Heavy Metal Analysis on Babylonia Areolata

Heavy Metal Analysis on Babylonia Areolata Heavy Metal Analysis on Babylonia areolata CONTENTS PAGES 1.0 INTRODUCTION 1.1 Background of study 1.2 Problem statements 1.3 Objectives of study 1.4 Hypothesis 1.5 Scope of study 1.6 Significant of study 2.0 LITERATURE REVIEW 3.0 MATERIALS AND METHODS 3.1 Study area 3.2 Research instrument 3.3 Sampling and sampling material 3.4 Research procedure EXPECTED RESULTS 5.0 GANTT CHART 6.0 REFERENCES CHAPTER 1 INTRODUCTION BACKGROUND OF STUDY Mollusks can be found almost everywhere on land and its habitat was including coral reef, estuaries, freshwater lakes and also rivers. Its habitat ranging from deserts to rainforests (Lydeard Lindberg, 2003). Mollusks also had been identified as an important fisheries and mariculture food such as clams, scallops, abalone and conch instead of commercial pearl production (Landman et al., 2001). Babylonia areolata, ivory shell was categorized as a gastropod in family Buccinidae (Hualkasin et al., 2008). B. areolata can easily be recognized by its colour-pattern because it was the only member of the genus with three broadly separated rows of dark spots (Altena et al., 1981). This three widely separated rows of spots are visible on the body-whorl, enabling easy identification of this species (Altena et al.,1981). It can be found 10-20m deep in sandy bottom (Habe, 1997). B. areolata has a buccinoid shell with the aperture approximately half of the total height. There are no notch can be seen from the upper part as the outer lip of the aperture not clearly thickened inside. On the last whorl in the inner lip, a notch consisting of a strong callus can be seen for the umbilicus. The umbilicus is wide open and the initial whorls whitish follows by the reddish-brown spots on a white background for the following whorls (Altena et al., 1981). The spotted babylon, B. areolata which also known as the Hoy Wan in Thailand supports a commercial fishery (Chaitanawisuti Kritsanapuntu, 1999). This species can be found in the Gulf of Thailand by three different shell colors which are brown, cream and white. The different shell colors indicate different values. The brown shell has the highest price while the white shell has the lowest price (Hualkasin et al., 2008). High demand for the brown shell B. areolata was from China, Taiwan, Hong kong and Japan. In Thailand, the distribution of B.areolata was different at the upper and lower Gulf of Thailand. Phetchaburi and Rayong which located at the upper gulf of Thailand only have brown shells B. areolata while in Songkhla and Pattani, all three colors are found there (Hualkasin et al., 2008). B. areolata is a well-known and nutritious food which have been a popular mollusk model used for the study of heavy-metal toxicity and biologic poisoning toxins transmission (Chen Chou, 1998). As the B. areolata has a potential market in Thailand as well as in Malaysia it will be used in this experiment to study its heavy metal contents and concentration. The place chosen for the sample drawing of B. areolata is in Bachok, Kelantan. Table 1: Taxonomy of B. areolata . PROBLEM STATEMENT Since B. areolata are widely used for the food purpose, there should some study on the composition or content of the B. areolata itself in order to ensure it was safe for the human consumption. The B. areolata lives in place like beach and may consume or eat on heavy metal that comes from nearby industry which may become harmful when human consume it. This experiment then can prove or can ensure the safety of B. aerolata for the consumption if the result of the experiments shows it flesh was having small quantity of the heavy metal which was deemed harmless to human. Heavy metal poisoning in human was resulted from the toxic accumulation of heavy metals in soft tissues. There was some level of heavy metal that permitted in the human body which would not give any health problems to the human health. In this study, the level of the expected heavy metal in the flesh of B. areolata will be discover to investigate whether their level was below the acceptable amount. The concentration of the heavy metal and exposure time make the metal’s toxic effects establish in an organ as many toxicants tend to be bio accumulate. When they occur at certain levels, even essential elements that are critical for life, may lead to loss of organ function or death (Goyer, 1996). This determination also important as B. areolata has the potential to become one of the ingredients for the feed preparation. If B. areolata was safe for human consumption, it also can become the ingredients for the feed production. OBJECTIVE OF STUDY To determine the concentration of heavy metal (Arsenic, Cadmium, Copper, Lead, Mercury and Zinc) in the Babylonia areolata. HYPOTHESIS H0 = B. areolata contains heavy metal concentration. Ha = B. areolata do not contains heavy metal concentration. SCOPE OF STUDY The scopes of this research are as follow: Only B. areolata which was draw from Bachok, Kelantan, Malaysia. Only one parameter of were being used in this study, that heavy metal concentration. To determine the component and concentration of the heavy metal in the B. areolata. SIGNIFICANT OF STUDY The study was important to get more knowledge about the contamination of the seafood which is B. areolata by the heavy metals. The importance of the study is to identify the concentration of the heavy metal in the B. areolata compared to the amount that permissible for the human consumption. As the contents of the heavy metal in the B. areolata was safe for human consumption, so the species can be the potential ingredients for the feed preparation. CHAPTER 2 LITERATURE REVIEW Distribution and background of Babylonia areolata B. areolata can be easily identify as it has three widely separated rows of spots which visible on its body whorl. The size of the shells can be up to 93 mm high and 52 mm broad. This species inhabits in sandy or muddy bottoms in shallow water. The distribution of this species is from Ceylon and the Nicobar Islands through the Gulf of Thailand, along the Vietnamese and Chinese coasts to Taiwan (Altena Gittenberger, 1981). B. areolata is well-known for domestic and international consumption which make it one of the economically important aquatic species. The price of this species was quite high which around 300- 350 Baht/kg in Thailand (Sutthinon et al., 2007). B. areolata will be a target species of commercial fisheries in Thailand. Nowadays, the aquaculture activity have been increase and improve to ensure the increment and sustainability of the stock as the number and the size of mollusk catch from the Thai coast is small (Hualkasin et al., 2008). In Thailand, the expanding domestic market of seafood and increasing demand of B. areolata results to the many interest to the commercial culture of this species. This also results due to the catastrophic decline in its populations in the gulf of Thailand. At present, the culture of B. areolata in large-scale production using the flow-through seawater system in concrete or canvas ponds shows a success for the species to survive from juveniles to marketable size (Chaitanawisuti et al., 2011). B. areolata with brown shell has the highest price while the white shell has the lowest price. High demand from countries such as China, Taiwan, Hong Kong, and Japan is for the brown shells (Hualkasin et al., 2008) This species has been cultured and consumed widespread throughout Asia which can be introduce as a new commercial gastropod. In recent years, market demand for this species has increased which results to the decrease in the wild population and shortage of seed stock to support its aquaculture industry. In order to support the increasing demand, the B. areolata should be produced in high quantity and quality by artificial method (Abol-munafi et al., 2010). 2.2 Category and hazards of heavy metal Heavy metal analysis on the source food was very important studies as it will ensure the safety of the food for the human consumption. Seafood was one of the food sources that have a high risk on the contamination with the heavy metal. Seafood may live in the sea where the components of heavy metals may be dissolved in it from the many sources such as the industrial activity nearby it. Heavy metal was divide into two categorized which is biological essential and non-biological essential metals (Kie, 2013) Biological essential metal can be refers to the metal that are needed to fulfill wide and variety range of human body functions. On the other hand, non-biological essential metals are considered to be toxic, nevertheless, modern medicine utilized them in a diverse range of applications including diagnostics, imaging and therapeutic applications (Dyson, 2011). Some examples of non-biological essential metal are lead, mercury, cadmium, chromium and tin. All heavy metals can be toxic when they exceed the threshold concentrations (Kie, 2013). 2.3 Heavy metal analysis in fish Heavy metals can harm human health by contaminating or accumulating in aquatic life and enter the food chain if the contamination and exposure is significant (Fernandes et al. 2007). In addition, this heavy metal are categorizes by the United States Environmental Protection Agency (USEPA) based on their potential for human exposure and health risk (Birungi et al. 2007). Fish is consumed by large population especially those who live nearby the river as a source of protein and the accumulating of heavy metal in fish will be an important issues (Roshasliney et al., 2010) Fish which has low saturated fat and sufficient omega fatty acid are also important in supporting good health to human. Growing rates, metabolism, feeding pattern and ecological need will influence the level of heavy metal contamination in fish (Yilmaz et al. 2005; Yilmaz et al. 2010). Besides, the exposure of fish to heavy metals also depends on the differences in life history patterns among species (including trophic levels and geographical distribution of life stages (Allen-Gil Martynov 1995). 2.4 Heavy metal analysis in bivalve and gastropod Mollusks are able to accumulate heavy metals which will give a hazard to the consumers (Qiang et al., 2001). According to Qiang et al. (2001), the heavy metal concentrations in the local seafood being monitored for many years to ensure the safety of the seafood. The study conducted by Qiang et al. (2001) was to access the current status of heavy metal pollution in shellfish available in major markets in Pearl River Delta and to compare with the tolerable limits. The costal environments of Pearl River become polluted with the liquid waste since the industrial development and the rapid population growth occur there (Qiang et al., 2001). MATERIAL AND METHODS 3.1 STUDY AREA Study area for this experiment is in Bachok, Kelantan. 3.2 RESEARCH INSTRUMENT Instrument that will be used for the analyzing of the heavy metal contents was Atomic Absorption Spectrometer (AAS). 3.3 SAMPLING AND SAMPLING MATERIAL Sample that will be collect is B. areolata 3.4 RESEARCH PROCEDURE Sample of B. areolata is collected from the sampling area which is in Bachok, Kelantan. 25 g of wet tissue of B. areolata (5 g dry weight) will be weighed out into crucible, and samples will be dried at 135 Â °C for 2 hour to obtain a dry weight. The dry sample then transfer to a cool muffle furnace and the temperature will slowly rise to 450Â °C-500Â °C. The ash will be left overnight. The samples then removed from the muffle furnace and let to cool to room temperature. Next, 2 ml of nitric acid (HNO3) will be added cautiously and swirled. The sample will be evaporated carefully just to dryness on warm hot plate or steam bath. It then transfers to cooled furnace, and the temperature slowly rises to 450 Â °C- 500 Â °C and hold at this temperature for 1 hour. The crucible will be removed and cool. To obtain clean, practically carbon-free ash the nitric acid (HNO3) treatment will be repeated if necessary. 10 ml of 1N hydrochloric acid (HCl) will be added and ash will dissolve by heating cautiously on a hot plate. The ash then transfers to a volumetric flask and hydrochloric acid (HCl) add as necessary. The ash then cool and dilute to a volume. As the sample ready, the sample will be test with Atomic Absorption Spectrometer (AAS) for the heavy metal analysis. Atomic Absorption Spectrometer general procedures consist of: 1. The hollow cathode lamp or electrode discharge lamp and D2-lamp were lighted if such background correction is used. The lamp current was set to the value specified by the manufacturer. 2. The monochromator was positioned at wavelength 213.9 nm. 3. The intensity of the hollow cathode lamp and the D2-lamp was carefully balanced if such background correction is used. 4. The burner head was aligned to assure that the center of the light beam passes over the burner slot. 5. The flame was lighted and the flow of fuel and oxidant was regulated to produce an oxidizing flame (lean blue). 6. Calibration blank was aspirate and a zero point was established. 7. Standard solutions were aspirated and a calibration curve was constructed. 8. Distilled water was aspirated after each standard or sample. EXPECTED RESULTS The B. areolata was live in deep sandy bottom which may be in sea or beach. For this experiment, the sample was draw near the industrial place. The expected heavy metals that will be analyzed from this experiment are Arsenic (As), Cadmium (Cd), Copper (Cu) and Zinc (Zn), Lead (Pb) and Mercury (Hg) (Qiang et al., 2001). These heavy metals was hazardous if accumulated in human tissue with exceeding value that recommended by the expertise. Arsenic can be found naturally on earth in small concentration. It occurs in soils and minerals and it may enter air, water and land through wind-blown dust and water run-off. This could be the reason for the contamination in B. areolata. The cadmium can be contaminated in the B. areolata by the exposure with the anticorrosion agent used by the ship for the coat of the ship itself. As the cadmium was mostly used as the anticorrosion agent, this would be the reasons of the cadmium absorption that release from the ship coat by B. areolata. Next, for the copper, it could be released into the environment by both natural sources and human activities. Examples of natural sources are wind-blown dust, decaying vegetation, forest fires and sea spray. Apart from that, it is applied in the industries and in agriculture which eventually will contaminate the sea water. For lead, although native lead is rare in nature but the contamination could be occur due to the lead cycle results from human production such as from the car exhaust. For mercury it can found naturally in the environment such as in metal form and mercury salts. This could be the source of the contamination. Lastly for the zinc, zinc occurs naturally in air, water and soil, but zinc concentrations are rising unnaturally, due to addition of zinc through human activities. Some soils are heavily contaminated with zinc, and these are to be found in areas where zinc has to be mined or refined, or were sewage sludge from industrial areas has been used as fertilizer. This also could be the source of the heavy metal that contaminated in the B. areolata. GANTT CHART

The Transmission Electron Microscopy Biology Essay

The Transmission Electron Microscopy Biology Essay The transmission electron microscope operates on the same basic principles as the light microscope but uses electrons instead of light. What you can see with a light microscope is limited by the wavelength of light. TEMs use electrons as light source and their much lower wavelength make it possible to get a resolution a thousand times better than with a light microscope. TEM uses a technique whereby a beam of electrons is transmitted through an ultra-thin specimen, interacting with the specimen as it passes through. An image is formed from the interaction of the electrons transmitted through the specimen; the image is magnified and focused onto an imaging device, such as a fluorescent screen, on a layer of photographic film, or to be detected by a sensor such as a CCD camera. TEMs are capable of imaging at a significantly higher resolution than light microscopes, owing to the small de Broglie wavelength of electrons. This enables the instruments user to examine fine detail-even as small as a single column of atoms, which is tens of thousands times smaller than the smallest resolvable object in a light microscope. TEM forms a major analysis method in a range of scientific fields, in both physical and biological sciences. TEMs find application in cancer research, virology, materials science as well as pollution, nanotechnology, and semiconductor research. History of TEMs The first operational electron microscope was presented by Ernst Ruska and Max Knoll in 1932, and 6 years later Ruska had a first version on the market. In 1986 Ruska received a Nobel Prize in physics for his fundamental work in electron optics and for the design of the first electron microscope. The following table gives a basic outline of the history of the electron microscope by decades. Year Specimens Application/development Instrumentation/theory Resolution 1940s Replicas oxide carbon plastics surfaces slip steps extracted particles fractography -50kV, single condenser -little or no theory; a first basic theory of electron microscopy was published in 1949 by Heidenreich. ~10nm 1950s Thin foils: from bulk deposited defects phase transitions -100kV -contrast theory developed. ~0.5-2nm 1960s metals semiconductors ceramics minerals Dynamic in-situ studies substructure of solids radiation damage microdiffraction -high voltage electron microscopes (Toulouse: 1.2 and 3MeV) -scanning electron microscopes -accessories for in-situ studies -controlled experiments 0.3nm (transmission) ~15-20nm (scanning) 1970s catalysts quasicrystals High resolution imaging lattice imaging -Analytical transmission electron microscopy -scanning transmission electron microscopy -energy dispersive x-ray spectra -electron energy loss spectroscopy -commercial high voltage electron microscopy (0.4-1.5MeV) -high resolution imaging theory 0.2nm (transmission) 7nm (standard scanning) 1980s virtually all materials atomic resolution in close-packed solids surface imaging small particles -commercial medium-voltage high-resolution/analytical electron microscopy (300-400kV) -improved analytical capabilities -energy filtering imaging -ultra-high vacuum microscopes 0.15nm (transmission) 5nm (scanning at 1kV) 1990s fast computation for image simulation alloy design nanostructures integrated digital scanning and image processing -surface atomic microscopy -orientation imaging microscopy 0.1nm (transmission) 3nm (scanning at 1kV) 2000s Electron microscopy in the 1960s In 1969 RCA dropped out of the electron microscope business, having decided that they could make more money selling record albums and consumer electronic devices.   General Electric had never become a major power in the electron microscope business. This left the field wide open for companies such as JEOL, Hitachi, and Akashi in Japan, and Philips, Siemens, and Zeiss in Europe. The resolution of the best TEMs was now approximately 0.3 nm (3 Ã…); JEOL claimed a resolution of 0.2 nm (2 Ã…) for its 1968 model JEM-100B. Accelerating voltages were still typically in the 100 kV range, although JEOL marketed a 200 kV instrument in 1967 called the JEM-200. Philips marketed a very popular 100 kV microscope called the EM 300 in 1966. They claimed that this was the first fully-transistorized electron microscope, and that it could attain a point resolution of 0.5 nm (5 Ã…). More than 1,850 units of the EM 300 were sold. Another approach to the study of materials that emerged in the 1960s involved increasing the accelerating voltage of the electron gun to extreme levels up to 3 MeV in an effort to penetrate more deeply into thicker samples. CEMES-LOE/CNRS at Toulouse, France, developed a 3MeV instrument around 1965, followed closely by JEOL, which released a 1 MeV microscope, the JEM-1000, in 1966. (One MeV represents a million electron volts, while one kV is a thousand electron volts. So 1,000 kV= 1 MeV.) These ultrahigh voltage EMs were so large that they typically occupied their own two-story building. The electron gun and its associated high voltage electronics were located near the ceiling of the second story, while the operator sat at the bottom of the microscope column looking at the fluorescent screen. Hitachis 1964 model HU-500 stood 4 meters tall; later, higher MeV versions eventually made this look small. On the left is a photograph of the 1 MeV Atomic Resolution Microscope (ARM) at the Lawrence Berkeley Laboratory. Electron microscopy in the 1970s The 1970s were a time of rapid development on all fronts in the electron microscope industry. Further improvements in TEM came from brighter electron sources (lanthanum hexaboride and field emission guns). The resolution of the TEM was pushed to 0.2 nm (2 Ã…) in the 1970s, with better results reported in some cases for lattice imaging resolutions; Hitachi claimed a 1.4 Ã… lattice resolution for its 1975 model H-500 TEM, and JEOL claimed the same resolution for its 1973 model JEM-100C. Accelerating voltages of 100 kV maximum had become the norm. In contrast to the low cost instruments, Philips 1972 model EM 301 TEM was designed for high performance and versatility for the skilled operator who had the time to coax the best results from his instrument. The EM 400 introduced in 1975 used a LAB6 electron gun, which was ten times as bright as the standard tungsten filament at the time. On the down side, the reactivity of lanthanum hexaboride required an ultra-clean vacuum system of 10-6 Torr. In 1977 Philips introduced accessories for the EM 400, including a secondary electron detector for topographical studies and a field emission gun (FEG) a single crystal tungsten tipped filament that emits electrons from a very localized region of the tip to produce narrow, bright electron beams. FEGs can have100 to 1,000 times the brightness of a LAB6 filament, with electron beam diameters as small as 1 nm. Vacuum requirements for these FEGs are 10-10 Torr. JEOL started with the JEM-100B Analytical model in 1970, which added scanning ability and an EDX x-ray spectrometer to the TEM. This was improved upon by the JEM-100C in 1973, with its 1.4 Ã… resolution, and further upgraded by the JEM-100CX Analytical model in 1976, which added an ultraclean vacuum system and a LAB6 electron gun. In the ultrahigh voltage EM market, The Hitachi 3MeV HU-3000 was installed at Osaka University in 1970. This accelerating voltage was the highest ever for an electron microscope. A resolution of 4.6 Ã… was reported for this instrument. The 1976 model H-1250 had a maximum voltage of 1250 kV, but a superior resolution of 2.04 Ã…. Electron microscopy in the 1980s During the 1980s TEM resolutions were further reduced to 1.0 to 1.5Ã…, making imaging of atoms in lattice planes possible. Microprocessor control of microscopes and computerized analysis of data became common due to the emergence of the personal computer in the early 80s. This microprocessor control brought about such features as an auto-stigmator and auto-focus, freeing the microscope operator from the mundane tasks that had always been involved in using the instrument. Electron energy loss spectroscopy (EELS) detectors were incorporated in STEMs and AEMs, allowing detection of low atomic number elements that could not be seen using x-ray techniques. The demands of the fast-growing integrated circuits industry produced electron microscopes designed for non-destructive testing of semiconductor wafers and for functional testing of ICs. Smaller electron beam sizes made it possible to switch from microprobe to nanoprobe technology. Elemental mapping of a samples surface could now be done on a nanometer level. Development of low cost instruments was not a priority in the 1980s. Some that were developed in the 1970s continued to be sold, but development was focused on high-performance, high-resolution, microprocessor-controlled instruments. JEOL produced 7 new TEM units between 1980 and 1986. These included the JEM-1200 EX (1981), which added microprocessor control to the JEM-100 CX (1976). The same model equipped with an EDS x-ray spectrometer was called the JEM-1200 EX/Analytical microscope. The 1984 model JEM-2000 FX/Analytical had a maximum voltage of 200 kV and a resolution of 2.8 Ã…; this instrument marked the switch from a microprobe beam to a nanoprobe. The JEM-4000 FX/Analytical microscope introduced in 1986 raised the acceleration voltage to 400 kV, which produced a beam probe size only 2 nm in diameter. After years of a standard 100 kV accelerating voltage with a few ultrahigh voltage units thrown in, these medium-voltage microscopes finally became popular. Electron microscopy in the 1990s The 1990s produced several corporate mergers in the electron microscope industry. Carl Zeiss and Leica joined to form LEO Electron Microscopy, Inc. In 1996 Philips bought Electroscan, the developer of the environmental SEM in the 1980s, to form Philips Electroscan. The following year Philips Electron Optics and a company called FEI merged under the name FEI to continue manufacturing electron microscopes. Hitachi and JEOL remained independent entities. The resolution of TEMs had already reached its theoretical limit (the best possible resolution predicted by calculations), so the 1Ã… resolution obtained using field emission gun (FEG) electron sources remained the standard. Medium voltage range instruments up to 300 kV were common, although 100 kV instruments still kept their long lasting popularity. Computers were now a vital part of every electron microscope, with graphical user interfaces (GUIs) being the norm. They were involved in both the control of the instrument and the processing of data, including post-analysis enhancement of micrographs using contrast-enhancing software. JEOL offered TEMs with maximum accelerating voltages of 120, 200, and 300 kV. The 120 kV model JEM1230 had a resolution of 0.2 nm (2Ã…). The JEM-2010 F FasTEM (200 kV) and the JEM-3000 F FasTEM (300 kV) both used FEG sources and achieved resolutions of 0.1 nm (1.0 Ã…). Three meetings of the Electron Microscopy Society of America (1968, 1975, and 1980) The Electron Microscopy Society of America (now known as the Microscopy Society of America) was founded in 1942, when it began holding annual meetings for instrument makers and users to gather and discuss the technology and its applications. The topics of papers given at these meetings present a snapshot of the state of electron microscopy at the time. A brief look at three of these meetings shows the evolution of the technology and its applications over a 12-year period. In the brief twelve-year span of 1968 to 1980, the physical sciences overtook the biological sciences at EMSA meetings, judging solely on number of papers presented. A large part of this development is probably due to the emergence of the scanning electron microscope in 1965, which made examination of the surface of bulk specimens possible for the first time. Since physical scientists could now look at real samples instead of replicas or thin films, activity in microscopy of materials increased dramatically. With no similar dramatic development in biological microscopy, the balance shifted. The Science of TEMs Comparison of Light (LM) and Electron Microscopes. a. Similarities 1) Illumination system: produces required radiation and directs it onto the specimen. Consists of a source, which emits the radiation, and a condenser lens, which focuses the illuminating beam (allowing variations of intensity to be made) on the specimen. 2) Specimen stage: situated between the illumination and imaging systems. 3) Imaging system: Lenses which together produce the final magnified image of the specimen. Consists of i) an objective lens which focuses the beam after it passes through the specimen and forms an intermediate image of the specimen and ii) the projector lens(es) which magnifies a portion of the intermediate image to form the final image. 4) Image recording system: Converts the radiation into a permanent image (typically on a photographic emulsion) that can be viewed. b. Differences 1) Optical lenses are generally made of glass with fixed focal lengths whereas magnetic lenses are constructed with ferromagnetic materials and windings of copper wire producing a focal length which can be changed by varying the current through the coil. 2) Magnification in the LM is generally changed by switching between different power objective lenses mounted on a rotating turret above the specimen. It can also be changed if oculars (eyepieces) of different power are used. In the TEM the magnification (focal length) of the objective remains fixed while the focal length of the projector lens is changed to vary magnification. 3) The LM has a small depth of field, thus different focal levels can be seen in the specimen. The large (relative) depth of field in the TEM means that the entire (thin) specimen is in focus simultaneously. 4) Mechanisms of image formation vary (phase and amplitude contrast). 5) TEMs are generally constructed with the radiation source at the top of the instrument: the source is generally situated at the bottom of LMs. 6) TEM is operated at high vacuum (since the mean free path of electrons in air is very small) so most specimens (biological) must be dehydrated. 7) TEM specimens (biological) are rapidly damaged by the electron beam. 8) TEMs can achieve higher magnification and better resolution than LMs. 9) Price tag!!! (100x more than LM) Figure below shows the cross-sectional view of a standard TEM. Figure shows the transmission electron microscope at The Chinese University of Hong Kong. Figure shows a schematic outline of a TEM. A TEM contains four parts: electron source, electromagnetic lens system, sample holder, and imaging system. A. Electron Source The electron gun produces a beam of electrons whose kinetic energy is high enough to enable them to pass through thin areas of the TEM specimen. The gun consists of an electron source, also known as the cathode because it is at a high negative potential, and an electron-accelerating chamber. There are several types of electron source, operating on different physical principles, which we now discuss. i. Thermionic Emission Figure 3-1 shows a common form of electron gun. The electron source is a V-shaped (hairpin) filament made of tungsten (W) wire, spot-welded to straight-wire leads that are mounted in a ceramic or glass socket, allowing the filament assembly to be exchanged easily when the filament eventually burns out. A direct (dc) current heats the filament to about 2700 K, at which temperature tungsten emits electrons into the surrounding vacuum by the process known as thermionic emission. Figure 3-1. Thermionic electron gun containing a tungsten filament F, Wehnelt electrode W, ceramic high-voltage insulator C, and o-ring seal O to the lower part of the TEM column. An autobias resistor, RB (actually located inside the high-voltage generator, as in Fig. 3-6) is used to generate a potential difference between W and F; thereby controlling the electron-emission current, Ie. Arrows denote the direction of electron flow that gives rise to the emission current. Raising the temperature of the cathode causes the nuclei of its atoms to vibrate with increased amplitude. Because the conduction electrons are in thermodynamic equilibrium with the atoms, they share this thermal energy, and a small proportion of them achieve energies above the vacuum level, enabling them to escape across the metal/vacuum interface. The rate of electron emission can be represented as a current density Je(in A/m2) at the cathode surface, which is given by the Richardson law: Where T is the absolute temperature (in K) of the cathode and A is the Richardson constant (~106Am-2K-2), which depends to some degree on the cathode material but not on its temperature; k is the Boltzmann constant (1.38 x 10-23J/K), and kT is approximately the mean thermal energy of an atom. ii. Schottky emission The thermionic emission of electrons can be increased by applying an electrostatic field to the cathode surface. This field lowers the height of the potential barrier (which keeps electrons inside the cathode) by an amount, the so-called Schottky effect. A Schottky source consists of a pointed crystal of tungsten welded to the end of V-shaped tungsten filament. The tip is coated with zirconium oxide (ZrO) to provide a low work function (~2.8 eV) and needs to be heated to only about 1800 K to provide adequate electron emission. Because the tip is very sharp, electrons are emitted from a very small area, resulting in a relatively high current density ( Je ~ 107A/m2) at the surface. Because the ZrO is easily poisoned by ambient gases, the Schottky source requires a vacuum substantially better than that of a LaB6 source. iii. Field emission If the electrostatic field at a tip of a cathode is increased sufficiently, the width (horizontal in Fig.3-4) of the potential barrier becomes small enough to allow electrons to escape through the surface potential barrier by quantum-mechanical tunneling, a process known as field emission. The probability of electron tunneling becomes high when the barrier width, w is comparable to de Broglie wavelength of the electron. This wavelength is related to the electron momentum p by p=h/ÃŽÂ » where h= 6.63 x 10-34 Js is the Planck constant. Because the barrier width is smallest for electrons at the top of the conduction band, they are the ones most likely to escape. Because thermal excitation is not required, a field-emission tip can operate at room temperature, and the process is sometimes called cold field emission. As there is no evaporation of tungsten during normal operation, the tip can last for many months or even years before replacement. It is heated (flashed) from time to time to remove adsorbed gases, which affect the work function and cause the emission current to be unstable. Even so, cold field emission requires ultra-high vacuum (UHV: pressure ~ 10-8 Pa) to achieve stable operation, requiring an elaborate vacuum system and resulting in substantially greater cost of the instrument. B. Electromagnetic Lens System The TEM may be required to produce a highly magnified (e.g, M = 105) image of a specimen on a fluorescent screen, of diameter typically 15 cm. To ensure that the screen image is not too dim, most of the electrons that pass through the specimen should fall within this diameter, which is equivalent to a diameter of (15 cm)/M = 1.5  µm at the specimen. For viewing larger areas of specimen, however, the final-image magnification might need to be as low as 2000, requiring an illumination diameter of 75  µm at the specimen. In order to achieve the required flexibility, the condenser-lens system must contain at least two electron lenses. The first condenser (C1) lens is a strong magnetic lens, with a focal length f that may be as small as 2 mm. Using the virtual electron source(diameter ds) as its object, C1 produces areal image of diameter d1. Because the lens is located 20 cm or more below the object, the object distance, u ~ 20 cm >> f and so the image distance v ~ f. The second condenser (C2) lens is a weak magnetic lens ( f ~ several centimeters) that provides little or no magnification (M ~ 1) but allows the diameter of illumination (d) at the specimen to be varied continuously over a wide range. The C2 lens also contains the condenser aperture (the hole in the condenser diaphragm) whose diameter D can be changed in order to control the convergence semi-angle of the illumination, the maximum angle by which the incident electrons deviate from the optic axis. Figure shows lens action within the accelerating field of an electron gun, between the electron source and the anode. Curvature of the equipotential surfaces around the hole in the Wehnelt electrode constitutes a converging electrostatic lens (equivalent to a convex lens in light optics), whereas the non-uniform field just above the aperture in the anode creates a diverging lens (the equivalent of a concave lens in light optics). C. Sample Holder To allow observation in different brands or models of microscope, TEM specimens are always made circular with a diameter of 3 mm. Perpendicular to this disk, the specimen must be thin enough (at least in some regions) to allow electrons to be transmitted to form the magnified image. The specimen stage is designed to hold the specimen as stationary as possible, as any drift or vibration would be magnified in the final image, impairing its spatial resolution (especially if the image is recorded by a camera over a period of several seconds). But in order to view all possible regions of the specimen, it is also necessary to move the specimen horizontally over a distance of up to3 mm if necessary. The design of the stage must also allow the specimen to be inserted into the vacuum of the TEM column without introducing air. This is achieved by inserting the specimen through an airlock, a small chamber into which the specimen is placed initially and which can be evacuated before the specimen enters the TEM column. Not surprisingly, the specimen stage and airlock are the most mechanically complex and precision-machined parts of the TEM. There are two basic designs of the specimen stage: side-entry and top-entry. In a side-entry stage, the specimen is clamped (for example, by a threaded ring) close to the end of a rod-shaped specimen holder and is inserted horizontally through the airlock. The airlock-evacuation valve and a high-vacuum valve (at the entrance to the TEM column) are activated by rotation of the specimen holder about its long axis; see figure (a). One advantage of this side-entry design is that it is easy to arrange for precision motion of the specimen. Translation in the horizontal plane (x and y directions) and in the vertical (z) direction is often achieved by applying the appropriate movement to an end-stop that makes contact with the pointed end of the specimen holder. A further advantage of the side-entry stage is that heating of a specimen is easy to arrange, by installing a small heater at the end of the specimen holder, with electrical leads running along the inside of the holder to a power supply located outside the TEM. The ability to change the temperature of a specimen allows structural changes in a material (such as phase transitions)to be studied at the microscopic level. Specimen cooling can also be achieved, by incorporating (inside the side-entry holder) a heat-conducting metal rod whose outer end is immersed in liquid nitrogen (at 77 K). One disadvantage of the side-entry design is that mechanical vibration  picked up from the TEM column or from acoustical vibrations in the external air, is transmitted directly to the specimen. In addition, any thermal expansion of the specimen holder can cause drift of the specimen and of the TEM image. These problems have been largely overcome by careful design, including choice of materials used to construct the specimen holder. As a result, side-entry holders are widely used, even for high-resolution imaging. In a top-entry stage, the specimen is clamped to the bottom end of a cylindrical holder that is equipped with a conical collar; see Figure (b). The holder is loaded into position through an airlock by means of a sliding and tilting arm, which is then detached and retracted. Inside the TEM, the cone of the specimen holder fits snugly into a conical well of the specimen stage, which can be translated in the (x and y) horizontal directions by a precision gear mechanism. The major advantage of a top-entry design is that the loading arm is disengaged after the specimen is loaded, so the specimen holder is less liable to pick up vibrations from the TEM environment. In addition, its axially symmetric design tends to ensure that any thermal expansion occurs radially about the optic axis and therefore becomes small close to the axis. However, in disadvantage views, it is more difficult to provide tilting, heating, or cooling of the specimen. Although such facilities have all been implemented in top-entry stages, they require elaborate precision engineering, making the holder fragile and expensive. Because the specimen is held at the bottom of its holder, it is difficult to collect more than a small fraction of the x-rays that are generated  by the transmitted beam and emitted in the upward direction, making this design less attractive for high-sensitivity elemental analysis. D. Imaging System The sample is placed in front of the objective lens in a form of thin foil, thin section or fine particles transparent for the electron beam. (Figure. 3). The objective lens forms an image of the electron density distribution at the exit surface of the specimen based on the electron optical principles. The diffraction, projection and intermediate lenses below the objective lens are used to focus and magnify either the diffraction pattern or the image onto a fluorescent screen, which converts the electrons into visible light signal. There are three important mechanisms, which produce image contrast in the electron microscope: mass-thickness contrast, phase contrast and diffraction or amplitude contrast. i. Mass-thickness contrast arises from incoherent elastic scattering of electrons. As electrons go through the specimen they are scattered off axis by elastic nuclear interaction also called Rutherford scattering. The cross section for elastic scattering is a function of the atomic number (Z). As the thickness of the specimen increases the elastic scattering also increases since the mean-free path remains fixed. Also specimens consisting of higher Z elements will scatter more electrons than low-Z specimens. This will create differential intensity in an image formed from thicker regions where fewer electrons will be transmitted to the image compared to a thinner or low atomic number region, which will be brighter in the image plane. In TEM, the mass-thickness contrast is affected by the size of the objective aperture and the accelerating voltage. Smaller apertures will increase the difference in the ratio of scattered and transmitted electrons and as a consequence will increase the contrast between regions of different thickness of mass. Lowering the accelerating voltage will lead to similar effect since the scattering angle and the cross section increase which also will cause increase in the relative contrast between higher mass and lower mass regions. ii. Phase contrast. Some of the electrons leaving the specimen are recombined to form the image so that phase differences present at the exit surface of the specimen are converted into intensity differences in the image. Phase contrast is the dominant mechanism for object detail iii. Diffraction contrast. Diffracted electrons leaving the lower surface of a crystalline specimen are intercepted by the objective aperture and prevented from contributing to the image. Alternatively only one diffracted beam forms the image. Diffraction contrast is the dominant mechanism delineating object detail >15 Ã… in crystalline specimens and is important and widely used contrast mechanism for study of crystal defects. Using this approach considerable quantitative information about the defect structure of the specimen may be obtained without operating the microscope at maximum resolution. Vacuum System Electron microscopes cannot operate in air for a number of reasons. The penetration of electrons through air is typically no more than 1 meter, so after coming on meter from the gun, the whole beam would be lost to collisions of the electrons with the air molecules. It is also not possible to generate the high charge difference between the anode and cathode in the gun because air is not a perfect insulator. Finally, the beam on the specimen while in air would trap all sorts of rubbish (air is full of hydrocarbon molecules) on the specimen, crack them (removing hydrogen, oxygen, etc.) and thus leave a thick carbon contamination layer on the specimen. Each electron microscope therefore has a vacuum system. The degree of sophistication of the vacuum system depends on the requirements. Simple imaging of biological thin sections is much less demanding than cryo applications or small-probe analysis in materials science and a thermionic gun can operate under much worse vacuum than a Field E mission Gun (FEG). The most basic vacuum system consists of a vessel connected to a pump that removes the air. The vacuum system of an electron microscope is considerably more complicated, containing a number of vessels, pumps, valves (to separate different vessels) and gauges (to measure vacuum pressures). From the bottom up we can distinguish four vessels in the vacuum system: The buffer tank The projection chamber The column (specimen area) The electron gun area Sometimes a tubomolecular pump (TMP), essentially a high-speed turbine fan, is used in place of (or to supplement) a diffusion pump. Usually an ion pump is used to achieve pressures below 10-4Pa, as required to operate a LaB6, Schottky, or field-emission electron source. By applying a potential difference of several kilovolts between large electrodes, a low-pressure discharge is set up (aided by the presence of a magnetic field) which removes gas molecules by burying them in one of the electrodes. Figure shows cross section through a diffusion pump. The arrows show oil vapor leaving jets within the baffle assembly. Water flowing within a coiled metal tube keeps the walls cool. Frequently, liquid nitrogen is used to help in achieving adequate vacuum inside the TEM, through a process known as cryo

Nelson on Descartess Theory of Perception and Judgment Essay -- Desca

Nelson on Descartes?s Theory of Perception and Judgment ABSTRACT: One tension in Descartes?s account of human error stems from the idea that we may be faulted for our acts of will, despite the fact that God is our omnipotent and omniscient creator. In the present essay, I describe a second tension in Descartes?s account of human error. After describing the tension, I consider Alan Nelson?s characterization of the means by which Descartes?s intended to relieve it. Although Nelson's interpretation is almost correct, I think that it obscures some of the interesting details of Descartes?s theory of perception and judgment. These details are revealed by the taxonomy of sensory responses that Descartes articulates in the Sixth Set of Replies to the Meditations. I. In the Fourth Meditation, Descartes is confronted with the problem of reconciling his conclusion that God exists and is no deceiver with apparent instances of human error. Described generally, Descartes attempts to square his assertions regarding God, with the fact that humans are subject to error, by claiming that any error made by a human being originates in a free act of will for which God should not be attributed fault. There is, of course, enormous tension between Descartes?s claim that human beings may be faulted for their acts of will, and his claim that God is our omnipotent and omniscient creator. In what respect is it appropriate to regard us as culpable for our acts, assuming that God is antecedently the author of these acts through his creation of the Universe? This is a difficult question to answer. However, even if we set this question aside (as I will), we find that considerable tension remains in Descartes?s account of the etiology of perceptual error. .. ...escartes, Volume II, pp. 295. 21 The same sort of confusion is also described in the last sentence of both principle 70 and 71, in Book One of the Principles. 22 In fact, the categories of the objects of confusion mentioned in principle 46 (perceptions and judgments) are precisely the constituents of the second and third categories of sensory response described in the Sixth Set of Replies. 23 The Philosophical Writings of Descartes, Volume I, pp. 208. References Descartes, Renï ¿ ½: 1985, The Philosophical Writings of Descartes (Vol. 1,2, and 3), Cambridge University Press, New York. Hare, R.M.: 1952, The Language of Morals, Clarendon Press, Oxford. Locke, John: 1975, An Essay Concerning Human Understanding, Clarendon Press, Oxford. Nelson, Alan: 1997, ?Descartes?s Ontology of Thought?, Topoi 16, 163-178. DESCARTES?S THEORY OF PERCEPTION AND JUDGMENT 11

Complex Systems Are Very Likely to Experience Accidents :: Challenger Accidents Accident Papers

Complex Systems Are Very Likely to Experience Accidents Many people in today’s industrial countries have experienced the frustration and inconvenience of having their car break down. That event, while troublesome, often does not pose any significant danger to people. It is a useful microcosm, however, because cars, like other complex systems, will almost certainly malfunction at some point during use. While we cannot prove the following assertion for sure, empirical data and observations strongly suggest that complex systems that are made of unreliable components will inevitably experience accidents so long as there exist flaws in the system that have no reliable safeguards. Numerous studies have investigated such a ‘Normal Accident Theory,’ and two notable cases very strongly indicate its validity: petroleum refinery accidents and the space shuttle Challenger, both of which will be discussed in this paper. Normal Accident Theory (NAT) is the label for a school of thought that considers accidents in complex systems to be inevitable. Two characteristics of complex systems that are very important to NAT are the interactive complexity of a system and a system’s coupling. Coupling is determined primarily by the time between processes in a system, the independent or dependent progression of such processes, and the number of different ways that a system’s goal can be achieved (Piccard, 1999). Systems are classified as ‘tightly coupled,’ meaning that the time between processes is small, the processes are highly interdependent, and there are few paths, if not one, to the goal; or ‘loosely coupled,’ which is the opposite. These characteristics are particularly useful for comparing different complex systems and evaluating them to determine which are at the highest risk for accidents. The results can then be used to minimize, but not elimina te, the possibility that an accident will occur. Sociologist Charles Perrow is generally credited with developing NAT. In order to understand the principles of NAT, several definitions that it uses are essential. An accident is defined as â€Å"an event that is unintended, unfortunate, damages people or objects, affects the functioning of the system of interest, and is non-trivial.† (Perrow, 1994) There are two types of accidents: component failure accidents, which â€Å"involve one or more component failures (part, unit, or subsystem) that are linked in an anticipated sequence,† and ‘normal accidents,’ or system accidents as they can be called (Perrow, 1994).

Norman Rockwell :: essays research papers

Norman Rockwell was one of America’s greatest illustrators of this century who made many significant contributions to the field of graphic design with his works that promoted patriotic unity, conveyed the national scene, and often time just evoked or inspired emotions in his audiences. Ironically this painter was regarded as an illustrator in the eyes of other freelance artists due to his occupational limitations, and his supervisor’s restrictions characteristic of the Saturday Evening Post where he did most of his work from 1916 to 1963. Rockwell was born on February 3, 1894 and since his childhood years had always aspired to be an artist. Instead of finishing high school Rockwell left high school to attend classes at the National Academy of Design and later on the Art Students League in New York. Here Rockwell was recognized as an above average illustrator with good potential. Rockwell then after developing his skills and contributing many illustrations to childre n’s magazines, managed to muster up the courage to show his work to a bigger periodical, the Saturday Evening Post. Happy with the quality of Rockwell’s work the Post gave Rockwell a job creating illustrations and cover art for its periodicals. This would be his arena, revealing his works to thousands of people, for over forty years. During this period Rockwell painted portraits of various celebrities and persona. Rockwell was a "people painter" and predominantly worked with the depiction of emotions inspired by his models. Rockwell always took particular care in picking and choosing his models as he was very pragmatic and wanted them to exhibit characteristics that met with his peculiar standards. During his time with the Post, Rockwell often made illustrations that effectively conveyed events taking place on the national scene. During different periods in American history Rockwell used his special skill in detail to capture and portray illustrations that ac curately reflected the emotions felt in the hearts of Americans at the time. Rockwell made several illustrations exhibiting events like the Great Depression and World War I. In fact during the second World War Rockwell was motivated by President Roosevelt himself to create one of his greatest projects, The Four Freedoms Paintings, illustrating each of America’s fundamental freedoms and revealing the reason behind the United States’ participation in the war. This Four Freedoms Project is one that reflects Rockwell’s great generosity and kindness as a person. Rockwell agreed to

Ethical Dilemmas Essay

There are three situations presented in the simulation which poses different ethical dilemmas on the part of the decision-maker. The symptoms of the respective dilemmas and their root causes shall be discussed individually because â€Å"analysis would be proper if they are able to locate the root cause of the conflict† (Lee). The Indiscreet Relationship The first situation presented was an indiscreet relationship between a boss and his secretary. The boss took the secretary along with him during business trips at the expense of the company. He even promoted the secretary to junior account executive. This problem created a stir within the company and corridor talks went around saying that the way to make it through the ladder of success in the company was through less than ethical means. This has caused an unrest among the employees of the organization that an ethical stand should be taken. However, the decision-maker had an ethical dilemma in making his decision. The boss, Patrick, is his former friend and colleague who was the one instrumental in landing him his job. Patrick also helped him during his early days with the company in getting hold of the ropes of the business of the company. On the other hand, company morale is going down because the employees think he is an unethical leader for allowing Patrick have his way in maintaining an indiscreet relations with his subordinate and in spending company resources in the process. This is what defines the ethical dilemma here. Sniffdog The second situation presented by the simulation which involved an ethical dilemma is the decision to represent SilverPill and their Sniffdog account. Sniffdog is a computer program which could sneak into the user’s hardware and retrieve many confidential data without the user’s knowledge. The ethical dilemma comes in when taking the account means allowance of the intrusion of privacy while not taking the account will make the company lose a lot of money by losing the account. The fact that compounds these all is that SilverPill informed the company that they will give all their accounts to McKinley should they choose to endorse Sniffdog. The ethics rulebook of McKinley states that the employees will maintain impeachable integrity in all its business dealings. Allowing Sniffdog to push through will not reflect well of this ethical rule. On its face, the business being dealt with here is plainly business and nothing will be objectionable about it. McKinley will just seek to endorse the Sniffdog program. However, when the program has capabilities of sneaking into private information, an ethical issue arises for McKinley will be signing itself to be part of such intrusion. Although SilverPill promised not to use any information that may be gathered for any illegal or extralegal use nor to sell it to a third party, the fact alone that there will be intrusion into the private lives of the users of the program will already present a grave ethical issue. Thus, the root cause of the problem here is whether or not to be a part of a project which can intrude into the private lives of clients by collecting confidential information from them without their knowledge. Think Eddie  And the third situation with an ethical dilemma presented by the simulation is whether or not to reveal certain information about the program Sniffdog to Think Eddie which is a competitor of SilverPill. At this point, SilverPill is no longer associated with McKinley and has moved on to another PR company. Think Eddie has entered the picture and wants McKinley to represent them for a computer program which has the same features as that of SilverPill’s Sniffdog. Think Eddie is a big client. And now it wants information about the Sniffdog program without, however, threats of any sanctions given to McKinley in case of non-compliance. The ethical dilemma here is whether to reveal the requested information to Think Eddie or not. Though Think Eddie did not give any threats for non-disclosure, surely there was an unwritten statement accompanying the request that non-disclosure might strain the relationship between the two companies. On the other hand, the ethics rule book of McKinley prescribes them not to hold conflicting interests. SilverPill, though a former client, still has the right that every information given by it to McKinley be kept confidential by the latter. Because of the mentioned rule, McKinley is duty-bound not to divulge confidential client information, especially in this case where the revelation will be made to a competitor. The root cause of the problem, therefore, is whether or not to reveal information obtained from a former engagement in order to establish a better business relationship with a new engagement even though the two have conflicting interests and the former engagement has already been severed. In all, the ethical dilemmas arise not because of the ethics rule books established by company but mostly because of moral grounds. â€Å"If doing what is right produces something bad, or if doing what is wrong produces something good, the force of moral obligation may seem balanced by the reality of the good end. We can have the satisfaction of being right, regardless of the damage done; or we can aim for what seems to be the best outcome, regardless of what wrongs must be committed† (Ross, 2007). Thus, the root of these dilemmas is simply because there are moral standards to which, companies as well as persons, must adhere.

A Child Special Place

All children have a special place, whether chosen by a conscious decision or not this is a place where one can go to sort their thoughts. Nature can often provide comfort by providing a nurturing surrounding where a child is forced to look within and choices can be made untainted by society. Mark Twain once said â€Å"Don't let school get in the way of your education. † Twain states that this education which is provided by society, can actually hinder human growth and maturity. Although a formal education shouldn't be completely shunned, perhaps true life experience, in society and nature, are a key part of development. In the novel Adventures of Huckleberry Finn, Mark Twain throws the curious yet innocent mind of Huck Finn out into a very hypocritical, judgmental, and hostile world, yet Huck has one escape–the Mississippi River constantly flowing nearby. Here nature is presented as a thought provoking environment when experienced alone. The river is quiet and peaceful place where Huck can revert to examine any predicament he might find himself in: â€Å"They went off, and I got aboard the raft, feeling bad and low†¦ Then I thought a minute, and says to myself, hold on,- s'pose you'd a done right and give Jim up; would you felt better than you do now? No, says I, I'd feel bad†¦ † (p. 127). Only a few weeks with Jim and still feeling great ambivalence, Huck returns to the river to think. Twain tries here to tell the reader how strong the â€Å"mob† really is, and only when totally alone is Huck able to make the morally correct decision. The natural flowing and calm of the river cause this deep-thought, show! ing how unnatural the collective thought of a society can be. The largest and most obvious test of Huck's character is his relationship with Jim. The friendship and assistance which he gives to Jim go completely against all that â€Å"sivilization† has taught him; at first this concept troubles Huck and causes him a great deal of pain, but over time, through his life experiences and shared times with Jim, Huck crosses the line upheld by the racist South and comes to know Jim as a human being. Huck is at a point in his life where opinions are formed, and by growing on the river, Huck can stand back from society and form his own. Eventually he goes as far as to risk his life for Jim:†And got to thinking of our trip down the river; and I see Jim before me, all the time, in the day, and in the night-time, sometimes moonlight, sometimes storms, and we a floating along, talking, and singing, and laughing. But somehow I couldn't see no places to harden me against him, but only the other kind†¦ I studied a minute sort of holding my breath, and then I s! ays to myself: ‘All right, then, I'll go to hell'†¦ † (pp. 270-271). After a long and thought-provoking adventure, Huck returns to the raft one final time to decide the fate of his friend. Symbolically, Huck makes the morally correct decision away from all others, thinking on the river. Although it might not be evident to himself, Huck causes the reader to see that â€Å"sivilization†, in their treatment of blacks especially, is not civilized at all. Every person Huck and Jim come across seems to just be following someone else blindly, as the whole country were some sort of mob. In the last few chapters, Tom Sawyer is re-introduced and the reader is left to examine how different environments: â€Å"sivilization† and nature (the river), have affected the children's growth. It is distinctly evident that Huck has turned out to be the one with a clear and intelligent mind, and Tom, although he can regurgitate worthless facts about Louis XVI and Henry VIII, shows no real sign of maturity. â€Å"The first time I catched up to Tom, private, I asked him what was his idea, time of the evasion? – what it was he planned to do if the evasion worked out all right and he managed to set a nigger free that was already free before? And he said, what he had planned in his head, from the start, if we got Jim out, all safe, was for us to run him down the river, on the raft, and have adventures plumb to the mouth†¦ † (p. 360). Huck has always thought of Tom as more intelligent than himself, but he cannot understand how Tom could toy with Jim's life in such a way. For much time, Huck is! without the river and it is though his mind clouds; he follows along with Tom playing a sick game until the end when he is once again threatened with being â€Å"sivilized†. But I reckon I got to light out for the Territory ahead of the rest, because aunt Sally she's going to adopt me and sivilize me and I can't stand it. I been there before† (p. 362). Huck's adventure, if nothing else, has given him a wary eye towards â€Å"sivilized† society. When the prospect of settling down with Sally is presented he light's out for the Territory to distance himself from a restrictive, formal education. Twain ends his novel by setting Huck up for a new experience and personal growth. The Adventures of Huckleberry Finn taught an important lesson, one that showed the importance of the self in the maturing process. We saw Huck grow up by having the river as a place of solitude and thought, where he was able to participate in society at times, and also sit back and observe society. Through the child's eye we see how ignorant and mob-like we can all be. Then nature, peace, and logic are presented in the form of the river where Huck goes to think. Though no concise answer is given, the literature forces the reader to examine their surroundings, and question their leaders.