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The temperature dependent of ac susceptibility studies are carried out on interacting 9.0 nm size MnFe2O4 particles in a wide frequency range (10–103 Hz) and in various external applied magnetic fields. At low external fields, the real part of ac susceptibility exhibit a maximum near room temperature. Interestingly, the imaginary part exhibits two maximum, one near 40 K and the other near room temperature. The former is interpreted as due to a spin-glass-like transition and the latter to the superparamagnetic blocking of the particles. The frequency dependence analysis of the spin-glass-like transition by Arrhenius and Volger–Fulcher laws is found to be unsatisfactory. The dynamic scaling analysis on frequency dependence of spin-glass-like transition temperature fits the model of a transition at finite temperature and yields critical exponents and parameters as: zν = 6.0, Tc = 34.4 K, τ0 = 10−7 s and that confirms the occurrence of spin-glass-like transition in 9.0 nm MnFe2O4 particles. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

IrMn based MTJs prepared under a low magnetic field of 30 Oe show pseudospin valve type behavior in the magnetoresistance and magnetization studies with no interlayer coupling or exchnage bias in the as-deposited state. The high field TMR curve shows a coercivity above 500 Oe with a wide distribution in switching fields with a low TMR value of 4%. The low field TMR curve shows sharp switching for the free layer without any interlayer coupling. However, after field annealing at 250 °C in a magnetic field of 1 kOe, MTJs show large MR values up to 35% with substantial bias around 1000 Oe for the pinned layer. It also shows an interlayer coupling of 3 Oe for the free layer. The loops corresponding to both the free and pinned layer show sharper switching behavior after annealing. During deposition in presence of the small magnetic field of 30 Oe, possibly, the spin ordering at the AFM/FM interface could not be attained due to the large anisotropy as indicated by the large coercivity for the pinned layer in the as-deposited state. Our results for the field annealed samples show that we can get good magnetoresistive properties in our MTJs after field annealing and cooilng despite no bias state in the as deposited MTJs.

High quality epitaxial indium zinc oxide (heavily indium oxide doped) (epi-n-IZO) thin films were optimized by laser-molecular beam epitaxy (L-MBE) i.e., pulsed laser deposition (PLD) technique for fabricating novel iso- and hetero-semiconductor–insulator–semiconductor (SIS) type solar cells using Johnson Matthey “specpure”- grade 90% In 2 O 3 mixed 10% ZnO (as commercial indium tin oxide (ITO) composition) pellets. The effects of substrate temperatures, substrates and heavy indium oxide incorporation on IZO thin film growth, opto-electronic properties with 〈1 0 0〉 silicon (Si), gallium arsenide (GaAs) and indium phosphide (InP) wafers were studied. As well as the feasibility of developing some novel models of iso- and hetero-SIS type solar cells using epi-IZO thin films as transparent conducting oxides (TCOs) and 〈1 0 0〉 oriented Si, GaAs and InP wafers as base substrates was also studied simultaneously. The optimized films were highly oriented, uniform, single crystalline approachment, nano-crystalline, anti-reflective (AR) and epitaxially lattice matched with 〈1 0 0〉 Si, GaAs and InP wafers without any buffer layers. The optical transmission T (max) ⩾ 95% is broader and absolute rivals that of other TCOs such as ITO. The highest conductivity observed is σ =0.47×10 3 Ω −1 cm −1 (n-type), carrier density n =0.168×10 20 cm −3 and mobility μ =123 cm 2 /V s. From opto-electronic characterizations, the solar cell characteristics and feasibilities of fabricating respective epi-n-TCO/〈1 0 0〉 wafer SIS type solar cells were confirmed. Also, the essential parameters of these cells were calculated and tabulated. We hope that these data be helpful either as a scientific or technical basis in semiconductor processing.

Highly textured zinc oxide (ZnO) thin films have been optimized and deposited by pulsed laser deposition (PLD), i.e., laser-molecular beam epitaxy technique on 〈100〉 Si, GaAs and InP wafers compatible with current semiconductor processing techniques. To our knowledge this is the first time that the PLD deposited zinc oxide thin films on semiconductor wafers have been applied to semiconductor–insulator–semiconductor type multi junction (homo and hetero) solar cell structures as wide band gap transparent conducting oxide (TCO) front electrode-emitter layers. In this present work, the effects of various substrate temperatures and substrates on ZnO thin film growth, structural and compositional properties were analyzed and the feasibility of developing high-quality TCO thin films for opto-electronic devices was also studied simultaneously. Increasing the deposition temperature leads the thin films to fine nano-structures. Our achievement in this work is elimination of any buffer layer like GaN and we have obtained good epitaxial lattice matching between the ZnO functional layers and the 〈100〉 substrates suitable for III–V-based high-speed opto- and micro-electronic devices.

This paper provides a brief overview of the current evidence for cancer predisposition and for an increased sensitivity of individuals carrying such predisposing mutations to cancers induced by ionizing radiations. We also discuss the use of a Mendelian one-locus, two-allele autosomal dominant model for predicting the impact of cancer predisposition and increased radiosensitivity on the risk of radiation-induced cancers in the population and in relatives of affected individuals using breast cancer due to BRCA1 mutations as an example. The main conclusions are the following: (1) The relative risk ratio of the risks of radiation-induced cancer in a heterogeneous population which has subgroups of normal and cancer-predisposed individuals to the risks in a homogeneous population (i.e., one which does not have these subgroups) increases with increasing dose; however, the dose dependence of the RR decreases at higher doses because of the fact that at high doses, the radiation risk to a homogeneous population will already be high. (2) The attributable risk (the proportion of cancers attributable to increased cancer susceptibility and increased radiosensitivity) follows a similar pattern. (3) When the proportion of cancers due to the susceptible genotypes is small (10%), as is likely to be the case for breast cancers in non-Ashkenazi Jewish women, the increases in risk ratios and attributable risks are small, and become marked only when there are very large increases in cancer susceptibility (1000-fold) and radiosensitivity (100-fold) in the susceptible group. (4) When the proportion of cancers due to the susceptible genotypes is appreciable (or = 10%), as may be the case for breast cancers in Ashkenazi Jewish women, there may be significant increases in the risk ratios and attributable risk for comparatively moderate increases in cancer susceptibility (10-fold) and radiosensitivity (100-fold) in the susceptible subpopulation. (5) The ratio of the risk of radiation-induced cancer in relatives to that in unrelated individuals in the population increases with the biological relatedness of the relative, being higher for close than for distant relatives; however, even when the mutant BRCA1 gene frequency and the proportion of breast cancers due to these mutations are high, as in Ashkenazi Jewish women, for values of predisposition strength and radiosensitivity differential10, the increase in breast cancer risks is only marginal, even for first-degree relatives.

Highly c-axis oriented ZnO thin films were epitaxially grown on semi-insulating 〈1 0 0〉 oriented InP substrates (SI-InP) held at room temperature (RT), 200°C and 300°C by laser molecular beam epitaxy (L-MBE) i.e., pulsed laser deposition. Through X-ray diffraction analysis, the material, the crystalline quality and the epitaxial lattice matching of the film were confirmed. The obtained high intense peak shows that the most preferential orientation was (0 0 2), i.e; along the ‘c-axis’. Results obtained from the optical studies indicated that the deposited film showed nearly 95% transparency and acts as anti-reflection medium. Photoluminescence (PL) study confirms the high electrical conductivity of the film and the obtained low-intensity PL spectrum indicates high O/Zn ratio. Further, the elemental peaks for Zn, O, In and P were identified by EDAX and the spectrum shows the stoichiometry of the ZnO thin films. From the optical absorption spectrum, the optical band gap and the thickness were calculated. The sheet resistance of the deposited ZnO thin films was measured for various deposition temperatures. Structural, compositional, surface morphological, optical and photoluminescence characterization results are discussed.

This paper provides an overview of the concept of doubling dose, changes in the database employed for calculating it over the past 30 years and recent advances in this area. The doubling dose is estimated as a ratio of the average rates of spontaneous and induced mutations in a defined set of genes. The reciprocal of the doubling dose is the relative mutation risk per unit dose and is one of the quantities used in estimating genetic risks of radiation exposures. Most of the doubling dose estimates used thus far have been based on mouse data on spontaneous and induced rates of mutations. Initially restricted to mutations in defined genes (with particular focus on the seven genes at which induced recessive mutations were studied in different laboratories), the doubling dose concept was subsequently expanded to include other endpoints of genetic damage. At least during the past 20 years, the magnitude of the doubling dose has remained unchanged at approximately 1 Gy for chronic low LET radiation exposures. One of the assumptions underlying the use of the doubling dose based on mouse data for predicting genetic risks in humans, namely, that the spontaneous rates of mutations in mouse and human genes are similar, is incorrect; this is because of the fact that, unlike in the mouse, the mutation rate in humans differs between the two sexes (being higher in males than in females) and increases with paternal age. Further, an additional source of uncertainty in spontaneous mutation rate estimates in mice has been uncovered. This is related to the non-inclusion of mutations which arise as germinal mosaics and which result in clusters of identical mutations in the following generation. In view of these reasons, it is suggested that a prudent way forward is to revert to the use of human data on spontaneous mutation rates and mouse data on induced mutation rates for doubling dose calculations as was first done in the 1972 BEIR report of the US National Academy of Sciences. The advantages of this procedure are the following: (i) estimates of spontaneous mutation rates in humans, which are usually presented as sex-averaged rates, automatically include sex differences and paternal age-effects; (ii) since human geneticists count all mutations that arise anew irrespective of whether they are part of a cluster or not, had clusters occurred, they would have been included in mutation rate calculations and (iii) one stays close to the aim of risk estimation, namely, estimation of the risk of genetic diseases in humans. On the basis of detailed analyses of the pertinent data, it is now estimated that the average spontaneous mutation rate of human genes (n=135 genes) is: (2.95+/-0.64)x10(-6) per gene and the average induced mutation rate of mouse genes (n=34) is: (0.36+/-0.10)x10(-5) per gene per Gy for chronic low LET radiation. The resultant doubling dose is (0.82+/-0.29) Gy. The standard error of the doubling dose estimate incorporates sampling variability across loci for estimates of spontaneous and induced mutation rates as well as variability in induced mutation rates in individual mouse experiments on radiation-induced mutations. We suggest the use of a rounded doubling dose value of 1 Gy for estimating genetic risks of radiation. Although this value is the same as that used previously, its conceptual basis is different and the present estimate is based on more extensive data than has so far been the case.

The habits of NMBA crystals grown with 10 different organic solvents having different dipole moments were studied. Solubility of NMBA in all the above solvents at various temperatures in the range 293–318 K was determined by Gravimetric method and the corresponding solubility coefficients at different growth temperatures were calculated. Crystals were grown by restricted evaporation method. Crystals with three different habits were obtained viz; needles (one-dimensional), platelets (two-dimensional) and octahedral (three-dimensional). All the grown crystals were found to be monoclinic which was confirmed by X-ray powder diffraction analysis and the lattice parameters calculated from this study are in line with the literature value.

This paper provides a broad overview of the epidemiological and genetical aspects of common multifactorial diseases in man with focus on three well-studied ones, namely, coronary heart disease (CHD), essential hypertension (EHYT) and diabetes mellitus (DM). In contrast to mendelian diseases, for which a mutant gene either in the heterozygous or homozygous condition is generally sufficient to cause disease, for most multifactorial diseases, the concepts of genetic susceptibility' and risk factors' are more appropriate. For these diseases, genetic susceptibility is heterogeneous. The well-studied diseases such as CHD permit one to conceptualize the complex relationships between genotype and phenotype for chronic multifactorial diseases in general, namely that allelic variations in genes, through their products interacting with environmental factors, contribute to the quantitative variability of biological risk factor traits and thus ultimately to disease outcome. Two types of such allelic variations can be distinguished, namely those in genes whose mutant alleles have (i) small to moderate effects on the risk factor trait, are common in the population (polymorphic alleles) and therefore contribute substantially to the variability of biological risk factor traits and (ii) profound effects, are rare in the population and therefore contribute far less to the variability of biological risk factor traits. For all the three diseases considered in this review, a positive family history is a strong risk factor. CHD is one of the major contributors to mortality in most industrialized countries. Evidence from epidemiological studies, clinical correlations, genetic hyperlipidaemias etc., indicate that lipids play a key role in the pathogenesis of CHD. The known lipid-related risk factors include: high levels of low density lipoprotein cholesterol, low levels of high density lipoprotein cholesterol, high apoB levels (the major protein fraction of the low density lipoprotein particles) and elevated levels of Lp(a) lipoprotein. Among the risk factors which are not related to lipids are: high levels of homocysteine, low activity of paraoxonase and possibly also elevated plasma fibrinogen levels. In addition to the above, hypertension, diabetes and obesity (which themselves have genetic determinants) are important risk factors for CHD. Among the environmental risk factors are: high dietary fat intake, smoking, stress, lack of exercise etc. About 60% of the variability of the plasma cholesterol is genetic in origin. While a few genes have been identified whose mutant alleles have large effects on this trait (e.g., LDLR, familial defective apoB-100), variability in cholesterol levels among individuals in most families is influenced by allelic variation in many genes (polymorphisms) as well as environmental exposures. A proportion of this variation can be accounted for by two alleles of the apoE locus that increase (e4) and decrease (e2) cholesterol levels, respectively. A polymorphism at the apoB gene (XbaI) also has similar effects, but is probably not mediated through lipids. High density lipoprotein cholesterol levels are genetically influenced and are related to apoA1 and hepatic lipase (LIPC) gene functions. Mutations in the apoA1 gene are rare and there are data which suggest a role of allelic variation at or linked LIPC gene in high density lipoprotein cholesterol levels. Polymorphism at the apoA1--C3 loci is often associated with hypertriglyceridemia. The apo(a) gene which codes for Lp(a) is highly polymorphic, each allele determining a specific number of multiple tandem repeats of a unique coding sequence known as Kringle 4. The size of the gene correlates with the size of the Lp(a) protein. The smaller the size of the Lp(a) protein, the higher are the Lp(a) levels. (ABSTRACT TRUNCATED)

Ethyl P-amino benzoate (EPAB) is also known as benzocaine was recently identified as new organic non linear optical (NLO) material which is having nearly six times higher SHG efficiency than that of KDP. Hence, growth of unidirectional EPAB crystal gains importance for phase matching studies and this is the first melt growth report of EPAB single crystal. Seeding with the microtube in the present technique eliminates the need for pre-grown seed and has more probability to grow bulk single crystal. Growth direction of the μT-Cz grown EPAB single crystals was identified as using X-ray powder diffraction studies. Thermal properties and optical transparency of the grown material were analyzed by TG and DTA and UV-VIS spectroscopic studies respectively. Laser damage threshold study shows nearly five times high damage threshold than KDP.

The effects of cancer predisposition and increased tumorigenic radiosensitivity of the predisposed genotypes on radiation cancer risks (in the general population and in sisters and first cousins of affected probands) are studied using an autosomal dominant model of cancer predisposition and radiosensitivity. The model assumes that the predisposing alleles, which confer enhanced tumorigenic radiosensitivity, are incompletely penetrant. In addition, the model also allows for sporadic cancers, unrelated to the predisposing locus. The predictions of the model are illustrated using current estimates of BRCA1 mutant gene frequencies; the estimates of the strength of predisposition and radiosensitivity differentials used are based on animal and human studies. It is shown that, unless both the strength of predisposition and radiosensitivity differential are large (say, >100-fold in comparison with normal homozygotes), (i) the effect of risk heterogeneity on cancer risk is marginal; (ii) dose-dependent radiation effect remains virtually the same as in a homogeneous irradiated population that has no predisposed subgroups; (iii) for the same radiation dose, relatives of affected probands show an enhancement of cancer risks; and (iv) most extra cancers in relatives can be attributed to radiosensitivity differentials. This simple model can give an upper bound of the effect of risk heterogeneity on radiation-induced breast cancer risks even when the cumulative breast cancer risk is age-dependent. Further, our model predicts that the benefits of mammography outweigh the risks.

A novel microtube seeding has been proposed in the conventional Czochralski pulling technique to grow a bulk single crystal. The versatility of the technique has been shown by adopting this method for the growth of benzil. Benzil single crystals having hexagonal facets are grown by this technique called the microtube-Czochralski technique (μT-CZ). Due to capillary rise, a fine column of melt was crystallized inside the microtube, which leads to the formation of the single crystal nucleation and ends up with hexagonal morphology. The reproducibility for getting single crystal is about 80%. It is evident that this technique is more viable to grow a bulk single crystal from the melt without a pregrown-seed. Further, the proposed μT-CZ technique can also be extended to other newer materials with the proper choice of the microtube.

Estimates of genetic risks of radiation exposure of humans are traditionally expressed as expected increases in the frequencies of genetic diseases (single-gene, chromosomal and multifactorial) over and above those of naturally-occurring ones in the population. An important assumption in expressing risks in this manner is that gonadal radiation exposures can cause an increase in the frequency of mutations and that this would result in an increase in the frequency of genetic diseases under study. However, despite compelling evidence for radiation-induced mutations in experimental systems, no increases in the frequencies of genetic diseases of concern or other adverse effects (i.e., those which are not formally classified as genetic diseases), have been found in human studies involving parents who have sustained radiation exposures. The known differences between spontaneous mutations that underlie naturally-occurring single-gene diseases and radiation-induced mutations studied in experimental systems now permit us to address and resolve these issues to some extent. The fact that spontaneous mutations (among which are point mutations and DNA deletions generally restricted to the gene) originate through a number of different mechanisms and that the latter are intimately related to the DNA organization of the genes, are now well-documented. Further, spontaneous mutations include those that cause diseases through loss of function as well as gain of function of genes. In contrast, most radiation-induced mutations studied in experimental systems (although identified through the phenotypes of the marker genes) are predominantly multigene deletions which cause loss of function; the recoverability of an induced deletion in a livebirth seems dependent on whether the gene and the genomic region in which it is located can tolerate heterozygosity for the deletion and yet be compatible with viability. In retrospect, the successful mutation test systems (such as the mouse specific locus test) used in radiation studies have involved genes which are non-essential for survival and are also located in genomic regions, likewise non-essential for survival. In contrast, most of the human genes at which induced mutations have been looked for, do not seem to have these attributes. The inference therefore is that the failure to find induced germline mutations in humans is not due to the resistance of human genes to induced mutations but due to the structural and functional constraints associated with their recoverability in livebirths. Since the risk of inducible genetic diseases in humans is estimated using rates of "recovered" mutations in mice, there is a need to introduce appropriate correction factors to bridge the gap between these rates and the rates at which mutations causing diseases are potentially recoverable in humans. Since the whole genome is the "target" for radiation-induced genetic damage, the failure to find increases in the frequencies of specific single-gene diseases of societal concern does not imply that there are no genetic risks of radiation exposures: the problem lies in delineating the phenotypes of recoverable genetic damage that are recognizable in livebirths. Data from studies of naturally-occurring microdeletion syndromes in humans and those from mouse radiation studies are instructive in this regard. They (i) support the view that growth retardation, mental retardation and multisystem developmental abnormalities are likely to be among the quantitatively more important adverse effects of radiation-induced genetic damage than mutations in a few selected genes and (ii) underscore the need to expand the focus in risk estimation from known genetic diseases (as has been the case thus far) to include these induced adverse developmental effects although most of these are not formally classified as "genetic diseases". (ABSTRACT TRUNCATED)

Multifactorial diseases, which include the common congenital abnormalities (incidence: 6%) and chronic diseases with onset predominantly in adults (population prevalence: 65%), contribute substantially to human morbidity and mortality. Their transmission patterns do not conform to Mendelian expectations. The model most frequently used to explain their inheritance and to estimate risks to relatives is a Multifactorial Threshold Model (MTM) of disease liability. The MTM assumes that: (i) the disease is due to the joint action of a large number of genetic and environmental factors, each of which contributing a small amount of liability, (ii) the distribution of liability in the population is Gaussian and (iii) individuals whose liability exceeds a certain threshold value are affected by the disease. For most of these diseases, the number of genes involved or the environmental factors are not fully known. In the context of radiation exposures of the population, the question of the extent to which induced mutations will cause an increase in the frequencies of these diseases has remained unanswered. In this paper, we address this problem by using a modified version of MTM which incorporates mutation and selection as two additional parameters. The model assumes a finite number of gene loci and threshold of liability (hence, the designation, Finite-Locus Threshold Model or FLTM). The FLTM permits one to examine the relationship between broad-sense heritability of disease liability and mutation component (MC), the responsiveness of the disease to a change in mutation rate. Through the use of a computer program (in which mutation rate, selection, threshold, recombination rate and environmental variance are input parameters and MC and heritability of liability are output estimates), we studied the MC-heritability relationship for (i) a permanent increase in mutation rate (e.g., when the population sustains radiation exposure in every generation) and (ii) a one-time increase in mutation rate. Our investigation shows that, for a permanent increase in mutation rate of 15%, MC in the first few generations is of the order of 1-2%. This conclusion holds over a broad range of heritability values above about 30%. At equilibrium, however, MC reaches 100%. For a one-time increase in mutation rate, MC reaches its maximum value (of 1-2%) in the first generation, followed by a decline to zero in subsequent generations. These conclusions hold for so many combinations of parameter values (i.e., threshold, selection coefficient, number of loci, environmental variance, spontaneous mutation rate, increases in mutation rate, levels of 'interaction' between genes and recombination rates) that it can be considered to be relatively robust. We also investigated the biological validity of the FLTM in terms of the minimum number of loci, their mutation rates and selection coefficients needed to explain the incidence of multifactorial diseases using the theory of genetic loads. We argue that for common multifactorial diseases, selection coefficients are small in present-day human populations. Consequently, with mutation rates of the order known for Mendelian genes, the FLTM with a few loci and weak selection provides a good approximation for studying the responsiveness of multifactorial diseases to radiation exposures.

We have carried out a systematic investigation of the development of exchange bias in an NiFe/FeMn/NiFe trilayer and in a trilayer with a nonmagnetic interlayer, in order to understand the development of bias in FeMn-based rf magnetron-sputtered multilayers. The trilayer shows two bias loops corresponding to the two NiFe layers where the seed layer shows a greater bias. The bias shows the expected 1/t variation with increasing seed layer thickness. The bias for the top NiFe layer of 5 nm constant thickness increases initially in the 2–6-nm range to reach a maximum value, and thereafter shows a surprising increase in bias at larger seed-layer thicknesses. The introduction of an Al layer of increasing thickness at the top FeMn surface causes the vanishing of the bias for the top NiFe layer and an increase in bias for the seed layer up to 1-nm thickness of Al layer and a decrease thereafter. The seed layer interestingly shows greater bias when an Al layer is present.

ZnAl2O4 is a spinel oxide, widely used as high-temperature material, catalyst, catalyst support, optical coating for spacecrafts and emerging as one of the best wide band gap compound semiconductor (Eg=3.8eV) for UV optoelectronic applications. In this work, spinel oxide is synthesized by the simple, in situ, acid-based chemical reaction and the thin film was deposited as a product of reaction by liquid-phase deposition (LPD). Material to be grown as metal incorporated thin film was taken as precursor and put into a bath containing acid, catalyst. The acid also serves as solvent with a metal foil as cation scavenger. Uniform and highly adherent ZnAl2O4 thin films were prepared. Structural, compositional and surface morphological properties of thin films were studied using Philips, Xpert—MPD: X-ray diffractometer and Philips, ESEM—TMP+EDAX, Hitachi S-450: SEM, Nanoscope—III: AFM.

With a historical setting for research in the field of radiation genetics, this chapter captures the essence of developments (concepts, assumptions, and databases) which contributed to the evolution of the estimates of genetic risks of radiation exposure of human populations from the mid-1950s to the year 2000. It presents the latest estimates of genetic risks, reflects upon the future of the field, and argues that progress in genetic risk estimation in the twenty-first century will be driven by the integration of the ever-increasing knowledge of the human genome with that of DNA repair mechanisms.

Copper Sulphide thin films have been prepared on different substrates using electrodeposition technique. X-ray diffraction analysis showed that the prepared films possess polycrystalline in nature with cubic structure. Microstructural parameters such as crystallite size, strain and dislocation density are determined using X-ray dif- fraction data. Film composition and surface morphology have been analyzed using Scanning electron microscopy and Energy dispersive analysis by X-rays. Optical absorption analysis showed that the prepared films possess band gap value in the range between 2.2 and 2.4 eV for films obtained on different substrates.

In the present investigations, a new etchant, viz., Bi(NO 3 ) 3 H 2 O 2 HCI (“BNCL etchant”) has been established for GaAs to reveal the subsurface damage induced during the polishing procedures. The investigated (1 0 0) oriented, silicon-doped n-type GaAs and undoped semi-insulating GaAs wafers were polished with slurries having pH 8 and 9. After etching, the shallow scratches are visible in addition to the wave-like defects. The etching rate was 6.5 μm/min for n-type and 8 μm/min for semi-insulating. When the etching was carried out for 2 min, all the observed damage vanished and most of the surface of both (n-type and semi-insulating) samples were found to be uniformly etched. The capability of the etchant to reveal the subsurface damage has been confirmed.

As a consequence of the U.S. Atomic Weapons Testing Program in the Trust Territory of the Pacific, now the Republic of the Marshall Islands, numerous scientists have advised the Marshallese on matters of radiation and radioactive contamination. Some of the previous advice has appeared to vary or conflict resulting in consequent uncertainty for the people. In a new initiative in 1989, the RMI Government engaged a five member multi-disciplinary Scientific Advisory Panel to oversee the assessment of, and to advise on, the radiological status of the entire nation. The formation of the Panel was accompanied by the establishment of a Resident Scientist position, and ultimately a small scientific team and laboratory on Majuro. The nationwide radiological study was conducted using ground survey methods over the period 1990-1994. Tasks undertaken by the Panel included formulating reasonable objectives for the study and attempting to establish effective communication and understanding of issues with political leaders and RMI Government agencies and people, as well as advising on and monitoring the scientific integrity of the study itself. The attempt was also made to initiate investigations to address matters of concern that emerged. The problem was faced of providing not only technical guidance on radioactivity and radiation measurements, but also explaining the significance of measured values and concepts, such as risk and probability of health effects to a diverse but nontechnical audience, generally across cultural and language barriers. The experience of the Panel in providing advice and guidance to the Republic of the Marshall Islands, while unique in many ways, parallels the difficulties experienced elsewhere in communicating information about risks from radiation exposure.

The protective effects of misoprostol (MP), an analogue of prostaglandin E1, on X-ray-induced chromosomal aberrations, were studied in normal or mutant Chinese hamster cell lines grown as spheroids in vitro and on cell-killing in stem-cell spermatogonia of a mutant (acid) mouse strain or its wild-type. The mutant hamster cell lines chosen for this purpose are known to be either hypersensitive to the killing effects of X-rays and/or deficient in the repair of DNA double-strand breaks. The scid mice are deficient in the repair of DNA double-strand breaks. The results show that MP manifests varying degrees of radioprotection in all these systems, but the magnitude of these effects in the mutants is markedly reduced compared to their respective wild-type counterparts. These findings suggest a link between ionizing radiation sensitivity, DNA double-strand break repair capability and MP-mediated radioprotection.

Zinc aluminate ZnAl2O4 is a well known wide band gap compound semiconductor (E g=3·8 eV) used in UV photoelectronic devices, antithermal coatings for spacecraft, and ceramic and catalyst materials. In the present work, the development of a single step process to synthesise and grow ZnAl2O4 spinel at low temperature is described. In this context, novel, economical and spontaneous growth of a bulk crystal of a ternary oxide material is reported. ZnAl2O4 crystals were grown at room temperature (30°C). Material to be grown as metal incorporated single crystals was taken as precursor and put into a neutral bath containing acid as reaction acceleration reagent (catalyst) as well as solvent with a metal foil (cation scavenger). Zinc aluminate crystals have been grown in a single step process using a chemical bath under optimised conditions in an average period of 15 days. Crystals were grown with hexagonal facets and XRD measurement confirmed the growth of a single crystal. Elemental (Zn, Al, O) and chem...

Computer graphics applications especially the applications which produce complex color images produce very large file sizes. Data with very large size creates several problems such as requirement of very large storage space, the need to quickly transmit image data across networks, etc. Hence, image compression has become an active area of research in the field of image processing to reduce file size. Wavelet and curvelet transformations are widely used transformations techniques to carry out compression. But both have their own limitations which affects overall performance of the compression process. This research work focuses on presenting a non-linear image compression technique that compresses images both radically and angularly. Wavelet-based Contourlet Transformation (WBCT) has the potential to approximate the natural images comprising contours and oscillatory patterns. In addition to this transformation scalar quantization technique is used to eliminate the redundancies in the images. Finally, this technique uses Modified Set Partitioning in Hierarchical Trees (MSPIHT) for the efficient encoding process. The experimental results of wavelet-based contourlet transformation with scalar quantization and MSPIHT are better when compared with existing transformations techniques.

The green lasers are attractive and highly useful for lot of practical applications. It is more than fifty times brighter when compared to a red laser and thus it can be seen from miles away. Due to these features, the green lasers can be used in high-tech weapons for aiming purposes. More‐ over, the green lasers are highly useful for laser televisions and medical applications. Most of the commercially available green lasers are based on the diode pumped solid state frequencydoubled (DPSSFD) laser technology. For the past several decades, researchers and several in‐ dustries were trying to develop the laser diodes based on the compound semiconductors such as Gallium nitride (GaN) and Indium Gallium nitride (InGaN) especially in the blue and green region of wavelengths [1]. However, it is very difficult to grow bulk crystal of these materials with reasonable quality. Moreover, for the preparation of epitaxial thin films of these materi‐ als on substrates, highly sophisticated and expensive techniques like molecular beam epitaxy (MBE) and metal organic chemical vapour deposition (MOCVD) are needed. Apart from these growth aspects, the relatively low power and limited wavelength range restricts their use in important applications [2]. Therefore, laser sources based on Second harmonic generation (SHG) is a better choice for the applications which requires higher powers or longer wave‐ lengths (>400nm). As a consequence, the green laser technology still depends on the nonlinear optical phenomena such as frequency doubling.

The generation of tritium during the electrolysis of aqueous light water alkali carbonate (K{sup 2}CO{sup 3} and Li{sup 2}CO{sup 3}) solutions by nickel cathodes, first reported by us at the International Conference on Cold Fusion-3 (Nagoya, Japan, October 1992) has once again been verified and confirmed. During 1993, 10 out of 23 cells, whose electrolytes were analyzed using a newly set up dedicated liquid scintillation counting unit, indicated low tritium levels in the electrolyte, in the range of 0.5 to 4.8 Bq/ml. Except one cell, which contained 25% D{sup 2}O, the remaining nine cells, which produced tritium, were charged with natural light water solutions only. Two of these cells, which were monitored for tritium every few days, and excluding cell OM-3, which was set up in 1992, indicated tritium level variations in a sawtooth fashion, suggesting the possible presence of an as yet unidentified mechanism responsible for periodically removing tritium from the electrolyte. 7 refs., 3 figs., 6 tabs.

The last three decades have witnessed substantial progress in the development and use of a variety of in vitro and in vivo assay systems for the testing of environmental chemicals which may pose a mutagenic hazard to humans. This is also true of basic studies in chemical mutagenesis on mechanisms, DNA repair, molecular dosimetry, structure-activity relationships, etc. However, the field of quantitative evaluation of genetic risks of environmental chemicals to humans is still in it infancy. This commentary addresses the question of how our experience in estimating genetic risks of exposure to ionizing radiation can be helpful in similar endeavors with environmental chemical mutagens. 24 refs., 3 tabs.

The radioprotective effects of prostaglandins (PGE2, PGE1 and its analogue misoprostol (MP) were investigated in cultures of V79 Chinese hamster (CHO) cells grown as spheroids and as monolayers, CHO cells grown as monolayers, and in bone marrow polychromatic erythrocytes and spermatogonial stem cells in mouse. The X-ray doses were 0.75 Gy (hamster cells) and 5, 8 and 10 Gy (mouse experiments). Prostaglandin pre-irradiation treatment resulted in a marked reduction in the frequencies of chromosomal aberrations in V79 spheroids and of reciprocal translocations in mouse stem cell spermatogonia. The amount of mouse spermatogonial stem cell killing was likewise significantly reduced. No radioprotective effects of prostaglandins could be demonstrated, however, for chromosomal aberrations in hamster cells grown as monolayers, for survival of V79 cells grown as spheroids, and for the induction of micronuclei in bone marrow polychromatic erythrocytes of mouse.

Biologically essential drug material of Paracetamol was crystallized with the nonessential amino acid in equimolar ratio by slow solvent evaporation method. Good quality of transparent drug crystals was grown within 3 weeks and its stability was analyzed by thermal studies. The unit cell parameters of the grown crystals were determined by single X-ray diffraction studies. FTIR, optical, and dielectric studies were also carried out to the grown biomolecular crystal which is very important in the drug development phase.

The predominant compliance in the dynamic response of the PUMA 560 robot manipulator arises in joints two and three. Considering compliance of these two joints, the effects of user controlled variables on system stability are studied using Floquet theory. Specifically, manipulator configuration, operating speed and trajectory amplitude are considered. For some configurations, instabilities are expected for ranges of operating frequencies which are significantly removed from the neighborhood of multiples of resonant frequencies of the stationary system. Results demonstrate overall trends in stability regions for several ranges of system configuration. Results also identify regions of rapidly changing stability of this industrial manipulator.

The growth aspects of 50 mm diameter gallium arsenide single crystals using LEC technique are presented. Defect investigations are made using photoluminescence studies. Photoluminescence studies on the wafers reveal the presence of the EL2 level, the presence of transition metal impurity copper which cannot be eliminated by surface treatments, and the presence of carbon. Photoluminescence scans are also obtained at room temperature to study the uniformity. The presence of carbon is also revealed by FTIR measurements.

This paper discusses (a) data on the epidemiological and etiological aspects of human congenital abnormalities, (b) the multifactorial threshold model and other models which have been proposed to explain their inheritance patterns and recurrence risks in families and (c) current concepts on mechanisms on the prevalence of heritable variation for quantitative traits in populations. Congenital abnormalities, which afflict an estimated 6% of all live births, are etiologically heterogeneous. The majority of these do not follow Mendelian transmission patterns, but do ‘run’ in families. The multifactorial threshold model is an extension of genetic principles developed for quantitative traits to all-or-none traits; in its simplest formulation, it assumes the existence in the population of an underlying normally distributed ‘liability’ (which is due to numerous genetic and environmental factors acting additively, each contributing a small amount of liability) and of a ‘threshold’ beyond which the individual is affected. For most congenital abnormalities, the nature of these factors remains unknown. Other models assume fewer causal factors although, again, these remain to be identified. The question of how considerable heritable variation for most quantitative / polygenic traits has come to exist is a long-standing one in evolutionary population genetics. Models postulating that its existence is consistent with a balance between recurrent mutation and stabilizing selection or suggesting the possible operation of other mechanisms have been published in the literature.

Ultrafine rare-earth iron garnets (RIG) in the crystalline size range 1.0–35 nm, prepared by the citrate precursor method have been investigated by Mossbauer spectroscopy at room temperature. The crystallites of 10–35 nm size show two six-line spectra corresponding to tetrahedral and octahedral Fe3+ with isomer shifts, δ, and magnetic hyperfine fields, H hf, comparable to the bulk polycrystalline garnets. However, 1.0–1.5 nm crystallites (X-ray amorphous) show a quadrupole split doublet due to superparamagnetic nature with isomer shifts (0.3 mms−1) internediate between tetrahedral and octahedral values of bulk garnets. The relative increase of tetrahedral δ and the decrease in the octahedral δ indicate, respectively, an increase of tetrahedral Fe-O bond distance and a decrease of octahedral Fe-O bond distance in the ultrafine state, in complete agreement with the observations made earlier in the spectrochemical investigations. The lines are broad (linewidth=0.65 mms−1) and the quadrupole splittings are relatively larger (ΔE Q = 1.0 mms−1) indicating large deviation from cubic symmetry at the Fe3+ sites.

This paper discusses the growth of gallium arsenide single crystals using the LEC technique. The Semi-insulating gallium arsenide was studied. The defect investigations were made by DLTS and etching studies. The variation of deep level concentration along the wafer was estimated using DLTS. The fabrication and efficiency of the PEC Solar cells are also reported.

This paper examines the impact of advances in knowledge on the molecular biology of human Mendelian diseases on the estimation of genetic risks of exposure to ionizing radiation and to chemical mutagens. More specifically, it addresses the question of whether and to what extent naturally occurring Mendelian diseases can be used as a baseline for efforts in this area. Data on the molecular nature and mechanisms of origin of spontaneous mutations underlying naturally occurring Mendelian diseases and on radiation-induced mutations in experimental systems suggest that for ionizing radiation, naturally occurring Mendelian diseases may not constitute an entirely adequate frame of reference and the current risk estimates for this class of diseases are conservative; these estimates however provide a margin of safety in formulating radiation protection guidelines. Currently available data on mechanisms and specificities of action of chemical mutagens, molecular dosimetry, repair of chemically induced adducts in the DNA, adduct-mutation relationships etc., permit the tentative conclusion that naturally occurring Mendelian diseases may provide a better baseline for genetic risk estimation for chemical mutagens than for ionizing radiation. With both ionizing radiation and chemical mutagens, the question of which Mendelian diseases are potentially inducible will become answerable in the near future when more molecular data on human genetic diseases become available. It is therefore essential that risk estimators keep abreast of advances in human genetics and integrate these into their conceptual framework. However, induced Mendelian diseases (especially the dominant ones which are of more immediate concern) are likely to represent a very small fraction of the adverse genetic effects of induced mutations. More attention therefore needs to be devoted to studies on the heterozygous effects of induced mutations.

Our study indicates that indeed it is possible to control the proliferation of adult hMScs. These results could be used to arrest cancer stem cells from proliferation and thus pave the way for a physical cancer therapy that can be out-patient-based using reduced doses of highly toxic chemo drugs, thus enhancing quality of life by reducing cost and side effects.

This article traces the development of the field of mutagenesis and its metamorphosis into the research area we now call genetic toxicology. In 1969, this transitional event led to the founding of the Environmental Mutagen Society (EMS). The charter of this new Society was to "encourage interest in and study of mutagens in the human environment, particularly as these may be of concern to public health." As the mutagenesis field unfolded and expanded, new wording appeared to better describe this evolving area of research. The term "genetic toxicology" was coined and became an important subspecialty of the broad area of toxicology. Genetic toxicology is now set for a thorough reappraisal of its methods, goals, and priorities to meet the challenges of the 21st Century. To better understand these challenges, we have revisited the primary goal that the EMS founders had in mind for the Society's main mission and objective, namely, the quantitative assessment of genetic (hereditary) risks to human populations exposed to environmental agents. We also have reflected upon some of the seminal events over the last 40 years that have influenced the advancement of the genetic toxicology discipline and the extent to which the Society's major goal and allied objectives have been achieved. Additionally, we have provided suggestions on how EMS can further advance the science of genetic toxicology in the postgenome era. Any oversight or failure to make proper acknowledgment of individuals, events, or the citation of relevant references in this article is unintentional.

MANET is a special kind of wireless network. It is a collection of mobile nodes without having aid of established infrastructure. Mobile Adhoc network removes the dependence on a fixed network infrastructure by treating every available mobile node as an intermediate switch, thereby extending the range of mobile nodes well beyond that of their base transceivers. Other advantages of Manet include easy installation and upgrade, low cost and maintenance, more flexibility, and the ability to employ new and efficient routing protocols for wireless communication. In this paper we present four routing algorithm, classifications, discuss their advantages and disadvantages.

Presents a broad overview of the following themes: (i) naturally occurring genetic diseases in man; (ii) how genetic risk estimates are obtained and used in the sphere of radiation protection; (iii) the significance of the genetic results from the studies of A-bomb survivors in Japan; (iv) the association between paternal radiation exposures and risk of leukaemia in the children noted by Gardner and colleagues (1990) and (v) a reassessment of the conceptual framework of risk estimation and of estimated risks in the light of recent advances in the molecular biology of human genetic diseases.

This paper (1) presents an analysis of published data on the molecular nature of spontaneously arising and radiation-induced mutations in mammalian somatic cell systems and (2) examines whether the molecular nature and mechanisms of origin of radiation-induced mutations, in mammalian in vivo and in vitro systems, as currently understood, are consistent with expectations based on the biophysical and microdosimetric properties of ionizing radiation. Depending on the test system (CHO cells, human T lymphocytes and human lymphoid cell line TK6), 80-97% of spontaneous HPRT mutations show normal Southern patterns; the remainder is due to gross changes, predominantly partial (intragenic) deletions. Total gene deletions at the HPRT locus are rare except in the TK6 cell line. At the APRT locus in CHO cells, 80-97% of spontaneous mutations are due to base-pair changes, the remainder being, mostly, partial deletions. The latter can extend upstream in the 5' direction but not beyond the APRT gene in the 3' direction. At the human HLA-A locus (T lymphocytes), the percentage of mutations with normal Southern patterns is lower than that for HPRT, and in the range of 50-60%. At the HLA-A locus, mitotic recombination contributes substantially to the mutation spectrum (approximately 30% of mutations recovered) and this is likely to be true of the TK locus in the TK6 cell line as well. With a few exceptions, most of the radiation-induced mutations show altered Southern patterns and are consistent with their being deletions and/or other gross changes (HPRT, 70-90% (CHO); 50-85% (TK6); 50-75% (T lymphocytes); TK, 60-80% (TK6); HLA-A, 80% (T lymphocytes); DHFR, 100% (CHO]. The exceptions are APRT mutations in CHO cells (16-20% of mutants with deletions or other changes) and HPRT mutations in T lymphocytes from A-bomb survivors (15-25%); the latter finding is consistent with the occurrence of in vivo selection against HPRT mutant cells. In cases of HPRT intragenic deletions analyzed (CHO cells and V79 Chinese hamster cells), there is evidence for a non-random distribution of breakpoints. The spontaneous mutation frequencies vary widely, from about 0.04/10(6) cells (sickle cell mutations at the human HBB locus) to 30.8/10(6) cells (HLA-A mutations in T lymphocytes) and are dependent on the locus, the system employed and a number of other factors. Those for the other loci fall between these limits.(ABSTRACT TRUNCATED AT 400 WORDS)

This paper reviews the currently available information on naturally occurring Mendelian diseases in man; it is aimed at providing a background and framework for discussion of experimental data on radiation-induced mutations (papers II and III) and for the estimation of the risk of Mendelian disease in human populations exposed to ionizing radiation (paper IV). Current consensus estimates indicate that a total of about 125 per 104 livebirths are directly affected by one or another naturally occurring Mendelian disease (autosomal dominants, 95/104; X-linked ones, 5/104; and autosomal recessives, 25/104). These estimates are conservative and take into account conditions which are very rare and for which prevalence estimates are unavailable. Most, although not all, of the recognized “common” dominants have onset in adult ages while most sex-linked and autosomal recessives have onset at birth or in childhood. Autosomal dominant and X-linked diseases (i.e., the responsible mutant alleles) presumed to be maintained in the population due to a balance between mutation and selection are the ones which may be expected to increase in frequency as a result of radiation exposures. Viewed from this standpoint, the above assumption seems safe only for a small proportion of such diseases; for the remainder, there is no easy way to discriminate between different mechanisms that may be responsible or to rigorously exclude some in favor of some others. Mutations in genes that code for enzymic proteins are more often recessive in contrast to those that code for non-enzymic proteins, which are more often dominant. At the molecular level, with recessives, a wide variety of changes is possible and these include specific types of point mutations, small and large intragenic deletions, multilocus deletions and rearrangements. In the case of dominants, however, the kinds of recoverable point mutations and deletion-type changes are less extensive because of functional constraints. The mutational potential of genes varies, depending on the gene, its size, sequence content and arrangement, location and its normal functions, and can be grouped into three groups: those in which only point mutations have been found to occur, those in which only deletions or other gross changes have been recovered and those in which both kinds of changes are known. Molecular data are available for about 75 Mendelian conditions and these suggest that in approximately 50% of them, the changes categorized to date are point mutations and in the remainder, intragenic deletions or other gross changes; there does not seem to be any fundamental difference between dominants and recessives with respect to the underlying molecular defect. Onset age for Mendelian diseases appears related to the normal function disrupted or abolished by the mutation and not necessarily to the underlying molecular change. Point mutations do not appear to be distributed at random throughout the gene; CpG dinucleotide sequences, when present in the gene, provide “hot-spots” for transition-type mutations, but not all transitions occur at CpG sequences. The breakpoints involved in intragenic deletions also are not distributed at random within the gene. In cases analyzed, the length of the deletion per se is not correlated with the severity of the clinical effect. The data from a number of well-analyzed gene deletions are consistent with mechanisms that assume base mispairing between repeat sequences and slippage during replication, homologous unequal recombination between evolutionarily related genes, homologous unequal recombination between repetitive sequences such as Alu and non-homologous recombination. Not all deletions involve Alu sequences. There is circumstantial evidence supporting the hypothesis that repetitive sequences may play an important role in chromosome pairing; if true, the deletions and duplications that have been found to be associated with some diseases may represent the inevitable by-products of occasional mispairing.

This paper is aimed at a synthesis of conclusions and concepts from the first three papers of this series and an inquiry of their relevance to the estimation of the risk of autosomal dominant and X-linked diseases in man, due to exposure to ionizing radiation. For a population under conditions of continuous irradiation, the doubling-dose method (DD method) enables the prediction of the excess risk of dominant and X-linked diseases at equilibrium. Per unit dose, this quantity is the product of the natural prevalence of these diseases (assumed to be 10,000/10(6) livebirths) and the reciprocal of the DD. The DD currently used is 1 Gy and is based primarily on data on the induction of recessive specific-locus mutations in male mice. The estimate of risk to the first generation is derived from that at equilibrium; the figure is about 15% of the equilibrium value (i.e., 15 cases/10(6) livebirths/cGy). With the direct method, the first-generation risk of dominant disease is estimated using data on the induction of dominant skeletal and cataract mutations in male mice and a number of correction factors. The estimates are about 10-20 cases and 0-9 cases, respectively, for irradiation of males and females, per 10(6) livebirths/cGy. In the Japanese studies, no significant adverse genetic effects, attributable to exposure of the parents to the atomic bombs, could be demonstrated with respect to any of the endpoints used. Most of the latter are clinically and socially relevant but mutationally insensitive. On the basis of these data, Neel and colleagues have estimated that the gametic DD for genetic effects of radiation in man is at least about 4-5 times the 1 Gy value thus far used. The concepts, assumptions, and the data-base used with the DD method have been re-examined. Arguments are advanced to support the thesis that ionizing radiation is probably not very efficient in inducing the very specific molecular changes that are known to underlie spontaneous mutations which cause naturally occurring dominant genetic diseases. It is suggested that (i) the DD estimate of 1 Gy that is used to estimate risk for autosomal dominant and X-linked diseases is conservative and (ii) the 1% prevalence figure for these diseases that is used for this purpose may be too high. If these suggestions are correct, then the estimate of risk for the dominant and X-linked diseases may need to be revised downwards.(ABSTRACT TRUNCATED AT 400 WORDS)

A large quantity of high purity InP crystal material has been produced by the phosphorus in-situ injection synthesis. In the injection method, phosphorus reacts with indium very quickly so that the rapid polycrystalline synthesis is possible. The injection speed, melt temperature, phosphorus excess, and so on are also important for a successful synthesis process. About 3200-4800 g stoichiometric high purity poly InP is synthesized reproducibly by improved P-injection method in the high-pressure puller. Twin-Free InP single crystals with diameter of 50-110 mm can be pulled after the synthesis. In the present work, the characterization of InP polycrystalline was studied by van der Pauw method, GDMS, and PL.

Cardiovascular and other chronic diseases are becoming the major causes of morbidity and mortality in most of the third world countries including India, especially in the southern Indian States, like Kerala, where most of the health indicators match closely with those of any developed country. Various behavioural risk factors (BRF) namely smoking, unhealthy diet, stress at home and work place, consumption of alcohol, sedentary life style, etc., are known to be risk factors for many such diseases. The present study was carried out to estimate the prevalence of various behavioural risk factors for chronic diseases, and to identify their biosocial correlates.A cross-sectional study was done in which the data were collected from a sample of 6579 individuals of age 30 to 74 yr, randomly selected following a stratified multi-stage cluster sampling design covering Kerala State. The important factors investigated include various behavioural risk factors, presenting chronic diseases and family histories among close relatives. The data were analysed using both univariate and multivariate analyses.The two major risk factors observed among males were smoking and alcohol consumption. About two fifths (40%) of them were current smokers as well as current users of alcohol (41%). The median age at initiation was 21 yr for both smoking habits and for alcohol consumption. Nearly a quarter of the target population were inactive (23% males and 22% females) based on work and leisure time activities. More than one-fifth of them (23%) reported stress. Obesity was found more among females (33%) than males (17%). Low socio-economic background was found to be a high predictor (high risk group) for habit of smoking, alcohol consumption, stress and unhealthy diet.Substantially high levels of the various behavioural risk factors among adults in Kerala suggests an urgent need for adopting healthy life style modifications among the population in general. The increased risk observed among the younger generation for behavioural risk factors such as smoking and alcohol consumption calls for urgent corrective steps and measures for long-term monitoring of all major risk factors as well as the major chronic disease conditions.

This paper presents a two dimensional numerical model for determining the d.c. characteristics of uniformly doped GaAs-MESFET (Metal semiconductor field effect transistor). The model takes into account all the major effects that determine the device characteristics in the illuminated condition. The 2-D potential distribution function in the active layer of the device is approximated as a parabolic function and the 2-D Poisson's equation has been solved with suitable boundary conditions to obtain the surface potential. The calculations have been carried out for uniform doping profile in two dimensions. Calculations have been carried out numerically for a GaAs-MESFET to examine the effect of illumination on current-voltage characteristics, depletion capacitance (C dP ), internal gate-to-source capacitance (C gs ), drain-to-source resistance (R ds ) and transconductance (g m ). The model takes into account the effect of photo-generation in the semi -insulating substrate region. The estimation of the channel voltage profile and the drain current characteristics has been obtained for the calculation of photo induced voltages at the Schottky contact under illumination. The model can be used to obtain the drain and the transfer characteristics under dark and illuminated conditions. The results show that the performance of the device is good and it can be used as photodetector for OEICs (Opto Electronic Integrated Circuits) applications. The proposed model is simple and easy to understand the behavior of the uniformly doped MESFET as compared to the other models reported in the literature.