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Background: Small concentration of magnetic material, in general, the transition metal atoms (TM), when doped into a semiconductor, behaves as a diluted magnetic semiconductor (DMS). It has an application to Quantum computing & spintronic devices. DMS silicon carbide has strong coupling and high Curie temperature. The magnetic and electronic properties of SiC with TMs impurities have been in focus for theoretical and experimental researchers. Objective: The objective of this work is to study the electrical and magnetic properties of tungsten doped cubic SiC. Comparing the density of states plot with and without impurity, the change in property happening due to the presence of tungsten is observed. Partial density of states is also plotted and interpreted. Self-consistent spin polarized calculations are done to study the magnetic properties. Magnetic Moment is also calculated for substitutional doping of SiC at different sites. Methods: Tungsten doped 3C-SiC is investigated by using the first-principle energy code, Quantum Espresso, which uses pseudopotential within Density Functional Theory (DFT). The calculations are done by density functional pseudopotential energy calculations in periodic systems by solving iteratively the Kohn Sham equation in a plane wave basis set. Both norm conserving and Vanderbilt USPP are used. Self-consistent iterations were performed until convergence of total energy and total charge was obtained. We used different k-point meshes for different supercells with 16, 54 and 128 atoms giving results for carious impurity percentages. Results: The formation energy values obtained indicate that the W impurity prefers the Si site to the C site in cubic SiC. The presence of a narrow band towards the conduction band minimum is due to the W-d states for Si site substitution. Both spin-up and spin-down states contribute towards the valence band, and a small contribution goes towards the conduction band. The magnetic moment values for C site substitution are lower than Si site substitution. Conclusion: It is observed W doped with Si site of cubic silicon carbide shows ferromagnetic behavior. Hence, there is a possibility of 3C SiC doped with W at the C site to behave as a semi-insulating material.

Intraflagellar transport (IFT) sculpts the proteome of cilia and flagella; the antenna-like organelles found on the surface of virtually all human cell types. By delivering proteins to the growing ciliary tip, recycling turnover products, and selectively transporting signalling molecules, IFT has critical roles in cilia biogenesis, quality control, and signal transduction. IFT involves long polymeric arrays, termed IFT trains, which move to and from the ciliary tip under the power of the microtubule-based motor proteins kinesin-II and dynein-2. Recent top-down and bottom-up structural biology approaches are converging on the molecular architecture of the IFT train machinery. Here we review these studies, with a focus on how kinesin-II and dynein-2 assemble, attach to IFT trains, and undergo precise regulation to mediate bidirectional transport.

Cytoplasmic dynein-2 is a motor protein complex that drives the movement of cargoes along microtubules within cilia, facilitating the assembly of these organelles on the surface of nearly all mammalian cells. Dynein-2 is crucial for ciliary function, as evidenced by deleterious mutations in patients with skeletal abnormalities. Long-standing questions include how the dynein-2 complex is assembled, regulated, and switched between active and inactive states. A combination of model organisms, in vitro cell biology, live-cell imaging, structural biology and biochemistry has advanced our understanding of the dynein-2 motor. In this Cell Science at a Glance article and the accompanying poster, we discuss the current understanding of dynein-2 and its roles in ciliary assembly and function.

Trypanosomes of the genus Leishmania swim by undulating motions of a single flagellum driven by axonemal dynein ATPases, essential for parasite survival and infectivity. The flagellum possesses two waveforms; flagellar (tip-to-base) responsible for forward movements and ciliary (base-to-tip) possibly responsible for reorientation in response to changes in surroundings. However, the role of dyneins in regulating the two waveforms remains unknown. Moreover, the unpredictable nature of the parasite ciliary waveform makes it difficult to study. We have previously reported a detergent-extracted, ATP-reactivated model ideal for investigating flagellar motility regulation in Leishmania that allows one to generate reactivated Leishmania flagella with constitutively beating ciliary waves in presence of cyclic-AMP. Here, using three dynein inhibitors [erythro-9-(2-hydroxy-3-nonyl) adenine, ciliobrevin A and vanadate] we investigated the role of dyneins in regulating the two waveforms of Leishmania. Using high speed videomicroscopy we observed differential inhibition of beat frequencies and waveforms of flagellar and ciliary beats in live (in vivo) and ATP-reactivated (in vitro) parasites. Beat frequency of flagellar waveform was more strongly reduced than ciliary waveform. Surprisingly, inhibition of the ciliary waveform led to an altered phenotype with the distal half of the flagellum paralysed. ATPase assays confirmed that dynein activity of flagellar cells was more strongly inhibited compared to ciliary cells irrespective of the mechanism of inhibition. Possibly the two different waveforms are an outcome of changes in the mechanical properties of axonemal dyneins present at the tip of the flagellum that contains a sliding resistive structure. Our study suggests that dyneins responsible for the two waveforms in Leishmania bear different structural and functional conformations. Moreover, during ciliary beating, there is heterogeneity along the flagellum.

Mitogen-activated protein kinases (MAPKs) have been demonstrated to regulate flagellar/ciliary motility of spermatozoa and miracidia of Schistosoma mansoni . However, the role of MAPKs in mediating flagella-driven motility of Leishmania donovani is unexplored. We investigated the function of MAPKs in motility regulation of L. donovani using pharmacological inhibitors and activators of various MAPKs and fast-capture videomicroscopy. Our studies have revealed that the inhibitor of p38 MAPK, PD 169316, significantly affected various motility parameters such as flagellar beat frequency, parasite swimming speed, waveform of the flagellum and resulted in reduced parasite motility. Together, our results suggest that a MAPK, similar to human p38 MAPK, is implicated in flagellar motility regulation of L. donovani .

We have previously reported the involvement of cyclic AMP in regulating flagellar waveforms in Leishmania. Here, we investigated the roles of calcium, calmodulin, and calcineurin in flagellar motility regulation in L. donovani. Using high-speed videomicroscopy, we show that calcium-independent calmodulin and calcineurin activity is necessary for motility in Leishmania. Inhibition of calmodulin and calcineurin induced ciliary beats interrupting flagellar beating in both live (in vivo) and ATP-reactivated (in vitro) parasites. Our results indicate that signaling mediated by calmodulin and calcineurin operates antagonistically to cAMP signaling in regulating the waveforms of Leishmania flagellum. These two pathways are possibly involved in maintaining the balance between the two waveforms, essential for responding to environmental cues, survival, and infectivity.

Axonemal dyneins are members of AAA+ proteins involved in force generation and are responsible for flagellar motility in eukaryotes. In this study, we characterized the effects of ciliobrevin A (CbA), a dynein ATPase inhibitor, on flagella driven motility of the protozoan parasite Leishmania donovani. Using fast-capture video microscopy, we observed that CbA decreased flagellar beat frequency of swimming parasites in a concentration-dependent manner. Beat frequency of live and reactivated L. donovani decreased by approximately 89% and 41% respectively in the presence of 250μM CbA. This inhibition was lost when CbA was removed, suggesting its effects were reversible. CbA also altered wavelength and amplitude of the flagellum of live parasites. Waveform analysis of live and reactivated L. donovani revealed that CbA significantly affected flagellar waveform by inducing non-uniform bends with the flagellum beating away from the cell axis. These results suggest that CbA sensitive dynein ATPases possibly are responsible for power generation and waveform maintenance of the flagellum of L. donovani. This ability to inhibit axonemal dyneins also emphasizes the use of dynein inhibitors as valuable tools in studying functional roles of axonemal dyneins of flagellated eukaryotes.

Dynein-2 assembles with polymeric intraflagellar transport (IFT) trains to form a transport machinery that is crucial for cilia biogenesis and signaling. Here we recombinantly expressed the ~1.4-MDa human dynein-2 complex and solved its cryo-EM structure to near-atomic resolution. The two identical copies of the dynein-2 heavy chain are contorted into different conformations by a WDR60-WDR34 heterodimer and a block of two RB and six LC8 light chains. One heavy chain is steered into a zig-zag conformation, which matches the periodicity of the anterograde IFT-B train. Contacts between adjacent dyneins along the train indicate a cooperative mode of assembly. Removal of the WDR60-WDR34-light chain subcomplex renders dynein-2 monomeric and relieves autoinhibition of its motility. Our results converge on a model in which an unusual stoichiometry of non-motor subunits controls dynein-2 assembly, asymmetry, and activity, giving mechanistic insight into the interaction of dynein-2 with IFT trains and the origin of diverse functions in the dynein family.

Dyneins are high molecular weight microtubule based motor proteins responsible for beating of the flagellum. The flagellum is important for the viability of trypanosomes like Leishmania. However, very little is known about dynein and its role in flagellar motility in such trypanosomatid species. Here, we have identified genes in five species of Leishmania that code for outer-arm dynein (OAD) heavy chains α and β, and inner-arm dynein (IAD) heavy chains 1α and 1β using BLAST and MSA. Our sequence analysis indicates that unlike the three-headed outer-arm dyneins of Chlamydomonas and Tetrahymena, the outer-arm dyneins of the genus Leishmania are two-headed, lacking the γ chain like that of metazoans. N-terminal sequence analysis revealed a conserved IQ-like calmodulin binding motif in the outer-arm α and inner-arm 1α dynein heavy chain in the five species of Leishmania similar to Chlamydomonas reinhardtii outer-arm γ. It was predicted that both motifs were incapable of binding calmodulin. Phosphorylation site prediction revealed conserved serine and threonine residues in outer-arm dynein α and inner-arm 1α as putative phosphorylation sites exclusive to Leishmania but not in Trypanosoma brucei suggesting that regulation of dynein activity might be via phosphorylation of these IQ-like motifs in Leishmania sp., Highlights • Identified outer and inner-arm dynein heavy chain genes in five Leishmania species. • Outer-arm dyneins of the genus Leishmania are two-headed like metazoans. • Conserved IQ-like motif present in outer-arm α and inner-arm 1α in Leishmania sp. • Conserved serine and threonine residues in dynein arms exclusive to Leishmania sp. • Possible regulation of dynein activity via phosphorylation of these IQ-like motifs.

We present ab initio density functional theory (DFT) calculations on the effect of in-plane equi-biaxial strain on the structural and electronic properties of graphene-like GaN monolayer (ML-GaN). For compressive strain in excess of 7.2%, ML-GaN gets buckled; buckling parameter increases quadratically with compressive strain. The 2D bulk modulus of ML-GaN was found to be smaller than that of graphene and graphene-like ML-BN, which reflects weaker bond in ML-GaN. More importantly, the bandgap and effective masses of charge carriers in ML-GaN were found to be tunable by application of in-plane equi-biaxial strain. In particular, when compressive biaxial strain of about 3% was reached, a transition from indirect to direct bandgap-phase occurred with change in the value and nature of effective masses of charge carriers; buckling and tensile strain reduced the bandgap — the bandgap reduced to 50% of its unstrained value at 6.36% tensile strain and to 0 eV at an extrapolated tensile strain of 12.72%, which is well within its predicted ultimate tensile strain limit of 16%. These predictions of strain-engineered electronic properties of highly strain sensitive ML-GaN may be exploited in future for potential applications in strain sensors and other nanodevices such as the nano-electromechanical systems (NEMS).

OBJECTIVE : to critically analyze the prevention of parent to child transmission (PPTCT) services offered by a teaching institute located in the Darjeeling district of West Bengal, since it started five years ago. METHOD : All the women registered in the antenatal clinic from 1st January 2004 to 31 st December 2008 were tested for HIV after counseling. Spouse counseling and testing of spouse and children was done where possible. Antiretroviral prophylaxis with Nevirapine was given to laboring mothers and their neonates. All data were compiled retrospectively and analyzed. RESULTS : A total 26319 women were offered counseling during the period. The acceptance of testing rose from 66.32% in 2004 to 90.7% in 2008. The highest seroprevalence was observed in 2007(0.84%) which had dropped in 2008(0.44%). The majority of the 112 seropositive women were rural residents, housewives, practicing no contraception, yet with some knowledge about HIV and its mode of transmission. There has been an increase in institutional delivery and cesarean section from 2004 to 2008. ARV prophylaxis with Nevirapine was given to all 35 women identified to be HIV positive before delivery. Out of 48 live born babies 46 received Nevirapine syrup. CONCLUSION : Seroprevalence has dropped with a greater awareness and acceptance of PPTCT program in the

In this study, inspired by the work of K. Nakazato and K. Kitahara [Prog. Theor. Phys. 64, 2261 (1980)], we consider the theoretical problem of tracer particle diffusion in an environment of diffusing hardcore interacting crowder particles. The tracer particle has a different diffusion constant from the crowder particles. Based on a transformation of the generating function, we provide an exact formal expansion for the tracer particle probability density, valid for any lattice in the thermodynamic limit. By applying this formal solution to dynamics on regular Bravais lattices we provide a closed form approximation for the tracer particle diffusion constant which extends the Nakazato and Kitahara results to include also b.c.c. and f.c.c. lattices. Finally, we compare our analytical results to simulations in two and three dimensions., Comment: 28 pages with appendix, 5 figure. To appear in JSTAT

The flagellum of parasitic trypanosomes is a multifunctional appendage essential for its viability and infectivity. However, the biological mechanisms that make the flagellum so dynamic remains unexplored. No method is available to access and induce axonemal motility at will to decipher motility regulation in trypanosomes. For the first time we report the development of a detergent-extracted/demembranated ATP-reactivated model for studying flagellar motility in Leishmania. Flagellar beat parameters of reactivated parasites were similar to live ones. Using this model we discovered that cAMP (both exogenous and endogenous) induced flagellar wave reversal to a ciliary waveform in reactivated parasites via cAMP-dependent protein kinase A. The effect was reversible and highly specific. Such an effect of cAMP on the flagellar waveform has never been observed before in any organism. Flagellar wave reversal allows parasites to change direction of swimming. Our findings suggest a possible cAMP-dependent mechanism by which Leishmania responds to its surrounding microenvironment, necessary for its survival. Our demembranated-reactivated model not only serves as an important tool for functional studies of flagellated eukaryotic parasites but has the potential to understand ciliary motility regulation with possible implication on human ciliopathies.

Using full-potential density functional calculations within local density approximation (LDA), we predict that mechanically tunable band-gap and quasi-particle-effective-mass are realizable in graphene/hexagonal-BN hetero-bilayer (C/h-BN HBL) by application of in-plane homogeneous biaxial strain. While providing one of the possible reasons for the experimentally observed gap-less pristine-graphene-like electronic properties of C/h-BN HBL, which theoretically has a narrow band-gap, we suggest a schematic experiment for verification of our results which may find applications in nano-electromechanical systems (NEMS), nano opto-mechanical systems (NOMS) and other nano-devices based on C/h-BN HBL., Comment: 9 pages, 8 figures

Degradation by human impact, poverty and limited ecological knowledge pose challenges for aquatic macrophyte restoration in India. The present paper proposes a framework for restoration of aquatic macrophytes in both freshwater and wastewater lentic ecosystems. The framework includes both ecological and economic aspects of aquatic macrophytes.

The optical properties of a material are characterized by its electric and magnetic susceptibilities. Finding analytical expressions for those quantities for a nanoparticle of arbitrary shape is generally a formidable task. A great deal of insight in to the basic phenomena can be obtained by studying analytically solvable cases, for nanoparticles of ellipsoidal and spherical shapes. We present here our study on the scattering and absorptive properties of multiply coated magnetic spherical and elliptical nanoparticles as functions of frequency of an incident electromagnetic radiation. We will present our results based on the analytical expressions for the dielectric and magnetic susceptibilities derived for such multiply coated nanoparticles. To our knowledge, the latter results are new. We will also present our results based on Maxwell-Garnett theory for a material having uniform distribution of mono dispersed multiply coated nanoparticles.

A study was conducted to ascertain monthly changes in biomass of the plant and nutrient content in various organs of Nymphoides hydrophylla grown in a tropical pond during September 1999–August 2000 in relation to environmental factors. Biomass of N. hydrophylla ranged from 25 to 247 g dry weight m−2. Among the various organs, leaf blade showed highest nitrogen (3.0–4.6%) and phosphorus content (0.9–2.4%). Comparative data of three Nymphoides species showed that N. peltata, the temperate species, had maximum potential of biomass production while long flowering period, year around growth, higher nitrogen content in various organs and presence of other associated flora were unique features of tropical species (N. hydrophylla and N. indica). Both water temperature and water level together appeared to be the best environmental variables that significantly explained the variability in biomass of N. hydrophylla.

The presence of different species of hydrophytes was investigated in relation to Secchi disk visibility, pH, dissolved oxygen, electrical conductivity, total Kjeldahl nitrogen, total phosphorus and chlorophyll-a concentration in two tropical ponds nearby Kolkata, India, during a three years period (June 1999 to May 2002). The dominant flora in the ponds namely, Alternanthera philoxeroides, Nymphoides hydrophylla, Lemna aequinoctialis, and Vallisneria spiralis were found to subsist over a wide amplitude of nutrient levels thereby showing their adaptability to highly eutrophic ecosystems, a common feature of the tropics. However, the presence of some minor species could be associated with a narrow range of specific limnological variables.

The ability of aquatic macrophytes to maintain water clarity was investigated in two tropical ponds [1999–2001]. Low chlorophyll‐a concentration (0.2–3.5 mg/m3) was observed throughout the study period, which reflected the absence of any algal bloom. At a high coverage (≥ 90%), the ability of Vallisneria spiralis to maintain Secchi disk transparency (> 2 m) extended to the deepest point (3.5–4.4 m) even at high Kjeldahl nitrogen (1.2–29.8 mg/l) and total phosphorus levels (0.2–1.2 mg/l).

The variability in water chemistry of samples taken on a monthly basis (March 1999 to February 2000) from two shallow tropical ponds was studied. The effect of location and pond depth on water chemistry was also examined. The study demonstrated that intra-annual variability in nutrient concentration is high. Thus, a high annual sampling frequency is required to provide representative annual mean water quality data. Routine monitoring during the monsoons is important for studies on dissolved oxygen and macrophyte growth. Significant differences were found between the topmost and bottommost points for samples of dissolved oxygen collected from the deepest part of both ponds. For nutrient analysis (nitrogen and phosphorus), sample from any location was found to be representative of the whole pond.

Using full-potential density functional theory (DFT) calculations we show that the band gap and effective masses of charge carriers in SiC monolayer (ML-SiC) in graphene-like two-dimensional honeycomb structure are tunable by strain engineering. ML-SiC was found to preserve its flat 2D graphene-like structure under compressive strain up to 7%. A transition from indirect-to-direct gap-phase is predicted to occur for a strain value lying within the interval (1.11 %, 1.76%). In both gap-phases band gap decreases with increasing strain, although the rate of decrease is different in the two gap-phases. Effective mass of electrons show a non-linearly decreasing trend with increasing tensile strain in the direct gap-phase. The strain-sensitive properties of ML-SiC, may find applications in future strain-sensors, nanoelectromechanical systems (NEMS) and nano-optomechanical systems (NOMS) and other nano-devices.

In this paper, we present a new method along the spirit of the constant coupling (CC) method for a pair, but now extended to a cluster of spins. We shall call this the constant coupling cluster (CCC) method. It is known that the CC approximation can be obtained as an approximation from the cluster expansion method. This gives us some justification for the use of this approximation. We present a comparative study of the present CCC method with the Bethe-Peierls-Weiss (BPW) and CC method. We find that it does not have the defects of the BPW method nor does it have the defects of the CC method and yet it is easily amenable for applications to complicated magnetic structures, which require multisublattice description.

We present a study of a group of B-site spinel ferrimagnetic compounds having magnetic properties dominated by strong ferromagnetic interactions, using a modified Bethe-Peierls-Weiss (BPW) method. We obtain the exchange parameters by studying the transition temperature and the inverse susceptibility curves. We use a method for obtaining the exchange constants using the ratio between the transition temperatures obtained by the Weiss molecular field theory and a more advanced theory, such as high temperature expansion, and compare the ratio with the experimental data. We also study the inverse magnetic susceptibility curves which, for the case of dominant ferromagnetic interactions, are linear in the high temperature limit and have nonlinear behaviour near the transition temperature. In particular, we study systems such as MCr2X4, where M = Cd,Hg and X = S,Se, which are ferrimagnetic spinels, for which we find excellent fits to the experimental magnetic susceptibility data using the modified BPW method.

A quasi 1-D quantum mechanical compact model for the gate tunneling current of the metal gate(TiN)/high-k(HfO2)/SiO2/p-Si nMOS capacitor is presented. With this model, measured gate leakage data is investigated using direct tunneling, multiphonon inelastic tunneling, and the Poole-Frenkel conduction mechanism. The thicker devices present a Poole-Frenkel like behaviour. The relative contributions of direct tunneling and the Poole-Frenkel like conduction to the gate leakage for intermediate thickness devices remain unresolved, while the thinner devices exhibit direct tunneling and inelastic tunneling as the dominant mechanisms.

Our First-principles Full-Potential Density Functional Theory (DFT) calculations show that a monolayer of ZnS (ML-ZnS), which is predicted to adopt a graphene-like planar honeycomb structure with a direct band gap, undergoes strain-induced modifications in its structure and band gap when subjected to in-plane homogeneous biaxial strain ($\delta$). ML-ZnS gets buckled for compressive strain greater than 0.92%; the buckling parameter $\Delta$ (= 0.00 \AA\, for planar ML-ZnS) linearly increases with increasing compressive strain ($\Delta = 0.435$ \AA \,at $\delta = - 5.25$%). A tensile strain of 2.91% turns the direct band gap of ML-ZnS into indirect. Within our considered strain values of $|\delta| < 6%$, the band gap shows linearly decreasing (non-linearly increasing as well as decreasing) variation with tensile (compressive) strain. These predictions may be exploited in future for potential applications in strain sensors and other nano-devices such as the nano-electromechanical systems (NEMS)., Comment: 8 pages including the cover page. 5 figures. arXiv admin note: text overlap with arXiv:1210.3309

Previously, we discussed a purely classical model for analysing surface plasmons of the molecule. The molecule was described as an abrupt spherical shell containing an effective number of or electrons. This simple model was found to be quite applicable for analysis of electron energy loss spectra (EELS), describing the main features of the experimentally observed collective resonances of electrons. In this study we have extended our earlier classical model using spherically averaged radial charge distributions of constructed using different numbers of valence electrons. These charge distributions have been obtained from a self-consistent local density calculation, based on a molecular-orbital linear combination of atomic orbitals (MO-LCAO) approach. Use of this type of smooth charge distribution introduces, together with causality, a natural broadening of the collective resonances.

We have previously demonstrated the existence of a rich spectrum of collective resonances for both carbon tubes and carbon onions using a classical electrodynamic model. Collective resonances in these systems are predicted to dominate their respective UV spectra. In this study we present results which demonstrate how the coupling between the shells via the Coulomb interaction completely determines the absorption cross section. The outermost shells are strongly screened for low frequencies and frequencies close to the effective plasma frequency of the shells.

Using full-potential density functional theory (DFT) calculations, we found a small asymmetry in the Fermi velocity of electrons and holes in graphene. These Fermi velocity values and their average were found to decrease with increasing in-plane homogeneous biaxial strain; the variation in Fermi velocity is quadratic in strain. The results, which can be verified by Landau level spectroscopy and quantum capacitance measurements of bi-axially strained graphene, promise potential applications in graphene based straintronics and flexible electronics., Comment: 4 pages, 3 figures. SOLID STATE PHYSICS: Proceedings of the 57th DAE Solid State Physics Symposium 2012, Indian Institute of Technology Bombay, Mumbai, India, 3-7 December 2012, Editors: A. K. Chauhan, Chitra Murli and S. C. Gadkari

Using full-potential density functional calculations we have investigated the structural and electronic properties of graphene and some of its structural analogues, viz., monolayer (ML) of SiC, GeC, BN, AlN, GaN, ZnO, ZnS and ZnSe. While our calculations corroborate some of the reported results based on different methods, our results on ZnSe, the two dimensional bulk modulus of ML-GeC, ML-AlN, ML-GaN, ML-ZnO and ML-ZnS and the effective masses of the charge carriers in these binary mono-layers are something new. With the current progress in synthesis techniques, some of these new materials may be synthesized in near future for applications in nano-devices., Comment: 16 pages including the cover page, 6 figures. A lot of errors (some of which are significant) in published version in the "World Journal of Engineering" have been rectified in this e-print version

We present ab initio calculations which show that the direct-band-gap, effective masses and Fermi velocities of charge carriers in ZnO monolayer (ML-ZnO) in graphene-like honeycomb structure are all tunable by application of in-plane homogeneous biaxial strain. Within our simulated strain limit of $\pm 10$%, the band gap remains direct and shows a strong non-linear variation with strain. Moreover, the average Fermi velocity of electrons in unstrained ML-ZnO is of the same order of magnitude as that in graphene. The results promise potential applications of ML-ZnO in mechatronics/straintronics and other nanodevices such as the nano-electromechanical systems (NEMS) and nano-optomechanical systems (NOMS)., Comment: 6 pages, 5 figures

In a large number of diverse phenomena one encounters the response of nano-particles to electromagnetic fields; for example, the winter fog or smog etc., are the response of nano-sized particles in the atmosphere towards scattering and absorption of light. In this lecture, we will first discuss the scattering and absorption of light by spherical particles and then dipolar response of spheres.

We report here our study on SiC doped with transition metals using first principle density functional theory calculations. We have considered cubic SiC with 3d transition metals as substitutional impurities for Si and C site separately. Cubic SiC doped with Cr, Mn, show ferromagnetism whereas with Sc, Ti, V and Co show site dependency of magnetic properties. Rests of the impurities are found to be non-magnetic., Presented in the 55th DAE-Solid State Physics Symposium, 26th to 30th December, 2010, Manipal University, Manipal, India; AIP Conf. Proc. 1349, 1087-1088 (2011)

The ground state structural and electronic properties of germanene (the germanium analogue of graphene) are investigated using first-principles calculations. On structure optimization, the graphene-like honeycomb structure of germanene turns out as buckled (buckling parameter $\Delta = 0.635$ \AA) in contrast with graphene's planar structure (buckling parameter $\Delta = 0.0$ \AA). In spite of this, germanene has similar electronic structure as that of graphene. While corroborating the reported results, we newly predict the in-plane contraction of hexagonal Ge with (thermal) stretching along the "c" axis, akin to a phenomenon observed in graphite., Comment: Presented in Solid State Physics, Proceedings of the 55th DAE Solid State Physics Symposium 2010, 26-30 December 2010, Manipal, India; Editors: Alka B. Garg, R. Mittal and R. Mukhopadhyay, Bhabha Atomic Research Centre, Mumbai, India; AIP Conference Proceedings 1349, 823-824 (2011). Few typographic errors in the published version corrected; 2pagges, 1 figure

We present here a mathematical formulation determining the enhancement factors of Raman scattered light from molecules adsorbed on to multiply coated ellipsoidal particles. We use this formulation to present enhancement of Raman scattering from molecules, such as pyridine and CV from nanoparticles of gold and silver as well as their core-shell structures with magnetic metal cobalt. The nanoparticles of these metals are widely used in biomedical applications. We also present results for the cases when the nanoparticle is covered with a monolayer of Raman active molecules and dispersed randomly in a medium. Our results can be of importance in medical technology.

Large memory window (6–9V) program/erase (P/E) cycling endurance is studied for evaluating their suitability for MLC operation. Effect of NC area coverage and device size is evaluated using statistical method. Constant voltage stress (CVS) measurements and 2-D simulations are extensively used to evaluate the impact of carrier; type, fluence, and energy on the defect generation process in the gate stack. Degradation during P and E are isolated to allow individual optimization for improving the cycling reliability. P/E cycling endurance ≫104 at 8V MW and ≫2.5×103 at 9V MW are shown for first time in metal NC memory devices using the proposed distributed cycling scheme.

In the presence of applied magnetic fields, magnetic nanoparticles suspended in a colloidal ferrofluid align themselves in chains if the inter-particle force due to induced dipolar interactions within the chain dominates over the thermal randomization. The variation of this chain force with the interparticle separation and particle volume has been studied in the past for the special case of spherical particles. In the present paper the dependence of the chain-force on the shape of the suspended nanoparticles of prolate spheroidal type has been investigated. Starting with the case of a sphere (eccentricity e = 0), the shape is evolved by varying the eccentricity of the spheroid up to the limiting case of a nano-rod (eccentricity e = 1) while keeping the particle volume and the inter-particle separation fixed. For the first time in our knowledge, the expressions for the bulk susceptibility and hence the induced magnetization of ellipsoidal nanoparticles have been derived and used for the present problem. The variation of chain-force with the inter-particle separation for a fixed shape is also presented.

This paper reviews recent advances in Charge Trap Flash (CTF) memories. CTFs are predicted to replace the traditional floating-gate flash devices beyond the 32 nm node. The paper focuses on work done at IIT Bombay in the areas of both nitride-based SONOS devices as well as nanocrystal (NC)-based devices. For SONOS devices, results are presented for optimization of the nitride layer to obtain the best characteristics, and the simulation of the program/erase transients. For NC devices, experimental characteristics of single and dual layer cells, as well as simulation results are presented.

Nanocrystal (NC) based memory devices are considered a possible alternative for floating gate (FG) replacement below 30nm node. In this work, endurance reliability of Pt NC devices is investigated for single layer (SL) and dual layer (DL) structures. The degradation in the devices due to Program/Erase (P/E) stress is investigated. Relative improvement in reliability of DL structure over SL structure is shown. A physical model for defect generation in the gate stack is proposed which is able to explain endurance and post-cycling characteristics. Dual layer structure is shown to have better inherent reliability over single layer structure.

The scattering of electromagnetic (e.m.) waves by small ellipsoidal particles having non-zero dielectric or magnetic susceptibility have been studied extensively. The studies in case the particles have non-zero dielectric as well as magnetic susceptibility have been limited to small uncoated particles of spherical shapes. We present here a study of the scattering of e.m. waves by small ellipsoidal particles having non-zero dielectric as well as magnetic susceptibility. We refer to such particles as magnetic particles. The ellipsoidal particles in our case can have multiple ellipsoidal coatings having common focii and axes. By deriving analytical expressions for the magnetic and electric scattering coefficients for such particles, we show that there is drastic difference between the backscattering as well as forward scattering patterns of the non-magnetic and magnetic particles. We also compare the scattering patterns of magnetic ellipsoidal and spherical particles. Furthermore, we derive Maxwell-Garnett formula for multiply coated magnetic ellipsoidal particles. To our knowledge, our results are new and should be useful for plasmonics and meta-materials designs.

©2006 The American Physical Society "selected for the February 27, 2006 issue of Virtual Journal of Nanoscale Science & Technology available at http://www.vjnano.org.", We present an analytic theory for the optical properties of ellipsoidal plasmonic particles covered by anisotropic molecular layers. The theory is applied to the case of a prolate spheroid covered by chromophores oriented parallel and perpendicular to the metal surface. For the case that the molecular layer resonance frequency is close to being degenerate with one of the particle plasmon resonances strong hybridization between the two resonances occurs. Approximate analytic expressions for the hybridized resonance frequencies, their extinction cross-section peak heights, and widths are derived. The strength of the molecular-plasmon interaction is found to be strongly dependent on olecular orientation and suggests that this sensitivity could be the basis for novel nanoparticle based bio- and chemo-sensing applications.

Awareness of attitudes to different types of medicine is very important for estabishment of cancer prevention programs. Alternative medicine has become an important feature of oncology regardless of geographic region, and in India, the majority of cancer patients present at late advance stage of disease when curative treatment cannot be initiated. Given the lack of facilities it is no surprise that many Indian cancer patients try various complementary and alternative medicines, depsite the fact that little is known about their therapeutic efficacy and toxicity. A study was conducted in 300 biopsy proven cancer patients undergoing alternative cancer therapy with Psorinum in Kolkata. The main aim of the study was to analyze the patients'/caregivers narratives regarding the therapy they have been trying. One hundred and ninety five patients (65%) have consulted their oncologists before trying this therapy. About 18.5% of the patients expressed satisfaction with the therapy due to the holistic nature and team approach employed for patient management. The cost of the therapy was within the reach of many cancer patients belonging to the underprivileged segment of the society, contributing to its immense popularity in Kolkata. Whether this can be translated into a willingness to use similar natural compounds for cancer prevention and treatment purposes now needs to be analysed.

©2005 The American Physical Society, A cluster consisting of many atoms or molecules may be considered, in some circumstances, to be a single large molecule with a well-defined polarizability. Once the polarizability of such a cluster is known, one can evaluate certain properties—e.g. the cluster’s van der Waals interactions, using expressions derived for atoms or molecules. In the present work, we evaluate the static polarizability of a cluster using a microscopic method that is exact within the linear and dipolar approximations. Numerical examples are presented for various shapes and sizes of clusters composed of identical atoms, where the term “atom” actually refers to a generic constituent, which could be any polarizable entity. The results for the clusters’ polarizabilities are compared with those obtained by assuming simple additivity of the constituents’ atomic polarizabilities; in many cases, the difference is large, demonstrating the inadequacy of the dditivity approximation. Comparison is made for symmetrical geometries with results obtained from continuum models of the polarizability. Also, the surface effects due to the nonuniform local field near a surface or edge are shown to be significant.