Intrinsic Limits of Subthreshold Slope in Biased Bilayer Graphene Transistor

In this work, we investigate the intrinsic limits of subthreshold slope in a dual gated bilayer graphene transistor using a coupled self-consistent Poisson-bandstructure solver. We benchmark the solver by matching the bias dependent bandgap results obtained from the solver against published experimental data. We show that the intrinsic bias dependence of the electronic structure and the self-consistent electrostatics limit the subthreshold slope obtained in such a transistor well above the Boltzmann limit of 60mV/decade at room temperature, but much below the results experimentally shown till date, indicating room for technological improvement of bilayer graphene.Comment: 10 pages, 2 figure

External Bias Dependent Direct To Indirect Bandgap Transition in Graphene Nanoribbon

In this work, using self-consistent tight-binding calculations, for the first time, we show that a direct to indirect bandgap transition is possible in an armchair graphene nanoribbon by the application of an external bias along the width of the ribbon, opening up the possibility of new device applications. With the help of Dirac equation, we qualitatively explain this bandgap transition using the asymmetry in the spatial distribution of the perturbation potential produced inside the nanoribbon by the external bias. This is followed by the verification of the bandgap trends with a numerical technique using Magnus expansion of matrix exponentials. Finally, we show that the carrier effective masses possess tunable sharp characters in the vicinity of the bandgap transition points.Comment: Accepted for publication in Nano Letter

Large magnetoresistance anomalies in Dy7Rh3

The compound Dy7Rh3 ordering antiferromagnetically below (TN=) 59 K has been known to exhibit a temperature (T) dependent electrical resistivity (rho) behavior in the paramagnetic state unusual for intermetallic compounds in the sense that there is a broad peak in rho(T) in the paramagnetic state (around 130 K) as though there is a semi-conductor to metal transition. In addition, there is an upturn below T_N due to magnetic super-zone gap effects. Here we report the influence of external magnetic field (H) on the rho(T) behavior of this compound below 300 K. The rise of rho(T) found below TN could be suppressed at very high fields (>> 60 kOe), thus resulting in a very large magnetoresistance (MR) in the magnetically ordered state. The most notable finding is that the magnitude of MR is large for moderate applications of H (say 80 kOe) in a temperature range far above T_N as well, which is untypical of intermetallic compounds. Thus, this compound is characterized by large MR anomalies in the entire T range of investigation.Comment: IOP Selec

The Persistence of Long-Term Memory A Molecular Approach to Self-Sustaining Changes in Learning-Induced Synaptic Growth

AbstractRecent cellular and molecular studies of both implicit and explicit memory storage suggest that experience-dependent modulation of synaptic strength and structure is a fundamental mechanism by which these diverse forms of memory are encoded and stored. For both forms of memory storage, some type of synaptic growth is thought to represent the stable cellular change that maintains the long-term process. In this review, we discuss recent findings on the molecular events that underlie learning-related synaptic growth in Aplysia and discuss the possibility that an active, prion-based mechanism is important for the maintenance of the structural change and for the persistence of long-term memory

Magnetized Plasma Sheath in the Presence of Negative Ions

The sheath formation in a weakly magnetized collisionless electronegative plasma consisting of electrons, negative and positive ions has been numerically investigated using the hydrodynamic equations. The electrons and negative ions are assumed to follow Boltzmann relation. A sheath formation criterion has been analytically derived. The paper focuses on studying the sheath structure by varying the electronegativity. It has been observed that the presence of negative ions has a substantial effect on the sheath structure. The observations made in the present work have profound significance on processing plasmas, especially in the semiconductor industry as well as in fusion studies

Cooperative polymer dynamics under nanoscopic pore confinements probed by field-cycling NMR relaxometry

Reptational dynamics of bulk polymer chains on a time scale between the Rouse mode relaxation time and the so-called disengagement time is not compatible with the basic thermodynamic law of fluctuations of the number of segments in a given volume. On the other hand, experimental field-cycling NMR relaxometry data of perfluoropolyether melts confined in Vycor, a porous silica glass of nominal pore dimension of 4 nm, closely display the predicted signatures for the molecular weight and frequency dependences of the spin-lattice relaxation time in this particular limit, namely T1 M-12 12. It is shown that this contradiction is an apparent one. In this paper a formalism is developed suggesting cooperative chain dynamics under nanoscopic pore confinements. The result is a cooperative reptational displacement phenomenon reducing the root-mean-squared displacement rate correspondingly but showing the same characteristic dependences as the ordinary reptation model. The tube diameter effective for cooperative reptation is estimated on this basis for the sample system under consideration and is found to be of the same order of magnitude as the nominal pore diameter of Vycor. © 2007 American Institute of Physics

An anomalous magnetic phase transition at 10 K in Nd7Rh3

The compound, Nd7Rh3, crystallizing in Th7Fe3-type hexagonal structure, has been shown recently by us to exhibit a signature of magnetic phase-coexistence phenomenon below 10 K after a field cycling, uncharacteristic of stoichiometric intermetallic compounds, bearing a relevance to the trends in the field of electronic phase-separation. In order to characterize this compound further, we have carried out dc magnetic susceptibility (chi), electrical resistivity, magnetoresistance and heat-capacity measurements as a function temperature (T= 1.8 to 300 K). The results reveal that this compound exhibits another unusual finding at the 10K-transition in the sense that the plot of chi(T) shows a sharp increase in the field-cooled cycle, whereas the zero-field-cooled curve shows a downturn below the transition. In addition, the sign of magnetoresistance is negative and the magnitude is large over a wide temperature range in the vicinity of magnetic ordering temperature, with a sharp variation at 10 K. The results indicate that the transition below 10 K is first-order in its character.Comment: Appeared in JPCM (Letters) 18 (2006) L40

Recurrent miscarriage in North Indian population: a study of association of polymorphisms in genes coding for the natural killer: cell receptor natural killer group 2, member D and its ligand MHC class I chain-related protein A

Background: The objective of this present study was to investigate the possible association of natural killer group (NKG) receptors gene polymorphisms and MHC class I chain-related protein A (MICA) gene polymorphism with recurrent spontaneous abortion (RSA).Methods: Three single-nucleotide polymorphism (SNPs) in NKG2D gene (rs2255336, rs2617160 and rs2617170) and one SNP in MICA gene (MICA129) rs1051792 were assessed in 100 controls and 100 patients employing polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and agarose gel electrophoresis.Results: NKG2D (rs2617160) and MICA 129 (rs1051792) variants are associated with RSA risk in North Indian women.Conclusions: The NKG2D and MICA129 gene polymorphisms may influence the success of pregnancy in North Indian women population