Suppression of random dopant-induced threshold voltage fluctuations in sub-0.1-μm MOSFET's with epitaxial and delta-doped channels

A detailed three-dimensional (3-D) statistical 'atomistic' simulation study of fluctuation-resistant sub 0.1-μm MOSFET architectures with epitaxial channels and delta doping is presented. The need for enhancing the fluctuation resistance of the sub-0.1-μm generation transistors is highlighted by presenting summarized results from atomistic simulations of a wide range of conventional devices with uniformly doped channels. According to our atomistic results, the doping concentration dependence of the random dopant-induced threshold voltage fluctuations in conventional devices is stronger than the analytically predicted fourth-root dependence. As a result of this, the scaling of such devices will be restricted by the �intrinsic� random dopant-induced fluctuations earlier than anticipated. Our atomistic simulations confirm that the introduction of a thin epitaxial layer in the MOSFET's channel can efficiently suppress the random dopant-induced threshold voltage fluctuations in sub-0.1-μm devices. For the first time, we observe an �anomalous� reduction in the threshold voltage fluctuations with an increase in the doping concentration behind the epitaxial channel, which we attribute to screening effects. Also, for the first time we study the effect of a delta doping, positioned behind the epitaxial layer, on the intrinsic threshold voltage fluctuations. Above a certain thickness of epitaxial layer, we observe a pronounced anomalous decrease in the threshold voltage fluctuation with the increase of the delta doping. This phenomenon, which is also associated with screening, enhances the importance of the delta doping in the design of properly scaled fluctuation-resistant sub-0.1-μm MOSFET's

Allele-specific primer based identification of dimeric alpha-amylase inhibitor

Wheat is one of the most important staple food crops cultivated over 200 mha in the range of environment throughout the world. Wheat production must continue to increase by 2% annually, more particularly in developing world including south-east Asia. Besides increasing the inherent productivity of wheat, it is important to minimize the losses caused to production by various abiotic and biotic factors. Alpha–amylase inhibitors are attractive candidates for the control of seed weevils as these insects are highly dependent on starch as the energy source. They play an important role in the carbohydrate metabolism of many heterotrophic and autotrophic organisms. In this study, we aimed to make sequence comparison and phylogenetic relationship among dimeric alpha-amylase inhibitor genes. These genes were clustered into two major groups based on phylogenetic analysis. Multiple alignments show at least 24 candidates single nucleotide polymorphisms in inhibitor genes, which could further be exploited for SNPs based haplotype diversity among Indian released wheat genotype. We have detected dimeric alpha-amylase inhibitor genes in cultivated and wild ancestors of wheat using genome specific primers. Genes encoding dimeric alpha-amylase belong to the family of 24 kDa alpha-amylase inhibitors. In this study, specific primer pairs were designed based on SNPs of these genes and chromosome locations of inhibitor genes confirmed by amplification in accession of T. urartu, A. tauschii, and A. speltoides. Results obtained under this study support that inhibitor genes amplified with primer PSWDAIAF1/PSWDAIAF2 and PSWDAIBF1/PSWDAIBF2 is present on genome B. These results further support evidence at molecular level that dimeric alpha-amylase inhibitor in cultivated wheat is encoded by a multigene family.

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Slow pressure modes in thin accretion discs

Thin accretion discs around massive compact objects can support slow pressure modes of oscillations in the linear regime that have azimuthal wavenumber $m=1$. We consider finite, flat discs composed of barotropic fluid for various surface density profiles and demonstrate--through WKB analysis and numerical solution of the eigenvalue problem--that these modes are stable and have spatial scales comparable to the size of the disc. We show that the eigenvalue equation can be mapped to a Schr\"odinger-like equation. Analysis of this equation shows that all eigenmodes have discrete spectra. We find that all the models we have considered support negative frequency eigenmodes; however, the positive eigenfrequency modes are only present in power law discs, albeit for physically uninteresting values of the power law index $\beta$ and barotropic index $\gamma$.Comment: 9 pages, 7 figures, 1 table, accepted in MNRAS for pulicatio

What will anisotropies in the clustering pattern in redshifted 21 cm maps tell us?

The clustering pattern in high redshift HI maps is expected to be anisotropic due to two distinct reasons, the Alcock-Paczynski effect and the peculiar velocities, both of which are sensitive to the cosmological parameters. The signal is also expected to be sensitive to the details of the HI distribution at the epoch when the radiation originated. We use simple models for the HI distribution at the epoch of reionizaation and the post-reionization era to investigate exactly what we hope to learn from future observations of the anisotropy pattern in HI maps. We find that such observations will probably tell us more about the HI distribution than about the background cosmological model. Assuming that reionization can be described by spherical, ionized bubbles all of the same size with their centers possibly being biased with respect to the dark matter, we find that the anisotropy pattern at small angles is expected to have a bump at the characteristic angular size of the individual bubbles whereas the large scale anisotropy pattern will reflect the size and the bias of the bubbles. The anisotropy also depends on the background cosmological parameters, but the dependence is much weaker. Under the assumption that the HI in the post-reionization era traces the dark matter with a possible bias, we find that changing the bias and changing the background cosmology has similar effects on the anisotropy pattern. Combining observations of the anisotropy with independent estimates of the bias, possibly from the bi-spectrum, may allow these observations to constrain cosmological parameters.Comment: Minor changes, Accepted to MNRA