Metal-insulator transition in perovskite oxides: Tunneling experiments

In this paper we have investigated the composition-driven metal-insulator (MI) transitions in two ABO3 classes of perovskite oxides (LaNixCo1-xO3 and NaxTayW1-yO3) in the composition range close to the critical region by using the tunneling technique. Two types of junctions (point-contact and planar) have been used for the investigation covering the temperature range 0.4 Kjunction conductance G(V) [=dI/dV] decreases near the zero-bias region as the MI transition is approached. However, there is a fairly strong thermal-smearing effect near the zero-bias region for ?V?<10kBT/e. $G(V)� has been found to follow a power law of the type G(V)=G0(1+{?V?/V*}n) with V*=const and with n=0.5 for samples in the weak-localization region. However, as the critical region of the MI transition is approached G0?0 and n?1. We also find that for samples lying in the weak-localization region ?=eV* has a well-defined dependence on ?0, the zero-temperature conductivity. The observed behavior can be explained either as a manifestation of depletion of density of states at the Fermi level as the MI transition is approached or as a manifestation of strong inelastic scattering in the junction region.

Molecular organization of the gene encoding Xenopus laevis transforming growth factor-beta 5

Transforming growth factor-beta s (TGF-beta 5) are multifunctional polypeptides, known to influence proliferation and differentiation of many cell types. TGF-beta 5 cDNA was cloned from Xenopus laevis and this isoform is unique to the amphibians. Here, we report the isolation and characterization of the TGF-beta 5 genomic clones to determine the structure of TGF-beta 5 gene. The gene consists of seven exons and all intron-exon boundaries follow the GT-AG consensus. The organization of TGF-beta 5 gene was identical to that of the mammalian TGF-beta isoforms, with the exception of position of the first splice junction. We determined the size of TGF-beta 5 gene to be approximately 20 kb.

Popular mixed matchings

We study the problem of matching applicants to jobs under one-sided preferences; that is, each applicant ranks a non-empty subset of jobs under an order of preference, possibly involving ties. A matching M is said to be more popular than T if the applicants that prefer M to T outnumber those that prefer T to M. A matching is said to be popular if there is no matching more popular than it. Equivalently, a matching M is popular if phi(M, T) >= phi(T, M) for all matchings T, where phi(X, Y) is the number of applicants that prefer X to Y. Previously studied solution concepts based on the popularity criterion are either not guaranteed to exist for every instance (e.g., popular matchings) or are NP-hard to compute (e.g., least unpopular matchings). This paper addresses this issue by considering mixed matchings. A mixed matching is simply a probability distribution over matchings in the input graph. The function phi that compares two matchings generalizes in a natural manner to mixed matchings by taking expectation. A mixed matching P is popular if phi(P, Q) >= phi(Q, P) for all mixed matchings Q. We show that popular mixed matchings always exist and we design polynomial time algorithms for finding them. Then we study their efficiency and give tight bounds on the price of anarchy and price of stability of the popular matching problem. (C) 2010 Elsevier B.V. All rights reserved.

Thiophene adsorption studies on clean and hydrogen-preadsorbed MoS2(100) surface

It is known from temperature-programmed desorption studies that the binding energy of thiophene over Mo/gamma-Al2O3 and Co-Mo/gamma-Al2O3, hydrodesulfurization catalysts, is lower in the presence of hydrogen. The adsorption of thiophene on clean and hydrogen-adsorbed MoS2 was modelled using extended Huckel tight binding band structure calculations. In the eta(1) adsorption configuration the calculations show a lower binding energy for adsorption on the hydrogen-preadsorbed surface similar to that observed experimentally. The lowering is due to an increased occupancy of the Mo density of states in the presence of hydrogen.

Real-time kinetic analysis of hCG-monoclonal antibody interaction using radiolabeled hCG probe: presence of two forms of Ag-mAb complex as revealed by solid phase dissociation studies

Real-time kinetics of ligand-ligate interaction has predominantly been studied by either fluorescence or surface plasmon resonance based methods. Almost all such studies are based on association between the ligand and the ligate. This paper reports our analysis of dissociation data of monoclonal antibody-antigen (hCG) system using radio-iodinated hCG as a probe and nitrocellulose as a solid support to immobilize mAb. The data was analyzed quantitatively for a one-step and a two-step model. The data fits well into the two-step model. We also found that a fraction of what is bound is non-dissociable (tight-binding portion (TBP)). The TBP was neither an artifact of immobilization nor does it interfere with analysis. It was present when the reaction was carried out in homogeneous solution in liquid phase. The rate constants obtained from the two methods were comparable. The work reported here shows that real-time kinetics of other ligand-ligate interaction can be studied using nitrocellulose as a solid support. (C) 2002 Elsevier Science B.V. All rights reserved.

Ab initio, DFT and transition state theory calculations on 1,2-HF, HCI and CIF elimination reactions from CH2F-CH2Cl

This paper reports ab intio, DFT and transition state theory (TST) calculations on HF, HCI and CIF elimination reactions from CH2Cl-CH2F molecule. Both the ground state and the transition state for HX elimination reactions have been optimized at HF, MP2 and DFT calculations with 6-31G*, 6-31G** and 6-311++G** basis sets. In addition, CCSD(T) single point calculations were carried out with MP2/6-311++G** optimized geometry for more accurate determination of the energies of the minima and transition state, compared to the other methods employed here. Classical barriers are converted to Arrhenius activation energy by TST calculations for comparisons with experimental results. The pre-exponential factors, A, calculated at all levels of theory are significantly larger than the experimental values. For activation energy, E-a DFT gives good results for HF elimination, within 4-8 W mol(-1) from experimental values. None of the methods employed, including CCSD(T), give comparable results for HCI elimination reactions. However, rate constants calculated by CCSD(T) method are in very good agreement with experiment for HCI elimination and they are in reasonable agreement for HF elimination reactions. Due to the strong correlation between A and E., the rate constants could be fit to a lower A and E-a (as given by experimental fitting, corresponding to a tight TS) or to larger A and E-a (as given by high level ab initio calculations, corresponding to a loose TS). The barrier for CIF elimination is determined to be 607 U mol(-1) at HF level and it is unlikely to be important for CH2FCH2Cl. Results for other CH2X-CH2Y (X,Y = F/Cl) are included for comparison.

A convenient enantiospecific methodology for (-)-(1R,5S)-1,5-dimethylbicyclo[3.3.0]octa-2,7-dione: A formal total synthesis of (-)-ceratopicanol

An enantiospecific formal total synthesis of (-)-ceratopicanol starting from the readily and abundantly available monoterpene (R)-limonene is described. A combination of Claisen rearrangement-intramolecular diazo-ketone cyclopropanation-regiospecific reductive cyclopropane cleavage reactions are employed for the stereo- and regiospecific generation of the two vicinal ring junction quaternary carbon atoms.

Model of resistances in systems of Tomonaga-Luttinger liquid wires

In a recent paper, we combined the technique of bosonization with the concept of a Rayleigh dissipation function to develop a model for resistances in one-dimensional systems of interacting spinless electrons Europhys. Lett. 93, 57007 (2011)]. We also studied the conductance of a system of three wires by using a current splitting matrix M at the junction. In this paper, we extend our earlier work in several ways. The power dissipated in a three-wire system is calculated as a function of M and the voltages applied in the leads. By combining two junctions of three wires, we examine a system consisting of two parallel resistances. We study the conductance of this system as a function of the M matrices and the two resistances; we find that the total resistance is generally quite different from what one expects for a classical system of parallel resistances. We do a sum over paths to compute the conductance of this system when one of the two resistances is taken to be infinitely large. We study the conductance of a three-wire system of interacting spin-1/2 electrons, and show that the charge and spin conductances can generally be different from each other. Finally, we consider a system of two wires that are coupled by a dissipation function, and we show that this leads to a current in one wire when a voltage bias is applied across the other wire.

Molecular insights into the mechanism of phenotypic tolerance to rifampicin conferred on mycobacterial RNA polymerase by MsRbpA

The protein MsRbpA from Mycobacterium smegmatis rescues RNA polymerase (RNAP) from the inhibitory effect of rifampicin (Rif). We have reported previously that MsRbpA interacts with the beta-subunit of RNAP and that the effect of MsRbpA on Rif-resistant (Rif(R)) RNAP is minimal. Here we attempted to gain molecular insights into the mechanism of action of this protein with respect to its role in rescuing RNAP from Rif-mediated transcription inhibition. Our experimental approach comprised multiple-round transcription assays, fluorescence spectroscopy, MS and surface plasmon resonance in order to meet the above objective. Based on our molecular studies we propose here that Rif is released from its binding site in the RNAP-Rif complex in the presence of MsRbpA. Biophysical studies reveal that the location of MsRbpA on RNAP is at the junction of the beta- and beta'-subunits, close to the Rif-binding site and the (i + 1) site on RNAP.

Guessing and compression subject to distortion

The problem of guessing a random string is revisited. The relation-ship between guessing without distortion and compression is extended to the case when source alphabet size is countably in¯nite. Further, similar relationship is established for the case when distortion allowed by establishing a tight relationship between rate distortion codes and guessing strategies.

Electrical and magneto-resistance of Co/CNT/epoxy thin film for strain and magnetic field sensing

Cobalt and iron nanoparticles are doped in carbon nanotube (CNT)/polymer matrix composites and studied for strain and magnetic field sensing properties. Characterization of these samples is done for various volume fractions of each constituent (Co and Fe nanoparticles and CNTs) and also for cases when only either of the metallic components is present. The relation between the magnetic field and polarization-induced strain are exploited. The electronic bandgap change in the CNTs is obtained by a simplified tight-binding formulation in terms of strain and magnetic field. A nonlinear constitutive model of glassy polymer is employed to account for (1) electric bias field dependent softening/hardening (2) CNT orientations as a statistical ensemble and (3) CNT volume fraction. An effective medium theory is then employed where the CNTs and nanoparticles are treated as inclusions. The intensity of the applied magnetic field is read indirectly as the change in resistance of the sample. Very small magnetic fields can be detected using this technique since the resistance is highly sensitive to strain. Its sensitivity due to the CNT volume fraction is also discussed. The advantage of this sensor lies in the fact that it can be molded into desirable shape and can be used in fabrication of embedded sensors where the material can detect external magnetic fields on its own. Besides, the stress-controlled hysteresis of the sample can be used in designing memory devices. These composites have potential for use in magnetic encoders, which are made of a magnetic field sensor and a barcode.

Faster Algorithms for Incremental Topological Ordering.Robert Tarjan

We present two online algorithms for maintaining a topological order of a directed acyclic graph as arcs are added, and detecting a cycle when one is created. Our first algorithm takes O(m 1/2) amortized time per arc and our second algorithm takes O(n 2.5/m) amortized time per arc, where n is the number of vertices and m is the total number of arcs. For sparse graphs, our O(m 1/2) bound improves the best previous bound by a factor of logn and is tight to within a constant factor for a natural class of algorithms that includes all the existing ones. Our main insight is that the two-way search method of previous algorithms does not require an ordered search, but can be more general, allowing us to avoid the use of heaps (priority queues). Instead, the deterministic version of our algorithm uses (approximate) median-finding; the randomized version of our algorithm uses uniform random sampling. For dense graphs, our O(n 2.5/m) bound improves the best previously published bound by a factor of n 1/4 and a recent bound obtained independently of our work by a factor of logn. Our main insight is that graph search is wasteful when the graph is dense and can be avoided by searching the topological order space instead. Our algorithms extend to the maintenance of strong components, in the same asymptotic time bounds.

Memory Architecture Exploration Framework for Cache Based Embedded SoC

Today's feature-rich multimedia products require embedded system solution with complex System-on-Chip (SoC) to meet market expectations of high performance at a low cost and lower energy consumption. The memory architecture of the embedded system strongly influences critical system design objectives like area, power and performance. Hence the embedded system designer performs a complete memory architecture exploration to custom design a memory architecture for a given set of applications. Further, the designer would be interested in multiple optimal design points to address various market segments. However, tight time-to-market constraints enforces short design cycle time. In this paper we address the multi-level multi-objective memory architecture exploration problem through a combination of exhaustive-search based memory exploration at the outer level and a two step based integrated data layout for SPRAM-Cache based architectures at the inner level. We present a two step integrated approach for data layout for SPRAM-Cache based hybrid architectures with the first step as data-partitioning that partitions data between SPRAM and Cache, and the second step is the cache conscious data layout. We formulate the cache-conscious data layout as a graph partitioning problem and show that our approach gives up to 34% improvement over an existing approach and also optimizes the off-chip memory address space. We experimented our approach with 3 embedded multimedia applications and our approach explores several hundred memory configurations for each application, yielding several optimal design points in a few hours of computation on a standard desktop.

Field emission properties of carbon nanotube arrays with defects and impurities

Field emission from carbon nanotubes (CNTs) in the form of arrays or thin films give rise to several strongly correlated process of electromechanical interaction and degradation. Such processes are mainly due to (1) electron-phonon interaction (2) electromechanical force field leading to stretching of CNTs (3) ballistic transport induced thermal spikes, coupled with high dynamic stress, leading to degradation of emission performance at the device scale. Fairly detailed physics based models of CNTs considering the aspects (1) and (2) above have already been developed by these authors, and numerical results indicate good agreement with experimental results. What is missing in such a system level modeling approach is the incorporation of structural defects and vacancies or charge impurities. This is a practical and important problem due to the fact that degradation of field emission performance is indeed observed in experimental I-V curves. What is not clear from these experiments is whether such degradation in the I-V response is due to dynamic reorientation of the CNTs or due to the defects or due to both of these effects combined. Non-equilibrium Green’s function based simulations using a tight-binding Hamiltonian for single CNT segment show up the localization of carrier density at various locations of the CNTs. About 11% decrease in the drive current with steady difference in the drain current in the range of 0.2-0.4V of the gate voltage was reported in literature when negative charge impurity was introduced at various locations of the CNT over a length of ~20nm. In the context of field emission from CNT tips, a simplistic estimate of defects have been introduced by a correction factor in the Fowler-Nordheim formulae. However, a more detailed physics based treatment is required, while at the same time the device-scale simulation is necessary. The novelty of our present approach is the following. We employ a concept of effective stiffness degradation for segments of CNTs, which is due to structural defects, and subsequently, we incorporate the vacancy defects and charge impurity effects in the Green’s function based approach. Field emission induced current-voltage characteristics of a vertically aligned CNT array on a Cu-Cr substrate is then simulated using a detailed nonlinear mechanistic model of CNTs coupled with quantum hydrodynamics. An array of 10 vertically aligned and each 12 m long CNTs is considered for the device scale analysis. Defect regions are introduced randomly over the CNT length. The result shows the decrease in the longitudinal strain due to defects. Contrary to the expected influence of purely mechanical degradation, this result indicates that the charge impurity and hence weaker transport can lead to a different electromechanical force field, which ultimately can reduce the strain. However, there could be significant fluctuation in such strain field due to electron-phonon coupling. The effect of such fluctuations (with defects) is clearly evident in the field emission current history. The average current also decreases significantly due to such defects.

Energy-insensitive Guidance of Solid Motor Propelled Long Range Flight Vehicles Using MPSP and Dynamic Inversion

A energy-insensitive explicit guidance design is proposed in this paper by appending newlydeveloped nonlinear model predictive static programming technique with dynamic inversion, which render a closed form solution of the necessary guidance command update. The closed form nature of the proposed optimal guidance scheme suppressed the computational difficulties, and facilitate realtime solution. The guidance law is successfully verified in a solid motor propelled long range flight vehicle, for which developing an effective guidance law is more difficult as compared to a liquid engine propelled vehicle, mainly because of the absence of thrust cutoff facility. The scheme guides the vehicle appropriately so that it completes the mission within a tight error bound assuming that the starting point of the second stage to be a deterministic point beyond the atmosphere. The simulation results demonstrate its ability to intercept the target, even with an uncertainty of greater than 10% in the burnout time