Universal Conductance Fluctuations as a direct probe to valley coherence and universality class of disordered graphene

We demonstrate that the universal conductance fluctuations (UCF) can be used as a direct probe to study the valley quantum states in disordered graphene. The UCF magnitude in graphene is suppressed by a factor of four at high carrier densities where the short-range disorder essentially breaks the valley degeneracy of the K and K' valleys, leading to a density dependent crossover of symmetry class from symplectic near the Dirac point to orthogonal at high densities.

Direct Characterizing of Densification Mechanisms during Spark Plasma Sintering

Spark plasma sintering (SPS) is a convenient and rapid means of producing dense ceramic compacts. However, the mechanisms responsible for rapid densification have not been identified satisfactorily, with different studies using an indirect approach yielding varied values for the densification parameters. This study involved SPS in high purity nanocrystalline alumina with temperatures ranging from 1173 to 1423K and stresses from 25 to 100MPa. A direct approach, with analyses at a constant density, revealed a stress exponent of similar to 1 and an inverse grain size dependence of similar to 3, consistent with Coble creep process. Whereas the direct approach gives a stress exponent of similar to 1, the indirect approach used previously gives stress exponents ranging from similar to 2.2 to 3.5 with the same data, thereby revealing potentially spurious values of the densification parameters from conventional indirect approaches to characterizing densification. The rapid densification during SPS is related to the finer grain sizes retained with the rapid heating rates and the imposed stress that enhances the driving force for densification.

Local and remote impacts of direct aerosol forcing on Asian monsoon

The impact of heating by black carbon aerosols on Indian summer monsoon has remained inconclusive. Some investigators have predicted that black carbon aerosols reduce monsoon rainfall while others have argued that it will increase monsoon rainfall. These conclusions have been based on local influence of aerosols on the radiative fluxes. The impact of aerosol-like heating in one region on the rainfall in a remote region has not been examined in detail. Here, using an atmospheric general circulation model, it has been shown that remote influence of aerosol-like heating can be as important as local influence on Indian summer monsoon. Precipitation in northern Arabian Sea and north-west Indian region increased by 16% in June to July when aerosol-like heating were present globally. The corresponding increase in precipitation due to presence of aerosol-like heating only over South Asia (local impact) and East Asia (remote impact) were 28 and 13%, respectively. This enhancement in precipitation was due to destabilization of the atmosphere in pre-monsoon season that affected subsequent convection. Moreover, pre-monsoon heating of the lower troposphere changed the circulation substantially that enabled influx of more moisture over certain regions and reduced the moist static stability of the atmosphere. It has been shown that regional aerosol heating can have large impact on the phase of upper tropospheric Rossby wave in pre-monsoon season, which acts as a primary mechanism behind teleconnection and leads to the change in precipitation during monsoon season. These results demonstrate that changes in aerosol in one region can influence the precipitation in a remote region through changes in circulation.

Direct control of type IIA topoisomerase activity by a chromosomally encoded regulatory protein

Precise control of supercoiling homeostasis is critical to DNA-dependent processes such as gene expression, replication, and damage response. Topoisomerases are central regulators of DNA supercoiling commonly thought to act independently in the recognition and modulation of chromosome superstructure; however, recent evidence has indicated that cells tightly regulate topoisomerase activity to support chromosome dynamics, transcriptional response, and replicative events. How topoisomerase control is executed and linked to the internal status of a cell is poorly understood. To investigate these connections, we determined the structure of Escherichia coil gyrase, a type HA topoisomerase bound to YacG, a recently identified chromosomally encoded inhibitor protein. Phylogenetic analyses indicate that YacG is frequently associated with coenzyme A (CoA) production enzymes, linking the protein to metabolism and stress. The structure, along with supporting solution studies, shows that YacG represses gyrase by sterically occluding the principal DNA-binding site of the enzyme. Unexpectedly, YacG acts by both engaging two spatially segregated regions associated with small-molecule inhibitor interactions (fluoroquinolone antibiotics and the newly reported antagonist GSK299423) and remodeling the gyrase holo enzyme into an inactive, ATP-trapped configuration. This study establishes a new mechanism for the protein-based control of topoisomerases, an approach that may be used to alter supercoiling levels for responding to changes in cellular state.

Direct regulation of topoisomerase activity by a nucleoid-associated protein

The topological homeostasis of bacterial chromosomes is maintained by the balance between compaction and the topological organization of genomes. Two classes of proteins play major roles in chromosome organization: the nucleoid-associated proteins (NAPs) and topoisomerases. The NAPs bind DNA to compact the chromosome, whereas topoisomerases catalytically remove or introduce supercoils into the genome. We demonstrate that HU, a major NAP of Mycobacterium tuberculosis specifically stimulates the DNA relaxation ability of mycobacterial topoisomerase I (TopoI) at lower concentrations but interferes at higher concentrations. A direct physical interaction between M. tuberculosis HU (MtHU) and TopoI is necessary for enhancing enzyme activity both in vitro and in vivo. The interaction is between the amino terminal domain of MtHU and the carboxyl terminal domain of TopoI. Binding of MtHU did not affect the two catalytic trans-esterification steps but enhanced the DNA strand passage, requisite for the completion of DNA relaxation, a new mechanism for the regulation of topoisomerase activity. An interaction-deficient mutant of MtHU was compromised in enhancing the strand passage activity. The species-specific physical and functional cooperation between MtHU and TopoI may be the key to achieve the DNA relaxation levels needed to maintain the optimal superhelical density of mycobacterial genomes.

Direct correlation between non-random distribution of cations and ion transport mechanism in soda-lime silicate glasses

We report a direct correlation between dissimilar ion pair formation and alkali ion transport in soda-lime silicate glasses established via broad band conductivity spectroscopy and local structural probe techniques. The combined Raman and Nuclear Magnetic Resonance (NMR) spectroscopy techniques on these glasses reveal the coexistence of different anionic species and the prevalence of Na+-Ca2+ dissimilar pairs as well as their distributions. The spectroscopic results further confirm the formation of dissimilar pairs atomistically, where it increases with increasing alkaline-earth oxide content These results, are the manifestation of local structural changes in the silicate network with composition which give rise to different environments into which the alkali ions hop. The Na+ ion mobility varies inversely with dissimilar pair formation, i.e. it decreases with increase of non-random formation of dissimilar pairs. Remarkably, we found that increased degree of non-randomness leads to temperature dependent variation in number density of sodium ions. Furthermore, the present study provides the strong link between the dynamics of the alkali ions and different sites associated with it in soda-lime silicate glasses. (C) 2014 Elsevier B.V. All rights reserved.

Oxygen-participated electrochemistry of new lithium-rich layered oxides Li3MRuO5 M = Mn, Fe)

We describe the synthesis, crystal structure and lithium deinsertion-insertion electrochemistry of two new lithium-rich layered oxides, Li3MRuO5 (M = Mn, Fe), related to rock salt based Li2MnO3 and LiCoO2. The Li3MnRuO5 oxide adopts a structure related to Li2MnO3 (C2/m) where Li and (Li0.2Mn0.4Ru0.4) layers alternate along the c-axis, while the Li3FeRuO5 oxide adopts a near-perfect LiCoO2 (R (3) over barm) structure where Li and (Li0.2Fe0.4Ru0.4) layers are stacked alternately. Magnetic measurements indicate for Li3MnRuO5 the presence of Mn3+ and low spin configuration for Ru4+ where the itinerant electrons occupy a pi*-band. The onset of a net maximum in the chi vs. T plot at 9.5 K and the negative value of the Weiss constant (theta) of -31.4 K indicate the presence of antiferromagnetic superexchange interactions according to different pathways. Lithium electrochemistry shows a similar behaviour for both oxides and related to the typical behaviour of Li-rich layered oxides where participation of oxide ions in the electrochemical processes is usually found. A long first charge process with capacities of 240 mA h g(-1) (2.3 Li per f.u.) and 144 mA h g(-1) (1.38 Li per f.u.) is observed for Li3MnRuO5 and Li3FeRuO5, respectively. An initial sloping region (OCV to ca. 4.1 V) is followed by a long plateau (ca. 4.3 V). Further discharge-charge cycling points to partial reversibility (ca. 160 mA h g(-1) and 45 mA h g(-1) for Mn and Fe, respectively). Nevertheless, just after a few cycles, cell failure is observed. X-ray photoelectron spectroscopy (XPS) characterisation of both pristine and electrochemically oxidized Li3MRuO5 reveals that in the Li3MnRuO5 oxide, Mn3+ and Ru4+ are partially oxidized to Mn4+ and Ru5+ in the sloping region at low voltage, while in the long plateau, O2- is also oxidized. Oxygen release likely occurs which may be the cause for failure of cells upon cycling. Interestingly, some other Li-rich layered oxides have been reported to cycle acceptably even with the participation of the O2- ligand in the reversible redox processes. In the Li3FeRuO5 oxide, the oxidation process appears to affect only Ru (4+ to 5+ in the sloping region) and O2- (plateau) while Fe seems to retain its 3+ state.

Image-Segmentation Technique to Analyze Deformation Profiles in Different Direct Shear Tests

Results from interface shear tests on sand-geosynthetic interfaces are examined in light of surface roughness of the interacting geosynthetic material. Three different types of interface shear tests carried out in the frame of direct shear-test setup are compared to understand the effect of parameters like box fixity and symmetry on the interface shear characteristics. Formation of shear bands close to the interface is visualized in the tests and the bands are analyzed using image-segmentation techniques in MATLAB. A woven geotextile with moderate roughness and a geomembrane with minimal roughness are used in the tests. The effect of surface roughness of the geosynthetic material on the formation of shear bands, movement of sand particles, and interface shear parameters are studied and compared through visual observations, image analyses, and image-segmentation techniques.

A comparative study of a direct discretization and an operator-splitting solver for population balance systems

A direct discretization approach and an operator-splitting scheme are applied for the numerical simulation of a population balance system which models the synthesis of urea with a uni-variate population. The problem is formulated in axisymmetric form and the setup is chosen such that a steady state is reached. Both solvers are assessed with respect to the accuracy of the results, where experimental data are used for comparison, and the efficiency of the simulations. Depending on the goal of simulations, to track the evolution of the process accurately or to reach the steady state fast, recommendations for the choice of the solver are given. (C) 2015 Elsevier Ltd. All rights reserved.

Direct measurements of growing amorphous order and non-monotonic dynamic correlations in a colloidal glass-former

The transformation of flowing liquids into rigid glasses is thought to involve increasingly cooperative relaxation dynamics as the temperature approaches that of the glass transition. However, the precise nature of this motion is unclear, and a complete understanding of vitrification thus remains elusive. Of the numerous theoretical perspectives(1-4) devised to explain the process, random first-order theory (RFOT; refs 2,5) is a well-developed thermodynamic approach, which predicts a change in the shape of relaxing regions as the temperature is lowered. However, the existence of an underlying `ideal' glass transition predicted by RFOT remains debatable, largely because the key microscopic predictions concerning the growth of amorphous order and the nature of dynamic correlations lack experimental verification. Here, using holographic optical tweezers, we freeze a wall of particles in a two-dimensional colloidal glass-forming liquid and provide direct evidence for growing amorphous order in the form of a static point-to-set length. We uncover the non-monotonic dependence of dynamic correlations on area fraction and show that this non-monotonicity follows directly from the change in morphology and internal structure of cooperatively rearranging regions(6,7). Our findings support RFOT and thereby constitute a crucial step in distinguishing between competing theories of glass formation.

Ultrasound-modulated optical tomography: direct recovery of elasticity distribution from experimentally measured intensity autocorrelation

Based on an ultrasound-modulated optical tomography experiment, a direct, quantitative recovery of Young's modulus (E) is achieved from the modulation depth (M) in the intensity autocorrelation. The number of detector locations is limited to two in orthogonal directions, reducing the complexity of the data gathering step whilst ensuring against an impoverishment of the measurement, by employing ultrasound frequency as a parameter to vary during data collection. The M and E are related via two partial differential equations. The first one connects M to the amplitude of vibration of the scattering centers in the focal volume and the other, this amplitude to E. A (composite) sensitivity matrix is arrived at mapping the variation of M with that of E and used in a (barely regularized) Gauss-Newton algorithm to iteratively recover E. The reconstruction results showing the variation of E are presented. (C) 2015 Optical Society of America

Copper-Catalyzed Direct Transformation of Secondary Allylic and Benzylic Alcohols into Azides and Amides: An Efficient Utility of Azide as a Nitrogen Source

A mild and convenient method for the synthesis of amides has been explored by using secondary alcohols, Cu(ClO4)(2)6H(2)O as a catalyst, and trimethylsilyl azide (TMSN3) as a nitrogen source in the presence of 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) at ambient temperature. This method has been successfully adapted to the preparation of azides directly from their corresponding alcohols and offers excellent chemoselectivity in the formation of -halo azides and the azidation of allylic alcohols in the presence of a benzyl alcohol moiety. In addition, this strategy provides an opportunity to synthesize azides that can serve as precursors to -amino acids.

Direct Link-Aware Optimal Relay Selection and a Low Feedback Variant for Underlay CR

Cooperative relaying combined with selection has been extensively studied in the literature to improve the performance of interference-constrained secondary users in underlay cognitive radio (CR). We present a novel symbol error probability (SEP)-optimal amplify-and-forward relay selection rule for an average interference-constrained underlay CR system. A fundamental principle, which is unique to average interference-constrained underlay CR, that the proposed rule brings out is that the choice of the optimal relay is affected not just by the source-to-relay, relay-to-destination, and relay-to-primary receiver links, which are local to the relay, but also by the direct source-to-destination (SD) link, even though it is not local to any relay. We also propose a simpler, practically amenable variant of the optimal rule called the 1-bit rule, which requires just one bit of feedback about the SD link gain to the relays, and incurs a marginal performance loss relative to the optimal rule. We analyze its SEP and develop an insightful asymptotic SEP analysis. The proposed rules markedly outperform several ad hoc SD link-unaware rules proposed in the literature. They also generalize the interference-unconstrained and SD link-unaware optimal rules considered in the literature.

Direct Measurement of Three-Dimensional Forces in Atomic Force Microscopy

Direct measurement of three-dimensional (3-D) forces between an atomic force microscope (AFM) probe and the sample benefits diverse applications of AFM, including force spectroscopy, nanometrology, and manipulation. This paper presents the design and evaluation of a measurement system, wherein the deflection of the AFM probe is obtained at two points to enable direct measurement of all the three components of 3-D tip-sample forces in real time. The optimal locations for measurement of deflection on the probe are derived for a conventional AFM probe. Further, a new optimal geometry is proposed for the probe that enables measurement of 3-D forces with identical sensitivity and nearly identical resolution along all three axes. Subsequently, the designed measurement system and the optimized AFM probe are both fabricated and evaluated. The evaluation demonstrates accurate measurement of tip-sample forces with minimal cross-sensitivities. Finally, the real-time measurement system is employed as part of a feedback control system to regulate the normal component of the interaction force, and to perform force-controlled scribing of a groove on the surface of polymethyl methacrylate.