Large Parameter Changes Research Articles

Illumination and Voltage Dependence of Electrical Characteristics of Au/0.03 Graphene-Doped PVA/n-Si Structures via Capacitance/Conductance-Voltage Measurements

Au/n-Si (MS) structures with a high dielectric interlayer (0.03 graphene-doped PVA) are fabricated to investigate the illumination and voltage effects on electrical and dielectric properties by using capacitance-voltage (C-V) and conductance-voltage (G/ω-V) measurements at room temperature and at 1 MHz. Some of the main electrical parameters such as concentration of doping atoms (ND), barrier height (ϕB(C - V)), depletion layer width (WD) and series resistance (Rs) show fairly large illumination dispersion. The voltage-dependent profile of surface states (Nss) and resistance of the structure (Ri) are also obtained by using the dark-illumination capacitance (Cdark-Cill) and Nicollian-Brews methods, respectively. For a clear observation of changes in electrical parameters with illumination, the values of ND, WD, ϕB(C - V) and Rs are drawn as a function of illumination intensity. The values of ND and WD change almost linearly with illumination intensity. On the other hand, Rs decreases almost exponentially with increasing illumination intensity whereas ϕB(C - V) increases. The experimental results suggest that the use of a high dielectric interlayer (0.03 graphene-doped PVA) considerably passivates or reduces the magnitude of the surface states. The large change or dispersion in main electrical parameters can be attributed to generation of electron-hole pairs in the junction under illumination and to a good light absorption. All of these experimental results confirm that the fabricated Au/0.03 graphene-doped PVA/n-Si structure can be used as a photodiode or a capacitor in optoelectronic applications.

Kinetic Detection of Orthogonal Protein and Chemical Coordinates in Enzyme Catalysis: Double Mutants of Soybean Lipoxygenase.

Soybean lipoxygenase-1 (SLO-1) is a paradigmatic enzyme system for studying the contribution of hydrogen tunneling to enzymatic proton-coupled electron transfer processes. In this study, the impact of pairs of double mutants on the properties of SLO-1 is presented. Steady-state rates and their deuterium kinetic isotope effects (KIEs) have been measured for the bimolecular reaction of enzyme with free substrate (kcat/Km) and compared to the unimolecular rate constant, kcat. A key kinetic finding is that the competitive KIEs on the second-order rate constant (kcat/Km) are all reduced from Dkcat and, despite large changes in rate and activation parameters, remain essentially unaltered under a variety of conditions. These data implicate a protein reaction coordinate that is orthogonal to the chemical reaction coordinate and controls the concentration of the active enzyme. This study introduces a new means to interrogate the alteration of conformational landscapes that can occur following site-specific mutagenesis.

Automatic generation control of a multi-area ST – Thermal power system using Grey Wolf Optimizer algorithm based classical controllers

This paper present automatic generation control (AGC) of a three area thermal system incorporating solar thermal power plant (STPP) in one of the area. Single reheat turbine and appropriate generation rate constraints is provided in the conventional thermal system. The performances of integral (I), proportional plus integral (PI), and proportional plus integral plus derivative (PID) controller are evaluated in the system with and without incorporating STPP. A new computational evolutionary technique called grey wolf optimizer algorithm (GWO) is used for the optimization of secondary controller gains for first time in AGC. Investigations reveal that GWO optimized PID controller’s performance is better than others in terms of settling time, peak overshoot and magnitude of oscillations in the system with or without STPP. Sensitivity analysis reveals that that GWO optimized PID controller gains obtained in nominal conditions and parameters are healthy and not necessary to reset for large change in system conditions and parameters.

MRI-Tracked Tumor Vascular Changes in the Hours after Single-Fraction Irradiation.

The purpose of this study was to characterize changes in tumor vascular parameters hours after a single radiation exposure in an orthotopic brain tumor model. U-251 human brain tumors were established intracerebrally in rat brains, and tumor blood flow, forward volume transfer constant (K(trans)) and interstitial volume fraction (v(e)) were measured using magnetic resonance imaging (MRI). Tumors were exposure to a single stereotactic radiation treatment of 20 Gy. Vascular parameters were assessed one additional time between 2 and 24 h after irradiation. After the second MRI session, brain tissue histology was examined for gross changes and apoptosis. In separate studies, cerebral blood flow was measured in nonimplanted controls before radiation exposure and 2 and 24 h after 20 Gy irradiation, and in implanted rats before radiation exposure and at 2 and 24 h after 6 Gy irradiation. Significant changes were observed in tumor-bearing rat brains in the hours after 20 Gy irradiation. Two hours after 20 Gy irradiation, tumor blood flow decreased nearly 80% and ve decreased by 30%. At 4 h, the K(trans) increased by 30% over preirradiation values. Extensive vacuolization and an increase in apoptosis were evident histologically in rats imaged 2 h after irradiation. Between 8 and 12 h after irradiation, all vascular parameters including blood flow returned to near preirradiation values. One day after irradiation, tumor blood flow was elevated 40% over preirradiation values, and other vascular parameters, including K(trans) and ve, were 20-40% below preirradiation values. In contrast, changes in vascular parameters observed in the normal brain 2 or 24 h after 20 Gy irradiation were not significantly different from preirradiation values. Also, tumor blood flow appeared to be unchanged at 2 h after 6 Gy irradiation, with a small increase observed at 24 h, unlike the tumor blood flow changes after 20 Gy irradiation. Large and significant changes in vascular parameters were observed hours after 20 Gy irradiation using noninvasive MRI techniques. It is hypothesized that cellular swelling hours after a high dose of radiation, coinciding with vacuolization, led to a decrease in tumor blood flow and v(e). Four hours after radiation exposure, K(trans) increased in concert with an increase in tumor blood flow. Vascular permeability normalized, 24 h after 20 Gy irradiation, as characterized by a decrease in K(trans). Vascular parameters did not change significantly in the normal brain after 20 Gy irradiation or in the tumor-bearing brain after 6 Gy irradiation.

Bucket-Filling: An Asymptotically Optimal Video-on-Demand Network With Source Coding

There has recently been growing interest for content providers to provide video-on-demand (VoD) as a cloud service. In such a network, the content provider may rent heterogeneous resources (such as streaming and storage capacities ) from geographically distributed data centers deployed close to user pools. These data centers (or proxy servers) collaboratively share content with each other to serve their local users. A critical challenge is to optimize movie storage and retrieval to minimize the deployment cost consisting of streaming, storage, and network transmission between data centers. We propose a novel and effective movie storage and retrieval using linear source coding. All the movies are source-encoded once at the repository, by taking every $q$ source symbols of movie $m$ to generate ${n^{(m)}}$ coded symbols. These coded symbols are then distributed to the servers in the cloud. Based on a general and comprehensive cost model, we optimize ${n^{(m)}}$ and the number of symbols to retrieve from remote servers for a local movie request. The optimal solution can be efficiently computed with a linear programming (LP) formulation . Our solution is proved to asymptotically approach the global minimum cost as $q$ increases. Even when $q$ is low, near optimality can be achieved. To accommodate large movie pool and system parameter changes, we propose algorithms for movie grouping and on-line re-optimization which significantly reduce the computational complexity with little compromise on optimality. Through extensive simulation, our algorithm is shown to achieve the lowest cost, outperforming traditional and state-of-the-art heuristics with a substantially wide margin.

An entropy-like index of bifurcational robustness for metabolic systems.

Natural and synthetic metabolic pathways need to retain stability when faced against random changes in gene expression levels and kinetic parameters. In the presence of large parameter changes, a robust system should specifically avoid moving to an unstable region, an event that would dramatically change system behavior. Here we present an entropy-like index, denoted as S, for quantifying the bifurcational robustness of metabolic systems against loss of stability. We show that S enables the optimization of a metabolic model with respect to both bifurcational robustness and experimental data. We then demonstrate how the coupling of ensemble modeling and S enables us to discriminate alternative designs of a synthetic pathway according to bifurcational robustness. Finally, we show that S enables the identification of a key enzyme contributing to the bifurcational robustness of yeast glycolysis. The different applications of S demonstrated illustrate the versatile role it can play in constructing better metabolic models and designing functional non-native pathways.

A study of the alterability of basaltic lithotypes from the Itaipu Dam site (southern Brazil)

The alteration of geological materials is a natural process and the measurement of these effects is of great importance in ensuring the safety of engineering works. This study presents results from a set of simple and low-cost tests using specimens lacking a specific geometry. The principal objective of this study was the geological-geotechnical characterization of various basaltic lithotypes, focusing on evaluating the alterability of the rock. Accordingly, this study included tests of point load strength, physical properties (apparent density, apparent porosity, and water absorption), natural alteration, pH, and electrical conductivity (dissolution of ions). Laboratory test results showed good correlation between these parameters, but the results should be interpreted with caution because they were strongly associated with the presence of secondary minerals, the size and distribution of vesicles and amygdules, and the state of alteration of the rock. The specimens subjected to natural alteration in the laboratory failed to develop a significant degree of alteration and, therefore, did not present large changes in point load strength parameters and physical rock properties throughout the alteration cycling tests. Nevertheless, the influence of plagioclase alteration on various laboratory parameters was clearly observed when specimens were analysed microscopically (200×).

Topological nature of optical bound states in the continuum.

Optical bound states in the continuum (BICs) have recently been realized in photonic crystal slabs, where the disappearance of out-of-plane radiation turns leaky resonances into guided modes with infinite lifetimes. We show that such BICs are vortex centers in the polarization directions of far-field radiation. They carry conserved and quantized topological charges, defined by the winding number of the polarization vectors, which ensure their robust existence and govern their generation, evolution, and annihilation. Our findings connect robust BICs in photonics to a wide range of topological physical phenomena.

Evolutionary tipping points in the capacity to adapt to environmental change.

In an era of rapid climate change, there is a pressing need to understand how organisms will cope with faster and less predictable variation in environmental conditions. Here we develop a unifying model that predicts evolutionary responses to environmentally driven fluctuating selection and use this theoretical framework to explore the potential consequences of altered environmental cycles. We first show that the parameter space determined by different combinations of predictability and timescale of environmental variation is partitioned into distinct regions where a single mode of response (reversible phenotypic plasticity, irreversible phenotypic plasticity, bet-hedging, or adaptive tracking) has a clear selective advantage over all others. We then demonstrate that, although significant environmental changes within these regions can be accommodated by evolution, most changes that involve transitions between regions result in rapid population collapse and often extinction. Thus, the boundaries between response mode regions in our model correspond to evolutionary tipping points, where even minor changes in environmental parameters can have dramatic and disproportionate consequences on population viability. Finally, we discuss how different life histories and genetic architectures may influence the location of tipping points in parameter space and the likelihood of extinction during such transitions. These insights can help identify and address some of the cryptic threats to natural populations that are likely to result from any natural or human-induced change in environmental conditions. They also demonstrate the potential value of evolutionary thinking in the study of global climate change.

Normal and inverse magnetocaloric effects in the ferromagnetic shape memory alloys

The field-induced entropy change and the magnetocaloric effect (MCE) of the ferromagnetic shape memory alloys Ni2Mn1−xCuxGa and Ni2Mn1+xIn1−x are studied theoretically on the basis of a phenomenological free energy. The free energy is expanded in powers of the mangetization M and the tetragonal distortion e3, which are the order parameters for the ferromagnetic and martensitic transitions, respectively. Through the magneto-structural interaction term in the free energy, magnetic fields can affect also e3 to shift the martensitic first-order transition temperatures. This shift of the transition temperature results in large field-induced changes in the order parameters, which can be responsible for large MCEs. It is found that the resulting MCEs depend on the nature of the magneto-structural interaction. In Ni2Mn1−xCuxGa with the attractive magneto-structural interaction, magnetic fields cause the negative entropy change as in the normal MCE. In Ni2Mn1+xIn1−x with the repulsive interaction, on the other hand, magnetic fields can do the positive entropy change causing the inverse MCE. For both the alloy systems, the x dependences of the refrigerant capacity (RC) are studied to find the compositions optimum for large MCEs. Applicability of the Maxwell relation to the system with the first-order transition is also studied by simulating the field-induced entropy changes on the basis of the Maxwell relation.

On the use of one-step perturbation to investigate the dependence of NOE-derived atom–atom distance bound violations of peptides upon a variation of force-field parameters

The method of one-step perturbation can be used to predict from a single molecular dynamics simulation the values of observable quantities as functions of variations in the parameters of the Hamiltonian or biomolecular force field used in the simulation. The method is used to predict violations of nuclear overhauser effect (NOE) distance bounds measured in nuclear magnetic resonance (NMR) experiments by atom-atom distances of the NOE atom pairs when varying force-field parameters. Predictions of NOE distance bound violations between different versions of the GROMOS force field for a hexa-β-peptide in solution show that the technique works for rather large force-field parameter changes as well as for very different NOE bound violation patterns. The effect of changing individual force-field parameters on the NOE distance bound violations of the β-peptide and an α-peptide was investigated too. One-step perturbation, which in this case is equivalent to reweighting configurations, constitutes an efficient technique to predict many values of different quantities from a single conformational ensemble for a particular system, which makes it a powerful force-field development technique that easily reduces the number of required separate simulations by an order of magnitude.

Significant Atomic Displacement at Isostructural Transition in Li<sub>0.99</sub>Cu<sub>0.01</sub>CrO<sub>2</sub> and its Effects

LiCrO2 is a triangular lattice antiferromagnetic compound exhibiting geometrically frustrated two dimensional arrangement of Cr ions with TN = 62 K at which an isostructural transition occurs. We show, using temperature dependent high energy synchrotron X-ray diffraction studies, that upon a nominal 1% Cu doping at the Li site, there are large changes in structural parameters and the (coupled) magnetic and dielectric properties.

Diagenetic modulation of the magnetic properties in sediments from the Northern Indian Ocean

Large changes in magnetic mineral concentration dependent parameters by more than 1 order of magnitude occur over 50–150 cm intervals in two marine sediment cores from the oxygen minimum zone in the Gulf of Aden. High‐resolution sedimentological and chemical analyses indicate that these intervals are not associated with turbiditic events or sediment reworking, they do not result from changes in carbonate dilution or differences in sediment properties, and they do not correspond to volcanic layers. Magnetic mineralogical analyses reveal a change in magnetic mineral concentration from a magnetite‐goethite assemblage to pure magnetite within the peak. The peaks almost disappear when the abundance of magnetic minerals is calculated after correcting for the magnetic moments of each magnetic mineral. Therefore, under the assumption that the variability of the magnetic parameters results from postdepositional mineralogical transformations, a relatively constant amount of magnetite was present at the surface of the sediment. Changes in redox conditions and nonsteady state diagenesis transformations have effectively been observed along both cores. Large values of total organic carbon coincide with poor preservation of biogenic and detrital magnetite, which reflects reductive dissolution of the finer magnetite grains. At the same levels, Fe2+ release from reductively dissolved magnetite favored precipitation of goethite. The susceptibility peaks coincide with episodes of magnetite preservation caused by reduced surface productivity and/or enhanced bottom‐water ventilation accompanying northward extension of Glacial Antarctic Intermediate Water into the Indian Ocean.

Strain-Engineered Cube Nanocrystals Ce1–yFeyO2 That Brought Forth Abnormal Structural and Magnetic Properties

Elucidating the relationship between internal strain and structural modification of metal oxide nanostructures expands our ability to fine tune their physical properties. However, this aspect of strain engineering is still challenging. Here, we employed two-step solution chemistry and prepared cube nanostructures Ce1–yFeyO2 with high sample uniformity. The solubility limit for Fe3+ ions doped in CeO2 nanostructures is determined to be around y = 0.15. Below the solubility limit, cube nanostructures showed a pronounced tensile strain that increased almost linearly with the doping levels. This tensile strain did not destroy the fluorite structure of parent CeO2 nanostructures but resulted in the smallest lattice constant ever reported for all CeO2-based solid solutions. In spite of a large change in lattice parameters, Raman phonon modes for these solid solutions did not shift at all with the strain, which differs from those under external compression or size effects. Further increasing the strain led to a ...

Restructuring of Membrane Bilayers due to Osmotic Pressure: Deuterium Solid-State NMR Study

Lipid membrane composition and biophysical properties have substantial influences on cellular functions. Studies of environmental effects on membrane bilayers are a prerequisite for understanding membrane protein functions. Experimental measures of structural parameters like cross-sectional area/lipid of membrane bilayers are vital for molecular dynamics simulations [1,2]. We used solid-state 2H NMR spectroscopy which gives site-specific orientational order parameters of the lipid segments to study structural fluctuations and deformations of phospholipid bilayers due to osmotic stress [1]. Model lipid membrane systems (DMPC and POPC) were subjected to osmotic pressure and temperature to establish their sensitivity to environmental changes in the liquid-crystalline state. Osmotic stress was applied by addition of osmolytes (polyethylene glycol) as well as by gravimetric dehydration. We observed very large changes in segmental order parameters with the application of osmotic pressures in the biological range. The NMR order parameters represent the area/lipid and show large changes in mean-square fluctuations of the lipid structure [3,4]. Stresses from these pressures are thermodynamically equivalent because changing chemical potential when transferring water from the interlamellar space to the bulk water phase corresponds to an induced pressure, as verified experimentally [1]. By employing mean-torque analysis of the NMR observables [3] we calculated the mean area per lipid and the volumetric bilayer thickness, which change up to 20% upon introduction of osmotic stress. These 2H NMR studies [4] show striking bilayer deformation due to the application of osmotic pressure. They distinguish molecular-level force regimes associated with lipids that can play a significant role in biological processes.[1] K.J. Mallikarjunaiah et al. (2011) BJ 100, 98-107. [2] A. Leftin et al. (2011) BBA1808, 818-839. [3] H.I. Petrache et al. (2000) BJ79, 3172-3192. [4] K.J. Mallikarjunaiah et al. (2012) to be submitted to PCCP.

Effect of Bi additive on structure and optical properties of amorphous BixIn25−xSe75 chalcogenide films

We report the structure and optical properties of thermally evaporated BixIn25−xSe75 (0 ≤ x ≤ 7) films by using X-ray diffraction and optical spectroscopic techniques. The as-prepared samples were found to be amorphous by X-ray diffraction while the crystallization of Se, In2Se3 and Bi2Se3 phases has been observed upon annealing the films at 440 K. The enhancement in the main diffraction peak intensity was accepted as the increase in the crystalline character for the devitrified films with Bi content. The addition of 5 at.% of Bi results in the large change in the electrical parameters due to the carrier type reversal in the as-prepared samples. The red shift in the absorption edge along with a decrease in the transmittance has been observed for the as-prepared samples. The inverse relationship between optical gap and the tailing parameter (except x = 1) were observed with the increase in Bi content. The optical gap was found to increase up to x ≤ 1 and thereafter, resulted in the decrease in it for the thermally annealed samples. These results have been discussed in conjunction with the structural relaxation and impurity mediated heterogeneous crystallization of the film network.

Interconversion of Active and Inactive Conformations of Urokinase-Type Plasminogen Activator

The catalytic activity of serine proteases depends on a salt-bridge between the amino group of residue 16 and the side chain of Asp194. The salt-bridge stabilizes the oxyanion hole and the S1 specificity pocket of the protease. Some serine proteases exist in only partially active forms, in which the amino group of residue 16 is exposed to the solvent. Such a partially active state is assumed by a truncated form of the murine urokinase-type plasminogen activator (muPA), consisting of residues 16-243. Here we investigated the allosteric interconversion between partially active states and the fully active state. Both a monoclonal antibody (mU3) and a peptidic inhibitor (mupain-1--16) stabilize the active state. The epitope of mU3 is located in the 37- and 70-loops at a site homologous to exosite I of thrombin. The N-terminus((Ile16)) of muPA((16--243)) was less exposed upon binding of mU3 or mupain-1--16. In contrast, introduction of the mutations F40Y or E137A into muPA((16--243)) increased exposure of the N-terminus((Ile16)) and resulted in large changes in the thermodynamic parameters for mupain-1--16 binding. We conclude that the distorted state of muPA((16--243)) is conformationally ordered upon binding of ligands to the active site and upon binding of mU3 to the 37- and 70-loops. Our study establishes the 37- and 70-loops as a unique site for binding to compounds stabilizing the active state of serine proteases.

Interfacing of DNA with carbon nanotubes for nanodevice applications

In nanotechnology, carbon nanotubes are evolving as ‘hot spot’ due to their applications as most sensitive biosensors. Thus, study of effect of biomolecular interaction is prerequisite for their electrical application in biosensors and bioelectronics. Here, we have explored this effect on electrical properties of carbon nanotubes with DNA as a model biomolecule. A stable conjugate of carbon nanotubes with DNA is formed via covalent methodology employing quantum dot as fluoropore and characterized with various spectroscopic, fluoroscopic and microscopic techniques. CNT–DNA adduct showed decreased transconductance (from 614.46 μS to 1.34 μS) and shift of threshold voltage (from −0.85 V to 2.5 V) due to change in Schottky barriers at metal–nanotube contact. In addition, decrease in hole mobility (from 4.46 × 106 to 9.72 × 103 cm2 V−1 s−1) and increase in ON-linear resistance (from 74 kΩ to 0.44 MΩ) conclude large change in device parameters. On the one hand, this substantial change in device parameters after interfacing with biomolecules supports application of carbon nanotubes in the field of biosensors while on the other hand, the same can limit their use in future power electronic devices where stability in device parameters is essential.

In Situ Investigations of SEI Layer Growth on Electrode Materials for Lithium-Ion Batteries Using Spectroscopic Ellipsometry

Thin film electrodes of a-Si and TiN were prepared by magnetron sputtering for use with a custom-designed tubular in-situ spectroscopic ellipsometry (SE) electrochemical cell. Ellipsometric measurements on Li/a-Si in-situ cells with 0.1 M LiPF6/EC:DEC (1:2) electrolyte were made while cells were charged and discharged. Large reversible changes in the ellipsometric parameters, Ψ and Δ, were closely related to the state of charge of the in-situ cell. The transformation of semiconducting a-Si to metallic a-LixSi alloy and the formation of an SEI layer contributed to these large changes, which we were unable to decouple. Li/TiN cells were made so that the SEI forming process could be studied without competing reactions. The effect of vinylene carbonate (VC) and fluoroethylene carbonate (FEC) additives on SEI formation were studied. SEI thicknesses for cells containing no additives, VC, and FEC were roughly 18 nm, 25 nm and 30 nm, respectively, after a 10 h hold at 0.1 V vs Li/Li+.

Electronic interaction and bipolar resistive switching in copper oxide-multilayer graphene hybrid interface: Graphene as an oxygen ion storage and blocking layer

This study reports a bipolar resistive switching device based on copper oxide (CuO)-multilayer graphene (MLG) hybrid interface in complete contrast to the ohmic and rectifying characteristics of junctions based on individual MLG and CuO layers. The observed shift and the occurrence of additional O1s, Cu2p, and C1s core level peaks indicate electronic interaction at the hybrid interfacial layer. Large changes in the resistive switching parameters on changing the ambient conditions from air to vacuum establish the important role of MLG as oxygen ion storage and blocking layer towards the observed resistive switching effect.