Density Modification Research Articles

Effects of current density on anodizing behavior, micro-structure, and electrical properties of ZrO2-coated Al foils

The effect of current density on the anodizing behaviors, micro-structure, and electric properties of ZrO2-coated Al samples is reported. The experiment is performed by coating ZrO2 on the surface of etched Al foils and anodizing in 2-methyl-1,3-propanediol (MPD)-boric acid electrolyte at current densities of 0.01, 0.05, and 0.10 A/cm2 at 700 V. The samples are characterized using X-ray diffraction, field emission transmission electron microscopy, and electrochemical impedance spectroscopy. Marked enhancements in anodization rate, and specific capacitance are achieved by the increase in current density during anodization. A maximum enhancement of 14.8% in specific capacitance and increase of 25.7% in charging ability are realized by anodizing at 0.10 A/cm2. The specific capacitance is finally increased by 54.3% after ZrO2 coating and current density modification. This work provides a valuable forerunner for research into the effect of current density on the anodizing behavior, micro-structure, and electric properties of valve metal oxide-coated Al foils.

An introduction to experimental phasing of macromolecules illustrated by SHELX; new autotracing features.

For the purpose of this article, experimental phasing is understood to mean the determination of macromolecular structures by exploiting small intensity differences of Friedel opposites and possibly of reflections measured at different wavelengths or for heavy-atom derivatives, without the use of specific structural models. The SHELX programs provide a robust and efficient route for routine structure solution by the SAD, MAD and related methods, but involve a number of simplifying assumptions that may limit their applicability in borderline cases. The substructure atoms (i.e. those with significant anomalous scattering) are first located by direct methods, and the experimental data are then used to estimate phase shifts that are added to the substructure phases to obtain starting phases for the native reflections. These are then improved by density modification and, if the resolution of the data and the type of structure permit, polyalanine tracing. A number of extensions to the tracing algorithm are discussed; these are designed to improve its performance at low resolution. Given native data to 2.5 Å resolution or better, a correlation coefficient greater than 25% between the structure factors calculated from such a trace and the native data is usually a good indication that the structure has been solved.

Fluidized Bed Catalytic Pyrolysis of Eucalyptus over HZSM-5: Effect of Acid Density and Gallium Modification on Catalyst Deactivation

Catalytic fast pyrolysis of eucalyptus wood was performed on a continuous laboratory-scale fluidized bed fast pyrolysis system. Catalytic activity was monitored from use of fresh catalyst up to a cumulative biomass/catalyst ratio (B/C) of 4:1 over extruded pellets of three different ZSM-5 catalysts by tracking CO, CO2, H2, and C2H4 production and bio-oil quality. The catalysts employed were extruded HZSM-5 with two different silica/alumina ratios (30 and 80) as well as one modified with Ga (SiO2/Al2O3 = 30) by ion exchange, which was reduced under H2 prior to pyrolysis. The deactivation of the catalysts over the course of the experiment was reflected in the decline in deoxygenation activity, following the order HZSM-5 (30) > HZSM-5 (80) > GaZSM-5 (30). HZSM-5 (30) lost most of its activity before a cumulative B/C of 2:1 was reached, while HZSM-5 (80) still showed significant deoxygenated activity at this exposure level. GaZSM-5 (30) still showed deoxygenation activity at B/C of >4:1. The improvement exhib...

Controlling Mobility in Perovskite Oxides by Ferroelectric Modulation of Atomic-Scale Interface Structure.

Coherent and epitaxial interfaces permit the realization of electric field driven devices controlled by atomic-scale structural and electronic effects at interfaces. Compared to conventional field effect devices where channel conductivity is modulated by carrier density modification, the propagation of atomic-scale distortions across an interface can control the atomic scale bonding, interatomic electron tunneling rates and thus the mobility of the channel material. We use first-principles theory to design an atomically abrupt epitaxial perovskite heterostructure involving an oxide ferroelectric (PbZr0.2Ti0.8O3) and conducting oxide channel (LaNiO3) where coupling of polar atomic motions to structural distortions can induce large, reversible changes in the channel mobility. We fabricate and characterize the heterostructure and measure record values, larger than 1000%, for the conductivity modulation. Our results describe how purely interfacial effects can be engineered to deliver unique electronic device properties and large responses to external fields.

Evaluating the electron density model by applying an imaginary modification

A function has been proposed to evaluate the electron density model constructed by inverse Fourier transform using the observed structure amplitudes and trial phase set. The strategy of this function is applying an imaginary electron density modification to the model, and then measuring how well the calculated structure amplitudes of the modified model matches the expected structure amplitudes for the modified correct model. Since the correct model is not available in advance, a method has been developed to estimate the structure amplitudes of the modified correct model. With the estimated structure amplitudes of the modified correct model, the evaluation function can be calculated approximately. Limited tests on simulated diffraction data indicate that this evaluation function may be valid at the data resolution better than 2.5 Å.

Experimental Observation of Convective Cell Formation due to a Fast Wave Antenna in the Large Plasma Device.

An experiment in a linear device, the Large Plasma Device, is used to study sheaths caused by an actively powered radio frequency (rf) antenna. The rf antenna used in the experiment consists of a single current strap recessed inside a copper box enclosure without a Faraday screen. A large increase in the plasma potential was observed along magnetic field lines that connect to the antenna limiter. The electric field from the spatial variation of the rectified plasma potential generated E[over →]×B[over →]_{0} flows, often referred to as convective cells. The presence of the flows generated by these potentials is confirmed by Mach probes. The observed convective cell flows are seen to cause the plasma in front of the antenna to flow away and cause a density modification near the antenna edge. These can cause hot spots and damage to the antenna and can result in a decrease in the ion cyclotron range of frequencies antenna coupling.

Building the atomic model of a boreal lake virus of unknown fold in a 3.9 Å cryo-EM map.

We report here the protocol adopted to build the atomic model of the newly discovered virus FLiP (Flavobacterium infecting, lipid-containing phage) into 3.9 Å cryo-electron microscopy (cryo-EM) maps. In particular, this report discusses the combination of density modification procedures, automatic model building and bioinformatics tools applied to guide the tracing of the major capsid protein (MCP) of this virus. The protocol outlined here may serve as a reference for future structural determination by cryo-EM of viruses lacking detectable structural homologues.

Solving proteins at non-atomic resolution by direct methods: update

Direct methods can be used to solve proteins of great structural complexity even when diffraction data are at non-atomic resolution. However, one of the main obstacles to the wider application of direct methods is that they reliably phase only a small fraction of the observed reflections, those with a sufficiently large value of the normalized structure factor amplitude. The subsequent phase expansion and refinement required for full structure solution are difficult. Here a new phase refinement procedure is described, which combines (1–2) difference Fourier synthesis with electron density modification techniques and thevive la differenceand Free Lunch algorithms. This procedure is able to solve data resistant to other direct space refinement procedures.

Subcycle Extreme Nonlinearities in GaP Induced by an Ultrastrong Terahertz Field

We report on the experimental observation of extreme laser spectral broadening and a change in optical transmission in gallium phosphite induced by 25 MV/cm terahertz (THz) single-cycle internal field. Such intense THz radiation leads to twofold transient modifications of the optical properties in the electro-optical crystal. First, the electric field provokes extensive cross-phase modulation via the χ^{(2)} and χ^{(3)} nonlinearities on a copropagating 50fs near infrared laser pulse which turns into 500% spectral broadening. Second, we observe an instantaneous change of the optical transmission occurring at the THz field which is alleged to interband Zener tunneling and charge carrier density modification by impact ionization turning the semiconductor in a metal-like transient state. The presented scheme displays a pathway to coherently control the optical properties of semiconductors on an ultrafast time scale by a strong THz field.

Experimental Phasing: Substructure Solution and Density Modification as Implemented in SHELX.

This chapter describes experimental phasing methods as implemented in SHELX. After introducing fundamental concepts underlying all experimental phasing approaches, the methods used by SHELXC/D/E are described in greater detail, such as dual-space direct methods, Patterson seeding and density modification with the sphere of influence algorithm. Intensity differences from data for experimental phasing can also be used for the generation and usage of difference maps with ANODE for validation and phasing purposes. A short section describes how molecular replacement can be combined with experimental phasing methods. The second half covers practical challenges, such as prerequisites for successful experimental phasing, evaluation of potential solutions, and what to do if substructure search or density modification fails. It is also shown how auto-tracing in SHELXE can improve automation and how it ties in with automatic model building after phasing.

A Hybrid K-Means Algorithm Improving Low-Density Map Based Medical Image Segmentation with Density Modification

Segmentation is grouping of a set of pixels, which are mapped from the structures inside the prostate and the background image. The main aim of this research is to provide a better segmentation technique for medical images by solving the drawbacks that currently exist in the density map-based discriminability of feature values. In this paper, we have proposed a method for image segmentation-based density map segmentation properties medical image. The accurateness of the resultant value possibly not up to the level of anticipation while the dimension of the dataset is high because we cannot say that the dataset chosen are free from noises and faults. The kernel change, i.e., segmentation is made by using hybrid K-means clustering algorithm. Thus this method is used to provide the segmentation processing information as well as also be noise free output in an efficient way. Hence, the developed model is implemented in the working platform of MATLAB and the output is compared with the existing techniques such as FCM, K-means to evaluate the performance of our proposed system.

Anion-π recognition between [M(CN)6]3- complexes and HAT(CN)6: structural matching and electronic charge density modification.

Hexacyanidometalates (M = FeIII, CoIII) and multisite anion receptor HAT(CN)6 (1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile) recognize each other in acetonitrile solution and self-assemble into the novel molecular networks (PPh4)3[M(CN)6][HAT(CN)6] (M = Fe, 1; Co, 2) and (AsPh4)3[M(CN)6][HAT(CN)6]·2MeCN·H2O (M = Fe, 3; Co, 4). 1-4 contain the stacked columns {[M(CN)6]3-;[HAT(CN)6]}∞ separated by the organic cations. All of the M-C[triple bond, length as m-dash]N vectors point collectively towards the centroids of pyrazine rings on neighboring HAT(CN)6 molecules, with Ncyanidecentroidpyrazine distances that are under 3 Å. The directional character and structural parameters of the new supramolecular synthons correspond to collective triple anion-π interactions between the CN- ligands of the metal complexes and the π-deficient areas of HAT(CN)6. Physicochemical characterisation (IR spectroscopy, UV-Vis spectroscopy, cyclic voltammetry) and dispersion-corrected DFT studies reveal the dominating charge-transfer (CT) and polarisation characters of the interactions. The electronic density flow occurs from the CN- ligands of [M(CN)6]3- to the HAT(CN)6 orbital systems and further, toward the peripheral -CN groups of HAT(CN)6. Solid-state DFT calculations determined the total interaction energy of HAT(CN)6 to be ca. -125 kcal mol-1, which gives ca. -15 kcal mol-1 per one CN-HAT(CN)6 contact after subtraction of the interaction with organic cations. The UV-Vis electronic absorption measurements prove that the intermolecular interactions persist in solution and suggest a 1 : 1 composition of the anion-π {[M(CN)6]3-;[HAT(CN)6]} chromophore, with the formation constant Kadd = (5.8 ± 6) × 102 dm3 mol-1 and the molar absorption coefficient εadd = 180 ± 9 cm-1 dm3 mol-1 at 600 nm, as estimated from concentration-dependent studies.

Nucleosome Density ChIP-Seq Identifies Distinct Chromatin Modification Signatures Associated with MNase Accessibility

Nucleosome position, density, and post-translational modification are widely accepted components of mechanisms regulating DNA transcription but still incompletely understood. We present a modified native ChIP-seq method combined with an analytical framework that allows MNase accessibility to be integrated with histone modification profiles. Application of this methodology to the primitive (CD34+) subset ofnormal human cord blood cells enabled genomic regions enriched in one versus two nucleosomes marked by histone 3 lysine 4 trimethylation (H3K4me3) and/or histone 3 lysine 27 trimethylation (H3K27me3) to be associated with their transcriptional and DNA methylation states. From this analysis, we defined four classes of promoter-specific profiles and demonstrated that a majority of bivalent marked promoters are heterogeneously marked at a single-cell level in this primitive cell type. Interestingly, extension of this approach to human embryonic stem cells revealed an altered relationship between chromatin modification state and nucleosome content at promoters, suggesting developmental stage-specific organization of histone methylation states.

Effect of ligand density and PEG modification on octreotide-targeted liposome via somatostatin receptor in vitro and in vivo

Octreotide had been exploited as a targeting ligand for nanoparticle tumor localization overexpressing somatostatin receptor. In addition to particle size and other physiochemical properties, ligand density had great influence on the delivery of active targeted nanoparticles. Herein, octreotide-targeted liposomal doxorubicin was constructed with different ligand density by post-inserting HSPE-PEG4000-Octreotide into pre-formed liposome. The octreotide ligand insertion was confirmed by activity detection of octreotide in HSPE-PEG4000-Octreotide with synchronous fluorescence. 1% octreotide density could achieve the best uptake efficiency on NCI-H-446 and SMMC-7721 cell lines among all liposomes. Octreotide-grafted long-circulating liposome (Oct-SSL) was prepared based on 1% octreotide density. The results showed that the insertion of PEG reduced cellular uptake and cytotoxicity. However, Oct-SSL showed a higher MRT compared with Oct-L showing the relative higher long circulating effect in pharmacokinetic study. Oct-SSL also showed tumor growth inhibition of twofold compared with other groups in Heps xenograft model mice. Oct-SSL with suitable ligand density and PEG modification exhibited significant effective tumor targeting for antitumor drug delivery.

Exploring HF‐induced ionospheric turbulence by Doppler sounding and stimulated electromagnetic emissions at the High Frequency Active Auroral Research Program heating facility

AbstractWe report on the features of the F region plasma perturbations during HF heating experiments at the High Frequency Active Auroral Research Program facility in March–April 2011 and May–June 2014. The diagnostics included multifrequency Doppler (phase) sounding (MDS) and stimulated electromagnetic emission (SEE). The results concern modification of the electron density profile near the reflection and upper hybrid heights, as well as correlation of the density modification with temporal behavior of narrow continuum, downshifted maximum, and broad continuum SEE spectral features. We reveal also a new SEE spectral feature which appears in the SEE spectra for the pump frequency f0 near the third and fourth electron gyroharmonics. It is located in the SEE spectrum well below the pump wave frequency, f − f0 ~ −(40–220) kHz, occupies a wide frequency range till 100–150 kHz, and is termed the broad downshifted emission.

The galactoside 2-α-L-fucosyltransferase FUT1 from Arabidopsis thaliana: crystallization and experimental MAD phasing.

The plant cell wall is a complex network of polysaccharides made up of cellulose, hemicelluloses and pectins. Xyloglucan (XyG), which is the main hemicellulosic component of dicotyledonous plants, has attracted much attention for its role in plant development and for its many industrial applications. The XyG-specific fucosyltransferase (FUT1) adds a fucose residue from GDP-fucose to the 2-O position of the terminal galactosyl residues on XyG side chains. Recombinant FUT1 from Arabidopsis thaliana was crystallized in two different crystal forms, with the best diffracting crystals (up to 1.95 Å resolution) belonging to the monoclinic space group P21, with unit-cell parameters a = 87.6, b = 84.5, c=150.3 Å, β = 96.3°. Ab initio phases were determined using a two-wavelength anomalous dispersion experiment on a tantalum bromide-derivatized crystal with data collected at the rising and descending inflection points of the Ta white line. An interpretable electron-density map was obtained after elaborate density modification. Model completion and structural analysis are currently under way.

Potential role of kinetic Alfvén waves and whistler waves in solar wind plasmas

Spacecraft observations indicate the signatures of highly oblique kinetic Alfven waves (KAWs) and whistler waves in the solar wind plasma. In the present work, we explore the possible role of KAWs and whistler waves in the observed solar wind magnetic turbulent spectrum. The nonlinear spatial evolution of KAW is studied including the effects of the ponderomotive force which results in intense localized structures due to the background density modification. Weak quasi-transverse whistler wave propagating through these localized structures also gets localized in the form of small-scale localized structures. We present numerically calculated magnetic power spectra for both KAW as well as for whistler wave. Our obtained results demonstrate the important role that KAWs and whistler waves play in the energy cascading from larger to smaller scales. The relevance of these results to recent spacecraft observations is also pointed out.

Electron acceleration considering pondermotive force effect in a plasma-filled rectangular waveguide by microwave radiation

The electron acceleration inside the plasma-filled rectangular waveguide is numerically investigated for the externally injected single-electron model considering the effects of density modification under a balance between the ponderomotive force and the pressure gradient force. Using Maxwell’s equations, we evaluate the field components of the fundamental mode in the plasma-filled rectangular waveguide, where the obtained equations are solved numerically using the fourth-order Runge–Kutta method for the electric field amplitude of the microwave. Besides, by solving the relativistic momentum and energy equations using the fourth-order Runge–Kutta method, the deflection angle and the total energy of the electron in the waveguide are obtained. Furthermore, it is shown that the electron energy gain can be controlled using superposing microwave fundamental modes. Effects of various parameters on the results are graphically presented.

Phase improvement via the Phantom Derivative technique: ancils that are related to the target structure.

Density modification is a general standard technique which may be used to improve electron density derived from experimental phasing and also to refine densities obtained by ab initio approaches. Here, a novel method to expand density modification is presented, termed the Phantom derivative technique, which is based on non-existent structure factors and is of particular interest in molecular replacement. The Phantom derivative approach uses randomly generated ancil structures with the same unit cell as the target structure to create non-existent derivatives of the target structure, called phantom derivatives, which may be used for ab initio phasing or for refining the available target structure model. In this paper, it is supposed that a model electron density is available: it is shown that ancil structures related to the target obtained by shifting the target by origin-permissible translations may be employed to refine model phases. The method enlarges the concept of the ancil, is as efficient as the canonical approach using random ancils and significantly reduces the CPU refinement time. The results from many real test cases show that the proposed methods can substantially improve the quality of electron-density maps from molecular-replacement-based phases.

Efficient quantum capacitance enhancement in DSSC by gold nanoparticles plasmonic effect

Charge collection, transport and the recombination, which can be described by a capacitance of the device, in a dye-sensitized solar cell determine the performance of the device. High capacitance renders efficient charge collection, transport and suppressing the recombination in the device. Here, we report the existence of quantum capacitance or electrochemical capacitance like phenomenon effect in the improvement of the performance of the DSSC device in the presence of Au nanoparticles. By comparing the photovoltaic performances of plasmonic DSSC (ITO|TiO2:Au:dye(N719)|Iodolyte|Pt) with normal DSSC (without gold nanoparticles), it is found that the power conversion efficiency is enhanced by 15.23%, namely from 4.07 to 4.69%, when the Au nanoparticles presence in the device. Electrochemical impedance and optical absorption and X-ray photoelectron spectroscopy analysis suggested that the improvement of the device performance is related to the enhancement of the optical activity of the TiO2 nanostructure via plasmonic effect and defect or oxygen vacancy density modification and the enhancement of carrier transport due to existence of the quantum capacitance effect in the device. The mechanism of the performance enhancement will be discussed in detail.