Changes In Average Structure Research Articles

Online available bandwidth estimation using multiclass supervised learning techniques

In order to answer how much bandwidth is available to an application from one end to another in a network, state-of-the-art estimation techniques, based on active probing, inject artificial traffic with a known structure into the network. At the receiving end, the available bandwidth is estimated by measuring the structural changes in the injected traffic, which are caused by the network path. However, bandwidth estimation becomes difficult when packet distributions are distorted by non-fluid bursty cross traffic and multiple links. This eventually leads to an estimation bias. One known approach to reduce the bias in bandwidth estimations is to probe a network with constant-rate packet trains and measure the average structural changes in them. However, one cannot increase the number of packet trains in a designated time period as much as needed because high probing intensity overloads the network and results in packet losses in probe and cross traffic, which distorts probe packet gaps and inflicts more bias. In this work, we propose a machine learning-based, particularly classification-based, method that provides reliable estimates utilizing fewer packet trains. Then, we implement supervised learning techniques. Furthermore, considering the correlated changes over time in traffic in a network, we apply filtering techniques on estimation results in order to track the changes in the available bandwidth. We set up an experimental testbed using the Emulab software and a dumbbell topology in order to create training and testing data for performance analysis. Our results reveal that our proposed method identifies the available bandwidth significantly well in single-link networks as well as networks with heavy cross traffic burstiness and multiple links. It is also able to estimate the available bandwidth in randomly generated networks where the network capacity and the cross traffic intensity vary substantially. We also compare our technique with the others that use direct probing and regression approaches, and show that ours has better performance in terms of standard deviation around the actual bandwidth values.

Evidence of structural modifications in the region around the broad dielectric maxima in the 30% Sn-doped barium titanate relaxor

The structural and dielectric characterization of 30% Sn-doped ${\mathrm{BaTiO}}_{3}$ (${{\mathrm{BaSn}}_{0.3}{\mathrm{Ti}}_{0.7}\mathrm{O}}_{3}$) as a function of temperature is carried out combining, complementary probes to reveal structural modifications associated to the relaxor behavior. Dielectric data confirms the existence of relaxor-type behavior in ${{\mathrm{BaSn}}_{0.3}{\mathrm{Ti}}_{0.7}\mathrm{O}}_{3}$. The local and average structural changes as a function of temperature have been investigated in the region of broad changes of dielectric response. Local probes, such as x-ray absorption fine structure spectroscopy and M\ossbauer spectroscopy reveal a special trend of the lattice related to the diffuse dielectric phase transition as observed from dielectric data. The analysis of Raman spectra as a function of temperature reveals a peculiar behavior in the temperature region corresponding to the dielectric transition. The analysis of x-ray diffraction patterns points out a pseudocubic structure throughout the temperature range while the volume exhibits a negative thermal expansion in the region of broad dielectric maximum. Our results suggest structural modifications occurring in the system throughout a wide temperature range, interestingly, associated with changes in macroscopic properties of relaxors such as dispersion in dielectric constants and raising of dipole moments.

VIS3COS

We study the impact of local density and stellar mass on the structure and morphology of approximately 500 quiescent and star-forming galaxies from the VIMOS Spectroscopic Survey of a Superstructure in COSMOS (VIS3COS). We perform bulge-to-disc decomposition of the surface brightness profiles and find ∼41 ± 3% of > 1010 M⊙ galaxies to be best fitted with two components. We complement our analysis with non-parametric morphological measurements and qualitative visual classifications. We find that both galaxy structure and morphology depend on stellar mass and environment for our sample as a whole. We only find an impact of the environment on galaxy size for galaxies more massive than 1011 M⊙. We find higher Sérsic indices (n) and bulge-to-total ratios (B/T) in high-density regions when compared to low-density counterparts at similar stellar masses. We also find that galaxies with higher stellar mass have steeper light profiles (high n, B/T) compared to galaxies with lower stellar mass. Using visual classifications, we find a morphology–density relation at z ∼ 0.84 for galaxies more massive than 1010 M⊙, with elliptical galaxies being dominant at high-density regions and disc galaxies more common in low-density regions. However, when splitting the sample into colour–colour-selected star-forming and quiescent sub-populations, there are no statistically significant differences between low- and high-density regions. We find that quiescent galaxies are smaller, have higher Sérsic indices (for single profiles, around n ∼ 4), and higher bulge-to-total light ratios (for decomposed profiles, around B/T ∼ 0.5) when compared to star-forming counterparts (n ∼ 1 and B/T ∼ 0.3, for single and double profiles, respectively). We confirm these trends with non-parametric quantities, finding quiescent galaxies to be smoother (lower asymmetry, lower M20) and to have most of their light over smaller areas (higher concentration and Gini coefficient) than star-forming galaxies. Overall, we find a stronger dependence of structure and morphology on stellar mass than on local density and these relations are strongly correlated with the quenching fraction. The change in average structure or morphology corresponds to a change in the relative fractions of blue disc-like galaxies and red elliptical galaxies with stellar mass and environment. We hypothesise that the processes responsible for the quenching of star formation must also affect the galaxy morphology on similar timescales.

Nuclear Magnetic Resonance Spectroscopy

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Local and Average Structural Changes in Zeolite A upon Ion Exchange

The infamous ‘structure–property relationship’ is a long-standing problem for the design, study and development of novel functional materials. Most conventional characterization methods, including diffraction and crystallography, give us a good description of long-range order within crystalline materials. In recent decades, methods such as Solid State NMR (SS NMR) are more widely used for characterization of crystalline solids, in order to reveal local structure, which could be different from long-range order and sometimes hidden from long-range order probes. In particular for zeolites, this opens a great avenue for characterization through studies of the local environments around Si and Al units within their crystalline frameworks. In this paper, we show that some structural modifications occur after partially exchanging the extraframework Na + ions with monovalent, Li + , K + , Rb + and NH 4 + and divalent, Ca 2 + cations. Solid state NMR is deployed to study the local structure of exchanged materials, while average stricture changes can be observed by powder diffraction (PXRD). To corroborate our findings, we also employ Fourier Transform Infrared spectroscopy (FT-IR), and further characterization of some samples was done using Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray spectroscopy (EDX).

Temperature-induced local and average structural changes in BaTiO3−xBi(Zn1/2Ti1/2)O3 solid solutions: The origin of high temperature dielectric permittivity

The existence of local tetragonal distortions is evidenced in the BaTiO3–xBi(Zn1/2Ti1/2)O3 (BT–xBZT) relaxor dielectric material system at elevated temperatures. The local and average structures of BT-xBZT with different compositions are characterized using in situ high temperature total scattering techniques. Using the box-car fitting method, it is inferred that there are tetragonal polar clusters embedded in a non-polar pseudocubic matrix for BT-xBZT relaxors. The diameter of these polar clusters is estimated as 2–3 nm at room temperature. Sequential temperature series fitting shows the persistence of the tetragonal distortion on the local scale, while the average structure transforms to a pseudocubic paraelectric phase at high temperatures. The fundamental origin of the temperature stable permittivity of BT-xBZT and the relationship with the unique local scale structures are discussed. This systematic structural study of the BT-xBZT system provides both insight into the nature of lead-free perovskite relaxors, and advances the development of a wide range of electronics with reliable high temperature performance.

Observation of dynamic atom-atom correlation in liquid helium in real space

Liquid 4He becomes superfluid and flows without resistance below temperature 2.17 K. Superfluidity has been a subject of intense studies and notable advances were made in elucidating the phenomenon by experiment and theory. Nevertheless, details of the microscopic state, including dynamic atom–atom correlations in the superfluid state, are not fully understood. Here using a technique of neutron dynamic pair-density function (DPDF) analysis we show that 4He atoms in the Bose–Einstein condensate have environment significantly different from uncondensed atoms, with the interatomic distance larger than the average by about 10%, whereas the average structure changes little through the superfluid transition. DPDF peak not seen in the snap-shot pair-density function is found at 2.3 Å, and is interpreted in terms of atomic tunnelling. The real space picture of dynamic atom–atom correlations presented here reveal characteristics of atomic dynamics not recognized so far, compelling yet another look at the phenomenon.

Designing tunable band-gap and magnetization at room-temperature in Pb(Ti1-xMx)O3-δ (M=Ni and Pd) thin films

The Pb(Ti1-xMx)O3-δ (M=Ni and Pd) ferroelectric thin films prepared by a sol-gel technique have been studied by means of structural characterizations, optical and magnetic measurements. X-ray diffraction and Raman scattering results reflect the visible changes in average structure. Moreover, d8M2+ doping has important effects on the energy band structure and magnetic orderings. Optical transmittance spectra analysis indicates that Pb(Ti0.85Ni0.15)O3-δ and Pb(Ti0.85Pd0.15)O3-δ thin films present small band-gaps of 2.67eV and 2.55eV, respectively. Also, the as-grown Pb(Ti0.85M0.15)O3-δ thin films show room-temperature ferromagnetism, in contrast to PbTiO3 which is diamagnetic. A bound magnetic polaron model can be employed to explain the observed ferromagnetic behavior.

Optical modulation and magnetic transition in PbTi1−xPdxO3−δ ferroelectric thin films

The PbTi1−xPdxO3−δ (xPTPO) thin films prepared by chemical solution deposition have been investigated by means of structural characterizations, optical and magnetic measurements. X-ray diffraction patterns show that all the films have a pseudotetragonal perovskite structure, but also exhibit a lattice dilatation behavior and increased internal strain as the x increases. A possible mechanism for strain-induced structural evolution is discussed. Raman scattering further corroborates this change in average structure, where the characteristic variation of phonon modes, indirectly reveal the incorporation of Pd2+ ions into host lattice. Transmittance spectra analysis indicates that Pd doping has a key effect on the energy band structure. The optical bandgap of xPTPO films decreases significantly with increasing Pd content, expressed by (3.5–9.0x) eV (0≤x≤0.09). Also, magnetic switching driven by doping has been confirmed in the films, which is attributed to the competition between ferromagnetic and paramagnetic/antiferromagnetic components.

Structural and superconducting features of Tl-1223 prepared at ambient pressure

This study provides an account of the bulk preparation of TlBa2Ca2Cu3O9−δ (Tl-1223) superconductor at ambient pressure, and the critical temperature (Tc) features under thermal-annealing conditions. The ‘as-prepared’ Tl-1223 (Tc = 106 K) presents a significantly higher Tc = 125 K after annealing the polycrystalline material in either flowing Ar + 4% H2, or N2 gases. In order to understand the fundamental reasons for a particular Tc, we refined the average bulk structures using powder x-ray diffraction data. Although Ar + 4%H2 annealed Tl-1223 shows an increased ‘c’ lattice parameter, it shrinks by 0.03% (approximately unchanged) upon N2 anneal. Due to such indeterminate conclusions on the average structural changes, local structures were investigated at using aberration-corrected scanning-transmission electron microscopy technique. Similar compositional changes in the atomic arrangements of both annealed-samples of Tl-1223 were detected in which the plane containing a Ca atomic layer gives a non-uniform contrast, due to substitution of some heavier Tl. In this report, extensive bulk properties are summarized through temperature-dependent resistivity, and shielding and Meissner fractions of magnetic susceptibility results; the bulk and local structures are investigated to correlate to properties.

Modified structure and optical properties of multiferroic Pb(Zr0.53Ti0.47)x(Fe0.5Nb0.5)(1−x)O3 ceramics

The Pb(Zr0.53Ti0.47)x(Fe0.5Nb0.5)(1−x)O3 (xPZTFN) multiferroic ceramics synthesized by a solid state reaction method have been investigated by means of structural characterizations and optical measurement. All the samples show polycrystalline perovskite structures with dense microstructures, but exhibit a gradual transition behavior from cubic to tetragonal structure with increasing x. The xPZTFN (0≤x≤0.2) ceramics have an average crystal structure described as the centrosymmetric cubic perovskite, whereas x≥0.4 ceramics are consistent with a non-centrosymmetric tetragonal structure. Coexistence of both cubic and tetragonal symmetries is observed for x=0.3. Raman spectroscopy analysis corroborates the change in average structure with the x but also show the local crystal symmetry for 0≤x≤0.2 ceramics to deviate from the idealized cubic perovskite. Optical absorption spectra indicate that Pb(Zr0.53Ti0.47)O3 (PZT) doping has an effect on the energy band structure. The band gap (Eg) of xPZTFN (0≤x≤0.7) ceramics is in the range of 2.08–2.33eV, much smaller than the 3.21eV Eg of the PZT material. This result shows that the modification of optical property can be achieved by manipulating the composition in xPZTFN materials.

Thermally Stable BaTiO3-Bi(Mg0.75W0.25)O3 Solid Solutions: Sintering Characteristics, Phase Evolution, Raman Spectra, and Dielectric Properties

(1 − x)BaTiO3-xBi(Mg0.75W0.25)O3 [(1 − x)BT-xBMW, 0.02 ≤ x ≤ 0.24] ceramics were synthesized by a two-step solid-state reaction technique. X-ray diffraction (XRD) patterns show that a systematic structure evolution from tetragonal to pseudocubic phase was observed at x = 0.07. Raman spectra analysis illustrates that a change in average structure was observed with increasing x, and the local crystal symmetry which deviated from the idealized cubic perovskite structure appeared as x ≥ 0.07. Temperature dependence of dielectric properties indicates that the phase transition temperature (Tc) decreased with increasing x. Moreover, (1 − x)BT-xBMW (0.07 ≤ x ≤ 0.24) ceramics show good dielectric thermal stability over a wide temperature range, which indicates that these ceramics are candidates for thermal stability devices.

The structure of (Ca,Co)CoSi2O6 pyroxenes and the Ca-M2+ substitution in (Ca,M2+)M2+Si2O6 pyroxenes (M2+ = Co, Fe, Mg)

The crystal structure of three C2/c clinopyroxenes with composition (Ca 0.8 Co 0.2 )CoSi 2 O 6 , (Ca 0.6 Co 0.4 ) CoSi 2 O 6 and (Ca 0.4 Co 0.6 )CoSi 2 O 6 was refined down to R4σ = 2.6% by single-crystal X-ray diffraction. The crystals were synthesized at P = 3 GPa by cooling from 1500 to 1200 °C in a piston-cylinder apparatus. At the end of the refinement cycles, electron density residuals (up to 2.1 e-) were observed close to the M2 site and related to the site splitting of Ca and Co in the M2 polyhedron in the two subsites M2 and M2′. Split refinement significantly improved the agreement factor and decreased the uncertainty in the atomic coordinates. Similar features were found in (Ca,Mg)MgSi 2 O 6 and (Ca,Fe) FeSi 2 O 6 intermediate pyroxenes. The average structural changes related to the cation substitution at the M2 site in (Ca,Co)CoSi 2 O 6 , (Ca,Mg)MgSi 2 O 6 , and (Ca,Fe)FeSi 2 O 6 pyroxenes are similar: the T tetrahedron becomes more regular, the difference between M1-O bond lengths increases, and the M2-O3 bond lengths with the furthermost O3 oxygen atoms become longer. The changes in the M2-O bond distances are, however, not linear, and they are higher for more increased substitution. The largest structural deformation occurs on the (010) plane, with higher deformation at about 60° from the c axis for any composition. The orientation of the deformation ellipsoid is most related to a shift in tetrahedral chains. The scalar deformation for the cation substitution, εs, is linearly related to the cation radius of the average M2 site (IRM2), i.e., the deformation is higher as the cation size decreases, following the equation: εs = -0.0072(12)IRM2 + 0.0082(13), R 2 = 0.75. Increasing deformation with cation substitution is supported as the major limiting factor for solid solution. The displacement parameters for unsplit M2, O2, and O3 atoms increase up to the intermediate composition, indicating a local configuration for the M2 polyhedron centered by Ca and Co. However no significant change in U eq of the O3 atom is observed up to 20% substitution of the smaller cation in the M2 site. Comparison with Raman spectral data suggests that local chain structural configurations occur only for the substitution of the smaller cation in the M2 site higher than 20%, and that the substitution mechanism is different for C2/c clinopyroxenes with lower and higher Ca content

Soft modes and local structural transitions in Pb-free Ba(Ti0.8Zr0.2)O3-x (Ba0.7Ca0.3)TiO3 (x = 0.5): Pressure- and temperature-dependent Raman studies

We report our Raman studies of a new lead-free relaxor ferroelectrics, Ba0.85Ca0.15Ti0.9Zr0.1O3 (BCTZO). The Raman modes of BCTZO are compared with those of BaTi0.8Zr0.2O3 (BTZO), and BaTiO3 (BTO). Also, they are compared with the eigenmodes of BTO calculated by using an ab-initio quantum-mechanical frozen-phonon method. The sharp mode at 321 cm-1 of BTO, reported as a coupled mode showing an interference effect, becomes progressively broader in BTZO and BCTZO. This behavior, together with a broadening of the 527-cm-1 mode, suggests that the mode-coupling is weakened in BTZO and BCTZO. The structural transitions of BCTZO were investigated as functions of pressure at pressures below 20 GPa and of temperature at temperatures below 600 K. Three characteristic pressure-induced transitions, on each at 2.5, 5.0, and 13.0 GPa, were found. The transitions are suggested by the drastic changes in phonon modes (two softening modes, one each at ~ 300 and ~ 530 cm-1) and by the transformation of the intensity profile. A temperature-induced transition was found at a Curie temperature of ~ 380 K, where the average structure changes from tetragonal to cubic. It is accompanied by a softening mode at ~ 530 cm-1. The phonon spectrum of BCTZO suggests that its local environment is close to that of BTZO. However, the characteristic pressures of BCTZO are close to those of BTO. The sequence of pressure-induced transitions in both BCTZO and BTZO illustrate rich interplay between the long-range averaged structure and the short-range local order such that four distinguishable phases are suggested: tetragonal, locally ordered but compensated cubic, disordered cubic, and ideal cubic. We found that the critical pressures are plausibly related to the average crystal lattice.

Structure–property relationships in BaTiO3–BiFeO3–BiYbO3 ceramics

Ba1−xBixTi1−xYbx/2Fex/2O3 ceramics were fabricated by the solid state reaction method. X-ray diffraction analyses show 0 ≤ x ≤ 0.04 ceramics to have an average crystal structure described by the non-centrosymmetric tetragonal P4 mm space group, whereas x ≥ 0.08 ceramics are consistent with a centrosymmetric cubic perovskite (space group Pm-3 m). Coexistence of both tetragonal and cubic symmetries is observed for x = 0.06. Raman spectroscopy analysis corroborate a change in average structure with increasing x, but also show the local crystal symmetry for x ≥ 0.08 ceramics to deviate from the idealized cubic perovskite structure. Dielectric data show a ferroelectric-to-relaxor crossover, which occurs in conjunction with the change in both the average and local crystal symmetry as indicated by X-ray and Raman data. For x ≥ 0.08, ceramics exhibit relaxor behavior, which is also accompanied by a shift of the permittivity maxima towards higher temperatures with increasing x.

Average Structures of a Single Knotted Ring Polymer

Two types of average structure of a single knotted ring polymer are studied by Brownian dynamics simulations. For a ring polymer with N segments, its structure is represented by a 3 N -dimensional conformation vector consisting of the Cartesian coordinates of the segment positions relative to the center of mass of the ring polymer. The average structure is given by the average conformation vector, which is self-consistently defined as the average of the conformation vectors obtained from a simulation each of which is rotated to minimize its distance from the average conformation vector. From each conformation vector sampled in a simulation, 2 N conformation vectors are generated by changing the numbering of the segments. Among the 2 N conformation vectors, the one closest to the average conformation vector is used for one type of average structure. The other type of average structure uses all the conformation vectors generated from those sampled in a simulation. In the case of the former average structure, the knotted part of the average structure is delocalized for small N and becomes localized as N increases. In the case of the latter average structure, the average structure changes from a double loop structure for small N to a single loop structure for large N , which indicates the localization–delocalization transition of the knotted part.

Effects of TMAO on the Structure and Aggregation Properties of Tau

Alzheimer’s disease is characterized by accumulation of neurofibrillary tangles composed principally of the microtubule-associated protein, tau. It is known that tau is a naturally unfolded protein that acquires secondary structure during aggregation into insoluble fibers. However, the structural changes important for the aggregation process are not known. We have found that in the presence of trimethylamine-N-oxide (TMAO), a C-terminal fragment of human tau (255-441) acquires regular secondary structure and its rate of aggregation is enormously enhanced. NMR studies reveal significant sharpening of resonance cross peaks without apparent changes in peak dispersion in the presence of TMAO suggesting overall increased conformational constraint with minimal changes in average structure. Furthermore, NH-NOE experiments reveal increased stiffening of three specific regions in the molecule: 311–316 in the 2nd inter-repeat, 344–350 in the 3rd inter-repeat, and 378-390 in the C-terminus. A single point mutation, Y310A, dramatically attenuates aggregation, but has no effect on promoting normal microtubule assembly. Thus, the mechanism by which this residue links structure with function is of particular interest. NMR analysis showed no appreciable change in the NH-NOE spectra in response to this mutation. But, significant changes in chemical shift values in the 2nd inter-repeat region 308-320, reflecting significantly altered chemical environment, were observed. We propose that some or all of these specific changes in tau dynamics may be critical for aggregation leading to neurodegeneration.

Extratropical Transition of Southwest Pacific Tropical Cyclones. Part I: Climatology and Mean Structure Changes

A database of tropical cyclone best track and intensity information for the southwest Pacific Ocean basin is used to construct a 28-year climatology for tropical cyclones that move into middle latitudes. Of the nine or so tropical cyclones that form each year, an average of about three can be expected to migrate south of 35°S, with the greatest fraction in March. Storms entering the Tasman Sea west of New Zealand (NZ) move almost due south on average and retain greater intensity than those to the east of NZ, where storms decay quickly while moving rapidly away to the southeast. Storms east of NZ are embedded in a stronger, more zonal flow than those to the west, which move poleward ahead of a larger-amplitude trough. During El Niño years, tropical cyclones that move into middle latitudes exhibit stronger zonal motion and occur over a wider range of longitudes than during La Niña years. Storm intensity is only weakly correlated with concurrent SST anomalies, suggesting that atmospheric circulation is the dominant influence on storm properties. Average structure changes during extratropical transition (ET) are identified using the NCEP–NCAR reanalysis dataset, for a subset of 33 transitioning storms during 1980–97. Composites are used to construct a three-dimensional conceptual model of the transformation from a mature hurricane to an asymmetric baroclinic midlatitude cyclone. Southwest Pacific tropical cyclones encounter the baroclinic westerlies early in their lives, accounting for their average eastward (and poleward) motion. At maximum average intensity near 20°S, baroclinic effects are already important, with warm frontogenesis appearing in the southeast quadrant and outflow aloft into a downstream subtropical wind maximum that moves poleward with the storm. By 25°S, the average TC has lost the characteristic symmetric anticyclonic outflow aloft and acquired the characteristics of a baroclinic midlatitude storm, including regions of warm and cold frontogenesis, a vertical motion dipole and a westward tilt with height. From about 30°S poleward, a second upper-tropospheric wind maximum appears west of the storm, with strengthening cyclonic vorticity advection aloft. Below about 400 hPa, the storm retains the vertical, warm cyclonic core as it migrates poleward.

Ab initio Monte Carlo simulation using multicanonical algorithm: temperature dependence of the average structure of water dimer

A multicanonical Monte Carlo simulation has been performed to investigate average structural changes in the water dimer with temperature. Potential energy was calculated by the ab initio MO method at the RHF/6-31G∗ level at each step of the simulation. By combining the reweighting technique with the multicanonical algorithm various thermodynamic properties have been evaluated over a wide range of temperature from a single production run. The technique is an ideal tool for studying temperature dependence properties, and the temperature dependence of the distribution functions of various geometric parameters has been examined in detail. It was found that the probability of finding structures similar to that of the transition state increases as the temperature is increased.

Ab initio Monte Carlo simulation using multicanonical algorithm: temperature dependence of the average structure of water dimer

A multicanonical Monte Carlo simulation has been performed to investigate average structural changes in the water dimer with temperature. Potential energy was calculated by the ab initio MO method at the RHF/6-31G* level at each step of the simulation. By combining the reweighting technique with the multicanonical algorithm various thermodynamic properties have been evaluated over a wide range of temperature from a single production run. The technique is an ideal tool for studying temperature dependence properties, and the temperature dependence of the distribution functions of various geometric parameters has been examined in detail. It was found that the probability of finding structures similar to that of the transition state increases as the temperature is increased.