231 research outputs found
First-principles calculations of electric field gradients in complex perovskites
Various experimental and theoretical work indicate that the local structure and chemical ordering play a crucial role in the different physical behaviors of lead-based complex ferroelectrics with the ABO 3 perovskite structure. First-principles linearized augmented plane wave (LAPW) with the local orbital extension method within local density approximation (LDA) are performed on structural models of Pb(Zr1/2Ti1/2 )O3 (PZT), Pb(Sc1/2Ta1/2)O3 (PST), Pb(Sc2/3W1/3)O3 (PSW), and Pb(Mg 1/3Nb2/3)O3 (PMN) to calculate electric field gradients (EFGs). In order to simulate these disordered alloys, various structural models were constructed with different imposed chemical orderings and symmetries. Calculations were carried out as a function of B-site chemical ordering, applied strain, and imposed symmetry. Large changes in the EFGs are seen in PZT as the electric polarization rotates between the tetragonal and rhombohedral directions. The onset of polarization rotation in monoclinic Cm symmetry strongly correlates with the shearing of the TiO6 octahedron, and there is a sharp change in slope in plots of Ti EFGs versus octahedral distortion index. The same changes in EFGs and the BO6 shearing corresponding to the change of off-centering direction are also seen in PST. In PSW and PMN, the calculated B cation EFGs showed more sensitivity to the surrounding nearest B neighboring environments. Calculated B atom EFGs in all alloys are considerably larger than those inferred from the NMR measurements. Based on comparisons with experiments, the calculated results are interpreted in terms of static and dynamic structural models of these materials
Estimate of halo ellipticity as a function of radius with flexions
The cold dark matter theory predicts triaxial dark matter haloes. The radial
distribution of halo ellipticity depends on baryonic processes and the nature
of dark matter particles (collisionless or collisional). Here we show that we
can use lensing flexion ratios to measure the halo ellipticity as a function of
radius. We introduce a weight function and study the relationship between the
first and second order statistics of flexion ratios, both of which can be used
to reduce the bias in the estimate of ellipticity. we perform numerical tests
for our method, and demonstrate that it can reduce the bias and determine the
halo ellipticity as a function of radius. We also point out that the minimum
mean flexion ratio can be used to trace the centres of galaxy clusters.Comment: 9 pages,9 figures, MNRAS accepte
The origin and properties of massive prolate galaxies in the Illustris simulation
We study galaxy shapes in the Illustris cosmological hydrodynamic simulation.
We find that massive galaxies have a higher probability of being prolate. For
galaxies with stellar mass larger than , 35 out of total
839 galaxies are prolate. For 21 galaxies with stellar mass larger than
, 9 are prolate, 4 are triaxial while the others are
close to being oblate. There are almost no prolate galaxies with stellar mass
smaller than . We check the merger history of the
prolate galaxies, and find that they are formed by major dry mergers. All the
prolate galaxies have at least one such merger, with most having mass ratios
between and . The gas fraction (gas mass to total baryon mass) of
the progenitors is 0-3 percent for nearly all these mergers, except for one
whose second progenitor contains gas mass, while its main
progenitor still contains less than . For the 35 massive prolate galaxies
that we find, 18 of them have minor axis rotation, and their angular momenta
mostly come from the spin angular momenta of the progenitors (usually that of
the main progenitor). We analyse the merger orbits of these prolate galaxies
and find that most of them experienced a nearly radial merger orbit. Oblate
galaxies with major dry mergers can have either radial or circular merger
orbits. We further discuss various properties of these prolate galaxies, such
as spin parameter , spherical anisotropy parameter ,
dark matter fraction, as well as inner density slopes for the stellar, dark
matter and total mass distributions.Comment: Accepted for publication in MNRAS. 24 pages, 14 figure
Milk-run routing problem with progress-lane in the collection of automobile parts
In recent years, the automotive industry has faced an unprecedented crisis. In particular, the zero-inventory approach, which has been widely pursued by many automobile companies, seems to be impractical in some real production contexts since it requires an inventory of all parts but in low amounts. In this paper, we investigate a new logistics method which collects automobile parts by integrating the progress-lane (P-LANE) into the corresponding vehicle routing problem. We propose a mixed integer programming formulation for this new model, which can simultaneously determines the trip routes to collect automobile parts, as well as the P-LANE that each collected part should be assigned to, so as to minimize the total costs of the production and inbound logistics. The comparison with the zero-inventory model shows that the use of the P-LANE within the milk-run system could significantly decrease the total costs and also improve the transportation efficiency. To be specific, for small and large size instances, the total costs of the zero-inventory model are about 10% and 30% higher than the ones with P-LANE, respectively, which suggests that the periodic part collection model with P-LANE could be more appropriate for automobile manufacturing
MaNGA DynPop -- V. The dark-matter fraction versus stellar velocity dispersion relation and initial mass function variations: dynamical models and full spectrum fitting of integral-field spectroscopy
Using the final MaNGA sample (DR17) of 10K galaxies, we investigate the dark
matter fraction within one half-light radius for about
6K galaxies with good kinematics spanning a wide range of morphologies and
stellar velocity dispersion (). We employ two techniques to estimate
: (i) Jeans Anisotropic Modelling (JAM), which performs dark matter
decomposition based on the stellar kinematics and (ii) comparing the total
dynamical mass-to-light ratios and the from Stellar Population Synthesis (SPS). We find that both methods
consistently show a significant trend of increasing with
decreasing , for and very low at larger
. For the 235 early-type galaxies with the best dynamical
models, we explore the variation of the stellar initial mass function (IMF) by
comparing the stellar mass-to-light ratios from JAM
and SPS. We confirm that the stellar mass excess , which reflects the IMF shape,
increases with , in agreement with previous studies that
reported a transition from Chabrier-like to Salpeter IMF among galaxies. We
also detect weak positive correlations between and age, but
no correlations with metallicity (). Finally, we stack galaxy spectra
according to their to search for differences in
IMF-sensitive spectral features (e.g. the doublet). We only
find marginal evidence for such differences, which casts doubt on the validity
of one or both methods to measure the IMF.Comment: 17 pages, 9 figures, 2 tables; Submitted to MNRAS on 21 September
202
Design and preparation of a novel colon-targeted tablet of hydrocortisone
The objective of this research was to design a new colon-targeted drug delivery system based on chitosan. The properties of the films were studied to obtain useful information about the possible applications of composite films. The composite films were used in a bilayer system to investigate their feasibility as coating materials. Tensile strength, swelling degree, solubility, biodegradation degree, Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), Scanning Electron Microscope (SEM) investigations showed that the composite film was formed when chitosan and gelatin were reacted jointly. The results showed that a 6:4 blend ratio was the optimal chitosan/gelatin blend ratio. In vitro drug release results indicated that the Eudragit- and chitosan/gelatin-bilayer coating system prevented drug release in simulated intestinal fluid (SIF) and simulated gastric fluid (SGF). However, the drug release from a bilayer-coated tablet in SCF increased over time, and the drug was almost completely released after 24h. Overall, colon-targeted drug delivery was achieved by using a chitosan/gelatin complex film and a multilayer coating system
A study of stellar orbit fractions: simulated IllustrisTNG galaxies compared to CALIFA observations
Motivated by the recently discovered kinematic "Hubble sequence" shown by the
stellar orbit-circularity distribution of 260 CALIFA galaxies, we make use of a
comparable galaxy sample at z = 0 with a stellar mass range from 5E9 to 5E11
solar masses, selected from the IllustrisTNG simulation and study their stellar
orbit compositions in relation to a number of other fundamental galaxy
properties.We find that the TNG100 simulation broadly reproduces the observed
fractions of different orbital components and their stellar mass dependencies.
In particular, the mean mass dependencies of the luminosity fractions for the
kinematically warm and hot orbits are well reproduced within model
uncertainties of the observed galaxies. The simulation also largely reproduces
the observed peak and trough features at a stellar mass of 1-2E10 solar masses,
in the mean distributions of the cold- and hot-orbit fractions, respectively,
indicating fewer cooler orbits and more hotter orbits in both more- and
less-massive galaxies beyond such a mass range. Several marginal disagreements
are seen between the simulation and observations: the average cold-orbit
(counter-rotating) fractions of the simulated galaxies below (above) a stellar
mass of 6E10 solar masses, are systematically higher than the observational
data by < 10% (absolute orbital fraction); the simulation also seems to produce
more scatter for the cold-orbit fraction and less so for the non-cold orbits at
any given galaxy mass. Possible causes that stem from the adopted heating
mechanisms are discussed.Comment: 12 pages, 6 figures, 3 tables, submitted to MNRAS. Comments are
welcome
Biomaterials research of China from 2013 to 2017 based on bibliometrics and visualization analysis
Objectives This study aims to evaluate the changes of development trends and research hotspots of biomaterials research from 2013 to 2017, which can identify the general information of papers and explore the changes of research content, thus providing perspectives for the development of biomaterials in China and other countries. Methods Data of the paper were retrieved from the Web of Science Core Collection, and then analyzed by the bibliometric and CiteSpace visualization analysis. Results It was found that a total of 3,839 related papers had been published from the year 2013 to 2017. The analysis of the articles showed that the annual quantity and quality of the articles in the biomaterials research have been increasing since 2013, and the Wang L / Chinese Academy of Sciences were the most productive author/institution. Meanwhile, the keywords “in vitro”, “scaffold”, “nanoparticle” , “mechanical property”, and “biocompatibility” have the relatively higher frequency, and the keywords “apatite”, “deposition”, and “surface modification” have the strongest burst citation. Conclusions After statistics and analysis, we found that biomaterials is a promising research field. The study may be helpful in understanding research trends in this field
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