1,524 research outputs found
Convergence of the Many-Body Expansion of Interaction Potentials: From van der Waals to Covalent and Metallic Systems
The many-body expansion of the interaction potential between atoms and molecules is analyzed in detail for different types of interactions involving up to seven atoms. Elementary clusters of Ar, Na, Si, and, in particular, Au are studied, using first-principles wave-function- and density-functional-based methods to obtain the individual n-body contributions to the interaction energies. With increasing atom number the many-body expansion converges rapidly only for long-range weak interactions. Large oscillatory behavior is observed for other types of interactions. This is consistent with the fact that Au clusters up to a certain size prefer planar structures over the more compact three-dimensional Lennard-Jones-type structures. Several Au model potentials and semi-empirical PM6 theory are investigated for their ability to reproduce the quantum results. We further investigate small water clusters as prototypes of hydrogen-bonded systems. Here, the many-body expansion converges rapidly, reflecting the localized nature of the hydrogen bond and justifying the use of two-body potentials to describe water-water interactions. The question of whether electron correlation contributions can be successfully modeled by a many-body interaction potential is also addressed
Outcome of a questionnaire within European pharmaceutical aerosol group (EPAG) companies concerning the implementation of the abbreviated impactor measurement (AIM) concept for the assessment of orally inhaled product (OIP) aerosol aerodynamic particle size properties
The AIM Concept as an augmentation of full resolution cascade impactor (CI) measurements of the aerodynamic properties of aerosols emitted by OIPs has been in existence for about ten years. A previous EPAG-based survey undertaken five years ago indicated significant interest in the approach, particularly for the screening of candidate products in early stage product development. We report the outcome of a further questionnaire with the goals of establishing: (a) the types of AIM-based equipment currently in use; and (b) insight into perceived hurdles towards full implementation within the product lifecycle. Responses were received in October 2016 from 17 out of 22 organizations from people involved directly with the in vitro testing of pressurized metered dose inhaler (pMDI)
and dry powder inhaler (DPI) products. The survey has shown that the AIM concept has sufficient popularity within the EPAG respondent organizations to be considered a viable augmentation to existing full resolution CI methodology. The main conclusions are: (1) The Fast Screening Andersen (FSA), reduced Next Generation
Impactor (rNGI) and Fast Screening Impactor (FSI) are all used as AIM-based impactor configurations for both dry powder inhaler (DPI) and pressurized metered dose inhaler (pMDI) applications; (2) AIM-based methods are used almost entirely for the early development phase of the OIP life cycle; (3) Organizations in general do not have confidence to use the AIM concept more widely in the product life cycle whilst no compendial/regulatory
guidance is available to provide standard procedures and precautions/regulatory acceptance respectively
Extreme gravitational lensing in vicinity of Schwarzschild-de Sitter black holes
We have developed a realistic, fully general relativistic computer code to
simulate optical projection in a strong, spherically symmetric gravitational
field. The standard theoretical analysis of optical projection for an observer
in the vicinity of a Schwarzschild black hole is extended to black hole
spacetimes with a repulsive cosmological constant, i.e, Schwarzschild-de Sitter
spacetimes. Influence of the cosmological constant is investigated for static
observers and observers radially free-falling from the static radius.
Simulations include effects of the gravitational lensing, multiple images,
Doppler and gravitational frequency shift, as well as the intensity
amplification. The code generates images of the sky for the static observer and
a movie simulations of the changing sky for the radially free-falling observer.
Techniques of parallel programming are applied to get a high performance and a
fast run of the BHC simulation code
Comparison of Coulomb Blockade Thermometers with the International Temperature Scale PLTS-2000
The operation of the primary Coulomb blockade thermometer (CBT) is based on a
measurement of bias voltage dependent conductance of arrays of tunnel junctions
between normal metal electrodes. Here we report on a comparison of a CBT with a
high accuracy realization of the PLTS-2000 temperature scale in the range from
0.008 K to 0.65 K. An overall agreement of about 1% was found for temperatures
above 0.25 K. For lower temperatures increasing differences are caused by
thermalization problems which are accounted for by numerical calculations based
on electron-phonon decoupling.Comment: 6 pages, 5 figure
Holographic Uniformization
We derive and study supergravity BPS flow equations for M5 or D3 branes
wrapping a Riemann surface. They take the form of novel geometric flows
intrinsically defined on the surface. Their dual field-theoretic interpretation
suggests the existence of solutions interpolating between an arbitrary metric
in the UV and the constant-curvature metric in the IR. We confirm this
conjecture with a rigorous global existence proof.Comment: 52 pages, 3 figure
Double-Layer Systems at Zero Magnetic Field
We investigate theoretically the effects of intralayer and interlayer
exchange in biased double-layer electron and hole systems, in the absence of a
magnetic field. We use a variational Hartree-Fock-like approximation to analyze
the effects of layer separation, layer density, tunneling, and applied gate
voltages on the layer densities and on interlayer phase coherence. In agreement
with earlier work, we find that for very small layer separations and low layer
densities, an interlayer-correlated ground state possessing spontaneous
interlayer coherence (SILC) is obtained, even in the absence of interlayer
tunneling. In contrast to earlier work, we find that as a function of total
density, there exist four, rather than three, distinct noncrystalline phases
for balanced double-layer systems without interlayer tunneling. The newly
identified phase exists for a narrow range of densities and has three
components and slightly unequal layer densities, with one layer being spin
polarized, and the other unpolarized. An additional two-component phase is also
possible in the presence of sufficiently strong bias or tunneling. The
lowest-density SILC phase is the fully spin- and pseudospin-polarized
``one-component'' phase discussed by Zheng {\it et al.} [Phys. Rev. B {\bf 55},
4506 (1997)]. We argue that this phase will produce a finite interlayer Coulomb
drag at zero temperature due to the SILC. We calculate the particle densities
in each layer as a function of the gate voltage and total particle density, and
find that interlayer exchange can reduce or prevent abrupt transfers of charge
between the two layers. We also calculate the effect of interlayer exchange on
the interlayer capacitance.Comment: 35 pages, 19 figures included. To appear in PR
Temperature dependent resistivity of spin-split subbands in GaAs 2D hole system
We calculate the temperature dependent resistivity in spin-split subbands
induced by the inversion asymmetry of the confining potential in GaAs 2D hole
systems. By considering both temperature dependent multisubband screening of
impurity disorder and hole-hole scattering we find that the strength of the
metallic behavior depends on the symmetry of the confining potential (i.e.,
spin-splitting) over a large range of hole density. At low density above the
metal-insulator transition we find that effective disorder reduces the
enhancement of the metallic behavior induced by spin-splitting. Our theory is
in good qualitative agreement with existing experiments
Escape from planarity in fragment-based drug discovery : A synthetic strategy analysis of synthetic 3D fragment libraries
In fragment-based drug discovery (FBDD), there is a developing appreciation that 3D fragments could offer opportunities that are not provided by 2D fragments. This review provides an overview of the synthetic strategies that have been used to prepare 3D fragments, as discussed in 25 papers published from 2011 to mid-May 2020. Three distinct strategies are highlighted: (i) diversity-oriented synthesis; (ii) the synthesis and diversification of scaffolds; and (iii) computational design and synthesis (where 3D fragments were computationally enumerated and filtered on the basis of computationally generated 3D shape descriptors and other properties). We conclude that a workflow that combines computational design and one other strategy, together with a consideration of fragment properties, 3D shape and ‘fragment sociability’, could allow 3D fragments to feature more widely in fragment libraries and could facilitate fragment-to-lead optimisation
The non-random walk of stock prices: The long-term correlation between signs and sizes
We investigate the random walk of prices by developing a simple model
relating the properties of the signs and absolute values of individual price
changes to the diffusion rate (volatility) of prices at longer time scales. We
show that this benchmark model is unable to reproduce the diffusion properties
of real prices. Specifically, we find that for one hour intervals this model
consistently over-predicts the volatility of real price series by about 70%,
and that this effect becomes stronger as the length of the intervals increases.
By selectively shuffling some components of the data while preserving others we
are able to show that this discrepancy is caused by a subtle but long-range
non-contemporaneous correlation between the signs and sizes of individual
returns. We conjecture that this is related to the long-memory of transaction
signs and the need to enforce market efficiency.Comment: 9 pages, 5 figures, StatPhys2
Intestinal Inflammation Induced by Soybean Meal Ingestion Increases Intestinal Permeability and Neutrophil Turnover Independently of Microbiota in Zebrafish
Indexación: Scopus.Intestinal inflammation is a condition shared by several intestinal chronic diseases, such as Crohn's disease and ulcerative colitis, with severely detrimental consequences in the long run. Current mammalian models have considerably increased understanding of this pathological condition, highlighting the fact that, in most of the cases, it is a highly complex and multifactorial problem and difficult to deal with. Thus, there is an increasingly evident need for alternative animal models that could offer complementary approaches that have not been exploited in rodents, thereby contributing to a different view on the disease. Here, we report the effects of a soybean meal–induced intestinal inflammation model on intestinal integrity and function as well as on neutrophil recruitment and microbiota composition in zebrafish. We find that the induced intestinal inflammation process is accompanied by an increase in epithelial permeability in addition to changes in the mRNA levels of different tight junction proteins. Conversely, there was no evidence of damage of epithelial cells nor an increase in their proliferation. Of note, our results show that this intestinal inflammatory model is induced independently of the presence of microbiota. On the other hand, this inflammatory process affects intestinal physiology by decreasing protein absorption, increasing neutrophil replacement, and altering microbiota composition with a decrease in the diversity of cultivable bacteria. © Copyright © 2020 Solis, Hamilton, Caruffo, Garcia-Lopez, Navarrete, Guillemin and Feijoo.https://www.frontiersin.org/articles/10.3389/fimmu.2020.01330/ful
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