5,898 research outputs found
Preparation of monotectic alloys having a controlled microstructure by directional solidification under dopant-induced interface breakdown
Monotectic alloys having aligned spherical particles of rods of the minor component dispersed in a matrix of the major component are prepared by forming a melt containing predetermined amounts of the major and minor components of a chosen monotectic system, providing in the melt a dopant capable of breaking down the liquid solid interface for the chosen alloy, and directionally solidfying the melt at a selected temperature gradient and a selected rate of movement of the liquid-solid interface (growth rate). Shaping of the minor component into spheres or rods and the spacing between them are controlled by the amount of dopant and the temperature gradient and growth rate values. Specific alloy systems include Al Bi, Al Pb and Zn Bi, using a transition element such as iron
Ground-state degeneracies leave recognizable topological scars in the one-particle density
In Kohn-Sham density functional theory (KS-DFT) a fictitious system of
non-interacting particles is constructed having the same ground-state (GS)
density as the physical system of interest. A fundamental open question in DFT
concerns the ability of an exact KS calculation to spot and characterize the GS
degeneracies in the physical system. In this article we provide theoretical
evidence suggesting that the GS density, as a function of position on a 2D
manifold of parameters affecting the external potential, is "topologically
scarred" in a distinct way by degeneracies. These scars are sufficiently
detailed to enable determination of the positions of degeneracies and even the
associated Berry phases. We conclude that an exact KS calculation can spot and
characterize the degeneracies of the physical system
Exact results for a charged, harmonically trapped quantum gas at arbitrary temperature and magnetic field strength
An analytical expression for the first-order density matrix of a charged,
two-dimensional, harmonically confined quantum gas, in the presence of a
constant magnetic field is derived. In contrast to previous results available
in the literature, our expressions are exact for any temperature and magnetic
field strength. We also present a novel factorization of the Bloch density
matrix in the form of a simple product with a clean separation of the
zero-field and field-dependent parts. This factorization provides an
alternative way of analytically investigating the effects of the magnetic field
on the system, and also permits the extension of our analysis to other
dimensions, and/or anisotropic confinement.Comment: To appear in Phys. Rev.
Ecdysteroids: A novel class of anabolic agents?
Increasing numbers of dietary supplements with ecdysteroids are marketed as “natural anabolic agents”. Results of recent studies suggested that their anabolic effect is mediated by estrogen receptor (ER) binding. Within this study the anabolic potency of ecdysterone was compared to well characterized anabolic substances. Effects on the fiber sizes of the soleus muscle in rats as well the diameter of C2C12 derived myotubes were used as biological readouts. Ecdysterone exhibited a strong hypertrophic effect on the fiber size of rat soleus muscle that was found even stronger compared to the test compounds metandienone (dianabol), estradienedione (trenbolox), and SARM S 1, all administered in the same dose (5 mg/kg body weight, for 21 days). In C2C12 myotubes ecdysterone (1 µM) induced a significant increase of the diameter comparable to dihydrotestosterone (1 µM) and IGF 1 (1.3 nM). Molecular docking experiments supported the ERβ mediated action of ecdysterone. To clarify its status in sports, ecdysterone should be considered to be included in the class “S1.2 Other Anabolic Agents” of the list of prohibited substances of the World Anti-Doping Agency
Two electrons on a hypersphere: a quasi-exactly solvable model
We show that the exact wave function for two electrons, interacting through a
Coulomb potential but constrained to remain on the surface of a
-sphere (), is a polynomial in the
interelectronic distance for a countably infinite set of values of the
radius . A selection of these radii, and the associated energies, are
reported for ground and excited states on the singlet and triplet manifolds. We
conclude that the model bears the greatest similarity to normal
physical systems.Comment: 4 pages, 0 figur
A systematic benchmark of the ab initio Bethe-Salpeter equation approach for low-lying optical excitations of small organic molecules
The predictive power of the ab initio Bethe-Salpeter equation (BSE) approach,
rigorously based on many-body Green's function theory but incorporating
information from density functional theory, has already been demonstrated for
the optical gaps and spectra of solid-state systems. Interest in photoactive
hybrid organic/inorganic systems has recently increased, and so has the use of
the BSE for computing neutral excitations of organic molecules. However, no
systematic benchmarks of the BSE for neutral electronic excitations of organic
molecules exist. Here, we study the performance of the BSE for the 28 small
molecules in Thiel's widely-used time-dependent density functional theory
benchmark set [M. Schreiber et al. J. Chem. Phys. 128, 134110 (2008)]. We
observe that the BSE produces results that depend critically on the mean-field
starting point employed in the perturbative approach. We find that this
starting point dependence is mainly introduced through the quasiparticle
energies obtained at the intermediate GW step, and that with a judicious choice
of starting mean-field, singlet excitation energies obtained from BSE are in
excellent quantitative agreement with higher-level wavefunction methods. The
quality of the triplet excitations is slightly less satisfactory
Determination of the gaseous hydrogen ductile-brittle transition in copper-nickel alloys
A series of copper-nickel alloys were fabricated, notched tensile specimens machined for each alloy, and the specimens tested in 34.5 MPa hydrogen and in air. A notched tensile ratio was determined for each alloy and the hydrogen environment embrittlement (HEE) determined for the alloys of 47.7 weight percent nickel to 73.5 weight percent nickel. Stacking fault probability and stacking fault energies were determined for each alloy using the x ray diffraction line shift and line profiles technique. Hydrogen environment embrittlement was determined to be influenced by stacking fault energies; however, the correlation is believed to be indirect and only partially responsible for the HEE behavior of these alloys
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Developing professionalism in new IT graduates? Who needs it?
A new graduate may require a period of ‘acclimatisation’ through a process of ‘developing their professionalism’ to fit into their work environment. The e-Skills UK Technology Counts Insights 2010 report suggests that 110,500 new entrants a year are required to fill IT & Telecoms professional job roles, with 20,800 coming from education (predominantly graduate level and higher). However, 43% of recruiters were reporting a lack of suitable candidates for IT & Telecoms posts where growing importance will be placed on relationship management, business process analysis and design, project and programme management. IT & Telecoms professionals are increasingly expected to be multi-skilled, with sophisticated business and interpersonal skills as well as technical competence. As the report also says: ‘UK growth will continue to be primarily in high-value roles with an increasing need for customer and business-oriented skills as well as sophisticated technical competencies.’
The diverse needs and requirements of the IT sector, as specified by various employer groups and professional bodies including BCS, IET, eSkills, the CBI and the SFIA Foundation, are discussed. According to the CBI, ‘62% of entrants to the IT sector need to draw on managerial and professional business skills almost immediately.’ For organisations to succeed, their IT graduate recruits must supplement their IT skills with managerial and professional business skills. Well considered CPD will ensure that recent graduates can enhance their ‘academic’ skills with the necessary work-based skills for the benefit of both themselves and their new employer. The focus of the improvement will balance the student-centred needs for development and the engaging employer’s commercial needs
Hooke's law correlation in two-electron systems
We study the properties of the Hooke's law correlation energy (\Ec),
defined as the correlation energy when two electrons interact {\em via} a
harmonic potential in a -dimensional space. More precisely, we investigate
the ground state properties of two model systems: the Moshinsky atom (in
which the electrons move in a quadratic potential) and the spherium model (in
which they move on the surface of a sphere). A comparison with their Coulombic
counterparts is made, which highlights the main differences of the \Ec in
both the weakly and strongly correlated limits. Moreover, we show that the
Schr\"odinger equation of the spherium model is exactly solvable for two values
of the dimension (), and that the exact wave function is
based on Mathieu functions.Comment: 7 pages, 5 figure
Density-density functionals and effective potentials in many-body electronic structure calculations
We demonstrate the existence of different density-density functionals
designed to retain selected properties of the many-body ground state in a
non-interacting solution starting from the standard density functional theory
ground state. We focus on diffusion quantum Monte Carlo applications that
require trial wave functions with optimal Fermion nodes. The theory is
extensible and can be used to understand current practices in several
electronic structure methods within a generalized density functional framework.
The theory justifies and stimulates the search of optimal empirical density
functionals and effective potentials for accurate calculations of the
properties of real materials, but also cautions on the limits of their
applicability. The concepts are tested and validated with a near-analytic
model.Comment: five figure
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