8,049 research outputs found
Ground and excited states of Li, Be through a density-based approach
Density functional calculations are performed for ground [He]2s
S, and three metastable bound excited states, 1s2s2p P,
1s2p S, 1s2s2p3p P of Li and [He]2s2p P,
[He]2p S, 1s2s2p S of Be each. The
work-function-based exchange potential is used, while the correlation effects
are included by employing the Lee-Yang-Parr potential. The relevant
nonrelativistic KS equation is solved by means of a generalized pseudospectral
discretization scheme offering nonuniform and optimal spatial grid. Computed
total energies, radial densities, selected density moments, as well as two
transition wavelengths (1s2s2p P1s2p S of Li,
[He]2s2p P [He]2p S of Be) show reasonably good
agreement with the available theoretical and experimental data. The term
energies show an absolute deviation of 0.007--0.171% with the largest deviation
being observed for the even-parity P state of Li. The transition
wavelengths of Li, Be are calculated within 0.891 and 0.438% of the
experimental values. This offers a simple practical route towards accurate
reliable calculation of excited states of anions within density functional
theory.Comment: 12 pages, 35 ref
Synchrotron spectral index and interstellar medium densities of star-forming galaxies
The spectral index of synchrotron emission is an important parameter in
understanding the properties of cosmic ray electrons (CREs) and the
interstellar medium (ISM). We determine the synchrotron spectral index
() of four nearby star-forming galaxies, namely NGC 4736, NGC
5055, NGC 5236 and NGC 6946 at sub-kpc linear scales. The was
determined between 0.33 and 1.4 GHz for all the galaxies. We find the spectral
index to be flatter () in regions with total neutral (atomic +
molecular) gas surface density, , typically in the arms and inner parts of the galaxies. In regions
with , especially in the
interarm and outer regions of the galaxies, the spectral index steepens sharply
to . The flattening of is unlikely to be caused due to
thermal free--free absorption at 0.33 GHz. Our result is consistent with the
scenario where the CREs emitting at frequencies below GHz are
dominated by bremsstrahlung and/or ionization losses. For denser medium
(), having strong magnetic
fields (G), is seen to be flatter than ,
perhaps caused due to ionization losses. We find that, due to the clumpy nature
of the ISM, such dense regions cover only a small fraction of the galaxy
( percent). Thus, the galaxy-integrated spectrum may not show
indication of such loss mechanisms and remain a power-law over a wide range of
radio frequencies (between to 10 GHz).Comment: 10 pages, 4 figures, 2 tables, Accepted to be published in MNRA
High Quality a-axis outgrowth on c-axis YlCa1-xBa2Cu3O7-d
The large amplitude of the high Tc (HTS) superconducting gap is attractive
for improved electronic applications. However, the study of such HTS cuprates
has uncovered that unlike the s-wave order parameter of the low Tc, an angle
dependent dx2-y2 wave function is the dominant order parameter in such
compounds. This symmetry causes low energy surface bound states, detrimental
for applications, except at (100) oriented surfaces. It is therefore essential
to have a smooth and well oriented surface of the crystallographic a-axis
(100). In this work we present a study of an unconventional way to attain such
surfaces in the form of a-axis outgrowth on a c-axis surface of sputtered
Y1-xCaxBa2Cu3O7-d thin film. The grains topography was tested using X-ray, SEM
and AFM together with Point Contact and Tunnel Junctions measurements.Comment: 15 pages, 5 figure
Determination of the critical current density in the d-wave superconductor YBCO under applied magnetic fields by nodal tunneling
We have studied nodal tunneling into YBa2Cu3O7-x (YBCO) films under magnetic
fields. The films' orientation was such that the CuO2 planes were perpendicular
to the surface with the a and b axis at 450 form the normal. The magnetic field
was applied parallel to the surface and perpendicular to the CuO2 planes. The
Zero Bias Conductance Peak (ZBCP) characteristic of nodal tunneling splits
under the effect of surface currents produced by the applied fields. Measuring
this splitting under different field conditions, zero field cooled and field
cooled, reveals that these currents have different origins. By comparing the
field cooled ZBCP splitting to that taken in decreasing fields we deduce a
value of the Bean critical current superfluid velocity, and calculate a Bean
critical current density of up to 3*10^7 A/cm2 at low temperatures. This
tunneling method for the determination of critical currents under magnetic
fields has serious advantages over the conventional one, as it avoids having to
make high current contacts to the sample.Comment: 8 pages, 2 figure
Order and disorder in intermediate filament proteins
AbstractIntermediate filaments (IFs), important components of the cytoskeleton, provide a versatile, tunable network of self-assembled proteins. IF proteins contain three distinct domains: an α-helical structured rod domain, flanked by intrinsically disordered head and tail domains. Recent studies demonstrated the functional importance of the disordered domains, which differ in length and amino-acid sequence among the 70 different human IF genes. Here, we investigate the biophysical properties of the disordered domains, and review recent findings on the interactions between them. Our analysis highlights key components governing IF functional roles in the cytoskeleton, where the intrinsically disordered domains dictate protein–protein interactions, supramolecular assembly, and macro-scale order
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