1,597 research outputs found
A first-principles study of the structural, electronic, optical, and vibrational properties for paramagnetic half-Heusler compound TiIrBi by GGA and GGA
The structural, electronic, optical, and vibrational properties of half-Heusler compound TiIrBi have been investigated by using the Generalized Gradient Approximation (GGA) and GGA plus modified Becke and Johnson (GGA + mBJ) functional within the Density Functional Theory (DFT). The obtained formation enthalpies and energy-volume curves for the three different atomic arrangements (alpha, beta and gamma) show that gamma phase is the most energetically favorable phase. Additionally, among the paramagnetic (PM), ferromagnetic (FM), and antiferromagnetic (AFM) magnetic systems considered for the gamma-phase of this compound, the paramagnetic system is found to be the most stable. The spin-polarized electronic band calculations of the TiIrBi compound demonstrate that this material has a semiconductor nature in both the majority and minority spin channels with the direct bandgap of 0.56 and 0.87 eV using the GGA and GGA + mBJ approach, respectively. The obtained formation enthalpy and phonon dispersion curves for gamma-crystal structure of TiIrBi compound show that this material is both thermodynamically and dynamically stable. We have also examined the optical properties by computing the optical parameters such as real and imaginary parts of the dielectric function, refractive index, extinction coefficient, optical conductivity, and reflectivity of the half-Heusler compound TiIrBi in the photon energy range of 0-16 eV. The collected results indicate that the TiIrBi compound has a direct bandgap semiconductor, which makes it a convenient material for technological applications in optoelectronics
Real Space Visualization of Thermomagnetic Irreversibility within Supercooling and Superheating Spinodals in using Scanning Hall Probe Microscopy
Phase coexistence across disorder-broadened and magnetic-field-induced first
order antiferromagnetic to ferrimagnetic transition in polycrystalline
has been studied mesoscopically by Scanning Hall Probe
Microscope at 120K and up to 5 Tesla magnetic fields. We have observed
hysteresis with varying magnetic field and the evolution of coexisting
antiferromagnetic and ferrimagnetic state on mesoscopic length scale. These
studies show that the magnetic state of the system at low field depends on the
path followed to reach 120 K. The low field magnetic states are mesoscopically
different for virgin and second field increasing cycle when 120 K is reached by
warming from 5K, but are the same within measurement accuracy when the
measuring temperature of 120K is reached from 300K by cooling
Photoluminescence transient study of surface defects in ZnO nanorods grown by chemical bath deposition
Two deep level defects (2.25 and 2.03 eV) associated with oxygen vacancies
(V) were identified in ZnO nanorods (NRs) grown by low cost chemical bath
deposition. A transient behaviour in the photoluminescence (PL) intensity of
the two V states was found to be sensitive to the ambient environment and
to NR post-growth treatment. The largest transient was found in samples dried
on a hot plate with a PL intensity decay time, in air only, of 23 and 80 s for
the 2.25 and 2.03 eV peaks, respectively. Resistance measurements under UV
exposure exhibited a transient behaviour in full agreement with the PL
transient indicating a clear role of atmospheric O on the surface defect
states. A model for surface defect transient behaviour due to band bending with
respect to the Fermi level is proposed. The results have implications for a
variety of sensing and photovoltaic applications of ZnO NRs
Scattering of elastic waves by periodic arrays of spherical bodies
We develop a formalism for the calculation of the frequency band structure of
a phononic crystal consisting of non-overlapping elastic spheres, characterized
by Lam\'e coefficients which may be complex and frequency dependent, arranged
periodically in a host medium with different mass density and Lam\'e
coefficients. We view the crystal as a sequence of planes of spheres, parallel
to and having the two dimensional periodicity of a given crystallographic
plane, and obtain the complex band structure of the infinite crystal associated
with this plane. The method allows one to calculate, also, the transmission,
reflection, and absorption coefficients for an elastic wave (longitudinal or
transverse) incident, at any angle, on a slab of the crystal of finite
thickness. We demonstrate the efficiency of the method by applying it to a
specific example.Comment: 19 pages, 5 figures, Phys. Rev. B (in press
Single-particle and collective excitations in quantum wires made up of vertically stacked quantum dots: Zero magnetic field
We report on the theoretical investigation of the elementary electronic
excitations in a quantum wire made up of vertically stacked self-assembled
InAs/GaAs quantum dots. The length scales (of a few nanometers) involved in the
experimental setups prompt us to consider an infinitely periodic system of
two-dimensionally confined (InAs) quantum dot layers separated by GaAs spacers.
The the Bloch functions and the Hermite functions together characterize the
whole system. We then make use of the Bohm-Pines' (full) random-phase
approximation in order to derive a general nonlocal, dynamic dielectric
function. Thus developed theoretical framework is then specified to work within
a (lowest miniband and) two-subband model that enables us to scrutinize the
single-particle as well as collective responses of the system. We compute and
discuss the behavior of the eigenfunctions, band-widths, density of states,
Fermi energy, single-particle and collective excitations, and finally size up
the importance of studying the inverse dielectric function in relation with the
quantum transport phenomena. It is remarkable to notice how the variation in
the barrier- and well-widths can allow us to tailor the excitation spectrum in
the desired energy range. Given the advantage of the vertically stacked quantum
dots over the planar ones and the foreseen applications in the single-electron
devices and in the quantum computation, it is quite interesting and important
to explore the electronic, optical, and transport phenomena in such systems
Impact of 50% ethanolic extract of Calendula officinalis (flower) on the reproductive function of male albino rats (Rattus norvegicus)
Oral administration to male rats of 200mg kg-1 body weight of an extract of Calendula officinalis flowers every day for 60 days did not cause loss of body weight, but decreased significantly the weight of the testis, epididymis, seminal vesicle and ventral prostate. Sperm motility as well as sperm density were reduced significantly, resulting in 80% loss of fertility.Serum testosterone levels showed highly significant reduction. Total protein and sialic acid in the testis, epididymis, seminal vesicles and ventral prostate decreased significantly, and testicular cholesterol was elevated. All measured haematological parameters were unchanged
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