98 research outputs found
Maximally-localized Wannier Functions in Antiferromagnetic MnO within the FLAPW Formalism
We have calculated the maximally-localized Wannier functions of MnO in its
antiferromagnetic (AFM) rhombohedral unit cell, which contains two formula
units. Electron Bloch functions are obtained with the linearized augmented
plane-wave method within both the LSD and the LSD+U schemes. The thirteen
uppermost occupied spin-up bands correspond in a pure ionic scheme to the five
Mn 3d orbitals at the Mn_1 (spin-up) site, and the four O 2s/2p orbitals at
each of the O_1 and O_2 sites. Maximal localization identifies uniquely four
Wannier functions for each O, which are trigonally-distorted sp^3-like
orbitals. They display a weak covalent bonding between O 2s/2p states and
minority-spin d states of Mn_2, which is absent in a fully ionic picture. This
bonding is the fingerprint of the interaction responsible for the AFM ordering,
and its strength depends on the one-electron scheme being used. The five Mn
Wannier functions are centered on the Mn_1 site, and are atomic orbitals
modified by the crystal field. They are not uniquely defined by the criterion
of maximal localization and we choose them as the linear combinations which
diagonalize the r^2 operator, so that they display the D_3d symmetry of the
Mn_1 site.Comment: 11 pages, 6 PostScript figures. Uses Revtex4. Hi-res figures
available from the author
Transition from tunneling to direct contact in tungsten nanojunctions
We apply the mechanically controllable break junctions technique to
investigate the transition from tunneling to direct contact in tungsten. This
transition is quite different from that of other metals and is determined by
the local electronic properties of the tungsten surface and the relief of the
electrodes at the point of their closest proximity. The conductance traces show
a rich variety of patterns from the avalanche-like jump to a mesoscopic contact
to the completely smooth transition between direct contact and tunneling. Due
to the occasional absence of an adhesive jump the conductance of the contact
can be continuously monitored at ultra-small electrode separations. The
conductance histograms of tungsten are either featureless or show two distinct
peaks related to the sequential opening of spatially separated groups of
conductance channels. The role of surface states of tungsten and their
contribution to the junction conductance at sub-Angstrom electrode separations
are discussed.Comment: 6 pages, 6 figure
Electronic dielectric constants of insulators by the polarization method
We discuss a non-perturbative, technically straightforward, easy-to-use, and
computationally affordable method, based on polarization theory, for the
calculation of the electronic dielectric constant of insulating solids at the
first principles level. We apply the method to GaAs, AlAs, InN, SiC, ZnO, GaN,
AlN, BeO, LiF, PbTiO, and CaTiO. The predicted \einf's agree well
with those given by Density Functional Perturbation Theory (the reference
theoretical treatment), and they are generally within less than 10 % of
experiment.Comment: RevTeX 4 pages, 2 ps figure
Оцінка ефективності внутрішньовенного введення лідокаїну гідрохлориду в інтраопераційному періоді
The aim of the work: to prove the fact of intravenous administration of lidocaine hydrochloride during general anesthesia to reduce the total dose of narcotic analgesics without loss of analgesic effect.
Dynamic active prospective two-center study of two statistically homogeneous groups of patients was performed: in group 1 general anesthesia with fentanyl analgesia was performed, in group 2 – a combination of fentanyl and lidocaine hydrochloride. The study was performed during the anesthesiology of patients who underwent metalostesynthesis for multiple fracture with displacement of bone fragments of the upper extremity and patients undergoing laparoscopic cholecystectomy for cholelithiasis, chronic cholecystosis. It was found that the use of 1 % lidocaine hydrochloride in combination with fentanyl can significantly reduce the total dose the last one, namely the total dose of fentanyl in the group 1 was, on average, (8.63±0.72) µg/kg/h, whereas in group 2 managed to reduce the dose to (6.27±0.44) µg/kg/h to achieve adequate analgesia.Цель работы: доказать, что внутривенное введение лидокаина гидрохлорида при проведении общей анестезии позволяет уменьшить суммарную дозу наркотических анальгетиков без потери обезболивающего эффекта.
Проведено динамическое активное проспективное двухцентровое исследование двух статистически однородных групп пациентов: в первой группе проводилась общая анестезия с анальгезией фентанилом, во второй – сочетание фентанила и лидокаина гидрохлорида. Исследование проводилось при анестезиологическом обеспечении больным, которым выполняли металлоостесинтез по поводу многоосколочного перелома со смещением костных отломков верхней конечности и пациентам, которым выполнялась лапароскопическая холецистэктомия по поводу желчнокаменной болезни, хронического калькулезного холецистита в стадии обострения. Было установлено, что использование 1 % лидокаина гидрохлорида в сочетании с фентанилом позволяет существенно сократить общую дозу последнего, а именно суммарная доза фентанила в первой группе составляла, в среднем (8,63 ± 0,72) мкг/кг/ч, тогда как во второй группе удалось снизить дозу до (6,27 ± 0,44) мкг/кг/ч для достижения адекватной аналгезии.Мета роботи: обґрунтувати твердження, що внутрішньовенне введення лідокаїну гідрохлориду під час проведення загальної анестезії дозволяє зменшити сумарну дозу наркотичних аналгетиків без втрати знеболювального ефекту.
Проведено динамічне активне проспективне двоцентрове дослідження двох статистично однорідних груп пацієнтів: в першій групі проводилась загальна анестезія з аналгезією фентанілом, в другій – поєднання фентанілу та лідокаїну гідрохлориду. Дослідження проводилось під час анестезіологічного забезпечення хворим, яким виконували металоостеосинтез з приводу багатоуламкового перелому зі зміщенням кісткових уламків верхньої кінцівки та пацієнтам, яким виконувалась лапароскопічна холецистектомія з приводу жовчнокам’яної хвороби, хронічного калькульозного холециститу в стадії загострення. Було встановлено, що використання 1 % лідокаїну гідрохлориду в поєднанні з фентанілом дозволяє суттєво скоротити загальну дозу останнього, а саме сумарна доза фентанілу в першій групі складала, в середньому (8,63±0,72) мкг/кг/год, тоді як у другій групі вдалося зменшити дозу до 6,27±0,44 мкг/кг/год для досягнення адекватної аналгезії
Polarity in GaN and ZnO: Theory, measurement, growth, and devices
This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Rev. 3, 041303 (2016) and may be found at https://doi.org/10.1063/1.4963919.The polar nature of the wurtzite crystalline structure of GaN and ZnO results in the existence of a spontaneous electric polarization within these materials and their associated alloys (Ga,Al,In)N and (Zn,Mg,Cd)O. The polarity has also important consequences on the stability of the different crystallographic surfaces, and this becomes especially important when considering epitaxial growth. Furthermore, the internal polarization fields may adversely affect the properties of optoelectronic devices but is also used as a potential advantage for advanced electronic devices. In this article, polarity-related issues in GaN and ZnO are reviewed, going from theoretical considerations to electronic and optoelectronic devices, through thin film, and nanostructure growth. The necessary theoretical background is first introduced and the stability of the cation and anion polarity surfaces is discussed. For assessing the polarity, one has to make use of specific characterization methods, which are described in detail. Subsequently, the nucleation and growth mechanisms of thin films and nanostructures, including nanowires, are presented, reviewing the specific growth conditions that allow controlling the polarity of such objects. Eventually, the demonstrated and/or expected effects of polarity on the properties and performances of optoelectronic and electronic devices are reported. The present review is intended to yield an in-depth view of some of the hot topics related to polarity in GaN and ZnO, a fast growing subject over the last decade
Heterovalent and A-atom effects in A(B'B'')O3 perovskite alloys
Using first-principles supercell calculations, we have investigated
energetic, structural and dielectric properties of three different A(B'B'')O_3
perovskite alloys: Ba(Zn_{1/3}Nb_{2/3})O_3 (BZN), Pb(Zn_{1/3}Nb_{2/3})O_3
(PZN), and Pb(Zr_{1/3}Ti_{2/3})O_3 (PZT). In the homovalent alloy PZT, the
energetics are found to be mainly driven by atomic relaxations. In the
heterovalent alloys BZN and PZN, however, electrostatic interactions among B'
and B'' atoms are found to be very important. These electrostatic interactions
are responsible for the stabilization of the observed compositional long-range
order in BZN. On the other hand, cell relaxations and the formation of short
Pb--O bonds could lead to a destabilization of the same ordered structure in
PZN. Finally, comparing the dielectric properties of homovalent and
heterovalent alloys, the most dramatic difference arises in connection with the
effective charges of the B' atom. We find that the effective charge of Zr in
PZT is anomalous, while in BZN and PZN the effective charge of Zn is close to
its nominal ionic value.Comment: 7 pages, two-column style with 2 postscript figures embedded. Uses
REVTEX and epsf macros. Also available at
http://www.physics.rutgers.edu/~dhv/preprints/index.html#lb_he
Ab initio Hartree-Fock Born effective charges of LiH, LiF, LiCl, NaF, and NaCl
We use the Berry-phase-based theory of macroscopic polarization of dielectric
crystals formulated in terms of Wannier functions, and state-of-the-art
Gaussian basis functions, to obtain benchmark ab initio Hartree-Fock values of
the Born effective charges of ionic compounds LiH, LiF, LiCl, NaF, and NaCl. We
find excellent agreement with the experimental values for all the compounds
except LiCl and NaCl, for which the disagreement with the experiments is close
to 10% and 16%, respectively. This may imply the importance of many-body
effects in those systems.Comment: 11 pages, Revtex, 2 figures (included), to appear in Phys. Rev. B
April 15, 200
Phonons and related properties of extended systems from density-functional perturbation theory
This article reviews the current status of lattice-dynamical calculations in
crystals, using density-functional perturbation theory, with emphasis on the
plane-wave pseudo-potential method. Several specialized topics are treated,
including the implementation for metals, the calculation of the response to
macroscopic electric fields and their relevance to long wave-length vibrations
in polar materials, the response to strain deformations, and higher-order
responses. The success of this methodology is demonstrated with a number of
applications existing in the literature.Comment: 52 pages, 14 figures, submitted to Review of Modern Physic
Effects of erythropoietin on depressive symptoms and neurocognitive deficits in depression and bipolar disorder
<p>Abstract</p> <p>Background</p> <p>Depression and bipolar disorder are associated with reduced neural plasticity and deficits in memory, attention and executive function. Drug treatments for these affective disorders have insufficient clinical effects in a large group and fail to reverse cognitive deficits. There is thus a need for more effective treatments which aid cognitive function. Erythropoietin (Epo) is involved in neuroplasticity and is a candidate for future treatment of affective disorders. The investigators have demonstrated that a single dose of Epo improves cognitive function and reduces neurocognitive processing of negative emotional information in healthy and depressed individuals similar to effects seen with conventional antidepressants. The current study adds to the previous findings by investigating whether repeated Epo administration has antidepressant effects in patients with treatment resistant depression and reverses cognitive impairments in these patients and in patients with bipolar disorder in remission.</p> <p>Methods/design</p> <p>The trial has a double-blind, placebo-controlled, parallel-group design. 40 patients with treatment-resistant major depression and 40 patients with bipolar disorder in remission are recruited and randomised to receive weekly infusions of Epo (Eprex; 40,000 IU) or saline (NaCl 0.9%) for 8 weeks. Randomisation is stratified for age and gender. The primary outcome parameters for the two studies are: depression severity measured with the Hamilton Depression Rating Scale 17 items (HDRS-17) <abbrgrp><abbr bid="B1">1</abbr></abbrgrp> in study 1 and, in study 2, verbal memory measured with the Rey Auditory Verbal Learning Test (RAVLT) <abbrgrp><abbr bid="B2">2</abbr><abbr bid="B3">3</abbr></abbrgrp>. With inclusion of 40 patients in each study we obtain 86% power to detect clinically relevant differences between intervention and placebo groups on these primary outcomes.</p> <p>Trial registration</p> <p>The trial is approved by the Local Ethics Committee: H-C-2008-092, Danish Medicines Agency: 2612-4020, EudraCT: 2008-04857-14, Danish Data Agency: 2008-41-2711 and ClinicalTrials.gov: NCT 00916552.</p
Placebo Response of Non-Pharmacological and Pharmacological Trials in Major Depression: A Systematic Review and Meta-Analysis
Background: Although meta-analyses have shown that placebo responses are large in Major Depressive Disorder (MDD) trials; the placebo response of devices such as repetitive transcranial magnetic stimulation (rTMS) has not been systematically assessed. We proposed to assess placebo responses in two categories of MDD trials: pharmacological (antidepressant drugs) and non-pharmacological (device- rTMS) trials. Methodology/Principal Findings: We performed a systematic review and meta-analysis of the literature from April 2002 to April 2008, searching MEDLINE, Cochrane, Scielo and CRISP electronic databases and reference lists from retrieved studies and conference abstracts. We used the keywords placebo and depression and escitalopram for pharmacological studies; and transcranial magnetic stimulation and depression and sham for non-pharmacological studies. All randomized, double-blinded, placebo-controlled, parallel articles on major depressive disorder were included. Forty-one studies met our inclusion criteria - 29 in the rTMS arm and 12 in the escitalopram arm. We extracted the mean and standard values of depression scores in the placebo group of each study. Then, we calculated the pooled effect size for escitalopram and rTMS arm separately, using Cohen's d as the measure of effect size. We found that placebo response are large for both escitalopram (Cohen's d - random-effects model - 1.48; 95%C.I. 1.26 to 1.6) and rTMS studies (0.82; 95%C.I. 0.63 to 1). Exploratory analyses show that sham response is associated with refractoriness and with the use of rTMS as an add-on therapy, but not with age, gender and sham method utilized. Conclusions/Significance: We confirmed that placebo response in MDD is large regardless of the intervention and is associated with depression refractoriness and treatment combination (add-on rTMS studies). The magnitude of the placebo response seems to be related with study population and study design rather than the intervention itself
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