12,809 research outputs found
Ab-initio determined electronic and magnetic properties of half-metallic NiCrSi and NiMnSi Heusler alloys; the role of interfaces and defects
Using state-of-the-art first-principles calculations we study the properties
of the ferromagnetic Heusler compounds NiYSi where Y stands for V, Cr or Mn.
NiCrSi and NiMnSi contrary to NiVSi are half-metallic at their equilibrium
lattice constant exhibiting integer values of the total spin magnetic moment
and thus we concentrate on these two alloys. The minority-spin gap has the same
characteristics as for the well-known NiMnSb alloy being around 1 eV.
Upon tetragonalization the gap is present in the density of states even for
expansion or contraction of the out-of-plane lattice parameter by 5%. The Cr-Cr
and Mn-Mn interactions make ferromagnetism extremely stable and the Curie
temperature exceeds 1000 K for NiMnSi. Surface and interfaces with GaP, ZnS and
Si semiconductors are not half-metallic but in the case of NiCrSi the Ni-based
contacts present spin-polarization at the Fermi level over 90%. Finally, we
show that there are two cases of defects and atomic-swaps. The first-ones which
involve the Cr(Mn) and Si atoms induce states at the edges of the gap which
persists for a moderate-concentration of defects. Defects involving Ni atoms
induce states localized within the gap completely destroying the
half-metallicity. Based on single-impurity calculations we associate these
states to the symmetry of the crystal
3d-electron induced magnetic phase transition in half-metallic semi-Heusler alloys
We study the effect of the non-magnetic 3\textit{d} atoms on the magnetic
properties of the half-metallic (HM) semi-Heusler alloys CoCuMnSb
and NiCuMnSb () using first-principles
calculations. We determine the magnetic phase diagram of both systems at zero
temperature and obtain a phase transition from a ferromagnetic to an
antiferromagnetic state. For low Cu concentrations the ferromagnetic RKKY-like
exchange mechanism is dominating, while the antiferromagnetic superexchange
coupling becomes important for larger Cu content leading to the observed
magnetic phase transition. A strong dependence of the magnetism in both systems
on the position of the Fermi level within the HM gap is obtained. Obtained
results are in good agreement with the available experimental data
Interpretation of Solar Magnetic Field Strength Observations
This study based on longitudinal Zeeman effect magnetograms and spectral line
scans investigates the dependence of solar surface magnetic fields on the
spectral line used and the way the line is sampled in order to estimate the
magnetic flux emerging above the solar atmosphere and penetrating to the corona
from magnetograms of the Mt. Wilson 150-foot tower synoptic program (MWO). We
have compared the synoptic program \lambda5250\AA line of Fe I to the line of
Fe I at \lambda5233\AA since this latter line has a broad shape with a profile
that is nearly linear over a large portion of its wings. The present study uses
five pairs of sampling points on the \AA line. We recommend
adoption of the field determined with a line bisector method with a sampling
point as close as possible to the line core as the best estimate of the
emergent photospheric flux. The combination of the line profile measurements
and the cross-correlation of fields measured simultaneously with \lambda5250\AA
and \lambda5233\AA yields a formula for the scale factor 1/\delta that
multiplies the MWO synoptic magnetic fields. The new calibration shows that
magnetic fields measured by the MDI system on the SOHO spacecraft are equal to
0.619+/-0.018 times the true value at a center-to-limb position 30 deg. Berger
and Lites (2003) found this factor to be 0.64+/-0.013 based on a comparison the
the Advanced Stokes Polarimeter.Comment: Accepted by Solar Physic
Generation of spin-motion entanglement in a trapped ion using long-wavelength radiation
Applying a magnetic-field gradient to a trapped ion allows long-wavelength radiation to produce a mechanical force on the ion's motion when internal transitions are driven. We demonstrate such a coupling using a single trapped Yb+171 ion and use it to produce entanglement between the spin and motional state, an essential step toward using such a field gradient to implement multiqubit operations
Using the LANDSAT data collection system for field geophysics: Operations in the British Virgin Islands
This particular application was to vertical geodesy by tide gauge and tiltmeter on a small desert island in the British Virgin Islands. The performance of the LANDSAT system under potentially marginal circumstances was found to be excellent
Еще об одном русском ключевом концепте
В статье показаны основные составляющие русского концепта "разлука", который, судя по встречаемости имени "разлука" в текстах русской культуры, является одним из ключевых. Показывается, что этот концепт связан с другими ключевыми русскими концептами - "дом", "свобода". Основная мысль статьи - содержание этого концепта подверглось значительным социокультурным модификациям.У статті показано основні складові російского концепта "розлука", який, судячи по вживанню імені "розлука" в текстах російскої культури, є одним з ключовіх. Показується, що цей концепт пов'язаний з іншими ключовіми російскими концептами " будинок", "свобода". Основна думка статті - зміст цього концепта зазнав значних социокультурних модифікацій.In article basic components of Russian concept "separation" ("parting") are analysed. An author considers this concept to be one of key Russian concepts according to usage of word "razluka" in Russian culture texts. Interdependence of concept "separation" and other Russian key concepts such as "home", "freedom" is shown. A main author's idea is that value of this concept was being a subject of considerable sociocultural modifications
A Novel Gonadotropin-Releasing Hormone 1 (Gnrh1) Enhancer-Derived Noncoding RNA Regulates Gnrh1 Gene Expression in GnRH Neuronal Cell Models.
Gonadotropin-releasing hormone (GnRH), a neuropeptide released from a small population of neurons in the hypothalamus, is the central mediator of the hypothalamic-pituitary-gonadal axis, and is required for normal reproductive development and function. Evolutionarily conserved regulatory elements in the mouse, rat, and human Gnrh1 gene include three enhancers and the proximal promoter, which confer Gnrh1 gene expression specifically in GnRH neurons. In immortalized mouse hypothalamic GnRH (GT1-7) neurons, which show pulsatile GnRH release in culture, RNA sequencing and RT-qPCR revealed that expression of a novel long noncoding RNA at Gnrh1 enhancer 1 correlates with high levels of GnRH mRNA expression. In GT1-7 neurons, which contain a transgene carrying 3 kb of the rat Gnrh1 regulatory region, both the mouse and rat Gnrh1 enhancer-derived noncoding RNAs (GnRH-E1 RNAs) are expressed. We investigated the characteristics and function of the endogenous mouse GnRH-E1 RNA. Strand-specific RT-PCR analysis of GnRH-E1 RNA in GT1-7 cells revealed GnRH-E1 RNAs that are transcribed in the sense and antisense directions from distinct 5' start sites, are 3' polyadenylated, and are over 2 kb in length. These RNAs are localized in the nucleus and have a half-life of over 8 hours. In GT1-7 neurons, siRNA knockdown of mouse GnRH-E1 RNA resulted in a significant decrease in the expression of the Gnrh1 primary transcript and Gnrh1 mRNA. Over-expression of either the sense or antisense mouse GnRH-E1 RNA in immature, migratory GnRH (GN11) neurons, which do not express either GnRH-E1 RNA or GnRH mRNA, induced the transcriptional activity of co-transfected rat Gnrh1 gene regulatory elements, where the induction requires the presence of the rat Gnrh1 promoter. Together, these data indicate that GnRH-E1 RNA is an inducer of Gnrh1 gene expression. GnRH-E1 RNA may play an important role in the development and maturation of GnRH neurons
Ground-state cooling of a trapped ion Using long-wavelength radiation
We demonstrate ground-state cooling of a trapped ion using radio-frequency (rf) radiation. This is a powerful tool for the implementation of quantum operations, where rf or microwave radiation instead of lasers is used for motional quantum state engineering. We measure a mean phonon number of n¯=0.13(4) after sideband cooling, corresponding to a ground-state occupation probability of 88(7)%. After preparing in the vibrational ground state, we demonstrate motional state engineering by driving Rabi oscillations between the |n=0⟩ and |n=1⟩ Fock states. We also use the ability to ground-state cool to accurately measure the motional heating rate and report a reduction by almost 2 orders of magnitude compared with our previously measured result, which we attribute to carefully eliminating sources of electrical noise in the system
Magnetic phase separation in ordered alloys
We present a lattice model to study the equilibrium phase diagram of ordered
alloys with one magnetic component that exhibits a low temperature phase
separation between paramagnetic and ferromagnetic phases. The model is
constructed from the experimental facts observed in CuAlMn and it
includes coupling between configurational and magnetic degrees of freedom which
are appropriated for reproducing the low temperature miscibility gap. The
essential ingredient for the occurrence of such a coexistence region is the
development of ferromagnetic order induced by the long-range atomic order of
the magnetic component. A comparative study of both mean-field and Monte Carlo
solutions is presented. Moreover, the model may enable the study of the
structure of the ferromagnetic domains embedded in the non-magnetic matrix.
This is relevant in relation to phenomena such as magnetoresistance and
paramagnetism.Comment: 12 pages, 11 figures, accepted in Phys. Rev.
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