1,582 research outputs found
Spin properties of single electron states in coupled quantum dots
Spin properties of single electron states in laterally coupled quantum dots
in the presence of a perpendicular magnetic field are studied by exact
numerical diagonalization. Dresselhaus (linear and cubic) and Bychkov-Rashba
spin-orbit couplings are included in a realistic model of confined dots based
on GaAs. Group theoretical classification of quantum states with and without
spin orbit coupling is provided. Spin-orbit effects on the g-factor are rather
weak. It is shown that the frequency of coherent oscillations (tunneling
amplitude) in coupled dots is largely unaffected by spin-orbit effects due to
symmetry requirements. The leading contributions to the frequency involves the
cubic term of the Dresselhaus coupling. Spin-orbit coupling in the presence of
magnetic field leads to a spin-dependent tunneling amplitude, and thus to the
possibility of spin to charge conversion, namely spatial separation of spin by
coherent oscillations in a uniform magnetic field. It is also shown that spin
hot spots exist in coupled GaAs dots already at moderate magnetic fields, and
that spin hot spots at zero magnetic field are due to the cubic Dresselhaus
term only.Comment: 16 pages, 12 figure
Higher order contributions to Rashba and Dresselhaus effects
We have developed a method to systematically compute the form of Rashba- and
Dresselhaus-like contributions to the spin Hamiltonian of heterostructures to
an arbitrary order in the wavevector k. This is achieved by using the double
group representations to construct general symmetry-allowed Hamiltonians with
full spin-orbit effects within the tight-binding formalism. We have computed
full-zone spin Hamiltonians for [001]-, [110]- and [111]-grown zinc blende
heterostructures (D_{2d},C_{4v},C_{2v},C_{3v} point group symmetries), which
are commonly used in spintronics. After an expansion of the Hamiltonian up to
third order in k, we are able to obtain additional terms not found previously.
The present method also provides the matrix elements for bulk zinc blendes
(T_d) in the anion/cation and effective bond orbital model (EBOM) basis sets
with full spin-orbit effects.Comment: v1: 11 pages, 3 figures, 8 table
A Microscopic T-Violating Optical Potential: Implications for Neutron-Transmission Experiments
We derive a T-violating P-conserving optical potential for neutron-nucleus
scattering, starting from a uniquely determined two-body -exchange
interaction with the same symmetry. We then obtain limits on the T-violating
-nucleon coupling from neutron-transmission
experiments in Ho. The limits may soon compete with those from
measurements of atomic electric-dipole moments.Comment: 8 pages, 2 uuencoded figures in separate files (replaces version sent
earlier in the day with figures attached), in RevTeX 3, submitted to PR
Reply to "Comment on 'Charge transport in disordered semiconducting polymers driven by nuclear tunneling'"
The authors reply to the Comment by Nenashev et al
Resonance-Induced Effects in Photonic Crystals
For the case of a simple face-centered-cubic photonic crystal of homogeneous
dielectric spheres, we examine to what extent single-sphere Mie resonance
frequencies are related to band gaps and whether the width of a gap can be
enlarged due to nearby resonances. Contrary to some suggestions, no spectacular
effects may be expected. When the dielectric constant of the spheres
is greater than the dielectric constant of the
background medium, then for any filling fraction there exists a critical
above which the lowest lying Mie resonance frequency falls inside
the lowest stop gap in the (111) crystal direction, close to its midgap
frequency. If , the correspondence between Mie
resonances and both the (111) stop gap and a full gap does not follow such a
regular pattern. If the Mie resonance frequency is close to a gap edge, one can
observe a resonance-induced widening of a relative gap width by .Comment: 14 pages, 3 figs., RevTex. For more info look at
http://www.amolf.nl/external/wwwlab/atoms/theory/index.htm
Local Electronic Structure of Defects in Superconductors
The electronic structure near defects (such as impurities) in superconductors
is explored using a new, fully self-consistent technique. This technique
exploits the short-range nature of the impurity potential and the induced
change in the superconducting order parameter to calculate features in the
electronic structure down to the atomic scale with unprecedented spectral
resolution. Magnetic and non-magnetic static impurity potentials are
considered, as well as local alterations in the pairing interaction. Extensions
to strong-coupling superconductors and superconductors with anisotropic order
parameters are formulated.Comment: RevTex source, 20 pages including 22 figures in text with eps
Optimal numerical design of bucket elevators using discontinuous deformation analysis
Bucket elevators are efficient machines to transport granular materials in industrial and civil engineering applications. These materials are composed of hundreds, thousands or even more particles, the global behavior of which is defined by contact interactions. The first attempts to analyze the transportation of granular materials were treated by very simple continuum methods that do not take into account these interactions, producing simulations that do not fit the experimental results accurately. Given the internal discontinuity nature of granular media, it is reasonable to use numerical methods to model their behavior, such as discontinuous deformation analysis (DDA)-a member of the discrete element method family that started to be used in the 90s to analyze similar problems. The version of DDA used in the current work treats grains as rigid circular particles with friction, damping and eventually cohesion with the objective of simulating and analyzing in detail the discharge of granular materials with bucket elevators. A deterministic computer code has been implemented and validated against simplified analytical formulae and experimental results taken from the literature. This computer code is then used to obtain optimum two-dimensional bucket geometries under specific working conditions. The optimization aims to maximize transport distance and to minimize remaining material, taking into account bucket velocity and the properties of the grains. The resulting geometries are discussed and compared against standard designs.J.L. Perez-Aparicio, R. Bravo were partially supported by the MFOM I+D (2004/38), both by MICIIN #BIA 2008-00522 and the first also by Polytechnic University of Valencia under grant PAID 05-10-2674. J.J. Gomez-Hernandez was partially supported by MICIIN #CGL 2011-23295.Pérez Aparicio, JL.; Bravo, R.; Gómez-Hernández, JJ. (2014). Optimal numerical design of bucket elevators using discontinuous deformation analysis. Granular Matter. 16(4):485-498. https://doi.org/10.1007/s10035-014-0485-5S485498164Rademacher, F.: Non-spill discharge characteristics of bucket elevators. Powder Technol. 22(2), 215–241 (1979)Koster, K.: Bulk material discharge of bucket elevators, especially high-capacity bucket elevators. [zum schuettgutabwurf bei becherwerken, insbesondere bei hochleistungsbecherwerken]. Aufbereitungs-Technik 25(8), 450–463 (1984)Koster, K.: Use of high-capacity bucket elevators in the cement industry. [zum einsatz von hochleistungsbecherwerken in der zementindustrie]. Zement-Kalk-Gips 33(3), 116–119 (1980)Koster, K.: Development and state of the art in heavy-duty bucket elevators with central chains—part 2 [entwicklung und stand der technik von hochleistungs-becherwerken mit zentralkette—teil 2]. ZKG Int. 49(4), 173–187 (1996)Koster, K.: Centrifugal discharge of bucket elevators. Bulk Solids Handl. 5(2), 449–460 (1985)Koster, K.: Problem of complete emptying of high-speed elevator buckets. Aufbereitungs-Technik 27(9), 471–481 (1986)Korzen, Z.: Mechanics of gravitational discharge of cell-less bucket wheels in reclaiming machines. Bulk Solids Handl. 7(6), 801–812 (1987)Korzen, Z., Dudek, K.: Mathematical model of the operational efficiency of a multibucket centrifugal discharge wheel [model matematyczny wydajnosci roboczego procesu kola wieloczerpakowego z odsrodkowym wysypem]. Politechnika Warszawska Prace Naukowe Mechanika 1(121), 187–199 (1989)Shi, G., Goodman, R.: Two dimensional discontinuous deformation analysis. Int. J. Numer. Anal. Methods Geomech. 9(6), 541–556 (1985)Pérez-Aparicio, J., Bravo, R.: Discrete Elements, vol. 2, pp. 41–77. Consorcio TCN (2006)Shi, G.: Discontinuous Deformation Analysis: A New Model for the Statics and Dynamics of Block Systems. Ph.D. thesis, University of California, Berkeley (1988)Moosavi, M., Grayeli, R.: A model for cable bolt-rock mass interaction: integration with discontinuous deformation analysis (DDA) algorithm. Int. J. Rock Mech. Min. Sci. 43(4), 661–670 (2006)Pérez-Aparicio, J., Bravo, R., Ortiz, P.: Refined element discontinuous numerical analysis of dry-contact masonry arches. Eng. Struct. 48, 578–587 (2013)McBride, W., Sinnott, M., Cleary, P.: Discrete element modelling of a bucket elevator head pulley transition zone. Granul. Matter 13(2), 169–174 (2011)Kruggel-Emden, H., Sudbrock, F., Wirtz, S., Scherer, V.: Experimental and numerical investigation of the bulk behavior of wood pellets on a model type grate. Granul. Matter 14(6), 681–693 (2012)Walton, O., Moor, C., Gill, K.: Effects of gravity on cohesive behavior of fine powders: implications for processing lunar regolith. Granul. Matter 9(5), 353–363 (2007)Gao, Y., Muzzio, F., Ierapetritou, M.: Optimizing continuous powder mixing processes using periodic section modeling. Chem. Eng. Sci. 80, 70–80 (2012)Shmulevich, I.: State of the art modeling of soil-tillage interaction using discrete element method. Soil Tillage Res. 111(1), 41–53 (2010)Moon, T., Oh, J.: A study of optimal rock-cutting conditions for hard rock tbm using the discrete element method. Rock Mech. Rock Eng. 45(5), 837–849 (2012)Makokha, A., Moys, M., Bwalya, M., Kimera, K.: A new approach to optimising the life and performance of worn liners in ball mills: experimental study and DEM simulation. Int. J. Miner. Process. 84(1–4), 221–227 (2007)Balevičius, R., Kačianauskas, R., Mroz, Z., Sielamowicz, I.: Discrete element method applied to multiobjective optimization of discharge flow parameters in hoppers. Struct. Multidiscip. Optim. 31(3), 163–175 (2006)Hu, L.: Gradual deformation and iterative calibration of Gaussian-related stochastic models. Math. Geol. 32(1), 87–108 (2000)Bravo, R., Pérez-Aparicio, J., Laursen, T.: An energy consistent frictional dissipating algorithm for particle contact problems. Int. J. Numer. Methods Eng. 92(9), 753–781 (2012)Belytschko, T., Liu, W., Moran, B.: Nonlinear Finite Elements for Continua and Structures. Wiley, New York (2000)Beckert, R., Föll, R.: Untersuchung der abwurfverhältnisse an kettenbecherwerken. Förden Heben 1(15), 833–836 (1966)Jaskulski, A.: Engineer-to-order approach to high speed bucket elevator design in a small-enterprise. Appl. Eng. Agric. 24(5), 545–557 (2008)Beverley, G.: Mechanics of High Speed Bucket Elevator Discharge. Ph.D. thesis. University of Newcastle (1986)Beverley, G., Roberts, A., Hayes, J.: Mechanics of high speed elevator discharge. Bulk Solids Handl. 3(4), 853–859 (1983)Korzen, Z., Dudek, K.: Reclaiming with a high-speed bucket wheel with centrifugal discharge. Bulk Solids Handl. 11(3), 615–626 (1991)Bravo, R., Pérez-Aparicio, J., Laursen, T.: An enhanced energy conserving time stepping algorithm for frictionless particle contacts. Int. J. Numer. Methods Eng. 85(11), 1415–1435 (2011)Jaskulski, A.: Methodology of Multi-Criteria Optimization of Appliances for Vertical Grain Transportation. Ph.D. thesis. Warsaw University of Technology (1992
Gene Expression Profiling in a Mouse Model Identifies Fetal Liver- and Placenta-Derived Potential Biomarkers for Down Syndrome Screening
BACKGROUND: As a first step to identify novel potential biomarkers for prenatal Down Syndrome screening, we analyzed gene expression in embryos of wild type mice and the Down Syndrome model Ts1Cje. Since current Down Syndrome screening markers are derived from placenta and fetal liver, these tissues were chosen as target. METHODOLOGY/PRINCIPAL FINDINGS: Placenta and fetal liver at 15.5 days gestation were analyzed by microarray profiling. We confirmed increased expression of genes located at the trisomic chromosomal region. Overall, between the two genotypes more differentially expressed genes were found in fetal liver than in placenta. Furthermore, the fetal liver data are in line with the hematological aberrations found in humans with Down Syndrome as well as Ts1Cje mice. Together, we found 25 targets that are predicted (by Gene Ontology, UniProt, or the Human Plasma Proteome project) to be detectable in human serum. CONCLUSIONS/SIGNIFICANCE: Fetal liver might harbor more promising targets for Down Syndrome screening studies. We expect these new targets will help focus further experimental studies on identifying and validating human maternal serum biomarkers for Down Syndrome screening
Local Electronic Structure of a Single Magnetic Impurity in a Superconductor
The electronic structure near a single classical magnetic impurity in a
superconductor is determined using a fully self-consistent Koster-Slater
algorithm. Localized excited states are found within the energy gap which are
half electron and half hole. Within a jellium model we find the new result that
the spatial structure of the positive-frequency (electron-like) spectral weight
(or local density of states), can differ strongly from that of the negative
frequency (hole-like) spectral weight. The effect of the impurity on the
continuum states above the energy gap is calculated with good spectral
resolution for the first time. This is also the first three-dimensional
self-consistent calculation for a strong magnetic impurity potential.Comment: 13 pages, RevTex, change in heuristic picture, no change in numerical
result
Quasiparticle transport equation with collision delay. II. Microscopic Theory
For a system of non-interacting electrons scattered by neutral impurities, we
derive a modified Boltzmann equation that includes quasiparticle and virial
corrections. We start from quasiclassical transport equation for
non-equilibrium Green's functions and apply limit of small scattering rates.
Resulting transport equation for quasiparticles has gradient corrections to
scattering integrals. These gradient corrections are rearranged into a form
characteristic for virial corrections
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