4,753 research outputs found
A structure marker study for Pd_2Si formation: Pd moves in epitaxial Pd_2Si
A sample with the configuration Si (111)/single crystalline Pd_2Si/polycrystalline Pd_2Si/Pd is used to study the dominant moving species during subsequent Pd_2Si formation by annealing at 275 °C. The interface between monocrystalline and polycrystalline Pd_2Si is used as a marker to monitor the dominant moving species. The result shows that Pd is the dominant moving species in the monocrystal
Determination of the Spin-Hall-Effect-Induced and the Wedged-Structure-Induced Spin Torque Efficiencies in Heterostructures with Perpendicular Magnetic Anisotropy
We report that by measuring current-induced hysteresis loop shift versus
in-plane bias magnetic field, the spin Hall effect (SHE) contribution of the
current-induced effective field per current density, , can be
estimated for Pt and Ta-based magnetic heterostructures with perpendicular
magnetic anisotropy (PMA). We apply this technique to a Pt-based sample with
its ferromagnetic (FM) layer being wedged-deposited and discover an extra
effective field contribution, , due to the asymmetric nature of
the deposited FM layer. We confirm the correlation between and
the asymmetric depinning process in FM layer during magnetization switching by
magneto-optical Kerr (MOKE) microscopy. These results indicate the possibility
of engineering deterministic spin-orbit torque (SOT) switching by controlling
the symmetry of domain expansion through the materials growth process
Superfluid-Insulator transition of ultracold atoms in an optical lattice in the presence of a synthetic magnetic field
We study the Mott insulator-superfluid transition of ultracold bosonic atoms
in a two-dimensional square optical lattice in the presence of a synthetic
magnetic field with p/q (p and q being co-prime integers) flux quanta passing
through each lattice plaquette. We show that on approach to the transition from
the Mott side, the momentum distribution of the bosons exhibits q precursor
peaks within the first magnetic Brillouin zone. We also provide an effective
theory for the transition and show that it involves q interacting boson fields.
We construct, from a mean-field analysis of this effective theory, the
superfluid ground states near the transition and compute, for q=2,3, both the
gapped and the gapless collective modes of these states. We suggest experiments
to test our theory.Comment: 4 pages, 4 figs; v
Zero Temperature Insulator-Metal Transition in Doped Manganites
We study the transition at T=0 from a ferromagnetic insulating to a
ferromagnetic metallic phase in manganites as a function of hole doping using
an effective low-energy model Hamiltonian proposed by us recently. The model
incorporates the quantum nature of the dynamic Jahn-Teller(JT) phonons strongly
coupled to orbitally degenerate electrons as well as strong Coulomb correlation
effects and leads naturally to the coexistence of localized (JT polaronic) and
band-like electronic states. We study the insulator-metal transition as a
function of doping as well as of the correlation strength U and JT gain in
energy E_{JT}, and find, for realistic values of parameters, a ground state
phase diagram in agreement with experiments. We also discuss how several other
features of manganites as well as differences in behaviour among manganites can
be understood in terms of our model.Comment: To be published in Europhysics Letter
Density wave and supersolid phases of correlated bosons in an optical lattice
Motivated by the recent experiment on the Bose-Einstein condensation of
Cr atoms with long-range dipolar interactions (Werner J. et al., Phys.
Rev. Lett., 94 (2005) 183201), we consider a system of bosons with repulsive
nearest and next-nearest neighbor interactions in an optical lattice. The
ground state phase diagram, calculated using the Gutzwiller ansatz, shows,
apart from the superfluid (SF) and the Mott insulator (MI), two modulated
phases, \textit{i.e.}, the charge density wave (CDW) and the supersolid (SS).
Excitation spectra are also calculated which show a gap in the insulators,
gapless, phonon mode in the superfluid and the supersolid, and a mode softening
of superfluid excitations in the vicinity of the modulated phases. We discuss
the possibility of observing these phases in cold dipolar atoms and propose
experiments to detect them
Minimal Impairment in a Rat Model of Duration Discrimination Following Excitotoxic Lesions of Primary Auditory and Prefrontal Cortices
We present a behavioral paradigm for the study of duration perception in the rat, and report the result of neurotoxic lesions that have the goal of identifying sites that mediate duration perception. Using a two-alternative forced-choice paradigm, rats were either trained to discriminate durations of pure tones (range = [200,500] ms; boundary = 316 ms; Weber fraction after training = 0.24 ± 0.04), or were trained to discriminate frequencies of pure tones (range = [8,16] kHz; boundary = 11.3 kHz; Weber = 0.16 ± 0.11); the latter task is a control for non-timing-specific aspects of the former. Both groups discriminate the same class of sensory stimuli, use the same motions to indicate decisions, have identical trial structures, and are trained to psychophysical threshold; the tasks are thus matched in a number of sensorimotor and cognitive demands. We made neurotoxic lesions of candidate timing-perception areas in the cerebral cortex of both groups. Following extensive bilateral lesions of the auditory cortex, the performance of the frequency discrimination group was significantly more impaired than that of the duration discrimination group. We also found that extensive bilateral lesions of the medial prefrontal cortex resulted in little to no impairment of both groups. The behavioral framework presented here provides an audition-based approach to study the neural mechanisms of time estimation and memory for durations
Privacy and Truthful Equilibrium Selection for Aggregative Games
We study a very general class of games --- multi-dimensional aggregative
games --- which in particular generalize both anonymous games and weighted
congestion games. For any such game that is also large, we solve the
equilibrium selection problem in a strong sense. In particular, we give an
efficient weak mediator: a mechanism which has only the power to listen to
reported types and provide non-binding suggested actions, such that (a) it is
an asymptotic Nash equilibrium for every player to truthfully report their type
to the mediator, and then follow its suggested action; and (b) that when
players do so, they end up coordinating on a particular asymptotic pure
strategy Nash equilibrium of the induced complete information game. In fact,
truthful reporting is an ex-post Nash equilibrium of the mediated game, so our
solution applies even in settings of incomplete information, and even when
player types are arbitrary or worst-case (i.e. not drawn from a common prior).
We achieve this by giving an efficient differentially private algorithm for
computing a Nash equilibrium in such games. The rates of convergence to
equilibrium in all of our results are inverse polynomial in the number of
players . We also apply our main results to a multi-dimensional market game.
Our results can be viewed as giving, for a rich class of games, a more robust
version of the Revelation Principle, in that we work with weaker informational
assumptions (no common prior), yet provide a stronger solution concept (ex-post
Nash versus Bayes Nash equilibrium). In comparison to previous work, our main
conceptual contribution is showing that weak mediators are a game theoretic
object that exist in a wide variety of games -- previously, they were only
known to exist in traffic routing games
Glycine decarboxylase deficiency causes neural tube defects and features of non-ketotic hyperglycinemia in mice.
Glycine decarboxylase (GLDC) acts in the glycine cleavage system to decarboxylate glycine and transfer a one-carbon unit into folate one-carbon metabolism. GLDC mutations cause a rare recessive disease non-ketotic hyperglycinemia (NKH). Mutations have also been identified in patients with neural tube defects (NTDs); however, the relationship between NKH and NTDs is unclear. We show that reduced expression of Gldc in mice suppresses glycine cleavage system activity and causes two distinct disease phenotypes. Mutant embryos develop partially penetrant NTDs while surviving mice exhibit post-natal features of NKH including glycine accumulation, early lethality and hydrocephalus. In addition to elevated glycine, Gldc disruption also results in abnormal tissue folate profiles, with depletion of one-carbon-carrying folates, as well as growth retardation and reduced cellular proliferation. Formate treatment normalizes the folate profile, restores embryonic growth and prevents NTDs, suggesting that Gldc deficiency causes NTDs through limiting supply of one-carbon units from mitochondrial folate metabolism
Superfluid, Mott-Insulator, and Mass-Density-Wave Phases in the One-Dimensional Extended Bose-Hubbard Model
We use the finite-size density-matrix-renormalization-group (FSDMRG) method
to obtain the phase diagram of the one-dimensional () extended
Bose-Hubbard model for density in the plane, where and
are, respectively, onsite and nearest-neighbor interactions. The phase diagram
comprises three phases: Superfluid (SF), Mott Insulator (MI) and Mass Density
Wave (MDW). For small values of and , we get a reentrant SF-MI-SF phase
transition. For intermediate values of interactions the SF phase is sandwiched
between MI and MDW phases with continuous SF-MI and SF-MDW transitions. We
show, by a detailed finite-size scaling analysis, that the MI-SF transition is
of Kosterlitz-Thouless (KT) type whereas the MDW-SF transition has both KT and
two-dimensional-Ising characters. For large values of and we get a
direct, first-order, MI-MDW transition. The MI-SF, MDW-SF and MI-MDW phase
boundaries join at a bicritical point at (.Comment: 10 pages, 15 figure
Best chirplet chain: near-optimal detection of gravitational wave chirps
The list of putative sources of gravitational waves possibly detected by the
ongoing worldwide network of large scale interferometers has been continuously
growing in the last years. For some of them, the detection is made difficult by
the lack of a complete information about the expected signal. We concentrate on
the case where the expected GW is a quasi-periodic frequency modulated signal
i.e., a chirp. In this article, we address the question of detecting an a
priori unknown GW chirp. We introduce a general chirp model and claim that it
includes all physically realistic GW chirps. We produce a finite grid of
template waveforms which samples the resulting set of possible chirps. If we
follow the classical approach (used for the detection of inspiralling binary
chirps, for instance), we would build a bank of quadrature matched filters
comparing the data to each of the templates of this grid. The detection would
then be achieved by thresholding the output, the maximum giving the individual
which best fits the data. In the present case, this exhaustive search is not
tractable because of the very large number of templates in the grid. We show
that the exhaustive search can be reformulated (using approximations) as a
pattern search in the time-frequency plane. This motivates an approximate but
feasible alternative solution which is clearly linked to the optimal one.
[abridged version of the abstract]Comment: 23 pages, 9 figures. Accepted for publication in Phys. Rev D Some
typos corrected and changes made according to referee's comment
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