2,224 research outputs found
Parents and children talk: the family dynamics of English language proficiency
This paper extends the analysis of the acquisition of destination language proficiency
among immigrants by explicitly incorporating dynamics among family membersâ
mother, father and children. Single equation, bivariate, and four-state (multivariate)
probit analyses are employed. Immigrant English language skills are greater the
younger the age at migration, the longer the duration of residence, the higher the
level of education, and for immigrants not from Asia. Large positive correlations in
the unmeasured determinants of proficiency exist between spouses, between
siblings, and between parents and children, although the latter relationship is
stronger for the mother
Multimodal segmentation of lifelog data
A personal lifelog of visual and audio information can be very helpful as a human memory augmentation tool. The SenseCam, a passive wearable camera, used in conjunction with an iRiver MP3 audio recorder, will capture over 20,000 images and 100 hours of audio per week. If used constantly, very soon this would build up to a substantial collection of personal data. To gain real value from this collection it is important to automatically segment the data into meaningful units or activities. This paper investigates the optimal combination of data sources to segment personal data into such activities. 5 data sources were logged and processed to segment a collection of personal data, namely: image processing on captured SenseCam images; audio processing on captured iRiver audio data; and processing of the temperature, white light level, and accelerometer sensors onboard the SenseCam device. The results indicate that a combination of the image, light and accelerometer sensor data segments our collection of personal data better than a combination of all 5 data sources. The accelerometer sensor is good for detecting when the user moves to a new location, while the image and light sensors are good for detecting changes in wearer activity within the same location, as well as detecting when the wearer socially interacts with others
Finite size effects and localization properties of disordered quantum wires with chiral symmetry
Finite size effects in the localization properties of disordered quantum
wires are analyzed through conductance calculations. Disorder is induced by
introducing vacancies at random positions in the wire and thus preserving the
chiral symmetry. For quasi one-dimensional geometries and low concentration of
vacancies, an exponential decay of the mean conductance with the wire length is
obtained even at the center of the energy band. For wide wires, finite size
effects cause the conductance to decay following a non-pure exponential law. We
propose an analytical formula for the mean conductance that reproduces
accurately the numerical data for both geometries. However, when the
concentration of vacancies increases above a critical value, a transition
towards the suppression of the conductance occurs.
This is a signature of the presence of ultra-localized states trapped in
finite regions of the sample.Comment: 5 figures, revtex
Dephasing of Electrons on Helium by Collisions with Gas Atoms
The damping of quantum effects in the transport properties of electrons
deposited on a surface of liquid helium is studied. It is found that due to
vertical motion of the helium vapour atoms the interference of paths of
duration is damped by a factor . An expression is
derived for the weak-localization lineshape in the case that damping occurs by
a combination of processes with this type of cubic exponential damping and
processes with a simple exponential damping factor.Comment: 7 pages, 2 figures, Revte
Fermi edge singularities in X-ray spectra of strongly correlated fermions
We discuss the problem of the X-ray absorption in a system of interacting
fermions and, in particular, those features in the X-ray spectra that can be
used to discriminate between conventional Fermi-liquids and novel "strange
metals". Focusing on the case of purely forward scattering off the core-hole
potential, we account for the relevant interactions in the conduction band by
means of the bosonization technique. We find that the X-ray Fermi edge
singularities can still be present, although modified, even if the density of
states vanishes at the Fermi energy, and that, in general, the relationship
between the two appears to be quite subtle.Comment: Latex, 16 pages, Princeton preprin
Superconductivity in CoO Layers and the Resonating Valence Bond Mean Field Theory of the Triangular Lattice t-J model
Motivated by the recent discovery of superconductivity in two dimensional
CoO layers, we present some possibly useful results of the RVB mean field
theory applied to the triangular lattice. Away from half filling, the order
parameter is found to be complex, and yields a fully gapped quasiparticle
spectrum. The sign of the hopping plays a crucial role in the analysis, and we
find that superconductivity is as fragile for one sign as it is robust for the
other. NaCoOHO is argued to belong to the robust case, by
comparing the LDA Fermi surface with an effective tight binding model. The high
frequency Hall constant in this system is potentially interesting, since it is
pointed out to increase linearly with temperature without saturation for T
T.Comment: Published in Physical Review B, total 1 tex + 9 eps files. Erratum
added as separate tex file on November 7, 2003, a numerical factor corrected
in the erratum on Dec 3, 200
Conductance Fluctuations of Open Quantum Dots under Microwave Radiation
We develop a time dependent random matrix theory describing the influence of
a time-dependent perturbation on mesoscopic conductance fluctuations in open
quantum dots. The effect of external field is taken into account to all orders
of perturbation theory, and our results are applicable to both weak and strong
fields. We obtain temperature and magnetic field dependences of conductance
fluctuations. The amplitude of conductance fluctuations is determined by
electron temperature in the leads rather than by the width of electron
distribution function in the dot. The asymmetry of conductance with respect to
inversion of applied magnetic field is the main feature allowing to distinguish
the effect of direct suppression of quantum interference from the simple
heating if the frequency of external radiation is larger than the temperature
of the leads .Comment: 7 pages, 5 figure
Nonuniversality in quantum wires with off-diagonal disorder: a geometric point of view
It is shown that, in the scaling regime, transport properties of quantum
wires with off-diagonal disorder are described by a family of scaling equations
that depend on two parameters: the mean free path and an additional continuous
parameter. The existing scaling equation for quantum wires with off-diagonal
disorder [Brouwer et al., Phys. Rev. Lett. 81, 862 (1998)] is a special point
in this family. Both parameters depend on the details of the microscopic model.
Since there are two parameters involved, instead of only one, localization in a
wire with off-diagonal disorder is not universal. We take a geometric point of
view and show that this nonuniversality follows from the fact that the group of
transfer matrices is not semi-simple. Our results are illustrated with
numerical simulations for a tight-binding model with random hopping amplitudes.Comment: 12 pages, RevTeX; 3 figures included with eps
Unitarity in Dirichlet Higgs Model
We show that a five dimensional Universal Extra Dimension model, compactified
on a line segment, is consistently formulated even when the gauge symmetry is
broken solely by non-zero Dirichlet boundary conditions on a bulk Higgs field,
without any quartic interaction. We find that the longitudinal W+W- elastic
scattering amplitude, under the absence of the Higgs zero-mode, is unitarized
by exchange of infinite towers of KK Higgs bosons. Resultant amplitude scales
linearly with the scattering energy, exhibiting five dimensional nature. A
tree-level partial-wave unitarity condition is satisfied up to 6.7 (5.7) TeV
for the KK scale 430 (500) GeV, favored by the electroweak data within 90% CL.Comment: 14pages, 2 figures (v1); References added (v2); Trivial error
corrected: u -> t and \cos\theta -> -\cos\theta, references added (v3);
comments added, a reference added, version to appear in Eur. Phys. J. C (v4);
Expressions matched to EPJC style, obsolete affiliation (on leave) has been
removed (v5
Transcranial Magnetic theta-burst stimulation of the human cerebellum distinguishes absolute, duration-based from relative, beat-based perception of subsecond time intervals
Cerebellar functions in two types of perceptual timing were assessed: the absolute (duration-based) timing of single intervals and the relative (beat-based) timing of rhythmic sequences. Continuous transcranial magnetic theta-burst stimulation (cTBS) was applied over the medial cerebellum and performance was measured adaptively before and after stimulation. A large and significant effect was found in the TBS (n = 12) compared to the SHAM (n = 12) group for single-interval timing but not for the detection of a regular beat or a deviation from it. The data support the existence of distinct perceptual timing mechanisms and an obligatory role of the cerebellum in absolute interval timing with a functional dissociation from relative timing of interval within rhythmic sequences based on a regular beat
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