27,791 research outputs found
The effects on topic familiarity on online search behaviour and use of relevance criteria
This paper presents an experimental study on the effect of topic familiarity on the assessment behaviour of online searchers. In particular we investigate the effect of topic familiarity on the resources and relevance criteria used by searchers. Our results indicate that searching on an unfamiliar topic leads to use of more generic and fewer specialised resources and that searchers employ different relevance criteria when searching on less familiar topics
Constraint on the early Universe by relic gravitational waves: From pulsar timing observations
Recent pulsar timing observations by the Parkers Pulsar Timing Array and
European Pulsar Timing Array teams obtained the constraint on the relic
gravitational waves at the frequency , which provides the
opportunity to constrain , the Hubble parameter when these waves crossed
the horizon during inflation. In this paper, we investigate this constraint by
considering the general scenario for the early Universe: we assume that the
effective (average) equation-of-state before the big bang nucleosynthesis
stage is a free parameter. In the standard hot big-bang scenario with ,
we find that the current PPTA result follows a bound H_*\leq
1.15\times10^{-1}\mpl, and the EPTA result follows H_*\leq
6.92\times10^{-2}\mpl. We also find that these bounds become much tighter in
the nonstandard scenarios with . When , the bounds become
H_*\leq5.89\times10^{-3}\mpl for the current PPTA and
H_*\leq3.39\times10^{-3}\mpl for the current EPTA. In contrast, in the
nonstandard scenario with , the bound becomes H_*\leq7.76\mpl for the
current PPTA.Comment: 8 pages, 3 figures, 1 table, PRD in pres
Evaluation of Formal posterior distributions via Markov chain arguments
We consider evaluation of proper posterior distributions obtained from
improper prior distributions. Our context is estimating a bounded function
of a parameter when the loss is quadratic. If the posterior mean of
is admissible for all bounded , the posterior is strongly
admissible. We give sufficient conditions for strong admissibility. These
conditions involve the recurrence of a Markov chain associated with the
estimation problem. We develop general sufficient conditions for recurrence of
general state space Markov chains that are also of independent interest. Our
main example concerns the -dimensional multivariate normal distribution with
mean vector when the prior distribution has the form on the parameter space . Conditions on for strong
admissibility of the posterior are provided.Comment: Published in at http://dx.doi.org/10.1214/07-AOS542 the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Relic gravitational waves: latest revisions and preparations for new data
The forthcoming release of data from the Planck mission, and possibly from
the next round of Wilkinson Microwave Anisotropy Probe (WMAP) observations,
make it necessary to revise the evaluations of relic gravitational waves in the
existing data and, at the same time, to refine the assumptions and data
analysis techniques in preparation for the arrival of new data. We reconsider
with the help of the commonly used CosmoMC numerical package the previously
found indications of relic gravitational waves in the 7-year (WMAP7) data. The
CosmoMC approach reduces the confidence of these indications from approximately
2 level to approximately 1 level, but the indications do not
disappear altogether. We critically analyze the assumptions that are currently
used in the Cosmic Microwave Background (CMB) data analyzes and outline the
strategy that should help avoid the oversight of relic gravitational waves in
the future CMB data. In particular, it is important to keep away from the
unwarranted assumptions about density perturbations. The prospects of confident
detection of relic gravitational waves by the Planck satellite have worsened,
but they are still good. It appears that more effort will be required in order
to mitigate the foreground contamination.Comment: 11 pages, 4 figures, 3 tables; v.3: improvements, published versio
Geometrical Expression for the Angular Resolution of a Network of Gravitational-Wave Detectors
We report for the first time general geometrical expressions for the angular
resolution of an arbitrary network of interferometric gravitational-wave (GW)
detectors when the arrival-time of a GW is unknown. We show explicitly elements
that decide the angular resolution of a GW detector network. In particular, we
show the dependence of the angular resolution on areas formed by projections of
pairs of detectors and how they are weighted by sensitivities of individual
detectors. Numerical simulations are used to demonstrate the capabilities of
the current GW detector network. We confirm that the angular resolution is poor
along the plane formed by current LIGO-Virgo detectors. A factor of a few to
more than ten fold improvement of the angular resolution can be achieved if the
proposed new GW detectors LCGT or AIGO are added to the network. We also
discuss the implications of our results for the design of a GW detector
network, optimal localization methods for a given network, and electromagnetic
follow-up observations.Comment: 13 pages, for Phys. Rev.
Food Consumption and Demographics in Japan: Implications for an Aging Population
This study estimates a cross-sectional model based on the Almost Ideal Demand System (AIDS) to examine the determinants of food consumption patterns in Japan over life-cycle periods. The test of structural changes, the analysis of the effects of demographic characteristics, and the estimation of expenditure and price elasticities are conducted from a random sample of 1,281 households from a Japanese household survey in 1997. Results show that each economic or non-economic factor has a different impact on food consumption over a lifetime. Changes in consumption of some food groups can be explained by price and income effects where others can be explained by demographic characteristics. Financial constraint is not binding and residential location is likely to have little or no impact on predicting consumers’ food choices at different periods of their lives. Other key factors that affect consumption pattern include family size, number of children, lifestyle and health concern.Japan, Food Demand, Life-Cycle, AIDS, Household
Mosaic spin models with topological order
We study a class of two-dimensional spin models with the Kitaev-type
couplings in mosaic structure lattices to implement topological orders. We show
that they are exactly solvable by reducing them to some free Majorana fermion
models with gauge symmetries. The typical case with a 4-8-8 close packing is
investigated in detail to display the quantum phases with Abelian and
non-Abelian anyons. Its topological properties characterized by Chern numbers
are revealed through the edge modes of its spectrum.Comment: 4 pages, 3 figures. Final version to appear in Phys. Rev. B as a
Rapid Communicatio
Temperature dependence and resonance effects in Raman scattering of phonons in NdFeAsOF single crystals
We report plane-polarized Raman scattering spectra of iron oxypnictide
superconductor NdFeAsOF single crystals with varying fluorine
content. The spectra exhibit sharp and symmetrical phonon lines with a weak
dependence on fluorine doping . The temperature dependence does not show any
phonon anomaly at the superconducting transition. The Fe related phonon
intensity shows a strong resonant enhancement below 2 eV. We associate the
resonant enhancement to the presence of an interband transition around 2 eV
observed in optical conductivity. Our results point to a rather weak coupling
between Raman-active phonons and electronic excitations in iron oxypnictides
superconductors.Comment: 4 pages, 3 figures, to appear in Phys. Rev.
Mode-Locking in Quantum-Hall-Effect Point Contacts
We study the effect of an ac drive on the current-voltage (I-V)
characteristics of a tunnel junction between two fractional Quantum Hall fluids
at filling an odd integer. Within the chiral Luttinger liquid model
of edge states, the point contact dynamics is described by a driven damped
quantum mechanical pendulum. In a semi-classical limit which ignores electron
tunnelling, this model exhibits mode-locking, which corresponds to current
plateaus in the I-V curve at integer multiples of , with
the ac drive angular frequency. By analyzing the full quantum model at
non-zero using perturbative and exact methods, we study the effect of
quantum fluctuation on the mode-locked plateaus. For quantum
fluctuations smear completely the plateaus, leaving no trace of the ac drive.
For smeared plateaus remain in the I-V curve, but are not
centered at the currents . For rounded plateaus
centered around the quantized current values are found. The possibility of
using mode locking in FQHE point contacts as a current-to-frequency standard is
discussed.Comment: 12 pages, 8 figures, minor change
Sharp and Smooth Boundaries of Quantum Hall Liquids
We study the transition between sharp and smooth density distributions at the
edges of Quantum Hall Liquids in the presence of interactions. We find that,
for strong confining potentials, the edge of a liquid is described by
the Fermi Liquid theory, even in the presence of interactions, a
consequence of the chiral nature of the system. When the edge confining
potential is decreased beyond a point, the edge undergoes a reconstruction and
electrons start to deposit a distance magnetic lengths away from the
initial QH Liquid. Within the Hartree-Fock approximation, a new pair of
branches of gapless edge excitations is generated after the transition. We show
that the transition is controlled by the balance between a long-ranged
repulsive Hartree term and a short-ranged attractive exchange term. Such
transition also occurs for Quantum Dots in the Quantum Hall Regime, and should
be observable in resonant tunneling experiments. Electron tunneling into the
reconstructed edge is also discussed.Comment: 28 pages, REVTeX 3.0, 18 figures available upon request,
cond-mat/yymmnn
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