29,875 research outputs found
Practical Certificateless Aggregate Signatures From Bilinear Maps
Aggregate signature is a digital signature with a striking property that anyone can aggregate n individual signatures on n different messages which are signed by n distinct signers, into a single compact signature to reduce computational and storage costs. In this work, two practical certificateless aggregate signature schemes are proposed from bilinear maps. The first scheme CAS-1 reduces the costs of communication and signer-side computation but trades off the storage, while CAS-2 minimizes the storage but sacrifices the communication costs. One can choose either of the schemes by consideration of the application requirement. Compare with ID-based schemes, our schemes do not entail public key certificates as well and achieve the trust level 3, which imply the frauds of the authority are detectable. Both of the schemes are proven secure in the random oracle model by assuming the intractability of the computational Diffie-Hellman problem over the groups with bilinear maps, where the forking lemma technique is avoided
Effects of relative orientation of the molecules on electron transport in molecular devices
Effects of relative orientation of the molecules on electron transport in
molecular devices are studied by non-equilibrium Green's function method based
on density functional theory. In particular, two molecular devices, with the
planer Au and Ag clusters sandwiched between the Al(100) electrodes
are studied. In each device, two typical configurations with the clusters
parallel and vertical to the electrodes are considered. It is found that the
relative orientation affects the transport properties of these two devices
completely differently. In the Al(100)-Au-Al(100) device, the conductance
and the current of the parallel configuration are much larger than those in the
vertical configuration, while in the Al(100)-Ag-Al(100) device, an
opposite conclusion is obtained
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Revisiting individual and group differences in thermal comfort based on ASHRAE database
Different thermal demands and preferences between individuals lead to a low occupant satisfaction rate, despite the high energy consumption by HVAC system. This study aims to quantify the difference in thermal demands, and to compare the influential factors which might lead to those differences. With the recently released ASHRAE Database, we quantitatively answered the following two research questions: which factors would lead to marked individual difference, and what the magnitude of this difference is. Linear regression has been applied to describe the macro-trend of how people feel thermally under different temperatures. Three types of factors which might lead to different thermal demands have been studied and compared in this study, i.e. individual factors, building characteristics and geographical factors. It was found that the local climate has the most marked impact on the neutral temperature, with an effect size of 3.5 °C; followed by country, HVAC operation mode and body built, which lead to a difference of more than 1 °C. In terms of the thermal sensitivity, building type and local climate are the most influential factors. Subjects in residential buildings or coming from Dry climate zone could accept 2.5 °C wider temperature range than those in office, education buildings or from Continental climate zone. The findings of this research could help thermal comfort researchers and designers to identify influential factors that might lead to individual difference, and could shed light on the feature selection for the development of personal comfort models
Spin correlated interferometry for polarized and unpolarized photons on a beam splitter
Spin interferometry of the 4th order for independent polarized as well as
unpolarized photons arriving simultaneously at a beam splitter and exhibiting
spin correlation while leaving it, is formulated and discussed in the quantum
approach. Beam splitter is recognized as a source of genuine singlet photon
states. Also, typical nonclassical beating between photons taking part in the
interference of the 4th order is given a polarization dependent explanation.Comment: RevTeX, 19 pages, 1 ps figure, author web page at
http://m3k.grad.hr/pavici
Four dual AGN candidates observed with the VLBA
According to hierarchical structure formation models, merging galaxies are
expected to be seen in different stages of their coalescence. However,
currently there are no straightforward observational methods neither to select
nor to confirm a large number of dual active galactic nuclei (AGN) candidates.
Most attempts involve the better understanding of double-peaked narrow emission
line sources, to distinguish the objects where the emission lines originate
from narrow-line kinematics or jet-driven outflows from those which might
harbour dual AGN. We observed four such candidate sources with the Very Long
Baseline Array (VLBA) at 1.5 GHz with 10 milli-arcsecond angular
resolution where spectral profiles of AGN optical emission suggested the
existence of dual AGN. In SDSS J210449.13-000919.1 and SDSS J23044.82-093345.3,
the radio structures are aligned with the optical emission features, thus the
double-peaked emission lines might be the results of jet-driven outflows. In
the third detected source SDSS J115523.74+150756.9, the radio structure is less
extended and oriented nearly perpendicular to the position angle derived from
optical spectroscopy. The fourth source remained undetected with the VLBA but
it has been imaged with the Very Large Array at arcsec resolution a few months
before our observations, suggesting the existence of extended radio structure.
In none of the four sources did we detect two radio-emitting cores, a
convincing signature of duality.Comment: 35 pages, 3 figures, 2 tables, accepted for publication in Ap
Exact solution of gyration radius of individual's trajectory for a simplified human mobility model
Gyration radius of individual's trajectory plays a key role in quantifying
human mobility patterns. Of particular interests, empirical analyses suggest
that the growth of gyration radius is slow versus time except the very early
stage and may eventually arrive to a steady value. However, up to now, the
underlying mechanism leading to such a possibly steady value has not been well
understood. In this Letter, we propose a simplified human mobility model to
simulate individual's daily travel with three sequential activities: commuting
to workplace, going to do leisure activities and returning home. With the
assumption that individual has constant travel speed and inferior limit of time
at home and work, we prove that the daily moving area of an individual is an
ellipse, and finally get an exact solution of the gyration radius. The
analytical solution well captures the empirical observation reported in [M. C.
Gonz`alez et al., Nature, 453 (2008) 779]. We also find that, in spite of the
heterogeneous displacement distribution in the population level, individuals in
our model have characteristic displacements, indicating a completely different
mechanism to the one proposed by Song et al. [Nat. Phys. 6 (2010) 818].Comment: 4 pages, 4 figure
Quakes in Solid Quark Stars
A starquake mechanism for pulsar glitches is developed in the solid quark
star model. It is found that the general glitch natures (i.e., the glitch
amplitudes and the time intervals) could be reproduced if solid quark matter,
with high baryon density but low temperature, has properties of shear modulus
\mu = 10^{30~34} erg/cm^3 and critical stress \sigma_c = 10^{18~24} erg/cm^3.
The post-glitch behavior may represent a kind of damped oscillations.Comment: 11 pages, 4 figures (but Fig.3 is lost), a complete version can be
obtained by http://vega.bac.pku.edu.cn/~rxxu/publications/index_P.htm, a new
version to be published on Astroparticle Physic
Luminous Infrared Galaxies in the Local Universe
We study the morphology and star formation properties of 159 local luminous
infrared galaxy (LIRG) using multi-color images from Data Release 2 (DR2) of
the Sloan Digital Sky Survey (SDSS). The LIRGs are selected from a
cross-correlation analysis between the IRAS survey and SDSS. They are all
brighter than 15.9 mag in the r-band and below redshift ~ 0.1, and so can be
reliably classified morphologically. We find that the fractions of
interacting/merging and spiral galaxies are ~ 48% and ~ 40% respectively. Our
results complement and confirm the decline (increase) in the fraction of spiral
(interacting/merging) galaxies from z ~1 to z ~ 0.1, as found by Melbourne, Koo
& Le Floc'h (2005). About 75% of spiral galaxies in the local LIRGs are barred,
indicating that bars may play an important role in triggering star formation
rates > 20 M_{sun}/yr in the local universe. Compared with high redshift LIRGs,
local LIRGs have lower specific star formation rates, smaller cold gas
fractions and a narrower range of stellar masses. Local LIRGs appear to be
either merging galaxies forming intermediate mass ellipticals or spiral
galaxies undergoing high star formation activities regulated by bars.Comment: 22 pages, 5 figures, accepted for publication in ApJ, title changed,
typos corrected,major revisions following referee's comments,updated
reference
Measuring Dark Energy with Gamma-Ray Bursts and Other Cosmological Probes
It has been widely shown that the cosmological parameters and dark energy can
be constrained by using data from type-Ia supernovae (SNe Ia), the cosmic
microwave background (CMB) anisotropy, the baryon acoustic oscillation (BAO)
peak from Sloan Digital Sky Survey (SDSS), the X-ray gas mass fraction in
clusters, and the linear growth rate of perturbations at z=0.15 as obtained
from the 2dF Galaxy Redshift Survey. Recently, gamma-ray bursts (GRBs) have
also been argued to be promising standard candles for cosmography. In this
paper, we present constraints on the cosmological parameters and dark energy by
combining a recent GRB sample including 69 events with the other cosmological
probes. First, we find that for the LambdaCDM cosmology this combination makes
the constraints stringent and the best fit is close to the flat universe.
Second, we fit the flat Cardassian expansion model and find that this model is
consistent with the LambdaCDM cosmology. Third, we present constraints on
several two-parameter dark energy models and find that these models are also
consistent with the LambdaCDM cosmology. Finally, we reconstruct the dark
energy equation-of-state parameter w(z) and the deceleration parameter q(z). We
see that the acceleration could have started at a redshift from
z_T=0.40_{-0.08}^{+0.14} to z_T=0.65_{-0.05}^{+0.10}. This difference in the
transition redshift is due to different dark energy models that we adopt. The
most stringent constraint on w(z) lies in the redshift range z\sim 0.3-0.6.Comment: 28 pages, 13 figures, accepted for publication in ApJ. One reference
added, one minor change in the final paragraph of section
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