19,042 research outputs found
Model checking a server - side micro payment protocol
Many virtual payment systems are available on the world
wide web for micropayment, and as they deal with money, correctness is important. One such payment system is Netpay. This paper examines the server-side version of the Netpay protocol and provides its formalization
as a CSP model. The PAT model checker is used to prove three properties essential for correctness: impossibility of double spending, validity of an ecoin during the execution and the absence of deadlock. We prove that the protocol is executing according to its description based on the assumption that the customers and vendors are cooperative. This is a very strong assumption for system built to prevent abuse, but further analysis suggests that without it the protocol does no longer guarantee
all correctness properties
Late-Time Optical Afterglow Observations with LBT and MDM
Using the 2.4m MDM and 8.4m Large Binocular Telescope, we observed nine GRB
afterglows to systematically probe the late time behaviors of afterglows
including jet breaks, flares, and supernova bumps. In particular, the LBT
observations have typical flux limits of 25-26 mag in the Sloan r' band, which
allows us to extend the temporal baseline for measuring jet breaks by another
decade in time scale. We detected four jet breaks (including a "textbook" jet
break in GRB070125) and a fifth candidate, all of which are not detectable
without deep, late time optical observations. In the other four cases, we do
not detect the jet breaks either because of contamination from the host galaxy
light, the presence of a supernova bump, or the intrinsic faintness of the
optical afterglow. This suggests that the basic picture that GRBs are
collimated is still valid and that the apparent lack of Swift jet breaks is due
to poorly sampled afterglow light curves, particularly at late times. Besides
the jet breaks, we also detected late time flares, which could attribute to
late central engine activities, and two supernova bumps.Comment: 5 pages, 5 figures, 2008 NANJING GAMMA-RAY BURST CONFERENCE. AIP
Conference Proceedings, Volume 1065, pp. 93-97 (2008), Eds. Y.F. Huang, Z.G.
Dai, B. Zhan
The Luminosity - E_p Relation within Gamma--Ray Bursts and Implications for Fireball Models
Using a sample of 2408 time-resolved spectra for 91 BATSE gamma-ray bursts
(GRBs) presented by Preece et al., we show that the relation between the
isotropic-equivalent luminosity (L_iso) and the spectral peak energy (E_p) in
the cosmological rest frame, L_iso \propto E_p^2, not only holds within these
bursts, but also holds among these GRBs, assuming that the burst rate as a
function of redshift is proportional to the star formation rate. The possible
implications of this relation for the emission models of GRBs are discussed. We
suggest that both the kinetic-energy-dominated internal shock model and the
magnetic-dissipation-dominated external shock model can well interpret this
relation. We constrain the parameters for these two models, and find that they
are in a good agreement with the parameters from the fittings to the afterglow
data (abridged).Comment: 3 pages plus 5 figures, emulateapj style, accepted for publication in
ApJ Letter
Solar modulation of cosmic ray intensity and solar flare events inferred from (14)C contents in dated tree rings
The delta 14C values in 42 rings of a white spruce grown in Mackenzie Delta was measured as a continuing effort of tracing the history of solar modulation of cosmic ray intensity. The delta 14C values in six rings were measured, in search of a 14C increase due to two large solar flares that occurred in 1942. The results are presented
Quantum criticality and nodal superconductivity in the FeAs-based superconductor KFe2As2
The in-plane resistivity and thermal conductivity of
FeAs-based superconductor KFeAs single crystal were measured down to 50
mK. We observe non-Fermi-liquid behavior at =
5 T, and the development of a Fermi liquid state with when
further increasing field. This suggests a field-induced quantum critical point,
occurring at the superconducting upper critical field . In zero field
there is a large residual linear term , and the field dependence of
mimics that in d-wave cuprate superconductors. This indicates that
the superconducting gaps in KFeAs have nodes, likely d-wave symmetry.
Such a nodal superconductivity is attributed to the antiferromagnetic spin
fluctuations near the quantum critical point.Comment: 4 pages, 4 figures - replaces arXiv:0909.485
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Community Networks and the Growth of Private Enterprise in China
This paper identifies and quantifies the role played by birth-county-based community networks in the growth of private enterprise in China. We develop a network-based model that generates predictions for the dynamics of firm entry, concentration, and firm size across birth counties with varying social connectedness (measured by population density). These predictions are verified over the 1990-2009 period with administrative data covering the universe of registered firms. Competing non-network-based explanations can explain some, but not all, of the results. Moreover, supplementary evidence indicates that network spillovers occur within the birth county and, going down even further, within clans within the county. Having validated the model, we estimate its structural parameters and conduct counter-factual simulations, which estimate that entry over the 1995-2004 period would have been 40% lower (with a comparable decline in the stock of capital) in the absence of community networks. Additional counter-factual simulations shed light on misallocation and industrial policy in economies where networks are active
Observable Optimal State Points of Sub-additive Potentials
For a sequence of sub-additive potentials, Dai [Optimal state points of the
sub-additive ergodic theorem, Nonlinearity, 24 (2011), 1565-1573] gave a method
of choosing state points with negative growth rates for an ergodic dynamical
system. This paper generalizes Dai's result to the non-ergodic case, and proves
that under some mild additional hypothesis, one can choose points with negative
growth rates from a positive Lebesgue measure set, even if the system does not
preserve any measure that is absolutely continuous with respect to Lebesgue
measure.Comment: 16 pages. This work was reported in the summer school in Nanjing
University. In this second version we have included some changes suggested by
the referee. The final version will appear in Discrete and Continuous
Dynamical Systems- Series A - A.I.M. Sciences and will be available at
http://aimsciences.org/journals/homeAllIssue.jsp?journalID=
Gamma-Ray Burst Afterglows with Energy Injection: Homogeneous Versus Wind External Media
Assuming an adiabatic evolution of a gamma-ray burst (GRB) fireball
interacting with an external medium, we calculate the hydrodynamics of the
fireball with energy injection from a strongly magnetic millisecond pulsar
through magnetic dipole radiation, and obtain the light curve of the optical
afterglow from the fireball by synchrotron radiation. Results are given both
for a homogeneous external medium and for a wind ejected by GRB progenitor. Our
calculations are also available in both ultra-relativistic and non-relativistic
phases. Furthermore, the observed R-band light curve of GRB{000301C} can be
well fitted in our model, which might provide a probe of the properties of GRB
progenitors.Comment: revised version for publication in Chin. Phys. Let
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