58,484 research outputs found
Heavy-tailed statistics in short-message communication
Short-message (SM) is one of the most frequently used communication channels
in the modern society. In this Brief Report, based on the SM communication
records provided by some volunteers, we investigate the statistics of SM
communication pattern, including the interevent time distributions between two
consecutive short messages and two conversations, and the distribution of
message number contained by a complete conversation. In the individual level,
the current empirical data raises a strong evidence that the human activity
pattern, exhibiting a heavy-tailed interevent time distribution, is driven by a
non-Poisson nature.Comment: 4 pages, 4 figures and 1 tabl
The triple degenerate star WD1704+481
WD1704+481 is a visual binary in which both components are white dwarfs. We
present spectra of the H-alpha line of both stars which show that one component
(WD1704+481.2 = Sanduleak B = GR 577) is a close binary with two white dwarf
components. Thus, WD1704+481 is the first known triple degenerate star. From
radial velocity measurements of the close binary we find an orbital period of
0.1448d, a mass ratio, q=Mbright/Mfaint of q=0.70+-0.03 and a difference in the
gravitational redshifts of 11.5+-2.3km/s. The masses of the close pair of white
dwarfs predicted by the mass ratio and gravitational redshift difference
combined with theoretical cooling curves are 0.39+-0.05 solar mass and
0.56+-0.07 solar masses. WD1704+481 is therefore also likely to be the first
example of a double degenerate in which the less massive white dwarf is
composed of helium and the other white dwarf is composed of carbon and oxygen.Comment: 5 pages, 4 figure
Commuting Simplicity and Closure Constraints for 4D Spin Foam Models
Spin Foam Models are supposed to be discretised path integrals for quantum
gravity constructed from the Plebanski-Holst action. The reason for there being
several models currently under consideration is that no consensus has been
reached for how to implement the simplicity constraints. Indeed, none of these
models strictly follows from the original path integral with commuting B
fields, rather, by some non standard manipulations one always ends up with non
commuting B fields and the simplicity constraints become in fact anomalous
which is the source for there being several inequivalent strategies to
circumvent the associated problems. In this article, we construct a new
Euclidian Spin Foam Model which is constructed by standard methods from the
Plebanski-Holst path integral with commuting B fields discretised on a 4D
simplicial complex. The resulting model differs from the current ones in
several aspects, one of them being that the closure constraint needs special
care. Only when dropping the closure constraint by hand and only in the large
spin limit can the vertex amplitudes of this model be related to those of the
FK Model but even then the face and edge amplitude differ. Curiously, an ad hoc
non-commutative deformation of the variables leads from our new model
to the Barrett-Crane Model in the case of Barbero-Immirzi parameter goes to
infinity.Comment: 41 pages, 4 figure
Distribution of parallel vortices studied by spin-polarized neutron reflectivity and magnetization
We present the studies of non-uniformly distributed vortices in Nb/Al
multilayers at applied field near parallel to film surface by using
spin-polarized neutron reflectivity (SPNR) and DC magnetization measurements.
We have observed peaks above the lower critical field, Hc1, in the M-H curves
from the multilayers.
Previous works with a model calculation of minimizing Gibbs free energy have
suggested that the peaks could be ascribed to vortex line transitions for
spatial commensuration in a thin film superconductor. In order to directly
determine the distribution of vortices, we performed SPNR measurements on the
multilayer and found that the distribution and density of vortices are
different at ascending and descending fields. At ascending 2000 Oe which is
just below the first peak in the M-H curve, SPNR shows that vortices are mostly
localized near a middle line of the film meanwhile the vortices are distributed
in broader region at the descending 2000 Oe. That is related to the observation
of more vortices trapped at the descending field. As the applied field is
sightly tilted (< 3.5degree), we observe another peak at a smaller field. The
peak position is consistent with the parallel lower critical field (Hc1||). We
discuss that the vortices run along the applied field below Hc1|| and rotate
parallel to the surface at Hc1||.Comment: 17 pages, 9 figure
Anomalous t-c-g coupling: The connection between single top production and top decay
Continuing earlier work, we examine the constraint on an anomalous t-c-g
coupling from top quark decay. We find that from current CDF measurements of
the branching ratio , the minimum scale at which new physics
can strongly modify the t-c-g coupling is \Ltcg about 950 GeV. At the
upgraded Tevatron, single top production can constrain \Ltcg 4.5 TeV.
The connection between t-c production and the decay is
examined, showing how constraints on one lead to a constraint on the other.Comment: 5 pages. Requires epsf.sty to process .eps formatted figure
A Path-integral for the Master Constraint of Loop Quantum Gravity
In the present paper, we start from the canonical theory of loop quantum
gravity and the master constraint programme. The physical inner product is
expressed by using the group averaging technique for a single self-adjoint
master constraint operator. By the standard technique of skeletonization and
the coherent state path-integral, we derive a path-integral formula from the
group averaging for the master constraint operator. Our derivation in the
present paper suggests there exists a direct link connecting the canonical Loop
quantum gravity with a path-integral quantization or a spin-foam model of
General Relativity.Comment: 19 page
Variation in ecosystem service values in response to land use changes in Zhifanggou watershed of Loess plateau: a comparative study
Background: Anthropological activities could lead to various land use changes. This subsequently exerts impacts on the Ecological status as the land is the carrier of Ecosystems and their services. Ecosystem Services Values (ESVs) are monetary assessment of ecosystems services. The choice of ecosystem services valuation methods highly depends on the type and conditions of the ecological environment.
Results: In this paper, Zhifangou watershed, a watershed with fragile environments in Loess Plateau, is analyzed in terms of the historical changes of land uses and their impact on Ecosystem Services Values (ESVs). The analysis presents that the watershed had seen a large cover of forest (689.8 hectare) and grassland (97.08 hectare) until 1938, which were substituted with a cropland of 663.56 hectare in the following years, and then a gradual recovery of natural land from 1978. During these years, the human activities have ranged from little disruption, to excessive cultivation, and finally to an integrated management of the watershed. The ESVs were highest at 43.75 × 104 in 1958, and then rebounded to $113.44 × 104 in 1999.
Conclusions: The analysis reveals that the values of soil formation and retention, biodiversity protection, and climate regulation have been associated with the largest share of the total ESVs. Among them, soil formation and retention was recognized as the most impacted service by land use changes
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