8,370 research outputs found
ASGR: An Artificial Spider-Web-Based Geographic Routing in Heterogeneous Vehicular Networks
Recently, vehicular ad hoc networks (VANETs) have been attracting significant attention for their potential for guaranteeing road safety and improving traffic comfort. Due to high mobility and frequent link disconnections, it becomes quite challenging to establish a reliable route for delivering packets in VANETs. To deal with these challenges, an artificial spider geographic routing in urban VAENTs (ASGR) is proposed in this paper. First, from the point of bionic view, we construct the spider web based on the network topology to initially select the feasible paths to the destination using artificial spiders. Next, the connection-quality model and transmission-latency model are established to generate the routing selection metric to choose the best route from all the feasible paths. At last, a selective forwarding scheme is presented to effectively forward the packets in the selected route, by taking into account the nodal movement and signal propagation characteristics. Finally, we implement our protocol on NS2 with different complexity maps and simulation parameters. Numerical results demonstrate that, compared with the existing schemes, when the packets generate speed, the number of vehicles and number of connections are varying, our proposed ASGR still performs best in terms of packet delivery ratio and average transmission delay with an up to 15% and 94% improvement, respectively
Cyclic cosmology from Lagrange-multiplier modified gravity
We investigate cyclic and singularity-free evolutions in a universe governed
by Lagrange-multiplier modified gravity, either in scalar-field cosmology, as
well as in one. In the scalar case, cyclicity can be induced by a
suitably reconstructed simple potential, and the matter content of the universe
can be successfully incorporated. In the case of -gravity, cyclicity can
be induced by a suitable reconstructed second function of a very
simple form, however the matter evolution cannot be analytically handled.
Furthermore, we study the evolution of cosmological perturbations for the two
scenarios. For the scalar case the system possesses no wavelike modes due to a
dust-like sound speed, while for the case there exist an oscillation
mode of perturbations which indicates a dynamical degree of freedom. Both
scenarios allow for stable parameter spaces of cosmological perturbations
through the bouncing point.Comment: 8 pages, 3 figures, references added, accepted for publicatio
Heavily electron-doped electronic structure and isotropic superconducting gap in AxFe2Se2 (A=K,Cs)
The low energy band structure and Fermi surface of the newly discovered
superconductor, AxFe2Se2 (A=K,Cs), have been studied by angle-resolved
photoemission spectroscopy. Compared with iron pnictide superconductors,
AxFe2Se2 (A=K,Cs) is the most heavily electron-doped with Tc~30 K. Only
electron pockets are observed with an almost isotropic superconducting gap of
~10.3 meV, while there is no hole Fermi surface near the zone center, which
indicates the inter-pocket hopping or Fermi surface nesting is not a necessary
ingredient for the unconventional superconductivity in iron-based
superconductors. Thus, the sign changed s pairing symmetry, a leading
candidate proposed for iron-based superconductors, becomes conceptually
irrelevant in describing the superconducting state here. A more conventional
s-wave pairing is a better description.Comment: 4 pages, 4 figures, published online in Nature Materials 201
High temperature superconductivity (Tc onset at 34K) in the high pressure orthorhombic phase of FeSe
We have studied the structural and superconducting properties of tetragonal
FeSe under pressures up to 26GPa using synchrotron radiation and diamond anvil
cells. The bulk modulus of the tetragonal phase is 28.5(3)GPa, much smaller
than the rest of Fe based superconductors. At 12GPa we observe a phase
transition from the tetragonal to an orthorhombic symmetry. The high pressure
orthorhombic phase has a higher Tc reaching 34K at 22GPa.Comment: 15 pages, 4 figure
Measurement of Neutrino-Electron Scattering Cross-Section with a CsI(Tl) Scintillating Crystal Array at the Kuo-Sheng Nuclear Power Reactor
The elastic scattering cross-section was measured with
a CsI(Tl) scintillating crystal array having a total mass of 187kg. The
detector was exposed to an average reactor flux of
at the Kuo-Sheng Nuclear Power
Station. The experimental design, conceptual merits, detector hardware, data
analysis and background understanding of the experiment are presented. Using
29882/7369 kg-days of Reactor ON/OFF data, the Standard Model(SM) electroweak
interaction was probed at the squared 4-momentum transfer range of . The ratio of experimental to SM cross-sections
of was measured. Constraints on
the electroweak parameters were placed, corresponding to a weak
mixing angle measurement of \s2tw = 0.251 \pm 0.031({\it stat}) \pm
0.024({\it sys}) . Destructive interference in the SM \nuebar -e process was
verified. Bounds on anomalous neutrino electromagnetic properties were placed:
neutrino magnetic moment at \mu_{\nuebar}< 2.2 \times 10^{-10} \mu_{\rm B}
and the neutrino charge radius at -2.1 \times 10^{-32} ~{\rm cm^{2}} <
\nuchrad < 3.3 \times 10^{-32} ~{\rm cm^{2}}, both at 90% confidence level.Comment: 18 Figures, 7 Tables; published version as V2 with minor revision
from V
Free energy barrier for melittin reorientation from a membrane-bound state to a transmembrane state
An important step in a phospholipid membrane pore formation by melittin
antimicrobial peptide is a reorientation of the peptide from a surface into a
transmembrane conformation. In this work we perform umbrella sampling
simulations to calculate the potential of mean force (PMF) for the
reorientation of melittin from a surface-bound state to a transmembrane state
and provide a molecular level insight into understanding peptide and lipid
properties that influence the existence of the free energy barrier. The PMFs
were calculated for a peptide to lipid (P/L) ratio of 1/128 and 4/128. We
observe that the free energy barrier is reduced when the P/L ratio increased.
In addition, we study the cooperative effect; specifically we investigate if
the barrier is smaller for a second melittin reorientation, given that another
neighboring melittin was already in the transmembrane state. We observe that
indeed the barrier of the PMF curve is reduced in this case, thus confirming
the presence of a cooperative effect
The genome and transcriptome of Trichormus sp NMC-1: insights into adaptation to extreme environments on the Qinghai-Tibet Plateau
The Qinghai-Tibet Plateau (QTP) has the highest biodiversity for an extreme environment worldwide, and provides an ideal natural laboratory to study adaptive evolution. In this study, we generated a draft genome sequence of cyanobacteria Trichormus sp. NMC-1 in the QTP and performed whole transcriptome sequencing under low temperature to investigate the genetic mechanism by which T. sp. NMC-1 adapted to the specific environment. Its genome sequence was 5.9 Mb with a G+C content of 39.2% and encompassed a total of 5362 CDS. A phylogenomic tree indicated that this strain belongs to the Trichormus and Anabaena cluster. Genome comparison between T. sp. NMC-1 and six relatives showed that functionally unknown genes occupied a much higher proportion (28.12%) of the T. sp. NMC-1 genome. In addition, functions of specific, significant positively selected, expanded orthogroups, and differentially expressed genes involved in signal transduction, cell wall/membrane biogenesis, secondary metabolite biosynthesis, and energy production and conversion were analyzed to elucidate specific adaptation traits. Further analyses showed that the CheY-like genes, extracellular polysaccharide and mycosporine-like amino acids might play major roles in adaptation to harsh environments. Our findings indicate that sophisticated genetic mechanisms are involved in cyanobacterial adaptation to the extreme environment of the QTP
Evolution of the Reactor Antineutrino Flux and Spectrum at Daya Bay
The Daya Bay experiment has observed correlations between reactor core fuel
evolution and changes in the reactor antineutrino flux and energy spectrum.
Four antineutrino detectors in two experimental halls were used to identify 2.2
million inverse beta decays (IBDs) over 1230 days spanning multiple fuel cycles
for each of six 2.9 GW reactor cores at the Daya Bay and Ling
Ao nuclear power plants. Using detector data spanning effective Pu
fission fractions, , from 0.25 to 0.35, Daya Bay measures an average
IBD yield, , of
cm/fission and a fuel-dependent variation in the IBD yield,
, of cm/fission.
This observation rejects the hypothesis of a constant antineutrino flux as a
function of the Pu fission fraction at 10 standard deviations. The
variation in IBD yield was found to be energy-dependent, rejecting the
hypothesis of a constant antineutrino energy spectrum at 5.1 standard
deviations. While measurements of the evolution in the IBD spectrum show
general agreement with predictions from recent reactor models, the measured
evolution in total IBD yield disagrees with recent predictions at 3.1.
This discrepancy indicates that an overall deficit in measured flux with
respect to predictions does not result from equal fractional deficits from the
primary fission isotopes U, Pu, U, and Pu.
Based on measured IBD yield variations, yields of and cm/fission have been determined for the two
dominant fission parent isotopes U and Pu. A 7.8% discrepancy
between the observed and predicted U yield suggests that this isotope
may be the primary contributor to the reactor antineutrino anomaly.Comment: 7 pages, 5 figure
Gate-Controlled Ionization and Screening of Cobalt Adatoms on a Graphene Surface
We describe scanning tunneling spectroscopy (STS) measurements performed on
individual cobalt (Co) atoms deposited onto backgated graphene devices. We find
that Co adatoms on graphene can be ionized by either the application of a
global backgate voltage or by the application of a local electric field from a
scanning tunneling microscope (STM) tip. Large screening clouds are observed to
form around Co adatoms ionized in this way, and we observe that some intrinsic
graphene defects display a similar behavior. Our results provide new insight
into charged impurity scattering in graphene, as well as the possibility of
using graphene devices as chemical sensors.Comment: 19 pages, 4 figure
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