1,802 research outputs found
Strength Reduction in Electrical and Elastic Networks
Particular aspects of problems ranging from dielectric breakdown to metal
insu- lator transition can be studied using electrical o elastic networks. We
present an expression for the mean breakdown strength of such networks.First,
we intro- duce a method to evaluate the redistribution of current due to the
removal of a finite number of elements from a hyper-cubic network of
conducatances.It is used to determine the reduction of breakdown strength due
to a fracture of size .Numerical analysis is used to show that the
analogous reduction due to random removal of elements from electrical and
elastic networks follow a similar form.One possible application, namely the use
of bone density as a diagnostic tools for osteorosporosis,is discussed.Comment: one compressed file includes: 9 PostScrpt figures and a text fil
A comprehensive study of shower to shower fluctuations
By means of Monte Carlo simulations of extensive air showers (EAS), we have
performed a comprehensive study of the shower to shower fluctuations affecting
the longitudinal and lateral development of EAS. We split the fluctuations into
physical fluctuations and those induced by the thinning procedure customarily
applied to simulate showers at EeV energies and above. We study the influence
of thinning on the calculation of the shower to shower fluctuations in the
simulations. For thinning levels larger than 10^(-5) - 10^(-6), the
determination of the shower to shower fluctuations is hampered by the
artificial fluctuations induced by the thinning procedure. However, we show
that shower to shower fluctuations can still be approximately estimated, and we
provide expressions to calculate them. The influence of fluctuations of the
depth of first interaction on the determination of shower to shower
fluctuations is also addressed.Comment: 17 pages, 15 figure
Experimental investigation of the impact of optical injection on vital parameters of a gain-switched pulse source
An analysis of optical injection on a gain-switched distributed feedback (DFB) laser and its impact on pulse parameters that influence the performance of the pulse source in high-speed optical communication systems is presented in this paper. A range of 10 GHz in detuning and 5 dB in injected power has been experimentally identified to attain pulses, from an optically injected gain-switched DFB laser, with durations below 10 ps and pedestal suppression higher than 35 dB. These pulse features are associated with a side mode suppression ratio of about 30 dB and a timing jitter of less than 1 ps. This demonstrates the feasibility of using optical injection in conjunction with appropriate pulse compression schemes for developing an optimized and cost-efficient pulse source, based on a gain-switched DFB laser, for high-speed photonic systems
Prevalence of Tritrichomonas foetus in beef bulls slaughtered at two abattoirs in northern Australia
Bovine trichomoniasis, caused by the protozoal parasite Tritrichomonas foetus, is a highly contagious venereal disease characterised by early pregnancy loss, abortion and pyometra. Persistently infected bulls and cows are the primary reservoirs of infection in infected herds. This research investigated the prevalence of T. foetus infection in bulls from properties located across northern Australia and New South Wales. Preputial samples were collected from 606 bulls at slaughter and tested for T. foetus using the VetMAX-Gold Trich Detection Kit (Thermo Fisher Scientific). The apparent prevalence of T. foetus infection varied between regions, with northern regions in the Northern Territory, Queensland and Western Australia showing a prevalence of 15.4%, 13.8% and 11.4%, respectively. There was some evidence of an association between infection and postcode (P = 0.06) and increasing bull age (P = 0.054). This study confirms that T. foetus infection is likely to be present in many beef breeding herds and contributing to lower than expected reproductive performance, particularly across northern Australia
Using Nonlinear Response to Estimate the Strength of an Elastic Network
Disordered networks of fragile elastic elements have been proposed as a model
of inner porous regions of large bones [Gunaratne et.al., cond-mat/0009221,
http://xyz.lanl.gov]. It is shown that the ratio of responses of such
a network to static and periodic strain can be used to estimate its ultimate
(or breaking) stress. Since bone fracture in older adults results from the
weakening of porous bone, we discuss the possibility of using as a
non-invasive diagnostic of osteoporotic bone.Comment: 4 pages, 4 figure
Ordering Effects in Benzo[1,2-b:4,5- bâČ]difuran-thieno[3,4- c]pyrrole-4,6-dione Polymers with >7% Solar Cell Efficiency
Benzo[1,2-b:4,5-b\u27]difuranâthieno[3,4-c]pyrrole-4,6-dione (PBDFTPD) polymers prepared by microwave-assisted synthesis can achieve power conversion efficiencies (PCEs) >7% in bulk-heterojunction solar cells with phenyl-C61/71-butyric acid methyl ester (PCBM). In âas-castâ PBDFTPD-based devices solution-processed without a small-molecule additive, high PCEs can be obtained in spite of the weak propensity of the polymers to self-assemble and form Ï-aggregates in thin films
Gastric cancer and Helicobacter pylori: a combined analysis of 12 case control studies nested within prospective cohorts
BACKGROUND: The magnitude of the association
between Helicobacter pylori and
incidence of gastric cancer is unclear. H
pylori infection and the circulating antibody
response can be lost with development
of cancer; thus retrospective studies
are subject to bias resulting from classifi-
cation of cases as H pylori negative when
they were infected in the past.
AIMS: To combine data from all case control
studies nested within prospective
cohorts to assess more reliably the relative
risk of gastric cancer associated with H
pylori infection.To investigate variation in
relative risk by age, sex, cancer type and
subsite, and interval between blood sampling
and cancer diagnosis.
METHODS: Studies were eligible if blood
samples for H pylori serology were collected
before diagnosis of gastric cancer in
cases. Identified published studies and two
unpublished studies were included. Individual
subject data were obtained for
each. Matched odds ratios (ORs) and 95%
confidence intervals (95% CI) were calculated
for the association between H pylori
and gastric cancer.
RESULTS: Twelve studies with 1228 gastric
cancer cases were considered. The association
with H pylori was restricted to noncardia
cancers (OR 3.0; 95% CI 2.3â3.8)
and was stronger when blood samples for
H pylori serology were collected 10+ years
before cancer diagnosis (5.9; 3.4â10.3). H
pylori infection was not associated with an
altered overall risk of cardia cancer (1.0;
0.7â1.4).
CONCLUSIONS: These results suggest that
5.9 is the best estimate of the relative risk
of non-cardia cancer associated with H
pylori infection and that H pylori does not
increase the risk of cardia cancer. They
also support the idea that when H pylori
status is assessed close to cancer diagnosis,
the magnitude of the non-cardia
association may be underestimated
Current constraints on Cosmological Parameters from Microwave Background Anisotropies
We compare the latest observations of Cosmic Microwave Background (CMB)
Anisotropies with the theoretical predictions of the standard scenario of
structure formation. Assuming a primordial power spectrum of adiabatic
perturbations we found that the total energy density is constrained to be
while the energy density in baryon and Cold Dark
Matter (CDM) are and ,
(all at 68% C.L.) respectively. The primordial spectrum is consistent with
scale invariance, () and the age of the universe is
Gyrs. Adding informations from Large Scale Structure and
Supernovae, we found a strong evidence for a cosmological constant
and a value of the Hubble parameter
. Restricting this combined analysis to flat universes, we put
constraints on possible 'extensions' of the standard scenario. A gravity waves
contribution to the quadrupole anisotropy is limited to be (95%
c.l.). A constant equation of state for the dark energy component is bound to
be (95% c.l.). We constrain the effective relativistic degrees
of freedom and the neutrino chemical potential and (massless neutrinos).Comment: The status of cosmological parameters before WMAP. In press on Phys.
Rev. D., Rapid Communication, 6 pages, 5 figure
Two-domains bulklike Fermi surface of Ag films deposited onto Si(111)-(7x7)
Thick metallic silver films have been deposited onto Si(111)-(7x7) substrates
at room temperature. Their electronic properties have been studied by using
angle resolved photoelectron spectroscopy (ARPES). In addition to the
electronic band dispersion along the high-symmetry directions, the Fermi
surface topology of the grown films has been investigated. Using ARPES, the
spectral weight distribution at the Fermi level throughout large portions of
the reciprocal space has been determined at particular perpendicular
electron-momentum values. Systematically, the contours of the Fermi surface of
these films reflected a sixfold symmetry instead of the threefold symmetry of
Ag single crystal. This loss of symmetry has been attributed to the fact that
these films appear to be composed by two sets of domains rotated 60 from
each other. Extra, photoemission features at the Fermi level were also
detected, which have been attributed to the presence of surface states and
\textit{sp}-quantum states. The dimensionality of the Fermi surface of these
films has been analyzed studying the dependence of the Fermi surface contours
with the incident photon energy. The behavior of these contours measured at
particular points along the Ag L high-symmetry direction puts forward
the three-dimensional character of the electronic structure of the films
investigated.Comment: 10 pages, 12 figures, submitted to Physical Review
- âŠ