42,936 research outputs found
Wormholes in String Theory
A wormhole is constructed by cutting and joining two spacetimes satisfying
the low energy string equations with a dilaton field. In spacetimes described
by the "string metric" the dilaton energy-momentum tensor need not satisfy the
weak or dominant energy conditions. In the cases considered here the dilaton
field violates these energy conditions and is the source of the exotic matter
required to maintain the wormhole. There is also a surface stress-energy, that
must be produced by additional matter, where the spacetimes are joined. It is
shown that wormholes can be constructed for which this additional matter
satisfies the weak and dominant energy conditions, so that it could be a form
of "normal" matter. Charged dilaton wormholes with a coupling between the
dilaton and the electromagnetic field that is more general than in string
theory are also briefly discussed.Comment: 9 pages, LaTex, submitted to Phys. Rev.
Calcium intake, physical activity and bone health status among Chinese early adolescents
The objective of this cross-sectional study was to determine the relationship between calcium
intake and physical activity with bone health status among Chinese early adolescents. A selfadministered
questionnaire was used to obtain socio-demographic background, family history of
osteoporosis, lifestyle practices and eating habits; while daily calcium intake was assessed using
one-day dietary recall and two-day dietary record. Physical activity was examined using PAQ-A
(Physical Activity Questionnaire for Adolescents). Height, weight and bone health status was
assessed using stadiometer, weighing scale (TANITA), and ultrasonometry QUS-2, respectively.
Data was analysed using the Statistical Package for Social Sciences (SPSS), version 15.0. A total of
236 Chinese subjects were recruited into this study. The mean age of subjects was 13.6 ± 0.5 years
old. Mean daily calcium intake was low, that is 573.4 ± 405.1mg. The mean score of PAQ-A was 2.14
± 0.64. Mean weight, height, and BMI were 50.9 ± 11.4kg, 1.62 ± 0.08m and 19.40 ± 3.72kg/m2,
respectively. Based on CDC classification of BMI-for-age (2000), 68.2% of subjects were in the
normal category, 16.1% were underweight, 11.4% were at risk of overweight and 4.2% overweight.
Mean Broadband Ultrasound Attenuation (BUA) was 77.55 ± 11.73dB/MHz. According to diagnostic
criteria for osteoporosis by WHO (1994), 49.2% of subjects had normal bone mass (t-score > -1.0),
more than half of the subjects were either osteopenic (49.6%) or osteopototic (1.3%). This might be
due to subjects being in the early adolescents state and their peak bone mass has yet to be attained.
T-test showed that there was significant difference between mean body weight among male and
female subjects. There was also significant higher mean BUA among female subjects than their
counterparts. Pearson correlation test showed that there was no significant relationship between
BUA with calcium intake (r= -0.05, p= 0.42) or physical activity (r= 0.03, p= 0.69). However, weight
had a significant positive correlation with BUA (r= 0.39, p<0.05). In conclusion, female subjects
have better bone health status as compared to males. Although no significant relationship was
shown between calcium intake and physical activity with bone health, these two factors are
known to reduce future risk of osteoporosis. It is recommended that prevention and management
of low bone mass should be focused on factors recognised as determinants of bone health status
among early adolescents. This is to ensure optimal bone health being attained among the young
population in reducing risk of osteoporosis in future
Master Equation for Hydrogen Recombination on Grain Surfaces
Recent experimental results on the formation of molecular hydrogen on
astrophysically relevant surfaces under conditions similar to those encountered
in the interstellar medium provided useful quantitative information about these
processes. Rate equation analysis of experiments on olivine and amorphous
carbon surfaces provided the activation energy barriers for the diffusion and
desorption processes relevant to hydrogen recombination on these surfaces.
However, the suitability of rate equations for the simulation of hydrogen
recombination on interstellar grains, where there might be very few atoms on a
grain at any given time, has been questioned. To resolve this problem, we
introduce a master equation that takes into account both the discrete nature of
the H atoms and the fluctuations in the number of atoms on a grain. The
hydrogen recombination rate on microscopic grains, as a function of grain size
and temperature, is then calculated using the master equation. The results are
compared to those obtained from the rate equations and the conditions under
which the master equation is required are identified.Comment: Latex document. 14 pages of text. Four associated figs in in PS
format on separate files that are "called-in" the LaTeX documen
Monte Carlo simulations of bosonic reaction-diffusion systems
An efficient Monte Carlo simulation method for bosonic reaction-diffusion
systems which are mainly used in the renormalization group (RG) study is
proposed. Using this method, one dimensional bosonic single species
annihilation model is studied and, in turn, the results are compared with RG
calculations. The numerical data are consistent with RG predictions. As a
second application, a bosonic variant of the pair contact process with
diffusion (PCPD) is simulated and shown to share the critical behavior with the
PCPD. The invariance under the Galilean transformation of this boson model is
also checked and discussion about the invariance in conjunction with other
models are in order.Comment: Publishe
Black plane solutions in four dimensional spacetimes
The static, plane symmetric solutions and cylindrically symmetric solutions
of Einstein-Maxwell equations with a negative cosmological constant are
investigated. These black configurations are asymptotically anti-de Sitter not
only in the transverse directions, but also in the membrane or string
directions. Their causal structure is similar to that of Reissner-Nordstr\"{o}m
black holes, but their Hawking temperature goes with , where is
the ADM mass density. We also discuss the static plane solutions in
Einstein-Maxwell-dilaton gravity with a Liouville-type dilaton potential. The
presence of the dilaton field changes drastically the structure of solutions.
They are asymptotically ``anti-de Sitter'' or ``de Sitter'' depending on the
parameters in the theory.Comment: 8 pages, RevTex, to appear in Phys. Rev.
Assessment Of Co2 Emission Mitigation For A Brazilian Oil Refinery
Currently the oil refining sector is responsible for approximately 5% of the total Brazilian energy related CO2 emissions. Possibilities to reduce CO2 emissions and related costs at the largest Brazilian refinery have been estimated. The abatement costs related to energy saving options are negative, meaning that feasibility exists without specific income due to emission reductions. The assessment shows that short-term mitigation options, i.e., fuel substitution and energy efficiency measures, could reduce CO2 emissions by 6% of the total current refinery emissions. It is further shown that carbon capture and storage offers the greatest potential for more significant emission reductions in the longer term (up to 43%), but costs in the range of 64 to162 US$/t CO2, depending on the CO2 emission source (regenerators of FCC units or hydrogen production units) and the CO2 capture technology considered (oxyfuel combustion or post-combustion). Effects of uncertainties in key parameters on abatement costs are also evaluated via sensitivity analysis.334835850Universidade Estadual de Campinas (UNICAMP)11th Latin American Symposium on Anaerobic Digestion (DAAL)2014Havana, CUB
Stereotactic ablative radiotherapy for medically inoperable early stage lung cancer: early outcomes
Objective To evaluate the clinical outcome and safety of stereotactic ablative radiotherapy for medically inoperable stage I non- small-cell lung carcinoma. Design Retrospective case series. Setting Pamela Youde Nethersole Eastern Hospital, Hong Kong. Patients All patients with medically inoperable stage I non-small-cell lung carcinoma receiving stereotactic ablative radiotherapy since its establishment in 2008. Main outcome measures Disease control rate, overall survival, and treatment toxicities. Results Sixteen stage I non-small-cell lung carcinoma patients underwent the procedure from June 2008 to November 2011. The median patient age was 82 years and the majority (81%) had moderate-tosevere co-morbidity based on the Adult Comorbidity Evaluation 27 index. With a median follow-up of 22 months, the 2-year primary tumour control rate, disease-free survival and overall survival rates were 91%, 71% and 87%, respectively. No grade 3 (National Cancer Institute Common Terminology Criteria for Adverse Events) or higher treatment-related complications were reported. Conclusion Stereotactic ablative radiotherapy can achieve a high degree of local control safely in medically inoperable patients with early lung cancer.published_or_final_versio
Unique gap structure and symmetry of the charge density wave in single-layer VSe
Single layers of transition metal dichalcogenides (TMDCs) are excellent
candidates for electronic applications beyond the graphene platform; many of
them exhibit novel properties including charge density waves (CDWs) and
magnetic ordering. CDWs in these single layers are generally a planar
projection of the corresponding bulk CDWs because of the quasi-two-dimensional
nature of TMDCs; a different CDW symmetry is unexpected. We report herein the
successful creation of pristine single-layer VSe, which shows a () CDW in contrast to the (4 4) CDW for the layers in
bulk VSe. Angle-resolved photoemission spectroscopy (ARPES) from the single
layer shows a sizable () CDW gap of 100 meV at the
zone boundary, a 220 K CDW transition temperature twice the bulk value, and no
ferromagnetic exchange splitting as predicted by theory. This robust CDW with
an exotic broken symmetry as the ground state is explained via a
first-principles analysis. The results illustrate a unique CDW phenomenon in
the two-dimensional limit
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