539 research outputs found
Self-force Regularization in the Schwarzschild Spacetime
We discuss the gravitational self-force on a particle in a black hole
space-time. For a point particle, the full (bare) self-force diverges. The
metric perturbation induced by a particle can be divided into two parts, the
direct part (or the S part) and the tail part (or the R part), in the harmonic
gauge, and the regularized self-force is derived from the R part which is
regular and satisfies the source-free perturbed Einstein equations. But this
formulation is abstract, so when we apply to black hole-particle systems, there
are many problems to be overcome in order to derive a concrete self-force.
These problems are roughly divided into two parts. They are the problem of
regularizing the divergent self-force, i.e., ``subtraction problem'' and the
problem of the singularity in gauge transformation, i.e., ``gauge problem''. In
this paper, we discuss these problems in the Schwarzschild background and
report some recent progress.Comment: 34 pages, 2 figures, submitted to CQG, special volume for Radiation
Reaction (CAPRA7
HIV and cancer registry linkage identifies a substantial burden of cancers in persons with HIV in India.
We utilized computerized record-linkage methods to link HIV and cancer databases with limited unique identifiers in Pune, India, to determine feasibility of linkage and obtain preliminary estimates of cancer risk in persons living with HIV (PLHIV) as compared with the general population.Records of 32,575 PLHIV were linked to 31,754 Pune Cancer Registry records (1996-2008) using a probabilistic-matching algorithm. Cancer risk was estimated by calculating standardized incidence ratios (SIRs) in the early (4-27 months after HIV registration), late (28-60 months), and overall (4-60 months) incidence periods. Cancers diagnosed prior to or within 3 months of HIV registration were considered prevalent.Of 613 linked cancers to PLHIV, 188 were prevalent, 106 early incident, and 319 late incident. Incident cancers comprised 11.5% AIDS-defining cancers (ADCs), including cervical cancer and non-Hodgkin lymphoma (NHL), but not Kaposi sarcoma (KS), and 88.5% non-AIDS-defining cancers (NADCs). Risk for any incident cancer diagnosis in early, late, and combined periods was significantly elevated among PLHIV (SIRs: 5.6 [95% CI 4.6-6.8], 17.7 [95% CI 15.8-19.8], and 11.5 [95% CI 10-12.6], respectively). Cervical cancer risk was elevated in both incidence periods (SIRs: 9.6 [95% CI 4.8-17.2] and 22.6 [95% CI 14.3-33.9], respectively), while NHL risk was elevated only in the late incidence period (SIR: 18.0 [95% CI 9.8-30.20]). Risks for NADCs were dramatically elevated (SIR > 100) for eye-orbit, substantially (SIR > 20) for all-mouth, esophagus, breast, unspecified-leukemia, colon-rectum-anus, and other/unspecified cancers; moderately elevated (SIR > 10) for salivary gland, penis, nasopharynx, and brain-nervous system, and mildly elevated (SIR > 5) for stomach. Risks for 6 NADCs (small intestine, testis, lymphocytic leukemia, prostate, ovary, and melanoma) were not elevated and 5 cancers, including multiple myeloma not seen.Our study demonstrates the feasibility of using probabilistic record-linkage to study cancer/other comorbidities among PLHIV in India and provides preliminary population-based estimates of cancer risks in PLHIV in India. Our results, suggesting a potentially substantial burden and slightly different spectrum of cancers among PLHIV in India, support efforts to conduct multicenter linkage studies to obtain precise estimates and to monitor cancer risk in PLHIV in India
Aminoglycosides for Intra-Abdominal Infection: Equal to the Challenge?
Background: Aminoglycosides, combined with antianaerobic agents, have been used widely for the treatment of intra-abdominal infection. However, some prospective randomized controlled trials and other data suggested that aminoglycosides were less efficacious than newer comparators for the treatment of these infections. We therefore performed a meta-analysis of all prospective randomized controlled trials utilizing aminoglycosides to reevaluate the efficacy of these agents for the treatment of intra-abdominal infection.
Methods: Published English-language prospective randomized controlled trials comparing aminoglycosides with other agents for treatment of intra-abdominal infection were identified by MEDLINE search. For each study, data were collected regarding the number of patients enrolled and evaluated, their basic demographic characteristics, the sources of the intra-abdominal infections, the number of failures as determined by the study investigators, quality score, and the use of serum drug concentrations to monitor aminoglycoside therapy. These data were combined to calculate odds ratios for risk of therapeutic failure, which were assessed for significance using Chi-square analysis.
Results: Forty-seven prospective randomized controlled trials comparing aminoglycosides to other agents were identified. These were published between 1981 and 2000, and included a total of 5,182 evaluable patients. Analysis of all studies combined revealed an odds ratio that slightly, but significantly, favored the comparators. After excluding six trials using comparators that lacked accepted antianaerobic efficacy, the odds ratio more strongly favored comparators. Trials published since 1990 also notably favored comparators. Analyzing results by quality score or the use of aminoglycoside monitoring did not alter these findings.
Conclusions: In this meta-analysis, aminoglycosides were less efficacious than newer comparators for the treatment of intra-abdominal infection. Given the well-known toxicities of these agents, we conclude that they should not be used as first-line therapy for these infections
Orbit optimization for ASTROD-GW and its time delay interferometry with two arms using CGC ephemeris
ASTROD-GW (ASTROD [Astrodynamical Space Test of Relativity using Optical
Devices] optimized for Gravitation Wave detection) is an optimization of ASTROD
to focus on the goal of detection of gravitation waves. The detection
sensitivity is shifted 52 times toward larger wavelength compared to that of
LISA. The mission orbits of the 3 spacecraft forming a nearly equilateral
triangular array are chosen to be near the Sun-Earth Lagrange points L3, L4 and
L5. The 3 spacecraft range interferometrically with one another with arm length
about 260 million kilometers. In order to attain the requisite sensitivity for
ASTROD-GW, laser frequency noise must be suppressed below the secondary noises
such as the optical path noise, acceleration noise etc. For suppressing laser
frequency noise, we need to use time delay interferometry (TDI) to match the
two different optical paths (times of travel). Since planets and other
solar-system bodies perturb the orbits of ASTROD-GW spacecraft and affect the
(TDI), we simulate the time delay numerically using CGC 2.7 ephemeris
framework. To conform to the ASTROD-GW planning, we work out a set of 20-year
optimized mission orbits of ASTROD-GW spacecraft starting at June 21, 2028, and
calculate the residual optical path differences in the first and second
generation TDI for one-detector case. In our optimized mission orbits for 20
years, changes of arm length are less than 0.0003 AU; the relative Doppler
velocities are less than 3m/s. All the second generation TDI for one-detector
case satisfies the ASTROD-GW requirement.Comment: 17 pages, 7 figures, 1 tabl
Avoiding selection bias in gravitational wave astronomy
When searching for gravitational waves in the data from ground-based
gravitational wave detectors it is common to use a detection threshold to
reduce the number of background events which are unlikely to be the signals of
interest. However, imposing such a threshold will also discard some real
signals with low amplitude, which can potentially bias any inferences drawn
from the population of detected signals. We show how this selection bias is
naturally avoided by using the full information from the search, considering
both the selected data and our ignorance of the data that are thrown away, and
considering all relevant signal and noise models. This approach produces
unbiased estimates of parameters even in the presence of false alarms and
incomplete data. This can be seen as an extension of previous methods into the
high false rate regime where we are able to show that the quality of parameter
inference can be optimised by lowering thresholds and increasing the false
alarm rate.Comment: 13 pages, 2 figure
Seismic topographic scattering in the context of GW detector site selection
In this paper, we present a calculation of seismic scattering from irregular
surface topography in the Born approximation. Based on US-wide topographic
data, we investigate topographic scattering at specific sites to demonstrate
its impact on Newtonian-noise estimation and subtraction for future
gravitational-wave detectors. We find that topographic scattering at a
comparatively flat site in Oregon would not pose any problems, whereas
scattering at a second site in Montana leads to significant broadening of wave
amplitudes in wavenumber space that would make Newtonian-noise subtraction very
challenging. Therefore, it is shown that topographic scattering should be
included as criterion in the site-selection process of future low-frequency
gravitational-wave detectors.Comment: 16 pages, 7 figure
Numerical simulation of time delay interferometry for eLISA/NGO
eLISA/NGO is a new gravitational wave detection proposal with arm length of
10^6 km and one interferometer down-scaled from LISA. Just like LISA and
ASTROD-GW, in order to attain the requisite sensitivity for eLISA/NGO, laser
frequency noise must be suppressed to below the secondary noises such as the
optical path noise, acceleration noise etc. In previous papers, we have
performed the numerical simulation of the time delay interferometry (TDI) for
LISA and ASTROD-GW with one arm dysfunctional by using the CGC 2.7 ephemeris.
The results are well below their respective limits which the laser frequency
noise is required to be suppressed. In this paper, we follow the same procedure
to simulate the time delay interferometry numerically. To do this, we work out
a set of 1000-day optimized mission orbits of the eLISA/NGO spacecraft starting
at January 1st, 2021 using the CGC 2.7 ephemeris framework. We then use the
numerical method to calculate the residual optical path differences in the
second-generation TDI solutions as in our previous papers. The maximum path
length difference, for all configurations calculated, is below 13 mm (43 ps).
It is well below the limit which the laser frequency noise is required to be
suppressed for eLISA/NGO. We compare and discuss the resulting differences due
to the different arm lengths for various mission proposals -- eLISA/NGO, an
NGO-LISA-type mission with a nominal arm length of 2 x 10^6 km, LISA and
ASTROD-GW.Comment: 17 pages, 13 figures, 3 tables, minor changes in description to match
the accepted version of Classical and Quantum Gravity. arXiv admin note: text
overlap with arXiv:1102.496
Improved Survival Associated with Neoadjuvant Chemoradiation in Patients with Clinical Stage IIIA(N2) Non–Small-Cell Lung Cancer
IntroductionOptimal management of clinical stage IIIA-N2 non–small-cell lung cancer (NSCLC) is controversial. This study examines whether neoadjuvant chemoradiation plus surgery improves survival rates when compared with other recommended treatment strategies.MethodsAdult patients from the National Cancer Database, with clinical stage IIIA-N2 disease definitively treated between 1998 and 2004 at American College of Surgeons Commission on Cancer accredited facilities, were included in the study. Treatment was defined as neoadjuvant chemoradiation plus either lobectomy (NeoCRT+L) or pneumonectomy (NeoCRT+P), lobectomy plus adjuvant therapy (L+AT), pneumonectomy plus adjuvant therapy (P+AT), and concurrent chemoradiation (CRT). Median follow-up and overall survival (OS) were defined from date of diagnosis to last contact. Five-year OS was estimated using Kaplan–Meier methods. Cox proportional hazard regression was used to estimate hazard ratios and 95% confidence intervals (CIs), adjusting for sociodemographic, clinical, and facility characteristics.ResultsMedian follow-up was 11.8 months for 11,242 eligible patients. Five-year OS was 33.5%, 20.7%, 20.3%, 13.35%, and 10.9% for NeoCRT+L, NeoCRT+P, L+AT, P+AT, and CRT, respectively (p < 0.0001). On multivariable analysis, the estimated hazard ratio was 0.51 (CI: 0.45–0.58) for NeoCRT+L; 0.77 (0.63–0.95) for NeoCRT+P; 0.66 (0.59–0.75) for L+AT; 0.69 (0.54–0.88) for P+AT; and 1.0 (reference) for the CRT group. Comorbidity did not attenuate the relationship between treatment and survival.ConclusionThis large study demonstrates that patients with clinical stage IIIA-N2 NSCLC, who underwent neoadjuvant chemoradiation followed by lobectomy, were associated with an improved survival
Feasibility of measuring the Shapiro time delay over meter-scale distances
The time delay of light as it passes by a massive object, first calculated by
Shapiro in 1964, is a hallmark of the curvature of space-time. To date, all
measurements of the Shapiro time delay have been made over solar-system
distance scales. We show that the new generation of kilometer-scale laser
interferometers being constructed as gravitational wave detectors, in
particular Advanced LIGO, will in principle be sensitive enough to measure
variations in the Shapiro time delay produced by a suitably designed rotating
object placed near the laser beam. We show that such an apparatus is feasible
(though not easy) to construct, present an example design, and calculate the
signal that would be detectable by Advanced LIGO. This offers the first
opportunity to measure space-time curvature effects on a laboratory distance
scale.Comment: 13 pages, 6 figures; v3 has updated instrumental noise curves plus a
few text edits; resubmitted to Classical and Quantum Gravit
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