2,676 research outputs found
Second order perturbation theory for embedded eigenvalues
We study second order perturbation theory for embedded eigenvalues of an
abstract class of self-adjoint operators. Using an extension of the Mourre
theory, under assumptions on the regularity of bound states with respect to a
conjugate operator, we prove upper semicontinuity of the point spectrum and
establish the Fermi Golden Rule criterion. Our results apply to massless
Pauli-Fierz Hamiltonians for arbitrary coupling.Comment: 30 pages, 2 figure
The effect of geometry on charge confinement in three dimensions
We show that, in contrast to the flat case, the Maxwell theory is not
confining in the background of the three dimensional BTZ black-hole (covering
space). We also study the effect of the curvature on screening behavior of
Maxwell-Chern-Simons model in this space-time.Comment: 8 pages. To be published in Europhysics Letter
Шестые Чупинские чтения. Предисловие
Quality-of-life studies are ideally suited to fulfilling the new international youth research agenda, which focuses on ‘positive youth development’ to make recommendations for policy and practice. The paper reports a South African case study conducted among disadvantaged youth for this purpose. A sample survey of close on 900 African youth, aged 15-24 years, sought to identify indicators of positive development to serve as goals of youth and community work in Grahamstown East/Rini, in the Eastern Cape province of South Africa. The setting is unique. This mainly rural province is among the poorest, least developed, and has one of highest unemployment rates. Nevertheless, Grahamstown may offer special development opportunities for local youth due to the proximity of the city centre and diverse extension projects for youth. The survey found that development opportunities were unequally distributed with the materially advantaged youth being more exposed to development opportunities through their schools, spare time activities, and community contacts. They were more ambitious than others and more aware of risks facing contemporary youth. Advantaged youth also reported higher levels of subjective well-being and optimism, findings consistent with earlier studies conducted among adult populations, which report remarkable congruence between material and subjective well-being among South Africans. The analysis used overall life satisfaction as key indicator of successful youth development to learn more about major youth aspirations and goals. In conclusion, the study was able to identify a youth development initiative based on the aspirations of the youth, which might be pursued as a researcher-practitioner partnership project in line with the new international youth research agenda
On the Possibility of Measuring the Abraham Force using Whispering Gallery Modes
Critical experimental tests of the time-dependent Abraham force in
phenomenological electrodynamics are scarce. In this paper we analyze the
possibility of making use of intensity-modulated whispering gallery modes in a
microresonator for this purpose. Systems of this kind appear attractive, as the
strong concentration of electromagnetic fields near the rim of the resonator
serves to enhance the Abraham torque exerted by the field. We analyze mainly
spherical resonators, although as an introductory step we consider also the
cylinder geometry. The order of magnitude of the Abraham torques are estimated
by inserting reasonable values for the various input parameters. As expected,
the predicted torques turn out to be very small, although probably not beyond
any reach experimentally. Our main idea is essentially a generalization of the
method used by G. B. Walker et al. [Can. J. Phys. 53, 2577] for low-frequency
fields, to the optical case.Comment: 6 pages, no figures. Minor typos corrected, acknowledgment added. To
appear in Phys. Rev.
Completeness of case ascertainment and survival time error in English cancer registries: impact on 1-year survival estimates
BACKGROUND: It has been suggested that cancer registries in England are too dependent on processing of information from death certificates, and consequently that cancer survival statistics reported for England are systematically biased and too low. METHODS: We have linked routine cancer registration records for colorectal, lung, and breast cancer patients with information from the Hospital Episode Statistics (HES) database for the period 2001-2007. Based on record linkage with the HES database, records missing in the cancer register were identified, and dates of diagnosis were revised. The effects of those revisions on the estimated survival time and proportion of patients surviving for 1 year or more were studied. Cases that were absent in the cancer register and present in the HES data with a relevant diagnosis code and a relevant surgery code were used to estimate (a) the completeness of the cancer register. Differences in survival times calculated from the two data sources were used to estimate (b) the possible extent of error in the recorded survival time in the cancer register. Finally, we combined (a) and (b) to estimate (c) the resulting differences in 1-year cumulative survival estimates. RESULTS: Completeness of case ascertainment in English cancer registries is high, around 98-99%. Using HES data added 1.9%, 0.4% and 2.0% to the number of colorectal, lung, and breast cancer registrations, respectively. Around 5-6% of rapidly fatal cancer registrations had survival time extended by more than a month, and almost 3% of rapidly fatal breast cancer records were extended by more than a year. The resulting impact on estimates of 1-year survival was small, amounting to 1.0, 0.8, and 0.4 percentage points for colorectal, lung, and breast cancer, respectively. INTERPRETATION: English cancer registration data cannot be dismissed as unfit for the purpose of cancer survival analysis. However, investigators should retain a critical attitude to data quality and sources of error in international cancer survival studies
The equivalence principle, uniformly accelerated reference frames, and the uniform gravitational field
The relationship between uniformly accelerated reference frames in flat
spacetime and the uniform gravitational field is examined in a relativistic
context. It is shown that, contrary to previous statements in the pages of this
journal, equivalence does not break down in this context. No restrictions to
Newtonian approximations or small enclosures are necessary
How does Casimir energy fall? III. Inertial forces on vacuum energy
We have recently demonstrated that Casimir energy due to parallel plates,
including its divergent parts, falls like conventional mass in a weak
gravitational field. The divergent parts were suitably interpreted as
renormalizing the bare masses of the plates. Here we corroborate our result
regarding the inertial nature of Casimir energy by calculating the centripetal
force on a Casimir apparatus rotating with constant angular speed. We show that
the centripetal force is independent of the orientation of the Casimir
apparatus in a frame whose origin is at the center of inertia of the apparatus.Comment: 8 pages, 2 figures, contribution to QFEXT07 proceeding
ALLSMOG: an APEX Low-redshift Legacy Survey for MOlecular Gas. I - molecular gas scaling relations, and the effect of the CO/H2 conversion factor
We present ALLSMOG, the APEX Low-redshift Legacy Survey for MOlecular Gas.
ALLSMOG is a survey designed to observe the CO(2-1) emission line with the APEX
telescope, in a sample of local galaxies (0.01 < z < 0.03), with stellar masses
in the range 8.5 < log(M*/Msun) < 10. This paper is a data release and initial
analysis of the first two semesters of observations, consisting of 42 galaxies
observed in CO(2-1). By combining these new CO(2-1) emission line data with
archival HI data and SDSS optical spectroscopy, we compile a sample of low-mass
galaxies with well defined molecular gas masses, atomic gas masses, and
gas-phase metallicities. We explore scaling relations of gas fraction and gas
consumption timescale, and test the extent to which our findings are dependent
on a varying CO/H2 conversion factor. We find an increase in the H2/HI mass
ratio with stellar mass which closely matches semi-analytic predictions. We
find a mean molecular gas fraction for ALLSMOG galaxies of MH2/M* = (0.09 -
0.13), which decreases with stellar mass. We measure a mean molecular gas
consumption timescale for ALLSMOG galaxies of 0.4 - 0.7 Gyr. We also confirm
the non-universality of the molecular gas consumption timescale, which varies
(with stellar mass) from ~100 Myr to ~2 Gyr. Importantly, we find that the
trends in the H2/HI mass ratio, gas fraction, and the non-universal molecular
gas consumption timescale are all robust to a range of recent
metallicity-dependent CO/H2 conversion factors.Comment: 25 pages, 15 figures. Accepted for publication in MNRA
Incidence of multiple primary cancers in a cohort of women diagnosed with breast cancer in southeast England
Among women in the Thames Cancer Registry database with a first breast cancer diagnosed between 1961–1995 observed numbers of subsequent cancers were compared with expected numbers and standardized incidence ratios were calculated. The occurrence of breast cancers subsequent to cancers at other sites was also examined. Women diagnosed with breast cancer before age 50 had significantly elevated risks for 9 cancer sites namely, oesophagus, stomach, lung, bone, connective tissue, breast, corpus uteri, ovary and myeloid leukaemia compared with 2 sites (corpus uteri and myeloid leukaemia) in women diagnosed at age 50 and above. Some of these associations are consistent with the effects of known inherited cancer susceptibility genes, shared environmental factors, or therapy. © 2001 Cancer Research Campaign http://www.bjcancer.co
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