234 research outputs found
Universality of Regge and vibrational trajectories in a semiclassical model
The orbital and radial excitations of light-light mesons are studied in the
framework of the dominantly orbital state description. The equation of motion
is characterized by a relativistic kinematics supplemented by the usual funnel
potential with a mixed scalar and vector confinement. The influence of finite
quark masses and potential parameters on Regge and vibrational trajectories is
discussed. The case of heavy-light mesons is also presented.Comment: 12 page
Preventive and curative effect of melatonin on mammary carcinogenesis induced by dimethylbenz[a]anthracene in the female Sprague–Dawley rat
INTRODUCTION: It has been well documented that the pineal hormone, melatonin, which plays a major role in the control of reproduction in mammals, also plays a role in the incidence and growth of breast and mammary cancer. The curative effect of melatonin on the growth of dimethylbenz [a]anthracene-induced (DMBA-induced) mammary adenocarcinoma (ADK) has been previously well documented in the female Sprague–Dawley rat. However, the preventive effect of melatonin in limiting the frequency of cancer initiation has not been well documented. METHODS: The aim of this study was to compare the potency of melatonin to limit the frequency of mammary cancer initiation with its potency to inhibit tumor progression once initiation, at 55 days of age, was achieved. The present study compared the effect of preventive treatment with melatonin (10 mg/kg daily) administered for only 15 days before the administration of DMBA with the effect of long-term (6-month) curative treatment with the same dose of melatonin starting the day after DMBA administration. The rats were followed up for a year after the administration of the DMBA. RESULTS: The results clearly showed almost identical preventive and curative effects of melatonin on the growth of DMBA-induced mammary ADK. Many hypotheses have been proposed to explain the inhibitory effects of melatonin. However, the mechanisms responsible for its strong preventive effect are still a matter of debate. At least, it can be envisaged that the artificial amplification of the intensity of the circadian rhythm of melatonin could markedly reduce the DNA damage provoked by DMBA and therefore the frequency of cancer initiation. CONCLUSION: In view of the present results, obtained in the female Sprague–Dawley rat, it can be envisaged that the long-term inhibition of mammary ADK promotion by a brief, preventive treatment with melatonin could also reduce the risk of breast cancer induced in women by unidentified environmental factors
Work at night and breast cancer - report on evidence-based options for preventive actions
In 2007, the International Agency for Research on Cancer classified shift work involving circadian disruption as probably carcinogenic to humans (group 2A), primarily based on experimental and epidemiologic evidence for breast cancer. In order to examine options for evidence-based preventive actions, 16 researchers in basic, epidemiological and applied sciences convened at a workshop in Copenhagen 26-27 October 2011. This paper summarizes the evidence from epidemiological and experimental studies and presents possible recommendations for prevention of the effects of night work on breast cancer. Among those studies that quantified duration of shift work, there were statistically significant elevations in risk only after about 20 years working night shift. It is unclear from these studies whether or not there is a modest but real elevated risk for shorter durations. Hence, restriction of the total number of years working night shift could be one future preventive recommendation for shift workers. The diurnal secretion of melatonin by the pineal gland with peak in secretory activity durin Work during the night is widespread worldwide. To provide additional evidence-based recommendations on prevention of diseases related to night shift work, large studies on the impact of various shift schedules and type of light on circadian rhythms need to be conducted in real work environments
Low-lying spectrum of the Y-string three-quark potential using hyper-spherical coordinates
We calculate the energies of three-quark states with definite permutation
symmetry (i.e. of SU(6) multiplets) in the N=0,1,2 shells, confined by the
Y-string three-quark potential. The exact Y-string potential consists of one,
so-called three-string term, and three angle-dependent two-string terms. Due to
this technical complication we treat the problem at three increasingly accurate
levels of approximation: 1) the (approximate) three-string potential expanded
to first order in trigonometric functions of hyper-spherical angles; 2) the
(approximate) three-string potential to all orders in the power expansion in
hyper-spherical harmonics, but without taking into account the transition(s) to
two-string potentials; 3) the exact minimal-length string potential to all
orders in power expansion in hyper-spherical harmonics, and taking into account
the transition(s) to two-string potentials. We show the general trend of
improvement %convergence of these approximations: The exact non-perturbative
corrections to the total energy are of the order of one per cent, as compared
with approximation 2), yet the exact energy differences between the
-plets are shifted to 2:2:0.9,
from the Bowler and Tynemouth separation rule 2:2:1, which is obeyed by
approximation 2) at the one per cent level. The precise value of the energy
separation of the first radial excitation ("Roper") -plet
from the -plet depends on the approximation, but does not become
negative, i.e. the "Roper" remains heavier than the odd-parity
-plet in all of our approximations.Comment: 19 pages, 6 figure
Bohr-Sommerfeld quantization and meson spectroscopy
We use the Bohr-Sommerfeld quantization approach in the context of
constituent quark models. This method provides, for the Cornell potential,
analytical formulae for the energy spectra which closely approximate numerical
exact calculations performed with the Schrodinger or the spinless Salpeter
equations. The Bohr-Sommerfeld quantization procedure can also be used to
calculate other observables such as r.m.s. radius or wave function at the
origin. Asymptotic dependence of these observables on quantum numbers are also
obtained in the case of potentials which behave asymptotically as a power-law.
We discuss the constraints imposed by these formulae on the dynamics of the
quark-antiquark interaction.Comment: 13 page
Unified description of light- and strange-baryon spectra
We present a chiral constituent quark model for light and strange baryons
providing a unified description of their ground states and excitation spectra.
The model relies on constituent quarks and Goldstone bosons arising as
effective degrees of freedom of low-energy QCD from the spontaneous breaking of
chiral symmetry. The spectra of the three-quark systems are obtained from a
precise variational solution of the Schr\"odinger equation with a
semirelativistic Hamiltonian. The theoretical predictions are found in close
agreement with experiment.Comment: 9 pages, including 2 figure
Radioprotectors and Mitigators of Radiation-Induced Normal Tissue Injury
The article reviews agents in clinical use or in development as radioprotectors and mitigators of radiation-induced normal tissue injury
Night-sky brightness monitoring in Hong Kong - a city-wide light pollution assessment
Results of the first comprehensive light pollution survey in Hong Kong are
presented. The night-sky brightness was measured and monitored around the city
using a portable light sensing device called the Sky Quality Meter over a
15-month period beginning in March 2008. A total of 1,957 data sets were taken
at 199 distinct locations, including urban and rural sites covering all 18
Administrative Districts of Hong Kong. The survey shows that the environmental
light pollution problem in Hong Kong is severe - the urban night-skies (sky
brightness at 15.0 mag per arcsec square) are on average ~100 times brighter
than at the darkest rural sites (20.1 mag per arcsec square), indicating that
the high lighting densities in the densely populated residential and commercial
areas lead to light pollution. In the worst polluted urban location studied,
the night-sky at 13.2 mag per arcsec square can be over 500 times brighter than
the darkest sites in Hong Kong. The observed night-sky brightness is found to
be affected by human factors such as land utilization and population density of
the observation sites, together with meteorological and/or environmental
factors. Moreover, earlier night-skies (at 9:30pm local time) are generally
brighter than later time (at 11:30pm), which can be attributed to some public
and commercial lightings being turned off later at night. On the other hand, no
concrete relationship between the observed sky brightness and air pollutant
concentrations could be established with the limited survey sampling. Results
from this survey will serve as an important database for the public to assess
whether new rules and regulations are necessary to control the use of outdoor
lightings in Hong Kong.Comment: 33 pages, 13 figures, Environmental Monitoring and Assessment, in
pres
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