12 research outputs found
Winds, B-Fields, and Magnetotails of Pulsars
We investigate the emission of rotating magnetized neutron stars due to the
acceleration and radiation of particles in the relativistic wind and in the
magnetotail of the star. We consider that the charged particles are accelerated
by driven collisionless reconnection. Outside of the light cylinder, the star's
rotation acts to wind up the magnetic field to form a predominantly azimuthal,
slowly decreasing with distance, magnetic field of opposite polarity on either
side of the equatorial plane normal to the star's rotation axis. The magnetic
field annihilates across the equatorial plane with the magnetic energy going to
accelerate the charged particles to relativistic energies. For a typical
supersonically moving pulsar, the star's wind extends outward to the standoff
distance with the interstellar medium. At larger distances, the power output of
pulsar's wind of electromagnetic field and relativistic particles
is {\it redirected and collimated into the magnetotail} of the star. In the
magnetotail it is proposed that equipartition is reached between the magnetic
energy and the relativistic particle energy. For such conditions, synchrotron
radiation from the magnetotails may be a significant fraction of
for high velocity pulsars. An equation is derived for the radius of the
magnetotail as a function of distance from the star.
For large distances , of the order of the distance travelled by the
star, we argue that the magnetotail has a `trumpet' shape owing to the slowing
down of the magnetotail flow.Comment: 11 pages, 4 figures, accepted for publication in Ap
Precision Prediction for the Big-Bang Abundance of Primordial Helium
Within the standard models of particle physics and cosmology we have
calculated the big-bang prediction for the primordial abundance of \he to a
theoretical uncertainty of less than 0.1 \pct ,
improving the current theoretical precision by a factor of 10. At this accuracy
the uncertainty in the abundance is dominated by the experimental uncertainty
in the neutron mean lifetime, . The following
physical effects were included in the calculation: the zero and
finite-temperature radiative, Coulomb and finite-nucleon-mass corrections to
the weak rates; order- quantum-electrodynamic correction to the plasma
density, electron mass, and neutrino temperature; and incomplete neutrino
decoupling. New results for the finite-temperature radiative correction and the
QED plasma correction were used. In addition, we wrote a new and independent
nucleosynthesis code designed to control numerical errors to be less than
0.1\pct. Our predictions for the \EL[4]{He} abundance are presented in the form
of an accurate fitting formula. Summarizing our work in one number, . Further,
the baryon density inferred from the Burles-Tytler determination of the
primordial D abundance, , leads to the
prediction: . This ``prediction'' and an accurate measurement of the primeval \he
abundance will allow an important consistency test of primordial
nucleosynthesis.Comment: Replaced fitting formulas - new versions differ by small but
significant amount. Other minor changes. 30 pages, 17 figures, 5 table
Effect of Finite Mass on Primordial Nucleosynthesis
We have calculated the small effect of finite nucleon mass on the
weak-interaction rates that interconvert protons and neutrons in the early
Universe. We have modified the standard code for primordial nucleosynthesis to
include these corrections and find a small, systematic increase in the 4He
yield, , depending slightly on the
baryon-to-photon ratio. The fractional changes in the abundances of the other
light elements are a few percent or less for interesting values of the
baryon-to-photon ratio.Comment: 15 pages, 8 figures, uses psfig.st
A exposição ocupacional ao mercúrio metálico no módulo odontológico de uma unidade básica de saúde localizada na cidade de São Paulo Occupational exposure to metallic mercury in the dentist's office of a public primary health care clinic in the city of São Paulo
Este artigo visa discutir a exposição ocupacional ao mercúrio metálico de dentistas e assistentes, enfocando a avaliação biológica, os efeitos na saúde e a avaliação ambiental. Os métodos utilizados foram visitas à unidade, avaliação ambiental, mapas de riscos, dosagens de mercúrio urinário e avaliação da saúde. Os resultados referentes ao ambiente e processos de trabalho mostraram: 1) as concentrações de vapor de mercúrio que impregnavam o revestimento ou tubulações de encanamentos variaram entre 0,001 e 0,051 mg/m3 de ar; 2) exposição ocupacional, havendo 62,5% dos trabalhadores com dosagens de mercúrio urinário entre 10 e 49µg/l e 37,5% abaixo de 10 µg/l em 1994. Estes trabalhadores estiveram expostos desde 1992, sendo suas dosagens de mercúrio urinário de 1992 inferiores às atuais; 3) vazamento de mercúrio e amalgamação inadequada, em função de um amalgamador defeituoso; 4) a necessidade de usar um pedaço de camurça para obter um amalgama homogêneo e remover o excesso de mercúrio; 5) a existência de riscos combinados e simultâneos na situação de trabalho. Os resultados concernentes à saúde mostraram: 1) a prevalência de sintomas relativos ao Sistema Nervoso Central; 2)sinais do quadro neurológico e/ou do quadro psíquico, mas não do quadro gastrintestinal; 3) intoxicações crônicas de leves a moderadas em 62,5% dos trabalhadores.<br>This paper discusses occupational exposure to metallic mercury among dentists and dental assistants, focusing on biological evaluation, effects on heaith, and environmental evaluation. Methods included visits to the clinic, hazard maps, urinary and environmental mercury measurements, and evaluation of health status. Results for the environment and work processes showed that mercury vapor concentrations impregnating surfaces and piping varied from 0.001 to 0.051 mg/m3 in air; occupational exposure with 62.5% of health workers having HgU ranging from 10 to 49 mg/l and 37.5% having HgU below 10 mg/l in 1994, while workers' previous measures (from 1992) were lower in every single case; an outflow of mercury and inadequate amalgamation due to a faulty amalgamator, the need for using a piece of chamois to obtain a homogeneous amalgam and remove excess mercury; the existence of combined hazards in the environment, and that all workers had been exposed since 1992. Results for workers' health showed a prevalence of symptoms from lesions to the central nervous system; central nervous system signs; and that mild-to-moderate chronic poisoning was found in 62.5% of workers
Correlação entre os níveis séricos de DDT e os títulos de anticorpos antidiftéricos em meninas
Foram determinados níveis séricos de DDT e títulos de anticorpos antidiftéricos em 28 meninas vacinadas, com a finalidade de estabelecer uma possível correlação. Para a determinação dos níveis de DDT empregou-se o método da cromatografia gasosa. Para a titulação de anticorpos empregou-se o método da inibição da hemaglutinação passiva. A análise estatística dos resultados, feita por métodos não paramétricos, mostrou existir correlação positiva entre presença de op'DDT, quantidade de pp'DDT e títulos de anticorpos. A possível influência do DDT no sistema AMP-cíclico das células imunocomponentes é discutida no trabalho, tentando explicar a correlação positiva encontrada
Metabolite and lipoprotein responses and prediction of weight gain during breast cancer treatment
Background: Breast cancer treatment has metabolic side effects, potentially affecting risk of cardiovascular disease (CVD) and recurrence. We aimed to compare alterations in serum metabolites and lipoproteins during treatment between recipients and non-recipients of chemotherapy, and describe metabolite profiles associated with treatment-related weight gain.
Methods: This pilot study includes 60 stage I/II breast cancer patients who underwent surgery and were treated according to national guidelines. Serum sampled pre-surgery and after 6 and 12 months was analysed by MR spectroscopy and mass spectrometry. In all, 170 metabolites and 105 lipoprotein subfractions were quantified.
Results: The metabolite and lipoprotein profiles of chemotherapy recipients and non-recipients changed significantly 6 months after surgery (p < 0.001). Kynurenine, the lipid signal at 1.55–1.60 ppm, ADMA, 2 phosphatidylcholines (PC aa C38:3, PC ae C42:1), alpha-aminoadipic acid, hexoses and sphingolipids were increased in chemotherapy recipients after 6 months. VLDL and small dense LDL increased after 6 months, while HDL decreased, with triglyceride enrichment in HDL and LDL. At baseline, weight gainers had less acylcarnitines, phosphatidylcholines, lyso-phosphatidylcholines and sphingolipids, and showed an inflammatory lipid profile.
Conclusion: Chemotherapy recipients exhibit metabolic changes associated with inflammation, altered immune response and increased risk of CVD. Altered lipid metabolism may predispose for treatment-related weight gain