33 research outputs found
Positrons from particle dark-matter annihilation in the Galactic halo: propagation Green's functions
We have made a calculation of the propagation of positrons from dark-matter
particle annihilation in the Galactic halo in different models of the dark
matter halo distribution using our 3D code, and present fits to our numerical
propagation Green's functions. We show that the Green's functions are not very
sensitive to the dark matter distribution for the same local dark matter energy
density. We compare our predictions with computed cosmic ray positron spectra
(``background'') for the ``conventional'' CR nucleon spectrum which matches the
local measurements, and a modified spectrum which respects the limits imposed
by measurements of diffuse Galactic gamma-rays, antiprotons, and positrons. We
conclude that significant detection of a dark matter signal requires favourable
conditions and precise measurements unless the dark matter is clumpy which
would produce a stronger signal. Although our conclusion qualitatively agrees
with that of previous authors, it is based on a more realistic model of
particle propagation and thus reduces the scope for future speculations.
Reliable background evaluation requires new accurate positron measurements and
further developments in modelling production and propagation of cosmic ray
species in the Galaxy.Comment: 8 pages, 6 ps-figures, 3 tables, uses revtex. Accepted for
publication in Physical Review D. More details can be found at
http://www.gamma.mpe-garching.mpg.de/~aws/aws.htm
Diffuse continuum gamma rays from the Galaxy
A new study of the diffuse Galactic gamma-ray continuum radiation is
presented, using a cosmic-ray propagation model which includes nucleons,
antiprotons, electrons, positrons, and synchrotron radiation. Our treatment of
the inverse Compton (IC) scattering includes the effect of anisotropic
scattering in the Galactic interstellar radiation field (ISRF) and a new
evaluation of the ISRF itself. Models based on locally measured electron and
nucleon spectra and synchrotron constraints are consistent with gamma-ray
measurements in the 30-500 MeV range, but outside this range excesses are
apparent. A harder nucleon spectrum is considered but fitting to gamma rays
causes it to violate limits from positrons and antiprotons. A harder
interstellar electron spectrum allows the gamma-ray spectrum to be fitted above
1 GeV as well, and this can be further improved when combined with a modified
nucleon spectrum which still respects the limits imposed by antiprotons and
positrons. A large electron/IC halo is proposed which reproduces well the
high-latitude variation of gamma-ray emission. The halo contribution of
Galactic emission to the high-latitude gamma-ray intensity is large, with
implications for the study of the diffuse extragalactic component and
signatures of dark matter. The constraints provided by the radio synchrotron
spectral index do not allow all of the <30 MeV gamma-ray emission to be
explained in terms of a steep electron spectrum unless this takes the form of a
sharp upturn below 200 MeV. This leads us to prefer a source population as the
origin of the excess low-energy gamma rays.Comment: Final version accepted for publication in The Astrophysical Journal
(vol. 537, July 10, 2000 issue); Many Updates; 20 pages including 49
ps-figures, uses emulateapj.sty. More details can be found at
http://www.gamma.mpe-garching.mpg.de/~aws/aws.htm
A Measurement of the Spatial Distribution of Diffuse TeV Gamma Ray Emission from the Galactic Plane with Milagro
Diffuse -ray emission produced by the interaction of cosmic-ray
particles with matter and radiation in the Galaxy can be used to probe the
distribution of cosmic rays and their sources in different regions of the
Galaxy. With its large field of view and long observation time, the Milagro
Gamma Ray Observatory is an ideal instrument for surveying large regions of the
Northern Hemisphere sky and for detecting diffuse -ray emission at very
high energies. Here, the spatial distribution and the flux of the diffuse
-ray emission in the TeV energy range with a median energy of 15 TeV
for Galactic longitudes between 30 and 110 and between
136 and 216 and for Galactic latitudes between -10 and
10 are determined. The measured fluxes are consistent with predictions
of the GALPROP model everywhere except for the Cygnus region
(). For the Cygnus region, the flux is twice the
predicted value. This excess can be explained by the presence of active cosmic
ray sources accelerating hadrons which interact with the local dense
interstellar medium and produce gamma rays through pion decay.Comment: 15 pages, 3 figures, accepted by Ap
Production and propagation of cosmic-ray positrons and electrons
We have made a new calculation of the cosmic-ray secondary positron spectrum
using a diffusive halo model for Galactic cosmic-ray propagation. The code
computes self-consistently the spectra of primary and secondary nucleons,
primary electrons, and secondary positrons and electrons. The models are first
adjusted to agree with the observed cosmic-ray Boron/Carbon ratio, and the
interstellar proton and Helium spectra are then computed; these spectra are
used to obtain the source function for the secondary positrons/electrons which
are finally propagated with the same model parameters. The primary electron
spectrum is evaluated, again using the same model. Fragmentation and energy
losses are computed using realistic distributions for the interstellar gas and
radiation fields, and diffusive reacceleration is also incorporated. Our study
includes a critical re-evaluation of the secondary decay calculation for
positrons.
The predicted positron fraction is in good agreement with the measurements up
to 10 GeV, beyond which the observed flux is higher than that calculated. Since
the positron fraction is now accurately measured in the 1-10 GeV range our
primary electron spectrum should be a good estimate of the true interstellar
spectrum in this range, of interest for gamma ray and solar modulation studies.
We further show that a harder interstellar nucleon spectrum, similar to that
suggested to explain EGRET diffuse Galactic gamma ray observations above 1 GeV,
can reproduce the positron observations above 10 GeV without requiring a
primary positron component.Comment: 25 pages including 8 figures and 1 table, latex, aaspp4.sty. To be
published in ApJ 1998, v.493 (February 1 issue). Details can be found at
http://www.gamma.mpe-garching.mpg.de/~aws/aws.htm
GLAST: Understanding the High Energy Gamma-Ray Sky
We discuss the ability of the GLAST Large Area Telescope (LAT) to identify,
resolve, and study the high energy gamma-ray sky. Compared to previous
instruments the telescope will have greatly improved sensitivity and ability to
localize gamma-ray point sources. The ability to resolve the location and
identity of EGRET unidentified sources is described. We summarize the current
knowledge of the high energy gamma-ray sky and discuss the astrophysics of
known and some prospective classes of gamma-ray emitters. In addition, we also
describe the potential of GLAST to resolve old puzzles and to discover new
classes of sources.Comment: To appear in Cosmic Gamma Ray Sources, Kluwer ASSL Series, Edited by
K.S. Cheng and G.E. Romer
Diffuse Gamma Rays: Galactic and Extragalactic Diffuse Emission
"Diffuse" gamma rays consist of several components: truly diffuse emission
from the interstellar medium, the extragalactic background, whose origin is not
firmly established yet, and the contribution from unresolved and faint Galactic
point sources. One approach to unravel these components is to study the diffuse
emission from the interstellar medium, which traces the interactions of high
energy particles with interstellar gas and radiation fields. Because of its
origin such emission is potentially able to reveal much about the sources and
propagation of cosmic rays. The extragalactic background, if reliably
determined, can be used in cosmological and blazar studies. Studying the
derived "average" spectrum of faint Galactic sources may be able to give a clue
to the nature of the emitting objects.Comment: 32 pages, 28 figures, kapproc.cls. Chapter to the book "Cosmic
Gamma-Ray Sources," to be published by Kluwer ASSL Series, Edited by K. S.
Cheng and G. E. Romero. More details can be found at
http://www.gamma.mpe-garching.mpg.de/~aws/aws.htm
Dinitrophenol
Dinitrofenol (DNP) – mieszanina izomerów: 2,3- DNP, 2,4- DNP i 2,6-DNP z przewagą 2,4-DNP, jest stosowany w produkcji barwników, kwasu pikrynowego i pikraminowego, wywoływaczy fotograficznych i materiałów wybuchowych oraz jako pestycyd w rolnictwie i sadownictwie. Dinitrofenol jest trucizną metaboliczną, a mechanizm jego działania toksycznego polega na rozprzęganiu fosforylacji oksydatywnej. Zawodowe narażenie na pary i pyły 2,4-DNP może wywoływać objawy wzmożonego metabolizmu. 2,4-DNP nie jest kancerogenem, nie wykazuje także działania genotoksycznego ani mutagennego. Za podstawę wyliczenia wartości NDS dla 2,4-DNP przyjęto wartość LOAEL dla skutków metabolicznych. Wartość ta u człowieka wynosi 1,2 mg/kg/dzień. W warunkach narażenia drogą oddechową taką dawkę pracownik może wchłonąć, gdy stężenie 2,4-DNP we wdychanym powietrzu wynosi 10,5 mg/m3. Przyjmując współczynnik niepewności równy 16 (2 dla różnic we wrażliwości osobniczej, 2 dla przejścia z wartości LOAEL do wartości NOAEL, 2 dla różnicy w sposobie narażenia i 2 dla ekstrapolacji z narażenia średnioterminowego do przewlekłego), to wyliczona wartość normatywu będzie wynosiła 0,66 mg/m3. W związku z powyższym proponuje się przyjęcie stężenia 0,5 mg/m3 za wartość NDS dla 2,4-DNP. Przyjmując, że 2,4-DNP jest najbardziej toksycznym izomerem dinitrofenolu oraz, że udział tego izomeru w dinitrofenolu – mieszaninie izomerów jest dominujący, proponujemy przyjęcie dla dinitrofenolu – mieszaniny również takiej samej wartości NDS jaką zaproponowano dla 2,4-DNP.Dinitrophenol (DNP) is a mixture of 2,4-DNP and smaller amounts of 2,3-DNP and 2,6-DNP). It is a yellow, crystalline solid. DNP is used in synthesis of dyes, picric acid, picramic acid, wood preservatives, photographic developers, explosives, and insecticides. In the 1930s, 2,4-DNP was used as a weight-reducing drug. Short-term exposure to DNP may affect metabolism resulting in hyperthermia. High-level exposure may be fatal. The existing data concerning the health effects of 2,4-DNP oral exposure in humans indicate that the characteristic effects of 2,4-DNP for this route are: increased basal metabolic rate and perspiration, weight loss, a sensation of warmth, and – at higher dosage – increased heart and respiratory rate, and increased body temperature. Repeated or prolonged contact with the skin may cause dermatitis. Exposure to DNP may result in changes in the functional state of the peripheral nervous system, cardiovascular system and gastrointestinal system. It may also induce cataracts. Taking into account the results obtained in clinical studies on people ingesting 2,4-DNP (LOAEL for metabolic effects was 1.2 mg/kg/day), a concentration 0.5 mg of dinitrophenol/m3 is proposed as a maximum exposure limit (maximum admissible concentration) with a skin notation. With regard to systemic effects of DNP no STEL value has beeen established
Bromoethane
Bromoetan jest bezbarwną, lotną, łatwo palną cieczą o eterycznym zapachu. W ubiegłym wieku bromoetan był używany podczas zabiegów chirurgicznych jako środek znieczulający. Obecnie jest wykorzystywany w przemyśle chemicznym i farmaceutycznym jako rozpuszczalnik oraz związek alkilujący w procesie syntezy związków organicznych. Do niedawna był również stosowany w systemach chłodniczych jako środek chłodzący. Bromoetan działa drażniąco na skórę, śluzówkę górnych dróg oddechowych i oczy. Wywiera szkodliwe działanie na układ nerwowy, krążenia i oddechowy, a także na wątrobę i nerki. Działa mutagennie na szczepy TA100 i TA1535 Salmonella typhimurium w warunkach aktywacji metabolicznej i bez aktywacji metabolicznej. Mutagenne właściwości bromoetanu stwierdzono także w badaniach na komórkach Escherichia coli ze szczepu WP2(hc-). U szczurów i myszy narażanych chronicznie (dwa lata) na bromoetan o stężeniach 445 - 1780 mg/m3 (100 - 400 ppm) stwierdzono częstsze występowanie nowotworów nadnerczy, płuc i macicy. Pod względem kancerogenności bromoetan został zaklasyfikowany do grupy A2 przez NTP (Narodowy Program Toksykologiczny, USA) i do grupy A3 przez ACGIH. Ze względu na fakt, iż niewątpliwie kancerogenne działanie bromoetanu wykazano tylko u myszy, a nie ma dowodów kancerogennego działania tego związku u człowieka, nie zostały uwzględniowe, w wyliczeniach proponowanej wartości NDS, wyniki badania kancerogenności. Podstawę wyliczeń stanowiły wyniki badań toksyczności ogólnej w doświadczeniu długoterminowym (2 lata) na szczurach i myszach. Na podstawie uzyskanych w tym doświadczeniu wyników można sądzić, że u szczurów i myszy narażenie na bromoetan o stężeniu 890 mg/m3 5 dni w tygodniu, 6 h/dzień przez dwa lata nie wywołuje efektów toksycznych. Przyjmując stężenie 890 mg/m3 za wartość NOAEL, a także następujące współczynniki niepewności: B = 2 (różnice we wrażliwości osobniczej), A = 2 (różnice we wrażliwości gatunkowej) oraz E = 3 (współczynnik modyfikujący udokumentowane działanie kancerogenne u niektórych szczepów gryzoni), wyliczona wartość NDS bromoetanu wyniesie 74,2 mg/m3. Ponieważ jest ona zbliżona do obowiązującej w Polsce wartości NDS bromoetanu (50 mg/m3), dokonywanie zmiany tej wartości nie jest uzasadnione. Wartość NDSCh bromoetanu proponuje się ustalić tak jak dla substancji o działaniu drażniącym (2 razy wartość NDS), tj. na poziomie 100 mg/m3. Związek powinien zostać oznaczony literami „Sk”, wskazującymi na wchłanianie się substancji przez skórę.Bromoethane is a colorless, volatile, flammable liquid. Bromoethane is an alkylating agent used in organic synthesis, in the manufacture of pharmaceuticals. It has been used as a refrigerant and solvent. In the last century bromoethane was used as an anesthetic. Bromoethane is the eyes, skin and mucous membranes tract irritant. The vapor can cause hepatic, cardiovascular and nervous system damage. The substance is mutagenic to Salmonella typhimurium TA100, TA1535 strain and Escherichia coli both with and without metabolic activation. The results of 2-year studies showed that inhalation exposure to bromoetane at the concentration of 445 ÷ 1780 mg/m3 (100 ÷ 400 ppm) significantly increases the number of adrenal glands, lungs and uterus tumors. Bromoethane is classified by ACGIH to A3 group and by NTP to A2 group. The TLV value for bromoethane was estimated on the basis of 2-year studies (rats and mice). The concentration of 890 mg/m3, 5 days/week, and 6h/day is a NOAEL value. The following uncertainty factors were used: 2 for differences between individuals, 2 for differences between species and modifying factor-3. Based on these data, the TLV value for bromoethane is proposed as 50 mgm/m3, STEL value as 100 mg/m3. Due to dermal absorption bromoethane should be mark as Sk