2,317 research outputs found
The Galactic black hole transient H1743-322 during outburst decay: connections between timing noise, state transitions and radio emission
Multi-wavelength observations of Galactic black hole transients during
outburst decay are instrumental for our understanding of the accretion geometry
and the formation of outflows around black hole systems. H1743-322, a black
hole transient observed intensely in X-rays and also covered in the radio band
during its 2003 decay, provides clues about the changes in accretion geometry
during state transitions and also the general properties of X-ray emission
during the intermediate and the low-hard states. In this work, we report on the
evolution of spectral and temporal properties in X-rays and the flux in the
radio band with the goal of understanding the nature of state transitions
observed in this source. We concentrate on the transition from the thermal
dominant state to the intermediate state that occurs on a timescale of one day.
We show that the state transition is associated with a sudden increase in
power-law flux. We determine that the ratio of the power-law flux to the
overall flux in the 3--25 keV band must exceed 0.6 to observe strong timing
noise. Even after the state transition, once this ratio was below 0.6, the
system transited back to the thermal dominant state for a day. We show that the
emission from the compact radio core does not turn on during the transition
from the thermal dominant state to the intermediate state but does turn on when
the source reaches the low-hard state, as seen in 4U 1543-47 and GX 339-4. We
find that the photon index correlates strongly with the QPO frequency and
anti-correlates with the rms amplitude of variability. We also show that the
variability is more likely to be associated with the power-law emission than
the disk emission.Comment: 23 pages, 5 Figures, 1 Table, accepted for publication in Ap
Target Mass Effects in Polarized Virtual Photon Structure Functions
We study target mass effects in the polarized virtual photon structure
functions , in the kinematic
region , where is the mass squared of
the probe (target) photon. We obtain the expressions for and in closed form by inverting the
Nachtmann moments for the twist-2 and twist-3 operators. Numerical analysis
shows that target mass effects appear at large and become sizable near
, the maximal value of , as the ratio
increases. Target mass effects for the sum rules of and
are also discussed.Comment: 24 pages, LaTeX, 9 eps figure
Problematising international placements as a site of intercultural learning
This paper theorises some of the learning outcomes of a three-year project concerning student learning in international social work placements in Malaysia. The problematic issue of promoting cultural and intercultural competence through such placements is examined, where overlapping hegemonies are discussed in terms of isomorphism of social work models, that of the nation state, together with those relating to professional values and knowledge, and the tyrannies of received ideas. A critical discussion of cultural competence as the rationale for international placements is discussed in terms of the development of the graduating social worker as a self-reflexive practitioner. The development of sustainable international partnerships able to support student placement and the issue of non-symmetrical reciprocation, typical of wide socio-economic differentials across global regions, is additionally discussed
Interferometry of Direct Photons in Central 280Pb+208Pb Collisions at 158A GeV
Two-particle correlations of direct photons were measured in central
208Pb+208Pb collisions at 158 AGeV. The invariant interferometric radii were
extracted for 100<K_T<300 MeV/c and compared to radii extracted from charged
pion correlations. The yield of soft direct photons, K_T<300 MeV/c, was
extracted from the correlation strength and compared to theoretical
calculations.Comment: 5 pages, 4 figure
Systematics of Inclusive Photon Production in 158 AGeV Pb Induced Reactions on Ni, Nb, and Pb Targets
The multiplicity of inclusive photons has been measured on an event-by-event
basis for 158 AGeV Pb induced reactions on Ni, Nb, and Pb targets. The
systematics of the pseudorapidity densities at midrapidity (rho_max) and the
width of the pseudorapidity distributions have been studied for varying
centralities for these collisions. A power law fit to the photon yield as a
function of the number of participating nucleons gives a value of 1.13+-0.03
for the exponent. The mean transverse momentum, , of photons determined
from the ratio of the measured electromagnetic transverse energy and photon
multiplicity, remains almost constant with increasing rho_max. Results are
compared with model predictions.Comment: 16 pages including 4 figure
Scaling of Particle and Transverse Energy Production in 208Pb+208Pb collisions at 158 A GeV
Transverse energy, charged particle pseudorapidity distributions and photon
transverse momentum spectra have been studied as a function of the number of
participants (N_{part}) and the number of binary nucleon-nucleon collisions
(N_{coll}) in 158 A GeV Pb+Pb collisions over a wide impact parameter range. A
scaling of the transverse energy pseudorapidity density at midrapidity as
N_{part}^{1.08 \pm 0.06} and N_{coll}^{0.83 \pm 0.05} is observed. For the
charged particle pseudorapidity density at midrapidity we find a scaling as
N_{part}^{1.07 \pm 0.04} and N_{coll}^{0.82 \pm 0.03}. This faster than linear
scaling with N_{part} indicates a violation of the naive Wounded Nucleon Model.Comment: 13 pages, 16 figures, submitted to European Physical Journal C
(revised results for scaling exponents
Efeito da ferrugem e da supressão de nitrogênio no nível transcricional do gene nitrato redutase (CaNR) em Coffea arabica L.
O objetivo do trabalho é avaliar se a ferrugem do cafeeiro (Hemileia vastatrix) pode modular a resposta transcricional de um gene-chave na assimilação de nitrogênio (N), a nitrato redutase, em função da restrição do nutriente e da resposta do cultivar ao patógeno. Sabe-se que o estado nutricional da planta pode influenciar a severidade do ataque por patógenos. A ferrugem no cafeeiro é um problema recorrente em todas as regiões de cultivo, afetando desde a produtividade até a qualidade final da bebida. A despeito da importância da nutrição mineral para a produtividade e seu impacto na resposta à ferrugem, existem poucos estudos relacionados ao estabelecimento da relação molecular entre o estado nutricional do cafeeiro e resposta de defesa a patógenos. Duas cultivares ? uma resistente e uma suscetível à ferrugem do cafeeiro - foram submetidas a regimes diferenciais de N e inoculadas com H. vastatrix. A análise por qPCR do gene CaNR em três períodos pós-inoculação evidenciou padrões transcricionais distintos entre as duas cultivares - a cultivar suscetível apresentou um pico de expressão em período anterior a cultivar resistente. Este estudo preliminar evidencia que fatores genotípicos e nutricionais podem influenciar na atividade de genes relacionados ao metabolismo de N, dando suporte a futuras análises bioquímicas que auxiliem na compreensão de respostas fisiológicas e moleculares relacionadas com a interação da resposta de defesa e o estado nutricional
A Preshower Photon Multiplicity Detector for the WA98 Experiment
A high granularity preshower detector has been fabricated and installed in the WA98 Experiment at the CERN SPS for measuring the spatial distribution of photons produced in the forward region in lead ion induced interactions. Photons are counted by detecting the preshower signal in plastic scintillator pads placed behind a 3 radiation length thick lead converter and applying a threshold on the scintillator signal to reject the minimum ionizing particles. Techniques to improve the imaging of the fibre and performance of the detector in the high multiplicity environment of lead-lead collisions are described. Using Monte-Carlo simulation methods and test beam data of pi- and e- at various energies the photon counting efficiency is estimated to be 68% for central and 73% for peripheral Pb+Pb collisions
Centrality Dependence of Neutral Pion Production in 158 A GeV Pb + Pb Collisions
The production of neutral pions in 158AGeV Pb+Pb collisions has been studied
in the WA98 experiment at the CERN SPS. Transverse momentum spectra are studied
for the range 0.3 GeV/c < mT-m0 < 4.0 GeV/c. The results for central collisions
are compared to various models. The centrality dependence of the neutral pion
spectral shape and yield is investigated. An invariance of the spectral shape
and a simple scaling of the yield with the number of participating nucleons is
observed for centralities with greater than about 30 participating nucleons
which is most naturally explained by assuming an equilibrated system.Comment: 5 pages, Latex, including 3 eps figures, submitted to Phys.Rev.Lett;
updated pQCD comparison due to new input from the author, updated references,
corrected plotting error in figure
Event-by-Event Fluctuations in Particle Multiplicities and Transverse Energy Produced in 158.A GeV Pb+Pb collisions
Event-by-event fluctuations in the multiplicities of charged particles and
photons, and the total transverse energy in 158 GeV Pb+Pb collisions
are studied for a wide range of centralities. For narrow centrality bins the
multiplicity and transverse energy distributions are found to be near perfect
Gaussians. The effect of detector acceptance on the multiplicity fluctuations
has been studied and demonstrated to follow statistical considerations. The
centrality dependence of the charged particle multiplicity fluctuations in the
measured data has been found to agree reasonably well with those obtained from
a participant model. However for photons the multiplicity fluctuations has been
found to be lower compared to those obtained from a participant model. The
multiplicity and transverse energy fluctuations have also been compared to
those obtained from the VENUS event generator.Comment: To appear in Physical Review C; changes : more detailed discussion on
errors and few figures modifie
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