428 research outputs found
Time-dependent radio emission from evolving jets
We investigated the time-dependent radiative and dynamical properties of
light supersonic jets launched into an external medium, using hydrodynamic
simulations and numerical radiative transfer calculations. These involved
various structural models for the ambient media, with density profiles
appropriate for galactic and extragalactic systems. The radiative transfer
formulation took full account of emission, absorption, re-emission, Faraday
rotation and Faraday conversion explicitly. High time-resolution intensity maps
were generated, frame-by-frame, to track the spatial hydrodynamical and
radiative properties of the evolving jets. Intensity light curves were computed
via integrating spatially over the emission maps. We apply the models to jets
in active galactic nuclei (AGN). From the jet simulations and the
time-dependent emission calculations we derived empirical relations for the
emission intensity and size for jets at various evolutionary stages. The
temporal properties of jet emission are not solely consequences of intrinsic
variations in the hydrodynamics and thermal properties of the jet. They also
depend on the interaction between the jet and the ambient medium. The
interpretation of radio jet morphology therefore needs to take account of
environmental factors. Our calculations have also shown that the environmental
interactions can affect specific emitting features, such as internal shocks and
hotspots. Quantification of the temporal evolution and spatial distribution of
these bright features, together with the derived relations between jet size and
emission, would enable us to set constraints on the hydrodynamics of AGN and
the structure of the ambient medium.Comment: 16 pages, 18 figures, MNRAS in press
Heat Conduction in -(BEDT-TTF)Cu(NCS)
The first study of thermal conductivity, , in a quasi-two-dimensional
organic superconductor of the -(BEDT-TTF)X family reveals features
analogous to those already observed in the cuprates. The onset of
superconductivity is associated with a sudden increase in which can be
suppressed by the application of a moderate magnetic field. At low
temperatures, a finite linear term - due to a residual electronic contribution-
was resolved. The magnitude of this term is close to what is predicted by the
theory of transport in unconventional superconductors.Comment: 5 pages, 4 figures include
Prevalence of intestinal microsporidiosis in Human Immunodeficiency Virus-infected patients with diarrhea in major United States cities
To determine the prevalence of intestinal microsporidiosis in HIV-infected patients, we performed a prospective study of HIV-infected patients with diarrheal illnesses in three US hospitals and examined an observational database of HIV-infected patients in 10 US cities. Among 737 specimens from the three hospitals, results were positive for 11 (prevalence 1.5%); seven (64%) acquired HIV through male-to-male sexual contact, two (18%) through male-to-male sexual contact and injection drug use, and one (9%) through heterosexual contact; one (9%) had an undetermined mode of transmission. Median CD4 count within six months of diagnosis of microsporidiosis was 33 cells/µL (range 3 to 319 cells/µL). For the national observational database (n = 24,098), the overall prevalence of microsporidiosis was 0.16%. Prevalence of microsporidiosis among HIV-infected patients with diarrheal disease is low, and microsporidiosis is most often diagnosed in patients with very low CD4+ cell counts. Testing for microsporidia appears to be indicated, especially for patients with very low CD4+ cell counts.Para determinar a prevalência de microsporidiose intestinal em pacientes infectados pelo HIV foi realizado um estudo prospectivo em três hospitais dos Estados Unidos da América do Norte (EUA) e analizada uma base de dados nacional composta de dados coletados de pacientes infectados pelo HIV em 10 cidades dos EUA. De um total de 737 amostras de fezes de pacientes infectados pelo HIV que apresentavam diarréia, amostras de 11 pacientes (prevalência de 1,5%) foram positivas para microsporídios. Todos os positivos eram do sexo masculino e, entre eles, sete (64%) pacientes adquiriram a infecção pelo HIV através de relação homossexual, dois (18%) através de relação sexual e drogas injetáveis e um (9%) através de contato heterosexual, enquanto que em um paciente o modo de transmissão do HIV não foi determinado. A contagem média de linfócitos CD4 realizada até seis meses do diagnóstico de microsporidiose foi de 33 células/microlitro (3 a 319 células/microlitro). A análise da base de dados nacional (n = 24.098) mostrou uma prevalência de microsporidiose de 0,16%. A prevalência de microsporidiose em pacientes HIV-positivos com diarréia é baixa. Entretando, como a microsporidiose é mais frequentemente diagnosticada em pacientes com contagens de CD4 muito baixas, a indicação de pesquisa de microsporídios é justificada, especialmente para estes pacientes
Quasiparticle dynamics and gap structure in Hg1223 investigated with femtosecond spectroscopy
Measurements of the temperature dependence of the quasiparticle (QP) dynamics
in Hg1223 with femtosecond time-resolved optical spectroscopy are reported.
From the temperature dependence of the amplitude of the photoinduced
reflection, the existence of two gaps is deduced, one temperature dependent Dc
that closes at Tc, and another temperature independent ''pseudogap'' Dp. The
zero-temperature magnitudes of the two gaps are Dc/kTc = 6 +/- 0.5 and Dp/kTc =
6.4 +/- 0.5 respectively. The quasiparticle lifetime is found to exhibit a
divergence as T -> Tc from below, which is attributed to the existence of a
superconducting gap which closes at Tc. Above Tc the relaxation time is longer
than expected for metallic relaxation, which is attributed to the presence of
the ''pseudogap''. The QP relaxation time is found to increase significantly at
low temperatures. This behavior is explained assuming that at low temperatures
the relaxation of photoexcited quasiparticles is governed by a bi-particle
recombination process.Comment: accepted for publication in Phys.Rev.
The effects of healthy aging, amnestic mild cognitive impairment, and Alzheimer's disease on recollection, familiarity and false recognition, estimated by an associative process-dissociation recognition procedure
Given the uneven experimental results in the literature regarding whether or not familiarity declines with healthy aging and cognitive impairment, we compare four samples (healthy young people, healthy older people, older people with amnestic mild cognitive impairment - aMCI -, and older people with Alzheimer's disease - AD -) on an associative recognition task, which, following the logic of the process-dissociation procedure, allowed us to obtain corrected estimates of recollection, familiarity and false recognition. The results show that familiarity does not decline with healthy aging, but it does with cognitive impairment, whereas false recognition increases with healthy aging, but declines significantly with cognitive impairment. These results support the idea that the deficits detected in recollection, familiarity, or false recognition in older people could be used as early prodromal markers of cognitive impairment
Gravitational Lensing
Gravitational lensing has developed into one of the most powerful tools for
the analysis of the dark universe. This review summarises the theory of
gravitational lensing, its main current applications and representative results
achieved so far. It has two parts. In the first, starting from the equation of
geodesic deviation, the equations of thin and extended gravitational lensing
are derived. In the second, gravitational lensing by stars and planets,
galaxies, galaxy clusters and large-scale structures is discussed and
summarised.Comment: Invited review article to appear in Classical and Quantum Gravity, 85
pages, 15 figure
Sonification and Music as Support to the Communication of Alcohol-Related Health Risks to Young People : Study design and results
Excessive consumption of alcohol has been recognised as a significant risk factor impacting the health of young people. Effective communication of such risk is considered to be one key step to improve behaviour. We evaluated an innovative multimedia intervention that utilised audio (sonification—using sound to display data—and music) and interactivity to support the visual communication of alcohol health risk data. A 3-arm pilot experiment was undertaken. The trial measures included health knowledge, alcohol risk perception and user experience of the intervention. Ninety-six subjects participated in the experiment. At 1 month follow-up, alcohol knowledge and alcohol risk perception improved significantly in the whole sample. However, there was no difference between the intervention groups that experienced (1) visual presentation with interactivity (VI-Exp group) and, (2) visual presentation with audio (sonification and music) and interactivity (VAI-Exp group), when compared to the control group which experienced a (3) visual only presentation (V-Cont group). Participants reported enjoying the presentations and found them educational. The majority of participants indicated that the audio, music and sonification helped to convey the information well, and, although a larger sample size is needed to fully establish the effectiveness of the different interventions, this study provides a useful model for future similar studies
A Maximum Stellar Surface Density in Dense Stellar Systems
We compile observations of the surface mass density profiles of dense stellar
systems, including globular clusters in the Milky Way and nearby galaxies,
massive star clusters in nearby starbursts, nuclear star clusters in dwarf
spheroidals and late-type disks, ultra-compact dwarfs, and galaxy spheroids
spanning the range from low-mass cusp bulges and ellipticals to massive core
ellipticals. We show that in all cases the maximum stellar surface density
attained in the central regions of these systems is similar, Sigma_max ~ 10^11
M_sun/kpc^2 (~20 g/cm^2), despite the fact that the systems span 7 orders of
magnitude in total stellar mass M_star, 5 in effective radius R_e, and have a
wide range in effective surface density M_star/R_e^2. The surface density limit
is reached on a wide variety of physical scales in different systems and is
thus not a limit on three-dimensional stellar density. Given the very different
formation mechanisms involved in these different classes of objects, we argue
that a single piece of physics likely determines Sigma_max. The radiation
fields and winds produced by massive stars can have a significant influence on
the formation of both star clusters and galaxies, while neither supernovae nor
black hole accretion are important in star cluster formation. We thus conclude
that feedback from massive stars likely accounts for the observed Sigma_max,
plausibly because star formation reaches an Eddington-like flux that regulates
the growth of these diverse systems. This suggests that current models of
galaxy formation, which focus on feedback from supernovae and active galactic
nuclei, are missing a crucial ingredient.Comment: 6 pages, 2 figures, accepted to MNRAS Letters (matches accepted
version
How to detect fluctuating order in the high-temperature superconductors
We discuss fluctuating order in a quantum disordered phase proximate to a
quantum critical point, with particular emphasis on fluctuating stripe order.
Optimal strategies for extracting information concerning such local order from
experiments are derived with emphasis on neutron scattering and scanning
tunneling microscopy. These ideas are tested by application to two model
systems - the exactly solvable one dimensional electron gas with an impurity,
and a weakly-interacting 2D electron gas. We extensively review experiments on
the cuprate high-temperature superconductors which can be analyzed using these
strategies. We adduce evidence that stripe correlations are widespread in the
cuprates. Finally, we compare and contrast the advantages of two limiting
perspectives on the high-temperature superconductor: weak coupling, in which
correlation effects are treated as a perturbation on an underlying metallic
(although renormalized) Fermi liquid state, and strong coupling, in which the
magnetism is associated with well defined localized spins, and stripes are
viewed as a form of micro-phase separation. We present quantitative indicators
that the latter view better accounts for the observed stripe phenomena in the
cuprates.Comment: 43 pages, 11 figures, submitted to RMP; extensively revised and
greatly improved text; one new figure, one new section, two new appendices
and more reference
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