10,935 research outputs found
Detection of X-ray emission from the host clusters of 3CR quasars
We report the detection of extended X-ray emission around several powerful
3CR quasars with redshifts out to 0.73. The ROSAT HRI images of the quasars
have been corrected for spacecraft wobble and compared with an empirical
point-spread function. All the quasars examined show excess emission at radii
of 15 arcsec and more; the evidence being strong for the more distant objects
and weak only for the two nearest ones, which are known from other wavelengths
not to lie in strongly clustered environments. The spatial profiles of the
extended component is consistent with thermal emission from the intracluster
medium of moderately rich host clusters to the quasars. The total luminosities
of the clusters are in the range 4x10^44 - 3x10^45 erg/s, assuming a
temperature of 4keV. The inner regions of the intracluster medium are, in all
cases, dense enough to be part of a cooling flow.Comment: 21 pages including 4 figures and 4 tables. To be published in MNRA
Does evolution lead to maximizing behavior?
A long-standing question in biology and economics is whether individual organisms evolve to behave as if they were striving to maximize some goal function. We here formalize this "as if" question in a patch-structured population in which individuals obtain material payoffs from (perhaps very complex multimove) social interactions. These material payoffs determine personal fitness and, ultimately, invasion fitness. We ask whether individuals in uninvadable population states will appear to be maximizing conventional goal functions (with population-structure coefficients exogenous to the individual's behavior), when what is really being maximized is invasion fitness at the genetic level. We reach two broad conclusions. First, no simple and general individual-centered goal function emerges from the analysis. This stems from the fact that invasion fitness is a gene-centered multigenerational measure of evolutionary success. Second, when selection is weak, all multigenerational effects of selection can be summarized in a neutral type-distribution quantifying identity-by-descent between individuals within patches. Individuals then behave as if they were striving to maximize a weighted sum of material payoffs (own and others). At an uninvadable state it is as if individuals would freely choose their actions and play a Nash equilibrium of a game with a goal function that combines self-interest (own material payoff), group interest (group material payoff if everyone does the same), and local rivalry (material payoff differences)
XMM-Newton observation of the ULIRG NGC 6240: The physical nature of the complex Fe K line emission
We report on an XMM-Newton observation of the ultraluminous infrared galaxy
NGC 6240. The 0.3-10 keV spectrum can be successfully modelled with: (i) three
collisionally ionized plasma components with temperatures of about 0.7, 1.4,
and 5.5 keV; (ii) a highly absorbed direct power-law component; and (iii) a
neutral Fe K_alpha and K_beta line. We detect a significant neutral column
density gradient which is correlated with the temperature of the three plasma
components. Combining the XMM-Newton spectral model with the high spatial
resolution Chandra image we find that the temperatures and the column densities
increase towards the center.
With high significance, the Fe K line complex is resolved into three distinct
narrow lines: (i) the neutral Fe K_alpha line at 6.4 keV; (ii) an ionized line
at about 6.7 keV; and (iii) a higher ionized line at 7.0 keV (a blend of the Fe
XXVI and the Fe K_beta line). While the neutral Fe K line is most probably due
to reflection from optically thick material, the Fe XXV and Fe XXVI emission
arises from the highest temperature ionized plasma component.
We have compared the plasma parameters of the ultraluminous infrared galaxy
NGC 6240 with those found in the local starburst galaxy NGC 253. We find a
striking similarity in the plasma temperatures and column density gradients,
suggesting a similar underlying physical process at work in both galaxies.Comment: 8 pages including 9 figures. Accepted for publication in A&
Impact of the COVID-19 pandemic on adherence to infection prevention and control measures between 2019 and 2021 in Swiss sentinel private practices: repeated cross-sectional surveys.
The COVID-19 pandemic has shown the importance of infection prevention and control (IPC) measures in health care settings, including primary care. We aimed to describe how it influenced adherence to infection prevention and control measures in private practices in the Swiss sentinel network (Sentinella).
An online cross-sectional survey was sent to the 181 Sentinella practices in 2021 that included questions on the practice's spatial organisation, staff habits and vaccination coverage, ventilation, mask wearing, hand hygiene, as well as triage and separation of patients with suspected infection. Results were compared with those of a 2019 survey conducted in the same setting.
We received 127 valid questionnaires (70.2% response rate). At the time of the study, SARS-CoV-2 vaccination was underway among physicians (51.3%). Between 2019 and 2021, an absence of specific recommendations on mask wearing for staff (55.7%) changed into a recommendation for continuous wearing (93.7%); hand hygiene improved, especially upon arrival at the practice (63.9% vs 85.8%; p <0.001) and before examining patients (74.6% vs 88.2%; p <0.010); impossibility of distancing symptomatic patients dropped (27.9% vs 3.9%, p <0.001); and ventilation and cleaning improved (p <0.001).
The COVID-19 pandemic led to important changes in adherence to the recommended IPC measures
Electrical control of spins and giant g-factors in ring-like coupled quantum dots
Emerging theoretical concepts for quantum technologies have driven a
continuous search for structures where a quantum state, such as spin, can be
manipulated efficiently. Central to many concepts is the ability to control a
system by electric and magnetic fields, relying on strong spin-orbit
interaction and a large g-factor. Here, we present a new mechanism for spin and
orbital manipulation using small electric and magnetic fields. By hybridizing
specific quantum dot states at two points inside InAs nanowires, nearly perfect
quantum rings form. Large and highly anisotropic effective g-factors are
observed, explained by a strong orbital contribution. Importantly, we find that
the orbital and spin-orbital contributions can be efficiently quenched by
simply detuning the individual quantum dot levels with an electric field. In
this way, we demonstrate not only control of the effective g-factor from 80 to
almost 0 for the same charge state, but also electrostatic change of the ground
state spin
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