394 research outputs found
Comparing non-safety with safety device sharps injury incidence data from two different occupational surveillance systems
The United States Occupational Safety and Health Administration (OSHA) Bloodborne Pathogens Standard as amended by the Needlestick Safety and Prevention Act requiring the use of safety-engineered medical devices to prevent needlesticks and sharps injuries has been in place since 2001. Injury changes over time include differences between those from non-safety compared with safety-engineered medical devices. This research compares two US occupational incident surveillance systems to determine whether these data can be generalized to other facilities and other countries either with legislation in place or considering developing national policies for the prevention of sharps injuries among healthcare personnel
On-disk coronal rain
Small and elongated, cool and dense blob-like structures are being reported
with high resolution telescopes in physically different regions throughout the
solar atmosphere. Their detection and the understanding of their formation,
morphology and thermodynamical characteristics can provide important
information on their hosting environment, especially concerning the magnetic
field, whose understanding constitutes a major problem in solar physics. An
example of such blobs is coronal rain, a phenomenon of thermal non- equilibrium
observed in active region loops, which consists of cool and dense chromospheric
blobs falling along loop-like paths from coronal heights. So far, only off-limb
coronal rain has been observed and few reports on the phenomenon exist. In the
present work, several datasets of on-disk H{\alpha} observations with the CRisp
Imaging SpectroPolarimeter (CRISP) at the Swedish 1-m Solar Telescope (SST) are
analyzed. A special family of on-disk blobs is selected for each dataset and a
statistical analysis is carried out on their dynamics, morphology and
temperatures. All characteristics present distributions which are very similar
to reported coronal rain statistics. We discuss possible interpretations
considering other similar blob-like structures reported so far and show that a
coronal rain interpretation is the most likely one. Their chromospheric nature
and the projection effects (which eliminate all direct possibility of height
estimation) on one side, and their small sizes, fast dynamics, and especially,
their faint character (offering low contrast with the background intensity) on
the other side, are found as the main causes for the absence until now of the
detection of this on-disk coronal rain counterpart.Comment: 18 pages, 10 figures. Accepted for Solar Physic
Three sites and you are out: Ternary synergistic allostery controls aromatic amino acid biosynthesis in Mycobacterium tuberculosis.
3-Deoxy-D-arabino-heptulosonate 7-phosphate synthase (DAH7PS) catalyzes the first step in the shikimate
pathway, the pathway responsible for the biosynthesis of the aromatic amino acids Trp, Phe, and Tyr. Unlike
many other organisms that produce up to three isozymes, each feedback-regulated by one of the aromatic
amino acid pathway end products, Mycobacterium tuberculosis expresses a single DAH7PS enzyme that can
be controlled by combinations of aromatic amino acids. This study shows that the synergistic inhibition of this
enzyme by a combination of Trp and Phe can be significantly augmented by the addition of Tyr.We used X-ray
crystallography, mutagenesis, and isothermal titration calorimetry studies to show that DAH7PS from M.
tuberculosis possesses a Tyr-selective site in addition to the Trp and Phe sites, revealing an unusual and
highly sophisticated network of three synergistic allosteric sites on one enzyme. This ternary inhibitory
response, by a combination of all three aromatic amino acids, allows a tunable response of the protein to
changing metabolic demands
Particle creation, classicality and related issues in quantum field theory: II. Examples from field theory
We adopt the general formalism, which was developed in Paper I
(arXiv:0708.1233) to analyze the evolution of a quantized time-dependent
oscillator, to address several questions in the context of quantum field theory
in time dependent external backgrounds. In particular, we study the question of
emergence of classicality in terms of the phase space evolution and its
relation to particle production, and clarify some conceptual issues. We
consider a quantized scalar field evolving in a constant electric field and in
FRW spacetimes which illustrate the two extreme cases of late time adiabatic
and highly non-adiabatic evolution. Using the time-dependent generalizations of
various quantities like particle number density, effective Lagrangian etc.
introduced in Paper I, we contrast the evolution in these two limits bringing
out key differences between the Schwinger effect and evolution in the de Sitter
background. Further, our examples suggest that the notion of classicality is
multifaceted and any one single criterion may not have universal applicability.
For example, the peaking of the phase space Wigner distribution on the
classical trajectory \emph{alone} does not imply transition to classical
behavior. An analysis of the behavior of the \emph{classicality parameter},
which was introduced in Paper I, leads to the conclusion that strong particle
production is necessary for the quantum state to become highly correlated in
phase space at late times.Comment: RevTeX 4; 27 pages; 18 figures; second of a series of two papers, the
first being arXiv:0708.1233 [gr-qc]; high resolution figures available from
the authors on reques
Particle creation, classicality and related issues in quantum field theory: I. Formalism and toy models
The quantum theory of a harmonic oscillator with a time dependent frequency
arises in several important physical problems, especially in the study of
quantum field theory in an external background. While the mathematics of this
system is straightforward, several conceptual issues arise in such a study. We
present a general formalism to address some of the conceptual issues like the
emergence of classicality, definition of particle content, back reaction etc.
In particular, we parametrize the wave function in terms of a complex number
(which we call excitation parameter) and express all physically relevant
quantities in terms it. Many of the notions -- like those of particle number
density, effective Lagrangian etc., which are usually defined using asymptotic
in-out states -- are generalized as time-dependent concepts and we show that
these generalized definitions lead to useful and reasonable results. Having
developed the general formalism we apply it to several examples. Exact analytic
expressions are found for a particular toy model and approximate analytic
solutions are obtained in the extreme cases of adiabatic and highly
non-adiabatic evolution. We then work out the exact results numerically for a
variety of models and compare them with the analytic results and
approximations. The formalism is useful in addressing the question of emergence
of classicality of the quantum state, its relation to particle production and
to clarify several conceptual issues related to this. In Paper II
(arXiv:0708.1237), which is a sequel to this, the formalism will be applied to
analyze the corresponding issues in the context of quantum field theory in
background cosmological models and electric fields.Comment: RevTeX 4; 32 pages; 28 figures; first of a series of two papers, the
second being arXiv:0708.1237 [gr-qc]; high resolution figures available from
the authors on reques
Acoustic Power Absorption and its Relation with Vector Magnetic Field of a Sunspot
The distribution of acoustic power over sunspots shows an enhanced absorption
near the umbra--penumbra boundary. Earlier studies revealed that the region of
enhanced absorption coincides with the region of strongest transverse potential
field. The aim of this paper is to (i) utilize the high-resolution vector
magnetograms derived using Hinode SOT/SP observations and study the
relationship between the vector magnetic field and power absorption and (ii)
study the variation of power absorption in sunspot penumbrae due to the
presence of spine-like radial structures. It is found that (i) both potential
and observed transverse fields peak at a similar radial distance from the
center of the sunspot, and (ii) the magnitude of the transverse field, derived
from Hinode observations, is much larger than the potential transverse field
derived from SOHO/MDI longitudinal field observations. In the penumbra, the
radial structures called spines (intra-spines) have stronger (weaker) field
strength and are more vertical (horizontal). The absorption of acoustic power
in the spine and intra-spine shows different behaviour with the absorption
being larger in the spine as compared to the intra-spine.Comment: 18 pages, 7 figures, In Press Solar Physics, Topical Issue on
Helio-and-Astroseismolog
The influence of cosmic-rays on the magnetorotational instability
We present a linear perturbation analysis of the magnetorotational
instability in the presence of the cosmic rays. Dynamical effects of the cosmic
rays are considered by a fluid description and the diffusion of cosmic rays is
only along the magnetic field lines. We show an enhancement in the growth rate
of the unstable mode because of the existence of cosmic rays. But as the
diffusion of cosmic rays increases, we see that the growth rate decreases.
Thus, cosmic rays have a destabilizing role in the magnetorotational
instability of the accretion discs.Comment: Accepted for publication in Astrophysics & Space Scienc
Large-scale magnetic fields from inflation due to a -even Chern-Simons-like term with Kalb-Ramond and scalar fields
We investigate the generation of large-scale magnetic fields due to the
breaking of the conformal invariance in the electromagnetic field through the
-even dimension-six Chern-Simons-like effective interaction with a fermion
current by taking account of the dynamical Kalb-Ramond and scalar fields in
inflationary cosmology. It is explicitly demonstrated that the magnetic fields
on 1Mpc scale with the field strength of G at the present time
can be induced.Comment: 18 pages, 6 figures, version accepted for publication in Eur. Phys.
J.
Stability and collapse of localized solutions of the controlled three-dimensional Gross-Pitaevskii equation
On the basis of recent investigations, a newly developed analytical procedure
is used for constructing a wide class of localized solutions of the controlled
three-dimensional (3D) Gross-Pitaevskii equation (GPE) that governs the
dynamics of Bose-Einstein condensates (BECs). The controlled 3D GPE is
decomposed into a two-dimensional (2D) linear Schr\"{o}dinger equation and a
one-dimensional (1D) nonlinear Schr\"{o}dinger equation, constrained by a
variational condition for the controlling potential. Then, the above class of
localized solutions are constructed as the product of the solutions of the
transverse and longitudinal equations. On the basis of these exact 3D
analytical solutions, a stability analysis is carried out, focusing our
attention on the physical conditions for having collapsing or non-collapsing
solutions.Comment: 21 pages, 14 figure
Modeling the Subsurface Structure of Sunspots
While sunspots are easily observed at the solar surface, determining their
subsurface structure is not trivial. There are two main hypotheses for the
subsurface structure of sunspots: the monolithic model and the cluster model.
Local helioseismology is the only means by which we can investigate
subphotospheric structure. However, as current linear inversion techniques do
not yet allow helioseismology to probe the internal structure with sufficient
confidence to distinguish between the monolith and cluster models, the
development of physically realistic sunspot models are a priority for
helioseismologists. This is because they are not only important indicators of
the variety of physical effects that may influence helioseismic inferences in
active regions, but they also enable detailed assessments of the validity of
helioseismic interpretations through numerical forward modeling. In this paper,
we provide a critical review of the existing sunspot models and an overview of
numerical methods employed to model wave propagation through model sunspots. We
then carry out an helioseismic analysis of the sunspot in Active Region 9787
and address the serious inconsistencies uncovered by
\citeauthor{gizonetal2009}~(\citeyear{gizonetal2009,gizonetal2009a}). We find
that this sunspot is most probably associated with a shallow, positive
wave-speed perturbation (unlike the traditional two-layer model) and that
travel-time measurements are consistent with a horizontal outflow in the
surrounding moat.Comment: 73 pages, 19 figures, accepted by Solar Physic
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