527 research outputs found
An algebraic approach to manifold-valued generalized functions
We discuss the nature of structure-preserving maps of varies function
algebras. In particular, we identify isomorphisms between special Colombeau
algebras on manifolds with invertible manifold-valued generalized functions in
the case of smooth parametrization. As a consequence, and to underline the
consistency and validity of this approach, we see that this generalized version
on algebra isomorphisms in turn implies the classical result on algebras of
smooth functions.Comment: 7 page
Isomorphisms of algebras of Colombeau generalized functions
We show that for smooth manifolds X and Y, any isomorphism between the
special algebra of Colombeau generalized functions on X, resp. Y is given by
composition with a unique Colombeau generalized function from Y to X. We also
identify the multiplicative linear functionals from the special algebra of
Colombeau generalized functions on X to the ring of Colombeau generalized
numbers. Up to multiplication with an idempotent generalized number, they are
given by an evaluation map at a compactly supported generalized point on X.Comment: 10 page
Charge conservation and time-varying speed of light
It has been recently claimed that cosmologies with time dependent speed of
light might solve some of the problems of the standard cosmological scenario,
as well as inflationary scenarios. In this letter we show that most of these
models, when analyzed in a consistent way, lead to large violations of charge
conservation. Thus, they are severly constrained by experiment, including those
where is a power of the scale factor and those whose source term is the
trace of the energy-momentum tensor. In addition, early Universe scenarios with
a sudden change of related to baryogenesis are discarded.Comment: 4 page
Magnetic Fields, Relativistic Particles, and Shock Waves in Cluster Outskirts
It is only now, with low-frequency radio telescopes, long exposures with
high-resolution X-ray satellites and gamma-ray telescopes, that we are
beginning to learn about the physics in the periphery of galaxy clusters. In
the coming years, Sunyaev-Zeldovich telescopes are going to deliver further
great insights into the plasma physics of these special regions in the
Universe. The last years have already shown tremendous progress with detections
of shocks, estimates of magnetic field strengths and constraints on the
particle acceleration efficiency. X-ray observations have revealed shock fronts
in cluster outskirts which have allowed inferences about the microphysical
structure of shocks fronts in such extreme environments. The best indications
for magnetic fields and relativistic particles in cluster outskirts come from
observations of so-called radio relics, which are megaparsec-sized regions of
radio emission from the edges of galaxy clusters. As these are difficult to
detect due to their low surface brightness, only few of these objects are
known. But they have provided unprecedented evidence for the acceleration of
relativistic particles at shock fronts and the existence of muG strength fields
as far out as the virial radius of clusters. In this review we summarise the
observational and theoretical state of our knowledge of magnetic fields,
relativistic particles and shocks in cluster outskirts.Comment: 34 pages, to be published in Space Science Review
The Similarity Hypothesis in General Relativity
Self-similar models are important in general relativity and other fundamental
theories. In this paper we shall discuss the ``similarity hypothesis'', which
asserts that under a variety of physical circumstances solutions of these
theories will naturally evolve to a self-similar form. We will find there is
good evidence for this in the context of both spatially homogenous and
inhomogeneous cosmological models, although in some cases the self-similar
model is only an intermediate attractor. There are also a wide variety of
situations, including critical pheneomena, in which spherically symmetric
models tend towards self-similarity. However, this does not happen in all cases
and it is it is important to understand the prerequisites for the conjecture.Comment: to be submitted to Gen. Rel. Gra
Associated Links Among Smoking, Chronic Obstructive Pulmonary Disease, and Small Cell Lung Cancer: A Pooled Analysis in the International Lung Cancer Consortium.
Background
The high relapse and mortality rate of small-cell lung cancer (SCLC) fuels the need for epidemiologic study to aid in its prevention.
Methods
We included 24 studies from the ILCCO collaboration. Random-effects panel logistic regression and cubic spline regression were used to estimate the effects of smoking behaviors on SCLC risk and explore their non-linearity. Further, we explored whether the risk of smoking on SCLC was mediated through COPD.
Findings
Significant dose–response relationships of SCLC risk were observed for all quantitative smoking variables. Smoking pack-years were associated with a sharper increase of SCLC risk for pack-years ranged 0 to approximately 50. The former smokers with longer cessation showed a 43%quit_for_5–9 years to 89%quit_for_≥ 20 years declined SCLC risk vs. subjects who had quit smoking < 5 years. Compared with non-COPD subjects, smoking behaviors showed a significantly higher effect on SCLC risk among COPD subjects, and further, COPD patients showed a 1.86-fold higher risk of SCLC. Furthermore, smoking behaviors on SCLC risk were significantly mediated through COPD which accounted for 0.70% to 7.55% of total effects.
Interpretation
This is the largest pooling study that provides improved understanding of smoking on SCLC, and further demonstrates a causal pathway through COPD that warrants further experimental study.
Abbreviations
COPD, chronic obstructive pulmonary disease; CPG, cigarettes per day; ILCCO, International Lung Cancer Consortium; MeSH, medical subject headings; NSCLC, non-small cell lung cancer; OR, odds ratio; SCLC, small cell lung cancer
Culture, Burnout, and Engagement: A Meta-Analysis on National Cultural Values as Moderators in JD-R Theory
Despite prominence and increasing application of the Job Demands‐Resources (JD‐R) theory across national contexts, the role of culture has not yet been systematically explored. We conducted a meta‐analysis of 132 independent samples from 120 studies across 5 global regions (total N = 101,073) to fill this void. Our paper responds to long‐standing concerns around neglecting differences in the relationships of workplace factors with burnout and engagement across national cultures by testing for a moderating role within JD‐R theory. Results suggest strong support for the direct job demands‐burnout and job resources‐engagement pathways. Regarding the role of culture, our study reveals moderating roles for five out of six cultural dimensions using Hofstede’s framework. Interestingly, these cultural dimensions present a moderating impact towards relationships with either job demands or job resources, yet not both. Our findings offer a valuable starting point for further theoretical developments that can impact international business and global mobility. While these insights suggest a role of national cultural context in JD‐R studies, sensitivity analyses showed that the findings were only partly stable
Basophil-derived Amphiregulin is essential for UVB irradiation-induced immune suppression
UVB irradiation (290–320nm) is used to treat skin diseases like psoriasis and atopic dermatitis, and is known to
suppress contact hypersensitivity (CHS) reactions in mouse models. Regulatory T cells (Treg cells) have been
shown to be responsible for this UVB-induced suppression of CHS. The epidermal growth factor (EGF)-like
growth factor amphiregulin (AREG) engages EGFR on Treg cells and, in different disease models, it was shown that
mast cell–derived AREG is essential for optimal Treg cell function in vivo. Here we determined whether AREG has a
role in UVB-induced, Treg cell–mediated suppression of CHS reactions in the skin. Our data show that AREG is
essential for UVB-induced CHS suppression. In contrast to the general assumption, however, mast cells were
dispensable for UVB-induced immune suppression, whereas basophil-derived AREG was essential. These data
reveal, to our knowledge, a previously unreported function for basophils in the homeostasis of immune
responses in the skin. Basophils thus fulfill a dual function: they contribute to the initiation of effective type 2
immune responses and, by enhancing the suppressive capacity of local Treg cell populations, also to local immune
regulation in the skin.A stimulation grant from the University of Utrecht and a grant from the Dutch Technology Foundation (STW-NWO).http://www.nature.com/jid/hb201
The Scientific Foundations of Forecasting Magnetospheric Space Weather
The magnetosphere is the lens through which solar space weather phenomena are focused and directed towards the Earth. In particular, the non-linear interaction of the solar wind with the Earth's magnetic field leads to the formation of highly inhomogenous electrical currents in the ionosphere which can ultimately result in damage to and problems with the operation of power distribution networks. Since electric power is the fundamental cornerstone of modern life, the interruption of power is the primary pathway by which space weather has impact on human activity and technology. Consequently, in the context of space weather, it is the ability to predict geomagnetic activity that is of key importance. This is usually stated in terms of geomagnetic storms, but we argue that in fact it is the substorm phenomenon which contains the crucial physics, and therefore prediction of substorm occurrence, severity and duration, either within the context of a longer-lasting geomagnetic storm, but potentially also as an isolated event, is of critical importance. Here we review the physics of the magnetosphere in the frame of space weather forecasting, focusing on recent results, current understanding, and an assessment of probable future developments.Peer reviewe
Plasticity in Diurnal Activity and Temporal Phenotype During Parental Care in European Starlings, Sturnus Vulgaris
We used an automated radiotelemetry system to determine diurnal patterns of activity and temporal phenotype (onset and cessation of activity) in female European starlings during breeding. Parental care is thought to be the most ‘costly’ part of reproduction, with high rates of intense activity due to foraging and provisioning for chicks, so we predicted that variation in timing of activity should be closely related to breeding success. Diurnal variation in activity varied systematically with breeding stage in a way consistent with specific demands of each phase of parental care: incubating females were more active late in the day (1600–1800 hours), while chick-rearing females were more active early in the morning (0700–1100 hours). There was marked individual variation in timing of onset, and to a lesser extent cessation, of activity, e.g. chick-rearing females first became active 7–127 min after morning civil twilight, with low to moderate repeatability within and among breeding stages (individual explained 2–62% of total variation). On average, females were active later, and ceased being active earlier, during chick rearing compared with incubation. Chick-rearing birds had a longer active day, but only by 2.3% (36% of the seasonal increase in total available daylength). Thus, chick-rearing females were relatively less active (‘lazier’), which is consistent with the idea that parents work more efficiently rather than simply working harder. We found little evidence that chick-rearing activity was associated with variation in measures of current reproduction (provisioning rate, number and quality of chicks), future fecundity (initiating a second brood, cumulative 2-year productivity) or survival (local return rate). Our study demonstrates that time-keeping mechanisms show plasticity in response to reproductive state and can be modulated by ‘biotic’ (e.g. prey availability) or ‘social’ time (demands of parental care)
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