534 research outputs found
Second law of thermodynamics for macroscopic mechanics coupled to thermodynamic degrees of freedom
Based only on classical Hamiltonian dynamics, we prove the maximum work
principle in a system where macroscopic dynamical degrees of freedom are
intrinsically coupled to microscopic degrees of freedom. Unlike recent
identities between irreversible work and free energy, such as in the Jarzynski
relation, the macroscopic dynamics is not governed by an external action but
undergoes the back reaction of the microscopic degrees of freedom. Our theorems
cover such physical situations as impact between macroscopic bodies,
thermodynamic machines, and molecular motors.Comment: 4 pages, RevTe
Cometary charge exchange diagnostics in UV and Xâray
Since the initial discovery of cometary charge exchange emission, more than 20 comets have been observed with a variety of Xâray and UV observatories. This observational sample offers a broad variety of comets, solar wind environments and observational conditions. It clearly demonstrates that solar wind charge exchange emission provides a wealth of diagnostics, which are visible as spatial, temporal, and spectral emission features. We review the possibilities and limitations of each of those in this contribution (© 2012 WILEYâVCH Verlag GmbH & Co. KGaA, Weinheim)Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/91138/1/335_ftp.pd
Distinct Frontal Networks Are Involved in Adapting to Internally and Externally Signaled Errors
Errors trigger changes in behavior that help individuals adapt to new situations. The dorsal anterior cingulate cortex (dACC) is thought to be central to this response, but more lateral frontal regions are also activated by errors and may make distinct contributions. We investigated error processing by studying 2 distinct error types: commission and timing. Thirty-five subjects performed a version of the Simon Task designed to produce large number of errors. Commission errors were internally recognized and were not accompanied by explicit feedback. In contrast, timing errors were difficult to monitor internally and were explicitly signaled. Both types of error triggered changes in behavior consistent with increased cognitive control. As expected, robust activation within the dACC and bilateral anterior insulae (the Salience Network) was seen for commission errors. In contrast, timing errors were not associated with activation of this network but did activate a bilateral network that included the right ventral attentional system. Common activation for both error types occurred within the pars operculari and angular gyri. These results show that the dACC does not respond to all behaviorally salient errors. Instead, the error-processing system is multifaceted, and control can be triggered independently of the dACC when feedback is unexpected
Solar system Xârays from charge exchange processes
While Xâray astronomy began in 1962 and has made fast progress since then in expanding our knowledge about where in the Universe Xârays are generated by which processes, it took one generation before the importance of a fundamentally different process was recognized. This happened in our immediate neighborhood, when in 1996 comets were discovered as a new class of Xâray sources, directing our attention to charge exchange reactions. Charge exchange is fundamentally different from other processes which lead to the generation of Xârays, because the Xârays are not produced by hot electrons, but by ions picking up electrons from cold gas. Thus it opens up a new window, making it possible to detect cool gas in Xârays (like in comets), while all the other processes require extremely high temperatures or otherwise extreme conditions. After having been overlooked for a long time, the astrophysical importance of charge exchange for the generation of Xârays is now receiving increased general attention. In our solar system, charge exchange induced Xârays have now been established to originate in comets, in all the planets from Venus to Jupiter, and even in the heliosphere itself. In addition to that, evidence for this Xâray emission mechanism has been found at various locations across the Universe. Here we summarize the current knowledge about solar system Xârays resulting from charge exchange processes (© 2012 WILEYâVCH Verlag GmbH & Co. KGaA, Weinheim)Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/91180/1/324_ftp.pd
On Blowup for time-dependent generalized Hartree-Fock equations
We prove finite-time blowup for spherically symmetric and negative energy
solutions of Hartree-Fock and Hartree-Fock-Bogoliubov type equations, which
describe the evolution of attractive fermionic systems (e. g. white dwarfs).
Our main results are twofold: First, we extend the recent blowup result of
[Hainzl and Schlein, Comm. Math. Phys. \textbf{287} (2009), 705--714] to
Hartree-Fock equations with infinite rank solutions and a general class of
Newtonian type interactions. Second, we show the existence of finite-time
blowup for spherically symmetric solutions of a Hartree-Fock-Bogoliubov model,
where an angular momentum cutoff is introduced. We also explain the key
difficulties encountered in the full Hartree-Fock-Bogoliubov theory.Comment: 24 page
Constructing Self-Dual Strings
We present an ADHMN-like construction which generates self-dual string
solutions to the effective M5-brane worldvolume theory from solutions to the
Basu-Harvey equation. Our construction finds a natural interpretation in terms
of gerbes, which we develop in some detail. We also comment on a possible
extension to stacks of multiple M5-branes.Comment: 1+19 pages, presentation improved, minor corrections, published
versio
Rebirth of X-ray Emission from the Born-Again Planetary Nebula A 30
The planetary nebula (PN) A30 is believed to have undergone a very late
thermal pulse resulting in the ejection of knots of hydrogen-poor material.
Using HST images we have detected the angular expansion of these knots and
derived an age of 850+280-150 yr. To investigate the spectral and spatial
properties of the soft X-ray emission detected by ROSAT, we have obtained
Chandra and XMM-Newton observations of A30. The X-ray emission from A30 can be
separated into two components: a point-source at the central star and diffuse
emission associated with the hydrogen-poor knots and the cloverleaf structure
inside the nebular shell. To help us assess the role of the current stellar
wind in powering this X-ray emission, we have determined the stellar parameters
of the central star of A 30 using a non-LTE model fit to its optical and UV
spectrum. The spatial distribution and spectral properties of the diffuse X-ray
emission is suggestive that it is generated by the post-born-again and present
fast stellar winds interacting with the hydrogen-poor ejecta of the born-again
event. This emission can be attributed to shock-heated plasma, as the
hydrogen-poor knots are ablated by the stellar winds, under which circumstances
the efficient mass-loading of the present fast stellar wind raises its density
and damps its velocity to produce the observed diffuse soft X-rays. Charge
transfer reactions between the ions of the stellar winds and material of the
born-again ejecta has also been considered as a possible mechanism for the
production of diffuse X-ray emission, and upper limits on the expected X-ray
production by this mechanism have been derived. The origin of the X-ray
emission from the central star of A 30 is puzzling: shocks in the present fast
stellar wind and photospheric emission can be ruled out, while the development
of a new, compact hot bubble confining the fast stellar wind seems implausible.Comment: 29 pages, 11 figures, 4 tables; accepted for publication by Ap
Chromogranin A as serum marker for neuroendocrine neoplasia: comparison with neuron-specific enolase and the alpha-subunit of glycoprotein hormones
Chromogranin A (CgA) is gaining acceptance as a serum marker of
neuroendocrine tumors. Its specificity in differentiating between
neuroendocrine and nonneuroendocrine tumors, its sensitivity to detect
small tumors, and its clinical value, compared with other neuroendocrine
markers, have not clearly been defined, however. The objectives of this
study were to evaluate the clinical usefulness of CgA as neuroendocrine
serum marker. Serum levels of CgA, neuron-specific enolase (NSE), and the
alpha-subunit of glycoprotein hormones (alpha-SU) were determined in 211
patients with neuroendocrine tumors and 180 control subjects with
nonendocrine tumors. The concentrations of CgA, NSE, and alpha-SU were
elevated in 50%, 43%, and 24% of patients with neuroendocrine tumors,
respectively. Serum CgA was most frequently increased in subjects with
gastrinomas (100%), pheochromocytomas (89%), carcinoid tumors (80%),
nonfunctioning tumors of the endocrine pancreas (69%), and medullary
thyroid carcinomas (50%). The highest levels were observed in subjects
with carcinoid tumors. NSE was most frequently elevated in patients with
small cell lung carcinoma (74%), and alpha-SU was most frequently elevated
in patients with carcinoid tumors (39%). Most subjects with elevated
alpha-SU levels also had elevated CgA concentrations. A significant
positive relationship was demonstrated between the tumor load and serum
CgA levels (P < 0.01, by chi 2 test). Elevated concentrations of CgA, NSE,
and alpha-SU were present in, respectively, 7%, 35%, and 15% of control
subjects. Markedly elevated serum levels of CgA, exceeding 300
micrograms/L, were observed in only 2% of control patients (n = 3)
compared to 40% of patients with neuroendocrine tumors (n = 76). We
conclude that CgA is the best general neuroendocrine serum marker
available. It has the highest specificity for the detection of
neuroendocrine tumors compared to the other neuroendocrine markers, NSE
and alpha-SU. Elevated levels are strongly correlated with tumor volume;
therefore, small tumors may go undetected. Although its specificity cannot
compete with that of the specific hormonal secretion products of most
neuroendocrine tumors, it can have useful clinical applications in
subjects with neuroendocrine tumors for whom either no marker is available
or the marker is inconvenient for routine clinical use
Zero modes, beta functions and IR/UV interplay in higher-loop QED
We analyze the relation between the short-distance behavior of quantum field
theory and the strong-field limit of the background field formalism, for QED
effective Lagrangians in self-dual backgrounds, at both one and two loop. The
self-duality of the background leads to zero modes in the case of spinor QED,
and these zero modes must be taken into account before comparing the
perturbative beta function coefficients and the coefficients of the
strong-field limit of the effective Lagrangian. At one-loop this is familiar
from instanton physics, but we find that at two-loop the role of the zero
modes, and the interplay between IR and UV effects in the renormalization, is
quite different. Our analysis is motivated in part by the remarkable simplicity
of the two-loop QED effective Lagrangians for a self-dual constant background,
and we also present here a new independent derivation of these two-loop
results.Comment: 15 pages, revtex
Technical Design Report for the Upgrade of the ALICE Time Projection Chamber
An interaction rate of 50 kHz is expected for the Pb-Pb periods after the luminosity upgrade of the LHC during LS2, and the ALICE upgrade plans foresee to operate the experiment at these interaction rates. For this purpose, the MWPC-based TPC readout chambers will be replaced by Gas Electron Multipliers (GEMs), allowing a continuous readout of the TPC. The details of this upgrade are described in this Technical Design Report
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