4,539 research outputs found
Superthermal electron processes in the upper atmosphere of Uranus: Aurora and electroglow
Strong ultraviolet emissions from the upper atmosphere of Uranus suggest that both auroral and electroglow phenomena are of significant aeronomical consequences in the structure of the upper atmosphere. Combined modeling and data analysis were performed to determine the effect of electroglow and auroral phenomena on the global heat and atomic hydrogen budgets in the Uranus upper atmosphere. The results indicate that the auroral and electroglow heat sources are not adequate to explain the high exospheric temperature observed at Uranus, but that the atomic hydrogen supplied by these processes is more than sufficient to explain the observations. The various superthermal electron distributions modeled have significantly different efficiencies for the various processes such as UV emission, heating, ionization, and atomic hydrogen production, and produce quite different H2 band spectra. However, additional information on the UV spectra and global parameters is needed before modeling can be used to distinguish between the possible mechanisms for electroglow
Holevo's bound from a general quantum fluctuation theorem
We give a novel derivation of Holevo's bound using an important result from
nonequilibrium statistical physics, the fluctuation theorem. To do so we
develop a general formalism of quantum fluctuation theorems for two-time
measurements, which explicitly accounts for the back action of quantum
measurements as well as possibly non-unitary time evolution. For a specific
choice of observables this fluctuation theorem yields a measurement-dependent
correction to the Holevo bound, leading to a tighter inequality. We conclude by
analyzing equality conditions for the improved bound.Comment: 5 page
Derivation of Boltzmann Principle
We present a derivation of Boltzmann principle
based on classical mechanical models of thermodynamics. The argument is based
on the heat theorem and can be traced back to the second half of the nineteenth
century with the works of Helmholtz and Boltzmann. Despite its simplicity, this
argument has remained almost unknown. We present it in a modern, self-contained
and accessible form. The approach constitutes an important link between
classical mechanics and statistical mechanics
Berry's conjecture and information theory
It is shown that, by applying a principle of information theory, one obtains
Berry's conjecture regarding the high-lying quantal energy eigenstates of
classically chaotic systems.Comment: 8 pages, no figure
Review Essay: Biopolitics 2.0 – Reclaiming the Power of Life in the Anthropocene
Biopolitics was once the preserve of critical Foucauldian-influenced theorists. This is no longer the case. The rise of new materialisms, networked and object-oriented ontologies and demands for the ‘renaturalization of politics’ (Grosz, 2011; Sharp, 2011) have turned the political into the biopolitical in much of radical contemporary political theory. Here, the biopolitical is often in tension with the Foucauldian discourses of the last few decades, affirming alternative possibilities rather than merely critiquing regimes of power (Malabou, 2008; Kirby, 2011; Taussig, 2018). One factor in this shift has been the impact of anthropogenic climate change and global warming on the contemporary political imagination, increasingly refracted through conceptualizations of the Anthropocene (Tsing, 2015; Cohen et al, 2016; Chandler, 2018). A second factor has been that the life sciences no longer appear to support understandings of deterministic differences but rather to cast evolution in sympoietic and entangled ways, making biology appear as no longer essentialising but as increasingly importable into politics, in ways which disrupt modernist or liberal conceptions of the culture/nature divide (Haraway, 2016). Two important but very different engagements, which reflect these affirmative readings of biopolitics, are reviewed here, from the fields of postcolonial literature and gender and race in international politics
Effects of tunnelling and asymmetry for system-bath models of electron transfer
We apply the newly derived nonadiabatic golden-rule instanton theory to
asymmetric models describing electron-transfer in solution. The models go
beyond the usual spin-boson description and have anharmonic free-energy
surfaces with different values for the reactant and product reorganization
energies. The instanton method gives an excellent description of the behaviour
of the rate constant with respect to asymmetry for the whole range studied. We
derive a general formula for an asymmetric version of Marcus theory based on
the classical limit of the instanton and find that this gives significant
corrections to the standard Marcus theory. A scheme is given to compute this
rate based only on equilibrium simulations. We also compare the rate constants
obtained by the instanton method with its classical limit to study the effect
of tunnelling and other quantum nuclear effects. These quantum effects can
increase the rate constant by orders of magnitude.Comment: 10 pages, 3 figure
Power Law Scaling for a System of Interacting Units with Complex Internal Structure
We study the dynamics of a system composed of interacting units each with a
complex internal structure comprising many subunits. We consider the case in
which each subunit grows in a multiplicative manner. We propose a model for
such systems in which the interaction among the units is treated in a mean
field approximation and the interaction among subunits is nonlinear. To test
the model, we identify a large data base spanning 20 years, and find that the
model correctly predicts a variety of empirical results.Comment: 4 pages with 4 postscript figures (uses Revtex 3.1, Latex2e,
multicol.sty, epsf.sty and rotate.sty). Submitted to PR
Transient x-ray diffraction used to diagnose shock compressed Si crystals on the Nova laser
Transient x-ray diffraction is used to record time-resolved information about the shock compression of materials. This technique has been applied on Nova shock experiments driven using a hohlraum x-ray drive. Data were recorded from the shock release at the free surface of a Si crystal, as well as from Si at an embedded ablator/Si interface. Modeling has been done to simulate the diffraction data incorporating the strained crystal rocking curves and Bragg diffraction efficiencies. Examples of the data and post-processed simulations are presented
"Even if the test result is negative, they should be able to tell us what is wrong with us": a qualitative study of patient expectations of rapid diagnostic tests for malaria.
BACKGROUND: The debate on rapid diagnostic tests (RDTs) for malaria has begun to shift from whether RDTs should be used, to how and under what circumstances their use can be optimized. This has increased the need for a better understanding of the complexities surrounding the role of RDTs in appropriate treatment of fever. Studies have focused on clinician practices, but few have sought to understand patient perspectives, beyond notions of acceptability. METHODS: This qualitative study aimed to explore patient and caregiver perceptions and experiences of RDTs following a trial to assess the introduction of the tests into routine clinical care at four health facilities in one district in Ghana. Six focus group discussions and one in-depth interview were carried out with those who had received an RDT with a negative test result. RESULTS: Patients had high expectations of RDTs. They welcomed the tests as aiding clinical diagnoses and as tools that could communicate their problem better than they could, verbally. However, respondents also believed the tests could identify any cause of illness, beyond malaria. Experiences of patients suggested that RDTs were adopted into an existing system where patients are both physically and intellectually removed from diagnostic processes and where clinicians retain authority that supersedes tests and their results. In this situation, patients did not feel able to articulate a demand for test-driven diagnosis. CONCLUSIONS: Improvements in communication between the health worker and patient, particularly to explain the capabilities of the test and management of RDT negative cases, may both manage patient expectations and promote patient demand for test-driven diagnoses
Records in a changing world
In the context of this paper, a record is an entry in a sequence of random
variables (RV's) that is larger or smaller than all previous entries. After a
brief review of the classic theory of records, which is largely restricted to
sequences of independent and identically distributed (i.i.d.) RV's, new results
for sequences of independent RV's with distributions that broaden or sharpen
with time are presented. In particular, we show that when the width of the
distribution grows as a power law in time , the mean number of records is
asymptotically of order for distributions with a power law tail (the
\textit{Fr\'echet class} of extremal value statistics), of order
for distributions of exponential type (\textit{Gumbel class}), and of order
for distributions of bounded support (\textit{Weibull class}),
where the exponent describes the behaviour of the distribution at the
upper (or lower) boundary. Simulations are presented which indicate that, in
contrast to the i.i.d. case, the sequence of record breaking events is
correlated in such a way that the variance of the number of records is
asymptotically smaller than the mean.Comment: 12 pages, 2 figure
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