31,486 research outputs found
Global Dimension of Polynomial Rings in Partially Commuting Variables
For any free partially commutative monoid , we compute the global
dimension of the category of -objects in an Abelian category with exact
coproducts. As a corollary, we generalize Hilbert's Syzygy Theorem to
polynomial rings in partially commuting variables.Comment: 11 pages, 2 figure
Partially incoherent gap solitons in Bose-Einstein condensates
We construct families of incoherent matter-wave solitons in a repulsive
degenerate Bose gas trapped in an optical lattice (OL), i.e., gap solitons, and
investigate their stability at zero and finite temperature, using the
Hartree-Fock-Bogoliubov equations. The gap solitons are composed of a coherent
condensate, and normal and anomalous densities of incoherent vapor co-trapped
with the condensate. Both intragap and intergap solitons are constructed, with
chemical potentials of the components falling in one or different bandgaps in
the OL-induced spectrum. Solitons change gradually with temperature. Families
of intragap solitons are completely stable (both in direct simulations, and in
terms of eigenvalues of perturbation modes), while the intergap family may have
a very small unstable eigenvalue (nevertheless, they feature no instability in
direct simulations). Stable higher-order (multi-humped) solitons, and bound
complexes of fundamental solitons are found too.Comment: 8 pages, 9 figures. Physical Review A, in pres
Media freedom and the escalation of state violence
When governments face severe political violence, they regularly respond with violence. Yet not all governments escalate repression under such circumstances. We argue that to understand the escalation of state violence, we need to pay attention to the potential costs leaders might face in doing so. We expect that the decision to escalate state violence is conditional on being faced with heightened threats and on possessing an information advantage that mitigates the expected cost of increasing state violence. In an environment where media freedom is constrained, leaders can deny or reframe an escalation of violations and so expect to reduce potential domestic and international costs attached to that decision. Using a global dataset from 1981 to 2006, we show that state violence is likely to escalate in response to increasing violent threats to the state when media freedom is curtailed – but not when the media are free from state intervention. A media environment that the government knows is free to sound the alarm is associated with higher political costs of repression and effectively reduces the risk of escalating state violence, even in the face of mounting armed threats
Controlling the uncontrolled: Are there incidental experimenter effects on physiologic responding?
The degree to which experimenters shape participant behavior has long been of interest in experimental social science research. Here, we extend this question to the domain of peripheral psychophysiology, where experimenters often have direct, physical contact with participants, yet researchers do not consistently test for their influence. We describe analytic tools for examining experimenter effects in peripheral physiology. Using these tools, we investigate nine data sets totaling 1,341 participants and 160 experimenters across different roles (e.g., lead research assistants, evaluators, confederates) to demonstrate how researchers can test for experimenter effects in participant autonomic nervous system activity during baseline recordings and reactivity to study tasks. Our results showed (a) little to no significant variance in participants' physiological reactivity due to their experimenters, and (b) little to no evidence that three characteristics of experimenters that are well known to shape interpersonal interactions-status (using five studies with 682 total participants), gender (using two studies with 359 total participants), and race (in two studies with 554 total participants)-influenced participants' physiology. We highlight several reasons that experimenter effects in physiological data are still cause for concern, including the fact that experimenters in these studies were already restricted on a number of characteristics (e.g., age, education). We present recommendations for examining and reducing experimenter effects in physiological data and discuss implications for replication
A study to assess the impact of continuing profession development (CPD) on doctors performance and patient/service outcomes. Final report for the GMC
Certified quantum non-demolition measurement of material systems
An extensive debate on quantum non-demolition (QND) measurement, reviewed in
Grangier et al. [Nature, {\bf 396}, 537 (1998)], finds that true QND
measurements must have both non-classical state-preparation capability and
non-classical information-damage tradeoff. Existing figures of merit for these
non-classicality criteria require direct measurement of the signal variable and
are thus difficult to apply to optically-probed material systems. Here we
describe a method to demonstrate both criteria without need for to direct
signal measurements. Using a covariance matrix formalism and a general noise
model, we compute meter observables for QND measurement triples, which suffice
to compute all QND figures of merit. The result will allow certified QND
measurement of atomic spin ensembles using existing techniques.Comment: 11 pages, zero figure
Hot String Soup
Above the Hagedorn energy density closed fundamental strings form a long
string phase. The dynamics of weakly interacting long strings is described by a
simple Boltzmann equation which can be solved explicitly for equilibrium
distributions. The average total number of long strings grows logarithmically
with total energy in the microcanonical ensemble. This is consistent with
calculations of the free single string density of states provided the
thermodynamic limit is carefully defined. If the theory contains open strings
the long string phase is suppressed.Comment: 13 pages, no figures, uses LaTex, some errors in equations have been
corrected, NSF-ITP-94-83, UCSBTH-94-3
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