20,090 research outputs found
Dynamical trapping and relaxation of scalar gravitational fields
We present a framework for nonlinearly coupled scalar-tensor theory of
gravity to address both inflation and core-collapse supernova problems. The
unified approach is based on a novel dynamical trapping and relaxation of
scalar gravity in highly energetic regimes. The new model provides a viable
alternative mechanism of inflation free from various issues known to affect
previous proposals. Furthermore, it could be related to observable violent
astronomical events, specifically by releasing a significant amount of
additional gravitational energy during core-collapse supernovae. A recent
experiment at CERN relevant for testing this new model is briefly outlined.Comment: 4 pages; version to appear in PL
Prediction of the bottomonium D-wave spectrum from full lattice QCD
We calculate the full spectrum of D-wave states in the Upsilon system in
lattice QCD for the first time, using an improved version of NonRelativistic
QCD on coarse and fine "second generation" gluon field configurations from the
MILC collaboration that include the effect of up, down, strange and charm
quarks in the sea. Taking the 2S-1S splitting to set the lattice spacing, we
determine the ^3D_2 - 1S splitting to 2.3%, and find agreement with experiment.
Our prediction of the fine structure relative to the ^3D_2 gives the ^3D_3 at
10.181(5) GeV and the ^3D_1 at 10.147(6) GeV. We also discuss the overlap of
^3D_1 operators with ^3S_1 states.Comment: 4 pages, 5 figure
Massless interacting particles
We show that classical electrodynamics of massless charged particles and the
Yang--Mills theory of massless quarks do not experience rearranging their
initial degrees of freedom into dressed particles and radiation. Massless
particles do not radiate. We consider a version of the direct interparticle
action theory for these systems following the general strategy of Wheeler and
Feynman.Comment: LaTeX; 20 pages; V4: discussion is slightly modified to clarify some
important points, relevant references are adde
Heavy-Light Mesons with Quenched Lattice NRQCD: Results on Decay Constants
We present a quenched lattice calculation of heavy-light meson decay
constants, using non-relativistic (NRQCD) heavy quarks in the mass region of
the quark and heavier, and clover-improved light quarks. The NRQCD
Hamiltonian and the heavy-light current include the corrections at first order
in the expansion in the inverse heavy quark mass. We study the dependence of
the decay constants on the heavy meson mass , for light quarks with the tree
level ( = 1), as well as the tadpole improved clover coefficient. We
compare decay constants from NRQCD with results from clover () heavy
quarks.
Having calculated the current renormalisation constant in one-loop
perturbation theory, we demonstrate how the heavy mass dependence of the
pseudoscalar decay constants changes after renormalisation. For the first time,
we quote a result for from NRQCD including the full one-loop matching
factors at .Comment: 45 pages, latex, 24 postscript figure
Semicausal operations are semilocalizable
We prove a conjecture by DiVincenzo, which in the terminology of Preskill et
al. [quant-ph/0102043] states that ``semicausal operations are
semilocalizable''. That is, we show that any operation on the combined system
of Alice and Bob, which does not allow Bob to send messages to Alice, can be
represented as an operation by Alice, transmitting a quantum particle to Bob,
and a local operation by Bob. The proof is based on the uniqueness of the
Stinespring representation for a completely positive map. We sketch some of the
problems in transferring these concepts to the context of relativistic quantum
field theory.Comment: 4 pages, 1 figure, revte
Density of critical points for a Gaussian random function
Critical points of a scalar quantitiy are either extremal points or saddle
points. The character of the critical points is determined by the sign
distribution of the eigenvalues of the Hessian matrix. For a two-dimensional
homogeneous and isotropic random function topological arguments are sufficient
to show that all possible sign combinations are equidistributed or with other
words, the density of the saddle points and extrema agree. This argument breaks
down in three dimensions. All ratios of the densities of saddle points and
extrema larger than one are possible. For a homogeneous Gaussian random field
one finds no longer an equidistribution of signs, saddle points are slightly
more frequent.Comment: 11 pages 1 figure, changes in list of references, corrected typo
Oscillation mode linewidths and heights of 23 main-sequence stars observed by Kepler
Solar-like oscillations have been observed by Kepler and CoRoT in many
solar-type stars, thereby providing a way to probe the stars using
asteroseismology. We provide the mode linewidths and mode heights of the
oscillations of various stars as a function of frequency and of effective
temperature. We used a time series of nearly two years of data for each star.
The 23 stars observed belong to the simple or F-like category. The power
spectra of the 23 main-sequence stars were analysed using both maximum
likelihood estimators and Bayesian estimators, providing individual mode
characteristics such as frequencies, linewidths, and mode heights. We study the
source of systematic errors in the mode linewidths and mode heights, and we
present a way to correct these errors with respect to a common reference fit.
Using the correction, we could explain all sources of systematic errors, which
could be reduced to less than 15% for mode linewidths and heights, and
less than 5% for amplitude, when compared to the reference fit. The effect
of a different estimated stellar background and a different estimated splitting
will provide frequency-dependent systematic errors that might affect the
comparison with theoretical mode linewidth and mode height, therefore affecting
the understanding of the physical nature of these parameters. All other sources
of relative systematic errors are less dependent upon frequency. We also
provide the dependence of the so-called linewidth dip, in the middle of the
observed frequency range, as a function of effective temperature. We show that
the depth of the dip decreases with increasing effective temperature. The
dependence of the dip on effective temperature may imply that the mixing length
parameter or the convective flux may increase with effective
temperature.Comment: Accepted by A&A, 38 pages, 35 figures, 26 table
JHK Observations of Faint Standard Stars in the Mauna Kea Near-Infrared Photometric System
JHK photometry in the Mauna Kea Observatory (MKO) near-IR system is presented
for 115 stars. Of these, 79 are UKIRT standards and 42 are LCO standards. The
average brightness is 11.5 mag, with a range of 10 to 15. The average number of
nights each star was observed is 4, and the average of the internal error of
the final results is 0.011 mag. These JHK data agree with those reported by
other groups to 0.02 mag. The measurements are used to derive transformations
between the MKO JHK photometric system and the UKIRT, LCO and 2MASS systems.
The 2MASS-MKO data scatter by 0.05 mag for redder stars: 2MASS-J includes H2O
features in dwarfs and MKO-K includes CO features in giants. Transformations
derived for stars whose spectra contain only weak features cannot give accurate
transformations for objects with strong absorption features within a filter
bandpasses. We find evidence of systematic effects at the 0.02 mag level in the
photometry of stars with J<11 and H,K<10.5. This is due to an underestimate of
the linearity correction for stars observed with the shortest exposure times;
very accurate photometry of stars approaching the saturation limits of infrared
detectors which are operated in double-read mode is difficult to obtain. Four
stars in the sample, GSPC S705-D, FS 116 (B216-b7), FS 144 (Ser-EC84) and FS 32
(Feige 108), may be variable. 84 stars in the sample have 11< J< 15 and
10.5<H,K<15, are not suspected to be variable, and have magnitudes with an
estimated error <0.027 mag; 79 of these have an error of <0.020 mag. These
represent the first published high-accuracy JHK stellar photometry in the MKO
photometric system; we recommend these objects be employed as primary standards
for that system [abridged].Comment: Accepted for publication in MNRAS, 14 pages, 5 Figure
Overseeing oversight: governance of quality and safety by hospital boards in the English NHS
Objectives:
To contribute towards an understanding of hospital Board composition and oversight of patient safety and health care quality in the NHS.
Methods:
A review of the theory related to hospital Board governance and two national surveys undertaken about Board management in NHS hospital trusts in England. The first was issued to 150 Trusts in 2011/12 and completed online via a dedicated web tool. A total of 145 replies were received (97% response rate). The second online survey undertaken in 2012/13 targeted individual Board members using the Board Self Assessment Questionnaire (BSAQ). A total of 334 responses were received from 165 executive and 169 non-executive board members, providing at least one response from 95 of the 144 NHS Trusts then in existence (66% response rate).
Results:
Around 42% of Boards had 10-12 members and around 51% had 13-15 members. We found no significant difference in Board size between Foundation and non Foundation trusts. Around 62% of Boards had three or fewer serving Board members with clinical backgrounds. For about two-thirds of the Trusts (63%), Board members with a clinical background comprised less than 30% of the Board members. Boards were using a wide range of hard performance metrics and soft intelligence to monitor their organisation with regard to patient safety. Hard, quantitative data were reportedly used at every Board meeting across most hospital Trusts (>80%), including a range of clinical outcomes measures, infection rates and process measures such as medication errors and readmission rates. A much smaller proportion of Trusts (57%) routinely report morbidity rates at every Board meeting. Softer intelligence, used organisationally and reported at all Board meetings, was more variably reported, with discussions with clinicians (in 89% of Trusts) and executive walk-arounds (88%) being most often reported, alongside use of patient stories (83%). However, in only about two-thirds of Trusts did Board members shadow clinicians and report back to the Board (65%). The BSAQ data showed general high or very high levels of agreement with desirable statements of practice in each of the six dimensions. Aggregate levels of agreement within each dimension ranged from 73% (interpersonal) to 85% (political).
Conclusions:
The study provides the best account to-date of English NHS Boards and their actions around health care quality and patient safety. While systematic differences between Trusts of different types were rare, there was nonetheless variation between individual Trusts on both Board composition and Board practices. These findings lay the groundwork for further empirical research exploring the dynamics, influences and impacts of Boards
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