613 research outputs found
On the connection between Quantum Mechanics and the geometry of two-dimensional strings
On the basis of an area-preserving symmetry in the phase space of a
one-dimensional matrix model - believed to describe two-dimensional string
theory in a black-hole background which also allows for space-time foam - we
give a geometric interpretation of the fact that two-dimensional stringy black
holes are consistent with conventional quantum mechanics due to the infinite
gauged `W-hair' property that characterises them.Comment: 19 page
Semi-classical stability of AdS NUT instantons
The semi-classical stability of several AdS NUT instantons is studied.
Throughout, the notion of stability is that of stability at the one-loop level
of Euclidean Quantum Gravity. Instabilities manifest themselves as negative
eigenmodes of a modified Lichnerowicz Laplacian acting on the transverse
traceless perturbations. An instability is found for one branch of the
AdS-Taub-Bolt family of metrics and it is argued that the other branch is
stable. It is also argued that the AdS-Taub-NUT family of metrics are stable. A
component of the continuous spectrum of the modified Lichnerowicz operator on
all three families of metrics is found.Comment: 18 pages, 3 figures; references adde
Perceptions of healthcare professionals and managers regarding the effectiveness of GP-led walk-in centres in the UK.
OBJECTIVES: This study aimed to identify the perceptions of healthcare professionals regarding the effectiveness and the impact of a new general practitioner-led (GP-led) walk-in centre in the UK. SETTING: This qualitative study was conducted in a large city in the North of England. In the past few years, there has been particular concern about an increase in the use of emergency department (ED) services provided by the National Health Service and part of the rationale for introducing the new GP-led walk-in centres has been to stem this increase. The five institutes included in the study were EDs, a minor injuries unit, a primary care trust, a GP-led walk-in centre and GP surgeries. PARTICIPANTS: Semistructured interviews were conducted with healthcare providers at an adult ED, an ED at a children's hospital, a minor injuries unit, a GP-led walk-in centre, GPs from surrounding surgeries and GPs. RESULTS: 11 healthcare professionals and managers were interviewed. Seven key themes were identified within the data: the clinical model of the GP-led walk-in centre; public awareness of the services; appropriate use of the centre; the impact of the centre on other services; demand for healthcare services; choice and confusion and mixed views (positive and negative) of the walk-in services. There were discrepancies between the managers and healthcare professionals regarding the usefulness of the GP-led walk-in centre in the current urgent care system. CONCLUSIONS: Participants did not notice declines in the demand for EDs after the GP-led walk-in centre. Most of the healthcare professionals believed that the GP-led walk-in centre duplicated existing healthcare services. There is a need to have a better communication system between the GP-led walk-in centres and other healthcare providers to have an integrated system of urgent care delivery
World-Sheet Duality, Space-Time Foam, and the Quantum Fate of a Stringy Black Hole
We interpret Minkowski black holes as world-sheet {\it spikes } which are
related by world-sheet { \it duality} to {\it vortices } that correspond to
Euclidean black holes. These world-sheet defects induce defects in the gauge
fields of the corresponding coset Wess-Zumino descriptions of
spherically-symmetric black holes. The low-temperature target space-time foam
is a Minkowski black hole (spike) plasma with confined Euclidean black holes
(vortices). The high-temperature phase is a {\it dense} vortex plasma described
by a topological gauge field theory on the world-sheet, which possesses
enhanced symmetry as in the target space-time singularity at the core of a
black hole. Quantum decay via higher-genus effects induces a back-reaction
which causes a Minkowski black hole to lose mass until it is indistinguishable
from intrinsic fluctuations in the space-time foam.Comment: 16 pages, CERN-TH.6534/92, (correction of a minor typographical error
on page 12
Searching for massive galaxies at z>=3.5 in GOODS-North
We constrain the space density and properties of massive galaxy candidates at
redshifts of z>=3.5 in the GOODS-N field. By selecting sources in the
Spitzer+IRAC bands, a highly stellar mass-complete sample is
assembled,including massive galaxies which are very faint in the
optical/near-IR bands that would be missed by samples selected at shorter
wavelengths. The z>=3.5 sample was selected down to 23 mag at 4.5 micron using
photometric redshifts that have been obtained by fitting the galaxies SEDs at
optical, near-IR and IRAC bands. We also require that the brightest band in
which candidates are detected is the IRAC 8 micron band in order to ensure that
the near-IR 1.6 micron (rest-frame) peak is falling in or beyond this band. We
found 53 z>=3.5 candidates, with masses in the range of M~10^10-10^11M_sun. At
least ~81% of these galaxies are missed by traditional Lyman Break selection
methods based on UV light. Spitzer+MIPS emission is detected for 60% of the
sample of z>=3.5 galaxy candidates. Although in some cases this might suggest a
residual contamination from lower redshift star-forming galaxies or AGN, 37% of
these objects are also detected in the sub-mm/mm bands in recent SCUBA,AzTEC
and MAMBO surveys, and have properties fully consistent with vigorous starburst
galaxies at z>=3.5. The comoving number density of galaxies with stellar masses
>= 5x10^10M_sun(a reasonable stellar mass completeness limit for our sample) is
2.6x10^-5Mpc^-3 (using the volume within 3.5<z<5), and the corresponding
stellar mass density is ~2.9x10^6M_sunMpc^-3, or~3% of the local density above
the same stellar mass limit.For the sub-sample of MIPS-undetected galaxies,we
find a number density of ~0.97x10^-5Mpc^-3 and a stellar mass density of
~1.15x10^6M_sun Mpc^-3.[abridged]Comment: Accepted by A&A; 35 pages, 15 figures, references update
Optically faint X-ray sources in the CDFN: Spitzer constraints
We investigate the properties of the most optically faint sources in the
GOODS-N area (R > 26.5 AB). Such extremely optically faint populations present
an uncharted territory despite the fact that they represent an appreciable
fraction of the X-ray sources in the GOODS-N field. They are believed to
contain either red AGN at moderate redshifts or possibly QSO at very high
redshift. We compile our sample by first finding the 3.6um IRAC counterparts of
the X-ray sources and searching for the optical counterparts of the IRAC
sources. 35 sources do not have counterparts in the R-band Subaru optical
images. Of these, 18 have HST-ACS counterparts while the remaining have no
optical counterparts. The vast majority of our 35 sources are classified as
Extremely Red Objects (EROs) on the basis of their V-K lower limits. Their
photometric redshifts show that these populate moderate redshifts (median
z~2.8), being markedly different from the already spectroscopically identified
population which peaks at z~0.7. The Spitzer-IRAC mid-IR colours of the sources
which have no HST counterparts tend to lie within the mid-IR colour diagram AGN
"wedge", suggesting either QSO, ULIRG (Mrk231), or early-type galaxy templates
at z>3. A large fraction of our sources (17/35), regardless of whether they
have HST counterparts, can be classified as mid-IR bright/optically faint
sources (Dust Obscured Galaxies) a class which is believed to include many
heavily absorbed AGN. The co-added X-ray spectrum of the optically faint
sources is very flat having a spectral index of Gamma~0.87, significantly
flatter than the spectrum of the X-ray background. The optically faint R>26.5
X-ray sources constitute more than 50% of the total X-ray population at
redshifts z>2 bearing important implications for the luminosity function and
its evolution; considering X-ray sources with 2<z<4 we find good agreement with
a modified PLE model.Comment: Accepted for publication in A&
Beyond communication:The role of standardized protocols in a changing health care environment
Background: Communication errors have grave consequences in health care settings. The situationYbackgroundY assessmentYrecommendation (SBAR) protocol has been theorized to improve communication by creating a common language between nurses and physicians in acute care situations. This practice is gaining acceptance across the health care field. However, as yet, there has been little investigation of the ways in which SBAR may have an impact on how health care professionals operate beyond the creation of a common language. Purpose: The purposes of the study were to explore the implementation of the SBAR protocol and investigate the potential impact of SBAR on the day-to-day experiences of nurses. Methods: We performed a qualitative case study of 2 hospitals that were implementing the SBAR protocol. We collected data from 80 semistructured interviews with nurses, nurse manager, and physicians; observation of nursing and other hospital activities; and documents that pertained to the implementation of the SBAR protocol. Data were analyzed using a thematic approach. Findings: Our analysis revealed 4 dimensions of impact that SBAR has beyond its use as a communication tool: schema formation, development of legitimacy, development of social capital, and reinforcement of dominant logics
Symmetries of Holographic Minimal Models
It was recently proposed that a large N limit of a family of minimal model
CFTs is dual to a certain higher spin gravity theory in AdS_3, where the 't
Hooft coupling constant of the CFT is related to a deformation parameter of the
higher spin algebra. We identify the asymptotic symmetry algebra of the higher
spin theory for generic 't Hooft parameter, and show that it coincides with a
family of W-algebras previously discovered in the context of the KP hierarchy.
We furthermore demonstrate that this family of W-algebras controls the
representation theory of the minimal model CFTs in the 't Hooft limit. This
provides a non-trivial consistency check of the proposal and explains part of
the underlying mechanism.Comment: 25 pages; references added and minor corrections (published version
Discrete Information from CHL Black Holes
AdS_2/CFT_1 correspondence predicts that the logarithm of a Z_N twisted index
over states carrying a fixed set of charges grows as 1/N times the entropy of
the black hole carrying the same set of charges. In this paper we verify this
explicitly by calculating the microscopic Z_N twisted index for a class of
states in the CHL models. This demonstrates that black holes carry more
information about the microstates than just the total degeneracy.Comment: LaTeX file, 24 pages; v2: references adde
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