925 research outputs found
Geometry and BMS Lie algebras of spatially isotropic homogeneous spacetimes
Simply-connected homogeneous spacetimes for kinematical and aristotelian Lie
algebras (with space isotropy) have recently been classified in all dimensions.
In this paper, we continue the study of these "maximally symmetric" spacetimes
by investigating their local geometry. For each such spacetime and relative to
exponential coordinates, we calculate the (infinitesimal) action of the
kinematical symmetries, paying particular attention to the action of the
boosts, showing in almost all cases that they act with generic non-compact
orbits. We also calculate the soldering form, the associated vielbein and any
invariant aristotelian, galilean or carrollian structures. The (conformal)
symmetries of the galilean and carrollian structures we determine are typically
infinite-dimensional and reminiscent of BMS Lie algebras. We also determine the
space of invariant affine connections on each homogeneous spacetime and work
out their torsion and curvature.Comment: 62 pages, 3 figures, 4 tables, v2: Matches published version, mistake
corrected in Section 4.1.3., 10.2, 10.3, other minor improvements, added
reference
The particle number in Galilean holography
Recently, gravity duals for certain Galilean-invariant conformal field
theories have been constructed. In this paper, we point out that the spectrum
of the particle number operator in the examples found so far is not a necessary
consequence of the existence of a gravity dual. We record some progress towards
more realistic spectra. In particular, we construct bulk systems with
asymptotic Schrodinger symmetry and only one extra dimension. In examples, we
find solutions which describe these Schrodinger-symmetric systems at finite
density. A lift to M-theory is used to resolve a curvature singularity. As a
happy byproduct of this analysis, we realize a state which could be called a
holographic Mott insulator.Comment: 29 pages, 1 rudimentary figure; v2: typo in eqn (3.4), added comments
and ref
GCA in 2d
We make a detailed study of the infinite dimensional Galilean Conformal
Algebra (GCA) in the case of two spacetime dimensions. Classically, this
algebra is precisely obtained from a contraction of the generators of the
relativistic conformal symmetry in 2d. Here we find quantum mechanical
realisations of the (centrally extended) GCA by considering scaling limits of
certain 2d CFTs. These parent CFTs are non-unitary and have their left and
right central charges become large in magnitude and opposite in sign. We
therefore develop, in parallel to the usual machinery for 2d CFT, many of the
tools for the analysis of the quantum mechanical GCA. These include the
representation theory based on GCA primaries, Ward identities for their
correlation functions and a nonrelativistic Kac table. In particular, the null
vectors of the GCA lead to differential equations for the four point function.
The solution to these equations in the simplest case is explicitly obtained and
checked to be consistent with various requirements.Comment: 45 pages; v2: 47 pages. Restructured introduction, minor corrections,
added references. Journal versio
Predicting the peak growth velocity in the individual child: validation of a new growth model
Predicting the peak growth velocity in an individual patient with adolescent idiopathic scoliosis is essential or determining the prognosis of the disorder and timing of the (surgical) treatment. Until the present time, no accurate method has been found to predict the timing and magnitude of the pubertal growth spurt in the individual child. A mathematical model was developed in which the partial individual growth velocity curve was linked to the generic growth velocity curve. The generic curve was shifted and stretched or shrunk, both along the age axis and the height velocity axis. The individual age and magnitude of the PGV were obtained from the new predicted complete growth velocity curve. Predictions were made using 2, 1.5, 1 and 0.5Â years of the available longitudinal data of the individual child, starting at different ages. The predicted values of 210 boys and 162 girls were compared to the childâs own original values of the PGV. The individual differences were compared to differences obtained when using the generic growth velocity curve as a standard. Using 2Â years of data as input for the model, all predictions of the age of the PGV in boys and girls were significantly better in comparison to using the generic values. Using only 0.5Â years of data as input, the predictions with a starting age from 13 to 15.5Â years in boys and from 9.5 to 14.5Â years in girls were significantly better. Similar results were found for the predictions of the magnitude of the PGV. This model showed highly accurate results in predicting the individual age and magnitude of the PGV, which can be used in the treatment of patients with adolescent idiopathic scoliosis
Galilean quantum gravity with cosmological constant and the extended q-Heisenberg algebra
We define a theory of Galilean gravity in 2+1 dimensions with cosmological
constant as a Chern-Simons gauge theory of the doubly-extended Newton-Hooke
group, extending our previous study of classical and quantum gravity in 2+1
dimensions in the Galilean limit. We exhibit an r-matrix which is compatible
with our Chern-Simons action (in a sense to be defined) and show that the
associated bi-algebra structure of the Newton-Hooke Lie algebra is that of the
classical double of the extended Heisenberg algebra. We deduce that, in the
quantisation of the theory according to the combinatorial quantisation
programme, much of the quantum theory is determined by the quantum double of
the extended q-deformed Heisenberg algebra.Comment: 22 page
Finite Temperature Aging Holography
We construct the gravity background which describes the dual field theory
with aging invariance. We choose the decay modes of the bulk scalar field in
the internal spectator direction to obtain the dissipative behavior of the
boundary correlation functions of the dual scalar fields. In particular, the
two-time correlation function at zero temperature has the characteristic
features of the aging system: power law decay, broken time translation and
dynamical scaling. We also construct the black hole backgrounds with asymptotic
aging invariance. We extensively study characteristic behavior of the finite
temperature two-point correlation function via analytic and numerical methods.Comment: 38 pages and 5 figures, expanded discussions on correlator, one
mistake is fixed, modified discussion on shear viscosity, to appear in JHE
How managers can build trust in strategic alliances: a meta-analysis on the central trust-building mechanisms
Trust is an important driver of superior alliance performance. Alliance managers are influential in this regard because trust requires active involvement, commitment and the dedicated support of the key actors involved in the strategic alliance. Despite the importance of trust for explaining alliance performance, little effort has been made to systematically investigate the mechanisms that managers can use to purposefully create trust in strategic alliances. We use Parkheâs (1998b) theoretical framework to derive nine hypotheses that distinguish between process-based, characteristic-based and institutional-based trust-building mechanisms. Our meta-analysis of 64 empirical studies shows that trust is strongly related to alliance performance. Process-based mechanisms are more important for building trust than characteristic- and institutional-based mechanisms. The effects of prior ties and asset specificity are not as strong as expected and the impact of safeguards on trust is not well understood. Overall, theoretical trust research has outpaced empirical research by far and promising opportunities for future empirical research exist
"It's a can of worms": understanding primary care practitioners' behaviours in relation to HPV using the Theoretical Domains Framework
Background: The relationship between infection with high-risk human papillomavirus (HPV) and cervical cancer is transforming cervical cancer prevention. HPV tests and vaccinations have recently become available. In Ireland, as elsewhere, primary care practitioners play a key role in prevention. ATHENS (A Trial of HPV Education and Support) aims to develop a theorybased intervention to support primary care practitioners in their HPV-related practice. This study, the first step in the intervention development process, aimed to: identify HPV-related clinical behaviours that the intervention will target; clarify general practitionersâ (GPsâ) and practice nursesâ roles and responsibilities; and determine factors that potentially influence clinical behaviour. A secondary objective was to informally assess the utility of the Theoretical Domains Framework (TDF) in understanding clinical behaviours in an area with an evolving evidence-base.
Methods: In-depth semi-structured telephone interviews were conducted with GPs and practice nurses. The topic guide, which contained open questions and HPV-related clinical scenarios, was developed through literature review and clinical experience. Interview transcripts were content-analysed using the TDF as the coding framework.
Results: 19 GPs and 14 practice nurses were interviewed. The major HPV-related clinical behaviours were: initiating a discussion about HPV infection with female patients; offering/recommending HPV vaccination to appropriate patients; and answering patientsâ questions about HPV testing. While the responsibility for taking smears was considered a female role, both male and female practitioners dealt with HPV-related issues. All 12 theoretical domains arose in relation to HPV infection; the domains judged to be most important were: knowledge, emotion, social influences, beliefs about capabilities and beliefs about consequences. Eleven domains emerged in relation to HPV vaccination, with beliefs about consequences, social influences, knowledge and environmental context and resources judged to be the most important. Nine domains were relevant to HPV testing, with knowledge and beliefs about capabilities judged to be the most important.
Conclusions: The findings confirm the need for an intervention to support primary care practitioners around HPV and suggest it should target a range of theoretical domains. The TDF proved valuable in analysing qualitative data collected using a topic guide not specifically designed to capture TDF domains and understanding clinical behaviours in an area with an evolving evidence-base
Charged, conformal non-relativistic hydrodynamics
We embed a holographic model of an U(1) charged fluid with Galilean
invariance in string theory and calculate its specific heat capacity and
Prandtl number. Such theories are generated by a R-symmetry twist along a null
direction of a N=1 superconformal theory. We study the hydrodynamic properties
of such systems employing ideas from the fluid-gravity correspondence.Comment: 31 pages, 1 figure, JHEP3 style, refs added, typos corrected, missing
terms in spatial charge current and field corrections added, to be published
in JHE
The three-dimensional easy morphological (3-DEMO) classification of scoliosis, part II: repeatability
BACKGROUND: In the first part of this study we proposed a new classification approach for spinal deformities (3-DEMO). To be valid, a classification needs to overcome the repeatability issue which is inherent both in the used classificatory system and in the measured object. AIM: The aim of this study is to present procedures and results obtained within the repeatability of 3-DEMO classification for scoliosis analysis. METHOD: We acquired the data of 100 pathological and 20 normal spines with an optoelectronic system (AUSCAN) and of two dummies with simulated spine deformity. On the obtained 3D reconstruction of the spine, we considered the coronal view with a spinal reference system (Top View) and its three related parameters, defined in part I, constituting the 3-DEMO classification. We calculated the repeatability coefficient for the subjects (two acquisitions for each subject with a time interval of 26 ± 12 sec), whereas we evaluated the system measurement error calculating the standard deviation of 50 consecutive acquisitions for each dummy. RESULTS: Comparing the results of the two types of acquisition, it emerged that the main part of parameters variability was due to postural adjustments The proportion of agreement for the 3-DEMO parameters gives a k value above 0.8; almost 10% of patients changed classification because of postural adjustments, but none had a "mirror-like" variation nor a change in more of one parameter at a time Repeatability coefficient is lower than the previously calculated normative limits. DISCUSSION: The 3-DEMO classification has a high repeatability when evaluated with an optoelectronic system such as the AUSCAN System, whose systematic error is very low. This means that the implied physiological phenomenon is consistent and overcomes the postural variability inherent in the measured object (normal or pathological subject)
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