867 research outputs found
Top ranking economics journals impact variability and a ranking update to the year 2002
In this paper I address four questions concerning the quality of scientific economic papers. First, I validate the ex-ante procedure of computing the average impact of economic papers by comparing its results with the expost values. Second, I calibrate an estimator of papers normalised impact. Third, I compute the ranking variability of journals using a bootstrap procedure. Fourth, I test the statistical hypothesis that journalsâ ranking did not changed over the time interval between 1980 and 2000. I concluded that this hypothesis is rejected only for the âQuarterly Journal of Economicsâ and âEconometricaâ, which saw their citation impact improved.
Image quality of myocardial perfusion-gated studies: effect of ingestion of different fat content in the reduction of extra-myocardial abdominal signal
Myocardial perfusion-gated-SPECT (MP-gated-SPECT) imaging often shows radiotracer uptake in abdominal organs. This accumulation interferes frequently with qualitative and quantitative assessment of the infero-septal region of myocardium. The objective of this study is to evaluate the effect of ingestion of different fat content on the reduction of extra-myocardial uptake and to improve MP-gated-SPECT image quality. In this study, 150 patients (65 ^ 18 years) who were referred for MP-gated-SPECT underwent a 1-day-protocol including imaging after stress (physical or pharmacological) and resting conditions. All patients gave written informed consent. Patients were subdivided into five groups: GI, GII, GIII, GIV and GV. In the first four groups, patients ate two chocolate bars with different fat content. Patients in GV â control group (CG) â had just water. Uptake indices (UI) of myocardium (M)/liver(L) and M/stomachâproximal bowel(S) revealed lower UI of M/S at rest in all groups. Both stress and rest studies using different food intake indicate that patients who ate chocolate with
different fat content showed better UI of M/L than the CG. The UI of M/L and M/S of groups obtained under physical stress are clearly superior to that of groups obtained under pharmacological stress. These differences are only significant in patients who ate high-fat chocolate or drank water. The analysis of all stress studies together (GI, GII, GIII and GIV) in comparison with CG shows higher mean ranks of UI of M/L for those who ate high-fat chocolate. After pharmacological stress, the mean ranks of UI of M/L were higher for patients who ate high- and low-fat chocolate. In conclusion, eating food with fat content after radiotracer injection increases, respectively, the UI of M/L after stress and rest in MP-gated-SPECT studies. It is, therefore, recommended that patients eat a chocolate bar after radiotracer injection and before image acquisition
Games on Cellular Spaces: How Mobility Affects Equilibrium
In this work we propose a new model for spatial games. We present a definition of mobility in terms of the satisfaction an agent has with its spatial location. Agents compete for space through a non-cooperative game by using mixed strategies. We are particularly interested in studyig the relation between Nash equilibrium and the winner strategy of a given model with mobility, and how the mobility can affect the results. The experiments show that mobility is an important variable concerning spatial games. When we change parameters that affect mobility, it may lead to the success of strategies away from Nash equilibrium.Spatial Games, Agent-Based Modelling, Mobility, Satisfaction, Chicken Game, Nash Equilibrium
Correlation Functions of Huge Operators in AdS/CFT: Domes, Doors and Book Pages
We describe solutions of asymptotically AdS Einstein gravity that are
sourced by the insertion of operators in the boundary CFT, whose dimension
scales with the central charge of the theory. Previously, we found that the
geometry corresponding to a black hole two-point function is simply related to
an infinite covering of the Euclidean BTZ black hole. However, here we find
that the geometry sourced by the presence of a third black hole operator turns
out to be a Euclidean wormhole with two asymptotic boundaries. We construct
this new geometry as a quotient of empty AdS realized by domes and doors.
The doors give access to the infinite covers that are needed to describe the
insertion of the operators, while the domes describe the fundamental domains of
the quotient on each cover. In particular, despite the standard fact that the
Fefferman-Graham expansion is single-sided, the extended bulk geometry contains
a wormhole that connects two asymptotic boundaries. We observe that the
two-sided wormhole can be made single-sided by cutting off the wormhole and
gluing on a "Lorentzian cap". In this way, the geometry gives the holographic
description of a three-point function, up to phases. By rewriting the metric in
terms of a Liouville field, we compute the on-shell action and find that the
result matches with the Heavy-Heavy-Heavy three-point function predicted by the
modular bootstrap. Finally, we describe the geometric transition between doors
and defects, that is, when one or more dual operators describe a conical defect
insertion, rather than a black hole insertion.Comment: 45 pages, 21 figure
Holography and Correlation Functions of Huge Operators: Spacetime Bananas
We initiate the study of holographic correlators for operators whose
dimension scales with the central charge of the CFT. Differently from light
correlators or probes, the insertion of any such maximally heavy operator
changes the AdS metric, so that the correlator itself is dual to a backreacted
geometry with marked points at the Poincar\'e boundary. We illustrate this new
physics for two-point functions. Whereas the bulk description of light or probe
operators involves Witten diagrams or extremal surfaces in an AdS background,
the maximally heavy two-point functions are described by nontrivial new
geometries which we refer to as "spacetime bananas". As a universal example, we
discuss the two-point function of maximally heavy scalar operators described by
the Schwarzschild black hole in the bulk and we show that its onshell action
reproduces the expected CFT result. This computation is nonstandard, and adding
boundary terms to the action on the stretched horizon is crucial. Then, we
verify the conformal Ward Identity from the holographic stress tensor and
discuss important aspects of the Fefferman-Graham patch. Finally we study a
Heavy-Heavy-Light-Light correlator by using geodesics propagating in the banana
background. Our main motivation here is to set up the formalism to explore
possible universal results for three- and higher-point functions of maximally
heavy operators.Comment: 45 pages, 14 figure
O DESENVOLVIMENTO DAS PESQUISAS EM FĂSICA NO BRASIL NAS DĂCADAS DE 1940 E 1950 E AS CONSEQUĂNCIAS ADVINDAS PARA O ESTUDO EM FĂSICA DE CAMPOS
O estudo dos Campos Ă© um tema muito importante para a formação dos profissionais em FĂsica, visto que sĂŁo essas entidades fĂsicas as responsĂĄveis pela propagação das interaçÔes fundamentais.No Brasil as dĂ©cadas de 1940 e 1950 sĂŁo de extrema importĂąncia para o desenvolvimento e consolidação das Pesquisas em FĂsica do paĂs, sobre tudo o desenvolvimento os estudos das teorias da FĂsica de Campos.TambĂ©m nessa Ă©poca surgem no Brasil algumas instituiçÔes importantes para a FĂsica no Brasil, como o Centro Brasileiro de Pesquisas FĂsicas (CBPF) em 1949 e o Conselho Nacional de Pesquisas (CNPq).A intenção desse trabalho Ă© traçar quais as consequĂȘncias ao desenvolvimento as pesquisas no paĂs apĂłs os avanços realizados nessas dĂ©cadas
Study of the influence of countâs number in myocardium in the determination of reproducible functional parameters in Gated-SPECT studies simulated with GATE
Myocardial Perfusion Gated Single Photon Emission Tomography (Gated-SPET) imaging is used for the combined evaluation of myocardial perfusion and left ventricular (LV) function. But standard protocols of the
Gated-SPECT studies require long acquisition times for each study. It is therefore important to reduce as much as possible the total duration of image acquisition. However, it is known that this reduction leads to decrease on counts statistics per projection and raises doubts about the validity of the functional parameters determined by Gated-SPECT. Considering that, itâs difficult to carry out this analysis in
real patients. For ethical, logistical and economical matters, simulated studies could be required for this analysis. Objective: Evaluate the influence of the total number of counts acquired from myocardium, in the calculation of myocardial functional parameters (LVEF â left ventricular ejection
fraction, EDV â end-diastolic volume, ESV â end-sistolic volume) using routine software procedures
Going green and sustainable : The influence of green HR practices on the organizational rationale for sustainability
Organizations that go green need their employees to perceive that sustainability is a priority in order to increase pro-sustainability behavior. Several factors can influence how employees perceive their organizationâs com- mitment to sustainability; however, no research has yet explored how green human resource management can influence that perception. This study thus examines the role of green hiring, green training, and green com- pensation, along with age and gender, in sustaining the organizational rationale for sustainability (ORS). Results from a sample of 275 Portuguese employees, analysed through the fuzzy-set qualitative comparative analysis (fsQCA), shows that perceived ORS is mainly grounded in green hiring, and to a lesser extent, in green training. Green hiring is especially important for older employees, whereas younger employees require green training. Green compensation is surprisingly irrelevant. The study is useful for researchers and practitioners who seek to understand employeesâ perception about the value and priority their organizations give to sustainability.info:eu-repo/semantics/publishedVersio
Thertact-System: A Virtual Reality Exoskeleton Gait Training Simulator Controlled by Brain-Computer Interface
This paper presents a developerâs overview of the Thertact system that combines virtual reality, brain-computer-interface and thermal-tactile stimulation in a gait training simulator for a reha- bilitation protocol focused in promoting neurological recovery in spinal cord injured patients. We describe each part of the system, with special focus on aspects that have impact on the resulting overall sense of embodiment. The system comprises innovative aspects, such as the simulation of exoskeleton gait movement and thermal-tactile haptic feedback, and have shown promising results on a first case study with one patient in real hospital setting
The S-matrix bootstrap. Part I : QFT in AdS.
We propose a strategy to study massive Quantum Field Theory (QFT) using conformal bootstrap methods. The idea is to consider QFT in hyperbolic space and study correlation functions of its boundary operators. We show that these are solutions of the crossing equations in one lower dimension. By sending the curvature radius of the background hyperbolic space to infinity we expect to recover flat-space physics. We explain that this regime corresponds to large scaling dimensions of the boundary operators, and discuss how to obtain the flat-space scattering amplitudes from the corresponding limit of the boundary correlators. We implement this strategy to obtain universal bounds on the strength of cubic couplings in 2D flat-space QFTs using 1D conformal bootstrap techniques. Our numerical results match precisely the analytic bounds obtained in our companion paper using S-matrix bootstrap techniques
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