638 research outputs found
Cybergeo and the Electronic Scientific Journals
International audienceThe purpose of this new topic is to bring elements of reflection on the contribution of the new technologies in the midst of the world of research, from the perspective of the distribution of scientific information as well as from the point of view of communication between the sciences. In this framework, we also wish to take stock of our experience in electronic publishing, and to undertake a comparative presentation
Evaluation Measures for Hierarchical Classification: a unified view and novel approaches
Hierarchical classification addresses the problem of classifying items into a
hierarchy of classes. An important issue in hierarchical classification is the
evaluation of different classification algorithms, which is complicated by the
hierarchical relations among the classes. Several evaluation measures have been
proposed for hierarchical classification using the hierarchy in different ways.
This paper studies the problem of evaluation in hierarchical classification by
analyzing and abstracting the key components of the existing performance
measures. It also proposes two alternative generic views of hierarchical
evaluation and introduces two corresponding novel measures. The proposed
measures, along with the state-of-the art ones, are empirically tested on three
large datasets from the domain of text classification. The empirical results
illustrate the undesirable behavior of existing approaches and how the proposed
methods overcome most of these methods across a range of cases.Comment: Submitted to journa
Quadratic-in-Spin Hamiltonian at from Scattering Amplitudes
We obtain the quadratic-in-spin terms of the conservative Hamiltonian
describing the interactions of a binary of spinning bodies in General
Relativity through and to all orders in velocity. Our
calculation extends a recently-introduced framework based on scattering
amplitudes and effective field theory to consider non-minimal coupling of the
spinning objects to gravity. At the order that we consider, we establish the
validity of the formula proposed in \cite{Bern:2020buy} that relates the
impulse and spin kick in a scattering event to the eikonal phase.Comment: 21 pages + references, 5 figures, 1 ancillary fil
Vision-Based Production of Personalized Video
In this paper we present a novel vision-based system for the automated production of personalised video souvenirs for visitors in leisure and cultural heritage venues. Visitors are visually identified and tracked through a camera network. The system produces a personalized DVD souvenir at the end of a visitorâs stay allowing visitors to relive their experiences. We analyze how we identify visitors by fusing facial and body features, how we track visitors, how the tracker recovers from failures due to occlusions, as well as how we annotate and compile the final product. Our experiments demonstrate the feasibility of the proposed approach
Consequences of patient position in the radiographic measurement of artificial disc replacement angles
Accurate clinical measurement of spinal range of motion (ROM) is essential in the evaluation of artificial disc performance. The effect of patient placement with respect to the X-ray beam source is yet to be reported and may be an influencing factor in radiographic artificial disc angle measurements. This study aims to evaluate how radiographic patient placement influences artificial disc angle measurements. An anatomically accurate synthetic L4-L5 motion segment was instrumented with an artificial disc and two pins. The instrumented motion segment was mounted onto a frame allowing for independent rotation and elevation while holding the artificial disc angle and anatomical position between L4 and L5 fixed. Analyses included descriptive statistics, evaluation of uncertainty, intra- and inter-observer, and a 2-way analysis of variance (ANOVA). The mean angle measurement range at the various positions was 1.26° for the pin, and 2.74° for the artificial disc endplates. The centered patient position had the highest inter- and intra-observer reliability. ANOVA results showed elevation effects to be statistically significant (P=0.021), and rotational effects to be extremely statistically significant (P<0.0001) for the pin angles. In terms of the mean artificial disc angle, however, the ANOVA showed a highly statistically significant interaction term (P=0.002). A significant difference was found in the angle measurements of a fixed artificial disc prosthesis based on a sample of patient radiographic placement positions. Since it is important to assess the success of an artificial disc replacement by evaluating the relatively small ROM present, it is crucial to aim at minimizing the error by placing the patient parallel to the plate with the beam centered not at the mid lumbar spine, but at the level of the arthroplasty, for both flexion and extension view
Incidence and management of pulmonary embolism following spinal surgery occurring while under chemical thromboprophylaxis
Patients undergoing spinal surgery are at risk of developing thromboembolic complications even though lower incidences have been reported as compared to joint arthroplasty surgery. Deep vein thrombosis (DVT) has been studied extensively in the context of spinal surgery but symptomatic pulmonary embolism (PE) has engaged less attention. We prospectively followed a consecutive cohort of 270 patients undergoing spinal surgery at a single institution. From these patients, only 26 were simple discectomies, while the largest proportion (226) was fusions. All patients received both low molecular weight heparin (LMWH) initiated after surgery and compressive stockings. PE was diagnosed with spiral chest CT. Six patients developed symptomatic PE, five during their hospital stay. In three of the six patients the embolic event occurred during the first 3 postoperative days. They were managed by the temporary insertion of an inferior vena cava (IVC) filter thus allowing for a delay in full-dose anticoagulation until removal of the filter. None of the PE patients suffered any bleeding complication as a result of the introduction of full anticoagulation. Two patients suffered postoperative haematomas, without development of neurological symptoms or signs, requiring emergency evacuation. The overall incidence of PE was 2.2% rising to 2.5% after exclusion of microdiscectomy cases. The incidence of PE was highest in anterior or combined thoracolumbar/lumbar procedures (4.2%). There is a large variation in the reported incidence of PE in the spinal literature. Results from the only study found in the literature specifically monitoring PE suggest an incidence of PE as high as 2.5%. Our study shows a similar incidence despite the use of LMWH. In the absence of randomized controlled trials (RCT) it is uncertain if this type of prophylaxis lowers the incidence of PE. However, other studies show that the morbidity of LMWH is very low. Since PE can be a life-threatening complication, LMWH may be a worthwhile option to consider for prophylaxis. RCTs are necessary in assessing the efficacy of DVT and PE prophylaxis in spinal patient
Gravitational Effective Field Theory Islands, Low-Spin Dominance, and the Four-Graviton Amplitude
We analyze constraints from perturbative unitarity and crossing on the
leading contributions of higher-dimension operators to the four-graviton
amplitude in four spacetime dimensions, including constraints that follow from
distinct helicity configurations. We focus on the leading-order effect due to
exchange by massive degrees of freedom which makes the amplitudes of interest
infrared finite. In particular, we place a bound on the coefficient of the
operator that corrects the graviton three-point amplitude in terms of the
coefficient. To test the constraints we obtain nontrivial effective
field-theory data by computing and taking the large-mass expansion of the
one-loop minimally-coupled four-graviton amplitude with massive particles up to
spin 2 circulating in the loop. Remarkably, we observe that the leading EFT
coefficients obtained from both string and one-loop field-theory amplitudes lie
in small islands. The shape and location of the islands can be derived from the
dispersive representation for the Wilson coefficients using crossing and
assuming that the lowest-spin spectral densities are the largest. Our analysis
suggests that the Wilson coefficients of weakly-coupled gravitational physical
theories are much more constrained than indicated by bounds arising from
dispersive considerations of scattering. The one-loop four-graviton
amplitudes used to obtain the EFT data are computed using modern amplitude
methods, including generalized unitarity, supersymmetric decompositions and the
double copy.Comment: 123 pages, 23 figure, 2 Mathematica ancillary file
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