Gravitational Collapse of Self-Similar and Shear-free Fluid with Heat Flow

A class of solutions to Einstein field equations is studied, which represents gravitational collapse of thick spherical shells made of self-similar and shear-free fluid with heat flow. It is shown that such shells satisfy all the energy conditions, and the corresponding collapse always forms naked singularities.Comment: 34 pages, 9 figures, late

Online Construction of Wavelet Trees

The wavelet tree (WT) is a flexible and efficient data structure for representing character strings in succinct space, while allowing for fast generalised rank, select and access operations. As such, they play an important role in modern text indexing methods. However, despite their popularity, not many algorithms have been published concerning their construction. In particular, while the WT is capable of representing a sequence of length n over an alphabet of size m in nlg m+o(nlg m) bits, much more space is typically used for its construction. Here we propose an O(nlg m)-time online method for the construction of the WT, requiring no prior knowledge about the input alphabet. The proposed algorithm is conceptually simpler than other state-of-the-art methods, while having comparable time performance and being more space-efficient in practice, since it performs just one pass over the input text and uses little extra space other than for the structure itself, as shown both theoretically and empirically

Identificación de áreas desertificadas y preservadas en una unidad de conservación en el Estado de Paraíba - Brasil

The objective of this study is to identify and analyse the main characteristics of areas potentially degraded by desertification and of preserved areas using the Soil Surface Moisture Index (SSMI), alongside the Land Surface Temperature (LST) and Normalized Difference Vegetation Index (NDVI). The study is based on a set of points obtained in the field and from the RGB false colour image for the Environmental Protection Areas (EPA) of the Cariri, in the semi-arid region of Paraíba, using a space-time cross-section covering both rainy and dry periods. The results showed that at all points in Desertified Areas, the main characteristics were a low SSMI, high LST and low NDVI in both periods. The Preserved Areas, on the other hand, presented a high SSMI, moderate LST and high NDVI in the rainy period, with the same characteristics repeated in the dry period for SSMI and NDVI, but with a low LST. Timely identification of these characteristics, both in areas degraded by desertification and in better preserved areas, can provide useful information for future decisions relating to the physical and territorial management of the Conservation Unit.El objetivo de este estudio fue identificar y analizar las principales características de áreas potencialmente degradadas por desertificación y de áreas preservadas. Para ello se utilizaron el Índice de Humedad Superficial del Suelo (IHSS), junto con la Temperatura de la Superficie de la Tierra (TS) y el Índice de Vegetación de Diferencia Normalizada (IVDN). El estudio está basado en un conjunto de puntos obtenidos en el campo y en la composición de la imagen de falso color RGB para el Área de Protección Ambiental (APA) del Carirí, en la región semiárida de Paraíba, utilizando un corte espacio-temporal que abarca la estación lluviosa y seca. Los resultados mostraron que en todos los puntos de las Áreas Desertificadas las principales características fueron el IHSS bajo, TS alto y IVDN bajo en ambos períodos. Las Áreas Preservadas, por su parte, presentaron IHSS alto, TS moderado e IVDN alto en la época de lluvias, con las mismas características repetidas en el periodo seco para IHSS y IVDN, pero con TS bajo. La identificación puntual de estas características, tanto en áreas degradadas por desertificación como en las más conservadas, puede aportar información útil para la toma de decisiones futuras relacionadas con la gestión territorial y física de la Unidad de Conservación

Multiple Photonic Shells Around a Line Singularity

Line singularities including cosmic strings may be screened by photonic shells until they appear as a planar wall.Comment: 6 page

Linear decomposition of approximate multi-controlled single qubit gates

We provide a method for compiling approximate multi-controlled single qubit gates into quantum circuits without ancilla qubits. The total number of elementary gates to decompose an n-qubit multi-controlled gate is proportional to 32n, and the previous best approximate approach without auxiliary qubits requires 32nk elementary operations, where k is a function that depends on the error threshold. The proposed decomposition depends on an optimization technique that minimizes the CNOT gate count for multi-target and multi-controlled CNOT and SU(2) gates. Computational experiments show the reduction in the number of CNOT gates to apply multi-controlled U(2) gates. As multi-controlled single-qubit gates serve as fundamental components of quantum algorithms, the proposed decomposition offers a comprehensive solution that can significantly decrease the count of elementary operations employed in quantum computing applications

On parameters of the Levi-Civita solution

The Levi-Civita (LC) solution is matched to a cylindrical shell of an anisotropic fluid. The fluid satisfies the energy conditions when the mass parameter $\sigma$ is in the range $0 \le \sigma \le 1$. The mass per unit length of the shell is given explicitly in terms of $\sigma$, which has a finite maximum. The relevance of the results to the non-existence of horizons in the LC solution and to gauge cosmic strings is pointed out.Comment: Latex, no figure

Levi-Civita Solutions Coupled with Electromagnetic Fields

The local and global properties of the Levi-Civita (LC) solutions coupled with an electromagnetic field are studied and some limits to the vacuum LC solutions are given. By doing such limits, the physical and geometrical interpretations of the free parameters involved in the solutions are made clear. Sources for both the LC vacuum solutions and the LC solutions coupled with an electromagnetic field are studied, and in particular it is found that all the LC vacuum solutions with $\sigma \ge 0$ can be produced by cylindrically symmetric thin shells that satisfy all the energy conditions, weak, dominant, and strong. When the electromagnetic field is present, the situation changes dramatically. In the case of a purely magnetic field, all the solutions with $\sigma \ge 1/\sqrt{8}$ or $\sigma \le - 1/\sqrt{8}$ can be produced by physically acceptable cylindrical thin shells, while in the case of a purely electric field, no such shells are found for any value of $\sigma$.Comment: Typed in Revtex, including two figure

Temperature Evolution Law of Imperfect Relativistic Fluids

The first-order general relativistic theory of a generic dissipative (heat-conducting, viscous, particle-creating) fluid is rediscussed from a unified covariant frame-independent point of view. By generalizing some previous works in the literature, we derive a formula for the temperature variation rate, which is valid both in Eckart's (particle) and in the Landau-Lifshitz (energy) frames. Particular attention is paid to the case of gravitational particle creation and its possible cross-effect with the bulk viscosity mechanism.Comment: 14 pages, no figure, revte

ABC 2 -SPH risk score for in-hospital mortality in COVID-19 patients: development, external validation and comparison with other available scores

Coronavirus SARS-CoV-2; COVID-19; 2019-nCoV; Hospitalitzacions; MortalitatCoronavirus SARS-CoV-2; COVID-19; 2019-nCoV; Hospitalizaciones; MortalidadCoronavirus SARS-CoV-2; COVID-19; 2019-nCoV; Hospitalizations; MortalityObjectives The majority of available scores to assess mortality risk of coronavirus disease 2019 (COVID-19) patients in the emergency department have high risk of bias. Therefore, this cohort aimed to develop and validate a score at hospital admission for predicting in-hospital mortality in COVID-19 patients and to compare this score with other existing ones. Methods Consecutive patients (≥ 18 years) with confirmed COVID-19 admitted to the participating hospitals were included. Logistic regression analysis was performed to develop a prediction model for in-hospital mortality, based on the 3978 patients admitted between March–July, 2020. The model was validated in the 1054 patients admitted during August–September, as well as in an external cohort of 474 Spanish patients. Results Median (25–75th percentile) age of the model-derivation cohort was 60 (48–72) years, and in-hospital mortality was 20.3%. The validation cohorts had similar age distribution and in-hospital mortality. Seven significant variables were included in the risk score: age, blood urea nitrogen, number of comorbidities, C-reactive protein, SpO 2 /FiO 2 ratio, platelet count, and heart rate. The model had high discriminatory value (AUROC 0.844, 95% CI 0.829–0.859), which was confirmed in the Brazilian (0.859 [95% CI 0.833–0.885]) and Spanish (0.894 [95% CI 0.870–0.919]) validation cohorts, and displayed better discrimination ability than other existing scores. It is implemented in a freely available online risk calculator (https://abc2sph.com/). Conclusions An easy-to-use rapid scoring system based on characteristics of COVID-19 patients commonly available at hospital presentation was designed and validated for early stratification of in-hospital mortality risk of patients with COVID-19.This study was supported in part by Minas Gerais State Agency for Research and Development ( Fundação de Amparo à Pesquisa do Estado de Minas Gerais – FAPEMIG ) [grant number APQ-00208-20], National Institute of Science and Technology for Health Technology Assessment ( Instituto de Avaliação de Tecnologias em Saúde – IATS )/ National Council for Scientific and Technological Development ( Conselho Nacional de Desenvolvimento Científico e Tecnológico – CNPq ) [grant number 465518/2014-1], and CAPES Foundation ( Coordenação de Aperfeiçoamento de Pessoal de Nível Superior ) [grant number 88887.507149/2020-00]. AS was supported by a postdoctoral grant “Juan Rodés” (JE18/00022) from Instituto de Salud Carlos III through the Ministry of Economy and Competitiveness, Spain