On the stability of the shear-free condition

The evolution equation for the shear is reobtained for a spherically symmetric anisotropic, viscous dissipative fluid distribution, which allows us to investigate conditions for the stability of the shear-free condition. The specific case of geodesic fluids is considered in detail, showing that the shear-free condition, in this particular case, may be unstable, the departure from the shear-free condition being controlled by the expansion scalar and a single scalar function defined in terms of the anisotropy of the pressure, the shear viscosity and the Weyl tensor or, alternatively, in terms of the anisotropy of the pressure, the dissipative variables and the energy density inhomogeneity.Comment: 19 pages Latex. To appear in Gen. Rel. Gra

Dissipative fluids out of hydrostatic equilibrium

In the context of the M\"{u}ller-Israel-Stewart second order phenomenological theory for dissipative fluids, we analyze the effects of thermal conduction and viscosity in a relativistic fluid, just after its departure from hydrostatic equilibrium, on a time scale of the order of relaxation times. Stability and causality conditions are contrasted with conditions for which the ''effective inertial mass'' vanishes.Comment: 21 pages, 1 postscript figure (LaTex 2.09 and epsfig.sty required) Submitted to Classical and Quantum Gravit

Some analytical models of radiating collapsing spheres

We present some analytical solutions to the Einstein equations, describing radiating collapsing spheres in the diffusion approximation. Solutions allow for modeling physical reasonable situations. The temperature is calculated for each solution, using a hyperbolic transport equation, which permits to exhibit the influence of relaxational effects on the dynamics of the system.Comment: 17 pages Late

Proximal, Microbiological and Color Evaluation and Comparison of the Meat of Llamas (Lama glama) and Alpacas (Vicugna pacos)

In this study, the meat of llama (Lama glama) and alpaca (Vicugna pacos) were examined. Data were analyzed through the analysis of variance (ANOVA) using the Centurion Statgraphics software. The bromatological characteristics of the meat were evaluated through proximal analysis. A high percentage of protein content was identified, with a higher value in the llama meat (24.025%). Regarding the ethereal extract, minimum values ​​were obtained in the alpaca meat (2.707%), indicating lean meat. The humidity was variable depending on the conditions of the conservation, and the organic matter present in the meat defined the ash content, which was not higher than 5%. In terms of the microbiological analyses, the value ​​of viable aereobic mesophiles in llama meat was 1330 cfu/g, and in alpaca meat it was 1490 cfu/g; and the values for E. coli were 0.500 cfu/g and 1,250 cfu/g, respectively. Keywords: software, Lama glama, Vicugna pacos, proximal analysis, microbiological requirements. RESUMEN La carne de Llama (Lama glama) y Alpaca (Vicugna pacos) cumple con los requisitos para ser considerada como carne; Mediante el análisis de varianza (ANOVA) utilizando el Software Statgraphics Centurion se evalúa los requisitos bromatológicos por medio del análisis proximal de las carnes en estudio, donde se identifica un alto porcentaje en el contenido de proteína, lo que conlleva a un elevado valor biológico en ambas especies, siendo más destacada, en la carne de llama con 24,025%; En cuanto a extracto etéreo  se obtiene valores mínimos en especial en la carne de alpaca con 2,707%, favoreciendo a la obtención de carne magra; En lo referente a humedad va a ser variable dependiendo de las condiciones de conservación de la misma, mientras tanto la materia orgánica presente en la carne define el contenido de cenizas, el cual no podrá ser mayor al 5%. En relación a los análisis microbiológicos los valores de Mesófilos Aereobios Viables en la carne de llama fueron 1330 ufc/g, en la carne de alpaca 1490 ufc/g, para E. Coli  de 0,500 ufc/g, y 1,250 ufc/g respectivamente encontrándose dentro de lo establecido en la Norma, y valores no permisibles por la presencia de Coliformes Totales.    Palabras clave: software, Lama glama, Vicugna pacos, análisis proximal, requerimientos microbiológicos

Why hyperbolic theories of dissipation cannot be ignored: Comments on a paper by Kostadt and Liu

Contrary to what is asserted in a recent paper by Kostadt and Liu ("Causality and stability of the relativistic diffusion equation"), experiments can tell apart (and in fact do) hyperbolic theories from parabolic theories of dissipation. It is stressed that the existence of a non--negligible relaxation time does not imply for the system to be out of the hydrodynamic regime.Comment: 8 pages Latex, to appear in Phys.Rev.

Spanish radiographers’ concerns about the COVID-19 pandemic

Introduction: The current outbreak of COVID-19 has caused worldwide healthcare and social emergency in which healthcare professionals were under extreme work conditions while being fearful of becoming infected or spreading the disease to their relatives. The perceived threat of COVID-19 has the potential to cause severe psychological maladjustment. The aim of the study is to explore Spanish radiographers' concerns about the COVID-19 pandemic. Methods: This study was quantitative, observational and cross-sectional. The sample was made up of 546 radiographers working in Spain during the outbreak. The instrument used for analysis was an ad hoc questionnaire with socio-demographic questions and the questionnaire on perception of threat from COVID-19 validate to spanish healthcare professionals. Results: The sample consisted of 70.1% of female, 29.7% of male and 0.2% undeclare sex participants. The results showed a high level of a perceived threat from COVID-19 (7.57 ± 0.088), furthermore we observed a high level of threat about the possibility of infecting family members (8.49 ± 0.25), patients (8.33 ± 0.086), and coworkers (8.35 ± 0.084). Furthermore, females have a higher level of a perception of threat to spread infection between patients (r = -0.136; p = 0.001) and coworkers (r = -0.118; p = 0.006), than males. Conclusion: COVID-19 pandemic is perceived as a serious threat, being especially concerned about the threat of spreading the infection to family, coworkers, and patients. The perception of risk depends partly on professionals' gender and family responsibilities. Implications for practice: Our findings suggest that it is recommended that healthcare professionals receive formation to reinforce and improve their emotional competencies for coping successfully with potentially stressful situations like COVI19 pandemic