We present the general analytical solution of the Riemann problem (decay of a jump discontinuity) for non-convex relativistic hydrodynamics. In convex dynamics, an elementary nonlinear wave, i.e. a ...rarefaction or a shock, originates at the discontinuity and travels towards one of the initial states. Between the left and right waves, an equilibrium state appears represented by a contact discontinuity. The exact solution to the Riemann problem in convex relativistic hydrodynamics was first addressed by Martí & Müller (J. Fluid Mech., vol. 258, 1994, pp. 317–333). In non-convex dynamics, two sequences of elementary nonlinear waves move towards the left and right initial states. Solving the Riemann problem involves determining the types of wave developing and the equilibrium state where they coincide. The procedure consists of constructing the wave curves associated with the nonlinear waves in the pressure–velocity phase space, where the intersection of the wave curves indicates the equilibrium state. We describe the relation between the wave curves, the explicit formulas for their calculation, and the outline of the process for a correct derivation and representation of the waves in the spatial domain. We present examples of the exact solution of a Riemann problem that illustrate the complex phenomena of non-convex dynamics by using the phenomenological non-convex equation of state proposed by Ibáñez et al. (Mon. Not. R. Astron. Soc., vol. 476, 2017, pp. 1100–1110).
The impact of coffee on health Cano-Marquina, A; Tarín, J.J; Cano, A
Maturitas,
05/2013, Letnik:
75, Številka:
1
Journal Article
Recenzirano
Abstract Objective Coffee is a beverage used worldwide. It includes a wide array of components that can have potential implication on health. We have reviewed publications on the impact of coffee on ...a series of health outcomes. Methods Articles published between January 1990 and December 2012 were selected after crossing coffee or caffeine with a list of keywords representative of the most relevant health areas potentially affected by coffee intake. Results Caffeine, chlorogenic acids and diterpenes are important components of coffee. Tolerance often acts as a modulator of the biological actions of coffee. There is a significant impact of coffee on the cardiovascular system, and on the metabolism of carbohydrates and lipids. Contrary to previous beliefs, the various forms of arterial cardiovascular disease, arrhythmia or heart insufficiency seem unaffected by coffee intake. Coffee is associated with a reduction in the incidence of diabetes and liver disease. Protection seems to exist also for Parkinson's disease among the neurological disorders, while its potential as an osteoporosis risk factor is under debate. Its effect on cancer risk depends on the tissue concerned, although it appears to favor risk reduction. Coffee consumption seems to reduce mortality. Conclusion The information gathered in recent years has generated a new concept of coffee, one which does not match the common belief that coffee is mostly harmful. This view is further supported by the discovery of a series of phyto-components with a beneficial profile. Reasonable optimism needs to be tempered, however, by the insufficiency of the clinical data, which in most cases stem from observational studies.
Abstract
The non-monotonicity of the local speed of sound in dense matter at baryon number densities much higher than the nuclear saturation density (n0 ≈ 0.16 fm−3) suggests the possible existence ...of a non-convex thermodynamics which will lead to a non-convex dynamics. Here, we explore the rich and complex dynamics that an equation of state (EoS) with non-convex regions in the pressure–density plane may develop as a result of genuinely relativistic effects, without a classical counterpart. To this end, we have introduced a phenomenological EoS, the parameters of which can be restricted owing to causality and thermodynamic stability constraints. This EoS can be regarded as a toy model with which we may mimic realistic (and far more complex) EoSs of practical use in the realm of relativistic hydrodynamics.
The novel disease produced by SARS-CoV-2 mainly harms the respiratory tract, but it has shown the capacity to affect multiple organs. Epidemiologic evidence supports the relationship between ...Coronavirus Disease 2019 (COVID-19) and pancreatic and hepatic injury development, identified by alterations in these organ function markers. In this regard, it is important to ascertain how the current prevalence of non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH) might affect COVID-19 evolution and complications. Although it is not clear how SARS-CoV-2 affects both the pancreas and the liver, a multiplicity of potential pathophysiological mechanisms seem to be implicated; among them, a direct viral-induced injury to the organ involving liver and pancreas ACE2 expression. Additionally, immune system dysregulation, coagulopathies, and drugs used to treat the disease could be key for developing complications associated with the patient's clinical decline. This review aims to provide an overview of the available epidemiologic evidence regarding developing liver and pancreatic alterations in patients with COVID-19, as well as the possible role that NAFLD/NASH might play in the pathophysiological mechanisms underlying some of the complications associated with COVID-19. This review employed a comprehensive search on PubMed using relevant keywords and filters. From the initial 126 articles, those aligning with the research target were selected and evaluated for their methodologies, findings, and conclusions. It sheds light on the potential pathophysiological mechanisms underlying this relationship. As a result, it emphasises the importance of monitoring pancreatic and hepatic function in individuals affected by COVID-19.
The total variation (TV) denoising method is a PDE-based technique that preserves edges well but has the sometimes undesirable staircase effect, namely, the transformation of smooth regions ( ramps) ...into piecewise constant regions ( stairs). In this paper we present an improved model, constructed by adding a nonlinear fourth order diffusive term to the Euler--Lagrange equations of the variational TV model. Our technique substantially reduces the staircase effect, while preserving sharp jump discontinuities (edges). We show numerical evidence of the power of resolution of this novel model with respect to the TV model in some 1D and 2D numerical examples.
The characterization of zinc oxide (ZnO) films, developed by a home-built chemical vapor deposition (CVD) system, working as an active layer for a
n
-channel depletion mode ...pseudo-metal-oxide-semiconductor field-effect transistor (MOSFET) is reported. A factorial experimental design was applied to analyze the behavior of the structural, optical, and morphological properties of the ZnO semiconductor. To study the behavior of the assembled equipment, the main parameters of substrate temperature, oxygen flow, and chamber pressure were varied at two levels. The ZnO films were studied by means of the characterization techniques of scanning electron microscopy (SEM), x-ray diffraction (XRD), Raman spectroscopy, photoluminescence, and cathodoluminescence. SEM images showed that the submicrometric ZnO morphologies were obtained from the interaction of the three growth parameters. XRD analysis exhibited an hexagonal wurtzite structure without the presence of other crystalline phases. The Raman response was analyzed according to the dependence of the oxygen flow, temperature, and growth pressure. The emission obtained under ultraviolet laser excitation showed two strong emissions, at 487 nm and 514 nm. In comparison, cathodoluminescence spectra of the ZnO samples exhibited a dominant transition centered at 380 nm. According to the results of the factorial design, one ZnO sample was selected as the active layer for the development of a pseudo-field effect transistor. The transfer and output characteristics of the device were used to study the threshold voltage, carrier mobility, and transconductance behavior. As a result, this work provides an alternative pathway to the fabrication of a
n
-channel depletion mode ZnO pseudo-transistor using a low-cost and home-built CVD system.
In this study, solid particle erosion tests were carried out to evaluate the performance of AISI 304, 316 and 420 stainless steels in relation to this wear process. These materials have several ...industrial applications such as turbine blades, valves, hard tools, fasteners, piping, storage tanks, water components, food processing equipment, etc. An erosion test rig similar to that shown in ASTM G76-95 standard was used to perform the tests. The abrasive particle used was angular silicon carbide (SiC) with a particle size of 420–450μm. Tests were carried out using different impact angles (30°, 45°, 60° and 90°) with a particle velocity of 24±2m/s and an abrasive flow rate of 150±0.5g/min. The room temperature during the tests was between 35°C to 40°C. The chemical composition of the tested materials was obtained by using energy dispersive X-ray analysis (EDS). In addition, SEM images were used to identify the wear mechanisms. In this particular case, wear damage similar to brittle fracture with the detachment of large fragments was observed on the surfaces of AISI 304 and 316 stainless steels. Plastic deformation characterised by pitting and cutting action was also observed. In respect to AISI 420, it was only damaged by plastic deformation, with pitting and ploughing action, some random scratches and irregular indentations on its surface for all impact angles. The results showed that AISI 304 and 316 presented a higher erosion rate at 60°, whereas AISI 420 exhibited the higher erosion damage at 30°. Finally, Atomic Force Microscopy (AFM) was used to compare the roughness of the surfaces before and after the tests at 30° and 90°, respectively.
Heterojunctions made of
n
-type cadmium sulfide (CdS) and
p
-type zinc telluride (ZnTe) thin films with rectifying behavior have been developed using an
in situ
approach based on pulsed laser ...deposition (PLD). The structure of the CdS and ZnTe thin films was observed by x-ray diffraction (XRD) analysis. Optical and electrical characterization of the semiconductor films and fabricated diodes is also reported herein. For this purpose, a set of CdS/ZnTe diodes was fabricated with circular gold contacts of varying diameters from 100
µ
m to 300
µ
m. The carrier concentrations of the semiconductor layers were determined using a Hall-effect measurement system, yielding values of 5.26 × 10
18
cm
−3
and 3.5 × 10
13
cm
−3
for CdS and ZnTe, respectively. Current–voltage (
I
–
V
) characteristic curves were used to observe the typical rectifier behavior over three orders of magnification. In addition, other parameters were obtained from the
I
–
V
curves, such as the density current, saturation current, series resistance, threshold voltage, and ideality factor. Also, capacitance–voltage (
C
–
V
) characteristic curves allowed the determination of the following parameters: depletion width, built-in voltage, and donor concentration. According to the results, such
n
-type CdS/
p
-type ZnTe heterojunctions with rectifying behavior could find potential applications in the development of photodetectors by modifying the difference in carrier concentration between the two materials.
•A microwave photonic filter that allows the generation of passband windows.•Bandwidth adjustment is controlled by using tunable optical bandpass filters.•Two approaches to demonstrate the adjusting ...of the bandwidth were described.•This proposal was achieved simultaneously for two passband microwave signals.
We propose a straightforward technique that allows adjusting the bandwidth of microwave filtered signals by using two tunable optical bandpass filters. The principle of operation of the microwave photonic filter that allows the generation of passband windows is described by a full mathematical analysis. The electrical bandwidth of each generated passband window is adjusted by optically filtering a multimode laser diode. We demonstrate that the proposed filter can generate passband windows located at 4.87 GHz and 9.63 GHz exhibiting a bandwidth of 284.54 MHz and 391.24 MHz, respectively. The electrical bandwidth of each passband window can be increased to a maximum value of 1000 MHz by means of an adequate adjustment of the optical bandwidth from 2 nm to 10 nm approximately. A potential application of this proposal resides in the fact that the microwave filtered signals can be used as electrical carriers in optical communication schemes taking advantage of the electrical bandwidth that can be tailored according to a data transmission.
In this work, ZnTe and ZnTe:Cu films were obtained by pulsed laser deposition using the co-deposition method. ZnTe and Cu
2
Te were used as targets and the shots ratio were varied to obtain 0.61, ...1.47, 1.72, and 3.46% Cu concentration. Doping of ZnTe films with Cu was performed with the purpose of increasing the p-type carrier concentration and establishing the effect of concentration of Cu on structural, optical, and electrical properties of ZnTe thin films to consider their potential application in electronic devices. According to X-ray diffraction, X-ray photoelectron spectroscopy, UV–visible spectroscopy, and Hall effect results, ZnTe and ZnTe:Cu films correspond to polycrystalline zinc–blende phase with preferential orientation in (111) plane. Optical characterization results indicate that as-deposited films (band gap = 2.16 eV) exhibit a band gap decrease as function of the increase of Cu concentration (2.09–1.64 eV), while, annealed films exhibit a decrease from 1.75 to 1.46 eV, as the Cu concentration increases. Lastly, Hall effect results show that ZnTe films correspond to a p-type semiconductor with a carrier concentration of 3 × 10
13
cm
−3
and a resistivity of 1.64 × 10
5
Ω∙cm. ZnTe:Cu films remain like a p-type material and present an increasing carrier concentration (from 3.8 × 10
15
to 1.26 × 10
19
cm
−3
) as function of Cu concentration and a decreasing resistivity (from 7.01 × 103 to 2.6 × 10
−1
Ω cm). ZnTe and ZnTe:Cu thin films, with the aforementioned characteristics, can find potential application in electronic devices, such as, solar cells and photodetectors.
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