A novel design of a grating-based optical pulse compressor is proposed. The proposed compressor provides a large group delay dispersion while keeping the compressor linear size small. The design of ...the proposed compressor is based on a traditional Treacy compressor with a straightforward modification of inserting two lenses between the compressor’s gratings. This simple alternation aims to substantially increase group delay dispersion of the compressor or alternatively to decrease the compressor size while maintaining its group delay dispersion. A theoretical description of the enhanced compressor has been developed in the paraxial approximation. A detailed numerical model has been built to calculate the compressor parameters more accurately. These theoretical studies have revealed that the enhanced optical compressor provides a significant increase in the group delay dispersion compared to a standard Treacy compressor.
A simple classification is given of the anisotropic relativistic star models, resembling the one of charged isotropic solutions. On the ground of this database, and taking into account the conditions ...for physically realistic star models, a method is proposed for generating all such solutions. It is based on the energy density and the radial pressure as seeding functions. Numerous relations between the realistic conditions are found and the need for a graphic proof is reduced just to one pair of inequalities. This general formalism is illustrated with an example of a class of solutions with linear equation of state and simple energy density. It is found that the solutions depend on three free constants and concrete examples are given. Some other popular models are studied with the same method.
A physically realistic stellar model with a simple expression for the energy density and conformally flat interior is found. The relations between the different conditions are used without graphic ...proofs. It may represent a real pulsar.
It is shown that the expressions for the tangential pressure, the anisotropy factor and the radial pressure in the Einstein–Maxwell equations may serve as generating functions for charged stellar ...models. The latter can incorporate an equation of state when the expression for the energy density is also used. Other generating functions are based on the condition for the existence of conformal motion (conformal flatness in particular) and the Karmarkar condition for embedding class one metrics, which do not depend on charge. In all these cases the equations are linear first order differential equations for one of the metric components and Riccati equations for the other. The latter may be always transformed into second order homogenous linear differential equations. These conclusions are illustrated by numerous particular examples from the study of charged stellar models.
Respiratory viruses cause infections of the upper or lower respiratory tract and they are responsible for the common cold-the most prevalent disease in the world. In many cases the common cold ...results in severe illness due to complications, such as fever or pneumonia. Children, old people, and immunosuppressed patients are at the highest risk and require fast diagnosis and therapeutic intervention. However, the availability and efficiencies of existing therapeutic approaches vary depending on the virus. Investigation of the pathologies that are associated with infection by respiratory viruses will be paramount for diagnosis, treatment modalities, and the development of new therapies. Changes in redox homeostasis in infected cells are one of the key events that is linked to infection with respiratory viruses and linked to inflammation and subsequent tissue damage. Our review summarizes current knowledge on changes to redox homeostasis, as induced by the different respiratory viruses.
Liver fibrosis is a regenerative process that occurs after injury. It is characterized by the deposition of connective tissue by specialized fibroblasts and concomitant proliferative responses. ...Chronic damage that stimulates fibrogenic processes in the long-term may result in the deposition of excess matrix tissue and impairment of liver functions. End-stage fibrosis is referred to as cirrhosis and predisposes strongly to the loss of liver functions (decompensation) and hepatocellular carcinoma. Liver fibrosis is a pathology common to a number of different chronic liver diseases, including alcoholic liver disease, non-alcoholic fatty liver disease, and viral hepatitis. The predominant cell type responsible for fibrogenesis is hepatic stellate cells (HSCs). In response to inflammatory stimuli or hepatocyte death, HSCs undergo trans-differentiation to myofibroblast-like cells. Recent evidence shows that metabolic alterations in HSCs are important for the trans-differentiation process and thus offer new possibilities for therapeutic interventions. The aim of this review is to summarize current knowledge of the metabolic changes that occur during HSC activation with a particular focus on the retinol and lipid metabolism, the central carbon metabolism, and associated redox or stress-related signaling pathways.
In this paper we give a generating function for solutions of the type of collapse mentioned in the title. It satisfies a simple Riccati equation, derived from a formula, which holds in the interior ...of the star. The generating function is unique, unlike in the neutral case. Every neutral solution has a charged companion with the same generating function. The charged solution has bigger radius, surface redshift, mass and compactness than the neutral one. Its rate of collapse is slower. A class of known exact neutral solutions, containing generalised travelling waves, is charged.
On general spherical fluid collapse Ivanov, B. V.
European physical journal. C, Particles and fields,
06/2019, Volume:
79, Issue:
6
Journal Article
Peer reviewed
Open access
A rather general form of spherical fluid collapse is formulated. The fluid is anisotropic, has shear, bulk and shear viscosities and is charged. It radiates energy through a heat flow or null ...radiation. The exterior solution is the charged Vaidya shining star solution. The general junction conditions are given. The main one represents a Riccati equation for the horizon function. We present a simple neutral solution, where the equation becomes a linear one. The whole mass of the star is radiated away without a remnant and the result is flat spacetime.
Arctic sea-ice loss is a leading indicator of climate change and can be attributed, in large part, to atmospheric forcing. Here, we show that recent ice reductions, weakening of the halocline, and ...shoaling of the intermediate-depth Atlantic Water layer in the eastern Eurasian Basin have increased winter ventilation in the ocean interior, making this region structurally similar to that of the western Eurasian Basin. The associated enhanced release of oceanic heat has reduced winter sea-ice formation at a rate now comparable to losses from atmospheric thermodynamic forcing, thus explaining the recent reduction in sea-ice cover in the eastern Eurasian Basin. This encroaching “atlantification” of the Eurasian Basin represents an essential step toward a new Arctic climate state, with a substantially greater role for Atlantic inflows.
Visible light synchronizes the human biological clock in the suprachiasmatic nuclei of the hypothalamus to the solar 24‐hour cycle. Short wavelengths, perceived as blue color, are the strongest ...synchronizing agent for the circadian system that keeps most biological and psychological rhythms internally synchronized. Circadian rhythm is important for optimum function of organisms and circadian sleep–wake disruptions or chronic misalignment often may lead to psychiatric and neurodegenerative illness. The beneficial effect on circadian synchronization, sleep quality, mood, and cognitive performance depends not only on the light spectral composition but also on the timing of exposure and its intensity. Exposure to blue light during the day is important to suppress melatonin secretion, the hormone that is produced by the pineal gland and plays crucial role in circadian rhythm entrainment. While the exposure to blue is important for keeping organism's wellbeing, alertness, and cognitive performance during the day, chronic exposure to low‐intensity blue light directly before bedtime, may have serious implications on sleep quality, circadian phase and cycle durations. This rises inevitably the need for solutions to improve wellbeing, alertness, and cognitive performance in today's modern society where exposure to blue light emitting devices is ever increasing.
Light is playing an important role beyond vision. The review summarizes the current and most recent knowledge on the role of light around 470 nm and its role in circadian rhythm. The circadian rhythm is essential for life. If it is not preserved, serious diseases might develop. Light and its role in synchronization, but also in disruption of the circadian rhythm is discussed.
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