The salient issues related to lightning protection of long wind-turbine blades are discussed in this paper. We show that the lightning protection of modern wind turbines presents a number of new ...challenges due to the geometrical, electrical, and mechanical particularities of the turbines. The risk assessment for the lightning-protection-system design is solely based today on downward flashes. We show in this paper that the majority of the strikes to modern turbines are expected to be upward lightning. Neglecting upward flashes, as implicitly done by the International Electrotechnical Commission, might result in an important underestimation of the actual number of strikes to a tall wind turbine. In addition, we show that the rotation of the blades may have a considerable influence on the number of strikes to modern wind turbines as these may be triggering their own lightning. Because wind turbines are tall structures, the lightning currents that are injected by return strokes into the turbines will be affected by reflections at the top, bottom, and junction of the blades with the static base of the turbine. This is of capital importance when calculating the protection of internal circuitry that may be affected by magnetically induced electromotive forces that depend directly on the characteristics of the current in the turbine. The presence of carbon-reinforced plastics (CRP) in the blades introduces a new set of problems to be dealt with in the design of the turbines' lightning protection system. One problem is the mechanical stress resulting from the energy dissipation in CRP laminates due to the circulation of eddy currents. We evaluate in this paper the dissipated energy and propose recommendations as to the number of down conductors and their orientation with respect to the CRP laminates so that the dissipated energy is minimized. It is also emphasized that the high static fields under thunderclouds might have an influence on the moving carbon-fiber parts. This issue needs to be addressed by lightning protection researchers and engineers. Representative full-scale blade tests are still complex because lightning currents from an impulse current generator are conditioned to the electrical characteristics of the element under test and return paths. It is therefore desirable to complement laboratory tests with theoretical and computer modeling for the estimation of fields, currents, and voltages within the blades.
Red supergiants are the most common final evolutionary stage of stars that have initial masses between 8 and 35 times that of the Sun
. During this stage, which lasts roughly 100,000 years
, red ...supergiants experience substantial mass loss. However, the mechanism for this mass loss is unknown
. Mass loss may affect the evolutionary path, collapse and future supernova light curve
of a red supergiant, and its ultimate fate as either a neutron star or a black hole
. From November 2019 to March 2020, Betelgeuse-the second-closest red supergiant to Earth (roughly 220 parsecs, or 724 light years, away)
-experienced a historic dimming of its visible brightness. Usually having an apparent magnitude between 0.1 and 1.0, its visual brightness decreased to 1.614 ± 0.008 magnitudes around 7-13 February 2020
-an event referred to as Betelgeuse's Great Dimming. Here we report high-angular-resolution observations showing that the southern hemisphere of Betelgeuse was ten times darker than usual in the visible spectrum during its Great Dimming. Observations and modelling support a scenario in which a dust clump formed recently in the vicinity of the star, owing to a local temperature decrease in a cool patch that appeared on the photosphere. The directly imaged brightness variations of Betelgeuse evolved on a timescale of weeks. Our findings suggest that a component of mass loss from red supergiants
is inhomogeneous, linked to a very contrasted and rapidly changing photosphere.
Full text
Available for:
GEOZS, IJS, IMTLJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK, ZAGLJ
Energy storage is a topic of great importance for the development of renewable energy, since it appears to be the only solution to the problem of intermittency of production, inherent to such ...technologies. In this paper, a new technology for energy storage, based on microwave-induced CO2 gasification of carbon materials is proposed. The tests carried out in this study on different carbon materials showed that charcoal consumes the least amount of energy. Two microwave heating mechanisms, a single-mode oven and a multimode device, were evaluated with the latter proving itself to be the more efficient in terms of energy consumption and recovery. The initial results obtained showed that this technology is able to achieve energy efficiencies of 45% at laboratory scale with every indication that these results can be improved upon to make this approach highly competitive against other energy storage technologies.
Full text
Available for:
GEOZS, IJS, IMTLJ, KISLJ, NUK, OILJ, SAZU, SBCE, UL, UM, UPCLJ, UPUK
Fossil Land Bermudez, A. J
The Kenyon review,
03/2023, Volume:
45, Issue:
2
Journal Article
All of this was underwater once. Nebraska is riddled with palaeoniscoid fishes and xenacanthid sharks. Chimaeroid scales and skeletons, petalodontoid teeth, violent and smooth, beneath all that ...grass. If you play the alphabet game along this route--west on Interstate 40, then north along 35 and 85--you thrive on the recurrence of antiques stores. Aside from license plates, they're almost the only way to get a q. In youth, Bermudez lived for these shops, mesmerized by the attempts at organization of so many disparate pieces of history, little tokens of this kitchen or that, gifts from people now dead to other people now dead, collectibles. If you've never been to one of these shops, the best and most overwhelming version is, by far, the antiques mall. These sprawling theme parks of antiquity are typically organized in long, narrow aisles lined with floor-to-ceiling glass cases stuffed as elegantly as possible with small trinkets, handwritten tags tethered to their hosts by strings.
Berries and red fruits are dietary sources of polyphenols with reported health benefits. As part of the diet, polyphenols are ingested as complex mixtures immersed in a food matrix which is digested ...in the gut. Epithelial cells lining the gut are regularly exposed to these digested mixtures. To understand the effects of dietary polyphenols on human gut health it is essential to determine their stability and fate in the lumen. In this work, we investigated the effects of an
in vitro gastric and pancreatic digestion on the stability and composition of the major polyphenols in chokeberry juice. Digestion was carried out with a mixture of pepsin-HCl for 2
h, followed by a 2
h incubation with pancreatin and bile salts at 37
°C with shaking, in the absence of light and under N
2. After digestion, the chokeberry samples were acidified, filtered and HPLC-DAD/HPLC–MS–MS analysed to determine the content of total soluble recovered phenolics. Gastric digestion had no substantial effect on any of the major phenolic compounds in chokeberry, namely anthocyanins, flavan-3-ols, flavonols and caffeic acid derivatives. However, these compounds were significantly altered during the pancreatic digestion and this effect was more marked for anthocyanins (approximately 43% was lost during the 2
h treatment with pancreatin). Flavonols and flavan-3-ols decreased by 26% and 19%, respectively. Neochlorogenic acid decreased by 28% whereas chlorogenic acid was increased by 24%.
In vitro digestion of standard phenolic compounds, representing each of the groups of phenolics in chokeberry, confirmed some of the observed changes. Interactions with the digestive enzymes were not responsible for the observed losses which were mostly due to the chemical conditions during pancreatic digestion. Our results, in accordance with previously published results, show that dietary polyphenols are highly sensitive to the mild alkaline conditions in the small intestine and that a good proportion of these compounds can be transformed into other unknown and/or undetected structural forms with different chemical properties and, consequently, different bioaccessibility, bioavailability and biological activity.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Family therapists know that clinical concerns are not separate from larger sociopolitical contexts. Attunement to clients’ sociocultural experience is foundational to good practice, yet few ...guidelines integrate attention to the larger societal processes or address social equity. The purpose of this article is to help therapists move from knowing about sociocontextual issues to doing socioculturally attuned practice. We offer an overarching framework that returns to Bateson and the roots of family therapy through a call for third order transformation. The approach is responsive to societal context and an analysis of power while working through enduring concepts of major family therapy models. Transtheoretical guidelines that can be integrated across practice models to promote third order change are illustrated with case examples.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, ODKLJ, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
17.
Scarring in Rough Rectangular Billiards Izrailev, Felix M; Luna-Acosta, German A; Mendez-Bermudez, J A
Entropy,
01/2023, Volume:
25, Issue:
2
Journal Article
Peer reviewed
Open access
We study the mechanism of scarring of eigenstates in rectangular billiards with slightly corrugated surfaces and show that it is very different from that known in Sinai and Bunimovich billiards. We ...demonstrate that there are two sets of scar states. One set is related to the bouncing ball trajectories in the configuration space of the corresponding classical billiard. A second set of scar-like states emerges in the momentum space, which originated from the plane-wave states of the unperturbed flat billiard. In the case of billiards with one rough surface, the numerical data demonstrate the repulsion of eigenstates from this surface. When two horizontal rough surfaces are considered, the repulsion effect is either enhanced or canceled depending on whether the rough profiles are symmetric or antisymmetric. The effect of repulsion is quite strong and influences the structure of all eigenstates, indicating that the symmetric properties of the rough profiles are important for the problem of scattering of electromagnetic (or electron) waves through quasi-one-dimensional waveguides. Our approach is based on the reduction of the model of one particle in the billiard with corrugated surfaces to a model of two artificial particles in the billiard with flat surfaces, however, with an effective interaction between these particles. As a result, the analysis is conducted in terms of a two-particle basis, and the roughness of the billiard boundaries is absorbed by a quite complicated potential.
Full text
Available for:
IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
18.
The Real India Bermudez, A. J
The Virginia quarterly review,
10/2022, Volume:
98, Issue:
3
Journal Article
Full text
Available for:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
► A Ni/γAl2O3 catalyst has been tested in the CO2 reforming of coke oven gas. ► Process occurs preferably through Reverse Water Gas Shift followed by steam reforming. ► Formation of Ni0 particles ...from a NiAl2O4 spinnel gave the catalyst great stability. ► Both organic and inorganic carbon deposits have been found in the spent catalyst.
The CO2 reforming of coke oven gases (COG) was carried out over a Ni/γAl2O3 catalyst in order to obtain a suitable syngas for methanol synthesis. The influence of different operating conditions, such as temperature and volumetric hourly space velocity (VHSV), was studied. It was found that the H2 present in the feed gas promotes the Reverse Water Gas Shift reaction (RWGS), which produces water. Nevertheless, the Ni/γAl2O3 catalyst showed a high selectivity to the CO2 reforming reaction and it was possible to avoid the RWGS under certain operating conditions. Moreover, a part of the reaction could take place via a different path (RWGS followed by the steam reforming of methane instead of the direct dry reforming of methane). The deactivation of the Ni/γAl2O3 catalyst was also studied. Both the methane and the carbon dioxide conversions remained steady for 50h without showing any sign of deactivation. However, the sinterization of the nickel particles and the presence of carbon deposits seemed to indicate that the catalyst would eventually loose catalytic activity.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
New synthetic hybrid materials and their increasing complexity have placed growing demands on crystal growth for single-crystal X-ray diffraction analysis. Unfortunately, not all chemical systems are ...conducive to the isolation of single crystals for traditional characterization. Here, small-molecule serial femtosecond crystallography (smSFX) at atomic resolution (0.833 Å) is employed to characterize microcrystalline silver n-alkanethiolates with various alkyl chain lengths at X-ray free electron laser facilities, resolving long-standing controversies regarding the atomic connectivity and odd–even effects of layer stacking. smSFX provides high-quality crystal structures directly from the powder of the true unknowns, a capability that is particularly useful for systems having notoriously small or defective crystals. We present crystal structures of silver n-butanethiolate (C4), silver n-hexanethiolate (C6), and silver n-nonanethiolate (C9). We show that an odd–even effect originates from the orientation of the terminal methyl group and its role in packing efficiency. We also propose a secondary odd–even effect involving multiple mosaic blocks in the crystals containing even-numbered chains, identified by selected-area electron diffraction measurements. We conclude with a discussion of the merits of the synthetic preparation for the preparation of microdiffraction specimens and compare the long-range order in these crystals to that of self-assembled monolayers.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
PDF
