Multi-Unmanned Aerial Vehicle (UAV) control is one of the major research interests in UAV-based networks. Yet few existing works focus on how the network should optimally react when the UAV lineup ...and user distribution change. In this work, proactive self-regulation (PSR) of UAV-based networks is investigated when one or more UAVs are about to quit or join the network, with considering dynamic user distribution. We target at an optimal UAV trajectory control policy which proactively relocates the UAVs whenever the UAV lineup is about to change, rather than passively dispatches the UAVs after the change. Specifically, a deep reinforcement learning (DRL)-based self-regulation approach is developed to maximize the accumulated user satisfaction (US) score for a certain period within which at least one UAV will quit or join the network. To handle the changed dimension of the state-action space before and after the lineup changes, the state transition is deliberately designed. To accommodate continuous state and action space, an actor-critic based DRL, i.e., deep deterministic policy gradient (DDPG), is applied with better convergence stability. To effectively promote learning exploration around the timing of lineup change, an asynchronous parallel computing (APC) learning structure is proposed. Referred to as PSR-APC, the developed approach is then extended to the case of dynamic user distribution by incorporating time as one of the agent states. Finally, numerical results are presented to demonstrate the convergence and superiority of PSR-APC over a passive reaction method, and its capability in jointly handling the dynamics of both UAV lineup and user distribution.
After over a decade of development, X-ray transient absorption (XTA) spectroscopy has become an increasingly important and common tool in following molecular structures in chemical reactions and to ...map out structural factors that could influence reaction pathways. The Perspective reviews current achievements and capabilities in chemical dynamics from XTA spectroscopy based mainly on studies by the authors, collaborators, and cousers of the same facility and then outlines some future challenges and impacts in chemical sciences using pulsed X-rays from the third-generation synchrotron and the fourth-generation X-ray free-electron light sources.
Earth-abundant oxygen evolution catalysts (OECs) with extended stability in acid can be constructed by embedding active sites within an acid-stable metal-oxide framework. Here, we report stable ...NiPbOₓ films that are able to perform oxygen evolution reaction (OER) catalysis for extended periods of operation (>20 h) in acidic solutions of pH 2.5; conversely, native NiOₓ catalyst films dissolve immediately. In situ X-ray absorption spectroscopy and ex situ X-ray photoelectron spectroscopy reveal that PbO₂ is unperturbed after addition of Ni and/or Fe into the lattice, which serves as an acid-stable, conductive framework for embedded OER active centers. The ability to perform OER in acid allows the mechanism of Fe doping on Ni catalysts to be further probed. Catalyst activity with Fe doping of oxidic Ni OEC under acid conditions, as compared to neutral or basic conditions, supports the contention that role of Fe3+ in enhancing catalytic activity in Ni oxide catalysts arises from its Lewis acid properties.
Fatigue properties of an extruded AZ31B magnesium alloy were evaluated using strain-controlled push–pull cyclic tests at different total strain amplitudes at room temperature. The alloy exhibited an ...asymmetric sigmoidal-shaped hysteresis loop due to twinning in compression during the unloading phase and detwinning during the loading phase. As the total strain amplitude increased, the asymmetry of hysteresis loops, plastic strain amplitude, mean stress, and stress amplitude increased, while the ratcheting strain and pseudoelastic modulus decreased. As the cyclic deformation progressed at a given total strain amplitude (greater than 0.3%), an abrupt increase in the plastic strain amplitude was observed, representing the onset of fatigue crack initiation. The extent of this increase process, which decreased with increasing total strain amplitude, corresponded to the fatigue crack propagation prior to the final fast failure. Fatigue crack initiation was observed to occur at the specimen surface, and fatigue crack propagation was characterized by typical striations. The smaller spacing of fatigue striations and larger fatigue crack propagation zone at the lower total strain amplitude gave rise to a longer fatigue life. The Coffin–Manson and Basquin's relationships can be used to describe the fatigue lifetime of this alloy.
Is dehydroepiandrosterone a hormone? Labrie, F; Luu-The, V; Bélanger, A ...
Journal of endocrinology,
11/2005, Letnik:
187, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Dehydroepiandrosterone (DHEA) is not a hormone but it is a very important prohormone secreted in large amounts by the adrenals in humans and other primates, but not in lower species. It is secreted ...in larger quantities than cortisol and is present in the blood at concentrations only second to cholesterol. All the enzymes required to transform DHEA into androgens and/or estrogens are expressed in a cell-specific manner in a large series of peripheral target tissues, thus permitting all androgen-sensitive and estrogen-sensitive tissues to make locally and control the intracellular levels of sex steroids according to local needs. This new field of endocrinology has been called intracrinology. In women, after menopause, all estrogens and almost all androgens are made locally in peripheral tissues from DHEA which indirectly exerts effects, among others, on bone formation, adiposity, muscle, insulin and glucose metabolism, skin, libido and well-being. In men, where the secretion of androgens by the testicles continues for life, the contribution of DHEA to androgens has been best evaluated in the prostate where about 50% of androgens are made locally from DHEA. Such knowledge has led to the development of combined androgen blockade (CAB), a treatment which adds a pure anti-androgen to medical (GnRH agonist) or surgical castration in order to block the access of the androgens made locally to the androgen receptor. In fact, CAB has been the first treatment demonstrated to prolong life in advanced prostate cancer while recent data indicate that it can permit long-term control and probably cure in at least 90% of cases of localized prostate cancer. The new field of intracrinology or local formation of sex steroids from DHEA in target tissues has permitted major advances in the treatment of the two most frequent cancers, namely breast and prostate cancer, while its potential use as a physiological HRT could well provide a physiological balance of androgens and estrogens, thus offering exciting possibilities for women’s health at menopause.
Significant interest exists in lead trihalides that present the perovskite structure owing to their demonstrated potential in photovoltaic, lasing, and display applications. These materials are also ...notable for their unusual phase behavior often displaying easily accessible phase transitions. In this work, time-resolved X-ray diffraction, performed on perovskite cesium lead bromide nanocrystals, maps the lattice response to controlled excitation fluence. These nanocrystals undergo a reversible, photoinduced orthorhombic-to-cubic phase transition which is discernible at fluences greater than 0.34 mJ cm
through the loss of orthorhombic features and shifting of high-symmetry peaks. This transition recovers on the timescale of 510 ± 100 ps. A reversible crystalline-to-amorphous transition, observable through loss of Bragg diffraction intensity, occurs at higher fluences (greater than 2.5 mJ cm
). These results demonstrate that light-driven phase transitions occur in perovskite materials, which will impact optoelectronic applications and enable the manipulation of non-equilibrium phase characteristics of the broad perovskite material class.
Molecular structures during chemical processes are crucial for predicting molecular reactivity and reaction mechanisms. Using a laser pulse as an internal clock for starting fundamental chemical ...processes, molecular structural dynamics can be characterized by coherent vibrational motions and by incoherent transitions between different intermediate states. Recent developments in pulsed X-ray facilities allow structural determination of discrete excited states and reaction intermediates using laser-initiated time-resolved X-ray absorption spectroscopy (LITR-XAS). Moreover, femtosecond X-ray sources have begun making significant contributions in monitoring coherent molecular motions. This review summarizes recent developments in the field, including technical and scientific challenges as well as several examples involving excited state molecular structure and electronic configuration determinations. Future applications of this technique with high time resolution will enable visualization of fundamental chemical events in many systems and further our understanding in photochemistry.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Shear-printing is a promising processing technique in organic electronics for microstructure/charge transport modification and large-area film fabrication. Nevertheless, the mechanism by which ...shear-printing can enhance charge transport is not well-understood. In this study, a printing method using natural brushes is adopted as an informative tool to realize direct aggregation control of conjugated polymers and to investigate the interplay between printing parameters, macromolecule backbone alignment and aggregation, and charge transport anisotropy in a conjugated polymer series differing in architecture and electronic structure. This series includes (i) semicrystalline hole-transporting P3HT, (ii) semicrystalline electron-transporting N2200, (iii) low-crystallinity hole-transporting PBDTT-FTTE, and (iv) low-crystallinity conducting PEDOT:PSS. The (semi-)conducting films are characterized by a battery of morphology and microstructure analysis techniques and by charge transport measurements. We report that remarkably enhanced mobilities/conductivities, as high as 5.7×/3.9×, are achieved by controlled growth of nanofibril aggregates and by backbone alignment, with the adjusted R² (R²adj) correlation between aggregation and charge transport as high as 95%. However, while shear-induced aggregation is important for enhancing charge transport, backbone alignment alone does not guarantee charge transport anisotropy. The correlations between efficient charge transport and aggregation are clearly shown, while mobility and degree of orientation are not always well-correlated. These observations provide insights into macroscopic charge transport mechanisms in conjugated polymers and suggest guidelines for optimization.
A variable annuity (VA) is equity-linked annuity product that has rapidly grown in popularity around the world in recent years. Research up to date on VA largely focuses on the valuation of ...guarantees embedded in a single VA contract. However, methods developed for individual VA contracts based on option pricing theory cannot be extended to large VA portfolios. Insurance companies currently use nested simulation to valuate guarantees for VA portfolios but efficient valuation under nested simulation for a large VA portfolio has been a real challenge. The computation in nested simulation is highly intensive and often prohibitive. In this paper, we propose a novel approach that combines a clustering technique with a functional data analysis technique to address the issue. We create a highly non-homogeneous synthetic VA portfolio of 100,000 contracts and use it to estimate the dollar Delta of the portfolio at each time step of outer loop scenarios under the nested simulation framework over a period of 25 years. Our test results show that the proposed approach performs well in terms of accuracy and efficiency.
PDF
