We study the infinite temperature dynamics of a prototypical one-dimensional system expected to exhibit many-body localization. Using numerically exact methods, we establish the dynamical phase ...diagram of this system based on the statistics of its eigenvalues and its dynamical behavior. We show that the nonergodic phase is reentrant as a function of the interaction strength, illustrating that localization can be reinforced by sufficiently strong interactions even at infinite temperature. Surprisingly, within the accessible time range, the ergodic phase shows subdiffusive behavior, suggesting that the diffusion coefficient vanishes throughout much of the phase diagram in the thermodynamic limit. Our findings strongly suggest that Wigner-Dyson statistics of eigenvalue spacings may appear in a class of ergodic but subdiffusive systems.
Heavily Doped Semiconductor Nanocrystal Quantum Dots Mocatta, David; Cohen, Guy; Schattner, Jonathan ...
Science (American Association for the Advancement of Science),
04/2011, Letnik:
332, Številka:
6025
Journal Article
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Doping of semiconductors by impurity atoms enabled their widespread technological application in microelectronics and optoelectronics. However, doping has proven elusive for strongly confined ...colloidal semiconductor nanocrystals because of the synthetic challenge of how to introduce single impurities, as well as a lack of fundamental understanding of this heavily doped limit under strong quantum confinement. We developed a method to dope semiconductor nanocrystals with metal impurities, enabling control of the band gap and Fermi energy. A combination of optical measurements, scanning tunneling spectroscopy, and theory revealed the emergence of a confined impurity band and band-tailing. Our method yields n- and p-doped semiconductor nanocrystals, which have potential applications in solar cells, thin-film transistors, and optoelectronic devices.
The quantum many-body problem is ultimately a curse of dimensionality: the state of a system with many particles is determined by a function with many dimensions, which rapidly becomes difficult to ...efficiently store, evaluate and manipulate numerically. On the other hand, modern machine learning models like deep neural networks can express highly correlated functions in extremely large-dimensional spaces, including those describing quantum mechanical problems. We show that if one represents wavefunctions as a stochastically generated set of sample points, the problem of finding ground states can be reduced to one where the most technically challenging step is that of performing regression-a standard supervised learning task. In the stochastic representation the (anti)symmetric property of fermionic/bosonic wavefunction can be used for data augmentation and learned rather than explicitly enforced. We further demonstrate that propagation of an ansatz towards the ground state can then be performed in a more robust and computationally scalable fashion than traditional variational approaches allow.
The peroxidation of n-3 and n-6 polyunsaturated fatty acids (PUFAs) and of their hydroperoxy metabolites is a complex process. It is initiated by free oxygen radical-induced abstraction of a hydrogen ...atom from the lipid molecule followed by a series of nonenzymatic reactions that ultimately generate the reactive aldehyde species 4-hydroxyalkenals. The molecule 4-hydroxy-2E-hexenal (4-HHE) is generated by peroxidation of n-3 PUFAs, such as linolenic acid, eicosapentaenoic acid, and docosahexaenoic acid. The aldehyde product 4-hydroxy-2E-nonenal (4-HNE) is the peroxidation product of n-6 PUFAs, such as arachidonic and linoleic acids and their 15-lipoxygenase metabolites, namely 15-hydroperoxyeicosatetraenoic acid (15-HpETE) and 13-hydroperoxyoctadecadienoic acid (13-HpODE). Another reactive peroxidation product is 4-hydroxy-2E,6Z-dodecadienal (4-HDDE), which is derived from 12-hydroperoxyeicosatetraenoic acid (12-HpETE), the 12-lipoxygenase metabolite of arachidonic acid. Hydroxyalkenals, notably 4-HNE, have been implicated in various pathophysiological interactions due to their chemical reactivity and the formation of covalent adducts with macromolecules. The progressive accumulation of these adducts alters normal cell functions that can lead to cell death. The lipophilicity of these aldehydes positively correlates to their chemical reactivity. Nonetheless, at low and noncytotoxic concentrations, these molecules may function as signaling molecules in cells. This has been shown mostly for 4-HNE and to some extent for 4-HHE. The capacity of 4-HDDE to generate such "mixed signals" in cells has received less attention. This review addresses the origin and cellular functions of 4-hydroxyalkernals.
Pruritoceptive (dermal) itch was long considered an accompanying symptom of diseases, a side effect of drug applications, or a temporary sensation induced by invading pruritogens, as produced by the ...stinging nettle. Due to extensive research in recent years, it was possible to provide detailed insights into the mechanism of itch mediation and modulation. Hence, it became apparent that pruritus is a complex symptom or disease in itself, which requires particular attention to improve patients' health. Here, we summarize recent findings in pruritoceptive itch, including how this sensation is triggered and modulated by diverse endogenous and exogenous pruritogens and their receptors. A differentiation between mediating pruritogen and modulating pruritogen seems to be of great advantage to understand and decipher the molecular mechanism of itch perception. Only a comprehensive view on itch sensation will provide a solid basis for targeting this long-neglected adverse sensation accompanying numerous diseases and many drug side effects. Finally, we identify critical aspects of itch perception that require future investigation.
In the ever-changing landscape of the Information Age, the development of self-regulated learning (SRL) skills has become increasingly important. Problem-solving is a critical SRL skill, and teachers ...play a vital role in fostering these abilities among their students. However, learners and teachers face challenges during the problem-solving process and in evaluating its incorporated strategies. To address these issues, this study explored students’ difficulties in problem-solving while implementing a video assisted SRL training program. This program was developed based on an integrative framework to facilitate a structured problem-solving process in disciplinary or generic contexts. The program aimed to activate additional SRL skills, such as time management, feedback, elaboration, and critical thinking, through a digital toolkit of learning support materials. This paper focuses on 241 students’ difficulties identified and classified according to the problem-solving framework that reported by teachers in different disciplines and grades (6-11). The analysis revealed that the most significant difficulties arose during the problem identification, followed by time planning and management, problem exploration, solution development, and solution evaluation. Based on this study, a dedicated map was developed called PS-SOS MAP to identify difficulties in different steps and tasks throughout the problem-solving process. The utilization of this mapping can also aid in the creation of feedback systems based on technology, such as chatbots or virtual assistants, that can provide valuable assistance to students during problem-solving training, facilitating the process of overcoming difficulties.
Experimental data from undoped-body gate-all-around (GAA) silicon nanowire (NW) MOSFETs with different sizes demonstrate the universality of short-channel effects as a function of L EFF /λ, where L ...EFF is the effective channel length and λ is the electrostatic scaling length. Data from undoped-body single-gate extremely thin SOI (ETSOI) devices additionally show that the universality of short-channel effects is valid for any undoped-body fully depleted SOI MOSFET. Our data indicate that L EFF of undoped GAA NW MOSFETs can be scaled down by ~2.5 times compared with undoped single-gate ETSOI MOSFETs while maintaining equivalent short-channel control.
The skin barrier and its endogenous protective mechanisms cope daily with exogenous stressors, of which ultraviolet radiation (UVR) poses an imminent danger. Although the skin is able to reduce the ...potential damage, there is a need for comprehensive strategies for protection. This is particularly important when developing pharmacological approaches to protect against photocarcinogenesis. Activation of NRF2 has the potential to provide comprehensive and long-lasting protection due to the upregulation of numerous cytoprotective downstream effector proteins that can counteract the damaging effects of UVR. This is also applicable to photodermatosis conditions that exacerbate the damage caused by UVR. This review describes the alterations caused by UVR in normal skin and photosensitive disorders, and provides evidence to support the development of NRF2 activators as pharmacological treatments. Key natural and synthetic activators with photoprotective properties are summarized. Lastly, the gap in knowledge in research associated with photodermatosis conditions is highlighted.
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•The deleterious action of ultraviolet radiation is summarized.•UV-induced damage is aggravated in light sensitive disorders.•Pharmacological activation of NRF2 can prevent photodamage and photocarcinogenesis.•The limitations of targeting NRF2 is presented.
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