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21.
22.
Introduction to the Special Issue on Meta-Learning 总被引:1,自引:0,他引:1
Recent advances in meta-learning are providing the foundations to construct meta-learning assistants and task-adaptive learners. The goal of this special issue is to foster an interest in meta-learning by compiling representative work in the field. The contributions to this special issue provide strong insights into the construction of future meta-learning tools. In this introduction we present a common frame of reference to address work in meta-learning through the concept of meta-knowledge. We show how meta-learning can be simply defined as the process of exploiting knowledge about learning that enables us to understand and improve the performance of learning algorithms. 相似文献
23.
Hassan Elhadidy Jan Franc Eduard Belas Pavel Hlídek Pavel Moravec Roman Grill Pavel Hoschl 《Journal of Electronic Materials》2008,37(9):1219-1224
Thermoelectric effect spectroscopy and photoluminescence techniques were used to study the defect levels in samples from three
crystals of CdTe:In grown by the vertical gradient freeze method. The main goal of the investigation was to study defects,
which strongly trap charge carriers or act as recombination centers in order to eliminate them from the technological process.
The main difference among detecting and non-detecting samples was the absence of electron traps with a very high capture cross-section
and energy 0.6 eV to 0.7 eV, which act as lifetime killers even at low concentrations. Recently published ab initio calculations show a complex of Te antisite and Cd vacancy within this energy range. 相似文献
24.
Marta Valkov Pavel Letinský Lenka Matjov Kateina Klemencov Michal Ritz Christian Schimpf Mykhailo Motylenko David Rafaja Jakub Blík 《International journal of molecular sciences》2022,23(15)
Hematite (α-Fe2O3) catalysts prepared using the precipitation methods was found to be highly effective, and therefore, it was studied with methane (CH4), showing an excellent stable performance below 500 °C. This study investigates hematite nanoparticles (NPs) obtained by precipitation in water from the precursor of ferric chloride hexahydrate using precipitating agents NaOH or NH4OH at maintained pH 11 and calcined up to 500 °C for the catalytic oxidation of low concentrations of CH4 (5% by volume in air) at 500 °C to compare their structural state in a CH4 reducing environment. The conversion (%) of CH4 values decreasing with time was discussed according to the course of different transformation of goethite and hydrohematites NPs precursors to magnetite and the structural state of the calcined hydrohematites. The phase composition, the size and morphology of nanocrystallites, thermal transformation of precipitates and the specific surface area of the NPs were characterized in detail by X-ray powder diffraction, transmission electron microscopy, infrared spectroscopy, thermal TG/DTA analysis and nitrogen physisorption measurements. The results support the finding that after goethite dehydration, transformation to hydrohematite due to structurally incorporated water and vacancies is different from hydrohematite α-Fe2O3. The surface area SBET of Fe2O3_NH-70 precipitate composed of protohematite was larger by about 53 m2/g in comparison with Fe2O3_Na-70 precipitate composed of goethite. The oxidation of methane was positively influenced by the hydrohematites of the smaller particle size and the largest lattice volume containing structurally incorporated water and vacancies. 相似文献
25.
UV‐Triggered Polydopamine Secondary Modification: Fast Deposition and Removal of Metal Nanoparticles
Yi Zeng Xin Du Wei Hou Xiaojiang Liu Cun Zhu Bingbing Gao Liangdong Sun Qiwei Li Junlong Liao Pavel A. Levkin Zhongze Gu 《Advanced functional materials》2019,29(34)
Since the first report in 2007, polydopamine (PDA) coating has shown great potential as a general and versatile method to create functional nanocoatings on arbitrary substrates. Slow kinetics and poor controllability of the coating and secondary modification processes, however, have limited the further development of this attractive method. In this work, it is demonstrated that UV irradiation at 365 nm significantly accelerates the process of secondary modification of a PDA‐coated surface. The kinetics of both thiol and amine modifications of PDA are increased 12‐fold via UV irradiation, while the kinetics of metal ion reduction at the PDA interface is increased more than 550 times. Moreover, it is demonstrated that irradiating a PDA/metal nanoparticle composite surface with UV light at 254 nm leads to dissolution of the deposited metal nanoparticles (MNPs). Finally, grayscale metallic patterns, dynamic deposition, and removal of MNPs on PDA surface are realized with the proposed method. 相似文献
26.
The failure prediction in sheet metal forming is typically realized by evaluating the so called forming limit curves (FLC). The standard experimental method is the Nakajima test, where sometimes also the Marciniak test setup is used. Up to now, the FLC determination was performed with failed specimens and an one-directional intersection line method or by manually analyzing the estimated strains before cracking. Both methods determine the failure by considering the occurrence of cracking and do not consider the possibility of time continuous recording of the Nakajima test. Consequently forming limit curves which have been evaluated in such way are often “laboratory dependent” and deviate for identical materials significantly. This paper presents an algorithm for a fully automatic and time-dependent determination of the beginning plastic instability based on physical effects. The algorithm is based on the evaluation of the strain distribution based on the displacement field which is evaluated by optical measurement and treated as a mesh of a finite element calculation. The critical deformation states are then defined by 2D-consideration of the strain distribution and their time derivates using a numerical evaluation procedure for detecting the beginning of the localization. The effectiveness of the proposed algorithm will be presented for different materials used for the Numisheet’08 Benchmark-1 with Nakajima test. 相似文献
27.
28.
Maria Pieralice Lucrezia Sergio Donato Di Venere Pavel Venediktov 《European Food Research and Technology》2011,232(5):919-923
The quality of leafy vegetables has to be guaranteed for consumers over the whole postharvest period, usually limited to 5–7 days. The analyses to evaluate the quality of vegetables are very time- and resource consuming, so the use of qualitative markers can be much useful. The aim of this work was to evaluate the use of thermoluminescence (TL) parameters as qualitative markers of fresh-cut leafy vegetables during the shelf life. TL is a technique consisting of a cooling, followed by the progressive warming, of a preilluminated sample to reveal the different types of charge pairs as successive emission bands, which are resolved better than the corresponding decay phases recorded at constant temperature. Experiments were performed on rocket (Diplotaxis tenuifolia L.) stored at 2 °C for 7 days. During storage, several changes in TL glow curves were found. The position of the peaks showed a shift to higher temperature. The area of the peaks, relating to the photosystem II (20–65 °C), grew up lightly; whereas in the temperature range that detects lipidic peroxidation (65–140 °C), the TL emission became more than twice. These changes demonstrated that, during the shelf life, a progressive destabilization of PSII centres occurred and that lipid peroxidation products were accumulated in membranes. TL could be used to estimate the damages immediately after as well as during the storage period. This is the first time that TL was used to evaluate the quality of fresh-cut vegetables products during the shelf life. 相似文献
29.
The phenomenon of spontaneous bubble nucleation in extremely supersaturated (superheated) polymer–solvent systems has been studied experimentally. Spontaneous boiling-up temperatures T* for polystyrene and poly(ethylene glycol) solutions in a number of solvents have been measured at different values of pressure p and weight fraction of polymer c by the pulse heating method. The heating rate Ṫ varied from 105 to 107 K/s. For all systems studied, the values of T* have been found to increase with increasing p and c. The T*(p, c) dependence is discussed with the use of the data on the degree of compatibility of components. The peculiarities of polymeric solutions manifest themselves in the region c → 1, as follows: (i) an abrupt increase (by 1–2 orders of magnitude) in the slope of the T*(c) dependence, and (ii) the appearance of the dependence of T* values on the heating rate. Our approach to the interpretation of this result assumes a change in the initial composition of a solution in the course of heating due to polymer decomposition. An example of the extended phase diagram of a polymer–solvent system including the kinetic surface of T*(p, c) is given. © 1996 John Wiley & Sons, Inc. 相似文献
30.
Libor Uttl Tom Hloek Pavel Mare Tom Plení
ek Hana Kubov 《International journal of molecular sciences》2022,23(1)
In spite of use of cannabidiol (CBD), a non-psychoactive cannabinoid, in pediatric patients with epilepsy, preclinical studies on its effects in immature animals are very limited. In the present study we investigated anti-seizure activity of CBD (10 and 60 mg/kg administered intraperitoneally) in two models of chemically induced seizures in infantile (12-days old) rats. Seizures were induced either with pentylenetetrazol (PTZ) or N-methyl-D-aspartate (NMDA). In parallel, brain and plasma levels of CBD and possible motor adverse effects were assessed in the righting reflex and the bar holding tests. CBD was ineffective against NMDA-induced seizures, but in a dose 60 mg/kg abolished the tonic phase of PTZ-induced generalized seizures. Plasma and brain levels of CBD were determined up to 24 h after administration. Peak CBD levels in the brain (996 ± 128 and 5689 ± 150 ng/g after the 10- and 60-mg/kg doses, respectively) were reached 1–2 h after administration and were still detectable 24 h later (120 ± 12 and 904 ± 63 ng/g, respectively). None of the doses negatively affected motor performance within 1 h after administration, but CBD in both doses blocked improvement in the bar holding test with repeated exposure to this task. Taken together, anti-seizure activity of CBD in infantile animals is dose and model dependent, and at therapeutic doses CBD does not cause motor impairment. The potential risk of CBD for motor learning seen in repeated motor tests has to be further examined. 相似文献