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排序方式: 共有467条查询结果,搜索用时 687 毫秒
21.
I. N. Tilikin T. A. Shelkovenko S. A. Pikuz S. N. Mishin A. R. Mingaleev D. A. Hammer 《Bulletin of the Russian Academy of Sciences: Physics》2018,82(4):386-389
Since the first experiments with hybrid X-pinches (HXP), it has been shown that a short wire between two conical tungsten electrodes produces the same radiation as a standard X-pinch. Since HXP has a simple construction, it is commonly used in many laboratories instead of standard pinches. Although details of the HXP dynamics remain poorly studied, the main factors governing HXP formation are investigated experimentally in this work. It is shown that the process of the electrode plasma formation is one of the main factors that lead to single hot spot bursts. Experimental results allow the fitting of HXP parameters and determination of the size of the source of X-ray radiation. It is also shown the radiation of HXP can be used as a source for point projection radiography in the wavelength range of soft to hard X-rays. Such sources can be also used for absorption spectroscopy and even electron beams. 相似文献
22.
Eva C. Sonnenschein Marc Stierhof Stephan Goralczyk Floriane M. Vabre Leonie Pellissier Kine Østnes Hanssen Mercedes de la Cruz Caridad Díaz Peter de Witte Daniëlle Copmans Jeanette Hammer Andersen Espen Hansen Venke Kristoffersen José R. Tormo Rainer Ebel Bruce F. Milne Hai Deng Lone Gram Jioji N. Tabudravu 《Tetrahedron》2017,73(18):2633-2637
A new siderophore containing a 4,5-dihydroimidazole moiety was isolated from Pseudoalteromonas piscicida S2040 together with myxochelins A and B, alteramide A and its cycloaddition product, and bromo- and dibromoalterochromides. The structure of pseudochelin A was established by spectroscopic techniques including 2D NMR and MS/MS fragmentation data. In bioassays selected fractions of the crude extract of S2040 inhibited the opportunistic pathogen Pseudomonas aeruginosa. Pseudochelin A displayed siderophore activity in the chrome azurol S assay at concentrations higher than 50 μM, and showed weak activity against the fungus Aspergillus fumigatus, but did not display antibacterial, anti-inflammatory or anticonvulsant activity. 相似文献
23.
Dr. Aron J. Huckaba Dr. Aswani Yella Dr. Louis E. McNamara April E. Steen J. Scott Murphy Casey A. Carpenter George D. Puneky Prof. Nathan I. Hammer Prof. Mohammad Khaja Nazeeruddin Prof. Michael Grätzel Prof. Jared H. Delcamp 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(43):15536-15542
Desirable components for dye‐sensitzed solar cell (DSC) sensitizers and fluorescent imaging dyes include strong donating building blocks coupled with well‐balanced acceptor functionalities for absorption beyond the visible range. We have evaluated the effects of increasing acceptor strengths and incorporation of dye morphology controlling groups on molar absorptivity and absorption breadth with indolizine donor‐based dyes. Indolizine‐based D –A and D –π–A sensitizers incorporating bis‐rhodanine, tricyanofuran (TCF), and cyanoacrylic acid functionalities were analyzed for performance in DSC devices. The TCF derivatives were also evaluated as near‐infrared (NIR)‐emissive materials with the AH25 emissions extending past 1000 nm. 相似文献
24.
Peter Hammer Fábio C. dos Santos Bianca M. Cerrutti Sandra H. Pulcinelli Celso V. Santilli 《Journal of Sol-Gel Science and Technology》2012,63(2):266-274
Siloxane-polymethyl methacrylate hybrid films were deposited on carbon steel substrates by dip-coating from a sol prepared by acid-catalyzed hydrolytic co-polycondensation of tetraethoxysilane (TEOS) and 3-methacryloxy propyl-trimethoxysilane (MPTS), followed by radical polymerization of methyl methacrylate (MMA). Structural properties of the hybrids were studied using 29Si and 13C nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA), as a function of the MMA/MPTS ratio, which ranged between 2 and 10. The efficiency of corrosion protection of hybrid-coated carbon steel was investigated by XPS, potentiodynamic polarization curves and electrochemical impedance spectroscopy after immersion of the material in acidic and neutral saline aqueous solution. The NMR and TGA results indicate a high degree of polycondensation (84%) and elevated thermal stability of 410?°C for the hybrid film with a MMA/MPTS ratio of 8, exhibiting also and excellent adhesion to the substrate. The XPS analysis confirmed the variation of the MMA phase in the hybrid, and showed that no corrosion-induced changes had occurred after 18?days immersion of the coated steel in 3.5% NaCl solution. Potentiodynamic polarization curves have shown that the hybrid coating prepared using a TEOS/MPTS ratio of 8 yielded the best anti-corrosion performance. It acts as a very efficient corrosion barrier, increasing the total impedance by almost 6 orders of magnitude and reducing the current densities by 4 orders of magnitude, compared to the bare electrode. The obtained results are discussed based on the correlation of structural information with impedance data presented for both electrolytes in the form of electrical equivalent circuits. 相似文献
25.
26.
Synthesis and Photophysical Properties of Multichromophoric Carbonyl‐Bridged Triarylamines
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Natalie Hammer Dr. Richard Hildner Dr. Milan Kivala Prof. Dr. Jürgen Köhler Prof. Hans‐Werner Schmidt 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(37):11708-11718
The synthesis and photophysical properties of two novel multichromophoric compounds is presented. Their molecular design comprises a carbonyl‐bridged triarylamine core and either naphthalimides or 4‐(5‐hexyl‐2,2′‐bithiophene)naphthalimides as second chromophore in the periphery. The lateral chromophores are attached to the core via an amide linkage and a short alkyl spacer. The synthetic approach demonstrates a straightforward functionalization strategy for carbonyl‐bridged triarylamines. Steady‐state and time‐resolved spectroscopic investigations of these compounds, in combination with three reference compounds, provide clear evidence for energy transfer in both multichromophoric compounds. The direction of the energy transfer depends on the lateral chromophore used. Furthermore, the compound bearing the lateral 4‐(bithiophene)naphthaimides is capable of forming fluorescent gels at very low concentrations in the sub‐millimolar regime whilst retaining its energy transfer properties. 相似文献
27.
?. Hammer 《The European physical journal. Special topics》2009,178(1):5-12
This article provides an overview of current and prospected climate changes, their causes and implied threats, and of a possible
route to keep the changes within a tolerable level. The global mean temperature has up to 2005 risen by almost 0.8°C, and
the change expected by 2100 is as large as glacial-interglacial changes in the past, which were commonly spread out over 10000
years. As is well known, the principle actor is man-made CO2, which, together with other anthropogenic gases, enhances the atmosphere’s greenhouse effect. The only man-made cooling agent
appears to be atmospheric aerosols. Atmospheric CO2 has now reached levels unprecedented during the past several million years. Principal threats are a greatly reduced biodiversity
(species extinction), changes in the atmospheric precipitation pattern, more frequent weather extremes, and not the least,
sea level rise. The expected precipitation pattern will enhance water scarcity in and around regions that suffer from water
shortage already, affecting many countries. Sea level rise will act on a longer time scale. It is expected to amount to more
than 50 cm by 2100, and over the coming centuries the potential rise is of the order of 10 m. A global-mean temperature increase
of 2°C is often quoted as a safe limit, beyond which irreversible effects must be expected. To achieve that limit, a major,
rapid, and coordinated international effort will be needed. Up to the year 2050, the man-made CO2 releases must be reduced by at least 50%. This must be accompanied by a complete overhaul of the global energy supply toward
depending increasingly on the Sun’s supply of energy, both directly and in converted form, such as wind energy. Much of the
information and insight available today has been generated by the Intergovernmental Panel on Climate Change (IPCC), in particular
its Fourth Assessment Report of 2007, which greatly advanced both public attention and political action. 相似文献
28.
Estephania Lira Jonas ?. Hansen Peipei Huo Ralf Bechstein Patrick Galliker Erik L?gsgaard Bj?rk Hammer Stefan Wendt Flemming Besenbacher 《Surface science》2010,604(21-22):1945-1960
High-resolution scanning tunneling microscopy (STM) and temperature-programmed desorption (TPD) were used to study the interaction of O2 with reduced TiO2(110)–(1 × 1) crystals. STM is the technique of choice to unravel the relation between vacancy and non-vacancy assisted O2 dissociation channels as a function of temperature. It is revealed that the vacancy-assisted, first O2 dissociation channel is preferred at low temperature (~ 120 K), whereas the non-vacancy assisted, second O2 dissociation channel operates at temperatures higher than 150 K–180 K. Based on the STM results on the two dissociative O2 interaction channels and the TPD data, a new comprehensive model of the O2 chemisorption on reduced TiO2(110) is proposed. The model explains the relations between the two dissociative and the molecular O2 interaction channels. The experimental data are interpreted by considering the available charge in the near-surface region of reduced TiO2(110) crystals, the kinetics of the two O2 dissociation channels as well as the kinetics of the diffusion and reaction of Ti interstitials. 相似文献
29.
Miller TJ Farquar HD Sheybani A Tallini CE Saurage AS Fronczek FR Hammer RP 《Organic letters》2002,4(6):877-880
[reaction: see text] The thiazole C-nucleoside analogue was synthesized by the Hantzsch cyclization method to form the thiazole ring and was then converted to the thiazole N-oxide C-nucleoside analogue by peracid oxidation of the heterocycle nitrogen. Incorporation of the thiazole and thiazole N-oxide phosphoramidites into DNA was successful though significant deoxygenation of the N-oxide occurred during DNA assembly. The mechanism proposed for the reduction of the thiazole N-oxide to thiazole involves the formation of an N-oxide phosphite ester. 相似文献
30.
Hammer B 《Physical review letters》2002,89(1):016102
The potential energy diagram for the NO+CO reaction on 1, 2, and 3 monolayer (ML) Pd films supported by MgO(100) is calculated using density functional theory. Thin Pd films are generally found to be more reactive than thick films, with a notable exception for nitrogen adsorption on 2 ML Pd/MgO(100). For this system an attractive through-the-metal adsorbate-oxide interaction of 0.5 eV is identified. Nitrogen adsorption is consequently estimated to provide a thermodynamic driving force for the reconstruction of MgO(100) supported 3 ML (or thicker) Pd clusters into thinner Pd clusters. 相似文献