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排序方式: 共有125条查询结果,搜索用时 15 毫秒
101.
Atkins R Benbow W Berley D Blaufuss E Coyne DG DeYoung T Dingus BL Dorfan DE Ellsworth RW Fleysher L Fleysher R Gisler G Gonzalez MM Goodman JA Haines TJ Hays E Hoffman CM Kelley LA Lansdell CP Linnemann JT McEnery JE Miller RS Mincer AI Morales MF Nemethy P Noyes D Ryan JM Samuelson FW Parkinson PM Shoup A Sinnis G Smith AJ Sullivan GW Williams DA Wilson ME Xu XW Yodh GB 《Physical review letters》2005,95(25):251103
Gamma-ray emission from a narrow band at the galactic equator has previously been detected up to 30 GeV. We report evidence for a TeV gamma-ray signal from a region of the galactic plane by Milagro, a large-field-of-view water Cherenkov detector for extensive air showers. An excess with a significance of 4.5 standard deviations has been observed from the region of galactic longitude l E (40 degrees, 100 degrees) and latitude /b/ < 5 degrees. Under the assumption of a simple power law spectrum, with no cutoff in the EGRET-Milagro energy range, the measured integral flux is phi gamma(>3.5 TeV) = (6.4 +/- 1.4 +/- 2.1) x 10(-11) cm(-2) s(-1) sr(-1). This flux is consistent with an extrapolation of the EGRET spectrum between 1 and 30 GeV in this galactic region. 相似文献
102.
Molecular iodine has been observed to lase on eight vibrational bands of the 3460–3015 Å band system. The laser was produced by electron-beam-pumping mixtures of a iodine-donor compound (HI, CF3I, or CH3I) and argon. The highest energy output obtained was 1.0 J in a 40 ns pulse, corresponding to an average power of 25 MW. 相似文献
103.
Zweiback J Cowan TE Smith RA Hartley JH Howell R Steinke CA Hays G Wharton KB Crane JK Ditmire T 《Physical review letters》2000,85(17):3640-3643
Exploiting the energetic interaction of intense femtosecond laser pulses with deuterium clusters, it is possible to create conditions in which nuclear fusion results from explosions of these clusters. We have conducted high-resolution neutron time-of-flight spectroscopy on these plasmas and show that they yield fast bursts of nearly monochromatic fusion neutrons with temporal duration as short as a few hundred picoseconds. Such a short, nearly pointlike source now opens up the unique possibility of using these bright neutron pulses, either as a pump or a probe, to conduct ultrafast studies with neutrons. 相似文献
104.
Zweiback J Smith RA Cowan TE Hays G Wharton KB Yanovsky VP Ditmire T 《Physical review letters》2000,84(12):2634-2637
Recent experiments on the interaction of intense, ultrafast laser pulses with large van der Waals bonded clusters have shown that these clusters can explode with substantial kinetic energy. By driving explosions in deuterium clusters with a 35 fs laser pulse, we have accelerated ions to sufficient kinetic energy to produce DD nuclear fusion. By diagnosing the fusion yield through measurements of 2.45 MeV fusion neutrons, we have found that the fusion yield from these exploding clusters varies strongly with the cluster size, consistent with acceleration of deuterons via Coulomb explosion forces. 相似文献
105.
Carsten von Hänisch PD Dr. 《无机化学与普通化学杂志》2008,634(1):23-29
The range of molecular silicon phosphorus compounds has been extended by some new species containing oligosilane ((R2Si)n; n ≥ 2) or oligosiloxane ((R2SiO)mSiR2; m ≥ 1) fragments bound to phosphorus atoms. Primary and secondary compounds of these types allow for the synthesis of metal derivatives. Such metalated species usually form oligomers and exhibit a versatile structural chemistry with cyclic, polycyclic, and cage‐like patterns. The main results obtained in the field of oligosilane‐ and oligosiloxane‐bridged phosphines will be presented below and the structures of the metal derivatives will be discussed. Moreover, the synthesis of an inorganic ligand on the basis of siloxane‐bridged phosphines will be presented. This compound opens up a new chapter in host‐guest chemistry. 相似文献
106.
Dennis Rottschäfer Beate Neumann Dr. Hans-Georg Stammler Dr. Ryohei Kishi Prof. Dr. Masayoshi Nakano PD Dr. Rajendra S. Ghadwal 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(13):3244-3247
Para-quinodimethane (pQDM) is a fundamental structural component in many π-conjugated organic molecules and materials. The incorporation of phosphorus atom into π-conjugated frameworks offers unique opportunities for controlling the properties of derived species. A phosphorus analogue of p-quinodimethane (pQDM), (IPrC)2P4 [ 5 , IPr=C{N(Ar)CH2}2; Ar=2,6-iPr2C6H3] featuring a planar P4 ring, was readily accessible by KC8-reduction of (IPrC)(PCl2)2 ( 2 ). Base-mediated C−H functionalization of IPrCH2 ( 1 ) with PCl3 afforded 2 . The formation of 5 was expected to occur through a dimerization of the transient 3H-diphosphirene (IPrC)P2 ( 4 ), which was theoretically suggested to have an intermediate diradical character. Compound 5 underwent photo-induced ring-contraction reaction to form the singlet diradicaloid (IPrCP)2 VI and white phosphorus (P4). The formation of and VI and P4 suggested the formal diphosphorus (P2) elimination from 5 . Indeed, photolysis of a mixture of 1,3-cyclohexadiene (CHD) and 5 led to the formation of P2-entrapped product (CHD)2P2 ( 6 ). The compound 5 represents the first organophosphorus species that functions as a P2 source. 相似文献
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109.
Christian Gebhardt Dr. Martin Lehmann Dr. Maria M. Reif Prof. Dr. Martin Zacharias PD Dr. Gerd Gemmecker Prof. Dr. Thorben Cordes 《Chemphyschem》2021,22(15):1566-1583
The use of fluorescence techniques has an enormous impact on various research fields including imaging, biochemical assays, DNA-sequencing and medical technologies. This has been facilitated by the development of numerous commercial dyes with optimized photophysical and chemical properties. Often, however, information about the chemical structures of dyes and the attached linkers used for bioconjugation remain a well-kept secret. This can lead to problems for research applications where knowledge of the dye structure is necessary to predict or understand (unwanted) dye-target interactions, or to establish structural models of the dye-target complex. Using a combination of optical spectroscopy, mass spectrometry, NMR spectroscopy and molecular dynamics simulations, we here investigate the molecular structures and spectroscopic properties of dyes from the Alexa Fluor (Alexa Fluor 555 and 647) and AF series (AF555, AF647, AFD647). Based on available data and published structures of the AF and Cy dyes, we propose a structure for Alexa Fluor 555 and refine that of AF555. We also resolve conflicting reports on the linker composition of Alexa Fluor 647 maleimide. We also conducted a comprehensive comparison between Alexa Fluor and AF dyes by continuous-wave absorption and emission spectroscopy, quantum yield determination, fluorescence lifetime and anisotropy spectroscopy of free and protein-attached dyes. All these data support the idea that Alexa Fluor and AF dyes have a cyanine core and are a derivative of Cy3 and Cy5. In addition, we compared Alexa Fluor 555 and Alexa Fluor 647 to their structural homologs AF555 and AF(D)647 in single-molecule FRET applications. Both pairs showed excellent performance in solution-based smFRET experiments using alternating laser excitation. Minor differences in apparent dye-protein interactions were investigated by molecular dynamics simulations. Our findings clearly demonstrate that the AF-fluorophores are an attractive alternative to Alexa- and Cy-dyes in smFRET studies or other fluorescence applications. 相似文献
110.