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51.
M. Siebold S. Bock U. Schramm B. Xu J. L. Doualan P. Camy R. Moncorgé 《Applied physics. B, Lasers and optics》2009,97(2):327-338
Here is presented and discussed the history, the spectroscopic, the thermo-mechanical and the laser properties of the new old laser crystal Yb:CaF2, of its Sr and Ba isotypes as well as of an Yb and Na codoped compound. It will be shown that Yb:CaF2 is a very particular luminescent material, in which the laser-active center probably consists of a complex hexameric cluster, that it is the most promising Yb-doped fluoride material for large-scale, high-power and high-energy laser systems and that it can compete in several aspects with the currently used Yb-doped oxide crystals and glasses. The opportunity of operating the crystals at cryogenic temperatures and the recently achieved improvements in the field of femtosecond pulsed laser operation and high peak power laser amplification is highlighted and evaluated. 相似文献
52.
Stephen J. Valentine Sarah T. Stokes Ruwan T. Kurulugama Fabiane M. Nachtigall David E. Clemmer 《Journal of the American Society for Mass Spectrometry》2009,20(5):738-750
The transport of ions through multiple drift regions is modeled to develop an equation that is useful for an understanding
of the resolving power of an overtone mobility spectrometry (OMS) technique. It is found that resolving power is influenced
by a number of experimental variables, including those that define ion mobility spectrometry (IMS) resolving power: drift
field (E), drift region length (L), and buffer gas temperature (T). However, unlike IMS, the resolving power of OMS is also influenced by the number of drift regions (n), harmonic frequency value (m), and the phase number (Φ) of the applied drift field. The OMS resolving power dependence upon the new OMS variables (n, m, and Φ) scales differently than the square root dependence of the E, L, and T variables in IMS. The results provide insight about optimal instrumental design and operation. 相似文献
53.
Ruwan T. Kurulugama Fabiane M. Nachtigall Sunyoung Lee Stephen J. Valentine David E. Clemmer 《Journal of the American Society for Mass Spectrometry》2009,20(5):729-737
A new method that allows a linear drift tube to be operated as a continuous ion mobility filter is described. Unlike conventional
ion mobility instruments that use an electrostatic gate to introduce a packet of ions into a drift region, the present approach
uses multiple segmented drift regions with modulated drift fields to produce conditions that allow only ions with appropriate
mobilities to pass through the instrument. In this way, the instrument acts as a mobility filter for continuous ion sources.
By changing the frequency of the applied drift fields it is possible to tune this instrument to transmit ions having different
mobilities. A scan over a wide range of drift field frequencies for a single ion species shows a peak corresponding to the
expected resonance time of the ions in one drift region segment and a series of peaks at higher frequencies that are overtones
of the resonant frequency. The measured resolving power increases for higher overtones, making it possible to resolve structures
that were unresolved in the region of the fundamental frequency. We demonstrate the approach by examining oligosaccharide
isomers, raffinose and melezitose as well as a mixture of peptides obtained from enzymatic digestion of myoglobin. 相似文献
54.
Valentine KG Pometun MS Kielec JM Baigelman RE Staub JK Owens KL Wand AJ 《Journal of the American Chemical Society》2006,128(50):15930-15931
Proteins encapsulated within the aqueous core of reverse micelles are found to partially align in a magnetic field. The degree of alignment is sufficient to result in sizable residual 15N-1H dipolar couplings that can be easily measured. It is found that the magnetic susceptibility of the reverse micelle particle is not dominated by the encapsulated protein. The residual dipolar couplings are found to be structurally meaningful. 相似文献
55.
Koder RL Valentine KG Cerda J Noy D Smith KM Wand AJ Dutton PL 《Journal of the American Chemical Society》2006,128(45):14450-14451
We show that a single internal polar interaction per helix is sufficient to engender structural specificity in that helix in helical bundle proteins. Furthermore, we use histidine-binding cofactors of different shapes which bind directly into the core, demonstrating that this structural specificity is not the result of a prescribed complimentary, "knobs in holes" core packing. We show that we can switch structural specificity of individual helices on and off by ligating cofactors, singly and in pairs, which bind either one or two histidine ligands. To our knowledge, this is the first demonstration of such extensive manipulation of protein structure by ligand binding, an important result of general interest to those working with self-assembled molecular systems. Finally, as these proteins were designed without the use of computational modeling, we not only demonstrate that designing a uniquely structured cofactor binding protein is not as difficult as is generally believed, we have determined why this is so: hydrophobic core complementarity, which is very difficult to design, is not necessary. Instead, a much simpler design process entails the creation of core polar interactions which themselves can drive conformational specificity. 相似文献
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58.
A.J. Kemp A.J. Maclean J.E. Hastie S.A. Smith J.-M. Hopkins S. Calvez G.J. Valentine M.D. Dawson D. Burns 《Applied physics. B, Lasers and optics》2006,83(2):189-194
Finite-element analysis is used to explore the practicalities and power-scaling potential of quasi-monolithic microchip vertical-external-cavity surface-emitting lasers: thermal lensing and its implications for transverse mode control are emphasised. A comparison is made between the use of sapphire and diamond heat spreaders. The experimental characterisation of an InGaAs/sapphire microchip VECSEL is presented as an exemplar system and the factors affecting slope efficiency, threshold and output power roll-over are examined. By comparing experimental measurements with the finite-element model, the key role of thermal lensing in transverse mode control is demonstrated. PACS 42.55.Xi; 42.55.Rz; 42.55.Px 相似文献
59.
Cover Picture: Dipole Effects on Electron Transfer are Enormous (Angew. Chem. Int. Ed. 38/2018)
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60.
Dr. Maciej Krzeszewski Eli M. Espinoza Dr. Ctirad Červinka James B. Derr John A. Clark Dr. Dan Borchardt Prof. Gregory J. O. Beran Prof. Daniel T. Gryko Prof. Valentine I. Vullev 《Angewandte Chemie (International ed. in English)》2018,57(38):12365-12369
Molecular dipoles present important, but underutilized, methods for guiding electron transfer (ET) processes. While dipoles generate fields of Gigavolts per meter in their vicinity, reported differences between rates of ET along versus against dipoles are often small or undetectable. Herein we show unprecedentedly large dipole effects on ET. Depending on their orientation, dipoles either ensure picosecond ET, or turn ET completely off. Furthermore, favorable dipole orientation makes ET possible even in lipophilic medium, which appears counterintuitive for non‐charged donor–acceptor systems. Our analysis reveals that dipoles can substantially alter the ET driving force for low solvent polarity, which accounts for these unique trends. This discovery opens doors for guiding forward ET processes while suppressing undesired backward electron transduction, which is one of the holy grails of photophysics and energy science. 相似文献