Synchronously pumped femtosecond optical parametric oscillator of congruent and stoichiometric MgO-doped periodically poled lithium niobate

A synchronously pumped femtosecond optical parametric oscillator based on congruent MgO-doped periodically poled lithium niobate (c-MgO:PPLN) is reported. The system, operating at room temperature, was pumped by a mode-locked Ti:sapphire laser. The wavelengths of the signal and idler waves were tuned from 870 nm to 1.54 μm and 1.58 to 5.67 μm, respectively, by changing the pump wavelength, the grating period or the cavity length. Pumped by 1.1 W of 755 nm laser radiation, the OPO generated 310 mW of 1080 nm radiation. This signal output corresponds to a total conversion efficiency of 50%. Without dispersion compensation the OPO generated phase-modulated signal pulses of 200 fs duration. Besides the OPO of c-MgO:PPLN, an OPO of stoichiometric (s) MgO:PPLN was investigated. Because of the reduced sensitivity to photorefractive damage, both crystals allowed efficient OPO operation at room temperature. Received: 19 August 2002 / Revised version: 11 December 2002 / Published online: 19 March 2003 RID="*" ID="*"Corresponding author. Fax: +49-631/205-3906, E-mail: andres@physik.uni-kl.de     

MCs+ secondary ion and sputtering yields of oxygen-exposed semiconductors and glasses

The emission of MCs⁺ molecular ions sputtered by Cs⁺ ion impact from a variety of elemental (Si and Ge) and compound (GaAs, InP, InSb, ZnSe, CdS, CdSe, CdTe and CdZnTe) semiconductors and a selection of glass samples of different composition has been investigated. For the glass samples a set of relative sensitivity factors has been determined which are largely composition-independent and provide the possibility of a reliable quantification of glasses by MCs⁺ SIMS. For the semiconductors fractional ion yields (i.e. the number of detected MCs⁺ ions per sputtered M atom) range from 10^–6 to some 10^–4 and exhibit little variation with the oxygen surface coverage of the specimen. Depending on M, the emission of MOCs⁺ molecular species becomes prominent (or even dominating) at high oxygen concentrations. Furthermore, total sputtering yields for 5.5 keV Cs⁺ impact and different oxygen partial pressures have been determined from sputtered craters.     

Search for isovector giant monopole resonances via the Pb(3He,tp) reaction

The (nat)Pb(3He,tp) reaction at E(3He) = 177 MeV was studied to identify 2Planck's over 2piomega isovector monopole strength in Bi isotopes. Monopole strength was found in the region -45相似文献   

Creatine kinase B deficient neurons exhibit an increased fraction of motile mitochondria

Background  

Neurons require an elaborate system of intracellular transport to distribute cargo throughout axonal and dendritic projections. Active anterograde and retrograde transport of mitochondria serves in local energy distribution, but at the same time also requires input of ATP. Here we studied whether brain-type creatine kinase (CK-B), a key enzyme for high-energy phosphoryl transfer between ATP and CrP in brain, has an intermediary role in the reciprocal coordination between mitochondrial motility and energy distribution. Therefore, we analysed the impact of brain-type creatine kinase (CK-B) deficiency on transport activity and velocity of mitochondria in primary murine neurons and made a comparison to the fate of amyloid precursor protein (APP) cargo in these cells, using live cell imaging.     

Critical petermann K factor for intensity noise squeezing

We investigate the impact of the Petermann-excess-noise factor K>/=1 on the possibility of intensity noise squeezing of laser light below the standard quantum limit. Using an N-mode model, we show that squeezing is limited to a floor level of 2(K-1) times the shot noise limit. Thus, even a modest Petermann factor significantly impedes squeezing, which becomes impossible when K>/=1.5. This appears as a serious limitation for obtaining sub-shot-noise light from practical semiconductor lasers. We present experimental evidence for our theory.     

The role of dimension in multivalent binding events: structure-activity relationship of dendritic polyglycerol sulfate binding to L-selectin in correlation with size and surface charge density

L ‐, P ‐, and E ‐Selectin are cell adhesion molecules that play a crucial role in leukocyte recruitment from the blood stream to the afflicted tissue in an acute and chronic inflammatory setting. Since selectins mediate the initial contact of leukocytes to the vascular endothelium, they have evolved as a valuable therapeutic target in diseases related to inflammation by inhibition of the physiological selectin–ligand interactions. In a previous study, it was demonstrated that dPGS, a fully synthetic heparin analogue, works as an efficient inhibitor towards L ‐ and P ‐selectin in vitro as well as in vivo. Herein, the focus is directed towards the effect of size and charge density of the polyanion. The efficiency of L ‐selectin inhibition via an SPR‐based in vitro assay and a cell‐based flow chamber assay is investigated with dPGS ranging from approximately 4 to 2000 kDa. SPR measurements show that the inhibitory potential of highly sulfated dPGS increases with size and charge density. Thereby, IC₅₀ values from the micromolar to the low picomolar range are determined. The same tendency could be observed in a cell‐based flow chamber assay with three representative dPGS samples. This structure–affinity relationship of dPGS suggests that the strong inhibitory potential of dPGS is not only based on the strong electrostatic interaction with areas of cationic surface potential on L ‐selectin but is also due to a steric shielding of the carbohydrate binding site by large, flexible dPGS particles.

     

Real‐time quantum chemistry

Significant progress in the development of efficient and fast algorithms for quantum chemical calculations has been made in the past two decades. The main focus has always been the desire to be able to treat ever larger molecules or molecular assemblies—especially linear and sublinear scaling techniques are devoted to the accomplishment of this goal. However, as many chemical reactions are rather local, they usually involve only a limited number of atoms so that models of about 200 (or even less) atoms embedded in a suitable environment are sufficient to study their mechanisms. Thus, the system size does not need to be enlarged, but remains constant for reactions of this type that can be described by less than 200 atoms. The question then arises how fast one can obtain the quantum chemical results. This question is not directly answered by linear‐scaling techniques. In fact, ideas such as haptic quantum chemistry (HQC) or interactive quantum chemistry require an immediate provision of quantum chemical information which demands the calculation of data in “real time.” In this perspective, we aim at a definition of real‐time quantum chemistry, explore its realm and eventually discuss applications in the field of HQC. For the latter, we elaborate whether a direct approach is possible by virtue of real‐time quantum chemistry. © 2012 Wiley Periodicals, Inc.     

Monitoring bacterial resistance to chloramphenicol and other antibiotics by liquid chromatography electrospray ionization tandem mass spectrometry using selected reaction monitoring

Antibiotic resistance is a growing problem worldwide. For this reason, clinical laboratories often determine the susceptibility of the bacterial isolate to a number of different antibiotics in order to establish the most effective antibiotic for treatment. Unfortunately, current susceptibility assays are time consuming. Antibiotic resistance often involves the chemical modification of an antibiotic to an inactive form by an enzyme expressed by the bacterium. Selected reaction monitoring (SRM) has the ability to quickly monitor and identify these chemical changes in an unprecedented time scale. In this work, we used SRM as a technique to determine the susceptibility of several different antibiotics to the chemically modifying enzymes β‐lactamase and chloramphenicol acetyltransferase, enzymes used by bacteria to confer resistance to major classes of commonly used antibiotics. We also used this technique to directly monitor the effects of resistant bacteria grown in a broth containing a specific antibiotic. Because SRM is highly selective and can also identify chemical changes in a multitude of antibiotics in a single assay, SRM has the ability to detect organisms that are resistant to multiple antibiotics in a single assay. For these reasons, the use of SRM greatly reduces the time it takes to determine the susceptibility or resistance of an organism to a multitude of antibiotics by eliminating the time‐consuming process found in other currently used methods. Copyright © 2013 John Wiley & Sons, Ltd.