High-energy handling capabilities of optical fibers: Application to pulse compression and direct generation of megawatt picosecond pulses

The compression of the output of a Q-switched, mode-locked Nd:YAG (130 ps, 1.06 m) is reported for a number of different core-size single mode, multimode and polarization preserving fibers at power levels near the damage threshold. In maximizing the energy throughput, the main limitations are dielectric breakdown and nonlinear induced birefringence. Compressed pulse stability is found to depend critically on core size at this power level. An optimized compressor has been obtained capable of compression factors up to 35 (3.7 ps) with peak power in excess of 2 MW. Second-harmonic generation has been observed in polarization preserving fibers.     

载有卟啉的介孔SBA-15表面光电压的性质研究

用表面光电压谱(SPS)和场诱导表面光电压谱(FISPS)技术对比研究了卟啉和介孔SBA-15及载有卟啉的介孔SBA-15的表面光伏特性.固载后同时显示了卟啉和介孔的光电压性质,但是光电压响应强度减弱,这是因为卟啉和介孔之间发生了电子传递的缘故.在外电场诱导下,它们的光伏响应强度随外加正电场光伏响应强度的增加而增强,随外加负电场光伏响应强度的增加而减弱.而装载后的SBA-15在334和425 nm处的光伏响应信号随外加电场的变化而有不同的变化.     

Determination of fluoride in sea-water by molecular absorption spectrometry of aluminium monofluoride after removal cation and anion interferences

Three procedures are proposed for the determination of trace levels of fluoride in sea-water, based on the formation of aluminium monofluoride in an electrothermal graphite furnace, followed by measurement of its molecular absorption at 227.45 nm. They involve the use of dilution, a matrix modifier, or a matrix modifier and an ion-exchange resin, and are all acceptably sensitive and specific for fluoride. Interferences from cations and anions are removed by a simple 20-fold dilution of the sample. At 10-fold sample dilution, chloride interference can be removed by adding 0.3M ammonium nitrate together with 0.01M aluminium + 0.01M strontium as a matrix modifier. The same matrix modifier is valid for use with 5-fold sample dilution and a cation-exchange step to avoid matrix affects from cations and chloride. The detection limit is about 8-10 ng/ml fluoride and the determination limit is 20 ng/ml. The precision of peak-height measurement at 0.2 mug/ml is 5-7%.     

Laser desorption/ablation combined with nuclear analytical methods for materials characterization

Ubiquitous elements like carbon and oxygen always contaminate surfaces and, therefore, are the soucre of important analytical errors at trace level. Even in the case of radioactivation (with charged particles), where the sample can be etched after irradiation, analytical problems exist. In this work, we show that laser desorption/ablation can efficiently clean surfacaes, in the case of GaAs samples, resulting in better analytical conditions. Under ultra high vacuum, these surfaces remain clean long enough, so that the analysis of carbon and oxygen can be carried out using various nuclear methods, according to the needs of the analyst.     

Three-dimensional synchronous fluorimetric determination of indole-type auxins after derivatization with o-phthalaldehyde

A sensitive fluorimetric method for teh determination of indole-derivative plant-growth regulators of the auxin group (indole-3-acetic acid, indole-3-butyric acid and indole-3-propanoic acid) is based on their eaction with o-phthaladehyde in concentrated sulphuric acid. The fluorescence spectra of the three derivatives are very similar, but the advantages offered by a three-dimensional plot of the spectra, the synchronous derivative approach and the optimization of experimental variables permit the individual and simultaneous quantitation of mixtures of these compounds at the ng ml^-1 level.     

Utilizing ion mobility to identify isobaric post-translational modifications: resolving acrolein and propionyl lysine adducts by TIMS mass spectrometry

Protein post-translational modifications provide critical proteomic details towards elucidating mechanisms of altered protein function due to toxic exposure, altered metabolism, or disease pathogenesis. Lysine propionylation is a recently described modification that occurs due to metabolic alterations in propionyl-CoA metabolism and sirtuin depropionylase activity. Acrolein is a toxic aldehyde generated through exogenous and endogenous pathways, such as industrial exposure, cigarette smoke inhalation, and non-enzymatic lipid peroxidation. Importantly, lysine modifications arising from propionylation and acroleination can be isobaric – indistinguishable by mass spectrometry – and inseparable via reverse-phase chromatography. Here, we present the novel application of trapped ion mobility spectrometry (TIMS) to resolve such competing isobaric lysine modifications. Specifically, the PTM products of a small synthetic peptide were analyzed using a prototype TIMS – time-of-flight mass spectrometer (TIMS-TOF). In that the mobilities of these propionylated and acroleinated peptides differ by only 1%, a high-resolution mobility analysis is required to resolve the two. We were able to achieve more than sufficient resolution in the TIMS analyzer (~170), readily separating these isobars.     

Some Aspects of Selectivity in the Reaction of Glycosyl Donors*

Some advantages, disadvantages, and anomalies of various donors in glycosidations are discussed. By studying several two‐component donor/acceptor‐diol reactions, it is shown that regiopreferences are not very sensitive to the type of donor used. However, in competitive glycosidations within a given type of donor and between different types of donor, it is shown that regio‐ and chemoselectivities must be indexed to donor reactivity.     

Efficient synthesis of phosphotyrosine building blocks using imidazolium trifluoroacetate

We have successfully employed imidazolium trifluoroacetate as a replacement for tetrazole for efficient synthesis of phosphotyrosine. This modification is compatible with the protecting groups commonly used in solution phase and Fmoc-solid phase peptide synthesis.