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Calculations are presented for the generation of an isolated attosecond pulse in a multicycle two-color strong-field regime. We show that the recollision of the electron wave packet can be confined to half an optical cycle using pulses of up to 40 fs in duration. The scheme is proven to be efficient using two intense beams, one producing a strong field at omega and the other a strong field detuned from 2omega. The slight detuning deltaomega of the second harmonic is used to break the symmetry of the electric field over many optical cycles and provides a coherent control for the formation of an isolated attosecond pulse.

We demonstrate the first example of a closed-loop adaptive control experiment in the soft-x-ray spectral region. The branching ratio of the dissociative photoionization of sulfur hexafluoride (SF(6)) can be maximized and minimized by applying tailored soft-x-ray femtosecond light fields. The spectrally shaped coherent soft-x-ray pulses are produced by high-harmonic generation driven by phase-shaped femtosecond laser pulses. The stability of the shaped high-harmonic output is high enough to perform adaptive control experiments, albeit its strong nonlinear dependence on the driving laser pulse shape. This experiment opens the door to the application of pulse-shaping and coherent-control techniques in the soft-x-ray range.

The concept of heterodyne mixing of laser fields is theoretically applied to the process of high-harmonic generation to enhance and modulate the kinetic energy of the active electron on subcycle time scales. A very small amount of intensity in the heterodyne field creates a significant modification of the electron kinetic energy, due to its amplification by the strong fundamental field in the kinetic-energy term, in which the heterodyne mixing occurs. Quantum calculations are carried out to verify the predictions of the classical results, demonstrating very good qualitative and quantitative agreement. Applications of the heterodyne-mixing concept are the extension of the harmonic cutoff to higher photon energies and the temporal gating of attosecond pulse production.

We experimentally demonstrate an efficient way to control and stabilize single optical filaments initiated by ultrashort laser pulses in a rare gas medium. This is done by the application of a stationary two-dimensional phase mask to the laser beam prior to focusing. Simple circular phase-step patterns of a given radius and relative phase are sufficient to stabilize the pointing of the filament output and to optimize the spectral bandwidth of the light without any resulting loss of input laser power.

We present a method of producing single attosecond pulses by high-harmonic generation with multicycle driver laser pulses. This can be achieved by tailoring the driving pulse so that attosecond pulses are produced only every full cycle of the oscillating laser field rather than every half-cycle. It is shown by classical and quantum-mechanical model calculations that even a minor addition (1%) of phase-locked second-harmonic light to the 800 nm fundamental driver pulse for high-harmonic generation leads to a major (15%) difference in the maximum kinetic energies of the recombining electrons in adjacent half-cycles.

Two major metabolites and one minor metabolite of sulfadiazine were found in pig manure, using a special combination of different MS techniques like parent and product ion scans, H/D exchange, accurate mass measurement, and MS/MS experiments with substructures. N4-acetylsulfadiazine and 4-hydroxysulfadiazine were identified as major metabolites. N4-acetylsulfadiazine could be verified by H/D exchange and comparison with product ion spectra of a synthetic reference compound. In the case of 4-hydroxysulfadiazine, the majority of possible isomers could be discounted after H/D exchange. Substructure-specific MS/MS experiments with fragment ions and comparison with product ion spectra of two references revealed the presence of 4-hydroxysulfadiazine. The minor metabolite was characterized to some degree using H/D exchange and tandem mass spectrometry in combination with a high-resolution time of flight mass spectrometer. The aminopyrimidine moiety contained an additional modification with a likely elemental composition of C2H4O and no further acidic hydrogen.

We demonstrate the control of high-harmonic generation in a hollow fiber by shaping the spatial structure of the generating laser pulse. We use a liquid-crystal-based two-dimensional spatial light modulator to control the spatial phase of the driver pulse. An evolutionary algorithm finds the spatial laser phase distribution that is optimal for reaching maximum total harmonic yield and for selectively enhancing the cutoff region of the spectrum. We show that enhacement of harmonic generation is related to coupling into a single fiber mode. Our results directly show that spatial properties of the laser are important parameters in fully controlling the high-harmonic spectrum. It is thus not possible to derive the controllability of the high-harmonic generation from the single-atom response only.

Introduction: Fibrin sealants (FS) have been used for many years to facilitate hemostasis and to provide suture support and sealing/adhesion of tissues after surgery. While their composition is similar, different formulations, application devices, and varying concentrations of key components mean that the properties of clots formed by individual FS can be diverse., Materials and Methods: We performed several studies, including animal models, to compare the properties of 12 different commercially available FS/application device combinations using partial liver and kidney resection models to assess hemostatic efficacy and a novel pig skin model to measure adhesive clot strength. The quality of mixing was determined using colored spray images., Results: Although the FS tested shared the principle of combining fibrinogen and thrombin, major differences were found between the individual preparations with regard to hemostatic efficacy. Two pre-requisites for successful early hemostasis were identified--adequate clottable protein content and the ability of the application device to effectively mix the fibrinogen and thrombin components of the FS. Factor XIII activity was a key determinant in prevention of re-bleeding and premature clot lysis. Furthermore, FS lacking measurable factor XIII activity formed the weakest, softest clots., Conclusions: Clearly, all FS are not the same, and their different characteristics may potentially translate into different clinical outcomes. In our studies, while all FS tested performed well on individual parameters, Beriplast P (Aventis Behring) was the foremost FS in consistently providing early hemostasis, minimizing the risk of re-bleeding, and providing strong adhesive clots capable of resisting mechanical forces.

A method for the determination of sulfonamides and trimethoprim in the complex matrix liquid manure has been developed using reversed-phase liquid chromatography and atmospheric pressure chemical ionization (APCI) tandem mass spectrometry. A comparison was made between electrospray and atmospheric pressure chemical ionization. APCI proved to be more robust and less sensitive to matrix effects. High-performance liquid chromatographic (HPLC) separation of the analytes was achieved in less than 7 min. The compounds were extracted with ethyl acetate and the extracts were cleaned up by solid-phase extraction on an aminopropyl column. Recoveries were not dependent on the concentration level. The mean recoveries were as follows: trimethoprim 79.0%, sulfadiazine 80.5%, N(4)-acetylsulfadiazine 91.0%, sulfamerazine 78.6%, sulfadimidine 77.2% and sulfamethoxazole 82.8%. Linearity was established over a concentration range of 5 to 5000 microg/kg with correlation coefficients greater than 0.99. The method had a limit of quantitation (LOQ) of 5 microg/kg manure., (Copyright 2002 John Wiley & Sons, Ltd.)