Versatile optical laser system for experiments at the European X-ray free-electron laser facility.

We present the main features of the final prototype of a pulsed optical laser, developed for pump-probe and other experiments in conjunction with the femtosecond x-ray beams at the European X-ray free-electron laser facility. Adapted to the temporal x-ray emission pattern of the facility, the laser provides 10 Hz bursts of up to 600 µs duration with intra-burst pulse frequencies as high as 4.5 MHz. In this mode, we have generated pulses as short as 12 fs at 350 W average power during the burst and with beam qualities close to the diffraction limit. This is, to the best of our knowledge, the highest power to date of a few-cycle laser operating at a center wavelength of 800 nm. Important for experimental flexibility, the laser can be configured in various unique ways, enabling, e.g., energy scaling to >3 mJ per pulse through a frequency change down to 100 kHz and the generation of nearly transform limited pulses between 12 fs and 300 fs. In addition to the 800 nm femtosecond beam line, a synchronized long pulse (0.8 ps or 400 ps) 1030 nm beam can be utilized, offering up to 4 kW burst average power, i.e. up to 40 mJ per pulse at 100 kHz. Efficient nonlinear wavelength conversion and tuning through intrinsic and external means further enhance the capabilities of the laser.

High power burst-mode optical parametric amplifier with arbitrary pulse selection.

We present results from a unique burst-mode femtosecond non-collinear optical parametric amplifier (NOPA) under development for the optical - x-ray pump-probe experiments at the European X-Ray Free-Electron Laser Facility. The NOPA operates at a burst rate of 10 Hz, a duty cycle of 2.5% and an intra-burst repetition rate of up to 4.5 MHz, producing high fidelity 15 fs pulses at a center wavelength of 810 nm. Using dispersive amplification filtering of the super-continuum seed pulses allows for selectable pulse duration up to 75 fs, combined with a tuning range in excess of 100 nm whilst remaining nearly transform limited. At an intra-burst rate of 188 kHz the single pulse energy from two sequential NOPA stages reached 180 µJ, corresponding to an average power of 34W during the burst. Acousto- and electro-optic switching techniques enable the generation of transient free bursts of required length and the selection of arbitrary pulse sequences inside the burst.

Compact picosecond mode-locked and cavity-dumped Nd:YVO4 laser.

We report on a diode pumped, semiconductor saturable absorber mirror mode-locked picosecond Nd:YVO(4) oscillator with cavity-dumping. In pure cw-mode-locking this laser produced up to 17W of average power at a pulse repetition rate of 9.7MHz, corresponding to a pulse energy of 1.7microJ. Using an electro-optic cavity dumper, we achieved average powers up to 7.8W at 500kHz and 10W at 1MHz dumping rate. With corresponding pulse energies of 15.6microJ and 10microJ respectively and pulsewidths around 10ps, this laser could become a compact source for materials processing applications, alternative to more complex schemes such as regenerative amplifiers or ultra-long resonator oscillators.

Femtosecond all-optical synchronization of an X-ray free-electron laser.

Many advanced applications of X-ray free-electron lasers require pulse durations and time resolutions of only a few femtoseconds. To generate these pulses and to apply them in time-resolved experiments, synchronization techniques that can simultaneously lock all independent components, including all accelerator modules and all external optical lasers, to better than the delivered free-electron laser pulse duration, are needed. Here we achieve all-optical synchronization at the soft X-ray free-electron laser FLASH and demonstrate facility-wide timing to better than 30 fs r.m.s. for 90 fs X-ray photon pulses. Crucially, our analysis indicates that the performance of this optical synchronization is limited primarily by the free-electron laser pulse duration, and should naturally scale to the sub-10 femtosecond level with shorter X-ray pulses.

Characterization of pseudo-islets formed from pancreatic islet cell suspensions of neonatal rats.

Well-preserved pancreatic islet cell suspensions were prepared from islets of Langerhans of neonatal rats by gentle trypsin treatment. Within a culture period of 4-6 days the islet cells reaggregate spontaneously and form pseudo-islets of different size and of a variable insulin content. While the ratio of insulin to glucagon in isolated islets of Langerhans is constant (18 +/- 1.9), the hormone ratio of the pseudo-islets is strongly variable and increased, indicating an excess of insulin. Glucose enhancement from 1.5 mmoles/l to 15 mmoles/l results in a significant stimulation of (pro)insulin biosynthesis whereas insulin secretion of the pseudo-islets is only slightly increased. At high glucose concentration (15 mmoles/l) insulin secretion of the pseudo-islets can be potentiated (by a factor of 4.5 +/- 0.46) by 3-isobutyl-l-methylxanthine (IBMX). Compared with the initial islet cell suspension, the cell aggregation during pseudo-islet formation did not result in an enhanced secretory response on glucose stimulation.

Evaluation of the efficacy of 2',3'-dideoxycytidine against adenovirus infection in a mouse pneumonia model.

The antiviral activity of 2',3'-dideoxycytidine (ddC) has been investigated in a mouse pneumonia model. Consolidation of lung, histopathological changes, DNA synthesis as well as levels of TNFalpha were assayed. In this in vivo model, the oral administration of ddC twice daily over 4 days, displayed an inhibitory effect. The drug significantly reduced histopathologic responses. Analysis indicated that under treatment pulmonary lesions were less severe than those of untreated controls. These data confirm the in vitro activity of ddC against adenovirus. Thus, ddC represents a potential therapeutic approach for inhibiting adenovirus infection and may offer promise as an anti-adenovirus agent for immunocompromised patients in whom serious adenovirus infection may prove fatal.

Inhibitory activity of 3'-fluoro-2' deoxythymidine and related nucleoside analogues against adenoviruses in vitro.

Antiviral effects of nucleoside analogues against human adenoviruses (ADV) belonging to subgroup B (ADV3) and C (ADV2) were comparatively analysed using focus reduction assay on Fogh and Lund (FL) cells. 3'-Fluoro-2'-deoxythymidine (FTdR), 3'-fluoro-2'-deoxyuridine (FUdR), 2',3'-dideoxycytidine (ddC) and 3'-fluoro-2'-deoxyguanosine (FGdR) emerged as potent and selective inhibitors. They were nontoxic for the FL cells at the tested doses. FTdR was proved to be the most effective inhibitor against both serotypes ADV2 and ADV3 (0.05 microM/0.02 microM). The inhibitory effect of FTdR was also analyzed on the level of viral proteins and viral DNA synthesis using radioimmunoprecipitation and PCR, respectively. Neither the main structural protein of ADV, the hexon, nor viral DNA could be detected in ADV-infected FL cells that had been exposed to FTdR.

Real-time PCR to improve the diagnosis of respiratory syncytial virus infection.

Respiratory syncytial virus (RSV) is one of the most important virus respiratory pathogens in infants and young children. A rapid and sensitive diagnosis is essential to focus any outbreak due to this virus. A real-time RT-PCR method was designed using a primer/probe pair from the F gene. Simultaneously with nested RT-PCR and antigen ELISA, 71 consecutive specimens from hospitalized children with clinical symptoms of acute respiratory distress were evaluated to confirm the incidence of RSV infection. RSV was detected in 25 (35.2 %) specimens by real-time RT-PCR and in 19 (26.7 %) by nested RT-PCR. The assay was specific for RSV. The procedure offers a rapid and sensitive alternative to conventional RT-PCR. Closed-tube detection eliminates the risk of contamination.

Fluorescent focus reduction assay for the screening of antiadenoviral agents.

A method for screening of antiviral compounds against adenoviruses was established. Test compounds were diluted and plated in chamber slides for tissue culture. Drug-treated, virus-infected cultures were stained with fluorescein isothiocyanate conjugated rabbit antibodies against adenovirus hexon type 2 and fluorescent cells were counted by microscopy. This assay is more sensitive than the colorimetric method and requires smaller volumes of compounds when compared with the standard method using plaque assay.

Functional characterization of a muscarinic receptor stimulating gastrin release from rabbit antral G-cells in primary culture.

In previous studies carbachol-induced stimulation of gastrin release from antral G-cells in primary culture suggested the presence of muscarinic acetylcholine receptors on this cell type. Therefore, we attempted to pharmacologically characterize the muscarinic acetylcholine receptor subtype involved. Enzymatically isolated rabbit antral mucosal cells (0.8% G-cells) were separated by counterflow elutriation yielding a fraction (1.7% G-cells) that was placed in culture on collagen-coated well plates. After 24-36 h of culture 13.0 +/- 2.4% of total adherent cells were immunoreactive for gastrin as shown by immunocytochemical staining using the avidin-biotin complex method. In this preparation basal gastrin release ranged from 3.3 +/- 0.3 to 4.1 +/- 0.3% of total cellular content. Maximal gastrin release in response to the acetylcholine receptor agonist carbachol (10(-4) M) or the selective muscarinic receptor agonist arecaidine propargyl ester (10(-4) M) was 8.5 +/- 0.4% and 7.6 +/- 0.4% of total cellular content, respectively. The EC50 values were 3.7 +/- 0.5 x 10(-6) M carbachol and 1.8 +/- 0.4 x 10(-6) M arecaidine propargyl ester. At a concentration of 10(-6) M the non-selective muscarinic receptor antagonist atropine and the muscarinic M3 receptor preferring antagonist hexahydro-sila-difenidol (HHSiD; M3 > or = M1 > M2) completely inhibited gastrin release in response to carbachol (Ki values: 52 x 10(-9) M atropine and 29 x 10(-9) M HHSiD) and arecaidine propargyl ester (Ki values: 11 x 10(-9) M atropine and 13 x 10(-9) M HHSiD).(ABSTRACT TRUNCATED AT 250 WORDS)

Response of cellular antioxidants to ozone in wheat flag leaves at different stages of plant development.

The effect of ozone (O3) on growth, yield and foliar antioxidants of spring wheat (Triticum aestivum L. cv. Turbo) was investigated in 1990 and 1991 in Braunschweig, Germany. Plants were grown full-season in pots in open-top chambers ventilated with charcoal-filtered (CF) air to which one or two levels of O3 were added. Mean 8 h day(-1) (10.00-18.00 h) O3 concentrations in the CF and CF + O3 treatments were 5.9, 61.2 and 92.5 nl litre(-1) in 1990, and 4.7 and 86.4 nl litre(-1) in 1991. Plants that received the high O3 level showed symptoms of premature senescence of the oldest leaves and yield reductions in both growing seasons. The contents of ascorbate and glutathione and the enzyme activities of ascorbate peroxidase and glutathione reductase were measured in symptomless flag leaves in weekly intervals before and after the beginning of anthesis. Leaf age had a significant effect on all antioxidants investigated. The O3 exposures of about 90 nl litre(-1) increased the activity of ascorbate peroxidase and the concentration of glutathione, but there were no pollutant effects on ascorbate content and glutathione reductase activity. Measurements of the antioxidant levels throughout one day showed no clear indications of diurnal changes in the antioxidative capacity in wheat flag leaves. The results are discussed in relation to the role of antioxidants in O3 detoxification.

Screening of Nepalese medicinal plants for antiviral activity.

In an ethnopharmacological screening, plants used in Nepalese traditional medicine were evaluated for antiviral activity. Methanolic and methanolic-aqueous extracts derived of 23 species were assayed in two in vitro viral systems, influenza virus/MDCK cells and herpes simplex virus/Vero cells. Two species, Bergenia ligulata and Nerium indicum showed the highest antiinfluenzaviral activity with 50% inhibitory dose of 10 microg/ml. Holoptelia integrifolia and N. indicum exhibited considerable antiviral activity against herpes simplex virus. None of these extracts showed cytotoxic effects. Additionally for B. ligulata and H. integrifolia partial protease inhibitory activity was estimated.

Antiviral lanostanoid triterpenes from the fungus Ganoderma pfeifferi.

Ganodermadiol, lucidadiol and applanoxidic acid G were isolated as first triterpenes from the European Basidiomycete Ganoderma pfeifferi. The compounds show antiviral activity against influenza virus type A and HSV type 1.

Inhibitory effect of Bergenia ligulata on influenza virus A.

Methanol water extract from rhizomes of Bergenia ligulata, a plant used in Nepalese ethnomedicine, inhibited in vitro the replication of influenza virus in a dose dependent manner and did not show virucidal activity at effective concentration. Pretreatment of cells with B. ligulata extract was shown to be most effective to prevent cell destruction. The extract inhibited viral RNA synthesis and reduced viral peptide synthesis at 10 microg/ml. The virus inhibitory effect is related to the presence of condensed tannins in the extract.

Single-shot pulse duration monitor for extreme ultraviolet and X-ray free-electron lasers.

The resolution of ultrafast studies performed at extreme ultraviolet and X-ray free-electron lasers is still limited by shot-to-shot variations of the temporal pulse characteristics. Here we show a versatile single-shot temporal diagnostic tool that allows the determination of the extreme ultraviolet pulse duration and the relative arrival time with respect to an external pump-probe laser pulse. This method is based on time-resolved optical probing of the transient reflectivity change due to linear absorption of the extreme ultraviolet pulse within a solid material. In this work, we present measurements performed at the FLASH free-electron laser. We determine the pulse duration at two distinct wavelengths, yielding (184±14) fs at 41.5 nm and (21±19) fs at 5.5 nm. Furthermore, we demonstrate the feasibility to operate the tool as an online diagnostic by using a 20-nm-thin Si3N4 membrane as target. Our results are supported by detailed numerical and analytical investigations.

Molecular and clinical characteristics of respiratory syncytial virus infections in hospitalized children.

The objective of this study was to determine the importance of respiratory syncytial virus (RSV) for hospitalization in the north east of Germany and to obtain molecular epidemiological data of the circulating strains. Using a rapid and sensitive reverse transcriptase-PCR, it was found that a quarter of pediatric respiratory disease admissions were due to RSV. Infections caused by RSV in hospitalized patients were determined over the whole year. Both RSV groups A and B were identified with a predominance of RSV A (86%) over the entire period. The analysis of the deduced amino acid sequences by direct sequencing showed that very similar RSV strains are circulating in the community.

Cyanobacteria a potential source of antiviral substances against influenza virus.

Aqueous and methanolic extracts of cultured cyanobacteria of several genera, Microcystis, Nodularia, Oscillatoria, Scytonema, Lyngbya and Calothrix were evaluated for their in vitro antiviral activity against influenza A virus in Madin Darby canine kidney cells. None of the methanolic extracts showed cytotoxic effects. The inhibitory concentration (IC(50)) of antiviral activity ranged between 20.0 micro g to 79.0 micro g extract/ml. The most active extract in this screening derived from genus Microcystis. The further analysis of methanolic extracts of cultured strains of genus Microcystis revealed a remarkable antiviral activity against influenza A virus for M. aeruginosa, M. ichthyoblabe and M. wesenbergii. The observed antiviral activity was associated with protease inhibitory activity of approximately 90% and suggest that protease inhibitory activity may be responsible for reducing virus replication. These results show that cyanobacteria are able to produce compounds with biological activity that may be of potential clinical interest.

Ultrasound for diagnosis of apophyseal injuries.

Avulsion injuries of the apophysis is a problem in young athletes. A correct diagnosis is necessary for establishing the appropriate treatment and the rehabilitation program. However, it is often difficult to distinguish between a simple muscle strain and an avulsion fracture. The X-ray examination is helpful only when an ossification center of the apophysis exists. Ultrasonography is considered the suitable diagnostic tool for these cases. From June 1988 to June 1993, 243 young athletes were seen with an anamnestic and clinically suspected apophyseal injury of the lower extremity. In all cases X-ray examination and ultrasound examination were performed. In 80 cases the diagnosis was confirmed by X-ray examination and in 97 by ultrasonography. Four criteria were defined for the sonographic examination: (a) a hypoechogenic zone, (b) increased distance to the apophysis, (c) dislocation of the apophysis, and (d) mobility of the apophysis on dynamic examination. These criteria are correlated to (a) edema, (b) lysis, (c) avulsion, and (d) unstable avulsion of the apophysis. Ultrasonography is a proven technique for the detection of apophyseal injuries. In comparison to X-ray examination, it has the advantages of no radiation exposure, early detection even without ossification center, and dynamic examination.