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T Schlegel

Publications and source records attributed to T Schlegel.

At least 19 recordsLinked to original sources
PubMed2006

Transverse characteristics of short-pulse laser-produced ion beams: a study of the acceleration dynamics.

We report on first measurements of the transverse characteristics of laser-produced energetic ion beams in direct comparison to results for laser accelerated proton beams. The experiments show the same low emittance for ion beams as already found for protons. Additionally, we demonstrate that the divergence is influenced by the charge over mass ratio of the accelerated species. From these observations we deduced scaling laws for the divergence of ions as well as the temporal evolution of the ion source size.

Journal Article↗
PubMed2005

The normal cellular prion protein (PrPc) is strongly expressed in bovine endocrine pancreas.

Expression of the cellular prion protein (PrP(c)) has been shown to be crucial for the development of transmissible spongiform encephalopathies and for the accumulation of the disease-associated conformer (PrP(sc)) in the brain and other tissues. One of the emerging hypotheses is that the conversion phenomenon could take place at the site where the infectious agent meets PrP(c). In this work we have studied whether PrP(c), a protein found predominantly in neurons, could also exist in pancreatic endocrine cells since neuroectoderm-derived cells and pancreatic islet cells share a large number of similarities. For this purpose we have examined the expression of PrP(c) in a series of fetal and postnatal bovine pancreatic tissue by immunohistochemistry and RT-PCR. Using immunostained serial sections and specific antibodies against bovine PrP(c), insulin, glucagon, somatostatin, chromogranin A and chromogranin B we found that PrP(c) is highly expressed in all endocrine cells of fetal and adult pancreatic islets with a particular strong expression in A-cells. Moreover it became evident that the PrP(c) gene-neighbour chromogranin B as well as chromogranin A are coexpressed together with PrP(c). The selective expression of PrP(c) in the bovine endocrine pancreas is of particular importance regarding possible iatrogenic transmission routes and demonstrates also that bovine pancreatic islet cells could represent an interesting model to study the control of PrP-gene expression.

Animals↗
PubMed2004

Responsiveness of C-fiber nociceptors to punctate force-controlled stimuli in isolated rat skin: lack of modulation by inflammatory mediators and flurbiprofen.

Although cutaneous C-fiber nociceptors show dramatic inflammatory sensitization to heat, they do not appear to get sensitized to the mechanical stimulation by von Frey hairs. We employed force-controlled punctate electromechanical stimulation to receptive fields of 61 characterized C-fibers in the isolated rat skin-saphenous nerve preparation. In general: low-in contrast to higher-threshold units showed greater dynamic sensitivity and response magnitude, an earlier onset and a stronger degree of adaptation, the latter due to the linear rise of the force stimulus. On this methodological basis three groups of units were subject to a mix of inflammatory mediators, to flurbiprofen or to control solution. Subsequent mechanostimulation revealed a good reproducibility of the control response and no significant changes in the treatment groups. In conclusion, even refined mechanostimulation was unable to demonstrate sensitization of the predominant nociceptor classes in the rat skin.

Action Potentials↗
PubMed2004

Harmonic emission from the rear side of thin overdense foils irradiated with intense ultrashort laser pulses.

The harmonic emission from thin solid carbon and aluminum foils, irradiated by 150 fs long frequency-doubled Ti:sapphire laser pulses at lambda=395 nm and peak intensities of a few 10(18) W/cm(2), has been studied. In addition to the harmonics emitted from the front side in the specular direction, we observe harmonics up to the 10th order, including the fundamental from the rear side in the direction of the incident beam, while the foil is still strongly overdense. The experimental observations are well reproduced by particle-in-cell simulations. They reveal that strong coupling between the laser-irradiated side and the rear side occurs via the nonlocal electron current driven by the laser light.

Journal Article↗
PubMed2003

Dynamic confinement of targets heated quasi-isochorically with heavy ion beams.

Isochoric heating of matter by intense heavy ion beams promises to become a fruitful approach to warm dense matter studies. For heating times that are long on the hydrodynamic time scale of the target response a tamped target is essential. The proposed dynamic confinement provides homogeneous target heating by a low-Z tamper, which allows one to apply powerful x-ray scattering diagnostics. To demonstrate the potential of the method, heating of a hydrogen sample with the SIS-18 beam at GSI Darmstadt is investigated numerically. The intense x-ray bursts for diagnostics can be provided by the PHELIX laser currently installed at GSI. In the optimized heating regime, density variations can be reduced to a level of 15% from the initial density value.

Journal Article↗
PubMed2003

IgA and secretory component (SC) in the third eyelid of domestic animals: a comparative study.

OBJECTIVE: The third eyelid of domestic animals is important for the production and distribution of tears, in removing ocular debris and in protection of the globe, and has significant immunologic functions. Although it is known that tears contain antibodies of the immunoglobulin A (IgA) isotype which are produced mainly by plasma cells of the lacrimal gland, very little is known about the antibody repertoires in the third eyelid of domestic animals. To assess whether IgA is derived from local synthesis, we analyzed the location of IgA-producing cells and the cellular distribution of secretory component (SC) in the third eyelid of domestic animals in a comparative study. ANIMAL STUDIED: A total of 83 third eyelids of dogs, cats, pigs, cows, sheep, goats and horses were investigated in the course of this study. PROCEDURES: Third eyelids were obtained immediately after death, cut length-wise, fixed overnight and processed for immunohistochemical detection of IgA and SC by the ABC technique. RESULTS: The results show that IgA-producing plasma cells are densely populated in subepithelial spaces of the surface epithelium as well as in the nictitating gland in a species-specific manner. In contrast, the SC could be demonstrated exclusively in glandular acinar and ductal epithelial cells and in different cell types of the surface epithelium, preferentially located on the bulbar side of the nictitating membrane. CONCLUSION: It is suggested that most of the SC is locally produced by resident plasma cells and subsequently transferred through the surface epithelium and glandular duct cells by transcytosis. This indicates that the third eyelid is an important member of the secretory immune system in domestic animals.

Animals↗
PubMed2001

The cartilage of the third eyelid: a comparative macroscopical and histological study in domestic animals.

The purpose of this comparative study was to evaluate morphological differences between the cartilages of the third eyelid in dogs, cats, pigs, cows, small ruminants and horses. For that reason a total of 83 third eyelids were investigated. By the aid of a modified maceration technique, the three-dimensional form of the cartilage could be demonstrated for the first time. Generally, the cartilage consists of a long narrow appendix which is followed by a variable crossbar. In dogs the appendix is cone shaped in the basal end and extends to form a triangular plate. The former is crescent-like in shape and has a marked bulge. The cartilage of the cat consists of an appendix which is enlarged in the proximal end as compared to the dog. The crossbar resembles a reverse s-form with ends tapering off to a point. In contrast pig and cow cartilage possess a typical anchorform whereas the cartilage of small ruminants starts with a thin rod which extends in a slightly curved form ending in an oval plate. The crossbar is crescent-like in these animals. In the horse the base of the cartilage is surrounded by a massive fatty tissue and the crossbar has a characteristic hook-form. Moreover, there are significant differences in regard to the quality of the cartilage, especially concerning the presence and distribution of elastic fibres. In cats and horses the elastic fibres of the adjacent connective tissue penetrate the perichondrium. Additionally, the centre of the cartilage shows a very dense network consisting of fine elastic fibres. In dogs, pigs, cows and small ruminants the cartilage consists of hyaline quality and only in the neighbouring connective tissue are some elastic fibres detectable.

Animals↗
PubMed2000

Hydrodynamic simulation of subpicosecond laser interaction with solid-density matter

The interaction of ultrashort subpicosecond laser pulses with initially cold and solid matter is investigated in a wide intensity range (10(11) to 10(17) W/cm(2)) by means of the hydrodynamic code MULTI-FS, which is an extension of the long pulse version of MULTI [R. Ramis, R. Schmalz, and J. Meyer-ter-Vehn, Comput. Phys. Commun. 49, 475 (1988)]. Essential modifications for the treatment of ultrashort pulses are the solution of Maxwell's equations in a steep gradient plasma, consideration of the nonequilibrium between electrons and ions, and a model for the electrical and thermal conductivity covering the wide range from the solid state to the high temperature plasma. The simulations are compared with several absorption measurements performed with aluminum targets at normal and oblique incidence. Good agreement is obtained by an appropriate choice of the electron-ion energy exchange time (characterized by 10 to 20 ps in cold solid Al). In addition we discuss the intensity scaling of the temperature, of the pressure, and of the density, where the laser energy is deposited in the expanding plasma, as well as the propagation of the heat wave and the shock wave into the solid. For laser pulse durations >/=150 fs considered in this paper the amount of isochorically heated matter at solid density is determined by the depth of the electron heat wave in the whole intensity range.

Journal Article↗
PubMed2000

Hot-electron generation in copper and photopumping of cobalt

Hot electrons generated upon interaction of p-polarized 130 fs laser pulses with copper and penetrating into the target material are characterized with respect to their energy distribution and directionality. "Experimental" data are obtained by comparing the rear-side x-ray emission from layered targets with Monte Carlo electron-photon transport simulations. Theoretical electron energy distributions are derived by means of a one and a half-dimensional particle-in-cell code. Both sets of data consist of a two-temperature distribution of electrons propagating in a direction almost perpendicular to the target surface. The "experimental" data contain a considerably higher population of the lower temperature electrons. The discrepancy is explained by the intensity distribution of the laser spot. The results are used to design an experiment for demonstrating photopumping of cobalt with copper Kalpha radiation. A 10 &mgr;m copper foil is backed with 1 mm of polyethylene (PE) followed by 10 &mgr;m of cobalt, the rear-side Kalpha emission of which is measured. The PE layer prevents fast electrons from reaching the cobalt. Comparing the cobalt Kalpha emission with that of nickel, which is not photopumped by copper Kalpha shows enhancement by almost a factor of 2.

Journal Article↗
PubMed1999

Comparison of measured and calculated X-ray and hot-electron production in short-pulse laser-solid interactions at moderate intensities.

Ultrashort pulse laser-solid interaction experiments with 4x10(16) W/cm(2),120 fs, 45 degrees incidence angle, p-polarized pulses are theoretically analyzed with the help of 1(1/2)-dimensional (1(1/2) D) particle-in-cell (PIC) simulations. The laser impinges upon preformed plasmas with a precisely controlled density-gradient scale-length. PIC electron distribution functions are used as an input to 3D Monte Carlo simulations to interpret measured electron distributions and Kalpha radiation emission. Satisfactory agreement between the experimental and simulation results is obtained for the measured absorption coefficient, the energy distribution of the back-scattered hot electrons, the hot-electron temperature in the bulk of the target, and the Kalpha yield, when the preplasma scale-length is varied.

Journal Article↗
PubMed1999

Hot-electron distribution functions in a subpicosecond laser interaction with solid targets of varying initial gradient scale lengths.

We have studied the distribution function of the hot electrons produced during the interaction of a 120-fs, 60-mJ, 800-nm wavelength and a p-polarized laser pulse with bilayered Al/Fe targets. The main pulse interacts with a preformed plasma, obtained with a controlled prepulse, whose density gradient scale length has been measured. The electron distribution function is characterized by means of the Kalpha emission of the two materials of the target as a function of the Al-layer thickness. The low-energy region (<50 keV) of the hot-electron distribution function shows no dependency in shape on the gradient scale length, but only a variation in the total number of the generated electrons. The comparison between the experimental results and the particle-in-cell and Monte Carlo calculations of the electron distribution function and the Kalpha emission is gratifying.

Journal Article↗
PubMed1996

Electromyographic and kinematic analysis of graded treadmill walking and the implications for knee rehabilitation.

Muscle activity, joints, angles, and heart rate during uphill walking were compared for application in knee rehabilitation. The objectives of this study were to quantify muscle activation levels at different treadmill grades and to determine the grade(s) at which knee range of motion would not further compromise the joint. Average and peak electromyographic activity of the quadriceps (vastus medialis oblique and vastus lateralis) and hamstrings (biceps femoris and medial hamstrings (semimembranosus/semitendinosus)] was recorded during walking at 0, 12, and 24% grade. Six subjects (age = 28.5 +/- 3.7 years, stature = 1.79 +/- .05 m, and mass = 74.7 +/- 7.9 kg) walked at self-selected speeds at each grade while ankle, knee and hip angles, heart rate, and electromyographic activity (surface electrodes) were recorded. Maximum voluntary contractions provided a relative reference for the electromyographic activity during walking. Average and peak electromyographic activity increased significantly across grades for the vastus medialis oblique (125 and 154%), vastus lateralis (109 and 139%), and biceps femoris (53 and 46%), but remained similar for the medial hamstrings. Maximum knee flexion at heel strike increased significantly with grade. Despite decreased self-selected speeds with increasing grade, there were significant increases in heart rate across grades. The results of this study provide a basic understanding of the quadriceps and hamstrings activity levels, lower extremity joint range of motion, and cardiovascular requirements of graded treadmill walking in normal subjects. The results also suggest that a grade just greater than 12% may be most beneficial for knee rehabilitation to minimize patellofemoral discomfort or potential strain on the anterior cruciate ligament. The benefits achieved through this functional activity encourage its implementation in rehabilitation and provide a basis for comparison with injured patients.

Adult↗
PubMed1990

[Automatic sleep analysis. I. Scoring of parameters].

EEG, EOG, EMG and motility are recorded and preprocessed by hardware filtering of EEG and hardware detection of sigma spindles, rapid eye movements (REMs) and delta-waves (greater than 45 microV). After AD-conversion calculation of mean values and smoothing, the sleep-wake-process can be represented by the time-curves of 8 parameters: mean amplitudes per epoch (30 s) of EMG, motility and EEG (in the delta- alpha- and beta-band), delta-time (time/epoch of counted delta-waves) and presence or absence of spindles and REMs per epoch. These parameters can be presented graphically or stored for further analysis of sleep stages, sleep structure or sleep periodicity.

Delta Rhythm↗
PubMed1990

[Automatic sleep analysis--II. Determination of sleep stages].

The presented automatic sleep analysis is based on the time courses of the mean amplitudes of EEG (delta, beta and alpha bands), EMG and motility and specific patterns (spindles, REMs, delta waves greater than 40 microV) detected automatically. The interindividual variability of the parameters is taken into consideration by interactively determining the threshold levels. Sleep stages are classified for every epoch using context free decision rules according to the manual of Rechtschaffen and Kales. The resulting cyclograms are smoothed and corrected using context sensitive rules which considers the successive epochs and the probability of stage transitions.

Autoanalysis↗