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Biomedical subjects

R Bartels

Publications and source records attributed to R Bartels.

At least 19 recordsLinked to original sources
PubMed2001

Generation of broadband VUV light using third-order cascaded processes.

We report the first demonstration of broadband VUV light generation through cascaded nonlinear wave mixing in a gas. Using a hollow-fiber geometry to achieve broad-bandwidth phase-matching, frequency conversion of ultrashort-pulse Ti:sapphire laser pulses from the visible into the deep UV around 200 and 160 nm is achieved. A new type of quasi-phase-matching is also observed in the VUV for the first time. Conversion using cascaded processes exhibits higher efficiencies, shorter pulse durations, and broader bandwidths than other schemes for generating light in the deep UV, and will enable many applications in science and technology.

Journal Article↗
PubMed2001

Attosecond time-scale intra-atomic phase matching of high harmonic generation.

Using a model of high-harmonic generation that couples a fully quantum calculation with a semiclassical electron trajectory picture, we show that a new type of phase matching is possible when an atom is driven by an optimal optical waveform. For an optimized laser pulse shape, strong constructive interference is obtained in the frequency domain between emissions from different electron trajectories, thereby selectively enhancing a particular harmonic order. This work demonstrates that coherent control in the strong-field regime is possible by adjusting the peaks of a laser field on an attosecond time scale.

Journal Article↗
PubMed2000

Shaped-pulse optimization of coherent emission of high-harmonic soft X-rays

When an intense laser pulse is focused into a gas, the light-atom interaction that occurs as atoms are ionized results in an extremely nonlinear optical process--the generation of high harmonics of the driving laser frequency. Harmonics that extend up to orders of about 300 have been reported, some corresponding to photon energies in excess of 500 eV. Because this technique is simple to implement and generates coherent, laser-like, soft X-ray beams, it is currently being developed for applications in science and technology; these include probing the dynamics in chemical and materials systems and imaging. Here we report that by carefully tailoring the shapes of intense light pulses, we can control the interaction of light with an atom during ionization, improving the efficiency of X-ray generation by an order of magnitude. We demonstrate that it is possible to tune the spectral characteristics of the emitted radiation, and to steer the interaction between different orders of nonlinear processes.

Journal Article↗
PubMed1998

Simple, rapid and sensitive determination of protionamide in human serum by high-performance liquid chromatography.

A simple high-performance liquid chromatography method has been developed that allows the sensitive determination of protionamide (2-n-propyl-pyridine-4-carboxylic acid thioamide, PTH) in human serum. After pretreatment of the serum with trichloroacetic acid (TCA) and centrifugation the supernatants were neutralized using NaHCO3. PTH was separated on a Kromasil 100 C4 column (acetonitrile-sodium tetraborate buffer pH 8-dibutylamine) and determined photometrically at 291 nm. The lower limit of quantification for 300 microl serum precipitated with 60 microl TCA and injection of 50 microl was 27 microg/l and linearity was observed up to 15 mg/l.

Antitubercular Agents↗
PubMed1997

[Effect of physical activity on incidence of sudden cardiac death. Study of the Berlin-Reinickendorf and Berlin-Spandau population].

AIM: Our investigation examined the influence of regular physical activity and sudden extrenious situations on the incidence of sudden cardiac death (scd) in two different Berlin districts with a total population of 219,251 in the examined age-groups. PATIENTS AND METHOD: All cases of scd which occurred outside of the hospital and were documented as been induced from ventricular fibrillation were examined over a time period of 18 months. For each case the amount of and the intensity of their regular physical activity was determined. In addition the stress of the sudden extrenious situations was survived. The study population was divided into various groups depending upon their level of regular physical activity. For each group the incidence of sudden cardiac death was determined. Then the relative risk for scd during strenuous activity compared to inactivity was determined for each group. The influence of preexisting disease was calculated. RESULTS: 77 patients with scd induced from ventricular fibrillation were included in our study. In the sedentary group we found an incidence of 4.69 scd per 10(5) person-years, in the group with a low level of regular physical activity we found an incidence of 4.25, in the group with a middle level of regular physical activity an incidence of 2.63 and in the most active group 0.92 scd per 10(5) person-years. We found the relative risk for scd during highly strenuous activity compared with inactivity to be 150 in the sedentary group as opposed to 4.0 in the most active group. The preexisting illness status of the case-groups had no influence on the outcome. CONCLUSIONS: The results show that the risk of scd for all persons regardless of their levels of regular physical activity and their preillness status is higher during strenuous activity than during inactivity. The increase of the risk for scd during activity is the highest for persons with sedentary lifestyles, whereas the risk increase for persons with active lifestyles is minimal. The protective effect of regular physical activity for scd by far exceeds the risk increase of the actual strenuous situation.

Adult↗
PubMed1996

Determination of rifabutin by high-performance liquid chromatography using on-line concentration and column switching.

A simple HPLC method has been developed that allows the sensitive determination of rifabutin (RBT) in human serum using on-line concentration and column switching. After pretreatment of the serum with acetonitrile and centrifugation, the samples were applied to a concentration column (CC) (Zorbax CN). Washing with phosphate buffer-methanol removed most of the contaminating substances. Via a six-port valve the CC was switched to the analytical mode. RBT was separated on a Chromspher RP 8 column (acetonitrile-phosphate buffer pH 7.4/sodium chloride) and determined photometrically at 278 nm. The lower limit of quantification for 200 microliters serum precipitated with 200 microliters acetonitrile and after injection of 2 x 150 microliters was 33 micrograms/l and linearity was observed up to 27 mg/l. Different modes of sample application (single, repeated, and different injection volume portions), as well as washing time, cycle time and different CC materials were investigated.

Antitubercular Agents↗
PubMed1990

Improved methods for the purification of enzymes of the folate pathway in Escherichia coli. I. Chromatographic methods.

A sequence of chromatographic procedures is described for the isolation of three consecutive enzymes of the folate pathway in Escherichia coli: hydroxymethyldihydropteridine pyrophosphokinase (E.C. 2.7.6.3) (I), 7,8-dihydropteroate synthase (E.C. 2.5.1.15) (II) and 7,8-dihydrofolate reductase, (E.C. 1.5.1.3) (III). Starting with the crude extract, ion-exchange chromatography on a DEAE-Sepharose CL-6B column with a salt gradient completely separated I, II and III. I and II were further purified by hydrophobic-interaction chromatography on Phenyl-Sepharose CL-4B, followed by size-exclusion chromatography on Ultrogel AcA 54. For III only size-exclusion chromatography was used. The overall enrichment factors, on the basis of protein, were 13,700-fold for I, 280-fold for II and 500-fold for III. Bacterial batches of more than 500 g were handled.

Chromatography, Ion Exchange↗
PubMed1985

The economic costs of schizophrenia. Implications for public policy.

The direct and indirect costs associated with schizophrenia in Australia were calculated using the incidence approach and compared with similar costings of myocardial infarction in Australia and the United States. In Australia schizophrenia affects one-twelfth as many people as does myocardial infarction, yet costs half as much. This is because the stream of costs associated with each case of schizophrenia is six times the stream of costs associated with myocardial infarction. To illustrate the utility of this costing approach, the information was used to estimate the cost-benefit ratio likely to follow the introduction of social intervention strategies. The information also showed that Australian support for research in schizophrenia is inadequate when compared with that for myocardial infarction and quite out of proportion to the cost of schizophrenia to the community.

Adolescent↗
PubMed1985

Estimating the economic costs of schizophrenia.

The economic costs of schizophrenia in New South Wales, Australia, were estimated using an incidence-based approach. The incidence of the disease was obtained from a case register. Direct treatment costs were calculated from length of stay data, the probability of readmission, and a direct costing of inpatient and outpatient care. Indirect costs were calculated from tables of average weekly earnings and work-force participation rates modified for the expected types of outcome. The prodrome was costed similarly. Costs were $139 million (in 1975 U.S. dollars), or $29 per head of the population of the State. A sensitivity analysis indicated that the likely margin of error of the estimate was plus or minus 15 percent. Comparison with the costs of myocardial infarction (in the same State at the same time and costed by the same methods) demonstrated that schizophrenia is a costly disease.

Adolescent↗
PubMed1981

Blood oxygen transport and organ weights of small bats and small non-flying mammals.

Blood oxygen transport properties and organ weights of five bat species in the weight range between 4.8 and 150 g have been investigated and compared to four similar-size non-flying mammals. In addition allometric organ weight-body weight relations have been compiled for both groups. All bats had higher relative heart weights than the terrestrial mammals. In both groups the relative heart weight increased with decreasing body weight. In bats hemoglobin concentrations (18.2--24.4 g Hb/dl), hematocrits (51--63%), and red blood cell counts (11.0 x 10(6)--26.2 x 10(6) RBC/microliter) were remarkably increased compared to non-flying mammals (15.3--17.4 g Hb/dl, 44--50% Hct, 8.8 x 10(6)--18.3 x 10(6) RBC/microliters). The highest values have been found in the smallest european bat Pipistrellus pipistrellus (4.8 g), they exceeded by far the results of the smallest terrestrial mammal, the shrew Suncus etruscus (2.5 g). Oxygen half saturation pressures and Bohr factors did not show considerable differences between similar-size flying and non-flying mammals. Our results indicate that the higher specific oxygen uptake of flying bats compared to exercising non-flying mammals is mainly enabled by larger hearts and larger blood oxygen capacities.

Animals↗
PubMed1979

Acclimatization of newborn rats and guinea pigs to 3000 to 5000 m simulated altitudes.

Two species of newborn rodents (guinea pigs and rats) were acclimatized to simulated altitudes of 3000 to 6000 m during 2 to 8 weeks after birth. Body weight increase was significantly retarded in both species at altitudes of 5000 m and higher. Heart weight relative to body weight increased by 50% at 3000 m and 300% at 5000 m (after 7 weeks) in rats but was only 17% increased even at 5000 (6 weeks) in guinea pigs. Relative lung weights increased by 40% at 3000 m in rats and 5000 m in guinea pigs; at 5000 m rats showed a 130% increase. Hb-concentration increase (20%) was not significantly different in rats at 3000 m and 5000 m, respectively, in guinea pigs it was below 10% at 3000 m and around 40% at 5000 m. Half saturation pressures of blood (P50) increased in rats significantly compared to controls but not in guinea pigs. The results suggest that relative maturity and high blood oxygen affinity in newborn guinea pigs favor high altitude acclimatization. Immaturity of newborn rats, their low blood oxygen affinity and immature enzyme patterns are considered as reasons for the smaller resistance against high altitude stress compared to guinea pigs.

Acclimatization↗
PubMed1979

Blood oxygen transport and organ weights of two shrew species (S. etruscus and C. russula).

Blood parameters concerning oxygen transport and relative organ weights of 11 Suncus etruscus and 13 Crocidura russula under light halothane anesthesia were investigated. Mean body weight of S. etruscus was 2.5 g and for C. russula was 9 g, hemoglobin concentration was 17.4 and 15.6 g/100 ml blood, hematocrit was 50 and 44%, red blood cells were 18 and 11 X 10(6)/microliter, respectively. Mean corpuscular volume was calculated to be 26 and 41 micron3, mean diameter 5.5 and 7 micron, and mean thickness 1.2 and 1.1 micron, respectively. Mean corpuscular hemoglobin concentration was in the normal range of mammalian red blood cells. A blood oxygen half-saturation pressure of 35 and 34 Torr at pH 7.4, 37 degrees C and a Bohr factor deltalog P50/deltapH of -0.61 and -0.66 was measured. Experiments with stripped hemoglobin showed that 2,3-diphosphoglycerate is the main oxygen affinity reducing allosteric factor. Relative weights of heart, kidney, and liver are remarkably high in S. etruscus. The maximal oxygen transport of 400 ml . kg-1 . min-1 of S. etruscus is feasible by an enormous heart rate, a large relative stroke volume, a high hemoglobin concentration combined with a low oxygen affinity, and a large Bohr effect.

Animals↗
PubMed1978

[Respiratory function of blood and relative weight of certain organs in two species of shrew: Crocidura russula and Suncus etruscus (Soricidae mammals)].

A high oxygen capacity combined with a low oxygen affinity and a large Bohr effect achieve a high oxygen transport capacity in small shrews. The high metabolic rate (Suncus estruscus: 100 to 350 ml O2/kg. min) can be explained by the combination of the favorable blood parameters with a high relative heart weight (1,2% of body weight) and heart frequencies of 1,000 to 1,350 per minute.

Animals↗
PubMed1978

Regulation of oxygen affinity in blood of fetal, newborn and adult mouse.

Oxygen half saturation pressure (P50) of blood and the role of 2,3 diphosphoglycerate (DPG), adenosine-triphosphate and red cell pH regulating oxygen affinity were examined in fetuses (16,5-18,5 days of gestational age), neonatal (1-22 days post partum) and adult mice (Balb/c). The high oxygen affinity of fetal blood (P50 = 29 Torr at 37 degrees C, pH 7.4 and Pco2 = 40 Torr) decreases to an average adult value of 41 Torr within two weeks after birth, accompanied by an increase of DPG-concentration from 0.2 M/MHb4 to the average of 1.5 M/MHb4. At a constant pHe of 7.4 red cell pH decreases from pH 7.3 to 7.18 from 18.5 days of gestational age to ten days post partum. Electrophoretic mobility and functional characteristics of purified fetal and adult hemoglobin were identical. Changes in oxygen affinity occur only due to organic phosphate concentration variations. A rapid replacement of large size fetal red cells by smaller adult cells after birth fairly coincides with the increase of the 2,3-DPG concentration.

Adenosine Triphosphate↗