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Biomedical subjects

M Drescher

Publications and source records attributed to M Drescher.

At least 19 recordsLinked to original sources
PubMed2002

Time-resolved atomic inner-shell spectroscopy.

The characteristic time constants of the relaxation dynamics of core-excited atoms have hitherto been inferred from the linewidths of electronic transitions measured by continuous-wave extreme ultraviolet or X-ray spectroscopy. Here we demonstrate that a laser-based sampling system, consisting of a few-femtosecond visible light pulse and a synchronized sub-femtosecond soft X-ray pulse, allows us to trace these dynamics directly in the time domain with attosecond resolution. We have measured a lifetime of 7.9(-0.9)(+1.0) fs of M-shell vacancies of krypton in such a pump-probe experiment.

Journal Article↗
PubMed2002

Experimental verification of quadrupole-dipole interference in spin-resolved photoionization.

We have measured the spin polarization of Xe (4p)(-1) photoelectrons after ionization with circularly polarized light at photon energies close to the ionization threshold where a resonant enhancement of quadrupole transitions has recently been predicted. At a reaction angle of 90 degrees a nonvanishing longitudinal spin polarization component of about 4% clearly indicates a quadrupole contribution to the photoexcitation. This is the first experimental evidence for the influence of nondipole transitions on the photoionization process at excitation energies much below 1 keV in an observable other than the intensity angular distribution.

Journal Article↗
PubMed2002

Steering attosecond electron wave packets with light.

Photoelectrons excited by extreme ultraviolet or x-ray photons in the presence of a strong laser field generally suffer a spread of their energies due to the absorption and emission of laser photons. We demonstrate that if the emitted electron wave packet is temporally confined to a small fraction of the oscillation period of the interacting light wave, its energy spectrum can be up- or downshifted by many times the laser photon energy without substantial broadening. The light wave can accelerate or decelerate the electron's drift velocity, i.e., steer the electron wave packet like a classical particle. This capability strictly relies on a sub-femtosecond duration of the ionizing x-ray pulse and on its timing to the phase of the light wave with a similar accuracy, offering a simple and potentially single-shot diagnostic tool for attosecond pump-probe spectroscopy.

Journal Article↗
PubMed2001

Attosecond metrology.

The generation of ultrashort pulses is a key to exploring the dynamic behaviour of matter on ever-shorter timescales. Recent developments have pushed the duration of laser pulses close to its natural limit-the wave cycle, which lasts somewhat longer than one femtosecond (1 fs = 10-15 s) in the visible spectral range. Time-resolved measurements with these pulses are able to trace dynamics of molecular structure, but fail to capture electronic processes occurring on an attosecond (1 as = 10-18 s) timescale. Here we trace electronic dynamics with a time resolution of </= 150 as by using a subfemtosecond soft-X-ray pulse and a few-cycle visible light pulse. Our measurement indicates an attosecond response of the atomic system, a soft-X-ray pulse duration of 650 +/- 150 as and an attosecond synchronism of the soft-X-ray pulse with the light field. The demonstrated experimental tools and techniques open the door to attosecond spectroscopy of bound electrons.

Journal Article↗
PubMed2001

X-ray pulses approaching the attosecond frontier.

Single soft-x-ray pulses of approximately 90-electron volt (eV) photon energy are produced by high-order harmonic generation with 7-femtosecond (fs), 770-nanometer (1.6 eV) laser pulses and are characterized by photoionizing krypton in the presence of the driver laser pulse. By detecting photoelectrons ejected perpendicularly to the laser polarization, broadening of the photoelectron spectrum due to absorption and emission of laser photons is suppressed, permitting the observation of a laser-induced downshift of the energy spectrum with sub-laser-cycle resolution in a cross correlation measurement. We measure isolated x-ray pulses of 1.8 (+0.7/-1.2) fs in duration, which are shorter than the oscillation cycle of the driving laser light (2.6 fs). Our techniques for generation and measurement offer sub-femtosecond resolution over a wide range of x-ray wavelengths, paving the way to experimental attosecond science. Tracing atomic processes evolving faster than the exciting light field is within reach.

Journal Article↗
PubMed2000

Sudden interchannel interaction in the Tl 6p ionization above the 5d threshold

The linear magnetic dichroism in the angular distribution of Tl 5d and 6p photoelectrons and their dynamical spin polarization have been measured between hnu = 30 and 50 eV. In contrast to the Xe 5p photoionization at the 4d threshold, our results show that above the Tl 5d threshold strong interchannel coupling effects induce a sudden increase in the asymptotic phase difference of the s and d waves for the Tl 6p ionization. This shows that the valence excitation is different for resonant (Xe 4d) and nonresonant (Tl 5d) excitation from subvalence shells.

Journal Article↗
PubMed2000

How Stable Are Epoxides? A Novel Synthesis of Epothilone B.

Remarkable stability of the oxirane function is displayed over a number of synthetic operations in a novel synthesis of the antitumor compound epothilone B (see scheme). The cis-epoxide, generated very early by dihydroxylation of an (E)-olefin, was resistant to more than ten synthetic steps under a wide variety of reaction conditions. TBS=tert-butyldimethylsilyl.

Journal Article↗
PubMed1996

De novo AML with dysplastic hematopoiesis: cytogenetic and prognostic significance.

Dysplastic hematopoiesis is the morphological hallmark of myelodysplastic syndromes. Dysplastic features in one or more lineages are also found frequently in bone marrow aspirates from patients with de novo AML and have been associated with an unfavorable prognosis. We asked whether dyshematopoiesis is an independent prognostic factor or an indicator of unrecognized secondary leukemia, identified by characteristic chromosomal abnormalities. Bone marrow aspirates from 102 patients with newly diagnosed AML were analyzed. Morphological analysis was obtained in all patients, flow cytometric analysis in 96 and successful cytogenetic analysis in 65 bone marrow aspirates. Dysgranulopoiesis (DysG) was found in 55, dysmegakaryopoiesis (DysM) in 32 and dyserythropoiesis (DysE) in 23 patients. Decreased side scatter signals of neutrophils in the flow cytometric analysis (DysS) were detected in 32 patients. DysG and DysS showed a highly significant correlation (P = 0.0005). DysG was an adverse negative prognostic factor for remission rate and event-free survival (P = 0.04, P = 0.02). An unfavorable karyotype was associated with a significantly lower chance for event-free survival (P = 0.002). The incidence of an unfavorable karyotype was significantly higher in patients with DysG (P = 0.01), DysM (P = 0.02) and DysS (P = 0.01). In patients with an unfavorable karyotype, dysplasia had no additional prognostic influence, however, in patients with a normal, favorable or prognostically uncertain karyotype DysG remained a predictor of lower remission rate (P = 0.03). We conclude that dysgranulopoiesis, dysmegakaryopoiesis and decreased side scatter signals of neutrophils are indicators of secondary leukemias in bone marrow aspirates from patients with de novo AML.

Bone Marrow↗
PubMed1994

Utility of postmortem computed tomography in trauma victims.

A possible way to circumvent the continuing decline in the number of autopsies is to perform computed tomography after death. The present study compares the pathologic findings of postmortem CT tomography (PMCT) in trauma fatalities with those disclosed upon conventional forensic autopsy. Within 6 hours of death, the bodies of 25 trauma victims underwent total body CT scanning, all with permission of the relatives, followed by conventional autopsy in 13 cases under court order. The pathologist and roentgenologist were unaware of each other's findings. The pathologic findings of PMCT plus conventional autopsy provided more information than either examination alone. Of the total 127 pathologic findings, 44.9% were diagnosed by both conventional autopsy and PMCT, 29.9% were not revealed by PMCT, whereas conventional autopsy missed 25.2%, and PMCT detected more bone injuries than did autopsy, whereas the latter was superior to PMCT in discovering soft-tissue pathologic states. In all, PMCT revealed 70.5% and autopsy 74.8% of the pathologic states. Although PMCT was not more effective than conventional autopsy in exposing pathologic entities, it increased the yield of findings when combined with conventional autopsy. Where conventional autopsy is unattainable, PMCT may be effective in shedding light on the pathologic state and mechanism of death in trauma fatalities.

Adult↗
PubMed1992

Nonspecific immunostimulation with low doses of cyclophosphamide (LDCY), thymostimulin, and Echinacea purpurea extracts (echinacin) in patients with far advanced colorectal cancers: preliminary results.

Outpatients (n = 15) with metastasizing far advanced colorectal cancers received immunotherapy consisting of low-dose cyclophosphamide (LDCY) 300 mg/m2 every 28 days i.v., thymostimulin 30 mg/m2, days 3-10 after low-dose cyclophosphamide i.m. once daily, then twice a week, and echinacin 60 mg/m2 together with thymostimulin i.m. All patients had had previous surgery and/or chemotherapy and had progressive disease upon entering the study. Two months after onset of therapy a partial tumor regression was documented in one and a stable disease in 6 other patients by abdominal ultrasonography, decrease of the tumor markers carcinoembryonic antigen (CEA), CA 19-9, CA 15-3, and/or chest roentgenography, which may also be attributed to the natural course of disease. Mean survival time was 4 months, 2 patients survived for more than 8 months. Immunotherapy was well tolerated by all patients without side effects.

Adjuvants, Immunologic↗
PubMed1992

Flow cytometric characterization of acute myeloid leukemia: IV. Comparison to the differentiation pathway of normal hematopoietic progenitor cells.

Gradual increase of CD38 on cells expressing CD34 characterizes the early cell differentiation pathway of normal human hematopoietic progenitors. In this study the coordinated expression pattern of CD34 and CD38 was assessed on leukemic blasts from bone marrow aspirates of 95 patients with newly diagnosed acute myeloid leukemia (AML). Expression was divided into six categories analogous to the differentiation pathway of normal bone marrow. The CD38 antigen was expressed on the leukemic cells of all patients and CD34+ leukemic cells were found in 79 patients (83%). In 93 patients, the leukemic cells were found along the differentiation pathway defined by CD34 and CD38. In 33 of the 93 patients, a part of the CD34+ cells did not express the CD38 antigen (categories 1 and 2). In another 33 patients, all CD34+ cells expressed CD38 (categories 3 and 4). In the remaining 27 patients, only cells were found which dimly expressed CD34 or did not express CD34 (categories 5 and 6). Of the 93 patients, 88 were treated with intensive chemotherapy according to the protocol of the German AML Cooperative Group. Of these, 21 died early and were not evaluable for treatment response. Complete remission was achieved in 14 of 22 patients (64%) in categories 1 and 2, in 19 of 26 patients (73%) in categories 3 and 4, and in 18 of 19 patients (95%) in categories 5 and 6. The event-free survival was significantly longer in patients of categories 5 and 6 compared to patients in categories 1 and 2 (p less than 0.01) and categories 3 and 4 (p less than 0.05), respectively. We conclude that in the majority of AML patients the immunophenotype of leukemic cells follows the early cell differentiation pathways defined by coordinated expression of CD34 and CD38 similar to that of normal hematopoietic progenitors. The presence of cells in the late cell differentiation stages (CD34+/-, CD38 /+) identifies patients with a higher complete remission rate and longer complete remission duration.

ADP-ribosyl Cyclase↗
PubMed1991

[Massive and multi-transfusions in polytraumatized patients: long-term serologic markers of hepatitis B, hepatitis C and AIDS].

302 out of 712 (42%) consecutive polytraumatized ICU patients received ten or more units of stored blood during primary and/or intensive care (1982 to 1987) treatment. 120 of the 197 surviving patients with an average number of transfusions of 23 (10 to 89) units were followed up after a mean interval of 70 (20 to 104) months. Mean duration of continuous post-ICU hospital stay was 17 (2 to 160) weeks, mean number of additional operative procedures was three (0 to 23). Manifest hepatitis had not occurred, all samples were negative for HIV testing. In nine samples (7.5%), anti-HBc-antibodies were positive, while HBs-antigen was negative. Ten patients (8.3%) tested positive for anti-HCV-antibodies (one combined with positive anti-HBc). The rate of serologically positive samples increased with the number of blood units given, duration of overall hospital stay and/or number of secondary surgery; all these findings failed to prove statistically significant. The rate of seropositivity for anti-HBc-antibodies corresponded well with the rate found in voluntary donors in FRG. Manifest or chronic hepatitis B was not observed. As to hepatitis C, the incidence of seropositivity for anti-HCV was found tenfold higher than in healthy blood donors in FRG. The relevance of this result remains unclear, but might indicate chronic post-transfusional hepatitis with high risk of cirrhosis. Among the patients testing positive for anti-HCV, too, acute manifest hepatitis had not occurred. Recently developed RIBA kits might improve specificity and sensitivity of anti-HCV testing. Thus, the frequency of PTH-C could decrease considerably.

Acquired Immunodeficiency Syndrome↗