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M Meister

Publications and source records attributed to M Meister.

At least 19 recordsLinked to original sources
PubMed2004

Shell structure of the near-dripline nucleus 23O.

Breakup reactions were used to study the ground-state configuration of the neutron-rich isotope 23O. The 22O fragments produced in one-nucleon removal from 23O at 938 MeV/nucleon in a carbon target were detected in coincidence with deexciting gamma rays. The widths of the longitudinal momentum distributions of the 22O fragments and the one-neutron removal cross sections were interpreted in the framework of a simple theoretical model which favors the assignment of Ipi = 1/2+ to the 23O ground state.

Journal Article↗
PubMed2003

The t+n+n system and 5H.

The one-proton knockout channel from 6He (240 MeV/u) impinging on a carbon target has been investigated. The triton fragments originating from this channel were detected in coincidence with the two neutrons. A broad structure, peaked at 3 MeV above the t+2n threshold, is observed in the t+n+n-relative energy spectrum. It is shown that this structure is mainly due to a I(pi)=1/2(+) resonance as expected for the 5H ground state, and from the observed angular and energy correlations, being used for the first time in 5H studies, that the neutrons to a large extent occupy the p shell.

Journal Article↗
PubMed2003

Clarification of the three-body decay of 12C (12.71 MeV).

Using beta decays of a clean source of 12N produced at the IGISOL facility, we have measured the breakup of the 12C (12.71 MeV) state into three alpha particles with a segmented particle detector setup. The high quality of the data permits solving the question of the breakup mechanism of the 12.71 MeV state, a longstanding problem in few-body nuclear physics. Among existing models, a modified sequential model fits the data best, but systematic deviations indicate that a three-body description is needed.

Journal Article↗
PubMed2003

Dissipative discrete breathers: periodic, quasiperiodic, chaotic, and mobile.

The properties of discrete breathers in dissipative one-dimensional lattices of nonlinear oscillators subject to periodic driving forces are reviewed. We focus on oscillobreathers in the Frenkel-Kontorova chain and rotobreathers in a ladder of Josephson junctions. Both types of exponentially localized solutions are easily obtained numerically using adiabatic continuation from the anticontinuous limit. Linear stability (Floquet) analysis allows the characterization of different types of bifurcations experienced by periodic discrete breathers. Some of these bifurcations produce nonperiodic localized solutions, namely, quasiperiodic and chaotic discrete breathers, which are generally impossible as exact solutions in Hamiltonian systems. Within a certain range of parameters, propagating breathers occur as attractors of the dissipative dynamics. General features of these excitations are discussed and the Peierls-Nabarro barrier is addressed. Numerical scattering experiments with mobile breathers reveal the existence of two-breather bound states and allow a first glimpse at the intricate phenomenology of these special multibreather configurations.

Journal Article↗
PubMed2002

Evidence for a new low-lying resonance state in 7He.

Low-lying resonance states in 7He(6He+n), formed after fragmentation reactions of a 227 MeV/nucleon 8He beam on a carbon target, have been studied. Coincidences between 6He nuclei and neutrons, corresponding to the one-neutron knockout channel in 8He, were selected. The relative energy spectrum in the 6He+n system shows a structure, which is interpreted as the 7He ( Ipi = 3/2(-)) ground state, unbound with 0.43(2) MeV relative to the 6He+n system and a width of Gamma = 0.15(8) MeV overlapping with an excited ( Ipi = 1/2(-)) state observed at 1.0(1) MeV with a width of Gamma = 0.75(8) MeV.

Journal Article↗
PubMed2001

Postembryonic hematopoiesis in Drosophila.

We have investigated the blood cell types present in Drosophila at postembryonic stages and have analysed their modifications during development and under immune conditions. The anterior lobes of the larval hematopoietic organ or lymph gland contain numerous active secretory cells, plasmatocytes, few crystal cells, and a number of undifferentiated prohemocytes. The posterior lobes contain essentially prohemocytes. The blood cell population in larval hemolymph differs and consists mainly of plasmatocytes which are phagocytes, and of a low percentage of crystal cells which reportedly play a role in humoral melanisation. We show that the cells in the lymph gland can differentiate into a given blood cell lineage when solicited. Under normal nonimmune conditions, we observe a massive differentiation into active macrophages at the onset of metamorphosis in all lobes. Simultaneously, circulating plasmatocytes modify their adhesion and phagocytic properties to become pupal macrophages. All phagocytic cells participate in metamorphosis by ingesting doomed larval tissues. The most dramatic effect on larval hematopoiesis was observed following infestation by a parasitoid wasp. Cells within all lymph gland lobes, including prohemocytes from posterior lobes, massively differentiate into a new cell type specifically devoted to encapsulation, the lamellocyte.

Animals↗
PubMed2001

Tuning and topography in an odor map on the rat olfactory bulb.

The sense of smell originates in a diverse array of receptor neurons, comprising up to 1000 different types. To understand how these parallel channels encode chemical stimuli, we recorded the responses of glomeruli in the olfactory bulbs of the anesthetized rat, by optical imaging of intrinsic signals. Odor stimulation produced two kinds of optical responses at the surface of the bulb: a broad diffuse component superposed by discrete small spots. Histology showed that the spots correspond to individual glomeruli, and that approximately 400 of them can be monitored in this way. Based on its wavelength-dependence, this optical signal appears to derive from changes in light scattering during neural activity. Pure odorants generally activated several glomeruli in a bilaterally symmetric pattern, whose extent varied greatly with concentration. A simple formalism for ligand binding accounts quantitatively for this concentration dependence and yields the effective affinity with which a glomerulus responds to an odorant. When tested with aliphatic molecules of increasing carbon chain length, many glomeruli were sharply tuned for one or two adjacent chain lengths. Glomeruli with similar tuning properties were located near each other, producing a systematic map of molecular chain length on the surface of the olfactory bulb. Given local inhibitory circuits within the olfactory bulb, this can account for the observed functional inhibition between related odors. We explore several parallels to the function and architecture of the visual system that help interpret the neural representation of odors.

Administration, Inhalation↗
PubMed2001

Predicting every spike: a model for the responses of visual neurons.

In the early visual system, neuronal responses can be extremely precise. Under a wide range of stimuli, cells in the retina and thalamus fire spikes very reproducibly, often with millisecond precision on subsequent stimulus repeats. Here we develop a mathematical description of the firing process that, given the recent visual input, accurately predicts the timing of individual spikes. The formalism is successful in matching the spike trains from retinal ganglion cells in salamander, rabbit, and cat, as well as from lateral geniculate nucleus neurons in cat. It adapts to many different response types, from very precise to highly variable. The accuracy of the model allows a compact description of how these neurons encode the visual stimulus.

Action Potentials↗
PubMed2001

The domino gene of Drosophila encodes novel members of the SWI2/SNF2 family of DNA-dependent ATPases, which contribute to the silencing of homeotic genes.

The Drosophila domino gene has been isolated in a screen for mutations that cause hematopoietic disorders. Generation and analysis of loss-of-function domino alleles show that the phenotypes are typical for proliferation gene mutations. Clonal analysis demonstrates that domino is necessary for cell viability and proliferation, as well as for oogenesis. domino encodes two protein isoforms of 3202 and 2498 amino acids, which contain a common N-terminal region but divergent C termini. The common region includes a 500 amino acid DNA-dependent ATPase domain of the SWI2/SNF2 family of proteins, which function via interaction with chromatin. We show that, although domino alleles do not exhibit homeotic phenotypes by themselves, domino mutations enhance Polycomb group mutations and counteract Trithorax group effects. The Domino proteins are present in large complexes in embryo extracts, and one isoform binds to a number of discrete sites on larval polytene chromosomes. Altogether, the data lead us to propose that domino acts as a repressor by interfering with chromatin structure. This activity is likely to be performed as a subunit of a chromatin-remodeling complex.

Adenosine Triphosphatases↗
PubMed2001

The ethics of health care professionals' opinions for hire.

BACKGROUND: Serving as a forensic consultant or medical expert witness is a professional duty and social responsibility. While objectivity is a hallmark of ethical health care evaluation, conflict arises when medical experts exhibit bias and serve the hiring party's interests instead of the public's. METHODS: The authors define different types of expert witnesses and examine the means for improving the quality of testimony. They evaluate professional association codes of ethics, health care education, neutral medical experts and the field of bioethics. RESULTS: Incorporating case-based analysis of medical expert testimony in the education of health care professionals may elevate the caliber of testimony. Court-appointed neutral experts may overcome some of the problems inherent in professional and product liability litigation. Neutral bioethicists may play a constructive role in mediating medicolegal disputes. Adopting strong professional association codes of ethics requires the consent of all members, and loss of membership for ethics violations may not be a powerful enough deterrent to biased testimony. CONCLUSION: Biased testimony contributes to scientifically unfounded liability verdicts. The public ultimately pays for huge monetary settlements via higher costs for all goods and services. Financial incentives in the current professional and product liability system will make it difficult to institute court-appointed neutral expert panels on a widespread basis. PRACTICE IMPLICATIONS: Dentists should view themselves as clinicians and evaluators. Rendering expert opinions on forensic matters is an ethical part of dental practice. By doing so with honesty and objectivity, dentists serve as a bridge to justice and fulfill a social responsibility.

Bioethics↗
PubMed2001

PDL neuron-associated neurotransmitters in orthodontic tooth movement: identification and proposed mechanism of action.

The remodeling of the PDL and alveolar bone that occurs during orthodontic tooth movement (OTM) has long been associated with an inflammatory process. The vascular and cellular changes that occur have been well documented, and several inflammatory mediators, growth factors and neuropeptides have been found in increased levels in the periodontal supporting tissues during orthodontic tooth movement. It recently was found that peripheral nerve fibers participate in the inflammatory process (neurogenic inflammation) by releasing various neuropeptides. Calcitonin gene-related peptide (CGRP) and substance P (SP), two PDL neuropeptides, play a role in inflammation by serving as vasodilators and inducing increased vascular permeability. They also stimulate plasma extravasation and proliferation of endothelial cells and fibroblasts; upregulate the expression of endothelial cell adhesion molecules; and act as neurotransmitters. The increase in concentration of these PDL neuropeptides during OTM indicates their importance to the process. This paper will review the current research and summarize the roles and proposed mechanism of these two main PDL neurotransmitters in OTM.

Calcitonin Gene-Related Peptide↗
PubMed2000

Responses of vomeronasal neurons to natural stimuli.

The vomeronasal organ (VNO) of mammals plays an essential role in the detection of pheromones. We obtained simultaneous recordings of action potentials from large subsets of VNO neurons. These cells responded to components of urine by increasing their firing rate. This chemosensory activation required phospholipase C function. Unlike most other sensory neurons, VNO neurons did not adapt under prolonged stimulus exposure. The full time course of the VNO spiking response is captured by a simple quantitative model of ligand binding. Many individual VNO neurons were strongly selective for either male or female mouse urine, with the effective concentrations differing as much as a thousandfold. These results establish a framework for understanding sensory coding in the vomeronasal system.

Action Potentials↗
PubMed1999

Signal transduction in atria and ventricles of mice with transient cardiac expression of activated G protein alpha(q).

We recently showed that the transient expression of a hemagglutinin (HA) epitope-tagged, constitutively active mutant of the G protein alpha(q) subunit (HAalpha(q)*) in the hearts of transgenic mice is sufficient to induce cardiac hypertrophy and dilatation that continue to progress after HAalpha(q)* protein becomes undetectable. We demonstrated that the activity of phospholipase Cbeta, the immediate downstream target of activated Galpha(q), is increased at 2 weeks, when HAalpha(q)* is expressed, but also at 10 weeks, when HAalpha(q)* is no longer detectable. This observation suggested that the transient HAalpha(q)* expression causes multiple, persistent changes in cellular signaling pathways. We now demonstrate changes in the level, activity, or both of several signaling components, including changes in the amount and hormone responsiveness of phospholipase Cbeta enzymes, in the basal level of diacylglycerol (which predominantly reflects activation of phospholipase D), in the amount or distribution of protein kinase C (PKC) isoforms (PKCalpha, PKCdelta, and PKCepsilon), and in the amount of several endogenous G proteins. These changes vary depending on the isoform of the signaling molecule, the chamber in which it is expressed, and the presence or absence of HAalpha(q)*. Our results suggest that a network of linked signaling functions determines the development of hypertrophy. They also suggest that atria and ventricles represent different signaling domains. It is likely that such changes occur in other model systems in which the activity of a single signaling component is increased, either due to an activating mutation or due to overexpression of the wild type.

Animals↗