6,644 research outputs found

    Universal Time Tunneling

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    How much time does a tunneling wave packet spent in traversing a barrier? Quantum mechanical calculations result in zero time inside a barrier . In the nineties analogous tunneling experiments with microwaves were carried out. The results agreed with quantum mechanical calculations. Electron tunneling time is hard to measure being extremely short and parasitic effects due to the electric charge of electrons may be dominant. However, quite recently the atomic ionization tunneling time has been measured. Experimental data of photonic, phononic, and electronic tunneling time is available now and will be presented. It appears that the tunneling time is a universal property independent of the field in question.Comment: 3 pages, 1 figure, 1 tabl

    Oral Protein Therapy for the Future - Transport of Glycolipid-Modified Proteins: Vision or Fiction?

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    The reliable and early diagnosis of common complex multifactorial diseases depends on the individual determination of all (or as many as possible) polymorphisms of each susceptibility gene together with amount and type of the corresponding gene products and their downstream effects, including the synthesis and flux of metabolites and regulation of signalling processes. In addition, this system's biology-driven personalized diagnosis must be accompanied by options for personalized reliable and early therapy. In the midterm, the direct substitution or inhibition of the proteins encoded by the corresponding defective gene products of the susceptibility genes exerting lower or higher activity by administration of the `normal' proteins or inhibitory antibodies, respectively, seems to be most promising. The critical hurdle of oral bioavailability as well as transport into the cytoplasm of the target cells, if required, could be overcome by therapeutic proteins with carboxy-terminal modification by glycosylphosphatidylinositol (GPI). This may be deduced from recent experiments with rat adipocytes. Here this membrane-anchoring glycolipid structure induces the sequential transport of proteins from special regions of the plasma membrane via the surface of intracellular lipid droplets to special membrane vesicles, which are finally released from the adipocytes together with the associated GPI proteins. It remains to be studied whether similar molecular mechanisms operate in intestinal epithelial cells and may enable the transport of GPI proteins from the intestinal lumen into the blood stream. If so, modification of proteins encoded by (combinations of) susceptibility genes with GPI could significantly facilitate the personalized therapy of common diseases on the basis of `inborn' safety, efficacy, rapid realization and oral application. Copyright (C) 2010 S. Karger AG, Base

    Weak Interactions in Supernova Cores and Saturation of Nucleon Spin Fluctuations

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    Extrapolation of perturbative nucleon spin fluctuation rates seems to suggest a strong suppression of weak interactions in supernova cores. We derive a new sum rule for the dynamical spin-density structure function which relates the spin fluctuation rate to the average nuclear interaction energy. For a bremsstrahlung like structure function profile we show that instead of strongly decreasing, the neutrino scattering cross section is roughly density independent and axion emission rates increase somewhat slower than the lowest order emissivities towards the center of a hot supernova core.Comment: 9 latex pages, 1 uuencoded postscript figure added via figures comman

    Cosmic Radiation Constraints on Low String Scale and Extra Dimension Cross Sections

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    The observed interaction energy of cosmic rays with atmospheric nuclei reaches up to a PeV in the center of mass. We compute nucleon-nucleon and nucleon-neutrino cross sections for various generic parton cross sections appearing in string and brane world scenarios for gravity and compare them with cosmic ray data. Scenarios with effective energy scales in the TeV range and parton cross sections with linear or stronger growth with the center of mass energy appear strongly constrained or ruled out. String-inspired scenarios with infinite-volume extra dimensions may require a fundamental scale above 100 eV for which they are probably in conflict with gravity on parsec scales.Comment: 4 revtex pages, 1 postscript figur

    The SMC Experiment: New Data on the Deuteron from the 1994 Run

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    An overview of the SMC data taking and the polarized deep inelastic scattering experiment is given. The new data on the deuteron extend the kinematic range and have considerably reduced statistical and systematic errors. The evaluation of the first moment of the spin dependent structure function is presented and the result for the Bjorken sum rule from SMC data alone is given. The spin contribution of the quarks to the spin of the nucleon is obtained with information from weak decays of baryons. In a new polarized semi-inclusive analysis the asymmetry of the difference between the number of positive and negative charged hadrons was studied. Preliminary results are shown.Comment: 14 pages including 8 figures, uuencoded gz-compressed ps-file, to be published in the Proceedings of the Seventh Conference on Perspectives in Nuclear Physics at Intermediate Energies, ICTP Trieste on 8-12 May 199

    Electroproduction of Dijets at Small Jet Separation

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    Dijet production in deep-inelastic scattering (DIS) in the range 150 < Q^2 < 35000 GeV^2 has been measured by the H1 collaboration using the Durham jet algorithm in the laboratory frame. QCD calculations in next-to-leading order (NLO) are found to give a good description of the data when requiring a small minimum jet separation, which selects a dijet sample containing 1/3 of DIS events in contrast to approximately 1/10 with more typical jet analyses.Comment: On behalf of the H1 collab., X International Workshop on Deep-Inelastic Scattering, DIS 2002, Cracow, 30 April - 4 May 2002, 4 pages, to be published in Acta Phys. Pol.

    Personalized Prognosis and Diagnosis of Type 2 Diabetes - Vision or Fiction?

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    Typical civilization diseases, such as type 2 diabetes, share several features: their worldwide frequency, the complexity of the underlying pathogenic mechanisms, heterogeneity in the phenotypes and their multifactorial nature due to a wide variety of possible combinations of disease susceptibility or protective genes in different tissues and negative or positive environmental factors. This is in sharp contrast to classical inherited diseases, such as Huntington's chorea, which are often caused by complete loss- or gain-of-function mutations in a single gene. The causative polymorphisms of susceptibility genes, however, are characterized by relatively subtle alterations in the function of the corresponding gene products, i.e. low penetrance and effect size, which do not support the pathogenesis per se, and by their high frequency; these two characteristics result in high expenditures for their identification and a rather low predictive value. In the future, the reliable and early diagnosis of common diseases will thus depend on the determination of all (or as many as possible) polymorphisms of each susceptibility gene together with the corresponding gene products and the metabolites emerging thereof for each individual. Great hopes are currently associated with systems biology to cover these demands in time (i.e. along the pathogenesis) and space (i.e. in all relevant tissues). Copyright (C) 2010 S. Karger AG, Base

    Macroscopic Virtual Particles Exist

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    Virtual particles expected to occur in microscopic processes as they are introduced, for instance by Feynman in the Quantum Electro Dynamics, as photons performing in an anonymous way in the interaction between two electrons. This note describes macroscopic virtual particles as they appear in classical evanescent modes and in quantum mechanical tunneling particles. Remarkably, these large virtual particles are present in wave mechanics of elastic, electromagnetic, and Schr\"odinger fields.Comment: 17 pages, 5 figure
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