6,746 research outputs found
Universal Time Tunneling
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
Cosmic Radiation Constraints on Low String Scale and Extra Dimension Cross Sections
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
Oral Protein Therapy for the Future - Transport of Glycolipid-Modified Proteins: Vision or Fiction?
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
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
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The SMC Experiment: New Data on the Deuteron from the 1994 Run
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
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?
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
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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