1,998 research outputs found
Quasi-free (p,2p) and (p,pn) reactions with unstable nuclei
We study (p,2p) and (p,pn) reactions at proton energies in the range of 100
MeV -- 1 GeV. Our purpose is to explore the most sensitive observables in
unpolarized reactions with inverse kinematics involving radioactive nuclei. We
formulate a model based on the eikonal theory to describe total cross sections
and momentum distributions of the recoiled residual nucleus. The model is
similar to the one adopted for knockout reactions with heavy ions. We show that
momentum distributions are sensitive to the angular momentum of the ejected
nucleon which can be used as an spectroscopic tool. The total cross sections
are sensitive to the nucleon separation energies and to multiple scattering
effects. Our calculations also indicate that a beam energy around 500
MeV/nucleon has a smaller dependence on the anisotropy of the nucleon-nucleon
elastic scattering.Comment: 17 pages, 12 figures, Accepted for publication in the Physical review
Creation of ventricular septal defects on the beating heart in a new pig model
Background/ Aims: So far, surgical and interventional therapies for muscular ventricular septal defects ( mVSDs) beyond the moderator band have had their limitations. Thus, alternative therapeutic strategies should be developed. We present a new animal model for the evaluation of such strategies. Methods: In a pig model ( n = 9), anterolateral thoracotomy was performed for exposure of the left ventricle. mVSDs were created under two- and three- dimensional echocardiography with a 7.5- mm sharp punch instrument, which was forwarded via a left ventricular puncture without extracorporeal circulation. Results: Creation of mVSDs was successful in all animals ( n = 9) confirmed by echocardiography, hemodynamic measurements and autopsy. The defects were located in the midmuscular ( n = 4), apical ( n = 1), inlet ( n = 2) and anterior part ( n = 2) of the muscular septum. All animals were hemodynamically stable for further procedures. The diameter and shunt volume of the mVSDs were 4.8 - 7.3 mm ( mean: 5.9 mm) and 12.9 - 41.3% ( mean: 22.1%), respectively. Autopsy confirmed in all animals the creation of a substantial defect. Conclusion: The described new technique for creation of an mVSD on the beating heart in a pig model is suitable for the evaluation of new therapeutic strategies for mVSD closure. Copyright (C) 2008 S. Karger AG, Basel
Anharmonicities of giant dipole excitations
The role of anharmonic effects on the excitation of the double giant dipole
resonance is investigated in a simple macroscopic model.Perturbation theory is
used to find energies and wave functions of the anharmonic ascillator.The cross
sections for the electromagnetic excitation of the one- and two-phonon giant
dipole resonances in energetic heavy-ion collisions are then evaluated through
a semiclassical coupled-channel calculation.It is argued that the variations of
the strength of the anharmonic potential should be combined with appropriate
changes in the oscillator frequency,in order to keep the giant dipole resonance
energy consistent with the experimental value.When this is taken into
account,the effects of anharmonicities on the double giant dipole resonance
excitation probabilities are small and cannot account for the well-known
discrepancy between theory and experiment
Strong Completeness for Markovian Logics
In this paper we present Hilbert-style axiomatizations for three logics for reasoning about continuous-space Markov processes (MPs): (i) a logic for MPs defined for probability distributions on measurable state spaces, (ii) a logic for MPs defined for sub-probability distributions and (iii) a logic defined for arbitrary distributions.These logics are not compact so one needs infinitary rules in order to obtain strong completeness results.
We propose a new infinitary rule that replaces the so-called Countable Additivity Rule (CAR) currently used in the literature to address the problem of proving strong completeness for these and similar logics. Unlike the CAR, our rule has a countable set of instances; consequently it allows us to apply the Rasiowa-Sikorski lemma for establishing strong completeness. Our proof method is novel and it can be used for other logics as well
Sensitive PCR method for the detection and real-time quantification of human cells in xenotransplantation systems
The sensitive detection of human cells in immunodeficient rodents is a prerequisite for the monitoring of micrometastasis of solid tumours, dissemination of leukaemic cells, or engraftment of haematological cells. We developed a universally applicable polymerase chain reaction method for the detection of a human-specific 850-bp fragment of the α-satellite DNA on human chromosome 17. The method allows the detection of one human cell in 106 murine cells and could be established as both, a conventional DNA polymerase chain reaction-assay for routine screening, and a quantitative real-time polymerase chain reaction-assay using TaqMan-methodology. It was applied to the following xenotransplantation systems in SCID and NOD/SCID mice: (1) In a limiting dilution assay, cells of the MDA-MB 435 breast carcinoma were injected into the mammary fat pad of NOD/SCID mice. It could be shown that 10 cells mouseâ1 were sufficient to induce a positive polymerase chain reaction signal in liver and lung tissue 30 days after transplantation as an indicator for micrometastasis. At this time a palpable tumour was not yet detectable in the mammary fat pad region. (2) Cells of a newly established human acute lymphatic leukaemia were administered intraperitoneally to SCID mice. These cells apparently disseminated and were detectable as early as day 50 in the peripheral blood of living mice, while the leukaemia manifestation was delayed by day 140. (3) In a transplantation experiment using mature human lymphocytes we wanted to standardise conditions for a successful survival of these cells in NOD/SCID mice. It was established that at least 5Ă107âcells given intravenously were necessary and that the mice had to be conditioned by 2âGy body irradiation to get positive polymerase chain reaction bands in several organs. (4) Engraftment studies with blood stem cells originating from cytapheresis samples of tumour patients or from cord blood were undertaken in NOD/SCID mice in order to define conditions of successful engraftment and to use this model for further optimisation strategies. The polymerase chain reaction method presented allowed a reliable prediction of positive engraftment and agreed well with the results of immunohistochemical or FACS analysis. All together, the polymerase chain reaction method developed allows a sensitive and reliable detection of low numbers of human cells in immunodeficient hosts. In combination with real-time (TaqMan) technique it allows an exact quantification of human cells. As this method can be performed with accessible material of living animals, follow up studies for the monitoring of therapeutic interventions are possible in which the survival time of mice as evaluation criteria can be omitted
Neutron radioactivityâLifetime measurements of neutron-unbound states
A new technique to measure the lifetime Ï of a neutron-radioactive nucleus that decays in-flight via neutron emission is presented and demonstrated utilizing MonteCarlo simulations. The method is based on the production of the neutron-unbound nucleus in a target, which at the same time slows down the produced nucleus and the residual nucleus after (multi-) neutron emission. The spectrum of the velocity difference of neutron(s) and the residual nucleus has a characteristic shape, that allows to extract the lifetime. If the decay happens outside the target there will be a peak in the spectrum, while events where the decay is in the target show a broad flat distribution due to the continuous slowing down of the residual nucleus. The method itself and the analysis procedure are discussed in detail for the specific candidate 26O. A stack of targets with decreasing target thicknesses can expand the measurable lifetime range and improve the sensitivity by increasing the ratio between decays outside and inside the target. The simulations indicate a lower limit of measurable lifetime ÏâŒ0.2 ps for the given conditions
Chaotic zone boundary for low free eccentricity particles near an eccentric planet
We consider particles with low free or proper eccentricity that are orbiting
near planets on eccentric orbits. Via collisionless particle integration we
numerically find the location of the boundary of the chaotic zone in the
planet's corotation region. We find that the distance in semi-major axis
between the planet and boundary depends on the planet mass to the 2/7 power and
is independent of the planet eccentricity, at least for planet eccentricities
below 0.3. Our integrations reveal a similarity between the dynamics of
particles at zero eccentricity near a planet in a circular orbit and with zero
free eccentricity particles near an eccentric planet. The 2/7 law has been
previously explained by estimating the semi-major at which the first order mean
motion resonances are large enough to overlap. Orbital dynamics near an
eccentric planet could differ due to first order corotation resonances that
have strength proportional to the planet's eccentricity. However, we find the
corotation resonance width at low free eccentricity is small. Also the first
order resonance width at zero free eccentricity is the same as that for a zero
eccentricity particle near a planet in a circular orbit. This accounts for
insensitivity of the chaotic zone width to planet eccentricity. Particles at
zero free eccentricity near an eccentric planet have similar dynamics to those
at zero eccentricity near a planet in a circular orbit.Comment: accepted for publication in MNRA
Privacy-Preserving Trust Management Mechanisms from Private Matching Schemes
Cryptographic primitives are essential for constructing privacy-preserving
communication mechanisms. There are situations in which two parties that do not
know each other need to exchange sensitive information on the Internet. Trust
management mechanisms make use of digital credentials and certificates in order
to establish trust among these strangers. We address the problem of choosing
which credentials are exchanged. During this process, each party should learn
no information about the preferences of the other party other than strictly
required for trust establishment. We present a method to reach an agreement on
the credentials to be exchanged that preserves the privacy of the parties. Our
method is based on secure two-party computation protocols for set intersection.
Namely, it is constructed from private matching schemes.Comment: The material in this paper will be presented in part at the 8th DPM
International Workshop on Data Privacy Management (DPM 2013
- âŠ