235 research outputs found
Solution of a One-Dimensional Reaction-Diffusion Model with Spatial Asymmetry
Full text linkWe study classical particles on the sites of an open chain which diffuse,
coagulate and decoagulate preferentially in one direction. The master equation
is expressed in terms of a spin one-half Hamiltonian and the model is shown
to be completely solvable if all processes have the same asymmetry. The
relaxational spectrum is obtained directly from and via the equations of
motion for strings of empty sites. The structure and the solvability of these
equations are investigated in the general case. Two phases are shown to exist
for small and large asymmetry, respectively, which differ in their stationary
properties.Comment: 18 pages, latex, 1 PostScript figure, uuencode
On Matrix Product States for Periodic Boundary Conditions
Full text linkThe possibility of a matrix product representation for eigenstates with
energy and momentum zero of a general m-state quantum spin Hamiltonian with
nearest neighbour interaction and periodic boundary condition is considered.
The quadratic algebra used for this representation is generated by 2m operators
which fulfil m^2 quadratic relations and is endowed with a trace. It is shown
that {\em not} every eigenstate with energy and momentum zero can be written as
matrix product state. An explicit counter-example is given. This is in contrast
to the case of open boundary conditions where every zero energy eigenstate can
be written as a matrix product state using a Fock-like representation of the
same quadratic algebra.Comment: 7 pages, late
Boiling Liquid Expanding Vapour Explosion (BLEVE) of Peroxy-fuels: Experiments and Computational Fluid Dynamics (CFD) Simulation
Get PDFAbstractFire and explosion hazards associated with storage and transportation of flammable materials have been a matter of great interest in the recent times. BLEVE is a scenario that occurs when a closed fuel container is subjected to heat for a longer duration. Such events are disastrous to human beings and assets both. In the past there have been numerous studies on BLEVEs and fireballs of hydrocarbon fuels, e.g. kerosene, gasoline, LPG, LNG and others. Though, the fireballs of peroxy-fuels are not looked into detail as such. This article tries to overcome this lack of knowledge. Both, experimental investigation and CFD simulations are performed to measure and predict the fireball characteristics of a peroxy-fuel. Due to thermal decomposition in the liquid phase and active oxygen content a peroxy-fuel fireball burns at a very fast rate and emit higher thermal radiation whereas exhibits smaller diameter and elevation compared to hydrocarbons. That eventually leads to consideration of larger safety distances from them which are also verified by CFD results
A novel malformation complex of bilateral and symmetric preaxial radial ray-thumb aplasia and lower limb defects with minimal facial dysmorphic features: a case report and literature review
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Projektbericht: Rehabilitation in der Geriatrie
Full text linkProblemstellung, Design und Erhebungsinstrumente einer empirischen Studie zu Fragen der Rehabilitation von über 60jährigen Schlaganfallpatienten werden dargestellt. Bei dieser Studie geht es vor allem um die Beschreibung der Akutphase und des Verlaufs der Rehabilitation unter differenzierenden Gesichtspunkten, wobei auch die Wirksamkeit der Rehabilitationsverfahren evaluiert werden soll. Die Daten werden in zwei Rehabilitationskliniken und in 10 Krankenhäusern erhoben, die mit der Basisversorgung während der akuten Krankheitsphase befaßt sind. Durch mehrere Erhebungsbögen wird der Gesamtkrankheitsverlauf der Patienten erfaßt. Die Evaluation der therapeutischen Maßnahmen erfolgt durch Verlaufs- und Aufwandsanalysen. Die Untersuchung in den Krankenhäusern richtet sich auf die deskriptive Erfassung des Auftretens von Schlaganfallerkrankungen und die damit verbundenen Anfälligkeits- und Sterblichkeitsraten innerhalb eines abgegrenzten regionalen und zeitlichen Raumes. Darüber hinaus wird in den Kliniken ein Teilprojekt durchgeführt, das Daten über die Notwendigkeit und den Bedarf an psychotherapeutischer Betreuung von Schlaganfallpatienten liefern soll. Der derzeitige Stand der Arbeiten, einschließlich erster Pretestergebnisse, wird dargestellt. (GB
The Effect of Co Incorporation on the CO Oxidation Activity of LaFe1−xCoxO3 Perovskites
Get PDFPerovskite oxides are versatile materials due to their wide variety of compositions of-
fering promising catalytic properties, especially in oxidation reactions. In the presented study,
LaFe1−xCoxO3 perovskites were synthesized by hydroxycarbonate precursor co-precipitation and
thermal decomposition thereof. Precursor and calcined materials were studied by scanning electron
microscopy (SEM), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR),
thermogravimetric analysis (TG), and X-ray powder diffraction (XRD). The calcined catalysts were in
addition studied by transmission electron microscopy (TEM) and N2 physisorption. The obtained
perovskites were applied as catalysts in transient CO oxidation, and in operando studies of CO
oxidation in diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). A pronounced
increase in activity was already observed by incorporating 5% cobalt into the structure, which contin-
ued, though not linearly, at higher loadings. This could be most likely due to the enhanced redox
properties as inferred by H2-temperature programmed reduction (H2-TPR). Catalysts with higher
Co contents showing higher activities suffered less from surface deactivation related to carbonate
poisoning. Despite the similarity in the crystalline structures upon Co incorporation, we observed a
different promotion or suppression of various carbonate-related bands, which could indicate different
surface properties of the catalysts, subsequently resulting in the observed non-linear CO oxidation
activity trend at higher Co contents
Matrix Product Eigenstates for One-Dimensional Stochastic Models and Quantum Spin Chains
Full text linkWe show that all zero energy eigenstates of an arbitrary --state quantum
spin chain Hamiltonian with nearest neighbor interaction in the bulk and single
site boundary terms, which can also describe the dynamics of stochastic models,
can be written as matrix product states. This means that the weights in these
states can be expressed as expectation values in a Fock representation of an
algebra generated by operators fulfilling quadratic relations which
are defined by the Hamiltonian.Comment: 11 pages, Late
Finite-Size Scaling Studies of Reaction-Diffusion Systems Part III: Numerical Methods
Full text linkThe scaling exponent and scaling function for the 1D single species
coagulation model are shown to be universal, i.e. they are
not influenced by the value of the coagulation rate. They are independent of
the initial conditions as well. Two different numerical methods are used to
compute the scaling properties: Monte Carlo simulations and extrapolations of
exact finite lattice data. These methods are tested in a case where analytical
results are available. It is shown that Monte Carlo simulations can be used to
compute even the correction terms. To obtain reliable results from finite-size
extrapolations exact numerical data for lattices up to ten sites are
sufficient.Comment: 19 pages, LaTeX, 5 figures uuencoded, BONN HE-94-0
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