22 research outputs found

### Semi-quantitative Risk Evaluation for the Occurrence of Salmonella spec. in Swine Herds and Slaughter Plants

The implementation of a “Salmonella Monitoring and Reduction Programme” in the framework of the emerging national quality assurance programme (it is called the “QS-System”) for food products (starting with pork) in Germany has led to the necessity to provide farmers and slaughter plants with guidelines for a) how to identify the critical points on their own farm and in their own slaughter plant that could be “responsible” for a high Salmonella load of the final product (= live slaughter pigs in case of the farm or carcasses and cut meat in case of the slaughter plant), and b) how to develop a “HACCP-like” plan for a measurable reduction of the salmonella load. The paper describes the development of check lists that can be used for both benchmarking and identifying “weak points” as basis for targeted intervention strategies in the framework of continuous improvement programmes

### Matrix Models, Emergent Gravity, and Gauge Theory

Matrix models of Yang-Mills type induce an effective gravity theory on
4-dimensional branes, which are considered as models for dynamical space-time.
We review recent progress in the understanding of this emergent gravity. The
metric is not fundamental but arises effectively in the semi-classical limit,
along with nonabelian gauge fields. This leads to a mechanism for protecting
certain geometries from corrections due to the vacuum energy.Comment: 8 pages. Based on invited talks given at the Conferences "Quantum
Spacetime and Noncommutative Geometry", Rome, 2008 and at "Workshop on
quantum gravity and nocommutative geometry", Lisbon, 2008 and at "Emergent
Gravity", Boston, 2008 and at DICE2008, Italy, 2008 and at "QG2 2008 Quantum
Geometry and Quantum Gravity", Nottingham, 200

### Absence of a fuzzy $S^4$ phase in the dimensionally reduced 5d Yang-Mills-Chern-Simons model

We perform nonperturbative studies of the dimensionally reduced 5d
Yang-Mills-Chern-Simons model, in which a four-dimensional fuzzy manifold,
``fuzzy S$^{4}$'', is known to exist as a classical solution. Although the
action is unbounded from below, Monte Carlo simulations provide an evidence for
a well-defined vacuum, which stabilizes at large $N$, when the coefficient of
the Chern-Simons term is sufficiently small. The fuzzy S$^{4}$ prepared as an
initial configuration decays rapidly into this vacuum in the process of
thermalization. Thus we find that the model does not possess a ``fuzzy S$^{4}$
phase'' in contrast to our previous results on the fuzzy S$^{2}$.Comment: 11 pages, 2 figures, (v2) typos correcte

### Dynamical aspects of the fuzzy CP$^{2}$ in the large $N$ reduced model with a cubic term

``Fuzzy CP^2'', which is a four-dimensional fuzzy manifold extension of the
well-known fuzzy analogous to the fuzzy 2-sphere (S^2), appears as a classical
solution in the dimensionally reduced 8d Yang-Mills model with a cubic term
involving the structure constant of the SU(3) Lie algebra. Although the fuzzy
S^2, which is also a classical solution of the same model, has actually smaller
free energy than the fuzzy CP^2, Monte Carlo simulation shows that the fuzzy
CP^2 is stable even nonperturbatively due to the suppression of tunneling
effects at large N as far as the coefficient of the cubic term ($\alpha$) is
sufficiently large. As \alpha is decreased, both the fuzzy CP$^2$ and the fuzzy
S^2 collapse to a solid ball and the system is essentially described by the
pure Yang-Mills model (\alpha = 0). The corresponding transitions are of first
order and the critical points can be understood analytically. The gauge group
generated dynamically above the critical point turns out to be of rank one for
both CP^2 and S^2 cases. Above the critical point, we also perform perturbative
calculations for various quantities to all orders, taking advantage of the
one-loop saturation of the effective action in the large-N limit. By
extrapolating our Monte Carlo results to N=\infty, we find excellent agreement
with the all order results.Comment: 27 pages, 7 figures, (v2) References added (v3) all order analyses
added, some typos correcte

### Nonperturbative studies of fuzzy spheres in a matrix model with the Chern-Simons term

Fuzzy spheres appear as classical solutions in a matrix model obtained via
dimensional reduction of 3-dimensional Yang-Mills theory with the Chern-Simons
term. Well-defined perturbative expansion around these solutions can be
formulated even for finite matrix size, and in the case of $k$ coincident fuzzy
spheres it gives rise to a regularized U($k$) gauge theory on a noncommutative
geometry. Here we study the matrix model nonperturbatively by Monte Carlo
simulation. The system undergoes a first order phase transition as we change
the coefficient ($\alpha$) of the Chern-Simons term. In the small $\alpha$
phase, the large $N$ properties of the system are qualitatively the same as in
the pure Yang-Mills model ($\alpha =0$), whereas in the large $\alpha$ phase a
single fuzzy sphere emerges dynamically. Various `multi fuzzy spheres' are
observed as meta-stable states, and we argue in particular that the $k$
coincident fuzzy spheres cannot be realized as the true vacuum in this model
even in the large $N$ limit. We also perform one-loop calculations of various
observables for arbitrary $k$ including $k=1$. Comparison with our Monte Carlo
data suggests that higher order corrections are suppressed in the large $N$
limit.Comment: Latex 37 pages, 13 figures, discussion on instabilities refined,
references added, typo corrected, the final version to appear in JHE

### Electrolyte Imbalance Determination of a Vanadium Redox Flow Battery by Potential‐Step Analysis of the Initial Charging

Vanadium redox flow batteries (VRFB) suffer from capacity fades owing to side reactions and crossover effects through the membrane. These processes lead to a deviation of the optimal initial average oxidation state (AOS=+3.5) of vanadium species in both half‐cell electrolytes. To rebalance the electrolyte solutions, it is first necessary to determine the current AOS. In this study, a new method was developed that enables an accurate determination of the AOS. A potential‐step analysis was performed with mixed electrolyte solutions of both half‐cells during the initial charging. The potential was recorded with a simple open‐circuit voltage (OCV) cell, and the potential‐steps were analyzed. A correlation between the duration of the potential plateaus in the OCV and the amount of vanadium ions of a certain oxidation state in the half‐cell electrolytes was found and used to precisely determine the AOS with a maximum error of 3.6 %

### Scalar Solitons on the Fuzzy Sphere

We study scalar solitons on the fuzzy sphere at arbitrary radius and
noncommutativity. We prove that no solitons exist if the radius is below a
certain value. Solitons do exist for radii above a critical value which depends
on the noncommutativity parameter. We construct a family of soliton solutions
which are stable and which converge to solitons on the Moyal plane in an
appropriate limit. These solutions are rotationally symmetric about an axis and
have no allowed deformations. Solitons that describe multiple lumps on the
fuzzy sphere can also be constructed but they are not stable.Comment: 24 pages, 2 figures, typo corrected and stylistic changes. v3:
reference adde

### Emergent Geometry and Gravity from Matrix Models: an Introduction

A introductory review to emergent noncommutative gravity within Yang-Mills
Matrix models is presented. Space-time is described as a noncommutative brane
solution of the matrix model, i.e. as submanifold of \R^D. Fields and matter on
the brane arise as fluctuations of the bosonic resp. fermionic matrices around
such a background, and couple to an effective metric interpreted in terms of
gravity. Suitable tools are provided for the description of the effective
geometry in the semi-classical limit. The relation to noncommutative gauge
theory and the role of UV/IR mixing is explained. Several types of geometries
are identified, in particular "harmonic" and "Einstein" type of solutions. The
physics of the harmonic branch is discussed in some detail, emphasizing the
non-standard role of vacuum energy. This may provide new approach to some of
the big puzzles in this context. The IKKT model with D=10 and close relatives
are singled out as promising candidates for a quantum theory of fundamental
interactions including gravity.Comment: Invited topical review for Classical and Quantum Gravity. 57 pages, 5
figures. V2,V3: minor corrections and improvements. V4,V5: some improvements,
refs adde

### Layered composite membranes based on porous PVDF coated with a thin, dense PBI layer for vanadium redox flow batteries

A commercial porous polyvinylidene fluoride membrane (pore size 0.65 μm, nominally 125 μm thick) is spray coated with 1.2–4 μm thick layers of polybenzimidazole. The area resistance of the porous support is 36.4 mΩ cm2 in 2 M sulfuric acid, in comparison to 540 mΩ cm2 for a 27 μm thick acid doped polybenzimidazole membrane, and 124 mΩ cm2 for PVDF-P20 (4 μm thick blocking layer). Addition of vanadium ions to the supporting electrolyte increases the resistance, but less than for Nafion. The expected reason is a change in the osmotic pressure when the ionic strength of the electrolyte is increased, reducing the water contents in the membrane. The orientation of the composite membranes has a strong impact. Lower permeability values are found when the blocking layer is oriented towards the vanadium-lean side in ex-situ measurements. Cells with the blocking layer on the positive side have significantly lower capacity fade, also much lower than cells using Nafion 212. The coulombic efficiency of cells with PVDF-PBI membranes (98.4%) is higher than that of cells using Nafion 212 (93.6%), whereas the voltage efficiency is just slightly lower, resulting in energy efficiencies of 85.1 and 83.3%, respectively, at 80 mA/cm2

### Semi-quantitative Risk Evaluation for the Occurrence of Salmonella spec. in Swine Herds and Slaughter Plants

The implementation of a “Salmonella Monitoring and Reduction Programme” in the framework of the emerging national quality assurance programme (it is called the “QS-System”) for food products (starting with pork) in Germany has led to the necessity to provide farmers and slaughter plants with guidelines for a) how to identify the critical points on their own farm and in their own slaughter plant that could be “responsible” for a high Salmonella load of the final product (= live slaughter pigs in case of the farm or carcasses and cut meat in case of the slaughter plant), and b) how to develop a “HACCP-like” plan for a measurable reduction of the salmonella load. The paper describes the development of check lists that can be used for both benchmarking and identifying “weak points” as basis for targeted intervention strategies in the framework of continuous improvement programmes.</p