Enhanced low-temperature entropy and flat-band ferromagnetism in the t-J model on the sawtooth lattice

Using the example of the sawtooth chain, we argue that the t-J model shares important features with the Hubbard model on highly frustrated lattices. The lowest single-fermion band is completely flat (for a specific choice of the hopping parameters $t_{i,j}$ in the case of the sawtooth chain), giving rise to single-particle excitations which can be localized in real space. These localized excitations do not interact for sufficient spatial separations such that exact many-electron states can also be constructed. Furthermore, all these excitations acquire zero energy for a suitable choice of the chemical potential $\mu$. This leads to: (i) a jump in the particle density at zero temperature, (ii) a finite zero-temperature entropy, (iii) a ferromagnetic ground state with a charge gap when the flat band is fully occupied and (iv) unusually large temperature variations when $\mu$ is varied adiabatically at finite temperature.Comment: 2 pages including 2 figures, uses elsart style files; (proceedings of ICM 2006

Comment on "Density of States and Critical Behavior of the Coulomb Glass"

In a recent numerical investigation of the Coulomb glass, Surer et al. [Phys. Rev. Lett. 102, 067205 (2009)] concluded that their simulation results are consistent with the Efros Shklovskii prediction for the density of states in the three-dimensional case. Here, we show that this statement has no relevance concerning the problem of the asymptotic behavior in the Coulomb gap since it is based on unjustified assumptions. Moreover, for the random-displacement Coulomb glass model, we demonstrate that a part of the density of states data by Surer et al. erroneously exhibit a broad gap. This is related to the staggered occupation being instable contrary to their findings.Comment: Submitted to Physical Review Letters, 1 page, 1 figur

Random Matrices and Chaos in Nuclear Physics: Nuclear Reactions

The application of random-matrix theory (RMT) to compound-nucleus (CN) reactions is reviewed. An introduction into the basic concepts of nuclear scattering theory is followed by a survey of phenomenological approaches to CN scattering. The implementation of a random-matrix approach into scattering theory leads to a statistical theory of CN reactions. Since RMT applies generically to chaotic quantum systems, that theory is, at the same time, a generic theory of quantum chaotic scattering. It uses a minimum of input parameters (average S-matrix and mean level spacing of the CN). Predictions of the theory are derived with the help of field-theoretical methods adapted from condensed-matter physics and compared with those of phenomenological approaches. Thorough tests of the theory are reviewed, as are applications in nuclear physics, with special attention given to violation of symmetries (isospin, parity) and time-reversal invariance.Comment: 50 pages, 26 figure

Video switcher for coupling video cameras to single TV monitor

Device couples up to 60 TV cameras to single monitor. Video switching is provided by diode matrix arranged in a 60-by-1 configuration. Switcher can be operated manually or automatically

Comment on "138La-138Ce-136Ce nuclear cosmochronometer of the supernova neutrino process"

The nuclear chosmochronometer suggested by Hayakawa et al. [Phys. Rev.C 77, 065802 (2008)] based on the 138La-138Ce-136Ce abundance ratio in presolar grains would be affected by the existence of a hitherto unknown low-energy 1+ state in 138La. Results of a recent high-resolution study of the 138Ba(3He,t) reaction under kinematics selectively populating 1+ states in 138La through Gamow-Teller transitions provides strong evidence against the existence of such a hypothetical state.Comment: Comment on Phys. Rev. C 77, 065802 (2008), submittted to Phys. Rev.

Possibilities and limitations of protein supply in organic poultry and pig production

It is one of the general recommendations in animal nutrition that the diet should be formulated according to the specific requirements of animals at the various stages of their development. To which degree the farmer can adapt the nutrient supply to the specific requirements of the animals depends primarily on the production goal and on the availability of nutrient resources. This report gives a general introduction to the present situation for dietary protein supply to poultry and pig production in relation to the principles for organic agriculture and husbandry production. Furthermore it includes partly literature based on research from conventional animal production, as the requirements on the level of the animals are not different in both systems. Moreover, there only few research projects of organic production systems available. This report is primarily focussing on the question whether a nutrient supply of 100% organic feed can and should be realised. In this context, it is not possible to cover all aspects in detail as the report cannot replace a textbook. The main emphasis is laid on a coherent argumentation based on the leading ideas of organic agriculture. Concerning further relevant aspects it is referred to the report ”Supply and demand for concentrated organic feed in the EU in 2002 and 2003” by Susanne Padel as part of the same EU-project: ‘Research to support the EU-regulation on Organic Agriculture’ (www.organic-revision.org) and to the project “Availability of organically reared livestock” (S. Gomez, JRC, Institute for Prospective Technological Studies, this study is expected to be completed in November 2005). In conventional animal production, a nutrient supply that is closely related to the requirements is an important tool in the performance-oriented production (FLACHOWSKY, 1998). The objective of animal nutrition is to adapt the nutrient supply as accurately as possible to the requirements resulting from maintenance and performance need. Soybean meal, due to the high protein content and high protein quality, has developed into the most important protein source in the nutrition of monogastric animals. Additionally, synthetic amino acids (DL-methionine) and industrial amino acids (produced from microbial fermentation, L-amino acids) are used to balance the supply of essential amino acids. While the use of soybean meal and synthetic amino acids is normal practice in conventional animal production, the Council-Regulation No. 2092/91, amended by Council Regulation No. 1804/99 on organic livestock production bans the use of chemically extracted soybean meal and synthetic amino acids on organic farms as livestock must be fed primarily on organically produced feedstuffs (Annex 1, paragraph 4.2). By way of a derogation from paragraph 4.2, for a transitional period expiring on 24 August 2005, the use of a limited proportion of non-organic feedstuffs is authorised where farmers can show to the satisfaction of the inspection body that they are unable to obtain feed exclusively from organic production (paragraph 4.8). The derogation, although with a declining percentage of non-organic feedstuffs over the next years, has been prolonged in July 2005. The preferable use of home-grown feedstuffs and limitations in the choice of boughtin feedstuffs can be the cause of considerable variation in the composition of the diets, and considerably restrict the possibilities for the adaptation of the feed ration to the specific requirements. Due to the limited availability of essential amino acids in particular, there is concern that nutritional imbalances encountered in practice might lead to deteriorating animal health and welfare. On the other hand, there is also the concern that allowing conventional feedstuffs to be fed in organic livestock production will result in intensification of production. The intensification might cause the same problems in organic production as conventional production already shows (animal health problems, risk of residues and GM contamination etc.). Thus, the use of non-organic feedstuffs may have a damaging effect on consumer confidence in organic products of animal origin. In the following the nutritional-physiological effects of a variation in protein supply with respect to growth performance and protein accretion in broilers, turkeys, laying hens, and pigs are examined by means of a literature review. Additionally, the potential effects of the protein content in the diet on product quality, animal health and environmental damage are addressed. It is the aim of the report to provide an overview of the many different aspects of the protein supply in organic poultry and pig production. Many different aspects are taken into account to elaborate possibilities to handle the use of organic and non-organic feedstuffs with respect to the objectives and framework conditions of organic livestock production. However, due to the complex interactions not all aspects can be covered. There is room and need for explanation and for further research

Dynamics of many-particle fragmentation in a Cellular Automaton model

A 3D Cellular Automaton model developed by the authors to deal with the dynamics of N-body interactions has been adapted to investigate the head-on collision of two identical bound clusters of particles, and the ensuing process of fragmentation. The range of impact energies is chosen low enough, to secure that a compound bound cluster can be formed. The model is devised to simulate the laboratory set-up of fragmentation experiments as monitored by 4pi detectors. The particles interact via a Lennard-Jones potential. At low impact energies the numerical experiments following the dynamics of the individual particles indicate a phase of energy sharing among all the particles of the compound cluster. Fragments of all sizes are then found to evaporate from the latter cluster. The cluster sizes, measured in our set-up by simulated 4pi detectors, conform to a power law of exponent around 2.6.Comment: 27 pages, 10 figures, submitted to Phys. Rev.

Discrete symmetries from hidden sectors

We study the presence of abelian discrete symmetries in globally consistent orientifold compactifications based on rational conformal field theory. We extend previous work [1] by allowing the discrete symmetries to be a linear combination of U(1) gauge factors of the visible as well as the hidden sector. This more general ansatz significantly increases the probability of finding a discrete symmetry in the low energy effective action. Applied to globally consistent MSSM-like Gepner constructions we find multiple models that allow for matter parity or Baryon triality.Comment: 20 page