Elementary excitations in antiferromagnetic Heisenberg systems

The structure of the (eigen)states of antiferromagnetic Heisenberg systems is discussed. These systems are shown to be equivalent to classical systems of coupled harmonic oscillators. Most attention will be paid to the first excited state. This state is supposed to be a triplet. An approximation method, which is a generalization of a method, used to describe the ground state of Heisenberg systems, will be used to describe elementary excitations. The working of the method is demonstrated by some small-system calculations

Exact spectrum for n electrons in the single band Hubbard model

The energy spectrum and the correlation functions for n electrons in the one-dimensional single band Hubbard model with periodic boundary conditions are calculated exactly. For that purpose the Hamiltonian is transformed into a set of Hamiltonians, corresponding to systems of spinless fermions.\ud Our results include the results of Mei and Chen, presented in a recent paper

A mechanism for symmetry breaking in antiferromagnetic Heisenberg systems

An approximation method, based on dimer coverings, for the ground state of the antiferromagnetic Heisenberg lattice is described. The working of the method is demonstrated by some small-system calculations. The method introduces a possible mechanism for symmetry breaking for two- and higher-dimensional systems

A thermodynamic approximation of the ground state of antiferromagnetic heisenberg spin−1/2 lattices

The exact ground state of finite Heisenberg spin−1/2 lattices isstudied. The coefficients of the so-called Ising configurations contributing to the ground state are approximated by Boltzmann-like expressions. These expressions contain a parameter that may be related to an inverse temperature

Image reconstruction from scattered Radon data by weighted positive definite kernel functions

We propose a novel kernel-based method for image reconstruction from scattered Radon data. To this end, we employ generalized Hermite–Birkhoff interpolation by positive definite kernel functions. For radial kernels, however, a straightforward application of the generalized Hermite–Birkhoff interpolation method fails to work, as we prove in this paper. To obtain a well-posed reconstruction scheme for scattered Radon data, we introduce a new class of weighted positive definite kernels, which are symmetric but not radially symmetric. By our construction, the resulting weighted kernels are combinations of radial positive definite kernels and positive weight functions. This yields very flexible image reconstruction methods, which work for arbitrary distributions of Radon lines. We develop suitable representations for the weighted basis functions and the symmetric positive definite kernel matrices that are resulting from the proposed reconstruction scheme. For the relevant special case, where Gaussian radial kernels are combined with Gaussian weights, explicit formulae for the weighted Gaussian basis functions and the kernel matrices are given. Supporting numerical examples are finally presented

Kernel-based Image Reconstruction from Scattered Radon Data

Computerized tomography requires suitable numerical methods for the approximation of a bivariate function f from a finite set of discrete Radon data, each of whose data samples represents one line integral of f . In standard reconstruction methods, specific assumptions concerning the geometry of the Radon lines are usually made. In relevant applications of image reconstruction, however, such assumptions are often too restrictive. In this case, one would rather prefer to work with reconstruction methods allowing for arbitrary distributions of scattered Radon lines. This paper proposes a novel image reconstruction method for scattered Radon data, which combines kernel-based scattered data approximation with a well-adapted regularization of the Radon transform. This results in a very flexible numerical algorithm for image reconstruction, which works for arbitrary distributions of Radon lines. This is in contrast to the classical filtered back projection, which essentially relies on a regular distribution of the Radon lines, e.g. parallel beam geometry. The good performance of the kernel-based image reconstruction method is illustrated by numerical examples and comparisons

Utilization of pork and pork by-products for nutritional and behavioral management of captive exotic felids

Currently two protein sources (beef or horse) comprise the majority of raw meat diet formulations for exotic carnivores in zoological institutions. Pork-based diets have traditionally not been fed to managed exotic carnivores, primarily because of microbial and pathogenic concerns, and nutrient digestibility of pork has not been evaluated in captive exotic carnivores, such as felids. Additionally, commercially prepared raw meat diets, while nutritionally complete, rarely meet nonnutritive requirements of cats, such as locating, capturing, and killing prey as well as psychological aspects related to the feeding process, and oral health needs. The pork industry currently sends many by-products to rendering that have the potential to be used in raw carnivore diets or as environmental enrichment. The overall objectives of this research were to evaluate a raw, pork-based diet for small and large captive exotic felids, including diet compositional analyses, fecal scores, palatability, and microbial loads. Additionally, the use of pork by-products as environmental enrichment devices for large captive exotic felids was evaluated. Our first aim was to determine apparent total tract macronutrient digestibility, fecal scores, and palatability of a pork-based diet compared with standard zoological carnivore diets formulated with either horse or beef, in large captive exotic felids. Our second aim was to determine if a pork-based diet had similar apparent total tract macronutrient digestibility and fecal scores as standard zoological carnivore diets formulated with either horse or beef, in small exotic felids, and evaluate microbial populations in raw diets. Our third aim was to evaluate 11 pork by-products for macronutrient and mineral composition and determine if a pig head would be a biologically relevant environmental enrichment device for large felids kept in a zoological setting. In general, a raw pork-based diet was well digested and utilized by large and small captive exotic felids. All raw meat diets used in these studies were highly digestible, and the pork-based diet was similarly or more digested compared to other protein sources. Fecal scores were healthy when felids were fed the pork-based diet and the diet was determined palatable for the tested cats. The use of raw pork by-products also provides opportunity as potential environmental enrichment. In our first aim, we demonstrated that a raw pork-based diet was highly digestible in large exotic felids by using four raw meat dietary treatments: one horse-based (Horse), two beef-based (B1, B2), and one pork-based diet (Pork). Dry matter (DM) and crude protein (CP) apparent digestibilities were higher (P\u3c0.05) in cats fed Pork (87.97 and 95.74%) compared with cats fed Horse (83.59 and 92.71%) and B2 (85.60 and 93.14%). Apparent organic matter (OM) digestibility was higher (P\u3c0.05) in cats fed Pork (90.76%) than cats fed Horse (88.53%). Apparent fat digestibility values were high across all treatments but were higher (P\u3c0.05) in cats fed Pork (98.51%) compared with cats fed B1 (95.51%) or B2 (96.45%). Gross energy (GE) digestibility values were higher in cats fed Pork (92.38%) compared with B1 (90.21%). Using a scale of 1 to 5, with 3 considered ideal, average fecal scores were 2.30, 2.94, 3.42, and 3.54 for Horse, Pork, B1 and B2, respectively; and were different between every treatment with the exception of B1 and B2 which were not statistically different. The pork-based diet was palatable and was selected in 24 of 37 total (64.86%) observations of first approached and 23 out of 33 total (69.70%) observations for first tasted, compared to a raw beef-based diet. In our second aim, we showed that a raw pork-based diet was highly digestible in small exotic felids by using raw horse (Horse), beef (Beef), beef/horse blend (Blend), and pork-based (Pork) dietary treatments. All diets were highly digestible, especially fat digestibility (98.58 to 99.73%) in which there were no statistical differences between diets. Digestibility of OM was higher (P\u3c0.05) when cats consumed the Blend diet (97.15%) compared to the Pork diet (93.10%). Fecal scores ranged from 1.55 to 2.63, with Beef (2.63) being statistically higher (P\u3c0.05) than Horse (1.55) and Pork (1.91). Additionally, microbial counts were shown to be highly variable in dietary treatments (E. Coli: 110 to 10,000 cfu/g; total coliforms: 150 to 28,000 cfu/g; yeast: 20 to 4,000 cfu/g; mold count: not detectable to 10 cfu/g; aerobic plate count: 23,000 to 26,000,000 cfu/g). Staphylococcus aureus was not detected in any of the diets. Salmonella was presumptive positive in the Pork and Blend diet, and was negative in the other three diets, but no signs of clinical illness were observed in cats fed any of the evaluated diets. In our third aim, it was demonstrated that pork by-products ranged widely in composition and have potential for use as biologically relevant environmental enrichment for captive exotic felids. Ranges of macronutrient composition for 11 pork by-products were: DM: 26.01-71.23%; OM: 53.04-96.79%; CP: 22.90-79.29%; fat: 22.01-63.15%; CF: 0.25-19.54%; total dietary fiber (TDF): 0.04-3.44%; GE: 3.73-7.45 kcal/g. Potential use of these by-products as environmental enrichment was demonstrated by offering five large exotic felids a pig head, and observing their behavior on Baseline (before head offered), Enrichment (head offered), and Post enrichment (head removed) days, over 4 weeks, using instantaneous scan sampling at one minute intervals for 2 hours in the morning. Active behaviors were observed to be 55.70% higher (P\u3c0.0001) on Enrichment days compared to Baseline and 26.42% higher (P\u3c0.0001) compared to Post enrichment days. Active behaviors were 39.79% higher (P\u3c0.0001) on Post enrichment days compared to Baseline days. Total active behaviors were observed to increase 44.24, 49.42, and 64.27% (P\u3c0.0001) in week 3 compared to weeks 1, 2, and 4, respectively, and increased 35.93 and 29.36% in weeks 1 and 2, respectively, compared to 4. Number of location changes were greater (P\u3c0.05) in week 3 compared to 2 or 4. Fecal scores were not statistically different across days or weeks. Time to approach the head (seconds) and loss in head weight from before to after offering to the cat (grams) were not statistically different (P\u3e0.05) across weeks. Dietary variety is important for exotic felid health as well as managerial flexibility. Enrichment also has been an area of increasing interest for zoos over the past several decades. This research has demonstrated that a pork-based raw meat diet can be included among dietary options for captive exotic felids and that, while microbial populations in these diets are high, felids can tolerate microbial load present in raw meat diets. Additionally, pork by-products can provide valuable nutrients while fulfilling nonnutritive needs of exotic felids that are not provided by commercially prepared soft, raw meat diets

Methodologische Fragen der Verwendung von Bild-, Ton- und Textdaten zur Navigationsanalyse

Lernende eignen sich bei der Navigation in Online-Lernumgebungen Wissen an. Studien, die diese Aneignung von Wissen untersuchen, stellen dabei häufig die Frage nach dem Resultat des Aneignungsprozesses in den Mittelpunkt. Dieser Zugang mit der Frage nach Effektivität und Effizienz dominiert die gegenwärtige Perspektive auf E-Learning – gerade auch im Vergleich zu traditionellen Medien wie dem Buch

Influence of nutrient intake on oxidative stress in zoo-managed species

A paucity of research exists investigating influence of diet on oxidative stress (OS) in zoo-managed animals. Many zoo-managed species have unknown nutrient requirements and OS can be used as a measure to evaluate dietary nutrient concentrations and narrow dietary recommendations. The overall dissertation objective was to evaluate influence of diet and nutrient intakes on markers of OS in zoo-managed animals through three objectives: 1) evaluate influence of five commercial gut-loading diets on resulting live cricket nutrient composition and impact on markers of OS in two zoo-managed toad species 2) evaluate dietary nutrient intake and nutritional husbandry influence on markers of OS in male snow leopards maintained in U.S. zoos and 3) assess the impact of three dietary vitamin E concentrations on OS, maze learning performance, and anxiety behaviors in feeder rats. Results demonstrated that 1) potassium and high protein to fat ratios increased markers of OS in toads 2) OS is influenced by copper and sodium intakes and whole prey consumption in male snow leopards 3) dietary vitamin E intakes five to 22 times above nutrient requirements are positively correlated with increased OS and are not beneficial for feeder rat welfare in relation to maze learning performance. This novel research in zoo-managed species provides some of the first data of its kind evaluating influence of dietary vitamin and mineral concentrations and ratios in relation to OS. The results presented provide some additional clarity to nutrient target ranges for future research in amphibians, felids, and rodents via an approach that has not been taken in exotic animal nutrition. Additionally, results provide valuable information to animal managers for improved health and advancements in husbandry to ensure success of assurance populations. Nutrition affects a myriad of processes in the body including OS, defined as an imbalance between pro-oxidants and antioxidants, in favor of pro-oxidants. Both nutrition and OS can affect many physiologies and phenotypes such as animal growth, reproduction, learning, and behavior. For zoo-managed species this is a critical issue because specific nutrient requirements for a majority of exotic species are not known. To address the overall dissertation objective, two research chapters (2-3) were completed using species managed in zoo breeding programs with challenges affecting their sustainability that are potentially linked with nutrition and OS (toads and snow leopards). Chapter 4 utilized a unique zoo-managed model (feeder rats) to evaluate controlled concentrations of one dietary antioxidant (vitamin E) to evaluate influence on maze learning performance and anxious behaviors that could be potential indicators of animal welfare. In Chapter 2, two toad species were utilized to evaluate OS when fed five different, live cricket, dietary treatments (crickets fed different diets (gut-loading diets)). With more than 50% of known amphibian species threatened with extinction, assurance populations are vital to sustain wild populations via reintroduction programs; however dietary nutrient deficiencies may be hindering amphibian health in zoos. The objective of Chapter 2 was to evaluate, for the first time in amphibians, correlations of dietary nutrients (proximates, vitamins A and E, and minerals) and markers of OS. We hypothesized that live crickets would differ in nutrient composition based on the diet they were fed, and toads fed crickets containing higher concentrations of vitamins A and E would have lower levels of OS. The hypotheses were partially supported as crickets did vary in nutrient composition (particularly protein, fat, calcium, and carotenoids) and nutrient intake did influence glutathione peroxidase (GPx) activity in toads. Contrary to our hypotheses, vitamin E did not impact markers of OS; however, GPx activity did decrease with increasing dietary retinol but this requires further investigation to determine positive or negative OS impacts. Additionally, higher cricket protein:fat ratios and potassium concentrations were correlated with increased GPx activity. Results of Chapter 2 indicate dietary imbalances in vitamins and minerals and very high protein to fat ratios (above 10.0) are correlated with increases in markers of OS. Results indicate that crickets should be monitored for low fat concentrations to prevent excessively high protein:fat ratios that could affect fat-soluble vitamin absorption. Evaluation of ideal ratios requires further investigation through controlled dietary studies. Our results also suggest the use of some products (Vita Bug®) for gut-loading, requires specific supplementation of nutrients (calcium) for amphibian health. In Chapter 3, the objective was to evaluate the influence of dietary nutrient intakes and nutritional husbandry on markers of OS in male snow leopards maintained in U.S. zoos. Snow leopards are an endangered species and zoo populations have been declining over the past two decades. Dietary inadequacies may be a contributing factor to disease and abnormal physiologies affecting zoo-managed snow leopards, possibly through OS. Improvement of nutritional understanding in zoo-managed settings is likely a vital component of managing this assurance population. Diets of each cat were collected and analyzed as well as weekly feeding amounts to yield weekly nutrient (proximates, minerals, vitamins A and E, and fatty acids) intakes. It was hypothesized that dietary nutrients, particularly higher intakes of vitamins A and E, would reduce markers of OS and that trace mineral balance would also influence OS. Our hypothesis was not supported as dietary vitamin intakes did not directly impact OS. In support of our hypothesis, dietary minerals (copper and sodium) were correlated with alterations in OS in male snow leopards. Reduction in oxidative DNA/RNA damage was correlated with increases in copper intakes; however, some snow leopards consumed less copper than recommended, highlighting the need to carefully evaluate concentrations in exotic cat diets. Very high intakes of some minerals such as iron also support the need to carefully evaluate mineral concentrations and mineral balance in zoo carnivore diet formulations. Additionally, the use of supplemental whole prey positively influenced superoxide dismutase (SOD) activity. These results suggest alteration of diet, specifically with attention to mineral premixes and addition of whole prey, may be beneficial for improving snow leopard OS and potentially improving the sustainability of zoo-managed snow leopard populations. Chapter 4 utilized growing feeder rats (raised to be fed to other animals) to achieve objectives of assessing the impact of specific dietary vitamin E concentrations on OS markers, maze learning performance, and anxious behaviors. While rats are not an exotic species, they do have published nutrient requirements allowing for dietary manipulation to assess target concentrations. Additionally, they can be useful as models for other zoo-managed species. We hypothesized that rats fed higher concentrations of dietary vitamin E would have suppressed OS levels, superior maze learning performance, and fewer anxiety behaviors. Oxidative stress did appear to be influenced by dietary vitamin E; however, not as anticipated because SOD activity was lowest and concentrations of PC highest in rats fed highest dietary vitamin E concentrations. Our hypothesis was not supported by results of Chapter 4, which demonstrated that feeding excessive concentrations of dietary vitamin E, did not impact rat maze learning performance. Diets containing the lowest concentrations of dietary vitamin E, resulted in more anxiety behaviors in rats and thus did support our hypothesis. Conclusions from Chapter 4 indicated that dietary vitamin E intakes 5-22 times above nutrient requirements were not beneficial for 13-ek old feeder rat maze learning performance and OS markers. Results indicate the potential risks of feeding super doses of vitamin E and can aid in supplementation decisions in diet formulation for exotic animal and feeder animal diets