The Phase Diagram and Spectrum of Gauge-Fixed Abelian Lattice Gauge Theory

We consider a lattice discretization of a covariantly gauge-fixed abelian gauge theory. The gauge fixing is part of the action defining the theory, and we study the phase diagram in detail. As there is no BRST symmetry on the lattice, counterterms are needed, and we construct those explicitly. We show that the proper adjustment of these counterterms drives the theory to a new type of phase transition, at which we recover a continuum theory of (free) photons. We present both numerical and (one-loop) perturbative results, and show that they are in good agreement near this phase transition. Since perturbation theory plays an important role, it is important to choose a discretization of the gauge-fixing action such that lattice perturbation theory is valid. Indeed, we find numerical evidence that lattice actions not satisfying this requirement do not lead to the desired continuum limit. While we do not consider fermions here, we argue that our results, in combination with previous work, provide very strong evidence that this new phase transition can be used to define abelian lattice chiral gauge theories.Comment: 42 pages, 30 figure

Shocks in unmagnetized plasma with a shear flow: Stability and magnetic field generation

A pair of curved shocks in a collisionless plasma is examined with a two-dimensional particle-in-cell (PIC) simulation. The shocks are created by the collision of two electron-ion clouds at a speed that exceeds everywhere the threshold speed for shock formation. A variation of the collision speed along the initially planar collision boundary, which is comparable to the ion acoustic speed, yields a curvature of the shock that increases with time. The spatially varying Mach number of the shocks results in a variation of the downstream density in the direction along the shock boundary. This variation is eventually equilibrated by the thermal diffusion of ions. The pair of shocks is stable for tens of inverse ion plasma frequencies. The angle between the mean flow velocity vector of the inflowing upstream plasma and the shock's electrostatic field increases steadily during this time. The disalignment of both vectors gives rise to a rotational electron flow, which yields the growth of magnetic field patches that are coherent over tens of electron skin depths.Comment: 10 pages, 10 figures accepted for publication in Physics of Plasma

Parametric motion control of robotic arms: A biologically based approach using neural networks

A neural network based system is presented which is able to generate point-to-point movements of robotic manipulators. The foundation of this approach is the use of prototypical control torque signals which are defined by a set of parameters. The parameter set is used for scaling and shaping of these prototypical torque signals to effect a desired outcome of the system. This approach is based on neurophysiological findings that the central nervous system stores generalized cognitive representations of movements called synergies, schemas, or motor programs. It has been proposed that these motor programs may be stored as torque-time functions in central pattern generators which can be scaled with appropriate time and magnitude parameters. The central pattern generators use these parameters to generate stereotypical torque-time profiles, which are then sent to the joint actuators. Hence, only a small number of parameters need to be determined for each point-to-point movement instead of the entire torque-time trajectory. This same principle is implemented for controlling the joint torques of robotic manipulators where a neural network is used to identify the relationship between the task requirements and the torque parameters. Movements are specified by the initial robot position in joint coordinates and the desired final end-effector position in Cartesian coordinates. This information is provided to the neural network which calculates six torque parameters for a two-link system. The prototypical torque profiles (one per joint) are then scaled by those parameters. After appropriate training of the network, our parametric control design allowed the reproduction of a trained set of movements with relatively high accuracy, and the production of previously untrained movements with comparable accuracy. We conclude that our approach was successful in discriminating between trained movements and in generalizing to untrained movements

The Herschel Space Observatory view of dust in M81

We use Herschel Space Observatory data to place observational constraints on the peak and Rayleigh-Jeans slope of dust emission observed at 70−500 μm in the nearby spiral galaxy M81. We find that the ratios of wave bands between 160 and 500 μm are primarily dependent on radius but that the ratio of 70 to 160 μm emission shows no clear dependence on surface brightness or radius. These results along with analyses of the spectral energy distributions imply that the 160−500 μm emission traces 15−30 K dust heated by evolved stars in the bulge and disc whereas the 70 μm emission includes dust heated by the active galactic nucleus and young stars in star forming regions

Instability tests for air-jet textured yarns

The air-jet texturing process is briefly introduced and its advantages over other texturing processes are summarized. Characteristics of air-jet textured yarns are stated with special reference to the stability of the yarns. Test methods used in industry and research to determine the "stability" or "instability" of air-jet textured yarns are critically reviewed. These methods involve different basic principles and therefore inevitably give different results. There is no consensus on a standard method. Effects of various test parameters, such as specimen length, test duration, and the alternatives of using a single yarn, a hank, or a skein as a test specimen are investigated. An improved test method is suggested as a standard instability test, and various existing methods are compared with it. Results of all the methods show similar trends for varying values of air pressure. Other yarn characteristics such as linear density, breaking elongation, and tenacity are also determined, and their indications of yarn quality are compared with the indications of instability tests. Stability test results alone provide misleading information regarding air-jet textured yarn quality

A simulation-based approach to business model design and organizational Change

While several practice-based approaches of business model design suggest ways to create new business models, there is limited understanding of why and how business models change. This exploratory study employs neural network analysis to simulate business model design and business model change. We conceptualise business model design as a schema of the organisation’s critical resources, transactions, and value proposition. Elements of the schema are connected in a simple neural network. The network evolves based on a constraint satisfaction network until it converges to a stable state of a coherent business model. An in-depth case study of an entrepreneurial venture provides a real-world example to test the analytical framework. Using data from the case study, we run multiple simulations of business model design and business model change. The results suggest that business model change can be understood as a form of constraint satisfaction, linking managerial cognition with business model change. The simulation approach also helps identify possible, but unrealized business models. This novel approach paves the way for new research and practice in business model design and change

Hyperuricaemia in cyclosporin-treated patients: a GFR-related effect

Background Hyperuricaemia is a well known side-effect of cyclosporin A (CsA) treatment. The pathogenic mechanisms, however, remain controversial. There is no convincing evidence that hyperuricaemia is due to CsA-induced, impaired tubular handling of uric acid. The impact of diminished GFR in this particular context has never been investigated. Methods We prospectively studied plasma uric acid, inulin clearances, and fractional clearances of uric acid in two groups of CsA-treated patients (bone-marrow transplant patients, n=50; renal transplant patients, n=32), and one healthy control group without CsA (living related kidney donors, n=28). Bone-marrow transplant patients were examined before transplantation and 6, 12, 18, 24 months after transplantation, renal transplant patients 1 year after transplantation, and living related kidney donors before and 1 year after unilateral nephrectomy. Results After 1 year of CsA treatment, hyperuricaemia was found in 36% of bone-marrow transplant patients and in 53% of renal transplant patients. Thirty per cent of living related kidney donors were borderline hyperuricaemic 1 year after unilateral nephrectomy. The fractional clearance of uric acid, measured serially in bone-marrow transplant patients did not change significantly over time; it was, however, slightly higher during CsA treatment than after CsA withdrawal. Moreover, the bone-marrow transplant patients' fractional clearance of uric acid was not statistically different from the renal transplant patients' and the living related kidney donors' (values 1 year after transplantation/unilateral nephrectomy: bone-marrow transplant patients, 15.3±2.3%; renal transplant patients, 11.9±0.9%; living related kidney donors, 11.1±0.8%). The GFR at 1 year, measured by inulin clearance, was identical in the CsA-treated groups and slightly higher in the living related kidney donors (bone-marrow transplant patients, 51±6 ml/min per 1.73 m2 renal transplant patients, 49±3 ml/min per 1.73 m2 living related kidney donors, 61±2 ml/min per 1.73 min2). Conclusions There is no evidence for impaired tubular handling of uric acid, induced by a CsA-specific tubulotoxic effect. Hyperuricaemia in CsA-treated transplant patients can therefore be attributed to the cyclosporin associated decrease of GF

Excellent uricosuric efficacy of benzbromarone in cyclosporin-A-treated renal transplant patients: a prospective study

Patients on cyclosporin A (CsA) often develop hyperuricaemia and gout. In transplant patients the use of uricosuric drugs for treating hyperuricaemia may be preferable to allopurinol because of the known interaction of the latter with azathioprine. We therefore prospectively studied the uricosuric efficacy of 100 mg benzbromarone (Bbr;Desuric®) daily in 25 CsA-treated renal transplant patients with stable graft function and hyperuricaemia (>359 μmol/l for females, >491 μmol/l for males). Benzbromarone decreased plasma uric acid from 579±18 μmol/l to 313±24 μmol/l (mean±SEM; P25 ml/min. Due to its excellent efficacy and lack of significant side-effects, benzbromarone appears to be preferable to allopurinol in CsA-treated renal transplant recipients with a creati nine clearance over 25 ml/mi