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At least 397 records · Page 22Linked to original sources
PubMed2006

Asymptotic freedom, non-Gaussian perturbation theory, and the application of renormalization group theory to isotropic turbulence.

A model equation with an extended range of asymptotic freedom is used as the basis of a non-Gaussian perturbation expansion in powers of the control parameter of the conditional average. Re-expansion in the local Reynolds number allows the systematic rederivation of an earlier, heuristic theory [W. D. McComb and A. G. Watt, Phys. Rev. Lett. 65, 3281 (1990)].

Journal Article↗
PubMed2000

Charge degree of freedom and the single-spin fluid model in YBa2Cu4O8

We present a 17O nuclear magnetic resonance study in the stoichiometric superconductor YBa2Cu4O8. A double irradiation method enables us to show that, below around 200 K, the spin-lattice relaxation rate of plane oxygen is not only driven by magnetic fluctuations, but also significantly by quadrupolar fluctuations, i. e., low-frequency charge fluctuations. In the superconducting state, on lowering the temperature, the quadrupolar relaxation diminishes faster than the magnetic one. These findings show that, with the opening of the spin pseudogap, a charge degree of freedom of mainly oxygen character is present in the electronic low-energy excitation spectrum.

Journal Article↗
PubMed2002

Coupling between spin and orbital degrees of freedom in KCuF3.

We present the results of resonant x-ray scattering experiments on KCuF3. Structurally forbidden reflections, corresponding to magnetic and 3d-orbital long-range order, have been observed. Integrated intensities have been measured as a function of incident energy, polarization, azimuthal angle, and temperature. The results give evidence for a strong coupling between orbital and spin degrees of freedom. The interplay between magnetic and orbital order parameters is revealed by the temperature dependence of the intensity of orbital Bragg peaks.

Journal Article↗
PubMed2002

Quantitative study of macroscopic quantum tunneling in a dc SQUID: a system with two degrees of freedom.

To test whether the theory of macroscopic quantum tunneling (MQT) is applicable to systems with 2 degrees of freedom, we experimentally investigated the switching current distribution of a dc SQUID. Using sample parameters determined from measurements at T=4.2 K, we are able to make quantitative comparison to the theories from 8 mK to 4.2 K. The excellent agreement between the data and the MQT theory demonstrates that tunneling from the zero-voltage state of the dc SQUID is well described by the quantum mechanics.

Journal Article↗
PubMed2003

Generalized synchronization of chaos in identical systems with hidden degrees of freedom.

We demonstrate generalized synchronization of chaos in a two-mode laser system. The total intensity of the laser output (the sum of the individual mode intensities) is used as the drive signal. This lumped variable transmitted to the identical response system does not generate identical synchronization. Generalized synchronization is observed instead of identical synchronization because of the hidden internal degrees of freedom.

Feedback↗
PubMed2004

Evidence for nonhadronic degrees of freedom in the transverse mass spectra of kaons from relativistic nucleus-nucleus collisions?

We investigate transverse hadron spectra from relativistic nucleus-nucleus collisions within two independent transport approaches that are based on quark, diquark, string, and hadronic degrees of freedom. Both transport models show their reliability for elementary pp as well as light-ion (C+C, Si+Si) reactions. However, for central Au+Au (Pb+Pb) collisions above approximately 5A GeV the measured K+/- transverse mass spectra have a larger inverse slope parameter than expected from the calculation. Thus, the pressure generated by hadronic interactions in the transport models above approximately 5A GeV is lower than observed in the experimental data. This finding shows that the additional pressure--as expected from lattice QCD calculations at finite quark chemical potential and temperature--is generated by strong partonic interactions in the early phase of central Au+Au (Pb+Pb) collisions.

Journal Article↗
PubMed2005

Energy exchange between mesoparticles and their internal degrees of freedom.

We present mesoscale equations of motion that lead to a thermodynamically accurate description of the energy exchange between mesoparticles and their internal degrees of freedom. In our approach, energy exchange is done through particle coordinates, rather than momenta, resulting in Galilean invariant equations of motion. The total linear momentum and total energy (including the internal energy of the mesoparticles) are conserved, and no coupling occurs when a mesoparticle is in free flight. We test our method for shock wave propagation in a crystalline polymer, poly(vinylidene fluoride); the mesodynamics results agree very well with all-atom molecular dynamics.

Journal Article↗
PubMed2005

Spin degree of freedom in the nu=1 bilayer electron system investigated by nuclear spin relaxation.

The nuclear-spin-relaxation rate 1/T(1) has been measured in a bilayer electron system at and around total Landau level filling factor nu=1. The measured 1/T(1), which probes electron spin fluctuations, is found to increase gradually from the quantum Hall (QH) state at low fields through a phase transition to the compressible state at high fields. Furthermore, 1/T(1) in the QH state shows a noticeable increase away from nu=1. These results demonstrate that, as opposed to common assumption, the electron spin degree of freedom is not completely frozen either in the QH or the compressible states.

Journal Article↗
PubMed2005

Nonsingular black holes and degrees of freedom in quantum gravity.

Spherically symmetric space-times provide many examples for interesting black hole solutions, which classically are all singular. Following a general program, space-like singularities in spherically symmetric quantum geometry, as well as other inhomogeneous models, are shown to be absent. Moreover, one sees how the classical reduction from infinitely many kinematical degrees of freedom to only one physical one, the mass, can arise, where aspects of quantum cosmology such as the problem of initial conditions play a role.

Journal Article↗
PubMed2006

Bose-Einstein condensation of S = 1 nickel spin degrees of freedom in NiCl2-4SC(NH2)2.

It has recently been suggested that the organic compound NiCl2-4SC(NH2)2 (DTN) undergoes field-induced Bose-Einstein condensation (BEC) of the Ni spin degrees of freedom. The Ni S = 1 spins exhibit three-dimensional XY antiferromagnetism above a critical field H(c1) approximately 2 T. The spin fluid can be described as a gas of hard-core bosons where the field-induced antiferromagnetic transition corresponds to Bose-Einstein condensation. We have determined the spin Hamiltonian of DTN using inelastic neutron diffraction measurements, and we have studied the high-field phase diagram by means of specific heat and magnetocaloric effect measurements. Our results show that the field-temperature phase boundary approaches a power-law H - H(c1) proportional variant T(alpha)(c) near the quantum critical point, with an exponent that is consistent with the 3D BEC universal value of alpha = 1.5.

Journal Article↗
PubMed2000

Rotation and direction judgment from visual images head-slaved in two and three degrees-of-freedom.

The contribution to spatial awareness of adding a roll degree-of-freedom (DOF) to telepresence camera platform yaw and pitch was examined in an experiment where subjects judged direction and rotation of stationary target markers in a remote scene. Subjects viewed the scene via head-slaved camera images in a head-mounted display. Elimination of the roll DOF affected rotation judgment, but only at extreme yaw and pitch combinations, and did not affect azimuth and elevation judgement. Systematic azimuth overshoot occurred regardless of roll condition. Observed rotation misjudgments are explained by kinematic models for eye-head direction of gaze.

Adult↗
PubMed2002

A novel multi-degree-of-freedom thick-film ultrasonic motor.

This paper describes a new multi-degree-of-freedom (MDOF) ultrasonic motor that comprises few parts and is based on low-cost thick-film technology. Conventional ultrasonic motors using bulk lead zirconate titanate (PZT) or thin-film PZT layers are relatively expensive at the present time. Thick-film printed PZT technology provides the opportunity to reduce the costs of ultrasonic motors. To demonstrate the feasibility of this approach, an ultrasonic motor was fabricated from alumina using thick-film printed PZT actuators. The thick-film PZT and electrode layers were printed on a thin alumina plate, and a tiny cylinder was mounted at its center. This cylinder magnifies the lateral displacement of the stator, holds the spherical rotor, and transmits the driving force to the sphere. Three bending vibrations, B22, B30, B03, of the plate were applied to rotate the sphere. Sufficient displacements for rotating the sphere were obtained near the resonance of B22 by applying an excitation voltage of 200 V peak-to-peak via a three-phase drive circuit. Rotations in three orthogonal directions have been observed by controlling the phase of the driving signal to the PZT electrodes, and a MDOF ultrasonic motor was successfully realized.

Journal Article↗
PubMed1999

Implantable transducer for two-degree of freedom joint angle sensing.

An implantable joint angle transducer (IJAT) was developed to provide command-control and feedback-control information for chronic use with functional neuromuscular stimulation (FNS) neuroprostheses. The IJAT uses Hall effect sensors to transduce joint angle. A titanium encapsulated array of Hall effect sensors and support circuitry is surgically implanted in one bone, and a similarly encapsulated permanent magnet in an opposing bone, across a joint. The IJAT provides consistent, reliable, high quality signals that reflect joint movement from midsized two-degree-of-freedom joints. IJAT's were implanted using a chronic in vivo dog model to demonstrate the feasibility of implantation and periodic measurement techniques, and to validate modeling techniques used for prediction of function and calibration. The flexion resolution ranged from 0.4 to 3.0 degrees over a range of 115 degrees. The maximum deviation from a linear response was 9 degrees. The resolution and linearity depend on several transducer and joint geometry parameters, and can be predicted prior to implantation and calibrated after implantation. The results of this study 1) defined the most appropriate hermetic capsule designs for the IJAT sensor and magnet, 2) defined the best orientation of the magnetic field to optimize device function, 3) provided a computer model of the IJAT to aid in placement, calibration, and evaluation of the device, 4) verified the surgical techniques used to implant the device, and 5) verified the long-term functionality and the biocompatibility of the device.

Animals↗
PubMedDate not supplied

Six degree-of-freedom haptic rendering using spatialized normal cone search.

This paper describes a haptic rendering algorithm for arbitrary polygonal models using a six degree-of-freedom haptic interface. The algorithm supports activities such as virtual prototyping of complex polygonal models and adding haptic interaction to virtual environments. The underlying collision system computes local extrema in distance between the model controlled by the haptic device and the rest of the scene. The haptic rendering computes forces and torques on the moving model based on these local extrema. The system is demonstrated on models with tens of thousands of triangles and developed in an accessibility application for finding collision-free paths.

Computer Simulation↗
PubMed2004

Sample size calculations for surveys to substantiate freedom of populations from infectious agents.

We develop a Bayesian approach to sample size computations for surveys designed to provide evidence of freedom from a disease or from an infectious agent. A population is considered "disease-free" when the prevalence or probability of disease is less than some threshold value. Prior distributions are specified for diagnostic test sensitivity and specificity and we test the null hypothesis that the prevalence is below the threshold. Sample size computations are developed using hypergeometric sampling for finite populations and binomial sampling for infinite populations. A normal approximation is also developed. Our procedures are compared with the frequentist methods of Cameron and Baldock (1998a, Preventive Veterinary Medicine34, 1-17.) using an example of foot-and-mouth disease. User-friendly programs for sample size calculation and analysis of survey data are available at http://www.epi.ucdavis.edu/diagnostictests/.

Animals↗
PubMed2004

Cost-effectiveness of flexible intensive insulin management to enable dietary freedom in people with Type 1 diabetes in the UK.

AIMS: To determine the cost-effectiveness of a structured treatment and teaching programme (STTP) combining dietary freedom with insulin adjustment for Type 1 diabetes. METHODS: Incremental cost-effectiveness analysis based on effectiveness data from three RCTs in Germany, Austria, and Dose Adjustment for Normal Eating (DAFNE) in the UK, to model the long-term microvascular complications of Type 1 diabetes. RESULTS: The STTP approach yields effectiveness gains at a lower cost compared with current standard practice for treatment of Type 1 diabetes. STTPs are likely to save 0.05 life years, yield 0.12 EuroQol 5 dimensions (EQ-5D) and 0.09 visual analogue scale (VAS) incremental quality-adjusted life years, and save approximately pound 2200 per patient treated discounted over 10 years. CONCLUSIONS: Introducing STTPs as standard treatment for people with Type 1 diabetes in the UK may help to achieve the primary goal of the National Service Framework (NSF) for Diabetes by enabling individuals to manage their own lifestyle and condition. In doing so it could save valuable resources for the NHS and yield important morbidity and mortality gains.

Blood Glucose↗
PubMed1984

Freedom, dependency, and the care of the very old.

Difficulties exist in making treatment decisions for the very old and dependent patient. In the years to come, these difficulties will increase. It is argued that such persons should not be abandoned to their "rights" as autonomous persons; yet quality of life judgments should also be avoided except in limited circumstances. Since aging is a process of becoming more dependent, the author proposes a dependency rule, by which greater responsibility for treatment decisions falls on care-givers as a person's dependency increases. In place of quality of life judgments he suggests a medical indications policy, if the latter includes restoration of some affective function. Five kinds of freedom are proposed, of which only some are lost in chronic illness and old age. Finally, it is suggested that life itself involves greater interdependence than the autonomy criterion itself can allow. The author focuses on the problem of dependency in the aged and the role an increase in this dependency plays, with corresponding loss of personal autonomy, in quality of life judgments. These, in turn, form the basis for treatment decisions.

Activities of Daily Living↗
PubMed1997

A national serological survey to verify Australia's freedom from porcine reproductive and respiratory syndrome.

OBJECTIVE: To provide serological data to support Australia's claim of freedom from porcine reproductive and respiratory syndrome. DESIGN: A national serological survey was designed to provide 99% confidence of detecting at least one infected pig herd in Australia, assuming that at least 5% of herds would have been exposed to porcine reproductive and respiratory syndrome virus and that at least 25% of the 'finisher' pigs in these herds would have antibodies to the virus. PROCEDURE: A two-stage testing regime was used. All samples were tested with a commercially available enzyme-linked immunosorbent assay. If assay reactions were found, all samples from the herd were to be tested using the indirect immunofluorescence antibody assay. RESULTS: Of the 875 samples from 163 herds from all States in Australia, there was some evidence of reactivity in only four samples from four herds on the enzyme-linked immunosorbent assay. Further testing using the indirect immunofluorescence antibody assay according to the study protocol demonstrated that the reactions were not due to the presence of specific porcine reproductive and respiratory syndrome virus antibodies in the sera. CONCLUSION: The results of this study support the view that Australian pigs are free of porcine reproductive and respiratory syndrome virus.

Animals↗