Physica B Condensed Matter

Free-volume type defects, such as vacancies, vacancy-agglomerates, dislocations, and grain boundaries represent a key parameter in the properties of ultrafine-grained and nanocrystalline materials. Such free-volume type defects are introduced in high excess concentration during the processes of structural refinement by severe plastic deformation. The direct method of time-differential dilatometry is applied in the present work to determine the total amount and the kinetics of free volume by measuring the irreversible length change upon annealing of bulk nanocrystalline metals (Fe, Cu, Ni) prepared by high-pressure torsion (HPT). In the case of HPT-deformed Ni and Cu, distinct substages of the length change upon linear heating occur due to the loss of grain boundaries in the wake of crystallite growth. The data on dilatometric length change can be directly related to the fast annealing of free-volume type defects studied by in situ Doppler broadening measurements performed at the high-intensity positron beam of the FRM II (Garching, Munich, Germany).

Densitometric results about local myocardial perfusion are compared with those derived from a quantitative analysis of TL-201 single photon emission computer tomograms (TL-201 SPECT). Ten patients underwent conventional TL-201 SPECT at rest and after maximum bicycle stress and dipyridamole infusion the day prior to the investigation. SPECT was applied to provide improved spatial resolution for the detection of perfusion abnormalities. During the catheterization procedure four digital subtraction coronary angiograms were performed, two of the left and two of the right coronary artery both before and after pharmacologically induced hyperemia by intracoronary papaverine. The densitometric parameter results were compared with the quantitative results of TL-201 SPECT. Both correlations were obtained for the densitometric parameters rise time and mean ascending time, worst for maximum intensity

A real-time signal acquisition, display, analysis, and storage system is developed for multichannel intracardiac electrograms. Four channels of data may be acquired simultaneously including signals measured from the high right atrium, right ventricular apex, His bundle, and a surface lead. Signals are displayed in a scrolling mode on the monitor as they occur. Waveform analysis consists of a multistage algorithm in which atrial, His, and ventricular depolarizations are detected. Beat-by-beat waveform intervals are measured online and displayed along with the scrolling waveforms. The accuracy of the system has been validated. Of waveforms correctly found, 87/4963 (1.7%) had measurement errors exceeding 10 ms. The triggering algorithm has been tested for robustness by insertion of 60 Hz noise in which 364 beats were reanalyzed and only in 2 (0.5%) was the time of occurrence shifted by more than 20 ms. Stimulus control software has been added to the analysis system. Stimulation and analysis can be done simultaneously, allowing for automatic detection of myocardial capture following programmed stimulation

Ultrasonic attenuation and sound velocity were measured at frequencies ranging from 25 MHz to 305 MHz in a large single crystal of La_2-xSr_xCuO₄ with nominal x of about 0.15. The observed features in attenuation and velocity suggest a relaxation process of magnetic origin at about 27 K, and those at ~37.9 K originate in the superconducting transition and a possible structural instability slightly above it

Summary form only given. Research related to computers and heart and vascular diseases is supported in the United States through the National Heart, Lung and Blood Institute (NHLBI) of the National Institutes of Health (NIH). Within NHLBI, the majority of this type of research is funded through the Devices and Technology Branch. Investigator-initiated research grants account for the greatest number of grants, and for most of the funding. In addition, each year several million dollars is set aside to support grant and contact programs in special research areas identified by NHLBI. Research grants include diagnostic and therapeutic areas of electrophysiology, imaging, mechanical circulatory support, drug infusion systems, metabolic and stereoscopic studies, flow modeling, and biomaterials. The NHLBI also supports research grants through a set-aside Small Business Innovation Research (SBIR) program with the aim of providing seed money to small businesses to develop and market biomedical instruments or processes

Results of computer simulations obtained by a finite-element package, FLUXMECA, are presented and compared with experimental measurements of vibrations of static inductors. The objective is to reduce the vibrations' level and the acoustic noise of the transformers. Resonant frequencies and the mechanical behavior of the inductors are predicted with a mechanical finite-element model coupled with Maxwell's equations. A homogenization algorithm allows representation of a stratified structure by a homogenized one. Two kinds of inductors have been tested: cylindrical ones without iron cores and classical iron-cored inductors. A study of the electromagnetic forces and the mechanical structures is presented, clarifying the generation of noise and vibrations in static electrical apparatus

The power spectra of an excessive high-frequency artifact (that obscures the QRS complex), narrow complex or supraventricular tachycardia (SVT), and wide complex tachyarrhthmias, including ventricular tachycardia (VT) and ventricular fibrillation (VF) are examined quantitatively for distinguishing features of these signals. Of 12 features examined, four differ significantly among these groups. It is found that SVT has more peaks spaced at longer intervals than monomorphic VT (mVT). Polymorphic VT (pVT) and VF have higher primary frequencies than mVT. Severe and excessive ripple artifacts have more peaks than SVT, mVT, and pVT, and are more irregular than SVT and mVT. Although the populations differ significantly, there is considerable overlap by individual samples. These features may be useful in the development of a noise-characterizing preprocessor that would allow QRS detection and delineation algorithms to vary their parameters automatically to optimize sensitivity and specificity for the incoming electrocardiogram signal

Signal averaged electrocardiograms (SAECGs) were studied with the Corazonix Predictor and the Marquette MAC 12/15 in a group of 27 patients. The two devices agreed on the interpretation of the SAECG in 81.5% of the patients. The sensitivity, specificity, and predictive value for these devices in predicting sustained monomorphic ventricular tachycardia are fairly good and comparable with values in the literature. Different methodologies and different criteria for an abnormal SAECG account in large part for the great range of predictive values reported in the literature

Active damping has been shown to offer increased suspension performance in terms of vehicle isolaton, suspension packaging, and road-tire contact force. It can even approximate the performance of full state feedback control without requiring the difficult measurement of tire deflection. Many semi-active damping strategies have been introduced to approximate the response of active damping with the modulation of passive damping parameters. These strategies have typically required a relatevely high bandwidth for actuator response. This paper investigates the simulation performance and "frequency response" of two concepts in low-bandwidth semi-active suspension control. The first strategy controls the pressure drop in a hydraulic flow path, the second controls a hydraulic resistance. The bandwidth of these actuators is approximately an order of magnitude less than other semi-active devices. A quarter-car model is studied with the controlled damping replacing both passive and active damping of typical control schemes. Both low-bandwidth damping strategies perform remarkably well compared to both active and high-bandwidth, semi-active damping.

Patients with sustained ventricular tachycardia (SVT) need intensive electrophysiological testing for a treatment decision. A computer-based support for this decision has to take into account the clinical experience with SVT, the facets of the required electrophysiological tests, and the general characteristics of the potential therapy. A Bayesian belief network (BBN) is developed that allows the test-therapy relationships to be modeled. In the arrhythmological context, the events (the nodes in the network) are cardiological findings, pathophysiological states, test results, and therapeutic decisions. The basics of BBN as a tool for the design of medical decision support are presented and the essential knowledge issues of the arrhythmological problem are treated

The destruction of carbon dioxide gas in simulated gaseous mixtures corresponding to an exit gas composition from a coal-burning thermal power station is investigated. The project is intended to address the issue of the greenhouse effect. The energy consumption evaluation of a coal power plant with proposed CO₂ reduction processes is also investigated. The performance tests and modifications of a corona torch plasma reactor have been conducted. The results show that the system pressure drop is at a minimum at 0.08 kPa/channel for 0.7 l/min of gas flow rate per channel, the CO₂ concentration is reduced from 10% to 8%, and 2.5 kg of CO₂ are reduced by 1 kWh of energy used in the corona-induced plasma reactor at all optimum reactor diameter of 25 mm and length of 60 mm

A discrete model was developed which reproduces the intercellular electrophysiological processes within a block of myocardial tissue. The behavior of individual elements is introduced in the form of the digitized physiologic and premature action potentials which are comprehended as series of jumps between discrete polarization levels. For each cellular element, the model introduces the excitation threshold as the minimum electric flow in the surrounding which can excite the cell, and the sensitivity towards the electronic interactions which can advance or slow down the depolarization and repolarization processes of the cell. The excitation threshold and the electronic sensitivity are dependent on the current polarity of the element. The numerical solution of the model is based on discrete planning of asynchronous events. The time increments are dynamically computed according to the chosen precision of the discrete polarity levels. The model enables efficient simulation of the electrophysiological properties in three-dimensional models of the myocardial tissue. A detailed formal description of the model is given and two series of experiments are presented

Stochastic resonance (SR) is generally considered as an enhancement of the system response for certain finite values of the noise strength. In particular the signal to noise ratio (SNR) and the signal amplification show a maximum as a function of the noise intensity. This effect has been experimentally observed in many physical systems and also in magnetic systems. However, as far as magnetic systems are concerned, the dynamic features of the systems have been neglected and it has been assumed that the typical relaxation time is negligible. However this is clearly a rough approximation. In order to clarify this relation, in this paper we numerically study magnetic stochastic resonance in several magnetic systems described by dynamic Preisach model.

The extended Euclidean algorithm (XEA) is the basis of one of the methods used for solving the key equation which arises in decoding Reed-Solomon error correcting codes. The algorithm is implemented using an Advanced Micro Devices electrically programmable gate array (EPGA) development system. This PC based software uses ORCAD schematic entry and simulation in conjunction with an AMD interface. EPGAs were chosen for the circuit design because of the ease of obtaining a silicon prototype once the circuit has been verified. The facility for direct programming of the IC from the PC means circuit revisions in hardware are quickly realized; this, coupled with efficient entry and simulation package, gives a much speedier design cycle than conventional masked silicon approaches. The advantages of the algorithm over existing designs are noted

The variable-voltage variable-frequency (VVVF) drive of an induction motor requires careful designing of the output voltage of a voltage source inverter, especially the fundamental component of the output voltage. A simplified measuring technique for obtaining the fundamental component of the output voltage is presented. The mean value of the PWM waveform is used for the purpose. It is found that the fundamental component of the PWM waveform can be expressed by the contents of zero vectors in the space vector expression. The analysis of this space vector voltage equation makes it possible to use the mean value of the voltage as the fundamental component. Experimental results show that the indicated value of the rectifier-type voltmeter approximates the RMS-value of the fundamental component

One of the major concepts in an advanced robotic manipulator control system is the ability of transforming the world Cartesian coordinates of the end-effector into joint coordinates, on which the control actions are developed. This transform is non-unique, while the analytic algebraic approach and the numerical iterative approach only give one solution. This paper applies a geometric approach to a translation-roll-roll type RTX robot with a roll-pitch-yaw wrist. The geometric approach is a straightforward method and especially effective for six-degree-of-freedom non-redundant robots with three wrist joint axes intersecting at one point. Through introducing configuration parameters the non-uniqueness of the inverse transform equation has been solved. The optimal configuration for each moving step can be calculated based on a suitable performance criterion.

The dielectric and piezoelectric properties of SrBi4−xHoxTi4O15 (x=0.00, 0.02, 0.04 and 0.06) ceramics were investigated. SrBi4−xHoxTi4O15 (x=0.00, 0.02, 0.04 and 0.06; SBHT-x) ceramics were synthesized by the conventional solid state reaction sintering method. An X-ray diffraction measurement indicated that a single phase layered perovskite was obtained for all compositions. Studies of dielectric properties with temperature at different frequencies and piezoelectric properties have been carried out.

The low temperature phase transitions in a (1 − x)CH4 − xCD4 mixture for x = 0.125 have been investigated by means of proton spin-lattice relaxation time measurements up to 700 bar.The II–III transition as it occurs in the pure substances was not found in the mixture at this CD4 concentration. Instead, another transition to a low temperature phase was found. Once this phase is produced at a pressure above 500 bar it can be maintained down to zero pressure. The experimental results indicate that this low temperature phase is metastable.Spin conversion in this mixture was observed as an increase of the proton relaxation time below 8 K.

Single-U-ion properties of heavy-electron compound URu2Si2 have been investigated by a series of diluting experiments on R1−xUxRu2Si2 (R=Th, Y, and La; x⩽0.07). A strong uniaxial magnetic anisotropy of local 5f moments is commonly observed throughout the dilutions. From a large enhancement of χ and C/T as T→0, we suggest a non-Kramers, magnetic doublet Γ5 (f2) to be eminently suitable for the crystal-field lowest level, contrary to general views of low-lying singlets for the periodic system. We further demonstrate the absence of the conventional Kondo effect in all these dilutions. A strong suppression of 5f moments at low temperatures accompanies a non-trivial ln T decrease in ρ and a small change in the magnetic entropy. Specific-heat measurements in magnetic fields up to 12 T have revealed no sign of the residual entropy, eliminating the simple application of the two-channel Kondo theory to the present alloys. We also discuss a puzzling phase transition at 17.5 K of URu2Si2 in relation to the single-ion physics, providing our latest results of neutron-scattering experiments under high pressure.

We investigate contribution of a single U ion to the electrical resistivity (Δρ) in the dilute U alloys for x⩽0.07. Contrary to the conventional Kondo behavior, in both systems Δρ exhibits an unusual decrease with reducing temperature below a characteristic temperature (T∗) of and 40 K (Y). At higher temperatures, Δρ is almost independent of T with the amplitude (ΔρRT) of ∼ 59 (95) for . The dependence below T∗ and the relationship are found similarly between these two dilutions irrespective of T∗ and ΔρRT, suggesting that these are universal features in the dilute limit of URu2Si2. The decrease in Δρ is approximately proportional to the increase in the magnetic susceptibility, which provides a remarkable distinction between the present systems and known reverse-Kondo alloys.

We report inelastic neutron scattering measurements performed on a single crystal of the heavy fermion compound Ce$_{0.925}$La$_{0.075}$Ru$_{2}$Si$_{2}$, which is at the borderline between an antiferromagnetically ordered and a paramagnetic ground state. Intensity maps as a function of wavevector and energy ($0.1<E<1.2$ meV) were obtained at temperatures $T=0.1$ and 2 K, using the time-of-flight spectrometer IRIS. An unexpected saturation of the relaxation rate and static susceptibility of the spin fluctuations is found at low temperatures.

Polycrystalline La1−xAgxMnO3 perovskite compounds (with x=0.10–0.30) have been synthesised by both the conventional solid-state reaction and the sol–gel method. While all samples with Ag concentrations up to 0.20 consist of single-phase perovskites with rhombohedral structure, unreacted Ag was found in the samples with Ag concentrations of 0.22 and higher. Magnetic properties of the as-prepared materials have been investigated. The magneto-caloric effect in these compounds has been found to be considerably large and higher than that in other perovskite compounds in which La is substituted by divalent alkali-earth elements.

μ+SR data on La1.875Ba0.075Sr0.050CuO4 confirm the magnetic character of the LTT-phase and demonstrate that superconductivity is limited to the orthorhombic domains.

In this paper we present transport, magnetic and electron paramagnetic resonance (EPR) studies of electron doped manganites NdxCa1−xMnO3(x=0.2,0.3) with a view to compare and contrast their properties with those of the hole doped Nd0.5Ca0.5MnO3 and other manganites. The samples were prepared by the solid-state reaction method and the composition was verified using X-ray and EDAX measurements. Magnetization measurements on the x=0.2 sample (NCMO 0.2) show a peak at accompanied by a sharp increase in the resistivity. In the case of x=0.3 sample (NCMO 0.3) a peak in the magnetization along with an increase in the resistivity is observed at . From a comparison of the EPR results in the two compounds, we conclude that the transition in NCMO 0.2 is an antiferromagnetic transition which is likely to be a charge ordering transition as well and that in NCMO 0.3 is only a charge ordering transition at which long-range magnetic order is not established. We infer that in this compound the long-range antiferromagnetic order sets in at a much lower temperature below which the EPR signal disappears due to the opening of an antiferromagnetic gap.

We report on a detailed study of the electrical resistivity and the magnetoresistance of the metallic members of the LaNi1−xCoxO3 series with 0.3≤x≤0.6. The low-temperature resistivity of the compounds with 0.3≤x≤0.5 exhibits a logarithmic temperature dependence that is characteristic of systems with enhanced spin disorder. We attribute the decreasing contribution of the −ln T term to resistivity with increasing magnetic field to the suppression of spin disorder in an electronically phase separated matrix by the application of magnetic field, and suggest that this mechanism is primarily responsible for the magnetoresistive behavior of these compounds. We propose two models that are based on inter-cluster scattering which could explain the observed effects.