Coercivity and wall motion

The process of magnetization reversal in ferromagnets with uniaxial crystal anisotropy is discussed. It is shown that the "critical-size concept" has no relevance to coercivity. Critical fields are distinguished as nucleation fields and propagation, or pinning, fields. The pinning of walls is discussed and illustrated by experiments on various substances. Intrinsic pinning in highly anisotropic materials is predicted.     

Noninvasive evaluation of local myocardial thickening and itscolor-coded imaging

For the noninvasive diagnosis of heart disease based on the acoustic characteristics of the heart muscle, we have developed a new method for accurately tracking the movement of the heart wall. By this method, a velocity signal of the heart wall with a small amplitude of less than 10 μm on the motion resulting from a heartbeat with large amplitude of 10 mm can be successfully detected with sufficient reproducibility in the frequency range up to several hundred Hertz continuously for periods of about 10 heartbeats. In this paper, the method is applied to multiple points preset in the left ventricular (LV) wall along the ultrasonic beam so that the spatial (depth) distributions of the velocity at these points are simultaneously obtained. The motion of the heart wall is divided into the following two components: parallel global motion of the heart wall and the change in myocardial layer thickening at each depth across the LV wall during myocardial contraction/relaxation. The latter component is superimposed on the M (motion) mode image using a color code to map contraction as red and expansion as blue. By preliminary human studies, the principle of the method proposed in this paper is verified and the frequency band of the components generated by thickening and/or thinning in the myocardium is identified. This new approach offers potential for research on noninvasive acoustical diagnosis of myocardial local motility, that is, the myocardial layer function at each depth in the ventricular wall     

Evaluation of an ultrasonic echo-tracking method for measurements of arterial wall movements in two dimensions

The longitudinal movement of blood vessel walls has so far gained little or no attention, as it has been presumed that these movements are of a negligible magnitude. However, modern high-resolution ultrasound scanners can demonstrate that the inner layers of the arterial wall exhibit considerable movements in the longitudinal direction. This paper evaluates a new, noninvasive, echo-tracking technique, which simultaneously can track both the radial and the longitudinal movements of the arterial wall with high resolution in vivo. Initially, the method is evaluated in vitro using a specially designed ultrasound phantom, which is attached to and moved by an X-Y system, the movement of which was compared with two high-resolution triangulation lasers. The results show an inaccuracy of 2.5% full scale deflection (fsd), reproducibility of 12 microm and a resolution of 5 microm, which should be more than sufficient for in vivo studies. The ability of the method is also demonstrated in a limited in vivo study in which a preselected part of the inner vessel wall of the right common carotid artery of a healthy volunteer is tracked in two dimensions over many cardiac cycles. The results show well reproducible x-y movement loops in which the recorded radial and longitudinal movements both are of the magnitude millimetre.     

Micromagnetic simulation of domain wall pinning and domain wall motion

Domain wall pinning is the coercivity mechanism of permanent magnets used in high temperature applications. In SmCo based magnets domain walls get trapped at the cellular precipitation structure causing a high coercive field. The motion of domain walls and their propagation velocity are important in soft magnets as used in sensor applications. A finite element micromagnetic algorithm was developed to study the motion of domain walls in complex microstructures. The cellular microstructure of SmCo magnets or the cylindrical soft wires can be easily built using tetrahedral finite elements. The pinning of the domain walls has been studied for different material compositions. Attractive and repulsive domain wall pinning are observed and their behaviour for increasing thickness of the precipitation structure is explained. The motion of domains in magnetic nanowires was calculated using adaptive mesh refinement. The wall velocity strongly depends on the domain wall structure. Transverse and vortex walls have been observed and their velocity in wires of different thickness has been studied.     

Real-time diode laser measurements of vapor-phase benzene

An absorption spectrometer equipped with a IV-VI semiconductor tunable mid-IR diode laser was used to make sensitive measurements of benzene (C(6)H(6)) gas in the 5.1-microm spectral range. Wavelength modulation coupled with second-harmonic detection achieved accurate real-time quantification of benzene concentrations down to a minimum detection limit of 1 ppmv with an integration time of 4 s. A variety of calibrated benzene-sensing measurements were made, including the determination of the benzene concentrations in vehicle exhaust and headspace vapors from unleaded gasoline and other liquids. Kinetic phenomena, including the monitoring of benzene evaporation and absorption/desorption by granulated activated carbon were observed with the instrument. Measurements were performed that allowed experimental determination of the activation energy for desorption of benzene from activated carbon, which was found to be 198 meV/molecule (19.0 kJ/mol).     

Turbulent wall motion of a viscoelastic fluid

Qualitative agreement between the theoretically calculated parameters and published experimental data is obtained for turbulent wall flow of a drag-reducing aqueous polymer solution treated as a viscoelastic medium.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 30, No. 1, pp. 109–114, January, 1976.     

Domain wall types and field-induced domain wall motion in L-shaped nanowires

The formation and behavior of domain walls were studied in L-shaped nanowires via micro-magnetic simulation using the Objective Oriented Micro-Magnetic Frame program. We induced three types of domain walls by varying the thickness of the nanowire. A transverse wall, an asymmetric transverse wall, and a vortex wall were induced in 10, 20, and 40 nm-thick nanowires, respectively. The type of domain walls formed was determined by the competition between exchange and magnetostatic energy. The depinning field of the domain wall was the largest for the 20 nm-thick and the smallest for the 10 nm-thick nanowires. Domain wall behaviors were quite different from one another. The transverse wall in the 10 nm-thick nanowire was annihilated without changing its type. In the case of the 40 nm-thick nanowire, the vortex wall was not transformed to another type, but did switch its polarity throughout the depinning process. The wall in the 20 nm-thick nanowire underwent repetitions of the transformation of type and the switching of polarity until annihilation. Our results confirm that the behavior of a domain wall at a corner or a rounded part of nanowires is very complex and it originates from the different spin structures of a domain wall.     

A multilayered wall model of arterial growth and remodeling

Adaptations of large arteries to sustained alterations in hemodynamics that cause changes in both caliber and stiffness are increasingly recognized as important initiators or indicators of cardiovascular risk to high flow, low resistance organs such as the brain, heart, and kidney. There is, therefore, a pressing need to understand better the underlying causes of geometric and material adaptations by large arteries and the associated time courses. Although such information must ultimately come from well designed experiments, mathematical models will continue to play a vital role in the design of these experiments and their interpretation. In this paper, we present a new multilayered model of the time course of basilar artery growth and remodeling in response to sustained alterations in blood pressure and flow. We show, for example, that single- and multi-layered models consistently predict similar changes in caliber and wall thickness, but multilayered models provide additional insight into other important metrics such as the residual stress related opening angle and the axial prestress, both of which are fundamental to arterial homeostasis and responses to injury or insult.     

Integration of local motion is normal in amblyopia

We investigate the global integration of local motion direction signals in amblyopia, in a task where performance is equated between normal and amblyopic eyes at the single element level. We use an equivalent noise model to derive the parameters of internal noise and number of samples, both of which we show are normal in amblyopia for this task. This result is in apparent conflict with a previous study in amblyopes showing that global motion processing is defective in global coherence tasks [Vision Res. 43, 729 (2003)]. A similar discrepancy between the normalcy of signal integration [Vision Res. 44, 2955 (2004)] and anomalous global coherence form processing has also been reported [Vision Res. 45, 449 (2005)]. We suggest that these discrepancies for form and motion processing in amblyopia point to a selective problem in separating signal from noise in the typical global coherence task.     

Comparison of the spatial-frequency selectivity of local and global motion detectors

Convergent physiological and behavioral evidence indicates that the initial receptive fields responsible for motion detection are spatially localized. Consequently, the perception of global patterns of movement (such as expansion) requires that the output of these local mechanisms be integrated across visual space. We have differentiated local and global motion processes, with mixtures of coherent and incoherent moving patterns composed of bandpass filtered dots, and have measured their spatial-frequency selectivity. We report that local motion detectors show narrow-band spatial-frequency tuning (i.e., they respond only to a narrow range of spatial frequencies) but that global motion detectors show broadband spatial-frequency tuning (i.e., they integrate across a broad range of spatial frequencies), with a preference for low spatial frequencies.     

Experimental detection of entanglement via witness operators and local measurements

Abstract

In this paper we address the problem of detection of entanglement using only few local measurements when some knowledge about the state is given. The idea is based on an optimized decomposition of witness operators into local operators. We discuss two possible ways of optimizing this local decomposition. We present several analytical results and estimates for optimized detection strategies for NPT states of 2 × 2 and N × M systems, entangled states in 3 qubit systems, and bound entangled states in 3 × 3 and 2 × 4 systems.     

Determinants of hemodialysis‐induced segmental wall motion abnormalities

Patients who demonstrate worsening of cardiac wall motion (WM) during hemodialysis have higher 1‐year mortality. We sought to identify risk factors for dialysis‐induced WM abnormalities. Additionally, we examined the effects of hemodialysis on other parameters of cardiac function. Forty patients underwent echocardiography directly before dialysis and during the last hour of dialysis (79 dialysis sessions). Candidate predictors for intradialytic worsening of WM included age, a history of heart failure (HF) or coronary artery disease, changes in blood pressure or heart rate, high sensitivity cardiac troponin T and N‐terminal brain natriuretic peptide. Among 40 patients, WM worsened segmentally in eight patients (20%), worsened globally in one patient (3%), and improved segmentally in four patients (10%). Diastolic function worsened in 44% of patients, and left ventricular ejection fraction was largely unchanged during dialysis. The case of globally worsened WM occurred in the setting of intradialytic hypertension in a patient without HF. Surprisingly, history of coronary artery disease, hemodynamics, and serologic factors were not associated with worsened segmental WM during dialysis. After adjustment for history of coronary artery disease and other cardiac risk factors, patients with a history of HF had a threefold higher risk of worsening segmental WM during dialysis (RR 3.1, 95% CI [1.1, 9], p = 0.04). In conclusion, patients with a history of clinical HF were at higher risk of intradialytic worsening of segmental WM. Further studies are needed to determine the mechanism of this association and whether cardioprotective medications could ameliorate this adverse cardiac effect of hemodialysis.     

Real-time amperometric measurements of zeptomole quantities of dopamine released from neurons

Amperometry with carbon-fiber microelectrodes provides a unique way to measure very small chemical concentration changes at the surface of biological cells. In this work, an investigation of dopamine release from individual neurons isolated from the mouse retina is described. The mice were genetically modified so that, in cells that expressed the protein responsible for catecholamine synthesis, tyrosine hydroxylase, the marker protein, placental alkaline phosphatase, was also expressed. This modification allowed for identification of the dopamine-containing cells among the many present in the freshly dissociated retina. Release of dopamine was evoked by chemical secretagogues delivered from micropipets that were calibrated with respect to response time and concentration delivered. Amperometric measurements were recorded with low-noise patch clamp amplifiers, and the primary noise source was found to be the electrode capacitance. Dopamine release occurred in the form of transient concentration spikes, consistent with release from small intracellular vesicles. With optimized filtering of the data, the quantity secreted during each release event could be determined. The average quantity determined at one cell was 52 zmol. However, the spikes were quite variable in size and the amount released per event ranged from 8 to 170 zmol. These measurements allow an estimation of the concentration of released transmitter in a synapse.     

Theory of domain wall motion induced by microwave magnetic fields

A general theory is developed that applies to arbitrary polarization and takes account of damping and of the dipolar interaction between domains. The effect of the microwave field on the domain structure can be characterized by a pressure on the domain walls and by an alignment energy, both of which are proportional to the square of the rf magnetic field and become large in the vicinity of a resonance. For circular polarization the pressure tends to decrease the Larmor-domains (domains in which the imposed sense of polarization coincides with the sense of the natural spin precession) for frequencies outside the resonance region. Inside the resonance region, however, the pressure tends to increase the Larmor-domains. A linearly polarized field also exerts a pressure on the domain walls, with the polarity dependent upon the orientation of the field to the wall normal. In a linearly polarized magnetic field the domain walls tend to become aligned parallel to the rf field at frequencies ω near the low-frequency resonance (ω =γHa, γ = gyromagnetic ratio, Ha= anisotropy field) and perpendicular to the rf field at frequencies near the high-frequency resonance (ω = γ[Ha(Ha+ 4πM0)]^1/2, M0= saturation magnetization).     

Real-time impedance measurements during electrochemical experiments and their application to aniline oxidation

Development of an in situ technique for measuring electrochemical impedance spectra in real time during an electrochemical experiment is described. The technique is based on staircase voltammetry with relatively large step heights, in which a series of increasing potential steps are applied to an electrochemical system, and the resulting currents are sampled. The first derivatives of the currents thus obtained are then converted to ac current signals in frequency domain, and impedances are computed from them. To demonstrate the technique as a tool for studying the electrode/electrolyte interface during the electrochemical reaction, we chose an electrochemical oxidation reaction of aniline, whose reaction products have been known to continuously change the electrode surface due to the polymer film growth on its surface, and report a number of observations that would not have been obtained without such in situ experiments. A suggestion is also made on the use of staircase voltammetry for mechanistic studies on complex electrochemical reactions by simply varying the sampling time.     

NMR measurements of grain and gas motion in a gas-fluidized granular bed

Nuclear magnetic resonance (NMR) experiments are described for gas-fluidized granular beds, which are important systems for many materials-processing operations. Using pulsed field gradient, magnetic resonance imaging, and hyperpolarized gas NMR, detailed information is obtained for the density and motions of both grains and interstitial gas. In particular, dynamic correlations in the grain density are used to measure the bubble velocity and hyperpolarized xenon gas NMR is used to measure the bubble-emulsion exchange rate. A goal of these measurements is to verify in earth gravity first-principles theories of granular flows.     

Development of childhood fall motion database and browser based on behavior measurements

This paper describes the development of a fall motion database and a browser designed to facilitate investigations into fall-related injury risk. First, child-related daily activities were collected at a “sensor home”, which is a model of a normal living environment equipped with an embedded video-surveillance system and within which child test subjects were equipped with wearable acceleration-gyro sensors. As of this report, measurements have been conducted for 19 children (months age: mean = 23.8, standard deviation = 10.5), and data has been obtained on 105 fall incidents. During our research, falls were detected from the accumulated sensor data using a detection algorithm developed by the authors, and then video clips of detected falls were extracted from the recorded video streams automatically. The extracted video clips were then used for fall motion analysis. A computer vision (CV) algorithm, which was developed to automate fall motion analysis, facilitates accumulation of fall motion data into the abovementioned database, and the associated database browser allows users to perform conditional searches of fall data by inputting search conditions, such as child attributes and specific fall situations. Before this study, there was no database which contains child's actual fall motion data, and it has the potential to facilitate injury risk reduction related to falls in daily living environments.     

A simplified approach for real-time detection of arterial wall velocity and distension

Arterial stiffness is known to increase with age and with many vascular diseases, but its noninvasive assessment in patients still represents a difficult task. The measurement of diameter change during the cardiac cycle (distension) has been proposed as a means to estimate arterial compliance and stiffness. Therefore, we have developed a simple PC-based device and algorithm for noninvasive quantification of vessel wall motion and diameter change in humans. This goal is achieved in real-time by processing the base-band signals from a commercial ultrasound Doppler system. Real-time operation is of crucial importance, because it allows a rapid achievement of optimal measurement conditions. The system was evaluated in a laboratory using a string phantom and was tested on the carotid arteries of 10 volunteers. Wall velocities from 0.05 to 600 mm/s and displacements lower than 2 μm were detected with phantoms. The measured carotid diameter change in the volunteers ranged from 7.5 to 11.8% (mean=9.8%) and agrees closely with values reported in the literature. The difference between values taken one hour apart ranged from 0.2 to 0.5%. We conclude that the new system provides rapid, accurate, and repeatable measurements of vessel distension in humans