Resistance Change Rate Research Articles

What does the Ashworth scale really measure and are instrumented measures more valid and precise?

This study aimed to explore the limitations of the Ashworth scale for measuring spasticity. An isokinetic dynamometer to quantify resistance to passive stretch and surface EMG was used to verify if a stretch response occurred and, if so, at what joint angle. The authors sought to determine which components of passive resistance (magnitude, rate of change, onset angle of stretch, or velocity dependence) were most related to Ashworth scores and which were related to motor function in cerebral palsy (CP). Twenty-two individuals with spastic CP (11 males, 11 females; mean age 11.9 years, SD 4.3) and a comparison group of nine children without CP (four males, five females; mean age 11.3 years, SD 2.5) participated in the study. The group with CP included those with a diagnosis of spastic diplegia, hemiplegia, or quadriplegia, distributed across Gross Motor Functional Classification Levels. Procedures included: (1) clinical assessment at the knee joint, (2) functional assessments, and (3) isokinetic assessment of passive resistance torque in hamstrings and quadriceps at three velocities. EMG data were recorded simultaneously to identify stretch responses. Detecting stretch responses using the Ashworth scale compared with instrumented measures showed near complete agreement at extremes of the scale, with marked inconsistencies in mid-range values. Ashworth scores were correlated with instrumented measures, particularly for the quadriceps, with higher correlations to the rate of change in resistance (stiffness) and onset angle of stretch than to peak resistance torque. Those with greater resistance tended to have poorer function with isokinetic relations typically stronger.

What does the Ashworth scale really measure and are instrumented measures more valid and precise?

This study aimed to explore the limitations of the Ashworth scale for measuring spasticity. An isokinetic dynamometer to quantify resistance to passive stretch and surface EMG was used to verify if a stretch response occurred and, if so, at what joint angle. The authors sought to determine which components of passive resistance (magnitude, rate of change, onset angle of stretch, or velocity dependence) were most related to Ashworth scores and which were related to motor function in cerebral palsy (CP). Twenty‐two individuals with spastic CP (11 males, 11 females; mean age 11.9 years, SD 4.3) and a comparison group of nine children without CP (four males, five females; mean age 11.3 years, SD 2.5) participated in the study. The group with CP included those with a diagnosis of spastic diplegia, hemiplegia, or quadriplegia, distributed across Gross Motor Functional Classification Levels. Procedures included: (1) clinical assessment at the knee joint, (2) functional assessments, and (3) isokinetic assessment of passive resistance torque in hamstrings and quadriceps at three velocities. EMG data were recorded simultaneously to identify stretch responses. Detecting stretch responses using the Ashworth scale compared with instrumented measures showed near complete agreement at extremes of the scale, with marked inconsistencies in mid‐range values. Ashworth scores were correlated with instrumented measures, particularly for the quadriceps, with higher correlations to the rate of change in resistance (stiffness) and onset angle of stretch than to peak resistance torque. Those with greater resistance tended to have poorer function with isokinetic relations typically stronger.

Magnetoresistance of boron-doped chemical vapor deposition polycrystalline diamond films

The electrical properties and magnetoresistance of boron-doped polycrystalline diamond films grown on p-typed Si (100) by hot filament chemical vapor deposition have been investigated. As the atomic boron concentration increases from 3×10 17 to 3×10 19 cm −3, and grain size from 5 to 15 μm, the quality of diamond is improved, which causes the carrier mobility μ and longitudinal magnetoresistance change rate Δρ ///ρ 0 to increase. For a magnetic field ( B) of 20 tesla and temperature 300 K, the longitudinal resistance change rate Δρ ///ρ 0 is up to 20%. Meanwhile, Δρ ///ρ 0 is proportional to μ 2 B 2 in a low field and proportional to μ 1.5 B in a high field. It is the first time that a result is obtained in a high field.

Characteristics of films developed in fretting experiments on tin plated contacts

A series of experiments were conducted to characterize oxide films that develop during fretting degradation. It was found that while the rate of change in resistance depends on contact force, the oxide film characteristics depend strongly on the number of fretting cycles. Moreover, after about 1000 fretting cycles, the oxygen content reaches a saturation level which corresponds to tin volume fractions below the percolation limit for metallic conduction (<0.4). Consequently, it is concluded that conduction is primarily due to the semi-conductor properties of tin oxide (SnO). In addition, sub-micron size particles, composed of tin and tin oxide, were found dispersed over the surface. These particles had tin fractions near the percolation limit and may play a role in the mechanism that causes short-term discontinuities in contact resistance.

Spatial variations in endothelial barrier function in disturbed flows in vitro.

Hindered barrier function has been implicated in the initiation and progression of atherosclerosis, a disease of focal nature associated with altered hemodynamics. In this study, endothelial permeability to macromolecules and endothelial electrical resistance were investigated in vitro in monolayers exposed to disturbed flow fields that model spatial variations in fluid shear stress found at arterial bifurcations. After 5 h of flow, areas of high shear stress gradients showed a 5.5-fold increase in transendothelial transport of dextran (molecular weight 70,000) compared with no-flow controls. Areas of undisturbed fully developed flow, within the same monolayer, showed a 2.9-fold increase. Monolayer electrical resistance decreased with exposure to flow. The resistance measured during flow and the rate of change in monolayer resistance after removal of flow were lowest in the vicinity of flow reattachment (highest shear stress gradients). These results demonstrate that endothelial barrier function and permeability to macromolecules are regulated by spatial variations in shear stress forces in vitro.

Advanced electrochemical methods for food can evaluation

Electrochemical measurements have been used to investigate the corrosion resistance of food cans produced from a steel–polymer laminate material, Ferrolite, over periods of up to 30 days. The aim of this work was to develop a predictive corrosion test procedure, whereby short term results could be used to predict long term container performance. Electrochemical impedance spectroscopy (EIS) and dc linear polarisation techniques were used to study the effect of increasing polymer laminate film thickness, and to compare Ferrolite performance with that of a conventional vinyl organosol lacquer. Testing was carried out using a sealed in electrode system, where electrodes were fitted to commercial can ends before filling. This electrode system was found to perform well over a 30 day period, and the results indicate that Ferrolite cans possessed a significantly greater resistance to corrosion than conventionally lacquered cans. Predictably, as the Ferrolite film thickness increased, coating and polarisation resistance values also increased. Under pack test conditions, coating and polarisation resistance parameters initially decreased rapidly, which is consistent with hydration and ion migration processes occurring within the film. After 30–40 days, the rate of change in resistance decreased and was consistent with longer term degenerative effects such as corrosion. Coating resistance, as determined by EIS, was found to be largely independent of the electrolytic oxygen concentration; however, polarisation resistance, determined by dc measurements, showed a strong inverse dependence on oxygen concentration.

Vasoconstrictor actions of atrial natriuretic peptide in the splanchnic circulation of anesthetized dogs

Intravenous atrial natriuretic peptide (ANP) usually results in splanchnic vasoconstriction in humans or experimental animals that is accompanied by falls in blood pressure and/or cardiac output. To determine direct in vivo effects in the present study, ANP was infused (12 ng. kg-1. min-1) directly into the mesenteric (iMA) and hepatic (iHA) arterial beds of anesthetized dogs, thereby minimizing changes in blood pressure. Over the first 2 min of iMA infusion, rate of change in mesenteric vascular resistance was 19.6 +/- 5.4 mmHg. l-1. min-1/min, reaching a maximum increase in resistance of 22 +/- 4% compared with baseline after approximately 10 min. There was no evidence of vasodilatation at any stage. The mesenteric response was similar whether ANP was infused iMA, iHA, or via the femoral vein (30 ng. kg-1. min-1). In contrast, hepatic vasoconstrictor response to ANP infusion iHA or into the portal vein was only evident after approximately 5 min, reaching a maximum increase in hepatic vascular resistance of 11 +/- 6% after approximately 15 min iHA infusion. When preinfused through the gut vasculature (iMA), ANP increased hepatic vascular resistance earlier and reached similar levels (14 +/- 3%), despite a lower arterial concentration of ANP. It is proposed that a vasoconstrictor agent from the intestinal circulation contributed to ANP-induced splanchnic vasoconstriction.

Tribological effects of roughness and running-in on oil-lubricated line contacts

A gear/cam adapter was employed to study various aspects of line-contact lubrication, using oil with extreme-pressure additive at two different concentrations. The effect of run-in on the tribological performance of rollers with two different surface roughnesses was investigated in terms of friction coefficient, wear loss, oil temperature, specimen roughness and electrical resistance. The relation between roller wear loss and the time rate of electrical resistance change was established. Electrical resistance versus oil temperature underwent a dramatic change during testing, a period of rising oil temperature and relatively constant low electrical resistance abruptly becoming a period of relatively constant oil temperature and rising electrical resistance, low wear rates correlating strongly with the second period. The run-in effect on roller wear loss in smooth rollers ( Ra = 0.076 μm) is opposite to that in rough rollers ( Ra = 0.463 μm). The asperity height of the smooth rollers was increased by wear testing irrespective of run-in; however, run-in enhanced the increase in surface roughness. The extreme-pressure additive concentration instead of run-in was the decisive factor in electrical resistance. Friction coefficients during testing showed a strong positive relation with composite surface roughness.

Rate of coronary flow adaptation in response to changes in heart rate before and during anesthesia for coronary artery surgery.

The rate of adaptation of coronary blood flow in response to stepwise changes in heart rate (HR) has been extensively studied in dogs and goats to improve our understanding of the dynamics of coronary regulation processes and their pathophysiology and to obtain time constants for mathematical modeling of the coronary regulation. However, little is known about the dynamic characteristics of coronary flow adaptation in humans. In patients undergoing coronary artery surgery, we investigated the rate of coronary adaptation in response to stepwise changes in HR, in the awake and anesthetized states. In 11 patients with stable coronary artery disease, arterial blood pressure, right atrial pressure, and coronary sinus blood flow, measured by continuous thermodilution, were calculated per beat. The ratio of beat-averaged arterial blood pressure minus right atrial pressure and coronary sinus blood flow was calculated to obtain an index of coronary resistance. The rate of change of coronary resistance index was quantified by t50, defined as the time required to establish 50% of the total change in coronary resistance index. Responses of coronary resistance index after HR changes, before and after induction of anesthesia, were compared. The anesthesia technique consisted of 100 micrograms.kg-1 fentanyl and 0.1 mg.kg-1 pancuronium bromide in combination with oxygen in air ventilation (FIO2 = 0.5). In the awake situation, t50 values of the dilating and constricting responses, induced by an increase and a decrease in HR were 5.0 +/- 2.1 (SD) s (range 2.6-9.0 s) and 5.7 +/- 1.2 s (range 4.1-7.8 s), respectively. During fentanyl/pancuronium anesthesia, the rate of coronary flow adaptation was significantly slower, with t50 values of 10.2 +/- 2.1 s (range 7.7-13.1 s) after an HR step-up and 9.8 +/- 2.1 s (range 6.6-13.2 s) after an HR step-down. Compared to the awake situation, arterial blood pressure was significantly reduced during anesthesia, but coronary vascular resistance remained unchanged. This implies that the steady-state static regulation of coronary blood flow had not changed. These preliminary data suggest that, in patients with coronary artery disease, the rate of change in coronary vascular resistance in response to pacing-induced changes in HR is mitigated by fentanyl/pancuronium anesthesia during positive pressure ventilation. A further qualification of our findings in a larger number of patients is warranted.

Dynamic and Static Cerebral Autoregulation during Isoflurane, Desflurane, and Propofol Anesthesia

Although inhalation anesthetic agents are thought to impair cerebral autoregulation more than intravenous agents, there are few controlled studies in humans. In the first group (n = 24), dynamic autoregulation was assessed from the response of middle cerebral artery blood flow velocity (Vmca) to a transient step decrease in mean arterial blood pressure (MABP). The transient hypotension was induced by rapid deflation of thigh cuffs after inflation for 3 min. In the second group (n = 18), static autoregulation was studied by observing Vmca in response to a phenylephrine-induced increase in MABP. All patients were studied during fentanyl (3 micrograms.kg-1.h-1)/nitrous oxide (70%) anesthesia, followed by, in a randomized manner, isoflurane, desflurane, or propofol in a low dose (0.5 MAC or 100 micrograms.kg-1.min-1) and a high dose (1.5 MAC or 200 micrograms.kg-1.min-1). The dynamic rate of regulation (dROR) was assessed from the rate of change in cerebrovascular resistance (MABP/Vmca) with the blood pressure decreases using computer modeling, whereas the static rate of regulation (sROR) was assessed from the change in Vmca with the change in MABP. Low-dose isoflurane delayed (dROR decreased) but did not reduce the autoregulatory response (sROR intact). Low-dose desflurane decreased both dROR and sROR. During 1.5 MAC isoflurane or desflurane, autoregulation was ablated (both dROR and sROR impaired). Neither dROR nor sROR changed with low- or high-dose propofol. At 1.5 MAC, isoflurane and desflurane impaired autoregulation whereas propofol (200 micrograms.kg-1.min-1) preserved it.

Activation energy in the early stage of electromigration in Al-1% Si/TiN/Ti bamboo lines

The activation energy of electromigration in 'bamboo'-type, passivated Al-1% Si/TiN/Ti lines was determined by means of high resolution resistance measurements at wafer level. Both the very early stages, with a nonlinear behaviour of the resistance, and the subsequent stages, characterized by an approximately constant rate of resistance change, were analysed with an existing model that correlates electromigration and mechanical stress evolution. An activation energy could be extracted only in the phase of linear resistance increase, where a value of 0.95 eV was found. Diffusion at the interface between Al-Si and the barrier metal or the passivation could be responsible for this value of the activation energy.

Reliability Study of On-Chip Interconnects : Prediction of Electromigration Resistance on A Short Time Scale

ABSTRACTA new method is presented to evaluate the resistance to electromigration (EM) of on-chip interconnects. The method is based on high resolution in-situ electrical measurements. In this way, the electrical resistance is measured with high accuracy during electromigration at high temperature. After careful analysis of the isothermal results, it was found that the metallization can be characterized by one parameter: the rate of resistance change (RRC). It is shown that the RRC is very sensistive to the electromigration performance. The performance level of the different metallizations can easily be detected and can be qualified in a quantitative way. The results are also compared with classic Mean Time To Failure (MTTF) results and it is found that there exists an almost linear relationship between the RRC results and the MTTF results. However, the in-situ technique offers the benifit that a metallization can be characterized on a time scale as short as a few days, which is certainly not the case for the classical techniques.

Joining of displays using thermosetting anisotropically conductive adhesives

This paper describes the reliability of using thermosetting anisotropically conductive adhesives for two applications: (1) joining LCD modules to rigid boards via flexible circuitry in a large panel video screen application; and (2) joining of LCD modules directly to flexible circuitry in a camera application. Three different types of thermosetting adhesive, one mixed type of thermosetting and thermoplastic anisotropically conductive adhesive and two heatseal connectors were used in the present investigation. The heatseal connectors are currently used in production and were used in the present investigation as reference materials. In the present study, ITO glass was used instead of real LCD devices. The interconnections were made using conventional heatseal press equipment for the two applications. The reliability of the adhesives was investigated in terms of a temperature-cycling test from −40 to 85oC for 1000 cycles using a temperature change rate of approximately 20oC/min, a constant-humidity test at 60oC, 95% RH for 1000 h, and a humidity-cycling test from 5 to 75oC at 95% RH for 1000 h. Both mechanical and electrical properties were measured before and after the environmental tests. The results indicate that control of process parameters such as bonding temperature, bonding pressure and time is critical for good bonding quality. Under the right process conditions, thermosetting anisotropically conductive adhesives are much better in environmental performance than heatseal connectors. The resistance change with time in the humidity test has been explained by oxidation of metal fillers or by oxidation of metallizations on interconnecting materials. It is shown that the oxide layer thickness and type control the rate of resistance change in a humid environment.

Transient response of a high T c superconducting thin film

The transient response of a YBCO thin film to a current pulse is reported. The measured rate of change of resistance across the superconductor is consistent with the thermal propagation of a normal region in a thin superconducting film. It appears that the normal region occurs at an ohmic contact and propagates across the length of the film, thus switching the film from its superconducting state to its normal state. The rate of resistance change shows a strong dependence on the bias temperature and current.

Determination of the diffusion coefficient of hydrogen in metals from the rate of change in the electrical resistance in desorption

A proposed method of measuring the diffusion coefficient of hydrogen D from the rate of change in electrical resistance in degassing of hydrogenimpregnated specimens is presented. Distinguished by simplicity, the method makes it possible to determine the coefficients with any method of hydrogen impregnation in a broad temperature range.

Strain Measurement in Optical Fiber Cable Using Resistance Wire

A resistance wire method is proposed for measuring the longitudinal strain in the glass fiber in an optical cable. In this method, the strain is evaluated by measuring the resistance change of a wire coated with the same material as the glass fiber. It is confirmed that the resistance change rate ΔR/R is proportional to the strain. An optical cable containing both a coated resistance wire and coated fibers was manufactured, and the strain in the cable was measured under tension, bending and vibration. The results are useful for the mechanical design of fiber cable, and the resistance wire method was found to be a simple and useful method of estimating the strain in the fibers inside such a cable.

Electron radiation damage in the rare-earth metals yttrium, samarium and ytterbium at low temperatures

The rare-earth metals Y, Sm and Yb have been irradiated with electrons over the energy range 0.4 to 1.7 MeV at a temperature of Tirr<or approximately=12K, and the damage production as well as the annealing spectra were determined. By fitting the electrical resistivity change rates to theoretical displacement cross sections, the authors have determined the minimum threshold energies for atomic displacement: TdY=(14.6+or-1) eV, Td1Sm=(9.5+or-1.5) eV, Td1Yb=(8.7+or-0.7) eV. Tentative values for the Frenkel pair (FP) resistivities have been proposed taking into account the magnetic order of Sm: rho FY=(50+or-20)*10-4 Omega cm (FP)-1, rho FSm=(140+or-30)*10-4 Omega cm (FP)-1, rho FYb=(75+or-25)*10-4 Omega cm (FP)-1. The threshold energies and the temperatures for interstitial long-range migration for the three metals have been compared with empirical expressions deduced from earlier work and their dependence on the corresponding crystallographic structure and on the ionic configuration has been emphasised.

Defect production and interdiffusion in electron irradiated α-brass

The residual electrical resistivity of α-Cu/Zn alloys containing 20, 30 and 36 at.% Zn has been measured during 0.4–3 MeV electron irradiation at temperatures between 30 K and 150 K as well as during isochronal annealing up to 360 K. The dependence of the resistivity change rate on electron energy has been investigated at 30 K and 150 K irradiation temperature. Above 100 K upon isochronal annealing or isothermal irradiation, negative resistivity changes due to an increase of short range order are found. The observed ordering kinetics of the alloy Cu/30 at% Zn are consistently interpreted by interstitialcy diffusion. The obtained reaction parameters were found in reasonable orders of magnitude. The equilibrium resistivity increases linearly with increasing temperature between 300 K and 483 K.

Characteristics of static and dynamic regulatory mechanisms in myogenic microvascular control.

The recently described static and dynamic components in myogenic microvascular control (Grände, Lundvall and Mellander 1977) were analysed in this study with regard to their stimulus-effector characteristics. Total and microvascular resistance responses in the sympathectomized vascular bed of skeletal muscle were analysed during graded changes of vascular transmural pressure (PT) applied at different rates (dPT/dt) in the range from +7.5 to -7.5 mmHg/s. The dynamic microvascular resistance responses, developing during the phase of changing PT, were pronounced and distinctly graded in relation to the magnitude of the dPT/dt stimulus, both with regard to amplitude of resistance response and rate of resistance change per unit time (dRmicro/dt). The static responses, revealed in the steady state phase of constant increased PT, were comparatively small and graded in relation to the amplitude of the PT increase. Rate-sensitivity in microvascular myogenic control was bi-directional, eliciting excitatory effects (constriction) in response to positive, and inhibitor effects (dilation) in response to negative, values of dPT/dt. The dynamic constrictor response to a given dPT/dt stimulus increased with increasing amplitude of PT and, thereby, increased duration of the dynamic stimulus. This effect might be explained by successive activation of myogenic "receptor units" with different thresholds. The described rate-sensitivity in the myogenic control system seems to increase its rapidity, stability, and sensitivity and thereby can contribute efficiently to well-adapted and refined microvascular adjustments.

Effects of Leaf Aging Upon Stomatal Resistance in Bean Plants1

The effect of leaf age on leaf resistance to gaseous diffusion was separated from three factors inherently related to leaf age: (a) progressive shading of lower leaves, (b) plant development, and (c) changes in stomatal size and density. Bush beans (Phaseolus vulgaris L., ‘Contender’) were grown and studied in an environmental chamber under constant conditions. Measurements of leaf resistance, light level, and stomatal density were made throughout the life of the plant (10 to 60 days from plant emergence). It was found that in a fully expanded leaf, exposed to constant light, the diffusive resistance of the whole leaf increased continuously with age until leaf abscission. The same was found true for leaves that were continuously shaded at 15% of the full light level (1,150 μ;einsteins m‐2 s‐l), but the resistances were higher. The rate of change in leaf resistance with time varied among the leaves within a plant, but the differences were eliminated when the time scale was expressed as the fractional lifespan of each leaf.Further, the effects of correlated factors such as shading, stage of plant development, and stomatal densities were negligible; and the leaf age effect occurred not only during the latter stages of senescence, when the leaf was becoming chlorotic or necrotic, but as a continuous process, beginning at leaf maturity and continuing until leaf abscission.