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Wave Amplitude (wave + amplitude)

Distribution by Scientific Domains

Medical Sciences	39%
Earth and Environmental Science	27%
Physics and Astronomy	9%
Life Sciences	6%

Distribution within Medical Sciences

Cardiovascular Disease	46%
Anesthesia & Pain Management	15%

Kinds of Wave Amplitude

pulse wave amplitude

r wave amplitude

Selected Abstracts

The effect of strength training on the force of twitches evoked by corticospinal stimulation in humans

ACTA PHYSIOLOGICA, Issue 2 2009
T. J. Carroll
Abstract Aim:, Although there is considerable evidence that strength training causes adaptations in the central nervous system, many details remain unclear. Here we studied neuromuscular responses to strength training of the wrist by recording electromyographic and twitch responses to transcranial magnetic stimulation (TMS) and cervicomedullary stimulation of the corticospinal tract. Methods:, Seventeen participants performed 4 weeks (12 sessions) of strength training for the radial deviator (RD) muscles of the wrist (n = 8) or control training without external load (n = 9). TMS recruitment curves were constructed from stimuli at five to eight intensities ranging between 15% below resting motor threshold and maximal stimulator output, both at rest and during isometric wrist extension (EXT) and RD at 10% and 50% of maximal voluntary contraction (MVC). Responses to weak TMS and cervicomedullary stimulation (set to produce a response of 10% maximal M wave amplitude during 10% MVC EXT contraction) were also compared at contraction strengths ranging from 10% to 75% MVC. Results:, Isometric strength increased following strength training (10.7% for the RD MVC, 8.8% for the EXT MVC), but not control training. Strength training also significantly increased the amplitude of TMS- and cervicomedullary-evoked twitches during low-force contractions. Increases in the force-generating capacity of the wrist extensor muscles are unlikely to account for this finding because training did not affect the amplitude of twitches elicited by supra-maximal nerve stimulation. Conclusion:, The data suggest that strength training induces adaptations that increase the net gain of corticospinal-motor neuronal projections to the trained muscles. [source]

Stability of surface waves at magnetized plasma , metal interface

CONTRIBUTIONS TO PLASMA PHYSICS, Issue 7 2003
Yu. A. Akimov
Abstract The stability of high-frequency potential surface waves at a dense magnetized plasma , metal interface with respect to a low-frequency plasma density modulation is studied in the point of view of the surface waves control. The discussion is addressed to the situation, when an external steady magnetic field is directed perpendicularly to the interface. The nonlinear interaction process of the high-frequency surface wave, its satellites and the low-frequency plasma density perturbation is investigated. It is shown that the low-frequency plasma density perturbation can be represented as a superposition of forced waves of surface and volume types and can lead to an additional attenuation of the surface waves. This attenuation arises when the surface wave amplitude exceeds the threshold value. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Microtubule sliding movement in tilapia sperm flagella axoneme is regulated by Ca2+/calmodulin-dependent protein phosphorylation

CYTOSKELETON, Issue 8 2006
Masaya Morita
Abstract Demembranated euryhaline tilapia Oreochromis mossambicus sperm were reactivated in the presence of concentrations in excess of 10,6 M Ca2+. Motility features changed when Ca2+ concentrations were increased from 10,6 to 10,5 M. Although the beat frequency did not increase, the shear angle and wave amplitude of flagellar beating increased, suggesting that the sliding velocity of microtubules in the axoneme, which represents dynein activity, rises with an increase in Ca2+. Thus, it is possible that Ca2+ binds to flagellar proteins to activate flagellar motility as a result of the enhanced dynein activity. One Ca2+ -binding protein (18 kDa, pI 4.0), calmodulin (CaM), was detected by 45Ca overlay assay and immunologically. A CaM antagonist, W-7, suppressed the reactivation ratio and swimming speed, suggesting that the 18 kDa Ca2+ -binding protein is CaM and that CaM regulates flagellar motility. CaMKIV was detected immunologically as a single 48 kDa band in both the fraction of low ion extract of the axoneme and the remnant of the axoneme, suggesting that CaMKIV binds to distinct positions in the axoneme. It is possible that CaMKIV phosphorylates the axonemal proteins in a Ca2+/CaM-dependent manner for regulating the dynein activity. A 32P-uptake in the axoneme showed that 48, 75, 120, 200, 250, 380, and 400 kDa proteins were phosphorylated in a Ca2+/CaM kinase-dependent manner. Proteins (380 kDa) were phosphorylated in the presence of 10,5 M Ca2+. It is possible that an increase in Ca2+ induces Ca2+/CaM kinase-dependent regulation, including protein phosphorylation for activation/regulation of dynein activity in flagellar axoneme. Cell Motil. Cytoskeleton 2006. © 2006 Wiley-Liss, Inc. [source]

Time asymmetric quantum theory , III.

FORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 6 2003
Decaying states, the causal Poincaré semigroup
Abstract These Gamow kets span an irreducible representation space for Poincaré transformations which, similar to the Wigner representations for stable particles, are characterized by spin (angular momentum of the partial wave amplitude) and complex mass (position of the resonance pole). The Poincaré transformations of the Gamow kets, as well as of the Lippmann-Schwinger plane wave scattering states, form only a semigroup of Poincaré transformations into the forward light cone. Their transformation properties are derived. From these one obtains an unambiguous definition of resonance mass and width for relativistic resonances. The physical interpretation of these transformations for the Born probabilities and the problem of causality in relativistic quantum physics is discussed. [source]

Regional tomographic inversion of the amplitude and phase of Rayleigh waves with 2-D sensitivity kernels

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2006
Yingjie Yang
SUMMARY In this study, we test the adequacy of 2-D sensitivity kernels for fundamental-mode Rayleigh waves based on the single-scattering (Born) approximation to account for the effects of heterogeneous structure on the wavefield in a regional surface wave study. The calculated phase and amplitude data using the 2-D sensitivity kernels are compared to phase and amplitude data obtained from seismic waveforms synthesized by the pseudo-spectral method for plane Rayleigh waves propagating through heterogeneous structure. We find that the kernels can accurately predict the perturbation of the wavefield even when the size of anomaly is larger than one wavelength. The only exception is a systematic bias in the amplitude within the anomaly itself due to a site response. An inversion method of surface wave tomography based on the sensitivity kernels is developed and applied to synthesized data obtained from a numerical simulation modelling Rayleigh wave propagation over checkerboard structure. By comparing recovered images to input structure, we illustrate that the method can almost completely recover anomalies within an array of stations when the size of the anomalies is larger than or close to one wavelength of the surface waves. Surface wave amplitude contains important information about Earth structure and should be inverted together with phase data in surface wave tomography. [source]

P-wave transmission across fractures with nonlinear deformational behaviour

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 11 2006
X. B. Zhao
Abstract Stress wave attenuation across fractured rock masses is a great concern of underground structure safety. When the wave amplitude is large, fractures experience nonlinear deformation during the wave propagation. This paper presents a study on normal transmission of P-wave across parallel fractures with nonlinear deformational behaviour (static Barton,Bandis model). The results show that the magnitude of transmission coefficient is a function of incident wave amplitude, nondimensional fracture spacing and number of fractures. Two important indices of nondimensional fracture spacing are identified, and they divide the area of nondimensional fracture spacing into three parts (individual fracture area, transition area and small spacing area). In the different areas, the magnitude of transmission coefficient has different trends with nondimensional fracture spacing and number of fractures. In addition, the study reveals that under some circumstances, the magnitude of transmission coefficient increases with increasing number of fractures, and is larger than 1. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Altered T Wave Dynamics in a Contracting Cardiac Model

JOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 2003
NICOLAS P. SMITH Ph.D.
Introduction: The implications of mechanical deformation on calculated body surface potentials are investigated using a coupled biophysically based model. Methods and Results: A cellular model of cardiac excitation-contraction is embedded in an anatomically accurate two-dimensional transverse cross-section of the cardiac ventricles and human torso. Waves of activation and contraction are induced by the application of physiologically realistic boundary conditions and solving the bidomain and finite deformation equations. Body surface potentials are calculated from these activation profiles by solving Laplace's equation in the passive surrounding tissues. The effect of cardiac deformation on electrical activity, induced by contraction, is demonstrated in both single-cell and tissue models. Action potential duration is reduced by 7 msec when the single cell model is subjected to a 10% contraction ramp applied over 400 msec. In the coupled electromechanical tissue model, the T wave of the ECG is shown to occur 18 msec earlier compared to an uncoupled excitation model. To assess the relative effects of myocardial deformation on the ECG, the activation sequence and tissue deformation are separated. The coupled and uncoupled activation sequences are mapped onto the undeforming and deforming meshes, respectively. ECGs are calculated for both mappings. Conclusion: Adding mechanical contraction to a mathematical model of the heart has been shown to shift the T wave on the ECG to the left. Although deformation of the myocardium resulting from contraction reduces the T wave amplitude, cell stretch producing altered cell membrane kinetics is the major component of this temporal shift. (J Cardiovasc Electrophysiol, Vol. 14, pp. S203-S209, October 2003, Suppl.) [source]

From intracranial pressure to intracranial pressure wave-guided intensive care management of a patient with an aneurysmal subarachnoid haemorrhage

ACTA ANAESTHESIOLOGICA SCANDINAVICA, Issue 4 2007
P. K. Eide
We report on a 65-year-old female with an aneurysmal subarachnoid hemorrhage (SAH) that was followed clinically, radiologically and electrophysiologically before and after converting from intracranial pressure (ICP)-guided to ICP wave-guided intensive care management. Intracranial pressure-guided management is aimed at keeping mean ICP < 15,20 mmHg, while ICP wave-guided management is aimed at keeping mean ICP wave amplitude < 5 mmHg. The aims of management were obtained by adjusting cerebrospinal fluid (CSF) draining volume from her external ventricular drain. No improvement was seen clinically or in cerebral magnetic resonance imaging (MRI) scans during the ICP-guided management. Clinical, MRI and neurophysiologic (electroencephalography and auditory evoked responses) improvements were obvious within 2 days after converting from ICP- to ICP wave-guided management. This case report describes how we used various ICP parameters to guide intensive care management of an aneurysmal SAH patient. [source]

Early Electrophysiological Changes In Transgenic Rat Model Of Charcot-Marie-Tooth

JOURNAL OF THE PERIPHERAL NERVOUS SYSTEM, Issue 1 2001
M Grandis
Recently, a reliable transgenic rat model of human Charcot-Marie-Tooth type 1 A has been developed. So far, neurophysiological studies have been performed only in advanced stages of rat disease. Moreover, axonal involvement, which is known to occur in human CMT1A, has never been observed in this rat model. Affected rats show overexpression of Peripheral Myelin Protein (PMP-22) and a peripheral hypomyelinating neuropathy. We perfomed an electrophysiological study in two heterozygous PMP-22 transgenic rats and in one normal control, matched for age (3 weeks) and weight (average: 60 g). Recordings were performed in vivo by stimulating the sciatic nerve at both sciatic notch and ankle sites and recording the Hoffman reflex and direct muscle responses (CMAP). The H-reflex related SNCV and MNCV were calculated by measuring the distance between the sciatic notch and the ankle sites and the respective latencies. The two transgenic rats showed different levels of PMP-22 overexpression, as judged by quantitative PCR. The rat with a lower PMP-22 gene level showed a 30% reduction of MNCV compared to the normal control, while SNCV was not reduced. The CMAP was sized approximately 45% of the normal rat while the ratio between H wave amplitude and CMAP was 30% of the normal, the H wave amplitude being more affected than the CMAP. The action potentials in the rat with a higher transgene level were not recordable. Our data demonstrate that slowing of MNCV is an early finding in the CMT1A rat model. The marked reduction of H wave amplitude in front of a normal SNCV suggests a possible early axonal damage of sensory fibers. The entity of electrophysiological compromission positively correlated with the number of copies for PMP-22 gene. All together these considerations prove the sensitivity of this method, however further studies are needed to confirm these results and to prove that this model may be suitable to investigate the effects of therapeutic approaches. [source]

Validation of 2 Techniques for Electrocardiographic Recording in Dogs and Cats

JOURNAL OF VETERINARY INTERNAL MEDICINE, Issue 4 2006
Luca Ferasin
Background: Standard electrocardiographic (ECG) recording in the dog and cat is commonly performed in right lateral recumbency, by connecting the ECG leads to the skin of the patient via metallic alligator clips. The jaws of the alligator clips are usually filed or flattened to reduce their uncomfortable pressure on the patient's skin. However, filed and flattened alligator clips can occasionally lose their grip to the skin, causing lead detachment during standard ECG recording. Hypothesis: The aim of the study was to validate two novel ECG recording techniques ("gel" and "pads"). Animals: Six-lead standard ECG recording was obtained from 42 dogs and 40 cats using the standard technique, as well as the two novel methods. Methods: Measurements were taken of the amplitude and duration of P waves and QRS complexes, duration of PQ and QT intervals, and mean electrical axis (MEA). In each recording, five representative complexes were measured, and the results were averaged for each parameter. Results: A good quality ECG recording was obtained with all the three different techniques, although a degree of wandering trace was observed in one third of cats with the "pads" technique. Bland-Altman analysis showed good agreement between the ECG values recorded with the two novel techniques and those recorded with the standard traditional technique. Furthermore, the observed differences were not clinically relevant, except for the R wave amplitude recorded with the "pads" method in cats (-0.35 to 0.37 mV). Conclusions and Clinical Importance: In conclusion, this study supports the reliability and clinical validity of the "gel" and "pads" techniques for ECG recording both in the dog and the cat, with some limitations for the "pads" technique in cats. [source]

Impact of nadir lower oesophageal sphincter pressure on bolus clearance assessed by combined manometry and multi-channel intra-luminal impedance measurement

NEUROGASTROENTEROLOGY & MOTILITY, Issue 1 2010
N. Q. Nguyen
Abstract, This study aimed to assess the relationship between nadir lower oesophageal sphincter pressure (LOSP) and wave amplitude (WA) in oesophageal bolus clearance. Concurrent oesophageal manometry and impedance were performed in 146 subjects [41 healthy, 24 non-obstructive dysphagia (NOD) and 81 gastro-oesophageal reflux (GOR)]. Patients with achalasia and diffuse oesophageal spasm were excluded. Swallow responses were categorized by nadir LOSP. For each category of nadir LOSP, WA at the distal 2 recording sites were grouped into bins of 10 mmHg and the proportion of waves in each bin associated with a normal bolus presence time (BPT) was determined. Nadir LOSP, distal BPT, total bolus transit time and the proportion of impaired oesophageal clearance in patients with NOD were greater than those of healthy subjects and patients with GOR. Overall, responses with impaired oesophageal clearance had significantly lower WA (54 ± 1 vs 81 ± 1 mmHg; P < 0.0001) and higher nadir LOSP (2.7 ± 0.4 vs 1.0 ± 0.1 mmHg, P < 0.001). For each level of nadir LOSP, there was a direct relationship between distal WA and successful bolus clearance of both liquid and viscous boluses from the distal oesophagus. As nadir LOSP increased, the relationship between WA and bolus clearance shifted to the right and higher amplitudes were required to achieve the same effectiveness of clearance. Hypotensive responses with nadir LOSP ,3 mmHg were less likely to clear than those with nadir LOSP <3 mmHg, for both liquid (7/29 vs 162/276; P < 0.001) or viscous boluses (11/46 vs 176/279; P < 0.0001). Nadir LOSP is an important determinant of bolus clearance from the distal oesophagus, particularly in patients with NOD. [source]

Compatibility of Automatic Threshold Tracking Pacemakers with Previously Implanted Pacing Leads in Children

PACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 11 2002
OSMAN KUCUKOSMANOGLU
KUCUKOSMANOGLU, O., et al.: Compatibility of Automatic Threshold Tracking Pacemakers with Previously Implanted Pacing Leads in Children. The Autocapture function controls and optimizes the amplitude of the pacing pulse and saves energy. The manufacturer recommends using a special low polarization, low threshold bipolar Pacesetter lead for the Autocapture function. The purpose of this study was to evaluate the compatibility of Autocapture with previously implanted pacing leads. The study included 15 patients (mean age 13.6 ± 3.4 years) who needed pulse generator replacement and received the VVIR pacemaker Regency SR+ or the DDDR pacemakers Affinity DR or Integrity DR with the Autocapture function. The new pulse generators connected to previously implanted ventricular leads. At the time of implantation the pacing threshold was 1.0 ± 0.35 V at 0.5 ms, the lead impedance was 580 ± 80 ,, and the spontaneous R wave amplitude was 7.89 ± 4.89 mV. The polarization signal (PS) was 3.8 ± 3.04 mV, and evoked response (ER) was 8.15 ± 4.57 mV at the predischarge testing. Follow-up telemetry was done at months 1, 3, 6, 12, and 18. The follow-up duration was 9.4 ± 5 months (range 1,18 months). If the results of PS and ER measurements were acceptable for Autocapture, it turned on at the 1-month visit. In six (40%) patients the results were found acceptable for Autocapture function. Age, lead impedance, pacing threshold, intrinsic R wave measurement, lead age, fixation mechanism, and ER measurements were not statistically different in Autocapture suitable and not suitable groups. The main reason not to activate Autocapture had been increased PS. Any significant fluctuations were not observed in pacing threshold, lead impedance, ER, and PS during follow-up. In conclusion, previously implanted pacing leads may be compatible with the Autocapture function. [source]

Development of an Echocardiographic Method for Choosing the Best Fitting Single-Pass VDD Lead

PACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 5 2002
WEI-HSIAN YIN
YIN, W.-H., et al.: Development of an Echocardiographic Method for Choosing the Best Fitting Single-Pass VDD Lead. To achieve stable single-lead VDD pacing, a selection of the electrode with the optimal distance between the lead tip and the floating atrial dipole (AV distance [AVD]) is important. The authors hypothesized that the size of the right heart chambers may affect atrial sensing, and that measurement of their internal dimension at end-diastole (RHIDd) in the apical four chamber view by transthoracic echocardiography may aid in choosing the proper AVD. Twenty-six consecutive cases that had undergone VDD pacer implantation using the conventional chest X ray were examined retrospectively by the echocardiographic method. The chest x-ray method properly selected a lead with optimal atrial sensing, defined as minimum P wave amplitude , 1.0 mV, for only 20 (77%) of 26 patients. By comparing these results with their respective RHIDd, a cut-off point of 13 cm was obtained that indicated a criterion for choosing the proper AVD. The indication was that if the RHIDd was , 13 cm, a lead with an AVD of 15.5/16 cm should have been used; if the RHIDd was < 13 cm, a lead with an AVD of 13/13.5 cm should have been chosen. Using the echocardiographic method, all six patients who had suboptimal atrial sensing could be identified and classified as having missized (four undersized; two oversized) permanent leads. In conclusion, the described method provides a promising preoperative assessment of the best fitting electrode length in single lead VDD pacing. A prospective study is ongoing to verify its applicability. [source]

Mapping the Coronary Sinus and Great Cardiac Vein

PACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 4 2002
MICHAEL GIUDICI
GIUDICI, M., et al.: Mapping the Coronary Sinus and Great Cardiac Vein. The purpose of this study was to develop a better understanding of the pacing and sensing characteristics of electrodes placed in the proximal cardiac veins. A detailed mapping of the coronary sinus (CS) and great cardiac vein (GCV) was done on 25 patients with normal sinus rhythm using a deflectable electrophysiological catheter. Intrinsic bipolar electrograms and atrial and ventricular pacing voltage thresholds were measured. For measurement purposes, the GCV and the CS were each subdivided into distal (D), middle (M), and proximal (P) regions, for a total of six test locations. Within the CS and GCV, the average atrial pacing threshold was always lower (P < 0.05) than the ventricle with an average ventricular to atrial ratio > 5, except for the GCV-D. The average atrial threshold in the CS and GCV ranged from 0.2, to 1.0-V higher than in the atrial appendage. Diaphragmatic pacing was observed in three patients. Atrial signal amplitude was greatest in the CS-M, CS-D, and GCV-P and smaller in the CS-P, GCV-M, and GCV-D. Electrode spacing did not significantly affect P wave amplitude, while narrower electrode spacing attenuated R wave amplitude. The average P:R ratio was highest with 5-mm-spaced electrodes compared to wider spaced pairs. The P:R ratio in the CS was higher (P < 0.05) than in all positions of the GVC. It is possible to pace the atrium independent of the ventricle at reasonably low thresholds and to detect atrial depolarization without undue cross-talk or noise using closely spaced bipolar electrode pairs. The areas of the proximal, middle, and distal CS produced the best combination of pacing and sensing parameters. [source]

Efficacy of Single Lead VDD Pacing in Patients with Impaired and Normal Left Ventricular Function

PACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 8 2000
ANDREAS SCHUCHERT
Atrial synchronous ventricular pacing seems to be the best pacing mode for patients with advanced AV block and impaired LV function. The long-term follow-up of single lead VDD pacing was studied in 33 patients with impaired LV function and compared to 42 patients with normal LV function. All patients received the same VDD lead and VDDR pacemaker. The lead model with 13-cm AV spacing between the atrial and ventricular electrode was implanted in 89% of the patients. Follow-ups were 1, 3, 6, and 12 months after implantation. The percentage of atrial sensing and the P wave amplitude were determined at each follow-up. Minimal P wave amplitude at implantation was 2.0 ± 1.4 mV in patients with impaired and 1.7 ± 0.9 mV with normal LV function (not significant). At the 12-month follow-up, 33 patients with normal and 23 patients with depressed LV function remained paced in the VDD mode. The remaining patients died in five (impaired LV function) and seven cases (normal LV function) or their pacemakers were programmed to the VVI/VVIR pacing mode in four (impaired LV function) and three cases (normal LV function). P wave amplitude did not differ in the two groups (e.g., at month 12: impaired: 1.17 ± 0.42 mV; normal: 1.09 ± 0.49 mV). The atrial sensitivity was programmed in most patients to sensitive settings with no differences between the two groups (e.g., at month 12: impaired: 0.13 ± 0.06 mV; normal: 0.13 ± 0.05 m V). The diagnostic counters indicated nearly permanent atrial sensing (e.g., at month 12: impaired: 99.3 ± 2.2%; normal: 99.0 ± 1.0 mV). In conclusions, single lead VDD pacing restored AV synchronous ventricular pacing in patients with normal and with impaired LV function indicating that it could be an alternative to DDD pacemakers, but not to dual-chamber pacing. [source]

Particle Size of Pneumatically Conveyed Powders Measured Using Impact Duration

PARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 6 2007
Peter J. Coghill
Abstract CSIRO Minerals has developed a technique for measuring particle size in pneumatically conveyed powders [1] by measurement of the acoustic waves produced by particle impacts upon a specially designed transducer. Previous work has focused on using the peak acoustic wave amplitude to determine particle size. This produces a spectrum that is hard to determine the particle size from, as the peak amplitude is a non-linear function of particle diameter, and is strongly affected by angle of incidence and velocity of the impacting particle. In this paper impact duration measurements are used to overcome these difficulties while retaining the advantages of being able to measure in high solids loadings of up to at least 0.5,kg/m3 of powder. In laboratory tests the impact size monitor's (ISM) results have been correlated with optical diffraction measurements of the mean (by number) powder size with a correlation coefficient of 0.985 and a relative error of 5.5,%. The ISM operated successfully in the laboratory at a loading of 0.5,kg/m3 of powder and measured particles down to 50,microns in size. [source]

Effects of task difficulty and invested mental effort on peripheral vasoconstriction

PSYCHOPHYSIOLOGY, Issue 5 2004
Cristina Iani
Abstract We ran two experiments to investigate whether peripheral arterial tone reflects changes in mental effort. Finger pulse wave amplitude, interpulse interval, and pulse variability in the mid- and high-frequency bands were recorded by means of a newly developed finger plethysmograph during both rest and cognitive performance. Using a modified version of the Sternberg memory task, we selectively manipulated either the difficulty of the task (Experiment 1) or the subjects' level of engagement in the task (Experiment 2). We found a significant difference in finger pulse wave amplitude between rest and task periods, suggesting that the measure reflects changes in sympathetic activity due to task engagement. In addition, our results suggest that reduced pulse wave amplitude, signaling vasoconstriction, occurs when subjects are investing effort. [source]

Do transient gravity waves in a shear flow break?

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 634 2008
M. Pulido
Abstract The propagation of transient gravity waves in a shear flow towards their critical levels is examined using a ray tracing approximation and a higher-degree (quasi-optic) approximation. Because of its transient forcing, the amplitude of transient waves decays to zero in the neighbourhood of the critical region so that it is not clear whether transient gravity waves will reach the convective instability threshold or not. The analysis shows that the horizontal perturbation decays asymptotically as the inverse of the square root of time, while the vertical wavenumber depends linearly on time, thus transient gravity waves attain convective instability for long times. The theoretical results are compared with numerical simulations. The ray path approximation is not able to reproduce the maximum amplitude, but the quasi-optic approximation gives a reasonable agreement at short and long times. There are three breaking regimes for transient gravity waves. For wave packets with a narrow frequency spectrum (quasi-steady waves) and large enough initial wave amplitude, the wave breaking is similar to the abrupt monochromatic wave overturning. On the other hand, highly transient wave packets will dissipate near the critical region for very long times with small wave amplitudes and high vertical wavenumber. The third regime is a transition between the two extremes; in this case both wave amplitude and vertical wavenumber are important to produce the convective threshold. The dependencies of the convective instability height (a quantity that may be useful for gravity wave parametrizations) on the Richardson number and the frequency spectral width are obtained. Copyright © 2008 Royal Meteorological Society [source]

Flow separation and rotor formation beneath two-dimensional trapped lee waves

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 620 2006
S. B. Vosper
Abstract Numerical simulations of trapped lee waves generated in flow over a two-dimensional ridge are presented. It is shown that for sufficiently large amplitude waves flow separation occurs beneath the wave crests when a no-slip lower boundary condition is applied. The occurrence of separation corresponds to rotor motion, or recirculation, under the wave crests. The dependence of the wave-induced horizontal flow perturbations near the ground on the wave amplitude, wavelength and surface roughness is examined. It is shown that the normalized critical wave amplitude, above which rotors form, is a function of the ratio of the lee-wave horizontal wavelength to the surface roughness length. This normalized wave amplitude is defined as the ratio of the lee-wave pressure amplitude within the boundary layer, to the square of the friction velocity. Linearized turbulent equations for motion beneath the wave crests are considered and numerical solutions to the linear problem are compared with results from the simulations. When the waves are of sufficiently small amplitude that flow separation does not occur, the linear flow perturbations are shown to agree closely with the results from the simulations. It is also shown that linear theory provides a useful prediction of the occurrence of rotor formation. © Crown copyright, 2006. [source]

Benjamin,Feir instability of Rossby waves on a jet

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 600 2004
J. G. Esler
Abstract Large-scale waves on the extratropical tropopause have been widely observed to spontaneously organize into groups or wave packets. Here, a simple paradigm for this wave packet formation is presented. Firstly, a weakly nonlinear theory of Rossby wave propagation on a potential-vorticity front, based on small non-dimensional wave amplitude ,, is developed. As is typical for systems allowing conservative one-dimensional wave propagation, the evolution of the wave envelope is governed by the nonlinear Schrödinger equation. The sense of the nonlinearity is consistent with Benjamin,Feir instability, where uniform wave trains are unstable to sideband modulations, leading to the formation of wave packets. Next, numerical results from contour dynamics integrations show that the weakly nonlinear predictions for sideband growth rates are quantitatively accurate up to ,,0.5, and that unstable sideband growth is qualitatively similar, but slower than predicted, at higher values of ,. For ,,0.6 the formation of wave packets leads to wave-breaking, this occuring at much lower initial wave amplitudes than for unmodulated uniform wave trains previously studied. The numerical results reveal that the length and time-scales of the Benjamin,Feir instability are broadly consistent with observed wave packet formation in the extratropics. Copyright © 2004 Royal Meteorological Society. [source]

Effect-site concentration of remifentanil attenuating surgical stress index responses to intubation of the trachea

ANAESTHESIA, Issue 6 2010
S. Mustola
Summary Surgical Stress Index has been proposed for assessment of surgical stress and analgesia. It is a numeric index based on the normalised pulse beat interval and photoplethysmographic pulse wave amplitude. We determined the effect-site concentration of remifentanil for attenuation of Surgical Stress Index responses to intubation of the trachea. Thirty ASA 1,2 patients received either deep or normal anaesthesia and then target-controlled remifentanil. Burst suppression was maintained in the deep group and state entropy at 40,60 (scale 0,91) in the normal group. Mean (SD) effect-site concentrations of remifentanil attenuating responses in 50% of patients were 2.13 (0.25) ng.ml,1 and 3.05 (0.27) ng.ml,1 in deep and normal groups, respectively (p = 0.034). From probit analysis, EC50 and EC95 of remifentanil (95% CI) were 2.34 (1.97,2.71) ng.ml,1 and 3.19 (2.69,3.69) ng.ml,1 in deep group and 3.17 (2.67,3.67) ng.ml,1 and 3.79 (3.21,4.37) ng.ml,1 in the normal group, respectively. The values from probit analysis and up-and-down method did not differ significantly. [source]

R-Wave Detection by Subcutaneous ECG.

ANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 1 2001
Possible Use for Analyzing R-R Variability
Background: Atrial arrhythmia (AA) discrimination remains a technological challenge for implanted cardiac devices. We examined the feasibility of R-wave detection by a subcutaneous far field ECG (SFFECG) and analysis of these signals for R to R variability as an indicator of atrial arrhythmia (AA). Methods: Surface ECG and SFFECG (from the pacemaker pocket) were recorded in sixteen patients (61.5 ± 11.4 years) with AA. The SFFECG was recorded with a pacemaker sized four electrode array acutely placed in the pacemaker pocket during implantation. The signals were analyzed to obtain peak-to-peak R wave amplitude and R to R interval variability (indicative of AAs). Results: In sixteen patients R waves were visually discernible in all recordings. The percentage over and under detection for automatic R wave recognition SFFECG was 3 and 9%, respectively. R to R variability analysis using the SFFECG produced results concordant to those using the surface ECG. Conclusion: SFFECG might be a helpful adjunct in implantable device systems for detection of R waves and may be used for measurement of R to R variability. A.N.E. 2001;6(1):18,23 [source]

2424: Pulsatile haemodynamics: potential for end-organ damage?

ACTA OPHTHALMOLOGICA, Issue 2010
C HUDSON
Purpose Increases in velocity pulse wave amplitude, or max:min velocity ratio, represent early haemodynamic disturbances associated with diabetic retinopathy (DR) and age-related macular degeneration. This change reflects an increase in vessel wall rigidity that is generally accepted to occur in the central vasculature but the peripheral vasculature is also implicated in this process. This presentation will highlight the implications of these changes in terms of end-organ damage in DR. Methods The sample comprised 4 groups: Group 1: 50 non-diabetic control subjects. Group 2: 56 diabetic patients without clinically visible DR. Group 3: 54 diabetic patients with micro-aneurysms and / or hard exudates within 2 disc diameters of the fovea in the absence of clinically manifest diabetic macular edema (DME). Group 4: 40 patients with clinically manifest DME. The diabetic patients were predominantly type 2. Retinal hemodynamics were assessed in the superior temporal retinal arteriole using the Canon Laser Blood Flowmeter. Intraocular pressure, blood pressure and relevant systemic markers of diabetes control and complications were also assessed. Results The velocity pulse wave amplitude was elevated with increasing risk of DME (p<0.0001). No significant differences were found between the groups with respect to diameter, velocity or flow. Pulse wave amplitude was correlated to age, duration of diabetes, blood pressure, pulse rate, IOP and serum potassium levels. Conclusion The increase in velocity pulse wave amplitude will induce excessive pressure pulsatility in the retinal arterioles and capillaries, changes in vascular function (e.g. loss of vascular regulation) and changes in vessel structure. Commercial interest [source]

Non-uniqueness with refraction inversion , the Mt Bulga shear zone

GEOPHYSICAL PROSPECTING, Issue 4 2010
Derecke Palmer
ABSTRACT The tau-p inversion algorithm is widely employed to generate starting models with many computer programs that implement refraction tomography. However, this algorithm can frequently fail to detect even major lateral variations in seismic velocities, such as a 50 m wide shear zone, which is the subject of this study. By contrast, the shear zone is successfully defined with the inversion algorithms of the generalized reciprocal method. The shear zone is confirmed with a 2D analysis of the head wave amplitudes, a spectral analysis of the refraction convolution section and with numerous closely spaced orthogonal seismic profiles recorded for a later 3D refraction investigation. Further improvements in resolution, which facilitate the recognition of additional zones with moderate reductions in seismic velocity, are achieved with a novel application of the Hilbert transform to the refractor velocity analysis algorithm. However, the improved resolution also requires the use of a lower average vertical seismic velocity, which accommodates a velocity reversal in the weathering. The lower seismic velocity is derived with the generalized reciprocal method, whereas most refraction tomography programs assume vertical velocity gradients as the default. Although all of the tomograms are consistent with the traveltime data, the resolution of each tomogram is comparable only with that of the starting model. Therefore, it is essential to employ inversion algorithms that can generate detailed starting models, where detailed lateral resolution is the objective. Non-uniqueness can often be readily resolved with head wave amplitudes, attribute processing of the refraction convolution section and additional seismic traverses, prior to the acquisition of any borehole data. It is concluded that, unless specific measures are taken to address non-uniqueness, the production of a single refraction tomogram that fits the traveltime data to sufficient accuracy does not necessarily demonstrate that the result is either correct, or even the most probable. [source]

Interictal and Postictal Contingent Negative Variation in Migraine Without Aura

HEADACHE, Issue 1 2001
E.J.C.M. Mulder MSc
Cortical hyperexcitability is thought to explain the more enhanced contingent negative variation (CNV) amplitudes and impaired CNV habituation that have been found during the interictal period in migraine without aura. These CNV characteristics have been shown to normalize to the level of healthy controls during an attack. This study aimed to replicate the interictal findings, and additionally examine whether migraineurs show reduced CNV amplitudes during the postattack period. Of 12 patients with migraine without aura and their sex- and age-matched healthy controls, CNV characteristics were recorded once in an interictal period, once during the postattack period within 30 hours after an attack that was treated with sumatriptan, and once after an attack that was treated with habitual nonvasoactive medication (counterbalanced). The present results did not confirm the enhanced CNV early and late wave amplitudes or impaired habituation, and cortical hyperexcitability that have previously been reported in the interictal period in patients with migraine without aura. During the postattack period, a decrease in CNV early and late amplitudes was found but only after sumatriptan use. This reduction in CNV amplitudes was most prominent over the frontal cortex and could reflect cortical hypoexcitability, possibly related to a suppression of central catecholaminergic activity by sumatriptan. [source]

Considerations of the discontinuous deformation analysis on wave propagation problems

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 12 2009
Jiong Gu
Abstract In rock engineering, the damage criteria of the rock mass under dynamic loads are generally governed by the threshold values of wave amplitudes, such as the peak particle velocity and the peak particle acceleration. Therefore, the prediction of wave attenuation across fractured rock mass is important on assessing the stability and damage of rock mass under dynamic loads. This paper aims to investigate the applications of the discontinuous deformation analysis (DDA) for modeling wave propagation problems in rock mass. Parametric studies are carried out to obtain an insight into the influencing factors on the accuracy of wave propagations, in terms of the block size, the boundary condition and the incident wave frequency. The reflected and transmitted waves from the interface between two materials are also numerically simulated. To study the tensile failure induced by the reflected wave, the spalling phenomena are modeled under various loading frequencies. The numerical results show that the DDA is capable of modeling the wave propagation in jointed rock mass with a good accuracy. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Tsunami generation and propagation from the Mjølnir asteroid impact

METEORITICS & PLANETARY SCIENCE, Issue 9 2007
S. Glimsdal
The geological structure resulting from the impact is today known as the Mjølnir crater. The present work attempts to model the generation and the propagation of the tsunami from the Mjølnir impact. A multi-material hydrocode SOVA is used to model the impact and the early stages of tsunami generation, while models based on shallow-water theories are used to study the subsequent wave propagation in the paleo-Barents Sea. We apply several wave models of varying computational complexity. This includes both three-dimensional and radially symmetric weakly dispersive and nonlinear Boussinesq equations, as well as equations based on nonlinear ray theory. These tsunami models require a reconstruction of the bathymetry of the paleo-Barents Sea. The Mjølnir tsunami is characteristic of large bolides impacting in shallow sea; in this case the asteroid was about 1.6 km in diameter and the water depth was around 400 m. Contrary to earthquake- and slide-generated tsunamis, this tsunami featured crucial dispersive and nonlinear effects: a few minutes after the impact, the ocean surface was formed into an undular bore, which developed further into a train of solitary waves. Our simulations indicate wave amplitudes above 200 m, and during shoaling the waves break far from the coastlines in rather deep water. The tsunami induced strong bottom currents, in the range of 30,90 km/h, which presumably caused a strong reworking of bottom sediments with dramatic consequences for the marine environment. [source]

Electrophysiological correlates of response inhibition in children and adolescents with ADHD: Influence of gender, age, and previous treatment history

PSYCHOPHYSIOLOGY, Issue 6 2007
Mario Liotti
Abstract Deficits in response inhibition may be at the core of the cognitive syndrome in ADHD. Here, inhibitory control mechanisms were studied in 36 ADHD-combined type and 30 healthy children by exploring the event-related brain activity during the Stop Signal task. The influence of age, gender, and previous treatment history was evaluated. The ADHD group showed reduced N200 wave amplitudes. For successful inhibitions, the N200 reduction was greatest over right inferior frontal scalp, and only the control group showed a success-related enhancement of such right frontal N200. Source analysis identified a source of the N200 group effect in right dorsolateral prefrontal cortex. Finally, a late positive wave to failed inhibitions was selectively reduced only in treatment-naïve ADHD children, suggesting that chronic stimulants may normalize late conscious error recognition. Both effects were independent of gender and age. [source]