Changes In Average Velocity Research Articles

Specific occupant and collision characteristics are associated with motor vehicle collision-related blunt cerebrovascular artery injury.

Blunt cerebrovascular artery injury (BCI) remains difficult to diagnose but is recognized with increasing frequency after motor vehicle collisions (MVCs). Failure to detect this injury in a timely fashion can be devastating. Criteria that can be used to heighten the suspicion of this injury have been suggested; however, more encompassing screening has been recommended. To address this need, we sought to describe occupant, vehicle, and collision characteristics among MVC occupants who sustained a BCI. All cases of BCI identified in the National Automotive Sampling System Crashworthiness Data System, a national probability sample of passenger vehicles involved in police-reported tow-away MVCs, between 1993 and 2001 were selected. Information on occupant (e.g., demographics, seating position, and restraint use), collision (e.g., collision type and severity), and vehicle characteristics were obtained and summarized using descriptive statistics. Nine-hundred forty individuals with BCI were identified in the Crashworthiness Data System data files. Over half were belted (57.4%) and 82.3% had airbag deployment; 16.2% were partially or completely ejected from the vehicle. Head and thoracic injuries were common (44.4% and 40.8%, respectively); 27.8% sustained a cervical spine fracture and 21.0% sustained a soft-tissue injury to the neck. The mean Injury Severity Score was 33.6. The case fatality rate was 44.5%. The majority of BCI occupants were drivers (76.0%). Among belted occupants, the lap/shoulder was the most commonly attributed as the injury source (61.4%). Among unbelted occupants, frequent injury sources included air bags (15.0%), windshield (13.7%), and other interior objects. With respect to collision characteristics, the average change in velocity (Delta V) was 43.3 km/h. The majority of collisions were frontal (76.2%). This study indicates that BCI is both a rare and lethal injury typified by specific occupant and collision characteristics. These characteristics provide insight as to the cause of this injury that may aid in the evaluation and management of the blunt trauma patient at risk for BCI.

Postural stability is compromised by fatiguing overhead work.

In a laboratory setting, 16 participants performed a repetitive overhead tapping task for 3 hours or until self-terminated due to substantial shoulder discomfort. Several measures of postural sway and stability were obtained using a force plate, both during quiet standing and during performance of the tapping task. Sway area and peak sway velocity showed consistent increases with time, whereas changes in average velocity and peak whole-body center-of-mass acceleration were either small or nonsignificant. Although relatively insensitive to several task variables, changes in sway areas and peak velocities were substantially larger in trials terminated by the participants. It is argued that fatigue plays a more important role than simple task duration in causing the observed increases in sway, and hence decreases in postural stability. Potential whole-body consequences of localized musculoskeletal stresses appear supported by the results, and implications for safety, risks of falls, and work scheduling are discussed.

Activación cerebral durante el movimiento de ambas manos. Estudio con Doppler transcraneal

In healthy persons, the force carried out by a group of muscles doing bilateral exercise with maximum effort is less than that done during unilateral exercise. The nervous control of movement is probably different in these two cases. Our objective was to study and compare cerebral activation on movement of one and of both hands by means of transcranial Doppler (TCD). We studied 30 healthy volunteers (19 men and 11 women; average age 65.4 +/- 9.5 years). Using transtemporal TCD we assessed the relative changes in average velocity of flow in both middle cerebral arteries during the exercise of sequential opposition of the fingers of one hand and of both hands. The activity due to the exercise of the hand contralateral to the hemisphere being studied was greater than that due to exercise of both hands together, both on the right side (p < 0.001) and on the left (p < 0.001). The functional activity of each cerebral hemisphere is not necessarily greater when both hands are exercised than when the contralateral hand is used, and may even be less. The possible increase in activity due to the additional contribution to ipsilateral movement in the first case may be compensated by simultaneous transhemispherical inhibition.

The Friction and Diffusion Coefficients with Maxwellian Scatters

The Fokker-Planck coefficients for Coulomb interaction, or the friction coefficient (the average change in velocity) and the diffusion coefficient , are evaluated by an appropriate variable change technique. This approach reduces the five-fold integral expressions of the Fokker-Planck coefficients to one-fold integral without meeting the divergence difficulties. A new Debye cutoff parameter , instead of the customary cutoff avoids the error incurred through the customary neglecting of velocity dependence of the Coulomb logarithm. The dominant terms of the new results are similar to Chandrasekhar's results. A non-dominant term, which can exceed the dominant one in the case of is added for .

Ultrasonic reflection mode computed tomography through a skullbone

An ultrasonic reflection-mode CT method was applied to transskull imaging of brain. The method involves only a single transducer and a single scan to acquire data from the object. In reconstruction an ordinary Fourier slice theorem is applied. The average velocity changes of ultrasound due to the skullbone can be compensated. In experiments the object immersed in water was scanned by a wide-angle transducer through the viewing angle of 360 degrees. When imaging through bone a simplified approach was employed in which a piece of skullbone (thickness 3-4 mm) was attached firmly to the transducer. For comparison, the same object was then imaged without the skullbone. A two-point resolution better than 3 mm was achieved for transskull imaging using 1 MHz ultrasound. The experiments with brain specimens show that transskull images compare well with the images of the same specimens obtained without the bone interference. The findings are clinically significant in terms of pediatric brain diagnosis and postoperative follow up. Based on the method, a clinical prototype imager is currently being developed especially for diagnosis of children's brain diseases.

Signal processor for laser Doppler tissue flowmeters.

Laser Doppler flowmeter for the assessment of tissue blood flow are generally equipped with a signal processor which generates the first moment of the unnormalised power spectral density as a continuous output signal. This signal is related to blood flow for low and moderate flow rates. At higher flow rates the interpretation of the output signal becomes ambiguous as a consequence of the multiple scattering in moving blood cells and the homodyne mixing of waves on the detector surface. The paper describes a new signal processor which takes these effects into account and establishes a linear relationship between the flowmeter output signal and blood flow for all flow rates. The performance of the signal processor was evaluated by an experimental fluid model which optically resembled the blood flow through the microvasculature. The transiently high blood flow in the initial phase of reactive hyperaemia, recorded from palmar skin, gave peak values which were almost double those recorded with the original signal processor of the flowmeter. In conjunction with these high peak values a high concentration of moving blood cells was recorded, indicating that the initially high flow rate is produced by an increased number of moving blood cells due to vasodulation rather than by a change in average velocity.

Optical coherent transient measurements of velocity-changing collisions in SF_6

Elastic velocity-changing collisions have been observed for the first time to our knowledge in a nonpolar molecule by photon-echo studies of SF(6) using a frequency-switched CO(2) laser that we have developed. The photon-echo decay is nonexponential and reveals the velocity-changing collision cross section to be sigma(vc) = 180 A(2), with an average velocity change per collision of Deltau = 155 cm/sec. Using delayed optical nutation, we also determine the cross section for the population decay rate (1/T(1)) to be sigma(pop)=335 A(2). To within experimental accuracy, we find that phaseinterrupting collisions are not important (T(1) approximately T(2)). A comparison of these cross sections with those for the polar molecule (13)CH(3)F is made.

Stimulated photon echo study of [formula omitted] velocity-changing collisions

Using the recently developed single-state stimulated photon echo technique, we have studied the velocity changes experienced by ground-state Na atoms in collisions with carbon monoxide molecules. We find that the ground-state Na atoms have a total cross section of ≈420 Å 2 for velocity-changing collisions with CO, and that they experience an average velocity change of ≈600 cm/s. A scattering kernel of exponential form is shown to be consistent with our results. We discuss the essential features of the estimated photon echo technique.

HOW VELOCITY LAYERING AND STEEP DIP AFFECT CDP

Normal moveout may be used to distinguish primary from multiple reflections when the average velocity changes with depth. Approximate values of normal moveout may be found using an average velocity formula, but such values are always too large. The error appears to be controlled by the ratio of the standard deviation of the velocities within the section to the average velocity. Ray tracing provides normal moveout values which agree much better with observations. As a consequence of large dip, the reflections added by the CDP method do not represent identical areas of the dipping bed. However, if the various reflection zones lie on an inclined plane, they are added in‐phase and assume the time of a reflection from a point on the plane.

Fokker-Planck Equation for an Inverse-Square Force

The contribution to the Fokker-Planck equation for the distribution function for gases, due to particle-particle interactions in which the fundamental two-body force obeys an inverse square law, is investigated. The coefficients in the equation, $〈\ensuremath{\Delta}\mathrm{v}〉$ (the average change in velocity in a short time) and $〈\ensuremath{\Delta}\mathrm{v}\ensuremath{\Delta}\mathrm{v}〉$, are obtained in terms of two fundamental integrals which are dependent on the distribution function itself. The transformation of the equation to polar coordinates in a case of axial symmetry is carried out. By expanding the distribution function in Legendre functions of the angle, the equation is cast into the form of an infinite set of one-dimensional coupled nonlinear integro-differential equations. If the distribution function is approximated by a finite series, the resultant Fokker-Planck equations may be treated numerically using a computing machine. Keeping only one or two terms in the series corresponds to the approximations of Chandrasekhar, and Cohen, Spitzer and McRoutly, respectively.