An application of the generalized Fokker–Planck equation to the dynamics of dilute polymer solutions

The nonlinear formalism developed by Zwanzig and Mori is utilized to derive a kinetic equation for the distribution of monomer phase space coordinates and a coarse‐grained momentum density. Several simplifying approximations are then introduced into the exact kinetic equation. The resulting approximate description is shown to be closely related to the starting equations of the Freed–Edwards theory. The former differs, however, due to the presence of a non‐Stoke’s frictional term which accounts for dissipation of monomer momentum fluctuations relative to the local velocity field of the solvent. Two applications of the approximate description are considered. A derivation of an equation for the two‐time configuration space distribution function ψ (y, y′, t) is presented, where y denotes the collection of monomer position vectors. It is demonstrated that ψ (y,y′,t ) satisfies an equation similar to the Kirkwood–Riseman equation. Nonlinear couplings of the polymer distribution function to monomer momenta and the momentum density of the solvent lead to a diffusion tensor in which hydrodynamic interactions are characterized by a coarse‐grained Oseen tensor. The correlation function formulation of the intrinsic viscosity proposed by Stockmayer et al. is extended to finite wavevectors and polymer concentrations. The specific viscosity is identified as the sum of two terms involving the mechanical contribution to the polymer momentum flux tensor and the diffusion current of chain segments.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70597/2/JCPSA6-69-6-2849-1.pd

The Effect of Poststenotic Vessel Wall Compliance upon the Pulsus Tardus Phenomenon

Recent studies have investigated the detection of significant arterial stenoses through identification of the "pulsus tardus" phenomenon in Doppler waveforms obtained distal to the stenosis. The etiology of this phenomenon, however, has not yet been determined. Using an in vitro model based upon an electrical circuit analogy, the authors had as their objective to determine whether the compliance of the vessel wall immediately distal to a stenosis, in conjunction with the stenosis, is the cause of pulsus tardus. For a constant stenosis, it was found that the degree of pulsus tardus, as quantitated by the acceleration index, increased as the compliance of the poststenotic segment increased. It is concluded that pulsus tardus distal to an arterial stenosis is likely due to the compliance of the normally distensible artery, in conjunction with the stenosis. Pathological conditions that alter the compliance of the poststenotic segment may affect the degree of pulsus tardus, perhaps limiting its usefulness for upstream stenosis detection.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68136/2/10.1177_000331979404500703.pd

An easily made, low-cost, tissue-like ultrasound phantom material

No Abstract.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/38198/1/1870230413_ftp.pd

A terrestrial search for dark contents of the vacuum, such as dark energy, using atom interferometry

We describe the theory and first experimental work on our concept for searching on earth for the presence of dark content of the vacuum (DCV) using atom interferometry. Specifically, we have in mind any DCV that has not yet been detected on a laboratory scale, but might manifest itself as dark energy on the cosmological scale. The experimental method uses two atom interferometers to cancel the effect of earth's gravity and diverse noise sources. It depends upon two assumptions: first, that the DCV possesses some space inhomogeneity in density, and second that it exerts a sufficiently strong non-gravitational force on matter. The motion of the apparatus through the DCV should then lead to an irregular variation in the detected matter-wave phase shift. We discuss the nature of this signal and note the problem of distinguishing it from instrumental noise. We also discuss the relation of our experiment to what might be learned by studying the noise in gravitational wave detectors such as LIGO.The paper concludes with a projection that a future search of this nature might be carried out using an atom interferometer in an orbiting satellite. The apparatus is now being constructed

Imaging of meniscal cyst of the knee in three cases

Three cases of solitary meniscal cyst in the knee have recently been diagnosed in our departments using ultrasound and nuclear magnetic resonance (MRI). Two cysts involved the lateral and one the medial meniscus. The appearance of these lesions on ultrasound and MR images is shown. All three cysts had low intensity on T1-weighted images and high intensity on T2-weighted images and clearly communicated with a large horizontal tear in the meniscus. Ultrasonography showed a relatively hypoechoic lesion and, in the two cases of lateral meniscal cyst, focal areas of relatively increased echoes which are probably due to meniscal debris. Ultrasound showed the abnormal meniscus in both of these cases. MRI is the best way of showing the cyst and an accompanying meniscal tear but, where MRI is not available, ultrasound may be an easy and inexpensive way of making a diagnosis whether or not it is used in conjunction with positive contrast arthrography.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46793/1/256_2004_Article_BF00368614.pd

Case report 725

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46804/1/256_2004_Article_BF00242137.pd

Gravitomagnetism in Quantum Mechanics

We give a systematic treatment of the quantum mechanics of a spin zero particle in a combined electromagnetic field and a weak gravitational field, which is produced by a slow moving matter source. The analysis is based on the Klein-Gordon equation expressed in generally covariant form and coupled minimally to the electromagnetic field. The Klein-Gordon equation is recast into Schroedinger equation form (SEF), which we then analyze in the non-relativistic limit. We include a discussion of some rather general observable physical effects implied by the SEF, concentrating on gravitomagnetism. Of particular interest is the interaction of the orbital angular momentum of the particle with the gravitomagnetic field.Comment: 9 page

Usefulness of an acoustic edge artifact in assessment of the Ilizarov corticotomy interval

Thirty-three ultrasound examinations of the corticotomy interval of patients undergoing Ilizarov procedures were retrospectively evaluated for the presence or absence of an acoustic edge artifact. This artifact, consisting of a fine anechoic band, has been previously described in phantom models and is presumed to be due to phase cancellation effects. We demonstrated this artifact in 8 of 33 examinations. The artifact proved helpful in identifying the location of the corticotomy margin, even when this margin was obscured by the presence of developing periosteal new bone. Attention to technical factors is, however, important. We believe that this artifact may have a useful role in the routine monitoring of the Ilizarov patient.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46805/1/256_2004_Article_BF00241766.pd

Phase cancellation: A cause of acoustical shadowing at the edges of curved surfaces in B-mode ultrasound images

Acoustical shadowing occurring at the edges of curved objects is one of the most frequently observed artifacts in ultrasound imaging. This artifact has been generally ascribed to refraction and reflection effects at the boundary between the curved object and the surrounding tissues. However, the shadowing that would be produced by pure refraction and reflection may not correspond in all circumstances to what is most often seen clinically, i.e., a sharp, discrete shadow projecting down from the edge. We used a tissue-mimicking contrast detail phantom, speed of sound (SOS) 1477 m/s, containing cylindrically shaped wells to investigate the origin of these shadows. Using solutions of relatively high SOS (20% ethylene glycol), approximately equivalent SOS (distilled water), and low SOS (70% isopropyl alcohol), the phantom was scanned with the scanhead face oriented perpendicular to and parallel to the central axes of the cylinders. Shadowing could be produced in both cases when there was a SOS difference between the contents of the cylinders and the phantom. When scanning perpendicular to the cylinders, refraction and reflection effects could have contributed to any shadowing produced, but when the scan planes were oriented parallel to the central axes of the cylinders, neither refraction nor reflection could be occurring to a significant degree. The shadowing produced in these circumstances could be better explained by a phenomenon well known in transmission ultrasonography called phase cancellation. Phase cancellation would produce shadowing independent of scan plane orientation, and could contribute to the shadowing generated in clinical imaging.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29542/1/0000630.pd

Quantitative tissue motion analysis of digitized m-mode images: Gestational differences of fetal lung

Quantitative analysis of transmitted cardiac motion in fetal lung is evaluated by applying correlation techniques to digitized M-mode images in 21 patients, subdivided into two subgroups by gestational age: (1) 25-30 weeks (11 patients), and (11) >=35 weeks (10 patients). The corresponding numbers of M-mode images analyzed for each group are 23 and 18, respectively. This partition is expected to reflect functionally "immature" and "mature" lungs. The estimated maximum mean radial deformation per unit epicardial excursion, r I = 0.79 +/- 0.11 (sem) and r II = 0.62 +/- 0.13 (sem). The analysis presented, albeit in a limited population, is indicative of a trend in accordance with qualitative observations of Birnholz and Farrell (1985). M-mode analysis, as indicated by Adler et al. (1989) is a potentially useful technique to quantify such tissue motion.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28898/1/0000735.pd