Disk Pressure Research Articles

Axial Compression Frame for MRI of Thoracolumbar Spine

Our objective was to present a method of performing thoracolumbar MRI with intervertebral disk pressure at 150 kPa without the patient being seated. Spine MRI with compression is more physiologic and will produce a higher yield than standard supine MRI.

Effects of Disk Design and Kinematics of Conditioners on Process Hydrodynamics during Copper CMP

This study focuses on determining the effect of conditioner disk design, kinematics, and pressure on the slurry distribution under the wafer as measured by the slurry film thickness between the wafer and the pad during actual polishing. Film thicknesses are measured using dual emission UV-enhanced fluorescence, which for thickness measurement requires the slurry to be tagged with two different fluorescent dyes. Results indicate that the wafer is tilted toward the center of the pad and that the extent of wafer tilt is a strong function of conditioning disk pressure. Increasing the oscillation frequency of the conditioner disk or the rotation rate decreases the slurry film thickness and the film thickness increases with slurry flow rate.

The Molecular Gas Distribution and Schmidt Law in M33

The relationship between the star formation rate and surface density of neutral gas within the disk of M33 is examined with new imaging observations of CO J=1-0 emission gathered with the FCRAO 14m telescope and IRAS HiRes images of the 60 micron and 100 micron emission. The Schmidt law, Sigma_SFR ~ Sigma_gas^n, is constructed using radial profiles of the HI 21cm, CO, and far infrared emission. A strong correlation is identified between the star formation rate and molecular gas surface density. This suggests that the condensation of giant molecular clouds is the limiting step to star formation within the M33 disk. The corresponding molecular Schmidt index, n_{mol}, is 1.36 +/- 0.08. The star formation rate has a steep dependence on total mass gas surface density, (Sigma_{HI}+Sigma_{H_2}), owing to the shallow radial profile of the atomic gas which dominates the total gas surface density for most radii. The disk pressure of the gas is shown to play a prominent role in regulating the molecular gas fraction in M33.

Swing Check Valve Characterization and Modeling During Transients

The hydraulic torque on the disk of a swing check valve strongly influences the dynamic valve-fluid interaction. This torque is difficult to quantify. In this study, the hydraulic torque is separated into a torque due to flow around a stationary disk and a torque due to disk rotation. Laboratory tests have been conducted to characterize these components. Numerical simulations of a check valve slam are made and the results compared with measured disk angle and pressure traces. The validity of the hydraulic torque characterization is demonstrated by the close agreement between the simulation results and the measurements.

Subcooled water critical pressure and critical flow rate in a safety valve

Subcooled water critical flow phenomena in a safety valve are investigated experimentally at various subcoolings between 10 and 125 K, and about 1 MPa of the inlet pressure with three different disk lifts, 1, 2, and 3 mm. The purpose of this experiment is to find the effects of subcooling and disk lift and to visualize flow patterns in a safety valve when the critical condition is established. All of the experiments show the critical characteristics such as constant throat pressure and constant flow rate when the back pressure is sufficiently decreased. Two correlations, critical pressure ratio and non-equilibrium factor, are developed by using the present experimental data represented in the form of non-dimensional disk lift, subcooling, and pressure. Critical pressure ratios and non-equilibrium factors are considerably affected by different subcoolings while the effect of disk lifts on them is relatively small. A non-equilibrium critical mass flow correlation for the safety valve is also developed based on Fauske's non-equilibrium model and the presented experimental data. The predictions of the correlation are within ±11% of the experimental data.

ITAL]HUBBLE SPACE TELESCOPE[/ITAL][ITAL]Hubble Space Telescope[/ITAL] Observations of the Interacting Galaxies NGC 2207 and IC 2163

Hubble Space Telescope (HST) images of the galaxies NGC 2207 and IC 2163 show star formation and dust structures in a system that has experienced a recent grazing encounter. Tidal forces from NGC 2207 compressed and elongated the disk of IC 2163, forming an oval ridge of star formation along a caustic where the perturbed gas rebounded after its inward excursion. Gas flowing away from this ridge has a peculiar structure characterized by thin parallel dust filaments transverse to the direction of motion. The filaments become thicker and longer as the gas approaches the tidal arm. Star formation that occurs in the filaments consistently lags behind, as if the exponential disk pressure gradient pushes outward on the gas but not on the young stars. Numerical models suggest that the filaments come from flocculent spiral arms that were present before the interaction. The arms stretch out into parallel filaments as the tidal tail forms. A dust lane at the outer edge of the tidal tail is a shock front where the flow abruptly changes direction. Gas at small-to-intermediate radii along this edge flows back toward the galaxy, while elsewhere in the tidal arm, the gas flows outward. A spiral arm of NGC 2207 that is backlit by IC 2163 is seen with HST to contain several parallel, knotty filaments spanning the full width of the arm. These filaments are probably shock fronts in a density wave. The parallel structure suggests that the shocks occur in several places throughout the arm, or that the interarm gas is composed of spiral-like wisps that merge together in the arms. Blue clusters of star formation inside the clumps of these dust lanes show density-wave triggering in unprecedented detail. The star formation process seems to be one of local gravitational collapse, rather than cloud collisions. Spiral arms inside the oval of IC 2163 have a familiar geometry reminiscent of a bar, although there is no obvious stellar bar. The shape and orientation of these arms suggest they could be the result of inner Lindblad resonance–related orbits in the cos 2θ tidal potential that formed the oval. Their presence suggests that tidal forces alone may initiate a temporary nuclear gas flow and eventual starburst without first forming a stellar bar. Several emission structures resembling jets or conical flows that are 100–1000 pc long appear in these galaxies. In the western arm of NGC 2207, there is a dense dark cloud with a conical shape 400 pc long and a bright compact cluster at the tip, and there is a conical emission nebula of the same length that points away from the cluster in the other direction. This region also coincides with a nonthermal radio continuum source that is ~1000 times the luminosity of Cas A at λ = 20 cm. Surrounding clusters in arclike patterns may have been triggered by enormous explosions.

Magnetized Accreting Stars: Studies of the Inner Accretion Disk Edge by a Magnetohydrodynamical Approach. I. Construction and Analysis of Magnetopause Equilibria

In this paper a numerical model of the interaction between the accretion disk and the magnetosphere of an accreting object (e.g., a neutron star) is used to study mechanisms that can lead to fast accretion of matter due to magnetic forces. The framework of magnetohydrodynamics (MHD) provides a simple but powerful tool for such a study on a semiglobal scale. The aim of this work is the construction of stationary states that describe the inner-edge region of the accretion disk with the star's rotating magnetosphere supporting the inner disk edge against gravitation. The equilibrium magnetic fields are computed numerically by a finite difference scheme using the magnetofriction method within ideal magnetohydrodynamics. To study the mass loading onto the magnetosphere we vary disk mass density and pressure. Magnetosphere rotation speed and magnetopause thickness are additonal variables contributing to the shape of the magnetosphere and the currents in the magnetopause at the disk edge.

Optimisation of procedures for microprojectile bombardment of microspore-derived embryos in wheat

Using the PDS-1000/He Biolistic® Particle Delivery System, the microprojectile travel distance, rupture disk pressure and DNA/gold particle concentrations were assessed in order to optimise short and longer-term β-glucuronidase reporter gene expression in microspore-derived embryos of wheat. The effects were also evaluated of using sterile filter paper to support explants and treatment with a high osmoticum medium (0.2 M mannitol/0.2 M sorbitol or 0.4 M maltose). In the optimised procedure, wheat microspore-derived embryos (MDEs), were placed on filter paper and incubated on medium containing 0.4 M maltose, for 4 h pre- and 45 h post-bombardment. Five μl pAHC25 (0.75 mg ml-1 in TE buffer) was precipitated onto 25 μl gold particles (60 mg ml-1 in sterile water), using 20 μl spermidine (0.1 M) and 50 μl CaCl2 (2.5 M). The particles were centrifuged and resuspended in 75 μl absolute ethanol prior to the preparation of 6 macrocarriers. A microprojectile travel distance of 70 mm, a rupture pressure of 1300 p.s.i., and a vacuum of 29′′ Hg were employed. Maltose at 0.4 M in the support medium was the most important factor influencing GUS activity in bombarded tissues. GUS activity, 1 day post-bombardment, reached 52 ± 17 GUS-positive foci/MDE (mean ± s.e.m, n=3), with 17 ± 4 foci/MDE at 15 days, giving a 3.0-fold increase (p<0.05) compared to expression in MDEs bombarded on medium without a high osmoticum treatment.

Transonic Magnetic Slim Accretion Disks and Kilohertz Quasi‐periodic Oscillations in Low‐Mass X‐Ray Binaries

The inner regions of accretion disks of weakly magnetized neutron stars are affected by general relativistic gravity and stellar magnetic fields. Even for field strengths sufficiently small so that there is no well-defined magnetosphere surrounding the neutron star, there is still a region in the disk where magnetic field stress plays an important dynamical role. We construct magnetic slim disk models appropriate for neutron stars in low-mass X-ray binaries (LMXBs), which incorporate the effects of both magnetic fields and general relativity (GR). The magnetic field-disk interaction is treated in a phenomenological manner, allowing for both closed- and open-field configurations. We show that even for surface magnetic fields as weak as 107-108 G, the sonic point of the accretion flow can be significantly modified from the pure GR value (near rGR = 6GM/c2 for slowly rotating neutron stars). We derive an analytical expression for the sonic radius in the limit of small disk viscosity and pressure. We show that the sonic radius mainly depends on the stellar surface field strength B0 and mass accretion rate ${u{M}{705F}}$ --> through the ratio b -->2 βB -->20/${u{M}{705F}}$ -->, where β |B/Bz| measures the azimuthal pitch angle of the magnetic field threading the disk. The sonic radius thus obtained approaches the usual Alfven radius for high b2 (for which a genuine magnetosphere is expected to form) and asymptotes to 6GM/c2 as b2 → 0. We therefore suggest that for neutron stars in LMXBs, the distinction between the disk sonic radius and the magnetosphere radius may not exist; there is only one generalized sonic radius, which is determined by both the GR effect and the magnetic effect. We apply our theoretical results to the kilohertz (kHz) quasi-periodic oscillations (QPOs) observed in the X-ray fluxes of LMXBs. If these QPOs are associated with the orbital frequency at the inner radius of the disk, then the QPO frequencies and their correlation with mass accretion rate can provide useful diagnostics on the (highly uncertain) nature of the magnetic field-disk interactions. In particular, a tight upper limit to the surface magnetic field B0 can be obtained, i.e., B0 3 × 10 -->7(${u{M}{705F}}$ --> -->17/β) -->1/2 G, where ${u{M}{705F}}$ --> -->17=${u{M}{705F}}$ -->/(10 -->17 g s-1), in order to produce kHz orbital frequency at the sonic radius. Current observational data may suggest that the magnetic fields in LMXBs have complex topology.

A REVIEW OF THE BIOMECHANICS AND EPIDEMIOLOGY OF WORKING POSTURES (IT ISN'T ALWAYS VIBRATION WHICH IS TO BLAME!)

Many vibrational environments also subject the worker to awkward, asymmetric and prolonged postures. This paper reviews the epidemiological, biomechanical and physiological factors involved in working postures which could lead to musculoskeletal problems. Too little or too much sitting leads to low back pain. Sedentary postures, including driving, also lead to a higher risk of a herniated disc. In sitting the pelvis rotates and higher pressures exist in the disk. A backrest inclined to 110° or more and with a lumbar support will reduce the disk pressure. Jobs involving excessive force application will be more apt to cause muscular and ligamentous damage. However, these excessive demands can occur in whole body vibration environments too. Neck, shoulder and arm problems are usually related to posture but can occur in WBV environments. Knee problems, in the standing worker, may be due to a flexed knee posture in an attempt to attenuate vibrations. Excessive postural demands on the neck, shoulder and arm will lead to higher muscle forces and higher joint forces. Recommendations are given to reduce risk of disability.

Hydrogen Embrittlement Characterization by Disk Pressure Tests: Test Analysis and Application to High Chromium Martensitic Steels

The paper reports and discusses the results of an experimental and numerical activity, aimed to the characterization of the influence of hydrogen on the mechanical properties of a few high chromium martensitic steels which are candidates for fusion reactor and chemical applications. Experiments were conducted with the Disk Pressure Test technique, according to which a circular thin specimen is loaded up to rupture by an uniform pressure. As a detailed analysis of the stress/strain distributions in the specimen was not available, this kind of test being mainly used to obtain comparative information about different materials, a nonlinear numerical (Finite Element) model of the specimen was set up, by which stress and strain could be accurately evaluated as a function of the applied pressure. This model was employed both for interpreting experimental results and to achieve a more general understanding of the capabilities of the Disk Pressure Test for the characterization of hydrogen embrittlement effects. The calculated strain at failure showed the typical dependence on hydrogen content, falling to very low levels as a threshold concentration is exceeded.

Autotraction Treatment for Low-Back Pain Syndromes

Autotraction (AT) is a form of exercise for low back pain. The patient lies on a specially designed bench with the pelvis anchored and while grasping an overhead bar, pulls him or herself. The patient should not feel any pain. To ensure painless pulling efforts during treatment, the table allows three-dimensional adjustments to the alignment of the patient's trunk. Although the method was originally designed for patients with acute pain, it has been found that 3-6 half-hr outpatient sessions provide relief from pain in 50−60% of patients with long-lasting low back pain with or without sciatic nerve involvement. This includes patients with verified lumbar disc herniation and those who have been refractory to previous conservative or surgical treatments. The aim of passive forms of traction and of conventional exercise regimens is to decrease intervertebral disk pressure; in contrast, studies have demonstrated that autotraction is associated with sharp rises in intervertebral disc pressure. This mechanism of action still needs to be verified. It has been suggested that relief of pain with autotraction may be due to favorable microscopic changes at the disc-nerve interface or to decongestion of engorged epidural veins.

Preparation of pore-free disk of La 1− xSr xCoO 3 mixed conductor and its oxygen permeability

Pore-free disks of La 1− x Sr x CoO 3 ( x=0.4, 0.5, 0.6) as one of the mixed conductive perovskite-type oxides were successfully prepared, where a powder precursor having not yet the perovskite structure was selected as a starting material. The rate of oxygen permeation through the La 1− x Sr x CoO 3 disk was found to increase with an increment in Sr content, and to be mainly controlled by the amount of oxygen vacancy. Effects of thickness of the disk and oxygen partial pressure on the oxygen permeation rate could be elucidated by the electrochemical transport equation. In conclusion, La 1− x Sr x CoO 3 is a promising material for oxygen permeation at high temperatures.

GENETIC TRANSFORMATION OF ROSE (ROSA SPP) USING THE BIOLISTIC PROCESS

Genetic transformation of cut roses may greatly facilitate cultivar improvement programs by shortening the time required to introduce new genes into elite germplasm. The biolistic process offers a very promising method for the genetic transformation of roses.Several factors that have a significant affect on transformation efficiency were examined in an effort to optimize the biolistic process for gene transfer in roses. The factors examined were type of tissue (leaf segments, petioles, callus, etc.), bombardment distance, the number of bombardments, DNA construct and microcarrier velocity.Two constructs of the reporter gene, β-GUS, were examined to determine which construct provided the highest level of expression. Only the construct designated pBI 426 provided β-GUS positive cells in leaf and callus tissue. This construct was used in all subsequent experiments.Experiments to find the optimum number of bombardments and rupture disk pressure were carried out using leaf and callus tissue and 1.6 μm gold particles. The optimum number of bombardments per sample was three for leaf tissue. The optimum rupture disk pressure was 900 p.s.i. for leaf and callus tissue.Meristems of axillary buds are being bombarded in situ on stem-bud explains. These should yield transgenic rose plantlets in 3 to 4 weeks.

Vibration of the Spine and Low Back Pain

There are now many studies suggesting a positive relationship between both low back pain and spinal degeneration and exposure to whole body vibration. Such relationships appear to be particularly marked in drivers of tractors, earth-moving equipment, and trucks. There is a tendency toward a greater incidence of complaints as exposure increases. Vibration affects the spine by exciting a 4-6-Hz resonance that is related to the biologic "soft spring" between S-1 and the seat. The muscle nerves fire sequentially under vibration and fatigue. In animals, vibration exposure leads to pronounced creep, increased disk pressure, and changes in the levels of neuropeptides in the dorsal root ganglia.

Nonlinear gross response analysis of a lumbar motion segment in combined sagittal loadings.

A 3-D nonlinear mathematical model is used to analyze the mechanical response of a lumbar L2-3 motion segment including the posterior elements when subjected to combined sagittal plane loads. The loadings consist of axial compression force, anterior and posterior shear forces, and flexion and extension moments. The facet articulation is modelled as a general moving contact problem and the ligaments as a collection of uniaxial elements. The disk nucleus is considered as an inviscid fluid and the annulus as a composite of collagenous fibers embedded in a matrix of ground substance. The presence of axial compression force reduces the segmental stiffness in flexion whereas a reverse trend is predicted in extension. In the presence of axial compression with and without sagittal shear force, flexion considerably increases the intradiscal pressure while extension reduces it. In other words, under an identical compression force, disk pressure is predicted to be noticeably larger in flexion than in extension. The segmental mechanical response in extension loadings is markedly influenced by the changes in the relative geometry of the articular surfaces at the lower regions. Finally, the deformation of the bony structures plays a significant role in the segmental mechanics under relatively large loads.

Augmentation of pressure in a vessel indenting the surface of the lung.

The lungs and intrathoracic cardiovascular structures compete for space within the thorax, interacting through their adjacent surfaces via the pleural space. Theoretical analysis and in vitro model studies (detailed here) established that when a vessel indents the lung surface, the increase in intravascular pressure with positive pressure lung inflation can be greater than the change in the pleural surface pressure measured outside of the interaction area. We define this phenomenon as intravessel pressure augmentation. We determined the average intravessel pressure gain as the slope of the linear regression of the pressure in a vascular structure or balloon indenting the lung on the pleural surface pressure measured by a flat disk-shaped device (disk). The analysis showed that the disk pressure overestimates the pleural pressure. Therefore, the derived pressure gain underestimated the pressure augmentation. In five dogs, the disk and a 2-ml balloon were placed in the lateral pleural space, and a segment of IVC was ligated at both ends and filled with saline. The dogs were ventilated with fixed tidal volumes, while the positive end-expiratory pressure was changed. The pressures were compared at the end of expiration. For the IVC segment, the pressure gains under four different tidal volumes were significantly greater than one [95% confidence interval of mean value (CIM) = 1.57 +/- 0.16, P less than 10(-4)], and for the small balloon, this was the case for three of four tidal volumes (95% CIM for all four volumes 1.13 +/- 0.04, P less than 10(-4)). We conclude that the surface interaction of the lungs with adjacent cardiovascular structures causes appreciable pressure augmentation in those structures during ventilation with the positive end-expiratory pressure.

Glaucoma without ocular hypertension. A clinical study

One hundred eighty-four glaucomatous eyes (125 patients) with visual field defects of Stage I and II in the central visual field were examined with the Octopus perimeter 201, Program 31 or 33, and were divided into 3 groups according to maximum intraocular pressures: (1) low-tension glaucoma (21 mm Hg), (2) glaucoma simplex (22-29 mm Hg), (3) glaucoma simplex (30-39 mm Hg). In these three groups of glaucomatous eyes the cupping of the optic disk, vision and blood pressure were examined and a further check for cardiovascular risk factors was carried out by the internist. All three groups proved to have an equally high incidence of cardiac insufficiency, abnormal EKG changes and diabetes. However, a low systolic blood pressure was found to be the risk factor more often in patients with low-tension glaucoma than with glaucoma simplex. Furthermore, intraocular pressures in the low-tension glaucoma group were higher than those in the normal population. The occurrence of cupping of the optic disk, which is not present with purely vascular optic nerve diseases, and the location of visual field defects in low-tension glaucoma, which is similar to that in glaucoma simplex but different from vascular diseases, as well as the increased diurnal tension variations of diurnal tension curves compared to the normal population are all factors which indicate that low-tension glaucoma is not a purely vascular optic nerve disease, and that pressure-lowering therapy is necessary.(ABSTRACT TRUNCATED AT 250 WORDS)

Self-regulating galaxy formation. I - H II disk and Lyman-alpha pressure

view Abstract Citations (23) References (11) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Self-regulating galaxy formation. I. H II disk and Lyman-alpha pressure. Cox, D. P. Abstract The nascent interstellar medium and star formation model are incorporated into a scenario for the formation epoch of spiral galaxies. The structure, star formation time scale, and luminosity of a self-gravitating isothermal disk are evaluated as functions of the disk surface density. The importance of radiation pressure, particularly that of Lyman-alpha, in maintaining an inflated disk and halting infall is discussed. The Lyman-alpha pressure also supports a considerable halo of material in the vicinity of the disk. A first-order infall scenario and the time-dependent properties of the system it constructs are presented. Disk properties are evaluated at the epoch at which further material is supportable against infall by Lyman-alpha pressure. The two-dimensional family of disk galaxies whose scales and surface density are expressible in terms of fundamental constants and which arise from the three parameter sets of perturbations in the Hubble flow are determined. Publication: The Astrophysical Journal Pub Date: January 1985 DOI: 10.1086/162812 Bibcode: 1985ApJ...288..465C Keywords: Disk Galaxies; Galactic Evolution; Hydrogen Clouds; Lyman Alpha Radiation; Radiation Pressure; Astronomical Models; Galactic Radiation; Interstellar Matter; Stellar Evolution; Astrophysics full text sources ADS | data products SIMBAD (2) NED (2)

Response of an advanced head-neck model to transient loading.

A second-generation mechanical head-neck model was constructed, instrumented and subjected to pendulum impact tests against both the head and torso and directed from the front, rear and side. The response history of the system was measured by thirty channels of instrumentation including disk pressure transducers and muscle displacement gages in the neck, and a central accelerometer, intracranial pressure transducers and skull strain gages for the cranium and its contents. The kinematics of the unit was observed by an intermediate speed framing camera and the input was determined by a calibrated force transducer located at the contact point. It was found that peak head linear acceleration and velocity occur either during or immediately after the impact, with corresponding peak rotational values manifested somewhat later, but well before maximum head displacement. Head accelerations were similar, albeit slightly lower than in corresponding cases for an earlier model and displacement values were also similar until large extensions were reached. For rear head or frontal base impact, the head experienced a significant period of translation without rotation immediately after loading, and the system appears to respond more violently to side than to corresponding front or rear impact. The muscle beahvior, which support the findings from the head kinematics, is analyzed in detail and shows its strong influence on limiting head excursions, with strain values up to 40 percent. Disk pressure histories were similar to those found in tests on an earlier model with the highest values between T2 and C4, while the intercranial pressure exhibited more realistic values, about an order of larger magnitude.