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At least 1,189 records · Page 66Linked to original sources
PubMed1983

Multiaxial strength characteristics of trabecular bone.

Bovine trabecular bone specimens were tested in multiaxial stress, including pure shear, in a special test device. Shear strength was proportional to apparent density to the exponent 1.65, in approximate agreement with theoretical and experimental studies on the shear strengths of porous foams. The mean shear strength was 6.60 +/- 1.66 MPa, after normalizing for apparent density. This compares well with normalized shear strengths from Saha and Gorman's (1981) study on human femora. A scanning electron microscope study indicated random trabecular architecture and a complex fracture mechanism at the level of the individual trabecular struts. Hoffmann's (1967) 3-D isotropic failure criterion was applied to the multiaxial test data, along with data from uniaxial compression tests, indicating a compressive strength approximately three times the tensile strength.

Animals↗
PubMed1994

PACS in Osaka University Hospital.

To develop the hospital information system, the radiological information system, and the picture archiving and communication system for our new hospital, we analysed the data volume at each step of the flow in our present film-based system. After that, we used a small PACS, and it indicated the problems in it. From the analysis of the data volume of the film-based system, it was found out that digital data should be compressed, and prefetching techniques should be employed for digital PACS. Several types of display terminals had been proved to be necessary for different purposes. An RIS connection was thought to be obligatory to avoid incorrect input of ID on the image. Image input terminals should have edit functions for easy recognition of the image information. Taking account of these requirements for digital PACS, we are developing an actual total PACS.

Computer Terminals↗
PubMed2006

Thermodynamic characterization of the prevailing molecular interactions in mixed floating monolayers of phospholipids and usnic acid.

The investigation of the characteristics of mixed floating monolayers of phospholipids and usnic acid (UA), an active metabolite from lichens, can provide valuable information on how to prepare stable liposomes that could serve as carriers of UA for therapeutic proposes. The present paper is concerned with the thermodynamic analysis of the behavior of Langmuir monolayers formed by mixing different phospholipids (dibehenoylphosphatidylcholine, DBPC, dipalmitoylphosphatidylcholine, DPPC, and dioleoylphosphatidylcholine, DOPC) and UA at varied molar fractions. Relevant thermodynamic parameters such as excess areas, excess free energies and free energy of mixing were derived from the surface pressure data obtained from compression measurements performed in a Langmuir trough. For the largest lateral pressure examined (25 mN/m), negative values of the excess free energy were found only for the DOPC/UA monolayer, which should be the most stable of them. Based on the calculated values of the free energy of mixing, we note that the DBPC/UA and DPPC/UA systems present the best mixed character at low pressures and when the molar fraction of the UA is 0.5; at that relative concentration and at low values of the external pressure, the UA molecules can better mix and interact with the phospholipid molecules. The compression isotherms for mixed monolayers show no visible transitions, exhibiting a more organized phase that corresponds to a negative free energy of mixing. We have established that the most stable monolayers were those corresponding to DOPC/UA mixtures with a UA molar fraction of 0.75.

Benzofurans↗
PubMed2006

Relative income, race, and mortality.

This paper examines the relationship between relative income and mortality. Our research is motivated by recent literature that posits that, holding individual income fixed, those whose income are low relative to the incomes of those in a reference group will have worse health. We develop an empirical model in which an individual's health is a function of his or her own income and the incomes of those who live in the same geographical area. We show how this individual-level model can be estimated using semi-aggregated data on the mortality rates of people categorized by age, race, gender, and place of residence. The model is estimated using mortality data from the 1980 and 1990 Compressed Mortality Files, merged with income data from the 1980 and 1990 5% Public Use samples of the US Census. We find no evidence that having relatively wealthy neighbors, holding own income fixed, is associated with higher mortality. Instead, we find evidence that among some demographic and age groups--in particular working-aged black males--having relatively wealthy neighbors is associated with lower mortality. For example, among younger (aged 25-64) black men, an increase in the income of others is estimated to have a beneficial effect on mortality that is 40% as large as an equivalent increase in own income.

Adolescent↗
PubMed2005

Carotid compression: investigation of cerebral autoregulative reserve in rats.

Easy-to-perform, reversible techniques to analyse cerebral autoregulation are still missing in animal research. The carotid compression technique has been established to investigate dynamic cerebral autoregulation in humans. Adapting the carotid compression technique, we compared data from the new application with that of a classical exsanguination method. Compressing the ipsilateral carotid artery with a non-traumatic clip device for 10s modulated cerebral perfusion pressure. After clip release, the peaking laser-Doppler flow velocity increase over the somatosensory cortex allowed calculation of the transient hyperaemic response ratio (THRR) in relation to baseline. Modulating blood-pressure levels maintenance of cerebral blood-flow velocity was compared with THRR responses. With decreasing blood-pressure levels, the THRR first increased (29+/-16% at 95+/-10 mmHg to 39+/-13% at 75+/-10 mmHg) before it returned to baseline values at 54+/-10 mmHg (27+/-14%). THRR significantly dropped to 11+/-12% at 34+/-11 mmHg when resting cerebral blood-flow velocity levels also started to decline. Based on the close correlation between blood-flow velocity levels and THRR responses, we have concluded that carotid compression is an alternative technique that can be used to assess cerebral autoregulation in rats. The technique allows less invasive and reversible testing of dynamic autoregulation to be performed, and the technique can easily be applied in conjunction with functional tests to potentially allow deeper insights into cerebral vasoregulative mechanisms.

Algorithms↗
PubMed1997

Hindered transport of macromolecules in isolated glomeruli. II. Convection and pressure effects in basement membrane.

The filtration rates for water and a polydisperse mixture of Ficoll across films of isolated glomerular basement membrane (GBM) were measured to characterize convective transport across this part of the glomerular capillary wall. Glomeruli were isolated from rat kidneys and the cells were removed by detergent lysis, leaving a preparation containing almost pure GBM that could be consolidated into a layer at the base of a small ultrafiltration cell. A Ficoll mixture with Stokes-Einstein radii ranging from about 2.0 to 7.0 nm was labeled with fluorescein, providing a set of rigid, spherical test macromolecules with little molecular charge. Filtration experiments were performed at two physiologically relevant hydraulic pressure differences (delta P), 35 and 60 mmHg. The sieving coefficient (filtrate-to-retentate concentration ratio) for a given size of Ficoll tended to be larger at 35 than at 60 mmHg, the changes being greater for the smaller molecules. The Darcy permeability also varied inversely with pressure, averaging 1.48 +/- 0.10 nm2 at 35 mmHg and 0.82 +/- 0.07 nm2 at 60 mmHg. Both effects could be explained most simply by postulating that the intrinsic permeability properties of the GBM change in response to compression. The sieving data were consistent with linear declines in the hindrance factors for convection and diffusion with increasing pressure, and correlations were derived to relate those hindrance factors to molecular size and delta P. Comparisons with previous Ficoll sieving data for rats in vivo suggest that the GBM is less size-restrictive than the cell layers, but that its contribution to the overall size selectivity of the barrier is not negligible. Theoretical predictions of the Darcy permeability based on a model in which the GBM is a random fibrous network consisting of two populations of fibers were in excellent agreement with the present data and with ultrastructural observations in the literature.

Animals↗
PubMed2001

An extensometer for global measurement of bone strain suitable for use in vivo in humans.

An axial extensometer able to measure global bone strain magnitudes and rates encountered during physiological activity, and suitable for use in vivo in human subjects, is described. The extensometer uses paired capacitive sensors mounted to intraosseus pins and allows measurement of strain due to bending in the plane of the extensometer as well as uniaxial compression or tension. Data are presented for validation of the device against a surface-mounted strain gage in an acrylic specimen under dynamic four-point bending, with square wave and sinusoidal loading inputs up to 1500 mu epsilon and 20 Hz, representative of physiological strain magnitudes and frequencies. Pearson's correlation coefficient (r) between extensometer and strain gage ranged from 0.960 to 0.999. Mean differences between extensometer and strain gage ranged up to 15.3 mu epsilon. Errors in the extensometer output were directly proportional to the degree of bending that occurs in the specimen, however, these errors were predictable and less than 1 mu epsilon for the loading regime studied. The device is capable of tracking strain rates in excess of 90,000 mu epsilon/s.

Bone and Bones↗
PubMed1999

The Telemedicine benchmark--a general tool to measure and compare the performance of video conferencing equipment in the telemedicine area.

In this paper, we describe the 'Telemedicine Benchmark' (TMB), which is a set of standard procedures, protocols and measurements to test reliability and levels of performance of data exchange in a telemedicine session. We have put special emphasis on medical imaging, i.e. digital image transfer, joint viewing and editing and 3D manipulation. With the TMB, we can compare the aptitude of different video conferencing software systems for telemedicine issues and the effect of different network technologies (ISDN, xDSL, ATM, Ethernet). The evaluation criteria used are length of delays and functionality. For the application of the TMB, a data set containing radiological images and medical reports was set up. Considering the Benchmark protocol, this data set has to be exchanged between the partners of the session. The Benchmark covers file transfer, whiteboard usage, application sharing and volume data analysis and compression. The TMB has proven to be a useful tool in several evaluation issues.

Benchmarking↗
PubMed1997

Effects of cholesterol on membrane surfaces as studied by high-pressure fluorescence spectroscopy.

We have studied the effects of cholesterol on membrane surfaces using fluorescence spectroscopy at high pressure. At atmospheric pressure, the dissociation state of a pH-sensitive fluorophore (6-decanylnaphthol or DECNA) incorporated into several types of membranes showed an apparent increase in dissociation with cholesterol content coming somewhat closer to its dissociation state in solution. Previous studies have shown that when DECNA is free in solution, pressure induces proton dissociation due to the volume decrease that occurs when water electrostricts around the ions. But in phosphatidylcholine (PC) bilayers, proton dissociation is inhibited, either due to the inability of the surface to expand and allow for increased hydration, or other changes in lipid structure. The pressure behavior of DECNA in dioleoyl-PC, dioleoylphosphatidic acid and dioleylphosphatidylglycerol bilayers shows that incorporation of 5-10% cholesterol causes DECNA to behave like it is in a more unrestricted environment. This trend is reversed at higher cholesterol concentrations. These data, together with compressibility measurements, support the model of Sankaram and Thompson [M. Sankaram, T.E. Thompson, Biochemistry 29 (1990) 10676.] whereby in the disordered phase, cholesterol can span the two leaflets causing an increase in the area between the head groups; whereas in the ordered phase, no expansion occurs. Thus, the effect of cholesterol on membrane surfaces depends on its phase diagram.

Journal Article↗
PubMed1999

A critical evaluation of the Heckel equation.

Great differences between published Heckel parameters, obtained from 'at pressure' data or the 'in-die' method, are outlined. The general validity of the concept of yield pressures derived from slopes of such Heckel plots is questioned. When the ability of the Heckel and the Walker equations is compared to fit density/pressure data from tabletting different pharmaceutical powders, a generally better fit is obtained with the Walker equation in the region of 5-100 MPa. The ability to discriminate between materials by data from the compression phase is improved by using the Walker model. For Emcompress(R), apparent yield pressures derived from Heckel plots are dependent strongly on the maximum pressure of the compression process.

Acetaminophen↗
PubMed2000

Risk of complications from bone metastases in breast cancer. implications for management.

A retrospective analysis of 859 patients who developed bone metastases from breast cancer between 1975 and 1991 was performed in order to identify factors that predict for complications from skeletal disease. The patients were divided into four groups based on the sites of disease at diagnosis of skeletal metastases: bone disease only; bone and soft tissue disease; bone and pleuro-pulmonary disease; bone and liver disease. Patients with metastatic disease confined to the skeleton were most likely to develop a pathological fracture. The time to long bone fracture was similar for all groups, but the least number of such fractures occurred in patients with bone and liver metastases since their survival was shortest (median: 5.5 months; P<0.001). Patients with bone metastases only were most likely to require radiotherapy to painful osseous deposits (P=0.0001) and most rapidly developed spinal cord compression (P=0.01, data not shown). The results suggest that patients with disease confined to the skeleton at the diagnosis of bone metastases are most likely to develop skeletal-related complications from advanced breast cancer. Such patients may benefit most from treatment with bisphosphonates.

Bone Neoplasms↗
PubMed2001

Olefin metathesis in supercritical carbon dioxide.

Liquid or supercritical carbon dioxide (scCO(2)) is a versatile reaction medium for ring-opening metathesis polymerization (ROMP) and ring-closing olefin metathesis (RCM) reactions using well-defined metal catalysts. The molybdenum alkylidene complex 1 and ruthenium carbenes 2 and 3 bearing PCy(3) or N-heterocyclic carbene ligands, respectively, can be used and are found to exhibit efficiency similar to that in chlorinated organic solvents. While compound 1 is readily soluble in scCO(2), complexes 2 and 3 behave like heterogeneous catalysts in this reaction medium. Importantly, however, the unique properties of scCO(2) provide significant advantages beyond simple solvent replacement. This pertains to highly convenient workup procedures both for polymeric and low molecular weight products, to catalyst immobilization, to reaction tuning by density control (RCM versus acyclic diene metathesis polymerization), and to applications of scCO(2) as a protective medium for basic amine functions. The latter phenomenon is explained by the reversible formation of the corresponding carbamic acid as evidenced by (1)H NMR data obtained in compressed CO(2). Together with its environmentally and toxicologically benign character, these unique physicochemical features sum up to a very attractive solvent profile of carbon dioxide for sustainable synthesis and production.

Journal Article↗
PubMed2001

Why do we SLIP to the basic level? Computational constraints and their implementation.

The authors introduce a new measure of basic-level performance (strategy length and internal practicability; SLIP). SLIP implements 2 computational constraints on the organization of categories in a taxonomy: the minimum number of feature tests required to place the input in a category (strategy length) and the ease with which these tests are performed (internal practicability). The predictive power of SLIP is compared with that of 4 other basic-level measures: context model, category feature possession, category utility, and compression measure, drawing data from other empirical work, and 3 new experiments testing the validity of the computational constraints of SLIP using computer-synthesized 3-dimensional artificial objects.

Adult↗
PubMed1999

Analysis of assisted-gait characteristics in persons with incomplete spinal cord injury.

UNLABELLED: Ambulatory assistive device use can improve functional independence following spinal cord injury and, potentially, quality of life. However, the interaction between aids and user in this population is poorly understood. OBJECTIVES: To determine the influence of walkers, crutches and canes on assisted-gait following incomplete spinal cord injury. STUDY DESIGN/METHODS: Outcome parameters evaluated in ten individuals included orthogonal forces exerted on instrumented assistive devices, walking speed, cadence, step length, trunk and thigh angles, as well as knee and ankle joint angles. Kinetic data included axial compressive force, and medio/lateral and antero/posterior bending forces. SETTING: Canada. RESULTS: Results indicated that walkers (n= 5) provided the greatest vertical support (up to 100% body weight), but resulted in slow gait with a forward flexed posture. Elbow crutch users (n = 3) walked faster (greater step length and cadence) and had a more upright posture than the walker users. Crutches supported up to 50% of the subject's body weight, granted lateral stability, and provided restraint in the antero/posterior direction. Canes (n = 2) offered restraining and propulsive assistance, some lateral stability, and the least amount of vertical support. CONCLUSION: Ambulatory devices affected posture and walking speed while fulfilling various assistive functions during locomotion. The conclusion drawn is that rehabilitation specialists are advised to match device characteristics to user needs when prescribing walking aids. SPONSORSHIP: Natural Sciences and Engineering Research Council of Canada (NSERC).

Adult↗
PubMed1990

The cold face test (diving reflex) in clinical autonomic assessment: methodological considerations and repeatability of responses.

1. Cold stimulus applied to the face causes bradycardia and peripheral vasoconstriction (i.e. the diving reflex), and has been suggested as a test of the autonomic pathways involved. The purpose of this study was to define standard procedures for conducting the test and analysing the responses to the cold face test, to evaluate variability in responses between subjects and within subjects when the same test is repeated, and to examine its usefulness in clinical autonomic assessment. 2. Sixteen (nine female, seven male) healthy adult (21-35 years old) subjects were used. Cold stimulus was applied with gel-filled compresses. Forehead temperature under the compress as an indication of stimulus magnitude, heart rate, blood flow in the finger, toe and calf by venous occlusion plethysmography, and systolic and diastolic blood pressure were monitored. Three protocols were carried out in which the temperature (0, 5, 10, 15 degrees C), placement (whole face, unilateral, forehead) and duration (20, 40, 60, 120 s) of the cold compress application were varied. 3. The data indicate that 0 degrees C compresses applied bilaterally for 40 s produced the maximum bradycardia and peripheral vasoconstriction. No subject found this test to be obnoxious, but a 120 s application was objectionable to some subjects. This cold face test resulted in 22%, 72%, 59% and 44% reductions in heart rate and blood flow to the finger, toe and calf, respectively. There was significant between-subject variability, but good consistency in responses to tests repeated in the same subject on different days, at different times of day and in different seasons.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2003

Comparison of diagnostic quality of motion picture experts group-2 digital video with super VHS videotape for echocardiographic imaging.

BACKGROUND: Motion Picture Experts Group-2 (MPEG2) is a broadcast industry standard that allows high-level compression of echocardiographic data. Validation of MPEG2 digital images compared with super VHS videotape has not been previously reported. METHODS: Simultaneous super VHS videotape and MPEG2 digital images were acquired. In all, 4 experienced echocardiographers completed detailed reporting forms evaluating chamber size, ventricular function, regional wall-motion abnormalities, and measures of valvular regurgitation and stenosis in a blinded fashion. Comparisons between the 2 interpretations were then performed and intraobserver concordance was calculated for the various categories. RESULTS: A total of 80 paired comparisons were made. The overall concordance rate was 93.6% with most of the discrepancies being minor (4.1%). Concordance was 92.4% for left ventricle, 93.2% for right ventricle, 95.2% for regional wall-motion abnormalities, and 97.8% for valve stenosis. The mean grade of valvular regurgitation was similar for the 2 techniques. CONCLUSIONS: MPEG2 digital imaging offers excellent concordance compared with super VHS videotape.

Aortic Valve Insufficiency↗
PubMed2000

Effect of frequency content on categorical loudness normalization.

In this study, increases in loudness with increases in bandwidth, termed loudness summation, were derived from loudness growth functions estimated using a loudness-scaling procedure. The results revealed that at equal loudness category, categorical loudness summation was generally larger in normal-hearing than in hearing-impaired subjects; furthermore, the increase in loudness summation at intermediate loudness levels observed in the former, was absent in the latter. These results, in broad agreement with recent data from the literature, can be explained in the light of physiological data on cochlear compression. One implication of these results regarding hearing aid fitting was that channel-by-channel loudness normalization was effective only when the incoming sound was closed in bandwidth to one of the test stimuli.

Adult↗
PubMed2006

Determination of elastomeric foam parameters for simulations of complex loading.

BACKGROUND: Finite element (FE) analysis has shown promise for the evaluation of elastomeric foam personal protection devices. Although appropriate representation of foam materials is necessary in order to obtain realistic simulation results, material definitions used in the literature vary widely and often fail to account for the multi-mode loading experienced by these devices. This study aims to provide a library of elastomeric foam material parameters that can be used in FE simulations of complex loading scenarios. METHOD OF APPROACH: Twelve foam materials used in footwear were tested in uni-axial compression, simple shear and volumetric compression. For each material, parameters for a common compressible hyperelastic material model used in FE analysis were determined using: (a) compression; (b) compression and shear data; and (c) data from all three tests. RESULTS: Material parameters and Drucker stability limits for the best fits are provided with their associated errors. The material model was able to reproduce deformation modes for which data was provided during parameter determination but was unable to predict behavior in other deformation modes. CONCLUSIONS: Simulation results were found to be highly dependent on the extent of the test data used to determine the parameters in the material definition. This finding calls into question the many published results of simulations of complex loading that use foam material parameters obtained from a single mode of testing. The library of foam parameters developed here presents associated errors in three deformation modes that should provide for a more informed selection of material parameters.

Cellulose↗