Elderly patients'' experiences of pain and distress in intensive care: a grounded theory study

Plasma membrane vesicles prepared from the bag region of the somatic muscle cell of the parasite Ascaris suum contain a large conductance, voltage-sensitive, calcium-activated chloride channel. The ability of this channel to conduct a variety of carboxylic acids, a number of which are products of anaerobic respiration, was investigated using the patch-clamp technique and isolated inside-out patches of muscle membrane. The channel has a conductance of 140 pS in symmetrical 140 mM chloride. Replacement of internal chloride with various carboxylic acids (140 mM) caused large hyperpolarizing shifts in the reversal potential. Permeability ratios, relative to chloride, were calculated for each acid. The relationship between permeability ratio and ionic size is inverse and linear predicting a pore diameter of 6.55 A. This simple relationship was not observed between ionic size and conductance. Calculation of the transition state energy required to transfer a single methyl group from aqueous phase to the binding site afforded a value that was low but favorable, indicating a cationic binding site of low field strength. As the channel is able to open fully at the resting membrane potential of Ascaris and is permeable to fatty acids produced by anaerobic respiration, the possible role of this channel in the removal of metabolic products across the muscle membrane is discussed.     

On dynamic effects at folding of coated papers

Folding of coated papers is examined numerically using the finite element method. The analysis is focused on the influence from dynamic effects on the folding process. In particular, the behaviour of field variables relevant for cracking of the coating layers are studied in some detail. The results presented indicate that dynamic effects are of little importance as regards maximum strain levels in the coating but will influence the stress and strain distributions. Accordingly, a quasi-static analysis of the problem will be sufficient in order to describe many of the important features related to cracking.     

Contractile studies of single human skeletal muscle fibers: a comparison of different muscles, permeabilization procedures, and storage techniques

The study of single muscle fibers has improved our understanding of muscle physiology and pathology. To compare three techniques for fiber preparation and storage, biopsies were obtained from the tibialis anterior and vastus lateralis muscles of a hemiparetic patient and a control subject. Single fibers were prepared with: (1) chemical skinning (CS) and storage at -20 degrees C; (2) chemical skinning followed by sucrose (SU) incubation and storage at -80 degrees C; or (3) freeze-drying (FD) and -80 degrees C storage. Cross-sectional area (CSA), resting, maximal (P0), and specific tension (P0/CSA), and maximum shortening velocity (V0) were determined in 189 cells. CSA was similar in all groups. Resting tension was higher and P0 and P0/CSA lower after FD. In general, V0 was the same in all groups. Our data suggest that CS and SU preserve the properties of single muscle fibers better than FD. SU may allow longer storage of fibers.     

Efficient collision detection for models deformed by morphing

Published online: 5 February 2003     

Parabolic-confocal unstable-resonator semiconductor lasers-Modelingand experiments

Surface-emitting all-grating-based unstable-resonator lasers, suitable for integration with diffractive beam-forming elements, have been experimentally and theoretically studied. The lasers exhibit single spatial mode operation for a device width of 160 μm. The device performance is modeled using a beam propagation method, which accounts for spatial hole burning as well as thermal and carrier diffusion effects. Near- and far-field calculations are incorporated to facilitate the comparison with the experimental results. To achieve high-quality beam forming, it is essential that the wavefront of the guided optical mode is well defined and stable. Using the model, we study the dependence of the wavefront distortion on various parameters and show how these distortions affect the far-field characteristics. The results from the simulations agree well with the experimental work. We find that the laser performance is to a large extent controlled by thermal effects. At low-power operation, these effects can be compensated for, for a range of the injection current, by modifications of the resonator or outcoupler grating geometries     

A comparative study of strain relaxation effects on the performanceof InGaAs quantum-well-based heterojunction phototransistors

The performance of a GaAs based heterojunction phototransistors (HPTs) using an n-p-i-n configuration, where the absorption is provided by InGaAs quantum wells (QWs) have been studied. Structures with differing numbers of QW were investigated. This allowed the tradeoff between the benefits of increased light absorption and the drawbacks of increased lattice relaxation, caused by the mis-match between InGaAs and the GaAs substrate, to be examined. All the HPT's investigated showed responsivities (A/W) far larger than unity, as well as large wavelength tolerance, for example 44 A/W±15% from 950-970 nm, for 10 μW incident optical. Electrical common-emitter current gains, of up to 3000 were measured for our HPT's and then confirmed by subsequent HBT measurements. Small relaxation levels (<10%) had no significant detrimental effects, allowing a large improvement in HPT performance. More heavily relaxed HPTs showed a degradation in both the inherent photodetector and transistor action, though this was not catastrophic in nature. A simple simulation of the results is carried out, suggesting that the dislocations adversely effect the carrier transport across the collector region, and also reduce the minority carrier diffusion length in the base     

Low-threshold grating-coupled surface-emitting lasers withetch-stop layer for precise grating positioning

The authors discuss the operation of InGaAs/AlGaAs grating-coupled surface-emitting lasers with threshold-current densities as low as 118 A/cm², to the best of our knowledge the lowest reported for a surface emitter. The low threshold-current density is the result of high reflectivity and low absorption gratings in conjunction with a lateral effective refractive index step in the gain section. The gratings were fabricated using electron-beam lithography and chemically assisted ion-beam etching, producing uniform rectangular gratings. A thin etch-stop layer incorporated in the epitaxial structure made it possible to combine precise control of the grating position with a strained-layer SQW-GRINSCH structure for optimum low-threshold currents     

Inhalation of cold air increases the number of inflammatory cells in the lungs in healthy subjects

Prolonged exposure to cold air may induce a chronic asthma-like condition in healthy subjects as has been demonstrated in cross-country skiers. In the present controlled study, our aim was to elucidate further the link between cold air exposure and airway inflammation by assessing the cellular influx and mediator levels within the airways following acute exposure to cold air. Bronchoalveolar (BAL) and nasal lavages were performed after exposure to cold air (-23 degrees C) and normal indoor air (+22 degrees C) during a light, intermittent work for 2 h in a cross-over design in eight healthy, nonsmoking, subjects. Analyses of inflammatory cell number, cell activation markers, pro-inflammatory cytokines, albumin and interleukin (IL)-8 in lavage fluids were performed. The number of granulocytes and of alveolar macrophages in BAL fluid was significantly higher after cold air exposure (p<0.05). No increase in BAL fluid lymphocytes and no signs of lymphocyte activation in BAL fluid were found. The concentration of IL-8 was unchanged. There were no signs of granulocyte activation (myeloperoxidase, eosinphilic cationic protein) in BAL fluid. Cold air did not influence the number of inflammatory cells or the concentration of albumin and IL-8 in nasal lavage fluid. In conclusion, exposure to cold air induces an increased number of granulocytes and macrophages in the lower airways in healthy subjects without influencing other inflammatory indices such as cellular activation, plasma leakage and pro-inflammatory cytokines. These findings support the hypothesis that cold air could be of pathogenetic importance in the asthma-like condition previously found in cross-country skiers.     

Intramedullary versus extramedullary fixation of subtrochanteric fractures. A biomechanical study

We compared two different subtrochanteric fracture fixation techniques, an intramedullary hip screw system (IMHS) and an extramedullary, dual sliding screw-plate system (MSP), to determine relative fixation stability. 6 matched pairs of osteosynthesized osteopenic cadaver femurs were axially loaded to 1000 N with concurrent, simulated abductor forces of 0%, 50%, or 86% of the applied head force. The initial loading sequence was made with uniaxial dynamization--the lag screw of the MSP locked and distal locking of the IMHS nail. Femoral head displacement and medial femoral strain were measured for intact femur controls, after fixation of a 2-part reverse oblique subtrochanteric fracture and finally a 3-part reverse oblique subtrochanteric fracture with a lateral wedge defect. The samples were then loaded at 750 N for 10(4) cycles with both devices uniaxially locked, followed by 10(4) cycles with both devices fully biaxially dynamized (unlocked). For the 2-part subtrochanteric fracture pattern, both devices exhibited similar inferior displacements of the femoral head (average 2.0 mm) and medial femoral strain (approximately 70% of intact). Increasing abductor forces decreased medial compressive strain but did not significantly affect head displacement. For the 3-part fracture model, the MSP demonstrated significantly less inferior displacement of the head (1.6 mm vs. 2.1 mm) and both devices demonstrated significantly decreased medial strain. After cycling, head displacement increased approximately 50% in both devices and medial strain increased slightly. After unlocking and cycling, the MSP group showed significant lateral displacement of the proximal fragment. The IMHS and MSP devices provide similar stability for fixation of 2-part and 3-part reverse oblique subtrochanteric fractures. In a biaxially dynamized, 3-part reverse oblique fracture, displacement of the proximal fragment can occur with the MSP.