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At least 829 records · Page 46Linked to original sources
PubMed1986

Guidelines for external fixation frame rigidity and stresses.

Using results from FEM analyses and experiments as references, analytical methods are applied to develop simple approximate formulas to relate frame rigidity, maximal pin stresses, and peak pin-bone stresses in external fracture fixation (EFF) configurations in axial loading to the most important frame, pin, and bone parameters. It is found that, in a realistic range, the parameters can be adapted to vary the frame rigidity from about 13 N/mm to 17,000 N/mm, thereby reducing the maximal stresses in the pins and at the pin-bone interface by a factor of 140. In particular, when compromises have to be established in the frame characteristics in order to ensure a flexible configuration and limit the stress values at the same time, the formulas presented can provide useful guidelines. The side-bar separation and the pin modulus, in particular, can be adapted to decrease the rigidity, while only moderately increasing the stresses, thereby reducing changes for pin failure, pin-bone loosening, and pin-tract infection. A nomogram is presented for a quick reference to estimated relations between frame characteristics, rigidity, and stresses. It is believed that this material may be of use in EFF design and applications in clinical and animal experimental trials.

Biomechanical Phenomena↗
PubMed1994

Electrophysiological and repetitive firing properties of neurons in the superficial/middle layers of the human neocortex maintained in vitro.

Conventional intracellular recordings were made from neurons located in the superficial/middle layers of human temporal neocortical slices obtained from patients undergoing neurosurgical procedures for the treatment of epilepsy or brain tumour. In most of the neurons, inward membrane rectification was observed when the cell was depolarized or hyperpolarized from rest by intracellular injection of positive or negative current pulses. Bath application of tetrodotoxin abolished the depolarizing inward rectification, but not the "anomalous rectification" in the hyperpolarizing direction. Single action potential firing was followed by a fast afterhyperpolarization, a depolarizing afterpotential and a medium afterhyperpolarization, while a slower afterhyperpolarization was seen following repetitive firing. Blockade of Ca2+ channels with Cd2+ diminished all three types of afterhyperpolarization. Although the repetitive firing pattern in all cells indicated that they discharge in a regular-spiking fashion, 63% of the cells fired tonically in the initial part of discharge, while the remaining 37% of the cells fired phasically. Frequency-current plot for the initial interspike intervals during long depolarizing pulses revealed primary and secondary ranges of firing. Spike frequency adaptation was also observed. In conclusion, our experiments indicate that human neocortical cells in the superficial/middle layers display electrophysiological characteristics that are similar to those described in rodent and feline neocortices.

Action Potentials↗
PubMed1991

Signal transmission through a metabolic cycle follows the compression hypothesis or a weak Weber's law.

Biological signal transduction often involves a metabolic cycle in which the flux at one point is driven by the input signal and the concentration of one of the metabolites of the cycle serves as the output signal. A kinetic analysis of such a metabolic cycle is made under an assumption that the law of mass action applies. The resultant kinetic model can produce a response that overshoots, quickens, and eventually saturates as the input intensity is increased. The possible model behavior ranges parametrically from non-adaptive (compression hypothesis) to weakly adaptive (limited Weber's law).

Adaptation, Physiological↗
PubMed1978

Functional mutants of yeast alcohol dehydrogenase affecting kinetics, cellular redox balance, and electrophoretic mobility.

Repeated selection of petite (respiratorily incompetent) Saccharomyces cerevisiae on medium containing allyl alcohol, both on plates and in the turbidostat, results in mutants with a remarkably similar response. Most of the mutations affect the constitutive alcohol dehydrogenase, resulting in enzymes with a cathodal shift in electrophoretic mobility, and none shows a significant anodal shift. The genetics, kinetics, and physiological effect of three of the mutants have been investigated in detail, and while all confer resistance to allyl alcohol through a shift in the NAD/NADH ratio, they do so in slightly different ways. The potential of this system for exploring the range of short-term adaptations open to this organism is discussed.

Alcohol Oxidoreductases↗
PubMed1998

Preparation of hair for measurement of elements by inductively coupled plasma-mass spectrometry (ICP-MS).

The preparation of hair for the determination of elements is a critical component of the analysis procedure. Open-beaker, closed-vessel microwave, and flowthrough microwave digestion are methods that have been used for sample preparation and are discussed. A new digestion method for use with inductively coupled plasma-mass spectrometry (ICP-MS) has been developed. The method uses 0.2 g of hair and 3 mL of concentrated nitric acid in an atmospheric pressure-low-temperature microwave digestion (APLTMD) system. This preparation method is useful in handling a large numbers of samples per day and may be adapted to hair sample weights ranging from 0.08 to 0.3 g. After digestion, samples are analyzed by ICP-MS to determine the concentration of Li, Be, B, Na, Mg, Al, P, S, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ge, As, Se, Rb, Sr, Zr, Mo, Pd, Ag, Cd, Sn, Sb, I, Cs, Ba, Pt, Au, Hg, Tl, Pb, Bi, Th, and U. Benefits of the APLTMD include reduced contamination and sample handling, and increased precision, reliability, and sample throughput.

Hair↗
PubMed2004

[Ureteroscopy under intravenous analgesia with remifentanil].

In a prospective study, from September 2000 to September 2001, all ureteroscopies ( n=140) were performed under local and intravenous patient controlled analgesia using continuous infusion of remifentanil (Ultiva). The dosage of 0.15 micro g/kg/min was adapted to changing intraoperative pain (range 0.08-0.30 micro g/kg/min). Preoperative sedation with midazolam 2 mg was given 5 min prior to ureteroscopy. The efficacy of monitored anesthesia care ("Big MAC") was quantified by the patient using a visual analogue pain scale. A total of 97.1% (136/140) of the procedures were performed and finished under remifentanil. Only four male patients underwent conversion to general anesthesia due to insufficient analgesia. All but one patient would choose remifentanil again for first line anesthesia. Significant differences in pain scale values were noticed for male/female patients and ureteroscopies above/below the iliac vessel crossing. Side effects were rare being mainly hypoxic events (pO(2)<90% in 5.1%). Indication, intraoperative procedure, average surgery time (24 min), complications and primary success rate (96.6/90/63.3% stone free for distal/mid/proximal ureter, respectively) did not differ from the control group under general anesthesia. Ureteroscopies with remifentanil are safe, universally applicable because of refifentanil's organ independent esterase metabolism and as effective as general anesthesia. There is no need for PACU stay for patients due to the ultra-short drug half-life, and therefore remifentanil is cost effective and perfect in an outpatient setting.

Carcinoma, Renal Cell↗
PubMed2007

Bacterial productivity distribution during a rainy year in an estuarine system.

Bacterial density and productivity were investigated along four salinity gradients within the estuary Ria de Aveiro. Bacterial variables and environmental parameters were measured at three to four stations spanning the entire salinity gradient of the four channels. The rather high variation in bacterial productivity (0.16-7.6 microg C L(-1) h(-1)) along the profiles of salinity indicates that bacterial activity shows a reactive behavior to environmental changing. Bacterial density (0.5-11.2 x 10(9) cells L(-1)) with a comparative smaller variation showed a more conservative behavior, mainly reflecting the phytoplankton distribution. Contrary to expectation, minimal values of bacterial productivity were not observed in November-December but in June. In fact, in November-December, the deep zone near the mouth showed the highest values of bacterial activity. At the upper stations, the highest values were observed in October. The relatively high values of bacterial production during the cold rainy season suggest that allochthonous substrates leached out from the surroundings by rain controlled the distribution of bacterial activity in the estuarine system. The substantial decrease in salinity during the rainy season negatively affected bacterial productivity, namely in the marine zone, where water column was highly stratified. Salinity seems to play an indirect role in the regulation of estuarine bacteria because there are different bacterial communities adapted to a wide salinity range.

Bacteria↗
PubMed2005

Land use, spatial scale, and stream systems: lessons from an agricultural region.

We synthesized nine studies that examined the influence of land use at different spatial scales in structuring biotic assemblages and stream channel characteristics in southeastern Minnesota streams. Recent studies have disagreed about the relative importance of catchment versus local characteristics in explaining variation in fish assemblages. Our synthesis indicates that both riparian- and catchment-scale land use explained significant variation in water quality, channel morphology, and fish distribution and density. Fish and macroinvertebrate assemblages can be positively affected by increasing the extent of perennial riparian and upland vegetation. Our synthesis is robust; more than 425 stream reaches were examined in an area that includes a portion of three ecoregions. Fishes ranged from coldwater to warmwater adapted. We suggest that efforts to rehabilitate stream system form and function over the long term should focus on increasing perennial vegetation in both riparian areas and uplands and on managing vegetation in large, contiguous blocks.

Agriculture↗
PubMed2004

From axenic spore germination to molecular farming. One century of bryophyte in vitro culture.

The first bryophyte tissue culture techniques were established almost a century ago. All of the techniques that have been developed for tissue culture of seed plants have also been adapted for bryophytes, and these range from mere axenic culture to molecular farming. However, specific characteristics of bryophyte biology--for example, a unique regeneration capacity--have also resulted in the development of methodologies and techniques different than those used for seed plants. In this review we provide an overview of the application of in vitro techniques to bryophytes, emphasising the differences as well as the similarities between bryophytes and seed plants. These are discussed within the framework of physiological and developmental processes as well as with respect to potential applications in plant biotechnology.

Bryophyta↗
PubMed2003

Differential responses of three fungal species to environmental factors and their role in the mycorrhization of Pinus radiata D. Don.

Three ectomycorrhizal (ECM) isolates of Rhizopogon luteolus, R. roseolus and Scleroderma citrinum were found to differ markedly in their in vitro tolerance to adverse conditions limiting fungal growth, i.e. water availability, pH and heavy metal pollution. S. citrinum was the most sensitive, R. luteolus intermediate and R. roseolus the most tolerant species. Pinus radiata D. Don seedlings were inoculated in the laboratory and in a containerised seedling nursery with spore suspensions of the three ECM species. Colonisation percentage was considerably lower under nursery conditions, probably due to competition by native fungi. The effects of nursery ECM inoculation on seedling growth depended on the fungal species. Only R. roseolus-colonised plants showed a significantly higher shoot growth than non-mycorrhizal plants. All three fungi induced significantly higher root dry weights relative to control plants. Despite the low mycorrhizal colonisation, mycorrhization with all three species improved the physiological status of nursery-grown seedlings, e.g. enhanced root enzyme activity, shoot nutrient and pigment content, net photosynthesis rate and water use efficiency. Of the three fungal species, R. roseolus was the most effective; this species was also the most adaptable and showed the greatest range of tolerance to adverse environmental conditions in pure culture. It is, therefore, proposed as a promising fungal species for ECM inoculation of P. radiata in the nursery.

Basidiomycota↗
PubMed2006

Skeletal tissues as nanomaterials.

Collagen is the most abundant protein in the body and, though the fibre-forming collagens have a 'common' structure, it is adapted to perform a large range of functions-from the differing mechanical needs of tendon versus bone to forming a transparent support structure in the cornea. This perfidy also suggests that collagen could form a generic basis for a range of scaffold needs for tissue engineering or medical device coating applications. We at the London Centre for Nanotechnology--a joint venture between University College London and Imperial College--are taking a bottom-up approach having decided that many of the 'accepted dogmas' of collagen biology may not be quite as soundly based as currently held. We are using several of the tools of 'hard' nanotechnology--such as atomic force microscopy--to re-examine collagen structure with the longer term aim of using such information to design materials with appropriate physical attributes. Examples of our current research on mineralised and soft tissue collagens are presented.

Animals↗
PubMed2005

A review of the factors affecting the survival of donkeys in semi-arid regions of sub-Saharan Africa.

The large fluctuations seen in cattle populations during periods of drought in sub-Saharan Africa are not evident in the donkey population. Donkeys appear to have a survival advantage over cattle that is increasingly recognized by smallholder farmers in their selection of working animals. The donkey's survival advantages arise from both socioeconomic and biological factors. Socioeconomic factors include the maintenance of a low sustainable population of donkeys owing to their single-purpose role and their low social status. Also, because donkeys are not usually used as a meat animal and can provide a regular income as a working animal, they are not slaughtered in response to drought, as are cattle. Donkeys have a range of physiological and behavioural adaptations that individually provide small survival advantages over cattle but collectively may make a large difference to whether or not they survive drought. Donkeys have lower maintenance costs as a result of their size and spend less energy while foraging for food; lower energy costs result in a lower dry matter intake (DMI) requirement. In donkeys, low-quality diets are digested almost as efficiently as in ruminants and, because of a highly selective feeding strategy, the quality of diet obtained by donkeys in a given pasture is higher than that obtained by cattle. Lower energy costs of walking, longer foraging times per day and ability to tolerate thirst may allow donkeys to access more remote, under-utilized sources of forage that are inaccessible to cattle on rangeland. As donkeys become a more popular choice of working animal for farmers, specific management practices need to be devised that allow donkeys to fully maximize their natural survival advantages.

Africa South of the Sahara↗
PubMed1988

The effect of rate of force application on the threshold of periodontal ligament mechanoreceptors in the cat canine tooth.

Mechanical stimuli in the form of ramp-plateau forces were applied to the tip of the crown of the left mandibular canine tooth in cats anaesthetized with alpha-chloralose. Electrophysiological recordings were made from functionally single fibres teased from the inferior alveolar nerve. The force threshold was determined for 34 periodontal ligament mechanoreceptors at different controlled rates of force application. Force threshold was dependent on the rate of force application to the crown tip. Rate sensitivity was present for all receptors across the range from rapidly to slowly adapting; the degree of rate sensitivity was graded according to the adaptation rate of the receptor. The results suggest that the velocity of mechanical stimulus application to teeth needs to be considered in studies involving periodontal mechanoreceptor responses and their reflexes.

Animals↗
PubMed1980

Field-dispersion profiles of the proton spin-lattice relaxation rate in chloroplast suspensions. Effect of manganese extraction by EDTA, Tris, and hydroxylamine.

Proton spin-lattice relaxation rates (R1) have been measured in a variety of dark-adapted chloroplast suspensions over a range of field stengths between 1 and 15 kG (4-65 MHz). When the effects of EDTA or Tris washing on chloroplast relaxivities are compared, the pool of Mn associated with oxygen evolution is seen not to contribute significantly to relaxivity. Instead, nearly all of the observed relaxivity, which is characterized by a paramagnetic maximum near 20.7 MHz in the field dispersion profile of R1, appears to arise from contaminating non-functional Mn(II) that can be removed by EDTA during the isolation procedure. These observations, which contradict previous reports ascribing chloroplast relaxivity to the water-oxidizing system, require a reevaluation of proposed models, derived from NMR studies, of the state of Mn in the water-splitting reaction. Chloroplasts from which loosely bound non-functional Mn has been removed by EDTA washing do show an enhancement of relaxivity when exposed to NH2OH at concentrations known to inactivate water oxidation. This NH2OH-induced relaxivity is comprised of Mn(II) in two distinct paramagnetic sites. One site is chelatable by EDTA, whereas the other site is not. This finding suggests that some Mn(II) tightly bound to thylakoid membranes can contribute to relaxivity after inactivation of the oxygen-evolving reaction.

Binding Sites↗
PubMed1983

The American leishmaniases: some observations on their ecology and epidemiology.

As the first species of Leishmania encountered were the agents of human visceral and cutaneous leishmaniasis, it is understandable that studies on these parasites for a long time concentrated on those organisms commonly causing disease in man. Epidemiological studies over the past 20 years or so, however, have led to the inescapable conclusion that the genus Leishmania is comprised of numerous species of well adapted parasites, in a wide range of mammals, throughout most of those tropical and subtropical regions of the world where phlebotomine sandflies exist (Diptera: Psychodidae). Many of the leishmanias probably never gain entrance into man: due either to an incapacity to survive in his tissues, or (more likely) because the natural sandfly vectors do not feed on him. The leishmanias that do infect man are, nevertheless, among the greatest protozoological scourges of mankind, and a better understanding of their life-cycles may well help in future prevention or control of the diseases they cause. With few exceptions the leishmaniases are zoonoses, with a major source of infection in wild or domestic animals. In the Americas, the disease is essentially a rural one, and most commonly acquired by those penetrating forested or wooded regions. The following paper deals with the better known human leishmaniases of the New World, and some new ones, and discusses the major historical events in the laborious task of elucidating their ecology and epidemiology.

Americas↗
PubMed2005

Regulation of hypoxia-inducible factor 1 by prolyl and asparaginyl hydroxylases.

Hypoxia-inducible factor 1 (HIF-1) functions as a master regulator of oxygen homeostasis by mediating a wide range of cellular and systemic adaptive physiological responses to reduced oxygen availability. In this review, we will summarize recent progress in elucidating the molecular mechanisms of HIF-1 activation, focusing on the role of oxygen-dependent prolyl and asparaginyl hydroxylases in hypoxia signal transduction.

Animals↗
PubMed2005

A protease stable in organic solvents from solvent tolerant strain of Pseudomonas aeruginosa.

A solvent tolerant strain of Pseudomonas aeruginosa (PseA) was isolated from soil samples by cyclohexane enrichment in medium. The strain was able to sustain and grow in a wide range of organic solvents. The adaptation of P. aeruginosa cell towards solvents was seen at membrane level in transmission electron micrographs. It also secreted a novel protease, which exhibited remarkable solvent stability and retained most of the activity at least up to 10 days in the presence of hydrophobic organic solvents (log P > or = 2.0) at 25% (v/v) concentrations. The protease was able to withstand as high as 75% concentration of solvents at least up to 48 h. P. aeruginosa strain and its protease, both seem promising for solvent bioremediation, wastewater treatment and carrying out biotransformation in non-aqueous medium.

Cell Proliferation↗
PubMed2005

Treatment of axillary burn scar contracture using opposite running Y-V-plasty.

Burn scar contractures are frequently observed following full-thickness burns of the axillary area. Such contractures are traditionally reconstructed sometime within the first year after injury with therapeutic methods including skin grafting, Z-plasty, local/regional flap, island flap, perforator flap, free flap or combination thereof. Flap methods have many advantages over split skin grafting, including less likelihood of recurrence of contracture as well as making prolonged splinting unnecessary. However these flaps are cumbersome, unattractive, and apparently distort the axillary hair. Moreover, they have a risk of flap necrosis or marginal vascular compromise. A new opposite running Y-V-plasty presented here is designed to overcome those dilemmas. This procedure was performed in eight cases with good functional recovery and cosmetic appearance. It is also a simple, adaptable, and reliable method. The range of motion of shoulder joint was also satisfactorily achieved since axillary contracture scars were almost completely released. Most of all the procedure can be repeated if the release is not enough. In short, the opposite running Y-V-plasty is a good alternative method when we consider the reconstruction of axillary burn contracture.

Adolescent↗