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At least 829 records · Page 46Linked to original sources

PubMed1997

Solution structure of neuropeptide tyrosine 13-36, a Y2 receptor agonist, as determined by NMR.

The three-dimensional structure of neuropeptide tyrosine (NPY) 13-36, a specific Y2 receptor agonist, has been investigated by two-dimensional 1H-NMR spectroscopy in solution. Analysis of the double-quantum-filtered correlation spectroscopy (DQFCOSY), total correlation spectroscopy (TOCSY) and nuclear Overhauser enhancement spectroscopy (NOESY) spectra provided a complete assignment of the proton signals. The interproton connectivities observed in the NOESY spectra comprised 166 intraresidue and 95 interresidue distance ranges which were used as constraints for molecular modeling by distance geometry, simulated annealing and energy minimization. The optimal structures are characterized by a helical C-terminal fragment Leu30-Tyr36 and a wide loop from Leu17 to Ser22. The structure of NPY 13-36 is analogous to the structure of NPY under the same solvent conditions. Comparison with other reported Y2 agonists suggests that the helical Leu30-Tyr36 fragment is the most critical for activity.

Animals↗

PubMed1996

Efficacy of corneal eye shields in protecting patients' eyes from laser irradiation.

BACKGROUND: The continuing development of new types and applications of lasers has appeared to surpass the development of specific eye protection for these lasers. There are a variety of eye shields on the market, but few are specifically designed for laser protection. OBJECTIVE: Our purpose was to test a variety of eye shields by two parameters, light transmission and temperature rise, and to determine from these measurements the most protective shield for patients. METHODS: We tested four plastic shields, one metal shield, and two sets of tanning goggles for temperature rise and light transmission when irradiated with a beam from a flashlamp-pumped, pulsed-dye laser. RESULTS: The temperature rise at the surface of the shield opposite the laser impacts was no more than 0.2 degree C in any case. White light was transmitted at significant levels through several of the shields, but yellow light transmittance was noted only through the green eye shield. CONCLUSION: Our measurements indicate that all except the green shield appeared safe from transmission of the 585-nm radiant energy. However, the optimal laser eye shield, in our opinion, would be a composite of several different shields' characteristics.

Color↗

PubMed1977

Total parenteral nutrition in infants. Blood levels of glucose, lactate, pyruvate, free fatty acids, glycerol, d-beta-hydroxybutyrate, triglycerides, free amino acids and insulin.

Two regimens (A and B) for TPN were designed to meet the requirements of newborn infants for calories, amino acids, fatty acids, electrolytes, trace elements and vitamins. Both "A" and "B" included fat emulsion (Intralipid). "A" contained fructose and glucose, "B" glucose only. "A" provided amino acids (Vamin) in proportions similar to those of whole egg, "B" similar to those of human milk. All nutrients were given simultaneously into peripheral veins by constant infusion. Nineteen patients (11 newborns, 8 infants) were studied for 1-28 days. Twelve infants recovered, 7 died. In none could TPN be regarded as the cause of death. Treatment was complicated by sepsis in 5 infants. During the course of treatment, blood levels of substrates and insulin were measured before, during and 30 min after discontinuation of TPN. Highly raised concentrations of circulating substrates seen in 3 infants seemed to be related to a poor clinical condition rather than to the regimen used. Infants in good condition tolerated TPN well. Low levels of branch-chained amino acids and tendency to ketonemia, when infusion was stopped, suggested that minimal rather than optimal supply of energy and of amino acids in relation to energy was provided with both regimens. Low insulin levels associated with elevated blood levels of substrates suggested that insulin administration to selected cases might be indicated. Fructose (0.30 g/kg X hour-1) given with regimen A increased blood lactate concentrations. Homocystinaemia appeared in 2 cases; disappearance after excess vitamin B6 administration indicated increased B6 requirement.

Amino Acids↗

PubMed2002

An accelerator based system for in vivo neutron activation analysis measurements of manganese in human hand bones.

Manganese (Mn) is an essential nutrient for growth and development. Unfortunately, overexposure can lead to neurological damage, which is manifested as a movement disorder marked by tremors. Preclinical symptoms have been found in populations occupationally exposed to the element, and it is suggested that in late stages of the disorder, removing the Mn exposure will not prevent symptoms from progressing. Hence, it is desirable to have a means of monitoring Mn body burden. In vivo neutron activation analysis (IVNAA) is a technique which allows the concentration of some elements to be determined within sites of the body without invasive procedures. Data in the literature suggests that the Mn concentration in bone is greater than other tissues, and that it may be a long term storage site following exposure. Therefore, using the McMaster KN-accelerator to produce neutrons through the 7Li(p,n)7Be reaction, the feasibility of IVNAA for measuring Mn levels in the human hand bone was investigated. Mn is activated through the 55Mn(n,gamma)56Mn reaction, and the 847 keV gamma rays emitted when 56Mn decays are measured outside the body using NaI(Tl) detectors. An optimal incident proton energy of 2.00 MeV was determined from indium foil and microdosimetry measurements. Hand phantom data suggest a minimum detectable limit of approximately 1.8 ppm could be achieved with a reasonably low dose of 50 mSv to the hand (normal manganese levels in the human hand are approximately 1 ppm). It is recommended the technique be developed further to make human in vivo measurements.

Bone and Bones↗

PubMed1997

A filtration method for improving film dosimetry in photon radiation therapy.

Successful radiotherapy requires accurate dosimetry for treatment verification. Existing dosimeters such as ion chambers, TLD, and diodes have drawbacks such as relatively long measurement time and poor spatial resolution. These disadvantages become serious problems for dynamic-wedged beams. Thus the clinical use of dynamic wedges requires an improved dosimetry method. X-ray film may serve this purpose. However, x-ray film is not clinically accepted as a dosimeter for photon beams, because it overresponds to photons with energies below about 400 keV. This paper presents and develops a method which was initially proposed by Burch to improve the dose response of x-ray film in a phantom. The method is based on placing high-atomic number foils next to the film. The foils are used as filters to preferentially remove low-energy photons. The optimal film and filter configuration in a phantom was determined using a mathematical scheme derived in this study and a Monte Carlo technique (ITS code). The optimal configuration thus determined is as follows: the filter-to-film distance of 6 mm and the filter thickness of 0.15 mm for percent depth-dose measurement; the distance of 1 cm and the thickness of 0.25 mm for off-axis (dose) ratio measurement. The configuration was then tested with photon beams from a 4 MV linac. The test result indicates that the in-phantom dose distribution based on the optimal configuration agrees well with those measured by ion chambers.

Calibration↗

PubMed1980

Physiological adaptations in response to environmental stress during an n(2)-fixing anabaena bloom.

Anabaena spiroides has the ability to maintain intense biomass production for extensive periods in the epilimnion of a small eutrophic lake characterized by conditions shown to cause photooxidative death in a number of other phytoplankton. By the enhancement of carotenoid synthesis chlorophyll a was protected from photooxidation and prevented from catalyzing other photooxidative reactions within the cells. By temporally separating CO(2) and N(2) fixation, maximum utilization of photosynthetically active radiation was achieved. Because CO(2) fixation was more sensitive than N(2) fixation to a high oxygen concentration, the former was maximized during morning hours, before the afternoon buildup of dissolved oxygen. The diurnal partitioning of carbon and N(2) fixation has two additional advantages; possible competition for reductant-generating compounds is minimized, and adequate endogenous pools of carbon skeletons are assured to accept newly fixed ammonia. Hence, Anabaena, far from undergoing photooxidative death, appears to utilize a physiological strategy which allows optimization of radiant energy use for reductive processes and dominance of surface waters and shading of deeper phytoplankton during summer blooms.

Journal Article↗

PubMed1997

Influence of respiratory distress syndrome on body composition after preterm birth.

AIM: To observe changes in body composition during the first week after birth, in preterm neonates with and without respiratory distress syndrome (RDS), so as to be able to provide optimal fluid and energy intake. METHODS: Twenty four babies with RDS and 19 healthy preterm babies, with gestational ages ranging from 26-36 weeks, were studied daily for the first week after birth. Total body water (TBW) was measured using bioelectrical impedance analysis. The babies were weighed daily and a record made of fluid and energy intake. Body solids were calculated as the difference between body weight and TBW. RESULTS: There was a highly significant reduction in body weight by the end of the week, with the RDS babies losing more than the healthy babies (RDS 7.6%; non-RDS 3.7%). There was no significant difference in the amount of TBW at birth in the babies with and without RDS (RDS 85.1%; non-RDS 85.5%) and both groups lost the same amount of body water (RDS 10.9%; non-RDS 9.9%) by the end of the first week. The amount of total body water lost was unrelated to the volume of fluid administered. There was a loss of body solids during the first day in the RDS group, but, overall, there was a highly significant increase in both groups between birth and day 7, which was greater in the healthy babies (RDS 13.0%; non-RDS 42.7%). CONCLUSIONS: Loss of body water after birth occurs to the same extent in healthy preterm neonates and in babies with RDS and is unrelated to the volume of fluid administered. Given adequate nutritional support, an increase in body solids can accompany early postnatal weight loss and begins almost immediately after birth, in both healthy preterm babies and babies with RDS.

Analysis of Variance↗

PubMed1976

Effects of treatment with pyruvate and tromethamine in experimental myocardial ischemia.

Failure of glycolysis to increase sufficiently to supply optimal levels of energy production in ischemic heart muscle is due in part to the cummulative restrainst of acidosis on rate-limiting enzymes, particularly glyceraldehyde-3-phosphate dehydrogenase. In an effort to modify this inhibition and salvage jeopardized myocardium, treatment with excess levels of pyruvate and tromethamine (Tris), designed to buffer intracellular hydrogen ion accumulations and improve the oxidation-reduction ratio, NAD+/NADH, was tested in 59 swine hearts in two separate preparations of global and regional ischemia. Global ischemia, per se, caused hemodynamic deterioration and shortened survival time (44.3 +/- 3.1 minutes). Myocardial oxygen consumption, fatty acid oxidation, and glucose uptake were all significantly (P less than 0.001) reduced as were estimates of glycolysis and tissue stores of creatine phosphate and ATP (P less than 0.01). Although treatment with Tris alone was inconclusive, administrations of pyruvate (40-50 mM) buffered with Tris (added directly into the coronary perfusate) effected an improvement in mechanical function and a significant prolongation in survival time (56.9 +/- 2.6 minutes. P less than 0.01). Glycogenolysis was enhanced and levels of key glycolytic intermediates were reduced, suggesting an acceleration of glycolytic flux. Excess levels of pyruvate (1.52 +/- 0.48 mumol/ml of coronary perfusate) provided added substrate for oxidation and led to a greater than 5-fold incrase in rates of pyruvate decarboxylation as compared to untreated ischemic hearts...

Animals↗

PubMed2000

Cardioplegia heat exchanger design modelling using computational fluid dynamics.

A new cardioplegia heat exchanger has been developed by Sorin Biomedica. A three-dimensional computer-aided design (CAD) model was optimized using computational fluid dynamics (CFD) modelling. CFD optimization techniques have commonly been applied to velocity flow field analysis, but CFD analysis was also used in this study to predict the heat exchange performance of the design before prototype fabrication. The iterative results of the optimization and the actual heat exchange performance of the final configuration are presented in this paper. Based on the behaviour of this model, both the water and blood fluid flow paths of the heat exchanger were optimized. The simulation predicted superior heat exchange performance using an optimal amount of energy exchange surface area, reducing the total contact surface area, the device priming volume and the material costs. Experimental results confirm the empirical results predicted by the CFD analysis.

Computer Simulation↗

PubMed2002

A new way to rapidly create functional, fluorescent fusion proteins: random insertion of GFP with an in vitro transposition reaction.

BACKGROUND: The jellyfish green fluorescent protein (GFP) can be inserted into the middle of another protein to produce a functional, fluorescent fusion protein. Finding permissive sites for insertion, however, can be difficult. Here we describe a transposon-based approach for rapidly creating libraries of GFP fusion proteins. RESULTS: We tested our approach on the glutamate receptor subunit, GluR1, and the G protein subunit, alphas. All of the in-frame GFP insertions produced a fluorescent protein, consistent with the idea that GFP will fold and form a fluorophore when inserted into virtually any domain of another protein. Some of the proteins retained their signaling function, and the random nature of the transposition process revealed permissive sites for insertion that would not have been predicted on the basis of structural or functional models of how that protein works. CONCLUSION: This technique should greatly speed the discovery of functional fusion proteins, genetically encodable sensors, and optimized fluorescence resonance energy transfer pairs.

Cell Line↗

PubMed1977

Oxidative metabolism in fetal rat brain during maternal halothane anesthesia.

The present study examines the effects of maternally administered halothane on fetal brain metabolism as determined by direct tissue analysis. Term pregnant rats were paralyzed, ventilated, and administered halothane in concentrations of 0.4, 1, or 2%. For comparison of fetal response to anesthetic agents, other maternal rats were administered pentobarbital (50 or 200 mg/kg). Dams receiving 0.4% halothane or 50 mg/kg pentobarbital remained normotensive, whereas 2% halothane or 200 mg/kg pentobarbital led to a 65% reduction in maternal blood pressure and a 3-fold increase in blood lactate. Fetal blood lactate tended to parallel the maternal lactacidemia. Fetuses of dams anesthetized with 0.4% halothane or 50 mg/kg pentobarbital exhibited concentrations of cerebral metabolities comparable to those of control animals. A 2% halothane level was associated with metabolic disturbances in fetal brain, indicative of cerebral hypoxia. Pentobarbital 200 mg/kg, although producing maternal hypotension and lactacidemia to a degree similar to 2% halothane, preserved a more optimal fetal cerebral energy state as reflected in a lower lactate/pyruvate ratio and normal ATP. The metabolic influence of pentobarbital may serve to protect the hypoxic fetus from neurological damage, an effect apparently not shared by maternally administered halothane.

Adenosine Triphosphate↗

PubMedDate not supplied

A sampler of marketing strategies for private practice.

When a practitioner sets out to develop a broad base of influence in order that referral sources are varied and active, marketing must address client, business and professional issues. When resources of money and time become scarce, a satisfied client must be and always will be the best recommendation. To maintain a long line of satisfied clients, credibility, reliability, and reputation must be fostered through personal drive, energy and eternal optimism. Other marketing alternatives must be evaluated for cost effectiveness and ultimate outcomes. All of this can be consumingly fun and rewarding.

Consumer Behavior↗

PubMed2003

Multilayer thin-film structures with high spatial dispersion.

We demonstrate how to design thin-film multilayer structures that separate multiple wavelength channels with a single stack by spatial dispersion, thus allowing compact manufacturable wavelength multiplexers and demultiplexers and possibly beam-steering or dispersion-control devices. We discuss four types of structure--periodic one-dimensional photonic crystal superprism structures, double-chirped structures exploiting wavelength-dependent penetration depth, coupled-cavity structures with dispersion that is due to stored energy, and numerically optimized nonperiodic structures utilizing a mixture of the other dispersion effects. We experimentally test the spatial dispersion of a 200-layer periodic structure and a 66-layer nonperiodic structure. Probably because of its greater design freedom, the nonperiodic structure can give both a linear shift with wavelength and a larger usable shift than the thicker periodic structure gives.

Journal Article↗

PubMed2005

Glass-batch composition monitoring by laser-induced breakdown spectroscopy.

Laser-induced breakdown spectroscopy is an almost ideal technique for the in situ monitoring of the composition of a glass batch before it enters the glass-melting furnace, saving a significant amount of energy by the optimization of the furnace parameters for a particular composition of the glass batch. We investigate this application of laser-induced breakdown spectroscopy by determining the elemental composition of the glass batch used (i) as a surrogate for radioactive glass waste and (ii) to manufacture the most common type of flat glass. The surrogate glass-batch and flat-glass calibration curves for the major constituents have been prepared using both the line intensity and the line-intensity ratio. The analytical figure of merit of the glass-batch data obtained from the two different detection systems, namely, the Czerny-Turner spectrometer with an intensified diode-array detector and the echelle spectrometer fitted with an intensified CCD camera, are compared.

Journal Article↗

PubMed2003

On the choice of a sparse prior.

An emerging paradigm analyses in what respect the properties of the nervous system reflect properties of natural scenes. It is hypothesized that neurons form sparse representations of natural stimuli: each neuron should respond strongly to some stimuli while being inactive upon presentation of most others. For a given network, sparse representations need fewest spikes, and thus the nervous system can consume the least energy. To obtain optimally sparse responses the receptive fields of simulated neurons are optimized. Algorithmically this is identical to searching for basis functions that allow coding for the stimuli with sparse coefficients. The problem is identical to maximizing the log likelihood of a generative model with prior knowledge of natural images. It is found that the resulting simulated neurons share most properties of simple cells found in primary visual cortex. Thus, forming optimally sparse representations is a very compact approach to describing simple cell properties. Many ways of defining sparse responses exist and it is widely believed that the particular choice of the sparse prior of the generative model does not significantly influence the estimated basis functions. Here we examine this assumption more closely. We include the constraint of unit variance of neuronal activity, used in most studies, into the objective functions. We then analyze learning on a database of natural (cat-cam) visual stimuli. We show that the effective objective functions are largely dominated by the constraint, and are therefore very similar. The resulting receptive fields show some similarities but also qualitative differences. Even for coefficient values for which the objective functions are dissimilar, the distributions of coefficients are similar and do not match the priors of the assumed generative model. In conclusion, the specific choice of the sparse prior is relevant, as is the choice of additional constraints, such as normalization of variance.

Algorithms↗

PubMed1995

Nutritional homeostatic capacity of a three-breed cross in poultry and associated effects of genotypes at the pea comb and endogenous viral element 1 loci.

The effect of varying combinations of dietary CP, at 16, 18, and 20%, with ME, at 2,900 and 3,100 kcal ME/kg, on BW and feed conversion (FC) at 2 to 6 wk of age for a three-breed cross was evaluated. Additionally, effect of genotypes at the pea comb (P) and endogenous viral element 1 (ev1) loci on dietary treatments were evaluated. Average weekly feed intake per bird varied from 25.6 to 32.6 g for birds on 16% CP, 3,100 kcal ME/kg and 20% CP, 2,900 kcal ME/kg diets, respectively. Weekly BW and FC were highest for birds on a combination of 20% CP and 3,100 kcal ME/kg diet. On 18% CP and 3,100 kcal/ME diet, males with pea comb had significantly higher BW than those with a single comb. At the ev1 locus, differences among genotypes were significant only for BW of females on a diet consisting of 20% CP and 2,900 kcal ME/kg. Pooled data from the dietary treatments revealed that males with pea comb had significantly higher BW than males with single comb at 3 to 6 wk of age. Birds heterozygous at the ev1 locus had higher BW than those homozygous at this locus. Results of the current studies provide information necessary to develop the optimal protein and energy combination for BW and FC for a three-breed cross involving Araucona, White Leghorn, and Rhode Island Red. These studies also provide additional evidence of the possible effects of the P locus and a gene linked to it, ev1, on production traits in chickens.

Animals↗

PubMed2000

[The metabolic characteristics of the adaptation of athletes to cyclic types of sports to the point of physical loading].

The article considers problems of peculiarities of energetic adaptation of athletics of cyclic sports activity for significant sports loadings by POL indices, antioxidant system. ATP before and after veloergometric test by PWC 170. Adaptation of high class sportsmen for acute and chronic stress was taking place at the expense of more economic consumption of ATP at rest. Optimal indices of energy supply and metabolic adaptation were found at sportsmen with high level of physical state, while a slight disbalance was found at the sportsmen with average level of physical state.

Adaptation, Physiological↗

PubMed2000

Oxidative phosphorylation in cardiolipin-lacking yeast mitochondria.

The role of cardiolipin in mitochondrial energy transformation was studied by comparing oxidative phosphorylation in the Saccharomyces cerevisiae cardiolipin synthase null mutant crd1Delta, and in isogenic wild type. Oxygen consumption experiments and membrane potential kinetics during the phosphorylation cycle in isolated mitochondria indicated that the absence of cardiolipin causes only a moderate deficiency of mitochondrial energy-transforming machinery at 25 degrees C. However, at 40 degrees C, respiration was completely uncoupled from phosphorylation for the mutant mitochondria, in contrast with that for the wild-type. Membranepotential kinetics demonstrated an increased susceptibility of the mutant mitochondria to gradual deterioration during in vitro incubation. These results suggest that cardiolipin, although normally associated with several of the major enzymes of oxidative phosphorylation and required in vitro for their maximal activity, is not absolutely necessary for mitochondrial energy transformation under optimal conditions. The role of cardiolipin is, rather, to improve efficiency of oxidative phosphorylation and its resistance to unfavourable conditions, such as increased temperature.

Adenosine Triphosphate↗