Ni(3)Si(Al)/a-SiO(x) core-shell nanoparticles: characterization, shell formation, and stability.

We have used an electrochemical selective phase dissolution method to extract nanoprecipitates of the Ni(3)Si-type intermetallic phase from two-phase Ni-Si and Ni-Si-Al alloys by dissolving the matrix phase. The extracted nanoparticles are characterized by transmission electron microscopy, energy-dispersive x-ray spectrometry, x-ray powder diffraction, and electron powder diffraction. It is found that the Ni(3)Si-type nanoparticles have a core-shell structure. The core maintains the size, the shape, and the crystal structure of the precipitates that existed in the bulk alloys, while the shell is an amorphous phase, containing only Si and O (SiO(x)). The shell forms around the precipitates during the extraction process. After annealing the nanoparticles in nitrogen at 700 °C, the tridymite phase recrystallizes within the shell, which remains partially amorphous. In contrast, on annealing in air at 1000 °C, no changes in the composition or the structure of the nanoparticles occur. It is suggested that the shell forms after dealloying of the matrix phase, where Si atoms, the main constituents of the shell, migrate to the surface of the precipitates.

Modelling the relationships between training, anxiety, and fatigue in elite athletes.

This study investigated the effects of 40-week training on anxiety and perceived fatigue in four elite triathletes. Anxiety and perceived fatigue were self-reported by the subjects twice a week by the way of a specific questionnaire and were linked by a mathematical model to the training loads calculated from the exercise heart rate. A significant relationship (r=0.32; p<0.001) between the training loads and anxiety was identified using a two-component model: a first, negative (i.e., anxiety decreased) short-term (tau (1)=23 days) function and a second, positive long-term (tau (2)=59 days) function. The relationship between the training loads and perceived fatigue was significant (r=0.30; p<0.001), with one negative function (tau (1)=4 days). This mathematical model can potentially describe the relationships between training loads and anxiety or perceived fatigue and may improve both the adjustment of the duration of tapering and the early detection of staleness.

The Perseus Exobiology mission on MIR: behaviour of amino acids and peptides in Earth orbit.

Leucine, alpha-methyl leucine and two peptides were exposed to space conditions on board the MIR station during the Perseus-Exobiology mission. This long duration space mission was aimed at testing the delivery of prebiotic building blocks. During this mission, two amino acids (leucine and alpha-methyl leucine) and two peptides (leucine-diketopiperazine and trileucine thioethylester) were exposed in Earth orbit for three months. Basalt, clay and meteorite powder were also mixed with the samples in order to simulate the effects of potential meteorite protection. Analysis of the material after the flight did not reveal any racemization or polymerisation but did provide information regarding photochemical pathways for the degradation of leucine and of the tripeptide. Amino acids appeared to be more sensitive to UV radiation than peptides, the cyclic dipeptide being found to be as particularly resistant. Meteorite powder which exhibits the highest absorption in Vacuum UltraViolet (VUV) afforded the best protection to the organic molecules whereas montmorillonite clay, almost transparent in VUV, was the least efficient. By varying the thickness of the meteorite, we found that the threshold for efficient protection against radiation was about 5 microm. The possible exogenous origin of biological building blocks is discussed with respect to the stability to the molecules and the nature of the associated minerals.

Digoxin poisoning and anuric acute renal failure: efficiency of the treatment associating digoxin-specific antibodies (Fab) and plasma exchanges.

Digoxin-specific antibodies (Fab) are currently the treatment of choice for digoxin intoxication. These fragments bind to digoxin, leading to Fab-digoxin complexes, and promote the release of receptor-bound digoxin. These complexes are renally excreted. In the case of anuria, they could be dissociated and lead to renewed intoxication. In this case plasma exchanges are proposed. We report the case of an anuric patient with digoxin intoxication, treated with a Fab injection, followed by a plasma exchange 16 hours later, a second Fab injection was given followed by two plasma exchanges, 38 and 86 hours later. The disappearance of cardiac abnormalities showed the efficiency of the Fab, the drop in serum digoxin concentration and the high digoxin concentration in the exchanged plasma indicate effective elimination. The association of Fab and plasma exchanges could be proposed in the case of digoxin intoxication in the anuric patient.

Amino acids from ultraviolet irradiation of interstellar ice analogues.

Amino acids are the essential molecular components of living organisms on Earth, but the proposed mechanisms for their spontaneous generation have been unable to account for their presence in Earth's early history. The delivery of extraterrestrial organic compounds has been proposed as an alternative to generation on Earth, and some amino acids have been found in several meteorites. Here we report the detection of amino acids in the room-temperature residue of an interstellar ice analogue that was ultraviolet-irradiated in a high vacuum at 12 K. We identified 16 amino acids; the chiral ones showed enantiomeric separation. Some of the identified amino acids are also found in meteorites. Our results demonstrate that the spontaneous generation of amino acids in the interstellar medium is possible, supporting the suggestion that prebiotic molecules could have been delivered to the early Earth by cometary dust, meteorites or interplanetary dust particles.

Modelling the transfers of training effects on performance in elite triathletes.

This study investigated the effects of 40-weeks training in swimming, cycling and running on performances in swimming, running and triathlon competitions in four elite triathletes. The training stimulus was calculated using the exercise heart rate. The level of performance was measured in running by a submaximal 30 min run, in swimming by a 5 x 400 m all-out test and subjectively in triathlon competitions. A mathematical model using one to three first order transfer functions linked actual and modelled performances by minimizing the residual sum of squares between them. The relationships between training and performances were significant in running (tau(1) = 20; tau(2) = 10; r = 0.74; p < 0.001) and in swimming (tau(1) = 31; r = 0.37; p = 0.03), supporting the principle of specificity of the training loads. Cross-transfer training effects were identified between cycling and running (tau(1 = )42; r = 0.56; p < 0.001), but not with swimming performances. In addition, the training loads completed in running were shown to have a major effect on performances in triathlon competition (tau(1 = )52; tau(2 = )4; r = 0.52; p < 0.001), indicating that running training is an essential part of triathlon performance. Swimming appears to be a highly specific activity, which does not gain nor provide benefits from/to other activities (i. e. cycling and running). The present study shows that cross-transfer training effects occur between cycling training and running performance in elite triathletes. A similar cross-training effect does not seem to occur for swimming performance.

Survival of microorganisms in space protected by meteorite material: results of the experiment 'EXOBIOLOGIE' of the PERSEUS mission.

During the early evolution of life on Earth, before the formation of a protective ozone layer in the atmosphere, high intensities of solar UV radiation of short wavelengths could reach the surface of the Earth. Today the full spectrum of solar UV radiation is only experienced in space, where other important space parameters influence survival and genetic stability additionally, like vacuum, cosmic radiation, temperature extremes, microgravity. To reach a better understanding of the processes leading to the origin, evolution and distribution of life we have performed space experiments with microorganisms. The ability of resistant life forms like bacterial spores to survive high doses of extraterrestrial solar UV alone or in combination with other space parameters, e.g. vacuum, was investigated. Extraterrestrial solar UV was found to have a thousand times higher biological effectiveness than UV radiation filtered by stratospheric ozone concentrations found today on Earth. The protective effects of anorganic substances like artificial or real meteorites were determined on the MIR station. In the experiment EXOBIOLOGIE of the French PERSEUS mission (1999) it was found that very thin layers of anorganic material did not protect spores against the deleterious effects of energy-rich UV radiation in space to the expected amount, but that layers of UV radiation inactivated spores serve as a UV-shield by themselves, so that a hypothetical interplanetary transfer of life by the transport of microorganisms inside rocks through the solar system cannot be excluded, but requires the shielding of a substantial mass of anorganic substances.

Simplified deceleration method for assessment of resistive forces in cycling.

PURPOSE: The purpose of this study was to develop and test a simplified deceleration technique for measurement of aerodynamic and rolling resistances in cycling. METHODS: Coast-down tests were performed in level hallways with an experienced cyclist as the rider. Average initial velocities were 2.5-12.8 m x s(-1)) The deceleration technique was simplified by the use on only three switches and a derivation that did not require an assumption that deceleration is constant. The effective frontal area (AC(D)) and coefficient of rolling resistance (CR) were then calculated through a derivation from the equation for resistive forces opposing motion. Method reproducibility was tested by comparison of results for four tests of 30 trials under identical conditions. Method sensitivity was tested by performing 30 trials with three different rider head positions and four different transported mass conditions. RESULTS: Analysis of variance revealed that there were no differences among the results in the reproducibility study for either AC(D) or C(R). Furthermore, the reproducibility tests revealed mean errors of only 0.66% and 0.70% for AC(D) and CR, respectively. ANOVA identified a significant increase (P < 0.001) in rolling resistance with external loading and a significant effect (P < 0.001) of head position on AC(D). Mean (+/-SD) values for AC(D) and C(R) from tests in a racing aeroposture with the head up, the head in line with the trunk, and the head in an intermediate position were 0.304 +/- 0.011, 0.268 +/- 0.010, and 0.262 +/- 0.013 m2, respectively. C(R) averaged 0.00368 in the three head positions. CONCLUSIONS: The findings indicate that this simplified deceleration technique is satisfactorily reproducible and sensitive for measurement of aerodynamic and rolling resistances in cycling.

Energy cost and running mechanics during a treadmill run to voluntary exhaustion in humans.

The aim of the present study was to examine the physiological and mechanical factors which may be concerned in the increase in energy cost during running in a fatigued state. A group of 15 trained triathletes ran on a treadmill at velocities corresponding to their personal records over 3000m [mean 4.53 (SD 0.28) m x s(-1)] until they felt exhausted. The energy cost of running (CR) was quantified from the net O2 uptake and the elevation of blood lactate concentration. Gas exchange was measured over 1 min firstly during the 3rd-4th min and secondly during the last minute of the run. Blood samples were collected before and after the completion of the run. Mechanical changes of the centre of mass were quantified using a kinematic arm. A significant mean increase [6.9 (SD 3.5)%, P < 0.001] in CR from a mean of 4.4 (SD 0.4) J x kg(-1) x m(-1) to a mean of 4.7 (SD 0.4) J x kg(-1) x m(-1) was observed. The increase in the O2 demand of the respiratory muscles estimated from the increase in ventilation accounted for a considerable proportion [mean 25.2 (SD 10.4)%] of the increase in CR. A mean increase [17.0 (SD 26.0)%, P < 0.05] in the mechanical cost (CM) from a mean of 2.36 (SD 0.23) J x kg m(-1) to a mean of 2.74 (SD 0.55) J x kg(-1) x m(-1) was also noted. A significant correlation was found between CR and CM in the non-fatigued state (r=0.68, P < 0.01), but not in the fatigued state (r=0.25, NS). Furthermore, no correlations were found between the changes (from non-fatigued to fatigued state) in CR and the changes in CM suggesting that the increase in CR is not solely dependent on the external work done per unit of distance. Since step frequency decreased slightly in the fatigued state, the internal work would have tended to decrease slightly which would not be compatible with an increase in CR. A stepwise regressions showed that the changes in CR were linked (r=0.77, P < 0.01) to the changes in the variability of step frequency and in the variability of potential cost suggesting that a large proportion of the increase in CR was due to an increase in the step variability. The underlying mechanisms of the relationship between CR and step variability remains unclear.

Delivery of extraterrestrial amino acids to the primitive Earth. Exposure experiments in Earth orbit.

A large collection of micrometeorites has been recently extracted from Antarctic old blue ice. In the 50 to 100 micrometers size range, the carbonaceous micrometeorites represent 80% of the samples and contain 2% of carbon. They might have brought more carbon to the surface of the primitive Earth than that involved in the present surficial biomass. Amino acids such as "-amino isobutyric acid have been identified in these Antarctic micrometeorites. Enantiomeric excesses of L-amino acids have been detected in the Murchison meteorite. A large fraction of homochiral amino acids might have been delivered to the primitive Earth via meteorites and micrometeorites. Space technology in Earth orbit offers a unique opportunity to study the behaviour of amino acids required for the development of primitive life when they are exposed to space conditions, either free or associated with tiny mineral grains mimicking the micrometeorites. Our objectives are to demonstrate that porous mineral material protects amino acids in space from photolysis and racemization (the conversion of L-amino acids into a mixture of L- and D-molecules) and to test whether photosensitive amino acids derivatives can polymerize in mineral grains under space conditions. The results obtained in BIOPAN-1 and BIOPAN-2 exposure experiments on board unmanned satellite FOTON are presented.

Improved detection of human antibodies to a Plasmodium antigen using a peptide modified with Aib residues.

A 17-mer sequence was selected as a model to study the influence of modifications of terminal ends both on the conformational of a peptide and on its antigenicity towards naturally developing antibodies. This sequence corresponded to a tandemly repeated motif, found in a long repetitive region, with high helical propensity, of a Plasmodium falciparum liver-stage antigen (LSA-1), immunogenic in man. Our model peptide was synthesized with ionizable or non-ionizable ends, or modified in both extremities by introduction of the helix-promoting residue alpha-aminoisobutyric acid (Aib). Helical contribution, absent in the 17 amino-acid sequence possessing ionizable ends, was detectable when non-ionizable ends were introduced, and dramatically increased in the Aib-modified analogue. The presence of ionizable ends totally abolished reactivity towards human sera, otherwise detectable with the peptide possessing non-ionizable ends. While modification by Aib residues was neither detrimental nor beneficial to antigenicity in solution, it clearly resulted in an improved sensitivity of the specific antibody detection when used as solid-phase antigen in ELISA.

Coronary arteries: new design for three-dimensional arterial phantoms.

Few three-dimensional (3D) anthropomorphic phantoms are available for testing 3D reconstruction and quantitation of vessels. The authors built a new realistic model of arteries with use of stereolithography, a computer-aided design and computer-aided manufacturing technique. Each phantom is composed of the physical object and its digital "twin." The entire coronary artery tree and complex stenoses were manufactured with a precision below 0.1 mm.

T helper cell epitopes of the human immunodeficiency virus (HIV-1) nef protein in rats and chimpanzees.

T helper cell antigenic and immunogenic determinants of the nef protein were investigated in the rat and chimpanzee models using recombinant nef protein and five synthetic peptides selected according to their amphipathic and alpha-helicity properties. The nef protein was shown to be immunogenic with both Freund's or aluminium hydroxide adjuvants. After immunization with the nef protein the 45-69 peptide was the most antigenic in rat and monkey models. In contrast, the 98-112 peptide, that required a carrier protein to induce in vitro rat T cell recall proliferation, was able to restimulate monkey T cells in the absence of a carrier. The amino acid sequence carrying the antigenic activity of the 45-69 peptide was further investigated by synthesizing short peptides overlapping this region. The antigenic sequence was precisely located in the middle of the peptide (region 50-59). This sequence was antigenic only when N alpha-acetylated. Circular dichroism analysis of the 45-69 peptide and the in vitro activity of the N-terminus group indicate in this case the involvement of the alpha-helical propensity for antigen presentation. However, the shorter sequence 50-64, able to induce a T cell reactivity, was determined as a beta-pleated sheet structure in aqueous solution. The 45-69 peptide was not only antigenic but also immunogenic and behaved in vivo as a functional T helper cell epitope. Indeed, the priming with the peptide or the transfer of peptide specific T cells to a naive recipient, followed by immunization with the nef protein, enhanced the subsequent antibody response to the nef protein. Together, these data indicate that the 45-69 peptide appears as a candidate for the in vivo elicitation of T cell immunity to the HIV-1 nef regulatory protein.

Pharmacokinetics of tolfenamic acid in the horse.

The pharmacokinetics of tolfenamic acid were studied in five ponies after an intravenous (iv) administration (2 mg/kg bodyweight [bwt]) and in four horses after an oral administration (30 mg/kg bwt) of tolfenamic acid. The plasma levels were determined by high pressure liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS). For the iv administration, a three-compartment model was used to represent the plasma concentration-time curve of the drug. The elimination half-life of the compound was 6.1 +/- 1.5 h, the total body clearance was 72.4 +/- 16.7 ml/kg bwt/h and the steady-state volume of distribution 0.32 +/- 0.11 litres/kg bwt. For the oral administration, absorbtion was delayed with a mean lag-time to absorption of 32 +/- 28 mins. The peak plasma concentration 11.1 +/- 0.69 micrograms/ml was observed after a highly variable delay ranging from 1.9 to 6.5 h post administration. The terminal half-life (4.2 +/- 0.48 h) was very similar to that obtained after iv administration. Tolfenamic acid could not be detected in equine plasma with the described analytical methods more than 48 h after drug administration.

Identification of a tolfenamic acid metabolite in the horse by gas chromatography-mass spectrometry.

A tolfenamic acid metabolite, a hydroxylated product, has been identified in equine plasma and urine samples using gas chromatography-mass spectrometry in the electron-impact and chemical-ionization modes. The method also allows the qualitative monitoring of the elimination of the drug and its metabolites from plasma. The two compounds are detected up to 48 and 24 h, respectively, after a single oral administration of a 30 mg/kg dose. The simultaneous detection of the two products increases the reliability of anti-doping control analysis.

Hydrolysis of oligoribonucleotides by alpha-helical basic peptides.

Poly(Leu-Lys-Lys-Leu) increases markedly the rate of hydrolysis of oligoribonucleotides. The polypeptide adopts and alpha-helical conformation in water in the presence of salt. Non-helical poly(Pro-Lys-Lys-Leu) is much less active. Ac-Leu-Lys-Lys-Leu-NHEt has no hydrolytic activity. Oligotetrapeptides Ac-(Leu-Lys-Lys-Leu)n-NHEt with increasing chain-length have been prepared by solid phase synthesis to evaluate the critical chain-length required for the hydrolytic activity. It is possible to correlate the activity to the propensity to form alpha-helices.

Chemical activity of simple basic peptides.

Alternating all-L poly(leucyl-lysyl) increases markedly the rate of hydrolysis of oligoribonucleotides. Pure D poly (leucyl-lysyl) is as active as the all-L polymer. The homochiral polypeptides adopt a beta-sheet structure when complexed to the oligonucleotides. Alternating poly(D,L-Leu-D,L-Lys) made of racemic amino acids is much less efficient and is unable to adopt a beta-sheet structure. A set of alternating poly (leucyl-lysyl) ranging from the racemic to the homochiral all-L polymer has been checked. Their conformations can be described as a mixture of random coil and beta-sheet conformations, the amount of beta-sheet increasing with the optical purity of the polymer. The hydrolytic activity follows the proportion of beta-sheets, suggesting that the chemical activity is related to the geometry of the chain. Short peptides were prepared in order to evaluate the critical chain length required for the hydrolytic activity. A decapeptide is long enough to present 90% of the activity of the corresponding polypeptide.

Search for catalytic properties of simple polypeptides.

Simple polypeptides were used as possible supports for nucleotide polymerization, in the absence of any preformed polynucleotide template. Sequential copolymers of alanine and glycine, water soluble polypeptides based on arginine and poly(Glu-Ser-Glu) have been tested. No catalytic effect has been found although poly(Glu-Ser-Glu) favors the 2'-5' internucleotide linkage. More interestingly, polypeptides containing arginine residues strongly accelerate the hydrolysis of oligoadenylic acids. The influence of pH, temperature, nature of the buffer and polypeptide sequence was investigated.

[Neonatal form of isovaleric acidemia. Apropos of a new case]. / Forme néo-natale de l'acidémie isovalérique. A propos d'une nouvelle observation.

The case reported concerns a 18 day-old girl who was hospitalized for severe toxemia. The nauseous smell, and significant ketonuria led us to suspect a disorder in amino-acids metabolism. Diagnosis was proven by gas chromatography. With adequate diet, evolution was favourable and the child had a normal psycho-motor development.