Laser temperature programmed desorption: A flexible technique to study ion-surface interaction.

Understanding the physical-chemical processes ruling the interaction of particles (atoms, molecules, and ions) with surfaces is fundamental in several research fields, such as heterogeneous catalysis, astrochemistry, and nuclear fusion. In particular, the interaction of hydrogen isotopes with plasma facing materials represents a high-priority research task in the fusion community. Such studies are essential to ensure the successful operation of experimental fusion reactors, such as the tokamak ITER. In this work, we present a surface science apparatus developed to study ion-surface interaction in fusion relevant systems. It combines laser-based techniques with contaminant-free ion/molecular beams, mass spectrometry, and surface science tools such as low-energy electron diffraction and Auger electron spectroscopy. It allows to cover a wide range of sample temperatures, from 130 to 2300 K, by changing the heating rate of samples from 0.1 to 135 K/s and maintaining the linearity of the heating ramps, a powerful feature to gain insight on adsorption, absorption, and desorption mechanisms. Experimental calibration and performance are presented in detail. Moreover, to provide a factual overview of the experimental capabilities, we focus on two different applications: the protocol used to clean a W(110) single crystal sample and the development of laser temperature programmed desorption to study helium retention in tungsten.

State-resolved reactivity of CH4(2nu3) on Pt(111) and Ni(111): effects of barrier height and transition state location.

Quantum state-resolved sticking coefficients on Pt(111) and Ni(111) surfaces have been measured for CH4 excited to the first overtone of the antisymmetric C-H stretch (2nu3) at well-defined kinetic energies in the range of 10-90 kJ/mol. The ground-state reactivity of CH4 is approximately 3 orders of magnitude lower on Ni(111) than on Pt(111) for kinetic energies in the range of 10-64 kJ/mol, reflecting a difference in barrier height of 28+/-6 kJ/mol. 2nu3 excitation of CH4 increases its reactivity by more than 4 orders of magnitude on Ni(111), whereas on Pt(111) the reactivity increase is lower by 2 orders of magnitude. We discuss the observed differences in the state-resolved reactivity for the ground state and 2nu3 excited state of methane in terms of a difference in barrier height and transition state location for the dissociation reaction on the two metal surfaces.

Cavity ring-down spectroscopy of jet-cooled silane isotopologues in the Si-H stretch overtone region.

Absorption spectra of silane in the region of the first overtone of the Si-H stretch vibration have been recorded in a seeded supersonic jet expansion by cavity ring-down spectroscopy as well as in a static gas cell at room temperature by photoacoustic spectroscopy. Spectral simplification due to strong rotational cooling in the jet expansion enables us to clearly resolve and assign the rovibrational transitions of the (2000) and (1100) bands of the three isotopologues, (28)SiH(4), (29)SiH(4), and (30)SiH(4), in their natural isotopic abundance. Interconversion between different nuclear spin species of SiH(4) is found to be absent during the jet expansion. Isotope shifts for (29)SiH(4) and (30)SiH(4) relative to (28)SiH(4) are measured and found to be suitable for selective vibrational excitation of any of three silane isotopologues by pulsed laser excitation in a jet expansion.

Concurrent total hip and knee replacements in a patient with haemophilia with inhibitors using recombinant factor VIIa by continuous infusion.

The introduction of activated recombinant factor VIIa (rFVIIa) has allowed elective surgery to be safely performed in haemophiliacs with inhibitors. The main problems associated with its use are the short half-life, necessitating frequent intravenous injections, and its very high cost. Here we describe, for the first time, the performance of total hip and knee replacements in a haemophiliac with inhibitors at the same operation. The amount of rFVIIa concentrate used (8.57 mg) was similar to that normally used for a single joint replacement. The use of continuous infusion allowed for easier administration and further contributed to the reduction in cost as it avoids the peak levels associated with bolus injections.

Subunits I and II of Dictyostelium cytochrome c oxidase are specified by a single open reading frame transcribed into a large polycistronic RNA.

A single open reading frame (ORF) encoding cytochrome c oxidase subunit I and II (cox1/2) was identified in the mitochondrial genome of the slime mold Dictyostelium discoideum. The cox1 coding region shares intron positions with its counterparts in fungi and algae. Northern blot analysis, using exon and intron-specific probes, suggests that the cox1/2 gene is transcribed as part of a large, efficiently processed, polycistronic RNA.

A single cell complementation class is common to several cases of cytochrome c oxidase-defective Leigh's syndrome.

A generalized defect of complex IV (cytochrome C oxidase, COX) is frequently found in subacute necrotizing encephalomyelopathy (Leigh's syndrome), the most common mitochondrial disorder in infancy. We previously demonstrated the nuclear origin of the COX defect in one case, by fusing nuclear DNA-less cytoplasts derived from normal fibroblasts with mitochondrial DNA (mtDNA)-less transformant fibroblasts derived from a patient with COX-defective [COX(-)] Leigh's syndrome. The resulting cybrid line showed a specific and serve COX(-) phenotype. Conversely, in the present study, we demonstrated that a COX(+) phenotype could be restored in hybrids obtained by fusing COX(-) transformant fibroblasts of seven additional Leigh's syndrome patients with mtDNA-less, COX(-) tumor-derived rho degree cells. Both these results are explained by the presence of a mutation in a nuclear gene. In a second set of experiments, in order to demonstrate whether COX(-) Leigh's syndrome is due to a defect in the same gene, or in different genes, we tested several hybrids derived by fusing our original COX(-) cell line with each of the remaining seven cell lines. COX activity was evaluated in situ by histochemical techniques and in cell extracts by a spectrophotometric assay. No COX complementers were found among the resulting hybrid lines. This result demonstrates that all our cases were genetically homogeneous, and suggests that a major nuclear disease locus is associated with several, perhaps most, of the cases of infantile COX(-) Leigh's syndrome. This information should make it easier to identify the gene responsible.

Subunit change in cytochrome c oxidase: identification of the oxygen switch in Dictyostelium.

Cytochrome c oxidase (COX) has a complex modular structure in eukaryotes. Depending on growth conditions, interchangeable isoforms of selected subunits are synthesized and combined to the evolutionarily conserved catalytic core of the enzyme. In Dictyostelium this structural make-up is regulated by oxygen and involves two forms of the smallest subunit, termed VIIe and VIIs. Here we show that, in spite of a considerable sequence divergency, they are encoded by adjacent genes, linked 'tail to head' by only 800 bp. Deletion analyses reveal the presence of a short intergenic segment acting as an oxygen transcriptional switch. This structural organization and the different stability of the two subunit isoforms offer a molecular explanation for the extraordinary sensitivity to oxygen of the switching mechanism.

Prevalence of decompression sickness among U-2 pilots.

BACKGROUND: Though it is rarely reported, decompression sickness (DCS) is an expected risk for U-2 aviators. The potential for chronic sequelae of untreated DCS in this population has never been addressed. METHODS: After conducting a preliminary survey at an active-duty U-2 squadron, a cohort of 416 U-2 pilots (active-duty and retired) were mailed two sequential anonymous surveys to assess demographic data, career prevalence of DCS symptoms, and overall health status with an emphasis on chronic musculoskeletal problems. RESULTS: The response rate for each mail-in survey was over 60%. During their career, 75.5% of pilots experienced DCS symptoms such as joint pain, skin manifestations, and/or various neurological problems. Symptoms generally started during flight and resolved upon descent. Many pilots voluntarily increased their oxygen prebreathing time, or inflated the pressure suit during flight to prevent or treat symptoms. At some point in their career 12.7% of those experiencing symptoms either altered the flight profile or aborted a mission as a result. The association of past DCS with current arthritic problems was not statistically significant. CONCLUSIONS: The career prevalence of DCS symptoms in U-2 pilots is higher than previously reported, and these symptoms sometimes affect mission completion. We found no evidence that chronic musculoskeletal sequelae (e.g., arthritis or dysbaric osteonecrosis) are causally associated with DCS in this population.

Nuclear DNA origin of cytochrome c oxidase deficiency in Leigh's syndrome: genetic evidence based on patient's-derived rho degrees transformants.

Defects of the respiratory chain carrying out oxidative phosphorylation (OXPHOS) are the biochemical hallmark of human mitochondrial disorders. Faulty OXPHOS can be due to mutations in either nuclear or mitochondrial genes, that are involved in the synthesis of individual respiratory subunits or in their post-translational control. The most common mitochondrial disorder of infancy and childhood is Leigh's syndrome, a severe encephalopathy, often associated with a defect of cytochrome c oxidase (COX). In order to demonstrate which genome is primarily involved in COX-deficient (COX(-))-Leigh's syndrome, we generated two lines of transmitochondrial cybrids. The first was obtained by fusing nuclear DNA-less cytoplasts derived from normal fibroblasts, with mitochondrial DNA-less (rho degree) transformant fibroblasts derived from a patient with COX(-))-Leigh's syndrome. The second cybrid line was obtained by fusing rho degree cells derived from 143B.TK- human osteosarcoma cells, with cytoplasts derived from the same patient. The first cybrid line showed a specific and severe COX(-) phenotype, while in the second all the respiratory chain complexes, including COX, were normal. These results indicate that the COX defect in our patient is due to a mutation of a nuclear gene. The use of cybrids obtained from 'customized', patient-derived rho degree cells can have wide applications in the identification of respiratory chain defects originated by nuclear DNA-encoded mutations, and in the study of nuclear DNA-mitochondrial DNA interactions.

Circadian rhythm desynchronosis in military deployments: a review of current strategies.

The combined problems of changing work schedules and work places are not uncommon in military operations. For example, during the Persian Gulf War, many military units underwent short notice transmeridian deployment with immediate commencement of 24-h operations upon arrival. Some of these individuals likely suffered from circadian desynchronosis, blunting their effectiveness. The United States Air Force approved limited use of one short acting hypnotic medication to assist aircrew sleep disorders in the operational theater and, until recently, one stimulant medication to enhance alertness. Multiple theoretical strategies for circadian rhythm management are available. However, many U.S. Air Force flight surgeons are not trained on how best to use medications in combination with other circadian rhythm strategies. We present a condensed review of current human circadian rhythm coping strategies pertinent to military operations.

Expression of cytochrome c oxidase during growth and development of Dictyostelium.

In the slime mold Dictyostelium discoideum, the subunit composition of cytochrome c oxidase depends on oxygen that inversely regulates the concentrations of two alternative isoforms of the smallest enzyme subunit (Schiavo, G., and Bisson, R. (1989) J. Biol. Chem. 264, 7129-7134). In order to investigate their role in the Dictyostelium life cycle, the expression of the oxidase subunits was monitored during cell growth and development. The results obtained demonstrate that exponentially growing amoebae respond rapidly and precisely to hypoxia by switching the expression of the two isoforms and also by increasing the levels of the mRNAs of the different oxidase subunits in a highly coordinated process. During normal development the "hypoxic" subunit is not synthesized, but its level of expression appears to parallel the sensitivity to oxygen of development, rising steeply below 10% oxygen when the differentiation program is virtually blocked. Under these conditions, the expression of the alternative subunit isoform is essentially oxygen-insensitive. These findings suggest that the physiological relevance of the subunit switching concerns primarily the vegetative phase of growth, possibly as part of a more general mechanism evolved in order to evade conditions that do not allow development. Taken together, the data obtained offer an intriguing example of the fine control exerted on the expression of a key respiratory enzyme in a strictly aerobic organism.

Subjective fatigue of C-141 aircrews during Operation Desert Storm.

Airlift crews were exposed to extended work periods, reduced sleep periods, night work, and circadian dysrhythmia caused by shift work and time-zone crossings during Operations Desert Shield and Desert Storm. This research reveals the extent to which severe subjective fatigue was experienced by the crews during Operation Desert Storm. In addition, through the evaluation of long-term and short-term work and sleep histories, this research shows that recent sleep and flight histories are correlated with high fatigue levels. Furthermore, we found a tendency for fatigue to correspond with pilot error. We recommend that the training of personnel involved in long-duration operations include fatigue management strategies and, further, that work policies and environments be designed to take into account the importance of regular and restorative sleep when unusual duty hours are required.

Crew fatigue during simulated, long duration B-1B bomber missions.

Crew fatigue associated with successive and unaugmented 36 h missions was evaluated in B-1B simulators. Data were obtained from 32 operationally qualified crewmembers. All crew-members completed three consecutive, long duration missions, each preceded by 33 to 35 h of crew rest. Oral temperature, salivary melatonin and cortisol, as well as actigraph and subjective measures, were collected during all missions. Temperature and melatonin data indicate that crews maintained their local home base circadian cycles. Elevated cortisol and subjective fatigue during the first mission indicate that it was the most difficult of the three. Furthermore, quality and duration of sleep were lowest during the first mission. These findings emphasize the need for realistic training in long duration fatigue management to improve the safety and effectiveness of the first and subsequent missions.

Inhibition of the synthesis of a cytochrome-c-oxidase subunit isoform by antisense RNA.

To investigate the role of subunit VIIe, an oxygen-regulated subunit isoform of Dictyostelium discoideum cytochrome-c oxidase, the full-length cDNA was inserted into an expression vector under the control of an actin promoter in the sense and antisense orientation. The DNA constructs were used for stable transformation of the slime mold amoebae. In most of the 28 antisense clones tested, the concentration of cytochrome-c oxidase was lowered compared to the wild type, while no significant changes were found in the sense mutants. Antisense RNA was abundantly expressed, leading to a drastic reduction of the steady-state level of the endogenous subunit VIIe mRNA, which was decreased up to 20-30% the level observed in parent cells. In these transformants, the amount of the target polypeptide and cytochrome c oxidase was 40-50% and 60-70% of control, respectively. A similar decrease was found in the level of the remaining nuclear and mitochondrial subunits. Unexpectedly, these changes affected neither basal nor uncoupled cell respiration suggesting an increase of the enzyme specific activity. Hypoxia completely relieved the cytochrome-c-oxidase deficit. These results indicate that subunit VII is needed for an efficient assembly of the protein complex and provide evidence for its involvement in the modulation of the enzyme activity.

Aircrew fatigue during Desert Shield C-5 transport operations.

The metrics used to define U.S. Air Force crew rest and flight duty limitations were not designed to manage surge operations such as Operation Desert Shield. Desert Shield provided an opportunity to obtain inflight data on acute and cumulative fatigue and the effect of other stressors during over-the-shoulder observations on 24 C-5 airlift crew members. Findings emphasize how sleep history, recent duty day cycles, subjective fatigue, scheduling patterns, nutrition, and billeting facilities contribute to fatigue and lower levels of alertness. The results of this fairly insignificant observational study attempt to preserve some of the aeromedical lessons of Desert Shield. The flight surgeon authors integrate their experience to outline development of a fatigue management and alertness enhancement doctrine.

Prediction of maximal oxygen uptake from submaximal exercise testing in aerobically fit and nonfit men.

Aerobic physical fitness, as determined by the body's maximal capacity to utilize oxygen (VO2max) during demanding work, is an important determinant of a person's ability to perform many military tasks. The present 2.4 km (1.5 mi) run has not proven itself capable of accurately estimating this important factor on a periodic basis. This paper reviews prior studies of heart rate response to known workloads on a cycle ergometer to estimate VO2max. This submaximal test, as revised by scientists at the USAF Armstrong Laboratory at Brooks AFB, TX, was validated on 22 male subjects by comparing the test results with laboratory measurements of VO2max obtained by analysis of expired air during maximal treadmill exercise. Two groups of subjects were selected; one consisting of highly trained runners and the other of inactive subjects who did not perform regular aerobic exercise. The cycle ergometry prediction underestimated measured VO2max by 8.1 ml.kg-1 x min-1 (SEE = 4.25) in all subjects, but there was a correlation of 0.95 between the estimated and measured values. Both estimated and measured VO2max were significantly higher in the group of trained runners than in the inactive subjects.