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Although theoretical calculations have predicted that layered GaS and GaSe should form nanotube and related structures, they have not been prepared experimentally to date. We have carried out laser irradiation as well as thermal treatment of GaS and GaSe to cause exfoliation, which yielded onionlike structures and nanotubes by the rolling of the exfoliated sheets.
The chemical evolution of poly(tetrafluoroethylene) (PTFE) that is brought about by increasing levels of irradiation with alpha particles is accompanied by the emergence and proliferation of functionalized moieties. Families of reaction products specifically identified in the alpha-irradiated polymer matrix include hydride-, hydroxide-, and oxide-functionalized fluorocarbons. The data also indicate the emergence of hydrogen peroxide (H2O2) and hydrazine (N2H4), but no distinct evidence suggesting the formation of perfluorinated amines, amides, or cyanogens is found. In this article we substantiate the speciation of emergent species and reveal evidence of intercalated molecular gases with which alpha particle-generated radicals may react to form the observed products. Furthermore, we present evidence to suggest that the kinetics of alpha particle-induced reaction is limited by the diffusion of radicals within the polymer matrix. That is to say, chemical additives in the polymer matrix are shown to be scavengers of H*, O*, and F* radicals and limit the rates of reaction that produce functionalized fluorocarbon moieties. Above a threshold dose of alpha particles, the concentration of radicals exceeds that of the scavenger species, and free radical diffusion commences as evidenced by a sudden increase in the yield of reaction products. Samples of PTFE were irradiated to alpha doses in the range of 10(7) to 5 x 10(10) rad with 5.5 MeV 4He2+ ions from a tandem accelerator. Residual gas analysis (RGA) was utilized to monitor the liberation of molecular gases from PTFE during alpha particle irradiation of samples in vacuum. Static time-of-flight SIMS (TOF-SIMS), equipped with a 20 keV C60+ source, was employed to probe chemical changes as a function of alpha particle irradiation. Chemical images and high-resolution mass spectra were collected in both the positive and negative polarities.
We present a new method for the prediction of the equilibrium properties of dense gases containing hydrogen isotopes. The proposed approach combines the Feynman-Hibbs effective potential method and a deconvolution scheme introduced by Weeks et al. The resulting equations of state and the chemical potentials as functions of pressure for each of the hydrogen isotope gases depend on a single set of Lennard-Jones parameters. In addition to its simplicity, the proposed method with optimized Lennard-Jones potential parameters accurately describes the equilibrium properties of hydrogen isotope fluids in the regime of moderate temperatures and pressures. The present approach should find applications in the nonlocal density functional theory of inhomogeneous quantum fluids and should also be of particular relevance to hydrogen (clean energy) storage and to the separation of quantum isotopes by novel nanomaterials.
Large-scale plasma was created in molecular gases (CO, CO2, N2, H2O) and their mixtures by high-power laser-induced dielectric breakdown (LIDB). Compositions of the mixtures used are those suggested for the early earth's atmosphere of neutral and/or mildly reducing character. Time-integrated optical spectra emitted from the laser spark have been measured and analyzed. The spectra of the plasma generated in the CO-containing mixtures are dominated by emission of both C2 and CN radicals. A vibrational temperature of approximately 10(4) K was determined according to an intensity distribution in a vibronic structure of the CN (B2Sigma(+)u-X2Sigma(+)g) violet band. For comparison, the NH3-CH4-H2-H2O mixture has been irradiated as a model of the strongly reducing version of the early earth's atmosphere. In this mixture, excited CN seems to be significantly less abundant than C2. The LIDB experiments were in the molecular gases carried out not only in the static cell but also using a large, double stream pulse jet (gas puff target) placed in the vacuum interaction chamber. The obtained soft X-ray emission spectra indicate the presence of highly charged atomic ions in the hot core of high-power laser sparks.
In this paper, we present the results of the prediction of the high-pressure adsorption equilibrium of supercritical gases (Ar, N2, CH4, and CO2) on various activated carbons (BPL, PCB, and Norit R1 extra) at various temperatures using a density-functional-theory-based finite wall thickness (FWT) model. Pore size distribution results of the carbons are taken from our recent previous work,(1,2) using this approach for characterization. To validate the model, isotherms calculated from the density functional theory (DFT) approach are comprehensively verified against those determined by grand canonical Monte Carlo (GCMC) simulation, before the theoretical adsorption isotherms of these investigated carbons calculated by the model are compared with the experimental adsorption measurements of the carbons. We illustrate the accuracy and consistency of the FWT model for the prediction of adsorption isotherms of the all investigated gases. The pore network connectivity problem occurring in the examined carbons is also discussed, and on the basis of the success of the predictions assuming a similar pore size distribution for accessible and inaccessible regions, it is suggested that this is largely related to the disordered nature of the carbon.
Direct electron transfer from InSe nanoparticles to GaSe nanoparticles in mixed solution-phase aggregates has been found to occur upon photoexcitation. Mixed aggregates exhibit a strong charge-transfer absorption band at an energy slightly higher than the InSe band gap. Photoexcitation of this band results in a polarized transient absorption spectrum and transient absorption kinetics characteristic of InSe valence-band holes and GaSe conduction-band electrons. The kinetics indicate that charge separation persists for at least several hundred picoseconds.
BACKGROUND: The effects of body position and feeding on lung mechanics and blood gases in very low birthweight infants with chronic lung disease (CLD) is not fully elucidated. METHODS: Seven very low birthweight infants who were being mechanically ventilated because of CLD were examined. They were enrolled in this study when their feeding volume exceeded 100 mL/kg per day. Each patient was kept on the same position (either prone or supine) during feeding. Feeding was given by a nasogastric tube for over 1 h every 3 h. Blood gases and lung mechanics were evaluated before, 20 min and 40 min after the initiation of the feeding and at the end of the feeding. RESULTS: The prone position resulted in a significant increase in arterial oxygen saturation during feeding. The tidal volume in the prone position was significantly larger than in the supine position only before feeding. There were no significant differences in minute ventilation between these positions during the study. Pulmonary resistance was not different in either position, but the static compliance and the work of breathing of spontaneous breaths were improved significantly when the infants were in the prone position. In the supine position, work of breathing increased and static compliance decreased significantly with time, while in the prone position, those values did not change significantly. CONCLUSION: The improvement in lung mechanics may partly explain better oxygenation obtained in the prone position. The prone position could decrease energy expenditure for spontaneous breathing and may shorten the period of ventilatory support for very low birthweight infants with CLD.
Nineteen women (mean +/- SD: 28 +/- 5 years) with small fetuses relative to gestational age (mean +/- SD: 32 +/- 2.2 weeks of gestation) were referred to our unit for cordocentesis for the determination of fetal karyotyping. Four of these 19 patients had small-for-gestational-age ultrasound-derived measurements under the third centile for gestational age. Fetal blood gases were measured in the umbilical vein. Umbilical artery and fetal internal carotid artery Doppler examinations were performed 15 min before cordocentesis. The results showed a progressive and proportional increase in umbilical artery resistance index with hypoxia (p < 0.001), hypercapnia (p < 0.025) and acidosis (p < 0.005). Moreover, the results showed a progressive and proportional decrease in fetal internal carotid artery resistance index with hypoxia (p < 0.01), hypercapnia (p < 0.01) and acidosis (p < 0.025). Fetal blood gases are therefore related to umbilical circulatory function and cerebral vasodilatation, suggesting fetal vascular redistribution.
Almitrine (A) and medroxyprogesterone acetate (MA) given separately improve arterial blood gases in some patients with chronic obstructive pulmonary disease (COPD); the aim of this study was to assess the effect of the two drugs given together. Forty-eight patients with irreversible COPD and hypoxaemia were prospectively enrolled into a 14-day run-in period and received single-blind oral treatment with double placebo. Patients whose PaO2 remained stable (less than 10% change; n = 29, 25 males, mean age 65.6 years) were included in a 14-day active treatment period and randomly assigned to three groups. They received double-blind oral treatment with: A (50 mg bid, group A, n = 10); MA (20 mg tid, group MA, n = 9); A (50 mg bid) and MA (20 mg tid, group A+MA, n = 10). Anthropometric and spirometric measurements were similar in the three groups and so were the arterial blood gas values at the beginning and the end of the run-in period. At the end of the active treatment period, blood gas changes (mean+/-SE) were significantly different between groups (P<0.05, Kruskal-Wallis test), with improvement in both hypoxaemia and hypercapnia in group A+MA only: delta PaO2 = 7.4+/-1.9 mmHg, delta PaCO2 = -5.1+/-1.7 m mHg (P<0.05, Wilcoxon test). In short-term treatment, the association of A and MA is more efficient than either drug alone at improving arterial blood gases in COPD patients.
Five fetuses with absent end-diastolic umbilical artery velocity had normal fetal acid-base status assessed by cordocentesis. Each fetus, despite widely differing pathologic conditions, deteriorated over the next several days. These cases confirm an earlier report of normal gases with absent umbilical artery end-diastolic velocity. Normal blood gases on cordocentesis cannot provide extended reassurance in fetuses with absent end-diastolic velocity.
We consider a general method for computing the sum of positive Lyapunov exponents for moderately dense gases. This method is based upon hierarchy techniques used previously to derive the generalized Boltzmann equation for the time-dependent spatial and velocity distribution functions for such systems. We extend the variables in the generalized Boltzmann equation to include a new set of quantities that describe the separation of trajectories in phase space needed for a calculation of the Lyapunov exponents. The method described here is especially suitable for calculating the sum of all of the positive Lyapunov exponents for the system, and may be applied to equilibrium as well as nonequilibrium situations. For low densities we obtain an extended Boltzmann equation, from which, under a simplifying approximation, we recover the sum of positive Lyapunov exponents for hard-disk and hard-sphere systems, obtained before by a simpler method. In addition we indicate how to improve these results by avoiding the simplifying approximation. The restriction to hard-sphere systems in d dimensions is made to keep the somewhat complicated formalism as clear as possible, but the method can be easily generalized to apply to gases of particles that interact with strong short-range forces. (c) 1998 American Institute of Physics.
This study collects information from absorption and luminescence excitation spectra recorded for Mn atoms isolated in the solid rare gases Ar, Kr, and Xe and presents an analysis of the site occupancy, based on the polarizabilities of the rare gases and the observed spectral shifts. Two thermally stable sites of isolation exist for atomic Mn in solid Ar and Kr, while a single thermally stable site is present in Mn/Xe. Site occupancy assignments are based on the application of a polarizability model to the z (6)P(5/2)<--a (6)S(5/2); z (8)P(5/2)<--a (6)S(5/2), and y (6)P(5/2)<--a (6)S(5/2) electronic transitions of atomic Mn. From an analysis of the observed RG matrix-to-gas phase energy shifts for P<--S type transitions, this model allows the association of certain site types occupied by metal atoms in the rare gas solids. The required condition being a linear dependence of the matrix shifts with rare gas polarizability for those metal atoms "trapped" in a particular site type. Application of the polarizability model in conjunction with trends observed in site dominance, established a connection between the blue sites in Ar and Kr and the single site in Xe. Use of the known MgRG ground state bond lengths facilitated an identification of the sites of Mn atom isolation assuming the transference of the known MgRG bond lengths to the MnRG systems. Substitutional site occupancy of atomic Mn is assigned to the blue sites in Ar and Kr and the single site in Xe, while tetra-vacancy site occupancy is assigned to the red sites in Ar and Kr. Consistent with these assignments, Mn atoms in solid Ar show a preference for trapping in tetra-vacancy sites whereas in solid Kr, single substitutional sites are preferred and in Xe, this is the only site observed.
We study the diffusion of tracers (self-diffusion) in a homogeneously cooling gas of dissipative particles, using the Green-Kubo relation and the Chapman-Enskog approach. The dissipative particle collisions are described by the coefficient of restitution epsilon which for realistic material properties depends on the impact velocity. First, we consider self-diffusion using a constant coefficient of restitution, epsilon=const, as frequently used to simplify the analysis. Second, self-diffusion is studied for a simplified (stepwise) dependence of epsilon on the impact velocity. Finally, diffusion is considered for gases of realistic viscoelastic particles. We find that for epsilon=const both methods lead to the same result for the self-diffusion coefficient. For the case of impact-velocity dependent coefficients of restitution, the Green-Kubo method is, however, either restrictive or too complicated for practical application, therefore we compute the diffusion coefficient using the Chapman-Enskog method. We conclude that in application to granular gases, the Chapman-Enskog approach is preferable for deriving kinetic coefficients.
BACKGROUND: Halogenated compounds in the atmosphere are of great environmental concern due to their demonstrated negative effect on atmospheric chemistry and climate. Detailed knowledge of the emission budgets of halogenated compounds has to be gained to understand better their specific impact on ozone chemistry and the climate. Such data are also highly relevant to guide policy decisions in connexion with international agreements about protection of the ozone layer. In selected cases, the relevance of specific emission sources for certain compounds were unclear. In this study we present new and comprehensive evidence regarding the existence and relevance of a volcanic contribution of chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs), hydrochlorofluorocarbons (HCFCs), halons (bromine containing halo(hydro)carbons), and fully fluorinated compounds (e.g. CF4 and SF6) to the atmospheric budget. METHODS: In order to obtain new evidence of a volcanic origin of these compounds, we collected repeatedly, during four field campaigns covering a period of two years, gases from fumaroles discharging over a wide range of temperatures at the Nicaraguan subduction zone volcanoes Momotombo, Cerro Negro and Mombacho, and analysed them with very sensitive GC/MS systems. RESULTS AND DISCUSSION: In most fumarolic samples certain CFCs, HFCs, HCFCs, halons, and the fully fluorinated compounds CF4 and SF6 were present above detection limits. However, these compounds occur in the fumarole gases in relative proportions characteristic for ambient air. CONCLUSION: This atmospheric fingerprint can be explained by variable amounts of air entering the porous volcanic edifices and successively being incorporated into the fumarolic gas discharges. Recommendation and Outlook. Our results suggest that the investigated volcanoes do not constitute a significant natural source for CFCs, HFCs, HCFCs, halons, CF4, SF6 and NF3.
OBJECTIVE: Our purpose was to evaluate the changes in intrauterine gases and acid-base gradients inside the human fetoplacental unit at 7 to 16 weeks' gestation. STUDY DESIGN: Respiratory gases and acid-base values were recorded by means of a multiparameter sensor and samples from inside the exocoelomic or amniotic cavity, placental tissue, decidua, and fetal blood of 30 early pregnancies. RESULTS: Before 11 weeks' gestation, placental PO(2) was 2.5 times lower than decidual PO(2). The PO(2) increased independently at both sites during gestation, but a PO(2) gradient of 13.3 mm Hg persisted during the fourth month. At 13 to 16 weeks, PO(2), oxygen saturation, and oxygen content gradients were observed between the fetal blood and the placenta and between the placenta and underlying decidual tissue. There was no fetoplacental gradient for pH and PCO(2) between 7 and 16 weeks, but fetal blood pH values were much lower and fetal PCO(2) values were much higher than those reported in older fetuses. CONCLUSIONS: Early human placental tissue develops in a physiologically low-oxygen environment compared with uterine tissue. This may be necessary to allow specific placental metabolic activities and to protect both placental and fetal tissues against toxic oxygen metabolites.
Here, direct noninvasive neutron reflectivity measurements reveal the presence of a reduced (deuterated) water density region, with a sigmoidal density profile at the hydrophobic silane-water interface that depends on the type and concentration of dissolved gases in the water. Removal of dissolved gases decreases the width of the reduced water density region, and their reintroduction leads to its increase. When compared with recent computer simulations, a locally fluctuating density profile is proposed, whereas preexisting nanobubbles are excluded. The presence of a fluctuating reduced water density region between two hydrophobic surfaces and the attractive "depletion force" to which it leads may help explain the hydrophobic force and its reported diminution in deaerated water. Our results are also quantitatively consistent with recent dynamic surface force apparatus results that drastically revise previous estimates of the slip length of water flowing past hydrophobic surfaces from microns to approximately 20 nm. Our observations, therefore, go a long way toward reconciling three quite different types of experiments and phenomena: water depletion at hydrophobic surfaces, water slip at hydrophobic surfaces, and the hydrophobic interaction.
In 1958 and subsequently we correlated properties of solutions of gases in liquids by using the "force constants," epsilon/k, and collision diameters, sigma, which serve as parameters in equations for molecular pair potential energy such as that of Lennard-Jones or its variants. Unfortunately, however, the figures for these parameters that have been published are so scattered for the same gas as to make it difficult to select "best" values; in 1967, therefore, I substituted for these indirectly determined molecular parameters the directly and accurately known molal energy of vaporization, DeltaE(b) (v), and the molal volume, v(b), of the liquefied gas, both at its boiling point. A plot of values of DeltaE(2) (v) against the most trustworthy values of epsilon/k reveals direct proportionality. The same is true for V(b) (1/3) versus sigma.Recent examples will be shown of excellent linear correlations with these parameters of thermodynamic properties of different gases in the same solvent.It is no less "scientific" and far more practical to regard molecules of a solute as immersed in the potential energy field of its solvent than it is to split this field into imperfectly known pair potentials of questionable additivity and to try to integrate them over an undetermined distribution function.
Regulatory agencies and photochemical models of ozone rely on self-reported industrial emission rates of organic gases. Incorrect self-reported emissions can severely impact on air quality models and regulatory decisions. We compared self-reported emissions of organic gases in Houston, Texas, to measurements at a receptor site near the Houston ship channel, a major petrochemical complex. We analyzed hourly observations of total nonmethane organic carbon and 54 hydrocarbon compounds from C-2 to C-9 for the period June through November, 1993. We were able to demonstrate severe inconsistencies between reported emissions and major sources as derived from the data using a multivariate receptor model. The composition and the location of the sources as deduced from the data are not consistent with the reported industrial emissions. On the other hand, our observationally based methods did correctly identify the location and composition of a relatively small nearby chemical plant. This paper provides strong empirical evidence that regulatory agencies and photochemical models are making predictions based on inaccurate industrial emissions.