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PubMed2006

On gas phase alpha-effects. 1. The gas-phase manifestation and potential SET character.

The possibility of a gas-phase alpha-effect has been explored for the methyl transfer from methyl formate to hydroxide, hydroperoxide, and ethoxide by computing barrier heights at the HF/6-311++G(2df,2p) level of theory. The alpha-nucleophile (hydroperoxide) is found to have a lower barrier than the gas-phase-acidity-matched normal nucleophile (ethoxide) by 3.6 kcal/mol, offering evidence for a gas phase alpha-effect. A Shi-Boyd analysis for these reactions indicates that there is more single-electron-transfer character in the hydroperoxide transition state than for either hydroxide or ethoxide, further bolstering the existence of a gas-phase alpha-effect and the appropriateness of the Hoz model for the alpha-effect.

Journal Article↗
PubMed2006

Noble gas-transition-metal complexes: coordination of VO2 and VO4 by Ar and Xe atoms in solid noble gas matrixes.

The matrix isolation infrared spectroscopic and quantum chemical calculation results indicate that vanadium oxides, VO2 and VO4, coordinate noble gas atoms in forming noble gas complexes. The results showed that VO2 coordinates two Ar or Xe atoms and that VO4 coordinates one Ar or Xe atom in solid noble gas matrixes. Hence, the VO2 and VO4 molecules trapped in solid noble gas matrixes should be regarded as the VO2(Ng)2 and VO4(Ng) (Ng = Ar or Xe) complexes. The total V-Ng binding energies were predicted to be 12.8, 18.2, 5.0, and 7.3 kcal/mol, respectively, for the VO2(Ar)2, VO2(Xe)2, VO4(Ar), and VO4(Xe) complexes at the CCSD(T)//B3LYP level of theory.

Journal Article↗
PubMed2000

Non-absorbable antibiotics for managing intestinal gas production and gas-related symptoms.

BACKGROUND: Simethicone, activated charcoal and antimicrobial drugs have been used to treat gas-related symptoms with conflicting results. AIM: To study the relationship between gaseous symptoms and colonic gas production and to test the efficacy of rifaximin, a new non-absorbable antimicrobial agent, on these symptoms. METHODS: Intestinal gas production was measured by hydrogen (H2) and methane (CH4) breath testing after lactulose in 21 healthy volunteers and 34 functional patients. Only the 34 functional patients took part in a double-blind, double-dummy controlled trial, receiving, at random, rifaximin (400 mg b.d per 7 days), or activated charcoal (400 mg b.d per 7 days). The following parameters were evaluated at the start of the study and 1 and 10 days after therapy: bloating, abdominal pain, number of flatus episodes, abdominal girth, and cumulative breath H2 excretion. RESULTS: Hydrogen excretion was greater in functional patients than in healthy volunteers. Rifaximin, but not activated charcoal, led to a significant reduction in H2 excretion and overall severity of symptoms. In particular, in patients treated with rifaximin, a significant reduction in the mean number of flatus episodes and of mean abdominal girth was evident. CONCLUSIONS: In patients with gas-related symptoms the colonic production of H2 is increased. Rifaximin significantly reduces this production and the excessive number of flatus episodes.

Absorption↗
PubMed2002

Control of exposure to hexavalent chromium and ozone in gas metal arc welding of stainless steels by use of a secondary shield gas.

Previous work has demonstrated that the shield gas composition in gas metal arc welding can have a considerable effect on hexavalent chromium [Cr(VI)] concentration in the fume and on ozone concentrations near the arc. Normally a single shield gas is used. This paper describes a double shroud torch that allows used of concentric shield gases of different compositions. A solid stainless steel wire was used for welding. The double shroud torch used secondary shield gases containing small amounts of the reducing agents NO and C2H4. The Cr(VI) concentration in the fume and ozone concentration at a fixed point relative to the arc were measured and compared with results when using a single shield gas. Use of the reducing agents in secondary shielding using the double shroud torch was found to offer advantages for ozone concentration reduction compared with use in a conventional torch, but this was not found to be an advantage for reducing Cr(VI) concentrations.

Chromium↗
PubMed1993

Fresh gas flow requirements during spontaneous ventilation: fresh gas flow to total ventilation ratio or ml kg-1 min-1?

Both the performance of breathing systems and recommendations for the fresh gas flows to be used in patients breathing spontaneously can be expressed in ml kg-1 min-1 or fresh gas: total ventilation ratio (VF:VE). We have examined the relationship between these two descriptions. The data of 106 subjects (awake volunteers and anaesthetized patients) were retrieved from the archives of previous work performed in our department. The two methods of describing the requisite fresh gas produced different results, with correlation coefficients (r) between the methods of r = 0.69 and r = 0.49 for the awake and anaesthetized groups, respectively. The results of the multiple regression models suggest that both baseline total ventilation and body weight may be used to predict the fresh gas flow requirements, but residual analysis did not discriminate which method was a better predictor.

Adolescent↗
PubMed2005

Analysis of complex samples by solvating gas chromatography (supercritical fluid to gas transition).

The various forms of chromatography are primarily determined by differences in the physical state of the mobile phases. The main chromatographic categories include gas chromatography (GC), liquid chromatography, and supercritical fluid chromatography. Adjusting a temperature and pressure will change the mobile phase from liquid to supercritical fluid to gas, with concomitant changes in their physical properties. In this paper, the technique transition-phase chromatography (TPC) is described. In TPC, different mobile phase conditions exist inside the column. This phase transformation within the column results in huge differences in density, solvating power, viscosity, diffusivity, and, as a consequence, in the chromatographic properties of the mobile phase. TPC experiments using capillary columns packed in our laboratory have shown that when the mobile phase is transformed from supercritical fluid to gas, high column efficiencies can be achieved. The transition from supercritical fluid to gas (also called solvating GC), a particular case of the TPC, is evaluated for the separation of complex real samples (environmental, food, and fuels).

Journal Article↗
PubMed1990

Design and validation of an indicator gas injector for multiple gas washout tests in mechanically ventilated patients.

A device to produce a stepwise indicator gas fraction variation to initiate a washout test in mechanically ventilated patients is described. The device, which can be used in conjunction with the commonly used Siemens-Elema series 900 ventilators, is based on simple, off-the-shelf technology. It features the simultaneous use of two indicator gases (so that the influence of diffusion processes in the gas exchange to the patient can be measured) and maintains a nearly constant FIO2 during a washout procedure. With this indicator gas injector, the transition time of the indicator gas fraction at the beginning of a washout proved to be short enough to detect ventilation inhomogeneity by visual inspection of the washout curves. Functional residual capacity measurements using this device are presented on a test lung with known volume, on healthy volunteers, and on critically ill patients.

Adolescent↗
PubMed2005

Quantum gas-liquid condensation in an attractive Bose gas.

Gas-liquid condensation (GLC) in an attractive Bose gas is studied on the basis of statistical mechanics. Using some results in combinatorial mathematics, the following are derived. (1) With decreasing temperature, the Bose-statistical coherence grows in the many-body wave function, which gives rise to the divergence of the grand partition function prior to Bose-Einstein condensation. It is a quantum-mechanical analogue to the GLC in a classical gas (quantum GLC). (2) This GLC is triggered by the bosons with zero momentum. Compared with the classical GLC, an incomparably weaker attractive force creates it. For the system showing the quantum GLC, we discuss a cold helium 4 gas at sufficiently low pressure.

Journal Article↗
PubMed2004

Dilute Fermi gas in quasi-one-dimensional traps: from weakly interacting fermions via hard core bosons to a weakly interacting Bose gas.

We study equilibrium properties of a cold two-component Fermi gas confined in a quasi-one-dimensional trap of the transverse size l(perpendicular). In the dilute limit (nl(perpendicular)<<1, where n is the 1D density) the problem is exactly solvable for an arbitrary 3D fermionic scattering length aF. When l(perpendicular)/aF goes from -infinity to +infinity, the system successively passes three regimes: weakly interacting Fermi gas, hard core Bose gas, and weakly coupled Bose gas. The regimes are separated by two crossovers at aF approximately +/-nl2(perpendicular). In conclusion, we discuss experimental implications of these results.

Journal Article↗
PubMed2006

Observations of density fluctuations in an elongated Bose gas: ideal gas and quasicondensate regimes.

We report in situ measurements of density fluctuations in a quasi-one-dimensional 87Rb Bose gas at thermal equilibrium in an elongated harmonic trap. We observe an excess of fluctuations compared to the shot-noise level expected for uncorrelated atoms. At low atomic density, the measured excess is in good agreement with the expected "bunching" for an ideal Bose gas. At high density, the measured fluctuations are strongly reduced compared to the ideal gas case. We attribute this reduction to repulsive interatomic interactions. The data are compared with a calculation for an interacting Bose gas in the quasicondensate regime.

Journal Article↗
PubMed1975

Effects on breathing mechanics and gas exchange of different inspiratory gas flow patterns during anaesthesia.

Ten patients without known cardiac or respiratory disease were investigated with breathing mechanics and gas exchange studies during anaesthesia and artifical ventilation. The effects of three different inspiratory gas flow patterns, namely, accelerating, constant and decelerating flows were studied. A decelerating flow resulted in an increase of total compliance when compared to an accelerating or a constant flow. However, at the same time, there was an increase in physiological dead space and a decrease in alveolar ventilation with a decelerating flow compared to an accelerating flow. These results seem to indicate an improved gas distribution in the greater airways with a decelerating flow pattern, but when the total effects of gas exchange were judged, the greatest benefits were with an accelerating flow.

Adult↗
PubMed1982

Pulmonary gas exchange during altered density gas breathing.

The alveolar-arterial O2 partial pressure difference (PAO2 - PaO2) has been shown to decrease as carrier-gas density increases. This study was designed to confirm or deny the hypothesis that the improvement in O2 exchange is a result of density-dependent changes in the alveolar ventilation-perfusion (VA/Q) distribution. On changing from heliox breathing to air breathing, there was an improvement in oxygen exchange along with a slight worsening of VA/Q distribution. The conclusion is reached that changes in VA/Q distribution due to altered carrier-gas density are not responsible for changes in O2 exchange. A possible explanation is related to the interaction of diffusion and convection on inspiration, which may cause inspired gas distribution to be different from overall ventilation distribution. The interesting implication is that gas exchange properties of gases eliminated from the blood and exhaled are not necessarily symmetrical to the properties of gases inhaled and taken up by the blood.

Acetone↗
PubMed2002

Hyperbaric oxygen may reduce gas bubbles in decompressed prawns by eliminating gas nuclei.

It is accepted that gas bubbles grow from preexisting gas nuclei in tissue. The possibility of eliminating gas nuclei may be of benefit in preventing decompression sickness. In the present study, we examined the hypothesis that hyperbaric oxygen may replace the resident gas in the nuclei with oxygen and, because of its metabolic role, eliminate the nuclei themselves. After pretreatment with oxygen, prawns were 98% saturated with nitrogen before explosive decompression at 30 m/min. Ten transparent prawns were exposed to four experimental profiles in a crossover design: 1) 10-min compression to 203 kPa with air; 2) 10-min compression with oxygen; 3) 10-min compression with oxygen to 203 kPa followed by 12 min air at 203 kPa; and 4) 10 min in normobaric oxygen followed by compression to 203 kPa with air. Bubbles were measured after explosive decompression. We found that pretreatment with hyperbaric oxygen (profile C) significantly reduces the number of bubbles and bubble volume. We suggest that hyperbaric oxygen eliminates bubble nuclei in the prawn.

Animals↗
PubMed2004

Trends in atmospheric trace gas measurement instruments with membrane-based gas diffusion scrubbers.

A diffusion scrubber (DS) is an excellent tool for gas analysis, and there are many types of DS devices, varying both in structure and construction. In this paper, recent work on atmospheric trace gas measurements by means of DS devices are reviewed. Theoretical considerations on representative DSs are summarized first. Then, the characteristics of the key material, a gas-diffusion membrane, are discussed, and recent improvements and novel scrubbers for highly effective collection are outlined. A chromatograph is a suitable tool for the multi-gas analysis of collected species. On the other hand, solid-state fluorescence/absorbance detectors have been developed for the continuous measurement of target gases. The methods based on DS collection and subsequent detection have high sensitivities, and the detection limits can be in the low-pptv levels. Accordingly, they are capable of measuring background levels, and detecting very low levels of contaminants in a cleanroom. Miniaturized advanced DS units, perhaps the next generation of DS devices, are introduced at the end of this review. DS systems have contributed significantly to our knowledge of the atmospheric dynamics and atmospheric chemistry.

Journal Article↗
PubMedDate not supplied

The effect of tubing length, gas flow, and number of heaters on maximum gas temperature for aerosol circuits used for cold water near-drowning or hypothermia.

BACKGROUND: Clinicians who treat patients suffering from cold water near-drowning or hypothermia routinely warm inspire gases greater than body temperature in accordance with care guidelines promulgated by the various organizations. However, humidifiers are designed to prevent heating gases beyond 41 C (assuming the use of a standard six foot aerosol circuit) in order to meet International Standards Organization regulations (ISO). Clinicians must modify equipment in order to deliver care. There are several factors, which can effect the highest temperature that a particular circuit will achieve. Among the factors that are considered most important for maximum circuit are tubing length, gas flow, and the number of heaters (heat source). METHODS: The maximum temperature that a circuit could achieve was measured after varying tubing lengths (1.5 feet, 3 feet, and 6 feet), gas flow (opening or closing a venturi receiving a fixed flow rate of 10 L/min), and the size of the heat source (one or two heated humidifiers in aerosol circuit). A total of ten runs were made in each of the possible twelve combinations. RESULTS: Univariate statistics showed significant differences for Venturi open/close (p = .0001) and the number of heaters (p = .0001) but not the tubing length (p = 0.19). However, the multivariate analysis revealed significance for tubing length, number of heaters, and venturi open/closed (p = .01). CONCLUSION: All factors (tubing length, number of heaters, and tubing length) were important determinants of maximum gas temperature. The effect of tubing length can be overwhelmed by higher gas flows.

Analysis of Variance↗
PubMed2003

The effect of breathing hyperoxic gas during simulated submarine escape on venous gas emboli and decompression illness.

Raised internal pressure in a distressed submarine rapidly increases the risk of decompression sickness (DCS) following submarine escape. The hypothesis that breathing a hyperoxic gas during escape may reduce the risk of DCS was tested using goats. Shallow air saturation and simulated submarine escape dives were carried out either singularly or in combination (saturation, escape, or saturation followed by escape) using air or 60% / 40% oxygen (O2) / nitrogen (N2) mixture as breathing gas during the escapes. Post-surfacing, animals were observed for signs of DCI and O2 toxicity. Precordial Doppler ultrasound was used to score venous gas emboli (VGE) using the Kisman Masurel (KM) scale. Following escape from 2.5 MPa, the rate at which VGE disappeared in the hyperoxic group (n = 8) was significantly faster(p < 0.05) than the air group (n = 7). One case of pulmonary barotrauma with arterial gas embolism occurred in the air group, but no cases of DCS were observed. After saturation at 0.18 MPa followed by escape from 2.5 MPa, DCS occurred in four of 15 animals in the air group and in two of 16 animals in the hyperoxic group. The rate of disappearance of VGE was significantly faster (p < 0.01) in the hyperoxic group. O2 toxicity was not discernible in any of the animals.

Air↗
PubMedDate not supplied

[Gas weapons as a variation on gas-propelled firearms].

Discusses the motion of gas weapons as defence weapons, including the group of gas barrel guns. Characterizes its design and ammunition. Presents arguments in favor of referring gas barrel guns to firearm devices. Shows the place of gas barrel guns in the general classification of ejecting devices and offers a classification of civil chemical weapons.

Chemical Warfare↗
PubMed1979

Inline blood gas analysis by gas chromatography in patients during and after coronary artery surgery.

A system was evaluated of measuring Pao2 and Pao2 by an inline sensor in the brachial artery and gas chromatography. Eight patients having coronary artery vein grafts were studied during anaesthesia, operation, perfusion and for 24 hours afterward. Compared to conventional blood gas analysis by polarography (electrodes), the chromatographic method gave readings for Pao2 which were not significantly different during normothermia. During hypothermic perfusion, the chromatographic system read significantly higher than the bench electrode, due at least in part to a difference in temperature correction. For Pao2 the correlation between the two methods was close and differences were clinically insignificant. The Sentorr blood-gas analyser provides a sensitive, accurate indicator of changes in oxygenation, ventilation and circulation during anaesthesia and in the intensive care unit.

Anesthesia, Inhalation↗