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At least 343 records · Page 19Linked to original sources
PubMed1985

Adult survival with intrahepatic portal venous gas secondary to acute gastric dilatation, with a review of portal venous gas.

The radiological observation of hepatic portal venous gas on plain abdominal radiography, ultrasonography or computed tomography is a highly significant finding. Its cause warrants urgent diagnosis and will usually require surgical management. Current overall mortality rate associated with this sign is 75%. A case of acute gastric dilatation with hepatic portal venous gas in an adult who survived without surgery is presented. Patients having this sign after double-contrast barium enemas with quiescent inflammatory bowel disease have also been reported to survive without surgery.

Acute Disease↗
PubMed1999

[Medical gas delivery systems. Activity report of the local commission for surveillance of gas delivery at the University Hospital of Nancy].

Local commissions for the surveillance of medical gas supply systems were made compulsory in France in 1985. This article analyses the activity of the local commission of the University hospital of Nancy. Main anomalies which occurred in the pipeline network, especially tightness problems, are discussed. Difficulties concerning the planning and the course of the visits of the gas supply systems by the commission are analysed. Finally, the actual power and responsibility of the commission members are considered.

Accidents, Occupational↗
PubMed1994

[Distribution of a hypoxic gas mixture by retro-pollution of a medical gas distribution system].

The authors report a case of retropollution through the defective gas mixer of a Logic O4T-IMV ventilator (Ohmeda) located in the recovery room. Due to a defective check valve inside the mixer, medical air entered into the oxygen pipeline when the O2 pressure decreased below the pressure inside the medical air pipeline. This incident resulted in episodes of hypoxic gas mixture delivery in the operating theatre, when nitrous oxide was associated with oxygen polluted with medical air. The occurrence of such an incident, rarely described so far, requires the association of several factors. It can be recognized without delay with the continuous use of an oxygen analyser.

Air↗
PubMed2001

Gas phase RNA and DNA ions 2. Conformational dependence of the gas-phase H/D exchange of nucleotide-5'-monophosphates.

The conformational dependence of the gas-phase hydrogen/deuterium (H/D) exchange of nucleotide-5-monophosphate anions with the H/D exchange reagent D2S is reported here. The electrospray-generated [M-H]- anions of adenosine-5'-monophosphate, adenosine-5'-carboxylic acid, ribitol-5-phosphate, and 2-deoxy-ribitol-5-phosphate were reacted with D2S in the gas phase. Their reactivity (adenosine-5'-monophosphate exchanged 2 of 5 labile hydrogens, adenosine-5'-carboxylic acid exchanged 1 of 4, ribitol-5-phosphate exchanged 2 of 3, and 2-deoxy-ribitol-5-phosphate exchanged 1 of 2) suggests that the hydroxyl group in the 2 position of the ribose sugar and the amino hydrogen on the nucleobase do not exchange readily with D2S. Semiempirical molecular orbital calculations suggest that the labile hydrogens in these positions are thermodynamically facile to exchange but as a conformation inaccessible to the presumed phosphate anion, consistent with a mechanism in which the phosphate anion complexes with the exchange reagent and assists H/D exchange at a neighboring site.

Adenosine↗
PubMed2000

Gas sampling glow discharge: a versatile ionization source for gas chromatography time-of-flight mass spectrometry

A gas chromatograph has been coupled to a direct-current gas sampling glow discharge (GSGD) ionization source for the mass spectrometric analysis of halogenated hydrocarbons. The continuous discharge is contained within the first vacuum stage of the differentially pumped spectrometer interface. The discharge can be operated statically or rapidly switched between atomic and molecular ionization modes; both atomic and molecular spectra could be generated in the helium-supported plasma. In the switched configuration, the duty cycle is 50% for each mode. The ionization mode is selected by application of either a positive (molecular) or negative (atomic) potential to the sample introduction electrode, and the two kinds of spectra can be sequentially collected by changing the voltage and current between two preset values. Similar ion-optical voltage settings could be employed for both modes of operation, with the exception of the steering-plate potential, which had to be modulated between two different values (at the plasma switching frequency) to obtain the greatest atomic and molecular signal levels. The source is capable of generating mass spectra resembling those from an electron-impact source while operated in the molecular ionization mode (both static and dynamic). The best atomic detection limits (1-25 fg of analyte/ second) were obtained when the plasma was operated in the static mode with single-channel gated ion counting. Atomic detection limits obtained with boxcar averager data collection were comparable for static and switched operation of the source (1-30 pg/s). Likewise, the molecular detection limits were similar for the static and switched modes and span the range of 7-140 pg/s (boxcar averagers). Precision was better than 7% RSD under all conditions. The atomic and molecular chromatographic peak heights were nearly unchanged over a range of modulation rates from 5 to 100 Hz. The elemental ratio (35Cl+/12C+) for chloroform was also measured over a range of plasma modulation rates (5-90 Hz) and found to be randomly distributed about the sample mean. Several chlorinated hydrocarbons were introduced into the discharge and could be successfully differentiated (or speciated) on the basis of their 35Cl+/12C+ ratios.

Journal Article↗
PubMed2006

Theoretical approximation for the linear flow of carrier gas through a rectangular gas chromatographic column.

A simple relationship for the average linear velocity of carrier gas flowing through a rectangular gas chromatographic column is derived. Since the relationship agrees remarkably well with published experimental data taken from a variety of sources, it should be very useful in practical application. This is particularly true for micro-fabricated etched silicon columns that often have a rectangular cross-section. Knowledge of the average linear velocity facilitates calculation of the height equivalent to a theoretical plate (HETP), a measure of resolution for the column.

Journal Article↗
PubMed2000

Determination of main and minor components of silicon based materials by a combustion with elemental fluorine. Separation of gaseous fluorination products by carrier gas distillation and gas mass spectrometry

For the determination of main and minor components in silicon-based ceramic powders, a decomposition by a combustion with elemental fluorine and separation of the volatile fluorination products by a carrier-gas distillation with a subsequent detection by quadrupole mass spectrometry is described. The necessity and success of the separation step is demonstrated for the determination of boron as a minor constituent in SiC, where the spectral interferences of silicon on the boron signals are decreased considerably. The method developed is shown to be directly applicable to determination of silicon in Si3N4, SiC, and SiO2. The determination of nitrogen in Si3N4 requires additional effort, to separate nitrogen from the excess of fluorine. For the determination of boron, a complete mobilization of BF3 is assured by the presence of an adequate amount of GeF4. Analysis results obtained with different types of calibration show a precision of 30 microg for boron at the milligram-per-gram level and a precision between 0.5 and 2% (m/m) for the main components, silicon and nitrogen. Within these standard deviations, the results agree well with the values expected from the stoichiometry, with the results for silicon and boron obtained by wet chemical decomposition and slurry techniques in combination with ICP-OES and with the results for nitrogen obtained by carrier gas heat extraction.

Journal Article↗
PubMed2004

Theoretical study of the gas-phase Fe(CO)5 catalyzed water gas shift reaction: a new mechanism proposed.

A novel mechanism for the gas-phase Fe(CO)(5) and base catalyzed water gas shift reaction has been examined. The reaction pathway described here is predicted at the B3LYP/6-31++G(d,p) level to be energetically competitive with the classic mechanism. The reaction path explored here involves the energetically barrierless formation of (CO)(4)FeCOOH(-) (the catalyst of the system) decarboxylation induced by the addition of CO to give (CO)(4)FeCHO, and evolution of H(2) upon addition of H(2)O to the (CO)(4)FeCHO intermediate. The energetic barriers predicted for the last two steps are 21.2 and 42.0 kcal/mol, respectively, using the B3LYP method.

Journal Article↗
PubMed1998

Gas-Phase Reaction of Tetraborane(10) and Ethyne: Molecular Structure of nido-1,2-C(2)B(3)H(7) in the Gas Phase.

The molecular structure of nido-1,2-C(2)B(3)H(7), 1, the principal volatile carborane generated in the quenched gas-phase reaction of B(4)H(10) and ethyne at 70 degrees C, has been determined by a combined analysis of gas-phase electron-diffraction data and rotation constants restrained by ab initio computations at the CCSD(T)/TZP' level. The structure is consistent with a geometry having C(s)() symmetry, similar to that of pentaborane(9). The apical position is occupied by a carbon atom, displaced toward B(4) from a position directly above the B(5).B(3) vector, and hydrogen atoms asymmetrically bridge the B-B bonds. The basal atoms are almost coplanar, C(2) lying ca. 2 degrees below the B(3)-B(4)-B(5) plane. Important experimental structural parameters (r(alpha) degrees /pm, angle(alpha)/ degrees ) are r[C(1)-C(2)] = 162.6(6); r[C(1)-B(3)] = 161.4(3); r[C(2)-B(3)] = 154.3(2); r[C(1)-B(4)] = 157.4(5); r[B(3)-B(4)] = 185.7(3); <B(3)-B(4)-B(5) = 80.9(1). In addition to this and the other previously reported carboranes, 2,3-C(2)B(4)H(8), 2-Me-2,3,4-C(3)B(3)H(6), and 4-Me-2-CB(5)H(8), several new derivatives have been identified among the volatile products. These include the dicarbahexaboranes 2,4-Me(2)-2,3-C(2)B(4)H(6) and 5-Et-2,3-C(2)B(4)H(7) (the major volatile products obtained when the reaction is allowed to go to completion, previously reported as tricarbahexaboranes) and the derivatives 2,5-Me(2)-2,3-C(2)B(4)H(6), 4-Et-2,3-C(2)B(4)H(7), 1-Me-2,3,4-C(3)B(3)H(6), 2-Me-2-CB(5)H(8), 3-Me-2-CB(5)H(8), and 2,3,4,5-C(4)B(2)H(6). The complex mechanism of the reaction is discussed in light of these new results.

Journal Article↗
PubMed2003

Noble gas-actinide complexes of the CUO molecule with multiple Ar, Kr, and Xe atoms in noble-gas matrices.

Laser-ablated U atoms react with CO in excess argon to produce CUO, which is trapped in a triplet state in solid argon at 7 K, based on agreement between observed and relativistic density functional theory (DFT) calculated isotopic frequencies ((12)C(16)O, (13)C(16)O, (12)C(18)O). This observation contrasts a recent neon matrix investigation, which trapped CUO in a linear singlet state calculated to be about 1 kcal/mol lower in energy. Experiments with krypton and xenon give results analogous to those with argon. Similar work with dilute Kr and Xe in argon finds small frequency shifts in new four-band progressions for CUO in the same triplet states trapped in solid argon and provides evidence for four distinct CUO(Ar)(4-n)(Ng)(n) (Ng = Kr, Xe, n = 1, 2, 3, 4) complexes for each Ng. DFT calculations show that successively higher Ng complexes are responsible for the observed frequency progressions. This work provides the first evidence for noble gas-actinide complexes, and the first example of neutral complexes with four noble gas atoms bonded to one metal center.

Journal Article↗
PubMed2004

Gas-phase hydrogen/deuterium exchange and conformations of deprotonated flavonoids and gas-phase acidities of flavonoids.

Gas-phase hydrogen/deuterium (H/D) exchange was used to probe the conformations, gas-phase acidities, and sites of deprotonation of isomeric flavonoid aglycons and glycosides. The flavonoids in each isomer series were differentiated on the basis of their relative rate constants and total numbers of exchanges. For example, flavonoids that possess neohesperidose-type disaccharides may undergo faster and far more extensive exchange than isomeric rutinoside flavonoids. The structural factors that promote or prevent H/D exchange were identified and correlated with collisionally activated dissociation (CAD) patterns and/or molecular modeling data (both high-level ab initio acidity calculations and conformational analysis with molecular dynamics (MD) simulations), thus providing a framework for the use of H/D exchange reactions in the structural elucidation of new flavonoids.

Carbohydrates↗
PubMed2004

Gas-phase kinetics and mechanism of the reactions of protonated hydrazine with carbonyl compounds. Gas-phase hydrazone formation: kinetics and mechanism.

The gas-phase reactions of protonated hydrazine (hydrazinium) with organic compounds were studied in a selected ion flow tube-chemical ionization mass spectrometer (SIFT-CIMS) at 0.5 Torr pressure and approximately 300 K and with hybrid density functional calculations. Carbonyl and other polar organic compounds react to form adducts, e.g., N(2)H(5)(+)(CH(3)CH(2)CHO). In the presence of neutral hydrazine, aldehyde adducts react further to form protonated hydrazones, e.g., CH(3)CH(2)CH[double bond]HNNH(2)(+) from propanal. Using deuterated hydrazine (N(2)D(4)) and butanal, we demonstrate that the gas-phase ion chemistry of hydrazinium and carbonyls operates by the same mechanisms postulated for the reactions in solution. Calculations provide insight into specific steps and transition states in the reaction mechanism and aid in understanding the likely reaction process upon chemical or translational activation. For most carbonyls, rate coefficients for adduct formation approach the predicted maximum collisional rate coefficients, k approximately 10(-9) cm(3) molecule(-1) s(-1). Formaldehyde is an exception (k approximately 2 x 10(-11) cm(3) molecule(-1) s(-1)) due to the shorter lifetime of its collision complex. Following adduct formation, the process of hydrazone formation may be rate limiting at thermal energies. The combination of fast reaction rates and unique chemistry shows that protonated hydrazine can serve as a useful chemical-ionization reagent for quantifying atmospheric carbonyl compounds via CIMS. Mechanistic studies provide information that will aid in optimizing reaction conditions for this application.

Journal Article↗
PubMed2005

Gas adsorption in active carbons and the slit-pore model 1: Pure gas adsorption.

We describe procedures based on the polydisperse independent ideal slit-pore model, Monte Carlo simulation and density functional theory (a 'slab-DFT') for predicting gas adsorption and adsorption heats in active carbons. A novel feature of this work is the calibration of gas-surface interactions to a high surface area carbon, rather than to a low surface area carbon as in all previous work. Our models are used to predict the adsorption of carbon dioxide, methane, nitrogen, and hydrogen up to 50 bar in several active carbons at a range of near-ambient temperatures based on an analysis of a single 293 K carbon dioxide adsorption isotherm. The results demonstrate that these models are useful for relatively simple gases at near-critical or supercritical temperatures.

Journal Article↗
PubMed2004

Gas-liquid and gas-liquid-solid catalysis in a mesh microreactor.

A microstructured mesh contactor that can offer residence time of more than minutes is used for gas-liquid-solid hydrogenations and gas-liquid asymmetric hydrogenations. Applications for catalyst/chiral inductor screening and for kinetic data acquisition are demonstrated.

Journal Article↗
PubMed2005

A comparative study of ethylene oxide gas, hydrogen peroxide gas plasma, and low-temperature steam formaldehyde sterilization.

OBJECTIVE: To compare the efficacies of ethylene oxide gas (EOG), hydrogen peroxide gas plasma (PLASMA), and low-temperature steam formaldehyde (LTSF) sterilization methods. METHODS: The efficacies of EOG, PLASMA, and LTSF sterilization were tested using metal and plastic plates, common medical instruments, and three process challenge devices with narrow lumens. All items were contaminated with Bacillus stearothermophilus spores or used a standard biological indicator. RESULTS: EOG and LTSF demonstrated effective killing of B. stearothermophilus spores, with or without serum, on plates, on instruments, and in process challenge devices. PLASMA failed to adequately sterilize materials on multiple trials in several experiments, including two of three plates, two of three instruments, and all process challenge devices. CONCLUSIONS: Our results suggest that PLASMA sterilization may be unsuccessful under certain conditions, particularly when used for items with complex shapes and narrow lumens. Alternatively, LTSF sterilization demonstrates excellent efficacy and is comparable to EOG sterilization. LTSF could potentially act as a substitute if EOG becomes unavailable due to environmental concerns.

Equipment and Supplies↗
PubMed2003

Conversion of an atomic Fermi gas to a long-lived molecular Bose gas.

We have converted an ultracold Fermi gas of 6Li atoms into an ultracold gas of 6Li2 molecules by adiabatic passage through a Feshbach resonance. Approximately 1.5 x 10(5) molecules in the least-bound, v=38, vibrational level of the X1Sigma(+)(g) singlet state are produced with an efficiency of 50%. The molecules remain confined in an optical trap for times of up to 1 s before we dissociate them by a reverse adiabatic sweep.

Journal Article↗
PubMed1978

Influence of abdominal gas on the Boyle's law determination of thoracic gas volume.

In a body plethysmograph we have demonstrated differences in total lung capacity (TLC) derived from panting maneuvers performed at different levels in the vital capacity. In almost all cases, the discrepancies were due to the magnitude of the abdominal gas volume (AGV) and the relative magnitude of abdominal and thoracic pressure swings during the panting mandeuver. When panting was performed at functional residual capacity (FRC), the effect of AGV compression on the determination of thoracid gas volume (TGV) was small. Of 11 individuals studied 2 were known to have mild asthma. Compression and decompression of AGV appeared to be an insufficient explanation for discrepancies in derived TLC's in these two, suggesting that other as yet unidentified factors may influence the plethysmographic determination of TGV.

Gases↗