Search Results - (Author, Cooperation:M. Chakrabarti)

2013-04-26

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

Aerobiosis ; Archaea/metabolism ; Bacteria/*metabolism ; Bacterial Proteins/chemistry/metabolism ; *Biocatalysis ; Deoxyadenosines/chemistry/metabolism ; Electron Spin Resonance Spectroscopy ; Glycine/chemistry/metabolism ; Hydrogen/metabolism ; Lyases/chemistry/metabolism ; Mass Spectrometry ; Methane/*biosynthesis/chemistry/metabolism ; Methionine/metabolism ; Mutant Proteins/chemistry/genetics/metabolism ; Pentosephosphates/chemistry/metabolism ; S-Adenosylmethionine/metabolism

2018-07-24

American Chemical Society (ACS)

1520-5207

Chemistry and Pharmacology

Physics

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

The generalized resonance enhanced two-photon dissociation (RETPD) cross sections of H2 are calculated for crossed and circular (same- and opposite-sense) polarizations of the two-photon fields using the reduced density operator formalism for the transitions X 1Σ+g(vg=0, Jg=0–4) →(ω1,εˆ1)VUVB 1Σ+u (C 1Πu)[vi=0, 3, Ji =0(1)–3]→(ω2,εˆ2)UV/visible [(EF+GK)1Σ+g+I 1Πg), Ef,Jf]. The wavelength (λ2) of the second photon is so chosen that ionization from the resonant B(C) state is energetically forbidden. The effects of polarizations on the wavelength and quantum number dependences of RETPD profiles have been studied. For vi=3 of both B and C states, a strong polarization dependence of RETPD cross sections is observed. The same- and opposite-sense circular polarizations have about the same RETPD profiles for the B state except at the shape resonance positions due to the final I state quasibound level, while the profiles are quite different for the C state.

Electronic Resource

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

The generalized resonance enhanced two-photon dissociation (RETPD) cross sections of H2 are calculated for linear parallel polarizations of the two photon fields. The reduced density operator formalism is used to study the wavelength and quantum number dependences for the transitions X 1Σ+g (vg=0, Jg=0–4) →vuv B 1Σ+u (C 1Πu) [vi=0,3, Ji=0(1)–3] →uv/visible [(EF+GK)1 Σ+g +I 1Πg, Ef, Jf]. By resonant absorption of the first photon an aligned population in the intermediate B(C) is created which is then dissociated by the second photon. The wavelength is so chosen that ionization from the resonant intermediate state is energetically forbidden. The contribution of the EF state to the total cross section is found to be negligible. The relative contribution of the GK and I states varies sharply with wavelength of the second photon and the resonant intermediate state. For both B and C states, dissociation through the I state is more prominent over a narrow range of wavelengths far from the dissociation threshold when the vibrational quantum number (vi) is large. For small vi the contribution of the I state is less. Due to the presence of a barrier above the dissociation threshold in the I state potential, narrow shape resonances occur. The cross sections at these shape resonances are a few orders of magnitude higher than the background. The detailed line shapes at these resonances have been presented for all the rotational quantum numbers considered for vi=0 and 3 of the B and C states.

Electronic Resource

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

We have studied the resonant two-photon dissociation (TPD) of vibrationally excited HD+ by both 1sσg→1sσg vibrational and 1sσg→2pσu electronic transitions. Following Armstrong et al., a quantum mechanical description of the laser field enabled us to define the intermediate resonant state as a "pseudodissociating state'' of the molecule–radiation system. This makes our theory formally similar to that of single-transition (photon) autoionization problem as formulated by Fano. This similarity has been exploited to obtain the intensity dependent line shapes of the resonant TPD of HD+. Resonant TPD cross sections from the vi=6, Ji=0 level of the ground 1sσg state of HD+ are calculated with a linearly polarized infrared laser radiation in the wavelength range 16 530–16 565 A(ring) and at different intensities ranging from 1.53×108–3.83×1013 W/cm2. Effects of laser intensity on the linewidth, line shift, and cross sections are found to be very different for the two types of transitions. Our previous results of nonresonant TPD cross sections are reproduced via this model.

Electronic Resource

1365-2044

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

We have examined the predictability of inspired isoflurane concentration during low-flow anaesthesia using a to-and-fro breathing system. Twenty one adult patients requiring mechanical ventilation of the lungs during surgery took part in this study. Using a fresh gas flow of 2 l.min-1, the ratio of inspired isoflurane concentration to isoflurane vaporizer setting was found to be approximately 4/5th after 5 min of anaesthesia. The ratio was maintained throughout the procedure, except for a few minutes following each change in vaporizer setting.

Electronic Resource

1365-2044

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

The insertion of a long deadspace tube between an anaesthetic breathing system and a ventilator produces only imperfect separation of the breathing system gas from the driving gas. This laboratory study has investigated different connecting tubes to establish the maximum tidal volume possible before ventilator gas contaminates the gas in a low-flow to-and-fro system (fresh gas flow 1 litre/minute). A larger volume tube enables the use of larger tidal volumes, and plastic corrugated tubes are slightly better than black rubber corrugated tubes in this respect. The maximum tidal volume possible without contamination decreases as ventilatory rate increases, but the maximum minute volume is increased. A 22 mm plastic corrugated tube of internal volume 1.5 litres should be adequate for clinical use with the to-and-fro system described in this study at afresh gas flow of 1 litre/minute.

Electronic Resource

1365-2044

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

A volume meter (Dräger Spirolog I) is evaluated for clinical use. It works on the principle of a constant temperature anemometer and displays tidal volume, minute volume and frequency. It was found that the volume recorded was hardly affected by oxygen concentration, humidity or temperature but was affected by high concentrations of nitrous oxide and during the operation of diathermy.

Electronic Resource

1365-2044

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Midazolam (15 mg), pentobarbitone (100 mg) and a placebo were administered orally to nine male volunteers in double-blind crossover studies and the effect on the ventilatory response to carbon dioxide was observed for periods of 6 hours. It was concluded that neither drug caused any significant degree of respiratory depression.

Electronic Resource

1365-2044

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Electronic Resource

1365-2044

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

The uptake of enflurane at a constant end-expired concentration of 2% in oxygen was studied in 38 patients, ASA 1 or 2, undergoing elective orthopaedic procedures. The anaesthetic was administered using a computer-controlled closed circle system. Following an initial 4 min period during which the expired concentration of enflurane was established, the rate of uptake of enflurane showed a triexponential decline. The mean cumulative use of enflurane after 60min was 10.7ml, and after 120min was 18.4ml.

Electronic Resource

1365-2044

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

A laboratory study of a new circle system is presented. The inspiratory limb encloses a coaxial tube, delivering fresh gas close to the patient, immediately upstream of the inspiratory one-way valve. The system is more efficient than the non-coaxial system and allows the expiratory valve to be situated conveniently at the canister end of the expiratory limb. A disadvantage of low flow anaesthesia is the sluggish response of the system to changes in vapour or oxygen concentrations in the fresh gas flow. This is markedly improved by the new system. The advantages of the system are largely independent of respiratory pattern.

Electronic Resource

1365-2044

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

The amount of desflurane required to maintain an end-expired concentration of 8% was measured in 30 ASA 1 and 2 patients undergoing elective spinal surgery. The anaesthetic was administered using a computer-controlled closed circle system. After an initial period during which the expired concentration of desflurane was stabilised (4 min) the rate of uptake showed a bi-exponential decline. Mean cumulative usage of desflurane was 10.1 ml of liquid at 30min, 14.8ml at 60min, 25.4ml at 120min, 35.8 at 180min.

Electronic Resource

1365-2044

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

It may be possible to overcome the classical disadvantages of a to-and-fro system by the use of a small soda lime canister. We report our experience of such a system in a series of 13 adult patients requiring mechanical ventilation of the lungs during surgery. The system was found to be convenient to use and the charge of soda lime had sufficient absorptive capacity to last throughout the great majority of surgical cases. Using afresh gas flow of 11.min−1, the ratio of inspired isoflurane concentration to isoflurane vaporizer setting was found to be approximately one half after 10 min of anaesthesia. This ratio was maintained throughout the procedure, except for a few minutes following each change in vaporizer setting. A to-and-fro system using a small soda lime canister is a convenient alternative to the circle system for low-flow anaesthesia.

Electronic Resource

1365-2044

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

The main disadvantages of the to-and-fro system (the bulky canister and the progressive increase in apparatus deadspace) may be overcome by the use of a smaller canister. In this laboratory study, we have evaluated a 160 g canister in a low-flow to-and-fro system (fresh gas flow 1 litre I minute). Two carbon dioxide productions of 150 and 200 ml/minute were simulated. The mean times to exhaustion, defined here as a 0.5 kPa rise in end-tidal Pco2, were 112 and 79 minutes in the 150 and 200 ml/minute carbon dioxide groups respectively. Ventilation to normacapnia or hypocapnia did not affect the times to exhaustion. The soda lime absorbed 16 litres of carbon dioxide before exhaustion, and this was not affected by minute volume or carbon dioxide production. A small soda lime canister is suitable for carbon dioxide absorption in a low-flow to-and-fro system for ventilated adults.

Electronic Resource

1365-2044

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

A prototype valveless ventilator was attached by open deadspace tubing to a circle system and used to ventilate the lungs of 12 patients with low flows of anaesthetic gases for periods between 60 and 120 minutes during intra-abdominal surgery. Anaesthesia was induced with thiopentone and maintained with nitrous oxide 50% in oxygen and enflurane. This was reduced to 2 litres/minute after a 10-minute period of nitrogen wash out and stabilisation of anaesthetic gas concentration, with an initial anaesthetic gas flow of 6 litres/minute. The concentration of oxygen, carbon dioxide, nitrous oxide and enflurane were measured in the outflow from both the anaesthetic machine and the inspiratory limb of the circle system. The measured mean inspired oxygen and nitrous oxide concentrations showed no significant variation throughout the low flow period of the study. This new low flow open circle ventilation system appears to offer some advantages in terms of safety and versatility over other systems which are discussed.

Electronic Resource

1365-2044

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

A circle breathing system was connected by deadspace tubing to an open system valveless ventilator. The minimum volume of this tubing, required to prevent dilution of anaesthetic gas in the breathing system by the driving gas of the ventilator, was determined at frequencies of 15, 30, 60, 100 and 150 breaths/minute, with tidal volumes that ranged from 100 to 1100 ml and a fresh gas supply to the circle system of 1, 2 and 4 litres/minute. At 15 breaths/minute, tidal volumes equal to or less than the deadspace volume could be used safely without any mixing with the ventilator driving gas, when a fresh gas flow of 2 litres/minute or above is supplied to the circle system. At 1 litre/minute of fresh gas flow, mixing occurred at tidal volumes less than the deadspace volume. Mixing of gas occurred in the system at frequencies greater than 30 breaths/minute even when the tidal volume was much less than the deadspace volume. However, at high frequencies of ventilation, since the tidal volume requirement decreases, deadspace tubing with a safe internal volume, that is greater than 600 ml, may be used up to 100 breaths/minute.

Electronic Resource

1365-2044

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Ten patients, whose lungs were ventilated initially with intermittent positive pressure ventilation at conventional rates after myocardial revascularisation or cardiac valvular surgery, were weaned using a valveless high frequency jet ventilator at a constant rate of 50 breaths/minute. The withdrawal of ventilation was achieved, when clinical criteria permitted, by reduction of the tidal volume preset on the jet ventilator in successive stages; this was effected by stepwise decreases in the jet driving pressure. This new mode of weaning at a constant rate of 50 breaths/minute is associated with minimum peak airway pressures. Synchronisation of the patient's breathing with the valveless ventilator is not required and weaning is tolerated well by the patient. Arterial oxygen tension and saturation were maintained throughout weaning and did not decline after extubation of the trachea.

Electronic Resource

1365-2044

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

A new electronic ventilator for application during closed breathing system anaesthesia is described (OAV7700, Ohmeda). It is easy to use and can be mounted on any conventional anaesthetic machine. It has several desirable features, such as a simple control and display panel, appropriate alarms and a patient breathing system that can be autoclaved. Observations were made on seven patients undergoing major surgery. Anaesthetic gases were introduced at 1, 2 and 4 litres/minute at three points in the breathing system, one conventionally in the closed system, one at the ventilator and one in the tracheal tube. Carbon dioxide homeostasis was maintained during this procedure. The application of fresh gas flows of 2 and 4 litres/minute in the tracheal tube allowed a small but significant reduction in the mean tidal volume. However, it was concluded that a fresh gas flow of 1 litre/minute applied conventionally either into the closed system or at the ventilator, provided optimal conditions.

Electronic Resource

1365-2044

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

The Ohmeda Rascal II is a multigas analyser and pulse oximeter for dedicated anaesthetic use. It uses the Raman scattering of laser light to identify and quantify oxygen, nitrogen, carbon dioxide, nitrous oxide and three volatile anaesthetic agents. Its response times equal or better the published response times of infrared or photo-acoustic devices. It is linear within the clinical ranges of all gases and vapours, simple to use, requires no maintenance, holds its calibration well, and is a suitable monitor for clinical and research use.

Electronic Resource