Ravi Tripathi

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$Research paper thumbnail of Pulse oximetry saturation to fraction inspired oxygen ratio as a measure of hypoxia under general anesthesia and the influence of positive end-expiratory pressure$

Pulse oximetry saturation to fraction inspired oxygen ratio as a measure of hypoxia under general anesthesia and the influence of positive end-expiratory pressure

Journal of Critical Care, 2010

Purpose: In ICU patients with acute lung injury, the pulse oximetry saturation (SpO 2 ) to fracti... more Purpose: In ICU patients with acute lung injury, the pulse oximetry saturation (SpO 2 ) to fraction of inspired oxygen (FIO 2 ) (S/F) ratio is a reliable surrogate measure for the P/F (PaO 2 /FIO 2 ) ratio. Our goal was to determine the correlation of the S/F to the P/F in a large sample of patients undergoing general anesthesia and the influence of positive end-expiratory pressure (PEEP) on this measure. Methods: We studied adult general anesthetics performed with arterial blood gas analysis. Intraoperative data were collected from an anesthesia information system. The S/F ratios corresponding to P/F ratios of 300 were determined. Results: A total of 4439 values were collected. Linear correlation between S/F and P/F was identified (r = 0.46; P b .01) with a P/F of 300 corresponding to an S/F of 206. The correlation was stronger in patients with 5 to 9 cm PEEP (r = 0.52; P b .01), more than 9 cm H 2 O PEEP (r = 0.68; P b .01), and a P/F ratio of 300 or less (r = 0.61; P b .01). Conclusion: The S/F correlates with the P/F in our cohort of patients undergoing general anesthesia, especially those ventilated with PEEP more than 9 cm H 2 O and/or with P/F less than 300. It has use as a noninvasive measure to screen for increased pulmonary dysfunction and to trend oxygenation during a general anesthetic.

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The most influential articles in critical care medicine

Journal of Critical Care, 2010

Purpose: The study aimed to examine query strategies that would provide an exhaustive search meth... more Purpose: The study aimed to examine query strategies that would provide an exhaustive search method to retrieve the most referenced articles within specific categories of critical care. Material and Methods: A comprehensive list of the most cited critical care medicine articles was generated by searching the Science Citation Index Expanded data set using general critical care terms keywords such as "critical care," critical care journal titles, and keywords for subsubjects of critical care. Results: The final database included 1187 articles published between 1905 and 2006. The most cited article was referenced 4909 times. The most productive search term was intensive care. However, this term only retrieved 25% of the top 100 articles. Furthermore, 662 of the top 1000 articles could not be found using any of the basic critical care search terms. Sepsis, acute lung injury, and mechanical ventilation were the most common areas of focus for the articles retrieved. Conclusion: Retrieving frequently cited, influential articles in critical care requires using multiple search terms and manuscript sources. Periodic compilations of most cited articles may be useful for critical care practitioners and researches to keep abreast of important information.

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Tc99m Ciprofloxacin Scans for Detection of Tubercular Bone Infection

Clinical Nuclear Medicine, 2007

Tc-99m MDP and Tc-99m ciprofloxacin scans were performed in 14 patients with suspected tubercular... more Tc-99m MDP and Tc-99m ciprofloxacin scans were performed in 14 patients with suspected tubercular bone disease and in 2 cases of nontubercular bone infection. In 5 patients the findings were true negative. There were no false positives and 1 was false negative. The sensitivity, specificity, and positive predictive value were found to be 93, 71, and 87.5%, respectively, for detection of bone tubercular lesions. However, the test does not distinguish TB osteomyelitis from other types of osteomyelitis. Delayed 24 hour scans were found useful to differentiate between inflammatory and infective lesions. The aim of this study was to evaluate the usefulness of the Tc-99m ciprofloxacin scan as a means to detect tubercular bone disease.

Magnetic properties of undoped YBa 2 Cu 3 O 6 + x system

European Physical Journal B, 2001

... 1/2π 0 0 0      7) Page 3. Govind et al.: Magnetic properties of undoped YBa2Cu3O6+x sys... more

Spin wave contribution to the thermal expansion of high- T c cuprate superconductors

Physica C-superconductivity and Its Applications, 1998

Superconducting properties of bilayer cuprates: role of CuO chains

Physica C-superconductivity and Its Applications, 2000

In the present paper, we report the role of CuO chains on the superconducting properties of bilay... more In the present paper, we report the role of CuO chains on the superconducting properties of bilayer cuprate superconductors. The model Hamiltonian incorporates the intra-bilayer, inter-bilayer and bilayer-chain interactions. The expressions of the superconducting order parameter, transition temperature, density of states and electronic specific heat have been obtained using Green's function technique. The numerical calculations show that these properties are sensitive to the chain contributions. Our results are qualitatively in accord with the experimentally observed superconducting properties in bilayer cuprates. q

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Role of interlayer interactions on transition temperature in high- T c cuprate superconductors

Physica C-superconductivity and Its Applications, 1997

... The doubletime temperature dependent retarded ( + ) and advance () Green's function invo... more ... The doubletime temperature dependent retarded ( + ) and advance () Green's function involving two opera tors A and B are defined by ((a(t)[B(t')))+ iO[+(tt')]([A(t),B(t')]o), (2) A jay, RS Tripathi Physica C 274 (1997) 7380 75 where [ A,B]n = AB rlBA, r = + 1 for bosons, r = 1 for ...

Role of Interlayer and Intersite Interactions in Superconducting State in HighT c Layered Cuprates

Journal of Superconductivity, 2000

We studied the role of interlayer and intersite interactions on transition temperature and specif... more We studied the role of interlayer and intersite interactions on transition temperature and specific heat of layered high-T c cuprates. We used double-time Green's function technique in the spirit of mean field approximation in order to obtain the expressions for hole density, transition temperature, and specific heat. These expressions are found to be dependent on the carrier concentration and intersite and interlayer interactions. The numerical analysis shows that the effect of intersite interaction on transition temperature and specific heat is qualitatively similar to that of interlayer interactions and provides favorable conditions to establish long-range order in the superconducting state.

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Pressure Dependence of T c in High Temperature Superconductors: Role of Interlayer Interactions

Journal of Superconductivity, 2000

We have studied the role of interlayer interactions (W) in the pressure dependence of T c of laye... more We have studied the role of interlayer interactions (W) in the pressure dependence of T c of layered superconductors. The expressions for dT c /dP are obtained by including the effects of layered structure within the framework of two different proposed models, namely the negative-U Hubbard model and the Hirsch model. We observe that the inclusion of interlayer interaction provides better explanation of pressure dependence of T c . Our numerical results show that the systems having one CuO2 layer per unit cell may be well described by small values of W while the larger values of W accounts for the systems having two or more superconducting layers in a unit cell. The calculated values of dT c /dP vs. W are found to be in good agreement with those of experimental results obtained for various high T c superconductors of cuprate family.

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Effect of interlayer interaction in high- T c cuprate superconductors

Journal of Superconductivity, 1996

We have studied the role of interlayer attractive interaction in a high-T c system having two lay... more We have studied the role of interlayer attractive interaction in a high-T c system having two layers per unit cell. The single band two-layer tight binding model Hamiltonian is considered and the double time Green's function technique is applied within the mean field approximation. The expressions for the hole density, transition temperature, and intra- and interlayer order parameters are obtained which are found to be dependent on the interlayer interaction and other parameters appearing in the Hamiltonian. The numerical analysis shows that the coupling of the charge carriers (holes) between the layers provides better conditions for the stabilization of long-range order and high superconducting transition temperature in layered superconductors. It is also observed that superconductivity is confined to a narrow region of hole concentration and the single particle tunneling suppresses the transition temperature.

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Effect of Interlayer Interaction on the Specific Heat of High T c Superconductors

Journal of Superconductivity, 1998

The effect of interlayer interactions on the electronic specific heat of high-T c layered superco... more The effect of interlayer interactions on the electronic specific heat of high-T c layered superconductors has been studied within the framework of the Hirsch model. In the present paper we extend our previous work in order to evaluate the expression for specific heat. It is shown that the inclusion of interlayer interactions suppresses the height of the jump in the specific heat at T c.

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Effect of interlayer coupling on Néel, temperature in copper oxide based antiferromagnets

Physica Status Solidi B-basic Solid State Physics, 1995

The role of interlayer coupling (J⟂ on the Néel temperature of (1–2–3) compounds is studied by ta... more The role of interlayer coupling (J⟂ on the Néel temperature of (1–2–3) compounds is studied by taking the three-dimensional anisotropic Heisenberg antiferromagnetic model. The two-sublattice model of the antiferromagnet is considered. The double-time Green function technique is employed and the higher-order Green functions are decoupled using the Callen decoupling approximation. The Néel temperature (TN) for YBa2Cu3O6+x (1–2–3) compounds as a function of doping concentrations (x) is estimated. The intraplanar coupling strength (J‖) is treated as a constant throughout the numerical calculations. The theoretical results are compared with that of the random phase approximation (RPA) and existing experimental results.

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Effect of interlayer interaction in highT c cuprate superconductors

Journal of Superconductivity, 1996

We have studied the role of interlayer attractive interaction in a high-To system having two laye... more We have studied the role of interlayer attractive interaction in a high-To system having two layers per unit cell. The single band two-layer tight binding model Hamiltonian is considered and the double time Green's function technique is applied within the mean field approximation. The expressions for the hole density, transition temperature, and intra-and interlayer order parameters are obtained which are found to be dependent on the interlayer interaction and other parameters appearing in the Hamiltonian. The numerical analysis shows' that the coupling of the charge carriers (holes) between the layers provides better conditions for the stabilization of long-range order and high superconducting transition temperature in layered superconductors. It is also observed that superconductivity is confined to a narrow region of hole concentration and the single particle tunneling suppresses the transition temperature.

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Role of interlayer interactions on transition temperature in high-Tc cuprate superconductors

Physica C-superconductivity and Its Applications, 1997

The effect of interlayer interactions on transition temperature in high-Tc layered superconductor... more The effect of interlayer interactions on transition temperature in high-Tc layered superconductors has been studied using a one-band two-layer tight binding Hamiltonian with intra- and interlayer attractive interactions. The double-time Green's function technique is employed and higher-order Green's functions are linearized by using a mean field decoupling approximation. The expressions for the transition temperature (Tc) and excitonic type interlayer correlation (γc) are obtained. It is shown that interlayer interactions play an important role in the enhancement of Tc in high-Tc cuprates. We have also explained the relevance of our results in high-Tc layered superconductors having two layers per unit cell under externally applied pressure.

Magnetic dynamics of bilayer cuprate superconductors

Physical Review B, 1999

Page 1. Magnetic dynamics of bilayer cuprate superconductors Amit Pratap,* Govind, and RS Tripath... more

57Fe Mössbauer investigation of nanostructured zinc ferrite irradiated by 100 MeV oxygen beam

Journal of Physics: Conference Series, 2010

... B 60 3400 [12] Sato T, Haneda K, Seki M and Iijima T 1990 Appl ... 1972) [22] Singh JP, Sriva... more

Effect of an interband interaction on narrow-band superconductivity

Physical Review B, 1995

... VOLUME 51, NUMBER 18 Effect of an interband interaction on narrow-band superconductivity Ajay... more

Magnetic properties of quasi-2D antiferromagnets

Physica Status Solidi B-basic Solid State Physics, 1996

We have studied the magnetic dynamics of quasi-2D high-Tc antiferromagnets within nonlinear spin-... more We have studied the magnetic dynamics of quasi-2D high-Tc antiferromagnets within nonlinear spin-wave approximation. The Green function method within the random phase approximation (RPA) is used to obtain the expressions for various magnetic properties such as staggered magnetization, specific heat, parallel and perpendicular susceptibilities. These properties have been analyzed by introducing an effective ratio (r2 = J⊥/J|) of interplanar to planar antiferromanetic (AFM) coupling strengths. The magnetic properties are found to be dependent on the renormalization factor (1 + α), r2, and temperature T, and it is shown that the magnon-magnon interaction plays a significant role in modifying the crossover temperature and other magnetic properties. Its effect in 2D is more pronounced than in 3D antiferromagnets. The various properties are estimated numerically and compared with the existing results.

Thermodynamic properties of bilayer cuprate superconductors

Physica C-superconductivity and Its Applications, 1999

... Thermodynamic properties of bilayer cuprate superconductors. Govind, A. Pratap, Ajay and RSTr... more

Role of Dipole-Dipole Interaction on the Magnetic Dynamics of Anisotropic Layered Cuprate Antiferromagnets

Physica Status Solidi B-basic Solid State Physics, 2001

ABSTRACT In the present paper, we report the role of dipole–dipole interaction on the magnetic dy... more ABSTRACT In the present paper, we report the role of dipole–dipole interaction on the magnetic dynamics of single layer antiferromagnets. For this, the model Hamiltonian includes the exchange Heisenberg Hamiltonian as well as dipole–dipole interactions. Within the linear spin-wave theory, we employ the double time Green&#39;s function technique to obtain expressions for the spin wave dispersion, sublattice magnetization and the magnetic contribution to specific heat as a function of various parameters of the model Hamiltonian. We observe through numerical calculations that in the absence of anisotropy in exchange couplings the dipole–dipole interaction works as an anisotropy and sustains the magnetization even in a pure 2D system.

Ravi Tripathi

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