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Biomedical subjects

B K Rao

Publications and source records attributed to B K Rao.

At least 19 recordsLinked to original sources
PubMed2006

Outcome predictors for non-invasive positive pressure ventilation in acute respiratory failure.

BACKGROUND: Noninvasive positive pressure ventilation (NIPPV) has emerged as a significant advancement in the management of acute respiratory failure. OBJECTIVE: To identify factors, based on clinical and laboratory parameters, for predicting the outcome of NIPPV in patients with acute respiratory failure. MATERIALS AND METHODS: Fifty patients were included in the study. Inclusion criteria were RR>30 breaths/ min, PaO2<60mmHg, PaO2/FiO2<300, pCO2< or = 45mmHg and signs of increased work of breathing. Baseline clinical parameters and arterial blood gas (ABG) were recorded before initiating NIPPV. Clinical parameters including heart rate, respiratory rate, oxygen saturation and ABG was revaluated at 1, 4, 12, 24 hrs after initiation of NIPPV. Change in these parameters and need for intubation was evaluated. RESULTS: Of the 50 patients, 37 (74%) showed clinical and ABG improvement. Out of 13 (26%) patients who failed to respond, 7 (52%) needed endotracheal intubation within 1 hr. There was significant improvement in clinical and ABG parameters within 1st hr in success group and these parameters continues to improve even after 4 hrs of NIPPV treatment (p<0.05). Failure group had higher baseline heart rate than success group (p<0.05). CONCLUSION: Determination of baseline clinical factors such as heart rate and respiratory rate, available at the time of initiation and after a short period, can predict the likelihood of success or failure of NIPPV. As a result, delay in intubation can be avoided which itself is associated with significant mortality.

Acute Disease↗
PubMed2005

Interaction of Pd and PdCl2 with cellulose: a theoretical investigation.

The pyrolytic fragmentation of cellulose in the presence of atomic palladium (Pd) and palladium(II) chloride (PdCl2) has been studied with use of hybrid density functional theory and cellobiose as a model for cellulose. The configuration changes in the host, rearrangement of geometries of the products, and the respective reaction energetics for different fragmentation pathways are analyzed. While Pd is found to undergo insertion at the beta-1,4-linkage oxygen (O1)-carbon (C-1) of the rings, Pd(II) chloride is observed to promote the cleavage of the chain as well as rearrangement of the rings. A detailed mechanism for the formation of levoglucosan from one of the fragments following the interaction with PdCl2 is also highlighted.

Cellobiose↗
PubMed2005

DFT study of structure and binding energies of Fe-corannulene complex.

Density functional theory (DFT) based theoretical calculations are performed to identify the ground-state geometries, the spin multiplicities, and the relevant energetics of neutral and positively charged Fe-corannulene complexes. Our calculations show that the on-top site of the six-membered ring (eta(6)) of corannulene molecule is the most preferred binding site for both Fe atom and Fe(+) ion. The electrostatic potential (ESP) surface picture is employed to explain the preference of the eta(6)- over the eta(5)-binding site (on-top site of central pentagon) of corannulene. Though in both neutral and cationic species the eta(6)-site is the most preferred binding site, the ground-state geometries of these complexes are different. The Fe(+) cation prefers to bind to the convex face of the corannulene, whereas the neutral Fe atom prefers slightly the concave to the convex face. The ionization-induced structural changes are reflected in the large energy difference between the vertical and adiabatic ionization potential values. We also show that the dissociation of Fe(+)-corannulene complex to corannulene + Fe(+) is just as likely as that to Fe + (corannulene)(+).

Iron↗
PubMed2005

Evolution of the electronic structure of Be clusters.

Using a modified symbiotic genetic algorithm approach and many-body interatomic potential derived from first principles, we have calculated equilibrium geometries and binding energies of the ground-state and low-lying isomers of Be clusters containing up to 41 atoms. Molecular-dynamics study was also carried out to study the frequency of occurrence of the various geometrical isomers as these clusters are annealed during the simulation process. For a selected group of these clusters, higher-energy isomers were more often found than their ground-state structures due to large catchment areas. The accuracy of the above ground-state geometries and their corresponding binding energies were verified by carrying out separate ab initio calculations based on molecular-orbital approach and density-functional theory with generalized gradient approximation for exchange and correlation. The atomic orbitals were represented by a Gaussian 6-311G** basis, and the geometry optimization was carried out using the GAUSSIAN 98 code without any symmetry constraint. While the ground-state geometries and their corresponding binding energies obtained from ab initio calculations do not differ much from those obtained using the molecular-dynamics approach, the relative stability of the clusters and the energy gap between the highest occupied and the lowest unoccupied molecular orbitals show significant differences. The energy gaps, calculated using the density-functional theory, show distinct shell closure effects, namely, sharp drops in their values for Be clusters containing 2, 8, 20, 34, and 40 electrons. While these features may suggest that small Be clusters behave free-electron-like and, hence, are metallic, the evolution of the structure, binding energies, coordination numbers, and nearest-neighbor distances do not show any sign of convergence towards the bulk value. We also conclude that molecular-dynamics simulation based on many-body interatomic potentials may not always give the correct picture of the evolution of the structure and energetics of clusters although they may serve as a useful tool for obtaining starting geometries by efficiently searching a large part of the phase space.

Journal Article↗
PubMed2004

Appearance of bulk properties in small tungsten oxide clusters.

Contrary to the conventional understanding that atomic clusters usually differ in properties and structure from the bulk constituents of which they are comprised, we show that even a dimer of tungsten oxide (WO(3))(2) possesses bulklike features and the geometry of a small cluster containing only 4 tungsten and 12 oxygen atoms bears the hallmarks of crystalline tungsten oxide, WO(3). This observation, based on a synergistic approach involving mass distributions under quasisteady state conditions, photoelectron spectroscopy, and first principles molecular orbital theory, not only illustrates the existence of a class of strongly covalent or ionic materials whose embryonic forms are tiny clusters but also lends the possibility that a fundamental understanding of complex processes such as catalytic reactions on surfaces may be achieved on an atomic scale with clusters as model systems.

Journal Article↗
PubMed2004

Electronic structure and bonding of Au on a SiO2 cluster: a nanobullet for tumors.

The binding of gold atoms to a small silica cluster has been studied by using density functional theory with generalized gradient approximation for exchange and correlation. It is shown that gold atoms bind to silicon atoms with dangling bonds and serve as seeds for the growth of Au islands. The large electron affinity of gold causes a significant change in the electronic structure of silica resulting in a substantial reduction in the highest occupied and the lowest unoccupied molecular orbital and the optical gap, thus allowing it to absorb near infrared radiation. This suggests that a small cluster can have a similar functionality in the treatment of cancer as the large size nanoshell, but for a different mechanism.

Breast Neoplasms↗
PubMed2004

Geometry and electronic structure of Vn(Bz)m complexes.

First-principles calculations based on the generalized gradient approximation to the density functional theory are performed to explore the global geometries, ground-state spin multiplicities, relative stabilities, and energetics of neutral and anionic V(n)(Bz)(m) (n=1-3, m=1-4, with n<m) complexes. The calculated results show that the V(n)(benzene)(m) complexes clearly prefer sandwich structures to rice-ball structures. The ground-state spin multiplicities of the V(n)(benzene)(n+1) complexes increased linearly with the size of the system (i.e., n). In the anionic complexes, the V(benzene)(2) complex is found to be unstable against the autodetachment of the extra electron. The energy difference between adiabatic and vertical electron affinities is found to be very less, indicating negligible ionization-induced structural changes in the ground-state geometries of V(n)(benzene)(n+1) complexes.

Journal Article↗
PubMed2003

Stabilization of Si60 cage structure.

A comprehensive search for the stable geometries of bare Si60 and Si60 supported on a C60 fullerene was carried out using first principles calculations based on density functional theory. In contrast to previous theoretical studies and in agreement with recent experiments, we show that Si60 and C(60)@Si(60) clusters are unstable in the fullerenelike cage structure. However, Si60 cage can be stabilized by including within it, as endohedral units, small magic clusters such as Al12X (X=Si, Ge, Sn, Pb) and Ba@Si(20).

Journal Article↗
PubMed2002

Giant magnetic moments of nitrogen-doped Mn clusters and their relevance to ferromagnetism in Mn-doped GaN.

Calculations based on density-functional theory show that the stability and magnetic properties of small Mn clusters can be fundamentally altered by the presence of nitrogen. Not only are their binding energies substantially enhanced, but also the coupling between the magnetic moments at Mn sites remains ferromagnetic irrespective of their size or shape. In addition, these nitrogen-doped Mn clusters carry giant magnetic moments ranging from 4mu(B) in MnN to 22mu(B) in Mn5N. It is suggested that the giant magnetic moments of MnxN clusters may play a key role in the ferromagnetism of Mn-doped GaN which exhibit a wide range (10-940 K) of Curie temperatures.

Journal Article↗
PubMed2002

Magic numbers in metallo-inorganic clusters: chromium encapsulated in silicon cages.

A systematic theoretical study of the equilibrium geometries and total energies of Cr encapsulated in Si clusters reveals that Cr@Si(12) is more stable than its neighbors. The origin of this enhanced stability is consistent with the 18-electron sum rule commonly used in the synthesis of stable chemical complexes, and may provide a criterion for a systematic search of magic numbers in metalloinorganic clusters. The 6 mu(B) magnetic moment of the caged Cr atom, the largest among the 3d transition metal atoms, is completely quenched. This effect of caging on the properties of transition metal atoms may lead to the synthesis of novel cluster based materials.

Journal Article↗
PubMed2001

Pyoderma vegetans.

BACKGROUND: Pyoderma vegetans is a rare condition that is clinically characterized by large verrucous plaques with elevated borders and multiple pustules. The etiology of this disorder remains unknown. OBJECTIVES: We describe a 24-year-old woman with rapidly evolving pyoderma vegetans. Our patient had the unique additional findings of a highly elevated serum IgE level and a history of hidradenitis suppurativa. CONCLUSIONS: Pyoderma vegetans is diagnosed on clinical and histological criteria. Differentiation must be made from disorders such as pyoderma gangrenosum, Sweet's syndrome, and deep fungal infections. We illustrate a case of pyoderma vegetans and review the literature on this rare disorder. Clinical and histological criteria for diagnosis are presented, as well as differentiation from some mimicking disorders.

Adult↗
PubMed2001

Electronic structure and properties of transition metal-benzene complexes.

A comprehensive theoretical study of the geometries, energetics, and electronic structure of neutral and charged 3d transition metal atoms (M) interacting with benzene molecules (Bz) is carried out using density functional theory and generalized gradient approximation for the exchange-correlation potential. The variation of the metal-benzene distances, dissociation energies, ionization potentials, electron affinities, and spin multiplicities across the 3d series in MBz complexes differs qualitatively from those in M(Bz)(2). For example, the stability of Cr(Bz)(2) is enhanced over that of CrBz by almost a factor of 30. On the other hand, the magnetic moment of Cr(Bz)(2) is completely quenched although CrBz has the highest magnetic moment, namely 6 mu(B), in the 3d metal-benzene series. In multidecker complexes involving V(2)(Bz)(3) and Fe(2)(Bz)(3), the metal atoms are found to couple antiferromagnetically. In addition, their dissociation energies and ionization potentials are reduced from those in corresponding M(Bz)(2) complexes. All of these results agree well with available experimental data and demonstrate the important role the organic support can play on the properties of metal atoms/clusters.

Journal Article↗
PubMed2001

AlH(3) and Al(2)H(6): magic clusters with unmagical properties.

Enhanced stability, low electron affinity, and high ionization potential are the hallmarks of a "magic" cluster. With an electron affinity of 0.28 eV, ionization potential of 11.43 eV, and a large binding energy, AlH(3) satisfies these criteria. However, unlike other magic clusters that interact only weakly with each other, two AlH(3) clusters bind to each other with an energy of 1.54 eV. The resulting Al(2)H(6), while also a magic cluster in its own right, possesses the most unusual property that the difference between its adiabatic and vertical detachment energy is about 2 eV--the largest of any known cluster. These results, based on density functional theory, are verified experimentally through photodetachment spectroscopy.

Journal Article↗
PubMed2001

Lipid peroxidation and antioxidant enzyme status in Type 2 diabetics with coronary heart disease.

Lipid peroxides are thought to be formed by free radicals and may play an important role in the development of atheromatous vascular diseases. The relationship between serum lipids, lipoproteins, lipid peroxides [thiobarbituric acid reactive substances (TBARS)] and erythrocyte antioxidant enzymes [catalase (CAT), glutathione peroxidase (GPx) and superoxide dismutase (SOD)] was investigated in non-insulin-dependent diabetic patients with and without coronary heart disease (CHD), and a comparison was made for all the above parameters with non-diabetic patients with CHD. Lipid peroxide concentrations were significantly increased in both groups of diabetic patients and also in non-diabetic patients with CHD, compared to those in control subjects. Diabetic patients with CHD had higher levels of TBARS compared to those diabetics without CHD. Hyperlipidaemia and abnormal lipoprotein levels were observed in all three groups of patients. Increased total cholesterol and LDL-cholesterol were observed in diabetics with CHD compared to those without CHD. Among the erythrocyte antioxidant enzymes, CAT activity was increased, GPx activity was decreased and no change was observed in SOD activity in both groups of diabetic patients and non-diabetic patients with CHD compared to those in controls. A clear correlation was observed between the CAT activity and lipid peroxide concentrations in all the diabetic patients. These observations suggest that there are similar abnormalities in lipid metabolism and erythrocyte antioxidant enzymes in diabetic patients and non-diabetic patients with CHD.

Catalase↗
PubMed2001

Antihyperglycemic activity of Momordica cymbalaria in alloxan diabetic rats.

Aqueous, ethanolic and hexane fractions of Momordica cymbalaria fruits were prepared and given individually at different doses to different batches of rats (both normal and alloxan diabetic rats) after an overnight fast. The blood glucose levels were measured at 0, 1, 3, 5 and 7 h after the treatment. The aqueous extract of Momordica cymbalaria at a dosage of 0.5 g/kg b.w. is showing maximal blood glucose lowering effect in diabetic rats. The same dosage did not produce any hypoglycemic activity in normal rats. The antihyperglycemic activity of Momordica cymbalaria fruit was compared with the treatment of Glibenclamide, an oral hypoglycemic agent.

Animals↗
PubMed2001

Typical dermoscopic patterns of benign melanocytic nevi.

Dermoscopy often is an effective diagnostic tool for differentiating benign and malignant pigmented skin lesions. The observed dermoscopic structures and patterns of lesions provide valuable sources of information that are not accessible by routine clinical examination. Recognition and interpretation of these dermoscopic structures and patterns require training and experience. Mentioned here are some fundamental guidelines for differentiating malignant and benign lesions. Some of the classic patterns associated with a list of benign melanocytic nevi also have been illustrated. Additional research is needed to identify other patterns of these benign lesions. More importantly, analysis of the prevalence of various patterns associated with the various benign lesions will be helpful to clinicians having the responsibility of making in vivo diagnoses of benign compared with malignant melanocytic neoplasms.

Dermatology↗
PubMed2001

Hypoglycemic and antihyperglycemic activity of Syzygium alternifolium (Wt.) Walp. seed extracts in normal and diabetic rats.

Aqueous, ethanolic and hexane fractions of Syzygium alternifolium seeds were prepared and given different doses of these extracts individually to different batches of rats (both normal and alloxan diabetic rats) after an overnight fast. The blood glucose levels were measured at 0, 1, 3, 5 and 7 hours after the treatment. The aqueous extract of Syzygium alternifolium at a dosage of 0.75 g/kg b.w. is showing maximum blood glucose lowering effect in both normal and alloxan diabetic rats. The ethanol and hexane fractions are also showing hypoglycemic and antihyperglycemic activity, but the effect is significantly less than that of aqueous extract. The antihyperglycemic activity of Syzygium alternifolium seed was compared with the treatment of Glibenclamide.

Alloxan↗