Showing papers by "Alok Chakrabarti published in 2009"

Characterization of the influenza A H5N1 viruses of the 2008-09 outbreaks in India reveals a third introduction and possible endemicity.

Abstract: Widespread infection of highly pathogenic avian influenza A H5N1 was reported from backyard and commercial poultry in West Bengal (WB), an eastern state of India in early 2008. Infection gradually spread to Tripura, Assam and Sikkim, the northeastern states, with 70 outbreaks reported between January 2008 and May 2009. Whole genome sequence analysis of three isolates from WB, one isolate from Tripura along with the analysis of hemagglutinin (HA) and neuraminidase (NA) genes of 17 other isolates was performed during this study. In the HA gene phylogenetic tree, all the 2008-09 Indian isolates belonged to EMA3 sublineage of clade 2.2. The closest phylogenetic relationship was found to be with the 2007-09 isolates from Bangladesh and not with the earlier 2006 and 2007 Indian isolates implying a third introduction into the country. The receptor-binding pocket of HA1 of two isolates from WB showed S221P mutation, one of the markers predicted to be associated with human receptor specificity. Two substitutions E119A (2 isolates of WB) and N294S (2 other isolates of WB) known to confer resistance to NA inhibitors were observed in the active site of neuraminidase. Several additional mutations were observed within the 2008-09 Indian isolates indicating genetic diversification. Overall, the study is indicative of a possible endemicity in the eastern and northeastern parts of the country, demanding active surveillance specifically in view of the critical mutations that have been observed in the influenza A H5N1 viruses.

A unique influenza A (H5N1) virus causing a focal poultry outbreak in 2007 in Manipur, India.

Abstract: A focal H5N1 outbreak in poultry was reported from Manipur, a north-eastern state, of India, in 2007. The aim of this study was to genetically characterize the Manipur isolate to understand the relationship with other H5N1 isolates and to trace the possible source of introduction of the virus into the country. Characterization of the complete genome revealed that the virus belonged to clade 2.2. It was distinctly different from viruses of the three EMA sublineages of clade 2.2 but related to isolates from wild migratory waterfowl from Russia, China and Mongolia. The HA gene, had the cleavage site GERRRRKR, earlier reported in whooper swan isolates from Mongolia in 2005. A stop codon at position 29 in the PB1-F2 protein could have implications on the replication efficiency. The acquisition of polymorphisms as seen in recent isolates of 2005–07 from distinct geographical regions suggests the possibility of transportation of H5N1 viruses through migratory birds. Considering that all eight genes of the earlier Indian isolates belonged to the EMA3 sublineage and similar strains have not been reported from neighbouring countries of the subcontinent, it appears that the virus may have been introduced independently.

Avian influenza surveillance in wild migratory, resident, domestic birds and in poultry in Maharashtra and Manipur, India, during avian migratory season 2006-07.

Abstract: India reported outbreaks of Highly Pathogenic Avian Influenza (HPAI) H5N1 in poultry in the states of Maharashtra, Gujarat and Madhya Pradesh (February-April 2006); Manipur (July 2007); West Bengal (January 2008) and Tripura (April 2008). The role of migratory birds in the transmission of the HPAI H5N1 remains a subject of debate. Avian Influenza (AI) surveillance in wild migratory, wild resident, domestic birds and poultry was undertaken by National Institute of Virology (NIV) jointly with Ela Foundation, Pune, India during 2006-07. A total of 1968 faecal specimens (1369 droppings from wild migratory and wild resident birds; 474 droppings from poultry and 125 cloacal swabs from chickens and ducks) were collected. These samples representing 10 avian families of wild migratory birds, four families of wild resident birds totalling 36 species, were from eight districts of Maharashtra covering 20 water bodies and two districts of Manipur. The samples were screened for AI viruses by reverse transcriptase polymerase chain reaction (RT-PCR), real-time PCR and were processed for virus isolation in embryonated chicken eggs and cell culture. Two samples from wild ducks were positive for viruses other than AI, newcastle disease virus (NDV) and infectious bursal disease virus (IBDV). During the study period no sample was positive for Influenza A viruses, Influenza A (H5N1) or any other strain of HPAI by RT-PCR and virus isolation. In view of the recent HPAI H5N1 outbreaks in poultry in India, continued and more widespread AI surveillance is necessary to elucidate the role of wild migratory, resident, domestic birds and poultry in the transmission of AI viruses.

β Decay of the proton-rich nucleus Si24 and its mirror asymmetry

Abstract: $\ensuremath{\beta}$-decay spectroscopy of the proton-rich nucleus $^{24}\mathrm{Si}$ was performed. The decay scheme was reconstructed from results of delayed $\ensuremath{\gamma}$-ray and proton measurements. We observed two $\ensuremath{\beta}$ branches to bound states in $^{24}\mathrm{Al}$ for the first time. The branching ratios were determined to be $31(4)%$ and $23.9(15)%$ for the ${1}_{1}^{+}$ state at $0.426$ MeV and the state at $1.090$ MeV, respectively. The observation of an allowed transition to the $1.090$-MeV state enabled us to firmly determine its spin-parity as ${1}^{+}$. In the proton measurements performed with the $\ensuremath{\Delta}E\text{\ensuremath{-}}E$ method, we observed a new unbound level at $6.735$ MeV. The branching ratios to three unbound states, including the new level, were also determined for the first time. Based on the decay scheme, the $B(\mathrm{GT})$ values of $^{24}\mathrm{Si}$ were deduced. The $B(\mathrm{GT})$ values were smaller than those of the mirror nucleus $^{24}\mathrm{Ne}$ by $22%$ and $10%$ for the ${1}_{1}^{+}$ and ${1}_{2}^{+}$ states, respectively. The mirror asymmetries of $B(\mathrm{GT})$, observed in both the ${1}_{1}^{+}$ and the ${1}_{2}^{+}$ states, indicate changes in configuration in the wave function associated with the Thomas-Ehrman shift. To clarify the mechanism of this asymmetry, a comparison with shell-model calculations is also discussed. The calculations attribute the changes in configuration to the lowering of the $1{s}_{1/2}$ orbital.

Coulomb explosion sputtering of selectively oxidized Si

Abstract: We have studied multiply charged Arq+ ion induced potential sputtering of a unique system comprising of coexisting Silicon and Silicon oxide surfaces. Such surfaces are produced by oblique angle oxygen ion bombardment on Si(100), where ripple structures are formed and one side of each ripple gets more oxidized. It is observed that higher the potential energy of Arq+ ion, higher the sputtering yield of the non conducting (oxide) side of the ripple as compared to the semiconducting side. The results are explained in terms of Coulomb explosion model where potential sputtering depends on the conductivity of the ion impact sites.

Observation of high ferromagnetic ordering in Fe implanted ZnO at room temperature

Abstract: Room temperature ferromagnetic ordering has been observed in ZnO by implanting 1.63 MeV 56 Fe 6+ ions. The total number of implanted Fe ions in ZnO is 1 × 10 16 , which is effectively 1 at.% doping of Fe in ZnO. The amount of saturation magnetic moment in Fe implanted ZnO, annealed to 500 °C, has been found to be two orders of magnitude more than that observed earlier in chemically prepared Zn 0.98 Mn 0.02 O and Zn 0.96 Mn 0.02 Fe 0.02 O samples.

Beta-decay study of Tz = - 2 proton-rich nucleus 24Si

Abstract: $ \beta$ -decay spectroscopy on a T z = - 2 proton-rich nucleus 24Si was performed. The decay scheme of 24Si was reconstructed by the $ \beta$ -delayed $ \gamma$ -ray and proton measurements. Two $ \beta$ branches to the bound 11 + and 12 + states in 24Al were observed for the first time. The observation of the allowed transition firmly established the spin-parity assignment for the 12 + states. The branching ratios to the 11 + and 12 + states were determined to be 31(4)% and 23.9(15)%, respectively. The branching ratios to three unbound states in 24Al including a new level at 6.735MeV were also determined for the first time. The level structure of 24Al was compared with its mirror nucleus 24Na . The Thomas-Ehrman shift on the 12 + state indicates s -wave dominance in the state as well as a characteristic behavior of the weakly bound s -wave proton in 24Al .

Modal response of 4-rod type radio frequency quadrupole linac.

Abstract: This paper deals with the analysis and experimental study of natural frequencies of vibration of a 4-rod type radio frequency quadrupole (RFQ) linear accelerator. The eigenvalue analysis of the structure has been done both analytically (multispan beam concept) as well as using blocked Lanczos eigenvalue finite element solver with an ability to extract the rigid body modes. This has been done in the mechanical design phase to find the level of agreement between the output of simplified analytical analysis results and the output of a commercial finite element method (FEM) solver, since a full scale RFQ structure is too complex to handle analytically. Experimental validation of the analysis results has been done on the physical 1.7 m RFQ at the installation site. The experimental data obtained were later analyzed and found to be in close agreement with the predicted frequencies in the lower frequency ranges. It gets more and more deviated in the higher frequency ranges. Also some frequencies were observed during experimentation, which were not found in the finite element analysis results. The source of those frequencies are to be further investigated as it may play a predominant role in the design high quality factor beam line cavities for higher operational efficiency.