Showing papers by "Alok Chakrabarti published in 2012"

Non structural protein of avian influenza A (H11N1) virus is a weaker suppressor of immune responses but capable of inducing apoptosis in host cells.

Abstract: The Non-Structural (NS1) protein of Influenza A viruses is an extensively studied multifunctional protein which is commonly considered as key viral component to fight against host immune responses. Even though there has been a lot of studies on the involvement of NS1 protein in host immune responses there are still ambiguities regarding its role in apoptosis in infected cells. Interactions of NS1 protein with host factors, role of NS1 protein in regulating cellular responses and apoptosis are quite complicated and further studies are still needed to understand it completely. NS1 genes of influenza A/Chicken/India/WBNIV2653/2008 (H5N1) and A/Aquatic bird/India/NIV-17095/2007(H11N1) were cloned and expressed in human embryonic kidney (293T) cells. Microarray based approach to study the host cellular responses to NS1 protein of the two influenza A viruses of different pathogenicity showed significant differences in the host gene expression profile. NS1 protein of H5N1 resulted in suppression of IFN-β mediated innate immune responses, leading to down-regulation of the components of JAK-STAT pathway like STAT1 which further suppressed the expression of pro-inflammatory cytokines like CXCL10 and CCL5. The degree of suppression of host immune genes was found considerable with NS1 protein of H11N1 but was not as prominent as with H5N1-NS1. TUNEL assay analyses were found to be positive in both the NS1 transfected cells indicating both H5N1 as well as H11N1 NS1 proteins were able to induce apoptosis in transfected cells. We propose that NS1 protein of both H5N1 and H11N1 subtypes of influenza viruses are capable of influencing host immune responses and possess necessary functionality to support apoptosis in host cells. H11N1, a low pathogenic virus without any proven evidence to infect mammals, contains a highly potential NS1 gene which might contribute to greater virus virulence in different gene combinations.

Key factors of ion induced nanopatterning

Abstract: We have reported the dependence of projectile mass, chemical reactivity and effect of molecular beams on ion induced nano structure formation, when 8 keV He 1+ , N 1+ , O 1+ , Ar 1+ atomic ions and 16 keV N 2 1 + and O 2 1 + molecular ions are used to bombard a Si(1 0 0) surface at an incidence angle of 60°. It is shown that the initiation and growth of ripple structures depend not only on the collision cascades but also on the chemical reactivity and molecular state of the projectiles. This experimental investigation explores the necessary requirements for ion induced controlled nanopatterning.

Photoluminescence and positron annihilation spectroscopic investigation on a H+ irradiated ZnO single crystal

Abstract: Low temperature photoluminescence and room temperature positron annihilation spectroscopy have been employed to investigate the defects incorporated by 6?MeV H+ ions in a hydrothermally grown ZnO single crystal Prior to irradiation, the emission from donor bound excitons is at 3378?eV (10?K) The irradiation creates an intense and narrow emission at 3368?eV (10?K) The intensity of this peak is nearly four times that of the dominant near band edge peak of the pristine crystal The characteristic features of the 3368?eV emission indicate its origin as a ?hydrogen at oxygen vacancy? type defect The positron annihilation lifetime measurement reveals a single component lifetime spectrum for both the unirradiated (164???1?ps) and irradiated crystal (175???1?ps) It reflects the fact that the positron lifetime and intensity of the new irradiation driven defect species are a little higher compared to those in the unirradiated crystal However, the estimated defect concentration, even considering the high dynamic defect annihilation rate in ZnO, comes out to be ?4???1017?cm?3 (using SRIM software) This is a very high defect concentration compared to the defect sensitivity of positron annihilation spectroscopy A probable reason is the partial filling of the incorporated vacancies (positron traps), which in ZnO are zinc vacancies The positron lifetime of ?175?ps (in irradiated ZnO) is consistent with recent theoretical calculations for partially hydrogen-filled zinc vacancies in ZnO Passivation of oxygen vacancies by hydrogen is also reflected in the photoluminescence results A possible reason for such vacancy filling (at both Zn and O sites) due to irradiation has also been discussed

Analysis and measurement of high power vacuum-tube RF transmitters: Matrix method

Abstract: High power radio frequency transmitters have been developed for the heavy ion linear accelerator of RIB project at VECC Kolkata. It works at 40 kW CW power in the frequency range of 32–39 MHz. The new approach of analysis and design of this transmitter has been carried out using ABCD matrix. It uses a linear small-signal AC model with input, output and inter stage matching circuits for Tetrode tube amplifier cascaded with Triode tube based diver amplifier. The analytical as well as measured S-parameter results are presented in this paper.

RF distribution and control system for accelerators of the VEC-RIB facility

Abstract: RIB facility at VECC has several heavy ion linear accelerators like RFQ, two IH-LINACs and one buncher cavity operating at 37.8 MHz and two IH-LINACs with one buncher cavity at 75.6 MHz. Some more RF cavities are being designed at the third harmonic of 37.8 MHz and will be added in the RIB beam line [1]. All the cavities have separate RF power amplifiers with proper amplitude, phase and resonance frequency tuning and control system for efficient and stable operation. The Low Level RF control system has been operational for the power amplifiers of the existing RF cavities and improved design and development is carried out. An embedded controller based data acquisition and processing system is being used for control and local/remote operation. The RF distribution system as well as the design details of RF control system and remote control system will be presented in this paper. RF DISTRIBUTION SYSTEM The RF sources for the RIB accelerators consist of three 30 kW RF transmitters operating at 37.8 MHz, one 2 kW RF transmitter operating at 37.8 MHz and a 5 kW RF transmitter operating at 75.6 MHz [2]. A single oscillator at 37.8 MHz drives all the RF power amplifiers of the RIB facility. This is done using a 6-way power splitter which divides the RF signal to the respective power amplifiers. For LINAC 3, which operates at 75.6 MHz, a frequency doubler is used to convert the 37.8 MHz signal to 75.6 MHz [3]. The forward and reflected power samples and pick-up signal from each of the RF accelerator cavities are fed to the low level RF control modules of the RF amplifiers. The schematic diagram for RF distribution is shown in Figure 1. LOW LEVEL RF CONTROL The Low Level RF (LLRF) control system regulates the amplitude and phase of the RF cavity voltage through fast electronic feedback mechanism. The frequency of the cavity is regulated through mechanical movement of a tuner loop in appropriate direction by sensing the frequency deviation. At present the control is based on the conventional amplitude and phase loop method. The scheme of the LLRF control is shown in Figure 2.