Indigenous development of ultra high vacuum (UHV) magnetron sputtering system for the preparation of Permalloy magnetic thin films

We have designed and developed an indigenous ultra high vacuum (UHV) sputtering system which can deposit magnetic thin films with high purity and good uniformity. The equipment consists of state-of the-art technologies and sophistication. With this system it is possible to deposit coatings of various materials on a sample size of 3”3” 3”. The Ni81Fe19 ferromagnetic thin films, with Tantalum (Ta) as a buffer and cap layers have been deposited on silicon substrates using this ultra high vacuum (UHV) sputtering system. The magneto transport measurement study indicated a significant variation in the AMR values of the films for varying thicknesses of tantalum and NiFe layers

Gunn Effect in Silicon Nanowires: Charge Transport under High Electric Field

Gunn (or Gunn-Hilsum) Effect and its associated negative differential resistivity (NDR) emanates from transfer of electrons between two different energy bands in a semiconductor. If applying a voltage (electric field) transfers electrons from an energy sub band of a low effective mass to a second one with higher effective mass, then the current drops. This manifests itself as a negative slope or NDR in the I-V characteristics of the device which is in essence due to the reduction of electron mobility. Recalling that mobility is inversely proportional to electron effective mass or curvature of the energy sub band. This effect was observed in semiconductors like GaAs which has direct bandgap of very low effective mass and its second indirect sub band is about 300 meV above the former. More importantly a self-repeating oscillation of spatially accumulated charge carriers along the transport direction occurs which is the artifact of NDR, a process which is called Gunn oscillation and was observed by J. B. Gunn. In sharp contrast to GaAs, bulk silicon has a very high energy spacing (~1 eV) which renders the initiation of transfer-induced NDR unobservable. Using Density Functional Theory (DFT), semi-empirical 10 orbital ($sp^{3}d^{5}s^{*}$) Tight Binding (TB) method and Ensemble Monte Carlo (EMC) simulations we show for the first time that (a) Gunn Effect can be induced in narrow silicon nanowires with diameters of 3.1 nm under 3 % tensile strain and an electric field of 5000 V/cm, (b) the onset of NDR in I-V characteristics is reversibly adjustable by strain and (c) strain can modulate the value of resistivity by a factor 2.3 for SiNWs of normal I-V characteristics i.e. those without NDR. These observations are promising for applications of SiNWs in electromechanical sensors and adjustable microwave oscillators.Comment: 18 pages, 6 figures, 63 reference

A novel method of staining acid-fast bacilli in sputum containers

Background & objectives: Making centrifuged deposit smears from sputum to detect acid-fast bacilli (AFB) is considered hazardous. We carried out this study to stain the centrifuged deposits with carbol-fuchsin in sputum containers and to decolourize and counterstain their smears made on glass slides. Methods: The centrifuged deposits of 180 sputum samples from pulmonary tuberculosis patients were used for making smears (initial deposit smears) and staining by Ziehl-Neelsen (ZN) method for the detection of AFB. Each of the sputum deposit was then treated with one ml of 1 per cent carbol-fuchsin and a smear made between 2 to 3 h was then decolourized and counterstained by the same procedures followed in ZN method (2 h stained deposit smear). The coded initial deposit smears and the corresponding 2 h stained deposit smears were read by the same readers and the results compared. Results: One hundred and fifty (70 positive and 80 negative) 2 h stained deposit smears were compared with initial deposit smears and the difference was not statistically significant. Interpretation & conclusion: Centrifuged deposits of sputum in sputum containers can be stained by carbol-fuchsin within 2-3 h and their smears made subsequently on glass slides can then be decolourized and counterstained by the procedures followed in ZN method for detection of AFB by light microscopy

In vitro susceptibility of Mycobacterium tuberculosis to trifluoperazine

The reference strain, Mycobacterium tuberculosis H37Rv, 19 drug-sensitive and 15 drug resistant clinical isolates of M. tuberculosis were tested for their in vitro susceptibility to trifluoperazine (TFP), an antipsychotic drug, by broth dilution method. The minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of TFP against M. tuberculosis H37Rv were 8 and 32 mg/l, respectively. The distribution of the sensitive and resistant isolates, with respect to the MIC of TFP, was similar. The distribution of the sensitive and resistant isolates, with respect to the MBC of TFP, was different and the difference was statistically significant. The findings suggest that TFP is more bactericidal to drug-resistant isolates than to the sensitive isolates

Single strand conformation polymorphism profiles with biotinylated PCR products to detect mutations in rpoB gene of Mycobacterium tuberculosis

A fragment of the rpoB gene, including the region shown to be involved in rifampicin resistance, was amplified from 15 rifampicin-resistant and 6 rifampicin- sensitive clinical isolates of Mycobacterium tuberculosis by the polymerase chain reaction (PCR). One of the primers, employed in PCR, was biotinylated. The biotinylated strand of the PCR product was separated from the unbiotinylated strand using streptavidin magnetic beads. Both the strands were subjected to single strand conformation polymorphism in polyacrylamide gel electrophoresis. The DNA bands were silver stained to study their migration pattern. A shift in the migration of either of the strands of the test strain compared to the strands from a control rifampicin-sensitive strain was considered as indicative of resistance. This strategy was found to ease the visualization of shift in the migration of the strands in 17 of 21 samples and thereby detection of mutations

Molecular analysis of isoniazid-resistant clinical isolates of Mycobacterium tuberculosis from India

The presence of mutations in specific regions of katG, inhA, oxyR–ahpC and kasA associated with isoniazid (INH)-resistant clinical isolates of Mycobacterium tuberculosis from India were analysed by DNA sequencing. Point mutations in the katG gene at codon 315 and a mutation at codon 138 were detected in 64.3% (45/70) and 4% (1/25) of isolates, respectively. Polymorphisms at codon 463 of the katG gene were found both in resistant and sensitive isolates. Mutation at the inhA and oxyR–ahpC promoter regions occurred in 11.4% (8/70) and 35.0% (14/40) of the isolates, respectively. No mutation was found to occur in kasA and inhA structural gene regions. Of the 70 resistant isolates studied, 55 (78.6%) showed mutation in the regions sequenced. This is the first comprehensive molecular analysis of INH resistance in India, which suggests that point mutation rather than deletion and insertion is the major cause of INH resistance

Bioluminescence assay of adenosine triphosphate in drug susceptibility testing of Mycobacterium tuberculosis

Twenty three clinical isolates of M. tuberculosis and the reference strain, M. tuberculosis H37Rv were tested for their susceptibility to trifluoperazine (TFP) by the standard broth dilution method and the bioluminescence assay. The results showed that in 15 of the 23 isolates, the minimal inhibitory concentration (MIC) was identical in both the methods and in the remaining 8 isolates the difference in the MIC values between the methods, was less than two fold and was not significant. The findings suggest that the measurement of adenosine triphosphate (ATP) by bioluminescence assay can be employed as an alternative method for the rapid screening of clinical isolates for their susceptibility to anti-mycobacterial agents

Use of streptavidin magnetic beads in single strand conformation polymorphism profiles to detect mutations in rpoB gene of M.tuberculosis

Single strand conformation polymorphism (SSCP) is one of the promising techniques to identify mutations in short pieces of DNA (Orita et al. 1989). In this technique, DNA of interest is often amplified by the polymerase chain reaction (PCR) and then denatured by heat or alkali treatment before electrophoresis on a non denaturing polyacrylamide gel. Differences in mobility of either of the single strands compared to the control DNA indicate mutations which affect the secondary structure and alter the mobility of the DNA. We applied PCR-SSCP for the detection of mutations in the rifampicin resistance determining region (RRDR) of the rpoB gene of M. tuberculosis (Telenti et al. 1993a; 1993b). A nested PCR was used to amplify the RRDR. In the first PCR, 293-bp product was amplified and in the second PCR a 103- bp of the first PCR product was amplified. However, in our experience using denaturation by alkali or heating, the denatured PCR product most often reannealed to form a large proportion of double stranded DNA during the electrophoresis (Selvakumar et al. 1997a). After visualisation by staining with ethidium bromide or silver staining, most of the DNA was in the double stranded form, with very little or no single stranded DNA. The single strands that could be observed often ran close together, making analysis of any difference in mobility difficult. Therefore an attempt was made to generate biotinylated PCR product using a biotinylated forward primer and later the biotinylated strand was separated using sterptavidin magnetic beads. The separated strands eliminated the problem of strand reannealing during SSCP and were silver stained to detect the shift in the mobility. Since the nested PCR requires more time and is more expensive. a biotinylated PCR product was generated in a single PCR using a biotinylated forward primer and an unbiotinylated reverse primer. This simplified protocol was applied to clinical isolates in an attempt to detect rifampicin resistance

Active community surveillance of the impact of different tuberculosis control measures, Tiruvallur, South India, 1968-2001

Background: Tuberculosis is curable, but community surveys documenting epidemiological impact of the WHO-recommended DOTS strategy on tuberculosis prevalence have not been published. We used active community surveillance to compare the impact of DOTS with earlier programmes. Methods: We conducted tuberculosis disease surveys using random cluster sampling of a rural population in South India approximately every 2.5 years from 1968 to 1986, using radiography as a screening tool for sputum examination. In 1999, DOTS was implemented in the area. Prevalence surveys using radiography and symptom screening were conducted at the start of DOTS implementation and after 2.5 years. Results: From 1968 to 1999, culture-positive and smear-positive tuberculosis declined by 2.3 and 2.5% per annum compared with 11.9 and 5.6% after DOTS implementation. The 2.5 year period of DOTS implementation accounted for one-fourth of the decline in prevalence of culture-positive tuberculosis over 33 years. Multivariate analysis showed that prevalence of culture-positive tuberculosis decreased substantially (10.0% per annum, 95% CI: 2.8–16.6%) owing to DOTS after only slight declines related to temporal trends (2.1% annual decline, 95% CI: 1.1–3.2%) and short-course chemotherapy (1.5% annual decline, 95% CI: �9.7% to 11.5%). Under DOTS, the proportion of total cases identified through clinical care increased from 81 to 92%. Conclusions: Following DOTS implementation, prevalence of culture-positive tuberculosis decreased rapidly following a gradual decline for the previous 30 years. In the absence of a large HIV epidemic and with relatively low levels of rifampicin resistance, DOTS was associated with rapid reduction of tuberculosis prevalenc