Pre-main-sequence population in NGC 1893 region: X-ray properties

Continuing the attempt to understand the properties of the stellar content in the young cluster NGC 1893 we have carried out a comprehensive multi-wavelength study of the region. The present study focuses on the X-ray properties of T-Tauri Stars (TTSs) in the NGC 1893 region. We found a correlation between the X-ray luminosity, $L_X$, and the stellar mass (in the range 0.2$-$2.0 \msun) of TTSs in the NGC 1893 region, similar to those reported in some other young clusters, however the value of the power-law slope obtained in the present study ($\sim$ 0.9) for NGC 1893 is smaller than those ($\sim$1.4 - 3.6) reported in the case of TMC, ONC, IC 348 and Chameleon star forming regions. However, the slope in the case of Class III sources (Weak line TTSs) is found to be comparable to that reported in the case of NGC 6611 ($\sim$ 1.1). It is found that the presence of circumstellar disks has no influence on the X-ray emission. The X-ray luminosity for both CTTSs and WTTSs is found to decrease systematically with age (in the range $\sim$ 0.4 Myr - 5 Myr). The decrease of the X-ray luminosity of TTSs (slope $\sim$ -0.6) in the case of NGC 1893 seems to be faster than observed in the case of other star-forming regions (slope -0.2 to -0.5). There is indication that the sources having relatively large NIR excess have relatively lower $L_X$ values. TTSs in NGC 1893 do not follow the well established X-ray activity - rotation relation as in the case of main-sequence stars.Comment: 10 pages, 7 figures, Accepted for publication in New Astronom

Cooperative Emission of a Coherent Superflash of Light

We investigate the transient coherent transmission of light through an optically thick cold stron-tium gas. We observe a coherent superflash just after an abrupt probe extinction, with peak intensity more than three times the incident one. We show that this coherent superflash is a direct signature of the cooperative forward emission of the atoms. By engineering fast transient phenomena on the incident field, we give a clear and simple picture of the physical mechanisms at play.Comment: 4 Fig., 5 page

Dissociative multi-photon ionization of isolated uracil and uracil-adenine complexes

Recent multi-photon ionization (MPI) experiments on uracil revealed a fragment ion at m/z 84 that was proposed as a potential marker for ring opening in the electronically excited neutral molecule. The present MPI measurements on deuterated uracil identify the fragment as C3H4N2O+ (uracil+ less CO), a plausible dissociative ionization product from the theoretically predicted open-ring isomer. Equivalent measurements on thymine do not reveal an analogous CO loss channel, suggesting greater stability of the excited DNA base. MPI and electron impact ionization experiments have been carried out on uracil-adenine clusters in order to better understand the radiation response of uracil within RNA. Evidence for C3H4N2O+ production from multi-photon-ionized uracil-adenine clusters is tentatively attributed to a significant population of π-stacked configurations in the neutral beam

Investigations of the Non-Linear LMC Cepheid Period-Luminosity Relation with Testimator and Schwarz Information Criterion Methods

In this paper, we investigate the linearity versus non-linearity of the Large Magellanic Cloud (LMC) Cepheid period-luminosity (P-L) relation using two statistical approaches not previously applied to this problem: the testimator method and the Schwarz Information Criterion (SIC). The testimator method is extended to multiple stages for the first time, shown to be unbiased and the variance of the estimated slope can be proved to be smaller than the standard slope estimated from linear regression theory. The Schwarz Information Criterion (also known as the Bayesian Information Criterion) is more conservative than the Akaike Information Criterion and tends to choose lower order models. By using simulated data sets, we verify that these statistical techniques can be used to detect intrinsically linear and/or non-linear P-L relations. These methods are then applied to independent LMC Cepheid data sets from the OGLE project and the MACHO project, respectively. Our results imply that there is a change of slope in longer period ranges for all of the data sets. This strongly supports previous results, obtained from independent statistical tests, that the observed LMC P-L relation is non-linear with a break period at/around 10 days.Comment: 9 pages, 5 figures and 3 tables, PASP accepte

Studies on Biodiesel Synthesis Using Nanosilica Immobilised Lipase in Inverse Fluidized Bed Bioreactors

Biodiesel synthesis from neem oil and methyl acetate using lipase catalyst immobilised in nanosilica particles in a continuous inverse fluidised bed bioreactor of modified design has been analysed. The process has been simulated mathematically by developing a multiparameter software package and subsequently verified through pilot plant tests(experiments).The improved performance characteristics of the bioreactor of proposed design have been highlighted. Graphical data have been presented to illustrate the dependence of reactor performance on system/operating parameters such as substrate flow rate, catalyst loading and molar ratio of oil to acetate in the blend(substrate solution).The downflow mode of operation is an added advantage of these bioreactors which tends to reduce their operating cost. Due to the use of nanoparticles, the effectiveness factor is close to unity and consequently, the global rate of transesterification is more or less equal to the intrinsic rate. This enhances the performance efficiency of the bioreactor

A high flux source of cold strontium atoms

We describe an experimental apparatus capable of achieving a high loading rate of strontium atoms in a magneto-optical trap operating in a high vacuum environment. A key innovation of this setup is a two dimensional magneto-optical trap deflector located after a Zeeman slower. We find a loading rate of 6x10^9/s whereas the lifetime of the magnetically trapped atoms in the 3P2 state is 54s.Comment: 12 pages, 16 figure

Radiation Processing: An Emerging Preservation Technique for Meat and Meat Products

Development of shelf stable meat and meat products is a challenging task due to physico-chemical, microbiological and sensory alterations during storage. Lot of thrust is being given in the application of radiation processing in meat sector due to its microbial safety. Maintaining and delivering quality and safety products both in civilian and service sectors is the need of the hour. Even though irradiation can ensure complete microbial sterility it can lead to lipid and protein oxidation due to the formation of free radicals which can cause flavour changes. Several studies on the usage of natural antioxidants which can arrest these changes have been reported. Irradiation can find excellent applications in the extension of shelf life of chilled and non chilled carcasses and birds in service sectors. There are several radiation processing plants in India commissioned in the private sector which can also be utilized by Armed forces for extending the shelf life of whole carcass and birds with an extension of shelf life. This will be of great significance to the defence forces.

Evaluation of Antioxidant Activity, Radical Scavenging, and Reducing Power of Clove Oil and Clove Oleoresin in Comparison with Natural and Synthetic Antioxidants in Chevon (Capra aegagrus hircus) and Chicken Meat

The antioxidant effects of clove oil (CO) and oleoresin (OR) in two species of meat i.e. chicken and chevon during refrigerated storage (4±1°C) were investigated. The antioxidant potential (AOP) and radical scavenging activities were compared with natural (α-Tocopherol & L-ascorbic acid) and synthetic antioxidants (BHA & TBHQ). CO & TBHQ, BHA & OR and L-ascorbic acid and α-Tocopherol produced 84-79%, 68-77% and 68-59% AOP respectively in both species. DPPH and ABTS methods of scavenging assay established better scavenging capability of CO and TBHQ in comparison with other treatments. Significant reduction (p<0.05) in FRAP values was observed in CO & TBHQ in both species of meat. The order of antioxidant potential, scavenging activity and reducing power was in the order of CO>TBHQ>OR>BHA>Tocopherol>L-ascorbic acid. All the antioxidant assays analysed demonstrated a very significant correlation (p<0.05) between each other. The results suggest that CO and OR through their antioxidant effects are potentially useful in preserving meat products