Nanodot to Nanowire: A strain-driven shape transition in self-organized endotaxial CoSi2 on Si (100)

We report a phenomenon of strain-driven shape transition in the growth of nanoscale self-organized endotaxial CoSi2 islands on Si (100) substrates. Small square shaped islands as small as 15\times15 nm2 have been observed. Islands grow in the square shape following the four fold symmetry of the Si (100) substrate, up to a critical size of 67 \times 67 nm2. A shape transition takes place at this critical size. Larger islands adopt a rectangular shape with ever increasing length and the width decreasing to an asymptotic value of ~25 nm. This produces long wires of nearly constant width.We have observed nanowire islands with aspect ratios as large as ~ 20:1. The long nanowire heterostructures grow partly above (~ 3 nm) the surface, but mostly into (~17 nm) the Si substrate. These self-organized nanostructures behave as nanoscale Schottky diodes. They may be useful in Si-nanofabrication and find potential application in constructing nano devices.Comment: 9 pages, 7 figure

MOLECULAR CHARA CTERIZATION OF METHICILLIN-RESISTANT STAPHYLOCOCCUS AUREUS (MRSA) ISOLATED FROM BOVINE MASTITIS IN AND AROUND KOLKATA, INDIA

The present investigation was carried out on 118 milk samples collected from suspected clinical and subclinical mastitis affected indigenous and cross-bred cattle in and around Kolkata and North 24 Parganas districts. A total of 38 samples were positive for Staphylococcus aureus. This indicates that considerable proportion of cattle with intramammary infection was colonized with S. aureus. However, sizeable populations of those pathogens (15 of 38) were methicillin resistant (MRSA) by phenotypic detection method. Methicillin resistance gene (mecA) was detected from 6 samples out of those 15 samples. Overuse or inadvertent use of antibiotics may be the cause of development of such resistant strains in livestock. This may have huge public health significance as these resistant strains may enter the food chain and infect the consumer with consequences of life-threatening infections

Using Local Public Goods to Attract and Retain the Creative Class: A Tale of Two Cities

We study the impact that the provision of a local public good (LPG) by two cities has on their ability to attract and retain members of the creative class. This creative class consists of two types of members known as engineers and artists. Engineers are wealthier than artists and they also value the LPG more. We first focus on each city in isolation. We compute the marginal value and the marginal cost of the LPG and then determine the provision of this LPG when the provision is determined by uniform contributions and majority voting. Next, we allow the creative class members to migrate between the two cities and analyze whether engineers or artists migrate, the equilibrium distribution of the creative class, and the efficiency of the LPG provision. Finally, we consider the situation in each city just before migration and study how much of the LPG is provided when proportional contributions and majority voting determine this provision. A related question we address is whether engineers or artists now have an incentive to migrate and, if yes, we identify who would like to migrate and to which city

BOVINE PLASMA FIBRINOGEN AS MARKER IN CLINICAL AND SUB-CLINICAL MASTITIS

Plasma samples were collected from healthy as well as clinical and sub-clinical mastitis affected cows from Barasat, West Bengal, India. Plasma samples, after ammonium sulphate precipitation, were dialyzed against several changes of PBS (pH 7.2) to remove the excess ammonium sulphate. Then plasma fibrinogens were purified by gel filtration chromatography on Sephacryl S-200 HR. SDS-PAGE (10%) of purified fibrinogen from plasma of healthy cow revealed polypeptide bands of 74, 67 and 57 kDa which represent the α (alpha), β (beta) and γ (gamma)- chains respectively. On the other hand, purified fibrinogen from plasma of sub-clinical and clinical mastitis affected cow revealed polypeptide bands of 73 (α-chain), 68 kDa (β-chain) and 72 (γ-chain), 68 kDa (β-chain) respectively. The SDS-PAGE analysis showed the absence of gamma (γ)- chain of fibrinogen in both the samples of sub-clinical and clinical mastitis positive cow. Single precipitin line was observed in double immunodiffusion test when purified fibrinogen from healthy, clinical and subclinical mastitis positive cows reacted with hyper immune sera raised in rabbit. No precipitin line was found against the normal control serum. These purified fibrinogens also showed cross reactivity against antibody raised in rabbit when analyzed by western blot technique

Low pH enhances the action of maximin H5 against Staphylococcus aureus and helps mediate lysylated phosphatidylglycerol induced resistance

Maximin H5 (MH5) is an amphibian antimicrobial peptide specifically targeting Staphylococcus aureus. At pH 6, the peptide showed an increased ability to penetrate (∆П = 6.2 mN m-1) and lyse (lysis = 48 %) S. aureus membrane mimics, which incorporated physiological levels of lysylated phosphatidylglycerol (Lys-PG, 60 %) as compared to pH 7 (∆П = 5.6 mN m-1 and lysis = 40 % at pH 7) where levels of Lys-PG are lower (40 %). The peptide therefore appears to have optimal function at pH levels known to be optimal for the organism’s growth. MH5 killed S. aureus (minimum inhibitory concentration = 90 µM) via membranolytic mechanisms that involved the stabilization of α-helical structure (circa 45-50 %) and which showed similarities to the ‘Carpet’ mechanism based on its ability to increase the rigidity (Cs-1 = 109.94 mN m-1) and thermodynamic stability (∆Gmix = -3.0) of physiologically relevant S. aureus membrane mimics at pH 6. Based on theoretical analysis this mechanism may involve the use of a tilted peptide structure and efficacy was noted to vary inversely with the Lys-PG content of S. aureus membrane mimics for each pH studied (R2 circa 0.97), which led to the suggestion that under biologically relevant conditions, low pH helps mediate Lys-PG induced resistance in S. aureus to MH5 antibacterial action. The peptide showed a lack of haemolytic activity (< 2 % haemolysis) and merits further investigation as a potential template for development as an anti-staphylococcal agent in medically and biotechnically relevant areas

The Mechanism of Substrate Inhibition in Human Indoleamine 2,3-Dioxygenase

Indoleamine 2,3-dioxygenase catalyzes the O(2)-dependent oxidation of L-tryptophan (L-Trp) to N-formylkynurenine (NFK) as part of the kynurenine pathway. Inhibition of enzyme activity at high L-Trp concentrations was first noted more than 30 years ago, but the mechanism of inhibition has not been established. Using a combination of kinetic and reduction potential measurements, we present evidence showing that inhibition of enzyme activity in human indoleamine 2,3-dioxygenase (hIDO) and a number of site-directed variants during turnover with L-tryptophan (L-Trp) can be accounted for by the sequential, ordered binding of O(2) and L-Trp. Analysis of the data shows that at low concentrations of L-Trp, O(2) binds first followed by the binding of L-Trp; at higher concentrations of L-Trp, the order of binding is reversed. In addition, we show that the heme reduction potential (E(m)(0)) has a regulatory role in controlling the overall rate of catalysis (and hence the extent of inhibition) because there is a quantifiable correlation between E(m)(0) (that increases in the presence of L-Trp) and the rate constant for O(2) binding. This means that the initial formation of ferric superoxide (Fe(3+)-O(2)(•-)) from Fe(2+)-O(2) becomes thermodynamically less favorable as substrate binds, and we propose that it is the slowing down of this oxidation step at higher concentrations of substrate that is the origin of the inhibition. In contrast, we show that regeneration of the ferrous enzyme (and formation of NFK) in the final step of the mechanism, which formally requires reduction of the heme, is facilitated by the higher reduction potential in the substrate-bound enzyme and the two constants (k(cat) and E(m)(0)) are shown also to be correlated. Thus, the overall catalytic activity is balanced between the equal and opposite dependencies of the initial and final steps of the mechanism on the heme reduction potential. This tuning of the reduction potential provides a simple mechanism for regulation of the reactivity, which may be used more widely across this family of enzymes