Charge transport and magnetic properties of coaxial composite fibrils of polypyrrole/multiwall carbon nanotubes at low temperature

We report the low temperature electrical and magnetic properties of polypyrrole (PPy)/multiwall carbon nanotube (MWNT) coaxial composite fibrils synthesized by the electro-polymerization method. The iron-filled MWNTs were first grown by chemical vapor deposition of a mixture of liquid phase organic compound and ferrocene by the one step method. Then the PPy/MWNT fibrils were prepared by the electrochemical polymerization process. Electron microscopy studies reveal that PPy coating on the surface of nanotube is quite uniform throughout the length. The temperature dependent electrical resistivity and magnetization measurements were done from room temperature down to 5 and 10 K, respectively. The room temperature resistivity (rho) of PPy/MWNT composite fibril sample is similar to 3.8 Omega m with resistivity ratio R-5 K/R-300 K] of similar to 300, and the analysis of rho(T) in terms of reduced activation energy shows that resistivity lies in the insulating regime below 40 K. The resistivity varies according to three dimensional variable range hopping mechanism at low temperature. The magnetization versus applied field (M-H loop) data up to a field of 20 kOe are presented, displaying ferromagnetic behavior at all temperatures with enhanced coercivities similar to 680 and 1870 Oe at room temperature and 10 K, respectively. The observation of enhanced coercivity is due to significant dipolar interaction among encapsulated iron nanoparticles, and their shape anisotropy contribution as well.

Mycobacterium tuberculosis mutT1 (Rv2985) and ADPRase (Rv1700) proteins constitute a two-stage mechanism of 8-Oxo-dGTP and 8-Oxo-GTP detoxification and adenosine to cytidine mutation avoidance

Approximately one third of the world population is infected with Mycobacterium tuberculosis, the causative agent of tuberculosis. A better understanding of the pathogen biology is crucial to develop new tools/strategies to tackle its spread and treatment. In the host macrophages, the pathogen is exposed to reactive oxygen species, known to damage dGTP and GTP to 8-oxo-dGTP and 8-oxo-GTP, respectively. Incorporation of the damaged nucleotides in nucleic acids is detrimental to organisms. MutT proteins, belonging to a class of Nudix hydrolases, hydrolyze 8-oxo-G nucleoside triphosphates/diphosphates to the corresponding nucleoside monophosphates and sanitize the nucleotide pool. Mycobacteria possess several MutT proteins. However, a functional homolog of Escherichia coli MutT has not been identified. Here, we characterized MtuMutT1 and Rv1700 proteins of M. tuberculosis. Unlike other MutT proteins, MtuMutT1 converts 8-oxo-dGTP to 8-oxo-dGDP, and 8-oxo-GTP to 8-oxo-GDP. Rv1700 then converts them to the corresponding nucleoside monophosphates. This observation suggests the presence of a two-stage mechanism of 8-oxo-dGTP/8-oxo-GTP detoxification in mycobacteria. MtuMutT1 converts 8-oxo-dGTP to 8-oxo-dGDP with a K-m of similar to 50 mu M and V-max of similar to 0.9 pmol/min per ng of protein, and Rv1700 converts 8-oxo-dGDP to 8-oxo-dGMP with a K-m of similar to 9.5 mu M and V-max of similar to 0.04 pmol/min per ng of protein. Together, MtuMutT1 and Rv1700 offer maximal rescue to E. coli for its MutT deficiency by decreasing A to C mutations (a hallmark of MutT deficiency). We suggest that the concerted action of MtuMutT1 and Rv1700 plays a crucial role in survival of bacteria against oxidative stress.

Can the viscosity in astrophysical black hole accretion disks be close to its string theory bound?

String theory and gauge/gravity duality suggest the lower bound of shear viscosity (eta) to entropy density (s) for any matter to be mu h/4 pi k(B), when h and k(B) are reduced Planck and Boltzmann constants respectively and mu <= 1. Motivated by this, we explore eta/s in black hole accretion flows, in order to understand if such exotic flows could be a natural site for the lowest eta/s. Accretion flow plays an important role in black hole physics in identifying the existence of the underlying black hole. This is a rotating shear flow with insignificant molecular viscosity, which could however have a significant turbulent viscosity, generating transport, heat and hence entropy in the flow. However, in presence of strong magnetic field, magnetic stresses can help in transporting matter independent of viscosity, via celebrated Blandford-Payne mechanism. In such cases, energy and then entropy produces via Ohmic dissipation. In,addition, certain optically thin, hot, accretion flows, of temperature greater than or similar to 10(9) K, may be favourable for nuclear burning which could generate/absorb huge energy, much higher than that in a star. We find that eta/s in accretion flows appears to be close to the lower bound suggested by theory, if they are embedded by strong magnetic field or producing nuclear energy, when the source of energy is not viscous effects. A lower bound on eta/s also leads to an upper bound on the Reynolds number of the flow.

Chemical unfolding of chicken villin headpiece in aqueous dimethyl sulfoxide solution: cosolvent concentration dependence, pathway, and microscopic mechanism

Unfolding of a protein often proceeds through partial unfolded intermediate states (PUIS). PUIS have been detected in several experimental and simulation studies. However, complete analyses of transitions between different PUIS and the unfolding trajectory are sparse. To understand such dynamical processes, we study chemical unfolding of a small protein, chicken villin head piece (HP-36), in aqueous dimethyl sulfoxide (DMSO) solution. We carry out molecular dynamics simulations at various solution compositions under ambient conditions. In each concentration, the initial step of unfolding involves separation of two adjacent native contacts, between phenyl alanine residues (11-18 and 7-18). This first step induces, under appropriate conditions, subsequent separation among other hydrophobic contacts, signifying a high degree of cooperativity in the unfolding process. The observed sequence of structural changes in HP-36 on increasing DMSO concentration and the observed sequence of PUIS, are in approximate agreement with earlier simulation results (in pure water) and experimental observations on unfolding of HP-36. Peculiar to water-DMSO mixture, an intervening structural transformation (around 15% of DMSO) in the binary mixture solvent retards the progression of unfolding as composition is increased. This is reflected in a remarkable nonmonotonic composition dependence of RMSD, radius of gyration and the fraction of native contacts. At 30% mole fraction of DMSO, we find the extended randomly coiled structure of the unfolded protein. The molecular mechanism of DMSO induced unfolding process is attributed to the initial preferential solvation of the hydrophobic side chain atoms through the methyl groups of DMSO, followed by the hydrogen bonding of the oxygen atom of DMSO to the exposed backbone NH groups of HP-36.

Crystal structures and binding studies of atovaquone and its derivatives with cytochrome bc(1): a molecular basis for drug design

Crystal structure of trans-atovaquone (antimalarial drug), its polymorph and its stereoisomer (cis) along with five other derivatives with different functional groups have been analyzed. Based on the conformational features of these compounds and the characteristics of the nature of intermolecular interactions, valuable insights into the atomistic details of protein-inhibitor interactions have been derived by docking studies. Atovaquone and its derivatives pack in the crystal lattice using intermolecular O-H center dot center dot center dot O hydrogen bond dimer motifs supported by surrogate weak interactions including C-H center dot center dot center dot O and C-H center dot center dot center dot Cl hydrogen bonds. The docking results of these molecules with cytochrome bc(1) show preferences to form N-H center dot center dot center dot O, O-H center dot center dot center dot O and O-H center dot center dot center dot Cl hydrogen bonds. The involvement of halogen atoms in the binding pocket appears to be significant and is contrary to the theoretically predicted mechanism of protein-ligand docking reported earlier based on mimicking experimental binding results of stigmatellin with cytochrome bc(1). The significance of subtle energy factors controlled by weak intermolecular interactions appears to play a major role in drug binding.

Quick recovery in transactional flash

Maintaining metadata consistency is a critical issue in designing a filesystem. Although satisfactory solutions are available for filesystems residing on magnetic disks, these solutions may not give adequate performance for filesystems residing on flash devices. Prabhakaran et al. have designed a metadata consistency mechanism specifically for flash chips, called Transactional Flash1]. It uses cyclic commit mechanism to provide transactional abstractions. Although significant improvement over usual journaling techniques, this mechanism has certain drawbacks such as complex protocol and necessity to read whole flash during recovery, which slows down recovery process. In this paper we propose addition of thin journaling layer on top of Transactional Flash to simplify the protocol and speed up the recovery process. The simplified protocol named Quick Recovery Cyclic Commit (QRCC) uses journal stored on NOR flash for recovery. Our evaluations on actual raw flash card show that journal writes add negligible penalty compared to original Transactional Flash's write performance, while quick recovery is facilitated by journal in case of failures.

Revisiting lepton flavor violation in a supersymmetric type II seesaw mechanism

In view of the recent measurement of the reactor mixing angle theta(13) and updated limit on BRd(mu -> e gamma) by the MEG experiment, we reexamine the charged lepton flavor violations in a framework of the supersymmetric type II seesaw mechanism. The supersymmetric type II seesaw predicts a strong correlation between BR(mu -> e gamma) and BR(tau -> mu gamma) mainly in terms of the neutrino mixing angles. We show that such a correlation can be determined accurately after the measurement of theta(13). We compute different factors that can affect this correlation and show that the minimal supergravity-like scenarios, in which slepton masses are taken to be universal at the high scale, predict 3.5 <= BR(tau -> mu gamma)/= BR(mu -> e gamma) <= 30 for normal hierarchical neutrino masses. Any experimental indication of deviation from this prediction would rule out the minimal models of the supersymmetric type II seesaw. We show that the current MEG limit puts severe constraints on the light sparticle spectrum in the minimal supergravity model if the seesaw scale lies within 10(13)-10(15) GeV. It is shown that these constraints can be relaxed and a relatively light sparticle spectrum can be obtained in a class of models in which the soft mass of a triplet scalar is taken to be nonuniversal at the high scale.

Method of designing an access mechanism for social networks

The rapid development of communication and networking has lessened geographical boundaries among actors in social networks. In social networks, actors often want to access databases depending upon their access rights, privacy, context, privileges, etc. Managing and handling knowledge based access of actors is complex and hard for which broad range of technologies need to be called. Access based on dynamic access rights and circumstances of actors impose major tasks on access systems. In this paper, we present an Access Mechanism for Social Networks (AMSN) to render access to actors over databases taking privacy and status of actors into consideration. The designed AMSN model is tested over an Agriculture Social Network (ASN) which utilises distinct access rights and privileges of actors related to the agriculture occupation, and provides access to actors over databases.

Exchange-spring mechanism of soft and hard ferrite nanocomposites

The paper reports exchange-spring soft and hard ferrite nanocomposites synthesized by chemical co-precipitation with or without the application of ultrasonic vibration. The composites contained BaFe12O19 as the hard phase and CoFe2O4/MgFe2O4 as the soft phase. X-ray diffraction patterns of the samples in the optimum calcined condition indicated the presence of soft ferrites as face-centred cubic (fcc) and hard ferrites as hexagonal close packed (hcp) structure respectively. Temperature dependence of magnetization in the range of 20-700 degrees C demonstrated distinct presence of soft and hard ferrites as magnetic phases which are characterized by wide difference in magnetic anisotropy and coercivity. Exchange-spring mechanism led these nanocomposite systems to exchange-coupled, which ultimately produced convex hysteresis loops characteristic of a single-phase permanent magnet. Fairly high value of coercivity and maximum energy product were observed for the samples in the optimum calcined conditions with a maximum applied field of 1600 kA/m (2 T).

Design and Analysis of an Acknowledgment-Aware Asynchronous MPR MAC Protocol for Distributed WLANs

Multi-packet reception (MPR) promises significant throughput gains in wireless local area networks (WLANs) by allowing nodes to transmit even in the presence of ongoing transmissions in the medium. However, the medium access control (MAC) layer must now be redesigned to facilitate rather than discourage - these overlapping transmissions. We investigate asynchronous MPR MAC protocols, which successfully accomplish this by controlling the node behavior based on the number of ongoing transmissions in the channel. The protocols use the backoff timer mechanism of the distributed coordination function, which makes them practically appealing. We first highlight a unique problem of acknowledgment delays, which arises in asynchronous MPR, and investigate a solution that modifies the medium access rules to reduce these delays and increase system throughput in the single receiver scenario. We develop a general renewal-theoretic fixed-point analysis that leads to expressions for the saturation throughput, packet dropping probability, and average head-of-line packet delay. We also model and analyze the practical scenario in which nodes may incorrectly estimate the number of ongoing transmissions.

Nanolipodendrosome-loaded glatiramer acetate and myogenic differentiation I as augmentation therapeutic strategy approaches in muscular dystrophy

Backgrond: Muscular dystrophies consist of a number of juvenile and adult forms of complex disorders which generally cause weakness or efficiency defects affecting skeletal muscles or, in some kinds, other types of tissues in all parts of the body are vastly affected. In previous studies, it was observed that along with muscular dystrophy, immune inflammation was caused by inflammatory cells invasion - like T lymphocyte markers (CD8+/CD4+). Inflammatory processes play a major part in muscular fibrosis in muscular dystrophy patients. Additionally, a significant decrease in amounts of two myogenic recovery factors (myogenic differentation 1 MyoD] and myogenin) in animal models was observed. The drug glatiramer acetate causes anti-inflammatory cytokines to increase and T helper (Th) cells to induce, in an as yet unknown mechanism. MyoD recovery activity in muscular cells justifies using it alongside this drug. Methods: In this study, a nanolipodendrosome carrier as a drug delivery system was designed. The purpose of the system was to maximize the delivery and efficiency of the two drug factors, MyoD and myogenin, and introduce them as novel therapeutic agents in muscular dystrophy phenotypic mice. The generation of new muscular cells was analyzed in SW1 mice. Then, immune system changes and probable side effects after injecting the nanodrug formulations were investigated. Results: The loaded lipodendrimer nanocarrier with the candidate drug, in comparison with the nandrolone control drug, caused a significant increase in muscular mass, a reduction in CD4+/CD8+ inflammation markers, and no significant toxicity was observed. The results support the hypothesis that the nanolipodendrimer containing the two candidate drugs will probably be an efficient means to ameliorate muscular degeneration, and warrants further investigation.

On the mechanism of metal nanoparticle synthesis in the brust-schiffrin method

Brust-Schiffrin synthesis (BSS) of metal nanoparticles has emerged as a major breakthrough in the field for its ability to produce highly stable thiol functionalized nanoparticles. In this work, we use a detailed population balance model to conclude that particle formation in BSS is controlled by a new synthesis route: continuous nucleation, growth, and capping of particles throughout the synthesis process. The new mechanism, quite different from the others known in the literature (classical LaMer mechanism, sequential nucleation-growth-capping, and thermodynamic mechanism), successfully explains key features of BSS, including size tuning by varying the amount of capping agent instead of the widely used approach of varying the amount of reducing agent. The new mechanism captures a large body of experimental observations quantitatively, including size tuning and only a marginal effect of the parameters otherwise known to affect particle synthesis sensitively. The new mechanism predicts that, in a constant synthesis environment, continuous nucleation-growth-capping mechanism leads to complete capping of particles (no more growth) at the same size, while the new ones are born continuously, in principle leading to synthesis of more monodisperse particles. This prediction is validated through new experimental measurements.

MECHANISM OF CELL LYSIS IN MICROFLUIDIC CHANNEL WITH INTEGRATED NANOCOMPOSITE ELECTRODES

This paper reports on the characterization of an integrated micro-fluidic platform for controlled electrical lysis of biological cells and subsequent extraction of intracellular biomolecules. The proposed methodology is capable of high throughput electrical cell lysis facilitated by nano-composite coated electrodes. The nano-composites are synthesized using Carbon Nanotube and ZnO nanorod dispersion in polymer. Bacterial cells are used to demonstrate the lysis performance of these nanocomposite electrodes. Investigation of electrical lysis in the microchannel is carried out under different parameters, one with continuous DC application and the other under DC biased AC electric field. Lysis in DC field is dependent on optimal field strength and governed by the cell type. By introducing the AC electrical field, the electrokinetics is controlled to prevent cell clogging in the micro-channel and ensure uniform cell dispersion and lysis. Lysis mechanism is analyzed with time-resolved fluorescence imaging which reveal the time scale of electrical lysis and explain the dynamic behavior of GFP-expressing E. coli cells under the electric field induced by nanocomposite electrodes. The DNA and protein samples extracted after lysis are compared with those obtained from a conventional chemical lysis method by using a UV-Visible spectroscopy and fluorimetry. The paper also focuses on the mechanistic understanding of the nano-composite coating material and the film thickness on the leakage charge densities which lead to differential lysis efficiency.

Metal based photosensitizers of tetradentate Schiff base: Promising role in anti-tumor activity through singlet oxygen generation mechanism

In the present investigation, a Schiff base N'(1),N'(3)-bis(Z)-(2-hydroxynapthyl)methylidene]benzene-1,3-dicarbod ihydrazide (L-1) and its Co(II), Ni(II) and Cu(II) complexes have been synthesized and characterized as novel photosensitizing agents for photodynamic therapy (PDT). The interaction of these complexes with calf thymus DNA (CT DNA) has been explored using absorption, thermal denaturation and viscometric studies. The experimental results revealed that Co(II) and Ni(II) complexes on binding to CT DNA imply a covalent mode, most possibly involving guanine N7 nitrogen of DNA, with an intrinsic binding constant K-b of 4.5 x 10(4) M-1 and 4.2 x 10(4) M-1, respectively. However, interestingly, the Cu(II) complex is involved in the surface binding to minor groove via phosphate backbone of DNA double helix with an intrinsic binding constant K-b of 5.7 x 10(4) M-1. The Co(II), Ni(II) and Cu(II) complexes are active in cleaving supercoiled (SC) pUC19 DNA on photoexposure to UV-visible light of 365 nm, through O-1(2) generation with quantum yields of 0.28, 0.25 and 0.30, respectively. Further, these complexes are cytotoxic in A549 lung cancer cells, showing an enhancement of cytotoxicity upon light irradiation. (C) 2013 Elsevier B.V. All rights reserved.

Evaluation of microwave assisted grafted sago starch as controlled release polymeric carrier

In the present investigation an attempt has been made to develop a new co-polymeric material for controlled release tablet formulations. The acrylamide grafting was successfully performed on the backbone of sago starch. The modified starch was tested for acute toxicity and drug-excipient compatibility study. The grafted material was used in making of controlled release tablets of lamivudine. The formulations were evaluated for physical characteristics such as hardness, friability, %drug content and weight variations. The in vitro release study showed that the optimized formulation exhibited highest correlation (R) value in case of Higuchi model and the release mechanism of the optimized formulation predominantly exhibited combination of diffusion and erosion process. There was a significant difference in the pharmacokinetic parameters (T-max, C-max, AUC, V-d, T-1/2 and MDT) of the optimized formulation as compared to the marketed conventional tablet Lamivir (R) was observed. The pharmacokinetics parameters were showed controlled pattern and better bioavailability. The optimized formulation exhibited good stability and release profile at the accelerated stability conditions. (c) 2013 Elsevier B.V. All rights reserved.