Supramolecular control of the magnetic anisotropy in two-dimensional high-spin Fe arrays at a metal interface

Magnetic atoms at surfaces are a rich model system for solid-state magnetic bits exhibiting either classical(1,2) or quantum(3,4) behaviour. Individual atoms, however, are difficult to arrange in regular patterns(1-5). Moreover, their magnetic properties are dominated by interaction with the substrate, which, as in the case of Kondo systems, often leads to a decrease or quench of their local magnetic moment(6,7). Here, we show that the supramolecular assembly of Fe and 1,4-benzenedicarboxylic acid molecules on a Cu surface results in ordered arrays of high-spin mononuclear Fe centres on a 1.5nm square grid. Lateral coordination with the molecular ligands yields unsaturated yet stable coordination bonds, which enable chemical modification of the electronic and magnetic properties of the Fe atoms independently from the substrate. The easy magnetization direction of the Fe centres can be switched by oxygen adsorption, thus opening a way to control the magnetic anisotropy in supramolecular layers akin to that used in metallic thin films.

Impact of Energy Quantization on the Performance of Current-Biased SET Circuits

The current-biased single electron transistor (SET) (CBS) is an integral part of almost all hybrid CMOS SET circuits. In this paper, for the first time, the effects of energy quantization on the performance of CBS-based circuits are studied through analytical modeling and Monte Carlo simulations. It is demonstrated that energy quantization has no impact on the gain of the CBS characteristics, although it changes the output voltage levels and oscillation periodicity. The effects of energy quantization are further studied for two circuits: negative differential resistance (NDR) and neuron cell, which use the CBS. A new model for the conductance of NDR characteristics is also formulated that includes the energy quantization term.

Metabolism of mandelic acid by Neurospora crassa

Preliminary studies on the metabolism of mandelic acid by Neurospora crassa reveal the operation of a pathway for its degradation which involves benzoyl formic acid, benzaldehyde, benzoic acid, 4-hydroxybenzoic acid, and protocatechuic acid as the intermediates. This pathway is different from that followed by bacterial systems and is the same as that observed in Aspergillus niger.

Mammalian spermatid specific protein, TP2, is a zinc metalloprotein with two finger motifs

An analysis of the recently reported cDNA derived amino acid sequences of mouse (Kleene and Flynn, J. Biol. Chem. , 17272–17277, 1987) and rat (Luersson Image ,Nucl. Acids Res. Image , 3585, 1989). TP2 has revealed the presence of two potential zinc finger motifs involving cysteine and histidine residues. TP2, as purified from rat elongating spermatids, is shown here to contain 0.2 atoms of zinc bound per molecule of the protein by atomic absorption spectroscopy. On incubation with 10 μM ZnCl2, Image , and subsequent exhaustive dialysis, TP2 had 2 atoms of zinc bound per molecule. The involvement of cysteine residues of TP2 in coordination with zinc was also suggested by the observation that TP2 could be labeled, Image , with iodoacetamidofluorescein only after preincubation of spermatid nuclei with EDTA. The zinc finger domains of TP2 may play an important role in initiation of chromatin condensation and /or cessation of transcriptional activity during mammalian spermiogenesis. DTT, Dithiothreitol; IAF, Iodoacetamido-fluorescein; SDS, Sodium dodecyl sulfate; PAGE, Polyacrylamide gel electrophoresis; PMSF, Phynyl methyl sulfonyl fluoride

Seawater Durability of Epoxy/Vinyl Ester Reinforced with Glass/Carbon Composites

Seawater aging response was investigated in marine-grade glass/epoxy, glass/vinyl ester, carbon/epoxy and carbon/vinyl ester composites with respect to water uptake, interlaminar shear strength, flexural strength, tensile strength, and tensile fracture surface observations. The reduction of mechanical properties was found to be higher in them initial stages which showed saturation in the longer durations of seawater immersion. The flexural strength and ultimate tensile strength (UTS) dropped by about 35% and 27% for glass/epoxy, 22% and 15% for glass/vinyl ester, 48% and 34% for carbon/epoxy 28%, and 21% carbon/vinyl ester composites respectively. The water uptake behavior of epoxy-based composites was inferior to that of the vinyl system.

Fabrication of device quality films of high loaded PPy/MWCNT nanocomposites using pulsed laser deposition

Polypyrrole (PPy) - multiwalled carbonnanotubes (MWCNT) nanocomposites with various MWCNT loading were prepared by in situ inversion emulsion polymerization technique. High loading of the nano filler were evaluated because of available inherent high interface area for charge separation in the nanocomposites. Solution processing of these conducting polymer nanocomposites is difficult because, most of them are insoluble in organic solvents. Device quality films of these composites were prepared by using pulsed laser deposition techniques (PLD). Comparative study of X-ray photoelectron spectroscopy (XPS) of bulk and film show that there is no chemical modification of polymer on ablation with laser. TEM images indicate PPy layer on MWCNT surface. SEM micrographs indicate that the MWCNT's are distributed throughout the film. It was observed that MWCNT in the composite held together by polymer matrix. Further more MWCNT diameter does not change from bulk to film indicating that the polymer layer remains intact during ablation. Even for very high loadings (80 wt.% of MWCNT's) of nanocomposites device quality films were fabricated, indicating laser ablation is a suitable technique for fabrication of device quality films. Conductivity of both bulk and films were measured using collinear four point probe setup. It was found that overall conductivity increases with increase in MWCNT loading. Comparative study of thickness with conductivity indicates that maximum conductivity was observed around 0.2 mu m. (C) 2010 Elsevier B.V. All rights reserved.

Giant magnetoresistance phenomenon in manganates

The discovery of giant magnetoresistance (GMR) in rare earth manganates of the general formula Ln(1-x)A(x)MnO(3) (Ln = rare earth, A = divalent cation) has aroused much interest not only because of its technological implications, but also due to the fascinating features and mechanism of the phenomemon in these oxides. GMR is observed in these manganates when they become ferromagnetic and transform from an insulating state to a metallic state close to the Curie temperature. The essential features of magnetoresistance in the manganates can be understood on the basis of the double-exchange mechanism, but this is too simplistic to account for all the observed data. The most curious property of the manganates relates to the high resistivity exhibited in the so-called metallic state. Charge ordering competes with the double-exchange interaction responsible for ferromagnetism and GMR in these materials. The charge-ordered (charge-crystal) insulating state in the rare earth manganates can be melted into a metallic and ferromagnetic charge-liquid state by applying a magnetic field, thus providing a unique case of charge and spin separation in solids. The observation of GMR in Tl2Mn2O7 shows that there can be causes other than double-exchange for the phenomenon.

An ab-initio study of the role of lone pairs in the structure and insulator-metal transition in SnO and PbO

We have performed density functional calculations on tetragonal SnO and PbO (litharge) in the space group P4/nmm with the specific intention of examining the role played by Sn 5s and Pb 6s lone pairs in stabilizing the structure, and in giving rise to semi-metallic behavior (of SnO at ambient pressure and of PbO in the gamma phase). Use of the electron localization function has permitted real-space visualization of the lone pair in these structures. We also discuss the electronic structure of the orthorhombic PbO (massicot, space group Pbma) which again has localized lone pairs, contrary to some earlier expectation. (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.

Multifaceted roles of curcumin: two sides of a coin!

Introduction: Curcumin has been a front-line topic of mainstream scientific research for a variety of diseases from cancer to Alzheimer's to infectious diseases. Curcumin suppresses the type 1 immune response, which might lead to alleviation of type 1 immune response disorders. However, the inhibition of type 1 immune response might invite infections with opportunistic pathogens. Considering its low bioavailability, several curcumin derivatives have been designed to improve its functionality. Areas covered: This is a consolidated review which aims to compare and contrast diverse aspects of curcumin in variety of diseases. The intricate underlying mechanisms and the functional determinants of curcumin are discussed. Expert opinion: Curcumin being considered as a spicy panacea, is not a remedy for all diseases. However, its ability to act differentially as an antioxidant or pro-oxidant akin to that of a double-edged sword/friend turning foe can be either beneficial or harmful for the host. It exhibits antioxidant properties at concentrations achievable in the body, making the host vulnerable to infections due to the suppression of innate immune responses. With the increase in knowledge of its functional groups, production of analogues of curcumin is underway to enhance its bioavailability and hence its therapeutic potency.

Targeting Mycobacterium tuberculosis Topoisomerase I by Small-Molecule Inhibitors

We describe inhibition of Mycobacterium tuberculosis topoisomerase I (MttopoI), an essential mycobacterial enzyme, by two related compounds, imipramine and norclomipramine, of which imipramine is clinically used as an antidepressant. These molecules showed growth inhibition of both Mycobacterium smegmatis and Mycobacterium tuberculosis cells. The mechanism of action of these two molecules was investigated by analyzing the individual steps of the topoisomerase I (topoI) reaction cycle. The compounds stimulated cleavage, thereby perturbing the cleavage-religation equilibrium. Consequently, these molecules inhibited the growth of the cells overexpressing topoI at a low MIC. Docking of the molecules on the MttopoI model suggested that they bind near the metal binding site of the enzyme. The DNA relaxation activity of the metal binding mutants harboring mutations in the DxDxE motif was differentially affected by the molecules, suggesting that the metal coordinating residues contribute to the interaction of the enzyme with the drug. Taken together, the results highlight the potential of these small molecules, which poison the Mycobacterium tuberculosis and Mycobacterium smegmatis topoisomerase I, as leads for the development of improved molecules to combat mycobacterial infections. Moreover, targeting metal coordination in topoisomerases might be a general strategy to develop new lead molecules.

A controller design method for 3 phase 4 wire grid connected VSI with LCL filter

Closed loop control of a grid connected VSI requires line current control and dc bus voltage control. The closed loop system comprising PR current controller and grid connected VSI with LCL filter is a higher order system. Closed loop control gain expressions are therefore difficult to obtain directly for such systems. In this work a simplified approach has been adopted to find current and voltage controller gain expressions for a 3 phase 4 wire grid connected VSI with LCL filter. The closed loop system considered here utilises PR current controller in natural reference frame and PI controller for dc bus voltage control. Asymptotic frequency response plot and gain bandwidth requirements of the system have been used for current control and voltage controller design. A simplified lower order model, derived for closed loop current control, is used for the dc bus voltage controller design. The adopted design method has been verified through experiments by comparison of the time domain response.

Covalent Postassembly Modification and Water Adsorption of Pd3 Self-Assembled Trinuclear Barrels

Three new ditopic imidazole ligands (2-4) were synthesized in high yields and characterized by various spectroscopic techniques. These ligands resulted in the formation of 3 + 6] self-assembled trinuclear barrels (5-7) in quantitative yields by stoichiometric combination of individual ligands and Pd(NO3)(2) in DMSO. All the three assemblies (5-7) were characterized by `H NMR and ESI-MS analysis, and subsequently, structures of the complexes 5 and 6 were confirmed by single-crystal X-ray diffraction studies. Structure analysis reveals the presence of NO3- counter anions in the intermolecular channels/pockets, which could potentially act as H-bonding sites between adsorbed water molecules within the channels. In fact, both the assemblies (5 and 6) showed water uptake (136.58, and 123.78 cm(3) g(-1), respectively) at ambient temperature under maximum allowable humidity. In addition, free aldehyde group present in the bridging ligand in complex 7 provides reactive site for postassembly modification. Herein, Knoevenagel condensation with Meldrum's acid was utilized under mild conditions by targeting aldehyde group appended in prefabricated complex 7 and transformed into a different complex (8) with altered functional group. Such postassembly functionalization enables incorporation of a new functional group without disrupting the integrity of the trifacial structure.

Space-Vector-Based Hybrid PWM Technique to Reduce Peak-to-Peak Torque Ripple in Induction Motor Drives

Constant-volts-per-hertz induction motor drives and vector-controlled induction motor drives utilize pulsewidth modulation (PWM) to control the voltage applied on the motor. The method of PWM influences the pulsations in the torque developed by the motor. A space-vector-based approach to PWM facilitates special switching sequences involving the division of active state time. This paper proposes a space-vector-based hybrid PWM technique, which is a combination of the conventional and special switching sequences. The proposed hybrid PWM technique results in a lower peak-to-peak torque ripple than conventional space vector PWM(CSVPWM) at high speeds of an induction motor drive. Furthermore, the magnitude of the dominant torque harmonic due to the proposed hybrid PWM is significantly lower than that due to CSVPWM at high speeds of the drive. Experimental results from a 3.75-kW sensorless vector-controlled induction motor drive under various load conditions are presented to support analytical and simulation results.