Grafting onto Wool. XXVI. Graft Copolymerization of Vinyl Monomers by Use of Cr(acac)3-TBHP as Initiator

Methyl methacrylate (MMA), methyl acrylate (MA), and ethyl acrylate (EA) have been graft copolymerized onto wool fiber in aqueous medium using the chromium acetylacetonate-tertiary-butyl hydroperoxide (Cr(acac)₃-TBHP) system as initiator. The percentage of grafting has been determined as a function of the concentrations of monomer, chelate, and TBHP, and the time and temperature under optimum conditions. MMA produced a maximum grafting of 119.8%, MA produced a maximum grafting of 56%, while EA afforded maximum grafting to the extent of 41.9%. Different vinyl monomers were found to follow the following reactivity order toward grafting onto wool fiber in the presence of the Cr(acac)₃-TBHP system: MMA > MA > EA.     

Spin-lock MRI with amplitude- and phase-modulated adiabatic waveforms: an MR simulation study

INTRODUCTION: Image contrast between tissue types can be generated based on their T1/T2 ratio using spin-lock MRI techniques. An interesting application of such a concept would be to generate contrast in tissue with tissue relaxation times modified using exogenous contrast agents. An amplitude-modulated adiabatic waveform has been shown in the past to perform spin-lock MRI. However, implementation of this waveform may not prove to be efficient and practical in research or a clinical setup due to high radiofrequency power deposition. Recent advancement in software and hardware MR technology allows implementation of amplitude- and phase-modulated adiabatic waveforms on MR systems. The aim of this work was to explore role of adiabatic waveforms in performing rho imaging and demonstrate that amplitude- and phase-modulated waveforms [e.g., hyperbolic secant, B1 independent rotation-4 (BIR-4) waveforms] can be used to distinguish materials that differ in T1/T2 ratio. METHODS AND RESULTS: MR simulation was performed using computer routines implemented in MATLAB environment (Mathworks, Natick, MA). Modified Bloch equations with trapezoidal, hyperbolic secant and BIR-4 waveforms were used to perform MR simulation. Trapezoidal waveforms were only used for comparison to other waveforms. Gadolinium DTPA (Gad-DTPA) (T1/T2 approximately 1) and manganese chloride (MnCl(2)) (T1/T2 approximately 10) were used as examples of contrast agents due to their routine use in clinical and research setups and more importantly because they provide good examples of materials differing in T1/T2 ratios. Results of spin locking using trapezoidal waveform agree very well with the previously published results, thereby validating the computer routines used in this MR simulation. Plots of M(rho) (magnetization vector in rho domain) vs. offset frequency show distinct curves for these materials differing in T1/T2 for the three waveforms. BIR-4 waveform demonstrated a 40% difference in M(rho) ( approximately 150 Hz) for the materials. Rate of spin lock with hyperbolic secant waveform was rapid compared to other waveforms. DISCUSSION: MR simulation using contrast agents Gad-DTPA and MnCl(2) provided a useful way to demonstrate that amplitude- and phase-modulated adiabatic waveforms can be used to perform spin-lock imaging. Future work involves implementation of these waveforms on MR scanners and performing in vivo imaging to generate tissue contrast based on relaxation times ratio.     

Nanostructured platform for the detection of Neisseria gonorrhoeae using electrochemical impedance spectroscopy and differential pulse voltammetry

We report on a nanocomposite based genosensor for the detection of Neisseria gonorrhoeae, a bacterium causing the sexually transmitted disease gonorrhoea. Amino-labeled probe DNA was covalently immobilized on electrochemically prepared polyaniline and iron oxide (PANI-Fe₃O₄) nanocomposite film on an indium tin oxide (ITO) electrode. Scanning electron microscopy, transmission electron microscopy, electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV) techniques have been employed to characterize surface of the modified electrode. The genosensor has detection limits of 1?×?10^-15 M and 1?×?10^-17 M, respectively, using the EIS and DPV techniques. This biosensor can discriminate a complementary sequence from a single-base mismatch and from non-complementary DNA, and has been utilized for detection of DNA extracted from N. gonorrhoeae culture, and from patient samples with N. gonorrhoeae. It is found to exhibit good specificity for N. gonorrhoeae species and shows no response towards non-gonorrhoeae type of Neisseria species (NgNs) and other gram-negative bacterias (GNBs). The affinity constant for hybridization calculated using the Langmuir adsorption isotherm model is found to be 3.39?×?10⁸ M^-1.

Graphene: The New Two‐Dimensional Nanomaterial

Every few years, a new material with unique properties emerges and fascinates the scientific community, typical recent examples being high‐temperature superconductors and carbon nanotubes. Graphene is the latest sensation with unusual properties, such as half‐integer quantum Hall effect and ballistic electron transport. This two‐dimensional material which is the parent of all graphitic carbon forms is strictly expected to comprise a single layer, but there is considerable interest in investigating two‐layer and few‐layer graphenes as well. Synthesis and characterization of graphenes pose challenges, but there has been considerable progress in the last year or so. Herein, we present the status of graphene research which includes aspects related to synthesis, characterization, structure, and properties.     

A qualocation method for parabolic partial differential equations

In this paper a qualocation method is analysed for parabolicpartial differential equations in one space dimension. Thismethod may be described as a discrete H¹-Galerkin method inwhich the discretization is achieved by approximating the integralsby a composite Gauss quadrature rule. An O (h^4-i) rate of convergencein the W^i.p norm for i = 0, 1 and 1 p is derived for a semidiscretescheme without any quasi-uniformity assumption on the finiteelement mesh. Further, an optimal error estimate in the H² normis also proved. Finally, the linearized backward Euler methodand extrapolated Crank-Nicolson scheme are examined and analysed.     

Microwave-assisted Vilsmeier-Haack synthesis of Pyrazole-4-carbaldehydes

The synthesis of 4-formylpyrazoles using Vilsmeier-Haack reagent is a common protocol in pyrazole chemistry. An efficient microwave-assisted synthesis of 4-formylpyrazoles by employing Vilsmeier-Haack reagent (OPC-VH) derived from phthaloyl dichloride/dimethylformamide has been described. This method offers the advantages of operational simplicity, avoiding the use of POCl₃ as toxic reagents and reuse of the by-product in the preparation of phthaloyl dichloride.     

Low-lying two-particle states in the nucleus236Np

The ambiguities and the uncertainties about the energy levels of the doubly odd actinide nucleus ₉₃ ²³⁶ Np₁₄₃ are sought to be removed by determination of the bandhead energies of various two-particle configurations expected to appear in the low energy spectrum of this nucleus. The calculations involve quantitative evaluation of the zero range neutron-proton residual interaction energy contribution to the bandhead energy for each configuration. It is concluded that the ground state is the long-lived isomer with spin-parityI ^π=6^- arising from the configuration {5/2⁺[642] _p +7/2^?[743] _n }. Bandhead energies for eight two-particle states appearing upto an excitation energy of 400 keV are presented and the results are discussed in the context of the available and further experiments.     

Nonvolatile unipolar resistive switching in ultrathin films of graphene and carbon nanotubes

We report unipolar resistive switching in ultrathin films of chemically produced graphene (reduced graphene oxide) and multiwalled carbon nanotubes. The two-terminal devices with yield >99% are made at room temperature by forming continuous films of graphene of thickness ∼20 nm on indium tin oxide coated glass electrode, followed by metal (Au or Al) deposition on the film. These memory devices are nonvolatile, rewritable with ON/OFF ratios up to ∼ 10⁵ and switching times up to 10 μs. The devices made of MWNT films are rewritable with ON/OFF ratios up to ∼400. The resistive switching mechanism is proposed to be nanogap formation and filamentary conduction paths.