Optimized pathway selection in intraresidual triple-resonance experiments

An optimized intraresidual pulse sequence element with better sensitivity and suppression of sequential cross peaks is presented. Concatenation of three magnetization transfer delays allows their independent setting, in accordance with the relaxation properties of the individual spins, without concomitantly prolonging the pulse sequence. Additionally, implementations of the scheme to HNCA, HNCACB, and the TROSY based triple-resonance experiments are proposed. The feasibility of the new element was verified by recording HNCA and HNCACB on the small 8.6 kDa protein ubiquitin. The corresponding HNCA-TROSY experiment was tested on a larger protein, the 30.4 kDa Cel6A from the thermophilic soil bacterium Thermobifida fusca at 800 (1)H MHz.     

Robust dangerous border-collision bifurcations in piecewise smooth systems

Physical and computer experiments involving systems describable by piecewise smooth continuous maps that are nondifferentiable on some surface in phase space exhibit novel types of bifurcations in which an attracting fixed point exists before and after the bifurcation. The striking feature of these bifurcations is that they typically lead to "unbounded behavior" of orbits as a system parameter is slowly varied through its bifurcation value. This new type of border-collision bifurcation is fundamental and robust. A method that prevents such "dangerous border-collision bifurcations" is given. These bifurcations may be found in a variety of experiments including circuits.     

Novel pulsed switched power supply for a fast field cycling NMR spectrometer

In this paper, we outline the operating principles of a pulsed switched power supply for a fast field-cycling nuclear magnetic resonance spectrometer. The power supply uses a variant of a four-quadrant chopper with a duty cycle that defines the average output current. With this topology only two semiconductors are necessary to drive hundreds of amperes with an output power of several kilowatts. The output current ripple has a well-defined shape that can be reduced to acceptable values by a careful design of the semiconductors' controlling circuits and drivers. A power supply prototype was tested with a home build air-core magnet operating with fields between 0 and 0.21 T. The system is computer controlled using pulse generator and data acquisition PC cards, and specific user-friendly home-developed software. A comparative proton relaxometry study in two well-known liquid crystal compounds 5CB and MBBA was performed to check the reproducibility of the T1 measurements.     

A suppression strategy for antibiotic discovery

High-throughput phenotype screening and target identification have been combined in an effort to isolate antimicrobial, small-molecule therapeutics. This approach, developed by Brown and colleagues and reported in this issue, is a major technological advance for antimicrobial drug discovery.     

Synthesis of a eta 2-2,3-diphosphabutadiene complex of zerovalent platinum from the corresponding eta 2-phosphaalkyne complex

Hydrozirconation of the eta 2-phosphaalkyne complex [Pt(dppe)(eta 2-tBuCP)] with [ZrHCl(eta 5-C5H5)2], followed by treatment with the chlorophosphaalkene ClP=C(SiMe3)2 affords the eta 2-2,3-diphosphabutadiene complex [Pt(dppe)(eta 2-tBuC(H)=PP=C(SiMe3)2]. In the presence of [Pt(PPh3)2] the latter undergoes an addition reaction with water to afford the structurally characterised Pt(II) complex [Pt(dppe)(tBuCH2P(O)HPC(SiMe3)2].     

Rank Properties in Finite Semigroups II: The Small Rank and the Large Rank

This paper is concerned with the application of two possible definitions of rank to certain well-known semigroups.AMS Subject Classification (2000), 20M10     

Large vertical loop shifts in mechanically synthesized (Mn,Fe)2O3−t nanograins

Magnetic properties of zero field cooled (ZFC) and field cooled (FC) sample of (Mn,Fe)₂O_3−t nanograins have been investigated by magnetometry (up to 70 kOe) and Mössbauer spectroscopy (up to 60 kOe) in the temperature interval 4.2–300 K. Large horizontal (up to 0.8 kOe) and vertical (up to 80%) shifts of the magnetization hysteresis loops are observed in the FC regime. The obtained results are discussed in terms of exchange interaction between an antiferromagnetic core and a spin-glass-like state of the nanograins boundaries. It is shown that hysteresis loop shifts (horizontal and vertical) depend on the field cooling magnitude, an effect that can be understood by the change of the boundary magnetic structure induced by the external magnetic field. The vertical magnetization shift is described by a phenomenological model, which takes into account the magnetic interaction between the spin-glass like boundary spins and the applied field.     

Thermal conductivity of lightweight aggregate based on coal fly ash

The article presents the results of physical and chemical properties of lightweight aggregates (LWA) obtained by the thermal treatments of raw composition based on fly ash, supplied by electric plants from Serbia. The production process of LWA consists of raw material preparation, plastic shaping?Cextrusion, granulation, and thermal treatment at three temperatures: 1100, 1150, and 1200?°C. The final firing temperature (T?=?1150?°C) is chosen based on the mechanical and physical properties of the designed aggregates. The particle-size distribution of the LWAs is unimodal (d????16?mm) while the density value varies from 0.98 to 1.99?g/cm³. The water absorption values are determined by use of two methods: 24?h of soaking in cold water and 5?h of boiling. The thermal conductivity of unbound, fired LWA particles is determined by measuring the amount of axially transferred heat in the stationary state. The obtained value of the LWA thermal conductivity (???=?0.0872?W/mK, T?=?1150?°C) is suitable for the production of structural concrete blocks with improved thermal insulating properties. Because of their high-porosity and -compressive strength values, the designed LWA could be used instead of the conventional aggregates in the production of concrete blocks. Consequently, a real valorization of the waste material such as fly ash in Serbia was established.     

Surface tension in field theory at finite temperature: Semiclassical fermionic plus bosonic contributions

We compute, within the one loop approximation, the temperature dependent surface tension for a model involving a scalar field coupled to a fermionic field. The fermionic and bosonic contributions have been computed in this approximation by evaluating explicitly the determinants in the presence of a domain wall.