New silyl ether reagents for the absolute stereochemical determination of secondary alcohols

[reaction: see text] Herein we report a new set of silyl ether reagents for determining the enantiomeric purity and absolute stereochemistry of secondary alcohols. These derivatives are easily synthesized, provide straightforward spectroscopic results, and allow for facile recovery of the original chiral alcohol.     

Effect of temperature on the electron field emission from aligned carbon nanofibers and multiwalled carbon nanotubes

Effect of temperature and aspect ratio on the field emission properties of vertically aligned carbon nanofiber and multiwalled carbon nanotube thin films were studied in detail. Carbon nanofibers and multiwalled carbon nanotube have been synthesized on Si substrates via direct current plasma enhanced chemical vapor deposition technique. Surface morphologies of the films have been studied by a scanning electron microscope, transmission electron microscope and an atomic force microscope. It is found that the threshold field and the emission current density are dependent on the ambient temperature as well as on the aspect ratio of the carbon nanostructure. The threshold field for carbon nanofibers was found to decrease from 5.1 to 2.6 V/μm when the temperature was raised from 300 to 650 K, whereas for MWCNTs it was found to decrease from 4.0 to 1.4 V/μm. This dependence was due to the change in work function of the nanofibers and nanotubes with temperature. The field enhancement factor, current density and the dependence of the effective work function with temperature and with aspect ratio were calculated and we have tried to explain the emission mechanism.     

Selective gravimetric method for direct determination of tin(IV) with N-o-toluoyl-N-o-tolylhydroxylamine and its application to brass and bronze analyses

A selective gravimetric method for determination of tin(IV) with N-o-toluoyl-N-o-tolylhydroxylamine by direct weighing as Sn(C(15)H(14)NO(2))(2)Cl(2) is recommended. The metal complex, dried at 110-120 degrees , gives reproducible results. The method is simple, rapid and quantitative over a wide range of acidity (1-4N sulphuric acid) and is superior to existing gravimetric methods. The method works satisfactorily for determining tin in brass and bronze.     

Nonuniqueness of the factorization scheme in quantum mechanics

We enquire into the consequences of the nonuniqueness of the factorizability of a quantum mechanical Hamiltonian in one dimension. This leads to a hierarchy of potentials, a particular class of which is endowed with the energy spectrum of the harmonic oscillator.     

Low-sensitivity bandpass filters using the operational-amplifier pole

The single-pole rolloff of the operational amplifier is used to realise 2nd-order bandpass filters with one external capacitor. These filters have low sensitivity to all the circuit parameters and are suitable for high-frequency medium-Qfactor operation.     

Low mobility materials and Debye dielectric loss due to electrons

It is shown that substances which exhibit Debye type of dielectric loss due to electrons in the bulk also show very low electronic mobility. Measurements are suggested to confirm this. Relevant substances are ionic crystals with positive ions of high charge, such as oxides, and possibly certain molecular solids. In substances of the above type the band model has broken down. Relevant theoretical methods are outlined, using electron wave functions centered on the positive ions, rather than (as in previously developed methods) on their lattice sites. The perturbation giving rise to transitions between these localized states is composed of four terms, each a different kind of average of the electron-lattice interaction. One of these terms explicitly contains the effect of the localized electron on the phonon spectrum.     

Dioxygen activation by a dinuclear nickel thiolate complex: structural characterization of the ligand oxidized product

A (mu-SR)2-nickel(II) dimer derived from a ligand with carboxamido nitrogen and thiolato sulfur donors reacts with O2 to afford an oxidized product in which phenyl groups of the ligand frames are oxidized to nickel-bound phenolates.     

Testing for Function and Performance: Towards an Integrated Processor Validation Methodology

Microprocessor design teams use a combination of simulation-based and formal verification techniques to validate the pre-silicon models prior to tape-out and chip fabrication. Pseudo-random test case generation to cover the architectural space is still relied upon as the principal means to identify design bugs. However, such methods are limited to functional bugs only. Detection and diagnosis of timing (performance) bugs at the architectural level is largely an expert job. Architects guide the performance team to run manually generated test cases to validate the design from a performance viewpoint. In this paper, we will review some of the new approaches being tried out to automate the generation of performance test cases. We will show how this can be done within the basic framework of current functional validation and testing of pre-silicon processor models. Three categories of reference specifications are used in determining the defect-free pipeline timing behavior associated with generated test cases: (a) axiomatic specifications of intrinsic machine latencies and bandwidths; (b) proven analytical models for simple basic block and loop test cases; and, (c) a stable reference behavioral/functional (pre-RTL) model of the processor under development. We report experimental results obtained in performance validation studies applied to real PowerPC processor development projects.     

Clustered ML Channel Estimation for Ultra-Wideband Signals

The multipath capture of ultrawideband (UWB) communications systems can be dependent on the accuracy of channel estimation. Furthermore, inefficient modeling of the channel often leads to over-parametrization and increased channel estimation error. Relying on a channel model based on clusters, this letter proposes a maximum likelihood estimation strategy which exploits the properties of the UWB channel and offers performance improvement of about 2 dB over less parametric schemes. The robustness of the proposed algorithm in the presence of pulse distortion is investigated and the corresponding BER degradation is observed to be small even when experimental data are employed.