bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical-pumping double-resonance NMR system for semiconductors
Authors: Goto Atsushi , Ohki Shinobu , Hashi Kenjiro , Shimizu Tadashi
Published: September 2006

We describe an optical-pumping double-resonance NMR system equipped with a single-coil double-tuning (XY) probe with an optical fiber attachment working in a helium-gas flow cryostat. The system enables simultaneous control of an infrared light and two radio-frequency fields irradiated to a sample, so that solid-state NMR techniques such as spin locking, decoupling, and cross polarization can be invoked under the optical-pumping condition. A nuclear hyperpolarization transfer experiment in optically pumped InP:Fe is presented.
Progress in understanding the intramolecular vibrational redistribution dynamics in the S1 state of para-fluorotoluene
Authors: Hammond Chris J. , Ayles Victoria L. , Bergeron Denis E. , Reid Katharine L. , Wright Timothy G.
Published: September 2006

We employ zero-kinetic-energy (ZEKE) photoelectron spectroscopy with nanosecond laser pulses to study intramolecular vibrational redistribution (IVR) in S1 para-fluorotoluene. The frequency resolution of the probe step is superior to that obtained in any studies on this molecule to date. We focus on the behavior of the 131 (C–CH3 stretch) and 7a1 (C–F stretch) vibrational states whose dynamics have previously received significant attention, but with contradictory results. We show conclusively that, under our experimental conditions, the 7a1 vibrational state undergoes significantly more efficient IVR than does the 131 state. Indeed, under the experimental conditions used here, the 131 state undergoes very little IVR. These two states are especially interesting because their energies are only 36cm−1 apart, and the two vibrational modes have the same symmetry. We discuss the role of experimental conditions in observations of IVR in some detail, and thereby suggest explanations for the discrepancies reported to date.
Examination of surface acoustic wave reflections by observing acoustoelectric current generation under pulse modulation
Authors: Astley M. R. , Kataoka M. , Schneble R. J. , Ford C. J. B. , Barnes C. H. W. , Anderson D. , Jones G. A. C. , Beere H. E. , Ritchie D. A. , Pepper M.
Published: September 2006

The authors investigate surface acoustic wave (SAW) reflections using the frequency dependence of the acoustoelectric current through a one-dimensional channel. By pulse modulating the transducer power with a short pulse width (0.2μs) and matching the pulse repetition period to the delay time of a specific reflection path, the authors detect individual reflected SAW wave packets. Fourier transform results show that reflections from the sample edge behind the transducer and Bragg reflections from the second transducer have the strongest effects. The reflection power coefficients for these are estimated to be ≈0.29 and ≈0.99, respectively.
Observation of negative differential resistance and hysteretic effect on buriti oil:polystyrene organic devices
Authors: Durães J. A. , Araújo Sales M. J. , Souto R. F. , Romariz A. , da Costa J. C. , Ceschin A. M. , Moreira S. G. C.
Published: September 2006

The authors have observed hysteretic behavior and negative differential resistance in single-layer devices made from buriti oil mixed with polystyrene and sandwiched between poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) and silver (Ag) electrodes. The hysteresis curve shows not only two different values of current but different behaviors as the increasing voltage curve shows negative differential resistance and the decreasing voltage curve does not. The fact that a simple fabrication technique yields reproducible conductance switching and hysteresis is relevant for the development of theories of organic electronic device behavior.
Correlation between plasma dynamics and porosity of Ge films synthesized by pulsed laser deposition
Authors: Riabinina Daria , Chaker Mohamed , Rosei Federico
Published: September 2006

The porosity of Ge films deposited by pulsed laser deposition in an inert gas atmosphere is observed to be directly correlated with the kinetic energy of ablated species. The deposition conditions were modified by varying the pressure and the target-substrate distance. The evolution of the kinetic energy of ablated species as a function of deposition parameters, such as distance from target and background gas pressure, is described in terms of a theoretical model. The relationship between the density of Ge films and the kinetic energy of ablated species is discussed.
Local environment surrounding S and Cd in CdS:O thin film photovoltaic materials probed by x-ray absorption fine structures
Authors: Soo Y. L. , Sun W. H. , Weng S. C. , Lin Y. S. , Chang S. L. , Jang L. Y. , Wu X. , Yan Y.
Published: September 2006

Local environments surrounding Cd and S in CdS:O thin films have been determined using extended x-ray absorption fine structure (EXAFS) and near-edge x-ray absorption fine structure (NEXAFS). As indicated by the Cd EXAFS, Cd atoms remain predominantly bonded with S. The S EXAFS and NEXAFS clearly demonstrate the presence of S–O bonds. The oxygen atoms actually combine with S to form SO3 and SO4 complexes. Combined with the transmission electron micrograph, these x-ray results suggest formation of oxygen-free CdS nanocrystals and provide an unambiguous explanation for the mystery of increased band gap that appears to violate the band anticrossing model.
Second harmonic generation in GaN∕Al50Ga50N films deposited by metal-organic chemical vapor deposition
Authors: Larciprete M. C. , Centini M. , Belardini A. , Sciscione L. , Bertolotti M. , Sibilia C. , Scalora M. , Passaseo A. , Potì B.
Published: September 2006

Second harmonic generation was observed experimentally from GaN∕Al50Ga50N multilayers grown on sapphire substrate by means of the rotational Maker fringe technique at a fundamental beam wavelength of 1064nm. From a single thick GaN layer (302nm), the d33 of GaN was evaluated and compared to the nonlinear coefficient obtained from measurements on several thin multilayer samples. Results show that the process of growing several thin, alternating layers does not cause the deterioration of the effective nonlinear susceptibility, which is 4.82pm∕V for GaN and 1.20pm∕V for Al50Ga50N, consistent with known values obtained for thick substrates.
Evolution of wurtzite CdTe through the formation of cluster assembled films
Authors: Neretina S. , Mascher P. , Hughes R. A. , Braidy N. , Gong W. H. , Britten J. F. , Preston J. S. , Sochinskii N. V. , Dippo P.
Published: September 2006

An approach has been developed to produce CdTe films with a high proportion of the metastable wurtzite phase. It involves the use of pulsed laser deposition to produce CdTe nanoparticles which are then collected on a substrate. Electron microscopy indicates that the nanoparticles produced have a relatively minor fraction of the wurtzite phase coexisting with the stable zinc blende phase. If these same nanoparticles arrive at a heated substrate they form a relatively dense cluster assembled film with an obvious wurtzite signature. Quite remarkable is that higher temperatures promote the metastable structure at the expense of the stable zinc blende phase.
Effect of third-order dispersion on subpicosecond pulse propagation in photonic-crystal waveguides
Authors: Tanaka Yu , Kuwatsuka Haruhiko , Kawashima Hitoshi , Ikeda Naoki , Sugimoto Yoshimasa , Hasama Toshifumi , Ishikawa Hiroshi
Published: September 2006

We have experimentally investigated the effects of dispersion on subpicosecond pulse propagation over two-dimensional (2D) photonic-crystal-slab line-defect waveguides by time domain measurements. Using a heterodyne detection technique, pulse shapes after propagating along the waveguide were recorded as cross-correlated traces. When the pulse central frequency approached the band edge of the guided mode, the pulses were temporally delayed and their shapes were found to be broadened asymmetrically; this effect originated from the group velocity dispersion (GVD), encompassing higher-order dispersion effects. Theoretical pulse shapes, including third-order dispersion (TOD), agreed well with the experimental results. When the group velocity (vg) reached 0.08c, c being the speed of light, we found a GVD of ∼5.0ps2∕mm and a TOD of ∼0.3ps3∕mm. Experimentally obtained vg, GVD, and TOD characteristics agreed well with those obtained from 2D plane-wave-expansion band calculations.
Glass formation mechanism of minor yttrium addition in CuZrAl alloys
Authors: Zhang Y. , Chen J. , Chen G. L. , Liu X. J.
Published: September 2006

Effects of yttrium additions on glass-forming ability of the model system (Cu0.48Zr0.48Al0.04)100−xYx (x=0–7at.%) were studied in detail by using a “perturbation theory” approach. Introduction of the atomic-level strain energy into the driving force for the crystal nucleation well explained the beneficial effects of yttrium additions. It was found that the atomic-level strain energy is related closely to the atomic packing efficiency of the precipitated crystals and less yttrium amount is needed to suppress the precipitation of crystal phase with a higher atomic packing efficiency, which is consistent with the experimental observations.
Photoexcitation effects on charge transports of Ge quantum-dot resonant tunneling diodes
Authors: Li P. W. , Kuo David M. T. , Hsu Y. C.
Published: September 2006

The authors have experimentally investigated photoexcitation effects on carrier transports through a Ge quantum-dot (QD)∕SiO2 system via a resonant tunneling diode (RTD). Features of resonant oscillation and negative differential conductance are observed from the tunneling current of Ge-QDs RTDs at room temperature. The tunneling current not only displays additional oscillatory peaks but also exhibits enhanced peak-to-valley current ratio under photoexcitation. This indicates that holes created in the QD by photoexcitation lead to additional channels via the electron-hole interaction for electron tunneling through the QD. The exciton binding energy in the Ge QD could also be extracted from the voltage separation of the tunneling current peaks.
Plasmonic waveguide ring resonator at terahertz frequencies
Authors: Wang Bing , Wang Guo Ping
Published: September 2006

The authors theoretically demonstrate a plasmonic waveguide ring resonator (WRR) working at terahertz frequencies considering that surface plasmon polaritons (SPPs) can effectively propagate on bended plasmonic waveguides with dielectric claddings possessing high refractive index. A free spectral region of 110GHz has been achieved by decreasing ring radius of the WRR, which could be much smaller than the operating wavelength. By introducing dielectric and plasmonic waveguides at both sides of the resonant ring, respectively, SPPs can be efficiently excited at the output of the WRR through mode coupling. The plasmonic WRRs may find great applications in the integration of terahertz generation and control platform.
Minority-carrier characteristics of InGaAs metal-oxide-semiconductor structures using atomic-layer-deposited Al2O3 gate dielectric
Authors: Xuan Y. , Ye P. D. , Lin H. C. , Wilk G. D.
Published: September 2006

Atomic layer deposition (ALD) provides a unique opportunity to integrate high-quality gate dielectrics on III-V compound semiconductors. ALD Al2O3 is a high-quality gate dielectric on III-V compound semiconductor with low interface trap density, low gate leakage, and high thermal stability. The authors study the minority-carrier response of Al2O3∕InGaAs metal-oxide-semiconductor (MOS) structures, which sheds light on the device physics for realizing high-performance inversion-type metal-oxide-semiconductor field-effect-transistor. The minority carriers in InGaAs do not respond to a small ac signal down to 100Hz at 300K, while they respond to up to 100kHz at 500K. Temperature dependent capacitance-voltage (C-V) measurement on the InGaAs MOS structure reveals the activation energy (Ea) of the minority-carrier recombination to be about 0.62eV.
Stress relaxation during the growth of 3C-SiC∕Si thin films
Authors: Zielinski M. , Leycuras A. , Ndiaye S. , Chassagne T.
Published: September 2006

In this work the authors study the strain of 3C-SiC thin films grown on (001) on-axis silicon substrates. They use ex situ wafer curvature measurements to monitor the residual strain of silicon carbide film. At high temperature creep effects take place and modify the intrinsic strain of silicon carbide film. From the time and temperature dependences of these effects, they determine the creep exponent and the creep activation energy for 3C-SiC. Obtained values of N=2.6±0.3 and Q=5.6±1.0eV are similar to those reported in literature for hexagonal polytypes of silicon carbide.
Observation of standing waves at steps on the GaN(0001) pseudo-(1×1) surface by scanning tunneling spectroscopy at room temperature
Authors: Harland M. L. , Li L.
Published: September 2006

Standing waves formed at steps of the GaN(0001) pseudo-(1×1) surface are observed with scanning tunneling spectroscopy (STS) at room temperature. The oscillatory behavior of the dI∕dV calculated for free electrons scattered by atomic steps agrees well with that measured by STS suggesting that surface state of the pseudo-(1×1) structure is nearly free-electron-like thereby confirming the metallic state of the GaN(0001) pseudo-(1×1) surface.
Effect of single-walled carbon nanotube purity on the thermal conductivity of carbon nanotube-based composites
Authors: Yu Aiping , Itkis Mikhail E. , Bekyarova Elena , Haddon Robert C.
Published: September 2006

Raw [as-prepared (AP)] and purified single-walled carbon nanotubes (SWNTs) were utilized for the preparation of SWNT-epoxy composites. Purified functionalized SWNTs provide a significantly greater enhancement of the thermal conductivity, whereas AP-SWNTs allow the best electrical properties because of their ability to form efficient percolating network. A series of SWNT samples of varying purity but identical chemical functionality was prepared to delineate the effect of SWNT purity on the thermal conductivity of SWNT-epoxy composites. The authors found that purified SWNTs provide approximately five times greater enhancement of the thermal conductivity than the impure SWNT fraction demonstrating the significance of SWNT quality for thermal management.
Vapor phase growth of Al whiskers induced by glancing angle deposition at high temperature
Authors: Suzuki Motofumi , Nagai Koji , Kinoshita Sadamu , Nakajima Kaoru , Kimura Kenji , Okano Tomoki , Sasakawa Kaoru
Published: September 2006

The authors demonstrate the growth of unusual Al whiskers by glancing angle deposition on a high temperature (HT-GLAD) substrate, while the usual columnar structures completely disappear due to accelerated surface diffusion. HT-GLAD is essential for the nucleation of the whiskers and efficient supply of Al atoms on the side surface of the vertically growing whiskers. HT-GLAD will, for the first time, reveal the mechanisms for the vapor growth of metal whiskers.
Near ultraviolet emission from nonpolar cubic AlxGa1−xN∕GaN quantum wells
Authors: Schörmann J. , Potthast S. , As D. J. , Lischka K.
Published: September 2006

In this contribution the authors studied the optical properties of cubic AlxGa1−xN∕GaN single and multiple quantum wells. The well widths ranged from 2.5to7.5nm. Samples were grown by rf-plasma assisted molecular beam epitaxy on free standing 3C-SiC (001) substrates. During growth of Al0.15Ga0.85N∕GaN quantum wells clear reflection high energy electron diffraction oscillations were observed indicating a two dimensional growth mode. They observe strong room temperature, ultraviolet photoluminescence at about 3.3eV with a minimum linewidth of 90meV. The peak energy of the emission versus well width is reproduced by a square-well Poisson-Schrödinger model calculation.
On the short-time limit of ring polymer molecular dynamics
Authors: Braams Bastiaan J. , Manolopoulos David E.
Published: September 2006

We examine the short-time accuracy of a class of approximate quantum dynamical techniques that includes the centroid molecular dynamics (CMD) and ring polymer molecular dynamics (RPMD) methods. Both of these methods are based on the path integral molecular dynamics (PIMD) technique for calculating the exact static equilibrium properties of quantum mechanical systems. For Kubo-transformed real-time correlation functions involving operators that are linear functions of positions or momenta, the RPMD and (adiabatic) CMD approximations differ only in the choice of the artificial mass matrix of the system of ring polymer beads that is employed in PIMD. The obvious ansatz for a general method of this type is therefore to regard the elements of the PIMD (or Parrinello-Rahman) mass matrix as an adjustable set of parameters that can be chosen to improve the accuracy of the resulting approximation. We show here that this ansatz leads uniquely to the RPMD approximation when the criterion that is used to select the mass matrix is the short-time accuracy of the Kubo-transformed correlation function. In particular, we show that the leading error in the RPMD position autocorrelation function is O(t8) and the error in the velocity autocorrelation function is O(t6), for a general anharmonic potential. The corresponding errors in the CMD approximation are O(t6) and O(t4), respectively.
L
1
ordered epitaxial FePt (001) thin films on TiN∕Si (100) by pulsed laser deposition
Authors: Trichy G. R. , Narayan J. , Zhou H.
Published: September 2006

Epitaxially oriented magnetic FePt (001) thin films were grown on Si (001) substrates with TiN as a template buffer by using pulsed laser deposition. The epitaxial relationship and presence of L10 ordering were studied by x-ray diffraction and further confirmed by detailed transmission electron microscopy. The effectiveness of using TiN (diamagnetic metal) as a template, for an epitaxial magnetic FePt heterostructure integrated with silicon and for inducing L10 order in the FePt films, has been demonstrated. Magnetic measurements show that the ordered FePt films are predominantly perpendicularly magnetized and have high values of coercivity suitable for magnetic recording applications.
Low temperature metallic state induced by electrostatic carrier doping of SrTiO3
Authors: Nakamura H. , Takagi H. , Inoue I. H. , Takahashi Y. , Hasegawa T. , Tokura Y.
Published: September 2006

Transport properties of SrTiO3-channel field-effect transistors with parylene organic gate insulator have been investigated. By applying gate voltage, the sheet resistance falls below R◻∼10kΩ at low temperatures, with carrier mobility exceeding 1000cm2∕Vs. The temperature dependence of the sheet resistance taken under constant gate voltage exhibits metallic behavior (dR∕dT>0). Results demonstrate an insulator to metal transition in SrTiO3 driven by electrostatic carrier density control.
Ferromagnetism in Mn-doped GaN nanocrystals prepared solvothermally at low temperatures
Authors: Biswas Kanishka , Sardar Kripasindhu , Rao C. N. R.
Published: September 2006

3% and 5% Mn-doped GaN nanocrystals of different sizes, with the average diameters in the range of 4–18nm, have been prepared by two independent routes under solvothermal conditions starting with two different precursors. The reaction temperature was around 350°C in all the preparations. The nanocrystals so prepared exhibit ferromagnetism with magnetization (M) and Curie temperature (TC) values increasing with percent of Mn and particle size. The observation of ferromagnetism in Mn-doped GaN nanocrystals prepared at relatively low temperatures is of significance in understanding this potential in spintronics materials.
Lubrication of Metal Surfaces by Silicone Films
Authors: Gregory JN , Newing MJ
Published: September 2006

Methods for the preparation of mono-, di-, and tri-isoamyl chlorsilanes, and the monocetyl chlorsilane have been developed. Molecular layers of the mono- and di-ethyl and mono- and di- soamyl silicones on various metal surfaces have been tested for their boundary lubricating properties. The layers have been shown to be excellent lubricants, with unusual thermal stability and resistance to wear.
"One-" and '"Two-dimensional" Partition Chromatographic Separations of Organic Acids on an Inert Sheet Support
Authors: Lugg JWH , Overell BT
Published: September 2006

Procedures have been described for "one-" and "two-dimensional" partition-chromatographic separations, on an inert sheet (paper) support, of mixtures of relatively non-volatile organic acids.
Ionization, and adsorption of the acids by the paper, have been suppressed by swamping both the stationary and mobile solvent phases with a volatile acid (acetic or formic). Formic acid is superior in that, at high concentration, it permits welldefined bands of the test acids to travel down the sheets and confers upon the bands highly characteristic RF values.
RF values for some acids (malic, citric, tartaric, succinic, fumaric, malonic, pyruvic, lactic, ketosuccinic (oxalacetic), α-ketoglutaric, monomethyl succinic, glutaric, and adipic) at 20°C., when Whatman No. 1 filter paper and various pairs of solvent phases are used. have been provided.
Some of the acids present in carrot tissue have been separated in "one-dimensional" work and identified by their RF values.
The Absolute Measurement of High-Energy Radiation
Authors: Spicer BM
Published: September 2006

The relationship between incident
intensity of X-rays and the ionization produced by them in a small cavity
behind an aluminium wall of given thickness has been derived, and calculations
performed for a specific case. The conditions of validity of Gray's relation
are the only ones imposed. The calculation was performed for monoenergetic
radiation, and extended to the case of a bremsstrahlung spectrum of the form
given by Schiff (Adams 1948). Comparison is made with the work of Fowler,
Lauritsen, and Lauritsen (1948) and Lawson (1950).
The Absorption and Reflection of Microwave Radiation by a Mercury-Vapour Discharge
Authors: Prime HA
Published: September 2006

The power transmission and reflection
coefficients of a limited volume of ionized gas (a mercury-vapour discharge)
located within a waveguide have been measured at a frequency of approximately
10,000 Mc/s. by a microwave method. From these coefficients the real and
imaginary components of the complex conductivity of the discharge are
evaluated. The results show that the real component of the conductivity бr is a linearly increasing function of
the discharge current, whereas the rate of increase of the imaginary component бi, which is negative, decreases with
increasing discharge current. The ratio бi/бr,
decreases with increase in current, but is of the order of unit;- due to the
fact that the gas pressure is sufficiently high (?1 atm.) to make бr comparable with бi.
The theoretical basis of the work is presented in an appendix in which the
particular case of high pressure conditions is discussed.
The Microwave Admittance of a Mercury-Vapour Discharge
Authors: Prime HA
Published: September 2006

The normalized conductance and susceptance
of a low-pressure mercury-vapour discharge hare been measured as a function of
the discharge current at a frequency of c. 10,000 Mc/s. by a microwave method.
The complex conductivity of the discharge is then calculated from the
admittance data by representing the discharge as a shunt admittance loading the
waveguide. The validity of this approximate representation is examined. The
conductivity results are in agreement with similar published results and the similarity
between the characteristics of a D.C. sustained discharge and a,
radio-frequency discharge are noted. It is deduced that the collision frequency
varies only slowly with change in discharge current.
The Condensation of a Vapour at a Crystalline Surface
Authors: Wylie RG
Published: September 2006

The theory of self-nucleation in a
supersaturated vapour has been developed with considerable success by Becker
and D�ring (1935), but little attention has hitherto been given to condensation
at a solid surface.

A theory is given for the nucleation of
liquid condensates on a plane surface and at lines and corners formed by the
intersection of plane surfaces. It is suggested that the line and corner sites
are representative of typical features of real crystalline surfaces. The
equilibrium properties and free energies of formation of embryos at these
sites, which are required for the nucleation theory, have been given in the
previous paper.

The theory shows that the supersaturation
for which nucleation proceeds at a just observable rate on a plane surface
increases rapidly as the contact angle increases from zero. Unless an edge free
energy is introduced, no supersaturation is necessary for nucleation at a line
or corner of intersection of plane surfaces when the contact angle 1s less than
a threshold value which depends on the angles between the planes. As the
contact angle Increases above the threshold value the supersaturation required
for observable condensation increases considerably.

The effect of contamination of the
substrate surfaces considered and the suggestions are made that, ~f a small
amount of soluble contamination is present it is likely to become localized at
surface steps and corners, sensitizing them as nucleation sites, and that
microscopic observation of incipient condensation on solid surfaces may provide
a tool for the investigation of surface structure.
The Frequency Dependence of the Dielectric Properties of Dipolar Substances
Authors: O'Dwyer JJ , Sack RA
Published: September 2006

A critical review of theories of the
frequency dependence of the dielectric constant of dipolar substances is given
and inconsistencies are pointed out in previous attempts to account for dipolar
interaction. A new theory is presented based on Debye's theory of molecular
relaxation and using Onsager's method for treating electrostatic inter- action.
Fluctuations are considered explicitly both in the orientation of an individual
dipole and in the local field acting on it ; a distinction is also made between
the experimentally measurable time constants and the relaxation times governing
molecular processes.

The results are presented m the form of a
series development in pourers of the dipolar concentration. In first
approximation the theory leads to a Debye frequency dependence of the
dielectric constant ; in second approximation a Debye dependence can be made
consistent with the molecular mechanism only for a more restricted
(two-position) model.
The Role of Surface Transport in the Stability and Breakdown of Foams
Authors: Ewers WE , Sutherland KL
Published: September 2006

A new theory of foam stability is proposed
which demonstrates that the transport of substrate. accompanying a movement of
the surface of the bubble film, is a dominant factor in the stability of foams
and in the action of foam breakers. The surface moves from a region of low
surface tension (high surface pressure) to a region of high surface tension.
The surface tension gradients arise from disturbances which may be caused by
mechanical or thermal shocks, or by the addition to the surface of particles,
droplets, or vapour of a surface-active material. When the surface tension is
highest at the centre of disturbance the film mill be stable ; when the surface
tension is lowest at this point the surface film and hence the substrate will
be moved away from this point and the film will rupture.
Thiohydantoins. I. The Preparation of Some 2-Thiohydantoins from Amino Acids and Acylamino Acids
Authors: Swan JM
Published: September 2006

A reinvestigation of the stepwise
degradation of peptides and proteins by the Schlack and Kumpf (1926) procedure,
which involves conversion of the terminal carboxyl residue to a
5-substituted-2-thiohydantoin; has been undertaken. The following amino acids
or their aoetyl derivatives have been converted by warming with acetic
anhydride and ammonium thiocyanate into the corresponding
1-acetyl-2-thio-hydantoins: valine, methionine, isoleucine, α-aminophenylacetic
acid, tryptophane, histidine, and tyrosine. These new
1-acetyl-2-thiohydantoins, as well as others, have been deacetylated by an
improved procedure. Certain 1-acyl-5-carbethoxy-2-thio- hydantoins on
hydrolysis give 2-thiohydantoin only. N-acetylthreonine, acetic anhydride, and
ammonium thiocyanate produce 5-ethylidene-2-thiohydantoin, also obtained by the
condensation of acetaldehyde with 2-thiohydantoin or its 1-acyl derivatives, or
from the interaction of ammonium thiocyanate with 2-phenyl-4-ethylideneoxazol-5-one.
This type of rearrangement occurs in other cases.
Thiohydantoins. III. Anhydride Intermediates in the Formation of 1-Acyl-2-thiohydantoins from Acylamino Acids
Authors: Swan JM
Published: September 2006

Linear anhydrides are formed by the action
of acetic anhydride on p-toluene-sulphonylglycine and carbobenzyloxy-glycine,
-phenylalanine, and -β-alanine. The
anhydrides from the first two acids yield the corresponding 2-thiohydantoin
with ammonium thiocyanate in acetic acid. Other methods for the preparation of
l-p-toluenesulphonylglycine anhydride, and its 2-thiohydantoin, are also given.

Hippuric acid, with ethyl chlorocarbonate
and triethylamine yields ethyl hippurate, probably via the mixed anhydride and
2-phenyloxazol-5-one. The inclusion of ammonium thiocyanate gives
1-benzoyl-2-thiohydantoin in high yield. The N-carboxy anhydride of
phenylalanine (4-benzyloxazolid-2,5-dione) also reacts with ammonium
thiocyanate to give carbon dioxide and 5-benzyl-2-thiohydantoin.
New Flavones from Pongamia pinnata (L.) Merr
Authors: Ramachandra Row L
Published: September 2006

From the root bark of Pongamia pinnata
(L.) Merr. (P. glabra Vent.) five flavones have been isolated. The two major
constituents are shown to be karanjin and a new furanoflavone named pongapin.
By degradation and synthesis the structure of the latter is established as
7,8-furano-3-methoxy-3?,4?-methylenedioxyflavone. Of the three minor products,
two appear to be isomeric with karanjin and pongapin respectively.
Dielectric Anisotropy in Crystalline Long-chain Alcohols
Authors: Hamon BV , Meakins RJ
Published: September 2006

Pressed disks made from powdered
crystalline long-chain n-primary and secondary alcohols have been shown to be
electrically anisotropic. At a particular frequency, the loss factor, when the
applied field is parallel to the faces of the disk, is from two to five times
greater than when the field is perpendicular to the faces. The observed
anisotropy is considered to be due to orientation of the flat crystals of the
alcohols parallel to the disk faces.

The effect of anisotropy on previously
published results for long-chain compounds is discussed. The observed
anisotropy is consistent with the main conclusions from this earlier work. The
application of the measuring technique to other materials is suggested.
The vibrational spectra of Methane Sulphonyl Chloride and Methane Sulphonyl Fluoride
Authors: Ham NS , Hambly AN
Published: September 2006

The Raman and infra-red spectra of methane
sulphonyl chloride and methane sulphonyl fluoride have been measured.
Assignments of the vibrational frequencies of the two molecules have been made
; the frequency 377 cm.-1 is characteristic of the S-Cl linkage and 1210 cm.-1 of the S-F linkage in
these compounds. An improved method for the preparation of methane sulphonyl
fluoride is described.
The chemistry of Quinones. I. Directive effects in the Substitution of Naphthoquinones
Authors: Cooke RG , Dowd H , Segal W
Published: September 2006

The reaction of dimethylamine with
5-methoxy-1,4-naphthoquinone gives approximately equal amounts of the two
possible substitution products and with 6-methyl-1,4-naphthoquinone followed by
acid hydrolysis 2-hydroxy-6-methyl-l,4-naphtho-quinone is the principal
product. Similar treatment of 5-methyl-1,4-naphthoquinone gives mostly
3-hydroxy-5-methyl-l,4-naphtlioquinone. The isomer, 2-hydroxy-5-
methyl-1,4-naphthoquinone, has been prepared by another method. The product of
Thiele-Winter addition of acetic anhydride to juglone is shown to be a mixture
of the two possible isomers, but authentic 1,3,4,5-tetra-acetoxynaphthalene has
been prepared from 3,5-dihydroxy-1,4-naphthoquinone. The reaction of acetic
anhydride with plumbagin gives three compounds, the composition of the mixture
depending on the time of contact. Juglone and plumbagin have been selectively
brominated in the 6-position and certain other halogen derivatives of these
quinones have been prepared. The preparation of 3-chloro-5-hydroxy-2-methyl-1,4-naphthoquinone
provides a new route by which droserone may be obtained from plumbagin.
The Synthesis and Reactivity of 5H-Cycloprop[f]isobenzofuran and Related Compounds. A Kinetic Probe for the Mills-Nixon Effect
Authors: Anthony IJ , Wege D
Published: September 2006

5H-Cycloprop[f]isobenzofuran (6) and the sulfur analogue 5H-cyclopropa[f][2] benzothiophen (18) have been prepared by a sequence of reactions involving trapping of 1,2-dibromocyclopropene with 3,4-dimethylidenetetrahydrofuran and 3,4-dimethylidenetetrahydrothiophen followed by sequential dehydrogenation and di-dehydrobromination. Both cyclopropa -fused heterocycles, like their parents, have limited stability. Several other 5,6-methylene-bridged and 5,6-disubstituted isobenzofurans (32) have been generated and characterized as their adducts with dimethyl fumarate . Second-order rate constants for the reaction of dimethyl fumarate with isobenzofuran, 5H-cycloprop[f] isobenzofuran as well as the series of substituted derivatives have been measured. The reactivity span is only one order of magnitude suggesting that π-bond fixation (the Mills-Nixon effect) does not play a significant role in determining the reactivity of (6).
Structural Characterization of Nickel(II) Tetraphenylporphyrin
Authors: Maclean AL , Foran GJ , Kennedy BJ , Turner P , Hambley TW
Published: September 2006

The structure of 5,10,15,20-tetraphenylporphinatonickel(II) ([Ni( tpp )]) has been studied by both X-ray diffraction (powder and single-crystal methods) and EXAFS. The bond lengths obtained from analysis of the EXAFS agree, within standard deviations, with those obtained from the X-ray diffraction studies. The Ni-N bond length of 1.93(1) Ǻ agrees especially well with the value of 1.931(2) Ǻ obtained from the single-crystal analysis. The powder X-ray diffraction pattern, collected by using synchrotron radiation, is presented.
Evidence for Silicon-Directed Acid-Catalysed Ring Opening of a β,γ-Epoxy Silane: Reaction of 1,1-Dimethyl-1-silacyclohex-3-ene Oxide With p-Nitrobenzoic Acid
Authors: Badali F , Karalis A , Tham WY , White JM
Published: September 2006

The ring-opening reaction of the β,γ-epoxy silane (4) with p-nitrobenzoic acid in chloroform occurs regiospecifically to give the two hydroxy esters (14) and (15). The mechanism involves regiospecific ring opening giving the β-silicon-stabilized carbenium ion (18) which is captured by the p-nitrobenzoate counter ion. The solution conformation of (14) provides evidence for the presence of σC- Si -σ* C-O interactions between the ring C- Si bonding orbital and the C-OCOC6H4NO2 antibonding orbital. In acetone, reaction of (4) with p-nitrobenzoic acid takes a different pathway and results in acyclic products from solvent attack at the silicon.
The Dichloroplatinum(II) and Dichloropalladium(II) Complexes of 1,4-Diazacycloheptane: Preparative, Structural and Conformational Studies
Authors: Allen GW , Ling ECH , Krippner LV , Hambley TW
Published: September 2006

The preparation and purification of [Pt( hpip )Cl2] and [Pd( hpip )Cl2] ( hpip = homopiperazine = 1,4-diazacycloheptane) are described. Crystal structures of [Pt( hpip )Cl2] and [Pd( hpip )Cl2] have been determined by X-ray diffraction methods and refined to R values of 0.023 (932 F) and 0.023 (948 F). The crystals of [Pt( hpip )Cl2] are orthorhombic, space group Pbcm , a 7.7019(8), b 9.8080(12), c 12.1944(14) Ǻ, and those of [Pd( hpip )Cl2] are monoclinic, space group P21/m, a 6.1001(9), b 11.527(2), c 6.458(I) Ǻ, β 106.30(2)°. The seven- membered rings of the ligands in both complexes adopt boat-like conformations in which the five- membered chelate ring has an eclipsed N-C-C-N group and the six- membered chelate ring adopts a chair conformation. Molecular mechanics methods were used to investigate whether this conformation was a crystallographic artefact but it was found to be real. An alternative conformation in which the six-membered chelate ring adopts a skew-boat conformation was also investigated. It was found to be less stable than the conformation observed in the crystal structures, but to a degree that depends on whether non-bonded interactions involving the metal atom were included or not.
The Influence of Alkyl Substituents on Carbon Acid Formaldehyde Condensation Reactions of Bis(alkane-1,2-diamine)copper(II) Ions
Authors: Rossignoli M , Lawrance GA , Maeder M , Hockless DCR , Skelton BW , White AH
Published: September 2006

The reaction of the bis (1,2-diamine)copper(II) complexes of ethane-1,2-diamine (en), propane-1,2-diamine ( pn ) and 2-methylpropane-1,2-diamine ( dmen ) with formaldehyde and nitroethane in methanol under basic conditions yields macrocyclic and acyclic condensation products with two or one new -NH-CH2-C(Me)(NO2)-CH2-NH- links introduced respectively between pairs of cis-disposed primary amines, and where the ratio of products is, surprisingly, significantly altered by C-methyl substitution on the parent ethane-1,2-diamine chelate . Under identical reaction conditions, the ratio of acyclic to macrocyclic product varied from 2:3 (en) to 10:1 ( pn ) to 50:1 ( dmen ) as first one methyl and then gem- dimethyl groups are attached to each parent chelate ring. That the reaction is influenced by substituent steric effects is supported by the structural characterization of the zinc-acid reduced and recomplexed acyclic species, which indicates that first ring formation occurs at amine pairs distant from the C-methyl substituents. The μ-chloro-bis (6-methyl-4,8-diazaundecane-2,6,10-triamine) dicopper (II) perchlorate crystallized in the space group C2/ c, a 23.003(6), b 12.641 (3), c 19.120(6) Ǻ, β 127.88(2)°, whereas the (2,6,10-trimethyl-4,8-diazaundecane-2,6,10-triamine)copper(II) perchlorate crystallized in the space group Cc2a, a 43.769(3), b 14.509(3), c 17.750(8) Ǻ. The copper ion is found in a distorted octahedral environment in the former with two complex units weakly bridged by a chloride anion, and in a square-based pyramidal environment in the latter.
A northern glacial refugium for bank voles (
Clethrionomys glareolus
)
Authors: Kotlík Petr , Deffontaine Valérie , Mascheretti Silvia , Zima Jan , Michaux Johan R. , Searle Jeremy B.
Published: September 2006

There is controversy and uncertainty on how far north there were glacial refugia for temperate species during the Pleistocene glaciations and in the extent of the contribution of such refugia to present-day populations. We examined these issues using phylogeographic analysis of a European woodland mammal, the bank vole (
Clethrionomys glareolus
). A Bayesian coalescence analysis indicates that a bank vole population survived the height of the last glaciation (≈25,000–10,000 years B.P.) in the vicinity of the Carpathians, a major central European mountain chain well north of the Mediterranean areas typically regarded as glacial refugia for temperate species. Parameter estimates from the fitted isolation with migration model show that the divergence of the Carpathian population started at least 22,000 years ago, and it was likely followed by only negligible immigration from adjacent regions, suggesting the persistence of bank voles in the Carpathians through the height of the last glaciation. On the contrary, there is clear evidence for gene flow out of the Carpathians, demonstrating the contribution of the Carpathian population to the colonization of Europe after the Pleistocene. These findings are consistent with data from animal and plant fossils recovered in the Carpathians and provide the clearest phylogeographic evidence to date of a northern glacial refugium for temperate species in Europe.
A theory for the atmospheric energy spectrum: Depth-limited temperature anomalies at the tropopause
Authors: Tulloch R. , Smith K. S.
Published: September 2006

The horizontal spectra of atmospheric wind and temperature at the tropopause have a steep −3 slope at synoptic scales, but transition to −5/3 at wavelengths of the order of 500–1,000 km [Nastrom, G. D. & Gage, K. S. (1985)
J. Atmos. Sci.
42, 950–960]. Here we demonstrate that a model that assumes zero potential vorticity and constant stratification
N
over a finite-depth
H
in the troposphere exhibits the same type of spectra. In this model, temperature perturbations generated at the planetary scale excite a direct cascade of energy with a slope of −3 at large scales, −5/3 at small scales, and a transition near horizontal wavenumber
k
t
=
f
/
NH
, where
f
is the Coriolis parameter. Ballpark atmospheric estimates for
N, f
, and
H
give a transition wavenumber near that observed, and numerical simulations of the previously undescribed model verify the expected behavior. Despite its simplicity, the model is consistent with a number of perplexing features in the observations and demonstrates that a complete theory for mesoscale dynamics must take temperature advection at boundaries into account.
The age incidence of chronic myeloid leukemia can be explained by a one-mutation model
Authors: Michor Franziska , Iwasa Yoh , Nowak Martin A.
Published: September 2006

Chronic myeloid leukemia (CML) is associated with the Philadelphia chromosome, which arises by a reciprocal translocation between chromosomes 9 and 22 and harbors the BCR-ABL fusion oncogene. It is unknown whether any other mutations are needed for the chronic phase of the disease. The CML incidence increases as a function of age with an exponent of ≈3. A slope of 3 could indicate that there are two mutations, in addition to the Philadelphia translocation, that have not yet been discovered. In this work, we explore an alternative hypothesis: We study a model of cancer initiation requiring only a single mutation. A mutated cell has a net reproductive advantage over normal cells and, therefore, might give rise to clonal expansion. The cancer is detected with a probability that is proportional to the size of the mutated cell clone. This model has three waiting times: (
i
) the time until a mutated cell is produced, (
ii
) the time of clonal expansion, and (
iii
) the time until the clone is detected. Surprisingly, this simple process can give rise to cancer incidence curves with exponents up to 3. Therefore, the CML incidence data are consistent with the hypothesis that the Philadelphia translocation alone is sufficient to cause chronic phase CML.
Preferential transfer of the complete glycan is determined by the oligosaccharyltransferase complex and not by the catalytic subunit
Authors: Castro Olga , Movsichoff Federico , Parodi Armando J.
Published: September 2006

Most eukaryotic cells show a strong preference for the transfer
in vivo
and
in vitro
of the largest dolichol-P-P-linked glycan (Glc
3
Man
9
GlcNAc
2
) to protein chains over that of biosynthetic intermediates that lack the full complement of glucose units. The oligosaccharyltransferase (OST) is a multimeric complex containing eight different proteins, one of which (Stt3p) is the catalytic subunit. Trypanosomatid protozoa lack an OST complex and express only this last protein. Contrary to the OST complex from most eukaryotic cells, the Stt3p subunit of these parasites transfers in cell-free assays glycans with Man
7–9
GlcNAc
2
and Glc
1–3
Man
9
GlcNAc
2
compositions at the same rate. We have replaced
Saccharomyces cerevisiae
Stt3p by the
Trypanosoma cruzi
homologue and found that the complex that is formed preferentially transfers the complete glycan both
in vivo
and
in vitro
. Thus, preference for Glc
3
Man
9
GlcNAc
2
is a feature that is determined by the complex and not by the catalytic subunit.
Reinvigorating exhausted HIV-specific T cells via PD-1–PD-1 ligand blockade
Authors: Freeman Gordon J. , Wherry E. John , Ahmed Rafi , Sharpe Arlene H.
Published: September 2006

The programmed death (PD)-1–PD-1 ligand (PD-L) pathway, which is part of the B7–CD28 family, consists of the PD-1 receptor and its two ligands PD-L1 and PD-L2. Engagement of PD-1 by its ligands inhibits immune responses, and recent work has shown that PD-1 is highly expressed on exhausted T cells during chronic lymphocytic choriomeningitis virus (LCMV) infection in mice. Blockade of this pathway reinvigorates the exhausted T cells, allowing them to expand and produce effector cytokines, raising the issue of whether this pathway has been exploited by a variety of viruses during chronic infection. New studies now extend these observations to HIV infection and human disease.
The Role of Intensity Upon Pitch Perception in Cochlear Implant Recipients
Authors: Arnoldner Christoph , Kaider Alexandra , Hamzavi Jafar
Published: September 2006

Objectives: Pitch plays a key role in the perception of speech and music, the recognition of a speaker's voice, and in analyzing complex auditory patterns. To date, little consideration has been given to the influence of stimulation level on pitch perception. The aim of this study was to investigate the impact of a sound's intensity on pitch perception in cochlear implant recipients using monopolar stimulation.

Study Design: Thirteen patients with an average implant use of 4.13 years took part in this study. All patients were implanted with MedEl Combi 40/40+ cochlear implants.

Methods: In the first part of the study, we performed a pitch ranking procedure to confirm that all patients were able to judge pitch changes. Using a visual scale, study participants were then asked to compare the pitch of an intensity‐constant reference tone with the pitch of a test tone of varying intensity.

Results: Eleven (85%) patients were found to perceive a clear change in pitch with changing stimulus intensity. Statistical analysis showed a strong positive correlation in 10 patients (correlation coefficients between 0.99 and 0.71) and a strong negative correlation in 1 patient (r = −0.92).

Conclusions: The results suggest that a distinct relationship exists between pitch perception and intensity of the stimulus. To date, speech coding strategies do not support these findings. Nevertheless, we believe that for the optimized most natural perception of sounds, especially music, the described particularities of pitch perception need to be respected, and further investigations on this topic are necessary.
‘Bow and Lean Test’ to Determine the Affected Ear of Horizontal Canal Benign Paroxysmal Positional Vertigo
Authors: Choung Yun‐Hoon , Shin You Ree , Kahng Hison , Park Keehyun , Choi Sung Jun
Published: September 2006

Objective: One of the problems in the management of horizontal semicircular canal benign paroxysmal positional vertigo (HSC‐BPPV) is the difficulty in determining the affected ear using Ewald's second law. The purpose of this study is to develop the new “bow and lean test (BLT)” to easily determine the affected ear of HSC‐BPPV and evaluate its efficiency.

Methods: We compared the efficiency between the classic method and BLT in 26 patients with HSC‐BPPV. The classic method is based on Ewald's second law comparing the intensity of nystagmus or symptoms in the head roll test. BLT is based on the direction of both “bowing nystagmus” and “leaning nystagmus” at the head's bowing and leaning state in a sitting position. The affected ear is the same direction of bowing nystagmus in canalolithiasis and the same direction of leaning nystagmus in cupulolithiasis.

Results: In 26 patents (15 canalolithiasis, 11 cupulolithiasis), 3 (11.5%) patients did not show a prominent affected ear in the classic method, and 7 (26.9%) patients showed the different affected ear between the two methods. All 10 patients were successfully treated with just one trial of barbecue rotation based on the affected ear in BLT. Three patients did not show any bowing or leaning nystagmus. The side with canal paresis in all four patients, who showed significant canal paresis in bithermal caloric tests, was equal to the affected ear based on BLT.

Conclusions: The “bow and lean test” (also called “Choung's test”) is a new method that can easily determine the affected ear of HC‐BPPV.