bluuebunny/crossref_metadata_2025 huggingface dataset:
Differential Rho‐kinase dependency of full and partial muscarinic receptor agonists in airway smooth muscle contraction
Authors: Schaafsma Dedmer , Boterman Mark , De Jong Anne‐Margreet , Hovens Iris , Penninks Jelte‐Maarten , Nelemans S Adriaan , Meurs Herman , Zaagsma Johan
Published: January 2006

In airway smooth muscle (ASM), full and partial muscarinic receptor agonists have been described to have large differences in their ability to induce signal transduction, including Ca2+‐mobilization. Despite these differences, partial agonists are capable of inducing a submaximal to maximal ASM contraction.

To further elucidate transductional differences between full and partial muscarinic receptor agonists, we investigated the contribution of Rho‐kinase (an important regulator of Ca2+‐sensitization) to methacholine‐, pilocarpine‐ and McN‐A‐343‐induced bovine tracheal smooth muscle (BTSM) contraction, using the selective Rho‐kinase inhibitor Y‐27632. In addition, we measured Ca2+‐mobilization and ‐influx in BTSM cells in response to these agonists in the absence and presence of Y‐27632.

Whereas treatment with Y‐27632 (1 μM) significantly decreased potency (pEC50) for all agonists, maximal contraction (Emax) was reduced by 23.4±2.8 and 50.4±7.9% for the partial agonists pilocarpine and McN‐A‐343, respectively, but was unaffected for the full agonist methacholine. However, Emax of methacholine became Rho‐kinase dependent after taking away its receptor reserve using the irreversible muscarinic receptor antagonist propylbenzilylcholine mustard.

Pilocarpine and McN‐A‐343 induced a very small Ca2+‐mobilization and ‐influx as compared to methacholine. In addition, an inverse relationship of these two parameters with the Rho‐kinase dependency was observed. Interestingly, no inhibitory effects of Y‐27632 were observed on Ca2+‐mobilization and‐influx for all three agonists, indicating that the effects of Y‐27632 on contraction are most likely on the level of Ca2+‐sensitization.

In conclusion, in contrast to the full agonist methacholine, the partial muscarinic receptor agonists pilocarpine and McN‐A‐343 are dependent on Rho‐kinase for their maximal contractile effects, presumably as a consequence of differences in transductional reserve, indicating an agonist‐dependent role for Rho‐kinase in ASM contraction. Moreover, an inverse relationship exists between Rho‐kinase dependency and both Ca2+‐mobilization and Ca2+‐influx for these agonists.

British Journal of Pharmacology (2006) 147, 737–743. doi:10.1038/sj.bjp.0706665
Compared pharmacology of human histamine H3and H4receptors: structure–activity relationships of histamine derivatives
Authors: Gbahou Florence , Vincent Ludwig , Humbert‐Claude Marie , Tardivel‐Lacombe Joel , Chabret Claude , Arrang Jean‐Michel
Published: January 2006

Various histamine derivatives were investigated at the human H3receptor (H3R) and H4receptor (H4R) stably expressed in human embryonic kidney (HEK)‐293 cells using [125I]iodoproxyfan and [3H]histamine binding, respectively.

In Tris buffer, [3H]histamine binding to membranes of HEK(hH4R) cells was monophasic (KDof 3.8±0.8 nM). In phosphate buffer, the Hill coefficient was decreased (nH=0.5±0.1) and a large fraction of the binding was converted into a low‐affinity component (KD=67±27 nM).

The inhibition of [3H]histamine binding by two agonists, a protean agonist and five antagonists/inverse agonists confirms that the potency of many H3R ligands is retained or only slightly reduced at the H4R.

Histamine derivatives substituted with methyl groups inα,βorNαposition of the side chain retained a nanomolar potency at the H3R, but their affinity was dramatically decreased at the H4R. With relative potencies to histamine of 282 and 0.13% at the H3R and H4R, respectively, (±)‐α,β‐dimethylhistamine is a potent and selective H3R agonist.

Chiralα‐branched analogues exhibited a marked stereoselectivity at the H3R and H4R, the enantiomers with a configuration equivalent toL‐histidine being preferred at both receptors.

The methylsubstitution of the imidazole ring was also studied. The relative potency to histamine of 4‐methylhistamine (4‐MeHA) at the H4R (67%) was similar to that reported at H2receptors but, owing to its high affinity at the H4R (Ki=7.0±1.2 nM) and very low potency at H1‐ and H3‐receptors, it can be considered as a potent and selective H4R agonist.

On inhibition of forskolin‐induced cAMP formation, all the compounds tested, including 4‐MeHA, behaved as full agonists at both receptors. However, the maximal inhibition achieved at the H4R (∼−30%) was much lower than at the H3R (∼−80%). Thioperamide behaved as an inverse agonist at both receptors and increased cAMP formation with the same maximal effect (∼+25%).

In conclusion, although the pharmacological profiles of the human H3R and H4R overlap, the structure–activity relationships of histamine derivatives at both receptors strongly differ and lead to the identification of selective compounds.

British Journal of Pharmacology(2006)147, 744–754. doi:10.1038/sj.bjp.0706666
Mechanisms of 5‐aminolevulic acid ester uptake in mammalian cells
Authors: Rodriguez Lorena , Batlle Alcira , Di Venosa Gabriela , Battah Sinan , Dobbin Paul , MacRobert Alexander J , Casas Adriana
Published: January 2006

The porphyrin precursor 5‐aminolevulinic acid (ALA) is being widely used in photodynamic therapy of cancer. Improvement in ALA delivery has been sought through the use of ALA derivatives, in particular the esterification of ALA with aliphatic alcohols, which in certain cases can improve cellular penetration and selectivity.

ALA uptake systems appear to be distinctive for each cell type. The LM3 mammary adenocarcinoma cell line takes ALA up by BETA transporters. In this work, we investigated ALA derivative transport systems through the inhibition of radiolabelled ALA uptake in the LM3 cells. We also performed inhibition studies of γ‐aminobutyric acid (GABA) uptake.

The more lipohilic ALA derivatives hexyl‐ALA and undecanoyl‐ALA inhibit ALA uptake, whereas methyl‐ALA, R, S‐ALA‐2‐(hydroxymethyl)tetrahydropyranyl ester and the dendron aminomethane tris methyl 5‐ALA does not inhibit ALA uptake. A similar pattern was found for GABA, except that the dendron inhibited GABA uptake. However, hexyl‐ALA and undecanoyl‐ALA are not taken up by BETA transporters, but by simple diffusion, although they still inhibit ALA uptake by binding to the cell membrane.

These results show that different modifications to the ALA molecule lead to different uptake mechanisms. Whereas ALA is taken up by BETA transporters, none of the ALA derivatives shares the same mechanism. Knowledge of the mechanisms of ALA derivatives entry into the cells is essential to understand and improve ALA‐mediated PDT and to the design of new ALA derivatives that may be taken up at a higher rate than ALA.

British Journal of Pharmacology (2006) 147, 825–833. doi:10.1038/sj.bjp.0706668
On the epitaxy of twin-free cubic (111) praseodymium sesquioxide films on Si(111)
Authors: Schroeder T. , Zaumseil P. , Weidner G. , Wenger Ch. , Dabrowski J. , Müssig H.-J. , Storck P.
Published: January 2006

Twin-free epitaxial cubic (111) praseodymium sesquioxide films were prepared on Si(111) by hexagonal-to-cubic phase transition. Synchrotron radiation grazing incidence x-ray diffraction and transmission electron microscopy were applied to characterize the phase transition and the film structure. As-deposited films grow single crystalline in the (0001)-oriented hexagonal high-temperature phase of praseodymium sesquioxide. In situ x-ray diffraction studies deduce an activation energy of 2.2eV for the hexagonal-to-cubic phase transition. Transmission electron microscopy shows that the phase transition is accompanied by an interface reaction at the oxide/Si(111) boundary. The resulting cubic (111) low-temperature praseodymium sesquioxide film is single crystalline and exclusively shows B-type stacking. The 180° rotation of the cubic oxide lattice with respect to the Si substrate results from a stacking fault at the substrate/oxide boundary.
Electronically activated boron-oxygen-related recombination centers in crystalline silicon
Authors: Bothe Karsten , Schmidt Jan
Published: January 2006

Two different boron- and oxygen-related recombination centers are found to be activated in crystalline silicon under illumination or electron injection in the dark, both leading to a severe degradation in the carrier lifetime. While one center forms on a time scale of seconds to minutes, the formation of the second center typically proceeds within hours. In order to reveal the electronic and microscopic properties of both defect centers as well as their formation and annihilation kinetics, we perform time-resolved lifetime measurements on silicon wafers and open-circuit voltage measurements on silicon solar cells at various temperatures. Despite the fact that the two centers are found to form independently of each other, their concentrations exhibit the same linear dependence on the substitutional boron (Bs) and quadratic dependence on the interstitial oxygen (Oi) content. Our results suggest that the fast- and the slowly forming recombination centers correspond to two different configurations of a BsO2i complex.
The finite state projection algorithm for the solution of the chemical master equation
Authors: Munsky Brian , Khammash Mustafa
Published: January 2006

This article introduces the finite state projection (FSP) method for use in the stochastic analysis of chemically reacting systems. One can describe the chemical populations of such systems with probability density vectors that evolve according to a set of linear ordinary differential equations known as the chemical master equation (CME). Unlike Monte Carlo methods such as the stochastic simulation algorithm (SSA) or τ leaping, the FSP directly solves or approximates the solution of the CME. If the CME describes a system that has a finite number of distinct population vectors, the FSP method provides an exact analytical solution. When an infinite or extremely large number of population variations is possible, the state space can be truncated, and the FSP method provides a certificate of accuracy for how closely the truncated space approximation matches the true solution. The proposed FSP algorithm systematically increases the projection space in order to meet prespecified tolerance in the total probability density error. For any system in which a sufficiently accurate FSP exists, the FSP algorithm is shown to converge in a finite number of steps. The FSP is utilized to solve two examples taken from the field of systems biology, and comparisons are made between the FSP, the SSA, and τ leaping algorithms. In both examples, the FSP outperforms the SSA in terms of accuracy as well as computational efficiency. Furthermore, due to very small molecular counts in these particular examples, the FSP also performs far more effectively than τ leaping methods.
Temperature-induced crystallization in concentrated suspensions of multiarm star polymers: A molecular dynamics study
Authors: Rissanou Anastassia N. , Yiannourakou Marianna , Economou Ioannis G. , Bitsanis Ioannis A.
Published: January 2006

In this work, we study temperature-induced crystallization in dense suspensions of multiarm star polymers. This is a continuation of a previous study, which identified and studied the emergence of “glassy” amorphous states, in accordance with experimental observations. We performed molecular dynamics simulations on two types of star polymers: 128-arm stars and 64-arm stars dissolved in n-decane in the temperature range of 20–60 °C. These supramolecules are modeled as “soft spheres” interacting via a theoretically developed potential of mean field. Both systems attain a crystalline structure with the characteristics of a face-centered-cubic (fcc) crystal beyond a certain temperature. Kinetics is sensitive on initial configuration. Interestingly, kinetic trapping in “temporary” energy wells leads to highly crystalline structures, yet less ordered than their genuine equilibrium fcc structure. This complication illustrates the difficulty in reaching the equilibrium state, which is crystalline at high temperatures. A structural analysis of the final conformations is presented. The effect of size dispersity and star functionality of soft spheres on microstructure is also examined. Both factors influence crystallization and their effect is quantified by our study.
n
-pentanol at high pressures: Rotational isomerism in the liquid phase and the liquid-solid phase transition
Authors: Baonza V. G. , Taravillo M. , Cazorla A. , Casado S. , Cáceres M.
Published: January 2006

The vibrational spectrum of liquids constituted of chain molecules is difficult to analyze because it may have contributions of different rotational isomers. In turn, with a proper vibrational assignment, this feature allows us to extract information about the effect of temperature or pressure on the molecular conformations in the liquid state. In this regard, the information on the vibrational spectrum in the solid phase greatly simplifies the vibrational analysis of the different rotational conformers existing in the liquid, as the molecules usually present all-trans conformations in the crystalline state. Here we report room-temperature Raman experiments on n-pentanol performed in a sapphire-anvil cell up to 3 GPa. A detailed analysis of the liquid-solid phase transition occurring at 1.3 GPa is provided. The analysis of the Raman spectrum in the solid phase allows the identification of the bands due to the different rotational isomers present in the liquid. The analysis of the spectral region corresponding to skeletal vibrations of the carbon chain (800–1200cm−1) indicates that gauche conformers are promoted by the application of pressure. The analysis of the intensity ratio of those bands assigned to trans and gauge conformations is used to calculate the change in molecular volume ascribed to the trans-gauge isomerization process. We find a value similar to that found in n-alkanes, i.e., −0.88cm3mol−1. In addition, we find indication that pressure varies the proportions of the different gauge conformers. Thus, it appears that the GTTt to TGTt transition in the carbon chain is favored at high pressures. As expected, a smaller change in the molecular volume accompanies this conformation change.
Role of dynamical screening in excitation kinetics of biased quantum wells: Nonlinear absorption and ultrabroadband terahertz emission
Authors: Turchinovich D. , Monozon B. S. , Jepsen P. Uhd
Published: January 2006

In this work we describe the ultrafast excitation kinetics of a biased quantum well, arising from the optically induced dynamical screening of a bias electric field. The initial bias electric field inside the quantum well is screened by the optically excited polarized electron-hole pairs. This leads to a dynamical modification of the properties of the system within an excitation pulse duration. We calculate the excitation kinetics of a biased quantum well and the dependency of resulting electronic and optical properties on the excitation pulse fluence, quantum well width, and initial bias field strength. Our calculations, in particular, predict the strongly nonlinear dependency of the effective optical absorption coefficient on the excitation pulse fluence, and ultrabroadband terahertz emission. Our theoretical model is free of fitting parameters. Calculations performed for internally biased InGaN∕GaN quantum wells are in good agreement with our experimental observations [Turchinovich et al., Phys. Rev. B 68, 241307(R) (2003)], as well as in perfect compliance with qualitative considerations.
Shear properties of glycerol by interface wave laser ultrasonics
Authors: Glorieux C. , Van de Rostyne K. , Goossens J. , Shkerdin G. , Lauriks W. , Nelson K. A.
Published: January 2006

Acoustic waves at the interface between a polymeric solid and a glass-forming liquid are studied through impulsive stimulated thermal scattering (ISTS), a photoacoustic method. The transverse character of the interface waves provides a unique window into the shear relaxation dynamics of supercooled liquids. Real and imaginary parts of the shear modulus of glycerol are extracted as functions of temperature and acoustic frequency. Extension of ISTS to interface waves permits characterization of shear dynamics even under conditions of very strong acoustic damping which preclude more conventional ultrasonic methods.
The effect of strained Si1−xGex and Si1−yCy layers for La0.75Sr0.25MnO3 films grown on oxide-buffered Si substrates
Authors: Kim J.-H. , Grishin A. M. , Radamson H. H.
Published: January 2006

We report the effect of strain on the structural and electrical properties of colossal magnetoresistive (CMR) La0.75Sr0.25MnO3 (LSMO) films grown on Bi4Ti3O12∕CeO2∕ yttrium-stabilized-zirconia-buffered Si1−xGex∕Si(x=0–0.20) and Si1−yCy∕Si(y=0–0.01) substrates. The strain in the buffer layer stack was tailored by varying the Ge and C contents in SiGe and SiC layers. It has been demonstrated that the relaxation of Bi4Ti3O12 layer is dependent on Ge content and this strongly affects the quality of the LSMO film. The surface roughness of LSMO was also strain dependent and samples grown on SiGe and SiC template layers were significantly smoother than that on Si. High resistivity and low values of the temperature coefficient of resistivity were obtained in LSMO films on Si0.8Ge0.2∕Si and Si0.99C0.01∕Si whereas Si0.9Ge0.1∕Si sample shows a slight improvement in the crystalline and electrical LSMO properties compared to the CMR film grown onto the Si substrate.
Raman spectroscopy studies of Ce-doping effects on Ba0.5Sr0.5TiO3 thin films
Authors: Wang S. Y. , Cheng B. L. , Wang Can , Dai S. Y. , Jin K. J. , Zhou Y. L. , Lu H. B. , Chen Z. H. , Yang G. Z.
Published: January 2006

Ba 0.5 Sr 0.5 TiO 3 (BST) thin films are among the best-known ferroelectric and dielectric materials. Ce-doped BST films have been fabricated by pulsed laser deposition in order to enhance their dielectric properties. X-ray diffraction, atomic force microscopy, and Raman spectroscopy have been used to study variations of crystal structure, surface morphologies, and phase stability of Ce-doped BST films, respectively. A strong influence of Ce doping on the properties of the BST films has been observed. First, a small amount of Ce dopant makes easy epitaxial growth of a BST film with a smooth surface on a MgO substrate. Second, residual stress in a BST film on a MgO substrate can be reduced by Ce doping, as demonstrated by the blueshift of phonon peaks in Raman spectroscopy.
Demonstration and analysis of reduced reverse-bias leakage current via design of nitride semiconductor heterostructures grown by molecular-beam epitaxy
Authors: Zhang H. , Yu E. T.
Published: January 2006

An approach for reducing reverse-bias leakage currents in Schottky contacts formed to nitride semiconductor heterostructures grown by molecular-beam epitaxy is described, demonstrated, and analyzed. By incorporation of a GaN cap layer atop a conventional AlxGa1−xN∕GaN heterostructure field-effect transistor epitaxial layer structure, the direction of the electric field at the metal-semiconductor interface of a Schottky contact is reversed, resulting in a suppression of electron flow into conductive screw dislocations that are known to dominate reverse-bias leakage currents in nitride semiconductors grown by molecular-beam epitaxy. Analysis of temperature-dependent current-voltage characteristics indicates that, in structures incorporating a GaN cap layer, reverse-bias leakage currents are reduced by one to three orders of magnitude, with the mechanism for leakage current flow differing from that established previously for the more conventional structure due to the alteration in the electric field at the metal-semiconductor interface. Scanned probe measurements of local, nanoscale current distributions confirm directly that current flow via conductive dislocations is suppressed in structures incorporating the GaN cap layer.
Fast pulse-excited spin waves in yttrium iron garnet thin films
Authors: Wu Mingzhong , Kalinikos Boris A. , Krivosik Pavol , Patton Carl E.
Published: January 2006

Fast pulse-driven spin-wave excitations in magnetic films have been studied experimentally and theoretically. The experiment was conducted on a low loss yttrium iron garnet thin-film strip with separate microstrip lines for excitation and detection. The theoretical analysis was based on the full spatio-temporal Fourier response of the input pulse/microstrip line configuration and the spin-wave dispersion for the film. The data and analysis provide a clear and precise picture of the manner in which the fast pulse-excited spin-wave signals are defined and controlled by the interplay of pulse rise time, excitation geometry, and spin-wave dispersion. The amplitude of the spin-wave wave packet associated with the leading or trailing edges of the drive decreases with the pulse rise time and the static magnetic field, and increases with the pulse amplitude. The spectral profile of the spin-wave excitation is highly asymmetric, with a steep lower-frequency edge and a gradual upper-frequency edge. The spectral bands are controllable; an increase in the static magnetic field pushes up the lower cutoff frequency, while an increase in the pulse rise time pushes down the higher cutoff frequency.
Predicting the amount of carbon in carbon nanotubes grown by CH4 rf plasmas
Authors: Okita Atsushi , Suda Yoshiyuki , Ozeki Atsushi , Sugawara Hirotake , Sakai Yosuke , Oda Akinori , Nakamura Junji
Published: January 2006

Carbon nanotubes (CNTs) were grown on Si substrates by rf CH4 plasma-enhanced chemical vapor deposition in a pressure range of 1–10Torr, and then characterized by scanning electron microscopy. At 1Torr, the CNTs continued growing up to 60min, while their height at 4Torr had leveled off at 20min. CNTs hardly grew at 10Torr and amorphous carbon was deposited instead. CH4 plasma was simulated using a one-dimensional fluid model to evaluate the production and transport of radicals, ions, and nonradical neutrals. The amount of simulated carbon supplied to the electrode surface via the flux of radicals and ions such as CH3, C2H5, and C2H5+ was consistent with estimations from experimental results.
Structure of V2AlC studied by theory and experiment
Authors: Schneider Jochen M. , Mertens Raphael , Music Denis
Published: January 2006

We have studied V2AlC (space group P63∕mmc, prototype Cr2AlC) by ab initio calculations. The density of states (DOS) of V2AlC for antiferromagnetic, ferromagnetic, and paramagnetic configurations have been discussed. According to the analysis of DOS and cohesive energy, no significant stability differences between spin-polarized and non-spin-polarized configurations were found. Based on the partial DOS analysis, V2AlC can be classified as a strongly coupled nanolaminate according to our previous work [Z. Sun, D. Music, R. Ahuja, S. Li, and J. M. Schneider, Phys. Rev. B 70, 092102 (2004)]. Furthermore, this phase has been synthesized in the form of thin films by magnetron sputtering. The equilibrium volume, determined by x-ray diffraction, is in good agreement with the theoretical data, implying that ab initio calculations provide an accurate description of V2AlC.
Triplet-triplet energy-transfer coupling: Theory and calculation
Authors: You Zhi-Qiang , Hsu Chao-Ping , Fleming Graham R.
Published: January 2006

Triplet-triplet (TT) energy transfer requires two molecular fragments to exchange electrons that carry different spin and energy. In this paper, we analyze and report values of the electronic coupling strengths for TT energy transfer. Two different methods were proposed and tested: (1) Directly calculating the off-diagonal Hamiltonian matrix element. This direct coupling scheme was generalized from the one used for electron transfer coupling, where two spin-localized unrestricted Hartree-Fock wave functions are used as the zero-order reactant and product states, and the off-diagonal Hamiltonian matrix elements are calculated directly. (2) From energy gaps derived from configuration-interaction-singles (CIS) scheme. Both methods yielded very similar results for the systems tested. For TT coupling between a pair of face-to-face ethylene molecules, the exponential attenuation factor is 2.59Å−1(CIS∕6-311+G**), which is about twice as large as typical values for electron transfer. With a series of fully stacked polyene pairs, we found that the TT coupling magnitudes and attenuation rates are very similar irrespective of their molecular size. If the polyenes were partially stacked, TT couplings were much reduced, and they decay more rapidly with distance than those of full-stacked systems. Our results showed that the TT coupling arises mainly from the region of close contact between the donor and acceptor frontier orbitals, and the exponential decay of the coupling with separation depends on the details of the molecular contacts. With our calculated results, nanosecond or picosecond time scales for TT energy-transfer rates are possible.
Linear polyelectrolytes in tetravalent salt solutions
Authors: Hsiao Pai-Yi
Published: January 2006

The effect of adding tetravalent salt of different sizes to a solution of linear and flexible polyelectrolytes is investigated by molecular dynamics simulations. Upon the addition of salt, a chain reexpansion takes place, following a well-known collapsed conformation. The degrees of collapse and reexpansion increase with ion size. In the solution, tetravalent counterions replace monovalent ones and condense onto the chains. The condensation for small ions displays a profile different from that for large ones. In a high-salt region, ions can form layering orders around a polyelectrolyte and locally overcompensate the charge inside. Consequently, the integrated charge distribution reveals an oscillatory behavior away from a chain. By studying the radial distribution function between monomers on different polyelectrolytes, like-charge attraction between chains is demonstrated. This attraction is a prerequisite to chain aggregation or precipitation. The results show a strong dependence of salt concentration and ion size on the properties of polyelectrolyte solutions.
Effects of an axial magnetic field on Z-pinch plasmas for extreme ultraviolet sources
Authors: Katsuki Sunao , Kimura Akihiro , Kondo Yoshihiro , Horita Hiroyuki , Namihira Takao , Sakugawa Takashi , Akiyama Hidenori
Published: January 2006

This paper describes the effect of an axial magnetic field (Bz) on plasma pinch dynamics and on the extreme ultraviolet (EUV) emission property of a compact Z-pinch device for EUV sources. The Z-pinch xenon plasma was driven by a pulse current with an amplitude of 27 kA and duration of 150 ns in an alumina tube with a diameter of 5 mm. A quasistatic magnetic field of up to 360 G is applied to the plasma. The EUV emission was evaluated for spectra, spatial distribution of the emission, and light energy at 13.5 nm with 2% bandwidth. A time-resolved interferogram provides the electron line density and pinch dynamics of the plasma. When a magnetic field of 160 G was applied to the plasma, the emission energy was approximately double that without the magnetic field. The spectroscopic measurement shows that the EUV spectrum drastically varies with magnetic-field strength. The time-resolved interferogram indicates that the axial magnetic field contributes by making the plasma compression smooth and by sustaining certain plasma conditions longer. From these experimental results, it was concluded that applying an axial magnetic field can be an effective method to improve EUV emission.
Influence of Ni Schottky contact area on two-dimensional electron-gas sheet carrier concentration of strained AlGaN∕GaN heterostructures
Authors: Lin Zhaojun , Lu Wu
Published: January 2006

The influence of Ni Schottky contact area on two-dimensional electron-gas (2DEG) sheet carrier concentration of strained AlGaN∕GaN heterostructures has been investigated by depositing different areas of Ni Schottky contact on the structure. With the measured capacitance-voltage (C-V) curves, the 2DEG sheet carrier concentrations with different Ni Schottky contact areas were calculated. It is shown that with the increased area of Ni Schottky contact on strained AlGaN∕GaN heterostructures, the 2DEG sheet carrier concentration is decreased, and when the area of Ni Schottky contact is increased to some extent, the decreased 2DEG sheet carrier concentration tends to be constant. A hypothetic model of the interaction among the electrons of Ni Schottky metal, the surface donor states of AlGaN barrier layer, and 2DEG electrons in strained AlGaN∕GaN heterostructures is proposed to explain the above results. The current-voltage (I-V) characteristics for the different areas of Ni Schottky contact confirm the results obtained by C-V characteristics.
Dynamic positive column in long-gap barrier discharges
Authors: Shvydky A. , Khudik V. N. , Theodosiou C. E. , Nagorny V. P.
Published: January 2006

A simple analytical model of the barrier discharge in a long gap between opposing plane electrodes is developed. It is shown that the plasma density becomes uniform over a large part of the gap in the course of the discharge development, virtually forming a dynamic positive column. The column completely controls the dynamics of the barrier discharge and determines such characteristics as the discharge current, discharge duration, light output, etc. Using the proposed model, one can easily evaluate many important discharge parameters.
Slab-thickness dependence of polarization change of terahertz waves transmitted through metal hole arrays
Authors: Miyamaru Fumiaki , Hangyo Masanori
Published: January 2006

Polarization characteristics of the terahertz wave transmitted through metal hole arrays with the triangular lattice structure are investigated in the subterahertz region. The metal hole arrays used in our experiments are thin metal slabs perforated periodically with circular holes. The polarization rotation of the terahertz wave transmitted through the metal hole arrays occurs only in the spectral range of the resonant frequency of the surface waves. By investigating the dependence of this phenomenon on the thickness of the metal hole array, we attribute such polarization phenomenon to the resonant excitation of the surface waves.
Determination of energy-band offsets between GaN and AlN using excitonic luminescence transition in AlGaN alloys
Authors: Westmeyer A. N. , Mahajan S. , Bajaj K. K. , Lin J. Y. , Jiang H. X. , Koleske D. D. , Senger R. T.
Published: January 2006

We report the determination of the energy-band offsets between GaN and AlN using the linewidth (full width at half maximum) of an extremely sharp excitonic luminescence transition in AlxGa1−xN alloy with x=0.18 at 10K. Our sample was grown on C-plane sapphire substrate by metal-organic chemical-vapor deposition at 1050°C. The observed value of the excitonic linewidth of 17meV is the smallest ever reported in literature. On subtracting a typical value of the excitonic linewidth in high-quality GaN, namely, 4.0meV, we obtain a value of 13.0meV, which we attribute to compositional disorder. This value is considerably smaller than that calculated using a delocalized exciton model [S. M. Lee and K. K. Bajaj, J. Appl. Phys. 73, 1788 (1993)]. The excitons are known to be strongly localized by defects and/or the potential fluctuations in this alloy system. We have simulated this localization assuming that the hole, being much more massive than the electron, is completely immobile, i.e., the hole mass is treated as infinite. Assuming that the excitonic line broadening is caused entirely by the potential fluctuations experienced by the conduction electron, the value of the conduction-band offset between GaN and AlN is determined to be about 57% of the total-band-gap discontinuity. Using our model we have calculated the variation of the excitonic linewidth as a function of Al composition in our samples with higher Al content larger than 18% and have compared it with the experimental data. We also compare our value of the conduction-band offset with those recently proposed by several other groups using different techniques.
Application of admittance spectroscopy to evaluate carrier mobility in organic charge transport materials
Authors: Tsang S. W. , So S. K. , Xu J. B.
Published: January 2006

We examine the feasibility of admittance spectroscopy (AS) and susceptance analysis in the determination of the charge-carrier mobility in an organic material. The complex admittance of the material is analyzed as a function of frequency in AS. We found that the susceptance, which is the imaginary part of the complex admittance, is related to the carrier transport properties of the materials. A plot of the computer-simulated negative differential susceptance versus frequency yields a maximum at a frequency τr−1. The position of the maximum τr−1 is related to the average carrier transit time τdc by τdc=0.56τr. Thus, knowledge of τr can be used to determine the carrier mobility in the material. Devices with the structure ITO/4,4′,4″ -tris[N, -(3-methylphenyl)-N-phenylamino] triphenylamine/Ag have been designed to investigate the validity of the susceptance analysis in the hole mobility determination. The hole mobilities were measured both as functions of the electric field and the temperature. The hole mobility data extracted by susceptance analysis were in excellent agreement with those independently obtained from time-of-flight (TOF) measurements. Using the temperature dependence results, we further analyzed the mobility data by the Gaussian disorder model (GDM). The GDM disorder parameters are also in good agreement with those determined from TOF.
Nonlinear absorption and refraction in indium arsenide
Authors: Haeri Mitchell B. , Kingham Steven R. , Milsom Philip K.
Published: January 2006

z -scan experiments and beam propagation modeling were conducted to determine the nonlinear absorption and refractive index cross sections of n-type indium arsenide (InAs). A doubled carbon dioxide pulsed laser operating at 4.78μm was used to generate free carriers via two-photon absorption. Using published values for the two-photon absorption coefficient in InAs, a nonlinear beam propagation model and a data fitting routine were used to extract the nonlinear absorption and refractive index cross sections.
Periodicity dependence of exchange bias in [Co∕Pt]N∕Co∕CoO multilayers with perpendicular anisotropy
Authors: Sang H. , Chien C. L. , Yang F. Y.
Published: January 2006

Perpendicular exchange bias has been realized in [Co(0.4nm)∕Pt(1nm)]N∕Co(1nm)∕CoO(1.5nm) multilayers with N from 3 to 36. The characteristics of exchange bias and the switching behavior of the multilayers strongly depend on the periodicity N. The exchange bias field and coercivity depend linearly on the inverse of the total thickness of the Co layers in the multilayer, while the surface anisotropy energy at the Co∕Pt interface is essentially independent of N.
Origin of the amplified spontaneous emission from thiophene/phenylene co-oligomer single crystals: Towards co-oligomer lasers
Authors: Bando Kazuki , Nakamura Toshiteru , Masumoto Yasuaki , Sasaki Fumio , Kobayashi Shunsuke , Hotta Shu
Published: January 2006

Photoluminescence (PL) and optical gain measurements have been performed for single crystals of thiophene/phenylene co-oligomer at room and low temperatures. Broad PL bands are transformed to be an ensemble of several spectrally narrower vibronic peaks with decreasing temperature. Very sharp lines as narrow as ∼3meV are observed at 10K under weak excitation. Intensities of sharp emission lines superlinearly increased at 10K under intense excitation, showing the amplified spontaneous emission (ASE). The ASE bands were clearly identified to the sidebands of B1 and A1+B1 vibronic modes. The ASE is also observed at room temperature under the intense excitation. Spectroscopic investigation at varied temperatures enabled us to identify the origin of the ASE band to the vibronic sidebands of the electronic transition of the thiophene/phenylene co-oligomer crystals. In addition, highly polarized optical gains ∼50cm−1 were obtained for the two ASE bands at room temperature.
Effect of strain on tunability in Ba0.60Sr0.40TiO3 thin films on Pt–Si substrates
Authors: Potrepka D. M. , Hirsch S. , Cole M. W. , Nothwang W. D. , Zhong S. , Alpay S. P.
Published: January 2006

Ba 0.6 Sr 0.4 Ti O 3 films with a thickness of 200nm were deposited on Pt–Si substrates at 400 and 700°C. Room-temperature tunability was measured and found to improve with deposition temperature, but losses also increased. The dielectric constant, tunability, and loss tangent are found to be 350, 52%, and 0.07 at 300kV∕cm for the 700°C deposition. The film grown at 700°C has a larger grain size, leading to approximately 5% higher tunability compared to the film deposited at 400°C. Supporting theoretical calculations were carried out using a modified Landau-Devonshire thermodynamic formalism that takes into account the internal stresses that arise from the differences of coefficients of thermal expansion between the film and the substrate.
Inelastic Takahashi hard-rod gas
Authors: Marini-Bettolo-Marconi Umberto , Natali Maurizio , Costantini Giulio , Cecconi Fabio
Published: January 2006

We study a one-dimensional fluid of hard rods interacting with each other via binary inelastic collisions and a short-ranged square-well potential. Upon tuning the depth and the sign of the well, we investigate the interplay between dissipation and cohesive or repulsive forces. Molecular-dynamics simulations of the cooling regime indicate that the presence of this simple interparticle interaction is sufficient to significantly modify the energy dissipation rates expected by Haff’s law for the free cooling. The simplicity of the model makes it amenable to an analytical approach based on the Boltzmann-Enskog transport equation which allows deriving the behavior of the granular temperature. Furthermore, in the elastic limit, the model can be solved exactly to provide a full thermodynamic description. A meaningful theoretical approximation explaining the properties of the inelastic system in interaction with a thermal bath can be directly extrapolated from the properties of the corresponding elastic system, upon a proper redefinition of the relevant observables. Simulation results both in the cooling and driven regimes can be fairly interpreted according to our theoretical approach and compare rather well to our predictions.
Binary nucleation of water and sodium chloride
Authors: Němec Tomáš , Maršík František , Palmer Donald A.
Published: January 2006

Nucleation processes in the binary water-sodium chloride system are investigated in the sense of the classical nucleation theory (CNT). The CNT is modified to be able to handle the electrolytic nature of the system and is employed to investigate the acceleration of the nucleation process due to the presence of sodium chloride in the steam. This phenomenon, frequently observed in the Wilson zone of steam turbines, is called early condensation. Therefore, the nucleation rates of the water-sodium chloride mixture are of key importance in the power cycle industry.
Flow-rate modulation epitaxy of wurtzite AlBN
Authors: Akasaka Tetsuya , Makimoto Toshiki
Published: January 2006

Wurtzite AlBN thin films were fabricated using flow-rate modulation epitaxy (FME), wherein group-III and group-V sources are alternatively supplied to the growing surface. A 350-nm-thick wurtzite Al1−xBxN (x∼0.015) film grown by FME exhibited a single sharp peak in the ω-2θ scan of x-ray diffraction, a smooth surface with the root-mean-square roughness of 3.4nm, and a sharp epitaxial interface with SiC(0001) substrate, whereas that prepared by conventional metalorganic chemical vapor deposition contained faceted columnar AlBN(11̱01) crystallites several ten nanometers in width in an AlBN(0001) matrix. FME is useful for fabricating high-quality wurtzite AlBN thin films, because it suppresses polycrystallization through enhancement of the surface migration of boron atoms.
Highly efficient stimulated Raman scattering of picosecond pulses in KTiOPO4
Authors: Pasiskevicius Valdas , Canalias Carlota , Laurell Fredrik
Published: January 2006

High-efficiency picosecond stimulated Raman scattering (SRS) by phonon-polaritons has been observed in KTiOPO4 in a single pass through a 10mm long crystal. For pulses longer than 10ps, the SRS waves formed a symmetric pattern consisting of four distinct beams: SRS Stokes and anti-Stokes wavelengths originating both from the near-infrared pump and from the scattering of the second harmonic of the pump. At peak intensities above 10GW∕cm2 and pulse length of 1.5ps, the SRS character changes into what can be called “runaway” Raman scattering with efficiencies exceeding 50% and Raman gain spreading over 60THz.
Magnetic nanocables—Silicon carbide sheathed with iron-oxide-doped amorphous silica
Authors: Liu C. , Li R. W. , Belik A. , Golberg D. , Bando Y. , Cheng H. M.
Published: January 2006

High-purity nanocables of iron-containing amorphous-silica-sheathed silicon carbide were synthesized by a thermal reaction method using silicon wafer as the silicon source and growth substrate, and ferrocene as the carbon and iron catalyst precursor. The nanocables were tens of μm in length and 40–60nm in diameter. Iron oxide nanoparticles with a mean diameter of 5nm were dispersed evenly in the amorphous silica layer. The nanocables were found to be ferromagnetic at both 10K and room temperature, which indicates that they may have important potential applications in electromagnetic nanodevices.
Ultrahigh-Q photonic crystal nanocavities realized by the local width modulation of a line defect
Authors: Kuramochi Eiichi , Notomi Masaya , Mitsugi Satoshi , Shinya Akihiko , Tanabe Takasumi , Watanabe Toshifumi
Published: January 2006

We propose an ultrahigh quality factor (Q) photonic crystal slab nanocavity created by the local width modulation of a line defect. We show numerically that this nanocavity has an intrinsic Q value of up to 7×107. Transmission measurements for fabricated Si photonic-crystal-slab nanocavities directly coupled to input/output waveguides have exhibited a loaded Q value of ∼800000. These theoretical and experimental Q values are very high for photonic crystal nanocavities. In addition, we demonstrate that simply shifting two holes away from a line defect is sufficient to achieve an ultrahigh Q value both theoretically and experimentally.
Mixing effect of hole-injecting and hole-transporting materials on the performance and lifetime of organic light-emitting devices
Authors: Kim Youngkyoo , Oh Eonseok , Lim Hyuntaek , Ha Chang-Sik
Published: January 2006

A hole-injecting-transporting layer (HITL), which was prepared by in situ mixing hole-injecting and hole-transporting (HTM) materials upon evaporating in vacuum, has been attempted to reduce the number of organic layers in organic light-emitting devices (OLEDs). OLEDs with HITLs showed lower current density and luminance than those with hole-injecting layer only or hole-transporting layer only, which is attributed to the charge transport change controlled by the HITL nanomorphology made upon mixing. The highest efficiency and the longest lifetime were achieved for the OLED having the HITL with 25% HTM content, while the OLED with HTM only exhibited very poor device lifetime despite the highest efficiency.
Effect of substitutions on the thermoelectric figure of merit of half-Heusler phases at 800 °C
Authors: Culp Slade R. , Poon S. Joseph , Hickman Nicoleta , Tritt Terry M. , Blumm J.
Published: January 2006

The merit of thermally stable MNiSn (M=Ti, Zr, Hf) half-Heusler phases, as n-type thermoelectric materials, for high-temperature power generation has been examined. Sb doping at the Sn site is shown to increase both the figure of merit, ZT, and the temperature at which ZT is maximized. The benefits of increased alloying at the M and Ni sites, on the thermal conductivity and thermoelectric transport properties, have also been investigated. The thermoelectric figure of merit, ZT∼0.8 at T∼800°C, for select Sb-doped MNiSn alloys was found to meet or exceed the industry benchmark set by SiGe alloys.
Signal amplitude and sensitivity of the Kelvin probe force microscopy
Authors: Ouisse T. , Martins F. , Stark M. , Huant S. , Chevrier J.
Published: January 2006

When the tip-sample distance is small, Kelvin probe force microscopy is affected by parametric amplification. This is due to the fact that the electric force has two components; the higher one having a frequency exactly twice as high as the lower. The oscillation amplitude may substantially depart from what is usually expected. Those phenomena are analytically modeled and experimentally shown, and the optimal parameter values which must be used for voltage detection are established.
Injury and Liability Associated with Monitored Anesthesia Care
Authors: Bhananker Sanjay M. , Posner Karen L. , Cheney Frederick W. , Caplan Robert A. , Lee Lorri A. , Domino Karen B.
Published: January 2006

Background

To assess the patterns of injury and liability associated with monitored anesthesia care (MAC) compared with general and regional anesthesia, the authors reviewed closed malpractice claims in the American Society of Anesthesiologists Closed Claims Database since 1990.

Methods

All surgical anesthesia claims associated with MAC (n = 121) were compared with those associated with general (n = 1,519) and regional (n = 312) anesthesia. A detailed analysis of MAC claims was performed to identify causative mechanisms and liability patterns.

Results

MAC claims involved older and sicker patients compared with general anesthesia claims (P < 0.025), often undergoing elective eye surgery (21%) or facial plastic surgery (26%). More than 40% of claims associated with MAC involved death or permanent brain damage, similar to general anesthesia claims. In contrast, the proportion of regional anesthesia claims with death or permanent brain damage was less (P < 0.01). Respiratory depression, after absolute or relative overdose of sedative or opioid drugs, was the most common (21%, n = 25) specific damaging mechanism in MAC claims. Nearly half of these claims were judged as preventable by better monitoring, including capnography, improved vigilance, or audible alarms. On-the-patient operating room fires, from the use of electrocautery, in the presence of supplemental oxygen during facial surgery, resulted in burn injuries in 20 MAC claims (17%).

Conclusion

Oversedation leading to respiratory depression was an important mechanism of patient injuries during MAC. Appropriate use of monitoring, vigilance, and early resuscitation could have prevented many of these injuries. Awareness and avoidance of the fire triad (oxidizer, fuel, and ignition source) is essential to prevent on-the-patient fires.