bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetic theory analysis of laser ablation of carbon: Applicability of one-dimensional models
Authors: Shusser Michael
Published: February 2007

The paper discusses the applicability of a one-dimensional approximation in a recently proposed model of ablation of carbon by a nanosecond laser pulse that considers the kinetics of the process. The model approximates the process as sublimation and combines conduction heat transfer in the target with the gas dynamics of the ablated plume which are coupled through the boundary conditions at the interface. The ablated mass flux and the temperature of the ablating material are obtained from the conservation relations at the interface derived from the moment solution of the Boltzmann equation for arbitrarily strong evaporation. It is shown that in the one-dimensional approximation the surface pressure and the ablation rate are too low and that the ablation rate is restricted most of the time by the kinetic theory limitation on the maximum mass flux that can be attained in a phase-change process. As a consequence, the model overpredicts the surface temperature and the duration of the process. However, it predicts the total ablated mass with good accuracy.
First-order excited state properties in the four-component Hartree-Fock approximation: The excited state electric dipole moments in CsAg and CsAu
Authors: Tellgren Erik , Henriksson Johan , Norman Patrick
Published: February 2007

An implementation of the second-order residue of the quadratic response function is presented in the four-component Hartree-Fock approximation, and the calculation of first-order properties of electronically excited states can thereby be achieved. Results are presented for the excited state electric dipole moments of the valence excited states in CsAg and CsAu. For CsAg, and even more so for CsAu, nonscalar relativistic effects on this property may be substantial, e.g., at the four-component level of theory, the excited-to-ground state dipole moment difference Δμ ranges from 1.994to4.110a.u. for the six components of the 1Π3 state in CsAg, whereas, at the scalar relativistic level of theory, the common value of Δμ is 2.494a.u.
Nuclear electric quadrupole moment of gold
Authors: Belpassi Leonardo , Tarantelli Francesco , Sgamellotti Antonio , Quiney Harry M. , van Stralen Joost N. P. , Visscher Lucas
Published: February 2007

The nuclear quadrupole moment for Au197 has been determined on the base of the state-of-art relativistic molecular calculations. The experimental shifts in the nuclear coupling constants in the series of molecules AuF, XeAuF, KrAuF, ArAuF, (OC)AuF, and AuH have been combined with highly accurate determinations of the electric field gradient (EFG) at the gold nucleus, obtained by molecular relativistic Dirac-Coulomb-Gaunt Hartree-Fock calculations. The electronic correlation contribution to the EFG is included with the CCSD(T) and CCSD-T approaches, also in the four-component framework, using a finite-difference method. In order to estimate the accuracy of their approach the authors have thoroughly investigated the convergence of the results with respect to the basis set employed and the size of the correlated orbital space. The effect of the full Breit electron-electron interaction on the nuclear quadrupole moment of gold has also been considered explicitly for the AuF molecule. They obtain for Au197 a nuclear quadrupole moment of 510±15mb, which deviates by about 7% from the currently accepted muonic value.
Sixfold bond orientational properties of a model liquid crystal in the dimensional crossover of B phases: A computer simulation study
Authors: De Gaetani Luca , Tani Alessandro
Published: February 2007

A wide range of NPT simulations of a bead necklace liquid crystal model in the crystal B, smectic B, smectic A, and nematic phases have been performed. Systems with up to 21600molecules have been studied to observe the behavior of slowly decaying spatial correlation functions. The pair correlation function and its in-plane restriction are consistent with a crystalline phase made of independent two-dimensional crystalline layers. Smectic B phase is studied by the bond orientational pair correlation functions g6 and its extension g6ext. The first reaches a constant value, which seems to rule out a classical hexatic phase. The latter shows a power-law decay within the layers: its typical decay exponent (η6ext) is evaluated. Relationships between multiple harmonics of the C6n order parameter have been evaluated through the whole range of existence of B phases (crystalline and smectic): the extension to the crystalline phase holds and provides an excellent fit of the simulation data.
Symmetry-based constant-time homonuclear dipolar recoupling in solid state NMR
Authors: Tycko Robert
Published: February 2007

Constant-time dipolar recoupling pulse sequences are advantageous in structural studies by solid state nuclear magnetic resonance (NMR) with magic-angle spinning (MAS) because they yield experimental data that are relatively insensitive to radio-frequency pulse imperfections and nuclear spin relaxation processes. A new approach to the construction of constant-time homonuclear dipolar recoupling sequences is described, based on symmetry properties of the recoupled dipole-dipole interaction Hamiltonian under cyclic displacements in time with respect to the MAS sample rotation period. A specific symmetry-based pulse sequence called PITHIRDS-CT is introduced and demonstrated experimentally. C13 NMR data for singly-C13-labeled amino acid powders and amyloid fibrils indicate the effectiveness of PITHIRDS-CT in measurements of intermolecular distances in solids. N15-detected and C13-detected measurements of intramolecular N15–N15 distances in peptides with α-helical and β-sheet structures indicate the utility of PITHIRDS-CT in studies of molecular conformations, especially measurements of backbone ψ torsion angles in peptides containing uniformly N15- and C13-labeled amino acids.
Proposal and achievement of novel structure InN∕GaN multiple quantum wells consisting of 1 ML and fractional monolayer InN wells inserted in GaN matrix
Authors: Yoshikawa A. , Che S. B. , Yamaguchi W. , Saito H. , Wang X. Q. , Ishitani Y. , Hwang E. S.
Published: February 2007

The authors propose and demonstrate the fabrication of InN∕GaN multiple quantum well (MQW) consisting of 1 ML and fractional monolayer InN well insertion in GaN matrix under In-polarity growth regime. Since the critical thickness of InN epitaxy on GaN is about 1 ML and the growth temperature for 1 ML InN insertion can be remarkably higher, the proposed MQW structure can avoid/reduce generation of misfit dislocation, resulting in higher quality MQW-structure nature in principle than former InN-based MQWs. The proposed InN∕GaN MQWs are potentially applicable to room temperature operating excitonic devices working in short-wavelength visible colors.
Diode pumped passive Q switching of Yb3+-doped GdAl3(BO3)4 nonlinear laser crystal
Authors: Brenier Alain , Tu Chaoyang , Zhu Zhaojie , Li Jianfu
Published: February 2007

The authors report the passive Q switching of a diode pumped Yb:GdAl3(BO3)4 (Yb:GAB) laser. The slopes of the average output power are 25% and 39.5% under different experimental conditions. The repetition rates occur in the 1–4.5kHz range and pulse energies of 125 and 165μJ with about 30ns duration are obtained. An experimental comparison with passively Q-switched Nd:GAB laser is provided. A theoretical analysis is performed. It is in reasonable agreement with the experimental data and it is shown to be a useful tool for predicting the optimization of the cavity parameters.
Electronic structure of NPB and BCP molecules probed by x-ray emission spectroscopy
Authors: Seo J. H. , Kim C. Y. , Kang S. J. , Yoo K.-H. , Whang C. N. , Moewes A. , Chang G. S.
Published: February 2007

Soft x-ray absorption and emission spectroscopies have been employed to investigate the electronic structure and chemical bonding of two prototypical molecules, N,N′-bis-(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) and bathocuproine (BCP), which are frequently chosen because of their hole-transporting and hole-blocking properties, respectively. The resulting resonant CKα x-ray emission spectra of these materials reveal different spectral features depending on the resonant excitation energy. According to the N absorption and emission spectra, the contribution of N atoms to the highest occupied and lowest unoccupied molecular orbitals is different for in NPB and in BCP. Detailed knowledge of these materials will allow tailoring charge transport properties of organic devices in order to develop high performance organic light-emitting diodes and photovoltaic cells.
Microfluidic four-roll mill for all flow types
Authors: Lee Joo Sung , Dylla-Spears Rebecca , Teclemariam Nerayo P. , Muller Susan J.
Published: February 2007

A microfluidic four-roll mill device that can cover the entire spectrum of flow types including purely rotational flow was designed using pseudo-three-dimensional simulations. In experiments using high aspect ratio devices etched in silicon, the authors observed the whole range of flow type by changing only the flow rate ratio. This microfluidic four-roll mill device can be applied to examining microdrop deformation and the dynamics of single molecules in a mixed flow or to enhancing mixing efficiency by sinusoidal changes of the inlet flow rate.
Emission of unidentified energy from growing ice crystals
Authors: Shen XiaoFeng
Published: February 2007

Power-compensated differential scanning calorimeter (DSC) was used to quantitatively measure the thermodynamic and kinetic course in the phase transition of water and gallium. When the media between the samples and the temperature sensor were changed, the ratio of the thermal energy given off by freezing water to that absorbed by melting ice was different. A type of unidentified energy was emitted from the growing ice crystals in supercooled water. The emission came off with greater part of latent energy released from the freezing water. Kinetic analysis of the DSC data further confirmed the above conclusion.
Magnetic properties of a melt-textured YBa2Cu3Ox ring with a perpendicular crack
Authors: Chen D.-X. , Pardo E. , Sanchez A. , Bartolomé E. , Puig T. , Obradors X.
Published: February 2007

The dc and ac magnetic properties of a melt-textured YBa2Cu3Ox ring with a perpendicular crack is studied. It is found that the crack behaves as a resistively shunted very long Josephson junction. However, besides the expected edge currents, certain inner currents have to occur in the junction. This anomaly may be a general feature of a very long junction with similar values of Josephson and London penetration depths, which is a case not yet studied theoretically.
Fabrication of deeply undercut GaN-based microdisk structures on silicon platforms
Authors: Vicknesh S. , Tripathy S. , Lin Vivian K. X. , Wang L. S. , Chua S. J.
Published: February 2007

The authors demonstrate the use of a dry releasing technique to achieve deeply undercut GaN-based microdisk structures supported by silicon platforms. Varying dimensions of microdisk structures on silicon posts with large air gaps are fabricated by a XeF2-based dry etching of the underlying silicon material. The residual stress variation in these microdisks is studied by high spectral resolution micro-Raman mapping. Such a fabrication technique may effectively improve the light extraction efficiency from GaN-based microdisk light emitting diodes on silicon substrates.
Local detection of enzymatic ion generation with polycrystalline silicon interdigitated electrodes and its application to biosensing
Authors: de la Rica Roberto , Baldi Antonio , Fernández-Sánchez César
Published: February 2007

Chips containing polycrystalline silicon interdigitated electrodes are modified with the enzyme urease. The sensors are able to detect changes in the resitivity of the solution near their surface, where the enzymatic reaction generates charged species. The electrodes are also grafted with an antigen and queried with different amounts of urease labeled antibody. The response of the modified electrodes is proportional to the amount of enzyme attached to the surface by the biorecognition event, thus validating the assay for biosensing applications.
High speed silicon photonic crystal waveguide modulator for low voltage operation
Authors: Gu Lanlan , Jiang Wei , Chen Xiaonan , Wang Li , Chen Ray T.
Published: February 2007

A high speed compact silicon modulator is experimentally demonstrated to work at a low driving voltage desirable for on-chip applications. As carrier injection is the only practical option for optical modulation in silicon, a lower limit of current density (∼104A∕cm2) exists for achieving gigahertz modulation in the p-i-n diode configuration. Exploiting the slow group velocity of light in photonic crystal waveguides, the interaction length of this Mach-Zehnder interferometer-type silicon modulator is reduced significantly compared to conventional modulators. The required high current density is achieved with a low voltage (2V) by scaling down the interaction length to 80μm.
Conductive mesh based flexible dye-sensitized solar cells
Authors: Fan Xing , Wang Fuzhi , Chu Zengze , Chen Lin , Zhang Chao , Zou Dechun
Published: February 2007

Conductive meshes are used to replace transparent conducting oxides (TCOs), which are commonly used in electrodes of dye-sensitized solar cells (DSSCs). The TCO-less flexible working electrode could be sintered under 400–500°C. A preliminary result that open-circuit voltage (VOC)=650mV, short-circuit current density (ISC)=4.5mA∕cm2, and efficiency (ηAM1.5)=1.49% (100mW∕cm2) is obtained from the liquid-type DSSC. The incident light could be dispersed uniformly inside the electrode. Testing results of the double-counterelectrode cell indicate that the transmission of electrolyte is not the rate-determining step. The dense TiO2 layer is critical in improving the cell’s performances.
Thermoelectric phase diagram in a CaTiO3–SrTiO3–BaTiO3 system
Authors: Yamamoto Masahiro , Ohta Hiromichi , Koumoto Kunihito
Published: February 2007

Herein the authors propose a compositional thermoelectric phase diagram, which includes the density of states effective mass (md*) carrier relaxation time (τ), and thermoelectric power factor (S2σ, where S and σ are Seebeck coefficient and electrical conductivity) for high-quality epitaxial films composed of 20%-Nb-doped CaTiO3–SrTiO3–BaTiO3 solid solutions [(Ca,Sr,Ba)(Ti0.8Nb0.2)O3]. The md* values almost proportionally increase with the in-plane lattice parameter of (Ca,Sr,Ba)(Ti0.8Nb0.2)O3 epitaxial film, while the τ values drastically decrease when Ca and/or Ba are substituted for Sr in Sr(Ti0.8Nb0.2)O3, indicating that the Sr-site substitution negatively affects the thermoelectric performance of Nb-doped SrTiO3.
Effect of intense chirped pulses on the coherent phonon generation in Te
Authors: Misochko O. V. , Dekorsy T. , Andreev S. V. , Kompanets V. O. , Matveets Yu. A. , Stepanov A. G. , Chekalin S. V.
Published: February 2007

The authors have studied the influence of chirped laser pulses on the coherent phonon generation in single crystal Te. They have shown that the pulse chirp affects the amplitude of coherent phonons with A1 symmetry in the case of intense excitation only. By varying the chirp of an intense exciting pulse, the authors demonstrated that negatively chirped pulses are almost twice more effective in the creation of lattice coherence than positively chirped pulses.
Subthreshold channels at the edges of nanoscale triple-gate silicon transistors
Authors: Sellier H. , Lansbergen G. P. , Caro J. , Rogge S. , Collaert N. , Ferain I. , Jurczak M. , Biesemans S.
Published: February 2007

The authors investigate the subthreshold behavior of triple-gate silicon field-effect transistors by low-temperature transport experiments. These three-dimensional nanoscale devices consist of a lithographically defined silicon nanowire surrounded by a gate with an active region as small as a few tens of nanometers down to 50×60×35nm3. Conductance versus gate voltage shows Coulomb blockade oscillations with a large charging energy due to the formation of a small potential well below the gate. According to dependencies on device geometry and thermionic current analyses, the authors conclude that subthreshold channels, a few nanometers wide, appear at the nanowire edges, hence providing an experimental evidence for the corner effect.
Diode-pumped 188fs mode-locked Yb3+:Y2O3 ceramic laser
Authors: Tokurakawa Masaki , Takaichi Kazunori , Shirakawa Akira , Ueda Ken-ichi , Yagi Hideki , Yanagitani Takagimi , Kaminskii Alexander A.
Published: February 2007

The authors have demonstrated a diode-pumped passively mode-locked Yb3+:Y2O3 ceramic laser by use of a semiconductor saturable absorber mirror. 188fs pulses at a center wavelength of 1038nm are obtained. The maximum output power is 220mW at an absorbed pump power of 2.4W with a diffraction-limited beam quality (M2<1.1). This is the shortest pulse generation from Yb-doped sesquioxide lasers and ceramic lasers ever reported.
Fabrication of high-Q chalcogenide photonic crystal resonators by e-beam lithography
Authors: Ruan Yinlan , Kim Myung-Ki , Lee Yong-He , Luther-Davies Barry , Rode Andrei
Published: February 2007

The authors report design, fabrication, and characterization of photonic crystal nanocavities in nonlinear chalcogenide glass using e-beam lithography and chemically assisted ion beam etching. The design indicated that three-hole missing cavities with simultaneously modified side hole position and radii showed the maximum quality factor of 14 000, which was insensitive to the fabrication error of side holes. The fabricated cavities presented coupling dips of −2.6dB at the wavelength of 1550nm and quality factors up to 10 000 when excited with the evanescent field from a tapered optical fiber.
Reduction in feature size of two-photon polymerization using SCR500
Authors: Tan Dengfeng , Li Yan , Qi Fengjie , Yang Hong , Gong Qihuang , Dong Xianzi , Duan Xuanming
Published: February 2007

Fabricated by femtosecond laser pulses at wavelength λ of 780nm, the feature size of two-photon polymerization using SCR500 was reduced to λ∕50. Lines with sub-25-nm width were produced by controlling the incident laser power and the laser focus scan speed up to 700μm∕s. Based on repolymerization between two structures close to each other, the feature size was further reduced to ∼15nm, which demonstrated the potential for three-dimensional nanofabrication with high spatial resolution.
Role of Si on the Al behavior in the reaction layer of Al∕UMo diffusion couples
Authors: Garcés Jorge E. , Bozzolo Guillermo , Hofman Gerard , Rest Jeffrey
Published: February 2007

The basic experimental features characterizing the Al–Si∕U–Mo interface are identified in this atomistic modeling effort, such as the formation of interfacial compounds, Si depletion in the Al matrix near the interface, reduced Al diffusion in the UMo solid solution, and the interaction between Mo and Si which inhibits Al and Si diffusion to the UMo bulk.
Single-crystal field-effect transistors of benzoannulated fused oligothiophenes and oligoselenophenes
Authors: Yamada Koichi , Okamoto Toshihiro , Kudoh Kenichi , Wakamiya Atsushi , Yamaguchi Shigehiro , Takeya J.
Published: February 2007

Recently synthesized benzoannulated fused oligothiophenes and oligoselenophenes are introduced as air-stable organic semiconductors for high-performance organic field-effect transistors. To evaluate electronic mobility intrinsic to the materials, the technique of single-crystal transistors is employed for two representative compounds of benzoannulated pentathienoacene f-B5TB and its selenium analog f-BT3STB. High mobility of approximately 1.1cm2∕Vs is achieved for the selenium compound due to its considerable Se---Se orbital interactions. The materials simultaneously bear features of high mobility and high duration in ambient atmosphere.
Copper phthalocyanine buffer layer to enhance the charge injection in organic thin-film transistors
Authors: Chen Fang-Chung , Kung Li-Jen , Chen Tung-Hsien , Lin Yung-Sheng
Published: February 2007

Copper phthalocyanine (CuPC) has been used as the buffer layer for source and drain electrodes to improve the performance of organic thin-film transistors. The mobility was improved by almost onefold after the modification. By incorporating with CuPC, the contact resistance was reduced, deduced from the line-transfer method. The higher hole current observed in the hole-only diode after adding CuPC further confirms the improvement of hole-injection efficiency. It is concluded that the device improvement is attributed to the reduction of contact resistance, which resulted from the Fermi level pinning at the induced gap states at the Au∕CuPC interface.
Negative differential resistance in tunneling transport through C60 encapsulated double-walled carbon nanotubes
Authors: Li Y. F. , Hatakeyama R. , Kaneko T. , Kato T. , Okada T.
Published: February 2007

The authors report electric transport properties of resonance tunneling field-effect transistors fabricated using C60-filled metallic double-walled carbon nanotubes. The devices exhibit strong resonance tunneling characteristics and the distinct negative differential resistance with high peak-to-valley current ratio about 1300 is observed at room temperature. In particular, at high bias voltages, the tunneling current is completely dominated by the Coulomb oscillation peaks with uniform conductance at room temperature, reflecting a strong single-electron tunneling effect.
Self-folding of single- and multiwall carbon nanotubes
Authors: Zhou W. , Huang Y. , Liu B. , Hwang K. C. , Zuo J. M. , Buehler M. J. , Gao H.
Published: February 2007

Long carbon nanotubes (CNTs) have many important applications. However, long CNTs may self-fold and therefore compromise their applications. The authors have determined the critical length for self-folding as 4πEI∕γ, where EI and γ are the CNT bending stiffness and binding energy, respectively. This simple expression has been verified by atomistic simulations. For single-wall CNTs, the critical self-folding length ranges from a few hundred nanometers to about 2μm. For multiwall CNTs, the critical length increases rapidly with the number of walls and exceeds 10μm for a 14-wall CNT.
Investigation of binary compounds using electron Rutherford backscattering
Authors: Went M. R. , Vos M.
Published: February 2007

High-energy (40keV) electrons, scattering over large angles, transfer a small fraction of their kinetic energy to the target atoms, in the same way as ions do in Rutherford backscattering experiments. The authors show here that this energy transfer can be resolved and used to determine the mass of the scattering atom. In this way information on the surface composition for thicknesses of the order of 10nm can be obtained. The authors refer to this technique as “electron Rutherford backscattering.” In addition the peak width reveals unique information about the vibrational properties (mean kinetic energy) of the scattering atoms. Here the authors demonstrate that the method can be used to identify a number of technologically important compounds.
Multiferroic thin film of Bi2NiMnO6 with ordered double-perovskite structure
Authors: Sakai Maiko , Masuno Atsunobu , Kan Daisuke , Hashisaka Masayuki , Takata Kazuhide , Azuma Masaki , Takano Mikio , Shimakawa Yuichi
Published: February 2007

Epitaxial thin films of Bi2NiMnO6 were synthesized on SrTiO3 substrates by pulsed laser deposition. The resulting film had the rock-salt-type arrangement of Ni2+ and Mn4+ ions in a double-perovskite unit cell. The films clearly showed multiferroic properties, both ferromagnetic behavior with a Curie temperature of about 100K and ferroelectric behavior with a saturated polarization of about 5μC∕cm2.
Laser-induced Ni(Pt) germanosilicide formation through a self-limiting melting phenomenon on Si1−xGex∕Si heterostructure
Authors: Setiawan Y. , Lee P. S. , Pey K. L. , Wang X. C. , Lim G. C. , Tan B. L.
Published: February 2007

Laser-induced Ni(Pt) germanosilicide formation on Si1−xGex∕Si substrate has resulted in the formation of smooth Ni(Pt) germanosilicide/Si interface with minimum interface roughness which is preferred as a contact material. A confined (self-limiting) melting phenomenon occurred during the laser-induced silicidation process at laser fluence of 0.4Jcm−2 (just at the melting threshold of the sample). This phenomenon is caused by significant differences in material properties of Si1−xGex alloy and Si substrates. Formation of highly textured [Ni1−v(Pt)v](Si1−yGey) phase was detected in the sample after 20-pulsed laser thermal annealing at 0.4Jcm−2. The formation mechanism of the Ni(Pt) monogermanosilicide is discussed.
Phase diagrams for growing ordered heteroepitaxial quantum dots and quantum rings by surface prepatterning
Authors: Liu P. , Zhang Y. W. , Lu C.
Published: February 2007

Three-dimensional computer simulations are performed to obtain the phase diagrams for heteroepitaxially grown ordered quantum dots and quantum rings by surface prepatterning. Concave patterning in a squared array may lead to the formation of ordered dots, whereas convex patterning in a squared array may initially lead to the formation of ordered quantum rings, then a transition into quantum dots with further growth. The evolution of the surface chemical potential during growth explains the formation of the ordered surface structures.
Laser welding of a single tungsten oxide nanotip on a handleable tungsten wire: A demonstration of laser-weld nanoassembly
Authors: She J. C. , An S. , Deng S. Z. , Chen Jun , Xiao Z. M. , Zhou J. , Xu N. S.
Published: February 2007

The authors demonstrate that individual nanotips (W18O49) may be laser welded onto the supporting microtip. The nanotip-microtip assembly can be handheld or ready for further manual manipulation, and thus is very useful for individual nanowire’s characterization, selection, and applications in nanoprobe analysis, nano-optical and nanoelectronic devices, and biostudy. Well mechanical and electrical connections are shown between the nanotip-microtip. Field emission characterization shows that the welded nanotip is a promising candidate for point electron source application.
Flame synthesis and characterization of rare-earth (Er3+, Ho3+, and Tm3+) doped upconversion nanophosphors
Authors: Qin Xiao , Yokomori Takeshi , Ju Yiguang
Published: February 2007

Rare-earth doped yttria upconversion nanophosphors were synthesized using a single-step gas-phase flame synthesis method. The phosphors were characterized by x-ray diffractometry, transmission electron microscopy, and fluorescence spectroscopy. The dependence of multiphoton emissions on excitation power was examined. The results show that particle size, morphology, and photoluminescence intensity are strongly affected by flame temperature. The as-prepared nanophosphors are mostly single crystallites with an average size less than 30nm. Under laser diode excitation, bright blue, green, and red emissions are visible from these phosphors which show potential applications in biological imaging and photodynamic therapy.
Comparison of the vacuum-ultraviolet radiation response of HfO2∕SiO2∕Si dielectric stacks with SiO2∕Si
Authors: Upadhyaya G. S. , Shohet J. L.
Published: February 2007

Vacuum ultraviolet (vuv) emitted during plasma processing degrades dielectrics by generating electron-hole pairs. VUV-induced charging of SiO2∕p-Si and HfO2∕SiO2∕p-Si dielectric stacks are compared. For SiO2∕p-Si, charging is observed for photon energies >15eV by ionization of dielectric atoms from photoinjected electrons. In HfO2∕SiO2∕p-Si, charging is observed for photon >10eV and is due to ionization by photoinjected electrons and by H+ trapping in the HfO2∕SiO2 bulk. Hydrogen appears during annealing at the Si–SiO2 interface forming Si–H, which, during irradiation, is depassivated by photoinjected electrons. The authors conclude that dielectric charging in thin oxides (<10nm) occurs more easily in HfO2∕SiO2 than in SiO2.
Single photon emission from an InGaAs quantum dot precisely positioned on a nanoplane
Authors: Hsieh Tung-Po , Chyi Jen-Inn , Chang Hsiang-Szu , Chen Wen-Yen , Hsu Tzu Min , Chang Wen-Hao
Published: February 2007

This work demonstrates single photon emissions from a site-controlled quantum dot (QD) grown on a self-constructed nanoplane. The size of the nanoplane on the micron-sized multifacet structure is accurately controlled by a low surface reducing rate (∼16nm∕min). Single QD spectral lines were resolved and identified. The antibunching behavior reveals that single photons are emitted from the positioned QD.
Imaging deep trap distributions by low vacuum scanning electron microscopy
Authors: Toth Milos , Knowles W. Ralph , Phillips Matthew R.
Published: February 2007

The distribution of deep traps in a bulk dielectric (Al2O3) is imaged by low vacuum scanning electron microscopy (LVSEM). The image contrast corresponds to spatial variations in radiation-induced, field-enhanced conductivity. A methodology is presented for identification of such contrast, the behavior of which is explained by a model of charge generation and transport in dielectrics imaged by LVSEM. The technique presented is applicable to studies of charge traps in dielectrics, device failure modes, and contrast mechanisms in electron microscopy.
N,N-Dialkyl-N′-Chlorosulfonyl Chloroformamidines in Heterocyclic Synthesis. IV. 3-Dialkylamino-1,1,8-trioxo-1H-1λ6-pyrano[3,4-e][1,4,3]oxathiazines
Authors: Cablewski Teresa , Francis Craig L. , Liepa Andris J.
Published: February 2007

N,N-dialkyl-N′-chlorosulfonylchloroformamidines 1 reacted regioselectively with 4-hydroxy-2-pyrone derivatives 2 to give 3-dialkylamino-1,1,8-trioxo-1H-1λ6-pyrano[3,4-e][1,4,3]oxathiazines 3. Dichloride 1b reacted regioselectively with 1,3-dimethylbarbituric acid 10 to give 3-diethylamino-5,7-dimethyl-1,1,6,8-tetraoxo-1H-1λ6-pyrimido[5,4-e][1,4,3]oxathiazine 11. The compounds 3 and 11 are derivatives of new ring systems.
Structural and Thermal Characterization of Cyclodextrin - Suprofen Complexes
Authors: Dean Pamela M.
Published: February 2007

Suprofen, α-methyl-4-(2-thienylcarbonyl)benzeneacetic acid, a non-steroidal anti-inflammatory drug (NSAID), forms an inclusion complex with β-cyclodextrin of formula (β-cyclodextrin)2·(suprofen)·20H2O 1 and with TRIMEB (a permethylated β-cyclodextrin) of formula (β-cyclodextrin)·(suprofen)·0H2O 2. These species were investigated by thermal analysis techniques (HSM, TGA, DSC), powder X-ray diffraction (PXRD), and single-crystal X-ray diffraction at 173 K. Thermal analysis of 1 revealed dehydration followed by decomposition at 311.0°C, and only melting at 161.0°C for 2. The host-to-drug stoichiometric ratio was determined by UV spectrophotometry, and found to be 2:1 for 1 and 1:1 for 2. Single-crystal X-ray methods revealed that 1 crystallizes in the orthorhombic space group C2221, with a 19.0409(1), b 24.1949(2), c 32.4707(2) Å, and Z 4 formula units. Complex 2 crystallizes in the orthorhombic space group P212121, with a 15.389(1), b 21.051(1), c 27.027(2) Å, and Z 4 formula units. The (S)-enantiomer of suprofen was preferentially included in both characterized crystals.
Microwave-Assisted Mild Conversion of Natural Dihydrotagetone into 5-Isobutyl-3-methyl-4,5-dihydro-2(3H)-furanone, an Analogue of Whisky Lactone
Authors: Sinha Arun K. , Joshi Bhupendra P. , Sharma Anuj , Kumar Vinod , Acharya Ruchi
Published: February 2007

A microwave-assisted mild protocol is developed for the synthesis of 5-isobutyl-3-methyl-4,5-dihydro-2(3H)-furanone, an analogue of whisky lactone, from dihydrotagetone, an acyclic monoterpenoid obtained from Tagetes minuta. The methodology involved oxidation of dihydrotagetone in the presence of sodium metaperiodate/potassium permanganate/alumina to give 2,6-dimethyl-4-oxo-heptanoic acid, which upon reduction and subsequent lactonization provided 5-isobutyl-3-methyl-4,5-dihydro-2(3H)-furanone. The reaction is also conducted under conventional conditions and is compared with the microwave method.
Microwave-Expedited One-Pot, Two-Component, Solvent-Free Synthesis of Functionalized Pyrimidines
Authors: Goswami Shyamaprosad , Jana Subrata , Dey Swapan , Adak Avijit Kumar
Published: February 2007

The synthesis of a series of diversely substituted pyrimidines under solvent-free conditions in good yields is described. Under microwave irradiation, a variety of nucleophilic substrates containing the N–C–N unit with β-dicarbonyl compounds, ethyl cyanoacetate, malononitrile, and chalcones was cyclized to give pyrimidines. A combinatorial type approach for a one-step synthesis has been developed where a ring-closing condensation is followed by spontaneous aromatization to afford 28 functionalized and aryl/alkyl substituted pyrimidines.
Structural Characterization of a Pentapeptide Derived from a Novel Carbohydrate α-Amino Acid
Authors: Scaffidi Adrian , Skelton Brian W. , Stick Robert V. , White Allan H.
Published: February 2007

Subsequent to our previous report describing several novel carbohydrate α-amino acid dipeptides (and the structural characterization of one of those), and their extension to higher peptides, a synchrotron radiation study of one of those—a pentapeptide—showing its structure to be a well-defined helical array in each of two independent molecules, stabilized by internal hydrogen bonds, is reported.
Thiazolamide - Ascorbic Acid Conjugate: a γ-Secretase Inhibitor with Enhanced Blood - Brain Barrier Permeation
Authors: Laras Younes , Sheha Mahmoud , Pietrancosta Nicolas , Kraus Jean-Louis
Published: February 2007

One of the major problems of the current therapy of brain diseases such as Alzheimer’s disease is the distribution of drugs to the central nervous system (CNS). Difficulties in traversing the blood–brain barrier (BBB) often impair the efficacy of valuable drugs. Using the ascorbic acid–drug conjugate concept, we have succeeded in developing a thiazolamide conjugate that shows an improved pharmacokinetic profile compared to the parent thiazolamide previously reported.
Molecular simulation studies on the adsorption of mercuric chloride
Authors: Kotdawala R. R. , Kazantzis Nikolaos , Thompson Robert W.
Published: February 2007

Environmental context. The Clean Air Act amendments of 1990 identified mercury and associated compounds as hazardous air pollutants of particular concern to human health and the environment. Coal-fired power plants and municipal solid waste incinerators are significant sources of mercury-containing emissions. Adsorption represents a common technique used to alleviate mercury contamination. The present study uses molecular simulations to study the correlation between key surface characteristics of the adsorbent and its mercury capturing ability with a view to the selection and design of novel adsorbents.
Abstract. In the present study, Monte Carlo simulations were used to model the physical adsorption of oxidised mercury (mercuric chloride) by zeolite NaX and activated carbon in the temperature range of 400–500 K. In particular, we considered zeolite NaX with spherical cavities and sodium cations, as well as activated carbon with slit carbon pores and hydroxyl, carboxyl and carbonyl sites, and layers of calcium hydroxide. The adsorption capacity and affinity of zeolite NaX were compared with those displayed by activated carbon with different acid sites and calcium hydroxide by assessing the impact on mercuric chloride adsorption within a practical range of magnitudes of the electrostatic interactions considered, namely charge-induced dipole and charge-quadrupole interactions, as well as dispersion interactions.
Potassium and sodium relations in salinised barley tissues as a basis of differential salt tolerance
Authors: Chen Zhonghua , Zhou Meixue , Newman Ian A. , Mendham Neville J. , Zhang Guoping , Shabala Sergey
Published: February 2007

A large-scale glasshouse trial, including nearly 70 barley cultivars (5300 plants in total), was conducted over 2 consecutive years to investigate plant physiological responses to salinity. In a parallel set of experiments, plant salt tolerance was assessed by non-invasive microelectrode measurements of net K+ flux from roots of 3-day-old seedlings of each cultivar after 1 h treatment in 80 mm NaCl as described in our previous publication (Chen et al. 2005). K+ flux from the root in response to NaCl treatment was highly (P < 0.001) inversely correlated with relative grain yield, shoot biomass, plant height, net CO2 assimilation, survival rate and thousand-seed weight measured in glasshouse experiments after 4–5 months of salinity treatment. No significant correlation with relative germination rate or tillering was found. In general, 62 out of 69 cultivars followed an inverse relationship between K+ efflux and salt tolerance. In a few cultivars, however, high salt tolerance (measured as grain yield at harvest) was observed for plants showing only modest ability to retain K+ in the root cells. Tissue elemental analysis showed that these plants had a much better ability to prevent Na+ accumulation in plant leaves and, thus, to maintain a higher K+/Na+ ratio. Taken together, our results show that a plant’s ability to maintain high K+/Na+ ratio (either retention of K+ or preventing Na+ from accumulating in leaves) is a key feature for salt tolerance in barley.
Leaf anatomy, gas exchange and photosynthetic enzyme activity in Flaveria kochiana
Authors: Sudderth Erika A. , Muhaidat Riyadh M. , McKown Athena D. , Kocacinar Ferit , Sage Rowan F.
Published: February 2007

Flaveria (Asteraceae) is one of the few genera known to contain both C3 and C4 species, in addition to numerous biochemically-intermediate species. C3-C4 and C4-like intermediate photosynthesis have arisen more than once in different phylogenetic clades of Flaveria. Here, we characterise for the first time the photosynthetic pathway of the recently described species Flaveria kochiana B.L. Turner. We examined leaf anatomy, activity and localisation of key photosynthetic enzymes, and gas exchange characteristics and compared these trait values with those from related C4 and C4-like Flaveria species. F. kochiana has Kranz anatomy that is typical of other C4 Flaveria species. As in the other C4 lineages within the Flaveria genus, the primary decarboxylating enzyme is NADP-malic enzyme. Immunolocalisation of the major C4 cycle enzymes, PEP carboxylase and pyruvate, orthophosphate dikinase, were restricted to the mesophyll, while Rubisco was largely localised to the bundle sheath. Gas exchange analysis demonstrated that F. kochiana operates a fully functional C4 pathway with little sensitivity to ambient oxygen levels. The CO2 compensation point (2.2 µbar) was typical for C4 species, and the O2-response of the CO2 compensation point was the same as the C4 species F. trinervia. Notably, F. vaginata (B.L. Robinson & Greenman), a putative C4-like species that is the nearest relative of F. kochiana, had an identical response of the CO2 compensation point to O2. Furthermore, F. vaginata, exhibited a carbon isotope ratio (–15.4‰) similar to C4 species including F. australasica Hooker, F. trinervia Spreng. C. Mohr and the newly characterised F. kochiana. F. vaginata could be considered a C4 species, but additional studies are necessary to confirm this hypothesis. In addition, our results show that F. kochiana uses an efficient C4 cycle, with the highest initial slope of the A/Ci curve of any C4 Flaveria species.
Substrate binding and protein conformational dynamics measured by 2D-IR vibrational echo spectroscopy
Authors: Finkelstein Ilya J. , Ishikawa Haruto , Kim Seongheun , Massari Aaron M. , Fayer M. D.
Published: February 2007

Enzyme structural dynamics play a pivotal role in substrate binding and biological function, but the influence of substrate binding on enzyme dynamics has not been examined on fast time scales. In this work, picosecond dynamics of horseradish peroxidase (HRP) isoenzyme C in the free form and when ligated to a variety of small organic molecule substrates is studied by using 2D-IR vibrational echo spectroscopy. Carbon monoxide bound at the heme active site of HRP serves as a spectroscopic marker that is sensitive to the structural dynamics of the protein. In the free form, HRP assumes two distinct spectroscopic conformations that undergo fluctuations on a tens-of-picoseconds time scale. After substrate binding, HRP is locked into a single conformation that exhibits reduced amplitudes and slower time-scale structural dynamics. The decrease in carbon monoxide frequency fluctuations is attributed to reduced dynamic freedom of the distal histidine and the distal arginine, which are key residues in modulating substrate binding affinity. It is suggested that dynamic quenching caused by substrate binding can cause the protein to be locked into a conformation suitable for downstream steps in the enzymatic cycle of HRP.
Experiments with probe masses
Authors: Braginsky V. B.
Published: February 2007

It is reasonable to regard the experiments performed by C. Coulomb and H. Cavendish in the end of the 18th century as the beginning of laboratory experimental physics. These outstanding scientists have measured forces (accelerations) produced by electric charges and by gravitational “charges” on probe masses that were attached to torque balance. Among the variety of different research programs and projects existing today, experiments with probe masses are still playing an important role. In this short review, the achieved and planned sensitivities of very challenging LIGO (Laser Interferometer Gravitational wave Observatory) and LISA (Laser Interferometer Space Antennae) projects are described, and a list of nonsolved problems is discussed as well. The role of quantum fluctuations in high precision measurements is also outlined. Apart from these main topics, the limitations of sensitivity caused by cosmic rays and the prospects of clock frequency stability are presented.
Multiscale responses of microbial life to spatial distance and environmental heterogeneity in a patchy ecosystem
Authors: Ramette Alban , Tiedje James M.
Published: February 2007

Spatial distance (SD) and environmental heterogeneity (EH) are currently thought to represent major factors shaping genetic variation and population abundance, but their relative importance is still poorly understood. Because EH varies at multiple spatial scales, so too are microbial variables expected to vary. The determination of SD × EH interactions at multiple scales is, however, not a trivial exercise, especially when one examines their effects on microbial abundance and genomic similarities. Here we assessed those interactions at all scales perceptible in a patchy environment composed of known plant species and of heterogeneous soil physical and chemical parameters. For free-living, soil-borne
Burkholderia ambifaria
, genomic similarities responded to most of the spatial scales that the experimental sampling scheme could reveal, despite limited dispersal of the individuals. Species abundance and community composition were, however, responding to much smaller scales more consistent with local responses to EH. Our results suggest that whole-genome similarities may reflect the simultaneous effects of both SD and EH in microbial populations, but the pure effects of each factor only contributed to <2% of the total genetic variation. The large amount of unexplained variation that remains after considering most environmental, spatial, and biological interactions is then posited to be the result of noise introduced by unmeasured environmental and spatial variability, sampling effects, and neutral ecological drift.
Gene expression and functional evidence of epithelial-to-mesenchymal transition in papillary thyroid carcinoma invasion
Authors: Vasko Vasily , Espinosa Allan V. , Scouten William , He Huiling , Auer Herbert , Liyanarachchi Sandya , Larin Alexander , Savchenko Victoria , Francis Gary L. , de la Chapelle Albert , Saji Motoyasu , Ringel Matthew D.
Published: February 2007

Papillary thyroid carcinomas (PTCs) that invade into local structures are associated with a poor prognosis, but the mechanisms for PTC invasion are incompletely defined, limiting the development of new therapies. To characterize biological processes involved in PTC invasion, we analyzed the gene expression profiles of microscopically dissected intratumoral samples from central and invasive regions of seven widely invasive PTCs and normal thyroid tissue by oligonucleotide microarray and performed confirmatory expression and functional studies. In comparison with the central regions of primary PTCs, the invasive fronts overexpressed TGF β, NFκB and integrin pathway members, and regulators of small G proteins and CDC42. Moreover, reduced levels of mRNAs encoding proteins involved in cell–cell adhesion and communication were identified, consistent with epithelial-to-mesenchymal transition (EMT). To confirm that aggressive PTCs were characterized by EMT, 34 additional PTCs were examined for expression of vimentin, a hallmark of EMT. Overexpression of vimentin was associated with PTC invasion and nodal metastasis. Functional,
in vitro
studies demonstrated that vimentin was required both for the development and maintenance of a mesenchymal morphology and invasiveness in thyroid cancer cells. We conclude that EMT is common in PTC invasion and that vimentin regulates thyroid cancer EMT
in vitro
.
Prion species barrier between the closely related yeast proteins is detected despite coaggregation
Authors: Chen Buxin , Newnam Gary P. , Chernoff Yury O.
Published: February 2007

Prions are self-perpetuating and, in most cases, aggregation-prone protein isoforms that transmit neurodegenerative diseases in mammals and control heritable traits in yeast. Prion conversion requires a very high level of identity of the interacting protein sequences. Decreased transmission of the prion state between divergent proteins is termed “species barrier” and was thought to occur because of the inability of divergent prion proteins to coaggregate. Species barrier can be overcome in cross-species infections, e.g., from “mad cows” to humans. We studied the counterparts of yeast prion protein Sup35, originated from three different species of the
Saccharomyces sensu stricto
group and exhibiting the range of prion domain divergence that overlaps with the range of divergence observed among distant mammalian species. All three proteins were capable of forming a prion in
Saccharomyces cerevisiae
, although prions formed by heterologous proteins were usually less stable than the endogenous
S. cerevisiae
prion. Heterologous Sup35 proteins coaggregated in the
S. cerevisiae
cells. However,
in vivo
cross-species prion conversion was decreased and
in vitro
polymerization was cross-inhibited in at least some heterologous combinations, thus demonstrating the existence of prion species barrier. Moreover, the barrier between the
S. cerevisiae
protein and its
Saccharomyces paradoxus
and
Saccharomyces bayanus
counterparts was asymmetric both
in vivo
and
in vitro
. Our data show that a decreased cross-species prion transmission does not necessarily correlate with a lack of cross-species coaggregation, suggesting that species-specificity of prion transmission is controlled at the level of conformational transition rather than coaggregation.