bluuebunny/crossref_metadata_2025 huggingface dataset:
Test Order Effects of Computerized Dynamic Posturography and Calorics
Authors: Bernstein Jill , Burkard Robert
Published: June 2009

Purpose

To determine whether there is a test order effect of the caloric subtest of videonystagmography on the Sensory Organization Test (SOT) of computerized dynamic posturography, and to assess the learning effect of multiple posturography test sessions on the SOT score.

Method

Scores on the 6 SOT conditions before and after caloric testing were compared for 10 participants age 18–36 years. Four SOT sessions were completed prior to caloric testing to assess the presence of a learning effect and establish precaloric baseline SOT scores. All participants had normal vestibular systems with no history of dizziness or imbalance.

Results

Caloric testing had a significant effect on the equilibrium score for only 1 of 6 test conditions. While meeting statistical significance, the actual change in score for this condition was very small. Equilibrium scores improved for the more difficult test conditions between the 1st and 2nd SOT sessions.

Conclusion

Results indicate that there are minimal test order effects of calorics on the SOT. Results confirm that a significant improvement in score for more challenging test conditions occurs between SOT Sessions 1 and 2 as a result of learning. Therefore, clinicians must be cautious when using posturography to monitor patient improvement.
Patient-Centered Tinnitus Management Tool: A Clinical Audit
Authors: Aazh Hashir , Moore Brian C. J. , Roberts Pete
Published: June 2009

Purpose

To evaluate the impact of an educational poster describing treatment options available to patients experiencing tinnitus.

Method

A patient-centered tinnitus management tool (PCTMT) was developed in the form of an educational poster that encouraged patients to decide how they wanted to deal with their tinnitus from the following options: (a) ignore the tinnitus and forget about it, (b) use a sound generator, (c) undertake tinnitus counseling with an expert, or (d) deal with the tinnitus using hearing aids (in the case of tinnitus and hearing loss). Fifty-five patients who were referred to the audiology department of a London hospital from the ENT department for tinnitus counseling were asked to read the PCTMT and to choose the option(s) that suited them the best.

Results

Forty-two percent of the patients wished to undertake counseling, 9% decided to try to ignore their tinnitus without help, 26% wanted to deal with their tinnitus with the help of a sound generator, and 24% decided to use hearing aids.

Conclusions

The PCTMT reduced the number of patients who would otherwise have been referred for tinnitus counseling by 58%. This reduced the length of the waiting list and increased the time available for counseling of those patients who wanted it.
Investigation of dynamic glass transitions and structural transformations in cryovacuum condensates of ethanol
Authors: Aldiyarov A. , Aryutkina M. , Drobyshev A. , Kaikanov M. , Kurnosov V.
Published: June 2009

An IR spectrometric investigation of the dynamic glass transition of ethanol from the rotationally disordered crystal to the orientationally disordered crystal is carried out. The samples considered are thin films formed from the gas phase at a substrate temperature of T=16K. The measurements are performed using the experimental apparatus which has been described in detail in our recent work. The sample thickness was d=2μm, and the typical rate of annealing is approximately 10K∕min. The results are compared with the phase diagram of solid ethanol proposed by M.A. Ramos et al. We observe good agreement between the temperature intervals of existence of the amorphous and crystalline states. The low-temperature amorphous phase (12–70K) is described by the present authors as amorphous solid ethanol by analogy with the amorphous solid water.
Phase transitions in clusters
Authors: Berry R. S. , Smirnov B. M.
Published: June 2009

General concepts of cluster phase transitions are reviewed as well as the cluster behavior near the melting point. Configuration excitation determines the nature of the cluster phase transitions, but a significant contribution to the entropy jump is given by thermal motion of atoms that allows one to characterize the phase transition through thermal atom motion in the Lindemann and other criteria. Phase coexistence near the melting point is a peculiarity of non-large clusters. The void concept of phase transitions with a void as an elementary configuration excitation allows one to describe the phase transition for clusters and macroscopic atomic systems. Phase transitions in metal clusters resemble those in clusters with pairwise atomic interactions, but their numerical parameters are different because of a large number of isomers and an additional electron degree of freedom. Cluster models are convenient for the analysis of macroscopic atomic systems. They allow us to understand the nature of glassy transitions and the reason for the absence of a stable infinite crystal lattice for gases at zero temperature and high pressure.
Heat transfer in solid halogenated methanes: trifluoromethane
Authors: Konstantinov V. A. , Revyakin V. P. , Sagan V. V.
Published: June 2009

The isochoric thermal conductivity of solid trifluoromethane is investigated for three samples of different densities in the interval from 75K to the onset of melting. The isochoric thermal conductivity first decreases with increasing temperature, passes through a minimum at T∼100K, and then starts to increase slowly. The results obtained are compared with the thermal conductivities of other freons of the methane series. The correlation between the temperature dependence of isochoric thermal conductivity and the character of the rotational molecular motion is discussed.
Evidence for high saturation of porous amorphous carbon films by noble gases
Authors: Krainyukova N. V.
Published: June 2009

Results of the electron diffraction study of Kr and Xe deposits on amorphous porous carbon substrates are reported. We have observed mixtures of crystallites typical of condensates formed at such substrates at low deposition temperatures. However, in the warming process at temperatures about three to five degrees below the sublimation point characteristic of flat substrates, the diffraction patterns demonstrate that large crystallites gradually disappear and a highly disordered matter forms. Such transformed samples are kept inside substrates several dozens degrees above the sublimation points which are typical of these substances on flat (e.g., metallic) substrates. We ascribe these features to specificity of composites formed from noble gases strongly bonded inside porous carbon matrices due to capillary filling at temperatures close to the sublimation points.
Localized electrons in dense heavy noble gases
Authors: Nazin S. , Shikin V.
Published: June 2009

The paper addresses counterintuitive behavior of electrons injected into dense cryogenic media with negative scattering length a0. Instead of the expected polaronic effect (formation of density enhancement clusters) which should substantially reduce the electron mobility, an opposite picture is observed: with increasing ∣a0∣ (the trend taking place for inert gases with the growth of atomic number) and the medium density, the electrons remain practically free. An explanation of this behavior is provided based on consistent accounting for the nonlinearity of electron interaction with the gaseous medium in the gas atom number density.
Cryocrystal phase transitions applied as temperature standards
Authors: Szmyrka-Grzebyk A. , Kowal A.
Published: June 2009

International temperature scales define several fixed points, the temperature values of which are determined with a very high precision. Some of them, which lie in a low-temperature range, are called gaseous fixed points because the reference substances under normal conditions—in a room-temperature range—are in a gaseous state. When occurring in a solid state at low temperature these reference substances are called cryocrystals or quantum crystals by physicists. These substances play an important role in a standard thermometry. The triple point of argon, oxygen, neon, and hydrogen are primary fixed points of the International Temperature Scale of 1990 (ITS-90) [H. Preston-Thomas, Metrologia 27, 3 (1990)].1 The triple points of nitrogen, methane, and carbon dioxide are secondary fixed points of the scale [R. E. Bedford, G. Bonnier, H. Maas, and F. Pavese, Metrologia 33, 133 (1996)].2 Also, the solid-solid phase transitions in the cryocrystals are secondary fixed points of the scale. The highest-accuracy methods of measurements applied in standard thermometry can be used to determine, with a very small uncertainty, the phase transition temperatures and their reproducibility and stability. The reproducibility and stability of the transition temperature are the most important factors deciding about usefulness of these points in thermometry. Using the highest-accuracy methods, better than 1mK, which at present are used only in metrology, can give new information about the nature and properties of the investigated substances, also of importance for physicists.
Electron traps in solid Xe
Authors: Khyzhniy I. V. , Uyutnov S. A. , Savchenko E. V. , Gumenchuk G. B. , Ponomaryov A. N. , Bondybey V. E.
Published: June 2009

Correlated real-time measurements of thermally stimulated luminescence and exoelectron emission from solid Xe pre-irradiated with an electron beam are performed. The study enables us to distinguish between surface and bulk traps in solid Xe and to identify a peak related to electronically induced defects. The activation energy corresponding to annihilation of these defects is estimated by the following methods: the method of different heating rates, the initial-rise method, and the curve cleaning technique with fitting of the thermally stimulated luminescence glow curve.
Optical constants of evaporation-deposited silicon monoxide films in the 7.1–800 eV photon energy range
Authors: Fernández-Perea Mónica , Vidal-Dasilva Manuela , Larruquert Juan I. , Aznárez José A. , Méndez José A. , Gullikson Eric , Aquila Andy , Soufli Regina
Published: June 2009

The transmittance of silicon monoxide films prepared by thermal evaporation was measured from 7.1 to 800 eV and used to determine the optical constants of the material. SiO films deposited onto C-coated microgrids in ultrahigh vacuum conditions were measured in situ from 7.1 to 23.1 eV. Grid-supported SiO films deposited in high vacuum conditions were characterized ex situ from 28.5 to 800 eV. At each photon energy, transmittance, and thickness data were used to calculate the extinction coefficient k. The obtained k values combined with data from the literature, and with interpolations and extrapolations in the rest of the electromagnetic spectrum provided a complete set of k values that was used in a Kramers–Kronig analysis to obtain the real part of the index of refraction, n. Two different sum-rule tests were performed that indicated good consistency of the data.
Liquid-like phase formation in Gd2Zr2O7 by extremely ionizing irradiation
Authors: Zhang Jiaming , Lang Maik , Lian Jie , Liu Jie , Trautmann Christina , Della-Negra Serge , Toulemonde Marcel , Ewing Rodney C.
Published: June 2009

Isometric Gd2Zr2O7 with the ordered, pyrochlore structure has an extremely high resistance to radiation-induced amorphization. Ion-beam irradiations at keV to GeV energies result in a disordered, defect-fluorite structure that remains crystalline to very large fluences. However, we report liquid-like phase formation of droplet-like surface hillocks and quenched molten tracks in Gd2Zr2O7. The extremely high energy density of 12-MeV C60 clusters creates tracks with substantial volumes of amorphous material, accompanied by the formation of nanocrystals of the disordered, defect-fluorite structure. This is the first evidence of irradiation-induced amorphization of Gd2Zr2O7. In contrast, irradiation of Gd2Zr2O7 pyrochlore with swift heavy ions of U resulted in an order-disorder transformation to defect-fluorite without any evidence of amorphization. Thermal-spike calculations highlight the dominance of the effect of deposited energy density, controlled by the projectile velocity, as compared with the energy loss.
Vertical alignment of liquid crystals on a fully oxidized HfO2 surface by ion bombardment
Authors: Lee Won-Kyu , Oh Byeong-Yun , Lim Ji-Hun , Park Hong-gyu , Kim Byoung-Yong , Na Hyun-Jae , Seo Dae-Shik
Published: June 2009

High-performance liquid crystals (LCs) driven at a 0.9 V threshold were demonstrated on very thin HfO2 films with vertical (homeotropic) alignment by ion bombardment. Atomic layer deposition was used to obtain LC orientation on ultrathin high-quality films of double-layer HfO2/Al2O3. X-ray photoelectron spectroscopy indicated that full oxidization of HfO2 film surfaces was induced by ion bombardment, shifting the Hf 4f spectra to lower binding energies. The increased intensities of the Hf 4f peaks after ion bombardment confirmed that nonstoichiometric HfOx was converted to the fully oxidized HfO2 surfaces.
Electrostatic condition for the termination of the opposite face of the slab in density functional theory simulations of semiconductor surfaces
Authors: Krukowski Stanisław , Kempisty Paweł , Strąk Paweł
Published: June 2009

It is proved that in slab simulations of uniform semiconductor surfaces the electric field in the vacuum space should vanish. In standard approach this condition was achieved by introduction of the dipole correction [J. Neugebauer and M. Scheffler, Phys. Rev. B 46, 16067 (1992)]. An effective and stable method of exact solution of Poisson equation, based on Laplace correction, which attains the zero field condition in the vacuum, is described. The dipole correction to the slab energy is removed. Additionally, a method of the control of electric field within the slab is introduced, applicable in direct simulations of Fermi level influence on the properties of semiconductor surfaces.
Numerical study of Rayleigh wave transmission through an acoustic barrier
Authors: Lamkanfi Ebrahim , Declercq Nico F. , Van Paepegem Wim , Degrieck Joris
Published: June 2009

Recent experiments [N. F. Declercq and E. Lamkanfi, Appl. Phys. Lett. 93, 2 (2008)] showed evidence of the relationship between the generation of leaky Rayleigh waves and the formation of the two reflected lobes and a null strip for bounded beam incidence at the Rayleigh angle. The evidence was based on an experimental setup using a sound barrier on a liquid solid interface. The current paper presents a finite element investigation of the experiments and confirms the earlier conclusions. In addition, unexplained experimental observations are clarified. Furthermore, a detailed investigation of the influence of the bonding properties between the barrier and the solid on the observed radiation patterns is achieved, which is of broader importance to the nondestructive characterization of bonding in general.
Effect of the gap on discharge characteristics of the three-electrode trigatron switch
Authors: Zhu H. H. , Huang L. , Cheng Z. H. , Yin J. , Tang H. Q.
Published: June 2009

A mathematical model was proposed to calculate the breakdown time based on the theoretical analysis of the discharging mechanism for three-electrode trigatron switch with the trigger electrode located inside the main electrode. The simulation result demonstrates that the breakdown time decreases with operating voltage increasing. The dependence on voltage is weak for the high voltages. A threshold voltage exists and threshold voltage increases with the main gap. If the charging voltage is enough high, the breakdown time is about same for both main gaps. Experimental result agrees with the simulation result very well.
Surface modification of polyhedral oligomeric silsesquioxane block copolymer films by 157 nm laser light
Authors: Sarantopoulou Evangelia , Kollia Zoe , Cefalas Alkiviadis Constantinos , Siokou Ageliki Elina , Argitis Panagiotis , Bellas Vassilios , Kobe Spomenka
Published: June 2009

Thin films of ethyl polyhedral oligomeric silsesquioxane (ethyl-POSS) containing polymers at different compositions were chemically modified using laser irradiation at 157 nm. The irradiation caused photodissociation of C–O and C–H bonds followed by the formation of new chemical bonds. The content of Si–O and C–O bonds increased, as did the surface hardness. Vacuum ultraviolet (VUV) absorption, mass spectrometry, x-ray photoelectron spectroscopy, and atomic force microscopy imaging and indentation were used to evaluate the effects of the 157 nm irradiation. The chemical modification was restricted to a thin surface layer. The layer depth was determined by the penetration depth of the 157 nm VUV photons inside the thin copolymer layer. With prolonged VUV irradiation, the absorbance of the polymers increased, eventually becoming saturated. The chemical changes were accompanied by surface hardening, as evidenced by the increase in the Young’s modulus from 4 to 24 GPa due to glassification of the irradiated parts. The chemically modified layer acts as a shield against photodissociation and degradation of the deeper portion of the POSS polymer by VUV radiation. Applications include the protection of solar cells on low orbit satellites from solar VUV photons.
Ultralow-power hydrogen sensing with single palladium nanowires
Authors: Offermans P. , Tong H. D. , van Rijn C. J. M. , Merken P. , Brongersma S. H. , Crego-Calama M.
Published: June 2009

Palladium nanowires were fabricated on silicon substrates using conventional microfabrication techniques. Sensors based on such nanowires show a reversible response to hydrogen concentrations as low as 27 ppm with response times varying from 5 s (H2 concentrations >20%) to 30 s (H2 concentrations <100 ppm) at room temperature. The response times can be reduced by increasing the applied bias due to resistive heating. The noise spectrum of the nanowires shows a 1/f behavior, sufficiently low to enables the detection of hydrogen with an ultralow-power consumption. The influence of oxygen on the nanowire response was also investigated.
Synchronized locomotion of freely suspended disjoint microbeads pairs
Authors: Bhat S. , Kurzweg T. P. , Guez A. , Friedman G.
Published: June 2009

The possibility of locomotion of a pair of disjoint spherical microbeads suspended in fluid is investigated experimentally. The beads interact magnetically and their nonreciprocal relative movements are coordinated using external uniform magnetic field. Locomotion is studied and demonstrated for cyclic swirling movements of the beads which mimics behavior often observed in bacterial swarms.
Effect of a guiding electric field on the melting of a 2D electron crystal above liquid helium
Authors: Nasedkin K. A. , Sivokon’ V. E.
Published: June 2009

The conductivity of a two-dimensional electron system with surface density 8⋅108cm−2 and 12⋅108cm−2 above a liquid-helium surface is investigated near a phase transition into the crystalline state (Wigner crystal). The measurements are performed in the frequency range 3–6MHz for different amplitudes of a guiding field. The phase transition was detected according to a sharp change of the amplitude and phase of the response signal. The temperature dependences of the real and imaginary components of the conductivity of two-dimensional system of electrons and the melting temperature are calculated. It is found that the temperature dependences of the imaginary part of the reciprocal of the conductivity, which reflect the inertial properties of the electron system, match well for different frequencies of the exciting signal, while the real component, which characterizes dissipation, increases with increasing frequency at the transition into an ordered state. It is found that at the transition into an ordered state both components of the reciprocal of the conductivity increase with increasing guiding electric field.
Photoluminescence of ZnSe nanocrystals at high excitation level
Authors: Tishchenko V. V. , Kovalenko A. V.
Published: June 2009

The excitation-dependent photoluminescence (PL) of ZnSe nanocrystals (NCs) grown on GaAs (100) substrate is studied. The PL spectra observed corroborate previous observations of a bimodal size distribution of the NCs grown, and, in addition, evidence the existence of spectral diffusion with an extent dependent on excitation power. Besides, it is also shown that at relatively intense excitation an extra band arises in the luminescence spectra due to biexcitons confined in NCs of 3.5–4.0nm size. The binding energy of these biexcitons is as large as 23meV.
Dynamic spin–electric and spin–thermal effects in a system of electrons on the surface of liquid helium
Authors: Kopeliovich A. I. , Pyshkin P. V.
Published: June 2009

A study is made of the natural spin-electric and thermoelectric oscillations in an electron ring and of forced oscillations of the spin density and temperature driven with the help of external electrodes. Effects that may be used to investigate the spin characteristics of the system, in particular, spin-flip processes, by means of electrical measurements are proposed.
Toward adaptive control of coherent electron transport in semiconductors
Authors: Solas Fernando , Ashton Jennifer M. , Markmann Andreas , Rabitz Herschel A.
Published: June 2009

This work explores the feasibility of using shaped electrostatic potentials to achieve specified final scattering distributions of an electron wave packet in a two dimensional subsurface plane of a semiconductor. When electron transport takes place in the ballistic regime, and features of the scattering potentials are smaller than the wavelength of the incident electron then coherent quantum effects can arise. Simulations employing potential forms based on analogous optical principles demonstrate the ability to manipulate quantum interferences in two dimensions. Simulations are presented showing that suitably shaped electrostatic potentials may be used to separate an initially localized Gaussian wave packet into disjoint components or concomitantly to combine a highly dispersed packet into a compact form. The results also indicate that highly complex scattering objectives may be achieved by utilizing adaptive closed-loop optimal control in the laboratory to determine the potential forms needed to manipulate the scattering of an incoming wave packet. An adaptive feedback algorithm can be used to vary individual voltages of multipixel gates on the surface of a solid state structure to thereby find the potential features in the transport plane needed to produce a desired scattering objective. A proposed experimental design is described for testing the concept of adaptive control of coherent electron transport in semiconductors.
The PLATO Dome A site-testing observatory: Power generation and control systems
Authors: Lawrence J. S. , Ashley M. C. B. , Hengst S. , Luong-Van D. M. , Storey J. W. V. , Yang H. , Zhou X. , Zhu Z.
Published: June 2009

The atmospheric conditions above Dome A, a currently unmanned location at the highest point on the Antarctic plateau, are uniquely suited to astronomy. For certain types of astronomy Dome A is likely to be the best location on the planet, and this has motivated the development of the Plateau Observatory (PLATO). PLATO was deployed to Dome A in early 2008. It houses a suite of purpose-built site-testing instruments designed to quantify the benefits of Dome A site for astronomy, and science instruments designed to take advantage of the observing conditions. The PLATO power generation and control system is designed to provide continuous power and heat, and a high-reliability command and communications platform for these instruments. PLATO has run and collected data throughout the winter 2008 season completely unattended. Here we present a detailed description of the power generation, power control, thermal management, instrument interface, and communications systems for PLATO, and an overview of the system performance for 2008.
Effects of nonmagnetic impurities on the spin transport property of a graphene nanoribbon device
Authors: Park Joonho , Yang Heok , Park K.-S. , Lee Eok-Kyun
Published: June 2009

Using a nonequilibrium density functional calculation, we investigated the electronic transport properties and fundamental mechanism of spin polarization as a function of the location of impurities from the center to an edge of a graphene nanoribbon device (GND) with zigzag edges. A center-located impurity enables both edges to be enhanced with respect to their spin transports whereas an edge-located impurity results in only the opposite edge channel being dominant. In the case of a center-located impurity, the ferromagnetic ground state induces new spin states near the Fermi level responsible for the spin-polarized current in the GND. We argue that the spin-polarized current can flow through the edge states induced by a nonmagnetic impurity around the Fermi level, especially on a GND with a center-located impurity.
Influence of heterogeneous profiles in carrier density measurements with respect to iron concentration measurements in silicon
Authors: Schubert Martin C. , Kerler Michael J. , Warta Wilhelm
Published: June 2009

Carrier density is a frequently examined parameter for silicon material characterization especially to determine carrier lifetime. Typically integrated values are obtained which ignore nonhomogeneities in the depth dependent carrier profile and result in mean values for lifetime and injection density. Due to the averaging together with nonlinear recombination processes, these values may be subjected to substantial systematic errors. This work demonstrates the effect on iron concentration measurements which are based on the comparison of carrier lifetime measurements before and after light induced splitting of FeB pairs. Although this technique has been proven to be very sensitive, simple, and thus attractive, systematic quantitative errors are revealed in this work which are inherent to this method. It is demonstrated that the errors, while small for certain conditions, may be substantial in many practical cases. Simulations based on the calculation of carrier profiles and virtual measurements provide a tool to estimate the influence of material and setup parameters to the total systematic error. A correction method is developed from this analysis.
Effect of exciton migration on the light emission properties in silicon nanocrystal ensembles
Authors: Gardelis S. , Nassiopoulou A. G. , Vouroutzis N. , Frangis N.
Published: June 2009

Different silicon nanocrystal (Si NC) systems in which Si NCs were either entirely isolated or loosely interconnected were studied by photoluminescence (PL) and time-resolved PL decay measurements in the range between 70 and 290 K, in order to investigate the role of exciton migration in the PL properties. We examined three kinds of samples: (a) two light emitting mesoporous Si (PSi) films with different porosities, grown on p-type Si, (b) a heavily oxidized light emitting anisotropic macroporous Si film, and (c) a film consisted of a Si NC superlattice with six Si NC/SiO2 bilayers, grown by low pressure chemical vapor deposition of amorphous Si (α-Si), followed by high temperature thermal oxidation. In the two mesoporous Si films of the first case, the Si NCs show a degree of interconnection that depends on the porosity, whereas in the two other cases the NCs were isolated by SiO2, the degree of electrical isolation depending on the thickness of the SiO2 interlayer between them. Temperature dependent PL spectra and PL decay times of the different systems correlate well with the ability of excitons to migrate from one NC to another (case of loosely correlated NCs) or remain strongly localized within the Si NCs (case of effectively isolated NCs).
Isoelectronic centers and type-II quantum dots: Mechanisms for the green band emission in ZnSeTe alloy
Authors: Chang L. W. , Cheng J. H. , Hsu C. H. , Chao H. Y. , Li W. , Chang Y. H. , Chen K. Y. , Chen Y. F. , Laing C.-T.
Published: June 2009

Te-doped and ZnTe-doped diluted ZnSeTe samples were grown by using metal-organic chemical vapor deposition. The green lights emitted from these two samples in the photoluminescence (PL) measurement have different peak emission energies and can be attributed to different emission mechanisms. For the Te-doped sample, the PL emission band is excitation laser power independent, the lifetime of the PL emission is short, and the PL emission could be attributed to the emission originated from Te isoelectronic centers. For the ZnTe-doped sample, the energy of the green emission band is laser power dependent, the PL lifetime is much longer than the Te-doped sample, and the PL emission could be attributed to the emission from type-II ZnTe∕ZnSe quantum dots. The results demonstrate that there are two different mechanisms responsible for the green PL emission in ZnSeTe system and our growth methods provide a way of selecting one of the two mechanisms for the green light emission in this system.
Emergence of molecular recognition phenomena in a simple model of imprinted porous materials
Authors: Dourado Eduardo M. A. , Sarkisov Lev
Published: June 2009

Polymerization in the presence of templates, followed by their consequent removal, leads to structures with cavities capable of molecular recognition. This molecular imprinting technology has been employed to create porous polymers with tailored selectivity for adsorption, chromatographic separations, sensing, and other applications. Performance of these materials crucially depends on the availability of highly selective binding sites. This parameter is a function of a large number of processing conditions and is difficult to control. Furthermore, the nature of molecular recognition processes in these materials is poorly understood to allow a more systematic design. In this work we propose a simple model of molecularly imprinted polymers mimicking the actual process of their formation. We demonstrate that a range of molecular recognition effects emerge in this model and that they are consistent with the experimental observations. The model also provides a wealth of information on how binding sites form and function in the imprinted structures. It demonstrates the capability to assess the role of various processing conditions in the final properties of imprinted materials, and therefore it can be used to provide some qualitative insights on the optimal values of processing parameters.
Performance analysis of statistical samples of graphene nanoribbon tunneling transistors with line edge roughness
Authors: Luisier Mathieu , Klimeck Gerhard
Published: June 2009

Using a three-dimensional, atomistic quantum transport simulator based on the tight-binding method, we investigate statistical samples of single-gate graphene nanoribbon (GNR) tunneling field-effect transistors (TFETs) with different line edge roughness probabilities. We find that as the nanoribbon edges become rougher, the device OFF-current drastically increases due to a reduction of the graphene band gap and an enhancement of source-to-drain tunneling leakage through the gate potential barrier. At the same time, the ON-current remains almost constant. This leads to a deterioration of the transistor subthreshold slopes and to unacceptably low ON/OFF current ratios limiting the switching performances of GNR TFETs.
Investigation into the vibrational yield of OH products in the OH+H+H channel arising from the dissociative recombination of H3O+
Authors: Zhaunerchyk Vitali , Geppert Wolf D. , Rosén Stefan , Vigren Erik , Hamberg Mathias , Kamińska Magdalena , Kashperka Iryna , af Ugglas Magnus , Semaniak Jacek , Larsson Mats , Thomas Richard D.
Published: June 2009

The vibrational population of the hydroxyl radical, OH, formed in the OH+H+H channel arising from the dissociative recombination of the hydronium ion, H3O+, has been investigated at the storage ring CRYRING using a position-sensitive imaging detector. Analysis shows that the OH fragments are predominantly produced in the v=0 and v=1 states with almost equal probabilities. This observation is in disagreement with earlier FALP experiments, which reported OH(v=0) as the dominant product. Possible explanations for this difference are discussed.
High spatial resolution confocal microscope with independent excitation and detection scanning capabilities
Authors: Marcet S. , Ouellet-Plamondon C. , Francoeur S.
Published: June 2009

We present the design of a confocal microscope adapted for optical spectroscopy and imaging at cryogenic temperatures. This system is based on the existing approach of partly inserting the optical components of the microscope inside a helium-bath cryostat. It provides a spatial resolution approaching the diffraction limit with a mechanical stability allowing uninterrupted integration times exceeding 10 h and allows keeping track of a single emitter for unlimited periods of time. Furthermore, our design allows scanning the excitation spot and detection area independently of the sample position. This feature provides the means to perform probeless transport experiments on one-dimensional nanostructures. The scanning capabilities of this microscope are fully detailed and characterized using the photoluminescence of single nitrogen dyads at 4.5 K.
Three-dimensional evolution of magnetic and velocity shear driven instabilities in a compressible magnetized jet
Authors: Bettarini Lapo , Landi Simone , Velli Marco , Londrillo Pasquale
Published: June 2009

The problem of three-dimensional combined magnetic and velocity shear driven instabilities of a compressible magnetized jet modeled as a plane neutral/current double vortex sheet in the framework of the resistive magnetohydrodynamics is addressed. The resulting dynamics given by the stream+current sheet interaction is analyzed and the effects of a variable geometry of the basic fields are considered. Depending on the basic asymptotic magnetic field configuration, a selection rule of the linear instability modes can be obtained. Hence, the system follows a two-stage path developing either through a fully three-dimensional dynamics with a rapid evolution of kink modes leading to a final turbulent state, or rather through a driving two-dimensional instability pattern that develops on parallel planes on which a reconnection+coalescence process takes place.
Properties of Hall magnetohydrodynamic waves modified by electron inertia and finite Larmor radius effects
Authors: Damiano P. A. , Wright A. N. , McKenzie J. F.
Published: June 2009

The linear wave equation (sixth order in space and time) and the corresponding dispersion relation is derived for Hall magnetohydrodynamic (MHD) waves including electron inertial and finite Larmor radius effects together with several limiting cases for a homogeneous plasma. We contrast these limits with the solution of the full dispersion relation in terms of wave normal (k⊥,k∥) diagrams to clearly illustrate the range of applicability of the individual approximations. We analyze the solutions in terms of all three MHD wave modes (fast, slow, and Alfvén), with particular attention given to how the Alfvén branch (including the cold ideal field line resonance (FLR) [D. J. Southwood, Planet. Space Sci. 22, 483 (1974)]) is modified by the Hall term and electron inertial and finite Larmor radius effects. The inclusion of these terms breaks the degeneracy of the Alfvén branch in the cold plasma limit and displaces the asymptote position for the FLR to a line defined by the electron thermal speed rather than the Alfvén speed. For a driven system, the break in this degeneracy implies that a resonance would form at one field line for small k⊥ and then shift to another as k⊥→∞. However for very large ωk⊥/VA, Hall term effects lead to a coupling to the whistler mode, which would then transport energy away from the resonant layer. The inclusion of the Hall term also significantly effects the characteristics of the slow mode. This analysis reveals an interesting “swapping” of the perpendicular root behavior between the slow and Alfvén branches.
Quasistatic displacement self-sensing method for cantilevered piezoelectric actuators
Authors: Ivan Ioan Alexandru , Rakotondrabe Micky , Lutz Philippe , Chaillet Nicolas
Published: June 2009

Piezoelectric meso- and microactuator systems required for manipulation or assembly of microscale objects demand reliable force and/or displacement information. Available sensors are prone to dimension restrictions or precision limitation. Self-sensing method, based on the electric charge measurement, may represent a solution in terms of cost-effectiveness and integration, the actuator performing simultaneously as its own sensor. This paper presents a self-sensing method dedicated to free uni- and bimorph piezocantilevers but can also be adapted to other piezoactuator types. The integrated electric current, used to convert the charge, can be compensated against piezoelectric material nonlinearities to provide accurate displacement information. The advantages relative to existing self-sensing methods consist in the ability to keep this displacement information for long-term periods (more than a thousand seconds) and in the reduction in signal noise. After introductive issues related to the method the base principle allowing the estimation of tip displacement is presented. Then, the identification procedure of the estimator parameters is depicted and representative experimental results are shown. Finally, a series of aspects related to electronic circuits are discussed, useful for successful system implementation.
Coupled-cluster calculations of C2H2Si and CNHSi structural isomers
Authors: Thorwirth Sven , Harding Michael E.
Published: June 2009

Results of large-scale coupled-cluster calculations of selected C2H2Si and CNHSi structural isomers are reported. Equilibrium molecular structures of a total of 12 molecules in their singlet electronic states have been calculated systematically employing the coupled-cluster singles and doubles model augmented by a perturbative correction for triple excitations (CCSD(T)) in combination with Dunning’s hierarchy of correlation consistent basis sets. In addition, anharmonic force fields were calculated to yield fundamental vibrational frequencies and rotation-vibration interaction constants αiA,B,C. The latter were used to determine empirical equilibrium structures reemp of two molecules — silacyclopropenylidene, c-C2H2Si, and silapropadienylidene, H2CCSi — for which sufficient isotopic data are available from literature. Very good agreement with theoretical equilibrium structures from CCSD(T) calculations employing core-valence basis sets of quadruple and quintuple-zeta quality — i.e., cc-pwCVQZ (337 basis functions), cc-pCV5Z, and cc-pwCV5Z (581 basis functions) is found — to within 0.001 Å for bond lengths and 0.1° for bond angles. Theoretical ground state rotational constants of HSiCN and HSiNC compare very favorably with experimental microwave data from literature, to within 0.15% (HSiCN) and 0.1% (HSiNC) for the B0 and C0 rotational constants. In the case of c-C2H2Si and H2CCSi this agreement is even better than 0.1%. For the latter two molecules effects of higher-level electron-correlation and relativity to the equilibrium geometry as well as the electronic contributions to the rotational constants are investigated. For eight molecules not yet studied at high spectral resolution in the gas-phase theoretical molecular parameters are provided to support future laboratory investigations. Theoretical vibrational fundamentals compare well with data of eight species studied previously with infrared matrix isolation spectroscopy.
High-speed liquid lens with 2 ms response and 80.3 nm root-mean-square wavefront error
Authors: Oku H. , Ishikawa M.
Published: June 2009

A liquid lens structure with a step response time of 2 ms, a refractive power range of 52 D, and a root-mean-square (rms) wavefront error of 80.3 nm is reported. This lens uses a liquid-liquid interface with a pinned contact line as a variable refractive surface, and its shape is controlled by a piezostack actuator via a built-in hydraulic amplifier. The measured wavefront error suggests that the method of pinning the contact line to a precise shape is an important factor in achieving higher optical performance.
Direct computation of the growth rate for the instability of a warm relativistic electron beam in a cold magnetized plasma
Authors: Timofeev I. V. , Lotov K. V. , Terekhov A. V.
Published: June 2009

The fully kinetic, fully electromagnetic dispersion equation for a warm relativistic electron beam in a cold magnetized plasma is numerically solved with no simplifying assumptions made. For magnetic fields of various strengths, the growth rate maps for the beam-plasma instability are plotted and dominant modes are identified. The exact solution is compared with available approximate solutions. The latter are shown to misinterpret the effect of the magnetic field on the instability of oblique waves.
Diagnoses of coaxial probes in shock compression
Authors: Sun Yue , Ci Jiaxiang , Yi Pengfei , Zhang Hongrun
Published: June 2009

A miniature diagnostic apparatus, which consists of a target, a guiding tube, a nail-gun, and a simple base, has been developed in the proposed research to estimate batches of pinlike coaxial probes with selectable collision speeds, 198.3, 361.0, and 420.6 mps, corresponding to thrust capabilities of certain minibullets. This work aims at filling the gap between typical two stage light gas gun (>500 mps) and pendulum machine (<100 mps) with low cost and risk in realistic shock compressions. As a part of the experiment, the κ coefficient and the statistical agreement and reliability are all evaluated.
Structural, electronic and magnetic properties of V2O5−x: An ab initio study
Authors: Xiao Z. R. , Guo G. Y.
Published: June 2009

Pure V2O5 is a diamagnetic layered semiconductor with many applications such as catalysis. In this paper, we study oxygen vacancy-induced changes in the atomic and electronic structures as well as magnetic properties of V2O5−x within spin density functional theory with generalized gradient approximation. Both the supercell approach and virtual crystal approximation are used to simulate the oxygen-deficient V2O5−x with vacancy concentration x up to 0.5. The 1×2×2 supercell calculations with one O vacancy predict that the formation energies of the apical (O1), bridge (O2), and chain (O3) oxygen vacancies are, respectively, 2.48, 4.17, and 4.44 eV/vacancy, and hence that the O vacancies in V2O5−x would be predominantly of the O1 type. The local structural distortions of the V atoms next to the O vacancies are found to be large for high vacancy density x(x>0.25), and for x∼0.5, even the crystal lattice changes from the orthorhombic to monoclinic symmetry. In all the cases considered, an O vacancy-induced stable or metastable ferromagnetic state with spin magnetic moment of ∼2.0μB/vacancy is found. For x below ∼0.13 and 0.19<x<∼0.45, the ferromagnetic state would be the ground state, while for 0.45≤x≤0.5, the antiferromagnetic state with the V spins on neighboring rungs (AF-2) being antiparallel is the ground state. Importantly, this suggests that undoped V2O5−x with x≤0.13 and 0.19<x<∼0.45 would be a diluted ferromagnetic semiconductor. The AF-2, however, disappears for x≤0.25, while the antiferromagnetic state with the V spins on neighboring ladders being antiparallel (AF-1) occurs for the entire range of x studied. Nevertheless, the AF-1 is energetically more favorable than the ferromagnetic state only in 0.13<x<∼0.19. For low O vacancy concentrations (x<0.25), the electronic structure of V2O5−x is very similar to that of the perfect bulk V2O5, except that 2x electrons now occupy the low V dxy dominant conduction bands which are exchange split. Majority of the magnetization is located on the dxy-orbitals of the V atoms near the O vacancy site. For larger x values, however, the electronic structure may change significantly, and, in particular, the V d-orbital character of the low conduction bands can be altered completely. Analysis of the calculated electronic structure reveals that the oxygen vacancy-induced magnetization in V2O5−x results primarily from the Stoner mechanism.
Coherent transfer via environment-induced vibronic resonance
Authors: Tamura Hiroyuki
Published: June 2009

We systematically analyze vibronic dynamics considering a high-frequency system mode and low-frequency environmental modes by using quantum dynamics calculations. We demonstrate how the vibronic resonance and environment dynamics induce a coherent transfer between coupled electronic states with a potential energy bias. The concerted dynamics of the low-frequency modes modulates the potential crossing, thereby inducing a coherent population transfer when the resonance condition is matched. This feature would underlie transfer phenomena in certain realistic systems.
The dependence of the ultrafast relaxation kinetics of the S2 and S1 states in β-carotene homologs and lycopene on conjugation length studied by femtosecond time-resolved absorption and Kerr-gate fluorescence spectroscopies
Authors: Kosumi Daisuke , Fujiwara Masazumi , Fujii Ritsuko , Cogdell Richard J. , Hashimoto Hideki , Yoshizawa Masayuki
Published: June 2009

The ultrafast relaxation kinetics of all-trans-β-carotene homologs with varying numbers of conjugated double bonds n(n=7–15) and lycopene (n=11) has been investigated using femtosecond time-resolved absorption and Kerr-gate fluorescence spectroscopies, both carried out under identical excitation conditions. The nonradiative relaxation rates of the optically allowed S2(1Bu+1) state were precisely determined by the time-resolved fluorescence. The kinetics of the optically forbidden S1(2Ag−1) state were observed by the time-resolved absorption measurements. The dependence of the S1 relaxation rates upon the conjugation length is adequately described by application of the energy gap law. In contrast to this, the nonradiative relaxation rates of S2 have a minimum at n=9 and show a reverse energy gap law dependence for values of n above 11. This anomalous behavior of the S2 relaxation rates can be explained by the presence of an intermediate state (here called the Sx state) located between the S2 and S1 states at large values of n (such as n=11). The presence of such an intermediate state would then result in the following sequential relaxation pathway S2→Sx→S1→S0. A model based on conical intersections between the potential energy curves of these excited singlet states can readily explain the measured relationships between the decay rates and the energy gaps.
Optical spectra obtained from amorphous films of rubrene: Evidence for predominance of twisted isomer
Authors: Kytka M. , Gisslen L. , Gerlach A. , Heinemeyer U. , Kováč J. , Scholz R. , Schreiber F.
Published: June 2009

In order to investigate the optical properties of rubrene we study the vibronic progression of the first absorption band (lowest π→π∗ transition). We analyze the dielectric function ε2 of rubrene in solution and thin films using the displaced harmonic oscillator model and derive all relevant parameters of the vibronic progression. The findings are supplemented by density functional calculations using B3LYP hybrid functionals. Our theoretical results for the molecule in two different conformations, i.e., with a twisted or planar tetracene backbone, are in very good agreement with the experimental data obtained for rubrene in solution and thin films. Moreover, a simulation based on the monomer spectrum and the calculated transition energies of the two conformations indicates that the thin film spectrum of rubrene is dominated by the twisted isomer.