bluuebunny/crossref_metadata_2025 huggingface dataset:
Resonance cones in a dusty magnetized plasma
Authors: Trottenberg Thomas , Brede Björn , Block Dietmar , Piel Alexander
Published: November 2003

A new diagnostic method for magnetized dusty plasmas, the excitation of lower hybrid resonance cones, is investigated experimentally. The resonance cone is excited with a small antenna, and the angular distribution of the wave field with respect to the magnetic field shows a resonant enhancement, which shifts according to the free electron density. It is demonstrated that dust reduces the free electron density in agreement with Langmuir probe results. Wave damping by scattering effects is found negligible.
Separatrix shapes and internal structures of a field-reversed configuration plasma
Authors: Gota Hiroshi , Fujimoto Kayoko , Ohkuma Yasunori , Takahashi Tsutomu , Nogi Yasuyuki
Published: November 2003

The separatrix shape of a field-reversed configuration plasma is determined in comparison with measured fluxes surrounding the plasma and the solution of the Grad–Shafranov equation with an edge-layer plasma in the open field region. A reconnection point of the bias field, an outgoing flow of torn plasmas and a large amplitude ripple on the separatrix surface are clearly observed at the formation phase. A smoothed separatrix shape having definite ends is observed at the quiescent phase. It is also estimated that the beta value at the separatrix and the thickness of the edge-layer plasma are, respectively, βs=0.5–0.7 and 4–6 ρi (ρi: ion gyroradius). The magnetic structure inside the separatrix is investigated by solving the Grad–Shafranov equation with the measured separatrix shape and βs. It is found that magnetic islands are formed near the magnetic axis not only at the formation phase but also at the quiescent phase. The appearance and coalescence of the islands are repeated during the discharge.
Virasoro structure and localized excitations of the LKR system
Authors: Lou S. Y. , Rogers C. , Schief W. K.
Published: November 2003

A symmetry analysis is conducted for a master 2+1-dimensional soliton system. The classical symmetries are shown to constitute an infinite dimensional Kac–Moody–Virasoro algebra. Finite symmetry group transformations are then used to construct localized excitations of the system.
Lax pair and super-Yangian symmetry of the nonlinear super-Schrödinger equation
Authors: Caudrelier V. , Ragoucy E.
Published: November 2003

We consider a version of the nonlinear Schrödinger equation with M bosons and N fermions. We first solve the classical and quantum versions of this equation, using a super-Zamolodchikov–Faddeev (ZF) algebra. Then we prove that the hierarchy associated to this model admits a super-Yangian Y(gl(M|N)) symmetry. We exhibit the corresponding (classical and quantum) Lax pairs. Finally, we construct explicitly the super-Yangian generators, in terms of the canonical fields on the one hand, and in terms of the ZF algebra generators on the other hand. The latter construction uses the well-bred operators introduced recently.
Screened occurrence scattering time for electron–dust grain collisions in dusty plasmas
Authors: Kim Chang-Geun , Lee Myoung-Jae , Jung Young-Dae
Published: November 2003

Plasma screening effects on occurrence time for electron–dust grain scattering in dusty plasmas are investigated using the eikonal method. The semiclassical path and the semiclassical wave function are applied to obtain the eikonal phase and amplitude. The interaction potential is obtained by using the image-charge method. The scaled semiclassical occurrence time is obtained as a function of the impact parameter, dust radius, scattering angle, and scattering energy. It has been found that the occurrence time delay is slightly increased as the scaled Debye length is increased for small scattering angles. However, the occurrence scattering time is increased sinusoidally with the increasing scattering angle.
High pressure electric discharge model applied to the halogen depletion instability development in a XeCl phototriggered laser
Authors: Belasri A. , Harrache Z. , Baba-Hamed T.
Published: November 2003

Theoretical studies of a phototriggered XeCl excimer laser have been performed through the development of a zero-dimensional model and used for conditions close to experiment for about 50–100 ns laser pulse duration with electron power deposition in the MW/cm3 range and inside a 300 cm3 chamber. The well-known parallel resistor network model is used. The plasma generated by the impulse discharge is represented by one or more resistance in parallel, whose conductivity is proportional to the electron density. Time variation of the electron density is obtained by integrating the transport equations coupled to the heavy species kinetic and the external circuit. This study provides the time variation of the discharge characteristics as well as the influence of the gas composition on these characteristics. The results have been discussed and analyzed. Calculated discharge current and voltage are also compared with experimental results. Finally, the use of the present model allows a good comprehension of the halogen depletion phenomena, which is the principal cause of laser ending and allows a simple study of the evolution of a large-scale heterogeneity in preionization density and its effect on electrical and chemical plasma properties.
Goursat distribution and sub-Riemannian structures
Authors: Anzaldo-Meneses A. , Monroy-Pérez F.
Published: November 2003

We obtain the Lie group whose action leaves invariant the sub-Riemannian structures associated with Goursat systems and Euclidean metrics. The group naturally contains the Heisenberg group, the nilpotent group associated with the Martinet case, and the group corresponding to systems of Engel type. We compute also the Casimir functions of the associated nilpotent Poisson algebra. Our results generalize previous works on this problem of nonholonomic systems. A particular physical problem described by our model is the motion of electric charges in certain static inhomogeneous magnetic fields. We define a new algebraic curve in total space and compute two examples of sub-Riemannian extremals in cotangent space.
Electromagnetic Weibel instability in intense charged particle beams with large energy anisotropy
Authors: Startsev Edward A. , Davidson Ronald C.
Published: November 2003

In plasmas with strongly anisotropic distribution functions, collective instabilities may develop if there is sufficient coupling between the transverse and longitudinal degrees of freedom. Our previous numerical and theoretical studies of intense charged particle beams with large temperature anisotropy [E. A. Startsev, R. C. Davidson, and H. Qin, Phys. Rev. ST Accel. Beams 6, 084401 (2003); Phys. Plasmas 9, 3138 (2002)] demonstrated that a fast, electrostatic, Harris-type instability develops, and saturates nonlinearly, for sufficiently large temperature anisotropy (T⊥b/T∥b≫1). The total distribution function after saturation, however, is still far from equipartitioned. In this paper the linearized Vlasov–Maxwell equations are used to investigate detailed properties of the transverse electromagnetic Weibel-type instability for a long charge bunch propagating through a cylindrical pipe of radius rw. The kinetic stability analysis is carried out for azimuthally symmetric perturbations about a two-temperature thermal equilibrium distribution in the smooth-focusing approximation. The most unstable modes are identified, and their eigenfrequencies, radial mode structure and instability thresholds are determined. The stability analysis shows that, although there is free energy available to drive the electromagnetic Weibel instability, the finite transverse geometry of the charged particle beam introduces a large threshold value for the temperature anisotropy [(T⊥b/T∥b)Weibel≫(T⊥b/T∥b)Harris] below which the instability is absent. Hence, unlike the case of an electrically neutral plasma, the Weibel instability is not expected to play as significant a role in the process of energy isotropization of intense unneutralized charged particle beams as the electrostatic Harris-type instability.
Boundary conformal fields and Tomita–Takesaki theory
Authors: Hannabuss K. C. , Semplice M.
Published: November 2003

Motivated by formal similarities between the continuum limit of the Ising model and the Unruh effect, this paper connects the notion of an Ishibashi state in boundary conformal field theory with the Tomita–Takesaki theory for operator algebras. A geometrical approach to the definition of Ishibashi states is presented, and it is shown that, when normalizable, the Ishibashi states are cyclic separating states, justifying the operator state corespondence. When the states are not normalizable Tomita–Takesaki theory offers an alternative approach based on left Hilbert algebras, making possible extensions of our construction and the state-operator correspondence.
Noncommutative geometry framework and the Feynman’s proof of Maxwell equations
Authors: Boulahoual A. , Sedra M. B.
Published: November 2003

The main focus of the present work is to study the Feynman’s proof of the Maxwell equations using the NC geometry framework. To accomplish this task, we consider two kinds of noncommutativity formulations going along the same lines as Feynman’s approach. This allows us to go beyond the standard case and discover nontrivial results. In fact, while the first formulation gives rise to the static Maxwell equations, the second formulation is based on the following assumption m[xj,ẋk]=δjk+imθjkf. The results extracted from the second formulation are more significant since they are associated to a nontrivial θ-extension of the Bianchi-set of Maxwell equations. We find divθ B=ηθ and (∂Bs/∂t)+εkjs(∂Ej/∂xk)=A1(d2f/dt2)+A2(df/dt)+A3, where ηθ, A1, A2, and A3 are local functions depending on the NC θ-parameter. The novelty of this proof in the NC space is revealed notably at the level of the corrections brought to the previous Maxwell equations. These corrections correspond essentially to the possibility of existence of magnetic charge sources that we can associate to the magnetic monopole since divθ B=ηθ is not vanishing in general.
Classical mode conversion description of neutrino oscillations in dense magnetized plasmas
Authors: Bingham R. , Silva L. O. , Cairns R. A. , Semikoz V. B. , Oraevsky V. N.
Published: November 2003

Neutrino oscillations in dense magnetized plasmas, similar to those found in supernovas, are described. The adopted model is similar to the classical mode conversion problems examined in fluid dynamics and plasma physics. This approach allows for the derivation of analytical results for the neutrino conversion probability for different combinations of background density profile and magnetic field profile.
Length scaling of dynamic-hohlraum axial radiation
Authors: Sanford T. W. L. , Mock R. C. , Slutz S. A. , Peterson D. L.
Published: November 2003

Radiation generated within a 10-mm-long foam-target DH (dynamic hohlraum) is used for high-temperature (>200 eV) radiation-flow and inertial-confinement-fusion studies [Sanford et al., Phys. Plasmas 9, 3573 (2002)]. The length of this DH is varied from 5 to 20 mm, keeping the mass/unit length constant in an effort to study the scaling of axial radiation power with length, and better understand its production. Measurements show a greater variation in this power with length than would be expected from simple arguments [Slutz et al., Phys. Plasmas 8, 1673 (2001)]. Maximum axial power of ∼10 TW is produced with a length of ∼7.5 mm, similar to the typical power for the baseline 10 mm DH. The decreasing axial power (at a rate of ∼0.65 TW per mm at longer lengths) is bounded by radiation-magnetohydrodynamic simulations [Peterson et al., Phys. Plasmas 6, 2178 (1999)] that include the development of the magnetic Rayleigh–Taylor instability in the r–z plane. The dramatic drop in axial power below 7.5 mm, by contrast, was unanticipated. This decrease suggests the presence of differing mechanisms for limiting power at short and long lengths.
Confinement and dynamical regulation in two-dimensional convective turbulence
Authors: Bian N. H. , Garcia O. E.
Published: November 2003

In this work the nature of confinement improvement implied by the self-consistent generation of mean flows in two-dimensional convective turbulence is studied. The confinement variations are linked to two distinct regulation mechanisms which are also shown to be at the origin of low-frequency bursting in the fluctuation level and the convective heat flux integral, both resulting in a state of large-scale intermittency. The first one involves the control of convective transport by sheared mean flows. This regulation relies on the conservative transfer of kinetic energy from tilted fluctuations to the mean component of the flow. Bursting can also result from the quasi-linear modification of the linear instability drive which is the mean pressure gradient. For each bursting process the relevant zero-dimensional model equations are given. These are finally coupled in a minimal model of convection in fluids and plasmas. The results of the modeling are used to discuss confinement scaling and intermittency, and in a heuristic way, more complex issues such as criticality and transport avalanches.
Analysis of stable resistive wall modes in a rotating plasma
Authors: Garofalo A. M. , Jensen T. H. , Strait E. J.
Published: November 2003

Measurements of the resistive wall mode (RWM) response to external resonant field pulses yield complete knowledge of the mode characteristics in the parameter range explored. An ideal magnetohydrodynamics model [Garofalo et al., Phys. Plasmas 9, 4573 (2002)] has been generalized to include the effects of plasma rotation and dissipation, and the new model is found to explain quantitatively the experimental observations. Rotation of the RWM with respect to the wall is often described as an essential feature of the mechanism by which plasma rotation stabilizes the RWM. This interpretation of the rotational stabilization of the RWM appears inconsistent with the measurements from recent DIII–D [Luxon and Davis, Fusion Technol. 8, 441 (1985)] experiments. It is found that the theoretically predicted mode rotation with respect to the wall is not needed for stabilization and is only a consequence of torque balance in the absence of magnetic-field nonaxisymmetries.
Characterization of ultrathin dopant segregation layers in nanoscale metal–oxide–semiconductor field effect transistors using scanning transmission electron microscopy
Authors: Topuria T. , Browning N. D. , Ma Z.
Published: November 2003

Silicide/Si source/drain interfaces (Co–silicide and Ti–silicide) in nanoscale metal–oxide–semiconductor field effect transistors (MOSFETs) were investigated using scanning transmission electron microscopy and electron energy loss spectroscopy. Z-contrast images of the N-type doped device show substitutional arsenic segregation on Si lattice sites with a very narrow profile precisely at the Co–silicide/Si interfaces. A detailed comparative electron energy loss study of As-doped and undoped devices reveals that arsenic remains electrically active and supplies additional charge carriers at the interface. These characteristics are desirable for optimum device performance with minimum contact resistance. A similar effect is also observed in MOSFETs with a Ti-silicided source/drain.
Identification of short-lived and localized coherent structures in plasma turbulence by window biorthogonal decomposition
Authors: Dong Lifang , Zhang Qingli , Wang Long
Published: November 2003

An alternative biorthogonal decomposition technique called the window biorthogonal decomposition (WBD) technique is introduced to analyze the coherent structures in the tokamak plasma turbulence. It can spot the short-lived and localized coherent structures in spatiotemporal turbulence signal and extract them out of the incoherence background. As an example, the localized and short-lived coherent structures existing stochastically in the CT-6B tokamak radial direction are analyzed by WBD.
Quasi-monochromatic flash x-ray generator utilizing weakly ionized linear copper plasma
Authors: Sato Eiichi , Hayasi Yasuomi , Germer Rudolf , Tanaka Etsuro , Mori Hidezo , Kawai Toshiaki , Ichimaru Toshio , Takayama Kazuyoshi , Ido Hideaki
Published: November 2003

In the plasma flash x-ray generator, a 200 nF condenser is charged up to 50 kV by a power supply, and flash x rays are produced by the discharging. The x-ray tube is a demountable triode with a trigger electrode, and the turbomolecular pump evacuates air from the tube with a pressure of approximately 1 mPa. Target evaporation leads to the formation of weakly ionized linear plasma, consisting of copper ions and electrons, around the fine target, and intense characteristic x rays are produced. At a charging voltage of 50 kV, the maximum tube voltage was almost equal to the charging voltage of the main condenser, and the peak current was about 20 kA. When the charging voltage was increased, the linear plasma formed, and the K-series characteristic x-ray intensities increased. The K lines were quite sharp and intense, and hardly any bremsstrahlung rays were detected at all. The x-ray pulse widths were approximately 700 ns, and the time-integrated x-ray intensity had a value of approximately 30 μC/kg at 1.0 m from the x-ray source with a charging voltage of 50 kV.
Higher harmonics imaging in tapping-mode atomic-force microscopy
Authors: Stark Robert W. , Heckl Wolfgang M.
Published: November 2003

In tapping-mode atomic-force microscopy usually amplitude and phase of the cantilever motion are acquired. These signals are related to the fundamental oscillation frequency neglecting information at higher frequencies. However, the nonlinear contact between tip and sample induces higher frequency vibrations that are harmonics of the fundamental. In order to recover the available information the full tip motion has to be analyzed. The higher harmonics can be employed for image formation. A setup that consists of two independently operated lock-in amplifiers is used to detect higher harmonics in the dynamic atomic-force microscopy signal. Higher harmonic imaging proves to be useful to monitor the imaging conditions in tapping mode and can be applied for nanoscale imaging with a material contrast.
The phosphorescence microphone: A device for testing oxygen sensors and films
Authors: McGraw Christina M. , Shroff Hari , Khalil Gamal , Callis James B.
Published: November 2003

A new concept in sound pressure detection, the phosphorescence microphone, is introduced. This device replaces the diaphragm of a microphone with a thin film of pressure sensitive paint. Dynamic changes in pressure are detected by monitoring the changes in phosphorescent intensity that are due to cyclical variations in oxygen partial pressure in the sound wave. To test this new device, the acoustic resonance spectrum of a closed cylinder is measured and compared to the spectrum obtained with a commercial electret microphone. Oscillations in phosphorescent intensity that occur at the frequency of sound are observed, and the magnitude of these oscillations is dependent on sound pressure. Several experiments are presented to confirm that the spectrum obtained with the phosphorescence microphone is due to the oxygen sensitivity of the pressure sensitive paint. In addition to detecting sound, this device has shown efficacy in testing pressure sensitive paints for high frequency, low differential pressure applications. The phosphorescence microphone was used to show that selected pressure sensitive paints could detect acoustic pressure changes as small as 6 Pa in the frequency range 150–3500 Hz on a background of 105 Pa.
A plasma-shielded, miniature Rogowski probe
Authors: Torbert E. , Furno I. , Intrator T. , Hemsing E.
Published: November 2003

The design and first results from an electrically isolated and plasma-shielded Rogowski probe, used in the reconnection scaling experiment (RSX), are presented. The probe is designed to withstand extreme thermal shock, plasma corrosion, and be vacuum sanitary, which is accomplished with a machinable boron nitride shell. The novel miniature design, with an inner detecting area of 0.79 cm2, allows accurate position detection of plasma current channels with ≈2 cm radius and to measure local current density profiles. The temporal resolution (<1 μs) is sufficiently high to resolve the dynamic evolution of RSX plasma current channels.
Automated spectro-goniometer: A spherical robot for the field measurement of the directional reflectance of snow
Authors: Painter Thomas H. , Paden Brad , Dozier Jeff
Published: November 2003

We describe an automated spectro-goniometer (ASG) that rapidly measures the spectral hemispherical-directional reflectance factor (HDRF) of snow in the field across the wavelength range 0.4⩽λ⩽2.5 μm. Few measurements of snow’s HDRF exist in the literature, in part caused by a lack of a portable instrument capable of rapid, repeatable sampling. The ASG is a two-link spherical robot coupled to a field spectroradiometer. The ASG is the first revolute joint and first automated field goniometer for use over snow and other smooth surfaces. It is light enough (∼50 kg) to be portable in a sled by an individual. The ASG samples the HDRF at arbitrary angular resolution and 0.5 Hz sampling rate. The arm attaches to the fixed-point frame 0.65 m above the surface. With vertical and oblique axes, the ASG places the sensor of the field spectroradiometer at any point on the hemisphere above a snow target. In standard usage, the ASG has the sun as the illumination source to facilitate in situ measurements over fragile surfaces not easily transported to the laboratory and to facilitate simultaneous illumination conditions for validation and calibration of satellite retrievals. The kinematics of the ASG is derived using Rodrigues’ formula applied to the 2 degree-of-freedom arm. We describe the inverse kinematics for the ASG and solve the inverse problem from a given view angle to the necessary rotation about each axis. Its two-dimensional hemispheric sampling space facilitates the measurement of spectral reflectance from snow and other relatively smooth surfaces into any direction. The measurements will be used to validate radiative transfer model results of directional reflectance and to validate/calibrate directional satellite measurements of reflectance from these smooth surfaces.
Flexible system for multiple plasma immersion ion implantation-deposition processes
Authors: Tian Xiubo , Fu Ricky K. Y. , Chu Paul K. , Anders Andre , Gong Chunzhi , Yang Shiqin
Published: November 2003

Multiple plasma immersion ion implantation-deposition offers better flexibility compared to other thin film deposition techniques with regard to process optimization. The plasmas may be based on either cathodic arc plasmas (metal ions) or gas plasmas (gas ions) or both of them. Processing parameters such as pulsing frequency, pulse duration, bias voltage amplitude, and so on, that critically affect the film structure, internal stress, surface morphology, and other surface properties can be adjusted relatively easily to optimize the process. The plasma density can be readily controlled via the input power to obtain the desirable gas-to-metal ion ratios in the films. The high-voltage pulses can be applied to the samples within (in-duration mode), before (before-duration mode), or after (after-duration mode) the firing of the cathodic arcs. Consequently, dynamic ion beam assisted deposition processes incorporating various mixes of gas and metal ions can be achieved to yield thin films with the desirable properties. The immersion configuration provides to a certain degree the ability to treat components that are large and possess irregular geometries without resorting to complex sample manipulation or beam scanning. In this article we describe the hardware functions of such a system, voltage–current behavior to satisfy the needs of different processes, as well as typical experimental results.
Brandaris 128: A digital 25 million frames per second camera with 128 highly sensitive frames
Authors: Chin Chien Ting , Lancée Charles , Borsboom Jerome , Mastik Frits , Frijlink Martijn E. , de Jong Nico , Versluis Michel , Lohse Detlef
Published: November 2003

A high-speed camera that combines a customized rotating mirror camera frame with charge coupled device (CCD) image detectors and is practically fully operated by computer control was constructed. High sensitivity CCDs are used so that image intensifiers, which would degrade image quality, are not necessary. Customized electronics and instruments were used to improve the flexibility and control precisely the image acquisition process. A full sequence of 128 consecutive image frames with 500×292 pixels each can be acquired at a maximum frame rate of 25 million frames/s. Full sequences can be repeated every 20 ms, and six full sequences can be stored on the in-camera memory buffer. A high-speed communication link to a computer allows each full sequence of about 20 Mbytes to be stored on a hard disk in less than 1 s. The sensitivity of the camera has an equivalent International Standards Organization number of 2500. Resolution was measured to be 36 lp/mm on the detector plane of the camera, while under a microscope a bar pattern of 400 nm spacing line pairs could be resolved. Some high-speed events recorded with this camera, dubbed Brandaris 128, are presented.
Comparison between the ultraviolet emission from pulsed microhollow cathode discharges in xenon and argon
Authors: Petzenhauser Isfried , Biborosch Leopold D. , Ernst Uwe , Frank Klaus , Schoenbach Karl H.
Published: November 2003

We measured the dynamic I–V characteristics and vacuum ultraviolet (VUV) emission lines of the second continuum in xenon (170 nm) and argon (130.5 nm) from pulsed microhollow cathode discharges (MHCD). For pulse lengths between 1 and 100 μs the dynamic I–V characteristics are similar in both inert gases. Only the time variation of the VUV emission line at 170 nm for xenon can be related to the dimer excited states. In argon the energy transfer between the Ar2* dimers and the oxygen impurity atoms is responsible for a qualitatively different time behavior of the resonance line at 130.5 nm. Consequently, the relative VUV efficiency reveals an inverse dependence on the electrical pulse lengths for the MHCD in xenon and argon, respectively.
Industrial application of ultrasound based in-line rheometry: Visualization of steady shear pipe flow of chocolate suspension in pre-crystallization process
Authors: Ouriev Boris , Windhab Erich , Braun Peter , Zeng Yuantong , Birkhofer Beat
Published: November 2003

In the present work an in-line ultrasonic method for investigation of the rheological flow behavior of concentrated suspensions was created. It is based on a nondestructive rheological measuring technique for pilot plant and industrial scale applications. Elsewhere the author discusses a tremendous need for in-line rheological characterization of highly concentrated suspensions exposed to pressure driven shear flow conditions. Most existing on-line methods are based on destructive macro actuators, which are not suitable for materials with sensitive to applied deformation structure. Since the process of our basic interest influences the structure of suspension it would be difficult to separate the effects of rheometric measurement and weakly pronounced structural changes arising from a fine adjustment of the process parameters. The magnitude of these effects is usually associated with the complex flow dynamics of structured liquids and is sensitive to density or temperature fluctuations around the moving rheometric actuator. Interpretation of the results of such measurements can be hindered by process parameter influences on liquid product structure. Therefore, the author introduces an in-line noninvasive rheometric method, which is implemented in a pre-crystallization process of chocolate suspension. Use of ultrasound velocity profile pressure difference (UVP-PD) technique enabled process monitoring of the chocolate pre-crystallization process. Influence of seeded crystals on Rheology of chocolate suspension was recorded and monitored on line. It was shown that even slight velocity pulsations in chocolate mainstream can strongly influence rheological properties besides influencing flow velocity profiles. Based on calculations of power law fit in raw velocity profiles and calculation of wall shear stress from pressure difference measurement, a viscosity function was calculated and monitored on line. On-line results were found to be in a good agreement with off-line data. The results of the industrial test of the UVP-PD system brought practical knowledge and stipulated further development of a Smart UVP-PD noninventive on-line rheometer.
Rapid scan Fourier transform detection of a frequency encoded quartz crystal microbalance array
Authors: Guan Shenheng , Nielsen Ralph B.
Published: November 2003

A detection method for thickness shear mode (TSM) or quartz crystal microbalance (QCM) sensor arrays is described. Each element of the sensor array is frequency encoded so that it has a unique resonant frequency and can be identified under any operating condition. Frequency encoding of TSM sensors can be realized (1) by creating individual sensors with different thicknesses of piezoelectric base material or (2) preferably by electroplating sensors of identical piezoelectric base material thickness with predetermined thicknesses of metal films. Frequency changes can be detected by use of pulsed Fourier transform method or rapid scan Fourier transform method with a heterodyne configuration in which frequency reference is generated by a local oscillator based on a device modified according to the frequency encoding procedure. The detection method allows high analysis speed and low cost in hardware construction. A four-sensor chemical vapor detection system is designed and constructed to demonstrate the principle of frequency encoding and rapid scan Fourier transform detection for QCM arrays.
Kolmogorov entropy of global attractor for dissipative lattice dynamical systems
Authors: Jia Qiuli , Zhou Shengfan , Yin Fuqi
Published: November 2003

We consider Kolmogorov’s ε-entropy of the global attractor for first and second order dissipative lattice dynamical systems. By using the element decomposition and the covering property of a polyhedron by balls of radii ε in the finite dimensional space, we obtain an estimate of the upper bound for Kolmogorov’s ε-entropy of the global attractor.
Charge evolution in dusty plasma expansion with negative ions
Authors: Djebli M.
Published: November 2003

The charge evolution of negatively charged dust grains during plasma expansion is investigated in the presence of Boltzmannian positive and negative ions. Using the self-similar treatment, it is found that the dust charge profile depends on the dust initial charge as well as on the negative ions density.
Anomalous electro-optic effect in Sr0.6Ba0.4Nb2O6 single crystals and its application in two-dimensional laser scanning
Authors: Tian L. , Scrymgeour D. A. , Sharan Alok , Gopalan Venkatraman
Published: November 2003

We report an anomalous electro-optic effect that results in laser scanning along the polarization direction of strontium barium niobate (Sr0.6Ba0.4Nb2O6, or SBN:60) single crystals under external fields. The origin of such unusual phenomenon is believed to arise from inhomogeneous index gradients near the crystal surfaces, possibly arising from space-charge fields. Based on this effect, two-dimensional scanning is demonstrated by using a combination of SBN:60 single crystal (for vertical scanning; full scan angle of 0.79°±0.07°) and lithium tantalate (LiTaO3) (for horizontal scanning; full scan angle of 3.68°±0.14°).
Integrable generalized spin ladder models based on the SU(1|3) and SU(3|1) algebras
Authors: Tonel Arlei Prestes , Foerster Angela , Hibberd Katrina , Links Jon
Published: November 2003

We present two integrable spin ladder models which possess a general free parameter besides the rung coupling J. The models are exactly solvable by means of the Bethe ansatz method and we present the Bethe ansatz equations. We analyze the elementary excitations of the models which reveal the existence of a gap for both models that depends on the free parameter.
Contactless electroreflectance of CdSe/ZnSe quantum dots grown by molecular-beam epitaxy
Authors: Muñoz Martı́n , Guo Shiping , Zhou Xuecong , Tamargo Maria C. , Huang Y. S. , Trallero-Giner C. , Rodrı́guez A. H.
Published: November 2003

The interband transitions of a capped CdSe quantum-dot structure have been investigated using contactless electroreflectance. The electroreflectance spectrum shows transitions originating from all the portions of the sample including the quantum dots and the wetting layer. The transitions of the two-dimensional layers have been modeled using an envelope approximation calculation which takes into account the biaxial strain in the wetting layer. A good agreement was found between the experimental values for the transition energies and the calculated ones. From atomic force microscopy measurements, a lens shape was observed for the uncapped quantum dots. Taking into account the lens shape geometry and assuming that the effective height-to-radius ratio is preserved, the size of the capped quantum dots was determined using the observed electroreflectance transitions, in the framework of the effective mass approximation.
Experimental study of nanoparticle detection by optical gradient forces
Authors: Ignatovich Filipp V. , Novotny Lukas
Published: November 2003

We experimentally investigate a particle detection scheme that makes use of optical gradient forces. The path of nanoscale particles carried in a microfluidic channel is perturbed by a strongly focused laser beam. The perturbation is interferometrically recorded with a quadrant detector and the temporal asymmetry of the detector signal yields information about the force exerted on the particles by the laser focus. Large particles experience strong forces, thus rendering a highly asymmetric signal whereas small particles pass the laser focus almost unperturbed thus rendering a symmetric signal. We analyze the influence of experimental parameters such as laser power and fluid speed on the precision of the method and discuss the influence of Brownian motion.
Simple, sensitive nitrogen analyzer based on pulsed miniplasma source emission spectrometry
Authors: Jin Zhe , Duan Yixiang
Published: November 2003

The development of pulsed miniplasma source emission spectrometry for trace nitrogen determination in inert gases is described in this article. The instrument consists of a pulsed miniplasma source generated by an in-house fabricated portable high-voltage supply, an optical beam collection system, an integrated small spectrometer with a charge-coupled-device detector, an interface card, and a notebook computer for controlling spectrometer parameters and signal processing. Trace nitrogen in the inert gases, such as helium and argon, was determined by monitoring the emission intensities from nitrogen molecules at 357 and 337 nm. The analytical performance was examined under various experimental conditions. The system has a detection limit of about 15 ppb (v/v) for nitrogen in helium with a relative standard deviation of 1.5%. The newly developed instrument offers a simple, low-cost, and sensitive method for continuously monitoring trace nitrogen in high-purity inert gases.
Device to increase the dynamic range of high-pressure ionization chambers used in environmental radiation monitoring
Authors: Balagi V. , Prasad K. R. , Jakati R. K. , Kataria S. K.
Published: November 2003

An electronic device that can raise the upper limit of detected gamma exposure from 5 mR/h up to 100 R/h, in the case of a high-pressure ionization chamber (HPIC), has been developed. The chamber has a 7 L sensitive volume filled with high-purity argon at 300 psi pressure and its current sensitivity is 16 nA/R/h. An empirical relationship between I and R has been used to program the electronic device. This device consists of an autoranging dc amplifier, an 8751 microcontroller, and an analog to digital converter/digital to analog converter. A single current reading obtained at 300 V is processed by the system to display the exposure rate instantaneously. Experiments have shown that the exposure rate values derived are comparable to the rates delivered within ±7.7%. The method has the advantage of using a single ion chamber over a very wide range and the device can be used with existing HPIC systems. Potential applications include area gamma monitoring in power reactors and other laboratories.
Dynamic and atomistic deformation of sp2-bonded boron nitride nanoarrays
Authors: Iwamoto C. , Yang H. S. , Watanabe S. , Yoshida T.
Published: November 2003

With the aim of developing a nanostructure, we produced an sp2-bonded boron nitride nanoarray (BNNA), and observed its dynamic deformation behavior using high-resolution transmission electron microscopy with a piezoceramic tube for three-axis positioning of an indenter. The BNNA has remarkable flexibility and resiliency, such that no permanent deformation occurred when it was bent repeatedly to the minimum radius of curvature of about 4 nm. Even in repeated bends to the minimum radius of curvature of about 0.3 nm, the BNNA underwent no catastrophic failure.
High-quality-factor and small-mode-volume hexapole modes in photonic-crystal-slab nanocavities
Authors: Ryu Han-Youl , Notomi Masaya , Lee Yong-Hee
Published: November 2003

Using finite-difference time-domain calculations, we investigate the hexapole mode of photonic-crystal-slab modified triangular single-defect cavity structures as a good candidate for a high-quality factor (Q) and small-mode volume (V) resonant mode. Structural parameters are optimized to obtain very large Q of even higher than 2×106 with small effective V of the order of cubic wavelength in material, the record value of theoretical Q/V. It is found, by the Fourier-space investigation of resonant modes, that such a high Q from the hexapole mode is achieved due both to the cancellation mechanism related to hexagonally symmetric whispering-gallery-mode distribution and to the mode delocalization mechanism.
Thickness dependence of leakage currents in high-permittivity thin films
Authors: Schroeder Herbert , Schmitz Sam
Published: November 2003

The leakage current through high-permittivity perovskite thin films in the nanometer range is of great technological interest because of the possible applications of these insulating films in future submicroelectronic devices such as dielectrics in Gbit dynamic random access memories or gate oxides in metal–oxide–semiconductor field-effect transistors. The experimental result of decreasing leakage current with decreasing thickness of the dielectric for the same externally applied field can be described by using a model combining thermionic emission at the electrode/dielectric interface and a low-mobility, high-permittivity dielectric with low-permittivity layers at the interfaces, the so-called dead layers.
In-plane strain fluctuation in strained-Si/SiGe heterostructures
Authors: Sawano K. , Koh S. , Shiraki Y. , Usami N. , Nakagawa K.
Published: November 2003

In-plane strain fluctuation in the strained-Si/relaxed-SiGe heterostructure was studied by micro-Raman spectroscopy. It was found that misfit dislocation, which is necessarily induced by strain relaxation of SiGe buffer layers, caused micrometer-scale inhomogeneous strain field in the strained-Si layer as well as SiGe buffer, which may degrade device performance. After annealing, the fluctuation was found to be enhanced due to partial strain relaxation of strained Si, particularly in the region where tensile strain was relatively high before annealing. From homoepitaxial growth of SiGe on planarized SiGe buffer layers, it was confirmed that the growth rate also fluctuated laterally, in correspondence with the in-plane strain variation.
Coordination of boron and phosphorous in borophosphosilicate glasses
Authors: Carboni R. , Pacchioni G. , Fanciulli M. , Giglia A. , Mahne N. , Pedio M. , Nannarone S. , Boscherini F.
Published: November 2003

We report boron K-edge x-ray absorption near-edge structure measurements on borophosphosilicate glasses and density functional theory calculations aimed at determining the most stable local geometries for boron and phosphorous. We demonstrate that phosphorous induces a modification in the local structure of boron, from a trigonal to a tetrahedral geometry. The microscopic mechanisms involved are discussed.
Temperature dependence of the trapped magnetic field in MgB2 bulk superconductors
Authors: Viznichenko R. V. , Kordyuk A. A. , Fuchs G. , Nenkov K. , Müller K.-H. , Prikhna T. A. , Gawalek W.
Published: November 2003

Based on dc magnetization measurements, the temperature dependencies of the trapped magnetic field have been calculated for two MgB2 samples prepared by two different techniques: high-pressure sintering and hot pressing. Experimentally measured trapped field values for the first sample coincide remarkably well with calculated ones over the whole temperature range. This shows, on one hand, the validity of the introduced calculation approach, and demonstrates, on the other hand, the great prospects of the hot pressing technology for large scale superconducting applications of the MgB2.
Transition from granular to dilute magnetic semiconducting multilayers in ion-beam-deposited ZnO/Co
Authors: Pakhomov A. B. , Roberts Bradley K. , Krishnan Kannan M.
Published: November 2003

Multilayers of Co/ZnO, with varying nominal thickness of metal (2–10 Å) and semiconductor (2–20 Å), were prepared by ion-beam sputtering. Magnetic, transport, and magnetotransport measurements were carried out over a temperature range of 2.5 to 300 K. Upon decreasing Co thickness and increasing ZnO thickness in the multilayer stack, the properties of the samples undergo a crossover from those of granular metallic Co/semiconductor multilayers to a dilute magnetic semiconductor superlattice. We interpret ferromagnetism in the latter case as due to ordering in the Co-rich layers, mediated by carriers from lightly doped, high carrier concentration layers.
Identification of a Br-correlated bandgap state in GaAs by radiotracer spectroscopy
Authors: Albrecht F. , Pasold G. , Grillenberger J. , Achtziger N. , Witthuhn W. , Risse M. , Vianden R. , Dietrich M. ,   The ISOLDE Collaboration
Published: November 2003

A deep energy level of bromine in the bandgap of GaAs was determined by means of Radiotracer deep-level transient spectroscopy (DLTS) measurements. For this purpose, the radioactive isotope 77Br was implanted in p-type as well as in n-type GaAs. In the course of repeated DLTS measurements at n-type GaAs, the spectra are dominated by the occurrence of one bandgap state with the trap parameters Et=EC−0.45(2) eV and σ=2×10−14 cm2. This level vanishes on time scales of the nuclear half-life of the elemental transmutation from 77Br to 77Se (T1/2=57 h). Thereby, a definite correlation can be drawn between the observed bandgap state and a Br-correlated defect.
Enhanced electrical properties of c-axis epitaxial Nd-substituted Bi4Ti3O12 thin films
Authors: Zhang S. T. , Zhang X. J. , Cheng H. W. , Chen Y. F. , Liu Z. G. , Ming N. B. , Hu X. B. , Wang J. Y.
Published: November 2003

High-quality c-axis epitaxial ferroelectric thin films of Bi4Ti3O12 (BTO) and Nd-substituted BTO, Bi3.15Nd0.85Ti3O12 (BNT), were prepared on (001)-LaNiO3-coated (001) LaAlO3 substrates by pulsed-laser deposition. The epitaxial alignments were established by the x-ray diffraction, including θ–2θ and φ scans. Compared to the BTO films, the BNT films have significantly improved electrical properties with about 2 times larger remanent polarization, 0.6 times lower coercive field, better fatigue-resisting characteristics, and 1.7 times larger dielectric constant. These results showed experimentally that Nd substitution could enhance the c-axis electrical properties of BTO. The reason for the improved properties of BNT films was discussed.
Size-exclusion chromatography using self-organized nanopores in anodic porous alumina
Authors: Sano Tohru , Iguchi Noriyuki , Iida Kazuhiro , Sakamoto Toshitsugu , Baba Masakazu , Kawaura Hisao
Published: November 2003

We have achieved the size separation of DNA molecules on a biochip using an anodic porous alumina as a separation matrix in electrophoresis. The bottom of the microfluid channel on the chip was made of a porous alumina membrane that has uniform nanoscale pores on its surface. Since smaller molecules are much more frequently trapped by nanopores than larger ones, larger molecules elute earlier than smaller molecules. This type of separation is the same process as that resulting from size-exclusion chromatography. When two kinds of DNA samples (3.2 and 0.3 kilobases) were applied to the biochip, they were clearly separated into two bands, with the larger molecules (3.2 kilobases) eluting earlier. Since nanopore formation does not require any nanolithography, the fabrication is easy and inexpensive. The matrix can be integrated with other biomicroelectromechanical systems reactors on a micro total analysis system chip.
Nonlinear current-voltage characteristics of Pt nanowires and nanowire transistors fabricated by electron-beam deposition
Authors: Rotkina L. , Lin J.-F. , Bird J. P.
Published: November 2003

We have fabricated Pt/C composite nanowires and nanowire transistors, using the technique of electron-beam-induced deposition. The current-voltage characteristics of the granular nanowires are strongly nonlinear at 4.2 K, and evidence for this nonlinearity is found to persist to room temperature. A voltage gap of order 0.1–0.2 V is observed at the lowest temperatures, and we suggest that this feature is consistent with single-electron tunneling via Pt nanocrystals that form in the wires during their fabrication. In order to further explore this possibility, we incorporate the nanowires into three-terminal transistor structures and find evidence for a gate-induced modulation of their voltage gap.
Transfer of nanoporous pattern of anodic porous alumina into Si substrate
Authors: Asoh Hidetaka , Matsuo Mamoru , Yoshihama Megumi , Ono Sachiko
Published: November 2003

Nanohole arrays in a Si substrate with a self-ordered configuration having a 100 nm hole periodicity were fabricated by the pattern transfer of the hole configuration of anodic porous alumina. The self-ordered anodic porous alumina used as a mask was directly prepared by anodizing an aluminum film sputtered on a Si substrate. The transfer of the nanoporous pattern of anodic alumina into the Si substrate could be achieved by removing silicon oxide, which was produced by the anodic oxidation of the local part of the Si substrate underneath the barrier layer corresponding to the pore base. In addition, we confirmed that the transformation of the nanostructure of porous alumina grown on a Si substrate is comparable to the current transient during alumina film formation.
Reversible shift of the transition temperature of manganites in planar field-effect devices patterned by atomic force microscope
Authors: Pallecchi I. , Pellegrino L. , Bellingeri E. , Siri A. S. , Marré D.
Published: November 2003

A planar side-gate device for field effect with a La0.67Ba0.33MnO3 channel on a SrTiO3 substrate is fabricated by means of the voltage-biased tip of an atomic force microscope. The peculiar geometry and the high dielectric permittivity of the substrate enhance the channel resistance modulation up to 20% at low temperature by a gate voltage of ±40 V. Moreover, a reversible shift by 1.3 K of the metal–insulator transition temperature (TMI) by field effect is observed. The signs of the changes of resistance and TMI both depend on the sign of the gate voltage, as expected for pure field effect; in particular, the TMI is raised (lowered) by accumulating (depleting) holes in the channel.