bluuebunny/crossref_metadata_2025 huggingface dataset:
Direct mask-free patterning of molecular organic semiconductors using organic vapor jet printing
Authors: Shtein Max , Peumans Peter , Benziger Jay B. , Forrest Stephen R.
Published: October 2004

We demonstrate the solvent-free, high-resolution direct printing of molecular organic semiconductors for use in low cost optoelectronic applications. In this method, called organic vapor jet printing, hot inert carrier gas picks up the molecular organic vapor and expands it through a microscopic nozzle, resulting in physisorption of the molecules onto a cooled substrate. Pattern resolution and printing speed are determined by the nozzle shape, nozzle-to-substrate distance, downstream pressure, and molecular mass of the carrier gas. Quantitative models are developed using a combination of scaling analysis, direct simulation Monte Carlo modeling, and printing experiments. Pattern resolutions of up to 1000dpi and local deposition rates exceeding 2300Å∕s are achieved. Pentacene channel thin film transistors are printed at a local deposition rate of 700Å∕s at both low and atmospheric pressures, resulting in a field-effect mobility of 0.25cm2∕Vs and a current on/off ratio of 7×105 for devices grown at a background pressure of 0.24Torr. The high directionality of the molecular jets and well-defined shape of the deposits enables combinatorial printing of structures and devices, while affording considerable control over film morphology. The method is also readily applicable to document printing using solvent-free inks.
Thermophoretic control of building units in the plasma-assisted deposition of nanostructured carbon films
Authors: Rutkevych P. P. , Ostrikov K. , Xu S. , Vladimirov S. V.
Published: October 2004

The possibility of the thermophoretic control of the plasma-grown building units in the plasma-assisted deposition of various carbon-based nanostructures on Ni-based catalyzed Si substrates is reported. It is experimentally demonstrated that varying the near-substrate temperature gradient, one can selectively deposit or levitate the carbon-based nanoparticles grown in the low-temperature reactive plasmas of Ar+H2+CH4 gas mixtures. When the nanoparticles are levitated in the plasma presheath, the arrays of vertically aligned carbon nanotips are assembled, whereas the enhanced deposition of the building units from the gas phase favors the formation of polymorphous nanostructured carbon films. The experimental observations are supported by the one-dimensional model of the nanoparticle dynamics in the near-electrode area. It is shown that the thermophoretic force is indeed a crucial factor that controls the deposition of the plasma-grown fine particles. The experimental and computation results suggest that it is likely that the aligned carbon nanotip structures are predominantly grown by the molecular or radical units, whereas the plasma-grown nanoparticles are presumably the most important component of polymorphous carbon films.
Quasi-spherical cavity resonators for metrology based on the relative dielectric permittivity of gases
Authors: May Eric F. , Pitre Laurent , Mehl James B. , Moldover Michael R. , Schmidt James W.
Published: October 2004

We evaluate a quasi-spherical, copper, microwave cavity resonator for accurately measuring the relative dielectric permittivity εr(p,T) of helium and argon. In a simple, crude approximation the cavity’s shape is a triaxial ellipsoid with axes of length a,1.001a and 1.005a, with a=5 cm. The unequal axes of the quasi-sphere separated each of the triply degenerate microwave resonance frequencies of a sphere (f11TM,f12TM,…,f11TE,f12TE,…) into three nonoverlapping, easily measured, frequencies. The frequency splittings are consistent with the cavity’s shape, as determined from dimensional measurements. We deduced εr(p,T) of helium and of argon at 289 K and up to 7 MPa from the resonance frequencies flnσ, the resonance half-widths glnσ, and the compressibility of copper. Simultaneous measurements of εr(p,T) with the quasi-spherical resonator and a cross capacitor agreed within 1×10−6 for helium, and for argon they differed by an average of only 1.4×10−6. This small difference is within the stated uncertainty of the capacitance measurements. For helium, the resonator results for εr(p,T) were reproducible over intervals of days with a standard uncertainty of 0.2×10−6, consistent with a temperature irreproducibility of 5 mK. We demonstrate that several properties of quasi-spherical cavity resonators make them well suited to εr(p,T) determinations. Ultimately, a quasi-spherical resonator may improve dielectric constant gas thermometry and realize a proposed pressure standard based on εr(p,T).
Microsystem with integrated capillary leak to mass spectrometer for high sensitivity temperature programmed desorption
Authors: Quaade Ulrich J. , Jensen Søren , Hansen Ole
Published: October 2004

Temperature programmed desorption (TPD) is a method for obtaining information about quantities and binding properties of adsorbed species on a surface. A microfabricated flow system for TPD with an integrated capillary leak to a mass spectrometer is presented. The use of an integrated capillary leak minimizes dead volumes in the system, resulting in increased sensitivity and reduced response time. These properties make the system ideal for TPD experiments in a carrier gas. With CO desorbing from platinum as model system, it is shown that CO desorbing in 105 Pa of argon from as little as 0.5 cm2 of platinum foil gives a clear desorption peak. By using the microfabricated flow system, TPD experiments can be performed in a carrier gas with a sensitivity approaching that of TPD experiments in vacuum.
Broadband precision wavelength meter based on a stepping Fabry–Pérot interferometer
Authors: Scholl T. J. , Rehse S. J. , Holt R. A. , Rosner S. D.
Published: October 2004

We have constructed a broadband apparatus for wavelength metrology capable of absolute accuracy at a level of better than 2 parts in 109. An evacuated plane-parallel Fabry–Pérot interferometer with continuously adjustable mirror separation is used to compare the wavelength of a single-frequency tunable laser with that of an iodine-stabilized HeNe laser used as a wavelength standard. This work details apparatus construction, a thorough investigation of systematic errors, and data analysis. The wavelengths of five Doppler-free Te2130 transitions in the region from 475.6 to 490.8 nm have been measured and are found to be in excellent agreement with previous measurements. In addition, the wavelengths of five previously unmeasured Te2130 transitions spanning the region from 424.9 to 462.3 nm have been determined for use as new reference wavelength standards.
Low cost multitarget holder for pulsed laser deposition system
Authors: Wang Xu , Pun Arthur F. , Xin Yan , Zheng Jim P.
Published: October 2004

A low cost multi-target holder (MTH) designed for pulsed laser deposition (PLD) systems fit for vacuum chamber ports of all size was designed and fabricated using only one rotary-linear motion feedthrough. This system can be used with vacuum chamber ports of small size because of the elimination of a second feedthrough. It provides current PLD chambers without enough large ports the ability to grow multi-layer films, and can decrease the required PLD chamber size. Its design of separate low cost MTH head and stud modules can be utilized to further prevent cross contamination from different multi-layer film fabrications. The MTH described was successfully utilized to grow SrRuO3–SrTiO3–SrRuO3 tri-layer films on LaAlO3 substrate.
Unsteady flow field in a square tube T-junction
Authors: Anagnostopoulos J. S. , Mathioulakis D. S.
Published: October 2004

This work constitutes an extension of two previous experimental studies, examining the flow field in a square tube T-junction with a time-dependent periodic inlet flow rate (zero to a maximum value) and equal branch flow rates. Based on numerical predictions, more details of the flow field are revealed, not being easily detectable by the experiment. Emphasis is given on the recirculation regions examining the velocity, pressure, and wall shear stress distributions as well as the limiting streamlines as a function of time. During acceleration an adverse pressure gradient builds up at the junction due to the streamlines curvature, causing flow separation before flow peak, which initiates at the corners of the tube cross section. Flow separation and reattachment lines, determined by the limiting streamline topology, move apart during deceleration. Streamwise cross-flow vortices appear in both branches, being much stronger in the 90° branch. The characteristics of the latter vortices, namely their circulation, swirl ratio, velocity distribution, as well as the process of their birth at the beginning of each cycle are examined in detail. Wall shear stress distributions exhibit maximum values at the entrance of the 90° branch, taking values proportional to the inlet time-dependent flow rate. Finally, comparisons with steady inlet conditions showed that in the unsteady case the flow can sustain much higher adverse pressure gradients before separating.
Prediction of barrier localization in modulated nanowires
Authors: Lew Yan Voon L. C. , Lassen B. , Melnik R. , Willatzen M.
Published: October 2004

It is shown that the phenomenon of inversion recently discovered in a one-band model [L. C. Lew Yan Voon and M. Willatzen, J. Appl. Phys. 93, 9997 (2003)] is much more general and is present in both multiband theories and in the excited states. Predictions of the one-band and of a four-band model are in good agreement for the ground state. A critical radius of around 15Å(7Å) is obtained for holes in InGaAs∕InP(GaAs∕AlAs) modulated nanowires. This phenomenon should be readily observable in both optical spectroscopy and transport.
Investigation of the optical properties of InGaAsN∕GaAs∕GaAsP multiple-quantum-well laser with 8-band and 10-band k·p model
Authors: Ng S. T. , Fan W. J. , Yoon S. F. , Wang S. Z. , Qu Yi , Liu C. Y. , Ma S. G. , Yuan Shu
Published: October 2004

We have used both 10-band and 8-band k·p Hamiltonian to investigate the maximum TE-mode optical gain for the triple quantum wells with In0.35Ga0.65As0.985N0.015 as the active layers and barriers comprised of two unstrained GaAs layers and one tensile-strained GaAs0.82P0.18 layer. The results were compared to a similar structure without the GaAsP layer and were discovered that the presence of the GaAsP barrier reduced the carrier density at threshold condition. However, the characteristics of the optical gain versus radiative current density for both structures are very similar. We also found the conduction band energy dispersion curves calculated by the 8-band model are flatter than the 10-band model due to the larger InGaAsN effective mass used. The transparent carrier density of the 10-band model is smaller than that of the 8-band model. The radiative recombination coefficient B calculated by the two models varies from 3.5×10−11cm3∕s for the 8-band model to 8.0×10−11cm3∕s for the 10-band model. Using Jtot=nwql(AN+BN2+CN3), the calculated Jth of 558A∕cm2 agrees very well with the experimentally observed threshold current density of a 10×1600μm2 broad-area laser.
Intervalence band absorption and carrier heating in type-II Sb-based lasers
Authors: Lobad Ahmed I. , Vern Schlie L. A.
Published: October 2004

The intervalence absorption in InAs∕InGaSb∕InAs type-II 4μm quantum well laser structure was investigated using band-edge nonlinear pump-probe spectroscopy techniques where two pump beams chopped at different frequencies are used to excite the sample. The spectrally resolved probe nonlinearity is measured at the sum frequency. Given their different characteristic nonlinearities, the contribution of the intervalence band absorption process (IVA) was resolved from that of the interband gain dynamics. The IVA absorption occurs at in-plane momentum k‖∼0.025Å and is not resonant with the interband lasing energy, therefore does not compete with the interband transition at low temperature and low carrier densities. A density dependent interband transition matrix element of N0.17 was deduced reflecting the enhancement of the electron hole wave function overlap due to the space-charge fields in the type-II wells. Significant lattice heating observed above 80K is reflected in the growth of an out of phase slow signal, resulting from the reduction of lattice thermal conductivity and a possible IVA resonance enhanced nonradiative Auger recombination transitions at higher temperatures. Thermal diffusion times of the order of ∼100μs that increases with temperature were measured.
Atomic scale stresses and strains in Ge∕Si(001) nanopixels: An atomistic simulation study
Authors: Makeev Maxim A. , Yu Wenbin , Madhukar Anupam
Published: October 2004

Recent progress in the growth of nanostructures on nonplanar (patterned) substrates has brought to the forefront issues related to atomic-level surface and subsurface stress and strain field variations, as these govern the process of formation of such nanostructures and strongly affect their physical properties. In this work, we use atomistic simulations to study the atomically resolved displacements, stresses, strains, and the strain energy in laterally finite nanoscale Si(001) mesas, uncovered and covered with the lattice-mismatched Ge overlayers. The spatial variations of the stress are examined both across the surface profile of the mesas and in the direction down to the substrate. We find that the hydrostatic stress and strain at the Ge∕Si interface undergo rapid changes from tensile in the interior of the Si mesa to compressive in the Ge overlayer, with the transition taking place over distances of the order of Si lattice constant. Substantial relaxation of the hydrostatic stress and strain, in both the lateral and vertical directions, is observed in the Ge overlayer, in the Si(001) mesa interior, and in the substrate. Atomic displacement fields, computed in the Ge overlayer and in the Si(001) mesa interior, demonstrate considerable inhomogeneity due to both finite geometry effects and the lattice-mismatched Ge overlayer–induced stresses. The maximum magnitude of displacements is as large as 0.7Å, even in the case of uncovered Si(001) mesa. Moreover, we find nonzero displacements in the Si substrate as far deep as 100ML (monolayer) from the Ge∕Si interface, showing that a substantial degree of the misfit-induced stress accommodation occurs through relaxation in the Si(001) mesa interior and the substrate. The topology of the equal displacement contours, in regions adjacent to the mesa edges and corners, is close to semielliptical. To reveal the impact of stress accommodation in the mesa interior and in the substrate, we compute the strain energies of the Ge overlayer atoms as a function of both the Si(001) mesa height and the Ge overlayer thickness. We find that the normalized (per Ge atom) elastic energy of a fixed thickness overlayer decreases with increasing mesa depth. At a fixed mesa height, the Ge overlayer energy per Ge atom increases as a function of Ge overlayer thickness. In both cases, the dependencies are shown to be adequately fitted with exponential forms. The shear stresses in both bare and 16ML thick Ge overlayer covered mesa systems show dramatic variations in both lateral and vertical directions. These variations are responsible for nonlinear stress-strain behavior in the regions around the finite geometry features (i.e., edges and corners).
The formation and dynamics of a blob on free and wall sheets induced by a drop impact on surfaces
Authors: Fedorchenko Alexander I. , Wang An-Bang
Published: October 2004

A physical model for describing an inviscid motion of free and wall liquid sheets induced by drop impact is presented. This model takes into account the formation of thick borders at the edge of a spreading drop, and the influence of advancing and receding contact angles on the dynamics of blob formation and motion. It has been shown that the blob motion on a free liquid sheet is described by a universal relationship (independent of the Weber number) in terms of dimensionless blob coordinates at both advancing and receding stages. For the case of blob formation and motion on a wall sheet at high Weber numbers, only the advancing stage is described by a universal relationship. The receding stage depends on the ratio of advancing and receding contact angles, but not on the Weber number. At the instant when the drop is at its maximum extension, the blob speed becomes equal to the liquid sheet velocity and the total kinetic energy of the drop is greater than zero. It is shown that the ratio of the instantaneous capillary wavelength to the sheet thickness is a constant 2.619 for a free sheet, when the capillary wave propagates away from the blob.
Electric field due to alternating current injected at the surface of a metal plate
Authors: Bowler N.
Published: October 2004

Closed form analytical expressions for the electric field interior and exterior to a metal plate, due to alternating current injected at its surface, are derived. Assuming that the current is injected and extracted by wires oriented perpendicular to the surface of the plate, the problem is decomposed into two cylindrically symmetric systems in which a single current-carrying wire lies on the coordinate axis. This simplified problem is formulated in terms of a single magnetic potential and the solution obtained by use of the Hankel transform. The resulting expression for the electric field in the plate takes the form of an analytic series. In exterior regions, the electric field is expressed in terms of Hankel transforms. The result for the physical system with two current-carrying wires is obtained by superposition.
Comment on “Low-resistance ohmic contacts to p-type GaN achieved by the oxidation of Ni∕Au films” [J. Appl. Phys. 86, 4491 (1999)]
Authors: Yu Lisheng , Qiao D.
Published: October 2004

A very low barrier height (∼0.055V) at the p-GaN side in energy band diagram of p-NiO∕p-GaN interface was obtained in the paper: “low-resistance ohmic contacts to p-type GaN achieved by the oxidation of Ni∕Au films.” They contributed the low contact resistance to the low energy barrier height for holes. We indicate the mistake of their calculation and obtain a barrier height of 2.28V and a notch of 0.19V on the p-GaN side and the p-NiO side, respectively, in this comment.
Magnetic switching depending on as-patterned magnetization state in Pac-man shaped Ni80Fe20 submicron elements
Authors: Pujada B. R. , Svendsen J. , Chipeniuk K. O. , Choi B. C. , Park M. H. , Hong Y. K. , Gee S. H. , Erickson D. W.
Published: October 2004

Magnetization configuration and magnetic switching of submiron “Pac-man” shaped Ni80Fe20 elements with conventional and modified (i.e., elongated) geometry have been studied using magnetic force microscopy, magneto-optical Kerr effect, and micromagnetic simulations. Experimental measurements and modeling analysis clearly demonstrate that the sensitive interplay between exchange, demagnetizing, and shape anisotropy energies leads to distinct magnetization configurations and magnetic switching mechanisms, even though the geometric shape of elements is only slightly modified. In a particular case, such as 40% elongated element, vortex-driven magnetic switching is replaced by well-defined coherent reversal.
Time-resolved cavity ringdown study of the Si and SiH3 surface reaction probability during plasma deposition of a-Si:H at different substrate temperatures
Authors: Hoefnagels J. P. M. , Barrell Y. , Kessels W. M. M. , van de Sanden M. C. M.
Published: October 2004

Time-resolved cavity ringdown spectroscopy (τ-CRDS) has been applied to determine the surface reaction probability β of Si and SiH3 radicals during plasma deposition of hydrogenated amorphous silicon (a-Si:H). In an innovative approach, our remote Ar-H2-SiH4 plasma is modulated by applying pulsed rf power to the substrate and the resulting time-dependent radical densities are monitored to yield the radical loss rates. It is demonstrated that the loss rates obtained with this τ-CRDS technique equal the loss rates in the undisturbed plasma and the determination of the gas phase reaction rates of Si and SiH3 as well as their surface reaction probability β is discussed in detail. It is shown that Si is mainly lost in the gas phase to SiH4 [reaction rate kr=(3.0±0.6)×10−16m3s−1], while the probability for Si to react at an a-Si:H surface is 0.95<βSi<1 for a substrate temperature of 200°C. SiH3 is only lost in reactions with the surface and measurements of β of SiH3 for substrate temperatures in the range of 50–450°C show that βSiH3=(0.30±0.03), independent of the substrate temperature. The implications for a-Si:H film growth are discussed.
Electrical and structural properties of MgB2 films prepared by sequential deposition of B and Mg on the NbN-buffered Si(100) substrate
Authors: Chromik Š. , Gaži Š. , Štrbík V. , Španková M. , Vávra I. , Beňačka Š. , van der Beek C. J. , Gierlowski P.
Published: October 2004

We introduce a simple method of a MgB2 film preparation using a sequential electron-beam evaporation of B-Mg bilayer (followed by in-situ annealing) on the NbN-buffered Si(100) substrate. The transmission electron microscopy analyses confirm a growth of homogeneous nanogranular MgB2 films without the presence of crystalline MgO. A sensitive measurement of temperature dependence of microwave losses shows a presence of intergranular weak links close to the superconducting transition only. The MgB2 films obtained, about 200-nm thick, exhibit a maximum zero resistance critical temperature of 36K and a critical current density of 3×107A∕cm2 at 13.2K.
Thin-film metal catalyst for the production of multi-wall and single-wall carbon nanotubes
Authors: Lacerda R. G. , Teo K. B. K. , Teh A. S. , Yang M. H. , Dalal S. H. , Jefferson D. A. , Durrell J. H. , Rupesinghe N. L. , Roy D. , Amaratunga G. A. J. , Milne W. I. , Wyczisk F. , Legagneux P. , Chhowalla M.
Published: October 2004

We present a detailed study of the growth of multiwall and single-wall carbon nanotubes (SWCNTs) by chemical-vapor deposition using a thin-film triple metal (Al∕Fe∕Mo) catalyst. Using Nanoauger spectroscopy, a full map of the metals in the sample surface is constructed and their evolution followed at different deposition temperatures. During the formation of SWCNTs at high temperatures (∼1000°C), the initial iron layer (∼1nm) is transformed into nanosized particles at the surface. In addition, the Al layer also plays a critical role during the annealing process by being altered into AlxOy particles. These particles act as a suitable underlayer to stabilize the nanosized Fe catalyst for nanotube growth. We also show that it is possible to resolve SWCNTs by mapping the areal intensity of carbon KVV Auger electrons.
Thermal response of nanocomposite materials under pulsed laser excitation
Authors: Rashidi-Huyeh Majid , Palpant Bruno
Published: October 2004

The optical properties of nanocomposite materials made of matrix-embedded noble metal nanoparticles strongly depend on thermal effects from different origins. We propose a classical model describing the energy exchanges within the nanoparticles and between the latter and the surrounding dielectric host subsequent to a light pulse absorption. This model, which accounts for the thermal interactions between neighboring particles, allows us to calculate numerically the temperature dynamics of the electrons, metal lattice and matrix as functions of particle size, and metal concentration of the medium, whatever be the pulsed excitation temporal regime. It is illustrated in the case of Au:SiO2 materials under femtosecond and nanosecond pulse excitation. It is shown that, in the femtosecond regime, the heat transfer to the matrix cannot be neglected beyond a few picosecond delay from which particle size and metal concentration play a significant role in the electron relaxation. In the nanosecond regime, these morphologic parameters influence crucially the material thermal behavior with the possibility of generating a thermal lens effect. The implications in the analysis of experimental results regarding both the electron relaxation dynamics and the nonlinear optical properties are also discussed. Finally, a method to adapt the model to the case of thin nanocomposite film is proposed.
The determination of a continuum mechanics equivalent elastic strain from the analysis of multiple diffraction peaks
Authors: Daymond Mark R.
Published: October 2004

Stress measurement by neutron or synchrotron x-ray diffraction is a nondestructive technique that provides insights into strain and/or stress fields deep within engineering components and structures. The technique is seeing increased use for the validation of finite element process models, however, present FE models predict a continuum elastic strain rather than diffraction strains. An expression is therefore derived for a physically realistic weighting of strains obtained from multiple single peak diffraction measurements of internal elastic strain in order to determine a macroscopic equivalent elastic strain, and hence stress. A practical approach to the use of the expression is suggested. A similar expression is derived for the equivalent weighting used in Rietveld refinements, for both polychromatic and monochromatic sources, which is applicable to both neutron and x-ray diffraction. The use of these expressions is illustrated for both textured and untextured, cubic (steel) and hexagonal (titanium) symmetry polycrystals. The physically realistic weighting is different from that used in the Rietveld refinement however both provide good estimates of the macroscopic equivalent elastic strain.
A model for the dissipation rate tensor in inhomogeneous and anisotropic turbulence
Authors: Perot Blair , Natu Sadbhaw
Published: October 2004

A model for the dissipation rate tensor in anisotropic inhomogeneous turbulence is developed. By including terms that depend on gradients a dissipation model is developed that is exact in the limit of very strong inhomogeneity (such as near solid walls or free surfaces). Rapid distortion theory and equilibrium theory are used to motivate the anisotropic terms in the model. The resulting model has only one free constant (from the equilibrium theory) which is determined via comparisons with turbulent channel flow at Re=590. A priori tests of the model for two shear-free boundary layers, channel flow at lower Reynolds numbers, and a backward facing step are presented. Full simulations using the model in channel flow are also performed. Comparisons are made with a variety of existing tensor dissipation rate models.
Use of linear wire array Z pinches to examine plasma dynamics in high magnetic fields
Authors: Bland S. N. , Lebedev S. V. , Chittenden J. P. , Ampleford D. J. , Tang G.
Published: October 2004

Planar arrangements of tungsten wires, with a flat, closely positioned current return surface, were driven by the Magpie generator (1 MA,240 ns) [I. H. Mitchell et al., Rev. Sci. Instrum. 67, 1553 (1996)]. This “linear array” configuration was expected to increase the magnetic field and forces experienced by the wires to the same level as created in experiments at the 20 MA Z facility. The wires in the linear array ablated, on average, (5–6)× faster than in 1 MA cylindrical array experiments—consistent with the expected increase in force at the wires. Streams of coronal plasma flowed from the wires to form a precursor column offset from the plane of the linear array. The dynamics of the column suggested that a much larger fraction of current flowed through it than in cylindrical array experiments (∼20%–30% cf. <7%). Inductance determined the division of current between the wires of the array; the lower inductance edge wires experienced higher currents and magnetic fields than the center wires, further increasing the ablation rate of the edge wires, resulting in an earlier start to their implosion. Timing of the implosion provided evidence that the “ablation velocity” of plasma in an array does not change with the level of drive current.
Vortex models based on similarity solutions of the two-dimensional diffusion equation
Authors: Satijn M. P. , van Buren M. G. , Clercx H. J. H. , van Heijst G. J. F.
Published: October 2004

In this paper, a class of two-dimensional (2D) vortex models is analyzed, which is based on similarity solutions of the diffusion equation. If the nonlinear advective term is neglected, the 2D Navier-Stokes equation reduces to a linear problem, for which a complete orthonormal set of eigenfunctions is known on an unbounded 2D domain. Some of the basic modes represent models for diffusing monopoles, dipoles, and tripolar vortices, which evolve self-similarly in time. Here, we mainly confine ourselves to an analysis of the dipole solution. In several respects, especially the decay and, to a lesser extent, the lateral expansion properties, the dipole model appears to be in fair agreement with the real evolution of dipolar vortices for finite Reynolds number, as obtained from numerical simulations of the full 2D Navier-Stokes equations. However, the simulations reveal that nonlinear effects result in small differences compared to the evolution according to the model. The most important nonlinear effect that was observed is the formation of “tails” of vorticity in the wake of the dipole. After a while, any initial condition leads to a vorticity distribution lying in between the viscous similarity solution and the Lamb dipole solution, which represents the limit of a stationary, inviscid flow. The exact form of the vorticity distribution is believed to be determined by an equilibrium between diffusion of vorticity through the separatrix and advection of vorticity into the wake of the dipole, which results in the formation of vorticity tails. A comparison revealed profound qualitative agreements between the model together with the simulations and dipolar vortex structures that were studied by laboratory experiments in stratified fluids.
Are There Lexicons?
Authors: Coltheart Max
Published: October 2004

Many models of the processing of printed or spoken words or objects or faces propose that systems of local representations of the forms of such stimuli—lexicons—exist. This is denied by partisans of the distributed-representation connectionist approach to cognitive modelling. An experimental paradigm of key theoretical importance here is lexical decision and its analogue in the domain of objects, object decision. How does each theoretical camp account for our ability to perform these two tasks? The localists say that the tasks are done by matching or failing to match a stimulus to a local representation in a lexicon. Advocates of distributed representations often do not seek to explain these two tasks; however, when they do, they propose that patterns of activation evoked in a semantic system can be used to discriminate between words and nonwords, or between real objects and false objects. Therefore the distributed-representation account of lexical and object decision tasks predicts that performance on these tasks can never be normal in patients with an impaired semantic system, nor in patients who cannot access semantics normally from the stimulus domain being tested. However, numerous such patients have been reported in the literature, indicating that semantic access is not needed for normal performance on these tasks. Such results support the localist form of modelling rather than the distributed-representation approach.
Evidence of the Intercalative Redox Polymerization of Ehylenedioxythiophene into V2O5 ;Achievement of Highly Conducting Poly(3,4‐Ethylenedioxythiophene)/V2O5 Nanohybrids
Authors: Murugan A. V. , Kwon C. W. , Hwang S. J. , Delville M. H. , Portier J. , Campet G.
Published: October 2004

We have established a novel method of inserting poly(3,4‐ethylenedioxythiophene) (PEDOT) between the layers of
V2O5 using a soft process of intercalation. The reaction takes place with the in situ polymerization of EDOT within the framework of crystalline V2O5 with different nominal EDOT/V2O5 ratios. The hybrids PEDOT/V2O5 exhibit a high electrical conductivity
New Cad Model of the Microstrip Interdigital Capacitor
Authors: Dib Nihad , Zhangb Qiu , Rohde Ulrich
Published: October 2004

A new model for the microstrip line interdigital capacitor is proposed. This model consists of calculating the
2N × 2N Y‐matrix of the N coupled lines using the multiple coupled line tool. Then, this matrix is reduced to a
2 × 2 matrix using simple circuit theory. The capacitance at the end of each finger is taken into consideration using closed‐form expression of the coplanar waveguide open‐end capacitance. This model can predict the resonances that might appear around the quarter‐wavelength frequency. These resonances are caused by the
coupling between the fingers and exist only in capacitors with four fingers or more. Very good agreement is obtained between the results of our model and those obtained using the software HFSS and measurements.
Structural and Optical Properties of In2S3 Thin Films Prepared by Flash Evaporation
Authors: Bouabid K. , Ihlal A. , Outzourhit A. , Ameziane E. L.
Published: October 2004

In2S3thin films were deposited by flash evaporation of In2S3 powder. The effect of annealing in vacuum and under
sulphur atmosphere on the structural and optical properties of these films was investigated. X‐ray diffraction studies reveal that the as‐deposited films are amorphous. The formation of β‐In2S3 phase is obtained after annealing under
vacuum at 693 K. Heat treatments under sulphur pressure lead to the formation of the above phase at a less annealing temperature (573 K). The energy dispersive X‐ray (EDX) analysis reveals that the sulphurized films are nearly stoichiometric and those annealed in vacuum are sulphur deficient. Optical transmission spectra showed a slight
shift of the absorption edge towards lower wavelengths. The optical gap value varied between 2.4 and 3 eV as a function of the film thickness and the annealing temperature.
A Novel Mixed‐Mode CCII‐Based Filter
Authors: Abuelma′atti Muhammad Taher , Bentrcia Abdulwahab
Published: October 2004

A new mixed‐mode biquad circuit is presented. The circuit uses five second‐generation current conveyors, seven resistors, and two grounded capacitors and can realize lowpass, highpass, bandpass , notch, lowpass notch, highpass notch and allpass responses from the same topology. The circuit can be driven by voltage or current and its output can be voltage or current. The parameters ωo and ωo/Qo enjoy independent electronic tunability. Simulation results are included.
Novel Cascadable Current Mode Translinear‐C Universal Filter
Authors: Maheshwari Sudhanshu , Khan Iqbal A.
Published: October 2004

A novel cascadable current‐mode universal filter employing three current‐controlled conveyors (translinear conveyors) and two grounded capacitors is proposed. The circuit with single input and three high‐impedance current outputs, ideal for cascading, realizes low‐pass, band‐pass, and inverting band‐reject transfer functions. Inverting high‐pass and inverting all‐pass transfer functions are obtained by simply connecting the available
outputs. The proposed circuit enjoys tuning through external currents, low total harmonic distortion (THD), good dynamic range, attractive sensitivity performance and is ideal for IC implementation.
A Subset of Liver NK T Cells Is Activated duringLeishmania donovaniInfection by CD1d-bound Lipophosphoglycan
Authors: Amprey Joseph L. , Im Jin S. , Turco Salvatore J. , Murray Henry W. , Illarionov Petr A. , Besra Gurdyal S. , Porcelli Steven A. , Späth Gerald F.
Published: October 2004

Natural killer (NK) T cells are activated by synthetic or self-glycolipids and implicated in innate host resistance to a range of viral, bacterial, and protozoan pathogens. Despite the immunogenicity of microbial lipoglycans and their promiscuous binding to CD1d, no pathogen-derived glycolipid antigen presented by this pathway has been identified to date. In the current work, we show increased susceptibility of NK T cell–deficient CD1d−/− mice to Leishmania donovani infection and Leishmania-induced CD1d-dependent activation of NK T cells in wild-type animals. The elicited response was Th1 polarized, occurred as early as 2 h after infection, and was independent from IL-12. The Leishmania surface glycoconjugate lipophosphoglycan, as well as related glycoinositol phospholipids, bound with high affinity to CD1d and induced a CD1d-dependent IFNγ response in naive intrahepatic lymphocytes. Together, these data identify Leishmania surface glycoconjugates as potential glycolipid antigens and suggest an important role for the CD1d–NK T cell immune axis in the early response to visceral Leishmania infection.
Imaging the Single Cell Dynamics of CD4+ T Cell Activation by Dendritic Cells in Lymph Nodes
Authors: Miller Mark J. , Safrina Olga , Parker Ian , Cahalan Michael D.
Published: October 2004

The adaptive immune response is initiated in secondary lymphoid organs by contact between antigen-bearing dendritic cells (DCs) and antigen-specific CD4+ T cells. However, there is scant information regarding the single cell dynamics of this process in vivo. Using two-photon microscopy, we imaged the real-time behavior of naive CD4+ T cells and in vivo–labeled DCs in lymph nodes during a robust T cell response. In the first 2 h after entry into lymph nodes, T cells made short-lived contacts with antigen-bearing DCs, each contact lasting an average of 11–12 min and occurring mainly on dendrites. Altered patterns of T cell motility during this early stage of antigen recognition promoted serial engagement with several adjacent DCs. Subsequently, T cell behavior progressed through additional distinct stages, including long-lived clusters, dynamic swarms, and finally autonomous migration punctuated by cell division. These observations suggest that the immunological synapse in native tissues is remarkably fluid, and that stable synapses form only at specific stages of antigen presentation to T cells. Furthermore, the serial nature of these interactions implies that T cells activate by way of multiple antigen recognition events.
SGS3 and SGS2/SDE1/RDR6 are required for juvenile development and the production of trans-acting siRNAs in Arabidopsis
Authors: Peragine Angela , Yoshikawa Manabu , Wu Gang , Albrecht Heidi L. , Poethig R. Scott
Published: October 2004

Higher plants undergo a transition from a juvenile to an adult phase of vegetative development prior to flowering. Screens for mutants that undergo this transition precociously produced alleles of two genes required for posttranscriptional gene silencing (PTGS)—SUPPRESSOR OF GENE SILENCING3 (SGS3) and SUPPRESSOR OF GENE SILENCING2(SGS2)/SILENCING DEFECTIVE1 (SDE1)/RNA-DEPENDENT POLYMERASE6 (RDR6). Loss-of-function mutations in these genes have a phenotype similar to that of mutations in the Argonaute gene ZIPPY (ZIP). Epistasis analysis suggests that ZIP, SGS3, SGS2/SDE1/RDR6, and the putative miRNA export receptor, HASTY (HST), operate in the same pathway(s). Microarray analysis revealed a small number of genes whose mRNA is increased in ZIP, SGS3, and SGS2/SDE1/RDR6 mutants, as well as genes that are up-regulated in SGS3 and SGS2/SDE1/RDR6 mutants, but not in ZIP mutants. One of these latter genes (At5g18040) is silenced posttranscriptionally in trans by the sRNA255 family of endogenous, noncoding, small interfering RNAs (siRNAs). The increase in At5g18040 mRNA in SGS3 and SGS2/SDE1/RDR6 mutants is attributable to the absence of sRNA255-like siRNAs in these mutants. These results demonstrate a role for endogenous siRNAs in the regulation of gene expression, and suggest that PTGS plays a central role in the temporal control of shoot development in plants.
Epigenetics and cancer
Authors: Lund Anders H. , van Lohuizen Maarten
Published: October 2004

Epigenetic mechanisms act to change the accessibility of chromatin to transcriptional regulation locally and globally via modifications of the DNA and by modification or rearrangement of nucleosomes. Epigenetic gene regulation collaborates with genetic alterations in cancer development. This is evident from every aspect of tumor biology including cell growth and differentiation, cell cycle control, DNA repair, angiogenesis, migration, and evasion of host immunosurveillance. In contrast to genetic cancer causes, the possibility of reversing epigenetic codes may provide new targets for therapeutic intervention.
A MyoD-generated feed-forward circuit temporally patterns gene expression during skeletal muscle differentiation
Authors: Penn Bennett H. , Bergstrom Donald A. , Dilworth F. Jeffrey , Bengal Eyal , Tapscott Stephen J.
Published: October 2004

The development and differentiation of distinct cell types is achieved through the sequential expression of subsets of genes; yet, the molecular mechanisms that temporally pattern gene expression remain largely unknown. In skeletal myogenesis, gene expression is initiated by MyoD and includes the expression of specific Mef2 isoforms and activation of the p38 mitogen-activated protein kinase (MAPK) pathway. Here, we show that p38 activity facilitates MyoD and Mef2 binding at a subset of late-activated promoters, and the binding of Mef2D recruits Pol II. Most importantly, expression of late-activated genes can be shifted to the early stages of differentiation by precocious activation of p38 and expression of Mef2D, demonstrating that a MyoD-mediated feed-forward circuit temporally patterns gene expression.
Bank Loan Availability and Trade Credit Demand
Authors: Danielson Morris G. , Scott Jonathan A.
Published: October 2004

This paper investigates the effects of bank loan availability on the trade credit and credit card demand of small firms, using firm‐level data from the 1995 Credit, Banks, and Small Business Survey, conducted by the National Federation of Independent Business. We find that firms increase their demand for trade credit and credit card debt when facing credit constraints imposed by banks. These results provide evidence of a pecking order of debt financing, where firms increase their reliance on potentially expensive sources of funds when bank loans are not available.
Cyclic Adenosine Monophosphate Inhibits Quinolone Alkaloid Evocarpine‐Induced Apoptosis via Activation of Protein Kinase A in Human Leukaemic HL‐60 Cells
Authors: Kim Na‐Young , Pae Hyun‐Ock , Kang Tai‐Hyun , Kim Youn‐Chul , Lee Ho‐Sub , Chung Hun‐Taeg
Published: October 2004

Evocarpine, an isoquinolone alkaloid isolated from the fruit of Evodia rutaecarpa, was found to induce apoptotic cell death in promyelocytic leukaemia HL‐60 cells in dose‐ and time‐dependent manners. We investigated the involvement of protein kinase A during the evocarpine‐induced apoptotic cell death. Evocarpine‐induced apoptosis was markedly inhibited by treatment of the cells with dibutyryl‐cyclic adenosine monophosphate. Similar results were obtained with other commonly used cyclic adenosine monophosphate analogues, chlorophenylthio‐cyclic adenosine monophosphate and the intracellular cyclic adenosine monophosphate‐elevating agent, forskolin. In contrast, pretreatment of HL‐60 cells with KT5720, an inhibitor of cyclic adenosine monophosphate‐dependent protein kinase A, abrogated the protective effects of cyclic adenosine monophosphate analogues and forskolin on evocrpine‐induced apoptosis. These findings suggest that cyclic adenosine monophosphate‐dependent activation of protein kinase A plays a crucial role in protecting HL‐60 cells from the evocarpine‐induced apoptotic cell death.
Chlorpyrifos‐Induced Hypothermia and Vasodilation in the Tail of the Rat: Blockade by Scopolamine
Authors: Gordon Christopher J. , Yang Yong‐Lu
Published: October 2004

Organophosphate pesticides such as chlorpyrifos reduce core temperature (Tc) in laboratory rodents. The mechanism(s) responsible for the chlorpyrifos‐induced hypothermia are not well known. This study assessed the role of a key effector for thermoregulation in the rat, vasomotor control of heat loss from the tail, and its possible cholinergic control during chlorpyrifos‐induced hypothermia. Tc and motor activity were monitored by telemetry in female Long‐Evans rats maintained at an ambient temperature (Ta) of 25°. Tail skin temperature (Tsk(t)) was measured hourly. Rats were dosed with chlorpyrifos (0 or 25 mg/kg orally). Two hr later the rats were dosed with saline or scopolamine (1.0 mg/kg intraperitoneally). Two hr after chlorpyrifos treatment there was a marked elevation in Tsk(t) concomitant with a 0.5° reduction in Tc. Scopolamine administered to control rats led to a marked elevation in Tc with little change in Tsk(t). Rats treated with chlorpyrifos and administered scopolamine underwent a marked vasoconstriction and elevation in Tc. Vasodilation of the tail is an important thermoeffector to reduce Tc during the acute stages of chlorpyrifos exposure. The blockade of the response by scopolamine suggests that the hypothermic and vasodilatory response to chlorpyrifos is mediated via a cholinergic muscarinic pathway in the CNS.
Four Weeks' Inhalation Exposure of Long Evans Rats to 4‐tert‐Butyltoluene: Effect on Evoked Potentials, Behaviour, and Brain Neurochemistry
Authors: Lam Henrik Rye , Ladefoged Ole , Østergaard Grete , Hass Ulla , Lund Søren Peter , Simonsen Leif
Published: October 2004

Long‐lasting central nervous system (CNS) neurotoxicity of 4‐tert‐butyltoluene (TBT) has been investigated using electrophysiology, behaviour, and neurochemistry in Long Evans rats exposed by inhalation to 0, 20, or 40 p.p.m. TBT 6 hr/day, 7 days/week for 4 weeks. Flash evoked potentials and somatosensory evoked potentials were not affected by TBT. In Auditory Brain Stem Response there was no shift in hearing threshold, but the amplitude of the first wave was increased in both exposed groups at high stimulus levels. Three to four months after the end of exposure, behavioural studies in Morris water maze and eight‐arm maze failed to demonstrate any TBT induced effects. Exposure was followed by a 5 months exposure‐free period prior to gross regional and subcellular (synaptosomal) neurochemical investigations of the brain. TBT reduced the NA concentration in whole brain minus cerebellum. Synaptosomal choline acetyltransferase activity increased and acetylcholinesterase activity was unchanged suggesting increased synaptosomal ability for acetylcholine synthesis. The relative and total yield of synaptosomal protein was reduced suggesting reduced density and total number of synapses in situ, respectively. We hypothesise that a reduced yield of synaptosomal protein reflects a more general effect of organic solvent exposure on the software of the brain. The synaptosomal concentration per mg synaptosomal protein and the total amount of 5‐hydroxytryptamine were not affected whereas the total amount of synaptosomal noradrenaline decreased. The concentration and the total amount of synaptosomal dopamine decreased. The noradrenergic and dopaminergic parts of CNS may be more vulnerable to TBT than the serotonergic, and these long‐lasting effects may cause or reflect TBT‐compromised CNS function.