bluuebunny/crossref_metadata_2025 huggingface dataset:
A Model for the Action of NMDA Conductances in the Visual Cortex
Authors: Fox Kevin , Daw Nigel
Published: March 2008

A model is presented for the behavior of N-methyl-D-aspartate (NMDA) receptors during neuronal responses to visual stimuli in visual cortex based on classical steady-state equations for membrane conductance, and for binding of transmitter with NMDA and non-NMDA receptors. Constraints in the equations and the equation for voltage dependency of the NMDA receptors come from measurements in hippocampus, embryonic CNS neurons, and cortex. An excitatory amino acid transmitter released from terminals in the visual cortex is assumed to be related to the contrast of the stimulus by a hyperbolic tangent formula. The transmitter is assumed to be glutamate. The model is a two compartment representation of a single neuron at steady state. The model fits results obtained from contrast-response curves measured in the visual cortex in control conditions and with iontophoresis of NMDA and non-NMDA agonists or antagonists. The model shows how NMDA receptors contribute to the visual response in a graded multiplicative fashion at all levels of contrast. NMDA receptors do not show switch behavior, that is, they are not turned on at high levels of stimulation only. The difference in NMDA receptor current between low and high levels of stimulation cannot be accounted for solely by the voltage dependency of the NMDA receptor. One needs, in addition, another factor, such as a difference in the Hill coefficient for binding of glutamate at the NMDA receptor.
On a Magnitude Preserving Iterative MAXnet Algorithm
Authors: Suter Bruce W. , Kabrisky Matthew
Published: March 2008

A new iterative maximum picking neural net (MAXnet) is presented. This formulation determines the value and the location either for a unique maximum or for multiple maxima. This new net converges, for many commonly occurring distributions, in O(log M) iterations using only simple computing elements.
A Network Simulation of Thalamic Circuit Operations in Selective Attention
Authors: LaBerge David , Carter Marc , Brown Vincent
Published: March 2008

The ability of a thalamic circuit to process information selectively from a spatial location was investigated in neural network models. Starting with the known general structure of the thalamic circuit, we considered three variations of the projections from the inhibitory cells of the reticular nucleus onto the cells of the pulvinar nucleus of the dorsal thalamus. The three circuits were modeled as systems of difference equations, and their operations were simulated by computer-based numerical integration. In all three circuits, when input from a target location was slightly larger than the input from neighboring locations, the time evolution of principal (relay) cell outputs showed substantial selective enhancement at the target location compared with neighboring locations. The selective enhancement effect was produced not only on ascending inputs but also on descending cortical inputs. Simulations separating the lateral inhibitory and feedback-enhancement components of the circuits suggested that the feedback-enhancement component substantially magnified the ability of lateral inhibition to produce a target/surround difference.
Simplifying Neural Networks by Soft Weight-Sharing
Authors: Nowlan Steven J. , Hinton Geoffrey E.
Published: March 2008

One way of simplifying neural networks so they generalize better is to add an extra term to the error function that will penalize complexity. Simple versions of this approach include penalizing the sum of the squares of the weights or penalizing the number of nonzero weights. We propose a more complicated penalty term in which the distribution of weight values is modeled as a mixture of multiple gaussians. A set of weights is simple if the weights have high probability density under the mixture model. This can be achieved by clustering the weights into subsets with the weights in each cluster having very similar values. Since we do not know the appropriate means or variances of the clusters in advance, we allow the parameters of the mixture model to adapt at the same time as the network learns. Simulations on two different problems demonstrate that this complexity term is more effective than previous complexity terms.
The Impact of Parallel Fiber Background Activity on the Cable Properties of Cerebellar Purkinje Cells
Authors: Rapp Moshe , Yarom Yosef , Segev Idan
Published: March 2008

Neurons in the mammalian CNS receive 104-105 synaptic inputs onto their dendritic tree. Each of these inputs may fire spontaneously at a rate of a few spikes per second. Consequently, the cell is bombarded by several hundred synapses in each and every millisecond. An extreme example is the cerebellar Purkinje cell (PC) receiving approximately 100,000 excitatory synapses from the parallel fibers (p.f.s) onto dendritic spines covering the thin dendritic branchlets. What is the effect of the p.f.s activity on the integrative capabilities of the PC? This question is explored theoretically using analytical cable models as well as compartmental models of a morphologically and physiologically characterized PC from the guinea pig cerebellum. The input of individual p.f.s was modeled as a transient conductance change, peaking at 0.4 nS with a rise time of 0.3 msec and a reversal potential of +60 mV relative to rest. We found that already at a firing frequency of a few spikes per second the membrane conductance is several times larger than the membrane conductance in the absence of synaptic activity. As a result, the cable properties of the PC significantly change; the most sensitive parameters are the system time constant (τ0) and the steady-state attenuation factor from dendritic terminal to soma. The implication is that the cable properties of central neurons in freely behaving animals are different from those measured in slice preparation or in anesthetized animals, where most of the synaptic inputs are inactive. We conclude that, because of the large conductance increase produced by the background activity of the p.f.s, the activity of the PC will be altered from this background level either when the p.f.s change their firing frequency for a period of several tens of milliseconds or when a large population of the p.f.s fires during a narrow time window.
Understanding Retinal Color Coding from First Principles
Authors: Atick Joseph J. , Li Zhaoping , Redlich A. Norman
Published: March 2008

A previously proposed theory of visual processing, based on redundancy reduction, is used to derive the retinal transfer function including color. The predicted kernels show the nontrivial mixing of space-time with color coding observed in experiments. The differences in color-coding between species are found to be due to differences among the chromatic autocorrelators for natural scenes in different environments.
Interaction between Transparency and Structure from Motion
Authors: Kersten Daniel , Bülthoff Heinrich H. , Schwartz Bennett L. , Kurtz Kenneth J.
Published: March 2008

It is well known that the human visual system can reconstruct depth from simple random-dot displays given binocular disparity or motion information. This fact has lent support to the notion that stereo and structure from motion systems rely on low-level primitives derived from image intensities. In contrast, the judgment of surface transparency is often considered to be a higher-level visual process that, in addition to pictorial cues, utilizes stereo and motion information to separate the transparent from the opaque parts. We describe a new illusion and present psychophysical results that question this sequential view by showing that depth from transparency and opacity can override the bias to see rigid motion. The brain's computation of transparency may involve a two-way interaction with the computation of structure from motion.
Information-Based Objective Functions for Active Data Selection
Authors: MacKay David J. C.
Published: March 2008

Learning can be made more efficient if we can actively select particularly salient data points. Within a Bayesian learning framework, objective functions are discussed that measure the expected informativeness of candidate measurements. Three alternative specifications of what we want to gain information about lead to three different criteria for data selection. All these criteria depend on the assumption that the hypothesis space is correct, which may prove to be their main weakness.
On the Information Storage Capacity of Local Learning Rules
Authors: Palm Günther
Published: March 2008

A simple relation between the storage capacity A for autoassociation and H for heteroassociation with a local learning rule is demonstrated: H = 2A. Both values are bounded by local learning bounds: A ≤ LA and H ≤ LH. LH = 2LA is evaluated numerically.
Ultrasound Tomography Imaging of Defects Using Neural Networks
Authors: Anthony Denis M. , Hines Evor L. , Hutchins David A. , Mottram J. T.
Published: March 2008

Simulations of ultrasound tomography demonstrated that artificial neural networks can solve the inverse problem in ultrasound tomography. A highly simplified model of ultrasound propagation was constructed, taking no account of refraction or diffraction, and using only longitudinal wave time of flight (TOF). TOF data were used as the network inputs, and the target outputs were the expected pixel maps, showing defects (gray scale coded) according to the velocity of the wave in the defect. The effects of varying resolution and defect velocity were explored. It was found that defects could be imaged using time of flight of ultrasonic rays.
Improving the Accuracy of an Artificial Neural Network Using Multiple Differently Trained Networks
Authors: Baxt William G.
Published: March 2008

When either detection rate (sensitivity) or false alarm rate (specificity) is optimized in an artificial neural network trained to identify myocardial infarction, the increase in the accuracy of one is always done at the expense of the accuracy of the other. To overcome this loss, two networks that were separately trained on populations of patients with different likelihoods of myocardial infarction were used in concert. One network was trained on clinical pattern sets derived from patients who had a low likelihood of myocardial infarction, while the other was trained on pattern sets derived from patients with a high likelihood of myocardial infarction. Unknown patterns were analyzed by both networks. If the output generated by the network trained on the low risk patients was below an empirically set threshold, this output was chosen as the diagnostic output. If the output was above that threshold, the output of the network trained on the high risk patients was used as the diagnostic output. The dual network correctly identified 39 of the 40 patients who had sustained a myocardial infarction and 301 of 306 patients who did not have a myocardial infarction for a detection rate (sensitivity) and false alarm rate (1-specificity) of 97.50 and 1.63%, respectively. A parallel control experiment using a single network but identical training information correctly identified 39 of 40 patients who had sustained a myocardial infarction and 287 of 306 patients who had not sustained a myocardial infarction (p = 0.003).
How to Incorporate New Pattern Pairs without Having to Teach the Previously Acquired Pattern Pairs
Authors: Wabgaonkar H. M. , Stubberud A. R.
Published: March 2008

In this paper, we deal with the problem of associative memory synthesis. The particular issue that we wish to explore is the ability to store new input-output pattern pairs without having to modify the path weights corresponding to the already taught pattern pairs. The approach to the solution of this problem is via interpolation carried out in a Reproducing Kernel Hilbert Space setting. An orthogonalization procedure carried out on a properly chosen set of functions leads to the solution of the problem.
Object Discrimination Based on Depth-from-Occlusion
Authors: Finkel Leif H. , Sajda Paul
Published: March 2008

We present a model of how objects can be visually discriminated based on the extraction of depth-from-occlusion. Object discrimination requires consideration of both the binding problem and the problem of segmentation. We propose that the visual system binds contours and surfaces by identifying “proto-objects”—compact regions bounded by contours. Proto-objects can then be linked into larger structures. The model is simulated by a system of interconnected neural networks. The networks have biologically motivated architectures and utilize a distributed representation of depth. We present simulations that demonstrate three robust psychophysical properties of the system. The networks are able to stratify multiple occluding objects in a complex scene into separate depth planes. They bind the contours and surfaces of occluded objects (for example, if a tree branch partially occludes the moon, the two "half-moons" are bound into a single object). Finally, the model accounts for human perceptions of illusory contour stimuli.
First-Principles Study of Silicon Nanocrystals: Structural and Electronic Properties, Absorption, Emission, and Doping
Authors: Ossicini Stefano , Bisi O. , Degoli Elena , Marri I. , Iori Federico , Luppi Eleonora , Magri Rita , Poli Raffaele , Cantele G. , Ninno D. , Trani F. , Marsili M. , Pulci O. , Olevano V. , Gatti M. , Gaal-Nagy K. , Incze A. , Onida G.
Published: March 2008

Total energy calculations within the Density Functional Theory have been carried out in order to investigate the structural, electronic, and optical properties of un-doped and doped silicon nano-structures of different size and different surface terminations. In particular the effects
induced by the creation of an electron-hole pair on the properties of hydrogenated silicon nanoclusters as a function of dimension are discussed in detail showing the strong interplay between the structural and optical properties of the system. The distortion induced on the structure by an
electronic excitation of the cluster is analyzed and considered in the evaluation of the Stokes shift between absorption and emission energies. Besides we show how many-body effects crucially modify the absorption and emission spectra of the silicon nanocrystals. Starting from the hydrogenated
clusters, different Si/O bonding at the cluster surface have been considered. We found that the presence of a Si—O—Si bridge bond originates significative excitonic luminescence features in the near-visible range. Concerning the doping, we consider B and P single- and co-doped
Si nanoclusters. The neutral impurities formation energies are calculated and their dependence on the impurity position within the nanocrystal is discussed. In the case of co-doping the formation energy is strongly reduced, favoring this process with respect to the single doping. Moreover
the band gap and the optical threshold are clearly red-shifted with respect to that of the pure crystals showing the possibility of an impurity based engineering of the absorption and luminescence properties of Si nanocrystals.
Self-Organization of Nanometer Periodic Structures of Clusters in Solids
Authors: Mirzade Fikret Kh. , Allakhverdiev Kerim R. , Salaeva Zehra Yu.
Published: March 2008

The formation of non-uniform spatial structures in irradiated solids (metals, semiconductors) is investigated, when the subsystem of nonequilibrium lattice defects (vacancies and interstitials) forms bonded states, nanoclusters. A set of kinetic equations is formulated which incorporates,
(i) generation of point defects by radiation, (ii) their diffusion and recombination, (iii) mutual pairwise elastic interaction among defects, (iv) formation and growth of the nanoclusters of point defects, and (v) losses of the nanoclusters due to removal from the nucleation zone by diffusion.
Linear stability analysis is used to show that, if the temperature (T) of medium is below a critical value (Tcr), due to the elastic interaction the homogeneous distribution of point defects and their clusters becomes unstable, and a periodic structure of a nanometer
scale arises. The criterion of self-organization of the clusters and the dependence of a super-lattice period on temperature of medium are determined analytically. The critical temperature for self-organization of periodic structures is governed by the dilatation volume of defects, by the
potential energy of elastic interaction, and the concentration of defects. Estimations showed that the period of super-lattices may change in the range of (20–80) nm. Obtained results agree with the experimental data.
Raman Scattering of Si Matrix with Randomly Distributed Nanoparticles of Semiconducting Silicides
Authors: Baleva M. , Atanassov A. , Marinova M. , Zlateva G. , Todorov N.
Published: March 2008

Samples, representing Si matrix with nanoformations of the semiconducting silicides β-FeSi2 and Mg2Si are studied by Raman scattering. The unpolarized Raman spectra of the samples are interpreted in the frameworkof the appearance of interface-phonon
polaritons. The theoretical dispersion relations of the interface-phonon polaritons in the system Si/silicide/Si are obtained from the Maxwell equations. The correspondence of the theoretical calculations and the experimental observations appeared to be sufficiently good. An evolution of the
features in the Raman spectra on the experimental conditions is observed.
Self-Organization of Cobalt-Silicide Nanoislands on Stepped Si(111) as a Function of Growth Method
Authors: Goldfarb I. , Levinshtein M.
Published: March 2008

When silicides, such as CoSi2, are grown in the form of nanoislands they frequently exhibit nanometer size effects, which can be useful for single electron devices. For such devices, however, lateral self-organization is required. In this work, step-aided self-organization
of CoSi2 nanoislands is demonstrated on a vicinal (stepped) Si(111) substrate. Straight and equidistant steps or step-bunches are routinely obtained on the vicinal Si(111), creating almost ideal template for self-organization. Two growth methods were examined: solid-phase epitaxy
(SPE), where Co was deposited at room temperature and annealed to promote silicide formation, and reactive deposition epitaxy (RDE) where Co was deposited at elevated temperature. While the latter did not result in any noticeable ordering, due to instantaneous reaction with Si in course of
deposition, the former lead to preferential occupation of step-bunch sites by the silicide nanoislands. Furthermore, self-limiting growth caused narrow distribution of island sizes and island–island separation distances.
Investigation of Multilayer Silicon Structures with Buried Iron Silicide Nanocrystallites: Growth, Structure, and Properties
Authors: Galkin N. G. , Goroshko D. L. , Polyarnyi V. O. , Chusovitin E. A. , Korobtsov V. V. , Balashev V. V. , Khang Y. , Dozsa L. , Gutakovsky A. K. , Latyshev A. V. , Shamirzaev T. S. , Zhuravlev K. S.
Published: March 2008

The growth of nanosize islands of iron silicides on Si(100) substrates and epitaxial silicon over-growth atop them have been studied by low energy electron diffraction and reflectance high energy electron diffraction methods. The near optimal formation conditions of iron silicide islands
with high density and minimal sizes have been determined by using of atomic force microscopy. Multilayer (8–10) monolithic structures with buried iron silicide nanocrystallites have been grown after the definition of monocrystalline burying conditions of iron silicides nanocrystallites
in silicon lattice. The structure of buried nanocrystallites has been studied in multilayer monolithic heterostructures by high resolution transmission electron microscopy. It was established that in multilayer samples the majority of nanocrystallites have β-FeSi2 structure,
but some of them have γ-FeSi2 structure. It was observed an influence of additional annealing at 850 °C on the morphology and structure of nanocrystallites. By means of deep level transient spectroscopy data one and two trap levels have been observed in multilayer
structures (without and with additional annealing, respectively). Photoluminescence spectra have been studied at 4.2 K and the causes of its absence from buried β-FeSi2 NC have been analyzed.
Synthesis of 1D Regular Arrays of Gold Nanoparticles and Modeling of Their Optical Properties
Authors: Dmitruk N. , Barlas T. , Dmytruk A. , Korovin A. , Romanyuk V.
Published: March 2008

Self-organized formation of uniform coating of semiconductor substrate by metal nanoparticles offers a convenient and efficient access to large-scale arrays of uniform metal-semiconductor nanostructures. We used a cheap and facile method of photoinduced chemical gold deposition from
an aqueous or alcohol gold salt solution onto semiconductor surface (GaAs, InP). By controlling of both the solution composition and the deposition conditions, gold particles of 10–50 nm in diameter were obtained and the gold covering degree of the semiconductor surface was varied in
a wide range. Morphology of the nano/micro structures formed was characterized by atomic force microscopy and scanned electron microscopy with local element analysis. The investigations show that the semiconductor surface patterning can be used for the selective deposition of gold nanoparticles,
because they are located predominantly at the tops of the microrelief. We have used specially textured by the anisotropic chemical etching microrelief surfaces of semiconductor single crystal as templates and have obtained nanoparticle arrays in the shape of 1D systems of near parallel quasiperiodical
wires. For the periodic 1D array of metal nanowires built into the air-semiconductor interface the spectral and angular dependencies of the transmittance/reflectance of the polarized light have been obtained theoretically using differential formalism. These dependencies demonstrate non-monotonic
behaviour at surface plasmon polariton excitation conditions and show possibility of designing functional subwavelength devices.
The Electronic Structure of Capped and Uncapped CdS Nanoparticles
Authors: Ercan İlke , Katırcıoglu Şenay
Published: March 2008

The electronic structure of spherical CdmSn nanoparticles having zinc-blende symmetry and the diameters of up to around 3 nm has been studied by Hartree-Fock theory to find out the effect of the cluster size on the optical energy gap between HOMO
and LUMO. The effect of encapsulation on the electronic structure has been also investigated for CdS4 and Cd13S4 clusters embedded in SiO2 matrix and sodalite cage by Hartree-Fock theory. It was found that the energy gap of CdS nanoparticles
can be regulated by both the cluster size and the interface provided by the SiO2 matrix and sodalite cage. The energy gap between HOMO and LUMO has been found to be increased to upper boundary of the visible spectra when CdS4 and Cd13S4 clusters
have been embedded in either SiO2 matrix or sodalite cage.
Simulation of Memory Behaviour of a Non-Volatile Si3N4 Structure ContainingSi Nanocrystals
Authors: Horváth Zs. J. , Hardy V. A.
Published: March 2008

Memory hysteresis, memory window and charge retention behaviour of an Al/Si3N4/Si structure with Si nanocrystals embedded in the Si3N4 layer are studied by fitting the results of a computer simulation to the experimental ones using simple
analytical expressions. It is concluded that the current through the control nitride layer during a charging voltage pulse is higher than the steady-state current. At high voltage pulses other effects, as transients, additional current mechanisms or charge injection and trapping from the metal
side, has to be considered. It is also obtained that the retention behaviour of the structure were determined by the Fowler-Nordheim tunneling.
Size and Surface Effects on Magnetic Properties of Fe3O4 Nanoparticles
Authors: Köseoglu Yüksel , Kavas Hüseyin
Published: March 2008

In this study, size and surface effects on temperature and frequency dependent magnetic properties of superparamagnetic Fe3O4 nanoparticles in a size range of 1.1–11 nm are investigated by SPR technique. We used a theoretical formalism based on a distribution
of diameters or volumes of the nanoparticles following lognormal proposed by Berger et al.18 The nanoparticles are considered as single magnetic domains with random orientations of magnetic moments and thermal fluctuations of anisotropic axes. The individual line shape function
is derived from the damped precession equation of Landau-Lifshitz. Magnetic properties of the samples were strongly temperature and size dependent. The increase in SPR line width, the decrease in the resonance field and also increase in anisotropy filed by decreasing the temperature core–shell
type structure of the nanoparticles and disordered magnetic structure (spin-glass like phase) of the particle surface. A linear microwave frequency dependence of the resonance field and the increase in the blocking temperature of the particles by the particle size were also observed.
Growth and Characterisation of Electrodeposited Co/Cu Superlattices
Authors: Şafak Mürşide , Alper Mürsel , Kockar Hakan
Published: March 2008

Ferromagnetic/non-ferromagnetic Co/Cu superlattices were grown on polycrystalline Titanium (Ti) from a single electrolyte by electrodeposition. Microstructure and magnetoresistance (MR) of the superlattices were investigated as a function of the electrolyte pH as well as the layer thicknesses.
Structural characterisation by X-ray diffraction (XRD) showed that the superlattices have face-centred cubic (fcc) structure with a strong (111) texture at the studied pH levels, but the texture degree is affected by the electrolyte pH. The scanning electron microscope (SEM) studies revealed
that the superlattices grown at low pH (2.0) have smoother surfaces compared to those grown at high pH (3.0). The superlattices exhibited either anisotropic magnetoresistance (AMR) or giant magnetoresistance (GMR) depending on the Cu layer thickness. The shape of MR curves changes depending
on the combination of Co and Cu layer thicknesses. The superlattices with Co layers less than 3 nm and Cu layers less than 2 nm have broad and non-saturating curves, indicating the predominance of a superparamagnetic contribution, possibly due to the discontinuous nature of the ferromagnetic
(Co) layer. For superlattices with the same bilayer and total thicknesses, the GMR magnitude decreased as the electrolyte pHincreased. Besides possible structural differences such as the texture degree and the surface roughness, this may arises from the variation in the Cu content of the ferromagnetic
layers caused by the electrolyte pH.
Rapid Synthesis and Characterization of Maghemite Nanoparticles
Authors: Tural Bilsen , Özenbaş Macit , Atalay Selçuk , Volkan Mürvet
Published: March 2008

Fe2O3–SiO2 nanocomposites were prepared by a sol–gel method using various evaporation surface to volume (S/V) ratios ranging from 0.03 to 0.2. The Fe2O3–SiO2 sols were gelated at various temperatures
ranging from 50 °C to 70 °C, and subsequently they were calcined in air at 400 °C for 4 hours. The structure and the magnetic properties of the prepared Fe2O3–SiO2 nanocomposites were characterized using X-ray diffraction (XRD), transmission
electron microscopy (TEM), differential thermal analysis (DTA), and vibrating sample magnetometer (VSM) measurements. The gelation temperature of the Fe2O3–SiO2 sols influenced strongly the particle size and crystallinity of the maghemite nanoparticles.
It was observed that the particle size of maghemite nanoparticles increased with the increasing of the gelation temperature of the sols, which may be due to the agglomeration of the maghemite particles at elevated temperatures inside the microporosity of the silica matrix during the gelation
process, and the subsequent calcination of these gels at 400 °C resulted in the formation of large size iron oxide particles. Magnetization studies at temperatures of 10, 195, and 300 K showed superparamagnetic behavior for all the nanocomposites prepared using the evaporation surface
to volume ratio (S/V) of 0.1, 0.2, 0.09, and 0.08. The saturation magnetization, Ms, values measured at 10K were 5.5, 8.5, and 9.5 emu/g, for the samples gelated at 50, 60, and 70 °C, respectively. At the gelation temperature of 70 °C, γ-Fe2O3
crystalline superparamagnetic nanoparticles with the particle size of 9±2 nm were formed in 12 hours for the samples prepared at the S/V ratio of 0.2.
Ni and Cu Incorporated Mesoporous Nanocomposite Catalytic Materials
Authors: Nalbant Asli , Dogu Timur , Balci Suna
Published: March 2008

Nickel and copper incorporated MCM-41-like mesoporous nanocomposite materials prepared by the direct hydrothermal synthesis and the impregnation procedures showed highly attractive pore structure and surface area results for catalytic applications. The XRD patterns showed that characteristic
MCM-41 structure was preserved for the materials synthesized following an impregnation procedure before the calcination step. The surface area of the Cu impregnated material with a quite high Cu/Si atomic ratio (0.19) was 631 m2/g. Very narrow pore size distributions with an average
pore diameter of about 2.7 nm were obtained as a result of plugging of some of the smaller pores by Cu nanoballs. For lower metal to Si ratios (for instance for Ni/Si = 0.06) much higher surface area values (1130 m2/g) were obtained. In the case of nanocomposite materials synthesized
by the direct hydrothermal route, MCM-41 structure was not destroyed for samples containing metal to Si atomic ratios as high as 0.12. In the case of materials containing Cu/Si and Ni/Si ratios over 0.2 wider pore size distributions and some decrease of surface area were observed.
Characterization of Iron Oxide Thin Films Prepared by Sol–Gel Processing
Authors: Karakuscu Aylin , Ozenbas Macit
Published: March 2008

Iron oxide thin films were prepared by spin-coating a gel solution of iron(III) nitrate dissolved in 2-methoxyethanol and acetylacetone on glass and quartz substrates. The film thickness was adjusted by changing the spinning rate of the spin coater. Annealing was carried out between
300 °C to 600 °C to investigate the phases present in the films. Viscosity of the main solution was found as 0.0035 Pa·s by viscosity measurement. TGA/DTA analyses showed that heat treatment should be done between 330 °C and 440 °C in order to produce maghemite thin
films. SEM studies showed that single layer thickness of the films were between 65 and 80 nm. The structural characteristics were evaluated by changing the experimental parameters which are annealing temperature, annealing time and thickness of the films. From the X-ray diffraction analysis,
maghemite formation was observed with decreasing annealing temperature, annealing time and film thickness. TEM results verified the presence of the maghemite phase by electron diffraction and selected area electron diffraction (SAED) methods. According to UV-Vis results transmittance of the
films decreases with increasing annealing temperature.
Particle Morphology of Various SiC-Based Nanocomposite Powders Made by the Aerosol-Assisted Synthesis Method
Authors: Czosnek Cezary , Janik Jerzy F.
Published: March 2008

Herein, we present a part of a study on the preparation of SiC-based composite nanopowders by the two-stage Aerosol-Assisted Vapor Phase Synthesis (AAVS) method from organosilicon precursors (neat hexamethyldisiloxane, neat tetramethoxysilane, ethanol solutions of polydimethylsiloxane).
Upon generation, liquid aerosol droplets were transported in a stream of argon through a ceramic reactor tube maintained at 1200 °C. The resulting solid by-products were collected on a nylon filter as bulk powders. Each raw powder was, subsequently, pyrolyzed in a furnace reactor heated
to 1650 °C under a flow of argon. After the final pyrolysis at 1650 °C, mostly nanocrystalline silicon carbide powder with small quantities of free excess carbon was obtained from the neat hexamethyldisiloxane system, composite powder of not fully converted silica and SiC was prepared
from the neat tetramethoxysilane system, and C-rich/SiC composite was made from the ethanol/polydimethylsiloxane solution system. The prevailing phase of the SiC component was the regular β-SiC polytype. Most of the powders were composed of spheroidal particles – morphology
imprinted during aerosol generation at 1200 °C and not much affected by the second-stage bulk pyrolysis at 1650 °C. The specifics of spheroidal morphology were characteristic of the applied precursor system.
Diffraction Effects in the Propagation of Radiation in Polarizable Layers
Authors: Dallacasa Valerio
Published: March 2008

The very low transmission of light through holes smaller than the wavelength has been found to be enhanced for subwavelength apertures in metallic surfaces with periodic corrugations. This effect has been attributed to the interaction of light with surface plasmons. Similar effects
obtained subsequently for non-metallic surfaces have been attributed to evanescent waves on the surface produced by the diffracted Bloch waves from different points in the array. We present an exact solution of Maxwell's equations in the discrete dipole approximation (DDA) for a periodic array
of polarizable point dipoles in a layer. Metallic as well as non metallic layers are described. When the wavelength is smaller than the lattice period there is a Bragg's scattered wave, while for subwavelength conditions an evanescent wave on the surface appears. The transmission/reflection
coefficients are found to oscillate as a function of frequency, with resonances occurring in a broad range of frequencies depending on the polarizability, at which the evanescent field is enhanced. A detailed study is presented for nanostructured arrays. We find that this model agrees with
features observed in experiments through hole arrays supporting the role played by diffraction during light transmission through such arrays without invoking surface plasmons and providing a base to analyze more complex geometries.
Influence of Composition and Particle Size on Spin Dynamics and Thermodynamic Properties of Magnetoresistive Perovskites
Authors: Tanasescu Speranta , Maxim Florentina , Teodorescu Florina , Giurgiu Liviu
Published: March 2008

The thermodynamic behavior and spin dynamics of the colossal magnetoresistive (CMR) perovskites of general formula La1−x(A)xMn1−y(B)yO3 (where A is an alkaline earth, and B = Al, In) have
been studied in order to evidence the effect of composition and the influence of nanocrystallinity on the thermodynamic and magnetic characteristics. By using electron paramagnetic resonance (EPR) spectroscopy, the behavior of the exchange coupling integral (J) between Mn spins and
the polaron activation energy (Ea) have been investigated. The thermodynamic properties represented by the relative partial molar free energies, enthalpies and entropies of oxygen dissolution in the perovskite phase, as well as the equilibrium partial pressures of oxygen
have been obtained by using solid electrolyte electrochemical cells method. The influence of the oxygen stoichiometry change on the thermodynamic properties was examined using the data obtained by a coulometric titration technique coupled with measurements of the electromotive force (EMF).
The results were correlated with the average Mn valence values as determined by redox titration. The properties of the rare-earth manganites are strongly affected by the A- and B-site substitution and by the oxygen nonstoichiometry. New features related to the modifications in properties connected
with the nanocrystalline state were evidenced. The correlation existing between the magnetic and thermodynamic characteristics were discussed in relation to significant changes in the overall concentration of defects.
Nanostructure of Pure Iron Anodically Oxidized in Borate Buffer Solution and Annealed by Infrared Radiation
Authors: Nanjo Hiroshi , Fujimura Motoaki , Xia Zhengbin , Ishikawa Ikuo , Kanakubo Mitsuhiro , Aizawa Takafumi , Izumisawa Miki , Onagawa Jun
Published: March 2008

The behavior of oxide film on pure iron passivated in a borate buffer solution and subsequently radiated by infrared light (IR) was investigated in comparing to that by just IR annealing without passivation, and was evaluated by film structure, etc. The effect of thermal annealing over
250 °C was observed with γ-Fe2O3 grain growth and sharp increase in surface roughness, film thickness and oxygen content. An ellipsometric parameter of tanΨ was sensitively reflected by annealing effect, and tanΨ curve had a shoulder at 150 °C
for 5 min and a peak of tanΨ was shifted from 350 nm to 450 nm in wavelength. This shift was also caused by the formation of γ-Fe2O3, because the peak was also observed in tanΨ of the bulk Fe2O3 family. Passivation effects at
800 mV prior to IR annealing on thickness and oxygen content changed at 150 °C, and decreased tanΨ at 350 nm and excessive film growth over 250 °C, and increased oxygen content under 100 °C and surface roughness at 50–250 °C. The terrace width with atomic scale flatness
was slightly increase by passivation prior to IR annealing at 50–250 °C, and the maximum terrace width reached larger than 10 nm by passivation and IR annealing at 100 °C for 30 min.
Fabrication and Characterization of ZnO Nanoneedle Array Using Metal Organic Chemical Vapor Deposition
Authors: Park Dongseok , Tak Youngjo , Yong Kijung
Published: March 2008

High density and vertically well-aligned ZnO nanoneedle arrays were fabricated on the ZnO thin film deposited on silicon substrates. The ZnO buffer layer and nanoneedles were synthesized by metal organic chemical vapor deposition using diethylzinc and oxygen gas. The ZnO buffer film
was grown at 250 °C and the growth temperature of nanoneedles was in the range of 480–500 °C. As-grown ZnO nanoneedles showed single crystalline structure of ZnO (002). The crystalline properties of three samples (A: as-deposited ZnO buffer layer, B: annealed buffer film, C:
ZnO nanoneedles) were compared using XRD and Raman spectroscopy. The synthesized ZnO nanoneedles (sample C) showed highest crystalline quality among three samples. The field emission properties of ZnO nanoneedles were investigated, which showed low turn on field of 4.8 V μm−1
and high field enhancement factor of 3.2 × 103.
Effect of Glass Phase on the Dissolution of Hydroxyapatite
Authors: Youn S. H. , Yang Z. X. , Hwang K. H. , Seo D. S. , Lee J. K. , Jun B. S. , Kim H.
Published: March 2008

Nano size defect formation at grain boundary during the dissolution of hydroxyapatite in water was evaluated by adding several sintering additives for sinterability enhancement. In the case of sintered pure hydroxyapatite, significant dissolution occurred after immersion in distilled
water or in simulated body fluid. The dissolution initiated at the grain boundaries creating nano-size defects like small pores that afterwards grew up to micro scale by increasing immersion time. This dissolution resulted in grain separation at the surfaces and finally in fracture. The dissolution
concentrated on the grains adjacent to pores rather than those in the dense region. So hydroxyapatite ceramics containing glass powders were prepared to prevent the dissolution by strengthening grain boundary. Calcium silicate and phosphate glasses were added at 0 to 10 mass% and sintered
at 1200 °C for 2 h in air with moisture protection. Glass phase was incorporated into hydroxyapatite to act as the sintering aid followed by crystallization in order to improve the mechanical properties without reducing biocompatibility. Dissolution tests, as well as X-ray diffraction
and SEM showed little decomposition of hydroxyapatite to secondary phases and the fracture toughness increased compared to pure hydroxyapatite.
Shape Memory Characteristics and Superelasticity of Ti-Ni-Cu Alloy Ribbons with Nano Ti2Ni Particles
Authors: Nam Tae-hyun , Yu Cheol-am , Nam Jung-min , Kim Hyun-gon , Kim Yeon-wook
Published: March 2008

Microstructures and deformation behaviour of Ti-45Ni-5Cu and Ti-46Ni-5Cu alloy ribbons prepared by melt spinning were investigated by transmission electron microscopy, thermal cycling tests under constant load and tensile tests. Spherical Ti2Ni particles coherent with the
B2 parent phase were observed in the alloy ribbons when the melt spinning temperature was higher than 1773 K. Average size of Ti2Ni particles in the ribbons obtained at 1873 K was 8 nm, which was smaller than that (10 nm) in the ribbons obtained at 1773 K. Volume fraction of Ti2Ni
phase in the ribbons obtained at 1873 K was 40%, which was larger than that (20%) in the ribbons obtained at 1773 K. The stress required at temperatures of Af + 10 K for the stress-induced martensitic transformation increased from 93 MPa to 229 MPa and apparent elastic modulus of
the B2 parent phase increased from 56 GPa to 250 GPa with increasing the melt spinning temperature from 1673 K to 1873 K in Ti-45Ni-5Cu alloy ribbons. The critical stress for slip deformation of the ribbons increased by coherent Ti2Ni particles, and thus residual elongation did
not occur even at 160 MPa, while considerable plastic deformation occurred at 60 MPa in the ribbons without Ti2Ni particles. Almost perfect superelastic recovery was found in the ribbons with coherent Ti2Ni particles, while only partial superelastic recovery was observed
in the ribbons without coherent Ti2Ni particles.
Adolescent Future Expectations of Work, Education, Family, and Community Development of a New Measure
Authors: McWhirter Ellen Hawley , McWhirter Benedict T.
Published: March 2008

The development and validation of a measure of adolescent future expectations associated with work, education, family, health, and church/community participation is presented. The 25-item measure was administered to a sample of 389 7th- to 12th-grade urban poor and working-class Chilean students. Results of an exploratory principal axis factor analysis with oblimin (oblique) rotation revealed a five-factor structure for the measure. Evidence of concurrent validity is supported by subscale correlations with a series of other measures, and internal consistency estimates for subscales and the full scale are strong. This promising measure has potential utility for understanding Chilean and other adolescents' future expectations in distinct domains. Recommendations for additional research are provided, including validation of this measure in other national and cultural contexts.
Parental Styles, Conscientiousness, and Academic Performance in High School: A Three-Wave Longitudinal Study
Authors: Heaven Patrick C. L. , Ciarrochi Joseph
Published: March 2008

This article assesses whether perceived parental style influenced the extent to which adolescents became increasingly conscientious and whether changes in conscientiousness influenced academic grades 1 year later. Parental styles, conscientiousness, verbal, and numerical ability at Time 1 were measured. One year later conscientiousness was again assessed, and 1 year after that end-of-year exam results were obtained. More than 784 students (mean age = 12.3 years, SD = 0.49) participated in the 1st year. The data of 563 students were matched across the 3 years. Conscientiousness tended to decrease from Time 1 to Time 2. Structural equation modeling showed that adolescents with more authoritative parents experienced less of a decrease in conscientiousness at Time 2 than did students with less authoritative parents and the same baseline level of conscientiousness at Time 1. Additionally, the decrease in conscientiousness at Time 2 predicted worse grades at Time 3, even after controlling for baseline levels of academic achievement.
The acquisition of articles in child second language English: fluctuation, transfer or both?
Authors: Zdorenko Tatiana , Paradis Johanne
Published: March 2008

The data for this study consisted of a longitudinal corpus of narratives from 17 English second language (L2) children, mean age of 5;4 years at the outset, with first languages (Lls) that do not have definite/indefinite articles (Chinese, Korean and Japanese) and Lls that do have article systems (Spanish, Romanian and Arabic). We examined these children's acquisition of articles in order to determine the role of L1 transfer and, in so doing, test the Fluctuation Hypothesis, and also to compare our findings to those from research on adult L2 learners. Three tendencies were found over two years: (1) All children substituted the for a in indefinite specific contexts (i.e. showed fluctuation) regardless of L1 background; (2) all children were more accurate with use of the in definite contexts than with a in indefinite contexts, regardless of L1 background; and (3) children with [-article] Lls had more omitted articles as error forms than children with [+article] L1s, but only at the early stages of acquisition. Overall, L1 influence in the children's developmental patterns and rates of article acquisition was limited. Child L2 learners converged on the target system faster than prior reports have indicated for adult L2 learners, even when their Lls lack articles. Thus, we conclude that fluctuation is a developmental process that overrides transfer in child L2 acquisition of English articles, in contrast to what has been reported for adult L2 learners.
Retrieving the Imperial: Empire and International Relations
Authors: Barkawi Tarak , Laffey Mark
Published: March 2008

This essay uses Michael Hardt and Antonio Negri's Empire, one of the most widely read accounts of international politics in recent years, as a vehicle to rethink International Relations' engagement with the notion of empire. We begin with the observation that Westphalian models of the international obscure the role of imperial relations in world politics. We go on to develop a conception of the international as a `thick' set of social relations, consisting of social and cultu ral flow s as wellas political-military and economic interactions, which often take place in a context of imperial hierarchy. Retrieving the imperial thus offers a way out of the `territorial trap' set by Westphalia and alerts us to a range of phenomena occluded by IR's central categories. From this perspective, we analyse Empire as an innovative but flawed effort to take seriously the imperial character of international relations. In particular, we focus on the role of the multitude in world politics, Hardt and Negri's genealogy of sovereignty, and their claim that imperialism in the old-fashioned sense is over.
Pragmatic Constructivism and the Study of International Institutions
Authors: Haas Peter M. , Haas Ernst B.
Published: March 2008

This article provides a pragmatic constructivist approach for progressing study in International Relations (IR) that sidesteps the ontological differences between major IR approaches, and that is capable of influencing practices in international relations. In particular, it looks at how international institutions can be studied and the possible consequences of how they are studied. While institutions are at times, as realists and neoliberal institutionalists contend, merely the artifacts of strategically and rationally motivated state actors, they are viewed differently by pragmatic constructivists. Institutions may, at times, be wilful actors on their own, but are also the venue in which reflexive new practices and policies develop. Pragmatic constructivism provides the explanatory lens through which this may be understood, as well as the methodological guidelines by which such a process may be pursued.