The influence of porous silicon on axonal outgrowth in vitro.

xonal outgrowth on smooth and porous silicon surfaces was studied in organ culture. The pore size of the silicon substrata varied between 100 and 1500 nm. We found that axons preferred to grow and elongate on porous silicon surfaces only when pores of (150-500 nm) are available.     

Efficient Algorithms for k Maximum Sums

We study the problem of computing the k maximum sum subsequences. Given a sequence of real numbers and an integer parameter k, the problem involves finding the k largest values of for The problem for fixed k = 1, also known as the maximum sum subsequence problem, has received much attention in the literature and is linear-time solvable. Recently, Bae and Takaoka presented a -time algorithm for the k maximum sum subsequences problem. In this paper we design an efficient algorithm that solves the above problem in time in the worst case. Our algorithm is optimal for and improves over the previously best known result for any value of the user-defined parameter k < 1. Moreover, our results are also extended to the multi-dimensional versions of the k maximum sum subsequences problem; resulting in fast algorithms as well.     

Hybrid time domain solvers for the Maxwell equations in 2D

We present a new approach to time domain hybrid schemes for the Maxwell equations. By combining the classical FD‐TD scheme with two unstructured solvers, one explicit finite volume solver and one implicit finite element solver, we achieve a very efficient and flexible second‐order scheme. The second‐order accuracy of the hybrid scheme is verified through convergence studies on perfectly conducting as well as dielectric and diamagnetic circular cylinders. The numerical results also show its superiority to the FD‐TD scheme. Copyright © 2002 John Wiley & Sons, Ltd.     

Suppression of the zero-order diffracted beam from a pixelated spatial light modulator by phase compression

Phase compression is used to suppress the on-axis zero-order diffracted (ZOD) beam from a pixelated phase-only spatial light modulator (SLM) by a simple modification to the computer generated hologram (CGH) loaded onto the SLM. After CGH design, the phase of each SLM element is identically compressed by multiplying by a constant scale factor and rotated on the complex unit-circle to produce a cancellation beam that destructively interferes with the ZOD beam. Experiments achieved a factor of 3 reduction of the ZOD beam using two different liquid-crystal SLMs. Numerical simulation analyzed the reconstructed image quality and diffraction efficiency versus degree of phase compression and showed that phase compression resulted in little image degradation or power loss.     

Space-time finite elements for a simplified thermo-metallurgical problem relevant to casting

The non-linear thermo-metallurgical problem, relevant for the cooling of a molten metal including the macro-segregation that occurs during the cooling process, is studied here. Due to the strong non-linearities involved in phase transformations, it is necessary to use a fine resolution in space-time in a finite element approximation in order to meet accuracy requirements. We derive space-time FE-methods based on the discontinuous and continuous Galerkin method in time for the energy equation. This formulation integrates the stored energy exactly for a given heat flux. When macro-segregation is incorporated into the model, the problem can be formulated in such a way that the phase-transition drives a flow of species. In addition, diffusion is possible throughout the domain. The model can be further rewritten using a potential approach. By this approach for modelling macro-segregation, we are able to obtain discretizations that guarantee that the balance equations are satisfied, and it is possible to solve the phase-transition problem either as a field problem or as a local problem (defined by a local evolution rule).     

Parameter extraction for bipolar transistors

Different methods of extracting the DC Gummel-Poon bipolar transistor model parameters are reviewed. First the shortcomings of the classical extraction schemes for the intrinsic model are presented together with some improved procedures. Finally the extraction of the series resistances is addressed.     

Characterization of the settling process for wastewater from a combined sewer system

Among the methods used for determining the parameters necessary for design of wastewater settling tanks, settling column tests are used most commonly, because of their simplicity and low costs. These tests partly mimic the actual settling processes and allow the evaluation of total suspended solids (TSS) removal by settling. Wastewater samples collected from the Liguori Channel (LC) catchment in Cosenza (Italy) were subject to settling column tests, which yielded iso-removal curves for both dry and wet-weather flow conditions. Such curves were approximated well by the newly proposed power law function containing two empirical parameters, a and b, the first of which is the particle settling velocity and the second one is a flocculation factor accounting for deviations from discrete particle settling. This power law function was tested for both the LC catchment and literature data and yielded a very good fit, with correlation coefficient values (R(2)) ranging from 0.93 to 0.99. Finally, variations in the settling tank TSS removal efficiencies with parameters a and b were also analyzed and provided insight for settling tank design.     

Current oscillations during chronoamperometric and cyclic voltammetric measurements in alkaline Cu(II)-citrate solutions

It is demonstrated that current oscillations can be observed during chronoamperometric and cyclic voltammetric experiments in solutions containing 0.4 M CuSO₄ and 1.2 M citrate at pH 11 and 50 °C. The oscillations, which are shown to originate from local variations in the pH, result in the deposition of nanostructured Cu and Cu₂O materials. It is concluded that the current oscillations are analogous to the previously described potential oscillations obtained under controlled current conditions in alkaline Cu(II)-lactate, -tartrate and -citrate solutions. Rotating disk electrode results clearly show that the reduction of the Cu(II)-complexes is kinetically controlled and that the rate of the reduction increases with increasing pH and temperature. It is also shown that the presence of a cathodic peak on the anodic scan in the cyclic voltammograms can be used to identify the experimental conditions leading to the spontaneous current (or potential) oscillations. Electrochemical quartz crystal microbalance results indicate that the cathodic peak stems from an increased rate of the reduction of the Cu(II)-citrate complexes due to a rapid increase in the local pH. This causes Cu₂O rather than Cu to be deposited which, however, results in a decrease in the local pH and a decreasing current. In situ ellipsometry data confirm that Cu₂O deposition replaces that of Cu in the potential region of the cathodic peak. The present findings should facilitate syntheses of nanolayered materials based on spontaneous potential or current oscillations.     

Distributed representations for extended syntactic transformation

This paper shows how the choice of representation substantially affects the generalization performance of connectionistnetworks. The starting point is Chalmers' simulations involving structure-sensitive processing. Chalmers argued that a connectionist network could handle structure sensitive processing without the use of syntactically structured representations. He trained a connectionist architecture to encode/decode distributed representations for simple sentences. These distributed representations were then holistically transformed such that active sentences were transformed into their passive counterpart. However, he noted that the recursive auto-associative memory (RAAM), which was used to encode and decode distributed representations for the structures, exhibited only a limited ability to generalize when trained to encode/decode a randomly selected sample of the total corpus. When the RAAM was trained to encode/decode all sentences, and a separate transformation network was trained to make some active-passive transformations of the RAAMencoded sentences, the transformation network demonstrated perfect generalization on the remaining test sentences. It is argued here that the main reason for the limited generalization is not the ability of the RAAM architecture per se, but the choice of representation for the tokens used. This paper shows that 100% generalization can be achieved for Chalmers' original set up (i.e. using only 30% of the total corpus for training). The key to this success is to use distributed representations for the tokens (capturing different characteristics for differentclasses of tokens, e.g. verbs or nouns).     

A method for structural dynamic contact problems with friction and wear

A method for structural dynamic contact problems with friction and wear is suggested. The method is obtained by including wear in the non‐smooth contact dynamics method of Moreau. A comparison of the method to the discrete energy‐momentum method of Simo and Tarnow is also outlined briefly. The fully discrete equations are treated using the augmented Lagrangian approach, where a non‐smooth Newton method is used as the equation solver. Two two‐dimensional examples are solved by the method. It is investigated how solutions of contact, friction and wear are influenced by inertia. It is shown that the quasi‐static assumption might be questionable for solving contact problems with friction and wear. Copyright © 2003 John Wiley & Sons, Ltd.