Semiconducting properties of anodic WO3 amorphous films

The semiconducting properties of amorphous WO₃ anodic films grown in different solutions and at different current densities have been investigated. The Mott—Schottky plots have shown that the donor density, N_d, of the grown films is strongly dependent on the films thickness and is not influenced by the nature of the anodizing solutions. The possible influence of the kinetics of anodization on N_d is discussed. The intersection voltages at 1/C²_sc = 0 in the Mott—Schottky plots show a complex dependence on the film thickness. The possibility of obtaining the flat band potential from these plots is also discussed.A linear relationship between the square of the photocurrent and the electrode potential has been observed as previously reported for single crystals. The dissolution rate of anodic WO₃ films is increased under illumination and strongly decreased in presence of Fe^{$\text{2+}\text{3+}$} couple. The kinetics of electron transfer between the amorphous WO₃ anodic films and the Fe^{$\text{2+}\text{3+}$} redox couple in the electrolyte seems to occur in accordance with the theory developed for single crystal semiconductors.     

Selective refinement queries for volume visualization of unstructured tetrahedral meshes

We address the problem of the efficient visualization of large irregular volume data sets by exploiting a multiresolution model based on tetrahedral meshes. Multiresolution models, also called Level-Of-Detail (LOD) models, allow encoding the whole data set at a virtually continuous range of different resolutions. We have identified a set of queries for extracting meshes at variable resolution from a multiresolution model, based on field values, domain location, or opacity of the transfer function. Such queries allow trading off between resolution and speed in visualization. We define a new compact data structure for encoding a multiresolution tetrahedral mesh built through edge collapses to support selective refinement efficiently and show that such a structure has a storage cost from 3 to 5.5 times lower than standard data structures used for tetrahedral meshes. The data structures and variable resolution queries have been implemented together with state-of-the art visualization techniques in a system for the interactive visualization of three-dimensional scalar fields defined on tetrahedral meshes. Experimental results show that selective refinement queries can support interactive visualization of large data sets.     

NMR structure of the (+)-CPI-indole/d(GACTAATTGAC)-d(GTCAATTAGTC) covalent complex

We report the NMR solution structure of (+)-CPI-indole (CPI, 1,2,8,8a-tetrahydrocyclopropa[c]pyrrolo[3,2-e]indol-4(5H)-one), an agent belonging to the CC-1065/duocarmycin family of antitumor compounds. This (+)-CPI-indole structure is covalently bound to d(G(1)ACTAATTGTC(11))-d(G(12)TCAATTAGTC(22)), a synthetic DNA duplex containing a high-affinity binding site. The three-dimensional structure has been determined by several cycles of restrained molecular dynamics calculations with a total of 563 NMR-derived constraints, both in vacuo and by using the generalized Born solvent continuum model. In-depth analysis of the structure of this ligand-DNA complex led to a detailed knowledge of the bound state conformation of the CPI-indole, the most simplified agent related to CC-1065 and duocarmycins, the parent members of a family of extremely potent antitumor compounds. Comparison of the CPI-indole bound conformation with those previously found for (+)-duocarmycin SA (DSA), its unnatural enantiomer (-)-DSA, and the demethoxylated analogue (+)-DSI in their DNA complexes provided additional evidence of the tight correlation between the catalytic effect exerted by DNA on the alkylation reaction and the extent of angular twist between the two planar heteroaromatic subunits of these agents. Additionally, comparison of the structural features of the DNA-bound state of a "naked" ligand, such as CPI-indole, with those of various other duocarmycin agents provided useful information for the interpretation of the observed effects on chemical reactivity of the different substitution patterns at the hemispheres of these types of complex.     

COMPLIANCE VERIFICATION OF AGENT INTERACTION: A LOGIC-BASED SOFTWARE TOOL

In open societies of agents, where agents are autonomous and heterogeneous, it is not realistic to assume that agents will always act so as to comply with interaction protocols. Thus, the need arises for a formalism to specify constraints on agent interaction, and for a tool able to observe and check for agent compliance with interaction protocols. In this paper we present a JAVA-PROLOG software component built on logic programming technology, which can be used to verify compliance of agent interaction to protocols, and that has been integrated with the PROSOCS platform.     

Quantifying the exploration performed by metaheuristics

In this article we propose a formalisation of the concept of exploration performed by metaheuristics. In particular, we define and test a method for studying this aspect regardless of the specific approach implemented. Understanding the behaviour of metaheuristics is important for being able to boost their results. Measuring the exploration performed may help increase this understanding. We propose an experimental analysis to show how the measure of exploration defined may be used to this aim. We quantify the different level of exploration implied by different parameter settings in an ant colony optimisation and in a genetic algorithm for the travelling salesman problem. The results suggest that it may be possible to establish a relation between exploration and performance of the algorithm.     

Winter and spring surface velocity fields in the Cape Blanc region as deduced with the maximum cross-correlation technique

The ocean surface velocity field in the Cape Blanc region, off Northwest Africa, is investigated with the maximum cross-correlation (MCC) method applied to channel-4 Advanced Very High Resolution Radiometer satellite images. An initial sensitivity analysis allows us to select the four parameters that provide maximum area coverage and the best velocity resolution, while limiting the standard deviation for each velocity component within reasonable values. These are (m, n, MV, CT)?=?(22, 32, 50, 0.6), where m and n are the number of pixels of the search window (SW) and reference window (RW), respectively, MV is the maximum possible velocity (in cm s^?1), and CT is a correlation threshold for a feature to be tracked. A total of 489 images, for years 2005 and 2006, are analysed, and 106 velocity maps are generated with good coverage of the coastal transition zone (CTZ), most of them for the winter (34) and spring (59) seasons. We remove spurious data using the method's own filters (MV, CT, and a neighbour-vector comparison), requesting the velocity components to have Gaussian distributions and smoothing the resulting velocity fields with a median-vector filter. The instantaneous velocity maps illustrate the response of the alongshore coastal jet north of Cape Blanc (and its extension along the Cape Verde frontal region) to wind forcing, as well as the presence of numerous mesoscalar features (100–300 km wide) superposed on a westward offshore transport south of Cape Blanc. We also produce mean and standard deviation winter and spring velocity maps, which are compared with the corresponding mean sea surface temperature fields. The along-shore and offshore flow is better defined and is more intense in spring than in winter, in concordance with cross-slope sharper temperature gradients during this season, and brings about a cooling of the whole region. We identify five different ubiquitous currents: a southwestward jet north of Cape Blanc, a northwestward jet off Banc d'Argin, an offshore convergent jet, a spring jet-like feature at 18° N, and a southward flow in the southwestern CTZ.     

MR imaging of focal liver lesions: comparison between turbo spin-echo and conventional spin-echo pulse sequences

The aim of this study was to compare conventional spin-echo (CSE)T ₂-weighted (T2W) images with turbo spin-echo (TSE) T2W pulse sequences in their ability to detect focal liver lesions. Seventy-eight consecutive patients with focal liver lesions were entered into this study. All patients were imaged using the gradient-echo (GE) sequence with the breath-hold technique forT ₁-weighted (T1W) images, and CSE and TSE sequences for T2W images. Qualitative evaluation included lesion detection (number of lesions detected) and conspicuity (extent of visualization of lesional borders); quantitative evaluation included the signal-to-noise (S/N) ratio and the contrast-to-noise (C/N) ratio. TSE showed the best performance in terms of lesion detection; however, the difference between TSE and CSE was significant only in the case of benign cysts (p<0.01). Conspicuity was higher with TSE and CSE, and lower with GE. The S/N and C/N ratios of the two T2W sequences were also comparable, and better than those of GE. However, the combined use of GE and TSE resulted in improved lesion detection. The results show that, because the acquisition time is greatly reduced with TSE sequences, these should be considered as first-line approach to magnetic resonance imaging of the liver for the study of focal lesions.     

Variants of constrained longest common subsequence

We consider a variant of the classical Longest Common Subsequence problem called Doubly-Constrained Longest Common Subsequence (DC-LCS). Given two strings s₁ and s₂ over an alphabet Σ, a set Cs of strings, and a function Co:Σ→N, the DC-LCS problem consists of finding the longest subsequence s of s₁ and s₂ such that s is a supersequence of all the strings in Cs and such that the number of occurrences in s of each symbol σ∈Σ is upper bounded by Co(σ). The DC-LCS problem provides a clear mathematical formulation of a sequence comparison problem in Computational Biology and generalizes two other constrained variants of the LCS problem that have been introduced previously in the literature: the Constrained LCS and the Repetition-Free LCS. We present two results for the DC-LCS problem. First, we illustrate a fixed-parameter algorithm where the parameter is the length of the solution which is also applicable to the more specialized problems. Second, we prove a parameterized hardness result for the Constrained LCS problem when the parameter is the number of the constraint strings (|Cs|) and the size of the alphabet Σ. This hardness result also implies the parameterized hardness of the DC-LCS problem (with the same parameters) and its NP-hardness when the size of the alphabet is constant.