Creation of TiN paths on titanium alloy OT4-1 by the use of a laser beam

TiN paths have been created on the surface of the titanium alloy OT4-1 by the use of a laser beam. The results of investigations of structure, phase composition, microhardness and surface roughness of the created TiN paths are given in the paper. The paths created in the work are inhomogenous two-phase mixtures of TiN and -Ti, in which the TiN phase with strong (2 0 0) texture is predominant over the other phase and presents a dendritic structure. © 1998 Chapman & Hall     

A clinical nude mouse metastatic model for highly malignant human pancreatic cancer

Pancreatic cancer is a highly aggressive and treatment-refractory cancer. A clinically-relevant animal model is necessary to develop therapy for metastatic pancreatic cancer. In this study we evaluated the efficacy of mitomycin C (MMC) and 5-FU against the human pancreatic adenocarcinoma cell line PAN-12 in an orthotopic human metastatic pancreatic cancer nude mice model. The model is constructed by surgical orthotopic implantation (SOI) of histologically intact tumor tissue in the tail portion of the pancreas near the spleen. PAN-12 grew very aggressively in the control group of nude mice with extensive local invasion and distant metastasis to various organs with a propensity for the lung but to other organs as well, including the liver, kidney and regional and distant lymph nodes. In a striking effect none of the mice in the MMC-treated group developed tumor. Although mice in the 5-FU treated group survived statistically significantly longer than those in the untreated control, the overall incidence of metastasis in these mice was equivalent to those in the control. However no liver or kidney metastases were found in the 5-FU treated animals perhaps accounting in part for their longer survival. This "clinical" nude mouse model of highly metastatic pancreatic cancer can now be used to discover new effective agents for this disease.     

Cooperative aspect-oriented programming

Aspect-oriented programming (AOP) seeks to improve software modularity via the separation of cross-cutting concerns. AOP proponents often advocate a development strategy where programmers write the main application (base code), ignoring cross-cutting concerns, and then aspect programmers, domain experts in their specific concerns, weave in the logic for these more specialized cross-cutting concerns. This purely oblivious strategy, however, has empirically been shown to tightly couple aspects to base code in many cases, hindering aspect modularity and reuse. In essence, the more intricate the weaving between the cross-cutting concern and the base code (lexically and/or semantically), the harder it becomes to: (a) robustly specify how to weave the aspects in at the required points, (b) capture interactions between aspects and base code, and (c) preserve the correct weaving as the base code evolves.We propose an alternate methodology, termed cooperative aspect-oriented programming (Co-AOP), where complete lexical separation of concerns is not taken as an absolute requirement. Instead, cross-cutting concerns are explicitly modeled as abstract interfaces through explicit join points (EJPs). Programmers specify where these interfaces interact with base code either through explicit lexical references or via traditional oblivious aspects. This explicit awareness allows base code and aspects to cooperate in ways that were previously not possible: arbitrary blocks of code can be advised, advice can be explicitly parameterized, base code can guide aspects in where to apply advice, and aspects can statically enforce new constraints upon the base code that they advise. These new techniques allow aspect modularity and program safety to increase, and bring us towards a cooperative AOP paradigm.We illustrate our methodology via an example on transactions, and also give an initial evaluation of cooperative AOP through an empirical study on program extensibility comparing both the traditional and cooperative AOP methodologies. Initial results show that cooperative AOP techniques result in code that is less complex with lower overall coupling, facilitating extensibility.     

A new framework for understanding educational digital library use: re-examining digital divides in U.S. schools

Despite their decade of deployment, educational digital libraries have not achieved sustained use in elementary and secondary schools in the United States. Barriers to accessing the Internet and computers have been widely targeted by myriad initiatives, but efforts aimed at bridging this first-level “digital divide” have not led to increased use of the Internet and digital library resources in U.S. classrooms. In fact, such programs have revealed additional divides that affect educators’ use. This paper examines the additional digital divide levels and proposes a new framework for understanding technology innovation in schools that can improve development and outreach approaches by digital library developers.     

Monomers of human beta 1 beta 1 alcohol dehydrogenase exhibit activity that differs from the dimer

A previously unreported enzymatic activity is described for monomers of the beta 1 beta 1 isoenzyme of human alcohol dehydrogenase that were prepared from dimeric enzyme by freeze-thaw in liquid nitrogen. Whereas the dimeric enzyme has optimal activity at low substrate concentrations (2.5 mM ethanol, 50 microM NAD+; "low Km" activity), the monomer has its highest activity at high substrate concentrations (1.5 M ethanol, 2.5 mM NAD+; "high Km" activity). While the activity of the monomer does not appear to be saturated at 1.5 M ethanol, its maximal activity at this high ethanol concentration exceeds the Vmax of the dimer by about 3-fold. The apparent Km of NAD+ with monomers is 270 microM, and no activity could be detected with nicotinamide mononucleotide as cofactor. During gel filtration the high Km activity elutes at a lower apparent molecular weight position than the dimer. The kinetics of monomer-to-dimer reassociation are consistent with a second-order process with a rate constant of 240 M-1 s-1. The reassociation rate is markedly enhanced by the presence of NAD+. During refolding of beta 1 beta 1 following denaturation in 6 M guanidine hydrochloride, an enzyme species with high Km activity and spectral properties similar to the freeze-thaw monomer is observed, indicating that a catalytically active monomer is an intermediate in the refolding pathway. The enzymatic activity of the monomer implies that the intersubunit contacts of beta 1 beta 1 are not crucial in establishing a catalytically competent enzyme. However, the differences in specific activity and Km between monomer and dimer suggest that dimerization may serve to modulate the catalytic properties.     

Habituation of the orienting response: a gating mechanism subserving selective attention

Possibilities of involution of changes in lesser circulation after closure of experimental aortopulmonary anastomosis were studied. 37 observations at various intervals after closure of anastomosis (several minutes to 13.5 months) in 25 dogs were analyzed. Before closure the anastomosis had functioned for 1-7 months. The results of histological examinations of lungs, pressure measurements in lesser circulation, heart weight, electrocardiographic and spirographic examinations were analyzed. It was found that complete involution of changes in lesser circulation was possible only in first month of existence of anastomosis, in this case with changes of both "early" and "late" types. "Late"-type changes after four months function of anastomosis had both reversible and irreversible character, whereas "early"-type changes became irreversible already after three-month duration of anastomosis. With the "late"-type changes, the operation itself (closure of anastomosis) was accompanied by symptoms of pulmonary vasomotor paresis and heart failure, whereas in the presence of "early"-type changes the operation elicited no morphological or functional changes.     

Imported measles. A potential control problem

From Dec 23, 1978, through Jan 31, 1979, an outbreak of five laboratory-confirmed cases and four clinical cases of measles occurred in a Vietnamese refugee population living in a single housing complex in Albuquerque, NM. The index cases were in two refugee siblings in whom measles was incubating on arrival in the United States. Despite spread through three subsequent generations of disease transmission within the Vietnamese population, there was no additional spread into the general Albuquerque population. Responsible factors included the age distribution of susceptible persons, the social isolation of the refugee population, and the physical structure of the housing complex. There is a need to identify the problem of imported measles in "ethnic islands" in need of vaccination.     

Formation mechanism of nano-diamond films from energetic species: From experiment to theory

In this paper, a particular class of nano-diamond films deposited by energetic species is described. Deposition is carried out using the direct-current glow-discharge (DC GD) deposition technique from a methane/hydrogen mixture. In this method, film growth occurs from energetic species being accelerated and incorporated into the film surface. The growth of the nano-diamond film occurs on top of a preferentially oriented graphitic precursor with its basal planes perpendicular to the substrate surface. The nano-diamond films consist of an agglomerate of diamond particles with particle sizes in the 3-5 nm range with amorphous grain boundaries. The hydrogen concentration in the graphitic precursor is only a few percent; however, it increases to ∼15-20 at.% in the nano-diamond film.From a microscopic perspective nano-diamond film and growth from energetic species is explained as a sub-surface process in terms of a four-step cyclic process. The DC GD-deposited nano-diamond films were comprehensively explored by a number of complementary techniques. The hydrogen content and its role in nano-diamond film formation were assessed. The experimental methods used in our studies comprise near-edge X-ray adsorption fine structure (NEXAFS) to prove the short-range coordination of the carbon films and indirectly their phase composition. The surface and grain boundary phase composition were investigated by a combination of electron energy loss spectroscopy (EELS) measured as a function of incident electron energy and hydrogen etching experiments. By transmission electron microscopy (TEM), the micro-structural evolution and their visualization were achieved. The density evolution of the films was determined by X-ray reflectivity (XRR). The hydrogen content and its distribution in the films were studied by secondary ion microscopy spectroscopy (SIMS) and elastic recoil detection (ERD). The hydrogen bonding was investigated by high-resolution electron energy loss spectroscopy (HREELS).Most likely, hydrogen is bonded within the amorphous grain boundaries and saturates the nano-diamond particles. The surface of the films is amorphous in nature.     

Multitarget miss distance via optimal assignment

The concept of miss distance-Euclidean, Mahalanobis, etc.-is a fundamental, far-reaching, and taken-for-granted element of the engineering theory and practice of single-target systems. In this paper we introduce a comprehensive L/sub p/-type theory of distance metrics for multitarget (and, more generally, multiobject) systems. We show that this theory extends, and provides a rigorous theoretical basis for, an intuitively appealing optimal-assignment approach proposed by Drummond for evaluating the performance of multitarget tracking algorithms. We describe tractable computational approaches for computing such metrics based on standard optimal assignment or convex optimization techniques. We describe the potentially far-reaching implications of these metrics for applications such as performance evaluation and sensor management. In the former case, we demonstrate the application of multitarget miss-distance metrics as measures of effectiveness (MoEs) for multitarget tracking algorithms.