In Situ ceramic particle-reinforced aluminum matrix composites fabricated by reaction pressing in the TiO2 (Ti)-Al-B (B2O3) systems

Particulate TiB₂ reinforced aluminum-based metal matrix composites (MMCs) were successfully fabricated by means of the reaction processing method. TiB₂ particulates were formed in situ through the reaction of Ti and B in Ti-Al-B, TiO₂ and B in TiO₂-Al-B, and TiO₂ and B₂O₃ in TiO₂-Al-B₂O₃ systems. The results showed that in situ TiB₂ particulates formed in the Ti-Al-B system had a size of 5 μm and they exhibited block and rodlike structures. Moreover, coarse Al₃Ti blocks several tens of micrometers in size were also formed simultaneously. On the other hand, equiaxed Al₂O₃ and TiB₂ particulates with a size of less than 2 μm were formed in situ in the TiO₂-Al-B and TiO₂-Al-B₂O₃ systems. The Al₃Ti phase was completely eliminated in the TiO₂-Al-B system with increasing B content. Tensile tests revealed that the Al₂O₃ · TiB₂/Al composite fabricated from the TiO₂-Al-B system exhibits excellent mechanical properties. The yield strength of the Al₂O₃ · TiB₂/Al composite appeared to increase with increasing TiB₂ content. The yield strength of the Al₂O₃ · TiB₂/Al composite could be further increased by introducing CuO into the TiO₂-Al-B system. Such an increment in mechanical strength arose from the strengthening effect caused by the Al₂Cu precipitates. The incorporation of CuO had no effect on the in situ reaction process of the TiO₂-Al-B system. Finally, the effect of SiC addition on the microstructure and mechanical properties of the composites fabricated from the TiO₂-Al-B and TiO₂-Al-B-CuO systems was also investigated.     

Detection of an anatoxin-a(s)-like anticholinesterase in natural blooms and cultures of cyanobacteria/blue-green algae from Danish lakes and in the stomach contents of poisoned birds

Ten natural bloom samples of cyanobacteria from the Danish lakes Knud s? (5), Ravn s? (4), and Salten Langs? (1) collected during 1993-1995 were assayed for toxicity by mouse bioassay, for acetylcholinesterase inhibiting activity by a colorimetric method, and for microcystins by enzyme-linked immunosorbent assay. In the mouse bioassay, seven samples were neurotoxic, two were non-toxic and one gave a protracted toxic response. One of the non-toxic and the single protracted toxic sample both contained anticholinesterase activity equivalent to 4 micrograms anatoxin-a(s) g-1. The neurotoxic samples contained equivalents to 20-3300 micrograms anatoxin-a(s) g-1. The highest anticholinesterase activities (equivalent to 2300 and 3300 micrograms anatoxin-a(s) g-1, respectively) were found in samples collected from Lake Knud s? in connection with bird-kills in 1993 and 1994. Small amounts of microcystins (0.1-0.9 microgram g-1) were detected in all samples but one. All Lake Knud s? and Lake Ravn s? samples were dominated by Anabaena lemmermannii, and the Lake Salten Langs? sample by several species of Anabaena. Gel filtration profiles indicated similarity between the toxic component from the Lake Knud s? 1994 bloom with registered bird-kills and anatoxin-a(s) isolated from Anabaena flos-aquae NRC-525-17. Anticholinesterase-producing cultures of A. lemmermannii were isolated from the Lake Knud s? 1993 bloom. These laboratory cultures produced anatoxin-a(s) equivalents of 29-743 micrograms g-1. Other cultures of A. lemmermannii isolated from Lake Knud s? and Lake Ravn s? were hepatotoxic or non-toxic. Dead birds collected from Lake Knud s? during the neurotoxic 1993 Anabaena bloom possibly died from cyanobacterial toxicosis. The stomach contents contained colonies and single trichomes of Anabaena, and anticholinesterase activities equivalent to 2.1-89.7 micrograms anatoxin-a(s) kg-1 body weight and microcystins (53-95 ng kg-1) were also detected.     

Laparoscopic operation of a Morgagni hernia

Morgagni hernias are the least common form of diaphragmatic hernias. Although they are congenital, most of them are not diagnosed until later in life. The indication for surgery is based on the patient's symptoms or on the radiological evidence of incarcerated tissue, and until quite recently involved a laparotomy or thoracotomy. Laparoscopy not only permits the suspected diagnosis to be confirmed--which is otherwise often difficult--but also makes it possible to close the hernia site by suturing. For improved security, the hernia site is augmented by fixing in place a non-absorbable mesh. The operative technique employed is described.     

Visualization of mitochondria with green fluorescent protein in cultured fibroblasts from patients with mitochondrial diseases

cDNAs for green fluorescent protein (GFP) and for a GFP fusion protein containing the presequence of human ornithine transcarbamylase (pOTC-GFP) were transfected into cultured human fibroblasts. GFP cDNA gave diffuse fluorescence throughout the cytoplasm and the nucleus, whereas pOTC-GFP cDNA gave mitochondria-associated fluorescence. Fluorescent mitochondrial structures could be classified into five patterns: thread-like mitochondria, fine thread-like ones, rod-like ones, granular ones, and granular ones with weak cytosolic fluorescence. pOTC-GFP mutants resulted in a loss of mitochondrial fluorescence and an appearance of weak fluorescence throughout the cytoplasm. pOTC-GFP cDNA was transfected into fibroblasts from patients with various mitochondrial diseases. Higher ratios of fibroblasts with granular mitochondria and those with fine thread-like ones were observed in a patient with Reye's syndrome and a patient with Kearns-Sayre syndrome. Weak cytosolic fluorescence was sometimes observed in fibroblasts from these patients. This method will be useful to analyze mitochondrial structural alterations and disorders of mitochondrial protein import.     

Effects of 17 beta-estradiol on nitric oxide and ventricular myocardium metabolism

BACKGROUND: Arrhythmias are frequent pathology in patients with chronic hemodialysis. We evaluated whether a relatively new technique, signal averaging, could be useful in predicting the development of complex arrhythmias in these patients. METHODS: Thirty-three patients, 18 male and 15 female, subjected to thrice weekly chronic hemodialytic treatment with various dialysis techniques, were studied. Exclusion criteria were the presence of antiarrhythmic and inotropic treatment. The following examinations were carried out in all patients: a Holter dynamic electrocardiography for a duration of 24 hours, begun on the day of dialysis, high resolution ECG pre- and post-dialysis to find out if there were any ventricular late potential (VLP). Four hundred beats were examined in order to obtain a background noise of less than 0.7 microV and a better definition of the signal. The following parameters were considered significant for the presence of VLP: a) filtered QRS duration > 120 msec; b) the root mean square of the signal expressed in the terminal portion of QRS (RMS) < 25 microV) high frequency low amplitude signals duration (HFLA) > 40 msec. A positive value in two of these parameters was considered indicative of the presence of VLP. In addition various pre and post-dialysis indices of dialytic efficiency and a mono and two-dimensional echocardiogram with pulsed and color Doppler were carried out. Of the 33 patients studied, ten were excluded because they presented too high a background noise at the high resolution ECG. Of the remaining 23 patients, 13 (56%) presented VLP and nine of these (69%) presented complex arrhythmias. Of the ten patients without VLP, 5 (50%) presented complex arrhythmias. The incidence of arrhythmias was highest during the last two hours of dialysis and in the two hours following it. The patients were then divided into two groups (A and B) according to the ejection fraction (EF) found at the echocardiogram. Group A was composed of 17 patients of whom 8 (47%) presented complex arrhythmias; group B (EF < 45%) was composed of the remaining six patients, who all presented complex arrhythmias. In group A nine patients (53%) out of 17 had LVP, in group B four out of six (66%) had it. All the patients except one presented an increase in the thickness of the ventricular wall and alterations of Doppler transmitral filling rate. Left ventricular hypertrophy was diagnosed in 22 out of the 23 patients. Four patients also had chronic ischaemic heart disease; of these three had LVP. There was no correlation between the presence of LVP and the hemodialytic indices and between the latter and complex arrhythmias. CONCLUSIONS: Our study showed that arrhythmias are more frequent in patients with LVP before dialysis than in those without. The difference was statistically significant (p < 0.006); the incidence of arrhythmias was higher in patients with FE < 45% (p < 0.001). The majority of patients (95%) had left ventricular hypertrophy; only four (17%) had ischaemic heart disease too. It is highly probable that the presence of LVP in our patients can be attributed to hypertension and subsequent left ventricular hypertrophy. As patients with LVP at the end of dialysis had a greater incidence of arrhythmias than those without LVP, we suggest that this method could be useful as a first screening in dialysed patients.     

Cultural adaptation and information design: two contrasting views

Approaches to using visual language in a cultural context can be placed on a continuum, with global (universal) on one end and culture-focused on the other. Each approach reveals contrasting assumptions about three central design issues: perception, aesthetics and pragmatics. The global approach is characterized by attempts to invent an objective, universal visual language or to define such a language through perceptual principles and empirical research. The culture-focused perspective is founded on the principle that visual communication is intimately bound to experience and hence can function only within a given cultural context, to which designers must be sensitive. While the modernist, universal approach has been losing ground to the postmodern, culture-focused approach, the two complement each other in a variety of ways and, depending on the rhetorical situation, offer pragmatic benefits and drawbacks     

Scientific and artistic investigation of multi-dimensional fractals on the AT & T pixel machine

The pipelined architecture and parallel organization of the AT&T Pixel Machine image computer are described and demonstrated with applications for the visualization of multidimensional fractals, particularly linear fractals and quaternion/ stacked Julia sets. Techniques for pushing the Pixel Machine to its peak abilities are described and apply to more recent parallel image computers as well.     

Function materialization in object bases: design, realization, andevaluation

View materialization is a well-known optimization technique of relational database systems. We present a similar, yet more powerful, optimization concept for object-oriented data models: function materialization. Exploiting the object-oriented paradigm-namely, classification, object identity, and encapsulation-facilitates a rather easy incorporation of function materialization into (existing) object-oriented systems. Only those types (classes) whose instances are involved in some materialization are appropriately modified and recompiled, thus leaving the remainder of the object system invariant. Furthermore, the exploitation of encapsulation (information hiding) and object identity provides for additional performance tuning measures that drastically decrease the invalidation and rematerialization overhead incurred by updates in the object base. First, it allows us to cleanly separate the object instances that are irrelevant for the materialized functions from those that are involved in the materialization of some function result, and this to penalize only those involved objects upon update. Second, the principle of information hiding facilitates fine-grained control over the invalidation of precomputed results. Based on specifications given by the data type implementor, the system can exploit operational semantics to better distinguish between update operations that invalidate a materialized result and those that require no rematerialization. The paper concludes with a quantitative analysis of function materialization based on two sample performance benchmarks obtained from our experimental object base system GOM     

Site and query scheduling policies in multicomputer databasesystems

We study run-time issues, such as site allocation and query scheduling policies, in executing read-only queries in a hierarchical, distributed memory, multicomputer system. The particular architecture considered is based on the hypercube interconnection. The data are stored in a base cube, which is controlled by a control cube and host node hierarchy. Input query trees are transformed into operation sequence trees, and the operation sequences become the units of scheduling. These sequences are scheduled dynamically at run-time. Algorithms for dynamic site allocation are provided. Several query scheduling policies that support interquery concurrency are also studied. Average query completion times and initiation delays are obtained for the various policies using simulations     

Partial indexing for nonuniform data distributions in relationalDBMS's

It is well known that the effectiveness of relational database systems is greatly dependent on the efficiency of the data access strategies. For this reason, much work has been devoted to the development of new access techniques, supported by adequate access structures such as the B⁺trees. The effectiveness of the B ⁺tree also depends on the data distribution characteristics; in particular, poor performance results when the data show strong key value distribution unbalancing. The aim of this paper is to present the partial index: a new access structure that is useful in such cases of unbalancing, as an alternative to the B⁺tree unclustered indexes. The access structures are built in the physical design phase, and at execution (or compilation) time, the optimizer chooses the most efficient access path. Thus, integration of the partial indexing technique in the design and in the optimization process are also described