Processing of ultrafine-size particulate metal matrix composites by advanced shear technology

Copyright @ 2009 ASM International. This paper was published in Metallurgical & Materials Transactions A 40A(3) and is made available as an electronic reprint with the permission of ASM International. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplications of any material in this paper for a fee or for commercial purposes, or modification of the content of this paper are prohibited.Lack of efficient mixing technology to achieve a uniform distribution of fine-size reinforcement within the matrix and the high cost of producing components have hindered the widespread adaptation of particulate metal matrix composites (PMMCs) for engineering applications. A new rheo-processing method, the melt-conditioning high-pressure die-cast (MC-HPDC) process, has been developed for manufacturing near-net-shape components of high integrity. The MC-HPDC process adapts the well-established high shear dispersive mixing action of a twin-screw mechanism to the task of overcoming the cohesive force of the agglomerates under a high shear rate and high intensity of turbulence. This is followed by direct shaping of the slurry into near-net-shape components using an existing cold-chamber die-casting process. The results indicate that the MC-HPDC samples have a uniform distribution of ultrafine-sized SiC particles throughout the entire sample in the as-cast condition. Compared to those produced by conventional high-pressure die casting (HPDC), MC-HPDC samples have a much improved tensile strength and ductility.EP-SR

Human T-cell lymphotropic virus types I and II infections in a cohort of patients with neurological disorders in Belém, Pará, Brazil Infecção pelos vírus linfotrópicos humanos de células T tipos I e II entre pacientes com doença neurológica em Belém, Pará, Brasil

Serum- and/or- cerebrospinal fluid (CSF) samples obtained from 190 patients suffering from chronic, progressive neurological disease were screened for the presence of human T-cell lymphotropic viruses type I (HTLV-I) and type II (HTLV-II) antibodies over a six-year period (1996 to 2001) in Belém, Pará, Brazil. Patients were of both sexes (male subjects, 52%) with ages ranging from 2 to 79 years (mean, 35.9). Overall, 15 (7.9%) subjects - of whom 12 (80%) were female adults - reacted HTLV-I/II-seropositive when screened by enzyme-linked immunosorbent assay (ELISA). Serum samples from 14 of these patients were also analyzed using a recombinant Western blot (WB) assay that yielded HTLV-I-, HTLV-II-, and HTLV-I/II- reactivities for 10 (71.4%), 3 (21.4%) and 1 (7.2%) of them, respectively. The yearly rates of HTLV-I/II antibodies ranged from 2.6% (2001) to 21.7% (2000), with progressively increasing seropositivities from 1998 to 2000. Altogether, walking difficulty (n = 5 subjects), spasticity (n = 4) and leg weakness (n = 3) accounted for 80% of symptoms recorded among the 15 patients whose sera had antibodies to HTLV-I/II as detected by ELISA. These findings provide evidence that both HTLV-I and HTLV-II play a role in the development of chronic myelopathy in Belém, Pará, Northern Brazil.<br>Amostras de soro e/ou líquido céfalo-raquidiano (LCR) foram obtidas de 190 pacientes com quadro de doença neurológica crônica e progressiva, com vistas à detecção de anticorpos para os vírus linfotrópicos humanos de células T dos tipos I (HTLV-I) e II (HTLV-II), durante um período de seis anos (1996 a 2001) em Belém, Pará, Brasil. O grupo compreendia ambos os sexos (homens, 52%), com idades variando de 2 a 79 anos (média, 35,9 anos). Tomando-se os resultados como um todo, 15 (7,9%) indivíduos, incluindo 12 (80%) mulheres adultas, apresentaram anticorpos para HTLV-I/II a partir da triagem pelo procedimento imunoenzimático (ELISA). Soros de 14 desses pacientes também foram testados utilizando-se procedimento de Western blot (WB), alcançando-se freqüências de anticorpos para HTLV-I, HTLV-II e dupla reação (HTLV-I e HTLV-II) em 10 (71,4%), 3 (21,4%) e 1 (7,2%) indivíduos, respectivamente. As freqüências anuais de positividade para HTLV-I/II variaram de 2,6% (2001) a 21,7% (2000), em escala crescente no período de 1998 a 2000. Em conjunto, dificuldade na deambulação (n = 5 pacientes), espasticidade (n = 4) e hipotonia crural compreenderam 80% das manifestações clínicas registradas entre os 15 pacientes cujas amostras de soro continham anticorpos para HTLV-I/II, com base em ELISA. Tais resultados oferecem indicadores quanto a uma possível associação do HTLV-I e do HTLV-II à gênese das mielopatias crônicas em Belém, norte do Brasil