Use of plasma nitriding to improve the wear and corrosion resistance of 18Ni-300 maraging steel manufactured by selective laser melting.

18Ni-300 maraging steel manufactured by selective laser melting was plasma nitrided to improve its wear and corrosion resistance. The effects of a prior solution treatment, aging and the combination of both on the microstructure and the properties after nitriding were investigated. The results were compared with conventionally produced 18Ni-300 counterparts subjected to the same heat- and thermo-chemical treatments. The plasma nitriding was performed under the same conditions (temperature of 520 °C and time of 6 h) as the aging in order to investigate whether the nitriding and the aging could be carried out simultaneously in a single step. The aim of this work was to provide a better understanding of the morphology and chemical composition of the nitrided layer in the additive-manufactured maraging steel as a function of the prior heat treatments and to compare the wear and corrosion resistance with those of conventional maraging steel. The results show that nitriding without any prior aging leads to cracks in the compound layer, while nitriding of the prior-heat-treated additive-manufactured maraging steel leads to benefits from the thermochemical treatment in terms of wear and corrosion resistance. Some explanations for the origins of the cracks and pores in the nitride layers are provided.

Microstructural Development in a Laser-Remelted Al-Zn-Si-Mg Coating.

In the last five decades, there has been intense development in the field of Zn-Al galvanic coating modification. Recently, Mg was added to improve corrosion properties. Further improvements to the coating are possible with additional laser surface treatment. In this article, we focus on remelting the Al-Zn-Mg-Si layer, using a diode laser with a wide-beam format, concentrating on the microstructure development during extreme cooling rates. Laser remelting of the Al-Zn-Mg-Si coating and rapid self-quenching produces a finer grain size, and a microstructure that is substantially refined and homogenized with respect to the phase distribution. Using EBSD results, we are able to understand microstructure modification. The laser modified coating has some porosity and intergranular cracking which are difficult to avoid, however this does not seem to be detrimental to mechanical properties, such as ductility on bending. The newly developed technology has a high potential for improved corrosion performance due to highly refined microstructure.

Coarsening behaviour of M23C6 carbides in creep-resistant steel exposed to high temperatures.

High operating temperatures can have very deleterious effects on the long-term performance of high-Cr, creep-resistant steels used, for example, in the structural components of power plants. For the popular creep-resistant steel X20CrMoV12.1 we analysed the processes of carbide growth using a variety of analytical techniques: transmission electron microscopy (TEM) and diffraction (TED), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD). The evolution of the microstructure after different aging times was the basis for a much better understanding of the boundary-migration processes and the growth of the carbides. We present an explanation as to why some locations are preferential for this growth, and using EBSD we were able to define the proper orientational relationship between the carbides and the matrix.

Surface and Bulk Carbide Transformations in High-Speed Steel.

We have studied the transformation of carbides in AISI M42 high-speed steels in the temperature window used for forging. The annealing was found to result in the partial transformation of the large, metastable M2C carbides into small, more stable grains of M6C, with an associated change in the crystal orientation. In addition, MC carbides form during the transformation of M2C to M6C. From the high-speed-steel production point of view, it is beneficial to have large, metastable carbides in the cast structure, which later during annealing, before the forging, transform into a structure of polycrystalline carbides. Such carbides can be easily decomposed into several small carbides, which are then randomly distributed in the microstructure. The results also show an interesting difference in the carbide-transformation reactions on the surface versus the bulk of the alloy, which has implications for in-situ studies of bulk phenomena that are based on surface observations.

Search for viral nucleic acid sequences in brain tissues of patients with schizophrenia using nested polymerase chain reaction.

BACKGROUND: We used polymerase chain reaction to search for nucleic acid sequences of several viruses in DNA and RNA extracted from brain tissues of schizophrenic and control subjects. METHODS: We extracted DNA and RNA templates from frozen brain specimens of 31 patients with schizophrenia and 23 nonschizophrenic control patients with other diseases. The extracts were subjected to polymerase chain reaction with oligonucleotide primers for 12 different viruses (cytomegalovirus, Epstein-Barr virus, herpes simplex virus type 1, human herpesvirus type 6, varicellazoster virus, measles virus, mumps virus, rubella virus, the picornavirus group, influenza A virus, human T-cell lymphotropic virus type I, and St Louis encephalitis virus), several of which have been suspected of involvement in schizophrenia. Nested primers were used to increase the sensitivity of the method. RESULTS: No amplified nucleic acid sequences encoded by the selected viral genomes were detected in extracts of any brain specimens from either schizophrenic or control patients. CONCLUSIONS: These data agree with previous studies that failed to find sequences of a number of viruses in the cerebrospinal fluid or selected areas of the brains of schizophrenic patients. Additional efforts should be undertaken to identify other known and unknown pathogens in schizophrenia, sampling more areas of the brain from subjects with a variety of clinical types of schizophrenia.

Widespread, restricted low-level measles virus infection of brain in a case of subacute sclerosing panencephalitis.

In situ reverse transcriptase-polymerase chain reaction amplification with labeled-probe hybridization (in situ RT-PCR/LPH) was used to detect measles virus RNA within formalin-fixed, paraffin-embedded brain tissue sections from a patient who died with subacute sclerosing panencephalitis (SSPE). Many more infected neurons and oligodendrocytes were detected by in situ RT-PCR/LPH than by immunohistochemistry or by in situ hybridization alone. In addition, infection of vascular endothelial cells was demonstrated only by in situ RT-PCR/LPH. The observation that many cells contained only a few copies of viral RNA without detectable antigen is consistent with a persistent viral infection of the central nervous system. In situ RT-PCR/LPH, combining the sensitivity of PCR with the tissue localization of in situ hybridization, should prove useful in further studies to detect nucleic acids in situ in the central nervous system.

Blood buffy coat from Alzheimer's disease patients and their relatives does not transmit spongiform encephalopathy to hamsters.

There was a report of spongiform encephalopathy transmitted to Syrian hamsters by intracerebral inoculation with the blood buffy coat of patients with Alzheimer's disease (AD) and their unaffected first-degree relatives. We attempted to verify that report, taking measures to reduce the risk of contaminating samples with agents causing spongiform encephalopathies. We obtained blood from 50 subjects, including six patients with familial AD, 21 unaffected first-degree relatives (siblings and offspring) of patients with familial AD, and 20 control subjects. We inoculated the buffy coats intracerebrally into Syrian LVG hamsters, observed them for signs of neurologic disease, examined their brains for neuropathologic changes at time of death, and performed serial (blind) passages by inoculating suspensions of all recovered brains into fresh LVG hamsters. We discerned no clinical illness or histopathologic changes resembling experimental spongiform encephalopathy in any hamster inoculated with human buffy coat nor in blind-passage hamsters, nor were the life spans of those hamsters shortened. We conclude that AD is not caused by an agent that transmits spongiform encephalopathy to hamsters.

Low-incidence latent infection with variant B or roseola type human herpesvirus 6 in leukocytes of healthy adults.

Nested primer-based polymerase chain reaction was employed to determine the frequency of latent infection with human herpesvirus 6 (HHV-6) among healthy adults from Bratislava, Slovak Republic. A 592-bp region, upstream from the gene encoding the putative large tegument protein of HHV-6, was amplified from DNA extracted from peripheral blood mononuclear cells (PBMC) of only one of 29 seropositive adults, suggesting that as few as 1 in 10(5) PBMC may be infected with the virus. Direct sequencing of the 592-bp fragment indicated that the virus harbored by the seropositive Slovak subject (designated B38) differed by only 3 nucleotides from an HHV-6 variant B strain (R-147) isolated from an American infant with a roseola-like illness and by 32 bases from the variant A strain GS isolated from a patient with lymphadenopathy (5.4% sequence divergence). None of these strains had a deoxyadenosine at base position 1251, when compared to the published sequence of strain GS clone pZVH14. Although this discrepancy did not affect the large tegument protein gene, it altered the predicted amino acid sequences of two putative proteins coded by open-reading frames 1 and 2 (ORF 1 and ORF 2) located upstream from this gene.

Sequence analysis of human T cell lymphotropic virus type I strains from southern India: gene amplification and direct sequencing from whole blood blotted onto filter paper.

Human T cell lymphotropic virus type I (HTLV-I) infection in India has been found to be associated with adult T cell leukaemia/lymphoma (ATLL) and HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP) among life-long residents of southern India. To examine the heterogeneity of HTLV-I strains from southern India and to determine their relationship with the sequence variants of HTLV-I from Melanesia, 1149 nucleotides spanning selected regions of the HTLV-I gag, pol, env and pX genes were amplified and directly sequenced from DNA extracted from whole blood blotted onto filter paper and from peripheral blood mononuclear cells, obtained from one patient with HAM/TSP, two with ATLL and eight asymptomatic carriers from Andhra Pradesh, Kerala and Tamil Nadu. Sequence alignments and comparisons indicated that the 11 HTLV-I strains from southern India were 99.2% to 100% identical among themselves and 98.7% to 100% identical to the Japanese prototype HTLV-I ATK. The majority of base substitutions were transitions and silent. No frameshifts, insertions, deletions or possibly disease-specific base changes were found in the regions sequenced. The observed clustering of the Indian HTLV-I strains with those from Japan, as determined by the maximum parsimony method, suggested a common source of HTLV-I infection with subsequent parallel evolution. Amplification of DNA from blood specimens collected on filter paper may be useful for the study of other blood-borne pathogens.

Belgrade virus, a cause of hemorrhagic fever with renal syndrome in the Balkans, is closely related to Dobrava virus of field mice.

Belgrade virus is a recently described hantavirus that causes severe hemorrhagic fever with renal syndrome (HFRS) in people living in various parts of the Balkan Peninsula. Nucleotide sequencing of the G2-encoding region in the medium (M) segment of the viral genome, reverse transcribed and amplified by the polymerase chain reaction, revealed the Belgrade virus to be substantially different from Hantaan virus and other major serotypes of hantavirus but identical to Dobrava virus, a virus isolated from a field mouse (Apodemus flavicollis) in Slovenia. Belgrade virus may be an important cause of HFRS in the Balkan Peninsula, extending north toward the Alps. It poses a special danger to humans who have close contact with field rodents.

Long-term observations of human immunodeficiency virus-infected chimpanzees.

Twenty-seven chimpanzees inoculated with material presumed to contain human immunodeficiency virus (HIV) between June 1983 and February 1985 were studied. The animals were examined on four to six occasions between 1989 and 1992 for serologic, virologic, hematologic, immunophenotypic, as well as clinical signs of HIV infection and compared to five uninfected control animals. The 19 animals that had seroconverted within 244 days of inoculation remained antibody positive, whereas those that did not seroconvert within 244 days of inoculation remained antibody negative 6 to 8 years later. HIV antigen was demonstrated at least once in lymphocyte cultures from 12 of the 19 antibody positive chimpanzees during this period. Nested polymerase chain reaction amplified proviral DNA in lymphocytes from 14 of the 19 animals. No proviral DNA was detected in antibody-negative animals. Antibody titers were generally higher in animals from which virus was recovered in lymphocyte cultures [granulocyte-macrophage (GM) titer, 1:8427] compared to virus-negative animals (GM titer, 1:3608). Mean total white blood cell and lymphocyte subtype counts were similar in the HIV-infected animals and uninfected controls. The high antibody levels and Western blot profiles, over periods as long as 9 years in these chimpanzees, suggest continuous stimulation of the immune system by HIV antigen although virus was detected only sporadically in the peripheral blood. No illness suggestive of immunodeficiency was seen.

Lack of JC viral genomic sequences in multiple sclerosis brain tissue by polymerase chain reaction.

With DNA extracted from brain specimens from 19 multiple sclerosis, 5 progressive multifocal leukoencephalopathy, 1 Alzheimer's disease, and 8 nonneurological control subjects, polymerase chain reaction was performed using nested sets of primer pairs amplifying segments of the large T and VP1 antigen-encoding sequences of JC virus. Both sequences were detected in each of the 5 brain specimens of progressive multifocal leukoencephalopathy but in none of the 19 multiple sclerosis, 1 Alzheimer's disease, or the 8 control brain specimens.

SSPE in Slovakia: immunocytochemical study.

In a retrospective study of two patients from Slovakia with clinical, virological and histopathological diagnosis of subacute sclerosing panencephalitis (SSPE), measles virus antigen was detected by immunocytochemical labelling studies. The formalin fixed, paraffin-embedded thin brain sections labelled with anti-measles antibodies and avidin-biotin complex peroxidase were counterstained with haematoxylin. Only a single area of brain was examined in each patient: cerebellum and parietal lobe. Viral antigen positive reaction was identified within Purkinje cells and extending along dendritic processes in cerebellum, and also in oligodendrocytes of subparietal white matter.

Absence of measles, mumps, and rubella viral genomic sequences from multiple sclerosis brain tissue by polymerase chain reaction.

We tested for measles, mumps, and rubella viruses in multiple sclerosis by polymerase chain reaction (PCR). Using RNA extracted from 19 multiple sclerosis and 8 control brain specimens, nested PCR was performed after reverse transcription (RT) of the RNA to cDNA using primer pairs directed against two regions in the genomes of measles and mumps viruses and one region in the rubella virus genome. Despite enhanced sensitivity of nested RT PCR, measles, mumps, and rubella viral genomic sequences were not found in any brain specimen.

Failure to isolate human T cell lymphotropic virus type I and to detect variant-specific genomic sequences by polymerase chain reaction in Melanesians with indeterminate western immunoblot.

The controversy over the endemicity of human T cell lymphotropic virus type I (HTLV-I) in Melanesia has been settled recently by the isolation of genetically distinct, highly divergent sequence variants of HTLV-I from unrelated inhabitants of Papua New Guinea and the Solomon Islands. Still at issue, however, is the significance of the high frequency of indeterminate HTLV-I Western blots (defined as reactivity to only gag-encoded proteins) among Melanesians. To investigate whether this indeterminate seroreactivity reflects specific reactivity to the Melanesian HTLV-I variants, 27 seroindeterminate Melanesians from Papua New Guinea and the Solomon Islands were studied for evidence of HTLV-I infection. Although antibodies against Melanesian variant-specific env gene products and variant-specific env gene sequences were detected by Western blot analysis and polymerase chain reaction, respectively, in all 11 HTLV-I Western blot-positive Melanesians, none of the 27 seroindeterminate Melanesians had such variant-specific antibodies or HTLV-I proviral sequences. In addition, attempts to isolate HTLV-I from seroindeterminate individuals were unsuccessful. These data indicate that HTLV-I infection is not the cause of the indeterminate Western blot reactivity seen in Melanesia.

Creutzfeldt-Jakob disease cosegregates with the codon 178Asn PRNP mutation in families of European origin.

We recently discovered an amino acid-altering heterozygous mutation in codon 178 of the PRNP amyloid precursor gene in patients with familial Creutzfeldt-Jakob disease. This mutation is now shown to be associated with the occurrence of disease in 7 unrelated families of Western European origin, among which a total of 65 members are known to have died from Creutzfeldt-Jakob disease. The mutation was detected in each of 17 tested patients, including at least 1 affected member of each family, and in 16 of 36 of their first-degree relatives, but not in affected families with other mutations, patients with the nonfamilial form of the disease, or 83 healthy control individuals. Linkage analysis in two informative families yielded a lod score of 5.30, which, because no recombinants were found, strongly suggests that codon 178Asn is the actual disease mutation.

Atypical Creutzfeldt-Jakob disease in an American family with an insert mutation in the PRNP amyloid precursor gene.

An American family of English origin with an unusually early onset and long-duration form of Creutzfeldt-Jakob disease (CJD) had a heterozygous insert mutation in the region of repeating octapeptide coding sequences between codons 51 and 91 of the PRNP gene on chromosome 20. Affected members were 23 to 35 years old at the onset of illnesses that lasted from 4 to 13 years, yet experimental transmission of disease from the proband (11-year duration) produced a typically brief incubation period and duration of illness in each of three inoculated primates. Also, the PrP amyloid protein that accumulates in CJD brain was only barely detectable in extracted brain tissue from one case with massive spongiform change and was undetectable in another case with no spongiform change, perhaps because of epitope shielding by a configurational change in the protein induced by the mutation. Analysis of this and other families with similar inserts suggests that such mutations in the PRNP gene not only predispose to CJD, but also modify its phenotypic expression.