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Fabrication of fully dense and highly conductive copper alloy parts via laser-based additive manufacturing (L-AM) is challenging due to the high optical reflectivity of copper at λ = 1060 – 1080 nm and high thermal conductivity. To overcome this, the use of optically absorptive surface-modified copper powders is being evaluated in the laser powder bed fusion (LPBF) process. Although the surface-modified powders exhibit high optical absorption at room temperature, not all of them allow the fabrication of fully dense parts at a laser power below 500 W. Accordingly, this article proposes the use of optically absorptive carburized CuCr1 powder for the consistent fabrication of copper parts. Moreover, a densification mechanism of parts is discussed to explain the distinct LPBF processing behavior of different surface-modified powders, such as carburized CuCr1 and carbon mixed CuCr1 powders, albeit having similar room temperature optical absorption. This investigation clearly outlines the advantage of a firmly bonded modified layer present on the surface of the carburized CuCr1 powder over a loosely attached carbon nanoparticle layer present in the carbon-mixed CuCr1 powder. Apart from the successful fabrication of CuCr1 parts, fabricated parts are subjected to two different post-heat treatments, and it is shown that the final properties can be customized by applying tailored post-heat treatments.
Mice infected with herpes simplex virus (HSV) were treated (separately) with the nucleoside analogues acyclovir or bromovinyldeoxyuridine by incorporating the drugs in the drinking water. This method of treatment was found to be effective for both drugs and compared favourably with intraperitoneal injection. Prompt treatment with either compound could prevent the establishment of latent infections but latent infections once established were intractable using prolonged courses of oral administration.
The antiviral activity and interferon-in- ducing ability of single-, double-, and triple-stranded poly- nucleotides, modified at pyrimidine C-5 or purine N-7, were evaluated in primary rabbit kidney cells challenged with vesicular stomatitis virus.(l) There is a parallel in- crease in antiviral activity and the temperature at which double-stranded polynucleotides rearrange to inactive triple-stranded complexes. (2) When the purine N-7 of (A)n is replaced by CH, all resulting double-stranded complexes fail to provide antiviral protection or to induce interferon, even though such complexes meet all requirements pre- viously recognized for interferon induction. (3) Competi- tion experiments between inactive and active polynucleo- tides indicate that single-stranded polynucleotides ap- parently do not bind to the cellular receptor sites for inter- feron induction, whereas triple-stranded complexes and inactive double-stranded complexes bind to such receptor sites but, probably for conformational reasons, fail to trig- ger the necessary message for interferon induction. An understanding of the structural parameters governing the induction of interferon by synthetic polynucleotides may be a prerequisite for the design of a clinically useful interferon inducer. The examination of a number of modified poly- nucleotides has led to the delineation of at least three charac- hypothesis; furthermore, the temperature at which (A)n, (U)0 rearranges to (A)n'2(U)n is 10--12 higher than the tempera- ture at which most antiviral assays are performed (Table 1). This would require the ad hoc assumption that the cellular environment produces conditions especially favorable for the rearrangement. We have explored two separate approaches in an attempt to define more clearly the importance of such strandwise (2 -* 3) rearrangements in the interferon system. I. Determination of the Antiviral Activity of M'odified (A)n' (U)n Systems That Differ in T2,(2-3), the Temperature at Which the Double-to-Triple-Strand Rearrangement Occurs. In addition to (A), (U),, we examined the (A),n (rT), and (A)n' (br5U), complexes, since the transitions occurring within these systems are well understood. Introduction of such sub- stituents as bromine or methyl at C-5 of the pyrimidine strand of (I),' (C)0 does not lead to a significant change in antiviral activity (11, 16). II. Evaluation of the Antiviral Activity of a Modified (A)n' (U)n System That Cannot Form a Triple-Stranded Complex under Any Conditions. The (c7A)n. (U)n system fits this de- scription, since it possesses the same hydrogen bonding scheme as (A). (U)n, but, due to the absence of the purine N-7, cannot form a complex equivalent to (A)n 2(U)0 by means of Hoogsteen base pairing. Since the duplex (c7A),. (U)n melts out to single-stranded structures at about 30° in 0.1 M salt (17), we prepared the complexes of (c7A)n with (rT)n and (br5U)n, since such substitutions lead to substantial elevations of Tm in the (A)n (U)n and (I)n ' (C)0 systems (18).
A system is described for assaying mouse interferon without using a viral "challenge" agent. Interferon-treated L cells were destroyed by exposure to polyriboinosinic.polyribocytidylic acid [poly(I).poly(C)], and the amount of destruction was dependent on both the concentration of interferon to which the cells were exposed and the amount of poly(I).poly(C) used as the "challenge" material. If the amount of poly(I).poly(C) was constant, the concentration of interferon could be determined by quantitating cell destruction 6 hr after addition of the double-stranded ribonucleic acid. In addition to eliminating the necessity for employing infectious virus for interferon assays, this system has the advantages of being quicker, easier, and more sensitive than other interferon assays. The sensitivity of the assay is related directly to the amount of poly(I).poly(C) applied to the cells, with each fivefold increase of poly(I).poly(C) giving about a fivefold increase of sensitivity.
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SummarySeveral interferon inducers including bacteria, viruses, and synthetic polycarboxylates demonstrated an antiviral effect against vaccinia virus challenge in mice. Various extracts of living materials were equally effective in stimulating interferon production. They provided rather transient protection in contrast with the prolonged protection following injection of either living microorganisms or plastics. The antiviral activity offered by injection of these different interferon inducers 1 day before virus challenge can be explained by interferon production. The protection observed at later times might or might not be mediated by interferon, but seems to depend on the continuous presence of the microorganisms or plastics in the host.The technical assistance of Mrs. L. Reghers-Aelvoet is gratefully acknowledged.
