The Electrolytic “Sintering” of Nickel Powder

Adherent and coherent deposits of nickel sponge similar to sintered nickel may be made from sulphate, chloride, fluoborate or sulphamate nickel plating solutions containing nickel powder in suspension, providing the concentration of free acid is maintained sufficiently high to inhibit co-depesition of Ni(OH) In nitrate solution, cathodic reduction of nitrate and deposition of Ni(OH)₂ predominates.     

Domain flexibility in retroviral proteases: structural implications for drug resistant mutations

Rigid body rotation of five domains and movements within their interfacial joints provide a rational context for understanding why HIV protease mutations that arise in drug resistant strains are often spatially removed from the drug or substrate binding sites. Domain motions associated with substrate binding in the retroviral HIV-1 and SIV proteases are identified and characterized. These motions are in addition to closure of the flaps and result from rotations of approximately 6-7 degrees at primarily hydrophobic interfaces. A crystal structure of unliganded SIV protease (incorporating the point mutation Ser 4 His to stabilize the protease against autolysis) was determined to 2.0 A resolution in a new space group, P3221. The structure is in the most "open" conformation of any retroviral protease so far examined, with six residues of the flaps disordered. Comparison of this and unliganded HIV structures, with their respective liganded structures by difference distance matrixes identifies five domains of the protease dimer that move as rigid bodies against one another: one terminal domain encompassing the N- and C-terminal beta sheet of the dimer, two core domains containing the catalytic aspartic acids, and two flap domains. The two core domains rotate toward each other on substrate binding, reshaping the binding pocket. We therefore show that, for enzymes, mutations at interdomain interfaces that favor the unliganded form of the target active site will increase the off-rate of the inhibitor, allowing the substrate greater access for catalysis. This offers a mechanism of resistance to competitive inhibitors, especially when the forward enzymatic reaction rate exceeds the rate of substrate dissociation.     

Modulation of T cell and monocyte function in the spleen following infection of pigs with African swine fever virus

Infection of pigs with many strains of African Swine Fever Virus (ASFV) has been shown to cause a loss or marked decrease in the ability of splenocytes to respond to mitogens. These observations have been extended by cell fractionation and reconstitution experiments to show that the mitogen stimulated proliferative capacity of both the CD4+ and CD8+ T cells is affected. Similarly, monocytes which are directly infectable by virus, are functionally defective as antigen presenting cells when added to mitogen stimulated normal T cells. Interestingly, the same T cells which respond poorly in mitogenic assays can be activated by stimulation through the CD3 receptor. In contrast to the defective mitogenic response of T cells, B cell function, as assessed by stimulation through the CD40 ligand in vitro remains intact. There is no evidence for apoptosis in either the T cells or the B cells recovered from the spleens of ASFV infected animals 1-5 days following infection. Although the number of leucocytes which can be recovered from the infected spleen decreases rapidly with progression of the disease, the proportion of the different cell phenotypes remains constant. Thus decreased activity of lymphocytes in lymphoid tissue from ASFV infected animals appears to be directly attributable to infection of the monocytes.     

Transport protocols for Internet-compatible satellite networks

We address the question of how well end-to-end transport connections perform in a satellite environment composed of one or more satellites in geostationary orbit (GEO) or low-altitude Earth orbit (LEO), in which the connection may traverse a portion of the wired Internet. We first summarize the various ways in which latency and asymmetry can impair the performance of the Internet's transmission control protocol (TCP), and discuss extensions to standard TCP that alleviate some of these performance problems. Through analysis, simulation, and experiments, we quantify the performance of state-of-the-art TCP implementations in a satellite environment. A key part of the experimental method is the use of traffic models empirically derived from Internet traffic traces. We identify those TCP implementations that can be expected to perform reasonably well, and those that can suffer serious performance degradation. An important result is that, even with the best satellite-optimized TCP implementations, moderate levels of congestion in the wide-area Internet can seriously degrade performance for satellite connections. For scenarios in which TCP performance is poor, we investigate the potential improvement of using a satellite gateway, proxy, or Web cache to “split” transport connections in a manner transparent to end users. Finally, we describe a new transport protocol for use internally within a satellite network or as part of a split connection. This protocol, which we call the satellite transport protocol (STP), is optimized for challenging network impairments such as high latency, asymmetry, and high error rates. Among its chief benefits are up to an order of magnitude reduction in the bandwidth used in the reverse path, as compared to standard TCP, when conducting large file transfers. This is a particularly important attribute for the kind of asymmetric connectivity likely to dominate satellite-based Internet access     

Interfacial reactions of Sn-Ag-Cu solders modified by minor Zn alloying addition

The near-ternary eutectic Sn-Ag-Cu alloys have been identified as leading Pb-free solder candidates to replace Pb-bearing solders in microelectronic applications. However, recent investigations on the processing behavior and solder joints reliability assessment have revealed several potential reliability risk factors associated with the alloy system. The formation of large Ag₃Sn plates in Sn-Ag-Cu joints, especially when solidified in a relatively slow cooling rate, is one issue of concern. The implications of large Ag₃Sn plates on solder joint performance and several methods to control them have been discussed in previous studies. The minor Zn addition was found to be effective in reducing the amount of undercooling required for tin solidification and thereby to suppress the formation of large Ag₃Sn plates. The Zn addition also caused the changes in the bulk microstructure as well as the interfacial reaction. In this paper, an in-depth characterization of the interfacial reaction of Zn-added Sn-Ag-Cu solders on Cu and Au/Ni(P) surface finishes is reported. The effects of a Zn addition on modification of the interfacial IMCs and their growth kinetics are also discussed.     

High resolution negative tone molecular resist based on di-functional epoxide polymerization

There is an urgent demand for higher performance resists with superior resolution, sensitivity, and line edge roughness for both electron-beam and extreme ultraviolet lithography applications. Chemically amplified resists provide superior sensitivity compared to non-chemically amplified resists, but often suffer from resolution limitations and poor line edge roughness. A new class of negative tone chemically amplified molecular resists has been developed based on epoxide cross-linking that combines high sensitivity with low line edge roughness and excellent resolution. The most recent compound of this class (2-Ep) simultaneously demonstrates resolution of 25 nm half-pitch, sensitivity of 38 μC/cm², and line edge roughness (3σ) of 2.9 nm under 100 keV e-beam exposure.     

Optimizing Router Performance in TCP/IP Networks

This article reviews the steps necessary to configure and implement a complex router internetwork. This article will specifically concentrate on Cisco routers, and since they support Transmission Control Protocol/Internet Protocol (TCP/IP) natively, it will concentrate on a backbone network employing that protocol.