Microwave diode amplifiers with low intermodulation distortion

Distortions can be greatly reduced in narrow-band applications by using the second harmonic. The ac behavior of simplified diode amplifier has negative resistance depending on slope of equivalent I-V curve

Image retrieval by hypertext links

This paper presents a model for retrieval of images from a large World Wide Web based collection. Rather than considering complex visual recognition algorithms, the model presented is based on combining evidence of the text content and hypertext structure of the Web. The paper shows that certain types of query are amply served by this form of representation. It also presents a novel means of gathering relevance judgements

Distribution of the cell substratum attachment (CSAT) antigen on myogenic and fibroblastic cells in culture.

Previous studies (Neff et al., 1982, J. Cell. Biol. 95:654-666; Decker et al., 1984. J. Cell. Biol. 99:1388-1404) have described a monoclonal antibody (CSAT Mab) directed against a complex of three integral membrane glycoproteins of 120,000-160,000 mol wt (CSAT antigen [ag]) involved in the cell matrix adhesion of myoblasts and fibroblasts. In localization studies on fibroblasts presented here, CSAT ag has a discrete, well-organized distribution pattern. It co-aligns with portions of stress fibers and is enriched at the periphery of, but not directly beneath vinculin-rich focal contacts. In this last location, it co-distributes with fibronectin, consistent with the suggestion that the CSAT ag participates in the mechanism by which fibroblasts attach to fibronectin. In prefusion myoblasts, which are rapidly detached by CSAT Mab, CSAT ag is distributed diffusely as are vinculin, laminin, and fibronectin. After fusion, myotubes become more difficult to detach with CSAT Mab. The CSAT ag and vinculin are organized in a much more discrete pattern on the myotube surface, becoming enriched at microfilament bundle termini and in lateral lamellae which appear to attach myotubes to the substratum. These results suggest that the organization of CSAT ag-adhesive complexes on the surface of myogenic cells can affect the stability of their adhesive contacts. We conclude from the sum of the studies presented that, in both myogenic and fibroblastic cells, the CSAT ag is localized in sites expected of a surface membrane mediator of cell adhesion to extracelluon of CSAT ag-adhesive complexes on the surface of myogenic cells can affect the stability of their adhesive contacts. We conclude from the sum of the studies presented that, in both myogenic and fibroblastic cells, the CSAT ag is localized in sites expected of a surface membrane mediator of cell adhesion to extracellular matrix. The results from studies that use fibroblasts in particular suggest the involvement of CSAT ag in the adhesion of these cells to fibronectin

On the interaction of ultrasound with cracks: Applications to fatigue crack growth

Partial contact of two rough fatigue crack surfaces leads to transmission and diffraction of an acoustic signal at those contacts. Recent experimental and theoretical efforts to understand and quantify such contact in greater detail are discussed. The objective is to develop an understanding of the closure phenomenon and its application to the interpretation of fatigue data, in particular the R-ratio, spike overload/underload and threshold effects on crack propagation

Doing Fractions: An Analysis of Partisanship in Post-Socialist Russia

Since its extrication from state socialism, Russia is notable for the ways in which coercive and, at times, violent displays of partisanship have divided its state. Drawing on evidence from ethnographic fieldwork and membership lists of civic organizations, the paper analyzes the composition and configuration of political factions in an in-depth case study of a Russian urban area, 1994-1999. The analysis demonstrates partisan antagonisms in the city emerged from a process of polarization that eliminated identification across factions. During the competition for state office, political groups became embroiled in a cycle of conflict setting the stage for partisans to purge themselves of coalition-builders

Characterization of Knots and Links Arising From Site-specific Recombination on Twist Knots

We develop a model characterizing all possible knots and links arising from recombination starting with a twist knot substrate, extending previous work of Buck and Flapan. We show that all knot or link products fall into three well-understood families of knots and links, and prove that given a positive integer $n$, the number of product knots and links with minimal crossing number equal to $n$ grows proportionally to $n^5$. In the (common) case of twist knot substrates whose products have minimal crossing number one more than the substrate, we prove that the types of products are tightly prescribed. Finally, we give two simple examples to illustrate how this model can help determine previously uncharacterized experimental data.Comment: 32 pages, 7 tables, 27 figures, revised: figures re-arranged, and minor corrections. To appear in Journal of Physics

CD28 interaction with B7 costimulates primary allogeneic proliferative responses and cytotoxicity mediated by small, resting T lymphocytes.

Engagement of the CD3/T cell antigen receptor complex on small, resting T cells is insufficient to trigger cell-mediated cytotoxicity or to induce a proliferative response. In the present study, we have used genetic transfection to demonstrate that interaction of the B7-BB1 B cell activation antigen with the CD28 T cell differentiation antigen costimulates cell-mediated cytotoxicity and proliferation initiated by either anti-CD2 or anti-CD3 monoclonal antibody (mAb). Moreover, a B7-negative Burkitt's lymphoma cell line that fails to stimulate an allogeneic mixed lymphocyte response is rendered a potent stimulator after transfection with B7. The mixed leukocyte reaction proliferative response against the B7 transfectant is inhibited by either anti-CD28 or B7 mAb. We also demonstrate that freshly isolated small, resting human T cells can mediate anti-CD3 or anti-CD2 mAb-redirected cytotoxicity against a murine Fc receptor-bearing mastocytoma transfected with human B7. These preexisting cytotoxic T lymphocytes in peripheral blood are present in both the CD4 and CD8 subsets, but are preferentially within the CD45RO+ "memory" population. While small, resting T cells apparently require costimulation by CD28/B7 interactions, this requirement is lost after T cell activation. Anti-CD3 initiates a cytotoxic response mediated by in vitro cultured T cell clones in the absence of B7 ligand. The existence of functional cytolytic T cells in the small, resting T cell population may be advantageous in facilitating rapid responses to immune challenge