Electromagnetic scattering and radiation from microstrip patch antennas and spirals residing in a cavity

A new hybrid method is presented for the analysis of the scattering and radiation by conformal antennas and arrays comprised of circular or rectangular elements. In addition, calculations for cavity-backed spiral antennas are given. The method employs a finite element formulation within the cavity and the boundary integral (exact boundary condition) for terminating the mesh. By virtue of the finite element discretization, the method has no restrictions on the geometry and composition of the cavity or its termination. Furthermore, because of the convolutional nature of the boundary integral and the inherent sparseness of the finite element matrix, the storage requirement is kept very low at O(n). These unique features of the method have already been exploited in other scattering applications and have permitted the analysis of large-size structures with remarkable efficiency. In this report, we describe the method's formulation and implementation for circular and rectangular patch antennas in different superstrate and substrate configurations which may also include the presence of lumped loads and resistive sheets/cards. Also, various modelling approaches are investigated and implemented for characterizing a variety of feed structures to permit the computation of the input impedance and radiation pattern. Many computational examples for rectangular and circular patch configurations are presented which demonstrate the method's versatility, modeling capability and accuracy

Scattering of Pruppacher-Pitter raindrops at 30 GHz

Optimum design of modern ground-satellite communication systems requires the knowledge of rain-induced differential attenuation, differential phase shift, and cross polarization factors. Different available analytical techniques for raindrop scattering problems were assessed. These include: (1) geometrical theory of diffraction; (2) method of moment; (3) perturbation method; (4) point matching methods; (5) extended boundary condition method; and (6) global-local finite element method. The advantages and disadvantages of each are listed. The extended boundary condition method, which was determined to yield the most scattering results, is summarized. The scattered fields for Pruppacher-Pitter raindrops with sizes ranging from 0.5 mm to 3.5 mm at 20 C and at 30 GHz for several incidence angles are tabulated

Cosmic Evolution of Black Holes and Spheroids. II: Scaling Relations at z=0.36

We combine Hubble Space Telescope images of a sample of 20 Seyfert galaxies at z=0.36 with spectroscopic information from the Keck Telescope to determine the black hole mass - spheroid luminosity relation (M-L), the Fundamental Plane (FP) of the host galaxies and the M-sigma relation. Assuming pure luminosity evolution, we find that the host spheroids had smaller luminosity and stellar velocity dispersion than today for a fixed M. The offsets correspond to Delta log L_B,0=0.40+-0.11+-0.15 (Delta log M = 0.51+-0.14+-0.19) and Delta log sigma = 0.13+-0.03+-0.05 (Delta log M = 0.54+-0.12+-0.21), respectively for the M-L and M-sigma relation. A detailed analysis of known systematic errors and selection effects shows that they cannot account for the observed offset. The data are inconsistent with pure luminosity evolution and the existence of universal and tight scaling relations. To obey the three local scaling relations by z=0 the distant spheroids have to grow their stellar mass by approximately 60% (\Delta log M_sph=0.20+-0.14) in the next 4 billion years. The measured evolution can be expressed as M/ M_sph ~ (1+z)^{1.5+-1.0}. Based on the disturbed morphologies of a fraction of the sample (6/20) we suggest collisional mergers with disk-dominated systems as evolutionary mechanism.Comment: 17 pages, 10 figures; accepted for publication in the Astrophysical Journa

Ballistic spin field-effect transistors: Multichannel effects

We study a ballistic spin field-effect transistor (SFET) with special attention to the issue of multi-channel effects. The conductance modulation of the SFET as a function of the Rashba spin-orbit coupling strength is numerically examined for the number of channels ranging from a few to close to 100. Even with the ideal spin injector and collector, the conductance modulation ratio, defined as the ratio between the maximum and minimum conductances, decays rapidly and approaches one with the increase of the channel number. It turns out that the decay is considerably faster when the Rashba spin-orbit coupling is larger. Effects of the electronic coherence are also examined in the multi-channel regime and it is found that the coherent Fabry-Perot-like interference in the multi-channel regime gives rise to a nested peak structure. For a nonideal spin injector/collector structure, which consists of a conventional metallic ferromagnet-thin insulator-2DEG heterostructure, the Rashba-coupling-induced conductance modulation is strongly affected by large resonance peaks that arise from the electron confinement effect of the insulators. Finally scattering effects are briefly addressed and it is found that in the weakly diffusive regime, the positions of the resonance peaks fluctuate, making the conductance modulation signal sample-dependent.Comment: 18 pages, 15 figure

Performance of a family of omni and steered antennas for mobile satellite applications

The design and performance of a family of vehicle antennas developed at JPL in support of an emerging US Mobile Satellite Service (MSS) system are described. Test results of the antennas are presented. Trends for future development are addressed. Recommendations on design approaches for vehicle antennas of the first generation MSS are discussed

Dynamics of Helping Behavior and Networks in a Small World

To investigate an effect of social interaction on the bystanders' intervention in emergency situations a rescue model was introduced which includes the effects of the victim's acquaintance with bystanders and those among bystanders from a network perspective. This model reproduces the experimental result that the helping rate (success rate in our model) tends to decrease although the number of bystanders $k$ increases. And the interaction among homogeneous bystanders results in the emergence of hubs in a helping network. For more realistic consideration it is assumed that the agents are located on a one-dimensional lattice (ring), then the randomness $p \in [0,1]$ is introduced: the $kp$ random bystanders are randomly chosen from a whole population and the $k-kp$ near bystanders are chosen in the nearest order to the victim. We find that there appears another peak of the network density in the vicinity of $k=9$ and $p=0.3$ due to the cooperative and competitive interaction between the near and random bystanders.Comment: 13 pages, 8 figure

Humoral and cellular immunopathology of hepatic and cardiac hamster-into-rat xenograft rejection: Marked stimulation of IgM^++bright/IgD^+dull splenic B cells

Normal Lewis rat serum contains antibodies (IgM > IgG) that bind to hamster leukocytes and endothelial cells. Transplantation of either the heart or liver from hamster rat results in release of hamster hematolymphoid cells from the graft, which lodge in the recipient spleen (cell migration), where recipient T- and B-cell populations initiate DNA synthesis within one day. There is marked stimulation of splenic IgM++(bright)/IgD+(dull) B cells in the marginal zone and red pulp, which account for 48% of the total splenic blast cell population by 4 days after liver transplantation. CD4+ predominant T-cell proliferation in the splenic periarterial lymphatic sheath and paracortex of peripheral lymph nodes occurs almost simultaneously. The effector phase of rejection in cardiac recipients is dominated by complement-fixing IgM antibodies, which increase daily and result in graft destruction in 3 to 4 days, even in animals treated with FK506. In liver recipients, combined antibody and cellular rejection, associated with graft infiltration by OX8+ natural killer, and fewer W3/25+ (CD4) lymphocytes, are responsible for graft failure in untreated recipients at 6 to 7 days. FK506 inhibits the T-cell response in liver recipients and significantly prolongs graft survival, but does not prevent the rise or deposition of IgM antibodies in the graft. However, a single injection of cyclophosphamide 10 days before transplantation effectively depletes the splenic IgM++(bright)/IgD+(dull) cells and in combination with FK506, results in 100% survival of both cardiac and hepatic xenografts for more than 60 days. Although extrapolation of morphological findings to functional significance is fraught with potential problems, we propose the following mechanisms of xenograft rejection. The reaction initially appears to involve primitive host defense mechanisms, including an IgM-producing subpopulation of splenic B cells and natural killer cells. Based on the reaction and distribution of OX8+ and W3/25+ cells, antibody dependent cell cytotoxicity and delayed-type hypersensitivity responses seem worthy of further investigation as possible effector mechanisms. Effective control of xenograft rejection is likely to require a dual pharmaceutical approach, one to contain T-cell immunity and another to blunt the primitive B-cell response

Effects of combined administration of FK 506 and the purine biosynthesis inhibitors mizoribine or mycophenolic acid on lymphocyte DNA synthesis and T cell activation molecule expression in human mixed lymphocyte cultures

Our objective was to obtain new information on the in vitro antilymphocytic action of the cytokine synthesis inhibitor FK 506 and the purine biosynthesis inhibitors mycophenolic acid (MPA; the active moiety of RS61443) and mizoribine (MZB) when used alone or in combination. When added at the initiation of six-day human mixed lymphocyte cultures (MLC), FK 506, MPA or MZB exhibited dose-dependent inhibition of T-lymphocyte DNA synthesis. FK 506, however, was 100-fold more potent than MPA, and 10000-fold more potent than MZB. Combination of FK 506 with either MPA or MZB, each at suboptional concentrations, produced no more than additive inhibitory effects on 3H thymidine incorporation. Two-colour flow cytometric analysis of lymphocytes revealed that none of the drugs affected cell surface activation molecule expression (CD25 = IL-2R 55 kD α-chain, HLA-DR or CD71 = transferrin receptor [TR]) on allostimulated CD4+ or CD8+ cells harvested at three days of culture. By day six, however, all three agents, at levels which markedly inhibited proliferation, suppressed the expression of activation markers on both CD4+ and CD8+ cells. Also at day six, inhibition of activation molecule expression on CD4+ cells was achieved with the combination of FK 506 and either MPA or MZB at concentrations which, on their own, were ineffective. These data provide new, additional information on the in vitro antilymphocytic action of FK 506, MPA and MZB when used alone and in combination. © 1993