Error Rate Analysis for Coded Multicarrier Systems Over Quasi-Static Fading Channels

Several standards such as IEEE 802.11a/g, IEEE 802.16, and the European Computer Manufacturers Association (ECMA) multiband orthogonal frequency division multiplexing (MB-OFDM) for high data-rate ultra-wideband employ bit-interleaved convolutionally coded multicarrier modulation over quasi-static fading channels. Motivated by the lack of appropriate error rate analysis techniques for this popular type of system and channel model, we present two novel analytical methods for bit error rate (BER) estimation of coded multicarrier systems operating over frequency-selective quasi-static channels with nonideal interleaving. In the first method, the approximate performance of the system is calculated for each realization of the channel, which is suitable for obtaining the outage BER performance (a common performance measure for, e.g., MB-OFDM systems). The second method assumes Rayleigh distributed frequency-domain subcarrier channel gains and knowledge of their correlation matrix, and can be used to directly obtain the average BER performance. Both methods are applicable to convolutionally coded interleaved multicarrier systems employing quadrature amplitude modulation, and are also able to account for narrowband interference (modeled as a sum of tone interferers). To illustrate the application of the proposed analysis, both methods are used to study the performance of a tone-interference-impaired MB-OFDM system.     

Cultivating Social Resources on Social Network Sites: Facebook Relationship Maintenance Behaviors and Their Role in Social Capital Processes

This study explores the relationship between perceived bridging social capital and specific Facebook‐enabled communication behaviors using survey data from a sample of U.S. adults (N=614). We explore the role of a specific set of Facebook behaviors that support relationship maintenance and assess the extent to which demographic variables, time on site, total and “actual” Facebook Friends, and this new measure (Facebook Relationship Maintenance Behaviors) predict bridging social capital. Drawing upon scholarship on social capital and relationship maintenance, we discuss the role of social grooming and attention‐signaling activities in shaping perceived access to resources in one's network as measured by bridging social capital.     

Gamma interferon production by cytotoxic T lymphocytes is required for resolution of Chlamydia trachomatis infection

In this study, we used mice in which the gene for gamma interferon (IFN-gamma) has been disrupted (IFN-gamma-/- mice) to study the role of this cytokine in the resolution of Chlamydia trachomatis infection. We show that IFN-gamma-/- mice are impaired in the ability to clear infection with C. trachomatis compared to IFN-gamma+/+ control mice. Activated CD8(+) cytotoxic T lymphocytes (CTL) secrete IFN-gamma in response to intracellular infection, and we have shown previously that a Chlamydia-specific CTL line can reduce C. trachomatis infection when adoptively transferred into infected mice. In the present study, we found that when these IFN-gamma+/+ CTL lines are transferred into Chlamydia-infected IFN-gamma-/- mice, the transferred CTL cannot overcome the immune defect seen in the IFN-gamma-/- mice. We also show that Chlamydia-specific CTL can be cultured from IFN-gamma-deficient mice infected with C. trachomatis; however, the adoptive transfer of IFN-gamma-/- CTL into infected IFN-gamma+/+ mice does not reduce the level of infection. These results suggest that IFN-gamma production by CTL is not sufficient to overcome the defect that IFN-gamma-/- mice have in the resolution of Chlamydia infection, yet IFN-gamma production by CTL is required for the protective effect seen upon adoptive transfer of CTL into IFN-gamma+/+ mice.