4,269 research outputs found
Variable Rate QAM for Mobile Radio
No full textQuadrature amplitude modulation (QAM) schemes which vary the number of modulation levels in accordance with the mobile radio fading channel variations are investigated. Important parameters considered are the fading rate and the block size used. We describe how the adaptive QAM modems can he employed and consider their use in a DECT-like TDD packet structure. System performance in the presence of cochannel interference is also considered. Simulations show that the variable rate system has about 5 dB improvement In channel SNR over a fixed 16-level QAM system for BER's between 10-2 and 10-5 and channel SNR's between 25 and 40 dB
Effects of PRMA on Objective Speech Quality
No full textWhen transmitting 32kbit/s adaptive differential pulse(ADPCM) speech using Reed-Solomon error correction coding and 16 level quadrature amplitude modulation(16-QAM), our 20 slot packet reservation multiple access(PRMA) assisted cordless telecommunications(CT) scheme supported 36-38 speech users with negligible objective and subjective speech degradation. The average number of users per slot was nearly doubled due to deploying PRMA and toll quality speech was transmitted in a user bandwidth ~11.6kHz. For a channel signal-to-noise(SNR) in excess of 25dB, a Rayleigh fading channel and mobile speeds above 2mph the speech segmental SNR degradation was less than 0.3dB
Cfp1 is required for gene expression dependent H3K4me3 and H3K9 acetylation in embryonic stem cells
No full textBackgroundTrimethylation of histone H3 lysine 4 (H3K4me3) accumulates at promoters in a gene activity dependent manner. The Set1 complex is responsible for most H3K4me3 in somatic cells and contains the conserved subunit Cfp1, which is implicated in targeting the Set1 complex to CpG islands in mammals. In mouse embryonic stem cells, Cfp1 is necessary for H3K4me3 accumulation at constitutively active gene promoters, but is not required to maintain steady-state transcription of the associated gene.ResultsHere we show that Cfp1 is instrumental for targeting H3K4me3 to promoters upon rapid transcriptional induction in response to external stimuli. Surprisingly, H3K4me3 accumulation is not required to ensure appropriate transcriptional output but rather plays gene specific roles. We also show that Cfp1-dependent H3K4me3 deposition contributes to H3K9 acetylation genome wide, suggesting that Cfp1 dependent H3K4me3 regulates overall H3K9 acetylation dynamics and is necessary for histone acetyl transferase recruitment. Finally, we observe increased antisense transcription at the start and end of genes that require Cfp1 for accurate deposition of H3K4me3 and H3K9ac.ConclusionsOur results assign a key role for Cfp1 in establishing a complex active promoter chromatin state and shed light on how chromatin signaling pathways provide context-dependent transcriptional outcomes.</p
Heterogeneous and tissue-specific regulation of effector T cell responses by IFN-gamma during Plasmodium berghei ANKA infection.
No full textIFN-γ and T cells are both required for the development of experimental cerebral malaria during Plasmodium berghei ANKA infection. Surprisingly, however, the role of IFN-γ in shaping the effector CD4(+) and CD8(+) T cell response during this infection has not been examined in detail. To address this, we have compared the effector T cell responses in wild-type and IFN-γ(-/-) mice during P. berghei ANKA infection. The expansion of splenic CD4(+) and CD8(+) T cells during P. berghei ANKA infection was unaffected by the absence of IFN-γ, but the contraction phase of the T cell response was significantly attenuated. Splenic T cell activation and effector function were essentially normal in IFN-γ(-/-) mice; however, the migration to, and accumulation of, effector CD4(+) and CD8(+) T cells in the lung, liver, and brain was altered in IFN-γ(-/-) mice. Interestingly, activation and accumulation of T cells in various nonlymphoid organs was differently affected by lack of IFN-γ, suggesting that IFN-γ influences T cell effector function to varying levels in different anatomical locations. Importantly, control of splenic T cell numbers during P. berghei ANKA infection depended on active IFN-γ-dependent environmental signals--leading to T cell apoptosis--rather than upon intrinsic alterations in T cell programming. To our knowledge, this is the first study to fully investigate the role of IFN-γ in modulating T cell function during P. berghei ANKA infection and reveals that IFN-γ is required for efficient contraction of the pool of activated T cells
Comparative Study Of The Influence Of Natural Convection On Directional Solidification Of Al-3.5 Wt% Ni And Al-7 Wt% Si Alloys
No full textWe present numerical simulations of thermosolutal convection for directional solidification of Al-3.5 wt% Ni and Al-7 wt% Si. Numerical results predict that fragmentation of dendrite arms resulting from dissolution could be favored in Al-7 wt% Si, but not in Al-3.5 wt% Ni. Corresponding experiments are in qualitative agreement with the numerical predictions. Distinguishing the two fragmentation mechanisms, namely dissolution and remelting, is critical during experiments on earth, when fluid flow is dominant. (C) 2007 COSPAR. Published by Elsevier Ltd. All rights reserved
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