Renaturation of formyltetrahydrofolate synthetase from urea and guanidinium chloride solutions

Formyltetrahydrofolate synthetase from Clostridium cylindrosporum and Clostridium acidi-urici was denatured in 6 M urea and 4 M guanidinium chloride. Viscometric, fluorimetric and ultracentrifugal measurements were used to determine that the protein is completely unfolded under these conditions. The polypeptide chains refold upon dilution of the denaturant-protein solutions to give final concentrations of 0.5 M urea or 0.1 M guanidinium chloride. In the presence of NH4+, but not in its absence, the refolded proteins associate to produce the catalytically active tetramer. Refolding and reassociation were followed by measuring changes in protein fluorescence and by determination of sedimentation constants. Under most conditions 80% of the enzymic activity is recovered.     

Optimal discrete-time control system with cost for observation

The problem of how to select the total number and the spacings of the observations optimally when a constant cost is incurred for each observation taken is discussed. Approximate expressions for the criterion function with a fixed number of observations are obtained and are used to determine the optimal total number of observations. For a class of multidimensional systems with a dominant eigenvalue, the problem is shown to reduce to that for scalar systems. Detailed discussion is then carded out for scalar systems including some sensitivity study.     

Strained n-Channel Transistors With Silicon Source and Drain Regions and Embedded Silicon/Germanium as Strain-Transfer Structure

We report the demonstration of 55 nm gate length strained n-channel field-effect transistors (n-FETs) having an embedded Si_1-xGe_x structure that is beneath the Si channel region and which acts as a strain-transfer structure (STS). The Si_1-xGe_x STS has lattice interactions with both the silicon source and drain regions and with the overlying Si channel region. This effectively results in a transfer of lateral tensile strain to the Si channel region for electron mobility enhancement. The mechanism of strain transfer is explained. Significant drive current I_on enhancement of 18% at a fixed off-state leakage I_off of 100 nA/mum is achieved, which is attributed to the strain-induced mobility enhancement. Furthermore, continuous downsizing of transistors leads to higher I_on enhancement in the strained n-FETs, which is consistent with the increasing transconductance G_m improvement when the gate length is reduced.     

Advances and Challenges with Data Broadcasting in Wireless Mesh Networks

Wireless mesh networks have become a promising means to provide low-cost broadband access. Many WMN applications require broadcasting data (IPTV etc.) over the WMN. This article studies how efficient data broadcast, measured in terms of broadcast latency, can be realized by exploiting two features of WMNs: the use of multiple transmission rates at the link layer and the use of multiple radio interfaces on each node. We demonstrate that by exploiting these features, broadcast latency can be reduced severalfold compared to the current default practice in wireless LANs of using the lowest transmission rate for broadcast traffic. We also discuss two important insights we have gained from our investigation. First, we find that when multiple radio interfaces are used, a channel assignment algorithm designed for unicast traffic may often perform poorly for broadcast flows. Second, we find that the efficiency of a transmission rate for reducing broadcast latency can be reasonably predicted by the product of the transmission rate and its coverage area.