CLTC: a cluster-based topology control for ad hoc networks

The topology of an ad hoc network has a significant impact on its performance in that a dense topology may induce high interference and low capacity, while a sparse topology is vulnerable to link failure and network partitioning. Topology control aims to maintain a topology that optimizes network performance while minimizing energy consumption. Existing topology control algorithms utilize either a purely centralized or a purely distributed approach. A centralized approach, although able to achieve strong connectivity (k-connectivity for k /spl ges/ 2), suffers from scalability problems. In contrast, a distributed approach, although scalable, lacks strong connectivity guarantees. We propose a hybrid topology control framework, cluster-based topology control (CLTC) that achieves both scalability and strong connectivity. By varying the algorithms utilized in each of the three phases of the framework, a variety of optimization objectives and topological properties can be achieved. In this paper, we present the CLTC framework; describe topology control algorithms based on CLTC and prove that k-connectivity is achieved using those algorithms; analyze the message complexity of an implementation of CLTC, namely, CLTC-A, and present simulation studies that evaluate the effectiveness of CLTC-A for a range of networks.     

Thoughts of agoraphobic people during scary tasks.

The authors examined the occurrence of theoretically derived patterns of thinking in 74 agoraphobic participants as they drove alone or tolerated an enclosed place. During the increasingly scary tasks in a behavioral test hierarchy, participants responded to a periodic beep by stating aloud what they were thinking at that moment, yielding more than 1,800 tape-recorded statements. Content analyses revealed that participants were mainly preoccupied with their current anxiety (expressed in 29% of the statements) and with their self-efficacy (15%). Despite participants' mounting feelings of anxiety, fewer than 1% of their statements expressed a thought of danger or an anticipation of future anxiety or panic. The rarity of danger thoughts poses an explanatory challenge for all cognitive theories of phobia and especially for the perceived danger theory of A. T. Beck (1976) and A. T. Beck, G. Emery, and R L. Greenberg (1985). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Identification of new components from anal glands ofTapinoma simrothi pheonicium

In addition to 2-methyl-4-heptanone, 6-methyl-5-hepten-2-one, and iridodials, the anal gland exudate of the dolichoderine ant,Tapinoma simrothi, contains 4-heptanone and 4-hydroxy-4-methyl-2-pentanone. The secretion functions as an alarm pheromone.     

The sequence of precipitation in the Al-Mg-Si-Cu alloy AA6111

The preciptation behavior of the aluminum alloy AA6111 in the advanced stages of aging has been studied using differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and high-resolution TEM (HRTEM). The results have demonstrated the formation of various precipitate types and morphologies of quaternaryQ phase andβ (Mg₂Si) families at the peak-aged condition and during overaging at different temperatures. The work has clarified the sequence ofQ phase formation and showed evidence for a new morphology of this phase. The sequence of precipitation in AA6111 is elaborated in light of the new findings.     

Recombinant human erythrocyte cytochrome b5

The gene encoding the human erythrocyte form of cytochrome b5 (97 residues in length) has been prepared by mutagenesis of an expression vector encoding lipase-solubilized bovine liver microsomal cytochrome b5 (93 residues in length) (Funk et al., 1990). Efficient expression of this gene in Escherichia coli has provided the first opportunity to obtain this protein in quantities sufficient for physical and functional characterization. Comparison of the erythrocytic cytochrome with the trypsin-solubilized bovine liver cytochrome b5 by potentiometric titration indicates that the principal electrostatic difference between the two proteins results from two additional His residues present in the human erythrocytic protein. The midpoint reduction potential of this protein determined by direct electrochemistry is -9 +/- 2 mV vs SHE at pH 7.0 (mu = 0.10 M, 25.0 degrees C), and this value varies with pH in a fashion that is consistent with the presence of a single ionizable group that changes pKa from 6.0 +/- 0.1 in the ferricytochrome to 6.3 +/- 0.1 in the ferrocytochrome with delta H degrees = -3.2 +/- 0.1 kcal/mol and delta S degrees = -11.5 +/- 0.3 eu (pH 7.0, mu = 0.10). The 1D 1H NMR spectrum of the erythrocytic ferricytochrome indicates that 90% of the protein binds heme in the "major" orientation and 10% of the protein binds heme in the "minor" orientation (pH 7.0, 25 degrees C) with delta H degrees = -2.9 +/- 0.3 kcal/mol and delta S degrees = -5.4 +/- 0.9 eu for this equilibrium.     

Scoring single-nucleotide polymorphisms at the single-molecule level by counting individual DNA cleavage events on surfaces

Single-nucleotide polymorphisms (SNPs) are the most frequent type of human genetic variation. Recent work has shown that it is possible to directly analyze SNPs in unamplified human genomic DNA samples using the surface-invasive cleavage reaction followed by rolling circle amplification (RCA) of the cleavage products. The ability of RCA to produce single-stranded DNA tens of thousands of nucleotides in length from a single cleaved DNA molecule on the surface suggested the possibility of detecting individual cleavage events on the surface. The feasibility of this approach to SNP scoring is shown here. Individual cleavage events on the surface are detected using fluorescence microscopy to visualize the single-stranded DNA product of the RCA reaction labeled with the fluorescent dye SYBR Green I. The surface density of fluorescent features observed is dependent upon the concentration of target DNA. Future reductions of the sample volume and optimization of the reaction conditions offer the potential of being able to perform such analyses on as little as a single copy of genomic DNA target.     

Platinum sulfated zirconia catalysts. Fate of chlorine during activation

The gases evolved during activation of a sulfated zirconia prepared by impregnation with chloroplatinic acid have been followed using mass spectrometry and infrared spectrometry. When the sample is heated in either helium or in air, the halogen is lost from the catalyst as HCl and Cl2. Heating the sample in hydrogen results in the loss of the halogen as HCl, and only traces as Cl2. The loss of halogen occurs over a wide temperature range (200-900°C). The data are consistent with the chloroplatinic acid being converted by loss of halide with the formation of Pt⁰. This revised version was published online in July 2006 with corrections to the Cover Date.