CROSS-LAYER SCHEDULING PROTOCOLS FOR MOBILE AD HOC NETWORKS USING ADAPTIVE DIRECT-SEQUENCE SPREAD-SPECTRUM MODULATION

We investigate strategies to improve the performance of transmission schedules for mobile ad hoc networks (MANETs) employing adaptive direct-sequence spread-spectrum (DSSS) modulation. Previously, scheduling protocols for MANETs have been designed under the assumption of an idealized, narrowband wireless channel. These protocols perform poorly when the channel model incorporates distance-based path loss and co-channel interference. Wideband communication systems, such as DSSS systems, are more robust in the presence of co-channel interference; however, DSSS also provides multiple-access capability that cannot be properly leveraged with a protocol designed for narrowband systems. We present a new transmission scheduling protocol that incorporates link characteristics, spreading factor adaptation, and packet capture capability into scheduling and routing decisions. This provides greater spatial reuse of the channel and better adaptability in mobile environments. Simulation results demonstrate the merits of this approach in terms of end-to-end packet throughput, delay, and completion rate for unicast traffic. We also discuss two variations of the protocol: one provides a method for enhancing the network topology through exchange of local information, and the other leverages multi-packet reception (MPR) capability to enhance the network topology. We show that each approach is useful in networks with sparse connectivity. We conclude by studying the capacity of the networks used in previous sections, providing insight on methods for realizing further performance gains

Sediment phosphorus flux in Beaver Lake in Northwest Arkansas

Internal phosphorus (P) loading may influence primary production in lakes, but the influence of sediment-derived P has not been well studied in Beaver Lake of Northwest Arkansas. Soluble reactive phosphorus (SRP), dissolved organic P (DOP), and total dissolved P (TDP) sediment-water fluxes were determined using intact sediment cores collected from deepwater environments in the riverine, transition zone, and lacustrine zones of Beaver Lake. The SRP, DOP, and TDP fluxes were also estimated from cores collected from shallow locations in the transition zone. There was a net positive SRP (0.001 – 0.005 µg P cm-2 h-1), DOP (0.005 – 0.01 µg P cm-2 h-1), and TDP (0.005 – 0.01 µg P cm-2 h-1) flux from deepwater sediments into the water column. However, DOP and TDP flux in shallow sediments were net negative (-0.004 and -0.002 µg P cm-2 h-1, respectively), suggesting that the majority of P was moving from water into sediment. The SRP flux from shallow sediments in the transition zone was similar to rates observed in deepwater sediments (0.002 µg P cm-2 h-1). However, the variability among flux rates, sites and depths was high, and therefore no statistical differences were found. Sediment oxygen demand was positively correlated with SRP and DOP flux rates from shallow transition zone sediments suggesting that microbial biomass and activity may have influenced sediment P flux. The P flux from shallow sediments supports approximately 1% to 5% of the daily P demand of phytoplankton. When compared to other lakes, sediment P flux in Beaver Lake appears minimal and is probably not an effective avenue to manage eutrophication in this system

A mechanistic study of the saponification of pivaloate esters

The reactions of the esters of trimethyl acetic acid (pivalic acid) have been followed kinetically (Walrath 1977 and Watkins 1986) in the presence of alkali in a 3:1 ethyl cellosolve: water solvent at 64°C. Through the use of both optically active pivaloates and O18 as a tracer, the positions of bond fission during saponification for several pivolates have been determined. With the secondary butyl ester bimolecular attack on both the acyl- and the alkyl- carbon atom is observed in the presence of alkali. Partial racemization of the product secondary butyl alcohols suggests that for a saponification of secondary butyl pivaloates a combination of the common Bac2 saponification mechanism and the rarer Bal2 saponification mechanism may occur in a purely aliphatic ester. In contrast to the secondary butyl ester, O18 studies show that the methyl ester undergoes biomolecular attack at only the acyl carbon atom in the presence of alkali. Apparently both the α tertiary butyl group and the secondary alcohol group are necessary to mask nucleophilic attack at the acyl carbon atom. The absence of a secondary alkyl group in methyl pivaloate allows nucleophilic attack at the acyl carbon to occur quite readily. Solvolysis experiments employing phenoxide ion (ՓO-) are under way to investigate the effect of the attacking nucleophile’s size on the reaction mechanism. Experiments employing O18 as a tracer for the saponification of ethyl-, n-butyl-, and secondary butyl pivaloate will begin shortly. This work should provide a more quantitative measure of the relative extent if each mechanism that occurs during the saponification of secondary butyl pivaloate and should provide insight into the effect of varying alkyl substituents on the mechanism of saponification of pivaloate esters

Milwaukee Parental Choice Program: Descriptive Report on Participating Schools 2010–11

This report is the fifth in a series of annual reports produced by the School Choice Demonstration Project (SCDP) that will provide descriptive information about the schools participating in the Milwaukee Parental Choice Program (MPCP)

Tasers and Community Controversy: Investigating Training Officer Perceptions of Public Concern Over Conducted Energy Weapons

Over the last several decades, “Tasers,” “stun guns” and other conducted energy devices (CEDs) have become a widely adopted, though publicly controversial, form of police restraint technology. While there is a growing body of research on the physiological effects of these types of weapons, less attention has been devoted to the social effects of this technology. This paper draws on in - depth interviews with a stratified random sample of police training officers from two states (n=27) to explore the effect that community controversy over the use of CEDs has had on police organizational practices. In particular, we explore how police training officers: (a ) Represent the sources of recent community controversies relating to CEDs; (b ) Characterize the effects that community controversy has on officer practices and policy development

Tasers, Accountability, and Less Lethal Force: Keying in on the Contentious Construction of Police Electroshock Weapons

Over the last decade, Tasers and other electroshock devices have become a nearly standard, though highly controversial, piece of police equipment for law enforcement. While a great deal of research focuses on the technical merits and health effects of this type of device, we adopt a constructionist framework and explore the manner in which different sets of actors compete to construct the “reality” of this type of technology within public media. By focusing on this issue, we seek to use the debate over Tasers to explore an underdeveloped area of social problems theory, i.e., how public problems are constructed publicly through the dynamic interaction of different sets of contentious claims-making actors. More specifically, we adopt Goffman’s concept of “keying” to examine how the opponents of the technology sought to appropriate and then re-deploy the claims made by proponents of the technology. By exploring the “keying” process, this paper will allow us to better understand the dynamic and iterative way in which the public claims offered by dominant and powerful groups are contested, appropriated and sometimes subverted, by less powerful groups

Holistic Hardware Counter Performance Analysis of Parallel Programs

The KOJAK toolkit has been augmented with refined hardware performance counter support, including more convenient measurement specification, additional metric derivations and hierarchical structuring, and an extended algebra for integrating multiple experiments. Comprehensive automated analysis of a hybrid OpenMP/MPI parallel program, the ASC Purple sPPM benchmark, is demonstrated with performance experiments on equisized POWER4-II-based IBM Regatta p690+ cluster, Opteron-based Cray XD1 cluster and UltraSPARC-IV-based Sun Fire E25000 systems. Automatically assessed communication and synchronisation performance properties, combined with a rich set of measured and derived counter metrics, provide a holistic analysis context and facilitate multi-platform comparison