BPC – A binary priority countdown protocol

In modern wireless ad hoc networks, with a high speed PHY, every collision means a significant loss of useful bandwidth. In the last few years different binary contention protocols have been introduced to address this problem. In this work we propose a novel binary contention protocol called binary priority countdown (BPC) protocol, whose goal is to reduce collisions as well as contention time. BPC uses a new priority countdown mechanism which exploits the efficiency of binary countdown, but the priority countdown process is not constrained to a single binary countdown round. This way, the priority space is not defined by the length of binary countdown round, like in other binary countdown protocols proposed in the literature, and arbitrary medium access priorities can be decremented through multiple binary countdown rounds if necessary. The ability of a new priority countdown mechanism to count down any priority number without changing the length of a binary countdown round, allows independent management of priority space. This “independence” of priority space introduces new optimization and adaptation possibilities. Collision memory effect is recognized and described. BPC protocol reveals connection between unary, binary and digit contention protocols. All three groups of protocols can now be seen as members of the same class of contention algorithms. Preliminary simulation results are shown.     

Multifunctional hydrogels that promote osteogenic hMSC differentiation through stimulation and sequestering of BMP2

The extracellular environment controls many cellular activities thereby linking external material cues to internal cell function. By better understanding these processes, synthetic extracellular material niches can be tailored to present cells with highly regulated physical and/or chemical cues that promote or suppress selected cell functions. Here, poly(ethylene glycol) (PEG) hydrogels were functionalized with fluvastatin-releasing grafts and growth factor binding heparin domains to enable the dynamic exchange of information between the material and cells from the outside-in and inside-out (i.e., bidirectional signaling). By incorporating a fluvastatin-releasing graft and carefully controlling the dose and temporal release, materials were designed to promote bone morphogenic protein (BMP2) and alkaline phosphatase (ALP) production by human mesenchymal stem cells (hMSCs). When the release of fluvastatin was controlled to occur over 2 weeks, BMP2 and ALP production was increased 2.2-fold and 1.7-fold, respectively, at day 28 compared to hMSCs cultured in the absence of fluvastatin. By introducing a heparin functionality into the gel to sequester and localize the hMSC-produced BMP2, the osteogenic differentiation of hMSCs was further augmented over fluvastatin delivery alone. Osteopontin and core binding factor α1 gene expression was 6-fold and 4-fold greater for hMSCs exposed to fluvastatin in the presence of the heparin functionalities, respectively. These results demonstrate how multifunctional gels that interact with cells in a bidirectional manner can efficiently promote selected cell functions, such as the osteogenic differentiation of hMSCs.     

A Blend of Ethanol and (−)-α-Pinene were Highly Attractive to Native Siricid Woodwasps (Siricidae,Siricinae) Infesting Conifers of the Sierra Nevada and the Allegheny Mountains

Woodwasps in Sirex and related genera are well-represented in North American conifer forests, but the chemical ecology of native woodwasps is limited to a few studies demonstrating their attraction to volatile host tree compounds, primarily monoterpene hydrocarbons and monoterpene alcohols. Thus, we systematically investigated woodwasp-host chemical interactions in California’s Sierra Nevada and West Virginia’s Allegheny Mountains. We first tested common conifer monoterpene hydrocarbons and found that (?)-α-pinene, (+)-3-carene, and (?)-β-pinene were the three most attractive compounds. Based on these results and those of earlier studies, we further tested three monoterpene hydrocarbons and four monoterpene alcohols along with ethanol in California: monoterpene hydrocarbons caught 72.3% of all woodwasps. Among monoterpene hydrocarbons, (+)-3-carene was the most attractive followed by (?)-β-pinene and (?)-α-pinene. Among alcohols, ethanol was the most attractive, catching 41.4% of woodwasps trapped. Subsequent tests were done with fewer selected compounds, including ethanol, 3-carene, and ethanol plus (?)-α-pinene in both Sierra Nevada and Allegheny Mountains. In both locations, ethanol plus (?)-α-pinene caught more woodwasps than other treatments. We discussed the implications of these results for understanding the chemical ecology of native woodwasps and invasive Sirex noctilio in North America. In California, 749 woodwasps were caught, representing five species: Sirex areolatus Cresson, Sirex behrensii Cresson, Sirex cyaneus Fabricius, Sirex longicauda Middlekauff, and Urocerus californicus Norton. In West Virginia 411 woodwasps were caught representing four species: Sirex edwardsii Brullé, Tremex columba Linnaeus, Sirex nigricornis F., and Urocerus cressoni Norton.     

Density of nafion exchanged with transition metal complexes and tetramethyl ammonium,ferrous, and hydrogen ions: commercial and recast films

The densities of commercial Nafion 117 and cast Nafion 1100 films were determined by the hydrostatic weighing method for films fully exchanged with hexaammineruthenium(III), tris(2,2' bipyridyl)ruthenium(II), tetramethylammonium, ferrous, and hydrogen ions. Films were pretreated in either water or concentrated nitric acid prior to cation exchange. All densities ranged between 1.65 and 2.19 g/cm3. Excluding the proton-exchanged films, the average density is 1.90 +/- 0.14 g/cm3, well in excess of the 1.58 g/cm3 commonly employed for Nafion. The density of acid-pretreated Nafion 1100 was constant at 1.95 +/- 0.03 g/cm3 for all cations except the proton. A simple, empirical model based on the Coulombic interaction between the intercalated cation and the sulfonate sites of the Nafion characterizes density for the commercial Nafion 117 films. A modified version of the model is appropriate for water-treated Nafion 1100. Water content of the films and implications for characterizing modified electrodes are discussed.     

Recognizing, assessing, and intervening with problems of professional competence.

Working collaboratively, psychologist educators and trainers at the doctoral, internship, and postdoctoral levels; credentialers; practitioners; and students offer 8 proposals for psychologists to consider in recognizing, assessing, and intervening with problems of professional competence in students and practicing professionals. In the proposals, the authors address the following topics: definitions and categories; preparing the system; self-assessment; remediation; diversity; communication across various levels of the system; confidentiality; and ethical, regulatory, and legal underpinnings. They also propose future directions for the assessment of problems in professional competence in both students and practicing psychologists. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A new approach to satellite-based estimation of precipitation over snow cover

Current satellite-based remote-sensing approaches are largely incapable of estimating precipitation over snow cover. This note reports a proof-of-concept study of a new satellite-based approach to the estimation of precipitation over snow-covered surfaces. The method is based on the principle that precipitation can be inferred from the changes in the snow water equivalent of the snowpack. Using satellite-based snow water equivalent measurements, we derived daily precipitation amounts for the northern hemisphere for three snow-accumulation seasons, and evaluated these against independent reference datasets. The new precipitation estimates captured realistic-looking storm events over largely un-instrumented regions. However, the data are noisy and, on a seasonal scale, the amount of precipitation is believed to be underestimated. Nevertheless, current uncertainty in snow measurements, albeit large (50–100%), is still lower than direct precipitation measurements over snow (100–140%) and therefore this approach is still useful. The method will become more feasible as the quality of remotely sensed snow measurements improves.     

Limited communication control

This work in limited communication control is directed towards bringing together classical control theory and communication theoretical issues that are of practical importance in the design of control systems. It is common to “decouple” the communication aspects from the underlying dynamics of a system, as this simplifies the analysis and generally works well for classical models. However, in situations where a single decision maker controls many subsystems over a communication channel of a finite capacity, the computation of control signals and their transmission to each system may take significant amounts of time. To address such cases, we consider a class of discrete-time models that jointly optimize over control and communication goals. Real-world examples where these models play a role include remotely controlled unmanned autonomous vehicles (UAVs), planetary rovers, arrays of microactuators and power control in mobile communication.