The Mason Test: A Defense Against Sybil Attacks in Wireless Networks Without Trusted Authorities

Wireless networks are vulnerable to Sybil attacks, in which a malicious node poses as many identities in order to gain disproportionate influence. Many defenses based on spatial variability of wireless channels exist, but depend either on detailed, multi-tap channel estimation - something not exposed on commodity 802.11 devices - or valid RSSI observations from multiple trusted sources, e.g., corporate access points - something not directly available in ad hoc and delay-tolerant networks with potentially malicious neighbors. We extend these techniques to be practical for wireless ad hoc networks of commodity 802.11 devices. Specifically, we propose two efficient methods for separating the valid RSSI observations of behaving nodes from those falsified by malicious participants. Further, we note that prior signalprint methods are easily defeated by mobile attackers and develop an appropriate challenge-response defense. Finally, we present the Mason test, the first implementation of these techniques for ad hoc and delay-tolerant networks of commodity 802.11 devices. We illustrate its performance in several real-world scenarios

Determination of Optical Constants for Titan Aerosol-, and Exoplanet and Brown Dwarf Cloud Particle Analogs from the Visible to the Far Infrared

Here we present optical constants covering a broad wavelength range, from the visible to the far infrared, for Titan aerosol analogs produced in the Titan Haze Simulation (THS) experiment at Ames COSmIC facility, as well as other exoplanet-relevant materials

Warming by 1°C drives species and assemblage level responses in Antarctica’s marine shallows

Forecasting assemblage-level responses to climate change remains one of the greatest challenges in global ecology [1 , 2 ]. Data from the marine realm are limited because they largely come from experiments using limited numbers of species [3 ], mesocosms whose interior conditions are unnatural [4 ], and long-term correlation studies based on historical collections [5 ]. We describe the first ever experiment to warm benthic assemblages to ecologically relevant levels in situ. Heated settlement panels were used to create three test conditions: ambient and 1°C and 2°C above ambient (predicted in the next 50 and 100 years, respectively [6]). We observed massive impacts on a marine assemblage, with near doubling of growth rates of Antarctic seabed life. Growth increases far exceed those expected from biological temperature relationships established more than 100 years ago by Arrhenius. These increases in growth resulted in a single “r-strategist” pioneer species (the bryozoan Fenestrulina rugula) dominating seabed spatial cover and drove a reduction in overall diversity and evenness. In contrast, a 2°C rise produced divergent responses across species growth, resulting in higher variability in the assemblage. These data extend our ability to expand, integrate, and apply our knowledge of the impact of temperature on biological processes to predict organism, species, and ecosystem level ecological responses to regional warming

Electro-kinetic technology as a low-cost method for dewatering food by-product

Increasing volumes of food waste, intense environmental awareness, and stringent legislation have imposed increased demands upon conventional food waste management. Food byproducts that were once considered to be without value are now being utilized as reusable materials, fuels, and energy in order to reduce waste. One major barrier to the valorization of food by-products is their high moisture content. This has brought about the necessity of dewatering food waste for any potential re-use for certain disposal options. A laboratory system for experimentally characterizing electro-kinetic dewatering of food by-products was evaluated. The bench scale system, which is an augmented filter press, was used to investigate the dewatering at constant voltage. Five food by-products (brewer’s spent grain, cauliflower trimmings, mango peel, orange peel, and melon peel) were studied. The results indicated that electro-kinetic dewatering combined with mechanical dewatering can reduce the percentage of moisture from 78% to 71% for brewer’s spent grain, from 77% to 68% for orange peel, from 80% to 73% for mango peel, from 91% to 74% for melon peel, and from 92% to 80% for cauliflower trimmings. The total moisture reduction showed a correlation with electrical conductivity (R2¼0.89). The energy consumption of every sample was evaluated and was found to be up to 60 times more economical compared to thermal processing

QED effective action at finite temperature and density

The QED effective action at finite temperature and density is calculated to all orders in an external homogeneous and time-independent magnetic field in the weak coupling limit. The free energy, obtained explicitly, exhibit the expected de\ Haas -- van\ Alphen oscillations. An effective coupling at finite temperature and density is derived in a closed form and is compared with renormalization group results.Comment: 10 pages, Latex, NORDITA-93/35 P, Goteborg ITP 92-2

Extreme phenotypic plasticity in metabolic physiology of Antarctic demosponges

Seasonal measurements of the metabolic physiology of four Antarctic demosponges and their associated assemblages, maintained in a flow through aquarium facility, demonstrated one of the largest differences in seasonal strategies between species and their associated sponge communities. The sponge oxygen consumption measured here exhibited both the lowest and highest seasonal changes for any Antarctic species; metabolic rates varied from a 25% decrease to a 5.8 fold increase from winter to summer, a range which was greater than all 17 Antarctic marine species (encompassing eight phyla) previously investigated and amongst the highest recorded for any marine environment. The differences in nitrogen excretion, metabolic substrate utilization and tissue composition between species were, overall, greater than seasonal changes. The largest seasonal difference in tissue composition was an increase in CHN (Carbon, Hydrogen, and Nitrogen) content in Homaxinella balfourensis, a pioneer species in ice-scour regions, which changed growth form to a twig-like morph in winter. The considerable flexibility in seasonal and metabolic physiology across the Demospongiae likely enables these species to respond to rapid environmental change such as ice-scour, reductions in sea ice cover and ice-shelf collapse in the Polar Regions, shifting the paradigm that polar sponges always live “life in the slow lane.” Great phenotypic plasticity in physiology has been linked to differences in symbiotic community composition, and this is likely to be a key factor in the global success of sponges in all marine environments and their dominant role in many climax communities

Seed bank dynamics govern persistence of Brassica hybrids in crop and natural habitats

Background and Aims: Gene flow from crops to their wild relatives has the potential to alter population growth rates and demography of hybrid populations, especially when a new crop has been genetically modified (GM). This study introduces a comprehensive approach to assess this potential for altered population fitness, and uses a combination of demographic data in two habitat types and mathematical (matrix) models that include crop rotations and outcrossing between parental species. Methods: Full life-cycle demographic rates, including seed bank survival, of non-GM Brassica rapa × B. napus F1 hybrids and their parent species were estimated from experiments in both agricultural and semi-natural habitats. Altered fitness potential was modelled using periodic matrices including crop rotations and outcrossing between parent species. Key Results: The demographic vital rates (i.e. for major stage transitions) of the hybrid population were intermediate between or lower than both parental species. The population growth rate (λ) of hybrids indicated decreases in both habitat types, and in a semi-natural habitat hybrids became extinct at two sites. Elasticity analyses indicated that seed bank survival was the greatest contributor to λ. In agricultural habitats, hybrid populations were projected to decline, but with persistence times up to 20 years. The seed bank survival rate was the main driver determining persistence. It was found that λ of the hybrids was largely determined by parental seed bank survival and subsequent replenishment of the hybrid population through outcrossing of B. rapa with B. napus. Conclusions: Hybrid persistence was found to be highly dependent on the seed bank, suggesting that targeting hybrid seed survival could be an important management option in controlling hybrid persistence. For local risk mitigation, an increased focus on the wild parent is suggested. Management actions, such as control of B. rapa, could indirectly reduce hybrid populations by blocking hybrid replenishment