HEURISTIC ALGORITHM FOR SPANNING TREE PROTOCOL ROOT BRIDGE DETERMINATION

Techniques are presented to avoid requiring network administrators to have Spanning Tree Protocol (STP) domain specific knowledge while still achieving a stable and high performing Layer 2 (L2) topology in their Virtual Local Area Networks (VLANs). Configuring the STP is easily ignored since it is operable initially, but networks might run at a suboptimal efficiency as a result

Deciphering the expression of climate change within the Lower Colorado River basin by stochastic simulation of convective rainfall

In drylands, convective rainstorms typically control runoff, streamflow, water supply and flood risk to human populations, and ecological water availability at multiple spatial scales. Since drainage basin water balance is sensitive to climate, it is important to improve characterization of convective rainstorms in a manner that enables statistical assessment of rainfall at high spatial and temporal resolution, and the prediction of plausible manifestations of climate change. Here we present a simple rainstorm generator, STORM, for convective storm simulation. It was created using data from a rain gauge network in one dryland drainage basin, but is applicable anywhere. We employ STORMto assess watershed rainfall under climate change simulations that reflect differences in wetness/ storminess, and thus provide insight into observed or projected regional hydrologic trends. Our analysis documents historical, regional climate change manifesting as a multidecadal decline in rainfall intensity, which we suggest has negatively impacted ephemeral runoff in the Lower Colorado River basin, but has not contributed substantially to regional negative streamflow trends

Portfolio Choice and Liquidity Constraints

This paper generalizes Deaton's (1991) approach to saving under borrowing constraints to incorporate portfolio choice. For infinite horizon, impatient consumers, effects of risk aversion, prudence and temperance on portfolios can be different from those obtained in atemporal models. We confirm the surprising result of portfolio specialization in stocks (Heaton and Lucas, 1997) using a different earnings process, and we provide a rationale for why risk aversion and habit persistence cannot reverse it. We then show that positive correlation of stock returns with permanent, but not transitory, earnings shocks can generate demand for bonds and zero stockholding. However, existing empirical estimates of such correlations are at variance with portfolio data. We offer an alternative explanation of observed stock holding patterns based on fixed stock market entry costs. The entry cost required to keep impatient households out of the stock market is surprisingly small. This suggests that entry costs could generate the observed reluctance of households to undertake stockholding and explain the slowness in the emergence of an "equity culture" among households.Precautionary Saving; Portfolio Choice; Liquidity Constraints; Buffer Stock

Benchmarking the performance of Density Functional Theory and Point Charge Force Fields in their Description of sI Methane Hydrate against Diffusion Monte Carlo

High quality reference data from diffusion Monte Carlo calculations are presented for bulk sI methane hydrate, a complex crystal exhibiting both hydrogen-bond and dispersion dominated interactions. The performance of some commonly used exchange-correlation functionals and all-atom point charge force fields is evaluated. Our results show that none of the exchange-correlation functionals tested are sufficient to describe both the energetics and the structure of methane hydrate accurately, whilst the point charge force fields perform badly in their description of the cohesive energy but fair well for the dissociation energetics. By comparing to ice Ih, we show that a good prediction of the volume and cohesive energies for the hydrate relies primarily on an accurate description of the hydrogen bonded water framework, but that to correctly predict stability of the hydrate with respect to dissociation to ice Ih and methane gas, accuracy in the water-methane interaction is also required. Our results highlight the difficulty that density functional theory faces in describing both the hydrogen bonded water framework and the dispersion bound methane.Comment: 8 pages, 4 figures, 1 table. Minor typos corrected and clarification added in Method

STORM 1.0: a simple, flexible, and parsimonious stochastic rainfall generator for simulating climate and climate change

Assessments of water balance changes, watershed response, and landscape evolution to climate change require representation of spatially and temporally varying rainfall fields over a drainage basin, as well as the flexibility to simply modify key driving climate variables (evaporative demand, overall wetness, storminess). An empirical–stochastic approach to the problem of rainstorm simulation enables statistical realism and the creation of multiple ensembles that allow for statistical characterization and/or time series of the driving rainfall over a fine grid for any climate scenario. Here, we provide details on the STOchastic Rainfall Model (STORM), which uses this approach to simulate drainage basin rainfall. STORM simulates individual storms based on Monte Carlo selection from probability density functions (PDFs) of storm area, storm duration, storm intensity at the core, and storm center location. The model accounts for seasonality, orography, and the probability of storm intensity for a given storm duration. STORM also generates time series of potential evapotranspiration (PET), which are required for most physically based applications. We explain how the model works and demonstrate its ability to simulate observed historical rainfall characteristics for a small watershed in southeast Arizona. We explain the data requirements for STORM and its flexibility for simulating rainfall for various classes of climate change. Finally, we discuss several potential applications of STORM

Embolization of a sporadic bleeding renal angiomyolipoma supplied by an aberrant renal artery

Spontaneous bleeding of a renal angiomyolipoma (AML) is a life threatening condition that necessitates prompt treatment. Herein we describe the first case of a spontaneously ruptured renal AML supplied solely by an aberrant renal artery that was successfully treated by selective transcatherer embolization

An unusual case of Multiple Inflammatory Myofibroblastic Tumors of the lung

Inflammatory myofibroblastic tumor (IMT) of the lung is a rare, usually solitary lesion that is considered nowadays as a true neoplasm with unpredictable clinical course. Herein we describe a case of multiple, bilateral IMTs of the lung in a 70 year-old asymptomatic woman, where diagnosis was established by CT guided core biopsy. To our knowledge only 10 cases of bilateral IMTs have been reported in a few case series and in only 2 cases of pulmonary IMTs, CT guided biopsy could establish the correct diagnosis

Perspective: How good is DFT for water?

Kohn-Sham density functional theory (DFT) has become established as an indispensable tool for investigating aqueous systems of all kinds, including those important in chemistry, surface science, biology and the earth sciences. Nevertheless, many widely used approximations for the exchange-correlation (XC) functional describe the properties of pure water systems with an accuracy that is not fully satisfactory. The explicit inclusion of dispersion interactions generally improves the description, but there remain large disagreements between the predictions of different dispersion-inclusive methods. We present here a review of DFT work on water clusters, ice structures and liquid water, with the aim of elucidating how the strengths and weaknesses of different XC approximations manifest themselves across this variety of water systems. Our review highlights the crucial role of dispersion in describing the delicate balance between compact and extended structures of many different water systems, including the liquid. By referring to a wide range of published work, we argue that the correct description of exchange-overlap interactions is also extremely important, so that the choice of semi-local or hybrid functional employed in dispersion-inclusive methods is crucial. The origins and consequences of beyond-2-body errors of approximate XC functionals are noted, and we also discuss the substantial differences between different representations of dispersion. We propose a simple numerical scoring system that rates the performance of different XC functionals in describing water systems, and we suggest possible future developments