Recent evidence suggests that slow anion channels in guard cells need to be activated to

The functional analysis of single ion channel proteins presents a serious bottleneck in the process of finding new pharmacologically active compounds. Single channel recording methods currently available (patch clamp, [1] black lipid membrane (BLM) [2] ) are not suited for automation and miniaturization. However, new techniques such as combinatorial chemistry [3] and combinatorial genetics, [4] which pro-

Selection procedures are used in a variety of applications to select the best of a finite set of alternatives. 'Best' is defined with respect to the largest mean, but the mean is inferred with statistical sampling, as in simulation optimization. There are a wide variety of procedures, which begs the question of which selection procedure to select. The main contribution of this paper is to identify, through extensive experimentation, the most effective selection procedures when samples are independent and normally distributed. We also (a) summarize the main structural approaches to deriving selection procedures, (b) formalize new sampling allocations and stopping rules, (c) identify strengths and weaknesses of the procedures, (d) identify some theoretical links between them, (e) and present an innovative empirical test bed with the most extensive numerical comparison of selection procedures to date. The most efficient and easiest to control procedures allocate samples with a Bayesian model for uncertainty about the means, and use new adaptive stopping rules proposed here.Selection procedures are intended to select the best of a finite set of alternatives, where best is determined with respect to the largest mean, but the mean must be inferred via statistical sampling (Bechhofer et al. 1995). Selection procedures can inform managers how to select the best of a small set of alternative actions whose effects are evaluated with simulation , and have been implemented in commercial simulation products. Selection procedures have also attracted interest in combination with tools like multiple attribute utility theory (Butler et al. 2001), evolutionary algorithms (Branke and Schmidt 2004), and discrete optimization via simulation (Boesel et al. 2003).Three main approaches to solving the selection problem are distinguished by their assumptions about how the evidence for correct selection is described and sampling allocations are made: the indifference zone (IZ, Kim and Nelson 2006), the expected value of information procedure (VIP, Chick and Inoue 2001a), and the optimal computing budget allocation (OCBA, Chen 1996) approaches. IZ procedures typically allocate samples in order to provide a guaranteed lower bound for the frequentist probability of correct selection (PCS), with respect to the sampling distribution, for selection problems in a specific class (e.g., the mean of the best is at least a prespecified amount better than each alternative). The VIP approach describes the evidence for correct selection with Bayesian posterior distributions, and allocates further samples using decision-theory tools to maximize the expected value of information in those samples. The OCBA is a heuristic that uses a normal distribution approximation for the Bayesian posterior distribution of the unknown mean performance of each alternative in order to sequentially allocate further samples. Each approach stipulates a number of different sampling assumptions, approximations, stopping rules and parameters that combine to define a pr...

Many advanced applications of X-ray free-electron lasers require pulse durations and time resolutions of only a few femtoseconds. To generate these pulses and to apply them in time-resolved experiments, synchronization techniques that can simultaneously lock all independent components, including all accelerator modules and all external optical lasers, to better than the delivered free-electron laser pulse duration, are needed. Here we achieve all-optical synchronization at the soft X-ray free-electron laser FLASH and demonstrate facility-wide timing to better than 30 fs r.m.s. for 90 fs X-ray photon pulses. Crucially, our analysis indicates that the performance of this optical synchronization is limited primarily by the free-electron laser pulse duration, and should naturally scale to the sub-10 femtosecond level with shorter X-ray pulses.

Closing of stomatal pores in the leaf epidermis of higher plants is mediated by long-term release of potassium and the anions chloride and malate from guard cells and by parallel metabolism of malate. Previous studies have shown that slowly activating anion channels in the plasma membrane of guard cells can provide a major pathway for anion efflux while also controlling K+ efflux during stomatal closing: Anion efflux produces depolarization of the guard cell plasma membrane that drives K+ efflux required for stomatal closing. The patch-clamp technique was applied to Vicia faba guard cells to determine the permeability of physiologically significant anions and halides through slow anion channels to assess the contribution of these anion channels to anion efflux during stomatal closing. Permeability ratio measurements showed that all tested anions were permeable with the selectivity sequence relative to CI-of NOs-> Br-> F--CI--I-> malate. Large malate concentrations in the cytosol (150 mM) produced a slow down-regulation of slow anion channel currents. Single anion channel currents were recorded that correlated with whole-cell anion currents. Single slow anion channels confirmed the large permeability ratio for nitrate over chloride ions. Furthermore, single-channel studies support previous indications of multiple condudance states of slow anion channels, suggesting cooperativity among anion channels. Anion conductances showed that slow anion channels can mediate physiological rates of CI-and initial malate efflux required for mediation of stomatal closure. l h e large optimize their atmospheric COZ and water vapor exchange by adjusting the aperture of stomatal pores in the leaf epidermis. Stomatal regulation depends on environmental conditions such as humidity, COZ levels, and light intensity. Guard cells surrounding stomata directly control the stomatal aperture. Stomatal opening is mediated by turgor and volume increases of guard cells, which result from ion uptake and intemal conversion of starch to osmotically active malate (Raschke, 1979). Efflux of potassium and anions (mainly chloride and to a small degree malate) from guard cells and malate metabolism produce turgor and volume reduction and the ensuing closure of stomatal pores (Raschke, 1979; MacRobbie, 1981; Outlaw et al., 1981).Anion channels in the plasma membrane of guard cells have been suggested to be central mediators of stomatal closing (Keller et al., 1989; Schroeder and Hagiwara, 1989). Recent studies have shown the presence of at least two different types or modes of anion channel currents in guard cells (Schroeder and Keller, 1992). Both anion channels are likely to be involved in stomatal closing, while showing significantly different activation times, voltage dependencies, and pharmacological properties (Schroeder and