A new method for estimating extreme sea levels from short sea-level records in a tide-dominated environment is presented. A short sea-level record is first decomposed into its constituent components ...such as tide, mean level of the sea, and storm surge. Monte Carlo simulations are then incorporated into an empirical simulation technique to randomly recombine the components to produce an annual series of sea levels at high tide from which the annual maximum is selected. The yearly simulation is repeated many thousands of times to yield robust statistics on extreme values. Comparison of the method with the traditional extreme-value analysis of annual maximum sea levels for a 33-year record shows that the methods give similar results. The method is likely to be most useful for estimation of extreme sea levels at locations where the available sea-level record is short (<15 years) and where the various sea-level components can be assumed to be largely independent.
In this paper we report the results of an experimental study of periphyton–flow
interactions conducted in a specially designed outdoor hydraulic flume. ‘Periphyton’
is a collective term for the ...micro-organisms which grow on stream beds, and includes
algae, bacteria, and fungi, with algae usually the dominant and most conspicuous
component. The main goals of the study are to identify potential effects of periphyton–flow interactions as
well as the potential mechanisms of mass transfer in the near-bed
region, which could influence periphyton growth and losses. The main results of the
study may be summarized as follows. A linear velocity distribution in the interfacial sublayer (i.e. below the roughness
tops), and a logarithmic distribution above the roughness tops appeared to be reasonable
approximations for both flow types, with and without periphyton on the
bed. However, the appearance of periphyton on a rough bed shifts the origin of the
bed upwards, increases the roughness length zo by 16–21%, and reduces the ratio of
the mean velocity at the level of roughness tops to the shear velocity by
≈30%. In general, below the roughness tops the periphyton suppresses the mean velocities, the
turbulent stresses, turbulence intensities, and vertical turbulent fluxes of the turbulent
energy and turbulent shear stresses. It was found that in flows without periphyton large-scale eddies successfully penetrate
the interfacial sublayer. However, tufts of periphyton on the tops of the
roughness elements significantly weaken the penetration processes leading to spatial
de-correlation in the velocity field within the interfacial sublayer. The appearance of
periphyton on the bed does not change appreciably the velocity spectra above the
roughness tops but reduces the total spectral energy and generates a wide spectral
peak in the interfacial sublayer. Most probably, this peak is formed by penetration
of sweep events into the interfacial sublayer, ‘filtered’ by the periphyton tufts. Thus,
sweep events may be the main mechanism responsible for the delivery of nutrients
from the outer region to the biologically active interfacial sublayer. The potential
effects of flow properties on the periphyton community are also discussed.
To determine potential targets of the S locus receptor kinase (SRK) during the Brassica self-incompatibility response, a yeast two-hybrid library was screened with the SRK-910 protein kinase domain. ...Two thioredoxin-h-like clones, THL-1 and THL-2, were found to interact specifically with the SRK-910 protein kinase domain and not to interact with the protein kinase domains from the Arabidopsis receptor-like protein kinases (RLK) RLK4 and RLK5. The interaction between THL-1 and the SRK-910 protein kinase domain was confirmed using coimmunoprecipitation experiments with fusion proteins produced in Escherichia coli. THL-1 has thioredoxin activity based on an insulin reduction assay, and THL-1 is weakly phosphorylated by the SRK-910 protein kinase domain. THL-1 and THL-2 are both expressed in a variety of tissues but show some differences in steady state mRNA levels, with THL-2 being preferentially expressed in floral tissues. This indicates a more general biological function for these thioredoxins in addition to a potential role as effector molecules in the self-incompatibility signal cascade
On gravel-bed roughness characterization Nikora, Vladimir I.; Goring, Derek G.; Biggs, Barry J. F.
Water resources research,
March 1998, Letnik:
34, Številka:
3
Journal Article
Recenzirano
Odprti dostop
The random field approach for gravel‐bed roughness characterization, which is based on the presentation of bed elevations as a three‐dimensional random field, is justified as an alternative to the ...characteristic particle size approach. We first show that the bed elevation distribution is close to Gaussian and then investigate gravel‐bed roughness using the second‐order structure function. The latter reveals two distinct regions: a scaling region at small spatial lags and a saturation region at large scales. The scaling exponent H (a form of Hurst exponent) appears to be isotropic and universal for both manually created “unworked” gravel beds (H=0.5) and natural water‐worked gravel beds (H=0.79). However, the gravel‐bed roughness, in general, is not isotropic and should be characterized by three independent characteristic scales. A simple model of gravel‐bed roughness based on the structure function parameterization is developed and compared with the characteristic particle size approach.
Previous studies have shown major differences in the way biomass of stream periphyton is controlled by spatial variations in velocity. We hypothesize that these differences may be the result of ...different growth forms within the community. Some dense and coherent growth forms (e.g. mucilaginous diatom/cyanobacterial mats) may be resistant to diffusion and also resistant to dislodgment by shear stress. Higher velocities applied to such communities could therefore be expected to enhance biomass accrual by increasing rates of mass transfer, but without greatly increasing losses through sloughing. Conversely, other growth forms (e.g. long filamentous green algae) have an open matrix, and high rates of diffusion into the mats can potentially occur even at low velocity. However, as velocities increase, high skin friction and form drag should lead to higher rates of sloughing. The overall result of these processes should be that maximum biomass occurs at low velocities. This “subsidy‐stress” hypothesis was tested twice with each of three different periphytal growth forms: a coherent, mucilaginous, diatom community; a moderately coherent, stalked/ short, filamentous diatom community; and an open‐weave, long, filamentous green algal community. A monotonic increase in chl a biomass occurred as a function of near‐bed velocities for the first of the two mucilaginous diatom communities investigated. No biomass‐velocity relationship was found, however, with the second mucilaginous community, probably because the waters were highly enriched and mass transfer driven by molecular diffusion was probably high throughout the velocity gradient. Biomass was moderate at low velocities, peaked at near‐bed velocities from 0.18 to 0.2 m·s−1 (∼0.40–0.45 m·s−1 mean column velocity), and then decreased at higher velocities in both of the stalked/ short filament communities of diatoms analyzed. With the long filamentous green algal communities, a monotonic reduction in biomass occurred as a function of increases in velocity. Proliferations greater than 100 mg·m−2 chl a occurred at low near‐bed velocities (i.e. <0.2 m·s−1), after which biomass declined nearly exponentially as a function of increasing velocity to less than 10 mg·m−2 chl a at velocities greater than 0.4 m·s−1. These biomass‐velocity trends support our hypothesis that community growth form determines periphytal responses to spatial variations in velocity within stream reaches.
Very high-energy gamma-ray emission from PKS 0447-439 was detected with the H.E.S.S. Cherenkov telescope array in December 2009. This blazar is one of the brightest extragalactic objects in the Fermi ...Bright Source List and has a hard spectrum in the MeV to GeV range. In the TeV range, a photon index of 3.89 +- 0.37 (stat) +- 0.22 (sys) and a flux normalisation at 1 TeV, Phi(1 TeV) = (3.5 +- 1.1 (stat) +- 0.9 (sys)) x 10^{-13} cm^{-2} s^{-1} TeV^{-1}, were found. The detection with H.E.S.S. triggered observations in the X-ray band with the Swift and RXTE telescopes. Simultaneous UV and optical data from Swift UVOT and data from the optical telescopes ATOM and ROTSE are also available. The spectrum and light curve measured with H.E.S.S. are presented and compared to the multi-wavelength data at lower energies. A rapid flare is seen in the Swift XRT and RXTE data, together with a flux variation in the UV band, at a time scale of the order of one day. A firm upper limit of z < 0.59 on the redshift of PKS 0447-439 is derived from the combined Fermi-LAT and H.E.S.S. data, given the assumptions that there is no upturn in the intrinsic spectrum above the Fermi-LAT energy range and that absorption on the Extragalactic Background Light (EBL) is not weaker than the lower limit provided by current models. The spectral energy distribution is well described by a simple one-zone Synchrotron Self-Compton (SSC) scenario, if the redshift of the source is less than z <~ 0.4.
A complex problem of turbulent-sediment interactions in an open-channel flow is approached experimentally, using specially designed field experiments in an irrigation canal. The experimental design ...included synchronous measurements of instantaneous three-dimensional (3D) velocities and suspended sediment concentration using acoustic Doppler velocimeters (ADV) and a water sampling system. Various statistical measures of sediment concentration fluctuations, turbulent sediment fluxes, and diffusion coefficients for fluid momentum and sediment are considered. Statistics, fractal behavior, and contributions of bursting events to vertical fluxes of fluid momentum and sediment are evaluated using quadrant analysis. It has been found that both turbulence and sediment events are organized in fractal clusters which introduce additional characteristic time and spatial scales into the problem and should be further explored. It is also shown that Barenblatt's theory of sediment-laden flows appears to be a good approximation of experimental data.
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