1,194 research outputs found
Spatial variability of hydrologic response on naturally vegetated hillslopes in a semi-arid environment.
Application of discriminant analysis to the soil/slope data validated the landsurface unit classification and identified the most useful mapping criteria. Seven variables measuring soil depth, soil texture, microroughness, and the areal percentage coverage of bare/eroded micro soil surfaces provided satisfactory discrimination of the six soil/slope groups.The hypothesis examined in this study suggests that spatial variability in overland flow and sediment yield on hillslopes in a semi-arid environment are related to the spatial distribution of specific soil/slope characteristics. Analysis of overland flow, sediment yield, and soil/slope data supports the research hypothesis by validating the field classification of erosional and depositional landsurface units, and in identifying distinctly different hydrologic responses between two landsurface units on three separate catenas.Four measures of hydrologic response were used to test for differences in overland flow and sediment yield between the landsurface units; overland flow response to individual rainfall events, sediment yield from individual rainfall events, total sediment yield for the six year period of recording, and rainsplash efficacy. All four attributes substantiated the hypothesized relationships
Bias in Zipf's Law Estimators
The prevailing maximum likelihood estimators for inferring power law models
from rank-frequency data are biased. The source of this bias is an
inappropriate likelihood function. The correct likelihood function is derived
and shown to be computationally intractable. A more computationally efficient
method of approximate Bayesian computation (ABC) is explored. This method is
shown to have less bias for data generated from idealised rank-frequency
Zipfian distributions. However, the existing estimators and the ABC estimator
described here assume that words are drawn from a simple probability
distribution, while language is a much more complex process. We show that this
false assumption leads to continued biases when applying any of these methods
to natural language to estimate Zipf exponents. We recommend that researchers
be aware of these biases when investigating power laws in rank-frequency data.Comment: 15 pages, 11 figure
High frequency dynamics in liquid nickel: an IXS study
Owing to their large relatively thermal conductivity, peculiar,
non-hydrodynamic features are expected to characterize the acoustic-like
excitations observed in liquid metals. We report here an experimental study of
collective modes in molten nickel, a case of exceptional geophysical interest
for its relevance in Earth interior science. Our result shed light on
previously reported contrasting evidences: in the explored energy-momentum
region no deviation from the generalized hydrodynamic picture describing non
conductive fluids are observed. Implications for high frequency transport
properties in metallic fluids are discussed.Comment: 6 pages, 4 figures, to appear in "Journal of Chemical Physics
Field Application of Spent Lime Water Treatment Residual for the Removal of Phosphorus and other Pollutants in Urban Stormwater Runoff
The threat of anthropogenic eutrophication and harmful algal blooms in lakes requires the development of innovative stormwater best management practices (BMPs) to reduce the external loading of phosphorus (P). This paper presents the findings of a 5-year study of a full-scale P removal structure constructed in Minnesota, USA with spent lime drinking water treatment residual (DWTR), a by-product of water softening at a local water treatment plant. Influent and effluent water samples were collected by auto-samplers during 43 storm events during the growing season. Samples were analyzed for P constituents, heavy metals, total suspended solids (TSS), and pH. Toxicity of the effluent was assessed using Ceriodaphnia dubia. Flow-weighted removal effectiveness was calculated for each storm event. Overall, the spent lime DWTR reduced total P loading by 70.9%, dissolved reactive P by 78.5%, dissolved P by 74.7%, and TSS by 58.5%. A significant reduction in heavy metals was also observed. Toxicity tests indicated the aquatic toxicity of the effluent treated with spent lime DWTR was not different from untreated stormwater. This study provided long-term real-world data that demonstrated that a full-scale P removal structure with spent lime DWTR significantly reduced P and other pollutants in stormwater discharging to an urban lake. Therefore, spent lime DWTR, which is currently treated as a waste product, is a promising filter material for stormwater treatment
The phonon theory of liquid thermodynamics
Heat capacity of matter is considered to be its most important property
because it holds information about system's degrees of freedom as well as the
regime in which the system operates, classical or quantum. Heat capacity is
well understood in gases and solids but not in the third state of matter,
liquids, and is not discussed in physics textbooks as a result. The perceived
difficulty is that interactions in a liquid are both strong and
system-specific, implying that the energy strongly depends on the liquid type
and that, therefore, liquid energy can not be calculated in general form. Here,
we develop a phonon theory of liquids where this problem is avoided. The theory
covers both classical and quantum regimes. We demonstrate good agreement of
calculated and experimental heat capacity of 21 liquids, including noble,
metallic, molecular and hydrogen-bonded network liquids in a wide range of
temperature and pressure.Comment: 7 pages, 4 figure
Evidence of short time dynamical correlations in simple liquids
We report a molecular dynamics (MD) study of the collective dynamics of a
simple monatomic liquid -interacting through a two body potential that mimics
that of lithium- across the liquid-glass transition. In the glassy phase we
find evidences of a fast relaxation process similar to that recently found in
Lennard-Jones glasses. The origin of this process is ascribed to the
topological disorder, i.e. to the dephasing of the different momentum
Fourier components of the actual normal modes of vibration of the disordered
structure. More important, we find that the fast relaxation persists in the
liquid phase with almost no temperature dependence of its characteristic
parameters (strength and relaxation time). We conclude, therefore, that in the
liquid phase well above the melting point, at variance with the usual
assumption of {\it un-correlated} binary collisions, the short time particles
motion is strongly {\it correlated} and can be described via a normal mode
expansion of the atomic dynamics.Comment: 7 pages, 7 .eps figs. To appear in Phys. Rev.
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Signal transduction in a covalent post-assembly modification cascade
Natural reaction cascades control the movement of biomolecules between cellular compartments. Inspired by these systems, we report a synthetic reaction cascade employing post-assembly modification reactions to direct the partitioning of supramolecular complexes between phases. The system is composed of a self-assembled tetrazine-edged FeII8L12 cube and a maleimide-functionalized FeII4L6 tetrahedron. Norbornadiene (NBD) functions as the stimulus that triggers the cascade, beginning with the inverse-electron-demand Diels–Alder reaction of NBD with the tetrazine moieties of the cube. This reaction generates cyclopentadiene as a transient by-product, acting as a relay signal that subsequently undergoes a Diels–Alder reaction with the maleimide-functionalized tetrahedron. Cyclooctyne can selectively inhibit the cascade by outcompeting NBD as the initial trigger. Initiating the cascade with 2-octadecyl NBD leads to selective alkylation of the tetrahedron upon cascade completion. The increased lipophilicity of the C18-tagged tetrahedron drives this complex into a non-polar phase, allowing its isolation from the initially inseparable mixture of complexes.B.S.P. acknowledges the Herchel Smith Research Fellowship, the Royal Commission for the Exhibition of 1851 Research Fellowship and the Fellowship from Corpus Christi College, Cambridge. D.A.R. acknowledges support from the Gates Cambridge Trust. This work was also supported by the UK Engineering and Physical Sciences Research Council (EPSRC, EP/M008258/1). The authors thank Diamond Light Source (UK) for synchrotron beamtime on I19 (MT11397), the NMR facility at the University of Cambridge Chemistry Department, and the EPSRC UK National Mass Spectrometry Facility
at Swansea University
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