2,209 research outputs found
Revisiting the phase diagram of hard ellipsoids
In this work the well-known Frenkel-Mulder phase diagram of hard ellipsoids
of revolution [Mol. Phys. 55, 1171 (1985)] is revisited by means of replica
exchange Monte Carlo simulations. The method provides good sampling of dense
systems and so, solid phases can be accessed without the need of imposing a
given structure. At high densities, we found plastic solids and fcc-like
crystals for semi-spherical ellipsoids (prolates and oblates), and SM2
structures [Phys. Rev. E 75, 020402 (2007)] for x:1-prolates and 1:x-oblates
with x>=3. The revised fluid-crystal and isotropic-nematic transitions
reasonably agree with those presented in the Frenkel-Mulder diagram. An
interesting result is that, for small system sizes (100 particles), we obtained
2:1 and 1.5:1-prolate equations of state without transitions, while some order
is developed at large densities. Furthermore, the symmetric oblate cases are
also reluctant to form ordered phases.Comment: 8 pages, 6 figure
The Honeycomb Conjecture
This article gives a proof of the classical honeycomb conjecture: any partition of the plane into regions of equal area has perimeter at least that of the regular hexagonal honeycomb tiling.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42423/1/454-25-1-1_10071.pd
Effects of decreased dietary roughage concentration on energy metabolism and nutrient balance in finishing beef cattle
The optimal roughage concentration required in feedlot diets changes continuously for many reasons such as source, availability, price, and interaction with other ingredients in the diet. Wet distillers grains and solubles (WDGS) are common in finishing diets and they contain relatively high amounts of fiber compared with other grains they replace. Therefore, concentration of roughage could be altered when WDGS are included in feedlot diets. There has been very little data published regarding the effects of roughage concentration on energy metabolism and nutrient balance in beef steers. Therefore, the effects of roughage concentration in dryrolled corn (DRC)–based diets containing 25% WDGS were evaluated in 8 steers (BW = 362 ± 3.71 kg) using a replicated Latin square. Data were analyzed with the fixed effects of dietary treatment and period and random effects of square and steer within square were included in the model. Diets consisted of 25% WDGS and the balance being DRC and coarsely ground alfalfa hay (AH) replacing corn at 2% (AH-2), 6% (AH-6), 10% (AH-10), and 14% (AH-14) of dietary dry matter. As a proportion of GE intake, fecal energy loss increased linearly (P = 0.02), and DE decreased linearly (P = 0.02) as dietary level of AH increased. Methane energy loss, as a proportion of GE intake, increased linearly (P \u3c 0.01) and ME decreased linearly (P \u3c 0.01) as dietary concentration of AH increased. Heat production tended (P = 0.10) to decrease reaching a minimum of 10% AH and increased from 10 to 14% AH inclusion. Moreover, as a proportion of GE intake, retained energy (RE) decreased (P \u3c 0.01) as AH level increased in the diet. Reasons for the decrease in RE are 1) the increase in fecal energy loss that is associated with decreased ruminal digestibility of NDF when AH replaced DRC and the shift in ruminal VFA produced, 2) the decreased energy available for animal retention when NDF increased linearly as AH increased in the diet, and 3) the methane and heat energy associated with digestion of the fibrous portion of the AH. Neutral detergent fiber and OM excretion also increased linearly (P \u3c 0.01) with increasing AH in the diet. The increased NDF and OM excretion were likely caused by the difference in digestibility of AH and DRC
Effects of decreased dietary roughage concentration on energy metabolism and nutrient balance in finishing beef cattle
The optimal roughage concentration required in feedlot diets changes continuously for many reasons such as source, availability, price, and interaction with other ingredients in the diet. Wet distillers grains and solubles (WDGS) are common in finishing diets and they contain relatively high amounts of fiber compared with other grains they replace. Therefore, concentration of roughage could be altered when WDGS are included in feedlot diets. There has been very little data published regarding the effects of roughage concentration on energy metabolism and nutrient balance in beef steers. Therefore, the effects of roughage concentration in dryrolled corn (DRC)–based diets containing 25% WDGS were evaluated in 8 steers (BW = 362 ± 3.71 kg) using a replicated Latin square. Data were analyzed with the fixed effects of dietary treatment and period and random effects of square and steer within square were included in the model. Diets consisted of 25% WDGS and the balance being DRC and coarsely ground alfalfa hay (AH) replacing corn at 2% (AH-2), 6% (AH-6), 10% (AH-10), and 14% (AH-14) of dietary dry matter. As a proportion of GE intake, fecal energy loss increased linearly (P = 0.02), and DE decreased linearly (P = 0.02) as dietary level of AH increased. Methane energy loss, as a proportion of GE intake, increased linearly (P \u3c 0.01) and ME decreased linearly (P \u3c 0.01) as dietary concentration of AH increased. Heat production tended (P = 0.10) to decrease reaching a minimum of 10% AH and increased from 10 to 14% AH inclusion. Moreover, as a proportion of GE intake, retained energy (RE) decreased (P \u3c 0.01) as AH level increased in the diet. Reasons for the decrease in RE are 1) the increase in fecal energy loss that is associated with decreased ruminal digestibility of NDF when AH replaced DRC and the shift in ruminal VFA produced, 2) the decreased energy available for animal retention when NDF increased linearly as AH increased in the diet, and 3) the methane and heat energy associated with digestion of the fibrous portion of the AH. Neutral detergent fiber and OM excretion also increased linearly (P \u3c 0.01) with increasing AH in the diet. The increased NDF and OM excretion were likely caused by the difference in digestibility of AH and DRC
Helical Tubes in Crowded Environments
When placed in a crowded environment, a semi-flexible tube is forced to fold
so as to make a more compact shape. One compact shape that often arises in
nature is the tight helix, especially when the tube thickness is of comparable
size to the tube length. In this paper we use an excluded volume effect to
model the effects of crowding. This gives us a measure of compactness for
configurations of the tube, which we use to look at structures of the
semi-flexible tube that minimize the excluded volume. We focus most of our
attention on the helix and which helical geometries are most compact. We found
that helices of specific pitch to radius ratio 2.512 to be optimally compact.
This is the same geometry that minimizes the global curvature of the curve
defining the tube. We further investigate the effects of adding a bending
energy or multiple tubes to begin to explore the more complete space of
possible geometries a tube could form.Comment: 10 page
Formal Verification of a Geometry Algorithm: A Quest for Abstract Views and Symmetry in Coq Proofs
This extended abstract is about an effort to build a formal description of a
triangulation algorithm starting with a naive description of the algorithm
where triangles, edges, and triangulations are simply given as sets and the
most complex notions are those of boundary and separating edges. When
performing proofs about this algorithm, questions of symmetry appear and this
exposition attempts to give an account of how these symmetries can be handled.
All this work relies on formal developments made with Coq and the mathematical
components library
Stacking Characteristics of Close Packed Materials
It is shown that the enthalpy of any close packed structure for a given
element can be characterised as a linear expansion in a set of continuous
variables which describe the stacking configuration. This enables us
to represent the infinite, discrete set of stacking sequences within a finite,
continuous space of the expansion parameters . These determine the
stable structure and vary continuously in the thermodynamic space of pressure,
temperature or composition. The continuity of both spaces means that only
transformations between stable structures adjacent in the space are
possible, giving the model predictive and well as descriptive ability. We
calculate the using density functional theory and interatomic potentials
for a range of materials. Some striking results are found: e.g. the
Lennard-Jones potential model has 11 possible stable structures and over 50
phase transitions as a function of cutoff range. The very different phase
diagrams of Sc, Tl, Y and the lanthanides are understood within a single
theory. We find that the widely-reported 9R-fcc transition is not allowed in
equilibrium thermodynamics, and in cases where it has been reported in
experiments (Li, Na), we show that DFT theory is also unable to predict it
Deep observations of the Super-CLASS super-cluster at 325 MHz with the GMRT: the low-frequency source catalogue
We present the results of 325 MHz GMRT observations of a super-cluster field,
known to contain five Abell clusters at redshift . We achieve a
nominal sensitivity of Jy beam toward the phase centre. We
compile a catalogue of 3257 sources with flux densities in the range
within the entire square degree
field of view. Subsequently, we use available survey data at other frequencies
to derive the spectral index distribution for a sub-sample of these sources,
recovering two distinct populations -- a dominant population which exhibit
spectral index trends typical of steep-spectrum synchrotron emission, and a
smaller population of sources with typically flat or rising spectra. We
identify a number of sources with ultra-steep spectra or rising spectra for
further analysis, finding two candidate high-redshift radio galaxies and three
gigahertz-peaked-spectrum radio sources. Finally, we derive the
Euclidean-normalised differential source counts using the catalogue compiled in
this work, for sources with flux densities in excess of Jy. Our
differential source counts are consistent with both previous observations at
this frequency and models of the low-frequency source population. These
represent the deepest source counts yet derived at 325 MHz. Our source counts
exhibit the well-known flattening at mJy flux densities, consistent with an
emerging population of star-forming galaxies; we also find marginal evidence of
a downturn at flux densities below Jy, a feature so far only seen
at 1.4 GHz.Comment: 25 pages, 18 figures, 10 tables. Accepted for publication in MNRA
Ecosystem processes at the watershed scale: Extending optimality theory from plot to catchment
The adjustment of local vegetation conditions to limiting soil water by either maximizing productivity or minimizing water stress has been an area of central interest in ecohydrology since Eagleson's classic study. This work has typically been limited to consider one-dimensional exchange and cycling within patches and has not incorporated the effects of lateral redistribution of soil moisture, coupled ecosystem carbon and nitrogen cycling, and vegetation allocation processes along topographic gradients. We extend this theory to the hillslope and catchment scale, with in situ and downslope feedbacks between water, carbon and nutrient cycling within a fully transient, distributed model. We explore whether ecosystem patches linked along hydrologic flow paths as a catena evolve to form an emergent pattern optimized to local climate and topographic conditions. Lateral hydrologic connectivity of a small catchment is calibrated with streamflow data and further tested with measured soil moisture patterns. Then, the spatial gradient of vegetation density within a small catchment estimated with fine-resolution satellite imagery and field measurements is evaluated with simulated vegetation growth patterns from different root depth and allocation strategies as a function of hillslope position. This is also supported by the correspondence of modeled and field measured spatial patterns of root depths and catchment-level aboveground vegetation productivity. We test whether the simulated spatial pattern of vegetation corresponds to measured canopy patterns and an optimal state relative to a set of ecosystem processes, defined as maximizing ecosystem productivity and water use efficiency at the catchment scale. Optimal carbon uptake ranges show effective compromises between multiple resources (water, light, and nutrients), modulated by vegetation allocation dynamics along hillslope gradient
Ecosystem processes at the watershed scale: extending optimality theory from plot to catchment
[1] The adjustment of local vegetation conditions to limiting soil water by either maximizing productivity or minimizing water stress has been an area of central interest in ecohydrology since Eagleson's classic study. This work has typically been limited to consider one-dimensional exchange and cycling within patches and has not incorporated the effects of lateral redistribution of soil moisture, coupled ecosystem carbon and nitrogen cycling, and vegetation allocation processes along topographic gradients. We extend this theory to the hillslope and catchment scale, with in situ and downslope feedbacks between water, carbon and nutrient cycling within a fully transient, distributed model. We explore whether ecosystem patches linked along hydrologic flow paths as a catena evolve to form an emergent pattern optimized to local climate and topographic conditions. Lateral hydrologic connectivity of a small catchment is calibrated with streamflow data and further tested with measured soil moisture patterns. Then, the spatial gradient of vegetation density within a small catchment estimated with fine-resolution satellite imagery and field measurements is evaluated with simulated vegetation growth patterns from different root depth and allocation strategies as a function of hillslope position. This is also supported by the correspondence of modeled and field measured spatial patterns of root depths and catchmentlevel aboveground vegetation productivity. We test whether the simulated spatial pattern of vegetation corresponds to measured canopy patterns and an optimal state relative to a set of ecosystem processes, defined as maximizing ecosystem productivity and water use efficiency at the catchment scale. Optimal carbon uptake ranges show effective compromises between multiple resources (water, light, and nutrients), modulated by vegetation allocation dynamics along hillslope gradient. Citation: Hwang, T., L. Band, and T. C. Hales (2009), Ecosystem processes at the watershed scale: Extending optimality theory from plot to catchment, Water Resour. Res., 45, W11425
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