1,042 research outputs found
Recommended from our members
Evapotranspiration Mapping for Forest Management in California's Sierra Nevada
We assessed the response of densely forested watersheds with little apparent annual water limitation to forest disturbance
and climate variability, by studying how past wildfires changed forest evapotranspiration, and what past evapotranspiration
patterns imply for the availability of subsurface water storage for drought resistance. We determined annual spatial patterns
of evapotranspiration using a top-down statistical model, correlating measured annual evapotranspiration from eddycovariance
towers across California with NDVI (Normalized Difference Vegetation Index) measured by satellite, and with
annual precipitation. The study area was the Yuba and American River watersheds, two densely forested watersheds in the
northern Sierra Nevada. Wildfires in the 1985-2015 period resulted in significant post-fire reductions in evapotranspiration
for at least 5 years, and in some cases for more than 20 years. The levels of biomass removed in medium-intensity fires (25-
75% basal area loss), similar to magnitudes expected from forest treatments for fuels reduction and forest health, reduced
evapotranspiration by as much 150-200 mm yr-1 for the first 5 years. Rates of recovery in post-wildfire evapotranspiration
confirm the need for follow-up forest treatments at intervals of 5-20 years to sustain lower evapotranspiration, depending
on local landscape attributes and interannual climate. Using the metric of cumulative precipitation minus evapotranspiration
(P-ET) during multi-year dry periods, we found that forests in the study area showed little evidence of moisture stress
during the 1985-2018 period of our analysis, owing to relatively small reliance on interannual subsurface water storage to
meet dry-year evapotranspiration needs of vegetation. However, more-severe or sustained drought periods will push some
lower-elevation forests in the area studied toward the cumulative P-ET thresholds previously associated with widespread
forest mortality in the southern Sierra Nevada
Glass bead shot peening retards stress corrosion failure of titanium tanks
Rigidly controlled shot peening retards the incompatibility between titanium alloys and nitrogen tetroxide in rocket-propellant storage tanks. This sets up a residual compressive stress in the surface of a material which reduces tensile stresses in the material fibers, alleviating stress corrosion
Controlled glass bead peening Patent
Method and apparatus for inducing compressive stresses in pressure vessel to prevent stress corrosio
Level Set Approach to Reversible Epitaxial Growth
We generalize the level set approach to model epitaxial growth to include
thermal detachment of atoms from island edges. This means that islands do not
always grow and island dissociation can occur. We make no assumptions about a
critical nucleus. Excellent quantitative agreement is obtained with kinetic
Monte Carlo simulations for island densities and island size distributions in
the submonolayer regime.Comment: 7 pages, 9 figure
Darwin\u27s Bee-Trap: The Kinetics of Catasetum, a New World Orchid
The orchid genera Catasetum employs a hair-trigger activated, pollen release mechanism, which forcibly attaches pollen sacs onto foraging insects in the New World tropics. This remarkable adaptation was studied extensively by Charles Darwin and he termed this rapid response sensitiveness. Using high speed video cameras with a frame speed of 1000 fps, this rapid release was filmed and from the subsequent footage, velocity, speed, acceleration, force and kinetic energy were computed
Epitaxial Growth Kinetics with Interacting Coherent Islands
The Stranski-Krastanov growth kinetics of undislocated (coherent)
3-dimensional islands is studied with a self-consistent mean field rate theory
that takes account of elastic interactions between the islands. The latter are
presumed to facilitate the detachment of atoms from the islands with a
consequent decrease in their average size. Semi-quantitative agreement with
experiment is found for the time evolution of the total island density and the
mean island size. When combined with scaling ideas, these results provide a
natural way to understand the often-observed initial increase and subsequent
decrease in the width of the coherent island size distribution.Comment: 4 pages, 4 figure
Profile scaling in decay of nanostructures
The flattening of a crystal cone below its roughening transition is studied
by means of a step flow model. Numerical and analytical analyses show that the
height profile, h(r,t), obeys the scaling scenario dh/dr = F(r t^{-1/4}). The
scaling function is flat at radii r<R(t) \sim t^{1/4}. We find a one parameter
family of solutions for the scaling function, and propose a selection criterion
for the unique solution the system reaches.Comment: 4 pages, RevTex, 3 eps figure
Dietary carbohydrate intake and high sensitivity C reactive protein in at-risk women and men
Background— The quality and quantity of dietary carbohydrate intake, measured as dietary glycemic load (GL), is associated with a number of cardiovascular disease (CVD) risk factors and, in healthy young women, is related to increased high sensitivity C-reactive protein (hsCRP) concentrations. Our objective was to determine if GL is related to hsCRP and other measures of CVD risk in a population of sedentary, overweight, dyslipidemic middle-aged women and men enrolled in an exercise intervention trial (STRRIDE).
Methods— This was a cross-sectional evaluation of the relationships between measures of dietary carbohydrate intake, calculated from food frequency questionnaire data, and CVD risk factors, including plasma hsCRP, measured in 171 subjects.
Results— After adjusting for energy intake, GL and other measures of carbohydrate intake were not independently related to hsCRP (P>0.05 for all). In analyses performed separately for each gender, only the quantity of carbohydrate intake was independently related to hsCRP (R2=0.28; P<0.04), and this relationship was present for women but not for men. The strongest relationship identified between GL and any CVD risk factor was for cardiorespiratory fitness (R2=0.12; P<0.02); an elevated GL was associated with a lower level of fitness in all subjects, and this relationship persisted even when the findings were adjusted for energy intake and gender (R2=0.48; P<0.03).
Conclusions— In middle-aged, sedentary, overweight to mildly obese, dyslipidemic individuals, consuming a diet with a low GL is associated with better cardiorespiratory fitness. Our findings suggest that the current literature relating carbohydrate intake and hsCRP should be viewed with skepticism, especially in the extension to at-risk populations that include men. Originally published American Heart Journal, Vol. 154, No. 5, Nov 200
Decay of one dimensional surface modulations
The relaxation process of one dimensional surface modulations is re-examined.
Surface evolution is described in terms of a standard step flow model.
Numerical evidence that the surface slope, D(x,t), obeys the scaling ansatz
D(x,t)=alpha(t)F(x) is provided. We use the scaling ansatz to transform the
discrete step model into a continuum model for surface dynamics. The model
consists of differential equations for the functions alpha(t) and F(x). The
solutions of these equations agree with simulation results of the discrete step
model. We identify two types of possible scaling solutions. Solutions of the
first type have facets at the extremum points, while in solutions of the second
type the facets are replaced by cusps. Interactions between steps of opposite
signs determine whether a system is of the first or second type. Finally, we
relate our model to an actual experiment and find good agreement between a
measured AFM snapshot and a solution of our continuum model.Comment: 18 pages, 6 figures in 9 eps file
A contiuum model for low temperature relaxation of crystal steps
High and low temperature relaxation of crystal steps are described in a
unified picture, using a continuum model based on a modified expression of the
step free energy. Results are in agreement with experiments and Monte Carlo
simulations of step fluctuations and monolayer cluster diffusion and
relaxation. In an extended model where mass exchange with neighboring terraces
is allowed, step transparency and a low temperature regime for unstable step
meandering are found.Comment: Submitted to Phys.Rev.Let
- …