2,484 research outputs found
Exciton resonances quench the photoluminescence of zigzag carbon nanotubes
We show that the photoluminescence intensity of single-walled carbon
nanotubes is much stronger in tubes with large chiral angles - armchair tubes -
because exciton resonances make the luminescence of zigzag tubes intrinsically
weak. This exciton-exciton resonance depends on the electronic structure of the
tubes and is found more often in nanotubes of the +1 family. Armchair tubes do
not necessarily grow preferentially with present growth techniques; they just
have stronger luminescence. Our analysis allows to normalize photoluminescence
intensities and find the abundance of nanotube chiralities in macroscopic
samples.Comment: 4 pages and 2 supplementary pages; 6 figure
Algebraic K-theory of group rings and the cyclotomic trace map
We prove that the Farrell-Jones assembly map for connective algebraic
K-theory is rationally injective, under mild homological finiteness conditions
on the group and assuming that a weak version of the Leopoldt-Schneider
conjecture holds for cyclotomic fields. This generalizes a result of
B\"okstedt, Hsiang, and Madsen, and leads to a concrete description of a large
direct summand of in terms
of group homology. In many cases the number theoretic conjectures are true, so
we obtain rational injectivity results about assembly maps, in particular for
Whitehead groups, under homological finiteness assumptions on the group only.
The proof uses the cyclotomic trace map to topological cyclic homology,
B\"okstedt-Hsiang-Madsen's functor C, and new general isomorphism and
injectivity results about the assembly maps for topological Hochschild homology
and C.Comment: To appear in Advances in Mathematics. 77 page
Exploring Movie Construction & Production: Whatâs So Exciting about Movies?
Exploring Movie Construction & Production contains eight chapters of the major areas of film construction and production. The discussion covers theme, genre, narrative structure, character portrayal, story, plot, directing style, cinematography, and editing. Important terminology is defined and types of analysis are discussed and demonstrated. An extended example of how a movie description reflects the setting, narrative structure, or directing style is used throughout the book to illustrate building blocks of each theme. This approach to film instruction and analysis has proved beneficial to increasing studentsâ learning, while enhancing the creativity and critical thinking of the student.https://knightscholar.geneseo.edu/oer-ost/1001/thumbnail.jp
SIMULATING OZONE EFFECTS ON FOREST PRODUCTIVITY: INTERACTIONS AMONG LEAFâ, CANOPYâ, AND STANDâLEVEL PROCESSES
Ozone pollution in the lower atmosphere is known to have adverse effects on forest vegetation, but the degree to which mature forests are impacted has been very difficult to assess directly. In this study, we combined leafâlevel ozone response data from independent ozone fumigation studies with a forest ecosystem model in order simulate the effects of ambient ozone on mature hardwood forests. Reductions in leaf carbon gain were determined as a linear function of ozone flux to the leaf interior, calculated as the product of ozone concentration and leaf stomatal conductance. This relationship was applied to individual canopy layers within the model in order to allow interaction with standâ and canopyâlevel factors such as light attenuation, leaf morphology, soil water limitations, and vertical ozone gradients.
The resulting model was applied to 64 locations across the northeastern United States using ambient ozone data from 1987 to 1992. Predicted declines in annual net primary production ranged from 3 to 16% with greatest reductions in southern portions of the region where ozone levels were highest, and on soils with high waterâholding capacity where drought stress was absent. Reductions in predicted wood growth were slightly greater (3â22%) because wood is a lower carbon allocation priority in the model than leaf and root growth. Interannual variation in predicted ozone effects was small due to concurrent fluctuations in ozone and climate. Periods of high ozone often coincided with hot, dry weather conditions, causing reduced stomatal conductance and ozone uptake. Withinâcanopy ozone concentration gradients had little effect on predicted growth reductions because concentrations remained high through upper canopy layers where net carbon assimilation and ozone uptake were greatest.
Sensitivity analyses indicate a tradeâoff between model sensitivity to available soil water and foliar nitrogen and demonstrate uncertainties regarding several assumptions used in the model. Uncertainties surrounding ozone effects on stomatal function and plant water use efficiency were found to have important implications on current predictions. Field measurements of ozone effects on mature forests will be needed before the accuracy of model predictions can be fully assessed
'Encore' Red Raspberry
'Encore' is a new red raspberry developed by Cornell University
at the New York State Agricultural Experiment Station in
Geneva, New York. 'Encore' is outstanding for its consistent
performance over many years of testing. 'Encore' is a late season
red raspberry cultivar developed for growers interested in
increasing their late season production. Specifically, it has excellent
winter hardiness in zone 5, very good plant production
and vigor, and commercial yields of large size fruit that peak in
production late in the harvest season. 'Encore' is adapted to upick,
retail, and wholesale markets. Its firm fruit withstand handling
and packing to produce an attractive pack for resale. 'Encore'
has potential to become a leading red raspberry cultivar
in the East Coast and Great Lakes regions
Relating multi-sequence longitudinal intensity profiles and clinical covariates in new multiple sclerosis lesions
Structural magnetic resonance imaging (MRI) can be used to detect lesions in
the brains of multiple sclerosis (MS) patients. The formation of these lesions
is a complex process involving inflammation, tissue damage, and tissue repair,
all of which are visible on MRI. Here we characterize the lesion formation
process on longitudinal, multi-sequence structural MRI from 34 MS patients and
relate the longitudinal changes we observe within lesions to therapeutic
interventions. In this article, we first outline a pipeline to extract voxel
level, multi-sequence longitudinal profiles from four MRI sequences within
lesion tissue. We then propose two models to relate clinical covariates to the
longitudinal profiles. The first model is a principal component analysis (PCA)
regression model, which collapses the information from all four profiles into a
scalar value. We find that the score on the first PC identifies areas of slow,
long-term intensity changes within the lesion at a voxel level, as validated by
two experienced clinicians, a neuroradiologist and a neurologist. On a quality
scale of 1 to 4 (4 being the highest) the neuroradiologist gave the score on
the first PC a median rating of 4 (95% CI: [4,4]), and the neurologist gave it
a median rating of 3 (95% CI: [3,3]). In the PCA regression model, we find that
treatment with disease modifying therapies (p-value < 0.01), steroids (p-value
< 0.01), and being closer to the boundary of abnormal signal intensity (p-value
< 0.01) are associated with a return of a voxel to intensity values closer to
that of normal-appearing tissue. The second model is a function-on-scalar
regression, which allows for assessment of the individual time points at which
the covariates are associated with the profiles. In the function-on-scalar
regression both age and distance to the boundary were found to have a
statistically significant association with the profiles
Predicting the effects of climate change on water yield and forest production in the northeastern United States
Rapid and simultaneous changes in temperature, precipitation and the atmospheric concentration of CO2 are predicted to occur over the next century. Simple, well-validated models of ecosystem function are required to predict the effects of these changes. This paper describes an improved version of a forest carbon and water balance model (PnET-II) and the application of the model to predict stand- and regional-level effects of changes in temperature, precipitation and atmospheric CO2 concentration. PnET-II is a simple, generalized, monthly time-step model of water and carbon balances (gross and net) driven by nitrogen availability as expressed through foliar N concentration. Improvements from the original model include a complete carbon balance and improvements in the prediction of canopy phenology, as well as in the computation of canopy structure and photosynthesis. The model was parameterized and run for 4 forest/site combinations and validated against available data for water yield, gross and net carbon exchange and biomass production. The validation exercise suggests that the determination of actual water availability to stands and the occurrence or non-occurrence of soil-based water stress are critical to accurate modeling of forest net primary production (NPP) and net ecosystem production (NEP). The model was then run for the entire NewEngland/New York (USA) region using a 1 km resolution geographic information system. Predicted long-term NEP ranged from -85 to +275 g C m-2 yr-1 for the 4 forest/site combinations, and from -150 to 350 g C m-2 yr-1 for the region, with a regional average of 76 g C m-2 yr-1. A combination of increased temperature (+6*C), decreased precipitation (-15%) and increased water use efficiency (2x, due to doubling of CO2) resulted generally in increases in NPP and decreases in water yield over the region
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