1,747 research outputs found
Lignum-Vitae: A Study of the Woods of the Zygophyllaceae with Reference to the True Lignum-Vitae of Commerce--Its Sources, Properties, Uses, and Substitutes
The true lignum-vitae of commerce belongs to the family Zygophyllaceae, of which only three genera, namely, Guaiacum, Porlieria, and Bulnesia, have representatives of tree size, and these are confined to the tropical and sub-tropical regions of the Western Hemisphere. Porlieria is of no commerical importance
Handbook for estimating toxic fuel hazards
Computer program predicts, from readily available meteorological data, concentration and dosage fields downwind from ground-level and elevated sources of toxic fuel emissions. Mathematical model is applicable to hot plume rise from industrial stacks and should also be of interest to air pollution meteorologists
Boxwoods
True boxwood, commonly called Turkish boxwood, is derived from a small group of plants, of which the common evergreen ·box of our gardens is the type. To this group the famous botanist Linnaeus gave the generic name of Buxis, the Latin for box tree. He called the best known member of it Buxis sempervirens, which is\u27 but another form of Ovid\u27s buxus perpetuo virens, the evergreen box. For long this was considered the only species, though various forms and varieties came to be recognized, several of which have since been elevated by other botanists to specific rank
Cocobolo
Cocobolo is a valuable timber of commerce that has been in use in this country, particularly for handles of cutlery, for more than fifty years. It is produced by certain species of Dalbergia indigenous to Central America and southwestern Mexico. The present commercial sources are Panama, Costa Rica, and Nicaragua
The Evergreen Forests of Liberia: A Report on Investigations made in the West African Republic of Liberia by the Yale University School of Forestry in Cooperation with the Firestone Plantations Company
Liberia is a forested country and a large proportion of it is covered with what is popularly known as jungle. This is the region of abundant rainfall and the forests are evergreen. The term \u27evergreen\u27 refers to the fact that the forest appears in full leaf the year round and does not signify conifers, for in all the country there is not a Pine or Fir or Hemlock or Cedar, such as constitute the evergreen forests of the North. The West African forests are composed of broadleaf trees and palms
Understanding Copepod Life-history and Diversity Using a Next-generation Zooplankton Model
Evolution has shaped the physiology, life history, and behavior of a species to the physical conditions and to the communities of predators and prey within its range. Within a community, the number of species is determined by both physical properties such as temperature and biological properties like the magnitude and timing of primary productivity, and ecological interactions such as predation. Despite well-known correlations between diversity and properties such as temperature, the mechanisms that drive these correlations are not well-described, especially in the oceans. The investigators will conduct a model-based investigation of diversity patterns in marine ecosystems, focusing on calanoid copepods. Diversity changes on both sides of the Atlantic suggest three main hypotheses, relating copepod diversity to environmental stability, productivity, and size-based predation. To test these, the investigators will develop a novel model of copepod population dynamics. The model treats developmental stage and mass as continua, leading to a single partial differential equation for abundance as a function of stage and mass. This approach facilitates the use of algorithms from computational fluid mechanics to resolve numerical dispersion problems that characterize many copepod abundance models. This new modeling framework will be tested by building a model for the species Calanus finmarchicus and Pseudocalanus newmani to compare the results of the model with prior observations and models for two contrasting ecosystems, the Gulf of Maine and Gulf of St. Lawrence. The model formalizes trade-offs between temperature-dependent development, mass-dependent and temperature-dependent growth, and mass-dependent mortality. A series of 1-D simulations will be conducted, encompassing a range of environmental conditions. Each simulation will be initialized with many distinct species, where a species is described by a set of parameters specifying key physiological and life history parameters. These will be coupled to a nutrient-phytoplankton-microzooplankton model and integrated for many years. This procedure will produce a community of copepods adapted to conditions in each simulated environment. By studying how the modeled copepod communities respond to changes in physical conditions, productivity, and predation, mechanisms accounting for copepod diversity patterns will be tested.The project will lead to improved models for important copepod species that can be incorporated into ongoing and future ecosystem forecasts. The information on copepod biogeographic limits developed by this study could support estimates of copepod distributions under climate change. The model will be designed to work in a basin-scale model. By allowing adaption to physical and biological conditions, the emergent copepod communities should provide more realistic estimates of the impact of climate change. The project will support the professional development of one graduate student and one postdoctoral associate. It will also engage one undergraduate summer intern each year. Concepts related to this project will be communicated to the wider public on a blog at SeascapeModeling.org
Understanding Copepod Life-History and Diversity using a Next-Generation Zooplankton Model
The main goal of our project is to understand the patterns of diversity and biogeography in marine copepods. To achieve this goal, we developed a unique modeling framework to simulate the trade-offs between growth, development, and fecundity in marine copepods.
We developed a new approach to modeling growth and development in metazoans. We applied this approach to marine copepods, and used it to understand relationships between copepod body size and temperature, copepod biodiversity patterns, and copepod biogeography. This project also provided support for experiments to look at how copepod body size impacts the particle size spectrum.
We used our model to explain why marine copepods and other organisms with strong associations between body size and temperature should be expected to deviate from the temperature-diversity relationship that emerges from classic metabolic theory. We also used a novel emergent modeling approach to explore how temperature and chlorophyll cycles influence copepod biogeography
Torsional Directed Walks, Entropic Elasticity, and DNA Twist Stiffness
DNA and other biopolymers differ from classical polymers due to their
torsional stiffness. This property changes the statistical character of their
conformations under tension from a classical random walk to a problem we call
the `torsional directed walk'. Motivated by a recent experiment on single
lambda-DNA molecules [Strick et al., Science 271 (1996) 1835], we formulate the
torsional directed walk problem and solve it analytically in the appropriate
force regime. Our technique affords a direct physical determination of the
microscopic twist stiffness C and twist-stretch coupling D relevant for DNA
functionality. The theory quantitatively fits existing experimental data for
relative extension as a function of overtwist over a wide range of applied
force; fitting to the experimental data yields the numerical values C=120nm and
D=50nm. Future experiments will refine these values. We also predict that the
phenomenon of reduction of effective twist stiffness by bend fluctuations
should be testable in future single-molecule experiments, and we give its
analytic form.Comment: Plain TeX, harvmac, epsf; postscript available at
http://dept.physics.upenn.edu/~nelson/index.shtm
Thermal denaturation of fluctuating finite DNA chains: the role of bending rigidity in bubble nucleation
Statistical DNA models available in the literature are often effective models
where the base-pair state only (unbroken or broken) is considered. Because of a
decrease by a factor of 30 of the effective bending rigidity of a sequence of
broken bonds, or bubble, compared to the double stranded state, the inclusion
of the molecular conformational degrees of freedom in a more general mesoscopic
model is needed. In this paper we do so by presenting a 1D Ising model, which
describes the internal base pair states, coupled to a discrete worm like chain
model describing the chain configurations [J. Palmeri, M. Manghi, and N.
Destainville, Phys. Rev. Lett. 99, 088103 (2007)]. This coupled model is
exactly solved using a transfer matrix technique that presents an analogy with
the path integral treatment of a quantum two-state diatomic molecule. When the
chain fluctuations are integrated out, the denaturation transition temperature
and width emerge naturally as an explicit function of the model parameters of a
well defined Hamiltonian, revealing that the transition is driven by the
difference in bending (entropy dominated) free energy between bubble and
double-stranded segments. The calculated melting curve (fraction of open base
pairs) is in good agreement with the experimental melting profile of
polydA-polydT. The predicted variation of the mean-square-radius as a function
of temperature leads to a coherent novel explanation for the experimentally
observed thermal viscosity transition. Finally, the influence of the DNA strand
length is studied in detail, underlining the importance of finite size effects,
even for DNA made of several thousand base pairs.Comment: Latex, 28 pages pdf, 9 figure
OLFACTORY RESPONSES OF DEER MICE TO DOUGLAS-FIR SEED VOLATILES
An attempt was made to identify the olfactory cues produced by Douglas-fir seeds which attract deer mice (Peromyscus maniculatus) to the seeds. The olfactometers used are described, and the merits of different statistical analyses of the data are discussed. The odors produced by whole Douglas-fir seed and by the endosperm were preferred among the fractions tested to date. Deer mice were repelled by Douglas-fir turpentine, cedar oil, and, to a lesser degree, one extract
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