36,633 research outputs found
Predicting species abundance distributions by simultaneously using number and biomass as units of measurement
The universal observation that some species in an ecological community are common, but many more are rare, is neatly encapsulated in a species abundance distribution (SAD)1. However, the shape of the distribution can depend on the currency used to measure abundance 2. Here we show how the SADs for numerical abundance and biomass are related and how this relationship can be used to predict the form of the SAD. When plotted in log numerical abundance, log biomass space, species points lie within an approximately triangular area the limits of which are set by body size range, and the upper limit of abundance in both metrics. Under the simplifying, but reasonable, assumption that the observed scatter of species within this region is random, the shape of the SAD is immediately derived from simple geometrical considerations. For the SAD of numerical abundance this is a power curve. The biomass SAD can be either a power curve or, more frequently, a unimodal curve, which can approximate a log normal. This log triangular random placement model serves as a null hypothesis against which actual communities can be compared. Data from two intensively surveyed local communities indicate that it can give a good approximation, with species scattered within a triangle. Further, we can predict the consequences, for the SAD, of size-selective sampling protocols. We argue that mechanistic models of SADs must be able to account for the relative abundance of species in alternative currencies. Moreover, this approach will shed light on niche packing and may have application in environmental monitoring
A dual-beam actinic light source for photosynthesis research
Simulation of photosynthetic process in plants is accomplished by using two separate and identical optical channels that provide independently adjustable wavelengths (filters), shutter sequencing, and control intensity of illumination. In addition to experiments using electron paramagnetic resonance spectroscopy, system may be applicable to other types of research in photosynthetic field
Investigating the Potential of Fee-Based Recreation on Private Lands in the Lower Mississippi River Delta
Private landowners may be willing to allow public access for fee-based wildlife-associated recreation. A survey and econometric techniques are proposed to determine what characteristics may influence the probability to decide to offer recreation, what organizational form landowners may prefer to manage and market fee-based recreation, and how liability concerns and other possible disincentives collectively influence landowners' access decisions.wildlife-associated recreation, liability perceptions, Resource /Energy Economics and Policy,
Geometry-induced phase transition in fluids: capillary prewetting
We report a new first-order phase transition preceding capillary condensation
and corresponding to the discontinuous formation of a curved liquid meniscus.
Using a mean-field microscopic approach based on the density functional theory
we compute the complete phase diagram of a prototypical two-dimensional system
exhibiting capillary condensation, namely that of a fluid with long-ranged
dispersion intermolecular forces which is spatially confined by a substrate
forming a semi-infinite rectangular pore exerting long-ranged dispersion forces
on the fluid. In the T-mu plane the phase line of the new transition is
tangential to the capillary condensation line at the capillary wetting
temperature, Tcw. The surface phase behavior of the system maps to planar
wetting with the phase line of the new transition, termed capillary prewetting,
mapping to the planar prewetting line. If capillary condensation is approached
isothermally with T>Tcw, the meniscus forms at the capping wall and unbinds
continuously, making capillary condensation a second-order phenomenon. We
compute the corresponding critical exponent for the divergence of adsorption.Comment: 5 pages, 4 figures, 5 movie
Predictors of refusal to participate: a longitudinal health survey of the elderly in Australia
BACKGROUND:
The loss of participants in longitudinal studies due to non-contact, refusal or death can introduce bias into the results of such studies. The study described here examines reasons for refusal over three waves of a survey of persons aged ≥ 70 years.
METHODS:
In a longitudinal study involving three waves, participants were compared to those who refused to participate but allowed an informant to be interviewed and to those who refused any participation.
RESULTS:
At Wave 1 both groups of Wave 2 non-participants had reported lower occupational status and fewer years of education, had achieved lower verbal IQ scores and cognitive performance scores and experienced some distress from the interview. Those with an informant interview only were in poorer physical health than those who participated and those who refused. Depression and anxiety symptoms were not associated with non-participation. Multivariate analyses found that verbal IQ and cognitive impairment predicted refusal. Results were very similar for refusers at both Waves 2 and 3.
CONCLUSIONS:
Longitudinal studies of the elderly may over estimate cognitive performance because of the greater refusal rate of those with poorer performance. However, there is no evidence of bias with respect to anxiety or depression
Charge exchange contribution to the decay of the ring current, measured by energetic neutral atoms (ENAs)
In this paper we calculate the contribution of charge exchange to the decay of the ring current. Past works have suggested that charge exchange of ring current protons is primarily responsible for the decay of the ring current during the late recovery phase, but there is still much debate about the fast decay of the early recovery phase. We use energetic neutral atom (ENA) measurements from Polar to calculate the total ENA energy escape. To get the total ENA escape we apply a forward modeling technique, and to estimate the total ring current energy escape we use the Dessler-Parker-Sckopke relationship. We find that during the late recovery phase of the March 10, 1998 storm ENAs with energies greater than 17.5 keV can account for 75% of the estimated energy loss from the ring current. During the fast recovery the measured ENAs can only account for a small portion of the total energy loss. We also find that the lifetime of the trapped ions is significantly shorter during the fast recovery phase than during the late recovery phase, suggesting that different processes are operating during the two phases
Fabrication of Nano-Gapped Single-Electron Transistors for Transport Studies of Individual Single-Molecule Magnets
Three terminal single-electron transistor devices utilizing Al/Al2O3 gate
electrodes were developed for the study of electron transport through
individual single-molecule magnets. The devices were patterned via multiple
layers of optical and electron beam lithography. Electromigration induced
breaking of the nanowires reliably produces 1-3 nm gaps between which the SMM
can be situated. Conductance through a single Mn12(3-thiophenecarboxylate)
displays the coulomb blockade effect with several excitations within +/- 40
meV.Comment: 10 pages, 5 figure
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