678 research outputs found
Downy brome seed bank dynamics in southwestern Saskatchewan
Non-Peer ReviewedIn order to study downy brome seed bank dynamics, a burial experiment was established near Maple Creek in August 1987. Downy brome seed was buried at four depths (2.5 to 20 cm), and placed on the soil surface, in nylon mesh bags. Seed was exhumed at monthly intervals in the fall of 1987 and throughout the 1988 growing season. Seed germination in the field in the fall of 1987 was greatest from the buried seed (almost 50 %) while the surface seed exhibited little germination. This germination occurred in response to fall precipitation. Seed on the soil surface was not in contact with moist soil for a sufficient time to stimulate germination, so 80-90 % of this seed had not germinated by freeze-up in 1987. However the surface collected seed had germination of 34 % when transferred to an incubator in the laboratory, indicating environmentally induced dormancy in the field. There was little recruitment from the seed bank
occurred in the spring of 1988 in spite of favorable moisture and temperature conditions. Seed on the soil surface remained viable until the 14th month but the buried seed at all depths had either germinated or deteriorated by the 9th month. This study was repeated in 1988, with similar results to date
Incorporating Distributed Debris Thickness in a Glacio-Hydrological Model: Khumbu Himalaya, Nepal
Understanding the future evolution of Himalayan glaciers is important in terms of runoff that provides an essential water source to local populations and has far-reaching downstream impacts. However, the climatic response of glaciers in High-Mountain Asia is complicated by ice stagnation and considerable supraglacial debris coverage, which insulates the ice from warming. Typical runoff modelling only crudely incorporates debris cover and there is currently no consensus on how significantly this may impact future glacier and runoff evolution. Here, a glacio-hydrological model is modified to incorporate fully distributed debris cover, using melt reduction factors that vary depending on debris thickness, and to redistribute mass losses according to observed surface elevation changes. A range of debris thickness data are implemented, including a remote-sensing survey and a modelled debris surface, to analyse the sensitivity of glacier evolution and runoff to possible future debris-cover changes in a series of experiments in the upper Khumbu catchment, Nepal. Simulations are undertaken using climate input data from Regional Climate Model simulations from CORDEX (Coordinated Regional Downscaling Experiment) which are further statistically downscaled using data from the Pyramid meteorological station. Results suggest that the accurate calibration of the model to volume change compensates for the inclusion of distributed debris cover but only if the climatic sensitivity of the calibration period (1999–2010) and the nature of the debris-covered surface remain constant during future simulations. Altering the nature of the debris surface has a significant impact on simulated ice volume, with melt rates under debris suppressed by up to 85 %. The sensitivity of runoff ranges from 60 to 140 million m3 yr-1, although there are considerable uncertainties relating to non-glacial snow melt. Moreover, incorporating locally enhanced melt at ice cliffs into the model also impacts upon volume loss and discharge, with a greater proportion of ice cliffs leading to enhanced volume losses compared to a homogeneous debris surface. Finally, using the most representative model configuration, the future evolution of Khumbu Glacier under various climate scenarios shows continued mass losses with a reduction in volume ranging from 60 % to 97 % by 2100. Runoff trends show an initial increase followed by an eventual decrease, with runoff in 2100 predicted to be 8 % lower than current levels
Mapping the Minds of Retirement Planners
This study explored the psychological mechanisms that underlie the retirement planning and saving tendencies of Dutch and American workers. Participants were 988 Dutch and 429 Americans, 25-64 years of age. Analyses were designed to: (a) examine the extent to which structural variables were related to planning tendencies, and (b) develop culture-specific path analysis models to identify the mechanisms that underlie perceived financial preparedness for retirement. Findings revealed striking differences across the Netherlands and the United States not only among structural variables predictive of key psychological and retirement planning constructs, but also in the robustness of the path models. These findings suggest that policy analysts should take into account both individual and cultural differences in the psychological predispositions of workers when considering pension reforms that stress individual responsibility for planning and saving
A Point's Point of View of Stringy Geometry
The notion of a "point" is essential to describe the topology of spacetime.
Despite this, a point probably does not play a particularly distinguished role
in any intrinsic formulation of string theory. We discuss one way to try to
determine the notion of a point from a worldsheet point of view. The derived
category description of D-branes is the key tool. The case of a flop is
analyzed and Pi-stability in this context is tied in to some ideas of
Bridgeland. Monodromy associated to the flop is also computed via Pi-stability
and shown to be consistent with previous conjectures.Comment: 15 pages, 3 figures, ref adde
Ising (anti-)ferromagnet on dynamical triangulations and quadrangulations
We write down matrix models for Ising spins with zero external field on the
vertices of dynamical triangulated random surfaces (DTRS) and dynamically
quadrangulated random surfaces (DQRS) and compare these with the standard
matrix model approach which places the spins on the dual and
graphs. We show that the critical temperatures calculated in the DTRS and DQRS
models agree with those deduced from duality arguments in the standard
approach. Using the DQRS model we observe that the Ising antiferromagnet still
undergoes a phase transition to a Neel (checkerboard) ordered ground state
which is absent because of frustration in the other cases.Comment: 5 pages, late
Uptake of minimally invasive surgery and stereotactic body radiation therapy for early stage non-small cell lung cancer in the USA
BACKGROUND: We aimed to assess the uptake of minimally invasive surgery (MIS) and stereotactic body radiation therapy (SBRT) among early stage (stage IA-IIB) non-small cell lung cancer (NSCLC) cases in the USA, and the rate of conversions from MIS to open surgery. MATERIALS AND METHODS: Data were obtained from the US National Cancer Database, a nationwide facility-based cancer registry capturing up to 70% of incident cancer cases in the USA. We included cases diagnosed with early stage (clinical stages IA-IIB) NSCLC between 2010 and 2014. In an ecological analysis, we assessed changes in treatment by year of diagnosis. Among surgically treated cases, we assessed the uptake of MIS and whether conversion to open surgery took place. For cases that received thoracic radiotherapy, we assessed the uptake of SBRT. RESULTS: Among 117 370 selected cases, radiotherapy use increased 3.4 percentage points between 2010 and 2014 (p<0.0001). Surgical treatments decreased 3.5 percentage points (p<0.0001). Rates of non-treatment remained stable (range: 10.0%-10.6% (p=0.4066)). Among surgically treated stage IA cases, uptake of MIS increased from 28.7% (95% CI 27.8% to 29.7%) in 2010 to 48.6% (95% CI 47.6% to 49
Quasi-particle Lifetimes in a d_{x^2-y^2} Superconductor
We consider the lifetime of quasi-particles in a d-wave superconductor due to
scattering from antiferromagnetic spin-fluctuations, and explicitly separate
the contribution from Umklapp processes which determines the electrical
conductivity. Results for the temperature dependence of the total scattering
rate and the Umklapp scattering rate are compared with relaxation rates
obtained from thermal and microwave conductivity measurements, respectively.Comment: 14 pages, 4 figure
Surface Instability in Windblown Sand
We investigate the formation of ripples on the surface of windblown sand
based on the one-dimensional model of Nishimori and Ouchi [Phys. Rev. Lett. 71,
197 (1993)], which contains the processes of saltation and grain relaxation. We
carry out a nonlinear analysis to determine the propagation speed of the
restabilized ripple patterns, and the amplitudes and phases of their first,
second, and third harmonics. The agreement between the theory and our numerical
simulations is excellent near the onset of instability. We also determine the
Eckhaus boundary, outside which the steady ripple patterns are unstable.Comment: 23 pages, 8 figure
The cost of simplifying air travel when modeling disease spread
Background: Air travel plays a key role in the spread of many pathogens. Modeling the long distance spread of infectious disease in these cases requires an air travel model. Highly detailed air transportation models can be over determined and computationally problematic. We compared the predictions of a simplified air transport model with those of a model of all routes and assessed the impact of differences on models of infectious disease. Methodology/Principal Findings: Using U.S. ticket data from 2007, we compared a simplified "pipe" model, in which individuals flow in and out of the air transport system based on the number of arrivals and departures from a given airport, to a fully saturated model where all routes are modeled individually. We also compared the pipe model to a "gravity" model where the probability of travel is scaled by physical distance; the gravity model did not differ significantly from the pipe model. The pipe model roughly approximated actual air travel, but tended to overestimate the number of trips between small airports and underestimate travel between major east and west coast airports. For most routes, the maximum number of false (or missed) introductions of disease is small (<1 per day) but for a few routes this rate is greatly underestimated by the pipe model. Conclusions/Significance: If our interest is in large scale regional and national effects of disease, the simplified pipe model may be adequate. If we are interested in specific effects of interventions on particular air routes or the time for the disease to reach a particular location, a more complex point-to-point model will be more accurate. For many problems a hybrid model that independently models some frequently traveled routes may be the best choice. Regardless of the model used, the effect of simplifications and sensitivity to errors in parameter estimation should be analyzed
Quenching 2D Quantum Gravity
We simulate the Ising model on a set of fixed random graphs, which
corresponds to a {\it quenched} coupling to 2D gravity rather than the annealed
coupling that is usually considered. We investigate the critical exponents in
such a quenched ensemble and compare them with measurements on dynamical
graphs, flat lattices and a single fixed graph.Comment: 8 page
- …