9,022 research outputs found
A global low order spectral model designed for climate sensitivity studies
A two level, global, spectral model using pressure as a vertical coordinate is developed. The system of equations describing the model is nonlinear and quasi-geostrophic. A moisture budget is calculated in the lower layer only with moist convective adjustment between the two layers. The mechanical forcing of topography is introduced as a lower boundary vertical velocity. Solar forcing is specified assuming a daily mean zenith angle. On land and sea ice surfaces a steady state thermal energy equation is solved to calculate the surface temperature. Over the oceans the sea surface temperatures are prescribed from the climatological average of January. The model is integrated to simulate the January climate
Characterising Place by Scene Depth
Turner and Penn introduced the notion of integration of isovist fields as a means to understand such fields syntactically - as a set of components with a structural
relationship to a global whole (1999). This research was further refined to put forward the concept of visibility graph analysis (VGA) as a tool for architectural analysis (Turner, Doxa, O’sullivan, & Penn, 2001), which has become widely used. We suggest a complementary method of characterising place that does not make use of integration or a graph yet which allows - as visibility graph analysis does - discrete view points to be dimensioned in relation to a set of such viewpoints. In our method, Principal Component Analysis (PCA), a statistical technique, is employed to infer salient characteristics of a set of views and then to situate these component views within a low dimensional space in order to compare the extent to which each
view corresponds to these characteristics. We demonstrate the method by reference to two distinct urban areas with differing spatial characteristics. Because PCA
operates on vectors, order of the data has important implications. We consider some of these implications including view orientation and chirality (handedness) and
assess the variance of results with regard to these factors
On a Kelvin-Voigt Viscoelastic Wave Equation with Strong Delay
An initial-boundary value problem for a viscoelastic wave equation subject to
a strong time-localized delay in a Kelvin & Voigt-type material law is
considered. Transforming the equation to an abstract Cauchy problem on the
extended phase space, a global well-posedness theory is established using the
operator semigroup theory both in Sobolev-valued - and BV-spaces. Under
appropriate assumptions on the coefficients, a global exponential decay rate is
obtained and the stability region in the parameter space is further explored
using the Lyapunov's indirect method. The singular limit is
further studied with the aid of the energy method. Finally, a numerical example
from a real-world application in biomechanics is presented.Comment: 34 pages, 4 figures, 1 set of Matlab code
Effects of Force Level and Hand Dominance on Bilateral Transfer of a Fine Motor Skill
Our research is about bilateral transfer, a concept in motor learning where skills
learned by one limb are "transferred", allowing the opposite limb to benefit from what
was learned by the first limb. Previous research into bilateral transfer has raised
questions about whether specific aspects of motor coordination are or are not
transferred. We wanted to see whether learning to control pinch force by the thumb
and index finger is transferable, and if it is, whether the learning transfers equally
from either hand. We also want to look into the effects of different force levels on
the degree of transfer. We designed a task using a program that takes force levels
as inputs and has the participant trace shapes on a screen. By having participants
perform with one hand, then practice with the other, and finally perform again with
the initial hand, we can measure transfer as the difference in performance before
and after practice with the other hand.Kinesiology and Health Educatio
Feshbach resonances in the 6Li-40K Fermi-Fermi mixture: Elastic versus inelastic interactions
We present a detailed theoretical and experimental study of Feshbach
resonances in the 6Li-40K mixture. Particular attention is given to the
inelastic scattering properties, which have not been considered before. As an
important example, we thoroughly investigate both elastic and inelastic
scattering properties of a resonance that occurs near 155 G. Our theoretical
predictions based on a coupled channels calculation are found in excellent
agreement with the experimental results. We also present theoretical results on
the molecular state that underlies the 155G resonance, in particular concerning
its lifetime against spontaneous dissociation. We then present a survey of
resonances in the system, fully characterizing the corresponding elastic and
inelastic scattering properties. This provides the essential information to
identify optimum resonances for applications relying on interaction control in
this Fermi-Fermi mixture.Comment: Submitted to EPJD, EuroQUAM special issues "Cold Quantum Matter -
Achievements and Prospects", v2 with updated calibration of magnetic field
(+4mG correction) and updated figures 4 and
Contexts can be Cheap: Solving Stochastic Contextual Bandits with Linear Bandit Algorithms
In this paper, we address the stochastic contextual linear bandit problem,
where a decision maker is provided a context (a random set of actions drawn
from a distribution). The expected reward of each action is specified by the
inner product of the action and an unknown parameter. The goal is to design an
algorithm that learns to play as close as possible to the unknown optimal
policy after a number of action plays. This problem is considered more
challenging than the linear bandit problem, which can be viewed as a contextual
bandit problem with a \emph{fixed} context. Surprisingly, in this paper, we
show that the stochastic contextual problem can be solved as if it is a linear
bandit problem. In particular, we establish a novel reduction framework that
converts every stochastic contextual linear bandit instance to a linear bandit
instance, when the context distribution is known. When the context distribution
is unknown, we establish an algorithm that reduces the stochastic contextual
instance to a sequence of linear bandit instances with small misspecifications
and achieves nearly the same worst-case regret bound as the algorithm that
solves the misspecified linear bandit instances.
As a consequence, our results imply a high-probability
regret bound for contextual linear bandits, making progress in resolving an
open problem in (Li et al., 2019), (Li et al., 2021).
Our reduction framework opens up a new way to approach stochastic contextual
linear bandit problems, and enables improved regret bounds in a number of
instances including the batch setting, contextual bandits with
misspecifications, contextual bandits with sparse unknown parameters, and
contextual bandits with adversarial corruption
Nephrogenic systemic fibrosis risk and liver disease.
Objective. Evaluate the incidence of nephrogenic systemic fibrosis (NSF) in patients with liver disease in the peritransplant period. Materials and Methods. This IRB approved study retrospectively reviewed patients requiring transplantation for cirrhosis, hepatocellular carcinoma (HCC), or both from 2003 to 2013. Records were reviewed identifying those having gadolinium enhanced MRI within 1 year of posttransplantation to document degree of liver disease, renal disease, and evidence for NSF. Results. Gadolinium-enhanced MRI was performed on 312 of 837 patients, including 23 with severe renal failure (GFR < 30 mL/min/1.73 cm(2)) and 289 with GFR > 30. Two of 23 patients with renal failure developed NSF compared to zero NSF cases in 289 patients with GFR > 30 (0/289; P < 0.003). High dose gadodiamide was used in the two NSF cases. There was no increased incidence of NSF with severe liver disease (1/71) compared to nonsevere liver disease (1/241; P = 0.412). Conclusion. Renal disease is a risk factor for NSF, but in our small sample our evidence suggests liver disease is not an additional risk factor, especially if a low-risk gadolinium agent is used. Noting that not all patients received high-risk gadolinium, a larger study focusing on patients receiving high-risk gadolinium is needed to further evaluate NSF risk in liver disease in the peritransplant period
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