Fresh-water dinoflagellates of Maryland

Collections were made in the summer of 1942 and again at different times in 1946 and 1947. Some collections were not sufficient in numbers to allow for proper identification, so the present paper does not give a complete list. Of the 20 identified species reported on in the paper, two are new to science and ten have not been reported previously for the United States

Influence of cardiac tissue anisotropy on re-entrant activation in computational models of ventricular fibrillation

The aim of this study was to establish the role played by anisotropic diffusion in (i) the number of filaments and epicardial phase singularities that sustain ventricular fibrillation in the heart, (ii) the lifetimes of filaments and phase singularities, and (iii) the creation and annihilation dynamics of filaments and phase singularities. A simplified monodomain model of cardiac tissue was used, with membrane excitation described by a simplified 3-variable model. The model was configured so that a single re-entrant wave was unstable, and fragmented into multiple re-entrant waves. Re-entry was then initiated in tissue slabs with varying anisotropy ratio. The main findings of this computational study are: (i) anisotropy ratio influenced the number of filaments Sustaining simulated ventricular fibrillation, with more filaments present in simulations with smaller values of transverse diffusion coefficient, (ii) each re-entrant filament was associated with around 0.9 phase singularities on the surface of the slab geometry, (iii) phase singularities were longer lived than filaments, and (iv) the creation and annihilation of filaments and phase singularities were linear functions of the number of filaments and phase singularities, and these relationships were independent of the anisotropy ratio. This study underscores the important role played by tissue anisotropy in cardiac ventricular fibrillation

ANOMALOUS SCALING OF THE PASSIVE SCALAR

We establish anomalous inertial range scaling of structure functions for a model of advection of a passive scalar by a random velocity field. The velocity statistics is taken gaussian with decorrelation in time and velocity differences scaling as $|x|^{\kappa/2}$ in space, with $0\leq\kappa < 2$. The scalar is driven by a gaussian forcing acting on spatial scale $L$ and decorrelated in time. The structure functions for the scalar are well defined as the diffusivity is taken to zero and acquire anomalous scaling behavior for large pumping scales $L$. The anomalous exponent is calculated explicitly for the 4^{\m\rm th} structure function and for small $\kappa$ and it differs from previous predictions. For all but the second structure functions the anomalous exponents are nonvanishing.Comment: 8 pages, late

The Royal City at War: The Military Mobilization of Guelph, Ontario during the First 18 Months of the Second World War

The story of a country at war can be told at various levels. Traditional histories speak of generals and statesmen, of decisions made in cabinet rooms, war rooms, and dimly-lit clubs. Others choose to concentrate upon particular instances or groups, such as the impact of the war upon women, a particular military unit, or even a specific family. This article seeks to combine those two traditions by examining the manner in which international events and political decisions made at the national level affected the way in which the nation’s military mobilization was carried out in one particular Canadian community

Infinitesimal invariants in a function algebra

Let G be a reductive connected linear algebraic group over an algebraically closed field of positive characteristic and let g be its Lie algebra. First we correct and generalise a well-known result about the Picard group of G. Then we prove that, if the derived group is simply connected and g satisfies a mild condition, the algebra K[G]^g of regular functions on G that are invariant under the action of g derived from the conjugation action, is a unique factorisation domain

Early afterdepolarisations and ventricular arrhythmias in cardiac tissue: a computational study

Afterdepolarisations are associated with arrhythmias in the heart, but are difficult to study experimentally. In this study we used a simplified computational model of 1D and 2D cardiac ventricular tissue, where we could control the size of the region generating afterdepolarisations, as well as the properties of the afterdepolarisation waveform. Provided the size of the afterdepolarisation region was greater than around 1 mm, propagating extrasystoles were produced in both 1D and 2D. The number of extrasystoles produced depended on the amplitude, period, and duration of the oscillatory EAD waveform. In 2D, re-entry was also initiated for specific combinations of EAD amplitude, period, and duration, with the afterdepolarisation region acting as a common pathway. The main finding from this modelling study is therefore that afterdepolarisations can act as potent sources of propagating extrasystoles, as well as a source of re-entrant activation

Determining optimal disassembly and recovery strategies

We present a stochastic dynamic programming algorithm fordetermining the optimal disassembly and recovery strategy, giventhe disassembly tree, the process dependent quality distributionsof assemblies, and the quality dependent recovery options andassociated profits for assemblies. This algorithm generalizes theone proposed by Krikke et al. \\cite{Krikke98} in two ways. First,there can be multiple disassembly processes. Second, partialdisassembly is allowed. Both generalizations are important forpractise.

An econometric evaluation of the firing of a coach on team performance

Firing the manager is a drastic measure employed by firms to deal with poor performance.However,data on within firm dynamics are scarce,and the firing of individual managers is rarely recorded in the firm level data currently available.This makes the val e of firing a manager difficult to assess. Data on sports offer a unique opportunity to study this phenomenon beca se the firing of a coach is usually well-publicized.Using data on soccer, the author evaluates the effect of the firing of a coach on team performance.As teams do not face the same opponents before and after a coach is fired, the issue of sample selectivity is addressed.

The multiple-job repair kit problem

The repair kit problem is that of finding the optimal set of partsin the kit of a repairman. An important aspect of this problem, inmany real-life situations, is that several job-sites are visitedbefore a kit is restocked. In this paper, we present twoheuristics for solving the multiple-job repair kit problem. Bothheuristics can be used to determine a solution under theservice-objective (minimal holding cost for a required job-fillrate) as well as the cost-objective (minimal expected total cost,including a penalty cost for each `broken' job). The `JobHeuristic (JH)' almost always determines the exact optimalsolution, as is shown in an extensive numerical experiment.However, it can not (easily) be used in cases where several partsof the same type may be needed on a job, or part failures aredependent, or the number of jobs in a tour varies. The `PartHeuristic (PH)' is simpler and easy to use in these cases also. Infact, it can be applied in a spreadsheet software package, as weillustrate. The numerical experiments show that it s leads tonear-optimal solutions (average `cost error' of less than 0.1 percent). Therefore, the PH is an excellent method for solving repairkit problems in practise.logistics;inventory;repair kit problem

Filament behavior in a computational model of ventricular fibrillation in the canine heart

The aim of this paper was to quantify the behavior of filaments in a computational model of re-entrant ventricular fibrillation. We simulated cardiac activation in an anisotropic monodomain with excitation described by the Fenton-Karma model with Beeler-Reuter restitution, and geometry by the Auckland canine ventricle. We initiated re-entry in the left and right ventricular free walls, as well as the septum. The number of filaments increased during the first 1.5 s before reaching a plateau with a mean value of about 36 in each simulation. Most re-entrant filaments were between 10 and 20 mm long. The proportion of filaments touching the epicardial surface was 65%, but most of these were visible for much less than one period of re-entry. This paper shows that useful information about filament dynamics can be gleaned from models of fibrillation in complex geometries, and suggests that the interplay of filament creation and destruction may offer a target for antifibrillatory therap