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Search Results: 1 - 10 of 302479 matches for " Kevin J. Mahoney "
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Increasing the Pensionable Age: What Changes Are OECD Countries Making? What Considerations Are Driving Policy?  [PDF]
Hila Axelrad, Kevin J. Mahoney
Open Journal of Social Sciences (JSS) , 2017, DOI: 10.4236/jss.2017.57005
Abstract: The average age of retirement used to be low in most countries due to numerous policies introduced 30 to 40 years ago which encouraged lower retirement ages. However, in response to the growth of the older segment of the population, increased life expectancy, the need for skilled workers, and the precarious financial state of public pension systems, pension reforms have been implemented in the U.S. and Europe, and are now geared towards improving employment rates for older workers, increasing retirement ages and pension eligibility. This paper surveys recent changes in retirement age and maps the changes that have occurred in the last decades using data from 34 OECD (The Organization for Economic Cooperation and Development) countries. This paper then reviews the arguments for and against these changes, the criteria for setting a certain retirement age, and the differences in statutory retirement age by gender, occupation, employment status, and other factors unique to particular countries. The purpose of this paper is to analyze current trends in terms of raising the pensionable age.
Community Structure in Large Networks: Natural Cluster Sizes and the Absence of Large Well-Defined Clusters
Jure Leskovec,Kevin J. Lang,Anirban Dasgupta,Michael W. Mahoney
Physics , 2008,
Abstract: A large body of work has been devoted to defining and identifying clusters or communities in social and information networks. We explore from a novel perspective several questions related to identifying meaningful communities in large social and information networks, and we come to several striking conclusions. We employ approximation algorithms for the graph partitioning problem to characterize as a function of size the statistical and structural properties of partitions of graphs that could plausibly be interpreted as communities. In particular, we define the network community profile plot, which characterizes the "best" possible community--according to the conductance measure--over a wide range of size scales. We study over 100 large real-world social and information networks. Our results suggest a significantly more refined picture of community structure in large networks than has been appreciated previously. In particular, we observe tight communities that are barely connected to the rest of the network at very small size scales; and communities of larger size scales gradually "blend into" the expander-like core of the network and thus become less "community-like." This behavior is not explained, even at a qualitative level, by any of the commonly-used network generation models. Moreover, it is exactly the opposite of what one would expect based on intuition from expander graphs, low-dimensional or manifold-like graphs, and from small social networks that have served as testbeds of community detection algorithms. We have found that a generative graph model, in which new edges are added via an iterative "forest fire" burning process, is able to produce graphs exhibiting a network community profile plot similar to what we observe in our network datasets.
Empirical Comparison of Algorithms for Network Community Detection
Jure Leskovec,Kevin J. Lang,Michael W. Mahoney
Computer Science , 2010,
Abstract: Detecting clusters or communities in large real-world graphs such as large social or information networks is a problem of considerable interest. In practice, one typically chooses an objective function that captures the intuition of a network cluster as set of nodes with better internal connectivity than external connectivity, and then one applies approximation algorithms or heuristics to extract sets of nodes that are related to the objective function and that "look like" good communities for the application of interest. In this paper, we explore a range of network community detection methods in order to compare them and to understand their relative performance and the systematic biases in the clusters they identify. We evaluate several common objective functions that are used to formalize the notion of a network community, and we examine several different classes of approximation algorithms that aim to optimize such objective functions. In addition, rather than simply fixing an objective and asking for an approximation to the best cluster of any size, we consider a size-resolved version of the optimization problem. Considering community quality as a function of its size provides a much finer lens with which to examine community detection algorithms, since objective functions and approximation algorithms often have non-obvious size-dependent behavior.
Pearl Harbor and Hiroshima : an Ironic Comparison = Pearl Harbor ve Hiro ima Sald rilar n n ronik bir Kar la t r lmas
Leo J. MAHONEY
Dogus University Journal , 2005,
Abstract: In the past century, veterans of America's wars have shown extraordinary human longevity in the postwar eras. As a result, contemporary public historical interpretations of the American second world war experience have been influenced by veterans' perceptions of historical issues for a longer time than was true of postwar eras before the twentieth centu y. Public historical debates in the United States have recently focused on the Japanese attack on Pearl Harbor (1941) and the American attacks on Hiroshima and Nagasaki (1945). These events may seem quite dated by now, but they have remarkable contemporary resonance in light of debates over proliferation of nuclear weapons and tactics of so-called pre-emptive warfare. Though the aerial attacks are often related in popular American perception, the truth is they were incommensurate events in terms of their military and political objectives, their physical scale and results, and the natures of their targets.
A Composition Formula for Asymptotic Morphisms
J. Matthew Mahoney
Mathematics , 2010,
Abstract: For graded $C^*$-algebras $A$ and $B$, we construct a semigroup ${\cal AP}(A,B)$ out of asymptotic pairs. This semigroup is similar to the semigroup $\Psi(A,B)$ of unbounded KK-modules defined by Baaj and Julg and there is a map $\Psi(A,B) \to {\cal AP}(A,B)$ when $B$ is stable. Furthermore, there is a natural semigroup homomorphism ${\cal AP}(A,B) \to E(A,B)$, where $E(A,B)$ is the E-theory group. We denote the image of this map $E'(A,B)$ and prove both that $E'(A,B)$ is a group and that the composition product of E-theory specializes to a composition product on these subgroups. Our main result is a formula for the composition product on $E'$ under certain operator-theoretic hypotheses about the asymptotic pairs being composed. This result is complementary to known results about the Kasparov product of unbounded KK-modules.
Invariant manifolds and the geometry of front propagation in fluid flows
Kevin A. Mitchell,John R. Mahoney
Physics , 2012, DOI: 10.1063/1.4746039
Abstract: Recent theoretical and experimental work has demonstrated the existence of one-sided, invariant barriers to the propagation of reaction-diffusion fronts in quasi-two-dimensional periodically-driven fluid flows. These barriers were called burning invariant manifolds (BIMs). We provide a detailed theoretical analysis of BIMs, providing criteria for their existence, a classification of their stability, a formalization of their barrier property, and mechanisms by which the barriers can be circumvented. This analysis assumes the sharp front limit and negligible feedback of the front on the fluid velocity. A low-dimensional dynamical systems analysis provides the core of our results.
A turnstile mechanism for fronts propagating in fluid flows
John R. Mahoney,Kevin A. Mitchell
Physics , 2013, DOI: 10.1063/1.4824675
Abstract: We consider the propagation of fronts in a periodically driven flowing medium. It is shown that the progress of fronts in these systems may be mediated by a turnstile mechanism akin to that found in chaotic advection. We first define the modified ("active") turnstile lobes according to the evolution of point sources across a transport boundary. We then show that the lobe boundaries may be constructed from stable and unstable \emph{burning invariant manifolds}---one-way barriers to front propagation analogous to traditional invariant manifolds for passive advection. Because the burning invariant manifolds (BIMs) are one-dimensional curves in a three-dimensional ($xy\theta$) phase space, their projection into $xy$-space exhibits several key differences from their advective counterparts: (lobe) areas are not preserved, BIMs may self-intersect, and an intersection between stable and unstable BIMs does not map to another such intersection. These differences must be accommodated in the correct construction of the new turnstile. As an application, we consider a lobe-based treatment protocol for protecting an ocean bay from an invading algae bloom.
Finite-time barriers to front propagation in two-dimensional fluid flows
John R. Mahoney,Kevin A. Mitchell
Physics , 2015,
Abstract: Recent theoretical and experimental investigations have demonstrated the role of certain invariant manifolds, termed burning invariant manifolds (BIMs), as one-way dynamical barriers to reaction fronts propagating within a flowing fluid. These barriers form one-dimensional curves in a two-dimensional fluid flow. In prior studies, the fluid velocity field was required to be either time-independent or time-periodic. In the present study, we develop an approach to identify prominent one-way barriers based only on fluid velocity data over a finite time interval, which may have arbitrary time-dependence. We call such a barrier a burning Lagrangian coherent structure (bLCS) in analogy to Lagrangian coherent structures (LCSs) commonly used in passive advection. Our approach is based on the variational formulation of LCSs using curves of stationary "Lagrangian shear", introduced by Farazmand, Blazevski, and Haller [Physica D 278-279, 44 (2014)] in the context of passive advection. We numerically validate our technique by demonstrating that the bLCS closely tracks the BIM for a time-independent, double-vortex channel flow with an opposing "wind".
Tolerance of Maize (Zea mays L.) and Soybean [Glycine max (L.) Merr.] to Late Applications of Postemergence Herbicides  [PDF]
Kris J. Mahoney, Robert E. Nurse, Peter H. Sikkema
Agricultural Sciences (AS) , 2014, DOI: 10.4236/as.2014.511109
Abstract: Seven maize (Zea mays L.) and three soybean [Glycine max (L.) Merr.] field experiments were conducted from 2006 to 2009 at various locations in southern Ontario, Canada to determine the tolerance of these crops to late applications of the maximum labeled herbicide dose. Single and sequential (simulating a spray overlap) applications were evaluated for visible injury, plant height, and crop yield in the absence of weed competition. Maize exhibited excellent tolerance to herbicides applied at the 9- to 10-leaf growth stage as visible injury levels for almost all tested herbicides was similar to the untreated control 7 days after treatment (DAT). However, the sequential application of dicamba/diflufenzopyr or foramsulfuron caused 6 and 8% injury 7 DAT and 8 and 14% reduction in maize height 28 DAT, respectively. The observed injury and stunting were transient as there were no differences in yield at harvest. Soybean displayed good tolerance to most herbicides applied at the 7th trifoliate leaf growth stage as visible injury levels were similar to the untreated control. However, thifensulfuron-methyl was injurious regardless of application and imazethapyr was injurious with sequential applications. For example, single thifensulfuron-methyl, sequential thifensulfuron-methyl, and sequential imazethapyr application treatments caused 35, 48, and 25% injury 7 DAT, respectively. Sequential thifensulfuron-methyl treatments also caused a 28 and 17% reduction in soybean height 14 and 28 DAT, respectively. Visual injury continued to be detected up to 56 DAT for single thifensulfuron-methyl, sequential thifensulfuron-methyl, and sequential imazethapyr treatments. But, soybean yields were reduced by 10% for only sequential thifensulfuron-methyl application treatments. For all other herbicides tested, the yields at harvest were similar to the untreated control. This research demonstrated that maize had exceptional tolerance to all the herbicides used in this study whereas soybean was tolerant to most of the herbicides used in this study.
Comparison of Glyphosate Formulations for Weed Control and Tolerance in Maize (Zea mays L.) and Soybean [Glycine max (L.) Merr.]  [PDF]
Kris J. Mahoney, Christy Shropshire, Peter H. Sikkema
Agricultural Sciences (AS) , 2014, DOI: 10.4236/as.2014.513142
Abstract:
Twenty-two field experiments (six maize (Zea mays L.) and five soybean [Glycine max (L.) Merr.] using low glyphosate doses to assess weed control and six maize and five soybean using high glyphosate doses to assess tolerance) were conducted from 2010 to 2012 at two locations in southern Ontario, Canada to compare the commercially available glyphosate formulations of Roundup Weather MAX?, Clearout?41 Plus, and Wise Up? (WeatherMAX, Clearout, and WiseUp, respectively). Inmaize and soybean, control of velvetleaf, pigweed species, common lambs quarters, and green foxtail 4 weeks after treatment (WAT) using 900 g·ae·ha-1 ranged from at least 85% to 99%, regardless of formulation. By 8 WAT with 900 g·ae·ha-1, control of these weeds generally declined, but still ranged from 82% to 97% across all formulations. At harvest, maize yields were similar to the weed-free control for 900 g·ae·ha-1 of glyphosate as WeatherMAX and Clearout; however, reduced weed control with WiseUp resulted in an 8.8% yield loss. For soybean, yields were similar to the weed-free control, regardless of formulation or dose. In the tolerance experiments, 2.1% and 2.8% injury was observed 4 WAT for maize treated with 3600 g·ae·ha-1 of glyphosate as WeatherMAX and WiseUp, respectively. However, maize yields were unaffected by glyphosate formulation or dose. In soybean, visible injury of 8.5%, 4.5%, and 3.7% was observed 1 WAT with 5400 g·ae·ha-1 of glyphosate as WeatherMAX, WiseUp, and Clearout, respectively; by 8 WAT, visible injury was similar to the untreated control, regardless of
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