in the absence of herbicides, cover crops play an important role for weed management in organic than in conventional farming. therefore, in order to evaluate the effects of cover crop management and plant density of buckwheat (fagopyrum esculentum) as cover crop on weed suppression, a field experiment was conducted at the research farm of university of zanjan, during the growing season of 2011....

Let G be a simple (i.e., no loops and no multiple edges) graph. We investigate the question of how to modify G combinatorially to obtain a sequentially CohenMacaulay graph. We focus on modifications given by adding configurations of whiskers to G, where to add a whisker one adds a new vertex and an edge connecting this vertex to an existing vertex in G. We give various sufficient conditions and...

Let G = (V,E) be a graph and R ⊆ E. A matching M in G is called R-feasible if the subgraph induced by the M -saturated vertices does not have an edge of R. We show that the general problem of finding a maximum size Rfeasible matching in G is NP-hard and identify several natural applications of this new concept. In particular, we use R-feasible matchings to give a necessary and sufficient condit...

A recurrent 2-dimensional (double) sequence t(m,n) is given by fixing particular sequences t(m, 0), t(0, n) as initial conditions and a rule of recurrence t(m,n) = t(a(m,n − 1), t(m − 1, n − 1), t(m − 1, n)) for m,n ≥ 1. We display such a sequence with values in the set {0, 1} and show that all rows are periodic and that the minimal period of the n-th row has length 2. We conclude that this 2-d...

This study concerns the relationship between gender and job performance among brokerage firm equity analysts. Women’s representation in analyst positions dropped from 16 percent in 1995 to 14 percent in 2005. The study found significant gender-based differences in performance on various dimensions. For example, women cover roughly 9 stocks, on average, as compared with 10 for men, and women’s e...

Let P be a simple polygon, and let Q be a set of points in P . We present an almostlinear time algorithm for computing a minimum cover of Q by disks that are contained in P . We then generalize the algorithm, so that it can compute a minimum cover of Q by homothets of any fixed compact convex set O of constant description complexity that are contained in P . This improves previous results of Ka...

a College of Earth, Ocean, and Atmospheric Science, Oregon State University, Corvallis, OR 97331, USA b Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada c Department of Geoscience, University of Wisconsin-Madison, 1215 West Dayton Street, Madison, WI 53706, USA d Department of Environmental, Earth & Atmospheric Sciences, University of Massac...

A k-dimensional box is the cartesian product R1 ×R2 × · · · ×Rk where each Ri is a closed interval on the real line. The boxicity of a graph G, denoted as box(G), is the minimum integer k such that G is the intersection graph of a collection of k-dimensional boxes. A unit cube in k-dimensional space or a k-cube is defined as the cartesian product R1 × R2 × · · · × Rk where each Ri is a closed i...