COINTEGRATION, ERROR CORRECTION, AND THE MEASUREMENT OF OLIGOPSONY CONDUCT IN THE U.S. CATTLE MARKET

US cattle producers often claim that cattle prices are below competitive levels. In this paper, short-run and long-run oligopsony conduct is estimated by utilizing an oligopsony dynamic model. Results of time-series analysis indicate that the hypothesis of competitive conduct in the short-run and in the long-run cannot be rejected.Demand and Price Analysis,

Rumor Spreading on Random Regular Graphs and Expanders

Broadcasting algorithms are important building blocks of distributed systems. In this work we investigate the typical performance of the classical and well-studied push model. Assume that initially one node in a given network holds some piece of information. In each round, every one of the informed nodes chooses independently a neighbor uniformly at random and transmits the message to it. In this paper we consider random networks where each vertex has degree d, which is at least 3, i.e., the underlying graph is drawn uniformly at random from the set of all d-regular graphs with n vertices. We show that with probability 1 - o(1) the push model broadcasts the message to all nodes within (1 + o(1))C_d ln n rounds, where C_d = 1/ ln(2(1-1/d)) - 1/(d ln(1 - 1/d)). In particular, we can characterize precisely the effect of the node degree to the typical broadcast time of the push model. Moreover, we consider pseudo-random regular networks, where we assume that the degree of each node is very large. There we show that the broadcast time is (1+o(1))C ln n with probability 1 - o(1), where C= 1/ ln 2 + 1, is the limit of C_d as d grows.Comment: 18 page

IS PRICING ABOVE MARGINAL COST AN INDICATION OF MARKET POWER IN THE U.S. MEATPACKING INDUSTRY?

There have been concerns about the increasing concentration in the meat packing industry. But this increased concentration may be due to various types of cost economies. In this paper we prove the existence of scale economies that might justify the increased consolidation in the industry.Demand and Price Analysis,

The environment of the wind-wind collision region of η\eta Carinae

$\eta$ Carinae is a colliding wind binary hosting two of the most massive stars and featuring the strongest wind collision mechanical luminosity. The wind collision region of this system is detected in X-rays and $\gamma$-rays and offers a unique laboratory for the study of particle acceleration and wind magneto-hydrodynamics. Our main goal is to use X-ray observations of $\eta$ Carinae around periastron to constrain the wind collision zone geometry and understand the reasons for its variability. We analysed 10 Nuclear Spectroscopic Telescope Array (NuSTAR) observations, which were obtained around the 2014 periastron. The NuSTAR array monitored the source from 3 to 30 keV, which allowed us to grasp the continuum and absorption parameters with very good accuracy. We were able to identify several physical components and probe their variability. The X-ray flux varied in a similar way as observed during previous periastrons and largely as expected if generated in the wind collision region. The flux detected within ~10 days of periastron is lower than expected, suggesting a partial disruption of the central region of the wind collision zone. The Fe K$\alpha$ line is likely broadened by the electrons heated along the complex shock fronts. The variability of its equivalent width indicates that the fluorescence region has a complex geometry and that the source obscuration varies quickly with the line of sight.Comment: to be published in A&A, 7 pages, 9 figure

Going after the k-SAT Threshold

Random $k$-SAT is the single most intensely studied example of a random constraint satisfaction problem. But despite substantial progress over the past decade, the threshold for the existence of satisfying assignments is not known precisely for any $k\geq3$. The best current results, based on the second moment method, yield upper and lower bounds that differ by an additive $k\cdot \frac{\ln2}2$, a term that is unbounded in $k$ (Achlioptas, Peres: STOC 2003). The basic reason for this gap is the inherent asymmetry of the Boolean value `true' and `false' in contrast to the perfect symmetry, e.g., among the various colors in a graph coloring problem. Here we develop a new asymmetric second moment method that allows us to tackle this issue head on for the first time in the theory of random CSPs. This technique enables us to compute the $k$-SAT threshold up to an additive $\ln2-\frac12+O(1/k)\approx 0.19$. Independently of the rigorous work, physicists have developed a sophisticated but non-rigorous technique called the "cavity method" for the study of random CSPs (M\'ezard, Parisi, Zecchina: Science 2002). Our result matches the best bound that can be obtained from the so-called "replica symmetric" version of the cavity method, and indeed our proof directly harnesses parts of the physics calculations

On the Insertion Time of Cuckoo Hashing

Cuckoo hashing is an efficient technique for creating large hash tables with high space utilization and guaranteed constant access times. There, each item can be placed in a location given by any one out of k different hash functions. In this paper we investigate further the random walk heuristic for inserting in an online fashion new items into the hash table. Provided that k > 2 and that the number of items in the table is below (but arbitrarily close) to the theoretically achievable load threshold, we show a polylogarithmic bound for the maximum insertion time that holds with high probability.Comment: 27 pages, final version accepted by the SIAM Journal on Computin