Improving understanding of collusion in intermediate microeconomics

Standard treatments of collusion in intermediate microeconomics textbooks frequently involve a Cournot duopoly facing linear demand with constant marginal costs of production. These presentations leave students with the misunderstanding that firms jointly behaving like a single-firm monopolist and profit maximising collusion are one and the same. We present a simple and effective way for improving student comprehension of collusion; this exercise results in collusion where the duopolists produce more total output than that of a monopolist while enjoying greater joint profits. The exercise can be used to clarify and lead to a better understanding of collusion and profit maximisation.

Teaching Mixed Strategy Nash Equilibrium to Undergraduates

The authors present a simple and effective method for improving student comprehension of mixed strategies. After reviewing available texts, and with some trial and error, we feel that this method eases the teaching of the information and increases the students' ability to understand and retain concepts. Through a simple alteration to the normal form of a game, students can clearly see the results of employing mixed strategies, practise calculating expected payoffs, visualise the accompanying 'indifference' in the payoffs, and recognise the mixed strategy Nash equilibrium in a familiar way.

Bubbles and Experience: An Experiment on Speculation

We investigate experimentally how the share of experienced traders in double-auction asset markets affects trading, in particular the occurrence of bubble-crash pricing patterns. In each session, six subjects trade in three successive market rounds and gain experience. In a fourth round, depending on the treatment, two or four experienced subjects are replaced by inexperienced subjects. The results are compared to earlier findings when all traders were either inexperienced or experienced. We explore what can be learned by analogy between these laboratory findings and the performance of naturally occurring markets.Asset Market; Bubble; Crash; Experience; Experiment; Speculation

Higher Education Marketing Through Digital Community: Understanding the Motivations of Joining and Participating in University-Sponsored Communities and the Effect on Yield.

As enrollment goals and student informational resources increase, universities are scrambling to be more competitive in the marketplace and implement more effective enrollment strategies. Digital closed online communities are one new method universities are using to reach students. Using an online survey, the authors investigated the motivations behind why students join these communities and how they participate in them. In addition, the research also tested how variables correlated to and predicted a student’s behavioral intention to yield, or enroll at, the university. Findings expand Situational Theory of Problem Solving literature and establish connections between certain attributes and enrolling at the university. Specifically, students who had a clear plan to make their college decision, joined the closed online community, and reported more communicative action in the closed online community also reported a higher behavioral intention to enroll at the university associated with the app

Invariant manifolds, discrete mechanics, and trajectory design for a mission to Titan

With an environment comparable to that of primordial Earth, a surface strewn with liquid hydrocarbon lakes, and an atmosphere denser than that of any other moon in the solar system, Saturn's largest moon Titan is a treasure trove of potential scientific discovery and is the target of a proposed NASA mission scheduled for launch in roughly one decade. A chief consideration associated with the design of any such mission is the constraint imposed by fuel limitations that accompany the spacecraft's journey between celestial bodies. In this study, we explore the use of patched three-body models in conjunction with a discrete mechanical optimization algorithm for the design of a fuel-efficient Saturnian moon tour focusing on Titan. In contrast to the use of traditional models for trajectory design such as the patched conic approximation, we exploit subtleties of the three-body problem, a classic problem from celestial mechanics that asks for the motion of three masses in space under mutual gravitational interaction, in order to slash fuel costs. In the process, we demonstrate the aptitude of the DMOC (Discrete Mechanics and Optimal Control) optimization algorithm in handling celestial mechanical trajectory optimization problems

On the spectrum of hypergraphs

Here we study the spectral properties of an underlying weighted graph of a non-uniform hypergraph by introducing different connectivity matrices, such as adjacency, Laplacian and normalized Laplacian matrices. We show that different structural properties of a hypergrpah, can be well studied using spectral properties of these matrices. Connectivity of a hypergraph is also investigated by the eigenvalues of these operators. Spectral radii of the same are bounded by the degrees of a hypergraph. The diameter of a hypergraph is also bounded by the eigenvalues of its connectivity matrices. We characterize different properties of a regular hypergraph characterized by the spectrum. Strong (vertex) chromatic number of a hypergraph is bounded by the eigenvalues. Cheeger constant on a hypergraph is defined and we show that it can be bounded by the smallest nontrivial eigenvalues of Laplacian matrix and normalized Laplacian matrix, respectively, of a connected hypergraph. We also show an approach to study random walk on a (non-uniform) hypergraph that can be performed by analyzing the spectrum of transition probability operator which is defined on that hypergraph. Ricci curvature on hypergraphs is introduced in two different ways. We show that if the Laplace operator, $\Delta$, on a hypergraph satisfies a curvature-dimension type inequality $CD (\mathbf{m}, \mathbf{K})$ with $\mathbf{m}>1$ and $\mathbf{K}>0$ then any non-zero eigenvalue of $- \Delta$ can be bounded below by $\frac{ \mathbf{m} \mathbf{K}}{ \mathbf{m} -1 }$. Eigenvalues of a normalized Laplacian operator defined on a connected hypergraph can be bounded by the Ollivier's Ricci curvature of the hypergraph

Characterization of Lysine Mutagenesis in the Bacillus thuringiensis Insecticidal Crystal Protein Cry1Ab

Graduating with research distinction in biochemistryThe insecticidal crystal proteins, known as Cry toxins, are naturally derived from Bacillus thuringiensis and provide an environmentally safe form of pest control. Though these proteins have been studied extensively, little is known regarding their specific mechanism of action and any conformational changes associated with this mechanism. In an effort to design a mutant Cry1Ab toxin with two individual lysine and cysteine residues for fluorophore ligation, this study focuses on the characterization of the structural effects of lysine mutagenesis leading to future development of such a toxin. In this study, the three lysines of active Cry1Ab toxin are mutated to alanine in different combinations, and the structural effects of these mutations are monitored by SDS-PAGE, bioassay, and circular dichroism wavelength scanning. Structural analyses have revealed that mutation of lysine 490 to alanine results in a toxin with increased protease sensitivity that makes isolation of pure, active toxin by the standardized procedure extremely difficult. Mutations of the other lysine residues are shown to have a lesser effect on toxin structure. The observations of this study contribute to data regarding potential sites on Cry1Ab for ligation of functional groups, and the structural and functional effects of mutagenesis at these sites.No embarg

THE ONSET, CESSATION, AND RATE OF GROWTH OF LOBLOLLY PINES IN THE FACE EXPERIMENT

The Duke Forest FACE experiment was set up to investigate the impact of elevated CO2 levels on a larger eco system. One of the studies dealt with the impact of elevated CO2 levels on the onset and cessation of growth of loblolly pine trees (Pinus taeda L.). In this study the times of these events were determined for each year, 1996 - 2002. The rate of growth, the growth duration, and actual growth were determined from the models of onset and cessation of growth. Adjusted for initial basal area, the rate of growth, the actual growth, and the current basal area were slightly greater for elevated CO2 levels. There was no difference between the two CO2 levels for any of the time variables, onset, cessation, and growth period

Interaction of Seed Dispersal and Environmental Filtering Affects Woody Encroachment Patterns in Coastal Grassland

Encroachment of woody plants into grasslands has occurred worldwide and includes coastal ecosystems. This conversion process is mediated by seed dispersal patterns, environmental filtering, and biotic interactions. As spatiotemporally heterogeneous, harsh environments, barrier islands present a unique set of challenges for dispersal and establishment. Environmental conditions act as filters on dispersed seeds, thereby influencing encroachment and distribution patterns. Seldom have patterns of propagule dispersal been considered in the context of woody encroachment. We quantified dispersal and post‐dispersal processes of an encroaching woody population of Morella cerifera relative to directional rate of encroachment and observed distribution patterns on an Atlantic coastal barrier island with strong environmental filtering. We analyzed historic foredune elevation as a proxy for reduced interior environmental stress. The dispersal kernel was leptokurtic, a common characteristic of expanding populations, but rate of encroachment has slowed since 2005. Expansion pattern was related to foredune elevation, which limits encroachment below a threshold elevation. This difference between dispersal kernel behavior and encroachment rate is due to limited availability of suitable habitat for Morella and temporal variability in chlorides during the time of germination. Our results demonstrate that processes mediating seeds and seedling success must be accounted for to better understand establishment patterns of encroaching woody plants

Structural features and near infra-red (NIR) luminescence of isomeric Yb(iii) bipyridyl-N,N'-dioxide coordination polymers

The synthesis and structural characterization of a series of lanthanide complexes formed from YbX3 salts (X = NO3(-) or CF3SO3(-)) and the isomeric 4,4'-bipyridine-N,N'-dioxide (4,4'-bpdo) or 3,3'-bipyridine-N,N'-dioxide (3,3'-bpdo) ligands has been undertaken by X-ray crystallography. Depending on the choice of anion, the complexes isolated with L = 4,4'-bpdo yield either an extended 1D linear chain {[Yb(L)(NO3)3(CH3OH)]}∞ or a coordination polymer network {[Yb(L)4](CF3SO3)3}∞ which are isostructural with previously reported compounds using other Ln(iii) metals. The isomeric 3,3'-bpdo ligand yields a similar extended 1D linear chain {[Yb(L)(NO3)3(CH3OH)]}∞ when NO3(-) is used as the anion. However, when substituted by the typically non-coordinating CF3SO3(-) anion, inner sphere coordination yields a coordination polymer {[Yb(L)3(CF3SO3)](CF3SO3)2}∞ with a (2(2)·4(8)·6(5)) network topology. In an effort to rationalize the observed difference in coordinating behavior, DFT calculations of the isomeric bipyridyl-N,N'-dioxide ligands have been undertaken, but revealed no significant differences in the charge distribution of the coordinating N-oxide groups. Lastly, sensitized Yb(iii) emission in the Near Infra-Red (NIR) region operating via the well-known antennae effect has been observed and compared for two of the coordination polymers