Opportunities for Producing Table Grapes in Egypt for the Export Market: A Decision Case Study

The Barakat Fruit Farm desires to increase their share of the exportable grape market in Egypt. Unfortunately, the grape cultivars currently cultivated by the farm bear fruit after the early market window to the European Union when prices are high. An analysis of the company, competition, consumer, market channel, and conditions, provides insight into possible solutions to the challenges faced by the farm management. Designed for undergraduate classroom use, this case encourages students to think outside of traditional production techniques to arrive at solutions that are viable from both crop culture and financial standpoints.Decision case, horticulture, agriculture economics, grape production, Production Economics, Teaching/Communication/Extension/Profession, Q10, Q11,

Study of the magnetic and structural properties of Mn-, Fe-, and Co-doped ZnO powder

AbstractA study of the magnetic and structural properties of Zn1−xMxO powder (where x=0 or 0.01, and M=Mn, Fe or Co) produced by the proteic sol–gel process was undertaken. The sample crystal structure was analyzed by XRD and magnetic measurements were carried out in a SQUID magnetometer. Of the XRD analysis, all samples had hexagonal wurtzite crystal structure with P63mc space group, and no secondary phase was observed. It is observed of the M(H) measures at 2K, that the Co- and Mn-doped ZnO displayed saturation magnetizations (Ms) of approximately 2 and 3.2emu/g, respectively, and no remanence (Mr) was observed, indicating a superparamagnetic behavior in these samples. However, the Fe-doped sample showed a ferromagnetic behavior with Ms∼0.34emu/g, Mr∼0.05emu/g, and coercivity (Hc)∼1090Oe. Already at room temperature, the M(H) measurements reveal a purely paramagnetic behavior for Mn- and Fe-doped ZnO, indicating that the Curie temperature (Tc) is below 300K. However, a weak superparamagnetic behavior was observed in the Co-doped sample, indicating that Tc>300K

Self-serving dictators and economic growth

We study the effect of fair institutions on growth. In our model, individuals are endowed with unequal entitlements to the economy's output. They can free-ride or cooperate. Cooperation is individually costly, but increases aggregate output and growth. Experimentally, we observe significantly less cooperation, when dictators chose high instead of low inequality. This effect is not observed when the degree of inequality is chosen randomly. Simple cross-country regressions provide basic macroeconomic support for interaction effects between the degree and the genesis of inequality. We conclude that economies granting equal opportunities are less likely to suffer retarded growth due to free-riding than economies with self-serving dictators

Gauge Independence of IR singularities in Non-Commutative QFT - and Interpolating Gauges

IR divergences of a non-commutative U(1) Maxwell theory are discussed at the one-loop level using an interpolating gauge to show that quadratic IR divergences are independent not only from a covariant gauge fixing but also independent from an axial gauge fixing.Comment: 11 pages, 2 figures, v1 minor correction

Communautés, biomasses et productions algales au sein d'un récif artificiel (acadja) en milieu lagunaire tropical

Dans un secteur oligohalin et turbide de la lagune Ebrié (Côte d'Ivoire), les communautés phytoplanctonique et périphytique d'une structure d'aquaculture extensive, localement dénommée acadja (bambous plantés verticalement dans le sédiment), sont étudiées en termes de biomasses, productions, rendements énergétiques et composition spécifique. Lors de cette étude, la biomasse algale au sein de l'acadja constituée à 73% par du périphyton était 4 fois supérieure à celle des eaux libres lagunaires. L'assimilation autotrophe totale estimée à 9,9 g C.m-2.J-1 dans l'acadja était 4,5 fois supérieure à celle des eaux lagunaires et 80% de cette activité sont dus au peuplement périphytique... Compte tenu des forts rendements photosynthétiques des communautés fixées (5,2% pour le périphyton contre 0,8% pour le phytoplancton), l'acadja permet une augmentation sensible de la productivité naturelle du milieu lagunaire. Au sein d'une telle structure, l'élevage de poissons à régime alimentaire phytophage constituerait un mode de valorisation possible de ce surcroît de production autotrophe. (D'après résumé d'auteur

Long Range Hops and the Pair Annihilation Reaction A+A->0: Renormalization Group and Simulation

A simple example of a non-equilibrium system for which fluctuations are important is a system of particles which diffuse and may annihilate in pairs on contact. The renormalization group can be used to calculate the time dependence of the density of particles, and provides both an exact value for the exponent governing the decay of particles and an epsilon-expansion for the amplitude of this power law. When the diffusion is anomalous, as when the particles perform Levy flights, the critical dimension depends continuously on the control parameter for the Levy distribution. The epsilon-expansion can then become an expansion in a small parameter. We present a renormalization group calculation and compare these results with those of a simulation.Comment: As-published version; two significant errors fixed, two references adde

Gravitational waves from self-ordering scalar fields

Gravitational waves were copiously produced in the early Universe whenever the processes taking place were sufficiently violent. The spectra of several of these gravitational wave backgrounds on subhorizon scales have been extensively studied in the literature. In this paper we analyze the shape and amplitude of the gravitational wave spectrum on scales which are superhorizon at the time of production. Such gravitational waves are expected from the self ordering of randomly oriented scalar fields which can be present during a thermal phase transition or during preheating after hybrid inflation. We find that, if the gravitational wave source acts only during a small fraction of the Hubble time, the gravitational wave spectrum at frequencies lower than the expansion rate at the time of production behaves as $\Omega_{\rm GW}(f) \propto f^3$ with an amplitude much too small to be observable by gravitational wave observatories like LIGO, LISA or BBO. On the other hand, if the source is active for a much longer time, until a given mode which is initially superhorizon ($k\eta_* \ll 1$), enters the horizon, for $k\eta \gtrsim 1$, we find that the gravitational wave energy density is frequency independent, i.e. scale invariant. Moreover, its amplitude for a GUT scale scenario turns out to be within the range and sensitivity of BBO and marginally detectable by LIGO and LISA. This new gravitational wave background can compete with the one generated during inflation, and distinguishing both may require extra information.Comment: 21 pages, 2 figures, added discussion about numerical integration and a new figure to illustrate the scale-invariance of the GW power spectrum, conclusions unchange

A Vector Supersymmetry in Noncommutative U(1) Gauge Theory with the Slavnov Term

We consider noncommutative U(1) gauge theory with the additional term, involving a scalar field lambda, introduced by Slavnov in order to cure the infrared problem. we show that this theory, with an appropriate space-like axial gauge-fixing, wxhibits a linear vector supersymmetry similar to the one present in the 2-dimensional BF model. This vector supersymmetry implies that all loop corrections are independent of the $\lambda AA$-vertex and thereby explains why Slavnov found a finite model for the same gauge-fixing.Comment: 18 pages, 3 figures; v2 Acknowledgments adde

A Generalization of Slavnov-Extended Non-Commutative Gauge Theories

We consider a non-commutative U(1) gauge theory in 4 dimensions with a modified Slavnov term which looks similar to the 3-dimensional BF model. In choosing a space-like axial gauge fixing we find a new vector supersymmetry which is used to show that the model is free of UV/IR mixing problems, just as in the previously discussed model in arXiv:hep-th/0604154. Finally, we present generalizations of our proposed model to higher dimensions.Comment: 25 pages, no figures; v2 minor correction