Canonical pure spinor (Fermionic) T-duality

We establish that the recently discovered fermionic T-duality can be viewed as a canonical transformation in phase space. This requires a careful treatment of constrained Hamiltonian systems. Additionally, we show how the canonical transformation approach for bosonic T-duality can be extended to include Ramond--Ramond backgrounds in the pure spinor formalism.Comment: 14 page

Renormalization of Lorentz non-invariant actions and manifest T-duality

We study general two-dimensional sigma-models which do not possess manifest Lorentz invariance. We show how demanding that Lorentz invariance is recovered as an emergent on-shell symmetry constrains these sigma-models. The resulting actions have an underlying group-theoretic structure and resemble Poisson-Lie T-duality invariant actions. We consider the one-loop renormalization of these models and show that the quantum Lorentz anomaly is absent. We calculate the running of the couplings in general and show, with certain non-trivial examples, that this agrees with that of the T-dual models obtained classically from the duality invariant action. Hence, in these cases solving constraints before and after quantization are commuting operations.Comment: V2: reference added, version to appear in Nucl. Phys.

Chen ranks and resonance

The Chen groups of a group $G$ are the lower central series quotients of the maximal metabelian quotient of $G$. Under certain conditions, we relate the ranks of the Chen groups to the first resonance variety of $G$, a jump locus for the cohomology of $G$. In the case where $G$ is the fundamental group of the complement of a complex hyperplane arrangement, our results positively resolve Suciu's Chen ranks conjecture. We obtain explicit formulas for the Chen ranks of a number of groups of broad interest, including pure Artin groups associated to Coxeter groups, and the group of basis-conjugating automorphisms of a finitely generated free group.Comment: final version, to appear in Advances in Mathematic

PRICE TRANSMISSION, THRESHOLD BEHAVIOR, AND ASYMMETRIC ADJUSTMENT IN THE U.S. PORK SECTOR

The US pork sector has experienced many significant structural changes in recent years. Such changes may have influenced price dynamics and transmission of shocks through marketing channels. We investigate linkages among farm, wholesale, and retail markets using weekly price data for the period covering 1987 through 1998. Our analysis uses a threshold cointegration model that permits asymmetric adjustment to positive and negative price shocks. Our results reveal important asymmetries. Our results are consistent with existing literature which has determined that price adjustment patterns are unidirectional and that information tends to flow from farm, to wholesale, to retail markets.asymmetric price transmission, vertical price transmission, error correction, thresholds, pork markets, Demand and Price Analysis, Livestock Production/Industries,

Stable quantum memories with limited measurement

We demonstrate the existence of a finite temperature threshold for a 1D stabilizer code under an error correcting protocol that requires only a fraction of the syndrome measurements. Below the threshold temperature, encoded states have exponentially long lifetimes, as demonstrated by numerical and analytical arguments. We sketch how this algorithm generalizes to higher dimensional stabilizer codes with string-like excitations, like the toric code.Comment: 11 Pages, 7 Figure

A Sufficient Condition for Power Flow Insolvability with Applications to Voltage Stability Margins

For the nonlinear power flow problem specified with standard PQ, PV, and slack bus equality constraints, we present a sufficient condition under which the specified set of nonlinear algebraic equations has no solution. This sufficient condition is constructed in a framework of an associated feasible, convex optimization problem. The objective employed in this optimization problem yields a measure of distance (in a parameter set) to the power flow solution boundary. In practical terms, this distance is closely related to quantities that previous authors have proposed as voltage stability margins. A typical margin is expressed in terms of the parameters of system loading (injected powers); here we additionally introduce a new margin in terms of the parameters of regulated bus voltages.Comment: 12 pages, 7 figure

Improving Information and Performance in Grain Marketing: an Assessment of Current Market Information Systems, and Recommendations for Developing a Public Grain MIS

This paper focuses on one dimension which is at the core of all modern economies: how to provide private and public agents with timely and accurate information regarding current and expected future market conditions. Its objective is to show the need for a public market information system for agricultural markets in Ethiopia, and to present concrete proposals that can be reviewed, debated, and modified as necessary by the relevant Ethiopian authorities in collaboration with Food Security Research Project (FSRP) personnel.food security, food policy, Crop Production/Industries, Marketing, Q18,

On resonance line profiles predicted by radiation driven disk wind models

We report on resonance line profiles predicted by radiation driven disk wind models which extend radially one order of magnitude farther out than our previous models. Our main result is that the inclusion of a disk wind at larger radii changes qualitatively and quantitatively the line profiles predicted by the models. Our new models predict line absorption that is significantly stronger than those predicted by old models. Some of the previous line profiles exhibit a doubled-humped structure near the line center which is now replaced by a more plausible single, blueshifted minimum. We emphasize that the improvements in the shape as well as the strength of the absorption were achieved without changing the gross properties of the wind. In particular, our new models do not predict a higher mass-loss rate than the previous models. The main changes in the line profiles are due to the fact that the ratio between the rotational velocity and poloidal velocity of the wind decreases downstream. The new line profiles reproduce well the line absorption of the nova-like variable, IX~Vel, and promise to reproduce observations of other cataclysmic variables. This success of the radiation driven disk wind model provides an important link between outflows in OB stars and outflows in active galactic nuclei.Comment: to appear in ApJ Lette