Conformal inversion and Maxwell field invariants in four- and six-dimensional spacetimes

Conformally compactified (3+1)-dimensional Minkowski spacetime may be identified with the projective light cone in (4+2)-dimensional spacetime. In the latter spacetime the special conformal group acts via rotations and boosts, and conformal inversion acts via reflection in a single coordinate. Hexaspherical coordinates facilitate dimensional reduction of Maxwell electromagnetic field strength tensors to (3+1) from (4 + 2) dimensions. Here we focus on the operation of conformal inversion in different coordinatizations, and write some useful equations. We then write a conformal invariant and a pseudo-invariant in terms of field strengths; the pseudo-invariant in (4+2) dimensions takes a new form. Our results advance the study of general nonlinear conformal-invariant electrodynamics based on nonlinear constitutive equations.Comment: 10 pages, birkjour.cls, submitted for the Proceedings of the XXXIInd Workshop on Geometric Methods in Physics, (Bialowieza, Poland, July 2013), v2: minor improvement

There is more to gesture than meets the eye: Visual attention to gesture’s referents cannot account for itsfacilitative effects during math instruction

Teaching a new concept with gestures – hand movements thataccompany speech – facilitates learning above-and-beyondinstruction through speech alone (e.g., Singer & Goldin-Meadow, 2005). However, the mechanisms underlying thisphenomenon are still being explored. Here, we use eyetracking to explore one mechanism – gesture’s ability todirect visual attention. We examine how children allocatetheir visual attention during a mathematical equivalencelesson that either contains gesture or does not. We show thatgesture instruction improves posttest performance, andadditionally that gesture does change how children visuallyattend to instruction: children look more to the problem beingexplained, and less to the instructor. However lookingpatterns alone cannot explain gesture’s effect, as posttestperformance is not predicted by any of our looking-timemeasures. These findings suggest that gesture does guidevisual attention, but that attention alone cannot account for itsfacilitative learning effects

There is More to Gesture Than Meets the Eye: Visual Attention to Gesture’s Referents Cannot Account for Its Facilitative Effects During Math Instruction

Teaching a new concept with gestures – hand movements that accompany speech – facilitates learning above-and-beyond instruction through speech alone (e.g., Singer & GoldinMeadow, 2005). However, the mechanisms underlying this phenomenon are still being explored. Here, we use eye tracking to explore one mechanism – gesture’s ability to direct visual attention. We examine how children allocate their visual attention during a mathematical equivalence lesson that either contains gesture or does not. We show that gesture instruction improves posttest performance, and additionally that gesture does change how children visually attend to instruction: children look more to the problem being explained, and less to the instructor. However looking patterns alone cannot explain gesture’s effect, as posttest performance is not predicted by any of our looking-time measures. These findings suggest that gesture does guide visual attention, but that attention alone cannot account for its facilitative learning effects

Prognostic significance of new onset ascites in patients with pancreatic cancer

BACKGROUND: The purpose of this study was to determine risk factors for development of malignant ascites and its prognostic significance in patients with pancreatic cancer. METHODS: A prospective database was queried to identify patients with pancreatic cancer who develop ascites. Stage at presentation, size, and location of primary tumor, treatment received and length of survival after onset of ascites were determined. RESULTS: A total of 15 patients were identified. Of which 4 patients (1 stage II, 3 stage III) underwent pancreaticoduodenectomy and manifested with ascites 2, 3, 24 and 47 months after surgery (tumor size 2.9 ± 1.32 cm). All but one of the remaining 11 patients (tumor size 4.4 ± 3.38 cm) presented with metastatic disease, and all developed malignant ascites 9 months after diagnosis, dying 2 months later. Resected patients lived longer before the onset of ascites, but not after. CONCLUSION: Once diagnosed, ascites in pancreatic cancer patients heralds imminent death. Limited survival should be considered when determining the aggressiveness of further intervention

Laparoscopic Drainage of a Hepatic Echinococcal Cyst: A Case Report

The Echinococcus granulosus tapeworm causes hepatic echinococcosis. It is endemic in the Mediterranean region, Middle East, and South America. Human infection is secondary to accidental consumption of ova in feces. Absorption through the bowel wall and entrance into the portal circulation leads to liver infection. This case involves a 34 y/o Moroccan male with an echinococcal liver cyst. His chief complaint was RUQ pain. The patient was treated with albendazole and praziquantel. His PMH and PSH was noncontributory. Patient was not on any other medications. ROS was otherwise unremarkable. The patient was AF VSS. He was tender to palpation in RUQ. Liver function tests were normal. Echinococcal titers were positive. CT demonstrated a large cystic lesion in the right lobe of the liver measuring 13.5 cm in diameter. The patient underwent successful laparoscopic drainage and excision of echinococcal cyst. Final pathology demonstrated degenerating parasites (E. granulosus) of echinococcal cyst

Generalizations of Nonlinear and Supersymmetric Classical Electrodynamics

We first write down a very general description of nonlinear classical electrodynamics, making use of generalized constitutive equations and constitutive tensors. Our approach includes non-Lagrangian as well as Lagrangian theories, allows for electromagnetic fields in the widest possible variety of media (anisotropic, piroelectric, chiral and ferromagnetic), and accommodates the incorporation of nonlocal effects. We formulate electric-magnetic duality in terms of the constitutive tensors. We then propose a supersymmetric version of the general constitutive equations, in a superfield approach.Comment: 15 pages, based on the presentation by G. A. Goldin at QTS

Freedom, Servitude and Voluntary Labor

We present an economic framework to revisit and reframe some important debates over the nature of free versus unfree labor and the economic consequences of emancipation. We use a simple general equilibrium model in which labor can be either free or coerced and where land and labor will be exchanged on markets that can be competitive or manipulated or via other non-market collusive arrangements. By working with variants of the same basic model under different assumptions about initial economy-wide factor endowments and asset ownership we can compare equilibrium distributional outcomes under different institutional and contractual arrangements including markets with free labor and free tenancy, slavery, and tenancy arrangements with tied labor-service obligations. Analysis of these different contractual and organizational forms yields insights that accord with common sense, but that are often overlooked or downplayed in academic debates, particularly amongst economists