Probing the Circular Polarization of Relativistic Jets on VLBI Scales

High resolution studies of circular polarization allow us see where it arises in a jet, study its local fractional level and spectrum, and compare these results to local measures of linear polarization and Faraday rotation. Here we not only review past results from Very Long Baseline Array (VLBA) circular polarization studies, but we also present preliminary new results on two quasars. In the core of PKS 0607-157, we find strong circular polarization at 8 GHz and much weaker levels at 15 GHz. Combined with the linear polarization data, we favor a simple model where the circular is produced by Faraday conversion driven by a small amount of Faraday rotation. In the core of 3C345, we find strong circular polarization at 15 GHz in a component with distinct linear polarization. This core component is optically thick at 8 GHz, where we detect no circular polarization. With opposite trends in frequency for PKS 0607-157 and 3C345, it seems clear that local conditions in a jet can have a strong effect on circular polarization and need to be taken into account when studying inhomogeneous objects with multi-frequency observations.Comment: To appear in the proceedings of "Circular Polarization of Relativistic Jet Sources", eds R. P. Fender and J.-P. Macquart, in Astrophysics and Space Science. 11 pgs, 2 fig

Theoretical Models for Producing Circularly Polarized Radiation in Extragalactic Radio Sources

We discuss the production of circular polarization in compact radio sources both by the intrinsic mechanism and by Faraday conversion. We pay particular attention to the magnetic field structure, considering partially ordered fiel ds and Laing sheets, and distinguishing between uniform and unidirectional fields. (The latter can be constrained b y flux conservation arguments.) In most cases, Faraday conversion is the more important mechanism. Conversion opera tes on Stokes U, which can be generated by internal Faraday rotation, or by magnetic field fluctuations, which can therefore produce circular polarization even in a pure pair plasma. We also show that the spectrum of circular pola rization in an inhomogeneous jet can be quite different from that in a uniform source, being flat or even inverted.Comment: To appear in the proceedings of "Circular Polarization of Relativistic Jet Sources", eds R. P. Fender and J.-P. Macquart, in Astrophysics and Space Science. 12 pgs, 0 fig

Spatial Labor Markets and Technology Spillovers - Analysis from the US Midwest

In this paper we examine the relation between geographic location and innovative behavior. Knowledge spillins, as opposed to knowledge spillovers, are modeled as an externality which exists between geographically close economic agents and enters the representative inventor production function explicitly from neighboring regions. To proxy new innovative behavior and new knowledge generated we use counts of patent filings per county. The proposed geographic spillin is tested for the US Midwestern States of Iowa, Minnesota, Missouri, Kansas, Nebraska, South Dakota and North Dakota using a newly constructed data set and implementing spatial statistical methods. The data set is comprised of primary inventor utility patent filings per county for the years 1975-2000. The results do indeed suggest spatial interaction does occur and innovative activity in surrounding counties is an important factor in explaining new innovative behavior. Further analysis also reveals lagged patenting behavior within the county also has a significant impact on patenting activity suggesting innovative externalities exist over both space and time.patents; employment growth; technology spillovers; spatial spillovers

Metabotropic Glutamate Receptor Activation in Cerebelar Purkinje Cells as Substrate for Adaptive Timing of the Classicaly Conditioned Eye Blink Response

To understand how the cerebellum adaptively times the classically conditioned nictitating membrane response (NMR), a model of the metabotropic glutamate receptor (mGluR) second messenger system in cerebellar Purkinje cells is constructed. In the model slow responses, generated postsynaptically by mGluR-mediated phosphoinositide hydrolysis, and calcium release from intracellular stores, bridge the interstimulus interval (ISI) between the onset of parallel fiber activity associated with the conditioned stimulus (CS) and climbing fiber activity associated with unconditioned stimulus (US) onset. Temporal correlation of metabotropic responses and climbing fiber signals produces persistent phosphorylation of both AMPA receptors and Ca2+-dependent K+ channels. This is responsible for long-term depression (LTD) of AMPA receptors. The phosphorylation of Ca2+-dependent K+ channels leads to a reduction in baseline membrane potential and a reduction of Purkinje cell population firing during the CS-US interval. The Purkinje cell firing decrease disinhibits cerebellar nuclear cells which then produce an excitatory response corresponding to the learned movement. Purkinje cell learning times the response, while nuclear cell learning can calibrate it. The model reproduces key features of the conditioned rabbit NMR: Purkinje cell population response is properly timed, delay conditioning occurs for ISIs of up to four seconds while trace conditioning occurs only at shorter ISIs, mixed training at two different ISis produces a double-peaked response, and ISIs of 200-400ms produce maximal responding. Biochemical similarities between timed cerebellar learning and photoreceptor transduction, and circuit similarities between the timed cerebellar circuit and a timed dentate-CA3 hippocampal circuit, are noted.Office of Naval Research (N00014- 92-J-4015, N00014-92-J-1309, N00014-95-1-0409); Air Force Office of Scientific Research (F49620-92-J-0225);National Science Foundation (IRI-90-24877

A Neural Model of Timed Response Learning in the Cerebellum

A spectral timing model is developed to explain how the cerebellum learns adaptively timed responses during the rabbit's conditioned nictitating membrane response (NMR). The model posits two learning sites that respectively enable conditioned excitation and timed disinhibition of the response. Long-term potentiation of mossy fiber pathways projecting to interpositus nucleus cells allows conditioned excitation of the response's adaptive gain. Long-term depression of parallel fiber- Purkinje cell synapses in the cerebellar cortex allows learning of an adaptively timed reduction in Purkinje cell inhibition of the same nuclear cells. A spectrum of partially timed responses summate to generate an accurately timed population response. In agreement with physiological data, the model Purkinje cell activity decreases in the interval following the onset of the conditioned stimulus, and nuclear cell responses match conditioned response (CR) topography. The model reproduces key behavioral features of the NMR, including the properties that CR peak amplitude occurs at the unconditioned stimulus (US) onset, a discrete CR peak shift occurs with a change in interstimulus interval (ISI) between conditioned stim- ulus (CS) and US, mixed training at two different ISis produces a double-peaked CR, CR acquisition and rate of responding depend unimodally on the lSI, CR onset latency decreases during training, and maladaptively-timed, small-amplitude CRs result from ablation of cerebellar cortex.National Science Foundation (IRI-90-24877); Office of Naval Research (N00014-92-J-1309); Air Force Office of Scientific Research (F49620-92-J-0225

A finite element formulation for scattering from electrically large 2-dimensional structures

A finite element formulation is given using the scattered field approach with a fictitious material absorber to truncate the mesh. The formulation includes the use of arbitrary approximation functions so that more accurate results can be achieved without any modification to the software. Additionally, non-polynomial approximation functions can be used, including complex approximation functions. The banded system that results is solved with an efficient sparse/banded iterative scheme and as a consequence, large structures can be analyzed. Results are given for simple cases to verify the formulation and also for large, complex geometries

Testing the General Validity of the Heckscher-Ohlin Theorem: The Natural Experiment of Japan

We exploit Japan's 19th century opening up to trade to test a general formulation of the Heckscher-Ohlin theorem. This formulation is based on Ohlin's measure of factor scarcity where autarky factor prices impose a refutable prediction on the economy's factor content of trade. Our test combines factor price data in Japan's autarky period with commodity trade data and a technology matrix in Japan's early free trade period. Our technology matrix is derived from a major Japanese survey of agricultural techniques during the early Meiji period, accounts by European visitors and numerous studies by Japanese and western scholars that draw on village records, business accounts and other historical sources. Evaluating Japan's factor content of trade during 1868-1875 at the corresponding autarky factor prices, we fail to reject the Heckscher-Ohlin prediction in each sample year.

Testing the general validity of the Heckscher-Ohlin Theorem: the natural experiment of Japan

We exploit Japan's 19th century opening up to trade to test a general formulation of the Heckscher-Ohlin theorem. This formulation is based on Ohlin's measure of factor scarcity where autarky factor prices impose a refutable prediction on the economy's factor content of trade. Our test combines factor price data in Japan's autarky period with commodity trade data and a technology matrix in Japan's early free trade period. Our technology matrix is derived from a major Japanese survey of agricultural techniques during the early Meiji period, accounts by European visitors and numerous studies by Japanese and western scholars that draw on village records, business accounts and other historical sources. Evaluating Japan's factor content of trade during 1868-1875 at the corresponding autarky factor prices, we fail to reject the Heckscher-Ohlin prediction in each sample year.