Entanglement Evolution in the Presence of Decoherence

The entanglement of two qubits, each defined as an effective two-level, spin 1/2 system, is investigated for the case that the qubits interact via a Heisenberg XY interaction and are subject to decoherence due to population relaxation and thermal effects. For zero temperature, the time dependent concurrence is studied analytically and numerically for some typical initial states, including a separable (unentangled) initial state. An analytical formula for non-zero steady state concurrence is found for any initial state, and optimal parameter values for maximizing steady state concurrence are given. The steady state concurrence is found analytically to remain non-zero for low, finite temperatures. We also identify the contributions of global and local coherence to the steady state entanglement.Comment: 12 pages, 4 figures. The second version of this paper has been significantly expanded in response to referee comments. The revised manuscript has been accepted for publication in Journal of Physics

Prices, Costs, and Margins of Florida Grapefruit -- Fresh and Processed

Florida is the leading producer of grapefruit, accounting for 76 percent of the 1973/74 U.S. crop. During the last decade processing has become the leading outlet for Florida grapefruit, with canned juice the most important processed product. This article traces trends in prices, costs, margins, and grower returns for Florida grapefruit, including fresh grapefruit, canned grapefruit juice, and canned grapefruit sections. Florida growers' share of the retail value in most seasons was larger for grapefruit juice than for either fresh grapefruit or canned sections. Florida growers have maintained their share of the consumer dollar for each of the three grapefruit products during the past 9 seasons

Florida Cucumbers and Green Peppers: Production, Marketing Patterns, Prices, and Margins

Florida is the leading domestic producer of many fall, winter, and spring vegetables. Increased competition from Mexican imports has hurt the Florida industry and, for some vegetables, has threatened the States's position as the major U.S. supplier. This report traces trends in production, marketing, prices, margins, and grower returns for Florida cucumbers and green peppers

Prices and Spreads for Selected Fruits Sold Fresh in Major Markets, 1967/68 - 1973/74

Prices and spreads are presented for Washington Red Delicious apples, eastern Red Delicious apples, midwestern Jonathan apples, Washington Winesap apples, Florida grapefruit, California Thompson Seedless grapes, California lemons, Florida oranges, California navel oranges, and California Valencia oranges, all sold fresh in major markets for six marketing seasons -- 1967/68 to 1972/73. Prices and spreads for 1973/74 are also presented for Florida grapefruit, and all apples, and oranges except California Valencia. Seasonal average retail price, shipping point price, and the total marketing spread for all fruits covered increased during 1967/68-1972/73. The weighted average retail price increased 17 percent, from 22.4 cents a pound in 1967/68 to 26.3 cents in 1972/73. Shipping point price (grower and packer return) increased 8 percent, from 10o6 cents a pound in 1967/68 to 11.4 cents in 1972/73, The total marketing spread increased 26 percent, from 11.8 cents a pound in 1967/68 to 14.9 cents in 1972/73

California-Arizona Fresh Oranges: Marketing Patterns, Prices, Costs, Margins, and Grower Returns

About one-fifth of the 1974/75 U.S. orange crop was used fresh. California and Arizona supplied two-thirds of the U.S. fresh crop that season. This report discusses trends in production and consumption of all oranges; marketing patterns for fresh California-Arizona oranges; and prices, costs, margins, and grower returns for fresh California-Arizona navel and Valencia oranges sold in New York City

California Celery Prices, Costs, and Margins

The retail value of celery sold in Chicago and New York City increased an average of 55 cents per crate per year between 1964 and 1973. The wholesale and retail margin increased 38 cents per crate per year; rail transportation costs went up 7 cents; harvesting, packing and selling costs rose 6 cents; and grower returns rose 4 cents. The wholesaler's and retailer's share of the retail value increased slightly and the share taken by harvesting, packing and selling costs declined slightly. Other market shares, including the grower's share, changed little