On the character of and distance between states in a binary switching net

Behavioral examination of binary switching net models has typically concerned itself with an examination of their cyclical character. This article considers two less frequently discussed behavioral variables-the density of 1's in net states and the (Hamming) distance between net states. These variables are studied under fully random nets and under nets controlled at levels of internal homogeneity, forcibility or threshold. A collection of theoretical and simulated results is presented.     

Thermal history of reef-associated environments during a record cold-air outbreak event

Summary Several polar continental air masses intruding into the south Florida/northern Bahama Bank region during January 1981 caused record low air temperatures and rapid chilling of extensive shallow-water carbonate systems. Numerous coral kills along the Florida reef tract and massive fish mortalities in Florida Bay were attributable to unusually cold waters generated at this time. Thermal evolution of Florida Bay/Florida reef tract and northern Bahama Bank waters from 8 to 21 January was assessed from thermal infrared data acquired by the NOAA-6 environmental satellite, in situ water temperatures, local meteorological data, and a computerized heat flux model. Field observations and laboratory experiments identify 16°C as a thermal stress threshold for most reef corals (Mayor 1915; Davis 1981). Temperaturecorrected digital satellite data indicated that water temperatures below 16°C were generated in Florida Bay and on Little and Great Bahama Banks during a 10-day period in January. Lowest temperatures on the Florida reef tract resulted from offshelf transport of Florida Bay water through major tidal channels. Offshelf movement of bay water is driven primarily by strong northerly winds, density gradients, and tidal pumping. Absence of reef development opposite major tidal passes along the Florida reef tract (Ginsburg and Shinn 1964) and aperiodic coral kills along bank margins can be attributed to this process, which has probably had a limiting influence on Holocene reef development in these areas.     

Bicarbonate assimilation by fresh-water charophytes and higher plants: I. Membrane transport of bicarbonate ions is not proven

Summary Although it is generally believed thatChara and some fresh-water angiosperms transport bicarbonate ions inwards across their plasma membranes, there has been no direct demonstration of such transport in these plants. The (indirect) arguments for their transporting HCO ₃ ^– are arguments against the inward diffusion of CO₂ at the observed rates. They rest on calculations of the equilibrium concentration of CO₂ or of the maximum rate at which CO₂ might be produced from HCO ₃ ^– at the pH of the medium outside the cells. SinceChara acidifies the medium over about half the cell surface during C assimilation, these calculations have been based on questionable premises.We propose a model forChara in which the acidification is attributed to active efflux of H⁺, and we calculate that both the equilibrium concentration of CO₂ and its rate of production outside the cell can be high enough to support the observed rates of C assimilation, without postulating transport of the species HCO ₃ ^– or H₂CO₃.Calculations are presented also for alternative models in which there is membrane transport of HCO ₃ ^– . The first includes symport of H⁺ with HCO ₃ ^– , again dependent on active H⁺ efflux. In the second, there is active electrogenic transport of HCO ₃ ^– . In this case the low pH in the medium outside the cell is caused by the dissociation of H₂CO₃ produced by hydration of CO₂ which leaks from the cell cytoplasm.All three models are consistent with the observations to date, but the first is more economical of postulates. It can also explain the apparent transport of HCO ₃ ^– by fresh-water angiosperms such asEgeria.     

Photosynthetic preparation and characterization of 13C-labeled carbohydrates in agmenellum quadruplicatum

The blue-green alga Agmenellum quadruplicatum (strain PR6) has been used to prepare photobiosynthetically ¹³C-labeled d-glucose, 2-O-(α-d-glucopyranosyl)-glyceric acid (glucosylglycerate), 2-hydroxy-1-(hydroxymethyl)ethyl α-d-gluco-pyranoside (glucosylglycerol), and α-d-glueopyranosyl β-d-fructofuranoside (sucrose). When grown to a cell density of 4.4 g.L^-1 (dry weight) under nitrate-nitrogen limiting growth conditions for 120 h, the algal cells contained 38% of the dry-cell weight as(1 → 4)-α-d-glucan (amylose). About 1% of the dry-cell weight was glucosylglycerol, glucosylglycerate, and sucrose. Glutamate was obtained, together with carbohydrates of low molecular weight, when the cells were extracted with chloroform-methanol; d-glucose was recovered from the extracted cells by acid hydrolysis of the starch. The algae were grown by using 20 mol% [¹³C] carbon dioxide for preparation of labeled carbohydrates and for cellular component identification by whole-cell n.m.r. spectroscopy.     

Diazepam induces relaxation of chick embryo muscle fibers in vitro and inhibits myosin synthesis

Diazepam (Valium/Roche) causes an immediate cessation of spontaneous contraction in chick embryo skeletal muscle fibers growing in vitro. Between 24–48 h later in the presence of 100 μM diazepam the relaxed muscle fibers no longer accumulate myosin as measured by the total amount of myosin heavy-chain peptide extracted from the cell cultures and identified by sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis. The myosin heavy chain assay procedure was standardized by quantitative precipitation of myosin with antibody to column purified chicken skeletal muscle myosin. Failure to accumulate myosin is related to a progressive inhibition of myosin synthesis. Diazepam-treated cultures showed an 80% inhibition of myosin heavy-chain synthesis over a period of 4 days. At the same time the rate of myosin heavy-chain degradation increases in diazepam-treated cultures relative to matched control cultures. Total protein synthesis was only marginally affected suggesting that diazepam may differentially inhibit myofibrillar protein synthesis. All of the observed effects of diazepam were reversible if drug exposure was limited to 48 h. The apparent specificity and reversibility of diazepam suggests that the drug will be useful in probing the mechanisms of terminal skeletal muscle cell differentiation and the hypotrophic relationship between chronic relaxation and inhibition of accumulation of myosin and perhaps other myofibrillar proteins.     

Effects of hyperthermia on the mouse testis and its response to X-rays, as assayed by weight loss.

The effects of both hyperthermia alone and X-rays combined with hyperthermia on mouse testis have been investigated. Testis weight on heating time was observed for temperatures in the range 39.5 to 43.75 degrees C. The relationship between the reaction rate and the reciprocal of absolute temperature indicated that, over the temperature range considered, the activation energy associated with such thermal damage was (646 +/- 45) x 10(3) J mol-1. No evidence was obtained to indicate a change in slope of the Arrhenius plot over this temperature range. Finally, despite the high sensitivity of the testis to heat and X-rays, no thermal enhancement of the weight loss after irradiation was observed when thermal treatments which, if given alone would produce some observable damage, were administered immediately after irradiation.     

The isolation, characterization and partial sequence of a peptide rich in glutamic acid and aspartic acid (HGA-2 peptide) from calf thymus non-histone chromosomal protein HMG 2. Comparison with a similar peptide (HGA-1 peptide) from calf thymus non-histone chromosomal protein HMG 1.

A 41-residue peptide (HGA-2) containing a continuous sequence of 35 glutamic and aspartic residues was isolated from non-histone chromosomal protein HMG 2. This highly acidic peptide is compared with a similar peptide (HGA-1) isolated from non-histone chromosomal protein HMG 1.