Materials with negative compressibilities in one or more dimensions

Rare crystal phases that expand in one or more dimensions when hydrostatically compressed are identified and shown to have negative Poisson's ratios. Some of these crystals (i) decrease volume and expand in two dimensions when stretched in a particular direction and (ii) increase surface area when hydrostatically compressed. Possible mechanisms for achieving such negative linear and area compressibilities are described for single crystals and composites, and sensor applications are proposed. Materials with these properties may be used to fabricate porous solids that either expand in all directions when hydrostatically compressed with a penetrating fluid or behave as if they are incompressible.     

Formation of nitrous oxide and dinitrogen by chemical decomposition of hydroxylamine in soils

Soil properties affecting formation of nitrous oxide (N₂O) and dinitrogen (N₂) by chemical decomposition of hydroxylamine (NH₂OH) in soils were studied using 19 soils selected to obtain a wide range in properties. It was found that production of N₂O by chemical decomposition of NH₂OH in soils is more rapid than production of N₂ and that, except with calcareous soils, N₂O production greatly exceeds N₂ production. Studies of the correlations between various soil properties and formation of N₂O and N₂ by decomposition of NH₂OH showed that production of N₂O was very highly correlated with exchangeable and oxidized Mn in the soils studied, and that production of N₂ was very highly correlated with pH, CaCO₃ equivalent, exchangeable Ca²⁺, and oxidized Mn. Production of N₂ in neutral and acidic soils was highly correlated with both exchangeable and oxidized Mn, and production of N₂ in calcareous soils was significantly correlated with oxidized Fe. The deductions from these correlations that Mn compounds are involved in the reactions leading to formation of N₂O and N₂ by chemical decomposition of NH₂OH in soils, and that CaCO₃ and Fe compounds are involved in the reactions leading to formation of N₂ in calcareous soils, were supported by studies of N₂O and N₂ production through reactions of Mn and Fe compounds with NH₂OH in the presence and absence of CaCO₃. Production of N₂O via chemical decomposition of NH₂OH in soils greatly exceeds production of N₂O through chemical decomposition of nitrite (i.e. via chemodenitrification), and the amount of N₂ produced by decomposition of NH₂OH in most soils exceeds the amount produced by decomposition of nitrite. Work reported indicates that, if N₂O is formed in soils through nonbiological transformations of NH₂OH produced by soil microorganisms, very little of this gas is generated by the reaction of NH₂OH with nitrite frequently postulated as a mechanism of N₂O production in soils (NH₂OH + HNO₂ → N₂O + 2H₂O).     

The effect of some cryoprotectants on dromedary camel frozen‐thawed semen

The cryopreserved camel semen is often associated with poor quality and fertility. This study aimed to improve the dromedary frozen semen quality by comparing the efficiency of four cryoprotectant agents (CPAs) on sperm freezability. Semen samples were collected from seven male Maghrabi camels, diluted with Shotor diluent supplemented with glycerol (Sh‐G), dimethyl formamide (DMF, Sh‐DF), dimethyl sulfoxide (DMSO, Sh‐DS) or ethylene glycol (EG, Sh‐EG), all at 6% final concentration, and the samples were subjected to cryopreservation. The results revealed the superiority of Sh‐DF over Sh‐G and Sh‐DS in terms of post‐thaw motility (55.83 ± 2.20 vs. 47.50 ± 4.33 and 45.00 ± 2.89%, respectively), sperm membrane (49.00 ± 0.58, 39.33 ± 3.33 and 42.67 ± 1.45%, respectively) and acrosomal integrities (53.00 ± 0.58, 57.33 ± 0.88 and 52.33 ± 1.45%, respectively). Sh‐EG group showed the lowest post‐thaw motility, plasma membrane and acrosome integrities (12.50 ± 1.44, 22.67 ± 1.45 and 30.67 ± 1.45, respectively). In conclusion, the protocols of dromedary camel semen cryopreservation could be enhanced using 6% DMF as a cryoprotectant agent.     

The physiological response of the turbot to multiple net confinements

The effects of multiple net confinements on the physiological stress response of the turbot (Scophthalmus maximus L.) were investigated. To allow for repeated blood sampling from individuals, fish were cannulated in the afferent branchial artery and were exposed to multiple 9 min net confinement episodes separated by either 4 h or 24 h. In fish stressed twice 4 h apart cumulative effects in plasma cortisol, glucose and free fatty acid concentrations were evident after the second handling stress. Although plasma Na⁺ and Cl⁻ concentrations were not increased further by the second net confinement, the elevation in plasma concentrations were more sustained compared to turbot handled only once. In a second experiment where turbot were net confined five times, with a 24 h recovery period between each net confinement episode, there was no evidence of any physiological accommodation with repeated exposures. For most circulatory parameters, there was also no evidence of any cumulative effect apparent. Plasma glucose concentrations were, however, elevated to a significantly higher degree with repeated net confinements. Although turbot were tolerant to the handling procedures, with no mortalities recorded, episodes of multiple handling of this species should be separated by at least 24 h if cumulative physiological disturbances are to be avoided. The significance of cumulative increases in plasma glucose concentrations is discussed. Present address: Aquaculture Associates International, The Firs, Glasshouse Hill, Codnor, Derbyshire, DE5 9QT, UK     

Sublethal effects of a carbamate pesticide on pheromonal mediated endocrine function in mature male Atlantic salmon (Salmo salar L.) parr

The sublethal effect of the carbamate pesticide carbofuran on the priming pheromonal system of Atlantic salmon (Salmo salar L.) was investigated. Previous studies have demonstrated that ovulated female salmon release a priming pheromone in their urine (considered to be an F-type prostaglandin) which is subsequently detected by mature male salmon and results in increased levels of plasma sex steroids and expressible milt. In the present study, electrophysiological recordings from the olfactory epithelium of mature male salmon parr indicated that the responses to prostaglandin F₂ (PGF₂) were significantly reduced at nominal concentrations of carbofuran as low as 1.0 µg l^-1, and the threshold of detection was reduced 10-fold. A 5 day exposure to carbofuran significantly reduced the ability of male parr to respond to PGF₂ stimulation. The priming effect of PGF₂ on milt and plasma 17,20-dihydroxy-4-pregnen-3-one levels were abolished at water concentrations at and above 2.7 µg l^-1. In addition, the priming effect of PGF₂ on plasma testosterone and 11-ketotestosterone concentrations was abolished at water carbofuran concentrations above 6.5 µg l^-1. Exposure to similar concentrations of carbofuran also resulted in a reduction in the levels of free and glucuronidated steroids in the bile of PGF₂ primed male parr. The effect of carbofuran on the priming response did not appear to be due to a direct effect on the testes, since the ability of testes to respond to pituitary extract stimulation in vitro was not impaired in carbofuran-exposed males. Carbofuran appeared to reduce significantly or abolish the priming pheromonal system in mature male parr by directly affecting the ability of the olfactory system to detect PGF₂, although the toxicological mechanism involved is as yet unknown. The results are therefore discussed in relation to the possible sublethal effects of carbofuran on reproduction in the Atlantic salmon.     

Net primary production of forests: a constant fraction of gross primary production?

Considerable progress has been made in our ability to model and measure annual gross primary production (GPP) by terrestrial vegetation. But challenges remain in estimating maintenance respiration (R(m)) and net primary production (NPP). To search for possible common relationships, we assembled annual carbon budgets from six evergreen and one deciduous forest in Oregon, USA, three pine plantations in New South Wales, Australia, a deciduous forest in Massachusetts, USA, and a Nothofagus forest on the South Island of New Zealand. At all 12 sites, a standard procedure was followed to estimate annual NPP of foliage, branches, stems, and roots, the carbon expended in synthesis of these organs (R(g)), their R(m), and that of previously produced foliage and sapwood in boles, branches, and large roots. In the survey, total NPP ranged from 120 to 1660 g C m(-2) year(-1), whereas the calculated fraction allocated to roots varied from 0.22 to 0.63. Comparative analysis indicated that the total NPP/GPP ratio was conservative (0.47 +/- 0.04 SD). This finding supports the possibility of greatly simplifying forest growth models. The constancy of the NPP/GPP ratio also provides an incentive to renew efforts to understand the environmental factors affecting partitioning of NPP above and belowground.     

Use of a physiological process model with forestry yield tables to set limits on annual carbon balances

We present an approach that sets limits on annual carbon fluxes for different aged forests by using a simple process-based model (3-PG) and information derived from yield tables and local weather stations. Given a measure of height-growth potential, model predictions are constrained to match stand dynamics described in yield tables. Thus constrained, the model can provide reasonable annual estimates of gross photosynthesis under a specified climate, even with inexact knowledge of soil properties. If we assume that leaf litterfall and fine-root turnover approach equilibrium at canopy closure, maximum net annual ecosystem exchange can also be predicted from modeled estimates of these two detrital components and estimates of foliage, branch, stem and coarse-root production. The latter four components of production are predicted from allometric relationships with mean stem diameter. The approach is demonstrated for Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) stands between Ages 20 and 150 years growing under conditions typical of those at Wind River, Washington, USA. Gross photosynthesis (Pg) by Douglas-fir at Ages 20, 70 and 150 years with leaf area indices (L) of 8.1, 6.9 and 4.0 was predicted at 1630, 1580 and 1160 g C m-2 year(1, respectively. Maximum net ecosystem production (Pe) for the same range in age classes was predicted to average 275, 294 and 207 g C m-2 year-1, respectively. The predicted reductions in L for older stands do not occur because other species fill the canopy gaps created by natural mortality of Douglas-fir. As a result of the development of an understory, total Pg is predicted to decrease only slightly with the aging of the overstory. Estimates of Pe exclude respiration from coarse woody debris, although additions of this component are provided annually by the model. The process-based modeling approach, constrained by yield table estimates of stand properties, sets reasonable limits on annual carbon exchange and suggests which environmental variables deserve careful monitoring to refine estimates of carbon fluxes.     

Integrated optoelectronic devices based on conjugated polymers

An all-polymer semiconductor integrated device is demonstrated with a high-mobility conjugated polymer field-effect transistor (FET) driving a polymer light-emitting diode (LED) of similar size. The FET uses regioregular poly(hexylthiophene). Its performance approaches that of inorganic amorphous silicon FETs, with field-effect mobilities of 0.05 to 0.1 square centimeters per volt second and ON-OFF current ratios of >10(6). The high mobility is attributed to the formation of extended polaron states as a result of local self-organization, in contrast to the variable-range hopping of self-localized polarons found in more disordered polymers. The FET-LED device represents a step toward all-polymer optoelectronic integrated circuits such as active-matrix polymer LED displays.