Comparing Stochastically Restricted Linear Estimators in a Regression Model

Conditions for superiority of the minimum dispersion estimator over another with respect to the covariance matrix are derived when the vector parameter of a regression model is subject to competing stochastic restrictions. The restrictions may also consist both of a deterministic part and a stochastic part.     

Effects on microbial activity by extraction of indigenous cells from soil slurries

Abstract: Possible effects on the physiological activity and culturability of soil microorganisms by different soil dispersion procedures, and effects on activity caused by extracting bacteria from soil, were investigated. There was no apparent difference in cfu's with dispersion of a silty loam soil and a loamy sand soil with pyrophosphate as compared to dispersion in NaCl. Substrate-induced respiration was reduced in the silty loam soil, and methanol oxidation was reduced in the loamy sand soil with dispersion in pyrophosphate, and the soil pH was irreversibly increased by the treatment. Extracted bacterial fractions had lower numbers of culturable cells as percentage of the total number of bacteria in each fraction, lower respiration rates and no methanol oxidation activity as compared to the soil slurry both before and after extraction. The physiological activity was apparently not affected by the number of cells extracted. This indicates that the increased extraction rate of indigenous soil bacteria obtained by effective disruption of aggregates and detachment of cells from surfaces, only results in increased extraction of cells that have been physiologically changed as a result of the extraction process.     

Dielectric analysis of mitochondria isolated from rat liver II. Intact mitochondria as simulated by a double-shell model

The dielectric dispersion of isolated intact mitochondria in suspension has been measured between 10 kHz and 500 MHz. In isotonic KCI media at 4°C, the mitochondria maintained their characteristic ‘double membrane’ structure as examined by electron microscopy, and the observed dispersion curves were successfully simulated in terms of a superposition of two sub-dispersions having different characteristic frequencies and different permittivity magnitudes. Taking these observations into account we analyzed the dispersion data on the basis of a ‘double-shell’ model in which two concentric shells are meant to represent the mitochondrial outer and inner membranes. The analyses by a computerized curve-fitting method revealed that: (i) electric capacities for the outer and the inner membrane are 1.7 and 0.5 μF/cm², respectively, (ii) relative permittivity for the inner compartment (or the equivalent homogeneous matrical space) = 50–60, (iii) outer compartment-to-external conductivity ratio = 0.4–0.6, and (iv) inner compartment-to-external conductivity ratio = 0.14. The implications of these parameter values are discussed with due attention paid to the limitations inherent in our ‘double-shell’ model approach.     

Metacercarial dispersion and intracellular parasitism in a strigeid trematode

Combes C. and Nassi H. 1977. Metacercarial dispersion and intracellular parasitism in a strigeid trematode. International Journal for Parasitology7: 501–503. The life cycle of Apatemon graciliformis Szidat, 1928 (Trematoda, Strigeidae), a parasite of Biorrphalaria glabrata in Guadeloupe, involves a novel mode of transmission, experimentally demonstrated, between the second intermediate host and the definitive host. The furcocercariae penetrate gravid females of the ovoviviparous fish, Poecilia reticulata, and develop into metacercariae in vitelline vesicles of the embryos where they encyst a short time before parturition. The young guppies are born infected with 1–3 metacercariae. It is considered that young infected fish are more prone to predation by the definitive host, thereby increasing the probability of the cycle being completed. Domestic ducks have been experimentally infected with these metacercariae. If cercariae penetrate non-gravid P. reticulata, they enter the oocytes; this represents a phase of intracellular parasitism.     

Dielectric probe of the electric-field-sensitive peptide alamethicin

Dielectric constant and loss of alamethicin in solvents of various degrees of lipophilicity (namely mixtures of n-octanol and dioxane) have been measured at frequencies from 5 kHz to 50 MHz. By means of a conventional Cole-Cole approach, dielectric properties were evaluated to obtain information about the structural and dipolar properties of the peptide in view of its function as a voltage-dependent pore former in membranes. The results for a pure octanol solvent (together with an apparent molecular weight determined by ultracentrifugation) indicate the existence of primarily monomeric particles of quite elongated shape and of comparatively high dipole moment. Adding dioxane was found to yield considerable aggregation and a decrease of polarity.     

Gonadotropin stimulation of steroidogenesis and cellular dispersion in cultured porcine cumuli oophori

The relationship between cellular dispersion and steroidogenesis was studied in culture using oocyte-cumulus complexes harvested from porcine follicles. The cells were cultured in modified TC 199 containing pig serum for one to two days. When oocyte-cumulus complexes were cultured in the absence of hormone the oocytes resumed meiosis, the cumulus cells grew out forming monolayers, and progesterone accumulation was low. Addition of ovine LH, purified human LH, or purified human FSH stimulated expansion of the cumulus mass as well as enhanced progesterone accumulation. Oocyte maturation was not affected by the hormones. In absence of hormone, oocyte-cumulus complexes obtained from large (6–12 mm) follicles showed increased cellular dispersion and higher progesterone accumulation as compared to complexes obtained from medium-sized (3–5 mm) follicles.     

Distribution of Polymorphus minutus among its intermediate hosts

Hirsch R. P. 1979. Distribution of Polymorphus minutus among its intermediate hosts. International journal for Parasitology10: 243–248. In 1971, Crofton investigated patterns of distribution of Polymorphus minutus in the intermediate host, Gammarus pulex. Among his conclusions were: (1) P. minutus populations occur in patterns similar to negative binomial distributions, and (2) parasite-induced host mortality results in patterns similar to truncated (high end) negative binomial distributions. Those conclusions, however, were not tested by statistical analyses. To test Crofton's observations, Chi-square goodness of fit tests were applied to data used by Crofton and an additional two stations sampled by Hynes & Nicholas in 1963. Analyses were expanded to include five theoretical distributions, four patterns of host mortality and various rates of host mortality. Truncated forms of negative binomial, positive binomial and Poisson distributions were also investigated where nontruncated distributions failed to fit observed distributions. It was found that negative binomial distributions most frequently describe patterns of P. minutus distribution with the exception of one population described by Poisson and another by positive binomial distributions. Crofton's assumption that truncated distributions result from parasite-induced host mortality seems unlikely in light of those analyses.     

Spatial and temporal structures of pheromone plumes in fields and forests

Wind‐borne odour stimuli from a small point‐source of pheromone are intermittent owing to the effects of atmospheric turbulence on the odour plume. The work reported here measures the characteristics of the intermittent stimulus in open fields and forests during typical daytime atmospheric conditions. To model the pheromone plume, negatively charged atmospheric ions were used as a tracer. They were released from an ion generator, and ion detectors measured the fluctuating flux of ions at positions up to 20 m downwind in the open field case and 10 m in the forest. In both the open field and in the forest, ion signals were highly intermittent, with a signal present only 20% of the time. Ion signals recorded in the forest consisted of bursts with gaps between them of at least three‐fold greater duration than those from the open field. In both environments, bursts generally each comprised a series of ‘spikes’, on average three in the field and seven in the forest. To validate the use of ionized air plumes as models of pheromone plumes, the antennae of male Lymantria dispar (gypsy moth) were used as detectors to quantify the plume of synthetic (+)‐disparlure emanating from a 2000 ng point source placed ≈ 10 cm from the ion source. A comparison of ion signals and EAGs (electronantennograms) suggests that the antennae respond to the main spikes within a burst, but no consistent relationship between the strength of the spikes and the magnitude of the EAG response was found. The average strengths of bursts in the ion detector signal decreased systematically as the distance from the ion generator to the ion detector increased. A similar trend, however, was not detected in the EAG response.     

Safety zones for a Sclerotinia sclerotiorum-based mycoherbicide: Accounting for regional and yearly variation in climate

Variation in the width of 'safety zones' for sheep and dairy pasture treated with a Sclerotinia sclerotiorum (Lib.) de Bary-based mycoherbicide was quantified using 10 years of climate data from each of five regions in New Zealand. Acceptable and risk-averse zones were defined as the maximum distances in any direction from a treated pasture where 'added:natural' ratios of air-borne S. sclerotiorum spores are 1:1 and 1:10, respectively. The 10-year mean 1:1 safety zone had zero width for sheep pasture at all locations, and was at most, 50 m wide for dairy pasture. The width of the 10-year mean 1:10 zone varied regionally from 314 to 443 m for sheep and from 175 to 280 m for dairy pasture, and the 90th percentile 1:10 zones were up to 41% wider. Linear relationships between safety zone width and mean wind speed were evident and these could be used to derive region-specific safety zones.