Decrease In Mean Size Research Articles

Superparamagnetic relaxation evidences large surface contribution for the magnetic anisotropy of MnFe204 nanoparticles of ferrofluids

Manganese ferrite nanoparticles, in the size range 3.3–9.0 nm, are prepared by a hydrothermal coprecipitation process and peptized in aqueous solution. The magnetization curves recorded at room temperature on diluted colloidal sols allow characterizing the distribution of magnetic moment by using a simple Langevin formalism. Mossbauer spectroscopy measurements performed on powder samples at 77 K exhibit a quadrupolar doublet which intensity grows at the expense of the hyperfine sextet pattern as the nanoparticles mean size decreases. The magnetic dynamics behavior is then investigated by measurements of magnetic hysteretic properties at 5 K and temperature dependence of the zero field cooling (ZFC) susceptibility. The values found for the effective anisotropy constant and the dependence of the irreversibility field, inversely proportional to the reference size, clearly indicate that the magnetic anisotropy of our nanoparticles finds its origin on the disordered surface layer.

Geographic and bathymetric trends in abundance, biomass and body size of four grenadier fishes along the Iberian coast in the western Mediterranean

The present study is a mesoscale analysis of latitude and depth related trends in abundance, biomass and body size of the four grenadier species Caelorinchus caelorhincus, Hymenocephalus italicus, Nezumia aequalis and Trachyrinchus scabrus inhabiting the deep western Mediterranean. We have analysed data from seven annual bottom trawl surveys, carried out down to 800 m depth along the Iberian Mediterranean coast covering a distance of approximately 1200 km. The objectives were to establish general patterns in the mesoscale distribution of abundance, biomass and body size of deep-water grenadier fishes and also analyse the consistency of the bathymetric distribution of these parameters along a large latitudinal gradient. Five complementary series of analyses have been completed. The first focussed on describing the general patterns of abundance and size by correspondence canonical analysis, CCA, in the area. The second and third series focussed on the existence of temporal, geographical and bathymetric trends of abundance, weight and mean size by analysis of covariance, ANCOVA and multiple regression analysis. The fourth series compared the frequency distributions of body length. Finally, the last series focussed on the patterns of abundance versus size. The total number of individuals of all four grenadier species captured in 260 bottom trawls amounted to 27,435 and their weight was 1404 kg. No general trends for the four species have been observed between years. All four species showed a general pattern of increasing size with depth, which, except in the case of C. caelorhincus, was consistent along a large latitudinal gradient. Nezumia aequalis was unique in showing the same noticeable trend of increasing abundance with depth along the entire latitudinal range, but with clear differences in the intercepts. The abundance of N. aequalis and C. caelorhincus decreased significantly northwards. Hymenocephalus italicus was the least abundant species and had a homogeneous distribution without any specific trend along the entire latitudinal range analysed. The distribution of T. scabrus in the Mediterranean seemed to be more localised. Higher abundances were found to the north and south of the latitudinal gradient with lower values between. The grenadiers studied also showed a general trend of decreasing mean size northwards, except in the case of the smallest species, H. italicus. The relation between abundance and body size differed between sectors for the whole grenadier population and species-specific variations were also observed. The relationship between individual body mass and population density fit well to a second-order polynomial function rather than to a linear regression, showing a significant trend for density to increase with increasing size until some mid-point, then to decline with increasing size thereafter. The observed latitudinal gradient in the distribution patterns of grenadiers along the upper slope of the western Mediterranean can be discussed in relation to direct and indirect factors of biogeographic, environmental and anthropogenic origin.

Do bigger fish arrive and spawn at the spawning grounds before smaller fish: Cod ( Gadus morhua) predation on beach spawning capelin ( Mallotus villosus) from coastal Newfoundland

A relationship between body size and time of spawning has often been described for both pelagic and non-pelagic fish species that migrate for the purpose of spawning. The present study investigates this relationship for capelin ( Mallotus villosus), a pelagic smelt-like species that spawns on the beaches of Newfoundland. Simple linear regressions were carried out separately for three groups of capelin: ovid females, spent females and males in three successive years (1982–1984). Bigger fish arrived near the spawning grounds first, for all three groups in all three years and was most obvious for female capelin. Analyses of stomach contents of Atlantic cod ( Gadus morhua), an important predator of capelin in the Newfoundland area, showed a similar decrease in mean size of capelin throughout the capelin spawning season in June, July and August. Furthermore, analyses strongly suggest that early in the spawning seasons, when capelin abundance was high, cod selected for bigger capelin, whereas towards the end of the spawning seasons, when capelin abundance was low, cod did not show any size preference.

Dynamics of black spot sea bream (Pagellus bogaraveo) mean length: evaluating the influence of life history parameters, recruitment, size selectivity and exploitation rates

Summary Stochastic simulations were used to evaluate the influence of recruitment pattern (log-normal, decreasing), size selectivity (normal, logistic model) and fishing mortality pattern (abrupt, continuous increase in fishing mortality) on the evolution of mean length and the dispersion of mean length for a relatively long-lived deep-water species, the black spot sea bream (Pagellus bogaraveo). An abrupt increase in fishing mortality resulted in mean size decreasing and stabilizing at a lower level while a steady increase in fishing mortality caused the continuous decrease in mean size that has been reported for many long-lived species. Decrease in mean size was greatest for logistic model simulations and for cases where fish were susceptible to capture at a small size. Logistic selectivity, with decreasing recruitment and increasing fishing mortality over time, resulted in mean length and variability in mean length trends similar to that observed for the Strait of Gibraltar fishery. Furthermore, it was found with the declining recruitment that moderate increases in fishing mortality can result in significant decreases in mean length. Given the importance of mean size as an indicator of the state of a resource, these simulations are a useful alternative or complement to standard fisheries assessment methods, helping to provide information on exploitation patterns and rates that can be used for conservation and management.

Ultrafast Photosynthetic Reduction of Elemental Sulfur by Au Nanoparticle-Loaded TiO2

Nanometer-sized gold particles with varying mean size from 3.2 to 12.2 nm were loaded on the surfaces of TiO2 particles in a highly dispersed state with the loading amount maintained constant (0.46 +/- 0.02 mass %) using the deposition-precipitation method. Light irradiation (lambda(ex) > 300 nm) to a deaerated ethanol TiO2 particle suspension containing elemental sulfur (S8) led to the energetically uphill reduction of S8 to H2S. It has been found that this reaction is dramatically enhanced with such a low level of Au loading on TiO2 and that the zero-order rate constant of reaction increases with decreasing mean size of Au nanoparticles (d). The effects of reaction parameters (substrate concentration, light intensity, temperature) on the rate of reaction were studied to infer the essential reaction mechanism. Further, a kinetic analysis has led to a conclusion that the increase in the rate of reaction with decreasing d results from the improvement of the charge separation efficiency.

Effects of flood abrasion of the Carpathian alluvial gravels

Floods occurred in the drainage basins of two large mountain tributaries of the Vistula—the Soła and the Skawa in 1996, 1997 and 2001. This paper shows changes in petrographical composition of gravel bars and characteristics of clasts in both rivers after the episodes of flood transport. The drainage basins of both rivers lie within the Carpathian mountains in their southern, headwater parts, and the in the Oświęcim Depression, belonging to the foreland, in the northern part. The Soła and Skawa are gravel-bed rivers which transport mostly sandstone and conglomerate gravels derived from erosion of flysch rocks. Both drainage basins share many characteristic features, the main difference being their hydrotechnical infrastructure. The Soła is regulated by three dams and the discharge below the dams is artificially controlled. There is no dam in the Skawa and its discharges are natural. Petrographical composition of gravels, roundness, shape and size of clasts were studied in 12 sites in the Soła valley and in 11 sites in the Skawa valley after each flood. More than 5000 clasts were studied in total. Granulometrical characteristics of the sediments changed markedly after the floods. Both increase and decrease in mean size of largest clasts in gravel bars were observed. The results point to the important role played by the tributaries, which control the characteristics of clasts in the main rivers. In the foreland, lateral supply is not so important, because the bedrock consists of argillaceous rocks which do not produce gravels. The processes observed there include selection of material and changes in its composition caused by the presence of dams. Conglomerates are the least resistant to flood transport among gravel components. The most resistant are quartz clasts, but they are present only in the finest size classes. The most persistent characteristic of the clasts is their shape. The influence of the dams on clasts characteristics, contrary to expectations, is only slight. It is visible only in the greater proportion of quartz clasts in the alluvium of the Soła where the dams are present.

Diet and condition of three fish species (Characidae) of the Andean foothills in relation to deforestation

I studied effects of deforestation on diet and condition of three characid species; Astyanax zonatus, Knodus gamma, and Prionobrama filigera in small streams in the Ecuadorian Amazon. The best condition of K. gamma was found at sites with low canopy cover, while the best condition of P. filigera was found at sites with high canopy cover. Deforestation changed population structure of A. zonatus by decreasing mean size of individuals, but this was not associated with lower fish condition. A. zonatus was omnivorous, and fed equally on invertebrate and plant food. A. zonatus increased feeding on aquatic food items (filamentous algae and fish scales) in the deforested sites (43%) compared to the forested sites (16%). K. gamma was an omnivorous species with preference for invertebrates. K. gamma was mainly feeding on terrestrial food sources in the forested sites, but switched to equal feeding between terrestrial and aquatic food sources in the deforested sites. P. filigera was an terrestrial insectivore feeder, and no differences in the overall food categories was found between stream groups. In contrast, there were no pronounced difference in the composition of invertebrate taxa in the stomachs of K. gamma between stream groups. However, less empty stomachs were observed among K. gamma in the deforested sites. The stomach contents of P. filigera showed great changes in composition of the predominating prey taxa between stream groups and less empty stomachs were observed among P. filigera in the forested sites. Food availability and utilisation seemed to be of main importance for the condition of these fish. Deforestation seems to favour species with high availability to utilise aquatic food items. In contrast, deforestation seems to have negative effects on species that are specialised on terrestrial invertebrates, and have low capacity to switch between aquatic and terrestrial food items.

A randomized placebo-controlled trial of low-dose monophasic pills in the treatment of functional ovarian cysts

Introduction: The purpose of this study was to determine the efficacy of low-dose monophasic pills in the treatment of functional cysts in a randomized triple-blind placebo-controlled trial. Methods: 186 women aged 15 to 45 with functional cysts were randomly assigned to either monophasic pills or placebo. The disappearance rate at 4 and 8 weeks and the mean decrease in size and mean percentage decrease in size of cysts at 8 weeks were primary outcome measures. Results: There were no significant difference between the two groups in the disappearance rate of functional cysts at 4 and 8 weeks ( p-value 0.53 and 0.41, respectively) and in the mean decrease size and mean percentage decrease in size of the cysts at 8 weeks ( p-value of 0.15 and 0.38, respectively). Conclusion: There was no sufficient evidence to say that treatment with low-dose monophasic pills is more effective than placebo in the disappearance of functional cysts at 4 and 8 weeks of treatment.

Implications of imaginal-size variation over the flight period in stoneflies (Plecoptera)

In the present study, the decrease in the mean size of specimens over the species flight period in Plecoptera (12 species, 5 families) was analysed, revealing a significant decrease in the adult mean size, for both males and female, in almost all the species without an extended flight-period pattern. Some of the data show that, in addition to temperature, other regulatory factors must govern these variations. Data support the explanation previously proposed for other insect groups that the individuals with appropriate development emerge at the beginning of the flight period or slightly afterwards, when environmental conditions are suitable, whereas individuals with suboptimal size emerge later trying to increase in size but under pressure to emerge during a specific period of the year. Nevertheless, our data suggest that maximum size does not necessarily coincide with the peak flight period (maximum reproductive possibility).

Cyprinid predation on zooplankton along the longitudinal profile of a canyon-shaped reservoir

In the deep, elongated řimov Reservoir (South Bohemia, Czech Republic), the diet composition of the three most abundant cyprinid species, as well as the fish and zooplankton distribution. were investigated at three sites (dam, middle, tributary) located along the longitudinal transect of the reservoir, and during two periods of the year. The studied fish were roach (Rutilus rutilus) and bream (Abramis brama) of two length classes (10-18 cm SL and >18 cm SL), and bleak (Alburnus alburnus) of one length class (10-18 cm SL). The diets of all cyprinids along the entire longitudinal transect constituted almost exclusively crustacean zooplankton. In May, Daphnia galeata was a highly preferred prey item of all fish, except for those of the 10-18 cm length class in the tributary station, which consumed mainly bosminids. In August, bleak and roach of both length classes preyed on D. galeata and Leptodora kindtii. Larger bream (> 18 cm SL) consumed these prey items as well and, moreover, fed significantly on Diaphanosoma brachyurum. Proportions of L. kindtii in the cyprinid diets were particularly conspicuous in the dam and middle sites In the tributary site, cyclopoid copepods were an important prey item in the diets of both length classes of bream, in contrast to their infrequency in the diets of roach and bleak. Densities of epilimnetic zooplankton declined gradually downstream in the reservoir, they were about two-fold higher in the tributary site compared to the dam site in both months, respectively. A relatively higher total fish catch per unit effort was found in the tributary site in comparison to the dam or middle site, and a decreasing mean size of D. galeata in zooplankton was observed from the dam to the tributary site in both months. Such results indicated stronger fish predation pressure in the upstream part of the reservoir during the two periods of the year. Moreover, lower diet overlaps within the cyprinid assemblage of the tributary site than within the cyprinid assemblages of the dam and middle sites suggested intense competition for food at the upstream end of the reservoir.

Abundance, distribution and size structure of zooplankton along a 20° west meridional transect of the northeast Atlantic Ocean in July

Zooplankton distribution, abundance and size structure were characterised on leg 2 of the PRIME cruise in the northeast Atlantic during July 1996. Latitudinal sampling was carried out from 60°N to 37°N along a meridian at approximately 20°W. Zooplankton were characterised using an Optical Plankton Counter (OPC), and from traditional depth-integrated net hauls for taxonomy and carbon. The former method allows zooplankton to be described in terms of biovolume and size. There was good agreement between the two methods for abundance and a good correlation between OPC biovolume and carbon analysis. These data also showed compatibility with concurrent acoustic measurements of zooplankton. Results for the cruise compared to recent studies in the region, show that, overall abundance was generally low, although most of the previous studies were closer to spring bloom conditions. The size structure over latitude shows that mean size fluctuated, but there was a general trend of decreasing mean size from the north of the transect to about 47°N. Further statistical treatment of the OPC data, using principal component analysis, showed that zooplankton size structure changed at five positions along the transect. Three of these coincided with changes in physical structure, one each side of the front at 48°N and the third on the outer edge of an eddy. The other two occurred in regions of high-surface chlorophyll concentration.

Control of soot emission of a turbulent diffusion flame by DC or AC corona discharges

The effects of DC or AC (14 kHz) corona discharges, formed between tips of opposed needle electrodes, on soot emission of a propane turbulent diffusion flame were investigated experimentally. It is shown that when a DC corona discharge (e.g., 3.6 W; 0.06% of the combustion energy released by the flame) or a discharge system composed of three AC coronas (e.g., 25.5 W in total; 0.43% of the combustion energy) is applied across the lower part of the flame, with a gap width such that the electrode tips are located outside the reaction zone, a marked reduction in soot emission is observed, without noticeable change in the shape of flame luminous region. When corona discharges are applied, increases of the density of charged species and/or charged soot particles are observed in the flame over the whole length downstream of the corona application. It is suggested that, in the case of DC corona application, additional air and inorganic charged species and electrons, produced in the air near the tip of the positive electrode, are carried into the flame mainly by corona winds, whereas in the case of the AC corona application the inorganic charged species and electrons are carried into the flame by diffusion processes. The charged species and electrons carried into the flame may influence the state of charging of incipient soot particles and also reduce the concentration of growing ions, i.e., soot precursors, which directly relate to the soot emission of the flame. In TEM photographs it was found that separate soot particles, or those forming chains in the flame, decrease in mean size with the application of corona discharges. Smaller size soot particles burn faster than larger size particles in the high-temperature oxidizing atmosphere at the flame top region.

Role of a surface active agent in the sol-emulsion-gel synthesis of spherical alumina powders

Spheroidal alumina particles of tailor-made size were prepared by the sol-emulsion-gel method under simultaneous mechanical agitation and sonication and by systematic variation of the concentration of a non-ionic surfactant in the organic solvent (“oil phase”) above or below the critical micelle concentration (CMC). The CMC of the surfactant in the organic solvent of low dielectric constant was determined from discernible breaks in surface tension, viscosity, optical absorption and dye fluorescence vs. concentration curves. The CMC of the surfactant played an important role in controlling the sol droplet size and accordingly, the size of the alumina particles obtained therefrom. Transmission electron microscopy (TEM) revealed that near (but below) CMC the nanospheroids (10–50 m) were in the state of chain-like agglomerates. Beyond CMC, spheroidal particles of larger dimensions were obtained. Particle size analysis showed a sharp decrease in mean size with increasing concentration of the surfactant up to CMC, above which a gentle upward trend was noticed.

Simultaneous estimation of all the parameters of a stepwise mutation model.

Minisatellite and microsatellite are short tandemly repetitive sequences dispersed in eukaryotic genomes, many of which are highly polymorphic due to copy number variation of the repeats. Because mutation changes copy numbers of the repeat sequences in a generalized stepwise fashion, stepwise mutation models are widely used for studying the dynamics of these loci. We propose a minimum chi-square (MCS) method for simultaneous estimation of all the parameters in a stepwise mutation model and the ancestral allelic type of a sample. The MCS estimator requires knowing the mean number of alleles of a certain size in a sample, which can be estimated using Monte Carlo samples generated by a coalescent algorithm. The method is applied to samples of seven (CA)n repeat loci from eight human populations and one chimpanzee population. The estimated values of parameters suggest that there is a general tendency for microsatellite alleles to expand in size, because (1) each mutation has a slight tendency to cause size increase and (2) the mean size increase is larger than the mean size decrease for a mutation. Our estimates also suggest that most of these CA-repeat loci evolve according to multistep mutation models rather than single-step mutation models. We also introduced several quantities for measuring the quality of the estimation of ancestral allelic type, and it appears that the majority of the estimated ancestral allelic types are reasonably accurate. Implications of our analysis and potential extensions of the method are discussed. SINCE the discovery that a large number of loci with tandemly repeated sequences in human and many eukaryote species are highly polymorphic because of copy number variation of the repeats in different individuals (Jeffreys 1985; Litt and Luty 1989; Weber and May 1989), allele size data from such loci are rapidly becoming the dominant source of genetic markers for genome mapping, forensic testing, and population studies. Loci with repeat sequences longer than 5 bp are generally referred to as minisatellite or variable number tandem repeat loci, and those with repeat sequences between 2 to 5 bp are referred to as microsatellite or short tandem repeat loci (Tautz 1993). Because mutations change the copy number of such loci in a stepwise fashion, rapid accumulation of population samples from minisatellite and microsatellite loci has resurrected the interest of the stepwise mutation model (SMM), which was popular in the 1970s.

Body size variation in Audouin's Gull Larus audouinii; a density‐dependent effect?

A significant decrease in the body size of Audouin's Gulls Larus audouinii breeding at the Chafarinas Islands is reported. The decrease in linear measurements in the current breeding population ranged from 2.5% to 5.6% in males and from 0.61% to 4.4% in females. This was detected when assessing the reliability of a sex‐discriminating function derived for the same colony 13 years earlier. When applied to the current population, this function failed to predict the sex of a large proportion of males (44%). The relative decrease in mean size was significantly greater in males than in females for culmen, nalospi and tarsus lengths, while for bill depth at culmen, wing length and body mass the relative decrease was similar in both sexes. Since the extent of differences depended on sex, these differences cannot be attributed to a systematic between‐observer bias. Mean body size reduction might be either the result of a greater proportion of small breeding birds in the current population, because of increased availability of nesting sites (competition relaxation hypothesis), or an outcome of environmental factors affecting growth parameters (environmental constraint hypothesis). According to the first hypothesis, the changes observed would be associated with higher variability values. Conversely, if the second is true, the degree of variability should be similar. Since there are no significant differences in the degree of variability shown in the two data sets, our results support the second hypothesis. The environmental constraint acting via growth parameters is probably related to the increase in the number of Audouin's Gull breeding pairs while food availability was depleted. Our data suggest that changes in the duration of the growth period, rather than in the growth rates themselves, are involved in the body size differences found.

Changes over time of the size structure in an exploited shelf fish community

After a long decline that began in the 1960s, the great fisheries of Newfoundland collapsed, and since 1992 a moratorium has applied to most stocks from Labrador to the U.S. border. Cold water temperatures and other environmental factors have been suggested as the underlying cause of the observed declines, but the data now emerging show that overfishing has been the prime agent. Study of scientific survey data for the years 1978–1993 shows that all species, commercial and non-commercial, in the fish community have undergone changes. Numbers and biomass decreased and for both target and non-target species mean size in the 90's has dropped dramatically from what it was in the early 80's. The decline in size results from the removal of the larger (and presumably older) individuals with the result that the population structure has been fundamentally changed. The trend of decreasing mean size over time is not an isolated occurrence on the Northeast Newfoundland and Labrador shelf, but is also observed in the groundfish community off west Greenland during a similar time period.

Growth Rate of Colon Polyps and Cancer

Malignancy potential of colorectal polyps increases with size. The growth rate and destiny of each polyp is virtually unknown. It was recently shown that polyps smaller than 10 mm left in situ may partly regress or partly increase in size, whereas one quarter of polyps are unchanged after 3 years. Polyps smaller than 5 mm show a mean increase in size, whereas polyps measuring 5 to 9 mm show a mean decrease in size. Methodologic problems with the measurement of polyps and cancer are discussed. More studies of polyp growth related to risk factors are warranted.

Changes in the population of American plaice ( Hippoglossoides platessoides) off Labrador and northeastern Newfoundland: A collapsing stock with low exploitation

Changes in the population dynamics of American plaice off southern Labrador and eastern Newfoundland (NAFO Subarea 2 and Division 3K) for the period 1977–1994 were investigated. Since the mid 1980s the population has declined dramatically and by the 1990s the stock had essentially collapsed. A higher proportion of what remained of the stock was found in deeper and warmer water than had previously been observed, coincident with a period of unusually cold ocean conditions. During the period of the greatest reductions in population size, the proportion of older, spawning-age fish declined much more rapidly than the younger ages and this decline was accompanied by a slight decrease in mean size at age. Also associated with these observations were declining trends in both size and age at maturity. Although exploitation has always been low, the fishery for American plaice in NAFO Subarea 2 and Division 3K has been regulated since the early 1970s. For the period investigated the average annual commercial exploitation rate was less than 2% with negligible bycatch in other fisheries. We conclude, therefore, that the collapse of this stock was not a result of fishing mortality. The causal mechanism for the decline remains unclear although unusual environmental conditions during the period continue to be investigated in relation to the observed changes in this population.

Rheological behaviour of coal-water mixtures. 1. Effects of coal type, loading and particle size

Factors affecting the rheological characteristics of coal-water mixture (CWM) were investigated, including the properties of the coal, the volume fraction of solids and the mean size and size distribution of the coal particles. The apparent viscosity was measured with a Brookfield viscometer, and the non-Newtonian properties based on the power-law model were investigated using a Haake rotational viscometer at shear rates up to 512 s −1. The results showed that the slurry exhibited shear thinning, i.e. pseudoplastic behaviour, and that it became more viscous as the mean particle size decreased, but less viscous with decreasing equilibrium moisture content. The degree of pseudoplasticity increased with increasing coal content and with decreasing mean size of particles. The mixing of coarse and fine coal particles was found to be very effective in obtaining mixtures characterized by high solids content and low viscosity. CWM viscosity was lowest when the blending ratio of fines was ∼0.35, irrespective of the mean-size ratio. The particle size distribution which gives high fluidity also appears to enhance the stability of the suspension.

Colloidal molybdoantimonic acids as ion exchangers

Colloidal particles with a c.c.p. structure were obtained from mixtures of antimonic and molybdic acids through a polymerization process. These particles were octahedral and their sizes fits the log-normal distributions. The mean size decreases and the polydispersity increases with increasing Mo content in the particles. The stability of the aqueous dispersions was due to the surface charge density of the particles which was enhanced when increasing the Mo content. Ion exchange reactions can occur with the dispersions. Two different routes lead to Ag+ fixation: substitution of core H+ without flocculation of the dispersion or cancellation of external charges with flocculation. Key words: inorganic exchangers, colloids, antimonic acid, molybdic acid.