Total Size Range Research Articles

Clustered trilobite assemblages in the Middle Devonian Hamilton Group

Clusters of well-preserved trilobites occur throughout lower and middle Paleozoic strata. This phenomenon, however, remains poorly understood. Several thin, regionally persistent beds in the Middle Devonian (Givetian) Hamilton Group of New York State display taphonomic and sedimentary features which indicate rapid burial by storm-generated clouds of fine-grained sediment. Furthermore, components in these units display little or no post-mortem disturbance and, therefore, reflect in faunal associations. These beds contain two types of clustered assemblages of the trilobites Phacops (Green), Greenops boothi (Green) and Dechenella rowi (Green). Body clusters comprise dense assemblages of three or more complete trilobite corpses. Moult clusters, in contrast, are composed of three more moult ensembles; i.e., articulated thoracopygidia in close proximity to corresponding cephala. Clusters are species-segregated and contain only a small portion of the total size range exhibited by trilobite species. Moreover, body clusters and moult clusters are morphometrically undifferentiated indicating that these two cluster modes represent related phenomena. Analogy with modern marine arthropods suggests that trilobites assembled into monospecific, age-segregated clusters and moulted prior to en masse copulation.

Population characteristics of the Burwash caribou herd in the southwestern Yukon estimated by capture–recapture analysis

Seasonal censuses (calving, rut, and winter periods) and other surveys were undertaken to apportion changes in mountain caribou (Rangifer tarandus caribou) numbers to changes in mortality, recruitment or ingress–egress, and to assess seasonal distribution. Data were collected from September 1978 to June 1982 in the St. Elias Mountains of the southwestern Yukon. Thirty-nine caribou were radiocollared and used in capture–recapture analysis. Estimates varied from a minimum herd size of 330 to a maximum of 560. Bulls comprised 33% of animals older than calves. Calving occurred between 15 May and 13 June from 1979 to 1982. Pregnancy rates varied from 78 to 82% during 1980 to 1982 while calves comprised 20% of the herd in calving periods, 19% during ruts, and 18% during midwinters. Recruitment (% yearlings) varied from 9% in 1980 to 13% in 1981 and 14% in 1982. Neonate mortality (birth to 3.5 weeks) varied from 13 to 49% between 1980 and 1982. An average of 56% of calves died within 5 months of birth. Natural mortality rates of adult–subadults varied between 6 and 9%. All evidence indicated stable or slowly increasing numbers until winter 1982 when movement from the study area was documented. The total range size was 1978 km2 with the herd occupying two distinct seasonal ranges in upland tundra plateaux separated by lowland boreal forest. Herd densities (based on seasonal range size) averaged 1.66 caribou/km2. The proportion of the herd in each upland area varied consistently between seasons and years such that variations in numbers could be accounted for by mortality, recruitment, and movement from the study area in the winter of 1982.

Direct Measurement of Aerosol Shape Factors

The dynamic shape factor K and the coagulation shape factor f of two metal-oxide aerosols, platinum oxide and uranium dioxide, are determined by means of experiments. For this purpose, special measuring and evaluating methods are developed that are independent of the shape of the particles examined. The dynamic shape factor is determined separately for the different size fractions, whereas the coagulation shape factor is calculated by averaging the entire size range examined. The experiments show that the results of experiments with a given aerosol system cannot be automatically transferred to other aerosol systems. The shape of particles of a given size depends on the specific properties of the material and on the prevailing experimental conditions during aerosol generation. For both aerosol systems that are examined, the mean dynamic shape factor—averaged over the total size range examined—agrees roughly with the coagulation shape factor.

The significance of the long chaetal form ofNephtys caeca(Polychaeta:Nephtyidae) and its relationship toN. longosetosa

Abstract A comparison of specimens of Nephtys caeca and N. longosetosa from the north east coast of England has shown that these two species can be reliably distinguished by examining:(a) the first setiger to bear mter-ramal cirri, (b) the pharyngeal papillae, and (c) the number of setigers in large specimens. Differences in parapodial morphology are also useful, though more variable. A long chaetal form of N. caeca, the var. ciliata of McIntosh (1908), has been shown to be present for only part of the year in the population at the mouth of the R. Tyne, and specimens belonging to this form were found to represent only a small part of the total size range of N. caeca. The length of the chaetae, relative to body size, shows a gradual transition from the var. ciliata condition to the condition characteristic of N. caeca non ciliata. It is suggested that this evidence indicates that the long chaetal form is a stage in the life history of N. caeca, possibly representing a pre-reproductive dispersive/migratory ...

Optimum Operating Conditions of14C-Methane Isotope Enrichment By Concentric Type Thermal Diffusion Columns for Use in Radiocarbon Dating

The optimum operating conditions providing minimum run-time and running costs have been studied theoretically for a thermal diffusion plant to be used for the enrichment of the radiocarbon isotope from finite sample size.The calculations are based on a simple approximate model of the enrichment process, regarding the isotope separation column as operating under quasi-stationary state conditions. The temporal variation of the isotope accumulation is given by a single exponential term. From comparison with the numerical solution of the separation tube equation, approximate models of this simple type appear hardly sufficient for analytical work but seem well suited for optimization calculations. For column operation not too close to the equilibrium state, the approximate run-times were found accurate within 0.2 d.The approximate model has been applied to a column of the concentric type, operated on gaseous methane. Cross-section configuration and temperatures were not varied (hot and cold wall radii: 2.0 and 2.6cm, respectively; hot and cold wall temperatures: 400°C and 14°C, respectively). The column transport coefficients used were derived from measurements. Run-time was minimized by optimizing both the operating pressure and the sample collection mode for different total sample size (range studied: 24 to 100 g), mass of enriched sample (1.8, 2.4, and 3.0 g), enrichment factor (12, 15, and 20) and column length (8 to 18 m). Optimum working pressures are between 1 and 2 atm. Usually, about 90 percent of the enriched sample mass is extracted favorably from the column itself, the length of the sampling section being about 2.5 to 5 m. Typical runtimes are between 3 days and 2 weeks, and isotope yield may reach 90 percent.Optimum operating conditions have also been calculated for other column configurations reported in literature and are compared with the experimental results.

Microanatomy of the ganglionic roots of the abdominal cord of the crayfish, Orconectes virilis (Hagen).

AbstractLow magnification electron micrographs were used to construct montage maps of cross sections of the three roots of the second abdominal ganglion of the crayfish Orconectes virilis. Arbitrary fiber diameter size ranges were established within the total size range of 0.2 μ to 55 μ. Fibers within each of the ranges were counted and their positions noted. The first root contains 2,451 fibers and is divided internally into distinct anterior and posterior halves. The posterior half contains 98.2% of the roots total number of fibers below 1 μ in diameter and these are contained primarily in 13 bundles. The second root is divided internally into five subregions and contains a total of 2,741 fibers. The size distribution of the fibers within each of the subregions is noted and compared with the fiber size distribution of the peripheral branches. The subregions are assigned functions based on their similarity to root branches of known activity. The third root contains two distinct elements, a phasic branch containing 13 fibers ranging from 6 μ to 55 μ and a tonic branch containing six fibers ranging from 3.5 μ to 21 μ.

The Structure and Taxonomic Status of Toddia from the Cottonmouth Snake Agkistrodon piscivorus leucostoma*

SYNOPSIS. Of 163 cottonmouth snakes Agkistrodon piscivorus leucostoma from Louisiana, 4 (2.4%) were infected with Toddia França, 1911, an erythrocytic parasite said to be a protozoon. In the 4 blood films, Toddia had an average size of 1.65–1.98 μ with a total size range of 0.88–3.4 μ. In Giemsa‐stained slides, the organisms were usually a round red‐staining mass which was either homogeneous or sometimes contained granules. A pattern of growth was seen in which the organisms increased in size and in which there was development of an erythrocytic inclusion. The inclusion, which was not a part of the parasite, developed first as a spheroid and then became altered in shape to a crystalloid square, possibly a break‐down product of the host cell hemoglobin. The first noticeable damage to the erythrocytes was to the nuclei, which became nearly round; later, when the crystalloid had formed, the host cell degenerated into a small mass containing a pycnotic nucleus, a remnant of cytoplasm and the Toddia.A review of the literature on Toddia and on Pirhemocyton Chatton & Blanc, 1914 leads to the conclusion that the organisms are closely related and that both are viruses of the DNA type.

Components of the flow stress of iron

Tensile tests have been made on a pure iron (99.97% pure; interstitial content 0.007 at.%) covering a total grain size range of 0.025–2 mm and a temperature range of −196 to +400°C. Dislocation densities were measured at various elongations up to 12 1 2% . Graphs of flow stress versus (dislocation density) 1 2 were unaffected by grain size, proving that the well-known effect of grain size on the stressstrain curve is less due to grain boundary barrier hardening than to an effect of grain size on the rate of dislocation multiplication. The efficiency of dislocation strengthening was little influenced by temperature despite variation in dislocation pattern. Three different methods of determining the friction stress, namely grain size analysis, extrapolating the stress-strain curve backwards, and dislocation analysis were compared, and the first and last in particular agree well when necessary corrections are made. The friction stress is close to zero between room temperature and 400°K although the lys, the flow stress, and k y all tend to rise in the blue-brittle region; because, it is believed, dislocations disappear less easily when strain-ageing takes place rather than because they are made faster as hitherto thought. The friction stress rises steeply below room temperature in some agreement with one branch of Friedel's theoretical expression for the Peierls force, while a theoretical calculation, made in an Appendix, of k y based on the Hall-Petch model agrees well with the experimental value.