Packing Ratios Research Articles

VARIATION OF KARYOTYPE COMPOSITION AND GENOME SIZE IN SOME MURICID GASTROPODS FROM THE NORTHERN HEMISPHERE

Members of the Muricidae in the Northern Hemisphere show striking variation in chromosome number. The majority of the species examined to date have chromosome numbers in the range 2n = 60−70, while the Atlantic dog‐whelk, Nucella lapillus is unique in having a Robertsonian polymorphism with 2n values in the range 26–36, and Ocinebrina aciculata; is newly recorded here as 2n = 86. The karyotype composition and genome size of eight muricid species from the N Atlantic and NE Pacific are described and compared. These results are discussed with reference to the evolution and biogeography of the family, and differences in the proportions of heterochromatin and packing ratios of the metaphase chromosomes. Evolution in N. lapillus, the derived form within the group, appears to have involved a reduction in chromosome number and haploid chromosome length, but an increase in both genome size and packing ratio.

An Experimental Study of Particle Damping for Beams and Plates

This paper describes an experimental investigation of a particle damping method for a beam and a plate. Tungsten carbide particles are embedded within longitudinal (and latitudinal) holes drilled in the structure, as a simple and passive means for vibration suppression. Unlike in traditional damping materials, mechanisms of energy dissipation of particle damping are highly nonlinear and primarily related to friction and impact phenomena. Experiments are conducted with a number of arrangements of the packed particles including different particle sizes and volumetric packing ratios. The results show that the particle damping is remarkably effective and that strong attenuations are achieved within a broad frequency range. The effects of the system parameters including particle size, packing ratio and particle material are studied by broadband and narrowband random excitations. The experimental results confirm a numerical prediction that shear friction in the longitudinal (and the latitudinal) directions is effective as the major contributing mechanism of damping in the case. Another unique feature of linear decay in free vibrations is also observed in this case of particle damping.

Evaluation of direct removal of nitrate with entrapped mixed microbial cell technology using ethanol as the carbon source.

Biological denitrification from simulated contaminated groundwater using ethanol as an external carbon source was investigated with an entrapped mixed microbial cell (EMMC) system. Ethanol was used as an external carbon source to serve both as the energy source for the nitrate removal reaction and substrate for microorganisms in the system. The hydraulic retention time and chemical oxygen demand (COD)/nitrogen ratio significantly affect nitrate removal performance and, therefore, must be monitored carefully to achieve high rates of nitrate and COD removal. The effect of packing ratios of carriers in the reactor on nitrate removal performance was also investigated. The removal of nitrate and COD in reactors with various carrier packing ratios (12, 22, and 35%) is not significantly different during steady-state operation. However, the start-up periods in these three reactors are significantly different. The highest packing ratio can result in a fast removal of nitrate during the start-up periods. Results of solids retention time (SRT) analysis indicate that a long SRT in the EMMC system contributes to the stable removal of nitrate and to fast start up of the system. The increase of SRT is related to the increase in days of operation, SRT is maintained at a level of more than 200 days.

Endovascular treatment of cerebral aneurysms: An in vitro study with detachable platinum coils and tricellulose acetate polymer.

The purpose of our experimental study was to determine the effectiveness of filling the cavity of in vitro aneurysms with detachable platinum coils and the combination of detachable platinum coils and liquid embolic agent. Silicone aneurysm models were connected to a circulatory system to simulate arterial flow. A microcatheter was used to introduce detachable coils into the aneurysm cavities. First, platinum coils were introduced until the point of minimal dense packing, indicated by aneurysmal circulatory exclusion. Packing was continued up to maximal dense packing, indicated by protrusion of the coil into the parent artery. Volumetric ratios (coil volume-aneurysm volume) were calculated for minimal and maximal dense packing. Then, after purposeful undercoiling of aneurysm models, a micropump system was used to fill the aneurysm by stepwise injection of tricellulose acetate polymer through the coil mesh until angiographic aneurysm exclusion was completed. The volumetric ratios of maximal packing with coils and tricellulose acetate polymer in relation to the aneurysm volume were calculated. Maximal dense packing ratios with coils (mean, 32.5%; standard deviation [SD], 3%) were slightly higher than those with the minimal dense packing (mean, 28. 2%; SD, 3%) but were always less than 37%. The ratios of packing with the combined use of coils and tricellulose acetate polymer were greater than 100% (mean, 124.4%; SD, 15%). Knowledge of the volumetric ratio of maximal dense packing was useful for effective filling with coils and tricellulose acetate polymer. The combined use of coils and liquid polymer appeared more effective than the use of coils alone for the complete occlusion of the aneurysm lumen.

Electronic spectra and optical band gap studies in neodymium chlorophosphate glasses

The present work aims to study the variation of optical band gaps, intensity parameters, and radiative lifetimes with different metal ions in various chlorophosphate glasses. Different chlorophosphate glasses in the composition range 50P 2O 5+30Na 2HPO 4+19.5RCl (R=Li, Na, K, Ca and Pb) with 0.5 mol% Nd 2O 3 were prepared by quenching melts consisting of the above chemicals (1100–1200°C, 1.5–2 h) between two brass plates. Using the optical absorption spectra, the optical properties have been systematically studied. The position of the absorption edge and hence, the values of optical band gaps have been reported. Except for potassium, the position of the fundamental absorption edge shifts to longer wavelengths with an increase of average molecular weight of the glass. Judd–Ofelt analysis is used along with a spectral analysis to calculate the intensity parameters, radiative lifetimes and branching ratios. The lifetime of all the states are high in these chlorophosphate glasses when compared with chloroborate glasses. There is no relation between the spontaneous emission probabilities and ion packing ratios in these phosphate glasses as observed in other glass systems. The predicted radiative transition probabilities ( A), radiative lifetimes ( τ R), branching ratios ( β) and integrated absorption cross-sections ( Σ) for certain excited states of Nd 3+ doped glasses have also been reported.

Technical evaluation of oxygen transfer rates of fish gills and artificial gills.

An artificial gill, which takes oxygen from water, would enhance the ability of people to function under water for extended periods. Increasing oxygen transfer rate, however, would be essential to the realization of compact, commercially viable equipment. Fish have evolved a variety of techniques to enable them to breathe under water, and their mechanisms must be clarified before compact, high-performance artificial gills can be developed. A model of the secondary lamellae of fish gills, through which oxygen is taken up from water to the blood, was devised, and its structure and oxygen transfer rate were evaluated by computer simulation analysis for carp and dogfish. Oxygen transfer rates were also found for an outside-water-flow artificial gill using a hollow fiber membrane at various fiber packing ratios. The biologic membrane is rate-determining for oxygen transfer through the secondary lamellae. Blood and water side boundary film resistances are small for fish because the blood and water channels are very narrow and numerous. When the fiber packing ratio of the artificial gill is raised, the oxygen transfer rate increases because of lower water side boundary film resistance. An optimum fiber packing ratio should be selected so that there is no major increase in pressure drop and no channeling occurs.

Suitability of Nd(III) absorption spectroscopy to probe the structure of glasses from the ternary system Na 2O–B 2O 3–SiO 2

Optical absorption spectra of glasses from the ternary system Na 2O–B 2O 3–SiO 2 with 20, 40, and 60 mol% SiO 2 and varying modifier contents containing 1 mol% Nd 2O 3 were measured at cryogenic temperatures. The glasses were obtained by quenching the liquids of appropriate composition between steel plates. For comparison doped glasses from the binary systems Na 2O–B 2O 3 and Na 2O–SiO 2 were included. The molar volumes and packing ratios of the doped ternary glasses were compared with those of undoped glasses with similar composition to make sure that the dopant ions do not affect the bulk glass properties. The position of the 4I 9/2 → 2P 1/2 transition was used to monitor the nephelauxetic effect and the hypersensitive 4I 9/2 → 4G 5/2, 2G 7/2 transition to monitor changes in the rare-earth environment with the glass composition. The observed changes of the spectral features are consistent with structural changes in the host glasses as proposed by models of these glasses derived from NMR and IR investigations on undoped glasses. Hence the suitability of Nd 3+ absorption spectroscopy to probe the structure of these glasses is established.

Rate of Spread of Free-Burning Fires in Woody Fuels in a Wind Tunnel

We describe the results of 357 experimental fires conducted in an environmentally controlled large wind tunnel. The fires were burned over a range of particle sizes, fuel bed depths, packing ratios, moisture contents and windspeeds. We find that spread rate decreases with moisture content in a way which depends on the fuel type and diameter. It decreases as the square root of the packing ratio. Fuel bed depth has little effect on spread rate, and fuel diameter has significant effect only for diameters above 1 mm. The relationship between rale or spread and windspeed is virtually linear We develop a predictive model for rate of-spread based on energy transfer considerations and the laboratory results. Other laboratory-based models for spread rate are compared with our model, and tested against the laboratory data. The other models have forms similar to ours, but do not predict our data well. Our model predicts well the spread rates for fires burned in windspeeds below 3 m/sec in other laboratories. The scale of the experiments and the similarity of the dependence on windspeed to that found in the field indicate that a field model may be developed from the laboratory model with relatively few modifications.

Structural-Properties and Dimensional Relations of Some Mediterranean Shrub Fuels

Structural properties of fuelbeds and particles of 60 plants of four shrub species (Ulex parviflorus,Lygos monosperma, Erica arborea, and Erica scoparia) common in the undergrowth of maritime pine forests were inventoried, namely total biomass, biomass distribution by diameter class, dead-to-live biomass ratios, bulk density, and surface-to-volume ratios. Porosity and packing ratios were calculated from the inventoried data. Results are compared with those reported for other shrub fuels of mediterranean and other plant communities. We developed dimensional relations to simplify prediction of total plant biomass, as well as biomass in the 1-hour, 10-hour, and 100-hour timelag size classes. Dimension analysis results are considered quite satisfactory for L. monosperma and Erica sp., while there seems to be some room for improvement regarding our ability to predict biomass of U. parviflorus, based on simple measurements of plant dimensions.

A comparative study of DNA amount and nuclear dry weight in four different species ( Rana catesbeiana, Salmo gairdneri, Gallus domesticus and Homo sapiens)

1. 1. Quantitative electron microscopic and cytophotometric determinations of average nuclear weight, unit weight of chromatin fiber, chromatin fiber diameter and DNA amount were made and compared from lymphocytes in human, chicken, frog and trout. 2. 2. From these determinations the “packing ratio” of DNA in chromatin fibers was calculated. 3. 3. Nuclear mass and DNA amounts were highest in frog and lowest in chicken, while fiber diameter and mass of unit fiber measured highest in trout followed by chicken, frog and man. 4. 4. The packing ratios were 21.4 in chicken, 35.2 in human, 47.0 in trout, 51.1 in frog and show a trend of being lower in amniotes than in anamniotes. 5. 5. As only four species were studied, no conclusions regarding evolutionary implications or relationships between them could be made from these measurements.

Sorption properties of zeolite rho

Zeolite rho possesses an unusual combination of selectivity and activity for the synthesis of dimethylamine from ammonia and methanol. Sorption measurements were used to examine the synthesis of zeolite rho and how it evolves to become a superior catalyst, to distinguish various preparations, and to determine the effects of calcination under different conditions. A term “packing ratio” was defined as the ratio of adsorbed weights at equilibrium of different molecules for the same sorption volume and was shown to provide a measure of the steric constraints imposed on guest molecules by the host framework. Statistical analysis of the sorption data for many samples reveals that methanol fills the available framework volume and packs according to its liquid density. Because of this feature, methanol sorption provides a measure of the crystallinity of the rho framework. Larger molecules are constrained by the framework in the order: n-hexane> n-propanol > ethanol > methanol. Reproducible packing ratios, ethanol/methanol and n-propanol/ethanol, were determined for the rho framework. Rates of filling used in conjunction with the packing ratios show the presence of extra-lattice material and its proximity to the double 8-rings of rho.

Study on the Densification Process of Pottery Body for Building Construction (Part 1)

Using the isothermal method, the densification process of the quartz-feldspar-kaolinite system, representative of ceramics used for building construction, was investigated at various packing ratios (65-69%). The Arrhenius equation can be established between the temperature and the time necessary for densification before the vitrification point. In addition, the particles show a rhombic dodecahedron orientation, as described by Sallam et al., irrespective of the packing ratio at forming. A linear relation can be established between the logarithm of the packing ratio and the logarithms of the gradient and intercept of the Arrhenius equation. The apparent activation energy necessary for vitrification is 104-117kcal/mol, and the apparent activation energy decreased with increasing packing ratio. This indicates a possibility that the body possesses a specific coefficient for densification which is extremely important industrially.

The Effect of Neutral Shade on the Structure of Mature, Sun-Acclimated Palisade Cells of Helianthus annuus L. II. 3-Day Exposure

Portions of mature leaves of Helianthus annuus var. Mammoth, field grown under full sunlight (FS), were shaded for 3 days at 40%, 25%, or 0% FS. Nonshaded leaf areas served as FS controls. The palisade cell structure of shaded and control leaf areas was analzyed stereologically. There were no detectable shade effects on the volume density values of the major organelle compartments except for a decrease in the starch compartment. The surface density values of chloroplast thylakoid membranes were significantly greater in shaded than in nonshaded chloroplasts at all levels of shading. The proportion of granal thylakoid surface area was greater than that for stromal thylakoids in shaded compared to nonshaded chloroplasts. There were no discernible shade effects on mean palisade cell volume. The total chlorophyll (chl)/mm3 of leaf and chl a/b ratios were lower in the shaded leaves than in the controls except for the full-shade sample (0%), which had higher chl a/b ratios than the control. Thylakoid packing ratios for palisade cells (mm2 thylakoid/mm2 leaf surface) were greater in the shade than in sun areas for 25% and 0% FS. Considering the overall response of thylakoid surface areas and changes in leaf anatomy, there was a greater light-gathering potential in the shaded half of the leaf. Although some shade response was observed in 40% FS (688 μmol s-1 m-2), the most pronounced responses occurred at 25% FS (347 μmol s-1 m-2). Thus, the threshold light level for shade response in sunflowers is near the latter value. These studies also show that cells within the same leaf respond independently to local irradiance levels.

The higher-order structure of chromatin: evidence for a helical ribbon arrangement.

Both intact and nuclease-isolated chromatin fibers have been examined at different degrees of salt-induced compaction, using a variety of preparation techniques. The results suggest that the initial folding step in nucleosome packing involves the formation of a zig-zag ribbon as has been proposed by others (Thoma F., T. Koller, and A. Klug, 1979, J. Cell Biol., 83:403-427; Worcel A., S. Strogartz, and D. Riley, 1981, Proc. Natl. Acad. Sci. USA, 78:1461-1465), and that subsequent compaction occurs by coiling of the ribbon to form a double helical structure. This type of folding generates a fiber in which the nucleosome-nucleosome contacts established in the zig-zag ribbon are maintained and in which the histone H1 molecules occupy equivalent sites. The diameter of the fiber is not dependent upon the nucleosome repeat length. Direct mass values for individual isolated fibers obtained from electron scattering measurements showed that the mass per length was dependent on ionic strength, and ranged from 6.0 X 10(4) daltons/nm at 10 mM NaCl to 27 X 10(4) daltons/nm at 150 mM salt. These values are equivalent to 2.5 nucleosomes/11 nm at 10 mM NaCl and to 11.6 nucleosomes/11 nm at 150 mM salt and are consistent with the range of packing ratios for the proposed helical ribbon.

Electron microscopic analysis of RNA transcription in preimplantation rabbit embryos.

We have examined directly RNA synthesis in several stages of preimplantation rabbit embryos by electron microscopic analysis of chromatin spreads. DNA/chromatin packing ratios were determined for non-transcribing regions (2.0) and for regions active in RNA synthesis (1.1). Significant amounts of RNA transcription were observed in all embryonic stages examined. Lengths of transcribed regions were calculated and range from 1.1 to 10.9 Kb of B-form DNA. The frequency of chromatin-associated ribonucleoprotein (RNP) fibrils was greatly reduced in samples prepared from embryos treated with alpha-amanitin indicating that the RNPs observed were growing chains. The frequency of single and multiple RNP fibrils attached to chromatin is the same at all stages examined implying the absence of extensive modulation of RNA chain initiation. These results are discussed in relation to the biochemical data on RNA synthesis in preimplantation rabbit embryos.

Characterization of active transcription units in Balbiani rings of chironomus tentans

Specific active transcription units on chromosome IV in the salivary glands of Chironomus tentans have been visualized by the Miller spreading technique and in situ by conventional electron microscopy. These units are likely to be located in the two most conspicuous puffs on chromosome IV, Balbiani ring 1 (BR 1) and Balbiani ring 2 (BR 2). The transcription units in these Balbiani rings generate 75S RNA molecules constituting putative messenger RNA species for the predominant cellular product, the salivary polypeptides. Solitary active transcription units with a mean length of 7.7 μm were observed most frequently. The lateral ribonucleoprotein (RNP) fibers of each unit formed a single length gradient. The number of fibers per unit was 123 (± 24), or about 16 growing RNP fibers per μm of chromosome fiber. The considerable variation in the number of RNP fibers per unit suggests that transcription can be modulated at the level of the individual gene. The modulation is probably achieved via the initiation event and/or via an early pretermination step, but a change in the elongation rate could not be excluded. The number of polymerases starting to traverse the whole gene was estimated to be six per min and transcription unit, and the rate of RNA chain elongation was calculated to be 31 nucleotides per second at 18°C. The properties of the chromosome fiber within the active 75S RNA units and also within their vicinity were studied in the Miller spreads. The inactive chromosome fiber exhibited a uniform beaded conformation, while the active fiber was sparsely and irregularly beaded. Furthermore, the chromosome fiber was more extended in the active 75S RNA unit than in inactive regions (DNA packing ratios of 1.6 and 1.9, respectively). By comparing the properties of the active 75S RNA gene with those of active genes in other systems, it was inferred that the loss of beads and the extension of the fiber in the active unit is probably directly related to the level of transcriptive activity. Finally, a smooth nonbeaded segment of 0.18 μm in length was found to precede the RNP fiber gradient. This segment may have a role in the process of transcriptional regulation. On the basis of comparison with the active transcription units in spread preparations, it was possible to identify active units in the Balbiani rings in sectioned material using conventional electron microscopy. In both BR 1 and BR 2 an active unit appeared as a loop, consisting of a fiber axis and having RNP granules attached to the loop axis by stalks. The growing RNP fibers therefore seem to be organized into granular structures during the transcription process, and the final products in BR 1 and BR 2 are granules, 500 Å in diameter, each containing a 75S RNA molecule.

Analysis of chromatin-associated fiber arrays

Electron microscopic examination of chromatin from embryonic nuclei of Oncopeltus fasciatus and Drosophila melanogaster reveals arrays of chromatin associated fibers. The lengths and spacings of these fibers were analyzed to provide a basis for defining and interpreting regions of transcriptionally active chromatin. The results of the analysis are consistent with the interpretation of some fibers as nascent RNA with associated protein (RNP). The chromatin segments underlying these fiber arrays were classified as ribosomal or non-ribosomal transcription units according to definitions and criteria described by Foe et al. (1976). Nascent fibers on active ribosomal transcription units were analyzed and compared for Drosophila melanogaster, Triturus viridescens, and Oncopeltus fasciatus. A common feature of the fiber patterns on ribosomal TUs is that origin-distal fibers exhibit greater length variability and a lower slope relative to proximal fibers. The region of increased variability in fiber lengths is correlated with the expected location of 28S ribosomal RNA sequences in the distal half of each ribosomal transcription unit. Because 28S ribosomal RNA appears to contain more extensive regions of base sequence complementarity, we suggest that the length of ribosomal RNP fibers is influenced under our spreading conditions by the secondary structure of the nascent RNA. In order to calculate the RNA content of RNP fibers, chromatin morphology was used to estimate lengths of transcribed DNA. The packing ratio of DNA in chromatin, which we express as the length of B-structure DNA divided by length of chromatin, is 1.1-1.2 and 1.6 for the DNA in active ribosomal and non-ribosomal chromatins, respectively. These DNA packing ratios are used to determine the extent to which nascent RNP fibers are shorter than the transcribed DNA (expressed as DNA/RNP length ratio). For non-ribosomal transcription units and for proximal fibers of ribosomal transcription units. DNA/RNP length ratios are relatively constant within each array. However, considerable variability in this ratio (4-23) is observed for different arrays of fibers. Possible sources of this variability are considered by comparing ratios derived from the presumably identical ribosomal transcription units. Further analysis of the morphology of nascent fibers may elucidate the contributions of proteins and successive RNA sequences to RNP structure.

New Periodic Close Packings of Identical Spheres

I DESCRIBE here very briefly eleven new periodic close packings of identical spheres. Current literature cites (at most) six, which are: “diamond”, (β-ZnS (“wurtzite”), Cubic-P, Cubic-I, Cubic-F and hexagonal closest packed (h.c.p.)—the first two having the (same) lowest packing ratios and four-fold coordination and the last two the (same) highest-possible packing ratios and twelve-fold coordination. The two notations (Table 1, columns 1 and 2) should be fairly obvious when related to the “old” packings. The detailed consideration of, for example, high planar densities, “continuous deformation” and spherical voids has been omitted here.

On random sequential packing in the plane and a conjecture of palasti

The random packing of geometric objects in one-, two- or three-dimensions may afford useful insights into the structure of crystals, liquids, absorbates on crystals, and in higher dimensions, into problems of pattern recognition. Random packing has accordingly received increasing attention in recent years. Two principal packing procedures have been formulated and each gives rise to different packing ratios. In one case, all possible configurations of a sphere-packed volume are assumed to be equally likely. In the other and most widely reported case, there is random sequential addition of spheres to the volume until it is packed. This is the situation we study in this paper. Most of the work to date has been limited to the theoretical study of the one-dimensional lattice or to continuous cases particularly in the limit for long lines. The higher dimensional cases have resisted theoretical attack but have been studied by computer simulation by Palasti [12] and Solomon [14] and by physical simulation by Bernal and Scott (see [14]).

On random sequential packing in the plane and a conjecture of palasti

The random packing of geometric objects in one-, two- or three-dimensions may afford useful insights into the structure of crystals, liquids, absorbates on crystals, and in higher dimensions, into problems of pattern recognition. Random packing has accordingly received increasing attention in recent years. Two principal packing procedures have been formulated and each gives rise to different packing ratios. In one case, all possible configurations of a sphere-packed volume are assumed to be equally likely. In the other and most widely reported case, there is random sequential addition of spheres to the volume until it is packed. This is the situation we study in this paper. Most of the work to date has been limited to the theoretical study of the one-dimensional lattice or to continuous cases particularly in the limit for long lines. The higher dimensional cases have resisted theoretical attack but have been studied by computer simulation by Palasti [12] and Solomon [14] and by physical simulation by Bernal and Scott (see [14]).