Closure Stages Research Articles

Poly (styrene) latex/modified Na-activated bentonite nanocomposite films: A fluorescence study

We studied film formation of composites of surfactant-free polystyrene (PS) nanoparticles and modified Na-activated bentonite (MLB), by steady state fluorescence (SSF) technique. The films were prepared from a mixture of pyrene (P)-labeled PS particles and MLB at various compositions at room temperature. These films were annealed at elevated temperatures above the glass transition ( T g) temperature of polystyrene for 10 min. Scattered light ( I s) and fluorescence intensities ( I P) from P were measured after each annealing step to monitor the stages of film formation. Evolution of transparency of the composite films was monitored by using photon transmission intensity, I tr. Atomic force microscopy (AFM) was used to detect the variation in physical structure of annealed composite films. The nanocomposite films exhibited a percolation threshold at 20 wt.% MLB content. Below this fraction two distinct film formation stages were observed which are known as void closure and interdiffusion and above this fraction no film formation was detected. At 0–20 wt.% MLB, minimum film formation, T 0, void closure, T v and healing, T h temperatures were determined. Void closure and interdiffusion stages were modeled and related activation energies were determined. Void closure activation energies decreased as the percent of MLB increased, no variation was observed in backbone activation energies.

Spatiotemporal changes of landscape pattern in response to deforestation in Northeastern Turkey: a case study in Rize

Recognition and understanding of landscape dynamics as a historical legacy of disturbances are necessary for sustainable management of forest ecosystems. This study analyzes spatial and temporal changes in land use and forest cover patterns in a typical mountain forest area in Rize Forest Enterprise of the Northeastern part of Turkey. The area is investigated by evaluated the temporal changes of spatial structure of forest conditions through spatial analysis of forest cover type maps from 1984 and 2007 using GIS and FRAGSTATS. The quantative evidences presented here showed that there were drastic changes in the temporal and spatial dynamics of land use/forest cover. As an overall change between 1984 and 2007, there was a net decrease of 2.30% in total forested areas. On one hand, productive forest areas decreased 12,506 ha, on the other hand, degraded forest areas increased 14,805 ha. In examining the changes of crown closure and development stages of forest ecosystem during the study period, the forest stand area with medium crown closures increased. Regenerated area increased while the other development stages were left to grow to mature development stages in the period. These results regarding to crown closure and development stage showed that forest quality has increased but total forest areas decreased. This is partially due to out-migration of rural population in Rize and Cayeli towns. In terms of spatial configuration, analysis of the metrics revealed that landscape structure in Study area had changed substantially over the 23-year study period, resulting in fragmentation of the landscape as indicated by the large patch numbers and the smaller mean patch sizes due to heavy timber subtraction, illegal cutting, and uncontrolled stand treatments.

Film formation from TiO2-polystyrene latex composite: a fluorescence study

This work reports the use of the steady state fluorescence (SSF) technique for studying film formation from TiO2 covered polystyrene (PS) latex particles. The composite films were prepared from pyrene (P)-labeled PS particles by covering them with TiO2 at room temperature and then annealed at elevated temperatures in 10 min time interval above glass transition (T g) temperature of polystyrene. Five different composite films were studied in various TiO2 layer contents. Fluorescence intensities I P from P were measured after each annealing step to monitor the stages of film formation. Films showed considerable increase in I P above the certain onset temperature called minimum film forming temperature, T 0. Void closure and interdiffusion stages were modeled and related activation energies were determined and found to be 23.12 and 92.80 kJ mol−1, respectively.

The effect of clay particles on film formation from polystyrene latex

AbstractFilm formation from surfactant‐free polystyrene (PS) latex was performed in the presence of 5% Na‐montmorillonite (NaMMT). The composite films were prepared from pyrene (P)‐labeled PS particles at room temperature and annealed at elevated temperatures above the glass‐transition (Tg) temperature of polystyrene. Scattered light (Is) and fluorescence intensity (IP) from P were measured after each annealing step to monitor the stages of composite film formation. Minimum film formation temperature, T0, and healing temperatures, Th, were determined. Void closure and interdiffusion stages were modeled and related activation energies were measured. From these results, it was found that the presence of NaMMT in the PS latex film only affects the minimum film formation, but does not affect the void closure and backbone motion activities. POLYM. COMPOS., 27:299–308, 2006. © 2006 Society of Plastics Engineers

Films formed from polystyrene latex/clay composites: A fluorescence study

This study reports a steady-state fluorescence (SSF) technique for studying film formation from surfactant-free polystyrene (PS) latex and Na-montmorillonite (SNaM) composites. The composite films were prepared from pyrene (P)-labeled PS particles and SNaM clay at room temperature and annealed at elevated temperatures in 10-min intervals above glass transition temperature (t3) of polystyrene. During the annealing processes, the transparency of the film improved considerably. Scattered light (Is) and fluorescence intensity (Ip) from P were measured after each annealing step to monitor the stages of film formation. Evolution of transparency of composite films was monitored by using photon transmission intensity, Itr. Scanning electron microscopy (SEM) was used to detect the variation in physical structure of annealed composite films. Minimum film formation temperature, Tq, and healing temperatures, Th, were determined. Void closure and interdiffusion stages were modeled and related activation energies were determined. It was observed that both activation energies increased as the percent of SNaM was increased in composite films.

Aspects of ecological development in managed stands of jack pine and black spruce in northern Ontario: Understory vegetation and nutrient relations

This study investigated relationships between understory vegetation and nutrient pools in managed stands of jack pine (Pinus banksiana Lamb.) and black spruce (Picea mariana [Mill.] BSP) in the Lake Nipigon region of northern Ontario. The species composition, biomass, and nutrient pool sizes in the understory vegetation, as well as biomass and nutrient pools in trees and soils, were determined in 16 managed stands ranging in age from 10 to 53 years since establishment and one mature, natural stand. Patterns of above-ground biomass accumulation in understory vegetation varied with overstory tree species and general site type (dry, sandy soils, or mesic, finer-textured soils). Understory vegetation contributed little (0.3 to 2.6%) to total above-ground organic matter (live biomass plus forest floor) but accounted for higher proportions of total above-ground nutrient pools (e.g., 0.7 to 3.4% of N; 3.2 to 11.7% of K) and net primary productivity (1.2 to 21.2%). The species composition of the understory vegetation was strongly related to stand basal area as well as to concentrations of nutrients (N, P, K, Ca, Mg) in the forest floor and mineral soil. The greatest amount of change in vegetation community composition occurred from the pre-to post-canopy closure stages of stand development; fewer differences were observed among stands of a given species and site type 35 to 50 years after establishment. The effects of silvicultural practices were detected in certain stands 35 years after establishment; for example the most severely treated (bladed and thinned) jack pine stand differed from other stands of similar age and soils with its Cladina/Vaccinium-dominated understory, and large amounts of biomass in the moss/lichen stratum. The understory vegetation communities in other managed jack pine stands, by 35 to 50 years, were similar to that of the mature, natural stand, indicating resilience to silvicultural disturbances. Silviculture may have lasting effects on understory vegetation biomass and species composition through its effects on stand basal area, overstory species, and soil nutrients. This research serves as baseline information for further studies into the ecology of managed stands in northern Ontario. Key words: understory, nutrients, managed forests, jack pine, black spruce, canonical correspondence analysis

Fluorescence study on Al2O3-polystyrene latex composite film formation

This work reports a steady state fluorescence (SSF) technique for studying film formation from mixture of Al2O3 and polystyrene (PS) latex particles. The composite films were prepared from dispersion of pyrene (P)-labeled PS particles in Al2O3 solution at room temperature and annealed at elevated temperatures in 10-min time interval above glass transition (Tg) temperature of polystyrene. Nine different composites film were studied in various latex contents. Fluorescence intensities (IP) from P were measured after each annealing step to monitor the stages of film formation. No variations in IP were detected for the films prepared with higher than 33 wt% Al2O3 content. However films prepared below 33 wt% Al2O3 content show considerable increase in IP above the certain onset temperature called minimum film forming temperature, T0. Healing temperatures Th, were determined from the maxima of IP. Void closure and interdiffusion stages were modeled and related activation energies were determined and found to be 20 and 97 kJ.mol–1, respectively. POLYM. COMPOS., 26:352–360, 2005. © 2005 Society of Plastics Engineers

Film formation from nano-sized polystyrene latex particles

This work reports on the steady state fluorescence (SSF) technique for studying film formation from surfactant-free, nano-sized polystyrene (PS) latex particles prepared via emulsion polymerization. The latex films were prepared from pyrene (P)-labeled PS particles at room temperature and annealed at elevated temperatures in 5, 10, 15, 20 and 30 min time intervals above the glass transition temperature (Tg) of PS. During the annealing processes, the transparency of the film was improved considerably. Monomer and excimer fluorescence intensities, IP and IE respectively, from P were measured after each annealing step to monitor the stages of film formation. Evolution of transparency of the latex films was monitored by using photon transmission intensity, Itr. Void closure and interdiffusion stages were modeled and related activation energies were determined and found to be 10.3 and 50.3 kJ mol−1. Void closure temperatures, Tv, were determined from the minima of Itr value. Copyright © 2005 John Wiley & Sons, Ltd.

Variability of Somatosensory Evoked Potential Monitoring During Scoliosis Surgery

Somatosensory evoked potentials (SEPs) of 65 patients undergoing scoliosis surgery were monitored by stimulation of posterior tibial nerve to observe variations in latencies and amplitudes. Monitoring was divided into five stages: pre incision, spine exposure, instrumentation loading, deformity correction, and wound closure (stages 1-5, respectively). We found the latency showed significant increase and the amplitude significant reduction from stages 1 to 2. There was no significant variability from stages 2, 3, and 4, but both latency and amplitude recovered significantly from stage 4 to 5. This variability correlated with the changes in mean arterial pressure and end-tidal concentrations of isoflurane and was not dependent on the type of surgical procedure. If either 50% amplitude reduction or 10% latency prolongation of SEP compared with baseline recordings at stage 1 (pre incision) was used as warning criterion, the overall false-positive rate was 23.1%. It was significantly reduced to 7.7% if stage 2 (spine exposure) recordings were used as the baseline (P < 0.05). The false-positive rate decreased to 0% if a combined 50% amplitude reduction and 10% latency prolongation of SEP compared with the stage 2 baseline were used (P < 0.001). Based on these findings, we concluded that the time to obtain SEP baseline data should be adjusted to be post incision instead of pre incision.

Film formation from surfactant-free, slightly crosslinked, fluorescein-labeled polystyrene particles

A steady state-fluorescence (SSF) technique for studying film formation from surfactant-free, slightly crosslinked polystyrene (PS) latex particles is reported. The powder films were prepared from fluorescein (F)-labeled PS particles at room temperature. The mechanically strong films were obtained by annealing these films at elevated temperatures in 5, 10, 20, and 30 min time intervals above the glass transition (Tg) temperature of polystyrene. Scattered light (Is) and fluorescence (IF) intensities from F were monitored after each annealing step to investigate the three different film formation stages called void closure, healing, and interdiffusion. The evolution of transparency of the latex films was monitored by using a photon transmission technique. Scanning electron microscopy (SEM) was employed to detect the variation in physical structure of the annealed latex films. Onset temperature for void closure, Tm’, and healing temperatures, Th, were determined and corresponding activation energies were measured. Void closure and interdiffusion stages were also modeled and the related activation energies were also determined. It was observed that lower energy is needed for the void closure process than interdiffusion of chains across the particle-particle boundaries.

Interrelationship between various aging methods, and their relevance to palaeodemography

Age estimations for 64 adult individuals from the Byzantine city of Rehovot-in-the-Negev were carried out using seven different aging methods. Correlation coefficients were calculated between five of the methods, which employed the following anatomical structures: teeth attrition rate, cranial sutures (closure stages), sternal end of ribs, symphysis pubis, and sacroiliac joints. Age estimations were checked against ‘summary age’ (Lovejoy et al., 1985a). Life tables were reconstructed based on summary ages and revised ages separately. It was found that ages obtained from the innominate bones correlated best with the summary age and showed less bias and inaccuracy, while ages obtained from the cranial sutures, showed the opposite. Reconstructing the ‘revised-age’ has no advantage over other aging methods when calculating demographic parameters.

Void closure and interdiffusion processes during latex film formation from surfactant-free polystyrene particles: a fluorescence study

This study reports a steady state fluorescence (SSF) technique for studying film formation from surfactant-free polystyrene (PS) latex particles. The latex films were prepared from pyrene (P)-labeled PS particles at room temperature and annealed at elevated temperatures for 5-, 10-, 20-, and 30-min time intervals above the glass transition ( T g) temperature of polystyrene. During the annealing processes, the transparency of the film changed considerably. Scattered light ( I sc) and fluorescence intensity ( I 0P) from P were measured after each annealing step to monitor the stages of film formation. Evolution of transparency of latex films were monitored using photon transmission intensity, I tr. Scanning electron microscopy (SEM) was used to detect variation in the physical structure of annealed films. Onset temperature for film formation, T 0, void closure, T v, and healing temperatures, T h, were determined and corresponding activation energies were measured. Void closure and interdiffusion stages were modeled and related activation energies were determined.

Germination and Establishment of Infection on Grape Berries by Single Airborne Conidia of Botrytis cinerea.

Table grapes (cv. Dauphine) at different phenological stages were dusted in a settling tower with dry conidia of Botrytis cinerea. The berries were incubated for periods of 3 to 96 h at high relative humidity (RH; ±93% RH, moist berries), or were covered with a film of water (wet berries). Germination of the solitary conidia, appressorium formation, stilbene and suberin induction by germlings, and germling viability were examined by fluorescence microscopy after each incubation period. Isolation and freezing studies were conducted to determine surface colonization (berries left unsterile) and penetration (surface-disinfested berries). Symptoms were determined on berries incubated at a specific wetness regime, kept dry for 10 days, and then incubated for 4 days at high RH. Microscopic observations indicated that germination was delayed on immature berries, but proceeded at a high rate on mature berries. Growth was invariably restricted on moist berries. Attempted penetration was always direct. Stilbene and suberin were generally induced early and were intense on berries at the pea-size and bunch closure stages. Dieback of conidia and germlings occurred at a significantly higher rate on wet than moist berries, and was more pronounced on immature than on mature berries. The segment isolation and freezing studies showed that infections in grape berry cheeks established by this infection mode were few. Extended incubation periods did not lead to substantially higher rates of surface colonization and skin penetration. Disease symptoms did not develop during the 14-day period on the berries transferred to dry perspex chambers, irrespective of phenological stage, incubation period, or wetness regime. According to these findings, this mode of infection should not contribute to a gradual build-up of secondary inoculum in the vineyard, and to B. cinerea epiphytotics.

Evolution of a conjugate passive margin pair in Mesozoic southern Turkey

In the western Tauride belt of southern Turkey, a north pointing cusp (Isparta Angle) occurs along the Mesozoic carbonate axis and encompasses passive continental margin sequences, rift assemblages, mantle peridotites, an ophiolite complex, and platform fragments. The contacts between these tectonostratigraphic units are commonly tectonic with the carbonate platforms forming the autochthonous basement to the west and east directed thrust sheets both in the west and the east. Rift assemblages consist of chert, pelagic limestone, mudstone, sandstone, and alkaline lavas ranging in age from Upper Triassic to Upper Cretaceous and locally include serpentinite lenses. Mantle peridotites are commonly harzburgitic, cut by numerous doleritic dikes, and underlain by a syntectonic mélange. The ophiolite complex occurs in the south, adjacent to and overlying the western platform (Bey Daglari), and consits mainly of peridotites and cumulate gabbros with a poorly developed dike complex and rare extrusive rocks. Platform fragments are represented by north‐south trending slivers of limestones that have affinity with the western platform. They are technically overlain by the rift assemblages and/or mantle rocks within the Isparta Angle. Rock types and associated structures within the Isparta Angle indicate a progressive evolution from continental rifting and passive margin development to ocean basin formation in the Tauride belt of the Neotethyan realm during Triassic to Late Cretaceous time. The pronounced asymmetry in the crustal architecture of the conjugate margins suggests that initial stages of rifting and subsequent extension were probably facilitated by crustal failure along an east dipping (in present coordinates) low‐angle fault. Continued rifting and associated crustal thinning resulted in upwelling and emplacement of the mantle beneath the lower plate and in partial melting of this elevated mantle generating alkaline lavas. Further extension in the south established a spreading system along which Cretaceous oceanic crust, now represented by the Tekirova ophiolite, was created. Contractional deformation in Late Cretaceous to Late Tertiary time caused telescoping of rock units within the Isparta Angle and emplacement of thrust sheets onto the platform carbonates both in the east and the west. The opening and closure stages of the ocean basin within the Isparta Angle were diachronous while the bounding carbonate platforms were probably revolved around a pivoting pole located at or near the apex of this sharp bend in the Tauride belt.

Conifer and Angiosperm Fine-Root Biomass in Relation to Stand Age and Site Productivity in Douglas-Fir Forests

(1) Conifer and angiosperm fine-root biomass were determined in an age sequence (range 13-160 years) of eight high-productivity and seven low-productivity Douglas-fir stands in western Washington, U.S.A. (2) No significant changes in total (conifer plus angiosperm) root biomass occurred among the different stand ages within each productivity class. Of the total fine-root biomass, however, the proportion of angiosperm to conifer roots varied significantly when stands were in the 'tree initiation' and 'competitive tree-stem exclusion' stages of stand development. (3) Conifer fine-root biomass reached a peak at canopy closure in both lowand highproductivity stands. After canopy closure, conifer fine-root and foliage biomass levelled off as basal area continued to increase in the low-productivity stands; however, conifer fine-root biomass decreased as basal area increased and foliage biomass levelled off in the high-productivity stands. (4) At all stand ages, the low-productivity stands had significantly more total (conifer plus angiosperm) fine-root biomass than those of high-productivity. At canopy closure and later stages of stand development, a significantly higher conifer fine-root biomass was maintained in low-productivity compared to high-productivity stands. (5) Conifer fine-root biomass was positively related to litterfall lignin content, litterfall lignin: nitrogen ratio and forest-floor nitrogen content in low-, but not in highproductivity stands; these patterns followed an asymptotic exponential curve.

Mesozoic unconformities in Israel: Characteristics, mode of origin and implications for the development of the Tethys

Nine breaks in the Mesozoic stratigraphic column of Israel are described in terms of their hiatus, type of contact, residual deposits and areal extent. Using these criteria, and by reference to published global eustatic sea level curves, three of the stratigraphic breaks are correlated with global eustatic sea level lowstands (Triassic/Jurassic boundary; Toarcian/ Aalenian; Late Turonian/Coniacian); one probably represents a condensed sequence resulting from a rapid sea level rise (Middle Callovian); four are related primarily to rifting and extension tectonics of the incipient (Anisian; Carnian; Pliensbachian-Sinemurian) or evolving (Early Neocomian) Tethys; and, one reflects a folding phase of the Syrian Arc fold system, related to the early closure stages of the Tethys (Campanian/Maastrichtian). By careful scrutiny of stratigraphic breaks on the margins of the Arabian Craton and by recognition of eustacy-related events, important stages in the tectonic evolution of the Tethys can be reconstructed.

Isolation of cell lines from embryos of the cockroach,Blattella germanica

Cell lines were isolated from three stages of embryos of Blattella germanica dissociated with trypsin. The lines have been subcultured 50 to 134 times in 3 years. Line UM-BGE-1 was isolated from germ band embryos at stages of segmentation and limb-bud formation (5 days old). Line UM-BGE-2 was derived from embryos at dorsal closure (7 days old). Line UM-BGE-4 arose from embryos in the germ band and dorsal closure stages (5 and 7 days old): these cells colonize as hollow spheres or vesicles. Line UM-BGE-5, isolated during organogenesis (10 days old), developed into two distinct sublines. Subline alpha is composed of round cells that do not attach to the flask. Subline beta grows as an attached monolayer; the cells can be removed with a saline solution containing 20 mM disodium dihydrogen Versenate. Most of the cells of these lines have the diploid chromosome number (23 or 24) excepting line UM-BGE-1 in which the tetraploid number predominates

Developmental stages and chemical composition in embryos of the cockroach, Diploptera punctata, with observations on the effect of diet

A developmental time-table has been established for the embryos of viviparous Diploptera punctata. The percentage of gestation time occupied by pre-dorsal closure stages is only 19 per cent compared to 40 or 50 per cent in non-viviparous species. The increase in wet weight of the embryos begins several days before dorsal closure and continues throughout gestation. The increase in dry weight, protein, carbohydrate, and uric acid does not begin until shortly after dorsal closure but thereafter parallels the increase in wet weight. The increase in oöcyte protein during vitellogenesis is tenfold, less than in oviparous or ovoviviparous species. But the increase in embryo protein during gestation is sixtyfold; this characterizes viviparity in D. punctata. Although total lipid increases during gestation, lipid as a percentage of wet weight decreases most rapidly before dorsal closure and less rapidly there-after. It is suggested that before dorsal closure lipid is the major energy source for development. After dorsal closure the embryos are able to drink through their mouths the fluid nutrient provided by the mother. The ultimate source of nutrients required by developing embryos is the maternal diet during gestation. Females starved from ecdysis do not produce young; females fed only sugar from ecdysis produce viable larvae but suffer loss in body weight. Embryos from such females, although normal in length, are deficient in protein.