Relative Timing Of Events Research Articles

Carbon dioxide budget in a temperate grassland ecosystem

Eddy correlation measurements of CO2 flux made during May–October 1987 and June–August 1989 were employed, in conjunction with simulated data, to examine the net exchange of CO2 in a temperate grassland ecosystem. Simulated estimates of CO2 uptake were used when flux measurements were not available. These estimates were based on daily intercepted photosynthetically active radiation, air temperature, and extractable soil water. Soil CO2 flux and dark respiration of the aerial part of plants were estimated using the relationships developed by Norman et al. (1992) and Polley et al. (1992) at the study site. Our results indicate that the CO2 exchange between this ecosystem and the atmosphere is highly variable. The net ecosystem CO2 exchange reached its peak value (12–18 g m−2 d−1) during the period when the leaf area index was maximum. Drought, a frequent occurrence in this region, can change this ecosystem from a sink to a source for atmospheric CO2. The degree to which this grassland can become a source of CO2 appears to depend not only on the severity and duration of the drought but also on the timing of the drought event in relation to the growth stage of the prairie vegetation. Comparison with data on dry matter indicated that the aboveground biomass accounted for about 45–70% of the net carbon uptake, suggesting the importance of the below ground biomass in estimating net primary productivity in this ecosystem.

Geochemical control on the evolutionary history of the Ballantrae Complex, SW Scotland, from comparisons with recent analogues

Abstract A combination of geochemical and field investigations of the Ballantrae Complex allows some control on the relative timing of events in its tectono-magmatic history. In particular, the presence of boninitic lava and hyaloclastite confirms an oceanic, supra-subduction zone origin for this early Ordovician ophiolite assemblage. Boninite eruption was preceded by a substantial phase of late Tremadoc island-arc volcanicity and the boninitic units themselves are interbedded with early Arenig primitive island-arc tholeiites. Various supra-subduction zone extensional processes have been invoked to explain boninite occurrences in recently active oceanic island arcs; interarc rifting as a precursor to marginal basin formation is preferred as a model for the Ballantrae Complex. Evidence to support this preference is drawn from the early to mid-Arenig part of the Complex where sandstones derived from mature volcanic arc lavas are conformably overlain by tholeiitic lavas erupted in a back-arc basin; a possible analogue is seen in the active Bransfield Strait marginal basin. Thus, an evolutionary sequence can be envisaged for the Ballantrae Complex which begins with the establishment of an oceanic island arc where supra-subduction zone extension led to the genesis of boninitic lavas. Next, as extension continued, a marginal basin developed wherein sandstones derived from the arc lavas were deposited and tholeiites of ocean island type were erupted. Imbrication of the back arc sequence and accretion of the ophiolite terrane was initiated in the late Arenig by arc-continent collision.

Histone-DNA interactions and their modulation by phosphorylation of -Ser-Pro-X-Lys/Arg- motifs.

The sea urchin sperm-specific histones H1 and H2B are multiply phosphorylated in spermatids, dephosphorylated in the final stages of spermatogenesis to give mature sperm, and rephosphorylated upon fertilization. Phosphorylation in spermatids, and probably at fertilization, occurs at repeated -Ser-Pro-X-Basic-motifs in the distinctive N-terminal basic domains of both histones and at the end of the much longer C-terminal domain of H1. Here we identify the consequences of multiple phosphorylation through comparison of some physical and biochemical properties of spermatid (phosphorylated) and sperm (dephosphorylated) chromatin and histones. Study of the DNA binding properties of the intact histones and isolated basic domains suggests that phosphorylation at three dispersed sites in the C-terminal tail of H1 has little effect on its overall DNA binding affinity, whereas, strikingly, binding of the N-terminal domains of H2B and H1 is abolished by phosphorylation at four or six tandemly repeated sites respectively. Together with the relative timing of events in vivo, this suggests that phosphorylation/dephosphorylation of the N-terminal (and distal end of the C-terminal) tail of H1, and/or the N-terminal tail of H2B, effectively controls intermolecular interactions between adjacent chromatin filaments, and hence chromatin packing in the sperm nucleus.

The September 1988 intracaldera avalanche and eruption at Fernandina volcano, Galapagos Islands

During 14–16 September 1988, a large intracaldera avalanche and an eruption of basaltic tephra and lava at Fernandina volcano, Galapagos, produced the most profound changes within the caldera since its collapse in 1968. A swarm of eight earthquakes (m b 4.7–5.5) occurred in a 14 h period on 24 February 1988 at Fernandina, and two more earthquakes of this size followed on 15 April and 20 May, respectively. On 14 September 1988, another earthquake (m b 4.6) preceded a complex series of events. A debris avalanche was generated by the failure of a fault-bounded segment of the east caldera wall, approximately 2 km long and 300 m wide. The avalanche deposit is up to 250 m thick and has an approximate volume of 0.9 km3. The avalanche rapidly displaced a preexisting lake from the southeast end of the caldera floor to the northwest end, where the water washed up against the lower part of the caldera wall, then gradually seeped into the avalanche deposit and was completely gone by mid-January 1989. An eruption began in the caldera within about 1–2 h of the earthquake, producing a vigorous tephra plume for about 12 h, then lava flows during the next two days. The eruption ended late on 16 September. Most of the eruptive activity was from vents on the caldera floor near the base of the new avalanche scar. Unequivocal relative timing of events is difficult to determine, but seismic records suggest that the avalanche may have occurred 1.6 h after the earthquake, and field relations show that lava was clearly erupted after the avalanche was emplaced. The most likely sequence of events seems to be that the 1988 feeder dike intruded upward into the east caldera wall, dislocated the unstable wall block, and triggered the avalanche. The avalanche immediately exposed the newly emplaced dike and initiated the eruption. The exact cause of the earthquakes is unknown.

The Effects of Running Speed on Lower Extremity Joint Moments Generated during the Support Phase

The investigation of the effects of speed related changes on joint moments may be an optimal method to study injury mechanisms indirectly and to identify accommodation strategies to the varied impact and loading forces incurred during running. Four skilled long-distance runners performed eight trials at each of four target speeds (3.06, 3.57, 4.09, and 4.60 m/s). Peak joint moments about the ankle, knee, and hip and the relative and absolute times for various temporal events were evaluated. The hip moment parameters exhibited the greatest number (59.0%) of significant speed related differences (p<.05) compared to the knee (27.1%) and ankle (25.0%). Increased hip extensor moments were used to decrease the braking forces, and increased knee and hip extensor moments were used to increase the propulsive forces. Absolute times decreased significantly, although relative times were fairly consistent, suggesting that the relative timing of events was invariant within this range of running speeds.

Geological history of Adélie Land and King George V Land, Antarctica: Evidence for a polycyclic metamorphic evolution

Abstract Metamorphic and structural studies in Adelie Land and King George V Land, East Antarctica, show that this part of the East Antarctic Shield can be divided into four different sections. The areas east of Commonwealth Bay show evidence for a polycyclic metamorphic evolution in which low-pressure granulite facies M 1 fabrics (4–4.5 kbar; ∼ 750°C) are overprinted by retrograde hydrated decompression textures of amphibolite facies during M 2 and by late, high-pressure, low-temperature coronas during M 3 (5.7–7.0 kbar, 500–600°C). The regional structure and relative timing of events in the other three areas is consistent with the recognition of these three metamorphic events. The Cape Denison orthogneiss in Commonwealth Bay was intruded after the pervasive low-pressure M 1 event but before the major ductile deformation phases and M 2 . The Cape Denison orthogneiss therefore only suffered the M 2 amphibolite facies metamorphic event and subsequent overprinting by M 3 mid-greenschist facies assemblages involving lawsonite. The Cape Hunter phyllites were deposited after M 2 but before M 3 and consequently were only affected by the mid-greenschist metamorphic event, which also overprinted the amphibolite facies fabrics at Cape Denison. The areas west of Commonwealth Bay underwent the low-pressure granulite facies metamorphism during M 1 , decompression during M 2 but no late M 3 overprint. The variation of the grade of M 3 in the different areas from granulite facies pressures east of Commonwealth Bay to no effect west of Cape Hunter is interpreted as a consequence of differential uplift along shear zones with a north-south strike, which exposed successively deeper levels towards North Victoria Land to the east. This spatial association and the age of M 3 may suggest that there is a connection between M 3 in King George V Land and Adelie Land and the Ross orogeny in North Victoria Land. The recognition of three metamorphic events can be correlated with three radiometric ages previously established for the Cape Denison orthogneiss.

Evaluation of Two Ankle Appliances Using Ground Reaction Force Data

The purpose of this study was to evaluate, using ground reaction force data, two ankle stabilizing techniques commonly used by athletic trainers; the closed Gibney taping procedure and the boot type ankle stabilizer. Each condition was examined in a pre- and postexercise bout. In addition, a no appliance condition was also tested. Eight healthy female athletes were required to perform ten satisfactory trials in each of the five conditions. Ten trial mean values of 34 descriptors of ground reaction force components for each subject/condition were evaluated using multivariate analyses of variance. No significant differences in any of the force or impulse variables were found across conditions. However, significant differences were found in three variables describing the relative timing of events in the footfall (p < 0.05). No significant differences were found between the pre- and postexercise conditions. The variability in the measured parameters. of the no appliance condition was consistently higher than the ankle appliance conditions. The implication of the study was that, in normal running, the ankle appliances did not appear to moderate or change foot function. J Orthop Sports Phys Ther 1986;7(5):244-249.

Surgical complications in Henoch-Schönlein purpura

Intestinal intussusception, perforation, and infarction constitute the major surgical complications in Henoch-Schönlein Purpura (HSP). This report reviews the surgical experience in 13 patients of the 58 treated for HSP at our institution in the past 10 years. In addition, the reported surgical cases of anaphylactoid purpura in the pediatric age are analyzed. Attention is focused on observations not previously emphasized in regard to the timing of the surgical event in relation to the cutaneous manifestation of HSP.

The Role of Timing in Motor Program Representation

A motor program is the representation in memory that controls the sequential structure of a motor skill. The present research was an attempt to determine the degree to which the timing and sequencing components of a motor skill are related in motor-program representation in a serial key-pressing task. Four groups practiced on event sequences varying in the form of the inherent temporal structure. Following training subjects attempted to execute the event sequences from memory as quickly as possible where the maintenance of the inherent temporal structure was not required. Under speed instructions the entire sequence was speeded up, but performance was still strongly influenced by the overall temporal structure acquired during training. The results suggested that the relative timing of events is an integral part of motor program representation, particularly in skills involving rhythmic timing structures. This paper is based on a doctoral dissertation at the University of Oregon, Dr. Steven W. Keele, sponsor. The research was supported by a contract from the Office of Naval Research, Contract No. N00014-67-A-0046-004 to S. W. Keele.

Some aspects of the production of oral and nasal labial stops.

Various measures were made of the electromyographic output of the muscles of the lips during the production of /p/, /b/, /m/, /mp/ and /mb/, to see if there was a difference in the amount or patterning of activity between sounds usually described as “tense” and “lax”. Overall, there is some slight average tendency for “tense” sounds to be produced more forcefully than “lax”, but this tendency is present only for some subjects and when large numbers of responses are averaged. It is not large enough to serve as the basis for a phonemic distinction based on muscular effort. We conclude that the essential difference between /p/ and /b/ lies elsewhere. The present results support a conclusion drawn from other studies that the real difference is in the relative timing of events at the glottis and at the place of oral occlusion.