Stages Of Fall Research Articles

Fatigue performance analysis of stainless steel cruciform joint with angular misalignment

AbstractWelding distortion causes the change of stress distribution of load‐carrying cruciform stainless steel welded joints, and the weld with angle less than 90° between steel plates became the fatigue performance control weld because of stress magnification. The effect of angular misalignment on fatigue performance of stainless steel cruciform welded joint was experimentally and numerically studied. The fatigue damage evolution equations, under different stress amplitudes, were derived using relative deformation increment as damage variable based on continuum damage mechanics to explain the process of damage transformation from micro to macro crack and finally rapid fracture. The hot spot stress magnification factor was positively correlated with the welding distortion angle and exhibited two discernible stages of rise and fall with increasing nominal stress taking the proportional limit as boundary. A proposed formula considering both misalignment angle and applied stress aimed to enhance accuracy in fatigue performance evaluation compared to current methods.

Availability of Technological Learning Applications and Tools, Science Teachers’ Levels of Use of Online Teaching, and Their Stages of Concerns

Using descriptive-correlational research design, this study determined the relationship between the availability of technological learning applications and tools, and science teachers’ levels of use of online teaching, and their stages of concern. It was conducted at the Schools Division of Laoag City involving all elementary science teachers who are teaching online for the SY 2021-2022. Hence, the purposive sampling technique was used to determine the teachers involved in the study. Findings revealed that the respondents are young adult. The majority of them are female. Most of them are teaching Science for less than five years. Their mean years of teaching Science is 9.44. Majority of them have masters’ units and they have attended trainings and seminars related to online teaching. The respondents have the availability of technological learning applications and tools in online teaching. The teachers’ level of use of online teaching falls at Level V (Integration Stage) while the teachers’ stages of concern fall at Stage 0 (Awareness). Findings also revealed that only the teachers’ number of years teaching in Science is significantly related to their level of use of online teaching.

Impact of meteoric water flushing on diagenesis of deep-marine turbidite sandstones: A case study from the Tertiary sandstones of Frigg and Grane fields, northern North sea

Meteoric water flushing into deep-marine environments is a topic of debate since the actual transport mechanism remains elusive. In order to evaluate the potential impact of meteoric water on early diagenesis of deep-marine sandstones, two submarine fan sandstone reservoirs, the Eocene Frigg (Frigg oilfield) and the Palaeocene Heimdal (Grane field) that have the same source area, were compared and contrasted. Petrographic studies reveal that both sandstone reservoirs are at the eodiagenesis stage (<70 °C) at the present day. However, the Eocene Frigg sandstones are characterized by geological features suggestive of potential meteoric water diagenesis, such as dissolution and kaolinization of the silicate grains, whereas the Palaeocene Heimdal sandstones show negligible alteration. The δ13CV-PDB and δ18OV-PDB values of siderites in the Eocene Frigg sandstones range from +5.2‰ to +16.7‰, and from −8.2‰ to −6.6‰, respectively, indicating siderite formation during methanogenesis in meteoric pore water. Results from generic hydrogeochemical modelling scenarios lend further support to the hypothesis of meteoric water flushing. Thus, we suggest that massive meteoric water might have been brought into the Frigg turbidite sands by basinward migration of the meteoric water. This occurred because the East Shetland Platform experienced two stages of relative sea-level fall (during and at the end of the Eocene, Priabonian), and flushing might have taken place via connected incised canyons. The location of the Frigg sands deposited immediately below the Shetland escarpment and the narrow palaeo-shelf area may have facilitated such meteoric water incursions. Our study suggests meteoric water intrusions as a possible diagenetic control of deep-marine sandstones, and, therefore, meteoric water diagenesis should be considered in the prediction of properties of deep-marine sandstone reservoirs.

Lagoonal reef island formation in Huvadhoo atoll, Maldives, highlights marked temporal variations in island building across the archipelago

Coral reef islands provide the only pedestals of human habitation in mid-ocean atoll archipelagoes. Understanding the environmental controls on island formation is critical for evaluating the future response of islands to environmental change and sea-level rise. This study examines the evolution of lagoonal reef islands in Huvadhoo atoll, southern Maldives. Using extensive ground penetrating radar (GPR) imaging of island sediment structure, combined with comprehensive analysis of island morphology, sedimentology, and 49 radiometric dates, detailed reconstructions of the evolution of two lagoonal islands is presented. A four-stage model shows a complex history of island formation across various stages of sea-level change during the late-Holocene: 1) lagoon infill occurring from ~3000–2000 years ago during a period of sea-level fall from the mid-Holocene highstand; 2) emergence of the island core through vertical aggradation during the latter stages of sea-level fall between ~2000 and 1500 yBP; 3) rapid lateral expansion of the islands between 1500 and 500 yBP coincident with the availability of sand-size sediments and during a period of sea-level oscillation; and, 4) subsequent minor expansion and modification of island shorelines through alongshore reworking of island sediments over the past 500 years. Results provide evidence of marked differences in the timing and mode of island formation within Huvadhoo atoll. Significantly, the formation of the lagoonal islands post-dates the formation of islands on the atoll rim by 1000–2000 years. Furthermore, the formation of sand islands over infilled shallow lagoons contrasts the formation of most atoll rim islands through the sequential deposition of storm-generated rubble deposited directly across reef surfaces that have reached their vertical growth limit. Results of lagoonal island formation in the southern Maldives provide comparative data for the northern Maldives. While the sequence of island formation follows the faro infill model identified in the northern archipelago, lagoonal islands in the south appear to have formed 2000 years after those in the north. This difference is likely to reflect lagged reef growth response from deeper foundations in the southern archipelago.

Rise and fall of interactions with brand communities

PurposeThis paper investigates the impact of consumer relationships with brand communities on behavioral interactions on Instagram. The objective is to identify different types and stages of relationships between consumers and brand communities on Instagram using social penetration theory and explain the behavioral interactions of consumers resulting from these relationships across different stages.Design/methodology/approachA mixed method strategy was employed combining a qualitative multi-case study and an online survey. Eight individuals following restaurant and apparel brands on Instagram participated in the first study and 202 samples participated in the online survey.FindingsFifteen different types of relationships were identified between consumers and brand communities on Instagram and were classified into five stages ranging from orientation to de-penetration. The results reveal that behavioral interactions (i.e. consuming and participating) rise across the first four stages of brand community relationship development and fall down at the fifth stage.Originality/valueThis paper introduces new relationship types and stages and brings together different pieces of extant literature to explain the rising and falling of behavioral interactions resulting from consumer relationships with brand communities on Instagram.

The nature, function, and destiny of the human body—Origen’s interpretation of 1 Cor 15

Abstract In this article, I will investigate Origen’s use of two metaphors: The seed metaphor and the clothing metaphor. Both metaphors are found in Paul’s first letter to the Corinthians, which Origen uses as his biblical foundation in the passage from On First Principles that will be analyzed in this article. My focus will be on how Origen understands the nature, the function, and the destiny of human beings and especially of human bodies. According to Origen, the nature of the human body is changeable and unstable. This is because the bodily matter has merely been added to the rational beings at a certain time and will disappear again when its function is fulfilled. The function of the human body is to clothe the rational being on its way through fall and spiritual progress towards perfection. Thus, the body allows the rational being to be punished and educated. The destiny of the human body is eventually to disappear, but this will only happen when the body has gone through many stages of fall and progress in its service of the rational being.

Karst Conduit Networks, Connectivity and Recharge Dynamics of a Sinkhole

Management of karst aquifers is often limited by a lack of understanding of recharge and flow dynamics. This article presents the identification of conduit networks and the connectivity, dynamic nature of recharge and inherent uncertainties in recharge assessment in karstic settings. The study was carried out at two large sinkholes located in the Poocher Swamp fresh water lens, south east of South Australia. Point recharge to the sinkholes was calculated using stream flow data at gauging stations and water balance of the swamp. Conduit system and their interconnectivity in the vicinity of sinkholes were characterized by the use of transient electromagnetic survey (TEM) to identify high potential porosity zones of the aquifer. Resistivity data were used to estimate aquifer porosities using Archie’s law. Recharge response to the karstic aquifer was monitored using four monitoring wells located at various distances from sinkholes. Measurements were taken during recharge and recession phases. Four dynamic stages of water level rise and fall were observed in response to filling of conduit zones, transmission and possible effects of entrapped air pressure within conduits. Electrical conductivity (EC) profiles were obtained at two stages. These confirmed interconnectivity of conduits, and re-adjustment to ambient groundwater quality following the recharge event. The lower EC water was found in the monitoring well furthest from the sinkholes indicating the complexity of conduit connection and the nature of mixing with ambient groundwater.

Study of the dynamic interaction between planetary vehicles and planets soft soil

This paper examines expanding the range of manoeuvrability, ease of motion and improving the mobility system of Mars rovers. The focus of the research is on the enhancement of rover's speed and mobility under numerous constraints imposed by rugged and difficult-to-navigate terrains that include abrupt change of ground level, soft soil, obstacles and rocks. The article presents a study and simulation of the dynamic response of a free fall of a quarter vehicle model with rigid wheel on a soft soil. A simplified form of Bekker's equation is incorporated in the numerical solution of the governing equations of motion. The response of the dynamic interaction of rigid wheel and soft soil has three stages: sinkage stage, equilibrium stage and pullout from soil stage. The rigid body mode of the dynamic response is required to let the sprung mass pullout the rigid wheel from soft soil. The simulation results demonstrate that the first three stages of the first fall are the most significant. They have larger sinkage, larger resistance force and larger amplitude of dynamic response. The existence of damping reduces the magnitudes and prevents the unsprung mass from pulling out the wheel from the soil. The normal force on the rigid wheel for this case can be approximated and replaced by a triangle-shaped distribution. The simulations results conform to the theoretical counterparts.

Biparental behavior in the burying beetleNicrophorus orbicollis: a role for dopamine?

Burying beetles Nicrophorus orbicollis exhibit facultative biparental care of young. To reproduce, a male–female burying beetle pair bury and prepare a small vertebrate carcass as food for its altricial young. During a breeding bout, male and female behavior changes synchronously at appropriate times and is coordinated to provide effective care for offspring. Although the ecological and evolutionary factors that shape this remarkable reproductive plasticity are well characterized, the neuromodulation of parental behavior is poorly understood. Juvenile hormone levels rise dramatically at the time beetle parents accept and feed larvae, remain highly elevated during the stages of most active care and fall abruptly when care is terminated. However, hormonal fluctuations alone cannot account for this elaborate control of reproduction. The biogenic amines octopamine (OA), dopamine (DA), and serotonin (5-HT) mediate a diversity of insect reproductive and social behaviors. In this study, we measured whole brain monoamine levels in individual male and female burying beetles and compared OA, DA, and 5-HT profiles between breeding (parental) and nonbreeding, unmated beetles. Remarkably, after 24 h of care, when parental feeding rates begin to peak, DA brain levels increase in breeding beetles when compared to nonbreeding controls. In contrast, brain OA and 5-HT levels did not change significantly. These results provide the first evidence for a potential role of DA in the modulation of burying beetle parental behavior.

Carbon and oxygen isotope variations of the Middle–Late Triassic Al Aziziyah Formation, northwest Libya

This study presents the δ13C and δ18O records from whole rock samples of the Middle-Late Triassic (Ladinian-Carnian) Al Aziziyah Formation that were deposited on a gently sloping carbonate ramp within the Jifarah Basin of Northwest Libya. The Al Aziziyah Formation consists of gray limestone, dolomite, and dolomitic limestone interbedded with shale. The Ghryan Dome and Kaf Bates sections were sampled and analyzed for carbon and oxygen isotope chemostratigraphy to integrate high-resolution carbon isotope data with an outcrop-based stratigraphy, to provide better age control of the Al Aziziyah Formation. This study also discusses the relation between the facies architecture of the Al Aziziyah Formation and the carbon isotope values. Seven stages of relative sea level rise and fall within the Ghryan Dome were identified based on facies stacking patterns, field observations and carbon stable isotopes. The Al Aziziyah Formation δ13C chemostratigraphic curve can be partially correlated with the Triassic global δ13C curve. This correlation indicates that the Al Aziziyah Formation was deposited during the Ladinian and early Carnian. No straight-forward relationship is seen between δ13C and relative sea level probably because local influences complicated systematic environmental and diagenetic isotopic effects associated with sea level change.

Multiple-year assessment of phenological plasticity within a beech (Fagus sylvatica L.) stand in southern Germany

Phenological traits such as unfolding of leaves in spring and onset of leaf coloring in autumn are powerful data that can be used to assess the local adaptation of plants to regional climate conditions and to track climate change in nature. Phenotypic variability in beech has been widely studied, but most of the investigations emphasize the variation between populations. The aim of this study was to explore phenotypic responses at the individual level within a beech population, comparing in a stand the annual phenological patterns as well as leaf area index (LAI) courses for three consecutive years (2010–2012). Thirty adult beech trees were randomly selected in a forest in southern Germany for which the seasonal pattern in LAI and different stages of leaf unfolding, leaf coloring and leaf fall were recorded biweekly/three times a week by hemispherical photographs and visual observations, respectively. Based on their phenological and LAI patterns we were able to analyze in detail the phenological variation of individual trees between seasons over a three year study. Our main results confirm that LAI based on hemispherical photographs was correlated with the ground phenological observations. Surprisingly, they suggest that the phenological patterns of individual beech trees compared to their stand neighbors were not necessarily fixed; instead they showed annually very plastic phenotypic responses. Not having a fixed phenological pattern may be a strategy to cope with a wide range of environmental conditions in an ever-changing climate.

Climate, duration, and mineralogy controls on meteoric diagenesis, La Molata, southeast Spain

We isolated the impact of climate, duration, and mineralogy on porosity enhancement and cementation associated with seven surfaces of subaerial exposure in Miocene carbonate strata of southeast Spain. We integrated new and published petrographic and geochemical studies on the same strata to quantify the approximate impact of each event of subaerial exposure. The results quantified that only minor dissolution and/or cementation occurred when subaerial exposure was short-lived ([Formula: see text] thousand years) and in an arid climate, or when carbonate sediments were composed primarily of calcite. For such exposure surfaces, alteration was confined to the uppermost 0.5–2 m with 2%–5% porosity from dissolution and 3% cementation. After deposition of the last Miocene carbonate sequence, dolomitization and dissolution occurred during the initial stages of sea-level fall, associated with mixing during influx of meteoric water. This resulted in dissolution to create 10%–20% porosity over 83% of the platform system, and this indicated that even incipient subaerial exposure can lead to major porosity enhancement during times of high freshwater recharge and hydrogeology that promotes mixing. During a long-lived period of subaerial exposure (greater than 5.3 million years) associated with wet climate, major amounts of cementation reduced porosity in the phreatic zone and some porosity was enhanced in the vadose zone. This included 25% freshwater calcite cement affecting 53% of the platform. Dissolution during and after calcite cementation was approximately 8% throughout the platform. These observations predict that duration and climate combine to have the most significant impacts on porosity associated with subaerial exposure.

Late Miocene sedimentary architecture of the Ebro Continental Margin (Western Mediterranean): implications to the Messinian Salinity Crisis

The Messinian Salinity Crisis (MSC) resulted from a significant multi-phase drop and subsequent reflooding of the Mediterranean Sea from 5.96 to 5.33 Ma. Well-developed drainage networks, characterized by step-like profiles and abrasion platforms, are associated to this event. The Ebro Continental Margin (Western Mediterranean) presents an additional complexity since the capture of the drainage of the adjacent subaerial Ebro Basin took place sometime prior to the Messinian stage. Using 3D seismic reflection data, this work provides new insights into the origin of the step-like profile of the Messinian erosional surface (MES) and timing of the capture of the subaerial Ebro Basin. The results obtained indicate a sedimentary-active continental slope and delta progradation during Middle-Late Miocene, in a normal regressive context associated to a pre-Messinian proto-Ebro River. The mature development attained by the Messinian Ebro River network during the MSC corroborates that the capture of the Ebro Basin occurred prior to the MSC. The configuration of the clinoforms below the MES suggests that deltaic sediments of the Messinian Paleo-Ebro River deposited during the Tortonian and initial Messinian sea-level drawdown. The MES formed at the top of the Tortonian Highstand, where a fluvial network was deeply carved, and in the topset region of the Messinian Falling Stage Systems Tract, where minor erosion occurred. Fluvial deposits are outstandingly preserved on the main valleys of the MES. Therefore, the step-like profile of the MES was not created during Zanclean inundation, but during the latest stages of the main Messinian sea-level fall and lowstand.

SEQUENCE STRATIGRAPHY OF DINOSAUR LAKE: SMALL SCALE FLUVIO-DELTAIC STRATAL RELATIONSHIPS OF A DINOSAUR ACCUMULATION AT THE AARON SCOTT QUARRY, MORRISON FORMATION, SAN RAFAEL SWELL, UTAH

Stratal geometries, cyclical stacking patterns, and taphonomic analysis of the Aaron Scott Quarry in the Jurassic Morrison Formation indicate that sediments accumulated within a prograding fluvio-deltaic lacustrine system. Sediments were deposited during the progressive fill of a large lake. Stratal geometries and stacking patterns display relationships similar to larger-scale deltaic sequences caused by fluctuations in base level. Stratigraphic, paleontologic, and sedimentologic analysis indicates that water-volume-driven, base-level changes were responsible for the accumulation and preservation of the assemblage. The assemblage accumulated during a lowering of base level during the late stages of an overall fall caused by drought and was buried by a rapid rise at the end of the drought. Fluvio-deltaic lake fill consists of numerous off-lapping beds of sparsely bioturbated, coarsening-upward mudstone capped by thin, bioturbated silty mudstones. Erosional surfaces dip to the west and cut older mudstone parasequences. Retrogradation, aggradation, and progradation of strata typify stratigraphic trends above the erosion surface. Coarse braided stream sands cap off successive sequences as accommodation is filled prior to the next lowstand and sequence boundary incisement. The quarry is a large, taxonomically diverse deposit formed by the concentration of animals at the margins of a lake during a drought. Animals congregated near the banks as smaller watering holes dried. Bone locations and orientations indicate reworking by fluvial and wave currents. Vertical preservational trends indicate accumulation over a period of years. Trace fossil, lake invertebrate distributions, and sedimentological evidence indicate that periodic establishment of oxygen stratification within lake waters may have contributed to conditions favorable for bone preservation.

Mapping tree species in temperate deciduous woodland using time‐series multi‐spectral data

AbstractQuestions: What is the optimum combination of image dates across a growing season for tree species differentiation in multi‐spectral data and how does species composition affect overstorey canopy density?Location: Monks Wood, Cambridgeshire, eastern England, UK.Methods: Six overstorey tree species were mapped using five Airborne Thematic Mapper images acquired across the 2003 growing season (17 March, 30 May, 16 July, 23 September, 27 October). After image pre‐processing, supervised maximum likelihood classification was performed on the images and on all two‐, three‐, four‐ and five‐date combinations. Relationships between tree species composition and canopy density were assessed using regression analyses.Results: The image with the greatest tree species discrimination was acquired on 27/10 when the overstorey species were in different stages of leaf tinting and fall. In this image, tree species were mapped with an overall classification accuracy (OCA) of 71% (kappa 0.63). A similar OCA was achieved from the other four images combined (OCA 72%, kappa 0.64). The highest classification accuracy was achieved by combining three images: 17 March, 16 July, 27 October. This achieved an OCA of 84% (kappa 0.79), increasing to 88% (kappa 0.85) after a post‐classification clump and sieve procedure. Canopy height and percentage cover of oak explained 72% of variance in canopy density.Conclusions: The ability to discriminate and map temperate deciduous tree species in airborne multi‐spectral imagery is increased using time‐series data. An autumn image supplemented with an image from both the green‐up and full‐leaf phases was optimum. The derived tree species map provides a more powerful ecological tool for determining woodland structural/compositional relationships than field‐based measures.

Biogeochemistry of a deep-sea whale fall: sulfate reduction, sulfide efflux and methanogenesis

Deep-sea whale falls create sulfidic habits Supporting chemoautotrophic communities, but microbial processes underlying the formation Of Such habitats remain poorly evaluated. Microbial degradation processes (sulfate reduction, methanogenesis) and biogeochemical gradients were studied in a whale-fall habitat created by a 30 t whale carcass deployed at 1675 m depth for 6 to 7 yr on the California margin. A variety of measurements were conducted including photomosaicking, microsensor measurements, radio-tracer incubations and geochemical analyses. Sediments were Studied at different distances (0 to 9 in) from the whale fall. Highest microbial activities and steepest vertical geochemical gradients were found within 0.5 m of the whale fall, revealing ex situ sulfate reduction and in vitro methanogenesis rates of up to 717 and 99 mmol m(-2) d(-1), respectively. In sediments containing whale biomass, methanogenesis was equivalent to 20 to 30%, of sulfate reduction. During in vitro sediment studies, sulfide and methane were produced within days to weeks after addition of whale biomass, indicating that chemosynthesis is promoted at early stages of the whale fall. Total sulfide production from sediments within 0.5 m of the whale fall was 2.1 +/- 3 and 1.5 +/- 2.1 mol d(-1) in Years 6 and 7, respectively, of which similar to 200 mmol d(-1) were available as free sulfide. Sulfate reduction in bones was much lower, accounting for a total availability of similar to 10 mmol sulfide d(-1). Over periods of at least 7 yr, whale falls can create sulfidic conditions similar to other chemosynthetic habitats Such as cold seeps and hydrothermal vents.

Controls on the degree of fluvial incision of continental shelves

During sea-level low stands continental shelves were dissected by a network of channels somewhat resembling today's coastal plain streams. The network was subsequently buried or erased by marine processes during sea-level transgression, so that only some tracts are still conserved in the geological record. Herein we use a numerical model to study the effect of base level change by sea-level fall on the total channel incision. We find that four factors control the total incision on the shelf: (i) the presence of convex deposits; (ii) the evolution of the rivers towards equilibrium (graded) conditions; (iii) geometrical differences between coastal plain and shelf; and (iv) the exposure of the continental slope. The conceptual model is then applied to the Adriatic Sea, Italy. Simulations show that incisions in the Adriatic shelf develop in high stand fluvial deposits in the early stages of sea-level fall. At lower sea level, fluvial incision occurs in the mid-Adriatic due to the regrading of the Po River after the capture of the Apennine streams in its drainage system.

Cyclicity in Pleistocene upper-slope cool-water carbonates: Unravelling sedimentary dynamics in deep-water sediments, Great Australian Bight, Odp Leg 182, Site 1131A

Ocean Drilling Program Site 1131, located in the central Great Australian Bight, recovered an expanded series of Pleistocene cool-water carbonates. Three distinct facies are arranged in repeating sedimentary cycles. Omission intervals form the base of the cycles and are overlain by laminated deposits. The upper part of the cycles consists of bioturbated sediments. Facies cyclicity parallels glacial–interglacial sea-level changes. Firmground/hardground surfaces formed during latest stages of sea-level falls. Laminated sediments were deposited during later sea-level fall and/or early phases of the sea-level lowstand, and the bioturbated intervals are related to interglacial sea-level highstands. Bottom current activity is interpreted to play an important control on facies and cycle development. During the late stages of sea-level fall, upwelling currents winnowed the slope sediments, leading to hardground formation. During latest sea-level falls and early sea-level lowstands, a relative increase in the ramp sediment supply to the slope leading to the formation of the laminated facies was also a response to the continued action of the near-bottom upwelling currents that reworked previously deposited sediments along the slope. During the early sea-level rises, laminated, upwelling-influenced facies were progressively covered by the bioturbated facies. The adopted approach to decipher sedimentary cyclicity, involving the integrated use of wireline logs, geochemical data, FMS images and sedimentological analysis of the lithofacies has allowed to recognise subtle facies changes in upper-slope settings of a distally-steepened carbonate ramp and their relationship with the sea level, as well as to unravel the importance of the oceanic-current regime in the deposition style on the ramp that otherwise would remain unsolved. This integrated method could be applied to study more precisely apparently homogeneous fine-grained calcareous sediment successions of distal-ramp outcrops.

CRYSTALLIZATION KINETICS OF SYNDIOTACTIC POLYPROPYLENE STUDIED BY TIME-DEPENDENT LIGHT ATTENUATION

Crystallization kinetics of syndiotactic polypropylene ( sPP) was observed by light attenuation measurements. The initial stages of temperature dependent sPP crystallization fall in the range of Rayleigh scattering and Rayleigh-Debye- Gans scattering. Initial time and growth time of crystallization were obtained, and the trend of crystallization temperature dependent linear attenuation coefficient on the radius and the index of the refraction of the spherulite were evaluated. of polymer crystallization are usually carried out by differential scanning calorimetry or X-ray scattering in the wide- and small-angle range, sometimes also by light scattering, dilatometry or time dependent vibrational spectroscopy. Although based on different properties there is not much difference in the sensitivity of all these methods. Reliable data are only obtained from values of the crystallinity in the range of some percent of the final values. This means that for growing spherulites, which usually reach end sizes in the order of several micrometers, measurements start only at sizes of several hundred nanometers. This, however, is already far away from the initial stages. Nuclei have sizes in the order of several to ten nanometers and these, together with the small hedrites and spherulites existing at the beginning, cannot be observed. To study the objects in these initial stages, one can now use atomic force microscopy (AFM), but this technique has also some shortcomings. Observations by AFM principally refer to the development and growth of spherulites at the free surface of a melt, and conditions here may differ from those in the bulk. In addition, deriving global properties from observations of the development of single objects is sometimes difficult, because a certain selectivity is usually involved. Presently, the work on polymer crystallization has given considerable attention to the possibility that the crystal phase in the final semicrystalline state could be preceded by a transient liquid phase with density different from that of the initial quenched bulk isotropic melt or annealed glassy state. A number of papers have explicitly criticized the spinodal hypothesis and associated experimental studies, favoring the traditional picture of nucleation and growth. Various studies have suggested that the denser transient phase involves chain orientation, and there are good reasons to assume a crystal nucleation and growth which include an intermediate phase in the form of a coverage of the whole volume by a prior mesomorphic phase developing by a mechanism which resembles a spinodal process (7) , or a nucleation into a mesomorphic phase (8) , or the existence of a

Eocene-Oligocene global climate and sea-level changes: St. Stephens Quarry, Alabama

We integrate upper Eocene–lower Oligocene lithostratigraphic, magnetostratigraphic, biostratigraphic, stable isotopic, benthic foraminiferal faunal, downhole log, and sequence stratigraphic studies from the Alabama St. Stephens Quarry (SSQ) core hole, linking global ice volume, sea level, and temperature changes through the greenhouse to icehouse transition of the Cenozoic. We show that the SSQ succession is dissected by hiatuses associated with sequence boundaries. Three previously reported sequence boundaries are well dated here: North Twistwood Creek–Cocoa (35.4–35.9 Ma), Mint Spring– Red Bluff (33.0 Ma), and Bucatunna-Chickasawhay (the mid-Oligocene fall, ca. 30.2 Ma). In addition, we document three previously undetected or controversial sequences: midPachuta (33.9–35.0 Ma), Shubuta-Bumpnose (lowermost Oligocene, ca. 33.6 Ma), and Byram-Glendon (30.5–31.7 Ma). An ~0.9‰ δ 18 O increase in the SSQ core hole is correlated to the global earliest Oligocene (Oi1) event using magnetobiostratigraphy; this increase is associated with the ShubutaBumpnose contact, an erosional surface, and a biofacies shift in the core hole, providing a fi rst-order correlation between ice growth and a sequence boundary that indicates a sea-level fall. The δ 18 O increase is associated with a eustatic fall of ~55 m, indicating that ~0.4‰ of the increase at Oi1 time was due to temperature. Maximum δ 18 O values of Oi1 occur above the sequence boundary, requiring that deposition resumed during the lowest eustatic lowstand. A precursor δ 18 O increase of 0.5‰ (33.8 Ma, mid-chron C13r) at SSQ correlates with a 0.5‰ increase in the deep Pacifi c Ocean; the lack of evidence for a sea-level change with the precursor suggests that this was primarily a cooling event, not an ice-volume event. Eocene–Oligocene shelf water temperatures of ~17–19 °C at SSQ are similar to modern values for 100 m water depth in this region. Our study establishes the relationships among ice volume, δ 18 O, and sequences: a latest Eocene cooling event was followed by an earliest Oligocene ice volume and cooling event that lowered sea level and formed a sequence boundary during the early stages of eustatic fall.