Time Of Maximum Expansion Research Articles

The cyclic expansion and contraction characteristics of a loess slope and implications for slope stability

Loess covers approximately 6.6% of China and forms thick extensive deposits in the northern and northwestern parts of the country. Natural erosional processes and human modification of thick loess deposits have produced abundant, potentially unstable steep slopes in this region. Slope deformation monitoring aimed at evaluating the mechanical behavior of a loess slope has shown a cyclic pattern of contraction and expansion. Such cyclic strain change on the slope materials can damage the loess and contribute to slope instability. The site showing this behavior is a 70-m high loess slope near Yan’an city in Shanxi Province, northwest China. A Ground-Based Synthetic Aperture Radar (GB-SAR) sensor and a displacement meter were used to monitor this cyclic deformation of the slope over a one-year period from September 2018 to August 2019. It is postulated that this cyclic behavior corresponds to thermal and moisture fluctuations, following energy conservation laws. To investigate the validity of this mechanism, physical models of soil temperature and moisture measured by hygrothermographs were used to simulate the observed cyclic deformations. We found good correlations between the models based on the proposed mechanism and the exhibited daily and annual cyclic contraction and expansion. The slope absorbed energy from the time of maximum contraction to the time of maximum expansion, and released energy from the time of maximum expansion to the time of maximum contraction. Recoverable cyclic deformations suggest stresses in the loess are within the elastic range, and non-recoverable cyclic deformations suggest damage of the loess material (breakage of bonds between soil grains), which could lead to instability. Based on these observations and the models, we developed a quantitative relationship between weather cycles and thermal deformation of the slope. Given the current climate change projections of temperature increases of up to 3.5 °C by 2100, the model estimates the loess slope to expand about 0.35 mm in average, which would be in addition to the current cyclic “breathing” behavior experienced by the slope.

Impact of climate and humans on the range dynamics of the woolly mammoth (Mammuthus primigenius) in Europe during MIS 2

AbstractThe woolly mammoth (Mammuthus primigenius) was widespread in almost all of Europe during the late Pleistocene. However, its distribution changed because of population fluctuations and range expansions and reductions. During Marine Oxygen Isotope Stage 2 (MIS 2), these processes were highly dynamic. Our analyses of 318 radiocarbon dates from 162 localities, obtained directly from mammoth material, confirmed important changes in mammoth range between ~28.6 and ~14.1 ka. The Greenland stadial 3 interval (27.5–23.3 ka) was the time of maximum expansion of the mammoth in Europe during MIS 2. The continuous range was soon fragmented and reduced, resulting in the disappearance of Mammuthus during the last glacial maximum from ~21.4 to ~19.2 ka in all parts of the North European Plain. It is not clear whether mammoths survived in the East European Plain. The mammoth returned to Europe soon after ~19.0 ka, and for the next 3–4 millennia played an important role in the lifeways of Epigravettian societies in eastern Europe. Mammoths became extinct in most of Europe by ~14.0 ka, except for core areas such as the far northeast of Europe, where they survived until the beginning of the Holocene. No significant correlation was found between the distribution of the mammoth in Europe and human activity.

Asymptotic Poincaré compactification and finite-time singularities

We provide an extension of the method of asymptotic decompositions of vector fields with finite-time singularities by applying the central extension technique of Poincaré to the dominant part of the vector field at approach to the singularity. This leads to a bundle of fan-out asymptotic systems whose equilibria at infinity govern the dynamics of the asymptotic solutions of the original system. We show how this method can be useful to describe a single-fluid isotropic universe at the time of maximum expansion, and discuss possible relations of our results to structural stability and non-compact phase spaces.

Fire resistance of concrete filled square steel tube columns subjected to eccentric axial load

The fire resistance of concrete filled square steel tube columns (CFT columns) without fire protection under a constant axial load has been previously examined. The purpose of this present study is to investigate the fire resistance of CFT columns when they are subjected to combined loads. This paper presents a nonlinear thermal stress analysis method for predicting the mechanical behavior and fire resistance of CFT columns under eccentric axial load (axial load and flexure moment). This method is based on the stress-strain characteristics of materials at high temperatures and on the mechanics of column deflection curves. From the results of the developed computational technique, it was demonstrated that as the yield stress and rigidity of the steel tube rapidly decreased for approximately 30 minutes, the decrease of flexure moment capacity increased significantly more than that of the axial load capacity. In addition, as the load eccentricity ratio increased, the fire resistance time drastically decreased. However, the time of maximum expansion under eccentric axial load was independent of the load eccentricity ratio.

Analytical expressions for primary Bjerknes force on inertial cavitation bubbles

The primary Bjerknes force is responsible for the quick translational motion of radially oscillating bubbles in a sound field. The problem is classical in the case of small-amplitude oscillations, for which an analytical expression of the force can be easily obtained, and predicts attraction of sub-resonant bubbles by pressure antinodes. But for high-amplitude sound fields the bubbles undergo large-amplitude nonlinear oscillations, so that no analytical expression for the force is available in this case. The bubble dynamics is approximated on physical grounds, following the method of Hilgenfeldt [J. Fluid Mech. 365, 171 (1998)], but carefully accounting for surface tension. The analytical expression of the maximum radius of the bubble is recovered, the time of maximum expansion is noticeably refined, and an estimation of the collapse time is found. An analytical expression for the time-varying bubble volume is deduced, and the Bjerknes force is obtained in closed form. The result is valid for any shape of the sound field, including purely standing or purely traveling waves, and is ready to use in a theoretical model of bubble cloud evolution. In addition, the well-known sign inversion of the Bjerknes force for large standing waves is recovered and the inversion threshold in the parameter space is obtained analytically. The results are in good agreement with numerical simulations and allow a quantitative assessment of the effects of physical parameters. It is found that either reduction of the surface tension or increase in the static pressure should produce a widening of the bubble-free region near high-amplitude pressure antinodes.

Origin of time asymmetry.

It is argued that the observed thermodynamic arrow of time must arise from the boundary conditions of the Universe. We analyze the consequences of the no-boundary proposal, the only reasonably complete set of boundary conditions that has been put forward. We study perturbations of a Friedmann model containing a massive scalar field, but our results should be independent of the details of the matter content. We find that gravitational wave perturbations have an amplitude that remains in the linear regime at all times and is roughly time symmetric about the time of maximum expansion. Thus gravitational wave perturbations do not give rise to an arrow of time. However, density perturbations behave very differently. They are small at one end of the Universe's history, but grow larger and become nonlinear as the Universe gets larger. Contrary to an earlier claim, the density perturbations do not get small again at the other end of the Universe's history. They therefore give rise to a thermodynamic arrow of time that points in a constant direction while the Universe expands and contracts again. The arrow of time does not reverse at the point of maximum expansion. One has to appeal to the weak anthropic principle to explain why we observe the thermodynamic arrow to agree with the cosmological arrow, the direction of time in which the Universe is expanding.

NADH- and Ferredoxin-Dependent Glutamate Synthase in the Life Span of the Second Leaf of Wheat Plant under Conditions of Senescence Induced by Nitrogen Deficiency and Natural Senescence

The aim of this paper was to study, in the second leaf of wheat plants with a long ontogenesis (47 d), the activity of the enzyme which catalyzes the synthesis of glutamic acid. The activity of the NADH-dependent glutamate synthase prevailed in young tissues of not yet fully expanded second leaf at the stage of incomplete autotrophy (at this stage, organic carbon and nitrogen substances are transferred into the leaf). This form was completely inhibited by azaserine (1 mmol1-1). The activity of the ferredoxin-dependent GOGAT increased with increasing leaf blade area, with its peak occuring at the time of maximum expansion of the assimilation area. Thus fd-GOGAT activity was characteristic for the photosynthetic fully autotrophic phase of leaf development which is materialized in completely mature leaf tissues. In plants grown in full-strength Knop's nutrient solution containing nitrogen, fd-GOGAT was active till the early and medium senescence, whereas only to the early senescence in plants grown in a solution lacking nitrogen. No fd-GOGAT could be detected at the stage of late leaf senescence.

Vashon Drift: definition of the formation in the Georgia Depression, southwest British Columbia

Vashon Drift was deposited during the Fraser Glaciation (late Wisconsinan) at the time of maximum expansion of the southwestern part of the Cordilleran ice sheet when it filled the Georgia Depression about 14 500 years ago. The drift is present throughout the depression and comprises till and glaciofluvial and glaciolacustrine sediments derived from source areas surrounding the coastal trough. It is overlain by Capilano Sediments and underlain by Quadra Sand, also of Fraser age. Drift deposition was diachronous and complex, probably caused by alpine glaciers coalescing in the trough with the ice margin repeatedly grounding and floating in seawater. Studies of bedrock striae, till fabrics, and clast provenance reveal that Vashon ice movement was generally southward, although locally controlled by topography. A time–space diagram is presented that confirms the long-held hypothesis that advance and decay of Vashon ice were rapid.

Further evidence of solar oscillations with a period of 160 minutes

Observations made at the Crimean Astrophysical Observatory and the Stanford Solar Observatory during 1979 provide evidence of the existence of oscillations of the sun with a period near 160 minutes. The new observations showed the same period with a phase of maximum expansion as predicted from earlier data; for 1979 the time of maximum expansion of the center of the solar disk was found to be 01:55 UT for the Crimean observatories and 01:58 UT for Stanford with a phase uncertainty of plus or minus 15 minutes. In addition, a new regression line can be found which yields a period of 160.01 minutes or a drift in phase of 31.5 minutes per year in an analysis at exactly 160 minutes. The continued agreement in phase (and amplitude) between the two observatories for four years, as well as the fact that the period of oscillations determined differs from exactly one-ninth of a day, supports the interpretation that solar oscillations are indeed being observed.

The development of auroral and geomagnetic substorm activity after a southward turning of the interplanetary magnetic field following several hours of magnetic calm

A comprehensive study of growth phase and substorm activity following a period of magnetic calm has been conducted through a network of all-sky camera stations, auroral zone magnetic observatories, and particle detectors aboard the Isis 1 satellite. We have carefully documented the observations with the following results. The preexpansive phase are which extended at least from 17 to 05 MLT was responsible for an energy input rate of approx. =3 x 10/sup 16/ ergs/s before breakup. An equatorward drift of this arc of 6 km/min, observed only in the evening sector, remained until after the expansive phase, when its motion stopped abruptly at the time of the maximum poleward displacement of the arcs. Electrons responsible for the prebreakup arc had energies of approx. =1--5 keV. Protons of approx. =4-keV energy were measured equatorward of the electron arc. During the expansive phase, symmetrically traveling disturbances were observed propagating eastward in the evening sector and westward in the morning sector. The propagation stopped for 1--2 min at the time of maximum expansion and then continued, thus suggesting a momentary variation in the rate of convection. Equivalent currents consistent with observed magnetic perturbations represented approximately the same DPZ (twin vortex) pattern before themore » expansive phase as during it; however, although the magnitude of the currents was greater during the expansive phase, the dominant feature during this phase was an intense westward auroral electrojet. The camera observations of diffuse cloudlike aurora showed an injection of approx. =40-keV electrons during the expansive phase along the auroral oval between midnight and 0400 corrected geomagnetic time. Movement of the cloud indicated an eastward gradient drift of the electron population.« less

Dynamics of SO(3, R)-homogeneous cosmologies

Cosmologies having spacelike 3-dimensional homogeneity surfaces on which the group of motions is SO(3, R) (Bianchi Type IX) are investigated. These models generalize the ordinary “closed” Robertson-Walker models. Detailed analytical and numerical treatment is given for those models containing pressureless fluid (dust). Included are proofs that infinite density regions and a time of maximum expansion occur in each model. Extensive discussion is devoted to the evolution of anisotropy and the possibility of “mixing,” a phenomenon characterized by the absence of a horizon in any direction. Numerical examples, illustrating the various types of models, are displayed graphically.