Natural Strata Research Articles

Laumon parahoric local models via quiver Grassmannians

Local models of Shimura varieties in type A can be realized inside products of Grassmannians via certain linear algebraic conditions. Laumon suggested a generalization which can be identified with a family over a line whose general fibers are quiver Grassmannians for the loop quiver and the special fiber is a certain quiver Grassmannian for the cyclic quiver. The whole family sits inside the Gaitsgory central degeneration of the affine Grassmannians. We study the properties of the special fibers of the (complex) Laumon local models for arbitrary parahoric subgroups in type A using the machinery of quiver representations. We describe the irreducible components and the natural strata with respect to the group action for the quiver Grassmannians in question. We also construct a cellular decomposition and provide an explicit description for the corresponding poset of cells. Finally, we study the properties of the desingularizations of the irreducible components and show that the desingularization construction is compatible with the natural projections between the parahoric subgroups.

Ensemble learning methods of inference for spatially stratified infectious disease systems.

Individual level models are a class of mechanistic models that are widely used to infer infectious disease transmission dynamics. These models incorporate individual level covariate information accounting for population heterogeneity and are generally fitted in a Bayesian Markov chain Monte Carlo (MCMC) framework. However, Bayesian MCMC methods of inference are computationally expensive for large data sets. This issue becomes more severe when applied to infectious disease data collected from spatially heterogeneous populations, as the number of covariates increases. In addition, summary statistics over the global population may not capture the true spatio-temporal dynamics of disease transmission. In this study we propose to use ensemble learning methods to predict epidemic generating models instead of time consuming Bayesian MCMC method. We apply these methods to infer disease transmission dynamics over spatially clustered populations, considering the clusters as natural strata instead of a global population. We compare the performance of two tree-based ensemble learning techniques: random forest and gradient boosting. These methods are applied to the 2001 foot-and-mouth disease epidemic in the U.K. and evaluated using simulated data from a clustered population. It is shown that the spatially clustered data can help to predict epidemic generating models more accurately than the global data.

Using natural strata when examining unmeasured biases in an observational study of neurological side effects of antibiotics

Abstract Fluoroquinolones are widely prescribed antibiotics that carry a US Food and Drug Administration warning about possible side-effects on the central and peripheral nervous system. We compare 436,891 patients with sinusitis treated with fluoroquinolones to two control groups treated with azithromycin or amoxicillin. In addition to looking for nervous system complications, we look for evidence of bias using outcomes for which an effect was not anticipated. The comparison uses ‘natural strata’ that form control groups proportional in size to the treated group and balance many covariates beyond those that define the strata. The main technical contribution is a new method for near-optimal construction of natural strata with multiple groups. The online supplement material contains proofs, details, and information about the R package natstrat and replication.

Forest trees as a natural metamaterial for surface wave attenuation in stratified soils

Forest trees have been shown to act as a natural metamaterial to attenuate elastic waves. However, the existing studies assumed that forest trees are located on homogeneous soils and did not consider the soil stratification that widely exists in natural strata. This study investigates the forest trees as a natural metamaterial to manipulate the propagation of elastic waves in stratified soils. A semi-analytical method is proposed to calculate the dynamic responses of a layered half-space coupled with arbitrary number of trees. A close-form Green’s function for a harmonic line load on a layered half-space is derived by the thin layer method, and subsequently used to determine the multiple scattered wavefield induced by forest trees as surface oscillators. The attenuation performance of forest trees on stratified soils is systematically investigated. Trees with a graded array of heights can provide a wide attenuation zone at frequencies below 80 Hz. Since the higher surface wave modes in a layered half-space can propagate forward without being affected by trees, the attenuation efficiency of trees on stratified soils is significantly lower than that of trees on corresponding homogeneous soils. The performance uncertainty induced by the randomness of the height, sizes, and spacing of trees is subsequently investigated through a Monte Carlo simulation. The forest trees can still obtain a significant attenuation efficiency at frequencies below 80 Hz even the randomness of tree properties being considered. The randomness in height and radius leads to significant uncertainty in attenuation performance, while the randomness in spacing results in reasonable uncertainty.

Influence of non-plastic fine on static iquefaction and undrained monotonic behavior of sandy gravel

Many geological hazards such as landslide, liquefaction, slope failure and rockfall occur in mixed gravelly alluvium or colluvium deposits, highlighting the importance of studying gravel–sand–silt mixtures. Although many natural strata are built using these mixtures, they are not entirely understood. A fundamental experimental study was designed to explore the influence of non-plastic fine content on the undrained behavior of gravel-sand-silt mixtures as common geomaterials in nature. Undrained monotonic triaxial tests were carried out. Three types of sandy gravels with different sand-to-gravel ratios were selected as base gravels. The impacts of the non-plastic fine content on the stress–strain behavior, static liquefaction potential, steady sate line, residual strength and critical state friction angle were studied. The laboratory results show that both sand-to-gravel ratio and non-plastic fine content have significant impacts on the undrained response of gravelly mixtures. It was observed that mixtures with zero non-plastic fines content exhibit the non-flow liquefaction behavior. However, adding silt content up to 45% shows the limited liquefaction or flow behavior, depending on the base gravelly soils and fine content percentage. A threshold for non-plastic fine content was found to be 35%–45%. Below this threshold, the steady state line shifts downward as silt content increases, and then shifts upward with further increase in the silt contents. The identical trend was also noted for residual strength and critical state friction angle. For silt contents below the threshold, the equivalent intergranular void ratio concept (modified with a new logical assumption) was used to analyze the behavior of gravelly mixtures. The results clearly indicate that the accurate value of equivalent intergranular void ratio can fully explain the behavior of sandy gravel-fine mixtures, similar to sand-fine mixtures. From a microstructure perspective, both sand and silt content act as fine-grains in gravelly mixtures and should be considered when studying the mechanical properties of theses mixtures.

Evaluating the Potential of Semi-Automated Image Analysis for Delimiting Soil and Sediment Layers

ABSTRACTEstablished methods for delineating anthropogenic and natural strata during fieldwork are based on the visual and tactile perception of excavators. Modern image analysis techniques can help to ensure objectivity and reproducibility when documenting sections and plana. Within this study we examine the unsupervised classification of digital images as a technique for delimiting layers and identifying stratigraphic features. Assessing the potential of this approach, we exemplarily captured soil profiles with high-contrast stratigraphy, located in the area of a historical vineyard (Brandenburg, Germany). Reproducible analyses were carried out using open-source software, allowing for the future advancement of the methodology utilized and providing a basis for the analysis of more complex stratigraphic sequences. We compare clustering results of high-resolution RGB and hyperspectral images (470–830 nm, 37 bands). Multiple pre-processing and processing steps are carried out to evaluate their influence. Our results render the semi-automatic analysis of RGB images helpful for stratigraphic interpretation.

Crack propagation and crack direction changes during the hydraulic fracturing of coalbed

Hydraulic fracturing is an effective treatment technology to improve reservoir permeability. In this paper, the dual effective stress was introduced into the theoretical analysis of water pressure during crack initiation, and the theoretical analysis results are about 37% more accurate than Hubbert and Willis theory based on the numerical results. Moreover, the artificial-macrocrack effects on fracturing crack propagation and direction changes have been analyzed and compared to hydraulic fracturing without the artificial-macrocrack. The water pressure required for crack initiation with the artificial-macrocracks is less than that without the artificial-macrocracks. When α (α is defined as the angle between the artificial-macrocrack and the horizontal direction) reached or exceeded π/4, crack growth began at the tip of the macrocrack with a higher box counting dimension than that at a lower values of α. Furthermore, a series of simulations have been conducted to obtain the point of fracturing crack direction change when α = 0. The fracturing crack starts to propagate at the artificial-macrocrack tip when λ = 0.95 (λ is defined as the ratio of horizontal stress to vertical stress), and the crack propagation direction becomes vertical when λ = 0.9625. By extracting the crack morphology from the simulation results, it was determined that the box-counting dimension, the crack perimeter, and the crack area proportion reach maximal values at λ = 0.95, λ = 0.9625 and λ = 0.975, respectively. Using image segmentation technology, the impact area proportion reached a maximum at λ = 0.9625 with a more effective treatment than at other values of λ. Finally, beddings and cracks in natural strata were taken into account for fracturing crack propagation, and beddings and cracks could guide the fracturing cracks. More microcracks could be generated along the beddings with the artificial-macrocrack effect at λ = 0.9. Case study indicated that the gas extraction achieved high production in the first 40 days, and the field data with fracturing treatment show that the average pure gas flux is about 4 times greater than that without fracturing. This research also provides a new idea to mine intact rock of construction aggregate.

Observations on seismically induced liquefactionfluidization in reclaimed land at Hinode, Honshu, Japan

As construction and reclamation activities become larger and more widespread the distribution of man-made strata is rapidly extending especially in developed countries. Such strata are often more likely to suffer geohazards or to contain harmful substances than natural strata. In particular, geological disasters are often associated with the unconformity between artificial and natural strata (known in Japan as the Jinji Unconformity) with highly consolidated strata beneath and less consolidated above. The flow of liquids within man-made strata is often less simple than in natural strata and a specific flow system tends to develop at the unconformity. The Great East Japan Earthquake on March 11, 2011 (Magnitude: M7.9, Epicenter: longitude 38°06.22 and latitude 142°51.62 and 24km in depth) affected the Kanto Plain near Tokyo. Large-scale liquefaction fluidization caused by the seismic vibrations was essentially confined to areas with man-made strata. The present study focused on land reclaimed by hydraulic filling at Hinode, a suburb of Itako City, which had been used subsequently for urban development and suffered significant damage. Cored boreholes and observation wells were made to assess evidence of liquefaction. Continuous cores were halved longitudinally and lacquer peels were made and examined using X-ray photograms. Samples taken from liquefaction zones, liquefaction-fluidization zones and non-liquefaction zones were subjected to grain size analysis. A large peel was made from the outcrop in a dewatered trench section. In the Hinode area, the Jinji Unconformity is relatively deep in the centre thinning towards each margin of the reclaimed area, essentially forming an irregular basin shape into which the man-made strata were emplaced. The reclaimed area is dominated by fine sand and silt which is generally more susceptible to liquefaction and fluidization. Therefore it is not surprising that sand eruptions caused by the earthquake of 11 th March 2011 demonstrate widespread liquefaction-fluidization. In the northern and eastern parts of the reclaimed area, where man-made strata, directly overlie the natural Sarawa Sand and Mud Formation and in areas underlain only by natural strata there were relatively few sand eruptions. Although a higher density of ground investigation and sampling points, particularly in a ring about half way between the central area and margins, would be needed to refine these observations and conclusions but it is already clear that the variations laterally and vertically in the distribution of the mobilized layers occurs at a scale of less than 1 meter. This calls into question current Japanese practice for assessing liquefaction and fluidization potential which relies on N-value SPT tests at 1 meter intervals. This needs to be reconsidered.

Rank One Local Systems and Forms of Degree One

Cohomology support loci of rank one local systems of a smooth quasiprojective complex algebraic variety are finite unions of torsion-translated complex subtori of the character variety of the fundamental group. Tangent spaces of the character variety are (partially) represented by logarithmic 1-forms. In this paper, we give a relation between cohomology support loci and the natural strata of 1-forms given by the dimension of the vanishing locus. This relation generalizes the one for the projective case due to Green and Lazarsfeld and also generalizes the partial relation due to Dimca in the quasi-projective case.

Cohomology jump loci of quasi-projective varieties

We prove that the cohomology jump loci in the space of rank one local systems over a smooth quasi-projective variety are finite unions of torsion translates of subtori. The main ingredients are a recent result of Dimca-Papadima, some techniques introduced by Simpson, together with properties of the moduli space of logarithmic connections constructed by Nitsure and Simpson. MB(X) = Hom(π1(X),C ∗ ) to be the variety of C ∗ representations of π1(X). Then MB(X) is a direct product of (C ∗ ) b1(X) and a finite abelian group. For each point ρ ∈ MB(X), there exists a unique rank one local system Lρ, whose monodromy representation is ρ. The cohomology jump loci of X are the natural strata � i (X) = {ρ ∈ MB(X) | dimC H i (X,Lρ) ≥ k}. � i (X) is a Zariski closed subset of MB(X). A celebrated result of Simpson says that if X is a smooth projective variety defined over C, theni (X) is a union of torsion

Prevention of Major Accidents of the Aboveground Parts of Natural Gas Storage Technologies and Shale Gas Production Facilities

This article is intended to describe the most significant hazards associated with the operation of the aboveground parts of shale gas production technology and to compare them with possible hazard of the aboveground parts of natural gas storage technologies in underground storage reservoirs (in natural or artificial spaces in underground geological formations). In both cases, in addition to hazards of treatment of methane (natural gas and shale gas), there are used hazardous chemical substances that may threaten employees and surrounding population. These chemical substances are used for extraction or storage of gas. The issue of prevention of serious accidents of aboveground part of technology for the extraction of shale gas has not yet been solved, but the information about safety and environmental aspects of extracting shale gas has already been described in the last two years, in the article (Pointet, 2011). Safety of chemical constituents used as propping agents is described in the study (Waxman at al., 2011). At present there is no specific legislation of European Union regarding the management of risks of shale gas production, but the update of the European directive 96/82/EC includes storage of natural gas in underground storage. The new Directive 2012/18/EU is generally applicable to all such forms of storage, including the storage in natural gas fields (onshore underground gas storage in natural strata, aquifers, salt cavities and disused mines, and chemical and thermal processing operations and storage related to those operations which involve dangerous substances, as well as operational tailings disposal facilities, including tailing ponds or dams containing dangerous substances shall be included within the scope of the Directive). Due to a larger volume of chemical substances stored in the aboveground part of the technology for extracting of shale gas (average amount about 230 m 3 in stage of hydraulic fracturing) compared with volumes of chemical substances used in the aboveground part of technology of underground storage of natural gas (about 50 m 3 ) the technology of shale gas extraction has significantly higher risk. However, in the case that the entire process of storage of chemical substances will be well managed and sufficient measures will be taken to minimize the risk, aboveground part of the technology for extracting of shale gas does not represent a significant difference from warehouses in chemical production plants. From the comparison of hazards of the aboveground parts of natural gas storage technologies in underground storage reservoirs with hazards associated with the operation of the aboveground parts of shale gas production technology is obvious, that future legislation of European Union in the field of major accident prevention should include also the shale gas production facilities. Although a research about hazards of the aboveground part of the shale gas extraction technology has been made to improve the knowledge on this risk source, more research would be required, especially with practical results of detailed risk analysis.

Using the copper-vapor laser to restore works of art

This paper shows that it is possible to use a copper-vapor laser to restore certain objects of historical and cultural heritage. The results of experiments on the use of such a laser to clean the surface of paper and marble from contaminants and natural strata are given as an example.

Seismic simulations of experimental strata

Experimental strata formed in the new Experimental Earthscape (XES) basin at the St. Anthony Falls Laboratory of the University of Minnesota offer a realistic model for simulating the seismic response of natural strata and thus for advancing understanding of the geologic information that can be extracted from seismic data. A new method is presented here for using digital photos of the experimental strata to generate synthetic seismic data at the length scales and frequencies relevant to oil and gas exploration. In the method, the digital photos are transformed into models of acoustic velocity and bulk density, which are then input into algorithms that generate synthetic seismic data. Three such algorithms are used to demonstrate the approach: a convolutional algorithm, which produces the equivalent of ideal, poststack, time-migrated seismic data; an exploding-reflector algorithm, which produces unmigrated, poststack seismic data; and a full-wave equation algorithm, which we use to produce a synthetic version of prestack, unmigrated, multichannel seismic data. Data generated by the latter two algorithms are processed to compare their information content against both the experimental strata and the ideal seismic data derived from the convolutional algorithm. The qualitative comparison nicely illustrates the filtering of geologic information in seismic data and its further degradation by wave-propagation phenomena, such as diffractions, multiples, and interbed reverberations.

Regimes of Dissociation of Gas Hydrates Coexisting with a Gas in Natural Strata

A mathematical model of decomposition of gas hydrates that coexist with a gas in natural strata is proposed; the model takes into account the mobility of the liquid phase. Conditions at the unknown boundary of dissociation are derived. In the self-similar approximation, the solution is represented in the form of probability integrals. The obtained system of transcendental equations at the moving boundary has been investigated numerically in a wide range of parameters. It is shown that different regimes of dissociation in collectors with a positive initial temperature exist; these regimes correspond to the decomposition of a hydrate into gas and water and gas and ice and have both a sharp phase-transition front and are accompanied by the formation of an extended region of dissociation. On the plane of the main parameters of the process, the critical diagram is constructed and the existence domains of the solution of each form are singled out.

A model for filtration in an aperiodic medium with double porosity

In this paper, the time-dependent equation for diffusion in an aperiodic porous medium with weakly penetrable inclusions is considered. The asymptotic behavior of its solutions is described by an averaged equation with memory. Effective parameters are calculated with the help of solutions to local problems. The general model obtained is shown to describe three qualitatively distinguished cases differing by the degree of inhomogeneity of a medium. 1. Introduction. We consider here transport processes in a porous medium representing the spatial alternation of two types of rocks with contrast transport properties. In this case, we cannot ignore the existence of a weakly conducting subsystem since, even being virtually impenetrable, it can contain a considerable quantity of a fluid. Objects of this type are widely met in hydrology or oil engineering, where natural porous strata are composed of rocks with sharply different petrographic properties or are dissected by nets of cracks. For the description of such objects, a model of media with double porosity is used. In the framework of this model, a medium is represented as a unified highly penetrable system (matrix) Ω e having weakly penetrable inclusions (blocks) F e . The porosity of blocks is considered to be not lower than that of the matrix. If the scale of an inhomogeneity e is small, the averaged behavior of the system is of interest. This behavior is complicated due to the fact that the medium involves the second substantial parameter ω ! 1 equal to the ratio between the conductivity of blocks and that of the matrix, so that the asymptotic degeneracy of coefficients of the equations occurs on the inclusions as ω 0 . The classical model of flow through a medium with double porosity [1] was based on the hypothesis of a quasisteady exchange process between the blocks and the matrix. In the general case, the exchange process is unsteady, and, by virtue of the Duhamel principle, the appearance of operators of the time-convolution type can be expected. A similar model with memory was proposed in [2, 3] for a particular relation between the medium parameters when ω ~ e 2 ( e 2 -model). In the more general case, media with double porosity correspond to all situations when ω ~ e 2 . Four classes of such media [4] can be distinguished. For ω ! e 2 , weakly penetrable blocks can be ignored; for ω ~ e 2 , the transport is described by the above model with a long-term memory; for ω ~ e 2 , the medium has a short-term memory; and, for e ! ω ! 1 , the medium behavior is moderately inhomogeneous without memory.

A front problem concerning the decomposition of gas hydrates in natural strata on exposure to high-frequency electromagnetic radiation

We consider a one-dimensional axial problem of gas filtration in front decomposition of gas hydrates in a porous medium on exposure to high-frequency electromagnetic radiation. Depending on the permeability of the medium, two basic regimes of the process are distinguished that differ in temperature distribution in the medium. The behavior of the hydrate decomposition front and of the pressure in this front depending on the absorption length of the medium is studied. The presence of an optimum regime for the most rapid decomposition of hydrate in a porous medium of prescribed dimensions is established.

The sunken lanes of Southern England: Engineering geological considerations

Abstract This paper examines the geological, geotechnical and environmental planning problems of the sunken lanes, or hollow ways, of Southern England. Sunken lanes are generally ascribed to the downcutting action of wheeled traffic on the formerly un-made road, augmenting and accelerating the natural processes of weathering and erosion. The road may be at least several metres below general ground level with a cutting slope in the natural strata and which may be wholly, or partly, vegetated. Sunken lanes must have evolved before road surfacing but the banks are still subject to degradation and although the rate is extremely slow, failure by spalling, debris-sliding or debris-flow may occur. From a site investigation point of view they are difficult to investigate geologically because of a variable extent of weathered mantle and because trial pitting is usually impractical. The materials of the bank can range from loose sand of the weathered mantle, weakly locked or locked sands and harder, cemented rock bands or masses. In most cases, stability cannot be quantified by traditional soil or rock mechanics methods. Where failure of the bank occurs, the Highway Authority may have the problem of assessing stability from engineering geological considerations. The question posed in such cases, is whether the failure represents an isolated occurrence or will it mean an accelerating rate of degradation with further, more frequent and/or larger failures. Since sunken lanes are usually narrow and winding, the fallen material becomes a traffic hazard and a decision may be made that engineering measures are required. These could include re-grading, retaining walls, revetting, gabions or protection by nylon or steel mesh. Sunken lanes are an attractive feature of the landscape, providing scenic variety, a window on the solid geology and a reminder of the past. It would be a loss were all potentially unstable cuttings 'engineered' to provide a safe but purely artificial road bank. This is a problem for environmental planners: to what extent can some hazard be accepted in the interests of conserving a very characteristic feature in the landscape?

Archaeological Investigations at 48Sw2302, a Sand Dune Site in Southwestern Wyoming

48SW2302 is a prehistoric site located in the Bridger Basin of southwestern Wyoming and is associated with a stabilized sand dune. Archaeological investigations were conducted here in 1980 and 1981 as part of the Mid-America Pipeline Co. (MAPCO) Project to mitigate the impact of pipeline construction and gather information about regional aboriginal settlement patterns. Five natural strata were defined, six cultural features were exposed, and hundreds of chipped stone artifacts and animal bones were collected. Charcoal from two features returned radiocarbon assays whose calibrated calendric ranges overlap between ca. A.D. 615 and 755. All evidence indicates that 48SW2302 was occupied by Late Prehistoric peoples who hunted artiodactyls and rabbits, cooked and ate those animals, and manufactured or modified their lithic tool kit. They responded to local climatic variations by dietary changes. The site is representative of a ubiquitous and relatively stable pattern of prehistoric settlement and subsistence in southwestern Wyoming.

Gamma radiation spectra of radioactive ores in their natural strata, determined by proportional counters

Gamma radiation spectra of radioactive ores in their natural strata, determined by proportional counters

ACROSTALAGMUS APHIDUM OUD. AND APHID CONTROL

1. A fungus, Acrostalagmus aphidum Oud., parasitizes aphids in Porto Rico. It had been reported as A. albus Preuss. 2. The size of the spores in the various natural strata is more or less uniform. 3. The size of the spores appears to be larger for those produced on the natural strata than those developing on oatmeal agar cultures. 4. There seems to be a wider range of length and width of spores on our form than on the A. aphidum Oud. described in Saccardo's "Sylloge Fungorum". 5. Some of the conidia become one-to several-septate prior to germination. 6. Conidia or head-like structures are produced on germinating spores. 7. Some young conidia germinate while still attached to the head or to the branch tips. 8. Spores germinate rapidly in sugar solutions. 9. Spores rapidly lose their germinating power when dried. 10. Experiments indicate a possible stimulating effect of aphid juices on germination and development of spores. There are probably variations in the degree of that influence, according to species. 11. The fungus grows best at reactions of pH 6.93 to 7.93. 12. So far as is known, Acrostalagmus aphidum attacks the aphids on 17 species of the higher plants. Of these 8 had been reported previously and the remaining 9 are new additions. Among these are important crop plants. 13. The aphids which may be parasitized comprise five different genera of which two are here first reported. Aphis pseudobrassicae is first here reported parasitized by the fungus. 14. The fungus does not parasitize the corn aphid under natural conditions. 15. The fungus has also been reported on the eggplant lace-bug, Corythaica monacha. 16. Acrostalagmus aphidum can be employed successfully and cheaply in the control of the aphids of the eggplant. The method will probably be effective in field control of the aphids of other vegetables. 17. The pathogene lives in greenhouse soil. No experiment proof is at hand which would demonstrate whether the fungus is eliminated by the application of fungicides used for the control of plant diseases.