Outer Sub-region Research Articles

Accretion and Uneven Depletion of the Main Asteroid Belt

The main asteroid belt (MAB) is known to be primarily composed of objects from two distinct taxonomic classes, generically defined here as S- and C-complex. The former probably originated from the inner solar system (interior to Jupiter’s orbit), while the latter probably originated from the outer solar system. Following this definition, (4) Vesta, a V-type residing in the inner MAB (a < 2.5 au), is the sole D > 500 km object akin to the S-complex that potentially formed in situ. This provides a useful constraint on the number of D > 500 km bodies that could have formed, or grown, within the primordial MAB. In this work, we numerically simulate the accretion of objects in the MAB region during the time when gas in the protoplanetary disk still existed while assuming different MAB primordial masses. We then account for the depletion of that population happening after gas disk dispersal. In our analysis, we subdivided the MAB into five subregions and showed that the depletion factor varies throughout the MAB. This results in uneven radial- and size-dependent depletion of the MAB. We show that the MAB primordial mass has to be ≲2.14 × 10−3 M ⊕. Larger primordial masses would lead to the accretion of tens to thousands of S-complex objects with D > 500 km in the MAB. Such large objects would survive depletion even in the outer subregions (a > 2.5 au), thus being inconsistent with observations. Our results also indicate that S-complex objects with D > 200–300 km, including (4) Vesta, are likely to be terrestrial planetesimals implanted into the MAB rather than formed in situ.

A Novel Hybrid Approach for Computing Electromagnetic Scattering from Objects with Honeycomb Structures

We propose in this paper a novel hybrid numerical modeling method for computing electromagnetic scattering from inhomogeneous targets containing honeycomb structures. In the proposed approach, the whole honeycomb structure is divided into the inner and outer two subregions. Each thin wall of a unit cell in the outer subregion is replaced by a zero-thickness surface, with the aid of a resistive sheet boundary condition (RSBC) to describe the electric and magnetic field discontinuities across the surface. Each unit cell in the inner subregion is homogenized by using the Hashin–Shtrikman and the Mori–Tanaka formulae. The two subregions are further divided into smaller subdomains by introducing the Robin-type transmission condition to couple subregion interfaces, as well as subdomain interfaces. The whole solution region is then discretized and solved using the nonconformal domain decomposition-based hybrid finite element–boundary integral–multilevel fast multipole algorithm (FE-BI-MLFMA). The numerical results demonstrate that the proposed approach exhibits a high accuracy, efficiency, and flexibility. Solutions of scattering by a wing-like object and a practical unmanned aerial vehicle (UAV) model with honeycomb radar-absorbing structures are presented, showing the superior performance of the proposed algorithm.

Localization in liquid phase separation: Coarsening and stable structures.

Dynamics of pattern formation in self-organizing systems subjected to spontaneous suppression of diffusion through a recently proposed source-sink-boundary templating technique is presented based on three-dimensional numerical simulations. This template disorder is introduced to divide the system into three different subregions, i.e., a source (outer subregion) at higher potential and a sink (inner subregion) region at a lower potential with the help of a boundary which is at the highest potential. The boundary allows only one-way diffusion from source to sink so diffusion stops completely whenever the sink is filled to its capacity. This technique was shown to be able to spontaneously form stable and complex patterns in the source and the sink parts. While the technique is applicable to any self-organizing or phase-separating system whenever certain conditions are met, a physically realizable system of liquid films supported on chemically heterogeneous substrates which self-organizes through morphological phase separation is chosen to study the dynamics. Free-energy functional of this system shows an asymmetric double-well potential and the Maxwell's double tangent construction on this free energy gives rise to two distinct and finite equilibrium phases. Disorder is introduced in the form of chemical heterogeneity to divide the whole system into different subregions each consisting of two equilibrium phases, thus enabling more finite equilibrium points in the same system. The dynamics uncovers two different pathways for stable localized structures, viz., the defect and the direct pathway. Thinner films are likely to favor the defect pathway whereby the equilibrium pattern forms after coarsening, whereas thicker films will predominantly choose the direct pathway of pattern formation by phase separation. The final localized structure is same irrespective of the chosen pathway. The dynamics also shows that the patterns formed in the inner subregion part can be seen as a result of "localization" and those formed in the outer subregion are due to arrested diffusion under geometric or curvature constraints. Simple measures of localization in terms of free energy and its constituents are also presented. The identification of localization in the above systems opens up the possibility of a systematic approach to create controlled structures at nano- and submicrometer scales with desired shape and size. These structures constitute new building blocks of advanced and tailored materials.

Self-Consistent Field Modeling of Homopolymers at Interfaces in the Long Chain Length Limit

According to de Gennes, the density profile for homopolymers adsorbing onto planar surfaces is characterized by a proximal, central and distal region. We have used self-consistent field calculations and focused on the central region in the limit of very long chain lengths. Our results complement earlier predictions for comparatively low molecular weights that basically only revealed a mean field scaling exponent of −2 for the power-law decay of the density. For very long chains, however, a more rich picture emerges. Apart from an inner sub-region where the loop conformations dominate and still the mean field exponent is found, there exists an outer sub-region where the tail conformations dominate with excluded volume scaling of ‒4/3. It is shown that the outer region grows logarithmically with chain length and only will exceed the decade when the length of the polymer chains exceeds N ≈ 3 × 107. We argue that ‘inner-adsorption blobs’ are visited twice by loop conformations (loops by definition return to the surface) and hence become overcrowded giving rise to mean field scaling. The ‘outer-adsorption blobs’ are visited just once by tails (tails do not need to return to the surface) and therefore provide the expected excluded volume scaling.

Segmentation of Regions of Interest Using Active Contours with SPF Function.

Segmentation of regions of interest is a well-known problem in image segmentation. This paper presents a region-based image segmentation technique using active contours with signed pressure force (SPF) function. The proposed algorithm contemporaneously traces high intensity or dense regions in an image by evolving the contour inwards. In medical image modalities these high intensity or dense regions refer to tumor, masses, or dense tissues. The proposed method partitions an image into an arbitrary number of subregions and tracks down salient regions step by step. It is implemented by enforcing a new region-based SPF function in a traditional edge-based level set model. It partitions an image into subregions and then discards outer subregion and partitions inner region into two more subregions; this continues iteratively until a stopping condition is fulfilled. A Gaussian kernel is used to regularize the level set function, which not only regularizes it but also removes the need of computationally expensive reinitialization. The proposed segmentation algorithm has been applied to different images in order to demonstrate the accuracy, effectiveness, and robustness of the algorithm.

Implementation of near-wall boundary conditions for modeling boundary layers with free-stream turbulence

The paper is devoted to the extension of the near-wall domain decomposition, earlier developed in some previous works by the authors, to modeling flat-plate boundary layers undergoing laminar-to-turbulent bypass transition. The steady-state wall boundary layers at high-intensity free-stream turbulence are studied on the basis of differential turbulence models with the use of non-overlapping domain decomposition. In the approach the near-wall resolution is replaced by the interface boundary conditions of Robin type. In contrast to the previous studies, the main attention is paid to the laminar–turbulent transitional regime. With the use of modified turbulence models we study an effect of free-stream parameters on the development of dynamic processes in the boundary layer including a transitional regime and fully developed turbulent flow. In addition, for the first time a full scale domain decomposition is realized via iterations between the inner and outer subregions until a convergence. The computational profiles of the velocity and intensity of the turbulence kinetic energy are compared with experimental data. A possible range of location of the near-wall interface boundary is found.

Risk associated with H2S evolution in sour aquifers during CO2 injection

Many aquifers suitable for CO2 sequestration contain measurable concentration of dissolved non-hydrocarbon species. In this paper, the compositional modelling of the CO2 injection into aquifers that contain dissolved hydrogen sulfide, described here as sour aquifers, is studied. According to the results of this study, when CO2 is injected into such aquifers, exsolution of dissolved components will occur and gaseous H2S will accumulate at the leading edge of the CO2 plume. At any time after the start of CO2 injection, the region swept by the plume consists of two sub-regions. An inner radial sub-region extending from the injection well is characterized by the absence of H2S in both the aqueous (brine) and gaseous (supercritical CO2) phases. The dissolved H2S in this first sub-region is almost completely removed from the brine and released to the migrating gas phase. The second sub-region extends from the outer edge of the first sub-region to the leading edge of the gas plume. In this outer sub-region, the mole fraction of H2S in the CO2 plume gradually increases toward a constant value at the edge (which is defined by the CO2-H2O-H2S phase equilibrium conditions at specific temperature, pressure, and salinity of the brine) and thereafter only the size of this sub-region progressively increases. For dissolved H2S concentrations typically found in the Western Canada Sedimentary Basin, mole fraction of gaseous H2S in the leading edge of the gas plume can be higher than 50%. This may have important implications for assessing the risk of CO2 injection into sour aquifers. Leakage into abandoned wells, for example, might plausibly occur when the gas phase first reaches the wellbore, so initial leakage may contain substantial amounts of H2S even though the average H2S fraction in the stored CO2 is quite small. H2S is highly toxic, with acute short term toxicity at 100 to 1000 times larger than that of CO2. This suggests that one need to account for this phenomenon when establishing risk assessment, monitoring and management strategies at planned CO2 geo-storage sites.

Evolution of hydrogen sulfide in sour saline aquifers during carbon dioxide sequestration

Many deep saline aquifers suitable for carbon dioxide (CO 2) sequestration contain measurable concentrations of hydrogen sulfide (H 2S). These aquifers are described here as sour saline aquifers and the other ones as ordinary saline aquifers. Sour saline aquifers occur wherever even minor amounts of anhydrite or other sulfate sources are present in the formation. In this paper, compositional modeling of CO 2 injection into such aquifers is studied. When CO 2 is injected into a sour saline aquifer, the H 2S initially dissolved in the brine will be exsolved and released into an expanding CO 2 plume. At any time after the start of CO 2 injection, the region swept by the plume consists of two sub-regions. The first of these is an inner sub-region extending from the injection well, and is characterized by the absence of H 2S in both aqueous and gaseous phases. The dissolved H 2S in this inner sub-region is nearly completely removed from the brine via an exsolution process. The second sub-region extends from the outer edge of the inner sub-region to the leading edge of the plume. In this outer sub-region, the mole fraction of H 2S in the gas plume gradually increases toward the leading edge and reaches a peak value. While the gas plume is expanding the size of the outer sub-region enlarges. Following the discussion of these phenomena, in the next part of the paper, injection of acid gases (mixtures of H 2S and CO 2) into sour saline aquifers and ordinary saline aquifers is explored. In contrast to sour aquifers, unsaturated water in an ordinary aquifer will strip away H 2S from the CO 2 stream and consequently the mole fraction of H 2S toward the gas front decreases. The highly toxic nature of H 2S gas suggests the need to account for dissolved H 2S in sour saline aquifers when establishing risk assessment, monitoring, and management strategies at CO 2 storage sites.

Natural Convection Reduction in a Composite Air/Porous Annular Region With Horizontal Orientation

This paper deals with a numerical investigation on natural convection heat transfer in a long horizontal annular region formed with a heated inner cylinder and a cooled outer cylinder. Identifying the annular region geometrically by its radius ratio, it is divided into two subregions: a thicker outer subregion is filled with a porous material saturated by air, whereas a thinner inner subregion is clear. Based on the general Darcy–Brinkman–Forchheimer model for flow in porous media, numerical calculations with the control volume method produce the velocity and temperature fields of the air motion in the two subregions. The baseline case corresponds to an annular region of same dimensions, but filled completely with a porous material saturated by air. Upon articulating the physical properties of a porous material with the clear gap size, the analyst will be able to tune those conditions that are conducive to heat transfer reduction across the concentric two-cylinder configuration. The outcome of this paper is equivalent to the determination of superior thermal insulation performance using lesser porous material. In other words, this paper boils down to beneficial energy conservation together with money savings in the purchase of the thermal insulation.

Analytical modeling and mitigation techniques for the energy hole problem in sensor networks

In this paper we investigate the problem of uneven energy consumption in a large class of many-to-one sensor networks. In a many-to-one sensor network, all sensor nodes generate constant bit rate (CBR) data and send them to a single sink via multihop transmissions. This type of sensor network has many potential applications such as environmental monitoring and data gathering. Based on the observation that sensor nodes sitting around the sink need to relay more traffic compared to other nodes in outer sub-regions, our analysis verifies that nodes in inner rings suffer much faster energy consumption rates (ECR) and thus have much shorter expected lifetimes. We term this phenomenon of uneven energy consumption rates as the “energy hole” problem, which may result in severe consequences such as early dysfunction of the entire network. We proposed analytical modeling for this problem, which can help understand the relevance of different factors on energy consumption rates. Using this model, we study the effectiveness of several existing approaches towards mitigating the “energy hole” problem, including deployment assistance, traffic compression and aggregation. We have used simulation results to validate our analysis.

Early neonatal and postweaning social emotional deprivation interferes with the maturation of serotonergic and tyrosine hydroxylase-immunoreactive afferent fiber systems in the rodent nucleus accumbens, hippocampus and amygdala

The impact of early emotional experience on the development of serotonergic and dopaminergic fiber innervation of the nucleus accumbens, hippocampal formation and the amygdala was quantitatively investigated in the precocious rodent Octodon degus. Two animal groups were compared: 1) degus which were repeatedly separated from their parents during the first three postnatal weeks, after weaning they were individually reared in chronic social isolation and 2) controls which were reared undisturbed with their families. In the deprived animals 5-hydroxytryptamine-immunoreactive fiber densities were increased in the core region of the nucleus accumbens (up to 126%), in the central nucleus of the amygdala (up to 112%) and in the outer subregion of the dentate gyrus stratum moleculare (up to 149%), whereas decreased fiber densities were detected in the dentate subgranular layer (down to 86%) and in the stratum lacunosum of the hippocampal cornu ammonis region 1 (down to 86%). Tyrosine hydroxylase-immunoreactive fiber densities were increased in the core (up to 115%) and shell region (up to 113%) of the nucleus accumbens of deprived animals, whereas decreased fiber densities (down to 84%) were observed in the hilus of the dentate gyrus. In the stratum granulosum and subgranular layer the fiber densities increased up to 168% and 127% respectively. In summary, these results indicate that the postnatal establishment of the monoaminergic innervation of limbic areas is modulated in response to early emotional experience, and that this environmental morphological adaptation is highly region specific.