Distribution of first-reaction times with target regions on boundaries of shell-like domains

We study the probability density function (PDF) of the first-reaction times between a diffusive ligand and a membrane-bound, immobile imperfect target region in a restricted "onion-shell" geometry bounded by two nested membranes of arbitrary shapes. For such a setting, encountered in diverse molecular signal transduction pathways or in the narrow escape problem with additional steric constraints, we derive an exact spectral form of the PDF, as well as present its approximate form calculated by help of the so-called self-consistent approximation. For a particular case when the nested domains are concentric spheres, we get a fully explicit form of the approximated PDF, assess the accuracy of this approximation, and discuss various facets of the obtained distributions. Our results can be straightforwardly applied to describe the PDF of the terminal reaction event in multi-stage signal transduction processes.

Probing Gas Kinematics and PDR Structure around O-type Stars in the Sh 2-305 H ii Region

We report an observational study of the Galactic H ii region Sh 2-305/S305 using the [C ii] 158 μm line data, which are used to examine the gas dynamics and structure of photodissociation regions. The integrated [C ii] emission map at [39.4, 49.5] km s−1 spatially traces two shell-like structures (i.e., inner and outer neutral shells) having a total mass of ∼565 M ⊙. The inner neutral shell encompasses an O9.5V star at its center and has a compact ring-like appearance. However, the outer shell is seen with more extended and diffuse [C ii] emission, hosting an O8.5V star at its center, and surrounds the inner neutral shell. The velocity channel maps and position–velocity diagrams confirm the presence of a compact [C ii] shell embedded in the diffuse outer shell, and both the shells seem to expand with v exp ∼ 1.3 km s−1. The outer shell appears to be older than the inner shell, hinting that these shells are formed sequentially. The [C ii] profiles are examined toward S305, which are either double peaked or blue skewed and have the brighter redshifted component. The redshifted and blueshifted components spatially trace the inner and outer neutral shell geometry, respectively. The ionized, neutral, and molecular zones in S305 are seen adjacent to one another around the O-type stars. The regularly spaced dense molecular and dust clumps (mass ∼10–103 M ⊙) are investigated around the neutral shells, which might have originated as a result of gravitational instability in the shell of collected materials.

Effect Of The Horizontal Component Of Earthquake On The Buckling Of Concrete Spherical Shells

The buckling failure of reinforced concrete spherical shell structures under the effect of the horizontal component of earthquake is investigated using a finite element method over a wide range of shell configurations. For this effect, two different loading case scenarios are considered; first, the shell is analyzed under the effects of the vertical seismic component alone. Then, the model is reanalyzed under the same loading conditions plus the horizontal earthquake component, taking into account two different horizontal-to-vertical earthquake spectral ratios. It is concluded that including the horizontal component of earthquake can result in a reduction in the buckling capacity of this type of structure; the impact of which is highly influenced by the horizontal-to-vertical earthquake spectral ratio and the shell geometry. It is also observed that the formulation adopted by ACI slightly overestimates the buckling capacity of spherical shells especially when horizontal seismic effects are included.

Effect Of The Horizontal Component Of Earthquake On The Buckling Of Concrete Spherical Shells

The buckling failure of reinforced concrete spherical shell structures under the effect of the horizontal component of earthquake is investigated using a finite element method over a wide range of shell configurations. For this effect, two different loading case scenarios are considered; first, the shell is analyzed under the effects of the vertical seismic component alone. Then, the model is reanalyzed under the same loading conditions plus the horizontal earthquake component, taking into account two different horizontal-to-vertical earthquake spectral ratios. It is concluded that including the horizontal component of earthquake can result in a reduction in the buckling capacity of this type of structure; the impact of which is highly influenced by the horizontal-to-vertical earthquake spectral ratio and the shell geometry. It is also observed that the formulation adopted by ACI slightly overestimates the buckling capacity of spherical shells especially when horizontal seismic effects are included.

How does salinity shape ocean circulation and ice geometry on Enceladus and other icy satellites?

Of profound astrobiological interest is that not only does Enceladus have a water ocean, but it also appears to be salty, important for its likely habitability. Here, we investigate how salinity affects ocean dynamics and equilibrium ice shell geometry and use knowledge of ice shell geometry and tidal heating rates to help constrain ocean salinity. We show that the vertical overturning circulation of the ocean, driven from above by melting and freezing and the temperature dependence of the freezing point of water on pressure, has opposing signs at very low and very high salinities. In both cases, heat and freshwater converges toward the equator, where the ice is thick, acting to homogenise thickness variations. In order to maintain observed ice thickness variations, ocean heat transport should not overwhelm tidal heating rates within the ice, which are small in equatorial regions. This can only happen when the ocean’s salinity has intermediate values, order 20 psu. In this case polar-sinking driven by meridional temperature variations is largely canceled by equatorial-sinking circulation driven by salinity variations and a consistent ocean circulation, ice shell geometry and tidal heating rate can be achieved.

Real-time Rendering of Small-scale Volumetric Structure on Animated Surfaces

There are a lot of methods for rendering of shell-space geometry, represented through voxel texture, known for today. While the topic is well studied in terms of techniques for applying this geometry onto surfaces, a little attention was paid to representation of sub-pixel details of the geometry. Such details are prone to produce aliasing artifacts and reduce performance due to bad cache utilization. In this paper we solve these problems by introducing levels of detail for voxel textures within shell mapping technique. The main problem here is that less detailed levels begin to contain semi-transparent voxels on the edge of an encoded surface, which requires additional handling. For this we present a new approach for order independent transparency rendering based on depth peeling. We extend the algorithm by adding additional resolving pass which allows to fully utilize hardware z-buffering to reduce amount of overdraw. This significantly reduces cost of each subsequent peeling pass. Empirically, 3-4 of such passes is enough to produce good quality results in most cases. Another issue with shell mapping techniques is that shell geometry is constructed offline, making base surface to be static. By slightly modifying the method, we made the construction to be performed on-the-fly on GPU and be applicable for animated surfaces.