A mixed finite element method for nearly incompressible multiple-network poroelasticity

In this paper, we present and analyze a new mixed finite element formulation of a general family of quasi-static multiple-network poroelasticity (MPET) equations. The MPET equations describe flow and deformation in an elastic porous medium that is permeated by multiple fluid networks of differing characteristics. As such, the MPET equations represent a generalization of Biot's equations, and numerical discretizations of the MPET equations face similar challenges. Here, we focus on the nearly incompressible case for which standard mixed finite element discretizations of the MPET equations perform poorly. Instead, we propose a new mixed finite element formulation based on introducing an additional total pressure variable. By presenting energy estimates for the continuous solutions and a priori error estimates for a family of compatible semi-discretizations, we show that this formulation is robust in the limits of incompressibility, vanishing storage coefficients, and vanishing transfer between networks. These theoretical results are corroborated by numerical experiments. Our primary interest in the MPET equations stems from the use of these equations in modelling interactions between biological fluids and tissues in physiological settings. So, we additionally present physiologically realistic numerical results for blood and tissue fluid flow interactions in the human brain

Single photon production by rephased amplified spontaneous emission

The production of single photons using rephased amplified spontaneous emission is examined. This process produces single photons on demand with high efficiency by detecting the spontaneous emission from an atomic ensemble, then applying a population-inverting pulse to rephase the ensemble and produce a photon echo of the spontaneous emission events. The theoretical limits on the efficiency of the production are determined for several variants of the scheme. For an ensemble of uniform optical density, generating the initial spontaneous emission and its echo using transitions of different strengths is shown to produce single photons at 70% efficiency, limited by reabsorption. Tailoring the spatial and spectral density of the atomic ensemble is then shown to prevent reabsorption of the rephased photon, resulting in emission efficiency near unity

Photodissociation of the OD radical at 226 and 243 nm

The photodissociation dynamics of state selected OD radicals has been examined at 243 and 226 nm using velocity map imaging to probe the angle–speed distributions of theD(2S) and O(3P2) products. Both experiment and complementary first principle calculations demonstrate that photodissociation occurs by promotion of OD from high vibrational levels of the ground X 2Π state to the repulsive 1 2Σ− state

Using Pilot Systems to Execute Many Task Workloads on Supercomputers

High performance computing systems have historically been designed to support applications comprised of mostly monolithic, single-job workloads. Pilot systems decouple workload specification, resource selection, and task execution via job placeholders and late-binding. Pilot systems help to satisfy the resource requirements of workloads comprised of multiple tasks. RADICAL-Pilot (RP) is a modular and extensible Python-based pilot system. In this paper we describe RP's design, architecture and implementation, and characterize its performance. RP is capable of spawning more than 100 tasks/second and supports the steady-state execution of up to 16K concurrent tasks. RP can be used stand-alone, as well as integrated with other application-level tools as a runtime system

Stabilizing All Geometric Moduli in Heterotic Calabi-Yau Vacua

We propose a scenario to stabilize all geometric moduli - that is, the complex structure, Kahler moduli and the dilaton - in smooth heterotic Calabi-Yau compactifications without Neveu-Schwarz three-form flux. This is accomplished using the gauge bundle required in any heterotic compactification, whose perturbative effects on the moduli are combined with non-perturbative corrections. We argue that, for appropriate gauge bundles, all complex structure and a large number of other moduli can be perturbatively stabilized - in the most restrictive case, leaving only one combination of Kahler moduli and the dilaton as a flat direction. At this stage, the remaining moduli space consists of Minkowski vacua. That is, the perturbative superpotential vanishes in the vacuum without the necessity to fine-tune flux. Finally, we incorporate non-perturbative effects such as gaugino condensation and/or instantons. These are strongly constrained by the anomalous U(1) symmetries which arise from the required bundle constructions. We present a specific example, with a consistent choice of non-perturbative effects, where all remaining flat directions are stabilized in an AdS vacuum.Comment: 24 pages, 2 figure

Graha Jurnalistik Expose Manado (Fleksibilitas Dalam Arsitektur)

Expose Manado sebagai media yang mewadahi karya foto para jurnalis Manado, yang didukung dengan kemajuan teknologi dan informasi, membuat majalah ini semakin berkembang. Namun perkembangan ini tidak didukung dengan fasilitas bangunan yang kompeten. Maka Graha Jurnalistik Expose Manado yang berfungsi sebagai tempat percetakan majalah, dan kantor jurnalis Manado, mampu mewadahi berbagai kegiatan jurnalis dalam peningkatan kualitas majalah Expose Manado lebih inovatif, serta mendukung kegiatan-kegiatan lain seperti, pameran foto, workshop, percetakan majalah dan lain sebagainya. Untuk mendukung rancangan objek maka tema Fleksibilitas dalam Arsitektur dipilih untuk diimplementasikan dalam rancangan karna dianggap mampu merepresentasikan fungsi objek dan dapat bekerja optimal mengikuti fungsi dan waktu. Fleksibilitas arsitektur sebagai konsep yang ditawarkan dirasa sesuai dengan kebutuhan bangunan saat ini. Sehingga sebuah desain dalam hal ini Graha Jurnalistik Expose Manado dapat berkesuaian dengan ruang tempat maupun waktu sesuai dengan penerapan konsep fleksibilitas dalam arsitektur. Metode rancangan yang dilakukan nantinya bersifat pragmatis dimana menghadirkan explorasi-explorasi bentuk mengikuti orientasi pada site perancangan yang berfungsi optimal untuk jurnalis dan percetakan majalah sebagai profil bangunan itu sendiri

Low temperature structural effects in the (TMTSF)2_2PF6_6 and AsF6_6 Bechgaard salts

We present a detailed low-temperature investigation of the statics and dynamics of the anions and methyl groups in the organic conductors (TMTSF)$_2$PF$_6$ and (TMTSF)$_2$AsF$_6$ (TMTSF : tetramethyl-tetraselenafulvalene). The 4 K neutron scattering structure refinement of the fully deuterated (TMTSF)$_2$PF$_6$-D12 salt allows locating precisely the methyl groups at 4 K. This structure is compared to the one of the fully hydrogenated (TMTSF)$_2$PF$_6$-H12 salt previously determined at the same temperature. Surprisingly it is found that deuteration corresponds to the application of a negative pressure of 5 x 10$^2$ MPa to the H12 salt. Accurate measurements of the Bragg intensity show anomalous thermal variations at low temperature both in the deuterated PF$_6$ and AsF$_6$ salts. Two different thermal behaviors have been distinguished. Low-Bragg-angle measurements reflect the presence of low-frequency modes at characteristic energies {\theta}$_E$ = 8.3 K and {\theta}$_E$ = 6.7 K for the PF$_6$-D12 and AsF$_6$-D12 salts, respectively. These modes correspond to the low-temperature methyl group motion. Large-Bragg-angle measurements evidence an unexpected structural change around 55 K which probably corresponds to the linkage of the anions to the methyl groups via the formation of F...D-CD2 bonds observed in the 4 K structural refinement. Finally we show that the thermal expansion coefficient of (TMTSF)$_2$PF$_6$ is dominated by the librational motion of the PF$_6$ units. We quantitatively analyze the low-temperature variation of the lattice expansion via the contribution of Einstein oscillators, which allows us to determine for the first time the characteristic frequency of the PF6 librations: {\theta}$_E$ = 50 K and {\theta}$_E$ = 76 K for the PF$_6$-D12 and PF$_6$-H12 salts, respectively

Benthic Foraminiferal response to sea level change in the mixed siliciclastic-carbonate system of southern Ashmore Trough (Gulf of Papua)

Ashmore Trough in the western Gulf of Papua (GoP) represents an outstanding modern example of a tropical mixed siliciclastic-carbonate depositional system where significant masses of both river-borne silicates and bank-derived neritic carbonates accumulate. In this study, we examine how benthic foraminiferal populations within Ashmore Trough vary in response to sea level–driven paleoenvironmental changes, particularly organic matter and sediment supply. Two 11.3-m-long piston cores and a trigger core were collected from the slope of Ashmore Trough and dated using radiocarbon and oxygen isotope measurements of planktic foraminifera. Relative abundances, principal component analyses, and cluster analyses of benthic foraminiferal assemblages in sediment samples identify three distinct assemblages whose proportions changed over time. Assemblage 1, with high abundances of Uvigerina peregrina and Bolivina robusta, dominated between ∼83 and 70 ka (early regression); assemblage 2, with high abundances of Globocassidulina subglobosa, dominated between ∼70 and 11 ka (late regression through lowstand and early transgression); and assemblage 3, with high abundances of neritic benthic species such as Planorbulina mediterranensis, dominated from ∼11 ka to the present (late transgression through early highstand). Assemblage 1 represents heightened organic carbon flux or lowered bottom water oxygen concentration, and corresponds to a time of maximum siliciclastic fluxes to the slope with falling sea level. Assemblage 2 reflects lowered organic carbon flux or elevated bottom water oxygen concentration, and corresponds to an interval of lowered siliciclastic fluxes to the slope due to sediment bypass during sea level lowstand. Assemblage 3 signals increased off-shelf delivery of neritic carbonates, likely when carbonate productivity on the outer shelf (Great Barrier Reef) increased significantly when it was reflooded. Benthic foraminiferal assemblages in the sediment sink (slopes of Ashmore Trough) likely respond to the amount and type of sediment supplied from the proximal source (outer GoP shelf)

Ultrafast Resonant Polarization Interferometry: Towards the First Direct Detection of Vacuum Polarization

Vacuum polarization, an effect predicted nearly 70 years ago, is still yet to be directly detected despite significant experimental effort. Previous attempts have made use of large liquid-helium cooled electromagnets which inadvertently generate spurious signals that mask the desired signal. We present a novel approach for the ultra-sensitive detection of optical birefringence that can be usefully applied to a laboratory detection of vacuum polarization. The new technique has a predicted birefringence measurement sensitivity of $\Delta n \sim 10^{20}$ in a 1 second measurement. When combined with the extreme polarizing fields achievable in this design we predict that a vacuum polarization signal will be seen in a measurement of just a few days in duration.Comment: 9 pages, 2 figures. submitted to PR