Using the Sirocco File System for high-bandwidth checkpoints.

The Sirocco File System, a file system for exascale under active development, is designed to allow the storage software to maximize quality of service through increased flexibility and local decision-making. By allowing the storage system to manage a range of storage targets that have varying speeds and capacities, the system can increase the speed and surety of storage to the application. We instrument CTH to use a group of RAM-based Sirocco storage servers allocated within the job as a high-performance storage tier to accept checkpoints, allowing computation to potentially continue asynchronously of checkpoint migration to slower, more permanent storage. The result is a 10-60x speedup in constructing and moving checkpoint data from the compute nodes. This demonstration of early Sirocco functionality shows a significant benefit for a real I/O workload, checkpointing, in a real application, CTH. By running Sirocco storage servers within a job as RAM-only stores, CTH was able to store checkpoints 10-60x faster than storing to PanFS, allowing the job to continue computing sooner. While this prototype did not include automatic data migration, the checkpoint was available to be pushed or pulled to disk-based storage as needed after the compute nodes continued computing. Future developments include the ability to dynamically spawn Sirocco nodes to absorb checkpoints, expanding this mechanism to other fast tiers of storage like flash memory, and sharing of dynamic Sirocco nodes between multiple jobs as needed

Dyons in N=4 Supersymmetric Theories and Three-Pronged Strings

We construct and explore BPS states that preserve 1/4 of supersymmetry in N=4 Yang-Mills theories. Such states are also realized as three-pronged strings ending on D3-branes. We correct the electric part of the BPS equation and relate its solutions to the unbroken abelian gauge group generators. Generic 1/4-BPS solitons are not spherically symmetric, but consist of two or more dyonic components held apart by a delicate balance between static electromagnetic force and scalar Higgs force. The instability previously found in three-pronged string configurations is due to excessive repulsion by one of these static forces. We also present an alternate construction of these 1/4-BPS states from quantum excitations around a magnetic monopole, and build up the supermultiplet for arbitrary (quantized) electric charge. The degeneracy and the highest spin of the supermultiplet increase linearly with a relative electric charge. We conclude with comments.Comment: 33 pages, two figures, LaTex, a footnote added, the figure caption of Fig.2 expanded, one more referenc

Relationship Between Static Mobility of the First Ray and First Ray, Midfoot, and Hindfoot Motion During Gait

The relationship between a static measure of dorsal first ray mobility and dynamic motion of the first ray, midfoot, and hindfoot during the stance phase of walking was investigated in healthy, asymptomatic subjects who represented the spectrum of static flexibility. Static first ray mobility of 15 subjects was measured by a load cell device and ranged from stiff (3.1 mm) to lax (8.0 mm). Using three-dimensional motion analysis, mean first ray dorsiflexion/eversion and mid-/hindfoot eversion peak motion, time-to-peak, and eversion excursion were evaluated. Subjects with greater static dorsal mobility of the first ray demonstrated significantly greater time-topeak hindfoot eversion and eversion excursion (p \u3c .01), and midfoot peak eversion and eversion excursion (p \u3c .01). No significant association was found between static first ray mobility and first ray motion during gait. This research provides evidence that the dynamic response of the foot may modulate the consequences of first ray mobility and that compensory strategies are most effective when static measures of dorsal mobility are most extreme

Modeling the resonant planetary system GJ876

The two planets about the star GJ 876 appear to have undergone extensive migration from their point of origin in the protoplanetary disk -- both because of their close proximity to the star (30 and 60 day orbital periods) and because of their occupying three stable orbital resonances at the 2:1 mean-motion commensurability. The resonances were most likely established by converging differential migration of the planets leading to capture into the resonances. A problem with this scenario is that continued migration of the system while it is trapped in the resonances leads to orbital eccentricities that rapidly exceed the observational upper limits of e_1 = 0.31 and e_2 = 0.05. As seen in forced 3-body simulations, lower eccentricities would persist during migration only for an applied eccentricity damping. Here we explore the evolution of the GJ 876 system using two-dimensional hydrodynamical simulations that include viscous heating and radiative effects. We find that a hydrodynamic evolution within the resonance, where only the outer planet interacts with the disk, always rapidly leads to large values of eccentricities that exceed those observed. Only if mass is removed from the disk on a time scale of the order of the migration time scale (before there has been extensive migration after capture), as might occur for photoevaporation in the late phases of planet formation, can we end up with eccentricities that are consistent with the observations.Comment: Paper accepted by A&A, 17 Pages, 17 Figure

Using a model of group psychotherapy to support social research on sensitive topics

This article describes the exploratory use of professional therapeutic support by social researchers working on a sensitive topic. Talking to recently bereaved parents about the financial implications of their child's death was expected to be demanding work, and the research design included access to an independent psychotherapeutic service. Using this kind of professional support is rare within the general social research community, and it is useful to reflect on the process. There are likely to be implications for collection and interpretation of data, research output and the role and experience of the therapist. Here, the primary focus is the potential impact on researcher well-being

Terahertz generation in Czochralski grown periodically poled Mg:Y:LiNbO3 via optical rectification

Using a canonical pump-probe experimental technique, we studied the terahertz (THz) waves generation and detection via optical rectification and mixing in Czochralski-grown periodically poled Mg:Y:LiNbO3 (PPLN) crystals. THz waves with frequencies at 1.37 THz and 0.68 THz as well as 1.8 THz were obtained for PPLN with nonlinear grating periods of 0.03 and 0.06 mm, respectively. A general theoretical model was developed by considering the dispersion and damping of low frequency phonon-polariton mode. Our results show that THz waves are generated in forward and backward directions via pumping pulse rectification. The generated THz waves depend on the spectral shape of the laser pulses, quasi-phase mismatches and dispersion characteristics of a crystal.Comment: 25 pages, 4 figure

The Hyperbolic Heisenberg and Sigma Models in (1+1)-dimensions

Hyperbolic versions of the integrable (1+1)-dimensional Heisenberg Ferromagnet and sigma models are discussed in the context of topological solutions classifiable by an integer `winding number'. Some explicit solutions are presented and the existence of certain classes of such winding solutions examined.Comment: 13 pages, 1 figure, Latex, personal style file included tensind.sty, Proof in section 3 altered, no changes to conclusion

Chern-Simons Solitons, Chiral Model, and (affine) Toda Model on Noncommutative Space

We consider the Dunne-Jackiw-Pi-Trugenberger model of a U(N) Chern-Simons gauge theory coupled to a nonrelativistic complex adjoint matter on noncommutative space. Soliton configurations of this model are related the solutions of the chiral model on noncommutative plane. A generalized Uhlenbeck's uniton method for the chiral model on noncommutative space provides explicit Chern-Simons solitons. Fundamental solitons in the U(1) gauge theory are shaped as rings of charge `n' and spin `n' where the Chern-Simons level `n' should be an integer upon quantization. Toda and Liouville models are generalized to noncommutative plane and the solutions are provided by the uniton method. We also define affine Toda and sine-Gordon models on noncommutative plane. Finally the first order moduli space dynamics of Chern-Simons solitons is shown to be trivial.Comment: latex, JHEP style, 23 pages, no figur