New Frontiers in Cosmology and Galaxy Formation: Challenges for the Future

(Abridged) Cosmology faces three distinct challenges in the next decade. (1) The dark sector, both dark matter and dark energy, dominates the Universe. Key questions include determining the nature of both. Improved observational probes are crucial. (2) Galaxy formation was initiated at around the epoch of reionization: we need to understand how and when as well as to develop probes of earlier epochs. (3) Our simple dark matter-driven picture of galaxy assembly is seemingly at odds with several observational results, including the presence of ULIRGS at high z, the `downsizing' signature, chemical signatures of alpha-element ratios and suggestions that merging may not be important in defining the Hubble sequence. Understanding the physical implications is a major challenge for theorists and refiniing the observational uncertainties a major goal for observers.Comment: To appear in "Structure Formation in the Universe", ed. Chabrier, G., Cambridge University Press. High resolution version on http://www.astro.caltech.edu/~rse/chamonix.pd

Symmetric Criticality for Tight Knots

We prove a version of symmetric criticality for ropelength-critical knots. Our theorem implies that a knot or link with a symmetric representative has a ropelength-critical configuration with the same symmetry. We use this to construct new examples of ropelength critical configurations for knots and links which are different from the ropelength minima for these knot and link types.Comment: This version adds references, and most importantly an acknowledgements section which should have been in the original postin

Experimental Study of Active LRC Circuits with PT-Symmetries

Mutually coupled modes of a pair of active LRC circuits, one with amplification and another with an equivalent amount of attenuation, provide an experimental realization of a wide class of systems where gain/loss mechanisms break the Hermiticity while preserving parity-time PT symmetry. For a value PT of the gain/loss strength parameter the eigen-frequencies undergo a spontaneous phase transition from real to complex values, while the normal modes coalesce acquiring a definite chirality. The consequences of the phase-transition in the spatiotemporal energy evolution are also presented.Comment: 4 pages, 4 figures, Rapid Communication in Physical Review A (2011

The stochastic background: scaling laws and time to detection for pulsar timing arrays

We derive scaling laws for the signal-to-noise ratio of the optimal cross-correlation statistic, and show that the large power-law increase of the signal-to-noise ratio as a function of the the observation time $T$ that is usually assumed holds only at early times. After enough time has elapsed, pulsar timing arrays enter a new regime where the signal to noise only scales as $\sqrt{T}$. In addition, in this regime the quality of the pulsar timing data and the cadence become relatively un-important. This occurs because the lowest frequencies of the pulsar timing residuals become gravitational-wave dominated. Pulsar timing arrays enter this regime more quickly than one might naively suspect. For T=10 yr observations and typical stochastic background amplitudes, pulsars with residual RMSs of less than about $1\,\mu$s are already in that regime. The best strategy to increase the detectability of the background in this regime is to increase the number of pulsars in the array. We also perform realistic simulations of the NANOGrav pulsar timing array, which through an aggressive pulsar survey campaign adds new millisecond pulsars regularly to its array, and show that a detection is possible within a decade, and could occur as early as 2016.Comment: Submitted to Classical and Quantum Gravity for Focus Issue on Pulsar Timing Arrays. 15 pages, 5 figure

On Coordinating Collaborative Objects

A collaborative object represents a data type (such as a text document) designed to be shared by a group of dispersed users. The Operational Transformation (OT) is a coordination approach used for supporting optimistic replication for these objects. It allows the users to concurrently update the shared data and exchange their updates in any order since the convergence of all replicas, i.e. the fact that all users view the same data, is ensured in all cases. However, designing algorithms for achieving convergence with the OT approach is a critical and challenging issue. In this paper, we propose a formal compositional method for specifying complex collaborative objects. The most important feature of our method is that designing an OT algorithm for the composed collaborative object can be done by reusing the OT algorithms of component collaborative objects. By using our method, we can start from correct small collaborative objects which are relatively easy to handle and incrementally combine them to build more complex collaborative objects.Comment: In Proceedings FOCLASA 2010, arXiv:1007.499

Compact Modeling for a Double Gate MOSFET

MOSFETs (metal-oxide-silicon field-effect transistors) are an integral part of modern electronics. Improved designs are currently under investigation, and one that is promising is the double gate MOSFET. Understanding device characteristics is critical for the design of MOSFETs as part of design tools for integrated circuits such as SPICE. Current methods involve the numerical solution of PDEs governing electron transport. Numerical solutions are accurate, but do not provide an appropriate way to optimize the design of the device, nor are they suitable for use in chip simulation software such as SPICE. As chips contain more and more transistors, this problem will get more and more acute. There is hence a need for analytic solutions of the equations governing the performance of MOSFETs, even if these are approximate. Almost all solutions in the literature treat the long-channel case (thin devices) for which the PDEs reduce to ODEs. The goal of this problem is to produce analytical solutions based on the underlying PDEs that are rapid to compute (e.g. require solving only a small number of algebraic equations rather than systems of PDEs). Guided by asymptotic analysis, a fast numerical procedure has been developed to obtain approximate solutions of the governing PDEs governing MOSFET properties, namely electron density, Fermi potential and electrostatic potential. The approach depends on the channel’s being long enough, and appears accurate in this limit

Archaeological Investigations for the Canyon Hydroelectric Project, Comal County, Texas

During January 1986, the Center for Archaeological Research from The University of Texas at San Antonio conducted a pedestrian survey along portions of a proposed Canyon Lake hydroelectric transmission line right-of-way in Comal County, Texas, for the Guadalupe-Blanco River Authority. The survey located six prehistoric sites (41 CM 160, 41 CM 161, 41 CM 162, 41 CM 163, 41 CM 164, and 41 CM 166) in the right-of-way, and one historic building complex (41 CM 165) adjacent to but well outside of the right-of-way. Recommendations were made for further testing of the prehistoric sites and background research for the historic site to determine their potential eligibility for nomination to the National Register of Historic Places and as a Texas Archeological Landmark. During April 1986, the Center conducted testing at prehistoric sites 41 CM 160, 41 CM 161, 41 CM 162, 41 CM 163, and 41 CM 164. Archival research was done for 41 CM 165. This work was done for the Guadalupe-Blanco River Authority as required by the Texas Historical Commission. All of the prehistoric sites were found to be lithic quarry sites that are deemed to have little potential for contributing significant new archaeological information. None are recommended as potentially eligible for nomination to the National Register or for Texas Archeological Landmark status. The historic site (41 CM 165) appears to have National Register potential. Further background research, building documentation, and selective testing are recommended, but not as part of this project