Four new T dwarfs identified in PanSTARRS 1 commissioning data

A complete well-defined sample of ultracool dwarfs is one of the key science programs of the Pan-STARRS 1 optical survey telescope (PS1). Here we combine PS1 commissioning data with 2MASS to conduct a proper motion search (0.1--2.0\arcsec/yr) for nearby T dwarfs, using optical+near-IR colors to select objects for spectroscopic followup. The addition of sensitive far-red optical imaging from PS1 enables discovery of nearby ultracool dwarfs that cannot be identified from 2MASS data alone. We have searched 3700 sq. deg. of PS1 y-band (0.95--1.03 um) data to y$\approx$19.5 mag (AB) and J$\approx$16.5 mag (Vega) and discovered four previously unknown bright T dwarfs. Three of the objects (with spectral types T1.5, T2 and T3.5) have photometric distances within 25 pc and were missed by previous 2MASS searches due to more restrictive color selection criteria. The fourth object (spectral type T4.5) is more distant than 25 pc and is only a single-band detection in 2MASS. We also examine the potential for completing the census of nearby ultracool objects with the PS1 3$\pi$ survey.Comment: 25 pages, 8 figures, 5 table, AJ accepted, updated to comply with Pan-STARRS1 naming conventio

HIP 38939B: A New Benchmark T Dwarf in the Galactic Plane Discovered with Pan-STARRS1

We report the discovery of a wide brown dwarf companion to the mildly metal-poor ([Fe/H]=-0.24), low galactic latitude (b = 1.88 deg) K4V star HIP 38939. The companion was discovered by its common proper motion with the primary and its red optical (Pan-STARRS1) and blue infrared (2MASS) colors. It has a projected separation of 1630 AU and a near-infrared spectral type of T4.5. As such it is one of only three known companions to a main sequence star which have early/mid-T spectral types (the others being HN Peg B and eps Indi B). Using chromospheric activity we estimate an age for the primary of 900{+1900,-600} Myr. This value is also in agreement with the age derived from the star's weak ROSAT detection. Comparison with evolutionary models for this age range indicates that HIP 38939B falls in the mass range 38+/-20 Mjup with an effective temperature range of 1090+/-60 K. Fitting our spectrum with atmospheric models gives a best fitting temperature of 1100 K. We include our object in an analysis of the population of benchmark T dwarfs and find that while older atmospheric models appeared to over-predict the temperature of the coolest objects compared to evolutionary models, more recent atmospheric models provide better agreement.Comment: ApJ, in press. Tiny changes incorporated into final version: added analysis of likelihood of companionship, clarified the fitting proceedure, and updated the benchmark analysis to highlight when the quoted evolutionary models use the atmospheric model they are being compared to as a boundary conditio

An analysis of software interface issues for SMT processors

Thesis (Ph. D.)--University of Washington, 2002Simultaneous Multithreading (SMT) has gradually progressed from a research concept to commercial processor technology. This thesis explores three software interface issues on SMT that are important to its real-world applicability. These issues are: operating system performance on SMT, the impact of spinning on SMT, and register file limitations to scaling SMT. We investigate these issues with a new, detailed simulation infrastructure capable of modeling all operating system activity.First, we present an analysis of operating system execution on SMT. Many of the applications most amenable to multithreading technologies, such as the Apache web server, spend a significant fraction of their time in kernel code. We compare Apache's user- and kernel-mode behavior to a multiprogrammed SPECInt workload. Overall, our results demonstrate the micro-architectural impact of an OS-intensive workload on an SMT processor. The synergy between the SMT processor and Web and OS software produces a greater throughput gain over superscalar execution than seen on any previously examined workloads, including commercial databases.Second, we study the cost of synchronization on SMT. Spinning can exact a large performance cost on SMT, because all threads share execution resources. We quantify the impact of spinning on SMT and the performance benefit of replacing spinning with SMT-lock-based code. We observe that spinning's degradation of performance ranges widely between more than 3x on multiprogrammed workloads to a negligible amount on the Apache workload.Finally, we explore architectural register sharing on SMT. A significant impediment to the construction of SMTs larger than two or four contexts is register file size. We introduce and evaluate mini-threads, a simple extension to SMT that increases thread-level parallelism without the commensurate increase in register hardware. A mini-threaded SMT CPU adds additional per-thread state to each hardware context; an application executing in a context can create mini-threads that will utilize its own per-thread state, but share the context's architectural register set. Our results quantify the factors affecting performance in detail and demonstrate that mini-threads can improve performance significantly, particularly on small-scale, space-sensitive CPU designs

Making sense of empathy with sociable robots: A new look at the "imaginative perception of emotion"

In the field of social robotics, empathy is somewhat of a "hot topic" for engineers and empirical researchers alike. In this chapter, I examine a philosophical contribution toward making sense of empathy with robots, namely: Misselhorn's (2009) proposal that empathy with robots occurs through the interplay between perception and imagination ("imaginative perception"). I argue that although Misselhorn's explanatory framework captures something true about why people feel empathy for robots, such emotional responses are better conceived of as analogous to perceptual illusions rather than as cases of imaginative perception. I subsequently modify Misselhorn's framework to accommodate this, and then explore whether this modified framework can help account for another emotional response toward robots, the uncanny valley phenomenon. Here, I draw from some examples of empirical research on the uncanny valley. I show that people can (mis)perceive that robots possess attributes like animacy, emotion, and mentation. If one also believes that robots lack these things, then the inconsistency between that belief and the aforementioned misperceptions can make a robot seem eerie. Finally, I conclude that examples of people feeling empathy for robots are not genuine cases of empathy

Paxos made live: an engineering perspective

We describe our experience building a fault-tolerant data-base using the Paxos consensus algorithm. Despite the existing literature in the field, building such a database proved to be non-trivial. We describe selected algorithmic and engineering problems encountered, and the solutions we found for them. Our measurements indicate that we have built a competitive system.

Algorithms for a Simple Point Placement Problem

. We consider algorithms for a simple one-dimensional point placement problem: given N points on a line, and noisy measurements of the distances between many pairs of them, estimate the relative positions of the points. Problems of this flavor arise in a variety of contexts. The particular motivating example that inspired this work comes from molecular biology; the points are markers on a chromosomeand the goal is to map their positions. The problem is NP-hard under reasonable assumptions. We present two algorithms for computing least squares estimates of the ordering and positions of the markers: a branch and bound algorithm and a highly effective heuristic search algorithm. The branch and bound algorithm is able to solve to optimality problems of 18 markers in about an hour, visiting about 10 6 nodes out of a search space of 10 16 nodes. The local search algorithm usually was able to find the global minimum of problems of similar size in about one second, and should c..