Spitzer spectroscopy of circumstellar disks in the 5 Myr old upper Scorpius OB association

We present mid-infrared spectra between 5.2 and 38 μm for 26 disk-bearing members of the ~5 Myr old Upper Scorpius OB association obtained with the Infrared Spectrograph (IRS) onboard the Spitzer Space Telescope. We find clear evidence for changes in the spectral characteristics of dust emission between the early-type (B+A) and late-type (K+M) infrared excess stars. The early-type members exhibit featureless continuum excesses that become apparent redward of ~8 μm. In contrast, 10 and 20 μm silicate features or polycyclic aromatic hydrocarbon emission are present in all but one of the late-type excess members of Upper Scorpius. The strength of silicate emission among late-type Upper Scorpius members is spectral-type dependent, with the most prominent features being associated with K5-M2-type stars. By fitting the spectral energy distributions (SED) of a representative sample of low-mass stars with accretion disk models, we find that the SEDs are consistent with models having inner disk radii ranging from ~0.2 to 1.2 AU. Complementary high-resolution (R ~ 33,000) optical (λλ4800-9200) spectra for the Upper Scorpius excess stars were examined for signatures of gaseous accretion. Of the 35 infrared excess stars identified in Upper Scorpius, only seven (all late-type) exhibit definitive signatures of accretion. Mass-accretion rates (M) for these stars were estimated to range from 10^–11 to 10^–8.9 M⊙ yr^–1. Compared to Class II sources in Taurus-Auriga, the disk population in Upper Scorpius exhibits reduced levels of near- and mid-infrared excess emission and an order of magnitude lower mass-accretion rates. These results suggest that the disk structure has changed significantly over the 2-4 Myr in age separating these two stellar populations. The ubiquity of depleted inner disks in the Upper Scorpius excess sample implies that such disks are a common evolutionary pathway that persists for some time

Controlling Network Latency in Mixed Hadoop Clusters: Do We Need Active Queue Management?

With the advent of big data, data center applications are processing vast amounts of unstructured and semi-structured data, in parallel on large clusters, across hundreds to thousands of nodes. The highest performance for these batch big data workloads is achieved using expensive network equipment with large buffers, which accommodate bursts in network traffic and allocate bandwidth fairly even when the network is congested. Throughput-sensitive big data applications are, however, often executed in the same data center as latency-sensitive workloads. For both workloads to be supported well, the network must provide both maximum throughput and low latency. Progress has been made in this direction, as modern network switches support Active Queue Management (AQM) and Explicit Congestion Notifications (ECN), both mechanisms to control the level of queue occupancy, reducing the total network latency. This paper is the first study of the effect of Active Queue Management on both throughput and latency, in the context of Hadoop and the MapReduce programming model. We give a quantitative comparison of four different approaches for controlling buffer occupancy and latency: RED and CoDel, both standalone and also combined with ECN and DCTCP network protocol, and identify the AQM configurations that maintain Hadoop execution time gains from larger buffers within 5%, while reducing network packet latency caused by bufferbloat by up to 85%. Finally, we provide recommendations to administrators of Hadoop clusters as to how to improve latency without degrading the throughput of batch big data workloads.The research leading to these results has received funding from the European Unions Seventh Framework Programme (FP7/2007–2013) under grant agreement number 610456 (Euroserver). The research was also supported by the Ministry of Economy and Competitiveness of Spain under the contracts TIN2012-34557 and TIN2015-65316-P, Generalitat de Catalunya (contracts 2014-SGR-1051 and 2014-SGR-1272), HiPEAC-3 Network of Excellence (ICT- 287759), and the Severo Ochoa Program (SEV-2011-00067) of the Spanish Government.Peer ReviewedPostprint (author's final draft

Interconnect Energy Savings and Lower Latency Networks in Hadoop Clusters: The Missing Link

An important challenge of modern data centres running Hadoop workloads is to minimise energy consumption, a significant proportion of which is due to the network. Significant network savings are already possible using Energy Efficient Ethernet, supported by a large number of NICs and switches, but recent work has demonstrated that the packet coalescing settings must be carefully configured to avoid a substantial loss in performance. Meanwhile, Hadoop is evolving from its original batch concept to become a more iterative type of framework. Other recent work attempts to reduce Hadoop's network latency using Explicit Congestion Notifications. Linking these studies reveals that, surprisingly, even when packet coalescing does not hurt performance, it can degrade network latency much more than previously thought. This paper is the first to analyze the impact of packet coalescing in the context of network latency. We investigate how to design and configure interconnects to provide the maximum energy savings without degrading cluster throughput performance or network latency.The research leading to these results has received funding from the European Unions Seventh Framework Programme (FP7/2007–2013) under grant agreement number 610456 (Euroserver). The research was also supported by the Ministry of Economy and Competitiveness of Spain under the contracts TIN2012-34557 and TIN2015-65316-P, Generalitat de Catalunya (contracts 2014-SGR-1051 and 2014-SGR-1272), HiPEAC-3 Network of Excellence (ICT- 287759), and the Severo Ochoa Program (SEV-2011-00067) of the Spanish Government.Peer ReviewedPostprint (author's final draft

Ejection Forces and Friction Coefficients from Injection Molding Experiments Using Rapid Tooling Inserts

Experiments have been performed with injection mold inserts made using solid freeform fabrication processes in an effort to further study such applications for economic production of small quantities of parts. Static friction coefficients were determined for HDPE and HIPS against P-20 steel, sintered LaserForm ST-100, and stereolithography SL 5170 using the ASTM D 1894 standard. Injection mold inserts were constructed of the same three materials and were used to inject cylindrical parts using HDPE and HIPS. Ejection forces were measured, and a model was used to calculate ejection forces and apparent coefficients of static friction. Statistical analyses were used to determine the effects of packing time, cooling time and packing pressure on ejection force for the three insert types. This paper compares experimental and calculated ejection forces, compares standard friction test results to calculated apparent coefficients of friction, summarizes the statistical results, and comments on the feasibility of using rapid tooled inserts for injection molding.Mechanical Engineerin

Inventory Investment, Internal-Finance Fluctuation, and the Business Cycle

macroeconomics, inventory investment, internal-finance fluctuation, business cycle

Evidence for Mass-dependent Circumstellar Disk Evolution in the 5 Myr Old Upper Scorpius OB Association

We present 4.5, 8, and 16 µm photometry from the Spitzer Space Telescope for 204 stars in the Upper Scorpius OB association. The data are used to investigate the frequency and properties of circumstellar disks around stars with masses between ~0.1 and 20 M_☉ at an age of ~5 Myr. We identify 35 stars that have emission at 8 or 16 µm in excess of the, stellar photosphere. The lower mass stars (~0.1–1.2M_☉) appear surrounded by primordial optically thick disks based on, the excess emission characteristics. Starsmoremassive than ~1.8M_☉ have lower fractional excess luminosities suggesting, that the inner ~10 AU of the disk has been largely depleted of primordial material. None of the G and F stars (~1.2–1.8 M_☉) in our sample have an infrared excess at wavelengths ≤16 µm. These results indicate that the mechanisms for, dispersing primordial optically thick disks operate less efficiently, on average, for low-mass stars, and that longer timescales are available for the buildup of planetary systems in the terrestrial zone for stars with masses ≾1 M_☉

Spin transition in Gd3_3N@C80_{80}, detected by low-temperature on-chip SQUID technique

We present a magnetic study of the Gd$_3$N@C$_{80}$ molecule, consisting of a Gd-trimer via a Nitrogen atom, encapsulated in a C$_{80}$ cage. This molecular system can be an efficient contrast agent for Magnetic Resonance Imaging (MRI) applications. We used a low-temperature technique able to detect small magnetic signals by placing the sample in the vicinity of an on-chip SQUID. The technique implemented at NHMFL has the particularity to operate in high magnetic fields of up to 7 T. The Gd$_3$N@C$_{80}$ shows a paramagnetic behavior and we find a spin transition of the Gd$_3$N structure at 1.2 K. We perform quantum mechanical simulations, which indicate that one of the Gd ions changes from a $^8S_{7/2}$ state ($L=0, S=7/2$) to a $^7F_{6}$ state ($L=S=3, J=6$), likely due to a charge transfer between the C$_{80}$ cage and the ion

Control of the cation occupancies of MnZn ferrite synthesized via reverse micelles

Variations in cation occupancy in mixed metal ferrite systems can affect their electronic and magnetic properties. It is known that different synthesis parameters can lead to various cation distributions and the ability to tune these distributions is of great interest. This study uses the extended x-ray-absorption fine structure–IR relationship to investigate the effect of various Fe2+/Fe3+ ratios in initial synthesis conditions on cation distribution for manganesezincferrite (MZFO). Differences in the precipitated material before firing could lead to differences in the final material if fired under similar conditions. This work uses several different ratios of Fe3+/Fe2+, which will affect the initial cell potential for the reaction, to synthesize nano MZFO. All samples were fired for 5h at 500°C under flowing nitrogen. Transmission electron microscopy micrographs reveal highly crystalline uniform nanoparticles of 16±2nm. The x-ray diffraction revealed single phase crystalline MZFO with an average crystallite size of around 14nm. The saturation magnetization ranged from 43to68emu∕g as measured by vibrating-sample magnetometry. The Fourier transform infrared (FTIR) analysis was used to determine the cation occupancies while changing the initial Fe3+/Fe2+ ratios from 10∕90 to90∕10. The FTIRspectra revealed a shift in the first absorption region in the far IR from 566.98to549.62cm−1 corresponding to the octahedral occupancies. This shift corresponds to a change in the percentage of octahedral sites occupied by manganese from roughly 25% to 12%. This change in manganese occupancy is also observed in the iron occupancies, which in turn help to explain the variation in saturation magnetization

Recognition of 3-D Objects from Multiple 2-D Views by a Self-Organizing Neural Architecture

The recognition of 3-D objects from sequences of their 2-D views is modeled by a neural architecture, called VIEWNET that uses View Information Encoded With NETworks. VIEWNET illustrates how several types of noise and varialbility in image data can be progressively removed while incornplcte image features are restored and invariant features are discovered using an appropriately designed cascade of processing stages. VIEWNET first processes 2-D views of 3-D objects using the CORT-X 2 filter, which discounts the illuminant, regularizes and completes figural boundaries, and removes noise from the images. Boundary regularization and cornpletion are achieved by the same mechanisms that suppress image noise. A log-polar transform is taken with respect to the centroid of the resulting figure and then re-centered to achieve 2-D scale and rotation invariance. The invariant images are coarse coded to further reduce noise, reduce foreshortening effects, and increase generalization. These compressed codes are input into a supervised learning system based on the fuzzy ARTMAP algorithm. Recognition categories of 2-D views are learned before evidence from sequences of 2-D view categories is accumulated to improve object recognition. Recognition is studied with noisy and clean images using slow and fast learning. VIEWNET is demonstrated on an MIT Lincoln Laboratory database of 2-D views of jet aircraft with and without additive noise. A recognition rate of 90% is achieved with one 2-D view category and of 98.5% correct with three 2-D view categories.National Science Foundation (IRI 90-24877); Office of Naval Research (N00014-91-J-1309, N00014-91-J-4100, N00014-92-J-0499); Air Force Office of Scientific Research (F9620-92-J-0499, 90-0083

Reduced Fine-Tuning in Supersymmetry with R-parity violation

Both electroweak precision measurements and simple supersymmetric extensions of the standard model prefer a mass of the Higgs boson less than the experimental lower limit of 114 GeV. We show that supersymmetric models with R parity violation and baryon number violation have a significant range of parameter space in which the Higgs dominantly decays to six jets. These decays are much more weakly constrained by current LEP analyses and would allow for a Higgs mass near that of the $Z$. In general, lighter scalar quark and other superpartner masses are allowed and the fine-tuning typically required to generate the measured scale of electroweak symmetry breaking is ameliorated. The Higgs would potentially be discovered at hadron colliders via the appearance of new displaced vertices. The lightest neutralino could be discovered by a scan of vertex-less events LEP I data.Comment: 5 pages, 2 figures. Significant detail added to the arguments regarding LEP limits - made more quantitative. Better figures used, plotting more physical quantities. Typos corrected and references updated. Conclusions unchange