Chain: A Dynamic Double Auction Framework for Matching Patient Agents

In this paper we present and evaluate a general framework for the design of truthful auctions for matching agents in a dynamic, two-sided market. A single commodity, such as a resource or a task, is bought and sold by multiple buyers and sellers that arrive and depart over time. Our algorithm, Chain, provides the first framework that allows a truthful dynamic double auction (DA) to be constructed from a truthful, single-period (i.e. static) double-auction rule. The pricing and matching method of the Chain construction is unique amongst dynamic-auction rules that adopt the same building block. We examine experimentally the allocative efficiency of Chain when instantiated on various single-period rules, including the canonical McAfee double-auction rule. For a baseline we also consider non-truthful double auctions populated with zero-intelligence plus"-style learning agents. Chain-based auctions perform well in comparison with other schemes, especially as arrival intensity falls and agent valuations become more volatile

Modern control concepts in hydrology

Two approaches to an identification problem in hydrology are presented based upon concepts from modern control and estimation theory. The first approach treats the identification of unknown parameters in a hydrologic system subject to noisy inputs as an adaptive linear stochastic control problem; the second approach alters the model equation to account for the random part in the inputs, and then uses a nonlinear estimation scheme to estimate the unknown parameters. Both approaches use state-space concepts. The identification schemes are sequential and adaptive and can handle either time invariant or time dependent parameters. They are used to identify parameters in the Prasad model of rainfall-runoff. The results obtained are encouraging and conform with results from two previous studies; the first using numerical integration of the model equation along with a trial-and-error procedure, and the second, by using a quasi-linearization technique. The proposed approaches offer a systematic way of analyzing the rainfall-runoff process when the input data are imbedded in noise

Canceling Quadratic Divergences in a Class of Two-Higgs-Doublet Models

The Newton-Wu conditions for the cancellation of quadratic divergences in a class of two-Higgs-doublet models are analyzed as to how they may be satisfied with a typical extension of the Standard Model of particle interactions.Comment: 5 pages, no figur

An Ironing-Based Approach to Adaptive Online Mechanism Design in Single-Valued Domains

Online mechanism design considers the problem of sequential decision making in a multi-agent system with self-interested agents. The agent population is dynamic and each agent has private information about its value for a sequence of decisions. We introduce a method ("ironing") to transform an algorithm for online stochastic optimization into one that is incentive-compatible. Ironing achieves this by canceling decisions that violate a form of monotonicity. The approach is applied to the CONSENSUS algorithm and experimental results in a resource allocation domain show that not many decisions need to be canceled and that the overhead of ironing is manageable.Engineering and Applied Science

The Taurus Boundary of Stellar/Substellar (TBOSS) Survey I: far-IR disk emission measured with Herschel

With Herschel/PACS 134 low mass members of the Taurus star-forming region spanning the M4-L0 spectral type range and covering the transition from low mass stars to brown dwarfs were observed. Combining the new Herschel results with other programs, a total of 150 of the 154 M4-L0 Taurus members members have observations with Herschel. Among the 150 targets, 70um flux densities were measured for 7 of the 7 ClassI objects, 48 of the 67 ClassII members, and 3 of the 76 ClassIII targets. For the detected ClassII objects, the median 70um flux density level declines with spectral type, however, the distribution of excess relative to central object flux density does not change across the stellar/substellar boundary in the M4-L0 range. Connecting the 70um TBOSS values with the results from K0-M3 ClassII members results in the first comprehensive census of far-IR emission across the full mass spectrum of the stellar and substellar population of a star-forming region, and the median flux density declines with spectral type in a trend analogous to the flux density decline expected for the central objects. SEDs were constructed for all TBOSS targets covering the optical to far-IR range and extending to the submm/mm for a subset of sources. Based on an initial exploration of the impact of different physical parameters; inclination, scale height and flaring have the largest influence on the PACS flux densities. From the 24um to 70um spectral index of the SEDs, 5 new candidate transition disks were identified. The steep 24um to 70um slope for a subset of 8 TBOSS targets may be an indication of truncated disks in these systems.Two examples of mixed pair systems that include secondaries with disks were measured. Finally, comparing the TBOSS results with a Herschel study of Ophiuchus brown dwarfs reveals a lower fraction of disks around the Taurus substellar population.Comment: 64 pages, 33 figures, 12 tables, accepted for publication in A&

Phyllosticta citriasiana sp. nov., the cause of Citrus tan spot of Citrus maxima in Asia

Guignardia citricarpa, the causal agent of Citrus Black Spot, is subject to phytosanitary legislation in the European Union and the U.S.A. This species is frequently confused with G. mangiferae, which is a non-pathogenic, and is commonly isolated as an endophyte from citrus fruits and a wide range of other hosts. Recently, necrotic spots similar to those caused by G. citricarpa were observed on fruit of Citrus maxima intercepted in consignments exported from Asia. In these spots, pycnidia and conidia of a Guignardia species closely resembling G. citricarpa were observed, and therefore measures were taken for the consignments in line with the European Union legislation for G. citricarpa. To determine the identity of the causal organism on this new host, fungal isolates were subjected to DNA sequence analysis of the internal transcribed spacer region (ITS1, 5.8S, ITS2), translation elongation factor 1-alpha (TEF1) and actin genes. A combined phylogenetic tree resolved three species correlating to G. citricarpa, G. mangiferae and a previously undescribed species, Phyllosticta citriasiana sp. nov., closely related to G. citricarpa. Morphologically P. citriasiana can be distinguished from G. citricarpa by having larger conidia, longer conidial appendages, and in not producing any diffuse yellow pigment when cultivated on oatmeal agar (OA). Furthermore, it is distinguishable from G. mangiferae by having smaller conidia, with a narrower mucoid sheath. In culture, colonies of P. citriasiana can also be distinguished from G. citricarpa and G. mangiferae by being darker shades of grey and black on OA, malt extract agar (MEA), potato-dextrose agar, and cornmeal agar. Furthermore, cultures of P. citriasiana achieved optimal growth after 2 weeks at 21-27°C, and ceased to grow at 30-33°C. In contrast, colonies of G. citricarpa and G. mangiferae achieved optimal growth at 27-30°C, and ceased to grow at 30-36°C Colonies of P. citriasiana also grew faster than those of G. citricarpa and G. mangiferae on OA and MEA. Phyllosticta citriasiana appears to be a harmful pathogen of Citrus maxima, causing a tan spot on fruit, underlining the need for further surveys and research to determine its distribution and host range

Efficiently Clustering Very Large Attributed Graphs

Attributed graphs model real networks by enriching their nodes with attributes accounting for properties. Several techniques have been proposed for partitioning these graphs into clusters that are homogeneous with respect to both semantic attributes and to the structure of the graph. However, time and space complexities of state of the art algorithms limit their scalability to medium-sized graphs. We propose SToC (for Semantic-Topological Clustering), a fast and scalable algorithm for partitioning large attributed graphs. The approach is robust, being compatible both with categorical and with quantitative attributes, and it is tailorable, allowing the user to weight the semantic and topological components. Further, the approach does not require the user to guess in advance the number of clusters. SToC relies on well known approximation techniques such as bottom-k sketches, traditional graph-theoretic concepts, and a new perspective on the composition of heterogeneous distance measures. Experimental results demonstrate its ability to efficiently compute high-quality partitions of large scale attributed graphs.Comment: This work has been published in ASONAM 2017. This version includes an appendix with validation of our attribute model and distance function, omitted in the converence version for lack of space. Please refer to the published versio

The Brown-dwarf Atmosphere Monitoring (BAM) Project II: Multi-epoch monitoring of extremely cool brown dwarfs

With the discovery of Y dwarfs by the WISE mission, the population of field brown dwarfs now extends to objects with temperatures comparable to those of Solar System planets. To investigate the atmospheres of these newly identified brown dwarfs, we have conducted a pilot study monitoring an initial sample of three late T-dwarfs (T6.5, T8 and T8.5) and one Y-dwarf (Y0) for infrared photometric variability at multiple epochs. With J-band imaging, each target was observed for a period of 1.0h to 4.5h per epoch, which covers a significant fraction of the expected rotational period. These measurements represent the first photometric monitoring for these targets. For three of the four targets (2M1047, Ross 458C and WISE0458), multi-epoch monitoring was performed, with the time span between epochs ranging from a few hours to ~2 years. During the first epoch, the T8.5 target WISE0458 exhibited variations with a remarkable min-to-max amplitude of 13%, while the second epoch light curve taken ~2 years later did not note any variability to a 3% upper limit. With an effective temperature of ~600 K, WISE0458 is the coldest variable brown dwarf published to-date, and combined with its high and variable amplitude makes it a fascinating target for detailed follow-up. The three remaining targets showed no significant variations, with a photometric precision between 0.8% and 20.0%, depending on the target brightness. Combining the new results with previous multi-epoch observations of brown dwarfs with spectral types of T5 or later, the currently identified variables have locations on the colour-colour diagram better matched by theoretical models incorporating cloud opacities rather than cloud-free atmospheres. This preliminary result requires further study to determine if there is a definitive link between variability among late-T dwarfs and their location on the colour-colour diagram.Comment: 9 pages, 6 figures, 3 tables, accepted for publication in MNRA