1,724,539 research outputs found
julianhong/TARS: Manuscript review
No full text<p>Under review for manuscript publication.</p>
TARS
No full textEfficient medium access control (MAC) is desirable for underwater sensor networks (UWSNs). However, designing an efficient underwater MAC protocol is challenging due to the long propagation delay of the underwater acoustic channel and spatial-temporal uncertainty. In this article, we propose a novel Traffic-Adaptive Receiver-Synchronized underwater MAC protocol, TARS, for throughput maximization. We divide time into equal-sized slots, each the size of one packet transmission time plus a guard time to cope with network dynamics. We adjust the packet transmission phase in a slot, determined by the sender-receiver distance, to align packet receptions for collision reduction. Both the sound propagation speed variation and the node mobility are considered in setting the transmission phase and slot size. We employ a queue-aware utility-optimization framework to determine the optimal transmission strategies dynamically, taking into account both the interference and data queue status. Extensive simulation results show that compared to the existing representative protocols, TARS achieves better performance with higher network throughput and lower packet delay (e.g., about 13%−146% higher in throughput and 13%−21% lower in delay than others in a mobile ad hoc network), as well as robustness under network mobility. Thus, TARS is highly suitable for mobile and traffic-varying UWSNs.</jats:p
A branching, positive relief network in the middle member of the Medusae Fossae Formation, equatorial Mars—Evidence for sapping?
Get PDFThe Medusae Fossae Formation (MFF) is a geological formation comprising three geological units (members) spread across five principal lobes. It dominates a quarter of the longitudinal extent of the equatorial region of Mars. Positive relief features referred to as ‘sinuous ridges’ (commonly interpreted as inverted paleoflow channel or valley fills) have been observed in the lowest member of the western MFF, but have not been identified within the central and eastern portions of the formation, in the middle and upper members. This paper presents the identification and analysis of a branching, positive relief system which occurs in the central lobe of the MFF in what appears to be an exposure of the middle member. A simple geomorphological map of the system is presented, from which we have adopted the working hypothesis that this is an inverted fill of a branching fluvial channel or valley system. A suite of morphological and topographic evidence supporting this hypothesis is presented, including analysis of the network using a ∼15 m/pixel digital terrain model derived from a Context Imager (CTX) stereo image pair. The evidence supporting this hypothesis includes: (1) the local slope and topography of the upper surface of the network are consistent with a contributory network; (2) the braided, fan-like form at the termination of the branching network is consistent in morphology with it being a depositional fan at the end of a fluvial system; (3) the terminal fan and surrounding deposits show layering and polygonization; and (4) there is strong association between the lower order branches and amphitheater shaped scarps in the depression walls. We evaluate the possible origins of this fluvial system and suggest that seepage sapping is the most probable. Two possible models for the evolution of the network and related features are presented; both require melt of ice within the MFF to form liquid water. We conclude that at least some portions of the Medusae Fossae Formation, if not the entire formation, were once volatile-rich. Finally, we note that our observations do not rule out the case that this network formed before MFF emplacement, and has since been exhumed. However, this conclusion would suggest that much of the surrounding terrain, currently mapped as middle-member MFF, is not in fact MFF material at all
Rollins' Students Become Tars
No full textRollins' students became Tars in support of their fellow students who were fighting in World War One. In honor of the troops, the college appointed a Tar as its mascot
The King of Tars
No full text"The King of Tars is an early fourteenth-century Middle English poem, a variation on the Constance- tale, celebrating the marriage of a Christian princess to a Muslim sultan and the sultan's conversion to Christianity." -
Characterization of acid tars
No full textAcid tars from the processing of petroleum and petrochemicals using sulfuric acid were characterized by gas chromatography/mass spectrometry (GC/MS), inductively coupled plasma/optical emission spectrometry (ICP/OES), differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectrometry, and scanning electron microscopy/energy dispersive X-ray (SEM/EDX) micro-analysis. Leaching of contaminants from the acid tars in 48 h batch tests with distilled water at a liquid-to-solid ratio 10:1 was also studied. GC/MS results show that the samples contained aliphatic hydrocarbons, cyclic hydrocarbons, up to 12 of the 16 USEPA priority polycyclic aromatic hydrocarbons (PAHs), and numerous other organic groups, including organic acids (sulfonic acids, carboxylic acids and aromatic acids), phenyl, nitrile, amide, furans, thiophenes, pyrroles, and phthalates, many of which are toxic. Metals analysis shows that Pb was present in significant concentration. DSC results show different transition peaks in the studied samples, demonstrating their complexity and variability. FTIR analysis further confirmed the presence of the organic groups detected by GC/MS. The SEM/EDX micro-analysis results provided insight on the surface characteristics of the samples and show that contaminants distribution was heterogeneous. The results provide useful data on the composition, complexity, and variability of acid tars; information which hitherto have been scarce in public domain. © 2009 Elsevier B.V. All rights reserved
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VAPOR PRESSURES AND HEATS OF VAPORIZATION OF PRIMARY COAL TARS
Get PDFThis project had as its main focus the determination of vapor pressures of coal pyrolysis tars. It involved performing measurements of these vapor pressures and from them, developing vapor pressure correlations suitable for use in advanced pyrolysis models (those models which explicitly account for mass transport limitations). This report is divided into five main chapters. Each chapter is a relatively stand-alone section. Chapter A reviews the general nature of coal tars and gives a summary of existing vapor pressure correlations for coal tars and model compounds. Chapter B summarizes the main experimental approaches for coal tar preparation and characterization which have been used throughout the project. Chapter C is concerned with the selection of the model compounds for coal pyrolysis tars and reviews the data available to us on the vapor pressures of high boiling point aromatic compounds. This chapter also deals with the question of identifying factors that govern the vapor pressures of coal tar model materials and their mixtures. Chapter D covers the vapor pressures and heats of vaporization of primary cellulose tars. Chapter E discusses the results of the main focus of this study. In summary, this work provides improved understanding of the volatility of coal and cellulose pyrolysis tars. It has resulted in new experimentally verified vapor pressure correlations for use in pyrolysis models. Further research on this topic should aim at developing general vapor pressure correlations for all coal tars, based on their molecular weight together with certain specific chemical characteristics i.e. hydroxyl group content
Structural features of full-length TarS.
No full text(A) Ribbon representation of TarS in complex with UDP (displayed in ball and stick form and colored according to heteroatom type) in two views related by a 90° rotation along the x-axis. Each monomer is indicated by color, and the catalytic and trimerization domains are indicated in the top view. Arrows in the bottom view demonstrate the 3-fold symmetry in the trimerization domain. (B) Overlay of TarS monomer trimerization domains displaying the relative positions of corresponding catalytic domains. The superimposed trimerization domain is represented by a light gray plane and the catalytic domains by colored planes corresponding to (A). (C) Electrostatic surface representation of TarS in two views related by a 180° rotation along the y-axis, with the left view in the same orientation as the bottom view in (A).</p
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Transverse Aeolian Ridges (TARs) on Mars
No full textAeolian processes are probably the dominant ongoing surface modification process on Mars, as demonstrated by observations of dunes, ripples, yardangs, ventifacts, wind streaks, dust devils and dust storms. Large Dark Dunes (LDDs) are particularly common and were first recognized in the 1960’s from Mariner data. However, another population of smaller, often brighter, ripple-like aeolian bed-forms that are morphologically distinct from LDDs has been observed in recent higher resolution images. Calculations of saltation path length under Martian conditions suggest these small bed-forms could have formed as small barchanoid dunes or as mega-ripples – also known as granule ripples. These features have therefore been called “Transverse Aeolian Ridges” (TARs) as this label has no genetic inference.
We have begun a study of TARs that examines all high resolution Mars Orbiter Camera data (1.5 to 8 m/pixel resolution) in a 45o longitude wide, pole-to-pole swath. We aim to determine the geographic distribution of TARs, assess whether they are active, and to identify possible sediment sources. We have already made some key observations: First, we present a new classification of TAR deposits based on crest-ridge morphology of individual forms and the size and degree of topographic control of the entire sediment mass. Second, we present associations of TARs with LDDs, slope streaks, dust devils tracks and small impact craters that provide clues as to whether TARs are currently active. Finally, we present preliminary pole-to pole survey results for the northern hemisphere that show clusters of TAR deposits in the low latitudes, suggesting possible unique sediment sources in these regions
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