We investigate the problem of sensor and source joint localization using time-difference of arrivals (TDOAs) of an ad-hoc array. A major challenge is that the TDOAs contain unknown time offsets ...between asynchronous sensors. To address this problem, we propose a low-rank approximation method that does not need any prior knowledge of sensor and source locations or timing information. At first, we construct a pseudo time of arrival (TOA) matrix by introducing two sets of unknown timing parameters (source onset times and device capture times) into the current TDOA matrix. Then we propose a Gauss-Newton low-rank approximation algorithm to jointly identify the two sets of unknown timing parameters, exploiting the low-rank property embedded in the pseudo TOA matrix. We derive the boundaries of the timing parameters to reduce the initialization space and employ a multi-initialization scheme. Finally, we use the estimated timing parameters to correct the pseudo TOA matrix, which is further applied to sensor and source localization. Experimental results show that the proposed approach outperforms state-of-the-art algorithms.
Submicrometer Metallic Barcodes Nicewarner-Peña, Sheila R.; Freeman, R. Griffith; Reiss, Brian D. ...
Science (American Association for the Advancement of Science),
10/2001, Letnik:
294, Številka:
5540
Journal Article
Recenzirano
We synthesized multimetal microrods intrinsically encoded with submicrometer stripes. Complex striping patterns are readily prepared by sequential electrochemical deposition of metal ions into ...templates with uniformly sized pores. The differential reflectivity of adjacent stripes enables identification of the striping patterns by conventional light microscopy. This readout mechanism does not interfere with the use of fluorescence for detection of analytes bound to particles by affinity capture, as demonstrated by DNA and protein bioassays.
Audio equalization is a vast and active research area. The extent of research means that one often cannot identify the preferred technique for a particular problem. This review paper bridges those ...gaps, systemically providing a deep understanding of the problems and approaches in audio equalization, their relative merits and applications. Digital signal processing techniques for modifying the spectral balance in audio signals and applications of these techniques are reviewed, ranging from classic equalizers to emerging designs based on new advances in signal processing and machine learning. Emphasis is placed on putting the range of approaches within a common mathematical and conceptual framework. The application areas discussed herein are diverse, and include well-defined, solvable problems of filter design subject to constraints, as well as newly emerging challenges that touch on problems in semantics, perception and human computer interaction. Case studies are given in order to illustrate key concepts and how they are applied in practice. We also recommend preferred signal processing approaches for important audio equalization problems. Finally, we discuss current challenges and the uncharted frontiers in this field. The source code for methods discussed in this paper is made available at https://code.soundsoftware.ac.uk/projects/allaboutaudioeq.
We report a virus-based scaffold for the synthesis of single-crystal ZnS, CdS, and freestanding chemically ordered CoPt and FePt nanowires, with the means of modifying substrate specificity through ...standard biological methods. Peptides (selected through an evolutionary screening process) that exhibit control of composition, size, and phase during nanoparticle nucleation have been expressed on the highly ordered filamentous capsid of the M13 bacteriophage. The incorporation of specific, nucleating peptides into the generic scaffold of the M13 coat structure provides a viable template for the directed synthesis of semiconducting and magnetic materials. Removal of the viral template by means of annealing promoted oriented aggregation-based crystal growth, forming individual crystalline nanowires. The unique ability to interchange substrate-specific peptides into the linear self-assembled filamentous construct of the M13 virus introduces a material tunability that has not been seen in previous synthetic routes. Therefore, this system provides a genetic toolkit for growing and organizing nanowires from semiconducting and magnetic materials.
•Present-day activity of one gully within a south polar pit in Sisyphi Cavi was detected.•Activity of the gully shows dark flows through the entire gully and new depositions at the terminus of the ...gully.•Activity was narrowed to occur in mid-spring between solar longitudes ∼218° and ∼226°.•Spectral investigations show, that the dark flows are most likely thin regolith flows on top of a CO2 slab ice cover.•Dark flows are most likely related to dry flows, possibly supported by ongoing sublimation of CO2 slab ice within the gully.
The large amount of multi-temporal high-resolution images acquired in the last few years offers the opportunity to identify morphological changes associated with recent geologic activity on the surface of Mars. In this study we focus on a single gully in Sisyphi Cavi, located in the south polar region at 1.44°E and 68.54°S. The gully incises the gullied equator-facing slope of an isolated polar pit within an infilled impact crater. It is important to notice that the following investigations describe the activity and modifications of an existing gully and not the formation of the gully itself. High-resolution image data analyses show new deposits at the terminus of the gully channel and on the gully apron within spring (after solar longitudes of 236°) of martian years (MY) 29 and 31. Our morphological investigations show that the identified new deposits were formed by dark flows through the entire gully deposited on top of the apron between solar longitudes (LS)∼218° and ∼226°. Thermal data show a temperature increase between LS ∼218° and ∼226°. Near-infrared spectral data show relatively constant band strengths of CO2 ice and H2O ice in this time range. After the formation of the dark flows (after LS∼226°), temperatures increase rapidly from ∼180K to >∼270K at LS∼250°. At this time, spectral data indicate that all volatiles on the surface sublimated. However, an earlier beginning of sublimation when the dark flows were observed (between LS∼218° and ∼226°) is likely, due to the fact that the instruments can only show the last phase of sublimation (decrease of volatile band strengths). Spectral modeling shows that from winter to mid-spring, the surface of the studied area is covered by translucent CO2 slab-ice contaminated by minor amounts of H2O ice and dust. Furthermore, our spectral modeling indicates that the dark material most likely flows on top of the CO2 slab-ice cover. Three different scenarios were proposed to explain the identified dark flows, including (1) flows supported by liquid H2O, (2) flows supported by CO2 gas, and (3) dry flows. On the basis of our study we find that scenario (1) is unlikely because of the very low temperatures. While scenario (2) is consistent with the observed beginning of CO2 ice sublimation in the study area, it is unlikely because of the limitation of the activity to only one gully compared to surrounding gullies that share the same morphologies, slope angles, and volatile contents. Also with scenario (3), dry flows, the activity of only one gully is difficult to explain. Thus, we propose a mixture of scenario (2 and 3), dry flows supported by the ongoing sublimation of CO2 ice within the gully, to be the most plausible scenario, when the observed active gully comprises different source material than the surrounding gullies, i.e., a higher content of probably sand-sized material from outcrops located in the alcove.
Endogenous retroviruses Maksakova, I. A.; Mager, D. L.; Reiss, D.
Cellular and molecular life sciences : CMLS,
11/2008, Letnik:
65, Številka:
21
Journal Article
Recenzirano
.
Endogenous retrovirus-like elements, or ERVs, are an abundant component of all eukaryotic genomes. Their transcriptional and retrotranspositional activities have great potential for deleterious ...effects on gene expression. Consequences of such activity may include germline mutagenesis and cancerous transformation. As a result, mammalian genomes have evolved means of counteracting ERV transcription and mobilization. In this review, we discuss epigenetic mechanisms of ERV and LTR retrotransposon control during mouse development, focusing on involvement of DNA methylation, histone modifications, small RNAs and their interaction with one another. We also address relevance of research performed in the mouse system to human and challenges associated with studying repetitive families. (Part of a Multi-author Review)
We study ultrafast magnetization quenching of ferromagnetic iron following excitation by an optical versus a terahertz pump pulse. While the optical pump (photon energy of 3.1 eV) induces a strongly ...nonthermal electron distribution, terahertz excitation (4.1 meV) results in a quasithermal perturbation of the electron population. The pump-induced spin and electron dynamics are interrogated by the magneto-optic Kerr effect (MOKE). A deconvolution procedure allows us to push the time resolution down to 130 fs, even though the driving terahertz pulse is about 500 fs long. Remarkably, the MOKE signals exhibit an almost identical time evolution for both optical and terahertz pump pulses, despite the 3 orders of magnitude different number of excited electrons. We are able to quantitatively explain our results using a nonthermal model based on quasielastic spin-flip scattering. It shows that, in the small-perturbation limit, the rate of demagnetization of a metallic ferromagnet is proportional to the excess energy of the electrons, independent of the precise shape of their distribution. Our results reveal that, for simple metallic ferromagnets, the dynamics of ultrafast demagnetization and of the closely related terahertz spin transport do not depend on the pump photon energy.
•We present a state-of-the-art map (1:2,000,000) of the entire Hellas basin floor based on USGS mapping standards.•Via crater-based model ages, stratigraphic analyses, and previous investigations of ...rim areas, we compiled a detailed, self-consistent geologic history for the entire basin.•Phreatomagmatic activity around Hellas basin ∼3.7Ga ago likely caused intense dissection along rim and deposition of interior formation.•Low-energy fluvial environments occurred along northern rim. No landforms indicating standing body of ice or water in basin are preserved.•Honeycomb terrain possibly canopy of truncated upwelling structures formed before lower wrinkle-ridged plains.•Banded terrain appears to be thin veneer occurring along wind-carved trough in eastern basin.
The Hellas basin on Mars is the second-largest topographically well-defined impact structure in the Solar System and has repeatedly been interpreted as a major sink of volcanic, glacio-fluvial and eolian materials. Based on established guidelines for planetary mapping, we compiled a comprehensive photogeological map of Hellas Planitia, i.e., the Hellas basin floor (1:2,000,000; ∼1.8×106km2; see Supplementary online material), using the Thermal Emission Imaging System (THEMIS-IR) day-time mosaic as basemap (supplemented by several other datasets). We identified 33 units, which were categorized into a “Rim Assemblage”, containing “Dissected units”, a “Layered rim sequence”, and “Other basin rim units”, as well as a “Floor Assemblage”, containing the “Honeycomb formation”, an “Interior formation”, and a “Plains sequence”. Relative dating of units was performed wherever contacts revealed stratigraphic relationships and was complemented by absolute model ages (AMAs) of all units that lend themselves to reliable crater-size frequency distribution (CSFDs) measurements. On the basis of our results, as well as AMAs of circum-Hellas volcanic provinces by previous authors, we compiled a chronostratigraphic model of the Hellas basin floor. The northern basin rim shows evidence (vast layered, hydrous mineral-bearing deposits containing meandering, channel-like valleys), that the early history of the basin until ∼3.8Ga ago experienced extended periods of low-energy fluvial, and possibly lacustrine, activity. Superposing the layered rim sequence, the majority of the Hellas basin infill (∼1.5–1.7×106km3) consists of volcanic material (a lower and an upper wrinkle-ridged plains unit), which was shortened by a compressive stress field relatively soon after its emplacement. Based on their ages and stratigraphic considerations, we identified Malea Patera (and possibly also Tyrrhena Patera) as a suitable source for the older, lower plains (∼3.8Ga), and Hadriaca and/or Amphitrites Paterae for the younger, upper plains (∼3.7Ga). Shortly after these volcanic episodes, the entire basin floor was covered by large amounts of deposits (>106km3) containing aqueously altered mafic materials. We interpret the deposits to have originated from Hesperia Planum and the Hesperia-Hellas trough, where they might have been removed by glacio-fluvial processes, which also sculpted the Hellas rim sections along northern Promethei Terra and Malea Planum around the same time. Such an apparent correlation between nearby volcanic activity and increased erosion/deposition is in agreement with previous models, which suggest outgassing by a maximum in global volcanism at that time caused warmer episodes enabling repeated subaerial water run-off. After the emplacement of these deposits, intense erosion, likely deflation along a rim-parallel annulus, began to exhume the outer parts of the wrinkle-ridged plains again, forming an interior formation of more elevated erosional remnants including the Alpheus Colles. Since ∼3.7Ga ago, fluvial activity of Dao/Niger and Harmakhis Valles dissected the eastern plains and emplaced pancake-shaped deposits in the basin center. Later, deflation and abrasion by katabatic winds moving through the Hellas basin in a clock-wise direction parallel to the basin floor outline carved out the northwestern Hellas Planitia trough (called Peneus Palus), possibly within a time span of few hundreds of Ma or less within the Amazonian. Being consistent with erosional patterns we observed within the basin, circulation models predict such winds to be ongoing today and might, thus, have recently exhumed the so called “honeycomb” formation on parts of Peneus Palus. This enigmatic, unique terrain was possibly formed by ductile deformation of pre-3.8Ga material and appears to be partially covered by another unique landform, the “banded terrain”. Although we cannot rule out that it is the surface expression of a thicker unit, the banded terrain might represent flows of volatile-rich airfall deposits emplaced along the edges of the Hellas wind alley by turbulent, marginal wind currents, which currently/recently prevail on both sides of the Hellas Planitia trough. In summary, our investigations enabled us to draw an updated, comprehensive and self-consistent picture of the geologic evolution of the Hellas basin floor, including volcanic, (peri-)glacial, fluvial and eolian processes, their possible interactions, and the implications on the climatic and geologic development of the circum-Hellas region and the entire planet.
•New method to derive motion of active features on Mars with CRISM and CTX/HiRISE data.•We derived the horizontal motion (speed and direction) of dust devils on Mars.•Comparison with Mars Climate ...Database (MCD) wind speeds and directions.•Broad agreement with ambient wind speeds and directions within the Planetary Boundary Layer (PBL).•Dust devils on Mars move faster than near-surface winds.
We derived the horizontal motion (speed and direction) of dust devils from time-delayed Mars Reconnaissance Orbiter (MRO) coordinated image data sets of the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) to the Context Camera (CTX) and/or the High Resolution Imaging Science Experiment (HiRISE) acquired between 2008 and 2011. In total, 47 dust devils were observed in 15 regions with diameters ranging from 15 to 280m with an average diameter of 100m and heights from 40 to 4400m. Horizontal speeds of 44 dust devils range from 4 to 25ms−1 with average speeds of 12ms−1. The majority of dust devils were observed in the northern hemisphere (79%), mainly in Amazonis Planitia (67.5% from the northern hemisphere dust devils). Seasonal occurrence of dust devils in the northern hemisphere is predominant in early and mid spring (76%). We compared our measured dust devil horizontal speeds and directions of motion to the monthly climatologies (wind speed and direction) released in the Mars Climate Database (MCD) derived from General Circulation Model (GCM) predictions. There is a broad agreement between dust devil horizontal speeds and MCD wind speed predictions within the Planetary Boundary Layer (PBL) as well as dust devil directions of motion and MCD predicted wind directions occurring within the PBL. Comparisons between dust devil horizontal speeds and MCD near-surface wind speed predictions at 10m height above the surface do not correlate well: dust devils move about a factor of 2 faster than MCD near-surface wind predictions. The largest offsets between dust devil motion and MCD predictions were related to three dust devils occurring near the Phoenix landing site when the lander was still active. The offsets could be explained by a regional weather front passing over the Phoenix landing site. In general, the good agreement between dust devil horizontal speeds and directions of motion, and ambient wind speeds and directions predicted within the PBL through GCM, show that dust devils on Mars move with ambient winds in the PBL, hence faster than near surface winds.
•Flows of mud were detected in the SW portion of Utopia Planitia.•Mud flows are spatially associated with giant polygons.•Rampart craters are concentrated at the periphery of Utopia Planitia.•Craters ...with pancake-like ejecta prevail in the center of Utopia Planitia.•A large body of water/ice likely existed in the center of Utopia Planitia.
Results of our detailed geological mapping and interpretation of the nature and relative and absolute model ages of units and structures in the SW portion of Utopia Planitia (20–45°N, 100–120°E) suggest the following. (1) The size–frequency distribution (SFD) of craters that both are buried by materials of the Vastitas Borealis units (VB) and superpose its surface indicate that the absolute model ages of terrain predating the emplacement of the VB is ∼3.7Ga. (2) Lack of craters that are partly embayed by materials of the VB in the SW portion of Utopia Planitia implies that the emplacement of the VB was faster than the rate of accumulation of impact craters and is consistent with the geologically short time of emplacement of the VB due to catastrophic release of water from outflow channels (e.g., Carr, M.H. 1996. Water on Mars. Oxford University Press, New York, p. 229). (3) The SFD of craters that superpose the surface of the VB indicates an absolute model age of ∼3.6–3.5Ga. The absolute model ages of etched flows, which represent the upper stratigraphic limit of the VB, are estimated to be ∼3.5Ga. (4) The majority of the larger (i.e., >1km) impact craters show ejecta morphologies (rampart and pancake-like ejecta) that are indicative of the presence of ice/water in the target materials. The distal portions of the pancake-like ejecta are heavily degraded (not due to embayment). This suggests that these craters formed in targets that contained higher abundances of volatiles. (5) The diameter ranges of the craters with either rampart- or pancake-like ejecta are overlapping (from ∼2 to ∼60km). Craters with pancake-like ejecta are concentrated within the central portion of the Utopia basin (less than ∼1000km from the basin center) and rampart craters occur at the periphery of the basin. This pattern of the crater spatial distribution suggests that materials within the center of Utopia Planitia contained more ice/water. (6) Etched flows around the central portion of Utopia Planitia were erupted from beneath of the surface of the VB. Their morphology and pattern of degradation, however, are inconsistent with lava and, instead, indicate formation of the flows due to mud volcanism. (7) Etched flows are spatially associated with giant polygons and there is evidence that these features populated the center portion of Utopia Planitia before it was covered by the Elysium-derived units. The outer (southern) edge of the zone of polygonal troughs and etched flows approximately corresponds to the transition from pancake-like ejecta to rampart ejecta. This suggest that the outer edge of the zone of the polygons and flows may outline the deeper portions of the large body (∼2000km across) of water/ice that likely existed in the center of Utopia Planitia in late Hesperian.
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