scholarly journals FRATs: Searching for fast radio transient in real-time with LOFAR

2012 ◽  
Vol 8 (S291) ◽  
pp. 233-233
Author(s):  
Heino Falcke ◽  
Keyword(s):  
Time Scales ◽  
Search Space ◽  
Large Field ◽  
New Radio ◽  
Wide Range ◽  
Imaging Observation ◽  
Previous Decade ◽  
First Results ◽  
Single Radio ◽  
Radio Transients

AbstractLOFAR is an innovative new radio interferometer operating at low radio frequencies from 10 to 270 MHz. It combines a large field-of-view, high fractional bandwidth, rapid response, and a wide range of baselines from tens of meters to thousand kilometers. Its use of phased-array technology and its digital nature make LOFAR an extremely versatile instrument to search for transient radio phenomena on all time scales. Here we discuss in particular the search for fast radio transients (FRATs) at sub-second time scales. In fact, at these time scales the radio sky is rather dynamic due to coherent emission processes. Objects like pulsars, flaring stars, or planets like Jupiter are able to produce bright short flares. For pulsars, most previous detection strategies made use of the rotation of pulsars to detect them, using Fourier techniques, but it is also possible to detect pulsars and other objects through their single pulses. Such surveys have, e.g., led in the previous decade to the detection of Rapid Radio Transients (RRATS), but the unprobed search space is still rather large. LOFAR is now conducting a rather unique survey over the entire northern sky, searching for bright dispersed single radio pulses. This FRATs survey makes use of the LOFAR transient buffer boards (TBBs), which had initially been used to detect nanosecond radio pulses from cosmic rays. The TBBs store the radio data from each single receiver element of LOFAR and allow one to look back in time. A trigger system that runs parallel to normal imaging observation allows one to detect single pulses in an incoherent beam of all LOFAR stations, covering several tens to hundred square degrees at once. Once triggered, the data can be used to localize the pulse and to discriminate cosmic sources from terrestrial interference through 3D localization. The system has been successfully tested with known pulsars and first results of the ongoing survey will be presented.

scholarly journals Star formation thresholds derived From THINGS

2006 ◽  
Vol 2 (S237) ◽  
pp. 397-397
Author(s):  
F. Bigiel ◽  
F. Walter ◽  
E. de Blok ◽  
E. Brinks ◽  
B. Madore
Keyword(s):  
Star Formation ◽  
Large Scale ◽  
Gravitational Instability ◽  
Critical Density ◽  
Nearby Galaxy ◽  
Uv Emission ◽  
Radial Profiles ◽  
Wide Range ◽  
First Results ◽  
Type Mass

AbstractWe present first results from THINGS (The HI Nearby Galaxy Survey), which consists of high quality HI maps obtained with the VLA of 34 galaxies across a wide range of galaxy parameters (Hubble type, mass/luminosity). We compare the distribution of HI to the UV emission in our sample galaxies. In particular we present radial profiles of the HI (tracing the neutral interstellar medium) and UV (mainly tracing regions of recent star formation) in our sample galaxies. The azimuthally averaged HI profiles are compared to the predicted critical density above which organized large-scale star formation is believed to start (this threshold is based on the Toomre-Q parameter, which in turn is a measure for local gravitational instability).

Strain-Rate Effect on the Tensile Behaviour of High Strength Alloys

2011 ◽  
Vol 82 ◽  
pp. 124-129 ◽  
Author(s):  
Ezio Cadoni ◽  
Matteo Dotta ◽  
Daniele Forni ◽  
Stefano Bianchi
Keyword(s):  
Strain Rate ◽  
Rate Sensitivity ◽  
High Strength ◽  
Constitutive Law ◽  
Tensile Behaviour ◽  
Strain Rates ◽  
Cross Sectional ◽  
Split Hopkinson Tensile Bar ◽  
Wide Range ◽  
First Results

In this paper the first results of the mechanical characterization in tension of two high strength alloys in a wide range of strain rates are presented. Different experimental techniques were used for different strain rates: a universal machine, a Hydro-Pneumatic Machine and a JRC-Split Hopkinson Tensile Bar. The experimental research was developed in the DynaMat laboratory of the University of Applied Sciences of Southern Switzerland. An increase of the stress at a given strain increasing the strain-rate from 10-3 to 103 s-1, a moderate strain-rate sensitivity of the uniform and fracture strain, a poor reduction of the cross-sectional area at fracture with increasing the strain-rate were shown. Based on these experimental results the parameters required by the Johnson-Cook constitutive law were determined.

scholarly journals EXPRESS: Sources of Variation In Search and Foraging A Theoretical Perspective

2021 ◽  
pp. 174702182110503
Author(s):  
Alastair David Smith ◽  
Carlo De Lillo
Keyword(s):  
Spatial Scales ◽  
Theoretical Perspective ◽  
Search Space ◽  
Visual Exploration ◽  
Two Dimensional ◽  
Search Behaviour ◽  
Wide Range ◽  
Search Processes ◽  
Sources Of Variation ◽  
The Individual

Search – the problem of exploring a space of alternatives in order to identify target goals – is a fundamental behaviour for many species. Although its foundation lies in foraging, most studies of human search behaviour have been directed towards understanding the attentional mechanisms that underlie the efficient visual exploration of two-dimensional scenes. With this review, we aim to characterise how search behaviour can be explained across a wide range of contexts, environments, spatial scales, and populations, both typical and atypical. We first consider the generality of search processes across psychological domains. We then review studies of interspecies differences in search. Finally, we explore in detail the individual and contextual variables that affect visual search and related behaviours in established experimental psychology paradigms. Despite the heterogeneity of the findings discussed, we identify that variations in control processes, along with the ability to regulate behaviour as a function of the structure of search space and the sampling processes adopted, to be central to explanations of variations in search behaviour. We propose a tentative theoretical model aimed at integrating these notions and close by exploring questions that remain unaddressed.

scholarly journals Shadow monochromatic backlighting: Large-field high resolution X-ray shadowgraphy with improved spectral tunability

2001 ◽  
Vol 19 (2) ◽  
pp. 285-293 ◽  
Author(s):  
T.A. PIKUZ ◽  
A. YA. FAENOV ◽  
M. FRAENKEL ◽  
A. ZIGLER ◽  
F. FLORA ◽  
...  
Keyword(s):  
High Resolution ◽  
High Spatial Resolution ◽  
Field Of View ◽  
Large Field ◽  
X Ray ◽  
Traditional Scheme ◽  
Wide Range ◽  
Wide Wavelength Range ◽  
Bent Crystals ◽  
First Time

The shadow monochromatic backlighting (SMB) scheme, a modification of the well-known soft X-ray monochromatic backlighting scheme, is proposed. It is based on a spherical crystal as the dispersive element and extends the traditional scheme by allowing one to work with a wide range of Bragg angles and thus in a wide spectral range. The advantages of the new scheme are demonstrated experimentally and supported numerically by ray-tracing simulations. In the experiments, the X-ray backlighter source is a laser-produced plasma, created by the interaction of an ultrashort pulse, Ti:Sapphire laser (120 fs, 3–5 mJ, 1016 W/cm2 on target) or a short wavelength XeCl laser (10 ns, 1–2 J, 1013 W/cm2 on target) with various solid targets (Dy, Ni + Cr, BaF2). In both experiments, the X-ray sources are well localized spatially (∼20 μm) and are spectrally tunable in a relatively wide wavelength range (λ = 8–15 Å). High quality monochromatic (δλ/λ ∼ 10−5–10−3) images with high spatial resolution (up to ∼4 μm) over a large field of view (a few square millimeters) were obtained. Utilization of spherically bent crystals to obtain high-resolution, large field, monochromatic images in a wide range of Bragg angles (35° < Θ < 90°) is demonstrated for the first time.

scholarly journals Workshop on Radio Transients

2011 ◽  
Vol 7 (S285) ◽  
pp. 272-272
Author(s):  
Steve Croft ◽  
Bryan Gaensler
Keyword(s):  
Best Practices ◽  
Common Ground ◽  
New Era ◽  
Software Packages ◽  
New Radio ◽  
The Status ◽  
Survey Strategy ◽  
Radio Transients ◽  
Single Pixel

SummaryWe are entering a new era in the study of variable and transient radio sources. This workshop discussed the instruments and the strategies employed to study those sources, how they are identified and classified, how results from different surveys can be compared, and how radio observations tie in with those at other wavelengths. The emphasis was on learning what common ground there is between the plethora of on-going projects, how methods and code can be shared, and how best practices regarding survey strategy could be adopted.The workshop featured the four topics below. Each topic commenced with a fairly brief introductory talk, which then developed into discussion. By way of preparation, participants had been invited to upload and discuss one slide per topic to a wiki ahead of the workshop.1. Telescopes, instrumentation and survey strategy. New radio facilities and on-going projects (including upgrades) are both studying the variability of the radio sky, and searching for transients. The discussion first centred on the status of those facilities, and on projects with a time-domain focus, both ongoing and planned, before turning to factors driving choices of instrumentation, such as phased array versus single pixel feeds, the field of view, spatial and time resolution, frequency and bandwidth, depth, area, and cadence of the surveys.2. Detection, pipelines, and classification. The workshop debated (a) the factors that influence decisions to study variability in the (u,v) plane, in images, or in catalogues, (b) whether, and how much, pipeline code could potentially be shared between one project and another, and which software packages are best for different approaches, (c) how data are stored and later accessed, and (d) how transients and variables are defined and classified.3. Statistics, interpretation, and synthesis. It then discussed how (i) the choice of facility and strategy and (ii) detection and classification schemes influence what is seen (in terms of types of object and rates) by different surveys, (iii) how results from different surveys could be compared, and (iv) how what we know from existing surveys drives choices (i) and (ii), particularly as regards finding new classes of object.4. Multiwavelength approaches. The workshop concluded by discussing what information is needed from wavelengths other than radio in order to classify transients and variables adequately and predict their rates as a function of topics (1), (2) and (3). It asked what the constraints are on responding to, and issuing triggers for, follow-up observations, and how that might feed back into considerations for designing our telescopes and surveys.

SAMPLE CLOCK OFFSET COMPENSATION IN THE FIFTH-GENERATION NEW RADIO UPLINK

2021 ◽  
Author(s):  
О.Г. ПОНОМАРЕВ ◽  
М. АСАФ
Keyword(s):  
Signal To Noise Ratio ◽  
Radio Channel ◽  
Estimation Method ◽  
Estimation Methods ◽  
Fifth Generation ◽  
New Radio ◽  
Shared Channel ◽  
Wide Range ◽  
Offset Compensation ◽  
Clock Offset

Рассмотрена проблема коррекции искажений OFDM-сигнала, вызванных смещением частоты дискретизации сигнала в приемном и передающем устройствах системы сотовой связи пятого поколения. Предлагаемый метод компенсации смещения частоты дискретизации основывается на прямой коррекции искажений, вносимых в передаваемый сигнал наличием смещения, и не предполагает какой-либо оценки величины смещения. Метод предназначен для коррекции сигналов в восходящем канале системы сотовой связи пятого поколения и основывается на использовании референсных сигналов, рекомендованных стандартами 3GPP. Результаты численного моделирования показали, что использование предлагаемого метода позволяет повысить эффективность передачи данных по многолучевому радиоканалу более чем на 15% в широком диапазоне значений отношения сигнал/шум. 5G-NR, CP-OFDM, synchronization, sample clock offset, PUSCH. О The paper investigates the issue of sampling clock offset ( SCO) in the fifth generation new radio systems. Due to the imperfect SCO estimation methods, the correction methods relying on the SCO estimation are not perfect, so the proposed method directly corrects the effect of SCO without using any kind of estimation method. Our method is designed to correct the signals in the physical uplink shared channel (PUSCH). The method uses reference signals as recommended by the 3rd generation partnership project (3GPP) standards. The results of the numerical simulation show that the use of the proposed method increases the efficiency of data transmission over the multipath radio channel by more than 15% in a wide range of signal-to-noise ratio values.

First results from coupling the Parallel Ice Sheet Model with the Modular Ocean Model via an Antarctic ice-shelf cavity module

2021 ◽  
Author(s):  
Moritz Kreuzer ◽  
Ronja Reese ◽  
Willem Huiskamp ◽  
Stefan Petri ◽  
Torsten Albrecht ◽  
...  
Keyword(s):  
Time Scales ◽  
General Circulation ◽  
Ice Sheet ◽  
Circulation Model ◽  
Ocean Model ◽  
Global Ocean ◽  
Ice Shelf ◽  
Antarctic Ice Sheet ◽  
First Results ◽  
The Antarctic

&lt;p&gt;The past and future evolution of the Antarctic Ice Sheet is largely controlled by interactions between the ocean and floating ice shelves. To investigate these interactions, coupled ocean and ice sheet model configurations are required. Previous modelling studies have mostly relied on high resolution configurations, limiting these studies to individual glaciers or regions over short time scales of decades to a few centuries. To study global and long term interactions, we developed a framework to couple the dynamic ice sheet model PISM with the global ocean general circulation model MOM5 via the ice-shelf cavity module PICO. Since ice-shelf cavities are not resolved by MOM5, but parameterized with the box model PICO, the framework allows the ice sheet and ocean model to be run at resolution of 16&amp;#8201;km and 3 degrees, respectively. We present first results from our coupled setup and discuss stability, feedbacks, and interactions of the Antarctic Ice Sheet and the global ocean system on millennial time scales.&lt;/p&gt;

Zoogeomorphosite: A concept for, and example of, linking geoheritage and biodiversity heritage

2021 ◽  
Author(s):  
François Bétard
Keyword(s):  
Mixed Forest ◽  
Slope Aspect ◽  
Major Influence ◽  
Termite Mounds ◽  
Morphometric Measurements ◽  
Small Surface ◽  
Formica Rufa ◽  
Wide Range ◽  
First Results ◽  
Ant Mounds

&lt;p&gt;Zoogeomorphosites can be defined as geomorphological sites of special interest for animal biodiversity and conservation. They appear as ideal places for linking geoheritage and biodiversity heritage because of the reciprocal effects and interactions between landforms and animals. On one hand, geomorphodiversity exerts an influence on animal biodiversity at alpha, beta and gamma levels, and many landforms constitute valuable habitats for a wide range of animal species. On the other hand, animals can have direct and indirect geomorphic effects by creating specific landforms (e.g., mounds) and by influencing geomorphic processes (e.g, runoff), respectively.&lt;/p&gt;&lt;p&gt;The aim of this presentation is (1) to illustrate a worldwide range of sites fitting the conceptual definition of a zoogeomorphosite, with a proposed typology, and (2) to present an example of zoogeomorphological survey conducted on a site in Northwest France (Bois-des-Jarries, Vend&amp;#233;e), where geoheritage meets with biodiversity heritage. The selected study site is a granitic geomorphosite composed of two hills with small tors and boulders outcropping at 230-260 m a.s.l., and franging a large fluvial paleo-valley of Ypresian age. The land cover is a mosaic of mixed forests and dry heathlands recognized for their high ecological interest, with many valuable species of vascular plants, birds and invertebrates. A major zoogeomorphic interest of the site is that it hosts an important population of mound-building red wood ants (&lt;em&gt;Formica rufa&lt;/em&gt;), a regionally rare and vulnerable species responsible for an impressive collection of biogenic microlandforms (ant mounds) on a small surface (62 ha). A zoogeomorphogical survey carried out in summer 2020 on these ant mounds involved a two-stage methodology: (1) linear surveys along forest paths, in order to calculate mound densities and to proceed with a general inventory of ant mounds; (2) morphometric measurements of mounds using strip transects in 13 representative habitat types, in order to calculate mound volumes and to evaluate their evolution on a 5-years period.&lt;/p&gt;&lt;p&gt;119 mounds of &lt;em&gt;Formica rufa&lt;/em&gt; have been inventoried in summer 2020 along the forest paths, indicating a density of 2-4 mounds ha&lt;sup&gt;&amp;#8211;1&lt;/sup&gt;. First results of the morphometric measurements indicate that the highest biovolumes are found in pine or mixed forest habitats, and that the geomorphology of the granitic hills (slope, aspect, height above drainage, etc.) is of major influence on their distribution and shape. In turn, ant mounds create environmental heterogeneity, or patch-scale geodiversity, highly favourable to biodiversity, notably because they offer microhabitats for various myrmecophilous insects. Finally, ant mounds can be viewed as a remarkable example of biogeomorphological heritage, hybrid and evolutionary in nature, but highly sensitive to environmental and human-induced changes (e.g., forest clear cuts, tourism pressure). Because ant mounds are an integral component of natural heritage and a key provider of ecosystem services, their inventory and protection as zoogeomorphosites &amp;#8211; just like that of termite mounds &amp;#8211; are of prime relevance in the wider scope of integrating geodiversity and biodiversity in nature conservation policies and strategies.&lt;/p&gt;

The Southern Ocean carbon sink 1985-2018: first results of the RECCAP2 project

2021 ◽  
Author(s):  
Judith Hauck ◽  
Luke Gregor ◽  
Cara Nissen ◽  
Eric Mortenson ◽  
Seth Bushinsky ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Seasonal Cycle ◽  
Carbon Sink ◽  
Global Ocean ◽  
Biogeochemical Models ◽  
Wide Range ◽  
Data Products ◽  
First Results ◽  
Ocean Carbon ◽  
Indian Sector

&lt;p&gt;The Southern Ocean is the main gateway for anthropogenic CO&lt;sub&gt;2&lt;/sub&gt; into the ocean owing to the upwelling of old water masses with low anthropogenic CO&lt;sub&gt;2&lt;/sub&gt; concentration, and the transport of the newly equilibrated surface waters into the ocean interior through intermediate, deep and bottom water formation. Here we present first results of the Southern Ocean chapter of RECCAP2, which is the Global Carbon Project&amp;#8217;s second systematic study on Regional Carbon Cycle Assessment and Processes. In the Southern Ocean chapter, we aim to assess the Southern Ocean carbon sink 1985-2018 from a wide range of available models and data sets, and to identify patterns of regional and temporal variability, model limitations and future challenges.&lt;/p&gt;&lt;p&gt;We gathered global and regional estimates of the air-sea CO&lt;sub&gt;2&lt;/sub&gt; flux over the period 1985-2018 from global ocean biogeochemical models, surface pCO&lt;sub&gt;2&lt;/sub&gt;-based data products, and data-assimilated models. The analysis on the Southern Ocean quantified geographical patterns in the annual mean and seasonal amplitude of air-sea CO&lt;sub&gt;2&lt;/sub&gt; flux, with results presented here aggregated to the level of large-scale ocean biomes.&lt;/p&gt;&lt;p&gt;Considering the suite of observed and modelled estimates, we found that the subtropical seasonally stratified (STSS) biome stands out with the largest air-sea CO&lt;sub&gt;2&lt;/sub&gt; flux per area and a seasonal cycle with largest ocean uptake of CO&lt;sub&gt;2&lt;/sub&gt; in winter, whereas the ice (ICE) biome is characterized by a large ensemble spread and a pronounced seasonal cycle with the largest ocean uptake of CO&lt;sub&gt;2&lt;/sub&gt; in summer. Connecting these two, the subpolar seasonally stratified (SPSS) biome has intermediate flux densities (flux per area), and most models have difficulties simulating the seasonal cycle with strongest uptake during the summer months.&lt;/p&gt;&lt;p&gt;Our analysis also reveals distinct differences between the Atlantic, Pacific and Indian sectors of the aforementioned biomes. In the STSS, the Indian sector contributes most to the ocean carbon sink, followed by the Atlantic and then Pacific sectors. This hierarchy is less pronounced in the models than in the data-products. In the SPSS, only the Atlantic sector exhibits net CO&lt;sub&gt;2&lt;/sub&gt; uptake in all years, likely linked to strong biological production. In the ICE biome, the Atlantic and Pacific sectors take up more CO&lt;sub&gt;2&lt;/sub&gt; than the Indian sector, suggesting a potential role of the Weddell and Ross Gyres.&lt;/p&gt;&lt;p&gt;These first results confirm the global relevance of the Southern Ocean carbon sink and highlight the strong regional and interannual variability of the Southern Ocean carbon uptake in connection to physical and biogeochemical processes.&lt;/p&gt;

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