Plane Coverage Research Articles

The GRAVITY young stellar object survey

Context. Temporal variability in the photometric and spectroscopic properties of protoplanetary disks is common in young stellar objects. However, evidence pointing toward changes in their morphology over short timescales has only been found for a few sources, mainly due to a lack of high-cadence observations at high angular resolution. Understanding this type of variation could be important for our understanding of phenomena related to disk evolution. Aims. We study the morphological variability of the innermost circumstellar environment of HD 98922, focusing on its dust and gas content. Methods. Multi-epoch observations of HD 98922 at milliarcsecond resolution with VLTI/GRAVITY in the K-band at low (R = 20) and high (R = 4000) spectral resolution are combined with VLTI/PIONIER archival data covering a total time span of 11 yr. We interpret the interferometric visibilities and spectral energy distribution with geometrical models and through radiative transfer techniques using the code MCMax. We investigated high-spectral-resolution quantities (visibilities and differential phases) to obtain information on the properties of the HI Brackett-γ (Brγ)-line-emitting region. Results. Comparing observations taken with similar (u,v) plane coverage, we find that the squared visibilities do not vary significantly, whereas we find strong variability in the closure phases, suggesting temporal variations in the asymmetric brightness distribution associated to the disk. Our observations are best fitted by a model of a crescent-like asymmetric dust feature located at ~1 au and accounting for ~70 % of the near-infrared (NIR) emission. The feature has an almost constant magnitude and orbits the central star with a possible sub-Keplerian period of ~12 months, although a 9 month period is another, albeit less probable, solution. The radiative transfer models show that the emission originates from a small amount of carbon-rich (25%) silicates, or quantum-heated particles located in a low-density region. Among different possible scenarios, we favor hydrodynamical instabilities in the inner disk that can create a large vortex. The high spectral resolution differential phases in the Brγ line show that the hot-gas compact component is offset from the star and in some cases is located between the star and the crescent feature. The scale of the emission does not favor magnetospheric accretion as a driving mechanism. The scenario of an asymmetric disk wind or a massive accreting substellar or planetary companion is discussed. Conclusions. With this unique observational data set for HD 98922, we reveal morphological variability in the innermost 2 au of its disk region. This property is possibly common to many other protoplanetary disks, but is not commonly observed due to a lack of high-cadence observation. It is therefore important to pursue this approach with other sources for which an extended dataset with PIONIER, GRAVITY, and possibly MATISSE is available.

Diagnostic accuracy of computed tomography brain perfusion in the prediction of acute ischemic stroke taking the findings of MRI as gold standard.

Objectives: To determine the diagnostic accuracy of computed tomography brain perfusion to predict acute ischemic stroke taking the findings of MRI as gold standard. Study Design: Cross-sectional Validation study. Setting: Department of Radiology Allied Hospital Faisalabad. Period: 20th May 2022 to 19th November 2022. Material & Methods: A total of 215 individuals, aged between 30 and 70, of both sexes, and exhibiting ischemic stroke symptoms lasting no more than 12 hours, were included. Patients with abnormal renal function tests having renal disease were excluded. The conventional non-contrast CT used in the CT stroke protocol had basal sections that were either 3 mm or 4 mm in thickness and supra tentorial sections that were either 3 mm or 4 mm in thickness. The acquisition parameters were 80kVp and 120mAs. Dynamic CT perfusion was carried out with 4 cm plane coverage. At the seventh day, all patients underwent a follow-up MRI using a 1.5 Tesla Philips MRI scanner. A radiologist examined CTP to look for signs of early ischemic changes. For CT perfusion (CTP), measurements were taken for time to peak (TTP), cerebral blood flow (CBF), and cerebral blood volume (CBV). Results: Overall sensitivity, specificity, positive predictive value, negative predictive value and diagnostic accuracy of computed tomography brain perfusion in the prediction of acute ischemic stroke taking the findings of MRI as gold standard was 85.37%, 76.09%, 82.68%, 79.55% and 81.40% respectively. Conclusion: This study led to the conclusion that diagnostic accuracy of computed tomography brain perfusion to predict acute ischemic stroke is quite high.

Advances in Optical/Infrared Interferometry

After decades of fast-paced technical advances, optical/infrared (O/IR) interferometry has seen a revolution in recent years: ▪The GRAVITY instrument at the Very Large Telescope Interferometer (VLTI) with four 8-m telescopes reaches thousand-times-fainter objects than possible with earlier interferometers, and the Center for High Angular Resolution Astronomy array (CHARA) routinely offers up to 330-m baselines and aperture synthesis with six 1-m telescopes.▪The observed objects are fainter than 19 mag, the images have submilliarcsecond resolution, and the astrometry reaches microarcsecond precision.▪This led to breakthrough results on the Galactic Center, exoplanets, active galactic nuclei, young stellar objects, and stellar physics. Following a primer in interferometry, we summarize the advances that led to the performance boost of modern interferometers: ▪Single-mode beam combiners now combine up to six telescopes, and image reconstruction software has advanced over earlier developments for radio interferometry.▪With a combination of large telescopes, adaptive optics (AO), fringe tracking, and especially dual-beam interferometry, GRAVITY has boosted the sensitivity by many orders of magnitude. Another order-of-magnitude improvement will come from laser guide star AO. In combination with large separation fringe tracking, O/IR interferometry will then provide complete sky coverage for observations in the Galactic plane and substantial coverage for extragalactic targets.

Design of Extensible Structured Interferometric Array Utilizing the “Coarray” Concept

The optimum placement of receiving telescope antennas is a central topic for designing radio interferometric arrays, and this determines the performance of the obtained information. A variety of arrays are designed for different purposes, and they perform poorly in scalability. In this paper, we consider a subclass of structured sparse arrays, namely nested arrays, and examine the important role of “coarray” in interferometric synthesis imaging, which is utilized to design nested array configurations for a complete uniform Fourier plane coverage in both supersynthesis and instantaneous modes. Both nested arrays and the theory of the coarray have rich research achievements, and we apply them to astronomy to design arrays with good scalability and imaging performance. Simulated celestial source image retrieval performance validates the effectiveness of nested interferometric arrays.

A Planar Orbicular Rectenna Array System With 3-D Uniform Coverage for Wireless Powering of IoT Nodes

Microwave power transfer (MPT) is a revolutionary technique for charging batteries of wireless sensor nodes in smart applications. However, sensor nodes can be positioned at any arbitrary orientation and location with respect to the microwave transmitter (Tx). Therefore, harvested DC power depends on the node’s position and orientation. Thus, to reduce this reliance, a novel, fully integrated planar multisector rectenna (Rx) array is designed to achieve a nearly uniform 3-D spherical DC coverage. To realize orientation insensitive azimuth and elevation plane coverage, the proposed Rx features eight radially arranged endfire Rx (EFR-antenna) elements, and a bore-sight Rx (BSR-antenna) element with multiarms for inherent DC combining is used at the center with orthogonally polarized ports. Furthermore, direct conjugate matching of antenna and rectifier circuit with integrated operation is applied to realize a fully integrated design. This reduces insertion losses and achieves the desired 3-D coverage along with miniaturization, shaping it suitable for deployment at space-constrained IoT sensor nodes for orientation oblivion wireless powering.

Multifrequency Black Hole Imaging for the Next-generation Event Horizon Telescope

The Event Horizon Telescope (EHT) has produced images of the plasma flow around the supermassive black holes in Sgr A* and M87* with a resolution comparable to the projected size of their event horizons. Observations with the next-generation Event Horizon Telescope (ngEHT) will have significantly improved Fourier plane coverage and will be conducted at multiple frequency bands (86, 230, and 345 GHz), each with a wide bandwidth. At these frequencies, both Sgr A* and M87* transition from optically thin to optically thick. Resolved spectral index maps in the near-horizon and jet-launching regions of these supermassive black hole sources can constrain properties of the emitting plasma that are degenerate in single-frequency images. In addition, combining information from data obtained at multiple frequencies is a powerful tool for interferometric image reconstruction, since gaps in spatial scales in single-frequency observations can be filled in with information from other frequencies. Here we present a new method of simultaneously reconstructing interferometric images at multiple frequencies along with their spectral index maps. The method is based on existing regularized maximum likelihood (RML) methods commonly used for EHT imaging and is implemented in the eht-imaging Python software library. We show results of this method on simulated ngEHT data sets as well as on real data from the Very Long Baseline Array and Atacama Large Millimeter/submillimeter Array. These examples demonstrate that simultaneous RML multifrequency image reconstruction produces higher-quality and more scientifically useful results than is possible from combining independent image reconstructions at each frequency.

Deep Reinforcement Learning-Based Optimization for End-to-End Network Slicing With Control- and User-Plane Separation

Control- and user-plane separation (CUPS) and network slicing are two key technologies to support increasing network traffic and diverse wireless services. However, the benefit of CUPS in decoupling the network coverage and data service functions has not been fully utilized to facilitate network slicing. In this paper, we present a novel CUPS-based end-to-end (CUPS-E2E) network slicing scheme. First, the base stations (BS) are classified into control BSs (CBS) that provide control plane (CP) coverage and traffic BSs (TBS) that deliver user plane (UP) traffic. Next, upon CBSs and TBSs being virtualized, we define four typical end-to-end (E2E) network slices: one for CP coverage, one for high-throughput services, one for computation-intensive services, and the other for delay-sensitive services. The utilities of the four E2E network slices are defined based on their coverage, throughput, computing capability and delay requirements, respectively. Then, a deep deterministic policy gradient (DDPG)-based algorithm is employed to maximize the long-term sum-utility of the four E2E network slices by jointly optimizing the allocation of communication and computing resources to the four network slices and the activation of virtual TBSs, while meeting the service requirements of all users. Simulation results show that our proposed CUPS-E2E network slicing scheme in conjunction with a DDPG-based sum-utility maximization algorithm can support the CP wide-coverage and massive access requirements as well as the UP high-throughput, computation-intensive and delay-sensitive services simultaneously, and outperforms the existing E2E network slicing schemes in terms of the sum-utility, coverage percentage, throughput and delay.

The Parameters Comparison of the “Starlink” LEO Satellites Constellation for Different Orbital Shells

Communications-integrated satellite-terrestrial networks used for global broadband services have gained a high degree of interest from scientists and industries worldwide. The most convenient structures for such use are low Earth orbit satellites, since they fly closer to the Earth compared to the other orbits, and consequently provide significantly lower latency, which is essential for reliable and safe communications. Among these efforts is the Starlink satellites constellation, developed and partly deployed by the United States Company SpaceX. The constellation is planned to be organized in three spatial shells, each of them made up of several hundreds of small-dimensioned and light-weighted low Earth orbit specially designed satellites to provide broadband services, intending to offer global Earth coverage through their interoperability, combined also with the ground stations as a part of the satellite-terrestrial integrated network. By October 24, 2020, 893 satellites are situated in orbit of altitudes of 550 km under different inclinations, determining the first Starlink orbital shell. Two next generations are planned to be situated at altitudes of 1,110 and 340 km, to complete the appropriate infrastructure of three Starlink satellite shells, toward a global presence of broadband internet services. These three orbital shells offer different space views seen from the ground station (user) because of their different altitudes, thus in this paper a few parameters which describe the satellite’s behavior considered from the ground station’s (user’s) point of view are compared. These parameters in fact stem from the space orbital parameters and are defined as: horizon plane wideness, slant range, latency, and coverage area. A comparison is given for the three Starlink orbit layers, with identification of appropriate drawbacks and advantages as performance indicators. By the end, these parameters are applied to geometrically interpret and confirm the handover process among satellites. This paper may serve to highlight the new challenges of the satellite-terrestrial integrated network, providing some theoretical analysis and performance comparisons for the satellites in different orbit layers seen from the ground station (user) perspective.

Labral tears with axial plane disorders.

Objectives This study aims to determine if there is an axial plane coverage insufficiency in patients with symptomatic labral tears compared to the contralateral asymptomatic side and healthy control subjects.Patients and methods This retrospective study was conducted between December 2017 and January 2019. Thirty patients (21 males, 9 females; mean age 28 years; range, 20 to 36 years) operated due to unilateral symptomatic acetabular labral tears secondary to femoroacetabular impingement were evaluated. Twenty asymptomatic patients (13 males, 7 females; mean age 27±9 years; range, 19 to 36 years) were included in the control group. The relationship between acetabular morphology and labral tear was investigated with the comparison of unilateral symptomatic hips with contralateral asymptomatic hips and the control group by using radiological parameters on plain radiographs and computed tomography.Results When the patient group symptomatic side was compared to the control group, acetabular anteversion angle (A A A) and alpha (a) angle were higher, while posterior acetabular sector angle and horizontal acetabular sector angle were lower. When the asymptomatic side was compared to the control group, AAA was higher in the patient group. There was no difference between the symptomatic and asymptomatic sides in the patient group; the symptomatic side yielded a higher α angle.ConclusionPosterior axial plane coverage deficiency in combination with cam deformity (increased a angle) seems to play a role in the pathogenesis of symptomatic acetabular labral tears, even creating a side-to-side difference in some individuals.

A Smithian (Early Triassic) ichnoassemblage from Lichuan, Hubei Province, South China: Implications for biotic recovery after the latest Permian mass extinction

A late Smithian ichnoassemblage is reported from the Lower Triassic succession from the Lichuan section, western Hubei Province, South China. This ichnoassemblage comprises 13 ichnogenera, which include simple, horizontal traces (Cochlichnus, Cosmorhaphe, Didymaulichnus, Gordia, Circulichnis, and Planolites), vertical traces (Arenicolites, Laevicyclus), oblique- or horizontal branching traces (Palaeophycus), slightly complex burrow networks (Thalassinoides, and Treptichnus), and grazing traces (Cosmorhaphe and Gyrochorte). These traces are also categorized into fodinichnia, domichnia, pascichnia, and repichnia ethologic types, suggesting a fairly high degree of behavioral complexity. Of these, the fodinichnia traces are most abundant. The ichnoassemblage horizons usually have rather high ichnofabric indices (ii), reaching ii 4–5. Bedding plane coverage is up to 70–90%, resulting in high bedding plane bioturbation index as well (BPBI 4–5). The Lichuan ichnoassemblage traces have mean and maximum diameters of 4.8mm and 9mm, respectively (n=342). The traces penetrate to a depth of up to 30mm into the sediment, with an average depth of penetration of 15mm, indicating third to fourth tiering levels (3–4). Overall, the Lichuan ichnofauna shows an abrupt increase in ichnodiversity, burrow width, behavioral complexity, and ecologic tiering level, which are indicative of recovery stages of 2–3 in the late Smithian. When compared to five coeval ichnoassemblages from other sections in South China (Yashan, Susong, Daxiakou, Gaimao, and Tianshengqiao) and coeval ichnoassemblages from elsewhere (northern Italy, Western Australia, western US), the Lichuan trace-fossil assemblage reaches similar level of diversity during this time interval. Paleoenvironmental analysis indicates that the late Smithian recovery pulse is typically confined to the offshore transition setting, whereas more distal zones record much lower levels of recovery. Therefore, time and environmental conditions were the two crucial factors controlling the rate and degree of recovery of trace-making organisms in the aftermath of the latest Permian mass extinction.

Robust high-contrast companion detection from interferometric observations

Context. Long-baseline interferometry is an important technique to spatially resolve binary or multiple systems in close orbits. By combining several telescopes together and spectrally dispersing the light, it is possible to detect faint components around bright stars in a few hours of observations.Aims. We provide a rigorous and detailed method to search for high-contrast companions around stars, determine the detection level, and estimate the dynamic range from interferometric observations.Methods. We developed the code CANDID (Companion Analysis and Non-Detection in Interferometric Data), a set of Python tools that allows us to search systematically for point-source, high-contrast companions and estimate the detection limit using all interferometric observables, i.e., the squared visibilities, closure phases and bispectrum amplitudes. The search procedure is made on a N × N grid of fit, whose minimum needed resolution is estimated a posteriori. It includes a tool to estimate the detection level of the companion in the number of sigmas. The code CANDID also incorporates a robust method to set a 3σ detection limit on the flux ratio, which is based on an analytical injection of a fake companion at each point in the grid. Our injection method also allows us to analytically remove a detected component to 1) search for a second companion; and 2) set an unbiased detection limit.Results. We used CANDID to search for the companions around the binary Cepheids V1334 Cyg, AX Cir, RT Aur, AW Per, SU Cas, and T Vul. First, we showed that our previous discoveries of the components orbiting V1334 Cyg and AX Cir were detected at >25σ and >13σ , respectively. The astrometric positions and flux ratios provided by CANDID for these two stars are in good agreement with our previously published values. The companion around AW Per is detected at more than 15σ with a flux ratio of f = 1.22 ± 0.30%, and it is located at ρ = 32.16 ± 0.29 mas and PA = 67.1 ± 0.3°. We made a possible detection of the companion orbiting RT Aur with f = 0.22 ± 0.11%, and at ρ = 2.10 ± 0.23 mas and PA = −136 ± 6°. It was detected at 3.8σ using the closure phases only, and so more observations are needed to confirm the dectection. No companions were detected around SU Cas and T Vul. We also set the detection limit for possible undetected companions around these stars. We found that there is no companion with a spectral type earlier than B7V, A5V, F0V, B9V, A0V, and B9V orbiting the Cepheids V1334 Cyg, AX Cir, RT Aur, AW Per, SU Cas, and T Vul, respectively. This work also demonstrates the capabilities of the MIRC and PIONIER instruments, which can reach a dynamic range of 1:200, depending on the angular distance of the companion and the (u,v ) plane coverage. In the future, we plan to work on improving the sensitivity limits for realistic data through better handling of the correlations.

A POLYNOMIAL-TIME ALGORITHM FOR COMPUTING THE RESILIENCE OF ARRANGEMENTS OF RAY SENSORS

Given an arrangement A of n sensors and two points s and t in the plane, the barrier resilience of A with respect to s and t is the minimum number of sensors whose removal permits a path from s to t such that the path does not intersect the coverage region of any sensor in A. When the surveillance domain is the entire plane and sensor coverage regions are unit line segments, even with restricted orientations, the problem of determining the barrier resilience is known to be NP-hard. On the other hand, if sensor coverage regions are arbitrary lines, the problem has a trivial linear time solution. In this paper, we study the case where each sensor coverage region is an arbitrary ray, and give an O(n2m) time algorithm for computing the barrier resilience when there are m ⩾ 1 sensor intersections.

MOJAVE: MONITORING OF JETS IN ACTIVE GALACTIC NUCLEI WITH VLBA EXPERIMENTS. XI. SPECTRAL DISTRIBUTIONS

We have obtained milliarcsecond-scale spectral index distributions for a sample of 190 extragalactic radio jets through the MOJAVE project. The sources were observed in 2006 at 8.1, 8.4, 12.1, and 15.4 GHz, and we study the four-frequency spectrum in individual jet features. We performed detailed simulations to study the effects of image alignment and (u,v)-plane coverage on the spectral index maps to verify our results. The core spectral indices are on average flat, while the jet spectrum is in general steep with a mean index of -1.04. A simple power-law fit is often inadequate for the core regions, as expected if the cores are partially self-absorbed. The overall jet spectrum steepens at a rate of about -0.001 to -0.004 per deprojected parsec when moving further out from the core with flat spectrum radio quasars having significantly steeper spectra than the BL Lac objects. The spectrum in both types of objects flattens at the locations of the jet components indicating particle acceleration or density enhancements along the jet. The mean spectral index at the component locations of -0.81 corresponds to a power-law index of ~2.6 for the electron energy distribution. We find a significant trend that jet components with linear polarization parallel to the jet (magnetic field perpendicular to the jet) have flatter spectra, as expected for transverse shocks. Compared to quasars, BL Lacs have more jet components with perpendicular magnetic field alignment, which may explain their generally flatter spectra. The overall steepening of the spectra with distance can be explained with radiative losses if the jets are collimating or with the evolution of the high-energy cutoff in the electron spectrum if the jets are conical. This interpretation is supported by a significant correlation with the age of the component and the spectral index, with older components having steeper spectra. (abridged)

Surface Coverage in Sensor Networks

Coverage is a fundamental problem in wireless sensor networks (WSNs). Conventional studies on this topic focus on 2D ideal plane coverage and 3D full space coverage. The 3D surface of a field of interest (FoI) is complex in many real-world applications. However, existing coverage studies do not produce practical results. In this paper, we propose a new coverage model called surface coverage. In surface coverage, the field of interest is a complex surface in 3D space and sensors can be deployed only on the surface. We show that existing 2D plane coverage is merely a special case of surface coverage. Simulations point out that existing sensor deployment schemes for a 2D plane cannot be directly applied to surface coverage cases. Thus, we target two problems assuming cases of surface coverage to be true. One, under stochastic deployment, what is the expected coverage ratio when a number of sensors are adopted? Two, if sensor deployment can be planned, what is the optimal deployment strategy with guaranteed full coverage with the least number of sensors? We show that the latter problem is NP-complete and propose three approximation algorithms. We further prove that these algorithms have a provable approximation ratio. We also conduct extensive simulations to evaluate the performance of the proposed algorithms.

Proliferation of MISS-forming microbial mats after the late Neoproterozoic glaciations: Evidence from the Kimberley region, NW Australia

A total of 20 morphological types of microbially induced sedimentary structures (MISS) are recognized from the late Neoproterozoic tillite-bearing successions of the Kimberley, northwestern Australia which include alpha-petees, triradiate cracks, multidirectional linear ridges, millimeter ripples, erosional remnants and pockets and so on. Of these, triradiate cracks, multidirectional linear ridges, and millimeter ripples are reported for the first time from the Neoproterozoic worldwide. Most Kimberley MISS are morphologically comparable with their ancient and present-day counterparts whose biogenicity have been well demonstrated.In the Kimberley, during the interglacial period MISS have colonization preference to relatively coarse sandy substrates (Ranford Formation) and their abundance decreased towards the younger strata (Throssell Shale). In contrast, MISS abundance increased from the older strata (Yurabi Formation) towards the younger strata (Flat Rock Formation) during the postglacial period. However, overall, both MISS abundance and bedding plane coverage percentage increased from the Marinoan-younger Marinoan/Gaskiers interglacial successions to younger Marinoan/Gaskiers postglacial successions, indicating a proliferation of microbial mats after the younger Marinoan/Gaskiers glaciation. The increase of microbial mats could have ameliorated marine biogeochemical conditions and ecosystems, and thus laid the foundation for the rise of Ediacaran biota in Australian basins.

Weighting interferometric data for direct imaging

The new generation interferometric arrays such as the Atacama Large Millimeter/submillimeter Array (ALMA) are composed of a large number of telescopes and their configurations are optimized for Fourier plane (a.k.a. uv-plane) coverage. As a consequence, solving for the missing information in the uv-plane is becoming less critical and the imaging algorithms can be revisited. The situation is getting similar to that encountered with single filled aperture telescopes and it is becoming possible to make images in a direct way. In this article a new weighting method is introduced to obtain “pseudo-clean” images without using prior information to solve for the Fourier transform of the source. This method is similar but not equivalent to the successive application of robust weighting and tapering at different scales. The idea is to weight the data to compensate for the imperfect distribution of natural weights in the uv-plane. The price to pay for this direct imaging technique is that the final point spread function (PSF or beam) may not follow a simple analytical shape such as a Gaussian (but this is also the case in optical astronomy) and some sensitivity is lost (but this is the case with any imaging algorithm in interferometry). Two parameters are introduced to control the trade-off between imaging quality and sensitivity, namely a threshold parameter and a coupling parameter. This method is applied to simulated ALMA observations with 16, 32 and 50 antennas. As expected this method is found to be more efficient with more antennas and for more compact configurations because the uv-plane coverage is more complete. With 50 antennas in compact configuration it is possible to reduce the amplitude of the inner sidelobes (outer sidelobes) by a factor >6 (>2) compared to natural weighting for ~10 % loss in sensitivity, leading to sidelobes lower than 1.6 % of the main lobe peak value. With 16 antennas only, the method can still be used to reduce the inner sidelobes of a compact configuration by a factor >2 for ~10 % loss in sensitivity. This method can therefore be used with the new generation interferometric arrays to efficiently produce images without relying on any assumptions about the sources. The dynamic range of the resulting images depend on the number of telescopes in the array, the source size and the acceptable level of sensitivity loss.

Imaging submilliarcsecond stellar features with intensity interferometry using air Cherenkov telescope arrays

Recent proposals have been advanced to apply imaging air Cherenkov telescope arrays to stellar intensity interferometry (SII). Of particular interest is the possibility of model-independent image recovery afforded by the good (u, v)-plane coverage of these arrays, as well as recent developments in phase retrieval techniques. The capabilities of these instruments used as SII receivers have already been explored for simple stellar objects, and here the focus is on reconstructing stellar images with non-uniform radiance distributions. We find that hot stars (T > 6000 K) containing hot and/or cool localized regions (T \sim 500 K) as small as \sim 0.1 mas can be imaged at short wavelengths ({\lambda} = 400 nm).

21 cm observation of large-scale structures atz ~ 1

Large Scale Structures (LSS) in the universe can be traced using the neutral atomic hydrogen HI through its 21cm emission. Such a 3D matter distribution map can be used to test the Cosmological model and to constrain the Dark Energy properties or its equation of state. A novel approach, called intensity mapping can be used to map the HI distribution, using radio interferometers with large instantaneous field of view and waveband. In this paper, we study the sensitivity of different radio interferometer configurations, or multi-beam instruments for the observation of large scale structures and BAO oscillations in 21cm and we discuss the problem of foreground removal. For each configuration, we determine instrument response by computing the (u,v) or Fourier angular frequency plane coverage using visibilities. The (u,v) plane response is the noise power spectrum, hence the instrument sensitivity for LSS P(k) measurement. We describe also a simple foreground subtraction method to separate LSS 21 cm signal from the foreground due to the galactic synchrotron and radio sources emission. We have computed the noise power spectrum for different instrument configuration as well as the extracted LSS power spectrum, after separation of 21cm-LSS signal from the foregrounds. We have also obtained the uncertainties on the Dark Energy parameters for an optimized 21 cm BAO survey. We show that a radio instrument with few hundred simultaneous beams and a collecting area of ~10000 m^2 will be able to detect BAO signal at redshift z ~ 1 and will be competitive with optical surveys.

Exceptionally preserved microbially induced sedimentary structures from the Ediacaran post-glacial successions in the Kimberley region, northwestern Australia

A set of exceptionally preserved microbially induced sedimentary structures (MISS) is described from the post-glacial Yurabi Formation of late Ediacaran age in the Kimberley region, northwestern Australia. These MISS comprise oriented grains, bamboo leaf-like cracks, polygonal cracks, worm-like cracks, sinuous cracks, gas domes, pyrite concentrated laminae, and micrite laminae. Most of the Yurabi MISS are morphologically comparable with their ancient and modern counterparts. Micrometre or nannometre-scale bacteria- or biofilm-like inorganic objects are detected from most MISS, and are interpreted as bacterial bodies or remains that have been replaced with inorganic minerals upon fossilization. Oriented grains indirectly support microbial control on their accumulation. Both pyrite conformable laminae and micrite laminae suggest degradation and decay of original microbial mats upon diagenesis. Sinuous cracks were likely generated in a soft sediment deformation process, whereas other sand cracks (bamboo leaf-like cracks, worm-like cracks, polygonal cracks) could have formed from sediment surface layer microbial organics shrinkage upon desiccation. Gas domes may have formed as the result of anoxic redox reactions and being filled with gases and sediments transported from below. Two proxies bedding plane coverage percentage and accumulative thickness of single MISS-bearing beds are developed to semi-quantitatively evaluate MISS abundance on bedding plane and vertical outcrop, respectively. The Yurabi MISS have substratum preference to fine sandstone facies and intertidal settings. The Yurabi Formation yields the most abundant and diverse post-glacial MISS assemblages during the Late Ediacaran worldwide. Both Kimberley and global fossil records indicate that MISS may have proliferated in shallow marine ecosystems soon after the retreat of Ediacaran/Gaskiers glaciation during late Neoproterozoic.

On Coverage of Wireless Sensor Networks for Rolling Terrains

Deriving the proper density to achieve the region coverage for random sensors deployment is a fundamentally important problem in the area of wireless sensor networks. Most existing works on sensor coverage mainly concentrate on the two-dimensional (2D) plane coverage which assume that all the sensors are deployed on an ideal plane. In contrast, sensors are also deployed on the three-dimensional (3D) rolling surfaces in many real applications. Toward this end, we study the coverage problem of wireless sensor networks for the rolling terrains, and derive the expected coverage ratios under the stochastic sensors deployment. According to the different terrain features, we investigate two kinds of terrain coverage problems: the regular terrain coverage problem and the irregular terrain coverage problem. Specifically, we derive the general expression of the expected coverage ratio for an arbitrary surface z=f(x, y) and build two models, cone model and Cos-revolution model, to estimate the expected coverage ratios for regular terrains. For irregular terrains, we propose a digital elevation model (DEM) based method to calculate the expected coverage ratio and design an algorithm to estimate the expected coverage ratio of an interested region by using only the contour map of this region. We also conduct extensive simulations to validate and evaluate our proposed models and schemes.