Meters In Diameter Research Articles

Maximizing Dust Devil Follow-Up Observations on Mars Using Cubesats and On-Board Scheduling

Several million dust devil events occur on Mars every day. These events last, on average, about 30 minutes and range in size from meters to hundreds of meters in diameter. Designing low-cost missions that will improve our knowledge of dust devil formation and evolution, and their connection to atmospheric dynamics and the dust cycle, is fundamental to informing future crewed Mars lander missions about surface conditions. In this paper we present a mission for a constellation of low orbiting Mars cubesats, each carrying imagers with agile pointing capabilities. The goal is to maximize the number of dust devil follow-up observations through real-time, on-board scheduling. We study scenarios where cubesats are equipped with a 2.5 degree boresight angle camera that accommodates twenty-one slew positions (including nadir). We assume a concept of operations where the cubesats autonomously survey the surface of Mars and can autonomously detect dust devils from their surface imagery. When a dust devil is detected, the constellation is autonomously re-tasked through an onboard distributed scheduler to capture as many follow-on images of the event as possible, so as to study its evolution. The cubesat orbits are propagated assuming two-body dynamics and the ground tracks and camera field of view are computed assuming a spherical Mars. Realistic inter-agent communication link opportunities are computed and included in our optimization, which allow for real-time event detection information to be shared within the constellation. We compare against a powerful “omniscient” oracle which has a priori knowledge of all dust devil activity to show the gap between predicted performance and the best possible outcome. In particular, we show that the communications are especially important for acquiring follow-up observations, and that a realistic distributed scheduling mechanism is able to capture a large fraction of all dust devil observations that are possible for a given orbit configuration, significantly outperforming a nadir-pointing heuristic.

Ontogeny, evolution and palaeogeographic distribution of the world's largest ammonite Parapuzosia (P.) seppenradensis (Landois, 1895).

The world’s largest ammonite, Parapuzosia (P.) seppenradensis (Landois, 1895), fascinated the world ever since the discovery, in 1895, of a specimen of 1.74 metres (m) diameter near Seppenrade in Westfalia, Germany, but subsequent findings of the taxon are exceedingly rare and its systematic position remains enigmatic. Here we revise the historical specimens and document abundant new material from England and Mexico. Our study comprises 154 specimens of large (< 1 m diameter) to giant (> 1m diameter) Parapuzosia from the Santonian and lower Campanian, mostly with stratigraphic information. High-resolution integrated stratigraphy allows for precise cross-Atlantic correlation of the occurrences. Our specimens were analysed regarding morphometry, growth stages and stratigraphic occurrence wherever possible. Our analysis provides insight into the ontogeny of Parapuzosia (P.) seppenradensis and into the evolution of this species from its potential ancestor P. (P.) leptophylla Sharpe, 1857. The latter grew to shell diameters of about 1 m and was restricted to Europe in the early Santonian, but it reached the Gulf of Mexico during the late Santonian. P. (P.) seppenradensis first appears in the uppermost Santonian- earliest Campanian on both sides of the Atlantic. Initially, it also reached diameters of about 1 m, but gradual evolutionary increase in size is seen in the middle early Campanian to diameters of 1.5 to 1.8 m. P. (P.) seppenradensis is characterized by five ontogenetic growth stages and by size dimorphism. We therefore here include the many historic species names used in the past to describe the morphological and size variability of the taxon. The concentration of adult shells in small geographic areas and scarcity of Parapuzosia in nearby coeval outcrop regions may point to a monocyclic, possibly even semelparous reproduction strategy in this giant cephalopod. Its gigantism exceeds a general trend of size increase in late Cretaceous cephalopods. Whether the coeval increase in size of mosasaurs, the top predators in Cretaceous seas, caused ecological pressure on Parapuzosia towards larger diameters remains unclear.

Boulders on Mercury

Boulders on the surfaces of planets, satellites and small bodies, as well as their geological associations, provide important information about surface processes. We analyzed all available images of the surface of Mercury that have sufficient resolution and quality to detect boulders, and we mapped all the boulders observed. The lower size limit of detectable boulders was ~5 m. All boulders found on Mercury are associated with fresh impact craters hundreds of meters in diameter or larger. We compared boulder population on Mercury with population of boulders of the same size on the Moon, and found that boulders on Mercury are ~30 times less abundant than in the lunar highlands. This exact quantitative estimate is inherently inaccurate due to the limitation in the source data; however, the significant relative rarity of boulders on Mercury can be firmly and reliably established. We discuss possible causes of the observed difference. Higher thermal stresses and more rapid material fatigue due to diurnal temperature cycling on Mercury may cause rapid disintegration of the upper decimeters of the boulder surface and thus contribute to more rapid boulder obliteration; however, these factors alone cannot account for the observed difference. A proposed thicker regolith on Mercury is likely to significantly reduce boulder production rate. A higher micrometeoritic flux on Mercury is likely to result in micrometeoritic abrasion being a dominant contributor to boulder degradation; this high abrasion rate likely shortens the boulder lifetime. A combination of these factors appears to be able to account for the relative rarity of boulders on Mercury.

Impact of age‐related macular degeneration on object searches in realistic panoramic scenes

BackgroundThis study investigated whether realistic immersive conditions with dynamic indoor scenes presented on a large, hemispheric panoramic screen covering 180° of the visual field improved the visual search abilities of participants with age‐related macular degeneration (AMD).MethodTwenty‐one participants with AMD, 16 age‐matched controls and 16 young observers were included. Realistic indoor scenes were presented on a panoramic five metre diameter screen. Twelve different objects were used as targets. The participants were asked to search for a target object, shown on paper before each trial, within a room composed of various objects. A joystick was used for navigation within the scene views. A target object was present in 24 trials and absent in 24 trials. The percentage of correct detection of the target, the percentage of false alarms (that is, the detection of the target when it was absent), the number of scene views explored and the search time were measured.ResultsThe search time was slower for participants with AMD than for the age‐matched controls, who in turn were slower than the young participants. The participants with AMD were able to accomplish the task with a performance of 75-per cent correct detections. This was slightly lower than older controls (79.2-per cent) while young controls were at ceiling (91.7-per cent). Errors were mainly due to false alarms resulting from confusion between the target object and another object present in the scene in the target‐absent trials.ConclusionThe outcomes of the present study indicate that, under realistic conditions, although slower than age‐matched, normally sighted controls, participants with AMD were able to accomplish visual searches of objects with high accuracy.

Planetary Defense Mission Using Guided Collision of Near-Earth Objects

The Baseline Instrumented Lithology Lander, Inspector, and Asteroid Redirection Demonstration System is a proposed demonstration mission to characterize a small asteroid less than 10 m in diameter and redirect it to collide with a larger asteroid hundreds of meters in diameter. This collision will disrupt the larger asteroid or alter its trajectory, thereby demonstrating a capability to prevent such an asteroid from colliding with Earth. The concept of redirecting a smaller asteroid into a larger asteroid is attractive for this type of mission because it uses natural kinetic energy available beyond Earth’s gravity well for the majority of the energy delivered to the larger asteroid. By contrast, a kinetic impactor launched directly from Earth to its target must have all of its mass lifted out of Earth’s gravity well. The proposed architecture allows for an impact energy of several terajoules without the use of nuclear devices. This work presents a novel approach to this type of kinetic impactor mission. In the proposed concept of operations, a spacecraft performs a controlled rendezvous and capture of the smaller asteroid. It then uses solar electric propulsion to redirect the asteroid over time onto a collision course. A high-thrust terminal guidance system is used to perform final trajectory adjustments in the hours leading to collision with the larger asteroid, ensuring a successful interception.

Experimental study on the motion process of radial retractable roof structures

In recent years, the use of retractable roofs is increasing to meet the demand of holding big-scale events. This article introduces a class of radial retractable roofs based on the foldable bar structure (FBS) mechanism. A radial retractable roof structure whose moveable section consisted of 6 segments and 6 rigid linkages was designed with appropriate parameters. An experimental study of a radial retractable roof was carried out. A scale model with a 3 metre diameter was constructed to study the roof deflection and vibration during the deployment process under four different load cases. Furthermore, based on the multi-flexible body dynamics theory, an ADAMS-ANSYS co-simulation was applied to simulate the motion process of the radial retractable roof structure. The experimental results were consistent with the numerical simulations. This indicates that the dynamic and fluctuation phenomena of structural behaviour are universal. The structural vibration was increased with the increase of external loads, and the vibration amplitude increased significantly when the roof was starting and braking. With the closing of the movable roof, the deflection of the fixed roof increased significantly. In the motion process, the bending moment of the fixed roof gradually increases, while that of the moving roof varies little. Vertical vibration is significant in the motion process by reason of the complex wheel-rail contact.

Research on individual pitch control below rated wind speed

The structure of the modern wind turbine is becoming larger and more complex, with the wind rotor exceeding hundreds of meters in diameter. The blade shear force is also becoming increasingly serious below the rated wind speed, which leads to structure fatigue loads and instability of the generator power. For improving the dynamic performance of large wind turbines, it was proposed that individual pitch control (IPC) method was operated below the rated wind speed. In this paper, we analyze the relationship between the aerodynamic characteristics of blades and the nonlinear time‐varying pitch control system based on wind shear and the tower shadow effect. The combination of IPC and torque control is used to optimize the control mode of the wind turbine. By fine‐tuning the pitch angle, the unbalanced force on the wind rotor was relieved to achieve the purpose of mitigating fatigue loads. Finally, our experimental results prove the validity of the proposed IPC method below the rated wind speed by showing that it can improve power quality and reduce fatigue loads of the key components without reducing the generator output power. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley &amp; Sons, Inc.

Opportunities and considerations for visualising neuroimaging data on very large displays

Neuroimaging experiments can generate impressive volumes of data and many images of the results. This is particularly true of multi-modal imaging studies that use more than one imaging technique, or when imaging is combined with other assessments. A challenge for these studies is appropriate visualisation of results in order to drive insights and guide accurate interpretations. Next-generation visualisation technology therefore has much to offer the neuroimaging community. One example is the Imperial College London Data Observatory; a high-resolution (132 megapixel) arrangement of 64 monitors, arranged in a 313 degree arc, with a 6 metre diameter, powered by 32 rendering nodes. This system has the potential for high-resolution, large-scale display of disparate data types in a space designed to promote collaborative discussion by multiple researchers and/or clinicians. Opportunities for the use of the Data Observatory are discussed, with particular reference to applications in Multiple Sclerosis (MS) research and clinical practice. Technical issues and current work designed to optimise the use of the Data Observatory for neuroimaging are also discussed, as well as possible future research that could be enabled by the use of the system in combination with eye-tracking technology.

Opportunities and considerations for visualising neuroimaging data on very large displays.

Neuroimaging experiments can generate impressive volumes of data and many images of the results. This is particularly true of multi-modal imaging studies that use more than one imaging technique, or when imaging is combined with other assessments. A challenge for these studies is appropriate visualisation of results in order to drive insights and guide accurate interpretations. Next-generation visualisation technology therefore has much to offer the neuroimaging community. One example is the Imperial College London Data Observatory; a high-resolution (132 megapixel) arrangement of 64 monitors, arranged in a 313 degree arc, with a 6 metre diameter, powered by 32 rendering nodes. This system has the potential for high-resolution, large-scale display of disparate data types in a space designed to promote collaborative discussion by multiple researchers and/or clinicians. Opportunities for the use of the Data Observatory are discussed, with particular reference to applications in Multiple Sclerosis (MS) research and clinical practice. Technical issues and current work designed to optimise the use of the Data Observatory for neuroimaging are also discussed, as well as possible future research that could be enabled by the use of the system in combination with eye-tracking technology.

Century-long monitoring of solar irradiance and Earth's albedo using a stable scattering target in space

Abstract An inert sphere of a few metres diameter, placed in a special stable geosynchronous orbit in perpetuo, can be used for a variety of scientific experiments. Ground-based observations of such a sphere, ‘GeoSphere’, can resolve very difficult problems in measuring the long-term solar irradiance. GeoSphere measurements will also help us understand the evolution of Earth's albedo and climate over at least the next century.

Zig-zag tape influence in NREL Phase VI wind turbine

Two bladed 10 metre diameter wind turbine was tested in the 24.4m × 36.6m NASA-Ames wind tunnel (Phase VI). These experiments have been extensively used for validation purposes for CFD and other engineering tools. The free transition case (S), has been, and is, the most employed one for validation purposes, and consist in a 3° pitch case with a rotational speed of 72rpm upwind configuration with and without yaw misalignment. However, there is another less visited case (M) where identical configuration was tested but with the inclusion of a zig-zag tape. This was called transition fixed sequence. This paper shows the differences between the free and the fix transition cases, that should be more appropriate for comparison with fully turbulent simulations. Steady k-ω SST fully turbulent computations performed with WMB CFD method are compared with the experiments showing, better predictions in the attached flow region when it is compared with the transition fixed experiments. This work wants to prove the utility of M case (transition fixed) and show its differences respect the S case (free transition) for validation purposes.

ATLAS MOTION PLATFORM MECANUM WHEEL JACOBIAN IN THE VELOCITY AND STATIC FORCE DOMAINS

Conventional training simulators commonly use the hexapod configuration to provide motion cues. While widely used, studies have shown that hexapods are incapable of producing the range of motion required to achieve high fidelity simulation required in many applications. Atlas is a six degree of freedom vehicle operating training simulator motion platform where orienting is decoupled from positioning, and unbounded rotation is possible about any axis. Angular displacements are achieved by manipulating the cockpit contained in a 2.9 metre (9.5 foot) diameter sphere with three Mecanum wheel actuators. The angular velocity Jacobian, Jω, maps the desired angular velocity of the sphere to the required speeds of the three Mecanum wheels, while the static force Jacobian, Jτ, maps the static moment vector required to statically orient the sphere to the static torques required by the three Mecanum wheels. In this paper, the two Jacobians are derived independently, and it is confirmed that , as it must. The implicat...

Effect of Lungeing and Circle Size on Movement Symmetry in Sound Riding Horses

IntroductionEvaluation of the movement during trot in circles is commonly used in clinical equine lameness examinations to exacerbate mild or bilateral lameness. Sound horses trotting in a straight line have a high degree of movement symmetry, which decreases with lameness. The aim of this study was to investigate the effect of lungeing and circle size on movement symmetry in sound horses.MethodsTwenty five riding horses categorized sound by inspection on straight line and lungeing were trotted in a straight line and in circles of 8, 10, 12, 14 and 16 metres diameter on both reins. Overall symmetry (S), symmetry of diagonal limb pair loading (A), and symmetry of diagonal limb pair timing (W) were calculated from trunk accelerations measured over the 13th thoracic vertebrae (T13) with a 3‐axis accelerometer. Data were analysed via ANOVA with horse as random effect.ResultsS, A, and W showed high degree of symmetry of straight line trot with mean ± SE = −6.0 ± 0.1, 0.01 ± 0.02 and −0.001 ± 0.003, respectively, that decreased with circular trot (P&lt;0.02 in pairwise tests). S and A showed decreasing symmetry with decreasing circle size. For 16 and 8 metres, respectively; S = −5.2 ± 0.1 and −4.7 ± 0.1; A = 0.10 ± 0.01 and 0.16 ± 0.01; W = −0.009 ± 0.002 and −0.012 ± 0.002.ConclusionsIn sound horses, movement symmetry measured over T13 decreased with circular trot and decreasing circle size as shown in earlier studies of movement of the poll and sacrum. The asymmetry mimicked inside diagonal lameness. Effect of circular movement and circle size should be considered in interpretation of lameness signs and asymmetry measured during circular trot.Ethical Animal ResearchThe study was approved by the department ethical committee. The horses belonged to the Danish army, who gave their informed consent. As no invasive procedures were applied approval from the Danish Animal Experimental board was not needed. Sources of funding: Foreningen KUSTOS af 1861. Competing interests: none.

Physical properties of asteroid 308635 (2005 YU55) derived from multi-instrument infrared observations during a very close Earth approach

The near-Earth asteroid (308635) 2005 YU55 is a potentially hazardous asteroid which was discovered in 2005 and passed Earth on November 8th 2011 at 0.85 lunar distances. This was the closest known approach by an asteroid of several hundred metre diameter since 1976 when a similar size object passed at 0.5 lunar distances. We observed 2005 YU55 from ground with a recently developed mid-IR camera (miniTAO/MAX38) in N- and Q-band and with the Submillimeter Array (SMA) at 1.3 mm. In addition, we obtained space observations with Herschel/PACS at 70, 100, and 160 micron. Our thermal measurements cover a wide range of wavelengths from 8.9 micron to 1.3 mm and were taken after opposition at phase angles between -97 deg and -18 deg. We performed a radiometric analysis via a thermophysical model and combined our derived properties with results from radar, adaptive optics, lightcurve observations, speckle and auxiliary thermal data. We find that (308635) 2005 YU55 has an almost spherical shape with an effective diameter of 300 to 312 m and a geometric albedo pV of 0.055 to 0.075. Its spin-axis is oriented towards celestial directions (lam_ecl, beta_ecl) = (60 deg +/- 30deg, -60 deg +/- 15 deg), which means it has a retrograde sense of rotation. The analysis of all available data combined revealed a discrepancy with the radar-derived size. Our radiometric analysis of the thermal data together with the problem to find a unique rotation period might be connected to a non-principal axis rotation. A low to intermediate level of surface roughness (r.m.s. of surface slopes in the range 0.1 - 0.3) is required to explain the available thermal measurements. We found a thermal inertia in the range 350-800 Jm^-2s^-0.5K^-1, very similar to the rubble-pile asteroid (25143) Itokawa and indicating a mixture of low conductivity fine regolith with larger rocks and boulders of high thermal inertia on the surface.

The Limoeiro Deposit: Ni-Cu-PGE Sulfide Mineralization Hosted Within an Ultramafic Tubular Magma Conduit in the Borborema Province, Northeastern Brazil

The Limoeiro deposit, located in a high-grade mobile belt of the Brasiliano orogenic cycle (650–500 Ma), represents one of the few magmatic Ni-Cu(-PGE) sulfide discoveries in recent years. The deposit is hosted by an ultramafic chonolith consisting in a partly deformed and metamorphosed tube-like body affected by brittle faults within high-grade gneiss and schist. The absolute age of the ultramafic intrusion that hosts the Limoeiro deposit is not yet known, but regional geologic constraints suggest that both intrusion and host rocks belong to a terrane older than the orogenic cycle. Peak metamorphic parageneses of the ultramafic intrusion and country rocks indicate granulite facies of metamorphism, interpreted as the result of the Neoproterozoic Brasiliano orogenic cycle. The Limoeiro deposit is the first significant discovery of Ni-Cu sulfide in the Borborema province, opening a new window for exploration in this large orogenic belt. Despite the high-grade metamorphism and the tectonic deformation, the primary magmatic structure of the intrusion hosting the Limoeiro deposit is remarkably well preserved. This intrusion forms a tube-like conduit (chonolith) with cross sections a few hundreds of meters in diameter and with a considerable length of more than 4 km. The conduit consists of two distinct sequences of ultramafic rocks, denominated Upper and Lower sequences, each one consisting of a core of harzburgite enveloped by orthopyroxenite, with an irregular and discontinuous outer shell of amphibolite. These ultramafic sequences, characterized by similar composition and structure, have distinctively different S contents resulting from the presence of disseminated Ni-Cu sulfide mineralization only in the Upper sequence. The magmatic system of the Limoeiro deposit is interpreted to result from the input of two major pulses of magma with similar composition, but sulfide saturation and segregation is restricted to the second magma pulse (Upper sequence). Nickel-Cu(-PGE) sulfide mineralization is broadly concordant with the Upper sequence and different orebodies resulted from tectonic slicing of the originally continuous tube-like structure. The bulk of the mineralization in all orebodies consists of thick (up to 150 m) and elongated (up to 1 km) masses of rock containing disseminated sulfides broadly concordant with the chonolithic structure. Thin layers of massive ore occur in the lower portions of some of the orebodies, and represent about 3 vol % of the Limoeiro deposit. The intrusion hosting the Limoeiro deposit is probably the best preserved chonolith that has been overprinted by granulite facies metamorphism within an orogenic terrane. This study indicates that reconstruction of small magma conduits, an important tool for exploration for Ni-Cu sulfide deposits, may be successfully achieved within high-grade orogenic terranes.

A Catastrophic tectonic event in summer 2011 in the Taman Peninsula

172 The territory of the Kerch Taman mud volcano zone is distinct for high neotectonic activity. Mud vol canoes erupt here both on land and in the Sea of Azov. In the latter case, islands of hundreds of meters in diameter and up to several meters high are formed from eruption products [1]. These islands are short lived though: active water erosion destroys them in the course of several months. Mud volcanoes are located in cryptodiapiric folds in Cenozoic deposits. Folds are grouped into long narrow subparallel anticline arrays divided by wider flat synclines. Anticlines are situated in the frontal parts of thrusts formed under tangential compression, and these structures are genetically interrelated [2, 3]. On land, anticlines are usually directly manifested in relief as topographic highs.

Assessment of the Diversity and Distribution of the Threatened Tree Species in a Logged Forest in Vietnam

Conservation of biodiversity and of endangered tree species in tropical forests represents a challenge in the era of deforestation and overlogging. Assessments of biodiversity and of conservation species are essential to estimating the conservation value of ecosystems in order to develop appropriate management measures. This paper discusses the floristic composition, the diversity, and the regeneration of the conservation species in a logged forest in southern Vietnam. Twenty five one hectare plots have been set up using circular sub-plots of 8 metres diameter and at a distance of 10m from the centre point of other sub-plots. The sampling is approximately 50% in each plot. Ten years after the last logging, the species richness appears low, when compared with the close protected area, but the diversity is quite high and conservation species still occur. Twelve conservation species have been studied from the point of view of their distribution and regeneration. Some are close to extinction but some others show promise in terms of regeneration. Six floristic groups have been identified and, among them, two are of interest from a conservation point of view. This logged forest still has a high conservation value, and the process that aims at developing protection measures is clearly relevant.

The spatial and temporal distribution of lunar mare basalts as deduced from analysis of data for lunar meteorites

In this work we analyze data for lunar meteorites with emphasis on the spatial and temporal distribution of lunar mare basalts. The data are mostly from the Lunar Meteorite Compendium ( http://www-curator.jsc.nasa.gov/antmet/lmc/contents.cfm cited hereafter as Compendium) compiled by Kevin Righter, NASA Johnson Space Center, and from the associated literature. Analysis of the data showed that (i) a significant part of the lunar meteorite source craters are not larger than hundreds of meters in diameter; (ii) cryptomaria seem to be rather abundant in lunar highlands; (iii) the ratios of lunar meteorites belonging to three broad petrologic groups (mare basalt/gabbro, feldspatic highland breccias, and mingled breccias which are a mixture of mare and highland components) seem to be roughly proportional to the areal distribution of these rocks on the lunar surface; and (iv) the meteorite mare basalt ages show a range from ∼2.5 to 4.3 Ga and fill the gaps in the Apollo/Luna basalt age distribution. The ages of mare basalt clasts from mingled breccias seem to be systematically higher than those of “normal” mare basalts, which supports the suggestion that mingled breccias originated mostly from cryptomaria.

HerschelSpace Observatory

Herschel was launched on 14 May 2009, and is now an operational ESA space observatory offering unprecedented observational capabilities in the far-infrared and submillimetre spectral range 55-671 {\mu}m. Herschel carries a 3.5 metre diameter passively cooled Cassegrain telescope, which is the largest of its kind and utilises a novel silicon carbide technology. The science payload comprises three instruments: two direct detection cameras/medium resolution spectrometers, PACS and SPIRE, and a very high-resolution heterodyne spectrometer, HIFI, whose focal plane units are housed inside a superfluid helium cryostat. Herschel is an observatory facility operated in partnership among ESA, the instrument consortia, and NASA. The mission lifetime is determined by the cryostat hold time. Nominally approximately 20,000 hours will be available for astronomy, 32% is guaranteed time and the remainder is open to the worldwide general astronomical community through a standard competitive proposal procedure.

Distributions of boulders ejected from lunar craters

We investigate the spatial distributions of boulders ejected from 18 lunar impact craters that are hundreds of meters in diameter. To accomplish this goal, we measured the diameters of 13,955 ejected boulders and the distance of each boulder from the crater center. Using the boulder distances, we calculated ejection velocities for the boulders. We compare these data with previously published data on larger craters and use this information to determine how boulder ejection velocity scales with crater diameter. We also measured regolith depths in the areas surrounding many of the craters, for comparison with the boulder distributions. These results contribute to understanding boulder ejection velocities, to determining whether there is a relationship between the quantity of ejected boulders and lunar regolith depths, and to understanding the distributions of secondary craters in the Solar System. Understanding distributions of blocky ejecta is an important consideration for landing site selection on both the Moon and Mars.