Belt Distances Research Articles

Impact of standing perturbation intensities on fall and stability outcomes in healthy young adults

Motorized treadmills have been extensively used in investigating reactive balance control and developing perturbation-based interventions for fall prevention. However, the relationship between perturbation intensity and its outcome has not been quantified. The primary purpose of this study was to quantitatively analyze how the treadmill belt’s peak velocity affects the perturbation outcome and other metrics related to the reactive balance in young adults while the total belt displacement is controlled at 0.36 m. Thirty-one healthy young adults were randomly assigned into three groups with different peak belt speeds: low (0.9 m/s), medium (1.2 m/s), and high (1.8 m/s). Protected by a safety harness, participants were exposed to a forward support surface translation while standing at an unexpected timing on an ActiveStep treadmill. The primary (perturbation outcome: fall vs. recovery) and secondary (dynamic stability, hip descent, belt distance at liftoff, and recovery step latency) outcome measures were compared among groups. Results revealed that a higher perturbation intensity is correlated with a greater faller rate (p < 0.001). Compared to the low- and medium-intensity groups, the high-intensity group was less stable (p < 0.001) with a larger hip descent (p < 0.001) and a longer belt distance (p < 0.001) at the recovery step liftoff. The results suggest that the increased perturbation intensity raises the risk of falling with larger instability and poorer reactive performance after a support surface translation-induced perturbation in healthy young adults. The findings could furnish preliminary guidance for us to design and select the optimal perturbation intensity that can maximize the effects of perturbation-based training protocols.

Cometary Activity Begins at Kuiper Belt Distances: Evidence from C/2017 K2

Abstract We study the development of activity in the incoming long-period comet C/2017 K2 over the heliocentric distance range 9 ≲ r H ≲ 16 au. The comet continues to be characterized by a coma of submillimeter-sized and larger particles ejected at low velocity. In a fixed co-moving volume around the nucleus we find that the scattering cross section of the coma, C, is related to the heliocentric distance by a power law, , with heliocentric index s = 1.14 ± 0.05. This dependence is significantly weaker than the r H −2 variation of the insolation as a result of two effects. These are, first, the heliocentric dependence of the dust velocity and, second, a lag effect due to very slow-moving particles ejected long before the observations were taken. A Monte Carlo model of the photometry shows that dust production beginning at r H ∼ 35 au is needed to match the measured heliocentric index, with only a slight dependence on the particle size distribution. Mass-loss rates in dust at 10 au are of order 103 kg s−1, while loss rates in gas may be much smaller, depending on the unknown dust to gas ratio. Consequently, the ratio of the nongravitational acceleration to the local solar gravity, α′, may, depending on the nucleus size, attain values of ∼10−7 ≲ α′ ≲ 10−5, comparable to values found in short-period comets at much smaller distances. Nongravitational acceleration in C/2017 K2 and similarly distant comets, while presently unmeasured, may limit the accuracy with which we can infer the properties of the Oort cloud from the orbits of long-period comets.

The First VERA Astrometry Catalog

AbstractWe present the first astrometry catalog from the Japanese VLBI (very long baseline interferometer) project VERA (VLBI Exploration of Radio Astrometry). We have compiled all the astrometry results from VERA, providing accurate trigonometric-annual-parallax and proper-motion measurements. In total, 99 maser sources are listed in the VERA catalog. Among them, 21 maser sources are newly reported, while the rest of the 78 sources are referred to in previously published results or those in preparation for forthcoming papers. The accuracy in the VERA astrometry is revisited and compared with that from the other VLBI astrometry projects such as BeSSeL (The Bar and Spiral Structure Legacy) Survey and GOBELINS (the Gould’s Belt Distances Survey) with the VLBA (Very Long Baseline Array). We have confirmed that most of the astrometry results are consistent with each other, and the largest error sources are due to source structure of the maser features and their rapid variation, along with the systematic calibration errors and different analysis methods. Combined with the BeSSeL results, we estimate the up-to-date fundamental Galactic parameters of $R_{0}=7.92\pm 0.16_{\rm {stat.}}\pm 0.3_{\rm {sys.}}\:$kpc and $\Omega _{\odot }=30.17\pm 0.27_{\rm {stat.}}\pm 0.3_{\rm {sys.}}\:$km$\:$s$^{-1}\:$kpc$^{-1}$, where $R_{0}$ and $\Omega _{\odot }$ are the distance from the Sun to the Galactic center and the Sun’s angular velocity of the Galactic circular rotation, respectively.

Hubble Space Telescope Search for Activity in High-perihelion Objects

Abstract Solar system objects with perihelia beyond the orbit of Jupiter (q &gt; 5 au) are too cold for water ice to generate an appreciable coma via sublimation. Despite this, numerous high-perihelion objects (HPOs) including many comets and recently escaped Kuiper Belt objects (Centaurs) are observed to be active out at least to the orbit of Saturn (q ∼ 10 au). Peak equilibrium temperatures at 10 au (∼125 K), while far too low to sublimate water ice, are sufficient to sublimate supervolatiles such as CO and CO2 ice. Temperatures at 10 au are also high enough to trigger the rapid crystallization of exposed amorphous ice, thus constituting another possible driver of distant activity. While supervolatile ices can sublimate strongly (as ) to at least Kuiper Belt (30 au) distances, crystallization is an exponential function of temperature that cannot be sustained much beyond ∼10 au. The heliocentric dependence of the activity thus suggests an observational test. If activity in high-perihelion objects is triggered by crystallization, then no examples of activity should be found with perihelia of q ≫ 10 au. If, on the other hand, activity is due to free sublimation of exposed supervolatile ices, or another cause, then distant activity might be detected. We obtained sensitive, high-resolution Hubble Space Telescope observations of HPOs to search for activity beyond the crystallization zone. No examples of activity were detected in 53 objects with q &gt; 15 au, consistent with the crystallization trigger hypothesis. However, sensitivity limits are such that we cannot reject the alternative hypothesis that mass loss is driven by the sublimation of supervolatile ices. We also searched for binary companions in our sample, finding none and setting an empirical 3σ limit to the binary fraction of &lt;8%.

Gaia-DR2 Confirms VLBA Parallaxes in Ophiuchus, Serpens, and Aquila

Abstract We present Gaia-DR2 astrometry of a sample of YSO candidates in Ophiuchus, Serpens Main, and Serpens South/W40 in the Aquila Rift, which had been mainly identified by their infrared excess with Spitzer. We compare the Gaia-DR2 parallaxes against published and new parallaxes obtained from our Very Long Baseline Array (VLBA) program Gould’s Belt Distances Survey. We obtain consistent results between Gaia and the VLBA for the mean parallaxes in each of the regions analyzed here. We see small offsets, when comparing mean values, of a few tens of microarcseconds in the parallaxes, which are either introduced by the Gaia zero-point error or due to a selection effect by Gaia toward the brightest, less obscured stars. Gaia-DR2 data alone conclusively places Serpens Main and Serpens South at the same distance, as we first inferred from VLBA data alone in a previous publication. Thus, Serpens Main, Serpens South, and W40 are all part of the same complex of molecular clouds, located at a mean distance of 436 ± 9 pc. In Ophiuchus, both Gaia and VLBA suggest a small parallax gradient across the cloud, and the distance changes from 144.2 ± 1.3 to 138.4 ± 2.6 pc when going from L1689 to L1688.

An Empirical Planetesimal Belt Radius–Stellar Luminosity Relation

Abstract Resolved observations of millimeter-sized dust, tracing larger planetesimals, have pinpointed the location of 26 Edgeworth–Kuiper Belt analogs. We report that a belt’s distance R to its host star correlates with the star’s luminosity L ⋆, following with a low intrinsic scatter of ∼17%. Remarkably, our Edgeworth–Kuiper Belt in the solar system and the two CO snow lines imaged in protoplanetary disks lie close to this R–L ⋆ relation, suggestive of an intrinsic relationship between protoplanetary disk structures and belt locations. To test the effect of bias on the relation, we use a Monte Carlo approach and simulate uncorrelated model populations of belts. We find that observational bias could produce the slope and intercept of the R–L ⋆ relation but is unable to reproduce its low scatter. We then repeat the simulation taking into account the collisional evolution of belts, following the steady-state model that fits the belt population as observed through infrared excesses. This significantly improves the fit by lowering the scatter of the simulated R–L ⋆ relation; however, this scatter remains only marginally consistent with the one observed. The inability of observational bias and collisional evolution alone to reproduce the tight relationship between belt radius and stellar luminosity could indicate that planetesimal belts form at preferential locations within protoplanetary disks. The similar trend for CO snow line locations would then indicate that the formation of planetesimals or planets in the outer regions of planetary systems is linked to the volatility of their building blocks, as postulated by planet formation models.

The Gould's Belt Distances Survey (GOBELINS). IV. Distance, Depth, and Kinematics of the Taurus Star-forming Region

Abstract We present new trigonometric parallaxes and proper motions of young stellar objects in the Taurus molecular cloud complex from observations collected with the Very Long Baseline Array as part of the Gould’s Belt Distances Survey. We detected 26 young stellar objects and derived trigonometric parallaxes for 18 stars with an accuracy of 0.3% to a few percent. We modeled the orbits of six binaries and determined the dynamical masses of the individual components in four of these systems (V1023 Tau, T Tau S, V807 Tau, and V1000 Tau). Our results are consistent with the first trigonometric parallaxes delivered by the Gaia satellite and reveal the existence of significant depth effects. We find that the central portion of the dark cloud Lynds 1495 is located at d =129.5 ± 0.3 pc, while the B216 clump in the filamentary structure connected to it is at d = 158.1 ± 1.2 pc. The closest and remotest stars in our sample are located at d = 126.6 ± 1.7 pc and d = 162.7 ± 0.8 pc, yielding a distance difference of about 36 pc. We also provide a new distance estimate for HL Tau that was recently imaged. Finally, we compute the spatial velocity of the stars with published radial velocity and investigate the kinematic properties of the various clouds and gas structures in this region.

THE GOULD’S BELT DISTANCES SURVEY (GOBELINS). II. DISTANCES AND STRUCTURE TOWARD THE ORION MOLECULAR CLOUDS

We present the results of the Gould's Belt Distances Survey (GOBELINS) of young star forming regions towards the Orion Molecular Cloud Complex. We detected 36 YSOs with the Very Large Baseline Array (VLBA), 27 of which have been observed in at least 3 epochs over the course of 2 years. At least half of these YSOs belong to multiple systems. We obtained parallax and proper motions towards these stars to study the structure and kinematics of the Complex. We measured a distance of 388$\pm$5 pc towards the Orion Nebula Cluster, 428$\pm$10 pc towards the southern portion L1641, 388$\pm$10 pc towards NGC 2068, and roughly $\sim$420 pc towards NGC 2024. Finally, we observed a strong degree of plasma radio scattering towards $\lambda$ Ori.

THE GOULD’S BELT DISTANCES SURVEY (GOBELINS). I. TRIGONOMETRIC PARALLAX DISTANCES AND DEPTH OF THE OPHIUCHUS COMPLEX

ABSTRACT We present the first results of the Gould’s Belt Distances Survey (GOBELINS), a project aimed at measuring the proper motion and trigonometric parallax of a large sample of young stars in nearby regions using multi-epoch Very Long Baseline Array (VLBA) radio observations. Enough VLBA detections have now been obtained for 16 stellar systems in Ophiuchus to derive their parallax and proper motion. This leads to distance determinations for individual stars with an accuracy of 0.3 to a few percent. In addition, the orbits of six multiple systems were modelled by combining absolute positions with VLBA (and, in some cases, near-infrared) angular separations. Twelve stellar systems are located in the dark cloud Lynds 1688; the individual distances for this sample are highly consistent with one another and yield a mean parallax for Lynds 1688 of mas, corresponding to a distance pc. This represents an accuracy greater than 1%. Three systems for which astrometric elements could be measured are located in the eastern streamer (Lynds 1689) and yield an estimate of mas, corresponding to a distance pc. This suggests that the eastern streamer is located about 10 pc farther than the core, but this conclusion needs to be confirmed by observations of additional sources in the eastern streamer (currently being collected). From the measured proper motions, we estimate the one-dimensional velocity dispersion in Lynds 1688 to be 2.8 ± 1.8 and 3.0 ± 2.0 km s−1, in R.A. and decl., respectively; these are larger than, but still consistent within of, those found in other studies.

THE GOULD’S BELT DISTANCES SURVEY (GOBELINS). III. THE DISTANCE TO THE SERPENS/AQUILA MOLECULAR COMPLEX

We report on new distances and proper motions to seven stars across the Serpens/Aquila complex. The observations were obtained as part of the Gould's Belt Distances Survey (GOBELINS) project between September 2013 and April 2016 with the Very Long Baseline Array (VLBA). One of our targets is the proto-Herbig AeBe object EC 95, which is a binary system embedded in the Serpens Core. For this system, we combined the GOBELINS observations with previous VLBA data to cover a total period of ~8 years, and derive the orbital elements and an updated source distance. The individual distances to sources in the complex are fully consistent with each other, and the mean value corresponds to a distance of $436.0\pm9.2$~pc for the Serpens/W40 complex. Given this new evidence, we argue that Serpens Main, W40 and Serpens South are physically associated and form a single cloud structure.

A method for measuring instantaneous treadmill speed

This paper presents a new method for measuring instantaneous treadmill speed. The method consists of two parts: (1) a motion-capture system and reflective squares placed directly on the treadmill belt, and (2) an algorithm for estimating belt speed and distance traveled from the measured positions of the reflective squares. The method was tested with a single subject walking on an instrumented treadmill. The method is easy to set up and results in an accurate estimate of treadmill speed that is conveniently synchronized with the output of the motion-capture system.

The Debiased Kuiper Belt: Our Solar System as a Debris Disk

AbstractThe dust measured in debris disks traces the position of planetesimal belts. In our Solar System, we are also able to measure the largest planetesimals directly and can extrapolate down to make an estimate of the dust. The zodiacal dust from the asteroid belt is better constrained than the only rudimentary measurements of Kuiper belt dust. Dust models will thus be based on the current orbital distribution of the larger bodies which provide the collisional source. The orbital distribution of many Kuiper belt objects is strongly affected by dynamical interactions with Neptune, and the structure cannot be understood without taking this into account. We present the debiased Kuiper belt as measured by the Canada-France Ecliptic Plane Survey (CFEPS). This model includes the absolute populations for objects with diameters &gt;100 km, measured orbital distributions, and size distributions of the components of the Kuiper belt: the classical belt (hot, stirred, and kernel components), the scattering disk, the detached objects, and the resonant objects (1:1, 5:4, 4:3, 3:2 including Kozai subcomponent, 5:3, 7:4, 2:1, 7:3, 5:2, 3:1, and 5:1). Because a large fraction of known debris disks are consistent with dust at Kuiper belt distances from the host stars, the CFEPS Kuiper belt model provides an excellent starting point for a debris disk model, as the dynamical interactions with planets interior to the disk are well-understood and can be precisely modelled using orbital integrations.

Belt distance between facets of space-filling zonotopes

To every d-dimensional polytope P with centrally symmetric facets one can assign a “subway map” such that every line of this “subway” contains exactly the facets parallel to one of the ridges of P. The belt diameter of P is the maximum number of subway lines one needs to use to get from one facet to another. We prove that the belt diameter of a d-dimensional space-filling zonotope does not exceed ⌈log2(4/5)d⌉.

The Gould's Belt Distances Survey

AbstractVery Long Baseline Interferometry (VLBI) observations can provide the positions of compact radio sources with an accuracy of order 50 micro-arcseconds. This is sufficient to measure the trigonometric parallax and proper motions of any object within 500 pc of the Sun to better than a few percent. Because they are magnetically active, young stars are often associated with compact radio emission detectable using VLBI techniques. Here we show how VLBI observations have already constrained the distance to the most often studied nearby regions of star formation (Taurus, Ophiuchus, Orion, etc.) and have started to provide information about their internal structure and kinematics. We will then briefly describe a large project, the ‘Gould's Belt Distances Survey,’ which has been designed to provide a detailed view of star formation in the solar neighborhood using VLBI observations.

MECHANICAL TRANSPLANTING OF POTATO USING STEM CUTTING

Decreasing food importation is a major concern for agricultural policy makers. Therefore, a special attention should be given to all projects and programs designed to promote crop production increase. First priority is to be given to production increase through, improved varieties, adapting and appropriate technologies transfer. Self–sufficiency in potato crop production may be by applying new technological inputs in agricultural mechanization, to optimize operation timeliness, and to promote a new method for potato by stem cuttings transplanting. Potato diseases and pests can be controlled using stem cutting that prevents contact with tuber and soil. Also, one potato tuber can produce 20 to 60 cuttings, each yielding half to one kg of tubers in the field, moreover each cutting produce five or more seed tubers. The main goal of this work is to develop and construct attachments for the transplanting machine to directly obtain stem cutting suitable for potato transplanting and reducing direct cost of importing practices. The auxiliary parts attached to the transplanter for transplanting stem cutting of potato may maximize transplanting machine exploitation. The developed machine was evaluated and tested at El-Gemeza Agr. Res. Station, El-Gharbia Gov. during season 2006 – 2007. A Massey Ferguson tractor of 26.11 kW (35 hp) and modified transplanter with attachments was tested at different operating conditions, tractor forward speed (0.28  0.06, 0.42  0.0.06, 0.56  0.06 and 0.69  0.06 m/s), speed ratio between ground wheel and horizontal belt (1:1, 1:2 and 1:3) distance between stem cuttings (0.2, 0.25 and 0.30 m) were also tested. The results show that the optimum tractor forward speed 0.28  0.06 m/s, speed ratio between ground wheel and horizontal belt 1:3 and distance between stem cuttings 0.30 m respectively. At these variable levels, the accuracy of distribution of stem cuttings and spunta tuber yield were maximized while missing seedling and operation cost was minimized. The developed transplanting machine reduced the operation costs to 50% compared to the local tubers method and saved 75% of the imported tubers costs.

A survey for pulsars in EGRET error boxes

As part of an effort to associate the unidentified EGRET gamma-ray sources with pulsars, error boxes for 19 sources were searched using Arecibo at 327-MHz. The sources were chosen to be out-of-plane and possibly associated with the Gould belt, a nearby starburst region with an enhanced production rate of core-collapse supernovae. The search revealed one new 597-ms pulsar, J2243+1518, within the error box of the EGRET source 3EG J2243+1509. The spin-down energy loss rate of the new pulsar is not nearly sufficient to power the gamma-ray source and so the pulsar is very unlikely to be associated. Simulations we have carried out show that any pulsars at Gould belt distances should have been detected by the survey. This suggests that either the EGRET sources associated with the Gould belt are not pulsars, or that the minimum of the pulsar luminosity function is lower than the ~1.5 mJy kpc^2 inferred from the population of normal pulsars.

Kuiper Belt Object Sizes and Distances from Occultation Observations

There are several observational campaigns underway to detect kilometer-sized foreground Kuiper belt objects (KBOs) through their occultation of background stars. The interpretation of an occultation light curve, unfortunately, is affected by a geometric degeneracy such that one is unable to determine the KBO size independently of its distance. This degeneracy can be broken through a precise measurement of the relative velocity obtained from simultaneous observations of individual events. While an array of telescopes spread over an area of few square kilometers can be employed, it is unlikely that the relative velocity can be measured to the required accuracy to help break this geometric degeneracy. The presence of diffraction fringes in KBO occultation light curves, when projected sizes of occulted stars are smaller than the Fresnel scale, improves determination of size and distance significantly. In this regard, we discuss the potential role of a dedicated satellite mission for KBO occultation observations. If dwarf stars at the V-band magnitudes of 14 and fainter can be monitored at time intervals of 0.1 s with normalized flux errors at the level of 1%, the occultation observations will allow individual KBO sizes and distances to be determined at the level of a few percent or better.

EFFECT OF INTERCROPPING DISTANCE ON CROP YIELD IN A PAULOWNIA-WHEAT AGROFORESTRY SYSTEM IN THE HUANG-HUAI-HAI PLAIN, CHINA

ABSTRACT A case study in a Paulownia (Paulownia elongata S. Y. Hu) -wheat intercropping system was conducted, and the relationship between tree belt distance (D), intercropping age (A) and annual relative wheat yield (Y) was estimated. The regression equation can be expressed as Y= 90.3290—1.9982 A+ 1.1924 D—0.3349 A2 + 0.2910 AD-0.0032 AD 2. Tree belt distance and intercropping tree age were the main factors influencing wheat yield. Optimized tree belt distance in each intercropping tree age within the rotation for maximum annual yield was expressed as Dm= 29.1496 + 2.6886 A. The optimized tree belt distance for different Paulownia rotation (T), which could cause the maximum accumulative average wheat yield, was shown as: Dm' = 0.600 + 11.042 T-0.787 T2 + 0.0273 T3 Further work is needed to develop a system to optimize the combined tree and wheat yields to meet the farmers' requirements.