Real-time Spatial Detection and Tracking of Resources in a Construction Environment

Construction accidents with heavy equipment and bad decision making can be based on poor knowledge of the site environment and in both cases may lead to work interruptions and costly delays. Supporting the construction environment with real-time generated three-dimensional (3D) models can help preventing accidents as well as support management by modeling infrastructure assets in 3D. Such models can be integrated in the path planning of construction equipment operations for obstacle avoidance or in a 4D model that simulates construction processes. Detecting and guiding resources, such as personnel, machines and materials in and to the right place on time requires methods and technologies supplying information in real-time. This paper presents research in real-time 3D laser scanning and modeling using high range frame update rate scanning technology. Existing and emerging sensors and techniques in three-dimensional modeling are explained. The presented research successfully developed computational models and algorithms for the real-time detection, tracking, and three-dimensional modeling of static and dynamic construction resources, such as workforce, machines, equipment, and materials based on a 3D video range camera. In particular, the proposed algorithm for rapidly modeling three-dimensional scenes is explained. Laboratory and outdoor field experiments that were conducted to validate the algorithm’s performance and results are discussed

Probing the Light Pseudoscalar Window

Very light pseudoscalars can arise from the symmetry-breaking sector in many extensions of the Standard Model. If their mass is below 200 MeV, they can be long-lived and have interesting phenomenology. We discuss the experimental constraints on several models with light pseudoscalars, including one in which the pseudoscalar is naturally fermiophobic. Taking into account the stringent bounds from rare K and B decays, we find allowed parameter space in each model that may be accessible in direct production experiments. In particular, we study the photoproduction of light pseudoscalars at Jefferson Lab and conclude that a beam dump experiment could explore some of the allowed parameter space of these models.Comment: 22 pages, 4 figure

Photoemission Spectra in t-J Ladders with Two Legs

Photoemission spectra for the isotropic two-leg t-J ladder are calculated at various hole-doping levels using exact diagonalization techniques. Low-energy sharp features caused by short-range antiferromagnetic correlations are observed at finite doping levels close to half-filling, above the naive Fermi momentum. These features should be observable in angle-resolved photoemission experiments. In addition, the formation of a d-wave pairing condensate as the ratio J/t is increased leads to dynamically generated spectral weight for momenta close to $k_F$ where the $d_{x^2-y^2 }$-order parameter is large.Comment: 9 pages, RevTex, to be published in Phys. Rev. B (RC

Validation and implication of segmentation on Empirical Bayes for highway safety studies

Typically, crash frequency is modelled as Poison where the variation is the square root of the expected number. If the expected number of crashes is small, the variation is a large percentage of the expected number of crashes, and the observed number of crashes provides a crude estimate for the expected number. A better estimate is obtained when the expected number is large. For a specific location, there are two approaches for performing measurements where the expected number of crashes is large. One approach is to measure over a long period of time. However, data are not often available for long periods. Even if available, changes in conditions over time, such as increase in traffic volumes or improvement in infrastructure, may limit the useful time frame. Another approach is to perform measurements over a large number of similar locations, providing a relatively precise estimate for the distribution. Then, one can use the Empirical Bayes (EB) approach to combine the relatively precise estimate for the distribution with the less precise estimate for the expected number at the location of interest, resulting is an improved estimate for the expected number at that location. This paper explores the two approaches. It uses multiple years of data from the Highway Safety Information System for California intersections and highway links from the State of Iowa. Data from a single year is used to estimate the expected number of crashes at locations, following the EB approach. Data from multiple years at each location is then used to estimate the expected number of crashes at those locations, and the results from the two approaches are compared. No such large scale validation has yet been performed. The effect of a priori segmentation of the highway system is also explored. Longer, homogeneous sections are found both to improve the statistical validity of models and to improve the EB correction of one-year section crash estimates

Generalized Hamiltonian structures for Ermakov systems

We construct Poisson structures for Ermakov systems, using the Ermakov invariant as the Hamiltonian. Two classes of Poisson structures are obtained, one of them degenerate, in which case we derive the Casimir functions. In some situations, the existence of Casimir functions can give rise to superintegrable Ermakov systems. Finally, we characterize the cases where linearization of the equations of motion is possible

Eddy genesis and manipulation in plane laminar shear flow

Eddy formation and presence in a plane laminar shear flow configuration consisting of two infinitely long plates orientated parallel to each other is investigated theoretically. The upper plate, which is planar, drives the flow; the lower one has a sinusoidal profile and is fixed. The governing equations are solved via a full finite element formulation for the general case and semi-analytically at the Stokes flow limit. The effects of varying geometry (involving changes in the mean plate separation or the amplitude and wavelength of the lower plate) and inertia are explored separately. For Stokes flow and varying geometry, excellent agreement between the two methods of solution is found. Of particular interest with regard to the flow structure is the importance of the clearance that exists between the upper plate and the tops of the corrugations forming the lower one. When the clearance is large, an eddy is only present at sufficiently large amplitudes or small wavelengths. However, as the plate clearance is reduced, a critical value is found which triggers the formation of an eddy in an otherwise fully attached flow for any finite amplitude and arbitrarily large wavelength. This is a precursor to the primary eddy to be expected in the lid-driven cavity flow which is formed in the limit of zero clearance between the plates. The influence of the flow driving mechanism is assessed by comparison with corresponding solutions for the case of gravity-driven fluid films flowing over an undulating substrate. When inertia is present, the flow generally becomes asymmetrical. However, it is found that for large mean plate separations the flow local to the lower plate becomes effectively decoupled from the inertia dominated overlying flow if the wavelength of the lower plate is sufficiently small. In such cases the local flow retains its symmetry. A local Reynolds number based on the wavelength is shown to be useful in characterising these large-gap flows. As the mean plate separation is reduced, the form of the asymmetry caused by inertia changes, and becomes strongly dependent on the plate separation. For lower plate wavelengths which do not exhibit a cinematically induced secondary eddy, an inertially induced secondary eddy can be created if the mean plate separation is sufficiently small and the global Reynolds number sufficiently large

Stratigraphy and palaeoceanography of a topography-controlled contourite drift in the Pen Duick area, southern Gulf of Cádiz

The northern part of the Gulf of Cádiz has and still is receiving a lot of attention from the scientific community due to (amongst others) the recent IODP Expedition 339. In contrast, its southern part, or the Moroccan margin has received far less attention, although mud volcanoes, diapiric ridges and cold-water corals are present in this region. The El Arraiche mud volcano field is characterized by a compressive regime creating several ridges and assisting the migration of hydrocarbon fluids towards the seabed surface. This study presents seismic and multibeam evidence for the existence of a contourite drift at water depths between 550 and 650 meters along the southwestern flank of the Pen Duick Escarpment and Gemini Mud Volcano, within the El Arraiche Mud Volcano field. From the onset of the Quaternary, when the escarpment started to lift and the local mud volcanism initiated, contouritic deposition was initiated as well at the foot of both topographic obstacles. Initially, fairly low-velocity bottom currents gave rise to sheeted drift deposits, affected by the uplift of the escarpment or mud extrusion. From the Middle Pleistocene onwards, separated mounded drift deposits were formed due to intensified bottom currents. An Antarctic Intermediate Water origin is inferred as driving mechanism for the drift development, although glacial conditions are not yet well constrained. The influence of Mediterranean Outflow Water (MOW) cannot be substantiated here. Moreover, the changes recorded within this contourite drift differ from the MOW-dominated contourite depositional system in the northern Gulf of Cádiz, as drift deposits only occur as early as the base of the Quaternary (compared to the Early Pliocene for the north) and mounded drift deposits only occur from the Middle Pleistocene onwards (compared to the Early Pleistocene). Cold-water coral mounds have been observed within and on top of the sedimentary sequence at the foot of the Pen Duick Escarpment. This implies that environmental conditions in which cold-water corals thrive were not necessarily restricted to the top of the Pen Duick Escarpment

Depolarisation cooling of an atomic cloud

We propose a cooling scheme based on depolarisation of a polarised cloud of trapped atoms. Similar to adiabatic demagnetisation, we suggest to use the coupling between the internal spin reservoir of the cloud and the external kinetic reservoir via dipolar relaxation to reduce the temperature of the cloud. By optical pumping one can cool the spin reservoir and force the cooling process. In case of a trapped gas of dipolar chromium atoms, we show that this cooling technique can be performed continuously and used to approach the critical phase space density for BECComment: 8 pages, 5 figure