6,786 research outputs found
Deep u*- and g-band Imaging of the Spitzer Space Telescope First Look Survey Field : Observations and Source Catalogs
We present deep u*-, and g-band images taken with the MegaCam on the 3.6 m
Canada-France-Hawaii Telescope (CFHT) to support the extragalactic component of
the Spitzer First Look Survey (hereafter, FLS). In this paper we outline the
observations, present source catalogs and characterize the completeness,
reliability, astrometric accuracy and number counts of this dataset. In the
central 1 deg2 region of the FLS, we reach depths of g~26.5 mag, and u*~26.2
mag (AB magnitude, 5 detection over a 3" aperture) with ~4 hours of
exposure time for each filter. For the entire FLS region (~5 deg2 coverage), we
obtained u*-band images to the shallower depth of u*=25.0--25.4 mag (5,
3" aperture). The average seeing of the observations is 0.85" for the central
field, and ~1.00" for the other fields. Astrometric calibration of the fields
yields an absolute astrometric accuracy of 0.15" when matched with the SDSS
point sources between 18<g<22. Source catalogs have been created using
SExtractor. The catalogs are 50% complete and greater than 99.3% reliable down
to g~26.5 mag and u*~26.2 mag for the central 1 deg2 field. In the shallower
u*-band images, the catalogs are 50% complete and 98.2% reliable down to
24.8--25.4 mag. These images and source catalogs will serve as a useful
resource for studying the galaxy evolution using the FLS data.Comment: 15 pages, 16 figure
Universal Robotic Gripper based on the Jamming of Granular Material
Gripping and holding of objects are key tasks for robotic manipulators. The
development of universal grippers able to pick up unfamiliar objects of widely
varying shape and surface properties remains, however, challenging. Most
current designs are based on the multi-fingered hand, but this approach
introduces hardware and software complexities. These include large numbers of
controllable joints, the need for force sensing if objects are to be handled
securely without crushing them, and the computational overhead to decide how
much stress each finger should apply and where. Here we demonstrate a
completely different approach to a universal gripper. Individual fingers are
replaced by a single mass of granular material that, when pressed onto a target
object, flows around it and conforms to its shape. Upon application of a vacuum
the granular material contracts and hardens quickly to pinch and hold the
object without requiring sensory feedback. We find that volume changes of less
than 0.5% suffice to grip objects reliably and hold them with forces exceeding
many times their weight. We show that the operating principle is the ability of
granular materials to transition between an unjammed, deformable state and a
jammed state with solid-like rigidity. We delineate three separate mechanisms,
friction, suction and interlocking, that contribute to the gripping force.
Using a simple model we relate each of them to the mechanical strength of the
jammed state. This opens up new possibilities for the design of simple, yet
highly adaptive systems that excel at fast gripping of complex objects.Comment: 10 pages, 7 figure
Dynamic Boundaries in Asymmetric Exclusion Processes
We investigate the dynamics of a one-dimensional asymmetric exclusion process
with Langmuir kinetics and a fluctuating wall. At the left boundary, particles
are injected onto the lattice; from there, the particles hop to the right.
Along the lattice, particles can adsorb or desorb, and the right boundary is
defined by a wall particle. The confining wall particle has intrinsic forward
and backward hopping, a net leftward drift, and cannot desorb. Performing Monte
Carlo simulations and using a moving-frame finite segment approach coupled to
mean field theory, we find the parameter regimes in which the wall acquires a
steady state position. In other regimes, the wall will either drift to the left
and fall off the lattice at the injection site, or drift indefinitely to the
right. Our results are discussed in the context of non-equilibrium phases of
the system, fluctuating boundary layers, and particle densities in the lab
frame versus the frame of the fluctuating wall.Comment: 13 page
Higher-Order Tarski Grothendieck as a Foundation for Formal Proof
We formally introduce a foundation for computer verified proofs based on higher-order Tarski-Grothendieck set theory. We show that this theory has a model if a 2-inaccessible cardinal exists. This assumption is the same as the one needed for a model of plain Tarski-Grothendieck set theory. The foundation allows the co-existence of proofs based on two major competing foundations for formal proofs: higher-order logic and TG set theory. We align two co-existing Isabelle libraries, Isabelle/HOL and Isabelle/Mizar, in a single foundation in the Isabelle logical framework. We do this by defining isomorphisms between the basic concepts, including integers, functions, lists, and algebraic structures that preserve the important operations. With this we can transfer theorems proved in higher-order logic to TG set theory and vice versa. We practically show this by formally transferring Lagrange\u27s four-square theorem, Fermat 3-4, and other theorems between the foundations in the Isabelle framework
Prototype ultrasonic wayfinder with haptic feedback for an IOT environment
Pervasive computing and the Internet of Things (IoT) have stimulated the development of many new assistive devices. It is possible to incorporate sensors such as acoustic, inductive, capacitive, temperature, humidity, pressure, location, and many more. Haptic feedback provides a person with sensory information through the skin using vibration or force-feedback responses. Commercial organizations have moved very quickly into this design space, particularly Sunu (smart-watch), HandSight (cameras on glove), and others. Arduino and Raspberry Pi are examples of the computing platforms currently in use. Sonar or ultrasonic transducers enable the production of lighter equipment with improved functionalities. Sonar as a means of assistive navigation has been used extensively in maritime environments to detect animals (D'Amico and Pittenger, 2009, Evans and Awbrey, 1988). As an assistive technology, there are projects for the blind which upgrade their walking sticks with an ultrasonic sensor (Amemiya and Sugiyama, 2010). Similar projects have been undertaken worldwide and most devices can only provide one or two designated functions. The size of the completed device is small enough to embed on a shoe, a walking stick, or on a wheelchair. A sonar sensor can detect something less than a meter from an individual user. This study uses a glove to attach a sonar sensor on a Raspberry Pi 0, whereas the Tacit glove (Hoefer, 2011) carries two sonar sensors with an Arduino controller actuating vibrating motors on a glove
Binaural advantages in users of bimodal and bilateral cochlear implant devices
This is the published version, also available here: http://dx.doi.org/10.1121/1.4831955.This paper investigates to what extent users of bilateral and bimodal fittings should expect to benefit from all three different binaural advantages found to be present in normal-hearing listeners. Head-shadow and binaural squelch are advantages occurring under spatially separated speech and noise, while summation emerges when speech and noise coincide in space. For 14 bilateral or bimodal listeners, speech reception thresholds in the presence of four-talker babble were measured in sound-field under various speech and noise configurations. Statistical analysis revealed significant advantages of head-shadow and summation for both bilateral and bimodal listeners. Squelch was significant only for bimodal listeners
A mathematical framework for the emergence of winners and losers in cell competition
Cell competition is a process in multicellular organisms where cells interact with their neighbours to determine a "winner" or "loser" status. The loser cells are eliminated through programmed cell death, leaving only the winner cells to populate the tissue. Cell competition is context-dependent; the same cell type can win or lose depending on the cell type it is competing against. Hence, winner/loser status is an emergent property. A key question in cell competition is: how do cells acquire their winner/loser status? In this paper, we propose a mathematical framework for studying the emergence of winner/loser status based on a set of quantitative criteria that distinguishes competitive from non-competitive outcomes. We apply this framework in a cell-based modelling context, to both highlight the crucial role of active cell death in cell competition and identify the factors that drive cell competition
Coulomb effects on growth of instabilities in asymmetric nuclear matter
We study the effects of the Coulomb interaction on the growth of unstable
modes in asymmetric nuclear matter. In order to compare with previous
calculations we use a semiclassical approach based on the linearized Vlasov
equation. Moreover, a quantum calculation is performed within the R.P.A.. The
Coulomb effects are a slowing down of the growth and the occurrence of a
minimal wave vector for the onset of the instabilities. The quantum corrections
cause a further decrease of the growth rates.Comment: 10 pages, revtex, 4 ps figures, to appear in Phys. Rev. C e-mail:
[email protected], [email protected]
- …