946 research outputs found
Landform classification of the Mamaku Plateau using a digital elevation model.
The Mamaku Plateau is a large, forest-covered ignimbrite plateau in the North Island of New Zealand. This study was launched to aid inquiries into the evolu-tion of the plateau by classifying its valleys (which con-stitute Mamaku’s main geomorphological feature).An automatic classification of the valley forms in the Mamaku Plateau was made using a Digital Elevation Model (DEM). A new algorithm was created for the Arc/Info Geographic Information System, to extract the valleys from the DEM. Preliminary results from this phase of the inquiry indi-cated that it was difficult to do a computer-aided classi-fication of valleys based only on valley form. Conven-tional classification of the plateau’s valleys had also been done using stereoscopy to assist in the geomorphological interpretation. The results of these classifications were compared, and it was concluded that DEMs are useful in landscape analysis especially if combined with traditional geomorphological analysis
CMB anisotropies seen by an off-center observer in a spherically symmetric inhomogeneous universe
The current authors have previously shown that inhomogeneous, but spherically
symmetric universe models containing only matter can yield a very good fit to
the SNIa data and the position of the first CMB peak. In this work we examine
how far away from the center of inhomogeneity the observer can be located in
these models and still fit the data well. Furthermore, we investigate whether
such an off-center location can explain the observed alignment of the lowest
multipoles of the CMB map. We find that the observer has to be located within a
radius of 15 Mpc from the center for the induced dipole to be less than that
observed by the COBE satellite. But for such small displacements from the
center, the induced quadru- and octopoles turn out to be insufficiently large
to explain the alignment.Comment: 8 pages (REVTeX4), 7 figures; v2: minor changes, matches published
versio
What triggers galaxy transformations? The environments of post-starburst galaxies
(abridged) There are good observational reasons to believe that the
progenitors of red galaxies have undergone starbursts, followed by a
post-starburst phase. We investigate the environments of post-starburst
galaxies by measuring \textsl{(1)} number densities in
radius comoving spheres, \textsl{(2)} transverse distances to nearest
Virgo-like galaxy clusters, and \textsl{(3)} transverse distances to nearest
luminous-galaxy neighbors. We compare the post-starburst galaxies to currently
star-forming galaxies identified solely by A-star excess or \Halpha emission.
We find that post-starburst galaxies are in the same kinds of environments as
star-forming galaxies; this is our ``null hypothesis''. More importantly, we
find that at each value of the A-star excess, the star-forming and
post-starburst galaxies lie in very similar distributions of environment. The
only deviations from our null hypothesis are barely significant: a slight
deficit of post-starburst galaxies (relative to the star-forming population) in
very low-density regions, a small excess inside the virial radii of clusters,
and a slight excess with nearby neighbors. None of these effects is strong
enough to make the post-starburst galaxies a high-density phenomenon, or to
argue that the starburst events are primarily triggered by external tidal
impulses (e.g., from close passages of massive galaxies). The small excess
inside cluster virial radii suggests that some post-starbursts are triggered by
interactions with the intracluster medium, but this represents a very small
fraction of all post-starburst galaxies.Comment: ApJ in pres
Modelling and control of a water jet cutting probe for flexible surgical robot
Surgical removal of cancerous tissue from the spine is limited by the inability of hand held drills and cutting tools to reach small crevices present in complex bones such as the spinal column, especially on the anterior side. In addition, the high speed rotating mechanisms used presently are subject to stability issues when manoeuvring around tortuous bone forms. We report on the design and experimental testing of a novel flexible robotic surgical system which addresses these issues. The robot consists of a flexible probe, a water jet cutting system, and a haptic feedback controller. The water jet cutting system consists of a flexible end effector capable of bending around the anterior of the spinal column for tissue removal. A new experimental method of controlling the depth of water jet cut is described. The haptic feedback controller is based on a constraint set approach to define 3D boundaries, based on five key types of constraints. Experimental outcomes of measuring the depth of water jet cut were combined with haptic regional constraints with the aim of improving the safety of surgical procedures. The reliability, accuracy and performance of the prototype robot were tested in a mock surgical procedure on the lower lumbar vertebrae. Results show promise for the implementation of water jet cutting for robotic surgical spinal procedures
Physics-Based Nozzle Design Rules for High-Frequency Liquid Metal Jetting
We present physics-based nozzle design rules to achieve high-throughput and
stable jetting in drop-on-demand liquid metal 3D printing. The design rules are
based on scaling laws that capture the change of meniscus oscillation
relaxation time with geometric characteristics of the nozzle's inner profile.
These characteristics include volume, cross-sectional area, and inner surface
area of the nozzle. Using boundary layer theory for a simple geometry, we show
that the meniscus settles faster when the ratio of inner surface area to volume
is increased. High-fidelity multiphase flow simulations verify this scaling. We
use these laws to explore several design concepts with parameterized classes of
shapes that reduce the meniscus relaxation time while preserving desired
droplet specs. Finally, we show that for various nozzle profile concepts, the
optimal performance can be achieved by increasing the ratio of the
circumferential surface area to the bulk volume to the extent that is allowable
by manufacturing constraints.Comment: Under Review in Physics of Fluids, AIP Publishin
Multiple Migration and Use of Ties: Bangladeshis in Italy and Beyond
This article analyses previous multiple migratory trajectories of Bangladeshifirst generationmigrants before their arrival in Italy and within Italy. It also uncovers the role of social net-works and transnational ties in their multiple migrations. Thefindings show that theirfirstinternational migration was mainly shaped by their family\u2019s socio-economic condition andtransnational kinship networks. They already had someone from their family or close relativesin the preferred country with whom they were connected. Their onward relocations until arriv-ing in Italy, in most cases, was to achieve the socio-economic success and legal status thatthey had failed to attain in theirfirst and subsequent destinations, but the transnational connec-tions with friends or acquaintances are a key resource facilitating these remigrations. Banglade-shis who arrived in Italy from various countries mostly had networks, either with someonefrom their local district in Bangladesh or with their earlier fellow migrants who moved to Italybefore the
Baryon Binding Energy in Sakai-Sugimoto Model
The binding energy of baryon has been studied in the dual
string theory with a black hole interior. In this picture baryon is constructed
of a brane vertex wrapping on and fundamental strings
connected to it. Here, we calculate the baryon binding energy in Sakai-Sugimoto
model with a in which the supersymmetry is completely
broken. Also we check the dependence of the baryon binding energy. We
believe that this model represents an accurate description of baryons due to
the existence of Chern-Simones coupling with the gauge field on the brane. We
obtain an analytical expression for the baryon binding energy . In that case we
plot the baryon binding energy in terms of radial coordinate. Then by using the
binding energy diagram, we determine the stability range for baryon
configuration. And also the position and energy of the stable equilibrium point
is obtained by the corresponding diagram. Also we plot the baryon binding
energy in terms of temperature and estimate a critical temperature in which the
baryon would be dissociated.Comment: 14 pages, 1 fi
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