60,638 research outputs found
The remote sensing of aquatic macrophytes Part 1: Color-infrared aerial photography as a tool for identification and mapping of littoral vegetation. Part 2: Aerial photography as a quantitative tool for the investigation of aquatic ecosystems
Research was initiated to use aerial photography as an investigative tool in studies that are part of an intensive aquatic ecosystem research effort at Lake Wingra, Madison, Wisconsin. It is anticipated that photographic techniques would supply information about the growth and distribution of littoral macrophytes with efficiency and accuracy greater than conventional methods
Growth, age and size of the Jurassic pachycormid Leedsichthys problematicus (Osteichthyes: Actinopterygii)
The Jurassic pachycormid osteichthyan Leedsichthys problematicus is renowned for having been able to achieve
prodigious size for a bony fish. Building on work of MARTILL (1986a), a thorough examination of all known
material was conducted in order to constrain estimates of the size of this animal and examine its rate of growth.
Important specimens of Leedsichthys are described for the first time. The histology of Leedsichthys is reviewed, and
the presence of growth annuli is used to establish ages for five specimens. Age and growth data were obtained
from gill rakers (n = 4) and lepidotrichia (n = 2). Lepidotrichia show upward curvilinear growth profiles and
ages ranging from 21 to 40 annuli, which are assumed to represent years. Both growth profiles start at a small
size (0.26 and 0.33 mm radial distance), which is assumed to represent age 1. However, annuli can be lost near
the margins of the elements. Gill rakers exhibit a sigmoidal growth profile. Age of gill rakers was estimated by
adjusting the alignment of the inflection points of the growth profiles thereby giving adjusted ages. Gill rakers
ranged in age from 19–38 annuli, but all show evidence of reabsorption of annuli near the focal points and at the
margins of most elements. Sizes for the five individuals range from 8.0-16.5 m for ages of 19-40 years. Growth
rate (0.01-0.05 K) was relatively slow as expected for a large, long-lived fish. At age 1, individuals were 1.6 m in
length. Estimates for the length of L. problematicus compare well with published lengths of other large suspension
feeders such as those for basking and whale sharks
The Ultimate Halo Mass in a LCDM Universe
In the far future of an accelerating LCDM cosmology, the cosmic web of
large-scale structure consists of a set of increasingly isolated halos in
dynamical equilibrium. We examine the approach of collisionless dark matter to
hydrostatic equilibrium using a large N-body simulation evolved to scale factor
a = 100, well beyond the vacuum--matter equality epoch, a_eq ~ 0.75, and 53/h
Gyr into the future for a concordance model universe (Omega_m ~ 0.3,
Omega_Lambda ~ 0.7). The radial phase-space structure of halos -- characterized
at a < a_eq by a pair of zero-velocity surfaces that bracket a dynamically
active accretion region -- simplifies at a > 10 a_eq when these surfaces merge
to create a single zero-velocity surface, clearly defining the halo outer
boundary, rhalo, and its enclosed mass, mhalo. This boundary approaches a fixed
physical size encompassing a mean interior density ~ 5 times the critical
density, similar to the turnaround value in a classical Einstein-deSitter
model. We relate mhalo to other scales currently used to define halo mass
(m200, mvir, m180b) and find that m200 is approximately half of the total
asymptotic cluster mass, while m180b follows the evolution of the inner zero
velocity surface for a < 2 but becomes much larger than the total bound mass
for a > 3. The radial density profile of all bound halo material is well fit by
a truncated Hernquist profile. An NFW profile provides a somewhat better fit
interior to r200 but is much too shallow in the range r200 < r < rhalo.Comment: 5 pages, 3 figures, submitted to MNRAS letter
Fluctuation Results from PHENIX
The PHENIX Experiment at the Relativistic Heavy Ion Collider has made
measurements of event-by-event fluctuations in the net charge, the mean
transverse momentum, and the charged particle multiplicity as a function of
collision energy, centrality, and transverse momentum in heavy ion collisions.
The results of these measurements will be reviewed and discussed.Comment: Proceedings for the Workshop on Correlations and Fluctuations in
Relativistic Nuclear Collisions, April 21-23, 2005; 10 pages, 17 figure
Flight/ground sample comparison relating to flight experiment M552, exothermic brazing
Comparisons were made between Skylab and ground-based specimens of nickel and stainless steel which were vacuum brazed using silver-copper-lithium alloy with various joint configurations. It was established that the absence of gravity greatly extends the scope of brazing since capillary flow can proceed without gravity interference. There was also evidence of enhanced transport, primarily in that liquid silver copper alloy dissolves nickel to a much greater extent in the zero gravity environment
Landau Collision Integral Solver with Adaptive Mesh Refinement on Emerging Architectures
The Landau collision integral is an accurate model for the small-angle
dominated Coulomb collisions in fusion plasmas. We investigate a high order
accurate, fully conservative, finite element discretization of the nonlinear
multi-species Landau integral with adaptive mesh refinement using the PETSc
library (www.mcs.anl.gov/petsc). We develop algorithms and techniques to
efficiently utilize emerging architectures with an approach that minimizes
memory usage and movement and is suitable for vector processing. The Landau
collision integral is vectorized with Intel AVX-512 intrinsics and the solver
sustains as much as 22% of the theoretical peak flop rate of the Second
Generation Intel Xeon Phi, Knights Landing, processor
Exchange Field-Mediated Magnetoresistance in the Correlated Insulator Phase of Be Films
We present a study of the proximity effect between a ferromagnet and a
paramagnetic metal of varying disorder. Thin beryllium films are deposited onto
a 5 nm-thick layer of the ferromagnetic insulator EuS. This bilayer arrangement
induces an exchange field, , of a few tesla in low resistance Be films
with sheet resistance , where is the quantum resistance.
We show that survives in very high resistance films and, in fact,
appears to be relatively insensitive to the Be disorder. We exploit this fact
to produce a giant low-field magnetoresistance in the correlated insulator
phase of Be films with .Comment: To be published in Physical Review Letter
Structural plasticity and associative memory in balanced neural networks with spike-time dependent inhibitory plasticity
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