10,100 research outputs found
Position-Based Multi-Agent Dynamics for Real-Time Crowd Simulation (MiG paper)
Exploiting the efficiency and stability of Position-Based Dynamics (PBD), we
introduce a novel crowd simulation method that runs at interactive rates for
hundreds of thousands of agents. Our method enables the detailed modeling of
per-agent behavior in a Lagrangian formulation. We model short-range and
long-range collision avoidance to simulate both sparse and dense crowds. On the
particles representing agents, we formulate a set of positional constraints
that can be readily integrated into a standard PBD solver. We augment the
tentative particle motions with planning velocities to determine the preferred
velocities of agents, and project the positions onto the constraint manifold to
eliminate colliding configurations. The local short-range interaction is
represented with collision and frictional contact between agents, as in the
discrete simulation of granular materials. We incorporate a cohesion model for
modeling collective behaviors and propose a new constraint for dealing with
potential future collisions. Our new method is suitable for use in interactive
games.Comment: 9 page
Asteroseismic modeling of 16 Cyg A & B using the complete Kepler data set
Asteroseismology of bright stars with well-determined properties from
parallax measurements and interferometry can yield precise stellar ages and
meaningful constraints on the composition. We substantiate this claim with an
updated asteroseismic analysis of the solar-analog binary system 16 Cyg A & B
using the complete 30-month data sets from the Kepler space telescope. An
analysis with the Asteroseismic Modeling Portal (AMP), using all of the
available constraints to model each star independently, yields the same age
( Gyr) and composition (, ) for both stars, as expected for a binary system. We quantify the
accuracy of the derived stellar properties by conducting a similar analysis of
a Kepler-like data set for the Sun, and we investigate how the reliability of
asteroseismic inference changes when fewer observational constraints are
available or when different fitting methods are employed. We find that our
estimates of the initial helium mass fraction are probably biased low by
0.02-0.03 from neglecting diffusion and settling of heavy elements, and we
identify changes to our fitting method as the likely source of small shifts
from our initial results in 2012. We conclude that in the best cases reliable
stellar properties can be determined from asteroseismic analysis even without
independent constraints on the radius and luminosity.Comment: 5 emulateapj pages, 1 table, 1 figure. ApJ Letters, accepte
1,3,4,6-Tetramethyl-1,4-dihydro-1,2,4,5-tetrazine, C_6H_(12)N_4
M_r =140∙19, monoclinic, P2_1/n, a = 10∙612(3), b=6∙820(1), c= 10∙975 (2) Å, β=95∙31(2)°, V=790.9(5) Å^3, Z=4, D_m=1.13(5) (flotation), D_x = 1∙177 g cm^(-3), Mo Kα, λ = 0.71073 Å, μ= 0.848 cm^(-1), F(000) = 304, T= 295 K, R = 0∙077 for 704 observed reflections. This potentially antiaromatic or homoaromatic ring system has a flattened boat conformation with both N-methyls in equatorial positions. Bond angles and distances (excluding H's) predicted to be symmetry equivalent exhibit variations of 0.002-0.014 Å and 0.0-2.0°. Substantial delocalization of the electron lone pairs of N(1) and N(4) is found
Balmer and Metal Absorption Feature Gradients in M32
Spectra from MDM Observatory are used to assess Lick/IDS feature strength
gradients inside the half-light radius of the compact Local Group elliptical
galaxy M32. All but a few (of 24 measured) indices show a statistically
significant gradient. Comparing with models, the index gradients indicate a
mean age and abundance gradient in the sense that the nucleus is a factor of
2.5 younger and a factor of 0.3 dex more metal-rich than at 1 effective radius.
This conclusion is only weakly dependent on which index combinations are used
and is robust to high accuracy. Stars near the M32 nucleus have a mean age and
heavy element abundance [M/H] of (4.7 Gyr, +0.02), judging from models by
Worthey with variable abundance ratios. This result has very small formal
random errors, although, of course, there is significant age-metallicity
degeneracy along an (age, abundance) line segment from (5.0 Gyr, 0.00) to (4.5
Gyr, +0.05). An abundance pattern of [C/M]=+0.077, [N/M]=-0.13, [Mg/M]=-0.18,
[Fe/M]~0.0, and [Na/M]=+0.12 is required to fit the feature data, with a
fitting precision of about 0.01 dex. Model uncertainties make the accuracies of
these values at least twice the magnitude of the precision. Forcing
scaled-solar abundances does not change the age very much, but it increases the
rms goodness of model-data fit by a factor of 3 and broadens the allowed range
of age to Gyr. The overall abundance pattern contrasts with larger
elliptical galaxies, in which all measurable lighter elements are enhanced
relative to iron and calcium.Comment: 23 pages, 9 figures, Astronomical Journal, in pres
Subscale, hydrogen-burning, airframe-integrated-scramjet: Experimental and theoretical evaluation of a water cooled strut airframe-integrated-scramjet: Experimental leading edge
A water-cooled leading-edge design for an engine/airframe integrated scramjet model strut leading edge was evaluated. The cooling design employs a copper cooling tube brazed just downstream of the leading edge of a wedge-shaped strut which is constructed of oxygen-free copper. The survival of the strut leading edge during a series of tests at stagnation point heating rates confirms the practicality of the cooling design. A finite difference thermal model of the strut was also proven valid by the reasonable agreement of calculated and measured values of surface temperature and cooling-water heat transfer
Stereociliary Myosin-1c Receptors Are Sensitive to Calcium Chelation and Absent from Cadherin 23 Mutant Mice
The identities of some of the constituents of the hair-cell transduction apparatus have been elucidated only recently. The molecular motor myosin-1c (Myo1c) functions in adaptation of the hair-cell response to sustained mechanical stimuli and is therefore an integral part of the transduction complex. Recent data indicate that Myo1c interacts in vitro with two other molecules proposed to be important for transduction: cadherin 23 (Cdh23), a candidate for the stereociliary tip link, and phosphatidylinositol 4,5-bisphosphate (PIP2), which is abundant in the membranes of hair-cell stereocilia. It is not known, however, whether these interactions occur in hair cells. Using an in situ binding assay on saccular hair cells, we demonstrated previously that Myo1c interacts with molecules at stereociliary tips, the site of transduction, through sequences contained within its calmodulin (CaM)-binding neck domain, which can bind up to four CaM molecules. In the current study, we identify the second CaM-binding IQ domain as a region of Myo1c that mediates CaM-sensitive binding to stereociliary tips and to PIP2 immobilized on a solid support. Binding of Myo1c to stereociliary tips of cochlear and vestibular hair cells is disrupted by treatments that break tip links. In addition, Myo1c does not bind to stereocilia from mice whose hair cells lack Cdh23 protein despite the presence of PIP2 in the stereociliary membranes. Collectively, our data suggest that Myo1c and Cdh23 interact at the tips of hair-cell stereocilia and that this interaction is modulated by CaM
Ensemble v-representable ab-initio density functional calculation of energy and spin in atoms: atest of exchange-correlation approximations
The total energies and the spin states for atoms and their first ions with Z
= 1-86 are calculated within the the local spin-density approximation (LSDA)
and the generalized-gradient approximation (GGA) to the exchange-correlation
(xc) energy in density-functional theory. Atoms and ions for which the
ground-state density is not pure-state v-representable, are treated as ensemble
v- representable with fractional occupations of the Kohn-Sham system. A newly
developed algorithm which searches over ensemble v-representable densities [E.
Kraisler et al., Phys. Rev. A 80, 032115 (2009)] is employed in calculations.
It is found that for many atoms the ionization energies obtained with the GGA
are only modestly improved with respect to experimental data, as compared to
the LSDA. However, even in those groups of atoms where the improvement is
systematic, there remains a non-negligible difference with respect to the
experiment. The ab-initio electronic configuration in the Kohn-Sham reference
system does not always equal the configuration obtained from the spectroscopic
term within the independent-electron approximation. It was shown that use of
the latter configuration can prevent the energy-minimization process from
converging to the global minimum, e.g. in lanthanides. The spin values
calculated ab-initio fit the experiment for most atoms and are almost
unaffected by the choice of the xc-functional. Among the systems with
incorrectly obtained spin there exist some cases (e.g. V, Pt) for which the
result is found to be stable with respect to small variations in the
xc-approximation. These findings suggest a necessity for a significant
modification of the exchange-correlation functional, probably of a non-local
nature, to accurately describe such systems. PACS numbers: 31.15.
- …