127,449 research outputs found
Scalable Co-Optimization of Morphology and Control in Embodied Machines
Evolution sculpts both the body plans and nervous systems of agents together
over time. In contrast, in AI and robotics, a robot's body plan is usually
designed by hand, and control policies are then optimized for that fixed
design. The task of simultaneously co-optimizing the morphology and controller
of an embodied robot has remained a challenge. In psychology, the theory of
embodied cognition posits that behavior arises from a close coupling between
body plan and sensorimotor control, which suggests why co-optimizing these two
subsystems is so difficult: most evolutionary changes to morphology tend to
adversely impact sensorimotor control, leading to an overall decrease in
behavioral performance. Here, we further examine this hypothesis and
demonstrate a technique for "morphological innovation protection", which
temporarily reduces selection pressure on recently morphologically-changed
individuals, thus enabling evolution some time to "readapt" to the new
morphology with subsequent control policy mutations. We show the potential for
this method to avoid local optima and converge to similar highly fit
morphologies across widely varying initial conditions, while sustaining fitness
improvements further into optimization. While this technique is admittedly only
the first of many steps that must be taken to achieve scalable optimization of
embodied machines, we hope that theoretical insight into the cause of
evolutionary stagnation in current methods will help to enable the automation
of robot design and behavioral training -- while simultaneously providing a
testbed to investigate the theory of embodied cognition
Networking Behavior in Thin Film and Nanostructure Growth Dynamics
Thin film coatings have been essential in development of several micro and
nano-scale devices. To realize thin film coatings various deposition techniques
are employed, each yielding surface morphologies with different characteristics
of interest. Therefore, understanding and control of the surface growth is of
great interest. In this paper, we devise a novel network-based modeling of the
growth dynamics of such thin films and nano-structures. We specifically map
dynamic steps taking place during the growth to components (e.g., nodes, links)
of a corresponding network. We present initial results showing that this
network-based modeling approach to the growth dynamics can simplify our
understanding of the fundamental physical dynamics such as shadowing and
re-emission effects
Dynamic evolution of interface roughness during friction and wear processes
Dynamic evolution of surface roughness and influence of initial roughness (Sa=0.282 to 6.73 µm) during friction and wear processes has been analyzed experimentally. The mirror polished and rough surfaces (28 samples in total) have been prepared by surface polishing on Ti-6Al-4V and AISI 1045 samples. Friction and wear have been tested in classical sphere/plane configuration using linear reciprocating tribometer with very small displacement from 130 to 200 microns. After an initial period of rapid degradation, dynamic evolution of surface roughness converges to certain level specific to a given tribosystem. However, roughness at such dynamic interface is still increasing and analysis of initial roughness influence revealed that to certain extent, a rheology effect of interface can be observed and dynamic evolution of roughness will depend on initial condition and history of interface roughness evolution. Multiscale analysis shows that morphology created in wear process is composed from nano, micro and macro scale roughness. Therefore, mechanical parts working under very severe contact conditions, like rotor/blade contact, screws, clutch etc. with poor initial surface finishing are susceptible to have much shorter lifetime than a quality finished parts
VSI: the VLTI spectro-imager
The VLTI Spectro Imager (VSI) was proposed as a second-generation instrument
of the Very Large Telescope Interferometer providing the ESO community with
spectrally-resolved, near-infrared images at angular resolutions down to 1.1
milliarcsecond and spectral resolutions up to R=12000. Targets as faint as K=13
will be imaged without requiring a brighter nearby reference object. The unique
combination of high-dynamic-range imaging at high angular resolution and high
spectral resolution enables a scientific program which serves a broad user
community and at the same time provides the opportunity for breakthroughs in
many areas of astrophysic including: probing the initial conditions for planet
formation in the AU-scale environments of young stars; imaging convective cells
and other phenomena on the surfaces of stars; mapping the chemical and physical
environments of evolved stars, stellar remnants, and stellar winds; and
disentangling the central regions of active galactic nuclei and supermassive
black holes. VSI will provide these new capabilities using technologies which
have been extensively tested in the past and VSI requires little in terms of
new infrastructure on the VLTI. At the same time, VSI will be able to make
maximum use of new infrastructure as it becomes available; for example, by
combining 4, 6 and eventually 8 telescopes, enabling rapid imaging through the
measurement of up to 28 visibilities in every wavelength channel within a few
minutes. The current studies are focused on a 4-telescope version with an
upgrade to a 6-telescope one. The instrument contains its own fringe tracker
and tip-tilt control in order to reduce the constraints on the VLTI
infrastructure and maximize the scientific return.Comment: 12 pages, to be published in Proc. SPIE conference 7013 "Optical and
Infrared Interferometry", Schoeller, Danchi, and Delplancke, F. (eds.). See
also http://vsi.obs.ujf-grenoble.f
Dynamic clonal progression in xenografts of acute lymphoblastic leukemia with intrachromosomal amplification of chromosome 21
Intrachromosomal amplification of chromosome 21 is a heterogeneous chromosomal rearrangement occurring in 2% of childhood precursor B-cell acute lymphoblastic leukemia. There are no cell lines with iAMP21 and these abnormalities are too complex to faithfully engineer in animal models. As a resource for future functional and pre-clinical studies, we have created xenografts from intrachromosomal amplification of chromosome 21 leukemia patient blasts and characterised them by in-vivo and ex-vivo luminescent imaging, FLOW immunophenotyping, and histological and ultrastructural analysis of bone marrow and the central nervous system. Investigation of up to three generations of xenografts revealed phenotypic evolution, branching genomic architecture and, compared with other B-cell acute lymphoblastic leukemia genetic subtypes, greater clonal diversity of leukemia initiating cells. In support of intrachromosomal amplification of chromosome 21 as a primary genetic abnormality, it was always retained through generations of xenografts, although we also observed the first example of structural evolution of this rearrangement. Clonal segregation in xenografts revealed convergent evolution of different secondary genomic abnormalities implicating several known tumour suppressor genes and a region, containing the B-cell adaptor, PIK3AP1, and nuclear receptor co-repressor, LCOR, in the progression of B-ALL. Tracking of mutations in patients and derived xenografts provided evidence for co-operation between abnormalities activating the RAS pathway in B-ALL and for their aggressive clonal expansion in the xeno-environment. Bi-allelic loss of the CDKN2A/B locus was recurrently maintained or emergent in xenografts and also strongly selected as RNA sequencing demonstrated a complete absence of reads for genes associated with the deletions
Radial Gas Flows in Colliding Galaxies: Connecting Simulations and Observations
(abridged) We investigate the detailed response of gas to the formation of
transient and long-lived dynamical structures induced in the early stages of a
disk-disk collision, and identify observational signatures of radial gas inflow
through a detailed examination of the collision simulation of an equal mass
bulge dominated galaxy. Stars respond to the tidal interaction by forming both
transient arms and long lived m=2 bars, but the gas response is more transient,
flowing directly toward the central regions within about 10^8 years after the
initial collision. The rate of inflow declines when more than half of the total
gas supply reaches the inner few kpc, where the gas forms a dense nuclear ring
inside the stellar bar. The average gas inflow rate to the central 1.8 kpc is
\~7 Msun/yr with a peak rate of 17 Msun/yr. The evolution of gas in a bulgeless
progenitor galaxy is also discussed, and a possible link to the ``chain
galaxy'' population observed at high redshifts is inferred. The evolution of
the structural parameters (the asymmetry and concentration) of both stars and
gas are studied in detail. Further, a new structural parameter (the compactness
parameter K) that traces the evolution of the size scale of the gas relative to
the stellar disk is introduced. Non-circular gas kinematics driven by the
perturbation of the non-axisymmetric structure can produce distinct emission
features in the "forbidden velocity quadrants'' of the position-velocity
diagram (PVD). The dynamical mass calculated using the rotation curve derived
from fitting the emission envelope of the PVD can determine the true mass to
within 20% to 40%. The evolution of the molecular fraction $M_H2/M_(H2 + HI)
and the compactness (K) are potential tracers to quantitatively assign the age
of the interaction.Comment: 52 pages, 20 figures (9 jpgs), accepted for publication in ApJ
Version with all figures at http://cfa-www.harvard.edu/~diono/ms.ps.g
- …