1,914 research outputs found
Trajectory Generation for Assembly Tasks Via Bilateral Teleoperation
Abstract in UndeterminedFor assembly tasks, the knowledge of both trajectory and forces are usually required. Consequently, we may use kinesthetics or teleoperation for recording human demonstrations. In order to have a more natural interaction, the operator has to be provided with a sense of touch. We propose a bilateral teleoperation system which is customized for this purpose. We introduce different coordinate frames to make the design of a 6-DOF teleoperation straightforward. Moreover, we suggest using tele-admittance, which simplifies instructing the robot. The compliance due to the slave controller allows the robot to react quickly and reduces the risk of damaging the workpiece
Feedback from Central Black Holes in Elliptical Galaxies: Two-dimensional Models Compared to One-dimensional Models
We extend the black hole (BH) feedback models of Ciotti, Ostriker, and Proga
to two dimensions. In this paper, we focus on identifying the differences
between the one-dimensional and two-dimensional hydrodynamical simulations. We
examine a normal, isolated galaxy subject to the cooling flow instability
of gas in the inner regions. Allowance is made for subsequent star formation,
Type Ia and Type II supernovae, radiation pressure, and inflow to the central
BH from mildly rotating galactic gas which is being replenished as a normal
consequence of stellar evolution. The central BH accretes some of the infalling
gas and expels a conical wind with mass, momentum, and energy flux derived from
both observational and theoretical studies. The galaxy is assumed to have low
specific angular momentum in analogy with the existing one-dimensional case in
order to isolate the effect of dimensionality. The code then tracks the
interaction of the outflowing radiation and winds with the galactic gas and
their effects on regulating the accretion. After matching physical modeling to
the extent possible between the one-dimensional and two-dimensional treatments,
we find essentially similar results in terms of BH growth and duty cycle
(fraction of the time above a given fraction of the Eddington luminosity). In
the two-dimensional calculations, the cool shells forming at 0.1--1 kpc from
the center are Rayleigh--Taylor unstable to fragmentation, leading to a
somewhat higher accretion rate, less effective feedback, and a more irregular
pattern of bursting compared to the one-dimensional case.Comment: 15 pages, 10 figures, ApJ 237:26. Updated to match published versio
Chemical evolution of local post-starburst galaxies: Implications for the mass-metallicity relation
We use the stellar fossil record to constrain the stellar metallicity
evolution and star-formation histories of the post-starburst regions within 45
local post-starburst galaxies from the MaNGA survey. The direct measurement of
the regions' stellar metallicity evolution is achieved by a new two-step
metallicity model that allows for stellar metallicity to change at the peak of
the starburst. We also employ a Gaussian process noise model that accounts for
correlated errors introduced by the observational data reduction or
inaccuracies in the models. We find that a majority of post-starburst regions
(69% at significance) increased in stellar metallicity during the
recent starburst, with an average increase of 0.8 dex and a standard deviation
of 0.4 dex. A much smaller fraction of PSBs are found to have remained constant
(22%) or declined in metallicity (9%, average decrease 0.4 dex, standard
deviation 0.3 dex). The pre-burst metallicities of the post-starburst galaxies
are in good agreement with the mass-metallicity relation of local star-forming
galaxies. These results are consistent with hydrodynamic simulations, which
suggest that mergers between gas-rich galaxies are the primary formation
mechanism of local PSBs, and rapid metal recycling during the starburst
outweighs the impact of dilution by any gas inflows. The final mass-weighted
metallicities of the post-starburst galaxies are consistent with the
mass-metallicity relation of local passive galaxies. Our results suggest that
rapid quenching following a merger-driven starburst is entirely consistent with
the observed gap between the stellar mass-metallicity relations of local
star-forming and passive galaxies.Comment: 18+4 pages, 8+2 figures, submitted to MNRA
The Growth of Massive Black Holes in Galaxy Merger Simulations with Feedback by Radiation Pressure
We study the growth of massive black holes (BH) in galaxies using smoothed
particle hydrodynamic simulations of major galaxy mergers with new
implementations of BH accretion and feedback. The effect of BH accretion on gas
in its host galaxy is modeled by depositing momentum at a rate ~ tau L/c into
the ambient gas, where L is the luminosity produced by accretion onto the BH
and tau is the wavelength-averaged optical depth of the galactic nucleus to the
AGN's radiation (a free parameter of our model). The accretion rate onto the BH
is relatively independent of our subgrid accretion model and is instead
determined by the BH's dynamical impact on its host galaxy: BH accretion is
thus self-regulated rather than `supply limited.' We show that the final BH
mass and total stellar mass formed during a merger are more robust predictions
of the simulations than the time dependence of the star formation rate or BH
accretion rate. In particular, the latter depend on the assumed interstellar
medium physics, which determines when and where the gas fragments to form star
clusters; this in turn affects the fuel available for further star formation
and BH growth. Simulations over a factor of ~ 30 in galaxy mass are consistent
with the observed M_BH-sigma relation for a mean optical depth of tau ~ 25.
This requires that most BH growth occur when the galactic nucleus is optically
thick to far-infrared radiation, consistent with the hypothesized connection
between ultra-luminous infrared galaxies and quasars. We find tentative
evidence for a shallower M_BH-sigma relation in the lowest mass galaxies, sigma
< 100 km/s. Our results demonstrate that feedback-regulated BH growth and
consistency with the observed M_BH-sigma relation do not require that BH
feedback terminate star formation in massive galaxies or unbind large
quantities of cold gas.Comment: 21 pages, 17 figures, submitted MNRA
Sustainable natural adsorbents for heavy metal removal from wastewater: Lead sorption on pine bark (Pinus radiata D.Don)
Aqueous Pb(II) adsorption on pine bark (Pinus Radiata D.Don), an inexpensive and sustainable natural sorbent material, has been evaluated and the mechanism of metal retention characterized by scanning electron microscopy (SEM), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and X-ray photoelectron spectroscopy (XPS). Bark pulp densities >1.5 g l-1 achieve near 100% Pb(II) removal from aqueous solutions containing 100 mg l-1 Pb(II). Adsorption rates increased with pulp density, although adsorption capacity diminished at high densities because of blockage of adsorption sites. The effects of washing and sulfuric acid activation were assessed and found to be less important than in previous metal sorption studies. Pb(II) sorption takes place mainly at the lignocellulosic C-O groups, with adsorption at phenolic sites appearing to be most significant
X-ray properties expected from AGN feedback in elliptical galaxies
The ISM evolution of elliptical galaxies experiencing feedback from accretion
onto a central black hole was studied recently with high-resolution 1D
hydrodynamical simulations including radiative heating and pressure effects, a
RIAF-like radiative efficiency, mechanical input from AGN winds, and
accretion-driven starbursts. Here we focus on the observational properties of
the models in the X-ray band (nuclear luminosity; hot ISM luminosity and
temperature; temperature and brightness profiles during quiescence and during
outbursts). The nuclear bursts last for ~10^7 yr, with a duty-cycle of a few X
(10^-3-10^-2); the present epoch bolometric nuclear emission is very
sub-Eddington. The ISM thermal luminosity \lx oscillates in phase with the
nuclear one; this helps reproduce statistically the observed large \lx
variation. In quiescence the temperature profile has a negative gradient;
thanks to past outbursts, the brightness profile lacks the steep shape typical
of inflowing models. Outbursts produce disturbances in these profiles. Most
significantly, a hot bubble from shocked hot gas is inflated at the galaxy
center; the bubble would be conical in shape, and show radio emission. The ISM
resumes a smooth appearance on a time-scale of ~200 Myr; the duty-cycle of
perturbances in the ISM is of the order of 5-10%. From the present analysis,
additional input physics is important in the ISM-black hole coevolution, to
fully account for the properties of real galaxies, as a confining external
medium and a jet. The jet will reduce further the mass available for accretion
(and then the Eddington ratio ), and may help, together with an external
pressure, to produce flat or positive temperature gradient profiles (observed
in high density environments). Alternatively, can be reduced if the switch
from high to low radiative efficiency takes place at a larger than
routinely assumed.Comment: 40 pages, submitted to Ap
Vibrotactile pedals : provision of haptic feedback to support economical driving
The use of haptic feedback is currently an underused modality in the driving environment, especially with respect to vehicle manufacturers. This exploratory study evaluates the effects of a vibrotactile (or haptic) accelerator pedal on car driving performance and perceived workload using a driving simulator. A stimulus was triggered when the driver exceeded a 50% throttle threshold, past which is deemed excessive for economical driving. Results showed significant decreases in mean acceleration values, and maximum and excess throttle use when the haptic pedal was active as compared to a baseline condition. As well as the positive changes to driver behaviour, subjective workload decreased when driving with the haptic pedal as compared to when drivers were simply asked to drive economically. The literature suggests that the haptic processing channel offers a largely untapped resource in the driving environment, and could provide information without overloading the other attentional resource pools used in driving
Genetic Variance in the Adiponutrin Gene Family and Childhood Obesity
AIM: The adiponutrin gene family consists of five genes (PNPLA1-5) coding for proteins with both lipolytic and lipogenic properties. PNPLA3 has previously been associated with adult obesity. Here we investigated the possible association between genetic variants in these genes and childhood and adolescent obesity. METHODS/RESULTS: Polymorphisms in the five genes of the adiponutrin gene family were selected and genotyped using the Sequenom platform in a childhood and adolescent obesity case-control study. Six variants in PNPLA1 showed association with obesity (rs9380559, rs12212459, rs1467912, rs4713951, rs10947600, and rs12199580, p0.05). When analyzing these SNPs in relation to phenotypes, two SNPs in the PNPLA3 gene showed association with insulin sensitivity (rs12483959: beta = -0.053, p = 0.016, and rs2072907: beta = -0.049, p = 0.024). No associations were seen for PNPLA2, PNPLA4, and PNPLA5. CONCLUSIONS: Genetic variation in the adiponutrin gene family does not seem to contribute strongly to obesity in children and adolescents. PNPLA1 exhibited a modest effect on obesity and PNPLA3 on insulin sensitivity. These data, however, require confirmation in other cohorts and ethnic groups
Hybrid Stiff/Compliant Workspace Control for Robotized Minimally Invasive Surgery
Abstract-This paper presents a novel control architecture for hybrid stiff and compliant control for minimally invasive surgery which satisfies the constraints of zero lateral velocity at the entry point for serial manipulators. For minimally invasive surgery it is required that there is no sideways motion at the point where the robots enter the abdomen. This is necessary to avoid any damage to the patient's body when the robot moves. We solve this at a kinematic level, i.e., we find a Jacobian matrix that maps the velocities in joint space to the end-effector velocities and at the same time guarantees that certain velocities at the entry point are zero. Because the new velocity variables are defined in the end-effector workspace we can use these for hybrid motion/force control. The approach is verified experimentally by implementing hybrid stiff and compliant control of the end effector and we show that the insertion point constraints are always satisfied
A Deep HST H-Band Imaging Survey of Massive Gas-Rich Mergers. II. The QUEST PG QSOs
We report the results from a deep HST NICMOS H-band imaging survey of 28 z <
0.3 QSOs from the Palomar-Green (PG) sample. This program is part of QUEST
(Quasar / ULIRG Evolution STudy) and complements a similar set of data on 26
highly-nucleated ULIRGs presented in Paper I. Our analysis indicates that the
fraction of QSOs with elliptical hosts is higher among QSOs with undetected
far-infrared (FIR) emission, small infrared excess, and luminous hosts. The
hosts of FIR-faint QSOs show a tendency to have less pronounced merger-induced
morphological anomalies and larger QSO-to-host luminosity ratios on average
than the hosts of FIR-bright QSOs, consistent with late-merger evolution from
FIR-bright to FIR-faint QSOs. The spheroid sizes and total host luminosities of
the radio-quiet PG QSOs in our sample are statistically indistinguishable from
the ULIRG hosts presented in Paper I, while those of radio-loud PG QSOs are
systematically larger and more luminous. ULIRGs and PG QSOs with elliptical
hosts fall near, but not exactly on, the fundamental plane of inactive
spheroids. We confirm the systematic trend noted in Paper I for objects with
small (< 2 kpc) spheroids to be up to ~1 mag. brighter than inactive spheroids.
The host colors and wavelength dependence of their sizes support the idea that
these deviations are due at least in part to non-nuclear star formation.
However, the amplitudes of these deviations does not depend on host R-H colors.
Taken at face value (i.e., no correction for extinction or the presence of a
young stellar population), the H-band spheroid-host luminosities imply BH
masses ~5 -- 200 x 10^7 M_sun and sub-Eddington mass accretion rates for both
QSOs and ULIRGs. These results are compared with published BH mass estimates
derived from other methods. (abridged)Comment: Accepted for publication in the Astrophysical Journal, Vol. 701,
August 20 issue. Paper with high-resolution figures can be downloaded at
http://www.astro.umd.edu/~veilleux/pubs/nicmos2.pd
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