2,093 research outputs found
Cavity optomechanics with stoichiometric SiN films
We study high-stress SiN films for reaching the quantum regime with
mesoscopic oscillators connected to a room-temperature thermal bath, for which
there are stringent requirements on the oscillators' quality factors and
frequencies. Our SiN films support mechanical modes with unprecedented products
of mechanical quality factor and frequency reaching Hz. The SiN membranes exhibit a low optical absorption
characterized by Im at 935 nm, representing a 15 times
reduction for SiN membranes. We have developed an apparatus to simultaneously
cool the motion of multiple mechanical modes based on a short, high-finesse
Fabry-Perot cavity and present initial cooling results along with future
possibilities.Comment: 4 pages, 5 figure
A sub-kpc-scale binary AGN with double narrow-line regions
We present the kinematic properties of a type-2 QSO, SDSS J132323.33-015941.9
at z~0.35, based on the analysis of Very Large Telescope integral field
spectroscopy and Hubble Space Telescope (HST) imaging, which suggest that the
target is a binary active galactic nucleus (AGN) with double narrow-line
regions. The QSO features double-peaked emission lines ([OIII] and Hb) which
can be decomposed into two kinematic components. The flux-weighted centroids of
the blue and red components are separated by ~0.2" (0.8 kpc in projection) and
coincide with the location of the two stellar cores detected in the HST
broad-band images, implying that both stellar cores host an active black hole.
The line-of-sight velocity of the blue component is comparable to the
luminosity-weighted velocity of stars in the host galaxy while the red
component is redshifted by ~240 km/s, consistent with typical velocity offsets
of two cores in a late stage of a galaxy merger. If confirmed, the target is
one of the rare cases of sub-kpc scale binary AGNs, providing a test-bed for
understanding the binary AGN population.Comment: 5 pages, 3 figure
Do Naked Singularities Form?
A naked singularity is formed by the collapse of a Sine-Gordon soliton in 1+1
dimensional dilaton gravity with a negative cosmological constant. We examine
the quantum stress tensor resulting from the formation of the singularity.
Consistent boundary conditions require that the incoming soliton is accompanied
by a flux of incoming radiation across past null infinity, but neglecting the
back reaction of the spacetime leads to the absurd conclusion that the total
energy entering the system by the time the observer is able to receive
information from the singularity is infinite. We conclude that the back
reaction must prevent the formation of the naked singularity.Comment: 7 pages (21 Kb), PHYZZX. Revised version to appear in Class. & Quant.
Grav. Letts. A discussion of the consistency of the Sine-Gordon model is
include
OPTIMASS: A Package for the Minimization of Kinematic Mass Functions with Constraints
Reconstructed mass variables, such as , , , and
, play an essential role in searches for new physics at hadron
colliders. The calculation of these variables generally involves constrained
minimization in a large parameter space, which is numerically challenging. We
provide a C++ code, OPTIMASS, which interfaces with the MINUIT library to
perform this constrained minimization using the Augmented Lagrangian Method.
The code can be applied to arbitrarily general event topologies and thus allows
the user to significantly extend the existing set of kinematic variables. We
describe this code and its physics motivation, and demonstrate its use in the
analysis of the fully leptonic decay of pair-produced top quarks using the
variables.Comment: 39 pages, 12 figures, (1) minor revision in section 3, (2) figure
added in section 4.3, (3) reference added and (4) matched with published
versio
Maximized performance of dye solar cells on plastic: a combined theoretical and experimental optimization approach
We demonstrate that a combined optimization approach based on the sequential alternation of theoretical analysis and experimental realization gives rise to plastic supported dye solar cells for which both light harvesting efficiency and electron collection are maximized. Rationalized configurations with optimized light trapping and charge extraction are realized to achieve photoanodes on plastic prepared at low temperature, showing a power conversion efficiency of 8.55% and a short circuit photocurrent of 16.11 mA cm 2, unprecedented for plastic based dye solar cell devices. Furthermore, the corresponding fully flexible designs present stable mechanical properties after several bending cycles, displaying 7.79% power conversion efficiency, an average broadband internal quantum efficiency above 90%, and a short circuit photocurrent of 15.94 mA cm 2, which is the largest reported value for bendable cells of this sort to dateEuropean Union 307081, 622533Ministerio de EconomÃa y Competitividad MAT2014-54852-R, MAT2011–2359
Lingulodinium machaerophorum expansion over the last centuries in the Caspian Sea reflects global warming
This article is made available through the Brunel Open Access Publishing Fund. Copyright @ Author(s) 2012. This work is distributed
under the Creative Commons Attribution 3.0 License.We analysed dinoflagellate cyst assemblages in four short sediment cores, two of them dated by radionuclides, taken in the south basin of the Caspian Sea. The interpretation of the four sequences is supported by a collection of 27 lagoonal or marine surface sediment samples. A sharp increase in the biomass of the dinocyst occurs after 1967, especially owing to Lingulodinium machaerophorum. Considering nine other cores covering parts or the whole of Holocene, this species started to develop in the Caspian Sea only during the last three millennia. By analysing instrumental data and collating existing reconstructions of sea level changes over the last few millennia, we show that the main forcing of the increase of L. machaerophorum percentages and of the recent dinocyst abundance is global climate change, especially sea surface temperature increase. Sea level fluctuations likely have a minor impact. We argue that the Caspian Sea has entered the Anthropocene
Path Tracking Controller of Quadruped Robot for Obstacle Avoidance Using Potential Functions Method
This paper proposes a tracking controller for obstacle avoidance of a quadruped robot using potential functions method. The followings are done for this task. At first, a ceiling-mounted camera system is installed for image processing. The goal point and obstacles are separated and recognized by a color recognition method. Second, a path planning algorithm using potential functions method is proposed to generate the path to avoid obstacles and to plan a path for the quadruped robot to reach from start point to goal point. Third, a quadruped robot is chosen as the mobile platform for this study and the kinematic model for the robot is presented. Fourth, a tracking controller is designed for the quadruped robot to track the trajectory based on the backstepping method using Lyapunov function. Finally, the simulation results are presented to show the effectiveness of the proposed trajectory planning algorithm and the tracking controller. [Keywords— Path tracking; back stepping; obstacles avoidance; potential functions; quadruped robot]
- …