35 research outputs found
Asynchronous Decentralized Task Allocation for Dynamic Environments
This work builds on a decentralized task allocation algorithm for networked agents communicating through an asynchronous channel, by extending the Asynchronous Consensus-Based Bundle Algorithm (ACBBA) to account for more real time implementation issues resulting from a decentralized planner. This paper specfically talks to the comparisons between global and local convergence in asynchronous consensus algorithms. Also a feature called asynchronous replan is introduced to ACBBA's functionality that enables e ffcient updates to large changes in local situational awareness. A real-time software implementation using multiple agents communicating through the user datagram protocol (UDP) validates the proposed algorithm.United States. Air Force (grant FA9550-08-1-0086)United States. Air Force Office of Scientific Research (grant FA9550-08-1-0086)Aurora Flight Sciences Corp. (SBIR - FA8750-10-C-0107
Ultra-high-resolution spectroscopy of trapped ion ensembles in the Lamb-Dicke regime: demonstration and determination of the proton-electron mass ratio
Optical spectroscopy in the gas phase is one of the key tools for the
elucidation of the structure of atoms and molecules and their interaction with
external fields. The line resolution is usually limited by a combination of
first-order Doppler broadening due to particle thermal motion and of a short
transit time through the excitation beam. For trapped particles, suitable laser
cooling techniques can lead to strong confinement (Lamb-Dicke regime, LDR) and
thus to optical spectroscopy free of these effects. For non-laser coolable
ions, this has so far only been achieved when trapping one or two atomic ions,
together with a single laser-coolable atomic ion. Here we show that one-photon
optical LDR spectroscopy can also be obtained with more easily prepared
ensembles of ions, if performed in the mid-infrared spectral range. We
demonstrate the method on molecular ions, for which LDR vibrational
spectroscopy has not before been achieved. We trap approximately 100 molecular
hydrogen ions (HD) within a Coulomb cluster of a few thousand
laser-cooled atomic ions and perform laser spectroscopy of the fundamental
vibrational transition. To generate the appropriate spectroscopy radiation (5.1
m), a metrology-grade, mid-infrared laser source was developed. We obtain
fractional vibrational linewidths of , times smaller
than previous best results for one-photon vibrational spectroscopy of molecular
ions. Transition frequencies were determined with lowest uncertainties
fractionally. As an application, we determine the
proton-electron mass ratio by matching a precise calculation with
the measured vibrational frequency. The mass ratio is in agreement with the
most precise recent measurements and has a similar uncertainty. The present
technique is relatively simple and applicable to a large variety of molecular
ions.Comment: This version was submitted to Nature Physics. After an embargo
period, this version will be replaced by the version accepted for publicatio
Development of a strontium optical lattice clock for the SOC mission on the ISS
Ultra-precise optical clocks in space will allow new studies in fundamental
physics and astronomy. Within an European Space Agency (ESA) program, the Space
Optical Clocks (SOC) project aims to install and to operate an optical lattice
clock on the International Space Station (ISS) towards the end of this decade.
It would be a natural follow-on to the ACES mission, improving its performance
by at least one order of magnitude. The payload is planned to include an
optical lattice clock, as well as a frequency comb, a microwave link, and an
optical link for comparisons of the ISS clock with ground clocks located in
several countries and continents. Within the EU-FP7-SPACE-2010-1 project no.
263500, during the years 2011-2015 a compact, modular and robust strontium
lattice optical clock demonstrator has been developed. Goal performance is a
fractional frequency instability below 1x10^{-15}, tau^{-1/2} and a fractional
inaccuracy below 5x10^{-17}. Here we describe the current status of the
apparatus' development, including the laser subsystems. Robust preparation of
cold {88}^Sr atoms in a second stage magneto-optical trap (MOT) is achieved.Comment: 27 Pages, 15 figures, Comptes Rendus Physique 201
The Space Optical Clocks Project: Development of high-performance transportable and breadboard optical clocks and advanced subsystems
The use of ultra-precise optical clocks in space ("master clocks") will allow
for a range of new applications in the fields of fundamental physics (tests of
Einstein's theory of General Relativity, time and frequency metrology by means
of the comparison of distant terrestrial clocks), geophysics (mapping of the
gravitational potential of Earth), and astronomy (providing local oscillators
for radio ranging and interferometry in space). Within the ELIPS-3 program of
ESA, the "Space Optical Clocks" (SOC) project aims to install and to operate an
optical lattice clock on the ISS towards the end of this decade, as a natural
follow-on to the ACES mission, improving its performance by at least one order
of magnitude. The payload is planned to include an optical lattice clock, as
well as a frequency comb, a microwave link, and an optical link for comparisons
of the ISS clock with ground clocks located in several countries and
continents. Undertaking a necessary step towards optical clocks in space, the
EU-FP7-SPACE-2010-1 project no. 263500 (SOC2) (2011-2015) aims at two
"engineering confidence", accurate transportable lattice optical clock
demonstrators having relative frequency instability below 1\times10^-15 at 1 s
integration time and relative inaccuracy below 5\times10^-17. This goal
performance is about 2 and 1 orders better in instability and inaccuracy,
respectively, than today's best transportable clocks. The devices will be based
on trapped neutral ytterbium and strontium atoms. One device will be a
breadboard. The two systems will be validated in laboratory environments and
their performance will be established by comparison with laboratory optical
clocks and primary frequency standards. In this paper we present the project
and the results achieved during the first year.Comment: Contribution to European Frequency and Time Forum 2012, Gothenburg,
Swede
Derivation of ODEs and Bifurcation Analysis of a Two-DOF Airfoil Subjected to Unsteady Incompressible Flow
An airfoil subjected to two-dimensional incompressible inviscid flow is considered.
The airfoil is supported via a translational and a torsional springs. The aeroelastic
integro-differential equations of motion for the airfoil are reformulated into a system of
six first-order autonomous ordinary differential equations. These are the simplest and
least number of ODEs that can present this aeroelastic system. The differential equations are then used for the bifurcation analysis of an airfoil with a structural nonlinearity in the pitch direction. Sample bifurcation diagrams
showing both stable and unstable limit cycle oscillation are presented. The types of
bifurcations are assessed by evaluating the Floquet multipliers. For a specific case, a
period doubling route to chaos was detected, and mildly chaotic behavior in a narrow
range of velocity was confirmed via the calculation of the Lyapunov exponents
A FLUID DYNAMICS STUDY OF A MODIFIED LOW-REYNOLDS-NUMBER FLAPPING MOTION
ABSTRACT The objective of the present study is to investigate the low Reynolds number (LRN) fluid dynamics of an elliptic airfoil performing a novel figure-eight-like motion. To this mean, the influence of phase angle between the pitching and translational (heaving and lagging) motions and the amplitude of translational motions on the fluid flow is simulated. NavierStokes (NS) equations with Finite Volume Method (FVM) are used and the instantaneous force coefficients and the fluid dynamics performance, as well as the corresponding vortical structures are analyzed. Both the phase angle and the amplitudes of horizontal and vertical motions are of great importance to the fluid dynamic characteristics of the model as they are shown to change the peaks of the fluid forces, fluid dynamic performance, and the vortical patterns around the model. INTRODUCTION Forced and flow-induced oscillations are highly prevalent in a wide range of fluid engineering applications. These unsteady conditions could be useful when assisting in the generation of the fluid forces such as wing flapping, or be destructive when becoming the undesired oscillations such as wing flutter. Flapping motions are the most common means of force generation in micro aerial vehicles and swimming robots. The physical characteristics and the fluid phenomena of such motions strongly depend on the governing flow and system parameters. LRN flapping flows are mostly accompanied with non-linear vortex dynamics, such as dynamic stal
Cytochrome Oxidase Content and Respiratory Rates of Etiolated Wheat and Barley Seedlings.
Conference agenda: http://www.aiaa.org/agenda.cfm?lumeetingid=1998This paper analyzes task assignment for heterogeneous air vehicles using a guaranteed
conflict-free assignment algorithm, the Consensus Based Bundle Algorithm
(CBBA). We extend this recently proposed algorithm to handle two realistic multi-
UAV operational complications. Our rst extension accounts for obstacle regions in
order to generate collision free paths for UAVs. Our second extension reduces task
planner sensitivity to sensor measurement noise, and thereby minimizes churning
behavior in flight paths. After integrating our enhanced CBBA module with a 3D
visualization and interaction software tool, we simulate multiple aircraft servicing
stationary and moving ground targets. Preliminary simulation results establish
that consistent, conflict-free multi-UAV path assignments can be calculated on the
order of a few seconds. The enhanced CBBA consequently demonstrates signfi cant
potential for real-time performance in stressing environments
A Challenging Issue in the Etiology of Speech Problems: The Effect of Maternal Exposure to Electromagnetic Fields on Speech Problems in the Offspring
Background: Nowadays, mothers are continuously exposed to different sources of
electromagnetic fields before and even during pregnancy. It has recently been shown
that exposure to mobile phone radiation during pregnancy may lead to adverse effects
on the brain development in offspring and cause hyperactivity. Researchers have
shown that behavioral problems in laboratory animals which have a similar appearance
to ADHD are caused by intrauterine exposure to mobile phones.
Objective: The purpose of this study was to investigate whether the maternal
exposure to different sources of electromagnetic fields affect on the rate and severity
of speech problems in their offspring.
Methods: In this study, mothers of 35 healthy 3-5 year old children (control group)
and 77 children and diagnosed with speech problems who had been referred to a speech
treatment center in Shiraz, Iran were interviewed. These mothers were asked whether
they had exposure to different sources of electromagnetic fields such as mobile phones,
mobile base stations, Wi-Fi, cordless phones, laptops and power lines.
Results: We found a significant association between either the call time (P=0.002)
or history of mobile phone use (months used) and speech problems in the offspring
(P=0.003). However, other exposures had no effect on the occurrence of speech problems.
To the best of our knowledge, this is the first study to investigate a possible association
between maternal exposure to electromagnetic field and speech problems in
the offspring. Although a major limitation in our study is the relatively small sample
size, this study indicates that the maternal exposure to common sources of electromagnetic
fields such as mobile phones can affect the occurrence of speech problems in the
offspring