98 research outputs found
Ultralow phase noise microwave generation with an Er:fiber-based optical frequency divider
We present an optical frequency divider based on a 200 MHz repetition rate
Er:fiber mode-locked laser that, when locked to a stable optical frequency
reference, generates microwave signals with absolute phase noise that is equal
to or better than cryogenic microwave oscillators. At 1 Hz offset from a 10 GHz
carrier, the phase noise is below -100 dBc/Hz, limited by the optical
reference. For offset frequencies > 10 kHz, the phase noise is shot noise
limited at -145 dBc/Hz. An analysis of the contribution of the residual noise
from the Er:fiber optical frequency divider is also presented.Comment: 4 pages, 3 figure
Improving the Voter Experience: Reducing Polling Place Wait Times by Measuring Lines and Managing Polling Place Resources
Long lines at the polls can undermine the voting experience, even to the point of discouraging people from voting. Reducing polling place wait times by measuring lines and managing polling place resources can improve the voting experience
The New Realities of Voting by Mail in 2016
The vote-by-mail process can be more convenient for voters who are unable or unwilling to contend with lines at polling places on Election Day. However, voting by mail is not a voting option without risk. Outdated laws, new administrative policies, and the realities of the political process today introduce obstacles voters may not be aware of. Without recognizing that voting by mail in 2016 is very different than in years past, voters are more likely to unwittingly disenfranchise themselves
Evaluation of the 13N(α,p)16O thermonuclear reaction rate and its impact on the isotopic composition of supernova grains
It has been suggested that hydrogen ingestion into the helium shell of
massive stars could lead to high C and N excesses when the shock
of a core-collapse supernova passes through its helium shell. This prediction
questions the origin of extremely high C and N abundances
observed in rare presolar SiC grains which is usually attributed to classical
novae. In this context N(,p)O the reaction plays an
important role since it is in competition with N -decay to
C. The N(,p)O reaction rate used in stellar
evolution calculations comes from the CF88 compilation with very scarce
information on the origin of this rate. The goal of this work is to provide a
recommended N(,p)O reaction rate, based on available
experimental data. Unbound nuclear states in the F compound nucleus were
studied using the spectroscopic information of the analog states in O
nucleus that were measured at the Alto facility using the
C(Li,t)O alpha-transfer reaction, and spectroscopic factors
were derived using a DWBA analysis. This spectroscopic information was used to
calculate a recommended N(,p)O reaction rate with
meaningful uncertainty using a Monte Carlo approach. The present
N(,p)O reaction rate is found to be within a factor of
two of the previous evaluation, with a typical uncertainty of a factor 2-3. The
source of this uncertainty comes from the three resonances at , 741 and 959 keV. This new error estimation translates to an overall
uncertainty in the C production of a factor of 50. The main source of
uncertainty on the re-evaluated N(,p)O reaction rate
currently comes from the uncertain alpha-width of relevant F states
Frequency-stabilization to 6x10^-16 via spectral-hole burning
We demonstrate two-stage laser stabilization based on a combination of Fabry-
Perot and spectral-hole burning techniques. The laser is first pre-stabilized
by the Fabry-Perot cavity to a fractional-frequency stability of sigma_y(tau) <
10^-13. A pattern of spectral holes written in the absorption spectrum of
Eu3+:Y2SiO5 serves to further stabilize the laser to sigma_y(tau) = 6x10^-16
for 2 s < tau < 8 s. Measurements characterizing the frequency sensitivity of
Eu3+:Y2SiO5 spectral holes to environmental perturbations suggest that they can
be more frequency stable than Fabry-Perot cavities
Gas accretion onto planetary cores: three-dimensional self-gravitating radiation hydrodynamical calculations
We present results from three-dimensional, self-gravitating radiation
hydrodynamical models of gas accretion by planetary cores. In some cases, the
accretion flow is resolved down to the surface of the solid core -- the first
time such simulations have been performed. We investigate the dependence of the
gas accretion rate upon the planetary core mass, and the surface density and
opacity of the encompassing protoplanetary disc. Accretion of planetesimals is
neglected.
We find that high-mass protoplanets are surrounded by thick circumplanetary
discs during their gas accretion phase but, contrary to locally-isothermal
calculations, discs do not form around accreting protoplanets with masses ~<
50M_Earth when radiation hydrodynamical simulations are performed, even if the
grain opacity is reduced from interstellar values by a factor of 100. We find
that the opacity of the gas plays a large role in determining the accretion
rates for low-mass planetary cores. For example, reducing the opacities from
interstellar values by a factor of 100 leads to roughly an order of magnitude
increase in the accretion rates for 10-20M_Earth protoplanets. The dependence
on opacity becomes less important in determining the accretion rate for more
massive cores where gravity dominates the effects of thermal support and the
protoplanet is essentially accreting at the runaway rate. Finally, for low-mass
planetary cores (~< 20M_Earth), we obtain accretion rates that are in agreement
with previous one-dimensional quasi-static models. This indicates that
three-dimensional hydrodynamical effects may not significantly alter the gas
accretion timescales that have been obtained from quasi-static models.Comment: 16 pages, 15 figures, accepted for publication in MNRAS. V2 includes
small corrections to the radiation hydrodynamical accretion rates for a
Jupiter mass core, including an updated figure 8; conclusions are unaffecte
American Society for Bone and Mineral Research-Orthopaedic Research Society Joint Task Force Report on Cell-Based Therapies.
Cell-based therapies, defined here as the delivery of cells in vivo to treat disease, have recently gained increasing public attention as a potentially promising approach to restore structure and function to musculoskeletal tissues. Although cell-based therapy has the potential to improve the treatment of disorders of the musculoskeletal system, there is also the possibility of misuse and misrepresentation of the efficacy of such treatments. The medical literature contains anecdotal reports and research studies, along with web-based marketing and patient testimonials supporting cell-based therapy. Both the American Society for Bone and Mineral Research (ASBMR) and the Orthopaedic Research Society (ORS) are committed to ensuring that the potential of cell-based therapies is realized through rigorous, reproducible, and clinically meaningful scientific discovery. The two organizations convened a multidisciplinary and international Task Force composed of physicians, surgeons, and scientists who are recognized experts in the development and use of cell-based therapies. The Task Force was charged with defining the state-of-the art in cell-based therapies and identifying the gaps in knowledge and methodologies that should guide the research agenda. The efforts of this Task Force are designed to provide researchers and clinicians with a better understanding of the current state of the science and research needed to advance the study and use of cell-based therapies for skeletal tissues. The design and implementation of rigorous, thorough protocols will be critical to leveraging these innovative treatments and optimizing clinical and functional patient outcomes. In addition to providing specific recommendations and ethical considerations for preclinical and clinical investigations, this report concludes with an outline to address knowledge gaps in how to determine the cell autonomous and nonautonomous effects of a donor population used for bone regeneration. © 2019 American Society for Bone and Mineral Research
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American Society for Bone and Mineral Research-Orthopaedic Research Society Joint Task Force Report on Cell-Based Therapies - Secondary Publication.
Cell-based therapies, defined here as the delivery of cells in vivo to treat disease, have recently gained increasing public attention as a potentially promising approach to restore structure and function to musculoskeletal tissues. Although cell-based therapy has the potential to improve the treatment of disorders of the musculoskeletal system, there is also the possibility of misuse and misrepresentation of the efficacy of such treatments. The medical literature contains anecdotal reports and research studies, along with web-based marketing and patient testimonials supporting cell-based therapy. Both the American Society for Bone and Mineral Research (ASBMR) and the Orthopaedic Research Society (ORS) are committed to ensuring that the potential of cell-based therapies is realized through rigorous, reproducible, and clinically meaningful scientific discovery. The two organizations convened a multidisciplinary and international Task Force composed of physicians, surgeons, and scientists who are recognized experts in the development and use of cell-based therapies. The Task Force was charged with defining the state-of-the art in cell-based therapies and identifying the gaps in knowledge and methodologies that should guide the research agenda. The efforts of this Task Force are designed to provide researchers and clinicians with a better understanding of the current state of the science and research needed to advance the study and use of cell-based therapies for skeletal tissues. The design and implementation of rigorous, thorough protocols will be critical to leveraging these innovative treatments and optimizing clinical and functional patient outcomes. In addition to providing specific recommendations and ethical considerations for preclinical and clinical investigations, this report concludes with an outline to address knowledge gaps in how to determine the cell autonomous and nonautonomous effects of a donor population used for bone regeneration. © 2020 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:485-502, 2020
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