22,207 research outputs found
Eliminating the Hadronic Uncertainty
The Standard Model Lagrangian requires the values of the fermion masses, the
Higgs mass and three other experimentally well-measured quantities as input in
order to become predictive. These are typically taken to be ,
and . Using the first of these, however, introduces a hadronic
contribution that leads to a significant error. If a quantity could be found
that was measured at high energy with sufficient precision then it could be
used to replace as input. The level of precision required for this to
happen is given for a number of precisely-measured observables. The boson
mass must be measured with an error of \,MeV, to \,MeV
and polarization asymmetry, , to that would seem to be the
most promising candidate. The r\^ole of renormalized parameters in perturbative
calculations is reviewed and the value for the electromagnetic coupling
constant in the renormalization scheme that is consistent
with all experimental data is obtained to be .Comment: 8 pages LaTeX2
Additional support for the TDK/MABL computer program
An advanced version of the Two-Dimensional Kinetics (TDK) computer program was developed under contract and released to the propulsion community in early 1989. Exposure of the code to this community indicated a need for improvements in certain areas. In particular, the TDK code needed to be adapted to the special requirements imposed by the Space Transportation Main Engine (STME) development program. This engine utilizes injection of the gas generator exhaust into the primary nozzle by means of a set of slots. The subsequent mixing of this secondary stream with the primary stream with finite rate chemical reaction can have a major impact on the engine performance and the thermal protection of the nozzle wall. In attempting to calculate this reacting boundary layer problem, the Mass Addition Boundary Layer (MABL) module of TDK was found to be deficient in several respects. For example, when finite rate chemistry was used to determine gas properties, (MABL-K option) the program run times became excessive because extremely small step sizes were required to maintain numerical stability. A robust solution algorithm was required so that the MABL-K option could be viable as a rocket propulsion industry design tool. Solving this problem was a primary goal of the phase 1 work effort
Ignorance is bliss: General and robust cancellation of decoherence via no-knowledge quantum feedback
A "no-knowledge" measurement of an open quantum system yields no information
about any system observable; it only returns noise input from the environment.
Surprisingly, performing such a no-knowledge measurement can be advantageous.
We prove that a system undergoing no-knowledge monitoring has reversible noise,
which can be cancelled by directly feeding back the measurement signal. We show
how no-knowledge feedback control can be used to cancel decoherence in an
arbitrary quantum system coupled to a Markovian reservoir that is being
monitored. Since no-knowledge feedback does not depend on the system state or
Hamiltonian, such decoherence cancellation is guaranteed to be general, robust
and can operate in conjunction with any other quantum control protocol. As an
application, we show that no-knowledge feedback could be used to improve the
performance of dissipative quantum computers subjected to local loss.Comment: 6 pages + 2 pages supplemental material, 3 figure
A planning language for activity scheduling
Mission planning and scheduling of spacecraft operations are becoming more complex at NASA. Described here are a mission planning process; a robust, flexible planning language for spacecraft and payload operations; and a software scheduling system that generates schedules based on planning language inputs. The mission planning process often involves many people and organizations. Consequently, a planning language is needed to facilitate communication, to provide a standard interface, and to represent flexible requirements. The software scheduling system interprets the planning language and uses the resource, time duration, constraint, and alternative plan flexibilities to resolve scheduling conflicts
Controlled Nanoparticle Formation by Diffusion Limited Coalescence
Polymeric nanoparticles (NPs) have a great application potential in science
and technology. Their functionality strongly depends on their size. We present
a theory for the size of NPs formed by precipitation of polymers into a bad
solvent in the presence of a stabilizing surfactant. The analytical theory is
based upon diffusion-limited coalescence kinetics of the polymers.
Two relevant time scales, a mixing and a coalescence time, are identified and
their ratio is shown to determine the final NP diameter. The size is found to
scale in a universal manner and is predominantly sensitive to the mixing time
and the polymer concentration if the surfactant concentration is sufficiently
high. The model predictions are in good agreement with experimental data. Hence
the theory provides a solid framework for tailoring nanoparticles with a priori
determined size.Comment: 4 pages, 3 figure
In vivo whole-cell recording from morphologically identified mouse superior colliculus neurons
In vivo whole-cell recording when combined with morphological
characterization after biocytin labeling is a powerful technique to study
subthreshold synaptic processing in cell-type-identified neuronal populations.
Here, we provide a step-by-step procedure for performing whole-cell recordings
in the superior colliculus of urethane-anesthetized mice, a major visual
processing region in the rodent brain. Two types of visual stimulation methods
are described. While we focus on superior colliculus neurons, this protocol is
applicable to other brain areas.Comment: 29 pages including 4 figure
Prospects for Redshifted 21-cm observations of quasar HII regions
The introduction of low-frequency radio arrays over the coming decade is
expected to revolutionize the study of the reionization epoch. Observation of
the contrast in redshifted 21cm emission between a large HII region and the
surrounding neutral IGM will be the simplest and most easily interpreted
signature. We find that an instrument like the planned Mileura Widefield Array
Low-Frequency Demonstrator (LFD) will be able to obtain good signal to noise on
HII regions around the most luminous quasars, and determine some gross
geometric properties, e.g. whether the HII region is spherical or conical. A
hypothetical follow-up instrument with 10 times the collecting area of the LFD
(MWA-5000) will be capable of mapping the detailed geometry of HII regions,
while SKA will be capable of detecting very narrow spectral features as well as
the sharpness of the HII region boundary. The MWA-5000 will discover
serendipitous HII regions in widefield observations. We estimate the number of
HII regions which are expected to be generated by quasars. Assuming a late
reionization at z~6 we find that there should be several tens of quasar HII
regions larger than 4Mpc at z~6-8 per field of view. Identification of HII
regions in forthcoming 21cm surveys can guide a search for bright galaxies in
the middle of these regions. Most of the discovered galaxies would be the
massive hosts of dormant quasars that left behind fossil HII cavities that
persisted long after the quasar emission ended, owing to the long recombination
time of intergalactic hydrogen. A snap-shot survey of candidate HII regions
selected in redshifted 21cm image cubes may prove to be the most efficient
method for finding very high redshift quasars and galaxies.Comment: 14 pages, 8 figures. Submitted to Ap
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