4,751 research outputs found
Dynamic modeling of fluid transmission lines of the DSN 70-meter antennas by using a lumped parameter model
Fluid transmission lines and fittings were found to significantly affect the dynamic and steady state operation of the engineering system in which they are incorporated. Therefore, a better understanding of the operation of a system can be obtained by including the performance of the transmission lines and fittings within the system model. The most accurate model of a transmission line or fitting is obtained by using a distributed parameter model. However, a distributed parameter model tends to be very complex. This complexity can be avoided without significant loss of model accuracy by using a lumped parameter model when the length of the fluid path through the transmission line or fitting is short. This article develops a lumped parameter model for short fluid transmission lines and fittings, describes the conditions under which the model is valid, and presents the model parameters associated with the servo hydraulic system of the Deep Space Network (DSN) 70-meter antennas
Reducing the net torque and flow ripple effects of multiple hydraulic piston motor drives
The torque and flow ripple effects which result when multiple hydraulic motors are used to drive a single motion of a mechanical device can significantly affect the way in which the device performs. This article presents a mathematical model describing the torque and flow ripple effects of a bent-axis hydraulic piston motor. The model is used to show how the ripple magnitude can be reduced when multiple motors are used to drive a motion. A discussion of the hydraulic servo system of the 70-m antennas located with the Deep Space Network is included to demonstrate the application of the concepts presented
Dynamic modeling of the servovalves incorporated in the servo hydraulic system of the 70-meter DSN antennas
As the pointing accuracy and service life requirements of the DSN 70 meter antenna increase, it is necessary to gain a more complete understanding of the servo hydraulic system in order to improve system designs to meet the new requirements. A mathematical model is developed for the servovalve incorporated into the hydraulic system of the 70 meter antenna and uses experimental data to verify the validity of the model and to identify the model parameters
Probing and manipulating valley coherence of dark excitons in monolayer WSe
Monolayers of semiconducting transition metal dichalcogenides are
two-dimensional direct-gap systems which host tightly-bound excitons with an
internal degree of freedom corresponding to the valley of the constituting
carriers. Strong spin-orbit interaction and the resulting ordering of the
spin-split subbands in the valence and conduction bands makes the lowest-lying
excitons in WX (X~being S or Se) spin-forbidden and optically dark. With
polarization-resolved photoluminescence experiments performed on a WSe
monolayer encapsulated in a hexagonal boron nitride, we show how the intrinsic
exchange interaction in combination with the applied in-plane and/or
out-of-plane magnetic fields enables one to probe and manipulate the valley
degree of freedom of the dark excitons.Comment: Manuscript: 6 pages, 3 figures; SM: 6 pages, 5 figure
Reassessing candidate eccentric binary black holes: Results with a model including higher-order modes
The detection of eccentricity from a gravitational wave signal is expected to
help distinguish between formation channels for a given binary. In this study,
we reassess all previously-reported binary black holes with previous claims of
possible eccentricity as well as a few binaries with more interesting source
parameters, for the first time using a model (TEOBResumSGeneral) which accounts
for the full eccentricity range possible and incorporates higher-order
gravitational emission critical to model emission from highly eccentric orbits.
We estimate the eccentricity of these five events. For the first time, we
present marginal evidence of eccentricity for one of the events: GW190929.
Contrary to previous work with different settings, we do not find evidence
supporting eccentric orbits for the same systems. We find the incorporation of
eccentricity in our analyses dramatically shifts the posterior in multiple
parameters for several events, features could negatively impact other analyses
Singlet and triplet trions in WS monolayer encapsulated in hexagonal boron nitride
Embedding a WS monolayer in flakes of hexagonal boron nitride allowed us
to resolve and study the photoluminescence response due to both singlet and
triplet states of negatively charged excitons (trions) in this atomically thin
semiconductor. The energy separation between the singlet and triplet states has
been found to be relatively small reflecting rather weak effects of the
electron-electron exchange interaction for the trion triplet in a WS
monolayer, which involves two electrons with the same spin but from different
valleys. Polarization-resolved experiments demonstrate that the helicity of the
excitation light is better preserved in the emission spectrum of the triplet
trion than in that of the singlet trion. Finally, the singlet (intravalley)
trions are found to be observable even at ambient conditions whereas the
emission due to the triplet (intervalley) trions is only efficient at low
temperatures.Comment: 11 pages, 4 figure
First version of the fiber injection unit for the Keck Planet Imager and Characterizer
Coupling a high-contrast imaging instrument to a high-resolution spectrograph has the potential to enable the most detailed characterization of exoplanet atmospheres, including spin measurements and Doppler mapping. The high-contrast imaging system serves as a spatial filter to separate the light from the star and the planet while the high-resolution spectrograph acts as a spectral filter, which differentiates between features in the stellar and planetary spectra. The Keck Planet Imager and Characterizer (KPIC) located downstream from the current W. M. Keck II adaptive optics (AO) system will contain a fiber injection unit (FIU) combining a high-contrast imaging system and a fiber feed to Keck’s high resolution infrared spectrograph NIRSPEC. Resolved thermal emission from known young giant exoplanets will be injected into a single-mode fiber linked to NIRSPEC, thereby allowing the spectral characterization of their atmospheres. Moreover, the resolution of NIRSPEC (R = 37,500 after upgrade) is high enough to enable spin measurements and Doppler imaging of atmospheric weather phenomenon. The module was integrated at Caltech and shipped to Hawaii at the beginning of 2018 and is currently undergoing characterization. Its transfer to Keck is planned in September and first on-sky tests sometime in December
First version of the fiber injection unit for the Keck Planet Imager and Characterizer
Coupling a high-contrast imaging instrument to a high-resolution spectrograph has the potential to enable the most detailed characterization of exoplanet atmospheres, including spin measurements and Doppler mapping. The high-contrast imaging system serves as a spatial filter to separate the light from the star and the planet while the high-resolution spectrograph acts as a spectral filter, which differentiates between features in the stellar and planetary spectra. The Keck Planet Imager and Characterizer (KPIC) located downstream from the current W. M. Keck II adaptive optics (AO) system will contain a fiber injection unit (FIU) combining a high-contrast imaging system and a fiber feed to Keck’s high resolution infrared spectrograph NIRSPEC. Resolved thermal emission from known young giant exoplanets will be injected into a single-mode fiber linked to NIRSPEC, thereby allowing the spectral characterization of their atmospheres. Moreover, the resolution of NIRSPEC (R = 37,500 after upgrade) is high enough to enable spin measurements and Doppler imaging of atmospheric weather phenomenon. The module was integrated at Caltech and shipped to Hawaii at the beginning of 2018 and is currently undergoing characterization. Its transfer to Keck is planned in September and first on-sky tests sometime in December
Contributions of semi-hadronic states to amm of muon, in frames of Nambu-Jona-Lasinio model
We calculate the contribution of semi-hadronic states with pseudoscalar
and scalar ((550))meson accompanied with real photon as
an intermediate state of a heavy photon to the anomalous magnetic moment of
muon. We consider the intermediate states with and as a
hadrons in frames of Nambu-Jona-Lasinio model. The contribution of
state is in agreement with results obtained in previous
theoretical considerations as well as with experimental data
, besides we estimate
We
discass as well the LbL mechanism with Comment: 6 pages, 2 figure
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