156 research outputs found
Using colocation to support human memory
The progress of health care in the western world has been
marked by an increase in life expectancy. Advances in life
expectancy have meant that more people are living with
acute health problems, many of which are related to impairment
of memory. This paper describes a pair of scenarios
that use RFID to assist people who may suffer frommemory
defects to extend their capability for independent living. We
present our implementation of an RFID glove, describe its
operation, and show how it enables the application scenarios
Los Angeles County Tree Canopy Assessment
This project applied the USDA Forest Service’s Tree Canopy Assessment protocols to the City of Los Angeles. The analysis was conducted using imagery and LiDAR acquired in 2016 provided through the Los Angeles Region Imagery Acquisition Consortium program.
The assessment was funded by a grant to TreePeople and carried out by SavATree in collaboration with the Center for Urban Resilience at Loyola Marymount University, the Spatial Analysis Laboratory at the University of Vermont’s Rubenstein School of the Environment and Natural Resources, and Dr. Dexter Locke.https://digitalcommons.lmu.edu/cures_reports/1005/thumbnail.jp
Femtosecond-Terawatt Hard X Ray Pulse Generation with Chirped Pulse Amplification on a Free Electron Laser
Advances of high intensity lasers have opened up the field of strong field
physics and led to a broad range of technological applications. Recent x ray
laser sources and optics development makes it possible to obtain extremely high
intensity and brightness at x ray wavelengths. In this paper, we present a
system design that implements chirped pulse amplification for hard x ray free
electron lasers. Numerical modeling with realistic experimental parameters show
that near-transform-limit single-femtosecond hard x ray laser pulses with peak
power exceeding 1 TW and brightness exceeding
smmmrad0.1\%bandwdith can be
consistently generated. Realization of such beam qualities is essential for
establishing systematic and quantitative understanding of strong field x-ray
physics and nonlinear x ray optics phenomena.Comment: 23 pages, 7 figures, Accepted by PR
Quantitative single-molecule microscopy reveals that CENP-A(Cnp1) deposition occurs during G2 in fission yeast
The inheritance of the histone H3 variant CENP-A in nucleosomes at centromeres following DNA replication is mediated by an epigenetic mechanism. To understand the process of epigenetic inheritance, or propagation of histones and histone variants, as nucleosomes are disassembled and reassembled in living eukaryotic cells, we have explored the feasibility of exploiting photo-activated localization microscopy (PALM). PALM of single molecules in living cells has the potential to reveal new concepts in cell biology, providing insights into stochastic variation in cellular states. However, thus far, its use has been limited to studies in bacteria or to processes occurring near the surface of eukaryotic cells. With PALM, one literally observes and 'counts' individual molecules in cells one-by-one and this allows the recording of images with a resolution higher than that determined by the diffraction of light (the so-called super-resolution microscopy). Here, we investigate the use of different fluorophores and develop procedures to count the centromere-specific histone H3 variant CENP-A(Cnp1) with single-molecule sensitivity in fission yeast (Schizosaccharomyces pombe). The results obtained are validated by and compared with ChIP-seq analyses. Using this approach, CENP-A(Cnp1) levels at fission yeast (S. pombe) centromeres were followed as they change during the cell cycle. Our measurements show that CENP-A(Cnp1) is deposited solely during the G2 phase of the cell cycle
Intrinsic ELMing in ASDEX Upgrade and global control system-plasma self-entrainment
It is well established that edge localized modes can be entrained to the frequency of applied global magnetic perturbations. These perturbations are delivered to the plasma using the vertical control system field coil currents. These field coils are part of an active control system that is required to maintain the plasma in a steady state. We perform time domain timeseries analysis of natural ELMing when there are no applied perturbations in the ASDEX Upgrade tokamak. We find that the plasma can transition into a state in which the control system field coil currents continually oscillate and are synchronized with oscillations in characteristic plasma parameters such as plasma edge position and total MHD energy. These synchronous oscillations have a one-to-one correlation with the naturally occurring ELMs; the ELMs all occur when the control system coil current is around a specific temporal phase. Large and small ELMs may be distinguished by the amplitude of inward movement of the edge following an ELM. Large ELMs are then found to occur preferentially around a specific temporal phase of the vertical position control coil current. Small ELMs are most likely in antiphase to this. The large and small natural ELMs occur at the opposite extrema of the oscillations in the control system vertical position control coil current. The control system coil current phase may thus provide a useful parameter to order the observed ELM dynamics. We have identified a class of natural ELMing which is a self-entrained state, in which there is a continual non-linear feedback between the global plasma dynamics and the active control system that is intrinsic to the cyclic dynamics of naturally occurring ELMs. Control system-plasma feedback thus becomes an essential component for integration into future models of natural ELM dynamics
Numerical study of tearing mode seeding in tokamak X-point plasma
A detailed understanding of island seeding is crucial to avoid (N)TMs and
their negative consequences like confinement degradation and disruptions. In
the present work, we investigate the growth of 2/1 islands in response to
magnetic perturbations. Although we use externally applied perturbations
produced by resonant magnetic perturbation (RMP) coils for this study, results
are directly transferable to island seeding by other MHD instabilities creating
a resonant magnetic field component at the rational surface. Experimental
results for 2/1 island penetration from ASDEX Upgrade are presented extending
previous studies. Simulations are based on an ASDEX Upgrade L-mode discharge
with low collisionality and active RMP coils. Our numerical studies are
performed with the 3D, two fluid, non-linear MHD code JOREK. All three phases
of mode seeding observed in the experiment are also seen in the simulations:
first a weak response phase characterized by large perpendicular electron flow
velocities followed by a fast growth of the magnetic island size accompanied by
a reduction of the perpendicular electron velocity, and finally the saturation
to a fully formed island state with perpendicular electron velocity close to
zero. Thresholds for mode penetration are observed in the plasma rotation as
well as in the RMP coil current. A hysteresis of the island size and electron
perpendicular velocity is observed between the ramping up and down of the RMP
amplitude consistent with an analytically predicted bifurcation. The transition
from dominant kink/bending to tearing parity during the penetration is
investigated
Project WISH: The Emerald City
Phase 3 of Project WISH saw the evolution of the Emerald City (E-City) from a collection of specialized independent analyses and ideas to a working structural design integrated with major support systems and analyses. Emphasis was placed on comparing and contrasting the closed and open cycle gas core nuclear rocket engines to further determine the optimum propulsive system for the E-City. Power and thermal control requirements were then defined and the question of how to meet these requirements was addressed. Software was developed to automate the mission/system/configuration analysis so changes dictated by various subsystem constraints could be managed efficiently and analyzed interactively. In addition, the liquid hydrogen propellant tank was statically designed for minimum mass and shape optimization using a finite element modeling package called SDRC I-DEAS. Spoke and shaft cross-sectional areas were optimized on ASTROS (Automated Structural Optimization System) for mass minimization. A structural dynamic analysis of the optimal structure also conducted using ASTROS enabled a study of the modes, frequencies, displacements, and accelerations of the E-City. Finally, the attitude control system design began with an initial mass moment of inertia analysis and was then designed and optimized using linear quadratic regulator control theory
MHD simulations of formation, sustainment and loss of Quiescent H-mode in the all-tungsten ASDEX Upgrade
Periodic edge localized modes (ELMs) are the non-linear consequences of
pressure-gradient-driven ballooning modes and current-driven peeling modes
becoming unstable in the pedestal region of high confinement fusion plasmas. In
future tokamaks like ITER, large ELMs are foreseen to severely affect the
lifetime of wall components as they transiently deposit large amounts of heat
onto a narrow region at the divertor targets. Several strategies exist for
avoidance, suppression, or mitigation of these instabilities, such as the
naturally ELM-free quiescent H-mode (QH-mode). In the present article, an ASDEX
Upgrade equilibrium that features a QH-mode is investigated through non-linear
extended MHD simulations covering the dynamics over tens of milliseconds. The
equilibrium is close to the ideal peeling limit and non-linearly develops
saturated modes at the edge of the plasma. A dominant toroidal mode number of
is found, for which the characteristic features of the edge harmonic
oscillation are recovered. The saturated modes contribute to heat and particle
transport preventing pedestal build-up to the ELM triggering threshold. The
non-linear dynamics of the mode, in particular its interaction with the
evolution of the edge safety factor is studied, which suggest a possible new
saturation mechanism for the QH-mode. The simulations show good qualitative and
quantitative agreement to experiments in AUG. In particular, the processes
leading to the termination of QH-mode above a density threshold is studied,
which results in the transition into an ELM regime. In the vicinity of this
threshold, limit cycle oscillations are observed.Comment: Revised version with modifications from review process include
A Galactic Dust Devil: far-infrared observations of the Tornado Supernova Remnant candidate
We present complicated dust structures within multiple regions of the
candidate supernova remnant (SNR) the `Tornado' (G357.7-0.1) using observations
with Spitzer and Herschel. We use Point Process Mapping, PPMAP, to investigate
the distribution of dust in the Tornado at a resolution of 8", compared to the
native telescope beams of 5-36". We find complex dust structures at multiple
temperatures within both the head and the tail of the Tornado, ranging from 15
to 60K. Cool dust in the head forms a shell, with some overlap with the radio
emission, which envelopes warm dust at the X-ray peak. Akin to the terrestrial
sandy whirlwinds known as `Dust Devils', we find a large mass of dust contained
within the Tornado. We derive a total dust mass for the Tornado head of 16.7
solar masses, assuming a dust absorption coefficient of kappa_300 =0.56m^2
kg^1, which can be explained by interstellar material swept up by a SNR
expanding in a dense region. The X-ray, infra-red, and radio emission from the
Tornado head indicate that this is a SNR. The origin of the tail is more
unclear, although we propose that there is an X-ray binary embedded in the SNR,
the outflow from which drives into the SNR shell. This interaction forms the
helical tail structure in a similar manner to that of the SNR W50 and
microquasar SS433.Comment: 16 pages, 10 figures + 3 appendix figures. Accepted to be published
in MNRA
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