10,092 research outputs found
Initial POLAR MFE observation of substorm signatures in the polar magnetosphere
This paper studies substorm influences in the polar magnetosphere using data from the POLAR magnetic field experiment (MFE). The POLAR spacecraft remains in the high altitude polar magnetosphere for extended periods around apogee. There it can stay at nearly constant altitude through all phases of a substorm, which was not possible on previous missions. We report such an event on March 28, 1996. Ground magnetometers monitored substorm activity, while the POLAR spacecraft, directly over the pole at (−0.8, −0.6, 8.5) RE in GSM coordinates, observed a corresponding perturbation in the total magnetic field strength. The total magnetic field first increased, then recovered toward quiet levels, consistent with erosion of magnetic flux from the dayside magnetosphere, followed by transport of that flux to the magnetotail, and eventual onset of tail reconnection and the return of that magnetic flux to the dayside magnetosphere
Fabric analysis of allende matrix using EBSD
Accepted versio
Direct observation of molecular cooperativity near the glass transition
We describe direct observations of molecular cooperativity near the glass
transition in poly-vinyl-acetate (PVAc), through nanometer-scale probing of
dielectric fluctuations. Molecular clusters switched spontaneously between two
to four distinct configurations, producing complex random-telegraph-signals
(RTS). Analysis of the RTS and their power spectra shows that individual
clusters exhibit both transient dynamical heterogeneity and non-exponential
kinetics.Comment: 14 pages pdf, need Acrobat Reade
The One-Way Communication Complexity of Group Membership
This paper studies the one-way communication complexity of the subgroup
membership problem, a classical problem closely related to basic questions in
quantum computing. Here Alice receives, as input, a subgroup of a finite
group ; Bob receives an element . Alice is permitted to send a
single message to Bob, after which he must decide if his input is an
element of . We prove the following upper bounds on the classical
communication complexity of this problem in the bounded-error setting: (1) The
problem can be solved with communication, provided the subgroup
is normal; (2) The problem can be solved with
communication, where is the maximum of the dimensions of the
irreducible complex representations of ; (3) For any prime not dividing
, the problem can be solved with communication,
where is the maximum of the dimensions of the irreducible
\F_p-representations of
MMS examination of FTEs at the earth's subsolar magnetopause
Determining the magnetic field structure, electric currents, and plasma distributions within flux transfer event (FTE)-type flux ropes is critical to the understanding of their origin, evolution, and dynamics. Here the Magnetospheric Multiscale mission's high-resolution magnetic field and plasma measurements are used to identify FTEs in the vicinity of the subsolar magnetopause. The constant-α flux rope model is used to identify quasi-force free flux ropes and to infer the size, the core magnetic field strength, the magnetic flux content, and the spacecraft trajectories through these structures. Our statistical analysis determines a mean diameter of 1,700 ± 400 km (~30 ± 9 d i ) and an average magnetic flux content of 100 ± 30 kWb for the quasi-force free FTEs at the Earth's subsolar magnetopause which are smaller than values reported by Cluster at high latitudes. These observed nonlinear size and magnetic flux content distributions of FTEs appear consistent with the plasmoid instability theory, which relies on the merging of neighboring, small-scale FTEs to generate larger structures. The ratio of the perpendicular to parallel components of current density, R J , indicates that our FTEs are magnetically force-free, defined as R J < 1, in their core regions ( < 0.6 R flux rope ). Plasma density is shown to be larger in smaller, newly formed FTEs and dropping with increasing FTE size. It is also shown that parallel ion velocity dominates inside FTEs with largest plasma density. Field-aligned flow facilitates the evacuation of plasma inside newly formed FTEs, while their core magnetic field strengthens with increasing FTE size
Closed-loop all-optical interrogation of neural circuits in vivo
Understanding the causal relationship between neural activity and behavior requires the ability to perform rapid and targeted interventions in ongoing activity. Here we describe a closed-loop all-optical strategy for dynamically controlling neuronal activity patterns in awake mice. We rapidly tailored and delivered two-photon optogenetic stimulation based on online readout of activity using simultaneous two-photon imaging, thus enabling the manipulation of neural circuit activity ‘on the fly’ during behavior
Physical Volcanology of Tseax Volcano, British Columbia, Canada
Tseax volcano erupted ∼ 250 years ago in NW British Columbia, Canada producing tephra deposits and lava flows. Field mapping has defined the stratigraphy of Tseax and the lava flow morphologies. Aerial photogrammetry and bathymetry surveys were used to create a high resolution digital elevation model of the volcano to facilitate mapping and estimates of erupted material volumes. Tseax volcano (∼ 10.4 ± 0.7 × 106 m3) comprises an outer breached spatter rampart and an inner conical tephra cone. Tseax is associated with a 32 km long and 0.49 ± 0.08 km3 basanite-to-tephrite lava flow field covering ∼ 36 km2 and divided into 4 distinct lava flows with heterogeneous surface morphologies. We present a volcanological map of Tseax volcano at a scale of 1:22,500. This will serve as supporting information for further research on the eruptive history of Tseax volcano and the lava flow field emplacement
Lithologic Mapping of HED Terrains on Vesta using Dawn Framing Camera Color Data
The surface composition of Vesta, the most massive intact basaltic object in
the asteroid belt, is interesting because it provides us with an insight into
magmatic differentiation of planetesimals that eventually coalesced to form the
terrestrial planets. The distribution of lithologic and compositional units on
the surface of Vesta provides important constraints on its petrologic
evolution, impact history and its relationship with Vestoids and
howardite-eucrite-diogenite (HED) meteorites. Using color parameters (band tilt
and band curvature) originally developed for analyzing lunar data, we have
identified and mapped HED terrains on Vesta in Dawn Framing Camera (FC) color
data. The average color spectrum of Vesta is identical to that of howardite
regions, suggesting an extensive mixing of surface regolith due to impact
gardening over the course of solar system history. Our results confirm the
hemispherical dichotomy (east-west and north-south) in albedo/color/composition
that has been observed by earlier studies. The presence of diogenite-rich
material in the southern hemisphere suggests that it was excavated during the
formation of the Rheasilvia and Veneneia basins. Our lithologic mapping of HED
regions provides direct evidence for magmatic evolution of Vesta with diogenite
units in Rheasilvia forming the lower crust of a differentiated object.Comment: Accepted for Meteoritics and Planetary Science special issue for
Composition of Vesta/Dawn Missio
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