9,978 research outputs found
The Role of CO2 in Aqueous Alteration of Ultra-Mafic Rocks and the Formation of MF-,FE-Rich Aqueous Solutons on Early Mars
An adequate understanding of water on Mars that moves beyond the simplistic "warmwet" vs. "cold-dry" dichotomy must include strong constraints on the variables: water/rock ratio, time, temperature, and chemical composition. By constraining these variables first on local, then regional and global scales we will be capable of precisely targeting landed missions to definitively understand the history of water on Mars and the possible existence of life. Data from remote sensing of Mars, landed missions, and martian meteorites indicate that secondary minerals formed from aqueous fluids on Mars are predominately Fe- and Mg-rich. The unique Mg-, Fe-rich carbonates in the ALH 84001 meteorite provide an excellent opportunity to provide strong constraints on an Fe-, Mg-rich aqueous system on early Mars. This work seeks to use the unusual chemical compositions of the ALH 84001 carbonates as a constraint for the composition of their formation fluid. These constraints can be used to better understand aqueous processes at a critical time in martian history
A purely reflective large wide-field telescope
Two versions of a fast, purely reflective Paul-Baker type telescope are
discussed, each with an 8.4-m aperture, 3 deg diameter flat field and f/1.25
focal ratio.
The first version is based on a common, even asphere type of surface with
zero conic constant. The primary and tertiary mirrors are 6th order aspheres,
while the secondary mirror is an 8th order asphere (referred to here for
brevity, as the 6/8/6 configuration). The D_80 diameter of a star image varies
from 0''.18 on the optical axis up to 0''.27 at the edge of the field (9.3-13.5
mcm).
The second version of the telescope is based on a polysag surface type which
uses a polynomial expansion in the sag z, r^2 = 2R_0z - (1+b)z^2 + a_3 z^3 +
a_4 z^4 + ... + a_N z^N, instead of the common form of an aspheric surface.
This approach results in somewhat better images, with D_80 ranging from 0''.16
to 0''.23, using a lower-order 3/4/3 combination of powers for the mirror
surfaces. An additional example with 3.5-m aperture, 3.5 deg diameter flat
field, and f/1.25 focal ratio featuring near-diffraction-limited image quality
is also presented.Comment: 14 pages, 6 figures; new examples adde
Phase diffusion and charging effects in Josephson junctions
The supercurrent of a Josephson junction is reduced by phase diffusion. For
ultrasmall capacitance junctions the current may be further decreased by
Coulomb blockade effects. We calculate the Cooper pair current by means of
time-dependent perturbation theory to all orders in the Josephson coupling
energy and obtain the current-voltage characteristic in closed form in a range
of parameters of experimental interest. The results comprehend phase diffusion
of the coherent Josephson current in the classical regime as well as the
supercurrent peak due to incoherent Cooper pair tunneling in the strong Coulomb
blockade regime.Comment: 4 pages, 3 figures, RevTe
Quantum Mechanics as a Framework for Dealing with Uncertainty
Quantum uncertainty is described here in two guises: indeterminacy with its
concomitant indeterminism of measurement outcomes, and fuzziness, or
unsharpness. Both features were long seen as obstructions of experimental
possibilities that were available in the realm of classical physics. The birth
of quantum information science was due to the realization that such
obstructions can be turned into powerful resources. Here we review how the
utilization of quantum fuzziness makes room for a notion of approximate joint
measurement of noncommuting observables. We also show how from a classical
perspective quantum uncertainty is due to a limitation of measurability
reflected in a fuzzy event structure -- all quantum events are fundamentally
unsharp.Comment: Plenary Lecture, Central European Workshop on Quantum Optics, Turku
2009
ALMA [NII] 205 micron Imaging Spectroscopy of the Interacting Galaxy System BRI 1202-0725 at Redshift 4.7
We present the results from Atacama Large Millimeter/submillimeter Array
(ALMA) imaging in the [NII] 205 micron fine-structure line (hereafter [NII])
and the underlying continuum of BRI 1202-0725, an interacting galaxy system at
4.7, consisting of an optical QSO, a sub-millimeter galaxy (SMG) and two
Lyman- emitters (LAEs), all within 25 kpc of the QSO. We detect
the QSO and SMG in both [NII] and continuum. At the (or 6.6 kpc)
resolution, both QSO and SMG are resolved in [NII], with the de-convolved major
axes of 9 and 14 kpc, respectively. In contrast, their continuum
emissions are much more compact and unresolved even at an enhanced resolution
of . The ratio of the [NII] flux to the existing CO (76) flux is
used to constrain the dust temperature () for a more accurate
determination of the FIR luminosity . Our best estimated equals K for both galaxies (assuming an emissivity index
). The resulting ratios are
statistically consistent with that of local luminous infrared galaxies,
confirming that traces the star formation (SF) rate (SFR) in
these galaxies. We estimate that the on-going SF of the QSO (SMG) has a SFR of
5.1 yr ( 30%) assuming Chabrier
initial mass function, takes place within a diameter (at half maximum) of 1.3
(1.5) kpc, and shall consume the existing 5 of
molecular gas in 10 years.Comment: 4 pages, 1 table, 4 figures; accepted for publication in the ApJ
Letter
A mapping approach to synchronization in the "Zajfman trap": stability conditions and the synchronization mechanism
We present a two particle model to explain the mechanism that stabilizes a
bunch of positively charged ions in an "ion trap resonator" [Pedersen etal,
Phys. Rev. Lett. 87 (2001) 055001]. The model decomposes the motion of the two
ions into two mappings for the free motion in different parts of the trap and
one for a compressing momentum kick. The ions' interaction is modelled by a
time delay, which then changes the balance between adjacent momentum kicks.
Through these mappings we identify the microscopic process that is responsible
for synchronization and give the conditions for that regime.Comment: 12 pages, 9 figures; submitted to Phys Rev
Exact and simple results for the XYZ and strongly interacting fermion chains
We conjecture exact and simple formulas for physical quantities in two
quantum chains. A classic result of this type is Onsager, Kaufman and Yang's
formula for the spontaneous magnetization in the Ising model, subsequently
generalized to the chiral Potts models. We conjecture that analogous results
occur in the XYZ chain when the couplings obey J_xJ_y + J_yJ_z + J_x J_z=0, and
in a related fermion chain with strong interactions and supersymmetry. We find
exact formulas for the magnetization and gap in the former, and the staggered
density in the latter, by exploiting the fact that certain quantities are
independent of finite-size effects
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