4,234 research outputs found
Stochastic Schroedinger equations and applications to Ehrenfest-type theorems
We study stochastic evolution equations describing the dynamics of open
quantum systems. First, using resolvent approximations, we obtain a sufficient
condition for regularity of solutions to linear stochastic Schroedinger
equations driven by cylindrical Brownian motions applying to many physical
systems. Then, we establish well-posedness and norm conservation property of a
wide class of open quantum systems described in position representation.
Moreover, we prove Ehrenfest-type theorems that describe the evolution of the
mean value of quantum observables in open systems. Finally, we give a new
criterion for existence and uniqueness of weak solutions to non-linear
stochastic Schroedinger equations. We apply our results to physical systems
such as fluctuating ion traps and quantum measurement processes of position
A Simulation Framework for Fast Design Space Exploration of Unmanned Air System Traffic Management Policies
The number of daily small Unmanned Aircraft Systems (sUAS) operations in
uncontrolled low altitude airspace is expected to reach into the millions. UAS
Traffic Management (UTM) is an emerging concept aiming at the safe and
efficient management of such very dense traffic, but few studies are addressing
the policies to accommodate such demand and the required ground infrastructure
in suburban or urban environments. Searching for the optimal air traffic
management policy is a combinatorial optimization problem with intractable
complexity when the number of sUAS and the constraints increases. As the
demands on the airspace increase and traffic patterns get complicated, it is
difficult to forecast the potential low altitude airspace hotspots and the
corresponding ground resource requirements. This work presents a Multi-agent
Air Traffic and Resource Usage Simulation (MATRUS) framework that aims for fast
evaluation of different air traffic management policies and the relationship
between policy, environment and resulting traffic patterns. It can also be used
as a tool to decide the resource distribution and launch site location in the
planning of a next-generation smart city. As a case study, detailed comparisons
are provided for the sUAS flight time, conflict ratio, cellular communication
resource usage, for a managed (centrally coordinated) and unmanaged (free
flight) traffic scenario.Comment: The Integrated Communications Navigation and Surveillance (ICNS)
Conference in 201
Impact of Salvage Surgery and Re-irradiation for Radiation Failed Recurrent Skull Base Meningiomas
View full abstracthttps://openworks.mdanderson.org/leading-edge/1052/thumbnail.jp
A Multiple System of Radio Sources at the Core of the L723 Multipolar Outflow
We present high angular resolution Very Large Array multi-epoch continuum
observations at 3.6 cm and 7 mm towards the core of the L723 multipolar outflow
revealing a multiple system of four radio sources suspected to be YSOs in a
region of only ~4 arcsecs (1200 AU) in extent. The 3.6 cm observations show
that the previously detected source VLA 2 contains a close (separation ~0.29
arcsecs or ~90 AU) radio binary, with components (A and B) along a position
angle of ~150 degrees. The northern component (VLA 2A) of this binary system is
also detected in the 7 mm observations, with a positive spectral index between
3.6 cm and 7 mm. In addition, the source VLA 2A is associated with extended
emission along a position angle of ~115 degrees, that we interpret as
outflowing shock-ionized gas that is exciting a system of HH objects with the
same position angle. A third, weak 3.6 cm source, VLA 2C, that is detected also
at 7 mm, is located ~0.7 arcsecs northeast of VLA 2A, and is possibly
associated with the water maser emission in the region. The 7 mm observations
reveal the presence of an additional source, VLA 2D, located ~3.5 arcsecs
southeast of VLA 2A, and with a 1.35 mm counterpart. All these radio continuum
sources have a positive spectral index, compatible with them being YSOs. We
also propose that the high velocity CO emission observed in the region could be
the superposition of multiple outflows (at least three independent bipolar
outflows) excited by the YSOs located at the core, instead of the previous
interpretations in terms of only one or two outflows.Comment: Accepted for publication in The Astrophysical Journal (2007 December
6
Not Waving but Striving: Research Collaboration in the Context of Stratification, Segmentation, and the Quest for Prestige
In this article we examine the ways in which institutional stratification and academic labor segmentation contribute to shaping faculty collaborative activities. We draw on interviews from science and engineering faculty at two institutions in the United States to highlight how collaboration, as an essential form of academic labor, is shaped by institutional factors like resource stress and isomorphic pressures to fit the ideal of the “world-class” research-intensive university. The findings suggest that a university’s relative position in the institutional status hierarchy has a significant impact on the types of resources faculty seeking to establish collaborations can access and mobilize, thus reinforcing existing patterns of institutional stratification where “striving” institutions can never catch up to their more prestigious peers. At the same time, the pressure to maximize institutional prestige can create paradoxical interinstitutional dynamics where seemingly successful “Mode 2” units that rely almost exclusively on external resources and partnerships with industry are expected to mold themselves more closely to the activity streams of traditional academic units
Bottom trawl selectivity and reduction of fisheries discards in European North Western Waters
Constraint on the time variation of the fine-structure constant with the SDSS-III/BOSS DR12 quasar sample
From the Sloan Digital Sky Survey (SDSS) Data Release 12, which covers the
full Baryonic Oscillation Spectroscopic Survey (BOSS) footprint, we investigate
the possible variation of the fine-structure constant over cosmological
time-scales. We analyse the largest quasar sample considered so far in the
literature, which contains 13175 spectra (10363 from SDSS-III/BOSS DR12 + 2812
from SDSS-II DR7) with redshift 1. We apply the emission-line method on
the [O III] doublet (4960, 5008 A) and obtain for the relative variation of the fine-structure
constant. We also investigate the possible sources of systematics:
misidentification of the lines, sky OH lines, H and broad line
contamination, Gaussian and Voigt fitting profiles, optimal wavelength range
for the Gaussian fits, chosen polynomial order for the continuum spectrum,
signal-to-noise ratio and good quality of the fits. The uncertainty of the
measurement is dominated by the sky subtraction. The results presented in this
work, being systematics limited, have sufficient statistics to constrain
robustly the variation of the fine-structure constant in redshift bins ( 0.06) over the last 7.9 Gyr. In addition, we study the [Ne III]
doublet (3870, 3969 A) present in 462 quasar spectra and discuss the systematic
effects on using these emission lines to constrain the fine-structure constant
variation. Better constraints on (10) using
the emission-line method would be possible with high-resolution spectroscopy
and large galaxy/qso surveys.Comment: 16 pages, 16 figures. Version published in MNRAS. Analysis enlarged,
public catalogue now availabl
FISHING SELECTIVITY AND REDUCTION OF DISCARDS IN BOTTOM TRAWL FISHERIES AT NORTH EUROPEAN ATLANTIC WATERS
Chemical tracers of Lusitanian amphorae kilns from the Tagus estuary (Portugal)
In this paper, the characterization of Roman amphorae from the Porto dos Cacos (PC) and Quinta do Rouxinol (QR) workshops, in the Tagus estuary, dating to a period between the 1st and 5th century AD was carried out on the basis of instrumental neutron activation analysis data on 260 amphorae fragments, together with mineralogical compositional studies obtained by X-ray diffraction.
Special attention was devoted to the study of the Dressel 14, Almagro 50/51c and Lusitana 3/9 amphorae in an attempt to establish whether or not it is possible to establish any correlation between the composition and typology, and between and within the production centres studied. A description of the geochemical patterns associated with each production centre was first carried out separately, followed by a discussion comparing the two centres situated in the same sedimentary basin, identifying diagnostic chemical tracers for each one; also, in certain cases, a relative correlation with the typology was achieved. Both the definition of reference groups and the attribution of amphorae to their workshop origin relied on the use of chemometric techniques for data structure analysis, coupled with geochemical data analysis, especially regarding trace element data and its geochemical behaviour and distribution according to the geological environment of the region.
This approach complements and reinforces the conclusions drawn from typological and archaeological analyses. Considering the two kiln sites studied, we may talk of the production of two types of Roman amphorae in the lower Tagus, with the establishment of compositional groups defined according to their corresponding chemical signatures. The products of the PC workshop are characterized by high concentrations of Co, As and U, and low concentrations of Fe, Zn, Sb, Rb, K; QR workshop amphorae show instead higher concentrations of Fe, Sb, and also of Rb and Zn, and lower amounts of U. These results make it possible to understand the crucial importance of the lower course of the Tagus River within the framework of the analysis of the economy of the estuary at the time. This, in turn, may lead to a better understanding of production and trade within Lusitania and also with other Roman provinces
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