11,588 research outputs found
The Virginia Sickle Cell Anemia Awareness Program: Education, Screening, and Counseling
In 1968, a program of screening for sickle trait carriers was begun as part of the work of the Hematology Division, Department of Medicine, at the Medical College of Virginia. It was felt that sickle cell anemia was more of a public health problem than was generally recognized, and in addition to instituting screening and education programs, data were collected to document the relative neglect of the problem
Achieving better than 1 minute accuracy in the Heliocentric and Barycentric Julian Dates
As the quality and quantity of astrophysical data continue to improve, the
precision with which certain astrophysical events can be timed becomes limited
not by the data themselves, but by the manner, standard, and uniformity with
which time itself is referenced. While some areas of astronomy (most notably
pulsar studies) have required absolute time stamps with precisions of
considerably better than 1 minute for many decades, recently new areas have
crossed into this regime. In particular, in the exoplanet community, we have
found that the (typically unspecified) time standards adopted by various groups
can differ by as much as a minute. Left uncorrected, this ambiguity may be
mistaken for transit timing variations and bias eccentricity measurements. We
argue that, since the commonly-used Julian Date, as well as its heliocentric
and barycentric counterparts, can be specified in several time standards, it is
imperative that their time standards always be reported when accuracies of 1
minute are required. We summarize the rationale behind our recommendation to
quote the site arrival time, in addition to using BJD_TDB, the Barycentric
Julian Date in the Barycentric Dynamical Time standard for any astrophysical
event. The BJD_TDB is the most practical absolute time stamp for
extra-terrestrial phenomena, and is ultimately limited by the properties of the
target system. We compile a general summary of factors that must be considered
in order to achieve timing precisions ranging from 15 minutes to 1 microsecond.
Finally, we provide software tools that, in principal, allow one to calculate
BJD_TDB to a precision of 1 microsecond for any target from anywhere on Earth
or from any spacecraft.Comment: Online BJD_TDB calculator at
http://astroutils.astronomy.ohio-state.edu/time/utc2bjd.html. PASP accepted,
11 pages, 6 figures, updated to match published versio
Epistemic Abstainers, Epistemic Martyrs, and Epistemic Converts
An intuitive view regarding the epistemic significance of disagreement says that when epistemic peers disagree, they should suspend judgment. This abstemious view seems to embody a kind of detachment appropriate for rational beings; moreover, it seems to promote a kind of conciliatory inclination that makes for irenic and cooperative further discussion. Like many strategies for cooperation, however, the abstemious view creates opportunities for free-riding. In this essay, the authors argue that the believer who suspends judgment in the face of peer disagreement is vulnerable to a kind of manipulation on the part of more tenacious peers. The result is that the abstemious view can have the effect of encouraging dogmatism
Automatic goal distribution strategies for the execution of committed choice logic languages on distributed memory parallel computers
There has been much research interest in efficient implementations of the Committed
Choice Non-Deterministic (CCND) logic languages on parallel computers. To take
full advantage of the speed gains of parallel computers, methods need to be found
to automatically distribute goals over the machine processors, ideally with as little
involvement from the user as possible.In this thesis we explore some automatic goal distribution strategies for the execu¬
tion of the CCND languages on commercially available distributed memory parallel
computers.There are two facets to the goal distribution strategies we have chosen to explore:DEMAND DRIVEN: An idle processor requests work from other processors. We describe
two strategies in this class: one in which an idle processor asks only neighbouring
processors for spare work, the nearest-neighbour strategy; and one where an idle
processor may ask any other processor in the machine for spare work, the allprocessors strategy.WEIGHTS: Using a program analysis technique devised by Tick, weights are attached to
goals; the weights can be used to order the goals so that they can be executed
and distributed out in weighted order, possibly increasing performance.We describe a framework in which to implement and analyse goal distribution strategies, and then go on to describe experiments with demand driven strategies, both with
and without weights. The experiments were made using two of our own implementations of Flat Guarded Horn Clauses — an interpreter and a WAM-like system —
executing on a MEIKO T800 Transputer Array configured in a 2-D mesh topology.Analysis of the results show that the all-processors strategies are promising (AP-NW),
adding weights had little positive effect on performance, and that nearest-neighbours
strategies can reduce performance due to bad load balancing.We also describe some preliminary experiments for a variant of the AP-NW strategy:
goals which suspend on one variable are sent to the processor that controls that variable,
the processes-to-data strategy. And we briefly look at some preliminary results of
executing programs on large numbers of processors (> 30)
Atemporal diagrams for quantum circuits
A system of diagrams is introduced that allows the representation of various
elements of a quantum circuit, including measurements, in a form which makes no
reference to time (hence ``atemporal''). It can be used to relate quantum
dynamical properties to those of entangled states (map-state duality), and
suggests useful analogies, such as the inverse of an entangled ket. Diagrams
clarify the role of channel kets, transition operators, dynamical operators
(matrices), and Kraus rank for noisy quantum channels. Positive (semidefinite)
operators are represented by diagrams with a symmetry that aids in
understanding their connection with completely positive maps. The diagrams are
used to analyze standard teleportation and dense coding, and for a careful
study of unambiguous (conclusive) teleportation. A simple diagrammatic argument
shows that a Kraus rank of 3 is impossible for a one-qubit channel modeled
using a one-qubit environment in a mixed state.Comment: Minor changes in references. Latex 32 pages, 13 figures in text using
PSTrick
Stably accessing octave-spanning microresonator frequency combs in the soliton regime
Microresonator frequency combs can be an enabling technology for optical
frequency synthesis and timekeeping in low size, weight, and power
architectures. Such systems require comb operation in low-noise, phase-coherent
states such as solitons, with broad spectral bandwidths (e.g., octave-spanning)
for self-referencing to detect the carrier-envelope offset frequency. However,
stably accessing such states is complicated by thermo-optic dispersion. For
example, in the Si3N4 platform, precisely dispersion-engineered structures can
support broadband operation, but microsecond thermal time constants have
necessitated fast pump power or frequency control to stabilize the solitons. In
contrast, here we consider how broadband soliton states can be accessed with
simple pump laser frequency tuning, at a rate much slower than the thermal
dynamics. We demonstrate octave-spanning soliton frequency combs in Si3N4
microresonators, including the generation of a multi-soliton state with a pump
power near 40 mW and a single-soliton state with a pump power near 120 mW. We
also develop a simplified two-step analysis to explain how these states are
accessed in a thermally stable way without fast control of the pump laser, and
outline the required thermal properties for such operation. Our model agrees
with experimental results as well as numerical simulations based on a
Lugiato-Lefever equation that incorporates thermo-optic dispersion. Moreover,
it also explains an experimental observation that a member of an adjacent mode
family on the red-detuned side of the pump mode can mitigate the thermal
requirements for accessing soliton states
Small viscosity behavior of a homogeneous, quasi-geostrophic, ocean circulation mode
Insensitivity to turbulent closure in the wind-driven nonlinear Stommel-Munk model is addressed theoretically and numerically. The QG energy equation is used to show that, with the assumption that the maximum velocities occur at inertial length scales or smaller, a Sverdrup interior is consistent with the small Rossby number assumption only when the frictional parameters exceed critical values. For frictional parameters smaller than these values, valid solutions must decrease the energy source. This is possible for non-Sverdrup solutions since the energy source is dependent on the solution. The steady-state behavior of the model was investigated via a pseudo-arclength continuation algorithm. Dependence on the boundary layer Reynolds number, Re, was investigated by varying the eddy viscosity for fixed wind forcing. A tendency to decrease the energy source was found for solutions that are nonsymmetric about the center latitude. Antisymmetric solutions displayed the opposite behavior and diverged more quickly with increasing Re. The robustness of the results to dynamic boundary condition, symmetry and strength of wind stress, time dependence and bottom friction were tested. Some aspects of the nonsymmetric solutions appeared insensitive to Re
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