21,406 research outputs found
Documentation of ice shapes accreted on the main rotor of a UH-1H helicopter in level flight
Icing tests were conducted on a UH-1H helicopter in level flight behind a spray tanker near Duluth, Minnesota, during the winter of 1983-84 as part of the joint NASA/Army HIFT program. On landing, the ice formations on the main rotor were documented by casting a set of ten-inch molds on the blade using a Dow-Corning silicone rubber compound which was initially liquid at sub-freezing temperatures. Such documentation was accomplished for eight flights in which the temperature ranged from -11 C to -22 C and the in-cloud flight times ranged from 5 to 9 minutes
Diagnostics Of Disks Around Hot Stars
We discuss three different observational diagnostics related to disks around hot stars: absorption line determinations of rotational velocities of Be stars; polarization diagnostics of circumstellar disks; and X-ray line diagnostics of one specific magnetized hot star, theta(1) Ori C. Some common themes that emerge from these studies include (a) the benefits of having a specific physical model as a framework for interpreting diagnostic data; (b) the importance of combining several different types of observational diagnostics of the same objects; and (c) that while there is often the need to reinterpret traditional diagnostics in light of new theoretical advances, there are many new and powerful diagnostics that are, or will soon be, available for the study of disks around hot stars
Malmquist Bias and the Distance to the Virgo Cluster
This paper investigates the impact of Malmquist bias on the distance to the
Virgo cluster determined by the H_0 Key Project using M100, and consequently on
the derived value of H_0. Malmquist bias is a volume-induced statistical effect
which causes the most probable distance to be different from the raw distance
measured. Consideration of the bias in the distance to the Virgo cluster raises
this distance and lowers the calculated value of H_0. Monte Carlo simulations
of the cluster have been run for several possible distributions of spirals
within the cluster and of clusters in the local universe. Simulations
consistent with known information regarding the cluster and the errors of
measurement result in a bias of about 6.5%-8.5%. This corresponds to an
unbiased distance of 17.2-17.4 Mpc and a value of H_0 in the range 80-82
km/s/Mpc.
The problem of determining the bias to Virgo illustrates several key points
regarding Malmquist bias. Essentially all conventional astronomical distance
measurements are subject to this bias. In addition, the bias accumulates when
an attempt is made to construct "distance ladders" from measurements which are
individually biased. As will be shown in the case of Virgo, the magnitude and
direction of the bias are sensitive to the spatial distribution of the parent
poputation from which the observed object is drawn - a distribution which is
often poorly known. This leads to uncertainty in the magnitude of the bias, and
adds to the importance of minimizing the number of steps in "distance ladders".Comment: 19 pages, 3 figures, Latex, To appear in Ap
Aquatic Vegetation, Largemouth Bass and Water Quality Responses to Low-Dose Fluridone Two Years Post Treatment
Whole-lake techniques are increasingly being used to selectively
remove exotic plants, including Eurasian watermilfoil
(
Myriophyllum spicatum
L.). Fluridone (1-methyl-3-phenyl-
5-[3-(trifluoromethyl)phenyl]-4(1
H
)-pyridinone), a systemic
whole-lake herbicide, is selective for Eurasian watermilfoil
within a narrow low concentration range. Because fluridone
applications have the potential for large effects on plant assemblages
and lake food webs, they should be evaluated at
the whole-lake scale. We examined effects of low-dose (5 to 8
ppb) fluridone applications by comparing submersed plant
assemblages, water quality and largemouth bass (
Micropterus
salmoides
) growth rates and diets between three reference
lakes and three treatment lakes one- and two-years post treatment.
In the treatment lakes, fluridone reduced Eurasian watermilfoil
cover without reducing native plant cover, although
the duration of Eurasian watermilfoil reduction varied among
treatment lakes. (PDF has 11 pages.
Spin-Dependent Tunneling of Single Electrons into an Empty Quantum Dot
Using real-time charge sensing and gate pulsing techniques we measure the
ratio of the rates for tunneling into the excited and ground spin states of a
single-electron AlGaAs/GaAs quantum dot in a parallel magnetic field. We find
that the ratio decreases with increasing magnetic field until tunneling into
the excited spin state is completely suppressed. However, we find that by
adjusting the voltages on the surface gates to change the orbital configuration
of the dot we can restore tunneling into the excited spin state and that the
ratio reaches a maximum when the dot is symmetric.Comment: 4 pages, 3 figure
Electrical control of spin relaxation in a quantum dot
We demonstrate electrical control of the spin relaxation time T_1 between
Zeeman split spin states of a single electron in a lateral quantum dot. We find
that relaxation is mediated by the spin-orbit interaction, and by manipulating
the orbital states of the dot using gate voltages we vary the relaxation rate
W= (T_1)^-1 by over an order of magnitude. The dependence of W on orbital
confinement agrees with theoretical predictions and from these data we extract
the spin-orbit length. We also measure the dependence of W on magnetic field
and demonstrate that spin-orbit mediated coupling to phonons is the dominant
relaxation mechanism down to 1T, where T_1 exceeds 1s.Comment: 4 pages, 3 figure
Measurement efficiency and n-shot read out of spin qubits
We consider electron spin qubits in quantum dots and define a measurement
efficiency e to characterize reliable measurements via n-shot read outs. We
propose various implementations based on a double dot and quantum point contact
(QPC) and show that the associated efficiencies e vary between 50% and 100%,
allowing single-shot read out in the latter case. We model the read out
microscopically and derive its time dynamics in terms of a generalized master
equation, calculate the QPC current and show that it allows spin read out under
realistic conditions.Comment: 5 pages, 1 figur
Population of human ventricular cell models calibrated with in vivo measurements unravels ionic mechanisms of cardiac alternans
Cardiac alternansis an important risk factor in cardiac physiology, and is related to the initiation of many pathophysiological conditions. However, the mechanisms underlying the generation of alternans remain unclear. In this study, we used a population of computational human ventricle models based onthe O’Hara model [1] to explore the effect of 11 key factors experimentally reported to be related to alternans. In vivo experimental datasets coming from patients undergoing cardiac surgery were used in the calibration of our in silico population of models. The calibrated models in the population were divided into two groups (Normal and Alternans) depending on alternans occurrence. Our results showed that there were significant differences in the following 5 ionic currents between the two groups: fast sodium current, sodium calcium exchanger current, sodium potassium pump current, sarcoplasmic reticulum (SR) calcium release flux and SR calcium reuptake flux. Further analysis indicated that fast sodium current and SR calcium uptake were the two most significant currents that contributed to voltage and calcium alternans generation, respectively
Political trials and the suppression of popular radicalism in England, 1799-1820
This chapter examines the decision-making process between the Home Office and the government’s law officers in prosecuting individuals for sedition and treason in the period 1799–1820. The term state trial suggests a more centralised and government-led repression of popular radicalism than the process was in practice. Provincial reformers also faced the complex layers of their local justice system, which was more loyalist, committed to stamping out political radicalism. The trial of the “Thirty Eight” Manchester radicals in June 1812 demonstrates the mutable definitions of treason, sedition and processes of justice in the theatre of the court.Peer reviewe
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