5,627 research outputs found
Numerical analysis of a downsized 2-stroke uniflow engine
In order to optimize the 2-stroke uniflow engine performance on vehicle applications, numerical analysis has been introduced, 3D CFD model has been built for the optimization of intake charge organization. The scavenging process was investigated and the intake port design details were improved. Then the output data from 3D CFD calculation were applied to a 1D engine model to process the analysis on engine performance. The boost system optimization of the engine has been carried out also. Furthermore, a vehicle model was also set up to investigate the engine in-vehicle performance
Attitudes to telecare among older people, professional care workers and informal carers: a preventative strategy or crisis management?
This paper reports findings from an attitudinal survey towards telecare that emerged from twenty-two focus groups comprising ninety-two older people, fifty-five professional stakeholders and thirty-nine carers. These were convened in three different regions of England as a precursor to telecare service development. The results from this study suggest that informants’ views were shaped by prior knowledge of conventional health and social care delivery in their locality and the implication is that expectations and requirements in respect of telecare services in general are likely to be informed by wider perceptions about the extent to which community care should operate as a preventative strategy or as a mechanism for crisis management
Brief of the Intellectual Property Amicus Brief Clinic of the University of New Hampshire School of Law as Amicus Curiae in Support of Neither Party
Amicus brief filed by the Intellectual Property Amicus Brief Clinic of the University of New Hampshire School of Law with the United States Court Of Appeals For The Ninth Circuit regarding United States v. Xavier Alvarez, Docket No. 11-21
The Effect of Resistivity on the Nonlinear Stage of the Magnetorotational Instability in Accretion Disks
We present three-dimensional magnetohydrodynamic simulations of the nonlinear
evolution of the magnetorotational instability (MRI) with a non-zero Ohmic
resistivity. The properties of the saturated state depend on the initial
magnetic field configuration. In simulations with an initial uniform vertical
field, the MRI is able to support angular momentum transport even for large
resistivities through the quasi-periodic generation of axisymmetric radial
channel solutions rather than through the maintenance of anisotropic
turbulence. Simulations with zero net flux show that the angular momentum
transport and the amplitude of magnetic energy after saturation are
significantly reduced by finite resistivity, even at levels where the linear
modes are only slightly affected. This occurs at magnetic Reynolds numbers
expected in low, cool states of dwarf novae, these results suggest that finite
resistivity may account for the low and high angular momentum transport rates
inferred for these systems.Comment: 8 figures, accepted for publication in Ap
What's the point of knowing how?
Why is it useful to talk and think about knowledge-how? Using Edward Craig’s discussion of the function of the concepts of knowledge and knowledge-how as a jumping off point, this paper argues that considering this question can offer us new angles on the debate about knowledge-how. We consider two candidate functions for the concept of knowledge-how: pooling capacities, and mutual reliance. Craig makes the case for pooling capacities, which connects knowledge-how to our need to pool practical capacities. I argue that the evidence is much more equivocal. My suggested diagnosis is that the concept of knowledge-how plays both functions, meaning that the concept of knowledge-how is inconsistent, and that the debate about knowledge-how is at least partly a metalinguistic negotiation. In closing, I suggest a way to revise the philosophical concept of knowledge how
Global MHD Simulations of Cylindrical Keplerian Disks
This paper presents a series of global three dimensional accretion disk
simulations carried out in the cylindrical limit in which the vertical
component of the gravitational field is neglected. The simulations use a
cylindrical pseudo-Newtonian potential to model the main dynamical properties
of the Schwarzschild metric. The disks are initially constant density with a
Keplerian angular momentum distribution and contain a weak toroidal or vertical
field. These simulations reaffirm many of the conclusions of previous local
simulations. The magnetorotational instability grows rapidly and produces MHD
turbulence with a significant Maxwell stress which drives accretion.
Tightly-wrapped low- spiral waves are prominent. In some simulations radial
variations in Maxwell stress concentrate gas into rings, creating substantial
spatial inhomogeneities. There is a nonzero stress at the marginally stable
orbit which produces a small decline in specific angular momentum inside the
last stable orbit. Detailed comparisons between simulations are used to examine
the effects of computational domain and equation of state. Simulations that
begin with vertical fields have greater field amplification and higher ratios
of stress to magnetic pressure compared with those beginning with toroidal
fields. In contrast to MHD, hydrodynamics alone neither creates nor sustains
turbulence.Comment: Submitted to the Astrophysical Journal Web version of paper and MPEG
animations can be found at http://www.astro.virginia.edu/~jh8h/cylinder
Accretion of low angular momentum material onto black holes: 2D magnetohydrodynamical case
We report on the second phase of our study of slightly rotating accretion
flows onto black holes. We consider magnetohydrodynamical (MHD) accretion flows
with a spherically symmetric density distribution at the outer boundary, but
with spherical symmetry broken by the introduction of a small,
latitude-dependent angular momentum and a weak radial magnetic field. We study
accretion flows by means of numerical 2D, axisymmetric, MHD simulations with
and without resistive heating. Our main result is that the properties of the
accretion flow depend mostly on an equatorial accretion torus which is made of
the material that has too much angular momentum to be accreted directly. The
torus accretes, however, because of the transport of angular momentum due to
the magnetorotational instability (MRI). Initially, accretion is dominated by
the polar funnel, as in the hydrodynamic inviscid case, where material has zero
or very low angular momentum. At the later phase of the evolution, the torus
thickens towards the poles and develops a corona or an outflow or both.
Consequently, the mass accretion through the funnel is stopped. The accretion
of rotating gas through the torus is significantly reduced compared to the
accretion of non-rotating gas (i.e., the Bondi rate). It is also much smaller
than the accretion rate in the inviscid, weakly rotating case.Our results do
not change if we switch on or off resistive heating. Overall our simulations
are very similar to those presented by Stone, Pringle, Hawley and Balbus
despite different initial and outer boundary conditions. Thus, we confirm that
MRI is very robust and controls the nature of radiatively inefficient accretion
flows.Comment: submitted in Ap
Coaxial microwave electrothermal thruster performance in hydrogen
The microwave electro thermal thruster (MET) is an electric propulsion concept that offers the promise of high performance combined with a long lifetime. A unique feature of this electric propulsion concept is its ability to create a microwave plasma discharge separated or floating away from any electrodes or enclosing walls. This allows propellant temperatures that are higher than those in resistojets and reduces electrode and wall erosion. It has been demonstrated that microwave energy is coupled into discharges very efficiently at high input power levels. As a result of these advantages, the MET concept has been identified as a future high power electric propulsion possibility. Recently, two additional improvements have been made to the coaxial MET. The first was concerned with improving the microwave matching. Previous experiments were conducted with 10-30 percent reflected power when incident power was in excess of 600 W(exp 6). Power was reflected back to the generator because the impedance of the MET did not match the 50 ohm impedance of the microwave circuit. To solve this problem, a double stub tuning system has been inserted between the MET and the microwave power supply. The addition of the double stub tuners reduces the reflected power below 1 percent. The other improvement has prepared the coaxial MET for hydrogen experiments. To operate with hydrogen, the vacuum window which separates the coaxial line from the discharge chamber has been changed from teflon to boron nitride. All the microwave energy delivered to the plasma discharge passes through this vacuum window. This material change had caused problems in the past because of the increased microwave reflection coefficients associated with the electrical properties of boron nitride. However, by making the boron nitride window electrically one-half of a wavelength long, power reflection in the window has been eliminated. This technical note summarizes the experimental performance of the improved coaxial MET when operating in nitrogen, helium, and hydrogen gases
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