43,598 research outputs found
Theoretical predictions of jet interaction effects for USB and OWB configurations
A wing jet interaction theory is presented for predicting the aerodynamic characteristics of upper surface blowing and over wing blowing configurations. For the latter configurations, a new jet entrainment theory is developed. Comparison of predicted results with some available data showed good agreement. Some applications of the theory are also presented
Highly frustrated spin-lattice models of magnetism and their quantum phase transitions: A microscopic treatment via the coupled cluster method
We outline how the coupled cluster method of microscopic quantum many-body
theory can be utilized in practice to give highly accurate results for the
ground-state properties of a wide variety of highly frustrated and strongly
correlated spin-lattice models of interest in quantum magnetism, including
their quantum phase transitions. The method itself is described, and it is
shown how it may be implemented in practice to high orders in a systematically
improvable hierarchy of (so-called LSUB) approximations, by the use of
computer-algebraic techniques. The method works from the outset in the
thermodynamic limit of an infinite lattice at all levels of approximation, and
it is shown both how the "raw" LSUB results are themselves generally
excellent in the sense that they converge rapidly, and how they may accurately
be extrapolated to the exact limit, , of the truncation
index , which denotes the {\it only} approximation made. All of this is
illustrated via a specific application to a two-dimensional, frustrated,
spin-half -- model on a honeycomb lattice with
nearest-neighbor and next-nearest-neighbor interactions with exchange couplings
and , respectively, where both
interactions are of the same anisotropic type. We show how the method can
be used to determine the entire zero-temperature ground-state phase diagram of
the model in the range of the frustration parameter and
of the spin-space anisotropy parameter. In particular,
we identify a candidate quantum spin-liquid region in the phase space
A frustrated spin-1/2 Heisenberg antiferromagnet on a chevron-square lattice
The coupled cluster method (CCM) is used to study the zero-temperature
properties of a frustrated spin-half () -- Heisenberg
antiferromagnet (HAF) on a 2D chevron-square lattice. Each site on an
underlying square lattice has 4 nearest-neighbor exchange bonds of strength
and 2 next-nearest-neighbor (diagonal) bonds of strength , with each square plaquette having only one diagonal bond.
The diagonal bonds form a chevron pattern, and the model thus interpolates
smoothly between 2D HAFs on the square () and triangular () lattices,
and also extrapolates to disconnected 1D HAF chains (). The
classical () version of the model has N\'{e}el order for and a form of spiral order for , where
. For the model we use both these classical
states, as well as other collinear states not realized as classical
ground-state (GS) phases, as CCM reference states, on top of which the
multispin-flip configurations resulting from quantum fluctuations are
incorporated in a systematic truncation scheme, which we carry out to high
orders and extrapolate to the physical limit. We calculate the GS energy, GS
magnetic order parameter, and the susceptibilities of the states to various
forms of valence-bond crystalline (VBC) order, including plaquette and two
different dimer forms. We find that the model has two quantum
critical points, at and ,
with N\'{e}el order for , a form of spiral order for
that includes the correct three-sublattice
spin ordering for the triangular-lattice HAF at , and
parallel-dimer VBC order for
Goal conflict, goal facilitation, and health professionals' provision of physical activity advice in primary care : An exploratory prospective study
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A tale of one city: intra-institutional variations in migrating VLE platform
City University London committed in 2009 to make Moodle the Virtual Learning Environment (VLE) at the core of a new Strategic Learning Environment (SLE) comprised of VLE, externally facing website and related systems such as video streaming and virtual classrooms. Previously, the WebCT VLE had been separate from most of the other systems at the institution with very limited connections to other tools. Each of the schools within the institution was able to pursue their own strategy and timeframe for the migration and embedding of Moodle within their subject areas, within an absolute limit of 2 years. This paper outlines the approaches taken by the various schools, highlighting similarities and differences, and draws out common aspects from the project to make recommendations for institutions seeking to undertake similar migrations
Resistive flow in a weakly interacting Bose-Einstein condensate
We report the direct observation of resistive flow through a weak link in a
weakly interacting atomic Bose-Einstein condensate. Two weak links separate our
ring-shaped superfluid atomtronic circuit into two distinct regions, a source
and a drain. Motion of these weak links allows for creation of controlled flow
between the source and the drain. At a critical value of the weak link
velocity, we observe a transition from superfluid flow to superfluid plus
resistive flow. Working in the hydrodynamic limit, we observe a conductivity
that is 4 orders of magnitude larger than previously reported conductivities
for a Bose-Einstein condensate with a tunnel junction. Good agreement with
zero-temperature Gross-Pitaevskii simulations and a phenomenological model
based on phase slips indicate that the creation of excitations plays an
important role in the resulting conductivity. Our measurements of resistive
flow elucidate the microscopic origin of the dissipation and pave the way for
more complex atomtronic devices.Comment: Version published in PR
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