10,625 research outputs found
Decay of far flow field in trailing vortices
A finite difference machine code is used in the wake vortex problems in the quasi-cylindrical boundary layer approximation. A turbulent energy model containing new features is developed that accounts for the major effects disclosed by more advanced models in which the parameters are not yet established. Several puzzles that arose in previous theoretical investigations of wake vortices are resolved
A site-specific standard for comparing dynamic solar ultraviolet protection characteristics of established tree canopies
A standardised procedure for making fair and comparable assessments of the ultraviolet protection of an established tree canopy that takes into account canopy movement and the changing position of the sun is presented for use by government, planning, and environmental health authorities. The technique utilises video image capture and replaces the need for measurement by ultraviolet radiometers for surveying shade quality characteristics of trees growing in public parks, playgrounds and urban settings. The technique improves upon tree shade assessments that may be based upon single measurements of the ultraviolet irradiance observed from a fixed point of view. The presented technique demonstrates how intelligent shade audits can be conducted without the need for specialist equipment, enabling the calculation of the Shade Protection Index (SPI) and Ultraviolet Protection Factor (UPF) for any discreet time interval and over a full calendar year
A typology for clients' multi-project environments
Construction management research and practice is dominated by a single project paradigm. This does not reflect the true nature of many construction clients who have large multi-project portfolios. Traditional single project management strategies are usually adopted for managing such portfolios - with limited success. The literature suggests that programmes, within portfolios, require different forms of management in order to optimize project delivery. In order to better understand these portfolios and thereby allow the exploration of new forms of management, a typology has been developed mapping out the various features of client's construction portfolios. The resultant typology provides a simple method for identifying the programme composition of a portfolio, highlighting the expected features of each programme type, and thereby directing management attention to the main aspects of each programme that can be optimized for efficiency. Six cases of client's construction project portfolios were studied using a highly structured, replication logic, case study methodology. A typology of clients' multi-project environments was developed and validated through literal and theoretical replication between cases. Three main types emerged as descriptive of programmes within client's construction portfolios: bounded programmes, target programmes and rolling programmes. The distinctive features of each type suggest that programme-specific approaches may be necessary for the successful delivery of projects within client's construction portfolios
Experimental study of optimal measurements for quantum state tomography
Quantum tomography is a critically important tool to evaluate quantum
hardware, making it essential to develop optimized measurement strategies that
are both accurate and efficient. We compare a variety of strategies using
nearly pure test states. Those that are informationally complete for all states
are found to be accurate and reliable even in the presence of errors in the
measurements themselves, while those designed to be complete only for pure
states are far more efficient but highly sensitive to such errors. Our results
highlight the unavoidable tradeoffs inherent to quantum tomography.Comment: 5 pages, 3 figure
Reorientation of the stripe Phase of 2D Electrons by a Minute Density Modulation
Interacting two-dimensional electrons confined in a GaAs quantum well exhibit
isotropic transport when the Fermi level resides in the first excited ()
Landau level. Adding an in-plane magnetic field () typically leads to
an anisotropic, stripe-like (nematic) phase of electrons with the stripes
oriented perpendicular to the direction. Our experimental data reveal
how a periodic density modulation, induced by a surface strain grating from
strips of negative electron-beam resist, competes against the -induced
orientational order of the stripe phase. Even a minute () density
modulation is sufficient to reorient the stripes along the direction of the
surface grating.Comment: Accepted for publication in Phys. Rev. Let
Anisotropic composite fermions and fractional quantum Hall effect
We study the role of anisotropy on the transport properties of composite
fermions near Landau level filling factor in two-dimensional holes
confined to a GaAs quantum well. By applying a parallel magnetic field, we tune
the composite fermion Fermi sea anisotropy and monitor the relative change of
the transport scattering time at along the principal directions.
Interpreted in a simple Drude model, our results suggest that the scattering
time is longer along the longitudinal direction of the composite fermion Fermi
sea. Furthermore, the measured energy gap for the fractional quantum Hall state
at decreases when anisotropy becomes significant. The decrease,
however, might partly stem from the charge distribution becoming bilayer-like
at very large parallel magnetic fields
Periods implying almost all periods, trees with snowflakes, and zero entropy maps
Let be a compact tree, be a continuous map from to itself,
be the number of endpoints and be the number of edges of .
We show that if has no prime divisors less than and has a
cycle of period , then has cycles of all periods greater than
and topological entropy ; so if is the least prime
number greater than and has cycles of all periods from 1 to
, then has cycles of all periods (this verifies a conjecture
of Misiurewicz for tree maps). Together with the spectral decomposition theorem
for graph maps it implies that iff there exists such that has
a cycle of period for any . We also define {\it snowflakes} for tree
maps and show that iff every cycle of is a snowflake or iff the
period of every cycle of is of form where is an odd
integer with prime divisors less than
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