22,324 research outputs found
Reversible signal transmission in an active mechanical metamaterial
Mechanical metamaterials are designed to enable unique functionalities, but
are typically limited by an initial energy state and require an independent
energy input to function repeatedly. Our study introduces a theoretical active
mechanical metamaterial that incorporates a biological reaction mechanism to
overcome this key limitation of passive metamaterials. Our material allows for
reversible mechanical signal transmission, where energy is reintroduced by the
biologically motivated reaction mechanism. By analysing a coarse grained
continuous analogue of the discrete model, we find that signals can be
propagated through the material by a travelling wave. Analysis of the continuum
model provides the region of the parameter space that allows signal
transmission, and reveals similarities with the well-known FitzHugh-Nagumo
system. We also find explicit formulae that approximate the effect of the
timescale of the reaction mechanism on the signal transmission speed, which is
essential for controlling the material.Comment: 20 pages, 7 figure
Two quantum Simpson's paradoxes
The so-called Simpson's "paradox", or Yule-Simpson (YS) effect, occurs in
classical statistics when the correlations that are present among different
sets of samples are reversed if the sets are combined together, thus ignoring
one or more lurking variables. Here we illustrate the occurrence of two
analogue effects in quantum measurements. The first, which we term
quantum-classical YS effect, may occur with quantum limited measurements and
with lurking variables coming from the mixing of states, whereas the second,
here referred to as quantum-quantum YS effect, may take place when coherent
superpositions of quantum states are allowed. By analyzing quantum measurements
on low dimensional systems (qubits and qutrits), we show that the two effects
may occur independently, and that the quantum-quantum YS effect is more likely
to occur than the corresponding quantum-classical one. We also found that there
exist classes of superposition states for which the quantum-classical YS effect
cannot occur for any measurement and, at the same time, the quantum-quantum YS
effect takes place in a consistent fraction of the possible measurement
settings. The occurrence of the effect in the presence of partial coherence is
discussed as well as its possible implications for quantum hypothesis testing.Comment: published versio
Survey of respiratory sounds in infants
Background: Over the last decade there
has been an apparent increase in childhood
wheeze. We speculated that much of
the reported increase may be attributed to
the term wheeze being adopted by parents
to describe a variety of other forms of
noisy breathing.
Aims: To investigate terminology used by
parents to describe their children’s breath
sounds.
Methods: An interview was carried out
with the parents of 92 infants with noisy
breathing, beginning with an open question
and then directed towards a more
detailed description. Finally, the parents
were asked to choose from a wheeze,
ruttle, and stridor on imitation by the
investigator and video clips of children.
Results: Wheeze was the most commonly
chosen word on initial questioning (59%).
Only 36% were still using this term at the
end of the interview, representing a decrease
of one third, whereas the use of the
word ruttles doubled.
Conclusions: Our results reflect the degree
of inaccuracy involved in the use of
the term wheeze in clinical practice,
which may be leading to over diagnosis.
Imprecise use of this term has potentially
important implications for therapy and
clinical trials
Fuselage shell and cavity response measurements on a DC-9 test section
A series of fuselage shell and cavity response measurements conducted on a DC-9 aircraft test section are described. The objectives of these measurements were to define the shell and cavity model characteristics of the fuselage, understand the structural-acoustic coupling characteristics of the fuselage, and measure the response of the fuselage to different types of acoustic and vibration excitation. The fuselage was excited with several combinations of acoustic and mechanical sources using interior and exterior loudspeakers and shakers, and the response to these inputs was measured with arrays of microphones and accelerometers. The data were analyzed to generate spatial plots of the shell acceleration and cabin acoustic pressure field, and corresponding acceleration and pressure wavenumber maps. Analysis and interpretation of the spatial plots and wavenumber maps provided the required information on modal characteristics, structural-acoustic coupling, and fuselage response
Electrical conduction of silicon oxide containing silicon quantum dots
Current-voltage measurements have been made at room temperature on a Si-rich
silicon oxide film deposited via Electron-Cyclotron Resonance Plasma Enhanced
Chemical Vapor Deposition (ECR-PECVD) and annealed at 750 - 1000C. The
thickness of oxide between Si quantum dots embedded in the film increases with
the increase of annealing temperature. This leads to the decrease of current
density as the annealing temperature is increased. Assuming the Fowler-Nordheim
tunneling mechanism in large electric fields, we obtain an effective barrier
height of 0.7 0.1 eV for an electron tunnelling
through an oxide layer between Si quantum dots. The Frenkel-Poole effect can
also be used to adequately explain the electrical conduction of the film under
the influence of large electric fields. We suggest that at room temperature Si
quantum dots can be regarded as traps that capture and emit electrons by means
of tunneling.Comment: 14 pages, 5 figures, submitted to J. Phys. Conden. Mat
UHB demonstrator interior noise control flight tests and analysis
The measurement and analysis of MD-UHB (McDonnell Douglas Ultra High Bypass) Demonstrator noise and vibration flight test data are described as they relate to passenger cabin noise. The analyses were done to investigate the interior noise characteristics of advanced turboprop aircraft with aft-mounted engines, and to study the effectiveness of selected noise control treatments in reducing passenger cabin noise. The UHB Demonstrator is an MD-80 test aircraft with the left JT8D engine replaced with a prototype UHB engine. For these tests, the UHB engine was a General Electric Unducted Fan, with either 8x8 or 10x8 counter-rotating propeller configurations. Interior noise level characteristics were studied for several altitudes and speeds, with emphasis on high altitude (35,000 ft), high speed (0.75 Mach) cruise conditions. The effectiveness of several noise control treatments was evaluated based on cabin noise measurements. The important airborne and structureborne transmission paths were identified for both tonal and broadband sources using the results of a sound intensity survey, exterior and interior noise and vibration data, and partial coherence analysis techniques. Estimates of the turbulent boundary layer pressure wavenumber-frequency spectrum were made, based on measured fuselage noise levels
Scoping recreational disturbance of shorebirds to inform the agenda for research and management in Tropical Asia
In addition to scoping the impacts of the four most reported sources of recreational disturbance on shorebirds, this study also advances the concept of Tropical Asia (TA) to collectively describe tourist destinations in the ecologically and geopolitically diverse part of the planet that incorporates the tourism megaregion of South and Southeast Asia. At a time of growing global concern about the rapid decline of shorebird populations, many governments in TA are embracing and capitalising on the exponential growth in demand for coastal recreation and tourism across the region. This political response is partly driven by efforts to deliver economic development, aligned to the United Nations Sustainable Development Goals, in order to secure the livelihoods of people living in less developed coastal areas. However, the rapid increase in visitor numbers and the development of infrastructure to support the booming demand for coastal tourism destinations in TA are further exacerbating the pressures on shorebird populations across the region. Despite these growing pressures and the wealth of research reporting on shorebird populations across the Asian flyways, this scoping study identified surprisingly little research that reports on the recreational disturbance of shorebirds in TA. While undertaken to inform future research, this study also provides a synthesis of management strategies reported in the global literature into a set of management recommendations for coastal destinations in TA
Spectral Analysis for Matrix Hamiltonian Operators
In this work, we study the spectral properties of matrix Hamiltonians
generated by linearizing the nonlinear Schr\"odinger equation about soliton
solutions. By a numerically assisted proof, we show that there are no embedded
eigenvalues for the three dimensional cubic equation. Though we focus on a
proof of the 3d cubic problem, this work presents a new algorithm for verifying
certain spectral properties needed to study soliton stability. Source code for
verification of our comptuations, and for further experimentation, are
available at http://www.math.toronto.edu/simpson/files/spec_prop_code.tgz.Comment: 57 pages, 22 figures, typos fixe
The interview as narrative ethnography : seeking and shaping connections in qualitative research.
Acts of counter-subjectification in qualitative research are always present but are often submerged in accounts that seek to locate the power of subjectification entirely with the researcher. This is particularly so when talking to people about sensitive issues. Based on an interview-based study of infertility and reproductive disruption among British Pakistanis in Northeast England, we explore how we, as researchers, sought and were drawn into various kinds of connections with the study participants; connections that were actively and performatively constructed through time. The three of us that conducted interviews are all female academics with Ph.Ds in anthropology, but thereafter our backgrounds, life stories and experiences diverge in ways that intersected with those of our informants in complex and shifting ways. We describe how these processes shaped the production of narrative accounts and consider some of the associated analytical and ethical implications
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