1,286 research outputs found
Percolation with long-range correlated disorder
Long-range power-law correlated percolation is investigated using Monte Carlo
simulations. We obtain several static and dynamic critical exponents as
function of the Hurst exponent which characterizes the degree of spatial
correlation among the occupation of sites. In particular, we study the fractal
dimension of the largest cluster and the scaling behavior of the second moment
of the cluster size distribution, as well as the complete and accessible
perimeters of the largest cluster. Concerning the inner structure and transport
properties of the largest cluster, we analyze its shortest path, backbone, red
sites, and conductivity. Finally, bridge site growth is also considered. We
propose expressions for the functional dependence of the critical exponents on
Benchmarking high fidelity single-shot readout of semiconductor qubits
Determination of qubit initialisation and measurement fidelity is important
for the overall performance of a quantum computer. However, the method by which
it is calculated in semiconductor qubits varies between experiments. In this
paper we present a full theoretical analysis of electronic single-shot readout
and describe critical parameters to achieve high fidelity readout. In
particular, we derive a model for energy selective state readout based on a
charge detector response and examine how to optimise the fidelity by choosing
correct experimental parameters. Although we focus on single electron spin
readout, the theory presented can be applied to other electronic readout
techniques in semiconductors that use a reservoir.Comment: 19 pages, 8 figure
Bodies, technologies and action possibilities: when is an affordance?
Borrowed from ecological psychology, the concept of affordances is often said to offer the social study of technology a means of re-framing the question of what is, and what is not, ‘social’ about technological artefacts. The concept, many argue, enables us to chart a safe course between the perils of technological determinism and social constructivism. This article questions the sociological adequacy of the concept as conventionally deployed. Drawing on ethnographic work on the ways technological artefacts engage, and are engaged by, disabled bodies, we propose that the ‘affordances’ of technological objects are not reducible to their material constitution but are inextricably bound up with specific, historically situated modes of engagement and ways of life
North Carolina Physician-Based Preventive Oral Health Services Improve Access And Use Among Young Medicaid Enrollees
To combat disparities in oral health and access to dental care among infants and toddlers, most state Medicaid programs now reimburse physician-based preventive oral health services, such as fluoride varnish applications. We used geospatial data to examine the distribution of dental and medical Medicaid providers of pediatric oral health services throughout North Carolina to determine if these services have improved access to care for Medicaid enrollees younger than three years old. We then used claims data to examine the association between distance from these practices and use of dental services for a cohort of approximately 1,000 young children. Among 100 counties, four counties had no physician-based preventive oral health services and nine counties had no dental practice. While children who lived further from the nearest dental practice were less likely to make dental visits, distance from physician-based preventive oral health services did not predict use. For young Medicaid enrollees, oral health services provided in medical offices can improve access and increase use
Residents\u27 perceptions of smart energy metres
Smart metres are a form of expert system with performance features beyond energy‐consumption record keeping, to include monitoring, analysing, and estimating metre readings. Although smart metres have great capabilities, this technology is still in its infancy in many developing countries, and little is known about the kinds of risks associated with smart metres from residents\u27 perspectives. This research therefore aims to fill this gap by examining the influence of four different types of perceived risk on residents\u27 intentions to use smart metres in Jordan. By following a quantitative approach, 242 survey responses were tested by using structural equation modelling–partial least squares. The statistical results indicated that perceived security and technical risks have a significant and negative impact on residents\u27 intentions to use smart metres. However, perceived privacy and health risks, surprisingly, were found to have no significant negative influence on intention to use. Theoretical and practical implications are indicated, and directions of future research are subsequently specified
Compilation of extended recursion in call-by-value functional languages
This paper formalizes and proves correct a compilation scheme for
mutually-recursive definitions in call-by-value functional languages. This
scheme supports a wider range of recursive definitions than previous methods.
We formalize our technique as a translation scheme to a lambda-calculus
featuring in-place update of memory blocks, and prove the translation to be
correct.Comment: 62 pages, uses pi
Impact of measurement backaction on nuclear spin qubits in silicon
Phosphorus donor nuclear spins in silicon couple weakly to the environment
making them promising candidates for high-fidelity qubits. The state of a donor
nuclear spin qubit can be manipulated and read out using its hyperfine
interaction with the electron confined by the donor potential. Here we use a
master equation-based approach to investigate how the backaction from this
electron-mediated measurement affects the lifetimes of single and multi-donor
qubits. We analyze this process as a function of electric and magnetic fields,
and hyperfine interaction strength. Apart from single nuclear spin flips, we
identify an additional measurement-related mechanism, the nuclear spin
flip-flop, which is specific to multi-donor qubits. Although this flip-flop
mechanism reduces qubit lifetimes, we show that it can be effectively
suppressed by the hyperfine Stark shift. We show that using atomic precision
donor placement and engineered Stark shift, we can minimize the measurement
backaction in multi-donor qubits, achieving larger nuclear spin lifetimes than
single donor qubits
Rupture by damage accumulation in rocks
The deformation of rocks is associated with microcracks nucleation and
propagation, i.e. damage. The accumulation of damage and its spatial
localization lead to the creation of a macroscale discontinuity, so-called
"fault" in geological terms, and to the failure of the material, i.e. a
dramatic decrease of the mechanical properties as strength and modulus. The
damage process can be studied both statically by direct observation of thin
sections and dynamically by recording acoustic waves emitted by crack
propagation (acoustic emission). Here we first review such observations
concerning geological objects over scales ranging from the laboratory sample
scale (dm) to seismically active faults (km), including cliffs and rock masses
(Dm, hm). These observations reveal complex patterns in both space (fractal
properties of damage structures as roughness and gouge), time (clustering,
particular trends when the failure approaches) and energy domains (power-law
distributions of energy release bursts). We use a numerical model based on
progressive damage within an elastic interaction framework which allows us to
simulate these observations. This study shows that the failure in rocks can be
the result of damage accumulation
Quantum point contact on graphite surface
The conductance through a quantum point contact created by a sharp and hard
metal tip on the graphite surface has features which to our knowledge have not
been encountered so far in metal contacts or in nanowires. In this paper we
first investigate these features which emerge from the strongly directional
bonding and electronic structure of graphite, and provide a theoretical
understanding for the electronic conduction through quantum point contacts. Our
study involves the molecular-dynamics simulations to reveal the variation of
interlayer distances and atomic structure at the proximity of the contact that
evolves by the tip pressing toward the surface. The effects of the elastic
deformation on the electronic structure, state density at the Fermi level, and
crystal potential are analyzed by performing self-consistent-field
pseudopotential calculations within the local-density approximation. It is
found that the metallicity of graphite increases under the uniaxial compressive
strain perpendicular to the basal plane. The quantum point contact is modeled
by a constriction with a realistic potential. The conductance is calculated by
representing the current transporting states in Laue representation, and the
variation of conductance with the evolution of contact is explained by taking
the characteristic features of graphite into account. It is shown that the
sequential puncturing of the layers characterizes the conductance.Comment: LaTeX, 11 pages, 9 figures (included), to be published in Phys. Rev.
B, tentatively scheduled for 15 September 1998 (Volume 58, Number 12
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