1,754 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
Text Entry in Immersive Head-Mounted Display-Based Virtual Reality Using Standard Keyboards
We study the performance and user experience of two popular mainstream text
entry devices, desktop keyboards and touchscreen keyboards, for use in Virtual
Reality (VR) applications. We discuss the limitations arising from limited
visual feedback, and examine the efficiency of different strategies of use. We
analyze a total of 24 hours of typing data in VR from 24 participants and find
that novice users are able to retain about 60% of their typing speed on a
desktop keyboard and about 40-45\% of their typing speed on a touchscreen
keyboard. We also find no significant learning effects, indicating that users
can transfer their typing skills fast into VR. Besides investigating baseline
performances, we study the position in which keyboards and hands are rendered
in space. We find that this does not adversely affect performance for desktop
keyboard typing and results in a performance trade-off for touchscreen keyboard
typing
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, âsocialâ 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 âaffordancesâ 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
Dark matter within high surface brightness spiral galaxies
We present results from a detailed dynamical analysis of five high surface
brightness, late type spirals, studied with the aim to quantify the
luminous-to-dark matter ratio inside their optical radii. The galaxies' stellar
light distribution and gas kinematics have been observed and compared to
hydrodynamic gas simulations, which predict the 2D gas dynamics arising in
response to empirical gravitational potentials, which are combinations of
differing stellar disk and dark halo contributions. The gravitational potential
of the stellar disk was derived from near-infrared photometry, color-corrected
to constant (M/L); the dark halo was modelled by an isothermal sphere with a
core. Hydrodynamic gas simulations were performed for each galaxy for a
sequence of five different mass fractions of the stellar disk and for a wide
range of spiral pattern speeds. These two parameters mainly determine the
modelled gas distribution and kinematics. The agreement between the
non-axisymmetric part of the simulated and observed gas kinematics permitted us
to conclude that the galaxies with the highest rotation velocities tend to
possess near-maximal stellar disks. In less massive galaxies, with v_max<200
km/s, the mass of the dark halo at least equals the stellar mass within 2-3
R_disk. The simulated gas morphology provides a powerful tool to determine the
dominant spiral pattern speed. The corotation radius for all galaxies was found
to be constant at R_corotation ~ 3 R_disk and encloses the strong part of the
stellar spiral in all cases.Comment: 28 pages, 7 figures; to appear in the Astrophysical Journal, Vol.
586, March 200
Effects of Physician-Based Preventive Oral Health Services on Dental Caries
Most Medicaid programs reimburse nondental providers for preventive dental services. We estimate the impact of comprehensive preventive oral health services (POHS) on dental caries among kindergarten students, hypothesizing improved oral health among students with medical visits with POHS
Benchmark and performance of long-range corrected time-dependent density functional tight binding (LC-TD-DFTB) on rhodopsins and light-harvesting complexes
The chromophores of rhodopsins (Rh) and light-harvesting (LH) complexes still represent a major challenge for a quantum chemical description due to their size and complex electronic structure. Since gradient corrected and hybrid density functional approaches have been shown to fail for these systems, only range-separated functionals seem to be a promising alternative to the more time consuming post-HartreeâFock approaches. For extended sampling of optical properties, however, even more approximate approaches are required. Recently, a long-range corrected (LC) functional has been implemented into the efficient density functional tight binding (DFTB) method, allowing to sample the excited states properties of chromophores embedded into proteins using quantum mechanical/molecular mechanical (QM/MM) with the time-dependent (TD) DFTB approach. In the present study, we assess the accuracy of LC-TD-DFT and LC-TD-DFTB for rhodopsins (bacteriorhodopsin (bR) and pharaonis phoborhodopsin (ppR)) and LH complexes (light-harvesting complex II (LH2) and FennaâMatthewsâOlson (FMO) complex). This benchmark study shows the improved description of the color tuning parameters compared to standard DFT functionals. In general, LC-TD-DFTB can exhibit a similar performance as the corresponding LC functionals, allowing a reliable description of excited states properties at significantly reduced cost. The two chromophores investigated here pose complementary challenges: while huge sensitivity to external field perturbation (color tuning) and charge transfer excitations are characteristic for the retinal chromophore, the multi-chromophoric character of the LH complexes emphasizes a correct description of inter-chromophore couplings, giving less importance to color tuning. None of the investigated functionals masters both systems simultaneously with satisfactory accuracy. LC-TD-DFTB, at the current stage, although showing a systematic improvement compared to TD-DFTB cannot be recommended for studying color tuning in retinal proteins, similar to some of the LC-DFT functionals, because the response to external fields is still too weak. For sampling of LH-spectra, however, LC-TD-DFTB is a viable tool, allowing to efficiently sample absorption energies, as shown for three different LH complexes. As the calculations indicate, geometry optimization may overestimate the importance of local minima, which may be averaged over when using trajectories. Fast quantum chemical approaches therefore may allow for a direct sampling of spectra in the near future
Correction: Benchmark and performance of long-range corrected time-dependent density functional tight binding (LC-TD-DFTB) on rhodopsins and light-harvesting complexes
Correction for âBenchmark and performance of long-range corrected time-dependent density functional tight binding (LC-TD-DFTB) on rhodopsins and light-harvesting complexesâ by Beatrix M. Bold et al., Phys. Chem. Chem. Phys., 2020, 22, 10500â10518, https://doi.org/10.1039/C9CP05753F.
The authors have recognised two errors in the data for the published version of this article. The first one concerns the reported QM/MM calculations on the FennaâMatthewsâOlson (FMO) complex, and the second error affects all Coulomb couplings presented.
In brief, the most important changes are: (i) the ZINDO site energies for the individual pigments are closer to each other and the ZINDO site energy fluctuations are smaller; (ii) the couplings are smaller and now in better agreement with reference data; and (iii) as a consequence, the exciton splitting is decreased. These errors do not change the conclusions of the study but only lead to small corrections of the reported results, as detailed below
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