3,472 research outputs found
WeChat Adoption among Older Adults and Urban-Rural Differences in China
At the intersection of social digitization and population aging, the challenge of older adults fitting into digital life is becoming more prominent. To understand how to help older adults adopt digital life, this study builds upon the Technology Acceptance Model (TAM) and developed the Digital Technology Motivation Interaction Model (DTMIM) to study the complex effects of autonomous motivation (perceived usefulness, perceived ease of use, perceived enjoyment), controlled motivation, and digital feedback on WeChat adoption among older adults, as well as the urban-rural differences. The results of the questionnaire survey and Fuzzy-set Qualitative Comparative Analysis (fsQCA) show that: First, no single construct is a necessary condition for a high (non-high) attitude toward using (ATU) or high (non-high) actual using (AU). Second, we identified two configurations that trigger high ATU including the autonomy-motivation type and digital feedback under motivational synergy, and three configurations that enable high AU including motivational synergy type, digital feedback under autonomous extrinsic motivation, and digital feedback under motivational synergy. Third, the configurations of high ATU and high AU show significant differences between urban and rural areas. Autonomy motivation plays a universal role in urban older adults’ WeChat adoption, while digital feedback is critical for rural older adults. The configuration analysis of DTMIM and urban-rural differences is not only an adaptive improvement of TAM but also provides new methods and perspectives for future research on the adoption of digital technology
Critical Current Density and Resistivity of MgB2 Films
The high resistivity of many bulk and film samples of MgB2 is most readily
explained by the suggestion that only a fraction of the cross-sectional area of
the samples is effectively carrying current. Hence the supercurrent (Jc) in
such samples will be limited by the same area factor, arising for example from
porosity or from insulating oxides present at the grain boundaries. We suggest
that a correlation should exist, Jc ~ 1/{Rho(300K) - Rho(50K)}, where Rho(300K)
- Rho(50K) is the change in the apparent resistivity from 300 K to 50 K. We
report measurements of Rho(T) and Jc for a number of films made by hybrid
physical-chemical vapor deposition which demonstrate this correlation, although
the "reduced effective area" argument alone is not sufficient. We suggest that
this argument can also apply to many polycrystalline bulk and wire samples of
MgB2.Comment: 11 pages, 3 figure
Thickness dependence of the properties of epitaxial MgB2 thin films grown by hybrid physical-chemical vapor deposition
We have studied the effect of deposition rate and layer thickness on the
properties of epitaxial MgB2 thin films grown by hybrid physical-chemical vapor
deposition on 4H-SiC substrates. The MgB2 film deposition rate depends linearly
on the concentration of B2H6 in the inlet gas mixture. We found that the
superconducting and normal-state properties of the MgB2 films are determined by
the film thickness, not by the deposition rate. When the film thickness was
increased, the transition temperature, Tc, increased and the residual
resistivity, rho0, decreased. Above about 300 nm, a Tc of 41.8 K, a rho0 of
0.28 mikroOhm.cm, and a residual resistance ratio RRR of over 30 were obtained.
These values represent the best MgB2 properties reported thus far.Comment: 10 pages, 4 figure
Object Picture of Quasinormal Modes for Stringy Black Holes
We study the quasinormal modes (QNMs) for stringy black holes. By using
numerical calculation, the relations between the QNMs and the parameters of
black holes are minutely shown. For (1+1)-dimensional stringy black hole, the
real part of the quasinormal frequency increases and the imaginary part of the
quasinormal frequency decreases as the mass of the black hole increases.
Furthermore, the dependence of the QNMs on the charge of the black hole and the
flatness parameter is also illustrated. For (1+3)-dimensional stringy black
hole, increasing either the event horizon or the multipole index, the real part
of the quasinormal frequency decreases. The imaginary part of the quasinormal
frequency increases no matter whether the event horizon is increased or the
multipole index is decreased.Comment: 4 pages, 5 figure
Superconducting properties of nanocrystalline MgB thin films made by an in situ annealing process
We have studied the structural and superconducting properties of MgB thin
films made by pulsed laser deposition followed by in situ annealing. The
cross-sectional transmission electron microscopy reveals a nanocrystalline
mixture of textured MgO and MgB with very small grain sizes. A
zero-resistance transition temperature () of 34 K and a zero-field
critical current density () of A/cm were obtained.
The irreversibility field was 8 T at low temperatures, although severe
pinning instability was observed. These bulk-like superconducting properties
show that the in situ deposition process can be a viable candidate for MgB
Josephson junction technologies
Coherent population trapping in a dressed two-level atom via a bichromatic field
We show theoretically that by applying a bichromatic electromagnetic field,
the dressed states of a monochromatically driven two-level atom can be pumped
into a coherent superposition termed as dressed-state coherent population
trapping. Such effect can be viewed as a new doorknob to manipulate a two-level
system via its control over dressed-state populations. Application of this
effect in the precision measurement of Rabi frequency, the unexpected
population inversion and lasing without inversion are discussed to demonstrate
such controllability.Comment: 14 pages, 6 figure
Nonorthogonal decoy-state Quantum Key Distribution
In practical quantum key distribution (QKD), weak coherent states as the
photon sources have a limit in secure key rate and transmission distance
because of the existence of multiphoton pulses and heavy loss in transmission
line. Decoy states method and nonorthogonal encoding protocol are two important
weapons to combat these effects. Here, we combine these two methods and propose
a efficient method that can substantially improve the performance of QKD. We
find a 79 km increase in transmission distance over the prior record using
decoy states method.Comment: 4 pages, 1 figure; Revtex4, submitted to PR
Fracture of Brittle Metallic Glasses: Brittleness or Plasticity
We report a brittle Mg-based bulk metallic glass which approaches the ideal brittle behavior. However, a dimple structure is observed at the fracture surface by high resolution scanning electron microscopy, indicating some type of "ductile" fracture mechanism in this very brittle glass. We also show, from the available data, a clear correlation between the fracture toughness and plastic process zone size for various glasses. The results indicate that the fracture in brittle metallic glassy materials might also proceed through the local softening mechanism but at different length scales
Mirror-enhanced super-resolution microscopy
Axial excitation confinement beyond the diffraction limit is crucial to the development of next-generation, super-resolution microscopy. STimulated Emission Depletion (STED) nanoscopy offers lateral super-resolution using a donut-beam depletion, but its axial resolution is still over 500 nm. Total internal reflection fluorescence microscopy is widely used for single-molecule localization, but its ability to detect molecules is limited to within the evanescent field of similar to 100 nm from the cell attachment surface. We find here that the axial thickness of the point spread function (PSF) during confocal excitation can be easily improved to 110 nm by replacing the microscopy slide with a mirror. The interference of the local electromagnetic field confined the confocal PSF to a 110-nm spot axially, which enables axial super-resolution with all laser-scanning microscopes. Axial sectioning can be obtained with wavelength modulation or by controlling the spacer between the mirror and the specimen. With no additional complexity, the mirror-assisted excitation confinement enhanced the axial resolution six-fold and the lateral resolution two-fold for STED, which together achieved 19-nm resolution to resolve the inner rim of a nuclear pore complex and to discriminate the contents of 120 nm viral filaments. The ability to increase the lateral resolution and decrease the thickness of an axial section using mirror-enhanced STED without increasing the laser power is of great importance for imaging biological specimens, which cannot tolerate high laser power.National Instrument Development Special Program [2013YQ03065102]; '973' Major State Basic Research Development Program of China [2011CB809101]; Natural Science Foundation of China [31327901, 61475010, 61428501]; Australian Research Council Centre of Excellence for Nanoscale BioPhotonics [CE140100003]; National Institute of Health [GM094198]SCI(E)PubMedä¸å›½ç§‘æŠ€æ ¸å¿ƒæœŸåˆŠ(ISTIC)[email protected]
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