932 research outputs found
The Resonant Theory Of Longitudinal Emittance Blowup By Phase modulated high Harmonic Cavities
Electric Switching of the Charge-Density-Wave and Normal Metallic Phases in Tantalum Disulfide Thin-Film Devices
We report on switching among three charge-density-wave phases - commensurate,
nearly commensurate, incommensurate - and the high-temperature normal metallic
phase in thin-film 1T-TaS2 devices induced by application of an in-plane
electric field. The electric switching among all phases has been achieved over
a wide temperature range, from 77 K to 400 K. The low-frequency electronic
noise spectroscopy has been used as an effective tool for monitoring the
transitions, particularly the switching from the incommensurate
charge-density-wave phase to the normal metal phase. The noise spectral density
exhibits sharp increases at the phase transition points, which correspond to
the step-like changes in resistivity. Assignment of the phases is consistent
with low-field resistivity measurements over the temperature range from 77 K to
600 K. Analysis of the experimental data and calculations of heat dissipation
suggest that Joule heating plays a dominant role in the electric-field induced
transitions in the tested 1T-TaS2 devices on Si/SiO2 substrates. The
possibility of electrical switching among four different phases of 1T-TaS2 is a
promising step toward nanoscale device applications. The results also
demonstrate the potential of noise spectroscopy for investigating and
identifying phase transitions in materials.Comment: 32 pages, 7 figure
A content analysis of the consumer-facing online information about my health record: Implications for increasing knowledge and awareness to facilitate uptake and use
© The Author(s) 2017. Background: Low health literacy, low levels of positive belief and privacy and security concerns have been identified as a significant barrier to personal electronic health record uptake and use. An important tool for overcoming these barriers is the consumer-facing information which accompanies the system. My Health Record (MyHR) is the Australian national e-health record system, for which a large suite of online resources exists to facilitate consumer registration and use. This study uses a number of different measures of health resource quality to assess the MyHR online consumer-facing information and identify any gaps or areas for improvement. Objective: To analyse the quality and content of the online consumer-facing resources which support the uptake and use of MyHR. Method: Australian information resources aimed at healthcare consumers about the MyHR were included in this study. A comprehensive search using Internet search engines was conducted to locate all online consumer-facing resources about MyHR from both government and non-government sources. Readability (measured by Flesch–Kincaid grade level), year of publication/review, publishing organisation type, presentation style, linked websites, target audience, and themes were identified as important measures of health information quality, and these were recorded and reported on for each resource. Results: Eighty resources met the inclusion criteria. The mean Flesch–Kincaid grade level was 11.8. Most resources were created by Australian government sources (n = 55), and the most common target audience was the general public (n = 65). Registration (n = 51), privacy/security (n = 49), and benefits of use (n = 46) were the most common resource themes. Conclusion: The authors identified a number of gaps and areas for improvement in the provision of consumer-facing information about MyHR. Readability is too high for the general Australian population, and there are few translated resources, which means that the information provided does not cater to people with low literacy levels, communication disability, and/or difficulties in understanding written English. The target audiences for resources do not reflect priority groups that were identified during the MyHR development processes. There are also gaps in information provision about how consumers can use MyHR as a tool to meaningfully engage with health professionals and services to support their own person-centred care
Optical and Acoustic Phonons in Turbostratic and Cubic Boron Nitride Thin Films on Diamond Substrates
We report an investigation of the bulk optical, bulk acoustic, and surface
acoustic phonons in thin films of turbostratic boron nitride (t-BN) and cubic
boron nitride (c-BN) grown on B-doped polycrystalline and single-crystalline
diamond (001) and (111) substrates. The characteristics of different types of
phonons were determined using Raman and Brillouin-Mandelstam light scattering
spectroscopies. The atomic structure of the films was determined using
high-resolution transmission electron microscopy (HRTEM) and correlated with
the Raman and Brillouin-Mandelstam spectroscopy data. The HRTEM analysis
revealed that the cubic boron nitride thin films consisted of a mixture of c-BN
and t-BN phases, with c-BN being the dominant phase. It was found that while
visible Raman spectroscopy provided information for characterizing the t-BN
phase, it faced challenges in differentiating the c-BN phase either due to the
presence of high-density defects or the overlapping of the Raman features with
those from the B-doped diamond substrates. In contrast, Brillouin-Mandelstam
spectroscopy clearly distinguishes the bulk longitudinal and surface acoustic
phonons of the c-BN thin films grown on diamond substrates. Additionally, the
angle-dependent surface Brillouin-Mandelstam scattering data show the peaks
associated with the Rayleigh surface acoustic waves, which have higher phase
velocities in c-BN films on diamond (111) substrates. These findings provide
valuable insights into the phonon characteristics of the c-BN and diamond
interfaces and have important implications for the thermal management of
electronic devices based on ultra-wide-band-gap materials.Comment: 27 pages; 4 figure
Thermal Conductivity and Thermal Rectification in Graphene Nanoribbons: a Molecular Dynamics Study
We have used molecular dynamics to calculate the thermal conductivity of
symmetric and asymmetric graphene nanoribbons (GNRs) of several nanometers in
size (up to ~4 nm wide and ~10 nm long). For symmetric nanoribbons, the
calculated thermal conductivity (e.g. ~2000 W/m-K @400K for a 1.5 nm {\times}
5.7 nm zigzag GNR) is on the similar order of magnitude of the experimentally
measured value for graphene. We have investigated the effects of edge chirality
and found that nanoribbons with zigzag edges have appreciably larger thermal
conductivity than nanoribbons with armchair edges. For asymmetric nanoribbons,
we have found significant thermal rectification. Among various
triangularly-shaped GNRs we investigated, the GNR with armchair bottom edge and
a vertex angle of 30{\deg} gives the maximal thermal rectification. We also
studied the effect of defects and found that vacancies and edge roughness in
the nanoribbons can significantly decrease the thermal conductivity. However,
substantial thermal rectification is observed even in the presence of edge
roughness.Comment: 13 pages, 5 figures, slightly expanded from the published version on
Nano Lett. with some additional note
Direct Observation of Martensitic Phase-Transformation Dynamics in Iron by 4D Single-Pulse Electron Microscopy
The in situ martensitic phase transformation of iron, a complex solid-state transition involving collective atomic displacement and interface movement, is studied in real time by means of four-dimensional (4D) electron microscopy. The iron nanofilm specimen is heated at a maximum rate of ∼10^(11) K/s by a single heating pulse, and the evolution of the phase transformation from body-centered cubic to face-centered cubic crystal structure is followed by means of single-pulse, selected-area diffraction and real-space imaging. Two distinct components are revealed in the evolution of the crystal structure. The first, on the nanosecond time scale, is a direct martensitic transformation, which proceeds in regions heated into the temperature range of stability of the fcc phase, 1185−1667 K. The second, on the microsecond time scale, represents an indirect process for the hottest central zone of laser heating, where the temperature is initially above 1667 K and cooling is the rate-determining step. The mechanism of the direct transformation involves two steps, that of (barrier-crossing) nucleation on the reported nanosecond time scale, followed by a rapid grain growth typically in ∼100 ps for 10 nm crystallites
Graphene -- Based Nanocomposites as Highly Efficient Thermal Interface Materials
We found that an optimized mixture of graphene and multilayer graphene -
produced by the high-yield inexpensive liquid-phase-exfoliation technique - can
lead to an extremely strong enhancement of the cross-plane thermal conductivity
K of the composite. The "laser flash" measurements revealed a record-high
enhancement of K by 2300 % in the graphene-based polymer at the filler loading
fraction f =10 vol. %. It was determined that a relatively high concentration
of single-layer and bilayer graphene flakes (~10-15%) present simultaneously
with thicker multilayers of large lateral size (~ 1 micrometer) were essential
for the observed unusual K enhancement. The thermal conductivity of a
commercial thermal grease was increased from an initial value of ~5.8 W/mK to
K=14 W/mK at the small loading f=2%, which preserved all mechanical properties
of the hybrid. Our modeling results suggest that graphene - multilayer graphene
nanocomposite used as the thermal interface material outperforms those with
carbon nanotubes or metal nanoparticles owing to graphene's aspect ratio and
lower Kapitza resistance at the graphene - matrix interface.Comment: 4 figure
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