2,290 research outputs found
Plasmon thermal conductivity of thin Au and Ag films
We investigated the thermal conductivity of surface plasmon polaritons (SPPs)
propagating along thin Au and Ag films on a SiO substrate with a Ti
adhesive layer. To determine the propagation length and skin depth of SPPs
along Au and Ag thin films, we numerically solved the dispersion relation while
considering the size effect of the permittivity of metal. Additionally, we
derived the spatial distribution of SPPs along the film thickness to analyze
the effect of the Ti adhesive layer on the plasmon thermal conductivity of Au
and Ag thin films. Our theoretical predictions revealed a decrease of
approximately 30\% in plasmon thermal conductivity when considering the size
effect of the permittivity of thin metal films. Furthermore, this causes the
film thickness at which maximum thermal conductivity occurs to increase by
about 30\%. Taking these factors into account, we calculated the optimal
thickness of Au and Ag films, along with Ti adhesive layers, on SiO
substrates to be approximately 20 nm. By fabricating a sample with the optimal
thickness of Au and Ag films, we experimentally demonstrated that the plasmon
thermal conductivity of Au and Ag films can be as high as about 20\% of their
electron contribution. This research will broaden the thermal design
applications of ballistic thermal transport by SPPs propagating along thin
metal coatings in microelectronics.Comment: 5 figure
PAGaN I: Multi-Frequency Polarimetry of AGN Jets with KVN
Active Galactic Nuclei (AGN) with bright radio jets offer the opportunity to
study the structure of and physical conditions in relativistic outflows. For
such studies, multi-frequency polarimetric very long baseline interferometric
(VLBI) observations are important as they directly probe particle densities,
magnetic field geometries, and several other parameters. We present results
from first-epoch data obtained by the Korean VLBI Network (KVN) within the
frame of the Plasma Physics of Active Galactic Nuclei (PAGaN) project. We
observed seven radio-bright nearby AGN at frequencies of 22, 43, 86, and 129
GHz in dual polarization mode. Our observations constrain apparent brightness
temperatures of jet components and radio cores in our sample to K
and K, respectively. Degrees of linear polarization are
relatively low overall: less than 10%. This indicates suppression of
polarization by strong turbulence in the jets. We found an exceptionally high
degree of polarization in a jet component of BL Lac at 43 GHz, with 40%. Assuming a transverse shock front propagating downstream along the
jet, the shock front being almost parallel to the line of sight can explain the
high degree of polarization.Comment: 14 pages, 17 figures, 4 tables. To appear in JKAS (received 2015 July
27; accepted 2015 October 25). Note the PAGaN II companion paper by J. Oh et
a
PAGaN II: The Evolution of AGN Jets on Sub-Parsec Scales
We report first results from KVN and VERA Array (KaVA) VLBI observations
obtained in the frame of our Plasma-physics of Active Galactic Nuclei (PAGaN)
project. We observed eight selected AGN at 22 and 43 GHz in single polarization
(LCP) between March 2014 and April 2015. Each source was observed for 6 to 8
hours per observing run to maximize the coverage. We obtained a total of
15 deep high-resolution images permitting the identification of individual
circular Gaussian jet components and three spectral index maps of BL Lac, 3C
111 and 3C 345 from simultaneous dual-frequency observations. The spectral
index maps show trends in agreement with general expectations -- flat core and
steep jets -- while the actual value of the spectral index for jets shows
indications for a dependence on AGN type. We analyzed the kinematics of jet
components of BL Lac and 3C 111, detecting superluminal proper motions with
maximum apparent speeds of about . This constrains the lower limits of the
intrinsic component velocities to and the upper limits of the angle
between jet and line of sight to 20. In agreement with global jet
expansion, jet components show systematically larger diameters at larger
core distances , following the global relation , albeit within
substantial scatter.Comment: 13 pages, 15 figures, 4 tables. To appear in JKAS (received 2015
August 31; accepted 2015 October 15). Note the PAGaN I companion paper by
J.-Y. Kim et a
Boosting thermal conductivity by surface plasmon polaritons propagating along a thin Ti film
We experimentally demonstrate a boosted in-plane thermal conduction by
surface plasmon polaritons (SPPs) propagating along a thin Ti film on a glass
substrate. Owing to a lossy nature of metal, SPPs can propagate over
centimeter-scale distance even with a supported metal film, and resulting
ballistic heat conduction can be quantitatively validated. Further, for a
100-nm-thick Ti film on glass substrate, a significant enhancement of in-plane
thermal conductivity compared to bulk value () is experimentally
shown. This study will provide a new avenue to employ SPPs for heat dissipation
along a supported thin film, which can be readily applied to mitigate hot-spot
issues in microelectronics.Comment: 3 figure
The effect of low temperature aging on the mechanical property & phase stability of Y-TZP ceramics
STATEMENT OF PROBLEM. Recently Yttrium-stabilized tetragonal zirconia polycrystal (Y-TZP) has been introduced due to superior flexural
strength and fracture toughness compared to other dental ceramic systems. Although zirconia has outstanding mechanical properties, the
phenomenon of decrease in the life-time of zirconia resulted from degradation in flexural strength after low temperature aging has been reported.
PURPOSE. The objective of this study was to investigate degradation of flexural strength of Y-TZP ceramics after various low temperature
aging treatments and to evaluate the phase stability and micro-structural change after aging by using X-ray diffraction analysis and a scanning
electron microscope (SEM). MATERIAL AND METHODS. Y-TZP blocks of Vita In-Ceram YZ (Vita Zahnfabrik, Bad Sa ¨ckingen,
Germany) were prepared in 40 mm (length) x 4 mm (width) x 3 mm (height) samples. Specimens were artificially aged in distilled water by heattreatment
at a temperature of 75, 100, 125, 150, 175, 200, and 225℃ for 10 hours, in order to induce the phase transformation at the surface.
To measure the mechanical property, the specimens were subjected to a four-point bending test using a universal testing machine (Instron model
3365; Instron, Canton, Mass, USA). In addition, X-ray diffraction analysis (DMAX 2500; Rigaku, Tokyo, Japan) and SEM (Hitachi s4700; Jeol
Ltd, Tokyo, Japan) were performed to estimate the phase transformation. The statistical analysis was done using SAS 9.1.3 (SAS institute,
USA). The flexural strength data of the experimental groups were analyzed by one-way analysis of variance and to detect statistically significant
differences (α= .05). RESULTS. The mean flexural strength of sintered Vita In-Ceram YZ without autoclaving was 798 MPa. When applied
aging temperature at below 125℃ for 10 hours, the flexural strength of Vita In-Ceram YZ increased up to 1,161 MPa. However, at above 150℃,
the flexural strength started to decrease. Although low temperature aging caused the tetragonal-to-monoclinic phase transformation related
to temperature, the minimum flexural strength was above 700 MPa. CONCLUSION. The monoclinic phase started to appear after aging treatment
above 100℃. With the higher aging temperature, the fraction of monoclinic phase increased. The ratio of monoclinic/tetragonal + monoclinic
phase reached a plateau value, circa 75% above 175℃. The point of monoclinic concentration at which the flexural strength begins to
decrease was between 12% and 54%.This work was supported by the Korea Science and Engineering Foundation (KOSEF) grant funded by the Korea government(MOST)
(No. R01-2007-000-10977-0)
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