An introduction to deep learning

Deep learning (DL) is currently being researched and implemented to solve civil engineering related problems, including autonomous inspection and inventory of civil infrastructure projects. The article introduces DL, specifically a convolutional neural network and the supervised learning process used to train a model that will enable professional structural engineers to automatically detect types of earthquake damage

Length dependence of current-induced breakdown in carbon nanofiber interconnects

Current-induced breakdown is investigated for carbon nanofibers (CNF) for potential interconnect applications. The measured maximum current density in the suspended CNF is inversely proportional to the nanofiber length and is independent of diameter. This relationship can be described with a heat transport model that takes into account Joule heating and heat diffusion along the CNF, assuming that breakdown occurs when and where the temperature reaches a threshold or critical value

Improved contact for thermal and electrical transport in carbon nanofiber interconnects

We study the performance and reliability of carbon nanofiber (CNF) interconnects under high-current stress by examining CNF breakdown for four test configurations, suspended/supported with/without tungsten deposition. The use of W is to improve the CNF-electrode contact. The supported cases show a larger current density just before breakdown than the suspended ones, suggesting an effective heat dissipation to the substrate. The W-deposited contacts reduce the initial total resistance from megaohm range without W to kilo-ohms. High-current stress does not change the total resistance of the test structures with W unlike those without W deposition

Tunneling between carbon nanofiber and gold electrodes

In a carbon nanofiber (CNF)-metal system such as a bridge between two gold electrodes, passing high current (current stressing) reduces the total resistance of the system (CNF resistance RCNF plus contact resistance Rc) by orders of magnitude. The role of current stressing is modeled as a reduction in the interfacial tunneling gap with transport characteristics attributed to tunneling between Au and CNF. The model predicts a reduction in Rc and gradual disappearance of the nonlinearity in the current-voltage (I-V) characteristics as Rc decreases. These results are consistent with measured I-V behavior

Thermoreflectance Measurement of Temperature and Thermal Resistance of Thin Film Gold

To improve performance and reliability of integrated circuits, accurate knowledge of thermal transport properties must be possessed. In particular, reduced dimensions increase boundary scattering and the significance of thermal contact resistance. A thermoreflectance measurement can be used with a valid heat transport model to experimentally quantify the contact thermal resistance of thin film interconnects. In the current work, a quasi-steady state thermoreflectance measurement is used to determine the temperature distribution of a thin film gold interconnect (100 nm) undergoing Joule heating. By comparing the data to a heat transport model accounting for thermal diffusion, dissipation, and Joule heating, a measure of the thermal dissipation or overall thermal resistance of unit area is obtained. The gold film to substrate overall thermal resistance of unit area beneath the wide lead (10 lm) and narrow line (1 lm) of the interconnect are 1.64 Â 10 À6 m 2 K=W and 5.94 Â 10 À6 m 2 K=W, respectively. The thermal resistance of unit area measurements is comparable with published results based on a pump-probe thermoreflectance measurement

Thermoreflectance small scale temperature measurement under ambient conditions

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.dc201

Observed 1970-2005 cooling of summer daytime temperatures in coastal California

This study evaluated 1950–2005 summer [June–August (JJA)] mean monthly air temperatures for two California air basins: the South Coast Air Basin (SoCAB) and the San Francisco Bay Area (SFBA). The study focuses on the more rapid post-1970 warming period, and its daily minima temperature Tmin and maxima temperature Tmax values were used to produce average monthly values and spatial distributions of trends for each air basin. Additional analyses included concurrent SSTs, 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) sea level coastal pressure gradients, and GCM-downscaled average temperature Tave values. Results for all 253 California National Weather Service (NWS) Cooperative Observer Program (COOP) sites together showed increased Tave values (0.23°C decade−1); asymmetric warming, as Tmin values increase faster than Tmax values (0.27° versus 0.04°C decade−1) and thus decreased daily temperature range (DTR) values (0.15°C decade−1). The spatial distribution of observed SoCAB and SFBA Tmax values exhibited a complex pattern, with cooling (−0.30°C decade−1) in low-elevation coastal areas open to marine air penetration and warming (0.32°C decade−1) in inland areas. Results also showed that decreased DTR values in the basins arose from small increases at inland sites (0.16°C decade−1) combined with large decreases (−0.58°C decade−1) at coastal sites. It is also possible that some of the current observed temperature trends could be associated with low-frequency decadal variability, expected even with a constant radiative forcing. Previous studies suggest that cooling JJA Tmax values in coastal California were a result of increased irrigation, coastal upwelling, or cloud cover. The current hypothesis is that they arise (as a possible “reverse reaction”) from the global warming of inland areas, which results in increased sea-breeze flow activity. GCM model Tave warming decreased from 0.13°C decade−1 at inland sites to 0.08°C decade−1 in coastal areas. Sea level pressure increased in the Pacific high and decreased in the thermal low. The corresponding gradient thus showed a trend of 0.04 hPa 100 km−1 decade−1, supportive of the hypothesis of increased sea-breeze activity

Performance of Commercially Available Supercapacitors

High energy density storage device exhibiting a reliable lifecycle is needed in the 21st century. Hence, energy storage research is critical for reducing energy consumption. Supercapacitors exhibit such characteristics via interfacial ion electrosorption and fast redox reactions. They are a feasible solution for transportation applications, among others, due to their superb characteristics. In this paper, we provide a background on supercapacitors, review public data on commercially available supercapacitors for performance characteristics, and finally summarize their performance in terms of energy density, equivalent series resistance, and device time consistency