Bottom-up photonic crystal lasers

The directed growth of III-V nanopillars is used to demonstrate bottom-up photonic crystal lasers. Simultaneous formation of both the photonic band gap and active gain region is achieved via catalyst-free selective-area metal-organic chemical vapor deposition on masked GaAs substrates. The nanopillars implement a GaAs/InGaAs/GaAs axial double heterostructure for accurate, arbitrary placement of gain within the cavity and lateral InGaP shells to reduce surface recombination. The lasers operate single-mode at room temperature with low threshold peak power density of ～625 W/cm2. Cavity resonance and lasing wavelength is lithographically defined by controlling pillar pitch and diameter to vary from 960 to 989 nm. We envision this bottom-up approach to pillar-based devices as a new platform for photonic systems integration.     

Transport modulation in Ge/Si core/shell nanowires through controlled synthesis of doped Si shells

Appropriately controlling the properties of the Si shell in Ge/Si core/shell nanowires permits not only passivation of the Ge surface states, but also introduces new interface phenomena, thereby enabling novel nanoelectronics concepts. Here, we report a rational synthesis of Ge/Si core/shell nanowires with doped Si shells. We demonstrate that the morphology and thickness of Si shells can be controlled for different dopant types by tuning the growth parameters during synthesis. We also present distinctly different electrical characteristics that arise from nanowire field-effect transistors fabricated using the synthesized Ge/Si core/shell nanowires with different shell morphologies. Furthermore, a clear transition in the modification of device characteristics is observed for crystalline shell nanowires following removal of the shell using a unique trimming process of successive native oxide formation/etching. Our results demonstrate that the preferred transport path through the nanowire structure can be modulated by appropriately tuning the growth conditions.     

Investigation of the emission mechanism in milled SrAl₂O₄:Eu, Dy using optical and synchrotron X-ray spectroscopy

There currently exists much debate as to the active state related to the "long afterglow" effect in europium doped oxide materials. Redox couples that consist of Eu(+/2+) and Eu(2+/3+) are discussed, but no common answer is currently accepted. Here, we present a comparison of the optical properties of a commercially available SrAl(2)O(4):Eu, Dy phosphor, as a function of nanoparticle size reduction via dry mechanical milling. X-ray and optical spectroscopic data indicate a significant decrease in phosphorescence efficiency and an increase in laser stimulated emission efficiency as near surface Eu(2+) ions are oxidized to Eu(3+) as a consequence of increased exposure during the milling process. These results show evidence only for Eu(2+/3+) oxidation states, suggesting the mechanism related to long afterglow effect does not arise from Eu(+) species. We also suggest that size reduction, as a rule, cannot be universally applied to improve optical properties of nanostructures.     

Charge injection engineering of ambipolar field-effect transistors for high-performance organic complementary circuits

Ambipolar π-conjugated polymers may provide inexpensive large-area manufacturing of complementary integrated circuits (CICs) without requiring micro-patterning of the individual p- and n-channel semiconductors. However, current-generation ambipolar semiconductor-based CICs suffer from higher static power consumption, low operation frequencies, and degraded noise margins compared to complementary logics based on unipolar p- and n-channel organic field-effect transistors (OFETs). Here, we demonstrate a simple methodology to control charge injection and transport in ambipolar OFETs via engineering of the electrical contacts. Solution-processed caesium (Cs) salts, as electron-injection and hole-blocking layers at the interface between semiconductors and charge injection electrodes, significantly decrease the gold (Au) work function (～4.1 eV) compared to that of a pristine Au electrode (～4.7 eV). By controlling the electrode surface chemistry, excellent p-channel (hole mobility ～0.1-0.6 cm(2)/(Vs)) and n-channel (electron mobility ～0.1-0.3 cm(2)/(Vs)) OFET characteristics with the same semiconductor are demonstrated. Most importantly, in these OFETs the counterpart charge carrier currents are highly suppressed for depletion mode operation (I(off) < 70 nA when I(on) > 0.1-0.2 mA). Thus, high-performance, truly complementary inverters (high gain >50 and high noise margin >75% of ideal value) and ring oscillators (oscillation frequency ～12 kHz) based on a solution-processed ambipolar polymer are demonstrated.     

Simulating Cities: Process,Product, and Prognosis

Problem, research strategy, and findings: Little research examines the effect of diversity on regional economic resilience to natural disasters. We examine whether economic diversity benefits regional economies in typical circumstances and in recovery after a natural disaster, using the case of the 1993 U.S. Midwest flood. By matching counties in the nine states affected by the flood to control counties, we isolate the influence of diversity on employment and income in normal circumstances and after a substantial shock. We found economic diversity to have mixed associations with employment and income in typical circumstances. On average, economically diverse counties tended to experience faster employment gains but slower growth in per capita income than less diverse areas. The effect of economic diversity upon resilience following a natural disaster was unambiguous. Economic diversity aided counties in weathering the downturn following the flood and sped their return to long-term patterns of employment and income growth.

Takeaway for practice: In promoting policies to enhance economic diversity, planners in communities located in areas prone to natural disasters should consider both the goal of disaster resilience and the potential tradeoffs between different aspects of economic performance.

Research support: None.     

Citizen Participation in Planning: The Relationship Between Objectives and Techniques

Problem: As Richard Florida's writings about the creative class garnered attention across the globe, planners and local government officials responded by enacting policies to attract and retain creative workers, often favoring spending for amenity and lifestyle attractions over more established economic development approaches. It is not clear, however, if the presence of these workers drives regional growth and development as effectively as more traditionally accepted place-based and institutional factors.

Purpose: In this article we explore the relationships between the presence of the creative class and regional economic performance, contrasting measures of regional creative capacity with traditional competitiveness factors.

Methods: We examine how Florida's creative class measures correlate with each other and with common indicators of economic performance for U.S. metropolitan areas. We also estimate multivariate regression models to compare the influence of Florida's measures to those of more traditional indicators of economic competitiveness on metropolitan job growth, income growth, and job instability.

Results and conclusions: We find that differences in Florida's measures of creativity are not generally associated with differences in metropolitan economic performance. Indicators of human capital and industry composition perform as well or better than talent, tolerance, and technology in explaining metropolitan job and income growth and job instability.

Takeaway for practice: Since we find measures derived from Florida's creative class hypotheses to be no more associated with positive economic outcomes than traditional competitiveness measures, we do not advocate replacing traditional economic development strategies with those based primarily on attracting the creative class. Programs supporting education, business creation, and industrial diversity are more likely to be effective tools for promoting economic well-being.

Research support: We received support from the Center for the Study of the American South and the Office of Economic and Business Development's Program on Southern Politics, Media, and Public Life, both of the University of North Carolina at Chapel Hill.     

The impact of cooling ponds in North Central Texas on dairy farm performance

The objective of this study was to determine whether measurable differences existed between farms with and without cooling ponds. Data from Dairy Herd Improvement records for 1999 through 2002 were obtained on 42 herds located in North Central Texas. Nineteen herds had installed cooling ponds, whereas 23 herds had not. Monthly somatic cell counts for each herd were obtained from the Federal Milk Market Administrator. Data were analyzed using the PROC MIXED regression model of SAS. Within and across herd groups, milk production from June to October was significantly lower compared with milk production for the rest of the year. Although there was numerically higher average milk production per cow per day throughout the year for herds that used cooling ponds, differences between herd groups that used or did not use cooling ponds were significant only for August production. Herds without a cooling pond had 4.8 kg/d per cow lower production in August than in the cool-season months of November to May (26.4 ± 0.6 vs. 31.2 ± 0.5 kg/d), whereas the difference in August production was only 2.9 kg/d per cow in herds that used cooling ponds (29.0 ± 0.7 vs. 31.9 ± 0.6 kg/d). Differences caused by seasonal use of a cooling pond in culling, days to first service, days open, percentage of estruses observed, and somatic cell counts were not significant. Bulk tank milk samples cultured for 10 different bacteria showed no difference between cooling pond and noncooling pond herds in 2002. Also, there was no difference in incidence of violations from the Texas Department of Health for herds that used or did not use cooling ponds. However, herds with cooling ponds did have a lower percentage of successful breedings, fewer days dry, and a higher percentage of cows in milk compared with dairy herds that used other forms of cooling. Such differences may or may not be attributed to seasonal use of a cooling pond. Therefore, cooling ponds may provide relief from heat stress without adversely affecting most important measures of herd performance.     

Artificial Intelligence-based Module Type Package-compatible Smart Sensors in the Process Industry

Image analysis presents a set of powerful methods to receive additional information about multiphase processes. It enables the development of advanced applications for process monitoring and optimization or, so-called, soft sensors. However, the integration of advanced smart sensor systems based on image analysis into the process control system presents a complex task. To address this challenge, a modular automation concept offers a standardized interface to integrate modules. This paper presents an integration profile as a service specification that allows a plug-and-measure integration of smart visual sensors into modular plants. To verify the concept, we applied it to three different use cases. At the end, we discuss open challenges in the integration of complex analysis systems with multidimensional data streams into modular plants.