Characteristics of rain and ice depolarization for a 19- and 28-GHz propagation path from a Comstar satellite

Relationships between rain and ice attenuation and depolarization for several incident polarizations have been determined experimentally for the first time. The relationships are based on measurements made using 19- and 28-GHz beacon transmissions from a Comstar satellite. Vertical and horizontal incident polarizations experience much less depolarization on the average than circular polarization or linear polarization incident at45deg. The measurements confirm that the usual orientations of the major symmetry axes of nonspherical raindrops and ice crystals are nearly horizontal. Joint cumulative distributions of attenuation and depolarization for one year of continuous measurement at 19 and 28 GHz are also presented. These distributions are useful for determining joint attenuation and depolarization margins required to meet outage objectives of specific satellite communication systems. For example, the outage of a 19-GHz dual-polarized system received with a polarization angle21degfrom horizontal and having an attenuation margin of 20 dB would be depolarization-dominated unless the system could also tolerate at least -15-dB depolarization.     

Correlation Bandwidth and Delay Spread Multipath Propagation Statistics for 910-MHz Urban Mobile Radio Channels

Distributions of delay spread and correlation bandwidth at 0.9 and 0.5 correlation for Gaussian wide-sense stationary uncorrelated scattering (GWSSUS) channels associated with 100 small-scale areas at different locations within a 2 × 2.5 km region of New York City are presented. For delay spread the maximum value observed was3frac{1}{2};mus and l0 percent of the areas exceeded2frac{1}{2}mus; for correlation bandwidth at 0.9 correlation the minimum was 20 kHz and 10 percent of the areas were less than 30 kHz; for correlation bandwidth at 0.5 correlation the minimum was 55 kHz and 10 percent of the areas were less than 130 kHz. The region is representative of the heavily built-up areas of many large cities in the United States.     

A small analytical quadrupole mass spectrometer designed for operation in high and ultra high vacuum systems

The characteristics of a small quadrupole mass spectrometer are described in detail. These show that the requirements of an analytical instrument for use in high and ultra high vacuum systems have been met. The performance is adequate for the measurement of partial pressures down to and below 10^?11 torr. This is achieved with constant sensitivity over the range 0–200 amu with a resolution adequate to separate completely individual peaks up to 50 amu. The instrument does not have an electron multiplier. The consequent disadvantages of a relatively slow response and a limitation to the minimum detectable pressure are compensated by a higher stability and a smaller, simpler, and reliable instrument. Observations with a number of units over a period of many months indicate a maximum change in sensitivity of any one and a difference between individual instruments to be of the order of ±20%. This is therefore a gauge head of approximately the same size as a modulated BA gauge with the same sensitivity, stability and baking characteristics.     

Possible and certain keys for SQL

Driven by the dominance of the relational model and the requirements of modern applications, we revisit the fundamental notion of a key in relational databases with NULL. In SQL, primary key columns are NOT NULL, and UNIQUE constraints guarantee uniqueness only for tuples without NULL. We investigate the notions of possible and certain keys, which are keys that hold in some or all possible worlds that originate from an SQL table, respectively. Possible keys coincide with UNIQUE, thus providing a semantics for their syntactic definition in the SQL standard. Certain keys extend primary keys to include NULL columns and can uniquely identify entities whenever feasible, while primary keys may not. In addition to basic characterization, axiomatization, discovery, and extremal combinatorics problems, we investigate the existence and construction of Armstrong tables, and describe an indexing scheme for enforcing certain keys. Our experiments show that certain keys with NULLs occur in real-world data, and related computational problems can be solved efficiently. Certain keys are therefore semantically well founded and able to meet Codd’s entity integrity rule while handling high volumes of incomplete data from different formats.     

Light Extraction Efficiency Enhancement of Colloidal Quantum Dot Light‐Emitting Diodes Using Large‐Scale Nanopillar Arrays

A colloidal quantum dot light‐emitting diode (QLED) is reported with substantially enhanced light extraction efficiency by applying a layer of large‐scale, low‐cost, periodic nanopillar arrays. Zinc oxide nanopillars are grown on the glass surface of the substrate using a simple, efficient method of non‐wetting templates. With the layer of ZnO nanopillar array as an optical outcoupling medium, a record high current efficiency (CE) of 26.6 cd/A is achieved for QLEDs. Consequently, the corresponding external quantum efficiency (EQE) of 9.34% reaches the highest EQE value for green‐emitting QLEDs. Also, the underlying physical mechanisms enabling the enhanced light‐extraction are investigated, which leads to an excellent agreement of the numerical results based on the mode theory with the experimental measurements. This study is the first account for QLEDs offering detailed insight into the light extraction efficiency enhancement of QLED devices. The method demonstrated here is intended to be useful not only for opening up a ubiquitous strategy for designing high‐performance QLEDs but also with respect to fundamental research on the light extraction in QLEDs.     

Application of an X-ray microscopy technique to evaluate tissue-engineered bone-scaffold constructs

Elemental composition and structural analysis are important considerations in evaluating osseous matrix formation in tissue-engineered bone constructs. Using X-ray spectroscopy techniques, such as the X-ray scanning analytical microscope (XSAM), enables the mapping of elements with simultaneous structural imaging. The aim of this study was to evaluate the feasibility of this microscopy technique to analyze tissue-engineered samples. Fused deposition modeling (FDM), a rapid prototyping technology, was used to fabricate 3-D scaffolds made of polycaprolactone (PCL)–hydroxylapatite (HA) (90/10 wt.%). The scaffolds had a regular architecture and the honeycomb-like pores were fully interconnected with a total matrix porosity of 70%. Biopsies of human calvarial corticocancellous bone were harvested and a primary explant system of the morcellized grafts was established within the PCL–HA constructs.

Tissue constructs were cultured in vitro for 3 weeks and then implanted into the back of Balb C nude mice. Grafts were explanted after 17 weeks and tissue formation was assessed via XSAM and CT scan and histology.

Outgrowth from osteoblasts from the bone chips started after 2 weeks in culture, with cells migrating radially into the composite constructs. Osteocalcin levels showed an increasing tendency during the 3-week culture period. After 17 weeks in vivo, areas of ectopic bone formation could be detected throughout the whole construct, compared to the control implants where only fibrous tissue formation was present. In the XSAM, calcium- and phosphorus-enriched bands presented a relatively even distribution with some dense spots. Quantitative elemental analysis revealed an average X-ray intensity of 131 cps for calcium in a mapped area of 2 mm². Trichrome Goldner staining showed good vascularization as well as irregular osteoid formation and mineralization of the newly formed woven bone-like tissue.

In this study, we were able to show that the XSAM is a useful analytical technique which enabled us to trace elements simultaneously and provides structural image with mapping information in tissue-engineered samples.     

The Third-Party Logistics Services and Globalization of Manufacturing

Cross-border production chains of manufacturing require coordination and logistics. Third-party logistics services have thus taken this role as a link in the globalization of economic activities. Distriparks, a provider of total logistics to manufacturing, have emerged in Singapore to offer customized distribution and inventory management. Established as a traditional entrepôt by international trading, the city-state has revamped its distribution industry when transnational corporations come to choose Singapore as regional centre and local firms venture into the region. Distribution has regained its vitality in the global economy. It is demonstrated that distriparks have facilitated the restructuring of Singapore manufacturing and altered the internal structure of firms in their space utilization. Thereafter, a changing profile of industrial landscape, high-density industrial land use, and industrial agglomeration ensues.