Dynamic Characteristics and Effective Stiffness Properties of Honeycomb Composite Sandwich Structures for Highway Bridge Applications

In this paper, a combined analytical and experimental study of dynamic characteristics of honeycomb composite sandwich structures in bridge systems is presented, and a relatively simple and reliable dynamic experimental procedure to estimate the beam bending and transverse shear stiffness is proposed. This procedure is especially practicable for estimating the beam transverse shear stiffness, which is primarily contributed by the core and is usually difficult to measure. The composite sandwich beams are made of E-glass fiber and polyester resins, and the core consists of the corrugated cells in a sinusoidal configuration. Based on the modeling of equivalent properties for the face laminates and core elements, analytical predictions of effective flexural and transverse shear stiffness properties of sandwich beams along the longitudinal and transverse to the sinusoidal core wave directions are first obtained. Using piezoelectric sensors, the dynamic response data are collected, and the dynamic characteristics of the sandwich structures are analyzed, from which the flexural and transverse shear stiffness properties are reduced. The experimental stiffness results are then compared to the analytical stiffness properties, and relatively good correlations are obtained. The proposed dynamic tests using piezoelectric sensors can be used effectively to evaluate the dynamic characteristics and stiffness properties of large sandwich structures suitable for highway bridge applications.     

DNA detection on plastic: surface activation protocol to convert polycarbonate substrates to biochip platforms

A mild and efficient surface activation protocol to convert polycarbonate (PC) substrates, e.g., plastic bases of compact disks, to biochip platforms for DNA probe immobilization and target detection is described. The preparation procedure (activation, patterning, and coupling) is simple and effective; the on-chip hybridization is sensitive and selective. Particularly, UV/ozone treatment of PC sheets produces a hydrophilic surface with a high density of reactive carboxylic acid groups [(4.8 +/- 0.2) x 10-10 mol/cm2] in less than 10 min at ambient conditions, and no significant aging or physical damage to the substrate is observed. Covalent immobilization of DNA probes via both passive (reagent-less photopatterning and coupling in bulk solution phase) and flow-through (creation of microarrays with microfluidic channel plates) procedures has been demonstrated. Subsequent hybridization shows uniform and strong fluorescent signals for complementary target DNA and allows clear discrimination between fully complementary targets and strands with a single base-pair mismatch. The surface chemistry described herein will facilitate the development of disposable plastic biochips (not limited to DNA microarrays) and the fabrication of biomedical devices that are readable with conventional optical drives.     

A simple method to control the diameter of carbon nanotubes and the effect of the diameter in field emission

We developed a simple method to control the diameter of carbon nanotubes (CNTs) and studied the effect of the diameter of CNTs in field emission. We fabricated Fe nanoparticle arrays of uniform size by filling Fe ion solution in the pores of the anodic aluminum oxide membrane bonded to a silicon wafer. Then we used them as catalysts to fabricate CNTs at a high temperature of 950 °C. The diameter of the nanoparticles could be controlled by changing the concentration of Fe ion solutions and consequently that of CNTs from 5 to 20 nm. Coating the Si wafers with gold greatly increased the field emission. The CNTs showed a good field emission property of a low turn-on field (1.8 V/μm), very high current density (94 mA/cm²) and long-term stability (5 h for 10% degradation of current density from 1 mA/cm²). Decreasing the diameter of the CNTs increased the field emission, while the field emission stability was almost unaffected by the diameter and length.     

Intra-Asia trade and foreign direct investment

This article reconsiders the patterns of intra-Asia trade and the linkages with foreign direct investment (FDI) in this region. The following conclusions are drawn. Firstly, by 1985 intra-Asia trade exhibited both distinct patterns of inter-industry trade on the one hand, and intra-industry trade on the other. Secondly, the patterns of trade in this region have not changed since 1985 from vertical to horizontal, but from a “flying-geese” to an “acrobatic” type, due to the sharp increase in FDI within the region. Thirdly, since the early 1990s, FDI began to shift to China due to the wage differentials between China and other East Asian countries. This made the countries of East Asia compete with one another, rushing to obtain capital and financial resources from all over the world – ultimately contributing to recent financial and economic turbulence in the region. The article concludes with some brief policy recommendations on how to avoid a recurrence of the Asian crisis in the 21 century. Received: 18 August 1997 / Accepted: 16 December 1998     

Flavonoids Seen through the Energy Perspective

In all life forms, opposing forces provide the energy that flows through networks in an organism, which fuels life. In this concept, health is the ability of an organism to maintain the balance between these opposing forces, which creates resilience, and a deranged flow of energy is the basis for diseases. Treatment should focus on adjusting the deranged flow of energy, e.g., by the redox modulating activity of antioxidants. A major group of antioxidants is formed by flavonoids, a group of polyphenolic compounds abundantly present in our diet. The objective here is to review how the redox modulation by flavonoids fits in the various concepts on the mode of action of bioactive compounds, so we can ‘see’ where there is overlap and where the missing links are. Based on this fundament, we should choose our research path aiming to ‘understand’ the redox modulating profile of specific flavonoids, so we can ultimately rationally apply the redox modulating power of flavonoids to improve our health.     

The miRNA-21-5p Payload in Exosomes from M2 Macrophages Drives Tumor Cell Aggression via PTEN/Akt Signaling in Renal Cell Carcinoma

M2 macrophages in the tumor microenvironment are important drivers of cancer metastasis. Exosomes play a critical role in the crosstalk between different cells by delivering microRNAs or other cargos. Whether exosomes derived from pro-tumorigenic M2 macrophages (M2-Exos) could modulate the metastatic behavior of renal cell carcinoma (RCC) is unclear. This study found that M2-Exos promotes migration and invasion in RCC cells. Inhibiting miR-21-5p in M2-Exos significantly reversed their pro-metastatic effects on RCC cells in vitro and in the avian embryo chorioallantoic membrane in vivo tumor model. We further found that the pro-metastatic mechanism of miR-21-5p in M2-Exos is by targeting PTEN-3′UTR to regulate PTEN/Akt signaling. Taken together, our results demonstrate that M2-Exos carries miR-21-5p promote metastatic features of RCC cells through PTEN/Akt signaling. Reversing this could serve as a novel approach to control RCC metastasis.     

National electricity planning in settings with low pre-existing grid coverage: Development of a spatial model and case study of Kenya

We develop a spatial electricity planning model to guide grid expansion in countries with low pre-existing electricity coverage. The model can be used to rapidly estimate connection costs and compare different regions and communities. Inputs that are modeled include electricity demand, costs, and geographic characteristics. The spatial nature of the model permits accurate representation of the existing electricity network and population distribution, which form the basis for future expansion decisions. The methodology and model assumptions are illustrated using country-specific data from Kenya. Results show that under most geographic conditions, extension of the national grid is less costly than off-grid options. Based on realistic penetration rates for Kenya, we estimate an average connection cost of $1900 per household, with lower-cost connection opportunities around major cities and in denser rural regions. In areas with an adequate pre-existing medium-voltage backbone, we estimate that over 30% of households could be connected for less than $1000 per connection through infilling. The penetration rate, an exogenous factor chosen by electricity planners, is found to have a large effect on household connection costs, often outweighing socio-economic and spatial factors such as inter-household distance, per-household demand, and proximity to the national grid.