Assessment of the effectiveness of two heat removal techniques for permafrost protection

Two mitigation techniques, an air convection embankment and an embankment of a granular material with an integrated heat drain, have been tested for the implementation in the shoulders of road and airfield embankments in permafrost regions. Both techniques will allow cold air to penetrate the embankment from the bottom, while warm air is dissipated at the top. The techniques have been tested in the laboratory, where a small-scale embankment (SSE) was build and placed in a cold room to measure the embankment temperatures during winter conditions. A numerical modeling has been developed and calibrated on the SSE to verify the effects on the thermal regime of full-scale embankments. The results have shown that both techniques will cause a decrease in temperature, which will minimize or even possibly avoid permafrost degradation underneath the embankments. The laboratory results have also shown that the effectiveness of the air convection embankment technique can be increased during winter conditions by ventilating the top and the bottom of the embankment shoulders. Installation of air intakes along the shoulders will facilitate air flow into the system during winter and will trap the cold air in the bottom of the embankment through the summer period. This solution has been verified using the numerical model.     

Modeling for temperature compensation and temperature characterizations of BAW resonators at GHz frequencies

This paper deals with the temperature dependence of electrical and physical features of various kinds of solidly mounted resonators (SMR). The presented bulk acoustic wave (BAW) devices are designed for the 2 GHz application. The temperature coefficient of frequency (TCF) is determined from measurements well above the temperature range defined for wireless telecommunication system specifications. Therefore, evolution of electromechanical coupling factors and quality factors at resonance and antiresonance are also monitored. Results of characterizations show the trend for a subsequent theoretical temperature compensation study by using analytical modeling. To improve accuracy of modeling, an attempt to extract temperature dependence of dielectric permittivity epsilon(33) and piezoelectric coefficient e(33) is made. Finally, a well-known analytical model is modified to take into account the temperature dependence of length, density, stiffness coefficient, dielectric permittivity, and piezoelectric coefficient. Modeling highlights the need to deposit a material with positive temperature coefficient of stiffness on the top electrode. Realistic thickness of such a layer is determined. At the same time, it is necessary to adjust piezoelectric and electrode thin film thicknesses for simultaneously keeping a constant antiresonance frequency, reaching a zero temperature coefficient of frequency for antiresonance, and minimizing the decrease in the coupling factor because of the mass-loading deposition.     

Sonochemical coating of silver nanoparticles on textile fabrics (nylon, polyester and cotton) and their antibacterial activity

Silver nanoparticles were synthesized and deposited on different types of fabrics using ultrasound irradiation. The structure of silver-fabric composites was studied by physico-chemical methods. The mechanism of the strong adhesion of silver nanoparticles to the fibers is discussed. The excellent antibacterial activity of the Ag-fabric composite against Escherichia coli (gram-negative) and Staphylococcus aureus (gram-positive) cultures was demonstrated.     

Bone tissue formation in sheep muscles induced by a biphasic calcium phosphate ceramic and fibrin glue composite

Some biomaterials are able to induce ectopic bone formation in muscles of large animals. The osteoinductive potential of macro- micro-porous biphasic calcium phosphate (MBCP) ceramic granules with fibrin glue was evaluated by intramuscular implantation for 6 months in six adult female sheep. The MBCP granules were 1–2 mm in size and were composed of hydroxyapatite (HA) and beta-tricalcium phosphate (β-TCP) in a 60/40 ratio. The fibrin glue was composed of fibrinogen, thrombin and other biological factors. After 6 months of implantation in the dorsal muscles of sheep, the explants were rigid. Histology, back-scattered electron microscopy and micro-computed tomography of the implants indicated that approximately 12% of mineralized bone had formed in between the MBCP granules. The ectopic bone appeared well-mineralized with mature osteocytes and Haversian structures. In addition, the number and thickness of bone trabeculae formed in between the MBCP particles were similar to those measured in trabecular bone in sheep. The overall results therefore confirmed the formation of well-mineralized ectopic bone tissue after intramuscular implantation of MBCP/fibrin glue composites. These bone substitutes exhibiting osteoinductive properties could be used for the reconstruction of large bone defects.     

By invitation only: uses and users of the ‘entrepreneurial city’

Large-scale urban development projects (LSUDPs) are embodying the diffusion of an entrepreneurial approach into urban policy and consequently to planning, with the built environment being transformed into spaces oriented towards specific users and uses. For planning practice, this entails including urban forms and discourses that support exclusion and polarization in planning projects. This paper asks how physical planning promotes and/or hinders spatial and socio-economic integration in these projects. The analysis focuses on two UDPs in Malmö, Sweden. Official planning documents, interviews with public officials and the media are used to illustrate the discourses and practices built around these projects to glance over aspects of equity and integration in a city that is plagued by socio-economic and spatial segregation. The paper contributes to the discussions on implications and dilemmas for physical planning derived from the adoption of entrepreneurial approaches in urban policy.     

The use of remote sensing in light use efficiency based models of gross primary production: a review of current status and future requirements

Global estimation and monitoring of plant photosynthesis (known as Gross Primary Production--GPP) is a critical component of climate change research. Modeling of carbon cycling requires parameterization of the land surface, which, in a spatially continuous mode, is only possible using remote sensing. The increasing availability of high spectral resolution satellite observations with global coverage and high temporal frequency has allowed the scientific community to revisit a number of existing approaches for modeling GPP, and reassess the potential for using remotely sensed inputs. In this paper we examine the current status and future requirements of modeling global GPP thereby focusing on the light use efficiency approach which expresses GPP as product of the photosynthetically active radiation (PAR), the fraction of PAR being absorbed by the plant canopy (f(PAR)) and the efficiency epsilon with which this absorbed PAR can be converted into biomass. The capacity of remote sensing to provide the critical input variables for this approach is reviewed and key issues are identified and discussed for future research.     

Two-degree-of-freedom inclined cable galloping—Part 2: Analysis and prevention for arbitrary frequency ratio

It has previously been shown that inclined cables and other slender structures can experience galloping instabilities in the critical Reynolds number region, due to the changes in force coefficients, and that coupling of the vibrations in two orthogonal planes can significantly affect the behaviour. It is shown in this paper that for more than a few percent detuning of the natural frequencies, the structural damping required to prevent galloping vibrations tends towards solutions for uncoupled single-degree-of-freedom (DOF) systems. However, the coupling can cause the trajectory of cable motion to be elliptical. Using measured force coefficients for an inclined circular cylinder in the critical Reynolds number range, calculated results of the effective damping and the cable trajectory have been obtained in good agreement with a separate full-scale dynamic cable model test that exhibited galloping behaviour under certain conditions. The special case of sub-critical Reynolds numbers is also addressed. The 1DOF and perfectly tuned 2DOF solutions are considered for inclined circular cables in a horizontal wind from any direction, leading to simple guidelines for the structural damping required in practice to prevent dry inclined cable galloping, for any frequency ratio. Finally, other factors in the behaviour and similarity to rain-wind excitation are discussed.     

A wavelet‐Fisz approach to spectrum estimation

Abstract. We propose a new approach to wavelet threshold estimation of spectral densities of stationary time series. Our proposal addresses the problem of heteroscedasticity and non‐normality of the (tapered) periodogram. We estimate thresholds for the empirical wavelet coefficients of the periodogram as appropriate linear combinations of the periodogram values similar to empirical scaling coefficients. Our solution introduces ‘asymptotically noise‐free reconstruction thresholds’ which parallels classical wavelet theory for nonparametric regression with independently and identically distributed Gaussian errors. Our simulations show promising results that clearly improve on existing approaches. In addition, we derive theoretical results on the near‐optimal rate of convergence of the minimax mean‐square risk for a class of spectral densities, including those of low regularity.