Sandstone response to salt weathering following simulated fire damage: a comparison of furnace heating and fire.

Fire has long been recognized as an agent of rock weathering. Our understanding of the impact of fire on stone comes either from early anecdotal evidence, or from more recent laboratory simulation studies, using furnaces to simulate the effects of fire. This paper suggests that knowledge derived from simulated heating experiments is based on the preconceptions of the experiment designer – when using a furnace to simulate fire, the operator decides on the maximum temperature and the duration of the experiment. These are key factors in determining the response of the stone to fire, and if these are removed from realworld observations then knowledge based on these simulations must be questioned. To explore the differences between heating sandstone in a furnace and a real fire, sample blocks of Peakmoor Sandstone were subjected to different stress histories in combination (lime rendering and removal, furnace heating or fire, frost and salt weathering). Block response to furnace heating and fire is discussed, with emphasis placed on the non-uniformity of the fire and of block response to fire in contrast to the uniform response to surface heating in a furnace. Subsequent response to salt weathering (by a 10% solution of sodium chloride and magnesium sulphate) was then monitored by weight loss. Blocks that had experienced fire showed a more unpredictable response to salt weathering than those that had undergone furnace heating – spalling of corners and rapid catastrophic weight loss were evidenced in blocks that had been subjected to fire, after periods of relative quiescence. An important physical side-effect of the fire was soot accumulation, which created a waxy, relatively impermeable layer on some blocks. This layer repelled water and hindered salt ingress, but eventually detached when salt, able to enter the substrate through more permeable areas, concentrated and crystallized behind it, resulting in rapid weight loss and accelerated decay. Copyright ©2007 John Wiley & Sons, Ltd.

Ultra-thin tunable microwave absorber using liquid crystals

A dynamically adaptive radar absorber is described which is based on a periodic array of microstrip patches that are printed on a 500 mu m-thick liquid crystal substrate. The measured reflectivity of the structure is less than -38 dB with a 200 MHz -10 dB bandwidth at 10.19 GHz when a +4 DC bias is applied. It is shown that a 34 dB reduction in signal loss occurs when the bias voltage is increased to 20 V.

Comparison of the volatile components of two cultivars of potato cooked by boiling, conventional baking and microwave baking

Tubers of two cultivars (Estima and Maris Piper) of potato were cooked by three different procedures, ie boiling, conventional baking and microwave baking. Peeled and sliced tubers were boiled, while intact potatoes were baked in their skins. Flavour components from the boiled slices and the flesh of the baked tubers were isolated by headspace adsorption onto Tenax and analysed by gas chromatography-mass spectrometry (GC-MS). For all cooking procedures, Estima gave stronger isolates than Maris Piper. The two main sources of flavour compounds (regardless of cooking procedure) were lipid degradation and the Maillard reaction and/or sugar degradation. The ratio (yield derived from lipid)/(yield derived from Maillard reaction and/or sugar) decreased from 8.5-9.1 (boiling) to 2.7-3.4 (microwave baking) and to 0.4-1.1 (conventional baking). Quantitative and qualitative differences among the cooking procedures are explained in terms of the variations in heat and mass transfer processes that occurred. Each cooking procedure resulted in a unique profile of flavour compounds. (C) 2002 Society of Chemical Industry.

Comparison of the volatile components of eight cultivars of potato after microwave baking

Eight cultivars of potato were baked in a microwave oven. The flavour components of the flesh were isolated by headspace trapping onto Tenax and analysed by gas chromatography-mass spectrometry. Lipid degradation and the Maillard reaction and/or sugar degradation were the main sources of the 80 flavour components identified. It is suggested that total levels of compounds and variations among their profiles may be attributed to differences in activities of lipid enzymes and levels of flavour precursors in the range of cultivars investigated. (C) 2002 Elsevier Science Ltd.

Plasma diagnostics of active-region evolution and implications for coronal heating

A detailed study is presented of the decaying solar-active region NOAA 10103 observed with the Coronal Diagnostic Spectrometer (CDS), the Michelson Doppler Imager (MDI) and the Extreme-ultraviolet Imaging Telescope (EIT) onboard the Solar and Heliospheric Observatory (SOHO). Electron-density maps formed using Si x (356.03 angstrom/347.41 angstrom) show that the density varies from similar to 10(10) cm(-3) in the active-region core to similar to 7 x 108 cm-3 at the region boundaries. Over the 5 d of observations, the average electron density fell by similar to 30 per cent. Temperature maps formed using Fe XVI (335.41 angstrom)/Fe XIV (334.18 angstrom) show electron temperatures of similar to 2.34 x 10(6) K in the active-region core and similar to 2.10 x 10(6) K at the region boundaries. Similarly to the electron density, there was a small decrease in the average electron temperature over the 5-d period. The radiative, conductive and mass-flow losses were calculated and used to determine the resultant heating rate (P-H). Radiative losses were found to dominate the active-region cooling process. As the region decayed, the heating rate decreased by almost a factor of 5 between the first and last day of observations. The heating rate was then compared to the total unsigned magnetic flux (Phi(tot) = integral dA vertical bar B-z vertical bar), yielding a power law of the form P-H similar to Phi(0.81 +/- 0.32)(tot) This result suggests that waves rather than nanoflares may be the dominant heating mechanism in this active region.

Design of asymmetrical RF and microwave bandpass filters by computer optimization

This paper presents an optimization-based approach to the design of asymmetrical filter structures having the maximum number of return- or insertion-loss ripples in the passband such as those based upon Chebyshev function prototypes. The proposed approach. has the following advantages over the general purpose optimization techniques adopted previously such as: less frequency sampling is required, optimization is carried out with respect to the Chebyshev (or minimax) criterion, the problem of local minima does not arise, and optimization is usually only required for the passband. When implemented around an accurate circuit simulation, the method can be used to include all the effects of discontinuities, junctions, fringing, etc. to reduce the amount of tuning required in the final filter. The design of asymmetrical ridged-waveguide bandpass filters is considered as an example. Measurements on a fabricated filter confirm the accuracy of the design procedure.

Improved preparations of ionic liquids using microwave irradiation

Controlled, multimode microwave irradiation has been employed in a generic solvent-free process to prepare a wide range of ionic liquids based on nitrogen-containing heterocycles. The developed method offers a flexible, small to large-scale approach to prepare ionic liquids, in either sealed or open vessels, in a faster and greener process than any previously described.

MODULATED BACKSCATTER MICROWAVE SECURITY SENSOR

A system capable of deployment as a microwave security sensor which can automatically reject background clutter is presented. The principle of operation is based on analog homodyne detection using 1. Q single side-band down conversion of an AM backscattered modulating signal envelope. A demonstrator is presented which operates with a carrier frequency of 2 GHz and 500 KHz backscattered signal. When deployed in a multipath rich open plan office environment the S/N ratio obtained at the detection output was better than 20 dB at 20 in range with 20 dBm EIRP in a 2 MHz detection bandwidth despite the presence of time varying and static clutter. (C) 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2492-2495, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24636

Characterisation of microwave phase conjugate signal generation using nonlinearly loaded wire frequency selective surface (FSS)

Both experimental and theoretical information regarding the scattering and phase conjugate mixing properties of a 2D double-periodic array of wires loaded with nonlinear/linear lumped elements have been provided. An experimental means for assessing the phase conjugate energy production capability for the array is given. These investigations enable identification of the fundamental operational characteristics and underlying mechanisms associated with the production of phase conjugate energy by this type of artificial electromagnetic media. Means for enhancing the phase conjugate energy production capability of the structure by using additional linear lumped loads is examined theoretically and limits on the production of phase conjugate energy established. Theoretical far-field prediction of the behaviour of the structure indicates that retro-directive reflector action as well as negative refraction should be possible.