Experimental investigation into the convective heat transfer and system-level effects of Al2O3-propanol nanofluid

It has been speculated that the application of nanofluids in real systems could lead to smaller, more compact heat exchangers and reductions in material cost. However, few studies have been conducted which have carefully measured the thermo-physical properties and thermal performance of these fluids as well as examine the system-level effects of using these fluids in traditional cooling systems. In this study, dilute suspensions of 10 nm aluminum oxide nanoparticles in propanol (0.5, 1, and 3 wt%) were investigated. Changes in density, specific heat, and thermal conductivity with particle concentration were measured and found to be linear, whereas changes in viscosity were nonlinear and increased sharply with particle loading. Nanofluid heat transfer performance data were generally commensurate with that measured for the baseline. For the 1 wt% concentration, a small but significant enhancement in the heat transfer coefficient was recorded for 1800 < Re < 2800, which is attributed to an earlier transition to turbulent flow. In the case of high particle loading (i.e. 3 wt%), the thermal performance was observed to deteriorate with respect to the baseline case. Discoloration of the fluid was also observed after being cycled at high flow rates and increased temperature.     

Laser printing of multi-layered polymer/metal heterostructures for electronic and MEMS devices

A laser forward transfer technique for the simultaneous printing of polymer/metal stacked micro-laminates is introduced. Several different material combinations as well as stacking architectures are presented including single laser pulse deposited dual layer capacitors, three-layer stacks for potentially printing organic thin-film transistors (OTFTs), and photo-definable polymer/metal laminates and free-standing membranes for MEMS based sensors.     

A moving grid finite element method applied to a model biological pattern generator

Many problems in biology involve growth. In numerical simulations it can therefore be very convenient to employ a moving computational grid on a continuously deforming domain. In this paper we present a novel application of the moving grid finite element method to compute solutions of reaction–diffusion systems in two-dimensional continuously deforming Euclidean domains. A numerical software package has been developed as a result of this research that is capable of solving generalised Turing models for morphogenesis.     

Experimental observations of a left-handed material that obeys Snell's law

We measure two-dimensional profiles of collimated microwave beams transmitted through composite wire and split-ring resonator prisms. Prior experiments suggest these structures have a negative index of refraction, though these claims have been questioned. Our 2D measurements demonstrate that transmission obeys Snell's law with a negative index, confirming the refractive nature of this signal and refuting alternatives posed in the criticisms. In addition, we present preliminary evidence that a flat rectangular slab of this material can focus power from a point source.     

Molecular contrast in optical coherence tomography by use of a pump-probe technique

We describe a novel technique for contrast enhancement in optical coherence tomography (OCT) that makes possible molecular-specific imaging for what is believed to be the first time. A pump-probe technique is employed in which a pulsed pump laser is tuned to ground-state absorption in a molecule of interest. The location of the target molecule population is derived from the resulting transient absorption of OCT sample-arm light acting as probe light. A signal processing technique for three-dimensional localization of the transient absorption signal is described, and preliminary results exhibiting OCT contrast from methylene blue dye in multilayer and scattering phantoms are presented.     

Growth model for atomic ordering: the case for quadruple-period ordering in GaAsSb alloys

Quadruple-period ordering in GaAsSb alloys is studied both theoretically and experimentally. A growth model is proposed to account for the observed three-dimensional (3D) ordered structure. The model is qualitatively different from the widely accepted surface reconstruction and dimerization-induced ordering models that strictly speaking explain only the in-plane 2D patterns. Here, we show that the already ordered substrate will affect the reconstruction of the growth front with respect to the substrate to ensure a correct stacking of the individual 2D ordered layers into the observed 3D lattice.     

Wet-etch optimization of free-standing terahertz frequency-selective structures

Free-standing frequency-selective surfaces consisting of approximately 10-microm-thick copper films with cross-aperture arrays are found to be tunable toward lower frequencies by means of wet chemical etching. Center frequencies were tuned from 1.57 to 1.53 THz while maintaining high transmittance. Wet etching also adjusts bandwidth, peak transmittance, and sidelobe transmittance. The advantage of the wet-etch technique is demonstrated by employment of these devices as bandpass filters for difluoromethane-based terahertz lasers. Adjustment in aperture dimensions because of etching results in suppression of a competing laser line (133.93 microm) by 15 dB while maintaining high transmittance at the operating wavelength of 192.06 microm.     

Phase transitions in the litharge and antilitharge structures

Abstract

The compounds PbO and LiOD possess the layered, tetragonal B10 structure and the corresponding antistructure respectively at 1 bar. They undergo very different phase transitions at moderate pressure. At 5 kbar, PbO undergoes a slight, reversible distortion to an orthorhombic phase. The structure is probably an expanded NaCl derivative.

The high-P LiOD phase begins to grow slowly above 17 kbar. Infrared and Raman data indicate that hydrogen bonding is present in the new phase. Neutron powder data indexed on a monoclinic cell. The structure is likely to be similar to that of T1I and NaOH, distorted by the H-bonding.