Polydimethylsiloxane (PDMS)-based microfluidic channel with integrated commercial pressure sensors

The precise characterisation of boiling in microchannels is essential for the optimisation of applications requiring two phase cooling. In this paper polydimethylsiloxane (PDMS) is employed to make microchannels for characterising microboiling. In particular the material properties of PDMS facilitate rapid prototyping and its optical transparency provides the capability to directly view any fluid flow. The production of microchannels is complicated by the need to integrate custom made sensors. This paper presents a PDMS microfluidic device with integrated commercial pressure sensors, which have been used to perform a detailed characterisation of microboiling phenomena. The proposed approach of integrating commercial pressure sensors into the channel also has potential applications in a range of other microsystems

Modification and characterisation of material hydrophobicity for surface acoustic wave driven microfluidics

Surface acoustic waves (SAW) generated in a piezoelectric substrate may be used to manipulate micro-scale droplets of liquid in a digital microfluidic system for lab-on-a-chip applications. The wettability of the surface over which a droplet is driven determines the ease and speed with which the droplet is propelled. This provides the opportunity to achieve fine control of SAW driven droplets simply by patterning of the surface into areas with different levels of wettability. This paper evaluates a number of different materials and surface preparation techniques and assesses their manufacturability and efficacy for this application. Test structures have been designed and developed to help optimise a fabrication process using the biocompatible polymer Parylene. Early results obtained using airflow as a driving force show that it is possible to manipulate droplets through direction changes of up to 60°. Additional work has been done using surface acoustic waves as the driving force to determine the extent to which droplets can be guided to desired locations

Cosmic Microwave Background constraint on residual annihilations of relic particles

Energy injected into the Cosmic Microwave Background at redshifts z<10^6 will distort its spectrum permanently. In this paper we discuss the distortion caused by annihilations of relic particles. We use the observational bounds on deviations from a Planck spectrum to constrain a combination of annihilation cross section, mass, and abundance. For particles with (s-wave) annihilation cross section, =\sigma_0, the bound is f[(\sigma_0/6e-27cm^3/s)(\Omega_{X\bar{X}}h^2)^2]/(m_X/MeV)<0.2, where m_X is the particle mass, \Omega_{X\bar{X}} is the fraction of the critical density the particle and its antiparticle contribute if they survive to the present time, h=H_0/(100km/s/Mpc), H_0 is the Hubble constant, and f is the fraction of the annihilation energy that interacts electromagnetically. We also compute the less stringent limits for p-wave annihilation. We update other bounds on residual annihilations and compare them to our CMB bound.Comment: submitted to Phys. Rev.

Schematic <i>Erlikosaurus andrewsi</i> skull in A, lateral and B, posterior views.

<p>Red represents skull originating from neural crest, blue, cephalic mesoderm origin, and green cephalic mesoderm origin. Modified from Clark, Perle, and Norell, 1994 with permission from American Museum of Natural History. Scale bar equals approximately 5 cm.</p

Latent variable modelling of the relationship between flow and exercise-induced feelings: an intuitive appraisal perspective

[Abstract]: The present study examined the relationship between self-reported levels of Flow (Csikszentmihalyi, 1975) and the post-exercise feelings of Positive Engagement, Revitalisation, Tranquillity, and Physical Exhaustion (Gauvin & Rejeski, 1993) using responses from 1, 231 aerobic dance exercise participants. Vallerand’s (1987) intuitive-reflective appraisal model of self-related affects and Csikszentmihalyi’s (1975) conceptual framework for optimal experience served as the guiding theoretical frameworks. It was hypothesised that self-reported flow would be positively associated with revitalisation, tranquillity and positive engagement while statistical independence was expected for physical exhaustion. First, participants completed the Flow State Scale (Jackson & Marsh, 1996) and second, the Exercise-induced Feeling Inventory (Gauvin & Rejeski, 1993) immediately after an aerobic dance exercise class. Latent variable analyses showed that the higher-order Flow factor was positively associated with post-exercise Positive Engagement, Revitalisation, and Tranquillity, but not with Physical Exhaustion. Flow state explained 35% of the variance in Positive Engagement, 31% of the variance in Revitalisation, and 22% of the variance in Tranquillity. It is concluded that self-reported flow in aerobic dance exercise is moderately associated with the experience of positive post-exercise feelings. Physical educators may wish to employ interventions to facilitate the flow experience during lessons that involve structured exercise

Electrochemical control of a DNA holliday junction nanoswitch by Mg2+ ions

The molecular conformation of a synthetic branched, 4-way DNA Holliday junction (HJ) was electrochemically switched between the open and closed (stacked) conformers. Switching was achieved by electrochemically induced quantitative release of Mg2+ ions from the oxidised poly(N-methylpyrrole) film (PPy), which contained polyacrylate as an immobile counter anion and Mg2+ ions as charge compensating mobile cations. This increase in the Mg2+ concentration screened the electrostatic repulsion between the widely separated arms in the open HJ configuration, inducing switching to the closed conformation. Upon electrochemical reduction of PPy, entrapment of Mg2+ ions back into the PPy film induced the reverse HJ switching from the closed to open state. The conformational transition was monitored using fluorescence resonance energy transfer (FRET) between donor and acceptor dyes each located at the terminus of one of the arms. The demonstrated electrochemical control of the conformation of the used probe-target HJ complex, previously reported as a highly sequence specific nanodevice for detecting of unlabelled target [Buck, A.H., Campbell, C.J., Dickinson, P., Mountford, C.P., Stoquert, H.C., Terry, J.G., Evans, S.A.G., Keane, L., Su, T.J., Mount, A.R., Walton, A.J., Beattie, J.S., Crain, J., Ghazal, P., 2007. Anal. Chem., 79, 4724–4728], allows the development of electronically addressable DNA nanodevices and label-free gene detection assays

Electrochemical deposition of Zn on TiN microelectrode arrays for microanodes

Zn was electrochemically deposited onto square TiN electrodes with edge dimensions of 490 μm and 40 μm. These were fabricated by standard microfabrication techniques, which provide an extremely reproducible electrode for experimentation. Reliable constant-potential electrodeposition of Zn on the TiN was performed at −1.2 V, just below the Zn/Zn2+ redox potential. At more negative potentials, the hydrogen evolution reaction on TiN interfered with bulk metal electrodeposition, resulting in poor quality Zn films. A two-step plating procedure was shown to be most efficient for electrochemical deposition of Zn, with Zn nucleation on the TiN substrate at high cathodic overpotential during the first step and a second step of bulk metal growth on the nucleated layer at low cathodic overpotential. These results were most consistent with 3D progressive nucleation of Zn on the TiN surface. Using this procedure, deposits of Zn on 490 μm TiN electrodes were uniform. In contrast, Zn deposits on 40 μm electrodes formed high-surface area and volume surface structures resulting from preferential growth at the electrode corners due to enhanced hemispherical diffusion at these sites. This should enable the formation of high surface area, high current density Zn anodes on biocompatible TiN microelectrodes, which could find application as improved microanodes for implantable miniature power supplies, e.g., implantable glucose sensors and internal cardioverter defibrillators. Keywords: Titanium nitride, Zinc, Microelectrode arrays, Electrochemical deposition, Microanode