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Wang K.,Buskerud and Vestfold University College | Liu G.,Buskerud and Vestfold University College | Liu G.,Anhui University of Technology | Hoivik N.,Buskerud and Vestfold University College | And 2 more authors.
Chemical Society Reviews | Year: 2014

Hollow nanoarchitectured materials with straight channels play a crucial role in the fields of renewable energy, environment and biotechnology due to their one-dimensional morphology and extraordinary properties. The current challenge is the difficulty on tailoring hollow nanoarchitectures with well-controlled morphology at a relatively low cost. As a conventional technique, electrochemistry exhibits its unique advantage on machining nanostructures. In this review, we present the progress of electrochemistry as a valuable tool in construction of novel hollow nanoarchitectures through pulse/step anodization, such as surface pre-texturing, modulated, branched and multilayered pore architectures, and free-standing membranes. Basic principles for electrochemical engineering of mono- or multi-ordered nanostructures as well as free-standing membranes are extracted from specific examples (i.e. porous silicon, aluminum and titanium oxide). The potential of such nanoarchitectures are further demonstrated for the applications of photovoltaics, water splitting, organic degradation, nanostructure templates, biosensors and drug release. The electrochemical techniques provide a powerful approach to produce nanostructures with morphological complexity, which could have far-reaching implications in the design of future nanoscale systems. © 2014 The Royal Society of Chemistry.

Shi Z.,Buskerud and Vestfold University College | Dong T.,Buskerud and Vestfold University College
Energy Conversion and Management | Year: 2014

Based on the second law of thermodynamics, an entropy generation investigation is carried out under given dimensionless parameters, i.e. heat exchanger duty, heat flux, with respect to heat transfer and frictional pressure drop in a rotating helical tube heat exchanger with laminar convective flow. The entropy generation from heat transfer across a finite temperature difference - Ψh decreases with increasing Dean number which represents the impact of centrifugal force induced secondary flow in enhancing heat transfer. Another aspect of increasing Dean number is that intensified momentum transfer in the radial direction also raises the entropy generation from frictional pressure drop - Ψf, the superposed effect of which yields a decreasing-increasing trend of the total entropy generation-Ψ, a local minimum located in between. The rotation of the helical tube in streamwise (co-rotation) or counter streamwise (counter-rotation) direction leads to a decrease in Ψh and a increase in Ψf which complicates the situation that whether or where the minimum of total entropy generation exists is dependent on whether Ψ is dominated by Ψh or Ψf or somewhere in between. No difference is discerned between pairs of cases with constant wall temperature and uniform wall heat flux but the same set of variables and parameters. A multi-objective optimization targeting Ψh and Ψf simultaneously is implemented using the non-dominated sorting genetic algorithm II (NSGA II). Five solution sets are selected and compared with the conventional optimization in regard of Ψ distinguishing the Ψh-dominated region from the Ψf-dominated region, the dimensionless variable η1 is found to be the most suitable representative in describing the trade-off between Ψh and Ψf. The Pareto solution sets is dominated by Ψh within the variable and parameter space under discussion. On the Pareto frontier, the counter rotational cases are distributed where the impact of Ψf is relatively higher while co-rotational cases dominate almost all the rest part. The proposed investigation procedure is a synthetic analysis concerning optimization of both Ψ and its components Ψh and Ψf, via which the dominating compartment and the key impact factors for irreversibility minimization can be obtained as a guidance for practical design of rotating helical tube heat exchangers. © 2014 Elsevier Ltd. All rights reserved.

Zhao X.,Buskerud and Vestfold University College | Dong T.,Buskerud and Vestfold University College
Analytical Chemistry | Year: 2012

This study reports a quantitative nucleic acid sequence-based amplification (Q-NASBA) microfluidic platform composed of a membrane-based sampling module, a sample preparation cassette, and a 24-channel Q-NASBA chip for environmental investigations on aquatic microorganisms. This low-cost and highly efficient sampling module, having seamless connection with the subsequent steps of sample preparation and quantitative detection, is designed for the collection of microbial communities from aquatic environments. Eight kinds of commercial membrane filters are relevantly analyzed using Saccharomyces cerevisiae, Escherichia coli, and Staphylococcus aureus as model microorganisms. After the microorganisms are concentrated on the membrane filters, the retentate can be easily conserved in a transport medium (TM) buffer and sent to a remote laboratory. A Q-NASBA-oriented sample preparation cassette is originally designed to extract DNA/RNA molecules directly from the captured cells on the membranes. Sequentially, the extract is analyzed within Q-NASBA chips that are compatible with common microplate readers in laboratories. Particularly, a novel analytical algorithmic method is developed for simple but robust on-chip Q-NASBA assays. The reported multifunctional microfluidic system could detect a few microorganisms quantitatively and simultaneously. Further research should be conducted to simplify and standardize ecological investigations on aquatic environments. © 2012 American Chemical Society.

Yang Z.,Buskerud and Vestfold University College | Halvorsen E.,Buskerud and Vestfold University College | Dong T.,Buskerud and Vestfold University College
Applied Physics Letters | Year: 2012

Generating electrical power from low frequency vibration to power portable devices is a challenge that potentially can be met by nonresonant electrostatic energy harvesters. We propose a generator employing a conductive droplet sliding on a microfabricated electret film which is sputtered onto an interdigital electrode and charged already during deposition. Droplet motion causes a capacitance variation that is used to generate electric power. A prototype of the fluidic energy harvester demonstrated a peak output power at 0.18 W with a single droplet having a diameter of 1.2 mm and sliding on a 2 -m thick electret film. © 2012 American Institute of Physics.

Nguyen S.D.,Buskerud and Vestfold University College | Halvorsen E.,Buskerud and Vestfold University College | Paprotny I.,University of California at Berkeley
Applied Physics Letters | Year: 2013

This paper presents experimental results on a microelectromechanical energy harvester with curved springs that demonstrates an extremely wide bandwidth. The springs display an asymmetrical bistable behavior obtained purely through their geometrical design. The frequency down-sweep shows that the harvester 3-dB bandwidth is about 587 Hz at 0.208-g acceleration amplitude. For white noise excitation at 4 × 10-3 g2/ Hz, we found that the bandwidth reaches 715 Hz, which is more than 250 times wider than in the linear-spring regime. By varying the bias voltage, an output power of 3.4 μW is obtained for frequency down-sweep at 1-g amplitude and 150-V bias. © 2013 American Institute of Physics.

Halvorsen E.,Buskerud and Vestfold University College
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2013

Mechanically nonlinear energy harvesters driven by broadband vibrations modeled as white noise are investigated. We derive an upper bound on output power versus load resistance and show that, subject to mild restrictions that we make precise, the upper-bound performance can be obtained by a linear harvester with appropriate stiffness. Despite this, nonlinear harvesters can have implementation-related advantages. Based on the Kramers equation, we numerically obtain the output power at weak coupling for a selection of phenomenological elastic potentials and discuss their merits. © 2013 American Physical Society.

Liu G.,Buskerud and Vestfold University College | Hoivik N.,Buskerud and Vestfold University College | Wang K.,Buskerud and Vestfold University College
Electrochemistry Communications | Year: 2013

We report ultraviolet (UV) light detection of thin wall TiO2 nanotubes (TNTs) with open diameter ~ 20 nm obtained by a two anodization procedure. This small diameter nanotubular geometry shows significant enhancement of the photoresponsivity and results in a large increase of photocurrent. The photocurrent is one order higher than that of classical nanotubes with diameter of 140 nm at - 1.0 V bias. We attribute this improvement to the modulation of hole carrier density as a result of field effects from the diameter-dependent population of the surface-trapped electrons. This finding demonstrates inherent size effects of internal gain in semiconductor nanotubes. © 2012 Elsevier B.V.

Zhang L.,Buskerud and Vestfold University College | Dong T.,Buskerud and Vestfold University College
Journal of Micromechanics and Microengineering | Year: 2013

A rapid and reliable detection system is needed in the area of label-free calorimetric measurement for monitoring biochemical reactions. In this paper, a thermal biosensor employing a Si/SiGe quantum well is proposed where the infrared radiation energy is carefully considered to increase the sensor's sensitivity. It applies a suspended functional film with a trench across the multilayers. A polydimethylsiloxane cover for the microfluidic channel is bonded with the sensor for the injection and removal of a small volume of solution (down to 500 nL). The resistance change of Si/SiGe quantum well material is read out through the wire bonding connection to the conductive pads of the sensor. A linear detection range from 0.5 to 150 mM and a relative standard deviation less than 1% are demonstrated in the enzymatic reaction test with urea solution. Characterizations on the quantum well film verifies a high temperature coefficient of resistance value and fine crystal lattice, which promises a notable sensitivity. The application of the wafer level transfer bonding process makes the sensor fabrication convenient and cost-effective. © 2013 IOP Publishing Ltd.

Nguyen S.D.,Buskerud and Vestfold University College | Halvorsen E.,Buskerud and Vestfold University College
Journal of Microelectromechanical Systems | Year: 2011

We experimentally investigate the usefulness of softening springs in a microelectromechanical systems electrostatic energy harvester under colored noise vibrations. It is shown that the nonlinear harvester has performance benefits when the vibration's center frequency varies in the frequency range of its softening response. With a vibration 3-dB bandwidth of 50 Hz, less than 3-dB variation in output power can be obtained over a 85-Hz wide range of vibration center frequencies. Compared to a simulated linear-spring device, the nonlinear device gives more output power for a wide range of vibration bandwidths. The nonlinear device shows less than 1-dB variation in output power when the vibration bandwidth varies from 12 to 120 Hz and is centered on the resonant frequency. © 2006 IEEE.

Buskerud and Vestfold University College | Date: 2011-03-02

Speckle reduction apparatus includes a radiation path and a mask arranged within the radiation path. The mask includes an array of electrically controllable cells configured to form a pattern on the mask that varies with time. The speckle reduction mask includes a first linear array including first parallel lines arranged to change the phase of incident radiation, and a second linear array including second parallel lines arranged to change the phase of incident radiation and further arranged such that cells are formed at the intersections of the first parallel lines and the second parallel lines. The speckle reduction mask includes a N_(1)N_(2 )array of cells, A, formed according to: A^(T)A=_(k,l), where A^(T )is the transpose of A, is a real and positive constant, d_(k,l )is Kronecker delta and N_(1)N_(2).

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