3,670 research outputs found
Dynamic acoustic field activated cell separation (DAFACS)
Advances in diagnostics, cell and stem cell technologies drive the development of application-specific tools
for cell and particle separation. Acoustic micro-particle separation offers a promising avenue for highthroughput,
label-free, high recovery, cell and particle separation and isolation in regenerative medicine.
Here, we demonstrate a novel approach utilizing a dynamic acoustic field that is capable of separating an
arbitrary size range of cells. We first demonstrate the method for the separation of particles with different
diameters between 6 and 45 μm and secondly particles of different densities in a heterogeneous medium.
The dynamic acoustic field is then used to separate dorsal root ganglion cells. The shearless, label-free and
low damage characteristics make this method of manipulation particularly suited for biological applications.
Advantages of using a dynamic acoustic field for the separation of cells include its inherent safety and
biocompatibility, the possibility to operate over large distances (centimetres), high purity (ratio of particle
population, up to 100%), and high efficiency (ratio of separated particles over total number of particles to
separate, up to 100%)
Interactive manipulation of microparticles in an octagonal sonotweezer
An ultrasonic device for micro-patterning and precision manipulation of micrometre-scale particles is demonstrated. The device is formed using eight piezoelectric transducers shaped into an octagonal cavity. By exciting combinations of transducers simultaneously, with a controlled phase delay between them, different acoustic landscapes can be created, patterning micro-particles into lines, squares, and more complex shapes. When operated with all eight transducers the device can, with appropriate phase control, manipulate the two dimensional acoustic pressure gradient; it thus has the ability to position and translate a single tweezing zone to different locations on a surface in a precise and programmable manner
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Mitigation of Moral Hazard and Adverse Selection in Venture Capital Financing: The Influence of the Country’s Institutional Setting
A venture capitalist (VC) needs to trade off benefits and costs when attempting to mitigate agency problems in their investor-investee relationship. We argue that signals of ventures complement the VC’s capacity to screen and conduct a due diligence during the pre-investment phase, but its attractiveness may diminish in institutional settings supporting greater transparency. Similarly, whereas a VC may opt for contractual covenants to curb potential opportunism by ventures in the post-investment phase, this may only be effective in settings supportive of shareholder rights enforcement. Using an international sample of VC contracts, our study finds broad support for these conjectures. It delineates theoretical and practical implications for how investors can best deploy their capital in different institutional settings whilst nurturing their relationships with entrepreneurs
MOSAIC: A Scalable reconfigurable 2D array system for NDT
This paper documents the development of a scalable 2D array system, or Mosaic that can be targeted at a wide range of NDT applications by way of a reconfigurable tile that can be tessellated to form arrays of any size and shape. Close coupling permits utilization of excitation voltages as low as +/-3.3V with insertion loss of 48dB on reflection from an aluminum back wall at 73mm achieved using 2D arrays without decoding
A Search for Pulsed and Bursty Radio Emission from X-ray Dim Isolated Neutron Stars
We have carried out a search for radio emission from six X-ray dim isolated
neutron stars (XDINSs) observed with the Robert C. Byrd Green Bank Radio
Telescope (GBT) at 820 MHz. No bursty or pulsed radio emission was found down
to a 4sigma significance level. The corresponding flux limit is 0.01-0.04 mJy
depending on the integration time for the particular source and pulse duty
cycle of 2%. These are the most sensitive limits yet on radio emission from
these objects.Comment: 3 pages, 3 figures, to be appeared in the Proceedings of the
conference "40 Years of Pulsars: Millisecond Pulsars, Magnetars, and More"
held on August 12-17, 2007, McGill University, Montreal, Canad
Impact ionisation electroluminescence in planar GaAs-based heterostructure Gunn diodes:Spatial distribution and impact of doping nonuniformities
When biased in the negative differential resistance regime, electroluminescence (EL) is emitted from planar GaAs heterostructure Gunn diodes. This EL is due to the recombination of electrons in the device channel with holes that are generated by impact ionisation when the Gunn domains reach the anode edge. The EL forms non-uniform patterns whose intensity shows short-range intensity variations in the direction parallel to the contacts and decreases along the device channel towards the cathode. This paper employs Monte Carlo models, in conjunction with the experimental data, to analyse these non-uniform EL patterns and to study the carrier dynamics responsible for them. It is found that the short-range lateral (i.e., parallel to the device contacts) EL patterns are probably due to non-uniformities in the doping of the anode contact, illustrating the usefulness of EL analysis on the detection of such inhomogeneities. The overall decreasing EL intensity towards the anode is also discussed in terms of the interaction of holes with the time-dependent electric field due to the transit of the Gunn domains. Due to their lower relative mobility and the low electric field outside of the Gunn domain, freshly generated holes remain close to the anode until the arrival of a new domain accelerates them towards the cathode. When the average over the transit of several Gunn domains is considered, this results in a higher hole density, and hence a higher EL intensity, next to the anode
Investigation of mechanical losses of thin silicon flexures at low temperatures
The investigation of the mechanical loss of different silicon flexures in a
temperature region from 5 to 300 K is presented. The flexures have been
prepared by different fabrication techniques. A lowest mechanical loss of
was observed for a 130 m thick flexure at around 10 K.
While the mechanical loss follows the thermoelastic predictions down to 50 K a
difference can be observed at lower temperatures for different surface
treatments. This surface loss will be limiting for all applications using
silicon based oscillators at low temperatures. The extraction of a surface loss
parameter using different results from our measurements and other references is
presented. We focused on structures that are relevant for gravitational wave
detectors. The surface loss parameter = 0.5 pm was obtained. This
reveals that the surface loss of silicon is significantly lower than the
surface loss of fused silica.Comment: 16 pages, 7 figure
The first Suzaku observation of SGR 1806-20
The soft gamma-ray repeater SGR 1806-20 has been attracting a lot of
attention owing to the fact that in December 2004 it emitted the most powerful
giant flare ever observed. Here we present the results of the first Suzaku
observation of SGR 1806-20, that seems to have reached a state characterized by
a flux close to the pre-flare level and by a relatively soft spectrum. Despite
this, the source remained quite active, as testified by several short bursts
observed by Suzaku. We discuss the broadband spectral properties of SGR 1806-20
in the context of the magnetar model, considering its recent theoretical
developments.Comment: 3 pages, 1 figure. Proceedings of the conference "40 Years of
Pulsars, Millisecond Pulsars, Magnetars and More", Montreal, August 12-17
2007. AIP, in pres
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