We discuss contrast formation in a propagating x-ray beam. We consider the validity conditions for linear relations based on the transport-of-intensity equation (TIE) and on contrast transfer functions (CTFs). From a single diffracted image, we recover the thickness of a homogeneous object which has substantial absorption and a phase-shift of --0.37 radian.
Phase singularities are a ubiquitous feature of waves of all forms and represent a fundamental aspect of wave topology. An optical vortex phase singularity occurs when there is a spiral phase ramp about a point phase singularity. We report an experimental observation of an optical vortex in a field consisting of 9-keV x-ray photons. The vortex is created with an x-ray optical structure that imparts a spiral phase distribution to the incident wave field and is observed by use of diffraction about a wire to create a division-of-wave-front interferometer.
We demonstrate here a new method to control the location of cells on surfaces in
two dimensions, which can be applied to a number of biomedical applications
including diagnostic tests and tissue engineered medical devices. Two-dimensional
control over cell attachment is achieved by generation of a spatially controlled
surface chemistry that allows control over protein adsorption, a process
which mediates cell attachment. Here, we describe the deposition of thin
allylamine plasma polymer coatings on silicon wafer and perfluorinated
poly(ethylene-co-propylene) substrates, followed by grafting of a protein resistant
layer of poly(ethylene oxide). Spatially controlled patterning of the surface
chemistry was achieved in a fast, one-step procedure by nanometer thickness
controlled laser ablation using a 248 nm excimer laser. X-ray photoelectron
spectroscopy and atomic force microscopy were used to confirm the production
of surface chemistry patterns with a resolution of approximately 1 µm,
which is significantly below the dimensions of a single mammalian cell.
Subsequent adsorption of the extracellular matrix proteins collagen I and
fibronectin followed by cell culture experiments using bovine corneal epithelial
cells confirmed that cell attachment is controlled by the surface chemistry pattern.
The method is an effective tool for use in a number of in vitro and in vivo
applications.
This paper describes a novel technique for bonding polymeric-microfluidic devices using microwave energy and a conductive polymer (polyaniline). The bonding is achieved by patterning the polyaniline features at the polymer joint interface by filling of milled microchannels. The absorbed electromagnetic energy is then converted into heat, facilitating the localized microwave bonding of two polymethylmethacrylate (PMMA) substrates. A coaxial open-ended probe was used to study the dielectric properties at 2.45 GHz of the PMMA and polyaniline at a range of temperatures up to 120 • C. The measurements confirm a difference in the dielectric loss factor of the PMMA substrate and the polyaniline, which means that differential heating using microwaves is possible. Microfluidic channels of 200 µm and 400 µm widths were sealed using a microwave power of 300 W for 15 s. The results of the interface evaluations and leak test show that strong bonding is formed at the polymer interface, and there is no fluid leak up to a pressure of 1.18 MPa. Temperature field of microwave heating was found by using direct measurement techniques. A numerical simulation was also conducted by using the finite-element method, which confirmed and validated the experimental results. These results also indicate that no global deformation of the PMMA substrate occurred during the bonding process.
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