27,894 research outputs found
Interrogation of spline surfaces with application to isogeometric design and analysis of lattice-skin structures
A novel surface interrogation technique is proposed to compute the
intersection of curves with spline surfaces in isogeometric analysis. The
intersection points are determined in one-shot without resorting to a
Newton-Raphson iteration or successive refinement. Surface-curve intersection
is required in a wide range of applications, including contact, immersed
boundary methods and lattice-skin structures, and requires usually the solution
of a system of nonlinear equations. It is assumed that the surface is given in
form of a spline, such as a NURBS, T-spline or Catmull-Clark subdivision
surface, and is convertible into a collection of B\'ezier patches. First, a
hierarchical bounding volume tree is used to efficiently identify the B\'ezier
patches with a convex-hull intersecting the convex-hull of a given curve
segment. For ease of implementation convex-hulls are approximated with k-dops
(discrete orientation polytopes). Subsequently, the intersections of the
identified B\'ezier patches with the curve segment are determined with a
matrix-based implicit representation leading to the computation of a sequence
of small singular value decompositions (SVDs). As an application of the
developed interrogation technique the isogeometric design and analysis of
lattice-skin structures is investigated. The skin is a spline surface that is
usually created in a computer-aided design (CAD) system and the periodic
lattice to be fitted consists of unit cells, each containing a small number of
struts. The lattice-skin structure is generated by projecting selected lattice
nodes onto the surface after determining the intersection of unit cell edges
with the surface. For mechanical analysis, the skin is modelled as a
Kirchhoff-Love thin-shell and the lattice as a pin-jointed truss. The two types
of structures are coupled with a standard Lagrange multiplier approach
Labeless and reversible immunosensor assay based upon an electrochemical current-transient protocol
A novel labeless and reversible immunoassay based upon an electrochemical
current-transient protocol is reported which offers many advantages in
comparison to classical immuno-biochemical analyses in terms of simplicity,
speed of response, reusability and possibility of multiple determinations.
Conducting polypyrrole films containing antibodies against 1) Bovine Serum
Albumin (BSA) and 2) Digoxin were deposited on the surface of platinum
electrodes to produce conductive affinity matrices having clearly defined
binding characteristics. The deposition process has been investigated using 125I
labelled anti-digoxin to determine optimal fabrication protocols. Antibody
integrity and activity, together with non-specific binding of antigen on the
conducting matrix have also been investigated using tritiated digoxin to probe
polypyrrole/anti-digoxin films. Amperometric responses to digoxin were recorded
in flow conditions using these films, but the technique was limited in use
mainly due to baseline instability. Anti-BSA - polypyrrole matrices were
investigated in more detail in both flow and quiescent conditions. No observable
response was found in flow conditions, however under quiescent conditions (in
non-stirred batch cell), anti-BSA – polypyrrole films have been demonstrated to
function as novel quantitative chronoamperometric immuno-biosensors when
interrogated using a pulsed potential waveform. The behaviour of the electrodes
showed that the antibody/antigen binding and/or interaction process underlying
the response observed was reversible in nature, indicating that the electrodes
could be used for multiple sensing protocols. Calibration profiles for BSA
demonstrated linearity for a concentration range of 0-50 ppm but tended towards
a plateau at higher concentrations. Factors relating to replicate sensor
production, sample measurement and reproducibility are discuss
Multi-channel SPR biosensor based on PCF for multi-analyte sensing applications
This paper presents a theoretical investigation of a novel holey fiber (Photonic Crystal Fiber (PCF)) multi-channel biosensor based on surface plasmon resonance (SPR). The large gold coated micro fluidic channels and elliptical air hole design of our proposed biosensor aided by a high refractive index over layer in two channels enables operation in two modes; multi analyte sensing and self-referencing mode. Loss spectra, dispersion and detection capability of our proposed biosensor for the two fundamental modes (HE x 11 and HE y 11 ) have been elucidated using a Finite Element Method (FEM) and Perfectly Matching Layers (PML)
Measurement of substrate thermal resistance using DNA denaturation temperature
Heat Transfer and Thermal Management have become important aspects of the developing field of uTAS systems particularly in the application of the the uTAS philosophy to thermally driven analysis techniques such as PCR. Due to the development of flowing PCR thermocyclers in the field of uTAS, the authors have previously developed a melting curve analysis technique that is compatible with these flowing PCR thermocyclers. In this approach a linear temperature gradient is induced along a sample carrying microchannel. Any flow passing through the microchannel is subject to linear heating. Fluorescent monitoring of DNA in the flow results in the generation of DNA melting curve plots. This works presents an experimental technique where DNA melting curve analysis is used to measure the thermal resistance of microchannel substrates. DNA in solution is tested at a number of different ramp rates and the di®erent apparent denaturation temperatures measured are used to infer the thermal resistance of the microchannel substrates. The apparent variation in denaturation temperature is found to be linearly proportional to flow ramp rate. Providing knowledge of the microchannel diameter and a non-varying cross-section in the direction of heat flux the thermal resistance measurement technique is independent of knowledge of substrate dimensions, contact surface quality and substrate composition/material properties. In this approach to microchannel DNA melting curve analysis the difference between the measured and actual denaturation temperatures is proportional to the substrate thermal resistance and the ramp-rate seen by the sample. Therefore quantitative knowledge of the substrate thermal resistance is required when using this technique to measure accurately DNA denaturation temperatur
Nanopipettes as Monitoring Probes for the Single Living Cell: State of the Art and Future Directions in Molecular Biology.
Examining the behavior of a single cell within its natural environment is valuable for understanding both the biological processes that control the function of cells and how injury or disease lead to pathological change of their function. Single-cell analysis can reveal information regarding the causes of genetic changes, and it can contribute to studies on the molecular basis of cell transformation and proliferation. By contrast, whole tissue biopsies can only yield information on a statistical average of several processes occurring in a population of different cells. Electrowetting within a nanopipette provides a nanobiopsy platform for the extraction of cellular material from single living cells. Additionally, functionalized nanopipette sensing probes can differentiate analytes based on their size, shape or charge density, making the technology uniquely suited to sensing changes in single-cell dynamics. In this review, we highlight the potential of nanopipette technology as a non-destructive analytical tool to monitor single living cells, with particular attention to integration into applications in molecular biology
Comparison between Vernier-cascade and MZI as transducer for biosensing with on-chip spectral filter
The Mach-Zehnder interferometer (MZI) and the Vernier-cascade are highly responsive photonic sensors with large design freedom. They are therefore very suitable for interrogation through a broadband source and an on-chip spectral filter, a sensing scheme that is well equipped for point-of-care applications. In this work, the MZI is shown to outperform the Vernier-cascade through a better minimum detectable wavelength shift as well as a higher power efficiency, indicating its superiority in this sensing scheme. Fabricated MZIs yield bulk detection limits down to 8.8 x 10(-7) refractive index units (RIU) in a point-of-care compatible measuring setup, indicating the potential of the proposed sensing scheme
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