14,022 research outputs found
Fabrication of alignment structures for a fiber resonator by use of deep-ultraviolet lithography
We present a novel method to mount and align an optical-fiber-based resonator
on the flat surface of an atom chip with ultrahigh precision. The structures
for mounting a pair of fibers, which constitute the fiber resonator, are
produced by a spin-coated SU-8 photoresist technique by use of deep-UV
lithography. The design and production of the SU-8 structures are discussed.
From the measured finesses we calculate the coupling loss of the SU-8
structures acting as a kind of fiber splice to be smaller than 0.013 dB.Comment: 4 pages, 3 figure
Direct hemoglobin measurement by monolithically integrated optical beam guidance
We present a concept for optical beam guidance by total internal reflection (TIR) at V-grooves as retro reflectors which are monolithically integrated on a microfluidic "lab-on-a-disk". This way, the optical path length through a measurement chamber and thus the sensitivity of colorimetric assays is massively enhanced compared to direct (perpendicular) beam incidence. With this rugged optical concept, we determine the concentration of hemoglobin (Hb) in human whole blood. Outstanding features are a high degree of linearity (R2 = 0.993) between the optical signal and the Hb together with a reproducibility of CV= 2.9 %, and a time-to-result of 100 seconds, only
The fractional Keller-Segel model
The Keller-Segel model is a system of partial differential equations
modelling chemotactic aggregation in cellular systems. This model has blowing
up solutions for large enough initial conditions in dimensions d >= 2, but all
the solutions are regular in one dimension; a mathematical fact that crucially
affects the patterns that can form in the biological system. One of the
strongest assumptions of the Keller-Segel model is the diffusive character of
the cellular motion, known to be false in many situations. We extend this model
to such situations in which the cellular dispersal is better modelled by a
fractional operator. We analyze this fractional Keller-Segel model and find
that all solutions are again globally bounded in time in one dimension. This
fact shows the robustness of the main biological conclusions obtained from the
Keller-Segel model
Parallelization of chip-based fluorescence immuno-assays with quantum-dot labelled beads
This paper presents an optical concept for the read-out of a parallel, bead-based fluorescence immunoassay conducted on a lab-on-a-disk platform. The reusable part of the modular setup comprises a detection unit featuring a single LED as light source, two emission-filters, and a color CCD-camera as standard components together with a spinning drive as actuation unit. The miniaturized lab-on-a-disk is devised as a disposable. In the read-out process of the parallel assay, beads are first identified by the color of incorporated quantum dots (QDs). Next, the reaction-specific fluorescence signal is quantified with FluoSpheres-labeled detection anti-bodies. To enable a fast and automated read-out, suitable algorithms have been implemented in this work. Based on this concept, we successfully demonstrated a Hepatitis-A assay on our disk-based lab-on-a-chip
Experimental and numerical study of error fields in the CNT stellarator
Sources of error fields were indirectly inferred in a stellarator by
reconciling computed and numerical flux surfaces. Sources considered so far
include the displacements and tilts (but not the deformations, yet) of the four
circular coils featured in the simple CNT stellarator. The flux surfaces were
measured by means of an electron beam and phosphor rod, and were computed by
means of a Biot-Savart field-line tracing code. If the ideal coil locations and
orientations are used in the computation, agreement with measurements is poor.
Discrepancies are ascribed to errors in the positioning and orientation of the
in-vessel interlocked coils. To that end, an iterative numerical method was
developed. A Newton-Raphson algorithm searches for the coils' displacements and
tilts that minimize the discrepancy between the measured and computed flux
surfaces. This method was verified by misplacing and tilting the coils in a
numerical model of CNT, calculating the flux surfaces that they generated, and
testing the algorithm's ability to deduce the coils' displacements and tilts.
Subsequently, the numerical method was applied to the experimental data,
arriving at a set of coil displacements whose resulting field errors exhibited
significantly improved quantitative and qualitative agreement with experimental
results.Comment: Special Issue on the 20th International Stellarator-Heliotron
Worksho
Radio-frequency operation of a double-island single-electron transistor
We present results on a double-island single-electron transistor (DISET)
operated at radio-frequency (rf) for fast and highly sensitive detection of
charge motion in the solid state. Using an intuitive definition for the charge
sensitivity, we compare a DISET to a conventional single-electron transistor
(SET). We find that a DISET can be more sensitive than a SET for identical,
minimum device resistances in the Coulomb blockade regime. This is of
particular importance for rf operation where ideal impedance matching to 50 Ohm
transmission lines is only possible for a limited range of device resistances.
We report a charge sensitivity of 5.6E-6 e/sqrt(Hz) for a rf-DISET, together
with a demonstration of single-shot detection of small (<=0.1e) charge signals
on microsecond timescales.Comment: 6 pages, 6 figure
Comparison of ultracold neutron sources for fundamental physics measurements
Ultracold neutrons (UCNs) are key for precision studies of fundamental
parameters of the neutron and in searches for new CP violating processes or
exotic interactions beyond the Standard Model of particle physics. The most
prominent example is the search for a permanent electric dipole moment of the
neutron (nEDM). We have performed an experimental comparison of the leading UCN
sources currently operating. We have used a 'standard' UCN storage bottle with
a volume of 32 liters, comparable in size to nEDM experiments, which allows us
to compare the UCN density available at a given beam port.Comment: 20 pages, 30 Figure
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