3,237 research outputs found
Optical quality assurance of GEM foils
An analysis software was developed for the high aspect ratio optical scanning
system in the Detec- tor Laboratory of the University of Helsinki and the
Helsinki Institute of Physics. The system is used e.g. in the quality assurance
of the GEM-TPC detectors being developed for the beam diagnostics system of the
SuperFRS at future FAIR facility. The software was tested by analyzing five
CERN standard GEM foils scanned with the optical scanning system. The
measurement uncertainty of the diameter of the GEM holes and the pitch of the
hole pattern was found to be 0.5 {\mu}m and 0.3 {\mu}m, respectively. The
software design and the performance are discussed. The correlation between the
GEM hole size distribution and the corresponding gain variation was studied by
comparing them against a detailed gain mapping of a foil and a set of six lower
precision control measurements. It can be seen that a qualitative estimation of
the behavior of the local variation in gain across the GEM foil can be made
based on the measured sizes of the outer and inner holes.Comment: 12 pages, 29 figure
Regularity analysis for patterned texture inspection
This paper considers regularity analysis for patterned texture material inspection. Patterned texture-like fabric is built on a repetitive unit of a pattern. Regularity is one of the most important features in many textures. In this paper, a new patterned texture inspection approach called the regular bands (RB) method is described. First, the properties of textures and the meaning of regularity measurements are presented. Next, traditional regularity analysis for patterned textures is introduced. Many traditional approaches such as co-occurrence matrices, autocorrelation, traditional image subtraction and hash function are based on the concept of periodicity. These approaches have been applied for image retrieval, image synthesis, and defect detection of patterned textures. In this paper, a new measure of periodicity for patterned textures is described. The Regular Bands method is based on the idea of periodicity. A detailed description of the RB method with definitions, procedures, and explanations is given. There is also a detailed evaluation using the Regular Bands of some patterned textures. Three kinds of patterned fabric samples are used in the evaluation and a high detection success rate is achieved. Finally, there is a discussion of the method and some conclusions. © 2006 IEEE.published_or_final_versio
Doping homogeneity in co-doped materials investigated at different length scales
Doping homogeneity is important for the properties of co-doped phosphors, as it can affect the energy transfer between sensitizer and activator ions. In a case study we apply different methods, that is
scanning electron microscopy (SEM) combined with energy dispersive X-ray spectroscopy (EDX)
mapping, SEM combined with cathodoluminescence (CL) and solid-state nuclear magnetic resonance
(NMR), to study the doping homogeneity of the host system monazite LaPO4 doped with two different
lanthanide ions on different length scales. A new criterion for doping heterogeneity in co-doped
systems is developed, which is based on the NMR visibility function, which for this purpose is extended
to doping with two or more paramagnetic dopants. A deviation from this function is indicative of doping
heterogeneity on the length-scale of the blind-spheres of the paramagnetic dopants. A discussion of the
advantages and disadvantages of the different methods is presented. The combined approach allows to
study doping homogeneity from the nm to the mm scale
Structural analysis of dilute bismide alloys by means of high resolution scanning transmission electron microscopy
Energy efficiency plays a key role in the development of new industrial as well as daily
life applications. There exists a strong demand for a new energy efficient generation of
optoelectronic devices, especially in the growing market of internet data transfer where
devices operate in the 1.55 µm wavelength regime. A promising material system that
could face the challenge of efficient devices is the dilute Bi containing Ga(AsBi) and
the dilute bismides in general. The novel material system Ga(AsBi) has been proven
that the incorporation of dilute Bi amounts reduces the bandgap energy. Furthermore, a
suppression of non-radiative loss mechanisms and a decreased temperature-dependency of
the emission wavelength could be verified which can be described by the valence band anti
crossing model. Moreover, first electrically pumped Ga(AsBi) based laser devices could be
fabricated which reveal once more the huge potential of dilute bismides.
In this work structural analysis of MOVPE grown Ga(AsBi), Ga(PAsBi) and Ga(NAsBi)
on GaAs substrates were carried out by means of spherical aberration corrected STEM. In
addition to STEM ADF measurements, ADF image simulations of Ga(AsBi) supercells
were performed which allowed the interpretation of the measurements as well as the Bi
quantification in Ga(AsBi)-QWs. Despite STEM measurements, image processing was
applied for further analysis, i.e., determination and separation of the crystal sublattices
in HR measurements via the MATLAB software. Image processing is mandatory since it
allows on the one hand a quantification of the Bi fraction in Ga(AsBi), and on the other
hand a further statistical evaluation of the atomic column intensities is possible.
The results of this work show that STEM is inevitable
for the characterization of novel semiconductors as well as for the detection of atomic
ordering. Finally, Bi has the ability to distribute homogeneously in dilute Bi-containing
materials, when MOVPE takes place under optimized growth conditions which is very
promising for the realization and fabrication of new energy efficient semiconductor devices
Body MRI artifacts in clinical practice: a physicist\u27s and radiologist\u27s perspective.
The high information content of MRI exams brings with it unintended effects, which we call artifacts. The purpose of this review is to promote understanding of these artifacts, so they can be prevented or properly interpreted to optimize diagnostic effectiveness. We begin by addressing static magnetic field uniformity, which is essential for many techniques, such as fat saturation. Eddy currents, resulting from imperfect gradient pulses, are especially problematic for new techniques that depend on high performance gradient switching. Nonuniformity of the transmit radiofrequency system constitutes another source of artifacts, which are increasingly important as magnetic field strength increases. Defects in the receive portion of the radiofrequency system have become a more complex source of problems as the number of radiofrequency coils, and the sophistication of the analysis of their received signals, has increased. Unwanted signals and noise spikes have many causes, often manifesting as zipper or banding artifacts. These image alterations become particularly severe and complex when they are combined with aliasing effects. Aliasing is one of several phenomena addressed in our final section, on artifacts that derive from encoding the MR signals to produce images, also including those related to parallel imaging, chemical shift, motion, and image subtraction
MIA and NIR Chemical Imaging for pharmaceutical product characterization
[EN] This paper presents a three step methodology based on the use of chemical oriented models (MCR and CLS) for extracting out the chemical distribution maps (CDMs) from hyperspectral images, afterwards performing multivariate image analysis (MIA) on the CDMs, and !nally extracting 'channel' and textural features from the score images related to quality characteristics These features show complementary properties to those directly obtained from the CDMs, since they take advantage of their internal correlation structure. The approach has been successfully applied to the evaluation of homogeneity and cluster presence of API in a novel formulation developed to improve the dissolution of poorly soluble drugs. © 2012 Elsevier B.V. All rights reserved.Research in this study was partially supported by the Spanish Ministry of Science and Innovation and FEDER funds from the European Union through grant DPI2011-28112-C04-02, and also by NSF-Engineering Research Center for Structured Organic Particulate Systems (ERC-SOPS, EEC-0540855) and the program NSF-Major Research Instrumentation grant 0821113.Prats-Montalbán, JM.; Jerez-Rozo, J.; Romanach, R.; Ferrer Riquelme, AJ. (2012). MIA and NIR Chemical Imaging for pharmaceutical product characterization. Chemometrics and Intelligent Laboratory Systems. 117(117):240-249. https://doi.org/10.1016/j.chemolab.2012.04.002S24024911711
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