172 research outputs found
Improved temperature measurement and modeling for 3D USCT II
Medical visualization plays a key role in the early diagnosis and detection of symptoms related to breast cancer. However, currently doctors must struggle to extract accurate and relevant information from the 2D models on which the medical field still relies. The problem is that 2D models lack the spatial definition necessary to extract all of the information a doctor might want. In order to address this gap, we are developing a machine capable of performing ultrasound computer tomography and reconstructing 3D images of the breasts - the KIT 3D USCT II.
In order to accurately reconstruct the 3D image using ultrasound, we must first have an accurate temperature model. This is because the speed of sound varies significantly based on the temperature of the medium (in our case, water). We address this issue in three steps: so-called super-sampling, calibration, and modeling. Using these three steps, we were able to improve the accuracy of the hardware from ±1°C to just under 0.1°C
FID NMR Studies of Suspensions and Porous Media
Nuclear Magnetic Resonance is used for the determination of the properties of porous media in Geophysics and oil exploration. As it stands, there is a challenge in understanding the connection between the times measured in Free Induction Decay Nuclear Magnetic Resonance experiments and the shape of samples. In this work, suspensions and watersaturated densely-packed porous media with the volume fraction of the glass solid phase in the range from 10â4 to âŒ1 are found to exhibit FID decay rates proportional to the square root of the volume fraction of the solid phase of the samples. A model of spheres in liquid is proposed for the description of such behavior
3D Ultrasound Computer Tomography for Breast Cancer Diagnosis at KIT: an Overview
3D Ultrasound Computer Tomography (USCT) emitting and receiving spherical wave fronts overcomes the limitations of 2D systems by offering a nearly isotropic 3D point spread function, a large depth of field, less loss of out-of-plane reflections, and fast 3D data acquisition.
3D devices for clinical practice require a more complex hard- and software due to the huge data rate, time-consuming image reconstruction, and large number of small transducers. The here reviewed KIT 3D USCT is a prototype for clinical studies, which realizes for the first time the full benefits of a 3D system
On the Number of Incipient Spanning Clusters
In critical percolation models, in a large cube there will typically be more
than one cluster of comparable diameter. In 2D, the probability of
spanning clusters is of the order . In dimensions d>6, when
the spanning clusters proliferate: for the spanning
probability tends to one, and there typically are spanning
clusters of size comparable to |\C_{max}| \approx L^4. The rigorous results
confirm a generally accepted picture for d>6, but also correct some
misconceptions concerning the uniqueness of the dominant cluster. We
distinguish between two related concepts: the Incipient Infinite Cluster, which
is unique partly due to its construction, and the Incipient Spanning Clusters,
which are not. The scaling limits of the ISC show interesting differences
between low (d=2) and high dimensions. In the latter case (d>6 ?) we find
indication that the double limit: infinite volume and zero lattice spacing,
when properly defined would exhibit both percolation at the critical state and
infinitely many infinite clusters.Comment: Latex(2e), 42 p, 5 figures; to appear in Nucl. Phys. B [FS
The Alexander-Orbach conjecture holds in high dimensions
We examine the incipient infinite cluster (IIC) of critical percolation in
regimes where mean-field behavior has been established, namely when the
dimension d is large enough or when d>6 and the lattice is sufficiently spread
out. We find that random walk on the IIC exhibits anomalous diffusion with the
spectral dimension d_s=4/3, that is, p_t(x,x)= t^{-2/3+o(1)}. This establishes
a conjecture of Alexander and Orbach. En route we calculate the one-arm
exponent with respect to the intrinsic distance.Comment: 25 pages, 2 figures. To appear in Inventiones Mathematica
Measurement of the cosmic ray spectrum above eV using inclined events detected with the Pierre Auger Observatory
A measurement of the cosmic-ray spectrum for energies exceeding
eV is presented, which is based on the analysis of showers
with zenith angles greater than detected with the Pierre Auger
Observatory between 1 January 2004 and 31 December 2013. The measured spectrum
confirms a flux suppression at the highest energies. Above
eV, the "ankle", the flux can be described by a power law with
index followed by
a smooth suppression region. For the energy () at which the
spectral flux has fallen to one-half of its extrapolated value in the absence
of suppression, we find
eV.Comment: Replaced with published version. Added journal reference and DO
Energy Estimation of Cosmic Rays with the Engineering Radio Array of the Pierre Auger Observatory
The Auger Engineering Radio Array (AERA) is part of the Pierre Auger
Observatory and is used to detect the radio emission of cosmic-ray air showers.
These observations are compared to the data of the surface detector stations of
the Observatory, which provide well-calibrated information on the cosmic-ray
energies and arrival directions. The response of the radio stations in the 30
to 80 MHz regime has been thoroughly calibrated to enable the reconstruction of
the incoming electric field. For the latter, the energy deposit per area is
determined from the radio pulses at each observer position and is interpolated
using a two-dimensional function that takes into account signal asymmetries due
to interference between the geomagnetic and charge-excess emission components.
The spatial integral over the signal distribution gives a direct measurement of
the energy transferred from the primary cosmic ray into radio emission in the
AERA frequency range. We measure 15.8 MeV of radiation energy for a 1 EeV air
shower arriving perpendicularly to the geomagnetic field. This radiation energy
-- corrected for geometrical effects -- is used as a cosmic-ray energy
estimator. Performing an absolute energy calibration against the
surface-detector information, we observe that this radio-energy estimator
scales quadratically with the cosmic-ray energy as expected for coherent
emission. We find an energy resolution of the radio reconstruction of 22% for
the data set and 17% for a high-quality subset containing only events with at
least five radio stations with signal.Comment: Replaced with published version. Added journal reference and DO
Measurement of the Radiation Energy in the Radio Signal of Extensive Air Showers as a Universal Estimator of Cosmic-Ray Energy
We measure the energy emitted by extensive air showers in the form of radio
emission in the frequency range from 30 to 80 MHz. Exploiting the accurate
energy scale of the Pierre Auger Observatory, we obtain a radiation energy of
15.8 \pm 0.7 (stat) \pm 6.7 (sys) MeV for cosmic rays with an energy of 1 EeV
arriving perpendicularly to a geomagnetic field of 0.24 G, scaling
quadratically with the cosmic-ray energy. A comparison with predictions from
state-of-the-art first-principle calculations shows agreement with our
measurement. The radiation energy provides direct access to the calorimetric
energy in the electromagnetic cascade of extensive air showers. Comparison with
our result thus allows the direct calibration of any cosmic-ray radio detector
against the well-established energy scale of the Pierre Auger Observatory.Comment: Replaced with published version. Added journal reference and DOI.
Supplemental material in the ancillary file
Noise Sensitivity in Continuum Percolation
We prove that the Poisson Boolean model, also known as the Gilbert disc
model, is noise sensitive at criticality. This is the first such result for a
Continuum Percolation model, and the first for which the critical probability
p_c \ne 1/2. Our proof uses a version of the Benjamini-Kalai-Schramm Theorem
for biased product measures. A quantitative version of this result was recently
proved by Keller and Kindler. We give a simple deduction of the
non-quantitative result from the unbiased version. We also develop a quite
general method of approximating Continuum Percolation models by discrete models
with p_c bounded away from zero; this method is based on an extremal result on
non-uniform hypergraphs.Comment: 42 page
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