392 research outputs found
Synchronization device for electrocardiography-gated echo-planar imaging
An electrocardiography (ECG) synchronization technique allowed triggering of 1.5-T echo-planar acquisitions of the heart, with high gradient slew rates. In 51 volunteers (37 men and 14 women, aged 21-48 years), the ECG signal was amplified, filtered, and converted into an optical signal directly above the heart and was transmitted optically outside the bore. Reliable and artifact-free ECG tracings were obtained in all cases, regardless of the gradient switching speed
MR-guided cholecystostomy: Assessment of biplanar, real-time needle tracking in three pigs
Purpose: To demonstrate the feasibility of magnetic resonance (MR)-guided cholecystostomy using active, real-time, biplanar MR tracking in animal experiments. Methods: Experiments were performed on three fully anesthetized pigs in an interventional MR system (GE open). The gallbladder was displayed in two orthogonal planes using a heavily T2-weighted fast spin-echo sequence. These "cholangio roadmaps” were displayed on LCD monitors positioned in front of the interventionalist. A special coaxial MR-tracking needle, equipped with a small receive-only coil at its tip, was inserted percutaneously into the gallbladder under continuous, biplanar MR guidance. The MR-tracking sequence allowed sampling of the coil (needle tip) position every 120 msec. The position of the coil was projected onto the two orthogonal "cholangio roadmap” images. Results: Successful insertion of the needle was confirmed by aspiration of bile from the gallbladder. The process of aspiration and subsequent instillation of Gd-DTPA into the gallbladder was documented with fast gradient-recalled echo imaging. Conclusion: Biplanar, active, real-time MR tracking in combination with "cholangio roadmaps” allows for cholecystostomies in an interventional MRI environmen
Formation of ultracold RbCs molecules by photoassociation
The formation of ultracold metastable RbCs molecules is observed in a double
species magneto-optical trap through photoassociation below the
^85Rb(5S_1/2)+^133Cs(6P_3/2) dissociation limit followed by spontaneous
emission. The molecules are detected by resonance enhanced two-photon
ionization. Using accurate quantum chemistry calculations of the potential
energy curves and transition dipole moment, we interpret the observed
photoassociation process as occurring at short internuclear distance, in
contrast with most previous cold atom photoassociation studies. The vibrational
levels excited by photoassociation belong to the 5th 0^+ or the 4th 0^-
electronic states correlated to the Rb(5P_1/2,3/2)+Cs(6S_1/2) dissociation
limit. The computed vibrational distribution of the produced molecules shows
that they are stabilized in deeply bound vibrational states of the lowest
triplet state. We also predict that a noticeable fraction of molecules is
produced in the lowest level of the electronic ground state
Ideal Multipole Ion Traps from Planar Ring Electrodes
We present designs for multipole ion traps based on a set of planar, annular,
concentric electrodes which require only rf potentials to confine ions. We
illustrate the desirable properties of the traps by considering a few simple
cases of confined ions. We predict that mm-scale surface traps may have trap
depths as high as tens of electron volts, or micromotion amplitudes in a 2-D
ion crystal as low as tens of nanometers, when parameters of a magnitude common
in the field are chosen. Several example traps are studied, and the scaling of
those properties with voltage, frequency, and trap scale, for small numbers of
ions, is derived. In addition, ions with very high charge-to-mass ratios may be
confined in the trap, and species of very different charge-to-mass ratios may
be simultaneously confined. Applications of these traps include quantum
information science, frequency metrology, and cold ion-atom collisions.Comment: Section on trapping of a single ion added, two figures added, one
formula corrected, otherwise minor change
Calibration of the Logarithmic-Periodic Dipole Antenna (LPDA) Radio Stations at the Pierre Auger Observatory using an Octocopter
An in-situ calibration of a logarithmic periodic dipole antenna with a
frequency coverage of 30 MHz to 80 MHz is performed. Such antennas are part of
a radio station system used for detection of cosmic ray induced air showers at
the Engineering Radio Array of the Pierre Auger Observatory, the so-called
Auger Engineering Radio Array (AERA). The directional and frequency
characteristics of the broadband antenna are investigated using a remotely
piloted aircraft (RPA) carrying a small transmitting antenna. The antenna
sensitivity is described by the vector effective length relating the measured
voltage with the electric-field components perpendicular to the incoming signal
direction. The horizontal and meridional components are determined with an
overall uncertainty of 7.4^{+0.9}_{-0.3} % and 10.3^{+2.8}_{-1.7} %
respectively. The measurement is used to correct a simulated response of the
frequency and directional response of the antenna. In addition, the influence
of the ground conductivity and permittivity on the antenna response is
simulated. Both have a negligible influence given the ground conditions
measured at the detector site. The overall uncertainties of the vector
effective length components result in an uncertainty of 8.8^{+2.1}_{-1.3} % in
the square root of the energy fluence for incoming signal directions with
zenith angles smaller than 60{\deg}.Comment: Published version. Updated online abstract only. Manuscript is
unchanged with respect to v2. 39 pages, 15 figures, 2 table
Ultrahigh-energy neutrino follow-up of Gravitational Wave events GW150914 and GW151226 with the Pierre Auger Observatory
On September 14, 2015 the Advanced LIGO detectors observed their first
gravitational-wave (GW) transient GW150914. This was followed by a second GW
event observed on December 26, 2015. Both events were inferred to have arisen
from the merger of black holes in binary systems. Such a system may emit
neutrinos if there are magnetic fields and disk debris remaining from the
formation of the two black holes. With the surface detector array of the Pierre
Auger Observatory we can search for neutrinos with energy above 100 PeV from
point-like sources across the sky with equatorial declination from about -65
deg. to +60 deg., and in particular from a fraction of the 90% confidence-level
(CL) inferred positions in the sky of GW150914 and GW151226. A targeted search
for highly-inclined extensive air showers, produced either by interactions of
downward-going neutrinos of all flavors in the atmosphere or by the decays of
tau leptons originating from tau-neutrino interactions in the Earth's crust
(Earth-skimming neutrinos), yielded no candidates in the Auger data collected
within s around or 1 day after the coordinated universal time (UTC)
of GW150914 and GW151226, as well as in the same search periods relative to the
UTC time of the GW candidate event LVT151012. From the non-observation we
constrain the amount of energy radiated in ultrahigh-energy neutrinos from such
remarkable events.Comment: Published version. Added journal reference and DOI. Added Report
Numbe
Multi-resolution anisotropy studies of ultrahigh-energy cosmic rays detected at the Pierre Auger Observatory
We report a multi-resolution search for anisotropies in the arrival
directions of cosmic rays detected at the Pierre Auger Observatory with local
zenith angles up to and energies in excess of 4 EeV ( eV). This search is conducted by measuring the angular power spectrum
and performing a needlet wavelet analysis in two independent energy ranges.
Both analyses are complementary since the angular power spectrum achieves a
better performance in identifying large-scale patterns while the needlet
wavelet analysis, considering the parameters used in this work, presents a
higher efficiency in detecting smaller-scale anisotropies, potentially
providing directional information on any observed anisotropies. No deviation
from isotropy is observed on any angular scale in the energy range between 4
and 8 EeV. Above 8 EeV, an indication for a dipole moment is captured; while no
other deviation from isotropy is observed for moments beyond the dipole one.
The corresponding -values obtained after accounting for searches blindly
performed at several angular scales, are in the case of
the angular power spectrum, and in the case of the needlet
analysis. While these results are consistent with previous reports making use
of the same data set, they provide extensions of the previous works through the
thorough scans of the angular scales.Comment: Published version. Added journal reference and DOI. Added Report
Numbe
Azimuthal asymmetry in the risetime of the surface detector signals of the Pierre Auger Observatory
The azimuthal asymmetry in the risetime of signals in Auger surface detector
stations is a source of information on shower development. The azimuthal
asymmetry is due to a combination of the longitudinal evolution of the shower
and geometrical effects related to the angles of incidence of the particles
into the detectors. The magnitude of the effect depends upon the zenith angle
and state of development of the shower and thus provides a novel observable,
, sensitive to the mass composition of cosmic rays
above eV. By comparing measurements with predictions from
shower simulations, we find for both of our adopted models of hadronic physics
(QGSJETII-04 and EPOS-LHC) an indication that the mean cosmic-ray mass
increases slowly with energy, as has been inferred from other studies. However,
the mass estimates are dependent on the shower model and on the range of
distance from the shower core selected. Thus the method has uncovered further
deficiencies in our understanding of shower modelling that must be resolved
before the mass composition can be inferred from .Comment: Replaced with published version. Added journal reference and DO
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