5,049 research outputs found
A steerable UV laser system for the calibration of liquid argon time projection chambers
A number of liquid argon time projection chambers (LAr TPC's) are being build
or are proposed for neutrino experiments on long- and short baseline beams. For
these detectors a distortion in the drift field due to geometrical or physics
reasons can affect the reconstruction of the events. Depending on the TPC
geometry and electric drift field intensity this distortion could be of the
same magnitude as the drift field itself. Recently, we presented a method to
calibrate the drift field and correct for these possible distortions. While
straight cosmic ray muon tracks could be used for calibration, multiple coulomb
scattering and momentum uncertainties allow only a limited resolution. A UV
laser instead can create straight ionization tracks in liquid argon, and allows
one to map the drift field along different paths in the TPC inner volume. Here
we present a UV laser feed-through design with a steerable UV mirror immersed
in liquid argon that can point the laser beam at many locations through the
TPC. The straight ionization paths are sensitive to drift field distortions, a
fit of these distortion to the linear optical path allows to extract the drift
field, by using these laser tracks along the whole TPC volume one can obtain a
3D drift field map. The UV laser feed-through assembly is a prototype of the
system that will be used for the MicroBooNE experiment at the Fermi National
Accelerator Laboratory (FNAL)
Measurement of the drift field in the ARGONTUBE LAr TPC with 266~nm pulsed laser beams
ARGONTUBE is a liquid argon time projection chamber (LAr TPC) with a drift
field generated in-situ by a Greinacher voltage multiplier circuit. We present
results on the measurement of the drift-field distribution inside ARGONTUBE
using straight ionization tracks generated by an intense UV laser beam. Our
analysis is based on a simplified model of the charging of a multi-stage
Greinacher circuit to describe the voltages on the field cage rings
A method to suppress dielectric breakdowns in liquid argon ionization detectors for cathode to ground distances of several millimeters
We present a method to reach electric field intensity as high as 400 kV/cm in
liquid argon for cathode-ground distances of several millimeters. This can be
achieved by suppressing field emission from the cathode, overcoming limitations
that we reported earlier
On the Electric Breakdown in Liquid Argon at Centimeter Scale
We present a study on the dependence of electric breakdown discharge
properties on electrode geometry and the breakdown field in liquid argon near
its boiling point. The measurements were performed with a spherical cathode and
a planar anode at distances ranging from 0.1 mm to 10.0 mm. A detailed study of
the time evolution of the breakdown volt-ampere characteristics was performed
for the first time. It revealed a slow streamer development phase in the
discharge. The results of a spectroscopic study of the visible light emission
of the breakdowns complement the measurements. The light emission from the
initial phase of the discharge is attributed to electro-luminescence of liquid
argon following a current of drifting electrons. These results contribute to
set benchmarks for breakdown-safe design of ionization detectors, such as
Liquid Argon Time Projection Chambers (LAr TPC).Comment: Minor revision according to editor report. 17 pages, 15 figures, 2
tables. Turboencabulato
Experimental study of electric breakdowns in liquid argon at centimeter scale
In this paper we present results on measurements of the dielectric strength
of liquid argon near its boiling point and cathode-anode distances in the range
of 0.1 mm to 40 mm with spherical cathode and plane anode. We show that at such
distances the applied electric field at which breakdowns occur is as low as 40
kV/cm. Flash-overs across the ribbed dielectric of the high voltage
feed-through are observed for a length of 300 mm starting from a voltage of 55
kV. These results contribute to set reference for the breakdown-free design of
ionization detectors, such as Liquid Argon Time Projection Chambers (LAr TPC)
Cosmology in massive gravity
We argue that more cosmological solutions in massive gravity can be obtained
if the metric tensor and the tensor defined by
St\"{u}ckelberg fields take the homogeneous and isotropic form. The standard
cosmology with matter and radiation dominations in the past can be recovered
and CDM model is easily obtained. The dynamical evolution of the
universe is modified at very early times.Comment: 4 pages, 1 figure,add more reference
Interprofessional differences in preoperative planning-the individualist surgeon
Background Perioperative processes have a great impact on the quality of surgery. In a high-risk surrounding, proper planning and communication is of upmost importance. We have identified other professions next to surgery with comparable circumstances and conducted a survey to elaborate on the impact of perioperative processes. Objective To identify standards in preoperative planning in high-risk professions and determine possible shortcomings in surgical practice. Methods Two surveys were constructed and distributed to surgeons, mountain guides, and soldiers. Questions were designed to investigate preoperative planning behavior and compare the different professions. Results Nearly every participant (97%) agreed to the fact that preoperative planning helps to avoid complications. Most surgeons agreed that the preoperative and postoperative phase of care had the greatest ability to improve overall quality of care. The opinions about planning were divided. The minority of surgeons agreed to the importance of sharing a plan preoperatively. Soldiers were the profession with the highest rate of plan sharing. Conclusion The readiness to communicate varies between professions and is lowest for surgeons. Missing standardization of procedures and the surgeon's ego might be explanations for this behavior. Interventions to overcome this shortcoming, like the preoperative team timeout, have already been implemented but further improvements are needed
The cost of surgical training: analysis of operative time for laparoscopic cholecystectomy
Background: Duration of surgery is a main cost factor of surgical training. The purpose of this analysis of operative times for laparoscopic cholecystectomies (LC) was to quantify the extra time and related costs in regards to the surgeons' experience in the operating room (OR). Methods: All LC performed between January 01, 2005 and December 31, 2008 in 46 hospitals reporting to the database of the Swiss Association for Quality Management in Surgery (AQC) were analyzed (n=10,010). Four levels of seniority were specified: resident (R), junior consultant (JC), senior consultant (SC), and attending surgeon (AS). The differences in operative time according to seniority were investigated in a multivariable log-linear and median regression analysis controlling for possible confounders. The OR costs were calculated by using a full cost rate in a teaching hospital. Results: A total of 9,208 LC were available for analysis; 802 had to be excluded due to missing data (n=212) or secondary major operations (n=590). Twenty-eight percent of the LC were performed by R as teaching operations (n=2,591). Compared with R, the multivariable analysis of operative time showed a median difference of −2.5min (−9.0; 4.8) for JC and −18min (−25; −11) for SC and −28min (−35; −10) for AS, respectively. The OR minute costs were €17.57, resulting in incremental costs of €492 (159; 615) per operation in case of tutorial assistance. Conclusions: The proportion of LC performed as tutorial assistance for R remains low. Surgical training in the OR causes relevant case-related extra time and therefore cost
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