253 research outputs found
Patient Reported Outcomes from Sacroiliac Joint Fusion
Study DesignRetrospective, case series.PurposeThe purpose of this study is to determine morbidity, complications, and patient reported outcomes from minimally invasive sacroiliac joint (SIJ) fusion.Overview of LiteratureLumbar back pain emanating from the SIJ can be surgically treated via a percutaneous approach in the appropriately selected patient with minimal morbidity and acceptable functional outcomes.MethodsPatients diagnosed by >2 physical examination maneuvers and subjective relief from a computed tomography–guided lidocaine-bupivacaine-steroid injection underwent SIJ fusion after failing conservative management with a combination of oral anti-inflammatory medications, physical therapy, and pelvic belt stabilization. Perioperative data collected include estimated blood loss (EBL) and operative time. Oswestry disability index, 12-item short form health survey (SF-12), visual analogue score, and functional status were analyzed. All complications were noted.ResultsThe study cohort of 45 cases (69% female) achieved postoperative survey follow-up at 9.9 and 32.3 months. SF-12 physical component summary statistically improved while all other scores were equivalent. Mean EBL and operative time were 22 mL and 36 minutes, respectively. Initial survey showed that 64% of patients discontinued narcotics (29/45), 71% do not use an assistive device (32/45), and 15.6% do not work due to pain (7/45). 73% of patients stated they would have the surgery again (33/45). For the second survey, 65% of patients discontinued narcotics (26/40), 70% did not use an assistive device (28/40), and 17.5% did not work due to pain (7/40). A history of thoracolumbar instrumentation (16/45) did not significantly affect outcomes. Three complications described by screw malposition with neurologic deficit (6.7%) were treated with screw repositioning (1 case) and removal of a single superior implant (2 cases) with time to revision of 2.2 months. All three ultimately had resolution of radicular pain.ConclusionsPercutaneous SIJ fusion offers minimal morbidity and acceptable functional outcomes. While women and those with a prior history of lumbar instrumentation may be at increased risk of having SIJ dysfunction requiring surgical intervention, it was not found to affect postoperative functional outcomes when compared to the non-instrumented group
A Compton reflection dominated spectrum in a peculiar accreting neutron star
We report on a puzzling event occurred during a long BeppoSAX observation of
the slow-rotating binary pulsar GX 1+4. During this event, lasting about 1 day,
the source X-ray flux was over a factor 10 lower than normal. The low-energy
pulsations disappeared while at higher energies they were shifted in phase. The
spectrum taken outside this low-intensity event was well fitted by an absorbed
cut-off power law, and exhibited a broad iron line at ~6.5 keV probably due to
the blending of the neutral (6.4 keV) and ionised (6.7 keV) K_alpha iron lines.
The spectrum during the event was Compton reflection dominated and it showed
two narrow iron lines at ~6.4 keV and ~7.0 keV, the latter never revealed
before in this source. We also present a possible model for this event in which
a variation of the accretion rate thickens a torus-like accretion disc which
hides for a while the direct neutron star emission from our line of sight. In
this scenario the Compton reflected emission observed during the event is well
explained in terms of emission reflected by the side of the torus facing our
line of sight.Comment: 10 pages; to be published in MNRA
State space modelling and data analysis exercises in LISA Pathfinder
LISA Pathfinder is a mission planned by the European Space Agency to test the
key technologies that will allow the detection of gravitational waves in space.
The instrument on-board, the LISA Technology package, will undergo an
exhaustive campaign of calibrations and noise characterisation campaigns in
order to fully describe the noise model. Data analysis plays an important role
in the mission and for that reason the data analysis team has been developing a
toolbox which contains all the functionalities required during operations. In
this contribution we give an overview of recent activities, focusing on the
improvements in the modelling of the instrument and in the data analysis
campaigns performed both with real and simulated data.Comment: Plenary talk presented at the 9th International LISA Symposium, 21-25
May 2012, Pari
A strategy to characterize the LISA-Pathfinder cold gas thruster system
The cold gas micro-propulsion system that will be used during the LISA-Pathfinder mission will be one of the most important component used to ensure the "free-fall" of the enclosed test masses. In this paper we present a possible strategy to characterize the effective direction and amplitude gain of each of the 6 thrusters of this system
Free-flight experiments in LISA Pathfinder
The LISA Pathfinder mission will demonstrate the technology of drag-free test
masses for use as inertial references in future space-based gravitational wave
detectors. To accomplish this, the Pathfinder spacecraft will perform drag-free
flight about a test mass while measuring the acceleration of this primary test
mass relative to a second reference test mass. Because the reference test mass
is contained within the same spacecraft, it is necessary to apply forces on it
to maintain its position and attitude relative to the spacecraft. These forces
are a potential source of acceleration noise in the LISA Pathfinder system that
are not present in the full LISA configuration. While LISA Pathfinder has been
designed to meet it's primary mission requirements in the presence of this
noise, recent estimates suggest that the on-orbit performance may be limited by
this `suspension noise'. The drift-mode or free-flight experiments provide an
opportunity to mitigate this noise source and further characterize the
underlying disturbances that are of interest to the designers of LISA-like
instruments. This article provides a high-level overview of these experiments
and the methods under development to analyze the resulting data.Comment: 13 pages, 5 figures. Accepted to Journal Of Physics, Conference
Series. Presented at 10th International LISA Symposium, May 2014,
Gainesville, FL, US
Beyond the required LISA free-fall performance: new LISA pathfinder results down to 20  μHz
In the months since the publication of the first results, the noise performance of LISA Pathfinder has improved because of reduced Brownian noise due to the continued decrease in pressure around the test masses, from a better correction of noninertial effects, and from a better calibration of the electrostatic force actuation. In addition, the availability of numerous long noise measurement runs, during which no perturbation is purposely applied to the test masses, has allowed the measurement of noise with good statistics down to 20  μHz. The Letter presents the measured differential acceleration noise figure, which is at (1.74±0.05)  fm s^{-2}/sqrt[Hz] above 2 mHz and (6±1)×10  fm s^{-2}/sqrt[Hz] at 20  μHz, and discusses the physical sources for the measured noise. This performance provides an experimental benchmark demonstrating the ability to realize the low-frequency science potential of the LISA mission, recently selected by the European Space Agency
In-flight thermal experiments for LISA pathfinder: simulating temperature noise at the inertial sensors
Thermal Diagnostics experiments to be carried out on board LISA Pathfinder (LPF) will yield a detailed characterisation of how temperature fluctuations affect the LTP (LISA Technology Package) instrument performance, a crucial information for future space based gravitational wave detectors as the proposed eLISA. Amongst them, the study of temperature gradient fluctuations around the test masses of the Inertial Sensors will provide as well information regarding the contribution of the Brownian noise, which is expected to limit the LTP sensitivity at frequencies close to 1 mHz during some LTP experiments. In this paper we report on how these kind of Thermal Diagnostics experiments were simulated in the last LPF Simulation Campaign (November, 2013) involving all the LPF Data Analysis team and using an end-to-end simulator of the whole spacecraft. Such simulation campaign was conducted under the framework of the preparation for LPF operations
The LISA pathfinder mission
ISA Pathfinder (LPF), the second of the European Space Agency's Small Missions for Advanced Research in Technology (SMART), is a dedicated technology validation mission for future spaceborne gravitational wave detectors, such as the proposed eLISA mission. LISA Pathfinder, and its scientific payload - the LISA Technology Package - will test, in flight, the critical technologies required for low frequency gravitational wave detection: it will put two test masses in a near-perfect gravitational free-fall and control and measure their motion with unprecedented accuracy. This is achieved through technology comprising inertial sensors, high precision laser metrology, drag-free control and an ultra-precise micro-Newton propulsion system. LISA Pathfinder is due to be launched in mid-2015, with first results on the performance of the system being available 6 months thereafter.
The paper introduces the LISA Pathfinder mission, followed by an explanation of the physical principles of measurement concept and associated hardware. We then provide a detailed discussion of the LISA Technology Package, including both the inertial sensor and interferometric readout. As we approach the launch of the LISA Pathfinder, the focus of the development is shifting towards the science operations and data analysis - this is described in the final section of the paper
A noise simulator for eLISA: migrating LISA pathfinder knowledge to the eLISA mission
We present a new technical simulator for the eLISA mission, based on state space modeling techniques and developed in MATLAB. This simulator computes the coordinate and velocity over time of each body involved in the constellation, i.e. the spacecraft and its test masses, taking into account the different disturbances and actuations. This allows studying the contribution of instrumental noises and system imperfections on the residual acceleration applied on the TMs, the latter reflecting the performance of the achieved free-fall along the sensitive axis. A preliminary version of the results is presented
Disentangling the magnetic force noise contribution in LISA pathfinder
Magnetically-induced forces on the inertial masses on-board LISA Pathfinder are expected to be one of the dominant contributions to the mission noise budget, accounting for up to 40%. The origin of this disturbance is the coupling of the residual magnetization and susceptibility of the test masses with the environmental magnetic field. In order to fully understand this important part of the noise model, a set of coils and magnetometers are integrated as a part of the diagnostics subsystem. During operations a sequence of magnetic excitations will be applied to precisely determine the coupling of the magnetic environment to the test mass displacement using the on-board magnetometers. Since no direct measurement of the magnetic field in the test mass position will be available, an extrapolation of the magnetic measurements to the test mass position will be carried out as a part of the data analysis activities. In this paper we show the first results on the magnetic experiments during an end- to-end LISA Pathfinder simulation, and we describe the methods under development to map the magnetic field on-board
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