We report a new limit on a possible short range spin-dependent interaction from the precise measurement of the ratio of Larmor precession frequencies of stored ultracold neutrons and Hg199 atoms ...confined in the same volume. The measurement was performed in a ∼1μT vertical magnetic holding field with the apparatus searching for a permanent electric dipole moment of the neutron at the Paul Scherrer Institute. A possible coupling between freely precessing polarized neutron spins and unpolarized nucleons of the wall material can be investigated by searching for a tiny change of the precession frequencies of neutron and mercury spins. Such a frequency change can be interpreted as a consequence of a short range spin-dependent interaction that could possibly be mediated by axions or axion-like particles. The interaction strength is proportional to the CP violating product of scalar and pseudoscalar coupling constants gSgP. Our result confirms limits from complementary experiments with spin-polarized nuclei in a model-independent way. Limits from other neutron experiments are improved by up to two orders of magnitude in the interaction range of 10−6<λ<10−4m.
Objective
Increasing construct stability of lumbosacral instrumentations using S2–ala screws as an alternate to iliac screws.
Indications
Revision surgery after failed lumbosacral fusion; long ...instrumentations to the sacrum; L5–S1 fusion without anterior support.
Contraindications
Lack of sacral bone stock.
Surgical technique
Midline approach. The entry point for S2–ala screws is caudal to the posterior S1 foramen and close to the lateral sacral crest. Screw tract preparation for S2–ala screws necessitates 30–45° angulation in the axial plane. Biplanar fluoroscopy with inlet and outlet views ensure screw accuracy. With S2–ala screws, bicortical fixation is the goal.
Postoperative management
Patients are mobilized under the surveillance of physiotherapists on day 1 and released from the hospital after 10 days. Clinical and radiographic controls are performed at 6, 12 and 24 months.
Results
Retrospective review of 80 patients undergoing S2–ala screw fixation. Main diagnosis was degenerative lumbar instability, adult scoliosis, high-grade listhesis, and nonidiopathic scoliosis. In 66% of patients, the instrumentation using S2–ala screws was part of a major lumbosacral revision surgery. Follow-up averaged 26 months. There were no deaths or major neurovascular complications. First time fusion rate at L5–S1 was greater than 90%. Eight patients (10%) experienced a complication which could be related to the S2–ala screws. Out of 160 S2-ala screws, 16 screws were judged to cause focal irritation and were removed, indicating a survival rate of 90% for the S2–ala screw.
Purpose
Recent literature shows that occult discoligamentous injuries still remain difficult to diagnose in the first instance. Thresholds as indicators for discoligamentous segmental instability ...were previously defined. But, since supine radiodiagnostic is prone to spontaneous reduction of a displaced injury, and even some highly unstable injuries reveal only slight radiographic displacement, these criteria might mislead in the traumatized patient. A highly accurate radiographic instrument to assess segmental motion is the computer-assisted quantitative motion analysis (QMA). The aim was to evaluate the applicability of the QMA in the setting of a traumatized patient.
Methods
Review of 154 patients with unstable cervical injuries C3–7. Seventeen patients (male/female: 1:5, age: 44.6 years) had history of initially hidden discoligamentous injuries without signs of neurologic impairment. Initial radiographs did not fulfill instability criteria by conventional analysis. Instability was identified by late subluxation/dislocation, persisting/increasing neck pain, and/or scheduled follow-up. For 16 patients plain lateral radiographs were subjected to QMA. QMA data derived were compared with normative data of 140 asymptomatic volunteers from an institutional database.
Results
Data analysis of measurements revealed mean spondylolisthesis of −1.0 mm (−3.7 to +3.4 mm), for segmental rotational angle mean angulation of −0.9° (−11.1° to +17.7°). Analysis of these figures indicated positive instability thresholds in 5 patients (31.3 %). Analysis of center of rotation (COR)-shifts was only accomplishable completely in 3/16 patients due to limited motion or inadequacy of radiographs. Two of these patients (12.5 %) showed a suspect shift of the COR.
Conclusions
Our data show a high rate of false negative results in cases of hidden discoligamentous injuries by using conventional radiographic analysis as well as QMA in plain lateral radiographs in a trauma setting. Despite the technical possibilities in a modern trauma center, our data and recent literature indicate a thorough clinical and radiographic follow-up of patients with cervical symptoms to avoid secondary complications from missed cervical spine injuries.
We present the result of an experiment to measure the electric dipole moment (EDM) of the neutron at the Paul Scherrer Institute using Ramsey's method of separated oscillating magnetic fields with ...ultracold neutrons. Our measurement stands in the long history of EDM experiments probing physics violating time-reversal invariance. The salient features of this experiment were the use of a ^{199}Hg comagnetometer and an array of optically pumped cesium vapor magnetometers to cancel and correct for magnetic-field changes. The statistical analysis was performed on blinded datasets by two separate groups, while the estimation of systematic effects profited from an unprecedented knowledge of the magnetic field. The measured value of the neutron EDM is d_{n}=(0.0±1.1_{stat}±0.2_{sys})×10^{-26} e.cm.
We have used copper-coated carbon fiber reinforced plastic (CuCFRP) for the construction of high and ultra-high vacuum chambers. The vacuum performance is found to be comparable to typical stainless ...steel used for this purpose. In test chambers we have reached pressures of 2 × 10−8 mbar and measured a desorption rate of 1 × 10−11 mbar l/s m2; no degradation over time (2 years) has been found. Suitability for baking has been found to depend on the CFRP production process, presumably on the temperature of the autoclave curing. Together with other unique properties of CuCFRP such as low weight and being nearly non-magnetic, this makes it an ideal material for many high-end vacuum applications.
•Copper coated carbon reinforced fiber was tested for vacuum properties.•Test chambers have shown a desorption rate of less then 1E-11 mbar l/s/cm2.•Lowest pressures measured (2E-8 mbar) were limited by fluoroelastomer gaskets.•Baking of high grade CuCFRP improved vacuum performance.•Low grade CuCFRP showed delamination after heat cycling.
Antioxidants can be divided into two broad classes, primary and secondary, depending upon their mode of action. The most broadly used primary antioxidants are hindered phenolics. Phenolic ...antioxidants have traditionally been based on 2,6-di-
t-butyl-4-methylphenol (BHT). This functional moiety has been incorporated into larger molecules affording products with lower volatility or greater polymer compatibility. More recently, molecules have been introduced which vary in steric hindrance about the phenol and also the way in which multiple phenol functional groups are linked to form larger molecules. This has led to structures which have lower colour contribution. Surprisingly, in some cases these molecules have shown higher levels of efficiency relative to other antioxidants with similar phenol/molecular weight ratios. This has included enhanced levels of synergism with secondary antioxidants. An attempt is made to correlate structural features of these molecules to the enhanced performance and/or lower colour.
Palladium catalyzes the regio- and stereoselective annulation of allenes by vinylic halides bearing alcohol-, amine-, sulfonamide-, carboxylic acid-, carboxamide- and carbanion-stabilizing groups to ...produce a variety of five- and six-membered-ring unsaturated heterocycles and carbocycles. The reaction appears to proceed by vinylic palladium formation and addition to the allene, followed by intramolecular nucleophilic displacement of the palladium. Six-membered rings are formed more readily than five-membered rings. The regioselectivity is generally high, with vinylic halides bearing alcohol, carboxylic acid, or carboxamide groups affording predominantly the product of intramolecular attack on the more substituted end of the π-allylpalladium intermediate, while amines and carbanions attack quite selectively at the less substituted end of the π-allylpalladium intermediate. Vinylic halides bearing tosylamides afford mixtures of regioisomers, where the predominant six-membered ring product arises by attack on the less substituted end of the allene, while the major five-membered ring products involve addition to the more substituted end of the allene.
Physics at the Planck scale could be revealed by looking for tiny violations of fundamental symmetries in low energy experiments. In 2008, a sensitive test of the isotropy of the universe has been ...performed with stored ultracold neutrons (UCN), this is the first clock-comparison experiment performed with free neutrons. During several days we monitored the Larmor frequency of neutron spins in a weak magnetic field using the Ramsey resonance technique. A nonzero cosmic axial field, violating rotational symmetry, would induce a daily variation of the precession frequency. Our null result constitutes one of the most stringent tests of Lorentz invariance to date.
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