Determination of Radiative Lifetimes In the 3d(10)np(2)p Sequence of Neutral Copper By Time-resolved Vuv Laser-spectroscopy

Lifetimes in the 3d(10)np(2)P sequence in neutral copper were measured by time-resolved laser spectroscopy. Excitation from the ground state was performed with pulsed laser radiation in the; vuv spectral region, generated by resonant sum-difference four-wave mixing in krypton gas. The lifetimes were evaluated from recorded optical transients. For the np(2)P(J) states we find the following: tau(n = 6, 5 = 3/2) = 5.2(8) ns, tau(6, 1/2) = 25.1(10) ns, tau(7; 3/2) = 15.0(12) ns, tau(7, 1/2) = 4.0(8) ns, tau(8,3/2) = 31(2) ns, tau(8, 1/2) = 15.8(12) us, tau(9, 3/2) = 123(6) ns, and tau(9, 1/2) = 51(6) ns. The data are compared with a recent multiconfiguration Hartree-Fock calculation

Insertion torque is not a good predictor of pedicle screw loosening after spinal instrumentation: a prospective study in 8 patients

<p>Abstract</p> <p>Background</p> <p>Pedicle screw loosening is a major safety concern in instrumented spinal surgery due to loosening with potential pseudarthrosis and possible loss of correction requiring revision surgery. Several cadaver studies have compared insertion torque of pedicle screws with resistance to pullout or cyclic loading. In most of these studies, a correlation has been found between these variables. Clinical studies have been made, comparing insertion torque to bone mineral density or radiological signs of screw loosening. There are no clinical studies comparing insertion torque to extraction torque or other biomechanical parameters in vivo. This study was designed to investigate whether the insertion torque of pedicle screws can be used to predict the purchase of the screws.</p> <p>Methods</p> <p>The insertion torque of stainless steel pedicle screws was recorded in eight patients undergoing lumbar fusion surgery with four-screw constructs. Torque gauge manometers were used for the recordings. The implants were removed after one year, and the extraction torque of the screws was recorded.</p> <p>Results</p> <p>The mean insertion torque was 76 ± 41 Ncm and the mean extraction torque 29 ± 36 Ncm. The r value was 0.591, suggesting that there was a correlation between the insertion and extraction torque. However, the scattergram revealed that the screws could be divided into two groups, six screws with a high correlation between insertion and extraction torque, and 26 screws where no correlation could be demonstrated.</p> <p>Conclusions</p> <p>In this unique human in-vivo study, the insertion torque could not be used to predict the purchase of lumbar pedicle screws one year after implantation. It could be demonstrated that in vivo insertion torque alone is of minor value to estimate pullout strength, and should be combined with or replaced by more accurate measures.</p

Natural Lifetimes of Excited-states of Neutral Nitrogen Determined By Time-resolved Laser Spectroscopy

Radiative lifetimes were determined for three quartet states of neutral nitrogen, and sequences of Rydberg states were studied using depletion spectroscopy. Free nitrogen atoms were generated by photodissociation of N2O using frequency-tripled dye-laser radiation that was two-photon resonant with the 2p(2)3p 4S or 4D states. Further quartet states were reached by a subsequent single-photon absorption. We obtain tau(2p(2)3p 4D7/2) = 44(2) ns, tau(2p(2)3p 4S3/2) = 26.0(1.5) ns, and tau(2p(2)6s4P5/2) = 41(7) ns

Two-color Time-resolved Spectroscopy of Helium Using High-order Harmonics

The radiative lifetime of the 1s2p(1)P state of helium is measured in a two-colour ionization experiment with a 5% accuracy. The state is excited by the 13th harmonic of a tunable 80 ps laser and ionized by a synchronous ultraviolet laser, with a variable time delay. This experiment demonstrates that the high harmonics generated in a jet of rare gas exposed to an intense laser field provide a tunable short-pulse xuv source ideally suited for pump/probe type of studies and, in particular, short lifetime measurements

High-order Harmonic-generation In Rare-gases With An Intense Short-pulse Laser

We present experimental studies of high-order harmonic generation in the rare gases performed with a short-pulse titanium sapphire laser operating at 794 nm in the 10(14)-10(15) W/cm2 range. The harmonic yields generated in neon and in argon are studied for all orders as a function of the laser intensity. They vary first rather steeply, in the cutoff region, then much more slowly in the plateau region, and, finally, they saturate when the medium gets ionized. The dependence of the high-order harmonic cutoff with the laser intensity in neon and argon is found to be lower than that predicted in single-atom theories. We observe high-order harmonics in argon and xenon (up to the 65th and 45th, respectively) at 10(15) W/cm2, which we attribute to harmonic generation from ions. We also show how the harmonic and fundamental spectra get blueshifted when the medium becomes ionized

Leisure Physical Activity and the Risk of Fracture in Men

From a large cohort study with 35 years of follow-up, Michaelsson and colleagues conclude that regular sport activities can reduce the risk of fractures in older men

In Vivo Evaluation of an Injectable Premixed Radiopaque Calcium Phosphate Cement

In this work a radiopaque premixed calcium phosphate cement (pCPC) has been developed and evaluated in vivo. Radiopacity was obtained by adding 0–40 % zirconia to the cement paste. The effects of zirconia on setting time, strength and radiopacity were evaluated. In the in vivo study a 2 by 3.5 mm cylindrical defect in a rat vertebrae was filled with either the pCPC, PMMA or bone chips. Nano-SPECT CT analysis was used to monitor osteoblast activity during bone regeneration. The study showed that by adding zirconia to the cement the setting time becomes longer and the compressive strength is reduced. All materials evaluated in the in vivo study filled the bone defect and there was a strong osteoblast activity at the injury site. In spite of the osteoblast activity, PMMA blocked bone healing and the bone chips group showed minimal new bone formation. At 12 weeks the pCPC was partially resorbed and replaced by new bone with good bone ingrowth. The radiopaque pCPC may be considered to be used for minimal invasive treatment of vertebral fractures since it has good handling, radiopacity and allows healing of cancellous bone in parallel with the resorption of the cement

Fungus covered insulator materials studied with laser-induced fluorescence and principal component analysis

A method combining laser-induced fluorescence and principal component analysis to detect and discriminate between algal and fungal growth on insulator materials has been studied. Eight fungal cultures and four insulator materials have been analyzed. Multivariate classifications were utilized to characterize the insulator material, and fungal growth could readily be distinguished from a clean surface. The results of the principal component analyses make it possible to distinguish between algae infected, fungi infected, and clean silicone rubber materials. The experiments were performed in the laboratory using a fiber-optic fluorosensor that consisted of a nitrogen laser and an optical multi-channel analyzer system