Heavy quark correlations ine + e − annihilations

In heavy quark jets the quark mass acts as a regulator of collinear singularities, making the quark momentum an infra-red safe variable in perturbative QCD. This allows a direct comparison of measured heavy hadron momentum spectra with perturbative calculations. We exploit the factorisation of heavy quark fragmentation to derive QCD predictions for momentum correlations between heavy hadrons produced ine ⁺ e ^? annihilations. We study the practical feasibility and model sensitivity of our approach using Monte Carlo simulations. Higher order perturbative corrections and contributions from non-perturbative effects are found to be at the level of 10%.     

Magnetic resonance imaging of the uterus at an ultra low (0.02 T) magnetic field.

In vivo pelvic imaging of 39 women and in vitro relaxation time measurements of four uterine specimens were performed using an ultra low field (0.02 T) MRI unit. Average T1 times measured in vitro at 37 degrees C for the myometrium and endometrium were 206 ms (SD 47 ms) and 389 ms (SD 21 ms), respectively. Corresponding T2 times were 95 ms (SD 20 ms) and 167 ms (SD 13 ms). The proton relaxation of almost all myometrial specimens proved to be biexponential, but of all endometrial specimens was monoexponential. Contrast measurements between endometrium versus myometrium and myometrium versus the junctional zone were performed after imaging 18 volunteer women using different pulse sequence parameters. Normal uterine structures were optimally demonstrated by SE 700/70. Relatively short repetition times could be used, because spin-lattice relaxation times were short at the low magnetic field. Consequently, the short repetition times allowed averaging of four excitations to create adequate images within an acceptable scanning time. In addition to T2-weighted images a T1-weighted inversion recovery sequence with a short inversion time of 50 ms (IR 1000/50/40) adequately differentiated the three uterine zones. Although pathologic lesions of the uterus including leiomyomas, anomalies and carcinomas were well demonstrated, especially with the T2-weighted spin echo pulse sequence, further investigations are needed to evaluate the optimal technique for ultra low field MR imaging of uterine tumors.     

P-N junctions in semiconducting TiO2 studied through computer modelling

The dependence of the formation of a p-n or p-p⁺ junction in semiconducting TiO₂ as a function of various parameters is investigated through a computer model. The effect of the polarizing conditions on the I–V characteristics is also discussed and related to experimental results. Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Sept. 15–22, 1996     

Possibilities for gamma-ray stimulated emissionexperiments

We show that gamma-ray stimulated emission experiments are comparatively easy and inexpensive. The registration of a double- (N_2γ/N_γ) and a triple-energy peak (N_3γ/N_γ) is possible and the relation between their intensities permits the calculation of the recoilles factor f_s (stimulated) and making a conclusion about constructing a working gamma-ray laser. This revised version was published online in August 2006 with corrections to the Cover Date.     

AUTOMATED WIND TUNNEL MEASUREMENTS

It is common practice in power transmission to use bundled overhead electrical conductors because the lower rate of corona discharge, compared with single conductors, makes the bundle attractive for high voltages. However, secondary problems may arise from the vibrations induced by the aerodynamic forces which act on the leeward conductors as a result of their immersion in the wake of a windward conductor. Thus, in addition to possible aeolian and galloping oscillations observed for a single conductor, bundle conductors may also be subjected to wake-induced oscillations. ^1,2 Although extensive research has been done on the aeroelastic behavior of single and bundled conductors which are bare, little is known about the galloping or wake oscillation characteristics of given bundle conductors which, depending upon the environmental conditions during the formation of ice, may have five or so representative shaped cross-sections. One important task involves the aerodynamic quasi-static force and moment measurements in a wind tunnel using full scale conductor cross-sections each of which must be rotated through many angles at different spacings. Such measurements are repetitive as well as tediously time consuming and, hence, are beneficially automated. A reliable, accurate and inexpensive automated apparatus is described in this paper which permits the aerodynamic measurements to be performed efficiently and without intervention. Most importantly, it relieves the operator of the usual responsibility for manually controlling the separation and orientation of the sections as well as the need to manually compensate fluctuations in the free stream air speed. For simplicity, the apparatus is detailed in the context of a twin bundle conductor.