Reabsorption in a neodymium fibre laser

Resonance absorption, the reabsorption of laser light by the laser transition of the dopant material itself, is found to be the limiting factor for fibre lasers when extremely long fibres are used. We report on measurements of the temperature dependence of the losses in a 8.5 m long commercial Nd³⁺ doped fibre (York, ND 95020/E). To determine the reabsorption losses, the threshold power has been measured as a function of temperature between 243 K and 413 K. The results are compared with theory assuming a ⁴l level energy of 2110 cm^-1 and an absorption cross-section of δ = 1.15 x 10^-20cm². The comparison shows that reabsorption from the thermally populated ⁴l level is the dominant contribution to the measured losses.     

Crystallization kinetics study on higher homologues of benzylidene aniline compounds: impact of phase variant on nucleation process

A systematic kinetic study leading to the crystallization process from the kinetophases (which occur prior to crystal phase) smectic B, crystal G and smectic F is performed on representative compounds of the homologous series p-phenylbenzylidene-p'-alkylanilines (PBnA) and p-n-alkoxybenzylidene-p'-alkylanilines (nO.m) these compounds are p-phenylbenzylidene-p'-nonylaniline (PB9A), p-phenylbenzylidene-p'-tetradecylaniline (PB14A), p-n-pentadecyloxybenzylidene p'-tetradecylaniline (15O.14) and p-n-octadecyloxybenzylidene-p'-nonylaniline (18O.9). The molecular mechanism and dimensionality in crystal growth from the kineto phases are computed from the Avrami equation, while the characteristic crystalline time (t*) at each crystallization temperature is deduced from the individual plots of log t vs. ΔH. The low magnitudes of the dimensionality parameter n infers the occurrence of diffusion-controlled transformations leading to the formation of plates or needles of finite size possessing impinged edges. The degree of variation in the value of n at each crystallization temperature also reveals the existence of an independent nucleation mechanism for any individual member of the series. The influence of the terminal alkyl chain lengths on the rate of crystallization is determined from a comparative study with the reported analogous compounds.     

A three-dimensional study of endometrial microvessels in women using the contraceptive subdermal levonorgestrel implant system, norplant

Recent evidence points towards a substantial disturbance of the process of angiogenesis within the endometrium in women who are exposed continuously to low dose contraceptive progestogens. This results in the patchy appearance of abnormally small and abnormally large, thin-walled vessels in the superficial regions of exposed endometrium. Three-dimensional pictures were developed from digitised images of serial tissue sections of endometrium in which microvascular endothelial cells were labelled with antibodies to the endothelial cell surface antigen, CD34 and their basement membranes labelled with anti-Collagen IV antibodies. Microvessels from endometrium exposed to continuous low-dose levonorgestrel from a subdermal implant system (Norplant) displayed considerable variations in size and shape. No spiral arterioles were identified. Some microvessels showed considerable dilatation, distortion and variability in the presence of surrounding basement membrane components. Other endothelial structures included narrow, solid cords of endothelial cells, without basement membranes, which often connected with normal or abnormal vessels containing lumens. Some areas, especially deeper in the tissue, contained microvessels of normal size and shape surrounded by basement membrane. These images have revealed an overall picture of great variability in superficial endometrial vascular structures in some women using a low-dose levonorgestrel implant system which appears substantially different from that seen in normal endometrium.     

The 65Cu(p,t)63Cu reaction and the structure of 63Cu

The ⁶⁵Cu(p, t)⁶³Cu reaction has been studied with 18.0 and 19.5 MeV protons. The states in ⁶³Cu at 1.547 and 2.498 MeV are each assigned $\text{J}{}^{\mathrm{\pi }}\text{=}\text{3}\text{2}{}^{\mathrm{?}}$ on the basis of angular distributions indicating mixed L = 0 and L = 2 transfer. Relative cross sections for L = 2 transfer to the low-lying states are compared with predictions of the shell model and particle-core model.     

Magnetic moments of (νi132)−n isomers in neutron-deficient lead isotopes

The magnetic moments of the 12⁺ isomers in ^{192, 196, 198, 200, 206}Pb and of the $\text{33}\text{2}{}^{\mathrm{+}}$ isomer in ²⁰⁵Pb have been measured using the PAD technique. The results for the g-factors are: g(192) = ?0.173(2), g(196) = ?0.1600(15), g(198) = ?0.1552(15), g(200) = ?0.1512(15), g(206) = ?0.1496(18), and g(205) = ?0.148(5). As all states have a rather pure $\text{(νi}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}\text{)}{}^{\mathrm{?n}}$ configuration, the values reflect directly the $\text{νi}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}$ orbital. They show a decrease towards the more neutron-deficient isotopes attributed to the reduced core polarisation as a result of decreasing occupation of the $\text{i}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}$ neutron shell. The measured systematics are discussed regarding core polarisation, mesonic corrections, and small admixtures of core-excited states to the $\text{i}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}$ wave function.     

NMR analysis and synthesis of 6- and 8-C-methylisoflavones

NMR data for eighteen 6- and 8-C-methylisoflavones provide conclusive evidence that in isoflavones, the C-8 proton and C-8 methyl signals occur downfield from the C-6 proton and C-6 methyl signals. Other useful NMR correlations and the synthesis of five new C-methylisoflavones are described.     

Mechanismus der durch Licht ausgel?sten Polymerisation von Methylmethacrylat auf Oberfl?chen von Zinkoxid

Ohne Zusammenfassung     

Factorization of nonnegative matrices—II

Suppose A is an n×n nonnegative matrix. Necessary and sufficient conditions are given for A to be factored as LU, where L is a lower triangular nonnegative matrix, and U is an upper triangular nonnegative matrix with u_ii = 1.     

Possible nuclear structure effects seen in (6Li,d) f-p shell reactions

A finite range DWBA analysis has been made of ground state angular distributions from (⁶Li, d) experiments on twelve fp shell nuclei at 28 or 32 MeV. Good fits were obtained. A systematic variation in bound-state radius was required. The interpretation of this effect using microscopic wavefunctions suggests that four-nucleon structure information may be obtained from the shapes of the angular distributions.     

Excitation of giant resonance in 90Zr by inelastic 6Li scattering

Inelastic ⁶Li scattering by ⁹⁰Zr was measured at 74 MeV. A broad structure, which appears to be the giant quadrupole resonance, was observed at 13.8 MeV excitation energy. This observation is in agreement with previous work done with ions lighter than ⁶Li.