The Effects of Deformation on Isovector Electromagnetic and Weak Transition Strengths

The summed strength for transitions from the ground state of $^{12}C$ via the operators $\vec{s}t, \vec{\ell}t, rY't, r[Y's]^{\lambda}t$ and $r[Y'\ell]^{\lambda}t$ are calculated using the $\Delta N = 0$ rotational model. If we choose the z component of the isospin operator $t_{z}$, the above operators are relevant to electromagnetic transitions; if we choose $t_{+}$ they are relevant to weak transitions such as neutrino capture. In going from the spherical limit to the asymptotic (oblate) limit the strength for the operator $\vec{s} t$ decreases steadily to zero; the strength for the operator $\vec{\ell}\tau$ (scissors mode) increases by a factor of three. For the last three operators - isovector dipole, spin dipole and orbital dipole (including the twist mode) it is shown that the summed strength is independant of deformation. The main difference in the behavior is that for the first two operators we have in-shell transitions whereas for the last three operators the transitions are out of shell.Comment: 14 pages, late

Correlation between the quenching of total GT+ strength and the increase of E2 strength

Relations between the total beta+ Gamow-Teller (GT+) strength and the E2 strength are further examined. It is found that in shell-model calculations for N=Z nuclei, in which changes in deformation are induced by varying the single-particle energies, the total GT+ or GT- strength decreases monotonically with increasing values of the B(E2) from the ground state to the first excited J=2+ state. Similar trends are also seen for the double GT transition amplitude (with some exceptions) and for the spin part of the total M1 strength as a function of B(E2).Comment: 11 pages and 3 figures (Figures will be sent on request

Pathophysiology of elevated ascites fluid cholesterol in malignant ascites

The existence of marked elevations of ascitic fluid cholesterol has been observed in patients with peritoneal carcinomatosis compared to patients with cirrhosis and has been found useful in differential diagnosis. This finding could be caused by an enhanced movement of plasma lipoproteins into the peritoneal cavity. To test this hypothesis we determined the fasting concentrations of total, high density lipoprotein (HDL)- and low density lipoprotein (LDL)-cholesterol, apolipoprotein-A1 (apo-A1) and apolipoprotein-B (apo-B) in serum and ascites of 17 patients with cirrhosis and 16 patients with peritoneal carcinomatosis. The movement of proteins from plasma to ascites was calculated from the ascites/serum concentration ratios of six different sized proteins with a molecular mass ranging from 54 kDa to 971 kDa. Mean values (mg/dl) for total cholesterol (92.6 vs. 21.0), HDL-cholesterol (15.6 vs. 1.8), LDL-cholesterol (63.4 vs. 16.1), apo-A1 (50.2 vs. 13.6) and apo-B (41.2 vs. 12.9) in ascites were significantly higher in peritoneal carcinomatosis than in cirrhosis. These differences could only partially be explained by the higher serum concentrations of these parameters in peritoneal carcinomatosis, but were mainly due to a lower selectivity for the movement of plasma proteins and lipoproteins into ascites (mean ascites/serum (A/S) ratio: 0.30–0.77) in peritoneal carcinomatosis as compared to cirrhosis (mean ascites/serum ratio: 0.11–0.21). In both groups about 85% of the total cholesterol in serum and ascites consisted of HDL- and LDL-cholesterol. These findings support the hypothesis that elevations in ascitic cholesterol in peritoneal carcinomatosis compared to cirrhosis are mainly caused by the increased movement of plasma HDL and LDL into the peritoneal cavity

Critical growth problems with singular nonlinearities on Carnot groups

We provide regularity, existence and non existence results for the semilinear subelliptic problem with critical growth −ΔGu=ψ^α|u|^(2∗(α)−2)u/d(ξ)^α+λu in ΩΩ, u=0 on ∂Ω, where ΔG is a sublaplacian on a Carnot group GG, 0<2, 2∗(α)=2(Q−α)/(Q−2), Ω is a bounded domain of G, d is the natural gauge associated with the fundamental solution of −ΔG on G and ψ:=|∇Gd|, ∇G being the subelliptic gradient associated to ΔG, λ is a real parameter

Long-Range Exciton Diffusion in Two-Dimensional Assemblies of Cesium Lead Bromide Perovskite Nanocrystals

F\"orster Resonant Energy Transfer (FRET)-mediated exciton diffusion through artificial nanoscale building block assemblies could be used as a new optoelectronic design element to transport energy. However, so far nanocrystal (NC) systems supported only diffusion length of 30 nm, which are too small to be useful in devices. Here, we demonstrate a FRET-mediated exciton diffusion length of 200 nm with 0.5 cm2/s diffusivity through an ordered, two-dimensional assembly of cesium lead bromide perovskite nanocrystals (PNC). Exciton diffusion was directly measured via steady-state and time-resolved photoluminescence (PL) microscopy, with physical modeling providing deeper insight into the transport process. This exceptionally efficient exciton transport is facilitated by PNCs high PL quantum yield, large absorption cross-section, and high polarizability, together with minimal energetic and geometric disorder of the assembly. This FRET-mediated exciton diffusion length matches perovskites optical absorption depth, opening the possibility to design new optoelectronic device architectures with improved performances, and providing insight into the high conversion efficiencies of PNC-based optoelectronic devices

Comparison of techniques for computing shell-model effective operators

Different techniques for calculating effective operators within the framework of the shell model using the same effective interaction and the same excitation spaces are presented. Starting with the large-basis no-core approach, we compare the time-honored perturbation-expansion approach and a model-space truncation approach. Results for the electric quadrupole and magnetic dipole operators are presented for $^6$Li. The convergence trends and dependence of the effective operators on differing excitation spaces and Pauli Q-operators is studied. In addition, the dependence of the electric-quadrupole effective charge on the harmonic-oscillator frequency and the mass number, for A=5,6, is investigated in the model-space truncation approach.Comment: 18 pages. REVTEX. 4 PostScript figure