Studies of the positive muon behavior in solid H2 and D2

Using a pulsed muon beam, we have investigated the microscopic μ⁺ behavior in solid H₂ and D₂ down to 0.6 K by the μ⁺SR method. From the studies of μ⁺ spin relaxation phenomena in solid para‐ H₂ and ortho‐ D₂, we have found that μ⁺ forms three distinct microscopic states; H₂μ⁺( D₂μ⁺)(20\sim25\%), muonium (15\sim20\%) and μ⁺(\sim60\%). In H₂μ⁺, the μ⁺ spin is depolarized in solid para‐ H₂ and a local magnetic field B_loc=1\sim2 G is deduced from LF‐μ⁺SR measurements. The magnitude of B_loc is inconsistent with the magnetic dipolar field (\sim25 G) expected from the magnetic moments of two protons in the H₂μ⁺ molecule and suggests that the H₂μ⁺ molecule might be in the rotationally excited state. From LF‐μ⁺SR measurements, muonium and μ⁺ have been found to diffuse in solid o‐ D_2. The diffusion rate of muonium is two order of magnitude larger than that of μ⁺. This revised version was published online in August 2006 with corrections to the Cover Date.     

Muonium desorption to vacuum from hot iridium surface

Slow muonium (Mu) emission from the surface of iridium (Ir) foil has been observed in vacuum above \sim1200\ K with a yield of 5(1)% Mu per incident muon stopped in the foil. The relative Mu signal was found to be thermally activated with E_a=1.86(1)\ eV. Analysis of the time‐differential evolution of Mu in vacuum at T_Ir=1580\ K showed that the trapping rate of positive muons during diffusion in the bulk Ir was nearly zero. In situ measurements of the surface of Ir with X‐ray photoelectron spectroscopy verified that the main source of impurities in the 99.9%‐Ir was molybdenum (Mo). This revised version was published online in August 2006 with corrections to the Cover Date.     

μ+SR study of two-dimensional antiferromagnets,delafossite-type compounds

⁺SR experiments were performed on delafossite-type compounds, CuCrO₂, AgCrO₂, CuFeO₂, which are model compounds of triangular lattice antiferromagnets. The initial asymmetries are much smaller than the expected value, implying muonium formation. The time spectra are composed of slow andfast relaxation components. We attributed the components to signals from ⁺ stopped at the center of O^2– ions andmuonium far from nuclear dipole moments, respectively. The asymmetries decrease belowT _N but no precession spectra were observed. Relaxation rates of slow andfast relaxation components show maxima atT _N.     

Anisotropic paramagnetic shift of μ−O in the highT c related materials LaSrCuO and LaCuO

The negative muon (^–) was used as a microscopic probe for the study of the electronic state at the oxygen site in highT _c related LaSrCuO materials. Using good single crystals, two types of signals are obtained corresponding to two different oxygen sites: one highly anisotropic, which shows a large (order of 1%) shift under the magnetic field inc-axis direction, the other less anisotropic and with a smaller amplitude (order of 0.2%). These results of ^–OSR show quit a difference with the result of¹⁷O-NMR, where the paramagnetic shift has axial symmetry along the Cu-O bond direction and a magnitude of the order of 0.2% and 0.05%.     

Location and associated hyperfine properties of μ+ in La2CuO4

The location of the positive muon used as a probe in highT _c systems is investigated using the unrestricted Hartree-Fock cluster procedure. Our calculations indicate that ⁺ is located in thea–c plane at a distance of 1.08 Å from the apical oxygen at a ⁺-O(a)-Cu angle of 25°. The hyperfine field at this site is also calculated. Our results show the importance of including the local contact and dipolar contributions to the hyperfine field which arise from the unpaired electron spin distribution in the vicinity of the muon.     

Slow and monoenergetic (3Heμ−)+ beam production and novel applications

Based upon the recent discovery at UT MSL/KEK, a new idea is proposed for producing a slow and monoenergetic (3.2 keV) (³He^–)⁺ ion beam by using particle decay of the (d³He) muon molecule formed during the (d) to³He transfer reaction. The proposed intense (³He) beam as well as the less intense (⁴He) beam will open up way to various new types of important CF experiments.     

Cellulose fiber biodegradation in natural waters: river water,brackish water,and seawater

Cellulose, the main component of plant cell walls, is degradable in nature. However, to the best of our knowledge, this is the first report that compares the biodegradability of cellulose fibers with different structures in natural waters. River water, brackish water, and seawater were collected from the Kamo River and Osaka Bay, Japan. Biodegradation of cellulose fibers with different structures and crystallinities, ramie, mercerized ramie, and regenerated cellulose fibers in the collected natural water was investigated in the dark at 20 °C for 30 days. The primary and aerobic ultimate biodegradability were evaluated by weight loss and biochemical oxygen demand (BOD) tests, respectively. In the weight-loss test, cellulose fibers were found to be degraded by more than 50% in any natural water within 30 days. However, in the BOD test, biodegradation was diminished, with values of 40%, 20–30%, and 2–10% in river water, brackish water, and seawater, respectively. These results indicate that cellulose fibers are easily degraded into fine fragments, but it is difficult to cause their ultimate decomposition into water and carbon dioxide. Existence of such a tendency in the degree of biodegradation among the cellulose fibers remains unclear. The molecular weight of cellulose fibers in natural water was also measured during their degradation. The degradation behavior in river water and seawater was observed to be different from that in brackish water. The results thus obtained indicate that the microorganisms and enzymes that degrade cellulose fibers differ depending on the natural water, which influences the degree and mechanism of biodegradation.

     

A collocation method for solving singular integro-differential equations

This paper describes a collocation method for numerically solving Cauchy-type linear singular integro-differential equations. The numerical method is based on the transformation of the integro-differential equation into an integral equation, and then applying a collocation method to solve the latter. The collocation points are chosen as the Chebyshev nodes. Uniform convergence of the resulting method is then discussed. Numerical examples are presented and solved by the numerical techniques.