Dissociative and molecular oxygen chemisorption channels on reduced rutile TiO2(110): An STM and TPD study

High-resolution scanning tunneling microscopy (STM) and temperature-programmed desorption (TPD) were used to study the interaction of O₂ with reduced TiO₂(110)–(1 × 1) crystals. STM is the technique of choice to unravel the relation between vacancy and non-vacancy assisted O₂ dissociation channels as a function of temperature. It is revealed that the vacancy-assisted, first O₂ dissociation channel is preferred at low temperature (~ 120 K), whereas the non-vacancy assisted, second O₂ dissociation channel operates at temperatures higher than 150 K–180 K. Based on the STM results on the two dissociative O₂ interaction channels and the TPD data, a new comprehensive model of the O₂ chemisorption on reduced TiO₂(110) is proposed. The model explains the relations between the two dissociative and the molecular O₂ interaction channels. The experimental data are interpreted by considering the available charge in the near-surface region of reduced TiO₂(110) crystals, the kinetics of the two O₂ dissociation channels as well as the kinetics of the diffusion and reaction of Ti interstitials.     

Fragment angular distributions in electron-induced fission of 232Th

Fission fragment angular distributions have been observed in electron-induced fission of ²³²Th for electron energies 8.7 MeV ≦ E_e ≦ 30 MeV. For low energies (though above the fission threshold) the angular distributions contain both a dipole and a quadrupole component. The (90°/0°) anisotropy decreases rapidly for higher electron energies but reveals smaller peaks after the onset of second-, third- and fourth-chance fission suggesting that the effective fission barriers for ²³¹Th and ²²⁹Th in second- and fourth-chance fission, respectively, are both characterized by $\text{K =}\text{1}\text{2}$.     

Geometry of the numerical range of matrices

Some techniques for the study of the algebraic curve C(A) which generates the numerical range W(A) of an n×n matrix A as its convex hull are developed. These enable one to give an explicit point equation of C(A) and a formula for the curvature of C(A) at a boundary point of W(A). Applied to the case of a nonnegative matrix A, a simple relation is found between the curvature of the function Φ(A)=p((1?α)A+ αA^T) (pbeingthePerronroot) at $\text{α=}\text{1}\text{2}$ and the curvature of W(A) at the Perron root of $\text{1}\text{2}\text{(A+A}{}^{\mathrm{T}}\text{)}$. A connection with 2-dimensional pencils of Hermitian matrices is mentioned and a conjecture formulated.     

Excitation functions of the analyzing power in elastic proton-proton scattering from 0.45 to 2.5 GeV

Excitation functions A_N(p_lab,_c.m.) of the analyzing power in elastic proton-proton scattering have been measured in an internal target experiment at the Cooler Synchrotron COSY with an unpolarized proton beam and a polarized atomic hydrogen target. Data were taken continuously during the acceleration and deceleration for proton kinetic energies T_lab (momenta p_lab) between 0.45 and 2.5 GeV (1.0 and 3.3 GeV/c) and scattering angles 30 ^° _c.m. 90^°. The results provide excitation functions and angular distributions of high precision and internal consistency. The data can be used as calibration standard between 0.45 and 2.5 GeV. They have significant impact on phase shift solutions, in particular on the spin triplet phase shifts between 1.0 and 1.8 GeV.     

A microfluidic system enabling Raman measurements of the oxygenation cycle in single optically trapped red blood cells

Using a lab-on-a-chip approach we demonstrate the possibility of selecting a single cell with certain properties and following its dynamics after an environmental stimulation in real time using Raman spectroscopy. This is accomplished by combining a micro Raman set-up with optical tweezers and a microfluidic system. The latter gives full control over the media surrounding the cell, and it consists of a pattern of channels and reservoirs defined by electron beam lithography that is moulded into rubber silicon (PDMS). Different buffers can be transported through the channels using electro-osmotic flow, while the resonance Raman response of an optically trapped red blood cell (RBC) is simultaneously registered. This makes it possible to monitor the oxygenation cycle of the cell in real time and to investigate effects like photo-induced chemistry caused by the illumination. The experimental set-up has high potential for in vivo monitoring of cellular drug response using a variety of spectroscopic probes.     

Direct observation of tunneling and nonlinear self-trapping in a single bosonic Josephson junction

We report on the first realization of a single bosonic Josephson junction, implemented by two weakly linked Bose-Einstein condensates in a double-well potential. In order to fully investigate the nonlinear tunneling dynamics we measure the density distribution in situ and deduce the evolution of the relative phase between the two condensates from interference fringes. Our results verify the predicted nonlinear generalization of tunneling oscillations in superconducting and superfluid Josephson junctions. Additionally, we confirm a novel nonlinear effect known as macroscopic quantum self-trapping, which leads to the inhibition of large amplitude tunneling oscillations.     

The influence of finite cavities on the sound insulation of double-plate structures

Lightweight walls are often designed as frameworks of studs with plates on each side--a double-plate structure. The studs constitute boundaries for the cavities, thereby both affecting the sound transmission directly by short-circuiting the plates, and indirectly by disturbing the sound field between the plates. The paper presents a deterministic prediction model for airborne sound insulation including both effects of the studs. A spatial transform technique is used, taking advantage of the periodicity. The acoustic field inside the cavities is expanded by means of cosine-series. The transmission coefficient (angle-dependent and diffuse) and transmission loss are studied. Numerical examples are presented and comparisons with measurement are performed. The result indicates that a reasonably good agreement between theory and measurement can be achieved.     

A Comparison of Splittings and Integral Equation Solvers for a Nonseparable Elliptic Equation

Iterative numerical schemes for solving the electrostatic partial differential equation with variable conductivity, using fast and high-order accurate direct methods for preconditioning, are compared. Two integral method schemes of this type, based on previously suggested splittings of the equation, are proposed, analyzed, and implemented. The schemes are tested for large problems on a square. Particular emphasis is paid to convergence as a function of geometric complexity in the conductivity. Differences in performance of the schemes are predicted and observed in a striking manner. AMS subject classification (2000) 31A10, 35C15, 65R20.Received May 2004. Accepted September 2004. Communicated by Anders Szepessy.Johan Helsing: This work was supported by the Swedish Science Research Council under contract 621-2001-2799.