Strong anisotropy of projected 3d moments in epitaxial CrO2 films

Soft x-ray magnetic circular dichroism (XMCD) spectra have been investigated for different crystallographic projections of CrO2. Strong anisotropic orbital Cr 3d contributions and a change of sign of the XMCD signal is observed and attributed to t(2g) majority states near the Fermi level. Additionally, moment analysis exhibits anisotropic behavior in the projected spin contributions of CrO2 assigned to a strong magnetic dipole term T(z), consistent with an intrinsic magnetic easy axis behavior along the CrO2 [001] axis. A reduced projected isotropic Cr 3d spin moment has been interpreted in terms of hybridization with oxygen.     

Thermoelectric properties of the interacting two dimensional electron gas in the diffusion regime?

We demonstrate that kinetic coefficients related to thermoelectric properties of the two dimensional electron gas in the diffusive regime are strongly influenced by electron-electron interaction. As an example we consider the thermoelectric coefficients of the diluted two-dimensional electron gas in Si(100) MOSFET’s in the presence of charged-impurity scattering. We find that the screening anomaly at q = 2k _F, also responsible for Friedel oscillations, leads at low electron densities to a large change in the thermoelectric coefficient for the thermopower.     

Design of Leaving Groups in Radical CC Fragmentations: Through‐Bond 2c–3e Interactions in Self‐Terminating Radical Cascades

Radical cascades terminated by β‐scission of exocyclic C?C bonds allow for the formation of aromatic products. Whereas β‐scission is common for weaker bonds, achieving this reactivity for carbon–carbon bonds requires careful design of radical leaving groups. It has now been found that the energetic penalty for breaking a strong σ‐bond can be compensated by the gain of aromaticity in the product and by the stabilizing two‐center, three‐electron “half‐bond” present in the radical fragment. Furthermore, through‐bond communication of a radical and a lone pair accelerates the fragmentation by selectively stabilizing the transition state. The stereoelectronic design of radical leaving groups leads to a new, convenient route to Sn‐functionalized aromatics.     

The Synthesis of (3,5-DI-tert-butyl-4-hydroxyphenyl)methyl-(3-pyridylalkyl)-ethers via 1-(3,5-Di-tert-butyl-4-hydroxyphenyl)methyl Pyridinium Salts.

The rearrangement of 1-(3,5-di-tert-butyl-4-hydroxyphenyl)methyl pyridinium salts under basic conditions is described. A method for the synthesis of (3,5-di-tert-butyl-4-hydroxyphenyl)methyl-(3-pyridylalkyl)-ethers is elaborated.     

Study of gain in C-band deflection cavities for afrequency-doubling magnicon amplifier

An experimental study of the gain between two half-wavelength, 5.7-GHz TM₁₁₀ mode pillbox cavities, separated by a quarter-wavelength drift space, and powered by a 170-A, 500-keV electron beam immersed in an 8.1-kG magnetic field is reported. These cavities constitute the first section of a planned multicavity deflection system, whose purpose is to spin up an electron beam to high transverse momentum (α≡υ⊥/υ_z⩾1) for injection into the output cavity of a frequency-doubling magnicon amplifier. A gain of ~15 dB was observed in the preferred circular polarization, at a frequency shift of approximately -0.18%, in the opposite circular polarization, at a frequency shift of approximately +0.06%. These results are in good agreement with theory     

A Markovian single server with upstream job and downstream demand arrival stream

In this paper we consider a Markovian single server system which processes items arriving from an upstream region (as usual in queueing systems) and is controlled by a demand arrival stream for finished items from a downstream area. A finite storage is available at the server to store finished items not immediately needed in the downstream area. The system considered corresponds to an assembly-like queue with two input streams. The system is stable in a strict sense only if all queues are finite, i.e., both random processes are synchronized via blocking. This notion leads to a complementary system with a very similar state space which is a pair of Markovian single servers with synchronous arrivals. In the mathematical analysis the main focus is on the state probabilities and expectation of minimum and maximum of the two input queues. This revised version was published online in June 2006 with corrections to the Cover Date.     

Elementary excitations in nanochannel arrays of quantum wires

We present an analytical model for the Coulomb interaction effects in quantum wires forming a nanochannel array. We study the elementary excitations (plasmons and electron-hole excitations) of electron arrays forming three-dimensional structures. The plasmon spectrum of boson arrays is also calculated. Our model applies to bulk material with one-dimensional conduction channels as realized in organic or polymer crystals and in nanochannel array glasses.     

Instability of layered quantum liquids: 6. Strongly correlated bosons

We calculate the local-field corrections G(q, q _z) for charged bosons at zero temperature in a superlattice with interlayer distance d. An analytical expression for the local-field correction is described. The sum-rule version of the self-consistent approach for the local-field correction is used to discuss the effects of correlation. The RPAparameter r _s and the ratio d/a* determine correlation effects. a* is the effective Bohr radius. The stability region for the Bose condensate r _s < r _sc as a function of d/a* is determined: r _sc ≈ (d/a*)^3/4. The ground-state energy of the layered Bose condensate is calculated and optical and acoustical plasmons are discussed. We predict a roton structure for optical plasmons for r _s > r _sr with r _sr ≈ 0.5 (d/a*)^3/4.     

Oxoferryl porphyrin cation radicals in model systems: Evidence for variable metal-radical spin coupling

Magnetic properties of frozen solutions of highly oxidized iron porphyrin complexes were investigated by EPR and Mössbauer spectroscopy. The Mössbauer spectra, recorded at low temperatures in various magnetic fields, were analyzed on the basis of spin Hamiltonian simulations. Spin coupling between ferryl iron (Fe^IV) and porphyrin cation radical was taken into account explicitly. Hyperfine and spin-coupling parameters are given for several complexes, together with zero-field parameters. One of the complexes exhibits weak spin coupling, it is the first model system exhibiting properties comparable to those of the oxoferryl cation radical enzyme Horse Radish Peroxidase I.     

The metal insulator transition in two-dimensional systems with charged impurities

The motion of interacting electrons in an array of charged impurities in two dimensions is discussed within a generalized selfconsistent current relaxation theory. The ratio of impurity density n_i to electron density n_c, where the metal insulator transition takes place, is shown to depend on n_c and varies between 0.2 and 10. A comparison of the theory with mobility measurements of Na⁺ drift experiments in inversion layers is made.