C-Fe chains due to segregated carbon impurities on Fe(1 0 0)

Bulk carbon impurities segregate at the Fe(1 0 0) surface and, upon thermal annealing, can form metastable surface phases with local and long range order and peculiar electronic properties. We present a surface science study of C-segregated Fe(1 0 0) with scanning tunneling microscopy, angle resolved photoemission, and ab initio calculations of the surface structure and electron states. In particular the c(3√2 × √2) structure, observed for 0.67 atomic layers of C segregated at the iron surface, is found to be due to self-organized carbon stripes made of zig-zag chains. The strong hybridization between C and Fe was observed in ARPES spectra.     

Spin polarized photoemission from the Fe 3s core levels

The origin of the core level splitting in the Fe 3s spectra has been investigated by spin resolved photoemission. The two Fe 3s spectral features, separated by 4.4 eV, are found to be characterized by large and opposite spin polarization. This observation proves that the exchange interaction is the main cause of the Fe 3s splitting.     

A complete treatment of a steady-state four-level model for the interpretation of OH laser-induced fluorescence measurements in atmospheric pressure flames

In order to obtain OH concentration measurements in atmospheric pressure flames from saturated fluorescence signal, we have developed a stationary four-level model. A general relationship between the measured upper state population and the total number density has been derived. The effects of the imbalance between the rotational transfer rates in the upper and ground states is analyzed. We show that in the case of comparable rotational rates, the results of our treatment are similar to the ones obtained with the balanced cross rate model. A set of complementary data which should facilitate absolute OH concentration measurements is also pointed out.     

Adaptive behaviour of the spinal cord in the transition from quiet stance to walking

Background

Parkinson??s disease is characterized by a continuous loss of neurons within the substantia nigra (SN) leading to a depletion of dopamine. Within the adult SN as a non-neurogenic region, cells with mainly oligodendrocytic precursor characteristics, expressing the neuro-glial antigen-2 (NG2) are continuously generated. Proliferation of these cells is altered in animal models of Parkinson??s disease (PD). Exercise and environmental enrichment re-increase proliferation of NG2⁺ cells in PD models, however, a possible mechanistic role of dopamine for this increase is not completely understood. NG2⁺ cells can differentiate into oligodendrocytes but also into microglia and neurons as observed in vitro suggesting a possible hint for endogenous regenerative capacity of the SN. We investigated the role of dopamine in NG2-generation and differentiation in the adult SN stimulated by physical activity and environmental enrichment.

Results

We used the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-model for dopamine depletion and analysed newborn cells in the SN at different maturation stages and time points depending on voluntary physical activity, enriched environment and levodopa-treatment. We describe an activity- induced increase of new NG2-positive cells and also mature oligodendrocytes in the SN of healthy mice. Running and enriched environment refused to stimulate NG2-generation and oligodendrogenesis in MPTP-mice, an effect which could be reversed by pharmacological levodopa-induced rescue.

Conclusion

We suggest dopamine being a key regulator for activity-induced generation of NG2-cells and oliogodendrocytes in the SN as a potentially relevant mechanism in endogenous nigral cellular plasticity.     

The Mean Field Theory of Spin Glasses: The Heuristic Replica Approach and Recent Rigorous Results

The mathematically correct computation of the spin glasses free energy in the infinite range limit crowns 25 years of mathematic efforts in solving this model. The exact solution of the model was found many years ago by using a heuristic approach; the results coming from the heuristic approach were crucial in deriving the mathematical results. The mathematical tools used in the rigorous approach are quite different from those of the heuristic approach. In this note we will review the heuristic approach to spin glasses in the light of the rigorous results; we will also discuss some conjectures that may be useful to derive the solution of the model in an alternative way.     

Achieving geodetic motion for LISA test masses: ground testing results

The low-frequency resolution of space-based gravitational wave observatories such as LISA (Laser Interferometry Space Antenna) hinges on the orbital purity of a free-falling reference test mass inside a satellite shield. We present here a torsion pendulum study of the forces that will disturb an orbiting test mass inside a LISA capacitive position sensor. The pendulum, with a measured torque noise floor below 10 fN m/square root of Hz from 0.6 to 10 mHz, has allowed placement of an upper limit on sensor force noise contributions, measurement of the sensor electrostatic stiffness at the 5% level, and detection and compensation of stray dc electrostatic biases at the millivolt level.     

The K-SAT Problem in a Simple Limit

In this work we compute the thermodynamic properties of the 3-satisfiability problem in the infinite connectivity limit. In this limit the computation can be strongly simplified and the thermodynamic properties can be obtained with a high accuracy. We find evidence for a continuous replica symmetry breaking in the region of high number of clauses, >_c.     

Spin–gravity coupling and gravity-induced quantum phases

External gravitational fields induce phase factors in the wave functions of particles. The phases are exact to first order in the background gravitational field, are manifestly covariant and gauge invariant and provide a useful tool for the study of spin–gravity coupling and of the optics of particles in gravitational or inertial fields. We discuss the role that spin–gravity coupling plays in particular problems.     

Properties and electronic structure of tetrahalogenocuprate (II)-complexes

Several salts containing the complex anions [CuCl ₄]= or [CuBr ₄]= have heen prepared, and their spectra have been measured and interpreted in terms of ligand-field theory. They exhibit a d-d band with about 8–9000 cm^–1, and several well defined charge-transfer bands in the visible and near ultraviolet spectral range. Several experimental facts, supported by theoretical considerations, indicate that the structure of the [CuX ₄]= anions is not a truly tetrahedral, but a flattened tetrahedral one, of symmetry D _2d . Details on the course of the endothermic solvolysis reactions which occur in polar organic solvents, and on the probable nature of the solvolysis products are reported and discussed.

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Zusammenfassung Mehrere Salze der komplexen Anionen [CuCl ₄]^2– und [CuBr ₄]^2– wurden dargestellt, ihre Spektren gemessen und ligandenfeldtheoretisch interpretiert. Die Spektren zeigen eine d d-Bande mit im Gebiet von 8000 bis 9000 cm^–1 und mehrere wohldefinierte Elektronenüberführungsbanden im sichtbaren und nahen ultravioletten Spektralbereich. Mehrere experimentelle Befunde, die von theoretischen Überlegungen unterstützt werden, deuten darauf hin, daß die [CuX ₄]^2/s--Anionen nicht rein tetraedrisch gebaut sind, sondern längs einer zweizähligen Achse gestauchte Tetraeder der Symmetrie D _2d darstellen.Einzelheiten über den Verlauf der endothermen Solvolysereaktionen in polaren organischen Lösungsmitteln und über die wahrscheinlichen Solvolyseprodukte werden mitgeteilt und diskutiert.

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Résumé Plusieurs sels des anions complexes [CuCl ₄]^2– et [CuBr ₄]^2– ont été préparés et leurs spectres mesurés et interprétés dans le cadre de la théorie du champ des ligands.Ils montrent une bande d d avec dans la région de 8000 à 9000 cm^–1 et plusieurs bandes bien définies du type «transfer de charges» dans le visible et l'ultraviolet proche. Plusieurs résultats expérimentaux, soutenus par des considérations théoriques, indiquent que la structure des ions [CuX ₄]^2– n'est pas celle d'un tétraèdre véritable mais celle d'un tétraèdre déformé, de symétrie D _2d , Des détails sur le cours des réactions endothermiques de solvolyse, qui ont lieu dans les solvants organiques polaires et sur la nature probable des produits de la solvolyse sont rapportés et discutés.

     

Current development of analytical affinity chromatography: Design and biotechnological uses of molecular recognition surfaces

Analytical high performance liquid affinity chromatography (analytical HPLAC) has been investigated as an experimental guide to both synthetic design and affinity technological use of peptide and protein recognition surfaces. This work has progressed from the ongoing use of analytical affinity chromatography to study interaction mechanisms of naturally-occurring peptides and proteins, including enzyme fragment complexes and neuroendocrine biosynthetic precursors. We recently initiated a study to use analytical HPLAC for de novo design of recognition peptides called “anti-sense peptides”. Present data suggest the potential to use anti-sense peptides as “synthetic antibodies”, in immobilized forms, for biomolecular separation and analysis. Analogous studies have been started with immobilized natural antibodies in analytical immuno HPLAC. Our present data typify the growing usefulness of analytical HPLAC when designing recognition molecules, analyzing their interaction characteristics, and devising ways to use them in affinity technology.