Depth-resolved profile of the magnetic field beneath the surface of a superconductor with a few nm resolution

The variation of a magnetic field as a function of depth beneath the surface of an YBa(2)Cu(3)O(7-delta) thin film in the Meissner state has been measured using low energy muons. The depth of implantation was varied from 20-150 nm by tuning the energy of the implanted muons from 3-30 keV. These are direct measurements of the penetration of a magnetic field beneath a superconducting surface which illustrate the power of low energy muons for near surface studies in superconductivity and magnetism.     

Electronic structure methods for studying surface-enhanced Raman scattering

This critical review highlights recent advances in using electronic structure methods to study surface-enhanced Raman scattering. Examples showing how electronic structure methods, in particular time-dependent density functional theory, can be used to gain microscopic insights into the enhancement mechanism are presented (150 references).     

Asymptotically exact a posteriori estimators for the pointwise gradient error on each element in irregular meshes. Part 1: A smooth problem and globally quasi-uniform meshes

A class of a posteriori estimators is studied for the error in the maximum-norm of the gradient on single elements when the finite element method is used to approximate solutions of second order elliptic problems. The meshes are unstructured and, in particular, it is not assumed that there are any known superconvergent points. The estimators are based on averaging operators which are approximate gradients, ``recovered gradients', which are then compared to the actual gradient of the approximation on each element. Conditions are given under which they are asympotically exact or equivalent estimators on each single element of the underlying meshes. Asymptotic exactness is accomplished by letting the approximate gradient operator average over domains that are large, in a controlled fashion to be detailed below, compared to the size of the elements.

     

Nuclear reaction analysis: A study on the interface formation in polymer mixtures below the critical point

We describe a method for directly determining the composition profile of deuterated polymer chains in polymer mixtures. Our technique, nuclear reaction analysis, is based on the ²H(³He, ⁴He)¹H nuclear reaction. By detecting ⁴He in a forward geometry, we achieve a spatial resolution of 14 nm (FWHM). We use this technique to probe the broadening of the interface between two partially miscible polymers. We found that such a system attains a finite interfacial width in equilibrium. For short times, we monitor the dynamics of interface formation. We found that the interfacial width increases significantly slower than in the case of free diffusion.     

Catalytic enantioselective conjugate addition en route to paxilline indoloterpenoids

Development of enantioselective synthesis of precursor en route to paxilline indoloterpenoids is described. Evaluation of 25 diphosphine-based ligands has led to identification of JosiPhos derivative that allows for asymmetric conjugate addition of homoprenyl Grignard reagent to 2-methylcyclopent-2-en-1-one in excellent yield and with appreciable levels of enantioinduction. Application to the conjugate addition of other Grignard reagents is demonstrated.     

Formation of [5.5]cyclopentadienidophanes by macrocyclization of [3-(methylammonio)propyl]cyclopentadienides under Mannich conditions

2-Acyl-1,4-bis(methoxycarbonyl)-3-[3-(methylammonio)propyl]cyclopentadienides 1 and aqueous formaldehyde can undergo a double Mannich reaction leading to the bisbetainic 2,12-diazonia-[5,5](1,3)cyclopentadienidophanes 2. The success of this macrocyclization reaction seems to depend on the length of the ω-ammonioalkyl chain and the individual acyl substituent. In the cases of ω-(methylammonio)butyl and ω-(methylammonio)pentyl chains, as well as with ω-ammoniopropyl derivatives bearing particularly electron-rich 4-methoxybenzoyl or 2-furoyl substituents, a mixture of oligomers is formed. On the other hand, DCC-assisted cyclocondensation of 1b,d (acyl=4-methoxybenzoyl and thiophene-2-carbonyl, respectively) occurs only intramolecularly, leading to the bicyclic 6-aminopentafulvenes 4b,d in good yields.     

Charge transport through extended molecular wires with strongly correlated electrons

Electron–electron interactions are at the heart of chemistry and understanding how to control them is crucial for the development of molecular-scale electronic devices. Here, we investigate single-electron tunneling through a redox-active edge-fused porphyrin trimer and demonstrate that its transport behavior is well described by the Hubbard dimer model, providing insights into the role of electron–electron interactions in charge transport. In particular, we empirically determine the molecule''s on-site and inter-site electron–electron repulsion energies, which are in good agreement with density functional calculations, and establish the molecular electronic structure within various oxidation states. The gate-dependent rectification behavior confirms the selection rules and state degeneracies deduced from the Hubbard model. We demonstrate that current flow through the molecule is governed by a non-trivial set of vibrationally coupled electronic transitions between various many-body ground and excited states, and experimentally confirm the importance of electron–electron interactions in single-molecule devices.

Experimental studies of electron transport through an edge-fused porphyrin oligomer in a graphene junction are interpreted within a Hubbard dimer framework.     

Mass measurements of neutron-deficient nuclei and their implications for astrophysics

During the years 2005-2010 the double-Penning-trap mass spectrometer JYFLTRAP has been used to measure the masses of 90 ground and 8 isomeric states of neutron-deficient nuclides with a typical precision of better than 10keV. The masses of 14 nuclides -- ⁸⁴Zr , ^{88, 89}Tc , ^90-92Ru , ^92-94Rh , ^{94, 95}Pd , ^{106, 108, 110}Sb -- have been experimentally determined for the first time. This article gives an overview on these measurements and their impact on the modeling of the astrophysical rp -process.