Mass measurements of neutron-deficient nuclides close to A = 80 with a Penning trap

The masses of ^{80, 81, 82, 83}Y, ^{83, 84, 85, 86, 88}Zr and ^{85, 86, 87, 88}Nb have been measured with a typical precision of 7keV by using the Penning trap setup at IGISOL. The mass of ⁸⁴Zr has been measured for the first time. These precise mass measurements have improved S_p and Q_EC values for astrophysically important nuclides.     

Stopping power in insulators and metals without charge exchange

The slowing-down process of pointlike charged particles in matter has been investigated by measuring the stopping power for antiprotons in materials of qualitatively very different nature. Whereas the velocity-proportional stopping power observed for metal-like targets such as aluminum over a wide energy range of 1-50 keV is in agreement with expectations, it is surprising that the same velocity dependence is seen for a large band-gap insulator such as LiF. The validity of these observations is supported by several measurements with protons and several checks of the target properties. The observations call for both a qualitative explanation and a quantitative theoretical model.     

Thermodynamic stability of clusters of molybdenum oxide

We show that a single geometrical rule underlies the stability of "polyoxomolybdates", the variety of clusters of molybdenum(VI) oxide in (acidified) aqueous solution that are found experimentally. We predict that upon increasing the proton or total molybdenum oxide concentration, the average size of the clusters increases. We compare our predictions with results from ultracentrifugation experiments and with data in the literature. Finally, it is shown that the formation of metal oxide clusters is thermodynamically equivalent to the formation of surfactant micelles.     

Activation mechanism of the human histamine H4 receptor--an explicit membrane molecular dynamics simulation study

Molecular dynamics (MD) simulations in a membrane-embedded environment were carried out on the homology model of the human histamine H4 receptor (hH4R) alone and in complex with its endogenous activator histamine and with the first reported selective hH4R antagonist JNJ7777120. During the simulation of the histamine-hH4R complex, considerable changes occurred in the hH4R structure as well as in the interaction pattern of histamine at the binding site. These changes are in agreement with experimental data published on GPCR activation. In particular, the intracellular side of TM helix VI moved significantly away from TM helices III and VII. Moreover, histamine formed an interaction with Asn147 (4.57) that was previously proved to be important in hH4R activation. Results of the MD simulations of the native hH4R and the JNJ7777120-hH4R complex suggest that these models represent an inactive conformation of hH4R. MD simulation in the presence of JNJ7777120 resulted in the movement of the intracellular side of TM helix VI in the direction of TM helix III. Snapshots of the simulations may serve as functionally relevant models in the development of novel hH4R ligands in the future.     

Computation of the Longitudinal and Transverse Dispersion Coefficient in an Adsorbing Porous Medium Using Homogenization

This article compares for the first time, local longitudinal and transverse dispersion coefficients obtained by homogenization with experimental data of dispersion coefficients in porous media, using the correct porosity dependence. It is shown that the longitudinal dispersion coefficient can be reasonably represented by a simple periodic unit cell (PUC), which consists of a single sphere in a cube. We present a slightly modified and simplified approach to derive the homogenized equations, which emphasizes physical aspects of homogenization. Subsequently, we give full dimensional expressions for the dispersion tensor based on a comparison with the convective dispersion equation used for contaminant transport, inclusive the correct dependence on porosity. For the PUC of choice, the dispersion relations are identical to the relations obtained for periodic media. We show that commercial finite element software can be readily used to compute longitudinal and transverse dispersion coefficients in 2D and 3D. The 3D results are for the first time obtained at relevant Peclet numbers. There is good agreement for longitudinal dispersion. The computed transverse dispersion coefficients for a single sphere in a cube are much too low. The effect of adsorption on the dispersion coefficient is also studied. Adsorption does not affect the transverse dispersion coefficient. However, adsorption enhances the longitudinal dispersion coefficient in agreement with an analysis of homogenization applied to Taylor dispersion discussed in the literature.     

Alpha-decay widths of neutron-deficient francium and astatine isotopes

The use of mass-separated samples of neutron-deficient francium isotopes, produced at the ISOLDE on-line mass-separator facility at the CERN 600 MeV synchro-cyclotron, has permitted precise determinations through genetic relationships of /(EC+β⁺) branching ratios for a range of light francium and astatine isotopes. The experiments verify previous mass assignments and provide improved values for the half-lives. The systematics of -widths and of β-strength functions is surveyed.