Shallow-underground accelerator sites for nuclear astrophysics: Is the background low enough?

In order to reliably estimate the rate of a charged particle induced nuclear reaction in a non-explosive astrophysical scenario, its cross-section must be measured far below the Coulomb barrier. However, at the corresponding energies the cross-section values are very low, so that the experimental counting rate is dominated by cosmic-ray induced background, even if a suitable anticoincidence shield is applied. This problem can be overcome by performing an accelerator-based experiment in a deep underground site, as has been done with great success at the LUNA 0.4MV accelerator in Gran Sasso, Italy. Several underground accelerators with higher beam energy are in the planning phase worldwide. All of them are shielded by over 1000m of rock, a depth at which cosmic-ray effects are negligible for the purposes of nuclear astrophysics experiments. It is shown here that a combined approach, using a shallow-underground laboratory below 47m of rock and an active shield to veto surviving muons in simple detectors, results in a background level that is not far from that of deep underground sites. Data have been obtained using two ??traveling?? ??-detectors. They have been transported both shallow underground, to the Dresden Felsenkeller in Germany, and deep underground, to the Gran Sasso laboratory in Italy. As shallow-underground facilities are more easily accessible than deep-underground ones, the present finding holds the promise of greatly accelerated progress in the field of cross-section measurements for nuclear astrophysics.     

Image formation in scanning electron microscopy of ultracold atoms

Imaging ultracold atoms by means of scanning electron microscopy involves several aspects that are different from standard optical imaging techniques. The quality of the images depends on the properties of the electron beam, and the signal depends on the details of the ionization process and subsequent detection strategy. We discuss the alignment and characterization procedure of the electron beam, the handling of different charge states that are produced upon electron impact, and correction algorithms to compensate for relative drifts between the field of view of the electron beam and the atomic target.     

FeAgMo2O8 — A novel oxygen evolution catalyst material for alkaline metal–air batteries

This paper reports about FeAgMo₂O₈ — a novel oxygen evolution catalyst material for secondary (rechargeable) metal–air batteries. Bifunctional air electrodes were made using FeAgMo₂O₈ as a charging catalyst for oxygen evolution reaction (OER) and silverized carbon black (Ag/C) was employed as a discharging catalyst for oxygen reduction reaction (ORR). Corresponding air electrodes were investigated using 10 M KOH as an electrolyte. At current densities between 20 and 50 mA per cm² we observed discharging and charging voltages of 1.20 to 1.15 V and 1.96 to 2.05 V, respectively.     

Moser’s Quadratic,Symplectic Map

In 1994, Jürgen Moser generalized Hénon’s area-preserving quadratic map to obtain a normal form for the family of four-dimensional, quadratic, symplectic maps. This map has at most four isolated fixed points. We show that the bounded dynamics of Moser’s six parameter family is organized by a codimension-three bifurcation, which we call a quadfurcation, that can create all four fixed points from none.The bounded dynamics is typically associated with Cantor families of invariant tori around fixed points that are doubly elliptic. For Moser’s map there can be two such fixed points: this structure is not what one would expect from dynamics near the cross product of a pair of uncoupled Hénon maps, where there is at most one doubly elliptic point. We visualize the dynamics by escape time plots on 2d planes through the phase space and by 3d slices through the tori.     

Ring current effects in [4m+2]annulenes and their di- and tetraanions

Simple MO theory of induced ring currents is used in order to rationalise the observed diatropism of neutral [4m+2]annulenes and their tetraanions and the paratropism of the corresponding dianions.     

Benzannelated annulenes -12. : Theoretical study of geometries and 1H chemical shifts of benzannelated [14] annulenes

The geometries and the ¹H chemical shifts of dihydropyrene $\text{1}$ and its benzannelated derivatives $\text{2}$–$\text{8}$ have been studied by means of semiempirical quantum chemical procedures. The calculated bond lengths of $\text{1}$ and proton shifts of $\text{1}$ – $\text{5}$ are in good accord with the corresponding experimental values. We show that monobenzannelation in $\text{2}$ – $\text{4}$ causes considerable bond length alternation in the [14] perimeter and hence reduced diatropocity. The same is true for the phenanth-fused dibenzannelated compounds $\text{4}$ and $\text{7}$. On the other hand we report evidence that anth-fused dibenzannelated dihydropyrenes $\text{5}$, $\text{6}$, and $\text{8}$ should be characterized by symmetric geometrical structures without significant bond length alternation thus leading to enhanced diatropicity.     

Building Block Approach to the Construction of Long-Lived Osmium(II) and Ruthenium(II) Multimetallic Complexes Incorporating the Tridentate Bridging Ligand 2,3,5,6-Tetrakis(2-pyridyl)pyrazine

Two classes of synthetically useful bimetallic complexes of the form [(tpy)M(tpp)RuCl(3)](PF(6)) and [(tpy)M(tpp)Ru(tpp)](PF(6))(4) have been prepared and their spectroscopic and electrochemical properties investigated (tpy = 2,2':6',2"-terpyridine, tpp = 2,3,5,6-tetrakis(2-pyridyl)pyrazine, and M = Ru(II) or Os(II)). Synthetic methods have been developed for the stepwise construction of tpp-bridged systems using a building block approach. In all four complexes, the tpp that serves as the bridging ligand is the site of localization of the lowest unoccupied molecular orbital (LUMO). The nature of the HOMO (highest occupied molecular orbital) varies depending upon the components present. In the systems of the type [(tpy)M(tpp)RuCl(3)](PF(6)), the ruthenium metal coordinated to tpp and three chlorides is the easiest to oxidize and is the site of localization of the HOMO. In contrast, for the [(tpy)M(tpp)Ru(tpp)](PF(6))(4) systems, the HOMO is based on the metal, M, that is varied, either Ru or Os. This gives rise to systems which possess a lowest lying excited state that is always a metal-to-ligand charge transfer state involving tpp but can be tuned to involve Os or Ru metal centers in a variety of coordination environments. The synthetic variation of the components within this framework has allowed for understanding the spectroscopic and electrochemical properties. Bimetallic systems incorporating this tpp ligand have long-lived excited states at room temperature (lifetimes of ca. 100 ns). The bimetallic system [(tpy)Ru(tpp)Ru(tpp)](PF(6))(4) has a longer excited state lifetime than the monometallic system from which it was constructed, [(tpy)Ru(tpp)](PF(6))(2). Details of the spectroscopic and electrochemical studies are reported herein.     

Analysis of serum protein precipitated with antiserum by matrix-assisted laser desorption ionization/time-of-flight and electrospray ionization mass spectrometry as a clinical laboratory test

Serum transferrin precipitated with specific antisera was analyzed by matrix-assisted laser desorption ionization/time-of-flight mass spectrometry (MALDI/TOF-MS) and electrospray ionization-mass spectrometry (ESI-MS). When analyzed by MALDI, transferrin showed signal peaks that clearly could be separated from ions of IgG present in the immunoprecipitate. By ESI-MS, when the immunoprecipitates were loaded through a microcapillary polymeric reversed-phase column connected to the electrospray ionization probe, the mass spectra of transferrin were observed with a high signal-to-noise ratio and good resolution. By MALDI/TOF-MS, the observed molecular weight of normal transferrin was ～ 1.2 ku smaller when analyzed in the reflectron mode than in the linear mode. The observed molecular weight of transferrin treated with sialidase was approximately the same in both modes. A comparison between the results obtained in both modes may help to estimate the number of sialic acids on the protein molecule. A transferrin isoform with a molecular weight of ～2.2 ku less than the normal species was identified in the serum of patients with a carbohydrate-deficient glycoprotein syndrome as well as in heavy alcohol consumers.