Tilted axis rotation, candidates for chiral bands, and wobbling motion in 138Nd

High-spin states in 138Nd were investigated using the reaction 94Zr(48Ca,4n), detecting coincident γ rays with the gasp spectrometer. A rich level scheme was constructed including four bands of negative parity at low spins, eight bands of dipole transitions, and eight bands of quadrupole transitions at medium spins. The cranked shell model and the tilted-axis cranking model are used to assign configurations to the observed bands, where zero pairing is assumed. For selected configurations the case of finite pairing is also considered. A consistent notation for configuration assignment that applies for both zero and finite pairing is introduced. The observed bands are interpreted as rotation around the short and long principal axes (quadrupole bands), as well as around a tilted axis (dipole bands). The dipole bands have an intermediate character, between magnetic and collective electric rotation. A pair of dipole bands is identified as candidates for chiral partners. The possible existence of the wobbling mode at low deformation and medium spins is discussed. The consistent interpretation of the multitude of observed bands strongly supports the existence of stable triaxial deformation at medium spins in 138Nd. ©2012 American Physical Societ

Algebraic structure of gravity in Ashtekar variables

The BRST transformations for gravity in Ashtekar variables are obtained by using the Maurer-Cartan horizontality conditions. The BRST cohomology in Ashtekar variables is calculated with the help of an operator $\delta$ introduced by S.P. Sorella, which allows to decompose the exterior derivative as a BRST commutator. This BRST cohomology leads to the differential invariants for four-dimensional manifolds.Comment: 19 pages, report REF. TUW 94-1

Anisotropic colloids through non-trivial buckling

We present a study on buckling of colloidal particles, including experimental, theoretical and numerical developments. Oil-filled thin shells prepared by emulsion templating show buckling in mixtures of water and ethanol, due to dissolution of the core in the external medium. This leads to conformations with a single depression, either axisymmetric or polygonal depending on the geometrical features of the shells. These conformations could be theoretically and/or numerically reproduced in a model of homogeneous spherical thin shells with bending and stretching elasticity, submitted to an isotropic external pressure.Comment: submitted to EPJ

Metallogenic implications of a new geodynamic model for the Eglab, Algeria

The Reguibat Shield is the northern part of the Archean-Proterozoic West African Craton. The Algerian portion of the Reguibat Shield is an extensive (~125,000 km2), long-lived Paleoproterozoic volcanic-plutonic tract. Previous workers (e.g., Lasserre et al., 1970; Sabate, 1973) have subdivided this basement into the Yetti domain to the west and the Eglab domain to the east, separated by a postulated terrane boundary called the “Yetti-Eglab shear zone.” Our Algerian Geological Survey Agency (ASGA) – U.S. Geological Survey (USGS) study area includes these domains and is known as the Eglab region. Magmatism in the Eglab region spanned more than 150 million years of Paleoproterozoic time during the Birimian (or Eburnian; ca. 2250-1900 Ma; Peucat et al., 2005) orogeny. Latest Birimian to possibly Mesoproterozoic dikes were the last major event in the region until onset of the Neoproterozoic Pan-African orogeny, which resulted in deformation in the Eglab region in the form of faulting and folding but little magmatism and no metamorphism. The youngest widespread magmatic event recorded in the Eglab region was the emplacement of Central Atlantic Magmatic Province (CAMP) mafic dikes and sills at ca. 200 Ma. Within the study area, the Tindouf (Cambrian or Ordovician to Devonian), Reggane (probably late Mesoproterozoic to Devonian), and Taoudeni (Mesoproterozoic to Cambrian or Ordovician) basins form the margins of the Eglab region on the north, east, and south flanks, respectively. The most widely accepted tectonic model for the Eglab region (Peucat et al., 2005) proposes that a 2.73 Ga relict of oceanic crust formed a cratonal core against which an eastward-dipping subduction zone developed, producing arc magmatism in the Eglab domain from 2.21-2.18 Ga. Closure of an intervening ocean and collision of the Yetti and Eglab domains at 2.09 Ga produced a second active margin magmatic event and deformation along the supposed Yetti-Eglab terrane boundary. Both domains were then intruded by large volumes of high-K, post-orogenic magmas triggered by slab roll-back and asthenospheric upwelling. Our work defines magmatic episodes at about 2210, 2150, 2090, and 2075 Ma. From ca. 2240 to 2100 Ma, magmatism was the product of east-dipping subduction, with the axis of magmatism migrating from east to west. The composite Paleoproterozoic arcs collided with the Archean craton in Mauritania at ca. 2090 Ma. The Paleoproterozoic Yetti, Akilet Deilel, and Oued Souss basins are intra-arc basins comprising continentally derived sedimentary rocks and dacite-rhyolite volcanic rocks. Oceanic sedimentary and basaltic volcanic rocks are rare to absent. Similarity of detrital zircon age populations and composition suggests absence of a major terrane boundary along the postulated Yetti-Eglab shear zone. Late collisional slab break-off resulted in a voluminous post-collisional igneous flareup and emplacement of early high-K calc-alkaline and later alkaline magmas throughout the Reguibat Shield at 2080-2060 Ma. Our preferred model for the geodynamic evolution of the Eglab region is shown in Figure 1. Our field observations, as well as igneous and detrital zircon geochronologic studies, do not support the presence of an Archean continental nucleus in the Eglab region. The absence of a significant Archean remnant in the Eglab region is also shown by neodymium model ages (TDM, “mantle separation ages”, 2.5 to 2.2 Ga; Peucat et al., 2005) that decrease from east to west, consistent with our igneous zircon data. All igneous rocks are overwhelmingly calc-alkaline, suggesting formation in an arc-subduction zone environment—probably as a series of continental margin arcs. The majority of the intrusive rocks are mixtures of metaluminous to peraluminous (I- and S-type) granites with a minor component of alkaline rocks; few igneous rocks exhibit A-type or peralkaline compositions, i.e., they are post-collision granites, not within-plate granites. Geophysical data do not show the presence of a major terrane boundary along the postulated Yetti-Eglab shear zone. The observed magnetic low over the Yetti granitic rocks is likely due to lower magnetite content in rocks with a higher component of metasedimentary protolith. This is supported by the slightly more peraluminous character of the Yetti basement compared to the Eglab basement. Based on our tectonic and metallogenic interpretations of the new data, a wide variety of mineral deposit types are permissible to occur in the Eglab. The most likely deposits include Mo-Cu porphyry deposits in arc magmatic rocks, epithermal base and precious metal vein deposits related to porphyry intrusions, and orogenic Au and Cu-Mo vein deposits in the Birimian volcano-sedimentary sequences. Also likely are U-Th-Nb-Ta-REE and possibly Au deposits related to alkaline/peralkaline granites, granite-hosted (shear) and calcrete-hosted (Hamada-type) uranium deposits, and Phanerozoic oolitic ironstones. Deposit types that are permissive, but less likely to occur, include PGE-Cr in layered gabbroic intrusions (sulfide-poor reef-type), Cu-Ni-PGE in unlayered mafic-ultramafic dikes/sills (sulfide-rich conduit-type), and iron/magnetite skarn and sedimentary rock-hosted U and Cu deposits in the marginal basins flanking the Eglab. The absence of a thick cratonic core in the Eglab region has important implications for diamond exploration. Previous studies have suggested that the Eglab may be a source region for headless diamond placers in Reggane, and several studies have noted the presence of a few harzburgitic “G9” and eclogitic garnets (Zerrouki, 2000; Kahoui et al., 2008). During the ASGA-USGS project, 74 regolith samples were collected and processed for kimberlite indicator minerals. Electron microprobe data for ~800 garnets were evaluated using the classification scheme of Schulze (2003). Our samples contained no peridotitic garnets; however, 74 eclogitic and 3 Cr-poor megacrystic garnets were detected. The majority of the eclogitic garnets are “group B”-type; of the remainder, a few are “group-C”-type and grospydite garnets. While eclogitic garnets are not as prospective for diamond potential as the presence of peridotitic garnets, the Eglab region remains permissive for primary diamonds in “off-craton” kimberlit

3D Brownian Diffusion of Submicron-Sized Particle Clusters

We report on the translation and rotation of particle clusters made through the combination of spherical building blocks. These clusters present ideal model systems to study the motion of objects with complex shape. Because they could be separated into fractions of well-defined configurations on a sufficient scale and their overall dimensions were below 300 nm, the translational and rotational diffusion coefficients of particle duplets, triplets and tetrahedrons could be determined by a combination of polarized dynamic light scattering (DLS) and depolarized dynamic light scattering (DDLS). The use of colloidal clusters for DDLS experiments overcomes the limitation of earlier experiments on the diffusion of complex objects near surfaces because the true 3D diffusion can be studied. When the exact geometry of the complex assemblies is known, different hydrodynamic models for calculating the diffusion coefficient for objects with complex shapes could be applied. Because hydrodynamic friction must be restricted to the cluster surface the so-called shell model, in which the surface is represented as a shell of small friction elements, was most suitable to describe the dynamics. A quantitative comparison of the predictions from theoretical modeling with the results obtained by DDLS showed an excellent agreement between experiment and theory

Absence of VHL gene alteration and high VEGF expression are associated with tumour aggressiveness and poor survival of renal-cell carcinoma

International audienceBACKGROUND: The von Hippel-Lindau gene (VHL) alteration, a common event in sporadic clear-cell renal-cell carcinoma (CCRCC), leads to highly vascularised tumours. Vascular endothelial growth factor (VEGF) is the major factor involved in angiogenesis, but the prognostic significance of both VHL inactivation and VEGF expression remain controversial. The aims of this study were to analyse the relationship between VHL genetic and epigenetic alterations, VHL expression and VEGF tumour or plasma expression, and to analyse their respective prognostic value in patients with CCRCC. METHODS: A total of 102 patients with CCRCC were prospectively analysed. Alterations in VHL were determined by sequencing, Multiplex Ligation-dependent Probe Amplification (MLPA) and methylation-specific MLPA. Expression of pVHL and VEGF was determined by immunohistochemistry. Plasma VEGF was measured by enzyme-linked immunosorbent assay (ELISA). RESULTS: VHL mutation, deletion and promoter methylation were identified in 70, 76 and 14 cases, respectively. Overall, at least one VHL-gene alteration occurred in 91 cases (89.2%). Both VEGF tumour and plasma expression appeared to be decreased in case of VHL alteration. Median progression-free survival and CCRCC-specific survival were significantly reduced in patients with wild-type VHL or altered VHL and high VEGF expression, which, therefore, represent two markers of tumour aggressiveness in CCRCC. CONCLUSION: Stratifying CCRCCs according to VHL and VEGF status may help tailor therapeutic strategy

Patterning symmetry in the rational design of colloidal crystals

Colloidal particles have the right size to form ordered structures with periodicities comparable to the wavelength of visible light. The tantalizing colours of precious opals and the colour of some species of birds are examples of polycrystalline colloidal structures found in nature. Driven by the demands of several emergent technologies, efforts have been made to develop efficient, self-assembly-based methodologies for generating colloidal single crystals with well-defined morphologies. Somewhat unfortunately, these efforts are often frustrated by the formation of structures lacking long-range order. Here we show that the rational design of patch shape and symmetry can drive patchy colloids to crystallize in a single, selected morphology by structurally eliminating undesired polymorphs. We provide a proof of this concept through the numerical investigation of triblock Janus colloids. One particular choice of patch symmetry yields, via spontaneous crystallization, a pure tetrastack lattice, a structure with attractive photonic properties, whereas another one results in a colloidal clathrate-like structure, in both cases without any interfering polymorphs

Low-lying octupole isovector excitation in Nd-144

International audienceThe nature of low-lying 3− levels in Nd144 was investigated in the Nd143(n,γγ) cold neutron-capture reaction. The combination of the high neutron flux from the research reactor at the Institut Laue-Langevin and the high γ-ray detection efficiency of the EXILL setup allowed the recording of γγ coincidences. From the coincidence data precise branching ratios were extracted. Furthermore, the octagonal symmetry of the setup allowed angular-distribution measurements to determine multipole-mixing ratios. Additionally, in a second measurement the ultra-high resolution spectrometer GAMS6 was employed to conduct lifetime measurements using the gamma-ray induced Doppler-shift technique (GRID). The confirmed strong M1 component in the 33−→31− decay strongly supports the assignment of the 33− level at 2779keV as low-lying isovector octupole excitation. Microscopic calculations within the quasiparticle phonon model confirm an isovector component in the wave function of the 33− level, firmly establishing this fundamental mode of nuclear excitation in near-spherical nuclei