Local stresses, dyke arrest and surface deformation in volcanic edificesand rift zones

Field studies indicate that nearly all eruptions in volcanic edifices and rift zones are supplied with magma through fractures (dykes) that are opened by magmatic overpressure. While (inferred) dyke injections are frequent during unrest periods, volcanic eruptions are, in comparison, infrequent, suggesting that most dykes become arrested at certain depths in the crust, in agreement with field studies. The frequency of dyke arrest can be partly explained by the numerical models presented here which indicate that volcanic edifices and rift zones consisting of rocks of contrasting mechanical properties, such as soft pyroclastic layers and stiff lava flows, commonly develop local stress fields that encourage dyke arrest. During unrest, surface deformation studies are routinely used to infer the geometries of arrested dykes, and some models (using homogeneous, isotropic half-spaces) infer large grabens to be induced by such dykes. Our results, however, show that the dyke-tip tensile stresses are normally much greater than the induced surface stresses, making it difficult to explain how a dyke can induce surface stresses in excess of the tensile (or shear) strength while the same strength is not exceeded at the (arrested) dyke tip. Also, arrested dyke tips in eroded or active rift zones are normally not associated with dyke-induced grabens or normal faults, and some dykes arrested within a few metres of the surface do not generate faults or grabens. The numerical models show that abrupt changes in Young's moduli(stiffnesses), layers with relatively high dyke-normal compressive stresses (stress barriers), and weak horizontal contacts may make the dyke-induced surface tensile stresses too small for significant fault or graben formation to occur in rift zones or volcanic edifices. Also, these small surface stresses may have no simple relation to the dyke geometry or the depth to its tip. Thus, for a layered crust with weak contacts, straightforward inversion of surface geodetic data may lead to unreliable geometries of arrested dykes in active rift zones and volcanic edifices

Sonoluminescing air bubbles rectify argon

The dynamics of single bubble sonoluminescence (SBSL) strongly depends on the percentage of inert gas within the bubble. We propose a theory for this dependence, based on a combination of principles from sonochemistry and hydrodynamic stability. The nitrogen and oxygen dissociation and subsequent reaction to water soluble gases implies that strongly forced air bubbles eventually consist of pure argon. Thus it is the partial argon (or any other inert gas) pressure which is relevant for stability. The theory provides quantitative explanations for many aspects of SBSL.Comment: 4 page

Skating on a Film of Air: Drops Impacting on a Surface

Drops impacting on a surface are ubiquitous in our everyday experience. This impact is understood within a commonly accepted hydrodynamic picture: it is initiated by a rapid shock and a subsequent ejection of a sheet leading to beautiful splashing patterns. However, this picture ignores the essential role of the air that is trapped between the impacting drop and the surface. Here we describe a new imaging modality that is sensitive to the behavior right at the surface. We show that a very thin film of air, only a few tens of nanometers thick, remains trapped between the falling drop and the surface as the drop spreads. The thin film of air serves to lubricate the drop enabling the fluid to skate on the air film laterally outward at surprisingly high velocities, consistent with theoretical predictions. Eventually this thin film of air must break down as the fluid wets the surface. We suggest that this occurs in a spinodal-like fashion, and causes a very rapid spreading of a wetting front outwards; simultaneously the wetting fluid spreads inward much more slowly, trapping a bubble of air within the drop. Our results show that the dynamics of impacting drops are much more complex than previously thought and exhibit a rich array of unexpected phenomena that require rethinking classical paradigms.Comment: 4 pages, 4 figure

Self-assembling DNA-caged particles: nanoblocks for hierarchical self-assembly

DNA is an ideal candidate to organize matter on the nanoscale, primarily due to the specificity and complexity of DNA based interactions. Recent advances in this direction include the self-assembly of colloidal crystals using DNA grafted particles. In this article we theoretically study the self-assembly of DNA-caged particles. These nanoblocks combine DNA grafted particles with more complicated purely DNA based constructs. Geometrically the nanoblock is a sphere (DNA grafted particle) inscribed inside a polyhedron (DNA cage). The faces of the DNA cage are open, and the edges are made from double stranded DNA. The cage vertices are modified DNA junctions. We calculate the equilibriuim yield of self-assembled, tetrahedrally caged particles, and discuss their stability with respect to alternative structures. The experimental feasability of the method is discussed. To conclude we indicate the usefulness of DNA-caged particles as nanoblocks in a hierarchical self-assembly strategy.Comment: v2: 21 pages, 8 figures; revised discussion in Sec. 2, replaced 2 figures, added new reference

Age adjustment of cancer survival rates: methods, point estimates and standard errors

We empirically evaluated the performance of a new method for age adjustment of cancer survival compared to traditional age adjustment using data from the Finnish Cancer Registry. We find that both methods provide almost identical results for absolute survival but the new method generally provides more meaningful estimates of relative survival with often a smaller standard error

Singular and regular solutions of a non-linear parabolic system

We study a dissipative nonlinear equation modelling certain features of the Navier-Stokes equations. We prove that the evolution of radially symmetric compactly supported initial data does not lead to singularities in dimensions $n\leq 4$. For dimensions $n>4$ we present strong numerical evidence supporting existence of blow-up solutions. Moreover, using the same techniques we numerically confirm a conjecture of Lepin regarding existence of self-similar singular solutions to a semi-linear heat equation.Comment: 16 page

Diagenetic modeling of siliciclastic systems: Status report

Basin analysis (the reconstruction of the dynamics and history of sedimentary basins) has entered a quantitative stage that requires analytical lithologic data. These data must include geologic parameters that describe the characteristics of sediments and the diagenetic changes that they undergo through time. Diagenesis is controlled by eight geologic parameters: sediment composition, temperature history, rate of accommodation (subsidence + sea-level changes + sediment compaction), rate of sediment accumulation, age (time that sediments have been exposed to other variables), internal sediment-body architecture (sedimentary texture and structure), sediment-body external geometry, and fluid chemistry and flow history. Tectonic and paleogeographic settings determine the primary compositions of both chemical and siliciclastic sediments. Siliciclastic provenances are reflected by the mineralogy of sandstones. The source or sources of sediment in sandstone units within genetic sequences and the contribution of each source need to be evaluated in terms of quantitative effects on the various diagenetic styles observed. With the use of modern settings as partial analogues, stratigraphic, sedimentologic, and petrographic data can be used to reconstruct sandstone architecture and to draw inferences about original pore fluid chemistry. Subsidence histories, isotopic signatures, trace element compositions, and fluid inclusion studies combined with petrographic observations can be used to set constraints on the geologic parameters for sandstone bodies within a time-temperature-basin setting framework. As more insight is gained into the reaction kinetics within specific paleotectonic and depositional settings, diagenetic modeling will become increasingly more quantitative and precise

Diagenetic modeling of siliciclastic systems: Status report

Basin analysis (the reconstruction of the dynamics and history of sedimentary basins) has entered a quantitative stage that requires analytical lithologic data. These data must include geologic parameters that describe the characteristics of sediments and the diagenetic changes that they undergo through time. Diagenesis is controlled by eight geologic parameters: sediment composition, temperature history, rate of accommodation (subsidence + sea-level changes + sediment compaction), rate of sediment accumulation, age (time that sediments have been exposed to other variables), internal sediment-body architecture (sedimentary texture and structure), sediment-body external geometry, and fluid chemistry and flow history. Tectonic and paleogeographic settings determine the primary compositions of both chemical and siliciclastic sediments. Siliciclastic provenances are reflected by the mineralogy of sandstones. The source or sources of sediment in sandstone units within genetic sequences and the contribution of each source need to be evaluated in terms of quantitative effects on the various diagenetic styles observed. With the use of modern settings as partial analogues, stratigraphic, sedimentologic, and petrographic data can be used to reconstruct sandstone architecture and to draw inferences about original pore fluid chemistry. Subsidence histories, isotopic signatures, trace element compositions, and fluid inclusion studies combined with petrographic observations can be used to set constraints on the geologic parameters for sandstone bodies within a time-temperature-basin setting framework. As more insight is gained into the reaction kinetics within specific paleotectonic and depositional settings, diagenetic modeling will become increasingly more quantitative and precise

Characteristics of phonon transmission across epitaxial interfaces: a lattice dynamic study

Phonon transmission across epitaxial interfaces is studied within the lattice dynamic approach. The transmission shows weak dependence on frequency for the lattice wave with a fixed angle of incidence. The dependence on azimuth angle is found to be related to the symmetry of the boundary interface. The transmission varies smoothly with the change of the incident angle. A critical angle of incidence exists when the phonon is incident from the side with large group velocities to the side with low ones. No significant mode conversion is observed among different acoustic wave branches at the interface, except when the incident angle is near the critical value. Our theoretical result of the Kapitza conductance $G_{K}$ across the Si-Ge (100) interface at temperature $T=200$K is 4.6\times10^{8} {\rm WK}^{-1}{\rmm}^{-2}. A scaling law $G_K \propto T^{2.87}$ at low temperature is also reported. Based on the features of transmission obtained within lattice dynamic approach, we propose a simplified formula for thermal conductanceacross the epitaxial interface. A reasonable consistency is found between the calculated values and the experimentally measured ones.Comment: 8 figure