908 research outputs found
Heat and extension at mid- and lower crustal levels of the Rio Grande rift
The process by which large amounts (50 to 200 percent) of crustal extension are produced was concisely described by W. Hamilton in 1982 and 1983. More recently, England, Sawyer, P. Morgan and others have moved toward quantifying models of lithospheric thinning by incorporating laboratory and theoretical data on rock rheology as a function of composition, temperature, and strain rate. Hamilton's description identifies three main crustal layers, each with a distinctive mechanical behavior; brittle fracturing and rotation in the upper crust, discontinuous ductile flow in the middle crust and laminar ductile flow in the lower crust. The temperature and composition dependent brittle-ductile transition essentially defines the diffuse boundary between upper and middle crust. It was concluded that the heat responsible for the highly ductile nature of the lower crust and the lensoidal and magma body structures at mid-crustal depths in the rift was infused into the crust by relatively modest ( 10 percent by mass) magmatic upwelling (feeder dikes) from Moho levels. Seismic velocity-versus-depth data, supported by gravity modeling and the fact that volumes of rift related volcanics are relatively modest ( 6000 cubic km) for the Rio Grande system, all imply velocities and densities too small to be consistent with a massive, composite, mafic intrusion in the lower crust
Bohmian Philosophy of Mind?
Bohm’s theory is in many ways an attractive solution to the measurement problem in quantum mechanics. It provides an intuitive explanation for the distinctive quantum phenomena of interference and entanglement without the need for any problematic “collapse” of the wave function. But it faces several serious difficulties. First, the dynamical law via which the wave function “pushes around” the Bohmian particles is explicitly non-local, against the spirit of
special relativity (Bell 1987, 115). Second, the Bohmian particles can be seen as redundant in the context of an Everettian solution to the measurement problem (Brown and Wallace 2005). And third, the Bohmian solution to the measurement problem apparently depends on an implausible and problematic account of mental awareness (Stone 1994; Brown and Wallace 2005). I do not wish to minimize the significance of the first two difficulties; they are serious
threats to the tenability of Bohm’s theory. But the third difficulty, I think, rests on a confusion concerning the way in which Bohmian particles encode the outcomes of measurements. In particular, my concern here is to respond to the accusations of Stone (1994) and Brown and Wallace (2005) that Bohm’s theory requires a mysterious kind of direct awareness of the positions of the Bohmian particles in our brains, and also to the claim of Brown and Wallace
(2005) that such direct awareness threatens the quantum no-signaling theorem
Raman microscopy of lithium-manganese-rich transition metal oxide cathodes
Lithium-rich and manganese-rich (LMR) layered transition metal (TM) oxide composites with general formula xLi2MnO3 • (1- x)LiMO2 (M = Ni, Co, Mn) are promising cathode candidates for high energy density lithium ion batteries. Lithium-manganese-rich TM oxides crystallize as a nanocomposite layered phase whose structure further evolves with electrochemical cycling. Raman spectroscopy is a powerful tool to monitor the crystal chemistry and correlate phase changes with electrochemical behavior. While several groups have reported Raman spectra of lithium rich TM oxides, the data show considerable variability in terms of both the vibrational features observed and their interpretation. In this study, Raman microscopy is used to investigate lithium-rich and manganese-rich TM cathodes as a function of voltage and electrochemical cycling at various temperatures. No growth of a spinel phase is observed within the cycling conditions. However, analysis of the Raman spectra does indicate the structure of LMR-NMC deviates significantly from an ideal layered phase. The results also highlight the importance of using low laser power and large sample sizes to obtain consistent data sets
Is photobleaching necessary for Raman imaging of bone tissue using a green laser?
AbstractRaman microspectroscopy is widely used for musculoskeletal tissues studies. But the fluorescence background obscures prominent Raman bands of mineral and matrix components of bone tissue. A 532-nm laser irradiation has been used efficiently to remove the fluorescence background from Raman spectra of cortical bone. Photochemical bleaching reduces over 80% of the fluorescence background after 2 h and is found to be nondestructive within 40 min. The use of electron multiplying couple charge detector (EMCCD) enables to acquire Raman spectra of bone tissues within 1–5 s range and to obtain Raman images less than in 10 min
T and CPT Symmetries in Entangled Neutral Meson Systems
Genuine tests of an asymmetry under T and/or CPT transformations imply the
interchange between in-states and out-states. I explain a methodology to
perform model-indepedent separate measurements of the three CP, T and CPT
symmetry violations for transitions involving the decay of the neutral meson
systems in B- and {\Phi}-factories. It makes use of the quantum-mechanical
entanglement only, for which the individual state of each neutral meson is not
defined before the decay of its orthogonal partner. The final proof of the
independence of the three asymmetries is that no other theoretical ingredient
is involved and that the event sample corresponding to each case is different
from the other two. The experimental analysis for the measurements of these
three asymmetries as function of the time interval {\Delta}t > 0 between the
first and second decays is discussed, as well as the significance of the
expected results. In particular, one may advance a first observation of true,
direct, evidence of Time-Reserval-Violation in B-factories by many standard
deviations from zero, without any reference to, and independent of,
CP-Violation. In some quantum gravity framework the CPT-transformation is
ill-defined, so there is a resulting loss of particle-antiparticle identity.
This mechanism induces a breaking of the EPR correlation in the entanglement
imposed by Bose statistics to the neutral meson system, the so-called
{\omega}-effect. I present results and prospects for the {\omega}-parameter in
the correlated neutral meson-antimeson states.Comment: Proc. DISCRETE 2010, Symposium on Prospects in the Physics of
Discrete Symmetries, December 2010, Rom
Have the changes introduced by the 2004 Higher Education Act made higher education admissions in England wider and fairer?
'Widening participation' and 'fair access' have been contested policy areas in English higher education since at least the early 1990s. They were key facets of the 2003 White Paper - The Future of Higher Education - and the subsequent 2004 Higher Education Act, with stated objectives that the reach of higher education should be wider and fairer. In particular, there has been considerable concern about admissions to 'top universities', which have remained socially as well as academically exclusive. The principal policy tools used by the Act were the introduction of variable tuition fees, expanded student grants, discretionary bursaries and the new Office for Fair Access (OFFA). This paper draws on publicly available statistics to assess whether the changes implemented by the 2004 Act have indeed made access to English higher education wider and fairer in relation to young people progressing from state schools and colleges and from lower socio-economic groups. It concludes that, while there is some evidence for modest improvements, these have been concentrated outside the 'top universities', which have seen slippage relative to the rest of the sector. The paper concludes with a discussion of the reasons why financial inducements appear to be a flawed and naive approach to influencing student demand. © 2011 Taylor & Francis
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