4,183 research outputs found
Flow in an experimental micro–magma chamber
The chemical evolution and eruptive behavior of magmas may be controlled largely by convective processes within magma chambers. According to a recent National Research Council Report [Committee on Physics and Chemistry of Earth Materials, 1987], “the style of convection itself, whether it is turbulent, laminar, large-scale, of multiple scales, tiered, or localized and intermittent, is very much at question.” In the U.S. National Report to the International Union of Geodesy and Geophysics, Marsh [1987] reviewed recent theoretical and experimental developments related to the style of convection in magma chambers, noting both significant quantitative advances and also the many remaining uncertainties. With regard to double-diffusive convection, he stated “as ever, the critical question concerns whether or not actual magma chambers convect in this style.” Similarly, Spera et al. [1986] , in discussion of double-diffusive convection, cautioned against “applying results from saltwater tanks to magma chambers.
James B. Macelwane Award: Citation and Acceptance of Robert Keith O'Nions
I have the pleasure to introduce Robert Keith O'Nions, a young man of 34, for the Macelwane Award, not because I have had anything to do with his education and research, but because I was a member of the committee this year, and we both originate from the same country. Keith O'Nions earned his B.Sc. from the University of Nottingham in 1966, traveled to Alberta for a Ph.D. in 1969, became a Postdoctoral Fellow in Oslo during 1970, joined the faculty at Oxford from 1971–1975, and moved to his present home at Columbia University in 1975.
When the time came to find a citationist [sic] for him it turned out that his colleagues at Lamont-Doherty, who were the obvious choices, were all at sea—and I admit that this is how I feel when I read some of Keith's papers. In a sense, this makes me well-suited for this introduction, because I cannot spend time explaining his research to you. Instead, I will read to you a couple of paragraphs from his nomination for the award, written by an anonymous friend
Breakdown of Angular Momentum Selection Rules in High Pressure Optical Pumping Experiments
We present measurements, using two complementary methods, of the breakdown of
atomic angular momentum selection rules in He-broadened Rb vapor. Atomic dark
states are rendered weakly absorbing due to fine-structure mixing during Rb-He
collisions. The effect substantially increases the photon demand for optical
pumping of dense vapors
Apoptosis: A Basic Biological Phenomenon with Wide-ranging Implications in Tissue Kinetics
The term apoptosis is proposed for a hitherto little recognized mechanism of controlled cell deletion, which appears to play a complementary but opposite role to mitosis in the regulation of animal cell populations. Its morphological features suggest that it is an active, inherently programmed phenomenon, and it has been shown that it can be initiated or inhibited by a variety of environmental stimuli, both physiological and pathological
Magic wavelengths for the transition in rubidium
Magic wavelengths, for which there is no differential ac Stark shift for the
ground and excited state of the atom, allow trapping of excited Rydberg atoms
without broadening the optical transition. This is an important tool for
implementing quantum gates and other quantum information protocols with Rydberg
atoms, and reliable theoretical methods to find such magic wavelengths are thus
extremely useful. We use a high-precision all-order method to calculate magic
wavelengths for the transition of rubidium, and compare the
calculation to experiment by measuring the light shift for atoms held in an
optical dipole trap at a range of wavelengths near a calculated magic value
Magnetocardiography with a modular spin-exchange relaxation free atomic magnetometer array
We present a portable four-channel atomic magnetometer array operating in the
spin exchange relaxation-free regime. The magnetometer array has several design
features intended to maximize its suitability for biomagnetic measurement,
specifically foetal magnetocardiography, such as a compact modular design, and
fibre coupled lasers. The modular design allows the independent positioning and
orientation of each magnetometer, in principle allowing for non-planar array
geometries. Using this array in a magnetically shielded room, we acquire adult
magnetocadiograms. These measurements were taken with a 6-11 fT Hz^(-1/2)
single-channel baseline sensitivity that is consistent with the independently
measured noise level of the magnetically shielded room.Comment: 15 pages, 5 figure
Phase equilibria constraints on Archean crustal genesis from crystallization experiments on trondhjemite with water at 10-17 kbar
The formation of continental crust during the Archean and early Proterozoic occurred through
a different mechanisms than the currently active processes of calc-alkaline volcanism in orogenic
regions. In view that most crustal growth models imply that by the end of the Archean a continental
mass equivalent to 75% or more of the current crust had evolved, it seems highly relevant to study
early crustal genesis
Hydrous Carbonatitic Liquids Drive CO2 Recycling From Subducted Marls and Limestones
This research was supported by the Italian Ministry of Education, University, and Research (MIUR) program PRIN2017 and by the Deep Carbon Observatory (DCO). We are greatly indebted to Andrea Risplendente for careful examination of run charges at the Electron Microprobe.Pelagic limestones are subducted in a variety of subduction zones worldwide. Despite the geochemical relevance
of systems enriched in CaCO3, previous experimental investigations mostly focused on carbonated pelites, with
low Ca/(Ca+Mg+Fe) ratio. We present the compositions and the formation conditions of liquids in the model
system CaO‐Al2O3‐SiO2‐H2O‐CO2 (CASHC), building on phase relationships in the subsystems CHC and
CSHC, where a second critical endpoint was suggested at temperatures as low as 515 °C, and 3.2 GPa. Multianvil
experiments were performed at 4.2 and 6.0 GPa on five bulk compositions at variable Ca/Si/Al ratios. H2O
contents
vary from 5.6 to 21 wt%. Aragonite + kyanite + vapor and minor lawsonite form at 700 °C, replaced by
zoisite/grossular at 800 °C. Between 850 °C and 950 °C, a complex sequence of textural features is observed
upon quenching of a single volatile‐rich liquid phase formed at run conditions. Precipitates include dendritic
CaCO3, silicate glass, and Al‐rich whiskers. The bulk composition of such hydrous carbonatitic liquids is
retrieved by image analysis on X‐ray maps, showing Ca/Si ratio increasing with pressure and temperature.
Hydrous Ca‐carbonatitic liquids are efficient media for scavenging volatiles from subducted crustal material and
for metasomatizing the mantle wedge.Ministry of Education, Universities and Research (MIUR)Deep Carbon Observatory (DCO
Solidity of viscous liquids. IV. Density fluctuations
This paper is the fourth in a series exploring the physical consequences of
the solidity of highly viscous liquids. It is argued that the two basic
characteristics of a flow event (a jump between two energy minima in
configuration space) are the local density change and the sum of all particle
displacements. Based on this it is proposed that density fluctuations are
described by a time-dependent Ginzburg-Landau equation with rates in k-space of
the form with where is the average
intermolecular distance. The inequality expresses a long-wavelength dominance
of the dynamics which implies that the Hamiltonian (free energy) may be taken
to be ultra local. As an illustration of the theory the case with the simplest
non-trivial Hamiltonian is solved to second order in the Gaussian
approximation, where it predicts an asymmetric frequency dependence of the
isothermal bulk modulus with Debye behavior at low frequencies and an
decay of the loss at high frequencies. Finally, a general
formalism for the description of viscous liquid dynamics, which supplements the
density dynamics by including stress fields, a potential energy field, and
molecular orientational fields, is proposed
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