4,291 research outputs found
Circular Dichroism of RbHe and RbN Molecules
We present measurements of the circular dichroism of optically pumped Rb
vapor near the D1 resonance line. Collisions with the buffer gases He and
N reduce the transparency of the vapor, even when fully polarized. We use
two methods to measure this effect, show that the He results can be understood
from RbHe potential curves, and show how this effect conspires with the
spectral profile of the optical pumping light to increase the laser power
demands for optical pumping of very optically thick samples
Liquid segregation parameters from amphibolite dehydration melting experiments
We have experimentally obtained some of the parameters necessary for understanding the segregation of silicate liquid from amphibolite undergoing dehydration melting at 1 GPa and 750–1000°C. The solidus for this calcic amphibolite (68% Mg-Hb, 32% Pl (An_(90))) is <750°C. Amphibolites begin to melt at relatively high temperatures in the garnet-absent field, but the solidus appears to backbend at ∼1 GPa, coincident with the garnet-in boundary. Hornblende breakdown due to garnet formation releases H_2O and causes melting. Thus, in the garnet-present field (≥1 GPa), the amphibolite dehydration melting solidus may be coincident with the H_2O-saturated solidus. Liquid interconnectivity may be achieved at <900°C and <5 vol % liquid, based on both physical and chemical data from solid rock runs. Mass balance calculations from powdered rock runs suggest that small amounts (∼5–15 vol %) of hydrous (≥4 wt % H_2O), low-viscosity (10^3–10^4 Pa s), heavy rare earth element-depleted, felsic liquid may be segregated during amphibolite dehydration melting at ≥875°C. The rapid breakdown of coarse-grained Hb cores may lead to the formation of transient H_2O-saturated liquids with even lower viscosities (∼10^2 Pa s). Although comprising only a small portion of the melting cycle, these H_2O-rich conditions may enhance the segregation of liquid by reduction of liquid viscosities and by mechanical effects on the restite (e.g., increased deformation and liquid fracturing). During anatexis of coarse-grained (natural) rocks, transient conditions may control the initial stages of liquid segregation
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
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
Functional assessment of triheteromeric NMDA receptors containing a human variant associated with epilepsy
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