9 research outputs found
Multi-polariton control in attosecond transient absorption of autoionizing states
Tunable attosecond transient absorption spectroscopy is an ideal tool for
studying and manipulating autoionization dynamics in the continuum. We
investigate near-resonant two-photon couplings between the bright 3s^-1 4p and
dark 3s^-1 4f autoionizing states of argon that lead to Autler-Townes like
interactions, forming entangled light-matter states, or polaritons. We observe
that one-photon couplings with intermediate dark states play an important role
in this interaction, leading to the formation of multiple polaritonic branches
whose energies exhibit avoided crossings as a function of the dressing-laser
frequency. Our experimental measurements and theoretical essential-state
simulations show good agreement and reveal how the delay, frequency, and
intensity of the dressing pulse govern the properties of autoionizing polariton
multiplets. These results demonstrate new pathways for quantum control of
autoionizing states with optical fields.Comment: 8 pages, 6 figure
The Safe Removal of Frozen Air from the Annulus of an LH2 Storage Tank
Large Liquid Hydrogen (LH2) storage tanks are vital infrastructure for NASA. Eventually, air may leak into the evacuated and perlite filled annular region of these tanks. Although the vacuum level is monitored in this region, the extremely cold temperature causes all but the helium and neon constituents of air to freeze. A small, often unnoticeable pressure rise is the result. As the leak persists, the quantity of frozen air increases, as does the thermal conductivity of the insulation system. Consequently, a notable increase in commodity boil-off is often the first indicator of an air leak. Severe damage can result from normal draining of the tank. The warming air will sublimate which will cause a pressure rise in the annulus. When the pressure increases above the triple point, the frozen air will begin to melt and migrate downward. Collection of liquid air on the carbon steel outer shell may chill it below its ductility range, resulting in fracture. In order to avoid a structural failure, as described above, a method for the safe removal of frozen air is needed. A thermal model of the storage tank has been created using SINDA/FLUINT modeling software. Experimental work is progressing in an attempt to characterize the thermal conductivity of a perlite/frozen nitrogen mixture. A statistical mechanics model is being developed in parallel for comparison to experimental work. The thermal model will be updated using the experimental/statistical mechanical data, and used to simulate potential removal scenarios. This paper will address methodologies and analysis techniques for evaluation of two proposed air removal methods
Pressure-Dependence of Poly( N -isopropylacrylamide) Mesoglobule Formation in Aqueous Solution
Above their cloud point, aqueous solutions of the thermoresponsive polymer poly(N-isopropylacrylamide) (PNIPAM) form large mesoglobules. We have carried out very small-angle neutron scattering (VSANS with q = 0.21–2.3 × 10–3 Å–1) and Raman spectroscopy experiments on a 3 wt % PNIPAM solution in D2O at atmospheric and elevated pressures (up to 113 MPa). Raman spectroscopy reveals that, at high pressure, the polymer is less dehydrated upon crossing the cloud point. VSANS shows that the mesoglobules are significantly larger and contain more D2O than at atmospheric pressure. We conclude that the size of the mesoglobules and thus their growth process are closely related to the hydration state of PNIPAM
Pressure-Dependence of Poly(<i>N</i>‑isopropylacrylamide) Mesoglobule Formation in Aqueous Solution
Above
their cloud point, aqueous solutions of the thermoresponsive
polymer polyÂ(<i>N</i>-isopropylacrylamide) (PNIPAM) form
large mesoglobules. We have carried out very small-angle neutron scattering
(VSANS with <i>q</i> = 0.21–2.3 × 10<sup>–3</sup> Å<sup>–1</sup>) and Raman spectroscopy experiments on
a 3 wt % PNIPAM solution in D<sub>2</sub>O at atmospheric and elevated
pressures (up to 113 MPa). Raman spectroscopy reveals that, at high
pressure, the polymer is less dehydrated upon crossing the cloud point.
VSANS shows that the mesoglobules are significantly larger and contain
more D<sub>2</sub>O than at atmospheric pressure. We conclude that
the size of the mesoglobules and thus their growth process are closely
related to the hydration state of PNIPAM