4,477 research outputs found
Microwave Absorption of Surface-State Electrons on Liquid He
We have investigated the intersubband transitions of surface state electrons
(SSE) on liquid He induced by microwave radiation at temperatures from 1.1
K down to 0.01 K. Above 0.4 K, the transition linewidth is proportional to the
density of He vapor atoms. This proportionality is explained well by Ando's
theory, in which the linewidth is determined by the electron - vapor atom
scattering. However, the linewidth is larger than the calculation by a factor
of 2.1. This discrepancy strongly suggests that the theory underestimates the
electron - vapor atom scattering rate. At lower temperatures, the absorption
spectrum splits into several peaks. The multiple peak structure is partly
attributed to the spatial inhomogeneity of the static holding electric field
perpendicular to the electron sheet.Comment: 15 pages, 7 figures, submitted to J. Phys. Soc. Jp
Feedback in the local LBG Analog Haro 11 as probed by far-UV and X-ray observations
We have re-analyzed FUSE data and obtained new Chandra observations of Haro
11, a local (D_L=88 Mpc) UV luminous galaxy. Haro 11 has a similar far-UV
luminosity (10^10.3 L_\odot), UV surface brightness (10^9.4 L_\odot kpc^-2),
SFR, and metallicity to that observed in Lyman Break Galaxies (LBGs). We show
that Haro 11 has extended, soft thermal (kT~0.68 keV) X-ray emission with a
luminosity and size which scales with the physical properties (e.g. SFR,
stellar mass) of the host galaxy. An enhanced alpha/Fe, ratio of ~4 relative to
solar abundance suggests significant supernovae enrichment. These results are
consistent with the X-ray emission being produced in a shock between a
supernovae driven outflow and the ambient material. The FUV spectra show strong
absorption lines similar to those observed in LBG spectra. A blueshifted
absorption component is identified as a wind outflowing at ~200-280 km/s.
OVI\lambda\lambda1032,1038 emission, the dominant cooling mechanism for coronal
gas at T~10^5.5 K is also observed. If associated with the outflow, the
luminosity of the OVI emission suggests that <20% of the total mechanical
energy from the supernovae and solar winds is being radiated away. This implies
that radiative cooling through OVI is not significantly inhibiting the growth
of the outflowing gas. In contradiction to the findings of Bergvall et al 2006,
we find no convincing evidence of Lyman continuum leakage in Haro 11. We
conclude that the wind has not created a `tunnel' allowing the escape of a
significant fraction of Lyman continuum photons and place a limit on the escape
fraction of f_{esc}<2%. Overall, both Haro 11 and a previously observed LBG
analogue VV 114, provide an invaluable insight into the X-ray and FUV
properties of high redshift LBGs.Comment: Accepted for publication in ApJ, 40 pages, 17 figure
Wigner Crystals in the lowest Landau level at low filling factors
We report on results of finite-size numerical studies of partially filled
lowest Landau level at low electron filling factors. We find convincing
evidence suggesting that electrons form Wigner Crystals at sufficiently low
filling factors, and the critical filling factor is close to 1/7. At nu=1/7 we
find the system undergoes a phase transition from Wigner Crystal to the
incompressible Laughlin state when the short-range part of the Coulomb
interaction is modified slightly. This transition is either continuous or very
weakly first order.Comment: 5 papges RevTex with 8 eps figures embedded in the tex
Microwave saturation of the Rydberg states of electrons on helium
We present measurements of the resonant microwave excitation of the Rydberg
energy levels of surface state electrons on superfluid helium. The temperature
dependent linewidth agrees well with theoretical predictions and is very small
below 300 mK. Absorption saturation and power broadening were observed as the
fraction of electrons in the first excited state was increased to 0.49, close
to the thermal excitation limit of 0.5. The Rabi frequency was determined as a
function of microwave power. The high values of the ratio of the Rabi frequency
to linewidth confirm this system as an excellent candidate for creating qubits.Comment: 4 pages, 4 figure
Transition from an electron solid to the sequence of fractional quantum Hall states at very low Landau level filling factor
At low Landau level filling of a two-dimensional electron system, typically
associated with the formation of an electron crystal, we observe local minima
in Rxx at filling factors nu=2/11, 3/17, 3/19, 2/13, 1/7, 2/15, 2/17, and 1/9.
Each of these developing fractional quantum Hall (FQHE) states appears only
above a filling factor-specific temperature. This can be interpreted as the
melting of an electron crystal and subsequent FQHE liquid formation. The
observed sequence of FQHE states follow the series of composite fermion states
emanating from nu=1/6 and nu=1/8
The development of life-cycle and risk assessment methodology using data from AWE Aldermaston
The research described in this thesis further develops Life-Cycle Assessment (LCA) methodology to include radiological releases to air, water and as waste. A new methodology has been developed to characterise radioactive aspects based on known effects to man and behaviour in the environment. Equivalency factors have been developed for nine radioisotopes (24'Am, 137Cs56 0Co, 239Pu52 41Pu53 HI 234U, 235U and 238U). A new LCA valuation method is developed for weighting environmental impacts in an Environmental Management System (EMS). A detailed LCA inventory of environmental burdens has been compiled from data from AWE Aldermaston and used as a case study to develop and demonstrate the methodologies developed in this work. As part of the research, the links between environmental aspects and impacts has been investigated using LCA, based on the high hazard facilities at AWE Aldermaston, which is a major industrial site. The case study also includes the contribution from vehicle use in the impact assessment. The results of this work have clearly identified which facilities and hence which processes are causing the most damaging environmental impact. New risk assessment methods are developed to quantify environmental accidents, that include revised consequence definitions that can be applied without the need for modelling and thus offer an economical alternative to existing methods. A new six-step screening methodology is presented to identify potential major accidents to the environment (MATTE) and to comply with the COMAH Regulations 1999. A method to prioritise MATTE scenarios has also been developed. The research has revealed that the current approach to significance assessment does not provide enough sophistication for sites as complex as AWE Aldermaston. The impacts of most concern are environmental irradiation, the generation of all categories of waste and global warming. The impacts associated with radioactive discharges (to air, water and as waste) are given the highest weighting largely reflecting the concern of the major stakeholder groups (local community, regulatory bodies and pressure groups). The methods proposed can be readily applied to any nuclear or chemical site.EThOS - Electronic Theses Online ServiceAEA Technology plcAWE plcUKAEAGBUnited Kingdo
Hexatic Order and Surface Ripples in Spherical Geometries
In flat geometries, two dimensional hexatic order has only a minor effect on
capillary waves on a liquid substrate and on undulation modes in lipid
bilayers. However, extended bond orientational order alters the long wavelength
spectrum of these ripples in spherical geometries. We calculate this frequency
shift and suggest that it might be detectable in lipid bilayer vesicles, at the
surface of liquid metals and in multielectron bubbles in liquid helium at low
temperatures. Hexatic order also leads to a shift in the threshold for the
fission instability induced in the later two systems by an excess of electric
charge.Comment: 5 pages, 1 figure; revised version; to appear in Phys. Rev. Let
Exchange Frequencies in the 2d Wigner crystal
Using Path Integral Monte Carlo we have calculated exchange frequencies as
electrons undergo ring exchanges in a ``clean'' 2d Wigner crystal as a function
of density. The results show agreement with WKB calculations at very low
density, but show a more rapid increase with density near melting. Remarkably,
the exchange Hamiltonian closely resembles the measured exchanges in 2d He.
Using the resulting multi-spin exchange model we find the spin Hamiltonian for
r_s \leq 175 \pm 10 is a frustrated antiferromagnetic; its likely ground state
is a spin liquid. For lower density the ground state will be ferromagnetic
The effect of pressure on statics, dynamics and stability of multielectron bubbles
The effect of pressure and negative pressure on the modes of oscillation of a
multi-electron bubble in liquid helium is calculated. Already at low pressures
of the order of 10-100 mbar, these effects are found to significantly modify
the frequencies of oscillation of the bubble. Stabilization of the bubble is
shown to occur in the presence of a small negative pressure, which expands the
bubble radius. Above a threshold negative pressure, the bubble is unstable.Comment: 4 pages, 2 figures, accepted for publication in Physical Review
Letter
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