120 research outputs found
Reconciling Conductance Fluctuations and the Scaling Theory of Localization
We reconcile the phenomenon of mesoscopic conductance fluctuations with the
single parameter scaling theory of the Anderson transition. We calculate three
averages of the conductance distribution: , and
where is the conductance in units of and is the resistance
and demonstrate that these quantities obey single parameter scaling laws. We
obtain consistent estimates of the critical exponent from the scaling of all
these quantities
Scaling of the conductance distribution near the Anderson transition
The single parameter scaling hypothesis is the foundation of our
understanding of the Anderson transition. However, the conductance of a
disordered system is a fluctuating quantity which does not obey a one parameter
scaling law. It is essential to investigate the scaling of the full conductance
distribution to establish the scaling hypothesis. We present a clear cut
numerical demonstration that the conductance distribution indeed obeys one
parameter scaling near the Anderson transition
Symmetry, dimension and the distribution of the conductance at the mobility edge
The probability distribution of the conductance at the mobility edge,
, in different universality classes and dimensions is investigated
numerically for a variety of random systems. It is shown that is
universal for systems of given symmetry, dimensionality, and boundary
conditions. An analytical form of for small values of is discussed
and agreement with numerical data is observed. For , is
proportional to rather than .Comment: 4 pages REVTeX, 5 figures and 2 tables include
Probability distribution of the conductance at the mobility edge
Distribution of the conductance P(g) at the critical point of the
metal-insulator transition is presented for three and four dimensional
orthogonal systems. The form of the distribution is discussed. Dimension
dependence of P(g) is proven. The limiting cases and are
discussed in detail and relation in the limit is proven.Comment: 4 pages, 3 .eps figure
Wavelength dependent collective effects in the multiphoton ionization of atomic deuterium
This paper presents the results of an experimental investigation into collective effects in the transient plasma
formed by multiphoton ionization of atomic deuterium with a pulsed laser. The laser wavelength is varied in a
narrow range around 243 nm, so that the photoionization is resonant with the metastable 2S1/2 state. The ion
yield, the ion time-of-flight spectra, and the yield of Lyman-a photons have been measured as a function of
laser intensity ~from 1 to 340 MW/cm2! and laser detuning around the 1S1/2-2S1/2 two-photon resonance.
During and shortly after the laser pulse, collective effects resulting from the mutual interaction of the photoelectrons
and the ions affect the spatial and temporal distribution of the ions. Because of the near-degeneracy
of the 2S1/2, 2P1/2 , and 2P3/2 states, the resonant multiphoton ionization is affected by the Stark mixing of
these states in the collective field. As a result, the time-dependent yields of ions and of Lyman-a photons are
modulated by the interplay of the multiphoton ionization of the atoms and the collective effects in the plasma.
From the measurements it is deduced that collective effects are important above a critical charge density of
33108 ions/cm3. An asymmetry is observed in the line profile of the total ion yield as a function of laser
detuning. This asymmetry is interpreted to be due to the effect of the collective field upon the intermediate
resonant 2S1/2 state of the photoionization process
Wavelength dependent collective effects in the multiphoton ionization of atomic deuterium
This paper presents the results of an experimental investigation into collective effects in the transient plasma
formed by multiphoton ionization of atomic deuterium with a pulsed laser. The laser wavelength is varied in a
narrow range around 243 nm, so that the photoionization is resonant with the metastable 2S1/2 state. The ion
yield, the ion time-of-flight spectra, and the yield of Lyman-a photons have been measured as a function of
laser intensity ~from 1 to 340 MW/cm2! and laser detuning around the 1S1/2-2S1/2 two-photon resonance.
During and shortly after the laser pulse, collective effects resulting from the mutual interaction of the photoelectrons
and the ions affect the spatial and temporal distribution of the ions. Because of the near-degeneracy
of the 2S1/2, 2P1/2 , and 2P3/2 states, the resonant multiphoton ionization is affected by the Stark mixing of
these states in the collective field. As a result, the time-dependent yields of ions and of Lyman-a photons are
modulated by the interplay of the multiphoton ionization of the atoms and the collective effects in the plasma.
From the measurements it is deduced that collective effects are important above a critical charge density of
33108 ions/cm3. An asymmetry is observed in the line profile of the total ion yield as a function of laser
detuning. This asymmetry is interpreted to be due to the effect of the collective field upon the intermediate
resonant 2S1/2 state of the photoionization process
Conductance fluctuations and boundary conditions
The conductance fluctuations for various types for two-- and
three--dimensional disordered systems with hard wall and periodic boundary
conditions are studied, all the way from the ballistic (metallic) regime to the
localized regime. It is shown that the universal conductance fluctuations (UCF)
depend on the boundary conditions. The same holds for the metal to insulator
transition. The conditions for observing the UCF are also given.Comment: 4 pages RevTeX, 5 figures include
Polarization Correlation Measurements of Electron Impact Excitation of Hs2pd at 54.4 eV
First direct measurements are reported of the linear reduced Stokes parameters P1,P2 for H(2p)
excited by electron impact at the benchmark energy of 54.4 eV. The results differ significantly from
previous values deduced from angular correlation measurements which are in serious conflict with all
sophisticated theoretical approaches. Our results support the trend of theoretical predictions for P2
and confirm that its value is negative at electron scattering angles above 100±, as predicted by theory
Polarization Correlation Measurements of Electron Impact Excitation of Hs2pd at 54.4 eV
First direct measurements are reported of the linear reduced Stokes parameters P1,P2 for H(2p)
excited by electron impact at the benchmark energy of 54.4 eV. The results differ significantly from
previous values deduced from angular correlation measurements which are in serious conflict with all
sophisticated theoretical approaches. Our results support the trend of theoretical predictions for P2
and confirm that its value is negative at electron scattering angles above 100±, as predicted by theory
Comparing the effects of sun exposure and vitamin D supplementation on vitamin D insufficiency, and immune and cardio-metabolic function: the Sun Exposure and Vitamin D Supplementation (SEDS) Study
BACKGROUND Adults living in the sunny Australian climate are at high risk of skin cancer, but vitamin D deficiency (defined here as a serum 25-hydroxyvitamin D (25(OH)D) concentration of less than 50 nmol/L) is also common. Vitamin D deficiency may be a risk factor for a range of diseases. However, the optimal strategies to achieve and maintain vitamin D adequacy (sun exposure, vitamin D supplementation or both), and whether sun exposure itself has benefits over and above initiating synthesis of vitamin D, remain unclear. The Sun Exposure and Vitamin D Supplementation (SEDS) Study aims to compare the effectiveness of sun exposure and vitamin D supplementation for the management of vitamin D insufficiency, and to test whether these management strategies differentially affect markers of immune and cardio-metabolic function. METHODS/DESIGN The SEDS Study is a multi-centre, randomised controlled trial of two different daily doses of vitamin D supplementation, and placebo, in conjunction with guidance on two different patterns of sun exposure. Participants recruited from across Australia are aged 18-64 years and have a recent vitamin D test result showing a serum 25(OH)D level of 40-60 nmol/L. DISCUSSION This paper discusses the rationale behind the study design, and considers the challenges but necessity of data collection within a non-institutionalised adult population, in order to address the study aims. We also discuss the challenges of participant recruitment and retention, ongoing engagement of referring medical practitioners and address issues of compliance and participant retention. TRIAL REGISTRATION Australia New Zealand Clinical Trials Registry: ACTRN12613000290796 Registered 14 March 2013
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