29,828 research outputs found
Light scattering from cold rolled aluminum surfaces
We present experimental light scattering measurements from aluminum surfaces
obtained by cold rolling. We show that our results are consistent with a scale
invariant description of the roughness of these surfaces. The roughness
parameters that we obtain from the light scattering experiment are consistent
with those obtained from Atomic Force Microscopy measurements
Applications and identification of surface correlations
We compare theoretical, experimental, and computational approaches to random
rough surfaces. The aim is to produce rough surfaces with desirable
correlations and to analyze the correlation functions extracted from the
surface profiles. Physical applications include ultracold neutrons in a rough
waveguide, lateral electronic transport, and scattering of longwave particles
and waves. Results provide guidance on how to deal with experimental and
computational data on rough surfaces. A supplemental goal is to optimize the
neutron waveguide for GRANIT experiments. The measured correlators are
identified by fitting functions or by direct spectral analysis. The results are
used to compare the calculated observables with theoretical values. Because of
fluctuations, the fitting procedures lead to inaccurate physical results even
if the quality of the fit is very good unless one guesses the right shape of
the fitting function. Reliable extraction of the correlation function from the
measured surface profile seems virtually impossible without independent
information on the structure of the correlation function. Direct spectral
analysis of raw data rarely works better than the use of a "wrong" fitting
function. Analysis of surfaces with a large correlation radius is hindered by
the presence of domains and interdomain correlations
Novel perspectives for the application of total internal reflection microscopy
Total Internal Reflection Microscopy (TIRM) is a sensitive non-invasive
technique to measure the interaction potentials between a colloidal particle
and a wall with femtonewton resolution. The equilibrium distribution of the
particle-wall separation distance z is sampled monitoring the intensity I
scattered by the Brownian particle under evanescent illumination. Central to
the data analysis is the knowledge of the relation between I and the
corresponding z, which typically must be known a priori. This poses
considerable constraints to the experimental conditions where TIRM can be
applied (short penetration depth of the evanescent wave, transparent surfaces).
Here, we introduce a method to experimentally determine I(z) by relying only on
the distance-dependent particle-wall hydrodynamic interactions. We demonstrate
that this method largely extends the range of conditions accessible with TIRM,
and even allows measurements on highly reflecting gold surfaces where multiple
reflections lead to a complex I(z).Comment: 11 pages, 7 figure
S-Matrix Unitarity, Impact Parameter Profiles, Gluon Saturation and High-Energy Scattering
A model combining perturbative and non-perturbative QCD is developed to
compute high-energy reactions of hadrons and photons and to investigate
saturation effects that manifest the S-matrix unitarity. Following a functional
integral approach, the S-matrix factorizes into light-cone wave functions and
the universal amplitude for the scattering of two color-dipoles which are
represented by Wegner-Wilson loops. In the framework of the non-perturbative
stochastic vacuum model of QCD supplemented by perturbative gluon exchange, the
loop-loop correlation is calculated and related to lattice QCD investigations.
With a universal energy dependence motivated by the two-pomeron (soft + hard)
picture that respects the unitarity condition in impact parameter space, a
unified description of pp, pip, Kp, gamma* p, and gamma gamma reactions is
achieved in good agreement with experimental data for cross sections, slope
parameters, and structure functions. Impact parameter profiles for pp and
longitudinal gamma* p reactions and the gluon distribution of the proton
xG(x,Q^2,b) are calculated and found to saturate in accordance with S-matrix
unitarity. The c.m. energies and Bjorken x at which saturation sets in are
determined.Comment: 65 pages with 13 figures, Introduction, Sec. 3, and Conclusion
extende
Scattering from surfaces with different roughness scales, analysis and interpretation
Statistical analysis and physical interpretation of scattering from surfaces with different roughness scale
Modeling surface roughness scattering in metallic nanowires
Ando's model provides a rigorous quantum-mechanical framework for
electron-surface roughness scattering, based on the detailed roughness
structure. We apply this method to metallic nanowires and improve the model
introducing surface roughness distribution functions on a finite domain with
analytical expressions for the average surface roughness matrix elements. This
approach is valid for any roughness size and extends beyond the commonly used
Prange-Nee approximation. The resistivity scaling is obtained from the
self-consistent relaxation time solution of the Boltzmann transport equation
and is compared to Prange-Nee's approach and other known methods. The results
show that a substantial drop in resistivity can be obtained for certain
diameters by achieving a large momentum gap between Fermi level states with
positive and negative momentum in the transport direction.Comment: 25 pages, 11 figure
Inversion of Randomly Corrugated Surfaces Structure from Atom Scattering Data
The Sudden Approximation is applied to invert structural data on randomly
corrugated surfaces from inert atom scattering intensities. Several expressions
relating experimental observables to surface statistical features are derived.
The results suggest that atom (and in particular He) scattering can be used
profitably to study hitherto unexplored forms of complex surface disorder.Comment: 10 pages, no figures. Related papers available at
http://neon.cchem.berkeley.edu/~dan
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