1,845 research outputs found
A Model for Conductive Percolation in Ordered Nanowire Arrays
The combined processes of anodization and electrodeposition lead to highly
ordered arrays of cylindrical nanowires. This template-based self-assembly
fabrication method yields nanowires embedded in alumina. Commonly, chemical
etching is used to remove the alumina and free the nanowires. However, it has
been experimentally observed during the etching process that the nanowires tend
to form clumps. In this work, the nanowires are modeled as elastic rods subject
to surface interaction forces. The dynamics of the model give rise to the
aforementioned clumping behavior which is studied via percolation theory. This
work finds that percolation takes place with probability ,
where the exponent and is the time at which percolation takes
place. The critical exponents which entirely determine the system are found to
be for (dimension) , and .Comment: 5 pages, 8 figure
A characteristic lengthscale causes anomalous size effects and boundary programmability in mechanical metamaterials
The architecture of mechanical metamaterialsis designed to harness geometry,
non-linearity and topology to obtain advanced functionalities such as shape
morphing, programmability and one-way propagation. While a purely geometric
framework successfully captures the physics of small systems under idealized
conditions, large systems or heterogeneous driving conditions remain
essentially unexplored. Here we uncover strong anomalies in the mechanics of a
broad class of metamaterials, such as auxetics, shape-changers or topological
insulators: a non-monotonic variation of their stiffness with system size, and
the ability of textured boundaries to completely alter their properties. These
striking features stem from the competition between rotation-based
deformations---relevant for small systems---and ordinary elasticity, and are
controlled by a characteristic length scale which is entirely tunable by the
architectural details. Our study provides new vistas for designing, controlling
and programming the mechanics of metamaterials in the thermodynamic limit.Comment: Main text has 4 pages, 4 figures + Methods and Supplementary
Informatio
Comparison of the COBE FIRAS and DIRBE Calibrations
We compare the independent FIRAS and DIRBE observations from the COBE in the
wavelength range 100-300 microns. This cross calibration provides checks of
both data sets. The results show that the data sets are consistent within the
estimated gain and offset uncertainties of the two instruments. They show the
possibility of improving the gain and offset determination of DIRBE at 140 and
240 microns.Comment: Accepted for publication in the Astrophysical Journal 11 pages, plus
3 figures in separate postscript files. Figure 3 has three part
Accuracy of site coordinates obtainable by a mobile lunar laser station
The accuracy with which a mobile lunar laser station can be located was the subject of a modeling study. The influence of the number and accuracy of fixed lunar ranging stations, the uncertainty in polar motion, and data loss due to weather and similar factors were considered, and the results are given in a cartographic form. In general, all three coordinates (for coordinates to latitude + or - 60 deg) were determined to better than the pole uncertainty, given three or more fixed sites and reasonable weather. This result indicates that one or more mobile stations would be suitable for the study of geotectonics
New CMB Power Spectrum Constraints from MSAMI
We present new cosmic microwave background (CMB) anisotropy results from the
combined analysis of the three flights of the first Medium Scale Anisotropy
Measurement (MSAM1). This balloon-borne bolometric instrument measured about 10
square degrees of sky at half-degree resolution in 4 frequency bands from 5.2
icm to 20 icm with a high signal-to-noise ratio. Here we present an overview of
our analysis methods, compare the results from the three flights, derive new
constraints on the CMB power spectrum from the combined data and reduce the
data to total-power Wiener-filtered maps of the CMB. A key feature of this new
analysis is a determination of the amplitude of CMB fluctuations at . The analysis technique is described in a companion paper by Knox.Comment: 9 pages, 6 included figure
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