604 research outputs found
Digital micromirror devices for laser-based manufacturing
Digital Micromirror Devices (DMDs), containing arrays of around one million individually-controllable ~10µm square mirrors, provide an extremely cost-effective and practical method to modulate the spatial beam profile of a pulsed laser source for both additive and subtractive laser processing and printing. When demagnified by a factor of ~100 in one dimension (hence ~10,000 in area) a ~1mJ/cm2 laser pulse reflected from the mirrors on the DMD surface that are switched to the 'on' position, attains a fluence of ~10J/cm2 at the workpiece, which is more than sufficient to ablate most materials of interest to the laser-manufacturing community. More familiar in the context of high values of magnification by the laser projection industry, reversing the role to use them for equally high values of demagnification opens up a wealth of possibilities for ablation, multiphoton polymerization, security marking and fabrication of features that perhaps surprisingly can be well below the wavelength of the laser used. Of key relevance is that very high-resolution patterning can be achieved by a single laser pulse, and step-and-repeat processes, when combined with the refresh rates of the DMD pattern that are currently at the 30kHz level, open up the possibility of processing areas of up to 1cm2 per second with micron-scale resolution where each ~100µm x 100µm area patterned per pulse can display arbitrary pixelated content. We will discuss the application of DMD-baser laser processing to the following areas of interest to the laser-manufacturing community
Multi-shot laser ablation and digital micromirror device mask translation for sub-diffraction-limit machining resolution
Digital Micromirror Devices (DMDs) can offer rapidly generated, bespoke intensity modulation masks for image-projection-based laser-machining. Recent work has shown repeatable sub-micron feature patterning [1], with proposed applications in the medical sciences and photonics. While DMDs can offer rapid patterning, with ~32kHz switching speeds available [2], they are not yet efficient reflectors at <300nm, thus limiting machining resolution to the diffraction limit at the near-visible wavelengths and above
Femtosecond laser-induced patterned transfer of intact semiconductor and polymer thin films via a digital micromirror device
The laser-induced forward transfer (LIFT) of thin films is an attractive technique to deposit materials on a size scale that can span nanometres to millimeters. During LIFT, the energy of a laser pulse is absorbed in a small volume of a thin film (donor) causing an explosive expansion which is used to propel a portion of the donor away from the carrier substrate and transfer it onto a receiver substrate as shown in Fig.1(a). Ultrashort laser systems can limit laser damage to remaining areas of the donor usually present using laser systems with longer (nanosecond) pulse widths
Simultaneous patterning and deposition of thin films via femtosecond laser-induced transfer using a digital micromirror device for spatial pulse shaping
The forward and backward femtosecond laser-induced transfer of thin films in an intact state with good adhesion, via a digital micromirror array acting as a dynamic object mask for spatial beam shaping is presented
Constraints on growth index parameters from current and future observations
We use current and future simulated data of the growth rate of large scale
structure in combination with data from supernova, BAO, and CMB surface
measurements, in order to put constraints on the growth index parameters. We
use a recently proposed parameterization of the growth index that interpolates
between a constant value at high redshifts and a form that accounts for
redshift dependencies at small redshifts. We also suggest here another
exponential parameterization with a similar behaviour. The redshift dependent
parametrizations provide a sub-percent precision level to the numerical growth
function, for the full redshift range. Using these redshift parameterizations
or a constant growth index, we find that current available data from galaxy
redshift distortions and Lyman-alpha forests is unable to put significant
constraints on any of the growth parameters. For example both CDM and
flat DGP are allowed by current growth data. We use an MCMC analysis to study
constraints from future growth data, and simulate pessimistic and moderate
scenarios for the uncertainties. In both scenarios, the redshift
parameterizations discussed are able to provide significant constraints and
rule out models when incorrectly assumed in the analysis. The values taken by
the constant part of the parameterizations as well as the redshift slopes are
all found to significantly rule out an incorrect background. We also find that,
for our pessimistic scenario, an assumed constant growth index over the full
redshift range is unable to rule out incorrect models in all cases. This is due
to the fact that the slope acts as a second discriminator at smaller redshifts
and therefore provide a significant test to identify the underlying gravity
theory.Comment: 13 pages, 5 figures, matches JCAP accepted versio
Precision Requirements for Space-based XCO2 Data
Precision requirements have been determined for the column-averaged CO2 dry air mole fraction (X(sub CO2)) data products to be delivered by the Orbiting Carbon Observatory (OCO). These requirements result from an assessment of the amplitude and spatial gradients in X(sub CO2), the relationship between X(sub CO2) precision and surface CO2 flux uncertainties calculated from inversions of the X(sub CO2) data, and the effects of X,,Z biases on CO2 flux inversions. Observing system simulation experiments and synthesis inversion modeling demonstrate that the OCO mission design and sampling strategy provide the means to achieve the X(sub CO2) precision requirements. The impact of X(sub CO2) biases on CO2 flux uncertainties depend on their spatial and temporal extent since CO2 sources and sinks are inferred from regional-scale X(sub CO2) gradients. Simulated OCO sampling of the TRACE-P CO2 fields shows the ability of X(sub CO2) data to constrain CO2 flux inversions over Asia and distinguish regional fluxes from India and China
A Soluble String Theory of Hadrons
We consider Penrose limits of the Klebanov-Strassler and Maldacena-Nunez
holographic duals to N =1 supersymmetric Yang-Mills. By focusing in on the IR
region we obtain exactly solvable string theory models. These represent the
nonrelativistic motion and low-lying excitations of heavy hadrons with mass
proportional to a large global charge. We argue that these hadrons, both
physically and mathematically, take the form of heavy nonrelativistic strings;
we term them "annulons." A simple toy model of a string boosted along a compact
circle allows us considerable insight into their properties. We also calculate
the Wilson loop carrying large global charge and show the effect of confinement
is quadratic, not linear, in the string tension.Comment: 40 pages, 1 figure; v2: typos correcte
Two refreshing views of Fluctuation Theorems through Kinematics Elements and Exponential Martingale
In the context of Markov evolution, we present two original approaches to
obtain Generalized Fluctuation-Dissipation Theorems (GFDT), by using the
language of stochastic derivatives and by using a family of exponential
martingales functionals. We show that GFDT are perturbative versions of
relations verified by these exponential martingales. Along the way, we prove
GFDT and Fluctuation Relations (FR) for general Markov processes, beyond the
usual proof for diffusion and pure jump processes. Finally, we relate the FR to
a family of backward and forward exponential martingales.Comment: 41 pages, 7 figures; version2: 45 pages, 7 figures, minor revisions,
new results in Section
Effect of initial conditions on the speed of reaction-diffusion fronts
The effect of initial conditions on the speed of propagating fronts in reaction-diffusion equations is examined in the framework of the Hamilton-Jacobi theory. We study the transition between quenched and nonquenched fronts both analytically and numerically for parabolic and hyperbolic reaction diffusion. Nonhomogeneous media are also analyzed and the effect of algebraic initial conditions is also discussed
Red Queen Coevolution on Fitness Landscapes
Species do not merely evolve, they also coevolve with other organisms.
Coevolution is a major force driving interacting species to continuously evolve
ex- ploring their fitness landscapes. Coevolution involves the coupling of
species fit- ness landscapes, linking species genetic changes with their
inter-specific ecological interactions. Here we first introduce the Red Queen
hypothesis of evolution com- menting on some theoretical aspects and empirical
evidences. As an introduction to the fitness landscape concept, we review key
issues on evolution on simple and rugged fitness landscapes. Then we present
key modeling examples of coevolution on different fitness landscapes at
different scales, from RNA viruses to complex ecosystems and macroevolution.Comment: 40 pages, 12 figures. To appear in "Recent Advances in the Theory and
Application of Fitness Landscapes" (H. Richter and A. Engelbrecht, eds.).
Springer Series in Emergence, Complexity, and Computation, 201
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