3,527 research outputs found
Signature of a Cosmic String Wake at
In this paper, we describe the results of N-body simulation runs, which
include a cosmic string wake of tension on top of the
usual fluctuations. To obtain a higher resolution of the wake in
the simulations compared to previous work, we insert the effects of the string
wake at a lower redshift and perform the simulations in a smaller volume. A
curvelet analysis of the wake and no-wake maps is applied, indicating that the
presence of a wake can be extracted at a three-sigma confidence level from maps
of the two-dimensional dark matter projection down to a redshift of .Comment: 8 pages, 6 figures; We have improved the analysis and results. The
text now agrees with the published versio
Resolving transition metal chemical space: feature selection for machine learning and structure-property relationships
Machine learning (ML) of quantum mechanical properties shows promise for
accelerating chemical discovery. For transition metal chemistry where accurate
calculations are computationally costly and available training data sets are
small, the molecular representation becomes a critical ingredient in ML model
predictive accuracy. We introduce a series of revised autocorrelation functions
(RACs) that encode relationships between the heuristic atomic properties (e.g.,
size, connectivity, and electronegativity) on a molecular graph. We alter the
starting point, scope, and nature of the quantities evaluated in standard ACs
to make these RACs amenable to inorganic chemistry. On an organic molecule set,
we first demonstrate superior standard AC performance to other
presently-available topological descriptors for ML model training, with mean
unsigned errors (MUEs) for atomization energies on set-aside test molecules as
low as 6 kcal/mol. For inorganic chemistry, our RACs yield 1 kcal/mol ML MUEs
on set-aside test molecules in spin-state splitting in comparison to 15-20x
higher errors from feature sets that encode whole-molecule structural
information. Systematic feature selection methods including univariate
filtering, recursive feature elimination, and direct optimization (e.g., random
forest and LASSO) are compared. Random-forest- or LASSO-selected subsets 4-5x
smaller than RAC-155 produce sub- to 1-kcal/mol spin-splitting MUEs, with good
transferability to metal-ligand bond length prediction (0.004-5 {\AA} MUE) and
redox potential on a smaller data set (0.2-0.3 eV MUE). Evaluation of feature
selection results across property sets reveals the relative importance of
local, electronic descriptors (e.g., electronegativity, atomic number) in
spin-splitting and distal, steric effects in redox potential and bond lengths.Comment: 43 double spaced pages, 11 figures, 4 table
Integrated micro X-ray fluorescence and chemometric analysis for printed circuit boards recycling
A novel approach, based on micro X-ray fluorescence (μXRF), was developed to define
an efficient and fast automatic recognition procedure finalized to detect and
topologically assess the presence of the different elements in waste electrical and
electronic equipment (WEEE). More specifically, selected end-of-life (EOL) iPhone
printed circuit boards (PCB) were investigated, whose technological improvement
during time, can dramatically influence the recycling strategies (i.e. presence of
different electronic components, in terms of size, shape, disposition and related
elemental content). The implemented μXRF-based techniques allow to preliminary
set up simple and fast quality control strategies based on the full recognition and
characterization of precious and rare earth elements as detected inside the electronic
boards. Furthermore, the proposed approach allows to identify the presence
and the physical-chemical attributes of the other materials (i.e. mainly polymers),
influencing the further physical-mechanical processing steps addressed to realize
a pre-concentration of the valuable elements inside the PCB milled fractions, before
the final chemical recovery
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