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Nanotailoring Stereolithography Resins for Unique Applications using Carbon Nanotubes
Nanostructured materials and exploiting their properties in stereolithography (SL) may open
new markets for unique rapidly manufactured functional devices. Controlled amounts of multiwalled carbon nanotubes (MWCNTs) were successfully dispersed in SL epoxy-based resins and
complex three-dimensional (3D) parts were successfully fabricated by means of a multi-material
SL setup. The effect of the nanosized filler was evaluated using mechanical testing. Small
dispersions of MWCNTs resulted in significant effects on the physical properties of the
polymerized resin. A MWCNT concentration of .05 wt% (w/v) in DSM Somos® WaterShed™
11120 resin increased the ultimate tensile stress and fracture stress an average of 17% and 37%,
respectively. Electron microscopy was used to examine the morphology of the nanocomposite
and results showed affinity between the MWCNTs and SL resin and identified buckled
nanotubes that illustrated strong interfacial bonding. These improved physical properties may
provide opportunities for using nanocomposite SL resins in end-use applications. Varying types
and concentrations of nanomaterials can be used to tailor existing SL resins for particular
applications.Mechanical Engineerin
Evaluation of the Use of UAV-Derived Vegetation Indices and Environmental Variables for Grapevine Water Status Monitoring Based on Machine Learning Algorithms and SHAP Analysis
(c) The Author/sfals
Searching for TeV DM evidence from Dwarf Irregular Galaxies with the HAWC Observatory
The dynamics of dwarf irregular (dIrr) galaxies are observed to be dominated by dark matter (DM). Recently, the DM density distribution has been studied for 31 dIrrs. Their extended DM halo (Burket type profile) makes these objects good candidates for DM searches. Located in Puebla (Mexico), the High Altitude Water Cherenkov (HAWC) Observatory is an optimal instrument to perform such DM searches, because of its large sky coverage (8.4 sr per day). We analyzed a set of two years of HAWC data and we found no significant DM signal from dIrr galaxies. We present the upper limits for DM annihilation cross-section with dIrr galaxies
Density-Matrix functional theory of strongly-correlated lattice fermions
A density functional theory (DFT) of lattice fermion models is presented,
which uses the single-particle density matrix gamma_{ij} as basic variable. A
simple, explicit approximation to the interaction-energy functional W[gamma] of
the Hubbard model is derived from exact dimer results, scaling properties of
W[gamma] and known limits. Systematic tests on the one-dimensional chain show a
remarkable agreement with theBethe-Ansatz exact solution for all interaction
regimes and band fillings. New results are obtained for the ground-state
energyand charge-excitation gap in two dimensions. A successful description of
strong electron correlations within DFT is achieved.Comment: 15 pages, 6 figures Submitted to PR
New Cataclysmic Variables and other Exotic Binaries in the Globular Cluster 47 Tucanae
We present 22 new (+3 confirmed) cataclysmic variables (CVs) in the non
core-collapsed globular cluster 47 Tucanae (47 Tuc). The total number of CVs in
the cluster is now 43, the largest sample in any globular cluster so far. For
the identifications we used near-ultraviolet (NUV) and optical images from the
Hubble Space Telescope, in combination with X-ray results from the Chandra
X-ray Observatory. This allowed us to build the deepest NUV CV luminosity
function of the cluster to date. We found that the CVs in 47 Tuc are more
concentrated towards the cluster center than the main sequence turnoff stars.
We compared our results to the CV populations of the core-collapsed globular
clusters NGC 6397 and NGC 6752. We found that 47 Tuc has fewer bright CVs per
unit mass than those two other clusters. That suggests that dynamical
interactions in core-collapsed clusters play a major role creating new CVs. In
47 Tuc, the CV population is probably dominated by primordial and old
dynamically formed systems. We estimated that the CVs in 47 Tuc have total
masses of approx. 1.4 M_sun. We also found that the X-ray luminosity function
of the CVs in the three clusters is bimodal. Additionally, we discuss a
possible double degenerate system and an intriguing/unclassified object.
Finally, we present four systems that could be millisecond pulsar companions
given their X-ray and NUV/optical colors. For one of them we present very
strong evidence for being an ablated companion. The other three could be CO- or
He-WDs.Comment: Published on MNRAS. 31 Pages, 23 Figures, 5 Tables. Minor changes
with respect to previous arXiv versio
Interaction energy functional for lattice density functional theory: Applications to one-, two- and three-dimensional Hubbard models
The Hubbard model is investigated in the framework of lattice density
functional theory (LDFT). The single-particle density matrix with
respect the lattice sites is considered as the basic variable of the many-body
problem. A new approximation to the interaction-energy functional
is proposed which is based on its scaling properties and which recovers exactly
the limit of strong electron correlations at half-band filling. In this way, a
more accurate description of is obtained throughout the domain of
representability of , including the crossover from weak to strong
correlations. As examples of applications results are given for the
ground-state energy, charge-excitation gap, and charge susceptibility of the
Hubbard model in one-, two-, and three-dimensional lattices. The performance of
the method is demonstrated by comparison with available exact solutions, with
numerical calculations, and with LDFT using a simpler dimer ansatz for .
Goals and limitations of the different approximations are discussed.Comment: 25 pages and 8 figures, submitted to Phys. Rev.
Discovery of near-ultraviolet counterparts to millisecond pulsars in the globular cluster 47 Tucanae
We report the discovery of the likely white dwarf companions to radio
millisecond pulsars 47 Tuc Q and 47 Tuc S in the globular cluster 47 Tucanae.
These blue stars were found in near-ultraviolet images from the Hubble Space
Telescope for which we derived accurate absolute astrometry, and are located at
positions consistent with the radio coordinates to within 0.016 arcsec
(0.2sigma). We present near-ultraviolet and optical colours for the previously
identified companion to millisecond pulsar 47 Tuc U, and we unambiguously
confirm the tentative prior identifications of the optical counterparts to 47
Tuc T and 47 Tuc Y. For the latter, we present its radio-timing solution for
the first time. We find that all five near-ultraviolet counterparts have
U300-B390 colours that are consistent with He white dwarf cooling models for
masses ~0.16-0.3 Msun and cooling ages within ~0.1-6 Gyr. The Ha-R625 colours
of 47 Tuc U and 47 Tuc T indicate the presence of a strong Ha absorption line,
as expected for white dwarfs with an H envelope.Comment: Accepted for publication on MNRAS. 12 pages, 5 figures, 3 table
Unstable fields in Kerr spacetimes
We show that both the interior region of a Kerr black
hole and the Kerr naked singularity admit unstable solutions of the
Teukolsky equation for any value of the spin weight. For every harmonic number
there is at least one axially symmetric mode that grows exponentially in time
and decays properly in the radial directions. These can be used as Debye
potentials to generate solutions for the scalar, Weyl spinor, Maxwell and
linearized gravity field equations on these backgrounds, satisfying appropriate
spatial boundary conditions and growing exponentially in time, as shown in
detail for the Maxwell case. It is suggested that the existence of the unstable
modes is related to the so called "time machine" region, where the axial
Killing vector field is time-like, and the Teukolsky equation, restricted to
axially symmetric fields, changes its character from hyperbolic to elliptic
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