370 research outputs found
An Electromagnetic Study of the Impact of Brain Anatomy on Deep Brain Stimulation
An electromagnetic simulation was performed to assess the volume of tissue activated on deep brain stimulation for two patients randomly selected. The finite element method is used to calculate the electric field distribution that predicts the volume of tissue activated. High-resolution magnetic resonance images are utilized to create patient-specific anatomical models of the subthalamic nucleus and the internal pallidum. The results confirmed the influence of brain anatomy leading to different shape and volume of tissue activated despite similar technical features. Thus, a patient-specific model and an adequate choice of stimulation parameters are crucial on deep brain stimulation outcomes.S
Electrical conductivity of oxidized-graphenic nanoplatelets obtained from bamboo: Effect of the oxygen content
The large-scale production of graphene and reduced-graphene oxide (rGO) requires low-cost and eco-friendly synthesis methods. We employed a new, simple, cost-effective pyrolytic method to synthetize oxidized-graphenic nanoplatelets (OGNP) using bamboo pyroligneous acid (BPA) as a source. Thorough analyses via high-resolution transmission electron microscopy and electron energy-loss spectroscopy provides a complete structural and chemical description at the local scale of these samples. In particular, we found that at the highest carbonization temperature the OGNP-BPA are mainly in a sp2 bonding configuration (sp2 fraction of 87%). To determine the electrical properties of single nanoplatelets, these were contacted by Pt nanowires deposited through focused-ion-beam-induced deposition techniques. Increased conductivity by two orders of magnitude is observed as oxygen content decreases from 17% to 5%, reaching a value of 2.3 103 S m-1 at the lowest oxygen content. Temperature-dependent conductivity reveals a semiconductor transport behavior, described by the Mott three-dimensional variable range hopping mechanism. From the localization length, we estimate a band-gap value of 0.22(2) eV for an oxygen content of 5%. This investigation demonstrates the great potential of the OGNP-BPA for technological applications, given that their structural and electrical behavior is similar to the highly reduced rGO sheets obtained by more sophisticated conventional synthesis methods
Somatostatin subtype-2 receptor-targeted metal-based anticancer complexes
Conjugates of a dicarba analogue of octreotide, a potent somatostatin agonist whose receptors are overexpressed on tumor cells, with [PtCl 2(dap)] (dap = 1-(carboxylic acid)-1,2-diaminoethane) (3), [(η 6-bip)Os(4-CO 2-pico)Cl] (bip = biphenyl, pico = picolinate) (4), [(η 6-p-cym)RuCl(dap)] + (p-cym = p-cymene) (5), and [(η 6-p-cym)RuCl(imidazole-CO 2H)(PPh 3)] + (6), were synthesized by using a solid-phase approach. Conjugates 3-5 readily underwent hydrolysis and DNA binding, whereas conjugate 6 was inert to ligand substitution. NMR spectroscopy and molecular dynamics calculations showed that conjugate formation does not perturb the overall peptide structure. Only 6 exhibited antiproliferative activity in human tumor cells (IC 50 = 63 ± 2 μ in MCF-7 cells and IC 50 = 26 ± 3 μ in DU-145 cells) with active participation of somatostatin receptors in cellular uptake. Similar cytotoxic activity was found in a normal cell line (IC 50 = 45 ± 2.6 μ in CHO cells), which can be attributed to a similar level of expression of somatostatin subtype-2 receptor. These studies provide new insights into the effect of receptor-binding peptide conjugation on the activity of metal-based anticancer drugs, and demonstrate the potential of such hybrid compounds to target tumor cells specifically. © 2012 American Chemical Society
K2-137 b: an Earth-sized planet in a 4.3-hour orbit around an M-dwarf
We report the discovery from K2 of a transiting terrestrial planet in an
ultra-short-period orbit around an M3-dwarf. K2-137 b completes an orbit in
only 4.3 hours, the second-shortest orbital period of any known planet, just 4
minutes longer than that of KOI 1843.03, which also orbits an M-dwarf. Using a
combination of archival images, AO imaging, RV measurements, and light curve
modelling, we show that no plausible eclipsing binary scenario can explain the
K2 light curve, and thus confirm the planetary nature of the system. The
planet, whose radius we determine to be 0.89 +/- 0.09 Earth radii, and which
must have a iron mass fraction greater than 0.45, orbits a star of mass 0.463
+/- 0.052 Msol and radius 0.442 +/- 0.044 Rsol.Comment: 12 pages, 9 figures, accepted for publication in MNRA
Detailed Radio to Soft Gamma-ray Studies of the 2005 Outburst of the New X-ray Transient XTE J1818-245
XTE J1818-245 is an X-ray nova that experienced an outburst in 2005, first
seen by the RXTE satellite. The source was observed simultaneously at various
wavelengths up to soft gamma-rays with the INTEGRAL satellite, from 2005
February to September. X-ray novae are extreme systems that often harbor a
black hole, and are known to emit throughout the electromagnetic spectrum when
in outburst. We analyzed radio, (N)IR, optical, X-ray and soft gamma-ray
observations and constructed simultaneous broad-band X-ray spectra. Analyzing
both the light curves in various energy ranges and the hardness-intensity
diagram enabled us to study the long-term behavior of the source. Spectral
parameters were typical of the Soft Intermediate States and the High Soft
States of a black hole candidate. The source showed relatively small spectral
variations in X-rays with considerable flux variation in radio. Spectral
studies showed that the accretion disc cooled down from 0.64 to 0.27 keV in 100
days and that the total flux decreased while the relative flux of the hot
medium increased. Radio emission was detected several times, and,
interestingly, five days after entering the HSS. Modeling the spectral energy
distribution from the radio to the soft gamma-rays reveals that the radio
flares arise from several ejection events. XTE J1818-245 is likely a black hole
candidate transient source that might be closer than the Galactic Bulge. The
results from the data analysis trace the physical changes that took place in
the system at a maximum bolometric luminosity of (0.4-0.9)e38 erg/s (assuming a
distance between 2.8-4.3 kpc) and they are discussed within the context of disc
and jet models.Comment: Accepted for publication in Astronomy and Astrophysics. 11 Figures, 3
Table
The transiting multi-planet system HD3167: a 5.7 MEarth Super-Earth and a 8.3 MEarth mini-Neptune
HD3167 is a bright (V=8.9 mag) K0V star observed by the NASA's K2 space
mission during its Campaign 8. It has been recently found to host two small
transiting planets, namely, HD3167b, an ultra short period (0.96 d)
super-Earth, and HD3167c, a mini-Neptune on a relatively long-period orbit
(29.85 d). Here we present an intensive radial velocity follow-up of HD3167
performed with the FIES@NOT, [email protected], and HARPS-N@TNG spectrographs. We
revise the system parameters and determine radii, masses, and densities of the
two transiting planets by combining the K2 photometry with our spectroscopic
data. With a mass of 5.69+/-0.44 MEarth, radius of 1.574+/-0.054 REarth, and
mean density of 8.00(+1.0)(-0.98) g/cm^3, HD3167b joins the small group of
ultra-short period planets known to have a rocky terrestrial composition.
HD3167c has a mass of 8.33 (+1.79)(-1.85) MEarth and a radius of
2.740(+0.106)(-0.100) REarth, yielding a mean density of 2.21(+0.56)(-0.53)
g/cm^3, indicative of a planet with a composition comprising a solid core
surrounded by a thick atmospheric envelope. The rather large pressure scale
height (about 350 km) and the brightness of the host star make HD3167c an ideal
target for atmospheric characterization via transmission spectroscopy across a
broad range of wavelengths. We found evidence of additional signals in the
radial velocity measurements but the currently available data set does not
allow us to draw any firm conclusion on the origin of the observed variation.Comment: 18 pages, 11 figures, 5 table
EPIC 219388192 b - an inhabitant of the brown dwarf desert in the Ruprecht 147 open cluster
We report the discovery of EPIC 219388192 b, a transiting brown dwarf in a
5.3-day orbit around a member star of Ruprecht-147, the oldest nearby open
cluster association, which was photometrically monitored by K2 during its
Campaign 7. We combine the K2 time-series data with ground-based adaptive
optics imaging and high resolution spectroscopy to rule out false positive
scenarios and determine the main parameters of the system. EPIC 219388192 b has
a radius of =~ and mass of
=~, yielding a mean density of
~. The host star is nearly a Solar twin with
mass =~, radius
=~, effective temperature
=~K and iron abundance [Fe/H]=~dex.
Its age, spectroscopic distance, and reddening are consistent with those of
Ruprecht-147, corroborating its cluster membership. EPIC 219388192 b is the
first brown dwarf with precise determinations of mass, radius and age, and
serves as benchmark for evolutionary models in the sub-stellar regime.Comment: 13 pages, 11 figures, 4 tables, submitted to AAS Journal
f(R) theories
Over the past decade, f(R) theories have been extensively studied as one of
the simplest modifications to General Relativity. In this article we review
various applications of f(R) theories to cosmology and gravity - such as
inflation, dark energy, local gravity constraints, cosmological perturbations,
and spherically symmetric solutions in weak and strong gravitational
backgrounds. We present a number of ways to distinguish those theories from
General Relativity observationally and experimentally. We also discuss the
extension to other modified gravity theories such as Brans-Dicke theory and
Gauss-Bonnet gravity, and address models that can satisfy both cosmological and
local gravity constraints.Comment: 156 pages, 14 figures, Invited review article in Living Reviews in
Relativity, Published version, Comments are welcom
Appraisal of MC2010 shear resistance approaches coupled with a residual flexural strength prediction model
In the present work the predictive performance of the two approaches proposed by
Model Code 2010 for the evaluation of the shear capacity of fiber reinforced concrete (FRC)
elements flexurally reinforced with conventional steel bars is assessed considering a database
(DBs) constituted by 80 FRC beams do not including conventional transverse reinforcements.
The accuracy of these shear models is evaluated by statistical analysis of the prediction ratio
between the experimental and estimated shear capacity of the beams of the DBs, and applying
the Demerit Points Classification approach for further information about the reliability of the
two approaches in design context. Due to the absence of the post-cracking experimental
characterization of the FRC used in several beams considered in the DBs, an approach was
developed for estimating the residual flexural strength parameters from the most relevant known
variables of steel fiber reinforcement mechanisms for concrete, namely the fiber volume and
aspect ratio, and the concrete compressive and tensile strength. The residual flexural strength
prediction model is assessed and its influence on the performance of the shear resistance models
is evaluatedSFRH/BDE/96381/2013 co-funded by CiviTest -
Pesquisa de Novos Materiais para a Engenharia Civil, Lda. and by FCT - Portuguese Foundation for
Science and Technology. The authors also acknowledge the support provided by the FCT project PTDC/ECM-EST/2635/201
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