368 research outputs found
Small variations in reaction conditions tune carbon dot fluorescence
The development of robust and reproducible synthetic strategies for the production of carbon dots with improved fluorescence quantum yields and distinct emission profiles is of great relevance given the vast range of applications of CDs. The fundamental understanding at a molecular level of their formation mechanism, chemical structure and how these parameters are correlated to their photoluminescence (PL) properties is thus essential. In this study, we describe the synthesis and structural characterization of a range of CDs with distinct physico-chemical properties. The materials were prepared under three minutes of microwave irradiation using the same common starting materials (GlcNH2·HCl 1 and EDA 2) but modifying the stoichiometry of the reagents. We show that small changes in reaction conditions leads to the tailoring of the fluorescent behaviour of the CDs from apparent blue to green emission. Structural analysis of the different CD samples suggested different reaction pathways during the CD formation and surface passivation, with the latter step being key to the observed differences. Moreover, we demonstrate that the different materials also respond reversibly to changes in pH, which we can attribute to different behaviour towards protonation/deprotonation events of distinct emission domains present within each nanomaterial. Our results highlight the importance of understanding the reaction pathways that lead to the formation of this carbon-based nanomaterials and how this can be exploited to develop tailored materials towards specific applications
Measuring the Refractive Index and Sub-Nanometre Surface Functionalisation of Nanoparticles in Suspension
Direct measurements to determine the degree of surface coverage of nanoparticles by functional moieties are rare, with current strategies requiring a high level of expertise and expensive equipment. Here, a practical method to determine the ratio of the volume of the functionalisation layer to the particle volume based on measuring the refractive index of nanoparticles in suspension is proposed. As a proof of concept, this technique is applied to poly(methyl methacrylate) (PMMA) nanoparticles and semicrystalline carbon dots functionalised with different surface moieties, yielding refractive indices that are commensurate to those from previous literature and Mie theory. In doing so, it is demonstrated that this technique is able to optically detect differences in surface functionalisation or composition of nanometre-sized particles. This non-destructive and rapid method is well-suited for in situ industrial particle characterisation and biological applications
Dynamic Edematous Response of the Human Heart to Myocardial Infarction Implications for Assessing Myocardial Area at Risk and Salvage
BACKGROUND: Clinical protocols aimed to characterize the post-myocardial
infarction (MI) heart by cardiac magnetic resonance (CMR) need to be
standardized to take account of dynamic biological phenomena evolving
early after the index ischemic event. Here, we evaluated the time course
of edema reaction in patients with ST-segment-elevation MI by CMR and
assessed its implications for myocardium-at-risk (MaR) quantification
both in patients and in a large-animal model.
METHODS: A total of 16 patients with anterior ST-segment-elevation MI
successfully treated by primary angioplasty and 16 matched controls were
prospectively recruited. In total, 94 clinical CMR examinations were
performed: patients with ST-segment-elevation MI were serially scanned
(within the first 3 hours after reperfusion and at 1, 4, 7, and 40
days), and controls were scanned only once. T2 relaxation time in the
myocardium (T2 mapping) and the extent of edema on T2-weighted short-tau
triple inversion-recovery (ie, CMR-MaR) were evaluated at all time
points. In the experimental study, 20 pigs underwent 40-minute
ischemia/reperfusion followed by serial CMR examinations at 120 minutes
and 1, 4, and 7 days after reperfusion. Reference MaR was assessed by
contrast-multidetector computed tomography during the index coronary
occlusion. Generalized linear mixed models were used to take account of
repeated measurements.
RESULTS: In humans, T2 relaxation time in the ischemic myocardium
declines significantly from early after reperfusion to 24 hours, and
then increases up to day 4, reaching a plateau from which it decreases
from day 7. Consequently, edema extent measured by T2-weighted short-tau
triple inversion-recovery (CMR-MaR) varied with the timing of the CMR
examination. These findings were confirmed in the experimental model by
showing that only CMR-MaR values for day 4 and day 7 postreperfusion,
coinciding with the deferred edema wave, were similar to values measured
by reference contrast-multidetector computed tomography.
CONCLUSIONS: Post-MI edema in patients follows a bimodal pattern that
affects CMR estimates of MaR. Dynamic changes in
post-ST-segment-elevation MI edema highlight the need for
standardization of CMR timing to retrospectively delineate MaR and
quantify myocardial salvage. According to the present clinical and
experimental data, a time window between days 4 and 7 post-MI seems a
good compromise solution for standardization. Further studies are needed
to study the effect of other factors on these variables.This study was partially supported by a competitive grant from the
Spanish Society of Cardiology (Proyectos de Investigacion Traslacional
en Cardiologia de la Sociedad Espanola de Cardiologia 2015, for the
project Caracterizacion tiSUlar miocaRdica con resonancia magnetica en
pacientes tras inFarto agudo de mioCardio con elevacioN de ST sometidos
a angloplastia Coronaria primaria. Estudio SURF-CNIC), by a competitive
grant from the Carlos III Institute of Health-Fondo de Investigacion
Sanitaria- and the European Regional Development Fund (ERDF/FEDER)
(PI10/02268 and PI13/01979), the Spanish Ministry of economy, industry,
and competitiveness (MEIC) and ERDF/FEDER SAF2013-49663-EXP. Dr
Fernandez-Jimenez holds a FICNIC fellowship from the Fundacio Jesus
Serra, the Fundacion Interhospitalaria de Investigacion Cardiovascular,
and the Centro Nacional de Investigaciones Cardiovasculares Carlos III
(CNIC), and Dr Aguero is a FP7-PEOPLE-2013-ITN-Cardionext fellow. This
study forms part of a Master Research Agreement between the CNIC and
Philips Healthcare, and is part of a bilateral research program between
Hospital de Salamanca Cardiology Department and the CNIC. This research
program is part of an institutional agreement between FIIS-Fundacion
Jimenez Diaz and CNIC. The CNIC is supported by the MEIC and the Pro
CNIC Foundation, and is a Severo Ochoa Center of Excellence (MEIC award
SEV-2015-0505).S
Towards a new generation axion helioscope
We study the feasibility of a new generation axion helioscope, the most
ambitious and promising detector of solar axions to date. We show that large
improvements in magnetic field volume, x-ray focusing optics and detector
backgrounds are possible beyond those achieved in the CERN Axion Solar
Telescope (CAST). For hadronic models, a sensitivity to the axion-photon
coupling of \gagamma\gtrsim {\rm few} \times 10^{-12} GeV is
conceivable, 1--1.5 orders of magnitude beyond the CAST sensitivity. If axions
also couple to electrons, the Sun produces a larger flux for the same value of
the Peccei-Quinn scale, allowing one to probe a broader class of models. Except
for the axion dark matter searches, this experiment will be the most sensitive
axion search ever, reaching or surpassing the stringent bounds from SN1987A and
possibly testing the axion interpretation of anomalous white-dwarf cooling that
predicts of a few meV. Beyond axions, this new instrument will probe
entirely unexplored ranges of parameters for a large variety of axion-like
particles (ALPs) and other novel excitations at the low-energy frontier of
elementary particle physics.Comment: 37 pages, 11 figures, accepted for publication in JCA
The International Axion Observatory (IAXO)
The International Axion Observatory (IAXO) is a new generation axion
helioscope aiming at a sensitivity to the axion-photon coupling of a few
10 GeV, i.e. 1 - 1.5 orders of magnitude beyond the one currently
achieved by CAST. The project relies on improvements in magnetic field volume
together with extensive use of x-ray focusing optics and low background
detectors, innovations already successfully tested in CAST. Additional physics
cases of IAXO could include the detection of electron-coupled axions invoked to
solve the white dwarfs anomaly, relic axions, and a large variety of more
generic axion-like particles (ALPs) and other novel excitations at the
low-energy frontier of elementary particle physics. This contribution is a
summary of our paper [1] to which we refer for further details.Comment: 4 pages, 2 figures. To appear in the proceedings of the 7th Patras
Workshop on Axions, WIMPs and WISPs, Mykonos, Greece, 201
CAST constraints on the axion-electron coupling
In non-hadronic axion models, which have a tree-level axion-electron
interaction, the Sun produces a strong axion flux by bremsstrahlung, Compton
scattering, and axio-recombination, the "BCA processes." Based on a new
calculation of this flux, including for the first time axio-recombination, we
derive limits on the axion-electron Yukawa coupling g_ae and axion-photon
interaction strength g_ag using the CAST phase-I data (vacuum phase). For m_a <
10 meV/c2 we find g_ag x g_ae< 8.1 x 10^-23 GeV^-1 at 95% CL. We stress that a
next-generation axion helioscope such as the proposed IAXO could push this
sensitivity into a range beyond stellar energy-loss limits and test the
hypothesis that white-dwarf cooling is dominated by axion emission
Epigenetic Silencing of Host Cell Defense Genes Enhances Intracellular Survival of the Rickettsial Pathogen Anaplasma phagocytophilum
Intracellular bacteria have evolved mechanisms that promote survival within hostile host environments, often resulting in functional dysregulation and disease. Using the Anaplasma phagocytophilum–infected granulocyte model, we establish a link between host chromatin modifications, defense gene transcription and intracellular bacterial infection. Infection of THP-1 cells with A. phagocytophilum led to silencing of host defense gene expression. Histone deacetylase 1 (HDAC1) expression, activity and binding to the defense gene promoters significantly increased during infection, which resulted in decreased histone H3 acetylation in infected cells. HDAC1 overexpression enhanced infection, whereas pharmacologic and siRNA HDAC1 inhibition significantly decreased bacterial load. HDAC2 does not seem to be involved, since HDAC2 silencing by siRNA had no effect on A. phagocytophilum intracellular propagation. These data indicate that HDAC up-regulation and epigenetic silencing of host cell defense genes is required for A. phagocytophilum infection. Bacterial epigenetic regulation of host cell gene transcription could be a general mechanism that enhances intracellular pathogen survival while altering cell function and promoting disease
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Surface brightness-colour relations of dwarf stars from detached eclipsing binaries: I. Calibrating sample
Aims. Surface brightness - colour relations (SBCRs) are very useful tools for predicting the angular diameters of stars. They offer the possibility to calculate very precise spectrophotometric distances by the eclipsing binary method or the Baade-Wesselink method. Double-lined Detached Eclipsing Binary stars (SB2 DEBs) with precisely known trigonometric parallaxes allow for a calibration of SBCRs with unprecedented precision. In order to improve such calibrations, it is important to enlarge the calibration sample of suitable eclipsing binaries with very precisely determined physical parameters. Methods. We carefully chose a sample of ten SB2 DEBs in the solar neighbourhood which contain inactive main-sequence components. The components have spectral types from early A to early K. All systems have high-precision parallaxes from the Gaia mission. We analysed high precision ground- and space-based photometry simultaneously with the radial velocity curves derived from HARPS spectra. We used spectral disentangling to obtain the individual spectra of the components and used these to derive precise atmospheric parameters and chemical abundances. For almost all components, we derived precise surface temperatures and metallicities. Results. We derived absolute dimensions for 20 stars with an average precision of 0.2% and 0.5% for masses and radii, respectively. Three systems show slow apsidal motion. One system, HD 32129, is most likely a triple system with a much fainter K6V companion. Also three systems contain metallic-line components and show strong enhancements of barium and ittrium. Conclusions. The components of all systems compare well to the SBCR derived before from the detached eclipsing binary stars. With a possible exception of HD 32129, they can be used to calibrate SBCRs with a precision better than 1% with available Gaia DR3 parallaxes
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