923 research outputs found
Sonochemical route for mesoporous silica-coated magnetic nanoparticles towards pH-triggered drug delivery system
This work reports a pH-triggered release system based on core@shell mesoporous magnetic nanoparticles (MNP@mSiO2) obtained using a simple and rapid ultrasound-assisted method. Performed characterization reveals magnetic cores of Fe2.9Mn0.1O4 (38 ± 6 nm) and specific loss power values adequate for hyperthermia (463 W/g), surrounded by a mesoporous silica shell (10 ± 2 nm) with large surface area (269 m2 g-1) functionalized with hydroxyl groups (-OH). MNP@mSiO2 were loaded with DOX and amino-silane grops, providing pH-triggered DOX release at acidic environments, driving by dipolar intermolecular interactions. The experimental DOX release kinetics at pH 5.5, 6.6 and 7.4 were determined and adjusted to Gompertz dissolution model (NashâSutcliffe efficiency coefficient (NSE>0.9)), where the only strongly pH-dependent variable is the percentage of DOX released. The pH-triggered response observed in the system was ~20% of the DOX loaded into the MNP@mSiO2 is released at pH 6.6 or 7.4, whereas up to 80 wt% is released at pH 5.5. Time to 50% of release and dissociation rate of the system remaining constant, suggesting no-pH influence on these parameters. The biological assays highlight negligible hemolytic effect and cytocompatibility of the hybrid material, pointing out the potential use of MNP@mSiO2 as a magnetic driven drug delivery system with pH-triggered drug release kinetics at acidic environments. These results probe the feasibility of sonochemical methods in the elaboration of biocompatible and controlled properties nanomaterials for drug release applications, with the advantage of accurately responses predictions by mathematical model and using minimal processing steps or laboratory equipment. © 2021 The Author
Quantum field theory approach to the optical conductivity of strained and deformed graphene
The computation of the optical conductivity of strained and deformed graphene is discussed within the framework of quantum field theory in curved spaces. The analytical solutions of the Dirac equation in an arbitrary static background geometry for one dimensional periodic deformations are computed, together with the corresponding Dirac propagator. Analytical expressions are given for the optical conductivity of strained and deformed graphene associated with both intra and interbrand transitions. The special case of small deformations is discussed and the result compared to the prediction of the tight-binding model.The authors acknowledge ïŹnancial supportfrom the Brazilian agencies FAPESP (Fundação de Amparo Ă Pesquisa do Estado de SĂŁo Paulo) and CNPq (Conselho Nacional de Desenvolvimento CientĂïŹco e TecnolĂłgico)
Soil organisms in organic and conventional cropping systems.
Apesar do crescente interesse pela agricultura orgĂąnica, sĂŁo poucas as informaçÔes de pesquisa disponĂveis sobre o assunto. Assim, num Argissolo Vermelho-Amarelo distrĂłfico foram comparados os efeitos de sistemas de cultivo orgĂąnico e convencional, para as culturas do tomate (Lycopersicum esculentum) e do milho (Zea mays), sobre a comunidade de organismos do solo e suas atividades. As populaçÔes de fungos,bactĂ©rias e actinomicetos, determinadas pela contagem de colĂŽnias em meio de cultura, foram semelhantes para os dois sistemas de produção. A atividade microbiana, avaliada pela evolução de CO2, manteve-se superior no sistema orgĂąnico, sendo que em determinadas avaliaçÔes foi o dobro da evolução verificada no sistema convencional. O nĂșmero de espĂ©cimes de minhoca foi praticamente dez vezes maior no sistema orgĂąnico. NĂŁo foi observada diferença na taxa de decomposição de matĂ©ria orgĂąnica entre os dois sistemas. De modo geral, o nĂșmero de indivĂduos de microartrĂłpodos foi superior no sistema orgĂąnico do que no sistema convencional, refletindo no maior Ăndice de diversidade de Shannon. As maiores populaçÔes de insetos foram as da ordem Collembola, enquanto para os ĂĄcaros a maior população foi a da superfamĂlia Oribatuloidea. IndivĂduos dos grupos Aranae, Chilopoda, Dyplopoda, Pauropoda, Protura e Symphyla foram ocasionalmente coletados e de forma similar entre os sistemas
The Fluorescence Detector of the Pierre Auger Observatory
The Pierre Auger Observatory is a hybrid detector for ultra-high energy
cosmic rays. It combines a surface array to measure secondary particles at
ground level together with a fluorescence detector to measure the development
of air showers in the atmosphere above the array. The fluorescence detector
comprises 24 large telescopes specialized for measuring the nitrogen
fluorescence caused by charged particles of cosmic ray air showers. In this
paper we describe the components of the fluorescence detector including its
optical system, the design of the camera, the electronics, and the systems for
relative and absolute calibration. We also discuss the operation and the
monitoring of the detector. Finally, we evaluate the detector performance and
precision of shower reconstructions.Comment: 53 pages. Submitted to Nuclear Instruments and Methods in Physics
Research Section
The exposure of the hybrid detector of the Pierre Auger Observatory
The Pierre Auger Observatory is a detector for ultra-high energy cosmic rays.
It consists of a surface array to measure secondary particles at ground level
and a fluorescence detector to measure the development of air showers in the
atmosphere above the array. The "hybrid" detection mode combines the
information from the two subsystems. We describe the determination of the
hybrid exposure for events observed by the fluorescence telescopes in
coincidence with at least one water-Cherenkov detector of the surface array. A
detailed knowledge of the time dependence of the detection operations is
crucial for an accurate evaluation of the exposure. We discuss the relevance of
monitoring data collected during operations, such as the status of the
fluorescence detector, background light and atmospheric conditions, that are
used in both simulation and reconstruction.Comment: Paper accepted by Astroparticle Physic
Update on the correlation of the highest energy cosmic rays with nearby extragalactic matter
Data collected by the Pierre Auger Observatory through 31 August 2007 showed
evidence for anisotropy in the arrival directions of cosmic rays above the
Greisen-Zatsepin-Kuz'min energy threshold, \nobreak{eV}. The
anisotropy was measured by the fraction of arrival directions that are less
than from the position of an active galactic nucleus within 75 Mpc
(using the V\'eron-Cetty and V\'eron catalog). An updated
measurement of this fraction is reported here using the arrival directions of
cosmic rays recorded above the same energy threshold through 31 December 2009.
The number of arrival directions has increased from 27 to 69, allowing a more
precise measurement. The correlating fraction is , compared
with expected for isotropic cosmic rays. This is down from the early
estimate of . The enlarged set of arrival directions is
examined also in relation to other populations of nearby extragalactic objects:
galaxies in the 2 Microns All Sky Survey and active galactic nuclei detected in
hard X-rays by the Swift Burst Alert Telescope. A celestial region around the
position of the radiogalaxy Cen A has the largest excess of arrival directions
relative to isotropic expectations. The 2-point autocorrelation function is
shown for the enlarged set of arrival directions and compared to the isotropic
expectation.Comment: Accepted for publication in Astroparticle Physics on 31 August 201
Advanced functionality for radio analysis in the Offline software framework of the Pierre Auger Observatory
The advent of the Auger Engineering Radio Array (AERA) necessitates the
development of a powerful framework for the analysis of radio measurements of
cosmic ray air showers. As AERA performs "radio-hybrid" measurements of air
shower radio emission in coincidence with the surface particle detectors and
fluorescence telescopes of the Pierre Auger Observatory, the radio analysis
functionality had to be incorporated in the existing hybrid analysis solutions
for fluoresence and surface detector data. This goal has been achieved in a
natural way by extending the existing Auger Offline software framework with
radio functionality. In this article, we lay out the design, highlights and
features of the radio extension implemented in the Auger Offline framework. Its
functionality has achieved a high degree of sophistication and offers advanced
features such as vectorial reconstruction of the electric field, advanced
signal processing algorithms, a transparent and efficient handling of FFTs, a
very detailed simulation of detector effects, and the read-in of multiple data
formats including data from various radio simulation codes. The source code of
this radio functionality can be made available to interested parties on
request.Comment: accepted for publication in NIM A, 13 pages, minor corrections to
author list and references in v
Search for First Harmonic Modulation in the Right Ascension Distribution of Cosmic Rays Detected at the Pierre Auger Observatory
We present the results of searches for dipolar-type anisotropies in different
energy ranges above eV with the surface detector array of
the Pierre Auger Observatory, reporting on both the phase and the amplitude
measurements of the first harmonic modulation in the right-ascension
distribution. Upper limits on the amplitudes are obtained, which provide the
most stringent bounds at present, being below 2% at 99% for EeV
energies. We also compare our results to those of previous experiments as well
as with some theoretical expectations.Comment: 28 pages, 11 figure
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