1,808 research outputs found
Effect of graphene substrate on the SERS Spectra of Aromatic bifunctional molecules on metal nanoparticles
The design of molecular sensors plays a very important role within nanotechnology and
especially in the development of different devices for biomedical applications. Biosensors can be classified according to various criteria such as the type of interaction established between the recognition element and the analyte or the type of signal detection from the analyte
(transduction). When Raman spectroscopy is used as an optical transduction technique the
variations in the Raman signal due to the physical or chemical interaction between the analyte and the recognition element has to be detected. Therefore any significant improvement in the amplification of the optical sensor signal represents a breakthrough in the design of molecular sensors. In this sense, Surface-Enhanced Raman Spectroscopy (SERS) involves an enormous enhancement of the Raman signal from a molecule in the vicinity of a metal surface.
The main objective of this work is to evaluate the effect of a monolayer of graphene oxide (GO)
on the distribution of metal nanoparticles (NPs) and on the global SERS enhancement of paminothiophenol (pATP) and 4-mercaptobenzoic acid (4MBA) adsorbed on this substrate.
These aromatic bifunctional molecules are able to interact to metal NPs and also they offer the
possibility to link with biomolecules. Additionally by decorating Au or Ag NPs on graphene sheets, a coupled EM effect caused by the aggregation of the NPs and strong electronic
interactions between Au or Ag NPs and the graphene sheets are considered to be responsible
for the significantly enhanced Raman signal of the analytes [1-2]. Since there are increasing
needs for methods to conduct reproducible and sensitive Raman measurements, Grapheneenhanced
Raman Scattering (GERS) is emerging as an important method [3].Universidad de Málaga. Campus de Excelencia Internacional AndalucÃa Tech
Structural elucidation of o-linked glycopeptides by high energy collision-induced dissociation
O-linked glycopeptides that bear a GalNAc core with and without the presence of sialic acid have been analyzed by high energy collision-induced dissociation (CID). We show that the CID spectra from the glycosylated precursor ions contain sufficient information to identify the peptide sequence and to determine the glycosylated site(s). Asialo O-linked glycopeptides, previously prepared from a tryptic digest of bovine fetuin were studied. One of the glycopeptides contained only a single Hex (hexose)-HexNAc (N-acetylhexosamine) substitution at Thr262, whereas the other exhibited Hex-HexNAc moieties at both Thr262 and Ser264. In addition, sialo and asialo fetuin glycopeptides from a pronase digest were derivatized with t-butoxycarbonyl-tyrosine, and characterized by high energy CID analysis. The presence of a Galβ(1,3)GalNAc core structure at Ser264 was confirmed by using the substrate specificity of endo-α-N-acetylgalactosaminidase. These studies revealed the presence of a β-galactosidase specific for β(1,4) linkages in the endo-α-N-acetylgalactosaminidase preparation employed. Finally, the relative stability of N-and O-glycosyl bonds to high energy CID is addressed based upon comparison of the behavior of a synthetic N-linked glycopeptide with analogous O-linked structures
Holographic description of Kerr-Bolt-AdS-dS Spacetimes
We show that there exists a holographic 2D CFT description of a
Kerr-Bolt-AdS-dS spacetime. We first consider the wave equation of a massless
scalar field propagating in extremal Kerr-Bolt-AdS-dS spacetimes and find in
the "near region", the wave equation in extremal limit could be written in
terms of the quadratic Casimir. This suggests that there exist dual
CFT descriptions of these black holes. In the probe limit, we compute the
scattering amplitudes of the scalar off the extremal black holes and find
perfect agreement with the CFT prediction. Furthermore we study the holographic
description of the generic four dimensional non-extremal Kerr-Bolt-AdS-dS black
holes. We find that if focusing on the near-horizon region, for the massless
scalar scattering in the low-frequency limit, the radial equation could still
be rewritten as the quadratic Casimir, suggesting the existence of
dual 2D description. We read the temperatures of the dual CFT from the
conformal coordinates and obtain the central charges by studying the
near-horizon geometry of near-extremal black holes. We recover the macroscopic
entropy from the microscopic counting. We also show that for the superradiant
scattering, the retarded Green's functions and the corresponding absorption
cross sections are in perfect match with CFT prediction.Comment: 17 pages, typos corrected, references adde
Fermi edge singularities in X-ray spectra of strongly correlated fermions
We discuss the problem of the X-ray absorption in a system of interacting
fermions and, in particular, those features in the X-ray spectra that can be
used to discriminate between conventional Fermi-liquids and novel "strange
metals". Focusing on the case of purely forward scattering off the core-hole
potential, we account for the relevant interactions in the conduction band by
means of the bosonization technique. We find that the X-ray Fermi edge
singularities can still be present, although modified, even if the density of
states vanishes at the Fermi energy, and that, in general, the relationship
between the two appears to be quite subtle.Comment: Latex, 16 pages, Princeton preprin
Sustainability Improvement of a composite materials’ industry through recycling and re-engineering process approaches
Recent Advances in Mechanics and Materials in DesignThis case study was aimed at measuring and assessing the potential improvements that could be made on the eco-efficiency performance of a composite materials’ industry, specifically a glass fibre reinforced plastic (GFRP) pultrusion manufacturing company. For this purpose, all the issues involved in the pultrusion process of GFRP profiles were analysed, the current ecoefficiency performance of the company was determined, all the procedures applied in the production process were revised, and improvement strategies were planned and investigated with basis on the performed analysis. The new eco-efficiency ratios were estimated taking into account the implementation of new proceedings and procedures through re-engineering the manufacturing process and recycling approaches. These features lead to significant improvements on the sequent assessed eco-efficiency ratios, yielding to a more sustainable product and manufacturing process of pultruded GFRP profiles
Vertex Cover Kernelization Revisited: Upper and Lower Bounds for a Refined Parameter
An important result in the study of polynomial-time preprocessing shows that
there is an algorithm which given an instance (G,k) of Vertex Cover outputs an
equivalent instance (G',k') in polynomial time with the guarantee that G' has
at most 2k' vertices (and thus O((k')^2) edges) with k' <= k. Using the
terminology of parameterized complexity we say that k-Vertex Cover has a kernel
with 2k vertices. There is complexity-theoretic evidence that both 2k vertices
and Theta(k^2) edges are optimal for the kernel size. In this paper we consider
the Vertex Cover problem with a different parameter, the size fvs(G) of a
minimum feedback vertex set for G. This refined parameter is structurally
smaller than the parameter k associated to the vertex covering number vc(G)
since fvs(G) <= vc(G) and the difference can be arbitrarily large. We give a
kernel for Vertex Cover with a number of vertices that is cubic in fvs(G): an
instance (G,X,k) of Vertex Cover, where X is a feedback vertex set for G, can
be transformed in polynomial time into an equivalent instance (G',X',k') such
that |V(G')| <= 2k and |V(G')| <= O(|X'|^3). A similar result holds when the
feedback vertex set X is not given along with the input. In sharp contrast we
show that the Weighted Vertex Cover problem does not have a polynomial kernel
when parameterized by the cardinality of a given vertex cover of the graph
unless NP is in coNP/poly and the polynomial hierarchy collapses to the third
level.Comment: Published in "Theory of Computing Systems" as an Open Access
publicatio
Electromagnetic form factors of light vector mesons
The electromagnetic form factors G_E(q^2), G_M(q^2), and G_Q(q^2), charge
radii, magnetic and quadrupole moments, and decay widths of the light vector
mesons rho^+, K^{*+} and K^{*0} are calculated in a Lorentz-covariant,
Dyson-Schwinger equation based model using algebraic quark propagators that
incorporate confinement, asymptotic freedom, and dynamical chiral symmetry
breaking, and vector meson Bethe-Salpeter amplitudes closely related to the
pseudoscalar amplitudes obtained from phenomenological studies of pi and K
mesons. Calculated static properties of vector mesons include the charge radii
and magnetic moments: r_{rho+} = 0.61 fm, r_{K*+} = 0.54 fm, and r^2_{K*0} =
-0.048 fm^2; mu_{rho+} = 2.69, mu_{K*+} = 2.37, and mu_{K*0} = -0.40. The
calculated static limits of the rho-meson form factors are similar to those
obtained from light-front quantum mechanical calculations, but begin to differ
above q^2 = 1 GeV^2 due to the dynamical evolution of the quark propagators in
our approach.Comment: 8 pages of RevTeX, 5 eps figure
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 (Nash–Sutcliffe 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
Experimental study on polyester based concretes filled with glass fibre reinforced plastic recyclates – a contribution to composite materials sustainability
The development and applications of thermoset
polymeric composites, namely fibre reinforced plastics
(FRP), have shifted in the last decades more and more
into the mass market [1]. Despite of all advantages
associated to FRP based products, the increasing
production and consume also lead to an increasing
amount of FRP wastes, either end-of-lifecycle
products, or scrap and by-products generated by the
manufacturing process itself. Whereas thermoplastic
FRPs can be easily recycled, by remelting and
remoulding, recyclability of thermosetting FRPs
constitutes a more difficult task due to cross-linked
nature of resin matrix. To date, most of the thermoset
based FRP waste is being incinerated or landfilled,
leading to negative environmental impacts and
supplementary added costs to FRP producers and
suppliers. This actual framework is putting increasing
pressure on the industry to address the options
available for FRP waste management, being an
important driver for applied research undertaken cost
efficient recycling methods. [1-2]. In spite of this,
research on recycling solutions for thermoset
composites is still at an elementary stage. Thermal
and/or chemical recycling processes, with partial fibre
recovering, have been investigated mostly for carbon
fibre reinforced plastics (CFRP) due to inherent value
of carbon fibre reinforcement; whereas for glass fibre
reinforced plastics (GFRP), mechanical recycling, by
means of milling and grinding processes, has been
considered a more viable recycling method [1-2].
Though, at the moment, few solutions in the reuse of
mechanically-recycled GFRP composites into valueadded
products are being explored.
Aiming filling this gap, in this study, a new waste
management solution for thermoset GFRP based
products was assessed. The mechanical recycling
approach, with reduction of GFRP waste to powdered
and fibrous materials was applied, and the potential
added value of obtained recyclates was experimentally
investigated as raw material for polyester based
mortars. The use of a cementless concrete as host
material for GFRP recyclates, instead of a
conventional Portland cement based concrete, presents
an important asset in avoiding the eventual
incompatibility problems arisen from alkalis silica
reaction between glass fibres and cementious binder
matrix. Additionally, due to hermetic nature of resin
binder, polymer based concretes present greater ability
for incorporating recycled waste products [3].
Under this scope, different GFRP waste admixed
polymer mortar (PM) formulations were analyzed
varying the size grading and content of GFRP powder
and fibre mix waste. Added value of potential
recycling solution was assessed by means of flexural
and compressive loading capacities of modified
mortars with regard to waste-free polymer mortars
A case study on the eco-efficiency performance of a composite processing industry: evaluation and quantification of potential improvements
In this study, an attempt was made in order to measure and evaluate the eco-efficiency performance of a pultruded composite processing company. For this purpose the recommendations of World Business Council for Sustainable Development (WCSD) and the directives of ISO 14301 standard were followed and applied. The main general indicators of eco-efficiency, as well as the specific indicators, were defined and determined. With basis on indicators’ figures, the value profile, the environmental profile, and the pertinent eco-efficiency ratios were established and analyzed.
In order to evaluate potential improvements on company eco-performance, new indicators values and eco-efficiency ratios were estimated taking into account the implementation of new proceedings and procedures, at both upstream and downstream of the production process, namely:
i) Adoption of a new heating system for pultrusion die-tool in the manufacturing process, more effective and with minor heat losses;
ii) Recycling approach, with partial waste reuse of scrap material derived from manufacturing, cutting and assembly processes of GFRP profiles.
These features lead to significant improvements on the sequent assessed eco-efficiency ratios of the present case study, yielding to a more sustainable product and manufacturing process of pultruded GFRP profiles
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