2,389 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 Andalucía Tech
Reducing computational time via order reduction of a class of reaction–diffusion systems
In this paper, we consider a class of reaction–
diffusion PDEs. For this class, a suitable state transformation
allows conversion to a heat equation together with a lower
order PDE set. By giving an explicit solution to the heat
equation we are able to obtain a complete solution to the
original PDE. By focusing on the computational load, we
give a comparison of the pure numerical, analytical/numerical,
analytical/approximated, and approximated methods of solving
the PDE. In some examples, we note an almost order of
magnitude improvement in computational load
Atherosclerotic carotid plaque composition: a 3T and 7T MRI-histology correlation study
Background and Purpose
Carotid artery atherosclerotic plaque composition may influence plaque stability and risk of
thromboembolic events, and non-invasive plaque imaging may therefore permit risk
stratification for clinical management. Plaque composition was compared using non-invasive
in-vivo (3T) and ex-vivo (7T) MRI and histopathological examination.
Methods
Thirty three endarterectomy cross sections, from 13 patients, were studied. The datasets
consisted of in-vivo 3T MRI, ex-vivo 7T MRI and histopathology. Semi-automated
segmentation methods were used to measure areas of different plaque components. Bland-
Altman plots and mean difference with 95% confidence interval were carried out.
Results
There was general quantitative agreement between areas derived from semi-automated
segmentation of MRI data and histology measurements. The mean differences and 95%
confidence bounds in the relative to total plaque area between 3T versus Histology were:
fibrous tissue 4.99 % (-4.56 to 14.56), lipid-rich/necrotic core (LR/NC) with haemorrhage -
1.81% (-14.11 to 10.48), LR/NC without haemorrhage -2.43% (-13.04 to 8.17), and
calcification -3.18% (-11.55 to 5.18). The mean differences and 95% confidence bounds in
the relative to total plaque area between 7T and histology were: fibrous tissue 3.17 % (-3.17
to 9.52), LR/NC with haemorrhage -0.55% (-9.06 to 7.95), LR/NC without haemorrhage -
12.62% (-19.8 to -5.45), and calcification -2.43% (-9.97 to 4.73).
Conclusions
This study provides evidence that semi-automated segmentation of 3T/7T MRI techniques
can help to determine atherosclerotic plaque composition. In particular, the high resolution of
ex-vivo 7T data was able to highlight greater detail in the atherosclerotic plaque composition.
High field MRI may therefore have advantages for in vivo carotid plaque MR imaging
Intra- and interspecies interactions between prion proteins and effects of mutations and polymorphisms
Recently, crystallization of the prion protein in a dimeric form was reported. Here we show that native soluble homogenous FLAG-tagged prion proteins from hamster, man and cattle expressed in the baculovirus system are predominantly dimeric. The PrP/PrP interaction was confirmed in Semliki Forest virus-RNA transfected BHK cells co-expressing FLAG- and oligohistidine-tagged human PrP. The yeast two-hybrid system identified the octarepeat region and the C-terminal structured domain (aa90-aa230) of PrP as PrP/PrP interaction domains. Additional octarepeats identified in patients suffering from fCJD reduced (wtPrP versus PrP+90R) and completely abolished (PrP+90R versus PrP+90R) the PrP/PrP interaction in the yeast two-hybrid system. In contrast, the Met/Val polymorphism (aa129), the GSS mutation Pro102Leu and the FFI mutation Asp178Asn did not affect PrP/PrP interactions. Proof of interactions between human or sheep and bovine PrP, and sheep and human PrP, as well as lack of interactions between human or bovine PrP and hamster PrP suggest that interspecies PrP interaction studies in the yeast two-hybrid system may serve as a rapid pre-assay to investigate species barriers in prion diseases
Entropy spectrum of a Kerr anti-de Sitter black hole
The entropy spectrum of a spherically symmetric black hole was derived
without the quasinormal modes in the work of Majhi and Vagenas. Extending this
work to rotating black holes, we quantize the entropy and the horizon area of a
Kerr anti-de Sitter black hole by two methods. The spectra of entropy and area
are obtained via the Bohr-Sommerfeld quantization rule and the adiabatic
invariance in the first way. By addressing the wave function of emitted
(absorbed) particles, the entropy and the area are quantized in the second one.
Both results show that the entropy and the area spectra are equally spaced.Comment: Accepted for publication in The European Physical Journal C, Volume
72, Issue
Aspects of Open-Closed Duality in a Background B-Field
We study closed string exchanges in background -field. By analysing the
two point one loop amplitude in bosonic string theory, we show that tree-level
exchange of lowest lying, tachyonic and massless closed string modes, have IR
singularities similar to those of the nonplanar sector in noncommutative gauge
theories. We further isolate the contributions from each of the massless modes.
We interpret these results as the manifestation of open/closed string duality,
where the IR behaviour of the boundary noncommutative gauge theory is
reconstructed from the bulk theory of closed strings.Comment: 33 pages, 4 figures, v2:references added, v3: minor changes, typos
corrected, references adde
Aspects of Open-Closed Duality in a Background B-Field II
It was shown in [hep-th/0503009], in the context of bosonic theory that the
IR singular terms that arise as a result of integrating out high momentum modes
in nonplanar diagrams of noncommutative gauge theory can be recovered from low
lying tree-level closed string exchanges. This follows as a natural consequence
of world-sheet open-closed string duality. Here using the same setup we study
the phenomenon for noncommutative gauge theory realised on a
fractional brane localised at the fixed point of . The IR
singularities from the massless closed string exchanges are exactly equal to
those coming from one-loop gauge theory. This is as a result of cancellation of
all contributions from the massive modes.Comment: 27 pages, 1 figure, references added, typos correcte
Expanding Universe: Thermodynamical Aspects From Different Models
The pivotal point of the paper is to discuss the behavior of temperature,
pressure, energy density as a function of volume along with determination of
caloric EoS from following two model: & .
The time scale of instability for this two models is discussed. In the paper we
then generalize our result and arrive at general expression for energy density
irrespective of the model. The thermodynamical stability for both of the model
and the general case is discussed from this viewpoint. We also arrive at a
condition on the limiting behavior of thermodynamic parameter to validate the
third law of thermodynamics and interpret the general mathematical expression
of integration constant (what we get while integrating energy
conservation equation) physically relating it to number of micro states. The
constraint on the allowed values of the parameters of the models is discussed
which ascertains stability of universe. The validity of thermodynamical laws
within apparent and event horizon is discussed.Comment: 16 pages, 3 figures(Accepted for publication in "Astrophysics and
Space Science"
Duality cascades and duality walls
We recast the phenomenon of duality cascades in terms of the Cartan matrix
associated to the quiver gauge theories appearing in the cascade. In this
language, Seiberg dualities for the different gauge factors correspond to Weyl
reflections. We argue that the UV behavior of different duality cascades
depends markedly on whether the Cartan matrix is affine ADE or not. In
particular, we find examples of duality cascades that can't be continued after
a finite energy scale, reaching a "duality wall", in terminology due to M.
Strassler. For these duality cascades, we suggest the existence of a UV
completion in terms of a little string theory.Comment: harvmac, 24 pages, 4 figures. v2: references added. v3: reference
adde
Non linear equation of state and effective phantom divide in brane models
Here, DGP model of brane-gravity is analyzed and compared with the standard
general relativity and Randall-Sundrum cases using non-linear equation of
state. Phantom fluid is known to violate the weak energy condition. In this
paper, it is found that this characteristic of phantom energy is affected
drastically by the negative brane-tension of the RS-II model. It is
found that in DGP model strong energy condition(SEC) is always violated and the
universe accelerates only where as in RS-II model even SEC is not violated for
and the universe decelerates
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