1,455 research outputs found
Graphene-based perfect optical absorbers harnessing guided mode resonances
We numerically and experimentally investigate graphene-based optical
absorbers that exploit guided mode resonances (GMRs) achieving perfect
absorption over a bandwidth of few nanometers (over the visible and
near-infrared ranges) with a 40-fold increase of the monolayer graphene
absorption. We analyze the influence of the geometrical parameters on the
absorption rate and the angular response for oblique incidence. Finally, we
experimentally verify the theoretical predictions in a one-dimensional,
dielectric grating and placing it near either a metallic or a dielectric
mirror
Graphene-based absorber exploiting guided mode resonances in one-dimensional gratings
A one-dimensional dielectric grating, based on a simple geometry, is proposed
and investigated to enhance light absorption in a monolayer graphene exploiting
guided mode resonances. Numerical findings reveal that the optimized
configuration is able to absorb up to 60% of the impinging light at normal
incidence for both TE and TM polarizations resulting in a theoretical
enhancement factor of about 26 with respect to the monolayer graphene
absorption (about 2.3%). Experimental results confirm this behaviour showing
CVD graphene absorbance peaks up to about 40% over narrow bands of few
nanometers. The simple and flexible design paves the way for the realization of
innovative, scalable and easy-to-fabricate graphene-based optical absorbers
Dynamically avoiding fine-tuning the cosmological constant: the "Relaxed Universe"
We demonstrate that there exists a large class of action functionals of the
scalar curvature and of the Gauss-Bonnet invariant which are able to relax
dynamically a large cosmological constant (CC), whatever it be its starting
value in the early universe. Hence, it is possible to understand, without
fine-tuning, the very small current value of the CC as compared to its
theoretically expected large value in quantum field theory and string theory.
In our framework, this relaxation appears as a pure gravitational effect, where
no ad hoc scalar fields are needed. The action involves a positive power of a
characteristic mass parameter, M, whose value can be, interestingly enough, of
the order of a typical particle physics mass of the Standard Model of the
strong and electroweak interactions or extensions thereof, including the
neutrino mass. The model universe emerging from this scenario (the "Relaxed
Universe") falls within the class of the so-called LXCDM models of the cosmic
evolution. Therefore, there is a "cosmon" entity X (represented by an effective
object, not a field), which in this case is generated by the effective
functional and is responsible for the dynamical adjustment of the cosmological
constant. This model universe successfully mimics the essential past epochs of
the standard (or "concordance") cosmological model (LCDM). Furthermore, it
provides interesting clues to the coincidence problem and it may even connect
naturally with primordial inflation.Comment: LaTeX, 63 pp, 8 figures. Extended discussion. Version accepted in
JCA
First measurement of the K−n →Λπ−non-resonant transition amplitude below threshold
We present the analysis of K−absorption processes on He4 leading to Λπ−final states, measured with the KLOE spectrometer at the DAΦNE e+e−collider and extract, for the first time, the modulus of the non-resonant K−n →Λπ−direct production amplitude about 33 MeV below the K‾N threshold. This analysis also allows to disentangle the K−nuclear absorption at-rest from the in-flight capture, for K−momenta of about 120 MeV. The data are interpreted with the help of a phenomenological model, and the modulus of the non-resonant K−n →Λπ−amplitude for K−absorption at-rest is found to be |AK−n→Λπ−|=(0.334±0.018stat−0.058+0.034syst)fm
Carbazole and simplified derivatives: Novel tools toward β-adrenergic receptors targeting
β-Adrenergic receptors (β-ARs) are G protein-coupled receptors involved in important physiological and pathological processes related to blood pressure and cardiac activity. The inhibition of cardiac β1-ARs could be beneficial in myocardial hypertrophy, ischemia and failure. Several carbazole-based compounds have been described as promising β-blockers. Herein, we investigate the capability of a carbazole derivative and three simplified indole analogs to interact with the active binding site of β1-AR by molecular docking studies. In the light of the obtained results, our compounds were tested by biological assays in H9c2 cardiomyocytes exposed to isoproterenol (ISO) to confirm their potential as β1-blockers agents, and two of them (8 and 10) showed interesting and promising properties. In particular, these compounds were effective against ISO-dependent in vitro cardiac hypertrophy, even at concentrations lower than the known β-AR antagonist propranolol. Overall, the data suggest that the indole derivatives 8 and 10 could act as potent β1-blockers and, active at low doses, could elicit limited side effects
Calibration of the length of a chain of single gold atoms
Using a scanning tunneling microscope or mechanically controllable break
junctions it has been shown that it is possible to control the formation of a
wire made of single gold atoms. In these experiments an interatomic distance
between atoms in the chain of ~3.6 Angstrom was reported which is not
consistent with recent theoretical calculations. Here, using precise
calibration procedures for both techniques, we measure length of the atomic
chains. Based on the distance between the peaks observed in the chain length
histogram we find the mean value of the inter-atomic distance before chain
rupture to be 2.6 +/- 0.2 A . This value agrees with the theoretical
calculations for the bond length. The discrepancy with the previous
experimental measurements was due to the presence of He gas, that was used to
promote the thermal contact, and which affects the value of the work function
that is commonly used to calibrate distances in scanning tunnelling microscopy
and mechanically controllable break junctions at low temperatures.Comment: 6 pages, 6 figure
Cyclic Fatigue of Different Nickel-Titanium Rotary Instruments: A Comparative Study
Since the introduction of nickel-titanium alloy to endodontics, there have been many changes in instrument design, but no significant improvements in the raw material properties, or enhancements in the manufacturing process. Recently, a new method to produce nickel-titanium rotary (NTR) instruments has been developed, in an attempt to obtain instruments that are more flexible and resistant to fatigue. NTR instruments produced using the process of twisting (TF, SybronEndo, Orange, CA) were compared to NTR instruments from different manufacturers produced by a traditional grinding process. The aim of the study was to investigate whether cyclic fatigue resistance is increased for TF NTR files. Tests were performed with a cyclic fatigue device that evaluated cycles to failure of rotary instruments inside curved artificial canals. Results indicated that size 06-25 TF instruments showed a significant increase (P< .05). In the mean number of cycles to failurewhen compared to the other tested 06-25 NTR. Hence, it can be concluded that size 06-25 TF NTR instruments were found to be significantly more resistant to fatigue than those produced with the traditional grinding process
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