1,173 research outputs found
Solid immersion lens at the aplanatic condition for enhancing the spectral bandwidth of a waveguide grating coupler
We report a technique to substantially boost the spectral
bandwidth of a conventional waveguide grating coupler by using a solid immersion cylindrical lens at the aplanatic condition to create a highly anamorphic beam and reach a much larger numerical aperture, thus enhancing the spectral bandwidth of a free-space propagating optical beam coupled into a single-mode planar integrated optical waveguide
(IOW). Our experimental results show that the broadband IOW spectrometer thus created almost doubles (94% enhancement) the coupled spectral bandwidth of a conventional configuration. To exemplify the benefits made possible by the developed approach, we applied the technique to
the broadband spectroscopic characterization of a protein submonolayer; our experimental data confirm the enhanced spectral bandwidth (around 380–nm) and illustrate the potentials of the developed technology. Besides
the enhanced bandwidth, the broadband coupler of the single-mode IOW spectrometer described here is more robust and user-friendly than those previously reported in the literature and is expected to have an important
impact on spectroscopic studies of surface-adsorbed molecular layers and surface phenomena
Dust content solutions for the Alcubierre warp drive spacetime
The Alcubierre metric is a spacetime geometry where a massive particle inside
a spacetime distortion, called warp bubble, is able to travel at velocities
arbitrarily higher than the velocity of light, a feature known as the warp
drive. This is a consequence of general relativity, which allows global
superluminal velocities but restricts local speeds to subluminal ones as
required by special relativity. In this work we solved the Einstein equations
for the Alcubierre warp drive spacetime geometry considering the dust matter
distribution as source, since the Alcubierre metric was not originally advanced
as a solution of the Einstein equations, but as a spacetime geometry proposed
without a source gravity field. We found out that all Einstein equations
solutions of this geometry containing pressureless dust lead to vacuum
solutions. We also concluded that these solutions connect the Alcubierre metric
to the Burgers equation, which describes shock waves moving through an inviscid
fluid. Our results also indicated that these shock waves behave as plane waves.Comment: 15 pages, 1 figure. LaTeX. Accepted for publication in the European
Physical Journal
On the nature of the (de)coupling of the magnetostructural transition in ErSi
In this report, a successful thermodynamical model was employed to understand
the structural transition in ErSi, able to explain the decoupling of
the magnetic and structural transition. This was achieved by the DFT
calculations which were used to determine the energy differences at 0 K, using
a LSDA+U approximation. It was found that the M structure as the stable phase
at low temperatures as verified experimentally with a 0.262 eV.
Finally, it was achieved a variation of Seebeck coefficient ( 6 V)
at the structural transition which allow to conclude that the electronic
entropy variation is negligible in the transition.Comment: 17 pages, 3 figures, 1 tabl
High‐Performance Ferroelectric–Dielectric Multilayered Thin Films for Energy Storage Capacitors
Use of Limpograss as an Alternative Feed During the Fall Forage Gap in Beef and Dairy Systems in Central and North Florida
In central and North Florida, the use of limpograss [Hemarthria altissima (Poir.) Stapf & C. E. Hubb.] for beef and dairy operations is limited and its potential use is not well documented. Two on-farm projects have been conducted in Central and North Florida to explore the use of limpograss as an alternative conserved forage during late fall and winter. The potential use of this forage as baleage for dairy farmers and as stockpiling for livestock producers would offer another alternative to reduce feed costs and fill the forage gap in the area when typical warm-season forages go dormant. In addition, the on-farm limpograss establishment would serve as dissemination for the limpograss planting material. Four dairy farms in Central and North Florida were enrolled in the study to evaluate two cultivars of limpograss for their potential when conserved as baleage. Four 0.2 ha strips were planted per farm, two for each variety (‘Kenhy’ and ‘Gibtuck’). The strips were arranged in a randomized complete block design, with two replicates in each location. Before wrapping the harvested forage for baleage, samples were taken to evaluate crude protein (CP) and in vitro digestible organic matter concentration (IVDOM). In addition, samples of fresh baleage at 60 and 90 d were analyzed for fermentation profile (pH, organic acids, and ammonia). Four beef cattle farms in North Florida allowed us to plant 1 ha of ‘Gibtuck’ for stockpiling evaluating the nutritive value at 30, 60, 90, and 120 days. Each plot was replicated four times and allocated in a randomized complete block design. The fermentation profile from the bales does not show differences between cultivars (P \u3e 0.05) and the pH is lower than 5 indicating that the fermentation process was successful. The CP and IVDOM of the stockpiling limpograss were different among the treatments (P \u3c 0.001)
Diffusion equations and different spatial fractional derivatives
We investigate for the diffusion equation the differences manifested by the solutions when three different types of spatial differential operators of noninteger (or fractional) order are considered for a limited and unlimited region. In all cases, we verify an anomalous spreading of the system, which can be connected to a rich class of anomalous diffusion processes
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