Nonlinear response of very high frequency contour mode resonators.

We explore the source of nonlinearities in Aluminum Nitride (AlN) Contour Mode Resonators (CMRs) operating in the Very High Frequency (VHF) range. We demonstrate that the red-shift of the resonance frequency found in VHF CMRs when the input RF power increases is due to nonlinear stiffness appearing from self-heating, and variable damping due to geometric nonlinearities. Moreover, we find a linear relationship between the variable damping coefficient and the resonator quality factor (Q).

Dual-band and spectrally selective infrared absorbers based on hybrid gold-graphene metasurfaces.

In this paper, we propose a dual-band and spectrally selective infrared (IR) absorber based on a hybrid structure comprising a patterned graphene monolayer and cross-shaped gold resonators within a metasurface. Rooted in full-wave numerical simulations, our study shows that the fundamental absorption mode of the gold metasurface hybridizes with the graphene pattern, leading to a second absorptive mode whose properties depend on graphene's electrical properties and physical geometry. Specifically, the central operation band of the absorber is defined by the gold resonators whereas the relative absorption level and spectral separation between the two modes can be controlled by graphene's chemical potential and its pattern, respectively.

Past, present and future in the geographical distribution of Mexican Tepezmaite cycads: Genus Ceratozamia.

Ceratozamia morettii, C. brevifrons, and C. tenuis are cycads considered endangered in montane forests in the center of Veracruz state.

Potential present and future distributions of the genus Atta of Mexico.

Temperature and precipitation influence insect distribution locally and drive large-scale biogeographical patterns. We used current and future climate data from the CHELSA database to create ensemble species distribution models for three Atta leaf-cutting ant species (Atta cephalotes, A. mexicana, and A.

Presence of Spodoptera frugiperda Multiple Nucleopolyhedrovirus (SfMNPV) Occlusion Bodies in Maize Field Soils of Mesoamerica.

The occlusion bodies (OBs) of lepidopteran nucleopolyhedroviruses can persist in soil for extended periods before being transported back on to the foliage for transmission to the host insect. A sensitive insect bioassay technique was used to detect OBs of Spodoptera frugiperda multiple nucleopolyhedrovirus (SfMNPV) in 186 soil samples collected from maize fields in the southern Mexican states of Chiapas, Tabasco, Campeche, Yucatán, and Quintana Roo, as well Belize and Guatemala. Overall, 35 (18.

Tunable optical traps over nonreciprocal surfaces.

We propose engineering optical traps over plasmonic surfaces and precisely controlling the trap position with an external bias by inducing in-plane nonreciprocity on the surface. The platform employs an incident Gaussian beam to polarize targeted nanoparticles, and exploits the interplay between nonreciprocal and spin-orbit lateral recoil forces to construct stable optical traps and manipulate their position within the surface. To model this process, we develop a theoretical framework based on the Lorentz force combined with nonreciprocal Green's functions and apply it to calculate the trapping potential.

Fused Raman spectroscopic analysis of blood and saliva delivers high accuracy for head and neck cancer diagnostics.

As a rapid, label-free, non-destructive analytical measurement requiring little to no sample preparation, Raman spectroscopy shows great promise for liquid biopsy cancer detection and diagnosis. We carried out Raman analysis and mass spectrometry of plasma and saliva from more than 50 subjects in a cohort of head and neck cancer patients and benign controls (e.g.

Multidimensional Characterization of Single-Molecule Dynamics in a Plasmonic Nanocavity.

Nanoscale manipulation and characterization of individual molecules is necessary to understand the intricacies of molecular structure, which governs phenomena such as reaction mechanisms, catalysis, local effective temperatures, surface interactions, and charge transport. Here we utilize Raman enhancement between two nanostructured electrodes in combination with direct charge transport measurements to allow for simultaneous characterization of the electrical, optical, and mechanical properties of a single molecule. This multi-dimensional information yields repeatable, self-consistent, verification of single-molecule resolution, and allows for detailed analysis of structural and configurational changes of the molecule in situ.

Slow light mediated by mode topological transitions in hyperbolic waveguides.

We show that slow light in hyperbolic waveguides is linked to topological transitions in the dispersion diagram as the film thickness changes. The effect appears in symmetric planar structures with type II films, whose optical axis (OA) lies parallel to the waveguide interfaces. The transitions are mediated by elliptical mode branches that coalesce along the OA with anomalously ordered hyperbolic mode branches, resulting in a saddle point.

Comparison Between Multicomponent Exercise and Walking Interventions in Long-Term Nursing Homes: A Randomized Controlled Trial.

Background And Objectives: There is evidence that exercise interventions counteract the functional and cognitive decline experienced by long-term nursing home (LTNH) residents. To determine the most effective exercise intervention, we compared the effects of a multicomponent exercise intervention and a walking intervention on physical and cognitive performance, habitual physical activity, affective function, and quality of life among older adults living in LTNHs.

Research Design And Methods: This 3-month single-blind randomized controlled trial (NCT03996083) involved 81 participants at 9 LTNHs randomly assigned to a multicomponent (MG) or a walking (WG) group.

Prevalence and Diversity of Endosymbionts in Cassava Whiteflies (Hemiptera: Aleyrodidae) From Colombia.

Whiteflies cause huge economic losses for cassava (Manihot esculenta Crantz) cultivation. Damage can be caused directly when the insects feed on the phloem and/or indirectly by the transmission of viruses. It has been found that whiteflies maintain a close relationship with some endosymbiotic bacteria and that this interaction produces different effects on host biology and can also facilitate viral transmission.

Diversity and composition of herbaceous angiosperms along gradients of elevation and forest-use intensity.

Terrestrial herbs are important elements of tropical forests; however, there is a lack of research on their diversity patterns and how they respond to different intensities of forest-use. The aim of this study was to analyze the diversity of herbaceous angiosperms along gradients of elevation (50 m to 3500 m) and forest-use intensity on the eastern slopes of the Cofre de Perote, Veracruz, Mexico. We recorded the occurrence of all herbaceous angiosperm species within 120 plots of 20 m x 20 m each.

Self-Assembled Epitaxial Au-Oxide Vertically Aligned Nanocomposites for Nanoscale Metamaterials.

Metamaterials made of nanoscale inclusions or artificial unit cells exhibit exotic optical properties that do not exist in natural materials. Promising applications, such as super-resolution imaging, cloaking, hyperbolic propagation, and ultrafast phase velocities have been demonstrated based on mostly micrometer-scale metamaterials and few nanoscale metamaterials. To date, most metamaterials are created using costly and tedious fabrication techniques with limited paths toward reliable large-scale fabrication.

Plasmonic piezoelectric nanomechanical resonator for spectrally selective infrared sensing.

Ultrathin plasmonic metasurfaces have proven their ability to control and manipulate light at unprecedented levels, leading to exciting optical functionalities and applications. Although to date metasurfaces have mainly been investigated from an electromagnetic perspective, their ultrathin nature may also provide novel and useful mechanical properties. Here we propose a thin piezoelectric plasmonic metasurface forming the resonant body of a nanomechanical resonator with simultaneously tailored optical and electromechanical properties.

Nonlocal response of hyperbolic metasurfaces.

We analyze and model the nonlocal response of ultrathin hyperbolic metasurfaces (HMTSs) by applying an effective medium approach. We show that the intrinsic spatial dispersion in the materials employed to realize the metasurfaces imposes a wavenumber cutoff on the hyperbolic isofrequency contour, inversely proportional to the Fermi velocity, and we compare it with the cutoff arising from the structure granularity. In the particular case of HTMSs implemented by an array of graphene nanostrips, we find that graphene nonlocality can become the dominant mechanism that closes the hyperbolic contour - imposing a wavenumber cutoff at around 300k(0) - in realistic configurations with periodicity L<π/(300k(0)), thus providing a practical design rule to implement HMTSs at THz and infrared frequencies.

Gradient Nonlinear Pancharatnam-Berry Metasurfaces.

We apply the Pancharatnam-Berry phase approach to plasmonic metasurfaces loaded by highly nonlinear multiquantum-well substrates, establishing a platform to control the nonlinear wave front at will based on giant localized nonlinear effects. We apply this approach to design flat nonlinear metasurfaces for efficient second-harmonic radiation, including beam steering, focusing, and polarization manipulation. Our findings open a new direction for nonlinear optics, in which phase matching issues are relaxed, and an unprecedented level of local wave front control is achieved over thin devices with giant nonlinear responses.

Hyperbolic Plasmons and Topological Transitions Over Uniaxial Metasurfaces.

We explore the unusual electromagnetic response of ultrathin anisotropic σ-near-zero uniaxial metasurfaces, demonstrating extreme topological transitions--from closed elliptical to open hyperbolic--for surface plasmon propagation, associated with a dramatic tailoring of the local density of states. The proposed metasurfaces may be implemented using nanostructured graphene monolayers and open unprecedented venues for extreme light confinement and unusual propagation and guidance, combined with large tunability via electric bias.

Self-biased reconfigurable graphene stacks for terahertz plasmonics.

The gate-controllable complex conductivity of graphene offers unprecedented opportunities for reconfigurable plasmonics at terahertz and mid-infrared frequencies. However, the requirement of a gating electrode close to graphene and the single 'control knob' that this approach offers limits the practical implementation and performance of these devices. Here we report on graphene stacks composed of two or more graphene monolayers separated by electrically thin dielectrics and present a simple and rigorous theoretical framework for their characterization.

Dehalogenation and coupling of a polycyclic hydrocarbon on an atomically thin insulator.

Catalytic activity is of pivotal relevance in enabling efficient and selective synthesis processes. Recently, covalent coupling reactions catalyzed by solid metal surfaces opened the rapidly evolving field of on-surface chemical synthesis. Tailored molecular precursors in conjunction with the catalytic activity of the metal substrate allow the synthesis of novel, technologically highly relevant materials such as atomically precise graphene nanoribbons.

Plane wave excitation-detection of non-resonant plasmons along finite-width graphene strips.

An approach to couple free-space waves and non-resonant plasmons propagating along graphene strips is proposed based on the periodic modulation of the graphene strip width. The solution is technologically very simple, scalable in frequency, and provides customized coupling angle and intensity. Moreover, the coupling properties can be dynamically controlled at a fixed frequency via the graphene electrical field effect, enabling advanced and flexible plasmon excitation-detection strategies.

Graphene-based plasmonic switches at near infrared frequencies.

The concept, analysis, and design of series switches for graphene-strip plasmonic waveguides at near infrared frequencies are presented. Switching is achieved by using graphene's field effect to selectively enable or forbid propagation on a section of the graphene strip waveguide, thereby allowing good transmission or high isolation, respectively. The electromagnetic modeling of the proposed structure is performed using full-wave simulations and a transmission line model combined with a matrix-transfer approach, which takes into account the characteristics of the plasmons supported by the different graphene-strip waveguide sections of the device.

Zygosaccharomyces bailii inactivation by means of UV light and low-frequency ultrasound treatments.

Zygosaccharomyces bailii inactivation suspended in apple juice was evaluated under the effects of selected treatments: short-wave UV light (UVC, using one or two lamps), or low-frequency ultrasound (US), or their simultaneous combination. US treatments (20 kHz, 120-μm wave amplitude) were performed at 35°C in a double-wall vessel by using a 13-mm probe. The UVC device consists of two 90-cm-long stainless steel tubes with 40-W UVC lamps covered with quartz tubes, each one inside a stainless steel tube (annular inside diameter of 2.

C-N coupling on transition metal surfaces: a density functional theory study.

We have investigated the formation of C-N bonds from individual atoms and single hydrogenated moieties on a series of transition metals. These reactions play a role in HCN formation at high oxygen coverage, also known as Andrussow oxidation, and they are fundamental to understand the ability of other materials to form part of alloys where Pt is the major component. Dehydrogenations take place quite easily under these high oxygen conditions and thus, the C+N, HC+N, and N+CH recombinations to form HCN or its isomer CNH might represent the rate-limiting steps for the reaction.