Physics

Acoustic wave resonators are promising for gravimetric biosensing. However, they generally suffer from strong acoustic radiation in liquid, which limits their quality factor and increases their frequency noise. This article presents an acoustic-radiation-free gravimetric biosensor based on a locally-resonant surface phononic crystal (SPC) consisting of periodic high aspect ratio electrodes to ad-dress the above issue. The acoustic wave generated in the SPC is slower than the sound wave in water, hence preventing acoustic propagation in the fluid and resulting in energy confinement near the electrode surface. This energy confinement results in a significant quality factor improvement and thus reduces the frequency noise. The proposed SPC resonator is numerically studied by finite element analysis and experimentally implemented by an electroplating based fabrication process. Experimental results show that the SPC resonator exhibits an in-liquid quality factor 15 times higher than a conventional Rayleigh wave resonator with a similar operating frequency. The proposed radiation suppression method using SPC can also be applied in other types of acoustic wave resonators. It can thus serve as a general technique for boosting the in-liquid quality factor and the sensing performance of many acoustic biosensors.

Dual-comb sources with equally spaced and low phase noise frequency lines are of great importance for high resolution spectroscopy and metrology. In the terahertz frequency range, electrically pumped semiconductor quantum cascade lasers (QCLs) are suitable candidates for frequency comb and dual-comb operation. For a single laser frequency comb, the repetition rate can be locked using a microwave injection locking and the carrier frequency can be locked to a highly stable source. However, for the locking of two laser combs, four frequencies (two repetition rates and two carrier offset frequencies) should be simultaneously locked; If one only refers to the dual-comb signal, two relative frequencies, i.e., the offset frequency and repetition frequency of one laser against those of the other laser, should be locked. Although the locking techniques that have been successfully used for a single laser comb can be, in principle, applied to a dual-comb laser source, the complete locking considerably complicates the implementation of such a system. Here, we propose a method to stabilize a terahertz QCL dual-comb source by phase locking one of the dual-comb lines to a radio frequency (RF) synthesizer. This technique forces one of the lasers to follow the tone of the other one (keeping the sum of the carrier offset frequency difference and repetition frequency difference between the two laser combs as a constant) by exploiting a laser self-detection that avoids the use of an external detector. Through the demonstration of this locking technique, we demonstrate that the dual-comb can generate periodic pulses over a 2 us time scale, showing that the terahertz QCL comb without a control of the repetition rate can produce pulsed-type waveforms.

Topological insulators, which allow edge or interface waves but forbid bulk waves, have revolutionized our scientific cognition of acoustic/elastic systems. Due to their nontrivial topological characteristics, edge (interface)waves are topologically protected against defects and disorders. This superior and unique characteristic could lead to a wealth of new opportunities in applications of quantum and acoustic/elastic information processing. However, current acoustic/elastic topological insulators are still at an infancy stage where the theory and prediction only work in laboratories and there are still many problems left open before promoting their practical applications. One of the apparent disadvantages is their narrow working frequency range, which is the main concern in this paper. We design a one-dimensional phononic beam system made of a homogeneous epoxy central beam sandwiched by two homogeneous piezoelectric beams, and covered with extremely thin electrodes, periodically and separately placed. These electrodes are connected to external electric circuits with negative capacitors. We show that a topological phase transition can be induced and tuned by changing the values of the negative capacitors. It follows that the working frequency of the topologically protected interface mode can be widely changed, such that the working frequency range of the topological insulator can be considerably `broadened'. This intelligent topological device may also find wide applications in intelligent technologies that need controllable information processing of high precision.

An all-epitaxial approach was demonstrated to create coaxial plasmon laser structures composed of an alumi-num plasmonic metal / SiNx dielectric / InGaN quantum well shell surrounding a p-GaN nanowire core. Strong UV lumi-nescence was observed from as-grown vertically-aligned arrays as well as horizontally-aligned nanowires transferred to a transparent carrier wafer.

We numerically demonstrate an all-optical nonlinearity pre-compensation module for state-of-the-art long-reach Raman-amplified unrepeatered links. The compensator design is optimized in terms of propagation symmetry to maximize the performance gains under WDM transmission, achieving 4.0dB and 2.6dB of SNR improvement for 250-km and 350-km links.

Developing MgO-bonded castables is still an important subject for refractory producers and end-users based on the expansive character of the in-situ Mg(OH)2 formation. Considering that magnesia undergoes hydration when exposed to water and the generated hydrated phase needs to be properly accommodated in the resulting microstructure to inhibit the generation of cracks, it is very important to find out alternatives to control the MgO hydration reaction rate. This research investigated the use of aluminum lactate (AL) as a likely additive to change the hydration and drying behavior of vibratable castables bonded with different MgO sources (dead burnt, caustic or fumed one). Firstly, XRD, TG and DSC measurements of magnesia-based aqueous suspensions were evaluated to identify the AL effect on changing the hydration reaction products during the curing and drying steps. After that, Al2O3-MgO refractories were prepared and their flowability, curing behavior, cold flexural strength, apparent porosity, permeability and explosion resistance were evaluated. The results indicated that, instead of Mg(OH)2, Mg6Al2(OH)16(OH)2.4.5H2O/ Mg6Al2(OH)16(CO3).4H2O was the main hydrated phase identified in the AL-containing compositions. Due to this change in the hydration behavior of the refractories, the mixtures prepared with dead-burnt or magnesia fumes plus organic salt presented a longer setting time. Besides that, crack-free samples with improved permeability and green mechanical strength could be obtained when adding 0.5 wt.% or 1.0 wt.% of aluminum lactate to the tested castable compositions. Consequently, 1.0 wt.% of the selected additive favored the design of refractories with enhanced properties and greater spalling resistance, as no explosion could be observed even when subjecting the prepared samples to severe heating conditions (20C/min).

In many cases, beam to column connections in structural frames are semi rigid, but they are considered to be ideally rigid or pinned due to their computational complexity and shortage of designing methods. In this paper, connections are considered as linear rotational springs with variable stiffness. Moreover, the main contribution of the present study is a preliminary design method of moment resisting frames, considering semi rigid behavior of connections, by means of presented diagrams for different frames. These diagrams relate three features of a frame together; stiffness of frames connections, geometrical properties of frames elements, and its lateral displacement. These diagrams can be used when the required stiffness of frames connections is needed while the desired response of the frame, dimensions of the frame and the ratio of second moment of inertia of its elements are known. On the other hand, they could be used to obtain the ratio of beams length to columns length and the ratio of second moment of inertia of beams to columns alongside the stiffness of frames connections while the only known data is the number of frames grids in X and Y directions and its desired response.

Structural health monitoring (SHM) using self-sensing cement-based materials has been reported before, where nano-fillers have been incorporated in cementitious matrices as functional sensing elements. A percolation threshold is always required in order for conductive nano-fillers modified concrete to be useful for SHM. Nonetheless, the best pressure/strain sensitivity results achieved for any self-sensing cementitious matrix are <0.01 MPa-1. In this work, we introduce novel reduced graphene oxide (RGO) based electronic textile (e-textile) embedded in plain and polymer-binder-modified cementitious matrix for SHM applications. As a proof of concept, it was demonstrated that these coated fabric-based sensors can be successfully embedded within the cement-based structures, which are independent of any percolation threshold due to the interconnected fabric inside the host matrix. The piezo-resistive response was measured by applying direct and cyclic compressive loads (0.1 to 3.9 MPa). A pressure sensitivity of 1.5 MPa-1 and an ultra-high gauge factor of 2000 was obtained for the system of the self-sensing cementitious structure with embedded e-textiles. The sensitivity of this new system with embedded e-textile is many orders of magnitude higher than nanoparticle based self-sensing of cementitious composites. The manufactured e-textile sensors showed mechanical stability and functional durability over long-term cyclic compression tests of 1000 cycles.

The dynamic behavior of AFM is studied taking into account the nonlinear interaction forces between probe and sample. The exerted forces on the free end of micro-beam are simulated with the third degree polynomial. The effect of some parameters on the dynamics of AFM is studied. The results show that the frequency response of AFM is not sensitive to the tip mass in the case of both the sample and cantilever vibration. The effect of sample vibration is studied in the case of in-phase and anti-phase vibration. The results show that although the vibration amplitude of sample is very small compared to the amplitude of cantilever, it has great effect on the resonant frequency of the cantilever.

The present work provides an analytic solution for the stiffness to crack length relation in microscopic cantilever shaped fracture specimens based on classical beam theory and substitution of the crack by a virtual rotational spring element. The resulting compact relationship allows for accounting of the actual beamgeometry and agrees very well with accompanying finite element simulations. Compared with the only other model present in literature the proposed relationship reduces the deviation between model and data to a maximum of 1.6% fromthe previous minimumof 15%. Thus, the novel solution will help to reduce the necessity for individual simulations and aim to increase the comparability of elastic-plastic microcantilever fracture experiments in the future.