Polarization-insensitive dual-wavelength dispersion tunable metalens achieved by global modulation method

SF$_6$ is widely used as a gas-insulator in high-voltage power electrical system. Detecting SF$_6$ leaks using unmanned aerial vehicle (UAV)-based thermal cameras allows efficient large-scale inspections during routine maintenance. The emergence of lightweight metalenses can increase the endurance of UAVs. Simultaneously controlling dispersion and polarization properties in metalens is significant for thermal camera applications. However, via a propagation phase modulation method in which the phase is tuned locally, it is difficult and time-consuming to obtain enough different nanostructures to control multiwavelength independently while maintain the polarization-insensitive property. To this end, by using a global modulation method, a polarization-insensitive dual-wavelength achromatic and super-chromatic metalens are designed respectively. The working wavelength is set at 10.6 and 12 $\rm\mu$m to match the absorption peaks of SF$_6$ and one of its decompositions (SO$_2$F$_2$), respectively. According to the operating wavelengths, only the geometric parameters of two nanofins are required to be optimized (through genetic algorithm). Then they are superimposed on each other to form cross-shaped meta-atoms. In order to control the influence between the two crossed nanofins, an additional term $\Delta f$ is introduced into the phase equation to modify the shape of the wavefront, whereby the phase dispersion can be easily engineered. Compared with local modulation, the number of unique nanostructures that need to be optimized can be reduced to two (operating at dual wavelengths) by the Pancharatnam-Berry (PB) phase based global modulation method. Therefore, the proposed design strategy is expected to circumvent difficulties in the local design approaches and can find widespread applications in multiwavelength imaging and spectroscopy

THE EFFECT OF POROSITY ON THE STRUCTURE AND PROPERTIES OF CALCIUM POLYPHOSPHATE BIOCERAMICS

Calcium polyphosphate (CPP) bioceramic with different porosities were prepared by controlling the concentration of the pore-foaming agent. Effect of porosity (0%, 15%, 30%, 45% and 60%) on the microstructure, pores interconnection, dissolution behavior and compressive strength of CPP bioceramic were investigated. Scanning electron microscope (SEM) and capillarity test results indicated that CPP with higher porosity (45% and 60%) exhibited three-dimensional interconnected pore structure with a pore size of about 200–400 μm, while the pores of lower porosity scaffold (0%, 15% and 30%) were isolated. The dissolution behavior in vitro indicated that the dissolution rate accelerated with the porosity increasing and the CPP with 60% porosity showed the highest dissolution velocity. The compressive strength of porosity CPP scaffolds were as much as the human cancellous bone, which decreased with the increase of porosity. While the dense CPP scaffolds lie in the same order of magnitude as compact bone

Preparation and evaluation of a biomimetic scaffold with porosity gradients in vitro

A novel biodegradable scaffold based on mimetic a natural bone tissue morphology with a porosity gradient structure was prepared in this paper. The result of surface morphology indicated that a graded porous structure was formed in the fabricated scaffold, where the dense layer (0%) was connected with the most porous layer (60%) by a middling porous layer (30%). To evaluate the degradability, graded porous scaffolds compared with homogeneous scaffolds were placed into a Tris-HCl buffer solution (pH = 7.4) for 28 days. It was found that both scaffolds presented the same degradation trend, and the graded porous structure did not change the original degradability of the scaffold. Moreover, the compressive strength of the graded porous scaffold was better than that of conventional homogeneous scaffold with the increase of degradation time, and the graded porous structure can enhanced the mechanical property of the scaffold. These findings suggest that this biodegradable and porosity-graded scaffold may be a new promising scaffold for loaded bone implant

Analysis and Properties of Time-Varying Modified DFT Filter Banks

<p/> <p>We provide a comprehensive analysis of the time-varying modified DFT (MDFT) filter bank based on the general time-varying filter bank theories (Wang, 2005, 2006, 2008, 2009) in both the time domain and frequency domain. We give firstly the description of the time-invariant MDFT filter bank including its perfect reconstruction (PR) condition, its mechanism of aliasing error cancellation and the relationship with the cosine-modulated filter bank in detail. Then, the time-varying MDFT filter bank is analyzed according to the time-domain description. Finally, the window switching method is introduced to design the prototype filter in the time-varying MDFT filter bank with examples. The error analysis shows that the introduced design approach is useful in practice.</p

VECTOR BOND GRAPH METHOD FOR UNIFIED MODELING AND SIMULATION OF JAW CRUSHER SYSTEM DYNAMICS

Aiming at the problem of unified modeling and simulation of system dynamics of simple swing jaw crusher driven by electric motor, the corresponding vector bond graph method was proposed. According to the constraint relation of the kinematic pair of the mechanism, the vector bond model of each component was bonded to each other, and the vector bond graph model of a six bar simple swing jaw crusher mechanism was made. By acting on the constraint force vectors of kinematic pair as the effort source vector at the corresponding 0-junction, the energy storage elements of the mechanism vector bond graph model were made have integral causality. Based on this, the vector bond graph model of the simple swing jaw crusher system was made, which takes into account the driving motor, crushing resistance force and the constraint force vector of the kinematic pair, and the unified computer modeling and dynamic simulation of the electromechanical system were realized. Compared with the results calculated by Newton-Euler dynamics method, the reliability of the proposed method was verified. The results show that the method described in this paper is effective, and its stylized modeling method improves the automation degree and reliability of electromechanical system dynamics modeling and simulation. In a movement cycle, the positive and reverse maximum of angular velocity for jaw crushing stroke and discharging stroke have little difference, and the time of crushing stroke and discharging stroke is close. At the beginning and the end of a motion cycle, the angular acceleration of the moving jaw and the constrained reaction force at both ends of the moving jaw will change greatly. In the final stage, the angular acceleration of the moving jaw increases from 0 to-83.36 rad/s~2, and the growth rate of the constrained reaction force at both ends is 2 576.44% and 249.10%, respectively. In addition, when the jaw is in the left limit position, the abrupt change of crushing force leads to large abrupt change of constrained reaction force at both ends of the jaw, with the reduction rates of 95.84% and 72.43%, respectively. This lays a foundation for the optimal design of the structure and parameters of the crusher, and further shows that the method presented in this paper has distinct characteristics and advantages

Degradation kinetics of calcium polyphosphate bioceramic: an experimental and theoretical study

In this work, the degradation kinetics of calcium polyphosphate bioceramic was studied. Liquid state31P nuclear magnetic resonance (NMR), X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to characterize the product. The in vitro degradation test was carried out at 37 ºC for up to 48 hours for both the simulation solution and the extreme solution. The ion concentrations were measured and analyzed by establishing a mathematical model referring to the chemical reaction kinetics. The results indicated that the degradability of calcium polyphosphate increased with the decrease of pH value, and the sample showed a rapid loss of ion concentration within the initial period of immersion followed by a slower loss ratio. The relationship between ion concentration and the degradation time coincided with Boxlucas model

Non-Invasive Electroretinogram Recording with Simultaneous Optogenetics to Dissect Retinal Ganglion Cells Electrophysiological Dynamics

Electroretinography (ERG) is a non-invasive electrophysiological recording technique that detects the electrical signaling of neuronal cells in the visual system. In conventional ERG recordings, the signals are considered a collective electrical response from various neuronal cell populations, including rods, cones, bipolar cells, and retinal ganglion cells (RGCs). However, due to the limited ability to control electrophysiological responses from different types of cells, the detailed information underlying ERG signals has not been analyzed and interpreted. Linking the features of ERG signals to the specific neuronal response will advance the understanding of neuronal electrophysiological dynamics and provide more evidence to elucidate pathological mechanisms, such as RGC loss during the progression of glaucoma. Herein, we developed an advanced ERG recording system integrated with a programmable, non-invasive optogenetic stimulation method in mice. In this system, we applied an automatic and unbiased ERG data analysis approach to differentiate a, b wave, negative response, and oscillatory potentials. To differentiate the electrophysiological response of RGCs in ERG recordings, we sensitized mouse RGCs with red-light opsin, ChRmine, through adeno-associated virus (AAV) intravitreal injection. Features of RGC dynamics under red-light stimulation were identified in the ERG readout. This non-invasive ERG recording system, associated with the programmable optogenetics stimulation method, provides a new methodology to dissect neural dynamics under variable physiological and pathological conditions in vivo. With the merits of non-invasiveness, improved sensitivity, and specificity, we envision this system can be further applied for early-stage detection of RGC degeneration and functional progression in neural degenerative diseases, such as glaucoma