A second order topological insulator is designed on a platform of a twodimensional (2D) square lattice with all coupling coefficients being positive. Simulated results show the existence of two types of nontrivial corner states in this system, with one type being identified as bound states in the continuum (BIC). The non-BIC corner states are also found by surrounding a nontrivial sample with a trivial one, and interestingly, these perfectly confined corner states can be gradually delocalized and merge into edge states by tuning the inter-system coupling coefficient. Both BIC and non-BIC corner states are originated from bulk dipole moments rather than the quantized quadrupole moments, with the corresponding topological invariant being the 2D Zak phase. Full wave simulations based on realistic acoustic waveguide structures are demonstrated. Our proposal provides an

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¶ These authors contributed equally. Abstract:We demonstrate that multiple topological transitions can occur, with high-sensitivity, by continuous change of the geometry of a simple 2D dielectric-frame photonic crystal consisting of circular air-holes. By changing the radii of the holes and/or the distance between them, multiple transitions between normal and topological photonic band gaps (PBGs) can appear. The time-reversal symmetric topological PBGs resemble the quantum spin-Hall insulator of electrons and have two counter-propagating edge states. We search for optimal topological transitions, i.e., sharp transitions sensitive to the geometry, and optimal topological PBGs, i.e., large PBGs with clean spectrum of edge states. Such optimizations reveal that dielectric-frame photonic crystals are promising for optical sensors and unidirectional waveguides.

A simple method of irreversibly sealing SU-8 microfluidic channels using PDMS is reported in this paper. The method is based on inducing a chemical reaction between PDMS and SU-8 by first generating amino groups on PDMS surface using N 2 plasma treatment, then allowing the amino groups to react with the residual epoxy groups on SU-8 surface at an elevated temperature. The N 2 plasma treatment of PDMS can be conducted using an ordinary plasma chamber and high purity N 2 , while the residual epoxy groups on SU-8 surface can be preserved by post-exposure baking SU-8 at a temperature no higher than 95 C. The resultant chemical bonding between PDMS and SU-8 using the method create an interface that can withstand a stress that is greater than the bulk strength of PDMS. The bond is permanent and is long-term resistant to water. The method was applied in fabricating SU-8 microfluidi-photonic integrated devices, and the obtained devices were tested to show desirable performance.

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Optofluidic devices combining micro-optical and microfluidic components bring a host of new advantages to conventional microfluidic devices. Aspects, such as optical beam shaping, can be integrated on-chip and provide high-sensitivity and built-in optical alignment. Optofluidic microflow cytometers have been demonstrated in applications, such as point-of-care diagnostics, cellular immunophenotyping, rare cell analysis, genomics and analytical chemistry. Flow control, light guiding and collecting, data collection and data analysis are the four main techniques attributed to the performance of the optofluidic microflow cytometer. Each of the four areas is discussed in detail to show the basic principles and recent developments. 3D microfabrication techniques are discussed in their use to make these novel microfluidic devices, and the integration of the whole system takes advantage of the miniaturization of each sub-system. The combination of these different techniques is a spur to the development of microflow cytometers, and results show the performance of many types of microflow cytometers developed recently.

The numerical modeling of actively Q-switched fiber lasers is systematically presented. On the basis of typical Q-switched ytterbium-doped double-clad fiber lasers under forward and backward pump, the dynamic characteristics of pulse energy, pulse width, population inversion, and stored energy at tens-of-kilohertz repetition rates are studied by using the traveling-wave method. The laser performance is further investigated for different fiber core diameters, doping rates, cavity lengths, fiber losses, signal and pump wavelengths, reflectivities of output coupler, and switching speed of an acousto-optic modulator; the laser optimization is also quantitatively discussed. Some simulation results are also compared with previous experimental results.

The objective of our study was to introduce community quarantine strategy against coronavirus disease 2019 (COVID-19) in Anhui and evaluate the effectiveness of community quarantine based on trauma center (TC) patients. Method: The structure of community quarantine strategy was illustrated. Distribution of injuries among patients in two TCs between January 24, 2020 and February 24, 2020 was described. Multiple linear regression was used to analyze the correlation between the distribution of Injuries in TCs and the number of COVID-19-associated cases. Results: A total of 757 TC patients in the two hospitals were enrolled. The number of traffic injuries and outdoor injuries showed a significant decrease in the early stage and began to increase on February 17. The number of indoor injuries neither decreased nor increased. Multiple linear regression analysis revealed a significant correlation between COVID-19-associated cases and traffic and outdoor injuries. Conclusion: From the perspective of the injuries in TCs, community quarantine strategy was effectively implemented and significantly slowed the outbreak of COVID-19 in Anhui. However, the implementation and maintenance of the strategy is costly and requires the participation of the entire population.