Topological operations around exceptional points-time-varying system configurations associated with non-Hermitian singularities-have been proposed as a robust approach to achieving far-reaching open-system dynamics, as demonstrated in highly dissipative microwave transmission and cryogenic optomechanical oscillator experiments. In stark contrast to conventional systems based on closed-system Hermitian dynamics, environmental interferences at exceptional points are dynamically engaged with their internal coupling properties to create rotational stimuli in fictitious-parameter domains, resulting in chiral systems that exhibit various anomalous physical phenomena. To achieve new wave properties and concomitant device architectures to control them, realizations of such systems in application-abundant technological areas, including communications and signal processing systems, are the next step. However, it is currently unclear whether non-Hermitian interaction schemes can be configured in robust technological platforms for further device engineering. Here we experimentally demonstrate a robust silicon photonic structure with photonic modes that transmit through time-asymmetric loops around an exceptional point in the optical domain. The proposed structure consists of two coupled silicon-channel waveguides and a slab-waveguide leakage-radiation sink that precisely control the required non-Hermitian Hamiltonian experienced by the photonic modes. The fabricated devices generate time-asymmetric light transmission over an extremely broad spectral band covering the entire optical telecommunications window (wavelengths between 1.26 and 1.675 micrometres). Thus, we take a step towards broadband on-chip optical devices based on non-Hermitian topological dynamics by using a semiconductor platform with controllable optoelectronic properties, and towards several potential practical applications, such as on-chip optical isolators and non-reciprocal mode converters. Our results further suggest the technological relevance of non-Hermitian wave dynamics in various other branches of physics, such as acoustics, condensed-matter physics and quantum mechanics.

Water distribution systems are complex environments frequently containing corroded iron pipes and biofilms. To thoroughly understand the fate of halogenated disinfection byproducts (DBPs) in these systems, two degradation processes were investigated: abiotic degradation (i.e. hydrolysis and reductive dehalogenation) and biodegradation. DBPs were selected from 6 different compound classes representing both regulated DBPs (i.e. trihalomethanes or THMs, and haloacetic acids or HAAs) and non-regulated or "emerging" DBPs. Batch experiments were conducted to investigate the pathways and kinetics of DBP degradation. As expected, the relative importance of hydrolysis, abiotic reductive dehalogenation, and biodegradation depends on the DBP structure and on the environmental conditions (i.e. pH, temperature, dissolved oxygen, Fe minerals present, bacteria present, etc.). From our results, chloropicrin (i.e. trichloronitromethane) and most brominated DBPs are highly susceptible to abiotic reductive dehalogenation, trichloracetonitrile and trichloropropanone are the most susceptible to hydrolysis, and HAAs are readily biodegraded under aerobic conditions. Knowledge of DBP degradation mechanisms and rates in distribution systems is important for selecting DBP monitoring locations, modeling DBP fate, and for predicting exposure to these compounds. Such information could also be useful for developing treatment systems for DBP removal. 334

We designed, fabricated, and characterized varifocal microlenses, whose focal length varies along with the deformation of a transparent elastomer membrane under hydraulic pressure tailored by electroactive polymer actuators. The microfluidic channel of the microlens was designed to be embedded between silicon and glass so that transient fluctuation of the optical fluid and elastomer membrane is effectively suppressed, and thus the microlens is optically stabilized in a reduced time. Multilayered poly(vinylidene fluoride-trifluoroethylene-clorotrifluoroethylene) actuators were also developed and integrated onto the microfluidic chambers. We demonstrated that the developed microlenses are suitable for use in microimaging systems to make their foci tunable.

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The integration of bottom-up fabrication techniques and top-down methods can overcome current limits in nanofabrication. For such integration, we propose a gradient area-selective deposition using atomic layer deposition to overcome the inherent limitation of 3D nanofabrication and demonstrate the applicability of the proposed method toward large-scale production of materials. Cp(CH3)5Ti(OMe)3 is used as a molecular surface inhibitor to prevent the growth of TiO2 film in the next atomic layer deposition process. Cp(CH3)5Ti(OMe)3 adsorption was controlled gradually in a 3D nanoscale hole to achieve gradient TiO2 growth. This resulted in the formation of perfectly seamless TiO2 films with a high-aspect-ratio hole structure. The experimental results were consistent with theoretical calculations based on density functional theory, Monte Carlo simulation, and the Johnson-Mehl-Avrami-Kolmogorov model. Since the gradient area-selective deposition TiO2 film formation is based on the fundamentals of molecular chemical and physical behaviours, this approach can be applied to other material systems in atomic layer deposition.