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Intrinsic disinfection byproducts are formed by reactions between disinfectant species and/or their decomposition products. In this review, we focus on a subset that accumulates in free chlorine and chloramine drinking water systems. First, we review the sequential formation of chlorite, chlorate, and perchlorate in hypochlorite feedstocks. Model simulations indicate chlorate and perchlorate can accumulate under realistic dosing conditions and can be managed with less concentrated feedstocks and climate-controlled storage. Second, we review the formation pathways of dichloramine and chloronitramide anion. Chloronitramide anion accumulation may be mitigated by increasing monochloramine stability and quenching reactive nitrogen species in its formation pathway. 

Abstract Optical phonon engineering through nonlinear effects has been utilized in ultrafast control of material properties. However, nonlinear optical phonons typically exhibit rapid decay due to strong mode-mode couplings, limiting their effectiveness in temperature or frequency sensitive applications. Here we report the observation of long-lived nonlinear optical phonons through the spontaneous formation of phonon frequency combs in the van der Waals material CrXTe₃(X=Ge, Si) using high-resolution Raman scattering. Unlike conventional optical phonons, the highestA_gmode in CrGeTe₃splits into equidistant, sharp peaks forming a frequency comb that persists for hundreds of oscillations and survives up to 200K. These modes correspond to localized oscillations of Ge₂Te₆clusters, isolated from Cr hexagons, behaving as independent quantum oscillators. Introducing a cubic nonlinear term to the harmonic oscillator model, we simulate the phonon time evolution and successfully replicate the observed comb structure. Similar frequency comb behavior is observed in CrSiTe₃, demonstrating the generalizability of this phenomenon. Our findings demonstrate that Raman scattering effectively probes high-frequency nonlinear phonon modes, offering insight into the generation of long-lived, tunable phonon frequency combs with potential applications in ultrafast material control and phonon-based technologies. 

Forming an interface between immiscible fluids incurs a free-energy cost that usually favors minimizing the interfacial area. An emulsion droplet of fixed volume therefore tends to form a sphere, and pairs of droplets tend to coalesce. Surfactant molecules adsorbed to the droplets' surfaces stabilize emulsions by providing a kinetic barrier to coalescence. Here, we show that the pressure exerted by bound surfactant molecules also competes with the droplet's intrinsic surface tension and can reverse the sign of the overall surface free energy. The onset of negative surface tension favors maximizing surface area and therefore favors elongation into a wormlike morphology. Analyzing this system in the Gibbs grand canonical ensemble reveals a phase transition between spherical and wormlike emulsions that is governed by the chemical potential of surfactant molecules in solution. Predictions based on this model agree with the observed behavior of an experimental model system composed of lipid-stabilized silicone oil droplets in an aqueous surfactant solution. 

BackgroundThe trachea, a vital conduit in the lower airway system, can be affected by various disorders, such as tracheal neoplasms and tracheoesophageal fistulas, that often necessitate reconstruction. While short-segment defects can sometimes be addressed with end-to-end anastomosis, larger defects require tracheal reconstruction, a complex procedure with no universally successful replacement strategy. Tissue engineering offers a promising solution for tracheal repair, particularly focusing on regenerating its epithelium, which plays a critical role in protecting the respiratory system and facilitating mucociliary clearance. However, replicating the complex structure and functionality of the tracheal epithelium remains a significant challenge, with key hurdles including proper cell differentiation, functional mucociliary clearance, and addressing the relative lack of vascular supply to the trachea.SummaryCurrent tissue engineering approaches, including biomaterial scaffolds, decellularized tissues, and scaffold-free methods, have shown varying levels of success, while in vitro air-liquid interface (ALI) cultures have provided valuable insights into epithelial modeling. Despite these advances, translating these findings into effective in vivo applications remains difficult due to challenges such as immune responses, inadequate integration with host tissue, and limited longterm functionality of engineered constructs. Overcoming these barriers requires further refinement of cell sources, scaffold materials and bioactive factors that promote vascularization and sustained epithelial function.Key MessagesThis review evaluates the current strategies and modeling, biomaterial scaffolds, cells, and bioactive factors used in tracheal epithelium regeneration, as well as the methods employed to assess their success through histological, functional, and molecular analyses. While significant progress has been made, the development of a safe, functional, and clinically viable trachealgraft remains elusive, underscoring the need for continued innovation in airway tissue engineering. Future advancements in biomaterial design, stem cell technology, and bioreactor-based tissue maturation hold promise for addressing challenges. 

The main focus of this article is radius-based (supplier) clustering in the two-stage stochastic setting with recourse, where the inherent stochasticity of the model comes in the form of a budget constraint. In addition to the standard (homogeneous) setting where all clients must be within a distance\(R\)of the nearest facility, we provide results for the more general problem where the radius demands may beinhomogeneous(i.e., different for each client). We also explore a number of variants where additional constraints are imposed on the first-stage decisions, specifically matroid and multi-knapsack constraints, and provide results for these settings. We derive results for the most general distributional setting, where there is only black-box access to the underlying distribution. To accomplish this, we first develop algorithms for thepolynomial scenariossetting; we then employ a novelscenario-discardingvariant of the standardSample Average Approximationmethod, which crucially exploits properties of the restricted-case algorithms. We note that the scenario-discarding modification to the SAA method is necessary to optimize over the radius.