Superomniphobic surfaces (i.e., surfaces that are extremely repellent to both high surface tension liquids like water and low surface tension liquid like oils) can be fabricated through a combination of surface chemistry that imparts low solid surface energy with a re-entrant surface texture. Recently, surface texturing with lasers has received significant attention because laser texturing is scalable, solvent-free, and can produce a monolithic texture on virtually any material. In this work, we fabricated nanostructured omniphobic and superomniphobic surfaces with a variety of materials using a simple, inexpensive and commercially available CO laser engraver. Further, we demonstrated that the nanostructured omniphobic and superomniphobic surfaces fabricated using our laser texturing technique can be used to design patterned surfaces, surfaces with discrete domains of the desired wettability, and on-surface microfluidic devices.
eutrophication and acidification of soils which lead to forest extinction and decline in biological diversity [3,4]. Ammonia also readily reacts with atmospheric species such as sulfuric acid (H 2 SO 4 ), nitric acid (HNO 3 ), and hydrochloric acid (HCl) to form fine particulate matter (PM 2.5 ) which can have harmful effects on human health [5]. The particles also cause haze which lead to visibility reduction and affect global radiation budgets [6][7][8]. Two major sources of ammonia are emissions resulting from domestic animals, and from motor vehicle combustion, meaning that most of the ammonia emitted to the atmosphere is directly or indirectly anthropogenic [9]. In spite of the importance of ammonia in the atmosphere, measurement of atmospheric ammonia concentrations and its regional variations have been relatively limited due to two important reasons:(1) Ambient concentrations are low and vary widely, and (2) ammonia is a sticky gas that introduces significant inlet challenges for typical closed-path instruments [8,10,11].We are primarily interested in ammonia emissions from concentrated animal feeding operations (CAFOs), such as feedlots and dairies, and in particular we seek to develop sensors for study of ammonia emissions and bidirectional fluxes and deposition [12,13]. Key sensor requirements are ppb level precision, and time response on the order of seconds, in order to measure turbulent (near-field) plumes that have concentrations typically ranging from 10 to 100 s of ppb. As will be discussed herein, widely used closedpath ammonia laser sensors typically have time response of ~30 s. While adequate for some applications, improving the time response to ~1 s would greatly benefit applications including: (1) moving toward widely used eddy-covariance methods that provide flux information [14], (2) quantifying fluxes from high emission transient/episodic events lasting for seconds to 10 s of seconds, e.g., manure handling/application, barn flushouts at dairies, and top dress application Abstract An open-path cavity ring-down spectroscopy (CRDS) sensor has been developed for measurement of atmospheric ammonia (NH 3 ) and represents the first use of open-path CRDS in the mid-infrared region. The sensor uses a continuous-wave distributed feedback quantum cascade laser at 10.33 μm to target strong absorption features. The optical cavity is constructed with two high-reflectivity mirrors (R = 0.9995). The open-path configuration removes inlet effects, which are very challenging for closed-path instruments, and can be enabling for compact, low-power designs. Sensor performance was validated in the laboratory by measuring known concentrations in a closed-path configuration. The open-path configuration was validated by comparison against a commercial closed-path CRDS instrument for outdoor measurements at a small feed lot. Ammonia concentrations from the two instruments showed good agreement with slope of 0.990 (R 2 = 0.92), for 5-min averages. The precision of the open-path instrument was found from Allan varianc...
The objective of the present work is to identify differences in elemental fingernail composition between opium-addicted and healthy adult human subjects using laser-induced breakdown spectroscopy. Thirty nails from normal, healthy male subjects and 30 nails from opium-addicted male individuals were analyzed. Measurements on 60 nail samples were carried out, identifying 13 key species including 11 neutral elements and 2 ions. Discriminant Function Analysis (DFA) was used to classify the samples between the two groups. Spectral line intensities of elements including Fe, C, Ti, Mg, Si, Al, Ca, H, K, O, and Na were considered variables in DFA. This analysis demonstrates the efficient discrimination between the two groups. However, the number of samples in this work is not sufficient for a decisive conclusion and further research is needed to generalize this idea.
Anthropogenic emissions of ammonia to the atmosphere, particularly those from agricultural sources, can be damaging to the environment and human health and can drive a need for sensor technologies that can be used to detect and quantify the emissions. Mobile sensing approaches that can be deployed on ground-based or aerial vehicles can provide scalable solutions for high throughput measurements but require relatively compact and low-power sensor systems. This contribution presents an ammonia sensor based on wavelength modulation spectroscopy (WMS) integrated with a Herriott multi-pass cell and a quantum cascade laser (QCL) at 10.33 µm oriented to mobile use. An open-path configuration is used to mitigate sticky-gas effects and achieve high time-response. The final sensor package is relatively small (~20 L), lightweight (~3.5 kg), battery-powered (<30 W) and operates autonomously. Details of the WMS setup and analysis method are presented along with laboratory tests showing sensor accuracy (<~2%) and precision (~4 ppb in 1 s). Initial field deployments on both ground vehicles and a fixed-wing unmanned aerial vehicle (UAV) are also presented.
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