Development and Application of Automated Vocal Fold Tracking Software in a Rat Surgical Model.

OBJECTIVE: The rat is a widely used model for studying vocal fold (VF) function after recurrent laryngeal nerve injury, but common techniques for evaluating rat VF motion remain subjective and imprecise. To address this, we developed a software package, called RatVocalTracker1.0 (RVT1.0), to quantify VF motion and tested it on rats with iatrogenic unilateral vocal fold paralysis (VFP). METHODS: A deep neural network was trained to identify the positions of the VFs and arytenoid cartilages (ACs) in transoral laryngoscope videos of the rat glottis. Software was developed to estimate glottic midline, VF displacement, VF velocity, and AC angle. The software was applied to laryngoscope videos of adult rats before and after right recurrent and superior laryngeal nerve transection (N = 15; 6M, 9F). All software calculated metrics were compared before and after injury and validated against manually calculated metrics. RESULTS: RVT1.0 accurately tracked and quantified VF displacement, VF velocity, and AC angle. Significant differences were found before and after surgery for all RVT1.0 calculated metrics. There was strong agreement between programmatically and manually calculated measures. Automated analysis was also more efficient than nearly all manual methods. CONCLUSION: This approach provides fast, accurate assessment of VF motion in rats with minimal labor and allows for quantitative comparison of lateral differences in movement. Through this novel analysis method, we can differentiate healthy movement from unilateral VFP. RVT1.0 is open-source and will be a valuable tool for researchers using the rat model for laryngology research. LEVEL OF EVIDENCE: NA Laryngoscope, 134:340-346, 2024.

A comparison of confocal and epifluorescence microscopy for quantification of RNAScope and immunohistochemistry fluorescent images.

BACKGROUND: Quantification of RNA expression and protein production in fluorescent stainings provides critical information concerning neurodevelopment. A trustable independent quantification technique requires acquisition of reliable images prior to image processing. There is uncertainty in existing literature regarding the use of confocal microscopy compared to standard epifluorescence microscopy, especially in the context of RNA in situ hybridization protocols. NEW METHOD: The hindbrains of developing rat embryos from embryologic day 14 (E14) to E20 were sectioned and stained for expression of Hoxb1, Hoxb2, and Phox2b using both RNAScope and immunohistochemistry. Islet1 was used for identification of hindbrain motoneuron cell bodies. Slides were imaged using both confocal and epifluorescence microscopy. RESULTS: Expression patterns of both mRNA and protein were similar in both imaging modalities. Analyses of Hoxb1 and Hoxb2 mRNA expression were particularly concordant between-scopes, with similar p-values and posthoc differences between timepoints. Confocal imaging of Hoxb2 protein yielded a significant peak at E18, but this level of significance was not reached using epifluorescence microscopy. Although similar trends were observed, only Phox2b RNAScope results were statistically significant when analyzed with confocal microscopy. In contrast, Phox2b immunostaining analyses showed significant differences using both microscopes. COMPARISON WITH EXISTING METHODS: Researchers may save time and financial resources if epifluorescence microscopy provides comparable or equal results as confocal. CONCLUSIONS: Epifluorescence microscopy appears sufficient for quantification of RNAScope experiments with relatively low puncta per cell, while confocal microscopy gives clearer definition to immunohistochemical protein relationships and may be preferable especially in targets with low protein production.

Temporal Expression of Hox Genes and Phox2b in the Rat Nucleus Ambiguus During Development: Implications on Laryngeal Innervation.

OBJECTIVES: Recurrent laryngeal nerve (RLN) injury results in synkinetic reinnervation and vocal fold paralysis. Investigation of cues expressed in the developing brainstem that influence correct selective targeting of intrinsic laryngeal muscles may elucidate post-injury abnormalities contributing to non-functional reinnervation. Primary targets of interest were Hoxb1 and Hoxb2, members of the Hox family that create overlapping gradients in the developing brain, and their target Phox2b, a transcription factor necessary for cranial nerve branchio- and visceromotoneuron survival. METHODS: Rat embryos at developmental days E14, E16, E18, and E20 (4 animals/age) were sectioned for RNA in situ hybridization to detect Hoxb1, Hoxb2, and Phox2b mRNA within the brainstem. Slides were costained with Islet1 antibody for identification of the nucleus ambiguus. Results were confirmed using immunohistochemistry. Sections were imaged on a confocal microscope. RNA and protein expressions were quantified using QuPath. Statistical analyses were performed using R. RESULTS: Hoxb1, Hoxb2, and Phox2b expressions varied according to embryologic age. Hoxb1 and Hoxb2 expression peaked at E16, with significant decreases at E18 and E20 (one-way ANOVA p = 0.001 for both). Phox2b expression was highest at E14 and trended downward with increased embryologic age (one-way ANOVA p = 0.005). CONCLUSION: Peak expression of Hoxb1 and Hoxb2 is observed at time points when the RLN arrives at the larynx and begins to branch toward individual muscles, positioning these gene products to be involved in cueing laryngeal motoneuron identity and target identification. Higher expression of Phox2b earlier in development suggests a role in laryngeal motoneuron formation. LEVEL OF EVIDENCE: NA Laryngoscope, 133:3462-3471, 2023.

Clinical parameters at time of admission as prognostic indicators in cats presented for trauma to an emergency centre in New Zealand: a retrospective analysis.

OBJECTIVES: The aims of this study were to describe the clinical features of cats presented for trauma in a first-opinion and referral teaching hospital in New Zealand, and to determine the relationship between those features and outcome. METHODS: The electronic medical records of cats presented for trauma to the Massey University Pet Emergency Centre between September 2013 and January 2019 were examined, from which the signalment, clinical parameters and patient outcomes were extracted. Cases were assigned an Animal Trauma Triage (ATT) score and Modified Glasgow Coma Scale (MGCS) score. Variables were selected for inclusion in a logistic regression model to predict survival, and backward elimination was used to find the minimal significant model. RESULTS: In total, 530 cats met the inclusion criteria. The cause of injury was not known in the majority of cases (38.0%). The most common location of injury was the hindlimbs/pelvis/tail (n = 247; 41%), and skin lacerations/abrasions were the most common specific injury. Multivariate analysis revealed altered mentation (odds ratio [OR] 0.31, P = 0.029), hypothermia (rectal temperature <37.8°C [<100.04°F]; OR 0.45, P = 0.015) and an ATT score ⩾5 (OR 0.13, P <0.001) to be statistically significantly associated with mortality. CONCLUSIONS AND RELEVANCE: Altered mentation and hypothermia are easily measurable perfusion parameter abnormalities associated with mortality in cats presenting with trauma. The ATT score appears to be an accurate prognostic indicator in cats presenting with trauma in New Zealand. These results highlight the importance of incorporating a hands-on triage examination in each cat that presents as an emergency after trauma.

Review and Analysis of National Monitoring Systems for Antimicrobial Resistance in Animal Bacterial Pathogens in Europe: A Basis for the Development of the European Antimicrobial Resistance Surveillance Network in Veterinary Medicine (EARS-Vet).

The monitoring of antimicrobial resistance (AMR) in bacterial pathogens of animals is not currently coordinated at European level. To fill this gap, experts of the European Union Joint Action on Antimicrobial Resistance and Healthcare Associated Infections (EU-JAMRAI) recommended building the European Antimicrobial Resistance Surveillance network in Veterinary medicine (EARS-Vet). In this study, we (i) identified national monitoring systems for AMR in bacterial pathogens of animals (both companion and food-producing) among 27 countries affiliated to EU-JAMRAI, (ii) described their structures and operations, and (iii) analyzed their respective strengths, weaknesses, opportunities and threats (SWOT). Twelve countries reported having at least one national monitoring system in place, representing an opportunity to launch EARS-Vet, but highlighting important gaps in AMR data generation in Europe. In total, 15 national monitoring systems from 11 countries were described and analyzed. They displayed diverse structures and operations, but most of them shared common weaknesses (e.g., data management and representativeness) and common threats (e.g., economic vulnerability and data access), which could be addressed collectively under EARS-Vet. This work generated useful information to countries planning to build or improve their system, by learning from others' experience. It also enabled to advance on a pragmatic harmonization strategy: EARS-Vet shall follow the European Committee on Antimicrobial Susceptibility Testing (EUCAST) standards, collect quantitative data and interpret AMR data using epidemiological cut-off values.

Defining the scope of the European Antimicrobial Resistance Surveillance network in Veterinary medicine (EARS-Vet): a bottom-up and One Health approach.

BACKGROUND: Building the European Antimicrobial Resistance Surveillance network in Veterinary medicine (EARS-Vet) was proposed to strengthen the European One Health antimicrobial resistance (AMR) surveillance approach. OBJECTIVES: To define the combinations of animal species/production types/age categories/bacterial species/specimens/antimicrobials to be monitored in EARS-Vet. METHODS: The EARS-Vet scope was defined by consensus between 26 European experts. Decisions were guided by a survey of the combinations that are relevant and feasible to monitor in diseased animals in 13 European countries (bottom-up approach). Experts also considered the One Health approach and the need for EARS-Vet to complement existing European AMR monitoring systems coordinated by the ECDC and the European Food Safety Authority (EFSA). RESULTS: EARS-Vet plans to monitor AMR in six animal species [cattle, swine, chickens (broilers and laying hens), turkeys, cats and dogs], for 11 bacterial species (Escherichia coli, Klebsiella pneumoniae, Mannheimia haemolytica, Pasteurella multocida, Actinobacillus pleuropneumoniae, Staphylococcus aureus, Staphylococcus pseudintermedius, Staphylococcus hyicus, Streptococcus uberis, Streptococcus dysgalactiae and Streptococcus suis). Relevant antimicrobials for their treatment were selected (e.g. tetracyclines) and complemented with antimicrobials of more specific public health interest (e.g. carbapenems). Molecular data detecting the presence of ESBLs, AmpC cephalosporinases and methicillin resistance shall be collected too. CONCLUSIONS: A preliminary EARS-Vet scope was defined, with the potential to fill important AMR monitoring gaps in the animal sector in Europe. It should be reviewed and expanded as the epidemiology of AMR changes, more countries participate and national monitoring capacities improve.

First detected case of rabbit Haemorrhagic disease virus 2 (RHDV2) in the Irish hare (Lepus timidus hibernicus).

BACKGROUND: Rabbit haemorrhagic disease virus (RHDV) is a Lagovirus, a subgroup of the family Caliciviridae. RHDV2 is a variant first described in France in 2010, and has since spread globally. It has been reported in several Lagomorph species (rabbits, hares, and their relatives) as well as other mammals including voles and shrews. The disease has raised international concerns for its potential impact on population abundance trajectories, particularly as 25% of Lagomorphs are currently Red-Listed by the International Union for the Conservation of Nature (IUCN). The Irish hare (Lepus timidus hibernicus) is a subspecies of the mountain hare, L. timidus, and is endemic to Ireland, making it an Evolutionarily Significant Unit of intrinsic value. CASE PRESENTATION: The first case of RHDV2 was detected in a wild Irish hare in July 2019. The individual exhibited atypical neurological behaviour (running in circles) prior to death. On necropsy, pink tinged foam was seen in the trachea and congestion was noted in the lungs, but there was no evidence of haemorrhages in any other organ. Both the liver and spleen were tested by reverse transcription real time qPCR confirming high levels of RHDV2 RNA. Histopathology confirmed multifocal necrotising hepatitis. CONCLUSION: The Irish hare is susceptible to RHDV2 infection. Further investigation is warranted to explore the clinical, epidemiological, and population biology implications.

Building the European Antimicrobial Resistance Surveillance network in veterinary medicine (EARS-Vet).

Antimicrobial resistance (AMR) should be tackled through a One Health approach, as stated in the World Health Organization Global Action Plan on AMR. We describe the landscape of AMR surveillance in the European Union/European Economic Area (EU/EEA) and underline a gap regarding veterinary medicine. Current AMR surveillance efforts are of limited help to veterinary practitioners and policymakers seeking to improve antimicrobial stewardship in animal health. We propose to establish the European Antimicrobial Resistance Surveillance network in Veterinary medicine (EARS-Vet) to report on the AMR situation, follow AMR trends and detect emerging AMR in selected bacterial pathogens of animals. This information could be useful to advise policymakers, explore efficacy of interventions, support antimicrobial stewardship initiatives, (re-)evaluate marketing authorisations of antimicrobials, generate epidemiological cut-off values, assess risk of zoonotic AMR transmission and evaluate the burden of AMR in animal health. EARS-Vet could be integrated with other AMR monitoring systems in the animal and medical sectors to ensure a One Health approach. Herein, we present a strategy to establish EARS-Vet as a network of national surveillance systems and highlight challenges of data harmonisation and bias. Strong political commitment at national and EU/EEA levels is required for the success of EARS-Vet.

Pharmacological management of cerebral ischemia in the elderly.

Introduction: For elderly adults in the United States, stroke is the fifth leading cause of death of which ischemic strokes comprise a vast majority. Optimal pharmacological management of elderly ischemic stroke patients involves both reperfusion and supportive care. Recent research into pharmacological management has focused on vascular, immunomodulatory, cytoprotective, and alternative agents, some of which have shown limited success in clinical trials. However, no treatments have been established as a reliable mode for management of cerebral ischemia for elderly adults beyond acute thrombolysis.Areas covered: The authors conducted a literature search for ischemic stroke management in the elderly and a search for human drug studies for managing ischemic stroke on clinicaltrials.gov. Here, they describe recent progress in the pharmacological management of cerebral ischemia in the elderly.Expert opinion: Many drug classes (antihypertensive, cytoprotective and immunomodulatory, and alternative agents) have been explored with limited success in managing ischemic stroke, though some have shown preventative benefits. We generally observed a broad gap in evidence on elderly patients from studies across all drug classes, necessitating further studies to gain an understanding of effective management of ischemic stroke in this large demographic of patients.

Resolving Atmospheric Mercury Loading and Source Trends from Isotopic Records of Remote North American Lake Sediments.

The strongest evidence for anthropogenic alterations to the global mercury (Hg) cycle comes from historical records of mercury deposition preserved in lake sediments. Hg isotopes have added a new dimension to these sedimentary archives, promising additional insights into Hg source apportionment and biogeochemical processing. Presently, most interpretations of historical changes are constrained to a small number of locally contaminated ecosystems. Here, we describe changes in natural Hg isotope records from a suite of dated sediment cores collected from various remote lakes of North America. In nearly all cases, the rise in industrial-use Hg is accompanied by an increase in δ202Hg and Δ199Hg values. These trends can be attributed to large-scale industrial emission of Hg into the atmosphere and are consistent with positive Δ199Hg values measured in modern-day precipitation and modeled increases in δ202Hg values from global emission inventories. Despite similar temporal trends among cores, the baseline isotopic values vary considerably among the different study regions, likely attributable to differences in the fractionation produced in situ as well as differing amounts of atmospherically delivered Hg. Differences among the study lakes in precipitation and watershed size provide an empirical framework for evaluating Hg isotopic signatures and global Hg cycling.

Tracheal Inflammatory Myofibroblastoma: A Rare Tumor of the Trachea.

Inflammatory myofibroblastic tumors (IMTs), also known as inflammatory pseudotumor are rarely reported in the trachea. Although initially considered benign, with the recent evidence of local recurrence after surgical resection, cases of metastatic spread, and advance in cytogenetic analysis, they are now categorized as tumors with malignant potential. Correct histological diagnosis is of utmost importance, as they closely resemble other benign and malignant spindle cell tumors with myofibroblasts predominance. Treatment remains challenging taking into account the location involving the airway. Here, we describe a case of tracheal IMF in an apparently healthy young adult presenting with recurrent hemoptysis.

Global and Local Sources of Mercury Deposition in Coastal New England Reconstructed from a Multiproxy, High-Resolution, Estuarine Sediment Record.

Historical reconstruction of mercury (Hg) accumulation in natural archives, especially lake sediments, has been essential to understanding human perturbation of the global Hg cycle. Here we present a high-resolution chronology of Hg accumulation between 1727 and 1996 in a varved sediment core from the Pettaquamscutt River Estuary (PRE), Rhode Island. Mercury accumulation is examined relative to (1) historic deposition of polycyclic aromatic hydrocarbons (PAHs) and lead (Pb) and its isotopes (206Pb/207Pb) in the same core, and (2) other reconstructions of Hg deposition in urban and remote settings. Mercury deposition in PRE parallels the temporal patterns of PAHs, and both track industrialization and regional coal use between 1850 and 1950 as well as rising petroleum use after 1950. There is little indication of increased Hg deposition from late 19th-century silver and gold mining in the western U.S. A broad maximum of Hg deposition during 1930-1980, and not found in remote sites, is consistent with the predicted influence of additional industrial sources and commercial products. Our results imply that a significant portion of global anthropogenic Hg emissions during the 20th century was deposited locally, near urban and industrial centers of Hg use and release.

A nationwide survey of anthelmintic treatment failure on sheep farms in Ireland.

BACKGROUND: Between 2013 and 2015 the Department of Agriculture, Food and the Marine (DAFM) administered a sheep technology adoption programme (STAP), with the aim of increasing profitability on Irish sheep farms by encouraging the adoption of best management practices. One of the options available to STAP participants was to test the efficacy of the anthelmintic treatment (benzimadazole, levamisole or macrocyclic lactone) used in their flocks by means of a drench test, which is a modification of the faecal egg count reduction test; individual faecal samples were collected from the same group of lambs before and after anthelmintic treatment, the number of eggs present pre and post treatment was subsequently determined from a pooled sample. RESULTS: In total, 4211 drench tests were undertaken by farmers during the 3 years of the programme. Information on the anthelmintic product used was available for 3771 of these tests; anthelmintics from the classes benzimidazole (BZ), levamisole (LV) and macrocyclic lactone (ML) (avermectins (AVM) plus moxidectin (MOX)) were used in 42.0%, 23.4% and 32.5% of tests, respectively. The remaining 2.1% of tests involved an inappropriate product. The efficacy of treatment against 'other trichostrongyles' (excluding Nematodirus spp and Strongyloides papillosus.) could be established for 1446 tests, and 51% of these tests were considered effective (i.e. a reduction of faecal egg count (FEC) ≥ 95%). There was a significant difference among the drug groups in efficacy; 31.5%, 51.9%, 62.5% and 84% of treatments were considered effective for BZ, LV, AVM, MOX, respectively. The efficacy of treatment against Nematodirus spp. could be established for 338 tests and the overall efficacy was 96%. CONCLUSIONS: Due to the significant difference among the anthelmintic classes for efficacy against 'other trichostrongyles' along with the high level of efficacy against Nematodirus spp., a genus for which anthelmintic resistance is rarely reported, it is concluded that anthelmintic resistance was responsible for the majority of the anthelmintic treatment failures observed.

Spatiotemporal patterns of mercury accumulation in lake sediments of western North America.

For the Western North America Mercury Synthesis, we compiled mercury records from 165 dated sediment cores from 138 natural lakes across western North America. Lake sediments are accepted as faithful recorders of historical mercury accumulation rates, and regional and sub-regional temporal and spatial trends were analyzed with descriptive and inferential statistics. Mercury accumulation rates in sediments have increased, on average, four times (4×) from 1850 to 2000 and continue to increase by approximately 0.2µg/m(2) per year. Lakes with the greatest increases were influenced by the Flin Flon smelter, followed by lakes directly affected by mining and wastewater discharges. Of lakes not directly affected by point sources, there is a clear separation in mercury accumulation rates between lakes with no/little watershed development and lakes with extensive watershed development for agricultural and/or residential purposes. Lakes in the latter group exhibited a sharp increase in mercury accumulation rates with human settlement, stabilizing after 1950 at five times (5×) 1850 rates. Mercury accumulation rates in lakes with no/little watershed development were controlled primarily by relative watershed size prior to 1850, and since have exhibited modest increases (in absolute terms and compared to that described above) associated with (regional and global) industrialization. A sub-regional analysis highlighted that in the ecoregion Northwestern Forest Mountains, <1% of mercury deposited to watersheds is delivered to lakes. Research is warranted to understand whether mountainous watersheds act as permanent sinks for mercury or if export of "legacy" mercury (deposited in years past) will delay recovery when/if emissions reductions are achieved.

Profiling oral and digital lesions in sheep in Ireland.

BACKGROUND: During the FMD outbreak in Ireland and the UK in 2001, there was significant uncertainty amongstveterinary practitioners and government veterinary inspectors surrounding the clinical diagnosis of FMD insheep. This situation was complicated by reports of idiopathic oral ulcers that closely resembled FMD ongross appearance which at that time were referred to as ovine mouth and gum obscure disease. METHODS: A field and abattoir study was carried out to determine the frequency, appearance and significance of oraland digital lesions in sheep in Ireland. A total of 3, 263 sheep were examined in 22 flocks, including 1, 969lambs and 1, 294 adults. A further 2,403 animals were examined by abattoir inspections. Animals bearing lesions of interest were identified, samples of the lesions were taken and subsequently examined by bacteriology, electron microscopy, serology, immunohistochemistry and histopathology. RESULTS: Forty four oral and 20 digital lesions were identified and characterised. Oral lesions were recorded mostfrequently in lambs, where the most common cause was orf virus infection. The majority of the oral lesions recorded in the adults was idiopathic and consistent with a diagnosis of idiopathic oral ulceration. A variety of digital lesions was observed, consistent with scald, foot-rot and contagious ovine digital dermatitis (CODD). All of the animals with lesions were seronegative to FMD virus (FMDV). CONCLUSIONS: There was no difficulty in differentiating these lesions from those caused by FMDV on the basis of flockhistory and careful clinical examination.

Atmospheric Hg emissions from preindustrial gold and silver extraction in the Americas: a reevaluation from lake-sediment archives.

Human activities over the last several centuries have transferred vast quantities of mercury (Hg) from deep geologic stores to actively cycling earth-surface reservoirs, increasing atmospheric Hg deposition worldwide. Understanding the magnitude and fate of these releases is critical to predicting how rates of atmospheric Hg deposition will respond to future emission reductions. The most recently compiled global inventories of integrated (all-time) anthropogenic Hg releases are dominated by atmospheric emissions from preindustrial gold/silver mining in the Americas. However, the geophysical evidence for such large early emissions is equivocal, because most reconstructions of past Hg-deposition have been based on lake-sediment records that cover only the industrial period (1850-present). Here we evaluate historical changes in atmospheric Hg deposition over the last millennium from a suite of lake-sediment cores collected from remote regions of the globe. Along with recent measurements of Hg in the deep ocean, these archives indicate that atmospheric Hg emissions from early mining were modest as compared to more recent industrial-era emissions. Although large quantities of Hg were used to extract New World gold and silver beginning in the 16th century, a reevaluation of historical metallurgical methods indicates that most of the Hg employed was not volatilized, but rather was immobilized in mining waste.

Methylmercury accumulation in plankton on the continental margin of the northwest Atlantic Ocean.

Accumulation of monomethylmercury (MMHg) by plankton is a key process influencing concentrations of this toxic mercury species in marine food webs and seafood. We examined bioaccumulation and biomagnification of MMHg in microseston and four size fractions of zooplankton on the continental shelf, slope, and rise of the northwest Atlantic Ocean. The bioaccumulation factor (BAF, L/kg) for MMHg in microseston averaged 10(4.3±0.3) among 21 locations, and concentrations were unrelated to those in colocated, filtered surface water. Instead, concentrations and the BAF of MMHg in microseston were related inversely with total suspended solids in surface water, a proxy for planktonic biomass at these remote locations. MMHg was biomagnified by a factor of 4 from microseston to zooplankton, and both concentrations of MMHg and the fraction of total mercury as MMHg increased with larger size fractions of zooplankton. These results suggest that the initial magnitude of MMHg uptake into pelagic marine food webs is influenced by the degree of primary production in surface waters and propagated up through large zooplankton. Accordingly, biological productivity, in addition to inputs of MMHg to surface waters, must be considered when predicting how MMHg bioaccumulation will vary spatially and temporally in the ocean.

Apportioning global and non-global components of mercury deposition through (210)Pb indexing.

Our previous work has documented a correlation between Hg concentrations and (210)Pb activity measured in wet deposition that might be used to help apportion sources of Hg in precipitation. Here we present the results of a 27-month precipitation collection effort using co-located samplers for Hg and (210)Pb designed to assess this hypothesis. Study sites were located on the east and west coasts of North America, in the continental interior, and on the Florida Peninsula. Relatively high variability in Hg/(210)Pb ratios was found at all sites regionally and seasonally (e.g., overall: 0.99-9.13ngdpm(-1)). The ratio of average volume-weighted Hg concentrations and (210)Pb activities showed consistent trends (higher in impacted area), with Glacier Bay in southeast Alaska, exhibiting the lowest value. Assuming that Glacier Bay represents a benchmark for a site with no regional contribution, we estimate less than 50% of the Hg input was "global" at the Seattle and Florida sites. Differences in Hg/(210)Pb in wet deposition could be due to either a regional/local source contribution of Hg, or a regional/local enhancement in the removal of Hg from the atmosphere (i.e., oxidants), however, this approach is not capable of discerning between these two possibilities. Thus, this method of source apportionment represents an estimate of the maximal amount of Hg contributed by regional sources and may be limited in regions of deep convective mixing.

Simultaneous measurement of magnitude and phase in interferometric sum-frequency vibrational spectroscopy.

We present a visible-infrared sum-frequency spectroscopic technique that is capable of simultaneously determining the magnitude and phase of the sample response from a single set of experimental conditions. This is especially valuable in cases where the phase stability is high, as in collinear beam geometries, as it enables multiple experiments to be performed without re-measuring the local oscillator phase or the reference phase. After illustrating the phase stability achievable with such a geometry, we provide a technique for quantitatively determining the magnitude and phase from a single set of two-dimensional spectral-temporal interference fringes. A complete demonstration is provided for the C-H stretching frequency region at the surface of an octadecyltricholosilane film.