US Government Employees Research Articles

Legacy and Contaminants of Emerging Concern in Tree Swallows Along an Agricultural to Industrial Gradient: Maumee River, Ohio.

Exposure to multiple classes of contaminants, both legacy and contaminants of emerging concern (CECs), were assessed in tree swallow (Tachycineta bicolor) tissue and diet samples from 6 sites along the Maumee River, Ohio, USA, to understand both exposure and possible effects of exposure to those CECs for which there are little avian data. The 6 sites represented a gradient from intensive agriculture upstream to highly urbanized and industrial landscapes downstream; 1 or 2 remote Wisconsin lakes were assessed for comparative purposes. Cytochrome P450 induction, DNA damage, and thyroid function were also assessed relative to contaminant exposure. Bioaccumulative CECs, such as polybrominated diphenyl ethers (PBDEs) and perfluorinated substances, did not follow any upstream to downstream gradient; but both had significantly greater concentrations along the Maumee River than at the remote lake sites. Greater exposure to PBDEs was apparent in swallows at or near wastewater-treatment facilities than at other sites. Total polychlorinated biphenyl and total polycyclic aromatic hydrocarbon concentrations were greater in swallows at downstream locations compared to upstream sites and were associated with higher ethoxyresorufin-O-dealkylase activity. Few herbicides or nonorganochlorine insecticides were detected in swallow tissues or their food, except for atrazine and its metabolite desethylatrazine. Few pharmaceuticals and personal care products were detected except for DEET and iopamidol. Both were detected in most liver samples but not in eggs, as well as detected at the remote lake sites. This is one of the most comprehensive assessments to date of exposure and effects of a wide variety of CECs in birds. Environ Toxicol Chem 2020;39:1936-1952. © 2020 SETAC. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Turnover behavior among US government employees

High employee turnover is a critical policy issue for public managers to solve. The US government is concerned about slowing turnover rates, which have accelerated from 14–15% to more than 18% since the Great Recession. Explanations for increases in employee departure are more difficult to pin down. The expected wave of baby-boomer retirements did not materialize and cannot explain turnover. The impact of the Great Recession on employment makes it more difficult to theorize about the relationship between employee–organizational fit and turnover. This study analyzes US government employees’ turnover using data from the 2003, 2006, 2010, and 2013 editions of the National Survey of College Graduates. The data provide a unique opportunity to study cohorts of US government workers before and after the recession. Statistical models of employee turnover focus on comparing the factors that lead to employee departure. The exodus of workers from government offices can be explained more by the fit between the individual and organizational needs than by a mismatch between the skills required in the job and the needs of the organization. The results show that when there is a mismatch between individual skill level and the skills in their job, individuals are more likely to move within government. Workers that made job changes after the recession (2010–2013) had a greater gap in organizational fit than those that made job changes prior to the recession (2003–2006). Points for practitioners This study describes turnover in public organizations and provides conclusions showing how managers can minimize the risk of turnover to ensure effective government. Public managers should modify management policies to meet the needs of modern-day employees and make the government more resilient within changing work environments. Organizations can begin to mitigate turnover rates during hiring by matching employment opportunities with the job skills and expectations of candidates through careful hiring, appropriate placement, and providing employee training and support.

Macroinvertebrate sensitivity thresholds for sediment in Virginia streams.

Sediment is the most commonly identified pollutant associated with macroinvertebrate community impairments in freshwater streams nationwide. Management of this physical stressor is complicated by the multiple measures of sediment available (e.g., suspended, dissolved, bedded) and the variability in natural "healthy" sediment loadings across ecoregions. Here we examine the relative importance of 9 sediment parameters on macroinvertebrate community health as measured by the Virginia Stream Condition Index (VSCI) across 5 ecoregions. In combination, sediment parameters explained 27.4% of variance in the VSCI in a multiregion data set and from 20.2% to 76.4% of variance for individual ecoregions. Bedded sediment parameters had a stronger influence on VSCI than did dissolved or suspended parameters in the multiregion assessment. However, assessments of individual ecoregions revealed conductivity had a key influence on VSCI in the Central Appalachian, Northern Piedmont and Piedmont ecoregions. In no case was a single sediment parameter sufficient to predict VSCI scores or individual biological metrics. Given the identification of embeddedness and conductivity as key parameters for predicting biological condition, we developed family-level sensitivity thresholds for these parameters, based on extirpation. Resulting thresholds for embeddedness were 68% for combined ecoregions, 65% for the Mountain bioregion (composed of Central Appalachian, Ridge and Valley, and Blue Ridge ecoregions), and 88% for the Piedmont bioregion (composed of Northern Piedmont and Piedmont ecoregions). Thresholds for conductivity were 366 μS/cm for combined ecoregions, 391 μS/cm for the Mountain bioregion, and 136 μS/cm for the Piedmont bioregion. These thresholds may help water quality professionals identify impaired and at-risk waters designated to support aquatic life and develop regional strategies to manage sediment-impaired streams. Inclusion of embeddedness as a restoration endpoint may be warranted; this could be facilitated by application of more quantitative, less time-intensive measurement approaches. We encourage refinement of thresholds as additional data and genus-based metrics become available. Integr Environ Assess Manag 2019;15:77-92. Published 2018. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

“Don't Do as I Do”—The US Response to Russian and Chinese Cyber Espionage and Public International Law

The Russian government is accused of hacking emails circulating among senior members of Hilary Clinton's campaign team to support President Trump's election in 2016. This was not the first time the United States was the target of massive cyber espionage: The Chinese government is believed to have gained sensitive information on 22.1 million US government employees through “cyber intrusions” in 2014. This Article will examine whether cyber espionage of this kind is unlawful under public international law and will conclude that it is. Specifically, such espionage can result in a violation of territorial sovereignty and will likely violate the principle of non-intervention in the internal affairs of other States. Yet, based on the controversial “clean-hands-doctrine,” past US actions in the realms of cyber espionage and intervention may well invalidate any claims it asserts against Russia or China.

How to control for unmeasured confounding in an observational time-to-event study with exposure incidence information: the treatment choice Cox model.

In an observational study of the effect of a treatment on a time-to-event outcome, a major problem is accounting for confounding because of unknown or unmeasured factors. We propose including covariates in a Cox model that can partially account for an unknown time-independent frailty that is related to starting or stopping treatment as well as the outcome of interest. These covariates capture the times at which treatment is started or stopped and so are called treatment choice (TC) covariates. Three such models are developed: first, an interval TC model that assumes a very general form for the respective hazard functions of starting treatment, stopping treatment, and the outcome of interest and second, a parametric TC model that assumes that the log hazard functions for starting treatment, stopping treatment, and the outcome event include frailty as an additive term. Finally, a hybrid TC model that combines attributes from the parametric and interval TC models. As compared with an ordinary Cox model, the TC models are shown to substantially reduce the bias of the estimated hazard ratio for treatment when data are simulated from a realistic Cox model with residual confounding due to the unobserved frailty. The simulations also indicate that the bias decreases or levels off as the sample size increases. A TC model is illustrated by analyzing the Women's Health Initiative Observational Study of hormone replacement for post-menopausal women. Published 2017. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Field Study of Variable Rate Irrigation Management in Humid Climates

AbstractComparison of variable rate irrigation (VRI) management with uniform rate irrigation (URI) management in soybean and corn crops was studied for 2 years in Stoneville, Mississippi, USA. The experiments were conducted on two 6.7 ha fields. Each of them was equally split into two sectors. VRI management was performed in one sector and URI management in the other. A centre pivot VRI system was used for delivering irrigation water. Soil apparent electrical conductivity (EC) of the fields was used to delineate VRI management zones and create a VRI prescription map. The VRI treatment used 25% less irrigation water and produced 2.8% more yield in soybean and 0.8% more yield in corn than the URI treatment. Irrigation water productivity (WP) of soybean under VRI management was 0.84 kg m−3 which is 31.2% higher than URI. The WP of corn under VRI management was 1.69 kg m−3, 27.1% higher than URI. Yield of the rainfed treatment was significantly lower than the VRI and URI treatments for both soybean and corn in the 2015 season (p < 0.05). Results in this study demonstrated that VRI management was superior to URI in terms of water use efficiency. Copyright © 2017. This article has been contributed to by US Government employees and their work is in the public domain in the USA. Copyright © 2017. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Adaptively tuned particle swarm optimization with application to spatial design

Particle swarm optimization (PSO) algorithms are a class of heuristic optimization algorithms that are attractive for complex optimization problems. We propose using PSO to solve spatial design problems, e.g. choosing new locations to add to an existing monitoring network. Additionally, we introduce two new classes of PSO algorithms that perform well in a wide variety of circumstances, called adaptively tuned PSO and adaptively tuned bare bones PSO. To illustrate these algorithms, we apply them to a common spatial design problem: choosing new locations to add to an existing monitoring network. Specifically, we consider a network in the Houston, TX, area for monitoring ambient ozone levels, which have been linked to out‐of‐hospital cardiac arrest rates. Published 2017. This article has been contributed to by US Government employees and their work is in the public domain in the USA

The amplitude of lee waves on the boundary‐layer inversion

This study presents an analytical model for the amplitude of lee waves on the boundary‐layer inversion in two‐dimensional flow. Previous linear lee wave models, in which the amplitude depends on the power spectrum of topography, can be inaccurate if the amplitude is large. Our model incorporates nonlinear effects by assuming that lee waves originate at a region of transition between super‐ and subcritical flow (internal jump) downstream of topography. Energy flux convergence at this location is compensated by the radiation of laminar lee waves. The available energy is estimated using a hydraulic jump model and the resulting wave amplitude is determined from linear theory. According to this model, the amplitude of lee waves depends essentially on their wavelength and on the inversion height difference across the jump. The new amplitude model is verified against numerical simulations and water tank experiments. The agreement between the model and the numerical results is excellent, while the verification with water tank experiments reveals that the accuracy of the model is comparable to that of numerical simulations. Finally, we derive a nonlinearity parameter for interfacial lee waves and discuss the regime transition from lee waves to hydraulic jumps in terms of the Froude number and the non‐dimensional mountain and inversion heights. The National Center for Atmospheric Research is sponsored by the National Science Foundation. This article has been contributed to by a US Government employee and her work is in the public domain in the USA.

Multivariate models for prediction of human skin sensitization hazard.

One of the Interagency Coordinating Committee on the Validation of Alternative Method's (ICCVAM) top priorities is the development and evaluation of non-animal approaches to identify potential skin sensitizers. The complexity of biological events necessary to produce skin sensitization suggests that no single alternative method will replace the currently accepted animal tests. ICCVAM is evaluating an integrated approach to testing and assessment based on the adverse outcome pathway for skin sensitization that uses machine learning approaches to predict human skin sensitization hazard. We combined data from three in chemico or in vitro assays - the direct peptide reactivity assay (DPRA), human cell line activation test (h-CLAT) and KeratinoSens™ assay - six physicochemical properties and an in silico read-across prediction of skin sensitization hazard into 12 variable groups. The variable groups were evaluated using two machine learning approaches, logistic regression and support vector machine, to predict human skin sensitization hazard. Models were trained on 72 substances and tested on an external set of 24 substances. The six models (three logistic regression and three support vector machine) with the highest accuracy (92%) used: (1) DPRA, h-CLAT and read-across; (2) DPRA, h-CLAT, read-across and KeratinoSens; or (3) DPRA, h-CLAT, read-across, KeratinoSens and log P. The models performed better at predicting human skin sensitization hazard than the murine local lymph node assay (accuracy 88%), any of the alternative methods alone (accuracy 63-79%) or test batteries combining data from the individual methods (accuracy 75%). These results suggest that computational methods are promising tools to identify effectively the potential human skin sensitizers without animal testing. Published 2016. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Revisiting the Effects of Anger on Risk‐Taking: Empirical and Meta‐Analytic Evidence for Differences Between Males and Females

AbstractThat anger elicited in one situation can carry over to drive risky behavior in another situation has been described since the days of Aristotle. The present studies examine the mechanisms through which and the conditions under which such behavior occurs. Across three experiments, as well as a meta‐analytic synthesis of the data, results reveal that incidental anger is significantly more likely to drive risky decision making among males than among females. Moreover, the experiments document that, under certain circumstances, such risk‐taking pays off financially. Indeed, the present experiments demonstrate that, because the expected‐value‐maximizing strategy in these studies rewarded risk‐taking, angry‐male individuals earned more money than did both neutral‐emotion males and angry females. In sum, these studies found evidence for robust disparities between males and females for anger‐driven risk‐taking. Importantly, although men did not experience more anger than women, they did show a heightened tendency to respond to anger with risk‐taking. Published 2016. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Flow Management for Hydropower Extirpates Aquatic Insects, Undermining River Food Webs

Published by Oxford University Press on behalf of American Institute of Biological Sciences 2016. This work is written by (a) US Government employee(s) and is in the public domain in the US. The published article can be found at: http://bioscience.oxfordjournals.org/content/66/7/561

Integrated decision strategies for skin sensitization hazard.

One of the top priorities of the Interagency Coordinating Committee for the Validation of Alternative Methods (ICCVAM) is the identification and evaluation of non-animal alternatives for skin sensitization testing. Although skin sensitization is a complex process, the key biological events of the process have been well characterized in an adverse outcome pathway (AOP) proposed by the Organisation for Economic Co-operation and Development (OECD). Accordingly, ICCVAM is working to develop integrated decision strategies based on the AOP using in vitro, in chemico and in silico information. Data were compiled for 120 substances tested in the murine local lymph node assay (LLNA), direct peptide reactivity assay (DPRA), human cell line activation test (h-CLAT) and KeratinoSens assay. Data for six physicochemical properties, which may affect skin penetration, were also collected, and skin sensitization read-across predictions were performed using OECD QSAR Toolbox. All data were combined into a variety of potential integrated decision strategies to predict LLNA outcomes using a training set of 94 substances and an external test set of 26 substances. Fifty-four models were built using multiple combinations of machine learning approaches and predictor variables. The seven models with the highest accuracy (89-96% for the test set and 96-99% for the training set) for predicting LLNA outcomes used a support vector machine (SVM) approach with different combinations of predictor variables. The performance statistics of the SVM models were higher than any of the non-animal tests alone and higher than simple test battery approaches using these methods. These data suggest that computational approaches are promising tools to effectively integrate data sources to identify potential skin sensitizers without animal testing. Published 2016. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Calibration and seasonal adjustment for matched case-control studies of vitamin D and cancer.

Vitamin D measurements are influenced by seasonal variation and specific assay used. Motivated by multicenter studies of associations of vitamin D with cancer, we formulated an analytic framework for matched case-control data that accounts for seasonal variation and calibrates to a reference assay. Calibration data were obtained from controls sampled within decile strata of the uncalibrated vitamin D values. Seasonal sine-cosine series were fit to control data. Practical findings included the following: (1) failure to adjust for season and calibrate increased variance, bias, and mean square error and (2) analysis of continuous vitamin D requires a variance adjustment for variation in the calibration estimate. An advantage of the continuous linear risk model is that results are independent of the reference date for seasonal adjustment. (3) For categorical risk models, procedures based on categorizing the seasonally adjusted and calibrated vitamin D have near nominal operating characteristics; estimates of log odds ratios are not robust to choice of seasonal reference date, however. Thus, public health recommendations based on categories of vitamin D should also define the time of year to which they refer. This work supports the use of simple methods for calibration and seasonal adjustment and is informing analytic approaches for the multicenter Vitamin D Pooling Project for Breast and Colorectal Cancer. Published 2016. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Development and application of a human PBPK model for bromodichloromethane to investigate the impacts of multi-route exposure.

As a result of its presence in water as a volatile disinfection byproduct, bromodichloromethane (BDCM), which is mutagenic, poses a potential health risk from exposure via oral, dermal and inhalation routes. We developed a refined human physiologically based pharmacokinetic (PBPK) model for BDCM (including new chemical-specific human parameters) to evaluate the impact of BDCM exposure during showering and bathing on important measures of internal dose compared with oral exposure. The refined model adequately predicted data from the published literature for oral, dermal and bathing/showering exposures. A liter equivalency approach (L-eq) was used to estimate BDCM concentration in a liter of water consumed by the oral route that would be required to produce the same internal dose of BDCM resulting from a 20-min bath or a 10-min shower in water containing 10 µg l(-1) BDCM. The oral liter equivalent concentrations for the bathing scenario were 605, 803 and 5 µg l(-1) BDCM for maximum venous blood concentration (Cmax), the area under the curve (AUCv) and the amount metabolized in the liver per hour (MBDCM), respectively. For a 10-min showering exposure, the oral L-eq concentrations were 282, 312 and 2.1 µg l(-1) for Cmax, AUC and MBDCM, respectively. These results demonstrate large contributions of dermal and inhalation exposure routes to the internal dose of parent chemical reaching the systemic circulation, which could be transformed to mutagenic metabolites in extrahepatic target tissues. Thus, consideration of the contribution of multiple routes of exposure when evaluating risks from water-borne BDCM is needed, and this refined human model will facilitate improved assessment of internal doses from real-world exposures. Published 2015. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

A 19 year old with Fever, rash, and conjunctivitis: a connection with the heart.

The patient was a 19-year-old African American male who presented to the hospital with complaints of fever, diffuse maculopapular rash (chest, bilateral upper extremities, and back), bilateral conjunctivitis, and abdominal pain. His symptoms began approximately 3 weeks prior to presentation to our hospital. Over the 3-week period he developed a constellation of symptoms to include a polymorphous eruption, right facial nerve palsy, and bilateral conjunctivitis (Figure 1). Before presenting to our hospital, he had multiple evaluations that included near normal evaluation including a normal head computed tomography (CT) scan, mildly elevated liver-associated enzymes (LAEs), negative human immunodeficiency virus, and syphilis serologies. On presentation to our facility he was febrile to 38.3°C, and his exam was notable for right facial palsy, edematous lips, and enlarged erythematous tongue with raised papilla (Figure 1). He also exhibited a mild leukocytosis, sterile pyuria, and elevated lipase and erythrocyte sedimentation rate (ESR) (Table 1). He was admitted for further evaluation and management. Infection, drug reaction, and rheumatologic process were all considered in the differential, and the various studies (laboratory tests, radiographs, electrocardiogram, and transthoracic echocardiogram [TTE]) performed to evaluate for these causes did not identify a clear etiology (Table 1). His abdominal pain, facial nerve palsy, and edematous lips and tongue improved with supportive care, and he was discharged with plans for follow-up examination. He was readmitted 6 days later with continued temperatures to 38.0°C (despite scheduled acetaminophen) and continued nonpurulent conjunctivitis. In addition, he now also had new severe bilateral lower extremity pain, swelling of bilateral ankle and feet, and desquamation of his palms and soles with notable periungual desquamation (Figure 1). This constellation of symptoms was suggestive of Kawasaki’s disease (KD). Laboratory markers were also supportive of the diagnosis leukocytosis (13.8 × 10/μL), normocytic anemia (11 g/dL), thrombocytosis (535 × 10/μL), elevated markers of inflammation (ESR, 94 mm/hour and C-reactive protein, 18 mg/dL), and elevated LAEs (alanine aminotransferase, 111 U/L and aspartate aminotransferase, 62 U/L). The second day of this admission, he developed complaints of dull substernal chest pain. A repeat TTE was performed and compared to one obtained a week prior. A new left anterior descending coronary artery dilatation and ectatic vessels were noted (Figure 2). Given the coronary artery changes, treatment for KD was deemed necessary. The patient was given intravenously administered immunoglobulin (2 mg/kg) and high-dose aspirin (50 mg/kg per day). As is typical with pediatric patients, our patient defervesced 1 day after initiation of therapy with dramatic overall clinical improvement. After 3 days, he was subsequently transitioned to 81 mg of aspirin per day. He had continued follow-up tests with CT angiography performed 4 months later, which showed normal coronary arteries without any evidence of aneurysmal changes. At that time, aspirin was discontinued and the patient was advised to arrange follow-up visits with the cardiology department annually. KD is a systemic vasculitis of unknown etiology that usually affects infants and children, with 76% of the cases in children in the United States occurring in individuals below the age of 5 [1]. Adult cases are far less reported, with approximately 100 cases reported in Received 1 December 2014; accepted 2 January 2015. Correspondence: Tida Lee, MD, PhD, Infectious Disease Fellow, Walter Reed National Military Medical Center, Infectious Diseases Clinic, Bldg 7, 1st Fl, Bethesda, MD 20889 (tida.k.lee.mil@mail.mil). Open Forum Infectious Diseases Published by Oxford University Press on behalf of the Infectious Diseases Society of America 2015. This work is written by (a) US Government employee(s) and is in the public domain in the US. DOI: 10.1093/ofid/ofv008

Quantifying photovoltaic fire danger reduction with arc‐fault circuit interrupters

AbstractUnmitigated arc‐faults present fire dangers, shock hazards, and cause system downtime in photovoltaic (PV) systems. The 2011 National Electrical Code® added section 690.11 to require a listed arc‐fault protection device on new PV systems. Underwriters Laboratories created the outline of investigation for PV DC arc‐fault circuit protection, UL 1699B, for certifying arc‐fault circuit interrupters (AFCIs) for arc suppression. Unfortunately, little is known about appropriate trip times for arc‐faults generated at different locations in the PV system, with different electrode and polymer encapsulant geometries and materials. In this investigation, a plasma model was developed, which determines fire danger with UL 1699B‐listed AFCIs and consequences of arc‐fault discharges sustained beyond UL 1699B trip time requirements. This model predicts temperatures for varying system configurations and was validated by 100 and 300 W arc‐faults experiments where combustion times and temperatures were measured. This investigation then extrapolated burn characteristics using this model to predict polymer ignition times for exposure to arc‐power levels between 100 and 1200 W. The numerical results indicate AFCI maximum trip times required by UL 1699B are sufficient to suppress 100–1200 W arc‐faults prior to fire initiation. Optical emission spectroscopy and thermochemical decomposition analysis were also conducted to assess spectral and chemical degradation of the polymer sheath. Published 2014. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Soft tissue sarcomas: staging principles and prognostic nomograms.

Soft tissue sarcomas (STS) are a rare and heterogenous group of tumors that often represent a management challenge. The American Joint Committee on Cancer system is currently used to stage tumors and direct treatment. Limitations of the current STS staging system, future potential direction for pre-operative staging, as well as the benefit of predictive nomograms for filling current knowledge gaps are all discussed. J. Surg. Oncol. 2015 111:532-539. Published 2014. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Climatic, ecophysiological, and phenological controls on plant ecohydrological strategies in seasonally dry ecosystems

AbstractLarge areas in the tropics and at mid‐latitudes experience pronounced seasonality and inter‐annual variability in rainfall and hence water availability. Despite the importance of these seasonally dry ecosystems (SDEs) for the global carbon cycling and in providing ecosystem services, a unifying ecohydrological framework to interpret the effects of climatic variability on SDEs is still lacking. A synthesis of existing data about plant functional adaptations in SDEs, covering some 400 species, shows that leaf phenological variations, rather than physiological traits, provide the dominant control on plant‐water‐carbon interactions. Motivated by this result, the combined implications of leaf phenology and climatic variability on plant water use strategies are here explored with a minimalist model of the coupled soil water and plant carbon balances. The analyses are extended to five locations with different hydroclimatic forcing, spanning seasonally dry tropical climates (without temperature seasonality) and Mediterranean climates (exhibiting out of phase seasonal patterns of rainfall and temperature). The most beneficial leaf phenology in terms of carbon uptake depends on the climatic regime: evergreen species are favoured by short dry seasons or access to persistent water stores, whereas high inter‐annual variability of rainy season duration favours the coexistence of multiple drought‐deciduous phenological strategies. We conclude that drought‐deciduousness may provide a competitive advantage in face of predicted declines in rainfall totals, while reduced seasonality and access to deep water stores may favour evergreen species. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Ann Starrs: enabling women to fulfil their potential

Ann Starrs: enabling women to fulfil their potential

Optimal control of continuous systems with impulse controls

Summary Impulse control problems, in which a continuously evolving state is modified by discrete control actions, have applications in epidemiology, medicine, and ecology. In this paper, we present a simple method for solving impulse control problems for systems of differential equations. In particular, we show how impulse control problems can be reformulated and solved as discrete optimal control problems. The method is illustrated with two examples. Published 2014. This article has been contributed to by US Government employees and their work is in the public domain in the USA.