Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “multivariate”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,585 records · Page 88
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Radiographic stool quantification: an equivalence study of 484 symptomatic and asymptomatic subjects

Purpose: To determine if symptomatic patients referred for radiographic stool quantification have equivalent stool burden to asymptomatic patients. Method: This was an IRB-approved HIPAA-compliant retrospective equivalence cohort study. An a priori equivalence power calculation was performed. Consecutive abdominal radiographs performed in adult outpatients with bloating, constipation, diarrhea, or abdominal pain to assess “fecal loading” [n = 242 (fecal cohort)] were compared to those performed in asymptomatic adult outpatients to assess “renal stones” [n = 242 (renal cohort)]. Radiographs were randomized and reviewed by two blinded independent abdominal radiologists. Exclusion criteria, designed to avoid unblinding, included urinary tract calculi ≥ 0.5 cm, multiple urinary tract calculi, and ureteral stent(s). Readers scored all radiographs (n = 484) for stool burden using validated Leech criteria [scale: 0 (none) to 15 (extreme diffuse)]. Mean Leech scores and 95% confidence intervals were calculated. Multivariable generalized linear modeling was performed to adjust for baseline medication use, age, and gender. The adjusted parameter estimate was used to test for equivalence in the mean difference between cohorts using Schuirmann’s method of two one-sided t-tests. Inter-reader agreement was assessed with intraclass correlation coefficients. Results: Overall mean Leech scores for fecal [6.9 (95% CI 6.7, 7.2)] and renal [7.3 (95% CI 7.1, 7.5)] cohorts were equivalent within a margin of 0.75 (adjusted mean difference: − 0.4 [90% CI − 0.7, − 0.04]; p value = 0.02). Inter-reader agreement was good [ICC: 0.62 (95% CI 0.56, 0.68)]. Conclusion: Radiographic stool quantification produces equivalent results in symptomatic and asymptomatic adults and is of uncertain value.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2019

Development and validation of an imaging and clinical scoring system to predict early mortality in spontaneous ruptured hepatocellular carcinoma treated with transarterial embolization

Purpose: To develop and validate a scoring system using a combination of imaging and clinical parameters to predict 30-day mortality in ruptured HCC (rHCC) patients after transarterial embolization (TAE). Methods: 98 consecutive patients with rHCC who underwent abdominal CT and subsequent TAE between January 2007 and December 2016 were retrospectively reviewed. The CT scans were reviewed by two radiologists blinded to the patient outcome. Clinical parameters including serum bilirubin, albumin, INR, creatinine, and hemoglobin were recorded. Independent risk factors for 30-day mortality after TAE were identified using multivariate binary logistic regression, for development of a scoring system. The scoring system was then validated in 20 patients between January 2017 and May 2018. Results: In the development cohort, bilobar tumor distribution (OR = 29.6), clinical parameters of bilirubin > 2.5 mg/dL (OR = 5.9), and albumin < 30 g/L (OR = 4.1) were independent predictors for 30-day mortality. A 6-point score was derived and yielded area-under-the-receiver-operating-characteristic-curve (AUC) of 0.904. A score ≥ 4 resulted in sensitivity of 80.5% and specificity of 91.2% for 30-day mortality. In the validation cohort, AUC for 30-day mortality was 0.939. A score ≥ 4 resulted in sensitivity of 81.2% and specificity of 88.9%. In both development and validation cohorts, the proposed scoring system was better than biochemical components of Child–Pugh score and serum bilirubin to predict 30-day mortality. Conclusion: Imaging and clinical parameters can be combined into a scoring system to accurately predict 30-day mortality after TAE in rHCC patients. The score may help identify and counsel high-risk patients.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2019

Can MRI be used to diagnose histologic grade in T1a (< 4 cm) clear cell renal cell carcinomas?

Objective: To assess whether MRI can differentiate low-grade from high-grade T1a cc-RCC. Materials and methods: With IRB approval, 49 consecutive solid < 4 cm cc-RCC (low grade [Grade 1 or 2] N = 38, high grade [Grade 3] N = 11) with pre-operative MRI before nephrectomy were identified between 2013 and 2018. Tumor size, apparent diffusion coefficient (ADC) histogram analysis, enhancement wash-in and wash-out rates, and chemical shift signal intensity index (SI index) were assessed by a blinded radiologist. Subjectively, two blinded Radiologists also assessed for (1) microscopic fat, (2) homogeneity (5-point Likert scale), and (3) ADC signal (relative to renal cortex); discrepancies were resolved by consensus. Outcomes were studied using Chi square, multivariate analysis, logistic regression modeling, and ROC. Inter-observer agreement was assessed using Cohen’s kappa. Results: Tumor size was 24 ± 7 (13–39) mm with no association to grade (p = 0.45). Among quantitative features studied, corticomedullary phase wash-in index (p = 0.015), SI index (p = 0.137), and tenth-centile ADC (p = 0.049) were higher in low-grade tumors. 36.8% (14/38) low-grade tumors versus zero high-grade tumors demonstrated microscopic fat (p = 0.015; Kappa = 0.67). Microscopic fat was specific for low-grade disease (100.0% [71.5–100.0]) with low sensitivity (36.8% [21.8–54.6]). Other subjective features did not differ between groups (p > 0.05). A logistic regression model combining microscopic fat + wash-in index + tenth-centile-ADC yielded area under ROC curve 0.98 (Confidence Intervals 0.94–1.0) with sensitivity/specificity 87.5%/100%. Conclusion: The combination of microscopic fat, higher corticomedullary phase wash-in and higher tenth-centile ADC is highly accurate for diagnosis of low-grade disease among T1a clear cell RCC.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2019

Microvascular invasion and grading in hepatocellular carcinoma: correlation with major and ancillary features according to LIRADS

Purpose: To assess major and ancillary parameters that could be correlated with Microvascular Invasion (MIV) and with histologic grade of HCC. Materials and methods: In this retrospective study, we assessed 62 patients (14 women–48 men; mean age, 63 years; range 38–80 years) that underwent hepatic resection for HCC. All patients were subject to Multidetector computed tomography (MDCT); 40 to Magnetic Resonance (MR) study. The radiologist assessed major and ancillary features according to LIRADS (v. 2018) and reported any radiological accessory findings if detected. Results: No major feature showed statistically significant differences and correlation with grading. Mean ADC value was correlated with grading and with MIV status. No major feature was correlated to MIV; progressive contrast enhancement and satellite nodules showed statistically different percentages with respect to the presence of MIV, so as at the monovariate correlation analysis, satellite nodules were correlated with the presence of MIV. At multivariate regression analysis, no factor proved to be strong predictors of grading while progressive contrast enhancement and satellite nodules were significantly associated with the MIV. Conclusion: Mean ADC value is correlated to HCC grading and MIV status. Progressive contrast enhancement and the presence of satellite nodules are correlated to MIV status.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2019

CT and MR imaging features of pancreatic adenosquamous carcinoma and their correlation with prognosis

Purpose: To retrospectively investigate the computed tomography (CT) and magnetic resonance (MR) imaging features of pancreatic adenosquamous carcinoma (PASC) and the association between imaging findings and prognosis. Materials and methods: CT, MR images of 26 patients with PASC were analyzed. Clinical symptoms, tumor markers, and patients’ survival were recorded. Tumor attenuation, enhancement pattern and degree, vessel involvement, adjacent tissue invasion and metastasis were evaluated. The association between imaging features and overall survival (OS) were also assessed using Cox proportional hazards ratio model. Results: Fourteen masses were found in the head of the pancreas and 12 in the body/tail. The mean tumor size was 4.47 ± 1.76 cm. PASC usually showed ill-defined (96.2%), lobulated (76.9%) and predominantly solid mass (92.3%). Ring enhancement in the peripheral area of the tumor was commonly seen (76.9%). Vessel invasion was seen in 17 cases (65.4%), encasement of adjacent arteries in 7 cases (26.9%), upstream main pancreatic duct (MPD) dilatation in 16 cases (61.5%) and double duct sign in 9 cases (34.6%). Multivariate Cox proportional hazards model demonstrated that patients with vessel invasion may predict a poor prognosis (p = 0.037). Conclusion: PASC tends to be an ill-defined solid mass with peripheral ring enhancement, and relatively poor enhancement in the central area. PASC may also show vessel invasion, vessel encasement and upstream MPD dilatation. Vessel invasion may indicate a poor prognosis.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2013

Patient Dose During Carotid Artery Stenting With Embolic-Protection Devices: Evaluation With Radiochromic Films and Related Diagnostic Reference Levels According to Factors Influencing the Procedure

To measure the maximum entrance skin dose (MESD) on patients undergoing carotid artery stenting (CAS) using embolic-protection devices, to analyze the dependence of dose and exposure parameters on anatomical, clinical, and technical factors affecting the procedure complexity, to obtain some local diagnostic reference levels (DRLs), and to evaluate whether overcoming DRLs is related to procedure complexity. MESD were evaluated with radiochromic films in 31 patients (mean age 72 {+-} 7 years). Five of 33 (15 %) procedures used proximal EPD, and 28 of 33 (85 %) procedures used distal EPD. Local DRLs were derived from the recorded exposure parameters in 93 patients (65 men and 28 women, mean age 73 {+-} 9 years) undergoing 96 CAS with proximal (33 %) or distal (67 %) EPD. Four bilateral lesions were included. MESD values (mean 0.96 {+-} 0.42 Gy) were <2 Gy without relevant dependence on procedure complexity. Local DRL values for kerma area product (KAP), fluoroscopy time (FT), and number of frames (N{sub FR}) were 269 Gy cm{sup 2}, 28 minutes, and 251, respectively. Only simultaneous bilateral treatment was associated with KAP (odds ratio [OR] 10.14, 95 % confidence interval [CI] 1-102.7, p < 0.05) and N{sub FR} overexposures (OR 10.8, 95 % CI 1.1-109.5, p < 0.05). Type I aortic arch decreased the risk of FT overexposure (OR 0.4, 95 % CI 0.1-0.9, p = 0.042), and stenosis {>=} 90 % increased the risk of N{sub FR} overexposure (OR 2.8, 95 % CI 1.1-7.4, p = 0.040). At multivariable analysis, stenosis {>=} 90 % (OR 2.8, 95 % CI 1.1-7.4, p = 0.040) and bilateral treatment (OR 10.8, 95 % CI 1.1-109.5, p = 0.027) were associated with overexposure for two or more parameters. Skin doses are not problematic in CAS with EPD because these procedures rarely lead to doses >2 Gy.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2015

Cone-Beam Computed Tomography (CBCT) Versus CT in Lung Ablation Procedure: Which is Faster?

AimTo compare cone-beam CT (CBCT) versus computed tomography (CT) guidance in terms of time needed to target and place the radiofrequency ablation (RFA) electrode on lung tumours.Materials and MethodsPatients at our institution who received CBCT- or CT-guided RFA for primary or metastatic lung tumours were retrospectively included. Time required to target and place the RFA electrode within the lesion was registered and compared across the two groups. Lesions were stratified into three groups according to their size (<10, 10–20, >20 mm). Occurrences of electrode repositioning, repositioning time, RFA complications, and local recurrence after RFA were also reported.ResultsForty tumours (22 under CT, 18 under CBCT guidance) were treated in 27 patients (19 male, 8 female, median age 67.25 ± 9.13 years). Thirty RFA sessions (16 under CBCT and 14 under CT guidance) were performed. Multivariable linear regression analysis showed that CBCT was faster than CT to target and place the electrode within the tumour independently from its size (β = −9.45, t = −3.09, p = 0.004). Electrode repositioning was required in 10/22 (45.4 %) tumours under CT guidance and 5/18 (27.8 %) tumours under CBCT guidance. Pneumothoraces occurred in 6/14 (42.8 %) sessions under CT guidance and in 6/16 (37.5 %) sessions under CBCT guidance. Two recurrences were noted for tumours receiving CBCT-guided RFA (2/17, 11.7 %) and three after CT-guided RFA (3/19, 15.8 %).ConclusionCBCT with live 3D needle guidance is a useful technique for percutaneous lung ablation. Despite lesion size, CBCT allows faster lung RFA than CT.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2016

Risk Factors for Immediate and Delayed-Onset Fever After Percutaneous Transhepatic Biliary Drainage

ObjectivesTo prospectively investigate the pre and intra-procedural risk factors for immediate (IF) and delayed-onset (DOF) fever development after percutaneous transhepatic biliary drainage (PTBD).MethodsInstitutional review board approval and informed patient consent were obtained. Between February 2013 and February 2014, 97 afebrile patients (77 at the Sapienza University of Rome, Italy and 20 at the Sun Yat-sen University of Guangzhou, China) with benign (n = 31) and malignant (n = 66) indications for a first PTBD were prospectively enrolled. Thirty pre- and intra-procedural clinical/radiological characteristics, including the amount of contrast media injected prior to PTBD placement, were collected in relation to the development of IF (within 24 h) or DOF (after 24 h). Fever was defined as ≥37.5 °C. Binary logistic regression analysis was used to assess independent associations with IF and DOF.ResultsFourteen (14.4 %) patients developed IF and 17 (17.5 %) developed DOF. At multivariable analysis, IF was associated with pre-procedural absence of intrahepatic bile duct dilatation (OR 63.359; 95 % CI 2.658–1510.055; P = 0.010) and low INR (OR 4.7 × 10{sup −4}; 95 % CI 0.000–0.376; P = 0.025), while DOF was associated with unsatisfactory biliary drainage at the end of PTBD (OR 4.571; 95 % CI 1.161–17.992; P = 0.030).ConclusionsThe amount of contrast injected is not associated with post-PTBD fever development. Unsatisfactory biliary drainage at the end of PTBD is associated with DOF, suggesting that complete biliary tree decompression should be pursued within the first PTBD. Patients with unsatisfactory drainage and those with the absence of pre-procedural intrahepatic bile duct dilatation, which is associated with IF, require tailored post-PTBD management.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2017

Peripheral Stent Thrombosis Leading to Acute Limb Ischemia and Major Amputation: Incidence and Risk Factors in the Aortoiliac and Femoropopliteal Arteries

PurposeTo report the real-world incidence and risk factors of stent thrombosis in the aortoiliac and femoropopliteal arteries in case of bare nitinol stent (BNS) or covered nitinol stent (CNS) placement from a single-centre retrospective audit.Materials and MethodsMedical records of consecutive patients treated with peripheral stent placement for claudication or critical limb ischemia were audited for definite stent thrombosis defined as imaging confirmed stent thrombosis that presented as acute limb-threatening ischemia. Cases were stratified between aortoiliac and femoropopliteal anatomy. Cox regression analysis was employed to adjust for baseline clinical and procedural confounders and identify predictors of stent thrombosis and major limb loss.Results256 patients (n = 277 limbs) were analysed over a 5-year period (2009–2014) including 117 aortoiliac stents (34 CNS; 12.8 ± 5.0 cm and 83 BNS; 7.8 ± 4.0 cm) and 160 femoropopliteal ones (60 CNS; 21.1 ± 11.0 cm and 100 BNS; 17.5 ± 11.9 cm). Median follow-up was 1 year. Overall stent thrombosis rate was 6.1% (17/277) after a median of 43 days (range 2–192 days) and affected almost exclusively the femoropopliteal segment (12/60 in the CNS cohort vs. 4/100 in the BNS; p = 0.001). Annualized stent thrombosis rates (per 100 person-years) were 12.5% in case of CNS and 1.4% in case of BNS (HR 6.3, 95% CI 2.4–17.9; p = 0.0002). Corresponding major amputations rates were 8.7 and 2.5%, respectively (HR 4.5, 95% CI 2.7–27.9; p = 0.0006). On multivariable analysis, critical leg ischemia and CNS placement were the only predictors of stent thrombosis. Diabetes, critical leg ischemia, femoropopliteal anatomy, long stents and CNS were independent predictors of major amputations.ConclusionsPlacement of long femoropopliteal covered nitinol stents is associated with an increased incidence of acute stent thrombosis and ensuing major amputation. Risks are significantly lower in the aortoiliac vessels and with use of bare nitinol stents.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2019

An evaluation of the consistency of extremes in gridded precipitation data sets

Noting a strong imperative to understand precipitation extremes, and that considerable uncertainty affects observational data sets, this paper compares the representation of extremes in a number of widely used daily gridded products, derived from rain gauge data, satellite retrieval and reanalysis for the conterminous United States. Analysis is based upon the concept of “tail dependence” arising in multivariate extreme value theory, and we infer the level of temporal dependence in the joint tail of the precipitation probability distribution for pairwise comparisons of products. In this way, we consider the range of products more like an ensemble and examine the relationships between members, and do not attempt to define, or compare products to, some ground truth. Linear correlation between products is also computed. Considerable discrepancy between groups of products, both annually and seasonally, is linked to source data and complex terrain. In particular, products based on rain gauge data showed remarkable similarity, but differed considerably, showing almost total loss of extremal dependence during DJF in mountainous regions, when compared with satellite products. Additionally, simulated re-forecasts revealed reasonable temporal agreement with large scale generated extremes. The diversity and extent of discrepancies identified across all products raises important questions about their use, and we urge caution, particularly for products derived from satellite data.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Projected changes in the terrestrial and oceanic regulators of climate variability across sub-Saharan Africa

Future changes in the sign and intensity of ocean–land–atmosphere interactions have been insufficiently studied, despite implications for regional climate change projections, extreme event statistics, and seasonal climate predictability. In response to this deficiency, the present study focuses on projected responses to the enhanced greenhouse effect in: (1) the mean state of the atmosphere and land surface; (2) oceanic and terrestrial drivers of sub-Saharan climate variability; and (3) total seasonal climate predictability of sub-Saharan Africa, a region known for its pronounced land–atmosphere coupling. Analysis focuses on output from 23 Earth System Models in the Coupled Model Intercomparison Project Phase Five for the late twentieth and twenty-first centuries. It is projected that the greatest warming across sub-Saharan Africa will occur over the Sahel, the monsoon season will become more persistent into late summer and autumn, short rains in the Horn of Africa (HOA) will intensify, and leaf area index will increase across the HOA. Stepwise Generalized Equilibrium Feedback Assessment, i.e. a multivariate statistical approach, is applied to the model output over sub-Saharan Africa in order to explore the oceanic and terrestrial drivers of regional climate. The models indicate that the study region’s climate variability is dominated by oceanic drivers, with secondary contributions from soil moisture and very modest impacts from vegetation. Overall, the general model consensus of future projections indicates a concerning diminished seasonal predictability of sub-Saharan African regional climate based on key oceanic and terrestrial predictors and an elevated role of the land surface (associated with soil moisture anomalies) compared to oceanic drivers in regulating regional climate variability.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Dietary B group vitamin intake and the bladder cancer risk: a pooled analysis of prospective cohort studies

Abstract Purpose Diet may play an essential role in the aetiology of bladder cancer (BC). The B group complex vitamins involve diverse biological functions that could be influential in cancer prevention. The aim of the present study was to investigate the association between various components of the B group vitamin complex and BC risk. Methods Dietary data were pooled from four cohort studies. Food item intake was converted to daily intakes of B group vitamins and pooled multivariate hazard ratios (HRs), with corresponding 95% confidence intervals (CIs), were obtained using Cox-regression models. Dose–response relationships were examined using a nonparametric test for trend. Results In total, 2915 BC cases and 530,012 non-cases were included in the analyses. The present study showed an increased BC risk for moderate intake of vitamin B1 (HR B1 : 1.13, 95% CI: 1.00–1.20). In men, moderate intake of the vitamins B1, B2, energy-related vitamins and high intake of vitamin B1 were associated with an increased BC risk (HR (95% CI): 1.13 (1.02–1.26), 1.14 (1.02–1.26), 1.13 (1.02–1.26; 1.13 (1.02–1.26), respectively). In women, high intake of all vitamins and vitamin combinations, except for the entire complex, showed an inverse association (HR (95% CI): 0.80 (0.67–0.97), 0.83 (0.70–1.00); 0.77 (0.63–0.93), 0.73 (0.61–0.88), 0.82 (0.68–0.99), 0.79 (0.66–0.95), 0.80 (0.66–0.96), 0.74 (0.62–0.89), 0.76 (0.63–0.92), respectively). Dose–response analyses showed an increased BC risk for higher intake of vitamin B1 and B12. Conclusion Our findings highlight the importance of future research on the food sources of B group vitamins in the context of the overall and sex-stratified diet.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2022

Long-term missing value imputation for time series data using deep neural networks

We present an approach that uses a deep learning model, in particular, a MultiLayer Perceptron, for estimating the missing values of a variable in multivariate time series data. We focus on filling a long continuous gap (e.g., multiple months of missing daily observations) rather than on individual randomly missing observations. Our proposed gap filling algorithm uses an automated method for determining the optimal MLP model architecture, thus allowing for optimal prediction performance for the given time series. We tested our approach by filling gaps of various lengths (three months to three years) in three environmental datasets with different time series characteristics, namely daily groundwater levels, daily soil moisture, and hourly Net Ecosystem Exchange. We compared the accuracy of the gap-filled values obtained with our approach to the widely used R-based time series gap filling methods ImputeTS and mtsdi. The results indicate that using an MLP for filling a large gap leads to better results, especially when the data behave nonlinearly. Thus, our approach enables the use of datasets that have a large gap in one variable, which is common in many long-term environmental monitoring observations.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2018

Impact of a Health Information Technology Intervention on the Follow-up Management of Pulmonary Nodules

Lung cancer is the leading cause of cancer deaths in the USA. The most common abnormalities suspicious for lung cancer on CT scan include pulmonary nodules. Recommendations to improve care for patients with pulmonary nodules require follow-up management. However, transitions in care, especially for patients undergoing transitions to ambulatory care sites from the emergency department (ED) and inpatient settings, can exacerbate failures in follow-up testing and compromise patient safety. We evaluate the impact of a discharge module that includes follow-up recommendations for further management of pulmonary nodules on the study outcome and follow-up management of patients with pulmonary nodules within 1 year after discharge. After IRB approval, we collected data on all patients undergoing chest or abdominal CT exams over a 12-month baseline and 12-month intervention period at an academic medical center. The inpatient discharge module was implemented in November 2011; the ED module was implemented in May 2012. Multivariable logistic regression was performed to account for care setting, imaging modality, recommendations, and patient demographics. Implementation of a discharge module resulted in improved follow-up of patients with pulmonary nodules within 1 year after discharge (OR = 1.64, p = 0.01); the ED implementation resulted in better follow-up compared to the inpatient module (OR = 2.24, p < 0.01). Twenty-seven percent of patients with pulmonary nodules received follow-up management, which, although significantly improved from the 18% baseline, remains low. An electronic discharge module is associated with improved follow-up management of patients with pulmonary nodules, and may be combined with interventions to further improve management of these patients.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2023

Association between soil organic carbon and calcium in acidic grassland soils from Point Reyes National Seashore, CA

Organo-mineral and organo-metal associations play an important role in the retention and accumulation of soil organic carbon (SOC). Recent studies have demonstrated a positive correlation between calcium (Ca) and SOC content in a range of soil types. However, most of these studies have focused on soils that contain calcium carbonate (pH > 6). To assess the importance of Ca-SOC associations in lower pH soils, we investigated their physical and chemical interaction in the grassland soils of Point Reyes National Seashore (CA, USA) at a range of spatial scales. Multivariate analyses of our bulk soil characterisation dataset showed a strong correlation between exchangeable Ca (Ca Exch ; 5–8.3 c.mol c kg –1 ) and SOC (0.6–4%) content. Additionally, linear combination fitting (LCF) of bulk Ca K-edge X-ray absorption near-edge structure (XANES) spectra revealed that Ca was predominantly associated with organic carbon across all samples. Scanning transmission X-ray microscopy near-edge X-ray absorption fine structure spectroscopy (STXM C/Ca NEXAFS) showed that Ca had a strong spatial correlation with C at the microscale. The STXM C NEXAFS K-edge spectra indicated that SOC had a higher abundance of aromatic/olefinic and phenolic C functional groups when associated with Ca, relative to C associated with Fe. In regions of high Ca-C association, the STXM C NEXAFS spectra were similar to the spectrum from lignin, with moderate changes in peak intensities and positions that are consistent with oxidative C transformation. Through this association, Ca thus seems to be preferentially associated with plant-like organic matter that has undergone some oxidative transformation, at depth in acidic grassland soils of California. Our study highlights the importance of Ca-SOC complexation in acidic grassland soils and provides a conceptual model of its contribution to SOC preservation, a research area that has previously been unexplored.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2015

Scenario generation for stochastic optimization problems via the sparse grid method

We study the use of sparse grids in the scenario generation (or discretization) problem in stochastic programming problems where the uncertainty is modeled using a continuous multivariate distribution. We show that, under a regularity assumption on the random function involved, the sequence of optimal objective function values of the sparse grid approximations converges to the true optimal objective function values as the number of scenarios increases. The rate of convergence is also established. We treat separately the special case when the underlying distribution is an affine transform of a product of univariate distributions, and show how the sparse grid method can be adapted to the distribution by the use of quadrature formulas tailored to the distribution. We numerically compare the performance of the sparse grid method using different quadrature rules with classic quasi-Monte Carlo (QMC) methods, optimal rank-one lattice rules, and Monte Carlo (MC) scenario generation, using a series of utility maximization problems with up to 160 random variables. The results show that the sparse grid method is very efficient, especially if the integrand is sufficiently smooth. In such problems the sparse grid scenario generation method is found to need several orders of magnitude fewer scenarios than MC and QMC scenario generation to achieve the same accuracy. As a result, it is indicated that the method scales well with the dimension of the distribution--especially when the underlying distribution is an affine transform of a product of univariate distributions, in which case the method appears scalable to thousands of random variables.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2021

Radiation effects on atherosclerosis in atomic bomb survivors: a cross-sectional study using structural equation modeling

Past reports indicated that total-body irradiation at low to moderate doses could be responsible for cardiovascular disease risks, but the mechanism remains unclear. The purpose of this study was to investigate the association between radiation exposure and atherosclerosis, an underlying pathology of cardiovascular diseases, in the Japanese atomic bomb survivors. We performed a cross-sectional study measuring 14 clinical-physiological atherosclerosis indicators during clinical exams from 2010 to 2014 in 3274 participants of the Adult Health Study cohort. Multivariable analyses were performed by using a structural equation model with latent factors representing underlying atherosclerotic pathologies: (1) arterial stiffness, (2) calcification, and (3) plaque as measured with indicators chosen a priori on the basis of clinical-physiological knowledge. Radiation was linearly associated with calcification (standardized coefficient per Gy 0.15, 95 % confidence interval: CI [0.070, 0.23]) and plaque (0.11, 95 % CI [0.029, 0.20]), small associations that were comparable to about 2 years of aging per Gy of radiation exposure, but not with arterial stiffness (0.036, 95 % CI [-0.025, 0.095]). The model fitted better and had narrower confidence intervals than separate ordinary regression models explaining individual indicators independently. The associations were less evident when the dose range was restricted to a maximum of 2 or 1 Gy. By combining individual clinical-physiological indicators that are correlated because of common, underlying atherosclerotic pathologies, we found a small, but significant association of radiation with atherosclerosis.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2016

Differentiable McCormick relaxations

McCormick's classical relaxation technique constructs closed-form convex and concave relaxations of compositions of simple intrinsic functions. These relaxations have several properties which make them useful for lower bounding problems in global optimization: they can be evaluated automatically, accurately, and computationally inexpensively, and they converge rapidly to the relaxed function as the underlying domain is reduced in size. They may also be adapted to yield relaxations of certain implicit functions and differential equation solutions. However, McCormick's relaxations may be nonsmooth, and this nonsmoothness can create theoretical and computational obstacles when relaxations are to be deployed. This article presents a continuously differentiable variant of McCormick's original relaxations in the multivariate McCormick framework of Tsoukalas and Mitsos. Gradients of the new differentiable relaxations may be computed efficiently using the standard forward or reverse modes of automatic differentiation. Furthermore, extensions to differentiable relaxations of implicit functions and solutions of parametric ordinary differential equations are discussed. A C++ implementation based on the library MC++ is described and applied to a case study in nonsmooth nonconvex optimization.

97 MATHEMATICS AND COMPUTING↗