Threshold Lines Research Articles

Threshold lines identification for non-Gaussian distributed diagnostic features

Machine condition monitoring systems are frequently used in the industry, especially for critical infrastructure. Decision making is still challenging due to the lack of limit values (called also thresholds). Identification of thresholds is in particular difficult for unique machines with specific Health Index (HI) data properties. Our contribution is a procedure for threshold values identification for HI data with time-varying characteristics and non-Gaussian behaviour. The proposed methodology consists of few crucial steps, such as data segmentation, data modelling, and Monte Carlo simulations for quantile lines identification based on the fitted models. The proposed methods are based on robust statistics dedicated to non-Gaussian distributed data. Novelty of the paper is related to the extension of simple ”Trend+Noise” model for HI data and model-based framework for threshold lines estimation. Thus, the method provides more accurate results for non-Gaussian, time-varying data. We demonstrate the superiority of the proposed procedure over the classical ones. The presented simulation study clearly indicates the efficiency of the approach for non-Gaussian HI data. The methodology is applied to two real datasets with different properties (level of non-Gaussianity and presence of interdependence in the random part). We believe that proposed procedure could be considered as a guideline for future research and may be implemented in commercial monitoring systems.

What is the best technique to estimate topographic thresholds of gully erosion? Insights from a case study on the permanent gullies of Rarh plain, India

The Rarh plain in the Lower Ganga Basin in India, best known for its lateritic landscape and gullied tracts, faces grave problems brought about by all types of soil erosion, of which gully erosion is the most conspicuous. The present study uses data collected through field measurements at 110 gully heads in ten sites of the Rarh plain, to first assess the applicability of various methods used to construct critical topographic threshold lines, and secondly, to characterise topographic threshold conditions of the permanent gullies in the Rarh plain as well as to identify main factors that promoted gully initiation in this region. It is concluded that thresholds defined though orthogonal regression are more appropriate than manual fitting of threshold line or employing quantile or nonlinear regression techniques for the same. The critical topographic threshold conditions of gullying in the Rarh plain, expressed by the relationship S = 0.118A−0.111 between the gully head slope gradient (S) and upslope catchment area (A) can be used to map areas under risk of gully head development in the lateritic terrain, mainly in the deforestation fronts. The value of the exponent (0.111) suggests that subsurface processes and mass failures are the main processes of gully growth at present, and it is suspected that gully erosion in this region is not a recent phenomenon, judging by rather small gully head catchment areas as well as the low AS2 range of 2–170 m2. Although statistical evidence in favour of distinct site-specific thresholds is not found, results of this study indicate that gullies under eucalyptus stands have a significantly lower threshold than those in other land cover types. Gully erosion in this region was most likely triggered by massive changes in land cover and land use that commenced from the middle of 19th century and continued into the first few decades of 20th century. However, gullies observed under eucalyptus stands are much younger, judging by their larger upslope catchment areas compared to gullies found in other land covers. Albeit it is observed that the lateritic terrain of Rarh plain offers more resistance to gully initiation than croplands or Mediterranean badlands, the threshold of gully head development is much lower than that of the primary laterites of the adjacent Chhotanagpur plateau fringe as well as other comparable soil types from around the world.

Laser Interstitial Thermal Therapy in the Treatment of Thalamic Brain Tumors: A Case Series.

Surgical options for patients with thalamic brain tumors are limited. Traditional surgical resection is associated with a high degree of morbidity and mortality. Laser interstitial thermal therapy (LITT) utilizes a stereotactically placed laser probe to induce thermal damage to tumor tissue. LITT provides a surgical cytoreduction option for this challenging patient population. We present our experience treating thalamic brain tumors with LITT. To describe our experience and outcomes using LITT on patients with thalamic tumors. We analyzed 13 consecutive patients treated with LITT for thalamic tumors from 2012 to 2017. Radiographic, clinical characteristics, and outcome data were collected via review of electronic medical records. Thirteen patients with thalamic tumors were treated with LITT. Most had high-grade gliomas, including glioblastoma (n=9) and anaplastic astrocytoma (n=2). The average tumor volume was 12.0 cc and shrank by 42.9% at 3 mo. The average hospital stay was 3.0 d. Median ablation coverage as calculated by thermal damage threshold (TDT) lines was 98% and 95% for yellow (>43°C for >2 min) or blue (>10 min), respectively. Median disease-specific progression-free survival calculated for 8 patients in our cohort was 6.1 mo (range: 1.1-15.1 mo). There were 6 patients with perioperative morbidity and 2 perioperative deaths because of intracerebral hematoma. LITT is a feasible treatment for patients with thalamic tumors. LITT offers a cytoreduction option in this challenging population. Patient selection is key. Close attention should be paid to lesion size to minimize morbidity. More studies comparing treatment modalities of thalamic tumors need to be performed.

Urban pluvial flooding prediction by machine learning approaches – a case study of Shenzhen city, China

Urban pluvial flooding is a threatening natural hazard in urban areas all over the world, especially in recent years given its increasing frequency of occurrence. In order to prevent flood occurrence and mitigate the subsequent aftermath, urban water managers aim to predict precipitation characteristics, including peak intensity, arrival time and duration, so that they can further warn inhabitants in risky areas and take emergency actions when forecasting a pluvial flood. Previous studies that dealt with the prediction of urban pluvial flooding are mainly based on hydrological or hydraulic models, requiring a large volume of data for simulation accuracy. These methods are computationally expensive. Using a rainfall threshold to predict flooding based on a data-driven approach can decrease the computational complexity to a great extent. In order to prepare cities for frequent pluvial flood events – especially in the future climate – this paper uses a rainfall threshold for classifying flood vs. non-flood events, based on machine learning (ML) approaches, applied to a case study of Shenzhen city in China. In doing so, ML models can determine several rainfall threshold lines projected in a plane spanned by two principal components, which provides a binary result (flood or no flood). Compared to the conventional critical rainfall curve, the proposed models, especially the subspace discriminant analysis, can classify flooding and non-flooding by different combinations of multiple-resolution rainfall intensities, greatly raising the accuracy to 96.5% and lowering the false alert rate to 25%. Compared to the conventional model, the critical indices of accuracy and true positive rate (TPR) were 5%-15% higher in ML models. Such models are applicable to other urban catchments as well. The results are expected to be used to assist early warning systems and provide rational information for contingency and emergency planning.

A New Framework for Advancement of Power Management Strategies in Hybrid Electric Vehicles

Power management strategies play a key role in the design process of hybrid electric vehicles. Electric Assist Control Strategy (EACS) is one of the popular power management strategies for hybrid electric vehicles (HEVs). The present investigation proposes a new framework to advance the EACS. Dynamic Programming method is applied to an HEV model in several drive cycles, and as a result, some optimal operating regions are found. The obtained regions are almost distinct, and consequently, some threshold lines can be defined to separate them. The obtained threshold lines are used to eliminate some parameters of the EACS to reduce its sensitivity to the driving behavior. It is shown that by applying the mentioned modification, the sensitivity of the EACS decreases without a significant increase in the HEV’s FC. All in all, our findings indicate the effectiveness of the proposed methodology to improve the EACS strategy for HEV supervisory control applications.

X-MP Radar for Developing a Lahar Rainfall Threshold for the Merapi Volcano Using a Bayesian Approach

Lahar flow is recognized as among the worst secondary hazards from volcanic disaster. Intense rainfall with long duration is frequently associated with lahar flow. In this study, estimation of a rainfall threshold likely to trigger lahar flow is presented in the first part. The second part discusses its implementation by assessing the growth of observed and predicted rainfall, including the uncertainties. The study area is Merapi Volcano, one of the most active volcanoes in Indonesia, including rivers on the flank of Mount Merapi that are vulnerable to debris flow. The rainfall indices needed to describe the conditions that generate lahars or not were determined empirically by evaluating the hourly and working rainfall using X-band multiparameter (X-MP) weather radar. Using past records of lahar flow, the threshold lines separating rainfall that triggers lahars or not were analyzed for the Putih, Gendol, Pabelan, and Krasak Rivers. The performance of several critical lines was evaluated using Bayesian probability based on skill rates from a contingency matrix. The study shows that the line intercept of the critical lines after a significant eruption in 2010 was higher than those lines developed before 2010, indicating that the rivers are currently at lesser risk. Good representation was shown by the thresholds verified with actual rainfall progression and lahar event information on February 17, 2016, at the Gendol and Pabelan Rivers. These rainfall critical lines were the basis for judging the debris flow occurrence by analyzing the track record of predicted rainfall progression. The uncertainty of rainfall short-term prediction from the extrapolation model was evaluated by perturbing the advection vector of rain echo motion. This ensemble forecast product could provide a plausible range of prediction possibility as assistance in gaining the confidence with which a lahar could be predicted. The scheme presented herein could serve as a useful tool for a lahar early warning system in the area of the Merapi Volcano.

Diagnosis of Pulmonary Arterial Hypertension in Children by Using Cardiac Computed Tomography.

To establish diagnostic criteria for pulmonary arterial hypertension (PAH) in children by using parameters obtained through noninvasive cardiac computed tomography (CCT). We retrospectively measured parameters from CCT images of children from a single institution in a multiple stepwise process. A total of 208 children with mean age of 10.5 years (range: 4 days-18.9 years) were assessed. The variables were classified into three groups: the great arteries; the ventricular walls; and the bilateral ventricular cavities. The relationship between the parameters obtained from the CCT images and mean pulmonary arterial pressure (mPAP) was tested and adjusted by the children's body size. Reference curves for the pulmonary trunk diameter (PTD) and ratio of diameter of pulmonary trunk to ascending aorta (rPTAo) of children with CCT images of normal hearts, adjusted for height, were plotted. Threshold lines were established on the reference curves. PTD and rPTAo on the CCT images were significantly positively correlated with mPAP (r > 0.85, p < 0.01). Height was the body size parameter most correlated with PTD (r = 0.91, p < 0.01) and rPTAo (r = -0.69, p < 0.01). On the basis of the threshold lines on the reference curves, PTD and rPTAo both showed 88.9% sensitivity for PAH diagnosis, with negative predictive values of 93.3% and 92.9%, respectively. PTD and rPTAo measured from CCT images were significantly correlated with mPAP in children. Reference curves and the formula of PTD and rPTAo adjusted for height could be practical for diagnosing PAH in children.

A Comparative Thermodynamic Study of Equilibrium Conditions for Carbon Deposition from Catalytic C–H–O Reformates

The importance of carbon deposition occurring during catalytic fuel reforming is briefly described along with former studies on the process. Thermodynamic fundamentals of modeling the critical conditions of the deposition equilibrium are presented. Computational results of ternary C–H–O diagrams with the threshold lines between the carbon deposition and deposition-free regions are discussed for two new pressure levels of 3 and 30 bar and a temperature range from 200 to 1000 °C. The process pressure does not affect the temperature range typical for the type of deposited carbon allotrope; either graphite, multi-walled carbon nanotubes, or single-walled carbon nanotubes in bundles. However, pressure has a profound influence on the location of the threshold lines for carbon deposition. Three reforming processes of two hydrocarbon fuels are analyzed; catalytic partial oxidation, and wet and dry reforming. Chord lines representing varied compositions of process mixtures are introduced to the ternary diagrams. The intersection points of the chord lines with the threshold lines are used in a novel interpretation of the functions of the oxygen-to-carbon critical ratio against temperature and pressure, which can be used in avoiding carbon deposition in catalytic reforming of natural gas and liquefied petroleum gas.

Multi-Index Seismic Capacity Evaluation of Buckling-Restrained Braced Frames

The seismic capacity of a structure is determined by the performance index that reaches its ultimate bearing or deformation capacity first. This paper presents a multi-index seismic capacity evaluation method for accurately evaluating the seismic capacity of a structure. The normalized response curves of several indices are concurrently plotted to form a multi-index seismic capacity evaluation figure, in which the seismic capacity and demand values that correspond to various indices can be determined by vertical and horizontal threshold lines. Based on an incremental dynamic analysis (IDA), a 6-story buckling-restrained braced frame (BRBF) and a series of comparable 6-story steel frames are analyzed using the proposed method to verify the method and investigate the seismic behavior of BRBFs. The results show that the seismic performance of buckling-restrained braces is not the only factor that determines the seismic capacity of BRBFs and indicate that the multi-index seismic capacity evaluation method can effectively identify the critical index of a structure and the weakest links that restrict the structural seismic capacity.

Shocks to the international prices of agricultural commodities and the effects on welfare and poverty. A simulation of the ex ante long-run effects for Uruguay

In countries with a large share of low- and medium–low-income households, an increase in agricultural commodity prices may have a damaging and widespread effect on the population through the rise in the cost of the consumption basket. A less obvious channel, changes in labor income, would be more beneficial to middle-income households. The simulations show that ex ante all households would experience losses of up to 7.5% of their initial expenditure, with poorer households being the most affected. Poverty would increase by 25% (7.2 p.p.), while indigence would increase even more by 35% (2.25 p.p.). The results also show that, on average, both poor and indigent households would move further away from the threshold lines, meaning that, within each category, poor and indigent households would become more homogeneous. Finally, since Uruguay has a comparative advantage in agricultural commodities, the improvement in the terms of trade is likely to increase the tax revenues, which could be used to compensate those who are negatively affected.

Liquid-liquid phase separation in dilute solutions of poly(styrene sulfonate) with multivalent cations: Phase diagrams, chain morphology, and impact of temperature.

The dilute solution behavior of sodium poly(styrene sulfonate) is studied in the presence of trivalent Al3+ and bivalent Ba2+ cations at various levels of excess NaCl. The study evaluates the phase behavior and the morphology of the polyelectrolyte chains with increasing extent of decoration with the Al3+ and Ba2+ cations and analyses the effect of temperature on these decorated chains. The phase behavior is presented in the form of the cation concentration versus the respective poly(styrene sulfonate) concentration, recorded at the onset of precipitation. Whereas poly(styrene sulfonate) with Al3+ exhibits a linear phase boundary, denoted as the "threshold line," which increases with increasing poly(styrene sulfonate) concentration, Ba2+ cations show a threshold line which is independent of the poly(styrene sulfonate) concentration. An additional re-entrant phase, at considerably higher cation content than those of the threshold lines, is observed with Al3+ cations but not with Ba2+ cations. The threshold line and the re-entrant phase boundary form parts of the liquid-liquid phase boundary observed at the limit of low polymer concentration. The dimensions of the polyelectrolyte chains shrink considerably while approaching the respective threshold lines on increase of the Al3+ and Ba2+ cation content. However, subtle differences occur between the morphological transformation induced by Al3+ and Ba2+. Most strikingly, coils decorated with Al3+ respond very differently to temperature variations than coils decorated with Ba2+ do. As the temperature increases, the poly(styrene sulfonate) chains decrease their size in the presence of Al3+ cations but increase in size in the presence of Ba2+ cations.

What do these scores mean? Presenting patient-reported outcomes data to patients and clinicians to improve interpretability.

BACKGROUNDPatient‐reported outcomes (PROs) (eg, symptoms, functioning) can inform patient management. However, patients and clinicians often have difficulty interpreting score meaning. The authors tested approaches for presenting PRO data to improve interpretability.METHODSThis mixed‐methods study included an Internet survey of cancer patients/survivors, oncology clinicians, and PRO researchers circulated via snowball sampling, plus individual in‐person interviews. Clinical importance was conveyed using 3 approaches (presented in random order): normal score range shaded green, concerning scores circled in red, and red threshold lines indicating normal versus concerning scores. Versions also tested 2 approaches to score directionality: higher = more (better for function, worse for symptoms) and higher = better for both function and symptoms. Qualitative data from online comments and in‐person interviews supplemented quantitative results on interpretation accuracy, clarity, and the “most useful” format.RESULTSThe survey included 1113 respondents: 627 survivors, 236 clinicians, and 250 researchers, plus 10 patients and 10 clinicians who were purposively sampled interviewees. Interpretation accuracy ranged from 53% to 100%. The formats in which higher = better were interpreted more accurately versus those in which higher = more (odds ratio [OR], 1.30; 95% confidence interval [CI], 1.07‐1.58) and were more likely to be rated “very”/“somewhat” clear (OR, 1.39; 95% CI, 1.13‐1.70) and “very” clear (OR, 1.36; 95% CI, 1.18‐1.58). Red circle formats were interpreted more accurately than green‐shaded formats when the first format presented (OR, 1.29; 95% CI, 1.00‐1.65). Threshold‐line formats were more likely to be rated “very” clear than green‐shaded (OR, 1.43; 95% CI, 1.19‐1.71) and red‐circled (OR, 1.22, 95% CI, 1.02‐1.46) formats. Threshold lines were most often selected as “most useful.”CONCLUSIONSThe current results support presenting PRO data with higher = better directionality and threshold lines indicating normal versus concerning scores. Cancer 2017;123:1848–1859. © 2017 The Authors. Cancer published byWiley Periodicals, Inc. on behalf of American Cancer Society. This is an open access article under the terms of the Creative Commons Attribution‐NonCommercial‐NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non‐commercial and no modifications or adaptations aremade.

Efficient soft demodulation schemes for the DVB-S2X system

Summary In this paper, we propose efficient soft demodulation methods for the 64, 128, and 256 amplitude and phase shift keying schemes defined in the digital video broadcasting via satellite second-generation system. We first derive hard decision threshold (HDT) lines for the constituent bits in a symbol and subsequently present compact equations to estimate the soft bit information. If the HDT line for a constituent bit is a simple continuous line, then the soft bit estimation is performed by simply calculating the distance between the detected symbol and the HDT line. High computational complexity and appreciable performance degradation may occur if HDT lines are too complex. In order to prevent this, we also propose a modified max-log demodulation method that achieves the same performance as the original max-log method but with reduced complexity. Depending on the application, a hybrid method can be utilized by combining the advantages of the HDT and modified max-log methods. The simulation results reveal that the proposed hybrid scheme produces almost the same performance as the original max-log method with greatly reduced computational complexity. Copyright © 2015 John Wiley & Sons, Ltd.

Rainfall thresholds for the occurrence of urban landslides in tegucigalpa, honduras: an application of the critical rainfall intensity

The occurrence of landslides on 134 days between 1980 and 2005 in Tegucigalpa, Honduras has been analyzed in order to determine the contribution of triggering and antecedent rainfall. For each of the 6344 days in the study period, the antecedent rainfall for 19 durations ranging between 1 and 60 days has been determined and the corresponding return period has been calculated using the umbel extreme value distribution. The critical rainfall intensity for every landslide day, denoting the antecedent rainfall amount yielding the highest return period divided by its antecedent duration, has been used for the construction of four rainfall thresholds with durations of 7, 15, 30 and 60 days. The accuracy of each threshold in discriminating between landside and non‐landslide days is determined by comparing the antecedent rainfall amounts of each day in the study period with the threshold's rainfall requirements. When threshold lines are allowed to underlie 15%, 50% and 85% of all landslide days, the best performance in the receiver operating characteristic space is achieved with the 7‐day threshold. To improve the threshold performance, landslide days whose triggering rainfall has higher return periods than their corresponding antecedent rainfall amounts are represented in the line x = 0.1 of the critical rainfall intensity–antecedent duration plot. Furthermore, a critical region where minimum triggering and antecedent rainfall amounts are necessary for landslide occurrence has been established to reduce the number of false alarms. Nonetheless, the threshold's low rainfall requirements suggest that human intervention has significantly predisposed egucigalpa's slopes to failure.

The role of laser interstitial thermal therapy in enhancing progression-free survival of difficult-to-access high-grade gliomas: a multicenter study.

Surgical extent-of-resection has been shown to have an impact on high-grade glioma (HGG) outcomes; however, complete resection is rarely achievable in difficult-to-access (DTA) tumors. Controlled thermal damage to the tumor may have the same impact in DTA-HGGs. We report our multicenter results of laser interstitial thermal therapy (LITT) in DTA-HGGs. We retrospectively reviewed 34 consecutive DTA-HGG patients (24 glioblastoma, 10 anaplastic) who underwent LITT at Cleveland Clinic, Washington University, and Wake Forest University (May 2011–December 2012) using the NeuroBlate® System. The extent of thermal damage was determined using thermal damage threshold (TDT) lines: yellow TDT line (43°C for 2 min) and blue TDT line (43°C for 10 min). Volumetric analysis was performed to determine the extent-of-coverage of tumor volume by TDT lines. Patient outcomes were evaluated statistically. LITT was delivered as upfront in 19 and delivered as salvage in 16 cases. After 7.2 months of follow-up, 71% of cases demonstrated progression and 34% died. The median overall survival (OS) for the cohort was not reached; however, the 1-year estimate of OS was 68 ± 9%. Median progression-free survival (PFS) was 5.1 months. Thirteen cases who met the following two criteria—(1) <0.05 cm3 tumor volume not covered by the yellow TDT line and (2) <1.5 cm3 additional tumor volume not covered by the blue TDT line—had better PFS than the other 21 cases (9.7 vs. 4.6 months; P = 0.02). LITT can be used effectively for treatment of DTA-HGGs. More complete coverage of tumor by TDT lines improves PFS which can be translated as the extent of resection concept for surgery.

Uncertainty assessment of ephemeral gully identification, characteristics and topographic threshold when using aerial photographs in agricultural settings

ABSTRACTManual digitizing on aerial photographs is still commonly used for characterizing gully erosion over large areas. Even when automated detection procedures are implemented, manual digitizing is frequently being resorted to in order to constitute reference datasets used for training and validation. In both cases, manual digitizing entails some subjective decisions on behalf of the operator, which introduces uncertainty into the resulting datasets. To assess the magnitude of this uncertainty, 11 experienced operators were asked to digitize and classify ephemeral gullies (EGs) on cropland following a standardized methodology. The resulting 11 datasets were compared in terms of number, type and location of EGs. Furthermore, for EGs located on a well‐defined runoff flow concentration axis, the slope versus contributing area topographic thresholds required for initiating gully channels were assessed using four thresholding methods, and compared across the 11 datasets. The operators identified 259 different EGs. However, the number (52–139) and sum total length (8.9–23.7 km) of EGs varied widely across operators. Only 34% of the EGs were digitized by more than half of the operators, and 7% were identified by all. Identification of EGs located on a well‐defined flow concentration axis proved least subjective. The longer the EG and the more fields the EG crossed, the larger the number of operators that were able to identify it. EGs were also most easily identified when located in sugar beet fields as compared to other crops. EG classification and topographic threshold lines were also found to be strongly operator‐dependent. Quantile regression appeared to be one of the most robust thresholding methods. Operator subjectivity when digitizing EGs on orthophotographs introduces uncertainty that should be taken into account in future remote sensing‐based studies of EG erosion whenever they rely, in part or in full, on manual photograph interpretation. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Stimulated emission of surface plasmon polaritons on smooth and corrugated silver surfaces

We have observed two regimes of stimulated emission of surface plasmon polaritons (SPPs) propagating at interfaces between dye-doped polymeric films and silver substrates. (i) On top of smooth silver substrates, the lasing threshold is very soft, and the relatively broad stimulated emission peak gradually narrows with increase of the pumping. We infer that this stimulated emission regime is dominated by amplification of SPPs in open paths, with a possible contribution from a diffusion feedback provided by unintentional scattering. (ii) At the same time, the laser action on top of roughened silver substrates is characterized by a sharp threshold and multiple narrow spectral lines. This novel stimulated emission effect has strong coherent feedback supported by strong scattering of SPPs at a roughened silver surface. The observed phenomena provide an addition to the family of surface plasmon lasers, enabling active metamaterials and plasmonics.

Rainfall intensity–duration thresholds for bedload transport initiation in small Alpine watersheds

Abstract. Although channel discharge represents one of the primary controls of bedload transport rates in mountain streams, it is rarely measured in small, steep catchments. Thus, it is often impossible to use it as a predictor of hazardous bedload events. In this study, the characteristics of rainfall events leading to bedload transport were investigated in five small Alpine catchments located in different geographical and morphological regions of Switzerland, Italy and France. Using rainfall data at high temporal resolution, a total of 370 rainfall events were identified that led to abundant sediment transport in the different catchments, and corresponding threshold lines were defined using a power law in intensity–duration space. Even though considerable differences in the distribution of the rainfall data were identified between catchments located in various regions, the determined threshold lines show rather similar characteristics. Such threshold lines indicate critical conditions for bedload transport initiation, but rainfall events that do not cause transport activity (so called no-bedload events) can still plot above them. With 0.67 overall in the Erlenbach (Swiss Prealps) and 0.90 for long-duration, low-intensity rainfall, the false alarm rate is considerable. However, for short-duration, high-intensity events, it is substantially smaller (0.33) and comparable to values determined in previous studies on the triggering of Alpine debris flows. Our results support the applicability of a traditional, generalized threshold for prediction or warning purposes during high-intensity rainfall. Such (often convective) rainfall events are unfortunately (i) difficult to measure, even by dense rain gauge networks, and (ii) difficult to accurately predict, both due to their small spatial and temporal scales. Still, for the protection of human life (e.g. along transportation infrastructure such as roads and railway) automated alerts based on power law threshold lines may be useful.

IDENTIFYING DESERT THRESHOLDS BY MAPPING INVERSE ERODIBILITY AND RECOVERY POTENTIALS IN PATCH PATTERNS USING SPECTRAL AND MORPHOLOGICAL ALGORITHMS

ABSTRACTDesert thresholds are narrow zones of spatial instability between semi‐arid and arid regions. Identifying and mapping such thresholds is difficult because of the high diversity of vegetation, soil and bare rock patterns in these regions. Here, we suggest incorporating pattern information from remote sensing imagery in the assessment of eco‐geomorphic transitions. A new methodology was developed for this purpose based on the analysis of potential inverse trends of erosion and recovery embedded in these patterns. The methodology applies spectral mixing analysis to map surface conditions and uses mathematical morphology algorithms of dilation and erosion to identify potential erodibility and recovery trends. Boundary lines are then delineated by classifying combinations of these inverse trends and assessed with reference to their separability. This approach is implemented along the climatic gradient between the Judean Mountains and the Dead Sea in central Israel using mid‐resolution Landsat TM data. The identified threshold lines fit well with lithological, soil and phytogeographical boundaries as delineated in low‐scale maps, yet add significant explicitness to their spatial definition. Such explicitness is instrumental for assessing future desert shifts because of global warming and extended overgrazing. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Development of Youth Aerobic-Capacity Standards Using Receiver Operating Characteristic Curves

Cardiovascular fitness has important implications for current and future health in children. In this paper, criterion-referenced standards are developed for aerobic capacity (an indicator of cardiovascular fitness) based on receiver operating characteristic (ROC) curves. The sample was drawn from participants aged 12-18 years in the National Health and Nutrition Examination Survey (1999-2002, N=1966). Subjects completed a treadmill exercise test from which maximal oxygen uptake (VO(2)max) was estimated from heart rate response. Metabolic syndrome was classified using previously published standards based on the National Cholesterol Education Program/Adult Treatment Panel III adult values at age 20 years. Using aerobic fitness z-scores as the test and metabolic syndrome as the criterion, ROC curve analysis was used to identify aerobic-capacity thresholds. The area under the curve (AUC) value for boys (83.1%) was high, indicating good utility for detecting risk of metabolic syndrome with aerobic fitness values. The AUC for girls (77.2%) was slightly below the recommended value of 80%. Although the ROC plots identified a defensible point for classifying levels of fitness, the approach in the present study was to establish two independent thresholds, one aimed at high specificity and one aimed at high sensitivity. The resulting z values for the low- and higher-risk threshold lines were then converted back to VO(2)max estimates using published LMS (L=skewness, M=median, and S=coefficient of variation) parameters. Values at the low-risk threshold ranged from 40 to 44 mL/kg/min for boys and from 38 to 40 mL/kg/min for girls. In summary, aerobic fitness can be used with moderate accuracy to differentiate between adolescents with and without metabolic syndrome. Age- and gender-specific aerobic-capacity thresholds for creating separate risk groups were identified using nationally representative growth percentiles.