Assumed Threshold Value Research Articles

Statistics of sea-effect snowfall along the Finnish coastline based on regional climate model data

Abstract. The formation of convective sea-effect snowfall (i.e., snow bands) is triggered by cold air outbreaks over a relatively warm and open sea. Snow bands can produce intense snowfall which can last for several days over the sea and potentially move towards the coast depending on wind direction. We defined the meteorological conditions which statistically favor the formation of snow bands over the north-eastern Baltic Sea of the Finnish coastline and investigated the spatio-temporal characteristics of these snow bands. A set of criteria, which have been previously shown to be able to detect the days favoring sea-effect snowfall for Swedish coastal area, were refined for Finland based on four case study simulations, utilizing a convection-permitting numerical weather prediction (NWP) model (HARMONIE-AROME). The main modification of the detection criteria concerned the threshold for 10 m wind speed: the generally assumed threshold value of 10 m s−1 was decreased to 7 m s−1. The refined criteria were then applied to regional climate model (RCA4) data, for an 11-year time period (2000–2010). When only considering cases in Finland with onshore wind direction, we found on average 3 d yr−1 with favorable conditions for coastal sea-effect snowfall. The heaviest convective snowfall events were detected most frequently over the southern coastline. Statistics of the favorable days indicated that the lower 10 m wind speed threshold improved the representation of the frequency of snow bands. For most of the favorable snow band days, the location and order of magnitude of precipitation were closely captured, when compared to gridded observational data for land areas and weather radar reflectivity images. Lightning were observed during one third of the favorable days over the Baltic Sea area.

Energy-based sidesway collapse fragilities for ductile structural frames under earthquake loadings

In assessing the likelihood of structural collapse under strong earthquake motions, uncertainties in structural properties and ground motions can be incorporated by use of a probabilistic analysis framework in conjunction with analysis methods such as incremental dynamic analysis (IDA). Maximum inter-story drift ratio (IDR) is typically selected as the key descriptor to characterize the global behavior of structural system in such a probabilistic assessment. The structural collapse capacity is often defined in terms of a threshold value of IDR or a reduced slope of the IDA curve between a selected seismic intensity measure and the corresponding IDR. However, collapse assessment approaches based on IDR may not accurately represent the overall structural collapse behavior due to redistribution and variation of local damage within the structure. Moreover, results of collapse predictions are found to be sensitive to variability in such drift measures, and assumed threshold values used in the collapse criterion. Recently, an energy-based seismic collapse criterion has been developed to describe collapse in terms of dynamic instability of the whole structural system caused by gravity loads. Using the energy-based collapse criterion, this paper proposes a more effective sidesway collapse risk assessment approach of ductile planar frames subjected to horizontal seismic loadings based on a new key descriptor of structural performance. The key descriptor, designated as the equivalent-velocity ratio, is related to the ratio of the energy dissipated through structural degradation to the seismic input energy. Using the equivalent-velocity ratio, a probabilistic collapse assessment method is developed for systematic treatment of uncertainties in the ground motions.

Energy-based seismic collapse criterion for ductile planar structural frames

One of the most common approaches to assess the collapse capacity of structures under earthquakes is incremental dynamic analysis (IDA), which tracks relationship between a structural damage measure and a ground motion intensity measure by so-called IDA curves. This IDA approach often uses collapse criteria given in terms of a large value of the maximum inter-story drift ratio, plastic hinge formations at structural components, or flattening of the IDA curve. However, these collapse criteria may not accurately represent the overall collapse behavior of structural systems due to redistribution and variation of damage within the structure. Moreover, collapse predictions by these subjective collapse limit-states are found to be sensitive to the assumed threshold values and to the characteristics of IDA curves. For more accurate assessment of collapse capacity and the likelihood of the collapse, this paper proposes a new collapse criterion that describes dynamic instability of frame structures in terms of the balance between the energies from the applied gravity loads and input ground motions. The collapse criterion is developed for planar frames under horizontally applied earthquakes and then tested using computational models of collapse behavior of ductile steel frame structures, which are validated by experiments reported in the literature. The collapse prediction results by the developed collapse criterion and existing criteria are compared in order to investigate sensitivity of the prediction results with respect to threshold values used by existing approaches. The results show that the proposed energy-based seismic collapse criterion is a more reliable option for assessing structural collapse of planar frames. The energy-based criterion can represent global dynamic instability of structural system more effectively by using aggregated quantities of energy responses of structural components instead of using assumed threshold values for structural responses such as story drifts.

Analysis of the Course and Frequency of High Water Stages in Selected Catchments of the Upper Vistula Basin in the South of Poland

The paper presents an analysis of the course and frequency of high water stages in selected catchments of the upper Vistula basin in the south of Poland. The following rivers were investigated: the Dunajec–Nowy Targ-Kowaniec cross-section, the Rudawa–Balice cross-section, the Kamienica–Nowy Sącz cross-section, the Wisłok–Tryńcza cross-section and the San–Przemyśl cross-section. Daily flows from the years 1983–2014 were used to determine maximum annual flows and maximum flows per summer and winter half-year. Selected floods were analyzed with reference to the following metrics: POTX (mean size of the flow determined based on high water stages exceeding the assumed threshold value), POT3F (number of high water stages exceeding the threshold value for each hydrological year), WPOT3F (number of high water stages exceeding the threshold value for the winter half-year and), LOPT3F (number of high water stages exceeding the threshold value for the summer half-year). The determined metrics were analyzed for trend (Mann-Kendall test), homogeneity (Kruskal-Wallis test), and heteroscedasticity (Levene test). Additionally, periodograms were used to determine periodicity of time series for maximum annual flows. The resulting computations indicated upward trends in the analyzed flood metrics but they were not significant in any case. Therefore, in the years 1983–2014 no factors were observed that would significantly affect the size and frequency of high water runoff from the investigated catchments.

Human fall detection on embedded platform using depth maps and wireless accelerometer

Since falls are a major public health problem in an aging society, there is considerable demand for low-cost fall detection systems. One of the main reasons for non-acceptance of the currently available solutions by seniors is that the fall detectors using only inertial sensors generate too much false alarms. This means that some daily activities are erroneously signaled as fall, which in turn leads to frustration of the users. In this paper we present how to design and implement a low-cost system for reliable fall detection with very low false alarm ratio. The detection of the fall is done on the basis of accelerometric data and depth maps. A tri-axial accelerometer is used to indicate the potential fall as well as to indicate whether the person is in motion. If the measured acceleration is higher than an assumed threshold value, the algorithm extracts the person, calculates the features and then executes the SVM-based classifier to authenticate the fall alarm. It is a 365/7/24 embedded system permitting unobtrusive fall detection as well as preserving privacy of the user.

Population genetics study of common (Pipistrellus pipistrellus) and soprano (Pipistrellus pygmaeus) pipistrelle bats from central Europe suggests interspecific hybridization

The discovery that the most widespread bat in Europe comprises cryptic species, Pipistrellus pipistrellus (Schreber, 1774) (common pipistrelle) and Pipistrellus pygmaeus (Leach, 1825) (soprano pipistrelle), provides a great opportunity to look at the mechanism of species coexistence. Based on eight nuclear microsatellite loci (n = 353), we observed similarities between the species in Poland with respect to heterozygosity, allelic richness, mean relatedness, and inbreeding coefficients. However, pronounced differences in migratory patterns (shown by assignment tests) suggest that P. pygmaeus is the more migratory species. The proportion of bats migrating between colonies differed significantly, with 17.1% and 41.8% individuals of P. pygmaeus and P. pipistrellus, respectively, confidently assigned to colonies of origin. Both species demonstrated a more migratory character in central Europe compared with the populations from the British Isles. Given the cryptic nature of the examined taxa, we also assessed whether they hybridize. Hybridization was confirmed by three methods—one based on genetic distance and two based on Bayesian approaches. The overall hybridization rate, depending on assumed threshold values, ranged from 1.7% to 13.3% for both species. We conclude that the population structuring in these pipistrelles is not homogenous across their range. Moreover, hybridization between them in continental Europe does occur and is not rare.

The "crowding effect" in the cestode Schistocephalus solidus: density-dependent effects on plerocercoid size and infectivity.

The occurrence of the crowding effect was demonstrated in plerocercoids of the cestode Schistocephalus solidus infecting threespine stickleback Gasterosteus aculeatus from Walby and Scout lakes, Alaska. Contrary to an earlier report, relatively large numbers of parasites (>3-4 plerocercoids) were observed to grow large enough in an intermediate host fish to become competent to infect and to mature in the definitive host under any of 3 assumed threshold values and 1 scenario of graded sizes for parasite competency. In Walby Lake, intensity and host body mass were significant predictors of mean plerocercoid mass per host, whereas intensity, host body mass, and combined parasite index were significant predictors in Scout Lake. Slopes of equations expressing the relationship between mean parasite mass and intensity for both lakes were less than 1, implying that processes other than or in combination with simple resource limitation might be producing the observed crowding effect. The causal mechanism for the crowding effect could include exploitative competition, interference competition, and host immune response. There were significant differences in infection between the two lakes, including different distributions of parasite intensities among hosts and different expressions of the crowding effect; however, an explanation of the differences awaits further investigation.

Some Statistical Characteristics of Monthly and Annual Pluviometric Irregularity for the Spanish Mediterranean Coast

Seven series of monthly pluviometric amounts, sometimes exceeding recording periods of 100 years and compiled by the Instituto Nacional de Meteorologia (Spain), are used to study the irregularity of the pluviometric regime along the Spanish Mediterranean coast and nearby Atlantic coast. First of all, three statistical functions (gamma, log-normal and a combination of Poisson and gamma distributions) and moment-ratio diagrams are used to model the monthly and annual empirical distributions of precipitation amounts, each distribution being tested by means of the Kolmogorov-Smirnov test. It is noteworthy that, whereas most of the monthly cases require the gamma distribution, the pluviometric behaviour of the summer months is well described by the Poisson-gamma distribution. Moreover, both the log-normal and the gamma distributions satisfactorily model empirical annual amounts. Consequently, rainfall amounts are not identically distributed along a year for each gauge tested. Second, temporal trends deduced for annual and seasonal amounts are computed and their statistical significance evaluated. The most notable fact is that, although some linear trends are close to 1 mm/year, their significance levels exceed the assumed threshold value and, excepting the winter season for Barcelona, they are considered non-significant from a statistical point of view. Finally, by again using monthly and annual amounts, three temporal irregularity indexes are computed for each pluviometric series, the temporal disparity of the rainfall patterns of the Mediterranean region being enhanced as a result. It addition to the temporal irregularity, a change with latitude is observed both in the parameters of the statistical distributions and the temporal irregularity indexes for the rain gauges analysed. The two most southerly rain gauges constitute a special case in comparison with the remaining stations, because they also receive the Atlantic influences due to their proximity to this ocean.

オブジェクト指向設計法によるチベット活字文字認識について

The set of Tibetan characters consist of basic 30 consents, 76 combination characters, and 4 vowels. Despite the limited number, there are many similar characters and thus, special treatment is necessary to recognize them automatically. In this paper, each Tibetan character is assigned to have an Object Oriented dictionary which is created by combining the categorization and the character identification procedures. When the Euclidean distance between the candidate characters becomes shorter than the assumed threshold values, these characters are categorized as similar characters.

A physically based distribution function for low flow

Abstract An attempt is made to incorporate the physical mechanism in a distribution function of low flow in terms of baseflow recession. The derived distribution function contains four parameters of which two are determined from a traditional recession analysis of low flow periods. The other two are derived from a statistical analysis of the maximum length of “dry weather” periods when precipitation is less than an assumed threshold value. The distribution function with the same parameters can be applied to calculate mean low flow for different durations. It is applied and tested for summer low flow in southern and western Norway.