Avalanche Statistics of Driven Granular Slides in a Miniature Mound

We examine avalanche statistics of rain- and vibration-driven granular slides in miniature sand mounds. A crossover from power-law to non power-law avalanche-size statistics is demonstrated as a generic driving rate $\nu$ is increased. For slowly-driven mounds, the tail of the avalanche-size distribution is a power-law with exponent $-1.97\pm 0.31$, reasonably close to the value previously reported for landslide volumes. The interevent occurrence times are also analyzed for slowly-driven mounds; its distribution exhibits a power-law with exponent $-2.670\pm 0.001$.Comment: 4 pages, 3 figures, 1 tabl

Pathology, microbiology, and genetic diversity associated with Erysipelothrix rhusiopathiae and novel Erysipelothrix spp. infections in southern sea otters (Enhydra lutris nereis)

Erysipelothrix spp., including E. rhusiopathiae, are zoonotic bacterial pathogens that can cause morbidity and mortality in mammals, fish, reptiles, birds, and humans. The southern sea otter (SSO; Enhydra lutris nereis) is a federally-listed threatened species for which infectious disease is a major cause of mortality. We estimated the frequency of detection of these opportunistic pathogens in dead SSOs, described pathology associated with Erysipelothrix infections in SSOs, characterized the genetic diversity and antimicrobial susceptibility of SSO isolates, and evaluated the virulence of two novel Erysipelothrix isolates from SSOs using an in vivo fish model. From 1998 to 2021 Erysipelothrix spp. were isolated from six of >500 necropsied SSOs. Erysipelothrix spp. were isolated in pure culture from three cases, while the other three were mixed cultures. Bacterial septicemia was a primary or contributing cause of death in five of the six cases. Other pathology observed included suppurative lymphadenopathy, fibrinosuppurative arteritis with thrombosis and infarction, bilateral uveitis and endophthalmitis, hypopyon, petechia and ecchymoses, mucosal infarction, and suppurative meningoencephalitis and ventriculitis. Short to long slender Gram-positive or Gram-variable bacterial rods were identified within lesions, alone or with other opportunistic bacteria. All six SSO isolates had the spaA genotype–four isolates clustered with spaA E. rhusiopathiae strains from various terrestrial and marine animal hosts. Two isolates did not cluster with any known Erysipelothrix spp.; whole genome sequencing revealed a novel Erysipelothrix species and a novel E. rhusiopathiae subspecies. We propose the names Erysipelothrix enhydrae sp. nov. and Erysipelothrix rhusiopathiae ohloneorum ssp. nov. respectively. The type strains are E. enhydrae UCD-4322-04 and E. rhusiopathiae ohloneorum UCD-4724-06, respectively. Experimental injection of tiger barbs (Puntigrus tetrazona) resulted in infection and mortality from the two novel Erysipelothrix spp. Antimicrobial susceptibility testing of Erysipelothrix isolates from SSOs shows similar susceptibility profiles to isolates from other terrestrial and aquatic animals. This is the first description of the pathology, microbial characteristics, and genetic diversity of Erysipelothrix isolates recovered from diseased SSOs. Methods presented here can facilitate case recognition, aid characterization of Erysipelothrix isolates, and illustrate assessment of virulence using fish models

Clustering regimes in a sandpile with targeted triggering

The sandpile is one of the earliest discrete models to have demonstrated the self-organisation believed to be at work in earthquakes and other nonlinear systems in nature. However, sandpile-based approaches are less utilised for modelling seismicity, due to the cascading behaviour of avalanches, which, in contrast to the bursty correlated earthquake dynamics, release all the accumulated energy in a single event. Here, the sandpile model is modified by introducing a preferential targeting of the most susceptible grid site, allowing it to generate simulated sequences that are statistically similar to those of earthquake events in space, time, and energy domains. In particular, the proposed model creates generalised space-time-magnitude “distance” between events akin to real aftershock sequences, and a comparison with real-world data from a catalogue of recent earthquakes is presented. The underlying mechanisms of earthquake generation are clearly very much complex, but discrete models such as this one provide easily reproducible results for statistical comparisons

Observing spatio-temporal clustering and separation using interevent distributions of regional earthquakes

Past studies that attempted to quantify the spatio-temporal organization of seismicity have defined the conditions by which an event and those that follow it can be related in space and/or time. In this work, we use the simplest measures of spatio-temporal separation: the interevent distances R and interevent times T between pairs of successive events. We observe that after a characteristic value R*, the distributions of R begin to follow that of a randomly shuffled sequence, suggesting that events separated by R > R* are more likely to be uncorrelated events generated independent of one another. Interestingly, the conditional T distributions for short-distance (long-distance) events, R ≤ R* (R > R*), peak at correspondingly short (long) T values, signifying the spatio-temporal clustering (separation) of correlated (independent) events. By considering different threshold magnitudes within a range that ensures substantial catalogue completeness, invariant quantities related to the spatial and temporal spacing of correlated events and the rate of generation of independent events emerge naturally

Comparing the sandpile model with targeted triggering and the Olami-Feder-Christensen model as models of seismicity using recurrence network analysis

Slowly driven sandpile models has found applications in modelling earthquakes due to the observed power law statistics in its magnitude distributions, like the behaviour of earthquakes. Adding a probability to target the most susceptible site in the grid, the sandpile model recovers even the spatio-temporal statistics of earthquake events. In this work, we compare the sandpile model with targeted triggering to the Olami-Feder-Christensen (OFC) model: a standard earthquake model that also exhibits self-organized criticality. The sandpile model captures the magnitude distributions of earthquake events at a value of targeted triggering probability p = [0.004,0.007]. The triggering probability value p = 1.0, showing that the most susceptible site is always triggered, follows the magnitude distribution of the OFC model. A comparison was done by constructing a record-breaking recurrence network for the events. Spatial and magnitude criteria set the temporally directed links between events across the entire record. Both the models recover power-law exponents comparable to those previously obtained for earthquake data, which is 1.0 for recurrence distance and recurrence time distributions, and 2.1 for the in-degree distributions for the farthest recurrence criteria. The sandpile model with targeted triggering exhibits a behaviour in between a slowly driven sandpile and the OFC model. © Published under licence by IOP Publishing Ltd

The role of intervention mechanisms on a self-organized system: dynamics of a sandpile with site reinforcement

We revisit the sandpile model and examine the effect of introducing site-dependent thresholds that increase over time based on the generated avalanche size. This is inspired by the simplest means of introducing stability into a self-organized system: the locations of collapse are repaired and reinforced. Statistically, for the case of finite driving times, we observe that the site-dependent reinforcements decrease the occurrence of very large avalanches, leading to an effective global stabilization. Interestingly, however, long simulation runs indicate that the system will persist in a state of self-organized criticality (SOC), recovering the power-law distributions with a different exponent as the original sandpile. These results suggest that tipping the heavy-tailed power-laws into more equitable and normal statistics may require unrealistic scales of intervention for real-world systems, and that, in the long run, SOC mechanisms still emerge. This may help explain the robustness of power-law statistics for many complex systems

A comparative study on the effect of privatization on the profitability of selected government owned and/or controlled corporations in the Philippines

The study discusses the effects of privatization on the profitability as measured by the return on equity of selected government owned and/or controlled corporations in the Philippines. The two GOCCs selected are Petron Corporation and Philippine National Bank. This study included the comparison of the pre- and post-financial conditions of the said companies, in which net profit margin, total asset turnover and financial leverage multiplier are used to evaluate profitability. A modified time frame of 15 years is used i.e. five years before and after privatization, excluding the five (5) years in between i.e. five year adjustment period wherein the GOCC underwent the privatization process. The Du Pont system of analysis and time series analysis are utilized in the study to compare the effects of privatiziation on the profitability of GOCCs. The study showed that privatization indeed affects the profitability of selected GOCCs. However, it is not solely privatization that influenced the firms but other factors such as political uncertainties and economic conditions