Financial fire sales as continuous-state complex contagion

Trading activities in financial systems create various channels through which systemic risk can propagate. An important contagion channel is financial fire sales, where a bank failure causes asset prices to fall due to asset liquidation, which in turn drives further bank defaults, triggering the next rounds of liquidation. This process can be considered as a complex contagion, yet it cannot be modeled using the conventional binary-state contagion models because there is a continuum of states representing asset prices. Here, we develop a threshold model of continuous-state cascades in which the states of each node are represented by real values. We show that the solution of a multistate contagion model, for which the continuous states are discretized, accurately replicates the simulated continuous state distribution as long as the number of states is moderately large. This discretization approach allows us to exploit the power of approximate master equations to trace the trajectory of the fraction of defaulted banks and obtain the distribution of asset prices that characterize the dynamics of fire sales through overlapping portfolios. We examine the accuracy of the proposed method using real data on asset-holding relationships in exchange-traded funds. Our methodology could contribute to evaluating and controlling systemic risk that would emerge in various real-world networked systems in the form of continuous-state complex contagion

Metastable GeV-scale particles as a solution to the cosmological lithium problem

The persistent discrepancy between observations of 7Li with putative primordial origin and its abundance prediction in Big Bang Nucleosynthesis (BBN) has become a challenge for the standard cosmological and astrophysical picture. We point out that the decay of GeV-scale metastable particles X may significantly reduce the BBN value down to a level at which it is reconciled with observations. The most efficient reduction occurs when the decay happens to charged pions and kaons, followed by their charge exchange reactions with protons. Similarly, if X decays to muons, secondary electron antineutrinos produce a similar effect. We consider the viability of these mechanisms in different classes of new GeV-scale sectors, and find that several minimal extensions of the Standard Model with metastable vector and/or scalar particles are capable of solving the cosmological lithium problem. Such light states can be a key to the explanation of recent cosmic ray anomalies and can be searched for in a variety of high-intensity medium-energy experiments.Comment: 50 pages, 13 figures; references added, typo correcte

Branching ratios of mesonic and nonmesonic antikaon absorptions in nuclear medium

The branching ratios of K^- absorption at rest in nuclear matter are theoretically investigated in order to understand the mechanism of K^- absorption into nuclei. For this purpose mesonic and nonmesonic absorption potentials are evaluated as functions of nuclear density, the kaon momentum and energy from one- and two-body K^- self-energy, respectively. By using a chiral unitary approach for the s-wave Kbar N amplitude we find that both the mesonic and nonmesonic absorption potentials are dominated by the Lambda(1405) contributions. The fraction of the mesonic and nonmesonic absorptions are evaluated to be respectively about 70% and 30% at the saturation density almost independently on the kaon momentum. We also observe different behavior of the branching ratios to pi ^+ Sigma^- and pi^- Sigma^+ channels in mesonic absorption due to the interference between Lambda(1405) and the I=1 nonresonant background, which is consistent with experimental results. The nonmesonic absorption ratios [Lambda p]/[Sigma^0 p] and [Lambda n]/[Sigma^0 n] are about unity while [Sigma^+ n]/[Sigma^0 p] and [Sigma^- p]/[Sigma^0 n] are about two due to the Lambda(1405) dominance in absorption. Taking into account the kaon momenta and energies, the absorption potentials become weaker due to the downward shift of the initial K^-N two-body energy, but this does not drastirally change the nonmesonic fraction. The Sigma(1385) contribution in the p-wave Kbar N amplitude is examined and found to be very small compared to the Lambda(1405) contribution in slow K^- absorption.Comment: 18 pages, 22 figure

Local variation of hashtag spike trains and popularity in Twitter

We draw a parallel between hashtag time series and neuron spike trains. In each case, the process presents complex dynamic patterns including temporal correlations, burstiness, and all other types of nonstationarity. We propose the adoption of the so-called local variation in order to uncover salient dynamics, while properly detrending for the time-dependent features of a signal. The methodology is tested on both real and randomized hashtag spike trains, and identifies that popular hashtags present regular and so less bursty behavior, suggesting its potential use for predicting online popularity in social media.Comment: 7 pages, 7 figure

Exploring concurrency and reachability in the presence of high temporal resolution

Network properties govern the rate and extent of spreading processes on networks, from simple contagions to complex cascades. Recent advances have extended the study of spreading processes from static networks to temporal networks, where nodes and links appear and disappear. We review previous studies on the effects of temporal connectivity for understanding the spreading rate and outbreak size of model infection processes. We focus on the effects of "accessibility", whether there is a temporally consistent path from one node to another, and "reachability", the density of the corresponding "accessibility graph" representation of the temporal network. We study reachability in terms of the overall level of temporal concurrency between edges, quantifying the overlap of edges in time. We explore the role of temporal resolution of contacts by calculating reachability with the full temporal information as well as with a simplified interval representation approximation that demands less computation. We demonstrate the extent to which the computed reachability changes due to this simplified interval representation.Comment: To appear in Holme and Saramaki (Editors). "Temporal Network Theory". Springer- Nature, New York. 201

Applying machine learning and predictive modeling to retention and viral suppression in South African HIV treatment cohorts

HIV treatment programs face challenges in identifying patients at risk for loss-to-follow-up and uncontrolled viremia. We applied predictive machine learning algorithms to anonymised, patientlevel HIV programmatic data from two districts in South Africa, 2016–2018. We developed patient risk scores for two outcomes: (1) visit attendance≤ 28 days of the next scheduled clinic visit and (2) suppression of the next HIV viral load (VL). Demographic, clinical, behavioral and laboratory data were investigated in multiple models as predictor variables of attending the next scheduled visit and VL results at the next test. Three classifcation algorithms (logistical regression, random forest and AdaBoost) were evaluated for building predictive models. Data were randomly sampled on a 70/30 split into a training and test set. The training set included a balanced set of positive and negative examples from which the classifcation algorithm could learn. The predictor variable data from the unseen test set were given to the model, and each predicted outcome was scored against known outcomes. Finally, we estimated performance metrics for each model in terms of sensitivity, specifcity, positive and negative predictive value and area under the curve (AUC). In total, 445,636 patients were included in the retention model and 363,977 in the VL model. The predictive metric (AUC) ranged from 0.69 for attendance at the next scheduled visit to 0.76 for VL suppression, suggesting that the model correctly classifed whether a scheduled visit would be attended in 2 of 3 patients and whether the VL result at the next test would be suppressed in approximately 3 of 4 patients. Variables that were important predictors of both outcomes included prior late visits, number of prior VL tests, time since their last visit, number of visits on their current regimen, age, and treatment duration. For retention, the number of visits at the current facility and the details of the next appointment date were also predictors, while for VL suppression, other predictors included the range of the previous VL value. Machine learning can identify HIV patients at risk for disengagement and unsuppressed VL. Predictive modeling can improve the targeting of interventions through diferentiated models of care before patients disengage from treatment programmes, increasing costefectiveness and improving patient outcomes.The American People and the President’s Emergency Plan for AIDS Relief (PEPFAR) through the United States Agency for International Development (USAID), including bilateral support through USAID South Africa’s Accelerating Program Achievements to Control the Epidemic; the NIH National Institute of Allergies and Infectious Diseases Award and Eunice Kennedy Shriver National Institute of Child Health & Human Development.https://www.nature.com/srepdm2022Human Nutritio

Peptide YY ablation in mice leads to the development of hyperinsulinaemia and obesity

Aims/hypothesis. Obese people exhibit reduced circulating peptide YY (PYY) levels, but it is unclear whether this is a consequence or cause of obesity. We therefore investigated the effect of Pyy ablation on energy homeostasis. Methods. Body composition, i.p. glucose tolerance, food intake and hypothalamic neuropeptide expression were determined in Pyy knock-out and wild-type mice on a normal or high-fat diet. Results. Pyy knock-out significantly increased bodyweight and increased fat mass by 50% in aged females on a normal diet. Male chow-fed Pyy −/− mice were resistant to obesity but became significantly fatter and glucose-intolerant compared with wild-types when fed a high-fat diet. Pyy knock-out animals exhibited significantly elevated fasting or glucose-stimulated serum insulin concentrations vs wild-types, with no increase in basal or fasting-induced food intake. Pyy knock-out decreased or had no effect on neuropeptide Y expression in the arcuate nucleus of the hypothalamus, and significantly increased proopiomelanocortin expression in this region. Male but not female knock-outs exhibited significantly increased growth hormone-releasing hormone expression in the ventromedial hypothalamus and significantly elevated serum IGF-I and testosterone levels. This sex difference in activation of the hypothalamo–pituitary somatotrophic axis by Pyy ablation may contribute to the resistance of chow-fed male knock-outs to late-onset obesity. Conclusions/interpretation. PYY signalling is important in the regulation of energy balance and glucose homeostasis, possibly via regulation of insulin release. Therefore reduced PYY levels may predispose to the development of obesity, particularly with ageing or under conditions of high-fat feeding

Human immunodeficiency virus: 25 years of diagnostic and therapeutic strategies and their impact on hepatitis B and C virus

The human immunodeficiency virus (HIV) had spread unrecognized in the human population as sexually transmitted disease and was finally identified by its disease AIDS in 1981. Even after the isolation of the causative agent in 1983, the burden and death rate of AIDS accelerated worldwide especially in young people despite the confection of new drugs capable to inhibit virus replication since 1997. However, at least in industrialised countries, this trend could be reversed by the introduction of combination therapy strategies. The design of new drugs is on going; besides the inhibition of the three enzymes of HIV for replication and maturation (reverse transcriptase, integrase and protease), further drugs inhibits fusion of viral and cellular membranes and virus maturation. On the other hand, viral diagnostics had been considerably improved since the emergence of HIV. There was a need to identify infected people correctly, to follow up the course of immune reconstitution of patients by measuring viral load and CD4 cells, and to analyse drug escape mutations leading to drug resistance. Both the development of drugs and the refined diagnostics have been transferred to the treatment of patients infected with hepatitis B virus (HBV) and hepatitis C virus (HCV). This progress is not completed; there are beneficial aspects in the response of the scientific community to the HIV burden for the management of other viral diseases. These aspects are described in this contribution. Further aspects as handling a stigmatising disease, education of self-responsiveness within sexual relationships, and ways for confection of a protective vaccine are not covered

Targeted Overexpression of Osteoactivin in Cells of Osteoclastic Lineage Promotes Osteoclastic Resorption and Bone Loss in Mice

This study sought to test whether targeted overexpression of osteoactivin (OA) in cells of osteoclastic lineage, using the tartrate-resistant acid phosphase (TRAP) exon 1B/C promoter to drive OA expression, would increase bone resorption and bone loss in vivo. OA transgenic osteoclasts showed ∼2-fold increases in OA mRNA and proteins compared wild-type (WT) osteoclasts. However, the OA expression in transgenic osteoblasts was not different. At 4, 8, and 15.3 week-old, transgenic mice showed significant bone loss determined by pQCT and confirmed by μ-CT. In vitro, transgenic osteoclasts were twice as large, had twice as much TRAP activity, resorbed twice as much bone matrix, and expressed twice as much osteoclastic genes (MMP9, calciton receptor, and ADAM12), as WT osteoclasts. The siRNA-mediated suppression of OA expression in RAW264.7-derived osteoclasts reduced cell size and osteoclastic gene expression. Bone histomorphometry revealed that transgenic mice had more osteoclasts and osteoclast surface. Plasma c-telopeptide (a resorption biomarker) measurements confirmed an increase in bone resorption in transgenic mice in vivo. In contrast, histomorphometric bone formation parameters and plasma levels of bone formation biomarkers (osteocalcin and pro-collagen type I N-terminal peptide) were not different between transgenic mice and WT littermates, indicating the lack of bone formation effects. In conclusion, this study provides compelling in vivo evidence that osteoclast-derived OA is a novel stimulator of osteoclast activity and bone resorption

Manovacuometria realizada por meio de traqueias de diferentes comprimentos

Manovacuometry is a simple, fast, and non-invasive test, with maximal inspiratory pressure (MIP) and maximal expiratory pressure (MEP) obtained to assist respiratory muscle assessment. Currently, there is a wide variety of models and brands of manovacuometers with different trachea diameters and lengths. However, the interference of these models in the measurements obtained by these equipments needs to be investigated. Thus, this study mainly aimed to verify the influence of tracheal length on maximal respiratory pressures (MRP), obtained by an analog manovacuometer, in healthy individuals. Our secondary objective was to verify the correlation between measurements. Fifty individuals, aged 18 to 30, of both sexes, were evaluated by spirometry and manovacuometry. MIP and MEP were performed using tracheas with same internal diameter (0.5 cm) and 30 cm, 60 cm, and 90 cm length. Significantly lower MIP values were observed when comparing a 90 cm trachea to 30 and 60 cm tracheas (Friedman’s ANOVA test and Wilcoxon test with Bonferroni adjustment). Tracheas with 30, 60, and 90 cm length and same diameter did not affect MIP and MEP values, except the 90 cm trachea for MIP values, which may interfere in the physical therapy clinical practice. Further studies are required to analyze the need for standardizing the trachea length used in manovacuometers.La manovacuometría es una prueba sencilla, rápida y no invasiva por la cual se obtienen la presión inspiratoria máxima (PImax) y la presión espiratoria máxima (PEmax), con el objetivo de ayudar en el examen muscular respiratorio. Hoy día se encuentran una gran variedad de modelos y marcas de manovacuometros, con diferentes diámetros y longitudes de las tráqueas, pero hacen falta estudios sobre la interferencia de estos modelos en las mediciones por este instrumento. En este texto se propone examinar en sujetos sanos, en primer lugar, la influencia en la longitud de las tráqueas en las presiones respiratorias máximas, obtenidas por manovacuometros analógicos, y en segundo lugar comprobar la existencia de correlación entre las mediciones. Se evaluaron a cincuenta sujetos entre 18 y 30 años de edad, tanto varones como mujeres, empleando la espirometría y la manovacuometría. Se midió la PImax y la PEmax empleando tráqueas de mismo diámetro interno (0,5 cm) y con longitudes de 30, 60 e 90 cm. Se observaron valores significativamente menores de PImax con la tráquea de longitud de 90 cm en comparación con las PImax con las tráqueas de 30 y 60 cm (prueba de Friedman’s ANOVA, la de Wilcoxon con ajustes de Bonferroni). Las tráqueas de 30, 60 y 90 cm de longitud y mismo diámetro no influyeron en los valores de la PEmax y de la PImax, con excepción de la tráquea de 90 cm en los valores de la PImax, lo que puede interferir la práctica clínica fisioterapéutica. Se necesitan más estudios para evaluar la necesidad de estándares de la longitud de tráqueas empleadas en manovacuometros.A manovacuometria é um teste simples, rápido e não invasivo por meio do qual a pressão inspiratória máxima (PImáx) e a pressão expiratória máxima (PEmáx) são obtidas, a fim de auxiliar na avaliação muscular respiratória. Atualmente, há grande variedade de modelos e marcas de manovacuômetros, com diferentes diâmetros e comprimentos de traqueias, no entanto, a interferência desses modelos nas medidas obtidas por esses equipamentos necessita de investigação. Desta forma, o objetivo primário deste estudo foi verificar a influência do comprimento de traqueias nas pressões respiratórias máximas, obtidas por meio de manovacuômetro analógico, em indivíduos saudáveis e, secundariamente, se há correlação entre as medidas. Foram avaliados 50 indivíduos, de 18 a 30 anos, de ambos os sexos, por meio da espirometria e manovacuometria. As PImáx e PEmáx foram realizadas com uso de traqueias de mesmo diâmetro interno (0,5 cm) e comprimentos de 30, 60 e 90 cm. Foram observados valores significativamente menores de PImáx obtidos com a traqueia de comprimento de 90 cm comparados às PImáx obtidas com as traqueias de 30 e 60 cm (teste de Friedman’s ANOVA com teste de Wilcoxon com ajuste de Bonferroni). As traqueias de 30, 60 e 90 cm de comprimento e mesmo diâmetro não influenciaram os valores de PEmáx e PImáx, exceto a traqueia de 90 cm para os valores de PImáx, o que pode interferir na prática clínica fisioterapêutica. Novos estudos são necessários para analisar a necessidade de padronização do comprimento da traqueia utilizada em manovacuômetros