Challenges for ATM management in times of market variability caused by the COVID-19 pandemic crisi.

One of the most important issues related to the management of an Automatic Teller Machine (ATM) network is the correct forecasting of the demand for cash. Typically, this demand, expressed as the value or number of ATM withdrawals, has some regularities that can be used to evaluate future values for these variables. However, forecasting becomes a challenge when a crisis occurs that could affect the behavior of ATM users. In this context, it is important to identify how the development of the crisis and the various information concerning it may affect people's attitudes to cash. This study aims to examine the impact of the COVID-19 pandemic on the behavior of ATM customers. On the basis of daily data from 81 ATMs, we analyze the changes in the value and number of withdrawals just before and during the COVID-19 pandemic in Poland. An event study analysis allows us to determine precisely the moments in which changes in user behavior took place. This means that it is also possible to examine the reaction of ATM users to the announcement and implementation of the pandemic restrictions, and to determine the factors that had an impact on the change in people's attitude to cash. Such a study is also important from a sociological point of view, as it enables one to understand people's reactions to the emerging crisis. Hence, its results may be useful not only for managers of ATM networks, but also for various authorities and policy makers.

Multi-feature evaluation of financial contagion.

Financial contagion refers to the spread of market turmoils, for example from one country or index to another country or another index. It is standardly assessed by modelling the evolution of the correlation matrix, for example of returns, usually after removing univariate dynamics with the GARCH model. However, significant events like crises visible in one financial market are usually reflected in other financial markets/countries simultaneously in several dimensions, i.e., in general, entire distributions of returns in other markets are affected. These distributions are determined/described by their expected value, variance, skewness, kurtosis and other statistics that determine the shape of the distribution function of returns, which can be based on higher (mixed) moments. These descriptive statistics are not constant over time, and, moreover, they can interreact within the given market and among the markets over time. In this article we propose, and use for the daily values of five indexes (CAC40, DAX30, DJIA, FTSE250 and WIG20) over the time period 2006-2017, a new, simple and computationally inexpensive methodology to automatically extend contagion evaluation from the evolution of the correlation matrix to the evolution of multiple higher mixed moments as well. Specifically, the joint distribution of normalized variables for each pair of indexes is modeled as a polynomial with time evolving coefficients estimated using an exponential moving average. As we can obtain any arbitrary number of evolving mixed moments this way, its dimensionality reduction using PCA (principal component analysis) is also discussed, obtaining a lower number of dominating and relatively independent features, which can each be interpreted through a polynomial that describes the corresponding perturbation of joint distribution. We obtain features that describe the interrelations among stock markets in several dimensions and that provide information about the current stage of crisis and the strength of the contagion process.

Experimental determination of the Stern layer thickness at the interface of the human arachnoid membrane and the cerebrospinal fluid.

The paper is part of an investigation of the electrostatic forces contributing to the interaction between colloidal molecules, suspended in the cerebrospinal fluid, with other molecules of the cerebrospinal fluid and with the surrounding environment. The study is based on experimental observations and theoretical considerations. We are reporting about the microscopic observation of particles suspended in the cerebrospinal fluid which was obtained by lumbar puncture of 27 neurosurgery patients. We found that the mean particle diameter and therefore the mean thickness of the Stern layer at the interface of the arachnoid membrane with the cerebrospinal fluid is a few micrometers. Individual variations of this diameter have been observed.

Atmospheric pressure and basic parameters of intracranial volume-pressure homeostasis.

BACKGROUND AND PURPOSE: There are only a few studies in the literature regarding the influence of atmospheric pressure on intracranial homeostasis and the mechanism of the relation has not been clarified. The aim of the study was to evaluate the influence of atmospheric pressure and ambient temperature on parameters of intracranial volume-pressure homeostasis including intracranial pressure and cerebral perfusion pressure as well as on blood pressure and body temperature. MATERIAL AND METHODS: The authors analyzed the influence of atmospheric pressure on intracranial pressure, blood pressure, cerebral perfusion pressure and body temperature in 14 patients who were monitored because of suspicion of having normal pressure hydrocephalus. RESULTS: Atmospheric pressure below 760 mm Hg (1013.3 hPa) significantly affects intracranial pressure, arterial blood pressure, cerebral perfusion pressure and body temperature. Atmospheric pressure above 770 mm Hg (1026.6 hPa) does not affect intracranial pressure, arterial blood pressure, cerebral perfusion pressure or body temperature. CONCLUSIONS: Atmospheric pressure range of 768 mm Hg (1023.9 hPa) to 770 mm Hg (1026.6 hPa) is the border range to preserve intracranial homeostasis, below which qualitative changes of cerebral blood flow occur. In the high range of atmospheric pressure its increase initiates biological protective mechanisms to maintain normal cerebral blood flow. The mechanism involved in the influence of atmospheric pressure and environmental factors in general on intracranial pressure and other parameters of pressure-volume homeostasis has not been explained.