Evaluation of the Lateral Vibration Response of Footbridges under Uncertainty Conditions

<p>The evaluation of the vibration performance of footbridges due to walking pedestrians is an issue of increasing importance in current footbridge design practice. The growing trend of slender footbridges with long spans and light materials has led to serviceability problems in lateral vibrations, which occur when the number of pedestrians reaches a “critical number”. Considering the mode of vibration in which the lateral instability is more likely to develop, the structural response depends on the modal characteristics of the footbridge; in particular, the natural frequency and the damping ratio. These modal parameters are stochastic variables, as it is not possible to determine them without a level of uncertainty. Thus, the purpose of this paper is to obtain the value of the lateral dynamic response of slender footbridges with a certain confidence level under uncertainty conditions. The uncertainties of those modal parameters are considered using a probabilistic approach. Both the natural frequency and the damping ratio are modelled as uncorrelated random variables that follow a predetermined probabilistic distribution function. Consequently, the structural response will also be described by a probabilistic distribution function, which can be estimated through Monte Carlo numerical simulations. As a result, the study allows the footbridge lateral response and the critical number of pedestrians to be calculated for different confidence levels and load scenarios, especially for crowd densities above the “critical number”.</p>

Research on the Possibility of Lowering the Manufacturing Accuracy of Cycloid Transmission Wheels with Intermediate Rolling Elements and a Free Cage

Purpose: In the present work, different combinations of fits and accuracies, in relation to the profiles of mating parts, have been analysed in order to assess the degree of the engagement of transmissions that contain intermediate rolling elements. The aim of this work is to determine which fits have decreased accuracy, but nevertheless provide a minimum manufacturing clearance for the transmission engagement in order to reduce the cost of parts production. Methods and materials: Considering the normal probabilistic distribution law in relation to the obtained dimensions of the manufacturing equipment, a combination of fits were selected using the incomplete interchangeability method, taking into account the peculiarities of the cycloid engagement in transmissions with intermediate rolling elements (IRE). Results: Having studied various combinations of fits of parts that are engaged in transmissions with intermediate rolling elements and a free cage (IREFC), a combination of fits for a “ring, rolling-element cam” were determined, in which a technological clearance of 3 µm is formed in the engagement. At the same time, cycloid disk profiles are manufactured according to the 9th tolerance grade, which reduces the laboriousness and cost of the production. Discussion. When reducing the manufacturing accuracy of cycloid disks, it is possible to obtain both very ample clearances and significant negative allowances. For example, having manufactured a ring with the H9 fit, rolling elements with h6 and a cam with js9, the maximum manufacturing clearance can reach 0.086 mm, while the clearance limits vary from 0.025 mm to 0.061 mm. Additionally, if mating parts are manufactured using a combination of K9-h6-js9 fits, a negative allowance varying from 0.014 mm to 0.026 mm will emerge in the engagement. Both described cases are unacceptable because both ample clearances and large negative allowances will negatively influence the working capacity of the mechanism. However, it is possible to select a combination of fits using the 9th tolerance grade of the basic parts, by which the parts will contact in the range from a small negative allowance of 1 µm to a clearance of 3–4 µm. Furthermore, if this is considered, taking into account the machine settings, it is possible to obtain parts according to the 9th accuracy tolerance grade and, at the same time, provide a clearance in the engagement that is almost equal to zero. Moreover, such a combination of fits is relevant for any transmission with IRE. This is a positive result because it reduces the laboriousness when manufacturing parts and, at the same time, provides high accuracy of the mechanism. Conclusions: It has been established that when lowering the accuracy of manufacturing transmission parts with IRE, both clearances and negative allowances may occur in the engagement, depending on the combination of fits. At the same time, it is possible to select such a combination of fits, by which the parts manufactured according to the 9th tolerance grade, will provide almost zero clearance of the engagement of the transmission. In this way, it is possible to reduce the cost of manufacturing the parts for gears with intermediate rolling elements and, at the same time, maintain a high accuracy of the transmission mechanism.

The ultimate publication activity of the Russian authors of the scientific journals

The paper deals with an approach to finding the ultimate number of papers Russian authors deliver to scientific journals. The approach is based on an assessment of the entire audience interested in publications in scientific journals, an assumption that each author personally pursues a research and writes a paper for the scientific journal, as well as an account for the co-authorship indicator, i.e. the involvement of colleagues into the research performed by the author. The research employs data by Rosstat, Higher School of Economics and Scientific Electronic Library to reveal all the authors interested in publication. This indicator is then multiplied by a value of co-authorship. The number of papers the authors publish per year is recommended to be taken as a random value, to be used later as a basis for building a probabilistic distribution of the ultimate number of papers among all authors. The distribution is built by the Monte Carlo method, and the analysis employs the apparatus of the probability theory and linear algebra. The obtained data and data from the Scientific electronic library have been exposed to comparative analysis. The work revealed that for the annual amount of more than one article the distribution of the number of papers received from the Russian audience can be approximated by a normal distribution, with all its parameters depending on maximum annual number of papers, scope of audience and co-authorship indicator. This gives the ultimate number of papers for any section (group of disciplines or a particular discipline). The article considers the examples of obtaining the distribution for the ultimate number of papers. The results can be used for correcting the research policy of an organization or an institute of higher education in the directions of activity being researched, and can serve as a guide to the necessary number of papers in various fields of science.

Influence of Material Toughness on Fracture Reliability in Steel Bridges

The fracture limit state of the AASHTO LRFD Bridge Design Specifications is addressed by requiring minimum impact toughness values for base material and mitigating potential fracture initiators through proper structural detailing. This fracture control approach has been successful in minimizing the number of fractures in steel bridges designed since its inception; however, it is not a calibrated limit state and the structural reliability against sudden brittle fracture has not been previously established. Accordingly, the objective of this study was to quantify the relationship between material toughness and fracture reliability in steel bridge members, considering the probabilistic distribution of fracture toughness and applied stress for a variety of structural steels and assumed crack sizes. The master curve approach is used to account for the probabilistic distribution of fracture toughness, and reliabilities are determined using Monte Carlo simulation and the Hasofer-Lind approach. The results indicate that the fracture reliability for modern bridge steels is consistent with the reliability of AASHTO strength limit states, and that certain steels currently available on the market can provide enough reliability against fracture to essentially eliminate brittle fracture as a limit state of concern. This finding holds the potential for a new way of approaching the design of fracture-critical members.

Enzymatic-metabolic support of oxidative homeostasis in patients with hypoxic-ischemic brain lesions in the stages of cardiosurgical interventions

To study the features of enzymatic and metabolic support of oxidative homeostasis in patients with hypoxic-ischemic brain lesions before and after cardiac surgery using artificial circulation we examined 38 patients, in particular: ischemic stroke — 14 people, encephalopathy — 15 people, severe cognitive dysfunction — 9 people ; diagnosis of neurological status was performed according to clinical protocols. Clinical and biochemical study was performed at the preoperative (3—5 days) and postoperative (5—7 days) stages: determined the content of superoxide dismutase, glutathione peroxidase, catalase in erythrocytes and α-tocopherol acetate in the serum of the blood, as well as the product cells: diene conjugates, metabolites of nitritanion in plasma. Variation statistics, probabilistic distribution of data with the subsequent estimation of reliability of results are applied; relative biochemical parameters were used: metabolic index, metabolic coefficient and metabolic effect for each. Standard methods using the program adapted to the “Excel” environment were used for calculations. The obtained data support the formation of patients with specific postoperative enzymatic-metabolic support of oxidative homeostasis, which should be considered as one of the triggers of hypoxic-ischemic brain lesions. In particular, at the level of the enzymatic chain of pro-, antioxidant protection and at the level of metabolic processes associated with peroxidation of phospholipids of cell membranes, a number of significant metabolic effects were revealed, which are generalized due to secondary oxidation products and NO‑dependent metabolites.

Coverage Strategy for Target Location in Marine Environments Using Fixed-Wing UAVs

In this paper, we propose a coverage method for the search of lost target or debris on the ocean surface. The OSCAR data set is used to determine the marine currents and the differential evolution genetic filter is used to optimize the sweep direction of the lawnmower coverage and get the sweep angle for the maximum probability of containment. The position of the target is determined by a particle filter, where the particles are moved by the ocean currents and the final probabilistic distribution is obtained by fitting the particle positions to a Gaussian probability distribution. The differential evolution algorithm is then used to optimize the sweep direction that covers the highest probability of containment cells before the less probable ones. The algorithm is tested with a variety of parameters of the differential evolution algorithm and compared to other popular optimization algorithms.

Two-Stream Deep Fusion Network Based on VAE and CNN for Synthetic Aperture Radar Target Recognition

Usually radar target recognition methods only use a single type of high-resolution radar signal, e.g., high-resolution range profile (HRRP) or synthetic aperture radar (SAR) images. In fact, in the SAR imaging procedure, we can simultaneously obtain both the HRRP data and the corresponding SAR image, as the information contained within them is not exactly the same. Although the information contained in the HRRP data and the SAR image are not exactly the same, both are important for radar target recognition. Therefore, in this paper, we propose a novel end-to-end two stream fusion network to make full use of the different characteristics obtained from modeling HRRP data and SAR images, respectively, for SAR target recognition. The proposed fusion network contains two separated streams in the feature extraction stage, one of which takes advantage of a variational auto-encoder (VAE) network to acquire the latent probabilistic distribution characteristic from the HRRP data, and the other uses a lightweight convolutional neural network, LightNet, to extract the 2D visual structure characteristics based on SAR images. Following the feature extraction stage, a fusion module is utilized to integrate the latent probabilistic distribution characteristic and the structure characteristic for the reflecting target information more comprehensively and sufficiently. The main contribution of the proposed method consists of two parts: (1) different characteristics from the HRRP data and the SAR image can be used effectively for SAR target recognition, and (2) an attention weight vector is used in the fusion module to adaptively integrate the different characteristics from the two sub-networks. The experimental results of our method on the HRRP data and SAR images of the MSTAR and civilian vehicle datasets obtained improvements of at least 0.96 and 2.16%, respectively, on recognition rates, compared with current SAR target recognition methods.

Hypoxic-ischemic brain injuries after cardiosurgical interventions: clinical options of somatogenic asthenic symptom complex in patients in the preoperative period

Annotation. The article presents the results of studying the symptomatology of different clinical variants of somatogenous asthenic symptom complex (SASC). The primary material of the study was a specially developed thematic map, the completion of which involved the implementation of clinical and anamnestic study and taking into account about 30 symptoms. Clinical and statistical methods were used: anamnestic quantitative analysis, variation statistics, probabilistic distribution of clinical signs with assessment of the reliability of the obtained results. It was found that in the structure of SASC the largest share belongs to the asthenic variant: is – 40.7%, while astheno-anxiety – 26.3%, astheno-subdepressive – 20.3%, and the smallest – dissomnic (12.7%). The symptomatic structure of SASC variants is characterized by the prevalence of the phenomena of physical and mental asthenia with symptoms of bodily synthesis, which allows to determine the most characteristic symptomatic complexes for cardiac surgery patients. The symptom complexes defined in research on each of variants of SASC allow to objectify at a preoperative stage a psychosomatic condition for maintenance of the integrated neurologic support of cardiosurgical patients.

Stochastic Modeling of Non-linear Terrorism Dynamics

Modeling terrorism is both necessary and difficult. While the necessity comes from the all too obvious real-world pressures our society is facing, the difficulty stems from the underlying complexity of the phenomena itself – there are many variables to account for, they are hard to measure, and the relationships between them are confounding. Since modeling terrorism is at its most onerous when it comes to predicting specific attacks, their timing and scale, we opted to work around this using observed probabilistic distribution and integrate power laws into our system dynamics model. After evaluating thousands of simulations runs, this allows us to replicate historical data as well as produce prognostic scenarios, while maintaining what we believe to be authentic behavior. Compromises need to be made, but we believe that this approach can be useful for systems highly dependent on events or parameters which we are unable to predict but whose distributions are known.