concentration problem
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2022 ◽  
Vol 12 (1) ◽  
Author(s):  
Cong Chen ◽  
Jiaxin Liu ◽  
Pingfei Xu

AbstractOne of the key issues that affect the optimization effect of the efficient global optimization (EGO) algorithm is to determine the infill sampling criterion. Therefore, this paper compares the common efficient parallel infill sampling criterion. In addition, the pseudo-expected improvement (EI) criterion is introduced to minimizing the predicted (MP) criterion and the probability of improvement (PI) criterion, which helps to improve the problem of MP criterion that is easy to fall into local optimum. An adaptive distance function is proposed, which is used to avoid the concentration problem of update points and also improves the global search ability of the infill sampling criterion. Seven test problems were used to evaluate these criteria to verify the effectiveness of these methods. The results show that the pseudo method is also applicable to PI and MP criteria. The DMP and PEI criteria are the most efficient and robust. The actual engineering optimization problems can more directly show the effects of these methods. So these criteria are applied to the inverse design of RAE2822 airfoil. The results show the criterion including the MP has higher optimization efficiency.


Symmetry ◽  
2022 ◽  
Vol 14 (1) ◽  
pp. 79
Author(s):  
Qiuwei Yang ◽  
Zhikun Ba ◽  
Zhuo Zhao ◽  
Xi Peng ◽  
Yun Sun

Blasting impact load may be encountered during the construction of some pile foundation projects. Due to the effect of blasting impact, hole collapse can easily occur in the hole-forming stage of pile foundation construction. In order to prevent hole collapse, it is very necessary to evaluate the stability of a pile hole wall before pile foundation construction. The calculation of hole collapse can usually be attributed to an axisymmetric circular hole stress concentration problem. However, the existing collapse failure theory of pile hole hardly considers the effect of blasting impact load. In view of this, this paper proposes the stability evaluation method of a pile hole wall under blasting impact. Compared with the existing collapse failure theory, the proposed method fully considers the effect of blasting impact stress. Using Mohr–Coulomb strength theory and symmetry analysis, the strength condition of collapse failure is established in this work for accurate evaluation of the stability of a hole wall. The proposed stability evaluation method is demonstrated by a pile foundation construction project of a bridge. Moreover, a shaking table test on the pile hole model was performed to verify the proposed method by experimental data. The results indicate the effectiveness and usability of the proposed method. The proposed method provides a feasible way for the stability analysis of a pile hole wall under blasting impact.


2021 ◽  
Vol 13 (20) ◽  
pp. 11329
Author(s):  
Glykeria Loupa ◽  
Zoi Panagiota Kryona ◽  
Varvara Pantelidou ◽  
Spyridon Rapsomanikis

A number of time series from two local PM2.5 monitoring stations were analyzed, for a small city, in North East Greece. They coincided with SARS-CoV-2 pandemic lockdowns and lifting restrictions. The aim of this analysis was to establish concentration exceedances and roughly apportion sources of the PM2.5 concentration problem. This was established by analyzing 24-h filter samples of trace elements using WD-XRF. It was found that the restrictions and their lifting did not significantly affect these concentrations. The main problems were assigned to emissions from biomass burning central heating and Saharan dust episodes. The study results indicate that even in small cities the air quality as far as PM2.5 is concerned can still be deleterious to the local population according to the WHO restricting levels but not according to the EU levels. The fact that PM2.5 is not a single chemical pollutant makes matters more complicated and renders such concentration upper levels, of little significance.


2021 ◽  
Author(s):  
GIOVANNI ZUCCO ◽  
MOHAMMAD ROUHI ◽  
OLIVERI VINCENZO ◽  
ENZO COSENTINO ◽  
RONAN O’HIGGINS ◽  
...  

Cut-outs are inevitable in many structural components such as in aircrafts to accommodate windows or openings for access purposes or fasteners. Engineers usually view cut-outs, especially in primary structures, with disfavour as they result in stress/strain concentration and consequently reduced load carrying capability. Local reinforcements usually increase cost and weight to the overall design which is not favourable in aerospace applications. In case of composite panels, emerging advanced manufacturing methods such as 3D printing of automated fiber placement made it possible to continuously steer fibers/tows around a cut-out to potentially alleviate stress/strain concentration problem. Another advantage of tow steering in this case is maintaining the continuity of fiber/tow paths without any fiber cut which precludes ply-level, 3D stress/strain concentration which could otherwise lead to delaminationinduced damage. In this study, potential capability of tow steering around an elliptical cut-out (manhole) in reducing stress/strain concentration in a composite wingbox is investigated Buckling response under compression loading together with stress and strain concentrations under both tensile and compression loads are examined. Under tensile loading, the maximum stress and strain concentration factors around the cut-out in the straight fiber design are shown to be approximately 29% and 32% larger than its counterpart with steered tows around the cut-out. For the compression loading condition, the direct strain of the panel with straight fiber orientations was found to be three times that of steered fiber trajectories in the vicinity of the cut-out.


Author(s):  
Asaf Ferber ◽  
Vishesh Jain ◽  
Yufei Zhao

Abstract Many problems in combinatorial linear algebra require upper bounds on the number of solutions to an underdetermined system of linear equations $Ax = b$ , where the coordinates of the vector x are restricted to take values in some small subset (e.g. $\{\pm 1\}$ ) of the underlying field. The classical ways of bounding this quantity are to use either a rank bound observation due to Odlyzko or a vector anti-concentration inequality due to Halász. The former gives a stronger conclusion except when the number of equations is significantly smaller than the number of variables; even in such situations, the hypotheses of Halász’s inequality are quite hard to verify in practice. In this paper, using a novel approach to the anti-concentration problem for vector sums, we obtain new Halász-type inequalities that beat the Odlyzko bound even in settings where the number of equations is comparable to the number of variables. In addition to being stronger, our inequalities have hypotheses that are considerably easier to verify. We present two applications of our inequalities to combinatorial (random) matrix theory: (i) we obtain the first non-trivial upper bound on the number of $n\times n$ Hadamard matrices and (ii) we improve a recent bound of Deneanu and Vu on the probability of normality of a random $\{\pm 1\}$ matrix.


Author(s):  
Aurpita Shaha ◽  
Mintu Sarker ◽  
Md. Nazmul Islam ◽  
Trishna Khatun ◽  
Md. Abdul Bashir ◽  
...  

The outburst of COVID-19 influenced the lives of all segment of society as people were requested to self-quarantine in their homes to stop the outspread of the virus. The lockdown had consequential impacts on mental health, triggering psychological problems encompassing frustration, stress, and depression. The outbreak of Covid-19 has significantly affected the lives of all parts of the society. One of the most instant changes launched was the closure of educational institutions to decelerate the spreading of the virus. Students no longer had availability of institution-based physical activities such as physical education, recess, and walking to/from universities/colleges/school. Inadequate physical activities and enormous sedentary behavior amid students exhibits a noteworthy problem because health behavior patterns can result in heightened risk for a number of hazardous health conditions (e.g., overweight/obesity, type II diabetes, and metabolic syndrome) in later. The objective of this study was to explore the pervasiveness of physical and mental health condition among Bangladeshi students during the COVID-19 pandemic. It also focuses on recognizing the stimulus of various states of physical and mental conditions throughout COVID-19 pandemic. The cross sectional data was gathered by means of interviews or self-responses among the university students from various districts of Bangladesh on July to August 2020. The study was performed with structured questionnaire. To reduce threats of Covid-19 infection, in this investigation, participants were interviewed over telephone instead of face to face interaction. In order to explore the effects of this pandemic on the lives of students, we performed a survey in which a total of 576 participants were participated. In this survey, among them 377 (66%) are male and 197 (34%) female. It was discovered that 92% of participants appreciate participating in physical activities & rest of them (8%) don’t like to participate in physical activities. In addition, our study also revealed 46% of the students having trouble in sleep and 45% students feels concentration problem. The findings of this study show that greater numbers of the students are not in sound physical or mental conditions. They are bored, helpless, anxious and depressed than previous.  This study shows that the mental conditions of female students are more affected by Covid-19 compared to male students. 82% of female students are stressed about their study, future life and so on. 46% female students are feeling helpless, 61% become upset and 60% feel bored during lockdown and close of education institution. COVID-19 is striking threat both on physical and mental health since its outbreak. During this challenging time, it is necessary to continue taking care of physical and mental health. 


Author(s):  
Manuel Aparicio-Alonso ◽  

The coronavirus disease 2019 (COVID19) has generated widespread healthcare concerns and has overburdened healthcare institutions. As the number of COVID19 patients recovers, so does the frequency of reports of COVID19-like symptoms following discharge. A telephone survey with standardized questions was undertaken in which participants were asked if they had had any of 25 possible sequelae after being diagnosed with COVID19 and treated with a Chlorine Dioxide Solution (CDS). One hundred sixty-one people completed the survey. We discovered that rising age is a risk factor (OR = 1.035, p = 0.028, 95% CI = 1.004-1.069), and the odds of having any symptoms in moderate patients is 0.077 compared to mild patients (P = 0.003). It was predicted that 64.6 percent of patients treated with CDS for SARS-CoV-2 infection experienced an average of 3.41 long-term effects. There were no variations in the number of sequelae reported by sex, age, COVID19 severity, or therapy method. The five most prevalent manifestations of the 25 distinct long-term symptoms observed in this study were fatigue, hair loss, dyspnea, concentration problem, and sleep difficulties. In addition, individuals treated with multiple drugs (COVID19 conventional treatment plus a CDS) had 2.7 fewer cases of sequelae, and patients treated exclusively with CDS had 6.14 fewer incidences of long-term effects. People who get a CDS are 19% less likely to experience long-term health effects than patients who receive standard COVID19 therapy. According to the findings of this study, patients who receive a CDS have a reduced probability of developing sequelae. Furthermore, the incidence of long-term effects is lower in individuals treated exclusively with a CDS. The recent findings involving Chlorine Dioxide support the development of clinical studies to evaluate its efficacy in preventing the development of COVID19 long-term effects.


Author(s):  
Musharrat Shabnam Shuchi ◽  
Sayeda Chandra Tabassum ◽  
MMK Toufique

Though there have been works highlighting the advantages and disadvantages of online learning, no study focused on university-level economics students. None of the studies explored students' opinions about improving the quality and effectiveness of online classes. Many used questionable samples, closed-ended questions, and all those researches were carried out at the beginning of online classes. In this paper, we overcome these limitations of earlier studies. Using a convenience sampling technique and open-ended questions, we collect data from 154 university-level economics students after being exposed to the online class for a year. Some advantages of online classes are: students can do classes from home without being exposed to health risks, easily accessible, flexible class schedule, students remained connected with the study, it saves costs, reduce the likelihood of semester loss, easy to understand, less stressful, and learning new technologies. Major problems from students' perspectives include network problems, difficulties in understanding the topic, unsuitable for mathematical courses, concentration problem, class not interactive, financial constraint, adverse health impacts, device issues, power outages, unfamiliarity with digital technology, internet problem, and unfixed class-schedule. Disadvantages outnumbered advantages. Students made several suggestions to improve the quality and effectiveness of online classes. Some of the vital suggestions are: using state-of-the-art digital tools, recording and uploading lectures, resolving internet issues, holding classes regularly, higher efforts to make the topics easier, resolving network issues, lowering class duration, institutional support, implementing a fixed class schedule, and introducing online evaluation system.


2021 ◽  
Vol 35 (1) ◽  
pp. 1-8
Author(s):  
Chairunnisa Djayadin ◽  
Wardah Wafiyah Mubarakah

Pembelajaran daring selama pandemik Covid-19 berhadapan dengan sejumlah permasalahan. Penelitian ini merupakan studi pendahuluan bagi penelitian terkait permasalahan konsentrasi mahasiswa saat melaksanakan pembelajaran daring. Penelitian ini bertujuan mendapatkan data untuk menegakkan diagnosis melalui tes asesmen diagnostik bahwa telah terjadi permasalahan pada konsentrasi mahasiswa selama  proses pembelajaran daring, yang akan menjadi dasar dalam tindakan penyelesaian atau intervensi. Metode penelitian yang digunakan adalah survei dengan teknik pengumpulan data melalui penyebaran kuesioner melalui googleform selama seminggu di Bulan Juni 2020. Pertanyaan bersifat tertutup dan terstruktur yang disesuaikan dengan karakteristik asesmen diagnostik berupa selected response. Kuesioner yang lengkap terisi sebanyak 163 buah. Partisipan penelitian adalah 163 mahasiswa dari PTKIN, dengan rincian 122 dari UIN, 36 mahasiswa dari IAIN, dan 5 mahasiswa STAIN. Hasil asesmen diagnostik terhadap konsentrasi mahasiswa dalam pembelajaran daring menunjukkan bahwa terdapat permasalahan konsentrasi belajar mahasiswa baik pada aspek kognitif, afektif, dan psikomotor, yang menjadi alat ukur konsentrasi dalam belajar. Hasil tersebut, menegakkan diagnosis bahwa telah terjadi permasalahan pada konsentrasi mahasiswa PTKIN saat mengikuti pembelajaran daring. Penelitian ini merekomendasikan untuk dilakukan intervensi pada proses pembelajaran terkait konsentrasi mahasiswa dalam belajar.   This study aims to proof that there is concentration problem faced by students during online learning process. This research is a preliminary study of a research  focusing on students concentration problems. The data was collected through survey with a questionnaire which sent to the participants via google form. The questionnaire distribution was started on June 21 to June 26, 2020. The participants who completed the questionnaire were 163 students with details of 122 students from UIN, 36 students from IAIN, and 5 STAIN students. The results of the diagnostic assessment show that there is a problem with student concentration in online learning on three aspects, namely cognitive, affective, and psychomotor as the measuring tools for concentration in learning. These results proofed the diagnosis that there has been a problem with the concentration of PTKIN students while participating in online learning. Based on the result showed, this study recommended further intervention to overcome the problems faced by the students.


2021 ◽  
Vol 30 (1) ◽  
Author(s):  
Jin-long Lai ◽  
Jin-liang Liu ◽  
Jian-yong An ◽  
Hang Jia ◽  
Jia Ma

In the process of metro station construction, the partition wall is usually used to prevent the displacement of the soil behind the wall to ensure the construction platform. This research aims to analyze the response of partition wall to keep the safety of the structure. The time-horizontal displacement and cracks of the partition wall are measured during the process of metro station construction. The finite element software FLAC 3D is used to simulate the response of partition wall, and the reasons of partition wall cracking and displacement are analyzed by finite element simulation and measurement data. The stiffness and self-stability of the partition wall in the station is powerful, the stress concentration appeared on the central area and caused cracks of the partition wall. Reducing the pressure exerted on the partition wall and shifting partial pressure exerted on the partition wall by the construction of the medium plate can solve the tress concentration problem. Through the data analysis of the strengthened partition wall, the reinforcement effect is good, ensuring the safety of the subsequent construction. The causes of partition wall cracking are found during process of metro station construction, and the solution proposed in this paper is effective. Engineers can refer to this paper to analyze the response of partition wall in the construction of similar structures, which can ensure construction safety and reduce construction cost.


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