Locality of Random Digraphs on Expanders

We study random digraphs on sequences of expanders with bounded average degree and weak local limit. The threshold for the existence of a giant strongly connected component, as well as the asymptotic fraction of nodes with giant fan-in or giant fan-out are local, in the sense that they are the same for two sequences with the same weak local limit. The digraph has a bow-tie structure, with all but a vanishing fraction of nodes lying either in the unique strongly connected giant and its fan-in and fan-out, or in sets with small fan-in and small fan-out. All local quantities are expressed in terms of percolation on the limiting rooted graph, without any structural assumptions on the limit, allowing, in particular, for non tree-like limits. In the course of proving these results, we prove that for unoriented percolation, there is a unique giant above criticality, whose size and critical threshold are again local. An application of our methods shows that the critical threshold for bond percolation and random digraphs on preferential attachment graphs is $p_c=0$, with an infinite order phase transition at $p_c$.Comment: Added a proof on infinite order phase transition of PA graphs. Revised introduction and moved the proof on applications to appendi

Examining the role of export competitive advantages on export performance

This paper investigates the role of export competitive advantage on export performance in food industry. The proposed study designs a questionnaire in Likert scale and distributes it among 280 randomly selected experts in food industry and Cronbach alpha has been calculated as 0.827. The study has applied factor analysis to find important factors influencing export performance. Kaiser-Meyer-Olkin Measure of Sampling Adequacy and Bartlett's Test of Sphericity have been performed to validate the results and they both validated the questionnaire. The results of the survey have determined six effective groups including product development, e-commerce, marketing planning, organizational performance, competitiveness and supply chain management

Sequential importance sampling for estimating expectations over the space of perfect matchings

This paper makes three contributions to estimating the number of perfect matching in bipartite graphs. First, we prove that the popular sequential importance sampling algorithm works in polynomial time for dense bipartite graphs. More carefully, our algorithm gives a $(1-\epsilon)$-approximation for the number of perfect matchings of a $\lambda$-dense bipartite graph, using $O(n^{\frac{1-2\lambda}{8\lambda}+\epsilon^{-2}})$ samples. With size $n$ on each side and for $\frac{1}{2}>\lambda>0$, a $\lambda$-dense bipartite graph has all degrees greater than $(\lambda+\frac{1}{2})n$. Second, practical applications of the algorithm requires many calls to matching algorithms. A novel preprocessing step is provided which makes significant improvements. Third, three applications are provided. The first is for counting Latin squares, the second is a practical way of computing the greedy algorithm for a card guessing game with feedback, and the third is for stochastic block models. In all three examples, sequential importance sampling allows treating practical problems of reasonably large sizes

Downregulating the Expression of CHID1 by Chitin Microparticles Mixed Leukocyte Culture

Abstract Background: chitin and its derivates microparticles (MPs) have immunomodulatory activities. In this study, we examined the effect of size, purity and acetylation degree of chitin MPs on CHID1- encoding SI-CLP, involved in inflammation- gene expression in mixed leukocyte culture. Materials and Methods: Small (<40) and medium(40-70) sized chitin MPs were prepared by sonication, and they were used in treatment of leukocyte mixed culture in comparison with chitosan and also shrimp shell small-sized MPs. Neutral red uptake assay and microscopic examination of apoptosis were used to assess cytotoxicity of MPs. Finally, following cell treatment with MPs (100 μg/mL) for 48h, expression levels of CHID1 gene were determined by Real Time PCR. Results: Different concentrations of chitinous MPs hadn’t any cytotoxic effects. In gene expression analysis, small-sized chitin MPs (<40 µ) resulted in down regulation of CHID1 gene expression (p=0.004), while other MPs didn’t change it significantly. Conclusion: Size, purity and acetylation degree of chitin MPs influence their interference in immune cells interactions and it seems small-sized chitin MPs can potentially modulate immune responses through decreasing CHID1 gene expression. Using small-sized chitin MPs may be effective to treat allergies which their treatment strategies rely on modulating the immune responses

Fractionally Log-Concave and Sector-Stable Polynomials: Counting Planar Matchings and More

We show fully polynomial time randomized approximation schemes (FPRAS) for counting matchings of a given size, or more generally sampling/counting monomer-dimer systems in planar, not-necessarily-bipartite, graphs. While perfect matchings on planar graphs can be counted exactly in polynomial time, counting non-perfect matchings was shown by [Jer87] to be #P-hard, who also raised the question of whether efficient approximate counting is possible. We answer this affirmatively by showing that the multi-site Glauber dynamics on the set of monomers in a monomer-dimer system always mixes rapidly, and that this dynamics can be implemented efficiently on downward-closed families of graphs where counting perfect matchings is tractable. As further applications of our results, we show how to sample efficiently using multi-site Glauber dynamics from partition-constrained strongly Rayleigh distributions, and nonsymmetric determinantal point processes. In order to analyze mixing properties of the multi-site Glauber dynamics, we establish two notions for generating polynomials of discrete set-valued distributions: sector-stability and fractional log-concavity. These notions generalize well-studied properties like real-stability and log-concavity, but unlike them robustly degrade under useful transformations applied to the distribution. We relate these notions to pairwise correlations in the underlying distribution and the notion of spectral independence introduced by [ALO20], providing a new tool for establishing spectral independence based on geometry of polynomials. As a byproduct of our techniques, we show that polynomials avoiding roots in a sector of the complex plane must satisfy what we call fractional log-concavity; this extends a classic result established by [Gar59] who showed homogeneous polynomials that have no roots in a half-plane must be log-concave over the positive orthant

The effect of age on driving performance in Iran using driving simulator

Background and Objectives: Nearly 16,000 people are killed in driving accidents in Iran each year. The purpose of this study was, therefore, to determine the effect of age on driving performance, using a driving simulator. Methods: This cross-sectional study was carried out on 16 young drivers, 16 middle-aged drivers, and 16 elderly drivers in Tehran. Driving simulators were used to check the drivers' performances. The main scenario was driving on a freeway at an average speed of 50 km/h, when pedestrians suddenly appeared at a distance of 40 m and the drivers had to brake immediately after noticing the pedestrian. The time interval between the emergence of the pedestrian and stepping on the brake pedal was continuously recorded as the reaction time and the amount of vehicle deviation from the center of the road as the lateral deviation of the vehicle. The drivers' mental workload was recorded after the simulated driving test, using the verbal online subjective opinion scale. Results: The elderly drivers had the highest mean reaction time, 963.8 ms, and there was no significant difference between the mean reaction time for youth and middle-aged drivers (858.3 ms vs. 860 ms). Elderly drivers showed high lateral deviation, 0.69 m, and mental workload, 6.19, whereas youth drivers had the lowest lateral deviation (0.55 m) and mental workload (3.60). MANOVA revealed a significant effect of age (Pillai's trace, V = 0.55, P P P P = 0.101). Poisson regression revealed no significant effect for age on the number of collisions (P = 0.357). Conclusion: Based on the variables under study, driving performance of the elderly group was poor as compared to that of the middle-aged and young ones. Old drivers were subjected to greater mental workload when responding to the stimulus of the driving environment

Validity and reliability of Verbal Online Subjective Opinion (VOSO) and Modified Cooper-Harper scales in measuring of mental workload

Introduction: High mental workload is one of the important factors that results in errors in safety and occupational health scope and its measurement has high importance. So, this study aimed to determine validity and reliability of Verbal Online Subjective Opinion (VOSO) and Modified Cooper-Harper (MCH) scales in measuring mental workload. Methods: This study was conducted on 90 male students of Iran University of Medical Sciences. In this study, the Forward-Backward translation was used for translation of scales. Moreover, Content Validity Ratio (CVR) and Content Validity Index (CVI) were calculated by having suggestion of 6 Ergonomics and Occupational health experts. The Hybrid Memory Search Task software was used to create mental workload. Convergent validity of scales was calculated using correlation of scales with reaction time and then Test-Retest method was used to determine the reliability of scales. Results: Content and convergent validity of scales were confirmed and correlation of both scales with reaction time were higher than 0.8. Moreover for determination of scales reliabilities, Pearson correlation coefficient between scales values in test and retest trials were 0.86 and 0.91 for VOSO and MCH respectively. Conclusion: It seems that in regard to confirmation of validity and reliability of VOSO and MCH in this study and their high correlation with reaction time, it can use these scales in measurement of mental workload