Acyclic edge coloring of graphs

An {\em acyclic edge coloring} of a graph $G$ is a proper edge coloring such that the subgraph induced by any two color classes is a linear forest (an acyclic graph with maximum degree at most two). The {\em acyclic chromatic index} \chiup_{a}'(G) of a graph $G$ is the least number of colors needed in an acyclic edge coloring of $G$. Fiam\v{c}\'{i}k (1978) conjectured that \chiup_{a}'(G) \leq \Delta(G) + 2, where $\Delta(G)$ is the maximum degree of $G$. This conjecture is well known as Acyclic Edge Coloring Conjecture (AECC). A graph $G$ with maximum degree at most $\kappa$ is {\em $\kappa$-deletion-minimal} if \chiup_{a}'(G) > \kappa and \chiup_{a}'(H) \leq \kappa for every proper subgraph $H$ of $G$. The purpose of this paper is to provide many structural lemmas on $\kappa$-deletion-minimal graphs. By using the structural lemmas, we firstly prove that AECC is true for the graphs with maximum average degree less than four (\autoref{NMAD4}). We secondly prove that AECC is true for the planar graphs without triangles adjacent to cycles of length at most four, with an additional condition that every $5$-cycle has at most three edges contained in triangles (\autoref{NoAdjacent}), from which we can conclude some known results as corollaries. We thirdly prove that every planar graph $G$ without intersecting triangles satisfies \chiup_{a}'(G) \leq \Delta(G) + 3 (\autoref{NoIntersect}). Finally, we consider one extreme case and prove it: if $G$ is a graph with $\Delta(G) \geq 3$ and all the $3^{+}$-vertices are independent, then \chiup_{a}'(G) = \Delta(G). We hope the structural lemmas will shed some light on the acyclic edge coloring problems.Comment: 19 page

Promoting Positive Development Among Rural, Left-Behind Youth in China: A Mixed-Methods Approach

The positive youth development (PYD) framework has shifted our attention from a deficit-based approach to a strength-based perspective to studying adolescent development (Lerner, 2005; Lerner & Steinberg, 2009). Integrating both the PYD and resilience science frameworks, this study developed and validated an instrument for assessing the individual strengths and environmental supports that enable a positive developmental trajectory for rural, left-behind youth (LBY) in China, a vulnerable group of youth who are endangered by prolonged parent-child separation. This newly developed instrument contains two scales: the Individual Strengths (IS) Scale and the Environmental Supports (ES) Scale. Utilizing an exploratory sequential design, this study was conducted in three steps: (1) conducting qualitative interviews to inform the creation of survey items, (2) developing an instrument based on qualitative findings and existing literature, and (3) conducting quantitative analyses to validate and revise the survey instrument. During the qualitative investigation, semi-structured interviews were conducted with 22 teachers and LBY. Thematic analysis revealed five individual strengths (i.e., achievement motivation, self-control, positive coping, academic engagement, and prosocial orientation ) and four categories of environmental support (i.e., social support, caring & belongingness, rules & high expectations, and extracurricular activity participation ) that were critical for the positive development among Chinese LBY. An original item pool was created based on qualitative findings and existing literature, and an iterative process of reviewing and revising items through expert reviews and field tests followed to refine the factor structure and individual items in both the IS and the ES scales. The finalized IS Scale contained 75 items that assessed eight individual strengths: achievement pursuit, self-control, positive coping, internal locus of control, hopeful future expectation, intention to contribute, social competencies, and obedience . The finalized ES Scale contained 91 items that assessed five categories of environmental support: social support, trust & acknowledgement, rules & role models, positive climates, and extracurricular support . Both scales were validated through quantitative analyses. During the quantitative investigation, a series of exploratory factor analysis (EFA) were conducted to reduce the number of items used to capture the constructs of individual strengths and environmental supports emerged from the qualitative study. The EFA process resulted in a 65-item scale for individual strengths with seven subscales: goals and future expectation, academic engagement, intention to contribute, prosociality, positive coping toward parental migration, positive coping, and academic motivation . Overall, the scale accounted for 74% of the total variance. The analyses resulted in a 68-item scale for environmental supports with eight subscales: school support, support of migrating parent(s), positive community and societal environment, support of caregiver(s), extracurricular support, family support, peer support, and support of peer relatives . The scale accounted for 70% of the total variance. An independent sample was recruited to validate the factor structures emerged from EFAs through confirmatory factor analysis. The 68-item measure of environmental supports was supported, while the 65-item measure of individual strengths was slightly adjusted to a 63-item scale. The Cronbach’s α of each scale and subscale ranged from 0.88 to 0.98, indicating strong internal consistency reliability. Both individual strengths and environmental supports were positively correlated with the PYD total score, PYD subscale scores, academic achievement, and subjective wellbeing, and were negatively correlated with externalizing problem behaviors. The findings were discussed and the implications of these findings for future PYD research among Chinese LBY were addressed. This research effort has the potential to expand our understanding of PYD as it applies to a new group of young people as well as to yield an important research tool for policy makers, educational practitioners, and youth workers who want to implement practices and policies that promote PYD among rural LBY in China

Time-Series Momentum in Nearly 100 Years of Stock Returns

We document strong time-series momentum effects in individual stocks in the US markets from 1927 to 2017. Time-series momentum is not specific to sub-periods, firm sizes, formation- and holding-period lengths, or geographic markets. The effects persist after controlling for standard risk factors. Time-series momentum effects are conditional on the market state, the information discreteness of the constituent stocks and investor sentiment. We propose two alternative implementations, revised time-series momentum and dual momentum, which generate even higher profits than standard time-series momentum

Preparation of nanofibre yarns from electrospun nonwoven strips

From ancient to modern time, humans have been trying to use finer fibres to make fibrous products for various purposes and believing that finer fibres have better aesthetic qualities. So far, the commercial fibres have been reduced to microns in diameter, but it seems difficult to further reduce the fibre fineness to submicrons using conventional fibre-making techniques.Electrospinning is a promising technique to produce continuous fibres with diameters on nanometre scales. This technique involves stretching a polymer fluid under a strong electric field into fine filaments, which are deposited randomly on the electrode collector forming a nonwoven nanofibre mat in most cases. Despite considerable efforts in exploring the applications of electrospun nanofibres in non-fibrous fields [1], very limited work has been conducted on using this material to process mechanically robust nanofibre yarns [2,3]

The Effort of Parent-Child Reading Activity in Chinese Traditional Family Education: A Practical Study in a Primary School of Shenzhen

China is a country with traditional family education. Parents greatly influence their children, especially under the one-child policy and urbanization background. Chinese teaching requires context and training. Reading and communication are important ways to improve Chinese. Parent-child reading can better help students in grades 1-3 to read. This article aims to compare students' performance and interview results of parents in an elementary school in the immigrant city, Shenzhen, Guangdong Province, China, to explore the supporting role of parents in this family education. Previously, similar language research work has examined the students' language development in Shenzhen Pontus' families for further research. This study used mixed methods to analyze the parent-child reading situation in a school in Shenzhen. This article also compared the students' Chinese performance to judge the impact of parent-child reading on students. The results show that the influence of parent-child reading in family education has an obvious positive effect. The specific auxiliary role is reflected in children's reading ability, Mandarin level, and literary knowledge. Therefore, this study suggests that teachers and parents promote parent-child reading work. Parent-child reading is not only conducive to the psychological growth of students but also conducive to the cultivation of students' language ability, especially for the cultivation of students' Mandarin and literary ability

D-STEM v2: A Software for Modelling Functional Spatio-Temporal Data

Functional spatio-temporal data naturally arise in many environmental and climate applications where data are collected in a three-dimensional space over time. The MATLAB D-STEM v1 software package was first introduced for modelling multivariate space-time data and has been recently extended to D-STEM v2 to handle functional data indexed across space and over time. This paper introduces the new modelling capabilities of D-STEM v2 as well as the complexity reduction techniques required when dealing with large data sets. Model estimation, validation and dynamic kriging are demonstrated in two case studies, one related to ground-level air quality data in Beijing, China, and the other one related to atmospheric profile data collected globally through radio sounding.Comment: 29 pages, 11 figure

Novel Restriction of HIV-1 by Chimeric Human APOBEC3A

The human apolipoprotein B mRNA editing enzyme catalytic peptide-like 3 (APOBEC3; A3) family of proteins are a family of seven cytidine deaminases (A3A, A3B, A3C, A3D, A3F, A3G and A3H) that restrict certain viral infections. These innate defense factors are best known for their ability to restrict the replication of human immunodeficiency virus type 1 (HIV-1) lacking a functional Vif protein (HIV-1Δvif) through the deamination of cytidine residues to uridines during reverse transcription, ultimately leading to lethal G-to-A changes in the viral genome. The best studied of the A3 proteins has been A3G because of its potent activity against HIV-1Δvif. However, one member of this family, A3A, has biological properties that make it unique among the A3 proteins. Despite potent restriction activity when expressed in myeloid cells, human A3A (hA3A) is generally known lacking inhibitory function towards HIV-1Δvif. Previous studies in our laboratory have shown that rhesus macaque A3A (rhA3A) is capable of restricting both simian–human immunodeficiency virus lacking vif gene (SHIVΔvif) and human immunodeficiency virus lacking vif gene (HIV-1Δvif) to a greater extent than hA3A. Chimeric studies by substituting amino acids 25–33 (AC loop 1 region) from rhA3A into hA3A showed that this region is critical in determining the restriction pattern against lentiviruses. Further studies identified three Old World Monkey A3As that were able to restrict HIV-1 replication. Restriction assays with various A3As from hominids, New World monkeys, and Old World monkeys found that agmA3A and colA3A restricted the replication of SHIVΔvif and that all three Old World monkey A3A proteins (agmA3A, colA3A, and rhA3A) restricted HIV-1Δvif to some extent. More impressively, it is also showed that the A3A protein from the black and white colobus monkey (mantled guereza; Colobus guereza; colA3A) potently inhibited not only HIV-1Δvif replication but also wild-type HIV- 1 in producer cells. Since previous studies indicated the importance of AC loop 1 region in determining the restriction ability and our sequence alignment analysis showed that A3A proteins from Mandrillus sphinx (mndA3A) and Cercopithecus neglectus (debA3A) had an AC-loop1 region that was almost identical to colA3A, we tested the restriction ability of mndA3A and debA3A. The restriction assay showed that both debA3A and mndA3A restricted HIV-1 similar as colA3A. Next, we used chimeric protein and amino acid deletion studies to show that AC loop 1 region, especially the 27WVS29 motif, is the key determinant for HIV-1 and AAV-2 restriction. First, by fusing the first 100 amino acids of colA3A and the C-terminal region of hA3A (h1–100 colA3A), or the first 100 amino acids of hA3A and the C-terminal region of colA3A (col1–100hA3A), we found that the N-terminal domain of colA3A contains the determinants for HIV-1 restriction. To further confirm that, we truncated the C-terminal off and constructed the mutant proteins that expressed only the N-terminal 100 amino acids (colA3A1–100, mndA3A1–100, debA3A1–100). The truncated colA3A, mndA3A and debA3A proteins were all able to restrict HIV-1 replication. We then narrowed the region down by examining chimeric proteins with the N-terminal 75, 50 and 33 amino acids of colA3A fused to hA3A (col1–75hA3A, col1–50hA3A, and col1–33hA3A). The results indicated that the first 33 amino acids harbor the critical determinants for HIV-1 restriction. As previous experiments indicate the importance of the AC loop 1 region, a chimeric hA3A containing the AC Loop1 region of mndA3A (mnd25–33hA3A) was made. Restriction assays revealed that the mnd25–33hA3A chimera was able to restrict HIV-1, indicating that the AC Loop1 region of mndA3A was critical to its restriction properties. As the hominids have a three amino acid deletion in this region of A3A, we constructed a chimeric hA3A with the WVS motif and found that this insertion completely restored the antiviral activity of hA3A. In addition, insertion of “WVS” or AC Loop-1 region into hA3A also changed the restriction pattern of adeno-associated virus 2 (AAV-2). Therefore, we conclude that this WVS motif is the key for both retrovirus and parvovirus restriction. As we found that the WVS motif in the AC loop 1 region plays a key role in HIV-1 restriction, we determined the role of each of these three amino acids in inhibiting HIV-1 replication. We constructed a series of single amino acid substitutions and single/double deletion mutants in this region and performed restriction assays on these mutants. The results suggested that the nature (charge and hydrophobicity) of the three amino acids was not as important as the length for restriction of HIV-1. Finally, we confirmed this by substituting the WVS motif with either AAA or GGG, and found that both hA3A[27AAA29] and hA3A[27GGG29] were able to inhibit HIV to the level similar as hA3A[27WVS29]. Finally, we explored the mechanism of hA3A[27WVS29] restriction of HIV-1 replication. First, we examined the viral replication in producer cells. We determined the viral protein synthesis in producer cells, using p24 and pulse-chase analysis, were similar in controls and cells expressing hA3A[27WVS29]. Next, we excluded the possibility of subcellular localization contributing to defective viruses production as hA3A and hA3A[27WVS29] were both expressed in cytoplasm and the nucleus at similar level in producer cells. Further, we examined the viral RNA packaging and found that viral RNA was packaged at similar levels in in progeny viruses from both control and hA3A[27WVS29] expressing cells. In addition, we showed that the viral reverse transcriptase enzyme activity of the progeny viruses was not affected by the presence of hA3A[27WVS29]. We next examined restriction in target cells. We first confirmed that the viral replication was inhibited in target cells by showing that the viral protein biosynthesis was significantly lower in target cells using pulse-chase experiments. We also excluded that canonical hypermutation contributed to the restriction. We found the levels of early and late reverse transcription products were decreased approximately 10-fold in the presence of hA3A[27WVS29]. This was also reflected in decreased viral integration and viral transcripts in the target cell. Thus, we concluded that the restriction of HIV-1 by hA3A[27WVS29] occurred at the level of reverse transcription in the target cells. In summary, we were able to restore the ability of hA3A to restrict HIV-1 and abolish the ability of hA3A to restrict AAV-2 by inserting only three amino acids in the AC loop 1 region. This reveals that the AC loop 1 region harbors key determinants for both retrovirus and parvovirus restriction, and provides promising preliminary data for further translational application such as gene therapy

Electrospinning of Continuous Nanofiber Bundles and Twisted Nanofiber Yarns

Spinning is a prehistoric technology in which endless filaments, shorter fibers or twisted fibers are put together to produce yarns that serve as key element to assemble multifarious structural designs for diverse functions. Electrospinning has been regarded as the most effective and versatile technology to produce nanofibers with controlled fiber morphology, dimension and functional components from various polymeric materials (Dersch et al., 2007, Frenot and Chronakis, 2003, Schreuder-Gibson et al., 2002). However, most electrospun fibers are produced in the form of randomly-oriented nonwoven fiber mats (Doshi and Reneker, 1995, Madhavamoorthi, 2005). The relatively low mechanical strength and difficulty in tailoring the fibrous structure have restricted their applications. With the rapid development in nanoscience and nanotechnology, yarns composed of nanofibers may uncover new opportunities for development of well-defined three dimensional nano fibrous architectures. This chapter focuses on recent research and advancement in electrospinning of nanofiber bundles and nanofiber yarns. The preparation, morphology, mechanical properties and potential applications of these fibrous materials are discussed in details

Strip twisted electrospun nanofiber yarns: Structural effects on tensile properties

Nanofiber yarns with controlled twist levels were prepared by twisting a narrow fibrous strip cut directly from electrospun nanofiber mats. The effects of fiber morphology, diameter and orientation, as well as the yarn twist level on the yarn tensile properties were examined. For the yarns made from randomly oriented fine uniform nanofibers (e.g., diameter 359 nm) and beaded nanofibers, the tensile strength increased with increasing the yarn twist level. Higher fiber diameter (e.g., 634 nm) led to the tensile strength having an initial increase and then decrease trend. The modulus increased with the twist level for all the yarns studied. However, the elongation at break increased initially with the twist level and subsequently decreased. The orientation of aligned fibers within the fiber strip greatly influenced the yarn tensile properties. When the fibers were oriented along the fiber length direction, both tensile strength and modulus were the largest