Negative Dependence Research Articles

Dependence of Charge Transport on the Degree of Ordering in Semicrystalline Conjugated Polymers

AbstractThe influence of ordering inside the crystalline regions of semi‐crystalline polymer thin films on charge transport is investigated by analyzing the electric field dependence of mobility calculated using Monte Carlo simulation. The degree of ordering inside the ordered regions is varied by changing the overlap between the hopping transport sites. Negative field dependence of mobility extending to higher electric field strengths along with an increase in the mobility are observed upon increasing the overlap between transport sites inside the ordered region. These observations are attributed to the variation in the charge transport, which affects the transit time that not only decreases but also shows a gradual shift from negative to positive field dependence at lower electric field strengths (∼<3 × 105 V/cm). Variations in the transit time are explained using the variation in the field dependence of hops performed by the carrier inside the ordered and disordered regions. Field dependence of mobility is also simulated with ballistic charge transport inside the ordered regions. At low concentrations of ordered regions (COR), higher carrier mobility is attained with hopping transport (∼<70%). Ballistic transport provides higher mobility at higher COR (∼>70%). This suggests that a very high order inside the ordered region may not necessarily provide higher mobility.

The Impact of Megatrends on the Business Environment of EU27 Countries

The global business environment is constantly evolving due to various megatrends. Understanding these shifts is crucial for economies, particularly for managers responsible for decisionmaking in diverse industries. Managers benefit from knowing both, the specific business environment they operate in, or plan to enter, and the interconnected environments of neighbouring countries or economically similar regions. This paper, therefore, analyses how current megatrends impact the quality of the business environment within EU27 countries. This understanding is especially critical for small and medium-sized enterprises. The paper aims to assess the effects of selected megatrends on the business environment quality using regression and correlation analysis. Five prominent megatrends have been identified: M1 - Shift in Economic Power, M2 - Resource Scarcity, M3 - Technological Breakthrough, M4 - Social Change, and M5 - Rapid Urbanization. Each of these trends has been assigned measurable indicators. Regression analysis indicates that three of the five megatrends adversely impact the business environment quality in the EU27. Furthermore, correlation analysis reveals a strong linear dependence between the Shift in Economic Power and business environment quality, along with a moderate negative dependence related to Social Change. This approach clarifies the influence of megatrends on business environments, providing valuable insights for decision-makers aiming to navigate a shifting economic landscape.

Integrating conspecifics negative density dependence, successional and evolutionary dynamics: Towards a theory of forest diversity

Tree successional diversity is evident even to casual observers and has a well-understood physiological basis. Various life history trade-offs, driven by interspecific variation in a single trait, help maintain this diversity. Conspecific negative density dependence (CNDD) is also well-documented and reduces tree vital rates independently of succession strategies. The CNDD hypothesis is frequently justified by specialist natural enemies at a separate trophic level. We integrate these processes into an analytical demographic model, spanning short-term plant physiological responses to the dynamics of a large forest mosaic connected to a metacommunity. Surprisingly, multiple trade-offs do not necessarily increase diversity, as suboptimal trait combinations lead to strategies that cannot compete for successional niches, explaining the weak correlation between functional traits and succession position. Succession alone can sustain half of the species in the metacommunity, with diversity increasing linearly with CNDD strength. The steeper increase with larger metacommunities suggests CNDD plays a greater role in tropical forests. However, if each successional type contains multiple equivalent species, CNDD maintains diversity but becomes less effective in promoting successional diversity, consistent with some tropical forests being less successional diverse. Additionally, CNDD enhances the likelihood of successful speciation and shifts life-history trait frequency by affecting more late-successional species.

Impact of Microtopography and Neighborhood Effects on Individual Survival Across Life History Stages.

Understanding drivers of plant community assembly and individual survival in forest ecosystems is crucial for effective conservation and management. While macro-scale factors influencing vegetation patterns are well documented, the combined impact of microtopographic variations and neighborhood effects at neighborhood scales, particularly in subtropical forests, requires further study. To contribute to this area of research, we established a 9.6 ha dynamic plot in a subtropical evergreen broad-leaved forest to examine the interplay between microtopographic factors and neighborhood effects on individual plant survival across different life stages. We conducted a comprehensive analysis of microtopographic variables and neighborhood effects, with individual plant survival censused through repeated surveys at 5-year intervals. Mixed-effects models were employed to assess the combined influence of these factors across life stages. Our results reveal that both microtopographic factors and neighborhood effects significantly influence plant survival, with their impacts varying across life stages. Water availability, represented by flow direction, emerged as a consistently critical factor throughout all life stages. Elevation and the topographic position index showed significant positive effects on survival, particularly in later life stages, possibly reflecting adaptations to light acquisition and water drainage. The influence of topographic factors intensified with succession, while the impact of neighborhood effects, particularly asymmetric competition and conspecific negative density dependence, changed as plants matured. This study enhances our understanding of forest community assembly, emphasizing the importance of considering abiotic and biotic factors across multiple scales for effective forest conservation and management. It provides insights into mechanisms driving spatial variation in community composition, crucial for preserving biodiversity in heterogeneous forest landscapes.

Improving shape memory effect in Fe-Mn-Si-based alloys by reducing annealing twin boundaries through trace boron doping

Previous work has shown that the shape memory effect (SME) exhibited a strong negative dependence on the density of annealing twin boundaries (ATBs) in Fe-Mn-Si-based alloys. Reducing the density of ATBs has thus been an effective way to improve the SME of Fe-Mn-Si-based alloys. This study investigated the effects of trace B doping on the density of ATBs and the resultant SME in solution-treated Fe-Mn-Si-based alloys. Results indicated that doping 89 ppm B effectively reduced the density of ATBs in the solution-treated Fe-Mn-Si-based alloy. Consequently, its SME was remarkably improved. The maximum shape recovery strain reached 2.7 % in the B-doped alloy, 1.3 % higher than in the alloy without B doping. This work demonstrates a new avenue to improve the SME by doping trace B, which is of significance for the fabrication of Fe-Mn-Si-based shape memory alloys in a more cost-effective manner.

Negative density dependence promotes persistence of a globally rare yet locally abundant plant species Oenothera coloradensis

Identifying the mechanisms underlying the persistence of rare species has long been a motivating question for ecologists. Classical theory implies that community dynamics should be driven by common species, and that natural selection should not allow small populations of rare species to persist. Yet, a majority of the species found on Earth are rare. Consequently, several mechanisms have been proposed to explain their persistence, including negative density dependence, demographic compensation, vital rate buffering, asynchronous responses of subpopulations to environmental heterogeneity, and fine‐scale source‐sink dynamics. Persistence of seeds in a seed bank, which is often ignored in models of population dynamics, can also buffer small populations against collapse. We used integral projection models (IPMs) to examine the population dynamics of Oenothera coloradensis, a rare, monocarpic perennial forb, and determine whether any of five proposed demographic mechanisms for rare species persistence contribute to the long‐term viability of two populations. We also evaluate how including a discrete seed bank stage changes these population models. Including a seed bank stage in population models had a significantly increased modeled O. coloradensis population growth rate. Using this structured population model, we found that negative density‐dependence was the only supported mechanism for the persistence of this rare species. We propose that high micro‐site abundances within a spatially heterogeneous environment enables this species to persist, allowing it to sidestep the demographic and genetic challenges of small population size that rare species typically face. The five mechanisms of persistence explored in our study have been demonstrated as effective strategies in other species, and the fact that only one of them had strong support here supports the idea that globally rare species can employ distinct persistence strategies. This reinforces the need for customized management and conservation strategies that mirror the diversity of mechanisms that allow rare species persistence.

Extreme comovements and downside/upside risk spillovers between oil prices and exchange rates

Abstract This paper examines the dependence structure and risk spillovers between oil prices and exchange rates in both oil-exporting and oil-importing countries. Using a flexible dependence switching copula model, we analyze both positive and negative dependence and transitions between the dependence regimes. Additionally, we investigate the directional risk spillovers between oil and currency markets in both their downsides and upsides. Based on empirical data from 1999 to 2024 for major oil-exporting and oil-importing countries, we find that oil price-currency dependence is predominantly positive for oil-exporting countries, with infrequent transitions, but mainly negative for oil-importing countries, with frequent transitions between the two dependence regimes. These transitions often occur around crisis or war times. Furthermore, we observe that during downturns in the oil market, tail dependence between oil prices and currencies becomes more pronounced than during upturns. Our results indicate the presence of risk spillovers between oil and currency markets, with the downside spillover effects outweighing the upside ones. Moreover, we find that risk spillover is stronger from oil markets to currency markets than the reverse direction. These insights substantially enrich the existing literature and would offer valuable implications for effective risk management strategies and policymaking.

Impact of evolutionary relatedness on species diversification and tree shape

Slowdowns in lineage accumulation are often observed in phylogenies of extant species. One explanation is the presence of ecological limits to diversity and hence to diversification. Previous research has examined whether and how species richness (SR) impacts diversification rates, but rarely considered the evolutionary relatedness (ER) between species, although ER can affect the degree of interaction between species, which likely sets these limits. To understand the influences of ER on species diversification and the interplay between SR and ER, we present a simple birth–death model in which the speciation rate depends on the ER. We use different metrics of ER that operate at different scales, ranging from branch/lineage-specific to clade-wide scales. We find that the scales at which an effect of ER operates yield distinct patterns in various tree statistics. When ER operates across the whole tree, we observe smaller and more balanced trees, with speciation rates distributed more evenly across the tips than in scenarios with lineage-specific ER effects. Importantly, we find that negative SR dependence of speciation masks the impact of ER on some of the tree statistics. Our model allows diverse evolutionary trajectories for producing imbalanced trees, which are commonly observed in empirical phylogenies but have been challenging to replicate with earlier models.

Redox Sensitive Mineral Magnetic Signatures of Seafloor Massive Sulfide Deposits

AbstractSeafloor massive sulfide (SMS) deposits in different geological settings can have variable magnetic mineralogy, but the mechanism and implications of their spatiotemporal diversity are poorly understood. Based on seabed shallow drilling and surficial sampling of the Yuhuang hydrothermal field, Southwest Indian Ridge, we investigate here whether ubiquitous oxidative weathering affects the magnetic properties of SMS deposits. Microscopic observation and ferrous iron concentrations reveal that seafloor SMS deposits are extensively oxidized; subseafloor SMS deposits are relatively fresh, but oxidation initiates immediately after sample recovery. Negative frequency dependence of magnetic susceptibility likely due to measurement eddy currents is observed for fresh samples but not for oxidized ones, which suggests that oxidative weathering reduces the electromagnetic detectability of SMS deposits in geophysical investigations. Pyrrhotite (and probably other magnetic iron sulfide minerals), magnetite, and hematite are recognized as dominating magnetic (ferromagnetic, sensu lato) minerals in SMS deposits. Electron and quantum diamond microscope observations reveal pyrrhotite mineralization from high‐temperature reducing hydrothermal fluids, while iron‐oxides are mostly oxidation products of primary sulfides. Oxidative weathering modifies paleomagnetic records of SMS deposits. Bulk magnetic parameters vary systematically with enhanced oxidation degree. Temperature‐dependent magnetic measurements are useful tools for distinguishing the oxidation state of SMS deposits. Overall, these findings explain magnetic mineral variability in SMS deposits, linking mineral magnetic properties with seafloor geophysical investigations. Mineral magnetism can also be a redox state proxy for tracing natural and artificial environmental fluctuations in seafloor hydrothermal fields, inspiring novel interdisciplinary research to understand interactions in the dynamic Earth System.

Negative Dependencies in Turkish

In this paper, we provide an overview of negative dependencies in Turkish. The first are elements such as hiçkimse, which sometimes seem to mean ‘anybody’ and sometimes ‘nobody’. We argue that unlike a standard Negative Polarity Item (NPI) like English anybody, these items should be analyzed as neg-words licensed under Negative Concord (NC). We also discuss further properties of these items, including whether they are universals or existentials. The second set of items that display a negative dependency are universal quantifiers such as herkes ‘everybody’. Unlike their counterparts in many languages, these items obligatorily scope under negation, which raises the question of why a universal is sensitive to negation in the way it is. We account for this behavior in terms of negative polarity sensitivity based on a referentiality requirement we dub the Non-Entailment-of-Non-Existence Condition, following a particular analysis of a class of NPIs in Mandarin. The final case of negative dependency we evaluate is modals that have to scope under or above negation. These cases constitute instances of polarity sensitivity in English and beyond, especially clearly in the case of modal PPIs. We show that in Turkish, however, they do not, and the apparent negative dependency follows from the syntax of Tense-aspect-modality (TAM) morphology.

Results of long-term studies of the annual growth of mosses of the genus <i>Sphagnum</i> L. In the central taiga of Karelia

The studies were carried out on the territory of the Kindasovo forest-bog research station of the Karelian Research Center, Russian Academy of Sciences, located in the middle taiga subzone (61°48′ N, 33°35′ E). The experiments were carried out in the Nenazvannoe natural mesoeutrophic bog of the aapa type in seven permanent bog areas located in different ecological and coenotic conditions. The paper presents long-term results (from 10 to 38 years) of studies of the dynamics of annual growth of 11 widespread hygro- and hydrophilic species of Sphagnum mosses. Based on fluctuations in the average annual growth data during the years of study, the largest increases were observed for Sphagnum riparium (140 mm) and S. obtusum (93 mm), growing in heavily watered bog areas and not withstanding drying out; medium growths of S. fallax (65 mm), S. subsecundum (57 mm), S. majus (42 mm), S. balticum (36 mm), and S. warnstorfii (28 mm) are found in low-flow watered bogs, hollows, and on carpets; the lowest growth was shown for S. divinum (17 mm), S. centrale (15 mm), S. papillosum (12 mm), and S. fuscum (8 mm), growing on ridges, low hummocks, and carpets under conditions of sharply variable conditions hydration. A correlation analysis to study the influence of precipitation and average temperature on the annual growth of Sphagnum mosses did not show any significant dependence of moss growth on temperature during the growing season. For S. fuscum, S. obtusum, and S. warnstorfii, negative dependences on the temperature of individual months are observed in different months of the growing season. Precipitation during the growing season is the main factor determining the dependence of the annual growth of Sphagnum mosses. A significant dependence of annual growth on precipitation during the growing season was shown for species S. obtusum, S. papillosum, S. centrale, S. fallax, and S. subsecundum, while the significance was weak for S. divinum, S. fuscum, and S. majus.

Path dependence in environment-related innovation: evidence from listed firms in China

ABSTRACT This paper studies the path dependence effect in corporate innovation based on the patent data of Chinese listed firms. The results provide robust evidence of the path dependence in technology innovation. The accumulated stock of brown patents reduces the ratio of green patents to total patents newly granted, thus inhibiting green structural changes in innovation. The accumulated stock of green patents increases the ratio of green patents in total patents granted, promoting structural change towards green innovation. The path dependence effect exists in both green inventions and green utility model patents. The heterogeneity analysis shows that both brown and green patent stocks of heavy polluting firms have a weaker effect on the ratio of green inventions than non-heavy polluting firms. The negative path dependence effect of brown patents on green innovation is stronger in firms with large scale, state ownership, and a high level of environmental regulation. However, the negative path dependence effects on green innovation can be alleviated for firms with superior environmental and financial performance. This suggests that the government has to create economic incentives to break the path dependence and encourage firms to engage in green innovation.

Effect of grain size on tensile behavior and the underlying deformation modes in a Mg-5Y sheet

This work aims to further understand the grain size effects on individual slip/twining activities at grain scale and their correlation with the tensile behavior, for a Mg-5Y sheet with mean grain size range of 3–130 μm, based on slip trace/electron backscatter diffraction (EBSD) analysis. The correlation between tensile yield strength and the corresponding grain size fitted well with the Hall-Petch relationship, i.e., the k value was 191 MPa·μm1/2, with an R2 of 0.96. According to the identified 1004 sets of slip traces in 2477 grains, basal <a> slip was always dominant and tended to increase (from 47.2% to 71.5%) with grain size increased from 3 to 85 μm. Meanwhile, the percentage of pyramidal II <c+a> slip exhibited a marked decline from 34.5% to 8.9%, while that of prismatic <a> and pyramidal I <c+a> slip changed slightly. The decreased pyramidal II <c+a> slip activity was consistent with the decreased tensile yield strength as grain size increased. The twinning activity was limited and insensitive to grain size. In addition, the geometrically necessary dislocation (GND) density was increased with increasing grain size. Based on the slip activity statistics, the critical resolved shear stress (CRSS) ratios were estimated, which exhibited a significant grain size effect. Specifically, CRSSpris/CRSSbas showed negative grain size dependence, while the opposite was true for CRSSpyrIICA/CRSSbas. This study provides valuable grain-scale experimental evidence for the grain size effect on individual slip activity and CRSS ratios, which contributes to a better understanding of the Hall-Petch relationship in Mg-Y alloy.

Phylogenetic relatedness and habitat affect seedling abundance of a mid-montane humid evergreen broad-leaved forest in the Gaoligong Mountains, Southwestern China

The neighborhood effect has become an important framework with which to study the mechanisms that maintain the coexistence of tree species. Phylogenetic relatedness among neighboring plants directly affects species coexistence and the maintenance of tree diversity. And some studies have reported that seedling performance is negatively correlated with phylogenetic relatedness, which termed phylogenetic negative density dependence. Soil-borne fungal pathogens affected seedling performance of phylogenetically related host species, i.e., phylogenetic Janzen–Connell effect. Seedlings may be particularly vulnerable to habitat and neighbor characteristics. Although previous studies have demonstrated the influence of neighborhood effects, phylogenetic relatedness, and habitat filtering on seedling survival, growth, and mortality, the effect of variation in these factors on seedling abundance remains unclear. To address this question, we used a 4-ha (200 m × 200 m) and monitored four-year (2020–2023) seedling dataset from a mid-montane humid evergreen broad-leaved subtropical forest in the Gaoligong Mountains, Yunnan, Southwestern China, and which consisted of 916 seedlings belonging to 56 species. The results of generalized linear mixed models showed no significant effect of conspecific adult neighbors on seedling abundance at any of the intervals evaluated. In contrast, we found evidence of phylogenetic distance density dependence in the forests of the Gaoligong Mountains. Specifically, there was a significant positive effect of the relative average phylogenetic distance between heterospecific adult neighbors and focal seedlings on focal seedling abundance in 2020; however, the relative average phylogenetic distance between heterospecific seedling neighbors and focal seedlings had a significant negative effect on seedling abundance over the four-year period (2020–2023). Among the habitat factors, only light (canopy opening) had a negative effect on seedling abundance in all four years. Light resources may be a limiting factor for seedlings, and determine seedling dynamics in subtropical forests. Overall, our results demonstrated that phylogenetic density dependence and habitat filtering affected subtropical seedling abundance. Our findings provide new evidence of the impact of phylogenetic density dependence on seedling abundance in a subtropical mid-montane humid evergreen broad-leaved forest and highlight the need to incorporate the neighborhood effect, phylogenetic relatedness, and habitat factors in models assessing seedling abundance.

Microbial Dormancy Supports Multi-Species Coexistence Under Resource Fluctuations.

The ability for microbes to enter dormant states is adaptive under resource fluctuations and has been linked to the maintenance of diversity. Nevertheless, the mechanism by which microbial dormancy gives rise to the density-dependent feedbacks required for stable coexistence under resource fluctuations is not well understood. Via analysis of consumer-resource models, we show that the stable coexistence of dormancy and non-dormancy strategists is a consequence of the former benefiting more from resource fluctuations while simultaneously reducing overall resource variability, which sets up the requisite negative frequency dependence. Moreover, we find that dormants can coexist alongside gleaner and opportunist strategies in a competitive-exclusion-defying case of three species coexistence on a single resource. This multi-species coexistence is typically characterised by non-simple assembly rules that cannot be predicted from pairwise competition outcomes. The diversity maintained via this three-way trade-off represents a novel phenomenon that is ripe for further theoretical and empirical inquiry.

Connectedness between artificial intelligence, clean energy, and conventional energy markets: Fresh findings from CQ and WLMC techniques

In line with achieving the objectives of COP27 and SDG7, this paper examines the interdependence of the Artificial Intelligence market, clean energy, and conventional energy markets from 19th December 2017 to 5th May 2023 by using Cross-Quantilogram (CQ) and Wavelet Locale Multiple correlations (WLMC) techniques. Heatmaps of CQ show a bidirectional relationship between the AI market and clean energy at lag one with negative cross-quantile dependence evident throughout most quantiles, especially in normal market conditions. It also indicates a positive relationship between AI return rates and the clean energy market, but only when both datasets are in the same extreme quantiles (10th and 90th). Additionally, WMLC results reveal that time, scale, and investment horizons influence the interaction between AI and clean and non-clean energy industries. A considerable positive association exists between the AI market and traditional energy markets, ranging from 0.6 to 0.8. However, during the pandemic, this dependency turned negative, and it has since been minor, with an uptick in co-movement during Russia – Ukraine conflict. Several policy implications are suggested for the clean energy and conventional energy markets in line with AI.

Probabilistic characterizations of flood hazards in deltas: Application to Hoek van Holland (Netherlands)

Coastal flooding events pose a critical risk in delta areas, since they are characterized by population growth and urban expansion. A better understanding of Extreme Water Levels (EWLs), the mechanisms generating them, and their components, i.e., astronomical tide and storm surge is of great importance as they drive the maintenance and design of flood protection systems. Therefore, a statistical investigation of them can provide new insights for more reliable flood risk mitigation infrastructures. In this study, we analyse these components and compare different probabilistic methods i.e., univariate extreme value analysis, copula functions, and Joint Probability Method (JPM) for the better estimation of EWLs. We use Hoek van Holland (NL) as a representative case study, since the dynamic conditions of this deltaic environment with man-made infrastructures render the area of strategic importance. The results indicate that a more accurate estimate of the declustering time between extreme events can be achieved using correlation of high surges and high wind speeds, taking into consideration also the wind direction. In the Southwest Delta this time estimated to be around 4 days. Furthermore, the EWLs components, i.e., surge and astronomical tide, show negative dependence. From the comparison between statistical approaches to model EWLs, results show that EWLs estimated via EVA and JPM do not vary significantly, while copulas’ seems to outperform the other methods. However, the selection of the proper copula to show the dependence is critical. As a conclusion, the analysis of the dependence between tides and storm surges can lead to more robust inferences of EWLs.

Viral plasticity facilitates host diversity in challenging environments

The antagonistic coevolution of microbes and viruses influences fundamentally the diversity of microbial communities. Information on how environmental variables interact with emergent defense-counterdefense strategies and community composition is, however, still scarce. Following biological intuition, diversity should increase with improved growth conditions, which offset evolutionary costs; however, laboratory and regional data suggest that microbial diversity decreases in nutrient-rich conditions. Moreover, global oceanic data show that microbial and viral diversity decline for high latitudes, although the underlying mechanisms are unknown. This article addresses these gaps by introducing an eco-evolutionary model for bacteria-virus antagonistic coevolution. The theory presented here harmonizes the observations above and identifies negative density dependence and viral plasticity (dependence of virus performance on host physiological state) as key drivers: environmental conditions selecting for slow host growth also limit viral performance, facilitating the survival of a diverse host community; host diversity, in turn, enables viral portfolio effects and bet-hedging strategies that sustain viral diversity. From marine microbes to phage therapy against antibiotic-resistant bacteria or cancer cells, the ubiquity of antagonistic coevolution highlights the need to consider eco-evolutionary interactions across a gradient of growth conditions.

Structural evolution of ultrasonic microinjection molded sterecomplexes of poly(lactide) during heating process

Two stereocomplexes (SCs) with different molecular weights in poly(L-lactide) (PLLA-49k and PLLA-163k) were prepared by mixing equal amounts of poly(D-lactide) (PDLA) and PLLA via the solution method. The exclusive formation of SCs was achieved in SC-PLLA-49k, whereas both homocrystallites (HCs) and SCs were observed in SC-PLLA-163k. Two blends were subjected to further processing via the ultrasonic microinjection molding technique at varying mold temperatures, yielding amorphous samples. As the samples were heated, the heating induced structural reorganization occurs with the concurrent SCs and HCs for all samples at ca. 80 °C. The degree of crystallinity for HCs XHC exhibits a positive correlation with the mold temperature, whereas the degree of crystallinity for SCs XSC shows a negative dependence on mold temperature for both systems. This behavior can be tentatively explained as follows. Firstly, the demixing of enantiomeric PLA chains occurs in the melt state as evidenced by twice heating measurements of blends. The degree of chain segregation is expected to increase with the increase in mold temperature due to lower supercooling, resulting in a decrease of PLLA/PDLA clusters (SC nuclei). Secondly, a high mold temperature is beneficial for the formation of HC nuclei as the chain mobility is improved. The reformulation of SC nuclei is difficult because of a longer diffusion distance required for PLA molecules. The coexistence of SC and HC nuclei causes the simultaneous appearance of SCs and HCs during heating of samples. As HCs start to melt, a transition from HCs to SCs occurs accompanied by a continuous increase in XSC. For both systems, a maximum of XSC is reached when SCs begin to melt followed by a mold temperature independent evolution of XSC upon further heating. Such a maximum is larger in the low molar mass system because it is less entangled. The reservation of SC nuclei is demonstrated by a comparison of the structural evolution and isothermal cold crystallization behavior between the two blends and their ultrasonic microinjection molded samples.

Hedge and safe haven functions of gold and Bitcoin around COVID-19: evidence from U.S. financial assets

ABSTRACT The COVID-19 outbreak triggered an unparalleled health crisis and financial shock. We re-examine whether gold and Bitcoin can function as hedges and safe havens for U.S. financial assets before and after the COVID-19 outbreak. This study employs the quantile-on-quantile and causality-in-quantiles methods to detect the nonlinear and asymmetric relationship of gold and Bitcoin with U.S. financial assets. The results reveal negative dependence of the U.S. dollar, real estate, crude oil, and natural gas on gold and Bitcoin in some quantiles during both periods, indicating that gold and Bitcoin are hedges for these four assets. Following the COVID-19 outbreak, the negative correlations that exist for stock and clean energy with Bitcoin almost all turn positive, gold and Bitcoin lose their ability to hedge stocks and clean energy. Bitcoin can still hedge bonds in middle and high quantiles, whereas gold does not possess this capability against the bond. Additionally, there is an asymmetric causality in the mean and variance from U.S. financial assets to gold and Bitcoin, which generally exists in the middle quantiles but not in the extreme (high and low) quantiles. Our findings provide clear guidelines to market participants on risk management and policy decisions according to market conditions.