AIDing Contraception: HIV and Recent Trends in Abortion Rates

Since the onset of HIV/AIDS awareness in the early 1980s, much attention has centered around the substantial negative effects of the disease throughout the world. This paper provides evidence of a secondary effect the disease has had on sexual behavior in the United States. Using a difference-in-differences estimation framework and state level data, we show that the perceived threat of HIV resulted in a drop in unwanted pregnancies, as demonstrated by a lower incidence of abortions. Our results suggest that each additional reported case of HIV per 1,000 individuals resulted in 85.5 fewer abortions per 1,000 live births.

High-throughput screening of coherent topologically close-packed precipitates in hexagonal close-packed metallic systems

The nanoscale, coherent topologically close-packed (TCP) precipitate plates in magnesium alloys are found beneficial to the strength and creep resistance of alloys. However, the conventional trial-and-error method is too time-consuming and costly, which impedes the application of TCP precipitates to hcp-based metallic alloys. Here, we systematically screen the potential coherent TCP precipitate plates in the three most common hcp alloys, magnesium (Mg), titanium (Ti), and zirconium (Zr) alloys, using an efficient high-throughput screening methodology. Our findings indicate that the hcp-to-TCP structural transformations readily occur in Mg alloys, leading to abundant precipitation of TCP plates. However, hcp-Ti and Zr alloys exhibit a preference for hcp-to-bcc structural transformations, rather than the in situ precipitation of TCP plates. These screening results are largely consistent with experimental observations. The insights gained contribute to a deeper understanding of precipitation behavior in various hcp-based alloys at the atomic level and provide insightful reference results for designing novel alloys containing TCP phases.Comment: arXiv admin note: substantial text overlap with arXiv:2307.0667

Structural pathway for nucleation and growth of topologically close-packed phase from parent hexagonal crystal

The solid diffusive phase transformation involving the nucleation and growth of one nucleus is universal and frequently employed but has not yet been fully understood at the atomic level. Here, our first-principles calculations reveal a structural formation pathway of a series of topologically close-packed (TCP) phases within the hexagonally close-packed (hcp) matrix. The results show that the nucleation follows a nonclassical nucleation process, and the whole structural transformation is completely accomplished by the shuffle-based displacements, with a specific 3-layer hcp-ordering as the basic structural transformation unit. The thickening of plate-like TCP phases relies on forming these hcp-orderings at their coherent TCP/matrix interface to nucleate ledge, but the ledge lacks the dislocation characteristics considered in the conventional view. Furthermore, the atomic structure of the critical nucleus for the Mg2Ca and MgZn2 Laves phases was predicted in terms of Classical Nucleation Theory (CNT), and the formation of polytypes and off-stoichiometry in TCP precipitates is found to be related to the nonclassical nucleation behavior. Based on the insights gained, we also employed high-throughput screening to explore several common hcp-metallic (including hcp-Mg, Ti, Zr, and Zn) systems that may undergo hcp-to-TCP phase transformations. These insights can deepen our understanding of solid diffusive transformations at the atomic level, and constitute a foundation for exploring other technologically important solid diffusive transformations

Description of a new species of Eucinetidae (Coleoptera, Scirtoidea) from Cretaceous Burmese amber

Eucinetus parvus sp. nov. is described from late Cretaceous Burmese amber, representing the second record of Eucinetidae from the Burmese amber and the first species of the family with simple, not piercing, mouthparts. A comparison between Mesocinetidae and Eucinetidae is provided

Soil carbon, nitrogen and phosphorus ecological stoichiometry shifts with tree species in subalpine plantations

Understanding ecological stoichiometric characteristics of soil nutrient elements, such as carbon (C), nitrogen (N) and phosphorus (P) is crucial to guide ecological restoration of plantations in ecologically vulnerable areas, such as alpine and subalpine regions. However, there has been only a few related studies, and thus whether and how different tree species would affect soil C:N:P ecological stoichiometry remains unclear. We compared soil C:N:P ecological stoichiometry of Pinus tabulaeformis, Larix kaempferi and Cercidiphyllum japonicum to primary shrubland in a subalpine region. We observed strong tree-specific and depth-dependent effects on soil C:N:P stoichiometry in subalpine plantations. In general, the C:N, C:P and N:P of topsoil (0–10 cm) are higher than subsoil (>10 cm) layer at 0–30 cm depth profiles. The differences in C:N, N:P and C:P at the topsoil across target tree species were significantly linked to standing litter stock, tree biomass/total aboveground biomass and Margalef’s index of plant community, respectively, whereas the observed variations of C:N, N:P and C:P ratio among soil profiles are closely related to differences in soil bulk density, soil moisture, the quantity and quality of aboveground litter inputs as well as underground fine root across plantations examined. Our results highlight that soil nutrients in plantation depend on litter quantity and quality of selected tree species as well as soil physical attributes. Therefore, matching site with trees is crucial to enhance ecological functioning in degraded regions resulting from human activity

Thinning-induced canopy opening exerted a specific effect on soil nematode community

Changes in microclimate, soil physicochemical properties, understory vegetation cover, diversity, and composition as well as soil microbial community resulting from silvicultural practices are expected to alter soil food webs. Here, we investigated whether and how contrasting-sized canopy openings affect soil nematode community within a 30year-aged spruce plantation. The results indicated that the responses of soil nematodes to canopy opening size were dependant on their feeding habit. The abundance of total nematodes and that of free-living nematodes was negatively correlated with soil bulk density, whereas the abundance of omnivore-predators was negatively correlated with soil bulk density and shrubs cover, respectively. The ratio of the sum abundance of predators and omnivores to the plant parasites' abundance, Simpson's dominance index, Pielou's evenness index, and sigma maturity index, maturity index (MI), MI2-5, basal index, enrichment index, and structure index was sensitive to alteration in canopy opening size. Multivariate analysis indicated that thinning-induced gap size resulted in contrasting nematode assemblages. In conclusion, soil nematodes should be integrated as an indicator to monitor soil multifunctionality change due to thinning

Gap thinning improves soil water content, changes the vertical water distribution, and decreases the fluctuation

Although it is clear that gap thinning significantly increases the soil water content (SWC) of the topsoil, less is known about whether and how this treatment affects deeper layers. From December 2008 to April 2012, we monitored the SWC at depths of 10, 20, 30, 45, 60, and 90 cm in gap creation treatments (small gap size of 30 m(2), intermediate gap size of 80 m(2), and unthinned plots) in a typical pine plantation in the eastern Tibetan Plateau. Among gap treatments, differences in SWC and its coefficient of variation (CV) at each depth and the soil water content proportion (SWCP) of the whole soil profile at specific depths were compared. Gap thinning improved SWC and decreased the CV at each depth. The SWCPs in thinned plots were lower at depths from 10 to 30 cm compared with unthinned plots but higher at depths of 45 and 60 cm. Also, in each season, the patterns were similar to the general results. In conclusion, gap thinning improves the SWC, changes the vertical soil water distribution, and decreases the SWC heterogeneity. The soil water conditions in intermediate gaps are more appropriate for local forest restoration

Differential responses of Picea asperata and Betula albosinensis to nitrogen supply imposed by water availability

A pot experiment was conducted to investigate the effects of nitrogen (N) addition (0, 20, 40 g N m(-2) year(-1), N0, N20, N40, respectively) on the growth, and biomass accumulation and allocation of coniferous and deciduous (Picea asperata Mast. and Betula albosinensis Burk.) seedlings under a range of soil moisture limitation (40%, 50%, 60%, 80% and 100% of field capacity, FC). At 100% FC, growth of shade-tolerant P. asperata increased with N supply, while that of shade-intolerant B. albosinensis reached a maximum at N20, declining somewhat thereafter. At 60% FC and lower moisture content, water availability limited the growth of P. asperata seedlings, while N availability became progressively limiting to growth with moisture increasing above 60% FC. The transition from principally water-limited response to N-limited response in B. albosinensis occurred at lower moisture content. For P. asperata, these patterns reflected the responses of roots, consistent with changes in root/shoot biomass. For B. albosinensis the response reflected changes in shoot dimensions and root biomass fraction, the latter decreasing with size and foliar [N]. We are not aware of another study demonstrating such differences in the shape of the growth responses of seedlings of differing potential growth rate, across a range in belowground resource supply. The responses of leaf photosynthesis (as well as photosynthetic water and N-use efficiencies) were consistent with the observed growth response of P. asperata to water and N availability, but not of B. albosinensis, suggesting that leaf area dynamics (not measured) dominated the response of this species. Betula albosinensis, a fast-growing species, has a relative narrow range of soil water and N availability for maximum growth, achieved by preferential allocation to the shoot as resources meet the requirements at moderate N and water supply. In contrast, P. asperata increases shoot biomass progressively with increasing resources up to moderate water supply, preferentially growing more roots when resources are not limiting, suggesting that its capacity to produce shoot biomass may reach a biological limit at moderate levels of resource supply