A Bimodal Pattern and Age-Related Growth of Intra-Annual Wood Cell Development of Chinese Fir in Subtropical China

Age plays an important role in regulating the intra-annual changes in wood cell development. Investigating the effect of age on intra-annual wood cell development would help to understand cambial phenology and xylem formation dynamics of trees and predict the growth of trees accurately. Five intermediate trees in each stand (total of 5 stands) in five age groupings of Chinese fir (Cunninghamia lanceolata Hook.) plantations in subtropical China were monitored on micro-cores collected weekly or biweekly from January to December in 2019. We modeled the dynamics of wood cell development with a mixed effects model, analyzed the age effect on intra-annual wood cell development, and explored the contribution of rate and duration of wood cell development on intra-annual wood cell development. We found a bimodal pattern of wood cell development in all age classes, and no matter the date of peak or the maximal number of cells the bimodal patterns were similar in all age classes. In addition, compared with the older trees, the younger trees had the longest duration of wood cell development because of the later end of wood cell development and a larger number of wood cells. The younger trees had the faster growth rate than the older trees, but the date of the maximal growth rate in older trees was earlier than younger trees, which led to the production of more wood cells in the younger trees. Moreover, we found that the number of cells in wood cell formation was mostly affected by the rate (92%) rather than the duration (8%) of wood cell formation.

A mantle-source solution to the enigma of bimodal arc volcanism

Silicate melts in arc environments are dominated by mafic (low-silica) and silicic (high-silica) compositions, often generating a characteristic bimodal pattern. We investigate the whole arc crust and show that the plutonic lower crust shares the bimodal pattern of melts from volcanoes. This key observation reveals that, contrary to some explanations of bimodal volcanism, variation in mantle source and mantle processes must fundamentally control bimodalism. We also recognise bimodalism in Th/La composition of the whole arc crust and suggest a new working hypothesis: bimodalism originates by melting of distinct sub-arc mantle sources, one dominated by relatively dry peridotite and the other by hydrous pyroxenite. The two groups of primary melts fractionate along distinct liquid lines of descent that lead to relatively dry mafic melts (Th/La~0.1) versus hydrous silicic melts (Th/La>0.2) by 65–80% fractional crystallisation. Common crustal processes such as crystal fractionation, assimilation, reactive flow and/or magma mixing may also lead to differentiation of both groups.

Entering a Golden Age of Sustained Superiority: Entrepreneurial Creation or Discovery?

To better understand the origins of sustained superior firm performance, we consider processes of entrepreneurial creation and discovery. Discovering new opportunities requires speed and flexibility, and although many discoveries are easy to implement, this makes them easy to imitate. By comparison, creation is more complex, iterative, and cumulative, making these opportunities slower to implement yet harder to copy. In formal simulation modeling and analyses of the U.S. Compustat population from 1966 to 2015, we found a bimodal pattern of entry into golden eras of sustained superiority. One peak consisted of an initial spike as firms went public, and evidence suggests this was driven by entrepreneurial discovery. The other peak involved a long-term inverted U-shaped trajectory that reached its high point about 17 years later. Evidence suggests this was driven by entrepreneurial creation, which first enabled then later constrained durable superiority. Our results have implications for research on sustained superiority, entrepreneurial opportunities, and strategic renewal.

Differential Seasonality of Legionnaires’ Disease by Exposure Category

Legionnaires’ disease (LD) shows a seasonal pattern with most cases occurring in summer. We investigate if seasonality can be observed for all three exposure categories (community-acquired (CALD), travel-associated (TALD) and healthcare-associated (HCA)). Methods: LD cases (2005–2015) were classified by exposure categories and we calculated the relative case ratio for each month from February to December using January as reference. The TALD relative case ratio was compared with flight frequencies. Results: Overall case numbers in Germany (N = 7351) peaked in August. CALD had a curve similar to all cases. TALD displayed a bimodal curve with peaks in June/July and October. The latter was attributable to LD cases aged 60+. The relative case ratio of TALD surpassed clearly that of CALD. The curve was similar to that of the relative flight frequencies, but was shifted by about one month. HCA showed no apparent seasonality. Conclusions: Although the overall seasonality in LD is heavily influenced by CALD, seasonal differences are more pronounced for TALD which may reflect travel behavior. The bimodal pattern of TALD is attributable to the curve among those aged 60+ and may reflect their preference to travel outside school holiday periods. Heightened vigilance for HCA cases is necessary throughout the entire year.

High-resolution analysis of Vegetated Linear Dune construction - The northwestern Negev dunefield, Israel

<p>Vegetated Linear Dunes (VLDs) are common in arid environments such as in Australia and southern-Africa. They propagate in a linearly fashion in accordance with strong unidirectional winds. Their elongation and accumulation mechanisms are not well-understood (Telfer, 2011). Here we report on VLD construction based on high-resolution Portable Optically Stimulated Luminescence (POSL), particle-size distribution (PSD), Optically Stimulated Luminescence (OSL) and inorganic carbon content of a rare, exposed and consolidated 8-m high section of a VLD axis, at the margins of the northwestern Negev dunefield, Israel.</p><p>The POSL profile results of sand (<300µm) samples (25 cm interval) in the Infra-Red (IR) and Blue (B) spectra display a similar pattern and are differentiated into three statistically distinct clusters, using an unclassified clustering (Mean-Shift) algorithm. Mean values and standard deviation of the B net values (Sanderson & Murphy, 2010) of the three clusters are: 858.1±62 [10<sup>3</sup>], 702.8±39.5 [10<sup>3</sup>] and 552.9±50.7 [10<sup>3</sup>] counts. ANOVA single factor analysis illustrate significant variation between the groups (p.<0.05). These discrete clusters plotted with depth, nicely fit observed stratigraphic units and CaCO<sub>3</sub> content, interpreted to represent episodes of sand accumulation. PSD analysis shows a (classic for Negev VLDs) unimodal distribution for sand (peak at 225mm) of the upper unit but a bimodal pattern (peaks at 65-70mm and 200-225mm) for samples of the two lower units. This rare bimodal pattern suggests short-distance fine-grained aeolian contribution from exposed sediments of dune-dammed water bodies that developed around the construction time of the VLD.</p><p>OSL ages fit previous studies (Roskin et al., 2011) but could not be discretely differentiated into the three units since both the middle- and upper-units date to the Younger Dryas event. Partial bleaching of some of the samples may have impaired dating accuracies. OSL ages of the lower unit date to the time of the Heinrich 1 event.</p><p>The finds, the first of their kind in high-resolution with POSL, demonstrate that VLDs accrete in discrete accumulation phases. The results strengthen the prevailing hypothesis based on lower resolution OSL dating (Roskin et al. 2011, 2014), advocating VLD construction in the Negev by several rapid phases of sand accumulation during periods of high wind power.</p><ul><li>Telfer, M. W. 2011. Growth by extension, and reworking, of a south-western Kalahari linear dune. Earth Surface Processes and Landforms, 36: 1125-1135.</li> <li>Roskin, J., Tsoar, H., Porat, N., & Blumberg, D. G. 2011. Palaeoclimate interpretations of Late Pleistocene vegetated linear dune mobilization episodes: Evidence from the northwestern Negev dunefield, Israel. Quaternary Science Reviews, 30(23–24), 3364–3380.</li> <li>Roskin, J., Blumberg, D. G., & Katra, I. 2014. Last Millenium development and dynamics of vegetated linear dunes inferred from ground-penetrating radar and optically stimulated luminescence ages. Sedimentology. 61: 1240-1260.</li> <li>Sanderson, D. C. W., & Murphy, S. 2010. Using simple portable OSL measurements and laboratory characterisation to help understand complex and heterogeneous sediment sequences for luminescence dating. Quaternary Geochronology, 5(2–3): 299–305.</li> </ul>