83 research outputs found
Enhanced Piezocapacitive Effect in CaCu<sub>3</sub>Ti<sub>4</sub>O<sub>12</sub>–Polydimethylsiloxane Composited Sponge for Ultrasensitive Flexible Capacitive Sensor
No full textHighly sensitive flexible piezocapacitive (PC) pressure sensor demonstrates wide applications in wearable electronics. In this paper, we first theoretically proposed an effective strategy to improve the sensitivity of the PC pressure sensor, by constructing a porous dielectric layer composted of inorganics with high dielectric constant (ϵH) and organics with low dielectric constant (ϵL). By using CaCu3Ti4O12 (CCTO) nanocrystals with giant ϵ as the dopant and polydimethylsiloxane (PDMS) with a low ϵ as the matrix, an ultrasoft CCTO-PDMS dielectric sponge was fabricated, via a simple porogen-assisted process. The CCTO-PDMS composited sponge exhibits an ultralow compression modulus of 6.3 kPa, a highly enhanced sensitivity with the gauge factor of up to 1.66 kPa-1 in a range of 0-640 Pa, and a response time of 33 ms, and the sensitivity outperforms that of pure PDMS and other PC sensors reported recently. This sensitivity enhancement is attributed to the hybridization of two phases of ϵH/ϵL in the composites, which provides an effective route to other novel flexible PC sensors. In practical applications, CCTO-PDMS-based PC sensor demonstrates potential applications, such as recording wrist pulse wave with fine accuracy and fidelity, bending and twisting detection, and Moss code simulating. The low-cost fabrication process in conjunction with its superior sensitivity, robustness of the functional versatility, and mechanical flexibility make the CCTO-PDMS-based pressure sensor widely promising for applications in wearable devices, flexible electronics, robotics, etc
Global warming reduces plant reproductive output for temperate multi-inflorescence species on the Tibetan plateau
No full textTemperature is projected to increase more during the winter than during the summer in cold regions. The effects of winter warming on reproductive effort have not been examined for temperate plant species. Here, we report the results of experimentally induced seasonal winter warming (0.4 and 2.4 degrees C increases in growing and nongrowing seasons, respectively, using warmed and ambient open-top chambers in a Tibetan Plateau alpine meadow) for nine indeterminate-growing species producing multiple (single-flowered or multi-flowered) inflorescences and three determinate-growing species producing single inflorescences after a 3-yr period of warming. Warming reduced significantly flower number and seed production per plant for all nine multi-inflorescence species, but not for the three single-inflorescence species. Warming had an insignificant effect on the fruit to flower number ratio, seed size and seed number per fruit among species. The reduction in seed production was largely attributable to the decline in flower number per plant. The flowering onset time was unaffected for nine of the 12 species. Therefore, the decline in flower production and seed production in response to winter warming probably reflects a physiological response (e.g. metabolic changes associated with flower production). Collectively, the data indicate that global warming may reduce flower and seed production for temperate herbaceous species and will probably have a differential effect on single- vs multi-inflorescence species
Petal Color, Flower Temperature, and Behavior in an Alpine Annual Herb, Gentiana leucomelaena (Gentianaceae)
No full textGentiana leucomelaena (Gentianaceae), an alpine herbaceous species of the Qinghai-Tibetan Plateau, has two colors of flowers (blue and white) that bloom in early spring. In order to determine the effect of petal color on flower interior temperature and behavior in the gentian, we investigated the differences in timing of flower opening and closure and the interior temperature of blooming flowers between the two colors, while recording the ambient temperature, light intensity, and relative humidity over the flowering season from March to May of 2009. When the flowers were open, the anther temperature was higher in the white flowers than in the blue flowers in various weather patterns; in particular it was about 2 degrees C higher on sunny days. Relative to the ambient temperature, the anther temperature was 1.27 degrees C higher in the white flowers, but was 0.41 degrees C lower in the blue flowers. Compared to blue flowers, white flowers opened later but closed earlier in the day at a higher ambient temperature. The two-factor two-level experiment (10 degrees C vs. 20 degrees C and 10,000 lux vs. darkness) indicates that temperature is the factor eventually determining the timing of flower opening and opening rates, but light may accelerate flower opening at the same temperature. The dye experiment, in which blue flowers were painted with red and purple food coloring, showed that the purple flowers had higher anther temperature, opened later but closed earlier, relative to the red ones. These results suggest that flower interior temperature is affected by both flower color and behavior in the species. In addition, we surveyed the percentages of the two flower colors in the field during the flowering season and also experimentally placed individuals with flower buds into growth chambers with contrasting day/night temperatures (12 degrees C/2 degrees C, 15 degrees C/2 degrees C, and 20 degrees C/2 degrees C), so as to examine the temperature effect on flower color frequency. A greater proportion of white flowers emerged in the early stage of the flowering season and in the low-temperature chambers, but blue ones dominated the late season and in the high-temperature chambers. This suggests that the color differentiation in the species is associated with temperature. The different strategies of adaptation to temperature might have allowed for flower color polymorphism
Artificial asymmetric warming reduces nectar yield in a Tibetan alpine species of Asteraceae
No full textBackground and Aims Asymmetric warming is one of the distinguishing features of global climate change, in which winter and night-time temperatures are predicted to increase more than summer and diurnal temperatures. Winter warming weakens vernalization and hence decreases the potential to flower for some perennial herbs, and night warming can reduce carbohydrate concentrations in storage organs. This study therefore hypothesized that asymmetric warming should act to reduce flower number and nectar production per flower in a perennial herb, Saussurea nigrescens, a key nectar plant for pollinators in Tibetan alpine meadows. Methods A long-term (6 years) warming experiment was conducted using open-top chambers placed in a natural meadow and manipulated to achieve asymmetric increases in temperature, as follows: a mean annual increase of 0 center dot 7 and 2 center dot 7 A degrees C during the growing and non-growing seasons, respectively, combined with an increase of 1 center dot 6 and 2 center dot 8 A degrees C in the daytime and night-time, respectively, from June to August. Measurements were taken of nectar volume and concentration (sucrose content), and also of leaf non-structural carbohydrate content and plant morphology. Key Results Six years of experimental warming resulted in reductions in nectar volume per floret (64 center dot 7 % of control), floret number per capitulum (8 center dot 7 %) and capitulum number per plant (32 center dot 5 %), whereas nectar concentration remained unchanged. Depletion of leaf non-structural carbohydrates was significantly higher in the warmed than in the ambient condition. Overall plant density was also reduced by warming, which, when combined with reductions in flower development and nectar volumes, led to a reduction of similar to 90 % in nectar production per unit area. Conclusions The negative effect of asymmetric warming on nectar yields in S. nigrescens may be explained by a concomitant depletion of leaf non-structural carbohydrates. The results thus highlight a novel aspect of how climate change might affect plant-pollinator interactions and plant reproduction via induction of allocation shifts for plants growing in communities subject to asymmetric warming
A Globally Conforming Lattice Structure for 2D Stress Tensor Visualization
No full textWe present a visualization technique for 2D stress tensor fields based on the construction of a globally conforming lattice. Conformity ensures that the lattice edges follow the principal stress directions and the aspect ratio of lattice elements represents the stress anisotropy. Since such a lattice structure cannot be space-filling in general, it is constructed from multiple intersecting lattice beams. Conformity at beam intersections is ensured via a constrained optimization problem, by computing the aspect ratio of elements at intersections so that their edges meet when continued along the principal stress lines. In combination with a coloring scheme that encodes relative stress magnitudes, a global visualization is achieved. By introducing additional constraints on the positional variation of the beam intersections, coherent visualizations are achieved when external loads or material parameters are changed. In a number of experiments using non-trivial scenarios, we demonstrate the capability of the proposed visualization technique to show the global and local structure of a given stress field.Accepted Author ManuscriptMaterials and Manufacturin
Difference in Floral Traits, Pollination, and Reproductive Success between White and Blue Flowers of Gentiana leucomelaena (Gentianaceae) in an Alpine Meadow
No full textThe blue-white gentian, Gentiana leucomelaena (Gentianaceae), bears two colors of flowers (blue and white) within populations and on individual plants. We tested the hypothesis that these flower morphs have different mating systems associated with differences in pollinator species and visitation rates. This hypothesis was driven by the fact that colorful flowers are often more likely to be pollinated by diverse animal pollinators, and by the observation that white G. leucomelaena flowers always blossom earlier than blue ones in early spring, when few pollinators are available. This hypothesis was investigated by determining the pollination success, daily duration of flower opening, flower life span, the number of pollen grains and ovules per flower, pollinator visitation rates, and seed output for both color morphs during the flowering season of 2009. Hand-pollination and pollinator-exclusion experiments were also conducted to determine whether the two color morphs differed in their ability to self-pollinate. In general, blue flowers were found to have a trait combination that favors a significantly higher degree of pollinator specificity and cross fertilization, whereas white flowers were characterized as pollinator generalists and self-fertilizing. We speculate that the difference in the floral structure and function between blue and white flowers and their coexistence are likely adaptive in unpredictable and often pollinator-limited environments such as those found in the alpine meadows of the Qinghai-Tibet Plateau
Key driving forces of desertification in the Mu Us Desert, China
No full textAbstractThe temporal trends and key driving forces of desertification in the Mu Us Desert are representatives of most arid regions of Asia with a high risk of desertification. We analyzed the significance of Aeolian transport on desertification in the Mu Us Desert by field investigations, sampling, wind tunnel experiments, particle size and nutrient measurements, and statistics on aeolian transport potentials. The results showed that high intensities of aeolian processes may result in low differences in aeolian transport despite differences in the underlying sediments. When high desertification occurred in the 1970s, the annual losses of the ammonium N, nitrate N, available K, and available P were approximately 116, 312, 46,436, and 1,251 kg km−2, respectively. After 2010, the losses were only 8, 20, 3,208, and 84 kg km−2, which were generally only 6.7% of those in the 1970s. The results showed that although human activity may trigger desertification, the dramatic decline of aeolian transport and low nutrient loss may be the key driving forces for the occurrence of rehabilitation in this region.</jats:p
Stress topology analysis for porous infill optimization
No full textThe optimization of porous infill structures via local volume constraints has become a popular approach in topology optimization. In some design settings, however, the iterative optimization process converges only slowly, or not at all even after several hundreds or thousands of iterations. This leads to regions in which a distinct binary design is difficult to achieve. Interpreting intermediate density values by applying a threshold results in large solid or void regions, leading to sub-optimal structures. We find that this convergence issue relates to the topology of the stress tensor field that is simulated when applying the same external forces on the solid design domain. In particular, low convergence is observed in regions around so-called trisector degenerate points. Based on this observation, we propose an automatic initialization process that prescribes the topological skeleton of the stress field into the density field as solid simulation elements. These elements guide the material deposition around the degenerate points, but can also be remodelled or removed during the optimization. We demonstrate significantly improved convergence rates in a number of use cases with complex stress topologies. The improved convergence is demonstrated for infill optimization under homogeneous as well as spatially varying local volume constraints.Materials and Manufacturin
Can mechanized pesticide application help reduce pesticide use and increase crop yield? Evidence from rice farmers in Jiangsu province, China
No full textThis study is devoted to analyzing the effects of outsourcing machinery-intensive farming activities vis-à-vis using mechanized equipment in-house on pesticide use, utilizing cross-sectional data collected from rice farmers in Jiangsu province, China. The control function approach is utilized to address the endogeneity of the decision to outsource pesticide application or complete the task in-house. Our results suggest that outsourcing pesticide application decreases pesticide expenditure but in-house application using mechanized equipment increases it. Specifically, outsourcing pesticide application reduces pesticide expenditure by about 81 yuan per mu or around 0.18 yuan per kilogram of rice produced. In comparison, the in-house application using mechanized equipment increases pesticide expenditure by 118 yuan per mu or by 0.14 yuan per kilogram of rice output. We also find that both outsourcing and in-house pesticide applications increase rice yield
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