14,124 research outputs found
Contrasting patterns of leaf solute accumulation and salt adaptation in four phreatophytic desert plants in a hyperarid desert with saline groundwater
No full textThe seasonal variation of leaf solutes was investigated in four perennial phreatophytes in the natural vegetation surrounding a river oasis in the Chinese Taklamakan desert in order to elucidate their adaptation to saline groundwater. Leaves of the herbaceous perennial legume Alhagi sparsifolia, the poplar tree Populus euphratica, the salt cedar Tamarix ramosissima, and the C(4) shrub Calligonum caput-medusae were collected at the end of each month during the growing season 1999 and analysed for cation, anion, organic acid, carbohydrate, glycinebetaine, and proline concentrations. The species revealed considerable differences in the foliar solute composition and their seasonal variation. Tamarix had high foliar mineral salt concentrations throughout the season but excreted the accumulated salts via salt glands. The three other species showed different degrees of ion regulation and ion selectivity. Calligonum had generally very low mineral ion concentrations, tolerated moderate Cl(-) concentrations and excluded Na(+). Populus effectively excluded Cl(-) from its leaves but Na(+) and total solute concentrations increased towards the end of the season which lead to K:Na ratio smaller than one in October. Alhagi showed the highest degree of ion selectivity by excluding Na(+) but accumulating Ca(2+) in its leaves. Mineral salt composition of xylemsap in Alhagi and Calligonian indicated that both species showed a similar degree of ion selectivity in the roots and that ion retransloction is probably another important mechanism to maintain low salt concentrations in the leaf. The cyclitols chiro-inositol and pinitol were the major compatible solutes in the plants and N-containing solutes like proline or glycinebetaine occurred only in minor concentrations or were absent, respectively. All plant species were well adapted to the moderate salinity of the NaCl dominated groundwater and no signs of salt related drought stress, ion toxicity or nutrient imbalance were observed. (C) 2003 Elsevier Ltd. All rights reserved
Potential hop reachable domain over surface of small bodies
No full textThe propagation of hopping trajectories with uncertainties is investigated over the surface of small celestial bodies. An intuitive geometric description of the accessible area referred to as the potential hop reachable domain, is provided when considering the uncertainties of the hopping rover’s state variables as well as the asteroid’s system parameters. A method to solve the envelope of the potential hop reachable domain is proposed by taking into account multi-hopping trajectories, which is applied to the asteroid 101955 Bennu. The influences of the state variables and asteroid physical parameters’ uncertainties on the propagation of hopping trajectories are discussed in detail. A comparison between the solved potential hop reachable domain and the Monte Carlo simulation is carried out to show the effectiveness of the method in this paper
Numerical Study on Low-Velocity Impact Between Asteroid Lander and Deformable Regolith
No full textInvestigating the impact process between the hopping lander and the regolith surfaces is of great significance for the
in situ asteroid explorations. The high-efficiency description of the regolith-interaction dynamics of the lander
remains to be analyzed. This paper presents a new method for effectively simulating the six-degree-of-freedom
motion of the lander when it impacts the regolith at a low velocity. The Bekker terramechanics theory is utilized for
calculating the impact force and torque, considering the notable deformable characteristic of the regolith.
Deformation of the regolith surfaces is tracked to simulate the formation of the impact crater. Parametric
simulations are implemented to verify this method by varying the regolith physical properties and the initial
lander state, respectively. The velocity and angular velocity of the lander are utilized as indicators for comparing
the hopping dynamics. Energy dissipation is discussed by calculating the restitution coefficients of different contact
scenarios
Wrinkling analysis of solar-photon sails
No full textThis paper regards small/midsize square sails on which a field of wrinkles appears owing to the necessary sail-membrane operations
before and during the deployment. We collected a large amount of data in our laboratory. Many ten thousands of measurements had
been statistically processed for characterizing some sail’s sampled membranes consisting of aluminized-polyimide layers ð2:5 þ 0:1Þlm
thin, and loaded at vertices. Such samples have exhibited area and orientation alterations, as a whole, which can affect the propulsive
acceleration of a sailcraft. Wrinkled-sail orientation has been given a thrust-specialized meaning for trajectory computation. Threedimensional
heliocentric minimum-time orbit transfer between Earth and Mercury orbits had been investigated. This had resulted in
wrinkled-sail sailcraft moving on trajectories remarkably different from those ones of the corresponding ideal unwrinkled-sail sailcraft.
Nevertheless, at least in the current framework, the most important result is that sail-wrinkled sailcraft’s interplanetary trajectories could
be optimized without resorting to stochastic differential equations
Analysis of the solar sail deformation based on the point cloud method
No full textThe deformation of the solar-sail membrane is an important factor for causing inaccuracies in the solar-sail missions. This paper
describes the solar sail under deformation by using a new modelling technique based on point cloud and triangular mesh generation.
Two types of deformation, stemming from wrinkling and billowing, are modelled. The changes in the solar radiation pressure force
and the moment caused by deformation are calculated and compared to the ideal non-deformed case. The heliocentric spiral trajectory
and the orbital angular momentum reversal trajectory are taken as examples to quantify the influence of the deformation from an orbit
point of view. Additionally, point cloud simplification, based on the normal vector and bounding box, is utilized to simplify the original
deformed-sail model. It involves a reasonable reduction and renewal of the points in the model considering the variation of surface curvature.
The simplification and its modelling accuracy are numerically investigated as well as computational efficiency
"Chemical blowing" of thin-walled bubbles: high-throughput fabrication of large-area, few-layered BN and C(x) -BN nanosheets
No full textMono- and few-atomic-layered BN and C x-BN nanosheets are fabricated in high yield through the blowing B- and N-containing polymers into large, thin-walled bubbles by chemically released hydrogen gas followed by subsequent annealing. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.link_to_subscribed_fulltex
Measurement of the Absolute Branching Fraction of the Inclusive Decay Lambda(+)(c) -> Lambda plus X
No full textBased on an e(+)e(-) collision data sample corresponding to an integrated luminosity of 567 pb(-1) taken at the center-of-mass energy of root s = 4.6 GeV with the BESIII detector, we measure the absolute branching fraction of the inclusive decay Lambda(+)(c) -> Lambda + X to be B(Lambda(+)(c) -> Lambda + X) = (38.2(-2.2)(+2.8) +/- 0.9)% using the double-tag method, where X refers to any possible final state particles. In addition, we search for direct CP violation in the charge asymmetry of this inclusive decay for the first time, and obtain A(CP) [B(Lambda(+)(c) -> Lambda + X) - B((Lambda) over bar (-)(c) -> (Lambda) over bar + X)]/[B(Lambda(+)(c) -> Lambda + X) + B((Lambda) over bar (-)(c) -> (Lambda) over bar + X)] = (2.1(-6.6)(+7.0) +/- 1.6)%, a statistically limited result with no evidence of CP violation
FIGURE. Specimens of Reevesia formosana Sprague (A) from Taiwan and R. thyrsoidea (B) from Guangdong. A: China. Taiwan, Pingtung, C. C. Chuang 2220 (HAST6559). B: China. Guangdong, Guangzhou, X. Q. Liu & C. X. Zeng 3447 (SZG00000091). in Taxonomic studies on the genus Reevesia (Malvaceae: Helicteroideae) I: the identities of R. thyrsoidea
No full textFIGURE. Specimens of Reevesia formosana Sprague (A) from Taiwan and R. thyrsoidea (B) from Guangdong. A: China. Taiwan, Pingtung, C. C. Chuang 2220 (HAST6559). B: China. Guangdong, Guangzhou, X. Q. Liu & C. X. Zeng 3447 (SZG00000091).Published as part of Feng, Hui-Zhe, Meng, Kai-Kai & Wang, Long-Yuan, 2022, Taxonomic studies on the genus Reevesia (Malvaceae: Helicteroideae) I: the identities of R. thyrsoidea, pp. 1-19 in Phytotaxa 547 (1) on page 5, DOI: 10.11646/phytotaxa.547.1.1, http://zenodo.org/record/655703
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