共查询到20条相似文献,搜索用时 31 毫秒
1.
O. V. Mingalev I. V. Mingalev M. N. Mel’nik A. V. Artemyev H. V. Malova V. Yu. Popov Shen Chao L. M. Zelenyi 《Plasma Physics Reports》2012,38(4):300-314
Thin current sheets, whose existence in the Earth’s magnetotail is confirmed by numerous spacecraft measurements, are studied
analytically and numerically. The thickness of such sheets is on the order of the ion Larmor radius, and the normal component
of the magnetic field (B
z
) in the sheet is almost constant, while the tangential (B
x
) and shear (B
y
) components depend on the transverse coordinate z. The current density in the sheet also has two self-consistent components (j
x
and j
y
, respectively), and the magnetic field lines are deformed and do not lie in a single plane. To study such quasi-one-dimensional
current configurations, two kinetic models are used, in particular, a numerical model based on the particle-in-cell method
and an analytical model. The calculated results show that two different modes of the self-consistent shear magnetic field
B
y
and, accordingly, two thin current sheet configurations can exist for the same input parameters. For the mode with an antisymmetric
z profile of the B
y
component, the magnetic field lines within the sheet are twisted, whereas the profiles of the plasma density, current density
component j
y
, and magnetic field component B
x
differ slightly from those in the case of a shearless magnetic field (B
y
= 0). For the symmetric B
y
mode, the magnetic field lines lie in a curved surface. In this case, the plasma density in the sheet varies slightly and
the current sheet is two times thicker. Analysis of the dependence of the current sheet structure on the flow anisotropy shows
that the sheet thickness decreases significantly with decreasing ratio between the thermal and drift plasma velocities, which
is caused by the dynamics of quasi-adiabatic ions. It is shown that the results of the analytical and numerical models are
in good agreement. The problems of application of these models to describe current sheets at the magnetopause and near magnetic
reconnection regions are discussed. 相似文献
2.
To investigate how complex food-webs can develop through repeated evolutionary diversification, a predator–prey model was
analyzed. In the model, each individual has two traits: trait x as a predator and trait y as a prey. These traits constitute a two-dimensional phenotype space, in which the whole group of individuals are represented
as a phenotype distribution. Predator–prey interactions among the phenotypes are determined by their relative positions in
the phenotype space. Each phenotypic cluster was treated as a species. Each species evolves in y to escape from predation, while it evolves in x to chase their prey. Analytical investigation provided two predictions. First, coupled evolutionary diversifications of y and x may occur when the x of predators have caught up with their prey’s y, which may be repeated. Second, complex food-webs may develop when species’ competitive strengths are kept similar within
the communities. If the functional response is close to the ratio-dependent response, the competitive strengths of all species
are similar when the relationship between predators and prey corresponds to the ideal free distribution (IFD). These predictions
were confirmed by numerical simulations.
Electronic supplementary material The online version of this article doi:() contains supplementary material, which is available to authorized users. 相似文献
3.
We examined properties of adaptive walks by the fittest on “rough Mt. Fuji-type” fitness landscapes, which are modeled by
superposing small uncorrelated random component on an additive fitness landscape. A single adaptive walk is carried out by
repetition of the evolution cycle composed of (1) mutagenesis process that produces random d-fold point mutants of population size N and (2) selection process that picks out the fittest mutant among them. To comprehend trajectories of the walkers, the fitness
landscape is mapped into a (x, y, z)-space, where x, y and z represent, respectively, normalized Hamming distance from the peak on the additive fitness landscape, scaled additive fitness
and scaled non-additive fitness. Thus a single adaptive walk is expressed as the dynamics of a particle in this space. We
drew the “hill-climbing” vector field, where each vector represents the most probable step for a walker in a single step.
Almost all of the walkers are expected to move along streams of vectors existing on a particular surface that overlies the
(x, y)-plane, toward the neighborhood of a characteristic point at which a mutation-selection-random drift balance is reached.
We could theoretically predict this reachable point in the case of random sampling search strategy.
Received: 1 March 2000 / Published online: 3 August 2000 相似文献
4.
F. Alba D. Nieto-Lugilde P. Comtois C. Díaz de la Guardia C. De Linares L. Ruiz 《Aerobiologia》2006,22(2):107-116
Estimations based upon geostatistics and mapping have enabled the construction of a spatial model to predict the presence of biological particles in a particular region. This methodological proposal has been tested in a case study, at a regional scale, of airborne Olea pollen, using the data acquired from␣various sampling stations that are designed for the aerobiological monitoring of pollen levels. These sampling stations have been set up in cities throughout the region of Andalusia (southern Spain) at sites with very different characteristics in terms of biogeography, bioclimate, topography and vegetation. Pollen counts were made daily at all sites during 2003 using a volumetric spore-trap. Data were comparatively analysed in classical diagrams and by means of spatial-temporal maps. Space-time models were constructed using three coordinates, x, y (the UTM coordinates of each sampling station) and z, (the aerobiological data compiled for a specific period). The aerobiological data were interpolated by applying the traditional geostatistical method of Kriging. The introduction of the variable “space” into the model allowed us to predict pollen levels in different areas throughout the region. The interpolation method was used to make weekly estimations of Olea pollen values in areas where there was no aerobiological sampling station. In addition, the maps generated present a two-dimensional vision of the study area, showing that bioclimatic diversity of this region promotes a step-wise flowering of Olea. 相似文献
5.
Fish and fisheries in the Upper Mekong: current assessment of the fish community, threats and conservation 总被引:2,自引:0,他引:2
Bin Kang Daming He Lisa Perrett Hongyuan Wang Wenxian Hu Weide Deng Yunfei Wu 《Reviews in Fish Biology and Fisheries》2009,19(4):465-480
The Mekong flows north to south, through six countries in south–east Asia. Many studies have concentrated on fish and fisheries
in the Lower Mekong, which has been identified as one of the largest inland fisheries in the world with an incredibly rich
diversity of species. In contrast, fish and fisheries in the Upper Mekong (Lancang River) have remained relatively undocumented.
In this paper, we synthesized information on freshwater fish biodiversity and fisheries in the Upper Mekong and documented
173 species and subspecies (including 87 endemic species) among 7 orders, 23 families and 100 genera. We divided the Upper
Mekong into 17 sub-basins based on Digital Elevation Model (DEM) and then used fish species data to cluster the sub-basins.
Four parts (the headwater, the upper reach, the middle reach and the lower reach) and one lake have distinct fish species
communities associated with them. There was a linear relationship between fish species (x) and endemic species (y) as y = 0.5464x − 3.2926. Relationship between species number or endemic species number (y) and mean altitude (x) can be described as y = −54.352 ln(x) + 460.79 or y = −30.381 ln(x) + 253.85, respectively. Fisheries kept as about 6,000 t from 1989 to 1998, and then steadily increased to 10,000 t in 2004.
We reviewed the overall threats to the Upper Mekong fish and fisheries, and found that hydrological alteration is the largest
threat in the basin, followed by over fishing and the introduction of exotic species. In terms of specific river sections,
water pollution was the most serious threat to fishes in the upper reach of the Upper Mekong, whilst migratory fishes in the
lower reach of the Upper Mekong are seriously threatened by the construction of cascade dams. The Buyuan River and the Nanla
River were identified as important feeding and spawning habitats for upstream migrant species and should be considered as
a priority for conservation. 相似文献
6.
The magnetic surface polaritons (MSPs) mode rarely exists in natural materials, mainly due to their limited magnetic response.
In order to understand the relationship between the MSPs mode and the limited magnetic response, we theoretically derive a
general dispersion equation of the MSPs mode for two kinds of biaxial anisotropic media. The dispersion equation suggests
the requirements of μ
x
< 0 < ε
z
, μ
x
μ
y
> 1, and momentum conservation need to be satisfied, which guides us to design a planar biaxial magnetic metamaterials (PBMM)
with two orthogonal negative permeabilities (i.e., μ
x
< 0 and μ
y
< 0). In addition, the results of the retrieval magnetic permeability and electric permittivity indeed point out that our
PBMM satisfies the aforementioned requirements. Meanwhile, we investigate the mechanism of the magnetic field by a consideration
of an induced current loop, and subsequently we demonstrate the artificial MSPs mode under transverse electric excitation
by numerical simulation. After a numerical fit of simulation results, we find that the field of the MSPs mode is in good agreement
with the analytical calculation of Maxwell’s equations. Moreover, we also simulate three unsatisfied aforementioned requirements
as control conditions to verify the general dispersion equation of the MSPs mode. 相似文献
7.
Following our established theoretical model to deal with the second-harmonic generation (SHG) excited by a linearly polarized
focused beam in type I collagen, in this paper, we further quantitatively characterize the differences between SHG emissions
in type I collagen excited by collimated and focused beams. The effects of the linear polarization angle (α) and the fibril polarity characterized by the hyperpolarizability ratio ρ on SHG emission has been compared under collimated and focused beam excitation, respectively. In particular, SHG emission
components along the i axis ( I2w,i )\left( {I_{2\omega {,}i} } \right) (i = x,y,z), the induced SHG emission deviation angle γ
ij
, and the detected SHG signals (I
2ω,ij
) in the ij plane by rotating the applied polarizer angle φ
ij
have been investigated (i = x, x, y; j = y, z, z). Results show that under our simulation model, SHG emission in the xy plane, such as I
2ω,x
,I
2ω,y
,γ
xy
and I
2ω,xy
varying as polarization angle (α) under collimated and focused light, presents no significant difference. The reverse of the fibril polarity has induced great
impact on I
2ω,x
,γ
xy
and I
2ω,xy
in both collimated and focused light. I
2ω,x
and γ
xy
show similarity, but I
2ω,xy
at α = 30° demonstrates a slight difference in focused light to that in collimated light. Under focused light, the reverse of
fibril polarity causes obvious changes of the collected SHG intensity I
2ω,xz
and I
2ω,yz
at a special polarization angle α = 60° and γ
xz
, γ
yz
along α. 相似文献
8.
Juan Guevara Roger D. Knapp John Spurlino B. V. Venkataram Prasad Joel D. Morrisett 《Journal of Protein Chemistry》1992,11(6):653-656
The three-dimensional coordinates for the -carbon atoms of crambin and basic pancreatic trypsin inhibitor (BPTI) were determined from the respective -carbon trace stereograms using an improved Simplex algorithm. This algorithm was used in a two-step process to estimate thez-coordinate values. In one approach, an average interatomic distance value, an approximate viewing angle, and a table of digitized values forx
left,y
left andx
right,y
right are provided in the first step. In the second step, thez-coordinate values are derived by varyingz to minimize the bond distance error (Rossmann and Argos, 1980). In another approach, only a reference bond distance table is provided along with the table ofx
left,y
left andx
right,y
right digitized values. In the first step, the viewing angle (), a combined scale and viewing distance parameter (q), a rotational angular distortion from digitizing and/or photocopying (z), and translational distortion factors (x
err andy
err) are calculated. In the second step, thez-coordinate values are varied to minimize the bond distance error. RMS difference values of less than 1.5 Å were obtained for both crambin and BPTI -carbon atoms. 相似文献
9.
The central-place forager in a social-insect colony, e.g., the bumblebee, has been expected to maximize its net rate of energy
gain to increase the success of its colony. In addition to foraging behavior, the nest location is an important factor for
the success of the colony. The bumblebee’s nest location would be affected by the spatial distribution of flowers and their
food quality. In this study, we constructed a model to estimate bumblebee nest sites, using the net energy intake rate at
available food sites for workers foraging from the nest site. We hypothesized that the probability of colony establishment
at a site in coordinates (x, y) was high as the sum of the net energy intake rate I(x, y) increased. To obtain I(x, y), nectar standing crop, sugar concentration, and foraging time were measured for ten plant species in the study site covering
6.25 km2. As available flowers changed seasonally, I(x, y) was calculated for three periods: the end of April, the beginning of May, and the middle of May. To verify our hypothesis,
we compared the estimations in our model with the actual nest sites of Bombus ardens found in the beginning of May and June by means of tracking bumblebees. From the results, we considered that the net energy
intake rate at mid-May might represent the probability of colony establishment, because it could affect colony persistence
and reproductive success. 相似文献
10.
Chantal N. van den Broek Arjen van der Horst Marcel C. M. Rutten Frans N. van de Vosse 《Biomechanics and modeling in mechanobiology》2011,10(2):249-258
Constitutive models describing the arterial mechanical behavior are important in the development of catheterization products,
to be used in arteries with a specific radius. To prove the possible existence of a constitutive model that, provided with
a generic set of material and geometric parameters, is able to predict the radius-specific mechanical behavior of a coronary
artery, the passive pressure–inner radius (P–r
i
) and pressure–axial force change (P–ΔF
z
) relations of seven porcine left anterior descending coronary arteries were measured in an in-vitro set-up and fitted with
the model of Driessen et al. in J Biomech Eng 127(3):494–503 (2005), Biomech Model Mechanobiol 7(2):93–103 (2008). Additionally,
the collagen volume fraction, physiological axial pre-stretch, and wall thickness to inner radius ratio at physiological loading
were determined for each artery. From this, two generic parameter sets, each comprising four material and three geometric
parameters, were obtained. These generic sets were used to compute the deformation of each tested artery using a single radius
measurement at physiological loading as an artery-specific input. Artery-specific P–r
i
and P–ΔF
z
relations were predicted with an accuracy of 32 μm (2.3%) and 6 mN (29% relative to ΔF
z
-range) on average compared to the relations measured in-vitro. It was concluded that the constitutive model provided with
the generic parameters found in this study can well predict artery-specific mechanical behavior. 相似文献
11.
Bending of z-lines by mechanical stimuli: An input signal for integrin dependent modulation of ion channels? 总被引:1,自引:1,他引:0
V. Dyachenko A. Christ R. Gubanov G. Isenberg 《Progress in biophysics and molecular biology》2008,97(2-3):196
We studied which components of mechanical cell deformation are involved in “stretch modulated ion currents” (SMIC). Murine ventricular myocytes were attached to glass coverslips and deformed in x, y and z with a 16 μm thin glass stylus (S) of calibrated stiffness. Three-dimensional confocal microscopy characterized cell deformation (T-tubular membranes, mitochondria) and bending of S (indicative of the applied force). Axial (x-) displacement of S sheared the upper cell part versus the attached bottom, close to S, it changed sarcomere length and bent z-lines (“z-line displacement”). Vertical (z-press) or transversal (y-shear) displacement of S bulged cytoplasm and mitochondria transversally without detectable z-line displacement.Axial stiffness increased with the extent of stress (“stress stiffening”). Depolymerization of F-actin or block of integrin receptors reduced stiffness. SMIC served as a proxy readout of deformation-induced signaling. Axial deformation activated a non-selective cation conductance (Gns) and deactivated an inwardly rectifying K+ conductance (GK1), z-press or y-shear did not induce SMIC. Depolymerization of F-actin or block of integrin receptors reduced SMIC. SMIC did not depend on changes in sarcomere length but correlated with the extent of z-line bending. We discuss that both shear stress at the attached cell bottom and z-line bending could activate mechanosensors. Since SMIC was absent during deformations without z-line bending we postulate that z-line bending is a necessary component for SMIC signaling. 相似文献
12.
Predictive models in aerobiology: data transformation 总被引:1,自引:1,他引:0
Francisco Javier Toro Marta Recio María del Mar Trigo Baltasar Cabezudo 《Aerobiologia》1998,14(2-3):179-184
This paper attempts to evaluate the effect of mathematical transformations of pollen and meteorogical data used in aerobiological
forecasting models. Stepwise multiple regression equations were developed in order to facilitate short term forecasts during
the pre-peak period. The daily mean pollen data (x
i) expressed as number of pollen grains per cubic metre of air were used directly and transformed into different scales: log(x
i + 1), ln((x
11000/Σp) + 1) and √x
i, where Σp is the sum of the daily mean values throughout the season. Thirteen meteorological parameters and the variable time were
used as forecasting variables. The most reliable forecasts were obtained with data transformed by ‘square root’ and with untransformed
data. Based on the results obtained, we recommend that the data be transformed by means of the square root if they do not
show a normal distribution and that non-linear statistics be used in this kind of study. 相似文献
13.
Porta A Furlan R Rimoldi O Pagani M Malliani A van de Borne P 《Biological cybernetics》2002,86(3):241-251
The coherence function measures the amount of correlation between two signals x and y as a function of the frequency, independently of their causal relationships. Therefore, the coherence function is not useful
in deciding whether an open-loop relationship between x and y is set (x acts on y, but the reverse relationship is prevented) or x and y interact in a closed loop (x affects y, and vice versa). This study proposes a method based on a bivariate autoregressive model to derive the strength of the causal
coupling on both arms of a closed loop. The method exploits the definition of causal coherence. After the closed-loop identification
of the model coefficients, the causal coherence is calculated by switching off separately the feedback or the feedforward
path, thus opening the closed loop and fixing causality. The method was tested in simulations and applied to evaluate the
degree of the causal coupling between two variables known to interact in a closed loop mainly at a low frequency (LF, around
0.1 Hz) and at a high frequency (HF, at the respiratory rate): the heart period (RR interval) and systolic arterial pressure
(SAP). In dogs at control, the RR interval and the SAP are highly correlated at HF. This coupling occurs in the causal direction
from the RR interval to the SAP (the mechanical path), while the coupling on the reverse causal direction (the baroreflex
path) is not significant, thus pointing out the importance of the direct effects of respiration on the RR interval. Total
baroreceptive denervation, by opening the closed loop at the level of the influences of SAP on RR interval, does not change
these results. In elderly healthy men at rest, the RR interval and SAP are highly correlated at the LF and the HF. At the
HF, a significant coupling in both causal directions is found, even though closed-loop interactions are detected in few cases.
At the LF, the link on the baroreflex pathway is negligible with respect to that on the reverse mechanical one. In heart transplant
recipients, in which SAP variations do not cause RR interval changes as a result of the cardiac denervation, the method correctly
detects a significant coupling only on the pathway from the RR interval to the SAP.
Received: 28 June 2001 / Accepted in revised form: 23 October 2001 相似文献
14.
A new system for understanding the biodiversity in different nature reserves: capacity, connectivity and quality of biodiversity 总被引:1,自引:0,他引:1
Zhenji Li Jiakuan Chen Yunqiu Ruan Ying Chang Wen Ye Luzhen Chen Dongliang Zhou 《Frontiers of Biology in China》2009,4(1):69-74
In this paper, we propose a new system for understanding the biodiversity in different conservation areas. It includes three
aspects: the capacity, the connectivity and the quality. The capacity refers to the numbers of biodiversity, including absolute
and relative richness of the vegetation types N
v
and D
v
=(N
v
−1)/lnA, species numbers S and richness of species d
Gl
=(S − 1)/lnA, and germ plasm resources within a nature reserve, and also the potential biological living space offered by the natural
resource. It comprises the total biological resources in a nature reserve. The connectivity refers to the flux of biodiversity,
including similarity and connected status of the vegetation types SI
Li
=2z/(x + y) and species numbers SI
C
=2z/(x + y) among different nature reserves. The quality refers to the stability of biodiversity, including relative species richness
index RS
Li
=d/d
max, relative vegetation richness index RV
Li
=D
v
/D
maxv
, fastness to invasion species ƒ
Li
=1−S
i
/S
t
, weighted values, representativeness and vulnerability of special vegetations, special species, CITES species and rare species
as the protected targets. 相似文献
15.
Charles Walter 《Bulletin of mathematical biology》1974,36(2):215-217
Models of biological development, evolution and control should take into account that very small numbers of cells or chemicals
or individuals eventually grow into stable, large populations. The simplified two-component model used in these studies includes
the following: (1) first-order decay; (2) first-order autocatalysis; (3) negative feedback; (4) positive feedback; (5) second-order
decay; (6) second-order autocatalysis. A positive definite Lyapunov function is constructed and shown to have a negative definite
total derivative. The stationary statex>0,y>0, therefore possesses global asymptotic stability. This means that sustained oscillations cannot occur. Another stationary
state,x=y=0, is shown to be unstable. This means that infinitesimally small perturbations ofx=y=0 will result in evolution of the variables to the stable stationary state. This result contrasts with that obtained with
the Lotka-Volterra model in that small perturbations ofx=y=0 for that model result in sustained, oscillating excursions; the smaller the initial perturbations, the larger these excursions
will be.
A simulation illustrates that stable populations of 1020
x's andy's can arise from a singlex andy.x grows more or less continuously, buty remains extremely small for 80 per cent of the time interval required for the variables to approach their stable populations.
Proceedings article from the Dissipative Structures section of the Tenth Symposium on Biomathematics and Computer Science
in the Life Sciences, University of Texas, Houston. March 29–31, 1973. Symposium Chairman: Stuart O. Zimmerman. Session Chairman
and Proceedings Editors: Charles Walter and Hugo M. Martinez. 相似文献
16.
Fangjun Bao Hao Chen Ye Yu Jiguo Yu Shi Zhou Jing Wang QinMei Wang Ahmed Elsheikh 《PloS one》2013,8(8)
Purpose
To investigate the bilateral symmetry of the global corneal topography in normal corneas with a wide range of curvature, astigmatism and thickness valuesDesign
Cross-Sectional StudyMethods
Topography images were recorded for the anterior and posterior surfaces of 342 participants using a Pentacam. Elevation data were fitted to a general quadratic model that considered both translational and rotational displacements. Comparisons between fellow corneas of estimates of corneal shape parameters (elevation, radius in two main directions, Rx and Ry, and corresponding shape factors, Qx and Qy) and corneal position parameters (translational displacements: x0, y0 and z0, and rotational displacements: α, β and γ) were statistically analyzed.Results
The general quadratic model provided average RMS of fit errors with the topography data of 1.7±0.6 µm and 5.7±1.3 µm in anterior and posterior corneal surfaces. The comparisons showed highly significant bilateral correlations with the differences between fellow corneas in Rx, Ry, Qx and Qy of anterior and posterior surfaces remaining insignificantly different from zero. Bilateral differences in elevation measurements at randomly-selected points in both corneal central and peripheral areas indicated strong mirror symmetry between fellow corneas. The mean geometric center (x0, y0, z0) of both right and left corneas was located on the temporal side and inferior-temporal side of the apex in anterior and posterior topography map, respectively. Rotational displacement angle α along X axis had similar distributions in bilateral corneas, while rotation angle β along Y axis showed both eyes tilting towards the nasal side. Further, rotation angle γ along Z axis, which is related to corneal astigmatism, showed clear mirror symmetry.Conclusions
Analysis of corneal topography demonstrated strong and statistically-significant mirror symmetry between bilateral corneas. This characteristic could help in detection of pathological abnormalities, disease diagnosis, measurement validation and surgery planning. 相似文献17.
In this work we address the problem of the robust identification of unknown parameters of a cell population dynamics model
from experimental data on the kinetics of cells labelled with a fluorescence marker defining the division age of the cell.
The model is formulated by a first order hyperbolic PDE for the distribution of cells with respect to the structure variable
x (or z) being the intensity level (or the log10-transformed intensity level) of the marker. The parameters of the model are the rate functions of cell division, death, label
decay and the label dilution factor. We develop a computational approach to the identification of the model parameters with
a particular focus on the cell birth rate α(z) as a function of the marker intensity, assuming the other model parameters are scalars to be estimated. To solve the inverse
problem numerically, we parameterize α(z) and apply a maximum likelihood approach. The parametrization is based on cubic Hermite splines defined on a coarse mesh
with either equally spaced a priori fixed nodes or nodes to be determined in the parameter estimation procedure. Ill-posedness
of the inverse problem is indicated by multiple minima. To treat the ill-posed problem, we apply Tikhonov regularization with
the regularization parameter determined by the discrepancy principle. We show that the solution of the regularized parameter
estimation problem is consistent with the data set with an accuracy within the noise level in the measurements.
相似文献
18.
Kram Rodger; Griffin Timothy M.; Donelan J. Maxwell; Chang Young Hui 《Journal of applied physiology》1998,85(2):764-769
Weconstructed a force treadmill to measure the vertical, horizontal andlateral components of the ground-reaction forces (Fz,Fy,Fx, respectively) and the ground-reaction force moments(Mz,My,Mx), respectively exerted bywalking and running humans. The chassis of a custom-built, lightweight(90 kg), mechanically stiff treadmill was supported along its length bya large commercial force platform. The natural frequencies of vibrationwere >178 Hz for Fz and >87Hz for Fy, i.e., well above thesignal content of these ground-reaction forces. Mechanical tests andcomparisons with data obtained from a force platform runway indicatedthat the force treadmill recordedFz,Fy,Mx andMy ground-reaction forces andmoments accurately. Although the lowest natural frequency of vibrationwas 88 Hz for Fx, thesignal-to-noise ratios for Fx andMz were unacceptable. This devicegreatly decreases the time and laboratory space required for locomotionexperiments and clinical evaluations. The modular design allows forindependent use of both treadmill and force platform. 相似文献
19.
Structure, above-ground biomass and dynamics of mangrove ecosystems: new data from French Guiana 总被引:5,自引:0,他引:5
The article presents new results on the structure and the above-ground biomass of the various population types of mangroves
in French Guiana. Nine mangrove stands were studied, each composed of three to ten adjoining plots with areas that varied
depending on the density of the populations. Structural parameters and indices were calculated. Individuals representative
of the three groups of taxa present were felled:Avicennia germinans (L) Stearn, Rhizophora spp., and Laguncularia racemosa (L) Gaertn. The trunks, branches and leaves were sorted and weighed separately. The biomass was obtained by determining the
allometric relationships, the general equation selected being of the type y = a
o
x
a1, where the diameter (x) is the predictive variable. The total above-ground biomass varied from 31 t ha−1 for the pioneer stages to 315 t ha−1 for mature coastal mangroves, but with large variations depending on the structural characteristics at each site. The results
place the Guianese mangroves among those with high biomass, although lower than those reported for Asia. Based on the relationships
between structural parameters and standing biomass, in particular with the use of the “self-thinning rule”, population dynamics
models are proposed.
Received: 16 August 1996 / Accepted 17 January 1998 相似文献
20.
The flowering integrator gene FLOWERING LOCUS T (FT) in Arabidopsis thaliana is conserved between diverse plant species and is thought to be the flowering signal ‘‘florigen’’, a universal long-distance
mobile signal. In soybean, two FT homologs having a function to induce flowering in Arabidopsis have been identified. In this study, we showed that the expression
of FT from Arabidopsis by the Apple latent spherical virus (ALSV) vector promoted precocious flowering and terminated vegetative growth in a wide range of genotypes of soybean, without
using a short-day treatment. Four determinate and two indeterminate cultivars, infected with ALSV expressing FT (FT-ALSV), set flower buds on shoot apices and terminated vegetative growth at the fourth- to seventh-node stages under long-day
conditions. In contrast, non-infected, healthy plants did not set flower buds on shoot apices at the same stage under the
same conditions. After flowering, soybean cultivars infected with FT-ALSV, belonging to different maturity groups and stem
growth habits, matured and produced seeds. The results suggest that the basic flowering pathway controlled by FT in A. thaliana might also be conserved in soybean. A system for precocious flowering and shortening of generation time using FT-ALSV would
be a useful and novel technology for efficient soybean breeding. 相似文献