Comparative reproductive biology of two southwestern Atlantic populations of the hermit crab Pagurus exilis (Crustacea: Anomura: Paguridae)     

Mariana Terossi  Lucas S. Torati  Ivana Miranda  Marcelo A. Scelzo  Fernando L. Mantelatto 《Marine Ecology》2010,31(4):584-591

Pagurus exilis (Benedict, 1892) is an endemic South Atlantic hermit crab with a distribution ranging from Rio de Janeiro State, Brazil, to Buenos Aires Province, Argentina. The present study analyzed the reproduction of two populations at the extremes of this geographical distribution, and compared their reproductive period, fecundity, and changes in egg size and egg volume during the incubation period in order to assess the variability over this latitudinal range. Hermit crabs were collected monthly over a 2‐year period. In total, 108 females were analyzed for Brazil (44 non‐ovigerous and 64 ovigerous), and 141 for Argentina (87 non‐ovigerous and 54 ovigerous). Reproduction in Brazil occurs year‐round, with peaks in the fall and winter seasons; in Argentina reproduction occurs only in spring and summer. The Brazilian ovigerous females were significantly larger than the Argentina ones (Brazil: SL = 5.33 ± 1.45 mm; Argentina: SL = 4.15 ± 0.52 mm; P < 0.001). The fecundity was 1447 ± 831 eggs (317 to 2885) in Brazil and 987 ± 711 eggs (114 to 2665) in Argentina, with a trend towards higher fecundity in Brazil. Eggs in the Argentina population were larger than those in Brazil for all the three stages investigated, and no changes in egg volume were found during egg development for both populations. The reproductive traits of the two populations showed some important differences, which may reflect adaptations to local environmental conditions, demonstrating a high plasticity of reproductive features of the species in Brazilian and Argentine waters. The strategy adopted by the Argentina population involves a lower production of larger eggs compared to the population in Brazil; this lower production is associated with reproduction in cold‐water regions.  相似文献   

Evaluation of damping reduction factors for estimating elastic response of structures with high damping     

Yu‐Yuan Lin  Eduardo Miranda  Kuo‐Chun Chang 《地震工程与结构动力学》2005,34(11):1427-1443

The damping reduction factors are used in a few building codes in order to estimate the elastic response spectrum with high damping ratios from its 5%‐damped counterpart. At present, much research regarding this factor has been published. The purpose of this paper is to evaluate the accuracy of five different models of damping reduction factors. In addition, the damping reduction factors adopted in the recent U.S.A. seismic codes are also evaluated. Statistical studies are carried out according to a total of 216 earthquake ground motions recorded on firm sites in California. Considered here are elastic single‐degree‐of‐freedom (SDOF) systems with natural vibrating periods between 0.1 and 6.0 s. Mean ratios and dispersion of approximate to exact maximum elastic displacement demands corresponding to various damping reduction factors are computed as functions of the natural vibrating period and the viscous damping ratio. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Angular velocities of Nubia and Somalia from continuous GPS data: implications on present-day relative kinematics   总被引：3，自引：0，他引：3  

R.M.S Fernandes  B.A.C Ambrosius  L Bastos  J.M Miranda 《Earth and Planetary Science Letters》2004,222(1):197-208

This study focuses on the break-up of the African tectonic plate into separate Nubian and Somalian blocks, based on recent Global Positioning System (GPS) data. A new, unique velocity field has been obtained by processing all available observations of permanent GPS stations on Africa since 1996. The quantity and distribution of the stations and the length of the time-series of observations exceed that of previous studies by a considerable margin, allowing one to derive a reliable estimate of the differential motion between the Nubia and Somalian plates, which are considered as a single (African) block in the prevailing global tectonic plate models. The estimated relative pole of rotation of Somalia with respect to Nubia is located at 54.8°S; 37.0°E with magnitude −0.069°/Ma, implying distinct opening in the Ethiopian Rift of magnitude ≈7 mm/year and azimuth ≈N94°E, whereas in southeastern South Africa this value is reduced to ≈2 mm/year in almost the same direction. This is in accordance with some of the independent geological and geophysical tectonic models of the Nubia-Somalia plate boundary region. However, the spatial density of the current tracking network is still not optimal to establish the exact location of the entire Somalia-Nubia plate boundary; in particular, the possible branch east of Lake Victoria and heading towards the Mozambique Channel is impossible to confirm or reject at this moment.  相似文献   

Geographic Training and Urban Planning     

Russell B. Adams  Edward G. Miranda 《The Professional geographer》1967,19(3):151-153

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Climatic change and rainfall patterns: Effects on semi-arid plant communities of the Iberian Southeast     

J.D. Miranda  C. Armas  F.M. Padilla  F.I. Pugnaire 《Journal of Arid Environments》2011,75(12):1302-1309

The structure and functioning of semi-arid ecosystems are strongly influenced by precipitation patterns. Water availability in such environments is highly pulsed, and discrete rainfall events interspersed with drought periods are important components of the annual water supply. Plant communities do not only respond to rainfall quantity, but also to variations in time, so that relatively small changes in rainfall frequency (i.e., pulsed inputs) may have strong effects on communities. Within the Mediterranean basin, climate change models forecast a decrease in mean annual precipitation and more extreme events (i.e., less rainy days and longer drought periods between events), along with seasonal changes. However, little is known on the consequences of these future precipitation changes on plant communities, especially in semi-arid environments. Here, we summarize the few experiments that have manipulated rainfall patterns in arid and semi-arid areas worldwide, and introduce the first results of a pioneer, long-term rainfall exclusion in the semi-arid southeast region of the Iberian Peninsula. The experiment is not only manipulating the amount of rainfall, but also its frequency and seasonal distribution in a grassland-shrubland in the Tabernas desert (Almería, Spain). This work monitored the effect of precipitation changes on different ecosystem processes for five years, at the species and community level, concluding that this plant community (as other communities studied in the same area) exhibited great resilience to changes in rainfall availability, likely caused by plant adaptation to large intra- and inter-annual precipitation variability.  相似文献   

Seed magnetic Fields Generated by Primordial Supernova Explosions     

Oswaldo D. Miranda  Merav Opher  & Reuven Opher 《Monthly notices of the Royal Astronomical Society》1998,301(2):547-550

The origin of the magnetic field in galaxies is an open question in astrophysics. Several mechanisms have been proposed related, in general, to the generation of small seed fields amplified by a dynamo mechanism. In general, these mechanisms have difficulty in satisfying both the requirements of a sufficiently high strength for the magnetic field and the necessary large coherent scales. We show that the formation of dense and turbulent shells of matter, in the multiple explosion scenario of Miranda &38; Opher for the formation of the large-scale structures of the Universe, can naturally act as a seed for the generation of a magnetic field. During the collapse and explosion of Population III objects, a temperature gradient not parallel to a density gradient can naturally be established, producing a seed magnetic field through the Biermann battery mechanism. We show that seed magnetic fields ∼ 10⁻¹²–10⁻¹⁴ G can be produced in this multiple explosion scenario on scales of the order of clusters of galaxies (with coherence length L  ∼ 1.8 Mpc) and up to ∼ 4.5 × 10⁻¹⁰ G on scales of galaxies ( L  ∼ 100 kpc).  相似文献   

An improved implicit-explicit time integration method for structural dynamics     

Isidoro Miranda  Robert M. Ferencz  Thomas J. R. Hughes 《地震工程与结构动力学》1989,18(5):643-653

An explicit predictor-corrector algorithm is derived from the implicit α-method. This explicit algorithm is shown to have better stability and accuracy properties than its Newmark-based predecessor. This algorithm is then combined with the implicit α-method, resulting in an implicit-explicit α-method which can be effectively utilized for linear and non-linear structural dynamics calculations.  相似文献   

Changes in zooplankton diversity and distribution pattern under varying precipitation regimes in a southern temperate estuary     

Ana Lígia Primo  Ulisses Miranda AzeiteiroSónia Cotrim Marques  Filipe MartinhoMiguel Ângelo Pardal 《Estuarine, Coastal and Shelf Science》2009

The influence of climate variability on the diversity and distribution patterns of zooplankton communities was investigated in the Mondego estuary (Portugal) during four consecutive years characterized by highly variable precipitation and, consequently, river flow regime. Monthly samples were collected along the estuarine gradient at five sampling stations. Seasonal, inter-annual and spatial distributions were evaluated by multivariate analyses and three diversity indices were applied (Species number, Shannon Diversity and Average Taxonomic Distinctness). A two-year drought period presented significant differences in salinity values, especially in 2005 (extreme drought event). During the study period, copepoda was the main dominant group and Acartia tonsa the most abundant species, with the exception of autumn 2006, where high abundances of the cladoceran Penilia avirostris were noticed. Multivariate analysis indicated that zooplankton communities changed from a pre- to a post-drought period indicating the influence of hydrological parameters in communities' structure. The dry period was associated with an increase in zooplankton density, a reduction in seasonality and higher abundance and prevalence of marine species throughout the year. Seasonally, winter/spring communities were distinct from those in summer/autumn. Spatially, salinity-associated differences between upstream and downstream communities were reduced during the drought years, but during the post-drought year, these differences were detected again.  相似文献   

Truncated Gaussian Simulation to Map the Spatial Heterogeneity of Rock Mass Rating     

Marisa Pinheiro  Xavier Emery  Tiago Miranda  Javier Vallejos 《Rock Mechanics and Rock Engineering》2016,49(8):3371-3376

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Use of spatial regression models in the analysis of burnings and deforestation occurrences in forest region,Amazon, Brazil     

Camil Wadih Salame  Joaquim Carlos Barbosa Queiroz  Gilberto de Miranda Rocha  Mario Miguel Amin  Edson Paulino da Rocha 《Environmental Earth Sciences》2016,75(3):274

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