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Since tropical rain forests are widely threatened by conversion to agriculture, even within protected areas, an understanding of recovery processes is important for restoration of forest ecosystems and thus conservation of their biodiversity. Secondary succession following land clearance and crop cultivation was studied in a lower montane rain forest in a protected area of the Venezuelan Cordillera de la Costa Central. Forest recovery was studied using a chronosequence of eight 20 × 20 m plots which represented four forest types ca.10 year-old Secondary Forest, ca. 20 year-old Secondary Forest, ca. 35 year-old (uncultivated) secondary forest and mature forest. Species richness and structural complexity increased during succession, with the oldest secondary forest having a physiognomy comparable to the mature forest. Species diversity was lower in the secondary forests than the mature forest, and their floristic composition was distinct. Four phases are hypothesized to occur in the succession process, each with a distinctive species assemblage: initial colonisation by non-woody vegetation; establishment and canopy closure by short-lived small-seeded woody pioneer species; replacement by longer-lived secondary species; and gradual replacement by mature forest large-seeded climax species. Full recovery of the forests in the protected area is likely to take many years, although it may be assisted through conservation management measures.  相似文献   
123.
In this paper, we apply mixture theory to quantitatively predict the transient behavior of drug delivery by using a microneedle array inserted into tissue. In the framework of mixture theory, biological tissue is treated as a multi-phase fluid saturated porous medium, where the mathematical behavior of the tissue is characterized by the conservation equations of multi-phase models. Drug delivery by microneedle array imposes additional requirements on the simulation procedures, including drug absorption by the blood capillaries and tissue cells, as well as a moving interface along its flowing pathway. The contribution of this paper is to combine mixture theory with the moving mesh methods in modeling the transient behavior of drug delivery into tissue. Numerical simulations are provided to obtain drug concentration distributions into tissues and capillaries.  相似文献   
124.
Binocular rivalry occurs when incongruent patterns are presented to corresponding regions of the retinas, leading to fluctuations of awareness between the patterns . One attribute of a stimulus may rival whereas another may combine between the eyes , but it is typically assumed that the dominant features are perceived veridically. Here, we show this is not necessarily the case and that a suppressed visual feature can alter dominant perception. The cortical representations of oriented gratings can interact even when one of them is perceptually suppressed, such that the perceived orientation of the dominant grating is systematically biased depending on the orientation of the suppressed grating. A suppressed inducing pattern has the same qualitative effect as a visible one, but suppression reduces effective contrast by a factor of around six. A simple neural model quantifies and helps explain these illusions. These results demonstrate that binocular rivalry suppression operates in a graded fashion across multiple sites in the visual hierarchy rather than truncating processing at a single site and that suppressed visual information can alter dominant vision in real-time.  相似文献   
125.
Despite concerns regarding the environmental impacts of microplastics, knowledge of the incidence and levels of synthetic particles in large marine vertebrates is lacking. Here, we utilize an optimized enzymatic digestion methodology, previously developed for zooplankton, to explore whether synthetic particles could be isolated from marine turtle ingesta. We report the presence of synthetic particles in every turtle subjected to investigation (n = 102) which included individuals from all seven species of marine turtle, sampled from three ocean basins (Atlantic [ATL]: n = 30, four species; Mediterranean (MED): n = 56, two species; Pacific (PAC): n = 16, five species). Most particles (n = 811) were fibres (ATL: 77.1% MED: 85.3% PAC: 64.8%) with blue and black being the dominant colours. In lesser quantities were fragments (ATL: 22.9%: MED: 14.7% PAC: 20.2%) and microbeads (4.8%; PAC only; to our knowledge the first isolation of microbeads from marine megavertebrates). Fourier transform infrared spectroscopy (FT‐IR) of a subsample of particles (n = 169) showed a range of synthetic materials such as elastomers (MED: 61.2%; PAC: 3.4%), thermoplastics (ATL: 36.8%: MED: 20.7% PAC: 27.7%) and synthetic regenerated cellulosic fibres (SRCF; ATL: 63.2%: MED: 5.8% PAC: 68.9%). Synthetic particles being isolated from species occupying different trophic levels suggest the possibility of multiple ingestion pathways. These include exposure from polluted seawater and sediments and/or additional trophic transfer from contaminated prey/forage items. We assess the likelihood that microplastic ingestion presents a significant conservation problem at current levels compared to other anthropogenic threats.  相似文献   
126.
DetectionandAnalysisofanEstrous-associatedOviductalGlycoproteinDNAFragmentfromPrimatesbyPCR¥CHENQing-xuan(陈清轩);ClaytonE.Walto...  相似文献   
127.
ATP binding cassette transporter A1 (ABCA1) is a widely expressed lipid transporter essential for the generation of HDL. ABCA1 is particularly abundant in the liver, suggesting that the liver may play a major role in HDL homeostasis. To determine how hepatic ABCA1 affects plasma HDL cholesterol levels, we treated mice with an adenovirus (Ad)-expressing human ABCA1 under the control of the cytomegalovirus promoter. Treated mice showed a dose-dependent increase in hepatic ABCA1 protein, ranging from 1.2-fold to 8.3-fold using doses from 5 x 108 to 1.5 x 109 pfu, with maximal expression observed on Day 3 posttreatment. A selective increase in HDL cholesterol occurred at Day 3 in mice treated with 5 x 108 pfu Ad-ABCA1, but higher doses did not further elevate HDL cholesterol levels. In contrast, total cholesterol, triglycerides, phospholipids, non-HDL cholesterol, and apolipoprotein B levels all increased in a dose-dependent manner, suggesting that excessive overexpression of hepatic ABCA1 in the absence of its normal regulatory sequences altered total lipid homeostasis. At comparable expression levels, bacterial artificial chromosome transgenic mice, which express ABCA1 under the control of its endogenous regulatory sequences, showed a greater and more specific increase in HDL cholesterol than Ad-ABCA1-treated mice. Our results suggest that appropriate regulation of ABCA1 is critical for a selective increase in HDL cholesterol levels.  相似文献   
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129.
Few techniques are suited to probe the structure and dynamics of molecular complexes at the mesoscale level (100–1000 nm). We have developed a single-molecule technique that uses tracking fluorescence correlation spectroscopy (tFCS) to probe the conformation and dynamics of mesoscale molecular assemblies. tFCS measures the distance fluctuations between two fluorescently labeled sites within an untethered, freely diffusing biomolecule. To achieve subdiffraction spatial resolution, we developed a feedback scheme that allows us to maintain the molecule at an optimal position within the laser intensity gradient for fluorescence correlation spectroscopy. We characterized tFCS spatial sensitivity by measuring the Brownian end-to-end dynamics of DNA molecules as short as 1000 bp. We demonstrate that tFCS detects changes in the compaction of reconstituted nucleosome arrays and can assay transient protein-mediated interactions between distant sites in an individual DNA molecule. Our measurements highlight the applicability of tFCS to a wide variety of biochemical processes involving mesoscale conformational dynamics.  相似文献   
130.
Thraustochytrids are large-celled marine heterokonts and classified as oleaginous microorganisms due to their production of docosahexaenoic (DHA) and eicosapentaenoic (EPA) ω-3-fatty acids. The applications of microbial DHA and EPA for human health are rapidly expanding, and a large number of clinical trials have been carried out to verify their efficacy. The development of refined isolation and identification techniques is important for the cultivation of thraustochytrids. With a high proportion of lipid biomass, thraustochytrids are also amenable to various production strategies which increase omega-3 oil output. Modifications to the existing lipid extraction methods and utilisation of sophisticated analytical instruments have increased extraction yields of DHA and EPA. Other metabolites such as enzymes, carotenoids and extracellular polysaccharides can also be obtained from these marine protists. Approaches such as the exploration for more diverse isolates having fast growth rates, metabolic engineering including gene cloning, and growing thraustochytrids on alternate low cost carbon source, will further enhance the biotechnological potential of thraustochytrids.  相似文献   
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