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排序方式: 共有780条查询结果,搜索用时 15 毫秒
101.
Eric Tabacchi Eduardo Gonzlez Dov Corenblit Virginia Garfano‐Gmez Anne‐Marie Planty‐Tabacchi Johannes Steiger 《河流研究与利用》2019,35(8):1228-1240
Plant communities and dynamics can be characterized according to species composition or plant traits. Here, we used species composition and plant traits to compare their effectiveness in discriminating the biogeomorphological (involving reciprocal feedbacks between physical and biological processes) and ecological (mainly biologically driven) phases of the fluvial biogeomorphological succession (FBS) model. The comparison was done between two French rivers, the largely unchannelized lower Allier and the channelized middle Garonne. One reach representative of each river section was selected for the study. Within each river reach, we chose two contrasted study sites in terms of channel and floodplain dynamics: a reference site (least altered channel and floodplain dynamics) and an altered site (laterally stabilized by riprap and constrained). In the four study sites, we sampled vegetation in 402 plots of 4 m2. The 512 species identified in the plots were characterized in terms of plant traits (20) from a literature review. When comparing reaches in unconstrained ordinations and permutational multivariate analyses of variance, both species composition and plant traits led to a similar identification of the biogeomorphological and the ecological successional trajectories. Nevertheless, the trait approach was less influenced by local and regional bioclimatic, hydrogeomorphological, and anthropogenic settings and thus produced a more comprehensive and general classification of the biogeomorphological and ecological phases of the FBS model. A lower than expected contrast between the four sites was found, because neither species composition nor plant traits could entirely characterize distinct successional trajectories occurring in our reference or altered sites. Furthermore, our results contributed to a better understanding of the multiple successional trajectories that can occur in midlatitude river corridors. It also showed that relating plant traits to their effects on fluvial landform dynamics remains a core challenge in explaining succession including feedback mechanisms between hydrology, morphodynamics, and vegetation dynamics. 相似文献
102.
The acrosome of the mature spermatozoon functions as a regulated secretory vesicle which performs several critical functions in mammalian fertilization. Acrosome assembly occurs throughout spermiogenesis and continues during posttesticular sperm maturation in the epididymis, resulting in a structurally polarized membrane-bounded organelle that contains an assortment of hydrolases and a stable infrastructure termed the acrosomal matrix. The role of stable acrosomal matrix assemblies in acrosomal biogenesis and function are poorly understood. This article presents ultrastructural, immunocytochemical, and biochemical data on the remodeling of the hamster acrosomal matrix during spermiogenesis and posttesticular sperm maturation in the epididymis. Specific posttranslational modifications of the major acrosomal matrix protein are evident in late, step 16, spermatids and matrix protein processing continues within specific acrosomal subdomains of caput epididymal spermatozoa. At the completion of sperm maturation, the acrosomal matrix consists of two structurally distinct domains which are adherent to the outer acrosomal membrane and exhibit a localized distribution pattern. Coincident with acrosomal matrix differentiation, a paracrystalline cytoskeletal complex is assembled onto the outer acrosomal membrane of epididymal spermatozoa. This cytoskeletal network appears to establish transmembrane structural interactions with the acrosomal matrix and may maintain attachment of the acrosomal cap to the sperm head during the early steps of the acrosome reaction. 相似文献
103.
Cathren E. Gowenlock Virginia Gomez James D. McGettrick Enrico Andreoli Andrew R. Barron 《Journal of Coatings Technology and Research》2017,14(1):195-205
Isonicotinate self-assembled monolayers (SAM) were prepared on alumina surfaces (A) using isonicotinic acid (iNA). These functionalized layers (iNA-A) were used for the seeded growth of copper films (Cu-iNA-A) by hydrazine hydrate-initiated electroless deposition. The films were characterized by scanning electron microscopy (SEM), electron-dispersive X-ray spectroscopy, atomic force microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and advancing contact angle measurements. The films are Cu0 but with surface oxidation, and show a faceted morphology, which is more textured (R q = 460 ± 90 nm) compared to the SAM (R q = 2.8 ± 0.5 nm). In contrast, growth of copper films by SnCl2/PdCl2 catalyzed electroless deposition, using formaldehyde (CH2O) as the reducing agent, shows a nodular morphology on top of a relatively smooth surface. No copper films are observed in the absence of the isonicotinate SAM. The binding of Cu2+ to the iNA is proposed to facilitate reduction to Cu0 and create the seed for subsequent growth. The films show good adhesion to the functionalized surface. 相似文献
104.
An anaerobic sludge blanket process, termed the anaerobic baffled reactor (ABR), has been developed and shows promise for industrial wastewater treatment. It combines the advantages of high stability and reliability with a high void volume. The risk of clogging and sludge bed expansion with resulting high microbial losses is reduced and there is no need for special gas collection or biological solids separation systems. Organic loadings as high as 36 g COD l?1day?1 have been achieved with COD removal rates of more than 24 g COD l?1 day?1 and methane production rates exceeding 6 volumes per day per unit volume of reactor. The hypothesis, that the ABR may be adequately modeled as a fixed-film reactor, has been supported. Therefore, a unified approach, based on fundamentals of bacterial kinetics and mass transport, appears useful for modeling this and similar systems. Pilot plant studies are necessary to determine the scaling factors of the system as well as the overall efficiency and costs. 相似文献
105.
Perfusion in microfluidic cross-flow: separation of white blood cells from whole blood and exchange of medium in a continuous flow 总被引:1,自引:0,他引:1
We describe a microfluidic technique for separation of particles and cells and a device that employs this technique to separate white blood cells (WBC) from whole human blood. The separation is performed in cross-flow in an array of microchannels with a deep main channel and large number of orthogonal, shallow side channels. As a suspension of particles advances through the main channel, a perfusion flow through the side channels gradually exchanges the medium of the suspension and washes away particles that are sufficiently small to enter the shallow side channels. The microfluidic device is tested with a suspension of polystyrene beads and is shown to efficaciously exchange the carrier medium while retaining all beads. In tests with whole human blood, the device is shown to reduce the content of red blood cells (RBC) by a factor of approximately 4000 with retention of 98% of WBCs. The ratio between WBCs and RBCs reached at an outlet of the device is 2.4 on average. The device is made of a single cast of poly(dimethylsiloxane) sealed with a cover glass and is simple to fabricate. The proposed technique of separation by perfusion in continuous cross-flow could be used to enrich rare populations of cells based on differences in size, shape, and deformability. 相似文献
106.
In this work, we report on the applicability of two-dimensional high-performance liquid chromatography (2D-HPLC) for the comprehensive characterization of inactivated influenza vaccine proteins. This novel procedure features minimal sample treatment and combines the on-line coupling of size exclusion HPLC to reversed-phase HPLC. A comparative analysis of commercial vaccines from three different manufacturers showed the method to be highly selective by providing characteristic reproducible chromatographic profiles for each vaccine. In addition, the method provided enhanced sensitivity for most constituents as a result of the use of native fluorescence detection in the reversed-phase HPLC step. The limits of detection (at a signal-to-noise ratio of >3) for hemagglutinin (HA) antigens were 105 and 172 ng/mL for influenza A/New Caledonia/20/99 and B/Jiangsu/10/2003 strains, respectively. The potential of this 2D-HPLC procedure in terms of quantitative antigen analysis was assessed by determination of the HA content of commercial vaccines. Results provided very good correlation with nominal HA values. The reproducibility (RSD) of the whole procedure was also evaluated and was found to be better than 2 and 3% for calculated antigen concentrations expressed as micrograms of HA per milliliter in commercial vaccines for samples of the same lot (n = 5) or different lots (n = 3), respectively. In addition, it allowed the selective detection of several influenza constituents including nucleoproteins from type A and B viruses and the highly hydrophobic matrix protein 1 from both virus strains. 相似文献
107.
de Paula M Goissis G Martins VC 《Journal of materials science. Materials in medicine》2007,18(9):1683-1690
The present paper describes the rheological properties of anionic collagen gels and anionic collagen:rhamsan composites gels
in the concentration of 0.7, 4 and 6%, estimated to be used as injectable biomaterials for plastic reconstruction. Rheological
studies of these gels showed that independently of pH, composition and concentration the viscoelastic behavior was dependent
on the frequency, with the storage modulus always greater than the loss modulus (G′ > G″ and δ < 45°). Creep experiments showed
that anionic collagen:rhamsan composites equilibrated at pH 7.4 were less elastic and more susceptible to deformation in comparison
to gels equilibrated at pH 3.5. Flow experiments indicated that the force needed for the extrusion of anionic collagen:rhamsan
composites, in comparison to anionic collagen, was significantly smaller and with a smoother flow, suggesting the association
with rhamsan may be a good alternative in the replacement of glutaraldehyde to stabilize the microfibril assembly of commercial
collagen gel preparations. Finally, on the basis of dynamic viscosity profiles found for different preparations, some of these
composites are potential candidates to be utilized in laryngology. 相似文献
108.
The susceptibility of 440 Listeria monocytogenes strains isolated from food (n=401) and clinical cases (n=39) between 1995 and 2005 was determined by standard agar dilution and E-test methods. Antimicrobial drugs currently used in veterinary and human therapy were tested, and they included penicillin G, ampicillin, cephalothin, gentamicin, chloramphenicol, tetracycline, doxycycline, trimethoprim, erythromycin, and clindamycin. The sensitivity of strains was established using Clinical and Laboratory Standards Institute (formerly NCCLS) breakpoints and MIC50 (the MIC for 50% of the strains) to MIC90 values. In general, isolates were susceptible to the majority of the antimicrobials tested, including beta-lactamics and aminoglycosides, which are normally used in the treatment of listeriosis. Resistance to tetracycline and doxycycline was found in five strains isolated from fresh trout belonging to the same fish farm. Molecular analysis by restriction endonuclease analysis showed a similar profile, suggesting the persistence of a strain well adapted to the presence of tetracycline in the environment of a fish farm, which is frequently used in aquaculture in order to prevent infections of fish. 相似文献
109.
Almela L Rabe V Sánchez B Torrella F López-Pérez JP Gabaldón JA Guardiola L 《Food microbiology》2007,24(4):319-327
The occurrence of ochratoxin A (OA) in paprika elaborated from peppers grown in several countries (Peru, Brazil, Zimbabwe and Spain) was studied, using an immunoaffinity clean-up column coupled to liquid chromatography and fluorescence detection. The preparation of the methyl ester (OA-Me) and liquid chromatography-electrospray-ion trap-mass spectrometry was used both to confirm the identity of the chromatographic peak that correspond to OA and to quantify it at low levels or in dirty fractions. A total of 115 strains of moulds were isolated; 85 of the fungal strains were obtained from OA contaminated paprika samples and identified as belonging to the Aspergillus Section Circumdati group (A. ochraceus) and Section Nigri group (A. niger, A. carbonarius). Among the latter ones, 31% of the A. ochraceus isolates and one A. niger were OA producers in vitro. None of the mould strains isolated from paprika samples with undetectable levels of OA or concentrations below 1 microg kg(-1) were toxin producers. Great differences in OA content in paprika samples were found, and a relationship with the climatic conditions of the geographic origin of the samples, and with cultural and technical practices in pepper manipulation is suggested. 相似文献
110.
Jacobs BW Ayres VM Petkov MP Halpern JB He M Baczewski AD McElroy K Crimp MA Zhang J Shaw HC 《Nano letters》2007,7(5):1435-1438
We report a new biphasic crystalline wurtzite/zinc-blende homostructure in gallium nitride nanowires. Cathodoluminescence was used to quantitatively measure the wurtzite and zinc-blende band gaps. High-resolution transmission electron microscopy was used to identify distinct wurtzite and zinc-blende crystalline phases within single nanowires through the use of selected area electron diffraction, electron dispersive spectroscopy, electron energy loss spectroscopy, and fast Fourier transform techniques. A mechanism for growth is identified. 相似文献