518 research outputs found
UV-isomerisation in nematic elastomers as a route to photo-mechanical transducer
The macroscopic shape of liquid crystalline elastomers strongly depends on
the order parameter of the mesogenic groups. This order can be manipulated if
photoisomerisable groups, e.g. containing N=N bonds, are introduced into the
material. We have explored the large photo-mechanical response of such an
azobenzene-containing nematic elastomer at different temperatures, using force
and optical birefringence measurements, and focusing on fundamental aspects of
population dynamics and the related speed and repeatability of the response.
The characteristic time of ``on'' and ``off'' regimes strongly depends on
temperature, but is generally found to be very long. We were able to verify
that the macroscopic relaxation of the elastomer is determined by the nematic
order dynamics and not, for instance, by the polymer network relaxation.Comment: Latex (EPJE class) 12 figure
Nematic elastomers with aligned carbon nanotubes: new electromechanical actuators
We demonstrate, for the first time, the large electromechanical response in
nematic liquid crystalline elastomers filled with a very low (~0.01%)
concentration of carbon nanotubes, aligned along the nematic director at
preparation. The nanotubes create a very large effective dielectric anisotropy
of the composite. Their local field-induced torque is transmitted to the
rubber-elastic network and is registered as the exerted uniaxial stress of
order ~1kPa in response to a constant field of order ~1MV/m. We investigate the
dependence of the effect on field strength, nanotube concentration and
reproducibility under multiple field-on and -off cycles. The results indicate
the potential of the nanotube-nematic elastomer composites as electrically
driven actuators
Parasitic Infection of an Endemic Fish (Blicca bjoerkna) and an Exotic Fish (Hemiculter beucisculus) In Anzali Lagoon, Caspian Sea, Iran
Background: In Anzali Lagoon, there are some endemic and exotic fishes. The present study was conducted to compare the parasitic fauna of Blicca bjeorkna, as an endemic fish and HemiculÂter leucisculus, as an introduced fish to the lagoon.Methods: A parasitological investigation was done on 78 specimens of B. bjoerkna and 114 of H. leuÂcisculus. The fishes were collected from August 2009 to April 2010 by the electro fishing from Anzali Lagoon.Results: Eleven parasites species were found in 192 fish samples. The prevalence and mean intenÂsity of parasites in each host were as follows: Parasites from B. bjorkna were Trichodina perforata (53.85%); Myxobolus musayevi (27.19%, 1±0.79); Dactylogyrus difformis (88.05%, 8±7.24) and D. sphyrna (5.18%, 0.95±0.51), Diplostomum spataceum (98.72%, 9.51±9.01), PostÂhodiplostomum cuticula (15.38%, 4.25±2.5), Ripidocotyle sp. (1.28%, 2±0.74); Contracaecum osculatum (17.95%, 1.64±0.79), Philometra rischta (12.8%, 1.4±0.54), and Raphidascaris acus (1.04%, 0.03±0.26). The H. leucisculus were infected with T. perforata (27.19%), D. spataceum (7.89%, 1.33±0.54), Ps. tomentosa (7.02%, 1.62±0.49) and R. acus (0.88%, 3±0.28). B. bjoerkna was presented as a new host for M. musayevi and C. osculatum, while H. leucisculus was introÂduced as a new host for T. perforata and Ps. tomentosa.Conclusion: The prevalence of parasites was significantly more in native fish than that of exotic fish (P<0.05). This reduction in parasitic infection in H. leucisculus may be due to its immune system resistance, well adaptation to the new environment, host-specific limitation for endemic parasites and disability of introduced parasite to complete its life cycle in the new host as well
The first record of Philometra rischta (Nematoda: Philometridae) in Blicca bjoerkna of Anzali wetland, Iran
The aim of the present study was to report Philometra rischta from Blicca bjoerkna from the Caspian Sea. During this study, from August (2008) to April (2009), 78 fish specimens were collected and transferred to the aquatic research laboratory of Shahid Beheshti University and were examined for parasitic infection. Parasites were fixed in formalin (10%). The parasites were indentified according to standard keys (Moravec, 1994, 1998). Prevalence (total of infected fish per total of fish) and mean intensity (number of parasite per total of infected of fish) were calculated for this parasite
Detection of Pseudomonas aeruginosa in sputum samples by modified fluorescent in situ hybridization
Pseudomonas aeruginosa is the most common and dominant infectious agent that causes chronic pneumonia in patients with cystic fibrosis (CF). Fluorescent in situ hybridization (FISH) is a powerfulmolecular method for the specific and rapid diagnosis of bacteria, including the detection of P. aeruginosa in sputum samples from CF patients. High background fluorescence of viscous sputumsamples obtained from CF patients may impede detection of microorganisms by FISH. The aim of this study was to test the application of biotin during FISH technique to reduce unspecific background fluorescence in sputum samples to facilitate and improve detection of P. aeruginosa. Sixty-three sputum samples from CF patients were tested by FISH to detect P. aeruginosa. All the 63 samples were also examined by a modified FISH procedure including biotin treatment. The FISH results were compared with those of conventional culture method. The specificity of FISH was 100%. The sensitivity of FISH for detection of P. aeruginosa from samples without biotin treatment was 83.3%, whereas in biotin-treated samples was 88.1%. Biotin reduced background fluorescence of 12 sputum samples of CF patients and it did not show any adverse effect on FISH results of the remaining sputum samples. Therefore, using of biotin in FISH procedure seems to facilitate and improve the detection of respiratorytract infections by P. aeruginosa in this population
Critical fluctuations and random-anisotropy glass transition in nematic elastomers
We carry out a detailed deuterium NMR study of local nematic ordering in
polydomain nematic elastomers. This system has a close analogy to the
random-anisotropy spin glass. We find that, in spite of the quadrupolar nematic
symmetry in 3-dimensions requiring a first-order transition, the order
parameter in the quenched ``nematic glass'' emerges via a continuous phase
transition. In addition, by a careful analysis of the NMR line shape, we deduce
that the local director fluctuations grow in a critical manner around the
transition point. This could be the experimental evidence for the Aizenman-Wehr
theorem about the quenched impurities changing the order of discontinuous
transition
Analysis of a key regulatory region upstream of the Myf5 gene reveals multiple phases of myogenesis, orchestrated at each site by a combination of elements dispersed throughout the locus
Myf5 is the first myogenic regulatory factor to be expressed in the mouse embryo and it determines the entry of cells into the skeletal muscle programme. A region situated between -58 kb and -48 kb from the gene directs Myf5 transcription at sites where muscles will form. We now show that this region consists of a number of distinct regulatory elements that specifically target sites of myogenesis in the somite, limbs and hypoglossal cord, and also sites of Myf5 transcription in the central nervous system. Deletion of these sequences in the context of the locus shows that elements within the region are essential, and also reveals the combinatorial complexity of the transcriptional regulation of Myf5. Both within the -58 kb to -48 kb region and elsewhere in the locus, multiple sequences are present that direct transcription in subdomains of a single site during development, thus revealing distinct phases of myogenesis when subpopulations of progenitor cells enter the programme of skeletal muscle differentiation.This work in M.B.'s laboratory was supported by the Pasteur Institute and the CNRS and by grants from the ACI Integrative Biology Programme of the MJER, the AFM and the European Community (QLK3-CT-99/02). J.H. benefited from fellowships from ARC and the AFM, L.B. from funding from the MJER, and T.C. from fellowships from NIH and the AFM. The work in P.R.'s laboratory was supported by a grant from The Institute of Cancer Research.Peer reviewe
Chromatin signatures at Notch-regulated enhancers reveal large-scale changes in H3K56ac upon activation.
The conserved Notch pathway functions in diverse developmental and disease-related processes, requiring mechanisms to ensure appropriate target selection and gene activation in each context. To investigate the influence of chromatin organisation and dynamics on the response to Notch signalling, we partitioned Drosophila chromatin using histone modifications and established the preferred chromatin conditions for binding of Su(H), the Notch pathway transcription factor. By manipulating activity of a co-operating factor, Lozenge/Runx, we showed that it can help facilitate these conditions. While many histone modifications were unchanged by Su(H) binding or Notch activation, we detected rapid changes in acetylation of H3K56 at Notch-regulated enhancers. This modification extended over large regions, required the histone acetyl-transferase CBP and was independent of transcription. Such rapid changes in H3K56 acetylation appear to be a conserved indicator of enhancer activation as they also occurred at the mammalian Notch-regulated Hey1 gene and at Drosophila ecdysone-regulated genes. This intriguing example of a core histone modification increasing over short timescales may therefore underpin changes in chromatin accessibility needed to promote transcription following signalling activation.This work was supported by a BBSRC project grant [BB/J008842/1] to SJB, BA and SR and by a MRC programme grant [G0800034] to SJB. JL is the recipient of a scholarship from the China Scholarship Council Cambridge.This is the author accepted manuscript. The final version is available from Wiley via http://dx.doi.org/10.15252/embj.20148992
Early In Vitro Differentiation of Mouse Definitive Endoderm Is Not Correlated with Progressive Maturation of Nuclear DNA Methylation Patterns
The genome organization in pluripotent cells undergoing the first steps of differentiation is highly relevant to the reprogramming process in differentiation. Considering this fact, chromatin texture patterns that identify cells at the very early stage of lineage commitment could serve as valuable tools in the selection of optimal cell phenotypes for regenerative medicine applications. Here we report on the first-time use of high-resolution three-dimensional fluorescence imaging and comprehensive topological cell-by-cell analyses with a novel image-cytometrical approach towards the identification of in situ global nuclear DNA methylation patterns in early endodermal differentiation of mouse ES cells (up to day 6), and the correlations of these patterns with a set of putative markers for pluripotency and endodermal commitment, and the epithelial and mesenchymal character of cells. Utilizing this in vitro cell system as a model for assessing the relationship between differentiation and nuclear DNA methylation patterns, we found that differentiating cell populations display an increasing number of cells with a gain in DNA methylation load: first within their euchromatin, then extending into heterochromatic areas of the nucleus, which also results in significant changes of methylcytosine/global DNA codistribution patterns. We were also able to co-visualize and quantify the concomitant stochastic marker expression on a per-cell basis, for which we did not measure any correlation to methylcytosine loads or distribution patterns. We observe that the progression of global DNA methylation is not correlated with the standard transcription factors associated with endodermal development. Further studies are needed to determine whether the progression of global methylation could represent a useful signature of cellular differentiation. This concept of tracking epigenetic progression may prove useful in the selection of cell phenotypes for future regenerative medicine applications
LAMP: Large Deep Nets with Automated Model Parallelism for Image Segmentation
Deep Learning (DL) models are becoming larger, because the increase in model
size might offer significant accuracy gain. To enable the training of large
deep networks, data parallelism and model parallelism are two well-known
approaches for parallel training. However, data parallelism does not help
reduce memory footprint per device. In this work, we introduce Large deep 3D
ConvNets with Automated Model Parallelism (LAMP) and investigate the impact of
both input's and deep 3D ConvNets' size on segmentation accuracy. Through
automated model parallelism, it is feasible to train large deep 3D ConvNets
with a large input patch, even the whole image. Extensive experiments
demonstrate that, facilitated by the automated model parallelism, the
segmentation accuracy can be improved through increasing model size and input
context size, and large input yields significant inference speedup compared
with sliding window of small patches in the inference. Code is
available\footnote{https://monai.io/research/lamp-automated-model-parallelism}.Comment: MICCAI 2020 Early Accepted paper. Code is
available\footnote{https://monai.io/research/lamp-automated-model-parallelism
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