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1.
PLoS One ; 13(7): e0198131, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-29966021

RESUMO

This study has used dense reconstructions from serial EM images to compare the neuropil ultrastructure and connectivity of aged and adult mice. The analysis used models of axons, dendrites, and their synaptic connections, reconstructed from volumes of neuropil imaged in layer 1 of the somatosensory cortex. This shows the changes to neuropil structure that accompany a general loss of synapses in a well-defined brain region. The loss of excitatory synapses was balanced by an increase in their size such that the total amount of synaptic surface, per unit length of axon, and per unit volume of neuropil, stayed the same. There was also a greater reduction of inhibitory synapses than excitatory, particularly those found on dendritic spines, resulting in an increase in the excitatory/inhibitory balance. The close correlations, that exist in young and adult neurons, between spine volume, bouton volume, synaptic size, and docked vesicle numbers are all preserved during aging. These comparisons display features that indicate a reduced plasticity of cortical circuits, with fewer, more transient, connections, but nevertheless an enhancement of the remaining connectivity that compensates for a generalized synapse loss.


Assuntos
Envelhecimento/patologia , Neurópilo/ultraestrutura , Córtex Somatossensorial/ultraestrutura , Sinapses/ultraestrutura , Animais , Axônios/ultraestrutura , Humanos , Imagem Tridimensional , Camundongos , Microscopia Eletrônica , Neurônios/patologia , Neurônios/ultraestrutura , Neurópilo/patologia , Córtex Somatossensorial/irrigação sanguínea , Córtex Somatossensorial/patologia , Sinapses/patologia
2.
Nano Lett ; 18(8): 5167-5171, 2018 08 08.
Artigo em Inglês | MEDLINE | ID: mdl-30040904

RESUMO

Exploiting additional degrees of freedom in solid-state materials may be the most-promising solution when approaching the quantum limit of Moore's law for the conventional electronic industry. Recently discovered topologically nontrivial spin textures, skyrmions, are outstanding among such possibilities. However, the controlled creation of skyrmions, especially by electric means, remains a pivotal challenge in technological applications. Here, we report that skyrmions can be created locally via electric field in the magnetoelectric helimagnet Cu2OSeO3. Using Lorentz transmission electron microscopy, we successfully write skyrmions in situ from a helical-spin background. Our discovery is highly coveted because it implies that skyrmionics can be integrated into modern field effect transistor based electronic technology, in which very low energy dissipation can be achieved and, hence, realize a large step forward toward its practical applications.

3.
Nat Commun ; 9(1): 1327, 2018 04 17.
Artigo em Inglês | MEDLINE | ID: mdl-29666368

RESUMO

Planetary formation models show that terrestrial planets are formed by the accretion of tens of Moon- to Mars-sized planetary embryos through energetic giant impacts. However, relics of these large proto-planets are yet to be found. Ureilites are one of the main families of achondritic meteorites and their parent body is believed to have been catastrophically disrupted by an impact during the first 10 million years of the solar system. Here we studied a section of the Almahata Sitta ureilite using transmission electron microscopy, where large diamonds were formed at high pressure inside the parent body. We discovered chromite, phosphate, and (Fe,Ni)-sulfide inclusions embedded in diamond. The composition and morphology of the inclusions can only be explained if the formation pressure was higher than 20 GPa. Such pressures suggest that the ureilite parent body was a Mercury- to Mars-sized planetary embryo.

4.
Ultramicroscopy ; 184(Pt A): 116-124, 2018 01.
Artigo em Inglês | MEDLINE | ID: mdl-28888106

RESUMO

Deriving accurate three-dimensional (3-D) structural information of materials at the nanometre level is often crucial for understanding their properties. Tomography in transmission electron microscopy (TEM) is a powerful technique that provides such information. It is however demanding and sometimes inapplicable, as it requires the acquisition of multiple images within a large tilt arc and hence prolonged exposure to electrons. In some cases, prior knowledge about the structure can tremendously simplify the 3-D reconstruction if incorporated adequately. Here, a novel algorithm is presented that is able to produce a full 3-D reconstruction of curvilinear structures from stereo pair of TEM images acquired within a small tilt range that spans from only a few to tens of degrees. Reliability of the algorithm is demonstrated through reconstruction of a model 3-D object from its simulated projections, and is compared with that of conventional tomography. This method is experimentally demonstrated for the 3-D visualization of dislocation arrangements in a deformed metallic micro-pillar.

5.
Proc Natl Acad Sci U S A ; 113(40): 11127-11130, 2016 10 04.
Artigo em Inglês | MEDLINE | ID: mdl-27647917

RESUMO

We performed laser-heated diamond anvil cell experiments combined with state-of-the-art electron microanalysis (focused ion beam and aberration-corrected transmission electron microscopy) to study the distribution and valence of iron in Earth's lower mantle as a function of depth and composition. Our data reconcile the apparently discrepant existing dataset, by clarifying the effects of spin (high/low) and valence (ferrous/ferric) states on iron partitioning in the deep mantle. In aluminum-bearing compositions relevant to Earth's mantle, iron concentration in silicates drops above 70 GPa before increasing up to 110 GPa with a minimum at 85 GPa; it then dramatically drops in the postperovskite stability field above 116 GPa. This compositional variation should strengthen the lowermost mantle between 1,800 km depth and 2,000 km depth, and weaken it between 2,000 km depth and the D" layer. The succession of layers could dynamically decouple the mantle above 2,000 km from the lowermost mantle, and provide a rheological basis for the stabilization and nonentrainment of large low-shear-velocity provinces below that depth.

6.
Proc Natl Acad Sci U S A ; 112(46): 14212-7, 2015 Nov 17.
Artigo em Inglês | MEDLINE | ID: mdl-26578765

RESUMO

Magnetic skyrmions are promising candidates as information carriers in logic or storage devices thanks to their robustness, guaranteed by the topological protection, and their nanometric size. Currently, little is known about the influence of parameters such as disorder, defects, or external stimuli on the long-range spatial distribution and temporal evolution of the skyrmion lattice. Here, using a large (7.3 × 7.3 µm(2)) single-crystal nanoslice (150 nm thick) of Cu2OSeO3, we image up to 70,000 skyrmions by means of cryo-Lorentz transmission electron microscopy as a function of the applied magnetic field. The emergence of the skyrmion lattice from the helimagnetic phase is monitored, revealing the existence of a glassy skyrmion phase at the phase transition field, where patches of an octagonally distorted skyrmion lattice are also discovered. In the skyrmion phase, dislocations are shown to cause the emergence and switching between domains with different lattice orientations, and the temporal fluctuation of these domains is filmed. These results demonstrate the importance of direct-space and real-time imaging of skyrmion domains for addressing both their long-range topology and stability.

7.
Nat Mater ; 14(10): 985-90, 2015 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-26259103

RESUMO

Ferroelectrics are widespread in technology, being used in electronics and communications, medical diagnostics and industrial automation. However, extension of their operational temperature range and useful properties is desired. Recent developments have exploited ultrathin epitaxial films on lattice-mismatched substrates, imposing tensile or compressive biaxial strain, to enhance ferroelectric properties. Much larger hydrostatic compression can be achieved by diamond anvil cells, but hydrostatic tensile stress is regarded as unachievable. Theory and ab initio treatments predict enhanced properties for perovskite ferroelectrics under hydrostatic tensile stress. Here we report negative-pressure-driven enhancement of the tetragonality, Curie temperature and spontaneous polarization in freestanding PbTiO3 nanowires, driven by stress that develops during transformation of the material from a lower-density crystal structure to the perovskite phase. This study suggests a simple route to obtain negative pressure in other materials, potentially extending their exploitable properties beyond their present levels.

8.
Microsc Microanal ; 20(5): 1544-55, 2014 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-24960631

RESUMO

This paper presents a method developed to quantify three-dimensional energy dispersive spectrometry (3D EDS) data with voxel size smaller than the volume from which X-rays are emitted. The influence of the neighboring voxels is corrected by applying recursively a complex quantification, improving thereby the accuracy of the quantification of critically small features. The enhanced quantification method is applied to simulated and measured data. A systematic improvement is obtained compared with classical quantification, proving the concept and the prospect of this method.

9.
Nat Protoc ; 9(6): 1354-66, 2014.
Artigo em Inglês | MEDLINE | ID: mdl-24833174

RESUMO

This protocol describes how in vivo-imaged dendrites and axons in adult mouse brains can subsequently be prepared and imaged with focused ion beam scanning electron microscopy (FIBSEM). The procedure starts after in vivo imaging with chemical fixation, followed by the identification of the fluorescent structures of interest. Their position is then highlighted in the fixed tissue by burning fiducial marks with the two-photon laser. Once the section has been stained and resin-embedded, a small block is trimmed close to these marks. Serially aligned EM images are acquired through this region, using FIBSEM, and the neurites of interest are then reconstructed semiautomatically by using the ilastik software (http://ilastik.org/). This reliable imaging and reconstruction technique avoids the use of specific labels to identify the structures of interest in the electron microscope, enabling optimal chemical fixation techniques to be applied and providing the best possible structural preservation for 3D analysis. The entire protocol takes ∼4 d.


Assuntos
Axônios/ultraestrutura , Encéfalo/citologia , Dendritos/ultraestrutura , Imagem Tridimensional/métodos , Microscopia Eletrônica de Varredura/métodos , Animais , Lasers , Camundongos , Software
10.
PLoS One ; 8(2): e57405, 2013.
Artigo em Inglês | MEDLINE | ID: mdl-23468982

RESUMO

Correlating in vivo imaging of neurons and their synaptic connections with electron microscopy combines dynamic and ultrastructural information. Here we describe a semi-automated technique whereby volumes of brain tissue containing axons and dendrites, previously studied in vivo, are subsequently imaged in three dimensions with focused ion beam scanning electron microcopy. These neurites are then identified and reconstructed automatically from the image series using the latest segmentation algorithms. The fast and reliable imaging and reconstruction technique avoids any specific labeling to identify the features of interest in the electron microscope, and optimises their preservation and staining for 3D analysis.


Assuntos
Córtex Cerebral/citologia , Microscopia Eletrônica de Varredura/métodos , Neurônios/citologia , Animais , Camundongos , Fótons
11.
Med Image Comput Comput Assist Interv ; 16(Pt 3): 413-20, 2013.
Artigo em Inglês | MEDLINE | ID: mdl-24505788

RESUMO

Scanning Electron Microscopy (SEM) is an invaluable tool for biologists and neuroscientists to study brain structure at the intracellular level. While able to image tissue samples with up to 5 nm isotropic resolution, image acquisition is prohibitively slow and limits the size of processed samples. In this work, we propose a novel approach to speeding up imaging when looking for specific structures. Unlike earlier methods, we explicitly balance the conflicting requirements of spending enough time scanning potential regions of interest to ensure that all targets are found while not wasting time on unpromising regions. This is achieved by using a Markov Random Field to model target locations and optimizing scanning locations by using a Branch-and-Bound strategy. We show that our approach significantly outperforms state-of-the-art methods to locate mitochondria in brain tissue.


Assuntos
Algoritmos , Encéfalo/ultraestrutura , Interpretação de Imagem Assistida por Computador/métodos , Microscopia Eletrônica de Varredura/métodos , Mitocôndrias/ultraestrutura , Reconhecimento Automatizado de Padrão/métodos , Humanos , Aumento da Imagem/métodos , Reprodutibilidade dos Testes , Sensibilidade e Especificidade
12.
Chem Commun (Camb) ; 48(52): 6484-6, 2012 Jul 04.
Artigo em Inglês | MEDLINE | ID: mdl-22627998

RESUMO

The activities of a series of MoS(2)-based hydrogen evolution catalysts were studied by biphasic reactions monitored by UV/Vis spectroscopy. Carbon supported MoS(2) catalysts performed best due to an abundance of catalytic edge sites and strong electronic coupling of catalyst to support.


Assuntos
Carbono/química , Dissulfetos/química , Hidrogênio/química , Molibdênio/química , Catálise , Espectrofotometria
13.
ACS Nano ; 6(3): 2790-7, 2012 Mar 27.
Artigo em Inglês | MEDLINE | ID: mdl-22375932

RESUMO

Theory predicts that periodic photonic nanostructures should outperform their random counterparts in trapping light in solar cells. However, the current certified world-record conversion efficiency for amorphous silicon thin-film solar cells, which strongly rely on light trapping, was achieved on the random pyramidal morphology of transparent zinc oxide electrodes. Based on insights from waveguide theory, we develop tailored periodic arrays of nanocavities on glass fabricated by nanosphere lithography, which enable a cell with a remarkable short-circuit current density of 17.1 mA/cm(2) and a high initial efficiency of 10.9%. A direct comparison with a cell deposited on the random pyramidal morphology of state-of-the-art zinc oxide electrodes, replicated onto glass using nanoimprint lithography, demonstrates unambiguously that periodic structures rival random textures.

14.
Acta Neuropathol ; 123(5): 653-69, 2012 May.
Artigo em Inglês | MEDLINE | ID: mdl-22361813

RESUMO

α-Synuclein (α-syn) is a presynaptic protein present at most nerve terminals, but its function remains largely unknown. The familial forms of Parkinson's disease associated with multiplications of the α-syn gene locus indicate that overabundance of this protein might have a detrimental effect on dopaminergic transmission. To investigate this hypothesis, we use adeno-associated viral (AAV) vectors to overexpress human α-syn in the rat substantia nigra. Moderate overexpression of either wild-type (WT) or A30P α-syn differs in the motor phenotypes induced, with only the WT form generating hemiparkinsonian impairments. Wild-type α-syn causes a reduction of dopamine release in the striatum that exceeds the loss of dopaminergic neurons, axonal fibers, and the reduction in total dopamine. At the ultrastructural level, the reduced dopamine release corresponds to a decreased density of dopaminergic vesicles and synaptic contacts in striatal terminals. Interestingly, the membrane-binding-deficient A30P mutant does neither notably reduce dopamine release nor it cause ultrastructural changes in dopaminergic axons, showing that α-syn's membrane-binding properties are critically involved in the presynaptic defects. To further determine if the affinity of the protein for membranes determines the extent of motor defects, we compare three forms of α-syn in conditions leading to pronounced degeneration. While membrane-binding α-syns (wild-type and A53T) induce severe motor impairments, an N-terminal deleted form with attenuated affinity for membranes is inefficient in inducing motor defects. Overall, these results demonstrate that α-syn overabundance is detrimental to dopamine neurotransmission at early stages of the degeneration of nigrostriatal dopaminergic axons.


Assuntos
Corpo Estriado/metabolismo , Dopamina/deficiência , Proteínas de Filamentos Intermediários/metabolismo , Atividade Motora/fisiologia , Substância Negra/metabolismo , Vesículas Sinápticas/metabolismo , Ácido 3,4-Di-Hidroxifenilacético/metabolismo , Anfetamina/farmacologia , Análise de Variância , Animais , Apomorfina/farmacologia , Cromatografia Líquida de Alta Pressão/métodos , Corpo Estriado/efeitos dos fármacos , Agonistas de Dopamina/farmacologia , Inibidores da Captação de Dopamina/farmacologia , Neurônios Dopaminérgicos/efeitos dos fármacos , Neurônios Dopaminérgicos/ultraestrutura , Eletroquímica , Ensaio de Imunoadsorção Enzimática/métodos , Comportamento Exploratório/efeitos dos fármacos , Comportamento Exploratório/fisiologia , Feminino , Lateralidade Funcional , Regulação da Expressão Gênica/efeitos dos fármacos , Regulação da Expressão Gênica/genética , Vetores Genéticos/metabolismo , Proteínas de Fluorescência Verde/genética , Proteínas de Fluorescência Verde/metabolismo , Ácido Homovanílico/metabolismo , Humanos , Técnicas In Vitro , Proteínas de Filamentos Intermediários/genética , Proteínas de Filamentos Intermediários/ultraestrutura , Microscopia Eletrônica de Transmissão , Atividade Motora/efeitos dos fármacos , Mutação/genética , Potássio/farmacologia , Ratos , Ratos Sprague-Dawley , Substância Negra/efeitos dos fármacos , Substância Negra/ultraestrutura , Vesículas Sinápticas/ultraestrutura , Fatores de Tempo , Transdução Genética , Proteínas Vesiculares de Transporte de Monoamina/metabolismo
15.
PLoS One ; 6(10): e24899, 2011.
Artigo em Inglês | MEDLINE | ID: mdl-22031814

RESUMO

We describe a protocol for fully automated detection and segmentation of asymmetric, presumed excitatory, synapses in serial electron microscopy images of the adult mammalian cerebral cortex, taken with the focused ion beam, scanning electron microscope (FIB/SEM). The procedure is based on interactive machine learning and only requires a few labeled synapses for training. The statistical learning is performed on geometrical features of 3D neighborhoods of each voxel and can fully exploit the high z-resolution of the data. On a quantitative validation dataset of 111 synapses in 409 images of 1948×1342 pixels with manual annotations by three independent experts the error rate of the algorithm was found to be comparable to that of the experts (0.92 recall at 0.89 precision). Our software offers a convenient interface for labeling the training data and the possibility to visualize and proofread the results in 3D. The source code, the test dataset and the ground truth annotation are freely available on the website http://www.ilastik.org/synapse-detection.


Assuntos
Microscopia Eletrônica de Varredura/métodos , Córtex Somatossensorial/ultraestrutura , Sinapses/ultraestrutura , Algoritmos , Animais , Ratos , Software
16.
J Vis Exp ; (53): e2588, 2011 Jul 06.
Artigo em Inglês | MEDLINE | ID: mdl-21775953

RESUMO

This protocol describes how biological samples, like brain tissue, can be imaged in three dimensions using the focussed ion beam/scanning electron microscope (FIB/SEM). The samples are fixed with aldehydes, heavy metal stained using osmium tetroxide and uranyl acetate. They are then dehydrated with alcohol and infiltrated with resin, which is then hardened. Using a light microscope and ultramicrotome with glass knives, a small block containing the region interest close to the surface is made. The block is then placed inside the FIB/SEM, and the ion beam used to roughly mill a vertical face along one side of the block, close to this region. Using backscattered electrons to image the underlying structures, a smaller face is then milled with a finer ion beam and the surface scrutinised more closely to determine the exact area of the face to be imaged and milled. The parameters of the microscope are then set so that the face is repeatedly milled and imaged so that serial images are collected through a volume of the block. The image stack will typically contain isotropic voxels with dimenions as small a 4 nm in each direction. This image quality in any imaging plane enables the user to analyse cell ultrastructure at any viewing angle within the image stack.


Assuntos
Encéfalo/ultraestrutura , Microscopia Eletrônica de Varredura/métodos , Animais , Humanos , Processamento de Imagem Assistida por Computador/métodos , Imagem Tridimensional/métodos , Microtomia/métodos , Fixação de Tecidos/métodos
17.
Nat Nanotechnol ; 3(10): 589-94, 2008 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-18838996

RESUMO

Nanoparticles play an important role in chemical and biological sciences due to their ability to bind and concentrate many molecules on their surface. Polymers and silica are widely used to make nanoparticles, but efforts to make nanoparticles from borosilicate glass--which exhibits high tolerance to chemicals and solvents, combined with excellent mechanical and thermal stability--have proved unsuccessful. Here we show that borosilicate nanoparticles (100-500 nm in size) can be synthesized by simply mixing a silicon-boron binary oxide solution, prepared using non-aqueous organic solvents, with water. This induces a vigorous exothermic phase separation in which borosilicate nanoparticles burst out of a silica phase. In addition to potential applications in the life sciences, monodisperse borosilicate particles could also have applications in the production of photonic bandgap devices with high optical contrast, contrast agents for ultrasonic microscopy or chemical filtration membranes.


Assuntos
Compostos de Boro/química , Nanopartículas Metálicas/química , Transição de Fase , Silicatos/química , Transferência de Energia , Esterificação , Dióxido de Silício/química
18.
Artigo em Inglês | MEDLINE | ID: mdl-16889341

RESUMO

Polycrystalline A1N thin films were deposited by RF reactive magnetron sputtering on Pt(111)/Ti electrode films. The substrates were tilted by an angle ranging from 40 degrees to 70 degrees with respect to the target normal. A low deposition temperature and a high sputter gas pressure were found ideal for tilted growth. The resulting grain tilt angle amounts to about half the substrate tilt angle. For coupling evaluation, 5 GHz solidly mounted resonator structures have been realized. The tilted grain A1N films exhibited a permittivity in the 9.5-10.5 range and loss tangent of 0.3%. Two shear modes as well as the longitudinal mode could be clearly identified. The coupling coefficient k2(eff) of the fundamental thickness shear mode (TS0) was found to be about 0.5%, which is compatible with a c-axis tilt of about 6 degrees.

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