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Learning and memory are thought to require hippocampal long-term potentiation (LTP), and one of the few central dogmas of molecular neuroscience that has stood undisputed for more than three decades is that LTP induction requires enzymatic activity of the Ca2+/calmodulin-dependent protein kinase II (CaMKII)1-3. However, as we delineate here, the experimental evidence is surprisingly far from conclusive. All previous interventions inhibiting enzymatic CaMKII activity and LTP4-8 also interfere with structural CaMKII roles, in particular binding to the NMDA-type glutamate receptor subunit GluN2B9-14. Thus, we here characterized and utilized complementary sets of new opto-/pharmaco-genetic tools to distinguish between enzymatic and structural CaMKII functions. Several independent lines of evidence demonstrated LTP induction by a structural function of CaMKII rather than by its enzymatic activity. The sole contribution of kinase activity was autoregulation of this structural role via T286 autophosphorylation, which explains why this distinction has been elusive for decades. Directly initiating the structural function in a manner that circumvented this T286 role was sufficient to elicit robust LTP, even when enzymatic CaMKII activity was blocked.
Assuntos
Proteína Quinase Tipo 2 Dependente de Cálcio-Calmodulina , Potenciação de Longa Duração , Proteína Quinase Tipo 2 Dependente de Cálcio-Calmodulina/antagonistas & inibidores , Proteína Quinase Tipo 2 Dependente de Cálcio-Calmodulina/química , Proteína Quinase Tipo 2 Dependente de Cálcio-Calmodulina/metabolismo , Ácido Glutâmico/metabolismo , Hipocampo/fisiologia , Aprendizagem/fisiologia , Potenciação de Longa Duração/fisiologia , Optogenética , Fosforilação , Ligação ProteicaRESUMO
Learning, memory, and cognition are thought to require synaptic plasticity, specifically including hippocampal long-term potentiation and depression (LTP and LTD). LTP versus LTD is induced by high-frequency stimulation versus low-frequency, but stimulating ß-adrenergic receptors (ßARs) enables LTP induction also by low-frequency stimulation (1 Hz) or theta frequencies (â¼5 Hz) that do not cause plasticity by themselves. In contrast to high-frequency stimulation-LTP, such ßAR-LTP requires Ca2+-flux through L-type voltage-gated Ca2+-channels, not N-methyl-D-aspartate-type glutamate receptors. Surprisingly, we found that ßAR-LTP still required a nonionotropic scaffolding function of the N-methyl-D-aspartate-type glutamate receptor: the stimulus-induced binding of the Ca2+/calmodulin-dependent protein kinase II (CaMKII) to its GluN2B subunit that mediates CaMKII movement to excitatory synapses. In hippocampal neurons, ß-adrenergic stimulation with isoproterenol (Iso) transformed LTD-type CaMKII movement to LTP-type movement, resulting in CaMKII movement to excitatory instead of inhibitory synapses. Additionally, Iso enabled induction of a major cell-biological feature of LTP in response to LTD stimuli: increased surface expression of GluA1 fused with super-ecliptic pHluorein. Like for ßAR-LTP in hippocampal slices, the Iso effects on CaMKII movement and surface expression of GluA1 fused with super-ecliptic pHluorein involved L-type Ca2+-channels and specifically required ß2-ARs. Taken together, these results indicate that Iso transforms LTD stimuli to LTP signals by switching CaMKII movement and GluN2B binding to LTP mode.
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Proteína Quinase Tipo 2 Dependente de Cálcio-Calmodulina , Potenciação de Longa Duração , Proteína Quinase Tipo 2 Dependente de Cálcio-Calmodulina/metabolismo , Receptores Adrenérgicos beta/metabolismo , Ácido D-Aspártico/metabolismo , Ácido D-Aspártico/farmacologia , Depressão Sináptica de Longo Prazo/fisiologia , Hipocampo/metabolismo , Sinapses/metabolismo , Receptores de N-Metil-D-Aspartato/metabolismoRESUMO
The Drosophila apical photoreceptor membrane is defined by the presence of two distinct morphological regions, the microvilli-based rhabdomere and the stalk membrane. The subdivision of the apical membrane contributes to the geometrical positioning and the stereotypical morphology of the rhabdomeres in compound eyes with open rhabdoms and neural superposition. Here we describe the characterization of the photoreceptor specific protein PIP82. We found that PIP82's subcellular localization demarcates the rhabdomeric portion of the apical membrane. We further demonstrate that PIP82 is a phosphorylation target of aPKC. PIP82 localization is modulated by phosphorylation, and in vivo, the loss of the aPKC/Crumbs complex results in an expansion of the PIP82 localization domain. The absence of PIP82 in photoreceptors leads to misshapped rhabdomeres as a result of misdirected cellular trafficking of rhabdomere proteins. Comparative analyses reveal that PIP82 originated de novo in the lineage leading to brachyceran Diptera, which is also characterized by the transition from fused to open rhabdoms. Taken together, these findings define a novel factor that delineates and maintains a specific apical membrane domain, and offers new insights into the functional organization and evolutionary history of the Drosophila retina.
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Membrana Celular/metabolismo , Proteínas de Drosophila/genética , Drosophila melanogaster/genética , Peptídeos e Proteínas de Sinalização Intracelular/genética , Células Fotorreceptoras de Invertebrados/metabolismo , Retina/crescimento & desenvolvimento , Animais , Animais Geneticamente Modificados , Evolução Biológica , Diferenciação Celular/genética , Membrana Celular/genética , Membrana Celular/ultraestrutura , Polaridade Celular/genética , Proteínas de Drosophila/metabolismo , Drosophila melanogaster/crescimento & desenvolvimento , Feminino , Regulação da Expressão Gênica no Desenvolvimento , Peptídeos e Proteínas de Sinalização Intracelular/metabolismo , Mutação com Perda de Função , Masculino , Microscopia Eletrônica de Transmissão , Fosforilação , Células Fotorreceptoras de Invertebrados/citologia , Células Fotorreceptoras de Invertebrados/ultraestrutura , Filogenia , Proteína Quinase C/metabolismo , Retina/citologia , Retina/ultraestrutura , Transcrição GênicaRESUMO
COVID-19 has had a profound impact on orthopaedic services and surgical training. AIM: This study aims to identify changes in lag screw position and Tip Apex Distance (TAD) in dynamic hip screw fixation due to changes in practice during the coronavirus pandemic and determine whether the changes resulted in improved patient outcomes and enhanced training opportunities. MATERIALS AND METHODS: Retrospective evaluation of two patient cohorts - pre-covid (n=27) and during covid (n=26) - to evaluate the TAD and lag screw position for each patient and record the grade of operating surgeon. A total of 53 patients were included. RESULTS: A mean TAD of 19.78mm and 19.80mm was calculated for cohort 1 and 2 respectively with no significant difference identified. When considering both key risk factors for lag screw cut-out (lag screw position and TAD) the number of patients with both a "satisfactory position" of the screw and a TAD <20mm, were 8/27 (29.6%) and 11/26 (42.3%), respectively. In cohort 1 3/27 cases had a consultant documented as the primary surgeon, while no consultants were documented as being present for the remaining 24 cases. 21/26 cases in cohort 2 had a consultant present some capacity, either as primary surgeon (15/21) or assistant (6/21). CONCLUSIONS: Changes in practice due to the pandemic have had some positive effects for both patients and trainees. This study has highlighted the importance of Consultant led trauma lists for improving training and surgical outcomes with a demonstrated improvement when considering both key factors associated with screw cut-out together. Ultimately some of the changes in practice should be continued in the post-covid era.
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COVID-19 , Fixação Intramedular de Fraturas , Fraturas do Quadril , Parafusos Ósseos , Humanos , Estudos Retrospectivos , SARS-CoV-2RESUMO
A new general de novo synthesis of pharmaceutically important N-(hetero)aryl piperidines is reported. This protocol uses a robustly diastereoselective reductive amination/aza-Michael reaction sequence to achieve rapid construction of complex polysubstituted ring systems starting from widely available heterocyclic amine nucleophiles and carbonyl electrophiles. Notably, the diastereoselectivity of this process is enhanced by the presence of water, and DFT calculations support a stereochemical model involving a facially selective protonation of a water-coordinated enol intermediate.
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A mechanistic study on the origin of the difference in reactivity between Ir catalysts for C-H borylation reactions is reported. Catalytic reactions of B2pin2 with a series of substrates that require high temperatures and long reaction times were conducted. These reactions catalyzed by the combination of [Ir(COD)(OMe)]2 and 3,4,7,8-tetramethylphenanthroline (tmphen) occur in yields that are substantially higher than those of reactions catalyzed by [Ir(COD)(OMe)]2 and 4,4'-di-tert-butylbipyridine (dtbpy). The electronic properties of Ir catalysts ligated by dtbpy or tmphen and their stoichiometric reactivity were investigated. It was found that a longer lifetime rather than higher reactivity of the catalyst leads to higher yields of reactions catalyzed by Ir-tmphen. The catalyst ligated by dtbpy decomposes principally by dissociation of the ligand and rapid borylation at the positions alpha to nitrogen. Thus, the greater stability of the catalyst containing tmphen results from its greater binding constant.
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Compostos de Boro/química , Irídio/química , Hidrocarbonetos Policíclicos Aromáticos/química , Catálise , Ligação de Hidrogênio , Ligantes , Estrutura MolecularRESUMO
Discovery of an unusual rectal gland in the Atlantic sixgill shark Hexanchus vitulus led us to examine the rectal glands of 31 species of sharks to study diversity in rectal-gland morphology. Twenty-four of 31 species of sharks had digitiform glands (mean width-length ratio ± SD = 0.17 ± 0.04) previously assumed to be characteristic of all elasmobranchs regardless of habitat depth or phylogenetic age. Rectal glands from the family Somniosidae were kidney bean-shaped (mean width: length ± SD = 0.46 ± 0.05); whereas those from families Echinorhinidae and Hexanchidae were lobulate (mean width: length ± SD = 0.55 ± 0.06). Rectal gland width: length were different among species with digitiform morphology and lobulate morphology (ANOVA; R2 = 0.9; df = 15, 386; 401, F = 219.24; P < 0.001). Histological and morphological characteristics of the digitiform morphology from deep-sea sharks were similar to those from shallow-water sharks. Histology of lobulate rectal glands from hexanchids were characterised by tubule bundles separated by smooth muscle around a central lumen. Additionally, we examined plasma chemistry of four species of sharks with digitiform rectal glands and two species with lobulate rectal-gland morphology to see if there were differences between morphologies. Plasma chemistry analysis showed that urea and trimethylamine N-oxide (TMAO) followed the piezolyte hypothesis, with TMAO being highest and urea being lowest in deep-sea sharks. Among electrolytes, Na+ was highest in species with lobulate rectal glands. Hexanchids and echinorhinids both have lobulate rectal glands similar to those of holocephalans, despite the more than 400 million years separating these two groups. The morphological similarities between the lobulate rectal-gland anatomy of primitive sharks and the secretory morphology of holocephalans may represent an intermediate state between Holocephali and derived shark species.
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Osmorregulação , Tubarões/anatomia & histologia , Adaptação Fisiológica , Animais , Evolução Biológica , Ecossistema , Filogenia , Alimentos Marinhos , Tubarões/fisiologiaRESUMO
We report the iridium-catalyzed borylation of primary and secondary alkyl C-H bonds directed by a Si-H group to form alkylboronate esters site selectively. The reactions occur with high selectivity at primary C-H bonds γ to the hydrosilyl group to form primary alkyl bisboronate esters. In the absence of such primary C-H bonds, the borylation occurs selectively at a secondary C-H bond γ to the hydrosilyl group, and these reactions of secondary C-H bonds occur with high diastereoselectivity. The hydrosilyl-containing alkyl boronate esters formed by this method undergo transformations selectively at the carbon-boron or carbon-silicon bonds of these products under distinct conditions to give the products of amination, oxidation, and arylation.
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Ácidos Borônicos/síntese química , Ésteres/síntese química , Irídio/química , Compostos Organometálicos/química , Silanos/química , Ácidos Borônicos/química , Catálise , Ésteres/química , Estrutura MolecularRESUMO
CONTEXTE: La recherche sur les défis de la prise en charge du diabète chez les personnes itinérantes qui en sont atteintes n'a pas tendance à prendre en considération le point de vue des personnes touchées. Nous avons utilisé une approche de recherche participative avec la communauté pour explorer ces défis. MÉTHODES: Nous avons recruté des cochercheurs ayant une connaissance expérientielle de l'itinérance et du diabète. Les chercheurs principaux leur ont offert une formation en recherche et ont préparé le terrain avec eux pour ce projet. Les cochercheurs ont collectivement choisi d'utiliser la méthode photovoix pour illustrer la difficulté de bien s'alimenter quand on est en situation d'itinérance et explorer en quoi cet écueil affecte plus largement la gestion du diabète. Après une formation en photographie et en éthique, les cochercheurs ont pris des photos en lien avec les objectifs du projet et rédigé des récits connexes au moyen de techniques de rédaction inspirée par des photos. Les chercheurs principaux ont analysé les photos et les récits, et ils en ont dégagé des thèmes qui se sont précisés lors de discussions de groupe. RÉSULTATS: Les 8 cochercheurs étaient atteints de diabète de type 2 (diagnostiqué de 18 mois à 23 ans auparavant) et avaient vécu en situation d'itinérance pendant des périodes allant de 8 mois à 12 ans. Nous avons dégagé 4 thèmes à partir de 17 photos et récits produits. L'itinérance affecte grandement la santé émotionnelle et mentale des personnes, ce qui nuit à leur capacité de bien gérer leur diabète. Les aliments servis dans les refuges sont rarement nutritifs ou appétissants. L'obtention d'une forme de logement peut faciliter la prise en charge du diabète en créant un environnement stable qui favorise l'autonomie, mais les coûts et le manque de connaissances sont des obstacles à la préparation de repas sains. L'itinérance complique aussi l'accès aux professionnels de la prise en charge du diabète et aux médicaments d'ordonnance. INTERPRÉTATION: Les images et les récits associés permettent de dresser un tableau frappant, complet et fidèle des défis auxquels sont confrontées les personnes en situation d'itinérance qui essaient de gérer leur diabète. Comprendre ces défis est la première étape qui permettra aux intervenants et aux décideurs de répondre aux besoins de cette population.
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Diabetes Mellitus/terapia , Pessoas Mal Alojadas/psicologia , Fotografação/métodos , Diabetes Mellitus/psicologia , Pessoas Mal Alojadas/estatística & dados numéricos , Humanos , Ontário , Fotografação/estatística & dados numéricos , Pesquisa QualitativaRESUMO
Primary benzylic boronate esters are useful intermediates in organic synthesis, but these reagents cannot be prepared by hydroboration. The benzylic C-H borylation of methylarenes would be a method to form these products, but such reactions without neat methylarene or a directing group are unknown. We report an approach to divert the borylation of methylarenes from aromatic positions to benzylic positions with a silylborane as reagent and a new iridium catalyst containing an electron-deficient phenanthroline as ligand. This system forms benzylic boronate esters selectively over the corresponding aryl boronate esters. An Ir diboryl monosilyl complex ligated by the phenanthroline was isolated and determined to be the resting state of the catalyst. Mechanistic studies show that this complex is kinetically competent to be an intermediate in the catalytic process. Kinetic studies of benzylic and aryl C-H borylation catalyzed by various Ir complexes show that the rate of aryl C-H borylation decreases with decreasing electron density at the metal center of the Ir catalyst, but that the rate of benzylic C-H borylation is less sensitive to the degree of electron density at the metal center of the Ir catalyst. Kinetic and computational studies suggest that the two borylation reactions respond differently to the degree of electron density at the metal center because they occur with different turnover-limiting steps. The turnover-limiting step in the borylation of aryl C-H bonds is known to be C-H oxidative addition, but the turnover-limiting step of the borylation of benzylic C-H bonds appears to be an isomerization prior to C-B reductive elimination.
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World War II and its subsequent GI Bill have been widely credited with playing a transformative role in American society, but there have been few quantitative analyses of these historical events' broad social effects. We exploit between-cohort variation in the probability of military service to investigate how WWII and the GI Bill altered the structure of marriage, and find that it had important spillover effects beyond its direct effect on men's educational attainment. Our results suggest that the additional education received by returning veterans caused them to "sort" into wives with significantly higher levels of education. This suggests an important mechanism by which socioeconomic status may be passed on to the next generation.
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Casamento/história , Cônjuges/estatística & dados numéricos , Veteranos/história , Veteranos/legislação & jurisprudência , II Guerra Mundial , Adolescente , Adulto , Escolaridade , História do Século XX , Humanos , Guerra da Coreia , Masculino , Casamento/estatística & dados numéricos , Pessoa de Meia-Idade , Militares/história , Militares/estatística & dados numéricos , Dinâmica Populacional , Fatores Socioeconômicos , Veteranos/estatística & dados numéricos , Adulto JovemRESUMO
A study on the iridium-catalyzed C-H borylation of heteroarenes is reported. Several heteroarenes containing multiple heteroatoms were found to be amenable to C-H borylation catalyzed by the combination of an iridium(I) precursor and tetramethylphenanthroline. The investigations of the scope of the reaction led to the development of powerful rules for predicting the regioselectivity of borylation, foremost of which is that borylation occurs distal to nitrogen atoms. One-pot functionalizations are reported of the heteroaryl boronate esters formed in situ, demonstrating the usefulness of the reported methodology for the synthesis of complex heteroaryl structures. Application of this methodology to the synthesis and late-stage functionalization of biologically active compounds is also demonstrated. Mechanistic studies show that basic heteroarenes can bind to the catalyst and alter the resting state from the olefin-bound complex observed during arene borylation to a species containing a bound heteroarene, leading to catalyst deactivation. Studies on the origins of the observed regioselectivity show that borylation occurs distal to N-H bonds due to rapid N-H borylation, creating an unfavorable steric environment for borylation adjacent to these bonds. Computational studies and mechanistic studies show that the lack of observable borylation of C-H bonds adjacent to basic nitrogen is not the result of coordination to a bulky Lewis acid prior to C-H activation, but the combination of a higher-energy pathway for the borylation of these bonds relative to other C-H bonds and the instability of the products formed from borylation adjacent to basic nitrogen.
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Compostos de Boro/síntese química , Compostos Heterocíclicos/química , Irídio/química , Compostos de Boro/química , Catálise , Estrutura Molecular , EstereoisomerismoRESUMO
High-resolution electron microscopy is a well-suited tool for characterizing the nanoscale structure of materials. However, the interaction of the sample and the high-energy electrons of the beam can often have a detrimental impact on the sample structure. This effect can only be alleviated by decreasing the number of electrons to which the sample is exposed but will come at the cost of a decreased signal-to-noise ratio in the resulting image. Images with low signal to noise ratios are often challenging to interpret as parts of the sample with a low interaction with the electron beam are reproduced with very low contrast. Here we suggest simple measures as alternatives to the conventional signal-to-noise ratio and investigate how these can be used to predict the interpretability of the electron microscopy images. We test the models on a sample consisting of gold nanoparticles supported on a cerium dioxide substrate. The models are evaluated based on series of images acquired at varying electron dose.
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Alzheimer's Disease (AD) is associated with brain accumulation of synaptotoxic amyloid-ß (Aß) peptides produced by the proteolytic processing of amyloid precursor protein (APP). Cognitive impairments associated with AD correlate with dendritic spine and excitatory synapse loss, particularly within the hippocampus. In rodents, soluble Aß oligomers impair hippocampus-dependent learning and memory, promote dendritic spine loss, inhibit NMDA-type glutamate receptor (NMDAR)-dependent long-term potentiation (LTP), and promote synaptic depression (LTD), at least in part through activation of the Ca2+-CaM-dependent phosphatase calcineurin (CaN). Yet, questions remain regarding Aß-dependent postsynaptic CaN signaling specifically at the synapse to mediate its synaptotoxicity. Here, we use pharmacologic and genetic approaches to demonstrate a role for postsynaptic signaling via A kinase-anchoring protein 150 (AKAP150)-scaffolded CaN in mediating Aß-induced dendritic spine loss in hippocampal neurons from rats and mice of both sexes. In particular, we found that Ca2+-permeable AMPA-type glutamate receptors (CP-AMPARs), which were previously shown to signal through AKAP-anchored CaN to promote both LTD and Aß-dependent inhibition of LTP, are also required upstream of AKAP-CaN signaling to mediate spine loss via overexpression of APP containing multiple mutations linked to familial, early-onset AD and increased Aß production. In addition, we found that the CaN-dependent nuclear factor of activated T-cells (NFAT) transcription factors are required downstream to promote Aß-mediated dendritic spine loss. Finally, we identified the E3-ubiquitin ligase Mdm2, which was previously linked to LTD and developmental synapse elimination, as a downstream NFAT target gene upregulated by Aß whose enzymatic activity is required for Aß-mediated spine loss.Significance Statement Impaired hippocampal function and synapse loss are hallmarks of AD linked to Aß oligomers. Aß exposure acutely blocks hippocampal LTP and enhances LTD and chronically leads to dendritic spine synapse loss. In particular, Aß hijacks normal plasticity mechanisms, biasing them toward synapse weakening/elimination, with previous studies broadly linking CaN phosphatase signaling to this synaptic dysfunction. However, we do not understand how Aß engages signaling specifically at synapses. Here we elucidate a synapse-to-nucleus signaling pathway coordinated by the postsynaptic scaffold protein AKAP150 that is activated by Ca2+ influx through CP-AMPARs and transduced to nucleus by CaN-NFAT signaling to transcriptionally upregulate the E3-ubiquitin ligase Mdm2 that is required for Aß-mediated spine loss. These findings identify Mdm2 as potential therapeutic target for AD.
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3',5'-Cyclic adenosine monophosphate (cAMP), the first identified second messenger, is implicated in diverse cellular processes involving cellular metabolism, cell proliferation and differentiation, apoptosis, and gene expression. cAMP is synthesized by adenylyl cyclase (AC), which converts ATP to cAMP upon activation of Gαs-protein coupled receptors (GPCRs) in most cases and hydrolyzed by cyclic nucleotide phosphodiesterases (PDEs) to 5'-AMP. Dysregulation of cAMP signaling is implicated in a wide range of pathophysiological conditions such as cardiovascular diseases, neurodegenerative and behavioral disorders, cancers, diabetes, obesity, cataracts, and others. Therefore, cAMP targeted therapies have been and are still undergoing intense investigation for the treatment of these and other diseases. This highlights the need for developing assays to detect and monitor cAMP levels. In this study, we show cAMP Lumit assay as a highly specific homogeneous bioluminescent assay suitable for high throughput screenings with a large assay window and a wide dynamic range for cAMP detection. We believe that this assay will aid and simplify drug discovery screening efforts for cAMP signaling targeted therapies.
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AMP Cíclico , Transdução de Sinais , AMP Cíclico/metabolismo , Adenilil Ciclases/metabolismo , Diferenciação Celular , Descoberta de DrogasRESUMO
We develop a combined theoretical and experimental method for estimating the amount of heating that occurs in metallic nanoparticles that are being imaged in an electron microscope. We model the thermal transport between the nanoparticle and the supporting material using molecular dynamics and equivariant neural network potentials. The potentials are trained to Density Functional Theory (DFT) calculations, and we show that an ensemble of potentials can be used as an estimate of the errors the neural network make in predicting energies and forces. This can be used both to improve the networks during the training phase, and to validate the performance when simulating systems too big to be described by DFT. The energy deposited into the nanoparticle by the electron beam is estimated by measuring the mean free path of the electrons and the average energy loss, both are done with Electron Energy Loss Spectroscopy (EELS) within the microscope. In combination, this allows us to predict the heating incurred by a nanoparticle as a function of its size, its shape, the support material, and the electron beam energy and intensity.
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The visualization of results while the simulation is running is increasingly common in extreme scale computing environments. We present a novel approach for in situ generation of image databases to achieve cost savings on supercomputers. Our approach, a hybrid between traditional inline and in transit techniques, dynamically distributes visualization tasks between simulation nodes and visualization nodes, using probing as a basis to estimate rendering cost. Our hybrid design differs from previous works in that it creates opportunities to minimize idle time from four fundamental types of inefficiency: variability, limited scalability, overhead, and rightsizing. We demonstrate our results by comparing our method against both inline and in transit methods for a variety of configurations, including two simulation codes and a scaling study that goes above 19 K cores. Our findings show that our approach is superior in many configurations. As in situ visualization becomes increasingly ubiquitous, we believe our technique could lead to significant amounts of reclaimed cycles on supercomputers.
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Motivated by the need for low electron dose transmission electron microscopy imaging, we report the optimal frame dose (i.e.e-/Å2) range for object detection and segmentation tasks with neural networks. The MSD-net architecture shows promising abilities over the industry standard U-net architecture in generalising to frame doses below the range included in the training set, for both simulated and experimental images. It also presents a heightened ability to learn from lower dose images. The MSD-net displays mild visibility of a Au nanoparticle at 20-30 e-/Å2, and converges at 200 e-/Å2 where a full segmentation of the nanoparticle is achieved. Between 30 and 200 e-/Å2 object detection applications are still possible. This work also highlights the importance of modelling the modulation transfer function when training with simulated images for applications on images acquired with scintillator based detectors such as the Gatan Oneview camera. A parametric form of the modulation transfer function is applied with varying ranges of parameters, and the effects on low electron dose segmentation is presented.
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Reconstruction of the exit wave function is an important route to interpreting high-resolution transmission electron microscopy (HRTEM) images. Here we demonstrate that convolutional neural networks can be used to reconstruct the exit wave from a short focal series of HRTEM images, with a fidelity comparable to conventional exit wave reconstruction. We use a fully convolutional neural network based on the U-Net architecture, and demonstrate that we can train it on simulated exit waves and simulated HRTEM images of graphene-supported molybdenum disulphide (an industrial desulfurization catalyst). We then apply the trained network to analyse experimentally obtained images from similar samples, and obtain exit waves that clearly show the atomically resolved structure of both the MoS2 nanoparticles and the graphene support. We also show that it is possible to successfully train the neural networks to reconstruct exit waves for 3400 different two-dimensional materials taken from the Computational 2D Materials Database of known and proposed two-dimensional materials.