Direct observation of 3D atomic packing in monatomic amorphous materials

Liquids and solids are two fundamental states of matter. However, due to the lack of direct experimental determination, our understanding of the 3D atomic structure of liquids and amorphous solids remained speculative. Here we advance atomic electron tomography to determine for the first time the 3D atomic positions in monatomic amorphous materials, including a Ta thin film and two Pd nanoparticles. We observe that pentagonal bipyramids are the most abundant atomic motifs in these amorphous materials. Instead of forming icosahedra, the majority of pentagonal bipyramids arrange into networks that extend to medium-range scale. Molecular dynamic simulations further reveal that pentagonal bipyramid networks are prevalent in monatomic amorphous liquids, which rapidly grow in size and form icosahedra during the quench from the liquid state to glass state. The experimental method and results are expected to advance the study of the amorphous-crystalline phase transition and glass transition at the single-atom level

Padronização da pesquisa de linfonodos sentinelas em estômago por métodos combinados

Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Ciências Médicas, Pós-Graduação em Ciências da Cirurgia, Campinas, 2012.Introdução - Com os estudos de Gould et al. (1960), Cabanas (1977) e Morton et al. (1992), estabeleceu-se o conceito da pesquisa do linfonodo sentinela. Esse se baseia na teoria de que ao identificar a presença ou ausência de metástase no primeiro linfonodo que recebe a drenagem linfática a partir do tumor (sentinela), poderia representar o estado de acometimento dos outros linfonodos. Isto evitaria a realização desnecessária de linfadenectomias. Com o passar dos anos, foi consagrada para ser aplicada em casos de melanoma e câncer de mama. Nesta última década, tenta-se estender os princípios da utilização da pesquisa de linfonodo sentinela para os cânceres do aparelho digestivo. Entretanto, no caso do estômago, existem algumas dificuldades, como: presença de sistema de drenagem linfática multidirecional, ocorrência de metástases saltatórias e identificação de mais de um linfonodo sentinela por indivíduo. Objetivo - Criar e padronizar um modelo animal para o treinamento de pesquisa de linfonodos sentinelas em estômago. Método - Trinta e dois coelhos, saudáveis, foram submetidos à anestesia exclusivamente intramuscular. Por meio de laparotomia, foi injetado na subserosa da parede anterior do corpo gástrico, 0,1 ml de fitato marcado com tecnécio-99m (0,2 mCi), em seguida pelo mesmo orifício, de 0,2 ml de Azul Patente V® 2,5%. A cavidade abdominal foi avaliada, in vivo , para pesquisa de suspeitas de linfonodos azuis (corados em azul) e com detector manual de radiação gamma aos 5, 10 e 20 minutos para detecção de suspeitas de linfonodos radioativos (radioatividade identificada superior a 10X o valor apresentado pelo fundo). Após 20 minutos, realizou-se ressecção e exérese total do estômago, baço e suspeitas de linfonodos, para posterior avaliação da radioatividade ex vivo . A seguir, encaminharam-se as suspeitas de linfonodos para estudo histológico para identificação de tecido linfóide. Resultados - Foram identificados linfonodos em 30 coelhos (93,75%) com média de 2,2 por animal. Das 90 suspeitas de linfonodos detectadas, em 70 casos (77,77%) obteve-se confirmação histológica para tecido linfóide. Dessas, a maioria foi identificada e localizada na região entre o esôfago e o fundo gástrico durante a avaliação in vivo aos 5 minutos. Dois coelhos faleceram durante os experimentos (Taxa de mortalidade = 6,25%). Conclusão - O modelo experimental em coelhos para pesquisa de linfonodos sentinelas em estômago por métodos combinados foi factível, de fácil execução e baixa mortalidade, podendo ser usado para treinamento.Abstract : Introduction - The concept of sentinel lymph node was established by the studies of Gould et al. (1960), Cabanas (1977) and Morton et al. (1992). It is based on the theory that, whenever the presence or absence of metastasis is identified in the first lymph node that receives the lymphatic drainage from the tumor (sentinel) the status of involvement of other lymph nodes might be infered. This could avoid the performance of unnecessary lymphadenectomies. Over the years, its use was consecrated by its application in melanoma and breast cancer. In the last decade, attempts have been made to extend the principles of sentinel lymph node investigation to cancers of the digestive tract. In the case of stomach cancer, additional difficulties were found, such as multiple and aberrant lymphatic routes, the occurrence of skip metastasis and the possible identification of more than one sentinel lymph node in the same patient. Aim - To develop and evaluate an animal model for training sentinel lymph node navigation in the stomach. Methods - Thirtytwo healthy rabbits, were prepped and given intramuscular anesthesia. Through a formal laparotomy, they received a subserosal injection of 0.1 ml of phytate labeled with technetium-99m (0.2 mCi) in the anterior wall of the gastric corpus, followed by 0.2 ml of Blue Patent ® V 2.5%, through the same puncture site. Suspicious lymph nodes were searched in-vivo at 5, 10 and 20 minutes, both visually (Blue Patent stained lymph nodes) and with a manual gamma radiation detector (to detect suspected radioactive lymph nodes, displaying radioactivity levels over 10X the value displayed by the background). En-block resection of the stomach, spleen, visible limph nodes and local fat tissue was then performed and the specimen was assessed "ex vivo" for radioactivity. Suspected lymph nodes were sent for histological study to evaluate the presence of lymphoid tissue. Results Radiolabeled or stained lymph nodes were identified in 30 rabbits (93.75%) with an average of 2.2 specimens per animal; of the 90 suspicious lymph nodes detected, histology confirmed lymphoid tissue in 70 cases (77.77%). Most lymph nodes were identified at the 5-minute in-vivo evaluation and their most common location was found to be in the region between the esophagus and the gastric fundus. Two rabbits died during the procedure resulting in a 6.25% mortality. Conclusion - The rabbit model proved adequate for training in sentinel node navigation in the stomach by combined methods (dye and radiocolloid) being easy to execute and associated with low mortality

Structural Control of Nanocrystal Superlattices Using Organic Guest Molecules

We report a host–guest chemistry approach to controlling the structures of nanocrystal superlattices through a molecular inclusion process. Upon addition of an appropriate amount of guest molecules such as squalane, polyisoprene, and 4-cyano-4′-pentylbiphenyl into a nanocrystal suspension, the resulting nanocrystal superlattices adopted non-close-packed structures (e.g., from face-centered cubic to body-centered cubic) and changed their morphologies to form superparticles. Our mechanistic studies revealed that these guest molecules can strongly tailor the kinetic process in superlattice formation, resulting in the formation of non-close-packed nanocrystal superlattices. The insights gained in this study are not only important for making nanocrystal superlattices with desirable architectures but also open a new way of synthesizing novel organic/inorganic composite materials

Algorithm to demodulate an electromyogram signal modulated by essential tremor

Abstract Essential tremor is a disorder that causes involuntary oscillations in patients both while they are engaged in actions and when maintaining a posture. Such patients face serious difficulties in performing daily living activities such as meal movement. We have been developing an electromyogram (EMG)-controlled exoskeleton to suppress tremors to support the movements of these patients. The problem is that the EMG signal of the patients is modulated by the tremor signal as multiplicative noise. In this paper, we proposed a novel signal processing method to demodulate patients’ EMG signals. We modelled the multiplicative tremor signal with a powered sine wave and the tremor signal in the EMG signal was removed by dividing the modelled tremor signal into the EMG signal. To evaluate the effectiveness of the demodulation, we applied the method to a real patient’s EMG signal, extracted from biceps brachii while performing an elbow flexion. We quantified the effect of the demodulation by root mean square error between two kinds of muscle torques, an estimated torque from the EMG signal and calculated torque from inverse dynamics based on the motion data. The proposed method succeeded in reducing the error by approximately 15–45% compared with using a low-pass filter, typical processing for additive noise, and showed its effectiveness in the demodulation of the patients’ EMG signal

Three-dimensional atomic packing in amorphous solids with liquid-like structure.

Liquids and solids are two fundamental states of matter. However, our understanding of their three-dimensional atomic structure is mostly based on physical models. Here we use atomic electron tomography to experimentally determine the three-dimensional atomic positions of monatomic amorphous solids, namely a Ta thin film and two Pd nanoparticles. We observe that pentagonal bipyramids are the most abundant atomic motifs in these amorphous materials. Instead of forming icosahedra, the majority of pentagonal bipyramids arrange into pentagonal bipyramid networks with medium-range order. Molecular dynamics simulations further reveal that pentagonal bipyramid networks are prevalent in monatomic metallic liquids, which rapidly grow in size and form more icosahedra during the quench from the liquid to the glass state. These results expand our understanding of the atomic structures of amorphous solids and will encourage future studies on amorphous-crystalline phase and glass transitions in non-crystalline materials with three-dimensional atomic resolution

Pressure-Enabled Synthesis of Hetero-Dimers and Hetero-Rods through Intraparticle Coalescence and Interparticle Fusion of Quantum-Dot-Au Satellite Nanocrystals

This report presents the fabrication and pressure-driven processing of heterostructural nanocrystal superlattices (HNC-SLs) self-assembled from quantum-dot-Au (QD-Au) satellite-type HNCs. <i>In situ</i> small/wide-angle X-ray scattering and electron microscopic measurements showed that the HNC-SLs underwent structural transformation at both atomic- and mesoscales during the pressure processing. Upon deviatoric stress-driven orientational migration, the intraparticle coalescence of Au satellites at QD surfaces transforms individual HNCs into heterodimers, whereas the interparticle fusion drives assembled HNCs into ordered heterorod arrays. These results demonstrate high-pressure-processing as a clean and fast means for conversion of HNCs into novel heteromaterials that are difficult to achieve through conventional synthetic routes