bluuebunny/crossref_metadata_2025_split huggingface dataset:
Induction of conoid extrusion is asociated to
MIC
secretion in Toxoplasma gondii tachyzoites
Authors: del Carmen Manuel Gonzalez , Calvo Lizbeth Cariño , Mondragón Ricardo 
Published: December 2016

INTRODUCTION

Toxoplasma
gondii
is an intracellular protozoan parasite which affects animals and humans causing encephalitis, chorioretinitis and death. The tachyzoite has structures that allow it to perform cell invasion. During the invasion, the tachyzoite adheres to the target cell membrane through proteins MIC that come from micronemes and then projects a highly dynamic structure called conoid [1,2]. Subsequently the parasite enters the cell and is housed in a parasitophorous vacuole proliferating by endodyogeny. After several cycles of replication, the parasites leave the infected cell by mechanisms such as conoid extrusion and secretion, which enables the parasite to invade neighboring cells. This replication cycle results in cell destruction and is responsible for the major clinical manifestations of toxoplasmosis. Ethanol is a well‐characterized inductor calcium‐dependent events in different cell models. In this work we used ethanol and we analyze the asociation between conoid extrusion and MIC secretion.

METHODS

Cell culture
. The cell model used for our invasion, proliferation and egress assays was HEP‐2 cells (human epithelial laryngeal carcinoma cells) (Hep‐2,ATCCCCL‐23).

Parasites
and conoid extrusion
. The RH strain of
T. gondii
was maintained in BALB/c mice, purified and incubated with 0.5M ethanol, fixed, and processed for electron microscopy and immunofluorescence.

Eletronic
microscopy
. The samples were fixed, dehydrated and infiltrated in resin or processed for scanning electron microscopy. Thin sections obtained were contrasted with uranyl acetate and examined in a transmission electron microscope (Jeol 2000 EX).

Immunodetection
. MIC2 protein detection was performed without permeating in extracellular tachyzoites. The samples were fixed and incubated with specific primary antibodies and analyzed using confocal microscopy.

RESULTS
The exposure of tachyzoites to ethanol induces reversible conoid extrusion, clearly observed the projection of the apical part of tachyzoites (Fig. 1). We also observed the presence of vesicle components accumulating in the back of tachyzoites, associated with some changes in the plasma membrane. We could detected that these vesicular components presenting on its surface was always associated with the extruded conoid(Fig. 1). For immunofluorescence, we showed that the secreted products during extrusion conoid micronemes come from. These results suggest a similar mechanism of secretion and induction for extrusion.
EMCD
investigation of the Verwey‐transition in magnetite
Authors: Hetaba Walid , Stöger‐Pollach Michael 
Published: December 2016

Magnetite is of interest in physics as well as in chemistry, for example because of its surface chemistry [1]. Furthermore, the investigation of the magnetic properties is worthwhile as the material exhibits a magnetic phase transition (the so‐called Verwey‐transition) at 125 K [2]. Magnetite shows a drop in its magnetisation when cooled down below the transition temperature, together with a change in electronic and structural properties. This behaviour was subject to a number of investigations [2]. However, the details of the transformation mechanism are still under discussion.

EMCD (energy‐loss magnetic chiral dichroism) is a versatile technique to investigate magnetic properties in the TEM on a nanoscale [3]. When performing EMCD on magnetite, the Fe L
2,3
‐edge, acquired using two different scattering conditions, is compared. The difference signal corresponds to the magnetic properties of the investigated material. Using current TEMs, EMCD can be performed in‐situ with a high spatial resolution, thus giving information about local changes of the magnetic moments [4].

We used a FEI Tecnai TF20 TEM, operated at 200 kV, equipped with a Gatan GIF Tridiem, and a Gatan Cryo‐Transfer sample holder to investigate magnetite samples close to the transition temperature. Thus, not the whole specimen was transformed. Figure 1(a) shows a bright field image of the investigated sample area. Due to variations from the perfect stoichiometry, regions that already transformed are visible alongside sample regions still in the high‐temperature phase. The diffraction patterns shown in Fig. 1(b,c) were acquired at two different regions, marked in Fig. 1(a), to check whether the material has already transformed.
The EMCD spectra that were recorded in the two marked sample regions are depicted in Fig. 2. It can be seen that in the non‐transformed region a strong EMCD signal of 13.5% is visible, while in the transformed region no EMCD effect is observed. This indicates changes in the local magnetic moments due to the phase transition. The results are faced to Bloch‐wave simulations [5], carried out for the same settings used in the EMCD measurements. Thus, the influence of different channelling conditions due to structural changes induced by the Verwey‐transition is compared to the measured EMCD signal. It is shown that the difference in the EMCD effect is mainly caused by local changes of the magnetic moments and not by different channelling conditions due to the structural changes.
EMCD in combination with the versatility of a wide variety of analytical techniques in a TEM is an ideal tool to gain knowledge about the magnetic properties of a material on the nanoscale. The necessary combination of experiments with simulations (as elastic scattering strongly influences the measured signal) provides insight into the mechanisms of magnetic phase transitions.
Electron microscopy investigations of cation exchange in colloidal
P
b
S
e/
C
d
S
e nanocrystals
Authors: Yalcin Anil , Goris Bart , Fan Zaochuan , Vlugt Thijs , van Blaaderen Alfons , Vanmaekelbergh Daniel , Bals Sara , van Huis Marijn 
Published: December 2016

Cation exchange is a very powerful method for creating heterogeneous nanocrystals (NCs), such as core‐shell or rod‐tip nanostructures. Here we present an overview of the experimental and simulation efforts made to elucidate the atomic mechanism underlying cation exchange in PbSe/CdSe nanocrystals.
When pure PbSe nanorods are in a colloidal solution, adding Cd precursors molecules to the solution will lead to the exchange of Pb ions by Cd ions, resulting in PbSe/CdSe core‐shell nanorods. High‐resolution high angle annular dark field scanning transmission electron microscopy (HAADF‐STEM) analysis of partly exchanged PbSe/CdSe core‐shell nanorods showed clearly defined interfaces in the nanorods, dominated by PbSe‐rocksalt/CdSe‐zinc blende {111}/{111} crystal planes [1]. However, from an atomic‐resolution 3D reconstruction of the PbSe core within such a core‐shell nanorod [2], it became clear that the interfaces are not as straight and defect‐free as they appear to be when considering only 2D projections.

The opposite process of Cd‐for‐Pb cation exchange was recorded in real time when PbSe‐tipped CdSe nanorods were heated
in‐situ
in the transmission electron microscope [3]. Stills of a movie recorded in HAADF‐STEM mode at a temperature of 180 °C are shown in Figure 1. Here the PbSe domains at the tips grew at the expense of the CdSe domains, a process driven by the evaporation of Cd (or Cd molecular complexes), as confirmed by energy‐dispersive X‐ray spectroscopy (EDX) chemical mapping. It became clear that cation exchange is a very dynamic process whereby excess Pb cations were consumed from Pb‐oleate complexes that were covering the surface of the NCs.

Finally, very recently a force‐field molecular dynamics (FF‐MD) simulation study was conducted which elucidates the role of both cation and anions in the underlying physical mechanism [3,4]. Figure 2 shows the result of a simulation whereby two types of interfaces are present in the nanorods, exhibiting very different defectiveness of the atomic planes at both sides of the interfaces.
Future opportunities for studying cation exchange, including Liquid Cell investigations and performing cation exchange of 2D of 3D assemblies of nanocrystals, are discussed as well.
Three‐dimensional electron imaging of dislocations from a single sample tilt
Authors: Oveisi Emad , Antoine Letouzey , Pascal Fua , Cecile Hebert 
Published: December 2016

Linear crystal defects called dislocations are one of the most fascinating concepts in materials science that govern mechanical and optoelectronic properties of many materials across a broad range of application [1–3]. Three‐dimensional (3‐D) study of dislocation network is in principle accessible by conventional tomographic and stereoscopic techniques in Transmission Electron Microscopy (TEM) [4,5]. In these techniques in general the need to tilt the specimen for acquiring image series over large tilt ranges remain however an intricate problem, in particular when diffraction contrast or sensitivity to electron beam are involved [6].
Here, a novel method in scanning TEM (STEM) is presented that provides a reliable and fast assessment of the 3‐D configuration of dislocations using data acquired from just one sample tilt. This technique acquires a stereoscopic pair of images by selecting different ray paths of a convergent illumination in STEM mode. The resulting images are then treated with a dedicated stereovision reconstruction algorithm, yielding a full 3‐D reconstruction of dislocations arrangement. The success of this method is demonstrated by measurement of dislocation arrangements in two experimental cases.
Addressing Pseudo‐Symmetric Misindexing in
EBSD
Analysis of gamma ‐
TiAl
with High Accuracy Band Detection
Authors: Schmidt Niels‐Henrik , Mansour Haithem , Goulden Jenny , Palomares‐García Alberto , Muñoz‐Moreno Rocio 
Published: December 2016

Technological developments in EBSD has enabled great improvements in indexing reliability and accuracy [1]. However, some individual phases continue to pose challenges, especially those that present extremely similar Kikuchi patterns to the EBSD camera for different crystallographic orientations. This phenomenon is called “pseudosymmetry”, as it commonly involves relatively high intensity bands in certain patterns with an apparent higher symmetry than the crystal structure actually possesses. In many cases, only very slight differences in inter‐band angle separate candidate solutions, and only robust and accurate band detection may identify the correct one among them.
Conventional Hough‐based band detection methods are sufficiently accurate for most indexing requirements. High accuracy Hough transform settings improves band detection accuracy, and is useful in mitigating pseudosymmetric misindexing [2]. However, these settings result in reduced data acquisition speeds, and may not completely eliminate pseudosymmetry problems.
New band detection refinement methods improve EBSD indexing performance for some of the most chronic cases, at reasonable data acquisition speeds. Higher accuracy band detection is achieved by iteratively comparing the positions of simulated bands with bands in the actual Kikuchi pattern image, using expected versus actual band widths and, accounting for the hyperbolic shape of bands. In addition to delivering high precision crystallographic orientation data and helping discriminate different phases with similar Kikuchi patterns, this method is sufficiently sensitive to resolve fine differences in inter‐band angle to nearly eliminate many cases of pseudosymmetric misindexing.

An important application is γ‐TiAl alloys, which are promising jet engine turbine materials, combining low density with good oxidation and creep resistance. The high temperature deformation behaviour of these alloys must be better understood before they can widely replace the higher density Ni‐base superalloys; For example, an improved knowledge of the fundamentals of crystallographic slip and its interaction with the γ/γ lamellar variants could be critical. Pseudosymmetry, however, is a major issue here (Fig. 1a), arising from γ‐TiAl's close tetragonal c:a unit cell parameter ratio of 1.018, giving the Kikuchi patterns it generates a pseudo‐cubic configuration, resulting in indexing inaccuracies. These mistakes show the same misorientations as boundaries between real γ‐TiAl lamellae, causing problems in revealing the true microstructure. Phase discrimination between coexisting γ(TiAl) andα
2
(Ti
3
Al) phases is also difficult (Fig. 2a). Application of a new, automated band detection tool and system knowledge of the confronting pseudo‐symmetry almost completely eliminate these issues (Fig.'s 1b and 2b) and are used in real‐time during data collection, at normal acquisition speeds.
Short time of
Z
n
O
nanoparticles uptake induces
DNA
damage and specific mitochondrial degeneration in human colon carcinoma cells
Authors: Condello Maria , Meschini Stefania , Berardis Barbara De , Ammendolia Maria Grazia , Condello Giancarlo , Pellegrini Evelin 
Published: December 2016

Thanks to their unique physico‐chemical properties, ZnO nanoparticles are widely used in consumer and industrial products, due to their higher chemical reactivity, stronger oxidation and corrosion resistance, antimicrobial properties, as compared with larger micro‐sized counterparts (Madhumitha et al., 2016). Recent studies have shown that ZnO nanoparticles can be promising candidates for biomedical applications and therapeutic interventions, and also successful as drug carrier and in targeted gene delivery (Peng et al., 2015; Velmurugan et al.,2015). In our previous in vitro study, ZnO nanoparticles showed to induce oxidative stress in human colon carcinoma cells (LoVo), resulting in significant decrease of cell viability (De Berardis et al., 2010).
In order to gain insight into the mechanism of action at subcellular level, aim of the present investigation was to carry out an ultrastructural study by transmission electron microscopy (TEM) on the subcellular localization of ZnO nanoparticles and a semi‐quantitative analysis of cellular uptake at multiple time points (from a few minutes up to 24 h of exposure). Electron microscopy observations of ZnO treated cells revealed two different mechanisms of cellular uptake, passive diffusion and endocytosis. Control cells show a mitochondria and nuclear normal shape (Fig. 1A). Small particles entry by passive diffusion crossing the plasma membrane without altering its structure (30 min of treatment, Fig. 1B; arrow indicates the nanoparticle in the cell membrane area). After 1h of treatment ZnO nanoparticles are already visible in the mitochondria cristae (Fig. 1C). The induction of the apoptosis is clearly showed in Fig. 1D, after 24 h of treatment. Quantitative analysis of cell death has been performed by flow cytometry.

We also evaluated the intracellular ions release from ZnO nanoparticles, their genotoxic potential by determining 7,8‐dihydro‐8‐oxo‐deoxyguanosine (8‐oxodG) levels, and the expression of phosphorylated histone H2AX (γ‐H2AX). The simultaneous presence of ZnO nanoparticles and Zn
2+
ions in the LoVo cells determined the formation of reactive oxygen species at the mitochondrial and nuclear level, inducing severe DNA damage.

In conclusion, our observations showed that ZnO nanoparticles entered LoVo cells by either passive diffusion or endocytosis or both, depending on the agglomeration state of the nanomaterial. ZnO nanoparticles coming into contact with acid pH of lysosomes altered organelles structure, resulting in the release of Zn
2+
ions. Taken together, the results of this study provide the evidence that damage induced by ZnO nanoparticles in LoVo cells derives from a combined action between intact nanoparticles and Zn
2+
ions, leading new insights into their toxicity.
ColorSTEM
‐ A Novel
STEM
Detector for Advanced Materials Analysis in
SEM
Authors: Dluhoš Jiří , Bilík Michal , Petráš Stanislav 
Published: December 2016

Performing scanning transmission electron microscopy (STEM) in a scanning electron microscope (SEM) is a popular technique for laboratories without transmission electron microscopy (TEM) capabilities.
The new versatile STEM detector by TESCAN is optimized for both high‐sensitivity orientation contrast as well as materials composition contrast imaging.
Transmitted electrons scattered in different angles represent different types of information that arises within a thin foil in scanning transmission electron microscopy. The new retractable STEM detector design allows maximum manipulation capabilities with the sample, including changes in working distance or eucentric tilt above the detector. Changing the working distance also changes the angular distribution of electrons detected by the detector segments. The sample can be therefore navigated to optimum contrast conditions easily, using changes in the working distance (see Fig. 1).
The redesigned electronics and signal processing apparatus of the detector allows simultaneous acquisition of multiple signals from transmitted and diffracted electrons including bright field (BF), dark field (DF) and high angle dark field (HADF) channels. The newly implemented ColorSTEM concept allows simultaneous acquisition of all channels as a live, color‐coded image with no information loss in either compositional color coding (Fig. 2) or orientation contrast color mode (Fig. 3).
The STEM analysis can be further supplemented with high‐resolution transmission‐EDS or transmission‐EBSD microanalysis. Higher resolution with these techniques is possible by reducing sample thickness thereby minimizing the interaction volume within the sample [1]. This combination takes advantage of the fact that these analytical techniques are already available in the SEM.
Study of Thermally Tunable Coupled Magnetic Vortex Oscillators with Lorentz Transmission Electron Microscopy and Differential Phase Contrast Microscopy
Authors: Wild Johannes , Vogel Michael , Müller Michael , Schwarzhuber Felix , Back Christian , Zweck Josef 
Published: December 2016

Magnetic vortex oscillators are an ideal system to study the dynamics of magnetic systems at very small length scales and over a wide frequency range. Their dynamic behavior shows characteristics known from other fundamental physical systems like the harmonic oscillator [1] and is in many aspects well understood. Their lateral dimension vary from a few microns [2] down to the nanometer scale [3]. Due to their flux closure configuration they are magnetically stable and a potential candidate for high density magnetic logic devices and magnonic crystals [4]. The oscillations, which can be obtained in essentially zero external magnetic field (besides the driving field), exhibit a narrow line width and resonance frequencies starting from the MHz range up to GHz frequencies [5]. They can be excited using magnetic field pulses [6] and electric currents harnessing the Spin Transfer Torques (STT) [5].
Recently, the magnetization dynamics in neighbouring magnetic vortex oscillators coupled via their stray fields come into focus of research [7‐10]. The system behaves like damped coupled harmonic oscillators. It has been shown that the dynamics of such systems is strongly influenced by the strength of the magnetostatic interaction given by the distance between the elements and the relative configuration of the core polarizations, e.g., the directions of the out‐of‐plane magnetization components [9].

Here we present a study of coupled vortices with Lorentz Transmission Electron Microscopy (LTEM) and Differential Phase Contrast Microcopy (DPC) at zero magnetic field. We show a novel technique to control the interaction of two or more vortex oscillators by directly influencing their resonance frequencies. The resonance frequencies depend on the saturation magnetization M
s
of the magnetic material, in this case permalloy and is highly dependent on the temperature of the disk. We use Joule heating to electrically manipulate the resonance frequencies of one element to control its excitation by a second neighbouring disk. We systematically mapped the frequency response of both disks for different temperatures to fully understand the behavior of the system.
Examination of inas/insb heterointerfaces in nanowires
Authors: Gejl Aske , Kanne Thomas , Johnson Erik , Denneulin Thibaud , Jäger Wolfgang , Nygård Jesper , Krogstrup Peter 
Published: December 2016

Examination of InAs/InSb heterointerfaces in Nanowires
Antimony based semiconductor nanowires (NWs) have been widely studied in recent years due to their large spin‐orbit coupling, high Landé g‐factor, and single subband conductance. They may become a key material in the field of quantum information processing and are currently used in the search for Majorana fermions by electrical transport [1]. Theory predicts that Majorana bound states can be realized in a 1D semiconductor coupled to a superconductor when exposed to an external magnetic field and manipulated by electrostatic gates [2]. Using NWs as a mean to achieve this goal has become even more promising after a recent report on epitaxial semiconductor/superconductor NW interfaces [3,4]. InSb NWs are expected to be the optimal material in this endeavor as the large spin‐orbit interaction, and the possibility to induce superconductivity, in InSb makes it feasible to drive the wires into the topologically protected regime [2,5]. Realization of Majorana bound states in semiconductor/superconductor NWs would open the route to perform quantum information processing in networks by exploiting the unique non‐abelian braiding statistics and non‐trivial fusion rules which are inherent in Majorana Fermions [6].
In this work we present a detailed investigation of the growth of Au‐seeded InSb NWs grown by molecular beam epitaxy (MBE) on (111)B InAs substrate. As InSb has proven difficult to grow directly on InAs substrates, an InAs stem mediates the growth as seen in Fig. 1. In Fig. 2 the growth deformation in this region is analyzed using Geometric Phase Analysis (GPA) and the abrupt interface indicates that the compositional change occur rapidly. To explore the growth dynamics of InSb, the transition region between InAs/InSb is investigated in order to study how incorporation of Sb affects the system. This analysis is performed using HR‐TEM, Dark‐Field Electron Holography (DFEH) [7], and Energy Dispersive x‐ray Spectroscopy (EDS). In Fig. 3 a DFEH image is obtained by interfering the diffracted beam from the InAs part of the NW with that from the InSb part. Using DFEH the in‐plane deformation in the growth direction is shown in Fig. 4. Comparing the results from the aforementioned techniques with parameters used in the MBE during growth gives insight into the incorporation dynamics of Sb in NWs. Understanding the dynamics of NW growth is crucial in order to optimize and utilize these in novel devices. InSb NWs with two‐facet Al shell are also investigated to explore the epitaxy of the interface, since the interface plays the major role in utilizing InSb/Al heterostructures for topological superconductivity and devices.