Simultaneous differential scanning calorimetry – synchrotron X-ray powder diffraction : a powerful technique for physical form characterisation in pharmaceutical materials

© 2016 American Chemical Society. We report a powerful new technique: hyphenating synchrotron X-ray powder diffraction (XRD) with differential scanning calorimetry (DSC). This is achieved with a simple modification to a standard laboratory DSC instrument, in contrast to previous reports which have involved extensive and complex modifications to a DSC to mount it in the synchrotron beam. The high-energy X-rays of the synchrotron permit the recording of powder diffraction patterns in as little as 2 s, meaning that thermally induced phase changes can be accurately quantified and additional insight on the nature of phase transitions obtained. Such detailed knowledge cannot be gained from existing laboratory XRD instruments, since much longer collection times are required. We demonstrate the power of our approach with two model systems, glutaric acid and sulfathiazole, both of which show enantiotropic polymorphism. The phase transformations between the low and high temperature polymorphs are revealed to be direct solid-solid processes, and sequential refinement against the diffraction patterns obtained permits phase fractions at each temperature to be calculated and unit cell parameters to be accurately quantified as a function of temperature. The combination of XRD and DSC has further allowed us to identify mixtures of phases which appeared phase-pure by DSC

Probing for Exoplanets Hiding in Dusty Debris Disks: Disk Imaging, Characterization, and Exploration with HST/STIS Multi-Roll Coronagraphy

Spatially resolved scattered-light images of circumstellar (CS) debris in exoplanetary systems constrain the physical properties and orbits of the dust particles in these systems. They also inform on co-orbiting (but unseen) planets, systemic architectures, and forces perturbing starlight-scattering CS material. Using HST/STIS optical coronagraphy, we have completed the observational phase of a program to study the spatial distribution of dust in ten CS debris systems, and one "mature" protoplanetrary disk all with HST pedigree, using PSF-subtracted multi-roll coronagraphy. These observations probe stellocentric distances > 5 AU for the nearest stars, and simultaneously resolve disk substructures well beyond, corresponding to the giant planet and Kuiper belt regions in our Solar System. They also disclose diffuse very low-surface brightness dust at larger stellocentric distances. We present new results inclusive of fainter disks such as HD92945 confirming, and better revealing, the existence of a narrow inner debris ring within a larger diffuse dust disk. Other disks with ring-like sub-structures, significant asymmetries and complex morphologies include: HD181327 with a posited spray of ejecta from a recent massive collision in an exo-Kuiper belt; HD61005 suggested interacting with the local ISM; HD15115 & HD32297, discussed also in the context of environmental interactions. These disks, and HD15745, suggest debris system evolution cannot be treated in isolation. For AU Mic's edge-on disk, out-of-plane surface brightness asymmetries at > 5 AU may implicate one or more planetary perturbers. Time resolved images of the MP Mus proto-planetary disk provide spatially resolved temporal variability in the disk illumination. These and other new images from our program enable direct inter-comparison of the architectures of these exoplanetary debris systems in the context of our own Solar System.Comment: 109 pages, 43 figures, accepted for publication in the Astronomical Journa

Atomic resolution studies of oxide superlattices and ultrathin films

The ability to grow ultrathin films layer-by-layer with well-defined epitaxial relationships has allowed research groups worldwide to grow a range of artificial films and superlattices, first for semiconductors, and now with oxides. In the oxides thin film research community, there have been concerted efforts recently to develop a number of epitaxial oxide systems grown on single crystal oxide substrates that display a wide variety of novel interfacial functionality, such as enhanced ferromagnetic ordering, increased charge carrier density, increased optical absorption, etc, at interfaces. The magnitude of these novel properties is dependent upon the structure of thin films, especially interface sharpness, intermixing, defects, and strain, layering sequence in the case of superlattices and the density of interfaces relative to the film thicknesses. To understand the relationship between the interfacial thin film oxide atomic structure and its properties, atomic scale characterization is required. Transmission electron microscopy (TEM) offers the ability to study interfaces of films at high resolution. Scanning transmission electron microscopy (STEM) allows for real space imaging of materials with directly interpretable atomic number contrast. Electron energy loss spectroscopy (EELS), together with STEM, can probe the local chemical composition as well as local electronic states of transition metals and oxygen. Both techniques have been significantly improved by aberration correctors, which reduce the probe size to 1 Å, or less. Aberration correctors have thus made it possible to resolve individual atomic columns, and possibly probe the electronic structure at atomic scales. Separately, using electron probe forming lenses, structural information such as the crystal structure, strain, lattice mismatches, and superlattice ordering can be measured by nanoarea electron diffraction (NED). The combination of STEM, EELS, and NED techniques allows us to gain a fundamental understanding of the properties of oxide superlattices and ultrathin films and their relationship with the corresponding atomic and electronic structure. In this dissertation, I use the aforementioned electron microscopy techniques to investigate several oxide superlattice and ultrathin film systems. The major findings are summarized below. These results were obtained with stringent specimen preparation methods that I developed for high resolution studies, which are described in Chapter 2. The essential materials background and description of electron microscopy techniques are given in Chapter 1 and 2. In a LaMnO3-SrMnO3 superlattice, we demonstrate the interface of LaMnO3-SrMnO3 is sharper than the SrMnO3-LaMnO3 interface. Extra spectral weights in EELS are confined to the sharp interface, whereas at the rougher interface, the extra states are either not present or are not confined to the interface. Both the structural and electronic asymmetries correspond to asymmetric magnetic ordering at low temperature. In a short period LaMnO3-SrTiO3 superlattice for optical applications, we discovered a modified band structure in SrTiO3 ultrathin films relative to thick films and a SrTiO3 substrate, due to charge leakage from LaMnO3 in SrTiO3. This was measured by chemical shifts of the Ti L and O K edges using atomic scale EELS. The interfacial sharpness of LaAlO3 films grown on SrTiO3 was investigated by the STEM/EELS technique together with electron diffraction. This interface, when prepared under specific conditions, is conductive with high carrier mobility. Several suggestions for the conductive interface have been proposed, including a polar catastrophe model, where a large built-in electric field in LaAlO3 films results in electron charge transfer into the SrTiO3 substrate. Other suggested possibilities include oxygen vacancies at the interface and/or oxygen vacancies in the substrate. The abruptness of the interface as well as extent of intermixing has not been thoroughly investigated at high resolution, even though this can strongly influence the electrical transport properties. We found clear evidence for cation intermixing through the LaAlO3-SrTiO3 interface with high spatial resolution EELS and STEM, which contributes to the conduction at the interface. We also found structural defects, such as misfit dislocations, which leads to increased intermixing over coherent interfaces

Principles of Optical and Electron Microscopy

The aim of this lecture is to provide participants of ETIM-95 with a guide to the techniques and procedures which enable the microstructures of the metals and alloys to completely characterized. In general metals are opaque, lustrous and relatively heavy, easily fabri-cated and shaped, have good mechanical strength and high thermal and electricty conductivity conductivity. All these properties are a consequence of the metallic bond; metal atoms have only a fiw electron in the outer shell which are shared between atoms forming and electron cloud and by coulomb attraction.Changes in the strength of this bond cause differences in optical, electrical, mechanical and thermal properties of various metals and alloys. The simple regular crystalline structures of metals result from this non-specific and nondirectional bond which holds atoms in close packed arrangements so that the pure metals, generally, have one of the face centered cubic (fcc), body centered cubic (bcc) or hexagonal close packed (hcp) structures of the fourteen crystal systems shown in Fig. 1. These crystallographic arrangements give rise to mate-rials of relatively high ductility since they are resis-tant to tensile stresses and less resistant to shearing forces. However the overall mechanical properties of met-als are controlled by "defect" structure within the cryst-allographic arrangement of atoms such as dislocations, point defects, etc. Mechanical and chemical properties can be modified by the addition of alloying elements which are used to advance in a range of commercial materials. In many alloy systems, compositions and heat treatments are selected that produces complex distributions of phases to give the required properties. To understand the response of metals and alloys to static, dynamic and cyclic stresses, various environments and temperatures, it is essential to be able to describe the "total micro-structure". For this it may be necessary to combine a knowledge of the chemical composition, crystal and defect structure, and the proportion and distribution of various phases present. This branch of science dealing with the microstructure of metals and alloys are called metall-ography

Multidimensional Scaling of Schematically Represented Faces Based on Dissimilarity Estimates and Evoked Potentials of Differences Amplitudes

Este estudio investiga la entrada del córtex cerebral occipital y temporal en el análisis de la confirguración facial y de las características expresivas. El análisis se basa en la construcción de un modelo esférico de diferenciación de caras presentadas esquemáticamente cuando la curvatura de boca y cejas varía quantitativamente. El modelo se ha diseñado empleando el método de escalonamiento multidimensional de los juicios de disimilitud entre los estímulos (caras) y la amplitud de los potenciales evocados de las diferencias (PED) entre los cambios abruptos de los estímulos registrados desde el córtex occipital y temporal posterior. Dependiendo del lugar de inserción del electrodo y la latencia del componente PED, el análisis de la estructura del modelo esférico de diferenciación facial en de la duración de 120-240 ms ha demostrado que la actividad del córtex occipital y temporal posterior del hemisferio derecho se asocia con las características emocionales de la cara presentada, y que la confguración facial se refleja en la activación de los córtex temporal posterior y occipital del hemisferio izquierdo. En todos los lugares de inserción de los electrodos, la máxima información de la expresión y configuración emocional se representa en una amplitud inter-pico de P120-N180. Al incrementar la latencia, aumenta la distorsión de la esturtura de las diferencias en el modelo esférico de caras presentadas esquemáticamente, lo cual se interpreta como la atenuación de la actividad eléctrica asociada al análisis de la expresión emocional, el cual ocurre más rápidamente que el análisis configuracional.This study researches the input of the cerebral occipital and temporal cortex in the analysis of facial configuration and expressive characteristics. Analysis is based on the construction of a spherical model for the differentiation of schematically presented faces with quantitatively altering curvature of the mouth and brows. The model is designed using the method of multidimensional scaling of the dissimilarity judgments between stimuli (faces) and the amplitude of evoked potentials of differences (EPD) between abrupt stimulus changes recorded from the occipital and posterior temporal cortex. Analysis of the structure of the spherical model of facial differentiation depending on the electrode site and the latency of the EPD component within the duration of 120-240 ms has demonstrated that the activity of the occipital and posterior temporal cortex of the right hemisphere is associated with the emotional characteristics of the presented face, whereas facial configuration is reflected in the activation of both posterior temporal cortex and the occipital cortex of the left hemisphere. At all electrode sites maximum information of the emotional expression and configuration is represented in inter-peak amplitude P120-N180. With increasing latency there is increased distortion of the structure of differences in the spherical model of schematically presented faces, which is interpreted as an attenuation of electrical activity associated with the analysis of the emotional expression, which occurs more rapidly than configuration analysi

Mach Bands: How Many Models are Possible? Recent Experiemental Findings and Modeling Attempts

Mach bands are illusory bright and dark bands seen where a luminance plateau meets a ramp, as in half-shadows or penumbras. A tremendous amount of work has been devoted to studying the psychophysics and the potential underlying neural circuitry concerning this phenomenon. A number of theoretical models have also been proposed, originating in the seminal studies of Mach himself. The present article reviews the main experimental findings after 1965 and the main recent theories of early vision that have attempted to discount for the effect. It is shown that the different theories share working principles and can be grouped in three clsses: a) feature-based; b) rule-based; and c) filling-in. In order to evaluate individual proposals it is necessary to consider them in the larger picture of visual science and to determine how they contribute to the understanding of vision in general.Air Force Office of Scientific Research (F49620-92-J-0334); Office of Naval Research (N00014-J-4100); COPPE/UFRJ, Brazi

Optical devices - Lasers. A compilation

Laser applications in communications, industrial fabrication, and computer systems, and laser beam generation and control - technology utilizatio

Scaling Factor Threshold Estimator in Different Color Models Using a Discrete Wavelet Transform for Steganographic Algorithm

Two of the main problems with steganographic algorithms are insertion capability and minimization of distortion in the digital files where the hidden information is the information is inserted to hiding Digital filters are generally used as noise detectors, and they also suppress information outside the original information contained in the file. There are different types of filtering, one in the spatial domain and the other in the frequency domain or sometimes a combination of both domains to propose adaptive filters. One of the filters with greater application is the discrete wavelet transform (DWT) because it is easy to implement and has low computational complexity. The DWT computationally implemented in an image can be represented as a quadrature mirror filter, separating the frequency components: so high-high, high-low, low-high and low-low levels obtain different resolutions

Analysis of Strain Relaxation, Ion Beam Damage and Instrument Imperfections for Quantitative STEM Characterizations

It is illustrated that the preparation of thin specimens from bulk materials can have significant influence on the interpretability of (S)TEM data. The results of the presented measurements show that and the elastic strain relaxation in low dimensional structures alters the overall strain state of the material – and hence affects strain measurements – as well as the contrast of STEM measurements and is generally needed to be incorporated in comparative simulation studies that involve strained structures. Furthermore, the ion beam thinning process itself can introduce – even with relatively low energies – a serious alteration of the surface which can affect the contrast of STEM measurements. Hence, the correlation to thickness measurements is complicated due to the distinct difference in scattering behaviour between (partially) amorphized surface layers in comparison with crystalline material. Although parts of these effects cannot be avoided the inclusion of amorphous pseudo-oxide layers in simulations has been shown to provide reasonable agreement with the experimental data. Furthermore, the impact of a finite electron source with limited coherence has been investigated. It can be shown that a reproduction of experimental contrast by simulation can only be achieved by the inclusion of an additional focus spread as well as a lateral point spread due to partial spatial coherence. Finally, the previous results are combined to reconstruct the three-dimensional shape of several antiphase domains within gallium phosphide grown on silicon-(001). At first the concept was demonstrated for a simple but highly strained interface and second for large structures with thousands of atomic columns. It is shown that although the contrast mechanism for annular dark-field imaging is in principle straight forward and mathematically simple, the details of atomic resolution microscopy are still very challenging. Realistic assumptions about the specimen properties and the electron optics have been shown to be of great relevance for data evaluation. It is clear that the research should be extended to the regime of low angular dark-field imaging where strain and inelastic scattering play a even more relevant role. Furthermore, it is of great importance to investigate the aforementioned practical aspects of damage layers and optical imperfections for other advanced imaging techniques like diffraction imaging. In addition, it is worth investigating in how far through focus depth section can be utilized to increase the reliability of structure restoration along the transmission direction. It is expected that the improvement of accuracy and robustness of atomic counting techniques will greatly increase the power of a (S)TEM by providing simultaneously lateral and depth information about arrangement and composition. Furthermore, it is clear that the role of high performance simulations will have an even more important role in the future