202 research outputs found
Mesoscopic simulation of abnormal grain growth
No full textGrain growth is the process that takes place during annealing of polycrystalline materials; its major feature is a systematic increase in grain size. Two different types of grain growth can be distinguished: the normal and abnormal grain growth. During normal grain growth, the microstructure exhibits a uniform increase in grain size with time and the grain size distribution follows the log-normal distribution with the grain sizes ranging from 0 - 2.2 times the average grain size (R). On the contrary, when the abnormal grain growth is the dominant mechanism, there are certain grains (abnormal grains) in the microstructure that grow much faster than the majority of the grains and in the end consume the fine-grained matrix around them. There has been a lot of work done in the field of abnormal grain growth, but the actual mechanism of abnormal grain formation and development from a uniform grain size distribution is not fully understood. In this study, various aspects of abnormal grain growth are investigated using a mesoscopic simulation approach. Our investigation focuses on two possible venues that are, in general, considered as main sources promoting abnormal grain growth. The role of both the geometrical inhomogeneities (size effect) and grain boundary (GB) anisotropic properties are investigated. Simulations are done on various microstructures in which there are certain fraction of preexistent large grains (size greater than 2.2), as well as on microstructures in which a given fraction of grains has different GB properties (mobility and energy). Our simulation results indicate that the presence of some large grains in the initial microstructure does not promote the abnormal grain growth. However, when certain grains in the microstructure have grain boundary energies below a certain threshold or mobilities above a certain threshold value relative to the rest of the grains, the microstructure may evolve by abnormal grain growth
Current understanding of the influence of environmental factors on SARS-CoV-2 transmission, persistence, and infectivity
No full textCoronavirus disease 2019 (COVID-19) has emerged as a significant public health emergency in recent times. It is a respiratory illness caused by the novel virus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which was initially reported in late December 2019. In a span of 6 months, this pandemic spread across the globe leading to high morbidity and mortality rates. Soon after the identification of the causative virus, questions concerning the impact of environmental factors on the dissemination and transmission of the virus, its persistence in environmental matrices, and infectivity potential begin to emerge. As the environmental factors could have far-reaching consequences on infection dissemination and severity, it is essential to understand the linkage between these factors and the COVID-19 outbreak. In order to improve our current understanding over this topic, the present article summarizes topical and substantial observations made regarding the influences of abiotic environmental factors such as climate, temperature, humidity, wind speed, air, and water quality, solid surfaces/interfaces, frozen food, and biotic factors like age, sex, gender, blood type, population density, behavioural characteristics, etc. on the transmission, persistence, and infectivity of this newly recognized SARS-CoV-2 virus. Further, the potential pathways of virus transmission that could pose risk to population health have been discussed, and the critical areas have been identified which merits urgent research for the assessment and management of the COVID-19 outbreak. Where possible, the knowledge gaps requiring further investigation have been highlighted. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature
Closed Form HJB Solution for Path Planning of a Robot Manipulator with Warehousing Applications
No full textReal-time optimal path planning for robotic manipulations in task space is a very fundamental and important problem. In this paper, the problem of generating robot trajectories in an obstacle-ridden environment is formulated under an optimal control framework using Hamilton-Jacobi-Bellman (HJB) equation. The novel contribution of this paper is that a closed form HJB control solution (a necessary and sufficient condition for global optimality of a control solution with respect to a cost function) has been achieved for generating real-time optimal trajectories for a robot manipulator. In contrast with the decoupled end-effector path planning and subsequent trajectory generation, the proposed scheme can exploit sensory input for real-time trajectory generation where the end-effector path as well as the joint trajectory is recomputed online while satisfying the real-time constraints. The stability and the performance of the proposed control framework is shown theoretically via Lyapunov approach and also verified experimentally using a 6 degrees of freedom (DOF) Universal Robot (UR) 10 robot manipulator. It is shown that a significant saving in cost metrics can be obtained over similar trajectory generation approaches from the state-of-the-art with obstacle-ridden environment and also has better performance in high speed tracking applications. Warehouse applications of the proposed scheme in case of static and dynamic targets with respect to the robot manipulator is also included.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Learning & Autonomous Contro
ECHOCARDIOGRAPHIC ASSESSMENT OF HYPERTENSIVE CHANGES IN ELDERLY PATIENTS OF ISOLATED SYSTOLIC HYPERTENSION WITH SPECIAL REFERENCE TO CARDIOVASCULAR COMPLICATIONS
No full textObjective: The objective of the study was to assess the echocardiographic changes and cardiovascular complications in patients with isolated systolic hypertension (ISH).
Methods: This was an observational cross-sectional study done in the Departments of General Medicine, Cardiology, and Radiodiagnosis of MKCG Medical College and Hospital, Berhampur, Odisha, India. Seventy patients above the age of 65 years with systolic blood pressure (BP) ≥140 mm Hg and diastolic BP <90 mm Hg, without any secondary causes of hypertension and antihypertensive drug therapy were selected for this study. Echocardiography and electrocardiography studies were implemented for demonstrating the development of cardiovascular complications.
Results: Of 70 cases (41 males and 29 females), 64.3% were asymptomatic and 35.7% were symptomatic, with palpitation being the major symptom, 40% (28 cases) developed retinopathy, 45.71% developed increased left ventricular mass index (p=0.04), 18.57% had increased in LV volume (>90 ml/m2), 30% cases had regional wall motion abnormalities, 27.1% had reduced ejection fraction (<56%), and 52.66% showed LA enlargement in this study (p=0.048). Doppler measurements of diastolic filling were significant in patients with ISH with higher peak atrial velocity (A wave) of 79.71±11.79 cm/s and a lower ratio of peak early to atrial velocity of 0.82±0.29.
Conclusion: This study demonstrates that elderly patients with ISH had a prevalence of concentric left ventricular hypertrophy (LVH) which was found to be more in female patients than in male patients followed by left atrial enlargement
Impact of Thermal Annealing on Facet-Directed Epitaxial and Decorated Nonepitaxial Pd-CsPbBr<sub>3</sub> Nanocrystal Heterostructures
No full textHalide
perovskite nanocrystals are the subject of in-depth research
because of their bright color-tunable optical emissions. Synthesis
of these nanocrystals and their phase stability in different halide
compositions and reaction environments are also extensively studied.
However, going beyond these nanocrystals, the chemistry of epitaxial
growth of metallic crystals on selective facets of ionic crystals
has not been largely established yet. For the formation of heteronucleations
as well as retaining the epitaxial relation at the junction, a high
reaction temperature remains a key factor. However, with an increase
in temperature, there are possibilities for cross nucleations and
also detachment of metal particles from the host. Keeping these in
mind, herein, the thermal impacts on different structural combinations
of Pd-CsPbBr3 nanocrystal heterostructures are reported.
Following the high-temperature reaction protocol, two types of heterostructures,
facet-directive epitaxial and nonepitaxial decorated Pd-CsPbBr3, are first obtained, and these are further explored to study
the annealing impact. In these cases, smaller size Pd particles are
first grown epitaxially and form a one-to-one heterostructure, and
then with time, Pd cubes are observed to be decorated randomly. However,
the formation and growth of Pd particles remained sensitive to both
the reaction temperature and the time as these did not grow to beyond
a certain size in the heterostructure, rather facilitated cross nucleation
formation. This provides strong support that annealing does not hamper
the epitaxial junction and it only helps the successive growth of
nonepitaxially connected metal nanocrystals
α-Halo Ketone for Polyhedral Perovskite Nanocrystals: Evolutions, Shape Conversions, Ligand Chemistry, and Self-Assembly
No full textBright lead halide perovskite nanocrystals, which have been extensively studied in the past 5 years, are mostly confined to a six faceted hexahedron (cube/platelet) shape. With variations of ligand, precursor, reaction temperature, and surface modification, their brightness has been enhanced and phase became stable, but ultimate nanocrystals still retained the hexahedron cube or platelet shape in most of the hot injection reactions. In contrast, by exploration of α-halo ketone in amine as a halide precursor, different shaped nanocrystals without compromising the photoluminescence quantum yield (PLQY) are reported. Confining to orthorhombic CsPbBr3, the obtained nanocrystals are stabilized by 12 facets ({200}, {020}, {112}) and led to 12 faceted rhombic dodecahedrons. These facets are absolutely different from six ({110}, {002}) equivalent facets of widely reported orthorhombic cube shaped CsPbBr3 nanocrystals. These also retained the colloidal and phase stability, as well as showed near unity PLQY. With further annealing, these are transformed to 26 faceted rhombicuboctahedrons by dissolving all their vertices. Importantly, these 12 faceted nanocrystals showed wide area self-assembly in most of the reactions. It has also been concluded that primary ammonium ions led to six faceted nanocrystals, but tertiary ammonium ions obtained in this case stabilized different group of facets. While perovskite nanocrystals were broadly confined to only nanocubes, these new nanocrystals with intense emission would certainly provide a new avenue for continuing their further research
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