Metal halide perovskites have demonstrated strong potential for optoelectronic applications. Particularly, two-dimensional (2D) perovskites have emerged to be promising materials due to their tunable properties and superior stability compared to their three-dimensional counterparts. For high device performance, 2D perovskites need a vertical crystallographic orientation with respect to the electrodes to achieve efficient charge transport. However, the vertical orientation is difficult to achieve with various compositions due to a lack of understanding of the thin film nucleation and growth processes. Here we report a general crystallization mechanism for 2D perovskites, where solvent evaporation and crystal growth compete to influence the level of supersaturation and a low supersaturation is necessary to crystallize vertically oriented thin films starting from nucleation at the liquid–air interface. Factors influencing the supersaturation and crystallization dynamics, such as choices of organic spacers, solvents, and solvent drying rate, have a strong influence on the degree of crystallographic orientation. With this understanding of crystallization mechanism, we demonstrate direct crystallization of thin films with strong vertical orientation using three different organic spacers without any additives, and the vertically oriented 2D perovskites result in efficient and stable solar cell operation.

Medical ultrasound imaging with Doppler plays an essential role in the diagnosis of vascular disease. This study intended to review the clinical use of "to-and-fro" waveform at duplex Doppler ultrasonography (DDU) in the diagnosis of pseudoaneurysms in the arterial vessels of upper and lower extremities, abdominal aorta, carotid and vertebral arteries as well as to review our personal experiences of "to-and-fro" waveform at DDU also. After receiving institutional review board approval, an inclusive literature review was carried out in order to review the scientific foundation of "to-and-fro" waveform at DDU and its clinical use in the diagnosis of pseudoaneurysms in various arterial vessels. Articles published in the English language between 2000 and 2013 were evaluated in this review study. Pseudoaneurysms in arterial vessels of the upper and lower extremities, abdominal aorta, carotid and vertebral arteries characterized by an extraluminal pattern of blood flow, which shows variable echogenicity, interval complexity, and "to-and-fro" flow pattern on color Doppler ultrasonography. In these arterial vessels, Duplex ultrasonography can demonstrate the degree of clotting, pseudoaneurysm communication, the blood flow patterns and velocities. Spectral Doppler applied to pseudoaneurysms lumen revealed systolic and diastolic turbulent blood flow with traditional "to-and-fro" waveform in the communicating channel. Accurate diagnosis of pseudoaneurysm by spectral Doppler is based on the documentation of the "to-and-fro" waveform. The size of pseudoaneurysm determines the appropriate treatment approach as surgical or conservative.

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Robot-assisted ultrasound-guided breast biopsy combines ultrasound (US) imaging with a robotic system for medical interventions. This study was designed to provide a literature review of a robotic US-guided breast biopsy system to delineate its efficacious impact on current medical practice. In addition, the strengths and limitations of this approach were also addressed. Articles published in the English language between 2000 and 2016 were appraised in this review. A wide range of systems that bind robotics with US imaging and guided breast biopsy were examined in this article. The fundamental safety and real-time imaging capabilities of US, together with the accuracy and maneuverability of robotic devices, is clearly an effective association with unmatched capabilities. Numerous experimental systems have obvious benefits over old-fashioned techniques, and the future of robot-assisted US-guided breast biopsy will be characterized by increasing levels of automation, and they hold tremendous possibility to impact doctor achievement, patient recovery, and clinical management.