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•The correlation of molecular shape and conformations with the Ntb phase and transitional properties was investigated.•The onset of the Ntb phase and transition temperatures turned ...out to be very sensitive to these structural features.•Observed differences were attributed to the changes in molecular bend, which is the only difference among these dimers.
In view of the importance of molecular structural features, particularly the molecular curvature, that form the basis for the appearance and stabilization of the twist-bend nematic (Ntb) phase, the present work reports a computational study on a set of cyanobiphenyl dimers. In these dimers, the chemical nature of the linkage between the spacer and mesogenic units has been systematically varied by incorporating either methylene, ether, or thioether groups. Through computational modeling, we calculated the bend angle between the two mesogenic arms from all-trans conformations as well as Boltzmann-weighted average bend angle from conformational ensembles for each dimer. It was observed that the incidence of the Ntb phase is not only sensitive to the degree of molecular bend angle but also the conformational distribution. The present analysis recognized that the Ntb phase is only seen in liquid crystal dimers that have a sufficiently bent molecular structure. In addition, we have found a strong dependency of transitional properties upon these molecular factors. The changes in the phase transition temperatures appear to be a direct consequence of discrete changes in the molecular bend angle, as this is the major difference when comparing these dimers.
Liquid crystals are molecular systems that exhibit partial ordering of molecules similar to solids while maintaining the ability to flow like liquids. Depending upon the amount of ordering in the ...material, there are many types of liquid crystalline phases. The nematic phase is the most common and technologically most important one due to its use in display applications. In the nematic phase, the molecules tend to have the same alignment, but their positions are not correlated. In part due to fundamental scientific interest and driven by new technological motivations apart from displays, the existence of new stable nematics has been continuously searched. The continuing search led to a recent discovery of a new type of nematic phase,1,2 known as the twist-bend nematic (Ntb), in certain bent-shaped liquid crystal dimers that have been supported by various independent experimental studies. Since the Ntb phase has been discovered recently, its properties have not been fully explored and a detailed description and understanding at the molecular level are still far from complete.3
The Ntb phase’s formation is highly sensitive to any slight changes in the molecular shape arising from the chemical makeup of the linking spacer, terminal moieties and mesogenic units.4, Such structural features are not accessible directly through experiments. Thus, in this work, we present a set of DFT calculations on a series of liquid crystal dimers. This work aims to probe the role of certain structural features in driving the formation of the Ntb phase. This study also reveals why this phase occurs in certain bent molecules, but not in all. Since the constituent molecules are flexible and exist in a range of conformers, comparing the conformational landscapes of the dimers-exhibiting-the-Ntb-phase against those-do-not would identify the molecular conformations promoting the formation of the Ntb phase. Overall, this study evaluates ideal molecular structural features and conformational ensembles potentially responsible for the appearance of the Ntb phase.
A nanofinishing process using ball end magnetorheological (MR) finishing tool was developed for finishing 3D workpiece surfaces. In this process a ball end shape of MR polishing fluid is generated at ...the tip surface of the rotating tool which is used as a finishing spot. This paper is focused on surface finishing and performance evaluation of a typical three-dimensional ferromagnetic workpiece using a ball end magnetorheological finishing process. A typical 3D workpiece surfaces were made by milling process at different angles of projection such as flat, 30°, 45° and curve surfaces. The experiments were performed on these typical workpiece surfaces by ball end MR finishing setup to study the effect of number of finishing passes on final surface roughness. The experiments were also performed on a flat ground surface to study the process performance as compared with the milled workpiece surfaces. The finite element analysis has been done to study the distribution of magnetic flux density at tip surface of the tool with an inserted typical 3D workpiece surfaces. When these typical workpiece surfaces were finished by proposed MR finishing process, the surface roughness were reduced as low as 16.6nm, 30.4nm, 71nm and 123.7nm respectively on flat, 30°, 45° and curve surfaces for 60 passes of finishing. The roughness of flat ground surface was reduced as low as 19.7nm for 120min of finishing. The experimental results demonstrated that the newly developed ball end magnetorheological finishing process was effective in finishing typical 3D ferromagnetic workpiece surfaces.
► Modified ball end MR finishing process was used for finishing of the typical 3D surfaces. ► Process capability was demonstrated on 3D milled surfaces and flat ground surface. ► Variation in magnetic normal forces and flux density zones were found by finite element analysis. ► Effects of finishing forces were observed on final surface roughness of 3D typical surfaces. ► Variation in normal forces can be minimized by providing a tilting motion to MR finishing tool.
Prostate cancer is the second leading cause of cancer-related death among the American male population, and the cost of treating prostate cancer patients is about $10 billion/year in the United ...States. Current treatments are mostly ineffective against advanced-stage prostate cancer and are often associated with severe side effects. Driven by these factors, we report a multifunctional, nanotechnology-driven, gold nano-popcorn-based surface-enhanced Raman scattering (SERS) assay for targeted sensing, nanotherapy treatment, and in situ monitoring of photothermal nanotherapy response during the therapy process. Our experimental data show that, in the presence of LNCaP human prostate cancer cells, multifunctional popcorn-shaped gold nanoparticles form several hot spots and provide a significant enhancement of the Raman signal intensity by several orders of magnitude (2.5 × 10(9)). As a result, it can recognize human prostate cancer cells at the 50-cells level. Our results indicate that the localized heating that occurs during near-infrared irradiation can cause irreparable cellular damage to the prostate cancer cells. Our in situ time-dependent results demonstrate for the first time that, by monitoring SERS intensity changes, one can monitor photothermal nanotherapy response during the therapy process. Possible mechanisms and operating principles of our SERS assay are discussed. Ultimately, this nanotechnology-driven assay could have enormous potential applications in rapid, on-site targeted sensing, nanotherapy treatment, and monitoring of the nanotherapy process, which are critical to providing effective treatment of cancer.
•Introduce a new MR fluid based process for nano-finishing of diamagnetic materials such as copper and its alloys which is a difficult task but new finishing tool made it easy.•Nano-finishing of ...diamagnetic materials with least possible finishing time.•Simplified and more productive magnetorheological finishing setup by using permanent magnets instead of electromagnet.•Fulfill the requirement of industries for highly finished copper mirrors in laser, aerospace, dentistry, interconnecting material in electronics parts etc. and nano-finish of EDM electrodes.
Nano-finishing of a material surface is one of the most required properties in industry. There is high need of nano-finishing of diamagnetic materials such as copper and its alloys in electronic industries and electrode of electric discharge machining. Some industries like laser, aerospace, dentistry and metal optics etc. widely use highly finished copper mirrors. As copper is soft and chemically reactive material, its surface finishing at nano level is a difficult tasked. To fulfill this need, a new magnetorheological technique for precise surface finishing of diamagnetic materials has been conceptualized. Two cylindrical permanent magnets along with magnetorheological polishing fluid have been used to finish the diamagnetic copper alloy workpiece. The cylindrical permanent magnets tool with magnetorheological polishing fluid at its tip surface is rotated over the copper alloy workpiece surface and performs finishing by the stiffened magnetorheological polishing fluid. The permanent magnets finishing tool along with magnetorheological polishing fluid at its tip surface and diamagnetic copper workpiece have been modeled as well as simulated in Maxwell Ansoft V13 (student version) software. Distribution of magnetic flux density in the working gap is obtained and analyzed. Experiments are performed on the copper alloy workpiece and least Ra value of 28.8nm is achieved in finishing time of 7.5min from its initial value of 273.6nm. Surface characteristics of both polished and unpolished workpiece are analyzed with the scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results obtained from finite element analysis and experimentation assures that the new design of magnetorheological finishing tool using permanent magnets is capable to nano-finish of diamagnetic materials such as copper alloy etc.
The modern trend toward miniaturization has provided an innovative push toward the creation of micro-fabrication parts. Micro-extrusion is one such emerging process. It finds its various industrial ...applications in mechanical, electronic and micro-fabrication parts. Micro-punches are the main part of the micro-extrusion process. In the extrusion process, high contact forces are generated due to the sliding between the punch and billet. These high contact forces are governed by the surface topography of the punch. When the punches are finely finished, lesser contact forces are generated. To fulfill this requirement, the rotating rectangular core magnetorheological finishing process is used. On the basis of the applications, four industrial micro-punches are used for the present investigation. After MR finishing, surface roughness values of the micro-punches of the initial ground surface 0.210, 0.230, 0.250 and 0.200 µm are reduced to 0.02, 0.02, 0.03, and 0.01 µm. The operative functionality of the magnetorheological finished micro-punch is examined for its improved performance in the micro-extrusion process. The decrease in the roughness value reduces the frictional force between the micro-punch surface and the billet. Improvement in surface topography of the magnetorheological finished micro-punches enhances the quality of the product outcome and more uniform deformation of billet material.
Cancer is the greatest challenge in human healthcare today. Cancer causes 7.6 million deaths and economic losses of around 1 trillion dollars every year. Early diagnosis and effective treatment of ...cancer are crucial for saving lives. Driven by these needs, we report the development of a multifunctional plasmonic shell-magnetic core nanotechnology-driven approach for the targeted diagnosis, isolation, and photothermal destruction of cancer cells. Experimental data show that aptamer-conjugated plasmonic/magnetic nanoparticles can be used for targeted imaging and magnetic separation of a particular kind of cell from a mixture of different cancer cells. A targeted photothermal experiment using 670 nm light at 2.5 W/cm(2) for 10 min resulted selective irreparable cellular damage to most of the cancer cells. We also showed that the aptamer-conjugated magnetic/plasmonic nanoparticle-based photothermal destruction of cancer cells is highly selective. We discuss the possible mechanism and operating principle for the targeted imaging, separation, and photothermal destruction using magnetic/plasmonic nanotechnology.
A new precision finishing process for nanofinishing of 3D surfaces using ball end MR finishing tool is developed. The newly developed finishing process is used to finish ferromagnetic as well as ...nonmagnetic materials of 3D shapes using specially prepared magnetorheological polishing (MRP) fluid. The existing MR finishing devices and methods are likely to incapable of finish 3D intricate surfaces such as grooves in workpiece or complex in-depth profiles in the mold due to restriction on relative movement of finishing medium and workpiece. In this newly developed finishing device, the ball end MR finishing tool is used for finishing different kinds of 3D surfaces, as there is no limitation on relative movement of finishing medium and workpiece. It can finish the work surfaces similarly as the machining of 3D surfaces by CNC ball end milling cutter and open a new era of its applications in future. The developed process may have its potential applications in aerospace, automotive and molds manufacturing industries. A computer controlled experimental setup is designed and manufactured to study the process characteristics and performance. The magnetostatic simulations were done on ferromagnetic as well as nonferromagnetic materials of 3D surfaces to observe the ball end shape of magnetic field at the tip of the MR finishing tool. The experiments were performed on flat EN31 and groove surface of copper workpieces in the developed MR finishing setup to study the effect of finishing time on final surface roughness.
This commentary highlights the potential consequences of the COVID-19 pandemic for India’s rural population. The rural health care system in India is not adequate or prepared to contain COVID-19 ...transmission, especially in many densely populated northern Indian States because of the shortage of doctors, hospital beds, and equipment. The COVID-19 pandemic creates a special challenge due to the paucity of testing services, weak surveillance system and above all poor medical care. The impacts of this pandemic, and especially the lockdown strategy, are multi-dimensional. The authors argue for the need to take immediate steps to control the spread and its aftereffects and to use this opportunity to strengthen and improve its primary health care system in rural India.
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