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Manipulation of colloidal objects with light is important in diverse fields. While performance of traditional optical tweezers is restricted by the diffraction-limit, recent approaches based on plasmonic tweezers allow higher trapping efficiency at lower optical powers but suffer from the disadvantage that plasmonic nanostructures are fixed in space, which limits the speed and versatility of the trapping process. As we show here, plasmonic nanodisks fabricated over dielectric microrods provide a promising approach toward optical nanomanipulation: these hybrid structures can be maneuvered by conventional optical tweezers and simultaneously generate strongly confined optical near-fields in their vicinity, functioning as near-field traps themselves for colloids as small as 40 nm. The colloidal tweezers can be used to transport nanoscale cargo even in ionic solutions at optical intensities lower than the damage threshold of living micro-organisms, and in addition, allow parallel and independently controlled manipulation of different types of colloids, including fluorescent nanodiamonds and magnetic nanoparticles. Current particle manipulation techniques using light are limited by optical effects, such as diffraction, or lack of dynamic capabilities. The authors report a strategy that combines conventional optical traps with plasmonic tweezers to gain maneuverability of the trapped particles while maintaining plasmonic trap efficiencies.

Selective control of single untethered robots within a collection is trivial in macroscale robotics since it is possible to address and actuate individual entities using various communication schemes. This strategy does not work at reduced (sub-µm) length scales, where the global field cannot differentiate or control a single nanobot selectively from within a collection of indistinguishable objects. Here, we propose and demonstrate strategies where identical magnetic nanobots can be selectively and independently actuated using global control fields. A key challenge for submicrometer magnetically actuated devices is achieving individual control under a global field. The authors present strategies to selectively and independently actuate identical nanobots, enabling distinct motions and complex collective behaviors at the nanoscale.

Soil liquefaction-induced damages in buildings and foundation during earthquakes increase the seismic hazard of densely populated urban cities dwelling on young alluvial soil deposits with a rising demand for infrastructural developments. Generally, liquefaction potential is evaluated for specific sites, which lacks the information related to the spatial extent of liquefaction effects. In the present study, liquefaction hazard maps of Kolkata metropolitan city is prepared for potential future earthquakes considering the spatial variability of soil parameters. The importance and application of geostatistical interpolation tools for hazard mapping are highlighted in this paper. Deterministic procedures of Boulanger and Idriss ( 2004 , 2014 ) were utilized to quantify the liquefaction potential of two types of soil deposits, silty clay and silty sand, in the study area. Probability of liquefaction ( P L ) was evaluated by first-order second moment (FOSM) reliability method for 2% and 10% probability of exceedance in 50 years. Python codes were developed for the calculation of factor of safety (FS) and P L values for silty sand and silty clay. Spatial distribution maps in terms of FS and P L were generated at 7 m, 15 m and 25 m depth of the study area using ordinary kriging technique in ArcGIS software. The regions of Maidan, Newtown, Rajarhat, Santoshpur, Sector V and Tangra were found to be vulnerable to liquefaction till 15 m depth. Additionally, correlations were also developed between P L and FS using non-linear regression analysis for all soils, silty clay and silty sand of the study area for both the probabilistic scenarios.

Nitrogen vacancy (NV) centers in diamonds are of current interest as quantum sensors, single photon sources, and biological nanomaterials due to their unique optical and spin properties, biocompatibility, and robust structure. Though NV center in diamonds demonstrates longer coherence time and has been used for more sensing and quantum operations compared to nanodiamonds (NDs), the prospect of selecting NDs with single, few, or multiple NV centers and moving the NDs to the location of interest makes NDs suitable for various applications, due to which there is a significant boost in the last decade to manipulate and position the NDs on the surface or to achieve dynamic control in the fluidic environment. This work covers some of the basics of the materials and optical properties of nanodiamonds and discusses the capabilities and challenges for practical applications, followed by a detailed review of the various static and dynamic manipulation methods of nanodiamonds in microfluidic environments (colloidal NDs). Fluorescent nanodiamonds (NDs) exhibit remarkable structural and optical properties, making them useful for diverse quantum applications ranging from single photon emission, nanophotonic devices to high‐resolution sensing. As a result, there is a strong focus on the selection, manipulation, and precise placement of NDs in specific locations, driving active research in this field, which is discussed in this review.

Acoustic cavitation is a powerful technique to probe electron bubbles inside the liquid helium. The critical pressure to explode a bubble depends on the number and quantum state of electrons inside the bubble and if the bubble is trapped on a vortex. Here, we report cavitation events that occur at pressure magnitudes approximately 70% lower compared to single electron bubbles. We have considered various possibilities, e.g., single electron bubbles trapped on vortex lines or primary electrons depositing the energy at the acoustic focus and compared the results of our experiments with past measurements reported in the literature. We consider the possibility these new species of bubbles are multielectron bubbles with a small (< 20) number of electrons and discuss future experiments to confirm the same.

Delivery of regenerative medicine in complex, microscale topographies can revolutionize multiple areas of healthcare, including but not limited to orthopaedics and dentistry. The technical challenges include navigation and regeneration of nanoscale biosimilars with spatial control, necessitating a different technological approach, as demonstrated here. The specific problem addressed here is dental hypersensitivity, which occurs when dentinal tubules are exposed to the external environment through enamel loss or cementum erosion of the tooth, thus stimulating nerves located in the peripheral odontoblast zone of the pulp. Existing treatments, such as sensitive toothpaste and adhesive resins, are limited to the surface and can only provide short‐term relief. Here, we deploy a confluence of distinct experimental strategies to develop a magnetic bioglass‐based nanomaterial called “CalBots,” consisting of a Calcium‐based colloidal gel that self‐assembles into short chains under optimized conditions of external magnetic fields and interparticle interactions and penetrates more than 300 µm deep inside the complex topography of the dentine tissue. Subsequently, it triggers the formation of a biocompatible seal, thus protecting the exposed tubules and their nerve fibers from external stimuli, for both human and murine teeth. The controlled animal trial shows a full recovery from dental hypersensitivity within the treatment group. Magnetically guided bioceramic nanoparticles (“CalBots”) achieve deep dentinal tubule occlusion via directed self‐assembly under externally applied magnetic field. Various visualization techniques and a novel mouse behavioral assay indicate that CalBot‐induced plugs may reduce dentinal sensitivity, offering a promising strategy for future dentin hypersensitivity treatments.

Investigations of two-dimensional electron systems (2DES) have been achieved with two model experimental systems, covering two distinct, non-overlapping regimes of the 2DES phase diagram, namely the quantum liquid phase in semiconducting heterostructures and the classical phases observed in electrons confined above the surface of liquid helium. Multielectron bubbles in liquid helium offer an exciting possibility to bridge this gap in the phase diagram, as well as to study the properties of electrons on curved flexible surfaces. However, this approach has been limited because all experimental studies have so far been transient in nature. Here we demonstrate that it is possible to trap and manipulate multielectron bubbles in a conventional Paul trap for several hundreds of milliseconds, enabling reliable measurements of their physical properties and thereby gaining valuable insight to various aspects of curved 2DES that were previously unexplored. Two-dimensional electron systems exhibit a range of interesting phenomena, and multielectron bubbles are a versatile platform in which to study them. Here, the authors show the use of a Paul ion trap to stably trap and manipulate such bubbles in liquid helium over a broad electron density.

We demonstrate an experimental setup to trap multielectron bubbles in bulk liquid He 4 using a point Paul trap. The experimental configuration is based on dc and rf electric fields applied to planar electrodes such as to trap the bubbles at a certain location. We have performed numerical simulations to estimate the experimental parameters at which stable trapping can occur, which matched with the experimental results. Compared to the linear Paul traps reported earlier by our group, point Paul traps allow more efficient loading and better optical access for viewing the trapped bubbles, and will allow simultaneous storage and investigation of multiple electron bubbles in the future.

The pressure applied to the tunnel face during excavation plays a significant role in ensuring the tunnel face stability. The tunnel face collapses at lower pressure and blasts out at higher pressure. In the present study, tunnel face stability analysis has been carried out under dry and seepage conditions for both φ and c - φ soil. The effects of tunnel geometry, including the tunnel diameter (D = 5.0, 7.5, 10.0) and cover-to-diameter ratio (C/D = 0.5, 1.0, 2.0, 4.0)] as well as the shear strength parameters of soil [Cohesion (c) and angle of internal friction (φ)] have been studied. A linearly proportional relationship has been observed between the face pressure and the tunnel diameter (D). The face pressure has been found to increase linearly with the increase in the value of the (H/D) ratio, irrespective of the soil type. Based on the observation of the parametric study, mathematical models have been developed to compute the stability numbers in dry ( N γ and N c ) and seepage ( N γ ′ and N c ′ ) conditions as a function of the angle of internal friction (φ) of soil. Based on soil types and drainage conditions, appropriate solutions have been proposed to find the face pressure. The face pressure predicted by the present model has also been validated with the experimental studies of previous researchers. Hence, the developed numerical model may find potential application for the assessment of face pressure in φ and c - φ soil under both dry and seepage conditions.