Development of Multi-Scale X-ray Fluorescence Tomography for Examination of Nanocomposite-Treated Biological Samples

Research in cancer nanotechnology is entering its third decade, and the need to study interactions between nanomaterials and cells remains urgent. Heterogeneity of nanoparticle uptake by different cells and subcellular compartments represent the greatest obstacles to a full understanding of the entire spectrum of nanomaterials’ effects. In this work, we used flow cytometry to evaluate changes in cell cycle associated with non-targeted nanocomposite uptake by individual cells and cell populations. Analogous single cell and cell population changes in nanocomposite uptake were explored by X-ray fluorescence microscopy (XFM). Very few nanoparticles are visible by optical imaging without labeling, but labeling increases nanoparticle complexity and the risk of modified cellular uptake. XFM can be used to evaluate heterogeneity of nanocomposite uptake by directly imaging the metal atoms present in the metal-oxide nanocomposites under investigation. While XFM mapping has been performed iteratively in 2D with the same sample at different resolutions, this study is the first example of serial tomographic imaging at two different resolutions. A cluster of cells exposed to non-targeted nanocomposites was imaged with a micron-sized beam in 3D. Next, the sample was sectioned for immunohistochemistry as well as a high resolution “zoomed in” X-ray fluorescence (XRF) tomography with 80 nm beam spot size. Multiscale XRF tomography will revolutionize our ability to explore cell-to-cell differences in nanomaterial uptake.

Theoretical Modeling for the Thermal Stability of Solid Targets in a Positron-Driven Muon Collider

A future multi-TeV muon collider requires new ideas to tackle the problems of muon production, accumulation and acceleration. In the Low EMittance Muon Accelerator concept a 45 GeV positron beam, stored in an accumulation ring with high energy acceptance and low angular divergence, is extracted and driven to a target system in order to produce muon pairs near the kinematic threshold. However, this scheme requires an intensity of the impinging positron beam so high that the energy dissipation and the target maintenance are crucial aspects to be investigated. Both peak temperature rises and thermomechanical shocks are related to the beam spot size at the target for a given material: these aspects are setting a lower bound on the beam spot size itself. The purpose of this paper is to provide a fully theoretical approach to predict the temperature increase, the thermal gradients, and the induced thermomechanical stress on targets, generated by a sequence of 45 GeV positron bunches. A case study is here presented for Beryllium and Graphite targets. We first discuss the Monte Carlo simulations to evaluate the heat deposited on the targets after a single bunch of 3 × 1011 positrons for different beam sizes. Then a theoretical model is developed to simulate the temperature increase of the targets subjected to very fast sequences of positron pulses, over different timescales, from ps regime to hundreds of seconds. Finally a simple approach is provided to estimate the induced thermomechanical stresses in the target, together with simple criteria to be fulfilled (i.e., Christensen safety factor) to prevent the crack formation mechanism.

Flexible welding of SiOx nanowire to macroporous carbon film and underlying new insights

With the continuous decreasing in sizes of functional materials and devices, people are being asked to perform a flexible, accurate, in-situ and non-thermal welding of nanowires at the nanoscale. In this work, a well deliberated procedure including three typical stages: sharpening, hooking and welding, was carried out in sequence by in-situ TEM to realize the high demand welding of SiOx nanowire to macroporous carbon film. It was found that the brittle SiOx nanowire was non-thermally softened under energetic e-beam irradiation, and the flexibility and accuracy of welding could be achieved by adjusting the beam spot size, irradiation location and irradiation time. It was demonstrated that the nanocurvature effect of SiOx nanowire and the ultra-fast energy deposition effect induced by energetic e-beam irradiation dominated the diffusion, evaporation and plastic flow of atoms and the resulting nanowire re-shaping and nanowelding processes. In contrast, the traditional knock-on mechanism and e-beam heating effect are inadequate to explain these phenomena. Therefore, such a study is crucial not only to the flexible technical controlling but also to the profound fundamental understanding of energetic e-beam-induced nanowire re-shaping and nanowelding.

Practical single-photon receiving efficiency model based on Gaussian beam propagation

Modern optical technology has greatly facilitated the implementation of free-space quantum key distribution. However, the influence of atmosphere on the beam propagation is always unpredictable and could impair the system performance to some extent. It is necessary to develop an efficient model that could describe the beam propagation and receiving. In this paper, a single-photon receiving efficiency model is proposed incorporating the single-photon acquisition probability and channel transmittance based on the Gaussian beam propagation. We also present simulation and experiment of beam-spot size widening through a 0.5 km free-space channel to verify the proposed model. The results show that with the increase of turbulence strengths, the single-photon acquisition probability will degrade more sharply. The single-photon receiving efficiency will decrease with the increment of the ratio between beam centroid deflection and the receiving aperture radius [Formula: see text].

Properties of Gaussian Beam Propagating in Ring Resonator Sensor

In this paper, we deduce the paraxial analytical expression for the Gaussian beam propagating in the sandwich slab system which contained double negative material based on light transfer matrix and generalized Huygens-Fresnel integral equation; the evolution properties of emerging Gaussian beam contour graph intensity distribution on the receiver plane, the relation between beam spot size and negative refractive index coefficient, and beam side transmission view in slab system changed with three negative refractive index parameters are illustrated through numerical examples. What is more, we propose a ring resonator sensor to measure the concentration of NaCl solution on the basis of above theory, of which the operating principle is deliberatively analyzed, the influence of the concave mirror curvature radius on the emerging beam evolution is acquired, the functional relation between the normalized central intensity of the emerging beam, the beam spot size, and NaCl solution concentration is further developed by fit linear method, and the mathematical statistics results reach high precision and linearity. It is expected that the proposed ring resonator sensor and the corresponding conclusions can be useful for precise optical measurement, especially for food safety inspection and medical services of health care.