基于L1范数的微分相位衬度CT稀疏角度重建算法

微分相位衬度成像及其计算层析(CT)技术是近年出现的无损检测新方法。但是,相位衬度CT往往需要对样品进行多次扫描,这必将导致非常长的辐射时间和巨大的辐射剂量。稀疏角度重建在降低辐射剂量方面有着非常明显的优势,因此,研究针对相位衬度CT的稀疏角度重建算法就显得尤为重要。在分析了相位衬度CT的特点之后,将压缩感知理论引入相位衬度CT重建中,并在该理论框架下将L1约束融入代数迭代重建(ART)算法中,提出了一种微分相位衬度CT重建算法。数值模拟和实际实验表明,该方法可以根据少量投影数据给出较好的重建结果。     

Advances in the FDTD design and modeling of nano- and bio-photonics applications

In this paper we focus on the discussion of two recent unique applications of the finite-difference time-domain (FDTD) simulation method to the design and modeling of advanced nano- and bio-photonic problems. The approach that is adopted here focuses on the potential of the FDTD methodology to address newly emerging problems and not so much on its mathematical formulation. We will first discuss the application of a traditional formulation of the FDTD approach to the modeling of sub-wavelength photonics structures. Next, a modified total/scattered field FDTD approach will be applied to the modeling of biophotonics applications including optical phase contrast microscope (OPCM) imaging of cells containing gold nanoparticles (NPs) as well as its potential application as a modality for in vivo flow cytometry configurations. The conclusion provides a justification for the selection of the two specific examples and summarizes some of the insights that could open the opportunity for the application of the FDTD approach in new research areas.     

All-reflective snapshot hyperspectral imager for ultraviolet and infrared applications

Snapshot hyperspectral imaging simultaneously acquires spatial and spectral information about a scene. We report on the first, to our knowledge, all-reflective snapshot hyperspectral imager in the form of a computed tomography imaging spectrometer (CTIS). The reflective design allows for instrument simplicity for applications in the ultraviolet and infrared. To realize a CTIS in a reflective Offner configuration, a reflective two-dimensional computer-generated hologram grating is fabricated on a convex spherical substrate by direct-write electron-beam lithography. Furthermore, a reconfigurable reflective field stop is implemented with a micromirror array to provide high-contrast spatial-spectral filtering, region-of-interest selection, and spatial structure formation.     

光子晶体光纤及其应用

光子晶体作为一种新兴的材料 ,将会对整个光子学和光子产业领域产生深远的影响 ,而其最重要的应用之一———光子晶体光纤已经在很多科研技术领域得到了应用 .文章综述了光子晶体光纤的研究进展 ,给出其分类 ,并重点介绍了光子晶体光纤在超短脉冲、光频测量、光纤通信等科研领域的重要应用以及未来的发展前景     

Nondiffracting random intensity patterns

We report a simple approach for generating nondiffracting random intensity patterns that do not change with propagation. Experimental results are shown where the generating patterns are encoded onto a phase-only liquid-crystal display. We expect that these results will be useful for encryption or surveillance applications.     

Structural markers for normal oral mucosa and oral sub-mucous fibrosis

This article presents a quantitative approach for the characterization of normal oral mucosa (NOM) in respect to thickness and textural properties of its entire epithelial layer. Histological images of oral mucosa depict that both thickness and tissue architecture at cellular and tissue level undergo change, as mucosa converts from normal to precancerous or cancerous state. In this study the thickness and fractal dimension of the mucosal epithelium of NOM and oral sub-mucous fibrosis (OSF) condition have been computed using 83 normal and 29 OSF images of oral mucosa. The result shows significant delineation between NOM and OSF in respect of both the epithelial thickness (in μm) and fractal dimensions. This quantitative characterization of oral epithelium will be of immense help for oral onco-pathologists and researchers to assess the biological nature of normal and diseased (OSF) mucosa with higher accuracy. Moreover, further differential applications may enable them to find out newer accurate quantitative diagnostic procedures to that of the usual histopathological gold standard for the assessment of malignant potentiality.     

Enhanced angular tolerance of resonant waveguide grating reflectors

We introduce an approach to enhance the angular tolerance of resonant waveguide gratings by stacking two resonant structures on top of each other. It is shown that reflectivities close to unity can be retrieved over the entire angular spectrum by a double T-shaped grating configuration. Although a combination of silicon as the high-index and diamond as the low-index material is considered, the principles of our new approach can also be used to realize monolithic silicon structures with similar properties. We illustrate that the functionality of the device can be understood by a decomposition into separated elements. Our approach might have compelling applications as new diffractive-reflective optical components with low-coating thermal noise in the field of high-precision metrology.     

Status of an R&D project of a positron gun at “Horia Hulubei” NIPNE Bucharest

A new positron gun (PG) will enable high sensitivity measurements in applications of positron annihilation spectroscopy in Romania. Some data concerning the design of a modular system for focussing, transport and acceleration of mono-energetic positrons in the range 0.8-50 keV have been obtained and experimenting on moderators and CDBS was performed. We present a short overview of the present status of the project and preliminary results from Coincidence Doppler Broadening Spectroscopy with a ²²NaCl source, on Al samples. The entire positron gun system will be designed as a high-vacuum dedicated extension operating with two options: a 50 mCi ²²NaCl source and in-line with the NIPNE cyclotron or a new intense compact cyclotron.     

Uniform Field Re-entrant Cylindrical TE$$_{01\text {U}}$$ Cavity for Pulse Electron Paramagnetic Resonance Spectroscopy at Q-band

Uniform field (UF) resonators create a region-of-interest, where the sample volume receives a homogeneous microwave magnetic field (\(B_1\)) excitation. However, as the region-of-interest is increased, resonator efficiency is reduced. In this work, a new class of uniform field resonators is introduced: the uniform field re-entrant cylindrical TE\(_{\text {01U}}\) cavity. Here, a UF cylindrical TE\(_{\text {01U}}\) cavity is designed with re-entrant fins to increase the overall resonator efficiency to match the resonator efficiency maximum of a typical cylindrical TE\(_{011}\) cavity. The new UF re-entrant cylindrical TE\(_{\text {01U}}\) cavity is designed for Q-band (34 GHz) and is calculated to have the same electron paramagnetic resonance (EPR) signal intensity as a TE\(_{011}\) cavity, a 60% increase in average resonator efficiency \(\Lambda _\mathrm{ave}\) over the sample, and has a \(B_1\) profile that is 79.8% uniform over the entire sample volume (98% uniform over the region-of-interest). A new H-type T-junction waveguide coupler with inductive obstacles is introduced that increases the dynamic range of a movable short coupler while reducing the frequency shift by 43% during over-coupling. The resonator assembly is fabricated and tested both on the bench and with EPR experiments. This resonator provides a template to improve EPR spectroscopy for pulse experiments at high frequencies.     

Experimental observation of an entire family of four-photon entangled states

A single linear-optical setup is used to observe an entire family of four-photon entangled states. This approach breaks with the inflexibility of present linear-optical setups usually designed for the observation of a particular multipartite entangled state only. The family includes several prominent entangled states that are known to be highly relevant for quantum information applications.     

Y模型四能级原子辅助光力学系统的多稳现象

本文对Y模型四能级原子辅助光力学系统的稳态特性进行了研究.结果发现,构成复合光力学系统的振动腔镜和被束缚在腔内的原子系综将随着弹簧劲度系数的减小,由单稳态过渡到多稳态.在劲度系数很大时,振动腔镜对整个光力学系统几乎无作用,光力学系统和处在腔中的原子系综都将出现一个稳态解.而当劲度系数足够小时,振动腔镜的稳态位移出现了多稳现象,随之对处于光力学腔中的原子系综的稳态行为也产生了影响,不但使得原子系综的极化率呈现出多个稳态解,同时使得腔中的原子系综对探测光的吸收和色散也发生了相应的变化.同时发现,通过调节劲度系数的取值可以控制整个系统稳态解的个数.这些研究结果在精密测量或量子信息处理等方面具有潜在应用价值.     

Analysis of input functions from different arterial branches with gamma variate functions and cluster analysis for quantitative blood volume measurements

Regional cerebral blood volume (rCBV) provides valuable information about the nature and progress of diseases of the central nervous system. While relative rCBV maps can be derived directly from dynamic susceptibility contrast data, the arterial input function (AIF) has to be measured for absolute rCBV quantification. For determination of the AIF pixels located completely within a feeding artery must be selected. However, by using a region-of-interest (ROI) based selection some confounding effects can occur, especially if single shot echo planar imaging (EPI) with low spatial resolution is used. In this study we analyzed the influence of partial volume effects and spatial misregistration due to frequency shifts induced by paramagnetic contrast agents. We analyzed AIFs from the internal carotid artery (ICA), the vertebral artery (VA) and the middle cerebral artery (MCA) using gamma variate function based parameterization. The concentration time curves (CTC) of several pixels which were selected on the basis of strong signal drop appeared distorted during the bolus passage. Moreover, the amplitudes of input functions derived from the MCA were smaller by a factor of three as compared to those of the ICA and VA. Simulations revealed that these effects can be attributed to a spatial shift of the vessel along phase-encoding direction during the passage of the bolus. We therefore developed a procedure for a pixel selection based on cluster analysis which classifies pixels according to the parameters of the fitted gamma variate functions. This approach accounted for misregistration of the vessel and yielded very consistent results for a group of normal subjects.     

The Ab Initio No-core Shell Model

This contribution reviews a number of applications of the ab initio no-core shell model (NCSM) within nuclear physics and beyond. We will highlight a nuclear-structure study of the A = 12 isobar using a chiral NN + 3NF interaction. In the spirit of this workshop we will also mention the new development of the NCSM formalism to describe open channels and to approach the problem of nuclear reactions. Finally, we will illustrate the universality of the many-body problem by presenting the recent adaptation of the NCSM effective-interaction approach to study the many-boson problem in an external trapping potential with short-range interactions.     

Elimination of beam walk-off in low-coherence off-axis photorefractive holography

Whole-field photorefractive holography can be combined with low-coherence interferometry for three-dimensional imaging and other applications, including imaging through turbid media, but the off-axis holographic recording geometry results in a limited field of view when light of low temporal coherence is used. We show that tilting the energy fronts with respect to the wave fronts by use of prisms can eliminate this problem and point out that this approach will be useful for many linear and nonlinear wave-mixing experiments.     

Towards Secure Big Data Analysis via Fully Homomorphic Encryption Algorithms

Privacy-preserving techniques allow private information to be used without compromising privacy. Most encryption algorithms, such as the Advanced Encryption Standard (AES) algorithm, cannot perform computational operations on encrypted data without first applying the decryption process. Homomorphic encryption algorithms provide innovative solutions to support computations on encrypted data while preserving the content of private information. However, these algorithms have some limitations, such as computational cost as well as the need for modifications for each case study. In this paper, we present a comprehensive overview of various homomorphic encryption tools for Big Data analysis and their applications. We also discuss a security framework for Big Data analysis while preserving privacy using homomorphic encryption algorithms. We highlight the fundamental features and tradeoffs that should be considered when choosing the right approach for Big Data applications in practice. We then present a comparison of popular current homomorphic encryption tools with respect to these identified characteristics. We examine the implementation results of various homomorphic encryption toolkits and compare their performances. Finally, we highlight some important issues and research opportunities. We aim to anticipate how homomorphic encryption technology will be useful for secure Big Data processing, especially to improve the utility and performance of privacy-preserving machine learning.     

Spectrum splitting using multi-layer dielectric meta-surfaces for efficient solar energy harvesting

We designed a high-efficiency dispersive mirror based on multi-layer dielectric meta-surfaces. By replacing the secondary mirror of a dome solar concentrator with this dispersive mirror, the solar concentrator can be converted into a spectrum-splitting photovoltaic system with higher energy harvesting efficiency and potentially lower cost. The meta-surfaces are consisted of high-index contrast gratings (HCG). The structures and parameters of the dispersive mirror (i.e. stacked HCG) are optimized based on finite-difference time-domain and rigorous coupled-wave analysis method. Our numerical study shows that the dispersive mirror can direct light with different wavelengths into different angles in the entire solar spectrum, maintaining very low energy loss. Our approach will not only improve the energy harvesting efficiency, but also lower the cost by using single junction cells instead of multi-layer tandem solar cells. Moreover, this approach has the minimal disruption to the existing solar concentrator infrastructures.     

Extremely-broad band metamaterial absorber for solar energy harvesting based on star shaped resonator

A new metamaterial absorber (MA) is investigated and shown numerically for solar energy harvesting for future solar cell applications. The structure consists of two metals and one dielectric layer having different thicknesses. Owing to this combination, the structure exhibits plasmonic resonance characteristics. In the entire spectrum of visible frequency region, the obtained results show that investigated structure has perfect absorptivity which is above 91.8%. Proposed structure also has 99.87% absorption at 613.94 THz and 99% absorption between 548 and 669 THz. The proposed structure also shows both polarization and angle independency for the entire visible region. The MA based solar cell proposes high absorption with an upper ratio of 90% in the widest range of visible spectrum comparing to the studies in literature. Hence, the proposed metamaterial absorber solar cells can be used for invisibility in entire spectrum of visible light. The absorption characteristics of the solar absorber are also investigated for infrared and ultraviolet region. The enhancement of absorption of the structure will provide new type of sensors in these frequency ranges.     

Analytical analysis of multi-pulse NMR

It is well known that in multi-pulse applications in high-resolution NMR and MRI a steady state is reached for the magnetisation vector by the effect of relaxation in combination with the pulse repetition time. In this paper, a mathematical model is developed to understand how the parameters of the pulse sequence and relaxation times T(1) and T(2) affect the behaviour of the magnetisation vector. It will be shown that even under strong simplifying conditions an analytical analysis becomes very complex and only an analytical solution can be found for 90 degrees pulses and T(1)=T(2). For other cases a numerical approach is needed. Nevertheless, the basic approach of the mathematical analysis provides a general tool for analytical multi-operator applications. Our results provide a quantitative insight in the process by which the magnetisation relaxes towards the steady-state situation in a multi-pulse sequence.     

Deterministic-statistical analysis of a structural-acoustic system

The purpose of this paper is to develop an efficient approach for vibro-acoustic analysis. Being simple and representative, an exited plate-acoustic system is selected as a validation case for the vibro-acoustic analysis as the system presents one two-dimensional statistical component (modal dense structure panel—plate) connected to the other component (deterministic acoustic volume—cavity) through the area junction over a surface domain, rather than at a line boundary. Potential industrial applications of the system vibro-acoustic analysis would be in acoustic modelling of vehicle body panels such as the cabin roof panel, and door panels for the boom noise analysis.A new deterministic-statistical analysis approach is proposed from a combination or hybrid of deterministic analysis and statistical energy analysis (SEA) approaches. General theory of the new deterministic-statistical analysis approach is introduced. The main advantage of the new deterministic-statistical analysis approach is its possibility in place of the time consuming Monte Carlo simulation. In order to illustrate and validate the new deterministic-statistical analysis approach, three approaches of the deterministic analysis, the statistical energy analysis and the new deterministic-statistical analysis are then applied to conduct the plate-acoustic system modelling, and their results will be compared. The vibro-acoustic energy coupling characteristic of the plate-acoustic system will be studied. The most suitable frequency range for the new approach will be identified in consideration of computational accuracy, information and speed.