Ostwald ripening of beta-carotene nanoparticles

Ostwald ripening, the interfacial-energy-driven dissolution and reprecipitation of solutes, becomes an increasingly significant problem for nanoparticle formulations. We present the first quantitative study of Ostwald ripening for nanoparticle dispersions. The Lifshitz-Slyozov-Wagner (LSW) theory of particle growth driven by diffusion is applied to study beta-carotene nanoparticles with sizes of O(100 nm) formed by our block-copolymer protected Flash Nanoprecipitation process. A numerical implementation of the LSW theory that accounts for the original particle size distribution is presented. The predicted particle sizes from the numerical simulation are compared with the experimental results measured by dynamical light scattering. The results show quantitative agreement with no adjustable parameters. The addition of antisolvent results in the reduction of the ripening rate by dramatically decreasing bulk solubility.     

Channeling chaos by building barriers

Chaotic diffusion often represents a severe obstacle for the setup of experiments, e.g., in fusion plasmas or particle accelerators. We present a complete test of a method of control of Hamiltonian chaos, with both its numerical test and its first experimental realization on a paradigm for wave-particle interaction, i.e., a travelling wave tube. The core of our approach is a small apt modification of the system which channels chaos by building barriers to diffusion. Its experimental realization opens the possibility to practically achieve the control of a wide range of systems at a low additional cost of energy.     

Strong and weak constraint variational assimilations for reduced order fluid flow modeling

In this work we propose and evaluate two variational data assimilation techniques for the estimation of low order surrogate experimental dynamical models for fluid flows. Both methods are built from optimal control recipes and rely on proper orthogonal decomposition and a Galerkin projection of the Navier Stokes equation. The techniques proposed differ in the control variables they involve. The first one introduces a weak dynamical model defined only up to an additional uncertainty time-dependent function whereas the second one, handles a strong dynamical constraint in which the dynamical system’s coefficients constitute the control variables. Both choices correspond to different approximations of the relation between the reduced basis on which is expressed the motion field and the basis components that have been neglected in the reduced order model construction. The techniques have been assessed on numerical data and for real experimental conditions with noisy particle image velocimetry data.     

Brownian dynamics simulations of colloidal hard spheres. Effects of sample dimensionality on self-diffusion

The self-diffusion coefficients of colloidal hard spheres were determined by Brownian dynamics (BD) computer simulations using a new efficient algorithm for treatment of the hard-sphere interactions. Calculations were done on an Apple PC type MacIIcx and on a Micro VAX 3000, considering samples in two and three dimensions at varying particle concentrations. Our results in three dimensions are compared with experimental results from our own group which were obtained by forced Rayleigh scattering (FRS), and with numerical results from a dynamical Monte Carlo simulation by Cichocki and Hinsen. Good agreement with the latter was found for particle volume fractions up to 0.40. Differences in the dynamical behavior of our numerically treated 2D and 3D samples are discussed using a simple geometrical model to enable comparison of particle concentrations in samples with different dimensionality.     

Study of the Z-Pinch Plasma Initiated by the Electron Beam

A lot of activities are carried out to develop compact laser accelerators. The transportation and focusing of beams in Z-pinch-type discharges, which requires thorough investigations into methods for the formation of these discharges, are important problems to be solved. At the ITEP, an experimental setup [1] is constructed to study Z-pinch plasma dynamics when the discharge is initiated by an electron beam. The first results of the experimental and numerical investigations show that development of the discharge initiated by an electron beam differs considerably from the ordinary Z-pinch formation process.     

机器学习在大型粒子加速器中的应用回顾与展望

机器学习技术在近十几年发展迅猛,并被广泛地用于解决复杂的科学和工程问题。最近十年间,基于机器学习的粒子加速器相关研究也开始呈现出井喷式发展趋势。国际上许多加速器实验室开始尝试用机器学习和大数据技术处理加速器中的海量复杂数据,以期解决加速器及其子系统中的诸多物理和技术问题。不过,迄今为止,机器学习在加速器中的应用仍处于初步探索阶段,不同机器学习算法在解决具体加速器问题的效果及其适用范围尚待摸索,机器学习在实际加速器中的应用仍非常有限。因此,有必要对加速器领域中的机器学习研究做一个整体回顾和总结。将回顾机器学习在大型粒子加速器（以储存环加速器和直线加速器为主）中的加速器技术、束流物理以及加速器整体性能优化等研究方向中已取得的研究成果,并探讨机器学习在加速器领域的未来发展方向和应用前景。     

RF focusing of ion beams in the axisymmetric periodic structure of a linac

A new approach to the analysis of charge particle motion in periodic resonant RF accelerators is suggested. A three-dimensional equation of motion in the Hamiltonian form is derived. This equation makes it possible to carefully study the relationship between the transverse and the longitudinal dynamics of the ion beams at low initial energies. General conditions for RF focusing in ion linacs are formulated. Basic results are compared with numerical simulation data for the beam dynamics in the polyharmonic field of the accelerating cavity. A version of an RF-focusing proton accelerator in which the current transmission coefficient is close to that in an accelerator with radio frequency quadrupole is described.     

Melting and crystallization dynamics of single-crystal silicon exposed to compression plasma flows

The melting and crystallization of single-crystal silicon wafers exposed to compression plasma flows generated by quasi-stationary plasma accelerators are studied by numerical simulation. The results include the phase transition kinetics described on the basis of the Kolmogorov equation. The space-time characteristics of the melting and crystallization processes for variously shaped plasma pulses are discussed. Based on the experimental data and estimates, it is concluded that thermoelectric instability plays an essential role in the formation of three-dimensional periodic structures.     

螺线管透镜的三级李映射

用李代数方法分析了带电粒子在螺线管透镜中的运动,得到六维相空间中粒子轨迹的三级近似解,并包含了运动的相对论效应.当需要时,还可以扩展到更高级像差.     

Nonequilibrium Linear Response for Markov Dynamics, I: Jump Processes and Overdamped Diffusions

Systems out of equilibrium, in stationary as well as in nonstationary regimes, display a linear response to energy impulses simply expressed as the sum of two specific temporal correlation functions. There is a natural interpretation of these quantities. The first term corresponds to the correlation between observable and excess entropy flux yielding a relation with energy dissipation like in equilibrium. The second term comes with a new meaning: it is the correlation between the observable and the excess in dynamical activity or reactivity, playing an important role in dynamical fluctuation theory out-of-equilibrium. It appears as a generalized escape rate in the occupation statistics. The resulting response formula holds for all observables and allows direct numerical or experimental evaluation, for example in the discussion of effective temperatures, as it only involves the statistical averaging of explicit quantities, e.g. without needing an expression for the nonequilibrium distribution. The physical interpretation and the mathematical derivation are independent of many details of the dynamics, but in this first part they are restricted to Markov jump processes and overdamped diffusions.     

Control-parameter-dependent Swift-Hohenberg equation as a model for bioconvection patterns

We consider a complex Swift-Hohenberg equation with control-parameter-dependent coefficients and use it as a model to describe dynamical features seen in an experimental bacterial bioconvection pattern. In particular, we give numerical results showing the development of a phase-unstable pattern behind a moving front.     

Investigation of the focusing of a 50-GeV proton beam using a new crystal device

Bent crystals are used at large accelerators to deflect particle beams for extraction and collimation. Not only the deflection but also the focusing of beams by bent crystals can be required for recently formulated proposals for investigations at the Large Hadron Collider (LHC) with a fixed target. The experimental results on the focusing of a 50-GeV proton beam with a new crystal device, which can be used in a circulating beam of a large accelerator such as the LHC, have been reported.     

Compact CC-18/9, CC-12, and MCC-30/15 cyclotrons for the production of medical radioisotopes

A compact cyclotron concept is presented, the design features of advanced compact cyclotrons are highlighted, the performance specifications of the accelerators are described, and the results of numerical simulation and experimental investigation of the main (magnetic and acceleration) systems are given.     

NESTOR: An underwater neutrino observatory in the Ionian sea

Deep underwater high energy neutrino detection is a very promising field in both elementary particle physics and astrophysics. On one side, the energy range of ground based accelerators cannot be extended much more respect to the present, leaving only astronomical sources for future investigations. In the astrophysics field, neutrinos are the tool to explore further in the universe due to their low interactions. By the same token, the experimental problems for a neutrino detector are enormous. The Cherenkov effect is practically the only possible tool, because it uses sea water both as shield and as detector. NESTOR is the first step toward a full fledged deep underwater neutrino experiment. While its area, of the order of 10000 m^**2, cannot hope to identify all possible celestial sources, it is nevertheless a necessary step toward the “Km^**3” experiment. The first deployment tests have already been performed, proving the feasibility of the mechanical design, and the electronics is almost completely ready. Additional tests are scheduled for this autumn and next year will see a relevant part of the experiment installed at the bottom of the Ionian sea.     

带电粒子加速器的基本类型及其技术实现

现代粒子加速器的发展已有100年的历史。给出了粒子加速器主要类型的简单分类图表,从粒子加速器发展过程中相关概念演变和加速器技术逻辑发展的角度,概述了粒子加速器的基本类型、基本工作原理、相应的技术实现途径以及各类加速器的典型的技术特征。     

Observation of shot noise suppression at optical wavelengths in a relativistic electron beam

Control of collective properties of relativistic particles is increasingly important in modern accelerators. In particular, shot noise affects accelerator performance by driving instabilities or by competing with coherent processes. We present experimental observations of shot noise suppression in a relativistic beam at the Linac Coherent Light Source. By adjusting the dispersive strength of a chicane, we observe a decrease in the optical transition radiation emitted from a downstream foil. We show agreement between the experimental results, theoretical models, and 3D particle simulations.     

Cosmic Imagery: Key Images in the History of Science,by John D. Barrow

Particle accelerators are finding increasing use in the study of materials. This review will concentrate on their application to study radiation damage effects. The first section will deal with the basic interaction of particle beams with solids, the production of defects and their agglomeration, and phenomena such as irradiation-enhanced diffusion and precipitation. The second part of the review complements the recent Contemporary Physics article by J. R. Matthews (1977) which deals with the behaviour of materials in fast reactors. It discusses in some detail the application of particle accelerators to technological problems such as void formation in fast reactor materials and irradiation enhanced creep.     

Exact results on cavity cooling in a system of a two-level atom and a cavity field

Using the algebraic dynamical method, this paper investigates the laser cooling of a moving two-level atom coupled to a cavity field. Analytical solutions of optical forces and the cooling temperatures are obtained. Considering Rb atoms as an example, it finds that the numerical results are relevant to the recent experimental laser cooling investigations.     

Realizing a laser-driven electron source applicable for radiobiological tumor irradiation

Laser-accelerated electron pulses have been used to irradiate human tumors grown on mice’s ears during radiobiological experiments. These experiments have been carried out with the JETI laser system at the Institute of Optics and Quantum Electronics in Jena, Germany. To treat a total of more than 50 mice, a stable and reliable operation of the laser-electron accelerator with a dose rate exceeding 1 Gy/min was necessary. To achieve this, a sufficient number of electrons at energies in excess of 5 MeV had to be generated. The irradiation time for a single mouse was a few minutes. Furthermore, the particle pulses’ parameters needed to remain achievable for a time period of several weeks. Due to the online detection of the radiation dose, the unavoidable shot-to-shot fluctuations, currently still typical for laser-based particle accelerators, could be compensated. The results demonstrate that particle pulses generated with laser-based accelerators have the potential to be a future alternative for conventional particle accelerators used for the irradiation of tumors.     

Heavy fermion quantum criticality

During the last few years, investigations of rare-earth materials have made clear that heavy fermion quantum criticality exhibits novel physics not fully understood. In this work, we write for the first time the effective action describing the low energy physics of the system. The f fermions are replaced by a dynamical scalar field whose nonzero expected value corresponds to the heavy fermion phase. The effective theory is amenable to numerical studies as it is bosonic, circumventing the fermion sign problem. Via effective action techniques, renormalization group studies, and Callan-Symanzik resummations, we describe the heavy fermion criticality and predict the heavy fermion critical dynamical susceptibility and critical specific heat. The specific heat coefficient exponent we obtain (0.39) is in excellent agreement with the experimental result at low temperatures (0.4).