Beam Decay Research Articles

利用柱透镜调控涡旋光束的拓扑结构

The topological transformation of vortex beams using cylindrical lens is experimentally and numerically demonstrated.The intensity distributions and phase structures of vortex beams with different topological charges were analyzed after the transformation by a cylindrical lens,which were generated using the computing generated holographic method.The results show that the transformation of the cylindrical lens results in the sign change of the topological charges of the vortex beams.In addition,the higher order vortex beams decay into a beam with multiple singularities with charge-one.These observations were analyzed based on the linear superposition of higher order laser modes and Gouy phase delay.Finally,the experiment results were verified by the numerical simulations.

Propagation of Airy-related beams generated from flat-topped Gaussian beams through a chiral slab

We derived the analytical expression for the propagation of Airy-related beams generated from flat-topped Gaussian beams through an ABCD optical system, and use it to study the propagation of this type of beams through a chiral slab. Several influence factors, such as the optical beams order N and the chiral parameter γ of the chiral medium, on the beam propagation properties both in near- and far-zones are discussed in detail. It is shown that the Airy tails of high order beams decay more quickly than those of low order beams in the chiral medium; the constructive interference effect between the LCP (left-circularly polarized) and RCP (right-circularly polarized) beams becomes more significant as the chiral parameter γ increases; the LCP and RCP beams are not separated in the near-zone, while the two beams are obviously separated in the far-zone, and accordingly the interference peaks decrease as the propagation distance increases in the chiral slab.

Rotation-managed dissipative solitons

We show that when spatially localized gain landscape performs accelerated motion in the transverse plane, i.e., when it rotates or oscillates around the light propagation axis, the effective gain experienced by the light beam considerably reduces with an increase of the amplitude of oscillations or frequency of rotation of the localized gain. In the presence of uniform background losses and defocusing nonlinearity, such gain landscapes may support dynamically oscillating gain-managed solitons, but if the amplitude of oscillations or the frequency of rotation of the localized gain exceeds a threshold, stable attractors disappear and any input beam decays.

Light controlling in transverse separation modulated photonic lattices

We numerically study the propagation of Gaussian beams in four different types of transverse separation modulated photonic lattices. We find the modulation obeying hyperbolic secant or rectangular functions can act as optical potentials, and the light waves can be localized or recur in the regions between such two positive potentials, respectively. While the beams decay in the regions between such two negative potentials since these structures could not support localized modes. Our results provide new ways for light controlling and manipulation in photonic lattices.

ELECTRON-ION RECOMBINATION OF Fe XII FORMING Fe XI: LABORATORY MEASUREMENTS AND THEORETICAL CALCULATIONS

We have measured electron–ion recombination for Fe xii forming Fe xi using a merged-beam configuration at the heavy-ion storage ring TSR located at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. The measured merged-beam recombination rate coefficient (MBRRC) for collision energies from 0 to 1500 eV is presented. This work uses a new method for determining the absolute MBRRC based on a comparison of the ion beam decay rate with and without the electron beam on. For energies below 75 eV, the spectrum is dominated by dielectronic recombination (DR) resonances associated with 3s → 3p and 3p → 3d core excitations. At higher energies, we observe contributions from 3 → N' and 2 → N' core excitation DR. We compare our experimental results to state-of-the-art multi-configuration Breit-Pauli (MCBP) calculations and find significant differences, both in resonance energies and strengths. We have extracted the DR contributions from the measured MBRRC data and transformed them into a plasma recombination rate coefficient (PRRC) for temperatures in the range of 103–107 K. We show that the previously recommended DR data for Fe xii significantly underestimate the PRRC at temperatures relevant for both photoionized plasmas (PPs) and collisionally ionized plasmas (CPs). This is contrasted with our MCBP PRRC results, which agree with the experiment to within 30% at PP temperatures and even better at CP temperatures. We find this agreement despite the disagreement shown by the detailed comparison between our MCBP and experimental MBRRC results. Last, we present a simple parameterized form of the experimentally derived PRRC for easy use in astrophysical modeling codes.

兰州重离子加速器冷却储存环中电子冷却性能

In order to investigate the one-dimensional beam ordering in HIRFL-CSR, the ion beam of 58Ni19+ with the energy of 6.39 MeV/u was accumulated in the main ring of HIRFL-CSR with the help of electron cooling. The maximum accumulated ion beam intensity in the 10 seconds was measured, and the lifetime of ion beams was measured. The momentum spread of the ion beam varying with the particle number was measured during the ion beam decay, the power exponent was derived from these data, in additional, the momentum spread in the case of a constant particle number was plotted with the angle between ion and electron beams and electron beam profile. The oscillation and shift of the central frequency of the ion beam were observed during the experiments when the angle was large.

Conceptual Designs of Dipole Magnet for Muon Collider Storage Ring

Conceptual designs of a superconducting dipole magnet for a Storage Ring of a Muon Collider with a 1.5 TeV center of mass (c.o.m.) energy and an average luminosity of 10 34 cm-2s-1 are presented. In contrast to proton machines, the dipoles for the Muon Collider should be able to handle ~0.5 kW/m of dynamic heat load from the muon beam decays. The magnets are based on Nb3Sn superconductor and designed to provide an operating field of 10 T in the 20-mm aperture with the critical current margin required for reliable machine operation. The magnet cross-sections were optimized to achieve the best possible field quality in the aperture occupied by beams. The developed mechanical structures provide adequate coil prestress and support at the maximum level of Lorentz forces in the coil. Magnet parameters are reported and compared with the requirements.

The new neutron decay spectrometer P erkeo III

We present the new large neutron decay spectrometer P erkeo III designed to study neutron β -decay in-beam. It offers largely improved statistics over its predecessor P erkeo II. When used with a pulsed neutron beam, leading sources of systematic errors in other experiments are strongly suppressed or eliminated. The instrument was commissioned in a first run at the high flux reactor of the Institut Laue-Langevin, Grenoble. With a continuous polarized neutron beam, a neutron decay rate of 5 × 10 4 s - 1 was obtained.

ACORN: An experiment to measure the electron–antineutrino correlation in neutron decay

The aCORN experiment is designed to make a precision ( < 1 % ) measurement of the electron–antineutrino angular correlation ( a-coefficient) in neutron beta decay. It uses a new method proposed in 1996 by Yerozolimsky and Mostovoy. Electrons and recoil protons from neutron decay in a cold beam are detected in coincidence. The momenta of the particles are selected so that the protons form two kinematically distinct time-of-flight groups as a function of electron energy. The count rate asymmetry in these two groups is proportional to the a-coefficient. Precision spectroscopy of the protons is not required. The apparatus is currently under construction. It will be integrated and tested at the Indiana University Cyclotron Facility (IUCF) and then moved to the NIST Center for Neutron Research for the initial physics run.

Nonlinear Waves in Subwavelength Waveguide Arrays: Evanescent Bands and the “Phoenix Soliton”

We formulate wave propagation in arrays of subwavelength waveguides with sharp index contrasts and demonstrate the collapse of bands into evanescent modes and lattice solitons with superluminal phase velocity. We find a self-reviving soliton ("phoenix soliton") comprised of coupled forward- and backward-propagating light, originating solely from evanescent bands. In the linear regime, all Bloch waves comprising this beam decay, whereas a proper nonlinearity assembles them into a propagating self-trapped beam. Finally, we simulate the dynamics of such a beam and observe breakup into temporal pulses, indicating a new kind of slow-light gap solitons, trapped in time and in one transverse dimension.

Discrete diffraction and shape-invariant beams in optical waveguide arrays

General properties of linear propagation of discretized light in homogeneous and curved waveguide arrays are comprehensively investigated and compared to those of paraxial diffraction in continuous media. In particular, general laws describing beam spreading, beam decay, and discrete far-field patterns in homogeneous arrays are derived using the method of moments and the steepest-descent method. In curved arrays, the method of moments is extended to describe evolution of global beam parameters. A family of beams which propagate in curved arrays maintaining their functional shape---referred to as discrete Bessel beams---is also introduced. Propagation of discrete Bessel beams in waveguide arrays is simply described by the evolution of a complex-$q$ parameter similar to the complex-$q$ parameter used for Gaussian beams in continuous lensguide media. A few applications of the $q$ parameter formalism are discussed, including beam collimation and polygonal optical Bloch oscillations.

Structure and Drug Release in a Crosslinked Poly(Ethylene Oxide) Hydrogel

Hydrogels are a continuously expanding class of pharmaceutical polymers designed for sustained or controlled drug release. The structure and intermolecular interactions in such systems define their macroscopic properties. The aim of this study was to investigate the mechanism of swelling, drug impregnation, and drug release from poly(ethylene oxide) (PEO) gel crosslinked by urethane bonds. A combination of SAXS/WAXS/SANS techniques enabled us to determine the phase transition between lamellar and extended gel network, and to apply different descriptions of crystallinity, based on lamellar and crystal lattice structures. It is shown that even low (1-7% w/w) loading of model drugs acetaminophen and caffeine, produced significant disorder in the polymer matrix. This effect was particularly pronounced for acetaminophen due to its specific ability to form complexes with PEO. The drug-release profiles were analyzed using a general cubic equation, proposed for this work, which allowed us to determine the gel hydration velocity. The results indicate that the release profiles correlate inversely with the polymer crystallinity.

Fluorescence Recovery Under Decaying Photobleaching Irradiation: Concept and Experiment

A novel modification of photobleaching method for measurement of lateral diffusion is developed. In this approach fluorescence recovery kinetics is measured under decaying photobleaching irradiation, termed as fluorescence recovery under decaying photobleaching (FRDP). The time evolution of fluorescence intensity normalized to input irradiation starts from the photobleaching kinetics and transforms into the kinetics of fluorescence recovery at a later stage resulting in appearance of minimum. The analytical solution for the kinetics of fluorescence for Gaussian lineshape of laser beam and hyperbolic decay of irradiation in the first order approximation on bleaching rate was obtained. The accuracy of the analytical function was evaluated with exact numerical solution computed with finite differentiates method. The FRDP method was successfully applied to fluorescein solution in the glycerol/water mixture (80%) under various experimental settings using home-made experimental set-up. The FRDP approach demonstrated 25-30 fold enhancement in signal intensity over classical fluorescence recovery after photobleaching (FRAP) method at 3-5 fold increase in total irradiation. Among other advantages of the FRDP is the opportunity to perform measurements on varying time scales under constant size of the bleaching spot, including "safe" long time measurements. The potential extra advantage of FRDP method for analysis of complex diffusion in the biological system is discussed.

PYTHIA 6.4 physics and manual

The PYTHIA program can be used to generate high-energy-physics `events', i.e. sets of outgoing particles produced in the interactions between two incoming particles. The objective is to provide as accurate as possible a representation of event properties in a wide range of reactions, within and beyond the Standard Model, with emphasis on those where strong interactions play a role, directly or indirectly, and therefore multihadronic final states are produced. The physics is then not understood well enough to give an exact description; instead the program has to be based on a combination of analytical results and various QCD-based models. This physics input is summarized here, for areas such as hard subprocesses, initial- and final-state parton showers, underlying events and beam remnants, fragmentation and decays, and much more. Furthermore, extensive information is provided on all program elements: subroutines and functions, switches and parameters, and particle and process data. This should allow the user to tailor the generation task to the topics of interest.

Time-dependent all-optical logic-gates with bacteriorhodopsin film

In this paper, we proposed time-dependent AND, NOT and A ¯ B operation based on the relation between input and output intensities of the first-order diffraction beams in degenerate multi-wave coupling. When two coherent green beams are coupled in bacteriorhodopsin (bR) film with a small angle, the intensities of the diffraction beams decrease along with writing time. Based on the phenomenon that the diffraction beams decay along with writing time and the relation between the intensities of input and output beams, we demonstrated the time-dependent optical AND, NOT and A ¯ B operations.

Deviation from the standard model in the decay π + → e + νγ

A precise investigation of radiative pion decay (π+ → e+νγ) in a pion beam from the meson factory of the Paul Scherrer Institute (Switzerland) was performed by the PIBETA Collaboration with the aid of the PIBETA detector. This resulted in finding 41 601 events of radiative pion decay in three kinematical regions. The absolute values of the branching ratio for radiative pion decay were determined in each of these regions. To a precision approximately four times higher than that known previously, the ratio of the axial-vector to the vector form factor was found to be γ ≡ FA/FV = 0.443 (15), the latter being fixed at FV = 0.0259. The number of events found in the kinematical region specified by photon energies of Eγ > 55.6 MeV, positron energies of Ee > 20.0 MeV, and angles of θγ, e > 40° between the momenta of the corresponding particles (B region) was 5233. In region B, the measured branching ratio for radiative pion decay, Rπ→evγ(expt) = 11.6(3) × 10−8, proved to be smaller by eight standard deviations than that which follows from the Standard Model, Rπ→evγ (theor) = 14.34(1) × 10−8.

Optical Neural Network Architecture in Photoferroelectrics

We present a novel, versatile optoelectronic neural network architecture for implementing supervised learning in photo-ferroelectrics (Sr x Ba1 − x Nb2O6, Bi12XO20; X=Ge, Si, Ti, LiNbO3: Fe, LiTaO3:Fe and LiTaO3:Cr). The system is based on spatial multiplexing rather than the more commonly used angular multiplexing of interconnect gratings. This sample, single-crystal architecture implements a variety of multi-propagations and Marr-Albus-Kanerva style algorithms. Extensive simulations show how suitable modified supervised learning algorithms compensate for beam depletion, re-scattering, absorption and decay effects of the crystals. This type of implementation also benefits strongly from recently discovered tunable stability phenomena in the read-write properties of anisotropic crystals like photo-ferroelectric.

Fast beam decay in an electron storage ring with low-energy injection

The phenomena of the fast beam decay which was often observed in electron storage rings with low-energy injection was studied. Drift motion of the trapped ions in the bending magnetic field was found to play an important role in the fast beam decay.

Three-dimensional structure of a human Fab with high affinity for tetanus toxoid

Background: The wide range of antibody specificity and affinity results from the differing shapes and chemical compositions of their binding sites. These shapes range from discrete grooves in antibodies elicited by linear oligomers of nucleotides and carbohydrates to shallow depressions or flat surfaces for accommodation of proteins, peptides and large organic compounds. Objectives: To determine the Fab structure of a high-affinity human antitoxin antibody. To explore structural features which enable the antibody to bind to intact tetanus toxoid, peptides derived from the sequence of the natural immunogen and antigenic mimics identified by combinatorial chemistry. To explain why this Fab shows a remarkable tendency to produce crystals consistently diffracting to d spacings of 1.7–1.8 Å. To use this information to engineer a strong tendency to crystallize into the design of other Fabs. Study design: The protein was crystallized in hanging or sitting drops by a microseeding technique in polyethylene glycol (PEG) 8000. Crystals were subjected to X-ray analysis and the three-dimensional structure of the Fab was determined by the molecular replacement method. Interactive computer graphics were employed to fit models to electron density maps, survey the structure in multiple views and discover the crystal packing motif of the protein. Results: Exceptionally large single crystals of this protein have been obtained, one measuring 5×3×2 mm (l×w×d). The latter was cut into six irregular pieces, each retaining the features of the original in diffracting to high resolution (1.8 Å) with little decay in the X-ray beam. In an individual Fab, the active site is relatively flat and it seems likely that the protein antigen and derivative peptides are tightly held on the outer surface without significant penetration into the interior. There is no free space to accommodate even a dipeptide between VH and VL. One of the unique features of the B7-15A2 Fab is a large aliphatic ridge dominating the center of the active site. The CDR3 of the H chain contributes significantly to this ridge, as well as to adjoining regions projected to be important for the docking of the antigen. Both the ease of crystallization and the favorable diffraction properties are mainly attributable to the tight packing of the protein molecules in the crystal lattice. Discussion: The B7-15A2 active site provides a stable and well defined platform for high affinity docking of proteins, peptides and their mimotopes. The advantages for future developments are suggested by the analysis of the crystal properties. It should be possible to incorporate the features promoting crystallization, close packing and resistance to radiation damage into engineered human antibodies without altering the desired specificities and affinities of their active sites.

Determination of the branching ratiosΓ(K L→3π0)/Γ(K L→π+ - 0) andΓ(K L→3π0)/Γ(K L→πev)

Improved branching ratios were measured for the $K_L \to 3 \pi^0 $ decay in a neutral beam at the CERN SPS with the NA31 detector: $\Gamma (K_L \to 3 \pi^0) / \Gamma (K_L \to \pi^+ \pi^- \pi^0) = 1.611 \pm 0.037$ and $\Gamma (K_L \to 3 \pi^0) / \Gamma (K_L \to \pi e \nu ) = 0.545 \pm 0.010$. From the first number an upper limit for $\Delta I =5/2$ and $\Delta I = 7/2 $ transitions in neutral kaon decay is derived. Using older results for the Ke3/K$\mu $3 fraction, the 3$\pi^0$ branching ratio is found to be $\Gamma (K_L \to 3 \pi^0 )/ \Gamma_{tot} = (0.211 \pm 0.003)$, about a factor three more precise than from previous experiments.