Current and current density limitations in existing electron storage rings

Storage rings dedicated for synchrotron light sources must show good beam performances in order to obtain high flux and brilliance. In particular bunch length, energy spread, beam intensity and transverse emittances have to satisfy special requirements.We intend here to briefly overview twenty years of experience obtained with small and medium size storage rings which were initially built as high energy physics facilities. The limiting effects will be extensively discussed by comparing theoretical models with systematic experimental studies.The possible means to remedy the inconveniences are also mentioned.     

Fano and Dicke effects in a double Rashba-ring system

The electronic transport in a system of two quantum rings side-coupled to a quantum wire is studied via a single-band tunneling tight-binding Hamiltonian. We derived analytical expressions for the conductance and spin polarization when the rings are threaded by magnetic fluxes with Rashba spin-orbit interaction. We show that by using the Fano and Dicke effects this system can be used as an efficient spin filter even for small spin-orbit interaction and small values of magnetic fluxes. We compare the spin-dependent polarization of this design and the polarization obtained with one ring side-coupled to a quantum ring. As a main result, we find better spin polarization capabilities as compared to the one-ring design.     

Development of copper beam ducts with antechambers for advanced high-current particle storage rings

There has been continuous progress at the High Energy Accelerator Research Organization (KEK) in R&D on vacuum beam ducts adaptable to future high-current particle storage rings. Here we proposed copper beam ducts with antechambers to deal with the severe issues attributed to the high beam currents. The proposed antechamber scheme can withstand intense synchrotron radiation (SR), provide a beam duct with low beam impedance, and effectively reduce the electron cloud effect (ECE) in positron/proton rings. Several trial models were manufactured by a pressing or cold-drawn method, and assembled with electron beam welding. Special vacuum components, such as connection flanges, distributed pumps, and gate valves, were customized for the beam ducts. TiN coating on the inner surface of the beam duct was also investigated as a mitigating measure for the ECE. Trial models of the copper beam ducts were installed into the KEK B-factory (KEKB), and their performances were evaluated using real positron and electron beams.     

Self-polarization of protons in storage rings

It has been proposed that stored proton or heavy ion beams can be polarized by spatially separating particles with opposite spin directions, using the Stern-Gerlach effect in alternating quadrupole fields. The growth rate of the vertival betatron amplitude is calculated for beam halves with opposite polarizations rotating in the horizontal plane, at intrinsic spin resonance aγ ± ν_y = integer. This polarization method would work best with rings having large diameter, low vertical emittance, low vertical betatron tune, and strong superconducting quadrupoles. Provided that suitable strong quadrupoles exist, the method might advantageously replace the present technique for obtaining polarized proton or heavy ion beams, where low energy polarized beams are first generated by a source and then accelerated through numerous depolarizing resonances up to the final energy. Although the proposed self-polarization in the present colliders and storage rings might be impractically slow, it is shown that in a purpose-built machine the vertical splitting rate of the beam might be reasonably fast compared with the beam blowup or decay.     

Magnetoresistance behavior of ferromagnetic nanorings in a ring-wire hybrid configuration

We present a technique for probing the magnetic configurations in ferromagnetic rings electrically without placing the electrical contact leads directly on the nanorings, but on wires attached to the ring structures. The magnetic configurations in pseudo spin valve rectangular and elliptical rings of width in the range from 60 to 300?nm have been systematically mapped using this technique. The giant magnetoresistance (GMR) responses for both the rings exhibit distinct switching fields and features corresponding to identifiable magnetization states in different segments of the nanostructures.     

Magnetoelectric Spin-FET for Memory,Logic, and Amplifier Applications

We propose a ballistic magneto-electric device that permits conductance modulation with both electric and magnetic fields applied perpendicular to its current conduction channel. Fields are applied through the ferromagnetic gates deposited on top of a HEMT heterostructure that contains a 2DEG for current conduction. The minimal-coupling Hamiltonian with spatially uniform electrical potentials, and delta Zeeman splitting is solved in the weak-coupling limit for which the Rashba spin orbit coupling is not considered. Ballistic transmission of electrons through a periodic system of zero-gauge double-pair magnetoelectric barriers is studied. Manipulation of barriers’ geometrical symmetry and configuration leads to the conception of a spin-FET for non-volatile storage and digital logic operations. The linear modulation of electron spin polarization (|P|) is also studied for its relevance to electrical signal amplification. Perpendicular magnetization of the ferromagnetic gates permits modulation of both |P| and electron transmission (T) threshold, the latter is particularly useful for spin logic design.     

Channel modeling and estimation for intrapage equalization in pixel-matched volume holographic data storage

We present two different channel models (the magnitude model and the intensity model) for a pixel-matched volume holographic data storage system that employs the 4-focal-length architecture. First, a framework to describe the channel models is developed. We evaluate the linearity of the channel models by comparing data values obtained from diffraction-limited interference with data values predicted by the channel models. The models are evaluated for linearity and equalization gain under different storage and read-back conditions, such as fill factors, apertures, and contrast ratios. Bit error rate results obtained by use of linear equalization methods in conjunction with the channel models developed are also presented. Our results suggest that the magnitude model leads to better performance when the fill factors are small, whereas the intensity model appears to be more appropriate for the high-fill-factor cases. The magnitude model, when suitable, appears to provide a storage density improvement of as great as 65%, whereas the intensity model seems capable of providing as much as 15% density gain through deconvolution. The optimum aperture for storage seems to be close to the Nyquist aperture.     

Analytical models for pick distances in fishbone warehouse based on exact distance contour

The pick distance models for a unit load warehouse employing fishbone layout conventionally use semicircular approximation for distance contour which can result in significant error. This paper develops discrete and continuous pick distance models for fishbone layout under random, full turnover, and class-based storage policies based on exact polygonal distance contour. Class-based storage policy with three classes was found to give pick distance comparable to full turnover policy over a range of demand skews and warehouse shapes studied. The discrete and continuous models are compared considering finite storage space, aisle width and discontinues in the ABC curve for a real life data. The sensitivity of warehouse performance over a range of warehouse parameters is studied. We also outline a methodology for class-based storage design where class partitions can be derived for a warehouse of any dimension from the results of a unit area warehouse.     

Frustration Effects in Magnetic Molecules

Besides being a fascinating class of new materials, magnetic molecules provide the opportunity to study concepts of condensed matter physics in zero dimensions. This contribution will exemplify the impact of molecular magnetism on concepts of frustrated spin systems. We will discuss spin rings and the unexpected rules that govern their low-energy behavior. Rotational bands, which are experimentally observed in various molecular magnets, provide a useful, simplified framework for characterizing the energy spectrum, but there are also deviations thereof with far-reaching consequences. It will be shown that localized independent magnons on certain frustrated spin systems lead to giant magnetization jumps, a new macroscopic quantum effect. In addition a frustration-induced metamagnetic phase transitions will be discussed, which demonstrates that hysteresis can exist without anisotropy. Finally, it is demonstrated that frustrated magnetic molecules could give rise to an enhanced magnetocaloric effect.     

集成模糊特征的Snakes模型分割图像纹理

对纹理图像进行局部一维离散傅里叶变换,把傅里叶变换能反映图像纹理的高频部分的振幅谱作为纹理的特征向量.利用模糊概念定义模糊特征向量,把模糊特征向量集成到Snakes模型.改进的Snakes模型使活动轮廓曲线在曲线内部力场、图像梯度力场和特征向量对区域的模糊隶属度确定大小的曲线法向力场的共同作用下运动.对纹理实验图像和真实图像的进行了分割实验,实验结果说明新的模型能对图像纹理进行有效的分割,模糊特征的融入扩大了Snakes模型分割图像的范围.     

Tunnelling spectra of individual magnetic endofullerene molecules

The manipulation of single magnetic molecules may enable new strategies for high-density information storage and quantum-state control. However, progress in these areas depends on developing techniques for addressing individual molecules and controlling their spin. Here, we report success in making electrical contact to individual magnetic N@C(60) molecules and measuring spin excitations in their electron tunnelling spectra. We verify that the molecules remain magnetic by observing a transition as a function of magnetic field that changes the spin quantum number and also the existence of non-equilibrium tunnelling originating from low-energy excited states. From the tunnelling spectra, we identify the charge and spin states of the molecule. The measured spectra can be reproduced theoretically by accounting for the exchange interaction between the nitrogen spin and electron(s) on the C(60) cage.     

Fixed-length two-dimensional modulation coding for imaging page-oriented optical data storage systems

We present a comprehensive discussion of modulation coding for page-oriented optical data storage (PODS) systems that write and read data in a two-dimensional (2-D) bit image format. We give several 2-D mathematical models for these systems, including two-photon optical data storage systems. Using these models, we describe the nature of intersymbol interference (ISI) in imaging PODS systems and find that its characteristics are different from ISI in conventional serial magnetic and optical data storage systems. To overcome the ISI in these imaging PODS systems, we present what is, to our knowledge, a novel 2-D modulation coding scheme. We also present many examples of fixed-length 2-D modulation codes with diverse properties. Finally, we analyze and compare the bit-error rate performance of these codes.     

Dose build up correction for radiation monitors in high-energy bremsstrahlung photon radiation fields

Conventional radiation monitors have been found to underestimate the personal dose equivalent in the high-energy bremsstrahlung photon radiation fields encountered near electron storage rings. Depth-dose measurements in a water phantom were carried out with a radiation survey meter in the bremsstrahlung photon radiation fields from a 450 MeV electron storage ring to find out the magnitude of the underestimation. Dose equivalent indicated by the survey meter was found to build up with increase in thickness of water placed in front of the meter up to certain depth and then reduce with further increase in thickness. A dose equivalent build up factor was estimated from the measurements. An absorbed dose build up factor in a water phantom was also estimated from calculations performed using the Monte Carlo codes, EGS-4 and EGSnrc. The calculations are found to be in very good agreement with the measurements. The studies indicate inadequacy of commercially available radiation monitors for radiation monitoring within shielded enclosures and in streaming high-energy photon radiation fields from electron storage rings, and the need for proper correction for use in such radiation fields.     

Decoherence of nuclear spin quantum memory in a quantum dot

Recently, an ensemble of nuclear spins in a quantum dot have been proposed as a long-lived quantum memory. A quantum state of an electron spin in the dot can be faithfully transfered into nuclear spins through controlled hyperfine coupling. Here we study the decoherence of this memory due to nuclear spin dipolar coupling and inhomogeneous hyperfine interaction during the storage period. We calculated the maximum fidelity of writing, storing, and reading operations. Our results show that nuclear spin dynamics can severely limit the performance of the proposed device for quantum information processing and storage based on nuclear spins.     

Collective magnetic behavior of graphene nanohole superlattices

We predict a new class of 2-D crystalline “bulk” magnets—the graphene nanohole (GNH) superlattices with each GNH acting like a “super” magnetic atom, using first principles calculations. We show that such superlattices can exhibit long-range magnetic order above room temperature, with a collective magnetic behavior governed by inter-NH spin spin interactions in additional to intra-NH spin ordering. Furthermore, magnetic semiconductors can be made by doping magnetic NHs into semiconducting NH superlattices. The possibility of engineering magnetic GNHs for storage media and spintronics applications is discussed. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users.     

Magnonics: Spin Waves on the Nanoscale

Magnetic nanostructures have long been in the focus of intense research in the magnetic storage industry. For data storage the nonvolatility of magnetic states is of utmost relevance. As information technology generates the need for higher and higher data‐transfer rates, research efforts have moved to understand magnetization dynamics. Here, spin waves and their particle‐like analog, magnons, are increasingly attracting interest. High‐quality nanopatterned magnetic media now offer new ways to transmit and process information without moving electrical charges. This new functionality is enabled by spin waves. They are confined by novel functioning principles, which render them especially suitable to operate at the nanoscale. Magnonic crystals are expected to provide full control of spin waves, similarly to what photonic crystals already do for light. Combined with nonvolatility, multifunctional metamaterials might be formed. We report recent advances in this rapidly increasing research field called magnonics.     

Finite Size Effects in Anisotropic <Emphasis Type="Italic">u</Emphasis> = ∞ Hubbard Ladder Rings

We apply perturbation theory and cyclic spin permutation formalism to study the lowest energy states of the infinite-repulsion Hubbard model on finite fragments of n-leg ladder rings and show jump-wise behavior of the ground state spin S ₀ as a function of fragment parameters.     

A New Class of 1D States for Liquid 3He

We examine the structure and energetics of ⁴He drops with added ³He atoms, deposited on flat alkali surfaces at zero temperature, and find that single ³He particles populate one dimensional bound states localized around the contact line. We analyze the possibility of a new type of Luttinger liquid behavior in mixtures of helium isotopes on Cs substrates, and examine possible measurable manifestations of the presence of these rings, such as the spectrum of undamped spin density fluctuations.     

Spin Rabi flopping in the photocurrent of a polymer light-emitting diode

Electron spin is fundamental in electrical and optical properties of organic electronic devices. Despite recent interest in spin mixing and spin transport in organic semiconductors, the actual spin coherence times in these materials have remained elusive. Measurements of spin coherence provide impartial insight into spin relaxation mechanisms, which is significant in view of recent models of spin-dependent transport and recombination involving high levels of spin mixing. We demonstrate coherent manipulation of spins in an organic light-emitting diode (OLED), using nanosecond pulsed electrically detected electron spin resonance to drive singlet-triplet spin Rabi oscillations. By measuring the change in photovoltaic response due to spin-dependent recombination, we demonstrate spin control of electronic transport and thus directly observe spin coherence over 0.5 s. This surprisingly slow spin dephasing underlines that spin mixing is not responsible for magnetoresistance in OLEDs. The long coherence times and the spin manipulation demonstrated are crucially important for expanding the impact of organic spintronics.     

Models for Understanding Flexible Manufacturing Systems

The basic features of flexible manufacturing systems are reviewed and models for determining the production capacity of such systems are developed. These models show the desirability of a balanced work load, the benefit of diversity in job routing if there is adequate control of the release of jobs (a job shop can be better than a flow shop), and the superiority of common storage for the system over local storage at machines. The models are extended to allow for material handling delays between machines and for unreliable machines. It is also shown that production capacity models can be used to develop good approximations to the mean number of jobs in the system for given job arrival rates and machine utilizations.