High-Flux Neutron Generator Based on Laser-Driven Collisionless Shock Acceleration.

A novel compact high-flux neutron generator with a pitcher-catcher configuration based on laser-driven collisionless shock acceleration (CSA) is proposed and experimentally verified. Different from those that previously relied on target normal sheath acceleration (TNSA), CSA in nature favors not only acceleration of deuterons (instead of hydrogen contaminants) but also increasing of the number of deuterons in the high-energy range, therefore having great advantages for production of high-flux neutron source. The proof-of-principle experiment has observed a typical CSA plateau feature from 2 to 6 MeV in deuteron energy spectrum and measured a forward neutron flux with yield 6.6×10^{7} n/sr from the LiF catcher target, an order of magnitude higher than the compared TNSA case, where the laser intensity is 10^{19} W/cm^{2}. Self-consistent simulations have reproduced the experimental results and predicted that a high-flux forward neutron source with yield up to 5×10^{10} n/sr can be obtained when laser intensity increases to 10^{21} W/cm^{2} under the same laser energy.

Tuning magnetic properties for domain wall pinning via localized metal diffusion.

Precise control of domain wall displacement in nanowires is essential for application in domain wall based memory and logic devices. Currently, domain walls are pinned by creating topographical notches fabricated by lithography. In this paper, we propose localized diffusion of non-magnetic metal into ferromagnetic nanowires by annealing induced mixing as a non-topographical approach to form pinning sites. As a first step to prove this new approach, magnetodynamic properties of permalloy (Ni80Fe20) films coated with different capping layers such as Ta, Cr, Cu and Ru were investigated. Ferromagnetic resonance (FMR), and anisotropy magnetoresistance (AMR) measurements were carried out after annealing the samples at different temperatures (T an ). The saturation magnetization of Ni80Fe20 film decreased, and damping constant increased with T an . X-Ray photoelectron spectroscopy results confirmed increased diffusion of Cr into the middle of Ni80Fe20 layers with T an . The resistance vs magnetic field measurements on nanowires showed intriguing results.

Large-charge quasimonoenergetic electron beams produced by off-axis colliding laser pulses in underdense plasma.

Electrons can be efficiently injected into a plasma wave by colliding two counterpropagating laser pulses in a laser wakefield acceleration. However, the generation of a high-quality electron beam with a large charge is difficult in the traditional on-axis colliding scheme due to the growth of the electron beam duration coming from the increase of the beam charge. To solve this problem, we propose an off-axis colliding scheme, in which the collision point is away from the axis of the driver pulse. We show that the electrons injected from the off-axis region are highly concentered on the tail of the bubble even for a large trapped charge, thus feeling almost the same accelerating field. As a result, quasimonoenergetic electron beams with a large charge can be produced. The validity of this scheme is confirmed by both the particle-in-cell simulations and the Hamiltonian model. Furthermore, it is shown that a Laguerre-Gauss (LG) laser can be adopted as the injection pulse to realize the off-axis colliding injection in three dimensions symmetrically, which may be useful in simplifying the technical layout of the real experiment setup.

Reduction of magnetic damping and isotropic coercivity and increase of saturation magnetization in Rh-incorporated CoIr system.

Replacing Ir with Rh in a CoIr system possessing negative uniaxial magnetocrystalline anisotropy (K u ) substantially reduces its magnetic damping and coercivity by more than half while retaining its high negative K u . Moreover, a higher saturation magnetization (M s ) and more isotropic coercivity are achieved. Such material development makes it particularly suitable for use as the soft underlayer (SUL) of magnetic recording media for reducing noise, and as the oscillation layer of a spin-torque oscillator (STO) for achieving higher oscillation frequency, larger AC magnetic field and lower driving current, which can be readily integrated with the current recording head for microwave-assisted magnetic recording. Finally, we recommend a composite free layer by coupling CoIr with a spin polarizer (Co or Co/Cu/Co) for the enhancement of the spin-polarization rate and, therefore, the improvement of STO efficiency. These could pave the way for CoIr-based materials to be implemented in devices requiring a negative Ku with low damping and high 'softness', such as oscillators.

Epigenetic changes of the Klotho gene in age-related cataracts.

OBJECTIVE: To determine the mRNA and protein expression, and methylation levels of the Klotho in lens epithelial cells (LECs) of normal transparent lenses and age-related cataracts (ARCs), and to explore the role of epigenetic changes of the Klotho gene in regulating the development of ARCs. PATIENTS AND METHODS: A total of 90 subjects were divided into three groups: a young adult group with normal transparent lenses aging from18 to30 years, a middle-aged group with ARC aging from 40 to 49 years, and an elderly group with ARC aging from 67 to 85 years. The LECs were collected through curvilinear capsulorhexis. The mRNA expression of the Klotho gene was determined using the reverse transcription polymerase chain reaction (RT-PCR). Protein expression of the Klotho gene in LECs was detected using immunohistochemical (IHC) staining. The methylation specific polymerase chain reaction (MSP) was used to detect the methylation level of the target gene. RESULTS: Decreased mRNA expression of the Klotho gene was reversely correlated with age. IHC results showed that the Klotho was mainly expressed in the cell membrane and cytoplasm of LECs. It was strongly positive in the young adult group (100.0%), with even distribution; weakly positive in the middle-aged group (36.7%), with expression distributed 4-5 mm away from the center of the anterior lens capsule; and negative in the elderly group (0.0%). MSP results showed that the Klotho gene was highly methylated in the elderly group (93.3%) and weakly methylated (56.7%) in the middle-aged group, but barely methylated in the young adult group (3.3%). CONCLUSIONS: Klotho were positively expressed in the LECs of normal individuals at the mRNA and protein level. Its promoter showed increased methylation as age increased, resulting in Klotho gene silencing as well as down-regulated expression or no expression of the Klotho protein. These epigenetic changes could affect the biological activities of LECs, which provided the basis for further studies of the association between the Klotho gene and ARC.

Wire network behavior in superconducting Nb films with diluted triangular arrays of holes.

We present results of transport measurements on superconducting Nb films with diluted triangular arrays (honeycomb and kagomé) of holes. The patterned films have large disk-shaped interstitial regions even when the edge-to-edge separations between nearest neighboring holes are comparable to the coherence length. Changes in the field interval of two consecutive minima in the field dependent resistance R(H) curves are observed. In the low field region, fine structures in the R(H) and T(c)(H) curves are identified in both arrays. Comparison of experimental data with calculation results reveals that these structures observed in honeycomb and kagomé hole arrays resemble those in wire networks with triangular and T(3) symmetries, respectively. The findings suggest that even in these specified periodic hole arrays with very large interstitial regions, the low field fine structures are determined by the connectivity of the nanostructures.