Resonant enhancement of spin Seebeck effect (SSE) due to phonons was recently discovered in YFormula: see textFeFormula: see textOFormula: see text (YIG). This effect is explained by hybridization ...between the magnon and phonon dispersions. However, this effect was observed at low temperatures and high magnetic fields, limiting the scope for applications. Here we report observation of phonon-resonant enhancement of SSE at room temperature and low magnetic field. We observe in LuFormula: see textBiFeFormula: see textGaOFormula: see text an enhancement 700% greater than that in a YIG film and at very low magnetic fields around 10Formula: see text T, almost one order of magnitude lower than that of YIG. The result can be explained by the change in the magnon dispersion induced by magnetic compensation due to the presence of non-magnetic ion substitutions. Our study provides a way to tune the magnon response in a crystal by chemical doping, with potential applications for spintronic devices.
Background
SPECT-derived dose estimates in tissues of diameter less than 3× system resolution are subject to significant losses due to the limited spatial resolution of the gamma camera. ...Incorporating resolution modelling (RM) into the SPECT reconstruction has been proposed as a possible solution; however, the images produced are prone to noise amplification and Gibbs artefacts. We propose a novel approach to SPECT reconstruction in a theranostic setting, which we term SPECTRE (single photon emission computed theranostic reconstruction); using a diagnostic PET image, with its superior resolution, to guide the SPECT reconstruction of the therapeutic equivalent. This report demonstrates a proof in principle of this approach.
Methods
We have employed the hybrid kernelised expectation maximisation (HKEM) algorithm implemented in STIR, with the aim of producing SPECT images with PET-equivalent resolution. We demonstrate its application in both a dual
68
Ga/
177
Lu IEC phantom study and a clinical example using
64
Cu/
67
Cu.
Results
SPECTRE is shown to produce images comparable in accuracy and recovery to PET with minimal introduction of artefacts and amplification of noise.
Conclusion
The SPECTRE approach to image reconstruction shows improved quantitative accuracy with a reduction in noise amplification. SPECTRE shows great promise as a method of improving SPECT radioactivity concentrations, directly leading to more accurate dosimetry estimates in small structures and target lesions. Further investigation and optimisation of the algorithm parameters is needed before this reconstruction method can be utilised in a clinical setting.
A novel direct core heating fusion process is introduced, in which a preimploded core is predominantly heated by energetic ions driven by LFEX, an extremely energetic ultrashort pulse laser. ...Consequently, we have observed the D(d,n)^{3}He-reacted neutrons (DD beam-fusion neutrons) with the yield of 5×10^{8} n/4π sr. Examination of the beam-fusion neutrons verified that the ions directly collide with the core plasma. While the hot electrons heat the whole core volume, the energetic ions deposit their energies locally in the core, forming hot spots for fuel ignition. As evidenced in the spectrum, the process simultaneously excited thermal neutrons with the yield of 6×10^{7} n/4π sr, raising the local core temperature from 0.8 to 1.8 keV. A one-dimensional hydrocode STAR 1D explains the shell implosion dynamics including the beam fusion and thermal fusion initiated by fast deuterons and carbon ions. A two-dimensional collisional particle-in-cell code predicts the core heating due to resistive processes driven by hot electrons, and also the generation of fast ions, which could be an additional heating source when they reach the core. Since the core density is limited to 2 g/cm^{3} in the current experiment, neither hot electrons nor fast ions can efficiently deposit their energy and the neutron yield remains low. In future work, we will achieve the higher core density (>10 g/cm^{3}); then hot electrons could contribute more to the core heating via drag heating. Together with hot electrons, the ion contribution to fast ignition is indispensable for realizing high-gain fusion. By virtue of its core heating and ignition, the proposed scheme can potentially achieve high gain fusion.
Abstract
A laser inertial fusion energy (IFE) reactor requires repetitive injection of fuel pellets and laser engagement to fuse fusion fuel beyond a few Hz. We demonstrate 10 Hz free-fall bead ...pellet injection and laser engagement with γ-ray generation. Deuterated polystyrene beads with a diameter of 1 mm were engaged by counter illuminating ultra-intense laser pulses with an intensity of 5 × 10
17
W cm
−2
at 10 Hz. The spatial distribution of free-fall beads was 0.86 mm in the horizontal direction and 0.18 mm in the vertical direction. The system operated for more than 5 min and 3500 beads were supplied with achieved frequencies of 2.1 Hz for illumination on the beads and 0.7 Hz for γ-ray generation; these frequencies were three times greater than with the previous 1 Hz injection system. The duration of operation was limited by the pellet supply. This injection and engagement system could be used for laser IFE research platforms.
•Oxygen deficiency δ was determined by thermo-gravimetric-analysis.•Crystal structural parameter was determined by Rietveld analysis.•The electrical and magnetic properties were greatly influenced by ...δ.•Two-dimensional character of Sr2−xLaxVO4−δ strongly enhanced the effect of δ.•The χ of SrLaVO4 (semiconductive) was nearly independent of temperature.
The effects of the oxygen deficiency, δ, on the electrical and magnetic properties of Sr2−xLaxVO4−δ were investigated. For this objective, single-phase polycrystalline materials of Sr2−xLaxVO4−δ (x=0, 0.04, 0.1, 0.2, 0.8 and 1) were synthesized. The value of δ was determined by thermo-gravimetric-analysis. The δ of Sr2−xLaxVO4−δ (x⩽0.2) was almost the same value, ∼0.2. The δ of x=0.8 was 0.05 and that of x=1 was ∼0. Electrical resistivity measurement showed that all the samples were semiconductive. For the low magnetic field (∼0.002T) measurement, the spin-glass-like behavior was clearly observed for larger δ samples (x=0.04, 0.1 and 0.2). This behavior became weak for smaller δ samples (x=0.8 and 1). It is considered that the random distribution of the oxygen vacancies in the two-dimensional VO2 plane lead to this result. From the high magnetic field (1T) measurement, it was found that the Curie–Weiss term, χcw, dominated in the magnetic susceptibility, χ, of Sr2−xLaxVO4−δ (x⩽0.2, δ∼0.2). The χcw considerably reduced for x=0.8 (δ=0.05) and almost disappeared for x=1 (δ∼0) i.e., SrLaVO4. Thus, the χcw is considered to be originated from oxygen vacancies. Hence, it is revealed that the δ is critical to the properties of Sr2−xLaxVO4−δ, in addition to x. It is worthy to note that almost temperature independent χ of SrLaVO4 is anomalous, because in this material, all the V are V3+ with S=1. The almost temperature independent susceptibility may be due to the spin fluctuation enhanced by the strong two-dimensionality of the crystal structure, quantum fluctuation or the spin frustration in VO2 square lattice.
A tailored-pulse-imploded core with a diameter of 70 μm is flashed by counterirradiating 110 fs, 7 TW laser pulses. Photon emission (>40 eV) from the core exceeds the emission from the imploded ...core by 6 times, even though the heating pulse energies are only one seventh of the implosion energy. The coupling efficiency from the heating laser to the core using counterirradiation is 14% from the enhancement of photon emission. Neutrons are also produced by counterpropagating fast deuterons accelerated by the photon pressure of the heating pulses. A collisional two-dimensional particle-in-cell simulation reveals that the collisionless two counterpropagating fast-electron currents induce mega-Gauss magnetic filaments in the center of the core due to the Weibel instability. The counterpropagating fast-electron currents are absolutely unstable and independent of the core density and resistivity. Fast electrons with energy below a few MeV are trapped by these filaments in the core region, inducing an additional coupling. This might lead to the observed bright photon emissions.
The concept of a novel approach to make a compact SMES unit composed of a stack of Si wafers using a well-established MEMS process was proposed. The concept was backed up by pilot estimations for ...energy storage capacity and mechanical strength to endure electromagnetic stress. The estimated volume density of the storable energy is comparable to that of rechargeable batteries and the mechanical strength of Si wafer endures the electromagnetic stress imposed on it. These estimations support the feasibility of this novel concept, although there needs to be more detailed design of the system for its practical realization. Furthermore, there are a lot of challenges to overcome. The first step of the experimental proof of this new concept was successfully performed through several repeated test fabrications. In one of these test fabrications, the theoretically estimated upper limit value of the energy storage corresponding to a pilot design of a spiral superconducting NbN coil in the spiral trench formed on a Si wafer 10.15 cm in diameter was attained.
A method to estimate the electricity storage capacity of our compact superconducting magnetic energy storage system composed of stacks of Si-wafers loaded with superconducting thin film coils in ...spiral trenches formed by MEMS process was developed and tested for initial 6 designs of wafer coils. The results show energy storage density as low as around 6 Wh/ℓ. This is not caused by the limitation of the hoop stress but by the limitation of the maximum magnetic flux density. Further calculations for optimum wafer coil designs will be continued in which the effect of the maximum magnetic flux energy and the effect of the maximum hoop stress on the limit of the amount of the electrical energy storage come into a good balance.
We have been developing a superconducting NbN thin film coil in a spiral trench on a Si-wafer using MEMS technology. Connecting the coils on the different wafers using waferbonding process, a ...cylindrical wafer stack is to be formed as a unit of a compact SMES. The critical current density of our NbN film was measured to be around 1100 A/mm2. We measured critical current Ic of 47 mA for the previously fabricated coil of the film thickness tf = 0.5 μm. Ic in the spiral coil increases with tf. However, if we make the NbN film thicker, the film is apt to have higher lateral force caused by tensile or compressive stress which can cause peeling of the film from the Si substrate. It is well known that the stress of the sputtered thin films can be controlled from tensile to compressive stress by controlling the bombardment of high energy particles including argon atoms backscattered from the target surface. Based on this knowledge, a specially designed sputter-deposition apparatus was fabricated in which the substrate can be located not only at the different target-to-substrate distances but also at several different lateral distances from the central axis of the target (off-axis lateral shift). Using this apparatus, various stress conditions could be realized which contributed to fabrication of thick NbN film spiral coil in the trench. The film stress was calculated from bending analysis of the substrate Si wafer by stylus method using Stoney's formula. The maximum compressive stress of 2.5 GPa was measured. By an off-axis lateral shift, tf could be increased from 0.5 to 1 μm. By increasing sputtering gas pressure from 0.7 to 2 Pa, the compressive stress could be mitigated and tf could be further increased from 1.0 to 3 μm. Up to now, we measured Ic of 220 mA for a NbN spiral coil at tf around 3 μm. More detailed adjustment of the deposition condition will bring further increase in tf, and hence Ic into sight.
PDF
