The average grain size (
d) arising from dynamic recrystallization (DRX) is often used as an indicator of flow stress (
σ); however, a theoretical basis for the scaling relation between
d and
σ has ...yet to be well established. In this paper, theories for the development of recrystallized grain size are reviewed and their applicability is examined. Special attention is paid to the dependence of the
d–
σ relation on DRX mechanisms. Steady-state DRX is classified into discontinuous DRX with bulging (BLG) nucleation
+
grain boundary migration (GBM) and continuous DRX with subgrain rotation (SGR) nucleation
+
GBM. The nucleation-and-growth model derived from Derby–Ashby theory describes the former case, whereas that derived from Shimizu theory applies to the latter. A static energy-balance model derived from Twiss theory is applicable to subgrain size, but not to recrystallized grain size. The lower limit of grain size is possibly constrained by a change in deformation mechanism from dislocation creep to diffusion creep, because deformation-induced grain size reduction ceases in the diffusion creep field. Scaling relations determined in the laboratory support the Shimizu model in the case of SGR
+
GBM. The theoretical piezometer calibrated for quartz suggests significant temperature effects under low-temperature metamorphic conditions.
The KamLAND-Zen experiment has provided stringent constraints on the neutrinoless double-beta (0νββ) decay half-life in ^{136}Xe using a xenon-loaded liquid scintillator. We report an improved search ...using an upgraded detector with almost double the amount of xenon and an ultralow radioactivity container, corresponding to an exposure of 970 kg yr of ^{136}Xe. These new data provide valuable insight into backgrounds, especially from cosmic muon spallation of xenon, and have required the use of novel background rejection techniques. We obtain a lower limit for the 0νββ decay half-life of T_{1/2}^{0ν}>2.3×10^{26} yr at 90% C.L., corresponding to upper limits on the effective Majorana neutrino mass of 36-156 meV using commonly adopted nuclear matrix element calculations.
We present an improved search for neutrinoless double-beta (0νββ) decay of ^{136}Xe in the KamLAND-Zen experiment. Owing to purification of the xenon-loaded liquid scintillator, we achieved a ...significant reduction of the ^{110m}Ag contaminant identified in previous searches. Combining the results from the first and second phase, we obtain a lower limit for the 0νββ decay half-life of T_{1/2}^{0ν}>1.07×10^{26} yr at 90% C.L., an almost sixfold improvement over previous limits. Using commonly adopted nuclear matrix element calculations, the corresponding upper limits on the effective Majorana neutrino mass are in the range 61-165 meV. For the most optimistic nuclear matrix elements, this limit reaches the bottom of the quasidegenerate neutrino mass region.
Abstract
We report on a search for electron antineutrinos (
ν
¯
e
) from astrophysical sources in the neutrino energy range 8.3–30.8 MeV with the KamLAND detector. In an exposure of 6.72 kton-year of ...the liquid scintillator, we observe 18 candidate events via the inverse beta decay reaction. Although there is a large background uncertainty from neutral current atmospheric neutrino interactions, we find no significant excess over background model predictions. Assuming several supernova relic neutrino spectra, we give upper flux limits of 60–110 cm
−2
s
−1
(90% confidence level, CL) in the analysis range and present a model-independent flux. We also set limits on the annihilation rates for light dark matter pairs to neutrino pairs. These data improve on the upper probability limit of
8
B solar neutrinos converting into
ν
¯
e
,
P
ν
e
→
ν
¯
e
<
3.5
×
10
−
5
(90% CL) assuming an undistorted
ν
¯
e
shape. This corresponds to a solar
ν
¯
e
flux of 60 cm
−2
s
−1
(90% CL) in the analysis energy range.
The KamLAND experiment has determined a precise value for the neutrino oscillation parameter Deltam21(2) and stringent constraints on theta12. The exposure to nuclear reactor antineutrinos is ...increased almost fourfold over previous results to 2.44 x 10(32) proton yr due to longer livetime and an enlarged fiducial volume. An undistorted reactor nuovere energy spectrum is now rejected at >5sigma. Analysis of the reactor spectrum above the inverse beta decay energy threshold, and including geoneutrinos, gives a best fit at Deltam21(2)=7.58(-0.13)(+0.14)(stat) -0.15+0.15(syst) x 10(-5) eV2 and tan2theta12=0.56(-0.07)+0.10(stat) -0.06+0.10(syst). Local Deltachi2 minima at higher and lower Deltam21(2) are disfavored at >4sigma. Combining with solar neutrino data, we obtain Deltam21(2)=7.59(-0.21)+0.21 x 10(-5) eV2 and tan2theta12=0.47(-0.05)+0.06.
Abstract
We use large cosmological smoothed particle hydrodynamics simulations to study the formation and evolution of submillimetre galaxies (SMGs). In our previous work, we studied the statistical ...properties of ultraviolet-selected star-forming galaxies at high redshifts. We populate the same cosmological simulations with SMGs by calculating the reprocessing of stellar light by dust grains into far-infrared to millimetre wavebands in a self-consistent manner. We generate light-cone outputs to compare directly the statistical properties of the simulated SMGs with available observations. Our model reproduces the submillimetre source number counts and the clustering amplitude. We show that bright SMGs with flux S > 1 mJy reside in haloes with masses of ∼1013 M⊙ and have stellar masses greater than 1011 M⊙. The angular cross-correlation between the SMGs and Lyman α emitters is significantly weaker than that between the SMGs and Lyman-break galaxies. The cross-correlation is also weaker than the autocorrelation of the SMGs. The redshift distribution of the SMGs shows a broad peak at z ∼ 2, where bright SMGs contribute significantly to the global cosmic star formation rate density. Our model predicts that there are hundreds of SMGs with S > 0.1 mJy at z > 5 per 1 deg2 field. Such SMGs can be detected by ALMA.
Abstract
Development of radio-purification for the large-volume
liquid scintillator detector is a key to enhance search
sensitivities in neutrino physics. In this paper, we describe
laboratory ...studies on the radio-purification of the liquid
scintillator detector by using the metal scavenger, aiming at the
improved search for the neutrinoless double beta decay in
KamLAND-Zen. In the purification tests, the
210
Pb reduction
efficiency was evaluated. Based on the purification performance in
small-scale system, we designed a large adsorption column for the
metal scavenging applicable to the KamLAND purification system. We
produced the column and constructed a purification test bench, and
confirmed the
212
Pb reduction efficiency, the process speed,
the LS contamination and quality changes, and the stability of
chemical components in the Xe-LS. We found that the metal scavenging
is a practical method for the large-volume LS purification, and will
be effective to reduce metallic radioactive elements.
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