A spin-transfer torque switched magnetic tunnel junction (MTJ) is a memory element in modern magnetic random access memory (MRAM), a CMOS-integrated technology that is being developed by ...semiconductor manufacturers. One electrode of the MTJ acts as a magnetically bi-stable “free-layer” (FL), determining the bit-state of a memory cell. Spin-transfer torque (or spin-torque, or STT) switches the magnetic state of the FL with respect to a reference-layer (RL) in the MTJ. Here I review our current understanding of the MTJ device physics governing spin-transfer-torque driven switching. Starting with some simple concepts based on macrospin assumptions, I will then review recent experimental results, and compare observations with macrospin expectation for a more realistic, observation-based quantitative description, beyond macrospin. I will also describe some unresolved scientific challenges that could further improve the MTJ performance for memory technology, and give a brief outlook.
In this work, the effects of surface mechanical attrition treatment (SMAT) and conventional shot peening (CSP) are comparatively studied on the surface characteristics and low cycle fatigue (LCF) ...properties of a 316L stainless steel. For this purpose, surface topography, residual stress and work hardening are evaluated on the treated samples. Both CSP and SMAT are performed with the same Almen intensity and the same coverage. Total strain controlled LCF tests are carried out in order to compare the effects of these two techniques on the fatigue properties of the studied steel. The results show that the samples treated by SMAT and CSP exhibit similar trends of cyclic stress amplitude evolution, and higher mechanical strength than the untreated samples. However, the samples treated by CSP manifest higher fatigue life under low strain amplitude (±0.5%), but lower fatigue life under high strain amplitude (±1.25%), compared to the SMATed samples. The fatigue life results are discussed based on the analysis of different characteristics including surface topography, microstructure, residual stress and its relaxation, as well as fracture surfaces.
•LCF properties of 316L steel processed by SMAT and shot peening are studied.•Same Almen intensity and coverage are applied to compare the two techniques.•Fatigue life is governed by competition between residual stress/surface topography.•Role of compressive residual stress is dominant under low strain amplitude.•Surface cracks and roughness are controlling factors under high strain amplitude.
Using a low background data sample of 9.7×10^{5} J/ψ→γη^{'}, η^{'}→γπ^{+}π^{-} events, which are 2 orders of magnitude larger than those from the previous experiments, recorded with the BESIII ...detector at BEPCII, the decay dynamics of η^{'}→γπ^{+}π^{-} are studied with both model-dependent and model-independent approaches. The contributions of ω and the ρ(770)-ω interference are observed for the first time in the decays η^{'}→γπ^{+}π^{-} in both approaches. Additionally, a contribution from the box anomaly or the ρ(1450) resonance is required in the model-dependent approach, while the process specific part of the decay amplitude is determined in the model-independent approach.
Abstract
Bulk Bi
0.5
Sr
0.5
Fe
0.5
Cr
0.5
O
3
(BSFCO) is a new compound comprising the
R3c
structure. The structural, magnetic property and exchange bias (EB) details are investigated. The material ...was in the super-paramagnetic (SP) state at room temperature. Exchange bias usually occurs at the boundary between different magnetic states after field cooling (
H
FC
) acts on the sample. Here the result shows that changing
H
FC
from 1 to 6 T reduces the
H
EB
value by 16% at 2 K at the same time. Meanwhile,
H
EB
diminishes as the ferromagnetic layer thickness increases. The variation of (the thickness of ferromagnetic layer)
t
FM
with the change of
H
FC
leads to the tuning of
H
EB
by
H
FC
in BSFCO bulk. These effects are obviously different from the phenomenon seen in other oxide types.
The exclusive process e+e−→ΛΛ¯, with Λ→pπ− and Λ¯→p¯π+, has been studied at s=2.396 GeV for measurement of the timelike Λ electric and magnetic form factors, GE and GM. A data sample, corresponding ...to an integrated luminosity of 66.9 pb−1, was collected with the BESIII detector for this purpose. A multidimensional analysis with a complete decomposition of the spin structure of the reaction enables a determination of the modulus of the ratio R=|GE/GM| and, for the first time for any baryon, the relative phase ΔΦ=ΦE−ΦM. The resulting values are R=0.96±0.14(stat)±0.02(syst) and ΔΦ=37°±12°(stat)±6°(syst), respectively. These are obtained using the recently established and most precise value of the asymmetry parameter αΛ=0.750±0.010 measured by BESIII. In addition, the cross section is measured with unprecedented precision to be σ=118.7±5.3(stat)±5.1(syst) pb, which corresponds to an effective form factor of |G|=0.123±0.003(stat)±0.003(syst). The contribution from two-photon exchange is found to be negligible. Our result enables the first complete determination of baryon timelike electromagnetic form factors.
Despite being only one-atom thick, defect-free graphene is considered to be completely impermeable to all gases and liquids
. This conclusion is based on theory
and supported by experiments
that ...could not detect gas permeation through micrometre-size membranes within a detection limit of 10
to 10
atoms per second. Here, using small monocrystalline containers tightly sealed with graphene, we show that defect-free graphene is impermeable with an accuracy of eight to nine orders of magnitude higher than in the previous experiments. We are capable of discerning (but did not observe) permeation of just a few helium atoms per hour, and this detection limit is also valid for all other gases tested (neon, nitrogen, oxygen, argon, krypton and xenon), except for hydrogen. Hydrogen shows noticeable permeation, even though its molecule is larger than helium and should experience a higher energy barrier. This puzzling observation is attributed to a two-stage process that involves dissociation of molecular hydrogen at catalytically active graphene ripples, followed by adsorbed atoms flipping to the other side of the graphene sheet with a relatively low activation energy of about 1.0 electronvolt, a value close to that previously reported for proton transport
. Our work provides a key reference for the impermeability of two-dimensional materials and is important from a fundamental perspective and for their potential applications.
This paper examines the optimal control of CO2 emissions from a perspective of efficiency analysis. Several centralized data envelopment analysis (DEA) models are introduced to study the optimal ...allocation of CO2 emissions under spatial, temporal and spatial–temporal allocation strategies, respectively. The models have been used to determine the optimal paths for controlling CO2 emissions at provincial and regional levels in China. A sensitivity analysis of the optimal path on the emission control coefficient under spatial–temporal allocation strategy is further carried out. Our empirical results show that more developed regions should take emission reduction responsibility earlier than less developed regions in China. Of the three allocation strategies, spatial–temporal allocation strategy seems to be a better choice for achieving the optimal control of CO2 emissions at country level since it is more encompassing by allowing both timing and spatial substitutions. It is also found that there exists an inverted U-shape relationship between the aggregate optimal GDP and the emission control coefficient, which shows that modest emission reduction policy might be more appropriate for China in order to achieve the joint goals of economic development and CO2 emission reduction.
•The optimal control of CO2 emissions in China is examined.•Centralized DEA models are used to allocate CO2 emissions under different strategies.•More developed regions should implement emission reduction earlier.•Modest emission reduction policy could be more appropriate for China.
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This work presents a comparative study on the in-situ alloying of NiTi shape memory alloys (SMAs) by directed energy deposition (DED), selective laser melting (SLM) and selective ...electron beam melting (SEBM) processes using pre-mixed Ni-Ti powders. The influence of process parameters on the microstructural homogeneity, phase formation and thermomechanical properties of NiTi alloy has been systematically studied. DED could build solid NiTi alloys with good interlayer fusion and phase transformation characteristics. However, a substantial amount of uniformly dispersed Ti2Ni intermetallics can embrittle this material. SLM-built NiTi parts show a tradeoff between microstructural inhomogeneity and keyhole defects when the energy densities are varied. In addition, the strong exothermic reaction in Ni-Ti powder mixtures during printing can disturb the melt pool, making it challenging to elaborate this material and obtain desired phases by using SLM. Moreover, SEBM is found to be unsuitable to in-situ synthesize this highly reactive material due to the lack-of-fusion vs. powder-ignition dilemma in the mandatory preheating step. It is suggested to adopt DED to in-situ alloy NiTi parts when using the elementally blended powders as feedstocks.
Cyclooxygenase (COX)-2 is upregulated in hepatocellular carcinoma (HCC). However, the direct causative effect of COX-2 in spontaneous HCC formation remains unknown. We thus investigate the role and ...molecular pathogenesis of COX-2 in HCC by using liver-specific COX-2 transgenic (TG) mice. We found spontaneous HCC formation with elevated inflammatory infiltrates and neovessels in male TG mice (3/21, 14.3%), but not in any of male WT mice (0/19). Reduced representation bisulfite sequencing (RRBS) and gene expression microarrays were performed in the HCC tumor and non-HCC liver tissues to investigate the molecular mechanisms of COX-2-driven HCC. By RRBS, DNA promoter hypermethylation was identified in HCC from TG mice. Induction of promoter hypermethylation was associated with reduced tet methylcytosine dioxygenase 1 (TET1) expression by COX-2. TET1 could catalyze the conversion of 5-methylcytosine into 5-hydroxymethylcytosine (5hmC) and prevents DNA hypermethylation. In keeping with this, loss of 5hmC was demonstrated in COX-2-induced HCC. Consistently, COX-2 overexpression in human HCC cell lines could reduce both TET1 expression and 5hmc levels. Integrative analyses of DNA methylation and gene expression profiles further identified significantly downregulated genes including LTBP1, ADCY5 and PRKCZ by promoter methylation in COX-2-induced HCC. Reduced expression of LTBP1, ADCY5 and PRKCZ by promoter hypermethylation was further validated in human HCCs. Bio-functional investigation revealed that LTBP1 inhibited cell proliferation in HCC cell lines, suggesting its potential role as a tumor suppressor in HCC. Gene expression microarrays revealed that signaling cascades (AKT (protein kinase B), STK33 (Serine/Threonine kinase 33) and MTOR (mechanistic target of rapamycin) pathways) were enriched in COX-2-induced HCC. In conclusion, this study demonstrated for the first time that enhanced COX-2 expression in hepatocytes is sufficient to induce HCC through inducing promoter hypermethylation by reducing TET1, silencing tumor-suppressive genes and activating key oncogenic pathways. Inhibition of COX-2 represents a mechanism-based target for HCC prevention.
Tumor metastasis is the leading cause of death among breast cancer patients. PELP1 (proline, glutamic acid and leucine rich protein 1) is a nuclear receptor coregulator that is upregulated during ...breast cancer progression to metastasis and is an independent prognostic predictor of shorter survival of breast cancer patients. Here, we show that PELP1 modulates expression of metastasis-influencing microRNAs (miRs) to promote cancer metastasis. Whole genome miR array analysis using PELP1-overexpressing and PELP1-underexpressing model cells revealed that miR-200 and miR-141 levels inversely correlated with PELP1 expression. Consistent with this, PELP1 knockdown resulted in lower expression of miR-200a target genes ZEB1 and ZEB2. PELP1 knockdown significantly reduced tumor growth and metastasis compared with parental cells in an orthotopic xenograft tumor model. Furthermore, re-introduction of miR-200a and miR-141 mimetics into PELP1-overexpressing cells reversed PELP1 target gene expression, decreased PELP1-driven migration/invasion in vitro and significantly reduced in vivo metastatic potential in a preclinical model of experimental metastasis. Our results demonstrated that PELP1 binds to miR-200a and miR-141 promoters and regulates their expression by recruiting chromatin modifier histone deacetylase 2 (HDAC2) as revealed by chromatin immunoprecipitation, small interfering RNA and HDAC inhibitor assays. Taken together, our results suggest that PELP1 regulates tumor metastasis by controlling the expression and functions of the tumor metastasis suppressors miR-200a and miR-141.
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