702 research outputs found
Bound magnetic polaron driven low-temperature ferromagnetism in Cu1−xMnxO compounds
AbstractPartial Mn atoms have been confirmed to enter the CuO lattice and form the Cu1−xMnxO compounds in the case of doping with 0≤x≤0.2 by the sol–gel method. With increasing Mn content, magnetism is observed. The magnetic critical transition temperature increases with enhanced magnetism, which obeys the bound magnetic polaron theory. The electronic transportation shows an insulating behavior as the band-gap decreases. Our results may indicate that CuO may be used as a candidate of magnetic semiconductor
Properties of the random field Ising model in a transverse magnetic field
We consider the effect of a random longitudinal field on the Ising model in a
transverse magnetic field. For spatial dimension , there is at low
strength of randomness and transverse field, a phase with true long range order
which is destroyed at higher values of the randomness or transverse field. The
properties of the quantum phase transition at zero temperature are controlled
by a fixed point with no quantum fluctuations. This fixed point also controls
the classical finite temperature phase transition in this model. Many critical
properties of the quantum transition are therefore identical to those of the
classical transition. In particular, we argue that the dynamical scaling is
activated, i.e, the logarithm of the diverging time scale rises as a power of
the diverging length scale
X-ray diffraction measurements of the c-axis Debye-Waller factors of YBa2Cu3O7 and HgBa2CaCu2O6
We report the first application of x-rays to the measurement of the
temperature dependent Bragg peak intensities to obtain Debye-Waller factors on
high-temperature superconductors. Intensities of (0,0,l) peaks of YBa2Cu3O7 and
HgBa2CaCu2O6 thin films are measured to obtain the c-axis Debye-Waller factors.
While lattice constant and some Debye-Waller factor measurements on high Tc
superconductors show anomalies at the transition temperature, our measurements
by x-ray diffraction show a smooth transition of the c-axis Debye-Waller
factors through T. This suggests that the dynamic displacements of the
heavy elements along the c-axis direction in these compounds do not have
anomalies at Tc. This method in combination with measurements by other
techniques will give more details concerning dynamics of the lattice.Comment: 4 pages, 2 figures. To be published in Physical Review B (Brief
Report
Measurement of Ultra-Low Potassium Contaminations with Accelerator Mass Spectrometry
Levels of trace radiopurity in active detector materials is a subject of
major concern in low-background experiments. Among the radio-isotopes, \k40
is one of the most abundant and yet whose signatures are difficult to reject.
Procedures were devised to measure trace potassium concentrations in the
inorganic salt CsI as well as in organic liquid scintillator (LS) with
Accelerator Mass Spectrometry (AMS), giving, respectively, the
\k40-contamination levels of and g/g.
Measurement flexibilities and sensitivities are improved over conventional
methods. The projected limiting sensitivities if no excess of potassium signals
had been observed over background are g/g and g/g for the CsI and LS, respectively. Studies of the LS samples
indicate that the radioactive contaminations come mainly in the dye solutes,
while the base solvents are orders of magnitude cleaner. The work demonstrate
the possibilities of measuring naturally-occurring isotopes with the AMS
techniques.Comment: 18 pages, 4 figures, 3 table
Measurement of Trace I-129 Concentrations in CsI Powder and Organic Liquid Scintillator with Accelerator Mass Spectrometry
Levels of trace radiopurity in active detector materials is a subject of
major concern in low-background experiments. Procedures were devised to measure
trace concentrations of I-129 in the inorganic salt CsI as well as in organic
liquid scintillator with Accelerator Mass Spectrometry (AMS) which leads to
improvement in sensitivities by several orders of magnitude over other methods.
No evidence of their existence in these materials were observed. Limits of < 6
X 10^{-13} g/g and < 2.6 X 10^{-17} g/g on the contaminations of I-129 in CsI
and liquid scintillator, respectively, were derived.These are the first results
in a research program whose goals are to develop techniques to measure trace
radioactivity in detector materials by AMS.Comment: Proceedings of 10th International Conference on Accelerator Mass
Spectrometr
Linear Response, Validity of Semi-Classical Gravity, and the Stability of Flat Space
A quantitative test for the validity of the semi-classical approximation in
gravity is given. The criterion proposed is that solutions to the
semi-classical Einstein equations should be stable to linearized perturbations,
in the sense that no gauge invariant perturbation should become unbounded in
time. A self-consistent linear response analysis of these perturbations, based
upon an invariant effective action principle, necessarily involves metric
fluctuations about the mean semi-classical geometry, and brings in the
two-point correlation function of the quantum energy-momentum tensor in a
natural way. This linear response equation contains no state dependent
divergences and requires no new renormalization counterterms beyond those
required in the leading order semi-classical approximation. The general linear
response criterion is applied to the specific example of a scalar field with
arbitrary mass and curvature coupling in the vacuum state of Minkowski
spacetime. The spectral representation of the vacuum polarization function is
computed in n dimensional Minkowski spacetime, and used to show that the flat
space solution to the semi-classical Einstein equations for n=4 is stable to
all perturbations on distance scales much larger than the Planck length.Comment: 22 pages: This is a significantly expanded version of gr-qc/0204083,
with two additional sections and two new appendices giving a complete,
explicit example of the semi-classical stability criterion proposed in the
previous pape
Association between first caesarean delivery and adverse outcomes in subsequent pregnancy: a retrospective cohort study
BACKGROUND:Few studies have explored the association between a previous caesarean section (CS) and adverse perinatal outcomes in a subsequent pregnancy, especially in women who underwent a non-indicated CS in their first delivery. We designed this study to compare the perinatal outcomes of a subsequent pregnancy in women who underwent spontaneous vaginal delivery (SVD) or CS in their first delivery. METHODS:This retrospective cohort study included women who underwent singleton deliveries at the International Peace Maternity and Child Health Hospital from January 2013 to December 2016. Data on the perinatal outcomes of all the women were extracted from the medical records. Multivariate logistic regression was conducted to assessed the association between CS in the first delivery and adverse perinatal outcomes in the subsequent pregnancy. RESULTS:CS delivery in the subsequent pregnancy was more likely for women who underwent CS in their first birth than for women with previous SVD (97.3% versus 13.2%). CS in the first birth was also associated with a significantly increased risk of adverse outcomes in the subsequent pregnancy, especially in women who underwent a non-indicated CS. Adverse perinatal outcomes included pregnancy-induced hypertension [adjusted odds ratio (OR), 95% confidence interval (CI): 2.20, 1.59-3.05], gestational diabetes mellitus (1.82, 1.57-2.11), gestational anaemia (1.27, 1.05-1.55), placenta previa (3.18, 2.15-4.71), placenta accreta (2.75, 1.75-4.31), and polyhydramnios (2.60, 1.57-4.31) in the mother and preterm delivery (1.37, 1.06-1.78), low birth weight (3.78, 2.07-6.90), macrosomia (5.04, 3.95-6.44), and neonatal jaundice (1.72, 1.39-2.14) in the baby. CONCLUSIONS:CS in the first delivery markedly increases the risk of repeated CS and maternal-fetal complications in the subsequent pregnancy, especially in women with a non-indicated CS.Hong-Tao Hu, Jing-Jing Xu, Jing Lin, Cheng Li, Yan-Ting Wu, Jian-Zhong Sheng, Xin-Mei Liu and He-Feng Huan
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Deforestation, leakage and avoided deforestation policies: a spatial analysis
This paper analyses the impact of several avoided deforestation policies within a patchy forested landscape. Central is the idea that deforestation choices in one area influence deforestation decisions in nearby patches. We explore the interplay between forest landscapes comprising heterogeneous patches, localised spatial displacement, and avoided deforestation policies. Avoided deforestation policies at a landscape level are respectively: two Payments for Environmental Services (PES) policies, one focused on deforestation hotspots, the second being equally available to all agents; a conservation area; and, an agglomeration bonus. We demonstrate how the "best" policy, in terms of reduced leakage, depends on landscape heterogeneity. Agglomeration bonuses are shown to be more effective where there is less landscape heterogeneity, whilst conservation areas are most effective where there is more spatial heterogeneity
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