4,922 research outputs found
First-order melting of a weak spin-orbit Mott insulator into a correlated metal
The electronic phase diagram of the weak spin-orbit Mott insulator
(Sr(1-x)Lax)3Ir2O7 is determined via an exhaustive experimental study. Upon
doping electrons via La substitution, an immediate collapse in resistivity
occurs along with a narrow regime of nanoscale phase separation comprised of
antiferromagnetic, insulating regions and paramagnetic, metallic puddles
persisting until x~0.04. Continued electron doping results in an abrupt,
first-order phase boundary where the Neel state is suppressed and a homogenous,
correlated, metallic state appears with an enhanced spin susceptibility and
local moments. As the metallic state is stabilized, a weak structural
distortion develops and suggests a competing instability with the parent
spin-orbit Mott state.Comment: 5 pages, 4 figure
Radio Afterglows of Gamma-Ray Bursts and Hypernovae at High Redshift, and their Potential for 21-cm Absorption Studies
We investigate the radio afterglows of gamma-ray bursts (GRBs) and hypernovae
(HNe) at high redshifts and quantify their detectability, as well as their
potential usefulness for 21 cm absorption line studies of the intergalactic
medium (IGM) and intervening structures. We examine several sets of source and
environment model parameters that are physically plausible at high redshifts.
The radio afterglows of GRBs would be detectable out to z ~ 30, while the
energetic HNe could be detectable out to z ~ 20 even by the current Very Large
Array (VLA). We find that the 21 cm absorption line due to the diffuse neutral
IGM is difficult to detect even by the proposed Square Kilometer Array (SKA),
except for highly energetic sources. We also find that the 21 cm line due to
collapsed gas clouds with high optical depth may be detected on rare occasions.Comment: 36 pages, 12 figures, 1 table, accepted for publication in Ap
The evolution of antiferromagnetic susceptibility to uniaxial pressure in Ba(Fe{1-x}Co{x})2As2
Neutron diffraction measurements are presented measuring the responses of
both magnetic and structural order parameters of parent and lightly Co-doped
Ba(Fe{1-x}Co{x})2As2 under the application of uniaxial pressure. We find that
the uniaxial pressure induces a thermal shift in the onset of antiferromagnetic
order that grows as a percentage of T_N as Co-doping is increased and the
superconducting phase is approached. Additionally, as uniaxial pressure is
increased within parent and lightly-doped Ba(Fe{1-x}Co{x})2As2 on the first
order side of the tricritical point, we observe a decoupling between the onsets
of the orthorhombic structural distortion and antiferromagnetism. Our findings
place needed constraints on models exploring the nematic susceptibility of the
bilayer pnictides in the tetragonal, paramagnetic regime.Comment: 10 pages, 7 figure
Spin ordering and electronic texture in the bilayer iridate SrIrO
Through a neutron scattering, charge transport, and magnetization study, the
correlated ground state in the bilayer iridium oxide SrIrO is
explored. Our combined results resolve scattering consistent with a high
temperature magnetic phase that persists above 600 K, reorients at the
previously defined K, and coexists with an electronic ground state
whose phase behavior suggests the formation of a fluctuating charge or orbital
phase that freezes below K. Our study provides a window into
the emergence of multiple electronic order parameters near the boundary of the
metal to insulator phase transition of the 5d Mott phase.Comment: Revised text and figures. 4 pages, 4 figure
Having a baby in your 40s with ART: the reproductive dilemma of autologous versus donor oocytes.
BACKGROUND:Increasing numbers of women ≥40 years old are accessing assisted reproductive technology (ART) due to age-related infertility. There is limited population-based evidence about the impact on the cumulative live birth rate (CLBR) of women aged ≥40 years using their own oocytes, compared to women of a similar age, using donor oocytes. AIMS:To compare the CLBR for women ≥40 years undergoing ART using autologous oocytes and women of similar age using donor oocytes. MATERIALS AND METHODS:This population-based retrospective cohort study used data from all women aged ≥40 years undergoing ART with donated (n = 987) or autologous oocytes (n = 19 170) in Victoria, Australia between 2009 and 2016. A discrete-time survival model was used to evaluate the CLBR following ART with donor or autologous oocytes. The odds ratio, adjusted for woman's age; male age; parity; cause of infertility; and the associated 95% confidence intervals (CI), were calculated. The numbers needed to be exposed (NNEs) were calculated from the adjusted odds ratio (aOR) and the CLBR in the autologous group. RESULTS:The CLBR ranged from 28.6 to 42.5% in the donor group and from 12.5% to 1.4% in the autologous group. The discrete-time survival analysis with 95% CI demonstrated significant aOR on CLBR across all ages (range aOR: 2.56, 95% CI: 1.62-4.01 to aOR: 15.40, 95% CI: 9.10-26.04). CONCLUSIONS:Women aged ≥40 years, using donor oocytes had a significantly higher CLBR than women using autologous oocytes. The findings can be used when counselling women ≥40 years about their ART treatment options and to inform public policy
Oocyte donor age has a significant impact on oocyte recipients' cumulative live-birth rate: a population-based cohort study
© 2019 Objective: To study the impact of the donor's and recipient's age on the cumulative live-birth rate (CLBR) in oocyte donation cycles. Design: A population-based retrospective cohort study. Setting: Not applicable. Patient(s): All women using donated oocytes (n = 1,490) in Victoria, Australia, between 2009 and 2015. Intervention(s): None. Main Outcome Measure(s): The association between the donor's and recipient's age and CLBR modeled by multivariate Cox proportional hazard regression with the covariates of male partner's age, recipient parity, and cause of infertility adjusted for, and donor age grouped as <30, 30–34, 35–37, 38–40, and ≥41 years, and recipient age as <35, 35–37, 38–40, 41–42, 43–44, and ≥45 years. Result(s): The mean age of the oocyte donors was 33.7 years (range: 21 to 45 years) with 49% aged 35 years and over. The mean age of the oocyte recipients was 41.4 years (range: 19 to 53 years) with 25.4% aged ≥45 years. There was a statistically significant relationship between the donor's age and the CLBR. The CLBR for recipients with donors aged <30 years and 30–34 years was 44.7% and 43.3%, respectively. This decreased to 33.6% in donors aged 35–37 years, 22.6% in donors aged 38–40 years, and 5.1% in donors aged ≥41 years. Compared with recipients with donors aged <30 years, the recipients with donors aged 38–40 years had 40% less chance of achieving a live birth (adjusted hazard ratio 0.60; 95% CI, 0.43–0.86) and recipients with donors aged ≥41 years had 86% less chance of achieving a live birth (adjusted hazard ratio 0.14; 95% CI, 0.04–0.44). The multivariate analysis showed no statistically significant effect of the recipient's age on CLBR. Conclusion(s): We have demonstrated that the age of the oocyte donor is critical to the CLBR and is independent of the recipient woman's age. Recipients using oocytes from donors aged ≥35 years had a statistically significantly lower CLBR when compared with recipients using oocytes from donors aged <35 years
Tunable Electron Multibunch Production in Plasma Wakefield Accelerators
Synchronized, independently tunable and focused J-class laser pulses are
used to release multiple electron populations via photo-ionization inside an
electron-beam driven plasma wave. By varying the laser foci in the laboratory
frame and the position of the underdense photocathodes in the co-moving frame,
the delays between the produced bunches and their energies are adjusted. The
resulting multibunches have ultra-high quality and brightness, allowing for
hitherto impossible bunch configurations such as spatially overlapping bunch
populations with strictly separated energies, which opens up a new regime for
light sources such as free-electron-lasers
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