250 research outputs found
Dynactin-dependent cortical dynein and spherical spindle shape correlate temporally with meiotic spindle rotation in Caenorhabditis elegans.
Oocyte meiotic spindles orient with one pole juxtaposed to the cortex to facilitate extrusion of chromosomes into polar bodies. In Caenorhabditis elegans, these acentriolar spindles initially orient parallel to the cortex and then rotate to the perpendicular orientation. To understand the mechanism of spindle rotation, we characterized events that correlated temporally with rotation, including shortening of the spindle in the pole-to pole axis, which resulted in a nearly spherical spindle at rotation. By analyzing large spindles of polyploid C. elegans and a related nematode species, we found that spindle rotation initiated at a defined spherical shape rather than at a defined spindle length. In addition, dynein accumulated on the cortex just before rotation, and microtubules grew from the spindle with plus ends outward during rotation. Dynactin depletion prevented accumulation of dynein on the cortex and prevented spindle rotation independently of effects on spindle shape. These results support a cortical pulling model in which spindle shape might facilitate rotation because a sphere can rotate without deforming the adjacent elastic cytoplasm. We also present evidence that activation of spindle rotation is promoted by dephosphorylation of the basic domain of p150 dynactin
Deep forecasting of translational impact in medical research
The value of biomedical research--a $1.7 trillion annual investment--is
ultimately determined by its downstream, real-world impact. Current objective
predictors of impact rest on proxy, reductive metrics of dissemination, such as
paper citation rates, whose relation to real-world translation remains
unquantified. Here we sought to determine the comparative predictability of
future real-world translation--as indexed by inclusion in patents, guidelines
or policy documents--from complex models of the abstract-level content of
biomedical publications versus citations and publication meta-data alone. We
develop a suite of representational and discriminative mathematical models of
multi-scale publication data, quantifying predictive performance out-of-sample,
ahead-of-time, across major biomedical domains, using the entire corpus of
biomedical research captured by Microsoft Academic Graph from 1990 to 2019,
encompassing 43.3 million papers across all domains. We show that citations are
only moderately predictive of translational impact as judged by inclusion in
patents, guidelines, or policy documents. By contrast, high-dimensional models
of publication titles, abstracts and metadata exhibit high fidelity (AUROC >
0.9), generalise across time and thematic domain, and transfer to the task of
recognising papers of Nobel Laureates. The translational impact of a paper
indexed by inclusion in patents, guidelines, or policy documents can be
predicted--out-of-sample and ahead-of-time--with substantially higher fidelity
from complex models of its abstract-level content than from models of
publication meta-data or citation metrics. We argue that content-based models
of impact are superior in performance to conventional, citation-based measures,
and sustain a stronger evidence-based claim to the objective measurement of
translational potential
Strain-engineering of the charge and spin-orbital interactions in Sr2IrO4
In the high spin-orbit coupled Sr2IrO4, the high sensitivity of the ground
state to the details of the local lattice structure shows a large potential for
the manipulation of the functional properties by inducing local lattice
distortions. We use epitaxial strain to modify the Ir-O bond geometry in
Sr2IrO4 and perform momentum-dependent Resonant Inelastic X-ray Scattering
(RIXS) at the metal and at the ligand sites to unveil the response of the low
energy elementary excitations. We observe that the pseudospin-wave dispersion
for tensile-strained Sr2IrO4 films displays large softening along the [h,0]
direction, while along the [h,h] direction it shows hardening. This evolution
reveals a renormalization of the magnetic interactions caused by a
strain-driven crossover from anisotropic to isotropic interactions between the
magnetic moments. Moreover, we detect dispersive electron-hole pair excitations
which shift to lower (higher) energies upon compressive (tensile) strain,
manifesting a reduction (increase) in the size of the charge gap. This behavior
shows an intimate coupling between charge excitations and lattice distortions
in Sr2IrO4, originating from the modified hopping elements between the t2g
orbitals. Our work highlights the central role played by the lattice degrees of
freedom in determining both the pseudospin and charge excitations of Sr2IrO4
and provides valuable information towards the control of the ground state of
complex oxides in the presence of high spin-orbit coupling.Comment: Published in Proceedings of the National Academy of Sciences,
September 202
Anisotropic magnetic excitations and incipient N\’eel order in \mathrm{Ba}{({\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x})}_{2}{\mathrm{As}}_{2}
It is currently understood that high temperature superconductivity (SC) in the transition metal (M) substituted iron arsenides Ba(Fe1−xMx)2As2 is promoted by magnetic excitations with wave vectors (π,0) or (0,π). It is known that while a small amount of Co substitution lead to SC, the same does not occur for Mn for any value of x. In this work, magnetic excitations in the iron arsenides Ba(Fe1−xMnx)2As2(x=0.0,0.007,0.009,0.08) are investigated by means of resonant inelastic x-ray scattering (RIXS) at the Fe L3 edge, for momentum transfer q along the high symmetry Brillouin zone (π,0) and (π,π) directions. It is shown that with increasing Mn content (x), the excitations become anisotropic both in dispersion and lineshape. Both effects are detected even for small values of x, evidencing a cooperative phenomenon between the Mn impurities, that we ascribe to emerging Néel order of the Mn spins. Moreover, for x=0.08, the excitations along q∥(π,0) are strongly damped and nearly nondispersive. This result suggests that phases of arsenides containing local moments at the FeAs layers, as in Mn or Cr substituted phases, do not support high temperature SC due to the absence of the appropriate magnetic excitations
Collective nature of orbital excitations in layered cuprates in the absence of apical oxygens
We have investigated the 3d orbital excitations in CaCuO2 (CCO), Nd2CuO4
(NCO) and La2CuO4 (LCO) using high-resolution resonant inelastic x-ray
scattering. In LCO they behave as well-localized excitations, similarly to
several other cuprates. On the contrary, in CCO and NCO the dxy orbital clearly
disperse, pointing to a collective character of this excitation (orbiton) in
compounds without apical oxygen. We ascribe the origin of the dispersion as
stemming from a substantial next-nearest-neighbor (NNN) orbital superexchange.
Such an exchange leads to the liberation of orbiton from its coupling to
magnons, which is associated with the orbiton hopping between nearest neighbor
copper sites. We show that the exceptionally large NNN orbital superexchange
can be traced back to the absence of apical oxygens suppressing the charge
transfer energy.Comment: 18 pages, 7 figure
Orbital dynamics during an ultrafast insulator to metal transition
Phase transitions driven by ultrashort laser pulses have attracted interest
both for understanding the fundamental physics of phase transitions and for
potential new data storage or device applications. In many cases these
transitions involve transient states that are different from those seen in
equilibrium. To understand the microscopic properties of these states, it is
useful to develop elementally selective probing techniques that operate in the
time domain. Here we show fs-time-resolved measurements of V Ledge Resonant
Inelastic X-Ray Scattering (RIXS) from the insulating phase of the Mott-
Hubbard material V2O3 after ultrafast laser excitation. The probed orbital
excitations within the d-shell of the V ion show a sub-ps time response, which
evolve at later times to a state that appears electronically indistinguishable
from the high-temperature metallic state. Our results demonstrate the potential
for RIXS spectroscopy to study the ultrafast orbital dynamics in strongly
correlated materials.Comment: 12 pages, 4 figure
Population mixing for leukaemia, lymphoma and CNS tumours in teenagers and young adults in England, 1996-2005
Background: Little aetiological epidemiological research has been undertaken for major cancers occurring in teenagers and young adults (TYA). Population mixing, as a possible proxy for infectious exposure, has been well researched for childhood malignancies. We aimed to investigate effects of population mixing in this older age group using an English national cancer dataset.Methods: Cases of leukaemia, lymphoma and central nervous system (CNS) tumours amongst 15-24 year olds in England (diagnosed 1996-2005) were included in the study. Data were obtained by ward of diagnosis and linked to 1991 census variables including population mixing (Shannon index); data on person-weighted population density and deprivation (Townsend score) were also used and considered as explanatory variables. Associations between TYA cancer incidence and census variables were investigated using negative binomial regression, and results presented as incidence rate ratios (IRR) with 95% confidence intervals (CI).Results: A total of 6251 cases of leukaemia (21%), lymphoma (49%) and CNS tumours (30%) were analysed. Higher levels of population mixing were associated with a significant decrease in the incidence of CNS tumours (IRR = 0.83, 95% CI = 0.75-0.91), accounted for by astrocytomas and 'other CNS tumours'; however, there was no association with leukaemia or lymphoma. Incidence of CNS tumours and lymphoma was 3% lower in more deprived areas (IRR = 0.97, 95% CI = 0.96-0.99 and IRR = 0.97, 95% CI =0.96-0.98 respectively). Population density was not associated with the incidence of leukaemia, lymphoma or CNS tumours.Conclusions: Our results suggest a possible role for environmental risk factors with population correlates in the aetiology of CNS tumours amongst TYAs. Unlike studies of childhood cancer, associations between population mixing and the incidence of leukaemia and lymphoma were not observed
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