1,646 research outputs found
Shadow of a Colossus: A z=2.45 Galaxy Protocluster Detected in 3D Ly-a Forest Tomographic Mapping of the COSMOS Field
Using moderate-resolution optical spectra from 58 background Lyman-break
galaxies and quasars at within a area of the
COSMOS field ( projected area density or mean transverse separation), we reconstruct a 3D
tomographic map of the foreground Ly forest absorption at
with an effective smoothing scale of
comoving. Comparing with 61
coeval galaxies with spectroscopic redshifts in the same volume, we find that
the galaxy positions are clearly biased towards regions with enhanced IGM
absorption in the tomographic map. We find an extended IGM overdensity with
deep absorption troughs at associated with a recently-discovered
galaxy protocluster at the same redshift. Based on simulations matched to our
data, we estimate the enclosed dark matter mass within this IGM overdensity to
be , and
argue based on this mass and absorption strength that it will form at least one
galaxy cluster with , although its elongated nature suggests that
it will likely collapse into two separate clusters. We also point out a compact
overdensity of six MOSDEF galaxies at within a radius and , which does not appear
to have a large associated IGM overdensity. These results demonstrate the
potential of Ly forest tomography on larger volumes to study galaxy
properties as a function of environment, as well as revealing the large-scale
IGM overdensities associated with protoclusters and other features of
large-scale structure.Comment: To be submitted to ApJ. Figure 3 can be viewed on Youtube:
https://youtu.be/KeW1UJOPMY
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Selective nitrogen adsorption via backbonding in a metal-organic framework with exposed vanadium sites.
Industrial processes prominently feature π-acidic gases, and an adsorbent capable of selectively interacting with these molecules could enable important chemical separations1-4. Biological systems use accessible, reducing metal centres to bind and activate weakly π-acidic species, such as N2, through backbonding interactions5-7, and incorporating analogous moieties into a porous material should give rise to a similar adsorption mechanism for these gaseous substrates8. Here, we report a metal-organic framework featuring exposed vanadium(II) centres capable of back-donating electron density to weak π acids to successfully target π acidity for separation applications. This adsorption mechanism, together with a high concentration of available adsorption sites, results in record N2 capacities and selectivities for the removal of N2 from mixtures with CH4, while further enabling olefin/paraffin separations at elevated temperatures. Ultimately, incorporating such π-basic metal centres into porous materials offers a handle for capturing and activating key molecular species within next-generation adsorbents
Imaging ultrafast excited state pathways in transition metal complexes by X-ray transient absorption and scattering using X-ray free electron laser source
This report will describe our recent studies of transition metal complex structural dynamics on the fs and ps time scales using an X-ray free electron laser source, Linac Coherent Light Source (LCLS). Ultrafast XANES spectra at the Ni K-edge of nickel(II) tetramesitylporphyrin (NiTMP) were successfully measured for optically excited state at a timescale from 100 fs to 50 ps, providing insight into its sub-ps electronic and structural relaxation processes. Importantly, a transient reduced state Ni(I) (π, 3d(x2−y2)) electronic state is captured through the interpretation of a short-lived excited state absorption on the low-energy shoulder of the edge, which is aided by the computation of X-ray transitions for postulated excited electronic states. The observed and computed inner shell to valence orbital transition energies demonstrate and quantify the influence of electronic configuration on specific metal orbital energies. A strong influence of the valence orbital occupation on the inner shell orbital energies indicates that one should not use the transition energy from 1s to other orbitals to draw conclusions about the d-orbital energies. For photocatalysis, a transient electronic configuration could influence d-orbital energies up to a few eV and any attempt to steer the reaction pathway should account for this to ensure that external energies can be used optimally in driving desirable processes. NiTMP structural evolution and the influence of the porphyrin macrocycle conformation on relaxation kinetics can be likewise inferred from this study
Chemokine CCL9 Is Upregulated Early in Chronic Kidney Disease and Counteracts Kidney Inflammation and Fibrosis
Inflammation and fibrosis play an important pathophysiological role in chronic kidney
disease (CKD), with pro-inflammatory mediators and leukocytes promoting organ damage with
subsequent fibrosis. Since chemokines are the main regulators of leukocyte chemotaxis and tissue
inflammation, we performed systemic chemokine profiling in early CKD in mice. This revealed
(C-C motif) ligands 6 and 9 (CCL6 and CCL9) as the most upregulated chemokines, with significantly higher levels of both chemokines in blood (CCL6: 3–4 fold; CCL9: 3–5 fold) as well as kidney
as confirmed by Enzyme-linked Immunosorbent Assay (ELISA) in two additional CKD models.
Chemokine treatment in a mouse model of early adenine-induced CKD almost completely abolished
the CKD-induced infiltration of macrophages and myeloid cells in the kidney without impact on circulating leukocyte numbers. The other way around, especially CCL9-blockade aggravated monocyte
and macrophage accumulation in kidney during CKD development, without impact on the ratio
of M1-to-M2 macrophages. In parallel, CCL9-blockade raised serum creatinine and urea levels as
readouts of kidney dysfunction. It also exacerbated CKD-induced expression of collagen (3.2-fold)
and the pro-inflammatory chemokines CCL2 (1.8-fold) and CCL3 (2.1-fold) in kidney. Altogether, this
study reveals for the first time that chemokines CCL6 and CCL9 are upregulated early in experimental
CKD, with CCL9-blockade during CKD initiation enhancing kidney inflammation and fibrosis
STAT1 Pathway Mediates Amplification of Metastatic Potential and Resistance to Therapy
BACKGROUND: Traditionally IFN/STAT1 signaling is connected with an anti-viral response and pro-apoptotic tumor-suppressor functions. Emerging functions of a constitutively activated IFN/STAT1 pathway suggest an association with an aggressive tumor phenotype. We hypothesized that tumor clones that constitutively overexpress this pathway are preferentially selected by the host microenvironment due to a resistance to STAT1-dependent cytotoxicity and demonstrate increased metastatic ability combined with increased resistance to genotoxic stress. METHODOLOGY/PRINCIPAL FINDINGS: Here we report that clones of B16F1 tumors grown in the lungs of syngeneic C57BL/6 mice demonstrate variable transcriptional levels of IFN/STAT1 pathway expression. Tumor cells that constitutively overexpress the IFN/STAT1 pathway (STAT1(H) genotype) are selected by the lung microenvironment. STAT1(H) tumor cells also demonstrate resistance to IFN-gamma (IFNgamma), ionizing radiation (IR), and doxorubicin relative to parental B16F1 and low expressors of the IFN/STAT1 pathway (STAT1(L) genotype). Stable knockdown of STAT1 reversed the aggressive phenotype and decreased both lung colonization and resistance to genotoxic stress. CONCLUSIONS: Our results identify a pathway activated by tumor-stromal interactions thereby selecting for pro-metastatic and therapy-resistant tumor clones. New therapies targeted against the IFN/STAT1 signaling pathway may provide an effective strategy to treat or sensitize aggressive tumor clones to conventional cancer therapies and potentially prevent distant organ colonization
Diabetes status and post-load plasma glucose concentration in relation to site-specific cancer mortality: findings from the original Whitehall study
ObjectiveWhile several studies have reported on the relation of diabetes status with pancreatic cancer risk, the predictive value of this disorder for other malignancies is unclear. Methods: The Whitehall study, a 25year follow-up for mortality experience of 18,006 men with data on post-challenge blood glucose and self-reported diabetes, allowed us to address these issues. Results: There were 2158 cancer deaths at follow-up. Of the 15 cancer outcomes, diabetes status was positively associated with mortality from carcinoma of the pancreas and liver, while the relationship with lung cancer was inverse, after controlling for a range of potential covariates and mediators which included obesity and socioeconomic position. After excluding deaths occurring in the first 10years of follow-up to examine the effect of reverse causality, the magnitude of the relationships for carcinoma of the pancreas and lung was little altered, while for liver cancer it was markedly attenuated. Conclusions: In the present study, diabetes status was related to pancreatic, liver, and lung cancer risk. Cohorts with serially collected data on blood glucose and covariates are required to further examine this area
Ultrafast Excited State Relaxation of a Metalloporphyrin Revealed by Femtosecond X-ray Absorption Spectroscopy
Photoexcited NickelÂ(II) tetramesitylporphyrin
(NiTMP), like many
open-shell metalloporphyrins, relaxes rapidly through multiple electronic
states following an initial porphyrin-based excitation, some involving
metal centered electronic configuration changes that could be harnessed
catalytically before excited state relaxation. While a NiTMP excited
state present at 100 ps was previously identified by X-ray transient
absorption (XTA) spectroscopy at a synchrotron source as a relaxed
(d,d) state, the lowest energy excited state (<i>J. Am. Chem.
Soc.</i>, <b>2007</b>, <i>129</i>, 9616 and <i>Chem. Sci.</i>, <b>2010</b>, <i>1</i>, 642),
structural dynamics before thermalization were not resolved due to
the ∼100 ps duration of the available X-ray probe pulse. Using
the femtosecond (fs) X-ray pulses of the Linac Coherent Light Source
(LCLS), the Ni center electronic configuration from the initial excited
state to the relaxed (d,d) state has been obtained via ultrafast Ni
K-edge XANES (X-ray absorption near edge structure) on a time scale
from hundreds of femtoseconds to 100 ps. This enabled the identification
of a short-lived NiÂ(I) species aided by time-dependent density functional
theory (TDDFT) methods. Computed electronic and nuclear structure
for critical excited electronic states in the relaxation pathway characterize
the dependence of the complex’s geometry on the electron occupation
of the 3d orbitals. Calculated XANES transitions for these excited
states assign a short-lived transient signal to the spectroscopic
signature of the NiÂ(I) species, resulting from intramolecular charge
transfer on a time scale that has eluded previous synchrotron studies.
These combined results enable us to examine the excited state structural
dynamics of NiTMP prior to thermal relaxation and to capture intermediates
of potential photocatalytic significance
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