3,575 research outputs found
Ultrafast light-induced response of photoactive yellow protein chromophore analogues
The fluorescence decays of several analogues of the photoactive yellow protein (PYP) chromophore in aqueous solution have been measured by femtosecond fluorescence up-conversion and the corresponding time-resolved fluorescence spectra have been reconstructed. The native chromophore of PYP is a thioester derivative of p-coumaric acid in its trans deprotonated form. Fluorescence kinetics are reported for a thioester phenyl analogue and for two analogues where the thioester group has been changed to amide and carboxylate groups. The kinetics are compared to those we previously reported for the analogues bearing ketone and ester groups. The fluorescence decays of the full series are found to lie in the 1–10 ps range depending on the electron-acceptor character of the substituent, in good agreement with the excited-state relaxation kinetics extracted from transient absorption measurements. Steady-state photolysis is also examined and found to depend strongly on the nature of the substituent. While it has been shown that the ultrafast light-induced response of the chromophore in PYP is controlled by the properties of the protein nanospace, the present results demonstrate that, in solution, the relaxation dynamics and pathway of the chromophore is controlled by its electron donor–acceptor structure: structures of stronger electron donor–acceptor character lead to faster decays and less photoisomerisation
Memory in narratives and stories: implications for nursing research
©2019 RCN Publishing Company Ltd. All rights reserved. Not to be copied, transmitted or recorded in any way, in whole or part, without prior permission of the publishers. BACKGROUND: Memory, as a concept, is rarely discussed or described in qualitative research. However, memories are central to the stories people tell about their experiences of health and illness, which are often the focus of nursing enquiry. Memories also have the potential to be sensitive or traumatic. AIM: To consider the implications of memory for qualitative research by exploring the following issues: What is memory? What are the implications for using it in research? How can research participants and researchers best be supported in qualitative research when sensitive or traumatic memories are involved? DISCUSSION: Memory is imperfect, complex and dependent on context. Memories are connected to meaning and are central to identity. Qualitative research should appreciate the complexities of memory. Nurses undertaking qualitative research should be mindful of the potentially sensitive or traumatic nature of memories. Both participants and researchers can be affected and care should be taken during the research. CONCLUSION: Memory should not be taken for granted. The meanings underpinning memories are central to qualitative enquiry and are to be valued. IMPLICATIONS FOR PRACTICE: The strategies described in this paper can support researchers and participants when dealing with traumatic or sensitive memories
Can Mg isotopes be used to trace cyanobacteria-mediated magnesium carbonate precipitation in alkaline lakes?
The fractionation of Mg isotopes was determined during the cyanobacterial mediated precipitation of hydrous magnesium carbonate precipitation in both natural environments and in the laboratory. Natural samples were obtained from Lake Salda (SE Turkey), one of the few modern environments on the Earth's surface where hydrous Mg-carbonates are the dominant precipitating minerals. This precipitation was associated with cyanobacterial stromatolites which were abundant in this aquatic ecosystem. Mg isotope analyses were performed on samples of incoming streams, groundwaters, lake waters, stromatolites, and hydromagnesite-rich sediments. Laboratory Mg carbonate precipitation experiments were conducted in the presence of purified Synechococcus sp cyanobacteria that were isolated from the lake water and stromatolites. The hydrous magnesium carbonates nesquehonite (MgCO3·3H2O) and dypingite (Mg5(CO3)4(OH)25(H2O)) were precipitated in these batch reactor experiments from aqueous solutions containing either synthetic NaHCO3/MgCl2 mixtures or natural Lake Salda water, in the presence and absence of live photosynthesizing Synechococcus sp. Bulk precipitation rates were not to affected by the presence of bacteria when air was bubbled through the system. In the stirred non-bubbled reactors, conditions similar to natural settings, bacterial photosynthesis provoked nesquehonite precipitation, whilst no precipitation occurred in bacteria-free systems in the absence of air bubbling, despite the fluids achieving a similar or higher degree of supersaturation. The extent of Mg isotope fractionation (?26Mgsolid-solution) between the mineral and solution in the abiotic experiments was found to be identical, within uncertainty, to that measured in cyanobacteria-bearing experiments, and ranges from ?1.4 to ?0.7 ‰. This similarity refutes the use of Mg isotopes to validate microbial mediated precipitation of hydrous Mg carbonate
Ethanol Vapours to Complement or Replace Sulfur Dioxide Fumigation of Table Grapes
Recent studies have shown that dipping table grapes in ethanol solutions at harvest improved storage of the fruit. We report here the first results obtained by treating "Chasselas" table grapes (Vitis vinifera) with ethanol vapours over the storage period. We tested the effect of ethanol at 0, 4 and 8 g/kg fruit during cold storage for 2, 4 and 6 weeks. We measured berry shatter, stem browning, Botrytis rot incidence and sensory appreciation by tasting panels. Ethanol vapours reduced Botrytis rot incidence and berry shatter, but hastened stem browning. Sensory analyses did not detect any differences between treatments
On the dynamical interaction between overshooting convection and an underlying dipole magnetic field -- I. The non-dynamo regime
Motivated by the dynamics in the deep interiors of many stars, we study the
interaction between overshooting convection and the large-scale poloidal fields
residing in radiative zones. We have run a suite of 3D Boussinesq numerical
calculations in a spherical shell that consists of a convection zone with an
underlying stable region that initially compactly contains a dipole field. By
varying the strength of the convective driving, we find that, in the less
turbulent regime, convection acts as turbulent diffusion that removes the field
faster than solely molecular diffusion would do. However, in the more turbulent
regime, turbulent pumping becomes more efficient and partially counteracts
turbulent diffusion, leading to a local accumulation of the field below the
overshoot region. These simulations suggest that dipole fields might be
confined in underlying stable regions by highly turbulent convective motions at
stellar parameters. The confinement is of large-scale field in an average sense
and we show that it is reasonably modeled by mean-field ideas. Our findings are
particularly interesting for certain models of the Sun, which require a
large-scale, poloidal magnetic field to be confined in the solar radiative zone
in order to explain simultaneously the uniform rotation of the latter and the
thinness of the solar tachocline.Comment: Accepted to MNRAS, 14 figure
Streptozocin Diabetes Elevates all Isoforms of TGF-β in the Rat Kidney
Transforming growth factor beta (TGF-β) is a major
promoter of diabetic nephropathy. While TGF-β1 is
the most abundaft renal isoform, types 2 and 3 are
present as well and have identical in vitro effects.
Whole kidney extracts were studied 2 weeks after
induction of streptozocin diabetes and in control
rats. Mean glomerular area was 25% greater in the
diabetic animals. TGF-β1 showed a 2-fold increase
in message with a 3-fold increase in protein. TGF-β2
mRNA increased approximately 6% while its
protein doubled. TGF-β-message increased by 25%,
producing a 35% increase in its protein. TGF-β-
inducible gene H3 mRNA was increased 35% in the
diabetic animals, consistent with increased activity
of this growth factor. All isoforms of TGF-β are
increased in the diabetic rat kidney. Future studies
need to address the specific role that each isoform
plays in diabetic nephropathy as well as the impact
of therapies on each isoform
Optical bistability in a GaAs based polariton diode
We report on a new type of optical nonlinearity in a polariton p-i-n
microcavity. Abrupt switching between the strong and weak coupling regime is
induced by controlling the electric field within the cavity. As a consequence
bistable cycles are observed for low optical powers (2-3 orders of magnitude
less than for Kerr induced bistability). Signatures of switching fronts
propagating through the whole 300 microns x 300 microns mesa surface are
evidenced.Comment: 5 pages 3 figure
Testing QUMOND theory with Galactic globular clusters in a weak external field
We developed self-consistent dynamical models of stellar systems in the
framework of quasi-linear modified Newtonian dynamics (QUMOND). The models are
constructed from the anisotropic distribution function of Gunn & Griffin
(1979), combined with the modified Poisson equation defining this gravitation
theory and take into account the external field effect. We have used these
models, and their Newtonian analogues, to fit the projected density and the
velocity dispersion profiles of a sample of 18 Galactic globular clusters,
using the most updated datasets of radial velocities and Gaia proper motions.
We have thus obtained, for each cluster, estimates of the dynamical
mass-to-light ratio () for each theory of gravity. The selected clusters
have accurate proper motions and a well sampled mass function down to the very
low mass regime. This allows us to constrain the degree of anisotropy and to
provide, from comparison with stellar evolution isochrones, a
dynamics-independent estimate of the minimum mass-to-light ratio .
Comparing the best-fitting dynamical with , we find that for
none of the analyzed clusters the two gravity theories are significantly
incompatible with the observational data, although for one of them (NGC 5024)
the dynamical predicted by QUMOND lies at below
. Though the proposed approach suffers from some limitations (in
particular the lack of a treatment of mass segregation), the obtained results
suggest that the kinematics of globular clusters in a relatively weak external
field can be a powerful tool to prove alternative theories of gravitation.Comment: Accepted for publication in MNRAS. Dedicated to the memory of Antonio
Sollima, who conceived, developed and carried out most of this wor
Secretion of Annexin II via Activation of Insulin Receptor and Insulin-like Growth Factor Receptor
Annexin II is secreted into the extracellular environment, where, via interactions with specific proteases and extracellular matrix proteins, it participates in plasminogen activation, cell adhesion, and tumor metastasis and invasion. However, mechanisms regulating annexin II transport across the cellular membrane are unknown. In this study, we used coimmunoprecipitation to show that Annexin-II was bound to insulin and insulin-like growth factor-1 (IGF-1) receptors in PC12 cells and NIH-3T3 cells overexpressing insulin (NIH-3T3(IR)) or IGF-1 receptor (NIH-3T3(IGF-1R)). Stimulation of insulin and IGF-1 receptors by insulin caused a temporary dissociation of annexin II from these receptors, which was accompanied by an increased amount of extracellular annexin II detected in the media of PC12, NIH-3T3(IR), and NIH-3T3(IGF-1R) cells but not in that of untransfected NIH-3T3 cells. Activation of a different growth factor receptor, the platelet-derived growth factor receptor, did not produce such results. Tyrphostin AG1024, a tyrosine kinase inhibitor of insulin and IGF-1 receptor, was shown to inhibit annexin II secretion along with reduced receptor phosphorylation. Inhibitors of a few downstream signaling enzymes including phosphatidylinositol 3-kinase, pp60c-Src, and protein kinase C had no effect on insulin-induced annexin II secretion, suggesting a possible direct link between receptor activation and annexin II secretion. Immunocytochemistry revealed that insulin also induced transport of the membrane-bound form of annexin II to the outside layer of the cell membrane and appeared to promote cell aggregation. These results suggest that the insulin receptor and its signaling pathways may participate in molecular mechanisms mediating annexin II secretion
The Lyman-continuum-leaking super star cluster in the Sunburst Arc and its surrounding nebula
Strong lensing offers a precious opportunity for studying the formation and
early evolution of super star clusters that are rare in our cosmic backyard.
The Sunburst Arc, a lensed Cosmic Noon galaxy, hosts a young super star cluster
with escaping Lyman continuum radiation. Analyzing archival HST images and
emission line data from VLT/MUSE and X-shooter, we construct a physical model
for the cluster and its surrounding photoionized nebula. We confirm that the
cluster is \sim 3\mbox{--}4\,Myr old, is extremely massive and yet has a central component as compact as several parsecs,
and we find a metallicity . The cluster is surrounded
by of dense clouds that have been pressurized to by perhaps stellar radiation at within ten
parsecs. These should have large neutral columns to survive rapid ejection by radiation pressure. The clouds are
likely dusty as they show gas-phase depletion of silicon, and may be conducive
to secondary star formation if or if they
sink further toward the cluster center. Detecting strong 1750,1752, we infer heavy nitrogen enrichment . This requires efficiently retaining of nitrogen in the high-pressure clouds from massive stars
heavier than up to 4 Myr. We suggest a physical origin of the
high-pressure clouds from partial or complete condensation of slow massive star
ejecta, which may have important implication for the puzzle of multiple stellar
populations in globular clusters.Comment: 25 pages, 10 figure
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