Search

Dust particles in lofted atmospheric layers may present a preferential orientation, which could be detected from the resulting dichroic extinction of the transmitted sunlight. The first indications were provided relatively recently on atmospheric dust layers using passive polarimetry, when astronomical starlight observations of known polarization were found to exhibit an excess in linear polarization, during desert dust events that reached the observational site. We revisit the previous observational methodology by targeting dichroic extinction of transmitted sunlight through extensive atmospheric dust layers utilizing a direct-sun polarimeter, which is capable to continuously monitor the polarization of elevated aerosol layers. In this study, we present the unique observations from the Solar Polarimeter (SolPol) for different periods within 2 years, when the instrument was installed in the remote monitoring station of PANGEA – the PANhellenic GEophysical observatory of Antikythera – in Greece. SolPol records polarization, providing all four Stokes parameters, at a default wavelength band centred at 550 nm with a detection limit of 10−7. We, overall, report on detected increasing trends of linear polarization, reaching up to 700 parts per million, when the instrument is targeting away from its zenith and direct sunlight propagates through dust concentrations over the observatory. This distinct behaviour is absent on measurements we acquire on days with lack of dust particle concentrations and in general of low aerosol content. Moreover, we investigate the dependence of the degree of linear polarization on the layers' optical depth under various dust loads and solar zenith angles and attempt to interpret these observations as an indication of dust particles being preferentially aligned in the Earth's atmosphere.

This paper addresses, for the first time, a key aspect of the phenomenology of compact symmetric objects (CSOs): the characteristics of their radio spectra. We present a radio-spectrum description of a complete sample of high-luminosity CSOs (CSO-2s), which shows that they exhibit the complete range of spectral types, including flat-spectrum sources ( α ≥ −0.5), steep-spectrum sources ( α < −0.5), and peaked-spectrum sources. We show that there is no clear correlation between spectral type and size, but there is a correlation between the high-frequency spectral index and both object type and size. We also show that, to avoid biasing the data and to understand the various classes of active galactic nuclei (AGN) involved, the complete range of spectral types should be included in studying the general phenomenology of compact jetted AGN, and that complete samples must be used, selected over a wide range of frequencies. We discuss examples that demonstrate these points. We find that the high-frequency spectral indices of CSO-2s span −1.3 < α _hi < −0.3 and hence that radio spectral signatures cannot be used to discriminate definitively between CSO-2s, binary galactic nuclei, and millilensed objects, unless they have α _hi > −0.3.

We use a sample of 54 compact symmetric objects (CSOs) to confirm that there are two unrelated CSO classes: an edge-dimmed, low-luminosity class (CSO 1), and an edge-brightened, high-luminosity class (CSO 2). Using blind tests, we show that CSO 2s consist of three subclasses: CSO 2.0, having prominent hot spots at the leading edges of narrow jets and/or narrow lobes; CSO 2.2, without prominent hot spots and with broad jets and/or lobes; and CSO 2.1, which exhibit mixed properties. Most CSO 2s do not evolve into larger jetted active galactic nuclei (AGN), but spend their whole life cycle as CSOs of size ≲500 pc and age ≲5000 yr. The minimum energies needed to produce the radio luminosity and structure in CSO 2s range from ∼10 ^−4 M _⊙ c ^2 to ∼7 M _⊙ c ^2 . We show that the transient nature of most CSO 2s, and their birth rate, can be explained through ignition in the tidal disruption events of stars. We also consider possibilities of tapping the spin energy of the supermassive black hole, and tapping the energy of the accretion disk. Our results demonstrate that CSOs constitute a large family of AGN in which we have thus far studied only the brightest. More comprehensive CSO studies, with higher sensitivity, resolution, and dynamic range, will revolutionize our understanding of AGN and the central engines that power them.

Compact symmetric objects (CSOs) are jetted active galactic nuclei (AGN) with overall projected size 700 mJy is between (6.8 ± 1.6)% and (8.5 ± 1.8)%.

Compact symmetric objects (CSOs) are compact (99%) of CSO 2s do not evolve into larger-scale radio sources. These CSO 2s belong to a distinct population of jetted AGN, which should be characterized as “short-lived,” as opposed to “young,” compared to the classes of larger jetted AGN. We show that there is a sharp upper cutoff in the CSO 2 size distribution at ≈500 pc. The distinct differences between most CSO 2s and other jetted AGN provides a crucial new time domain window on the formation and evolution of relativistic jets in AGN and the supermassive black holes that drive them.

We report on the electric field variations during Saharan dust advection over two atmospheric remote stations in Greece, using synergistic observations of the vertical atmospheric electric field strength (Ez) at ground level and the lidar-derived particle backscatter coefficient profiles. Both parameters were monitored for the first time with the simultaneous deployment of a ground-based field mill electrometer and a multi-wavelength polarization lidar. The field mill time series are processed to extract the diurnal variations of the global electric circuit and remove fast field perturbations due to peak lightning activity. In order to identify the influence of the elevated dust layers on the ground Ez, we extract a localized reference electric field from the time series that reflects the local fair-weather activity. Then, we compare it with the reconstructed daily average behaviour of the electric field and the Saharan dust layers' evolution, as depicted by the lidar. The observed enhancement of the vertical electric field (up to ∼100 V m−1), for detached pure dust layers, suggests the presence of in-layer electric charges. Although higher dust loads are expected to result in such an electric field enhancement, episodic cases that reduce the electric field are also observed (up to ∼60 V m−1). To quantitatively approach our results, we examine the dependency of Ez against theoretical assumptions for the distribution of separated charges within the electrified dust layer. Electrically neutral dust is approximated by atmospheric conductivity reduction, while charge separation areas within electrically active dust layers are approximated as finite-extent cylinders. This physical approximation constitutes a more realistic description of the distribution of charges, as opposed to infinite-extent geometries, and allows for analytical solutions of the electric field strength so that observed variations during the monitored dust outbreaks can be explained.

Backgound. The existence of a “placental clock” which determines the duration of gestation has been previously proposed. It is related to placental CRH secretion and is active from an early phase in human pregnancy. Urocortin is a specific ligand for the corticotropin-releasing factor (CRF) receptor expressed by human trophoblast and fetal membranes. The purpose of this study was to evaluate whether urocortin concentrations in the early second trimester amniotic fluid might serve to predict preterm delivery. Method. The urocortin concentrations in early second trimester amniotic fluid were measured in 41 pregnancies with term delivery and in 41 pregnancies with preterm delivery by using an immunoradiometric assay. Conditional logistic regression analysis was used for statistical analysis. Results. Mean amniotic fluid urocortin concentrations in women with preterm labor were 1.55±0.63 ng/mL while those in women with term labor were 1.6±0.49 ng/mL (p: NS). No statistical significant results were found when comparing amniotic fluid urocortin concentrations in women with preterm premature rupture of membranes leading to preterm labor (𝑛=19) to women with term delivery without premature rupture of membranes. Conclusion. These results suggest that urocortin concentrations in the amniotic fluid of genetic amniocentesis are not predictive of preterm labor and birth.

The magnetic field (B-field) of the starless dark cloud L1544 has been studied using near-infrared (NIR) background starlight polarimetry (BSP) and archival data in order to characterize the properties of the plane-of-sky B-field. NIR linear polarization measurements of over 1700 stars were obtained in the H band and 201 of these were also measured in the K band. The NIR BSP properties are correlated with reddening, as traced using the Rayleigh–Jeans color excess (H–M) method, and with thermal dust emission from the L1544 cloud and envelope seen in Herschel maps. The NIR polarization position angles change at the location of the cloud and exhibit their lowest dispersion there, offering strong evidence that NIR polarization traces the plane-of-sky B-field of L1544. In this paper, the uniformity of the plane-of-sky B-field in the envelope region of L1544 is quantitatively assessed. This allows evaluation of the approach of assuming uniform field geometry when measuring relative mass-to-flux ratios in the cloud envelope and core based on averaging of the radio Zeeman observations in the envelope, as done by Crutcher et al. In L1544, the NIR BSP shows the envelope B-field to be significantly non-uniform and likely not suitable for averaging Zeeman properties without treating intrinsic variations. Deeper analyses of the NIR BSP and related data sets, including estimates of the B-field strength and testing how it varies with position and gas density, are the subjects of later papers in this series. [ABSTRACT FROM AUTHOR]

Novel biophysical tools allow the structural dynamics of proteins and the regulation of such dynamics by binding partners to be explored in unprecedented detail. Although this has provided critical insights into protein function, the means by which structural dynamics direct protein evolution remain poorly understood. Here, we investigated how proteins with a bilobed structure, composed of two related domains from the periplasmic-binding protein-like II domain family, have undergone divergent evolution, leading to adaptation of their structural dynamics. We performed a structural analysis on ∼600 bilobed proteins with a common primordial structural core, which we complemented with biophysical studies to explore the structural dynamics of selected examples by single-molecule Förster resonance energy transfer and Hydrogen-Deuterium exchange mass spectrometry. We show that evolutionary modifications of the structural core, largely at its termini, enable distinct structural dynamics, allowing the diversification of these proteins into transcription factors, enzymes, and extracytoplasmic transport-related proteins. Structural embellishments of the core created interdomain interactions that stabilized structural states, reshaping the active site geometry, and ultimately altered substrate specificity. Our findings reveal an as-yet-unrecognized mechanism for the emergence of functional promiscuity during long periods of evolution and are applicable to a large number of domain architectures., Competing Interests: The authors declare no competing interest., (Copyright © 2021 the Author(s). Published by PNAS.)

Genetically encodable fluorescent proteins have revolutionized biological imaging in vivo and in vitro. Despite their importance, their photophysical properties, i. e., brightness, count-rate and photostability, are relatively poor compared to synthetic organic fluorophores or quantum dots. Intramolecular photostabilizers were recently rediscovered as an effective approach to improve photophysical properties of organic fluorophores. Here, direct conjugation of triplet-state quenchers or redox-active substances creates high local concentrations of photostabilizer around the fluorophore. In this paper, we screen for effects of covalently linked photostabilizers on fluorescent proteins. We produced a double cysteine mutant (A206C/L221C) of α-GFP for attachment of photostabilizer-maleimides on the β-barrel near the chromophore. Whereas labelling with photostabilizers such as trolox, a nitrophenyl group, and cyclooctatetraene, which are often used for organic fluorophores, had no effect on α-GFP-photostability, a substantial increase of photostability was found upon conjugation to azobenzene. Although the mechanism of the photostabilizing effects remains to be elucidated, we speculate that the higher triplet-energy of azobenzene might be crucial for triplet-quenching of fluorophores in the blue spectral range. Our study paves the way for the development of fluorescent proteins with photostabilizers in the protein barrel by methods such as unnatural amino acid incorporation., (© 2021 The Authors. ChemBioChem published by Wiley-VCH GmbH.)

The current model of active transport via ABC importers is mostly based on structural, biochemical and genetic data. We here establish single-molecule Förster resonance energy transfer (smFRET) assays to monitor the conformational states and heterogeneity of the osmoregulatory type I ABC importer OpuA from Lactococcus lactis. We present data probing both intradomain distances that elucidate conformational changes within the substrate-binding domain (SBD) OpuAC, and interdomain distances between SBDs or transmembrane domains. Using this methodology, we studied ligand-binding mechanisms, as well as ATP and glycine betaine dependences of conformational changes. Our work expands the scope of smFRET investigations towards a class of so far unstudied ABC importers, and paves the way for a full understanding of their transport cycle in the future., (© 2020 The Authors. FEBS Letters published by John Wiley & Sons Ltd on behalf of Federation of European Biochemical Societies.)

ABC transporters utilize ATP for export processes to provide cellular resistance against toxins, antibiotics, and harmful metabolites in eukaryotes and prokaryotes. Based on static structure snapshots, it is believed that they use an alternating access mechanism, which couples conformational changes to ATP binding (outward-open conformation) and hydrolysis (inward-open) for unidirectional transport driven by ATP Here, we analyzed the conformational states and dynamics of the antibacterial peptide exporter McjD from Escherichia coli using single-molecule Förster resonance energy transfer (smFRET). For the first time, we established smFRET for an ABC exporter in a native-like lipid environment and directly monitor conformational dynamics in both the transmembrane- (TMD) and nucleotide-binding domains (NBD). With this, we unravel the ligand dependences that drive conformational changes in both domains. Furthermore, we observe intrinsic conformational dynamics in the absence of ATP and ligand in the NBDs. ATP binding and hydrolysis on the other hand can be observed via NBD conformational dynamics. We believe that the progress made here in combination with future studies will facilitate full understanding of ABC transport cycles., (© 2018 The Authors. Published under the terms of the CC BY 4.0 license.)

Stars and planets are formed inside dense interstellar molecular clouds by processes imprinted on the three-dimensional (3D) morphology of the clouds. Determining the 3D structure of interstellar clouds remains challenging because of projection effects and difficulties measuring the extent of the clouds along the line of sight. We report the detection of normal vibrational modes in the isolated interstellar cloud Musca, allowing determination of the 3D physical dimensions of the cloud. We found that Musca is vibrating globally, with the characteristic modes of a sheet viewed edge on, not the characteristics of a filament as previously supposed. We reconstructed the physical properties of Musca through 3D magnetohydrodynamic simulations, reproducing the observed normal modes and confirming a sheetlike morphology., (Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

During the last decade we showed clearly that abiotic stress changes the cellular composition of polyamines, which in turn regulate the photochemical and non-photochemical quenching of the received light energy in the photosynthetic apparatus and that modulate substantially the level of plant tolerance. In the present contribution, we tried to change the bioenergetics of the leaf discs before the exposure to osmotic stress only by exogenously supplied putrescine, in order to enhance quickly the tolerance against the abiotic stress. Tobacco leaf discs treated with polyethylene-glycol reduced their water content about 24% within 1h. This relatively mild osmotic stress increased endogenous putrescine about 83% and decreased maximum photosystem II photochemical efficiency about 14%. In line with this, here we show that treatment with 1mM exogenous putrescine 1h before polyethylene-glycol addition protects the photochemical capacity and inhibits loss of water, confirming the key role of putrescine in the modulation of plant tolerance against osmotic stress. Furthermore, our recent works indicate that putrescine is accumulated in lumen during light reactions and may act as a permeable buffer and an osmolyte., (Copyright © 2013 Elsevier GmbH. All rights reserved.)

Aim: The objective is to present a rare case of late diagnosis of Cornelia de Lange syndrome., Case: A 27-year-old pregnant woman (gravida 1, para 0) was referred to our Fetal Medicine Department during her 33rd week of gestation due to intrauterine growth restriction (IUGR) and polyhydramnios. The ultrasound scanning confirmed the findings and furthermore, the 3-D examination revealed minor facial dysmorphisms, limb abnormalities, and hypertrichosis. The fetus died 1 week post-diagnosis due to unknown reason and the woman underwent an induction of labor. Postmortem examination confirmed the diagnosis of Cornelia de Lange syndrome., Conclusion: The prognosis of the syndrome is severe. Termination of pregnancy before viability is proposed. Genetic counseling is necessary.

Aim: Human beta defensins 2 (HBD2) and 3 (HBD3) are peptides expressed in the amnion and chorion. This is a matched case control study conducted in our Department to determine whether second trimester amniotic fluid HBD2 and HBD3 concentrations measured at the time of genetic amniocentesis could be potential markers of preterm labor prediction., Methods: Amniotic fluid HBD2 and HBD3 were determined by an enzyme-linked immunosorbent assay (ELISA) Women with preterm labor were defined as cases (N=41) while for each case a woman matched for age delivering at term served as control (N=41). Subgroup analysis was conducted to examine possible associations of HBD2 and HBD3 in cases of premature rupture of membranes. Nineteen women with preterm labor and premature rupture of membranes were defined as cases while for every case a woman matched for maternal age delivering at term served as control (N1=19). Results were presented as odds ratios (OR) and 95% confidence intervals. Statistical analysis used STATA 8.2 and SPSS 11.5 edition. A P-value of <0.05 was considered statistically significant., Results: Amniotic fluid concentrations of HBD2 at the time of genetic amniocentesis were positively associated with preterm premature rupture of membranes (P=0.028), but not with preterm labour. No association of HBD3 and preterm birth was documented., Conclusion: Second trimester amniotic fluid HBD2 might be a predictor of premature rupture of membranes.

Background: Adrenomedullin, secreted by decidua and trophoblast cells, is considered to participate in regulating uterine and placental blood flow, leading to control of placental hormonal secretion. Furthermore, adrenomedullin has an antimicrobial activity. The objective of this study was to determine whether adrenomedullin concentrations in midtrimester amniotic fluid can be used as a predictor of preterm delivery., Patients and Methods: Amniotic fluid samples were collected in a retrospective cross-matched study that included 362 women with singleton pregnancies who presented for genetic amniocentesis. Adrenomedullin concentrations were determined by ELISA in amniotic fluid taken from women with spontaneous preterm delivery (n=41) and maternal age-matched controls who had normal pregnancy at term (n=41)., Results: No difference was found in adrenomedullin concentrations between women with spontaneous preterm delivery (median: 1.33 ng/ml, range: 0.36-8.53 ng/ml) and controls (median: 1.32 ng/ml, range: 0.33-4.07 ng/ml), nor between a subset of cases of preterm premature rupture of membranes (n=19) and their controls (n=19)., Conclusion: Adrenomedullin concentration in amniotic fluid cannot serve as a predictor of preterm delivery.

Background: The existence of a "placental clock" which determines the duration of gestation has been previously proposed. It is related to placental CRH secretion and is active from an early phase in human pregnancy. Urocortin is a specific ligand for the corticotropin-releasing factor (CRF) receptor expressed by human trophoblast and fetal membranes. The purpose of this study was to evaluate whether urocortin concentrations in the early second trimester amniotic fluid might serve to predict preterm delivery., Method: The urocortin concentrations in early second trimester amniotic fluid were measured in 41 pregnancies with term delivery and in 41 pregnancies with preterm delivery by using an immunoradiometric assay. Conditional logistic regression analysis was used for statistical analysis., Results: Mean amniotic fluid urocortin concentrations in women with preterm labor were 1.55+/-0.63 ng/mL while those in women with term labor were 1.6+/-0.49 ng/mL (p: NS). No statistical significant results were found when comparing amniotic fluid urocortin concentrations in women with preterm premature rupture of membranes leading to preterm labor (n=19) to women with term delivery without premature rupture of membranes., Conclusion: These results suggest that urocortin concentrations in the amniotic fluid of genetic amniocentesis are not predictive of preterm labor and birth.