Glancing through the debris disk: Photometric analysis of DE Boo with CHEOPS

Aims. DE Boo is a unique system, with an edge-on view through the debris disk around the star. The disk, which is analogous to the Kuiper belt in the Solar System, was reported to extend from 74 to 84 AU from the central star. The high photometric precision of the Characterising Exoplanet Satellite (CHEOPS) provided an exceptional opportunity to observe small variations in the light curve due to transiting material in the disk. This is a unique chance to investigate processes in the debris disk. Methods. Photometric observations of DE Boo of a total of four days were carried out with CHEOPS. Photometric variations due to spots on the stellar surface were subtracted from the light curves by applying a two-spot model and a fourth-order polynomial. The photometric observations were accompanied by spectroscopic measurements with the 1m RCC telescope at Piszkésteto and with the SOPHIE spectrograph in order to refine the astrophysical parameters of DE Boo. Results. We present a detailed analysis of the photometric observation of DE Boo. We report the presence of nonperiodic transient features in the residual light curves with a transit duration of 0.3–0.8 days. We calculated the maximum distance of the material responsible for these variations to be 2.47 AU from the central star, much closer than most of the mass of the debris disk. Furthermore, we report the first observation of flaring events in this system. Conclusions. We interpreted the transient features as the result of scattering in an inner debris disk around DE Boo. The processes responsible for these variations were investigated in the context of interactions between planetesimals in the system

Single-nanoparticle phase transitions visualized by four-dimensional electron microscopy

The advancement of techniques that can probe the behaviour of individual nanoscopic objects is of paramount importance in various disciplines, including photonics and electronics. As it provides images with a spatiotemporal resolution, four-dimensional electron microscopy, in principle, should enable the visualization of single-nanoparticle structural dynamics in real and reciprocal space. Here, we demonstrate the selectivity and sensitivity of the technique by visualizing the spin crossover dynamics of single, isolated metal–organic framework nanocrystals. By introducing a small aperture in the microscope, it was possible to follow the phase transition and the associated structural dynamics within a single particle. Its behaviour was observed to be distinct from that imaged by averaging over ensembles of heterogeneous nanoparticles. The approach reported here has potential applications in other nanosystems and those that undergo (bio)chemical transformations

Lipids modulate the conformational dynamics of a secondary multidrug transporter

Direct interactions with lipids have emerged as key determinants of the folding, structure and function of membrane proteins, but an understanding of how lipids modulate protein dynamics is still lacking. Here, we systematically explored the effects of lipids on the conformational dynamics of the proton-powered multidrug transporter LmrP from Lactococcus lactis, using the pattern of distances between spin-label pairs previously shown to report on alternating access of the protein. We uncovered, at the molecular level, how the lipid headgroups shape the conformational-energy landscape of the transporter. The model emerging from our data suggests a direct interaction between lipid headgroups and a conserved motif of charged residues that control the conformational equilibrium through an interplay of electrostatic interactions within the protein. Together, our data lay the foundation for a comprehensive model of secondary multidrug transport in lipid bilayers

DNA breaks at fragile sites generate oncogenic RET/PTC rearrangements in human thyroid cells

Human chromosomal fragile sites are regions of the genome that are prone to DNA breakage, and are classified as common or rare, depending on their frequency in the population. Common fragile sites frequently coincide with the location of genes involved in carcinogenic chromosomal translocations, suggesting their role in cancer formation. However, there has been no direct evidence linking breakage at fragile sites to the formation of a cancer-specific translocation. Here, we studied the involvement of fragile sites in the formation of RET/PTC rearrangements, which are frequently found in papillary thyroid carcinoma (PTC). These rearrangements are commonly associated with radiation exposure; however, most of the tumors found in adults are not linked to radiation. In this study, we provide structural and biochemical evidence that the RET, CCDC6 and NCOA4 genes participating in two major types of RET/PTC rearrangements, are located in common fragile sites FRA10C and FRA10G, and undergo DNA breakage after exposure to fragile site-inducing chemicals. Moreover, exposure of human thyroid cells to these chemicals results in the formation of cancer-specific RET/PTC rearrangements. These results provide the direct evidence for the involvement of chromosomal fragile sites in the generation of cancer-specific rearrangements in human cell

Glancing through the debris disk: Photometric analysis of DE Boo with CHEOPS

DE Boo is a unique system, with an edge-on view through the debris disk around the star. The disk, which is analogous to the Kuiper belt in the Solar System, was reported to extend from 74 to 84 AU from the central star. The high photometric precision of the Characterising Exoplanet Satellite (CHEOPS) provided an exceptional opportunity to observe small variations in the light curve due to transiting material in the disk. This is a unique chance to investigate processes in the debris disk. Photometric observations of DE Boo of a total of four days were carried out with CHEOPS. Photometric variations due to spots on the stellar surface were subtracted from the light curves by applying a two-spot model and a fourth-order polynomial. The photometric observations were accompanied by spectroscopic measurements with the 1m RCC telescope at Piszk\'estet\H{o} and with the SOPHIE spectrograph in order to refine the astrophysical parameters of DE Boo. We present a detailed analysis of the photometric observation of DE Boo. We report the presence of nonperiodic transient features in the residual light curves with a transit duration of 0.3-0.8 days. We calculated the maximum distance of the material responsible for these variations to be 2.47 AU from the central star, much closer than most of the mass of the debris disk. Furthermore, we report the first observation of flaring events in this system. We interpreted the transient features as the result of scattering in an inner debris disk around DE Boo. The processes responsible for these variations were investigated in the context of interactions between planetesimals in the system

Convergence of solutions in a mean-field model of go-or-grow type with reservation of sites for proliferation and cell cycle delay

We consider the mean-field approximation of an individual-based model describing cell motility and proliferation, which incorporates the volume exclusion principle, the go-or-grow hypothesis and an explicit cell cycle delay. To utilise the framework of on-lattice agent-based models, we make the assumption that cells enter mitosis only if they can secure an additional site for the daughter cell, in which case they occupy two lattice sites until the completion of mitosis. The mean-field model is expressed by a system of delay differential equations and includes variables such as the number of motile cells, proliferating cells, reserved sites and empty sites. We prove the convergence of biologically feasible solutions: eventually all available space will be filled by mobile cells, after an initial phase when the proliferating cell population is increasing then diminishing. By comparing the behaviour of the mean-field model for different parameter values and initial cell distributions, we illustrate that the total cell population may follow a logistic-type growth curve, or may grow in a step-function-like fashion

A modular approach for the synthesis of nanometer-sized polynitroxide multi-spin systems

S.V. is supported by an EPSRC Doctoral Training Grant; B.E.B. acknowledges an EaStCHEM Hirst Academic Fellowship by the School of Chemistry, St Andrews and funding from the People Programme (Marie Curie Actions) of the European Union’s Seventh Framework Programme (REA 334496)The synthesis of rigid symmetric polyradical model systems with inter-spin distances between 1.4 and 4 nm and their room temperature continuous wave (CW) EPR spectra are reported. Conditions for attachment of the spin-label via esterification have been optimized on the direct synthesis of polyradicals from commercially available polyphenols and the carboxylic acid functionalized nitroxide TPC. A common synthetic protocol utilizing 4-hydroxy-4′-iodobiphenyl as a key building block has been used to synthesize an equilateral biradical and a triradical in only two steps from commercially available starting materials. The first synthesis of a tetraradical based upon an adamantane core bearing six equivalent nitroxide–nitroxide distances is also reported. These systems are very promising candidates for studying multi-spin effects in pulsed EPR distance measurements.Publisher PDFPeer reviewe