@article{21095, abstract = {Inspired by DNA mimic proteins, we have introduced aromatic foldamers bearing phosphonate groups as synthetic mimics of the charge surface of B-DNA and competitive inhibitors of some therapeutically relevant DNA-binding enzymes: the human DNA Topoisomerase 1 (Top1) and the human HIV-1 integrase (HIV-1 IN). We now report on variants of these anionic foldamers bearing carboxylates instead of phosphonates. Several new monomers have been synthesized with protecting groups suitable for solid phase synthesis (SPS). Six hexadecaamides have been prepared using SPS. Proof of their resemblance to B-DNA was brought by the first crystal structure of one of these DNA-mimic foldamers in its polyanionic form. While some of the foldamers were found to be as active as, or even more active than, the original phosphonate oligomers, others had no activity at all or could even stimulate enzyme activity in vitro. Some foldamers were found to have differential inhibitory effects on the two enzymes. These results demonstrate a strong dependence of inhibitory activity on foldamer structure and charge distribution. They open broad avenues for the development of new classes of derivatives that could inhibit the interaction of specific proteins with their DNA target thereby influencing the cellular pathways in which they are involved.}, author = {Corvaglia, Valentina and Carbajo, Daniel and Prabhakaran, Panchami and Ziach, Krzysztof and Mandal, Pradeep K and Santos, Victor Dos and Legeay, Carole and Vogel, Rachel and Parissi, Vincent and Pourquier, Philippe and Huc, Ivan}, issn = {1362-4962}, journal = {Nucleic Acids Research}, number = {11}, pages = {5511--5521}, publisher = {Oxford University Press}, title = {{Carboxylate-functionalized foldamer inhibitors of HIV-1 integrase and Topoisomerase 1: Artificial analogues of DNA mimic proteins}}, doi = {10.1093/nar/gkz352}, volume = {47}, year = {2019}, } @article{21538, abstract = {Extracting light from silicon is a longstanding challenge in modern engineering and physics. While silicon has underpinned the past 70 years of electronics advancement, a facile tunable and efficient silicon-based light source remains elusive. Here, we experimentally demonstrate the generation of tunable radiation from a one-dimensional, all-silicon nanograting. Light is generated by the spontaneous emission from the interaction of these nanogratings with low-energy free electrons (2–20 keV) and is recorded in the wavelength range of 800–1600 nm, which includes the silicon transparency window. Tunable free-electron-based light generation from nanoscale silicon gratings with efficiencies approaching those from metallic gratings is demonstrated. We theoretically investigate the feasibility of a scalable, compact, all-silicon tunable light source comprised of a silicon Field Emitter Array integrated with a silicon nanograting that emits at telecommunication wavelengths. Our results reveal the prospects of a CMOS-compatible electrically-pumped silicon light source for possible applications in the mid-infrared and telecommunication wavelengths.}, author = {Roques-Carmes, Charles and Kooi, Steven E. and Yang, Yi and Massuda, Aviram and Keathley, Phillip D. and Zaidi, Aun and Yang, Yujia and Joannopoulos, John D. and Berggren, Karl K. and Kaminer, Ido and Soljačić, Marin}, issn = {2041-1723}, journal = {Nature Communications}, publisher = {Springer Nature}, title = {{Towards integrated tunable all-silicon free-electron light sources}}, doi = {10.1038/s41467-019-11070-7}, volume = {10}, year = {2019}, } @article{21557, abstract = {A new optical processor for solving hard optimization problems breaks previous size records and is based on a highly scalable technology. }, author = {Roques-Carmes, Charles and Soljačić, Marin}, issn = {1943-2879}, journal = {Physics}, publisher = {American Physical Society}, title = {{Photonic ising machines go big}}, doi = {10.1103/physics.12.61}, volume = {12}, year = {2019}, } @inproceedings{21568, abstract = {Optical approaches to AI acceleration have gained intense interest recently due to the potentially breakthrough advantages of photonics: high bandwidth, low power consumption, and efficient data movement. We overview leading photonic AI platforms based on beamsplitter mesh networks, weight banks, and photoelectric multiplication. While the theoretical performance can be orders of magnitude beyond current state of the art, practical issues of chip area, input / output, and crosstalk paint a more nuanced near-term picture of photonic AI acceleration. Both fundamental and near-term limitations to energy efficiency are addressed, and bandwidth limitations due to temporal crosstalk are analyzed.}, author = {Hamerly, R. and Sludds, A. and Bernstein, L. and Prabhu, M. and Roques-Carmes, Charles and Carolan, J. and Yamamoto, Y. and Soljacic, M. and Englund, D.}, booktitle = {2019 IEEE International Electron Devices Meeting}, issn = {2156-017X}, location = {San Francisco, CA, United States}, publisher = {IEEE}, title = {{Towards large-scale photonic neural-network accelerators}}, doi = {10.1109/iedm19573.2019.8993624}, year = {2019}, } @inproceedings{21620, abstract = {We present the Photonic Recurrent Ising Sampler (PRIS), an algorithm tailored for photonic parallel networks, that can sample distributions of arbitrary Ising problems. The PRIS finds the ground state of general Ising problems and probes critical exponents of universality classes.}, author = {Roques-Carmes, Charles and Shen, Yichen and Zanoci, Cristian and Prabhu, Mihika and Atieh, Fadi and Jing, Li and Dubček, Tena and Čeperić, Vladimir and Joannopoulos, John D. and Englund, Dirk and Soljačić, Marin}, booktitle = {Conference on Lasers and Electro-Optics}, location = {San Jose, CA, United States}, publisher = {Optica Publishing Group}, title = {{Photonic Recurrent Ising Sampler}}, doi = {10.1364/cleo_qels.2019.ftu4c.2}, year = {2019}, } @inproceedings{21627, abstract = {We demonstrate an integrated silicon photonic Markov Chain Monte Carlo sampler capable of high-probability convergence to the ground state of various 4-spin Ising graphs. Robustness to getting trapped in local minima is enhanced by experimental system noise.}, author = {Roques-Carmes, Charles and Prabhu, Mihika and Shen, Yichen and Harris, Nicholas and Jing, Li and Carolan, Jacques and Hamerly, Ryan and Baehr-Jones, Tom and Hochberg, Michael and Ceperic, Vladimir and Joannopoulos, John D. and Englund, Dirk and Soljacic, Marin}, booktitle = {Conference on Lasers and Electro-Optics}, location = {San Jose, CA, United States}, publisher = {Optica Publishing Group}, title = {{Integrated nanophotonic ising sampler}}, doi = {10.1364/cleo_si.2019.sf1n.1}, year = {2019}, } @article{21814, abstract = {Photoisomerization of molecules dissolved in a polymer film can modulate its properties. In a previous paper (Mostafavi, S. H.; Macromolecules 2018, 51, 2388−2394), it was found that the ultraviolet light-induced photoisomerization of spiropyran dopants could substantially increase adhesion to a glass surface. In this work, a different photochromic reaction, the visible-light-induced cyclization of a donor–acceptor Stenhouse adduct (DASA), leads to the opposite effect: the deadhesion of a polystyrene film from a clean glass surface. Measurements of the shear and pull-off adhesion strengths before and after visible irradiation show a light-induced decrease of 20–30%. The time required for delamination in water shows an even more dramatic decrease of 90%. Changes in the water contact angle and other measurements suggest that molecular-level noncovalent interactions between the polymer and glass are weakened after photoisomerization, possibly due to the molecular contraction of the DASA that disrupts the interaction between its amine groups and the surface silanols. The ability to reduce polymer adhesion using visible light enables the controlled release of dye molecules from a glass container, where these have been stored as a dry powder, into an aqueous solution. Embedding photochromic molecules in a polymer can lead to new effects that may have practical applications in stimuli-responsive materials.}, author = {Mostafavi, Seyed Hossein and Li, Wangxiang and Clark, Kyle D. and Stricker, Friedrich J and Alaniz, Javier Read de and Bardeen, Christopher J.}, issn = {1520-5835}, journal = {Macromolecules}, number = {16}, pages = {6311--6317}, publisher = {American Chemical Society}, title = {{Photoinduced deadhesion of a polymer film using a photochromic donor-acceptor Stenhouse adduct}}, doi = {10.1021/acs.macromol.9b00882}, volume = {52}, year = {2019}, } @article{13366, abstract = {The ability to reversibly assemble nanoparticles using light is both fundamentally interesting and important for applications ranging from reversible data storage to controlled drug delivery. Here, the diverse approaches that have so far been developed to control the self-assembly of nanoparticles using light are reviewed and compared. These approaches include functionalizing nanoparticles with monolayers of photoresponsive molecules, placing them in photoresponsive media capable of reversibly protonating the particles under light, and decorating plasmonic nanoparticles with thermoresponsive polymers, to name just a few. The applicability of these methods to larger, micrometer-sized particles is also discussed. Finally, several perspectives on further developments in the field are offered.}, author = {Bian, Tong and Chu, Zonglin and Klajn, Rafal}, issn = {1521-4095}, journal = {Advanced Materials}, keywords = {Mechanical Engineering, Mechanics of Materials, General Materials Science}, number = {20}, publisher = {Wiley}, title = {{The many ways to assemble nanoparticles using light}}, doi = {10.1002/adma.201905866}, volume = {32}, year = {2019}, } @article{13369, abstract = {Arylazopyrazoles represent a new family of molecular photoswitches characterized by a near-quantitative conversion between two states and long thermal half-lives of the metastable state. Here, we investigated the behavior of a model arylazopyrazole in the presence of a self-assembled cage based on Pd–imidazole coordination. Owing to its high water solubility, the cage can solubilize the E isomer of arylazopyrazole, which, by itself, is not soluble in water. NMR spectroscopy and X-ray crystallography have independently demonstrated that each cage can encapsulate two molecules of E-arylazopyrazole. UV-induced switching to the Z isomer was accompanied by the release of one of the two guests from the cage and the formation of a 1:1 cage/Z-arylazopyrazole inclusion complex. DFT calculations suggest that this process involves a dramatic change in the conformation of the cage. Back-isomerization was induced with green light and resulted in the initial 1:2 cage/E-arylazopyrazole complex. This back-isomerization reaction also proceeded in the dark, with a rate significantly higher than in the absence of the cage.}, author = {Hanopolskyi, Anton I and De, Soumen and Białek, Michał J and Diskin-Posner, Yael and Avram, Liat and Feller, Moran and Klajn, Rafal}, issn = {1860-5397}, journal = {Beilstein Journal of Organic Chemistry}, keywords = {Organic Chemistry}, pages = {2398--2407}, publisher = {Beilstein Institut}, title = {{Reversible switching of arylazopyrazole within a metal–organic cage}}, doi = {10.3762/bjoc.15.232}, volume = {15}, year = {2019}, } @article{13370, abstract = {Efficient isomerization of photochromic molecules often requires conformational freedom and is typically not available under solvent-free conditions. Here, we report a general methodology allowing for reversible switching of such molecules on the surfaces of solid materials. Our method is based on dispersing photochromic compounds within polysilsesquioxane nanowire networks (PNNs), which can be fabricated as transparent, highly porous, micrometer-thick layers on various substrates. We found that azobenzene switching within the PNNs proceeded unusually fast compared with the same molecules in liquid solvents. Efficient isomerization of another photochromic system, spiropyran, from a colorless to a colored form was used to create reversible images in PNN-coated glass. The coloration reaction could be induced with sunlight and is of interest for developing “smart” windows.}, author = {Chu, Zonglin and Klajn, Rafal}, issn = {1530-6992}, journal = {Nano Letters}, keywords = {Mechanical Engineering, Condensed Matter Physics, General Materials Science, General Chemistry, Bioengineering}, number = {10}, pages = {7106--7111}, publisher = {American Chemical Society}, title = {{Polysilsesquioxane nanowire networks as an “Artificial Solvent” for reversible operation of photochromic molecules}}, doi = {10.1021/acs.nanolett.9b02642}, volume = {19}, year = {2019}, } @article{13371, abstract = {Diamondoid nanoporous crystals represent a synthetically challenging class of materials that typically have been obtained from tetrahedral building blocks. In this issue of Chem, Stoddart and coworkers demonstrate that it is possible to generate diamondoid frameworks from a hexacationic building block lacking a tetrahedral symmetry. These results highlight the great potential of self-assembly for rapidly transforming small molecules into structurally complex functional materials.}, author = {Białek, Michał J. and Klajn, Rafal}, issn = {2451-9294}, journal = {Chem}, keywords = {Materials Chemistry, Biochemistry (medical), General Chemical Engineering, Environmental Chemistry, Biochemistry, General Chemistry}, number = {9}, pages = {2283--2285}, publisher = {Elsevier}, title = {{Diamond grows up}}, doi = {10.1016/j.chempr.2019.08.012}, volume = {5}, year = {2019}, } @article{13372, abstract = {The capacity to respond or adapt to environmental changes is an intrinsic property of living systems that comprise highly-connected subcomponents communicating through chemical networks. The development of responsive synthetic systems is a relatively new research area that covers different disciplines, among which nanochemistry brings conceptually new demonstrations. Especially attractive are ligand-protected gold nanoparticles, which have been extensively used over the last decade as building blocks in constructing superlattices or dynamic aggregates, under the effect of an applied stimulus. To reflect the importance of surface chemistry and nanoparticle core composition in the dynamic self-assembly of nanoparticles, we provide here an overview of various available stimuli, as tools for synthetic chemists to exploit. Along with this task, the review starts with the use of chemical stimuli such as solvent, pH, gases, metal ions or biomolecules. It then focuses on physical stimuli: temperature, magnetic and electric fields, as well as light. To reflect on the increasing complexity of current architectures, we discuss systems that are responsive to more than one stimulus, to finally encourage further research by proposing future challenges.}, author = {Grzelczak, Marek and Liz-Marzán, Luis M. and Klajn, Rafal}, issn = {1460-4744}, journal = {Chemical Society Reviews}, keywords = {General Chemistry}, number = {5}, pages = {1342--1361}, publisher = {Royal Society of Chemistry}, title = {{Stimuli-responsive self-assembly of nanoparticles}}, doi = {10.1039/c8cs00787j}, volume = {48}, year = {2019}, } @article{13373, abstract = {The reversible photoisomerization of azobenzene has been utilized to construct a plethora of systems in which optical, electronic, catalytic, and other properties can be controlled by light. However, owing to azobenzene’s hydrophobic nature, most of these examples have been realized only in organic solvents, and systems operating in water are relatively scarce. Here, we show that by coadsorbing the inherently hydrophobic azobenzenes with water-solubilizing ligands on the same nanoparticulate platforms, it is possible to render them essentially water-soluble. To this end, we developed a modified nanoparticle functionalization procedure allowing us to precisely fine-tune the amount of azobenzene on the functionalized nanoparticles. Molecular dynamics simulations helped us to identify two distinct supramolecular architectures (depending on the length of the background ligand) on these nanoparticles, which can explain their excellent aqueous solubilities. Azobenzenes adsorbed on these water-soluble nanoparticles exhibit highly reversible photoisomerization upon exposure to UV and visible light. Importantly, the mixed-monolayer approach allowed us to systematically investigate how the background ligand affects the switching properties of azobenzene. We found that the nature of the background ligand has a profound effect on the kinetics of azobenzene switching. For example, a hydroxy-terminated background ligand is capable of accelerating the back-isomerization reaction by more than 6000-fold. These results pave the way toward the development of novel light-responsive nanomaterials operating in aqueous media and, in the long run, in biological environments.}, author = {Chu, Zonglin and Han, Yanxiao and Bian, Tong and De, Soumen and Král, Petr and Klajn, Rafal}, issn = {1520-5126}, journal = {Journal of the American Chemical Society}, keywords = {Colloid and Surface Chemistry, Biochemistry, General Chemistry, Catalysis}, number = {5}, pages = {1949--1960}, publisher = {American Chemical Society}, title = {{Supramolecular control of azobenzene switching on nanoparticles}}, doi = {10.1021/jacs.8b09638}, volume = {141}, year = {2019}, } @article{13468, abstract = {Hydrogen-rich supernovae, known as Type II (SNe II), are the most common class of explosions observed following the collapse of the core of massive stars. We used analytical estimates and population synthesis simulations to assess the fraction of SNe II progenitors that are expected to have exchanged mass with a companion prior to explosion. We estimate that 1/3 to 1/2 of SN II progenitors have a history of mass exchange with a binary companion before exploding. The dominant binary channels leading to SN II progenitors involve the merger of binary stars. Mergers are expected to produce a diversity of SN II progenitor characteristics, depending on the evolutionary timing and properties of the merger. Alternatively, SN II progenitors from interacting binaries may have accreted mass from their companion, and subsequently been ejected from the binary system after their companion exploded. We show that the overall fraction of SN II progenitors that are predicted to have experienced binary interaction is robust against the main physical uncertainties in our models. However, the relative importance of different binary evolutionary channels is affected by changing physical assumptions. We further discuss ways in which binarity might contribute to the observed diversity of SNe II by considering potential observational signatures arising from each binary channel. For supernovae which have a substantial H-rich envelope at explosion (i.e., excluding Type IIb SNe), a surviving non-compact companion would typically indicate that the supernova progenitor star was in a wide, non-interacting binary. We argue that a significant fraction of even Type II-P SNe are expected to have gained mass from a companion prior to explosion.}, author = {Zapartas, Emmanouil and de Mink, Selma E. and Justham, Stephen and Smith, Nathan and de Koter, Alex and Renzo, Mathieu and Arcavi, Iair and Farmer, Rob and Götberg, Ylva Louise Linsdotter and Toonen, Silvia}, issn = {1432-0746}, journal = {Astronomy & Astrophysics}, keywords = {Space and Planetary Science, Astronomy and Astrophysics}, publisher = {EDP Sciences}, title = {{The diverse lives of progenitors of hydrogen-rich core-collapse supernovae: The role of binary interaction}}, doi = {10.1051/0004-6361/201935854}, volume = {631}, year = {2019}, } @article{13469, abstract = {Stars stripped of their envelopes from interaction with a binary companion emit a significant fraction of their radiation as ionizing photons. They are potentially important stellar sources of ionizing radiation, however, they are still often neglected in spectral synthesis simulations or simulations of stellar feedback. In anticipating the large datasets of galaxy spectra from the upcoming James Webb Space Telescope, we modeled the radiative contribution from stripped stars by using detailed evolutionary and spectral models. We estimated their impact on the integrated spectra and specifically on the emission rates of H I-, He I-, and He II-ionizing photons from stellar populations. We find that stripped stars have the largest impact on the ionizing spectrum of a population in which star formation halted several Myr ago. In such stellar populations, stripped stars dominate the emission of ionizing photons, mimicking a younger stellar population in which massive stars are still present. Our models also suggest that stripped stars have harder ionizing spectra than massive stars. The additional ionizing radiation, with which stripped stars contribute affects observable properties that are related to the emission of ionizing photons from stellar populations. In co-eval stellar populations, the ionizing radiation from stripped stars increases the ionization parameter and the production efficiency of hydrogen ionizing photons. They also cause high values for these parameters for about ten times longer than what is predicted for massive stars. The effect on properties related to non-ionizing wavelengths is less pronounced, such as on the ultraviolet continuum slope or stellar contribution to emission lines. However, the hard ionizing radiation from stripped stars likely introduces a characteristic ionization structure of the nebula, which leads to the emission of highly ionized elements such as O2+ and C3+. We, therefore, expect that the presence of stripped stars affects the location in the BPT diagram and the diagnostic ratio of O III to O II nebular emission lines. Our models are publicly available through CDS database and on the STARBURST99 website.}, author = {Götberg, Ylva Louise Linsdotter and de Mink, S. E. and Groh, J. H. and Leitherer, C. and Norman, C.}, issn = {1432-0746}, journal = {Astronomy & Astrophysics}, keywords = {Space and Planetary Science, Astronomy and Astrophysics}, publisher = {EDP Sciences}, title = {{The impact of stars stripped in binaries on the integrated spectra of stellar populations}}, doi = {10.1051/0004-6361/201834525}, volume = {629}, year = {2019}, } @article{13470, abstract = {Context. Massive Wolf–Rayet (WR) stars dominate the radiative and mechanical energy budget of galaxies and probe a critical phase in the evolution of massive stars prior to core collapse. It is not known whether core He-burning WR stars (classical WR; cWR) form predominantly through wind stripping (w-WR) or binary stripping (b-WR). Whereas spectroscopy of WR binaries has so-far largely been avoided because of its complexity, our study focuses on the 44 WR binaries and binary candidates of the Large Magellanic Cloud (LMC; metallicity Z ≈ 0.5 Z⊙), which were identified on the basis of radial velocity variations, composite spectra, or high X-ray luminosities. Aims. Relying on a diverse spectroscopic database, we aim to derive the physical and orbital parameters of our targets, confronting evolution models of evolved massive stars at subsolar metallicity and constraining the impact of binary interaction in forming these stars. Methods. Spectroscopy was performed using the Potsdam Wolf–Rayet (PoWR) code and cross-correlation techniques. Disentanglement was performed using the code Spectangular or the shift-and-add algorithm. Evolutionary status was interpreted using the Binary Population and Spectral Synthesis (BPASS) code, exploring binary interaction and chemically homogeneous evolution. Results. Among our sample, 28/44 objects show composite spectra and are analyzed as such. An additional five targets show periodically moving WR primaries but no detected companions (SB1); two (BAT99 99 and 112) are potential WR + compact-object candidates owing to their high X-ray luminosities. We cannot confirm the binary nature of the remaining 11 candidates. About two-thirds of the WN components in binaries are identified as cWR, and one-third as hydrogen-burning WR stars. We establish metallicity-dependent mass-loss recipes, which broadly agree with those recently derived for single WN stars, and in which so-called WN3/O3 stars are clear outliers. We estimate that 45  ±  30% of the cWR stars in our sample have interacted with a companion via mass transfer. However, only ≈12  ±  7% of the cWR stars in our sample naively appear to have formed purely owing to stripping via a companion (12% b-WR). Assuming that apparently single WR stars truly formed as single stars, this comprises ≈4% of the whole LMC WN population, which is about ten times less than expected. No obvious differences in the properties of single and binary WN stars, whose luminosities extend down to log L ≈ 5.2 [L⊙], are apparent. With the exception of a few systems (BAT99 19, 49, and 103), the equatorial rotational velocities of the OB-type companions are moderate (veq ≲ 250 km s−1) and challenge standard formalisms of angular-momentum accretion. For most objects, chemically homogeneous evolution can be rejected for the secondary, but not for the WR progenitor. Conclusions. No obvious dichotomy in the locations of apparently single and binary WN stars on the Hertzsprung-Russell diagram is apparent. According to commonly used stellar evolution models (BPASS, Geneva), most apparently single WN stars could not have formed as single stars, implying that they were stripped by an undetected companion. Otherwise, it must follow that pre-WR mass-loss/mixing (e.g., during the red supergiant phase) are strongly underestimated in standard stellar evolution models.}, author = {Shenar, T. and Sablowski, D. P. and Hainich, R. and Todt, H. and Moffat, A. F. J. and Oskinova, L. M. and Ramachandran, V. and Sana, H. and Sander, A. A. C. and Schnurr, O. and St-Louis, N. and Vanbeveren, D. and Götberg, Ylva Louise Linsdotter and Hamann, W.-R.}, issn = {1432-0746}, journal = {Astronomy & Astrophysics}, keywords = {Space and Planetary Science, Astronomy and Astrophysics}, publisher = {EDP Sciences}, title = {{The Wolf–Rayet binaries of the nitrogen sequence in the Large Magellanic Cloud}}, doi = {10.1051/0004-6361/201935684}, volume = {627}, year = {2019}, } @article{13471, abstract = {We perform an extensive numerical study of the evolution of massive binary systems to predict the peculiar velocities that stars obtain when their companion collapses and disrupts the system. Our aim is to (i) identify which predictions are robust against model uncertainties and assess their implications, (ii) investigate which physical processes leave a clear imprint and may therefore be constrained observationally, and (iii) provide a suite of publicly available model predictions to allow for the use of kinematic constraints from the Gaia mission. We find that 22+26−8% of all massive binary systems merge prior to the first core-collapse in the system. Of the remainder, 86+11−9% become unbound because of the core-collapse. Remarkably, this rarely produces runaway stars (observationally defined as stars with velocities above 30 km s−1). These are outnumbered by more than an order of magnitude by slower unbound companions, or “walkaway stars”. This is a robust outcome of our simulations and is due to the reversal of the mass ratio prior to the explosion and widening of the orbit, as we show analytically and numerically. For stars more massive than 15 M⊙, we estimate that 10+5−8% are walkaways and only 0.5+1.0−0.4% are runaways, nearly all of which have accreted mass from their companion. Our findings are consistent with earlier studies; however, the low runaway fraction we find is in tension with observed fractions of about 10%. Thus, astrometric data on presently single massive stars can potentially constrain the physics of massive binary evolution. Finally, we show that the high end of the mass distributions of runaway stars is very sensitive to the assumed black hole natal kicks, and we propose this as a potentially stringent test for the explosion mechanism. We also discuss companions remaining bound that can evolve into X-ray and gravitational wave sources.}, author = {Renzo, M. and Zapartas, E. and de Mink, S. E. and Götberg, Ylva Louise Linsdotter and Justham, S. and Farmer, R. J. and Izzard, R. G. and Toonen, S. and Sana, H.}, issn = {1432-0746}, journal = {Astronomy & Astrophysics}, keywords = {Space and Planetary Science, Astronomy and Astrophysics}, publisher = {EDP Sciences}, title = {{Massive runaway and walkaway stars}}, doi = {10.1051/0004-6361/201833297}, volume = {624}, year = {2019}, } @article{13472, abstract = {Massive stars in binaries can give rise to extreme phenomena such as X-ray binaries and gravitational wave sources after one or both stars end their lives as core-collapse supernovae. Stars in close orbit around a stellar or compact companion are expected to explode as “stripped-envelope supernovae”, showing no (Type Ib/c) or little (Type IIb) signs of hydrogen in the spectra, because hydrogen-rich progenitors are too large to fit. The physical processes responsible for the stripping process and the fate of the companion are still very poorly understood. Aiming to find new clues, we investigate Cas A, which is a very young (∼340 yr) and near (∼3.4 kpc) remnant of a core-collapse supernova. Cas A has been subject to several searches for possible companions, all unsuccessfully. We present new measurements of the proper motions and photometry of stars in the vicinity based on deep HST ACS/WFC and WFC3-IR data. We identify stellar sources that are close enough in projection but using their proper motions we show that none are compatible with being at the location of center at the time of explosion, in agreement with earlier findings. Our photometric measurements allow us to place much deeper (order-of-magnitude) upper limits on the brightness of possible undetected companions. We systematically compare them with model predictions for a wide variety of scenarios. We can confidently rule out the presence of any stellar companion of any reasonable mass and age (main sequence, pre main sequence or stripped) ruling out what many considered to be likely evolutionary scenarios for Type IIb supernova (SN IIb). More exotic scenarios that predict the presence of a compact companion (white dwarf, neutron star or black hole) are still possible as well as scenarios where the progenitor of Cas A was single at the moment of explosion (either because it was truly single, or resulted from a binary that was disrupted, or from a binary merger). The presence of a compact companion would imply that Cas A is of interest to study exotic outcomes of binary evolution. The single-at-death solution would still require fine-tuning of the process that removed most of the envelope through a mass-loss mechanism yet to be identified. We discuss how future constraints from Gaia and even deeper photometric studies may help to place further constraints.}, author = {Kerzendorf, Wolfgang E. and Do, Tuan and de Mink, Selma E. and Götberg, Ylva Louise Linsdotter and Milisavljevic, Dan and Zapartas, Emmanouil and Renzo, Mathieu and Justham, Stephen and Podsiadlowski, Philipp and Fesen, Robert A.}, issn = {1432-0746}, journal = {Astronomy & Astrophysics}, keywords = {Space and Planetary Science, Astronomy and Astrophysics}, publisher = {EDP Sciences}, title = {{No surviving non-compact stellar companion to Cassiopeia A}}, doi = {10.1051/0004-6361/201732206}, volume = {623}, year = {2019}, } @article{138, abstract = {Autoregulation is the direct modulation of gene expression by the product of the corresponding gene. Autoregulation of bacterial gene expression has been mostly studied at the transcriptional level, when a protein acts as the cognate transcriptional repressor. A recent study investigating dynamics of the bacterial toxin–antitoxin MazEF system has shown how autoregulation at both the transcriptional and post-transcriptional levels affects the heterogeneity of Escherichia coli populations. Toxin–antitoxin systems hold a crucial but still elusive part in bacterial response to stress. This perspective highlights how these modules can also serve as a great model system for investigating basic concepts in gene regulation. However, as the genomic background and environmental conditions substantially influence toxin activation, it is important to study (auto)regulation of toxin–antitoxin systems in well-defined setups as well as in conditions that resemble the environmental niche.}, author = {Nikolic, Nela}, journal = {Current Genetics}, number = {1}, pages = {133--138}, publisher = {Springer}, title = {{Autoregulation of bacterial gene expression: lessons from the MazEF toxin–antitoxin system}}, doi = {10.1007/s00294-018-0879-8}, volume = {65}, year = {2019}, } @article{14001, abstract = {Chiral molecules interact and react differently with other chiral objects, depending on their handedness. Therefore, it is essential to understand and ultimately control the evolution of molecular chirality during chemical reactions. Although highly sophisticated techniques for the controlled synthesis of chiral molecules have been developed, the observation of chirality on the natural femtosecond time scale of a chemical reaction has so far remained out of reach in the gas phase. Here, we demonstrate a general experimental technique, based on high-harmonic generation in tailored laser fields, and apply it to probe the time evolution of molecular chirality during the photodissociation of 2-iodobutane. These measurements show a change in sign and a pronounced increase in the magnitude of the chiral response over the first 100 fs, followed by its decay within less than 500 fs, revealing the photodissociation to achiral products. The observed time evolution is explained in terms of the variation of the electric and magnetic transition-dipole moments between the lowest electronic states of the cation as a function of the reaction coordinate. These results open the path to investigations of the chirality of molecular-reaction pathways, light-induced chirality in chemical processes, and the control of molecular chirality through tailored laser pulses.}, author = {Baykusheva, Denitsa Rangelova and Zindel, Daniel and Svoboda, Vít and Bommeli, Elias and Ochsner, Manuel and Tehlar, Andres and Wörner, Hans Jakob}, issn = {1091-6490}, journal = {Proceedings of the National Academy of Sciences}, keywords = {Multidisciplinary}, number = {48}, pages = {23923--23929}, publisher = {Proceedings of the National Academy of Sciences}, title = {{Real-time probing of chirality during a chemical reaction}}, doi = {10.1073/pnas.1907189116}, volume = {116}, year = {2019}, }