@article{14008, abstract = {Time-resolved x-ray absorption spectroscopy (TR-XAS) has so far practically been limited to large-scale facilities, to subpicosecond temporal resolution, and to the condensed phase. We report the realization of TR-XAS with a temporal resolution in the low femtosecond range by developing a tabletop high-harmonic source reaching up to 350 electron volts, thus partially covering the spectral region of 280 to 530 electron volts, where water is transmissive. We used this source to follow previously unexamined light-induced chemical reactions in the lowest electronic states of isolated CF4+ and SF6+ molecules in the gas phase. By probing element-specific core-to-valence transitions at the carbon K-edge or the sulfur L-edges, we characterized their reaction paths and observed the effect of symmetry breaking through the splitting of absorption bands and Rydberg-valence mixing induced by the geometry changes.}, author = {Pertot, Yoann and Schmidt, Cédric and Matthews, Mary and Chauvet, Adrien and Huppert, Martin and Svoboda, Vit and von Conta, Aaron and Tehlar, Andres and Baykusheva, Denitsa Rangelova and Wolf, Jean-Pierre and Wörner, Hans Jakob}, issn = {1095-9203}, journal = {Science}, keywords = {Multidisciplinary}, number = {6322}, pages = {264--267}, publisher = {American Association for the Advancement of Science}, title = {{Time-resolved x-ray absorption spectroscopy with a water window high-harmonic source}}, doi = {10.1126/science.aah6114}, volume = {355}, year = {2017}, } @article{14009, abstract = {Attosecond delays between photoelectron wave packets emitted from different electronic shells are now well established. Is there any delay between electrons originating from the same electronic shell but leaving the cation in different fine-structure states? This question is relevant for all attosecond photoemission studies involving heavy elements, be it atoms, molecules or solids. We answer this fundamental question by measuring energy-dependent delays between photoelectron wave packets associated with the 2P3/2 and 2P1/2 components of the electronic groundstates of Xe+ and Kr+. We observe delays reaching up to 33±6 as in the case of Xe. Our results are compared with two state-of-the-art theories. Whereas both theories quantitatively agree with the results obtained for Kr, neither of them fully reproduces the experimental results in Xe. Performing delay measurements very close to the ionization thresholds, we compare the agreement of several analytical formulas for the continuum-continuum delays with experimental data. Our results show an important influence of spin-orbit coupling on attosecond photoionization delays, highlight the requirement for additional theory development, and offer a precision benchmark for such work.}, author = {Jordan, I. and Huppert, M. and Pabst, S. and Kheifets, A. S. and Baykusheva, Denitsa Rangelova and Wörner, H. J.}, issn = {2469-9934}, journal = {Physical Review A}, number = {1}, publisher = {American Physical Society}, title = {{Spin-orbit delays in photoemission}}, doi = {10.1103/physreva.95.013404}, volume = {95}, year = {2017}, } @article{14031, abstract = {High-harmonic spectroscopy driven by circularly polarized laser pulses and their counterrotating second harmonic is a new branch of attosecond science which currently lacks quantitative interpretations. We extend this technique to the midinfrared regime and record detailed high-harmonic spectra of several rare-gas atoms. These results are compared with the solution of the Schrödinger equation in three dimensions and calculations based on the strong-field approximation that incorporate accurate scattering-wave recombination matrix elements. A quantum-orbit analysis of these results provides a transparent interpretation of the measured intensity ratios of symmetry-allowed neighboring harmonics in terms of (i) a set of propensity rules related to the angular momentum of the atomic orbitals, (ii) atom-specific matrix elements related to their electronic structure, and (iii) the interference of the emissions associated with electrons in orbitals corotating or counterrotating with the laser fields. These results provide the foundation for a quantitative understanding of bicircular high-harmonic spectroscopy.}, author = {Baykusheva, Denitsa Rangelova and Brennecke, Simon and Lein, Manfred and Wörner, Hans Jakob}, issn = {1079-7114}, journal = {Physical Review Letters}, keywords = {General Physics and Astronomy}, number = {20}, publisher = {American Physical Society}, title = {{Signatures of electronic structure in bicircular high-harmonic spectroscopy}}, doi = {10.1103/physrevlett.119.203201}, volume = {119}, year = {2017}, } @article{1407, abstract = {We consider the problem of computing the set of initial states of a dynamical system such that there exists a control strategy to ensure that the trajectories satisfy a temporal logic specification with probability 1 (almost-surely). We focus on discrete-time, stochastic linear dynamics and specifications given as formulas of the Generalized Reactivity(1) fragment of Linear Temporal Logic over linear predicates in the states of the system. We propose a solution based on iterative abstraction-refinement, and turn-based 2-player probabilistic games. While the theoretical guarantee of our algorithm after any finite number of iterations is only a partial solution, we show that if our algorithm terminates, then the result is the set of all satisfying initial states. Moreover, for any (partial) solution our algorithm synthesizes witness control strategies to ensure almost-sure satisfaction of the temporal logic specification. While the proposed algorithm guarantees progress and soundness in every iteration, it is computationally demanding. We offer an alternative, more efficient solution for the reachability properties that decomposes the problem into a series of smaller problems of the same type. All algorithms are demonstrated on an illustrative case study.}, author = {Svoreňová, Mária and Kretinsky, Jan and Chmelik, Martin and Chatterjee, Krishnendu and Cěrná, Ivana and Belta, Cǎlin}, journal = {Nonlinear Analysis: Hybrid Systems}, number = {2}, pages = {230 -- 253}, publisher = {Elsevier}, title = {{Temporal logic control for stochastic linear systems using abstraction refinement of probabilistic games}}, doi = {10.1016/j.nahs.2016.04.006}, volume = {23}, year = {2017}, } @inproceedings{14205, abstract = {Two of the most fundamental prototypes of greedy optimization are the matching pursuit and Frank-Wolfe algorithms. In this paper, we take a unified view on both classes of methods, leading to the first explicit convergence rates of matching pursuit methods in an optimization sense, for general sets of atoms. We derive sublinear (1/t) convergence for both classes on general smooth objectives, and linear convergence on strongly convex objectives, as well as a clear correspondence of algorithm variants. Our presented algorithms and rates are affine invariant, and do not need any incoherence or sparsity assumptions.}, author = {Locatello, Francesco and Khanna, Rajiv and Tschannen, Michael and Jaggi, Martin}, booktitle = {Proceedings of the 20th International Conference on Artificial Intelligence and Statistics}, location = {Fort Lauderdale, FL, United States}, pages = {860--868}, publisher = {ML Research Press}, title = {{A unified optimization view on generalized matching pursuit and Frank-Wolfe}}, volume = {54}, year = {2017}, } @inproceedings{14206, abstract = {Greedy optimization methods such as Matching Pursuit (MP) and Frank-Wolfe (FW) algorithms regained popularity in recent years due to their simplicity, effectiveness and theoretical guarantees. MP and FW address optimization over the linear span and the convex hull of a set of atoms, respectively. In this paper, we consider the intermediate case of optimization over the convex cone, parametrized as the conic hull of a generic atom set, leading to the first principled definitions of non-negative MP algorithms for which we give explicit convergence rates and demonstrate excellent empirical performance. In particular, we derive sublinear (O(1/t)) convergence on general smooth and convex objectives, and linear convergence (O(e−t)) on strongly convex objectives, in both cases for general sets of atoms. Furthermore, we establish a clear correspondence of our algorithms to known algorithms from the MP and FW literature. Our novel algorithms and analyses target general atom sets and general objective functions, and hence are directly applicable to a large variety of learning settings.}, author = {Locatello, Francesco and Tschannen, Michael and Rätsch, Gunnar and Jaggi, Martin}, booktitle = {Advances in Neural Information Processing Systems}, isbn = {9781510860964}, location = {Long Beach, CA, United States}, title = {{Greedy algorithms for cone constrained optimization with convergence guarantees}}, year = {2017}, } @article{14286, abstract = {The bacteriophage M13 has found frequent applications in nanobiotechnology due to its chemically and genetically tunable protein surface and its ability to self-assemble into colloidal membranes. Additionally, its single-stranded (ss) genome is commonly used as scaffold for DNA origami. Despite the manifold uses of M13, upstream production methods for phage and scaffold ssDNA are underexamined with respect to future industrial usage. Here, the high-cell-density phage production with Escherichia coli as host organism was studied in respect of medium composition, infection time, multiplicity of infection, and specific growth rate. The specific growth rate and the multiplicity of infection were identified as the crucial state variables that influence phage amplification rate on one hand and the concentration of produced ssDNA on the other hand. Using a growth rate of 0.15 h−1 and a multiplicity of infection of 0.05 pfu cfu−1 in the fed-batch production process, the concentration of pure isolated M13 ssDNA usable for scaffolded DNA origami could be enhanced by 54% to 590 mg L−1. Thus, our results help enabling M13 production for industrial uses in nanobiotechnology. Biotechnol. Bioeng. 2017;114: 777–784.}, author = {Kick, Benjamin and Hensler, Samantha and Praetorius, Florian M and Dietz, Hendrik and Weuster-Botz, Dirk}, issn = {0006-3592}, journal = {Biotechnology and Bioengineering}, keywords = {Applied Microbiology and Biotechnology, Bioengineering, Biotechnology}, number = {4}, pages = {777--784}, publisher = {Wiley}, title = {{Specific growth rate and multiplicity of infection affect high-cell-density fermentation with bacteriophage M13 for ssDNA production}}, doi = {10.1002/bit.26200}, volume = {114}, year = {2017}, } @article{14287, abstract = {We describe an approach to bottom-up fabrication that allows integration of the functional diversity of proteins into designed three-dimensional structural frameworks. A set of custom staple proteins based on transcription activator–like effector proteins folds a double-stranded DNA template into a user-defined shape. Each staple protein is designed to recognize and closely link two distinct double-helical DNA sequences at separate positions on the template. We present design rules for constructing megadalton-scale DNA-protein hybrid shapes; introduce various structural motifs, such as custom curvature, corners, and vertices; and describe principles for creating multilayer DNA-protein objects with enhanced rigidity. We demonstrate self-assembly of our hybrid nanostructures in one-pot mixtures that include the genetic information for the designed proteins, the template DNA, RNA polymerase, ribosomes, and cofactors for transcription and translation.}, author = {Praetorius, Florian M and Dietz, Hendrik}, issn = {1095-9203}, journal = {Science}, number = {6331}, publisher = {American Association for the Advancement of Science}, title = {{Self-assembly of genetically encoded DNA-protein hybrid nanoscale shapes}}, doi = {10.1126/science.aam5488}, volume = {355}, year = {2017}, } @article{14290, abstract = {DNA nanotechnology, in particular DNA origami, enables the bottom-up self-assembly of micrometre-scale, three-dimensional structures with nanometre-precise features1,2,3,4,5,6,7,8,9,10,11,12. These structures are customizable in that they can be site-specifically functionalized13 or constructed to exhibit machine-like14,15 or logic-gating behaviour16. Their use has been limited to applications that require only small amounts of material (of the order of micrograms), owing to the limitations of current production methods. But many proposed applications, for example as therapeutic agents or in complex materials3,16,17,18,19,20,21,22, could be realized if more material could be used. In DNA origami, a nanostructure is assembled from a very long single-stranded scaffold molecule held in place by many short single-stranded staple oligonucleotides. Only the bacteriophage-derived scaffold molecules are amenable to scalable and efficient mass production23; the shorter staple strands are obtained through costly solid-phase synthesis24 or enzymatic processes25. Here we show that single strands of DNA of virtually arbitrary length and with virtually arbitrary sequences can be produced in a scalable and cost-efficient manner by using bacteriophages to generate single-stranded precursor DNA that contains target strand sequences interleaved with self-excising ‘cassettes’, with each cassette comprising two Zn2+-dependent DNA-cleaving DNA enzymes. We produce all of the necessary single strands of DNA for several DNA origami using shaker-flask cultures, and demonstrate end-to-end production of macroscopic amounts of a DNA origami nanorod in a litre-scale stirred-tank bioreactor. Our method is compatible with existing DNA origami design frameworks and retains the modularity and addressability of DNA origami objects that are necessary for implementing custom modifications using functional groups. With all of the production and purification steps amenable to scaling, we expect that our method will expand the scope of DNA nanotechnology in many areas of science and technology.}, author = {Praetorius, Florian M and Kick, Benjamin and Behler, Karl L. and Honemann, Maximilian N. and Weuster-Botz, Dirk and Dietz, Hendrik}, issn = {1476-4687}, journal = {Nature}, number = {7683}, pages = {84--87}, publisher = {Springer Nature}, title = {{Biotechnological mass production of DNA origami}}, doi = {10.1038/nature24650}, volume = {552}, year = {2017}, } @article{14308, abstract = {Here we describe an approach to bottom-up fabrication with nanometer-precision that allows integrating the functional diversity of proteins in designed three-dimensional structural frameworks. We reimagined the successful DNA origami design principle using a set of custom staple proteins to fold a double-stranded DNA template into a user-defined shape. Each staple protein recognizes two distinct double-helical DNA sequences and can carry additional functionalities. The staple proteins we present here are based on the transcription activator-like (TAL) effector proteins. Due to their repetitive structure these proteins offer a unique programmability that enables us to construct numerous staple proteins targeting any desired DNA sequence. Our approach is general, meaning that many different objects may be created using the same set of rules, and it is modular, because components can be modified or exchanged individually. We present rules for constructing megadalton-scale DNA-protein hybrid nanostructures; introduce important structural motifs, such as curvature, corners, and vertices; describe principles for creating multi-layer DNA-protein objects with enhanced rigidity; and demonstrate the possibility to combine our DNA-protein hybrid origami with conventional DNA nanotechnology. Since all components can be encoded genetically, our structures should be amenable to biotechnological mass-production. Moreover, since the target objects can self-assemble at room temperature in near-physiological buffer, our hybrid origami may also provide an attractive method to realize positioning and scaffolding tasks in vivo. We expect our method to find application both in scaffolding protein functionalities and in manipulating the spatial arrangement of genomic DNA.}, author = {Praetorius, Florian M and Dietz, Hendrik}, issn = {0006-3495}, journal = {Biophysical Journal}, keywords = {Biophysics}, number = {3}, publisher = {Elsevier}, title = {{Genetically encoded DNA-protein hybrid origami}}, doi = {10.1016/j.bpj.2016.11.171}, volume = {112}, year = {2017}, } @article{14309, abstract = {Establishing precise control over the shape and the interactions of the microscopic building blocks is essential for design of macroscopic soft materials with novel structural, optical and mechanical properties. Here, we demonstrate robust assembly of DNA origami filaments into cholesteric liquid crystals, one-dimensional supramolecular twisted ribbons and two-dimensional colloidal membranes. The exquisite control afforded by the DNA origami technology establishes a quantitative relationship between the microscopic filament structure and the macroscopic cholesteric pitch. Furthermore, it also enables robust assembly of one-dimensional twisted ribbons, which behave as effective supramolecular polymers whose structure and elastic properties can be precisely tuned by controlling the geometry of the elemental building blocks. Our results demonstrate the potential synergy between DNA origami technology and colloidal science, in which the former allows for rapid and robust synthesis of complex particles, and the latter can be used to assemble such particles into bulk materials.}, author = {Siavashpouri, M and Wachauf, CH and Zakhary, MJ and Praetorius, Florian M and Dietz, H and Dogic, Z}, issn = {1476-4660}, journal = {Nature Materials}, number = {8}, pages = {849--856}, publisher = {Springer Nature}, title = {{Molecular engineering of chiral colloidal liquid crystals using DNA origami}}, doi = {10.1038/nmat4909}, volume = {16}, year = {2017}, } @inproceedings{14310, author = {Siavashpouri, Mahsa and Wachauf, Christian and Zakhary, Mark and Praetorius, Florian M and Dietz, Hendrik and Dogic, Zvonimir}, booktitle = {APS March Meeting 2017}, publisher = {APS}, title = {{Molecular engineering of colloidal liquid crystals using DNA origami}}, year = {2017}, } @article{1433, abstract = {Phat is an open-source C. ++ library for the computation of persistent homology by matrix reduction, targeted towards developers of software for topological data analysis. We aim for a simple generic design that decouples algorithms from data structures without sacrificing efficiency or user-friendliness. We provide numerous different reduction strategies as well as data types to store and manipulate the boundary matrix. We compare the different combinations through extensive experimental evaluation and identify optimization techniques that work well in practical situations. We also compare our software with various other publicly available libraries for persistent homology.}, author = {Bauer, Ulrich and Kerber, Michael and Reininghaus, Jan and Wagner, Hubert}, issn = { 0747-7171}, journal = {Journal of Symbolic Computation}, pages = {76 -- 90}, publisher = {Academic Press}, title = {{Phat - Persistent homology algorithms toolbox}}, doi = {10.1016/j.jsc.2016.03.008}, volume = {78}, year = {2017}, } @article{15154, abstract = {Biofilm formation is critical for the infection cycle of Vibrio cholerae. Vibrio exopolysaccharides (VPS) and the matrix proteins RbmA, Bap1 and RbmC are required for the development of biofilm architecture. We demonstrate that RbmA binds VPS directly and uses a binary structural switch within its first fibronectin type III (FnIII-1) domain to control RbmA structural dynamics and the formation of VPS-dependent higher-order structures. The structural switch in FnIII-1 regulates interactions in trans with the FnIII-2 domain, leading to open (monomeric) or closed (dimeric) interfaces. The ability of RbmA to switch between open and closed states is important for V. cholerae biofilm formation, as RbmA variants with switches that are locked in either of the two states lead to biofilms with altered architecture and structural integrity.}, author = {Fong, Jiunn CN and Rogers, Andrew and Michael, Alicia Kathleen and Parsley, Nicole C and Cornell, William-Cole and Lin, Yu-Cheng and Singh, Praveen K and Hartmann, Raimo and Drescher, Knut and Vinogradov, Evgeny and Dietrich, Lars EP and Partch, Carrie L and Yildiz, Fitnat H}, issn = {2050-084X}, journal = {eLife}, keywords = {General Immunology and Microbiology, General Biochemistry, Genetics and Molecular Biology, General Medicine, General Neuroscience}, publisher = {eLife Sciences Publications}, title = {{Structural dynamics of RbmA governs plasticity of Vibrio cholerae biofilms}}, doi = {10.7554/elife.26163}, volume = {6}, year = {2017}, } @article{15155, abstract = {The C-terminal transactivation domain (TAD) of BMAL1 (brain and muscle ARNT-like 1) is a regulatory hub for transcriptional coactivators and repressors that compete for binding and, consequently, contributes to period determination of the mammalian circadian clock. Here, we report the discovery of two distinct conformational states that slowly exchange within the dynamic TAD to control timing. This binary switch results from cis/trans isomerization about a highly conserved Trp-Pro imide bond in a region of the TAD that is required for normal circadian timekeeping. Both cis and trans isomers interact with transcriptional regulators, suggesting that isomerization could serve a role in assembling regulatory complexes in vivo. Toward this end, we show that locking the switch into the trans isomer leads to shortened circadian periods. Furthermore, isomerization is regulated by the cyclophilin family of peptidyl-prolyl isomerases, highlighting the potential for regulation of BMAL1 protein dynamics in period determination.}, author = {Gustafson, Chelsea L. and Parsley, Nicole C. and Asimgil, Hande and Lee, Hsiau-Wei and Ahlbach, Christopher and Michael, Alicia Kathleen and Xu, Haiyan and Williams, Owen L. and Davis, Tara L. and Liu, Andrew C. and Partch, Carrie L.}, issn = {1097-2765}, journal = {Molecular Cell}, keywords = {Cell Biology, Molecular Biology}, number = {4}, pages = {447--457.e7}, publisher = {Elsevier}, title = {{A slow conformational switch in the BMAL1 transactivation domain modulates circadian rhythms}}, doi = {10.1016/j.molcel.2017.04.011}, volume = {66}, year = {2017}, } @article{15156, abstract = {Circadian clocks are ubiquitous timing systems that induce rhythms of biological activities in synchrony with night and day. In cyanobacteria, timing is generated by a posttranslational clock consisting of KaiA, KaiB, and KaiC proteins and a set of output signaling proteins, SasA and CikA, which transduce this rhythm to control gene expression. Here, we describe crystal and nuclear magnetic resonance structures of KaiB-KaiC,KaiA-KaiB-KaiC, and CikA-KaiB complexes. They reveal how the metamorphic properties of KaiB, a protein that adopts two distinct folds, and the post–adenosine triphosphate hydrolysis state of KaiC create a hub around which nighttime signaling events revolve, including inactivation of KaiA and reciprocal regulation of the mutually antagonistic signaling proteins, SasA and CikA.}, author = {Tseng, Roger and Goularte, Nicolette F. and Chavan, Archana and Luu, Jansen and Cohen, Susan E. and Chang, Yong-Gang and Heisler, Joel and Li, Sheng and Michael, Alicia Kathleen and Tripathi, Sarvind and Golden, Susan S. and LiWang, Andy and Partch, Carrie L.}, issn = {1095-9203}, journal = {Science}, keywords = {Multidisciplinary}, number = {6330}, pages = {1174--1180}, publisher = {American Association for the Advancement of Science}, title = {{Structural basis of the day-night transition in a bacterial circadian clock}}, doi = {10.1126/science.aag2516}, volume = {355}, year = {2017}, } @article{15157, abstract = {The basic helix–loop–helix PAS domain (bHLH-PAS) transcription factor CLOCK:BMAL1 (brain and muscle Arnt-like protein 1) sits at the core of the mammalian circadian transcription/translation feedback loop. Precise control of CLOCK:BMAL1 activity by coactivators and repressors establishes the ∼24-h periodicity of gene expression. Formation of a repressive complex, defined by the core clock proteins cryptochrome 1 (CRY1):CLOCK:BMAL1, plays an important role controlling the switch from repression to activation each day. Here we show that CRY1 binds directly to the PAS domain core of CLOCK:BMAL1, driven primarily by interaction with the CLOCK PAS-B domain. Integrative modeling and solution X-ray scattering studies unambiguously position a key loop of the CLOCK PAS-B domain in the secondary pocket of CRY1, analogous to the antenna chromophore-binding pocket of photolyase. CRY1 docks onto the transcription factor alongside the PAS domains, extending above the DNA-binding bHLH domain. Single point mutations at the interface on either CRY1 or CLOCK disrupt formation of the ternary complex, highlighting the importance of this interface for direct regulation of CLOCK:BMAL1 activity by CRY1.}, author = {Michael, Alicia Kathleen and Fribourgh, Jennifer L. and Chelliah, Yogarany and Sandate, Colby R. and Hura, Greg L. and Schneidman-Duhovny, Dina and Tripathi, Sarvind M. and Takahashi, Joseph S. and Partch, Carrie L.}, issn = {1091-6490}, journal = {Proceedings of the National Academy of Sciences}, keywords = {Multidisciplinary}, number = {7}, pages = {1560--1565}, publisher = {Proceedings of the National Academy of Sciences}, title = {{Formation of a repressive complex in the mammalian circadian clock is mediated by the secondary pocket of CRY1}}, doi = {10.1073/pnas.1615310114}, volume = {114}, year = {2017}, } @article{15158, abstract = {Cryptochromes are evolutionarily related to the light‐dependent DNA repair enzyme photolyase, serving as major regulators of circadian rhythms in insects and vertebrate animals. There are two types of cryptochromes in the animal kingdom: Drosophila‐like CRYs that act as nonvisual photopigments linking circadian rhythms to the environmental light/dark cycle, and vertebrate‐like CRYs that do not appear to sense light directly, but control the generation of circadian rhythms by acting as transcriptional repressors. Some animals have both types of CRYs, while others possess only one. Cryptochromes have two domains, the photolyase homology region (PHR) and an extended, intrinsically disordered C‐terminus. While all animal CRYs share a high degree of sequence and structural homology in their PHR domains, the C‐termini are divergent in both length and sequence identity. Recently, cryptochrome function has been shown to extend beyond its pivotal role in circadian clocks, participating in regulation of the DNA damage response, cancer progression and glucocorticoid signaling, as well as being implicated as possible magnetoreceptors. In this review, we provide a historical perspective on the discovery of animal cryptochromes, examine similarities and differences of the two types of animal cryptochromes and explore some of the divergent roles for this class of proteins.}, author = {Michael, Alicia Kathleen and Fribourgh, Jennifer L. and Van Gelder, Russell N. and Partch, Carrie L.}, issn = {1751-1097}, journal = {Photochemistry and Photobiology}, keywords = {Physical and Theoretical Chemistry, General Medicine, Biochemistry}, number = {1}, pages = {128--140}, publisher = {Wiley}, title = {{Animal cryptochromes: Divergent roles in light perception, circadian timekeeping and beyond}}, doi = {10.1111/php.12677}, volume = {93}, year = {2017}, } @article{15239, abstract = {Using images from the Hubble Space Telescope Advanced Camera for Surveys, we measure the rate of cooling of white dwarfs in the globular cluster 47 Tucanae and compare it to modelled cooling curves. We examine the effects of the outer convective envelope reaching the nearly isothermal degenerate core and the release of latent heat during core crystallization on the white dwarf cooling rates. For white dwarfs typical of 47 Tuc, the onset of these effects occur at similar times. The latent heat released during crystallization is a small heat source. In contrast, the heat reservoir of the degenerate core is substantially larger. When the convective envelope reaches the nearly isothermal interior of the white dwarf, the star becomes brighter than it would be in the absence of this effect. Our modelled cooling curves that include this convective coupling closely match the observed luminosity function of the white dwarfs in 47 Tuc.}, author = {Obertas, Alysa and Caiazzo, Ilaria and Heyl, Jeremy and Richer, Harvey and Kalirai, Jason and Tremblay, Pier-Emmanuel}, issn = {1365-2966}, journal = {Monthly Notices of the Royal Astronomical Society}, keywords = {Space and Planetary Science, Astronomy and Astrophysics}, number = {1}, pages = {677--682}, publisher = {Oxford University Press}, title = {{The onset of convective coupling and freezing in the white dwarfs of 47 Tucanae}}, doi = {10.1093/mnras/stx2759}, volume = {474}, year = {2017}, } @article{15240, abstract = {Multi-epoch observations with the Advanced Camera Survey and WFC3 on the Hubble Space Telescope provide a unique and comprehensive probe of stellar dynamics within 47 Tucanae. We confront analytic models of the globular cluster with the observed stellar proper motions that probe along the main sequence from just above 0.8–0.1M⊙ as well as white dwarfs younger than 1 Gyr. One field lies just beyond the half-light radius where dynamical models (e.g., lowered Maxwellian distributions) make robust predictions for the stellar proper motions. The observed proper motions in this outer field show evidence for anisotropy in the velocity distribution as well as skewness; the latter is evidence of rotation. The measured velocity dispersions and surface brightness distributions agree in detail with a rotating anisotropic model of the stellar distribution function with mild dependence of the proper-motion dispersion on mass. However, the best-fitting models underpredict the rotation and skewness of the stellar velocities. In the second field, centered on the core of the cluster, the mass segregation in proper motion is much stronger. Nevertheless the model developed in the outer field can be extended inward by taking this mass segregation into account in a heuristic fashion. The proper motions of the main-sequence stars yield a mass estimate of the cluster of at a distance of 4.7 kpc. By comparing the proper motions of a sample of giant and subgiant stars with the observed radial velocities we estimate the distance to the cluster kinematically to be 4.29 ± 0.47 kpc.}, author = {Heyl, J. and Caiazzo, Ilaria and Richer, H. and Anderson, J. and Kalirai, J. and Parada, J.}, issn = {1538-4357}, journal = {The Astrophysical Journal}, keywords = {Space and Planetary Science, Astronomy and Astrophysics}, number = {2}, publisher = {American Astronomical Society}, title = {{Deep HST imaging in 47 Tucanae: A global dynamical model}}, doi = {10.3847/1538-4357/aa974f}, volume = {850}, year = {2017}, }