Robust diffraction-limited near-infrared-to-near-ultraviolet wide-field imaging from stratospheric balloon-borne platforms-Super-pressure Balloon-borne Imaging Telescope performance

At a fraction of the total cost of an equivalent orbital mission, scientific balloon-borne platforms, operating above 99.7% of the Earth's atmosphere, offer attractive, competitive, and effective observational capabilities-namely, space-like seeing, transmission, and backgrounds-which are well suited for modern astronomy and cosmology. The Super-pressure Balloon-borne Imaging Telescope (SUPERBIT) is a diffraction-limited, wide-field, 0.5 m telescope capable of exploiting these observing conditions in order to provide exquisite imaging throughout the near-infrared to near-ultraviolet. It utilizes a robust active stabilization system that has consistently demonstrated a 48 mas 1σ sky-fixed pointing stability over multiple 1 h observations at float. This is achieved by actively tracking compound pendulations via a three-axis gimballed platform, which provides sky-fixed telescope stability at < 500 mas and corrects for field rotation, while employing high-bandwidth tip/tilt optics to remove residual disturbances across the science imaging focal plane. SUPERBIT's performance during the 2019 commissioning flight benefited from a customized high-fidelity science-capable telescope designed with an exceptional thermo- and opto-mechanical stability as well as a tightly constrained static and dynamic coupling between high-rate sensors and telescope optics. At the currently demonstrated level of flight performance, SUPERBIT capabilities now surpass the science requirements for a wide variety of experiments in cosmology, astrophysics, and stellar dynamics.

Nuclear microtubule filaments mediate non-linear directional motion of chromatin and promote DNA repair

Damaged DNA shows increased mobility, which can promote interactions with repair-conducive nuclear pore complexes (NPCs). This apparently random mobility is paradoxically abrogated upon disruption of microtubules or kinesins, factors that typically cooperate to mediate the directional movement of macromolecules. Here, we resolve this paradox by uncovering DNA damage-inducible intranuclear microtubule filaments (DIMs) that mobilize damaged DNA and promote repair. Upon DNA damage, relief of centromeric constraint induces DIMs that cooperate with the Rad9 DNA damage response mediator and Kar3 kinesin motor to capture DNA lesions, which then linearly move along dynamic DIMs. Decreasing and hyper-inducing DIMs respectively abrogates and hyper-activates repair. Accounting for DIM dynamics across cell populations by measuring directional changes of damaged DNA reveals that it exhibits increased non-linear directional behavior in nuclear space. Abrogation of DIM-dependent processes or repair-promoting factors decreases directional behavior. Thus, inducible and dynamic nuclear microtubule filaments directionally mobilize damaged DNA and promote repair.

Following DNA damage, different processes come to action to aid repair. The authors here find that microtubule filaments within the cell nucleus capture and non-randomly mobilize damaged chromatin to mediate DNA repair.

Modal Properties and Control System Design for Two-Link Flexible Manipulators

The vibration modes of a generic two-link fiexible manipulator are studied as a function of the link, rotor, and tip (statorlpayload) mass distribution. Necessary and sufficient conditions are devel oped for all vibration modes to exhibit a node at the manipulator endpoint. A rigorous treatment of the relevant kinematics and dy namics shows that this property can be closely achieved for large tip/link mass ratio and sufficiently small rotor inertia. The major impacts of this result on feedforward/feedback controller design are uncovered. First, the nonlinear joint torque to end-effector motion dynamics become essentially equivalent to those of the rigid case. Second, an output involving the endpoint rates and elastic motions is shown to possess the passivity property for suitably defined inputs. This permits the design of simple controllers that furnish endpoint stabilization with simultaneous vibration suppression. A numeri cal example is used to illustrate the results and demonstrate the achievable performance using the controller design concepts.