Preliminary Jitter Stability Results for the Large UV/Optical/Infrared (LUVOIR) Surveyor Concept Using a Non-Contact Vibration Isolation and Precision Pointing System

The need for high payload dynamic stability and ultra-stable mechanical systems is an overarching technology need for large space telescopes such as the Large Ultraviolet / Optical / Infrared (LUVOIR) Surveyor concept. The LUVOIR concept includes a 15-meter-diameter segmented-aperture telescope with a suite of serviceable instruments operating over a range of wavelengths between 100nm to 2.5 um. Wavefront error (WFE) stability of less than 10 picometers RMS of uncorrected system WFE per wavefront control step represents a drastic performance improvement over current space-based telescopes being fielded. Through the utilization of an isolation architecture that involves no mechanical contact between the telescope and the host spacecraft structure, a system design is realized that maximizes the telescope dynamic stability performance without driving stringent technology requirements on spacecraft structure, sensors or actuators. Through analysis of the LUVOIR finite element model and linear optical model, the wavefront error and Line-Of-Sight (LOS) jitter performance is discussed in this paper when using the Vibration Isolation and Precision Pointing System (VIPPS) being developed cooperatively with Lockheed Martin in addition to a multi-loop control architecture. The multi-loop control architecture consists of the spacecraft Attitude Control System (ACS), VIPPS, and a Fast Steering Mirror on the instrument. While the baseline attitude control device for LUVOIR is a set of Control Moment Gyroscopes (CMGs), Reaction Wheel Assembly (RWA) disturbance contribution to wavefront error stability and LOS stability are presented to give preliminary results in this paper. CMG disturbance will be explored in further work to be completed

Global wealth disparities drive adherence to COVID-safe pathways in head and neck cancer surgery

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On phasing the small-angle x-ray diffraction pattern from nerve myelin.

Using a method they developed, Stamatoff and Krimm (1976) have phased swelling data from nerve myelin. Although most phases agree with those I determined previously, there are a few differences. In this letter the two different phasings, theirs and my own, are used to compute the corresponding electron-density profiles, which are then closely compared. For both phasings, small differences are seen in the membrane profile at different degrees of swelling. The explanation that these differences are due simply to errors in measuring intensity is shown to be quite improbable; thus the differences indicate a real change in the profile. It follows that the assumption of a constant membrane profile appears to be invalid in the case of myelin swelling. The differences therefore are assumed to indicate a real change in the profile. It is shown that this change can be attributed consistently to interdigitation of protein molecules at the surfaces of neighboring membranes, while the membrane structure itself remains unchanged. In this case, valid phases still can be determined by swelling, but the phases determined by Stamatoff and Krimm are not valid

Myelin x-ray patterns reconciled.

Two different X-ray diffraction patterns have been published for frog sciatic myelin. Here the apparent discrepancy is attributed to different spacings between the myelin membranes in the two experiments. Assuming the single membrane has the same structure in the two cases, some restrictions on the phasing are indicated. Several possible profiles for the single membrane are then considered. A profile derived by assuming a lecithin cholesterol-like bilayer within the membrane accounts for all the published data. Three published profiles also are considered. These are not quite in as good agreement with observation, but they cannot be excluded at present

Treatment of Low Angle X-Ray Data from Planar and Concentric Multilayered Structures

Low angle X-ray diffraction can be recorded from planar and concentric multilayered (biological) structures. In order to proceed with the X-ray analysis the relation between the observed intensities and the Fourier transform of the unit cell is required. This relation is derived for planar structures such as retinal rods, mitochondria, and collagen; and also for nerve myelin