Cryogenic mechanisms for scanning and interchange of the Fabry-Perot interferometers in the ISO long wavelength spectrometer

The Infrared Space Observatory (ISO) is an ESA cornerstone mission for infrared astronomy. Schedules for launch in 1993, its four scientific instruments will provide unprecedented sensitivity and spectral resolution at wavelengths which are inaccessible using ground-based techniques. One of these, the Long Wavelength Spectrometer (LWS), will operate in the 45 to 180 micron region (Emery et. al., 1985) and features two Fabry-Perot interferometers mounted on an interchange mechanism. The entire payload module of the spacecraft, comprising the 60 cm telescope and the four focal plane instruments, is maintained at 2 to 4 K by an onboard supply of liquid helium. The mechanical design and testing of the cryogenic interferometer and interchange mechanisms are described

AMP Deaminase 3 in Skeletal Muscle Atrophy: Regulation of Protein Degradation and Contractile Performance

Skeletal muscle atrophy is characterized by depressed cellular energetics, increased rates of protein degradation, contractile deficits and loss of muscle mass. A potential regulator of these impairments is the metabolic enzyme AMP Deaminase 3, which is highly upregulated during most if not all types of atrophy. The goals of the present dissertation were: 1) to investigate the role of AMPD3 on energetics and contractile characteristics of skeletal muscle during atrophy and 2) to determine the effects of AMPD3 in muscle cells on adenine nucleotide content and protein degradation. AMPD3 was knocked down by electroporation of shRNA plasmids into mouse soleus muscle during denervation-induced atrophy. One week later, muscles were removed, electrically stimulated, and contractile function measured. Muscle homogenates were analyzed by UPLC and western blot. Denervation increased AMPD3 protein expression by 67%, while knockdown reduced AMPD3 by 60%. Knockdown of AMPD3 increased half relaxation times in both innervated and denervated muscles during tetanic and high intensity fatiguing contractions. Neither low intensity contractions nor overexpression of AMPD3 in non-atrophying muscles altered half relaxation time. To determine the effects of AMPD3 on protein degradation, AMPD3 was overexpressed by adenovirus in C2C12 myotubes. Adenine nucleotides, protein degradation rate, and indices of the major protein degradative pathways were measured. Overexpression of AMPD3 resulted in a 40% loss of ATP and an increase in IMP. Protein degradation rate was 38% greater while protein synthesis was unchanged, which resulted in a net loss of protein and myotube atrophy. Surprisingly, the autophagy activator ULK1 and apparent autophagic flux were unchanged. Further, proteasome subunit contents and in-vitro proteasome activity were similarly unchanged. However, consistent with greater protein degradation, total ubiquitinated conjugates decreased. The increase in half relaxation time with AMPD3 knockdown is consistent with the role of AMPD in preserving the free energy of ATP hydrolysis and SERCA function. Overexpression of AMPD3 also resulted in a loss of adenine nucleotides and acceleration of protein degradation, suggesting that a fall in ATP activates proteasomal degradation in-vivo. These exciting findings identify AMPD3 as a novel regulator of skeletal muscle performance and protein degradation during atrophy

Muscle Oxygen Demands of the Vastus Lateralis in Back and Front Squats

International Journal of Exercise Science 13(6): 734-743, 2020. In resistance training squats are often used to strengthen the muscles of the lower extremities and core muscles. There are two common forms of squats that use a barbell for loading, the back squat and the front squat. The technique and loading of each squat differ markedly. However, the energetic demands on the muscle between the two forms are not well understood. The purpose of this study was to investigate the difference in energy demands between front and back squats by measuring the change in skeletal muscle oxygen saturation (SmO2) through the use of near infrared spectroscopy (NIRS). Methods: Eleven resistance trained individuals, (5 female, 6 male) with an average age of 23.7 ± 1.4, completed 3 sets of 15 repetitions at 70% of their 1-RM weight for both back and front squats. Skeletal muscle oxygen saturation (SmO2) of the vastus lateralis was measured using a wireless NIRS device. Results: The ΔSmO2 was not significantly different between back and front squats but was different between sets 1-3 (44.76 ± 3.24% vs. 55.19 ± 2.75% vs. 56.30 ± 2.63%), main effect p ≤ 0.0001 . The recovery of SmO2 was significantly different between back (42.5 ± 3.4 sec) and front squats (30.9 ± 2.8 sec), main effect p ≤ 0.05. Conclusions: The findings of this study suggest that the energetic demands placed on the vastus lateralis during both front and back squats are similar with a slower recovery of energetics in the back squat

Primordial magnetic field and spectral distortion of cosmic background radiation

The role played by a primordial magnetic field during the pre-recombination epoch is analysed through the cyclotron radiation (due to the free electrons) it might produce in the primordial plasma. We discuss the constraint implied by the measurement or lack thereof COBE on this primordial field.Comment: to appear in International Journal of Mod. Phy

Lensing Properties of Lightlike Current Carrying Cosmic Strings

The lensing properties of superconducting cosmic strings endowed with a time dependent pulse of lightlike current are investigated. The metric outside the core of the string belongs to the $pp$--wave class, with a deficit angle. We study the field theoretic bosonic Witten model coupled to gravity, and we show that the full metric (both outside and inside the core) is a Taub-Kerr-Shild generalization of that for the static string with no current. It is shown that the double image due to the deficit angle evolves in an unambiguous way as a pulse of lightlike current passes between the source and the observer. Observational consequences of this signature of the existence of cosmic strings are briefly discussed.Comment: 21 pages, LaTeX-REVTeX, 7 figures available upon request, preprint # DAMTP-R94/1

Dynamical Stability of Witten Rings

The dynamical stability of cosmic rings, or vortons, is investigated for the particular equation of state given by the Witten bosonic model. It is found that there exists a finite range of the state parameter for which the vorton states are actually stable against dynamical perturbations. Inclusion of the electromagnetic self action into the equation of state slightly shrinks the stability region but otherwise yields no qualitative difference. If the Witten bosonic model represents a good approximation for more realistic string models, then the cosmological vorton excess problem can only be solved by assuming either that strings are formed at low energy scales or that some quantum instability may develop at a sufficient rate.Comment: 11 pages, LaTeX-ReVTeX (v.3), 2 figures available upon request, DAMTP R-94/1

Constraints on the perturbed mutual motion in Didymos due to impact-induced deformation of its primary after the DART impact

Binary near-Earth asteroid (65803) Didymos is the target of the proposed NASA Double Asteroid Redirection Test (DART), part of the Asteroid Impact & Deflection Assessment (AIDA) mission concept. In this mission, the DART spacecraft is planned to impact the secondary body of Didymos, perturbing mutual dynamics of the system. The primary body is currently rotating at a spin period close to the spin barrier of asteroids, and materials ejected from the secondary due to the DART impact are likely to reach the primary. These conditions may cause the primary to reshape, due to landslides, or internal deformation, changing the permanent gravity field. Here, we propose that if shape deformation of the primary occurs, the mutual orbit of the system would be perturbed due to a change in the gravity field. We use a numerical simulation technique based on the full two-body problem to investigate the shape effect on the mutual dynamics in Didymos after the DART impact. The results show that under constant volume, shape deformation induces strong perturbation in the mutual motion. We find that the deformation process always causes the orbital period of the system to become shorter. If surface layers with a thickness greater than ~0.4 m on the poles of the primary move down to the equatorial region due to the DART impact, a change in the orbital period of the system and in the spin period of the primary will be detected by ground-based measurement.Comment: 8 pages, 7 figures, 2 tables, accepted for publication in MNRA

X-ray Evaluation of the Marshall Grazing Incidence X-Ray Spectrometer (MaGIXS) Nickel-Replicated Mirrors

X-ray observations of astronomical objects provides diagnostics not available in any other wavelength regime, however the capability of making these observation at a high spatial resolution has proven challenging. Recently, NASA Marshall Space Flight Center (MSFC) has made good progress in employing computer numerical control (CNC) polishing techniques on electroless nickel mandrels as part of our replicated grazing incidence optics program. CNC polishing has afforded the ability to deterministically refine mandrel figure, thereby improving mirror performance. The Marshall Grazing Incidence X-ray Spectrometer (MaGIXS) is a MSFC-led sounding rocket instrument that is designed to make the first ever soft x-ray spectral observations of the Sun spatially resolved along a narrow slit. MaGIXS incorporates some of the first mirrors produced at MSFC using this polishing technique. Here we present the predicted mirror performance obtained from metrology, after completion of CNC polishing, as well as the results of X-ray tests performed on the MaGIXS telescope mirror before and after mounting