Application of fast Fourier transforms to EPR spectra of free radicals in solution

A method of reducing EPR spectra of free radicals in solution is presented in detail. This method is based on the use of the fast Fourier transform algorithm and curve fitting in the Fourier space by weighted least-squares minimization. Comparison with previous work is shown for EPR spectra of methyl viologen.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23183/1/0000110.pd

Non-Invasive Mouse Models of Post-Traumatic Osteoarthritis

SummaryAnimal models of osteoarthritis (OA) are essential tools for investigating the development of the disease on a more rapid timeline than human OA. Mice are particularly useful due to the plethora of genetically modified or inbred mouse strains available. The majority of available mouse models of OA use a joint injury or other acute insult to initiate joint degeneration, representing post-traumatic osteoarthritis (PTOA). However, no consensus exists on which injury methods are most translatable to human OA. Currently, surgical injury methods are most commonly used for studies of OA in mice; however, these methods may have confounding effects due to the surgical/invasive injury procedure itself, rather than the targeted joint injury. Non-invasive injury methods avoid this complication by mechanically inducing a joint injury externally, without breaking the skin or disrupting the joint. In this regard, non-invasive injury models may be crucial for investigating early adaptive processes initiated at the time of injury, and may be more representative of human OA in which injury is induced mechanically. A small number of non-invasive mouse models of PTOA have been described within the last few years, including intra-articular fracture of tibial subchondral bone, cyclic tibial compression loading of articular cartilage, and anterior cruciate ligament (ACL) rupture via tibial compression overload. This review describes the methods used to induce joint injury in each of these non-invasive models, and presents the findings of studies utilizing these models. Altogether, these non-invasive mouse models represent a unique and important spectrum of animal models for studying different aspects of PTOA

The Physics of Star Cluster Formation and Evolution

© 2020 Springer-Verlag. The final publication is available at Springer via https://doi.org/10.1007/s11214-020-00689-4.Star clusters form in dense, hierarchically collapsing gas clouds. Bulk kinetic energy is transformed to turbulence with stars forming from cores fed by filaments. In the most compact regions, stellar feedback is least effective in removing the gas and stars may form very efficiently. These are also the regions where, in high-mass clusters, ejecta from some kind of high-mass stars are effectively captured during the formation phase of some of the low mass stars and effectively channeled into the latter to form multiple populations. Star formation epochs in star clusters are generally set by gas flows that determine the abundance of gas in the cluster. We argue that there is likely only one star formation epoch after which clusters remain essentially clear of gas by cluster winds. Collisional dynamics is important in this phase leading to core collapse, expansion and eventual dispersion of every cluster. We review recent developments in the field with a focus on theoretical work.Peer reviewe

Added precision in 57Fe Mossbauer spectroscopy

This paper contains (1) the necessary mathematics for a precise interpretation of Mossbauer data, and (2) a characterization of a spectrometer designed specifically to maximize the information avalable from these data. The innovative aspects of this spectrometer are that it provides a known absorber lineshape, that it is quantitative, and that is provides information of the vibrational states of the absorber via the second order Doppler shift vs temperature and the total absorption vs temperature. The spectrometer allows sample temperature and applied magnetic field to be varied in any combination of 2-350 K or 0-6 T, respectively. Simultaneous collection of four data streams allows an accurate representation of the transmission spectrum. Sophisticated computer treatment with extensive use of least squares fitting procedures and fast Fourier transform techniques provides the final output display of sample cross-section vs standardized source velocity. The cross-section display is shown to be independent of the thickness of samples with Mossbauer optical densities up to 3. In addition, we report the method and results of measurements which must precede the operation of the spectrometer: (1) the absorption coefficient of iron at 14 keV: (498+/-7)cm-1, (2) the Debye temperature of our source (57Co in rhodium matrix): (361+/-20)K, (3) the source lineshape: three Lorentzians with Heisenberg linewidth, a center line with twice the intensity of the symmetrically placed outer lines which are spaced 0.055 mm/s apart, (4) the Mossbauer effect cross-section for 57Fe: (2.4+/-0.2) x 10-18 cm2, (5) the Debye temperature of iron (NBS # 1541): (430+/-30) K, and (6) the values for the Hamiltonian parameters of iron metal (NBS # 1541) at 290, 101 and 4.2 K. The precision of the determined Hamiltonian parameters is defined in terms of a statistic with a weighted [chi]2 distribution.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/22843/1/0000403.pd