Environmental interactions of the Space Station Freedom electric power system

The Space Station Freedom operates in a low earth orbit (LEO) environment. Such operation results in different potential interactions with the Space Station systems including the Electric Power System (EPS). These potential interactions result in environmental effects which include neutral species effects such as atomic oxygen erosion, effects of micrometeoroid and orbital debris impacts, plasma effects, ionizing radiation, and induced contamination degradation effects. The EPS design and its interactions with the LEO environment are briefly described and the results of analyses and testing programs planned and performed thus far to resolve environmental concerns related to the EPS and its function in LEO environment

Chronic Nicotine Selectively Enhances α4β2* Nicotinic Acetylcholine Receptors in the Nigrostriatal Dopamine Pathway

These electrophysiological experiments, in slices and intact animals, study the effects of in vivo chronic exposure to nicotine on functional α4β2* nAChRs in the nigrostriatal dopaminergic (DA) pathway. Recordings were made in wild-type and α4 nicotinic acetylcholine receptor (nAChR) subunit knock-out mice. Chronic nicotine enhanced methyllycaconitine citrate hydrate-resistant, dihydro-β-erythroidine hydrobromide-sensitive nicotinic currents elicited by 3–1000 µM ACh in GABAergic neurons of the substantia nigra pars reticulata (SNr), but not in DA neurons of the substantia nigra pars compacta (SNc). This enhancement leads to higher firing rates of SNr GABAergic neurons and consequently to increased GABAergic inhibition of the SNc DA neurons. In the dorsal striatum, functional α4* nAChRs were not found on the neuronal somata; however, nicotine acts via α4β2* nAChRs in the DA terminals to modulate glutamate release onto the medium spiny neurons. Chronic nicotine also increased the number and/or function of these α4β2* nAChRs. These data suggest that in nigrostriatal DA pathway, chronic nicotine enhancement of α4β2* nAChRs displays selectivity in cell type and in nAChR subtype as well as in cellular compartment. These selective events augment inhibition of SNc DA neurons by SNr GABAergic neurons and also temper the release of glutamate in the dorsal striatum. The effects may reduce the risk of excitotoxicity in SNc DA neurons and may also counteract the increased effectiveness of corticostriatal glutamatergic inputs during degeneration of the DA system. These processes may contribute to the inverse correlation between tobacco use and Parkinson's disease

Exploring the magnetic properties of the largest single molecule magnets

The giant {Mn₇₀} and {Mn₈₄} wheels are the largest nuclearity single-molecule magnets synthesized to date, and understanding their magnetic properties poses a challenge to theory. Starting from first-principles calculations, we explore the magnetic properties and excitations in these wheels using effective spin Hamiltonians. We find that the unusual geometry of the superexchange pathways leads to weakly coupled {Mn₇} subunits carrying an effective S = 2 spin. The spectrum exhibits a hierarchy of energy scales and massive degeneracies, with the lowest-energy excitations arising from Heisenberg-ring-like excitations of the {Mn₇} subunits around the wheel. We further describe how weak longer-range couplings can select the precise spin ground-state of the Mn wheels out of the nearly degenerate ground-state band

Theoretical prediction of magnetic exchange coupling constants from broken-symmetry coupled cluster calculations

Exchange coupling constants (J) are fundamental to the understanding of spin spectra of magnetic systems. Here, we investigate the broken-symmetry (BS) approaches of Noodleman and Yamaguchi in conjunction with coupled cluster (CC) methods to obtain exchange couplings. J values calculated from CC in this fashion converge smoothly toward the full configuration interaction result with increasing level of CC excitation. We compare this BS-CC scheme to the complementary equation-of-motion CC approach on a selection of bridged molecular cases and give results from a few other methodologies for context

Research Notes : Studies in polyploidy in soybeans: A simple and effective colchicine technique of chromosome doubling for soybean (Glycine max (L .) Merr.) and its wild relatives.

Tang and Loo (1940) first reported the induction of tetraploid soybeans by soaking day-old seedlings in 0.05 to 0.1% colchicine solution for 24 or 48 h. Oinuma (1952) obtained tetraploids by soaking dry soybean seeds in 0.1% colchicine solution for 24, 48 and 72 h. His results showed that the survival of resulting plants was poor

Seeking Equity, Agility, and Sustainability in the Provision of Emergency Remote Teaching During the COVID-19 Pandemic: A Center for Teaching and Learning Takes an Expanded Role

Objectives: The purpose of the study was to illuminate and assess the experiences and feelings of the staff of a center for teaching and learning at one South African university during the early months (April–June 2020) of the COVID-19 pandemic lockdowns when it switched from face-to-face teaching to emergency remote teaching (ERT). It explores the practical, operational, ethical, cultural, and emotional questions that the staff of this center dealt with as they supported the university in ERT provision. Method: This paper draws on in-depth interviews with 23 staff members of the Centre for Innovation in Learning and Teaching (CILT) who revealed not only the logistical, technical, and administrative challenges faced during the ERT rollout period but the efforts they made to ensure that their efforts promoted equity (for students), agility (for the university), and psychological sustainability (for themselves). Findings: Using cultural historical activity theory as a lens to assess CILT staff activities, findings indicate that a number of contradictions and tensions emerged during this period—concerning exacerbated inequities, pedagogical compromises, cultural anxieties, and psychological pressures—that could not be fully resolved but only managed. Implications for Research: CILT staff are interested not only in providing logistical, technical, and practical support to a university but also in dealing effectively with the ethical, cultural, and emotional concerns that arise in times of crisis and transition, such as the current one. Understanding what happened during COVID-19 may offer insights into how other centers for teaching and learning can adjust to what will likely remain an unstable future in higher education. Conclusion: The pandemic ruptured the previously organic change and growth that characterized CILT development, transforming it as the staff responded to this South African university’s need to provide support to academics and students engaging with ERT

A Novel Solution to the Gravitino Problem

In a general phenomenological model with local supersymmetry, the amount of massive gravitinos produced in early universe tends to violate the known dark matter density bound by many orders of magnitude. This problem is absent in the recently proposed non-linear supergravity model in the brane world scenario in Type IIB string theory, where we (i.e., the standard model of strong and electroweak interactions) live in a stack of $\overline{\rm D3}$-branes (i.e., anti-D3-branes) that span the 3 large spatial dimensions. These $\overline{\rm D3}$-branes break supersymmetry. As an open string mode in there, the Goldstino to be eaten by the gravitino is present only inside the $\overline{\rm D3}$-branes. So, although a gravitino can be massive (e.g., $\overline{m}_{3/2} \ge 100$ GeV) inside the $\overline{\rm D3}$-branes, it is (almost) massless outside the $\overline{\rm D3}$-branes. It follows that the massive gravitinos produced inside the $\overline{\rm D3}$-branes will be pushed out of the $\overline{\rm D3}$-branes, analogous to the Meissner effect for the massive photons in super-conductors. As a result, the massive gravitinos will be depleted so the gravitino problem is absent.Comment: 13 pages, 1 figure, 2 table