The Variation of Integrated Star IMFs among Galaxies

The integrated galaxial initial mass function (IGIMF) is the relevant distribution function containing the information on the distribution of stellar remnants, the number of supernovae and the chemical enrichment history of a galaxy. Since most stars form in embedded star clusters with different masses the IGIMF becomes an integral of the assumed (universal or invariant) stellar IMF over the embedded star-cluster mass function (ECMF). For a range of reasonable assumptions about the IMF and the ECMF we find the IGIMF to be steeper (containing fewer massive stars per star) than the stellar IMF, but below a few Msol it is invariant and identical to the stellar IMF for all galaxies. However, the steepening sensitively depends on the form of the ECMF in the low-mass regime. Furthermore, observations indicate a relation between the star formation rate of a galaxy and the most massive young stellar cluster in it. The assumption that this cluster mass marks the upper end of a young-cluster mass function leads to a connection of the star formation rate and the slope of the IGIMF above a few Msol. The IGIMF varies with the star formation history of a galaxy. Notably, large variations of the IGIMF are evident for dE, dIrr and LSB galaxies with a small to modest stellar mass. We find that for any galaxy the number of supernovae per star (NSNS) is suppressed relative to that expected for a Salpeter IMF. Dwarf galaxies have a smaller NSNS compared to massive galaxies. For dwarf galaxies the NSNS varies substantially depending on the galaxy assembly history and the assumptions made about the low-mass end of the ECMF. The findings presented here may be of some consequence for the cosmological evolution of the number of supernovae per low-mass star and the chemical enrichment of galaxies of different mass.Comment: 27 pages, accepted for publication by Ap

Folding of Cu, Zn superoxide dismutase and Familial Amyotrophic Lateral Sclerosis

Cu,Zn superoxide dismutase (SOD1) has been implicated in the familial form of the neurodegenerative disease Amyotrophic Lateral Sclerosis (ALS). It has been suggested that mutant mediated SOD1 misfolding/aggregation is an integral part of the pathology of ALS. We study the folding thermodynamics and kinetics of SOD1 using a hybrid molecular dynamics approach. We reproduce the experimentally observed SOD1 folding thermodynamics and find that the residues which contribute the most to SOD1 thermal stability are also crucial for apparent two-state folding kinetics. Surprisingly, we find that these residues are located on the surface of the protein and not in the hydrophobic core. Mutations in some of the identified residues are found in patients with the disease. We argue that the identified residues may play an important role in aggregation. To further characterize the folding of SOD1, we study the role of cysteine residues in folding and find that non-native disulfide bond formation may significantly alter SOD1 folding dynamics and aggregation propensity.Comment: 16 pages, 5 figure

Spontaneous Penile (Cavernosal) Abscess: Case Report with Discussion of Aetiology, Diagnosis, and Management with Review of Literature

The rare presentation of spontaneous, corpus cavernosal abscess with evident pus discharge is reported. The 19-year-old English man was successfully treated with surgical drainage and antibiotics with long-term sequelae in form of mild, left-sided penile deviation, but normal erectile function. Though he did not require any further surgical intervention for correction of chordee at that time, there remains a possibility of it getting worse over time, which may ultimately need surgery for correction. The possible aetiology, diagnosis, and treatment of this rare condition are briefly discussed

Raman signatures of charge ordering in K0.3WO3

We present polarization- and temperature-dependent Raman spectroscopic study of hexagonal tungsten bronze, K0.3WO3. The observed asymmetry in phonon line shapes indicate the presence of strong lattice anharmonicity arising due to the nonstoichiometry of the material. We observed a broad multipeak Raman feature at low frequency due to the local modes of K atoms known as local structural excitations. The observed vibrational features indicate a second-order phase transition around T=200 K accompanied by a frequency softening of low-frequency phonon modes. The observed phonon anomalies hint a physical picture involving a continuous symmetry change toward a charge-ordered state below 200 K. These observations indicate that K0.3WO3 may exhibit a weak charge-density-wave ground state at low temperatures.

Earth, humans, and metals: investigating the role of iron and other metals in the atmospheric, oceanic, and energy systems

Includes bibliographical references.2022 Fall.Metals such as iron and copper have been an integral component of the Earth system since its beginnings and have formed the basis for modern human civilization growth since the Bronze and Iron Ages. Human activities include metals at various levels, from burning coal in power plants and mining ores lead to emissions of particulate and gaseous metallic products into the atmosphere. While suspended in the air, metal oxides such as hematite and magnetite absorb solar radiation, thus warming the atmosphere. After falling into the oceans, metals such as iron and magnesium act as important nutrients for oceanic biota, and thus affect the marine nutrient and carbon cycles. Human activities have increased many-fold since the beginning of the Industrial Era, and as the world moves from fossil fuel to renewable energy to reduce carbon emissions, the demand for metals is also projected to increase many folds. Yet, the past, present, and future impacts of anthropogenic activities on the atmospheric and marine metal cycles, particularly iron, remain poorly understood.In Chapter 2, I estimate the atmospheric radiative and oceanic biological impacts of anthropogenic iron emissions over the Industrial Era. I perform simulations using a mineralogy-based inventory and an Earth System Model and estimate the 1850-to-2010 global mean direct radiative forcing by anthropogenic iron to be +0.02 to +0.10 W/m2. I estimate that the enhanced phytoplankton primary production due to anthropogenic soluble iron deposition over the last 150 years caused carbon dioxide (CO2) sequestration of 0.2-13 ppmv. This sequestered CO2 also led to an 'avoided' CO2 forcing of -0.002 to -0.16 W/m2. While globally small, these impacts can be higher in specific regions; the anthropogenic iron oxide direct radiative forcing is +0.5 W/m2 over areas such as East Asia and India with more coal combustion and metal smelting. Anthropogenic soluble iron sustains >10% of marine net primary productivity in the high-latitude North Pacific Ocean, a region vulnerable to thermal stratification due to climate change. In Chapter 3, I focus on evaluating anthropogenic total iron emissions using observations and models. Performing the model-observation comparison only at sites where the modeled anthropogenic contribution is the highest, I find that the current emission inventory underestimates anthropogenic total iron emissions from North America and Europe by a factor of 3-5. Further isolating anthropogenic sectoral emissions over North America using Positive Matrix Factorization, I find that smelting and coal combustion emissions are overestimated by a factor of 3-10 in the current emission inventory, whereas heavy fuel oil emissions from ships and industrial boilers are underestimated by a factor of 2-5. By comparing modeled concentrations of iron oxides with observations from Japan, I find that the current smelting and coal combustion emissions from East Asia are only slightly overestimated in the inventory, by a factor of 1.2-1.5. Finally, in Chapter 4, I explore the regionality and magnitude of PM2.5 emissions from metal mining and smelting to meet projected global renewable energy demand. I estimate future PM2.5 (particulate matter smaller than 2.5 μm diameter) emissions from mining and smelting to meet the metal demand of renewable energy technologies in two climate pathways to be 0.3-0.6 Tg/yr in the 2020-2050 period, which is projected to contribute 10-30% of total anthropogenic primary PM2.5 combustion emissions in many countries. The concentration of mineral reserves in a few regions means the impacts are also regionally concentrated. Rapid decarbonization could lead to a faster reduction of overall anthropogenic PM2.5 emissions but also could create more unevenness in the distributions of emissions relative to where demand occurs