Low-velocity collisions of centimeter-sized dust aggregates

Collisions between centimeter- to decimeter-sized dusty bodies are important to understand the mechanisms leading to the formation of planetesimals. We thus performed laboratory experiments to study the collisional behavior of dust aggregates in this size range at velocities below and around the fragmentation threshold. We developed two independent experimental setups with the same goal to study the effects of bouncing, fragmentation, and mass transfer in free particle-particle collisions. The first setup is an evacuated drop tower with a free-fall height of 1.5 m, providing us with 0.56 s of microgravity time so that we observed collisions with velocities between 8 mm/s and 2 m/s. The second setup is designed to study the effect of partial fragmentation (when only one of the two aggregates is destroyed) and mass transfer in more detail. It allows for the measurement of the accretion efficiency as the samples are safely recovered after the encounter. Our results are that for very low velocities we found bouncing as could be expected while the fragmentation velocity of 20 cm/s was significantly lower than expected. We present the critical energy for disruptive collisions Q*, which showed up to be at least two orders of magnitude lower than previous experiments in the literature. In the wide range between bouncing and disruptive collisions, only one of the samples fragmented in the encounter while the other gained mass. The accretion efficiency in the order of a few percent of the particle's mass is depending on the impact velocity and the sample porosity. Our results will have consequences for dust evolution models in protoplanetary disks as well as for the strength of large, porous planetesimal bodies

Mechanisms of Pain in Sickle Cell Disease

Pain is one of the most common features of sickle cell disease (SCD) lacking effective therapy. Pain in SCD is relatively more complicated than other conditions associated with pain requiring understanding of the pathobiology of pain specific to SCD. The characterization of pain to define the diverse modalities of nociception in SCD is currently under progress via human studies accompanied by transgenic mouse models of SCD. Sickle pathobiology characterized by oxidative stress, inflammation and vascular dysfunction contributes to both peripheral and central nociceptive sensitization via mast cell activation in the periphery, and reactive oxygen species and glial activation and endoplasmic reticulum stress in the spinal cord among other effectors. These effects are mediated via several cellular receptors, which can be targeted to produce positive therapeutic outcomes. In this chapter, we will discuss the present understanding of molecular mechanisms of SCD pain and outline the mechanism‐based translational potential of novel actionable targets to treat SCD pain

Compaction, cratering and collision frequency on chondritic parent objects

Calculamos el grado de compactación de un asteroide de 100 km de radio debido a un impacto con un asteroide pequeño para velocidades de impacto entre 3 y 5 km s−1. Calculamos el radio del cráter producto del impacto. Obtenemos además el número de impactos sobre el asteroide de 100 km de radio con toda la distribución de asteroides pequeños durante la edad del Sistema Solar.We calculate the compaction of an asteroid with radius 100 km due to an impact with a small asteroid for impact velocities between 3 and 5 km s−1. The crater formed on the target surface as a result of such an impact is calculated. The number of impacts on the target with the distribution of small asteroids during the age of the Solar System is computed.Fil: Parisi, Mirta Gabriela. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Beitz, E.. Technische Universitat Carolo Wilhelmina Zu Braunschweig.; AlemaniaFil: Blum, J.. Technische Universitat Carolo Wilhelmina Zu Braunschweig.; AlemaniaReunión anual de la Asociación Argentina de AstronomíaLa PlataArgentinaUniversidad Nacional de La Plata. Facultad de Ciencias Astronómicas y GeofísicasUniversidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plat

Progress Report on Iowa State University Burroughs Endowment Activities

Faculty in the Department of Animal Science initiated soliciting of funds in 1987 to establish a permanent endowment to recognize the distinguished career and major contributions of Dr. Wise Burroughs, a distinguished professor in animal science at Iowa State University. The endowment was established in the Iowa State University Foundation in 1991. The purpose of the fund is to support research and graduate education in the areas of fundamental factors regulating growth in food-producing animals, with emphasis on ruminants; to enhance growth of animals with the goal of improving the competitive position of ruminants as food-producing animals; and to develop innovative approaches to ruminant nutrition and/or growth enhancement as a means to improve desirability of meat produced by food animals. Dr. Burroughs’ research resulted in important and significant developments in technology for modern production systems for beef cattle. He was widely known for his ability to communicate complex ideas and research results for use by those involved in the animal industry. The current Burroughs Team has established three research projects: 1) Ghrelin--How does ghrelin affect blood and body composition in rats?; 2) Use of 25- hydroxyvitamin D3 to improve tenderness of beef; 3) Redesigning beef cattle to have a more healthful fatty acid composition

Osteosarcomagenesis: Biology, Development, Metastasis, and Mechanisms of Pain

Osteosarcoma is the most common primary cancer of the bone and third most common cancer in children and adolescents with approximately 900 new cases annually in the United States. A major facet of osteosarcoma is its high level of genomic instability, in particular chromosomal instability, which is the result of increased or decreased chromosome number in a cell. Furthermore, pain is the most common symptomatic feature of osteosarcoma that lacks effective therapy. Pain in osteosarcoma is relatively more complicated than many other painful conditions requiring a more thorough understanding of its etiology, pathobiology, and neurobiology to allow the development of better therapies for reducing pain in osteosarcoma patients. Studies are underway to define the diverse modalities of presentation, growth, development, metastases, and nociception in osteosarcoma. New data from human studies in combination with data from studies incorporating transgenic mouse models of osteosarcoma are providing valuable insights into the mechanisms underlying the development of both the tumor and the tumor-induced pain. These new data will undoubtedly lead to improved prognoses, as well as the development of novel therapeutics that will significantly decrease bone cancer pain

Crossing barriers in planetesimal formation: The growth of mm-dust aggregates with large constituent grains

Collisions of mm-size dust aggregates play a crucial role in the early phases of planet formation. We developed a laboratory setup to observe collisions of dust aggregates levitating at mbar pressures and elevated temperatures of 800 K. We report on collisions between basalt dust aggregates of from 0.3 to 5 mm in size at velocities between 0.1 and 15 cm/s. Individual grains are smaller than 25 \mum in size. We find that for all impact energies in the studied range sticking occurs at a probability of 32.1 \pm 2.5% on average. In general, the sticking probability decreases with increasing impact parameter. The sticking probability increases with energy density (impact energy per contact area). We also observe collisions of aggregates that were formed by a previous sticking of two larger aggregates. Partners of these aggregates can be detached by a second collision with a probability of on average 19.8 \pm 4.0%. The measured accretion efficiencies are remarkably high compared to other experimental results. We attribute this to the rel. large dust grains used in our experiments, which make aggregates more susceptible to restructuring and energy dissipation. Collisional hardening by compaction might not occur as the aggregates are already very compact with only 54 \pm 1% porosity. The disassembly of previously grown aggregates in collisions might stall further aggregate growth. However, owing to the levitation technique and the limited data statistics, no conclusive statement about this aspect can yet be given. We find that the detachment efficiency decreases with increasing velocities and accretion dominates in the higher velocity range. For high accretion efficiencies, our experiments suggest that continued growth in the mm-range with larger constituent grains would be a viable way to produce larger aggregates, which might in turn form the seeds to proceed to growing planetesimals.Comment: 9 pages, 20 figure

Improvement of Lipid Absorption in Young Pigs as a Model for Preterm Infants

Preterm infants and neonatal suckling piglets have a limited bile acid pool that may hinder absorption of dietary lipids such as fatty acids, triacylglycerols (TAGs), and other lipid-soluble nutrients. Because dietary lipids are a valuable source of energy for growth, it is important that they are efficiently absorbed. The hypothesis of this study is that oral administration of 0.2 g/kg body weight daily of cholylsarcosine, an artificial bile acid, would decrease fecal excretion of dietary fatty acids and TAGs in suckling piglets. Twelve 7-d-old piglets were housed individually and fed a commercial milk replacer with or without oral cholylsarcosine until 21 d of age. Cholylsarcosine treatment decreased fecal excretion of stearic acid (18:0) and palmitic acid (16:0) (P ≤ 0.02). Cholylsarcosine supplementation had no effect on absorption of unsaturated fatty acids of 16 or 18 carbons (P \u3e 0.05). Cholylsarcosine increased fecal excretion of deoxycholic acid (P = 0.03). Apparent absorption of dietary TAGs was increased from 77% in piglets not fed cholylsarcosine to 83% in the piglets that received oral cholylsarcosine. These results support the hypothesis that cholylsarcosine increases absorption of dietary TAGs

In defence of global egalitarianism

This essay argues that David Miller's criticisms of global egalitarianism do not undermine the view where it is stated in one of its stronger, luck egalitarian forms. The claim that global egalitarianism cannot specify a metric of justice which is broad enough to exclude spurious claims for redistribution, but precise enough to appropriately value different kinds of advantage, implicitly assumes that cultural understandings are the only legitimate way of identifying what counts as advantage. But that is an assumption always or almost always rejected by global egalitarianism. The claim that global egalitarianism demands either too little redistribution, leaving the unborn and dissenters burdened with their societies' imprudent choices, or too much redistribution, creating perverse incentives by punishing prudent decisions, only presents a problem for global luck egalitarianism on the assumption that nations can legitimately inherit assets from earlier generations – again, an assumption very much at odds with global egalitarian assumptions

Effects of Intensified Nutrition on Immune Cell Populations in Milk Replacer-Fed Neonatal Calves

Results from the present study confirm the growthpromoting benefits of feeding an intensified milk replacer to dairy calves. Effects of the elevated plane of nutrition on immune variables examined in the present study were minimal. The number of circulating leukocytes and the composition of the PBMC population as well as this population’s general responsiveness and capacity to secrete IgM were not affected by diet. Relative to responses of calves fed the traditional MR, calves fed the intensified MR demonstrated reduced IFN-γ responses and elevated NO responses during the latter stages of the study. Aberrant NO production, however, can result in undesirable host tissue destruction