Spectral properties and geology of bright and dark material on dwarf planet Ceres

Variations and spatial distributions of bright and dark material on dwarf planet Ceres play a key role in understanding the processes that have led to its present surface composition. We define limits for bright and dark material in order to distinguish them consistently, based on the reflectance of the average surface using Dawn Framing Camera data. A systematic classification of four types of bright material is presented based on their spectral properties, composition, spatial distribution, and association with specific geomorphological features. We found obvious correlations of reflectance with spectral shape (slopes) and age; however, this is not unique throughout the bright spots. Although impact features show generally more extreme reflectance variations, several areas can only be understood in terms of inhomogeneous distribution of composition as inferred from Dawn Visible and Infrared Spectrometer data. Additional material with anomalous composition and spectral properties are rare. The identification of the composition and origin of the dark, particularly the darkest material, remains to be explored. The spectral properties and the morphology of the dark sites suggest an endogenic origin, but it is not clear whether they are more or less primitive surficial exposures or excavated subsurface but localized material. The reflectance, spectral properties, inferred composition, and geologic context collectively suggest that the bright and dark material tends to gradually change toward the average surface over time. This could be because of multiple processes, i.e., impact gardening/space weathering, and lateral mixing, including thermal and aqueous alteration, accompanied by changes in composition and physical properties such as grain size, surface temperature, and porosity (compaction).Comment: Meteoritics and Planetary Science; Dawn at Ceres special issu

Rigorous conditions for the existence of bound states at the threshold in the two-particle case

In the framework of non-relativistic quantum mechanics and with the help of the Greens functions formalism we study the behavior of weakly bound states as they approach the continuum threshold. Through estimating the Green's function for positive potentials we derive rigorously the upper bound on the wave function, which helps to control its falloff. In particular, we prove that for potentials whose repulsive part decays slower than $1/r^{2}$ the bound states approaching the threshold do not spread and eventually become bound states at the threshold. This means that such systems never reach supersizes, which would extend far beyond the effective range of attraction. The method presented here is applicable in the many--body case

Air and Spray Mixture Temperature Effects on Atomization of Agricultural Sprays

spray drift associated with agrochemical operations is highly dependent upon the physical properties of the spray solution with respect to how they influence atomization.  This study examined two spray solutions across a wide range of solution temperatures for two nozzles spraying into two high speed airstreams.  The dynamic surface tension and viscosity of the spray solutions were also measured across the range of temperatures.  Generally as the solution temperature increased, the dynamic surface tension and viscosity both decreased.  This decrease in physical properties was directly related to the decrease in spray droplet size for all nozzles and airspeeds tested.  Monitoring of spray solution temperature throughout the spray system of a typical agricultural aircraft demonstrated that while changes in the spray solutions temperature do occur, the range is much less than the ranges across which this atomization study covered.  During a typical aerial application scenario, the temperature of a spray solution and the associated physical properties and atomization characteristics would not be expected to see significant variation

Efficiency of a thermodynamic motor at maximum power

Several recent theories address the efficiency of a macroscopic thermodynamic motor at maximum power and question the so-called "Curzon-Ahlborn (CA) efficiency." Considering the entropy exchanges and productions in an n-sources motor, we study the maximization of its power and show that the controversies are partly due to some imprecision in the maximization variables. When power is maximized with respect to the system temperatures, these temperatures are proportional to the square root of the corresponding source temperatures, which leads to the CA formula for a bi-thermal motor. On the other hand, when power is maximized with respect to the transitions durations, the Carnot efficiency of a bi-thermal motor admits the CA efficiency as a lower bound, which is attained if the duration of the adiabatic transitions can be neglected. Additionally, we compute the energetic efficiency, or "sustainable efficiency," which can be defined for n sources, and we show that it has no other universal upper bound than 1, but that in certain situations, favorable for power production, it does not exceed 1/2

KCNK5 is Functionally Down-Regulated Upon Long-Term Hypotonicity in Ehrlich Ascites Tumor Cells

Background/Aims: Regulatory volume decrease (RVD) in response to acute cell swelling is well described and KCNK5 (also known as TASK-2 or K2P5.1) has been shown to be the volume sensitive K+ channel in Ehrlich cells. Very little is, on the other hand, known about the effects of long-term hypotonicity on expression and function of KCNK5, thus we have investigated the effect of long-term hypotonicity (24h - 48h) on KCNK5 in Ehrlich cells on the mRNA, protein and physiological levels. Methods: Physiological effects of long-term hypotonicity were measured using patch-clamp and Coulter counter techniques. Expression patterns of KCNK5 on mRNA and protein levels were established using real-time qPCR and western blotting respectively. Results: The maximum swelling-activated current through KCNK5 was significantly decreased upon 48h of hypotonicity and likewise the RVD response was significantly impaired after both 24 and 48h of hypotonic stimulation. No significant differences in the KCNK5 mRNA expression patterns between control and stimulated cells were observed, but a significant decrease in the KCNK5 protein level 48h after stimulation was found. Conclusion: The data suggest that the strong physiological impairment of KCNK5 in Ehrlich cells after long-term hypotonic stimulation is predominantly due to down-regulation of the KCNK5 protein synthesis

The uses of Connes and Kreimer's algebraic formulation of renormalization theory

We show how, modulo the distinction between the antipode and the "twisted" or "renormalized" antipode, Connes and Kreimer's algebraic paradigm trivializes the proofs of equivalence of the (corrected) Dyson-Salam, Bogoliubov-Parasiuk-Hepp and Zimmermann procedures for renormalizing Feynman amplitudes. We discuss the outlook for a parallel simplification of computations in quantum field theory, stemming from the same algebraic approach.Comment: 15 pages, Latex. Minor changes, typos fixed, 2 references adde