Changes in Dark Matter Properties After Freeze-Out

The properties of the dark matter that determine its thermal relic abundance can be very different from the dark matter properties today. We investigate this possibility by coupling a dark matter sector to a scalar that undergoes a phase transition after the dark matter freezes out. If the value of Omega_DM h^2 calculated from parameters measured at colliders and by direct and indirect detection experiments does not match the astrophysically observed value, a novel cosmology of this type could provide the explanation. This mechanism also has the potential to account for the "boost factor" required to explain the PAMELA data.Comment: 5 pages; v2: Fixed minor typo, added short discussion of application to PAMELA and appropriate references, results unchange

A Summary of Some Typical Steel Failures in Machine Parts & Structural

The study of service failures results in continued improvement in the use of metals. The experience gained in individual cases becomes of general value when a fundamental concept of the cause can be derived. In this way engineers have learned to avoid notch effects and other stress raisers while other concepts such as stress corrosion are not so well defined

Learning to become an expert : reinforcement learning and the acquisition of perceptual expertise

To elucidate the neural mechanisms underlying the development of perceptual expertise, we recorded ERPs while participants performed a categorization task. We found that as participants learned to discriminate computer-generated "blob'' stimuli, feedback modulated the amplitude of the errorrelated negativity (ERN)-an ERP component thought to reflect error evaluation within medial-frontal cortex. As participants improved at the categorization task, we also observed an increase in amplitude of an ERP component associated with object recognition (the N250). The increase in N250 amplitude preceded an increase in amplitude of an ERN component associated with internal error evaluation (the response ERN). Importantly, these electroencephalographic changes were not observed for participants who failed to improve on the categorization task. Our results suggest that the acquisition of perceptual expertise relies on interactions between the posterior perceptual system and the reinforcement learning system involving medial-frontal cortex

Supersymmetric Baryogenesis from Exotic Quark Decays

In a simple extension of the minimal supersymmetric standard model, out-of-equilibrium decays of TeV scale exotic vector-like squarks may generate the baryon asymmetry of the universe. Baryon number and CP violation are present in the superpotential, so this mechanism does not rely on CP violation in supersymmetry breaking parameters. We discuss phenomenological constraints on the model as well as potential signals for the Large Hadron Collider and electronic dipole moment experiments. A variation on the TeV scale model allows the exotic squarks to be the messengers of gauge mediated supersymmetry breaking.Comment: 28 pages, 7 figures, 2 appendices, v2: typos corrected, results unchange

FUNCTIONAL MATURATION OF THYMIC LYMPHOCYTE POPULATIONS IN VITRO

Mouse thymocytes were cultured for short periods of time either alone or with one of two supporting cell populations, splenic adherent cells or thymic epithelial cells. The thymus-derived (T) cell activity of thymocytes cultured on supporting cell populations increased dramatically during 2 days of culture, as assayed in the mixed lymphocyte interaction (MLI), response to phytomitogens, and helper cell activity in the in vitro antibody response. The level of activity attained was equal to that of spleen and lymph node lymphocytes and greater than that of steroid-resistant thymocytes. The cultured thymocytes had surface antigens characteristic of mature T lymphocytes with regard to θ and H-2. The appearance of functionally active lymphocytes in vitro depended upon cell division. Most of the active cultured cells arose from cells already undergoing maturation, i.e., from cells with reduced θ determinants and increased H-2 determinants. We therefore have generated a population of thymocytes indistinguishable from peripheral T lymphocytes using simple in vitro techniques. The extent to which the production of these active lymphocytes depends upon in vitro differentiation is discussed

My Mother\u27s Evening Prayer

https://digitalcommons.library.umaine.edu/mmb-vp/4425/thumbnail.jp

Quantum Films Adsorbed on Graphite: Third and Fourth Helium Layers

Using a path-integral Monte Carlo method for simulating superfluid quantum films, we investigate helium layers adsorbed on a substrate consisting of graphite plus two solid helium layers. Our results for the promotion densities and the dependence of the superfluid density on coverage are in agreement with experiment. We can also explain certain features of the measured heat capacity as a function of temperature and coverage.Comment: 13 pages in the Phys. Rev. two-column format, 16 Figure

Reply to Kiers et al.: Economic and Biological Clarity in the Theory of Mutualism

Kiers et al. (1) make three main points. First, they noted that many mutualisms involve multiple symbionts interacting with a single host. We agree, and we explained that partner fidelity feedback (PFF) can function because plants generally “limit, withdraw, or even abscise investment in shoots, flowers, and roots (or subsets of any of these) after physical damage or deficits of… resources…” (2). This “modularity” of plant hosts (3) separates the effects of different symbionts and allows the host to react to individual symbionts. Modularity is easily incorporated into our model, because (with no change in our results) principal-agent theory allows the assumption of one agent per host to be replaced …Organismic and Evolutionary Biolog

Regional-Scale Relationships of Leaf Area Index to Specific Leaf Area and Leaf Nitrogen Content

Specific leaf area (SLA) is an important link between vegetation water and carbon cycles because it describes the allocation of leaf biomass per unit of leaf area. Several studies in many vegetation types have shown that canopy SLA is closely related to canopy leaf nitrogen (N) content and photosynthetic capacity. SLA increases as light is attenuated by leaf area down through a plant canopy. It therefore follows that across an individual biome the spatial patterns in canopy—average SLA and leaf N content should be significantly correlated with the spatial patterns in leaf area index (LAI) and canopy transmittance. In this paper, we show that the LAI across the Oregon transect is closely related to canopy—average SLA (R2 = 0.82) and leaf N content on a mass basis (R2 = 0.80). Canopy—average leaf N per unit area is highly correlated to canopy transmittance (R2 = 0.94) across the transect. At any given site, canopy—average SLA and leaf N per unit area do not vary significantly, either seasonally or between different codominant species occupying the same site. The results of this study suggest that the spatial distribution of canopy—average SLA and leaf nitrogen content (and perhaps canopy photosynthetic capacity) can be predicted across biomes from satellite estimates of LAI

Impact of multiscale dynamical processes and mixing on the chemical composition of the upper troposphere and lower stratosphere during the Intercontinental Chemical Transport Experiment–North America

We use high-frequency in situ observations made from the DC8 to examine fine-scale tracer structure and correlations observed in the upper troposphere and lower stratosphere during INTEX-NA. Two flights of the NASA DC-8 are compared and contrasted. Chemical data from the DC-8 flight on 18 July show evidence for interleaving and mixing of polluted and stratospheric air masses in the vicinity of the subtropical jet in the upper troposphere, while on 2 August the DC-8 flew through a polluted upper troposphere and a lowermost stratosphere that showed evidence of an intrusion of polluted air. We compare data from both flights with RAQMS 3-D global meteorological and chemical model fields to establish dynamical context and to diagnose processes regulating the degree of mixing on each day. We also use trajectory mapping of the model fields to show that filamentary structure due to upstream strain deformation contributes to tracer variability observed in the upper troposphere. An Eulerian measure of strain versus rotation in the large-scale flow is found useful in predicting filamentary structure in the vicinity of the jet. Higher-frequency (6–24 km) tracer variability is attributed to buoyancy wave oscillations in the vicinity of the jet, whose turbulent dissipation leads to efficient mixing across tracer gradients