Synthetic Spectra for Type Ia Supernovae at Early Epochs

We present the current status of our construction of synthetic spectra for type Ia supernovae. These properly take into account the effects of NLTE and an adequate representation of line blocking and blanketing. The models are based on a sophisticated atomic database. We show that the synthetic spectrum reproduces the observed spectrum of 'normal' SN-Ia near maximum light from the UV to the near-IR. However, further improvements are necessary before truly quantitative analyses of observed SN-Ia spectra can be performed. In particular, the inner boundary condition has to be fundamentally modified. This is due to the dominance of electron scattering over true absorption processes coupled with the flat density structure in these objectsComment: To appear in "Proceedings of the IAU Colloquium 192 - Supernovae (10 Years of SN1993J)", eds. J.M. Marcaide and K.W. Weile

Crucial Physical Dependencies of the Core-Collapse Supernova Mechanism

We explore with self-consistent 2D F{\sc{ornax}} simulations the dependence of the outcome of collapse on many-body corrections to neutrino-nucleon cross sections, the nucleon-nucleon bremsstrahlung rate, electron capture on heavy nuclei, pre-collapse seed perturbations, and inelastic neutrino-electron and neutrino-nucleon scattering. Importantly, proximity to criticality amplifies the role of even small changes in the neutrino-matter couplings, and such changes can together add to produce outsized effects. When close to the critical condition the cumulative result of a few small effects (including seeds) that individually have only modest consequence can convert an anemic into a robust explosion, or even a dud into a blast. Such sensitivity is not seen in one dimension and may explain the apparent heterogeneity in the outcomes of detailed simulations performed internationally. A natural conclusion is that the different groups collectively are closer to a realistic understanding of the mechanism of core-collapse supernovae than might have seemed apparent.Comment: 25 pages; 10 figure

Extended search for the invisible axion with the axion dark matter experiment

This Letter reports on a cavity haloscope search for dark matter axions in the Galactic halo in the mass range 2.81–3.31μeV. This search utilizes the combination of a low-noise Josephson parametric amplifier and a large-cavity haloscope to achieve unprecedented sensitivity across this mass range. This search excludes the full range of axion-photon coupling values predicted in benchmark models of the invisible axion that solve the strong CP problem of quantum chromodynamics

Bounds on the possible evolution of the Gravitational Constant from Cosmological Type-Ia Supernovae

Recent high-redshift Type Ia supernovae results can be used to set new bounds on a possible variation of the gravitational constant $G$. If the local value of $G$ at the space-time location of distant supernovae is different, it would change both the kinetic energy release and the amount of $^{56}$Ni synthesized in the supernova outburst. Both effects are related to a change in the Chandrasekhar mass $M_{Ch} \propto G^{-3/2}$. In addition, the integrated variation of $G$ with time would also affect the cosmic evolution and therefore the luminosity distance relation. We show that the later effect in the magnitudes of Type Ia supernovae is typically several times smaller than the change produced by the corresponding variation of the Chandrasekhar mass. We investigate in a consistent way how a varying $G$ could modify the Hubble diagram of Type Ia supernovae and how these results can be used to set upper bounds to a hypothetical variation of $G$. We find G/G_0 \la 1.1 and G'/G \la 10^{-11} yr^{-1} at redshifts $z\simeq 0.5$. These new bounds extend the currently available constrains on the evolution of $G$ all the way from solar and stellar distances to typical scales of Gpc/Gyr, i.e. by more than 15 orders of magnitudes in time and distance.Comment: 9 pages, 4 figures, Phys. Rev. D. in pres

Classification of Supernovae

The current classification scheme for supernovae is presented. The main observational features of the supernova types are described and the physical implications briefly addressed. Differences between the homogeneous thermonuclear type Ia and similarities among the heterogeneous core collapse type Ib, Ic and II are highlighted. Transforming type IIb, narrow line type IIn, supernovae associated with GRBs and few peculiar objects are also discussed.Comment: 16 Pages, 4 figures, to be published in "Supernovae and Gamma-Ray Bursters," ed. Kurt W. Weile

First- and second-order effects of consumers' institutional logics on firm-consumer relationships: a cross-market comparative analysis

Consumers’ conceptions of a market's institutional logic affect mechanisms of firm–consumer relationships, but are generally neglected in comparative studies of international marketing. This study bridges institutional and relationship marketing theories to examine two questions: do consumers hold meaningful mental models of a market's institutional logics, and do these mental models explain differentiated patterns of market relationships across international contexts? Building on contract-relational duality, we develop a market-level construct for capturing consumers’ socially constructed mental models for the institutional logics of market action. We theorize that differences in consumers’ institutional logics will influence both their evaluation of a firm's capabilities (first-order effect) and the degree to which they reward a firm through their commitment (second-order effect). These bridging predictions are tested using data from the insurance industry across three international markets. Our results show that the German insurance market is located in the relatively high contracts–low relational quadrant, whereas the US and Dutch markets are both located in the relatively low contracts – high relational quadrant. Our results also suggest that consumer commitment conforms to a principle of alignment such that commitment accrues to providers who align their capabilities with consumers’ prevalent institutional logics of the market, and penalizes those who deviate from it

Role of cold resistance and burial for winter survival and spring initiation of an Ulva spp. (Chlorophyta) bloom in a eutrophic lagoon (Veerse Meer lagoon, The Netherlands)

In the eutrophic Veerse Meer lagoon (The Netherlands) large amounts of free-floating thalli from Ulva spp. are present from May to October. In winter however, no algae seem to occur in the lagoon. Sexual reproduction appears to be negligible, as spore formation and germling growth are observed only sporadically. Results of a field survey showed that in winter, viable Ulva biomass is present buried in the sediment of the shallow parts of the lagoon. Freezing experiments demonstrated that the algae are able to survive temperatures of -5 degrees C for 2 weeks when kept in darkness. In spring, the buried Ulva thalli are liberated out of the sediment to initiate a bloom. A field experiment indicates that bioturbation by the lugworm Arenicola marina does not stimulate the release of the thalli. Burial and winter survival can explain the rapid increase in Ulva biomass in spring and suggest that the initial spring biomass is one of the major factors determining the maximal biomass in summer. [KEYWORDS: Dimethylsulphoniopropionate dmsp content arenicola-marina; wadden sea; macroalgae; growth; lactuca; requirements; strategies; waters; form]

Effect of grazing by isopods and amphipods on growth of Ulva spp. (Chlorophyta)

Eutrophication of shallow coastal waters often leads to blooms of macroalgae. Grazing by crustaceans, such as amphipods and isopods, can reduce macroalgal biomass accumulation. At the same time, growth of the macroalgae can be stimulated by epiphyte removal. The role of grazing by isopods and amphipods on Ulva spp. biomass development was investigated in the Veerse Meer, a brackish lagoon situated in the southwest Netherlands. Exclusion of grazing in the field did not stimulate Ulva spp. growth. In fact, growth rates were higher in exclosures that allowed grazers to enter. Edibility tests identified the amphipod Gammarus locusta, and the isopods Idotea chelipes and Sphaeroma hookeri as potential grazers on Ulva spp. However, when epiphytic diatoms were present on the Ulva spp. thalli, Gammarus and Sphaeroma grazed on ephiphytes and not on Ulva tissue. Only Idotea continued to graze on Ulva spp. A laboratory growth experiment revealed a positive effect of Gammarus presence on Ulva spp. growth, probably caused by preferential removal of epiphytic diatoms from the Ulva spp. thalli. The growth stimulation by epiphyte removing grazers such as Gammarus may explain the higher growth rates in the presence of grazers observed in the field. When determining the potential role of invertebrate grazers in controlling macroalgal biomass accumulation, it is important to include an assessment of the epiphyte abundance on the macroalgae, as preferential removal of epiphytes may stimulate growth and thus have the opposite effect. [KEYWORDS: epiphytes, grazing, growth, Ulva spp.]