Pitcher Plants (Sarracenia) Provide a 21st-Century Perspective on Infraspecific Ranks and Interspecific Hybrids: A Modest Proposal for Appropriate Recognition and Usage

The taxonomic use of infraspecific ranks (subspecies, variety, subvariety, form, and subform), and the formal recognition of interspecific hybrid taxa, is permitted by the International Code of Nomenclature for algae, fungi, and plants. However, considerable confusion regarding the biological and systematic merits is caused by current practice in the use of infraspecific ranks, which obscures the meaningful variability on which natural selection operates, and by the formal recognition of those interspecific hybrids that lack the potential for inter-lineage gene flow. These issues also may have pragmatic and legal consequences, especially regarding the legal delimitation and management of Threatened and Endangered Species. A detailed comparison of three contemporary floras highlights the degree to which infraspecific and interspecific variation are treated inconsistently. An in depth analysis of taxonomy of the North American flowering plant genus Sarracenia (Sarraceniaceae) provides an ideal case study illustrating the confusion that can arise from inconsistent and apparently arbitrary designation of infraspecific ranks and hybrid taxa. To alleviate these problems, we propose the abandonment of infraspecific ranks of “variety” and “form”, and discourage naming of sterile interspecific hybrids except for use in the horticultural or agronomic trade. Our recommendations for taxonomic practice are in accord with the objectives proposed in the Systematics Agenda 2000, Systematics Agenda 2020, and the Global Strategy for Plant Conservation.Organismic and Evolutionary Biolog

Thorium-Uranium-233 Oxide (Kilorod) Facility--Rod Fabrication Process and Equipment

A fabrication facility with related process equipment has been constructed to fabricate fuel rods containing /sup 233/U and thorium oxide by the bulk oxide-vibratory compaction route and is now in operation at the Oak Ridge National Laboratory. While the initial motivation for the facility was to fabricate /sup 233/U-bearing 1/2-in.-dia x 46-in.-long Zircaloy-2 clad fuel rods for criticality experiments at the Brookhaven National Laboratory, sufficient flexibility has been incorporated into the facility to accommodate a variety of development work on a pilot-plant scale. The facility consists of a number of permanent alpha-tight cubicles which are shielded with 41/4-in. steel. The fabrication process is carried out remotely in these cubicles with the exception of several gloved-hand operations which occur where the dexterity required for manipulation exceeds that of the remote castle-type tongs. The fabrication equipment that has been installed in the facility performs the operations associated with oxide powder comminution and classification, vibratory compaction of oxide in fuel tubes, tube closure, fuel rod decontamination, and fuel rod inspection. Both the facility and the process equipment are described in detail, and detailed assembly drawings of the process equipment are included. (auth

Acid pH activation of the PmrA/PmrB two-component regulatory system of Salmonella enterica

Acid pH often triggers changes in gene expression. However, little is known about the identity of the gene products that sense fluctuations in extracytoplasmic pH. The Gram-negative pathogen Salmonella enterica serovar Typhimurium experiences a number of acidic environments both inside and outside animal hosts. Growth in mild acid (pH 5.8) promotes transcription of genes activated by the response regulator PmrA, but the signalling pathway(s) that mediates this response has thus far remained unexplored. Here we report that this activation requires both PmrA's cognate sensor kinase PmrB, which had been previously shown to respond to Fe(3+) and Al(3+), and PmrA's post-translational activator PmrD. Substitution of a conserved histidine or of either one of four conserved glutamic acid residues in the periplasmic domain of PmrB severely decreased or abolished the mild acid-promoted transcription of PmrA-activated genes. The PmrA/PmrB system controls lipopolysaccharide modifications mediating resistance to the antibiotic polymyxin B. Wild-type Salmonella grown at pH 5.8 were > 100 000-fold more resistant to polymyxin B than organisms grown at pH 7.7. Our results suggest that protonation of the PmrB periplasmic histidine and/or of the glutamic acid residues activate the PmrA protein, and that mild acid promotes cellular changes resulting in polymyxin B resistance

The Imprint of Gravitational Waves on the Cosmic Microwave Background

Long-wavelength gravitational waves can induce significant temperature anisotropy in the cosmic microwave background. Distinguishing this from anisotropy induced by energy density fluctuations is critical for testing inflationary cosmology and theories of large-scale structure formation. We describe full radiative transport calculations of the two contributions and show that they differ dramatically at angular scales below a few degrees. We show how anisotropy experiments probing large- and small-angular scales can combine to distinguish the imprint due to gravitational waves.Comment: 11 pages, Penn Preprint-UPR-

Landau-De Gennes theory of nematic liquid\ud crystals: the Oseen-Frank limit and beyond

We study global minimizers of a continuum Landau-De Gennes energy functional for nematic liquid crystals, in three-dimensional domains, subject to uniaxial boundary conditions. We analyze the physically relevant limit of small elastic constant and show that global minimizers converge strongly, in W 1,2 , to a global minimizer predicted by the Oseen-Frank theory for uniaxial nematic liquid crystals with constant order parameter. Moreover, the convergence is uniform in the interior of the domain, away from the singularities of the limiting Oseen-Frank global minimizer. We obtain results on the rate of convergence of the eigenvalues and the regularity of the eigenvectors of the Landau-De Gennes global minimizer.\ud \ud \ud We also study the interplay between biaxiality and uniaxiality in Landau-De Gennes global energy minimizers and obtain estimates for various related quantities such as the biaxiality parameter and the size of admissible strongly biaxial regions

Reconciling inflation with openness

It is already understood that the increasing observational evidence for an open Universe can be reconciled with inflation if our horizon is contained inside one single huge bubble nucleated during the inflationary phase transition. In this frame of ideas, we show here that the probability of living in a bubble with the right $\Omega_0$ (now the observations require $\Omega_0 \approx .2$) can be comparable with unity, rather than infinitesimally small. For this purpose we modify both quantitatively and qualitatively an intuitive toy model based upon fourth order gravity. As this scheme can be implemented in canonical General Relativity as well (although then the inflation driving potential must be designed entirely ad hoc), inferring from the observations that $\Omega_0 < 1$ not only does not conflict with the inflationary paradigm, but rather supports therein the occurrence of a primordial phase transition.Comment: 4 pages, one postscript figure, to be published on Physical Review D PACS: 98.80. C

CMB polarization from secondary vector and tensor modes

We consider a novel contribution to the polarization of the Cosmic Microwave Background induced by vector and tensor modes generated by the non-linear evolution of primordial scalar perturbations. Our calculation is based on relativistic second-order perturbation theory and allows to estimate the effects of these secondary modes on the polarization angular power-spectra. We show that a non-vanishing B-mode polarization unavoidably arises from pure scalar initial perturbations, thus limiting our ability to detect the signature of primordial gravitational waves generated during inflation. This secondary effect dominates over that of primordial tensors for an inflationary tensor-to-scalar ratio $r<10^{-6}$. The magnitude of the effect is smaller than the contamination produced by the conversion of polarization of type E into type B, by weak gravitational lensing. However the lensing signal can be cleaned, making the secondary modes discussed here the actual background limiting the detection of small amplitude primordial gravitational waves.Comment: 14 pages, 3 figures, minor changes matching the version to be published in Phys. Rev.

Social and cultural origins of motivations to volunteer a comparison of university students in six countries

Although participation in volunteering and motivations to volunteer (MTV) have received substantial attention on the national level, particularly in the US, few studies have compared and explained these issues across cultural and political contexts. This study compares how two theoretical perspectives, social origins theory and signalling theory, explain variations in MTV across different countries. The study analyses responses from a sample of 5794 students from six countries representing distinct institutional contexts. The findings provide strong support for signalling theory but less so for social origins theory. The article concludes that volunteering is a personal decision and thus is influenced more at the individual level but is also impacted to some degree by macro-level societal forces

Heat release by controlled continuous-time Markov jump processes

We derive the equations governing the protocols minimizing the heat released by a continuous-time Markov jump process on a one-dimensional countable state space during a transition between assigned initial and final probability distributions in a finite time horizon. In particular, we identify the hypotheses on the transition rates under which the optimal control strategy and the probability distribution of the Markov jump problem obey a system of differential equations of Hamilton-Bellman-Jacobi-type. As the state-space mesh tends to zero, these equations converge to those satisfied by the diffusion process minimizing the heat released in the Langevin formulation of the same problem. We also show that in full analogy with the continuum case, heat minimization is equivalent to entropy production minimization. Thus, our results may be interpreted as a refined version of the second law of thermodynamics.Comment: final version, section 2.1 revised, 26 pages, 3 figure