Double ionization of helium by particle impact

Experimental results are reviewed of the ratio, R sq., of double to single ionization of He by proton, antiproton, electron and positron impact in the energy range from 0.15 to about 10 MeV/amu. At high velocities (greater than 1 to 2 MeV/amu) values of R sq. caused by electron impact merge with those for the proton with the antiproton, electron values being up to a factor of 2 greater than that for the p, positron. At these velocities the single ionization cross sections caused by impact of any of these four particles are indistinguishable

dd-abelian quotients of (d+2)(d+2)-angulated categories

Let ${\mathscr T}$ be a triangulated category. If $T$ is a cluster tilting object and $I = [ \operatorname{add} T ]$ is the ideal of morphisms factoring through an object of $\operatorname{add} T$, then the quotient category ${\mathscr T} / I$ is abelian. This is an important result of cluster theory, due to Keller-Reiten and K\"{o}nig-Zhu. More general conditions which imply that ${\mathscr T} / I$ is abelian were determined by Grimeland and the first author. Now let ${\mathscr T}$ be a suitable $( d+2 )$-angulated category for an integer $d \geqslant 1$. If $T$ is a cluster tilting object in the sense of Oppermann-Thomas and $I = [ \operatorname{add} T ]$ is the ideal of morphisms factoring through an object of $\operatorname{add} T$, then we show that ${\mathscr T} / I$ is $d$-abelian. The notions of $( d+2 )$-angulated and $d$-abelian categories are due to Geiss-Keller-Oppermann and Jasso. They are higher homological generalisations of triangulated and abelian categories, which are recovered in the special case $d = 1$. We actually show that if $\Gamma = \operatorname{End}_{ \mathscr T }T$ is the endomorphism algebra of $T$, then ${\mathscr T} / I$ is equivalent to a $d$-cluster tilting subcategory of $\operatorname{mod} \Gamma$ in the sense of Iyama; this implies that ${\mathscr T} / I$ is $d$-abelian. Moreover, we show that $\Gamma$ is a $d$-Gorenstein algebra. More general conditions which imply that ${\mathscr T} / I$ is $d$-abelian will also be determined, generalising the triangulated results of Grimeland and the first author.Comment: 19 pages. This is the final accepted version, which has been accepted for publication in the Journal of Algebr

Flight test techniques for wake-vortex minimization studies

Flight test techniques developed for use in a study of wake turbulence and used recently in flight studies of wake minimization methods are discussed. Flow visualization was developed as a technique for qualitatively assessing minimization methods and is required in flight test procedures for making quantitative measurements. The quantitative techniques are the measurement of the upset dynamics of an aircraft encountering the wake and the measurement of the wake velocity profiles. Descriptions of the instrumentation and the data reduction and correlation methods are given

Cattle trampling reduces the risk of nitrate leaching in organic dairy rotations

Organic dairy farming is characterized by grazing cows in contrast to Danish conventional farms where the majority of cows are kept indoors. Cattle trampling reduces the finer macroporosity in the top 5-10 cm of the soil. This causes a low infiltration capacity at the soil surface, giving a higher probability of macropore flow from the surface. Rapid water movement through macropores bypasses the soil matrix, reducing nitrate leaching. We investigated how three years of cattle trampling in organic grass-clover fields could influence the risk of nitrate leaching in the autumn. The experimental part of this study was situated in Denmark on a loamy sand within a long-term organic dairy crop rotation trial. Experimental plots were irrigated with a concentrated solution of potassium bromide (18.5 mm for an hour). The amount of bromide in the soil water was determined at five depths (0.1, 0.3, 0.4, 0.75 and 1.0 m) 24 h after irrigation. Macropores larger than 1 mm were recorded on horizontal surfaces (0.70 m2) at the same depths. Earthworm density and biomass were registered. Bromide concentration in soil was significantly larger with the grazing regime than with the cutting regime below 0.3 m depth to at least 1 m. We observed equivalent macropore densities between the two treatments, both at 0.1 and at 0.3 m depth. The dry bulk density measured at 10 cm depth was significantly larger in the plots with the grazing regime than with the cutting regime, indicating a reduction of the porosity at this depth for the plots subjected to cattle trampling. No epigeic species were present. Cattle trampling affected mainly endogeic earthworms. Deep-burrowing species (anecic) were the least sensitive to cattle trampling. The deeper infiltration of water in soil when subjected to cattle trampling indicated that preferential flow through large macropores occurred, and that rain water may bypass the soil matrix under similar or more extreme conditions than this experiment. We expect such hydraulic functioning to reduce the risk of leaching of soil water nitrate

Current Approaches to HR Strategies: Inside-Out vs. Outside-In

In an effort to determine the best practices with regard to Human Resource (HR) strategies, we conducted interviews with HR executives knowledgeable about their HR strategies from 20 companies, and gathered archival materials such as the HR strategy documents from 9 of the companies. We found that the content, process, and evaluation of the HR strategies can each be classified as focusing primarily on the HR function, the people of the firm, or the business. We provide some examples of ways that firms can move from an HR focused to a business-focused HR strategy

Extended two-level quantum dissipative system from bosonization of the elliptic spin-1/2 Kondo model

We study the elliptic spin-1/2 Kondo model (spin-1/2 fermions in one dimension with fully anisotropic contact interactions with a magnetic impurity) in the light of mappings to bosonic systems using the fermion-boson correspondence and associated unitary transformations. We show that for fixed fermion number, the bosonic system describes a two-level quantum dissipative system with two noninteracting copies of infinitely-degenerate upper and lower levels. In addition to the standard tunnelling transitions, and the transitions driven by the dissipative coupling, there are also bath-mediated transitions between the upper and lower states which simultaneously effect shifts in the horizontal degeneracy label. We speculate that these systems could provide new examples of continuous time quantum random walks, which are exactly solvable.Comment: 7 pages, 1 figur

Hard hexagon partition function for complex fugacity

We study the analyticity of the partition function of the hard hexagon model in the complex fugacity plane by computing zeros and transfer matrix eigenvalues for large finite size systems. We find that the partition function per site computed by Baxter in the thermodynamic limit for positive real values of the fugacity is not sufficient to describe the analyticity in the full complex fugacity plane. We also obtain a new algebraic equation for the low density partition function per site.Comment: 49 pages, IoP styles files, lots of figures (png mostly) so using PDFLaTeX. Some minor changes added to version 2 in response to referee report

Disruption of an RNA helicase/RNAse III gene in Arabidopsis causes unregulated cell division in floral meristems

Arabidopsis thaliana floral meristems are determinate structures that produce a defined number of organs, after which cell division ceases. A new recessive mutant, carpel factory (caf), converts the floral meristems to an indeterminate state. They produce extra whorls of stamens, and an indefinite number of carpels. Thus, CAF appears to suppress cell division in floral meristems. The function of CAF is partially redundant with the function of the CLAVATA (CLV) and SUPERMAN (SUP) genes, as caf clv and caf sup double mutants show dramatically enhanced floral meristem over-proliferation. caf mutant plants also show other defects, including absence of axillary inflorescence meristems, and abnormally shaped leaves and floral organs. The CAF gene was cloned and found to encode a putative protein of 1909 amino acids containing an N-terminal DExH/DEAD-box type RNA helicase domain attached to a C-terminal RNaseIII-like domain. A very similar protein of unknown function is encoded by a fungal and an animal genome. Helicase proteins are involved in a number of processes, including specific mRNA localization and mRNA splicing. RNase III proteins are involved in the processing of rRNA and some mRNA molecules. Thus CAF may act through some type of RNA processing event(s). CAF gives rise to two major transcripts of 2.5 and 6.2 kb. In situ hybridization experiments show that CAF RNA is expressed throughout all shoot tissues

Integrability vs non-integrability: Hard hexagons and hard squares compared

In this paper we compare the integrable hard hexagon model with the non-integrable hard squares model by means of partition function roots and transfer matrix eigenvalues. We consider partition functions for toroidal, cylindrical, and free-free boundary conditions up to sizes $40\times40$ and transfer matrices up to 30 sites. For all boundary conditions the hard squares roots are seen to lie in a bounded area of the complex fugacity plane along with the universal hard core line segment on the negative real fugacity axis. The density of roots on this line segment matches the derivative of the phase difference between the eigenvalues of largest (and equal) moduli and exhibits much greater structure than the corresponding density of hard hexagons. We also study the special point $z=-1$ of hard squares where all eigenvalues have unit modulus, and we give several conjectures for the value at $z=-1$ of the partition functions.Comment: 46 page