70 research outputs found
Non-Kaehler String Backgrounds and their Five Torsion Classes
We discuss the mathematical properties of six--dimensional non--K\"ahler
manifolds which occur in the context of supersymmetric heterotic
and type IIA string compactifications with non--vanishing background H--field.
The intrinsic torsion of the associated SU(3) structures falls into five
different classes. For heterotic compactifications we present an explicit
dictionary between the supersymmetry conditions and these five torsion classes.
We show that the non--Ricci flat Iwasawa manifold solves the supersymmetry
conditions with non--zero H--field, so that it is a consistent heterotic
supersymmetric groundstate.Comment: 33 pages, LaTeX; references added; one more reference adde
Superconformal N=2, D=5 matter with and without actions
We investigate N=2, D=5 supersymmetry and matter-coupled supergravity
theories in a superconformal context. In a first stage we do not require the
existence of a Lagrangian. Under this assumption, we already find at the level
of rigid supersymmetry, i.e. before coupling to conformal supergravity, more
general matter couplings than have been considered in the literature. For
instance, we construct new vector-tensor multiplet couplings, theories with an
odd number of tensor multiplets, and hypermultiplets whose scalar manifold
geometry is not hyperkaehler.
Next, we construct rigid superconformal Lagrangians. This requires some extra
ingredients that are not available for all dynamical systems. However, for the
generalizations with tensor multiplets mentioned above, we find corresponding
new actions and scalar potentials. Finally, we extend the supersymmetry to
local superconformal symmetry, making use of the Weyl multiplet. Throughout the
paper, we will indicate the various geometrical concepts that arise, and as an
application we compute the non-vanishing components of the Ricci tensor of
hypercomplex group manifolds. Our results can be used as a starting point to
obtain more general matter-couplings to Poincare supergravity.Comment: 67 pages; v2: title of reference changed and small editing
corrections; v3: small typing errors corrected, version published in JHEP;
v4: typos corrected; v5: additional term in (2.109) and (4.11); v6: change of
order of indices in (2.89
Diving into the vertical dimension of elasmobranch movement ecology
Knowledge of the three-dimensional movement patterns of elasmobranchs is vital to understand their ecological roles and exposure to anthropogenic pressures. To date, comparative studies among species at global scales have mostly focused on horizontal movements. Our study addresses the knowledge gap of vertical movements by compiling the first global synthesis of vertical habitat use by elasmobranchs from data obtained by deployment of 989 biotelemetry tags on 38 elasmobranch species. Elasmobranchs displayed high intra- and interspecific variability in vertical movement patterns. Substantial vertical overlap was observed for many epipelagic elasmobranchs, indicating an increased likelihood to display spatial overlap, biologically interact, and share similar risk to anthropogenic threats that vary on a vertical gradient. We highlight the critical next steps toward incorporating vertical movement into global management and monitoring strategies for elasmobranchs, emphasizing the need to address geographic and taxonomic biases in deployments and to concurrently consider both horizontal and vertical movements
Efeito do Grupo Genético e da Heterose na Composição Física e nas Características Qualitativas da Carcaça e da Carne de Vacas de Descarte Terminadas em Confinamento
Relevant aspects of golden retriever muscular dystrophy for the study of Duchenne muscular dystrophy in humans
Relative roles of cortical and trabecular thinning in reducing osteoporotic vertebral body stiffness: a modelling study
While the effects of reduced bone density on osteoporotic vertebral strength are well known, the relative roles of cortical shell and trabecular architecture thinning in determining vertebral stiffness and strength are less clear. These are important parameters in investigating the changing biome-chanics of the ageing spine, and in assessing the effect of stiff-ening procedures such as vertebroplasty on neighbouring spinal segments. This work presents the development of a microstructural computer model of the osteoporotic lumbar vertebral body, allowing detailed prediction of the effects of bone micro-architecture on vertebral stiffness and strength. Microstructural finite element models of an L3 human ver-tebral body were created. The cortex geometry was repre-sented with shell elements and the trabecular network with a lattice of beam elements. Trabecular architecture was varied according to age. Each beam network model was validated against experimental data. Models were generated to represent vertebral bodies of age 75y respectively. For all models, an initial cortical shell thickness of 0.5mm was used, followed by reductions in the age >75y models to 0.35mm and 0.2mm to represent cortical thinning in late stage osteoporosis. Loads were applied to simulate in vitro biomechanical testing, compressing the vertebra by 20% of its height. Predicted vertebral stiffness and strength reduced with pro-gressive age changes in microarchitecture, demonstrating a 44% reduction in stiffness and a 43% reduction in strength, between the age 75 models. Reducing cortical thickness in the age >75 models demonstrated a substantial reduction in stiffness and strength, resulting in a 48% reduc-tion in stiffness and a 62% reduction in strength between the 0.5mm and 0.2mm cortical thickness models. Cortical thinning in late stage osteoporosis may therefore play an even greater role in reducing vertebral stiffness and strength than earlier reductions due to trabecular thinning
Comparative susceptibility of Salmonella Typhimurium biofilms of different ages to disinfectants
There is a general consensus that with increasing age a biofilm shows increased resistance to antimicrobials. In this study the susceptibility of 3-, 5- and 7-day-old Salmonella enterica serovar Typhimurium biofilms to disinfectants was evaluated. It was hypothesized that 7-day-old biofilms would be more resistant to disinfectants compared to 3- and 5-day-old biofilms. Biofilms were formed using the MBEC™ system and treated with six chemical disinfectants for 1 and 5 min. Four disinfectants at the highest concentration available showed 100% reduction in viable cells from all ages of biofilms after exposure for 5 min, and ethanol at 70% v/v was the least effective against biofilms, followed by chlorhexidine gluconate (CG). At the recommended user concentrations, only sodium hypochlorite showed 100% reduction in viable cells from all ages of biofilms. Benzalkonium chloride and CG were the least effective against biofilms, followed by quaternary ammonium compound which only showed 100% reduction in viable cells from 5-day-old biofilms. Overall, the results from this study do not display enhanced resistance in 7-day-old biofilms compared to 3- and 5-day-old biofilms. It is concluded that under the conditions of this study, the age of biofilm did not contribute to resistance towards disinfectants. Rather, the concentration of disinfectant and an increased contact time were both shown to play a role in successful sanitization
The use of cetyltrimethylammonium bromide for the rapid isolation from Staphylococcus aureus of relaxable and non-relaxable plasmid DNA suitable for in vitro manipulation
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