305 research outputs found
Analysis of the carbon and nitrogen limitations to soybean yield
Soybeans are hypothesized to be âself-destructiveâ since they apparently need to translocate large amounts of nitrogen from vegetative tissues during seed-fill to sustain seed growth. To assess the possible limitations of this characteristic on soybean seed yield, a simple, dynamic simulation model is developed which accounts for the availability of nitrogen and photosynthate within the plant. The simulations show that the duration of seedfill and seed yield is clearly limited by the self-destructive characteristic. Increased availability of nitrogen within the plant is required for significant increases in soybean yields. Possible alterations of the model required to mimic actual soybean seed growth are presented
Spontaneous Breaking of N=2 Global Supersymmetry
We study spontaneous supersymmetry breaking in N=2 globally supersymmetric
theories describing a system of abelian vector multiplets. We find that the
most general form of the action admits, in addition to the usual
Fayet-Iliopoulos term, a magnetic Fayet-Iliopoulos term for the auxiliary
components of dual vector multiplets. In a generic case, N=2 supersymmetry is
broken down spontaneously to N=1. In some cases however, the scalar potential
can drive the theory towards a N=2 supersymmetric ground state where massless
dyons condense in the vacuum.Comment: 12 pages, LaTe
Perturbative Prepotential and Monodromies in N=2 Heterotic Superstring
We discuss the prepotential describing the effective field theory of N=2
heterotic superstring models. At the one loop-level the prepotential develops
logarithmic singularities due to the appearance of charged massless states at
particular surfaces in the moduli space of vector multiplets. These
singularities modify the classical duality symmetry group which now becomes a
representation of the fundamental group of the moduli space minus the singular
surfaces. For the simplest two-moduli case, this fundamental group turns out to
be a certain braid group and we determine the resulting full duality
transformations of the prepotential, which are exact in perturbation theory.Comment: 39 pages, LaTeX, no figures; section 6 expanded to include explicit
construction of the monodromy group in a (4,0) orbifold exampl
N=2 Heterotic Superstring and its Dual Theory in Five Dimensions
We study quantum effects in five dimensions in heterotic superstring theory
compactified on K_3 x S_1 and analyze the conjecture that its dual effective
theory is eleven-dimensional supergravity compactified on a Calabi-Yau
threefold. This theory is also equivalent to type II superstring theory
compactified on the same Calabi-Yau manifold, in an appropriate large volume
limit. In this limit the conifold singularity disappears and is replaced by a
singularity associated to enhanced gauge symmetries, as naively expected from
the heterotic description. Furthermore, we exhibit the existence of additional
massless states which appear in the strong coupling regime of the heterotic
theory and are related to a different type of singular points on Calabi-Yau
threefolds.Comment: 26 pages, LaTe
âIt is not fashionable to suffer nowadaysâ: Community motivations to repeatedly participate in outreach HIV testing indicate UHC potential in Tanzania
OBJECTIVE: This study examined peopleâs motivations for (repeatedly) utilizing HIV testing services during community-based testing events in urban and rural Shinyanga, Tanzania and potential implications for Universal Health Coverage (UHC). METHODS: As part of a broader multidisciplinary study on the implementation of a HIV Test and Treat model in Shinyanga Region, Tanzania, this ethnographic study focused on community-based testing campaigns organised by the implementing partner. Between April 2018 and December 2019, we conducted structured observations (24), short questionnaires (42) and in-depth interviews with HIV-positive (23) and HIV-negative clients (8). Observations focused on motivations for (re-)testing, and the counselling and testing process. Thematic analysis based on inductive and deductive coding was completed using NVivo software. RESULTS: Regular HIV testing was encouraged by counsellors. Most participants in testing campaigns were HIV-negative; 51.1% had tested more than once over their lifetimes. Testing campaigns provided an accessible way to learn oneâs HIV status. Motivations for repeat testing included: monitoring personal health to achieve (temporary) reassurance, having low levels of trust toward sexual partners, feeling at risk, seeking proof of (ill)-health, and acting responsibly. Repeat testers also associated testing with a desire to start treatment early to preserve a healthy-looking body, should they prove HIV positive. CONCLUSIONS: Community-based testing campaigns serve three valuable functions related to HIV prevention and treatment: 1) enable community members to check their HIV status regularly as part of a personalized prevention strategy that reinforces responsible behaviour; 2) identify recently sero-converted clients who would not otherwise be targeted; and 3) engage community with general prevention and care messaging and services. This model could be expanded to include routine management of other (chronic) diseases and provide an entry for scaling up UHC
âIt is not fashionable to suffer nowadaysâ: Community motivations to repeatedly participate in outreach HIV testing indicate UHC potential in Tanzania
Topological Amplitudes in String Theory
We show that certain type II string amplitudes at genus are given by the
topological partition function discussed recently by Bershadsky, Cecotti,
Ooguri and Vafa. These amplitudes give rise to a term in the four-dimensional
effective action of the form , where is the chiral
superfield of supergravitational multiplet. The holomorphic anomaly of
is related to non-localities of the effective action due to the
propagation of massless states. This result generalizes the holomorphic anomaly
of the one loop case which is known to lead to non-harmonic gravitational
couplings.Comment: 31 pages (LATEX) + 2 figures (available upon request as PS file or
hardcopy), NUB-3071 - IC/93/202 - CPTH-A258.079
N=2 Type II- Heterotic duality and Higher derivative F-terms
We test the recently conjectured duality between supersymmetric type II
and heterotic string models by analysing a class of higher dimensional
interactions in the respective low-energy Lagrangians. These are -terms of
the form where is the gravitational superfield. On the type II
side these terms are generated at the -loop level and in fact are given by
topological partition functions of the twisted Calabi-Yau sigma model. We show
that on the heterotic side these terms arise at the one-loop level. We study in
detail a rank 3 example and show that the corresponding couplings satisfy
the same holomorphic anomaly equations as in the type II case. Moreover we
study the leading singularities of 's on the heterotic side, near the
enhanced symmetry point and show that they are universal poles of order
with coefficients that are given by the Euler number of the moduli
space of genus- Riemann surfaces. This confirms a recent conjecture that the
physics near conifold singularity is governed by string theory at the
self-dual point.Comment: 33 pages, latex, no figure
On the Thermodynamic Geometry of BTZ Black Holes
We investigate the Ruppeiner geometry of the thermodynamic state space of a
general class of BTZ black holes. It is shown that the thermodynamic geometry
is flat for both the rotating BTZ and the BTZ Chern Simons black holes in the
canonical ensemble. We further investigate the inclusion of thermal
fluctuations to the canonical entropy of the BTZ Chern Simons black holes and
show that the leading logartithmic correction due to Carlip is reproduced. We
establish that the inclusion of thermal fluctuations induces a non zero scalar
curvature to the thermodynamic geometry.Comment: 1+17 pages, LaTeX, 4 eps figure
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