697 research outputs found
Spatial vegetation patterns and neighborhood competition among woody plants in an East African savanna
The majority of research on savanna vegetation dynamics has focused on the coexistence of woody and herbaceous vegetation. Interactions among woody plants in savannas are relatively poorly understood. We present data from a 10-year longitudinal study of spatially explicit growth patterns of woody vegetation in an East African savanna following exclusion of large herbivores and in the absence of fire. We examined plant spatial patterns and quantified the degree of competition among woody individuals. Woody plants in this semi-arid savanna exhibit strongly clumped spatial distributions at scales of 1 - 5 m. However, analysis of woody plant growth rates relative to their conspecific and heterospecific neighbors revealed evidence for strong competitive interactions at neighborhood scales of up to 5 m for most woody plant species. Thus, woody plants were aggregated in clumps despite significantly decreased growth rates in close proximity to neighbors, indicating that the spatial distribution of woody plants in this region depends on dispersal and establishment processes rather than on competitive, density-dependent mortality. However, our documentation of suppressive effects of woody plants on neighbors also suggests a potentially important role for tree-tree competition in controlling vegetation structure and indicates that the balanced-competition hypothesis may contribute to well-known patterns in maximum tree cover across rainfall gradients in Africa
Food additives: Sodium benzoate, potassium sorbate, azorubine, and tartrazine modify the expression of NFÎșB, GADD45α, and MAPK8 genes
It has been reported that some of the food additives may cause sensitization, inflammation of tissues, and potentially risk factors in the development of several chronic diseases. Thus, we hypothesized that expressions of common inflammatory molecules â known to be involved in the development of various inflammatory conditions and cancers â are affected by these food additives. We investigated the effects of commonly used food preservatives and artificial food colorants based on the expressions of NFÎșB, GADD45α, and MAPK8 (JNK1) from the tissues of liver. RNA was isolated based on Trizol protocol and the activation levels were compared between the treated and the control groups. Tartrazine alone could elicit effects on the expressions of NFÎșB (pâ=â0.013) and MAPK8 (pâ=â0.022). Azorubine also resulted in apoptosis according to MAPK8 expression (pâ=â0.009). Preservatives were anti-apoptotic in high dose. Sodium benzoate (from low to high doses) dose-dependently silenced MAPK8 expression (pâ=â0.004 to pâ=â0.002). Addition of the two preservatives together elicited significantly greater expression of MAPK8 at half-fold dose (pâ=â0.002) and at fivefold dose (pâ=â0.008). This study suggests that some of the food preservatives and colorants can contribute to the activation of inflammatory pathways
Partition Functions in Statistical Mechanics, Symmetric Functions, and Group Representations
Partition functions for non-interacting particles are known to be symmetric
functions. It is shown that powerful group-theoretical techniques can be used
not only to derive these relationships, but also to significantly simplify
calculation of the partition functions for particles that carry internal
quantum numbers. The partition function is shown to be a sum of one or more
group characters. The utility of character expansions in calculating the
partition functions is explored. Several examples are given to illustrate these
techniques.Comment: 16 pages of RevTe
Multiplicity distributions at high energies as a sum of Poissonian-like distributions
It is shown that at collider energies experimental multiplicity distributions
are well parameterized by a sum of Gupta-Sarma distributions. This extends
earlier description of the lower energy data by the two parameter sum of
Poissonians. Implications of the proposed parametrization for LHC are
discussed.Comment: 16 pages, Latex, 4 EPS figure
Matter-Antimatter Asymmetry in the Large Hadron Collider
The matter-antimatter asymmetry is one of the greatest challenges in the
modern physics. The universe including this paper and even the reader
him(her)self seems to be built up of ordinary matter only. Theoretically, the
well-known Sakharov's conditions remain the solid framework explaining the
circumstances that matter became dominant against the antimatter while the
universe cools down and/or expands. On the other hand, the standard model for
elementary particles apparently prevents at least two conditions out of them.
In this work, we introduce a systematic study of the antiparticle-to-particle
ratios measured in various and collisions over the last three
decades. It is obvious that the available experimental facilities turn to be
able to perform nuclear collisions, in which the matter-antimatter asymmetry
raises from at AGS to at LHC. Assuming that the final
state of hadronization in the nuclear collisions takes place along the
freezeout line, which is defined by a constant entropy density, various
antiparticle-to-particle ratios are studied in framework of the hadron
resonance gas (HRG) model. Implementing modified phase space and distribution
function in the grand-canonical ensemble and taking into account the
experimental acceptance, the ratios of antiparticle-to-particle over the whole
range of center-of-mass-energies are very well reproduced by the HRG model.
Furthermore, the antiproton-to-proton ratios measured by ALICE in
collisions is also very well described by the HRG model. It is likely to
conclude that the LHC heavy-ion program will produce the same particle ratios
as the program implying the dynamics and evolution of the system would not
depend on the initial conditions. The ratios of bosons and baryons get very
close to unity indicating that the matter-antimatter asymmetry nearly vanishes
at LHC.Comment: 9 pages, 5 eps-figures, revtex4-styl
QCD and models on multiplicities in and interactions
A brief survey of theoretical approaches to description of multiplicity
distributions in high energy processes is given. It is argued that the
multicomponent nature of these processes leads to some peculiar characteristics
observed experimentally. Predictions for LHC energies are presented. It is
shown that similarity of the energy dependence of average multiplicities in
different reactions is not enough alone to suggest the universal mechanism of
particle production in strongly-interacting systems. Other characteristics of
multiplicity distributions depend on the nature of colliding partners.Comment: 16 pages, 11 figures, Phys. Atom. Nuc
- âŠ