7,913 research outputs found
Cannibalism as a life boat mechanism
Under certain conditions a cannibalistic population can survive when food for the adults is too scarce to support a non-cannibalistic population. Cannibalism can have this lifeboat effect if (i) the juveniles feed on a resource inaccessible to the adults; and (ii) the adults are cannibalistic and thus incorporate indirectly the inaccessible resource. Using a simple model we conclude that the mechanism works when, at low population densities, the average yield, in terms of new offspring, due to the energy provided by one cannibalized juvenile is larger than one
Застосування меланіну як стреспротектора півкуль головного мозку в залежності від стресостійкості тварин
На модели острого стресса обоснована стрессоустойчивость полушарий головного мозга крыс и стресспротекторные свойства меланина. Меланин проявляет стресспротекторные свойства за счет уменьшения содержания окислительномодифицированных белков, ТБК-реактантов и увеличения антиоксидантной защиты в тканях полушарий головного мозга в условиях острого стресса.A stress-resistance of rats’ cerebral hemispheres and melanin’s stressprotective properties were substantiated on the model of an acute stress. Melanin shows its stressprotective properties at the expense of oxidatively-modificated proteins’ decrease, TBA-reactants’ decrease and antioxidative protection’s increase in the tissues of cerebral hemispheres in conditions of an acute stress
Ectopic Fat and Insulin Resistance: Pathophysiology and Effect of Diet and Lifestyle Interventions
The storage of triglyceride (TG) droplets in nonadipose tissues is called ectopic fat storage. Ectopic fat is associated with insulin resistance and type 2 diabetes mellitus (T2DM). Not the triglycerides per se but the accumulation of intermediates of lipid metabolism in organs, such as the liver, skeletal muscle, and heart seem to disrupt metabolic processes and impair organ function. We describe the mechanisms of ectopic fat depositions in the liver, skeletal muscle, and in and around the heart and the consequences for each organs function. In addition, we systematically reviewed the literature for the effects of diet-induced weight loss and exercise on ectopic fat depositions
Genotyping of Giardia in Dutch patients and animals: a phylogenetic analysis of human and animal isolates.
Giardia duodenalis (syn. Giardia lamblia, Giardia intestinalis) is a protozoan organism that can infect the intestinal tract of many animal species including mammals. Genetic heterogeneity of G. duodenalis is well described but the zoonotic potential is still not clear. In this study, we analysed 100 Giardia DNA samples directly isolated from human stool specimens, to get more insight in the different G. duodenalis assemblages present in the Dutch human population. Results showed that these human isolates could be divided into two main Assemblages A and B within the G. duodenalis group on the basis of PCR assays specific for the Assemblages A and B and the DNA sequences of 18S ribosomal RNA and the glutamate dehydrogenase (gdh) genes. Genotyping results showed that G. duodenalis isolates originating from Dutch human patients belonged in 35% of the cases to Assemblage A (34/98) and in 65% of the cases to Assemblage B (64/98) whereas two human cases remained negative in all assays tested. In addition, we compared these human samples with animal samples from the Netherlands and human and animal samples from other countries. A phylogenetic analysis was carried out on the DNA sequences obtained from these Giardia and those available in GenBank. Using gdh DNA sequence analysis, human and animal Assemblage A and B Giardia isolates could be identified. However, phylogenetic analysis revealed different sub-clustering for human and animal isolates where host-species-specific assemblages (C, D, E, F and G) could be identified. The geographic origin of the human and animal samples was not a discriminating factor
A general scheme for the effective-mass Schrodinger equation and the generation of the associated potentials
A systematic procedure to study one-dimensional Schr\"odinger equation with a
position-dependent effective mass (PDEM) in the kinetic energy operator is
explored. The conventional free-particle problem reveals a new and interesting
situation in that, in the presence of a mass background, formation of bound
states is signalled. We also discuss coordinate-transformed, constant-mass
Schr\"odinger equation, its matching with the PDEM form and the consequent
decoupling of the ambiguity parameters. This provides a unified approach to
many exact results known in the literature, as well as to a lot of new ones.Comment: 16 pages + 1 figure; minor changes + new "free-particle" problem;
version published in Mod. Phys. Lett.
Quantum entanglement and Bell violation of two coupled cavity fields in dissipative environment
We study the quantum entanglement between two coupled cavities, in which one
is initially prepared in a mesoscopic superposition state and the other is in
the vacuum in dissipative environment and show how the entanglement between two
cavities can arise in the dissipative environment. The dynamic behavior of the
nonlocality for the system is also investigated.Comment: 12 pages, 5 figure
Universality and its Origins at the Amorphous Solidification Transition
Systems undergoing an equilibrium phase transition from a liquid state to an
amorphous solid state exhibit certain universal characteristics. Chief among
these are the fraction of particles that are randomly localized and the scaling
functions that describe the order parameter and (equivalently) the statistical
distribution of localization lengths for these localized particles. The purpose
of this Paper is to discuss the origins and consequences of this universality,
and in doing so, three themes are explored. First, a replica-Landau-type
approach is formulated for the universality class of systems that are composed
of extended objects connected by permanent random constraints and undergo
amorphous solidification at a critical density of constraints. This formulation
generalizes the cases of randomly cross-linked and end-linked macromolecular
systems, discussed previously. The universal replica free energy is
constructed, in terms of the replica order parameter appropriate to amorphous
solidification, the value of the order parameter is obtained in the liquid and
amorphous solid states, and the chief universal characteristics are determined.
Second, the theory is reformulated in terms of the distribution of local static
density fluctuations rather than the replica order parameter. It is shown that
a suitable free energy can be constructed, depending on the distribution of
static density fluctuations, and that this formulation yields precisely the
same conclusions as the replica approach. Third, the universal predictions of
the theory are compared with the results of extensive numerical simulations of
randomly cross-linked macromolecular systems, due to Barsky and Plischke, and
excellent agreement is found.Comment: 10 pages, including 3 figures (REVTEX
Daphnias: from the individual based model to the large population equation
The class of deterministic 'Daphnia' models treated by Diekmann et al. (J
Math Biol 61: 277-318, 2010) has a long history going back to Nisbet and Gurney
(Theor Pop Biol 23: 114-135, 1983) and Diekmann et al. (Nieuw Archief voor
Wiskunde 4: 82-109, 1984). In this note, we formulate the individual based
models (IBM) supposedly underlying those deterministic models. The models treat
the interaction between a general size-structured consumer population
('Daphnia') and an unstructured resource ('algae'). The discrete, size and
age-structured Daphnia population changes through births and deaths of its
individuals and throught their aging and growth. The birth and death rates
depend on the sizes of the individuals and on the concentration of the algae.
The latter is supposed to be a continuous variable with a deterministic
dynamics that depends on the Daphnia population. In this model setting we prove
that when the Daphnia population is large, the stochastic differential equation
describing the IBM can be approximated by the delay equation featured in
(Diekmann et al., l.c.)
Generator coordinate method calculations of one-nucleon removal reactions on Ca
An approach to the Generator Coordinate Method (GCM) using Skyrme-type
effective forces and Woods-Saxon construction potential is applied to calculate
the single-particle proton and neutron overlap functions in Ca. The
relationship between the bound-state overlap functions and the one-body density
matrix has been used. These overlap functions are applied to calculate the
cross sections of one-nucleon removal reactions such as (), ()
and () on Ca on the same theoretical footing. A consistent
description of data for the different reactions is achieved. The shapes of the
experimental cross sections for transitions to the ground state and
the first excited state of the residual nuclei are well reproduced by
the overlap functions obtained within the GCM. An additional spectroscopic
factor accounting for correlations not included in the overlap function must be
applied to the calculated results to reproduce the size of the experimental
cross sections.Comment: 16 pages, 6 figures, to be published in Phys. Rev.
Randomly Crosslinked Macromolecular Systems: Vulcanisation Transition to and Properties of the Amorphous Solid State
As Charles Goodyear discovered in 1839, when he first vulcanised rubber, a
macromolecular liquid is transformed into a solid when a sufficient density of
permanent crosslinks is introduced at random. At this continuous equi- librium
phase transition, the liquid state, in which all macromolecules are
delocalised, is transformed into a solid state, in which a nonzero fraction of
macromolecules have spontaneously become localised. This solid state is a most
unusual one: localisation occurs about mean positions that are distributed
homogeneously and randomly, and to an extent that varies randomly from monomer
to monomer. Thus, the solid state emerging at the vulcanisation transition is
an equilibrium amorphous solid state: it is properly viewed as a solid state
that bears the same relationship to the liquid and crystalline states as the
spin glass state of certain magnetic systems bears to the paramagnetic and
ferromagnetic states, in the sense that, like the spin glass state, it is
diagnosed by a subtle order parameter.
In this review we give a detailed exposition of a theoretical approach to the
physical properties of systems of randomly, permanently crosslinked
macromolecules. Our primary focus is on the equilibrium properties of such
systems, especially in the regime of Goodyear's vulcanisation transition.Comment: Review Article, REVTEX, 58 pages, 3 PostScript figure
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