94 research outputs found
Complex Dynamics in Predator-prey Models with Nonmonotonic Functional Response and Seasonal Harvesting
In this paper we study the complex dynamics of predator-prey systems with nonmonotonic functional response and harvesting. When the harvesting is constant-yield for prey, it is shown that various kinds of bifurcations, such as saddle-node bifurcation, degenerate Hopf bifurcation, and Bogdanov-Takens bifurcation, occur in the model as parameters vary. The existence of two limit cycles and a homoclinic loop is established by numerical simulations. When the harvesting is seasonal for both species, sufficient conditions for the existence of an asymptotically stable periodic solution and bifurcation of a stable periodic orbit into a stable invariant torus of the model are given. Numerical simulations are carried out to demonstrate the existence of bifurcation of a stable periodic orbit into an invariant torus and transition from invariant tori to periodic solutions, respectively, as the amplitude of seasonal harvesting increases
A schematic model for fragmentation and phase transition in nuclear collisions
We develop here a simple yet versatile model for nuclear fragmentation in
heavy ion collisions. The model allows us to calculate thermodynamic properties
such as phase transitions as well as the distribution of fragments at
disassembly. In spite of its simplicity the model gives very good fit to recent
data taken at the Michigan National Superconducting Cyclotron Laboratory. The
model is an extension of a lattice gas model which itself has strong overlaps
with percolation models which have been used in the past to compare with
nuclear fragmentation data.Comment: 12 pages (RevTex), 4 figures (uuencoded ps file), To appear in Phys.
Lett.
Crystallization and preliminary X-ray analysis of \u3ci\u3eNa\u3c/i\u3e-ASP-1, a multi-domain pathogenesis-related-1 protein from the human hookworm parasite \u3ci\u3eNecator americanus\u3c/i\u3e
Human hookworm infection is a major cause of anemia and malnutrition in the developing world. In an effort to control hookworm infection, the Human Hookworm Vaccine Initiative has identified candidate vaccine antigens from the infective larval stage (L3) of the parasite, including a family of pathogenesis-related-1 (PR-1) proteins known as the ancylostoma-secreted proteins (ASPs). The functions of the ASPs are unknown. In addition, it is unclear why some ASPs have one while others have multiple PR-1 domains. There are no known structures of a multi-domain ASP and in an effort to remedy this situation, recombinant Na-ASP-1 has been expressed, purified and crystallized. Na-ASP-1 is a 406-amino-acid multi-domain ASP from the prevalent human hookworm parasite Necator americanus. Useful X-ray data to 2.2 A ° have been collected from a crystal that belongs to the monoclinic space group P21 with unit-cell parameters a = 67.7, b = 74.27, c = 84.60 Ă
, ÎČ = 112.12°. An initial molecular-replacement solution has been obtained with one monomer in the asymmetric unit
Crystallization and preliminary X-ray analysis of \u3ci\u3eNa\u3c/i\u3e-ASP-1, a multi-domain pathogenesis-related-1 protein from the human hookworm parasite \u3ci\u3eNecator americanus\u3c/i\u3e
Human hookworm infection is a major cause of anemia and malnutrition in the developing world. In an effort to control hookworm infection, the Human Hookworm Vaccine Initiative has identified candidate vaccine antigens from the infective larval stage (L3) of the parasite, including a family of pathogenesis-related-1 (PR-1) proteins known as the ancylostoma-secreted proteins (ASPs). The functions of the ASPs are unknown. In addition, it is unclear why some ASPs have one while others have multiple PR-1 domains. There are no known structures of a multi-domain ASP and in an effort to remedy this situation, recombinant Na-ASP-1 has been expressed, purified and crystallized. Na-ASP-1 is a 406-amino-acid multi-domain ASP from the prevalent human hookworm parasite Necator americanus. Useful X-ray data to 2.2 A ° have been collected from a crystal that belongs to the monoclinic space group P21 with unit-cell parameters a = 67.7, b = 74.27, c = 84.60 Ă
, ÎČ = 112.12°. An initial molecular-replacement solution has been obtained with one monomer in the asymmetric unit
Crystallization and preliminary X-ray analysis of Na-ASP-1, a multi-domain pathogenesis-related-1 protein from the human hookworm parasite Necator americanus. Corrigendum
A correction to the paper by Asojo et al. [(2005), Acta Cryst. F61, 391â394]
A unified description for nuclear equation of state and fragmentation in heavy ion collisions
We propose a model that provides a unified description of nuclear equation of
state and fragmentations. The equation of state is evaluated in Bragg-Williams
as well as in Bethe-Peierls approximations and compared with that in the mean
field theory with Skyrme interactions. The model shows a liquid-gas type phase
transition. The nuclear fragment distributions are studied for different
densities at finite temperatures. Power law behavior for fragments is observed
at critical point. The study of fragment distribution and the second moment
shows that the thermal critical point coincides with the percolation
point at the critical density. High temperature behavior of the model shows
characteristics of chemical equilibrium.Comment: 20 pages in RevTex, 11 figures (uuencoded ps files), to appear in
Phys. Rev.
Knee osteoarthritis pendulum therapy : in vivo evaluation and a randomised, single-blind feasibility clinical trial
Background.
Exercise is recommended as the first-line management for knee osteoarthritis (KOA); however, it is difficult to determine which specific exercises are more effective. This study aimed to explore the potential mechanism and effectiveness of a leg-swinging exercise practiced in China, called âKOA pendulum therapyâ (KOAPT). Intraarticular hydrostatic and dynamic pressure (IHDP) are suggested to partially explain the signs and symptoms of KOA. As such this paper set out to explore this mechanism in vivo in minipigs and in human volunteers alongside a feasibility clinical trial. The objective of this study is 1) to analyze the effect of KOAPT on local mechanical and circulation environment of the knee in experimental animals and healthy volunteers; and 2) to test if it is feasible to run a large sample, randomized/single blind clinical trial.
Methods.
IHDP of the knee was measured in ten minipigs and ten volunteers (five healthy and five KOA patients). The effect of leg swinging on synovial blood flow and synovial fluid content depletion in minipigs were also measured. Fifty KOA patients were randomly divided into two groups for a feasibility clinical trial. One group performed KOAPT (targeting 1000 swings/leg/day), and the other performed walking exercise (targeting 4000 steps/day) for 12 weeks with 12 weeks of follow-up.
Results.
The results showed dynamic intra-articular pressure changes in the knee joint, increases in local blood flow, and depletion of synovial fluid contents during pendulum leg swinging in minipigs. The intra-articular pressure in healthy human knee joints was â11.32 ± 0.21 (cmH2O), whereas in KOA patients, it was â3.52 ± 0.34 (cmH2O). Measures were completed by 100% of participants in all groups with 95â98% adherence to training in both groups in the feasibility clinical trial. There were significant decreases in the Oxford knee score in both KOAPT and walking groups after intervention (p < 0.01), but no significant differences between the two groups.
Conclusion.
We conclude that KOAPT exhibited potential as an intervention to improve symptoms of KOA possibly through a mechanism of normalising mechanical pressure in the knee; however, optimisation of the method, longer-term intervention and a large sample randomized-single blind clinical trial with a minimal 524 cases are needed to demonstrate whether there is any superior benefit over other exercises
First Order Phase Transition in Intermediate Energy Heavy Ion Collisions
We model the disassembly of an excited nuclear system formed as a result of a
heavy ion collision. We find that, as the beam energy in central collisions in
varied, the dissociating system crosses a liquid-gas coexistence curve,
resulting in a first-order phase transition. Accessible experimental signatures
are identified: a peak in specific heat, a power-law yield for composites, and
a maximum in the second moment of the yield distribution
Multiple Bifurcations in a Predator-Prey System of Holling and Lesile Type with Constant-Yield Prey Harvesting
The bifurcation analysis of a predatorâprey system of Holling and Leslie type with constant-yield prey harvesting is carried out in this paper. It is shown that the model has a BogdanovâTakens singularity (cusp case) of codimension at least 4 for some parameter values. Various kinds of bifurcations, such as saddle-node bifurcation, Hopf bifurcation, repelling and attracting BogdanovâTakens bifurcations of codimensions 2 and 3, are also shown in the model as parameters vary. Hence, there are different parameter values for which the model has a limit cycle, a homoclinic loop, two limit cycles, or a limit cycle coexisting with a homoclinic loop. These results present far richer dynamics compared to the model with no harvesting. Numerical simulations, including the repelling and attracting BogdanovâTakens bifurcation diagrams and corresponding phase portraits, and the existence of two limit cycles or an unstable limit cycle enclosing a stable multiple focus with multiplicity one, are also given to support the theoretical analysis
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