Permanence and Positive Periodic Solutions for Kolmogorov Competing Species Systems with Periodic Forced Terms

IIntroductionhnsldertheKolmogorovtypeequationswithforcedtermsforn－spedeswheremevectorfunctionIscontinuousandT－periodicInthet—variable（T＞0）andP。（t）IS。COntlnuOuST－period1CfUnCtlol（l—1，2，…，n），。nddoeSn。tCh。ngeitsSignSlfl［0，Inthispaper，wesaythatthesystem（1．1）lspermanent，Ifthereexiststwoconstantssuchthatanysolutionexistsgloballyon［0，＋OO）andthatthereexistsTO＞0suchthatPe。anenceofconslde。dspeczeshasbeenw；delydlscu。edInllte。ture（see［1，2．3Jandtherefer…     

Periodic disturbances,trophic gradient and phytoplankton characteristics related to cyanobacterial growth in Guarapiranga Reservoir,São Paulo State,Brazil

The relationships between phytoplankton assemblage, disturbance and trophic characteristics were investigated in Guarapiranga Reservoir, which supplies water to approximately 25% of the São Paulo metropolitan region. Two open-water stations were sampled weekly during 1991–92, in order to determine the main factors promoting of Cyanobacterial growth. These were found to include: rainfall-induced nutrient inputs via runoff and percolation from the drainage basin; circulation patterns that favored resurgence of nutrients and transported littoral algae to the open water; senescence of algae (especially Chlorococcales and Zygnemaphyceae) which increased the availability of nutrients in the water column; and high nutrient concentrations during the driest season. Restricting nutrient inputs and controlling eutrophication are necessary if the quality of water supplied from this reservoir is to be improved.     

Periodic Active Case Finding for TB: When to Look?

Objective

To investigate the factors influencing the performance and cost-efficacy of periodic rounds of active case finding (ACF) for TB.

Methods

A mathematical model of TB dynamics and periodic ACF (PACF) in the HIV era, simplified by assuming constant prevalence of latent TB infection, is analyzed for features that control intervention outcome, measured as cases averted and cases found. Explanatory variables include baseline TB incidence, interval between PACF rounds, and different routine and PACF case-detection rates among HIV-infected and uninfected TB cases.

Findings

PACF can be cost-saving over a 10 year time frame if the cost-per-round is lower than a threshold proportional to initial incidence and cost-per-case-treated. More cases are averted at higher baseline incidence rates, when more potent PACF strategies are used, intervals between PACF rounds are shorter, and when the ratio of HIV-negative to positive TB cases detected is higher. More costly approaches, e.g. radiographic screening, can be as cost-effective as less costly alternatives if PACF case-detection is higher and/or implementation less frequent.

Conclusion

Periodic ACF can both improve control and save medium-term health care costs in high TB burden settings. Greater costs of highly effective PACF at frequent (e.g. yearly) intervals may be offset by higher numbers of cases averted in populations with high baseline TB incidence, higher prevalence of HIV-uninfected cases, higher costs per-case-treated, and more effective routine case-detection. Less intensive approaches may still be cost-neutral or cost-saving in populations lacking one or more of these key determinants.     

Genes for all metals—a bacterial view of the Periodic Table

Bacterial chromosomes have genes for transport proteins for inorganic nutrient cations and oxyanions, such as NH₄ ⁺, K⁺, Mg²⁺, Co²⁺, Fe³⁺, Mn²⁺, Zn²⁺ and other trace cations, PO₄ ^3-, SO₄ ^2- and less abundant oxyanions. Together these account for perhaps a few hundred genes in many bacteria. Bacterial plasmids encode resistance systems for toxic metal and metalloid ions including Ag⁺ AsO₂ ^-, AsO₄ ^3-, Cd²⁺, Co²⁺, CrO₄ ²⁻, Cu²⁺, Hg²⁺, Ni²⁺, Pb²⁺, TeO₃ ²⁻, TI⁺ and Zn²⁺. Most resistance systems function by energy-dependent efflux of toxic ions. A few involve enzymatic (mostly redox) transformations. Some of the efflux resistance systems are ATPases and others are chemiosmotic ion/proton exchangers. The Cd²⁺-resistance cation pump of Gram-positive bacteria is membrane P-type ATPase, which has been labeled with ³²P from [γ-³²P]ATP and drives ATP-dependent Cd²⁺ (and Zn²⁺) transport by membrane vesicles. The genes defective in the human hereditary diseases of copper metabolism, Menkes syndrome and Wilson’s disease, encode P-type ATPases that are similar to bacterial cadmium ATPases. The arsenic resistance system transports arsenite [As(III)], alternatively with the ArsB polypeptide functioning as a chemiosmotic efflux transporter or with two polypeptides, ArsB and ArsA, functioning as an ATPase. The third protein of the arsenic resistance system is an enzyme that reduces intracellular arsenate [As(V)] to arsenite [As(III)], the substrate of the efflux system. In Gram-negative cells, a three polypeptide complex functions as a chemiosmotic cation/protein exchanger to efflux Cd²⁺, Zn²⁺ and Co²⁺. This pump consists of an inner membrane (CzcA), an outer membrane (CzcC) and a membrane-spanning (CzcB) protein that function together. Received 08 August 1997/ Accepted in revised form 01 November 1997     

A Periodic Droop Model for Two Species Competition in A Chemostat

Both uniform persistence and the existence of periodic coexistence state are established for a periodically forced Droop model on two phytoplankton species competition in a chemostat under some appropriate conditions. Numerical simulations using biological data are presented as well to illustrate the main result. Research supported in part by the NSERC of Canada and the MITACS of Canada.     

Mutations of Sodium Channel α-Subunit Genes in Chinese Patients with Normokalemic Periodic Paralysis

OBJECTIVE: In this study, we aim to investigate the clinical features and Mutations of sodium channel alpha-subunit (SCN4A) genes in Chinese patients with normokalemic periodic paralysis (normoKPP). METHODS: Six unrelated Chinese families with normoKPP were analyzed in clinical features. Genomic DNA was extracted from peripheral blood leukocytes and amplified with PCR. We screened all 24 exons of SCN4A gene with denaturing high performance liquid chromatography (DHPLC) technology, and then sequence analysis was performed in those who showed heteroduplex as compared with unaffected controls. RESULTS: The laboratory tests were within normal ranges. Electromyograms and electrocardiograms were normal. One muscle biopsy was performed with the patient in family 4 after a brief attack of normoKPP. Examination of light microscopy showed no changes, but electronic microscopy showed occasionally degenerating myofibers. The mutations of SCN4A genes were as follows: (1) Met1592Val occurred in family 1. (2) Val-781-Ile occurred with the patient and her father in family 4. (3) Both the patients had a novel mutation g2101a predicting the amino acid exchange Arg675Gln in family 5, which may be a disease-causing mutation. CONCLUSIONS: In addition to Val-781-Ile and Met1592Val, the mutation g2101a (Arg675Gln) may be the novel mutation of SCN4A genes in Chinese patients with normoKPP.     

Positive Catch & Economic Benefits of Periodic Octopus Fishery Closures: Do Effective,Narrowly Targeted Actions ‘Catalyze’ Broader Management?

Overview

Eight years of octopus fishery records from southwest Madagascar reveal significant positive impacts from 36 periodic closures on: (a) fishery catches and (b) village fishery income, such that (c) economic benefits from increased landings outweigh costs of foregone catch. Closures covered ~20% of a village’s fished area and lasted 2-7 months.

Fishery Catches from Each Closed Site

Octopus landings and catch per unit effort (CPUE) significantly increased in the 30 days following a closure’s reopening, relative to the 30 days before a closure (landings: +718%, p<0.0001; CPUE: +87%, p<0.0001; n = 36). Open-access control sites showed no before/after change when they occurred independently of other management (“no ban”, n = 17/36). On the other hand, open-access control sites showed modest catch increases when they extended a 6-week seasonal fishery shutdown (“ban”, n = 19/36). The seasonal fishery shutdown affects the entire region, so confound all potential control sites.

Fishery Income in Implementing Villages

In villages implementing a closure, octopus fishery income doubled in the 30 days after a closure, relative to 30 days before (+132%, p<0.001, n = 28). Control villages not implementing a closure showed no increase in income after “no ban” closures and modest increases after “ban” closures. Villages did not show a significant decline in income during closure events.

Net Economic Benefits from Each Closed Site

Landings in closure sites generated more revenue than simulated landings assuming continued open-access fishing at that site (27/36 show positive net earnings; mean +$305/closure; mean +57.7% monthly). Benefits accrued faster than local fishers’ time preferences during 17-27 of the 36 closures. High reported rates of illegal fishing during closures correlated with poor economic performance.

Broader Co-Management

We discuss the implications of our findings for broader co-management arrangements, particularly for catalyzing more comprehensive management.     

Periodic limb movements in sleep during pregnancy: a common but benign disorder?

Pregnant women have a two- to threefold increased prevalence of restless legs syndrome (RLS) compared to the general population, and the majority of RLS patients also experience periodic limb movements in sleep (PLMS). PLMS have been associated with sleep disturbance as well as autonomic heart rate and blood pressure responses; however, the prevalence, cause and significance of PLMS during pregnancy remain unknown. This study evaluated the presence of PLMS in late pregnancy and its relationship to hypertensive disorders of pregnancy. Ninety-one women in the third trimester of pregnancy underwent overnight polysomnography. An RLS questionnaire and the Multivariate Apnea Risk Index were administered and venous blood was sampled within 2 weeks of the sleep study. After exclusions due to obstructive sleep apnoea and signal loss, PLMS data were available for 73 women, 36 hypertensive women and 37 BMI- and gestation-matched controls. PLMS were found to be very common during pregnancy; 45% of women had a PLMS index > 5 and 25% had a PLMS index > 15. The number of PLMS per hour did not differ by hypertensive status. Sleep quality was mostly unaffected by PLMS, as was change in blood pressure overnight. While RLS was reported by 18.3% of the sample, this did not reliably predict the presence of PLMS. Despite iron deficiency being common in this population, it was not associated with PLMS. This novel study investigating the frequency and impact of PLMS during pregnancy revealed that PLMS are very common in the third trimester; however, this disorder appears to be benign in terms of objective sleep quality and relationship with pregnancy-related hypertension.

     

Periodic coupling strength-dependent multiple coherence resonance by time delay in Newman–Watts neuronal networks

Recently, multiple coherence resonance induced by time delay has been observed in neuronal networks with constant coupling strength. In this paper, by employing Newman–Watts Hodgkin–Huxley neuron networks with time-periodic coupling strength, we study how the temporal coherence of spiking behavior and coherence resonance by time delay change when the frequency of periodic coupling strength is varied. It is found that delay induced coherence resonance is dependent on periodic coupling strength and increases when the frequency of periodic coupling strength increases. Periodic coupling strength can also induce multiple coherence resonance, and the coherence resonance occurs when the frequency of periodic coupling strength is approximately multiple of the spiking frequency. These results show that for periodic coupling strength time delay can more frequently optimize the temporal coherence of spiking activity, and periodic coupling strength can repetitively optimize the temporal coherence of spiking activity as well. Frequency locking may be the mechanism for multiple coherence resonance induced by periodic coupling strength. These findings imply that periodic coupling strength is more efficient for enhancing the temporal coherence of spiking activity of neuronal networks, and thus it could play a more important role in improving the time precision of information processing and transmission in neural networks.     

Periodic ammonium pulses: are they important for the uptake kinetics of Isochrysis galbana?

In a megatidal coastal system, high tidal currents can lead to periodic reinjection of nutrients via the water/sediment interface. This study investigates the phytoplankton response to periodic ammonium pulses (every 5h20) in a nitrogen-limited culture of Isochrysis galbana. Results show that cells use additional ammonium. The cell response is not instantaneous and an adaptation period is observed in experiments. This period is characterized by (i) a decrease in latency stage during 10 mn after one pulse, (ii) an alternance of uptake/excretion processes decreasing throughout the experiment, (iii) an increasingly high and rapid surge-uptake phenomenon until pulse 6. We raise the question whether the Michaelis–Menten equation classically used to describe uptake processes is adequate in such an intermittent background.     

Four Biofuel Species’ Responses to Periodic Flooding and High Water Tables on a Florida Histosol

Rising energy costs, decreasing soil depth, and best management practices that require on-farm water retention have led to interest in flood-tolerant bioenergy crops for production in the Everglades Agricultural Area (EAA) of Florida. Information on the effects of high water tables on sugarcane (Saccharum spp. L.) is available; however, little is known about the bioenergy crops elephant grass (Pennisetum purpureum Schumach.), energycane (Saccharum spp. L.), and giant reed (Arundo donax L.). The objective of this study was to evaluate the role of water-table depth on the yields, morphology, physiology, and early season growth of these three bioenergy species in relation to sugarcane. The species were grown in a greenhouse and subjected to three water management strategies, ?40 or ?16 cm constant water-table depths, and bi-weekly flooding with drainage to ?40 cm. The experiment was conducted in plant-cane, first-ratoon, and successive plant-cane crop cycles.       Periodic flooding relative to a ?40 cm constant water table significantly reduced dry weights and leaf area index and increased aerenchyma development. Averaged among crops, dry weight declined by 32, 49, 37, and 52% while leaf area index (LAI) decreased by 31, 50, 46, and 57% for giant reed, elephant grass, energycane, and sugarcane, respectively, in response to flooding. Aerenchyma proportional area of the stalk increased by 52, 90, and 95% for elephant grass, energycane, and sugarcane, respectively, but aerenchyma in giant reed decreased by 11%. High yields and stalk populations for all water tables were observed in energycane and elephant grass. These two species show potential for bioenergy production in the EAA. Field trials are recommended to confirm production scale yield.     

Periodic 17β-Estradiol Pretreatment Protects Rat Brain from Cerebral Ischemic Damage via Estrogen Receptor-β

Although chronic 17β-estradiol (E₂) has been shown to be a cognition-preserving and neuroprotective agent in animal brain injury models, concern regarding its safety was raised by the failed translation of this phenomenon to the clinic. Previously, we demonstrated that a single bolus of E₂ 48 hr prior to ischemia protected the hippocampus from damage in ovariectomized rats via phosphorylation of cyclic-AMP response element binding protein, which requires activation of estrogen receptor subtype beta (ER-β). The current study tests the hypothesis that long-term periodic E₂-treatment improves cognition and reduces post-ischemic hippocampal injury by means of ER-β activation. Ovariectomized rats were given ten injections of E₂ at 48 hr intervals for 21 days. Hippocampal-dependent learning, memory and ischemic neuronal loss were monitored. Results demonstrated that periodic E₂ treatments improved spatial learning, memory and ischemic neuronal survival in ovariectomized rats. Additionally, periodic ER-β agonist treatments every 48 hr improved post-ischemic cognition. Silencing of hippocampal ER-β attenuated E₂-mediated ischemic protection suggesting that ER-β plays a key role in mediating the beneficial effects of periodic E₂ treatments. This study emphasizes the need to investigate a periodic estrogen replacement regimen to reduce cognitive decline and cerebral ischemia incidents/impact in post-menopausal women.     

Autophagosomes,phagosomes, autolysosomes,phagolysosomes, autophagolysosomes… Wait,I’m confused

When an autophagosome or an amphisome fuse with a lysosome, the resulting compartment is referred to as an autolysosome. Some people writing papers on the topic of autophagy use the terms “autolysosome” and “autophagolysosome” interchangeably. We contend that these words should be used to denote 2 different compartments, and that it is worthwhile maintaining this distinction—the autophagolysosome has a particular origin in the process of xenophagy that makes it distinct from an autolysosome.     

Autophagosomes,phagosomes, autolysosomes,phagolysosomes, autophagolysosomes… Wait,I’m confused

When an autophagosome or an amphisome fuse with a lysosome, the resulting compartment is referred to as an autolysosome. Some people writing papers on the topic of autophagy use the terms “autolysosome” and “autophagolysosome” interchangeably. We contend that these words should be used to denote 2 different compartments, and that it is worthwhile maintaining this distinction—the autophagolysosome has a particular origin in the process of xenophagy that makes it distinct from an autolysosome.