Threshold Quantity Research Articles

Computer Simulation of the Structure of Porous Electrodes with an Immobilized Enzyme and Nanosized Support Particles

The efficiency of the operation of a porous electrode with an immobilized enzyme is defined, in particular, by a lucky structure of its active layer, which can contain nanosized particles of the support. The composites of such a kind are prepared with the aid of methods of colloidal chemistry. The aim of this particular investigation is to perform a computer simulation of processes of coagulation of particles of the support and their possible heterocoagulation with molecules of the enzyme. Algorithms of the formation of nanocomposite structures in solution are suggested. Calculations show that the concentration of the enzyme molecules in the nanocomposite structures cannot exceed a certain critical value. On the other hand, at a fixed value of the concentration of the enzyme molecules, the concentration of the support particles must not fall below a certain threshold quantity, which provides for the passing of current through the active layer. In order for all the enzyme molecules, rather than for a fraction of these, in the composite to take part in the process of bioelectrocatalysis, the concentration of support particles must be increased even higher, to an optimum value.

Contaminant-induced current decline in capillary array electrophoresis

High-throughput capillary array electrophoresis (CAE) instruments for DNA sequencing suffer to varying degrees from read length degradation associated with electrophoretic current decline and inhibition or delay in the arrival of fragments at the detector. This effect is known to be associated with residual amounts of large, slow-moving fragments of template or genomic DNA carried through from sample preparation and sequencing reactions. Here, we investigate the creation and expansion of an ionic depletion region induced by overloading the capillary with low-mobility DNA fragments, and the effect of growth of this region on electrophoresis run failure. Slow-moving fragments are analytically and experimentally shown to reduce the ionic concentration of the downstream electrolyte. With injection of large fragments beyond a threshold quantity, the anode-side boundary of the nascent depletion region begins to propagate toward the anode at a rate faster than the contaminant DNA migration. Under such conditions, the depletion region expands, the capillary current declines dramatically, and the electrophoresis run yields a short read length or fails completely.

A mathematical model for assessing control strategies against West Nile virus

Since its incursion into North America in 1999, West Nile virus (WNV) has spread rapidly across the continent resulting in numerous human infections and deaths. Owing to the absence of an effective diagnostic test and therapeutic treatment against WNV, public health officials have focussed on the use of preventive measures in an attempt to halt the spread of WNV in humans. The aim of this paper is to use mathematical modelling and analysis to assess two main anti-WNV preventive strategies, namely: mosquito reduction strategies and personal protection. We propose a single-season ordinary differential equation model for the transmission dynamics of WNV in a mosquito–bird–human community, with birds as reservoir hosts and culicine mosquitoes as vectors. The model exhibits two equilibria; namely the disease-free equilibrium and a unique endemic equilibrium. Stability analysis of the model shows that the disease-free equilibrium is globally asymptotically stable if a certain threshold quantity ( R 0 ) , which depends solely on parameters associated with the mosquito–bird cycle, is less than unity. The public health implication of this is that WNV can be eradicated from the mosquito–bird cycle (and, consequently, from the human population) if the adopted mosquito reduction strategy (or strategies) can make R 0 < 1 . On the other hand, it is shown, using a novel and robust technique that is based on the theory of monotone dynamical systems coupled with a regular perturbation argument and a Liapunov function, that if R 0 > 1 , then the unique endemic equilibrium is globally stable for small WNV-induced avian mortality. Thus, in this case, WNV persists in the mosquito–bird population.

Bifurcation Analysis of an SIRS Epidemic Model with Generalized Incidence

An SIRS epidemic model, with a generalized nonlinear incidence as a function of the number of infected individuals, is developed and analyzed. Extending previous work, it is assumed that the natural immunity acquired by infection is not permanent but wanes with time. The nonlinearity of the functional form of the incidence of infection, which is subject only to a few general conditions, is biologically justified. The stability analysis of the associated equilibria is carried out, and the threshold quantity ($\R$) that governs the disease dynamics is derived. It is shown that $\R$, called the basic reproductive number, is independent of the functional form of the incidence. Local bifurcation theory is applied to explore the rich variety of dynamical behavior of the model. Normal forms are derived for the different types of bifurcation that the model undergoes, including Hopf, saddle-node, and Bogdanov--Takens. The first Lyapunov coefficient is computed to determine various types of Hopf bifurcation, such a...

Intelligent hybrid controlled structures with soil-structure interaction

A hybrid control system is presented for seismic-resistant building structures with and without soil-structure interaction (SSI). The hybrid control is a damper-actuator-bracing control system composed of passive and active controllers. An intelligent algorithm is developed for the hybrid system, in which the passive damper is designed for minor and moderate earthquakes and the active control is designed to activate when the structural response is greater than a given threshold quantity. Thus, the external energy for active controller can be optimally utilized. In the control of a multistory building, the controller placement is determined by evaluating the optimal location index (OLI) calculated from six earthquake sources. In the study, the soil-structure interaction is considered both in frequency domain and time domain analyses. It is found that the interaction can significantly affect the control effectiveness. In the hybrid control algorithm with intelligent strategy, the working stages of passive and active controllers can be different for a building with and without considering SSI. Thus SSI is essential to be included in predicting the response history of a controlled structure.

ENVIRONMENTAL CONTROL SYSTEMS FOR MIST PROPAGATION OF CUTTINGS

ENVIRONMENTAL CONTROL SYSTEMS FOR MIST PROPAGATION OF CUTTINGS

Review of threshold quantities for the control of explosives in health and safety legislation in The Netherlands

This paper describes a study undertaken for the Ministry of Social Affairs and Employment in The Netherlands, to examine systems and limits for the control of explosives. An important part of the study was the development of a questionnaire and its issue to 11, key countries to obtain information on controls for the storage of explosives, especially fireworks. The responses to the questionnaire are analysed and used in conjunction with published information as the basis for our recommendations. The paper concludes that the threshold quantity for explosives in Dutch regulations should continue to be that quantity equivalent to 1000 kg of TNT. The paper also concludes that two threshold quantities for professional fireworks should be added to the list of explosives in the regulations. These proposed, new entries will cover report shells and other types of professional fireworks.

Major hazard control: the Malaysian experience

Malaysia plans to be a fully developed and industrialized country by year 2020. Malaysia has achieved good progress in the industrial sector. The industrial sector is operating plants and factories using and storing hazardous substances in quantities exceeding the threshold quantities. The plants that are dealing with hazardous substances exceeding the threshold quantity are classified as major hazard installations (MHIs). Some MHIs are located in heavily populated areas. Experience shows that MHIs pose a risk to the workers and the neighbors of the plants. Malaysia has taken the preventive measures to protect the workers and the public. The preventive measures have been taken through establishment of authorities to set major hazard control regulations, enforcing the regulations, assessing the safety reports and emergency plans, conducting audits and accident investigations. This paper reviews, in brief, the international regulations and guidelines of major hazard control. The paper also reviews the Malaysian experience of major hazard control.

Technological disaster factors

Abstract Major Hazard Installations (MHIs) deal with the hazardous substances which exceed the threshold quantity. Although MHIs are safe organizations, they cannot fail due to a single error. However, due to their high complexity, the designer and the operator make errors during the design, and operation of the plants. Consequently, the technical, operational and organizational errors may lead to a major accident. The world has seen many incidents due to the operation of the MHIs. Malaysia has experienced several technological disasters. Four investigation reports have been reviewed in detail. This paper reviews the causes of the technological disasters in general. This paper also summarizes the causes of the technological disasters in Malaysia. Finally the paper rearranges the technological disaster causes and errors.

Threshold quantity criteria for risk management programs: recommendations for toxic releases

Facilities using hazardous substances are required to comply with risk management programs that aim to reduce the frequency of chemical accidents and the severity of consequences in the event of an accident. Both the European Union and the United States use chemical-specific weight thresholds for toxic substances to determine those facilities and processes that must comply with such programs. This study evaluates whether the establishment and use of these ‘threshold quantities’ is consistent and protective of public health. The chemical footprint or hazard zone length is calculated using current threshold quantities and ‘level of concern’ (LOC) concentrations for 77 toxic chemicals in the US regulations. Using the worst-case scenario and the recommended procedure involving the Risk Management Program (RMP) ∗Comp, footprint lengths range up to 40 km. However, the RMP ∗Comp program provides inconsistent results. Threshold quantities are then calculated using an atmospheric dispersion model and several meteorological and land-use scenarios. In the base scenario (winds at 4.3 m/s, neutral stability, urban conditions, and distances of 100, 250, and 1000 m), distance-based weight thresholds are considerably smaller than current listings for most toxic substances. Distance-based and current thresholds have low correlation (e.g. r=0.34) and large discrepancies (e.g. differences up to three orders of magnitude). Alternative scenarios evaluated for distance-based threshold quantities, which used using stable atmospheres and rural settings further reduce the distance-based weight thresholds and increase discrepancies. Linear relationships are shown between threshold quantities and level of concerns for each scenario and dispersion mode (neutral or dense) that allow simple calculation of threshold quantities. The current thresholds may exclude facilities that could pose significant off-site risks, and the thresholds are inconsistent with the off-site consequence analysis (OCA). Recommendations include revising the threshold quantities that determine covered facilities/processes; modifying RMP ∗Comp to eliminate errors; establishing threshold quantities using a more rational approach, e.g. based on hazard zones or distances using credible scenarios; and using the same health-based level of concern in both initial screening and subsequent off-site consequence analyses.

Localization of saturated karst aquifer with magnetic resonance sounding and resistivity imagery.

To answer one of the main questions of hydrogeologists implementing boreholes or working on pollution questions in a karst environment--i.e., where is the ground water?--numerous tools including geophysics are used. However, the contribution of geophysics differs from one method to the other. The magnetic resonance sounding (MRS) method has the advantage of direct detection of ground water over other geophysical methods. Eight MRSs were implemented over a known karst conduit explored and mapped by speleologists to estimate the MRS ability to localize ground water. Two direct current resistivity imageries (DC-2D imagery) were also implemented to check their capability to map a known cave. We found that the MRS is a useful tool to locate ground water in karst as soon as the quantity of water is enough to be detected. The threshold quantity is a function of depth and it was estimated by forward modeling to propose a support graph to hydrogeologists. The measured MRS's signals could be used to calculate transmissivity and permeability estimators. These estimators were used to map and to draw a cross section of the case study site, which underline accurately the known karst conduit location and depth. We also found that the DC-2D imagery could underline the karst structures: It was able to detect the known cave through its associated faults. We prepared a computer simulation to check the depth of such a cave to induce resistivity anomaly which could be measured in similar conditions.

A new method for estimating the effort required to control an infectious disease.

We propose a new threshold quantity for the analysis of the epidemiology of infectious diseases. The quantity is similar in concept to the familiar basic reproduction ratio, R0, but it singles out particular host types instead of providing a criterion that is uniform for all host types. Using this methodology we are able to identify the long-term effects of disease-control strategies for particular subgroups of the population, to estimate the level of control necessary when targeting control effort at a subset of host types, and to identify host types that constitute a reservoir of infection. These insights cannot be obtained by using R0 alone.

Effect of a preventive vaccine on the dynamics of HIV transmission

A deterministic mathematical model for the transmission dynamics of HIV infection in the presence of a preventive vaccine is considered. Although the equilibria of the model could not be expressed in closed form, their existence and threshold conditions for their stability are theoretically investigated. It is shown that the disease-free equilibrium is locally–asymptotically stable if the basic reproductive number R<1 (thus, HIV disease can be eradicated from the community) and unstable if R>1 (leading to the persistence of HIV within the community). A robust, positivity-preserving, non-standard finite-difference method is constructed and used to solve the model equations. In addition to showing that the anti-HIV vaccine coverage level and the vaccine-induced protection are critically important in reducing the threshold quantity R , our study predicts the minimum threshold values of vaccine coverage and efficacy levels needed to eradicate HIV from the community.

Review of an incident at a petrochemical plant

Major hazard installations (MHIs) are dealing with hazardous substances which exceed the threshold quantity. MHIs are characterized by tight coupling and high complexity. Due to their complexity, MHIs require well trained managers who have good experience at all levels to manage the operations successfully. The managements of major hazard installations play a vital role in the success or failure of their installation. The world has witnessed many incidents in major hazard installations due to failure of the management at all levels. This paper summarizes in brief the management errors for several incidents which occurred worldwide. Also, the paper reviews the management errors which led to an incident at a petrochemical plant in East Malaysia.

Food allergy diagnosis: are there any missing factors? A theoretical approach

Actual diagnostic criteria in food allergy frequently show a group of subjects with uncertain diagnosis, i.e., subjects with only occasional reactions to an offending food. These subjects are probably under- or misdiagnosed. It is possible that food itself may be only one of the factors involved in the allergic food reaction, at least in these subjects. In these cases, several factors besides food could modify either the allergenic potential of food or the absorption of allergens and may be relevant for a clinical response to occur. In order to investigate the possible relevance of missing factors, a theoretical model is elaborated by modifying the equation that represents the classical food allergy model: xAg+( IgE ∗ -cell)⇒ clinical response (mediators release…). In this classical model, it is assumed that if there is specific IgE against a food (IgE*-cell), the only limiting factor will be x (total amount of allergen ingested), being Ag, the allergen supposed to elicit a clinically relevant response. Always that x⩾ a (threshold quantity of allergen that elicits a reaction) a reaction should occur. The possible existence of missing factors, i.e., the presence of ‘modified allergens’ ( Ag ′, Ag ′′,…, Ag n ) induced by modification of the allergenic potential of food, are not considered in the equation, but these factors may have clinical relevance, and these relevance could be related to x 1, x 2,…, x n (relative quantities of ‘modified allergens’). So, a modified formula is proposed: {x−Σ(x 1,x 2,…,x n)]Ag+Σ(x 1Ag ′,x 1Ag ′′,…,x nAg n)}+ IgE ∗ -cell)⇒ clinical response . In this formula, depending of the relative amount of the limiting factors: x 1, x 2,…, x n and the relevant allergen ( Ag, Ag ′, Ag ′′… or Ag n ) to which the subject is sensitized an allergic reaction could or could not be elicited. So, factors other that the food itself and the threshold of sensitivity may be missed in the diagnosis of food allergy. When there are not any factors modifying Ag, the allergic response will depend only on the amount of x (‘classical equation’). But when there is some kind of modification the response will depend on the relevance of the modified allergens and on the relative amount of them. If the factors modifying the allergenicity cannot be controlled, the amount of the clinically relevant allergen cannot be estimated, and the clinical response may be only occasional, explaining the inconsistent findings of some subjects.

Analysis of an epidemic model with bistable equilibria using the Poincaré index

In most disease transmission models, disease eradication depends on a certain threshold quantity ( R 0 ), known as the basic reproductive number, such that if R 0<1 , then the disease-free equilibrium is stable and the disease can be eradicated from the population. However, several recent studies have shown that reducing R 0 to values less than unity is not sufficient to control the spread of a disease. These studies have considered epidemic models that have bistable equilibria, where both the disease-free equilibrium and an endemic equilibrium are locally asymptotically stable. This paper proposes a technique for analysing the models that exhibit such dynamics. It is shown that the stability of the equilibria for such models can be established using the Poincaré index of a piecewise Jordan curve defined as the boundary of a positively invariant region for the model. An application of this result to a vaccination model for the transmission dynamics of an infectious disease is given.

Subthreshold domain of bistable equilibria for a model of HIVepidemiology

A homogeneous‐mixing population model for HIV transmission, which incorporates an anti‐HIV preventive vaccine, is studied qualitatively. The local and global stability analysis of the associated equilibria of the model reveals that the model can have multiple stable equilibria simultaneously. The epidemiological consequence of this (bistability) phenomenon is that the disease may still persist in the community even when the classical requirement of the basic reproductive number of infection (ℛ0) being less than unity is satisfied. It is shown that under specific conditions, the community‐wide eradication of HIV is feasible if ℛ0 &lt; ℛ∗, where ℛ∗ is some threshold quantity less than unity. Furthermore, for the bistability case (which occurs when ℛ∗ &lt; ℛ0 &lt; 1), it is shown that HIV eradication is dependent on the initial sizes of the subpopulations of the model.

Ticks and tick-borne diseases in Africa: a disease transmission model

A general disease transmission model is developed for a tick-borne disease for cattle. Both the tick and cow are possible hosts for the disease parasite. The two species are therefore classified as infected or uninfected. The tick individual is further classified as sedentary (off-host) or feeding (on-host). First conditions for the persistence of the tick population are investigated. A threshold quantity for the disease is derived which is dependent on both the tick and host population parameters and the two transmission rates: from ticks to cattle and vice versa. From the analysis persistence and non-persistence conditions for both the tick population and the disease are investigated. The effect of the presence of a second host species is introduced as an additional feature in the analysis.

Technological man‐made disaster precondition phase model for major accidents

Major hazard organizations are dealing with hazardous material exceeding the threshold quantity. Major hazard organizations are relatively secure areas and cannot fail from single error. However, failure of an organization to control hazardous material usually results in a technological man‐made disaster. The conditions preceding the onset of technological man‐made disaster are collectively called the technological man‐made disaster precondition phase “incubation period”. A model has been developed representing the technological man‐made disaster pre‐condition phase where it focuses on the origin of the technological man‐made disaster. The model was based on detailed analysis of four technological man‐made disasters at major hazard installations in Malaysia.

Reproductive allocation by the blow fly Lucilia sericata in response to protein limitation

Abstract.Adult females of the anautogenous blow fly Lucilia sericata (Meigen) (Diptera: Calliphoridae) were fed standardized meals of liquidized liver, in quantities shown to range around the minimum required to initiate yolk deposition. Females from each feeding regime were dissected at daily intervals between 4 and 11 days of age; the number and stage of development of all oöcytes were recorded. Once an initial threshold quantity of protein was ingested, yolk deposition was initiated in all available oöcytes. Subsequently, one of two distinct developmental pathways was followed: arrested development in all oöcytes at an early stage of yolk deposition, or more extensive yolk deposition followed by progressive oösorbtion and the maturation of small batches of eggs. The proportion of females showing oösorbtion relative to arrested follicular development increased with increasing protein meal size, suggesting that the difference in response may be triggered by a second protein threshold, either side of which the arrested development or oösorbtion pathways are followed. The behaviour observed may reflect strategies to maximize reproductive output in this short‐lived, resource‐limited insect species. Flies that display arrested development may have sufficient protein to mature few if any complete eggs, but may subsequently be able to mature a full egg‐batch if they obtain further protein meals; this possibility is offset by the risk of death before finding such a meal. Flies that show oöcyte development and oösorbtion produce smaller egg batches more quickly and hence have a higher probability of achieving at least some reproductive output. By initiating yolk deposition in all oöcytes, female L. sericata retain the potential to adopt either developmental pathway, depending on subsequent protein intake.