Diseases and parasites play a major role in most ecosystem dynamics; yet, they have received relatively little attention in ecological modelling [1–3]. Traditionally, ecologists have mostly considered disease outbreaks as disturbances rather than as an integral part of the ecosystem dynamics [4]. However, there is mounting evidence that diseases and parasites play a vital role in the stability and dynamics of most ecosystems [5–9].

In this paper we will consider the effects of a disease that specifically infects juvenile individuals and subsequently prevents the infected individual from producing offspring. The work is inspired by the interaction between the tape worm Ligula intestinalis and its cyprinid fish host species roach (Rutilis rutilis). The parasite has a complex life cycle, involving three host species. The final host species of the parasite are fish eating birds, such as cormorant (Phalacrocorax carbo), grey herron (Ardea cinerea), and great crested grebe (Podiceps cristatus) [10]. In this final host the parasite completes its sexual cycle and produces eggs, which are shed to the water via the faeces of the birds. The larvae of the parasite are eaten by copepods, which in turn are a primary food source for the juvenile fish. After a fish is infected, the parasite settles and grows in the host gut system and may obtain a staggering weight of up to half the host weight [11]. Surprisingly, the physical condition of such a fish-parasite combination can be not noticeably different from uninfected individuals [12]. However, the consequences for the infected fish are severe, as the parasites supress gonad development and consequently prevent the individual from maturing. Even infection with a single parasite can act to sterilize the infected fish [12]. Furthermore, the parasite might induce behavioural changes, such as directing the infected fish to move to the littoral zone, where it can be caught more easily by the fish eating birds and thus complete the parasite life cycle [13,14].

Also the consequences of the parasite infection on the host population dynamics can be extensive. A well-documented case are the recurrent Ligula parasite outbreaks in the roach population of lake Slapton Ley [11,15,16]. The roach population in this lake shows a tendency to build-up a so-called stunted population. In this population state, small juvenile individuals are very numerous. This causes exploitation competition amongst juveniles to be so fierce, that individual growth rate substantially slows down, effectively preventing juveniles from reaching the size necessary for maturation [16,17].

In this stunted population situation, the Ligula parasite can cause a large epidemic, reaching a prevalence of more than 70% of all juveniles being infected [11]. This in turn seems to act to relieve the stuntedness in the juvenile population, causing a reduction in the juvenile population size, with a subsequent acceleration in juvenile growth and maturation, accompanied by a strong reduction of the parasite prevalence. However, hereafter, the stuntedness in the host population slowly rebuilds, after which a second epidemic of the parasite can occur. In the case of the Slapton Ley dataset, such recurrent epidemics were recorded three times, spanning a total period of 31 years [11].

In this paper we will study a mathematical model to investigate the interplay between ecological population dynamics of a potentially stunted population and a disease. Furthermore, we will study the interaction between the disease and a natural predator of the host. In the Ligula–Roach system there are several predators on Roach, including Northern Pike (Esox Lucius) and European Perch (Perca fluvitilis). Often, such predator species are of commercial or recreational interest for fisherman, and stunting of the prey species can greatly affect predator numbers or predator quality. Here, we will study the potential indirect influence of a prey disease on the predator species. For the ecological baseline, we will use a model that we have introduced before for the dynamics of a structured prey population and a predator that attacks adult prey [18,19]. In this model a stunted juvenile prey population can build up due to a maturation bottleneck, and it has a parameter region of bistability between a stunted and non-stunted equilibrium state [19]. To this system we will add a disease that specifically infects juvenile individuals, and that acts to sterilize these individuals and prevents maturation. In this way we can study the indirect interaction between a predator and a disease, that both attack the same host species, but each targeting a different host life stage. For mathematical simplicity, we model a disease that spreads through direct contact. This differs from the parasite infection in the Ligula-Roach system, where the parasite has to pass through two additional host stages. Our simplified model would roughly correspond to a constancy assumption in the copepod and bird populations. Furthermore, we do not explicitly account for individual parasite load, but instead we only distinguish between infected and uninfected individuals.

Our main objective in this paper is to study the effects of a disease that infects and sterilizes juvenile individuals on the population dynamics of its host species. In particular, we will focus on a system where the host population is in a stunted population state, which is strongly dominated by juvenile individuals and where individual growth rate and maturation are strongly reduced. We will map the dynamic consequences of introducing such a disease in a stunted host population state. It will turn out that these consequences strongly depend on the ability of infected juveniles to compete with uninfected conspecifics. We will discuss the biological implications of our results.

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@zaasmi said in MCM610 GDB1 Solution and discussion:

‘In the Public Interest’ is an excessively used cliché in mass media. What do you know about it?

Media are the communication outlets or tools used to store and deliver information or data. The term refers to components of the mass media communications industry, … By the mid-1960s, the term had spread to general use in North America and the … The meaning of electronic media, as it is known in various spheres, has …

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@zareen said in IT430 GDB1 Solution and discussion:

Do you think that in hash function can be decrypted and reversible?

No, they cannot be decrypted. These functions are not reversible. There is no deterministic algorithm that evaluates the original value for the specific hash.

However, if you use a cryptographically secure hash password hashing then you can may still find out what the original value was. These functions were designed to produce hash codes for big volumes of data / files. That is why they were designed to be very fast. It is relative easy to calculate MD5 and SHA1 hashes over a big number of inputs and use that to create a reverse lookup table.

Reff

@zaasmi said in ENG508 GDB1 Solution and discussion:

What are the benefits and barriers of e-learning with reference to linguistic courses? Do you find an effective guidance from the instructors for your course activities?

Online facilitated and instructor-led courses are usually organized into … used to the online learning platform and for administrators to see if there are any … The course consists of a series of learning activities that can be scheduled on a weekly … learners are too shy or lack language fluency to collaborate effectively in real …

FXAA is the most interesting group of anti-aliasing techniques, these algorithms perform their duties during scene post-processing, after the rendering process. They are all shader-based and cause little to no performance drop, which is their most important advantage. Image quality can vary from one algorithm to another. For example, FXAA is known to make the image look a bit blurry, obviously to the chagrine of some players. Another commonly used technique is SMAA, which usually provides better quality than FXAA while getting around, or at least reducing, the blur effect. Game developers tend to implement their own post-process anti-aliasing algorithms as well. Some of the notable examples are CMAA in Grid: Autosport, AAA (heavily modified FXAA to eliminate blurring) in Metro: Last Light, and T-AA in Rainbow Six: Siege. There are also “injectors” that enable these techniques in games that don’t support post-process anti-aliasing natively.

@zareen said in BT505 GDB1 Solution and discussion:

“Discuss Biosignals”

A biosignal is any signal in living beings that can be continually measured and monitored. The term biosignal is often used to refer to bioelectrical signals, but it may refer to both electrical and non-electrical signals.

Biosignals provide communication between biosystems and are our primary source of information on their behavior. Interpretation and transformation of signals are major topics of this text. Biosignals, like all signals, must be carried by some form of energy. Biosignals can be measured directly from their biological source, but often external energy is used to measure the interaction between the physiological system and external energy. Measuring a biosignal entails converting it to an electric signal using a device known as a biotransducer. The resultant analog signal is often converted to a digital (discrete-time) signal for processing in a computer.

Biosignals and the systems that produce them have several important properties: they can be stationary or nonstationary, linear or nonlinear, and deterministic or stochastic (i.e., random). Biosignals often contain noise, which is an unwanted signal component.

Biosystems modeling is a powerful analytical tool for investigating living systems. Two very different models have been developed to represent physiological systems: analog models and system models. Each representation has different strengths and weaknesses.

The goal of this book is to present the most important and fundamental of the many powerful signal and systems analysis tools available to biomedical engineers.

link text

In the two families of nucleic acids, ribonucleic acid (RNA) and deoxyribonucleic acid (DNA), the sequence of nucleotides in the DNA or RNA codes for the structure of proteins synthesized in the cell. The nucleotide adenosine triphosphate (ATP) supplies the driving force of many metabolic processes. Several nucleotides are coenzymes; they act with enzymes to speed up (catalyze) biochemical reactions.

The nitrogen-containing bases of nearly all nucleotides are derivatives of three heterocyclic compounds: pyrimidine, purine, and pyridine. The most common nitrogen bases are the pyrimidines (cytosine, thymine, and uracil), the purines (adenine and guanine), and the pyridine nicotinamide.

The nucleotides are of great importance to living organisms, as they are the building blocks of nucleic acids, the substances that control all hereditary characteristics.

@zareen said in BT201 GDB1 Solution and discussion:

Discuss some features of protists.

Characteristics of Protists?
What Is Kingdom Protista?

Imagine you are cleaning or organizing around your house. To assist in this process, you separate your items into categories to help you locate them later. Maybe you have a box for books, a drawer for school supplies, and a cubby for electronics. You start to realize, however, that you have a bunch of extra bits and pieces that do not fit into any of your other groups. So, you create a special container for them: your ‘other’ container. This is pretty much what happened with Kingdom Protista.

All the life on planet Earth is organized into five kingdoms based on whether or not the organism is single-celled, how it obtains energy, and how (or if) it moves. Kingdom Protista is the hodge-podge category. It contains the protists, or the organisms that do not fit into any of the other categories.

Protista is Greek for the very first. These organisms were traditionally considered the first eukaryotic forms of life, predecessors to the organisms in the plant, animal, and fungus kingdoms. Eukaryotes are organisms whose cells have membrane-bound organelles. This is opposed to prokaryotes, single-celled organisms lacking a nucleus.
Characteristics of Protists

Protists are eukaryotic organisms that cannot be classified as a plant, animal, or fungus. They are mostly unicellular, but some, like algae, are multicellular. Kelp, or ‘seaweed,’ is a large multicellular protist that provides food, shelter, and oxygen for numerous underwater ecosystems. Even though kelp resembles a plant, it is not classified into Kingdom Plantae because it lacks the cellular complexity of plant cells.

Protists can be heterotrophic, which means they obtain the energy they need to live by consuming other organisms. Or, they can be autotrophic, which means they obtain energy from the environment through photosynthesis, the process of capturing light energy and storing it in carbohydrates.

Protists primarily live in water, though some live in moist soil. They can be found almost anywhere on Earth where there is liquid water, even in humans.
Classification of Protists

Protists are grouped by how they move and how they obtain nutrients. They are arranged into three main categories: animal-like protists, plant-like protists, and fungus-like protists.

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