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When acids come into contact with concrete, they initiate a chemical reaction that dissolves the hydrated cement paste. This process leads to softening and structural weakening of the concrete. This issue is commonly observed in environments such as chimneys, sewers, and industrial settings. The severity of the damage increases as the pH of the water interacting with the concrete drops below 6.5. In particular, a pH under 4.5 can cause significant concrete damage.
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A reversible chemical reaction represents a chemical process that proceeds in both forward (left to right) and reverse (right to left) directions. When the rates of the forward and reverse reactions are equal, the concentrations of the reactant and product species remain constant over time and the system is at equilibrium. A special double arrow is used to emphasize the reversible nature of the reaction. The relative concentrations of reactants and products in equilibrium systems vary greatly;...
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In circuit analysis, situations often arise where resistors are neither in series nor parallel configurations. To tackle such scenarios, three-terminal equivalent networks like the wye (Y) (Figure 1 (a)) or tee (T) and delta (Δ) (Figure 1 (b)) or pi (π) networks come into play. These networks offer versatile solutions and are frequently encountered in various applications, including three-phase electrical systems, electrical filters, and matching networks.
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Related Experiment Video

Updated: Feb 2, 2026

Use of an Optical Trap for Study of Host-Pathogen Interactions for Dynamic Live Cell Imaging
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Pathogen dynamics under both bottom-up host resistance and top-down hyperparasite attack.

Steven R Parratt1, Anna-Liisa Laine1

  • 1Research Centre for Ecological Change University of Helsinki Helsinki Finland.

The Journal of Applied Ecology
|November 20, 2018
PubMed
Summary
This summary is machine-generated.

Host resistance significantly impacts plant pathogen spread, while hyperparasites are more effective against later pathogen life stages. Top-down control by natural enemies is crucial for managing powdery mildew.

Keywords:
Ampelomyces spp.Plantago lanceolataPodosphaera plantaginisbottom‐updisease biologyhyperparasiteplant pathogentop‐down

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Area of Science:

  • Ecology and Evolutionary Biology
  • Plant Pathology
  • Population Dynamics

Background:

  • Population dynamics are influenced by bottom-up (host resistance) and top-down (natural enemies) control.
  • Research in infectious disease biology often prioritizes bottom-up host resistance over top-down pathogen control.
  • The role of natural enemies, like hyperparasitic fungi, in controlling plant pathogens has been largely overlooked.

Purpose of the Study:

  • To investigate the effects of host genotype and hyperparasite infection on plant pathogen dynamics.
  • To explore the interaction between host resistance and hyperparasitism in controlling powdery mildew (Podosphaera plantaginis).
  • To determine the key factors influencing pathogen spread in semi-natural and laboratory settings.

Main Methods:

  • A semi-natural field experiment was conducted to assess hyperparasite infection, host resistance, and spatial structure impacts on pathogen spread.
  • A laboratory-based inoculation approach was used to test findings across multiple pathogen-host genetic combinations.
  • The study examined hyperparasite effects on pathogen establishment, early epidemic growth, transmission, and later life-history stages.

Main Results:

  • Hyperparasite infection showed negligible effects on early-stage within-host infection and between-host pathogen spread.
  • Host-plant resistance was the primary factor determining plant infection, while host genotype and proximity to the source influenced severity.
  • Laboratory studies indicated hyperparasitism reduced infection severity and negatively affected pathogen overwintering structure production.

Conclusions:

  • Bottom-up host resistance is critical for pathogen spread, but top-down control by hyperparasites is more effective against later pathogen life stages.
  • While hyperparasites can reduce pathogen growth in controlled lab conditions, this effect was not observed in a semi-natural environment.
  • Understanding hyperparasite impacts across a pathogen's life history is essential for developing effective biocontrol strategies.