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Children use one-to-one correspondence to establish equality after learning tocount
Humans make frequent and powerful use of external symbolsto express number exactly, leading some to question whetherexact number concepts are only available through the acqui-sition of symbolic number systems. Although prior work hasaddressed this longstanding debate on the relationship betweenlanguage and thought in innumerate populations and semi-numerate children, it has frequently produced conflicting re-sults, leaving the origin of exact number concepts unclear.Here, we return to this question by replicating methods pre-viously used to assess exact number knowledge in innumer-ate groups, such as the Pirah Ìa, with a large sample of semi-numerate US toddlers. We replicate previous findings fromboth innumerate cultures and developmental studies showingthat numeracy is linked to the concept of exact number. How-ever, we also find evidence that this knowledge is surprisinglyfragile even amongst numerate children, suggesting that nu-meracy alone does not guarantee a full understanding of exact-ness
Self-reporting dynamic covalent polycarbonate networks
Here, we report the first-time development of polycarbonate networks with self-reporting thermoreversible bonding/debonding on demand properties. The reversible linkages within the network are based on a HeteroâDielsâAlder (HDA) moiety, which is able to undergo cleavage and rebonding as a function of temperature within minutes. As HDA pair a phosphoryl dithioester and a cyclopentadiene moiety are employed as bonding and debonding take place in the temperature range between 25â120 °C. The degradation and rebonding can be readily traced by visible inspection due to the self-reporting nature of the HDA moiety. In order to prove the reversibility, linear polycarbonates (Mw = 4.200â20.000 g molâ1) including the reversible linkage in each repeating unit were generated and carefully analyzed using size exclusion chromatography (SEC), UV/Vis analysis and high temperature 1H NMR spectroscopy. Subsequently, polycarbonate networks bearing HDA units â allowing the networks to be fully degraded into small molecules â were synthesized, debonded and bonded several times in the temperature range between 25 and 120 °C within minutes. The present study thus introduces fully degradable polycarbonate networks based on a facile chemical concept as a viable alternative to networks based on CâC bond formation that disallow a complete degradation
Untapped toolbox of luminol based polymers
The objective of the current Perspective article is to highlight the present state of luminol based polymers, with a specific emphasis on how to include luminol derivatives into polymer chains using both electrochemical and chemical techniques with an underline on new synthetic methods. Importantly, the current limitations that limit the expansion of polymeric luminol derivatives will be discussed by drawing attention to the challenges of solubilising monomers, the harsh conditions leading to undesired side reactions during the polymerization process or the necessity of orthogonal post-modification reactions. Importantly, the article discusses the remaining challenges within the field, while suggesting strategies for the advancement of this versatile class of polymers
Prevent or Cure - The Unprecedented Need for Self-Reporting Materials
Selfâreporting smart materials are highly relevant in modern soft matter materials science, as they allow for the autonomous detection of changes in synthetic polymers, materials, and composites. Despite critical advantages of such materials, for example, prolonged lifetime or prevention of disastrous material failures, they have gained much less attention than selfâhealing materials. However, as diagnosis is critical for any therapy, it is of the utmost importance to report the existence of system changes and their exact location to prevent them from spreading. Thus, we herein critically review the chemistry of selfâreporting soft matter materials systems and highlight how current challenges and limitations may be overcome by successfully transferring selfâreporting research concepts from the laboratory to the real world. Especially in the space of diagnostic selfâreporting systems, the recent SARSâCoVâ2 (COVIDâ19) pandemic indicates an urgent need for such concepts that may be able to detect the presence of viruses or bacteria on and within materials in a selfâreporting fashion
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