Rheological and flow birefringence studies of rod-shaped pigment nanoparticle dispersions

We study rheological and rheo-optical properties of suspensions of anisometric pigment particles in a non-polar fluid. Different rheological regimes from the dilute regime to an orientationally arrested gel state were characterized and compared with existing theoretical models. We demonstrate the intricate flow behaviour in a wide range of volume fractions. A unique combination of the optical properties of the particles results in a giant rheo-optical effect: an unprecedentedly large shear stress-induced birefringence was found in the isotropic range, exhibiting a sharp pre-transitional behaviour

Comparison of winter and summer activity of ants in Icelandic geothermal areas

Maurar hafa borist um jarðkringluna alla með mönnum. Á síðustu árum hafa fundist um 25 tegundir maura á Íslandi. Einungis tvær þessara tegunda geta lifað óháð manngerðu umhverfi en það er Húsamaur (H. ergatandria) og Hveramaur (H. eduardi). Báðar tegundirnar hafa fundist á jarðhitasvæðum víðsvegar um landið. Rannsóknir síðustu ára hafa að mestu kannað útbreiðslu og þéttleika þessara tegunda að sumri til. Markmið þessa verkefnis var að meta útbreiðslu og þéttleika þessara tegundanna á hverasvæðum að vetri til. Skoðuð voru sjö svæði frá janúar til apríls, og til samanburðar voru notuð gögn frá fimm svæðum sem könnuð voru sumarið 2022. Í ljós kom að yfir veturinn voru einungis hveramaurar virkir í þeim hverasvæðum sem voru skoðuð en engir húsamaurar fundust. Líklegt er að húsamaurar grafi sig dýpra niður í jarðveginn og fari í vetrardvala. Áhugavert er að þéttleiki hveramaura var töluvert hærri að vetri til en að sumri, orsakir þess eru ekki þekktar. Ekkert fannst af eggjum, lirfum eða púpum mauranna í vetrarskoðununum en það gæti bent til þess að maurarnir stöðvi framleiðslu ungviðis yfir vetrarmánuðina. Auk maura var einnig dreifing annarra hryggleysingja metin. Þá kom í ljós að veikt samband var milli dreifingu maura og annarra hryggleysingja að vetri til en þetta samband var ekki að finna að sumri til. Sýru- og rakastig jarðvegs virtist hafa lítil áhrif á dreifingu beggja hryggleysingjahópanna en maurar virtust bundnir við ákveðin hitamörk. Í ljós kom að kjörhitastig maura að sumri og vetri var nánast hið sama (25,7°C að sumri, 26,1°C að vetri) sem bendir til að hveramaurarnir hafi mjög afmarkað hita og kuldaþol sem er líklegt til að hindra varanlega útbreiðslu út fyrir hverasvæði eða manngerð umhverfi. Niðurstöður þessarar rannsóknar sýna að Hveramaurar séu vel búnir fyrir líf á Íslenskum hverasvæðum. Þar að auki eru þessar niðurstöður mikilvægur liður að svari stóru ráðgátunnar um uppruna maura á Íslandi.Ants have spread around the globe with humans, and even invaded Iceland. In recent years some 25 different species of ants have been found in Iceland. Only two of these can, however, survive outside of human-made habitats for extended periods of time. These are the ponerine ants H. ergatandria and H. eduardi. Both species have been found in geothermal areas across Iceland though their distribution has only been surveyed during summer. This project aims to study the distribution, density and activity of these two species during the winter months. To this end we surveyed seven different areas between January and April of this year and compared these results to data gathered in five geothermal areas during the summer of 2022. It was revealed that only individuals of H. eduardi were active during the winter months, as no individuals of H. ergatandria were found in winter. It is likely that H. ergatandria buries further down into the ground and hibernates. Interestingly, the density of H. eduardi was found to be markedly higher during the winter months in the sampled patches though the reason for this remains unknown. No eggs, larvae, or pupae were found during the winter surveys, which may indicate a pause in the production of offspring by the colonies over the winter months. In addition to the ants, we also surveyed the abundance of other invertebrates. It became clear that there was some correlation between the number of ants and other invertebrates during winter though this correlation was absent during summer. Both acidity and humidity seemed to have no effect on the distribution of ants and invertebrates though the ants were found to be tied to a specific heat range. It was discovered that the thermal optimum of ants was nearly identical during winter and summer (25,7°C in summer, 26,1°C in winter). This observation could indicate that permanent habitation outside of geothermal areas in Iceland is unlikely for these species. The results of this study make it clear that H. eduardi is well suited to life in Icelandic geothermal areas. This study is also an important factor of the larger question about the origin of the amts in Iceland.Ameisen sind mit der Hilfe von Menschen rund um den Globus gereist. In den letzten Jahren sind in Island etwa 25 verschiedene Ameisenarten gefunden worden. Nur zwei dieser Arten können in Island ausserhalb von menschlich geschaffenen Lebensräumen existieren. Diese zwei Arten sind H. ergatandria und H. eduardi. Beide Arten können in isländischen Geothermalgebieten gefunden werden, weit von beheizten Gebäuden entfernt. In den letzten Jahren haben Feldstudien der isländischen Universität die Verbreitung von Ameisen während der Sommerzeit dokumentiert, aber es gab noch keine Studien über die Winteraktivität von Ameisen in isländischen geothermalen Gebieten. Das Ziel dieses Projekts war es, die Aktivität von Ameisen in isländischen geothermalen Gebieten während des Winters zu untersuchen. Zwischen Januar und April 2023 wurden sieben verschiedene Gebiete untersucht und mit fünf älteren Untersuchungen vom Sommer 2022 verglichen. Es zeigte sich, dass während des Winters nur H. eduardi in den geothermalen Gebieten sichtbar war, aber keine Individuen von H. ergatandria gefunden werden konnten. Wahrscheinlich ist, dass H. ergatandria sich tiefer in die Erde graben, um dort in Winterstarre verfallen. Interessant ist, dass die Dichte von H. eduardi während der Wintermonate höher war. Der Grund dafür ist noch unbekannt. Während der Winterzeit wurden keine Eier, Larven oder Puppen gefunden, was darauf hinweist, dass diese Ameisen im Winter die Produktion von Eiern einstellen. Es wurde auch festgestellt, dass sich die Ameisen während des Sommers und Winters in nahezu identischen Bodentemperaturbereichen aufhalten. Zusätzlich zu den Ameisen haben wir auch die Verbreitung anderer Wirbellosen untersucht. Im Winter ist eine gewisse Korrelation zwischen der Verbreitung von Ameisen und anderen Wirbellosen vorhanden, die jedoch im Sommer nicht zu finden ist. Sowohl die Säure als auch die Luftfeuchtigkeit schienen keinen Einfluss auf die Verbreitung von Ameisen und anderen Wirbellosen zu haben, obwohl festgestellt wurde, dass die Ameisen an einen bestimmten Temperaturbereich gebunden waren. Die Ergebnisse dieser Studie zeigen deutlich, dass H. eduardi gut an das Leben in den geothermalen Gebieten Islands angepasst ist. Diese Studie gibt wichtige Daten, die uns helfen werden, die größere Frage zu beantworten über den Ursprung der Ameisen in Island