We demonstrate an experimental method for measuring quantum state degeneracies in bound state energy spectra. The technique is based on the general principle of detailed balance, and the ability to perform precise and efficient measurements of energy-dependent tunnelling-in and -out rates from a reservoir. The method is realized using a GaAs/AlGaAs quantum dot allowing for the detection of time-resolved single-electron tunnelling with a precision enhanced by a feedback-control. It is thoroughly tested by tuning orbital and spin-degeneracies with electric and magnetic fields. The technique also lends itself for studying the connection between the ground state degeneracy and the lifetime of the excited states.
It is common to see students multitasking or switching between different tasks on the computer while also listening to the teacher lecture in the front of a classroom. In today's classrooms, students have much greater control over how they use their time, with the classroom integration of computers and mobile devices combined with social media and text-based chat tools. It is important to understand how students learn with the connected technologies. This study examines high- school students' ability to take notes and obtain information from a video while simultaneously carrying a conversation online with a friend. This study examines issues related to media multitasking and learning in educational environments. The rise of connected devices in the classroom has increased the level of multitasking during lectures and lessons. Students are often observed taking notes while texting a friend on their phone or updating their Facebook page. Students can be observed performing these types of dual-tasks throughout the day and it has become a natural part of how they function. What is the cognitive cost of this practice? Poldrack and Foerde (2007) found that people had a harder time learning new things when their brains were distracted by another activity. The Functional Magnetic Resonance Images (fMRIs) used by researchers showed that when people learned without distraction, an area of the brain known as the hippocampus was involved. This region of the brain is critical to the processing and storing of information. However, the hippocampus was not engaged when people learned while multitasking. Instead, the region of the brain called the striatum was activated. The striatum is activated by stimuli associated with reward or by stimuli associated with aversive, novel, unexpected or intense experiences (Schultz, 2010). Results indicated that learning while distracted or multitasking would alter the brain's learning processes and change the way people learn (Poldrack & Foerde, 2007). Foerde, Knowlton, and Poldrack (2006) found that learning new things is dependent on working memory where as habit learning is not as sensitive to working memory. Some tasks such as learning new skills may require high cognitive loads, while other familiar and automatic tasks may require lower cognitive loads. Lin and Bigenho (2012) examined undergraduate student's memory recall under nine conditions in a 3x3 study with three levels of environmental distraction and three levels of note-taking. The study found significant interactions between environment and method of note-taking as the computer seemed to mediate the effect of an auditory distraction during computer aided note taking. The study also found that students were more successful when taking notes at lower levels of distraction and that those who did not take notes consistently performed poorly on the recall tasks regardless of distraction level.
SUMMARY 1. Two experiments were performed with periphytic diatoms originating from the River Lot (France) and allowed to grow on clean substrata within indoor artificial streams. Three cadmium (Cd) levels (control, low Cd=10 μg L −1 and high Cd=100 μg L −1 ) were used to test the effects of Cd on (i) the settlement and development of diatom communities (Experiment 1, 4 weeks Cd exposure) and (ii) predeveloped communities grown over a 2‐week period without contamination (Experiment 2, 2 weeks Cd exposure). 2. Experiment 1 revealed that growth and taxonomic composition of diatom communities clearly differed with Cd exposure. Biofilms were more adpressed to substrata under low Cd concentration, and were thinner and patchy under high Cd concentration. 3. Exposure of developed diatom communities (Experiment 2) to Cd revealed only minor variations in taxonomic composition, possibly linked to the protective role of the developed organic matrix against metal stress. 4. These results support the validity of periphytic diatom communities as indicators of metal pollution, although significant structural changes would take longer within developed communities.
Une demarche methodologique en plusieurs etapes a ete developpee afin d'evaluer les effets de la pollution metallique sur la structure des communautes de diatomees periphytiques, associant des etudes multispecifiques realisees dans les conditions complexes du milieu naturel, puis dans les conditions simplifiees du laboratoire. Les etudes de terrain ont ete menees au niveau du gradient de pollution polymetallique (Cd/Zn) de la riviere Lot (SO, France). Les resultats des differentes approches experimentales ont globalement presente une tres grande complementarite. Une reduction marquee de l'architecture en trois dimensions des biofilms periphytiques a ete mise en evidence dans le cas d'une exposition a la pollution intervenant des la phase initiale du developpement des communautes. L'etude parallele de communautes exposees aux metaux a un stade avance de developpement (maturite) a permis de mettre en evidence le role protecteur exerce par la matrice organique des biofilms periphytiques vis-a-vis de la pollution metallique. Les resultats ont egalement apporte des informations sur le comportement de plusieurs especes de diatomees face aux metaux, certains taxons - comme Melosira varians ou Nitzschia dissipata - semblant presenter une grande sensibilite, alors que d'autres - comme Achnanthidium minutissimum, Encyonema minutum, Cyclostephanos dubius, Nitzschia palea, Rhoicosphenia abbreviata, Cocconeis placentula ou Fragilaria crotonensis -, ont presente une grande tolerance a la pollution par le cadmium, pour les niveaux experimentaux testes. Une etude complementaire monospecifique, menee au niveau d'une population d'Achnanthidium minutissimum cultivee en milieu controle, a permis de preciser le comportement de cette espece par rapport a la contamination par le cadmium. L'ensemble des ces etudes revele la pertinence des communautes de diatomees periphytiques en tant qu'indicateurs biologiques de la pollution metallique.
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