[1] A mathematical model describes silicate mineral weathering processes in modern soils located in the boreal coniferous region of northern Europe. The process model results demonstrate a stabilizing biological feedback mechanism between atmospheric CO 2 levels and silicate weathering rates as is generally postulated for atmospheric evolution. The process model feedback response agrees within a factor of 2 of that calculated by a weathering feedback function of the type generally employed in global geochemical carbon cycle models of the Earth's Phanerozoic CO 2 history. Sensitivity analysis of parameter values in the process model provides insight into the key mechanisms that influence the strength of the biological feedback to weathering. First, the process model accounts for the alkalinity released by weathering, whereby its acceleration stabilizes pH at values that are higher than expected. Although the process model yields faster weathering with increasing temperature, because of activation energy effects on mineral dissolution kinetics at warmer temperature, the mineral dissolution rate laws utilized in the process model also result in lower dissolution rates at higher pH values. Hence, as dissolution rates increase under warmer conditions, more alkalinity is released by the weathering reaction, helping maintain higher pH values thus stabilizing the weathering rate. Second, the process model yields a relatively low sensitivity of soil pH to increasing plant productivity. This is due to more rapid decomposition of dissolved organic carbon (DOC) under warmer conditions. Because DOC fluxes strongly influence the soil water proton balance and pH, this increased decomposition rate dampens the feedback between productivity and weathering. The process model is most sensitive to parameters reflecting soil structure; depth, porosity, and water content. This suggests that the role of biota to influence these characteristics of the weathering profile is as important, if not more important, than the role of biota to influence mineral dissolution rates through changes in soil water chemistry. This process-modeling approach to quantify the biological weathering feedback to atmospheric CO 2 demonstrates the potential for a far more mechanistic description of weathering feedback in simulations of the global geochemical carbon cycle.
A central aspect of learning chemistry is learning to relate observations of phenomena to models of the sub-microscopic level of matter, and hence being able to explain the observable phenomena. However, research shows that students have difficulties discerning and comprehending the meaning of the sub-micro level and its models, and that practical work in its traditional form fails to help students to discern the relation between observations and models. Consequently, there is a strong call for new teaching activities to address these issues. This paper emerges from a growing number of studies showing that learning is supported when students are set to cooperatively create their own multimodal representations of science phenomena. In this paper, we explore the approach of letting students create their own stop-motion animation as a means to explain observations during practical work. The students’ work of producing a phenomenon in the laboratory and creating an animation was recorded (audio–video) to capture students’ verbal and non-verbal interactions and use of resources. Data was analysed using a thematic content analysis with a deductive approach aimed at identifying the aspects of chemistry content that are being reasoned. The analysis showed that the task enabled students to engage in reasoning concerning both the observations and the sub-micro-level models, and how they relate to each other. The task also enabled students to reason about features of the representation that are needed to make sense of both the observational and sub-microscopic aspects of a phenomenon, as well as reflecting upon the meaning of a model.
Awareness of infant mental health has steadily been growing in South Africa. The University of Cape Town Parent-Infant Mental Health Service serves the under three population in two areas in Cape Town. The challenges that face professionals when working in a traditional community are numerous. Besides the problems that poverty bring, there are the differences in cultures that need to be understood and engaged with. Although South Africa is now in the phase of integrating its cultural diversity, professional training has been based on western models. These models place the emphasis on individual, personal relationships. The African worldview, however, includes a deep awareness of the importance of the collective community. The sense of person-hood is rooted in this consciousness. For psychotherapy in South Africa to be relevant and appropriate, professionals working in this field have to be aware and genuinely respectful of differences between the various cultural groups. The complexity of two cultures meeting without sufficient awareness of difference is illustrated in the failed psychotherapy of a mother-infant dyad that resulted in attempted infanticide. This highlights the shortcomings of a psychotherapy based on dyadic attachment models only.RESUMEN: El conocimiento de la salud mental infantil ha crecido constantemente en Sudáfrica. Los servicios de salud mental para padres e infantes en la Universidad de la Ciudad del Cabo ayudan a la triple población baja en dos áreas de esta capital. Los retos que los profesionales encuentran cuando trabajan en una comunidad tradicional son numerosos. Además de los problemas que aporta el estado de pobreza, están las diferencias culturales, las cuales necesitan ser comprendidas y asimiladas. Mientras que Sudáfrica está ahora en la fase de integración de su diversidad cultural, el entrenamiento profesional ha estado basado en los modelos occidentales. Estos modelos ponen énfasis en las relaciones individuales y personales. Sin embargo, la perspectiva mundial que tiene el africano incluye un profundo conocimiento de la importancia de la comunidad en forma colectiva. El sentido de lo que significa ser persona tiene raíces en este tipo de consciencia colectiva. Para que la sicoterapia tenga relevancia en Sudáfrica y al mismo tiempo sea apropiada, los prefesionales que trabajan en este campo tienen que estar conscientes y ser genuinamente respetuosos de las diferencias entre los varios grupos culturales. Lo complejo de dos culturas que se encuentran sin el suficiente conocimiento de las diferencias se ilustra en la fallida sico- 266• A. Berg terapia de una díada --madre e infante--, la cual resultó en un intento de infanticidio. Esto subraya los puntos débiles de la sicoterapia que se basa en los modelos de afectividad que solamente toman en cuenta una díada.RÉ SUMÉ : La prise de conscience de la santé mentale du nourrisson grandit régulièrement en Afrique du Sud. Le Service de Santé Mentale du Nourrisson de l'Université de Cape Town sert la population de moins de tr...
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