title: A hydrothermally precipitated catalytic iron sulphide membrane as a first step toward life

authors: Russell, Michael J.

subjects: botryoid

abstract: We propose that life emerged from growing aggregates of iron sulphide bubbles containing alkaline and highly reduced hydrothermal solution. These bubbles were inflated hydrostatically at sulphidic submarine hot springs sited some distance from oceanic spreading centers four billion years ago. The membrane enclosing the bubbles was precipitated in response to contact between the spring waters and the mildly oxidized, acidic and iron-bearing Hadean ocean water. As the gelatinous sulphide bubbles aged and were inflated beyond their strength they budded, producing contiguous daughter bubbles by the precipitation of new membrane. [Fe2S2]+/0 or [Fe4S4]2+/+ clusters, possibly bonded by hydrothermal thiolate ligands as proferredoxins, could have catalyzed oxidation of thiolates to disulphides, thereby modifying membrane properties. 
We envisage the earliest iron sulphide bubbles (pro botryoids) first growing by hydrostatic inflation with hydrothermal fluid, but evolving to grow mainly by osmosis (the protocellular stage), driven by (1) catabolism of hydrothermal abiogenic organics trapped on the inner walls of the membrane, catalyzed by the iron sulphide clusters; and (2) cleavage of hydrophobic compounds dissolved in the membrane to hydrophilic moieties which were translocated, by the proton motive force inherent in the acidic Hadean ocean, to the alkaline interior of the protocell. The organics were generated first within the hydrothermal convective system feeding the hot springs operating in the oceanic crust and later in the pyritizing mound developing on the sea floor, as a consequence of the reduction of CO, CO2, and formaldehyde by Fe2+- and S2–-bearing minerals.
We imagine the physicochemical interactions in and on the membrane to have been sufficiently complex to have engendered auto- and cross-catalytic replication. The membrane may have been constructed in such a way that a  successful  parent could have  informed  the daughters of membrane characteristics functional for the then-current level of evolution.

text: A hydrothermally precipitated catalytic iron sulphide membrane as a first step toward life We propose that life emerged from growing aggregates of iron sulphide bubbles containing alkaline and highly reduced hydrothermal solution. These bubbles were inflated hydrostatically at sulphidic submarine hot springs sited some distance from oceanic spreading centers four billion years ago. The membrane enclosing the bubbles was precipitated in response to contact between the spring waters and the mildly oxidized, acidic and iron-bearing Hadean ocean water. As the gelatinous sulphide bubbles aged and were inflated beyond their strength they budded, producing contiguous daughter bubbles by the precipitation of new membrane. [Fe2S2]+/0 or [Fe4S4]2+/+ clusters, possibly bonded by hydrothermal thiolate ligands as proferredoxins, could have catalyzed oxidation of thiolates to disulphides, thereby modifying membrane properties. 
We envisage the earliest iron sulphide bubbles (pro botryoids) first growing by hydrostatic inflation with hydrothermal fluid, but evolving to grow mainly by osmosis (the protocellular stage), driven by (1) catabolism of hydrothermal abiogenic organics trapped on the inner walls of the membrane, catalyzed by the iron sulphide clusters; and (2) cleavage of hydrophobic compounds dissolved in the membrane to hydrophilic moieties which were translocated, by the proton motive force inherent in the acidic Hadean ocean, to the alkaline interior of the protocell. The organics were generated first within the hydrothermal convective system feeding the hot springs operating in the oceanic crust and later in the pyritizing mound developing on the sea floor, as a consequence of the reduction of CO, CO2, and formaldehyde by Fe2+- and S2–-bearing minerals.
We imagine the physicochemical interactions in and on the membrane to have been sufficiently complex to have engendered auto- and cross-catalytic replication. The membrane may have been constructed in such a way that a  successful  parent could have  informed  the daughters of membrane characteristics functional for the then-current level of evolution.

year: 1994

title: Tyings in linear systems of equations modelled with positive and negative penalty functions

authors: Askes, Harm

subjects: constraints

abstract: In this short note, we focus on tyings (constraints that relate multiple degrees of freedom) modelled by means of penalty functions. In contrast to what is commonly thought, it is possible to obtain convergent results when negative penalty parameters are taken. A mathematical proof and an illustrating example are provided. In particular, we have proven that the results obtained with positive and negative penalty parameters enclose the exact solution from opposite sides. To this end, we have investigated a pseudo-force that is defined as the derivative of the constraint with respect to the inverse penalty parameter.

text: Tyings in linear systems of equations modelled with positive and negative penalty functions In this short note, we focus on tyings (constraints that relate multiple degrees of freedom) modelled by means of penalty functions. In contrast to what is commonly thought, it is possible to obtain convergent results when negative penalty parameters are taken. A mathematical proof and an illustrating example are provided. In particular, we have proven that the results obtained with positive and negative penalty parameters enclose the exact solution from opposite sides. To this end, we have investigated a pseudo-force that is defined as the derivative of the constraint with respect to the inverse penalty parameter.

year: 2008

title: Are they really at risk? Students' stories of success.

authors: Gray, Sheridan

subjects: Student engagement

abstract: In 2011, as the year level dean for year 13, I was surprised and pleased to see a group of students complete their fifth year of secondary schooling, contrary to teacher expectations, and in spite of earlier signs of disengagement and struggle.  Such students are frequently labelled “at risk” in our secondary schools. Truancy, lack of achievement, conduct issues, learning difficulties and health problems are seen as indicators of an at risk student by teachers. 

Statistically in Aotearoa, Māori and Pasifika students and students from low socio-economic families tend to be overrepresented among disengaged or early leavers from secondary schools, and so being from these cultures, and being from a low socio-economic group becomes a “risk” factor.   This can lead to assumptions among teachers about the students’ families, how parents value education, and even about the capacity of these groups to be able to succeed in education.  A range of strategies and programmes have been implemented in an attempt to address these issues, including Te Kotahitanga, Ka Hikitia and the Pasifika Education Plan, Resource Teachers Learning and Behaviour, Restorative Practice, and more recently Positive Behaviour for Learning

While there has been a shift in such approaches from deficit of students to emphasising more positive attitudes in teachers, the perspectives of the students themselves are missing from the discussion about these issues.  This study asks students what factors helped them to stay, and to achieve at least a level one NCEA qualification

The findings show that retention and engagement of “at risk” students requires careful attention to the quality of relationships across the school community: students, teachers and parents. They discredit some commonly held assumptions that “at risk” students and their parents do not value education and that teachers cannot support these students sufficiently. These quality relationships are respectful, responsive and tenacious showing a high level of respect for and interest in the students that goes beyond a teaching and learning relationship.  It also suggests that the discourse of “risk” invites a disrespectful response to retention and engagement of students.

text: Are they really at risk? Students' stories of success. In 2011, as the year level dean for year 13, I was surprised and pleased to see a group of students complete their fifth year of secondary schooling, contrary to teacher expectations, and in spite of earlier signs of disengagement and struggle.  Such students are frequently labelled “at risk” in our secondary schools. Truancy, lack of achievement, conduct issues, learning difficulties and health problems are seen as indicators of an at risk student by teachers. 

Statistically in Aotearoa, Māori and Pasifika students and students from low socio-economic families tend to be overrepresented among disengaged or early leavers from secondary schools, and so being from these cultures, and being from a low socio-economic group becomes a “risk” factor.   This can lead to assumptions among teachers about the students’ families, how parents value education, and even about the capacity of these groups to be able to succeed in education.  A range of strategies and programmes have been implemented in an attempt to address these issues, including Te Kotahitanga, Ka Hikitia and the Pasifika Education Plan, Resource Teachers Learning and Behaviour, Restorative Practice, and more recently Positive Behaviour for Learning

While there has been a shift in such approaches from deficit of students to emphasising more positive attitudes in teachers, the perspectives of the students themselves are missing from the discussion about these issues.  This study asks students what factors helped them to stay, and to achieve at least a level one NCEA qualification

The findings show that retention and engagement of “at risk” students requires careful attention to the quality of relationships across the school community: students, teachers and parents. They discredit some commonly held assumptions that “at risk” students and their parents do not value education and that teachers cannot support these students sufficiently. These quality relationships are respectful, responsive and tenacious showing a high level of respect for and interest in the students that goes beyond a teaching and learning relationship.  It also suggests that the discourse of “risk” invites a disrespectful response to retention and engagement of students.

year: 2012