Revising Z: part II - logical development

This is the second of two related papers. In "Revising Z: Part I - logic and semantics" (this journal) we introduced a simple specification logic ZC comprising a logic and a semantics (in ZF set theory). We then provided an interpretation for (a rational reconstruction of) the specification language Z within ZC. As a result we obtained a sound logic for Z, including the basic schema calculus. In this paper we extend the basic framework with more sophisticated features (including schema operations) and we mount a critique of a number of concepts used in Z. We further demonstrate that the complications and confusions which these concepts introduce can be avoided without compromising expressibility

Revising Z: part I - logic and semantics

This is the first of two related papers. We introduce a simple specification logic ZC comprising a logic and a semantics (in ZF set theory) within which the logic is sound. We then provide an interpretation for (a rational reconstruction of) the specification language Z within ZC. As a result we obtain a sound logic for Z, including a basic schema calculus

Results on formal stepwise design in Z

Stepwise design involves the process of deriving a concrete model of a software system from a given abstract one. This process is sometimes known as refinement. There are numerous refinement theories proposed in the literature, each of which stipulates the nature of the relationship between an abstract specification and its concrete counterpart. This paper considers six refinement theories in Z that have been proposed by various people over the years. However, no systematic investigation of these theories, or results on the relationships between them, have been presented or published before. This paper shows that these theories fall into two important categories and proves that the theories in each category are equivalent

An analysis of total correctness refinement models for partial relation semantics I

This is the first of a series of papers devoted to the thorough investigation of (total correctness) refinement based on an underlying partial relational model. In this paper we restrict attention to operation refinement. We explore four theories of refinement based on an underlying partial relation model for specifications, and we show that they are all equivalent. This, in particular, sheds some light on the relational completion operator (lifted-totalisation) due to Wookcock which underlines data refinement in, for example, the specification language Z. It further leads to two simple alternative models which are also equivalent to the others

Z Logic and its Consequences

This paper provides an introduction to the specification language Z from a logical perspective. The possibility of presenting Z in this way is a consequence of a number of joint publications on Z logic that Henson and Reeves have co-written since 1997. We provide an informal as well as formal introduction to Z logic and show how it may be used, and extended, to investigate issues such as equational logic, the logic of preconditions, the issue of monotonicity and both operation and data refinement

SunSat Design Competition 2014-2015 Second Place Winner – Team SunFlower: Thermal Power Satellite

Space-based Solar Power has failed to be competitive on cost in spite of decades of study. A new approach appears to resolve the cost issue, undercutting coal and opening huge markets for low cost solar power from space. There are two parts to the problem. First is the cost of lifting parts to Geosynchronous Earth Orbit (GEO; second is the mass of parts that make up a power satellite. Our team is proposing a combination that makes use of Skylon to Low Earth Orbit (LEO), and a 15,000 ton payload ground powered electric propulsion from LEO to GEO. This strategy reduces the cost to under $200/kg, a 100-to-one reduction from the current cost for lifting communication satellites to GEO. Reaching these numbers requires a Skylon flight rate in excess of 10,000 per year. Even at$200/kg, the economics cannot tolerate more than 6.5 kg/kW for power satellites to undercut coal, e.g., 32,500 tons for a 5 GWe satellite. Low (20%) efficient photovoltaic (PV) systems are very difficult to reduce below 10 kg/kW. A 60% efficient thermal design has one third of the light intercepting area of a 20% efficient PV power satellite. Carnot considerations require a high temperature ratio between boilers and radiators. The thermal cycles considered in our approach use concentrating mirrors to direct sunlight into high-temperature boilers. The first working fluid proposed is potassium. After passing through a high temperature turbine, the condensing potassium heats a second working fluid (water or super critical CO2). Waste heat is channeled to low-temperature condensing radiators. Analysis found the radiators to be a relatively small part of the power satellite mass. Concentrators, boilers, turbines, generators, heat radiators and the transmitter massed close enough to 32,500 tons to merit further detailed investigation. The total, including rectenna, parts cost, labor and transportation, came to ~$2400/kW. Levelized cost of electricity from$2400 capital expense came to 3 cents per kWh, comfortably undercutting coal at 4 cents. Displacing coal on financial merits bypasses debates about CO2 buildup and climatology. If designs and economics can be verified, and assuming rapid expansion beyond the first dozen power satellites, the human race could be off fossil fuels as early as the mid-2030s. To achieve this goal, power satellites must cost less than $2400/kW, installed. It all depends on keeping the power satellite reasonably low in mass and transportation costs extremely low. Click here to see this team video: Team SunFlower - 2015 SunSat Design Competitio

Aquilegia, Vol. 37 No. 3, Summer 2013, Newsletter of the Colorado Native Plant Society

https://epublications.regis.edu/aquilegia/1143/thumbnail.jp

All hat and no cattle: Accountability following the UN food systems summit

The United Nations Food Systems Summit (UNFSS) is an important moment to garner political and financial attention to the challenges that food systems face. It is a difficult moment with many competing national and global priorities including massive inequities, rapid climate change and a global pandemic. It will be important for the UNFSS to build in robust accountability mechanisms to ensure that commitments to address food systems challenges are upheld, and that these mechanisms align to already existing frameworks towards sustainable development. While the UNFSS may be impressive in its planning, without accountability of what, who, and by when, it could fall short in its execution. We, as the Editors of the Global Food Security Journal articulate the importance of accountability to ensure the UNFSS is not just ‘all hat and no cattle.

A research vision for food systems in the 2020s: Defying the status quo

As we enter the third decade of the 21st century, the world is at a crossroads. As the Editors of the journal Global Food Security, we share our perspectives on the food security challenges that face humanity and lay out our vision and call for stronger food systems research and science in this decade. The challenges and opportunities for food systems research that lay ahead are significant, requiring that high-quality science be translated into policy and action faster than ever before. Our vision is one in which research and science, and the evidence stemming from their application, not only inform food and environmental policy, but are adopted and mainstreamed into actions at the national, regional, and global levels. Global Food Security provides a platform where such evidence is shared in an accessible manner for those who need to use it and act on it