7,787 research outputs found
Structure and ionic conductivity in lithium garnets
Garnets are capable of accommodating an excess of lithium cations beyond that normally found in this prototypical structure. This excess lithium is found in a mixture of coordination environments with considerable positional and occupational disorder and leads to ionic conductivity of up to 4×10-4 S cm-1 at room temperature. This high value for total conductivity, combined with excellent thermal and (electro)chemical resistance makes these candidate materials for operation in all solid-state batteries. This review looks at garnets with a wide range of stoichiometries and lithium concentrations and the impact of complex lithium distributions and crystallographic order/disorder transitions on the transport properties of these materials
Power system requirements
An overview of electrical power requirements for each mission of a baseline and alternate plan for space activities in the 1990-2035 timeframe is presented. The specific missions included low earth orbit (LEO), geosynchronous earth orbit (GEO), lunar, Mars, and asteroid related projects
Energy-based Analysis of Biochemical Cycles using Bond Graphs
Thermodynamic aspects of chemical reactions have a long history in the
Physical Chemistry literature. In particular, biochemical cycles - the
building-blocks of biochemical systems - require a source of energy to
function. However, although fundamental, the role of chemical potential and
Gibb's free energy in the analysis of biochemical systems is often overlooked
leading to models which are physically impossible. The bond graph approach was
developed for modelling engineering systems where energy generation, storage
and transmission are fundamental. The method focuses on how power flows between
components and how energy is stored, transmitted or dissipated within
components. Based on early ideas of network thermodynamics, we have applied
this approach to biochemical systems to generate models which automatically
obey the laws of thermodynamics. We illustrate the method with examples of
biochemical cycles. We have found that thermodynamically compliant models of
simple biochemical cycles can easily be developed using this approach. In
particular, both stoichiometric information and simulation models can be
developed directly from the bond graph. Furthermore, model reduction and
approximation while retaining structural and thermodynamic properties is
facilitated. Because the bond graph approach is also modular and scaleable, we
believe that it provides a secure foundation for building thermodynamically
compliant models of large biochemical networks
Laser power transmission
An overview of previous studies related to laser power transmission is presented. Particular attention is given to the use of solar pumped lasers for space power applications. Three general laser mechanisms are addressed: photodissociation lasing driven by sunlight, photoexcitation lasing driven directly by sunlight, and photoexcitation lasing driven by thermal radiation
Cosmological matching conditions
We investigate the evolution of scalar metric perturbations across a sudden
cosmological transition, allowing for an inhomogeneous surface stress at the
transition leading to a discontinuity in the local expansion rate, such as
might be expected in a big crunch/big bang event. We assume that the transition
occurs when some function of local matter variables reaches a critical value,
and that the surface stress is also a function of local matter variables. In
particular we consider the case of a single scalar field and show that a
necessary condition for the surface stress tensor to be perturbed at the
transition is the presence of a non-zero intrinsic entropy perturbation of the
scalar field. We present the matching conditions in terms of gauge-invariant
variables assuming a sudden transition to a fluid-dominated universe with
barotropic equation of state. For adiabatic perturbations the comoving
curvature perturbation is continuous at the transition, while the Newtonian
potential may be discontinuous if there is a discontinuity in the background
Hubble expansion.Comment: 12 pages, no figure
Nest and Prey of \u3ci\u3eAgeniella (Leucophrus) Fulgifrons\u3c/i\u3e (Hymenoptera: Pompilidae)
Information on the habitat, nest-site, hunting, prey transport, closure, burrow structure, and prey of Ageniella (Leucophrus) fulgifrons is presented. Components of the nesting behaviors of other species of Ageniella are examined and compared with those of A. fulgifrons
Northern Distribution Records for Some Nearctic Pompilidae (Hymenoptera)
Distributional records and nomenclatural changes are presented for 20 species of Nearctic Pompilidae. The records extend the species\u27 ranges northward in North America, are peripheral on the northern boundaries of the ranges, or fill in sizeable gaps in the distributions. Flower records, habitat notes, and remarks on the prey are given for some of the species
Lagrangian Evolution of the Weyl Tensor
We derive the evolution equations for the electric and magnetic parts of the
Weyl tensor for cold dust from both general relativity and Newtonian gravity.
In a locally inertial frame at rest in the fluid frame, the Newtonian equations
agree with those of general relativity. We give explicit expressions for the
electric and magnetic parts of the Weyl tensor in the Newtonian limit. In
general, the magnetic part does not vanish, implying that the Lagrangian
evolution of the fluid is not purely local.Comment: 17 pages, AAS LateX v3.0, submitted to ApJ, MIT-CSR-94-0
- …