629 research outputs found
Negative Linear Compressibility
While all materials reduce their intrinsic volume under hydrostatic (uniform)
compression, a select few actually \emph{expand} along one or more directions
during this process of densification. As rare as it is counterintuitive, such
"negative compressibility" behaviour has application in the design of pressure
sensors, artificial muscles and actuators. The recent discovery of surprisingly
strong and persistent negative compressibility effects in a variety of new
families of materials has ignited the field. Here we review the phenomenology
of negative compressibility in this context of materials diversity, placing
particular emphasis on the common structural motifs that recur amongst known
examples. Our goal is to present a mechanistic understanding of negative
compressibility that will help inform a clear strategy for future materials
design.Comment: Submitted to PCC
Nanostructure determination from the pair distribution function: A parametric study of the INVERT approach
We present a detailed study of the mechanism by which the INVERT method
[Phys. Rev. Lett. 104, 125501] guides structure refinement of disordered
materials. We present a number of different possible implementations of the
central algorithm and explore the question of algorithm weighting. Our analysis
includes quantification of the relative contributions of variance and
fit-to-data terms during structure refinement, which leads us to study the
roles of density fluctuations and configurational jamming in the RMC fitting
process. We present a parametric study of the pair distribution function
solution space for C60, a-Si and a-SiO2, which serves to highlight the
difficulties faced in developing a transferable weighting scheme.Comment: 15 pages, 7 figures, formatted for JPCM (RMC issue
Incommensurate chirality density wave transition in a hybrid molecular framework
Using single-crystal X-ray diffraction we characterise the 235\,K
incommensurate phase transition in the hybrid molecular framework
tetraethylammonium silver(I) dicyanoargentate, [NEt]Ag(CN). We
demonstrate the transition to involve spontaneous resolution of chiral
[NEt] conformations, giving rise to a state in which molecular
chirality is incommensurately modulated throughout the crystal lattice. We
refer to this state as an incommensurate chirality density wave (XDW) phase,
which represents a fundamentally new type of chiral symmetry breaking in the
solid state. Drawing on parallels to the incommensurate ferroelectric
transition of NaNO we suggest the XDW state arises through coupling between
acoustic (shear) and molecular rotoinversion modes. Such coupling is
symmetry-forbidden at the Brillouin zone centre but symmetry-allowed for small
but finite modulation vectors . The importance of
long-wavelength chirality modulations in the physics of this hybrid framework
may have implications for the generation of mesoscale chiral textures, as
required for advanced photonic materials.Comment: 5 pages, 3 figure
The Broiler-Corn Ratio: Is it an Indicator of Fattened Broiler Profits?
As consumers eat healthier and obesity concerns increase, the poultry industry continues growth in sales and revenues. Data reflect ten years of broiler prices, exports, egg and chick production, cold storage stocks, company earnings and stock price. Expected results suggest a broiler-corn ratio is an indicator of company profits.Livestock Production/Industries,
A Comparative Assessment of the Broiler:Corn Ratio and Its Impact on Broiler Processors' Profitability
Input prices for broiler production, particularly corn, are becoming increasingly volatile due to increasing competition for corn from ethanol and biofuels production suggesting volatility in poultry profits will follow indicator of profits relating feed input prices and broiler meat output prices, such as a Broiler:corn ratios. Total chicken exports, total chicken ready-to-cook production, number of eggs set, number of chicks placed, and cold storage chicken inventory are used to estimate. Utilizing a distributed lag model, seventeen years of data for three Broiler:corn ratios, broiler exports, egg set, chick placements, cold storage stocks, and ready-to-cook broiler production were utilized to estimate stock share price for four major broiler producers.Demand and Price Analysis, Livestock Production/Industries,
- …