Reversible Control of Third-Order Optical Nonlinearity of DNA Decorated Carbon Nanotube Hybrids.

Positive and negative third-order optical nonlinearities have been investigated in single-stranded DNA wrapped semiconducting single-walled carbon nanotubes. It is found that the redox reactions of hydrogen peroxide can reverse the sign of the third-order nonlinearity. The observation proves that the lowest unoccupied molecular orbital has a lower density of electronic states than that of the highest occupied molecular orbital. A three-energy-level model is used to explain the effect of the redox reactions. Raman spectroscopy has also been used to investigate the interaction between single-walled carbon nanotubes and single-stranded DNA.

The influence of environmental conditions, lipid composition, and phase behavior on the origin of cell membranes.

At some point in life's development, membranes formed, providing barriers between the environment and the interior of the 'cell.' This paper evaluates the research to date on the prebiotic origin of cell membranes and highlights possible areas of continuing study. A careful review of the literature uncovered unexpected factors that influence membrane evolution. The major stages in primitive membrane formation and the transition to contemporary cell membranes appear to require an exacting relationship between environmental conditions and amphiphile composition and phase behavior. Also, environmental and compositional requirements for individual stages are in some instances incompatible with one another, potentially stultifying the pathway to contemporary membranes. Previous studies in membrane evolution have noted the effects composition and environment have on membrane formation but the crucial dependence and interdependence on these two factors has not been emphasized. This review makes clear the need to focus future investigations away from proof-of-principle studies towards developing a better understanding of the roles that environmental factors and lipid composition and polymorphic phase behavior played in the origin and evolution of cell membranes.

Getting the most out of all your customers.

Companies spend billions of dollars on direct marketing, targeting individual customers with ever more accuracy. Yet despite the power of the myriad data-collecting and analytical tools at their disposal, they're still having trouble optimizing their direct-marketing investments. Many marketers try to minimize costs by pursuing only those customers who are cheap to find and cheap to keep. Others try to get the most customers they possibly can and keep all of them for as long as they can. But a customer need not be loyal to be highly profitable, and many loyal customers turn out to be highly unprofitable. Companies can get more out of direct marketing if they see it as a single system for generating profits than if they try to maximize performance measures at each stage of the process. This article describes a tool for doing just that. Called ARPRO (Allocating Resources for Profits), the tool is essentially a complex regression analysis that can estimate the impact of a company's direct-marketing investments on the profitability of its customer pool. With data that companies already gather, the tool can show managers how much to spend on acquisition versus retention and even what percentage of their funds they should allocate to the different direct-marketing channels. Using the model, companies can easily see that even small deviations from the optimal levels of customer profitability are expensive. Applying it to one catalog retailer showed, for instance, that a 10% reduction in marketing costs would lead to a 1.8 million dollar drop in long-term customer profits. Conversely, spending 69% less on marketing would actually increase average customer profitability at one B2B service provider by 42%. What's more, the tool can show that finding the optimal balance between investments in acquisition and retention can be more important than finding the optimum amount to invest overall.