Determining Free Energy Differences Through Variational Morphing

Free energy calculations based on atomistic Hamiltonians and sampling are key to a first principles understanding of biomolecular processes, material properties, and macromolecular chemistry. Here, we generalize the Free Energy Perturbation method and derive non-linear Hamiltonian transformation sequences for optimal sampling accuracy that differ markedly from established linear transformations. We show that our sequences are also optimal for the Bennett Acceptance Ratio (BAR) method, and our unifying framework generalizes BAR to small sampling sizes and non-Gaussian error distributions. Simulations on a Lennard-Jones gas show that an order of magnitude less sampling is required compared to established methods.Comment: 7 pages, 5 figure

Laser-Directed Self-Organization and Reaction Control in Complex Systems

Pulsed lasers proved to be advantageous tools for the stimulation of pattern formation in complex systems. Their capability to support thermodynamic, kinetic and spatial control facilitates the direction of self-organization processes into selective channels. The short lifetime of laser-stimulated processes was identified to be the key aspect that enables for the synthesis of functional materials starting from complex systems. When self-organization is abruptly stopped after a few nanoseconds, this creates materials present in a non-equilibrium state, which are known to exhibit special properties. A prominent example is the distinctively different behavior of gold nanoparticles compared to bulk gold. Repeated laser stimulation was demonstrated to be a powerful method that enables selective adjustments of material properties emergent in the course of self-organized pattern formation in complex systems. This includes a broad spectrum of optical, electrical, magnetic and catalytic properties, which are not found in the starting materials prior to laser modification. The capability of lasers to trigger self-organization processes with spatial control was identified to be an interesting feature because it bears the potential to create materials with advanced functionality. In particular, the utilization of a phenomenon called laser-induced periodic surface structures (LIPSS) proved to be very efficient. LIPSS transformed the surface of stainless steel into hierarchical structures thus equipping this everyday material with a multifunctional surface. Considering the simplicity of the generation process this demonstrates the viability of nature’s low-effort-high-outcome-principle of order formation in complex systems. In addition to that, the application breath of laser-stimulated pattern formation was successfully expanded to temperature sensitive materials by including photochemistry into the concept. The large variety of reaction types accessible via photochemistry opens an even wider field of potential applications. In conclusion, it can be stated that the concept of nature to trigger selective reorganizations and pattern formation in complex systems can be imitated in its principles. The introduced concept of laser-directed self-organization and reaction control in complex systems prospects a large application potential. Presented insights into laser-stimulated reaction pathways and pattern formations processes provide a valuable basis for future studies in this field. Overall, the major challenge that must be met on the way to beneficial applications is the need for purposeful design of materials, which requires a thorough understanding of the fundamental principles behind self-organization

Variationally Derived Intermediates for Correlated Free Energy Estimates between Intermediate States

Free energy difference calculations based on atomistic simulations generally improve in accuracy when sampling from a sequence of intermediate equilibrium thermodynamic states that bridge the configuration space between two states of interest. For reasons of efficiency, usually the same samples are used to calculate the step-wise difference of such an intermediate to both adjacent intermediates. However, this procedure violates the assumption of uncorrelated estimates that is necessary to derive both the optimal sequence of intermediate states and the widely used Bennett acceptance ratio (BAR) estimator. In this work, via a variational approach, we derive the sequence of intermediate states and the corresponding estimator with minimal mean squared error that account for these correlations and assess its accuracy

Mixing effectiveness in the Apollo oxygen tanks of spin-up and rotation-reversal maneuvers

Two-dimensional simulations of stratified flows in the Apollo oxygen tanks have been used to estimate the mixing effectiveness of spin-up and rotation-reversal maneuvers. Calculations have been made for square and circular cylindrical tank geometries. Differences arising from heater position on the tank wall or near the center of the tank have been investigated. In the event of a prolonged period without normal maneuvers, the potential pressure decay (drop in pressure that would result from adiabatic mixing) can be suppressed by more than a factor of two through the use of spin-up and rotation-reversal maneuvers. Changes in rotation rate of order three revolutions per hour or greater are sufficient for this purpose

Not seeing the forest for the trees:The oversight of defaunation in REDD+ and global forest governance

Over the past decade, countries have strived to develop a global governance structure to halt deforestation and forest degradation, by achieving the readiness requirements for Reducing Emissions from Deforestation and forest Degradation (REDD+). Nonetheless, deforestation continues, and seemingly intact forest areas are being degraded. Furthermore, REDD+ may fail to consider the crucial ecosystem functions of forest fauna including seed dispersal and pollination. Throughout the tropics, forest animal populations are depleted by unsustainable hunting to the extent that many forests are increasingly devoid of larger mammals—a condition referred to as empty forests. Large mammals and birds, who often disperse seeds of larger more carbon-rich tree species, are preferentially targeted by hunters and the first to be depleted. Such defaunation has cascading ecosystem effects, changing forest structure and composition with implications for carbon storage capacity. Failure to address defaunation would therefore be a major oversight in REDD+, compromising its long-term viability. We carried out a desktop study reviewing REDD+ documents and national implementation efforts in Colombia, Ecuador, Nigeria, Tanzania, and Indonesia to assess the extent to which they address hunting and acknowledged the ecosystem functions of fauna. We also assessed sub-national REDD+ projects to determine whether they recognized hunting and if and how they incorporated hunting management and wildlife monitoring at the project level. Moreover, we assessed to what extent sub-national REDD+ projects addressed the long-term impacts of the sustainability of hunting on forest ecosystem function including carbon storage. We found that hunting, the risk of defaunation, and its effects have been ignored in the REDD+ policy process at both the international and national levels. At the project level, we found some reference to hunting and the risks posed by the loss of forest fauna, albeit only addressed superficially. Our results underline the fact that forest ecosystems are being reduced to their carbon content and that, despite the rhetoric of biodiversity co-benefits, fauna is not treated as a functional component of forests. This neglect threatens to undermine forest ecosystem function and service delivery as well as long-term forest carbon assimilation capacity and hence, ultimately, to compromise REDD+ objectives

IT Support for Intra-Organizational Innovation Networks – An Exploratory Study

The paper examines requirements for IT support in open innovation within companies. Based on an in-depth single-case study, we derive four major levels of IT requirements: incentive & inspiration, information & knowledge, communication & collaboration, and feedback & feed-forward. The multitude of requirements identified on each level clearly points to the need for IT support during the internal open innovation process. The paper concludes that many findings from prior research on innovation management systems apply to the internal open innovation context as well, but with some interesting differences. An IT system for open innovation within a company should pay particular attention to the incentives and inspiration of employees. The system should motivate all employees to participate in open innovation and stimulate innovative ideas by indicating clear benefits as well as recent needs, challenges and developments in their company’s context. Furthermore, a virtual community seems to be a powerful concept for driving open innovation in the company. It fosters the activity of and the interaction between employees, thereby addressing all of our requirement levels. To build and run such an intraorganizational open innovation community, social software offers useful concepts and applications. Based on the identified requirements, we present initial concepts for their implementation