Here is the second of this week’s bumper selection of research articles highly recommended by our reviewers. The topics covered include maths, physics and economics.

• Continuous Variable Quantum Key Distribution with a Noisy Laser
• Geometric Interpretation of Surface Tension Equilibrium in Superhydrophobic Systems
• Zeta Function Expression of Spin Partition Functions on Thermal AdS3
• Why Creativity Isn’t in IQ Tests, Why it Matters, and Why it Won’t Change Anytime Soon Probably
• Designing a Microfluidic Device with Integrated Ratiometric Oxygen Sensors for the Long-Term Control and Monitoring of Chronic and Cyclic Hypoxia
• Lie and Conditional Symmetries of a Class of Nonlinear (1 + 2)-Dimensional Boundary Value Problems
• Market-Based Instruments for Ecosystem Services between Discourse and Reality: An Economic and Narrative Analysis
• Metadata-Assisted Global Motion Estimation for Medium-Altitude Unmanned Aerial Vehicle Video Applications

Continuous Variable Quantum Key Distribution with a Noisy Laser

Christian S. Jacobsen, Tobias Gehring and Ulrik L. Andersen *

Existing experimental implementations of continuous-variable quantum key distribution require shot-noise limited operation, achieved with shot-noise limited lasers. However, loosening this requirement on the laser source would allow for cheaper, potentially integrated systems. Here, we implement a theoretically proposed prepare-and-measure continuous-variable protocol and experimentally demonstrate the robustness of it against preparation noise stemming for instance from technical laser noise. Provided that direct reconciliation techniques are used in the post-processing we show that for small distances large amounts of preparation noise can be tolerated in contrast to reverse reconciliation where the key rate quickly drops to zero. Our experiment thereby demonstrates that quantum key distribution with non-shot-noise limited laser diodes might be feasible.

Geometric Interpretation of Surface Tension Equilibrium in Superhydrophobic Systems

Michael Nosonovsky * and Rahul Ramachandran

Surface tension and surface energy are closely related, although not identical concepts. Surface tension is a generalized force; unlike a conventional mechanical force, it is not applied to any particular body or point. Using this notion, we suggest a simple geometric interpretation of the Young, Wenzel, Cassie, Antonoff and Girifalco–Good equations for the equilibrium during wetting. This approach extends the traditional concept of Neumann’s triangle. Substances are presented as points, while tensions are vectors connecting the points, and the equations and inequalities of wetting equilibrium obtain simple geometric meaning with the surface roughness effect interpreted as stretching of corresponding vectors; surface heterogeneity is their linear combination, and contact angle hysteresis is rotation. We discuss energy dissipation mechanisms during wetting due to contact angle hysteresis, the superhydrophobicity and the possible entropic nature of the surface tension.

Zeta Function Expression of Spin Partition Functions on Thermal AdS3

Floyd L.Williams

We find a Selberg zeta function expression of certain one-loop spin partition functions on three-dimensional thermal anti-de Sitter space. Of particular interest is the partition function of higher spin fermionic particles. We also set up, in the presence of spin, a Patterson-type formula involving the logarithmic derivative of zeta.

Why Creativity Isn’t in IQ Tests, Why it Matters, and Why it Won’t Change Anytime Soon Probably

James C. Kaufman

Creativity is a part of most theories of intelligence—sometimes a small part and sometimes a large part. Yet even IQ tests that assess aspects of intelligence that supposedly reflect creative abilities do not actually measure creativity. Recent work has argued that intelligence and creativity are more conceptually related than we have thought. In addition, creativity offers a potential way to counter issues of test bias from several different angles. That said, inherent difficulties in measuring creativity and inherent sluggishness in the test industry mean the odds are small that creativity will find its way into IQ tests as currently defined. However, there remain other potential possibilities in related fields.

Designing a Microfluidic Device with Integrated Ratiometric Oxygen Sensors for the Long-Term Control and Monitoring of Chronic and Cyclic Hypoxia

Samantha M. Grist, Jonathan C. Schmok, Meng-Chi (Andy) Liu, Lukas Chrostowski and Karen C. Cheung *

Control of oxygen over cell cultures in vitro is a topic of considerable interest, as chronic and cyclic hypoxia can alter cell behaviour. Both static and transient hypoxic levels have been found to affect tumour cell behaviour; it is potentially valuable to include these effects in early, in vitro stages of drug screening. A barrier to their inclusion is that rates of transient hypoxia can be a few cycles/hour, which is difficult to reproduce in traditional in vitro cell culture environments due to long diffusion distances from control gases to the cells. We use a gas-permeable three-layer microfluidic device to achieve spatial and temporal oxygen control with biologically-relevant switching times. We measure the oxygen profiles with integrated, ratiometric optical oxygen sensors, demonstrate sensor and system stability over multi-day experiments, and characterize a pre-bleaching process to improve sensor stability. We show, with both finite-element modelling and experimental data, excellent control over the oxygen levels by the device, independent of fluid flow rate and oxygenation for the operating flow regime. We measure equilibration times of approximately 10 min, generate complex, time-varying oxygen profiles, and study the effects of oxygenated media flow rates on the measured oxygen levels. This device could form a useful tool for future long-term studies of cell behaviour under hypoxia.

Lie and Conditional Symmetries of a Class of Nonlinear (1 + 2)-Dimensional Boundary Value Problems

Roman Cherniha 1,2,* and John R. King 1

A new definition of conditional invariance for boundary value problems involving a wide range of boundary conditions (including initial value problems as a special case) is proposed. It is shown that other definitions worked out in order to find Lie symmetries of boundary value problems with standard boundary conditions, followed as particular cases from our definition. Simple examples of direct applicability to the nonlinear problems arising in applications are demonstrated. Moreover, the successful application of the definition for the Lie and conditional symmetry classification of a class of (1 + 2)-dimensional nonlinear boundary value problems governed by the nonlinear diffusion equation in a semi-infinite domain is realised. In particular, it is proven that there is a special exponent, k ≠ -2, for the power diffusivity uk when the problem in question with non-vanishing flux on the boundary admits additional Lie symmetry operators compared to the case k ≠ -2. In order to demonstrate the applicability of the symmetries derived, they are used for reducing the nonlinear problems with power diffusivity uk and a constant non-zero flux on the boundary (such problems are common in applications and describing a wide range of phenomena) to (1 + 1)-dimensional problems. The structure and properties of the problems obtained are briefly analysed. Finally, some results demonstrating how Lie invariance of the boundary value problem in question depends on the geometry of the domain are presented.

Market-Based Instruments for Ecosystem Services between Discourse and Reality: An Economic and Narrative Analysis

Géraldine Froger 1,2,* , Valérie Boisvert 3, Philippe Méral 4, Jean-François Le Coq 5, Armelle Caron 6 and Olivier Aznar 7

Since the mid-1990s, the concept of ecosystem services has become increasingly popular in academic circles and among decision-makers. Because of its inclusive character, this concept has given rise to different interpretations in economics. Since its inception, it has been associated with the development of market-based instruments (MBIs) in conservation policies. From this perspective, the sustainable provision of ecosystem services is hindered by market failures (e.g., public good attributes, externalities) and prices that do not capture the full value of the natural assets. MBIs are therefore recommended. According to their promoters, they provide powerful incentives to conserve the environment while at the same time offering new sources of income to support rural livelihoods. Our paper contends that different economic narratives, and associated representations of the market failure at stake with the provision of ecosystem services, may support different policy instruments that are all coined as MBIs. As an illustration, we analyze the economic discourse underlying payments for ecosystem services and eco-labels, and we underline the variety of institutional forms to which they give rise in order to emphasize the differences between discourse and practice.

Metadata-Assisted Global Motion Estimation for Medium-Altitude Unmanned Aerial Vehicle Video Applications

Hongguang Li 1, Xinjun Li 2, Wenrui Ding 1,* and Yuqing Huang 3

Global motion estimation (GME) is a key technology in unmanned aerial vehicle remote sensing (UAVRS). However, when a UAV’s motion and behavior change significantly or the image information is not rich, traditional image-based methods for GME often perform poorly. Introducing bottom metadata can improve precision in a large-scale motion condition and reduce the dependence on unreliable image information. GME is divided into coarse and residual GME through coordinate transformation and based on the study hypotheses. In coarse GME, an auxiliary image is built to convert image matching from a wide baseline condition to a narrow baseline one. In residual GME, a novel information and contrast feature detection algorithm is proposed for big-block matching to maximize the use of reliable image information and ensure that the contents of interest are well estimated. Additionally, an image motion monitor is designed to select the appropriate processing strategy by monitoring the motion scales of translation, rotation, and zoom. A medium-altitude UAV is employed to collect three types of large-scale motion datasets. Peak signal to noise ratio (PSNR) and motion scale are computed. This study’s result is encouraging and applicable to other medium- or high-altitude UAVs with a similar system structure.