Casimir forces in the time domain II: Applications

Our preceding paper introduced a method to compute Casimir forces in arbitrary geometries and for arbitrary materials that was based on a finite-difference time-domain (FDTD) scheme. In this manuscript, we focus on the efficient implementation of our method for geometries of practical interest and extend our previous proof-of-concept algorithm in one dimension to problems in two and three dimensions, introducing a number of new optimizations. We consider Casimir piston-like problems with nonmonotonic and monotonic force dependence on sidewall separation, both for previously solved geometries to validate our method and also for new geometries involving magnetic sidewalls and/or cylindrical pistons. We include realistic dielectric materials to calculate the force between suspended silicon waveguides or on a suspended membrane with periodic grooves, also demonstrating the application of PML absorbing boundaries and/or periodic boundaries. In addition we apply this method to a realizable three-dimensional system in which a silica sphere is stably suspended in a fluid above an indented metallic substrate. More generally, the method allows off-the-shelf FDTD software, already supporting a wide variety of materials (including dielectric, magnetic, and even anisotropic materials) and boundary conditions, to be exploited for the Casimir problem.Comment: 11 pages, 12 figures. Includes additional examples (dispersive materials and fully three-dimensional systems

Achieving a Strongly Temperature-Dependent Casimir Effect

We propose a method of achieving large temperature sensitivity in the Casimir force that involves measuring the stable separation between dielectric objects immersed in fluid. We study the Casimir force between slabs and spheres using realistic material models, and find large > 2nm/K variations in their stable separations (hundreds of nanometers) near room temperature. In addition, we analyze the effects of Brownian motion on suspended objects, and show that the average separation is also sensitive to changes in temperature . Finally, this approach also leads to rich qualitative phenomena, such as irreversible transitions, from suspension to stiction, as the temperature is varied

Structural anisotropy and orientation-induced Casimir repulsion in fluids

In this work we theoretically consider the Casimir force between two periodic arrays of nanowires (both in vacuum, and on a substrate separated by a fluid) at separations comparable to the period. Specifically, we compute the dependence of the exact Casimir force between the arrays under both lateral translations and rotations. Although typically the force between such structures is well-characterized by the Proximity Force Approximation (PFA), we find that in the present case the microstructure modulates the force in a way qualitatively inconsistent with PFA. We find instead that effective-medium theory, in which the slabs are treated as homogeneous, anisotropic dielectrics, gives a surprisingly accurate picture of the force, down to separations of half the period. This includes a situation for identical, fluid-separated slabs in which the exact force changes sign with the orientation of the wire arrays, whereas PFA predicts attraction. We discuss the possibility of detecting these effects in experiments, concluding that this effect is strong enough to make detection possible in the near future.Comment: 12 pages, 9, figure. Published version with expanded discussio

Structural anisotropy and orientation-induced Casimir repulsion in fluids

In this work we theoretically consider the Casimir force between two periodic arrays of nanowires (both in vacuum, and on a substrate separated by a fluid) at separations comparable to the period. Specifically, we compute the dependence of the exact Casimir force between the arrays under both lateral translations and rotations. Although typically the force between such structures is well-characterized by the Proximity Force Approximation (PFA), we find that in the present case the microstructure modulates the force in a way qualitatively inconsistent with PFA. We find instead that effective-medium theory, in which the slabs are treated as homogeneous, anisotropic dielectrics, gives a surprisingly accurate picture of the force, down to separations of half the period. This includes a situation for identical, fluid-separated slabs in which the exact force changes sign with the orientation of the wire arrays, whereas PFA predicts attraction. We discuss the possibility of detecting these effects in experiments, concluding that this effect is strong enough to make detection possible in the near future.Comment: 12 pages, 9, figure. Published version with expanded discussio

Adapting usability techniques for application in open source Software: A multiple case study

Context: As a result of the growth of non-developer users of OSS applications, usability has over the last ten years begun to attract the interest of the open source software (OSS) community. The OSS community has some special characteristics (such as worldwide geographical distribution of both users and developers and missing resources) which are an obstacle to the direct adoption of many usability techniques as specified in the human-computer interaction (HCI) field. Objective: The aim of this research is to adapt and evaluate the feasibility of applying four usability techniques: user profiles, personas, direct observation and post-test information to four OSS projects from the viewpoint of the development team. Method: The applied research method was a multiple case study of the following OSS projects: Quite Universal Circuit Simulator, PSeInt, FreeMind and OpenOffice Writer. Results: We formalized the application procedure of each of the adapted usability techniques. We found that either there were no procedures for adopting usability techniques in OSS or they were not fully systematized. Additionally, we identified the adverse conditions that are an obstacle to their adoption in OSS and propose the special adaptations required to overcome the obstacles. To avoid some of the adverse conditions, we created web artefacts (online survey, wiki and forum) that are very popular in the OSS field. Conclusion: It is necessary to adapt usability techniques for application in OSS projects considering their idiosyncrasy. Additionally, we found that there are obstacles (for example, number of participant users, biased information provided by developers) to the application of the techniques. Despite these obstacles, it is feasible to apply the adapted techniques in OSS projectsThis research was funded by the Secretariat of Higher Education, Science, Technology and Innovation (SENESCYT) of the Government of Ecuador as part of an academic scholarship granted for postgradu- ate training, and Quevedo State Technical University through doctoral scholarships for university professors. Also this research was funded by the Spanish Ministry of Education, Culture and Sports FLEXOR ( TIN2014-52129-R ) and TIN2014-60490-P projects and the eMadrid- CM project ( S2013/ICE-2715 ). Finally, this research received funding from the University of Atacama “DIUDA 22316 ”projec

Frequency-selective near-field enhancement of radiative heat transfer via photonic-crystal slabs: a general computational approach for arbitrary geometries and materials

We demonstrate the possibility of achieving enhanced frequency-selective near-field radiative heat transfer between patterned (photonic crystal) slabs at designable frequencies and separations, exploiting a general numerical approach for computing heat transfer in arbitrary geometries and materials based on the finite-difference time-domain method. Our simulations reveal a tradeoff between selectivity and near-field enhancement as the slab--slab separation decreases, with the patterned heat transfer eventually reducing to the unpatterned result multiplied by a fill factor (described by a standard proximity approximation). We also find that heat transfer can be further enhanced at selective frequencies when the slabs are brought into a glide-symmetric configuration, a consequence of the degeneracies associated with the non-symmorphic symmetry group

Applying a Usability Technique in the Open Source Software Development Process: Experiences from the Trenches

The growth in the number of non-developer open source software (OSS) application users has drawn attention to usability in the OSS community. OSS communities do not generally know how to apply usability techniques and are unclear about which techniques to use in each activity of the development process. The aim of our research is to determine the feasibility of applying the focus groups technique in the OSS ERMaster project. To do this, we participated as project volunteers. We used the case study research method to investigate technique application and OSS community participation. As a result, we identified adverse conditions that were an obstacle to the application of the original technique. We then adapted the technique to make it applicable in an OSS project. We can conclude that was not easy to recruit OSS users and developers to participate in technique application

M2K: I. A Jovian mass planet around the M3V star HIP79431

Doppler observations from Keck Observatory reveal the presence of a planet with Msini of 2.1 Mjup orbiting the M3V star HIP79431. This is the sixth giant planet to be detected in Doppler surveys of M dwarfs and it is one of the most massive planets discovered around an M dwarf star. The planet has an orbital period of 111.7 days and an orbital eccentricity of 0.29. The host star is metal rich, with an estimated [Fe/H] = +0.4. This is the first planet to emerge from our new survey of 1600 M-to-K dwarf stars.Comment: 5 figure