Increasing the Directivity of Resonant Cavity Antennas with Nearfield Transformation Meta-Structure Realized with Stereolithograpy

A simple, nearfield transformation meta-structure is proposed to increase the directivity of resonant cavity antennas (RCA). The meta-structure is comprised of 14 × 14 meta-atoms or so called “unit-cells”, adding localized phase delays in the aperture of the RCA and thus increasing its broadside directivity. A prototype of the meta-structure is additively manufactured using the stereolithograpy process and has a profile of 0.56λ. With the meta-structure integrated with the RCA, it demonstrates a measured broadside directivity of 20.15 dBi without affecting its half-power directivity bandwidth. Benefiting from additive manufacturing, the proposed approach is a simple, light-weight, low-cost, and planar approach that can be tailored to achieve medium-to-high gains with RCAs.

Cone complementarity approach for dynamic analysis of multiple pendulums

The multibody system dynamics approach allows describing equations of motion for a dynamic system in a straightforward manner. This approach can be applied to a wide variety of applications that consist of interconnected components which may be rigid or deformable. Even though there are a number of applications in multibody dynamics, the contact description within multibody dynamics still remains challenging. A user of the multibody approach may face the problem of thousands or millions of contacts between particles and bodies. The objective of this article is to demonstrate a computationally straightforward approach for a planar case with multiple contacts. To this end, this article introduces a planar approach based on the cone complementarity problem and applies it to a practical problem of granular chains.

Bragg-Grating-Based Photonic Strain and Temperature Sensor Foils Realized Using Imprinting and Operating at Very Near Infrared Wavelengths

Thin and flexible sensor foils are very suitable for unobtrusive integration with mechanical structures and allow monitoring for example strain and temperature while minimally interfering with the operation of those structures. Electrical strain gages have long been used for this purpose, but optical strain sensors based on Bragg gratings are gaining importance because of their improved accuracy, insusceptibility to electromagnetic interference, and multiplexing capability, thereby drastically reducing the amount of interconnection cables required. This paper reports on thin polymer sensor foils that can be used as photonic strain gage or temperature sensors, using several Bragg grating sensors multiplexed in a single polymer waveguide. Compared to commercially available optical fibers with Bragg grating sensors, our planar approach allows fabricating multiple, closely spaced sensors in well-defined directions in the same plane realizing photonic strain gage rosettes. While most of the reported Bragg grating sensors operate around a wavelength of 1550 nm, the sensors in the current paper operate around a wavelength of 850 nm, where the material losses are the lowest. This was accomplished by imprinting gratings with pitches 280 nm, 285 nm, and 290 nm at the core-cladding interface of an imprinted single mode waveguide with cross-sectional dimensions 3 × 3 µm2. We show that it is possible to realize high-quality imprinted single mode waveguides, with gratings, having only a very thin residual layer which is important to limit bend losses or cross-talk with neighboring waveguides. The strain and temperature sensitivity of the Bragg grating sensors was found to be 0.85 pm/µε and −150 pm/°C, respectively. These values correspond well with those of previously reported sensors based on the same materials but operating around 1550 nm, taking into account that sensitivity scales with the wavelength.

2D wind clumping in hot, massive stars from hydrodynamical line-driven instability simulations using a pseudo-planar approach

Context. Clumping in the radiation-driven winds of hot, massive stars arises naturally due to the strong, intrinsic instability of line-driving (the line-deshadowing instability, hereafter LDI). But LDI wind models have so far mostly been limited to 1D, mainly because of the severe computational challenges regarding calculation of the multi-dimensional radiation force. Aim. In this paper we simulate and examine the dynamics and multi-dimensional nature of wind structure resulting from the LDI. Methods. We introduce a pseudo-planar, box-in-a-wind method that allows us to efficiently compute the line force in the radial and lateral directions, and then use this approach to carry out 2D radiation-hydrodynamical simulations of the time-dependent wind. Results. Our 2D simulations show that the LDI first manifests itself by mimicking the typical shell structure seen in 1D models, but that these shells quickly break up into complex 2D density and velocity structures, characterized by small-scale density “clumps” embedded in larger regions of fast and rarefied gas. Key results of the simulations are that density variations in the well-developed wind are statistically quite isotropic and that characteristic length scales are small; a typical clump size is ℓcl∕R*~ 0.01 at 2R*, thus also resulting in rather low typical clump masses mcl ~ 1017 g. Overall, our results agree well with the theoretical expectation that the characteristic scale for LDI generated wind-structure is on the order of the Sobolev length ℓSob. We further confirm some earlier results that lateral “filling in” of radially compressed gas leads to somewhat lower clumping factors in 2D simulations than in comparable 1D models. We conclude by discussing an extension of our method toward rotating LDI wind models that exhibit an intriguing combination of large- and small-scale structures extending down to the wind base.

Enhancing Mechanical Properties of Thin-Walled Structures Using Non-Planar Extrusion Based Additive Manufacturing

Traditional extrusion based additive manufacturing (AM) processes build parts by depositing material in planar layers. The development of processes that adopt a non-planar approach is becoming a subject of significant interest in AM research. It is expected that such processes will impart superior mechanical strength to anisotropic and thin-walled structures, and will especially be useful in exploiting continuous fiber reinforced composites in additive manufacturing. This paper presents an extrusion based non-planar additive manufacturing process. The process allows for the deposition of material along 3-dimensional paths, providing the capability to reorient deposition head, build objects on curved platforms, and create complete structures using one continuous strand. Two different parts are fabricated and tested in this paper. One is produced using the developed process, while the other is created using a commercial FDM 3D printer. The two specimens are then mechanically tested to examine their behavior in two different loading configurations, and to investigate the effect that the deposition method and orientation has on the failure mode.

Preoperative assessment of relative pulmonary lobar perfusion fraction in lung cancer patients

SummaryPreoperative quantification of (relative) pulmonary lobar perfusion fraction using scintigraphy is established in predicting lung function after pulmonary surgery. Aim was to develop an easy and truly anatomical method for relative pulmonary lobar perfusion fraction quantification using SPECT/CT and to compare results with those from planar analyses in lung cancer patients. Patients, methods: 36 patients with operable lung cancer, borderline lung function referred to pre-operative quantification. Perfusion SPECT-data were acquired p.i. of 163±9 MBq 99mTc-MAA, subsequent low-dose-CT (SymbiaT, Siemens). Iterative Flash3D-reconstruction, manual 3D segmentation of all lobes using PMOD. VOI transfer to coregistered perfusion SPECTdata, calculation of lobar fractions. Modelbased calculation of relative lobar fractions based on planar data, analysis of planar vs. 3D results using t-test. Results: Significant differences (p<0.05) between the results from 3D method and planar imaging were found for right upper and middle lobe and both lower lobes. Maximum differences ranged from 10.9% (left upper lobe) to 22.9% (right upper lobe). Conclusions: Relative pulmonary lobar perfusion fraction can easily be obtained by an anatomically driven 3D quantification. Results yielded by this method and the traditional planar approach differed greatly, possibly affecting eligibility for lung surgery in individual patients. Considering these results a 3D approach should be used whenever possible.

A Robust Method to Characterize Vertebral Geometry In Vivo

Wolff’s law postulates that bone will grow in the direction principal stress, as an effect of adaptation to this loading environment, and therefore will adjust their shape to prevent physiological imbalance. Altered geometry can be a mark of disease progression and degeneration just like a biomarker. For functional reasons, the vertebral body as a bone is not immune to these changes in geometry. Previous work in the literature has documented vertebral body geometry characteristics with age [1], its contribution to lordosis changes [2] and detected some asymmetric features [3]. These few descriptions available in the literature are limited due to their planar approach (radiography or individual CT slice cuts) [1, 2] or use of manual metrology devices that are subject to operator error, which might compromise its repeatability [3]. Based on the Wolff’s law premise, the hypothesis for this study is that a known alteration — spinal degeneration — of the spine configuration (lordosis) will also have an effect on the shape of the vertebral bodies. A common byproduct of spinal degeneration is also the presence of osteophytes in the intervertebral junction. To the best of the authors’ knowledge, no study has attempted to characterize hypothetical changes in vertebral geometry as in a population of low back pain symptomatic/ asymptomatic volunteers in vivo. The aim of this study is to prove said hypothesis by applying an accurate imaging technique that is insensitive to osteophytes and able to measure the vertebral body using subject-specific CT-based 3D models.