Geometric Asymmetry Research Articles

Geometry-induced rectification for an active object

The authors show that geometric asymmetry of an active particle rectifies its motion and induces unidirectional current.

Optimal asymmetry of transistor-based terahertz detectors

Detectors of terahertz radiation based on field-effect transistors (FETs) are among the most promising candidates for low-noise passive signal rectification both in imaging systems and wireless communications. However, it was not realized so far that geometric asymmetry of common FETs with respect to source-drain interchange is a strong objective to photovoltage harvesting. Here, we break the traditional scheme and reveal the optimally asymmetric FET structure, providing the maximization of THz responsivity. We fabricate a series of graphene transistors with variable top gate positions with respect to a mid-channel and compare their subterahertz responsivities in a wide range of carrier densities. We show that responsivity is maximized for input gate electrode shifted toward the source contact. Theoretical simulations show that for large channel resistance, exceeding the gate impedance, such a recipe for responsivity maximization is universal and holds for both resistive self-mixing and photo-thermoelectric detection pathways. In the limiting case of the small channel resistance, the thermoelectric and self-mixing voltages react differently upon changing the asymmetry, which may serve to disentangle the origin of nonlinearities in novel materials.

Estimation of Added Mass and Radiation Damping of Large Ocean Observation Buoy Using Numerical Analysis

Kim, D.; Shim, J.-S.; Min, Y.; Min, I.K., and Lim, H.S., 2021. Estimation of added mass and radiation damping of large ocean observation buoy using numerical analysis. In: Lee, J.L.; Suh, K.-S.; Lee, B.; Shin, S., and Lee, J. (eds.), Crisis and Integrated Management for Coastal and Marine Safety. Journal of Coastal Research, Special Issue No. 114, pp. 221–225. Coconut Creek (Florida), ISSN 0749-0208. A vane is to be installed to control the yawing behavior of a large ocean observation buoy (LOOB). The role of the vane is to control the yaw motion of the one-point mooring LOOB against current and waves. The lengths of the vanes were 0.8, 1.6, and 2.0 m, and the added mass tensor (6 × 6) and radiation damping tensor (6 × 6) at that time were estimated using computational fluid dynamics. In addition, the added mass tensor and radiation damping tensor according to the wave frequency domain are presented. Estimating the added mass and radiation damping of LOOB is important because it presents the hydrodynamic relationship between the structure and fluid. As a result of the analysis, the added mass was almost unchanged in other components except m66. On the other hand, m66 was proportional to the length of vane. When the length of the vane is 0.8 m, the maximum added mass is 1.28 × 104 kg (wave frequency 3.7 rad/s), and when the lengths are 1.6 and 2.0 m, it increases to 2.79 × 104 and 3.58 × 104 kg, respectively. This means that the length of the vane affects the resistance to rotational motion. In the case of radiation damping, the results were that the length of the vane and the radiation damping (component c66) were proportional. However, there is no significant difference depending on the length of the vane in the other components (c11 to c55). Radiation damping (c66) increased to 1.12 × 104, 3.56 × 104 and 4.46 × 104 kg, according to the length of the vane. In conclusion, it can be seen that the longer the vane, the better the yaw control effect. However, as the length of the vane increases, the geometric asymmetry of the LOOB increases. In addition, it can be cause fatal damage to small boats berthing the LOOB. Therefore, it is necessary to optimally design it by considering the advantages and disadvantages according to the length of the vane.

Auxin-dependent control of cytoskeleton and cell shape regulates division orientation in the Arabidopsis embryo

SummaryPremitotic control of cell division orientation is critical for plant development, as cell walls prevent extensive cell remodeling or migration. While many divisions are proliferative and add cells to existing tissues, some divisions are formative and generate new tissue layers or growth axes. Such formative divisions are often asymmetric in nature, producing daughters with different fates. We have previously shown that, in the Arabidopsis thaliana embryo, developmental asymmetry is correlated with geometric asymmetry, creating daughter cells of unequal volume. Such divisions are generated by division planes that deviate from a default “minimal surface area” rule. Inhibition of auxin response leads to reversal to this default, yet the mechanisms underlying division plane choice in the embryo have been unclear. Here, we show that auxin-dependent division plane control involves alterations in cell geometry, but not in cell polarity axis or nuclear position. Through transcriptome profiling, we find that auxin regulates genes controlling cell wall and cytoskeleton properties. We confirm the involvement of microtubule (MT)-binding proteins in embryo division control. Organization of both MT and actin cytoskeleton depends on auxin response, and genetically controlled MT or actin depolymerization in embryos leads to disruption of asymmetric divisions, including reversion to the default. Our work shows how auxin-dependent control of MT and actin cytoskeleton properties interacts with cell geometry to generate asymmetric divisions during the earliest steps in plant development.

Large eddy simulation of incident flows around polygonal cylinders

In this study, we carry out large eddy simulation of incident flow around polygonal cylinders of side number N=5−8 at Reynolds number Re=104. In total, six incidence angles (α) are studied on each cylinder ranging from face to corner orientations, thus covering the entire α spectrum. Special focus is put on the time-mean aerodynamic forces including lift, drag, and vortex shedding frequencies as well as the near wake flow features. It is found that because of y-plane asymmetry of polygonal cross sections at most incidence angles, the flow separation characteristics and hence the induced base pressure distribution and the aerodynamic forces exhibit unique and complex dependence on α and N. While the general inverse relation of drag coefficient and Strouhal number previously proposed from experimental observations at principal orientations still holds at arbitrary α, the variation of the two is found to be non-monotonic on both α and N. We also found that compared to the absolute time mean shear layer length measured from the final separation point, the extent of them stretched to the wake, measured from the cylinder center, is a powerful scaling factor for all the quantities investigated, including the wake characteristic length scales. In particular, the difference between the top and the bottom shear layer (due to geometrical asymmetry at arbitrary α) describes the variation of the non-zero time mean lift coefficient reasonably well, whose sign varies with N non-monotonically.

Analysis of angular dependent spatial frequency response of Digital Coplanar Translational Laminography

Digital Coplanar Translational Laminography (CTL) is a radiographic imaging technique that permits the visualization of structural details and discontinuities in the object of interest after 3D reconstruction from multiple projections. This technique becomes quite competitive regarding to computed tomography in situations of arrangements in which no complete rotation of the X-ray source - detector system around the object of interest is accessible or in cases where the part to be inspected has a high geometric asymmetry. The literature does not show many studies about image quality for different laminographic reconstructions and scan geometries. Different methodologies for measuring the Modulation Transfer Function (MTF) as a key image quality parameter for the aforementioned technique are applied. The MTF was measured using different approaches, pre-sampled MTF or sampled MTF, both based on the Fourier Transform-Magnitude Spectrum or the square wave MTF using line pattern gauges. A sample known as Siemens Star with a converging line pattern was used to measure the circular square wave MTF. This circular MTF provides information on the direction dependent contrast transfer related to the measurement conditions, the reconstruction algorithms and the translational scan direction. For this purpose, several MTF measurements were performed in multiple angular directions. Beyond it, reconstructions were performed using different algorithms (Filtered Shifted Average) and an iterative one (MART – Multiplicative Algebraic Reconstruction Technique). Image quality analysis were done for both reconstruction methods. MART showed an image quality improvement for challenging conditions for laminographic arrangements, such as for a low number of projections (down to 25 for this study, considered as limited view, limited angle reconstruction). Additionally, a Gadolinium gauge with parallel line patterns within a range from 10 μm to 1000 μm was used to compare the square wave MTF with the sine MTFs, measured by the different techniques mentioned above. The results show that the MTF techniques presented are equivalent in this study. The results obtained for this Gadolinium plate showed a good agreement between MTF10% and SRbimage measurements. The methodology presented here is used for the characterization of the frequency dependent spatial resolution of measurements obtained from different laminographic reconstruction techniques and scan geometries. Finally, from the acquisitions and reconstructions obtained with the Siemens Star, cross laminographic images were calculated in order to improve the direction dependent sensitivity. The results showed a better detectability for cross laminographic images in comparison to unidirectional coplanar translational laminographic images covering dead zones.

Asymmetric Cavity Mode Engineering in a Single Plasmonic Nanowire

Plasmon mode engineering enables the ability to manipulate the highly localized electromagnetic fields at the deep-subwavelength scale. Here, without introducing geometrical asymmetry, we propose a scheme to generate and control the asymmetric plasmon mode in a single nanowire cavity by the interference of cavity modes with opposite parities. Through a rigorous theoretical derivation and further verification with finite-element analysis, we show that the simultaneous excitation of odd and even cavity modes with mutual spectral and spatial overlap in a single nanowire enables a new hybridized plasmon mode with strong near-field directionality and high extinction ratio. By full exploitation of the incident electromagnetic field including its amplitude, phase, and spin components, the behavior of the asymmetric plasmon mode with its asymmetric field can be readily controlled over a broad wavelength range, offering versatility for controlling the cavity plasmon's spatial and spectral distribution at the nanoscale. Our approach can be applied to modulate the light-matter interaction and other functional devices in applications such as cavity quantum electrodynamics, information processing, sensing and lasing.

Uphill Anion Pumping through Triangular Nanofluidic Device of Reconstructed Layered Double Hydroxide

Numerous research efforts have been devoted to replicate the functioning of biological ion pumps in nanofluidic devices. Unlike previous reports of cationic pumps, positively charged CoAl layered double hydroxide (CoAl LDH) is exploited here for uphill pumping of anionic species. Nanofluidic membranes prepared by self-assembling exfoliated layers of CoAl LDH exhibit excellent anionic transport characteristics. At the surface-charge-governed regime, the positively charged CoAl LDH membrane (p-LDHM) showed a remarkable OH– ion conductivity of ∼2 mS cm–1. The remarkable mobility of OH– ions (4 × 10–4 cm2 V–1 S–1) in the atomically thin channel of p-LDHM is attributed to the tiny activation energy (0.09 eV) required for Grotthuss-like hopping of the ions between the positive charges of densely packed CoAl LDH layers. The lamellar p-LDHM was also found to be suitable for energy harvesting via salinity gradient, and a power density up to 0.7 Wm–2 was achieved under a 1000-fold concentration gradient. The triangular p-LDHM displays a diode-like nonlinear I–V curve, attributed to a combination of unipolar conductivity of counterions inside the two-dimensional (2D) nanochannels and geometrical asymmetry. The triangular p-LDHM pumps anions against the concentration gradient (up to 1000-fold), under fluctuating external potentials with a mean value of zero.

2D Particle-in-cell simulations of charged particle dynamics in geometrically asymmetric low pressure capacitive RF plasmas

Understanding the spatio-temporal dynamics of charged particles in low pressure radio frequency capacitively coupled plasmas (CCP) is the basis for knowledge based process development in these plasma sources. Due to the importance of kinetic non-local effects the particle in cell/Monte Carlo collision (PIC/MCC) simulation became the primary modeling approach. However, due to computational limitations most previous PIC/MCC simulations were restricted to spatial resolution in one dimension. Additionally, most previous studies were based on oversimplified treatments of plasma-surface interactions. Overcoming these problems could clearly lead to a more realistic description of the physics of these plasma sources. In this work, the effects of the reactor geometry in combination with realistic heavy particle and electron induced secondary electron emission coefficients (SEEC) on the charged particle dynamics are revealed by GPU based 2D3V PIC/MCC simulations of argon discharges operated at 0.5 Pa and at a high voltage amplitude of 1000 V. The geometrical reactor asymmetry as well as the SEECs are found to affect the power absorption dynamics and distribution functions of electrons and ions strongly by determining the sheath voltages and widths adjacent to powered and grounded surface elements as well as via the self-excitation of the plasma series resonance. It is noticed that secondary electrons play important roles even at low pressures. Electron induced secondary electrons (δ-electrons) are found to cause up to half of the total ionization, while heavy particle induced secondary electrons (γ-electrons) do not cause much ionization directly, but induce most of the δ-electron emission from boundary surfaces. The fundamental insights obtained into the 2D-space resolved charged particle dynamics are used to understand the formation of energy distribution functions of electrons and ions for different reactor geometries and surface conditions.

Sandwich "Ion Pool"-Structured Power Gating for Salinity Gradient Generation Devices.

Nanoconfinement ion transport, similar to that of biological ion channels, has attracted widespread research interest and offers prospects for broad applications in energy conversion and nanofluidic diodes. At present, various methods were adopted to improve the rectification performance of nanofluidic diodes including geometrical, chemical, and electrostatic asymmetries. However, contributions of the confinement effects within the channels were neglected, which can be a crucial factor for ion rectification behavior. In this research, we report an "ion pool"-structured nanofluidic diode to improve the confinement effect of the system, which was constructed based on an anodic aluminum oxide (AAO) nanoporous membrane sandwiched between zeolitic imidazolate framework 8 (ZIF-8) and tungsten oxide (WO3) thin membranes. A high rectification ratio of 192 is obtained through this nanofluidic system due to ions could be enriched or depleted sufficiently within the ion pool. Furthermore, this high-rectification-ratio ion pool-structured nanofluidic diode possessed pH-responsive and excellent ion selectivity. We developed it as a pH-responsive power gating for a salinity gradient harvesting device by controlling the surface charge density of the ion pool nanochannel narrow ends with different pH values, and hence, the ionic gate is switched between On and Off states, with a gating ratio of up to 27, which exhibited 8 times increase than ZIF-8-AAO and AAO-WO3 composite membranes. Significantly, the peculiar ion pool structure can generate high rectification ratios due to the confinement effect, which then achieves high gating ratios. Such ion pool-structured nanochannels created new avenues to design and optimize nanofluidic diodes and boosted their applications in energy conversion areas.

Electrically Tuning Characteristics of LC Selectively Infiltrated PCF Sagnac Interferometer

A photonic crystal fiber was selectively infiltrated only two of the air holes near the core with liquid crystal. The selective infiltration caused geometric asymmetry and created high birefringence. Because of the geometric asymmetry, the response to varying electric field is concerned with electric field direction. A Sagnac interferometer was set to investigate the electric tuning characteristics of the selectively infiltrated photonic crystal fiber. The effective refractive-indices of the fiber varies with electric field due to reorientation of liquid crystal molecules. The highest sensitivity was 1.12 nm/V (504 nm/kV/mm) with tuning range of 7 nm when electric field direction was parallel to the connecting line of infiltrated holes. The response time of the selectively infiltrated photonic crystal fiber was studied. The device can be utilized as voltage sensors, electro-optical modulators and filters.

Dynamically Tunable Friction via Subsurface Stiffness Modulation

Currently soft robots primarily rely on pneumatics and geometrical asymmetry to achieve locomotion, which limits their working range, versatility, and other untethered functionalities. In this paper, we introduce a novel approach to achieve locomotion for soft robots through dynamically tunable friction to address these challenges, which is achieved by subsurface stiffness modulation (SSM) of a stimuli-responsive component within composite structures. To demonstrate this, we design and fabricate an elastomeric pad made of polydimethylsiloxane (PDMS), which is embedded with a spiral channel filled with a low melting point alloy (LMPA). Once the LMPA strip is melted upon Joule heating, the compliance of the composite structure increases and the friction between the composite surface and the opposing surface increases. A series of experiments and finite element analysis (FEA) have been performed to characterize the frictional behavior of these composite pads and elucidate the underlying physics dominating the tunable friction. We also demonstrate that when these composite structures are properly integrated into soft crawling robots inspired by inchworms and earthworms, the differences in friction of the two ends of these robots through SSM can potentially be used to generate translational locomotion for untethered crawling robots.

Gas Monitoring in Human Frontal Sinuses-Stability Considerations and Gas Exchange Studies.

Acute rhinosinusitis is a common infectious disease, which, in more than 90% of cases, is caused by viruses rather than by bacteria. Even so, antibiotics are often unnecessarily prescribed, and in the long run this contributes to the alarming level of antibiotics resistance. The reason is that there are no good guiding tools for defining the background reason of the infection. One main factor for the clearance of the infection is if there is non-obstructed ventilation from the sinus to the nasal cavity. Gas in Scattering Media Absorption Spectroscopy (GASMAS) has potential for diagnosing this. We have performed a study of frontal sinuses of volunteers with a focus on signal stability and reproducibility over time, accurate oxygen concentration determination, and assessment of gas transport through passages, naturally and after decongestant spray administration. Different from earlier studies on frontal sinuses, water vapor, serving the purpose of oxygen signal normalization, was measured at 818 nm rather than earlier at 937 nm, now closer to the 760 nm oxygen absorption band and thus resulting in more reliable results. In addition, the action of decongestants was objectively demonstrated for the first time. Evaluated oxygen concentration values for left- and right-hand side sinus cavities were found to agree within 0.3%, and a left-right geometrical asymmetry parameter related to anatomical differences was stable within 10%.

Phenomenological Interpretations of Some Somatic Temporal and Spatial Patterns of Biophoton Emission in Humans

Biophoton emission remains controversial. The photo-genic origin of biophoton has been attributed to the oxidative stress or free radical production. However, there are considerable gaps in quantitative understanding of biophoton emission. I propose an analytical hypothesis for interpreting a few patterns of steady-state biophoton emission of human, including the dependency on age, the diurnal variation, and the geometric asymmetry associated with serious asymmetrical pathological conditions. The hypothesis is based on an alternative form of energy state, termed vivo-nergy, which is associated with only metabolically active organisms that are also under neuronal control. The hypothesis projects a decrease of the vivo-nergy in human during growth beyond puberty. The hypothesis also proposes a modification of the vivo-nergy by the phases of systematic or homeostatic physiology. The hypothesis further postulates that the deviation of the physiology-modified vivo-nergy from the pre-puberty level is deteriorated by acquired organ-specific pathological conditions. A temporal differential change of vivo-nergy is hypothesized to proportionally modulate oxidative stress that functions as the physical source of biophoton emission. The resulted steady-state diffusion of the photon emitted from a photo-genic source in a human geometry simplified as a homogeneous spherical domain is modeled by photon diffusion principles incorporating an extrapolated zero-boundary condition. The age and systematic physiology combined determines the intensity of the centered physiological steady-state photo-genic source. An acquired pathology sets both the intensity and the off-center position of the pathological steady-state photo-genic source. When the age-commemorated, physiology-commanded, and pathology-controlled modifications of the steady-state photo-genetic sources are implemented in the photon diffusion model, the photon fluence rate at the surface of the human-representing spherical domain reveals the patterns on age, the temporal variation corresponding to systematic physiology, and the geometric asymmetry associated with significant asymmetric pathological condition as reported for spontaneous biophoton emission. The hypothesis, as it provides conveniences for quantitative estimation of biophoton emission patterns, will be extended in future works towards interpreting the temporal characteristics of biophoton emission under stimulation.

Mechanical properties of PtS2 monolayer with rectangular defects: A molecular dynamics study

Using the classical molecular dynamics simulations, the mechanical properties of the PtS2 monolayer with rectangular defects have been investigated. Particularly, a counterintuitive defect enlargement method to recover from defect-induced mechanical degradation has been explored. As the rectangular defects are enlarged along the zigzag direction, the uniaxial tension has been firstly applied in the same direction. It's found that the Young’s modulus (Ys) increases slightly with the size of the defects. However, both the fracture strain and stress are increased obviously as the length of the rectangular defect increasing, indicating the recovery of the mechanical properties for the defective PtS2 monolayer. And this degradation recovery could be attributed to the higher degree of geometric asymmetry when the defect being lengthened. Then, the mechanical properties of the defective PtS2 monolayer under uniaxial tension in the armchair direction have also been studied. The calculations show that the Ys, fracture strain and stress decrease significantly as the rectangular defect enlarging. These results suggest even though the defect itself can induce the mechanical degradation, enlargement of the defect along a direction may promote the mechanical recovery in the same direction.

Cloud property trends in hot and ultra-hot giant gas planets (WASP-43b, WASP-103b, WASP-121b, HAT-P-7b, and WASP-18b)

Context. Ultra-hot Jupiters are the hottest exoplanets that have been discovered so far. Observations begin to provide insight into the composition of their extended atmospheres and their chemical day/night asymmetries. Both are strongly affected by cloud formation. Aims. We explore trends in cloud properties for a sample of five giant gas planets: the hot gas giant WASP-43b and the four ultra-hot Jupiters (UHJs) WASP-18b, HAT-P-7b, WASP-103b, and WASP-121b. This provides a reference frame for cloud properties for the JWST targets WASP-43b and WASP-121b. We further explore chemically inert tracers to observe geometrical asymmetries of UHJs and if the location of the inner boundary of a 3D global circulation model (3D GCM) matters for the clouds that form. Methods. A homogeneous set of 3D GCM results was used as input for a kinetic cloud formation code to evaluate the cloud opacity and gas parameters such as C/O, mean molecular weight, and degree of ionisation. We cast our results in terms of integrated quantities to enable a global comparison between the sample planets. Results. The large day/night temperature differences of UHJs cause the following chemical asymmetries: cloud-free days but cloudy nights, atomic versus molecular gases and their different mean molecular weights, deep thermal ionospheres versus low-ionised atmospheres, and undepleted versus enhanced C/O. WASP-18b, as the heaviest planet in the sample, has the lowest global C/O. Conclusions. The global climate may be considered as similar amongst UHJs, but different to that of hot gas giants. The local weather, however, is individual for each planet since the local thermodynamic conditions, and hence the local cloud and gas properties, differ. The morning and the evening terminator of UHJs will carry signatures of their strong chemical asymmetry such that ingress and egress asymmetries can be expected. An increased C/O ratio is a clear sign of cloud formation, making cloud modelling a necessity when utilising C/O (or other mineral ratios) as a tracer for planet formation. The changing geometrical extension of the atmosphere from the day to the nightside may be probed through chemically inert species such as helium. Ultra-hot Jupiters are likely to develop deep atmospheric ionospheres which may impact the atmosphere dynamics through magneto-hydrodynamic processes.

2D particle-in-cell simulations of geometrically asymmetric low-pressure capacitive RF plasmas driven by tailored voltage waveforms

The effects of the simultaneous presence of two different types of plasma asymmetry, viz, geometric and electrical, on low-pressure capacitively coupled argon discharges are studied by 2D3V graphics-processing-unit-based particle-in-cell/Monte Carlo simulations. The geometric asymmetry originates from the different powered vs grounded electrode surface areas, while the electrical asymmetry is established by applying peaks/valleys and sawtooth-up/-down driving voltage waveforms. While in geometrically symmetric discharges, the {peaks ↔ valleys} and the {sawtooth-down ↔ sawtooth-up} switching of the waveforms is equivalent to exchanging the powered and grounded electrodes, this transformation is violated when the geometric symmetry is broken. Under such conditions, the plasma characteristics and the DC self-bias generation behave differently, compared to the geometrically symmetric case. This leads to different sheath dynamics and, therefore, strongly influences the electron power absorption dynamics. For identical peak-to-peak voltages, the plasma density obtained for such tailored voltage waveforms is found to be higher compared to the classical single-frequency waveform case. Reduced plasma densities are found in the valleys- and sawtooth-down waveform cases, compared to the peaks- and sawtooth-up waveforms. By including realistic energy and material-dependent secondary electron emission (SEE) coefficients in the simulations, the electron-induced SEE is found to be reduced in the valleys- and sawtooth-down waveform cases, which explains the behaviour of the plasma density. Using such tailored waveforms in geometrically asymmetric discharges is also found to lead to the formation of different charged particle energy distributions at the boundary surfaces, compared to those in geometrically symmetric plasma sources.

On the need for simultaneous electrochemical testing of positive and negative electrodes in carbon supercapacitors

The lack of uniformity in the experimental conditions used for testing carbon supercapacitors by different authors highlights the need for standardized procedures to evaluate their performance. This study demonstrates the usefulness of a three-electrode arrangement in the investigation of electrochemical processes on both electrodes of double-layer carbon/carbon supercapacitors in a T-type sandwich-designed cell by performing simultaneous electrochemical measurements of positive and negative electrodes in six different acetonitrile-containing electrolytes. The testing employed electrochemical impedance spectroscopy, cyclic voltammetry, and constant current charging/discharging measurements. The results demonstrated that the impedance measurements were highly sensitive to the experimental arrangement and that the impedance data were distorted due to geometrical and electrical asymmetry within the cell. Such asymmetries did not affect cyclic voltammetry and constant current charging/discharging measurements, and the results proved valuable in the simultaneous investigations of both electrodes in supercapacitors. The study detected different behavior of anion and cation adsorption in the porous structure of carbon electrodes. While quaternary ammonium cations exhibit constant and even slightly increasing specific capacitances during successive cycling, specific capacitances of BF4− and PF6− anions exponentially decrease. Irreversible adsorption of anions inside the positive electrode explained such behavior. Overall, the results show the viability of a three-electrode arrangement in the investigation of electrochemical processes on both electrodes in supercapacitors and batteries. The results confirm that tetraethylammonium tetrafluoroborate is a superior electrolyte for carbon/carbon supercapacitors, while lithium tetrafluoroborate does not have adequate properties in acetonitrile for use in electrochemical power sources.

Magnetization reversal in shape asymmetric permalloy nanocaps

Symmetric and asymmetric ferromagnetic permalloy nanocaps of 100 nm diameter are investigated using micromagnetic simulations to study the influence of geometrical asymmetry on the magnetization reversal as a function of thickness. Symmetric nanocaps are featured by having a maximum thickness exactly at the center, whereas, in asymmetric nanocaps, the maximum thickness is at an oblique direction, 20° off to the center of the caps. Magnetization reversal and switching processes in asymmetric nanocaps are found to be strongly dependent on the field direction as well as on the thickness of the nanocaps. In the symmetric nanocaps, magnetization reversal happens via coherent rotation of the magnetic moments. On the other hand, magnetization reversal in asymmetric nanocaps happens via the formation of a non-uniform C-state. An increase in the nucleation field of C-state with the thickness of nanocaps indicates that the stability of the C-state increases with the thickness of the nanocaps. Formation of a C-state due to the shape-induced asymmetry results in distinct M-H loops that depends on the orientation of the nanocaps to the external field direction.

Investigation of an additively manufactured pentamode material using non-contact vibration transmissibility measurements

Pentamodal (PM) metamaterials are one potential means to enable concepts from transformation acoustics in underwater applications because they can be designed to support anisotropic longitudinal wave motion over wide frequency bands while simultaneously being impedance matched to water [Su et al., J. Acoust. Soc. Am. 141(6), (2017)]. In three dimensions, PM materials can be fabricated using additive manufacturing (AM) to create elastic lattice structures whose microstructure can be tailored to produce the desired anisotropic sound speed and impedance in a target frequency band. This work presents measurements of the vibrational response of a PM block designed to display anisotropic stiffness. The sample measures approximately 100x100x85 mm and is constructed from titanium using direct metal laser sintering. Measurements were made on a sample mounted on an electro-dynamic shaker providing base excitation between 0.05 and 20i kHz. A scanning laser Doppler vibrometer measured out-of-plane surface velocity with normals both parallel and orthogonal to the excitation axis. The finite extent of the sample introduces geometric asymmetry associated with domain truncation, which is observable in the vibrational modes. Measurements were made for various sample orientations and compared to full-featuredfinite element models. Simulation-experiment comparisons and other findings will be presented and discussed. [Work supported by ONR.]