Asymmetric Distortion Research Articles

Response to an applied electric field in an antiferroelectric 1/2 subphase: The role of thermal fluctuations.

The response to an applied electric field in the q_{T}=1/2 subphase of the MC881-MC452 binary mixture system is studied by using thick homeotropically aligned cells. In the ordinary antiferroelectric SmC_{A}^{*} and 1/2 (sub)phases, some nonplanar asymmetric distortions in the antiferroelectric unit cell structure produce induced polarization in the applied field direction, starts to unwind the helix from the beginning, and tends to align the averaged tilt plane direction parallel to the applied field. In the 1/2 subphase under consideration, however, the helix resists being deformed at the beginning and then the thresholdlike steep increase of birefringence Δn occurs in the transition from 1/2 to unwound SmC^{*} at a field of less than 0.5V/µm; we conclude that the thermal fluctuations play an important role in promoting the director flip-flopping in a single layer under the applied field and bring about additional induced polarization, which counteracts the aforementioned ordinary induced one and prevents the helix from unwinding. This suggests that the Langevin-like director reorientation is the mechanism of the V-shaped switching which was actually observed in the thin films of Mitsui mixture [Phys. Rev. Lett. 87, 015701 (2001)0031-900710.1103/PhysRevLett.87.015701] and must have been used in prototyped thresholdless antiferroelectric liquid-crystal displays.

Appearance and modeling of bubble artifacts in intracranial magnetic resonance-guided laser interstitial thermal therapy (MRg-LITT) temperature images

PurposeTo understand if unexplained signal artifacts in MRg-LITT proton resonance frequency- (PRF-) shift thermometry images are caused by air bubbles or hemorrhages, and to characterize their effects on temperature measurements. MethodsRetrospective image data from an IRB-approved clinical trial of intracranial MRg-LITT were inspected for asymmetric distortions observed in phase data during ablations, which have been previously reported as likely hemorrhages. A total of eight patient cases were selected: seven with artifact occurrence and one without. Mathematical image models for air bubbles or hemorrhages were implemented to estimate the size of the air bubble or hemorrhage needed to explain the clinically observed phase artifacts. Correlations and Bland-Altman analyses were used to determine if an air bubble model or a hemorrhage model was better correlated to the clinical data. The model was used to inject bubbles into clean PRF phase data without artifacts to examine how temperature profile distortions change with slice orientation. The simulated air-bubble injected data were compared to clinical data containing artifacts to examine the bubbles' effects on temperature and thermal damage estimates. ResultsThe model demonstrated that air bubbles up to approximately 1 cm in diameter could explain the clinically observed phase artifacts. The bubble model predicts that a hemorrhage would have to be 2.2 times as large as an air bubble in order to explain the same extent of phase distortion observed in clinical data. Air bubbles had 16% percent higher correlations to the clinical PRF phase data than hemorrhages, even after rescaling the hemorrhage phases to better match the data. The air bubble model also explains how the phase artifacts lead to both large positive and large negative temperature errors, up to ±100 °C, which could cascade to damage estimate errors of several millimeters. ConclusionResults showed that the artifacts are likely caused by air bubbles rather than hemorrhages, which may be introduced before heating or appear during heating. Manufacturers and users of devices that rely upon PRF-shift thermometry should be aware these phase distortions from bubble artifacts can result in large temperature errors.

Central nodes of canine functional brain networks are concentrated in the cingulate gyrus

Compared to the field of human fMRI, knowledge about functional networks in dogs is scarce. In this paper, we present the first anatomically-defined ROI (region of interest) based functional network map of the companion dog brain. We scanned 33 awake dogs in a “task-free condition”. Our trained subjects, similarly to humans, remain willingly motionless during scanning. Our goal is to provide a reference map with a current best estimate for the organisation of the cerebral cortex as measured by functional connectivity. The findings extend a previous spatial ICA (independent component analysis) study (Szabo et al. in Sci Rep 9(1):1.25. https://doi.org/10.1038/s41598-019-51752-2, 2019), with the current study including (1) more subjects and (2) improved scanning protocol to avoid asymmetric lateral distortions. In dogs, similarly to humans (Sacca et al. in J Neurosci Methods. https://doi.org/10.1016/j.jneumeth.2021.109084, 2021), ageing resulted in increasing framewise displacement (i.e. head motion) in the scanner. Despite the inherently different approaches between model-free ICA and model-based ROI, the resulting functional networks show a remarkable similarity. However, in the present study, we did not detect a designated auditory network. Instead, we identified two highly connected, lateralised multi-region networks extending to non-homotropic regions (Sylvian L, Sylvian R), including the respective auditory regions, together with the associative and sensorimotor cortices and the insular cortex. The attention and control networks were not split into two fully separated, dedicated networks. Overall, in dogs, fronto-parietal networks and hubs were less dominant than in humans, with the cingulate gyrus playing a central role. The current manuscript provides the first attempt to map whole-brain functional networks in dogs via a model-based approach.

ReLOAD: Using Reinforcement Learning to Optimize Asymmetric Distortion for Additive Steganography

Recently, the success of non-additive steganography has demonstrated that asymmetric distortion can remarkably improve security performance compared with symmetric cost functions. However, most of current existing additive steganographic methods are still based on symmetric distortion. In this paper, for the first time we optimize asymmetric distortion for additive steganography and propose an A3C(Asynchronous Advantage Actor-Critic) based steganographic framework, called ReLOAD. ReLOAD is composed of an actor and a critic, where the former guides action selection for pixel-wise distortion modulation, and the latter evaluates the performance of modulated distortion. Meanwhile, a reward function that considers embedding effects is proposed to unify the goal of steganography and reinforcement learning, so that the minimization of embedding effects can be achieved by learning secure policy to maximize total rewards. Statistical analysis shows that compared with non-additive steganography, ReLOAD achieves lower change rates and makes embedding traces more consistent with cover image textures. Comprehensive experiments conducted on both hand-crafted feature-based and deep learning-based steganalyzers show that ReLOAD significantly promotes the state-of-the-art security performance of current additive methods and even outperforms non-additive steganography when the modification distribution gets sparser.

A Study of Hypersonic Vehicle-Borne SAR Imaging Under Plasma Sheath

Hypersonic vehicle-borne synthetic aperture radar (SAR) imaging has promising application prospects for remote sensing owing to the characteristics of fast response and flexible trajectory. However, a newly observed phenomenon that occurs during hypersonic flight, called the plasma sheath, seriously affects hypersonic vehicle-borne SAR imaging. Therefore, in this study, the effect of plasma sheath on hypersonic vehicle-borne SAR imaging is investigated systematically. First, a hypersonic vehicle-borne SAR signal model under plasma sheath is developed. Then, the phase shift and amplitude attenuation which are critical in the SAR signal model under plasma sheath are deduced. Moreover, the analytical formulas for the linear and quadratic phase errors are derived. Based on the developed signal model, point target response and an SAR image of an area under plasma sheath show that linear phase error will cause image shift, and quadratic phase error will lead to pulse broadening. In addition, the amplitude attenuation will make the point target response submerged in noise, and signal amplitude nonlinear distortion will result in an asymmetric distortion phenomenon. To further explore the effect of plasma sheath on hypersonic vehicle-borne SAR imaging, quantitative evaluation and analysis of SAR imaging degradation are conducted under different electron densities, carrier frequencies, and bandwidths. The evaluation results in this study will benefit the application of hypersonic vehicle-borne SAR imaging under plasma sheath, and the analytical formulas of linear and quadratic phase error provide the possibility to compensate for SAR imaging degradation under plasma sheath in the future.

Probing the Structure of SDSS J1004+4112 through Microlensing Analysis of Spectroscopic Data

AbstractWe aim to uncover the structure of the continuum and broad emission line (BEL) emitting regions in the gravitationally lensed quasar SDSS J1004+4112 through unique microlensing signatures. Analyzing 20 spectroscopic observations from 2003 to 2018, we study the striking deformations of various BEL profiles and determine the sizes of their respective emitting regions. We use the emission line cores as a baseline for no microlensing and then apply Bayesian methods to derive the sizes of the Lyα, Si IV, C IV, C III], and Mg II emitting regions, as well as of the underlying continuum-emitting sources. We find that the sizes of the emitting regions for the BELs are a few light-days across, notably smaller than in typical lensed quasars. The asymmetric distortions observed in the BELs suggest that the broad-line region lacks spherical symmetry and is likely confined to a plane. The inferred continuum emitting region sizes are larger than predictions based on standard thin-disk theory by a factor of ∼ 4. We find that the size-wavelength relation is in agreement with that of a geometrically thin and optically thick accretion disk.

Error Analysis of Digital Electric Energy Metering Based on FPGA

With the emergence and development of smart grid, digital meters have been widely used in substations, so the research on digital energy metering error has become a research hotspot. The purpose of this paper is to analyze the error of digital power measurement based on FPGA, mainly take the analog input fusion module and digital power meter in the digital power measurement system as the research object, and analyze the source of measurement error. An FPGA-based energy metering error detection platform is built to analyze the energy metering error when there are harmonics in the full energy metering method currently used by most digital energy meter manufacturers. The comparative analysis of numerical integration algorithms shows that the asymmetric distortion rates of the simulated waveforms are approximate. The results of measurement error analysis under harmonic conditions show that when the number of sampling points per cycle is 60, the power measurement errors of the 2nd to 4th harmonics are equivalent. The magnitude of the measurement error is still consistent with other low-order harmonics, and the simulation results are consistent with the theoretical analysis results.

Cation Valences and Multiferroic Properties of EuTiO3 Co-Doped with Ba and Transition Metals of Co/Ni.

Eu1−xBaxTi1−yMyO3 (M = Co or Ni) was sintered at 1400 °C under a reduction atmosphere. X-ray photoelectron spectroscopy revealed the mixed valences of Eu2+/Eu3+ and Ti4+/Ti3+ in EuTiO3 and Eu0.7Ba0.3TiO3, as well as some oxygen vacancies required to keep the charge neutrality. The co-doping of Co2+/Ni2+ in Eu0.7Ba0.3TiO3 resulted in the disappearance of oxygen vacancies, as a result of a reduction in Ti3+ numbers and an increase in Eu3+ numbers. On the other hand, Ba2+ doping led to an increased lattice parameter due to its larger ionic size than Eu2+, whereas the Co2+/Ni2+ co-doping resulted in smaller lattice parameters because of the combined effects of ionic size and variation in the oxygen-vacancy numbers. Eu0.7Ba0.3TiO3 exhibited a clear ferroelectricity, which persisted in the Co2+/Ni2+ co-doped samples until the doping levels of y = 0.05 and 0.10, respectively. Eu0.7Ba0.3TiO3 remained to be antiferromagnetic with a reduced transition temperature of 3.1 K, but co-doping of Co2+/Ni2+ turned the samples from antiferromagnetic to ferromagnetic with transition temperatures of 2.98 K and 2.72 K, respectively. The cause for such a transition could not be explained by the larger lattice volume, oxygen vacancies and mixed valences of Eu2+/Eu3+, which were proposed in previous works. Instead, it was more likely to arise from a large asymmetric distortion of the Eu–O polyhedron introduced by the aliovalent doping, which promotes the admixture of Eu 5d and 4f states.

Microstructure and abrasive wear resistance evolution of water and liquid nitrogen forced cooling Fe-Cr-C deposit

Fe-Cr-C arc hardfacing deposits under air cooling (AC), water forced cooling (WC) and liquid nitrogen forced cooling (NC) were investigated. The fastest cooling rate and the lowest cooling finish temperature were obtained by WC and NC, respectively. Compared with AC and WC, NC led to the highest macro- and micro-hardness, and the most wear resistant. According to the three-body abrasive wear test results of dry sand/rubber wheel, the wear resistance of NC was 1.29 times that of AC. The cooling finish temperature (−125 ℃) of NC promoted the martensitic transformation. The martensite of NC was observed in the matrix of eutectic structure rather than in primary austenite (P-A), and showed a tetragonal structure, with lattice parameters a= 0.285 nm, c= 0.305 nm, because the high interstitial atom C in the lattice caused asymmetric lattice distortion.

Ultra-Long Lived Luminescent Triplet Excited States in Cyclic (Alkyl)(amino)carbene Complexes of Zn(II) Halides.

The high element abundance and d10 electron configuration make ZnII‐based compounds attractive candidates for the development of novel photoactive molecules. Although a large library of purely fluorescent compounds exists, emission involving triplet excited states is a rare phenomenon for zinc complexes. We have investigated the photophysical and ‐chemical properties of a series of dimeric and monomeric ZnII halide complexes bearing a cyclic (alkyl)(amino)carbene (cAAC) as chromophore unit. Specifically, [(cAAC)XZn(μ‐X)2ZnX(cAAC)] (X=Cl (1), Br (2), I (3)) and [ZnX2(cAAC)(NCMe)] (X=Br (4), I (5)) were isolated and fully characterized, showing intense visible light photoluminescence under UV irradiation at 297 K and fast photo‐induced transformation. At 77 K, the compounds exhibit improved stability allowing to record ultra‐long lifetimes in the millisecond regime. DFT/MRCI calculations confirm that the emission stems from 3XCT/LEcAAC states and indicate the phototransformation to be related to asymmetric distortion of the complexes by cAAC ligand rotation. This study enhances our understanding of the excited state properties for future development and application of new classes of ZnII phosphorescent complexes.

Experimental characterization and modeling of complex anisotropic hardening in quenching and partitioning (Q&P) steel subject to biaxial non-proportional loadings

Quenching and partitioning (Q&P) steels, as one of the third-generation advanced high strength steels, exhibit complex anisotropic hardening behavior under biaxial non-proportional loadings. In this study, a wide range of strain path changes (SPCs) defined as an angle (χ) between stress deviators before and after the SPC is experimentally applied to characterize the anisotropic hardening of a Q&P steel with a strength grade of 980 MPa (QP980). The investigated SPCs include uniaxial tension followed by compression (UT-UC; χ=180°), uniaxial compression followed by tension (UC-UT; χ=180°), uniaxial tension followed by plane strain (UT-PS; χ=30°), equi-biaxial tension followed by plane strain (EBT-PS; χ=30°), followed by uniaxial tension (EBT-UT; χ=60°) and followed by simple shear (EBT-SH; χ=90°). These SPCs are achieved by the program-controlled biaxial tensile testing equipment using novel arm-reinforced cruciforms. The experimental findings in the QP980 steel sheet are summarized as follows: (1) Strong strain-dependent Bauschinger effect, transient hardening and permanent softening are observed in both UT-UC and UC-UT loadings; (2) Bauschinger effect increases as strain increases, and it exhibits obvious tension-compression asymmetry; (3) The transient hardening behaviors are path-dependent under SPCs with various χ; (4) The Bauschinger coefficient is approximately a parabola function of cosχ; (5) The most significant strength softening occurs under EBT-SH loading. In order to describe the complex hardening behavior of the QP980 steel, a distortional hardening model is proposed on the basis of non-associated flow rule. A coupled quadratic and stress-invariant-based yield function is used to describe stress anisotropy, strength differential effect, and anisotropic hardening for proportional loadings. Then, the Bauschinger effect related hardening and path-dependent permanent softening are captured by a modified homogeneous anisotropic hardening model. The calibrated model parameters and experimental validations demonstrate that the strain- and path-dependent Bauschinger effect can be well predicted by the proposed constitutive model. Especially, the model enables to accurately describe both the asymmetric anisotropic hardening and yield surface distortions of the QP980 steel at various biaxial SPCs.

Regulating Pseudo-Jahn–Teller Effect and Superstructure in Layered Cathode Materials for Reversible Alkali-Ion Intercalation

The Jahn-Teller effect (JTE) is one of the most important determinators of how much stress layered cathode materials undergo during charge and discharge; however, many reports have shown that traces of superstructure exist in pristine layered materials and irreversible phase transitions occur even after eliminating the JTE. A careful consideration of the energy of cationic distortion using a Taylor expansion indicated that second-order JTE (pseudo-JTE) is more widespread than the aforementioned JTE because of the various bonding states that occur between bonding and antibonding molecular orbitals in transition-metal octahedra. As a model case, a P2-type Mn-rich cathode (Na3/4MnO2) was investigated in detail. MnO6 octahedra are well known to undergo either elongation or contraction in a specific direction due to JTE. Here, the substitution of Li for Mn (Na3/4(Li1/4Mn3/4)O2) helped to oxidize Mn3+ to Mn4+ suppressing JTE; however, the MnO6 octahedra remained asymmetric with a clear trace of the superstructure. With various advanced analyses, we disclose the pseudo-JTE as a general reason for the asymmetric distortions of the MnO6 octahedra. These distortions lead to the significant electrochemical degradation of Na3/4Li1/4Mn3/4O2. The suppression of the pseudo-JTE modulates phase transition behaviors during Na intercalation/deintercalation and thereby improves all of the electrochemical properties. The insight obtained by coupling a theoretical background for the pseudo-JTE with verified layered cathode material lattice changes implies that many previous approaches can be rationalized by regulating pseudo-JTE. This suggests that the pseudo-JTE should be thought more important than the well-known JTE for layered cathode materials.

3D saliency guided deep quality predictor for no-reference stereoscopic images

The use of 3D technologies is growing rapidly, and stereoscopic imaging is usually used to display the 3D contents. However, compression, transmission and other necessary treatments may reduce the quality of these images. Stereo Image Quality Assessment (SIQA) has attracted more attention to ensure good viewing experience for the users and thus several methods have been proposed in the literature with a clear improvement for deep learning-based methods. This paper introduces a new deep learning-based no-reference SIQA using cyclopean view hypothesis and human visual attention. First, the cyclopean image is constructed considering the presence of binocular rivalry that covers the asymmetric distortion case. Second, the saliency map is computed considering the depth information. The latter aims to extract patches on the most perceptual relevant regions. Finally, a modified version of the pre-trained Convolutional Neural Network (CNN) is fine-tuned and used to predict the quality score through the selected patches. Five distinct pre-trained models were analyzed and compared in term of results. The performance of the proposed metric has been evaluated on four commonly used datasets (3D LIVE phase I and phase II databases as well as Waterloo IVC 3D Phase 1 and Phase 2). Compared with the state-of-the-art metrics, the proposed method gives better outcomes. The implementation code will be made accessible to the public at: https://github.com/o-messai/3D-NR-SIQA

Analysis of Influence of Doppler Asymmetric Spatial Heterodyne Interferogram Distortion on Phase Inversion Accuracy

Analysis of Influence of Doppler Asymmetric Spatial Heterodyne Interferogram Distortion on Phase Inversion Accuracy

Reversible structural transition of two-dimensional copper selenide on Cu(111)

Structural engineering opens a door to manipulating the structures and thus tuning the properties of two-dimensional materials. Here, we report a reversible structural transition in honeycomb CuSe monolayer on Cu(111) through scanning tunneling microscopy and Auger electron spectroscopy (AES). Direct selenization of Cu(111) gives rise to the formation of honeycomb CuSe monolayers with one-dimensional moiré structures (stripe-CuSe), due to the asymmetric lattice distortions in CuSe induced by the lattice mismatch. Additional deposition of Se combined with post annealing results in the formation of honeycomb CuSe with quasi-ordered arrays of triangular holes (hole-CuSe), namely, the structural transition from stripe-CuSe to hole-CuSe. Further, annealing the hole-CuSe at higher temperature leads to the reverse structural transition, namely from hole-CuSe to stripe-CuSe. AES measurement unravels the Se content change in the reversible structural transition. Therefore, both the Se coverage and annealing temperature play significant roles in the reversible structural transition in CuSe on Cu(111). Our work provides insights in understanding of the structural transitions in two-dimensional materials.

Spinal deformity measurement using a low-density flexible array ultrasound transducer: A feasibility study with phantoms

Spinal deformities assessment using 3D ultrasound scanning has limitations in fitting onto different back surface contour as well as fitting within the gaps between subject and their spinal brace during bracing assessments. The study proposed a flexible array ultrasound transducer to overcome these limitations.The results demonstrated the feasibility of spinal deformity assessments with a flexible ultrasound array when arranged in four shapes, namely Linear, Concave, Convex, and S-shaped. For comparisons of imaging performance on spinous process using the four shapes, Convex and S-shaped transducer showed a depth dependence and lateral location dependence of the lateral intensity distribution of spinous process, respectively. S-shaped transducer had the least accurate prediction of the location of spinous process, with measurement error of 4.8 ​± ​3.2 ​mm, it also showed poorer prediction on spinal curvature measurements. This is suggested to be due to the asymmetrical distortion to the spinous process due to the lateral location dependence of the image. However, the coronal curve prediction of spine phantom performed well with R-squared values of >0.97 in all transducer shapes.The results of this study paved the way for further investigation on the improvement of image quality and measurement accuracy under different shapes for the flexible array, mechanism of dynamic shape change during the scanning to fit different body contour, as well as extension from 1D to 2D flexible array.

Inertial Cavitation Behaviors Induced by Nonlinear Focused Ultrasound Pulses.

Inertial cavitation induced by pulsed high-intensity focused ultrasound (pHIFU) has previously been shown to successfully permeabilize tumor tissue and enhance chemotherapeutic drug uptake. In addition to HIFU frequency, peak rarefactional pressure ( p- ), and pulse duration, the threshold for cavitation-induced bioeffects has recently been correlated with asymmetric distortion caused by nonlinear propagation, diffraction and formation of shocks in the focal waveform, and therefore with the transducer F -number. To connect previously observed bioeffects with bubble dynamics and their attendant physical mechanisms, the dependence of inertial cavitation behavior on shock formation was investigated in transparent agarose gel phantoms using high-speed photography and passive cavitation detection (PCD). Agarose phantoms with concentrations ranging from 1.5% to 5% were exposed to 1-ms pulses using three transducers of the same aperture but different focal distances ( F -numbers of 0.77, 1.02, and 1.52). Pulses had central frequencies of 1, 1.5, or 1.9 MHz and a range of p- at the focus varying within 1-18 MPa. Three distinct categories of bubble behavior were observed as the acoustic power increased: stationary near-spherical oscillation of individual bubbles, proliferation of multiple bubbles along the pHIFU beam axis, and fanned-out proliferation toward the transducer. Proliferating bubbles were only observed under strongly nonlinear or shock-forming conditions regardless of frequency, and only where the bubbles reached a certain threshold size range. In stiffer gels with higher agarose concentrations, the same pattern of cavitation behavior was observed, but the dimensions of proliferating clouds were smaller. These observations suggest mechanisms that may be involved in bubble proliferation: enhanced growth of bubbles under shock-forming conditions, subsequent shock scattering from the gel-bubble interface, causing an increase in the repetitive tension created by the acoustic wave, and the appearance of a new growing bubble in the proximal direction. Different behaviors corresponded to specific spectral characteristics in the PCD signals: broadband noise in all cases, narrow peaks of backscattered harmonics in the case of stationary bubbles, and broadened, shifted harmonic peaks in the case of proliferating bubbles. The shift in harmonic peaks can be interpreted as a Doppler shift from targets moving at speeds of up to 2 m/s, which correspond to the observed bubble proliferation speeds.

One-Cycle Fourier Finite Position Set PLL

This work introduces a new method for computing the angular position of the voltage of the grid—based on a finite set of angles—in the condition of failures in the distribution systems, as symmetrical and asymmetric voltage sags, unbalance, harmonic distortions, and frequency changes. This method is inspired in the model predictive control finite control set principles. In this way, the proposal employs the One-Cycle Fourier filter (OCF) to estimate the positive sequence of the voltage vector into the stationary αβ-frame. The positive sequence voltages extracted from this filter is then handled by an algorithm that is implemented by a finite position set (FPS) for estimating the phase angle. In this way, the minimized cost function chooses the optimal angular position while using the predicted behavior of the grid voltage vector elements in dq frame. The structure, called One-Cycle Fourier Finite position Set Phase Locked Loop (OCF-FS-PLL), here is a composition of the OCF and the FPS. The results that were obtained in an experimental test bench validate the proposed method.

Optical distortion correction considering radial and tangential distortion rates defined by optical design

This paper proposes a high-accuracy distortion correction method for optical imaging distortion mapping and computational image predistortion. Due to the establishment of the predistortion is based on the distortion evaluation in the common optical design software CODE V, it can be used in the broad field of optical imaging system. Two distortion correction methods considering radial and tangential distortion rates which defined by optical design are introduced to perform distortion correction, and the forward and inverse image warping interpolation methods are adopted, separately. Simulations are conducted to verify the effectiveness in correcting complex distortion for freeform off-axis optical system. Furthermore, we implement a distortion correction experiment for an augmented reality head-mounted display that suffers from an asymmetric distortion with the maximum tangential distortion over 7%. For the first method, fast and high-accuracy image warping is achieved, and the RMS error of the approximation predistortion image is less than 1 pixel. Meanwhile, the RMS errors of the corrected imaging points are approximately 1.93 pixels vertically and 2.16 pixels horizontally when using a 5-megapixel camera. The second method considers the additional influence of the actual machining and assembly errors of the optical system, and the RMS errors of 0.89 pixels vertically and 0.85 pixels horizontally are achieved.

Droplet asymmetry and wetting dynamics on irregularly roughened surfaces

This study illustrates pervasive challenges in studying wetting dynamics, including dynamic contact angles, on irregularly roughened surfaces. We demonstrate that asymmetric water droplet shapes occur more than 50% of the time during static and dynamic contact angle measurements on sandblasted Zn-plated stainless steel with a polymeric overcoat. The pinning that causes the asymmetric drop shape distortion on horizontal surfaces also influences the sliding behavior on inclined surfaces. These effects lead to a poor correlation between the measured dynamic contact angles and the observed sliding angles (critical tilt angles). Our work emphasizes that large variations in the values of these dynamic wetting parameters are inherent to the heterogeneity of the surface roughness, and thus they limit the usefulness of standard dynamic wetting criteria. These findings have implications for academic and industrial research focused on making coated materials that have consistent wettability properties throughout their usage life cycle.