Rotational Scanning Research Articles

Anisotropic cellular structure and texture microstructure of 316L stainless steel fabricated by selective laser melting via rotation scanning strategy

In this work, the effects of solidification and remelting under chessboard 67° rotation scanning strategy on the microstructure and properties of selective laser melted (SLMed) 316L stainless steel (316L SS) were studied, including dendrite microstructure, element distribution, grain orientation, dislocation structure, microhardness and corrosion resistance. We put forward a complete foundation relationship among texture, cellular structure and mechanical property influenced by anisotropy. Main results are summarized as follows: The 〈101〉 texture formation is the result of dendrite epitaxial growth. The cellular dislocation structure highly overlapped with dendrite significantly changed in remelting zone. Hence the high ratio of 〈101〉 texture signifies the anisotropy distribution of epitaxially growth dendrite which released the internal stress. The dislocation structure has a contribution to strength similar work hardening strengthening. Meanwhile, the 316L SS obtains Orowan strengthening via the nano oxide pinning effect in dislocation wall. Thus, the dislocation density and oxide distance obvious changed in different directions of cellular dislocation structure, resulting in the cellular dendrite regions performed higher microhardness than the columnar dendrite regions. The drastic change of dendrite increased the crack sensitivity of SLMed 316L SS, and the junction of different epitaxially growth direction dendrites formed high energy grain boundary.

Dark-field computed tomography reaches the human scale

X-ray computed tomography (CT) is one of the most commonly used three-dimensional medical imaging modalities today. It has been refined over several decades, with the most recent innovations including dual-energy and spectral photon-counting technologies. Nevertheless, it has been discovered that wave-optical contrast mechanisms-beyond the presently used X-ray attenuation-offer the potential of complementary information, particularly on otherwise unresolved tissue microstructure. One such approach is dark-field imaging, which has recently been introduced and already demonstrated significantly improved radiological benefit in small-animal models, especially for lung diseases. Until now, however, dark-field CT could not yet be translated to the human scale and has been restricted to benchtop and small-animal systems, with scan durations of several minutes or more. This is mainly because the adaption and upscaling to the mechanical complexity, speed, and size of a human CT scanner so far remained an unsolved challenge. Here, we now report the successful integration of a Talbot-Lau interferometer into a clinical CT gantry and present dark-field CT results of a human-sized anthropomorphic body phantom, reconstructed from a single rotation scan performed in 1 s. Moreover, we present our key hardware and software solutions to the previously unsolved roadblocks, which so far have kept dark-field CT from being translated from the optical bench into a rapidly rotating CT gantry, with all its associated challenges like vibrations, continuous rotation, and large field of view. This development enables clinical dark-field CT studies with human patients in the near future.

Eccentric-rotation-scanned ptychography and its application in multispectral watermarking

Due to the uncertainty that may occur during one experiment, the repetition of the same sample experiment is particularly important. Here we propose a novel eccentric-rotation-scanned ptychography (eRSP), eccentric rotation scanning is used to collect diffraction patterns instead of traditional mesh scanning. In the process of collecting diffraction patterns, only the single variable of rotation angle needs to be controlled. The position error is reduced from two-dimensional to one-dimensional, and the difficulty of experimental operation is greatly reduced. The repeatability of the experiment has been significantly improved. Rotating scanning can also avoid the raster grid pathology. In this paper, the theory of eRSP is introduced, and the feasibility of this method has been analyzed by simulation and optical experiment. A multi-spectral information hiding system based on eRSP was proposed. The double random-phase encoding system with a color random phase mask is embedded into a retractable cylinder. A super-continuum white laser source is used as the incident beam, records the ciphertext diffraction pattern by rotating the cylinder and embedded them into the host image. Additional eccentric distance key, rotation angle key, spectrum key and telescopic distance key are introduced, which greatly enhance the system security. Numerical simulations are implemented to demonstrate the feasibility, security and robustness of the proposed scheme.

S-wave anisotropy from two dipole sonic data processing methods, confronted with fracture permeability, logs and cores

The present paper consists in two parts, determined by the historical emerging production of Dipole Sonic Imager (DSI) measurements and results in the early 1990’s. The DSI data were processed following two methods simultaneously developed in France and in USA by Schlumberger. In the first part the early dipole sonic S-wave velocity results obtained in late 1993 are confronted with the other borehole data obtained in the scientific borehole MM-1, entirely cored and extensively logged, as part of the comprehensive scientific project named Géologie Profonde de la France (GPF), conducted by the Bureau de Recherches Géologiques et Minières (BRGM, i.e. the French Geological Survey), in Ardèche, southern France. In 1994, José Perrin summarized and integrated all the borehole information including the preliminary results from an azimuthal “rotation scan” of S-wave sonic slowness determination method quickly developed in Schlumberger-France and aiming at detecting only the presence of S-wave velocity anisotropy in a first step. The initial results were presented to the French industrial logging community in April 1994, prior to the commercialization of any S-wave splitting computer detection routine applied to dipole sonic data. The second part focuses on the comparison of the dipole sonic S-wave anisotropy detection results from two methods produced at a later time by Schlumberger, namely: a) results from the commercial S-wave anisotropy detection routine based on cross energy minimization, obtained in October 1994, and b) principal S-wave azimuth results sorted from the “rotation scan” azimuthal method, produced in 1995 and further improved in July 1997. After discussing the discrepancies of the principal fast S-wave azimuth derived from the two methods with diverse specialists in Schlumberger, over several years, and on a spare time basis, the authors expose constructive explanations in the present paper. A limited overview of the latest dipole sonic data processing developments has also been attempted to better understand the differing S-wave birefringence results obtained in MM-1, suggesting that the rock formation in the immediate borehole vicinity, up to three times the borehole radius, may not be homogeneous along the borehole depth depending on the local geological context. Besides, the Fast Azimuth split S-wave (FAZ) fits with the strike of major regional faults and parallel to the maximal horizontal palaeo-stress, which happens to be nearly orthogonal to the local present stress direction accepted by the geologists! The present case study suggests that the S-wave anisotropy results ought to become more reliable, mainly on the accuracy and precision of the FAZ. Additionally, the efficiency of the semblance parameter for S-wave attenuation anisotropy detection is pondered, where no S-wave velocity anisotropy is detected over the dipole sonic receiver array.

3D Multi-Track and Multi-Layer Epitaxy Grain Growth Simulations of Selective Laser Melting.

An integrated simulation framework consisting of the 3D finite element method and 3D cellular automaton method is presented for simulating the multi-track and multi-layer selective laser melting (SLM) process. The framework takes account of all the major multi-physics phenomena in the SLM process, including the initial grain structure, the growth kinetics, the laser scanning strategy, the laser–powder and laser–matter interactions, the melt flow, and the powder-to-liquid-to-solid transformations. The feasibility of the proposed framework is demonstrated by simulating the evolution of the epitaxy grain structure of Inconel 718 (IN718) during a 15-layer SLM process performed using a bi-directional 67° rotation scanning strategy and various SLM process parameters. The simulation results are found to be in good agreement with the experimental observations obtained in the present study and in the literature. In particular, a strong (001) texture is observed in the final component, which indicates that the grains with a preferred <001> orientation win the competitive epitaxy grain growth process. In addition, the size and shape of the IN718 grains are governed primarily by the cooling rate, where the cooling rate is determined in turn by the SLM parameters and the build height. Overall, the results show that the proposed framework provides an accurate approach for predicting the final microstructures of SLM components, and therefore, it can play an important role in optimizing the SLM processing parameters in such a way as to produce components with the desired mechanical properties.

PARAMETER’S INVESTIGATION ON Al2O3 CERAMIC USING LASER TURNING

The investigation deals with the turning of Alumina (Al2[Formula: see text] ceramic using various parameters of the input process. The experimental design has been used based on Taguchi technology to perform the experimentation. Pulse frequency, average laser power, work piece rotational speed and feed rate are the process inputs considered during investigation. The Signal-to-Noise ratio values are used for measuring various outputs. The best amount of spot overlap has been reached with various combined parameter settings. In addition, a better width of the rotational scan has been attained by varying axial feed rate as well as the rotational speed of the work piece. Micro-turned deviation (depth) and machined surface finish at different input parametric combinations were considered as output reactions for machining. During the laser turning operation, analyses learned the effect of overlaps on the various inputs considered for output measurements such as micro-degree deviation and surface roughness. The investigation reveals that the surface finish decreases with an increase in overlap in the circumferential direction and rotation of the work sample. The maximum surface finish is 0.507[Formula: see text][Formula: see text]m achieved at a frequency of 5000[Formula: see text]Hz, 300[Formula: see text]rpm work piece cutting speed, 8.5[Formula: see text]W power and 0.4[Formula: see text]mm/s feed.

Imaging characteristics and image restoration method for large field circular scanning system

Large field circular scanning system obtains remote sensing images by rotating scanning, which is one of the technical ways to effectively expand the field of view of geostationary orbit optical remote sensing imaging system. However, due to its special rotation scanning imaging mechanism, the on-orbit imaging process of this system is affected by the coupling of detector rotation sampling, satellite platform vibration, optical system aberration and other factors, so the image degradation characteristics are very complex. In this paper, the on-orbit imaging characteristics of large field circular scanning system are first analyzed to provide a theoretical basis for the subsequent research of image restoration method. Secondly, aiming at the problems of annular geometric distortion and spatial blur of the system image, the image restoration method is proposed based on ring block and regularization methodology. Experimental results show that under the condition of detector rotation speed ω <0.06 rad/s, the proposed method exhibited a satisfactory processing performance.

Detection of Mandibular Canal in Human Dry Mandibles with Cone Beam Computed Tomography using 270° and 360° Protocols under Continuous and Pulse Modes – A Comparative Study

Background: Cone beam computed tomography (CBCT) enables practitioner to accurately localize and mark the nerve canal. The rotation of the X-ray tube and the detector around the patient's head produces multiple projection images. A high number of projections is associated with increased radiation dose to the patient, higher spatial and contrast resolution. Shorter scan arc results in reduced scan time, reduced dose and smaller file sizes. The pulsed X-ray beam reduces the actual exposure time than the scanning time and the patient radiation exposure. Aim: (1) To assess and compare the diagnostic efficacy between pulse mode and continuous mode (2) To assess and compare the diagnostic efficacy between 270° and 360° CBCT rotational protocols Subjects and Methods: A total of 30 Intact Dentate or Partially dentate dry human mandibles consisting first, second, and third molars were subjected to a total of 4 CBCT scans: 270° rotation scans under continuous and pulse mode, 360° rotation scans under continuous and pulse mode using two CBCT units. Distance from the inferior cortical border of mandible (ICBM) to the roof of the inferior alveolar nerve canal (IANC) was measured at four locations: mental foramen, first, second and third molar. The results were then compared. Results: Comparison of the IANC length measurements for the two modes revealed no significant difference. Conclusion: Shorter scan arc and pulse mode can be adopted in patients finding it difficult to remain stable for prolonged periods of time, while maintaining appreciable clarity and quality of image. This could apply to geriatric patients, children, mentally challenged, in patients with trauma, neurological diseases, anxiety, claustrophobia, wherein the patient's movements might need re-scanning, which would lead to an extra radiation dose to the patient.

Three-Dimensional Map of Descemet Membrane Endothelial Keratoplasty Detachment: Development and Application of a Deep Learning Model.

PurposeTo develop and apply a neural network for quantification of endothelial corneal graft detachment using anterior segment (AS) OCT.DesignTraining and validation of a neural network and application within a prospective cohort.ParticipantsPatients two weeks after Descemet membrane endothelial keratoplasty.MethodsInvestigators manually labeled the posterior cornea and the graft in cross-sectional images of rotational AS OCT scans. Neural networks for image segmentation were trained to identify the area of graft detachment on cross-sectional images. The best-performing neural network with the lowest misclassification (Youden index) and highest spatial overlap with the ground truth (Dice coefficient) was selected and evaluated in a separate dataset. Three-dimensional maps of the area and volume of graft detachment were calculated. For application, the neural network’s rating on the detachment was compared with slit-lamp–based ratings of cornea specialists on the same day as the AS OCT imaging took place.Main Outcome MeasuresYouden index and Dice coefficient.ResultsNeural networks were trained on 27 AS OCT scans with 6912 labeled images. Among 48 combinations of probability thresholds and epoch states, the best-performing neural network showed a Youden index of 0.99 and a Dice coefficient of 0.77, indicating low misclassification and good spatial overlap on individual image segmentation. In the validation set unknown to the neural network with 20 scans (5120 images), the Youden index was 0.85 and the Dice coefficient was 0.73, and a high overall performance compared with the manually labeled ground truth (R2 = 0.90). In the application set with 107 eyes, the neural network estimated the mean percent detachment larger than the cornea specialist (mean difference, 8.2 percentage points; 95% confidence interval, 6.2–10.2). Masked review of 42 AS OCTs with more than ±10 percentage points difference in ratings showed that clinicians underestimated the true detachment in cases with significant detachment requiring intervention.ConclusionsDeep learning-based segmentation of AS OCT images quantified the percent and the volume of DMEK graft detachment with high precision. Fully automated 3-dimensional quantification of graft detachment is highly sensitive, particularly in corneas with a significant amount of detachment, and may support decision making.

The Importance of Subsurface Residual Stress in Laser Powder Bed Fusion IN718

The residual stress (RS) in laser powder bed fusion (LPBF) IN718 alloy samples produced using a 67°‐rotation scan strategy is investigated via laboratory X‐ray diffraction (XRD) and neutron diffraction (ND). The location dependence of the strain‐free (d0) lattice spacing in ND is evaluated using a grid array of coupons extracted from the far‐edge of the investigated specimen. No compositional spatial variation is observed in the grid array. The calculated RS fields show considerable non‐uniformity, significant stress gradients in the region from 0.6 to 2 mm below the surface, as well as subsurface maxima that cannot be accounted for via XRD. It is concluded that failure to determine such maxima would hamper a quantitative determination of RS fields by means of the stress balance method.

How 9-month-old crawling infants profit from visual-manual rotations in a mental rotation task

Studies show that visual-manual object exploration influences spatial cognition, and specifically mental rotation performance in infancy. The current work with 9-month-old infants investigated which specific exploration procedures (related to crawling experience) support mental rotation performance. In two studies, we examined the effects of two different exploration procedures, manual rotation (Study 1) and haptic scanning (Study 2), on subsequent mental rotation performance. To this end, we constrained infants’ exploration possibilities to only one of the respective procedures, and then tested mental rotation performance using a live experimental set-up based on the task used by Moore and Johnson (2008). Results show that, after manual rotation experience with a target object, crawling infants were able to distinguish between exploration objects and their mirror objects, while non-crawling infants were not (Study 1). Infants who were given prior experience with objects through haptic scans (Study 2) did not discriminate between objects, regardless of their crawling experience. Results indicated that a combination of manual rotations and crawling experience are valuable for building up the internal spatial representation of an object.

High resolution three- dimensional visualization using neutron computerized tomography images

This paper presents a modified Neutron Computerized Tomography (NCT) reconstruction method to obtain an effective and accurate 3D volume rendering with more cleared details that achieve the optimization for contrast, raise the resolution, real view and reduce noise. This proposed method depends on dealing with the slice duplication in case of full scan by dividing the sinogram into two halves by considering the rotation angle from 0° to 180° and from 180° to 360°. In this case, and after solving the center of rotation problem, three reconstructed slices will be obtained, the first one for the full scan from 0° to 360° that has two congruent slices, the second one for the first half of sinogram that represents the first half cycle of the full scan from 0° to 180°, the third one for the second half of sinogram that represents the second half cycle of the full scan from 180° to 360°. By building the 3D volume rendering to each of these three reconstructed slices, the 3D volume rendering of the first slice that resulted from the first half of sinogram proved a high-quality volume visualization compared to the 3D volume rendering resulted from half rotation scan (180° scan) and the 3D volume resulted from the current existing working software in the neutron computerized tomography facility in Egypt Second Research Reactor (ETRR-2).

Orientation dependent tensile properties of a selective-laser-melt 316L stainless steel

The effect of specimen inclination angle with respect to building direction on the tensile properties of a selective laser melt 316L alloy was investigated. Tensile test specimens were fabricated with the angles between 0° to 90° at 15° intervals using a rotation scanning. In addition, 316L alloy test specimens were generated in the ANSYS 2020R1 additive module and tensile tested in LS-DYNA in order to determine the effect of residual stresses on the tensile strengths. The microscopic analysis revealed a strong ⟨110⟩ fiber texture orientation along the building direction (the loading axis of 0° inclined specimens) and a weak <111> texture or nearly random distribution of directions in the normal to the building direction (tensile loading axis of 90° inclined specimens). The yield and tensile strength increased and ductility decreased with increasing inclination angle. The strength variation with the inclination angle was shown well-fitted with the Tsai-Hill failure criterion. Although, the used numerical models indicated an inclination-dependent residual stress, the difference in the residual stresses was much lower than the difference in the strengths between 0° and 90° inclined specimens. Predictions showed a lower twinning stress in 0° inclined specimens due to ⟨110⟩ fiber texture orientation in the tensile axis. The fiber texture resulted in extensive twinning; hence, higher ductility and tension-compression asymmetry in 0° inclined specimens. Based on these results, the variations in the strength and ductility of tested SLM-316L specimens with the inclination angle was ascribed to the variations in the angle between the fiber texture orientation and loading axis.

Rotational coronary angiography in heart transplant recipients

As a screening method for detecting coronary lesions, coronary angiography (CAG) is becoming increasingly important in the activities of transplant centers. Angiography examination of coronary arteries is performed in potential recipients of various organs, related donors, and annually in heart recipients. Given the grave condition of recipients in the early post-transplant period and annual angiographic studies, it is necessary to strive for reduction of radiation load on the body and reduction of dose of X-ray contrast agents used.Objective: to assess the possibilities of using rotational CAG in the activities of transplant centers.Materials and methods. We observed 254 patients who underwent CAG. Their ages ranged from 21 to 79 years (mean 46.92 ± 1), and 90% were men. All patients were divided into two groups: group 1 included 142 patients who underwent rotational CAG, while group 2 was the control group (where classical polyprojection CAG was performed) and included 112 patients. Group 1 was divided into 2 subgroups – the subgroup of patients after heart transplantation who underwent endomyocardial biopsy along with CAG (n = 51), and the subgroup of patients who underwent only rotational CAG.Results. In 91% of patients, CAG was performed by radial access. In group 1, stenotic lesions were detected in 33 patients: 19 had single-vessel lesions, 9 had two-vessel lesions, and 5 had three-vessel lesions. A total of 56 hemodynamically significant stenoses were detected, 9 of which were chronic total occlusions. In 83 patients (60%), performing only 2 series of rotational scans (one left and one right coronary artery) was sufficient. In 32 (23%) patients, one more clarifying projection was required, in 17 patients two and in 9 – 3–5 additional projections. In 3 cases, we switched to polyprojection CAG. The average amount of contrast agent used was 24.4 ± 0.9 ml, the average X-ray dose was 34561.3 ± 1695.2 mGycm2. The need for a contrast agent was significantly higher in the comparison group – 24.4 ± 0.9 mL and 103.5 ± 1.7 mL, respectively. The average X-ray dose in the main group was 34561.3 ± 1695.2 mGycm2, in the comparison group 41430.9 ± 4141.7 mGycm2. However, there was no significant difference between the groups. Subgroup analysis showed that patients who underwent only rotational CAG had lower radiation exposure compared to patients who underwent CAG combined with endomyocardial biopsy biopsy (EMB), as well as significantly lower load compared to the control group.Conclusion. Rotational CAG can be considered as the method of choice at transplant centers, where screening diagnostics of the state of the coronary bed is required, which is equivalent in terms of information content and safety. Rotational CAG allows to reduce the amount of injected contrast agent by more than three times, which in turn reduces the number of associated complications, as well as the radiation exposure of patients and medical personnel.

Efficient high cone-angle artifact reduction in circular cone-beam CT using deep learning with geometry-aware dimension reduction

High cone-angle artifacts (HCAAs) appear frequently in circular cone-beam computed tomography (CBCT) images and can heavily affect diagnosis and treatment planning. To reduce HCAAs in CBCT scans, we propose a novel deep learning approach that reduces the three-dimensional (3D) nature of HCAAs to two-dimensional (2D) problems in an efficient way. Specifically, we exploit the relationship between HCAAs and the rotational scanning geometry by training a convolutional neural network (CNN) using image slices that were radially sampled from CBCT scans. We evaluated this novel approach using a dataset of input CBCT scans affected by HCAAs and high-quality artifact-free target CBCT scans. Two different CNN architectures were employed, namely U-Net and a mixed-scale dense CNN (MS-D Net). The artifact reduction performance of the proposed approach was compared to that of a Cartesian slice-based artifact reduction deep learning approach in which a CNN was trained to remove the HCAAs from Cartesian slices. In addition, all processed CBCT scans were segmented to investigate the impact of HCAAs reduction on the quality of CBCT image segmentation. We demonstrate that the proposed deep learning approach with geometry-aware dimension reduction greatly reduces HCAAs in CBCT scans and outperforms the Cartesian slice-based deep learning approach. Moreover, the proposed artifact reduction approach markedly improves the accuracy of the subsequent segmentation task compared to the Cartesian slice-based workflow.

Metazoan activity facilitates passive sediment trapping in modern supratidal microbialites: Revealed using µ-CT-scanning and microscopy.

Microbialites are formed through two processes, the trapping and binding of sediment grains and mineral precipitation. Sediment trapping and binding result in coarse sandy textures, whereas fine micritic textures are produced by mineral precipitation. Although well-studied modern microbialites (e.g. Bahamas and Shark Bay) are formed through the former process, purely trapped-and-bound examples are rare throughout the geologic record and limited to shallow-marine environments. Through the use of conventional microscopy and 3D micro-computed tomography (µ-CT) scanning, this study found that South African coastal microbialites have a primarily mineral precipitated texture, although detrital material is included sporadically. Furthermore, these modern microbialites exhibit both micritic and fibrous layering with high porosity. The novel use of 3D microtomography rotational scans has revealed that microbialites are extensively burrowed by metazoan activity and was also able to distinguish the occurrence and distribution of heavy minerals and detrital shell material in the samples. Some of the detrital grains appeared to be accidental/random inclusions, while in other cases the metazoan burrows provided space for the accumulation of sediment once abandoned. In both cases, sediment was incorporated as a product of intermittent accumulation, rather than systematic trapping and binding. The microfabric texture of South African microbialites is therefore a function of both biological (e.g. microbially mediated precipitation) and environmental (e.g. sporadic sediment deposition and inorganic cementation) influence. Overall, the findings presented here highlight the importance of these systems regarding microbialite formation, ichnology and taphonomy.

Combined frameless stereotactical biopsy and intraoperative cerebral angiography by 3D-rotational fluoroscopy with intravenous contrast administration: a feasibility study

BackgroundMobile 3-dimensional fluoroscopes are an integral part of modern neurosurgical operating theatres and can also be used in combination with free available image post processing to depict cerebral vessels. In preparation of stereotactic surgery, preoperative Computed Tomography (CT) may be required for image fusion. Contrast CT may be of further advantage for image fusion as it regards the vessel anatomy in trajectory planning. Time-consuming in-hospital transports are necessary for this purpose. Mobile 3D-fluoroscopes may be used to generate a CT equal preoperative data set without an in-hospital transport. This study was performed to determine the feasibility and image quality of intraoperative 3-dimensional fluoroscopy with intravenous contrast administration in combination with stereotactical procedures.Methods6 patients were included in this feasibility study. After fixation in a radiolucent Mayfield clamp a rotational fluoroscopy scan was performed with 50 mL iodine contrast agent. The image data sets were merged with the existing MRI images at a planning station and visually evaluated by two observer. The operation times were compared between the frame-based and frameless systems (“skin-to-skin” and “OR entry to exit”).ResultsThe procedure proves to be safe. The entire procedure from fluoroscope positioning to the transfer to the planning station took 5–6 min with an image acquisition time of 24 s. In 5 of 6 cases, the fused imaging was able to reproduce the vascular anatomy accurately and in good quality. Both time end-points were significantly shorter compared to frame-based interventions.ConclusionThe images could easily be transferred to the planning and navigation system and were successfully merged with the MRI data set. The procedure can be completely integrated into the surgical workflow. Preoperative CT imaging or transport under anaesthesia may even be replaced by this technique in the future. Furthermore, hemorrhages can be successfully visualized intraoperatively and might prevent time delays in emergencies.

Absorption modes of M\xf6bius strip resonators

In this work, the electromagnetic response of a mathematically interesting shape—a Möbius strip—is presented, along with a ring resonator for comparison. Both resonators consist of a central lossy dielectric layer bounded by perfectly conducting layers. For the case of the Möbius strips, the computational results show that there are a family of half-integer wavelength modes within the dielectric layer. These additional modes result in increased absorption, and a corresponding reduction in the radar cross section. Interestingly, rotational scans show that these modes can be excited over a large angular range. This investigation gives an understanding of the electromagnetic response of these structures, paving the way for future experiments on Möbius strip resonators.

Rheology, Hydration, and Microstructure of Portland Cement Pastes Produced with Ground Açaí Fibers

Açaí (Euterpe oleracea) is a Brazilian typical fruit that is enveloped by natural fibers. This work investigated the effect of incorporating ground açaí fibers (in natura and chemically treated with NaOH and HCl) in 5–10 wt.% replacement of Portland cement on the rheology, hydration, and microstructure of pastes. Rotational rheometry, isothermal calorimetry, X-Ray Diffraction (XRD), and Scanning Electron Microscopy (SEM) were performed to evaluate the cement pastes, in addition to SEM-EDS, FTIR, zeta potential, and XRD for fiber characterization. The results showed that the chemical treatment reduced the cellulose and lignin contents in açaí fibers while increasing its surface roughness. The addition of 5% of either fiber slightly increased the yield stress and viscosity of paste, while 10% addition drastically increased these properties, reaching yield stress and viscosity values respectively 40 and 8 times higher than those of plain paste. The incorporation of 5% in natura fibers delayed the cement hydration by about 2.5 days while 10% in natura fibers delayed it by over 160 h. The chemical treatment significantly reduced this retarding effect, leading to a 3 h delay when 5% treated fibers were incorporated. Overall, the combined NaOH/HCl treatment was effective for açaí fibers functionalization and these fibers can be used in cementitious composites.

A Miniature High-Frequency Rotary Ultrasonic Encoder for Internal Ultrasound Imaging

High-speed mechanical rotation scanning is the main imaging method of current high-frequency internal ultrasound. Due to uneven drag on the catheter driveshaft leading to changes in the rotational speed, Nonuniform rotational deformity (NURD) is critically limited for the quantitative analysis of internal ultrasound use. To date there have been no techniques shown that provide effective and dynamic modulation of NURD. In this work, a micro structured high-frequency rotary ultrasonic encoder with cylinder gratings was developed, which can dynamically fix the NURD and get high quality restored image. Accordingly, a prototyped micro rotary 50-MHZ ultrasonic encoder with a miniature diameter of 3 mm and a selection of resolutions up to 64 pulses per revolution, which should be the smallest and highest frequency rotary ultrasonic encoder ever reported, was demonstrated based on an endoscopic ultrasound system. The miniature high-frequency rotary ultrasonic encoder shows great potential for ultrasonic endoscopy, OCT, and other mechanical scanning imaging.