Sample Rotation Research Articles

On-site in situ high-pressure ultrafast pump-probe spectroscopy instrument.

We conceive and construct an on-site in situ high-pressure time-resolved ultrafast optical spectroscopy instrument that facilitates ultrafast pump-probe dynamics measurements under high pressure conditions. We integrate an ultrafast pump-probe spectroscopy system with a diamond anvil cell (DAC) system. Significantly, both the DAC and the sample are fixed within the light path without motion and rotation throughout the whole ultrafast spectroscopy experiment, including tuning and calibrating the pressure. This instrument thus avoids introducing artifacts due to sample motion or rotation, enabling precision high-pressure ultrafast pump-probe dynamics investigations. As a demonstrating example, we compare the effect of on-site in situ conditions with off-site in situ conditions on the ultrafast dynamics of Sr2IrO4 under 0-44.5GPa high pressure. Our data and analysis show that conventional possible artifacts are greatly reduced by using the on-site in situ layout. Our work helps the high-pressure ultrafast science investigation develop into a promising new area, which enables the exploration of nonequilibrium excited quantum states in the high-pressure regime.

Maximizing efficiency of dipolar recoupling in solid-state NMR using optimal control sequences.

Dipolar recoupling is a central concept in the nuclear magnetic resonance spectroscopy of powdered solids and is used to establish correlations between different nuclei by magnetization transfer. The efficiency of conventional cross-polarization methods is low because of the inherent radio frequency (rf) field inhomogeneity present in the magic angle spinning (MAS) experiments and the large chemical shift anisotropies at high magnetic fields. Very high transfer efficiencies can be obtained using optimal control–derived experiments. These sequences had to be optimized individually for a particular MAS frequency. We show that by adjusting the length and the rf field amplitude of the shaped pulse synchronously with sample rotation, optimal control sequences can be successfully applied over a range of MAS frequencies without the need of reoptimization. This feature greatly enhances their applicability on spectrometers operating at differing external fields where the MAS frequency needs to be adjusted to avoid detrimental resonance effects.

Measurement of crystallographic orientation of quartz crystal using Raman spectroscopy: application to entrapped inclusions

Raman spectroscopy has been widely used in mineralogy and petrology for identifying mineral phases. Some recent applications of Raman spectroscopy involve measuring the residual pressure of mineral inclusions, such as quartz inclusions in garnet host, to recover the entrapment pressure condition during metamorphism. The crystallographic orientations of entrapped inclusions and host are important to know for the modelling of their elastic interaction. However, the analysis of tiny entrapped mineral inclusions using EBSD technique requires time consuming polishing. The crystallographic orientations can be measured using polarized Raman spectroscopy, as the intensities of Raman bands depend on the mutual orientation between the polarization direction of the laser and the crystallographic orientation of the crystal. In this study, the Raman polarizability tensor of quartz is first obtained and is used to fit arbitrary orientations of quartz grains. We have implemented two rotation methods: (1) sample rotation method, where the sample is rotated on a rotation stage, and (2) polarizer rotation method, where the polarization directions of the incident laser and the scattered Raman signal are parallel and can be rotated using a circular polarizer. The precision of the measured crystallographic orientation is systematically studied and is shown to be ca. 0.25 degrees using quartz wafers and quartz plates that are cut along known orientations. It is shown that the orientation of tiny mineral inclusions (ca. 2–5 μm) can be precisely determined and yield consistent results with EBSD.

Effect of Growth Parameters on MoS2 Film Quality Deposited by Low-Temperature MOCVD Using I-Pr2DADmo(CO)3 and (t-C4H9)2S2

This study investigates the effect of various deposition parameters on the MOCVD film growth and provide guidelines for process optimization for the film quality improvement. As a typical result, 93 % coverage with average grain size of 70-80 nm and maximum grain size of approximately 110 nm was achieved in 4 h deposition time at 450°C using non-toxic precursors. Further improvement can be expected by CVD apparatus refinement for uniform precursor supply and/or sample rotation.

Orthopedic Surgery Residency Program Website Content and Accessibility During the COVID-19 Pandemic: Observational Study.

BackgroundThe exceptional competitiveness of the orthopedic surgery specialty, combined with the unclear impact of the COVID-19 pandemic on residency recruitment, has presented significant challenges to applicants and residency program directors. With limited in-person opportunities in the 2020-2021 application cycle, applicants have been pressed to gauge chances and best fit by browsing program websites.ObjectiveThe aim of the study was to assess the accessibility and content of accredited orthopedic surgery residency program websites during the COVID-19 pandemic.MethodsUsing the online database of the Electronic Residency Application Service (ERAS), we compiled a list of accredited orthopedic surgery residency programs in the United States. Program websites were evaluated across four domains: program overview, education, research opportunities, and application details. Each website was assessed twice in July 2020, during a period of adjustment to the COVID-19 pandemic, and twice in November 2020, following the October ERAS application deadline.ResultsA total of 189 accredited orthopedic surgery residency programs were identified through ERAS. Of these programs, 3 (1.6%) did not have functional website links on ERAS. Data analysis of content in each domain revealed that most websites included program details, a description of the didactic curriculum, and sample rotation schedules. Between the two evaluation periods in July and November 2020, the percentage of program websites containing informative videos and virtual tours rose from 12.2% (23/189) to 48.1% (91/189; P<.001) and from 0.5% (1/189) to 13.2% (25/189; P<.001), respectively. However, the number of programs that included information about a virtual subinternship or virtual interview on their websites did not change. Over the 4-month period, larger residency programs with 5 or more residents were significantly more likely to add a program video (P<.001) or virtual tour (P<.001) to their websites.ConclusionsMost residency program websites offered program details and an overview of educational and research opportunities; however, few addressed the virtual transition of interviews and subinternships during the COVID-19 pandemic.

Deep depth profiling using gas cluster secondary ion mass spectrometry: Micrometer topography development and effects on depth resolution.

Secondary ion mass spectrometry using the argon cluster primary ion beam enables molecular compositional depth profiling of organic thin films with minimal loss of chemical information or changes in sputter rate. However, for depth profiles of thicker organic films (> 10 μm of sputtered depth) we have observed the rapid formation of micron-scale topography in the shape of pillars that significantly affect both the linearity of the sputter yield and depth resolution. To minimize distortions in the 3D reconstruction of the sample due to this topography, a step-wise, staggered sample rotation was employed. By using polymer spheres embedded in an organic film, it was possible to measure the depth resolution at the film-sphere interface as a function of sputtered depth and observe when possible distortions in the 3D image occurred. In this way, it was possible to quantitatively measure the effect of micron-scale topography and sample rotation on the quality of the depth profile.

DETERMINATION OF WOOD COMPOSITION USING SOLID-STATE 13C NMR SPECTROSCOPY

In recent years, solid-state 13C NMR spectroscopy using the technique of cross-polarization (CP) and sample rotation at a magic angle (MAS) has been widely used in the analysis of plant materials, including wood. Knowledge of the composition, structure and behavior of wood components under various conditions is of great importance, since the properties of wood materials depend on this. In this work, differences in the composition of wood belonging to various tree species growing in central Russia (spruce, aspen, birch, oak, linden, pine, poplar and larch) were revealed using CP MAS 13C NMR spectroscopy. The assignment of various peaks in CP MAS 13C NMR spectra to the main components of wood was carried out. It was shown that cellulose is present in its amorphous and crystalline forms, the presence of lignin was unambiguously confirmed by the signals of aromatic carbon atoms, and hemicelluloses were detected by the signals from the carbon atoms of methyl groups of acetylxylose and L-rhamnose. According to the integral intensities, the total ratio of cellulose and hemicelluloses to lignin was determined: the largest amount of lignin was found in coniferous wood (spruce, larch and pine), and the smallest amount of lignin was detected in deciduous species (aspen, oak, linden, birch and poplar).

Direct cross-sectional imaging using X-ray Compton scattering: application to commercial batteries.

A synchrotron-based technique using Compton scattering imaging is presented. This technique has been applied to a coin battery (CR2023), and the cross-sectional image has been obtained in 34 ms without sample rotation. A three-dimensional image of the whole structure has been reconstructed from 74 cross-sectional images taken consecutively by scanning the incident, wide X-ray beam along one direction. This work demonstrates that quick cross-sectional imaging of regions of interest and three-dimensional image reconstruction without sample rotation are feasible using Compton scattering imaging.

Measurement of the refractive index of glass with 10−4 level accuracy based on the lateral displacement method

The measurement of the refractive index of optical glass samples is a common and fundamental activity in numerous fields of expertise. Several measurement techniques exist with relative accuracies from 10 − 2 to, at least, 10 − 7 with complexities that are inversely related to the corresponding uncertainty. We describe an implementation of a technique based on the measurement of the lateral displacement variation of a collimated beam caused by the rotation of a parallel plate glass sample. The method was aimed to achieve an uncertainty in the range from 10 − 3 to 10 − 4 without increasing the complexity normally associated with techniques with this level of accuracy. The system was designed and optimized based on a detailed analysis of the uncertainty budget. We describe the implementation, the data processing, and the results obtained with calibrated samples, showing a relative uncertainty at the level of 10 − 4.

CP MAS 13C NMR SPECTROSCOPY IN DETERMINATION OF SPECIFIC DIFFERENCES IN COMPOSITION OF WOOD

In recent years solid-state 13C NMR spectroscopy using the technique of cross-polarization (CP) and sample rotation at a magic angle (MAS) has been used in the analysis of plant materials, including wood. Knowledge of the composition, structure and behavior of wood components in different conditions is of great importance, since the properties of wood materials depend on this. In this work differences in the composition of various tree species wood in central Russia (birch, aspen, spruce, and larch) were revealed using CP MAS 13C NMR spectroscopy. Assignment of various peaks in CP MAS 13C NMR spectra with the main components of wood was carried out. It was shown that cellulose is presented in amorphous and crystalline forms, the presence of lignin is unambiguously confirmed by signals of aromatic carbon atoms, and hemicellulose is detected by signals from carbon atoms of methyl groups of acetylxylose and L-rhamnose. According to the integral intensities, the total proportion of cellulose and hemicellulose in relation to lignin was determined: the largest amount of lignin was found in coniferous wood (spruce, larch), and the smallest amount of lignin was detected in deciduous species (aspen and birch).

Barnett field, rotational Doppler effect, and Berry phase studied by nuclear quadrupole resonance with rotation

We report the observation of the Barnett field, rotational Doppler effect, and Berry phase using the rotating nuclear quadrupole resonance (NQR) method. We have developed coil-spinning techniques that enable us to systematically study the effects of rotation in setups involving rotation of the signal detector, rotation of the sample, and simultaneous rotation of both the signal detector and sample. Applying these setups to NQR measurements, we observe NQR line splittings in which the spectral structures are clearly distinct among the setups. By analyzing these structures, we clarify the origin of the NQR line splittings and discuss the relationship between the rotational Doppler effect, Barnett field effect, and Berry phase in terms of the rotational degrees of freedom, such as the relative rotation and the sample rotation itself, and the observation frame of reference. We also provide clear evidence of the difference between the rotational Doppler effect and the Barnett field and the equivalence of the Barnett field and the Berry phase.

True-to-size surface mapping with neutral helium atoms

Three-dimensional mapping of microscopic surface structures is important in many applications of technology and research, including areas as diverse as microfluidics, MEMS, and geoscience. However, on the nanoscale, using established techniques for such imaging can be extremely challenging. Scanning helium microscopy is a technique that uses neutral helium atoms as a probe, enabling completely nondestructive imaging. The technique is broadly applicable and ideal for many otherwise difficult-to-image materials, such as insulators, ultrathin nanocoatings, and biological samples. Here we present a method for implementation and operation of a stereo helium microscope, by applying the photometric stereo method of surface reconstruction to helium microscopy. Four detectors around the sample are typically required, but we show how sample rotation can be used to perform stereo reconstruction with a single-detector instrument, or to improve the quality of the reconstructed surface by increasing the number of independent measurements. We examine the quality of the reconstructed surface and show that for low aspect ratio good absolute height is recovered. For features with height/width $\ensuremath{\sim}1$ the shape of the surface is still recovered well (8% error) despite multiple scattering and masking of the helium beam by surface topography. Therefore, it is possible to perform accurate reconstruction of the shape of nanoscale structures with a height to width ratio of at least unity.

Pneumatic angle adjustment for magic angle spinning spherical rotors

Precise alignment of the sample's spinning axis is vital for many magic angle spinning solid state NMR experiments. Spherical rotors are a new paradigm for magic angle spinning NMR, having been demonstrated to spin stably with little risk of rotor crash, but like cylindrical rotors, they have previously only utilized a mechanical adjustment method to set the sample's rotation axis to the magic angle. Here we show that by using a second gas aperture within the stator, a spherical rotor's axis of rotation may be precisely pitched about the magic angle without mechanical adjustment or motion of the stator. The 2H MAS sideband lineshape of the carboxylic acid deuteron resonance in d4-malonic acid is used as a measure of the rotor's absolute deviation above or below the magic angle by comparing the experimental data to simulated lineshapes. We observe a linear, monotonic relationship between the angle adjustment gas flow rate and the rotor's pitch angle, which is also accompanied by an increase in spinning rate. Precise and in operando control of the spinning axis angle is expected to have considerable advantages to future implementation of MAS within narrow-bore magnets, and for variable angle spinning (VAS) and dynamic angle spinning (DAS) experiments.

Oriented Bounding Boxes for Small and Freely Rotated Objects

A novel object detection method is presented that handles freely rotated objects of arbitrary sizes, including tiny objects as small as $2\times 2$ pixels. Such tiny objects appear frequently in remotely sensed images, and present a challenge to recent object detection algorithms. More importantly, current object detection methods have been designed originally to accommodate axis-aligned bounding box detection, and therefore fail to accurately localize oriented boxes that best describe freely rotated objects. In contrast, the proposed CNN-based approach uses potential pixel information at multiple scale levels without the need for any external resources, such as anchor boxes.The method encodes the precise location and orientation of features of the target objects at grid cell locations. Unlike existing methods which regress the bounding box location and dimension,the proposed method learns all the required information by classification, which has the added benefit of enabling oriented bounding box detection without any extra computation. It thus infers the bounding boxes only at inference time by finding the minimum surrounding box for every set of the same predicted class labels. Moreover, a rotation-invariant feature representation is applied to each scale, which imposes a regularization constraint to enforce covering the 360 degree range of in-plane rotation of the training samples to share similar features. Evaluations on the xView and DOTA datasets show that the proposed method uniformly improves performance over existing state-of-the-art methods.

Bypassing the resolution limit of diffractive zone plate optics via rotational Fourier ptychography

Diffractive zone plate optics uses a thin micro-structure pattern to alter the propagation direction of the incoming light wave. It has found important applications in extreme-wavelength (extreme ultraviolet or soft X-ray) imaging where conventional refractive lenses do not exist. The resolution limit of zone plate optics is determined by the smallest width of the outermost zone. In order to improve the achievable resolution, significant efforts have been devoted to the fabrication of very small zone width with ultrahigh placement accuracy. Here, we report the use of a diffractometer setup for bypassing the resolution limit of zone plate optics. In our prototype, we mounted the sample on two rotation stages and used a low-resolution binary zone plate to relay the sample plane to the detector. We then performed both in-plane and out-of-plane sample rotations and captured the corresponding raw images. The captured images were processed using a Fourier ptychographic procedure for resolution improvement. The final achievable resolution of the reported setup is not determined by the smallest width structures of the employed binary zone plate; instead, it is determined by the maximum angle of the out-of-plane rotation. In our experiment, we demonstrated 8-fold resolution improvement using both a resolution target and a titanium dioxide sample. The reported approach may be able to bypass the fabrication challenge of diffractive elements and open up new avenues for microscopy with extreme wavelengths.

Time-resolved x-ray stroboscopic phase tomography using Talbot interferometer for dynamic deformation measurements.

Time-resolved x-ray phase tomography using a Talbot interferometer and white synchrotron radiation can provide a three-dimensional movie for visualizing the structural change of materials consisting of light elements. In this study, time-resolved x-ray stroboscopic phase tomography using a Talbot interferometer is demonstrated for a vibrating object under 24Hz compression-stretch fatigue loading. Moiré patterns are recorded by synchronizing drivers for a shutter, grating displacement, and sample rotation with an x-ray camera with a 200 µs exposure, and phase tomograms are reconstructed at specific motion phases of the vibration. The measurement lasts for a few minutes and the δ value changes before breaking, which is considered due to plastic deformation of soft materials under external vibration are depicted three-dimensionally.

Strength comparative analysis of furniture joints made of various materials

The strength comparative analysis of furniture joints made of various materials. The influence of the load on the angular deformation of the furniture joint samples made of various materials was studied. The tests were carried out for six types of furniture materials: chipboard, MDF, hardwood plywood, glued pine wood, glued oak wood and HPL and for three types of fasteners with different ways of fixing in connected elements: shape-thread, expansion-expansion and expansion-thread way of anchoring in material of boards. The joint samples were loaded with a bending moment only (without inducing transverse loadings). The maximum load capacity and load capacity at the 3° (0.052 rad) sample rotation was measured and then the stiffness coefficients were calculated. Considerable differences were found between HPL and others lignocellulosic materials. Expansion fasteners offer incredibly low joint rigidity. This was observed for all tested furniture materials, from soft (chipboard) to very hard (HPL). Expansion connectors work better in soft lignocellulosic materials than in hard materials. The main advantage of expansion fasteners, in comparison to shape-thread fasteners, is its low visibility in the joint and the technological ease of assembly. On the other hand, thread-shaped connectors offer much greater strength and stiffness of joints.

Solid particle erosion resistance of Al alloy and Al alloy-fly ash composite subjected to equal-channel angular pressing

This paper describes the influence of deformation by equal-channel angular pressing (ECAP) on the solid particle erosion resistance of the AlSi7Mg0.3 alloy and AlSi7Mg0.3 based composite material reinforced with the addition of 4 % of fly ash (FA) particles. Both, alloy and composite samples were produced using the compo-casting method. The samples have been subjected to ECAP in multiple passes with the rotation of samples around the vertical axis for the angle of 90° after each pass. Particles of silicon carbide (SiC) have been used as erodent while their impact angle was varied (30° and 90°). Observed samples of AlSi7Mg0.3 alloy generally showed higher wear resistance at 90° angle where material fatigue predominates, than at a 30° angle where abrasion-related phenomena predominate. On the other hand, AlSi7Mg0.3 based composite material exhibited erosion wear at 30° angle less than at 90° angle after one ECAP pass. Evaluation of the erosion resistance has been made based on mass and volume loss. After two passes of ECAP, the matrix structure of the AlSi7Mg0.3 based composite material, as well as that of the AlSi7Mg0.3 alloy was improved from the aspect of erosion resistance.

Ptychographic optical coherence tomography.

Ptychography is a robust computational imaging technique that can reconstruct complex light fields beyond conventional hardware limits. However, for many wide-field computational imaging techniques, including ptychography, depth sectioning remains a challenge. Here we demonstrate a high-resolution three-dimensional (3D) computational imaging approach, which combines ptychography with spectral-domain imaging, inspired by optical coherence tomography (OCT). This results in a flexible imaging system with the main advantages of OCT, such as depth-sectioning without sample rotation, decoupling of transverse and axial resolution, and a high axial resolution only determined by the source bandwidth. The interferometric reference needed in OCT is replaced by computational methods, simplifying hardware requirements. As ptychography is capable of deconvolving the illumination contributions in the observed signal, speckle-free images are obtained. We demonstrate the capabilities of ptychographic optical coherence tomography (POCT) by imaging an axially discrete lithographic structure and an axially continuous mouse brain sample.

Influence of noise-reduction techniques in sparse-data sample rotation tomographic imaging

Data acquisition and processing is a critical issue for high-speed applications, especially in three-dimensional live cell imaging and analysis. This paper focuses on sparse-data sample rotation tomographic reconstruction and analysis with several noise-reduction techniques. For the sample rotation experiments, a live Candida rugosa sample is used and controlled by holographic optical tweezers, and the transmitted complex wavefronts of the sample are recorded with digital holographic microscopy. Three different cases of sample rotation tomography were reconstructed for dense angle with a step rotation at every 2°, and for sparse angles with step rotation at every 5° and 10°. The three cases of tomographic reconstruction performance are analyzed with consideration for data processing using four noise-reduction techniques. The experimental results demonstrate potential capability in retaining the tomographic image quality, even at the sparse angle reconstructions, with the help of noise-reduction techniques.