Stem Tilt Research Articles

Multislice Electron Tomography Using Four-Dimensional Scanning Transmission Electron Microscopy

Electron tomography offers useful three-dimensional (3D) structural information, which cannot be observed by two-dimensional imaging. By combining annular dark-field scanning transmission electron microscopy (ADF STEM) with aberration correction, the resolution of electron tomography has reached atomic resolution. However, tomography based on ADF STEM inherently suffers from several issues, including a high electron-dose requirement, poor contrast for light elements, and artifacts from image-contrast nonlinearity. Here, we develop an alternative method called multislice electron tomography (MSET) based on four-dimensional STEM tilt series. Our simulations show that multislice-based 3D reconstruction can effectively reduce undesirable reconstruction artifacts from the nonlinear contrast, allowing precise determination of atomic structures with improved sensitivity for low-Z elements, at considerably low electron-dose conditions. We expect that the MSET method can be applied to a wide variety of materials, including radiation-sensitive samples and materials containing light elements whose 3D atomic structures have never been fully elucidated due to electron-dose limitations or nonlinear imaging contrast.

Assessment of Effective Wind Loads on Individual Plantation-Grown Forest Trees

Quantifying wind loads acting on forest trees remains a major challenge of wind-tree-interaction research. Under wind loading, trees respond with a complex motion pattern to the external forces that displace them from their rest position. To minimize the transfer of kinetic wind energy, crowns streamline to reduce the area oriented toward the flow. At the same time, the kinetic energy transferred to the trees is dissipated by vibrations of all aerial parts to a different degree. This study proposes a method to estimate the effective wind load acting on plantation-grown Scots pine trees. It evaluates the hypothesis that the effective wind load acting on the sample trees can be estimated using static, non-destructive pulling tests, using measurements of stem tilt under natural wind conditions and static, non-destructive pulling tests. While the analysis of wind-induced stem displacement reconstructs the temporal tree response dynamics to the effective wind load, results from the pulling tests enable the effective wind load quantification. Since wind-induced stem displacement correlates strongly with the sample trees’ diameter at breast height, the effective wind load estimation can be applied to all other trees in the studied stand for which diameter data is available. We think the method is suitable for estimating the effective wind load acting on trees whose wind-induced response is dominated by sway in the fundamental mode.

Variability in Femoral Preparation and Implantation Between Surgeons Using Manual and Powered Impaction in Total Hip Arthroplasty.

BackgroundThe influence of the surgical process on implant loosening and periprosthetic fractures (PPF) as major complications in uncemented total hip arthroplasty (THA) has rarely been studied because of the difficulty in quantification. Meanwhile, registry analyses have clearly shown a decrease in complications with increasing experience. The goal of this study was to determine the extent of variability in THA stem implantation between highly experienced surgeons with respect to implant size, position, press-fit, contact area, primary stability, and the effect of using a powered impaction tool.MethodsPrimary hip stems were implanted in 16 cadaveric femur pairs by three experienced surgeons using manual and powered impaction. Quantitative CTs were taken before and after each process step, and stem tilt, canal-fill-ratio, press-fit, and contact determined. Eleven femur pairs were additionally tested for primary stability under cyclic loading conditions.ResultsManual impactions led to higher variations in press-fit and contact area between the surgeons than powered impactions. Stem tilt and implant sizing varied between surgeons but not between impaction methods. Larger stems exhibited less micromotion than smaller stems.ConclusionsLarger implants may increase PPF risk, while smaller implants reduce primary stability. The reduced variation for powered impactions indicates that appropriate measures may promote a more standardized process. The variations between these experienced surgeons may represent an acceptable range for this specific stem design. Variability in the implantation process warrants further investigations since certain deviations, for example, a stem tilt toward varus, might increase bone stresses and PPF risk.

The Relationship between Femoral Stem Tilt and Stem Length in Total Hip Arthroplasty: A Retrospective Case-Control Study.

BackgroundThe current trend of using short femoral stems in total hip arthroplasty (THA) is associated with angular deviation of the femoral stem towards the native femoral axis. The purpose of this study was to compare the difference in stem tilt angle between two different stems with a similar design except for the stem length.MethodsThis is a retrospective review of 66 patients who underwent primary THA between April 2012 and May 2016, using a trans-gluteal direct lateral approach by a single surgeon. We evaluated the femoral stem tilt angle in both the coronal and sagittal planes and performed multivariate logistic regression analysis to evaluate possible risk factors. We also simulated the range of motion (ROM) of the hip joint using three-dimensional computer-aided design software (SolidWorks, 2016) to examine the clinical significance of femoral stem tilt.ResultsThe mean coronal tilt angle was 1.8° ± 1.0° in the conventional stem group and 1.6° ± 1.1° in the short stem group, showing no statistically significant difference between the groups (p = 0.570). However, the mean sagittal tilt angle was 4.0° ± 2.0° in the conventional stem group and 7.8° ± 2.0° in the short stem group (p < 0.001). The stem type and stem length had a linear correlation with the sagittal tilt angle (p < 0.001) in multivariate regression analysis. A simulated hip ROM demonstrated a 3.8° decrease in extension in proportion to a 3.8° increase in the mean sagittal stem tilt angle of the short femoral stem.ConclusionsAnterior femoral stem tilting in the sagittal plane was prominent when the shorter stem was used, and anterior tilting was responsible for decreased ROM in hip extension.

Assessing the Self-Recovery Ability of Maize after Lodging Using UAV-LiDAR Data

Lodging is one of the main problems in maize production. Assessing the self-recovery ability of maize plants after lodging at different growth stages is of great significance for yield loss assessment and agricultural insurance claims. The objective of this study was to quantitatively analyse the effects of different growth stages and lodging severity on the self-recovery ability of maize plants using UAV-LiDAR data. The multi-temporal point cloud data obtained by the RIEGL VUX-1 laser scanner were used to construct the canopy height model of the lodging maize. Then the estimated canopy heights of the maize at different growth stages and lodging severity were obtained. The measured values were used to verify the accuracy of the canopy height estimation and to invert the corresponding lodging angle. After verifying the accuracy of the canopy height, the accuracy parameter of the tasselling stage was R2 = 0.9824, root mean square error (RMSE) = 0.0613 m, and nRMSE = 3.745%. That of the filling stage was R2 = 0.9470, RMSE = 0.1294 m, and nRMSE = 9.889%, which showed that the UAV-LiDAR could accurately estimate the height of the maize canopy. By comparing the yield, canopy height, and lodging angle of maize, it was found that the self-recovery ability of maize at the tasselling stage was stronger than that at the filling stage, but the yield reduction rate was 14.16~26.37% higher than that at the filling stage. The more serious the damage of the lodging is to the roots and support structure of the maize plant, the weaker is the self-recovery ability. Therefore, the self-recovery ability of the stem tilt was the strongest, while that of root lodging and root stem folding was the weakest. The results showed that the UAV-LiDAR could effectively assess the self-recovery ability of maize after lodging.

Variations in sagittal and coronal stem tilt and their impact on prosthetic impingement in total hip arthroplasty.

Optimization of the combined anteversion of cup and stem has been emphasized to avoid prosthetic impingement in total hip arthroplasty (THA). However, no study has focused on the impact of variations in sagittal and coronal stem tilt against the whole femur on prosthetic range of motion. The purposes of the present study were a) to quantify the anatomical variation of sagittal and coronal tilt of the proximal canal axis against the femoral retrocondylar coordinate system, that is variation of sagittal and coronal stem tilt and b) to determine their impact on the zone of impingement-free cup position using computer simulation. Preoperative computed tomography images of 477 femurs from 409 consecutive patients who underwent THA using computed tomography-based computer navigation were stored. Virtual implantation of an anatomical stem was performed on the navigation workstation. The safe zone of the cup position with regard to prosthetic impingement was determined by motion simulation in the range of sagittal and coronal stem tilt of the subjects. The sagittal and coronal stem tilt varied by 10°, which was smaller than the stem anteversion variation. However, there was about 3 times the difference in the impingement-free zone of cup position in the ranges of sagittal and coronal stem tilt. The safe zone was significantly decreased by posterior tilt and valgus tilt of the stem. Range of motion simulation revealed that the variations in sagittal or coronal stem tilt significantly influenced the safe zone of the cup. In conclusion, although the variations in sagittal and coronal stem tilt against the femoral retrocondylar coordinate system were small, their impact on prosthetic impingement was significant.

Pre-commercial thinning in naturally regenerated stands of European beech (Fagus sylvaticaL.): effects of thinning pattern, stand density and pruning on tree growth and stem quality

Pre-commercial thinning in naturally regenerated stands of European beech is often expensive and must be justified by improved development of the remaining crop. Based on a field experiment established in two 14-year-old naturally regenerated beech stands in Denmark, we investigated some effects of pre-commercial thinning and pruning on future crop tree growth and stem quality. The treatments included (1) no thinning, (2) moderate to heavy strip thinning, with or without subsequent selective thinning, and (3) extremely heavy strip thinning in two perpendicular directions (checkerboard thinning), with or without subsequent selective thinning and with or without pruning. The resulting residual stand densities ranged from 10⁵ to only 200 ha⁻¹. Treatment effects were evaluated on one potential future crop tree for every 100 m². Potential future crop trees were selected 32 years after germination based on spatial distribution, growth potential and stem quality. Total crop tree height was unaffected by strip thinning, but reduced by checkerboard thinning. Stem diameter at 1.30 m above ground level increased with decreasing stand density but, for checkerboard thinning, was reduced by pruning. The lower live branch was located at a lower position with heavy strip thinning and with checkerboard thinning without pruning. The frequency of crop trees with a forked stem was largest with checkerboard thinning and these forks were located at a lower position. Stem tilt and stem bend (stem straightness) were essentially unaffected by thinning practice. However, pruned trees tilted less and had straighter stems. The initial formation of epicormic branches on crop trees was unrelated to thinning and pruning practice, but crop trees that had been pruned for these were less prone to subsequently develop epicormic branches. In summary, moderate to heavy pre-commercial thinning had no effect on stem quality, while extremely heavy thinning without pruning resulted in unacceptably low stem quality. The no-thinning option resulted in acceptable growth and stem quality of the crop trees and this remains a viable management alternative for young beech.

The final implant position of a commonly used collarless straight tapered stem design (Corail\xae) does not correlate with femoral neck resection height in cement-free total hip arthroplasty: a retrospective computed tomography analysis

BackgroundIn total hip arthroplasty, inadequate femoral component positioning can be associated with instability, impingement and component wear and subsequently with patient dissatisfaction. In this study, we investigated the influence of femoral neck resection height on the final three-dimensional position of a collarless straight tapered stem (Corail®). We asked two questions—(1) is neck resection height correlated with version, tilt, and varus/valgus alignment of the femoral component, and (2) dependent on the resection height of the femoral neck, which area of the stem comes into contact with the femoral cortical bone?Materials and methodsThree-dimensional computed tomography scans of 40 patients who underwent minimally invasive, cementless total hip arthroplasty were analyzed retrospectively. We analyzed the relationship between femoral neck resection height and three-dimensional alignment of the femoral implant, as well as the contact points of the implant with the femoral cortical bone. This investigation was approved by the local Ethics Commission (No.10-121-0263) and is a secondary analysis of a larger project (DRKS00000739, German Clinical Trials Register May-02-2011).ResultsMean femoral neck resection height was 10.4 mm (± 4.8) (range 0–20.1 mm). Mean stem version was 8.7° (± 7.4) (range − 2° to 27.9°). Most patients had a varus alignment of the implant. The mean varus/valgus alignment was 1.5° (± 1.8). All 40 patients (100%) had anterior tilt of the implant with a mean tilt of 2.2° (± 1.6). Femoral neck resection height did not correlate with stem version, varus/valgus alignment, or tilt. Independent from femoral neck resection height, in most patients the implant had contact with the ventral and ventromedial cortical bone in the upper third (77.5%) and the middle third (52.5%). In the lower third, the majority of the implants had contact with the lateral and dorsolateral cortical bone (92.5%).ConclusionFemoral neck resection height ranging between 0 and 20.1 mm does not correlate with the final position of a collarless straight tapered stem design (Corail®).Level of evidenceLevel 3.

Alterações posturais em mulheres submetidas à cirurgia para retirada do câncer de mama

Introdução: A cirurgia para a retirada do câncer de mama leva a repercussões no corpo da mulher e influencia diretamente sua postura. Objetivo: Identificar as alterações posturais em mulheres submetidas a tal procedimento e compará-las com o tipo de cirurgia. Métodos: Foi avaliada a postura de 23 voluntárias selecionadas por conveniência por meio do software SAPO. Resultados: Das mulheres avaliadas, 52,2% apresentaram rotação de cabeça à esquerda e elevação de ombro à direita, 56,5%, elevação da pelve à esquerda, e 65,2%, inclinação de tronco à esquerda. Em 100% das mulheres observou-se anteriorização da cabeça, 87% tiveram deslocamento posterior do tronco e 82,6% demonstraram ter anteversão pélvica. Não foi encontrada diferença significativa entre os tipos de cirurgia. Conclusão: As mulheres apresentaram alterações no alinhamento da cabeça, do ombro, da pelve e do tronco. Porém, essas alterações não foram diferentes quando comparados os tipos de cirurgia.

Can tree tilting indicate mechanisms of slope movement?

Slope movements are a common natural hazard. That is why considerable funds are spent annually to limit their effects or to research their prevention. This study evaluates dendrometric approaches as a fast and low-cost alternative to classical methods of slope movement mechanism analysis. A total of 1688 trees growing on the Mazák landslide in the Moravskoslezské Beskydy Mts. and 100 reference trees growing out of the landslide area were analysed. The Mazák landslide is approximately 400m in length and presents varied morphological features (scarps, rotated blocks, scree slopes, shallow landslide areas, etc.). The slope and direction of stem inclination was recorded for each tree. The results were categorized into four distinct landforms (scarp with outcrops of bedrock, scree slope, front of partial landslide block, plateau of partial landslide block) and were then compared with parameters for the reference trees.The general model of tree tilting for the landslide area was verified and partially confirmed. Trees growing on the plateau of rotated blocks are predominantly oriented upslope; trees growing on scree slopes of shallow movement and creep are predominantly oriented downslope. Trees growing on rocky scars do not differ significantly from the reference trees. Trees growing from fronts of rotated blocks are oriented both upslope and downslope. From these results, several recommendations regarding dendrometric evidence of slope movement mechanisms are presented: (i) all trees growing on the landslide are to be analysed; (ii) old trees maintain stem tilt intensities and directions for long periods, but young trees are more sensitive to ground movements; (iii) tree root depth influences root sensitivity to movements of various depths; (iv) the general shape of a stem can denote specific mechanisms of slope movement and (v) comparisons with reference trees should always be conducted to exclude potential non-geomorphic effects on tree stem tilt.

Self-assembly of biaxial discorectangular lead carbonate nanosheets into stacked ribbons studied by SAXS and HAADF-STEM tomographic tilt series.

The self-assembling behaviour of 2.6 nm thin PbCO3 nanoplatelets with discorectangular shape and uniform width and thickness occurring after their formation in nonionic water-in-oil microemulsions has been investigated using synchrotron small angle X-ray scattering (SAXS) and (scanning) transmission electron microscopy ((S)TEM). The presence of attractive depletion forces originating from the ubiquitous microemulsion droplets triggers a new type of superstructure at low particle concentration. Instead of the universally observed formation of face-to-face assembled lamellar mesostructures, the nanosheets self-organise into extended ribbon structures, whereby each on top lying sheet is displaced by a constant shift in the length and width directions leading to a so far unprecedented staggered zigzag-type stack assembly with restricted height. This type of stacking gives rise to a complex interference pattern in the isotropic small angle scattering of the stacked ribbon assemblies (SRAs) in reverse micellar solution. Different to the, for lamellar-structured nanosheets typical, diffraction peaks at multiples of the wave vector corresponding to one particular repeat distance, the scattering peaks measured in this study are asymmetric, displaying a shoulder on their low wave vector side. The asymmetric shape of the observed face-to-face correlation peaks indicates that the SRAs do not extend in one direction only. Their scattering behaviour is analysed by expanding the Kratky-Porod structure factor for stacking plates into three dimensions. High-angle annular dark-field (HAADF)-STEM tilt series have complementary been acquired to retrieve three-dimensional structural information on the SRAs in the dry state and to confirm the model used for the refinement of the SAXS data.

Optimal anterior femoral offset for functional range of motion in total hip arthroplasty--a computer simulation study.

Compared to medial femoral offset (MFO), the role of anterior femoral offset (AFO) on range of motion (ROM) in total hip arthroplasty (THA) has not been fully examined. We therefore defined AFO as the anterior distance from the centre of the femoral head to the proximal femoral axis in the sagittal plane and determined the optimal AFO required for ROM needed for activities of daily living using a computer-simulated THA model. Various AFOs were obtained by changing stem anteversion (stem-AV) and stem tilt in the sagittal plane (stem-tilt) using a CT-based simulation software. The required ROM was defined as: flexion ≥ 110°, internal rotation at 90° flexion (IR) ≥ 30°, external rotation (ER) ≥ 30°, and extension ≥ 30°, and we determined AFO and MFO to satisfy required ROM. AFO was positively correlated with stem-AV and anterior stem-tilt. MFO was negatively correlated with stem-AV and not influenced by stem-tilt. Flexion and IR increased with both increased AFO and MFO, whereas extension and ER decreased with increased AFO. A smoothing spline curve showed the optimal AFO and MFO for required ROM to be from 15 mm to 25 mm on average and more than 32.1 mm, respectively. This is the first study to show that AFO directly influenced ROM in THA. Optimal AFO as well as MFO should be reconstructed to achieve sufficient ROM.

Influencing factors for the increased stem version compared to the native femur in cementless total hip arthroplasty

Stem version is not always equivalent to femoral neck version (native version) in cementless total hip arthroplasty (THA). We therefore examined the discrepancy of version between the native femoral neck and stem using pre- and postoperative computed tomography (CT), the level of the femur where the canal version most closely fit the stem version, and the factors influencing version discrepancy between the native femoral neck and stem. A total of 122 hips in 122 patients who underwent primary THA using a metaphyseal-fit stem through the postero-lateral approach were included. Pre- and postoperative CT images were utilized to measure native and stem version, and the version of the femoral canal at four levels relative to the lesser trochanter. The mean native and stem versions were 28.1 ± 11.0° and 38.0 ± 11.2°, respectively, revealing increased stem version with a mean difference of 9.8° (p < 0.0001). A total of 84 hips (68.9 %) revealed an increase in version greater than 5°. Femoral canal version at the level of the lesser trochanter most closely approximated that of stem version. Among the factors analysed, both univariate and multivariate analysis showed that greater degrees of native version and anterior stem tilt significantly reduced the version discrepancy between the native femoral neck and stem version. Since a cementless stem has little version adjustability in the femoral canal, these findings are useful for surgeons in preoperative planning and to achieve proper component placement in THA.

Stem Tilt in the Contact Plane of Epitaxially Grown Polylactide Lamellae and Its Direct Correlation with Lamellar Bending

Via transmission electron microscopy, it was revealed that epitaxial crystallization on hexamethylbenzene substrate led to oriented arrays of individual long-chain poly(l-lactide) edge-on lamellae. Selected-area electron diffraction patterns indicated orientational deviations of packed stems from lamellar normal, i.e., stem tilt on the bc contact plane as a result of stairlike stem packing. Upon growth beyond edges of underneath substrates, correlated bending of lamellae in a counterclockwise manner was developed. The direct relationship between the tilted stem orientation and the bending sense of lamellar growth supports the notion of more severe accumulation of fold surface stresses around acute corners of growth fronts created by the stairlike packing scheme. Selected molecular weights and growth temperatures caused the changes in the magnitude of stem tilt, further manifesting the role of fold-loop repulsion on lamellar basal planes in creating surface stresses. In contrast, the type of chiral center on polylactide backbone appears to have played an important role in tilted orientation of stem packing during lamellar growth.

Stem Tilt in α-Form Single Crystals of Isotactic Polypropylene: A Manifestation of Conformational Constraints Set by Stereochemistry and Minimized Fold Encumbrance

Two high molecular weight (MW) isotactic polypropylene (i-PP) samples, one containing a small amount of rr stereodefects denoted R1 and one conventional, commercial i-PP denoted S1, were used to grow single crystals in thin films at high temperatures (Tx = 145 °C for R1, Tx = 155 °C for S1). Elongated α2-form lathlike single crystals could be found in these two samples, indicating that the growth of this type of single crystal is a general phenomenon in i-PP and is independent of the small amount of tacticity defects. On the basis of our selected area electron diffraction (SAED) experimental results, the stems in these lathlike single crystals were tilted at an unusual 17° angle around the b-axis (i.e., a rotation of 17° of the c-axis within the ac-plane toward the a-axis direction), while in the traditional scheme of the α-form in i-PP, the stem axis is understood to be normal to the fold surface. This 17° stem tilt in the α2-form, lathlike single crystals grown at high Tx values appears to depend upon two constraints: (a) the conformational restrictions on chirality and clinicity of isotactic polyolefin stems linked by a fold, as analyzed by Petraccone et al. [Polymer 1986, 27, 1665; Eur. Polym. J. 1989, 25, 43], and (b) a minimized encumbrance at the fold surface can be achieved by those folds which start from and end on the chemical bonds normal to the fold surface with a favorable gauche conformation of i-PP chains. This is because in i-PP (and most isotactic polyolefins) with a helical stem conformation every other chemical bond is nearly parallel (in a trans conformation) or perpendicular (in a gauche conformation) to the stem axis (and thus, nearly within or normal to the fold surface). The combination of these two constraints favors a (102̅) fold surface in the i-PP case, as is observed in this study.

A practical method to determine the effective resolution in incoherent experimental electron tomography

It is not straightforward to determine resolution for a 3D reconstruction when performing an electron tomography experiment. Different contributions such as missing wedge and misalignment add up and often influence the final resolution in an anisotropic manner. The conventional resolution measures can not be used for all of the reconstruction techniques, especially for iterative techniques which are more commonly used for electron tomography in materials science. Here we define a quantitative resolution measure that determines the resolution in three orthogonal directions of the reconstruction. As an application we use this measure to determine the optimum number of simultaneous iterative reconstruction technique (SIRT) iterations to reconstruct the gold nanoparticles, based on a high angle annular dark field STEM (HAADF-STEM) tilt series.

Three-Dimensional Observation of Dislocations by Electron Tomography in a Silicon Crystal

Dislocations in a silicon single crystal introduced by three point-bending at a high temperature were observed by electron tomography in annular dark field-scanning transmission electron microscopy (ADF-STEM). Commercially available P type (001) single crystal wafers were employed. An ADF STEM tilt series was acquired from -60° to +60° in tilt range with 2° in tilt step. The diffraction vector was maintained close to g(hkl) = 220 during the acquisition by adjusting the [110] direction of the sample parallel to the tilt axis of the holder. The observed dislocations were reconstructed by simultaneous interactive reconstruction technique, exhibiting a 3-D configuration of dislocations introduced by the three-point bending.

Organisation and melting of solution grown truncated lozenge polyethylene single crystals

Abstract Morphological features and the melting behaviour of truncated lozenge crystals have been studied. For the crystals investigated, the heights of the (110) and the (200) sectors were measured to be 14.5 and 12.7 nm, respectively, using atomic force microscopy (AFM) in contact and non-contact mode. Moreover, melting temperatures of 123°C for the (110) sector and of 120°C for the (200) sector have been measured using real-time AFM during annealing experiments. Applying atomic force acoustic microscopy and the n-alkane decoration technique, no difference in the surface fold organisation of (110) and (200) sectors could be detected. For similar stem lengths, variations in stem tilt angle within the sectors might cause the thickness difference observed. However, a very high tilt angle difference above 20° is required. More likely, a shorter stem length within the (200) sector may cause its lower melting temperature.

Automatic selection of molecular images from dark field electron micrographs

A method is described which can be used objectively to select putative molecular images from dark field electron micrographs of unstained molecules. The only characteristic of the molecule required for automatic selection is an estimate of molecular weight. Structures are selected from micrographs by a series of steps including: low pass filtering, edge detection and mass determination. The procedure is shown to be reliable for images with signal-to-noise ratios of at least 4.0. Moreover, the method is insensitive to both the shape and the number of molecules in the image. Five different molecules with molecular weights between MW 330,000 and MW 4 000 are successfully selected from low dose STEM and high dose tilt beam dark field electron micrographs.