High Tilt Research Articles

Type-I and type-II smectic-C^{*} systems: A twist on the electroclinic critical point.

We conduct an in-depth analysis of the electroclinic effect in chiral, ferroelectric liquid crystal systems that have a first-order smectic-A^{*}-smectic-C^{*} (Sm-A^{*}-Sm-C^{*}) transition, and show that such systems can be either type I or type II. In temperature-field parameter space type-I systems exhibit a macroscopically achiral (in which the Sm-C_{M}^{*} helical superstructure is expelled) low-tilt (LT) Sm-C_{U}^{*}-high-tilt (HT) Sm-C_{U}^{*} critical point, which terminates a LT Sm-C_{U}^{*}-HT Sm-^{*}C_{U} first-order boundary. Notationally, Sm-C_{M}^{*} or Sm-C_{U}^{*} denotes the Sm-C^{*} phase with or without a modulated superstructure. This boundary extends to an achiral-chiral triple point at which the macroscopically achiral LT Sm-C_{U}^{*} and HT Sm-C_{U}^{*} phases coexist along with the chiral Sm-C_{M}^{*} phase. In type-II systems the critical point, triple point, and first-order boundary are replaced by a Sm-C_{M}^{*} region, sandwiched between LT and HT Sm-C_{U}^{*} phases, at low and high fields, respectively. Correspondingly, as the field is ramped up, the type-II system will display a reentrant Sm-C_{U}^{*}-Sm-C_{M}^{*}-Sm-C_{U}^{*} phase sequence. Moreover, discontinuity in the tilt of the optical axis at each of the two phase transitions means the type-II system is tristable, in contrast to the bistable nature of the LT Sm-C_{U}^{*}-HT Sm-C_{U}^{*} transition in type-I systems. Whether the system is type I or type II is determined by the ratio of two length scales, one of which is the zero-field Sm-C^{*} helical pitch. The other length scale depends on the size of the discontinuity (and thus the latent heat) at the zero-field first-order Sm-A^{*}-Sm-C^{*} transition. We note that this type-I vs type-II behavior in this ferroelectric smectic is the Ising universality class analog of type-I vs type-II behavior in XY universality class systems. Lastly, we make a complete mapping of the phase boundaries in all regions of temperature-field-enantiomeric-excess parameter space (not just near the critical point) and show that various interesting features are possible, including a multicritical point, tricritical points, and a doubly reentrant Sm-C_{U}^{*}-Sm-C_{M}^{*}-Sm-C_{U}^{*}-Sm-C_{M}^{*} phase sequence.

Analyse 3D pour prédire les résultats des fractures cervicales fémorales Garden 1 et 2 : une étude rétrospective multicentrique

IntroductionThe aim of our study was to (1) report our surgical outcomes of internal fixation in patients with nondisplaced or valgus impaction fractures of the femoral neck; (2) introduce our new three dimensional assessment method using a combination of X-ray and CT imaging, and (3) determine which radiologic measurements significantly predicted fixation failure. HypothesisWe hypothesized that high posterior tilt angle and retroversion angle are related to high incidence of non-union and osteonecrosis. Materials and methodsFrom January 2009 to December 2016, 64 elderly patients in two institutions with nondisplaced or valgus impaction fractures of the femoral neck who had internal fixation using multiple parallel cannulated screws were enrolled. To determine the independent predictors of non-union, osteonecrosis, and reoperation, various clinical variables and radiologic variables, including the valgus angle on coronal CT images, the posterior tilt angle on Lorenz images, and the retroversion angle on axial CT images, were analyzed. ResultsNon-union was identified in nine of the 64 patients (14.1%) and nine of the 55 patients (16.4%) who achieved bony union had femoral head osteonecrosis with subsequent segmental collapse. The multiple logistic regression model showed that a low bone mineral density of the femur, a higher posterior tilt angle on Lorenz image, and a higher retroversion angle on axial CT images were independent predictors of non-union and reoperation. DiscussionPrimary hip arthroplasty should be considered when a posterior tilt angle of more than 9 degrees on Lorenz images or a retroversion angle of more than 13 degrees on axial CT images is identified in patients with osteoporotic valgus impaction fractures. Type of study and level of proofIII, retrospective comparative study.

Nano scale tilt measurement using a polarizing phase shifting cyclic interferometer

This paper presents an improved method of high precision tilt measurement using a phase shifting cyclic interferometer. Tilt measurement with a cyclic interferometer is a highly stable and reliable experimental technique and tilts as low as 5 μrad has been reported using the same. Here we employ Polarizing Phase Shifting Interferometry (PPSI) as well as multiple reflections for improving the sensitivity. Using a combination of these two techniques tilts as low as 500 nrad has been measured.

Three-dimensional analyses to predict surgical outcomes in non-displaced or valgus impaction fractures of the femoral neck: A multicenter retrospective study

IntroductionThe aim of our study was to (1) report our surgical outcomes of internal fixation in patients with non-displaced or valgus impaction fractures of the femoral neck, (2) introduce our new three-dimensional assessment method using a combination of X-ray and CT imaging, and (3) determine which radiologic measurements significantly predicted fixation failure. HypothesisWe hypothesized that high posterior tilt angle and retroversion angle are related to high incidence of non-union and osteonecrosis. Materials and methodsFrom January 2009 to December 2016, 64 elderly patients in two institutions with non-displaced or valgus impaction fractures of the femoral neck who had internal fixation using multiple parallel cannulated screws were enrolled. To determine the independent predictors of non-union, osteonecrosis, and re-operation, various clinical variables and radiologic variables, including the valgus angle on coronal CT images, the posterior tilt angle on Lorenz images, and the retroversion angle on axial CT images, were analyzed. ResultsNon-union was identified in nine of the 64 patients (14.1%) and nine of the 55 patients (16.4%) who achieved bony union had femoral head osteonecrosis with subsequent segmental collapse. The multiple logistic regression model showed that a low bone mineral density of the femur, a higher posterior tilt angle on Lorenz image, and a higher retroversion angle on axial CT images were independent predictors of non-union and re-operation. DiscussionPrimary hip arthroplasty should be considered when a posterior tilt angle of more than 9 degrees on Lorenz images or a retroversion angle of more than 13 degrees on axial CT images is identified in patients with osteoporotic valgus impaction fractures. Type of study and level of proofIII, Retrospective comparative study.

Design of functional multicomponent liquid crystalline mixtures with nano-scale pitch fulfilling deformed helix ferroelectric mode demands

Design of new functional smectic liquid crystalline mixtures possessing polar behaviour remains quite highlighted task as those materials are highly requested by industry for specific applications in photonics. This work is devoted to specific practical method devoted to design of functional multicomponent ferroelectric liquid crystalline (FLC) mixtures based on chiral components exhibiting the ferroelectric and antiferroelectric polar order. The self-assembling behaviour, tilt angle, spontaneous polarization as well as dielectric properties of the prepared mixtures have been studied and discussed. The three resulting mixtures exhibit a broad range of the ferroelectric smectic phase, very low melting point, short helical pitch (below 180 nm) and relatively high tilt angle (about 40 degree). Excellent chemical stability and compatibility of components as well as moderate values of spontaneous polarization add another great deal to these FLCs materials for application in deformed helix ferroelectric mode in photonics and opto-electronics.

Anisotropic etching of β-Ga2O3 using hot phosphoric acid

We report a systematic investigation on the anisotropic etching behavior of β-Ga2O3. A wagon wheel pattern was designed and fabricated on (010)-oriented β-Ga2O3 substrates. The wet etching in hot phosphoric acid was found to be effective in reducing the sidewall roughness caused by plasma dry etching. The angular dependence of the sidewall etch rate and inclination angles after wet etching was evaluated. The fins aligned along the [001] direction showed nearly vertical sidewalls after wet etching and a fast sidewall etch rate, making it feasible for the fabrication of ultrascaled vertical channel devices. The fins aligned in the angular range between the [203] and [201] directions showed slanted sidewalls with high tilt angles, which could be useful in reducing the peak electric field near the corners of high power devices. The observed anisotropic etching in this work offers a low-cost, low damage, and controllable fabrication method for ultrascaled and advanced device structures.

A systematic study of grain boundary segregation and grain boundary formation energy using a new copper–nickel embedded-atom potential

In this atomistic study on the copper–nickel system, a new embedded-atom alloy potential between copper and nickel is fitted to experimental data on the mixing enthalpy, taking available potentials for the pure components from literature. The resulting phase boundaries of the new potential are in very good agreement with a recent CALPHAD prediction. Using this new potential, a high angle symmetrical tilt Σ5 and a coherent Σ3 twin grain boundary (GB) are chosen for a systematic investigation of equilibrium GB segregation in the semi-grandcanonical ensemble at temperatures from 400 K to 800 K. Applying thermodynamically accurate integration techniques, the GB formation energies are calculated exactly and as an absolute value for every temperature and composition, which also enables the evaluation of GB excess entropies. The thorough thermodynamic model of GBs developed by Frolov and Mishin is excellently confirmed by the simulations quantitatively, if the impact of both segregation and GB tension on the change in GB formation energy is accounted for. In the case of the Σ3 coherent GB, it turns out that the change in GB formation energy at low temperatures is for the most part attributed to the GB tension, while segregation only has a small influence. This demonstrated effect of GB tensions should also be taken into account in the interpretation of experiments.

Influence of the type of phase sequence and polymer-stabilization on the physicochemical and electro-optical properties of novel high-tilt antiferroelectric liquid crystalline materials

Antiferroelectric liquid crystal (AFLC) mixtures with two types of phase sequence, isotropic - smectic A* - smectic C* - smectic CA* and isotropic - smectic CA*, respectively, have been formulated from components having biphenyl benzoate rigid cores, a non-chiral terminal chain with either alkoxy groups as well as perfluorinated parts on one side, and a chiral chain with different structures on the other side. The properties of the mixtures have been examined by means of polarized optical microscopy, differential scanning calorimetry, as well as UV–Vis-NIR spectrophotometry, and their electrooptic performance have been characterized in device cells, before and after polymer-stabilization of the structures. For all mixtures we observed unusually broad temperature ranges of the smectic CA* phase, extending from at least −30 °C to about +70 °C or more, molecular tilt angles of 42–44°, helical pitches of several micrometers, and a spontaneous polarization of about 200 nC/cm2. The polymer network has a profound impact on the relaxation to the anticlinic state, especially in the mixtures with a direct smectic SmCA*- isotropic phase transition. A symmetric electrooptic response, with both on and off response times of about 140 μs, was obtained in cell gaps of 1.5 μm, which is, to our knowledge, unique among contemporary available high tilt AFLC material systems.

Wind Loads on a Solar Panel at High Tilt Angles

A solar photovoltaic system consists of tilted panels and is prone to extreme wind loads during hurricanes or typhoons. To ensure the proper functioning of the system, it is important to determine its aerodynamic characteristics. Offshore photovoltaic (PV) systems have been developed in recent years. Wind loads are associated with wind, wave climates, and tidal regimes. In this study, the orientation of a single panel is adjusted to different angles of tilt (10°–80°) and angles of incidence for wind (0°–180°) that are pertinent to offshore PV panels. The critical wind loads on a tilted panel are observed at lower angles of incidence for the wind, when the angle of tilt for the panel is greater than 30°.

Clinical and Radiological Predictors of Functional Outcome After Isolated Medial Patellofemoral Ligament Reconstruction at Midterm Follow-up

Background: Isolated medial patellofemoral ligament reconstruction (iMPFLR) is increasingly used for the surgical treatment of recurrent patellofemoral instability. Purpose: The purpose of this study was to identify the clinical and radiological predictors that can significantly influence the functional outcomes after an iMPFLR. Study Design: Case series; Level of evidence, 4. Methods: A total of 107 patients (112 ligament reconstructions) who underwent iMPFLR were evaluated with a mean ± SD follow-up of 59 ± 33 months (range, 12-123 months). Functional International Knee Documentation Committee (IKDC) and Kujala scores were assessed preoperatively and every 12 months. Radiological assessment of patellar height and tilt (Laurin angle, Merchant angle, Maldague classification) and computed tomography (CT) scan measurement of patellar tilt (contracted and relaxed quadriceps) and tibial tubercle–trochlear groove distance were performed preoperatively and at 6 months. Femoral tunnel position was assessed following the criteria formulated by Schöttle. The amount of femoral tunnel widening was measured by means of 3-dimensional CT scan at 6 months. Predictors were determined from univariate and multivariate regression analyses integrating clinical and radiological criteria pre- and postoperatively. The dependent variable was defined as the difference between pre- and postoperative scores. Results: Between pre- and postoperative measurement at last follow-up, a significant improvement for IKDC and Kujala functional scores was observed (Kujala: 57 ± 11.3 to 87 ± 12.9, P < .001; IKDC: 47.8 ± 13.1 to 79 ± 15.8, P < .001). Demographics (age, body mass index, sex), dislocation characteristics (number of dislocations, time between first dislocation and surgery, age at first dislocation, mechanism of first dislocation, knee side), clinical data (frontal limb alignment, hyperlaxity, recurvatum, pre- and postoperative range of motion), and complications (quadriceps atrophy, complex regional pain syndrome) did not influence functional scores. The predictors of lower improvement in functional scores included small correction of the patellar tilt reported on the CT scan measurement, malpositioning of the femoral tunnel, and a widening of this tunnel near the medial cortex. Malpositioning of the femoral tunnel was correlated with tunnel widening, and patients with anterior and proximal malpositioning experienced stiffness in flexion. Conclusion: Overall, iMPFLR demonstrated good outcomes. Predictors influencing the functional results were identified. Less improvement in clinical outcome was reported for patients with a high preoperative patellar tilt and only a small correction in tilt and for those who had femoral tunnel malpositioning, which was correlated with tunnel widening.

Effect of multi-walled carbon nanotubes on dielectric and electro-optic properties of a high tilt antiferroelectric liquid crystal

ABSTRACTBy dispersing a small amount of multi-walled carbon nanotubes in a high tilt antiferroelectric liquid crystal, a nano composite is prepared. Though the phase sequence remains the same, the transition temperatures of the composite get changed, the stability of SmA* and SmC* phases increases whereas that of SmCA* phase decreases. Pitch of the helicoidal structure shows a discontinuous change at SmC*–SmCA* transition. Absorption strength and critical frequency of the anti-phase antiferroelectric mode are reduced in the composite. The dielectric increment of the Goldstone mode (GM) decreases and the critical frequency increases due to increased elasticity of the composite. A two-fold increase in the critical field for suppression of the GM is observed which signifies more stable helical structure in the composite. The switching time is reduced by 56% in the nano composite as a result of decrease in rotational viscosity but the high tilt remains intact. An observed lower value of conductivity indicates ion trapping in the composite.

Numerical analysis of Bragg polarization gratings

Here we study Bragg regime polarization gratings (PGs) using an anisotropic rigorous coupled-wave analysis method. We simulate the most important diffraction properties without paraxial approximation, including the angular, spectral, and polarization responses. We first focus on the angular and spectral bandwidths of the transmissive and reflective Bragg PGs optimized for normal incidence. The effects of material birefringence and average index of refraction were investigated. Second, we examine the nonideal Bragg PGs with nonplanar director profiles and identified degradation in optical performance due to the high tilt of the liquid crystal director. Third, we simulate the polarization response of both types of Bragg PGs and observed complicated angular dependence of the polarization output. Qualitatively, good agreement can be observed between the simulation results and prior experimental work. Finally, we fit the measured angular and polarization data to retrieve actual grating parameters and demonstrated excellent quantitative correspondence, which can be particularly useful in closing the gap between design and fabrication.

Software for automated acquisition of electron tomography tilt series.

For automated acquisition of tilt series for electron tomography, software needs to handle complications such as movements of the sample in x/y and z, increased projected thickness at high tilt, specimen drift, etc. In addition, many applications require special functionality such as low dose acquisition, automated sequential (batch) tomography, or montage tomography. After reviewing how these difficulties can be addressed and a closer look at what advanced acquisition strategies are employed in biosciences, this chapter introduces acquisition software both developed in academia as well as by hardware vendors. It covers the hardware requirements and compatibility, the functional principle and workflow implemented, as well as what advanced functions are supported by the individual programs.

Development of MEMS Sensor-based High Resolution Tilt Monitoring System

Development of MEMS Sensor-based High Resolution Tilt Monitoring System

A Systematic Study of Grain Boundary Segregation and Grain Boundary Formation Energy Using a New Copper-Nickel Embedded-Atom Potential

Abstract In this atomistic study on the copper–nickel system, a new embedded-atom alloy potential between copper and nickel is fitted to experimental data on the mixing enthalpy, taking available potentials for the pure components from literature. The resulting phase boundaries of the new potential are in very good agreement with a recent CALPHAD prediction. Using this new potential, a high angle symmetrical tilt Σ 5 and a coherent Σ 3 twin grain boundary (GB) are chosen for a systematic investigation of equilibrium GB segregation in the semi-grandcanonical ensemble at temperatures from 400 K to 800 K. Applying thermodynamically accurate integration techniques, the GB formation energies are calculated exactly and as an absolute value for every temperature and composition, which also enables the evaluation of GB excess entropies. The thorough thermodynamic model of GBs developed by Frolov and Mishin is excellently confirmed by the simulations quantitatively, if the impact of both segregation and GB tension on the change in GB formation energy is accounted for. In the case of the Σ 3 coherent GB, it turns out that the change in GB formation energy at low temperatures is for the most part attributed to the GB tension, while segregation only has a small influence. This demonstrated effect of GB tensions should also be taken into account in the interpretation of experiments.

Surgical medial patellofemoral ligament reconstruction versus non-surgical treatment of acute primary patellar dislocation: a prospective controlled trial.

The acute primary (first-time) lateral patellar dislocation is associated with a high rate of functional disability. There is no consensus as to the choice of surgical or non-surgical treatment for these patients. The aim of this study is to compare the clinical results between the surgical (reconstruction of the medial patellofemoral ligament [MPFL]) and non-surgical treatments for acute primary patellar dislocations. Sixty-nine skeletally mature patients (69 knees) were included in this prospective non-randomized controlled trial. At least one predisposing factor for patellar dislocation (including patella alta, high lateral patellar tilt, trochlear dysplasia, and increased TT-TG distance) was identified in the included patients. Thirty patients were treated surgically with MPFL reconstruction, and the other 39 patients were treated non-surgically. The main outcome variable was patellar redislocation within a two year follow-up period. The Kujala questionnaire was applied for analyzing the pain and the quality of life. The additional surgeries due to patellofemoral problems were also recorded. Patellar redislocation occurred in eight patients in the non-surgical group, while no redislocation occurred in the surgical group (P < 0.05). Four patients in non-surgical group underwent further surgery due to patellar redislocation and poor function during the follow-up period. The Kujala score and the percentage of "good/excellent" results on the Kujala score of the surgical group were significantly better than that of the non-surgical group (P < 0.05). The surgical MPFL reconstruction achieved better clinical outcomes compared with non-surgical treatment for the acute primary patellar dislocation in the skeletally mature patients with the presence of abnormal patellofemoral anatomy. Surgery should be considered as the better choice for these specific patients.

A high-resolution dynamic fiber-optic inclinometer

We proposed a high-resolution dynamic fiber-optic inclinometer based on a Fabry-Perot (F-P) interferometer and a vertical cantilever structure with an inertial mass. The F-P cavity length variation approximates the vertical cantilever deflection corresponding to the tilt angle. As a fast demodulation mechanism is applied, the F-P cavity length is absolutely and dynamically measured. The tilt angle is obtained by extracting direct current component from the real-time signals of the F-P cavity length. An experiment is carried out by using an adjustable micro-tilt platform mounted on a vibration table. The experimental results show a high tilt resolution of 0.03″ within the measurement range of ±1°. The dynamic resolution of the tilt measurement in ambient vibration is also estimated to 0.66″ with the simulated vibration frequency and amplitude of 50 Hz and 20.9 μm. Due to the dynamic measurement method, the tilt angle readouts are tolerant of ambient vibration.

Effect of nucleation density on the crystallinity of graphene grown from mobile hot-wire-assisted CVD

Chemical vapor deposition (CVD) is widely used for producing high-quality graphene in large area. However, grain boundaries (GBs) are inevitably generated when isolated graphene domains, grown from numerous graphitic nuclei, unify, resulting in severe degradation of intrinsic material properties of graphene. Using mobile hot-wire-assisted CVD (MHW-CVD), here, we successfully demonstrated the progress toward single-crystal graphene; graphene grown from MHW-CVD on pure copper substrate generally has large density of high angle tilt boundary. The main strategy of the improvement is the composition control of catalytic substrate to copper-nickel alloy (4.25 at% of Ni), via both increasing the initial density of graphitic nuclei and facilitating the rotations of isolated graphene domains during the recrystallization process of 2D graphene. Compared to graphene grown from the pure copper substrate, the areal density of the single-crystal graphene from the alloy increases from 22% to 88%. The improvement of electrical property of graphene is also confirmed by the measurement of sheet resistance and mobility whose value is enhanced to 40% and 17%, respectively. Our findings will likely benefit facile CVD synthesis of large-area, high-quality graphene for future thermal, electronic or mechanical devices.

Patients with High Pelvic Tilt Achieve the Same Clinical Success as Those with Low Pelvic Tilt After Minimally Invasive Adult Deformity Surgery.

Pelvic tilt (PT) is a compensatory mechanism for adult spinal deformity patients to mitigate sagittal imbalance. The association between preop PT and postop clinical and radiographic outcomes has not been well studied in patients undergoing minimally invasive adult deformity surgery. To evaluate clinical and radiographic outcomes in adult spinal deformity patients with high and low preoperative PT treated surgically using less invasive techniques. Retrospective case-control, institutional review board-approved study. A multicenter, minimally invasive surgery spinal deformity patient database was queried for 2-yr follow-up with complete radiographic and health-related quality of life (HRQOL) data. Hybrid surgery patients were excluded. Inclusion criteria were as follows: age > 18 and either coronal Cobb angle > 20, sagittal vertical axis > 5 cm, pelvic incidence-lumbar lordosis (PI-LL) > 10 or PT > 20. Patients were stratified by preop PT as per Schwab classification: low (PT< 20), mid (PT 20-30), or high (>30). Postoperative radiographic alignment parameters (PT, PI, LL, Cobb angle, sagittal vertical axis) and HRQOL data (Visual Analog Scale Back/Leg, Oswestry Disability Index) were evaluated and analyzed. One hundred sixty-five patients had complete 2-yr outcomes data, and 64 patients met inclusion criteria (25 low, 21 mid, 18 high PT). High PT group had higher preop PI-LL mismatch (32.1 vs 4.7; P < .001). At last follow-up, 76.5% of patients in the high PT group had continued PI-LL mismatch compared to 34.8% in the low PT group (P < .006). There was a difference between groups in terms of postop changes of PT (-3.9 vs 1.9), LL (8.7 vs 0.5), and PI-LL (-9.5 vs 0.1). Postoperatively, HRQOL data (Oswestry Disability Index and Visual Analog Scale) were significantly improved in both groups (P < .001). Adult deformity patients with high preoperative PT treated with minimally invasive surgical techniques had less radiographic success but equivalent clinical outcomes as patients with low PT.

Coherent patterns of environmental change at multiple organic spring sites in northwest Australia: Evidence of Indonesian-Australian summer monsoon variability over the last 14,500 years

At present, knowledge of late Quaternary variability of the Indonesian-Australian summer monsoon in the Australian tropics is limited. Organic spring deposits, which occur throughout the Kimberley region of northwest Australia, are valuable archives that contain records spanning the past ∼14,500 years. In this study we compare multiple proxies from three organic springs. Principal Components Analyses demonstrates similar patterns of change in the elemental and non-pollen palynomorph (NPP) datasets between the springs, implying regional drivers are responsible for changes in these proxies. By comparison, the pollen records differ between each of the springs, with the assemblage at each thought to be influenced by spring recharge and evolution rather than climate variability. In order to empirically and objectively assess the synchronicity of changes, we applied Monte Carlo empirical orthogonal function (MCEOF) analysis to one variable in each μXRF and NPP dataset (Si/Ti ratios and Pseudoschizaea accumulation rates, as these proxies are expected to reflect hydrological conditions in springs) to assess regional patterns of change in site moisture. This analysis revealed periods of increased monsoonal precipitation from ∼14,500–7500 cal. yr BP corresponding with deglacial sea level rise, high orbital tilt coupled with warmer sea surface temperatures, and with possible links to a southward migration of the Inter Tropical Convergence Zone (ITCZ) during the Younger Dryas. Monsoonal precipitation was reduced from 7500 cal. yr BP coinciding with the culmination of deglacial sea level rise and a possible northward shift in the mean position of the ITCZ, in addition to between 2600 and 1000 cal. yr BP corresponding with increased moderate-to-strong ENSO events.