Position Of Stability Research Articles

Plane mirror-optical path coupling noise in telescope off-axis system dimensional stability measurement

The dimensional stability of the off-axis optical system affects its optical performance significantly and may even lead to its failure. Here, we report a heterodyne interferometry technology to measure the telescope’s dimensional stability. In this method, the standard plane mirror, which reflects the measurement laser, is a critical structural component. Additionally, it is one of the primary sources of the noise. The study focuses on the impact of the standard plane mirror’s positional misalignment instability on optical path noise. A mathematical model was established to depict the effects of mirror misalignment instability on the optical path, and experiments were conducted to decouple the noise. The results of the experiment show that the standard plane mirror introduces approximately 1nm/Hz1/2 at 10 mHz of optical path noise into the off-axis system, and the dimensional stability of the off-axis system is about 6.23nm/Hz1/2 at 10 mHz.

Precision in practice: Exploring the impact of AI and machine learning on ultrasound guided regional anaesthesia.

Ultrasound Guided Regional Anaesthesia (UGRA) is a commonly utilized practice in both elective and emergency situations during surgical procedures and for pain management. Its benefits include, being non-invasive, cost-effective, readily accessible, and providing the anaesthetist with clear visualization of essential anatomical landmarks, needle progression, and the spread of local anaesthetic. Ultrasonography has been shown to increase success rates for regional anaesthesia and decrease complications. One of the critical steps during UGRA is identifying relevant anatomical structures like nerves or vertebras. However, this aspect can be hindered by external influences such as variations in nerve structure and position, interference from noise, and positional instability. Machine learning is a promising branch of artificial intelligence. It is used to conduct predictive tasks without programming instructions by creating algorithms. Extensive research has been conducted to evaluate the influence of machine learning on innovative anaesthesia methods. In 2023, Lopez et al. published a systematic review on how Artificial Intelligence could positively impact traditional anaesthesia practices.1 Various studies included in the review employed different models to achieve variable targets during the induction of anaesthesia. In one experiment, Alkhatib et al. used Convolutional neural network (CNN) based deep trackers to track the median and sciatic nerve with a surprising accuracy of 0.87.2 Another study employed the same CNN model to locate and discriminate accurate images of sacrum, vertebral levels and intervertebral gaps during percutaneous spinal needle insertion.3 Another study used a different AI model called SVM (support vector machine) classification, image processing, and template matching to locate lumbar level L3-L4 and the ideal puncture site for epidural anaesthesia in real-time. In this experiment, anaesthetists with minimal experience in ultrasonography were able to successfully determine needle puncture sites accurately.4 All these studies utilizing AI models not only yielded beneficial results but also led to significant time savings. Considering this, anaesthesiologists nationwide must integrate effective AI models to improve their clinical practice. This would minimize adverse outcomes in regional anaesthesia and ultimately enhance patient care and satisfaction.

Combined, Pedicled Anterior Cruciate Ligament and Anterolateral Ligament Reconstruction - “PAAR” Technique

Despite constant development of surgical implants, instruments, and rehabilitation protocols, the outcomes of anterior cruciate ligament reconstruction remain unpredictable, and the failure rate of isolated procedures remains unacceptably high. Several factors possibly concerning suboptimal outcomes and risk of graft rerupture have been highlighted, among which are graft healing, tunnel position, and residual rotational instability. Recent studies have suggested that addressing anterolateral complex injury and enhancing graft healing properties might improve the outcomes of surgery. We propose a simple technique of combined anterior cruciate ligament and anterolateral ligament reconstruction using pedicled semitendinosus and gracilis tendons with a single femoral tunnel and no additional tibial tunnels.

Inertial mixing of acoustically levitated droplets for time‐lapse protein crystallography

AbstractVarying the chemical consistency of acoustically levitated droplets opens up an in situ study of chemical and biochemical reactions in small volumes. However, the optimization of the mixing time and the minimization of the positional instability induced by solution dispensing are necessary for practical applications such as the study of the transient state of macromolecules crystallography during the ligand binding processes. For this purpose, we study the inertial mixing in a configuration compatible with the room‐temperature crystallography using the acoustic levitation diffractometer, therein solution drops ejected at high velocity collide and coalesce with droplets dispensed on acoustically levitated and rotating polymer thin‐film sample holders. With the proposed method, we are able to achieve the mixing time of ∼0.1 s for sub‐micro and a few microliter droplets. The observed short mixing time is ascribed to the rapid penetration of the solution into the droplets and confirmed by a computational fluid dynamic simulation. The demonstrated accelerated solution mixing is tested in a pilot time‐lapse protein crystallography experiment using the acoustic levitation diffractometer. The results indicate the detection of transient ligand binding state within 2 s after the solution dispensing, suggesting the feasibility of the proposed method for studying slow biochemical processes.

Orthodontic treatment of an open bite after splint therapy for a patient with idiopathic condylar resorption

In the treatment of orthodontic patients with idiopathic condylar resorption, symptoms of temporomandibular joint disorders and constantly changing occlusions caused by an instability of mandibular position make it difficult for orthodontists to confirm definitive orthodontic diagnosis and treatment plans. Therefore, these patients' temporomandibular joint (TMJ) structures need to be stabilized with splint therapy before active tooth movement to identify and maintain the true mandibular position. For some idiopathic condylar resorption patients, orthognathic surgery can cause further resorption on the vulnerable condyles of the mandible; thus, effective orthodontic camouflage treatment after joint stabilization should be considered. During the orthodontic camouflage treatment, adverse loads on the TMJ structures, which could change the position of condyles, should be avoided, and TMJ-friendly mechanics must be applied.

Comparison of nutritional adequacy in adult patients with acute respiratory distress syndrome with and without veno-venous extracorporeal membrane oxygenation: a single-center experience

Objectives: Limited data is available regarding nutrition practices for patients with acute respiratory distress syndrome (ARDS) who are also receiving veno-venous-extracorporeal membrane oxygenation (VV-ECMO). The aim of the study was to describe the nutritional status of patients receiving VV-ECMO and compared with those who did not. Methods: Patients (>18 years-old) diagnosed with ARDS who received VV-ECMO (≥72 hours) were included in this retrospective study. The daily achievement of an energy target (%) and average protein intake during 2 weeks after initiation of VV-ECMO were calculated. Adequate feeding was defined as achieving 80-110% of the calculated target. The duration before initiating parenteral (PN) and enteral nutrition (EN), feeding route, length of intensive care, and hospital stay were evaluated. Data was compared between groups. Results: In this study, 24 patients were included, of whom 12 received VV-ECMO. EN was started in a median 1.5 and 1 days in the VV-ECMO and non-ECMO groups, respectively. In the VV-ECMO group, 75% of the patients could achieve nutritional adequacy (>80% energy goal) and 83.3% in the non-ECMO group (p = 0.615). PN being required in 4 (33.3%) patients who received VV-ECMO and 3 (25%) patients who did not (p = 0254). Ten of all patients experienced inadequate EN because of hemodynamic instability (n = 3), prone position (n=4), gastric distension (n = 2) and diarrhea (n = 1). Conclusions: VV-ECMO was not an obstacle for adequate nutrition, but prone position and hemodynamic instability were common causes of enteral feeding interruptions and inadequate energy delivery.

Cross-scale process quality control of variable polarity plasma arc welding based on predefined temperature field

This study investigates the underlying causes of Variable Polarity Plasma Arc Welding (VPPAW) spatial positional instability and its adverse impact on weld seam quality. Microstructural analysis reveals that the primary cause of poor transverse mechanical properties is the asymmetric distribution of grains. Through the study of heat and mass transfer in the molten pool, it was found that the asymmetric flow of molten metal under the influence of gravity is the main factor leading to uneven temperature distribution and asymmetric grain distribution in the weld pool. A novel approach based on a predefined temperature field is proposed to regulate the weld pool's stability and welding quality. The implementation of the predefined temperature field effectively improves VPPAW weld pool flow, leading to enhanced temperature distribution and grain size and distribution. These findings provide a theoretical foundation and valuable engineering recommendations for achieving high-quality spatial position welding in VPPAW.

Stability and dynamics of spike-type solutions to delayed Gierer-Meinhardt equations

<p style='text-indent:20px;'>For a specific set of parameters, we analyze the stability of a one-spike equilibrium solution to the one-dimensional Gierer-Meinhardt reaction-diffusion model with delay in the components of the reaction-kinetics terms. Assuming slow activator diffusivity, we consider instabilities due to Hopf bifurcation in both the spike position and the spike profile for increasing values of the time-delay parameter <inline-formula><tex-math id="M1">\begin{document}$ T $\end{document}</tex-math></inline-formula>. Using method of matched asymptotic expansions it is shown that the model can be reduced to a system of ordinary differential equations representing the position of the slowly evolving spike solution. The reduced evolution equations for the one-spike solution undergoes a Hopf bifurcation in the spike position in two cases: when the negative feedback of the activator equation is delayed, and when delay is in both the negative feedback of the activator equation and the non-linear production term of the inhibitor equation. Instabilities in the spike profile are also considered, and it is shown that the spike solution is unstable as <inline-formula><tex-math id="M2">\begin{document}$ T $\end{document}</tex-math></inline-formula> is increased beyond a critical Hopf bifurcation value <inline-formula><tex-math id="M3">\begin{document}$ T_H $\end{document}</tex-math></inline-formula>, and this occurs for the same cases as in the spike position analysis. In all cases, the instability in the profile is triggered before the positional instability. If however the degradation of activator is delayed, we find stable positional oscillations can occur in this system.</p>

Disconjugacy of Eye Movements during Attempted Fixation: A Sufficient Marker for Amblyopia?

To investigate whether detection of disconjugacy of eye movements during attempted fixation, or interocular position instability, may serve as a single sensitive test for amblyopia. Binocular eye movements were recorded at 500 Hz using the EyeLink 1000 eye tracker (SR Research Ltd., Kanata, Ontario, Canada) and analyzed using EyeLink software and Matlab (MathWorks, Natick, MA, USA). Eight subjects (four amblyopes, one successfully treated amblyope, and three non-amblyopes: 7 - 44 years) were asked to fixate on a stationary cross subtending 0.5° at 57 cm. Interocular position instability was quantified by calculating the minimum area bivariate contour ellipse (BCEA) encompassing 68% of the difference between right and left eye position points during 20-second viewing epochs. For statistical analysis, BCEA values, as well as visual acuity and stereoacuity, were normalized by base-10 logarithm transformation. The amblyopic subjects with persistent vision loss (one anisometropic, two strabismic, one deprivation; uncorrected visual acuity range 20/60 - 20/300, corrected stereoacuity range nil-400 arcsec) showed significantly higher interocular position instability (larger 68% BCEAs) than the non-amblyopic subjects (uncorrected visual acuity range 20/20 - 20/800, corrected stereoacuities of 20 arcsec) and the successfully treated strabismic amblyope (to the 20/20 level of visual acuity and 70 arcsec of stereoacuity) during binocular viewing trials; p < 0.01. Interocular position stability was strongly correlated with stereoacuity (in that better stereoacuity was associated with lower 68% BCEAs; r = 0.95), but not with visual acuity (r = 0.20). Interocular position instability appears to differentiate amblyopic from non-amblyopic subjects and appears to improve after successful treatment. Interocular position instability may therefore prove to be a single sensitive test for the presence of amblyopia. As a difference measure, it is inherently less susceptible to head motion and calibration error, as well as to conjugate eye motion, and as such is expected to be somewhat immune to latent nystagmus. Interocular position instability may also be useful to guide treatment, especially in preverbal children, and to assess the efficacy of novel treatments. Further research is required to establish optimal interocular position instability thresholds and to determine how specific this measure is to amblyopia.

Computational Analysis of Balloon Catheter Behaviour at Variable Inflation Levels.

Aortic valvuloplasty is a minimally invasive procedure for the dilatation of stenotic aortic valves. Rapid ventricular pacing is an established technique for balloon stabilization during this procedure. However, low cardiac output due to the pacing is one of the inherent risks, which is also associated with several potential complications. This paper proposes a numerical modelling approach to understand the effect of different inflation levels of a valvuloplasty balloon catheter on the positional instability caused by a pulsating blood flow. An unstretched balloon catheter model was crimped into a tri-folded configuration and inflated to several levels. Ten different inflation levels were then tested, and a Fluid-Structure Interaction model was built to solve interactions between the balloon and the blood flow modelled in an idealised aortic arch. Our computational results show that the maximum displacement of the balloon catheter increases with the inflation level, with a small step at around 50% inflation and a sharp increase after reaching 85% inflation. This work represents a substantial progress towards the use of simulations to solve the interactions between a balloon catheter and pulsating blood flow.

Technique for fine adjustment of snare size during endoscopic mucosal resection by a single endoscopist.

Performing endoscopic mucosal resection for polyps located in the hepatic flexure is always challenging. The two most important reasons that make removing polyps in the hepatic flexure difficult are the instability of the position of the endoscope and the difficulty in advancing the endoscope’s accessories while in that bent angle. To overcome the instability of the endoscopic position, the left pinkie maneuver can be applied [1]. The cases shown here demonstrate that an “open-and-retract maneuver of the snare” could solve the approach problem ([Video 1]).

Effect of equilibrium radial position on horizontal instability of middle single null divertor configuration in the iron core tokamak

The unique high-field side middle single null divertor configuration in the Joint-Texas Experimental Tokamak is attractive in studying detachment, impurity control, L-H transition, and negative triangularity. Its equilibrium configuration with a horizontally elongated (or flattened) poloidal cross section causes position instability and difficulty in equilibrium control. This work disassembles the vertical magnetic field of each group of poloidal field windings and calculates the field decay index (n-index) at different radial positions. It is found that the instability growth time τg of horizontal displacement increases as the equilibrium radial position of plasma moves outward, which is beneficial to the position control. The simulation and experiments verified the effect of equilibrium position on horizontal instability. The equilibrium position slightly outward from the geometric center of the vacuum chamber effectively decreases the horizontal displacement oscillation amplitude and guarantees the controllable horizontal displacement.

SEEKING FRIENDS IN TROUBLED TIMES: THE STRUCTURE AND DYNAMICS OF TRANSNATIONAL LGBT NETWORKS IN EUROPE*

Prior research demonstrates the importance of domestic associations joining transnational advocacy networks to create social change. Few studies, however, investigate how dynamic political opportunities influence the structure of crossnational networks. To address this gap, we analyze an original dataset of 3,103 domestic lesbian, gay, bisexual, and transgender (LGBT) associations in Europe connected through joint membership in 46 LGBT international nongovernmental organizations from 2010 to 2020. Results from network and multilevel analyses reveal a relatively unstable network that is centrally comprised of associations located in adverse political contexts. More specifically, advocacy associations located in adverse political contexts, but recently joining the European Union, are more likely to occupy central positions in the network. Although the structure of the network suggests LGBT organizations are countering traditional, hegemonic lines of stratification, the instability of central position undermines widely held assumptions about the relationship between power and centrality within these networks.

Déjà vu: economic determinants of Russia’s power in the historical perspective (1890–2020)

What reasons stood behind the instability of the power position of Russia over the last 130 years? This analysis, covering three periods of time: 1890–1913, 1980–1991, and 2000–2020, reveals astonishing similarities of structural economic problems that led to severe economic and socio-political crises. Despite different causes, each time the crisis was triggered by insufficient savings compared to needs resulting from a program of economic modernisation and imperial policy, low competitiveness of industry, and dependence on export of raw materials. These vulnerabilities of Russia became especially apparent under extraordinary circumstances (wars, economic blockades, sanctions).

Evaluation of the effect of instability of the spacecraft position on the synthesis of radar images

Evaluation of the effect of instability of the spacecraft position on the synthesis of radar images

Lessons Learned While Designing A Next-Generation Firefighting Hel- met: Preliminary Data

In this study, we evaluated the effects of weight and profile (center of gravity location) of three different most widely used firefighting helmets on the head-neck kinematics, positional instability, visual range,and comfort. we compared three different firefighter helmets: a traditional-look (with-brim) helmet (58 oz),a jet-style helmet (62.25 oz), and the jet-style helmet with lighting and communication systems (70.85 oz); all are large.. Since our preliminary investigation showed promising results for the jet-style helmet type, a thorough systematic analysis on a large sample is warranted. Some legitimate concerns that we observed in the preliminary study include: 1) excessive helmet weight caused neck hyper-flexion and imbalanced lateral bending, 2) the CoG of the helmet system lies away from the mid-sagittal plane, and 3) the weight and the displaced CoG poses the threat of an increased risk of cervical spinal disc loading, which can result in disc herniation and degenerated disc.

Beach Chair Versus Lateral Decubitus Positioning for Primary Arthroscopic Anterior Shoulder Stabilization: A consecutive series of 641 shoulders

Objectives:There are no studies that directly compare beach chair (BC) versus lateral decubitus (LD) position for anterior instability. In the only systematic review evaluating BC vs LD, bone loss is not accounted for in the recurrence rate. The purpose of this is to identify predictors of shoulder instability recurrence and revision after anterior shoulder stabilization surgery in a young, high demand population and evaluate surgical position and glenoid bone loss as independent predictors of the outcomes of interest, recurrence and revision.Methods:A consecutive series of 641 arthroscopic Bankart stabilizations were performed by sports-medicine certified and fellowship trained orthopaedic surgeons from 2009-2016 in either the BC or LD position. Patients were included if they underwent an isolated primary arthroscopic anterior capsulolabral repair. Patients were excluded if concomitant labral repair and/or Remplissage procedures were performed at the time of surgery. Shoulders were additionally excluded if magnetic resonance imaging (MRI) was not available at the time of preoperative evaluation or the patient was lost to follow-up. All shoulders were evaluated for glenohumeral bone loss using the perfect circle technique on the sagittal en-face MRI as well as for bipolar lesions according to the on/off-track method of Diagacomo et al. Glenoid bone loss was grouped into three categories: <5%, 5-13.5%, and >13.5%. The primary outcomes of interest were recurrent instability and revision stabilization. Recurrent instability was defined as the presence of a recurrent subluxation and or dislocation event and/or the presence of a positive apprehension. Multivariable logistic regression models were used to assess the relationships of outcomes with age, position, glenoid bone loss group, and, track.Results:641 shoulders with a mean age of 22.3 years (SD 4.46) underwent isolated arthroscopic Bankart repair and were followed for a mean 6 years. The overall recurrent instability and revision rates were 15.7% (101/641) and 11.5% (74/641). Recurrent instability was observed in 15.6% (24/154) and 15.9% (77/487) of LD and BC shoulders, respectively. After adjusting for confounders, multivariable logistic regression found no association between surgical position and recurrent instability (p=0.85). Age was an independent predictor for recurrence. The odds of recurrence were 1.58 times higher per 4.5 years (1 standard deviation) decrease in age (P<0.01, 95% CI 1.02 to 1.72). In a separate multivariable logistic regression model of revision surgery as the dependent variable, revision surgery was not associated with age, surgical position, glenoid bone loss group, or recurrence.Conclusions:Among fellowship-trained orthopaedic surgeons the overall failure of primary arthroscopic anterior shoulder stabilization was 15.7% in a high-demand population and equivalent outcomes may be anticipated with arthroscopic Bankart repair performed in the BC or LD position. In multivariable analysis, younger age, but not surgical position, was an independent risk factor for recurrence.

Characterizing the astrometric instability of extragalactic radio source positions measured with geodetic VLBI

Context. Geodetic very long baseline interferometry (VLBI) has been used to observe extragalactic radio sources for more than 40 yr. The absolute source positions derived from the VLBI measurements serve as a basis to define the International Celestial Reference Frame (ICRF). Despite being located at cosmological distances, an increasing number of these sources are found to show position instabilities, as revealed by the accumulation of VLBI data over the years. Aims. We investigate how to characterize the astrometric source position variations, as measured with geodetic VLBI data, in order to determine whether these variations occur along random or preferential directions. The sample of sources used for this purpose is made up of the 215 most observed ICRF sources. Methods. Based on the geodetic VLBI data set, we derived source coordinate time series to map the apparent trajectory drawn by the successively measured positions of each source in the plane of the sky. We then converted the coordinate time series into a set of vectors and used the direction of these vectors to calculate a probability density function (PDF) for the direction of variation of the source position. For each source, a model that matches the PDF and that comprises the smallest number of Gaussian components possible was further adjusted. The resulting components then identify the preferred directions of variation for the source position. Results. We found that more than one-half of the sources (56%) in our sample may be characterized by at least one preferred direction. Among these, about three-quarters are characterized by a unique direction, while the remaining sources show multiple preferred directions. The analysis of the distribution of these directions reveals an excess along the declination axis that is attributed to a VLBI network effect. Whether single or multiple, the identified preferred directions are likely due to source-intrinsic physical phenomena.

Avoidance of vertical displacement events in DIII-D using a neural network growth rate estimator

Robust disruption avoidance techniques are critical for the development of reliable fusion reactor devices. A viable reactor will require non-disruptive, long pulse operation where simply shutting down a discharge is undesirable. To achieve such performance, the plasma must be controlled to continuously avoid hazardous regimes instead of asynchronously aborting. A recent experiment on DIII-D demonstrated for the first time real-time control of proximity to a disruptive instability boundary. In particular, the vertical growth rate, an eigenvalue that characterizes the degree of instability of the plasma's vertical position, was regulated so as not to exceed DIII-D's vertical controllability limit. The open-loop growth rate was estimated in real time on the DIII-D plasma control system using a neural network model trained with tens of thousands of DIII-D shots. The model was trained to replicate the results of RZRIG [1], a rigid displacement code for calculating the growth rate. Once trained, producing an estimate using the neural network is multiple orders of magnitude faster than RZRIG, thereby making the calculation suitable for real-time execution. The control system regulated the estimated growth rate by adjusting plasma elongation and distance to the inner wall of the vessel, and this regulation was shown to reliably avoid vertical displacement event disruptions (i.e. uncontrolled vertical oscillations) of the plasma. This work presents these experimental results, including the dynamic performance and the effectiveness of the control technique. Details are presented on the training of the neural network model, including concerns such as hyperparameter tuning and uncertainty quantification. Additionally, the methodology for embedding the neural network into the control system is discussed.

Identification of deliberate catheter motion at the left atrial posterior wall during pulmonary vein isolation: Validity of respiratory motion adjustment.

During automated radiofrequency (RF) annotation-guided pulmonary vein isolation (PVI), respiratory motion adjustment (RMA) is recommended, yet lacks in vivo validation. Following contact force (CF) PVI (continuous RF, 30 W) using general anesthesia and automated RF annotation-guidance (VISITAG™: force-over-time 100% minimum 1 g; 2 mm position stability; ACCURESP™ RMA "off") in 25 patients, we retrospectively examined RMA settings "on" versus "off" at the left atrial posterior wall (LAPW). Respiratory motion detection occurred in eight, permitting offline retrospective comparison of RMA settings. Significant differences in LAPW RF auto-annotation occurred according to RMA setting, with curves displaying catheter position, CF and impedance data indicating "best-fit" for catheter motion detection using RMA "off."Comparing RMA "on" versus "off,"respectively: total annotated sites, 82 versus 98; median RF duration per-site, 13.3versus 10.6 s (p < 0.0001); median force time integral177versus 130 gs (p = 0.0002); mean inter-tag distance (ITD), 6.0versus 4.8 mm (p = 0.002). Considering LAPW annotated site 1-to-2 transitions resulting from deliberate catheter movement, 3 concurrent with inadvertent 0 g CF demonstrated < 0.6 s difference in RF duration. However, 13 deliberate catheter movements during constant tissue contact (ITD range: 2.1-7.0 mm) demonstrated (mean) site-1 RF duration difference 3.7 s (range: -1.3 to 11.3 s): considering multiple measures of catheter position instability, the appropriate indication of deliberate catheter motion occurred with RMA "off" in all. ACCURESP™ respiratory motion adjustment importantly delayed the identification of deliberate and clinically relevant catheter motion during LAPW RF delivery, rendering auto-annotated RF display invalid. Operators seeking greater accuracy during auto-annotated RF delivery should avoid RMA use.