Vertical Prism Research Articles

Vertical prism adaptation, but not sound presentation, modulates the visuospatial representation: A manual line-bisection study

The present study aimed at testing whether vertical prism adaptation (PA) can modulate vertical visuospatial representation, assessed with a vertical manual line-bisection (MLB) task (Experiment 1). In a second time, we wanted to investigate the potential influence of sound presentation during such a task. Sound is a spatially valued element that has previously been reported to modify horizontal visuospatial representation. In Experiment 2, we presented either a high pitch, a low pitch, or no sound during the same MLB as in Experiment 1. With this experiment, we also searched for an eventual interaction between the effect of sound presentation and the potential cognitive aftereffects of vertical PA on visual representation.Both Experiments 1 and 2 were constructed with the same design and conducted with two distinct groups of young healthy right-handed participants. First, we assessed the initial sensorimotor state with an open-loop pointing task, and the initial representational state through a vertical MLB (with addition of sound for Experiment 2). Then participants were submitted to a 16-minute PA procedure and were tested again on the open-loop pointing task and the MLB to assess the aftereffects following prism removal.Our results showed sensorimotor aftereffects following both upward and downward PA, in a direction opposed to the optical deviation used. The early aftereffects measured following PA were symmetrical, but at the end of the experiment the residual aftereffects were smaller following downward PA than upward PA. We also provide a new insight on the aftereffects of vertical PA on visuospatial representation, showing that downward PA (but not upward PA) can produce an upward bias on the manual line-bisection task. This is the first proof of such cognitive aftereffects following vertical PA. However, we found no effect of sound presentation on the vertical visual space representation and no interaction between PA and sound presentation.

Efficacy of Worth 4 Dot Test and Vertical prism dissociation Test in Screening of Amblyopia for School Going Children.

Introduction: Amblyopia is reduction of best corrected visual acuity in one or both eyes that cannot exclusively be attributed to structural abnormality of the eye. It can be better treated if diagnosed early in life. Fixation preference is assessed in Vertical prism dissociation test (VPDT) to predict amblyopia while in Worth 4 dot test (W4DT) degree of suppression is detected which tell us the presence of amblyopia.
 Objective: The objectives of this study were mainly, to assess the efficacy of Worth 4 dot test and Vertical prism dissociation test in screening of amblyopia in School going children and to screen the prevalence of amblyopia.
 Methods: It was a Descriptive cross-sectional study conducted from October 2020 to June 2021 at three Government Schools of Faisalabad, Pakistan. Non-probability random sampling Technique was used to screen out 400 subjects. All subjects were equally screened out with the help of VPDT and W4D test. Data was analyzed through chi-square and cross tabulation by using SPSS software version 20. Both VPD test and W4D test were performed in which fixation pattern and suppression were documented on self-designed proforma.
 Results: There was a good agreement between qualitative measures of fixation pattern with VPDT and suppression with W4DT for the clinical determination of amblyopia (p < 0.005).
 Conclusion: This study concluded that the prevalence of amblyopia was 8% in school going children and there was significant relationship in success rates and reliability of vertical prism dissociation test and worth four dot test in screening of amblyopia (p=0.00).

Surgical management of superior oblique palsy with coexisting exotropia

To analyze the surgical results of patients treated for superior oblique palsy with coexisting exotropia. The medical records of patients with superior oblique palsy and exotropia who underwent inferior oblique weakening and simultaneous lateral rectus recession by a single surgeon from 1996 to 2022 were reviewed retrospectively. Demographics, pre- and postoperative vertical and horizontal deviation, and presence of diplopia were recorded. Surgical success was defined as horizontal deviation <10Δ and vertical deviation ≤4Δ without overcorrection or diplopia. The decision to operate for the horizontal deviation was made based on fusion in free space when the vertical deviation was offset with a prism. A total of 27 patients were included. Mean age was 26.1 ± 22 years (range, 26 months to 78 years). Preoperatively, mean vertical deviation was 15.2Δ ± 7.5Δ (range, 4Δ-30Δ); mean exodeviation, 17Δ ± 5.5Δ (range, 10Δ-35Δ). Of the 27 patients, 25 underwent unilateral and 2 underwent bilateral lateral rectus recession, according to the magnitude of the horizontal deviation. Mean follow-up was 3 ± 3.8 months (range, 2 weeks to 17 months). Postoperative mean vertical alignment was 3.0 ± 5.9, and horizontal alignment was 3.4Δ ± 5.2Δ (esotropia of 7Δ to exotropia of 12Δ; P < 0.0001). Nineteen patients (70%) had a successful result; 2 patients had residual exotropia of >10Δ, 2 had vertical overcorrection (range, 3Δ-4Δ), and 6 had residual vertical deviation ≥4Δ (range, 5Δ-20Δ). None had secondary esotropia >10Δ. Horizontal deviation was corrected successfully with no consecutive esotropia in 25 patients. In our study cohort, patients with superior oblique palsy and exotropia in whom fusion required both horizontal and vertical prism correction had a high likelihood of successful horizontal alignment after lateral rectus weakening in combination with inferior oblique surgery.

Assessment of optical quality of ready-made reading spectacles for presbyopic correction.

Many presbyopic patients in both developed and developing countries use ready-made reading spectacles for their near vision correction even though the quality of these spectacles cannot always be assured. This study assessed the optical quality of ready-made reading spectacles for presbyopic correction in comparison with relevant international standards. A total of 105 ready-made reading spectacles with powers ranging from +1.50 to +3.50 dioptres (D) in +0.50 D steps were randomly procured from open markets in Ghana and assessed for their optical quality, including induced prisms and safety markings. These assessments were done in line with the International Organization for Standardization (ISO 16034:2002 [BS EN 14139:2010]) as well as the standards used in low-resource countries. All lenses (100%) had significant induced horizontal prism that exceeded the tolerance levels stipulated by the ISO standards, while 30% had vertical prism greater than the specified tolerances. The highest prevalence of induced vertical prism was seen in the +2.50 and +3.50 D lenses (48% and 43%, respectively). When compared with less conservative standards, as suggested for use in low-resource countries, the prevalence of induced horizontal and vertical prism reduced to 88% and 14%, respectively. While only 15% of spectacles had a labelled centration distance, none had any safety markings per the ISO standards. The high prevalence of ready-made reading spectacles in Ghana that fail to meet optical quality standards indicates the need for more robust, rigorous and standardised protocols for assessing their optical quality before they are sold on the market. This will alleviate unwanted side effects including asthenopia associated with their use. There is also the need to intensify public health awareness on the use of ready-made reading spectacles, especially by patients with significant refractive errors and ocular pathologies.

The role of transverse inclination on the flow phenomenology around cantilevered prisms and the tripole wake mode

This work conducted wind tunnel experiments and high-fidelity numerical simulations to study the flow phenomenology around and aerodynamic characteristics of a transversely inclined cantilever prism—a highly probable but unattended configuration when inclined civil structures are subjected to changing angle of attack. The velocity field, stream and spanwise vorticity, Q-criterion vortex structures, aerodynamic force and spectra, surface pressures, and shear layer morphology have been comprehensively analyzed. Results showed significant deviations from the vertical prism, deeming many classical observations on the prism wake untransferable to the inclined cases. The underlying flow phenomenology was subsequently clarified. Transverse inclination induces a fundamentally different, asymmetric wake morphology, especially near the fix- and free-end, suppressing the horseshoe vortices and intensifying near-wake turbulence. The prism base also experiences a remarkable intensification of wind load and vortical dynamics. The suppression of vortical activities on the near-wind side of the fix-end also gives rise to a new wake morphology – the tripole mode – unique to transverse inclination. Moreover, transversely inclined prisms experience different crosswind loads when angle of attack reverse in sign, which is attributed to changes in shear layer curvature. This work’s conclusions partially fill the gap in the fluid mechanics of inclined prisms and, more importantly, highlight the extra cautions needed for engineering applications involving inclined structures.

Observation on the curative effect of horizontal rectus transposition combining recess-resect treatment on monocular elevation deficiency with horizontal strabismus.

To explore the clinical effect of horizontal rectus transposition combining recess and resect treatment on monocular elevation deficiency (MED) with horizontal strabismus. Ten patients (10 eyes) scheduled to undergo horizontal rectus transposition combining recess-resect surgery to treat MED with horizontal strabismus in the ME Department of Ophthalmology of the First Affiliated Hospital of Guangxi Medical University between July 2016 and February 2022 were included in the study. The degree of vertical and horizontal prism strabismus, the grading of upper movement of the paralyzed eye, and the improvement of binocular vision were evaluated before and after the surgery. Horizontal rectus transposition combined with recess and resect treatment was used to treat 10 patients with MED combined with horizontal strabismus. A good curative effect was seen in eight patients. The differences in the degree of vertical strabismus, the degree of horizontal strabismus, and the movement function of the paretic eyes before and after surgery were significantly different (all P < 0.05). The binocular haplopia function in six patients was reconstructed in the primary position after surgery. Horizontal rectus transposition combining recess-resect is easy to perform, and the number of recti involved in the surgery is small. This approach can effectively correct the eye position, improve eye movement, and reconstruct binocular vision in patients with MED by combining horizontal strabismus.

Scale dependence of petrophysical measurements in reservoirs with Thalassinoides: Insights from CT scans

Subsurface reservoirs with Thalassinoides are well known. Using a CT scan of an 18.5 cm-diameter core (top cross section, 267.21 cm2; length, 26.5 cm) with Thalassinoides, this study demonstrates the scale dependence of sampling, and variables important in selecting representative sample dimensions for modeling these reservoirs. In the CT scan, 40 vertical square prism subsamples were extracted with cross sectional area ranging from 1.44 cm2 to 92.16 cm2. The results illustrate the scale dependence and sampling biases on Thalassinoides morphology, burrow percentage (BP), and connectivity of burrows from the top to bottom of subsamples (a proxy for permeability). Analysis of the entire scan shows a BP of ∼38%. The 40 subsamples vary in BP from 7% to 44% with the smallest cross sections showing the expected highest variance, but also showing the lowest mean BP. This illustrates that small-diameter vertical subsamples are likely to under sample Thalassinoides networks. In the full core, Thalassinoides connects across the top and bottom. Subsample cross sections >51.84 cm2 have 100% probability of showing this, whereas subsample cross sections <12.96 cm2 have 0% probability of showing this. To find the dimensions of representative samples to model Thalassinoides-bearing reservoirs, burrow diameter, BP, vertical length of sample, and core diameter must all be considered.

Recent Volumetric Deformations of Fault Zones

—Volumetric (non-shear) deformations of fault zones measured from leveling data are analyzed. It is shown that volumetric deformations within fault zones lead to symmetric local surface subsidence. Examples of anomalous subsidence identified in the Ashgabat fault zone (North Kopet Dag) and in the fault zones of the underground gas storage facility are presented. A mechanism describing the formation of these anomalous deformations based on the models of poroelastic inclusion and poroelastic inhomogeneity is proposed. The problem about surface displacements of elastic halfspace with a poroelastic region in the form of vertical extended rectangular prism simulating active fragment of a fault zone is solved. Analytical formulas for surface-displacement estimation are derived for two variants of poroelastic models: a model of inclusion and a model of heterogeneity. The comparison of the two models based on the case study of the Ashgabat fault has shown that the mechanism of anomalous deformations with poroelastic heterogeneity model much better describes the observed displacements than poroelastic inclusion model. The analysis of anomalous surface displacements at an underground gas storage facility indicates that local subsidence occurs during both gas withdrawal and injection. It is established that the formation of anomalous subsidence in the first case follows the poroelastic inclusion model, and in the second case it corresponds to the poroelastic heterogeneity model. This means that local subsidence in a fault zone during gas withdrawal is linearly related to the change in reservoir pressure. Anomalous subsidence during gas injection is nonlinearly linked to the change in reservoir pressure. This is a striking example of induced deformations in the fault zones when temporal variations of poroelastic parameters within a fault zone in the setting of external quasistatic loading induce local perturbation in the stress-strain state of rocks in the vicinity of fault.

A Neutron Diffraction Study of the Effect Produced by the Direction of Crystal Growth on the Distribution of Residual Stresses in Austenite Steel Prisms Manufactured by Selective Laser Melting

The effect affected by the choice of the direction of the crystal growth by selective laser melting on the distribution of residual stresses was studied on the example of initiated growing of a 20 × 20 × 70-mm prism of steel 316L. Prisms with different growth directions (along their long and short edges) have been investigated. Neutron stress diffractometry providing the measurement of all three stress tensor components in massive materials and products by a nondestructive method was used. Compressive stresses are formed in the central part of a prism in both cases. They are close to zero or transit to tensile stresses when approaching the surface. In the prism grown vertically along the long edge, tensile stresses are higher and occupy a larger volume as compared to the prism grown along the short edge. Maximum tensile stresses (~500 MPa) near the vertical prism edges are close to the ultimate yield strength of the material (~540 MPa). The maximum compressive stresses (~–400 MPa) are formed in the central part of the vertical prism.

Visuomanual Vertical Prism Adaptation: Aftereffects on Visuospatial and Auditory Frequency Representations.

Sensorimotor aftereffects have been widely studied after lateral prism adaptation but not after vertical prism adaptation. It is thus well-known that lateral prism adaptation produces aftereffects on visuospatial representation and, recently, on auditory perception. This study aimed to explore the sensorimotor after-effects of vertical prism adaptation as well as its aftereffects on vertical visuospatial representation (Experiment 1) and on auditory frequency representation (Experiment 2). The experimental procedure was similar in both experiments: before and after prism adaptation to an upward or a downward optical deviation, healthy young participants performed an visual open-loop pointing task and a visual (Experiment 1) or an auditory (Experiment 2) perceptual bisection task. In the visual task, the participants had to indicate if they perceived the bisection as higher or lower than the true center of a line. In the auditory task, the participants had to indicate if they perceived the target auditory frequency closer to the low or the high limit of an auditory interval. For sensorimotor aftereffects, pointing errors were computed by means of a vertical touchscreen. For the perceptual bisection task, we measured the percentage of “down” (Experiment 1) or “low” responses (Experiment 2), and we computed the visual (Experiment 1) or the auditory (Experiment 2) subjective center for each participant. Statistical analyses were carried out separately for each optical deviation in each experiment. Sensorimotor aftereffects were observed in both experiments, in the opposite direction to the optical deviation (all ps < 0.01). No significant aftereffects occurred on visuospatial representation (all ps > 0.5), whereas the percentage of “low” responses and the auditory subjective center significantly increased after adaptation to a downward optical deviation (all ps < 0.05). Unlike lateral prism adaptation aftereffects that have been previously shown in both visuospatial horizontal representation and auditory frequency representation, aftereffects of vertical prism adaptation occurred in the auditory frequency representation but not in the vertical visuospatial representation. These results suggest that both vertical and lateral prism adaptations share a common substrate dedicated to the auditory modality (probably the temporal cortex), and that vertical adaptation does not act on the neural substrate of vertical visuospatial representation.

Computational modelling of SLM additive manufacturing of metals

Additive manufacturing (AM) is a technology that can create 3D structures by depositing or melting material in a layer-by-layer manner. This paper focuses on the metal-based powder bed fusion AM approach, specifically the selective laser melting (SLM) technique. The repetitive hot and cold cycles associated with AM, causes localised compression and tension giving rise to significant residual stresses, which can lead to shape loss, structural failure, etc. Numerous parameters determine the thermal gradient; these include the thermal characteristics of the powder, the bed temperature, and the part size. This investigation describes the associated problem formulation and numerical resolution in the SLM simulation. An ANSYS-additive model is developed to determine the parameter dependence on the process. An efficient parameter calibration algorithm is proposed to generate an accurate numerical model. Three numerical studies are conducted using a vertical prism, a horizontal prism, and an L-shaped structure also compared with the experimental data. [Submitted 25 July 2020; Accepted 10 December 2020]

Optical Quality of Ready-Made Reading Spectacles and Symmetry during Manufacturing Process are Good Enough?

Purpose : This study aimed to assess whether the ready-made reading spectacles (RMS) in Korea comply with the required optical standard. In addition, symmetricity of RMS was also investigated. Methods : A total of 100 of RMS of power +1.00, +2.00, +3.00, and +4.00 D currently available in optical practice were collected. Optical quality of the RMS including refractive power, optical center distance (OCD) between right lens (RL) and left lens (LL), optical centre height (Oh) were measured. Optical quality tolerances was compared with the ISO standard (ISO 8980-1 and ISO 16034:2002) and the RAL-RG-915. Induced horizontal and vertical prism were calculated from discrepancy between OCD and average pupillary distance (PD) of male and female using the prentice rule. In addition, asymmetric RMS due to manufacturing error was measured by difference of monocular OCD and Oh. Results : Twenty-three percent of the 100 RMS did not meet the ISO 8980-1 in spectacle power. Average OCD of the RMS was 62.06±1.41 mm and induced horizontal prism due to discrepancy between OCD and PD were 0.53±0.54 △ BI (range of 0.18~1.06 △) for male and 0.98±0.68 △ BI (range of 0.37~1.78 △) for female. For monocular OCD from the centre of frame, 85% of RMS had more than 1 mm monocular OCD difference between RL and LL. Optical centre height difference between RL and LL was 1.26±0.83 mm and the range of induced vertical prism was 0.12~0.45 △. Conclusion : Large amount of RMS in the study did not meet the optical quality. As RMS cannot consider the wearer’s facial shape, there was a mismatch of OCD and PD which induced significant amount of horizontal prism. Therefore, wearing RMS with improper optical quality may not provide comfort vision rather than causing additional visual burden and intervention from professional to confirm the quality of RMS is strongly recommend.

Dielectric anisotropy as indicator of crystal orientation fabric in Dome Fuji ice core: method and initial results

AbstractPolycrystalline ice is known to exhibit macroscopic anisotropy in relative permittivity (ɛ) depending on the crystal orientation fabric (COF). Using a new system designed to measure the tensorial components of ɛ, we investigated the dielectric anisotropy (Δɛ) of a deep ice core sample obtained from Dome Fuji, East Antarctica. This technique permits the continuous nondestructive assessment of the COF in thick ice sections. Measurements of vertical prism sections along the core showed that the Δɛ values in the vertical direction increased with increasing depth, supporting previous findings of c-axis clustering around the vertical direction. Analyses of horizontal disk sections demonstrated that the magnitude of Δɛ in the horizontal plane was 10–15% of that in the vertical plane. In addition, the directions of the principal axes of tensorial ɛ in the horizontal plane corresponded to the long or short axis of the elliptically elongated single-pole maximum COF. The data confirmed that Δɛ in the vertical and horizontal planes adequately indicated the preferred orientations of the c-axes, and that Δɛ can be considered to represent a direct substitute for the normalized COF eigenvalues. This new method could be extremely useful as a means of investigating continuous and depth-dependent variations in COF.

Prospective Correlation of Risk of Obstructive Sleep Apnea With Severe Clinical Features of Thyroid Eye Disease.

To evaluate the association between risk of obstructive sleep apnea (OSA) and severity of thyroid eye disease (TED) using a validated OSA screening tool. A prospective, observational cohort study was performed. New adult TED patients were offered OSA screening with the Snoring Tired Observed Pressure (STOP)-Bang survey during their initial evaluation. Clinical examination and treatment for TED were standard of care and utilized the International Thyroid Eye Disease Society Vision Inflammation Strabismus Appearance system. At the conclusion of the study period, analysis was performed correlating maximum severity of TED signs and symptoms between high- and low-risk OSA groups. Multivariate logistic and linear regression analyses were also performed to analyze the association between the numerical STOP-Bang score and maximum severity of the potentially actionable clinical features of TED (compressive optic neuropathy, vertical prism deviation, horizontal prism deviation, exophthalmos, vertical fissure height). Eighty-five patients met inclusion criteria. Twenty-eight percent were at high risk of OSA (STOP-Bang score of 3 or higher). When comparing the low- and high-risk cohorts, increased risk of OSA was significantly associated with the development of TED compressive optic neuropathy (p = 0.014), conjunctival injection (p = 0.027), chemosis (p = 0.013), upper eyelid edema (p = 0.024), lower eyelid edema (p = 0.003), eyelid erythema (p = 0.037), and vertical strabismus (p = 0.047). In the multivariate regression analyses, higher STOP-Bang scores correlated with increased risk of TED compressive optic neuropathy (p = 0.006), vertical strabismus (p = 0.019), and higher subjective diplopia scores (p = 0.045). Increased risk of OSA, as determined by the STOP-Bang survey, is associated with increased severity of multiple clinical features of TED, including TED compressive optic neuropathy and strabismus.

Experimental study on rectangular cut-throated flume: Effects of flume walls slopes and channel longitudinal slope

This research conducted to study the flow through a rectangular cut-throated flume (RCTF). The flume is simply formed by placing two vertical triangular prisms (two vertical folded plates) on either side of a rectangular open channel. Both channel and flume cross-sections are rectangular. The investigated flume is inexpensive, easy to install and does not require high maintenance. A wide experimental investigation, carried out under free outflow conditions and under upstream subcritical flow regime to investigate the effects of the channel longitudinal slope, the flume throat width, and slopes of upstream and downstream flume walls on the stage-discharge relationship. The stage-discharge relationships were deduced by applying the dimensional analysis and were calibrated using the data of this study. The proposed stage-discharge equation for horizontal channel has an average absolute relative error of 2.97% with the relative errors restricted in the range of ±10%, and 80% of the data points are in the error range of ±5%. The proposed stage-discharge equation for sloping channel has an average absolute relative error of 3.97% with the relative errors restricted in the range of ±10%, and 66% of the data points are in the error range of ±5%. The measurements indicate that slopes of upstream and downstream walls affect the stage-discharge relationship of the CTFs only in sloping channels and flow discharge is not influenced by the flume walls slopes in a horizontal channel. The proposed unified stage-discharge equation for both horizontal and sloping channels has an average absolute relative error of 3.38% with the relative errors restricted in the range of ±10%, and 74% of the data points are in the error range of ±5%. The proposed stage-discharge model demonstrates favorable accurate and convenient estimation of discharge for flows through the CTFs.

Geosynthetic-reinforced soils above voids: Observation of soil and geosynthetic deformation mechanisms

Understanding how a geosynthetic-reinforced soil deforms in response to the formation of an underlying void is crucial to provide appropriate designs of these systems. Centrifuge models employing a trapdoor to simulate the void formation below a geosynthetic-reinforced sand were conducted to investigate the behaviour in a controlled environment at realistic stress levels. The plane-strain models allowed visual observations of the deformation mechanisms using Particle Image Velocimetry (PIV). These observations were used to validate assumptions about the geosynthetic behaviour made in current design recommendations, and address limitations related to the fill behaviour. Soil expansion was observed to be confined to a parabolic zone above the void related to the soil dilatancy, rather than with a single, unique coefficient of expansion. The zone of subsidence was characterised by an initial vertical prism with a funnel to the surface, with the surface settlement profile better described by a Gaussian distribution rather than the parabolic profile used historically. Detailed interpretation of the centrifuge tests has given new insight into the soil and geosynthetic behaviour relevant to how these systems deform in practice. This paves the way for more efficient design recommendations and consequently will facilitate better predictions of geosynthetic-reinforced soil behaviour above voids.

Fourier-domain modeling of gravity effects caused by a vertical polyhedral prism, with application to a water reservoir storage process

We have developed a new Fourier-domain algorithm for the modeling of gravity effects caused by a vertical polyhedral prism. Simplified and more compact Fourier-domain expressions are derived for the vertical gravity anomaly on a 2D plane either above, in the middle of, or below the vertical polyhedral prism. A new Fourier-domain algorithm, which combines a low-order Gauss fast Fourier transform (FFT) algorithm and a low-order nonuniform FFT algorithm, to permit polar sampling near the zero wave vector, is introduced. To validate the numerical efficiency of the new algorithm, we carry out a series of synthetic tests. Numerical results show that the new algorithm is superior in numerical accuracy and efficiency compared to a pure Gauss-FFT algorithm, and both Fourier methods run much faster than traditional space-domain analytical solutions. We then apply the Fourier forward algorithms to the prediction of vertical component of gravity at many survey points, as a function of the water level of a reservoir located in Xianlin, Hangzhou, China. The reservoir geometry is approximated by a single vertical polyhedral prism. Water storage corresponds to increased heights of the polyhedral prism. Detailed maps of vertical gravity value changes corresponding to a water level rise of 5 and 10 m, with spatial resolution [Formula: see text], on the local topography covering a study area of approximately [Formula: see text] around the water reservoir, are calculated using the new algorithm. Then, the gravity values are classified according to the accuracy of the gravimeter, providing a reference of optimal site selection for a proposed cold-atom gravimetry survey to be carried out in the near future.

Arching in granular soils: experimental observations of deformation mechanisms

Understanding soil arching is an important component of predicting soil behaviour in cases such as the progressive displacements above sinkholes and when predicting loads on buried structures, where the expected deformation mechanisms are used to predict the applied loads. Visual validation of these deformation mechanisms above a void at appropriate stress levels remains limited. Centrifuge tests on dense sand were conducted to allow visualisation of the deformation mechanisms and hence enable a more accurate prediction of the load–displacement curve. The results showed that at the point of maximum arching a triangular failure zone corresponding to the formation of an apparent active failure wedge forms with proposed angles of 45° − ϕp/2 to the vertical. If the soil height is large enough to allow the full formation of this initial wedge, the deformation mechanism progresses to a vertical prism. Otherwise, the soil collapses into the void. A modification of the classical arching theory is required to allow it to be used to more accurately predict the stresses at the point of maximum arching and in the ultimate state with large displacements.

Horizontal Transposition of the Vertical Rectus Muscles to Correct a Head Tilt in 5 Patients With Idiopathic Nystagmus Syndrome

Patients with idiopathic nystagmus syndrome often develop an abnormal head position. A horizontal face turn can be treated with the augmented Kestenbaum procedure, while patients with a chin up or chin down position can be treated with surgery on the vertical recti and/or oblique muscles. Although rare, some patients may have a head tilt with no face turn. We report 5 patients who underwent horizontal transposition of the vertical rectus muscles to correct a head tilt. Retrospective case series. Five cases from 2 different tertiary referral eye centers and 3 different surgeons were reviewed and analyzed. Surgery for the patients consisted of either a 7-mm or full tendon-width transposition of the vertical rectus muscles of each eye to induce cyclotorsion in the direction of the head tilt. The presenting clinical histories, measurements, and surgical outcomes were reviewed. The primary outcome measure was correction of head tilt. Of 5 patients, 2 had previous horizontal face turns that were corrected with an augmented Kestenbaum procedure and later developed a head tilt, while 3 patients presented primarily with a head tilt. Age at surgery ranged from 5 to 8 years. Initial tilts were measured between 20-45°. Surgery was performed bilaterally except in 1 patient with history of morning glory disc anomaly and therefore transposition surgery was only performed on fixating eye for that patient. Postoperatively, 3 of 5 patients had near complete (0-5°) resolution of their tilt. One patient had a persistent 5-degree head tilt and a small chin up that was nullified with vertical prisms in spectacles. Transposition of the vertical rectus to induce cyclotorsion in the direction of the head tilt improves abnormal head titling in patients who have idiopathic nystagmus syndrome. This procedure was safely performed in patients with previous augmented Kestenbaum procedures with no incidence of anterior segment ischemia in our cases.

ROADELS: discrete information objects for production planning and control of road construction

Road construction is fundamentally different to building construction, in terms of its products, the types of work and operations, and the resources used. One of the key differences from the point of view of planning and control of production flow is that roads are composed of geometrically continuous courses rather than discrete ‘products’, making work packaging difficult. Clearly defined work packages that comprise work performed on distinct products are central to lean construction methods of planning and control, such as the Last Planner System. We therefore propose a product schema which models road sections with distinct road course segments that are dynamically defined aggregations of 'roadels'. A roadel is a fine-grained vertical triangular prism object that can be dynamically aggregated with other roadels to represent a road course segment associated with a work package, a planned task, or an as-built section. The schema represents the continuous nature of road construction, and its discrete entities enable representation and computations of as-made work using the raw data obtained from machine-mounted sensors and land surveys. We describe the information schema and illustrate its use for computation and analysis of lean production flow metrics. The schema has been tested using case study data from a 25,000 m2 parking lot project, which was modeled with more than 560,000 roadels with as-made status data collected from 33 working days over a period of two months.