Fusion Conditions Research Articles

Dynamic assessment of direct-current mobility in field-assisted sintered oxide dispersion-strengthened V-4Cr-4Ti alloys

BackgroundVanadium alloy is one of the potential candidate material for structural applications in a commercial fusion reactor. Extended survival of a structural material has a direct consequence on the net energy produced in a fusion reaction, it is important to develop ultra-functional materials with tailored microstructures, to meet the harsh fusion environments. Microstructure of material, indeed depend upon the thermodynamics and kinetics of material processing.MethodsAiming to meet the harsh fusion conditions, we have developed oxide dispersion strengthened V-4Cr-4Ti alloys by high energy ball milling and field assisted sintering technique. Possible microstructural, morphological aftermaths observed in ball milled yttria dispersed V-4Cr-4Ti powders is explored.Results and conclusionElectron microscopy and laser particle analysis acknowledge that yttria addition aids powder agglomeration during ball milling. Ball milled powder was then consolidated (to a relative density of ~100%) using field assisted sintering technique, under optimal sintering conditions. Densification profile has implied that heterogeneous powder characteristic (apparent particle size and shape of powder) tends to impede the direct-current conductivity across the powder particle during various stages of field assisted sintering. In order to understand the kinetics of the field assisted sintering process on the starting powders, a new method was developed to compute the activation energy required for the direct-current conductivity across the individual powder particles. Relatively higher activation energy (for direct-current conductivity) is required for sintering yttria dispersed V-4Cr-4Ti powder than its V-4Cr-4Ti counterpart.Graphical Quantitative dynamic sintering kinetics analysis of FAST processed vanadium alloys

Automated inventory and material science scoping calculations under fission and fusion conditions

Abstract The FISPACT-II inventory simulation platform is a modern computational tool with advanced and unique capabilities. It is sufficiently flexible and efficient to make it an ideal basis around which to perform extensive simulation studies to scope a variety of responses of many materials (elements) to several different neutron irradiation scenarios. This paper briefly presents the typical outputs from these scoping studies, which have been used to compile a suite of nuclear physics materials handbooks, providing a useful and vital resource for material selection and design studies. Several different global responses are extracted from these reports, allowing for comparisons between materials and between different irradiation conditions. A new graphical output format has been developed for the FISPACT-II platform to display these “global summaries”; results for different elements are shown in a periodic table layout, allowing side-by-side comparisons. Several examples of such plots are presented and discussed.

Percutaneous pedicle screw placement under single dimensional fluoroscopy with a designed pedicle finder—a technical note and case series

Background ContextMinimally invasive spine surgery has become increasingly popular in clinical practice, and it offers patients the potential benefits of reduced blood loss, wound pain, and infection risk, and it also diminishes the loss of working time and length of hospital stay. However, surgeons require more intraoperative fluoroscopy and ionizing radiation exposure during minimally invasive spine surgery for localization, especially for guidance in instrumentation placement. In addition, computer navigation is not accessible in some facility-limited institutions. PurposeThis study aimed to demonstrate a method for percutaneous screws placement using only the anterior-posterior (AP) trajectory of intraoperative fluoroscopy. Study DesignA technical report (a retrospective and prospective case series) was carried out. Patient SamplePatients who received posterior fixation with percutaneous pedicle screws for thoracolumbar degenerative disease or trauma comprised the patient sample. MethodWe retrospectively reviewed the charts of consecutive 670 patients who received 4,072 pedicle screws between December 2010 and August 2015. Another case series study was conducted prospectively in three additional hospitals, and 88 consecutive patients with 413 pedicle screws were enrolled from February 2014 to July 2016. The fluoroscopy shot number and radiation dose were recorded. In the prospective study, 78 patients with 371 screws received computed tomography at 3 months postoperatively to evaluate the fusion condition and screw positions. ResultsIn the retrospective series, the placement of a percutaneous screw required 5.1 shots (2–14, standard deviation [SD]=2.366) of AP fluoroscopy. One screw was revised because of a medialwall breach of the pedicle. In the prospective series, 5.8 shots (2–16, SD=2.669) were required forone percutaneous pedicle screw placement. There were two screws with a Grade 1 breach (8.6%), both at the lateral wall of the pedicle, out of 23 screws placed at the thoracic spine at T9–T12. Forthe lumbar and sacral areas, there were 15 Grade 1 breaches (4.3%), 1 Grade 2 breach (0.3%), and 1 Grade 3 breach (0.3%). No revision surgery was necessary. ConclusionThis method avoids lateral shots of fluoroscopy during screw placement and thus decreases the operation time and exposes surgeons to less radiation. At the same time, compared with the computer-navigated procedure, it is less facility-demanding, and provides satisfactory reliability and accuracy.

Materials testing facilities and programmes for fission and ion implantation damage

Currently there is no fusion neutron dedicated source with a high enough flux to mimic irradiation conditions relevant to those to be experienced by the First Wall in a fusion reactor. Nevertheless, very valuable information can be obtained from existing irradiation sources, in particular Materials Test Reactors, Fast neutron reactors and Ion accelerators. Partial information is provided by these irradiation facilities that can be used to down select main materials candidates for DEMO fusion reactors and evaluate their performance under limited conditions. Modelling is an indispensable tool to interpret all the available information and build a test matrix of experiments to be carried out in a dedicated fusion neutron source.Available tools for testing materials exposed to ion or neutron irradiation, including their advantages and limitations when mimicking fusion conditions, are discussed in this paper. Next generation of fusion devices, such as DEMO, will need the input provided by a dedicated fusion neutron source to enable them to proceed in an efficient and safe manner to reach their full mission and performance.

Effect of collisions on drift instabilities in a field reversed configuration under conditions of magneto-inertial fusion

Drift instabilities in a field reversed configuration are studied under conditions of magneto-inertial fusion (MIF). Specifically, the collisional effect is taken into account because of high-density plasmas in MIF where the drift wave frequency is smaller than the electron-ion collision frequency. Dispersion relations are based on the two fluid equations including the collisional terms; meanwhile, the electromagnetic effect is also considered due to high β values (β is the ratio of plasma pressure to magnetic pressure). It is found that in the limit of low β, the behavior of instabilities described by the dispersion relations in the present paper would become like drift instabilities in tokamaks, where β ∼ 0.1. Therefore, in the MIF case, electromagnetic drift instabilities could be driven by electron-ion collisions due to the charge separation effect. The collisions also bring the phase difference between the perturbed density and the potential perturbation, which is significant for the particle transport.

Multi-soliton fusion phenomenon of Burgers equation and fission, fusion phenomenon of Sharma–Tasso–Olver equation

A direct rational exponential scheme is proposed to construct exact multi-soliton solutions and its fission, fusion phenomena after interaction of the solitons has been discussed. We have considered the Burgers and Sharma–Tasso–Olver equation as two concrete examples to show the fission and fusion of the solitary wave and the solitons, respectively. We improve different structured multi-soliton solutions with possible conditions for fission and fusion of the Burgers and the Sharma–Tasso–Olver equations arises in plasma physics and in ocean dynamics. The amplitude and velocity relations between solitons and/or solitary waves before and after interactions are given and a possible condition for fission and fusion is proposed. Furthermore, three-dimensional plots of the wave solutions are given to visualize the dynamics of the model.

Density modulation-induced absolute laser-plasma-instabilities: Simulations and theory

Fluid simulations show that when a sinusoidal density modulation is superimposed on a linear density profile, convective instabilities can become absolutely unstable. This conversion can occur for two-plasmon-decay and stimulated Raman Scattering instabilities under realistic direct-drive inertial confinement fusion conditions and can affect hot electron generation and laser energy deposition. Analysis of the three-wave model shows that a sufficiently large change of the density gradient in a linear density profile can turn convective instabilities into absolute ones. An analytical expression is given for the threshold of the gradient change for a two-slope density profile, which depends on the convective gain only.

Evaluation of fused imagery using eye movement-based measures of perceptual processing

Human performance measures were used to evaluate the perceptual processing efficiency of infrared and fused-infrared images. In two experiments, eye movements were recorded while subjects searched for and identified human targets in forested scenes presented on a computer monitor. The scenes were photographed simultaneously using short-wave infrared (SWIR), long-wave infrared (LWIR), and visible (VIS) spectrum cameras. Fused images were created through two-way combinations of these single-band images. In Experiment 1 the single band sensors were contrasted with a simple average fusion scheme (SWIR/LWIR). Analysis of subjects’ eye movements revealed differences between sensors in measures of central processing (gaze duration, response accuracy) and peripheral selection (detection interval, saccade amplitude). In Experiment 2 this methodology was applied to compare three two-way combinations of sensors (SWIR/LWIR, SWIR/VIS, VIS/LWIR), produced by state-of-the-art fusion methods. Peripheral selection for fused images tended to exhibit a compromise between the performance levels of component sensor images, while measures of central processing showed evidence that fused images matched or exceeded the performance level of component single-band sensor images. Stimulus analysis was conducted to link measures of central and peripheral processing efficiency to image characteristics (e.g. target contrast, target-background contrast), and these image characteristics were able to account for a moderate amount of the variance in the performance across fusion conditions. These findings demonstrate the utility of eye movement measures for evaluating the perceptual efficiency of fused imagery.

Central Schur rings over the projective special linear groups

ABSTRACTIn [1], Bannai presents a fusion condition and uses this to consider central Schur rings (S-rings) over the simple groups PSL(2,q) where q is a prime power. In this paper, we concretely describe all such S-rings in terms of symmetric S-rings over cyclic groups. The final section discusses counting these.

Neutralisation and transport of negative ion beams: physics and diagnostics

Neutral beam injection is one of the most important methods of plasma heating in thermonuclear fusion experiments, allowing the attainment of fusion conditions as well as driving the plasma current. Neutral beams are generally produced by electrostatically accelerating ions, which are neutralised before injection into the magnetised plasma. At the particle energy required for the most advanced thermonuclear devices and particularly for ITER, neutralisation of positive ions is very inefficient so that negative ions are used. The present paper is devoted to the description of the phenomena occurring when a high-power multi-ampere negative ion beam travels from the beam source towards the plasma. Simulation of the trajectory of the beam and of its features requires various numerical codes, which must take into account all relevant phenomena. The leitmotiv is represented by the interaction of the beam with the background gas. The main outcome is the partial neutralisation of the beam particles, but ionisation of the background gas also occurs, with several physical and technological consequences. Diagnostic methods capable of investigating the beam properties and of assessing the relevance of the various phenomena will be discussed. Examples will be given regarding the measurements collected in the small flexible NIO1 source and regarding the expected results of the prototype of the neutral beam injectors for ITER. The tight connection between measurements and simulations in view of the operation of the beam is highlighted.

Simple-ribbon fusions on non-split links

In [Simple ribbon fusions and genera for links, J. Math. Soc. Japan 68 (2016) 1033–1045], we introduced special types of fusions, so-called simple-ribbon fusions on links, and showed that they never decrease the genera of links. In this paper, we also gave a geometric condition for a simple-ribbon fusion to preserve a link type, and it turns out that a “complicated” simple-ribbon fusion may preserve a link type if the link is split. In this paper, we show that only “clearly trivial” simple-ribbon fusion preserves a link type if the link is non-split. This enables us to give a lower bound for the difference between genera of knots related by a simple-ribbon fusion.

Surgical strategies for cervical spine fracture combined with ankylosing spondylitis and cervicothoracic junction kyphosis

Objective To discuss the operative strategies for cervical spine fracture combined with ankylosing spondylitis and the deformity of cervicothoracic kyphosis. Methods Retrospectively analyzed 21 cases of cervical spine fracture combined with ankylosing spondylitis and the deformity of cervicothoracic kyphosis, who underwent surgeries from January, 2007 to August, 2014. Twenty males and 1 female were included. Mean age was (48.6±7.5) years (range, 36-65 years). The preoperative American Spine Injury Association (ASIA) classification distribution: 2 cases of Grade A, 6 cases of Grade B, 7 cases of Grade C, 5 cases of Grade D, and 1 case of of Grade E. The investigative surgical methods including posterior cervical open reduction, internal fixation and bone graft fusion; posterior cervical open reduction/decompression, internal fixation and bone graft fusion; or combined posterior and anterior cervical decompression, bone graft fusion and instrumentation. The operative time and blood loss were recorded, the clinical therapeutic effect was evaluated by visual analogue scale (VAS) score, ASIA grade improvement, cervical curvature (the angle between a line drawn parallel to the inferior endplate of C2 and a line drawn parallel to the inferior endplate of C7 in the lateral plane of an X-ray image) and radiological assessment (including bone graft fusion condition and internal fixation position). Results One case died from severe pulmonary infection and respiratory failure at the 45th day after operation. All the other 20 patients obtained complete follow-up with a mean time of (39.4±8.76) months (range, 25-59 months). 7 cases received posterior cervical open reduction, internal fixation and bone graft fusion, average operative time was (92.1±5.4) minutes and average blood loss was (96.1+23.7) ml. 9 cases received the posterior cervical open reduction and decompression, internal fixation and bone graft fusion, mean operation time was (121.4±14.0) minutes and blood loss was (250.0±38.9) ml. 3 cases experienced combined posterior and anterior cervical decompression, bone graft fusion and fixation, average operative time was (222.4±14.9) minutes and average blood loss was (354.3+46.7) ml. Mean of VAS scores at the 3th month postoperatively was 2.76±0.46, significantly lower than the preoperatively VAS scores (8.95±0.36). Mean of VAS scores at the 24th month postoperatively was 1.77±0.39, significantly lower than those at the 3th month postoperatively. The neurological function of spinal cord achieved significant improvement after operations and continued recovered gradually in the subsequent follow up. ASIA Classification distribution at the 24th month postoperatively was: 0 case of Grade A, 0 case of Grade B, 3 cases of Grade C, 8 cases of Grade D, 9 case of Grade E. Mean of the cervical curvature after operation was -7.1°±1.9°, significantly higher than preoperatively(-13.4°±3.3°) and did not have any loss of Cobb's angles at 24th month after operation. All the surviving cases achieved solid bone graft fusion. Mean bone graft fusion time was 5.8 months (range, 4-9 months). There was no internal fixation loose, fracture and dislocation occurred during follow up. Conclusion All procedures can significantly relieve the painful symptoms, effectively restore the normal cervical alignment and stability, and remarkably improve the neural function of the patients suffering cervical spine fracture combined with ankylosing spondylitis and the deformity of cervicothoracic junction kyphosis. Key words: Spondylitis, ankylosing; Cervical vertebrae; Spinal fractures; Thoracic vertebrae; Kyphosis

Development of target fabrication for laser-driven inertial confinement fusion at research center of laser fusion

As the basic conditions for laser inertial confinement fusion (ICF) research, the targets are required to be well specified and elaborately fabricated. Because of the characteristics of the targets, the research and fabrication process is a systematically tough task, which needs fundamental and deep insights into film deposition, mechanical machining, precise measurement and assembly, etc. As a result, knowledge of material science, physics, mechanical as well as electronics is a necessity for target researchers. In this paper, we give introductions to the state of art on target fabrication for ICF research at Research Center of Laser Fusion (RCLF) in China.

One-dimensional numerical investigation on the formation of Z-pinch dynamic hohlraum using the code MULTI

Z-pinch dynamic hohlraum can effectively convert Z-pinch plasma kinetic energy into radiation field energy, which has a potential to implode a pellet filled with deuterium-tritium fuel to fusion conditions when the drive current is sufficiently large. To understand the formation process of Z-pinch dynamic hohlraum on JULONG-I facility with a typical drive current of 8-10 MA, a new radiation magneto-hydrodynamics code is developed based on the program MULTI-IFE. MULTI-IFE is a one-dimensional, two-temperature, multi-group, open-source radiation hydrodynamic code, which is initially designed for laser and heavy ion driven fusion. The original program is upgraded to simulate Z-pinch related experiments by introducing Lorentz force, Joule heating and the evolution of magnetic field into the code. Numerical results suggest that a shock wave and a thermal wave will be launched when the high speed plasma impacts onto the foam converter. The thermal wave propagates much faster than shock wave, making the foam become hot prior to the arrival of shock wave. For the load parameters and drive current of shot 0180, the calculated propagation speed of thermal wave and shock wave are about 36.1 cm/s and 17.6 cm/s, respectively. The shock wave will be reflected when it arrives at the foam center and the speed of reflected shock wave is about 12.9 cm/s. Calculations also indicate that the plastic foam will expand obviously due to the high temperature radiation environment (~30 eV) around it before the collision between tungsten plasma and foam converter. The evolution of radial radiation temperature profile shows that a pair of bright strips pointing to the foam center can be observed by an on-axis streak camera and the radiation temperature in the foam center achieves its highest value when the shock arrives at the axis. A bright emission ring moving towards the foam center can also be observed by an on-axis X-ray frame camera. The best time to capture the bright strips and bright emission rings is before the thermal wave reaches the foam center. Even though some amount of X-ray radiation in the foam is expected to escape from the hohlraum via radiation transport process, simulation results suggest that the tungsten plasma can serve as a good hohlraum wall. The radiation temperature is about 80 eV when the dynamic hohlraum is created and can rise more than 100 eV before the shock arrives at the foam center. Most of the X-rays emitted by the wire-array plasma surface have energies below 1000 eV. In this paper, the physical model of the code MULTI-IFE and the simulation results of array implosions on Saturn facility are presented as well.

Non-equilibrium between ions and electrons inside hot spots from National Ignition Facility experiments

The non-equilibrium between ions and electrons in the hot spot can relax the ignition conditions in inertial confinement fusion [Fan et al., Phys. Plasmas 23, 010703 (2016)], and obvious ion-electron non-equilibrium could be observed by our simulations of high-foot implosions when the ion-electron relaxation is enlarged by a factor of 2. On the other hand, in many shots of high-foot implosions on the National Ignition Facility, the observed X-ray enhancement factors due to ablator mixing into the hot spot are less than unity assuming electrons and ions have the same temperature [Meezan et al., Phys. Plasmas 22, 062703 (2015)], which is not self-consistent because it can lead to negative ablator mixing into the hot spot. Actually, this non-consistency implies ion-electron non-equilibrium within the hot spot. From our study, we can infer that ion-electron non-equilibrium exists in high-foot implosions and the ion temperature could be ∼9% larger than the equilibrium temperature in some NIF shots.

Conceptual design of the beam source for the DEMO Neutral Beam Injectors

DEMO (DEMOnstration Fusion Power Plant) is a proposed nuclear fusion power plant that is intended to follow the ITER experimental reactor. The main goal of DEMO will be to demonstrate the possibility to produce electric energy from the fusion reaction. The injection of high energy neutral beams is one of the main tools to heat the plasma up to fusion conditions. A conceptual design of the Neutral Beam Injector (NBI) for the DEMO fusion reactor, is currently being developed by Consorzio RFX in collaboration with other European research institutes. High efficiency and low recirculating power, which are fundamental requirements for the success of DEMO, have been taken into special consideration for the DEMO NBI. Moreover, particular attention has been paid to the issues related to reliability, availability, maintainability and inspectability. A conceptual design of the beam source for the DEMO NBI is here presented featuring 20 sub-sources (two adjacent columns of 10 sub-sources each), following a modular design concept, with each sub-source featuring its radio frequency driver, capable of increasing the reliability and availability of the DEMO NBI. Copper grids with increasing size of the apertures have been adopted in the accelerator, with three main layouts of the apertures (circular apertures, slotted apertures and frame-like apertures for each sub-source). This design, permitting to significantly decrease the stripping losses in the accelerator without spoiling the beam optics, has been investigated with a self-consistent model able to study at the same time the magnetic field, the electrostatic field and the trajectory of the negative ions. Moreover, the status on the R&D carried out in Europe on the ion sources is presented.

Ex vivo loading of trussed implants for spine fusion induces heterogeneous strains consistent with homeostatic bone mechanobiology

A truss structure was recently introduced as an interbody fusion cage. As a truss system, some of the connected elements may be in a state of compression and others in tension. This study aimed to quantify both the mean and variance of strut strains in such an implant when loaded in a simulated fusion condition with vertebral body or contoured plastic loading platens ex vivo. Cages were each instrumented with 78 fiducial spheres, loaded between platens (vertebral body or contoured plastic), imaged using high resolution micro-CT, and analyzed for deformation and strain of each of the 221 struts. With repeated loading of a cage by vertebral platens, the distribution (variance, indicated by SD) of strut strains widened from 50N control (4±114με, mean±SD) to 1000N (−23±273με) and 2000N (-48±414με), and between 1000N and 2000N. With similar loading of multiple cages, the strain distribution at 2000N (23±389με) increased from 50N control. With repeated loading by contoured plastic platens, induced strains at 2000N had a distribution similar to that induced by vertebral platens (84±426με). In all studies, cages exhibited increases in strut strain amplitude when loaded from 50N to 1000N or 2000N. Correspondingly, at 2000N, 59–64% of struts exhibited strain amplitudes consistent with mechanobiologically-regulated bone homeostasis. At 2000N, vertically-oriented struts exhibited deformation of −2.87±2.04μm and strain of −199±133με, indicating overall cage compression. Thus, using an ex vivo 3-D experimental biomechanical analysis method, a truss implant can have strains induced by physiological loading that are heterogeneous and of amplitudes consistent with mechanobiological bone homeostasis.

Effect of collision cascades on dislocations in tungsten: A molecular dynamics study

Tungsten (W) is the prime candidate material for the divertor and other plasma-facing components in DEMO. The point defects (i.e. vacancies and self-interstitials) produced in collision cascades caused by incident neutrons aggregate into dislocation loops (and voids), which strongly affect the mechanical properties. The point defects also interact with existing microstructural features, and understanding these processes is crucial for modelling the long term microstructural evolution of the material under fusion conditions. In this work, we performed molecular dynamics simulations of cascades interacting with initially straight edge dislocation dipoles. It was found that the residual vacancy number usually exceeds the residual interstitial number for cascades interacting with vacancy type dipoles, but for interstitial type dipoles these are close. We observed that a cascade near a dislocation promotes climb, i.e. it facilitates the movement of point defects along the climb direction. We also observed that the dislocations move easily along the glide direction, and that kinks are formed near the centre of the cascade, which then facilitate the movement of the dipoles. Some dipoles are sheared off by the cascade, and this is dependent on PKA energy, position, direction, and the width of dipole.

SYNTHESIS AND ANTI-INFLAMMATORY ACTIVITY OF SOME NEW PYRAZOLO[3,4-d] PYRIMIDINES

5-Amino-3-methyl-1-phenyl-1 H -pyrazole-4-carbonitrile ( 5 ) was reacted with chloroacetyl chloride under fusion condition to afford two compounds, which identified as 6-chloromethylpyrazolo[3,4- d ]pyrimdine ( 3 ) and 4-amino-5-chloropyrazolo[3,4- b ]pyridine ( 7 ) ln different ratios. Treatment of compound ( 3 ) with aromatic amines, gave the arylaminomethyl derivatives ( 8a-c ). Compound ( 3 ) was reacted with sodium azide, phosphorous oxychloride, sulphanilamide to give new derivatives ( 9, 10, and 14 ). The 4-chloro derivative ( 11 ) underwent nucleophilic substitution using some reagent such as P 2 S 5 , sodium azide and hydrazine hydrate to furnish novel pyrazolo[3,4- d ]pyrimidines ( 12, 13, 15, 16, 17 ). All synthesized compounds were characterized using elemental analysis and spectral techniques. The anti-inflammatory activity of all the newly synthesized compounds was evaluated using the carrageenan induced paw oedema test in rats using indomethacin as the reference drug.

Compressive Force With 2-Screw and 3-Screw Subtalar Joint Arthrodesis With Headless Compression Screws.

Joint compression is an essential element of successful arthrodesis. Although subtalar joint compression generated by conventional screws has been quantified in the laboratory, compression obtainable with headless screws that rely on variable thread pitch to achieve bony contact has not been assessed. This study measured subtalar joint compression achieved by 2 posteriorly placed contemporary headless, variable-pitch screws, and quantified additional compression gained by placing a third screw anteriorly. Ten, unpaired fresh-frozen cadaveric subtalar joints were fixed sequentially using 2 diverging posterior screws (one directed into the talar dome, the other into the talar neck), 2 parallel posterior screws (both ending in the talar dome), and 2 parallel screws with an additional anterior screw inserted from the plantar calcaneus into the talar neck. Joint compression was quantified directly during screw insertion using a novel custom-built measuring device. The mean compression generated by 2 diverging posterior screws was 246 N. Two parallel posterior screws produced 294 N of compression, and augmentation of that construct with a third, anterior screw increased compression to 345 N (P < .05). Compression subsequent to 2-screw fixation was slightly less than that reported previously for subtalar joint fixation with 2 conventional lag screws, but was comparable when a third screw was added. Under controlled testing conditions, 2 tapered, variable-pitch screws generated somewhat less compression than previously reported for 2-screw fixation with conventional headed screws. A third screw placed anteriorly increased compression significantly. Because headless screws are advantageous where prominent screw heads are problematic, such as the load-bearing surface of the foot, their effectiveness compared to other screws should be established to provide an objective basis for screw selection. Augmenting fixation with an anterior screw may be desirable when conditions for fusion are suboptimal.