Ideal MHD Limited Electron Temperature in Spherical Tokamaks.

It is well documented that the central electron temperature in the national spherical torus experiment (NSTX) remains largely unchanged as the external heating power, and hence the normalized volume averaged plasma pressure ß increases [Stutman, Phys. Rev. Lett. 102, 115002 (2009)PRLTAO0031-900710.1103/PhysRevLett.102.115002]. Here we present a hypothesis that low n, pressure driven ideal magnetohydrodynamic (MHD) instabilities that are nondisruptive, can break magnetic surfaces in the central region and thereby flatten the electron temperature profiles. We demonstrate this mechanism in a 3D resistive MHD simulation of a NSTX discharge. By varying the toroidal magnetic field strength, and/or the heating power, we show that there is a critical value of ß, above which the central temperature profile no longer peaks on axis.

Observations of heteroclinic bifurcations in resistive magnetohydrodynamic simulations of the plasma response to resonant magnetic perturbations.

A class of topological magnetic island bifurcations that has not previously been observed in toroidal plasmas is described. Increasing an externally applied three-dimensional magnetic field in resistive magnetohydrodynamic simulations results in the asymmetric elongation of resonant island flux surfaces followed by a sequence of heteroclinic bifurcations. These bifurcations produce new sets of hyperbolic-elliptic fixed points as predicted by the Poincaré-Birkoff fixed point theorem. Field line calculations verify that the new fixed points do not connect to those of the prebifurcated islands as required for heteroclinic bifurcations on a torus with winding numbers composed of common integer factors.

Independent risk factors for long-term skeletal relapse after mandibular advancement with bilateral sagittal split osteotomy.

The purpose of this retrospective cohort study was to identify the independent risk factors for long-term skeletal relapse following mandibular advancement with bilateral sagittal split osteotomy. Univariate and multivariate linear regression analyses were performed including nine common risk factors for relapse as independent variables and horizontal/vertical long-term (≥2 years) skeletal relapse as dependent variables. Ninety-six patients were analyzed; 66 were female (68.8%) and the average age of the patients was 29.7±10.5 years. Over an average follow-up of 3.8±1.8 years after an initial mandibular advancement of 8.8±2.4 mm, long-term skeletal relapse of 1.6±1.0 mm horizontal and 0.9±0.7 mm vertical was found. Multivariate analysis identified age, preoperative mandibular plane angle (MPA), bimaxillary surgery, counterclockwise mandibular rotation, and the magnitude of mandibular advancement to be significantly associated with horizontal long-term skeletal relapse. Preoperative MPA, counterclockwise mandibular rotation, and the magnitude of mandibular advancement were significantly associated with vertical long-term skeletal relapse. Thus preoperative MPA, the magnitude of mandibular advancement, and counterclockwise mandibular rotation of the mandible were found to be independent risk factors for both horizontal and vertical long-term skeletal relapse. Although long-term skeletal relapse cannot be avoided entirely, understanding the independent risk factors and their contributions will optimize treatment planning and long-term stability.

Macrophage Transcriptional Profile Identifies Lipid Catabolic Pathways That Can Be Therapeutically Targeted after Spinal Cord Injury.

Although infiltrating macrophages influence many pathological processes after spinal cord injury (SCI), the intrinsic molecular mechanisms that regulate their function are poorly understood. A major hurdle has been dissecting macrophage-specific functions from those in other cell types as well as understanding how their functions change over time. Therefore, we used the RiboTag method to obtain macrophage-specific mRNA directly from the injured spinal cord in mice and performed RNA sequencing to investigate their transcriptional profile. Our data show that at 7 d after SCI, macrophages are best described as foam cells, with lipid catabolism representing the main biological process, and canonical nuclear receptor pathways as their potential mediators. Genetic deletion of a lipoprotein receptor, CD36, reduces macrophage lipid content and improves lesion size and locomotor recovery. Therefore, we report the first macrophage-specific transcriptional profile after SCI and highlight the lipid catabolic pathway as an important macrophage function that can be therapeutically targeted after SCI.SIGNIFICANCE STATEMENT The intrinsic molecular mechanisms that regulate macrophage function after spinal cord injury (SCI) are poorly understood. We obtained macrophage-specific mRNA directly from the injured spinal cord and performed RNA sequencing to investigate their transcriptional profile. Our data show that at 7 d after SCI, macrophages are best described as foam cells, with lipid catabolism representing the main biological process and canonical nuclear receptor pathways as their potential mediators. Genetic deletion of a lipoprotein receptor, CD36, reduces macrophage lipid content and improves lesion size and locomotor recovery. Therefore, we report the first macrophage-specific transcriptional profile after SCI and highlight the lipid catabolic pathway as an important macrophage function that can be therapeutically targeted after SCI.

Evidence of Toroidally Localized Turbulence with Applied 3D Fields in the DIII-D Tokamak.

New evidence indicates that there is significant 3D variation in density fluctuations near the boundary of weakly 3D tokamak plasmas when resonant magnetic perturbations are applied to suppress transient edge instabilities. The increase in fluctuations is concomitant with an increase in the measured density gradient, suggesting that this toroidally localized gradient increase could be a mechanism for turbulence destabilization in localized flux tubes. Two-fluid magnetohydrodynamic simulations find that, although changes to the magnetic field topology are small, there is a significant 3D variation of the density gradient within the flux surfaces that is extended along field lines. This modeling agrees qualitatively with the measurements. The observed gradient and fluctuation asymmetries are proposed as a mechanism by which global profile gradients in the pedestal could be relaxed due to a local change in the 3D equilibrium. These processes may play an important role in pedestal and scrape-off layer transport in ITER and other future tokamak devices with small applied 3D fields.

Self-Organized Stationary States of Tokamaks.

We demonstrate that in a 3D resistive magnetohydrodynamic simulation, for some parameters it is possible to form a stationary state in a tokamak where a saturated interchange mode in the center of the discharge drives a near helical flow pattern that acts to nonlinearly sustain the configuration by adjusting the central loop voltage through a dynamo action. This could explain the physical mechanism for maintaining stationary nonsawtoothing "hybrid" discharges, often referred to as "flux pumping."

Observation of a multimode plasma response and its relationship to density pumpout and edge-localized mode suppression.

Density pumpout and edge-localized mode (ELM) suppression by applied n=2 magnetic fields in low-collisionality DIII-D plasmas are shown to be correlated with the magnitude of the plasma response driven on the high-field side (HFS) of the magnetic axis but not the low-field side (LFS) midplane. These distinct responses are a direct measurement of a multimodal magnetic plasma response, with each structure preferentially excited by a different n=2 applied spectrum and preferentially detected on the LFS or HFS. Ideal and resistive magneto-hydrodynamic (MHD) calculations find that the LFS measurement is primarily sensitive to the excitation of stable kink modes, while the HFS measurement is primarily sensitive to resonant currents (whether fully shielding or partially penetrated). The resonant currents are themselves strongly modified by kink excitation, with the optimal applied field pitch for pumpout and ELM suppression significantly differing from equilibrium field alignment.

Pedestal bifurcation and resonant field penetration at the threshold of edge-localized mode suppression in the DIII-D Tokamak.

Rapid bifurcations in the plasma response to slowly varying n=2 magnetic fields are observed as the plasma transitions into and out of edge-localized mode (ELM) suppression. The rapid transition to ELM suppression is characterized by an increase in the toroidal rotation and a reduction in the electron pressure gradient at the top of the pedestal that reduces the perpendicular electron flow there to near zero. These events occur simultaneously with an increase in the inner-wall magnetic response. These observations are consistent with strong resonant field penetration of n=2 fields at the onset of ELM suppression, based on extended MHD simulations using measured plasma profiles. Spontaneous transitions into (and out of) ELM suppression with a static applied n=2 field indicate competing mechanisms of screening and penetration of resonant fields near threshold conditions. Magnetic measurements reveal evidence for the unlocking and rotation of tearinglike structures as the plasma transitions out of ELM suppression.

Tokamak operation with safety factor q95 < 2 via control of MHD stability.

Magnetic feedback control of the resistive-wall mode has enabled the DIII-D tokamak to access stable operation at safety factor q(95) = 1.9 in divertor plasmas for 150 instability growth times. Magnetohydrodynamic stability sets a hard, disruptive limit on the minimum edge safety factor achievable in a tokamak, or on the maximum plasma current at a given toroidal magnetic field. In tokamaks with a divertor, the limit occurs at q(95) = 2, as confirmed in DIII-D. Since the energy confinement time scales linearly with current, this also bounds the performance of a fusion reactor. DIII-D has overcome this limit, opening a whole new high-current regime not accessible before. This result brings significant possible benefits in terms of fusion performance, but it also extends resistive-wall mode physics and its control to conditions never explored before. In present experiments, the q(95) < 2 operation is eventually halted by voltage limits reached in the feedback power supplies, not by intrinsic physics issues. Improvements to power supplies and to control algorithms have the potential to further extend this regime.

Organic cleanliness of the Mars Science Laboratory sample transfer chain.

One of the primary science goals of the Mars Science Laboratory (MSL) Rover, Curiosity, is the detection of organics in Mars rock and regolith. To achieve this, the Curiosity rover includes a robotic sampling system that acquires rock and regolith samples and delivers it to the Sample Analysis at Mars (SAM) instrument on board the rover. In order to provide confidence that any significant organics detection result was Martian and not terrestrial in origin, a requirement was levied on the flight system (i.e., all sources minus the SAM instrument) to impart no more than 36 parts per billion (ppb by weight) of total reduced carbon terrestrial contamination to any sample transferred to the SAM instrument. This very clean level was achieved by a combination of a rigorous contamination control program on the project, and then using the first collected samples for a "dilution cleaning" campaign of the sample chain prior to delivering a sample to the SAM instrument. Direct cleanliness assays of the sample-contacting and other Flight System surfaces during pre-launch processing were used as inputs to determine the number of dilution cleaning samples needed once on Mars, to enable delivery of suitably clean samples to the SAM experiment. Taking into account contaminant redistribution during launch thorough landing of the MSL on Mars, the amount of residue present on the sampling hardware prior to the time of first dilution cleaning sample acquisition was estimated to be 60 ng/cm(2) on exposed outer surfaces of the sampling hardware and 20 ng/cm(2) on internal sample contacting surfaces; residues consisting mainly of aliphatic hydrocarbons and esters. After three dilution cleaning samples, estimated in-sample contamination level for the first regolith sample delivered to the SAM instrument at the Gale Crater "Rocknest" site was bounded at ≤10 ppb total organic carbon. A Project decision to forego ejecting the dilution cleaning sample and instead transfer the first drill-acquired sample at the "John Klein" site to SAM resulted in an estimated level of terrestrial contamination of ≤430 ppb. The estimated terrestrial contamination for portions from the second drill-acquired sample, at Cumberland, was ≤69 ppb; the estimate for a future, third, drilled sample is ≤38 ppb. These levels are comparable in magnitude to the SAM instrument blanks at the nanomole level (as chlorohydrocarbon).

Formation of collisionless high-beta plasmas by odd-parity rotating magnetic fields.

Odd-parity rotating magnetic fields (RMFo) applied to mirror-configuration plasmas have produced average electron energies exceeding 200 eV at line-averaged electron densities of approximately 10(12) cm-3. These plasmas, sustained for over 10(3)tauAlfven, have low Coulomb collisionality, vc* triple bond L/lambdaC approximately 10(-3), where lambdaC is the Coulomb scattering mean free path and L is the plasma's characteristic half length. Divertors allow reduction of the electron-neutral collision frequency to values where the RMFo coupling indicates full penetration of the RMFo to the major axis.

Fine-needle aspiration biopsy of intraosseous jaw lesions.

PURPOSE: This study assessed diagnostic accuracy, determined reasons for error, and evaluated modifications to improve the reliability of fine-needle aspiration biopsy (FNAB) of primary jaw lesions. PATIENTS AND METHODS: This was a retrospective review of 32 FNABs of intraosseous jaw lesions performed at the Massachusetts General and Children's Hospital between 1993 and 1998. A consistent, standardized technique was used, and each case was evaluated for 1) adequacy of cells to allow diagnosis, 2) presence of malignant cells, and 3) correlation between FNAB diagnosis and the final histopathology. RESULTS: Material obtained by FNAB was adequate for evaluation in 30 of 32 cases. No complications were reported. Malignant cells were found in 5 of 30 cases. FNAB diagnosis was confirmed by histopathology in all 5 of these specimens (100% accuracy). The FNAB diagnosis of benign lesions was confirmed in 17 of 25 cases (68%). The most common benign lesions were odontogenic cysts, ameloblastomas, and fibro-osseous and giant cell lesions. Incorrect diagnosis was related to lack of architectural context of the FNAB material, sampling of a nonrepresentative part of a large lesion, and inadequate quantity or quality of the aspirate. CONCLUSIONS: FNAB is a useful technique to distinguish between malignant and benign intraosseous jaw lesions. Its simplicity, suitability as an outpatient procedure, rapidity of interpretation, and minimal morbidity potentially make it the diagnostic tool of choice in the hospital setting.

Femoral shaft reconstruction using tissue-engineered growth of bone.

Tissue engineering is an interdisciplinary field that applies the principles and methods of engineering and the life sciences to the development of biologic substitutes. Bovine periosteum-derived cells were cultivated in vitro, put onto bioresorbable polymer fiber constructs, and allowed to grow until most of the fibers were coated with multiple layers of osteoblasts. Standardized 9-mm nonhealing defects were created in 24 male athymic rats femurs and bridged with titanium miniplates. In 12 animals, the defects were filled with polymer constructs containing periosteum-derived cells (experimental group); in another 12 animals, the defects were either left unfilled (control group I) or filled with polymer templates alone (control group II). After 12-week in vivo implantation, the new bone produced bridged the surgically created defects completely in seven of 10 cases. The animals of the control groups did not show significant bone formation in the gap. Histologic evaluation revealed bone formation in all experimental specimens with rests of cartilage islands showing hypertrophying chondrocytes indicative of enchondral bone formation. Tissue-engineered growth of bone resulted in healing of large segmental bone defects in an orthotopic site in an animal model. The findings of this study support potential applications of the technique of tissue-engineered growth of bone to clinical situations where local bone formation is needed.

Cervicofacial lymphatic malformation: clinical course, surgical intervention, and pathogenesis of skeletal hypertrophy.

This is a retrospective review of the clinical course and long-term soft-tissue/skeletal problems in 17 patients with large cervicofacial lymphatic malformations. Morbidity included infection (71 percent), airway compromise requiring tracheostomy (65 percent), poor dental health with aggressive caries (53 percent), abnormal articulatory patterns (47 percent), and episodic bleeding (35 percent). All patients underwent soft-tissue excision (mean four procedures per patient). Damage to facial nerve (76 percent) and hypoglossal nerve (24 percent) were common postoperative sequelae. Contour resection did not alter the progression of skeletal hypertrophy. Overgrowth most commonly occurred in the mandibular body, manifesting as anterior open bite deformity and class III occlusion (65 percent). Early mandibular body ostectomy was done in four children with grotesque hypertrophy. Jaw osteotomy was required in 71 percent of the patients to improve the maxillary/mandibular relationship. Histologic examination revealed intraosseous lymphatic malformation in areas of skeletal overgrowth in two-thirds of surgical specimens. The complexity of managing cervicofacial lymphatic malformation underscores the need for an interdisciplinary program in every major referral center.

Temporomandibular joint disc replacement made by tissue-engineered growth of cartilage.

OBJECTIVE: To test the effectiveness of the new technique of tissue-engineered growth of cartilage, temporomandibular joint (TMJ) disc replacements were created by seeding dissociated chondrocytes on synthetic, three-dimensional, bioresorbable polymer constructs of a predetermined anatomic shape, incubating the cell-polymer constructs in vitro, and transplanting them into test animals. MATERIALS AND METHODS: Twelve highly porous and bioresorbable cell-transplantation devices in the shape of TMJ discs were created using biodegradable polylactid and polyglycolic acid fibers. Bovine articular cartilage was dissociated into chondrocytes and the cells were allowed to attach to the three-dimensional polymer scaffolds and multiply in vitro. After 1 week, the cell-polymer constructs were implanted subcutaneously into nude mice. The neocartilage was assessed by magnetic resonance imaging (MRI) techniques, gross inspection, histology, and biomechanical and biochemical analysis after 12 weeks. RESULTS: All implants seeded with chondrocytes showed gross evidence of histologically organized hyaline cartilage. The scaffolds maintained their specific shape. They not only showed appropriate intrinsic stability during neomorphogenesis of cartilage in vitro and in vivo, but also seemed to guide the growth of cartilage. The presence of sulfated glycosaminoglycans was shown by aldehyde fuchsin alcian blue staining of the specimens. Type II collagen, considered to be indicative of cartilage formation, was found in the specimens tested. MRI showed signal characteristics similar to those of hyaline cartilage. Analysis of neocartilage force/displacement curves and aqueous phase compliance using a closed compression chamber suggested that the ability of the constructs to resist deformation was similar to that of native donor cartilage. CONCLUSION: The technology of tissue-engineered growth of cartilage on individually designed scaffolds may have many applications not only in reconstructive surgery of the TMJ, but also in craniomaxillofacial, plastic, and orthopedic surgery.

The use of prefabricated fascial flaps for lining of the oral and nasal cavities.

Twelve temporoparietal fascial flaps were prefabricated to line the oral and/or nasal cavities in 10 patients. Bilateral flaps were used both in a patient suffering from lye ingestion and in a patient undergoing bilateral lip reconstruction. All reconstructions were performed in two stages separated by 3 to 4 weeks. The first stage involved creation of an epithelial lining by placing a non-hair-bearing skin graft over the temporoparietal fascia. The second stage raised the fascial flaps as vascular islands and transferred them as either pedicled or free flaps. All 12 flaps survived and improved function for the patients involved. Although all possible applications for this flap have not been explored fully, there appears to be great potential for the use of this procedure in refined reconstructions of moderately sized intraoral and nasal defects.

The role of surgery in rhabdomyosarcoma of the head and neck in children.

The role of surgery in the treatment of rhabdomyosarcoma of the head and neck has diminished during the past 25 years. Treatment of this tumor in the pediatric population has involved radical radiation therapy and chemotherapy with little or no role for surgery. However, the potential effect of irradiation on facial growth and the appearance of secondary irradiation-induced tumors has raised the question as to whether surgery may once again play a role in the treatment of these patients. Advances in skull base and reconstructive surgery and microsurgical techniques have permitted a reconsideration of initial ablative surgery. The head and neck surgical team must be prepared to respond in those patients in whom craniofacial development is at risk or recurrence has occurred after radical chemotherapy and/or radiation therapy.

Respiratory muscle deoxygenation during exercise in patients with heart failure demonstrated with near-infrared spectroscopy.

Exertional dyspnea in patients with heart failure may be due, in part, to respiratory muscle underperfusion. Near-infrared spectroscopy is a new technique that permits noninvasive assessment of skeletal muscle oxygenation by monitoring changes in near-infrared light absorption. With use of near-infrared spectroscopy, serratus anterior muscle oxygenation during maximal bicycle exercise was compared in 10 patients with heart failure (ejection fraction 16 +/- 5%) and 7 age-matched normal subjects. Oxygen consumption (VO2), minute ventilation (VE) and arterial saturation were also measured. Changes in difference in absorption between 760 and 800 nm, expressed in arbitrary units, were used to detect muscle deoxygenation. Minimal change in this difference in absorption occurred in normal subjects during exercise, whereas patients with heart failure exhibited progressive changes throughout exercise consistent with respiratory muscle deoxygenation (peak exercise: normal 3 +/- 6, heart failure 12 +/- 4 near-infrared arbitrary units, p less than 0.001). At comparable work loads patients with heart failure had significantly greater minute ventilation and respiratory rate but similar tidal volume when contrasted with normal subjects. However, at peak exercise normal subjects achieved significantly greater minute ventilation and tidal volume with a comparable respiratory rate. No significant arterial desaturation occurred during exercise in either group. These findings indicate that respiratory muscle deoxygenation occurs in patients with heart failure during exercise. This deoxygenation may contribute to the exertional dyspnea experienced by such patients.