Structures induced by companions in galactic discs

Using N-body simulations we study the structures induced on a galactic disc by repeated flybys of a companion in decaying eccentric orbit around the disc. Our system is composed by a stellar disc, bulge and live dark matter halo, and we study the system's dynamical response to a sequence of a companion's flybys, when we vary i) the disc's temperature (parameterized by Toomre's Q-parameter) and ii) the companion's mass and initial orbit. We use a new 3D Cartesian grid code: MAIN (Mesh-adaptive Approximate Inverse N-body solver). The main features of MAIN are reviewed, with emphasis on the use of a new Symmetric Factored Approximate Sparse Inverse (SFASI) matrix in conjunction with the multigrid method that allows the efficient solution of Poisson's equation in three space variables. We find that: i) companions need to be assigned initial masses in a rather narrow window of values in order to produce significant and more long-standing non-axisymmetric structures (bars and spirals) in the main galaxy's disc by the repeated flyby mechanism. ii) a crucial phenomenon is the antagonism between companion-excited and self-excited modes on the disc. Values of $Q >1.5$ are needed in order to allow for the growth of the companion-excited modes to prevail over the the growth of the disc's self-excited modes. iii) We give evidence that the companion-induced spiral structure is best represented by a density wave with pattern speed nearly constant in a region extending from the ILR to a radius close to, but inside, corotation.Comment: Published in MNRA

A domain decomposing parallel sparse linear system solver

The solution of large sparse linear systems is often the most time-consuming part of many science and engineering applications. Computational fluid dynamics, circuit simulation, power network analysis, and material science are just a few examples of the application areas in which large sparse linear systems need to be solved effectively. In this paper we introduce a new parallel hybrid sparse linear system solver for distributed memory architectures that contains both direct and iterative components. We show that by using our solver one can alleviate the drawbacks of direct and iterative solvers, achieving better scalability than with direct solvers and more robustness than with classical preconditioned iterative solvers. Comparisons to well-known direct and iterative solvers on a parallel architecture are provided.Comment: To appear in Journal of Computational and Applied Mathematic

Explicit preconditioned domain decomposition schemes for solving nonlinear boundary value problems

AbstractA new class of inner-outer iterative procedures in conjunction with Picard-Newton methods based on explicit preconditioning iterative methods for solving nonlinear systems is presented. Explicit preconditioned iterative schemes, based on the explicit computation of a class of domain decomposition generalized approximate inverse matrix techniques are presented for the efficient solution of nonlinear boundary value problems on multiprocessor systems. Applications of the new composite scheme on characteristic nonlinear boundary value problems are discussed and numerical results are given

Manifold spirals, disc-halo interactions and the secular evolution in N-body models of barred galaxies

The manifold theory of barred-spiral structure provides a dynamical mechanism explaining how spiral arms beyond the ends of galactic bars can be supported by chaotic flows extending beyond the bar's co-rotation zone. We discuss its applicability to N-body simulations of secularly evolving barred galaxies. In these simulations, we observe consecutive `incidents' of spiral activity, leading to a time-varying disc morphology. Besides disc self-excitations, we provide evidence of a newly noted excitation mechanism related to the `off-centering' effect: particles ejected in elongated orbits at major incidents cause the disc center-of-mass to recoil and be set in a wobble-type orbit with respect to the halo center of mass. The time-dependent m=1 perturbation on the disc by the above mechanism correlates with the excitation of new incidents of non-axisymmetric activity beyond the bar. At every new excitation, the manifolds act as dynamical avenues attracting particles which are directed far from corotation along chaotic orbits. The fact that the manifolds evolve morphologically in time, due to varying non-axisymmetric perturbations, allows to reconcile manifolds with the presence of multiple patterns and frequencies in the disc. We find a time-oscillating pattern speed profile $\Omega_p(R)$ at distances R between the bar's corotation, at resonance with the succession of minima and maxima of the non-axisymmetric activity beyond the bar. Finally, we discuss disc thermalization, i.e., the evolution of the disc velocity dispersion profile and its connection with disc responsiveness to manifold spirals.Comment: 20 pages, 22 figures. Accepted for publication in MNRA

Comprehensive Evaluation of Hip Arthroscopy for Elite Athletes with Femoroacetabular Impingement and Associated Pathology

Femoroacetabular impingement (FAI) is a recognized source of debilitating hip pain among elite athletes. Hip arthroscopy, including labral repair, and FAI lesion correction have been gaining notoriety as methods to mitigate pain and enable athletes to return to their respective sports. PURPOSE: To provide a comprehensive understanding of the clinical presentation, surgical intervention, and outcomes of elite athletes suffering from hip pain attributed to FAI and associated pathology. METHODS: Elite athletes (n = 35; females = 12) from various sports, including basketball, soccer, martial arts, water polo, and weightlifting, participated. Following unsuccessful conservative management (e.g., analgesic medications, physical therapy), all participants consented to undergo hip arthroscopy. The surgical procedures were conducted under epidural anesthesia with patients in the supine position. We assessed the modified Harris hip score (MHHS) both preoperatively and at the 12-week postoperative mark. After surgery, athletes followed individualized physical therapy programs with physician supervision. RESULTS: The intraoperative findings revealed labral detachment in all 35 athletes, alongside various FAI lesions and cartilage defects. Surgical interventions included labral repair using bioabsorbable anchors, burring pincer and cam lesions, and inducing subchondral bone microfractures where necessary. Postoperatively, athletes exhibited statistically significant improvements, with a mean preoperative MHHS of 69 (at 1 week) rising to a mean postoperative MHHS of 92 (at 12 weeks) (t(34) = -9.62, p d = 2.29). Notably, 29 athletes (83%) reported being pain-free and returning to pre-surgical activity levels within 12 weeks. Three athletes (8.5%) endured residual pain due to iliopsoas tendinitis but resumed full activity between 15-18 weeks postoperatively. Three athletes (8.5%) developed heterotopic ossification but did not require reoperation. CONCLUSION: Hip arthroscopy involving classic labral and FAI lesion repair provides a successful approach for correcting hip pathology in elite athletes. This intervention, although continually evolving, remains a potent tool in the arsenal of sports medicine, allowing for the restoration of hip joint biomechanical function

The conjoined parascapular and latissimus dorsi free flap for reconstruction of extensive knee defects

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/146630/1/micr30361.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/146630/2/micr30361_am.pd

Sacral Stress Fracture — Wrestling

CASE HISTORY: During preseason, a 35-year-old wrestler complained of pain in his lower back concurrently with a tingling sensation in the left thigh and buttocks. PHYSICAL EXAM: The wrestler was examined by a physical therapist (PT) and, while discussing prior medical history, the athlete mentioned a previous diagnosis of a mild herniated disk (Grade 1). Upon clinical examination, the athlete demonstrated a full range of motion with some discomfort in passive hip extension. The PT suggested rest and rehabilitation through electrical stimulation, alongside the strengthening of the lumbar spine and hip abductor muscles. Ten days later, the athlete presented to an orthopedic surgeon (Ortho) complaining of the same discomfort. During the examination, the Ortho noticed the same localized tenderness over the left sacroiliac joint. Results for both the Lasegue and FABER tests were negative. Although there was no significant sign of fracture or edema, the Ortho suggested obtaining lumbar and pelvis X-Rays. He prescribed anti-inflammatory medication and performed a corticosteroid injection in the left sacroiliac joint. After treatment, the athlete had immediate relief and was able to compete the following day in his competitive event. One week later, the athlete returned to the outpatient clinic complaining that the pain was still localized in the left sacroiliac joint. The Ortho performed the hop test, which was positive. The athlete was then referred for an MRI of the spine and pelvis followed by a CT scan. DIFFERENTIAL DIAGNOSIS: 1. Spinal Disc Herniation Aggravation; 2. Sacroiliac Joint Misalignment; 3. Sciatic Neuritis; 4. Musculotendinous Strain; and 5. Sarcoma. TESTS & RESULTS: X-Ray: Clear; Hop test: Positive; MRI: a) Lumbar region: Mild L5-S1 herniation (Grade 1) with the lumbar spine curvature found to be within normal limits and b) Pelvis: Edema with associated marrow changes due to a non-displaced sacral stress fracture; CT Scan: Fracture line along with sclerosis parallel to the sacroiliac joint. FINAL DIAGNOSIS: Stress fracture on the left, anterior column of the sacrum. DISCUSSION: Clear X-Rays are associated with 20%-38% of misdiagnoses of sacral fractures. When a stress fracture is suspected, MRI should be the indicated exam, followed by a CT scan. Our clinical case gives an indication of the decision-making process so that other physicians can apply lateral thinking to their own cases. OUTCOME OF THE CASE: 1. Rehabilitation: Rest and light weight-bearing exercises (4 months) and 2. Anti-osteoporotic treatment: Calcium and Vitamin D. RETURN TO ACTIVITY AND FURTHER FOLLOW-UP: Return to participation: 5-12 months

Femur Stress Fracture - Marathon

HISTORY: During a race, a 35-year-old marathon runner complained of experiencing dull, achy pain in the right groin. After the race, he occasionally experienced radiating pain in the right thigh. The athlete was examined by a general practitioner (GP). During the clinical evaluation, the athlete had no signs of tenderness or swelling. The GP suggested rest and prescribed anti-inflammatory medication. PHYSICAL EXAMINATION: Ten days later, during training, the athlete felt the same discomfort after a challenging training session. He, then, decided to see an orthopedic physician. At the clinical examination, there was no localized pain. Focal pain was present during weight bearing activities only. Initial x-rays showed no significant abnormality or fracture. However, due to the complaints of the athlete, the doctor suggested additional x-rays and an MRI. DIFFERENTIAL DIAGNOSIS: Lumbar radiculopathy Rectus femoris strain Abductor strain Trochanteric bursitis TEST AND RESULTS: - X-ray showed a fracture of the middle shaft of the femur - MRI showed a medial periosteal reaction in the femoral shaft (high fluid signal) - Pain, especially during internal rotation - Pain on the affected side with a single-leg stance - Pain during activity, reproducible on passive range of motion FINAL / WORKING DIAGNOSIS: Stress fracture of the middle shaft of the right femur TREATMENT AND OUTCOMES: Tolerate weight bearing if no displacement occurs (four months max.) Treatment by a metabolic physician (Vitamin D deficiency or other) Continuing follow-up with repeated imaging: Verify resolution and minimize the progression to displacement Surgery if conservative management fails (see #1-3) Intramedullary rodding (surgical procedure

An Aggregation-Based Algebraic Multigrid Method with Deflation Techniques and Modified Generic Factored Approximate Sparse Inverses

In this paper, we examine deflation-based algebraic multigrid methods for solving large systems of linear equations. Aggregation of the unknown terms is applied for coarsening, while deflation techniques are proposed for improving the rate of convergence. More specifically, the V-cycle strategy is adopted, in which, at each iteration, the solution is computed by initially decomposing it utilizing two complementary subspaces. The approximate solution is formed by combining the solution obtained using multigrids and deflation. In order to improve performance and convergence behavior, the proposed scheme was coupled with the Modified Generic Factored Approximate Sparse Inverse preconditioner. Furthermore, a parallel version of the multigrid scheme is proposed for multicore parallel systems, improving the performance of the techniques. Finally, characteristic model problems are solved to demonstrate the applicability of the proposed schemes, while numerical results are given

Shoulder Arthroscopy After a Proximal Humeral Fracture Malunion: Athlete Care and Clinical Medicine in Middle-Aged Athletes

Malunion of the proximal humerus is operationally defined as healing of the fractured bone in a non-anatomical position, resulting in a painful and disabling deformity (e.g., a bone being shorter than normal, twisted or rotated in a bad position, or bent), which affects the range of motion (ROM) and functional movement. A correction and functional restoration are often needed in athletes, since their profession requires superior physical functioning. Shoulder arthroscopy has evolved dramatically over the past 15 years and has been used in cases of malunion of the humerus in athletes. However, there is a scarcity of evidence concerning middle-aged athletes. PURPOSE: To examine the benefits of shoulder arthroscopy after a proximal humeral fracture unified in malposition in middle-aged athletes. METHODS: Physical examination and imaging evaluation using 3D Computed Tomography(3D-CT), Magnetic Resonance Imaging (MRI), and shoulder radiographs (anteroposterior, internal rotation, and lateral scapular view) were used to evaluate shoulder dysfunction after proximal humeral fracture in malposition. Fourteen athletes (9 males, 5 females; Mage = 43.1, SD = 3.5) were included in this research. According to Neer classification before surgery, 11 (78%) had one part displaced and the rest three (22%) had two parts displaced. Post-operative clinical results were evaluated with self-reported pain score (1-10), UCLA scores, and shoulder abduction ROM measured with a goniometer. RESULTS: There was significant difference in pain scores (Mbefore = 8, Range: 6-9; Mafter = 4, Range: 2-6; p \u3c .001), in UCLA scores (Mbefore = 12, Range: 9-16; Mafter = 28, Range: 20-31; p \u3c .01), and in shoulder abduction ROM (Mbefore = 80, Range: 70-100; Mafter = 135, Range: 120-150; p \u3c .05). CONCLUSION: Our research provides evidence for clinical translation in improving health outcomes in middle-aged athletes with a history of proximal humeral fracture union in malposition: shoulder arthroscopy can be simultaneously beneficial in terms of decreasing pain level, increasing ROM, and restoring limb function