Flywheel energy storage system with homopolar electrodynamic magnetic bearing

The goal of this research was to evaluate the potential of homopolar electrodynamic magnetic bearings for flywheel energy storage systems (FESSs). The primary target was a FESS for Low Earth Orbit (LEO) satellites; however, the design can also be easily adapted for Earth-based applications. The main advantage of Homopolar Electrodynamic Bearings compared to more conventional Active Magnetic Bearings (AMB) is simplicity and very low power rating of its electronics, resulting in higher system reliability - a critical factor for space applications. For commercial applications this technologies may also be found very attractive due to a potentially lower cost compared to AMB.Center for Electromechanic

Rigidity and volume preserving deformation on degenerate simplices

Given a degenerate $(n+1)$-simplex in a $d$-dimensional space $M^d$ (Euclidean, spherical or hyperbolic space, and $d\geq n$), for each $k$, $1\leq k\leq n$, Radon's theorem induces a partition of the set of $k$-faces into two subsets. We prove that if the vertices of the simplex vary smoothly in $M^d$ for $d=n$, and the volumes of $k$-faces in one subset are constrained only to decrease while in the other subset only to increase, then any sufficiently small motion must preserve the volumes of all $k$-faces; and this property still holds in $M^d$ for $d\geq n+1$ if an invariant $c_{k-1}(\alpha^{k-1})$ of the degenerate simplex has the desired sign. This answers a question posed by the author, and the proof relies on an invariant $c_k(\omega)$ we discovered for any $k$-stress $\omega$ on a cell complex in $M^d$. We introduce a characteristic polynomial of the degenerate simplex by defining $f(x)=\sum_{i=0}^{n+1}(-1)^{i}c_i(\alpha^i)x^{n+1-i}$, and prove that the roots of $f(x)$ are real for the Euclidean case. Some evidence suggests the same conjecture for the hyperbolic case.Comment: 27 pages, 2 figures. To appear in Discrete & Computational Geometr

Extended Volumetric Follow-up of Juvenile Pilocytic Astrocytomas Treated with Proton Beam Therapy

Purpose: To describe volume changes following proton beam therapy (PBT) for juvenile pilocytic astrocytoma (JPA), we analyzed post-PBT magnetic resonance imaging (MRI) to clarify survivorship, response rate, and the concept of pseudoprogression. Materials and Methods: Pediatric patients with a histologic diagnosis of JPA after a biopsy or subtotal resection and at least 4 post-PBT MRIs were retrospectively reviewed. After PBT, tumors were contoured on follow-up T1-contrasted MRIs, and 3-dimensional volumes were plotted against time, with thresholds for progressive disease and partial response. Patterns of response, pseudoprogression, and progression were uncovered. Post-PBT clinical course was described by the need for further intervention and survivorship. Results: Fifteen patients with a median of 10 follow-up MRIs made up this report: 60% were heavily pretreated with multiple lines of chemotherapy, and 67% had undergone subtotal resection. With a median follow-up of 55.3 months after a median of 5400 centigray equivalents PBT, estimates of 5-year overall survival and intervention-free survival were 93% and 72%, respectively. The crude response rate of 73% included pseudoprogressing patients, who comprised 20% of the entire cohort; the phenomenon peaked between 3 and 8 months and resolved by 18 months. One nonresponder expired from progression. Post-PBT intervention was required in 53% of patients, with 1 patient resuming chemotherapy. There were no further resections or radiotherapy. One patient developed acute lymphoblastic leukemia, and another developed biopsy-proven radionecrosis. Conclusion: The PBT for inoperable/progressive JPA provided 72% 5-year intervention-free survival in heavily pretreated patients. Although most patients responded, 20% demonstrated pseudoprogression. The need for post-PBT surveillance for progression and treatment-induced sequelae should not be underestimated in this extended survivorship cohort

Complementary vertices and adjacency testing in polytopes

Our main theoretical result is that, if a simple polytope has a pair of complementary vertices (i.e., two vertices with no facets in common), then it has at least two such pairs, which can be chosen to be disjoint. Using this result, we improve adjacency testing for vertices in both simple and non-simple polytopes: given a polytope in the standard form {x \in R^n | Ax = b and x \geq 0} and a list of its V vertices, we describe an O(n) test to identify whether any two given vertices are adjacent. For simple polytopes this test is perfect; for non-simple polytopes it may be indeterminate, and instead acts as a filter to identify non-adjacent pairs. Our test requires an O(n^2 V + n V^2) precomputation, which is acceptable in settings such as all-pairs adjacency testing. These results improve upon the more general O(nV) combinatorial and O(n^3) algebraic adjacency tests from the literature.Comment: 14 pages, 5 figures. v1: published in COCOON 2012. v2: full journal version, which strengthens and extends the results in Section 2 (see p1 of the paper for details

Factors Associated with Recurrence of Varicose Veins after Thermal Ablation: Results of The Recurrent Veins after Thermal Ablation Study

Background. The goal of this retrospective cohort study (REVATA) was to determine the site, source, and contributory factors of varicose vein recurrence after radiofrequency (RF) and laser ablation. Methods. Seven centers enrolled patients into the study over a 1-year period. All patients underwent previous thermal ablation of the great saphenous vein (GSV), small saphenous vein (SSV), or anterior accessory great saphenous vein (AAGSV). From a specific designed study tool, the etiology of recurrence was identified. Results. 2,380 patients were evaluated during this time frame. A total of 164 patients had varicose vein recurrence at a median of 3 years. GSV ablation was the initial treatment in 159 patients (RF: 33, laser: 126, 52 of these patients had either SSV or AAGSV ablation concurrently). Total or partial GSV recanalization occurred in 47 patients. New AAGSV reflux occurred in 40 patients, and new SSV reflux occurred in 24 patients. Perforator pathology was present in 64% of patients. Conclusion. Recurrence of varicose veins occurred at a median of 3 years after procedure. The four most important factors associated with recurrent veins included perforating veins, recanalized GSV, new AAGSV reflux, and new SSV reflux in decreasing frequency. Patients who underwent RF treatment had a statistically higher rate of recanalization than those treated with laser

Six topics on inscribable polytopes

Inscribability of polytopes is a classic subject but also a lively research area nowadays. We illustrate this with a selection of well-known results and recent developments on six particular topics related to inscribable polytopes. Along the way we collect a list of (new and old) open questions.Comment: 11 page

Development of planar pixel modules for the ATLAS high luminosity LHC tracker upgrade

The high-luminosity LHC will present significant challenges for tracking systems. ATLAS is preparing to upgrade the entire tracking system, which will include a significantly larger pixel detector. This paper reports on the development of large area planar detectors for the outer pixel layers and the pixel endcaps. Large area sensors have been fabricated and mounted onto 4 FE-I4 readout ASICs, the so-called quad-modules, and their performance evaluated in the laboratory and testbeam. Results from characterisation of sensors prior to assembly, experience with module assembly, including bump-bonding and results from laboratory and testbeam studies are presented

Rigidity of escaping dynamics for transcendental entire functions

We prove an analog of Boettcher's theorem for transcendental entire functions in the Eremenko-Lyubich class B. More precisely, let f and g be entire functions with bounded sets of singular values and suppose that f and g belong to the same parameter space (i.e., are *quasiconformally equivalent* in the sense of Eremenko and Lyubich). Then f and g are conjugate when restricted to the set of points which remain in some sufficiently small neighborhood of infinity under iteration. Furthermore, this conjugacy extends to a quasiconformal self-map of the plane. We also prove that this conjugacy is essentially unique. In particular, we show that an Eremenko-Lyubich class function f has no invariant line fields on its escaping set. Finally, we show that any two hyperbolic Eremenko-Lyubich class functions f and g which belong to the same parameter space are conjugate on their sets of escaping points.Comment: 28 pages; 2 figures. Final version (October 2008). Various modificiations were made, including the introduction of Proposition 3.6, which was not formally stated previously, and the inclusion of a new figure. No major changes otherwis