Transient Astrophysical Pulses and Quantum Gravity

Searches for transient astrophysical pulses could open an exciting new window into the fundamental physics of quantum gravity. In particular, an evaporating primordial black hole in the presence of an extra dimension can produce a detectable transient pulse. Observations of such a phenomenon can in principle explore the electroweak energy scale, indicating that astrophysical probes of quantum gravity can successfully complement the exciting new physics expected to be discovered in the near future at the Large Hadron Collider.Comment: 7 pages, This essay received an honorable mention in the Gravity Research Foundation Essay Competition, 200

Online Learning with Ensembles

Supervised online learning with an ensemble of students randomized by the choice of initial conditions is analyzed. For the case of the perceptron learning rule, asymptotically the same improvement in the generalization error of the ensemble compared to the performance of a single student is found as in Gibbs learning. For more optimized learning rules, however, using an ensemble yields no improvement. This is explained by showing that for any learning rule $f$ a transform $\tilde{f}$ exists, such that a single student using $\tilde{f}$ has the same generalization behaviour as an ensemble of $f$-students.Comment: 8 pages, 1 figure. Submitted to J.Phys.

Cryptography based on neural networks - analytical results

Mutual learning process between two parity feed-forward networks with discrete and continuous weights is studied analytically, and we find that the number of steps required to achieve full synchronization between the two networks in the case of discrete weights is finite. The synchronization process is shown to be non-self-averaging and the analytical solution is based on random auxiliary variables. The learning time of an attacker that is trying to imitate one of the networks is examined analytically and is found to be much longer than the synchronization time. Analytical results are found to be in agreement with simulations

Intraluminal recanalization of long infrainguinal chronic total occlusions using the Crosser system

Purpose: To assess the safety and efficacy of a device for vibrational angioplasty in the percutaneous intraluminal recanalization of long infrainguinal chronic total occlusions (CTO). Technique: The Crosser CTO Recanalization System is a mechanical recanalization device that uses high-frequency vibrational energy to disrupt and channel through fibrocalcific plaque without harming the vessel wall, thus assisting in the recanalization of an occluded artery. In 12 diabetic patients (7 men; median age 71 years, range 58–80) with critical limb ischemia owing to long (median length 26 cm, range 21–32) infrainguinal CTOs resistant to conventional guidewire techniques, the Crosser CTO Recanalization System was successful in intraluminally crossing the occlusion in 9 (75%) patients in ,5 minutes (mean 4:03 minutes). The safety endpoint (distal lumen guidewire position with no vessel perforation or dissection) was achieved in all successful cases. Conclusion: In our preliminary experience, the Crosser CTO Recanalization Catheter decreased crossing time, was safe, and achieved a high rate of intraluminal recanalization of long infrainguinal CTOs. J Endovasc Ther. 2009;16:23–27 Key words: critical limb ischemia, chronic total occlusion, percutaneous interventions, infrainguinal occlusion, intraluminal recanalization, vibrational energ

Chronic Contained Rupture of an Abdominal Aortic Aneurysm: From Diagnosis to Endovascular Resolution

A male patient, 69 years old, presented with fever, leucocytosis, and persistent low back pain; he also had an abdominal aortic aneurysm (AAA), as previously diagnosed by Doppler UltraSound (US), and was admitted to our hospital. On multislice computed tomography (msCT), a large abdominal mass having no definite border and involving the aorta and both of the psoas muscles was seen. This mass involved the forth-lumbar vertebra with lysis, thus simulating AAA rupture into a paraspinal collection; it was initially considered a paraspinal abscess. After magnetic resonance imaging examination and culture of the fluid aspirated from the mass, no infective organisms were found; therefore, a diagnosisof chronically contained AAA rupture was made, and an aortic endoprosthesis was subsequently implanted. The patient was discharged with decreased lumbar pain. At 12-month follow-up, no evidence of leakage was observed. To our knowledge, this is the first case of endoprosthesis implantation in a patient, who was a poor candidate for surgical intervention due to renal failure, leucocytosis and high fever, having a chronically contained AAA ruptured simulatingspodilodiscitis abscess. Appropriate diagnosis and therapy resolved potentially crippling pathology and avoided surgical graftrelated complications. Keywords Abdominal aortic aneurysm Endoprosthesis implantation Vertebral erosio

On the Sensitivity of a Hollow Sphere as a Multi-modal Resonant Gravitational Wave Detector

We present a numerical analysis to simulate the response of a spherical resonant gravitational wave detector and to compute its sensitivity. Under the assump- tion of optimal filtering, we work out the sensitivity curve for a sphere first taking into account only a single transducer, and then using a coherent analysis of the whole set of transducers.Comment: 24 pages, 11 figures, published versio

Single-row vs. double-row arthroscopic rotator cuff repair: clinical and 3 Tesla MR arthrography results.

Background Arthroscopic rotator cuff repair has become popular in the last few years because it avoids large skin incisions and deltoid detachment and dysfunction. Earlier arthroscopic single-row (SR) repair methods achieved only partial restoration of the original footprint of the tendons of the rotator cuff, while double-row (DR) repair methods presented many biomechanical advantages and higher rates of tendon-to-bone healing. However, DR repair failed to demonstrate better clinical results than SR repair in clinical trials. MR imaging at 3 Tesla, especially with intra-articular contrast medium (MRA), showed a better diagnostic performance than 1.5 Tesla in the musculoskeletal setting. The objective of this study was to retrospectively evaluate the clinical and 3 Tesla MRA results in two groups of patients operated on for a medium-sized full-thickness rotator cuff tear with two different techniques. Methods The first group consisted of 20 patients operated on with the SR technique; the second group consisted of 20 patients operated on with the DR technique. All patients were evaluated at a minimum of 3 years after surgery. The primary end point was the re-tear rate at 3 Tesla MRA. The secondary end points were the Constant-Murley Scale (CMS), the Simple Shoulder Test (SST) scores, surgical time and implant expense. Results The mean follow-up was 40 months in the SR group and 38.9 months in the DR group. The mean postoperative CMS was 70 in the SR group and 68 in the DR group. The mean SST score was 9.4 in the SR group and 10.1 in the DR group. The re-tear rate was 60% in the SR group and 25% in the DR group. Leakage of the contrast medium was observed in all patients. Conclusions To the best of our knowledge, this is the first report on 3 Tesla MRA in the evaluation of two different techniques of rotator cuff repair. DR repair resulted in a statistically significant lower re-tear rate, with longer surgical time and higher implant expense, despite no difference in clinical outcomes. We think that leakage of the contrast medium is due to an incomplete tendon-to-bone sealing, which is not a re-tear. This phenomenon could have important medicolegal implications. Level of evidence III. Treatment study: Case–control study

Diffusion tensor imaging and magnetic resonance spectroscopy assessment of cancellous bone quality in femoral neck of healthy, osteopenic and osteoporotic subjects at 3T: Preliminary experience.

We assessed the potential of diffusion tensor imaging (DTI) in combination with proton magnetic resonance spectroscopy ((1)H-MRS), in cancellous bone quality evaluation of the femoral neck in postmenopausal women. INTRODUCTION: DTI allows for non-invasive microarchitectural characterization of heterogeneous tissue. In this work we hypothesized that DTI parameters mean diffusivity (MD) and fractional anisotropy (FA) of bone marrow water, can provide information about microstructural changes that occur with the development of osteoporosis disease. Because osteoporosis is associated with increased bone marrow fat content, which in principal can alter DTI parameters, the goal of this study was to examine the potential of MD and FA, in combination with bone marrow fat fraction (FF), to discriminate between healthy, osteopenic and osteoporotic subjects, classified according to DXA criteria. MATERIALS AND METHODS: Forty postmenopausal women (mean age, 68.7years; range 52-81years), underwent a Dual-energy X-ray absorptiometry (DXA) examination in femoral neck, to be classified as healthy (n=12), osteopenic (n=14) and osteoporotic (n=14) subjects. (1)H-MRS and DTI (with b value=2500s/mm(2)) of femoral neck were obtained in each subject at 3T. The study protocol was approved by local Ethics Committee. MD, FA, FF and MD/FF, FA/FF were obtained and compared among the three bone-density groups. One-way ANOVA with multiple comparisons Bonferroni test and Pearson correlation analysis were applied. Receiver operating characteristic (ROC) curve analysis was also performed. RESULTS: Reproducibility of DTI measures was satisfactory. CV was approximately 2%-3% for MD and 4%-5% for FA measurements. Moreover, no significant difference was found in both MD and FA measurements between two separate sessions (median 34days apart) comprised of six healthy volunteers. FF was able to discriminate between healthy and osteoporotic subjects only. Conversely MD and FA were able to discriminate healthy from osteopenic and healthy from osteoporotic subjects, but they were not able to discriminate between osteopenic and osteoporotic patients. A significant correlation between MD and FF was observed in healthy group only. A moderate correlation was found between MD and T-score when all groups together are considered. No significant correlation was found between MD and T-score within groups. A significant positive correlation between FA and FF was found in both osteopenic and osteoporotic groups. Vice-versa no correlation between FA and FF was observed in healthy group. A high significant positive correlation was found between FA and T-score in all groups together, in healthy and in osteoporotic groups. MD/FF and FA/FF are characterized by a higher sensitivity and specificity compared to MD and FA in the discrimination between healthy, and osteoporotic subjects. MD/FF vs FA/FF graph extracted from femoral neck, identify all healthy individuals according to DXA results. CONCLUSION: DTI-(1)H-MRS protocol performed in femoral neck seems to be highly sensitive and specific in identifying healthy subjects. A MR exam is more expensive when compared to a DXA investigation. However, even though DXA BMD evaluation has been the accepted standard for osteoporosis diagnosis, DXA result has a low predictive value on patients' risk for future fractures. Thus, new approaches for examining patients at risk for developing osteoporosis would be desirable. Preliminary results showed here suggest that future studies on a larger population based on DTI assessment in the femoral neck, in combination with (1)H-MRS investigations, might allow screening of high-risk populations and the establishment of cut-off values of normality, with potential application of the method to single subjects

Mutual learning in a tree parity machine and its application to cryptography

Mutual learning of a pair of tree parity machines with continuous and discrete weight vectors is studied analytically. The analysis is based on a mapping procedure that maps the mutual learning in tree parity machines onto mutual learning in noisy perceptrons. The stationary solution of the mutual learning in the case of continuous tree parity machines depends on the learning rate where a phase transition from partial to full synchronization is observed. In the discrete case the learning process is based on a finite increment and a full synchronized state is achieved in a finite number of steps. The synchronization of discrete parity machines is introduced in order to construct an ephemeral key-exchange protocol. The dynamic learning of a third tree parity machine (an attacker) that tries to imitate one of the two machines while the two still update their weight vectors is also analyzed. In particular, the synchronization times of the naive attacker and the flipping attacker recently introduced in [1] are analyzed. All analytical results are found to be in good agreement with simulation results

Evaluation of basal ganglia haemodynamic changes with perfusion-weighted magnetic resonance imaging in patients with Parkinson's disease

The aim of our study was to assess the regional cerebral blood flow (rCBF) of basal ganglia and thalami in patients with Parkinson’s disease (PD) using perfusion–weighted magnetic resonance imaging (PW–MRI)