1,408 research outputs found

    Conifold geometries, matrix models and quantum solutions

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    This paper is a continuation of hepth/0507224 where open topological B-models describing D-branes on 2-cycles of local Calabi--Yau geometries with conical singularities were studied. After a short review, the paper expands in particular on two aspects: the gauge fixing problem in the reduction to two dimensions and the quantum matrix model solutions.Comment: 17 p. To appear in proc. Symposium QTS-4, Varna (Bulgaria), August 200

    Proton and neutron polarized structure functions from low to high Q**2

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    Phenomenological parameterizations of proton and neutron polarized structure functions, g1p and g1n, are developed for x > 0.02 using deep inelastic data up to ~ 50 (GeV/c)**2 as well as available experimental results on photo- and electro-production of nucleon resonances. The generalized Drell-Hearn-Gerasimov sum rules are predicted from low to high values of Q**2 and compared with proton and neutron data. Furthermore, the main results of the power correction analysis carried out on the Q**2-behavior of the polarized proton Nachtmann moments, evaluated using our parameterization of g1p, are briefly summarized.Comment: Proceedings of the II International Symposium on the Gerasimov-Drell-Hearn sum rule and the spin structure of the nucleon, Genova (Italy), July 3-6, 200

    Possible evidence of extended objects inside the proton

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    Recent experimental determinations of the Nachtmann moments of the inelastic structure function of the proton F2p(x, Q**2), obtained at Jefferson Lab, are analyzed for values of the squared four-momentum transfer Q**2 ranging from ~ 0.1 to ~ 2 (GeV/c)**2. It is shown that such inelastic proton data exhibit a new type of scaling behavior and that the resulting scaling function can be interpreted as a constituent form factor consistent with the elastic nucleon data. These findings suggest that at low momentum transfer the inclusive proton structure function originates mainly from the elastic coupling with extended objects inside the proton. We obtain a constituent size of ~ 0.2 - 0.3 fm.Comment: 1 reference adde

    Comment on "Nucleon elastic form factors and local duality"

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    We comment on the papers "Nucleon elastic form factors and local duality" [Phys. Rev. {\bf D62}, 073008 (2000)] and "Experimental verification of quark-hadron duality" [Phys. Rev. Lett. {\bf 85}, 1186 (2000)]. Our main comment is that the reconstruction of the proton magnetic form factor, claimed to be obtained from the inelastic scaling curve thanks to parton-hadron local duality, is affected by an artifact.Comment: to appear in Phys. Rev.

    Neutron structure function moments at leading twist

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    The experimental data on F2 structure functions of the proton and deuteron were used to construct their moments. In particular, recent measurements performed with CLAS detector at Jefferson Lab allowed to extend our knowledge of structure functions in the large-x region. The phenomenological analysis of these experimental moments in terms of the Operator Product Expansion permitted to separate the leading and higher twist contributions. Applying nuclear corrections to extracted deuteron moments we obtained the contribution of the neutron. Combining leading twist moments of the neutron and proton we found d/u ratio at x->1 approaching 0, although 1/5 value could not be excluded. The twist expansion analysis suggests that the contamination of higher twists influences the extraction of the d/u ratio at x->1 even at Q2-scale as large as 12 (GeV/c)^2.Comment: To appear in proceedings of Quark Confinement and the Hadron Spectrum VII Conference, Ponta Delgada, Portugal, 2-7 September 200

    Self-tuning high-voltage and high-frequency sinusoidal power supply for dielectric barrier discharge plasma generation

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    In this paper a high-voltage sinusoidal power supply controlled by Arduino DUE micro-controller is described. This generator can feed a dielectric barrier discharge (DBD) load with sinusoidal voltages up to 20 kV peak and frequencies in the range 10\u201360 kHz, with a maximum output power of 200 W. Output voltage can be produced either in a continuous mode, or with on/off modulation cycles, according to treatment/application requirements. This power source is equipped with on-board diagnostics used to measure the output voltage and the charge delivered to the load. With a sample frequency of 500 kHz, Arduino DUE allows to evaluate both the high voltage and the average power feeding the discharge without the use of an expensive external measurement setup. Lissajous techniques are utilized to calculate discharge average power in a quasi-real-time manner. When a load is connected to high-voltage terminals, a self-tuning procedure is carried out to obtain the best working frequency. This parameter allows to minimize power-electronic component stress and to maximize generator efficiency

    A General Mathematical Formulation for the Determination of Differential Leakage Factors in Electrical Machines with Symmetrical and Asymmetrical Full or Dead-Coil Multiphase Windings

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    This paper presents a simple and general mathematical formulation for the determination of the differential leakage factor for both symmetrical and asymmetrical full and dead-coil windings of electrical machines. The method can be applied to all multiphase windings and considers Görges polygons in conjunction with masses geometry in order to find an easy and affordable way to compute the differential leakage factor, avoiding the adoption of traditional methods that refer to the Ossanna's infinite series, which has to be obviously truncated under the bound of a predetermined accuracy. Moreover, the method described in this paper allows the easy determination of both the minimum and maximum values of the differential leakage factor, as well as its average value and the time trend. The proposed method, which does not require infinite series, is validated by means of several examples in order to practically demonstrate the effectiveness and the easiness of application of this procedure

    Prosthetic bypass for restenosis after endarterectomy or stenting of the carotid artery

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    OBJECTIVE: The objective of this study was to evaluate the results of prosthetic carotid bypass (PCB) with polytetrafluoroethylene (PTFE) grafts as an alternative to carotid endarterectomy (CEA) in treatment of restenosis after CEA or carotid artery stenting (CAS). METHODS: From January 2000 to December 2014, 66 patients (57 men and 9 women; mean age, 71 years) presenting with recurrent carotid artery stenosis ‚Č•70% (North American Symptomatic Carotid Endarterectomy Trial [NASCET] criteria) were enrolled in a prospective study in three centers. The study was approved by an Institutional Review Board. Informed consent was obtained from all patients. During the same period, a total of 4321 CEAs were completed in the three centers. In these 66 patients, the primary treatment of the initial carotid artery stenosis was CEA in 57 patients (86%) and CAS in nine patients (14%). The median delay between primary and redo revascularization was 32 months. Carotid restenosis was symptomatic in 38 patients (58%) with transient ischemic attack (n = 20) or stroke (n = 18). In this series, all patients received statins; 28 patients (42%) received dual antiplatelet therapy, and 38 patients (58%) received single antiplatelet therapy. All PCBs were performed under general anesthesia. No shunt was used in this series. Nasal intubation to improve distal control of the internal carotid artery was performed in 33 patients (50%), including those with intrastent restenosis. A PTFE graft of 6 or 7 mm in diameter was used in 6 and 60 patients, respectively. Distal anastomosis was end to end in 22 patients and end to side with a clip distal to the atherosclerotic lesions in 44 patients. Completion angiography was performed in all cases. The patients were discharged under statin and antiplatelet treatment. After discharge, all of the patients underwent clinical and Doppler ultrasound follow-up every 6 months. Median length of follow-up was 5 years. RESULTS:No patient died, sustained a stroke, or presented with a cervical hematoma during the postoperative period. One transient facial nerve palsy and two transient recurrent nerve palsies occurred. Two late strokes in relation to two PCB occlusions occurred at 2 years and 4 years; no other graft stenosis or infection was observed. At 5 years, overall actuarial survival was 81% ¬Ī 7%, and the actuarial stroke-free rate was 93% ¬Ī 2%. There were no fatal strokes. CONCLUSIONS: PCB with PTFE grafts is a safe and durable alternative to CEA in patients with carotid restenosis after CEA or CAS in situations in which CEA is deemed either hazardous or inadvisable
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