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Search Results: 1 - 10 of 626565 matches for " S. M. Hsu "
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Experimental Identification of the Kink Instability as a Poloidal Flux Amplification Mechanism for Coaxial Gun Spheromak Formation
S. C. Hsu,P. M. Bellan
Physics , 2003, DOI: 10.1103/PhysRevLett.90.215002
Abstract: The magnetohydrodynamic kink instability is observed and identified experimentally as a poloidal flux amplification mechanism for coaxial gun spheromak formation. Plasmas in this experiment fall into three distinct regimes which depend on the peak gun current to magnetic flux ratio, with (I) low values resulting in a straight plasma column with helical magnetic field, (II) intermediate values leading to kinking of the column axis, and (III) high values leading immediately to a detached plasma. Onset of column kinking agrees quantitatively with the Kruskal-Shafranov limit, and the kink acts as a dynamo which converts toroidal to poloidal flux. Regime II clearly leads to both poloidal flux amplification and the development of a spheromak configuration.
Anomaly Matching in Gauge Theories at Finite Matter Density
S. D. Hsu,F. Sannino,M. Schwetz
Physics , 2000, DOI: 10.1142/S0217732301005217
Abstract: We investigate the application of 't Hooft's anomaly matching conditions to gauge theories at finite matter density. We show that the matching conditions constrain the low-energy quasiparticle spectrum associated with possible realizations of global symmetries.
On the jets, kinks, and spheromaks formed by a planar magnetized coaxial gun
S. C. Hsu,P. M. Bellan
Physics , 2004, DOI: 10.1063/1.1850921
Abstract: Measurements of the various plasma configurations produced by a planar magnetized coaxial gun provide insight into the magnetic topology evolution resulting from magnetic helicity injection. Important features of the experiments are a very simple coaxial gun design so that all observed geometrical complexity is due to the intrinsic physical dynamics rather than the source shape and use of a fast multiple-frame digital camera which provides direct imaging of topologically complex shapes and dynamics. Three key experimental findings were obtained: (1) formation of an axial collimated jet [Hsu and Bellan, Mon. Not. R. Astron. Soc. 334, 257 (2002)] that is consistent with a magnetohydrodynamic description of astrophysical jets, (2) identification of the kink instability when this jet satisfies the Kruskal-Shafranov limit, and (3) the nonlinear properties of the kink instability providing a conversion of toroidal to poloidal flux as required for spheromak formation by a coaxial magnetized source [Hsu and Bellan, Phys. Rev. Lett. 90, 215002 (2003)]. A new interpretation is proposed for how the n=1 central column instability provides flux amplification during spheromak formation and sustainment, and it is shown that jet collimation can occur within one rotation of the background poloidal field.
A Laboratory Plasma Experiment for Studying Magnetic Dynamics of Accretion Discs and Jets
S. C. Hsu,P. M. Bellan
Physics , 2002, DOI: 10.1046/j.1365-8711.2002.05422.x
Abstract: This work describes a laboratory plasma experiment and initial results which should give insight into the magnetic dynamics of accretion discs and jets. A high-speed multiple-frame CCD camera reveals images of the formation and helical instability of a collimated plasma, similar to MHD models of disc jets, and also plasma detachment associated with spheromak formation, which may have relevance to disc winds and flares. The plasmas are produced by a planar magnetized coaxial gun. The resulting magnetic topology is dependent on the details of magnetic helicity injection, namely the force-free state eigenvalue alpha_gun imposed by the coaxial gun.
Using an integrated method to estimate watershed sediment yield during heavy rain period: a case study in Hualien County, Taiwan
S. M. Hsu,H. Y. Wen,N. C. Chen,S. Y. Hsu
Natural Hazards and Earth System Sciences (NHESS) & Discussions (NHESSD) , 2012, DOI: 10.5194/nhess-12-1949-2012
Abstract: A comprehensive approach estimating sediment yield from a watershed is needed to develop better measures for mitigating sediment disasters and assessing downstream impacts. In the present study, an attempt has been made to develop an integrated method, considering sediment supplies associated with soil erosion, shallow landslide and debris flow to estimate sediment yield from a debris-flow-prone watershed on a storm event basis. The integrated method is based on the HSPF and TRIGRS models for predicting soil erosion and shallow landslide sediment yield, and the FLO-2D model for calculating debris flow sediment yield. The proposed method was applied to potential debris-flow watersheds located in the Sioulin Township of Hualien County. The available data such as hourly rainfall data, historical streamflow and sediment records as well as event-based landslide inventory maps have been used for model calibration and validation. Results for simulating sediment yield have been confirmed by comparisons of observed data from several typhoon events. The verified method employed a 24-h design hyetograph with the 100-yr return period to simulate sediment yield within the study area. The results revealed that the influence of shallow landslides on sediment supply as compared with soil erosion was significant. The estimate of landslide transport capacity into a main channel indicated the sediment delivery ratio on a typhoon event basis was approximately 38.4%. In addition, a comparison of sediment yields computed from occurrence and non-occurrence of debris flow scenarios showed that the sediment yield from an occurrence condition was found to be increasing at about 14.2 times more than estimated under a non-occurrence condition. This implied watershed sediment hazard induced by debris flow may cause severe consequences.
A Comparison of the American Society of Cataract and Refractive Surgery post-myopic LASIK/PRK Intraocular Lens (IOL) calculator and the Ocular MD IOL calculator
DeMill DL, Moshirfar M, Neuffer MC, Hsu M, Sikder S
Clinical Ophthalmology , 2011, DOI: http://dx.doi.org/10.2147/OPTH.S24131
Abstract: Comparison of the American Society of Cataract and Refractive Surgery post-myopic LASIK/PRK Intraocular Lens (IOL) calculator and the Ocular MD IOL calculator Original Research (3467) Total Article Views Authors: DeMill DL, Moshirfar M, Neuffer MC, Hsu M, Sikder S Published Date September 2011 Volume 2011:5 Pages 1409 - 1414 DOI: http://dx.doi.org/10.2147/OPTH.S24131 David L DeMill1, Majid Moshirfar1, Marcus C Neuffer1, Maylon Hsu1, Shameema Sikder2 1John A Moran Eye Center, University of Utah, Salt Lake City, UT, USA; 2Wilmer Eye Institute, Johns Hopkins University, Baltimore, MD, USA Background: To compare the average values of the American Society of Cataract and Refractive Surgery (ASCRS) and Ocular MD intraocular lens (IOL) calculators to assess their accuracy in predicting IOL power in patients with prior laser-in-situ keratomileusis (LASIK) or photorefractive keratectomy. Methods: In this retrospective study, data from 21 eyes with previous LASIK or photorefractive keratectomy for myopia and subsequent cataract surgery was used in an IOL calculator comparison. The predicted IOL powers of the Ocular MD SRK/T, Ocular MD Haigis, and ASCRS averages were compared. The Ocular MD average (composed of an average of Ocular MD SRK/T and Ocular MD Haigis) and the all calculator average (composed of an average of Ocular MD SRK/T, Ocular MD Haigis, and ASCRS) were also compared. Primary outcome measures were mean arithmetic and absolute IOL prediction error, variance in mean arithmetic IOL prediction error, and the percentage of eyes within ±0.50 and ±1.00 D. Results: The Ocular MD SRK/T and Ocular MD Haigis averages produced mean arithmetic IOL prediction errors of 0.57 and –0.61 diopters (D), respectively, which were significantly larger than errors from the ASCRS, Ocular MD, and all calculator averages (0.11, –0.02, and 0.02 D, respectively, all P < 0.05). There was no statistically significant difference between the methods in absolute IOL prediction error, variance, or the percentage of eyes with outcomes within ±0.50 and ±1.00 D. Conclusion: The ASCRS average was more accurate in predicting IOL power than the Ocular MD SRK/T and Ocular MD Haigis averages alone. Our methods using combinations of these averages which, when compared with the individual averages, showed a trend of decreased mean arithmetic IOL prediction error, mean absolute upper limit of IOL prediction error, and variance, while increasing the percentage of outcomes within ±0.50 D.
Fast Track Extubation Post Coronary Artery Bypass Graft: A Retrospective Review of Predictors of Clinical Outcomes*  [PDF]
Shelly Bansal, H. M. Thai, C. H. Hsu, C. B. Sai-Sudhakar, S. Goldman, B. E. Rhenman
World Journal of Cardiovascular Surgery (WJCS) , 2013, DOI: 10.4236/wjcs.2013.32014
Abstract: Introduction: Fast track (FT) cardiac surgery and early extubation (EE) are aimed at safe and effective rapid post-operative progression to discharge, and have been practiced for more than two decades. Their goal is to optimize patient care perioperatively in order to decrease costs without negatively affecting morbidity and mortality. However, the factors that predict successful EE are poorly understood, and patients with significant co-morbidities are frequently excluded from protocols. We hypothesize that independent of disease severity, early extubation leads to shorter hospital stays and can be performed safely without negatively affecting outcomes. Materials and Methods: We performed a retrospective review of 919 patients who underwent coronary artery bypass grafting (CABG) at the Southern Arizona Veteran’s Affairs Health Care System medical center over 7 years. We collected pre-operative data regarding patients’ NYHA classification, presence and severity of cerebral vascular disease, peripheral vascular disease, pulmonary disease, diabetes and hypertension. Intra-operative variables were also recorded including ASA scores, ischemic times, and time to extubation. Finally, post-operative variables such as rates of reintubation and tracheotomy, and both length of ICU and total hospital stay were also compared. Results: Prolonged periods of ischemia were found to predict a delayed extubation (HR = 0.992; CI = 0.988 - 0.997, p = 0.0015) while small body surface area (HR = 1.57; CI = 1.13, 2.17, p = 0.007) and higher pre-operative functional status of the patient, such as independent versus dependent status (HR =1.68; CI = 1.30 - 2.16, p < 0.0001), or partially dependent to fully dependent status (HR = 1.33; CI = 1.03 - 1.70, p = 0.03) were found to be associated with earlier extubation. The early extubation (EE) group (those extubated in less than the median 7.3 hours) had an average hospital stay of 5.1 ± 4.0 days, versus 7.8 ± 8.1 days in the delayed group (>4 hours), p < 0.0001. The EE group also
Topological Charge and $U(1)_A$ Symmetry in the High Temperature Phase of QCD
N. Evans,S. D. H. Hsu,M. Schwetz
Physics , 1996, DOI: 10.1016/0370-2693(96)00280-8
Abstract: We discuss the global symmetries of the high temperature phase of QCD with $N_f$ massless quarks. We show that the $U(N_f) \times U(N_f)$ symmetries are only violated by operators of dimension $\geq 3 N_f$. For $N_f > 2$ this implies that the thermal two-point correlation functions of the $\eta'$ and $\pi^a$'s are identical. We discuss the implications of this for the chiral phase transition at finite temperature.
Phase Transitions in Softly Broken N=2 SQCD at Non-zero Theta Angle
N. Evans,S. D. H. Hsu,M. Schwetz
Physics , 1996, DOI: 10.1016/S0550-3213(96)00595-0
Abstract: We investigate the behavior of softly broken $N=2$ SQCD at non-zero bare theta angle $\theta_0$, using superfield spurions to implement the SUSY breaking. We find a first-order phase transition as $\theta_0$ is varied from zero to $2 \pi$, in agreement with a prediction of `t Hooft. The low-energy theta angle $\theta_{eff}$, which determines the effective charges of dyonic excitations, has a complicated dependence on $\theta_0$ and breaking parameters.
QCD at Large $θ$ Angle and Axion Cosmology
N. Evans,S. D. H. Hsu,A. Nyffeler,M. Schwetz
Physics , 1996, DOI: 10.1016/S0550-3213(97)00174-0
Abstract: We use the chiral Lagrangian to investigate the global properties of the $N$-flavor QCD vacuum as a function of the $\theta$ parameter. In the case of exact quark degeneracy we find evidence for first order phase transitions at $\theta = \pi \cdot ({\rm odd~ integer})$. The first order transitions are smoothed by quark mass splittings, although interesting effects remain at realistic quark masses. We emphasize the role of the $\eta'$ condensate in our analysis. Finally, we discuss the implications of our results on the internal hadronic structure of axion domain walls and axion cosmology.
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