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In future fusion reactors, the confinement of α-particles is a crucial issue. The perfect omnigenity may be difficult to achieve in the quasi-isodynamic and quasi-symmetric stellarators when a multi-objective optimization is considered. Non-axisymmetric field can result in collisionless particles' transport via localized trapping by ripples. Specific loss channels have been revealed to essentially exist in quasi-axisymmetric stellarators [Yang et al., Europhys. Lett. 129, 35001 (2020)] and W7-X [J. M. Faustin et al., Nucl. Fusion 56, 092006 (2016)]. It indicates a drastic loss of collisionless ions through these channels. This paper is devoted to investigate the effects of axisymmetry-breaking magnetic fields on collisionless α-particle transport in the CFQS (Chinese First Quasi-axisymmetric Stellarator) -like reactor configuration. A semi-analytic representation of radial and poloidal drifts in Boozer coordinates is given, by which we found an effective route to mitigate α-particle losses, i.e., adjusting the location of the quasi-axisymmetric radial position. Such a route enables the enhancement of the poloidal drift and decrease of radial drift in peripheral regions of the identified loss channels. The particles launched inside the quasi-axisymmetric radial surface can be well confined because localized particles that may fall in loss channels can transit into blocked particles near the quasi-axisymmetric surface, escaping from loss channels, which is beneficial for the improvement of the particle confinement. Moreover, this paper may provide a set of proxy functions for suppression of energetic particle losses to optimize stellarator configurations. [ABSTRACT FROM AUTHOR]

Abstract: Obturator hernia (OH) is a rare cause of bowel obstruction. Although several surgical approaches, including the laparoscopic approach, have been reported to date, a standard approach for treating OH has not been established. A 101‐year‐old woman who presented with constipation and vomiting was admitted to our hospital. CT revealed an incarcerated small bowel within the left obturator foramen, and a diagnosis of left‐sided incarcerated OH with small bowel ileus was made. With the patient under general anesthesia, exploratory laparoscopy was performed; we identified an OH with an incarcerated small bowel, which was judged viable after hernia reduction. We repaired the hernia using an anterior preperitoneal approach under laparoscopic assistance and placed a prosthetic mesh over the obturator foramen. The patient recovered with no postoperative complications and was discharged on postoperative day 4. A hybrid laparoscopic and anterior preperitoneal approach is safe and effective for treating an incarcerated OH in an elderly patient. [ABSTRACT FROM AUTHOR]

We investigate how the neoclassical thermal diffusivity of an axisymmetric toroidal plasma is modified by the effect of resonant magnetic perturbations (RMPs), using a drift-kinetic simulation code for calculating the radial thermal diffusivity of ion in the perturbed region under an assumption of zero electric field. Here, the perturbed region is assumed to be generated on and near the resonance surfaces, and is wedged in between the regular closed magnetic surfaces. We find that the dependence of the radial thermal diffusivity on parameters of the toroidal plasma is represented as Χr = Χr(0) {1 + c0 (ωb/νeff∆b²) <∥δBr∥²>/|Bt0|²}, where Χr(0) is the neoclassical thermal diffusivity and c0 is a positive coefficient. Here, ωb is the bounce frequency, νeff is the effective collision frequency, ∆b is the banana width, <∥δBr∥²1/2 is the strength of the RMPs in the radial directions, and |Bt0| is the strength of the magnetic field on the magnetic axis. The value of c0 := c0/(qRax/ √∈t)² is significantly reduced to c0 ~ 10-4 in the simulations because of the drift motion affected by the Coulomb collision, as contrasted with c0 = π predicted by the so-called field-line diffusion theory, where q is the safety factor, Rax is the major radius of the magnetic axis, and ∈t is the inverse aspect ratio. [ABSTRACT FROM AUTHOR]

High electron temperature plasmas with steep temperature gradient in the core are obtained in recent experiments in the Large Helical Device [A. Komori et al., Fusion Sci. Technol. 58, 1 (2010)]. Such plasmas are called core electron-root confinement (CERC) and have attracted much attention. In typical CERC plasmas, the radial electric field shows a transition phenomenon from a small negative value (ion root) to a large positive value (electron root) and the radial electric field in helical plasmas are determined dominantly by the ambipolar condition of neoclassical particle flux. To investigate such plasmas' neoclassical transport precisely, the numerical neoclassical transport code, FORTEC-3D [S. Satake et al., J. Plasma Fusion Res. 1, 002 (2006)], which solves drift kinetic equation based on δf Monte Carlo method and has been applied for ion species so far, is extended to treat electron neoclassical transport. To check the validity of our new FORTEC-3D code, benchmark calculations are carried out with GSRAKE [C. D. Beidler et al., Plasma Phys. Controlled Fusion 43, 1131 (2001)] and DCOM/NNW [A. Wakasa et al., Jpn. J. Appl. Phys. 46, 1157 (2007)] codes which calculate neoclassical transport using certain approximations. The benchmark calculation shows a good agreement among FORTEC-3D, GSRAKE and DCOM/NNW codes for a low temperature (Te(0)=1.0 keV) plasma. It is also confirmed that finite orbit width effect included in FORTEC-3D affects little neoclassical transport even for the low collisionality plasma if the plasma is at the low temperature. However, for a higher temperature (5 keV at the core) plasma, significant difference arises among FORTEC-3D, GSRAKE, and DCOM/NNW. These results show an importance to evaluate electron neoclassical transport by solving the kinetic equation rigorously including effect of finite radial drift for high electron temperature plasmas. [ABSTRACT FROM AUTHOR]

Several dynamic load-balancing methods for web server clusters have been proposed. In order to realize effective load-balancing, they have required almost real-time server load information, which could be obtained by observation of client server interactions or by frequent polling from the load-balancer (dispatcher) to each server. However, observation provides indirect server load information and the polling interval produces a time lag. To overcome that problem, this paper proposes a load-balancing method based on server load estimation. Under our method, the load-balancer selects the estimated least-loaded server, then delivers arriving requests to that server. The estimation is based on the fact that the file transfer delay is proportional to the file size. The fact makes it possible to estimate the load on each server from the last request delivery time and the file size. A performance comparison with the previously proposed methods indicates that our method can achieve an effective load balancing of web server clusters. © 2011 Wiley Periodicals, Inc. Electron Comm Jpn, 94(2): 59-66, 2011; Published online in Wiley Online Library (). DOI 10.1002/ecj.10274 [ABSTRACT FROM AUTHOR]

In a wireless LAN, since two or more terminals randomly access a signal channel, frame collisions might occur. Under the standard IEEE 802.11 protocol, to avoid collisions, each terminal sets a random backoff before frame transmission. Although this measure avoids collisions, it results in useless standby duration and low throughput. To solve that problem, this paper proposes a media access method which has a fixed backoff after a successful transmission. It is shown by simulation that the proposed method reduces frame collisions and improves throughput. Furthermore, our method reduces the frame loss probability and the file transfer delay. 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 173(3): 30–39, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.21044 [ABSTRACT FROM AUTHOR]

For a system comprised of multiple Web servers that provide the same content, this paper proposes a method for the dynamic selection of servers that process requests, based on periodically obtained load information on servers. Previously proposed methods select servers probabilistically based on the weights calculated from server load information, and consequently, a server with a heavy load is selected by chance, often resulting in decreased performance. In contrast, the present method, instead of employing probabilistic server selection, selects servers by a round-robin scheme after eliminating any difference in load among the servers. A comparison of performance based on simulation studies with the conventional method indicates that the proposed method is immune to the impact of the intervals at which load information is acquired or the number of servers involved, and that it produces a low average response time even under heavy load conditions. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(10): 1–12, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20309 [ABSTRACT FROM AUTHOR]

Neoclassical transport theory around the magnetic axis of a tokamak is studied, in which relatively wide "potato" orbits play an important role in transport. Lagrangian formulation of transport theory, which has been investigated to reflect finiteness of guiding-center orbit widths to transport equations, is developed in order to analyze neoclassical transport near the axis for a low-collisionality plasma. The treatment of self-collision term in Lagrangian formulation is revised to retain momentum conservation property of it. By directly reflecting the orbital properties of all the types of orbits in calculation, the ion thermal conductivity around the axis is found to decrease from that predicted by conventional neoclassical theory. This result supports recent numerical simulations which show the reduction of thermal conductivity near the magnetic axis. [ABSTRACT FROM AUTHOR]

A global full-f gyrokinetic simulation code, GT5D, is extended to incorporate stellarator equilibria, provided by a widely used three-dimensional equilibrium code, VMEC [S. P. Hirshman and O. Betancourt, J. Comput. Phys. 96, 99 (1991)]. An interface code is newly developed, in which the so-called VMEC coordinates are transformed into the coordinates of GT5D. The following benchmark calculations in a typical LHD equilibrium are carried out for the numerical verification of GT5D in stellarator configurations. First, zonal flow damping tests are performed, and good agreement in the residual levels with an analytical theory is confirmed. Second, the neoclassical transport and the ambipolar radial electric field computed by a global δf neoclassical transport code, FORTEC-3D [S. Satake et al., Plasma Fusion Res. 3, S1062 (2008)], are successfully reproduced. [ABSTRACT FROM AUTHOR]