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The velocity required in IEC 61373 for long-life random vibration testing of Category-3 rolling stock equipment in the vertical direction is 2.7821 m/s, but the maximum velocity of existing electrodynamic shakers falls in the range of 2–2.5 m/s. In this study, an electrodynamic shaker with a velocity satisfying the requirements for vibration testing of Category-3 rolling stock equipment was developed. First, mechanical and equivalent circuit models of an electrodynamic shaker were developed. On this basis, reducing the impedance of the armature coil was identified as the best option for increasing the velocity of the shaker. However, owing to the impact of the back electromotive force of the armature coil, a decrease in the input impedance of the armature coil at low frequencies leads to an increase in its input impedance at high frequencies. To reduce the input impedance at high frequencies, a shading coil was incorporated into the circuit. The shading coil-incorporated new design was modeled using equivalent circuits and simulated numerically. The results showed that the improvement measures—incorporating a shading coil, increasing the cross-sectional area, and reducing the number of turns of the armature coil—effectively reduced the input impedance of the armature coil, thereby increasing the armature coil current and the velocity of the shaker. Finally, a shaker with a maximum velocity of 3.2 m/s was fabricated based on the new design and was validated to satisfy the high-velocity requirement for the long-life vibration test of Category-3 equipment in the vertical direction as specified in IEC 61373.

The parametric instability of homogeneous couplers with and without viscoelasticity has been the subject of many interests. Recently, an attention is given to the use of nonhomogeneous links to reduce the happening of dynamic instability of mechanisms. Therefore, the objective of this study is to perform qualitative analysis of beam-like members composed of periodically embedded arrays in transverse direction to diminish the possibility of occurrence of large amplitude vibration. By assuming that the member is an inhomogeneous continuum, the periodicity and matching conditions across the interfaces of arrays and layers are taken into account by the Fourier series. The embedded arrays have different geometric and material properties and carry linear viscoelastic Kelvin–Voigt model. The proposed model is evaluated by applying it as a coupler into a slider-crank mechanism to examine the influence produced by arrays to the primary and secondary parametric instability. Result shows that the stiffness ratio between arrays and basic layers has visible effect on narrowing the regions of dynamic instability. Meanwhile, even if the damping of basic layer is light, increasing the damping ratio of arrays increases the capability of the coupler to suppress resonant peaks of vibration. As the damping of basic layer is moderate, the combination of stiffness ratio and damping ratio produces significant influence on diminishing the occurrence of large amplitude vibration, even though the fundamental frequency of the coupler is close to the resonant frequency. It is concluded that the growth of small amplitude vibration into large motion regime caused by parametric resonance can be effectively attenuated if the material and geometric properties between arrays and basic layers of the coupler are properly arranged.

In order to avoid the effect of photon defect on the imaging during X-ray generation, an imaging integral filter based on quantum enhancement was proposed in this paper to effectively reduce the sensitivity of X-ray detection system for quantum noise. Firstly, the coupling constraint at the end of the image intensifier was analyzed by discussing the X-ray imaging mechanism. The effects of quantum thermal noise and defects on spectrum transfer were studied from the micro perspective. Then the effectiveness of the new integral filter method was verified from the view of the integral effect of fundamental space frequency transfer characteristics in Fourier spectrum. Finally, the superiority and real-time performance of the quantum enhancement filter method were verified by the comparison filter testing.

Full list of authors: Rast, Mark P.; Bello González, Nazaret; Bellot Rubio, Luis; Cao, Wenda; Cauzzi, Gianna; Deluca, Edward; de Pontieu, Bart; Fletcher, Lyndsay; Gibson, Sarah E.; Judge, Philip G.; Katsukawa, Yukio; Kazachenko, Maria D.; Khomenko, Elena; Landi, Enrico; Martínez Pillet, Valentín; Petrie, Gordon J. D.; Qiu, Jiong; Rachmeler, Laurel A.; Rempel, Matthias; Schmidt, Wolfgang; Scullion, Eamon; Sun, Xudong; Welsch, Brian T.; Andretta, Vincenzo; Antolin, Patrick; Ayres, Thomas R.; Balasubramaniam, K. S.; Ballai, Istvan; Berger, Thomas E.; Bradshaw, Stephen J.; Campbell, Ryan J.; Carlsson, Mats; Casini, Roberto; Centeno, Rebecca; Cranmer, Steven R.; Criscuoli, Serena; Deforest, Craig; Deng, Yuanyong; Erdélyi, Robertus; Fedun, Viktor; Fischer, Catherine E.; González Manrique, Sergio J.; Hahn, Michael; Harra, Louise; Henriques, Vasco M. J.; Hurlburt, Neal E.; Jaeggli, Sarah; Jafarzadeh, Shahin; Jain, Rekha; Jefferies, Stuart M.; Keys, Peter H.; Kowalski, Adam F.; Kuckein, Christoph; Kuhn, Jeffrey R.; Kuridze, David; Liu, Jiajia; Liu, Wei search; Longcope, Dana; Mathioudakis, Mihalis; McAteer, R. T. James; McIntosh, Scott W.; McKenzie, David E.; Miralles, Mari Paz; Morton, Richard J.; Muglach, Karin; Nelson, Chris J.; Panesar, Navdeep K.; Parenti, Susanna; Parnell, Clare E.; Poduval, Bala; Reardon, Kevin P.; Reep, Jeffrey W.; Schad, Thomas A.; Schmit, Donald; Sharma, Rahul; Socas-Navarro, Hector; Srivastava, Abhishek K.; Sterling, Alphonse C.; Suematsu, Yoshinori; Tarr, Lucas A.; Tiwari, Sanjiv; Tritschler, Alexandra; Verth, Gary; Vourlidas, Angelos; Wang, Haimin; Wang, Yi-Ming.-- This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/., The National Science Foundation’s Daniel K. Inouye Solar Telescope (DKIST) will revolutionize our ability to measure, understand, and model the basic physical processes that control the structure and dynamics of the Sun and its atmosphere. The first-light DKIST images, released publicly on 29 January 2020, only hint at the extraordinary capabilities that will accompany full commissioning of the five facility instruments. With this Critical Science Plan (CSP) we attempt to anticipate some of what those capabilities will enable, providing a snapshot of some of the scientific pursuits that the DKIST hopes to engage as start-of-operations nears. The work builds on the combined contributions of the DKIST Science Working Group (SWG) and CSP Community members, who generously shared their experiences, plans, knowledge, and dreams. Discussion is primarily focused on those issues to which DKIST will uniquely contribute. © 2021, The Author(s)., This work rests on many years of sustained vision, effort, and dedication by DKIST and DKIST instrument, team scientists, engineers, and administrative, support personnel, the unwavering commitment of the National Science Foundation, and the support of the US taxpayers. It includes contributions from members of the DKIST Science Working Group and the DKIST Critical Science Plan Community, all of whom generously shared their experiences, plans, knowledge, and dreams. The research reported herein was based in part on the National Science Foundation’s Daniel K. Inouye Solar Telescope (DKIST), a facility of the National Solar Observatory (NSO). NSO is managed by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the National Science Foundation., With funding from the Spanish government through the Severo Ochoa Centre of Excellence accreditation SEV-2017-0709.

Because of its distinctive compositional properties and variability, low-speed ($\lesssim 450$ km s$^{-1}$) solar wind is widely believed to originate from coronal streamers, unlike high-speed wind, which comes from coronal holes. An alternative scenario is that the bulk of the slow wind (excluding that in the immediate vicinity of the heliospheric current sheet) originates from rapidly diverging flux tubes rooted inside small coronal holes or just within the boundaries of large holes. This viewpoint is based largely on photospheric field extrapolations, which are subject to considerable uncertainties and do not include dynamical effects, making it difficult to be certain whether a source is located just inside or outside a hole boundary, or whether a high-latitude hole will be connected to Earth. To minimize the dependence on field-line extrapolations, we have searched for cases where equatorial coronal holes at central meridian are followed by low-speed streams at Earth. We describe 14 examples from the period 2014--2017, involving Fe XIV 21.1 nm coronal holes located near active regions and having equatorial widths of $\sim$3$^\circ$--10$^\circ$. The associated in situ wind was characterized by speeds $v\sim 300$--450 km s$^{-1}$ and by O$^{7+}$/O$^{6+}$ ratios of $\sim$0.05--0.15, with $v$ showing the usual correlation with proton temperature. In addition, consistent with other recent studies, this slow wind had remarkably high Alfv\'enicity, similar to that in high-speed streams. We conclude that small coronal holes are a major contributor to the slow solar wind during the maximum and early post-maximum phases of the solar cycle.

The strength of the radial component of the interplanetary magnetic field (IMF), which is a measure of the Sun's total open flux, is observed to vary by roughly a factor of two over the 11 yr solar cycle. Several recent studies have proposed that the Sun's open flux consists of a constant or "floor" component that dominates at sunspot minimum, and a time-varying component due to coronal mass ejections (CMEs). Here, we point out that CMEs cannot account for the large peaks in the IMF strength which occurred in 2003 and late 2014, and which coincided with peaks in the Sun's equatorial dipole moment. We also show that near-Earth interplanetary CMEs, as identified in the catalog of Richardson and Cane, contribute at most $\sim$30\% of the average radial IMF strength even during sunspot maximum. We conclude that the long-term variation of the radial IMF strength is determined mainly by the Sun's total dipole moment, with the quadrupole moment and CMEs providing an additional boost near sunspot maximum. Most of the open flux is rooted in coronal holes, whose solar cycle evolution in turn reflects that of the Sun's lowest-order multipoles.

Earlier studies using extreme-ultraviolet images and line-of-sight magnetograms from the Solar Dynamics Observatory (SDO) have suggested that active region (AR) plages and strong network concentrations often have small, looplike features embedded within them, even though no minority-polarity flux is visible in the corresponding magnetograms. Because of the unexpected nature of these findings, we have searched the SDO database for examples of inverted-Y structures rooted inside "unipolar" plages, with such jetlike structures being interpreted as evidence for magnetic reconnection between small bipoles and the dominant-polarity field. Several illustrative cases are presented from the period 2013--2015, all of which are associated with transient outflows from AR "moss." The triangular or dome-shaped bases have horizontal dimensions of $\sim$2--4 Mm, corresponding to $\sim$1--3 granular diameters. We also note that the spongy-textured Fe IX 17.1 nm moss is not confined to plages, but may extend into regions where the photospheric field is relatively weak or even has mixed polarity. We again find a tendency for bright coronal loops seen in the 17.1, 19.3, and 21.1 nm passbands to show looplike fine structure and compact brightenings at their footpoints. These observations provide further confirmation that present-day magnetograms are significantly underrepresenting the amount of minority-polarity flux inside AR plages and again suggest that footpoint reconnection and small-scale flux cancellation may play a major role in coronal heating, both inside and outside ARs.

Extreme-ultraviolet images from the Solar Dynamics Observatory often show looplike fine structure to be present where no minority-polarity flux is visible in magnetograms, suggesting that the rate of ephemeral region (ER) emergence inside "unipolar" regions has been underestimated. Assuming that this rate is the same inside coronal holes as in the quiet Sun, we show that interchange reconnection between ERs and open field lines gives rise to a solar wind energy flux that exceeds 10$^5$ erg cm$^{-2}$ s$^{-1}$ and that scales as the field strength at the coronal base, consistent with observations. In addition to providing Ohmic heating in the low corona, these reconnection events may be a source of Alfv{\'e}n waves with periods ranging from the granular timescale of $\sim$10 minutes to the supergranular/plume timescale of many hours, with some of the longer-period waves being reflected and dissipated in the outer corona. The asymptotic wind speed depends on the radial distribution of the heating, which is largely controlled by the rate of flux-tube expansion. Along the rapidly diverging flux tubes associated with slow wind, heating is concentrated well inside the sonic point (1) because the outward conductive heat-flux density and thus the outer coronal temperatures are reduced, and (2) because the net wave energy flux is dissipated at a rate proportional to the local Alfv{\'e}n speed. In this "hybrid" solar wind model, reconnection heats the lower corona and drives the mass flux, whereas waves impart energy and momentum to the outflow at greater distances.

On 2018 November 5, about 24 hours before the first close perihelion passage of Parker Solar Probe (PSP), a coronal mass ejection (CME) entered the field of view of the inner detector of the Wide-field Imager for Solar PRobe (WISPR) instrument onboard PSP, with the northward component of its trajectory carrying the leading edge of the CME off the top edge of the detector about four hours after its first appearance. We connect this event to a very small jet-like transient observed from 1 au by coronagraphs on both the SOlar and Heliospheric Observatory (SOHO) and the A component of the Solar TErrestrial RElations Observatory mission (STEREO-A). This allows us to make the first three-dimensional reconstruction of a CME structure considering both observations made very close to the Sun and images from two observatories at 1 au. The CME may be small and jet-like as viewed from 1 au, but the close-in vantage point of PSP/WISPR demonstrates that it is not intrinsically jet-like, but instead has a structure consistent with a flux rope morphology. Based on its appearance in the SOHO and STEREO-A images, the event belongs in the "streamer blob" class of transients, but its kinematic behavior is very unusual, with a more impulsive acceleration than previously studied blobs., Comment: 9 pages, 8 figures, to appear in The Astrophysical Journal Supplement

With the development of integrated circuits according to Moore’s law, traditional silicon-based devices have gradually reached their performance limitation. Nanoelectronics based on carbon nanomaterials provides a broad prospect for the continuation of Moore’s law. In particular, in the field of optoelectronic devices, it is necessary to further develop new types of nano-optoelectronic devices. Carbon nanotubes (CNTs) are one of the representative materials of nanoelectronics with excellent electrical and optical properties, e.g., high mobility, suitable band structure, and good infrared absorption. The application of CNTs in optoelectronic devices is a very attractive research topic, which has been developed rapidly in recent years. Until now, various prototypes of CNT-based optoelectronic devices have been developed. In this Review, we briefly introduce the structure and photoelectric properties of CNTs. Then, according to different photo-electron coupling mechanisms, four types of CNTs based on optoelectronic devices are introduced in detail, namely, solar cells, photodetectors, light-emitting diodes, and lasers. Intrinsic and composite CNT-based optoelectronic devices are presented in order to describe the development of CNT-based optoelectronic devices. Finally, different material preparation, separation, and mixing methods of CNTs are discussed, which are the methods for basic material preparation for the fabrication of high performance CNT-based optoelectronic devices. An in-depth study of the development trend of CNT-based optoelectronic devices will contribute to the future development of novel high-performance nanoelectronic devices.

To develop a NaI (Tl) detector for in situ radioactivity monitoring in the marine environment and enhance the confidence of the probability of the gamma-spectrum analysis, Monte Carlo simulations using the Monte Carlo N-Particle ( MNCP ) code were performed to provide the response spectra of some interested radionuclides and the background spectra originating from the natural radionuclides in seawater recorded by a NaI (Tl) detector. A newly developed 75 mm × 75 mm NaI (Tl) detector was calibrated using four reference radioactive sources 137Cs, 60Co, 40K and 54Mn in the laboratory before the field measurements in seawater. A simulation model was established for the detector immersed in seawater. The simulated spectra were all broadened with Gaussian pulses to reflect the statistical fluctuations and electrical noise in the real measurement. The simulated spectra show that the single-energy photons into the detector are mostly scattering low-energy photons and the high background in the low energy region mainly originates from the Compton effect of the high energy ?-rays of natural radionuclides in seawater. The simulated background spectrum was compared with the experimental one recorded in field measurement and they seem to be in good agreement. The simulation method and spectra can be used for the accurate analysis of the filed measurement results of low concentration radioactivity in seawater.

This paper studies the interaction dynamics of a vehicle traveling on a simply supported beam. A simple quarter-car planar model of the vehicle is taken into account. The system of the quarter-car model is treated as a moving mass with a massless harmonic force rolling on a simply supported beam. The objective of this paper is to present analytical and numerical methodologies to evaluate the vehicle–beam coupling effects when the vehicle moves under variable speed condition. Due to the presence of friction and convective acceleration, the vehicle can be accelerated by a forward force. Meanwhile, the vehicle is capable of reducing speed by applying a retard force to the vehicle and/or increasing the friction between the vehicle and beam. This results in variable velocity, acceleration, and deceleration, as well as unknown location of the vehicle along the beam. Result shows that as the spring stiffness of the suspension is close to the resonant value, strong commensurability between the oscillating frequency of the vehicle and the vibrant frequency of beam occurs when the instantaneous speed of the vehicle becomes a small quantity. In other words, a commensurable condition between the vehicle and beam is weakened when the vehicle is accelerated by a positive driving force; it becomes strong if the vehicle is decelerated by a negative reverse force and friction. If the vehicle reduces its traveling speed sharply, large amplitude and high oscillating frequency of the vehicle were generated. This significantly reduces the riding comfort for passengers in the vehicle. The applied force and coefficient of friction can be treated as tuning parameters to determine the resonant region of the interaction dynamics of a vehicle–beam system.

The objective of this paper is to present analytical and numerical methodologies to evaluate the transient dynamics of a moving mass rolling on an eccentric path along a finite simple-supported inextensible beam. The eccentric path of a beam exists due to either manufacturing imperfection or preset purpose to produce specified dynamic characteristics to satisfy special performances. The eccentricity of the eccentric path may have different shapes and is assumed to be a spatial variable which is the distance from the neutral axis of the beam to the path. The method used in the analysis is Newtonian. The mechanics of the interface between the moving mass and the beam is determined by modeling the mass as a rigid body that is rolling on the eccentric axis when the mass is set on motion; moment of the moving mass acting on the beam along the eccentric path is taken into account. Based on Euler–Bernoulli beam theory and inextensibility constraint, the mechanics, including effects due to friction and convective accelerations, of the interface between the mass and the beam is obtained. By employing Galerkin’s procedure to eliminate spatial dependence, the problem reduces to a multi-degrees-of-freedom dynamical system with time dependent coefficients. Result of present study indicates that the eccentricity of eccentric path plays an important role to the dynamics of a beam-mass system. If the shape of the eccentric path is concave upward, the amplitude of eccentricity amplifies not only the positive amplitude of the trajectory of mass but also the negative displacement of the beam even if the amplitude of eccentricity is tiny. However, if the shape of the eccentric path is convex upward, the amplitude of eccentricity attenuated the displacement of the beam. In addition, it is generally true that as the mass moves from the left end, the occurrence of negative displacement exists when the mass is subjected by a reverse force and approaches to the right terminal.

Because the two components have relative motion, pair clearance is inevitable. With the machine’s speed increasing, nonlinear vibration phenomenon caused by clearance is much obviously. The state of damping in pair clearance will often make mechanism’s nonlinear vibration appear different status. For the study of damping in joint clearances impact to nonlinear vibration, four-bar mechanism with clearance is taken as research object. A nonlinear dynamic model has been established based on continuous contact model. Through analysis the nonlinear vibration in different damping and clearance, it can be found that in weak damping condition, nonlinear vibration in small pair clearance is more sensitive to the small changes of damping than that in large pair clearance. So, it’s very important to keep the pair clearance in proper lubrication conditions.

The opening-up of the magnetic field during solar eruptive events is often accompanied by a dimming of the local coronal emission. From observations of filament eruptions recorded with the Extreme-Ultraviolet Imager on STEREO during 2008-2009, it is evident that these dimmings are much more pronounced in 19.5 nm than in the lower-temperature line 17.1 nm, as viewed either on the disk or above the limb. We conclude that most of the cooler coronal plasma is not ejected but remains gravitationally bound when the loops open up. This result is consistent with Doppler measurements by Imada and coworkers, who found that the upflow speeds in a transient coronal hole increased dramatically above a temperature of 1 MK; it is also consistent with the quasistatic behavior of polar plumes, as compared with the hotter interplume regions that are the main source of the fast solar wind. When the open flux reconnects and closes down again, the trapped plasma is initially heated to such high temperatures that it is no longer visible at Fe IX 17.1 nm. Correspondingly, 17.1 nm images show a dark ribbon or ``heat wave'' propagating away from the polarity inversion line and coinciding with the brightened Fe XV 28.4 nm and Fe XII 19.5 nm post-eruptive loops and their footpoint areas. Such dark ribbons provide a clear example of dimmings that are not caused by a density depletion. The propagation of the ``heat wave'' is driven by the closing-down, not the opening-up, of flux and can be observed both off-limb and on-disk., Comment: 5 figures, movies are available online on the ApJL website

Coronal helmet streamers show a continual tendency to expand outward and pinch off, giving rise to flux ropes that are observed in white light as "blobs" propagating outward along the heliospheric current/plasma sheet. The blobs form within the r ~ 2–6 R ⊙ heliocentric range of the Large Angle and Spectrometric Coronagraph (LASCO) C2 instrument, but the expected inward-moving counterparts are often not detected. Here we show that the height of blob formation varies as a function of the underlying photospheric field, with the helmet streamer loops expanding to greater heights when active regions (ARs) emerge underneath them. When the pinch-offs occur at r ~ 3–4 R ⊙, diverging inward/outward tracks sometimes appear in height–time maps constructed from LASCO C2 running-difference images. When the underlying photospheric field is weak, the blobs form closer to the inner edge of the C2 field of view and only the outward tracks are clearly visible. Conversely, when the emergence of large ARs leads to a strengthening of the outer coronal field and an increase in the total white-light radiance (as during late 2014), the expanding helmet-streamer loops pinch off beyond r ~ 4 R ⊙, triggering strong inflow streams whose outgoing counterparts are usually very faint. We deduce that the visibility of the blobs and inflows depends on the amount of material that the diverging components sweep up within the 2–6 R ⊙ field of view. We also note that the rate of blob production tends to increase when a helmet streamer is "activated" by underlying flux emergence.

A combination of heliospheric and solar data was used to identify open magnetic fields stretching from the lower corona to Earth orbit. 35 near-relativistic electron beams detected at the ACE spacecraft "labeled" the heliospheric segments of the open fields. An X-ray flare occurred

The objective of this paper is an analytical and numerical study of the transient dynamics of a beam–mass system carrying multiple masses moving along an initially curved beam. An attention is given to the phenomena arising due to the initial curvature, initial imperfection, of a beam and the motion produced by the existence of multiple moving masses. The method used in the analysis is Newtonian. The mechanics of the interface between the masses and the beam is determined by modeling the masses as rigid bodies that are rolling on an initially curved flexible structure when the moving masses are set on motion. Based on the Euler–Bernoulli beam theory, the mechanics, including effects due to friction and convective accelerations, of the interfaces between the moving masses and the beam are obtained. Result of present study shows that the initial curvature of a beam can result significant effects to the dynamics of the system even if the initial imperfection of the beam is small. The magnification of the amplitude of response of the system due to the initial deviation of beam depends on the initial speed of mass, the applied forward/retard force on the mass, and the friction between the mass and the beam.

The objective of this paper is to study the dynamics and dynamic instability of a slider-crank mechanism with an initially curved coupler under parametric resonance. An attention is given to the phenomena arising due to initial curvature, geometric imperfection, of a connecting rod and modal interactions produced by the existence of two-component parametric resonance. The two-component parametric resonance can occur, for example, when the fundamental frequency of the flexible part of a slider-crank mechanism is close to one-half of the excitation frequency and simultaneously the difference between the first and the second natural frequencies is near the frequency of excitation. It is known that for the case of one-component parametric resonance, an initially curved connecting rod enlarges the amplitude of fundamental mode of vibration significantly only if the motion is in the vicinity of the secondary region of instability. In other words, the initial curvature of a coupler plays no effects to the fundamental response of the system if the oscillation is near the primary region of instability. However, result of present study shows that under the condition of two-component parametric resonance, unlike the case of one-component parametric resonance, an initially curved linkage can result significant effects to the vibration of the system even if the motion is close to the primary region of instability. In addition, the result also indicates that the growth of small amplitude vibration into large motion regime occurs if vibrations arise near the boundary of stable region.

The Spallation Neutron Source (SNS) Superconducting RF (SRF) linear accelerator is operated with a pulsed beam. For the SRF control system to track the repetitive electromagnetic field reference trajectory, both feedback and feedforward controllers have been proposed. The feedback controller is utilized to guarantee the closed loop system stability and the feedforward controller is used to improve the tracking performance for the repetitive reference trajectory and to suppress repetitive disturbances. As the iteration number increases, the feedforward controller decreases the tracking error. Numerical simulations demonstrate that inclusion of the feedforward controller significantly improves the control system performance over its performance with just the feedback controller.

During times of high solar activity, the Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph C2 coronagraph has recorded multitudes of small features moving inward through its field of view. These outer-coronal inflows, which are concentrated around the heliospheric current sheet, tend to be poorly correlated with individual coronal mass ejection (CME) events. Using running-difference movies constructed from Solar Terrestrial Relations Observatory/COR1 coronagraph images taken during 2008–2014, we have identified large numbers of inward-moving features at heliocentric distances below , with the rate increasing with sunspot and CME activity. Most of these inner-coronal inflows are closely associated with CMEs, being observed during and in the days immediately following the eruptions. Here, we describe several examples of the pinching-off of tapered streamer structures in the wake of CMEs. This type of inflow event is characterized by a separation of the flow into incoming and outgoing components connected by a thin spike, which is interpreted as a continually elongating current sheet viewed edge-on; by the prior convergence of narrow rays toward the current sheet; and by a succession of collapsing loops that form a cusp-shaped structure at the base of the current sheet. The re-forming streamer overlies a growing post-eruption arcade that is visible in EUV images. These observations provide support for standard reconnection models for the formation/evolution of flux ropes during solar eruptive events. We suggest that inflow streams that occur over a relatively wide range of position angles result from the pinching-off of loop arcades whose axes are oriented parallel rather than perpendicular to the sky plane.

We discuss the nature of the small areas of rapidly diverging, open magnetic flux that form in the strong unipolar fields at the peripheries of active regions (ARs), according to coronal extrapolations of photospheric field measurements. Because such regions usually have dark counterparts in extreme-ultraviolet (EUV) images, we refer to them as coronal holes, even when they appear as narrow lanes or contain sunspots. Revisiting previously identified "AR sources" of slow solar wind from 1998 and 1999, we find that they are all associated with EUV coronal holes; the absence of well-defined He i 1083.0 nm counterparts to some of these holes is attributed to the large flux of photoionizing radiation from neighboring AR loops. Examining a number of AR-associated EUV holes during the 2014 activity maximum, we confirm that they are characterized by wind speeds of ~300–450 km s−1, O7+/O6+ ratios of ~0.05–0.4, and footpoint field strengths typically of order 30 G. The close spacing between ARs at sunspot maximum limits the widths of unipolar regions and their embedded holes, while the continual emergence of new flux leads to rapid changes in the hole boundaries. Because of the highly nonradial nature of AR fields, the smaller EUV holes are often masked by the overlying canopy of loops, and may be more visible toward one solar limb than at central meridian. As sunspot activity declines, the AR remnants merge to form much larger, weaker, and longer-lived unipolar regions, which harbor the "classical" coronal holes that produce recurrent high-speed streams.

We have developed an analytical physics model from fundamental physics principles and used the reduced one-dimensional model to derive a thermonuclear ignition criterion and implosion energy scaling laws applicable to inertial confinement fusion capsules. The scaling laws relate the fuel pressure and the minimum implosion energy required for ignition to the peak implosion velocity and the equation of state of the pusher and the hot fuel. When a specific low-entropy adiabat path is used for the cold fuel, our scaling laws recover the ignition threshold factor dependence on the implosion velocity, but when a high-entropy adiabat path is chosen, the model agrees with recent measurements.

Because of its distinctive compositional properties and high variability, the slow solar wind is widely believed to originate from coronal streamers, unlike high-speed wind, which emanates from coronal holes. Based on measurements from the Advanced Composition Explorer, it has been proposed that an oxygen charge-state ratio O7+/O6+ of 0.145 is the threshold that separates streamer from coronal hole wind. During the 2007–2009 sunspot minimum, however, the median value of O7+/O6+ fell to only 0.06, implying that almost all of the near-Earth wind came from coronal holes, despite the fact that the streamer belt lay much closer to the ecliptic plane at that time than at solar maximum. Employing extrapolations of photospheric field maps to derive the footpoint field strengths B 0 of the near-Earth wind, we find that the median value of B 0 decreased to only 2.6 G during 2007–2009, from a value of 21 G during 1998–2004. The factor of ~2 decrease in the median value of O7+/O6+ thus reflects the factor of ~8 decrease in the footpoint field strength. Variations in O7+/O6+ are strongly anticorrelated with the wind speed on timescales of days, but not on long timescales, which are dominated by changes in B 0. We suggest that the charge-state ratio is determined by the amount of energy deposited near the coronal base, which in turn depends on B 0 and the local flux-tube expansion rate. High values of O7+/O6+ are associated with rapidly diverging flux tubes rooted just inside the boundaries of coronal holes with strong footpoint fields.

We demonstrate the effect of preheat, hydrodynamic mix and vorticity on the adiabat of the deuterium-tritium (DT) fuel in fusion capsule experiments. We show that the adiabat of the DT fuel increases resulting from hydrodynamic mixing due to the phenomenon of entropy of mixture. An upper limit of mix, Mclean/MDT ≥ 0.98, is found necessary to keep the DT fuel on a low adiabat. We demonstrate in this study that the use of a high adiabat for the DT fuel in theoretical analysis and with the aid of 1D code simulations could explain some aspects of 3D effects and mix in capsule implosion. Furthermore, we can infer from our physics model and the observed neutron images the adiabat of the DT fuel in the capsule and the amount of mix produced on the hot spot.

Earlier studies have suggested that coronal plumes are energized by magnetic reconnection between unipolar flux concentrations and nearby bipoles, even though magnetograms sometimes show very little minority-polarity flux near the footpoints of plumes. Here we use high-resolution extreme-ultraviolet (EUV) images and magnetograms from the Solar Dynamics Observatory (SDO) to clarify the relationship between plume emission and the underlying photospheric field. We find that plumes form where unipolar network elements inside coronal holes converge to form dense clumps, and fade as the clumps disperse again. The converging flows also carry internetwork fields of both polarities. Although the minority-polarity flux is sometimes barely visible in the magnetograms, the corresponding EUV images almost invariably show loop-like features in the core of the plumes, with the fine structure changing on timescales of minutes or less. We conclude that the SDO observations are consistent with a model in which plume emission originates from interchange reconnection in converging flows, with the plume lifetime being determined by the approximately 1-day evolutionary timescale of the supergranular network. Furthermore, the presence of large EUV bright points and/or ephemeral regions is not a necessary precondition for the formation of plumes, which can be energized even by the weak, mixed-polarity internetwork fields swept up by converging flows.

We investigated the relationship between heavy-ion composition variability in gradual solar energetic particle (SEP) events and the source regions of the associated interplanetary magnetic field (IMF) along which these SEPs are transported. In particular, we found that the SEP elemental composition has a positive correlation with the unsigned photospheric magnetic field strength around the IMF footpoints. Furthermore, the IMF source region can be generally categorized into two classes, depending on whether the associated solar wind, and correspondingly the footpoints of the open magnetic field along which the SEPs are transported, are from a coronal hole (CH) near an active region (an ‘AR field-source’) or from a CH without an AR in its close proximity (a ‘CH field-source’). This study is based on 24 events observed in years 1998 and 2003-2006. We present in this paper the results for Fe/O as an example, and show that the observed SEP Fe/O ratio at 3-30 MeV/nucleon is preferentially enhanced in the case o...

The paper addresses the question of whether out-of-ecliptic measurements satisfy the inverse correlation between wind speed at 1 AU and flux-tube divergence in the corona, already found from measurements in the ecliptic. Using the in-ecliptic calibration, out-of-ecliptic speeds are derived from coronal expansion factors determined from global observations of photospheric field and their current-free coronal extension. These derived speeds are compared with speeds inferred from interplanetary scintillation measurements during 1972-1988 and with in situ speeds measured by the Pioneer 11 spacecraft at 16 deg N latitude during 1984-1988. These three sets of wind speed show the same overall variation with latitude and time during the sunspot cycle, with higher latitudes having more years of fast wind than lower latitudes and all latitudes having slow wind at sunspot maximum. Although some detailed discrepancies are also present, the overall agreement is comparable to that achieved in the ecliptic plane.

Empirical studies suggest a close relationship between the solar-wind speed near the earth and the magnetic structure of the solar corona. The correlation can be used to infer the latitudinal distribution of wind speed at different phases of the sunspot cycle, and to identify the sources of fast, high-latitude wind streams such as those that might be encountered by the Ulysses spacecraft on its journey toward the solar poles during 1992-1995.

We apply a recently developed analytical model of implosion and thermonuclear burn to fusion capsule experiments performed at the National Ignition Facility that used low-foot and high-foot laser pulse formats. Our theoretical predictions are consistent with the experimental data. Our studies, together with neutron image analysis, reveal that the adiabats of the cold fuel in both low-foot and high-foot experiments are similar. That is, the cold deuterium-tritium shells in those experiments are all in a high adiabat state at the time of peak implosion velocity. The major difference between low-foot and high-foot capsule experiments is the growth of the shock-induced instabilities developed at the material interfaces which lead to fuel mixing with ablator material. Furthermore, we have compared the NIF capsules performance with the ignition criteria and analyzed the alpha particle heating in the NIF experiments. Our analysis shows that alpha heating was appreciable only in the high-foot experiments.

Using white-light and extreme-ultraviolet imaging observations, we confirm that pseudostreamers (streamers that separate coronal holes of the same polarity) give rise to a different type of coronal mass ejection (CME) from that associated with helmet streamers (defined as separating coronal holes of opposite polarity). Whereas helmet streamers are the source of the familiar bubble-shaped CMEs characterized by gradual acceleration and a three-part structure, pseudostreamers produce narrower, fanlike ejections with roughly constant speeds. These ejections, which are typically triggered by underlying filament eruptions or small, flaring active regions, are confined laterally and channeled outward by the like-polarity open flux that converges onto the pseudostreamer plasma sheet from both sides. In contrast, helmet streamer CMEs are centered on the relatively weak field around the heliospheric current sheet and thus undergo greater lateral expansion. Pseudostreamer ejections have a morphological resemblance to white-light jets from coronal holes; however, unlike the latter, they are not primarily driven by interchange reconnection, and tend to have larger widths (~20°–30°), lower speeds (~250–700 km s−1), and more complex internal structure.

Magnetic fields play a crucial role in heating the outer atmospheres of the Sun and Sun-like stars, but the mechanisms by which magnetic energy in the photosphere is converted to thermal energy in the corona remain unclear. Observations show that magnetic fields emerge onto the solar surface as bipolar regions with a broad range of length scales. On large scales, the bipolar regions survive for months before dispersing diffusively1,2,3. On the smaller scales, individual bipolar regions disappear within days but are continuously replenished by new small flux concentrations, resulting in a sustained state of mixed polarity4. Here we determine the rate of emergence of these small bipolar regions and we argue that the frequent magnetic reconnections associated with these regions (an unavoidable consequence of continued flux replacement) will heat the solar atmosphere. The model that describes the details of these mixed-polarity regions4 is complementary to the traditional diffusion model for large-scale flux dispersal1,2,3 and a combination of the two should lead to a more complete understanding of the role of magnetic fields in stellar atmospheres.

In modern industrial control, a relay experiment can be used for auto-tuning a PI controller. It gives the ultimate frequency and ultimate gain of the open loop system. Based on the ultimate gain and the ultimate frequency, the PI control parameters, the proportional gain, and the integration time, are determined. A relay experiment can be used to determine the sensitivity of a closed loop system against external disturbances. This paper addresses a method to estimate the sensitivity represented by the gain margin of a closed loop low-level RF (LLRF) control system based on the Matlab/Simulink model of the Low Energy Demonstration Accelerator (LEDA) RFQ. This paper discusses some of the modeling performed and our operational experience to date.

A digital signal processor is implemented to control the resonant frequency of the RFQ prototype in APT/LEDA. Two schemes are implemented to calculate the resonant frequency of the RFQ. One uses the measurement of the forward and reflected fields. The other uses the measurement of the forward and transmitted fields. The former is sensitive and accurate when the operation frequency is relatively far from the resonant frequency. The latter gives accurate results when the operation frequency is close to the resonant frequency. Linearized algorithms are derived to calculate the resonant frequency of the RFQ efficiently using a fixed-point DSP. The control frequency range is about 100 kHz for 350 MHz operation frequency. A frequency agile scheme is employed using a dual direct digital synthesizer to drive the klystron at the cavity's resonant frequency (not necessarily the required beam resonant frequency) in power-up mode to quickly bring the cavity to the desired resonant beam frequency. This paper will address the algorithm implementation and error analysis, as well as related hardware design issues.

A high-intensity proton linac, such as that being planned for the SNS, requires accurate RF control of cavity fields for the entire pulse in order to avoid beam spill. The current design requirement for the SNS is RF field stability within /spl plusmn/0.5% and /spl plusmn/0.5/spl deg/. This RF control capability is achieved by the control electronics using the excess RF power to correct disturbances. To minimize the initial capital costs, the RF system is designed with 'just enough' RF power. All the usual disturbances exist, such as beam noise, klystron/HVPS noise, coupler imperfections, transport losses, turn-on and turn-off transients, etc. As a superconducting linac, there are added disturbances of large magnitude, including Lorentz detuning and microphonics. The effects of these disturbances and the power required to correct them are estimated, and the result shows that the highest power systems in the SNS have just enough margin, with little or no excess margin.

This paper addresses the modeling problem of the linear accelerator RF system for SNS. The cascade of the klystron and the cavity is modeled as a nominal system. In the real world, high voltage power supply ripple, Lorentz force detuning, microphonics, cavity RF parameter perturbations, distortions in RF components, and loop time delay imperfection exist inevitably, which must be analyzed. The analysis is based on the accurate modeling of the disturbances and uncertainties. In this paper, modern control theory is applied for modeling the disturbances, uncertainties, and for analyzing the closed loop system robust performance.

The axes of solar active regions are inclined relative to the east-west direction, with the tilt angle tending to increase with latitude (Joy's law). Observational determinations of Joy's law have been based either on white-light images of sunspot groups or on magnetograms, where the latter have the advantage of measuring directly the physically relevant quantity (the photospheric field), but the disadvantage of having been recorded routinely only since the mid-1960s. White-light studies employing the historical Mount Wilson (MW) database have yielded tilt angles that are smaller and that increase less steeply with latitude than those obtained from magnetic data. We confirm this effect by comparing sunspot-group tilt angles from the Debrecen Photoheliographic Database with measurements made by Li and Ulrich using MW magnetograms taken during cycles 21-23. Whether white-light or magnetic data are employed, the median tilt angles significantly exceed the mean values, and provide a better characterization of the observed distributions. The discrepancy between the white-light and magnetic results is found to have two main sources. First, a substantial fraction of the white-light tilt angles refer to sunspots of the same polarity. Of greater physical significance is that the magnetograph measurements include the contribution of plage areas, which are invisible in white-light images but tend to have greater axial inclinations than the adjacent sunspots. Given the large uncertainties inherent in both the white-light and the magnetic measurements, it remains unclear whether any systematic relationship exists between tilt angle and cycle amplitude during cycles 16-23.

We extend our previous counts of coronal inflows from the 5 yr interval 1996-2001 to the 18 yr interval 1996-2014. By comparing stackplots of these counts with similar stackplots of the source-surface magnetic field and its longitudinal gradient, we find that the inflows occur in long-lived streams with counting rates in excess of 18 inflows per day at sector boundaries where the gradient exceeds 0.22 G rad{sup –1}. These streams are responsible for the high (86%) correlation between the inflow rate and the longitudinal field gradient. The overall inflow rate was several times larger in sunspot cycle 23 than it has been so far in cycle 24, reflecting the relatively weak source-surface fields during this cycle. By comparison, in cycles 21-22, the source-surface field and its gradient had bursts of great strength, as if large numbers of inflows occurred during those cycles. We find no obvious relation between inflows and coronal mass ejections (CMEs) on timescales of days to weeks, regardless of the speeds of the CMEs, and only a 60% correlation on timescales of months, provided the CMEs are fast (V > 600 km s{sup –1}). We conclude that most of the flux carried out by CMEs is returnedmore » to the Sun via field line reconnection well below the 2.0 R {sub ☉} inner limit of the LASCO field of view, and that the remainder accumulates in the outer corona for an eventual return at sector boundaries.« less

Sustained thermonuclear fusion at the National Ignition Facility remains elusive. Although recent experiments approached or exceeded the anticipated ignition thresholds, the nuclear performance of the laser-driven capsules was well below predictions in terms of energy and neutron production. Such discrepancies between expectations and reality motivate a reassessment of the physics of ignition. We have developed a predictive analytical model from fundamental physics principles. Based on the model, we obtained a general thermonuclear ignition criterion in terms of the areal density and temperature of the hot fuel. This newly derived ignition threshold and its alternative forms explicitly show the minimum requirements of the hot fuel pressure, mass, areal density, and burn fraction for achieving ignition. Comparison of our criterion with existing theories, simulations, and the experimental data shows that our ignition threshold is more stringent than those in the existing literature and that our results are consistent with the experiments.

We analyzed 27 solar wind (SW) intervals during the declining phase of cycle 23, whose source coronal holes (CHs) can be unambiguously identified and are associated with one of the polar CHs. We found that the SW ions have a temporal trend of decreasing ionization state, and such a trend is different between the slow and fast SW. The photospheric magnetic field, both inside and at the outside boundary of the CH, also exhibits a trend of decrease with time. However, EUV line emissions from different layers of the atmosphere exhibit different temporal trends. The coronal emission inside the CH generally increases toward the CH boundary as the underlying field increases in strength and becomes less unipolar. In contrast, this relationship is not seen in the coronal emission averaged over the entire CH. For C and O SW ions that freeze-in at lower altitude, stronger correlation between their ionization states and field strength (both signed and unsigned) appears in the slow SW, while for Fe ions that freeze-in at higher altitude, stronger correlation appears in the fast SW. Such correlations are seen both inside the CH and at its boundary region. On the other hand, the coronal electron temperature correlates well with the SW ion composition only in the boundary region. Our analyses, although not able to determine the likely footpoint locations of the SW of different speeds, raise many outstanding questions for how the SW is heated and accelerated in response to the long-term evolution of the solar magnetic field.

Although sunspot numbers are roughly a factor of two lower in the current cycle than in cycle 23, the rate of coronal mass ejections (CMEs) appears to be at least as high in 2011-2013 as during the corresponding phase of the previous cycle, according to three catalogs that list events observed with the Large Angle and Spectrometric Coronagraph (LASCO). However, the number of CMEs detected is sensitive to such factors as the image cadence and the tendency (especially by human observers) to under-/overcount small or faint ejections during periods of high/low activity. In contrast to the total number, the total mass of CMEs is determined mainly by larger events. Using the mass measurements of 11,000 CMEs given in the manual CDAW catalog, we find that the mass loss rate remains well correlated with the sunspot number during cycle 24. In the case of the automated CACTus and SEEDS catalogs, the large increase in the number of CMEs during cycle 24 is almost certainly an artifact caused by the near-doubling of the LASCO image cadence after mid-2010. We confirm that fast CMEs undergo a much stronger solar-cycle variation than slow ones, and that the relative frequency of slow and less massive CMEs increases with decreasing sunspot number. We conclude that cycle 24 is not only producing fewer CMEs than cycle 23, but that these ejections also tend to be slower and less massive than those observed one cycle earlier.

This paper addresses part of the design of the LLRF control system for the Spallation Neutron Source. Based on the Matlab/Simulink model of the Klystron and Cavity, considered as a two input two output (TITO) system, we design a PID controller which achieves the tracking of the set point reference. The PID controller design method modifies a relay-feedback-based PID auto-tuner for a single input single output (SISO) system. The original modeling was developed for the Low Energy Demonstration Accelerator and has been modified for the SNS. The advantage of this method is that the only system information required for tuning the PID controller gains is the oscillation gain (critical gain) and the oscillation frequency (critical frequency) from the relay-feedback control of the open loop system. From the oscillation gain (critical gain), we obtain the proportional gain, and from the oscillation frequency (critical frequency), we obtain the integration time and the derivative time by applying some algebraic rules.

Gradual solar energetic particle (SEP) events are those in which ions are accelerated to their observed energies by interactions with a shock driven by a fast coronal mass-ejection (CME). Previous studies have shown that much of the observed event-to-event variability can be understood in terms of shock speed and evolution in the shock-normal angle. But an equally important factor, particularly for the elemental composition, is the origin of the suprathermal seed particles upon which the shock acts. To tackle this issue, we (1) use observed solar-wind speed, magnetograms, and the PFSS model to map the Sun-L1 interplanetary magnetic field (IMF) line back to its source region on the Sun at the time of the SEP observations; and (2) then look for correlation between SEP composition (as measured by Wind and ACE at approx. 2-30 MeV/nucleon) and characteristics of the identified IMF-source regions. The study is based on 24 SEP events, identified as a statistically-significant increase in approx. 20 MeV protons and occurring in 1998 and 2003-2006, when the rate of newly-emergent solar magnetic flux and CMEs was lower than in solar-maximum years and the field-line tracing is therefore more likely to be successful. We find that the gradual SEP Fe/O is correlated with the field strength at the IMF-source, with the largest enhancements occurring when the footpoint field is strong, due to the nearby presence of an active region. In these cases, other elemental ratios show a strong charge-to-mass (q/M) ordering, at least on average, similar to that found in impulsive events. These results lead us to suggest that magnetic reconnection in footpoint regions near active regions bias the heavy-ion composition of suprathermal seed ions by processes qualitatively similar to those that produce larger heavy-ion enhancements in impulsive SEP events. To address potential technical concerns about our analysis, we also discuss efforts to exclude impulsive SEP events from our event sample.

As observed in spectral lines originating from the chromosphere, transition region, and low corona, active regions are surrounded by an extensive "circumfacular" area which is darker than the quiet Sun. We examine the properties of these dark moat- or canopy-like areas using \ion{Fe}{9} 17.1 nm images and line-of-sight magnetograms from the {\it Solar Dynamics Observatory}. The 17.1 nm canopies consist of fibrils (horizontal fields containing EUV-absorbing chromospheric material) clumped into featherlike structures. The dark fibrils initially form a quasiradial or vortical pattern as the low-lying field lines fanning out from the emerging active region connect to surrounding network and intranetwork elements of the opposite polarity. The area occupied by the 17.1 nm fibrils expands as supergranular convection causes the active region flux to spread into the background medium; the outer boundary of the dark canopy stabilizes where the diffusing flux encounters a unipolar region of the opposite sign. The dark fibrils tend to accumulate in regions of weak longitudinal field and to become rooted in mixed-polarity flux. To explain the latter observation, we note that the low-lying fibrils are more likely to interact with small loops associated with weak, opposite-polarity flux elements in close proximity, than with high loops anchored inside strong unipolar network flux. As a result, the 17.1 nm fibrils gradually become concentrated around the large-scale polarity inversion lines (PILs), where most of the mixed-polarity flux is located. Systematic flux cancellation, assisted by rotational shearing, removes the field component transverse to the PIL and causes the fibrils to coalesce into long PIL-aligned filaments., Accepted for publication in ApJ