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We improve our filament automated detection method which was proposed in our previous works. It is then applied to process the full disk H$\alpha$ data mainly obtained by Big Bear Solar Observatory (BBSO) from 1988 to 2013, spanning nearly 3 solar cycles. The butterfly diagrams of the filaments, showing the information of the filament area, spine length, tilt angle, and the barb number, are obtained. The variations of these features with the calendar year and the latitude band are analyzed. The drift velocities of the filaments in different latitude bands are calculated and studied. We also investigate the north-south (N-S) asymmetries of the filament numbers in total and in each subclass classified according to the filament area, spine length, and tilt angle. The latitudinal distribution of the filament number is found to be bimodal. About 80% of all the filaments have tilt angles within [0{\deg}, 60{\deg}]. For the filaments within latitudes lower (higher) than 50{\deg} the northeast (northwest) direction is dominant in the northern hemisphere and the southeast (southwest) direction is dominant in the southern hemisphere. The latitudinal migrations of the filaments experience three stages with declining drift velocities in each of solar cycles 22 and 23, and it seems that the drift velocity is faster in shorter solar cycles. Most filaments in latitudes lower (higher) than 50{\deg} migrate toward the equator (polar region). The N-S asymmetry indices indicate that the southern hemisphere is the dominant hemisphere in solar cycle 22 and the northern hemisphere is the dominant one in solar cycle 23., Comment: 51 pages, 12 tables, 25 figures, accepted for publication in ApJS

The Jiangmen Underground Neutrino Observatory (JUNO) is proposed to determine the neutrino mass hierarchy using an underground liquid scintillator detector. It is located 53 km away from both Yangjiang and Taishan Nuclear Power Plants in Guangdong, China. The experimental hall, spanning more than 50 meters, is under a granite mountain of over 700 m overburden. Within six years of running, the detection of reactor antineutrinos can resolve the neutrino mass hierarchy at a confidence level of 3-4$\sigma$, and determine neutrino oscillation parameters $\sin^2\theta_{12}$, $\Delta m^2_{21}$, and $|\Delta m^2_{ee}|$ to an accuracy of better than 1%. The JUNO detector can be also used to study terrestrial and extra-terrestrial neutrinos and new physics beyond the Standard Model. The central detector contains 20,000 tons liquid scintillator with an acrylic sphere of 35 m in diameter. $\sim$17,000 508-mm diameter PMTs with high quantum efficiency provide $\sim$75% optical coverage. The current choice of the liquid scintillator is: linear alkyl benzene (LAB) as the solvent, plus PPO as the scintillation fluor and a wavelength-shifter (Bis-MSB). The number of detected photoelectrons per MeV is larger than 1,100 and the energy resolution is expected to be 3% at 1 MeV. The calibration system is designed to deploy multiple sources to cover the entire energy range of reactor antineutrinos, and to achieve a full-volume position coverage inside the detector. The veto system is used for muon detection, muon induced background study and reduction. It consists of a Water Cherenkov detector and a Top Tracker system. The readout system, the detector control system and the offline system insure efficient and stable data acquisition and processing., Comment: 328 pages, 211 figures

Two-ribbon brightenings are one of the most remarkable characteristics of an eruptive solar flare and are often used for predicting the occurrence of coronal mass ejections (CMEs). Nevertheless, it was called in question recently whether all two-ribbon flares are eruptive. In this paper, we investigate a two ribbon-like white-light (WL) flare that is associated with a failed magnetic flux rope (MFR) eruption on 2015 January 13, which has no accompanying CME in the WL coronagraph. Observations by \textit{Optical and Near-infrared Solar Eruption Tracer} and \textit{Solar Dynamics Observatory} reveal that, with the increase of the flare emission and the acceleration of the unsuccessfully erupting MFR, two isolated kernels appear at the WL 3600 {\AA} passband and quickly develop into two elongated ribbon-like structures. The evolution of the WL continuum enhancement is completely coincident in time with the variation of \textit{Fermi} hard X-ray 26--50 keV flux. Increase of continuum emission is also clearly visible at the whole FUV and NUV passbands observed by \textit{Interface Region Imaging Spectrograph}. Moreover, in one WL kernel, the \ion{Si}{4}, \ion{C}{2}, and \ion{Mg}{2} h/k lines display significant enhancement and non-thermal broadening. However, their Doppler velocity pattern is location-dependent. At the strongly bright pixels, these lines exhibit a blueshift; while at moderately bright ones, the lines are generally redshifted. These results show that the failed MFR eruption is also able to produce a two-ribbon flare and high-energy electrons that heat the lower atmosphere, causing the enhancement of the WL and FUV/NUV continuum emissions and chromospheric evaporation., Comment: 7 pages, 5 figures, 1 table, accepted for publication in ApJ

We attempt to propose a method for automatically detecting the solar filament chirality and barb bearing. We first introduce the unweighted undirected graph concept and adopt the Dijkstra shortest-path algorithm to recognize the filament spine. Then, we use the polarity inversion line (PIL) shift method for measuring the polarities on both sides of the filament, and employ the connected components labeling method to identify the barbs and calculate the angle between each barb and the spine to determine the bearing of the barbs, i.e., left or right. We test the automatic detection method with H-alpha filtergrams from the Big Bear Solar Observatory (BBSO) H-alpha archive and magnetograms observed with the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO). Four filaments are automatically detected and illustrated to show the results. The barbs in different parts of a filament may have opposite bearings. The filaments in the southern hemisphere (northern hemisphere) mainly have left-bearing (right-bearing) barbs and positive (negative) magnetic helicity, respectively. The tested results demonstrate that our method is efficient and effective in detecting the bearing of filament barbs. It is demonstrated that the conventionally believed one-to-one correspondence between filament chirality and barb bearing is not valid. The correct detection of the filament axis chirality should be done by combining both imaging morphology and magnetic field observations., Comment: 20 pages, 7 figures, accepted for publication in RAA

Magnetic reconnection, a change of magnetic field connectivity, is a fundamental physical process in which magnetic energy is released explosively. It is responsible for various eruptive phenomena in the universe. However, this process is difficult to observe directly. Here, the magnetic topology associated with a solar reconnection event is studied in three dimensions (3D) using the combined perspectives of two spacecraft. The sequence of extreme ultraviolet (EUV) images clearly shows that two groups of oppositely directed and non-coplanar magnetic loops gradually approach each other, forming a separator or quasi-separator and then reconnecting. The plasma near the reconnection site is subsequently heated from $\sim$1 to $\ge$5 MK. Shortly afterwards, warm flare loops ($\sim$3 MK) appear underneath the hot plasma. Other observational signatures of reconnection, including plasma inflows and downflows, are unambiguously revealed and quantitatively measured. These observations provide direct evidence of magnetic reconnection in a 3D configuration and reveal its origin., Comment: 16 pages, 4 figures, Nature Communications 6, Article number: 7598

Giant magneto-Seebeck (GMS) effect was observed in Co/Cu/Co and NiFe/Cu/Co spin valves. Their Seebeck coefficients in parallel state was larger than that in antiparallel state, and GMS ratio defined as (SAP-SP)/SP could reach -9% in our case. The GMS originated not only from trivial giant magnetoresistance but also from spin current generated due to spin polarized thermoelectric conductivity in ferromagnetic materials and subsequent modulation of the spin current by spin configurations in spin valves. Simple Mott two-channel model reproduced a -11% GMS for the Co/Cu/Co spin valves, qualitatively consistent with our observations. The GMS effect could be applied simultaneously sensing temperature gradient and magnetic field and also be possibly applied to determine spin polarization of thermoelectric conductivity and Seebeck coefficient in ferromagnetic thin films., Comment: 4 pages and 5 figures in maintext. 2 pages and figures in supplementary information

Recently, Seebeck coefficients of ferromagnetic conductors are found to be spin-dependent. However straightforward method of accurately determining its spin polarization is still to be developed. Here, we have derived a linear dependence of anomalous Nernst coefficient on anomalous Hall angle with scaling factor related to spin polarization of Seebeck coefficient, which has been experimentally verified in [Co/Pt]n superlattices. Based on the dependence, we have also evaluated spin polarization of Seebeck coefficient of some ferromagnetic conductors. Besides, we have also found a new mechanism to generate pure spin current from temperature gradient in ferromagnetic/nonmagnetic hybrid system, which could improve efficiency from thermal energy to spin current., Comment: 5 pages and 4 figures in maintext and a supplementary material with 4 supplementary figures

Ellerman bombs (EBs) are tiny brightenings often observed near sunspots. The most impressive characteristic of the EB spectra is the two emission bumps in both wings of the H$\alpha$ and \ion{Ca}{II} 8542 {\AA} lines. High-resolution spectral data of three small EBs were obtained on 2013 June 6 with the largest solar telescope, the 1.6 meter New Solar Telescope (NST), at the Big Bear Solar Observatory. The characteristics of these EBs are analyzed. The sizes of the EBs are in the range of 0.3\arcsec\--0.8\arcsec\ and their durations are only 3--5 minutes. Our semi-empirical atmospheric models indicate that the heating occurs around the temperature minimum region with a temperature increase of 2700--3000 K, which is surprisingly higher than previously thought. The radiative and kinetic energies are estimated to be as high as 5$\times$10$^{25}$--3.0$\times$10$^{26}$ ergs despite the small size of these EBs. Observations of the magnetic field show that the EBs appeared just in a parasitic region with mixed polarities and accompanied by mass motions. Nonlinear force-free field extrapolation reveals that the three EBs are connected with a series of magnetic field lines associated with bald patches, which strongly implies that these EBs should be produced by magnetic reconnection in the solar lower atmosphere. According to the lightcurves and the estimated magnetic reconnection rate, we propose that there is a three phase process in EBs: pre-heating, flaring and cooling phases., Comment: 12 pages, 7 figures, accepted for publication in RAA

Helical magnetic flux rope (MFR) is a fundamental structure of corona mass ejections (CMEs) and has been discovered recently to exist as a sigmoidal channel structure prior to its eruption in the extreme ultraviolet (EUV) high temperature passbands of the Atmospheric Imaging Assembly (AIA). However, when and where the MFR is built up are still elusive. In this paper, we investigate two MFRs (MFR1 and MFR2) in detail, whose eruptions produced two energetic solar flares and CMEs on 2014 April 18 and 2014 September 10, respectively. The AIA EUV images reveal that for a long time prior to their eruption, both MFR1 and MFR2 are under formation, which is probably through magnetic reconnection between two groups of sheared arcades driven by the shearing and converging flows in the photosphere near the polarity inversion line. At the footpoints of the MFR1, the \textit{Interface Region Imaging Spectrograph} Si IV, C II, and Mg II lines exhibit weak to moderate redshifts and a non-thermal broadening in the pre-flare phase. However, a relatively large blueshift and an extremely strong non-thermal broadening are found at the formation site of the MFR2. These spectral features consolidate the proposition that the reconnection plays an important role in the formation of MFRs. For the MFR1, the reconnection outflow may propagate along its legs, penetrating into the transition region and the chromosphere at the footpoints. For the MFR2, the reconnection probably takes place in the lower atmosphere and results in the strong blueshift and non-thermal broadening for the Mg II, C II, and Si IV lines., Comment: 12 pages, 13 figures, accepted for publication in ApJ, any comments are welocome

Modern electronic devices are unthinkable without the well-controlled formation of interfaces at heterostructures. These often involve at least one amorphous material. Modeling such interfaces poses a significant challenge, since a meaningful result can only be expected by using huge models or by drawing from many statistically independent samples. Here we report on the results of high throughput calculations for interfaces between crystalline silicon (c-Si) and amorphous silicon nitride (a-Si$_3$N$_{3.5}$:H), which are omnipresent in commercially available solar cells. The findings reconcile only partly understood key features. At the interface, threefold coordinated Si atoms are present. These are caused by the structural mismatch between the amorphous and crystalline part. The local Fermi level of undoped c-Si lies well below that of a-SiN:H. To align the Fermi levels in the device, charge is transferred from the a-SiN:H part to the c-Si part resulting in an abundance of positively charged, threefold coordinated Si atoms at the interface. This explains the existence of a positive, fixed charge at the interface that repels holes.

Various fossil evidences show that hunting is one of major means of ancient human to get foods. But the running speed of our ancestors was much slower than quadruped animals, and they did not have sharp claws and canines. So, they have to rely heavily on stone and wooden tools when they hunting or fighting against other predators, which are very different from the hunting behaviors of other carnivores. There are mainly two types of attack and defense action during human hunting, front or side hit with a wooden stick in hands and stone or wooden spears throwing, and throwing had play an important role in human evolution process. But there is almost no work to study the why only human chose to hunting by this way. Here we suppose that ancient human chose two-arm brachiation as main arboreal locomotion mode because of their suitable body weight. Human body traits include slim body, parallel arranged scapulas, long thumb and powerful grip ability are all evolved as results of two arm brachiation. The relevant adaptive evolution of the shoulder bone structure make human arms with a large range of movement and the long thumb makes human activities to be more accurate and controllable. These are two important body structure advantages of ancient human which makes them could get from arboreal life into a whole new hunting and fighting stage., Comment: 7pages,5 figures

Among all kinds of apes, only gibbons have the slim body as human. Gibbons can move in the forest by cross arm swing, what was the locomotion mode of our arboreal ancestor. Since our ancestor had much heavier body but weaker arms than gibbons, we suppose they had to move with two arm brachiation. Such mode of locomotion can account reasonably for the transition to bipedalism. Firstly, it needed our ancestor to straighten knee and hip joints and flex their lumbar spine. secondly, it evolved the feet of our ancestor with longitudinal arche. And most importantly, it made the ratio of the length of the upper limbs to that of the lower limbs unsuitable for quadruped walking., Comment: 10 pages, 4 figures

The dynamics of a filament channel are observed with imaging and spectroscopic telescopes before and during the filament eruption on 2011 January 29. The extreme ultraviolet (EUV) spectral observations reveal that there is no EUV counterparts of the H$\alpha$ counter-streamings in the filament channel, implying that the ubiquitous H$\alpha$ counter-streamings found by previous research are mainly due to longitudinal oscillations of filament threads, which are not in phase between each other. However, there exist larger-scale patchy counter-streamings in EUV along the filament channel from one polarity to the other, implying that there is another component of uni-directional flow (in the range of $\pm$10 km s$^{-1}$) inside each filament thread in addition to the implied longitudinal oscillation. Our results suggest that the flow direction of the larger-scale patchy counter-streaming plasma in the EUV is related to the intensity of the plage or active network, with the upflows being located at brighter areas of the plage and downflows at the weaker areas. Besides, we propose a new method to determine the chirality of an erupting filament based on the skewness of the conjugate filament drainage sites. It suggests that the right-skewed drainage corresponds to sinistral chirality, whereas the left-skewed drainage corresponds to dextral chirality., Comment: 17 pages, 10 figures, published in ApJ, title changed slightly from previous version

High-resolution H$\alpha$ observations indicate that filaments consist of an assembly of thin threads. In quiescent filaments, the threads are generally short, whereas in active region filaments, the threads are generally long. In order to explain these observational features, we performed one-dimensional radiative hydrodynamic simulations of filament formation along a dipped magnetic flux tube in the framework of the chromospheric evaporation-coronal condensation model. The geometry of a dipped magnetic flux tube is characterized by three parameters, i.e., the depth ($D$), the half-width ($w$), and the altitude ($h$) of the magnetic dip. The parameter survey in the numerical simulations shows that allowing the filament thread to grow in 5 days, the maximum length ($L_{th}$) of the filament thread increases linearly with $w$, and decreases linearly with $D$ and $h$. The dependence is fitted into a linear function $L_{th}=0.84w-0.88D-2.78h+17.31$ Mm. Such a relation can qualitatively explain why quiescent filaments have shorter threads and active region filaments have longer threads., Comment: 8 pages, 6 figures, accepted for publication in RAA

A new multi-wavelength solar telescope, Optical and Near-infrared Solar Eruption Tracer (ONSET) of Nanjing University, was constructed, being fabricated by Nanjing Institute of Astronomical Optics & Technology and run in cooperation with Yunnan Astronomical Observatory. ONSET is able to observe the Sun in three wavelength windows: He {\small I} 10830 \AA, H$\alpha$, and white-light at 3600 \AA and 4250 \AA, which are selected in order to obtain the dynamics in the corona, chromosphere, and the photosphere simultaneously. Full-disk or partial-disk solar images with a field of 10 arcmin at three wavelengths can be obtained nearly simultaneously. It is designed to trace solar eruptions with high spatial and temporal resolutions. This telescope was installed at a new solar observing site near Fuxian Lake in Yunnan Province, southwest China. The site is located at E102N24, with an altitude of 1722 m. The seeing is stable and of high quality. We give a brief description of the scientific objectives and the basic structure of the ONSET. Some preliminary results are also presented., Comment: 9 pages, 5 figures, to be published in Res. Astron. Astrophys. (RAA)

An X3.4 solar flare and a fast halo coronal mass ejection (CME) occurred on 2006 December 13, accompanied by a high flux of energetic particles recorded both in near-Earth space and at ground level. Our purpose is to provide evidence of flare acceleration in a major solar energetic particle (SEP) event. We first present observations from ACE/EPAM, GOES, and the Apatity neutron monitor. It is found that the initial particle release time coincides with the flare emission and that the spectrum becomes softer and the anisotropy becomes weaker during particle injection, indicating that the acceleration source changes from a confined coronal site to a widespread interplanetary CME-driven shock. We then describe a comprehensive study of the associated flare active region. By use of imaging data from HINODE/SOT and SOHO/MDI magnetogram, we infer the flare magnetic reconnection rate in the form of the magnetic flux change rate. This correlates in time with the microwave emission, indicating a physical link between the flare magnetic reconnection and the acceleration of nonthermal particles. Combining radio spectrograph data from Huairou/NOAC, Culgoora/IPS, Learmonth/RSTN, and WAVES/WIND leads to a continuous and longlasting radio burst extending from a few GHz down to several kHz. Based on the photospheric vector magnetogram from Huairou/NOAC and the nonlinear force free field (NFFF) reconstruction method, we derive the 3D magnetic field configuration shortly after the eruption. Furthermore, we also compute coronal field lines extending to a few solar radii using a potential-field source-surface (PFSS) model. Both the so-called type III-l burst and the magnetic field configuration suggest that open-field lines extend from the flare active region into interplanetary space, allowing the accelerated and charged particles escape.

We attempt to understand the white-light flare (WLF) that was observed on 2012 March 9 with a newly constructed multi-wavelength solar telescope called the Optical and Near-infrared Solar Eruption Tracer (ONSET). We analyzed WLF observations in radio, H-alpha, white-light, ultraviolet, and X-ray bands. We also studied the magnetic configuration of the flare via the nonlinear force-free field (NLFFF) extrapolation and the vector magnetic field observed by the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO). Continuum emission enhancement clearly appeared at the 3600 angstrom and 4250 angstrom bands, with peak contrasts of 25% and 12%, respectively. The continuum emission enhancement closely coincided with the impulsive increase in the hard X-ray emission and a microwave type III burst at 03:40 UT. We find that the WLF appeared at one end of either the sheared or twisted field lines or both. There was also a long-lasting phase in the H-alpha and soft X-ray bands after the white-light emission peak. In particular, a second, yet stronger, peak appeared at 03:56 UT in the microwave band. This event shows clear evidence that the white-light emission was caused by energetic particles bombarding the lower solar atmosphere. A two-step magnetic reconnection scenario is proposed to explain the entire process of flare evolution, i.e., the first-step magnetic reconnection between the field lines that are highly sheared or twisted or both, and the second-step one in the current sheet, which is stretched by the erupting flux rope. The WLF is supposed to be triggered in the first-step magnetic reconnection at a relatively low altitude., Comment: 4 pages, 4 figures, published in A&A Letter

A new code, named MAP, is written in Fortran language for magnetohydrodynamics (MHD) calculation with the adaptive mesh refinement (AMR) and Message Passing Interface (MPI) parallelization. There are several optional numerical schemes for computing the MHD part, namely, modified Mac Cormack Scheme (MMC), Lax-Friedrichs scheme (LF) and weighted essentially non-oscillatory (WENO) scheme. All of them are second order, two-step, component-wise schemes for hyperbolic conservative equations. The total variation diminishing (TVD) limiters and approximate Riemann solvers are also equipped. A high resolution can be achieved by the hierarchical block-structured AMR mesh. We use the extended generalized Lagrange multiplier (EGLM) MHD equations to reduce the non-divergence free error produced by the scheme in the magnetic induction equation. The numerical algorithms for the non-ideal terms, e.g., the resistivity and the thermal conduction, are also equipped in the MAP code. The details of the AMR and MPI algorithms are described in the paper., Comment: 44 pages, 16 figures

Microflares are small activities in solar low atmosphere, some are in the low corona, and others in the chromosphere. Observations show that some of the microflares are triggered by magnetic reconnection between emerging flux and a pre-existing background magnetic field. We perform 2.5D compressible resistive MHD simulations of magnetic reconnection with gravity considered. The background magnetic field is a canopy-type configuration which is rooted at the boundary of the solar supergranule. By changing the bottom boundary conditions in the simulation, new magnetic flux emerges up at the center of the supergranule and reconnects with the canopy-type magnetic field. We successfully simulate the coronal and chromospheric microflares, whose current sheets are located at the corona and the chromosphere, respectively. The microflare of coronal origin has a bigger size and a higher temperature enhancement than that of chromospheric origin. In the microflares of coronal origin, we also found a hot jet ($\sim$$1.8 \times 10^6$ K), which is probably related to the observational EUV/SXR jets, and a cold jet ($\sim$$10^4$ K), which is similar to the observational H$\alpha$/Ca surges, whereas there is only an H$\alpha$/Ca bright point in the microflares of chromospheric origin. The study of parameter dependence shows that the size and strength of the emerging magnetic flux are the key parameters which determine the height of the reconnection location, and further determine the different observational features of the microflares., Comment: 24 pages, 11 figures, accepted by ApJ

Coronal "EIT waves" appear as EUV bright fronts propagating across a significant part of the solar disk. The intriguing phenomenon provoked continuing debates on their nature and their relation with coronal mass ejections (CMEs). In this paper, we first summarize all the observational features of "EIT waves", which should be accounted for by any successful model. The theoretical models constructed during the past 10 years are then reviewed. Finally, the implication of the "EIT wave" research to the understanding of CMEs is discussed. The necessity is pointed out to revisit the nature of CME frontal loop., Comment: 10 pages, 3 figures, a review paper to be published in the Proc. of the 1st Asian-Pacific Solar Phys. Meeting

We performed three dimensional resistive magnetohydrodynamic simulations to study the magnetic reconnection using an initially shearing magnetic field configuration (force free field with a current sheet in the middle of the computational box). It is shown that there are two types of reconnection jets: the ordinary reconnection jets and fan-shaped jets, which are formed along the guide magnetic field. The fan-shaped jets are much different from the ordinary reconnection jets which are ejected by magnetic tension force. There are two driving forces for accelerating the fan-shaped jets. The one is the Lorentz force which dominates the motion of fluid elements at first and then the gas pressure gradient force accelerates the fluid elements in the later stage. The dependence on magnetic reconnection angle and resistivity value has also been studied. The formation and evolution of these jets provide a new understanding of dynamic magnetohydrodynamic jets., Comment: 26 pages, 22 figures, accepted for publication in Research in Astronomy and Astrophysics (RAA)

With gravity, ionization, and radiation being considered, we perform 2.5D compressible resistive MHD simulations of chromospheric magnetic reconnection using the CIP-MOCCT scheme. The temperature distribution of the quiet-Sun atmospheric model VALC and the helium abundance (10%) are adopted. Our 2.5D MHD simulation reproduces qualitatively the temperature enhancement observed in chromospheric microflares. The temperature enhancement $\Delta T$ is demonstrated to be sensitive to the background magnetic field, whereas the total evolution time $\Delta t$ is sensitive to the magnitude of the anomalous resistivity. Moveover, we found a scaling law, which is described as $\Delta T/\Delta t \sim {n_H}^{-1.5} B^{2.1} {\eta_0}^{0.88}$. Our results also indicate that the velocity of the upward jet is much greater than that of the downward jet and the X-point may move up or down., Comment: 31 pages; 9 figures; published in ApJ

Halo coronal mass ejections (CMEs) were found to be significantly faster than normal CMEs, which was a long-standing puzzle. In order to solve the puzzle, we first investigate the observed properties of 31 limb CMEs that display clearly loop-shaped frontal loops. The observational results show a strong tendency that slower CMEs are weaker in the white-light intensity. Then, we perform a Monte Carlo simulation of 20 000 artificial limb CMEs that have average velocity of $\sim$523 km s$^{-1}$. The Thomson scattering of these events is calculated when they are assumed to be observed as limb and halo events, respectively. It is found that the white-light intensity of many slow CMEs becomes remarkably reduced as they turn from being viewed as a limb event to as a halo event. When the intensity is below the background solar wind fluctuation, it is assumed that they would be missed by coronagraphs. The average velocity of "detectable" halo CMEs is $\sim$922 km s$^{-1}$, very close to the observed value. It also indicates that wider events are more likely to be recorded. The results soundly suggest that the higher average velocity of halo CMEs is due to that a majority of slow events and a part of narrow fast events carrying less material are so faint that they are blended with the solar wind fluctuations, and therefore are not observed., Comment: 12 pages, 10 figures, to be published in RAA

The unconventional superconductivity in the newly discovered iron-based superconductors is intimately related to its multi-band/multi-orbital nature. Here we report the comprehensive orbital characters of the low-energy three-dimensional electronic structure in BaFe$_{1.85}$Co$_{0.15}$As$_2$ by studying the polarization and photon energy dependence of angle-resolved photoemission data. While the distributions of the $d_{xz}$, $d_{yz}$, and $d_{3z^2-r^2}$ orbitals agree with the prediction of density functional theory, those of the $d_{xy}$ and $d_{x^2-y^2}$ orbitals show remarkable disagreement with theory. Our results point out the inadequacy of the existing band structure calculations, and more importantly, provide a foundation for constructing the correct microscopic model of iron pnictides., Comment: 7 pages, 8 figures, Add new data and detail results