Progressive internal gravity waves with bounded upper surface climbing a triangular obstacle

In this paper we discuss a theoretical model for the interfacial profiles of progressive non-linear waves which result from introducing a triangular obstacle, of finite height, attached to the bottom below the flow of a stratified, ideal, two layer fluid, bounded from above by a rigid boundary. The derived equations are solved by using a nonlinear perturbation method. The dependence of the interfacial profile on the triangular obstacle size, as well as its dependence on some flow parameters, such as the ratios of depths and densities of the two fluids, have been studied

Formability limits and process window based on fracture analysis of 5A02-O aluminium alloy in splitting spinning

Splitting spinning or rotary flow splitting is an advanced forming process for manufacturing axisymmetric integrated parts with bifurcated features and unique characteristics of high-performance and low-weight. During the process, under the kinematic effects of mandrel rotational movement and roller radial feed, plastic deformation occurs accompanied usually by undesirable fracture, which reduces the formability limit (FL). In this study, the kinematic effects on the FL of a 5A02-O aluminium alloy in the splitting spinning process were systematically investigated by finite element simulation based on a modified Lemaitre criterion and physical experiments. The results show that at a given roller feed speed or mandrel rotational speed (forming speed), the FL has a nonlinear relationship with forming speed, which increases firstly and then decreases. With the increase of forming speed, the maximum FL decreases, which appears at the larger forming speed. These variations of FL show that there exists a combined effect of the roller feed speed and mandrel rotational speed, thus a ratio between them, named as the roller feed ratio, is then used to investigate FL. It is found that there exists a critical roller feed ratio of approximately 2 mm/rev, independent of the speeds of roller and mandrel. Below this critical value, the FL increases with the roller feed ratio. While over the critical value, the FL decreases. In addition, the decrease of FL becomes more remarkable with the increase of mandrel rotational speed. Furthermore, the variations of stress triaxiality and tensile plastic strain were analyzed to see their effects on FL. The analyses show that the decrease of tensile plastic strain with the increasing roller feed ratio is dominant the increase of FL below the critical roller feed ratio value. The increase in the stress triaxiality is dominant in the decrease of FL when the roller feed ratio is over the critical value in combination with not too high forming speed, whereas both increases are dominant in the decrease of FL when it is over the critical roller feed ratio value in combination with high forming speed. Based on the kinematic effects of mandrel and roller, the process windows of the splitting spinning process were obtained to improve the FL. It is found that under the condition of the roller feed ratio within 1–2.5 mm/rev, the mandrel rotational speed within 8–100 rev/min and the roller feed speed within 0.5–4 mm/s are helpful to get high FL values. The experiments were carried out to verify the prediction on the FL and the process window. The research provides an in-depth understanding of FL and its affecting factors, and thus lays a basis for process optimization and process parameter configuration

The dependence of the EIT wave velocity on the magnetic field strength

"EIT waves" are a wavelike phenomenon propagating in the corona, which were initially observed in the extreme ultraviolet (EUV) wavelength by the EUV Imaging Telescope (EIT). Their nature is still elusive, with the debate between fast-mode wave model and non-wave model. In order to distinguish between these models, we investigate the relation between the EIT wave velocity and the local magnetic field in the corona. It is found that the two parameters show significant negative correlation in most of the EIT wave fronts, {\it i.e.}, EIT wave propagates more slowly in the regions of stronger magnetic field. Such a result poses a big challenge to the fast-mode wave model, which would predict a strong positive correlation between the two parameters. However, it is demonstrated that such a result can be explained by the fieldline stretching model, \emph{i.e.,} that "EIT waves" are apparently-propagating brightenings, which are generated by successive stretching of closed magnetic field lines pushed by the erupting flux rope during coronal mass ejections (CMEs).Comment: 11 pages, 8 figures, accepted for publication in Solar Phy

Large-scale Bright Fronts in the Solar Corona: A Review of "EIT waves"

``EIT waves" are large-scale coronal bright fronts (CBFs) that were first observed in 195 \AA\ images obtained using the Extreme-ultraviolet Imaging Telescope (EIT) onboard the \emph{Solar and Heliospheric Observatory (SOHO)}. Commonly called ``EIT waves", CBFs typically appear as diffuse fronts that propagate pseudo-radially across the solar disk at velocities of 100--700 km s$^{-1}$ with front widths of 50-100 Mm. As their speed is greater than the quiet coronal sound speed ($c_s\leq$200 km s$^{-1}$) and comparable to the local Alfv\'{e}n speed ($v_A\leq$1000 km s$^{-1}$), they were initially interpreted as fast-mode magnetoacoustic waves ($v_{f}=(c_s^2 + v_A^2)^{1/2}$). Their propagation is now known to be modified by regions where the magnetosonic sound speed varies, such as active regions and coronal holes, but there is also evidence for stationary CBFs at coronal hole boundaries. The latter has led to the suggestion that they may be a manifestation of a processes such as Joule heating or magnetic reconnection, rather than a wave-related phenomena. While the general morphological and kinematic properties of CBFs and their association with coronal mass ejections have now been well described, there are many questions regarding their excitation and propagation. In particular, the theoretical interpretation of these enigmatic events as magnetohydrodynamic waves or due to changes in magnetic topology remains the topic of much debate.Comment: 34 pages, 19 figure

A Model Study of Discrete Scale Invariance and Long-Range Interactions

We investigate the modification of discrete scale invariance in the bound state spectrum by long-range interactions. This problem is relevant for effective field theory descriptions of nuclear cluster states and manifestations of the Efimov effect in nuclei. As a model system, we choose a one dimensional inverse square potential supplemented with a long-range Coulomb interaction. We study the renormalization and bound-state spectrum of the system as a function of the Coulomb interaction strength. Our results indicate, that the counterterm required to renormalize the inverse square potential alone is sufficient to renormalize the full problem. However, the breaking of the discrete scale invariance through the Coulomb interaction leads to a modified bound state spectrum. The shallow bound states are strongly influenced by the Coulomb interaction while the deep bound states are dominated by the inverse square potential.Comment: 8 pages, 6 figures, EPJ style, published versio

Coronal Shock Waves, EUV Waves, and Their Relation to CMEs. III. Shock-Associated CME/EUV Wave in an Event with a Two-Component EUV Transient

On 17 January 2010, STEREO-B observed in extreme ultraviolet (EUV) and white light a large-scale dome-shaped expanding coronal transient with perfectly connected off-limb and on-disk signatures. Veronig et al. (2010, ApJL 716, 57) concluded that the dome was formed by a weak shock wave. We have revealed two EUV components, one of which corresponded to this transient. All of its properties found from EUV, white light, and a metric type II burst match expectations for a freely expanding coronal shock wave including correspondence to the fast-mode speed distribution, while the transient sweeping over the solar surface had a speed typical of EUV waves. The shock wave was presumably excited by an abrupt filament eruption. Both a weak shock approximation and a power-law fit match kinematics of the transient near the Sun. Moreover, the power-law fit matches expansion of the CME leading edge up to 24 solar radii. The second, quasi-stationary EUV component near the dimming was presumably associated with a stretched CME structure; no indications of opening magnetic fields have been detected far from the eruption region.Comment: 18 pages, 10 figures. Solar Physics, published online. The final publication is available at http://www.springerlink.co

The 3-3-1 model with S_4 flavor symmetry

We construct a 3-3-1 model based on family symmetry S_4 responsible for the neutrino and quark masses. The tribimaximal neutrino mixing and the diagonal quark mixing have been obtained. The new lepton charge \mathcal{L} related to the ordinary lepton charge L and a SU(3) charge by L=2/\sqrt{3} T_8+\mathcal{L} and the lepton parity P_l=(-)^L known as a residual symmetry of L have been introduced which provide insights in this kind of model. The expected vacuum alignments resulting in potential minimization can origin from appropriate violation terms of S_4 and \mathcal{L}. The smallness of seesaw contributions can be explained from the existence of such terms too. If P_l is not broken by the vacuum values of the scalar fields, there is no mixing between the exotic and the ordinary quarks at the tree level.Comment: 20 pages, revised versio

On the Nature and Genesis of EUV Waves: A Synthesis of Observations from SOHO, STEREO, SDO, and Hinode

A major, albeit serendipitous, discovery of the SOlar and Heliospheric Observatory mission was the observation by the Extreme Ultraviolet Telescope (EIT) of large-scale Extreme Ultraviolet (EUV) intensity fronts propagating over a significant fraction of the Sun's surface. These so-called EIT or EUV waves are associated with eruptive phenomena and have been studied intensely. However, their wave nature has been challenged by non-wave (or pseudo-wave) interpretations and the subject remains under debate. A string of recent solar missions has provided a wealth of detailed EUV observations of these waves bringing us closer to resolving their nature. With this review, we gather the current state-of-art knowledge in the field and synthesize it into a picture of an EUV wave driven by the lateral expansion of the CME. This picture can account for both wave and pseudo-wave interpretations of the observations, thus resolving the controversy over the nature of EUV waves to a large degree but not completely. We close with a discussion of several remaining open questions in the field of EUV waves research.Comment: Solar Physics, Special Issue "The Sun in 360",2012, accepted for publicatio

Calculation of the local density of relic neutrinos

Nonzero neutrino masses are required by the existence of flavour oscillations, with values of the order of at least 50 meV. We consider the gravitational clustering of relic neutrinos within the Milky Way, and used the N - one-body simulation technique to compute their density enhancement factor in the neighbourhood of the Earth with respect to the average cosmic density. Compared to previous similar studies, we pushed the simulation down to smaller neutrino masses, and included an improved treatment of the baryonic and dark matter distributions in the Milky Way. Our results are important for future experiments aiming at detecting the cosmic neutrino background, such as the Princeton Tritium Observatory for Light, Early-universe, Massive-neutrino Yield (PTOLEMY) proposal. We calculate the impact of neutrino clustering in the Milky Way on the expected event rate for a PTOLEMY-like experiment. We find that the effect of clustering remains negligible for the minimal normal hierarchy scenario, while it enhances the event rate by 10 to 20% (resp. a factor 1.7 to 2.5) for the minimal inverted hierarchy scenario (resp. a degenerate scenario with 150 meV masses). Finally we compute the impact on the event rate of a possible fourth sterile neutrino with a mass of 1.3 eV

What is the Nature of EUV Waves? First STEREO 3D Observations and Comparison with Theoretical Models

One of the major discoveries of the Extreme ultraviolet Imaging Telescope (EIT) on SOHO were intensity enhancements propagating over a large fraction of the solar surface. The physical origin(s) of the so-called `EIT' waves is still strongly debated. They are considered to be either wave (primarily fast-mode MHD waves) or non-wave (pseudo-wave) interpretations. The difficulty in understanding the nature of EUV waves lies with the limitations of the EIT observations which have been used almost exclusively for their study. Their limitations are largely overcome by the SECCHI/EUVI observations on-board the STEREO mission. The EUVI telescopes provide high cadence, simultaneous multi-temperature coverage, and two well-separated viewpoints. We present here the first detailed analysis of an EUV wave observed by the EUVI disk imagers on December 07, 2007 when the STEREO spacecraft separation was $\approx 45^\circ$. Both a small flare and a CME were associated with the wave cadence, and single temperature and viewpoint coverage. These limitations are largely overcome by the SECCHI/EUVI observations on-board the STEREO mission. The EUVI telescopes provide high cadence, simultaneous multi-temperature coverage, and two well-separated viewpoints. Our findings give significant support for a fast-mode interpretation of EUV waves and indicate that they are probably triggered by the rapid expansion of the loops associated with the CME.Comment: Solar Physics, 2009, Special STEREO Issue, in pres