Primordial Non-Gaussianity from LAMOST Surveys

The primordial non-Gaussianity (PNG) in matter density perturbation is a very powerful probe of the physics of the very early Universe. The local PNG can induce a distinct scale-dependent bias on the large scale structure distribution of galaxies and quasars, which could be used for constraining it. We study the detection limits on PNG from the surveys of the LAMOST telescope. The cases of the main galaxy survey, the luminous red galaxy (LRG) survey, and the quasar survey of different magnitude limits are considered. We find that the MAIN1 sample (i.e. the main galaxy survey with one magnitude deeper than the SDSS main galaxy survey, or r<18.8) could only provide very weak constraint on PNG. For the MAIN2 sample (r<19.8) and the LRG survey, the 2\sigma (95.5%) limit on the PNG parameter f_{NL} are |f_{NL}|<145 and |f_{NL}|<114 respectively, comparable to the current limit from cosmic microwave background (CMB) data. The quasar survey could provide much more stringent constraint, and we find that the 2\sigma limit for |f_{NL}| is between 50 and 103, depending on the magnitude limit of the survey. With Planck-like priors on cosmological parameters, the quasar survey with g<21.65 would improve the constraints to |f_{NL}|<43 (2\sigma). We also discuss the possibility of further tightening the constraint by using the relative bias method proposed by Seljak(2008).Comment: 8 pages, 2 figures, RAA accepte

Tunable pure spin currents in a triple-quantum-dot ring

Electron transport properties in a triple-quantum-dot ring with three terminals are theoretically studied. By introducing local Rashba spin-orbit interaction on an individual quantum dot, we calculate the charge and spin currents in one lead. We find that a pure spin current appears in the absence of a magnetic field. The polarization direction of the spin current can be inverted by altering the bias voltage. In addition, by tuning the magnetic field strength, the charge and spin currents reach their respective peaks alternately.Comment: 5 pages, 2 Figure

Electron confinement by laser-driven azimuthal magnetic fields during direct laser acceleration

A laser-driven azimuthal plasma magnetic field is known to facilitate electron energy gain from the irradiating laser pulse. The enhancement is due to changes in the orientation between the laser electric field and electron velocity caused by magnetic field deflections. Transverse electron confinement is critical for realizing this concept experimentally. We find that the phase velocity of the laser pulse has a profound impact on the transverse size of electron trajectories. The transverse size remains constant below a threshold energy that depends on the degree of the superluminosity and it increases with the electron energy above the threshold. This increase can cause electron losses in tightly focused laser pulses. We show using 3D particle-in-cell simulations that the electron energy gain can be significantly increased by increasing laser power at fixed intensity due to the increased electron confinement. This finding makes a strong case for designing experiments at multi-PW laser facilities

Quantifying and Transferring Contextual Information in Object Detection

(c) 2012 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other work

Generating Text Sequence Images for Recognition

Recently, methods based on deep learning have dominated the field of text recognition. With a large number of training data, most of them can achieve the state-of-the-art performances. However, it is hard to harvest and label sufficient text sequence images from the real scenes. To mitigate this issue, several methods to synthesize text sequence images were proposed, yet they usually need complicated preceding or follow-up steps. In this work, we present a method which is able to generate infinite training data without any auxiliary pre/post-process. We tackle the generation task as an image-to-image translation one and utilize conditional adversarial networks to produce realistic text sequence images in the light of the semantic ones. Some evaluation metrics are involved to assess our method and the results demonstrate that the caliber of the data is satisfactory. The code and dataset will be publicly available soon

Expanding the Reliable Paleomagnetic Constraints on Configurations of Pre-Pangean Supercontinents

Supercontinents embody perhaps the longest cyclic process on our planet, profoundly influencing the evolution of Earth’s biosphere, geosphere, and atmosphere on timescales of hundred-million years or more. Yet, the configurations of pre-Pangean supercontinents, Rodinia, Nuna, and/or Kenorland, as well as their transition processes remain the subjects of debate, hampering the understanding of the interactions between the global tectonics and Earth’s evolution in deep time. Compared to other approaches, paleomagnetism is the only quantitative method to reconstruct pre-Pangean supercontinents in an absolute paleogeographic framework. However, a recent summary of global paleomagnetic data of Precambrian age reveals two problems. First is that discordant paleomagnetic records exist in some cratons’ datasets, thus rendering paleogeographic interpretations difficult. Second is that some cratons (e.g., West African Craton) have heretofore essentially no reliable Precambrian paleomagnetic records, yielding large uncertainties in their paleogeography. This dissertation is dedicated to addressing these problems. Specifically, we studied three cases of discordant paleomagnetic records, one from Tonian data in Baltica, and a pair of Orosirian datasets from the Slave craton. By adding new data and carefully compiling and evaluating published results, we thoroughly discussed the possible causes of discordance in the paleomagnetic directions. For Baltica, using detailed laboratory demagnetization techniques on samples from the Dalarna-Blekinge dolerite dike suite, we attributed an abnormal direction within the Dalarna-Blekinge mafic dikes to unremoved overprints. In addition, by comparing our new Baltica poles around ~950 Ma with coeval poles from Laurentia, we proposed rapid latitudinal motions of these two cratons in early Tonian time. For the Slave craton, we proposed that although basin- or local-scale vertical-axis rotations could account for some discrepancies among time-correlative 2.02-1.88 Ga poles, the overall pattern of the Orosirian apparent polar wander path of the Slave craton is better explained by true polar wander. These findings are helpful for studying the dynamic movements of Rodinia and the amalgamation of Nuna. In addition, we reviewed the Precambrian paleomagnetic records of the West African Craton to understand the limitations of previous studies. We found that most of the low-quality published results from the West African Craton suffer from inadequate sampling, poor dating, and the lack of field tests. We conducted a paleomagnetic study on Proterozoic mafic dike swarms in the Anti-Atlas Belt, Morocco, combined with U-Pb geochronology. After detailed field and laboratory work, we provided two reliable paleomagnetic poles for the West African Craton, one at 2.04 Ga and the other at 1.4–1.36 Ga. These new poles help fill the large gaps in the paleomagnetic dataset of the West African Craton. Using the two poles, we proposed a new connection between the West African Craton and Amazonia before and within Nuna, of which the relative position between the two cratons is 180° different from their connection in Gondwana. Incorporating paleomagnetic and geological constraints from other major cratons, we revised the configuration of supercontinent Nuna. Our new reconstruction model sheds light on the plate motion pattern between neighboring cratons in deep time, as well as the style of Nuna-Rodinia supercontinental transition. To summarize, the outcome of this dissertation expands the reliable paleomagnetic constraints on configurations of pre-Pangean supercontinents, and promotes an understanding of the Earth’s evolution in a spatial perspective. The final establishment of a global paleogeographic framework in the Precambrian still awaits further integrations of robust paleomagnetic studies with geochronological, stratigraphical, geochemical, and paleontological constraints

Top quark spin and HtbHtb interaction in charged Higgs and top quark associated production at LHC

We study the charged Higgs production at LHC via its associated production with top quark. The kinematic cuts are optimized to suppress the background processes so that the reconstruction of the charged Higgs and top quark is possible. The angular distributions with respect to top quark spin are explored to study the $Htb$ interaction at LHC.Comment: 10 pages,5 figures, to appear in PR