Repeating fast radio bursts reveal the secret of pulsar magnetospheric activity

The puzzling mechanism of coherent radio emission remains unknown, but fortunately, repeating fast radio bursts (FRBs) provide a precious opportunity, with extremely bright subpulses created in a clear and vacuum-like pulsar magnetosphere. FRBs are millisecond-duration signals that are highly dispersed at distant galaxies but with uncertain physical origin(s). Coherent curvature radiation by bunches has already been proposed for repeating FRBs. The charged particles are created during central star's quakes, which can form bunches streaming out along curved magnetic field lines, so as to trigger FRBs. The nature of narrow-band radiation with time-frequency drifting can be a natural consequence that bunches could be observed at different times with different curvatures. Additionally, high linear-polarization can be seen if the line of sight is confined to the beam angle, whereas the emission could be highly circular-polarized if off-beam. It is also discussed that pulsar surface may be full of small hills (i.e., zits) which would help producing bulk of energetic bunches for repeating FRBs as well as for rotation-powered pulsars.     

Exploring the magnetized cosmic web through low-frequency radio emission

Recent improvements in the capabilities of low-frequency radio telescopes provide a unique opportunity to study thermal and non-thermal properties of the cosmic web. We argue that the diffuse, polarized emission from giant radio relics traces structure formation shock waves and illuminates the large-scale magnetic field. To show this, we model the population of shock-accelerated relativistic electrons in high-resolution cosmological simulations of galaxy clusters and calculate the resulting radio synchrotron emission. We find that individual shock waves correspond to localized peaks in the radio surface brightness map which enables us to measure Mach numbers for these shocks. We show that the luminosities and number counts of the relics strongly depend on the magnetic field properties, the cluster mass and dynamical state. By suitably combining different cluster data, including Faraday rotation measures, we are able to constrain some macroscopic parameters of the plasma at the structure formation shocks, such as models of turbulence. We also predict upper limits for the properties of the warm-hot intergalactic medium, such as its temperature and density. We predict that the current generation of radio telescopes [Low-Frequency Array (LOFAR), Giant Meter Radio Telescope (GMRT), the Murchison Wide-field Array (MWA) and Long Wavelength Array (LWA)] have the potential to discover a substantially larger sample of radio relics, with multiple relics expected for each violently merging cluster. Future experiments [(Square Kilometre Array (SKA)] should enable us to further probe the macroscopic parameters of plasma physics in clusters.     

Interpretation and implications of the non-detection of GeV spectrum excess by the Fermi Gamma-ray Space Telescope in most gamma-ray bursts

Since the launch of the Fermi Gamma-ray Space Telescope on 2008 June 11, significant detections of high-energy emission have been reported only in six gamma-ray bursts (GRBs) until now. In this work we show that the lack of detection of a GeV spectrum excess in almost all GRBs, though somewhat surprising, can be well understood within the standard internal shock model and several alternatives like the photosphere internal shock (gradual magnetic dissipation) model and the magnetized internal shock model. The delay of the arrival of the >100 MeV photons from some Fermi bursts can be interpreted too. We then show that with the polarimetry of prompt emission these models may be distinguishable. In the magnetized internal shock model, a high linear polarization level should be typical. In the standard internal shock model, a high linear polarization level is still possible but much less frequent. In the photosphere internal shock model, the linear polarization degree is expected to be roughly anticorrelated with the weight of the photosphere/thermal component, which may be a unique signature of this kind of model. We also briefly discuss the implications of the current Fermi GRB data on the detection prospects of the prompt PeV neutrinos. The influences of the intrinsic proton spectrum and the enhancement of the neutrino number at some specific energies, due to the cooling of pions (muons), are outlined.     

新场气田中侏罗统沙溪庙组一段的储集特征

通过岩心、薄片等方法对新场气田中侏罗统沙溪组一段的储集特征进行了详细研究,对其储集物性的主控因素展开探讨,认为成岩作用是影响物性的重要因素.得出方解石胶结是导致孔隙度减少的主要原因,衬垫(或环边)绿泥石则导致渗透率变差,溶蚀作用形成的次生孔隙对孔隙度增加作出了贡献,但对渗透率无明显的建设性.     

Vacation Field Work for Pupils

Abstract

A Magic Carpet Trip to Learning Geography provides successful hands on, student-tested activities for teaching elementary school students about continents and oceans. From the introductory “Magic Carpet” poem to the finale, Geography Pizza, students are activiely involved in learning: (1) why our earth is the “Blue Planet”; (2) the continent names, shapes, and locations; (3) about continental drift. In the article an evaluation tool is discussed that can be used to assess the growth of geography awareness in the classroom. Through the use of poetry, music, games, science, math, cooking, and student writing, geogrpahy comes alive in the elementary classroom.     

The Status of Geography in the Social Studies Curricula of Canadian Schools

Abstract

Successful curriculum development that will have impact upon individual American classrooms remains the key to maintaining the momentum of Geography for Life: National Geography Standards 1994. Teachers and students must be able to translate the national geography standards from the national stage to the local classroom setting to become geographically informed people. One example of this development for elementary urban geography is the Main Street lesson plan. It encourages observation and analysis required by Standard 4: The geographically informed student knows and understands the physical and human characteristics of places. After testing in a variety of Missouri classrooms, instructors thought that Main Street was a unique way of studying urban places and allowing students to gain a greater understanding of place.     

Geography and Multiple Abilities Program: Innovations in Teacher Education-Reconnecting Teaching to Students' Needs

Abstract

The University of Alabama is now offering a new and innovative, five-semester program that provides preservice teachers with both knowledge of and skill in using strategies and teaching methods associated with general and special education. The goal of the Multiple Abilities Program (MAP) is to enable teachers to accommodate the wide range of learning styles and developmental readiness for instruction of all learners in a given classroom, regardless of the labels with which the children are identified. This article describes MAP in light of the geography strand of the MAP curriculum. MAP students work with five topics in geography, which they use to develop a greater understanding of how authentic teaching and learning of geography are mediated by cognitive, affective, and social needs of children. MAP students take a particular topic in geography and design and implement instruction for it by creating authentic learning activities that offer elementary school students an opportunity to explore the topic. The variety that is systematically planned into the activities is the major means of accommodating differences in cognitive ability, learning style, level of physical and social development, and cultural, ethnic, and socioeconomic diversity.     

Going beyond location: Thematic maps in the early elementary grades

Abstract

Cartographic research has long suggested that preschool and early elementary children possess advanced mapping behaviors in terms of interpreting, making, and using locational and wayfinding maps. To improve instruction in geographic concepts, it is necessary to see if these advanced mapping behaviors apply to thematic or special purpose maps as well, as an understanding of these types of maps is integral to the five fundamental themes of geography. An experiment was conducted to evaluate the thematic mapping abilities of second-grade students. Students viewed maps at the neighborhood, city, and national scales displaying different types of symbolization and presented in a random order. Results indicated that the map tasks were appropriate for this age level, and a statistical test of reaction times did not identify a best symbol type or scale, as all were appropriate for this age level. Responses to discussion questions indicated the students also have the ability to describe spatial patterns. The interpretation of quantitative information on maps is within the ability level of second grade students, and materials currently used in second grade should be revised to include these maps.     

甘肃省阳山金矿床流体包裹体特征及其地质意义

甘肃省阳山金矿床是一个赋存于泥盆系浅变质岩中的似微细浸染型超大型金矿床.研究表明矿石中石英及方解石包裹体分为两种成因共9种物理状态类型,均一温度为105～310℃.成矿流体盐度w(NaCl)=1.6%～10.6%,密度为0.35～1.02 g/cm3,成矿压力为400×105～800×105 Pa.成矿流体呈中性偏弱碱性、弱还原性,以大气降水为主,岩浆水也不同程度地参与了成矿作用.     

长江中游地区洪泛沉积物与正常河流沉积物磁组构特征对比研究

在地层剖面中,洪泛沉积物与正常的河道沉积物的沉积学特征非常相似,仅靠沉积学特征很难将两者区分. 为了识别古洪灾事件,因而从环境磁学角度建立两种沉积物的识别标志是非常必要和有意义的. 本文通过对1998年长江黣洲湾溃口扇及其附近的长江现代河漫滩沉积物进行磁组构参数测量和对比分析,并结合长江下游河漫滩沉积物的磁组构参数特征,揭示出长江中游正常河流沉积物与河流溃口沉积物的磁组构参数特征具有明显的不同,并且它们与沉积时的沉积环境有着密切的关系. 因此,对长江中游地区沉积物磁组构参数的测试及磁化率各向异性量值椭球体形态的研究,是目前分辨洪泛沉积物和正常的河道沉积物的一个较有效的方法.