Anthropology of the Crowd, Blog 3

Student blog posts from the Great VCU Bike Race Book

Comoving acceleration of overdense electron-positron plasma by colliding ultra-intense laser pulses

Particle-in-cell (PIC) simulation results of sustained acceleration of electron-positron (e+e-) plasmas by comoving electromagnetic (EM) pulses are presented. When a thin slab of overdense e+e- plasma is irradiated with linear-polarized ultra-intense short laser pulses from both sides, the pulses are transmitted when the plasma is compressed to thinner than ~ 2 relativistic skin depths. A fraction of the plasma is then captured and efficiently accelerated by self-induced JxB forces. For 1 micron laser and 1021Wcm-2 intensity, the maximum energy exceeds GeV in a picosecond.Comment: 10 pages, 4 figure

Loop quantum cosmology of Bianchi IX: Effective dynamics

We study numerically the solutions to the effective equations of Bianchi IX spacetimes within Loop Quantum Cosmology. We consider Bianchi IX models with and without inverse triad corrections whose matter content is a scalar field without mass. The solutions are classified using the classical observables. We show that both effective theories --with lapse N=V and N=1-- solve the big bang singularity and reproduce the classical dynamics far from the bounce. Moreover, due to the spatial compactness, there is an infinity number of bounces and recollapses. We study the limit of large volume and show that both effective theories reproduce the same dynamics, thus recovering general relativity. We implement a procedure to identify amongst the Bianchi IX solutions, those that behave like k=0,1 FLRW as well as Bianchi I, II, and VII_0 models. The effective solutions exhibit Bianchi I phases with Bianchi II transitions and also Bianchi VII_0 phases, which had not been studied before, at the quantum nor effective level. We comment on the possible implications of these results for a quantum modification to the classical BKL behaviour.Comment: This version to be published in the CQG special issu

On distinguished orbits of reductive representations

Let $G$ be a real reductive Lie group and ${\tau}:G \longrightarrow GL(V)$ be a real reductive representation of $G$ with (restricted) moment map m_{\ggo}: V-{0} \longrightarrow \ggo. In this work, we introduce the notion of "nice space" of a real reductive representation to study the problem of how to determine if a $G$-orbit is "distinguished" (i.e. it contains a critical point of the norm squared of m_{\ggo}). We give an elementary proof of the well-known convexity theorem of Atiyah-Guillemin-Sternberg in our particular case and we use it to give an easy-to-check sufficient condition for a $G$-orbit of a element in a nice space to be distinguished. In the case where $G$ is algebraic and $\tau$ is a rational representation, the above condition is also necessary (making heavy use of recent results of M. Jablonski), obtaining a generalization of Nikolayevsky's nice basis criterium. We also provide useful characterizations of nice spaces in terms of the weights of $\tau$. Finally, some applications to ternary forms and minimal metrics on nilmanifolds are presented.Comment: 27 pages (with an appendix), 2 figures, 5 tables. This is a preliminary version; comments, criticisms and suggestions are welcom

Soft gamma rays from black holes versus neutron stars

The recent launches of GRANAT and GRO provide unprecedented opportunities to study compact collapsed objects from their hard x ray and gamma ray emissions. The spectral range above 100 keV can now be explored with much higher sensitivity and time resolution than before. The soft gamma ray spectral data is reviewed of black holes and neutron stars, radiation, and particle energization mechanisms and potentially distinguishing gamma ray signatures. These may include soft x ray excesses versus deficiencies, thermal versus nonthermal processes, transient gamma ray bumps versus power law tails, lines, and periodicities. Some of the highest priority future observations are outlines which will shed much light on such systems

PEMBELAJARAN KONSEP REDUCE, REUSE, RECYCLE DALAM MATA PELAJARAN ILMU PENGETAHUAN SOSIAL DENGAN MODEL PICTURE AND PICTURE UNTUK MENINGKATKAN EKOLITERASI PESERTA DIDIK : Penelitian Tindakan di Kelas VII Sunan Gresik SMP Islam Insan Rabbany Kota Tangerang Selatan

Penelitian ini dilatarbelakangi masih rendahnya kesadaran peserta didik menjaga lingkungan sekitar. Rendahnya kesadaran tersebut diantaranya peserta didik masih membuang sampah sembarangan, bersikap apatis terhadap sampah yang berserakan dan relatif belum sadar konsep 3R dalam penanganan sampah. Penelitian ini bertujuan untuk meningkatkan kepedulian peserta didik terhadap lingkungan sesuai dengan tujuan pembelajaran IPS kompetensi inti spiritual (KI 1) dan sikap (KI 2). Peningkatan kepedulian lingkungan peserta didik dalam penelitian ini dengan peningkatan ekoliterasi melalui konsep 3R dalam pembelajaran IPS. Metode penelitian yang digunakan dalam penelitian ini adalah Penelitian Tindakan Kelas pada peserta didik Kelas VII Sunan Gresik di SMP Islam Insan Rabbany Kota Tangerang Selatan. Instrumen yang digunakan diantaranya lembar observasi guru, lembar observasi peserta didik, lembar diskusi balikan, catatan lapangan dan wawancara. Hasil dari penelitian ini adalah peningkatan keterampilan guru dan peningkatan ekoliterasi peserta didik Kelas VII Sunan Gresik baik dimensi pengetahuan, keterampilan dan sikap. Guru berhasil merencanakan pembelajaran bersama guru mitra dengan baik, pelaksanaan penelitian tindakan kelas dilaksanakan dalam 3 siklus, berdasarkan refleksi dan data terdapat peningkatan pada setiap siklusnya. Hasil peningkatan ekoliterasi peserta didik pada siklus ketiga baik dimensi pengetahuan, ketrampilan dan sikap secara keseluruhan mencapai kategori ketuntasan minimal (KKM)

Sustained Acceleration of Over-dense Plasmas by Colliding Laser Pulses

We review recent PIC simulation results which show that double-sided irradiaton of a thin overdense plasma slab by ultra-intense laser pulses from both sides can lead to sustained comoving acceleration of surface electrons to energies much higher than the conventional ponderomotive limit. The acceleration stops only when the electrons drift transversely out of the laser beam. We show results of parameter studies based on this concept and discuss future laser experiments that can be used to test these computer results.Comment: 9 pages 6 figures. AIP Conference Proceedings for 2005 Varenna Conf. on Superstrong Fields in Plasmas (AIP, NY 2006