Conditions for Gravitational Instability in Protoplanetary Disks

Gravitational instability is one of considerable mechanisms to explain the formation of giant planets. We study the gravitational stability for the protoplanetary disks around a protostar. The temperature and Toomre's Q-value are calculated by assuming local equilibrium between viscous heating and radiative cooling (local thermal equilibrium). We assume constant $\alpha$ viscosity and use a cooling function with realistic opacity. Then, we derive the critical surface density $\Sigma_{\rm{c}}$ that is necessary for a disk to become gravitationally unstable as a function of $r$. This critical surface density $\Sigma_{\rm c}$ is strongly affected by the temperature dependence of the opacity. At the radius $r_{\rm c}\sim 20$AU, where ices form, the value of $\Sigma_{\rm c}$ changes discontinuously by one order of magnitude. This $\Sigma_{\rm c}$ is determined only by local thermal process and criterion of gravitational instability. By comparing a given surface density profile to $\Sigma_{\rm c}$, one can discuss the gravitational instability of protoplanetary disks. As an example, we discuss the gravitational instability of two semi-analytic models for protoplanetary disks. One is the steady state accretion disk, which is realized after the viscous evolution. The other is the disk that has the same angular momentum distribution with its parent cloud core, which corresponds to the disk that has just formed. As a result, it is found that the disks tend to become gravitationally unstable for $r\ge r_{\rm c}$ because ices enable the disks to become low temperature. In the region closer to the protostar than $r_{\rm c}$, it is difficult for a typical protoplanetary disk to fragment because of the high temperature and the large Coriolis force. From this result, we conclude that the fragmentation near the central star is possible but difficult.Comment: accepted for publication in PASJ. Draft version with 26 pages, 8 figures, 1 tabl

Hadron-hadron interaction from SU(2) lattice QCD

We evaluate interhadron interactions in two-color lattice QCD from Bethe-Salpeter amplitudes on the Euclidean lattice. The simulations are performed in quenched SU(2) QCD with the plaquette gauge action at $\beta = 2.45$ and the Wilson quark action. We concentrate on S-wave scattering states of two scalar diquarks. Evaluating different flavor combinations with various quark masses, we try to find out the ingredients in hadronic interactions. Between two scalar diquarks ($u C\gamma_5 d$, the lightest baryon in SU(2) system), we observe repulsion in short-range region, even though present quark masses are not very light. We define and evaluate the "quark-exchange part" in the interaction, which is induced by adding quark-exchange diagrams, or equivalently, by introducing Pauli blocking among some of quarks. The repulsive force in short-distance region arises only from the "quark-exchange part", and disappears when quark-exchange diagrams are omitted. We find that the strength of repulsion grows in light quark-mass regime and its quark-mass dependence is similar to or slightly stronger than that of the color-magnetic interaction by one-gluon-exchange (OGE) processes. It is qualitatively consistent with the constituent-quark model picture that a color-magnetic interaction among quarks is the origin of repulsion. We also find a universal long-range attractive force, which enters in any flavor channels of two scalar diquarks and whose interaction range and strength are quark-mass independent. The weak quark-mass dependence of interaction ranges in each component implies that meson-exchange contributions are small and subdominant, and the other contributions, {\it ex.} flavor exchange processes, color-Coulomb or color-magnetic interactions, are considered to be predominant, in the quark-mass range we evaluated.Comment: 14 pages, 20 figure

Cosmological Constraints on Neutrino Injection

We derive general constraints on the relic abundances of a long-lived particle which mainly decays into a neutrino (and something else) at cosmological time scales. Such an exotic particle may show up in various particle-physics models based on physics beyond the standard model. The constraints are obtained from big-bang nucleosynthesis, cosmic microwave background and diffuse neutrino and photon fluxes, depending on the lifetime and the electromagnetic and hadronic branching ratios.Comment: 33 pages, 23 figure

Opening Up Education: The Collective Advancement of Education through Open Technology, Open Content, and Open Knowledge

Given the abundance of open education initiatives that aim to make educational assets freely available online, the time seems ripe to explore the potential of open education to transform the economics and ecology of education. Despite the diversity of tools and resources already available -- from well-packaged course materials to simple games, for students, self-learners, faculty, and educational institutions -- we have yet to take full advantage of shared knowledge about how these are being used, what local innovations are emerging, and how to learn from and build on the experiences of others. Opening Up Education argues that we must develop not only the technical capability but also the intellectual capacity for transforming tacit pedagogical knowledge into commonly usable and visible knowledge: by providing incentives for faculty to use (and contribute to) open education goods, and by looking beyond institutional boundaries to connect a variety of settings and open source entrepreneurs.These essays by leaders in open education describe successes, challenges, and opportunities they have found in a range of open education initiatives. They approach -- from both macro and micro perspectives -- the central question of how open education tools, resources, and knowledge can improve the quality of education. The contributors (from leading foundations, academic institutions, associations, and projects) discuss the strategic underpinnings of their efforts first in terms of technology, then content, and finally knowledge. They also address the impact of their projects, and how close they come to achieving a vision of sustainable, transformative educational opportunities that amounts to much more than pervasive technology.Contributors:Richard Baraniuk, Randy Bass, Trent Batson, Dan Bernstein, John Seely Brown, Barbara Cambridge, Tom Carey, Catherine Casserly, James Dalziel, Bernadine Chuck Fong, Richard Gale, Gerard Hanley, Diane Harley, Mary Huber, Pat Hutchings, Toru Iiyoshi, David Kahle, M. S. Vijay Kumar, Andy Lane, Diana Laurillard, Stuart Lee, Steve Lerman, Marilyn Lombardi, Phil Long, Clifford Lynch, Christopher Mackie, Anne Margulies, Owen McGrath, Flora McMartin, Shigeru Miyagawa, Diana Oblinger, Neeru Paharia, Cheryl Richardson, Marshall Smith, Candace Thille, Edward Walker, and David WileyAbout the Editors:Toru Iiyoshi is Senior Scholar and Director of the Knowledge Media Lab at the Carnegie Foundation.M. S. Vijay Kumar is Senior Associate Dean and Director of the Office of Educational Innovation and Technology at MIT

Peierls instability, periodic Bose-Einstein condensates and density waves in quasi-one-dimensional boson-fermion mixtures of atomic gases

We study the quasi-one-dimensional (Q1D) spin-polarized bose-fermi mixture of atomic gases at zero temperature. Bosonic excitation spectra are calculated in random phase approximation on the ground state with the uniform BEC, and the Peierls instabilities are shown to appear in bosonic collective excitation modes with wave-number $2k_F$ by the coupling between the Bogoliubov-phonon mode of bosonic atoms and the fermion particle-hole excitations. The ground-state properties are calculated in the variational method, and, corresponding to the Peierls instability, the state with a periodic BEC and fermionic density waves with the period $\pi/k_F$ are shown to have a lower energy than the uniform one. We also briefly discuss the Q1D system confined in a harmonic oscillator (HO) potential and derive the Peierls instability condition for it.Comment: 9 pages, 3figure

Weak localization and spin splitting in inversion layers on p-type InAs

We report on the magnetoconductivity of quasi two-dimensional electron systems in inversion layers on p-type InAs single crystals. In low magnetic fields pronounced features of weak localization and antilocalization are observed. They are almost perfectly described by the theory of Iordanskii, Lyanda-Geller and Pikus. This allows us to determine the spin splitting and the Rashba parameter of the ground electric subband as a function of the electron density.Comment: Accepted for publication in Phys. Rev. B, 4 page

Non-Abelian Dual Superconductor Picture for Quark Confinement

We give a theoretical framework for defining and extracting non-Abelian magnetic monopoles in a gauge-invariant way in SU(N) Yang-Mills theory to study quark confinement. Then we give numerical evidences that the non-Abelian magnetic monopole defined in this way gives a dominant contribution to confinement of fundamental quarks in SU(3) Yang-Mills theory, which is in sharp contrast to the SU(2) case in which Abelian magnetic monopoles play the dominant role for quark confinement.Comment: 9 pages, 3 figures (4 ps files); The paper was extensively revised, focusing especially on the lattice par