Strings in pp-wave background and background B-field from membrane and its symplectic quantization

The symplectic quantization technique is applied to open free membrane and strings in pp-wave background and background gauge field obtained by compactifying the open membrane in the presence of a background anti-symmetric 3--form field. In both cases, first the Poisson brackets among the Fourier modes are obtained and then the Poisson brackets among the membrane(string) coordinates are computed. The full noncommutative phase-space structure is reproduced in case of strings in pp-wave background and background gauge field. We feel that this method of obtaining the Poisson algebra is more elegant than previous approaches discussed in the literature.Comment: Accepted in Physics Letters B, some minor corrections mad

The origin of noncommutativity?

Consistent boundary Poisson structures for open string theory coupled to background $B$-field are considered using the new approach proposed in hep-th/0111005. It is found that there are infinitely many consistent Poisson structures, each leads to a consistent canonical quantization of open string in the presence of background $B$-field. Consequently, whether the $D$-branes to which the open string end points are attached is noncommutative or not depends on the choice of a particular Poisson structure.Comment: Revtex4, published versio

Korean Immigrants’ Perceptions of Library Services and Library Multicultural Programs for Asian Communities Before and During COVID-19

This study explored 141 Korean immigrant parents’ use of local libraries to enhance their families’ social and cultural capital and adjust to the host country. We searched resources in Korean, and multicultural programs planned for the public and immigrants, Asian immigrants in particular, at two libraries before and during COVID-19. Parents reported dissatisfaction with library services because of language barriers (38%) and the lack of Korean resources (38%) and cultural programs (25%). Except for 18 books and 24 e-resources, no library resources in Korean were published after 2008. Before COVID-19, one multicultural program was offered for children. At Branches B and C, the number of adult programs related to Asian culture decreased to 0% from 6% and increased to 3% from 0%, respectively, during COVID-19, when hate crimes against Asians increased by 77%. The respondents’ concerns about the lack of programs supporting their adjustment and fostering multicultural dialogue were validated

Jamming transition in a highly dense granular system under vertical vibration

The dynamics of the jamming transition in a three-dimensional granular system under vertical vibration is studied using diffusing-wave spectroscopy. When the maximum acceleration of the external vibration is large, the granular system behaves like a fluid, with the dynamic correlation function G(t) relaxing rapidly. As the acceleration of vibration approaches the gravitational acceleration g, the relaxation of G(t) slows down dramatically, and eventually stops. Thus the system undergoes a phase transition and behaves like a solid. Near the transition point, we find that the structural relaxation shows a stretched exponential behavior. This behavior is analogous to the behavior of supercooled liquids close to the glass transition.Comment: 5 pages, 5 figures, accepted by Phys. Rev.

Competition graphs of degree bounded digraphs

If each vertex of an acyclic digraph has indegree at most $i$ and outdegree at most $j$, then it is called an $(i,j)$ digraph, which was introduced by Hefner~{\it et al.}~(1991). Whereas Hefner~{\it et al.} characterized $(i,j)$ digraphs whose competition graphs are interval, characterizing the competition graphs of $(i,j)$ digraphs is not an easy task. In this paper, we introduce the concept of $\langle i,j \rangle$ digraphs, which relax the acyclicity condition of $(i,j)$ digraphs, and study their competition graphs. By doing so, we obtain quite meaningful results. Firstly, we give a necessary and sufficient condition for a loopless graph being an $\langle i,j \rangle$ competition graph for some positive integers $i$ and $j$. Then we study on an $\langle i,j \rangle$ competition graph being chordal and present a forbidden subdigraph characterization. Finally, we study the family of $\langle i,j \rangle$ competition graphs, denoted by $\mathcal{G}_{\langle i,j \rangle}$, and identify the set containment relation on $\{\mathcal{G}_{\langle i,j \rangle}\colon\, i,j \ge 1\}$