Electron Spin Resonance in Quasi-One-Dimensional Quantum Antiferromagnets: Relevance of Weak Interchain Interactions

We discuss universal features on the electron spin resonance (ESR) of a temperature-induced Tomonaga-Luttinger liquid phase in a wide class of weakly coupled $S=1/2$ antiferromagnetic spin chains such as spin ladders, spin tubes and three-dimensionally coupled spin chains. We show that the ESR linewidth of various coupled chains increases with lowering temperature while the linewidth of a single spin chain is typically proportional to temperature. This broadening with lowering temperature is attributed to anisotropic interchain interactions and has been indeed observed in several kinds of three-dimensional (3D) magnets of weakly coupled spin chains above the 3D ordering temperature. We demonstrate that our theory can account for anomalous behaviors of the linewidths in an $S=1/2$ four-leg spin tube compound Cu$_2$Cl$_4 \cdot$H$_8$C$_4$SO$_2$ (abbreviated to Sul-Cu$_2$Cl$_4$) and a three-dimensionally coupled $S=1/2$ spin chain compound CuCl$_2\cdot 2$NC$_5$H$_5$

Warm Extended Dense Gas Lurking At The Heart Of A Cold Collapsing Dense Core

In order to investigate when and how the birth of a protostellar core occurs, we made survey observations of four well-studied dense cores in the Taurus molecular cloud using CO transitions in submillimeter bands. We report here the detection of unexpectedly warm (~ 30 - 70 K), extended (radius of ~ 2400 AU), dense (a few times 10^{5} cm^{-3}) gas at the heart of one of the dense cores, L1521F (MC27), within the cold dynamically collapsing components. We argue that the detected warm, extended, dense gas may originate from shock regions caused by collisions between the dynamically collapsing components and outflowing/rotating components within the dense core. We propose a new stage of star formation, "warm-in-cold core stage (WICCS)", i.e., the cold collapsing envelope encases the warm extended dense gas at the center due to the formation of a protostellar core. WICCS would constitutes a missing link in evolution between a cold quiescent starless core and a young protostar in class 0 stage that has a large-scale bipolar outflow.Comment: Accepted for publication in The Astrophysical Journal Letter

Boundary Resonances in S = 1/2 Antiferromagnetic Chains under a Staggered Field

We develop a boundary field theory approach to electron spin resonance in open $S=1/2$ Heisenberg antiferromagnetic chains with an effective staggered field. In terms of the sine Gordon effective field theory with boundaries,we point out the existence of boundary bound states of elementary excitations, and modification of the selection rules at the boundary. We argue that several "unknown modes" found in electron spin resonance experiments on KCuGaF$_6$ [I. Umegaki et al., Phys. Rev. B 79, 184401 (2009)] and Cu-PM [S. A. Zvyagin et al., Phys. Rev. Lett. 93, 027201 (2004)] can be understood as boundary resonances introduced by these effects

A Brief Note on Linearized, Unsteady, Supercavitating Flows

Three different models for the unsteady fluctuations of a slender cavity in the limit of small reduced frequency are compard with the results of quasi-steady calculations. Tullin's kinematically closed model in unsteady flow in soon to tend smoothly to a limiting quasi-steady motion having the same value for the compliance of the cavitating flow, unlike other models that have been used in the past

A Note on the Calculation of Supercavitating Hydrfoils with Rounded Noses

Practical supercavitating hydrfoils have rounded leading edges for mechanical strength. The prediction of pressures near the leading edge of such hydrofoils by linearized free streamline theory fails because singularities are usually required there by the theory. A simple method based on singular perturbations of avoiding these difficulties for hydrofoils which have parabolic noses but an arbitrary profile downstream of the leading edge is presented. The results of such a computation on a hydrofoil with a parabolic profile and with fixed cavity separation near the leading edge radius are shown and are compared with an exact free-streamline theory. The agreement is excellent