28,595 research outputs found
Phase Diagram of the 1/2-1/2-1-1 Spin Chain by the Nonlinear Sigma Model
We examine a periodic mixed spin chain with spin magnitudes 1/2 and 1 which
are arrayed as 1/2-1/2-1-1. The three independent parameters are ratios of the
four exchange couplings. We determine phase boundaries in the parameter space
by using the gapless condition which was previously derived by mapping a
general inhomogeneous spin chain to the nonlinear sigma model. We find two
gapless boundaries separating three disordered phases. The features of the
phases are explained in terms of singlet clusters.Comment: 2 pages, 2 Postscript figures, Submitted to Physica B (Proceedings of
the 22nd International Conference on Low temperature Physics
Observations of Ammonia in External Galaxies. II. Maffei 2
The ammonia (J,K) = (1,1), (2,2), (3,3), and (4,4) transitions at 23.7 --
24.1 GHz region were searched for in a nearby galaxy Maffei 2 to study relation
between molecular abundances and physical conditions in galaxies. The (1,1),
(2,2), and (3,3) emission lines were clearly detected. The rotational
temperatures and ortho-to-para abundance ratios obtained are about 30 K and
about 2.6, respectively. The abundance of NH3 relative to H2 in Maffei 2 was
found to be the largest among galaxies where NH3 is already detected, and the
abundance in Maffei 2 is more than an order of magnitude larger than the
already reported upper limit in M82. Hence, we further confirmed the
systematically peculiar molecular abundance in the aspect of formation
mechanisms of molecules already reported in M82.Comment: 6 pages, 2 fugure
Axiomatization of a Basic Logic of Logical Bilattices
A sequential axiomatization is given for the 16-valued logic that has been proposed by Shramko-Wansing (J Philos Logic 34:121–153, 2005) as a candidate for the basic logic of logical bilattices
Two Types of Social Grooming Methods depending on the Trade-off between the Number and Strength of Social Relationships
Humans use various social bonding methods known as social grooming, e.g. face
to face communication, greetings, phone, and social networking sites (SNS). SNS
have drastically decreased time and distance constraints of social grooming. In
this paper, I show that two types of social grooming (elaborate social grooming
and lightweight social grooming) were discovered in a model constructed by
thirteen communication data-sets including face to face, SNS, and Chacma
baboons. The separation of social grooming methods is caused by a difference in
the trade-off between the number and strength of social relationships. The
trade-off of elaborate social grooming is weaker than the trade-off of
lightweight social grooming. On the other hand, the time and effort of
elaborate methods are higher than lightweight methods. Additionally, my model
connects social grooming behaviour and social relationship forms with these
trade-offs. By analyzing the model, I show that individuals tend to use
elaborate social grooming to reinforce a few close relationships (e.g. face to
face and Chacma baboons). In contrast, people tend to use lightweight social
grooming to maintain many weak relationships (e.g. SNS). Humans with
lightweight methods who live in significantly complex societies use various
social grooming to effectively construct social relationships.Comment: Accepted by Royal Society Open Scienc
Spin-gap phase of a quantum spin system on a honeycomb lattice
We study a quantum spin system on a honeycomb lattice, when it includes
frustration and distortion in antiferromagnetic (AF) exchange interactions. We
transform the spin system onto a nonlinear sigma model (NLSM) in a new way
preserving the original spin degrees of freedom. Assisted by a renormalization-
group argument, the NLSM provides a ground-state phase diagram consisting of an
ordered AF phase and a disordered spin-gap phase.
The spin-gap phase extends from a strong frustration regime to a strong
distortion regime, showing that the disordered ground states are essentially
the same in both the regimes. In the spin-half case, the spin-gap phase for the
spin system on a honeycomb lattice is larger than that for the J1-J2 model on a
square lattice.Comment: 4 pages with 2 figures; accepted in Phys. Rev.
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