7,224 research outputs found
Cohomological non-rigidity of generalized real Bott manifolds of height 2
We investigate when two generalized real Bott manifolds of height 2 have
isomorphic cohomology rings with Z/2 coefficients and also when they are
diffeomorphic. It turns out that cohomology rings with Z/2 coefficients do not
distinguish those manifolds up to diffeomorphism in general. This gives a
counterexample to the cohomological rigidity problem for real toric manifolds
posed in \cite{ka-ma08}. We also prove that generalized real Bott manifolds of
height 2 are diffeomorphic if they are homotopy equivalent
Voter model with non-Poissonian interevent intervals
Recent analysis of social communications among humans has revealed that the
interval between interactions for a pair of individuals and for an individual
often follows a long-tail distribution. We investigate the effect of such a
non-Poissonian nature of human behavior on dynamics of opinion formation. We
use a variant of the voter model and numerically compare the time to consensus
of all the voters with different distributions of interevent intervals and
different networks. Compared with the exponential distribution of interevent
intervals (i.e., the standard voter model), the power-law distribution of
interevent intervals slows down consensus on the ring. This is because of the
memory effect; in the power-law case, the expected time until the next update
event on a link is large if the link has not had an update event for a long
time. On the complete graph, the consensus time in the power-law case is close
to that in the exponential case. Regular graphs bridge these two results such
that the slowing down of the consensus in the power-law case as compared to the
exponential case is less pronounced as the degree increases.Comment: 18 pages, 8 figure
Real Forms of the Oscillator Quantum Algebra and its Representations
We consider the conditions under which the -oscillator algebra becomes a
Hopf -algebra. In particular, we show that there are at least two real forms
associated with the algebra. Furthermore, through the representations, it is
shown that they are related to with different
conjugations.Comment: 10 pages, Ams-Tex, To be published in Letters in Mathematical physic
A likely detection of a local interplanetary dust cloud passing near the Earth in the AKARI mid-infrared all-sky map
Context. We are creating the AKARI mid-infrared all-sky diffuse maps. Through
a foreground removal of the zodiacal emission, we serendipitously detected a
bright residual component whose angular size is about 50 x 20 deg. at a
wavelength of 9 micron. Aims. We investigate the origin and the physical
properties of the residual component. Methods. We measured the surface
brightness of the residual component in the AKARI mid-infrared all-sky maps.
Results. The residual component was significantly detected only in 2007
January, even though the same region was observed in 2006 July and 2007 July,
which shows that it is not due to the Galactic emission. We suggest that this
may be a small cloud passing near the Earth. By comparing the observed
intensity ratio of I_9um/I_18um with the expected intensity ratio assuming
thermal equilibrium of dust grains at 1 AU for various dust compositions and
sizes, we find that dust grains in the moving cloud are likely to be much
smaller than typical grains that produce the bulk of the zodiacal light.
Conclusions. Considering the observed date and position, it is likely that it
originates in the solar coronal mass ejection (CME) which took place on 2007
January 25.Comment: 5 pages, 4 figures, accepted by Astronomy and Astrophysic
Thermal conductivity of Mg-doped CuGeO_3 at very low temperatures: Heat conduction by antiferromagnetic magnons
Thermal conductivity \kappa is measured at very low temperatures down to 0.28
K for pure and Mg-doped CuGeO_3 single crystals. The doped samples carry larger
amount of heat than the pure sample at the lowest temperature. This is because
antiferromagnetic magnons appear in the doped samples and are responsible for
the additional heat conductivity, while \kappa of the pure sample represents
phonon conductivity at such low temperatures. The maximum energy of the magnon
is estimated to be much lower than the spin-Peierls-gap energy. The result
presents the first example that \kappa at very low temperatures probes the
magnon transport in disorder-induced antiferromagnetic phase of spin-gap
systems
Cultural value orientations and work–family conflict : The mediating role of work and family demands
The current paper examined the associations between Schwartz's (2006) cultural value orientations and individuals' work-family conflict. Results of multilevel analyses across 19 European countries (N = 16,145) showed that the cultural value orientation of embeddedness vs. autonomy, hierarchy vs. egalitarianism, and mastery vs. harmony were related to individuals' higher levels of family-to-work conflict (FWC). Embeddedness vs. autonomy was positively related with work-to-family conflict (WFC). These results hold after controlling for both individual-level predictors of WFC and the GLOBE cultural values of in-group collectivism, gender egalitarianism, performance orientation, and power distance. Whereas gender egalitarianism was negatively related to WFC, in-group collectivism was not related to any form of work-family conflict. Also, performance orientation (PO) related to lower FWC and WFC. Further, our analysis yielded significant indirect effects of embeddedness vs. autonomy and hierarchy vs. egalitarianism on FWC via family demands (household size) and on WFC via working demands (total working hours). Implications for theory and practice are discussed.Peer reviewe
Magnetic versus nonmagnetic doping effects on the magnetic ordering in the Haldane chain compound PbNi2V2O8
A study of an impurity driven phase-transition into a magnetically ordered
state in the spin-liquid Haldane chain compound PbNi2V2O8 is presented. Both,
macroscopic magnetization as well as 51V nuclear magnetic resonance (NMR)
measurements reveal that the spin nature of dopants has a crucial role in
determining the stability of the induced long-range magnetic order. In the case
of nonmagnetic (Mg2+) doping on Ni2+ spin sites (S=1) a metamagnetic transition
is observed in relatively low magnetic fields. On the other hand, the magnetic
order in magnetically (Co2+) doped compounds survives at much higher magnetic
fields and temperatures, which is attributed to a significant anisotropic
impurity-host magnetic interaction. The NMR measurements confirm the predicted
staggered nature of impurity-liberated spin degrees of freedom, which are
responsible for the magnetic ordering. In addition, differences in the
broadening of the NMR spectra and the increase of nuclear spin-lattice
relaxation in doped samples, indicate a diverse nature of electron spin
correlations in magnetically and nonmagnetically doped samples, which begin
developing at rather high temperatures with respect to the antiferromagnetic
phase transition.Comment: 10 pages, 7 figure
Fast Collisionless Reconnection Condition and Self-Organization of Solar Coronal Heating
I propose that solar coronal heating is a self-regulating process that keeps
the coronal plasma roughly marginally collisionless. The self-regulating
mechanism is based on the interplay of two effects. First, plasma density
controls coronal energy release via the transition between the slow collisional
Sweet-Parker regime and the fast collisionless reconnection regime. This
transition takes place when the Sweet--Parker layer becomes thinner than the
characteristic collisionless reconnection scale. I present a simple criterion
for this transition in terms of the upstream plasma density (n_e), the
reconnecting (B_0) and guide (B_z) magnetic field components, and the global
length (L) of the reconnection layer: L < 6.10^9 cm [n_e/(10^{10}/cm^3)]^(-3)
(B_0/30G)^4 (B_0/B_z)^2. Next, coronal energy release by reconnection raises
the ambient plasma density via chromospheric evaporation and this, in turn,
temporarily inhibits subsequent reconnection involving the newly-reconnected
loops. Over time, however, radiative cooling gradually lowers the density again
below the critical value and fast reconnection again becomes possible. As a
result, the density is highly inhomogeneous and intermittent but,
statistically, does not deviate strongly from the critical value which is
comparable with the observed coronal density. Thus, in the long run, the
coronal heating process can be represented by repeating cycles that consist of
fast reconnection events (i.e., nanoflares), followed by rapid evaporation
episodes, followed by relatively long periods (1-hour) during which magnetic
stresses build up and simultaneously the plasma cools down and precipitates.Comment: 17 pages, no figures; accepted to the Astrophysical Journal; replaced
to match the accepted versio
Study of impurities in spin-Peierls systems including lattice relaxation
The effects of magnetic and non-magnetic impurities in spin-Peierls systems
are investigated allowing for lattice relaxation and quantum fluctuations. We
show that, in isolated chains, strong bonds form next to impurities, leading to
the appearance of magneto-elastic solitons. Generically, these solitonic
excitations do not bind to impurities. However, interchain elastic coupling
produces an attractive potential at the impurity site which can lead to the
formation of bound states. In addition, we predict that small enough chain
segments do not carry magnetic moments at the ends
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