7 research outputs found
Critical Exponents for Three-Dimensional Superfluid--Bose-Glass Phase Transition
The critical phenomenon of the zero temperature superfluid--Bose-glass phase
transition for hard-core bosons on a three-dimensional disordered lattice is
studied using a quantum real-space renormalization-group method. The
correlation-length exponent and the dynamic exponent z are computed. The
critical exponent z is found to be 2.5 for compressible states and 1.3 for
incompressible states. The exponent is shown to be insensitive to z as
that in the two-dimensional case, and has value roughly equal to 1.Comment: 11 pages, REVTE
Disordered Boson Systems: A Perturbative Study
A hard-core disordered boson system is mapped onto a quantum spin 1/2
XY-model with transverse random fields. It is then generalized to a system of
spins with an arbitrary magnitude S and studied through a 1/S expansion. The
first order 1/S expansion corresponds to a spin-wave theory. The effect of weak
disorder is studied perturbatively within such a first order 1/S scheme. We
compute the reduction of the speed of sound and the life time of the Bloch
phonons in the regime of weak disorder. Generalizations of the present study to
the strong disordered regime are discussed.Comment: 27 pages, revte
Onset of Superfluidity in 4He Films Adsorbed on Disordered Substrates
We have studied 4He films adsorbed in two porous glasses, aerogel and Vycor,
using high precision torsional oscillator and DC calorimetry techniques. Our
investigation focused on the onset of superfluidity at low temperatures as the
4He coverage is increased. Torsional oscillator measurements of the 4He-aerogel
system were used to determine the superfluid density of films with transition
temperatures as low as 20 mK. Heat capacity measurements of the 4He-Vycor
system probed the excitation spectrum of both non-superfluid and superfluid
films for temperatures down to 10 mK. Both sets of measurements suggest that
the critical coverage for the onset of superfluidity corresponds to a mobility
edge in the chemical potential, so that the onset transition is the bosonic
analog of a superconductor-insulator transition. The superfluid density
measurements, however, are not in agreement with the scaling theory of an onset
transition from a gapless, Bose glass phase to a superfluid. The heat capacity
measurements show that the non-superfluid phase is better characterized as an
insulator with a gap.Comment: 15 pages (RevTex), 21 figures (postscript
Evolution of chloroplast retrograde signaling facilitates green plant adaptation to land
Chloroplast retrograde signaling networks are vital for chloroplast biogenesis, operation, and signaling, including excess light and drought stress signaling. To date, retrograde signaling has been considered in the context of land plant adaptation, but not regarding the origin and evolution of signaling cascades linking chloroplast function to stomatal regulation. We show that key elements of the chloroplast retrograde signaling process, the nucleotide phosphatase (SAL1) and 3'-phosphoadenosine-5'-phosphate (PAP) metabolism, evolved in streptophyte algae-the algal ancestors of land plants. We discover an early evolution of SAL1-PAP chloroplast retrograde signaling in stomatal regulation based on conserved gene and protein structure, function, and enzyme activity and transit peptides of SAL1s in species including flowering plants, the fern Ceratopteris richardii, and the moss Physcomitrella patens Moreover, we demonstrate that PAP regulates stomatal closure via secondary messengers and ion transport in guard cells of these diverse lineages. The origin of stomata facilitated gas exchange in the earliest land plants. Our findings suggest that the conquest of land by plants was enabled by rapid response to drought stress through the deployment of an ancestral SAL1-PAP signaling pathway, intersecting with the core abscisic acid signaling in stomatal guard cells.Chenchen Zhao, Yuanyuan Wang, Kai Xun Chan, D. Blaine Marchant, Peter J. Franks, David Randall, Estee E. Tee, Guang Chen, Sunita Ramesh, Su Yin Phua, Ben Zhang, Adrian Hills, Fei Dai, Dawei Xue, Matthew Gilliham, Steve Tyerman, Eviatar Nevo, Feibo Wu, Guoping Zhang, Gane K.-S. Wong, James H. Leebens-Mack, Michael Melkonian, Michael R. Blatt, Pamela S. Soltis, Douglas E. Soltis, Barry J. Pogson, and Zhong-Hua Che