10,148 research outputs found
Theoretical prediction on the structural, electronic, and polarization properties of tetragonal Bi₂ZnTiO₆
Author name used in this publication: C. H. Woo2008-2009 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe
Interaction between concentric Tubes in DWCNTs
A detailed investigation of the Raman response of the inner tube radial
breathing modes (RBMs) in double-wall carbon nanotubes is reported. It revealed
that the number of observed RBMs is two to three times larger than the number
of possible tubes in the studied frequency range. This unexpected increase in
Raman lines is attributed to a splitting of the inner tube response. It is
shown to originate from the possibility that one type of inner tube may form in
different types of outer tubes and the fact that the inner tube RBM frequency
depends on the diameter of the enclosing tube. Finally, a comparison of the
inner tube RBMs and the RBMs of tubes in bundles gave clear evidence that the
interaction in a bundle is stronger than the interaction between inner and
outer tubes.Comment: 6 pages, 7 figures, submitted to Eur. Phys. J.
Effect of bilayer coupling on tunneling conductance of double-layer high T_c cuprates
Physical effects of bilayer coupling on the tunneling spectroscopy of high
T cuprates are investigated. The bilayer coupling separates the bonding
and antibonding bands and leads to a splitting of the coherence peaks in the
tunneling differential conductance. However, the coherence peak of the bonding
band is strongly suppressed and broadened by the particle-hole asymmetry in the
density of states and finite quasiparticle life-time, and is difficult to
resolve by experiments. This gives a qualitative account why the bilayer
splitting of the coherence peaks was not clearly observed in tunneling
measurements of double-layer high-T oxides.Comment: 4 pages, 3 figures, to be published in PR
Raman study of carrier-overdoping effects on the gap in high-Tc superconducting cuprates
Raman scattering in the heavily overdoped (Y,Ca)Ba_2Cu_3O_{7-d} (T_c = 65 K)
and Bi_2Sr_2CaCu_2O_{8+d} (T_c = 55 K) crystals has been investigated. For the
both crystals, the electronic pair-breaking peaks in the A_{1g} and B_{1g}
polarizations were largely shifted to the low energies close to a half of
2Delta_0, Delta_0 being the maximum gap. It strongly suggests s-wave mixing
into the d-wave superconducting order parameter and the consequent
manifestation of the Coulomb screening effect in the B_{1g}-channel. Gradual
mixing of s-wave component with overdoping is not due to the change of crystal
structure symmetry but a generic feature in all high-T_c superconducting
cuprates.Comment: 5 pages, 4 figures, to be published in Phys. Rev. B, Rapid
communicaito
Effects of Cyclin Dependent Kinase 9 inhibition on zebrafish larvae
CDK9 is a known regulator of cellular transcription, growth and proliferation. Small molecule inhibitors are currently being developed and assessed in clinical trials as anti-cancer drugs. The zebrafish embryo provides an ideal model to explore the effects of CDK9 inhibition in-vivo. This has not been adequately explored previously at the level of a whole organism. We have compared and contrasted the effects of pharmacological and molecular inhibition of CDK9 on somatic growth, apoptosis and cellular proliferation in zebrafish larvae between 0 to 120 hours post fertilisation (hpf) using flavopiridol, a selective CDK9 antagonist, and CDK9-targeting morpholino. We demonstrate that the inhibition of CDK9 diminishes cellular proliferation and increases apoptosis. Subsequently, it affects somatic growth and development of a number of key embryonic structures including the brain, heart, eye and blood vessels. For the first time, we have localized CDK9 at a subcellular level in whole-mounted larvae. This works shows, at a high-throughput level, that CDK9 clearly plays a fundamental role in early cellular growth and proliferation
Selective targeting of activating and inhibitory Smads by distinct WWP2 ubiquitin ligase isoforms differentially modulates TGFβ signalling and EMT
Ubiquitin-dependent mechanisms have emerged as essential regulatory elements controlling cellular levels of Smads and TGFß-dependent biological outputs such as epithelial–mesenchymal transition (EMT). In this study, we identify a HECT E3 ubiquitin ligase known as WWP2 (Full-length WWP2-FL), together with two WWP2 isoforms (N-terminal, WWP2-N; C-terminal WWP2-C), as novel Smad-binding partners. We show that WWP2-FL interacts exclusively with Smad2, Smad3 and Smad7 in the TGFß pathway. Interestingly, the WWP2-N isoform interacts with Smad2 and Smad3, whereas WWP2-C interacts only with Smad7. In addition, WWP2-FL and WWP2-C have a preference for Smad7 based on protein turnover and ubiquitination studies. Unexpectedly, we also find that WWP2-N, which lacks the HECT ubiquitin ligase domain, can also interact with WWP2-FL in a TGFß-regulated manner and activate endogenous WWP2 ubiquitin ligase activity causing degradation of unstimulated Smad2 and Smad3. Consistent with our protein interaction data, overexpression and knockdown approaches reveal that WWP2 isoforms differentially modulate TGFß-dependent transcription and EMT. Finally, we show that selective disruption of WWP2 interactions with inhibitory Smad7 can stabilise Smad7 protein levels and prevent TGFß-induced EMT. Collectively, our data suggest that WWP2-N can stimulate WWP2-FL leading to increased activity against unstimulated Smad2 and Smad3, and that Smad7 is a preferred substrate for WWP2-FL and WWP2-C following prolonged TGFß stimulation. Significantly, this is the first report of an interdependent biological role for distinct HECT E3 ubiquitin ligase isoforms, and highlights an entirely novel regulatory paradigm that selectively limits the level of inhibitory and activating Smads
A thermodynamic unification of jamming
Fragile materials ranging from sand to fire-retardant to toothpaste are able
to exhibit both solid and fluid-like properties across the jamming transition.
Unlike ordinary fusion, systems of grains, foams and colloids jam and cease to
flow under conditions that still remain unknown. Here we quantify jamming via a
thermodynamic approach by accounting for the structural ageing and the
shear-induced compressibility of dry sand. Specifically, the jamming threshold
is defined using a non-thermal temperature that measures the 'fluffiness' of a
granular mixture. The thermodynamic model, casted in terms of pressure,
temperature and free-volume, also successfully predicts the entropic data of
five molecular glasses. Notably, the predicted configurational entropy avoids
the Kauzmann paradox entirely. Without any free parameters, the proposed
equation-of-state also governs the mechanism of shear-banding and the
associated features of shear-softening and thickness-invariance.Comment: 16 pgs double spaced. 4 figure
Electronic structure of the trilayer cuprate superconductor BiSrCaCuO
The low-energy electronic structure of the trilayer cuprate superconductor
BiSrCaCuO near optimal doping is investigated by
angle-resolved photoemission spectroscopy. The normal state quasiparticle
dispersion and Fermi surface, and the superconducting d-wave gap and coherence
peak are observed and compared with those of single and bilayer systems. We
find that both the superconducting gap magnitude and the relative
coherence-peak intensity scale linearly with for various optimally doped
materials. This suggests that the higher of the trilayer system should be
attributed to parameters that simultaneously enhance phase stiffness and
pairing strength.Comment: 5 pages, 5 figre
Universality in the Screening Cloud of Dislocations Surrounding a Disclination
A detailed analytical and numerical analysis for the dislocation cloud
surrounding a disclination is presented. The analytical results show that the
combined system behaves as a single disclination with an effective fractional
charge which can be computed from the properties of the grain boundaries
forming the dislocation cloud. Expressions are also given when the crystal is
subjected to an external two-dimensional pressure. The analytical results are
generalized to a scaling form for the energy which up to core energies is given
by the Young modulus of the crystal times a universal function. The accuracy of
the universality hypothesis is numerically checked to high accuracy. The
numerical approach, based on a generalization from previous work by S. Seung
and D.R. Nelson ({\em Phys. Rev A 38:1005 (1988)}), is interesting on its own
and allows to compute the energy for an {\em arbitrary} distribution of
defects, on an {\em arbitrary geometry} with an arbitrary elastic {\em energy}
with very minor additional computational effort. Some implications for recent
experimental, computational and theoretical work are also discussed.Comment: 35 pages, 21 eps file
Precise Neutron Magnetic Form Factors
Precise data on the neutron magnetic form factor G_{mn} have been obtained
with measurements of the ratio of cross sections of D(e,e'n) and D(e,e'p) up to
momentum transfers of Q^2 = 0.9 (GeV/c)^2. Data with typical uncertainties of
1.5% are presented. These data allow for the first time to extract a precise
value of the magnetic radius of the neutron.Comment: 10 pages, 2 figures, submitted to Physics Letters
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