3,761 research outputs found
D-Terms from Generalized NS-NS Fluxes in Type II
Orientifolds of type II string theory admit a certain set of generalized
NS-NS fluxes, including not only the three-form field strength H, but also
metric and non-geometric fluxes, which are related to H by T-duality. We
describe in general how these fluxes appear as parameters of an effective N=1
supergravity theory in four dimensions, and in particular how certain
generalized NS-NS fluxes can act as charges for R-R axions, leading to D-term
contributions to the effective scalar potential. We illustrate these phenomena
in type IIB with the example of a certain orientifold of T^6/Z_4.Comment: 31+1 pages, uses utarticle.cls; v2: references adde
Dental Pulp Cell Behavior in Biomimetic Environments
There is emerging recognition of the importance of a physiologically relevant in vitro cell culture environment to promote maintenance of stem cells for tissue engineering and regenerative medicine purposes. In vivo, appropriate cellular cues are provided by local tissue extracellular matrix (ECM), and these are not currently recapitulated well in vitro using traditional cultureware. We therefore hypothesized that better replication of the in vivo environment for cell culture and differentiation could be achieved by culturing dental pulp cells with their associated ECM. Primary dental pulp cells were subsequently seeded onto pulp-derived ECM-coated cultureware. While at up to 24 h they exhibited the same level of adherence as those cells seeded on tissue culture–treated surfaces, by 4 d cell numbers and proliferation rates were significantly decreased in cells grown on pulp ECM compared with controls. Analysis of stem cell and differentiation marker transcripts, as well as Oct 3/4 protein distribution, supported the hypothesis that cells cultured on ECM better maintained a stem cell phenotype compared with those cultured on standard tissue culture–treated surfaces. Subsequent differentiation analysis of cells cultured on ECM demonstrated that they exhibited enhanced mineralization, as determined by alizarin red staining and mineralized marker expression. Supplementation of a 3% alginate hydrogel with pulp ECM components and dental pulp cells followed by differentiation induction in mineralization medium resulted in a time-dependent mineral deposition at the periphery of the construct, as demonstrated histologically and using micro–computed tomography analysis, which was reminiscent of tooth structure. In conclusion, data indicate that culture of pulp cells in the presence of ECM better replicates the in vivo environment, maintaining a stem cell phenotype suitable for downstream tissue engineering applications
Variability in H9N2 haemagglutinin receptor-binding preference and the pH of fusion
H9N2 avian influenza viruses are primarily a disease of poultry; however, they occasionally infect humans and are considered a potential pandemic threat. Little work has been performed to assess the intrinsic biochemical properties related to zoonotic potential of H9N2 viruses. The objective of this study, therefore, was to investigate H9N2 haemagglutinins (HAs) using two well-known correlates for human adaption: receptor-binding avidity and pH of fusion. Receptor binding was characterized using bio-layer interferometry to measure virus binding to human and avian-like receptor analogues and the pH of fusion was assayed by syncytium formation in virus-infected cells at different pHs. We characterized contemporary H9N2 viruses of the zoonotic G1 lineage, as well as representative viruses of the zoonotic BJ94 lineage. We found that most contemporary H9N2 viruses show a preference for sulphated avian-like receptor analogues. However, the ‘Eastern’ G1 H9N2 viruses displayed a consistent preference in binding to a human-like receptor analogue. We demonstrate that the presence of leucine at position 226 of the HA receptor-binding site correlated poorly with the ability to bind a human-like sialic acid receptor. H9N2 HAs also display variability in their pH of fusion, ranging between pH 5.4 and 5.85 which is similar to that of the first wave of human H1N1pdm09 viruses but lower than the pH of fusion seen in zoonotic H5N1 and H7N9 viruses. Our results suggest possible molecular mechanisms that may underlie the relatively high prevalence of human zoonotic infection by particular H9N2 virus lineages
Effective descriptions of branes on non-geometric tori
We investigate the low-energy effective description of non-geometric
compactifications constructed by T-dualizing two or three of the directions of
a T^3 with non-vanishing H-flux. Our approach is to introduce a D3-brane in
these geometries and to take an appropriate decoupling limit. In the case of
two T-dualities, we find at low energies a non-commutative T^2 fibered
non-trivially over an S^1. In the UV this theory is still decoupled from
gravity, but is dual to a little string theory with flavor. For the case of
three T-dualities, we do not find a sensible decoupling limit, casting doubt on
this geometry as a low-energy effective notion in critical string theory.
However, by studying a topological toy model in this background, we find a
non-associative geometry similar to one found by Bouwknegt, Hannabuss, and
Mathai.Comment: 22 pages, 4 figures, references adde
Effective actions and N=1 vacuum conditions from SU(3) x SU(3) compactifications
We consider compactifications of type II string theory on general SU(3) x
SU(3) structure backgrounds allowing for a very large set of fluxes, possibly
nongeometric ones. We study the effective 4d low energy theory which is a
gauged N=2 supergravity, and discuss how its data are obtained from the
formalism of the generalized geometry on T+T*. In particular we relate
Hitchin's special Kaehler metrics on the spaces of even and odd pure spinors to
the metric on the supergravity moduli space of internal metric and B-field
fluctuations. We derive the N=1 vacuum conditions from this N=2 effective
action, as well as from its N=1 truncation. We prove a direct correspondence
between these conditions and an integrated version of the pure spinor equations
characterizing the N=1 backgrounds at the ten dimensional level.Comment: 54 pages. v2, v3: minor change
Heterotic-type IIA duality with fluxes
In this paper we study a possible non-perturbative dual of the heterotic
string compactified on K3 x T^2 in the presence of background fluxes. We show
that type IIA string theory compactified on manifolds with SU(3) structure can
account for a subset of the possible heterotic fluxes. This extends our
previous analysis to a case of a non-perturbative duality with fluxes.Comment: 26 pages, minor corrections; version to appear in JHE
Competing magnetic states, disorder, and the magnetic character of Fe3Ga4
The physical properties of metamagnetic FeGa single crystals are
investigated to explore the sensitivity of the magnetic states to temperature,
magnetic field, and sample history. The data reveal a moderate anisotropy in
the magnetization and the metamagnetic critical field along with features in
the specific heat at the magnetic transitions K and K. Both
and are found to be sensitive to the annealing conditions of the
crystals suggesting that disorder affects the competition between the
ferromagnetic (FM) and antiferromagnetic (AFM) states. Resistivity measurements
reveal metallic transport with a sharp anomaly associated with the transition
at . The Hall effect is dominated by the anomalous contribution which
rivals that of magnetic semiconductors in magnitude ( cm at 2 T
and 350 K) and undergoes a change of sign upon cooling into the low temperature
FM state. The temperature and field dependence of the Hall effect indicate that
the magnetism is likely to be highly itinerant in character and that a
significant change in the electronic structure accompanies the magnetic
transitions. We observe a contribution from the topological Hall effect in the
AFM phase suggesting a non-coplanar contribution to the magnetism. Electronic
structure calculations predict an AFM ground state with a wavevector parallel
to the crystallographic -axis preferred over the experimentally measured FM
state by 50 meV per unit cell. However, supercell calculations with a
small density of Fe-antisite defects introduced tend to stabilize the FM over
the AFM state indicating that antisite defects may be the cause of the
sensitivity to sample synthesis conditions.Comment: 13 pages, 14 figures, and 4 supplementary table
Doping of a spin-1 chain: integrable model
An exactly soluble model describing a spin S=1 antiferromagnetic chain doped
with mobile S=1/2 carriers is constructed. In its continuum limit the undoped
state is described by three gapless Majorana fermions composing the SU(2)
triplet. Doping adds to this a scalar charge field and a singlet Majorana
fermion with different velocity. We argue that this mode survives when the
Haldane gap is added.Comment: RevTeX, 6 pages, 3 figures; final version, to appear in PR
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