14,603 research outputs found
Do Athermal Amorphous Solids Exist?
We study the elastic theory of amorphous solids made of particles with finite
range interactions in the thermodynamic limit. For the elastic theory to exist
one requires all the elastic coefficients, linear and nonlinear, to attain a
finite thermodynamic limit. We show that for such systems the existence of
non-affine mechanical responses results in anomalous fluctuations of all the
nonlinear coefficients of the elastic theory. While the shear modulus exists,
the first nonlinear coefficient B_2 has anomalous fluctuations and the second
nonlinear coefficient B_3 and all the higher order coefficients (which are
non-zero by symmetry) diverge in the thermodynamic limit. These results put a
question mark on the existence of elasticity (or solidity) of amorphous solids
at finite strains, even at zero temperature. We discuss the physical meaning of
these results and propose that in these systems elasticity can never be
decoupled from plasticity: the nonlinear response must be very substantially
plastic.Comment: 11 pages, 11 figure
Effects of salinity on the characteristics of biomass and membrane fouling in membrane bioreactors
New Physics Effects From B Meson Decays
In this talk, we point out some of the present and future possible signatures
of physics beyond the Standard Model from B-meson decays, taking R-parity
conserving and violating supersymmetry as illustrative examples.Comment: Talk given at the Sixth Workshop on High Energy Particle
Phenomenology (WHEPP-6), Chennai (Madras), India. Includes 2 epsf figure
Putative spin liquid in the triangle-based iridate BaIrTiO
We report on thermodynamic, magnetization, and muon spin relaxation
measurements of the strong spin-orbit coupled iridate BaIrTiO,
which constitutes a new frustration motif made up a mixture of edge- and
corner-sharing triangles. In spite of strong antiferromagnetic exchange
interaction of the order of 100~K, we find no hint for long-range magnetic
order down to 23 mK. The magnetic specific heat data unveil the -linear and
-squared dependences at low temperatures below 1~K. At the respective
temperatures, the zero-field muon spin relaxation features a persistent spin
dynamics, indicative of unconventional low-energy excitations. A comparison to
the isostructural compound BaRuTiO suggests that a concerted
interplay of compass-like magnetic interactions and frustrated geometry
promotes a dynamically fluctuating state in a triangle-based iridate.Comment: Physical Review B accepte
Collagen and bone morphogenetic protein-2 functionalized hydroxyapatite scaffolds induce osteogenic differentiation in human adipose-derived stem cells
Surface modification is one important way to fabricate successful biocompatible materials in bone tissue engineering. Hydroxyapatite (HAp) materials have received considerable attention as suitable bioceramics for manufacturing osseous implants because of their similarity to bone mineral in terms of chemical composition. In this study, the surface of porous HAp scaffold was modified by collagen treatment and bone morphogenetic protein‐2 (BMP‐2) conjugation. The surface modification did not affect the HAp scaffold's bulk properties. No significant difference in compressive strength was found among different scaffolds, with HAp, collagen modified HAp, and collagen–BMP‐2‐functionalized HAp having compressive strengths of 45.8 ± 3.12, 51.2 ± 4.09, and 50.7 ± 3.98 MPa, respectively. In vitro studies were performed to compare adhesion and osteogenic differentiation between human adipose‐derived stem cells (hADSCs) with modified surfaces and those unmodified HAp surfaces. Collagen or BMP‐2 alone was insufficient and that both collagen and BMP‐2 are necessary to get the desired results. The findings suggest the possibility of using three‐dimensional HAp scaffold treated with gold‐standard collagen coating and highly researched BMP‐2 growth factor as a platform to deliver hADSCs. Results of this study could be used to develop treatment strategy for regenerating completely transected models using more synergistic approaches
Orbitally driven spin-singlet dimerization in =1 LaRuO
Using x-ray absorption spectroscopy at the Ru- edge we reveal that
the Ru ions remain in the =1 spin state across the rare 4d-orbital
ordering transition and spin-gap formation. We find using local spin density
approximation + Hubbard U (LSDA+U) band structure calculations that the crystal
fields in the low temperature phase are not strong enough to stabilize the
=0 state. Instead, we identify a distinct orbital ordering with a
significant anisotropy of the antiferromagnetic exchange couplings. We conclude
that LaRuO appears to be a novel material in which the
orbital physics drives the formation of spin-singlet dimers in a quasi
2-dimensional =1 system.Comment: 5 pages, 4 figures, and 1 tabl
Tailoring a two-dimensional electron gas at the LaAlO3/SrTiO3 (001) interface by epitaxial strain
Recently a metallic state was discovered at the interface between insulating
oxides, most notably LaAlO3 and SrTiO3. Properties of this two-dimensional
electron gas (2DEG) have attracted significant interest due to its potential
applications in nanoelectronics. Control over this carrier density and mobility
of the 2DEG is essential for applications of these novel systems, and may be
achieved by epitaxial strain. However, despite the rich nature of strain
effects on oxide materials properties, such as ferroelectricity, magnetism, and
superconductivity, the relationship between the strain and electrical
properties of the 2DEG at the LaAlO3/SrTiO3 heterointerface remains largely
unexplored. Here, we use different lattice constant single crystal substrates
to produce LaAlO3/SrTiO3 interfaces with controlled levels of biaxial epitaxial
strain. We have found that tensile strained SrTiO3 destroys the conducting
2DEG, while compressively strained SrTiO3 retains the 2DEG, but with a carrier
concentration reduced in comparison to the unstrained LaAlO3/SrTiO3 interface.
We have also found that the critical LaAlO3 overlayer thickness for 2DEG
formation increases with SrTiO3 compressive strain. Our first-principles
calculations suggest that a strain-induced electric polarization in the SrTiO3
layer is responsible for this behavior. It is directed away from the interface
and hence creates a negative polarization charge opposing that of the polar
LaAlO3 layer. This both increases the critical thickness of the LaAlO3 layer,
and reduces carrier concentration above the critical thickness, in agreement
with our experimental results. Our findings suggest that epitaxial strain can
be used to tailor 2DEGs properties of the LaAlO3/SrTiO3 heterointerface
Double polarization hysteresis loop induced by the domain pinning by defect dipoles in HoMnO3 epitaxial thin films
We report on antiferroelectriclike double polarization hysteresis loops in
multiferroic HoMnO3 thin films below the ferroelectric Curie temperature. This
intriguing phenomenon is attributed to the domain pinning by defect dipoles
which were introduced unintentionally during film growth process. Electron
paramagnetic resonance suggests the existence of Fe1+ defects in thin films and
first principles calculations reveal that the defect dipoles would be composed
of oxygen vacancy and Fe1+ defect. We discuss migration of charged point
defects during film growth process and formation of defect dipoles along
ferroelectric polarization direction, based on the site preference of point
defects. Due to a high-temperature low-symmetry structure of HoMnO3, aging is
not required to form the defect dipoles in contrast to other ferroelectrics
(e.g., BaTiO3).Comment: 4 figure
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