16,513 research outputs found
Stress induced polarization switching and coupled hysteretic dynamics in ferroelectric materials
The dynamic responses of ferroelectric materials upon external mechanical and electrical stimulations are inherently nonlinear and coupled. In the current paper, a macroscopic differential model is constructed for the coupled hysteretic dynamics via modeling the orientation switching induced in the materials. A non-convex potential energy is constructed with both mechanic and electric field contributions. The governing equations are formulated as nonlinear ordinary differential equations by employing the Euler-Lagrange equation, and can be easily recast into a state space form. Hysteresis loops associated with stress induced polarization switching and butterfly-shaped behavior in ferroelectric materials are also successfully captured. The effects of mechanical loadings on the electrically induced switching are numerically investigated, as well as the mechanically-induced switching with various bias electric fields
Nutrition Mission--A Multimedia Educational Tool for Youth Grades 4 - 6
Nutrition Mission is a multimedia educational CD-ROM with an accompanying Web site designed to teach 4th - 6th grade students about making healthy food and activity choices. The CD-ROM incorporates a rich learning environment using graphics, audio, video, and interactive animations to excite students and make learning about nutrition fun. The CD includes lessons about the food guide pyramid, food labels, nutrient density, fast foods, snacking, physical activity, and food science experiments. Preliminary data indicates that the majority of youth acquire knowledge and skills related to foods, nutrition, and physical activity
Spores of Clostridium engineered for clinical efficacy and safety cause regression and cure of tumors in vivo.
Spores of some species of the strictly anaerobic bacteria Clostridium naturally target and partially lyse the hypoxic cores of tumors, which tend to be refractory to conventional therapies. The anti-tumor effect can be augmented by engineering strains to convert a non-toxic prodrug into a cytotoxic drug specifically at the tumor site by expressing a prodrug-converting enzyme (PCE). Safe doses of the favored prodrug CB1954 lead to peak concentrations of 6.3 μM in patient sera, but at these concentration(s) known nitroreductase (NTR) PCEs for this prodrug show low activity. Furthermore, efficacious and safe Clostridium strains that stably express a PCE have not been reported. Here we identify a novel nitroreductase from Neisseria meningitidis, NmeNTR, which is able to activate CB1954 at clinically-achievable serum concentrations. An NmeNTR expression cassette, which does not contain an antibiotic resistance marker, was stably localized to the chromosome of Clostridium sporogenes using a new integration method, and the strain was disabled for safety and containment by making it a uracil auxotroph. The efficacy of Clostridium-Directed Enzyme Prodrug Therapy (CDEPT) using this system was demonstrated in a mouse xenograft model of human colon carcinoma. Substantial tumor suppression was achieved, and several animals were cured. These encouraging data suggest that the novel enzyme and strain engineering approach represent a promising platform for the clinical development of CDEPT
Evolutions of helical edge states in disordered HgTe/CdTe quantum wells
We study the evolutions of the nonmagnetic disorder-induced edge states with
the disorder strength in the HgTe/CdTe quantum wells. From the supercell band
structures and wave-functions, it is clearly shown that the conducting helical
edge states, which are responsible for the reported quantized conductance
plateau, appear above a critical disorder strength after a gap-closing phase
transition. These edge states are then found to decline with the increase of
disorder strength in a stepwise pattern due to the finite-width effect, where
the opposite edges couple with each other through the localized states in the
bulk. This is in sharp contrast with the localization of the edge states
themselves if magnetic disorders are doped which breaks the time-reversal
symmetry. The size-independent boundary of the topological phase is obtained by
scaling analysis, and an Anderson transition to an Anderson insulator at even
stronger disorder is identified, in-between of which, a metallic phase is found
to separate the two topologically distinct phases.Comment: 7 pages, 5 figure
Orbital Diamagnetism of Weak-doped Bilayer Graphene in Magnetic Field
We investigate the orbital diamagnetism of a weak-doped bilayer graphene
(BLG) in spatially smoothly varying magnetic field and obtain the general
analytic expression of the orbital susceptibility of BLG, with finite wave
number and Fermi energy, at zero temperature. We find that the magnetic field
screening factor of BLG is dependent with the wave number, which results in a
more complicated screening behavior compared with that of monolayer graphene
(MLG). We also study the induced magnetization, electric current in BLG, under
nonuniform magnetic field, and find that they are qualitatively different from
that in MLG and two-dimensional electron gas (2DEG). However, similar to the
MLG, the magnetic object placed above BLG is repelled by a diamagnetic force
from BLG, approximately equivalent to a force produced by its mirror image on
the other side of BLG with a reduced amplitude dependent with the typical
length of the systems. BLG shows crossover behaviors in the responses to the
external magnetic field as the intermediate between MLG and 2DEG.Comment: 8 pages, 2 figure
Quickly routing searches without having to move content
Abstract. A great deal of work has been done to improve peer-to-peer routing by strategically moving or replicating content. However, there are many applications for which a peer-to-peer architecture might be appropriate, but in which content movement is not feasible. We argue that even in such applications, progress can be made in developing techniques that ensure efficient searches. We present several such techniques. First, we show that organizing the network into a square-root topology, where peer degrees are proportional to the square root of the popularity of their content, provides much better performance than power-law networks. Second, we present routing optimizations based on the amount of content stored at peers, and tracking the “best ” peers, that can further improve performance. These and other techniques can make searches efficient, even when content movement or replication is not feasible.
Electron Accumulation and Emergent Magnetism in LaMnO3/SrTiO3 Heterostructures
Emergent phenomena at polar-nonpolar oxide interfaces have been studied
intensely in pursuit of next-generation oxide electronics and spintronics. Here
we report the disentanglement of critical thicknesses for electron
reconstruction and the emergence of ferromagnetism in polar-mismatched
LaMnO3/SrTiO3 (001) heterostructures. Using a combination of element-specific
X-ray absorption spectroscopy and dichroism, and first-principles calculations,
interfacial electron accumulation and ferromagnetism have been observed within
the polar, antiferromagnetic insulator LaMnO3. Our results show that the
critical thickness for the onset of electron accumulation is as thin as 2 unit
cells (UC), significantly thinner than the observed critical thickness for
ferromagnetism of 5 UC. The absence of ferromagnetism below 5 UC is likely
induced by electron over-accumulation. In turn, by controlling the doping of
the LaMnO3, we are able to neutralize the excessive electrons from the polar
mismatch in ultrathin LaMnO3 films and thus enable ferromagnetism in films as
thin as 3 UC, extending the limits of our ability to synthesize and tailor
emergent phenomena at interfaces and demonstrating manipulation of the
electronic and magnetic structures of materials at the shortest length scales.Comment: Accepted by Phys. Rev. Let
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