5,037 research outputs found
Static friction on the fly: velocity depinning transitions of lubricants in motion
The dragging velocity of a model solid lubricant confined between sliding
periodic substrates exhibits a phase transition between two regimes,
respectively with quantized and with continuous lubricant center-of-mass
velocity. The transition, occurring for increasing external driving force F_ext
acting on the lubricant, displays a large hysteresis, and has the features of
depinning transitions in static friction, only taking place on the fly.
Although different in nature, this phenomenon appears isomorphic to a static
Aubry depinning transition in a Frenkel-Kontorova model, the role of particles
now taken by the moving kinks of the lubricant-substrate interface. We suggest
a possible realization in 2D optical lattice experiments.Comment: 5 pages, 4 figures, revtex, in print in Phys. Rev. Let
Quantum Stochastic Walk models for quantum state discrimination
Quantum Stochastic Walks (QSW) allow for a generalization of both quantum and
classical random walks by describing the dynamic evolution of an open quantum
system on a network, with nodes corresponding to quantum states of a fixed
basis. We consider the problem of quantum state discrimination on such a
system, and we solve it by optimizing the network topology weights. Finally, we
test it on different quantum network topologies and compare it with optimal
theoretical bounds
METCAN verification status
The status of the verification (comparisons of predictions with experimental data) of the METCAN (METal-matrix Composite ANalyzer) code at high temperature is summarized. Verification includes select available room temperature of W/Cu composites for different fiber volume ratios. It also includes high temperature properties for thermal expansion, moduli, strength and stress/strain behavior for SiC/Ti composites. Furthermore it includes limited cases for thermal fatigue strength degradation. The verification results summarized herein indicate that METCAN simulates complex high temperature metal matrix composite bahavior with reasonable accuracy and that it can be used with confidence to identify in-situ nonlinear behavior that influences composite properties
Direct evidence of electron spin polarization from an organic-based magnet: [FeII(TCNE)(NCMe)2][FeIII Cl4]
Journal ArticleDirect evidence of an organic-based magnet with a finite electron spin polarization at the Fermi edge is shown from spin-resolved photoemission of the [FeII(TCNE)(NCMe)2][FeIIICl4] organic-based magnet. The 23% majority-based spin polarization at the Fermi edge is observed at 80 K in zero applied field. Ab initio calculations at the density functional level (O K) are in accord with a semiconductor with 100% majority-based electron spin polarization at the band edges, commensurate with our experimental results and model prediction for a half-semiconductor. Organic-based magnets may prove to be important for realizing polarized electron injection into semiconductors for magnetoelectronic applications
Sustainable Materials Containing Biochar Particles: A Review
The conversion of polymer waste, food waste, and biomasses through thermochemical decomposition to fuels, syngas, and solid phase, named char/biochar particles, gives a second life to these waste materials, and this process has been widely investigated in the last two decades. The main thermochemical decomposition processes that have been explored are slow, fast, and flash pyrolysis, torrefaction, gasification, and hydrothermal liquefaction, which produce char/biochar particles that differ in their chemical and physical properties, i.e., their carbon-content, CHNOS compositions, porosity, and adsorption ability. Currently, the main proposed applications of the char/biochar particles are in the agricultural sector as fertilizers for soil retirement and water treatment, as well as use as high adsorption particles. Therefore, according to recently published papers, char/biochar particles could be successfully considered for the formulation of sustainable polymer and biopolymer-based composites. Additionally, in the last decade, these particles have also been proposed as suitable fillers for asphalts. Based on these findings, the current review gives a critical overview that highlights the advantages in using these novel particles as suitable additives and fillers, and at the same time, it shows some drawbacks in their use. Adding char/biochar particles in polymers and biopolymers significantly increases their elastic modulus, tensile strength, and flame and oxygen resistance, although composite ductility is significantly penalized. Unfortunately, due to the dark color of the char/biochar particles, all composites show brown-black coloration, and this issue limits the applications
Gapped Surface States in a Strong-Topological-Semimetal
A three-dimensional strong-topological-insulator or -semimetal hosts
topological surface states which are often said to be gapless so long as
time-reversal symmetry is preserved. This narrative can be mistaken when
surface state degeneracies occur away from time-reversal-invariant momenta. The
mirror-invariance of the system then becomes essential in protecting the
existence of a surface Fermi surface. Here we show that such a case exists in
the strong-topological-semimetal BiSe. Angle-resolved photoemission
spectroscopy and \textit{ab initio} calculations reveal partial gapping of
surface bands on the BiSe-termination of BiSe(111), where an 85
meV gap along closes to zero toward the mirror-invariant
azimuth. The gap opening is attributed to an interband
spin-orbit interaction that mixes states of opposite spin-helicity.Comment: 5 pages, 3 figure
Zero-point energy of massless scalar fields in the presence of soft and semihard boundaries in D dimensions
The renormalized energy density of a massless scalar field defined in a
D-dimensional flat spacetime is computed in the presence of "soft" and
"semihard" boundaries, modeled by some smoothly increasing potential functions.
The sign of the renormalized energy densities for these different confining
situations is investigated. The dependence of this energy on for the cases
of "hard" and "soft/semihard" boundaries are compared.Comment: 36 pages, LaTeX, 4 figure
Next Generation Neutron Detection for Next Generation Nuclear Reactors
Track I: Power GenerationIncludes audio file (31 min.)As the demand for nuclear energy increases worldwide, and MO reactors come online, so does
the availability of spent fuel that may be used as a medium of terror. That is, fuel for and waste
or byproducts from fissile material refining and nuclear reactors (e.g. plutonium) pose a serious
threat with respect to radiological dispersal and nuclear bomb detonation. Radiological dispersal
can include fallout by means of water or atmospheric transport (e.g., dumping waste in a river)
while fissile trafficking can include the transport of plutonium across a border by seaport entry.
In order to safely increase the use of nuclear energy in Missouri, sensitive techniques for nuclear
detection must be developed. Presently available commercial detectors are not sensitive enough
to detect even large (~3kg) quantities of weapons grade plutonium that are hidden in a barrel of
water; our borders are effectively open to critical mass sized plutonium transport. Profs. Caruso,
Ching and Kruger (UMKC Physics) are developing detectors capable of a ten times increase in
detection sensitivity over existing commercial detectors that will provide a critical component to
the future Missouri nuclear safeguarding infrastructure
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