49,269 research outputs found
Deconstruction and Gauge Theories in AdS_5
On a slice of AdS_5, despite having a dimensionful coupling, gauge theories
can exhibit logarithmic dependence on scale. In this paper, we utilize
deconstruction to analyze the scaling behavior of the theory, both above and
below the AdS curvature scale, and shed light on position-dependent
regularizations of the theory. We comment on applications to geometries other
than AdS.Comment: 15 pages, 1 figur
The effect of silicon on the glass forming ability of the Cu47Ti34Zr11Ni8 bulk metallic glass forming alloy during processing of composites
Composites of the Cu47Ti34Zr11Ni8 bulk metallic glass, reinforced with up to 30 vol % SiC particles are synthesized and characterized. Results based on x-ray diffraction, optical microscopy, scanning Auger microscopy, and differential scanning calorimetry (DSC) are presented. During processing of the composites, a TiC layer forms around the SiC particles and Si diffuses into the Cu47Ti34Zr11Ni8 matrix stabilizing the supercooled liquid against crystallization. The small Si addition between 0.5 and 1 at. % increases the attainable maximum thickness of glassy ingots from 4 mm for Cu–Ti–Zr–Ni alloys to 7 mm for Cu–Ti–Zr–Ni–Si alloys. DSC analyses show that neither the thermodynamics nor the kinetics of the alloy are affected significantly by the Si addition. This suggests that Si enhances the glass forming ability by chemically passivating impurities such as oxygen and carbon that cause heterogeneous nucleation in the melt
Gauge Theories in and Fine-Lattice Deconstruction
The logarithmic energy dependence of gauge couplings in AdS_5 emerges almost
automatically when the theory is deconstructed on a coarse lattice. Here we
study the theory away from the coarse-lattice limit. While we cannot
analytically calculate individual KK masses for a fine lattice, we can
calculate the product of all non-zero masses. This allows us to write down the
gauge coupling at low energies for any lattice-spacing and curvature. As
expected, the leading log behaviour is corrected by power-law contributions,
suppressed by the curvature. We then turn to intermediate energies, and discuss
the gauge coupling and the gauge boson profile in perturbation theory around
the coarse-lattice limit.Comment: 17 pages, 1 figure, typos in listing version of abstract correcte
Mechanical properties of Zr_(57)Nb_5Al_(10)Cu_(15.4)Ni_(12.6) metallic glass matrix particulate composites
To increase the toughness of a metallic glass with the nominal composition Zr_(57)Nb_5Al_(10)Cu_(15.4)Ni_(12.6), it was used as the matrix in particulate composites reinforced with W, WC, Ta, and SiC. The composites were tested in compression and tension experiments. Compressive strain to failure increased by more than 300% compared with the unreinforced Zr_(57)Nb_5Al_(10)Cu_(15.4)Ni_(12.6), and energy to break of the tensile samples increased by more than 50%. The increase in toughness came from the particles restricting shear band propagation, promoting the generation of multiple shear bands and additional fracture surface area. There was direct evidence of viscous flow of the metallic glass matrix within the confines of the shear bands
Kondo Effect and Josephson Current through a Quantum Dot between Two Superconductors
We investigate the supercurrent through a quantum dot for the whole range of
couplings using the numerical renormalization group method. We find that the
Josephson current switches abruptly from a - to a 0-phase as the coupling
increases. At intermediate couplings the total spin in the ground state depends
on the phase difference between the two superconductors. Our numerical results
can explain the crossover in the conductance observed experimentally by
Buitelaar \textit{et al.} [Phys. Rev. Lett. \textbf{89}, 256 801 (2002)].Comment: Fig.2 and corresponding text have been changed; Several other small
change
Origin of Electric Field Induced Magnetization in Multiferroic HoMnO3
We have performed polarized and unpolarized small angle neutron scattering
experiments on single crystals of HoMnO3 and have found that an increase in
magnetic scattering at low momentum transfers begins upon cooling through
temperatures close to the spin reorientation transition at TSR ~ 40 K. We
attribute the increase to an uncompensated magnetization arising within
antiferromagnetic domain walls. Polarized neutron scattering experiments
performed while applying an electric field show that the field suppresses
magnetic scattering below T ~ 50 K, indicating that the electric field affects
the magnetization via the antiferromagnetic domain walls rather than through a
change to the bulk magnetic order
Running of Gauge Couplings in AdS5 via Deconstruction
Running of gauge couplings on a slice of AdS5 is examined using the
deconstruction set-up. Logarithmic running instead of (linear) power law is
justified when the cutoff is lower than the curvature scale. Most of
interesting features in warped gauge theory including the localization of
Kaluza-Klein modes, the widening of higher Kaluza-Klein spectrum spacing are
well captured within the framework of the deconstruction.Comment: 20 pages, 3 figures, revtex, refereces added and typos corrected; the
version published in JHE
Optical Study of the Free Carrier Response of LaTiO3/SrTiO3 Superlattices
We used infrared spectroscopic ellipsometry to investigate the electronic
properties of LaTiO3/SrTiO3 superlattices (SLs). Our results indicated that,
independent of the SL periodicity and individual layer-thickness, the SLs
exhibited a Drude metallic response with sheet carrier density per interface
~3x10^14 cm^-2. This is probably due to the leakage of d-electrons at
interfaces from the Mott insulator LaTiO3 to the band insulator SrTiO3. We
observed a carrier relaxation time ~ 35 fs and mobility ~ 35 cm^2V^-1s^-1 at 10
K, and an unusual temperature dependence of carrier density that was attributed
to the dielectric screening of quantum paraelectric SrTiO3.Comment: 4 pages, 4 figure
Engineering Negative Differential Conductance with the Cu(111) Surface State
Low-temperature scanning tunneling microscopy and spectroscopy are employed
to investigate electron tunneling from a C60-terminated tip into a Cu(111)
surface. Tunneling between a C60 orbital and the Shockley surface states of
copper is shown to produce negative differential conductance (NDC) contrary to
conventional expectations. NDC can be tuned through barrier thickness or C60
orientation up to complete extinction. The orientation dependence of NDC is a
result of a symmetry matching between the molecular tip and the surface states.Comment: 5 pages, 4 figures, 1 tabl
Processing of carbon-fiber-reinforced Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 bulk metallic glass composites
Carbon-fiber-reinforced bulk metallic glass composites are produced by infiltrating liquid Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 into carbon fiber bundles with diameter of the individual fiber of 5 mum. Reactive wetting occurs by the formation of a ZrC layer around the fibers. This results in a composite with a homogeneous fiber distribution. The volume fraction of the fibers is about 50% and the density of the composite amounts to 4.0 g/cm(^3)
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