71,940 research outputs found
Spinning strings in AdS_5 x S^5: one-loop correction to energy in SL(2) sector
We consider a circular string with spin in wrapped around big
circle of and carrying also momentum . The corresponding N=4 SYM
operator belongs to the SL(2) sector, i.e. has tr structure. The
leading large term in its 1-loop anomalous dimension can be computed using
Bethe ansatz for the SL(2) spin chain and was previously found to match the
leading term in the classical string energy. The string solution is stable at
large , and the Lagrangian for string fluctuations has constant
coefficients, so that the 1-loop string correction to the energy is given
simply by the sum of characteristic frequencies. Curiously, we find that the
leading term in the zero-mode part of is the same as a 1/J correction to
the one-loop anomalous dimension on the gauge theory (spin chain) side that was
found in hep-th/0410105. However, the contribution of non-zero string modes
does not vanish. We also discuss the ``fast string'' expansion of the classical
string action which coincides with the coherent state action of the SL(2) spin
chain at the first order in \l, and extend this expansion to higher orders
clarifying the role of the winding number.Comment: 31 pages, 1 figure, latex; v3: minor changes and correction
Epitaxial growth of Cu (001) on Si (001): Mechanisms of orientation development and defect morphology
We describe the evolution of microstructure during ultrahigh vacuum ion beam sputter deposition of Cu (001) at room temperature on hydrogen-terminated Si (001). In situ reflection high energy electron diffraction indicates growth of an epitaxial Cu (001) film on Si (001) with the intensity of the Bragg rods sharpening during 5â20 nm of Cu film growth. Post-growth x-ray diffraction indicates the Cu film has a mosaic spread of (001) textures of about ±2° and that a small fraction (0.001â0.01) is of (111) textures. High-resolution transmission electron microscopy shows an abrupt Cu/Si interface with no interfacial silicide, and reveals an evolution in texture with Cu thickness so as to reduce the mosaic spread about (001). MoirĂ© contrast suggests a nearly periodic elastic strain field extending into the Cu and Si at the interface. Other aspects of film growth which are critical to epitaxy are also discussed
Use of scale models to determine the structural dynamic characteristics of space vehicles
Scale model designs for determining structural dynamic characteristics of future spacecraf
Fast and dense magneto-optical traps for Strontium
We improve the efficiency of sawtooth-wave-adiabatic-passage (SWAP) cooling
for strontium atoms in three dimensions and combine it with standard
narrow-line laser cooling. With this technique, we create strontium
magneto-optical traps with bosonic Sr (
fermionic Sr) atoms at phase-space densities of
(). Our method is simple to implement and is faster and more
robust than traditional cooling methods.Comment: 9 pages, 6 figure
The quantization of the chiral Schwinger model based on the BFT-BFV formalism II
We apply an improved version of Batalin-Fradkin-Tyutin (BFT) Hamiltonian
method to the a=1 chiral Schwinger Model, which is much more nontrivial than
the a>1.\delta\xi$ in the measure. As a result, we explicitly
obtain the fully gauge invariant partition function, which includes a new type
of Wess-Zumino (WZ) term irrelevant to the gauge symmetry as well as usual WZ
action.Comment: 17 pages, To be published in J. Phys.
Supergravity duals of gauge theories from F(4) gauged supergravity in six dimensions
We construct supergravity solutions dual to twisted field theories that are
the worldvolume theories of D4-branes wrapped on 2, 3-cycles, and NS-fivebranes
on 3-cycles. We first obtain the solutions for the Romans' six-dimensional
gauged supergravity theories and then up-lift them to ten dimensions. In
particular, we find solutions for field configurations with either non-Abelian
fields or B-fields being excited. One of these solutions, in the massless case,
is up-lifted to the massless type IIA string theory. This is the first example
of such a kind. The cases studied provide new examples of the AdS/CFT duality
involving twisted field theories.Comment: 26 pages, 3 figures, minor changes and references added to match the
published versio
Shuttling of Spin Polarized Electrons in Molecular Transistors
Shuttling of electrons in single-molecule transistors with magnetic leads in
the presence of an external magnetic field is considered theoretically. For a
current of partially spin-polarized electrons a shuttle instability is
predicted to occur for a finite interval of external magnetic field strengths.
The lower critical magnetic field is determined by the degree of spin
polarization and it vanishes as the spin polarization approaches 100%. The
feasibility of detecting magnetic shuttling in a -based molecular
transistor with magnetic (Ni) electrodes is discussed [A.~N.~Pasupathy et al.,
Science 306, 86 (2004)].Comment: Submitted to a special issue of "Synthetic Metals" to appear in March
201
Does Scientific Progress Consist in Increasing Knowledge or Understanding?
Bird argues that scientific progress consists in increasing knowledge. DellsĂ©n objects that increasing knowledge is neither necessary nor sufficient for scientific progress, and argues that scientific progress rather consists in increasing understanding. DellsĂ©n also contends that unlike Birdâs view, his view can account for the scientific practices of using idealizations and of choosing simple theories over complex ones. I argue that DellsĂ©nâs criticisms against Birdâs view fail, and that increasing understanding cannot account for scientific progress, if acceptance, as opposed to belief, is required for scientific understanding
Crossover in the Slow Decay of Dynamic Correlations in the Lorentz Model
The long-time behavior of transport coefficients in a model for spatially
heterogeneous media in two and three dimensions is investigated by Molecular
Dynamics simulations. The behavior of the velocity auto-correlation function is
rationalized in terms of a competition of the critical relaxation due to the
underlying percolation transition and the hydrodynamic power-law anomalies. In
two dimensions and in the absence of a diffusive mode, another power law
anomaly due to trapping is found with an exponent -3 instead of -2. Further,
the logarithmic divergence of the Burnett coefficient is corroborated in the
dilute limit; at finite density, however, it is dominated by stronger
divergences.Comment: Full-length paragraph added that exemplifies the relevance for dense
fluids and makes a connection to recently observed, novel long-time tails in
a hard-sphere flui
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