3,718 research outputs found
Detection of Tiny Mechanical Motion by Means of the Ratchet Effect
We propose a position detection scheme for a nanoelectromechanical resonator
based on the ratchet effect. This scheme has an advantage of being a dc
measurement. We consider a three-junction SQUID where a part of the
superconducting loop can perform mechanical motion. The response of the ratchet
to a dc current is sensitive to the position of the resonator and the effect
can be further enhanced by biasing the SQUID with an ac current. We discuss the
feasibility of the proposed scheme in existing experimental setups.Comment: 8 pages, 9 figure
Interest rate co-movements, global factors and the long end of the term spread
The disconnect between rising short and low long interest rates has been a distinctive
feature of the 2000s. Both research and policy circles have argued that international
forces, such as global monetary policy (e.g. Rogoff, 2006); international business cycles
(e.g. Borio and Filardo, 2007); or a global savings glut (e.g Bernanke, 2005) may be
responsible. In this paper, we employ recent advances in panel data econometrics to
document the disconnect and link it explicitly to the existence of a global latent factor that dominates the long end of the term spread for the recent period; the saving glut story emerges as the most likely contender for the global factor
The charge shuttle as a nanomechanical ratchet
We consider the charge shuttle proposed by Gorelik {\em et al.} driven by a
time-dependent voltage bias. In the case of asymmetric setup, the system
behaves as a rachet. For pure AC drive, the rectified current shows a complex
frequency dependent response characterized by frequency locking at fracional
values of the external frequency. Due to the non-linear dynamics of the
shuttle, the rachet effect is present also for very low frequencies.Comment: 4 pages, 4 figure
Possible complex annihilation and B -> K pi direct CP asymmetry
We point out that a sizable strong phase could be generated from the penguin
annihilation in the soft-collinear effective theory for B meson decays. Keeping
a small scale suppressed by O(Lambda/m_b), Lambda being a hadronic scale and
m_b the b quark mass, in the denominators of internal particle propagators
without expansion, the resultant strong phase can accommodate the data of the
B^0 -> K^-+ pi^+- direct CP asymmetry. Our study reconciles the opposite
conclusions on the real or complex penguin annihilation amplitude drawn in the
soft-collinear effective theory and in the perturbative QCD approach based on
k_T factorization theorem.Comment: 8 pages, 1 figure, added reference
Two-photon decay of heavy quarkonium from heavy-quark spin symmetry
With the recent measurements on and at CLEO,
Babar and Belle, and with the prospect of finding the at the
Tevatron, it seems appropriate to have another look at the two-photon decay of
heavy quarkonium from the standpoint of an effective Lagrangian based on local
operator expansion and heavy-quark spin symmetry. In this talk, I would like to
discuss a recent work on the two-photon decay rates of ground states and
excited states of and using the local operator expansion
approach and heavy-quark spin symmetry and taking into account the
binding-energy. We find that the predicted two-photon width for agrees
well with experiment, but the predicted value for is twice larger
than the CLEO estimation. We point out that the essentially model-independent
ratio of two-photon width to the leptonic width and the
two-photon width could be used to extract the strong coupling
constant .Comment: 9 pages, Talk given at the QCD@Work 2007 International Workshop on
QCD: Theory and Experiment}, Martina Franca, Italy, 16--20 June 200
New measurements of the cosmic infrared background fluctuations in deep Spitzer/IRAC survey data and their cosmological implications
We extend previous measurements of cosmic infrared background (CIB)
fluctuations to ~ 1 deg using new data from the Spitzer Extended Deep Survey.
Two fields, with depths of ~12 hr/pixel over 3 epochs, are analyzed at 3.6 and
4.5 mic. Maps of the fields were assembled using a self-calibration method
uniquely suitable for probing faint diffuse backgrounds. Resolved sources were
removed from the maps to a magnitude limit of AB mag ~ 25, as indicated by the
level of the remaining shot noise. The maps were then Fourier-transformed and
their power spectra were evaluated. Instrumental noise was estimated from the
time-differenced data, and subtracting this isolates the spatial fluctuations
of the actual sky. The power spectra of the source-subtracted fields remain
identical (within the observational uncertainties) for the three epochs
indicating that zodiacal light contributes negligibly to the fluctuations.
Comparing to 8 mic power spectra shows that Galactic cirrus cannot account for
the fluctuations. The signal appears isotropically distributed on the sky as
required for an extragalactic origin. The CIB fluctuations continue to diverge
to > 10 times those of known galaxy populations on angular scales out to < 1
deg. The low shot noise levels remaining in the diffuse maps indicate that the
large scale fluctuations arise from the spatial clustering of faint sources
well below the confusion noise. The spatial spectrum of these fluctuations is
in reasonable agreement with an origin in populations clustered according to
the standard cosmological model (LCDM) at epochs coinciding with the first
stars era.Comment: ApJ, to be publishe
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