40,221 research outputs found
Coopetition spectrum trading in cognitive radio networks
Spectrum trading is a promising method to improve spectrum usage efficiency. Several issues must be addressed, however, to enable spectrum trading that goes beyond conservative trading idle bands and achieve cooperation between primary and secondary users. In this paper, we argue that spectrum holes should be explicitly endogenous and negotiated by spectrum trading participants. To this end, we proposed an a Vickery auction based, coopetive framework to foster cooperation, while allowing competition for spectrum sharing. Incentive schemes and penalty for revocable spectrum are proposed to increase the spectrum access opportunities for SUs while protecting PUs spectrum value. A simultation study shows that the proposed framework outperforms conservative trading approaches, in a variety of scenarios with different levels of cooperation and bidding strategies. © 2013 IEEE
Pumped spin-current and shot noise spectra in a single quantum dot
We exploit the pumped spin-current and current noise spectra under
equilibrium condition in a single quantum dot connected to two normal leads, as
an electrical scheme for detection of the electron spin resonance (ESR) and
decoherence. We propose spin-resolved quantum rate equations with correlation
functions in Laplace-space for the analytical derivation of the zero-frequency
atuo- and cross-shot noise spectra of charge- and spin-current. Our results
show that in the strong Coulomb blockade regime, ESR-induced spin flip
generates a finite spin-current and the quantum partition noises in the absence
of net charge transport. Moreover, spin shot noise is closely related to the
magnetic Rabi frequency and decoherence and would be a sensitive tool to
measure them.Comment: 4 pages, 3 figures, to be published in Phys. Rev. Lette
Adjoint Chiral Supermultiplets and Their Phenomenology
Matter fields in the MSSM are chiral supermultiplets in fundamental (or
singlet) representations of the standard model gauge group. In this paper we
introduce chiral superfields in the adjoint representation of and
study the effective field theory and phenomenology of them. These states are
well motivated by intersecting D-brane models in which additional massless
adjoint chiral supermultiplets appear generically in the low energy spectrum.
Although it has been pointed out that the existence of these additional fields
may make it difficult to obtain asymptotic freedom, we demonstrate that this
consideration does not rule out the existence of adjoints. The QCD gauge
coupling can be perturbative up to a sufficiently high scale, and therefore a
perturbative description for a D-brane model is valid. The full supersymmetric
and soft SUSY breaking Lagrangians and the resulting renormalization group
equations are given. Phenomenological aspects of the adjoint matter are also
studied, including the decay and production processes. The similarity in gauge
interaction between the adjoint fermion and gluino facilitates our study on
these aspects. It is found that these adjoint multiplets can give detectable
signals at colliders and satisfy the constraints from cosmology.Comment: 18 pages, 3 figures; minor corrections, references adde
Shot noise in resonant tunneling through an interacting quantum dot with intradot spin-flip scattering
In this paper, we present theoretical investigation of the zero-frequency
shot noise spectra in electron tunneling through an interacting quantum dot
connected to two ferromagnetic leads with possibility of spin-flip scattering
between the two spin states by means of the recently developed bias-voltage and
temperature dependent quantum rate equations. For this purpose, a
generalization of the traditional generation-recombination approach is made for
properly taking into account the coherent superposition of electronic states,
i.e., the nondiagonal density matrix elements. Our numerical calculations find
that the Fano factor increases with increasing the polarization of the two
leads, but decreases with increasing the intradot spin-flip scattering.Comment: Some typos correction. 6 pages, 3 figures, based on work presented at
the 2004 IEEE NTC Quantum Device Technology Workshop, accepted for
publication by IEEE transactions on Nanotechnolog
Super-Poissonian shot noise in the resonant tunneling due to coupling with a localized level
We report our studies of the shot noise spectrum in tunneling through an
interacting quantum dot when an additional single-level quantum dot without
tunnel coupling to leads is coherently side-connected to it. We show that the
zero-frequency shot noise could reach a super-Poissonian value for appropriate
ratios between dot-dot hoppings and dot-lead couplings, but the current is
independent on the hopping. Moreover, the frequency spectrum of shot noise
shows an obvious peak at the Rabi frequency, which is controllable by tuning
the dot-lead couplings.Comment: 3 pages, 3 figures, Appl. Phys. Lett.(in press
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Coil combination using linear deconvolution in k-space for phase imaging
Background: The combination of multi-channel data is a critical step for the imaging of phase and susceptibility contrast in magnetic resonance imaging (MRI). Magnitude-weighted phase combination methods often produce noise and aliasing artifacts in the magnitude images at accelerated imaging sceneries. To address this issue, an optimal coil combination method through deconvolution in k-space is proposed in this paper.
Methods: The proposed method firstly employs the sum-of-squares and phase aligning method to yield a complex reference coil image which is then used to calculate the coil sensitivity and its Fourier transform. Then, the coil k-space combining weights is computed, taking into account the truncated frequency data of coil sensitivity and the acquired k-space data. Finally, combining the coil k-space data with the acquired weights generates the k-space data of proton distribution, with which both phase and magnitude information can be obtained straightforwardly. Both phantom and in vivo imaging experiments were conducted to evaluate the performance of the proposed method.
Results: Compared with magnitude-weighted method and MCPC-C, the proposed method can alleviate the phase cancellation in coil combination, resulting in a less wrapped phase.
Conclusions: The proposed method provides an effective and efficient approach to combine multiple coil image in parallel MRI reconstruction, and has potential to benefit routine clinical practice in the future
A programmable microsystem using system-on-chip for real-time biotelemetry
A telemetry microsystem, including multiple sensors, integrated instrumentation and a wireless interface has been implemented. We have employed a methodology akin to that for System-on-Chip microelectronics to design an integrated circuit instrument containing several "intellectual property" blocks that will enable convenient reuse of modules in future projects. The present system was optimized for low-power and included mixed-signal sensor circuits, a programmable digital system, a feedback clock control loop and RF circuits integrated on a 5 mm × 5 mm silicon chip using a 0.6 μm, 3.3 V CMOS process. Undesirable signal coupling between circuit components has been investigated and current injection into sensitive instrumentation nodes was minimized by careful floor-planning. The chip, the sensors, a magnetic induction-based transmitter and two silver oxide cells were packaged into a 36 mm × 12 mm capsule format. A base station was built in order to retrieve the data from the microsystem in real-time. The base station was designed to be adaptive and timing tolerant since the microsystem design was simplified to reduce power consumption and size. The telemetry system was found to have a packet error rate of 10<sup>-</sup><sup>3</sup> using an asynchronous simplex link. Trials in animal carcasses were carried out to show that the transmitter was as effective as a conventional RF device whilst consuming less power
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