4,572 research outputs found
Quantum state transfer via the ferromagnetic chain in a spatially modulated field
We show that a perfect quantum state transmission can be realized through a
spin chain possessing a commensurate structure of energy spectrum, which is
matched with the corresponding parity. As an exposition of the mirror inversion
symmetry discovered by Albanese et. al (quant-ph/0405029), the parity matched
the commensurability of energy spectra help us to present the novel
pre-engineered spin systems for quantum information transmission. Based on the
these theoretical analysis, we propose a protocol of near-perfect quantum state
transfer by using a ferromagnetic Heisenberg chain with uniform coupling
constant, but an external parabolic magnetic field. The numerical results shows
that the initial Gaussian wave packet in this system with optimal field
distribution can be reshaped near-perfectly over a longer distance.Comment: 5 pages, 2 figure
Unbalance Compensation of a Full Scale Test Rig Designed for HTR-10GT: A Frequency-Domain Approach Based on Iterative Learning Control
Unbalance vibrations are crucial problems in heavy rotational machinery, especially for the systems with high operation speed, like turbine machinery. For the program of 10 MW High Temperature gas-cooled Reactor with direct Gas-Turbine cycle (HTR-10GT), the rated operation speed of the turbine system is 15000 RPM which is beyond the second bending frequency. In that case, even a small residual mass will lead to large unbalance vibrations. Thus, it is of great significance to study balancing methods for the system. As the turbine rotor is designed to be suspended by active magnetic bearings (AMBs), unbalance compensation could be achieved by adequate control strategies. In the paper, unbalance compensation for the Multi-Input and Multi-Output (MIMO) active magnetic bearing (AMB) system using frequency-domain iterative learning control (ILC) is analyzed. Based on the analysis, an ILC controller for unbalance compensation of the full scale test rig, which is designed for the rotor and AMBs in HTR-10GT, is designed. Simulation results are reported which show the efficiency of the ILC controller for attenuating the unbalance vibration of the full scale test rig. This research can offer valuable design criterion for unbalance compensation of the turbine machinery in HTR-10GT
Quantum state transmission via a spin ladder as a robust data bus
We explore the physical mechanism to coherently transfer the quantum
information of spin by connecting two spins to an isotropic antiferromagnetic
spin ladder system as data bus. Due to a large spin gap existing in such a
perfect medium, the effective Hamiltonian of the two connected spins can be
archived as that of Heisenberg type, which possesses a ground state with
maximal entanglement. We show that the effective coupling strength is inversely
proportional to the distance of the two spins and thus the quantum information
can be transferred between the two spins separated by a longer distance, i.e.
the characteristic time of quantum state transferring linearly depends on the
distance.Comment: 7 pages, 5 figures, 1 tabl
Searching for Product-Market Fit with Externally Developed Components: Effects on Time to Product-Market Fit
Nascent digital start-ups that leverage digital technology (DT) could use externally developed components (EDCs) to search for DT features needed for product-market fit (PMF). Drawing on the organizational search literature, we investigate the relationship between nascent digital start-ups\u27 search breadth and search depth (in terms of EDCs use) on their time to achieve PMF (proxied by the receipt of Series A funding). We employ a survival analysis using data on startups and their EDC use from Crunchbase and LinkedIn. Our results reveal that higher search breadth reduces the time to PMF, whereas higher search depth increases it. Higher levels of interdependency between the DT and nascent digital start-ups’ business strengthen search breadth’s time reduction effect. Our findings contribute to the literature on digital entrepreneurship and organizational search and offer suggestions for how nascent digital start-ups should develop their DT in the early years
(2E,6E)-2,6-Difurfurylidenecyclohexanone
The complete molecule of the title compound, C16H14O3, is generated by crystallographic mirror symmetry, with two C atoms and one O atom lying on the mirror plane. The molecule adopts an E configuration about the C=C bond and the dihedral angle between the furan rings is 16.1 (2)°
On the Robustness, Generalization, and Forgetting of Shape-Texture Debiased Continual Learning
Tremendous progress has been made in continual learning to maintain good
performance on old tasks when learning new tasks by tackling the catastrophic
forgetting problem of neural networks. This paper advances continual learning
by further considering its out-of-distribution robustness, in response to the
vulnerability of continually trained models to distribution shifts (e.g., due
to data corruptions and domain shifts) in inference. To this end, we propose
shape-texture debiased continual learning. The key idea is to learn
generalizable and robust representations for each task with shape-texture
debiased training. In order to transform standard continual learning to
shape-texture debiased continual learning, we propose shape-texture debiased
data generation and online shape-texture debiased self-distillation.
Experiments on six datasets demonstrate the benefits of our approach in
improving generalization and robustness, as well as reducing forgetting. Our
analysis on the flatness of the loss landscape explains the advantages.
Moreover, our approach can be easily combined with new advanced architectures
such as vision transformer, and applied to more challenging scenarios such as
exemplar-free continual learning
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