52 research outputs found
Spin-dependent Rotating Wigner Molecules in Quantum dots
The spin-dependent trial wave functions with rotational symmetry are
introduced to describe rotating Wigner molecular states with spin degree of
freedom in four- and five-electron quantum dots under magnetic fields. The
functions are constructed with unrestricted Hartree-Fock orbits and projection
technique in long-range interaction limit. They highly overlap with the
exact-diagonalized ones and give the accurate energies in strong fields. The
zero points, i.e. vortices of the functions have straightforward relations to
the angular momenta of the states. The functions with different total spins
automatically satisfy the angular momentum transition rules with the increase
of magnetic fields and explicitly show magnetic couplings and characteristic
oscillations with respect to the angular momenta. Based on the functions, it is
demonstrated that the entanglement entropies of electrons depend on the
z-component of total spin and rise with the increase of angular momenta
Delta-Sigma Digitization and Optical Coherent Transmission of DOCSIS 3.1 Signals in Hybrid Fiber Coax Networks
We first demonstrate delta-sigma digitization and coherent transmission of data over cable system interface specification (DOCSIS) 3.1 signals in a hybrid fiber coax (HFC) network. Twenty 192-MHz DOCSIS 3.1 channels with modulation up to 16384QAM are digitized by a low-pass cascade resonator feedback (CRFB) delta-sigma analog-to-digital converter (ADC) and transmitted over 80 km fiber using coherent single-λ 128-Gb/s dual-polarization (DP)-QPSK and 256-Gb/s DP-16QAM optical links. Both one-bit and two-bit delta-sigma digitization are implemented and supported by the QPSK and 16QAM coherent transmission systems, respectively. To facilitate its practical application in access networks, the coherent system is built using a low-cost narrowband optical modulator and RF amplifiers. Modulation error ratio (MER) larger than 50 dB is successfully demonstrated for all 20 DOCSIS 3.1 channels, and high order modulation up to 16384QAM is delivered over fiber for the first time in HFC networks. The raw DOCSIS data capacity is 54 Gb/s with net user information ~45 Gb/s. Moreover, the bit error ratio (BER) tolerance is evaluated by measuring the MER performance as BER increases. Negligible MER degradation is observed for BER up to 1.5 × 10−6 and 1.7 × 10−4, for one-bit and two-bit digitization, respectively
The existence of positive solutions for high order fractional differential equations with sign changing nonlinearity and parameters
By constructing an auxiliary boundary value problem, the difficulty caused by sign changing nonlinearity terms is overcome by means of the linear superposition principle. Using the Guo-Krasnosel'skii fixed point theorem, the results of the existence of positive solutions for boundary value problems of high order fractional differential equation are obtained in different parameter intervals under a more relaxed condition compared with the existing literature. As an application, we give two examples to illustrate our results
Superconducting Diode Effect and Large Magnetochiral Anisotropy in T-MoTe Thin Film
In the absence of time-reversal invariance, metals without inversion symmetry
may exhibit nonreciprocal charge transport -- a magnetochiral anisotropy that
manifests as unequal electrical resistance for opposite current flow
directions. If superconductivity also sets in, the charge transmission may
become dissipationless in one direction while remaining dissipative in the
opposite, thereby realizing a superconducting diode. Through both
direct-current and alternating-current measurements, we study the nonreciprocal
effects in thin films of the noncentrosymmetric superconductor
T-MoTe\textsubscript{2} with disorders. We observe nonreciprocal
superconducting critical currents with a diode efficiency close to 20\%~, and a
large magnetochiral anisotropy coefficient up to
\SI{5.9e8}{\per\tesla\per\ampere}, under weak out-of-plane magnetic field in
the millitesla range. The great enhancement of rectification efficiency under
out-of-plane magnetic field is likely abscribed to the vortex ratchet effect,
which naturally appears in the noncentrosymmetric superconductor with
disorders. Intriguingly, unlike the finding in Rashba systems, the strongest
in-plane nonreciprocal effect does not occur when the field is perpendicular to
the current flow direction. We develop a phenomenological theory to demonstrate
that this peculiar behavior can be attributed to the asymmetric structure of
spin-orbit coupling in T-MoTe\textsubscript{2}. Our study highlights how
the crystallographic symmetry critically impacts the nonreciprocal transport,
and would further advance the research for designing the superconducting diode
with the best performance.Comment: 7 pages, 5figure
Quantum Dot Coherent Comb Laser Source for Converged Optical-Wireless Access Networks
We propose and experimentally demonstrate a converged optical-wireless WDM access network architecture enabled by a highly integrated quantum dot coherent comb laser. The converged optical-wireless WDM network features simultaneous delivery of coherent and millimeter wave (mmWave) / citizens broadband radio service (CBRS) signals over 50-km and 20 km fiber links, respectively
Ultra-Sensitive, Deformable and Transparent Triboelectric Tactile Sensor based on Micro-Pyramid Patterned Ionic Hydrogel for Interactive Human-Machine Interfaces
Rapid advances in wearable electronics and mechno-sensational human-machine interfaces impose great challenges in developing flexible and deformable tactile sensors with high efficiency, ultra-sensitivity, environment-tolerance and self-sustainability. Herein, we report a tactile hydrogel sensor (THS) based on micro-pyramid-patterned double-network (DN) ionic organohydrogels to detect subtle pressure changes by measuring the variations of triboelectric output signal without an external power supply. By the first time of pyramidal-patterned hydrogel fabrication method and laminated PDMS encapsulation process, the self-powered THS shows the advantages of remarkable flexibility, good transparency (~85), and excellent sensing performance, including extraordinary sensitivity (45.97 mV Pa-1 ), fast response (~20 ms), very low limit of detection (50 Pa) as well as high stability (36000 cycles). Moreover, with the LiBr immersion treatment method, the THS possesses excellent long-term hyper antifreezing and anti-dehydrating properties, broad environment tolerance (-20 to 60 ℃), and instantaneous peak power density of 20 μW cm-2 , providing reliable contact outputs with different materials and detecting very slight human motions. The THS shows no apparent output decline under the extreme environments of −29℃, 60℃ and even the vacuum conditions, demonstrating the excellent application potential in the field of harsh environments. By integrating the signal acquisition/process circuit, the THS with excellent self-power sensing ability is utilized as a switching button to control electric appliances and robotic hands by simulating human finger gestures, offering its great potentials for wearable and multi-functional electronic applications
Optical millimeter-wave signal generation, transmission and processing for symmetric super-broadband optical-wireless access networks
Three 40/60-GHz optical-wireless bidirectional architectures are designed with a centralized light source in the central office based on wavelength reuse. Three super-broadband access networks are proposed and experimentally demonstrated for simultaneously delivering wired and wireless services over an optical fiber and an air link in a single transport platform. The transport feasibility in metro and wide-area access networks with multiple reconfigurable optical add-drop multiplexers (ROADMs) nodes is explored for 40-GHz and 60-GHz optical millimeter-wave signals. Additionally, the optical-wireless systems using the orthogonal frequency division multiplexing (OFDM) modulation format are analytically and experimentally demonstrated to mitigate the chromatic dispersion in optical fiber. This thesis also successfully implements the testbed trial for the delivery of uncompressed 270-Mb/s standard-definition television (SDTV) and 1.485-Gb/s high-definition television (HDTV) video signals over optical fiber and air links. The demonstration represents the first ever reported real applications over hybrid wired and wireless access networks, showing that our developed up-conversion schemes and designed architectures are highly suitable for super-broadband applications in next-generation optical-wireless access networks.Ph.D.Committee Chair: Gee-Kung Chang; Committee Co-Chair: Jianjun Yu; Committee Member: John A. Buck; Committee Member: Joy Laskar; Committee Member: Umakishore Ramachandran; Committee Member: Ye L
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