179 research outputs found
Optimization design of mth-band FIR filters with application to image processing
Cone programming (CP) is a class of convex optimization technique, in which a linear objective function is minimized over the intersection of a set of affine constraints. Such constraints could be linear or convex, equalities or inequalities. Owing to its powerful optimization capability as well as flexibility in accommodating various constraints, the cone programming finds wide applications in digital filter design. In this thesis, fundamentals of linear-phase M th-band FIR filters are first introduced, which include the time-domain interpolation condition and the desired frequency specifications. The restriction of the interpolation matrix M for linear-phase two-dimensional (2-D) M th-band filters is also discussed by considering both the interpolation condition and the symmetry of the impulse response of the 2-D filter. Based on the analysis of the M th-band properties, a semidefinite programming (SOP) optimization approach is developed to design linear-phase 1-0 and 2-D M th-band filters. The 2-D SOP optimization design problem is modeled based on both the mini-max and the least-square error criteria. In contrast to the 1-D based design, the 2-D direct SDP design can offer an optimal equiripple result. A second-order cone programming (SOCP) optimization approach is then presented as an alternative for the design of M th-band filters. The performances as well as the design complexity of these two design approaches are justified through numerical design examples. Simulation results show that the performance of the SOCP approach is better than that of the SDP approach for 1-D M th-band filter design due to its reduced computational complexity for the worst-case, whereas the SDP approach is more appropriate for the 2-D M th-band filter design than the SOCP approach because of its efficient and simple optimization structure. Moreover, the designed M th-band filters are proved useful in image interpolation according to both the visual quality and the peak signal-to-noise ratio (PSNR) for the images with different levels of details
Trap characterization in composite of solid-liquid using dual-level trap model and TSDC method
Charge trap is considered to be one of the effective characteristic parameters for qualitatively evaluating the aging status of insulating material. In this paper, the trap characteristics in oil-impregnated paper with different aging types (non-treatment, thermal treatment and electrical treatment) are investigated using a dual-level (shallow and deep energy) trap model based on space charge profiles and thermally stimulated depolarization current (TSDC) data. The simulated results based on the model are well consistent with the experimental results. Onthe other hand, the TSDC method can acquire much information related to the shallower traps, and the dual–level trap model can obtain much charge dynamicscharacteristics. It has been observed that thermally aging makes the shallow trap energy become deeper while electrically aging makes it shallower. Moreover, thetrap density in oil-impregnated paper increases after aging regardless of thermal or electrical aging
Learn to Cluster Faces with Better Subgraphs
Face clustering can provide pseudo-labels to the massive unlabeled face data
and improve the performance of different face recognition models. The existing
clustering methods generally aggregate the features within subgraphs that are
often implemented based on a uniform threshold or a learned cutoff position.
This may reduce the recall of subgraphs and hence degrade the clustering
performance. This work proposed an efficient neighborhood-aware subgraph
adjustment method that can significantly reduce the noise and improve the
recall of the subgraphs, and hence can drive the distant nodes to converge
towards the same centers. More specifically, the proposed method consists of
two components, i.e. face embeddings enhancement using the embeddings from
neighbors, and enclosed subgraph construction of node pairs for structural
information extraction. The embeddings are combined to predict the linkage
probabilities for all node pairs to replace the cosine similarities to produce
new subgraphs that can be further used for aggregation of GCNs or other
clustering methods. The proposed method is validated through extensive
experiments against a range of clustering solutions using three benchmark
datasets and numerical results confirm that it outperforms the SOTA solutions
in terms of generalization capability
Signature of the coexistence of ferromagnetism and superconductivity at KTaO heterointerfaces
The coexistence of superconductivity and ferromagnetism is a long-standing
issue in the realm of unconventional superconductivity due to the antagonistic
nature of these two ordered states. Experimentally identifying and
characterizing novel heterointerface superconductors that coexist with
magnetism is challenging. Here, we report the experimental observation of
long-range ferromagnetic order at the verge of two-dimensional
superconductivity at KTaO heterointerfaces. Remarkably, we observe in-plane
magnetization hysteresis loop persisting up to room temperature with direct
current superconducting quantum interference device measurements. Furthermore,
first-principles calculations suggest that the observed robust ferromagnetism
is attributed to the presence of oxygen vacancies that localize electrons in
nearby Ta 5 states. Our findings not only indicate KTaO heterointerfaces
as unconventional superconductors with time-reversal symmetry breaking, but
also inject a new momentum to the study of the delicate interplay between
superconductivity and magnetism boosted by strong spin-orbit coupling inherent
to the heavy Ta in 5 orbitals of KTaO heterointerfaces.Comment: 7 pages, 3 figure
Two-dimensional superconductivity at heterostructure of Mott insulating titanium sesquioxide and polar semiconductor
Heterointerfaces with symmetry breaking and strong interfacial coupling could
give rise to the enormous exotic quantum phenomena. Here, we report on the
experimental observation of intriguing two-dimensional superconductivity with
superconducting transition temperature () of 3.8 K at heterostructure of
Mott insulator TiO and polar semiconductor GaN revealed by the
electrical transport and magnetization measurements. Furthermore, at the verge
of superconductivity we find a wide range of temperature independent resistance
associated with vanishing Hall resistance, demonstrating the emergence of
quantum metallic-like state with the Bose-metal scenario of the metallic phase.
By tuning the thickness of TiO films, the emergence of quantum
metallic-like state accompanies with the appearance of superconductivity as
decreasing in temperature, implying that the two-dimensional superconductivity
is evolved from the quantum metallic-like state driven by the cooperative
effects of the electron correlation and the interfacial coupling between
TiO and polar GaN. These findings provide a new platform for the study
of intriguing two-dimensional superconductivity with a delicate interplay of
the electron correlation and the interfacial coupling at the heterostructures,
and unveil the clues of the mechanism of unconventional superconductivity.Comment: 17 pages, 4 figure
Quantum metallic state in the titanium sesquioxide heterointerface superconductor
The emergence of the quantum metallic state marked by a saturating finite
electrical resistance in the zero-temperature limit in a variety of
two-dimensional superconductors injects a new momentum to the realm of
unconventional superconductivity. Despite much research efforts over last few
decades, there is not yet a general consensus on the nature of this unexpected
quantum metal. Here, we report the unique quantum metallic state within the
hallmark of Bose-metal characterized by the saturated resistance and
simultaneously vanished Hall resistance in the titanium sesquioxide
heterointerface superconductor TiO/GaN. Strikingly, the quantum bosonic
metallic state proximate to the two-dimensional superconductivity-metal
transition tuned by magnetic fields persists in the normal phase, suggesting
that the existence of composite bosons formed by electron Cooper pairs survives
even in the normal phase. Our work marks the observation of the preformed
electron Cooper pairs in heterointerface superconductor and sheds new light on
understanding the underlying pairing mechanism of unconventional
superconductivity.Comment: 6 pages, 4 figure
- …