4,082 research outputs found
Orthogonality catastrophe and quantum speed limit for dynamical quantum phase transition
We investigate the orthogonality catastrophe and quantum speed limit in the
Creutz model for dynamical quantum phase transitions. We demonstrate that exact
zeros of the Loschmidt echo can exist in finite-size systems for specific
discrete values. We highlight the role of the zero-energy mode when analyzing
quench dynamics near the critical point. We also examine the behavior of the
time for the first exact zeros of the Loschmidt echo and the corresponding
quantum speed limit time as the system size increases. While the bound is not
tight, it can be attributed to the scaling properties of the band gap and
energy variance with respect to system size. As such, we establish a relation
between the orthogonality catastrophe and quantum speed limit by referencing
the full form of the Loschmidt echo. Significantly, we find the possibility of
using the quantum speed limit to detect the critical point of a static quantum
phase transition, along with a decrease in the amplitude of noise induced
quantum speed limit.Comment: 10 pages, 8 figure
Spatio-Temporal Relation and Attention Learning for Facial Action Unit Detection
Spatio-temporal relations among facial action units (AUs) convey significant
information for AU detection yet have not been thoroughly exploited. The main
reasons are the limited capability of current AU detection works in
simultaneously learning spatial and temporal relations, and the lack of precise
localization information for AU feature learning. To tackle these limitations,
we propose a novel spatio-temporal relation and attention learning framework
for AU detection. Specifically, we introduce a spatio-temporal graph
convolutional network to capture both spatial and temporal relations from
dynamic AUs, in which the AU relations are formulated as a spatio-temporal
graph with adaptively learned instead of predefined edge weights. Moreover, the
learning of spatio-temporal relations among AUs requires individual AU
features. Considering the dynamism and shape irregularity of AUs, we propose an
attention regularization method to adaptively learn regional attentions that
capture highly relevant regions and suppress irrelevant regions so as to
extract a complete feature for each AU. Extensive experiments show that our
approach achieves substantial improvements over the state-of-the-art AU
detection methods on BP4D and especially DISFA benchmarks
Mechanical transistors for logic-with-memory computing
As a potential revolutionary topic in future information processing,
mechanical computing has gained tremendous attention for replacing or
supplementing conventional electronics vulnerable to power outages, security
attacks, and harsh environments. Despite its potential for constructing
intelligent matter towards nonclassical computing systems beyond the von
Neumann architecture, most works on mechanical computing demonstrated that the
ad hoc design of simple logic gates cannot fully realize a universal mechanical
processing framework involving interconnected arithmetic logic components and
memory. However, such a logic-with-memory computing architecture is critical
for complex and persistent state-dependent computations such as sequential
logic. Here we propose a mechanical transistor (M-Transistor), abstracting
omnipresent temperatures as the input-output mechanical bits, which consists of
a metamaterial thermal channel as the gate terminal driving a nonlinear
bistable soft actuator to selectively connect the output terminal to two other
variable thermal sources. This M-Transistor is an elementary unit to modularly
form various combinational and sequential circuits, such as complex logic
gates, registers (volatile memory), and long-term memories (non-volatile
memory) with much fewer units than the electronic counterparts. Moreover, they
can establish a universal processing core comprising an arithmetic circuit and
a register in a compact, reprogrammable network involving periodic read, write,
memory, and logic operations of the mechanical bits. Our work contributes to
realizing a non-electric universal mechanical computing architecture that
combines multidisciplinary engineering with structural mechanics, materials
science, thermal engineering, physical intelligence, and computational science.Comment: 25 pages, 4 figures, Articl
Quantum and classical correlations in the one-dimensional XY model with Dzyaloshinskii-Moriya interaction
We study the effect of Dzyaloshinskii-Moriya (DM) interaction on pairwise
quantum discord, entanglement, and classical correlation in the anisotropic XY
spin-half chain. Analytical expressions for both quantum and classical
correlations are obtained from the spin-spin correlation functions. We show
that these pairwise quantities exhibit various behaviors in relation to the
relative strengths of the DM interaction, the anisotropy and the magnetic
intensity. We observe non-analyticities of the derivatives of both quantum and
classical correlations with respect to the magnetic intensity at the critical
point, with consideration of the DM interaction.Comment: 18pages, 6figure
Evolution of thin protecting Si-layer on Mn0.5Si0.5 layer at low temperatures
Evolution of 2-nm-thick protecting Si-layer on amorphous Mn0.5Si0.5 films at elevated temperatures was investigated by using conductive atom force microscopy (CAFM) and other structure and composition characterization methods. At a temperature of 300 degrees C, a dramatic change was observed in surface morphology with many islands forming on the surface. Those islands were SiO2 islands rather than Si ones. Further studies showed that those islands formed via first oxidation of the Si cap layer followed by the agglomeration of this SiO2 layer. Because Si cap layer has widely been used as protecting materials to prevent the surface from oxidizing and contamination, this study provides an insight on the effectiveness of thin protecting Si-layer at low temperatures. (C) 2015 Elsevier B.V. All rights reserved
High-performance supercapacitors based on hierarchically porous carbons with a three-dimensional conductive network structure
Clews of polymer nanobelts (CsPNBs) have the advantages of inexpensive raw materials, simple synthesis and large output. Novel clews of carbon nanobelts (CsCNBs) have been successfully prepared by carbonizing CsPNBs and by KOH activation subsequently. From the optimized process, CsCNBs*4, with a specific surface area of 2291 m2 g−1 and a pore volume of up to 1.29 cm3 g−1, has been obtained. Fundamentally, the CsCNBs possess a three-dimensional conductive network structure, a hierarchically porous framework, and excellent hydrophilicity, which enable fast ion diffusion through channels and a large enough ion adsorption/desorption surface to improve electrochemical performance of supercapacitors. The product exhibits a high specific capacitance of 327.5 F g−1 at a current density of 0.5 A g−1 in a three-electrode system. The results also reveal a high-rate capacitance (72.2% capacitance retention at 500 mV s−1) and stable cycling lifetime (95% of initial capacitance after 15 000 cycles). Moreover, CsCNBs*4 provides a high energy density of 29.8 W h kg−1 at a power density of 345.4 W kg−1 in 1 M tetraethylammonium tetrafluoroborate/acetonitrile (TEABF4/AN) electrolyte. These inspiring results imply that this carbon material with a three-dimensional conductive network structure possesses excellent potential for energy storage
Optimized synthesis of ultrahigh-surface-area and oxygen-doped carbon nanobelts for high cycle-stability lithium-sulfur batteries
Hierarchical clews of carbon nanobelts (CsCNBs) with ultrahigh specific surface area (2300 m2 g−1) and large pore volume (up to 1.29 cm3 g−1) has been successfully fabricated through carbonization and KOH activation of phenolic resin based nanobelts. The product possesses hierarchically porous structure, three-dimensional conductive network framework, and polar oxygen-rich groups, which are very befitting to load sulfur leading to excellent cycling stability of lithium-sulfur batteries. The composites of CsCNBs/sulfur exhibit an ultrahigh initial discharge capacity of 1245 mA h g−1 and ultralow capacity decay rate as low as 0.162% per cycle after 200 cycles at 0.1 C. Even at high current rate of 4 C, the cells still display a high initial discharge capacity (621 mA h g−1) and ultralow capacity decay rate (only 0.039% per cycle) after 1000 cycles. These encouraging results indicate that polar oxygen-containing functional groups are important for improving the electrochemical performance of carbons. The oxygen-doped carbon nanobelts have excellent energy storage potential in the field of energy storage
Fragmentation fractal of sandstone under acid corrosion and coupled static-dynamic loads
The analysis results show that the fragment of broken rock is a fractal distribution, and the smaller the impact pressure is, the less specimen fragments is,the lower degree of fragmentation degree is, and the lower fractal dimension is. Research shows that fractal dimension increases with the dynamic compression strength of rock increasing, and the incident energy and the absorb energy increase linear with the fracture fractal dimension increasing. The fragmentation distribution of the specimens becomes more and more uniform with the increasing of the incident energy, and the characteristic scale of rupture decreased gradually
Revisiting the quantum Szilard engine with fully quantum considerations
By considering level shifting during the insertion process we revisit the
quantum Szilard engine (QSZE) with fully quantum consideration. We derive the
general expressions of the heat absorbed from thermal bath and the total work
done to the environment by the system in a cycle with two different cyclic
strategies. We find that only the quantum information contributes to the
absorbed heat, and the classical information acts like a feedback controller
and has no direct effect on the absorbed heat. This is the first demonstration
of the different effects of quantum information and classical information for
extracting heat from the bath in the QSZE. Moreover, when the well width
or the temperature of the bath
the QSZE reduces to the classical Szilard engine (CSZE), and the total work
satisfies the relation as obtained by
Sang Wook Kim et al. [Phys. Rev. Lett. 106, 070401 (2011)] for one particle
case.Comment: 17 pages, 3 figures, to be published in Annals of Physics(NY
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