Unsupervised domain adaptation for video recognition is challenging where the domain shift includes both spatial variations and temporal dynamics. Previous works have focused on exploring contrastive learning for cross-domain alignment. However, limited variations in intra-domain positives, false cross-domain positives, and false negatives hinder contrastive learning from fulfilling intra-domain discrimination and cross-domain closeness. This paper presents a non-contrastive learning framework without relying on negative samples for unsupervised video domain adaptation. To address the limited variations in intra-domain positives, we set unlabeled target videos as anchors and explored to mine "informative intra-domain positives" in the form of spatial/temporal augmentations and target nearest neighbors (NNs). To tackle the false cross-domain positives led by noisy pseudo-labels, we reversely set source videos as anchors and sample the synthesized target videos as "robust cross-domain positives" from an estimated target distribution, which are naturally more robust to the pseudo-label noise. Our approach is demonstrated to be superior to state-of-the-art methods through extensive experiments on several cross-domain action recognition benchmarks.

Recognizing Families In the Wild (RFIW): an annual large-scale, multi-track automatic kinship recognition evaluation that supports various visual kin-based problems on scales much higher than ever before. Organized in conjunction with the 15th IEEE International Conference on Automatic Face and Gesture Recognition (FG) as a Challenge, RFIW provides a platform for publishing original work and the gathering of experts for a discussion of the next steps. This paper summarizes the supported tasks (i.e., kinship verification, tri-subject verification, and search & retrieval of missing children) in the evaluation protocols, which include the practical motivation, technical background, data splits, metrics, and benchmark results. Furthermore, top submissions (i.e., leader-board stats) are listed and reviewed as a high-level analysis on the state of the problem. In the end, the purpose of this paper is to describe the 2020 RFIW challenge, end-to-end, along with forecasts in promising future directions.

Commercial products are now making use of the unique properties of nanoscale particles. However, common challenges of making nanoparticles into products still limit their impact. In this article, we review recent advances in nanoparticle manufacturing in liquids, clarifying the similarities between different processes and products at a system level. Our integrative survey emphasizes the fundamental challenge of heterogeneity, which propagates through manufacturing processes and increases the cost of quality control. We also consider the central constraint of production scale, external costs of safety and sustainability, and technology transfer from the laboratory to the market. We review applications of nanoparticles in nanocomposite materials, healthcare and medicine, electronics and photonics, and energy and the environment, and conclude with a summary of the critical issues.

We present results of self-consistent electronic structure calculations for an electromechanical memory cell consisting of a carbon nanotube (CNT) fabric between titanium leads to elucidate the mechanism whereby the applied bias works to close the current gaps in the CNT fabric. We demonstrate that the asymmetry in the bias conditions required to achieve the "SET" operation of the cell (changing it from a high resistivity to low resistivity) results from the nature of a voltage drop in a compensated semiconducting material and depends sensitively on the background charge as well as on the position of the layer where the conducting gaps occur. The calculations provide insight into the behavior of the material and suggest possible fabrication strategies to modify the functionality. (C) 2016 The Japan Society of Applied Physics

Excess charge stabilization of molecules in metallic environments is of particular importance for fields such as molecular electronics and surface chemistry. We study the energetics of benzene and its anion between two metallic plates. We observe that orientational effects are important at small interplate separation. This leads to benzene oriented perpendicular to the gates being more stable than the parallel case due to induced dipole effects. We find that the benzene anion, known for being unstable in the gas phase, is stabilized by the plates at zero bias and an interplate distance of 21 A. We also observe the effect of benzene under a voltage bias generated by the plates; under a negative bias, the anion becomes destabilized. We use the electron localization function to analyze the changes in electron density due to the bias. These findings suggest that image effects such as those present in nanoscale devices are able to stabilize excess charge and should be important to consider when modeling molecu...

We fabricated a quantum dot coupled laterally to a two-dimensional electron gas and vertically to a three-dimensional electron gas in order to investigate the eigenstate dependence of tunneling rate to these gases. We observed a bias-dependent "geometric" current blockade. By tunneling via the asymmetric couplings, population inversion is induced and a dark metastable triplet state is revealed. The metastable state stops the current transport process, suppresses the current, and asymmetrically widens the Coulomb diamond. By analyzing the current as a function of source-drain and gate voltage and the magnetic field, we concluded that this effect is due to the geometric shape of the electronic states in the dot and the current is limited by the tunneling rate due to the eigenstates, that is, artificial sigma coupling and pi coupling.

We theoretically investigate the controlled dynamic polarization of lattice nuclear spins in GaAs double quantum dots containing two electrons. Three regimes of long-term dynamics are identified, including the build up of a large difference in the Overhauser fields across the dots, the saturation of the nuclear polarization process associated with formation of so-called "dark states," and the elimination of the difference field. We show that in the case of unequal dots, build up of difference fields generally accompanies the nuclear polarization process, whereas for nearly identical dots, build up of difference fields competes with polarization saturation in dark states. The elimination of the difference field does not, in general, correspond to a stable steady state of the polarization process.

We discuss a feedback mechanism between electronic states in a two-electron double quantum dot and the underlying nuclear spin bath. We analyze two pumping cycles for which this feedback provides a force for the Overhauser fields of the two dots to either equilibrate or diverge. Which of these effects is favored depends on the g factor and Overhauser coupling constant of the material. The strength of the effect increases with the ratio of Overhauser coupling to electron exchange energy and also increases as the external magnetic field decreases.

Single-shot measurement of the charge arrangement and spin state of a double quantum dot are reported with measurement times down to 100 ns. Sensing uses radio-frequency reflectometry of a proximal quantum dot in the Coulomb blockade regime. The sensor quantum dot is up to 30 times more sensitive than a comparable quantum point-contact sensor and yields three times greater signal to noise in rf single-shot measurements. Numerical modeling is qualitatively consistent with experiment and shows that the improved sensitivity of the sensor quantum dot results from reduced lifetime broadening and screening.

Exciton transport in semiconductor nanoparticles underlies recent experiments on electrically controlled nanostructures and proposals for new artificial light-harvesting systems. In this work, we develop a novel method for the numerical evaluation of the Forster matrix element, based on a three-dimensional real space grid and the self-consistent solution of the mesoscopic exciton in a macroscopic dielectric environment. This method enables the study of the role of the nanoparticle shape, spatially varying dielectric environments, and externally applied electric fields. Depending on the orientation of the transition dipole, the Forster coupling is shown to be either increased or decreased as a function of the nanoparticle shape and of the properties of the dielectric environment. In the presence of an electric field, we investigate the relation between excitonic binding and confinement effects. We also study a type II core-shell quantum dot where electron and hole are spatially separated due to a particular configuration of the bandstructure.

Rectification properties of a quantum wire (QW) coupled asymmetrically to a quantum dot (QD) are studied for bias voltages up to 1 V. The QW-QD system is based on a modulation-doped GaAs/AlGaAs heterostructure with InGaAs self-assembled quantum dots in close vicinity to a two-dimensional electron gas. Due to an applied lateral electric field, the coupled QW-QD system is formed. By increasing the bias voltage, the QD becomes charged by electron tunneling from the wire and quantized rectification is observed in the QW. We attribute the rectifying behavior to a recently proposed charging rectifier [M. Stopa, Phys. Rev. Lett. 88, 146802 (2002)], whereas many electrons contribute to the charging rectification.

We study the effects of chemical bonding on Raman scattering from benzenethiol chemisorbed on silver clusters using time-dependent density functional theory (TDDFT). Raman scattering cross sections are computed using a formalism that employs analytical derivatives of frequency-dependent electronic polarizabilities, which treats both off-resonant and resonant enhancement within the same scheme. In the off-resonant regime, Raman scattering into molecular vibrational modes is enhanced by one order of magnitude and shows pronounced dependence on the orientation and the local symmetry of the molecule. Additional strong enhancement of the order of 10(2) arises from resonant transitions to mixed metal-molecular electronic states. The Raman enhancement is analyzed using Raman excitation profiles (REPs) for the range of excitation energies 1.6-3.0 eV, in which isolated benzenethiol does not have electronic transitions. The computed vibrational frequency shifts and relative Raman scattering cross sections of the metal-molecular complexes are in good agreement with experimental data on surface enhanced Raman scattering (SERS) from benzenethiol adsorbed on silver surfaces. Characterization and understanding of these effects, associated with chemical enhancement mechanism, may be used to improve the detection sensitivity in molecular Raman scattering.

Fig 2: Comparison between the normalized PL lineshapes of intrinsic and n-modulation doped T-shaped QWRs (n ≈ 1×10 cm). Excitation and detection polarizations are chosen parallel to the QWRs. In order to detect only the QWRs PL signal and to avoid an overlap with the SQW PL signal, excitation is performed on the (110)surface. The excitation power amounts to 1μW for a spot size of 0.8 μm (full width at half maximum), the excitation energy to 1656 meV. Bandgap renormalization of modulation doped quantum wires fabricated by the “Cleaved Edge Overgrowth” (CEO) technique

We employ density functional calculated eigenstates as a basis for exact diagonalization studies of semiconductor double quantum dots, with two electrons, through the transition from the symmetric bias regime to the regime where both electrons occupy the same dot. We calculate the singlet-triplet splitting J(epsilon) as a function of bias detuning epsilon and explain its functional shape with a simple, double anticrossing model. A voltage noise suppression "sweet spot," where dJ(epsilon)/d epsilon = 0 with nonzero J(epsilon), is predicted and shown to be tunable with a magnetic field B.

We measure Coulomb drag between displaced parallel quantum wires fabricated on a high-mobility two-dimensional electron gas using a split-gate technique. We observe a rectified Coulomb drag, in which the sign of the drag current is the same irrespective of the current direction in the drive wire, when the Coulomb interaction becomes dominant over kinetic energy for a low electron density, a high magnetic field, and low temperature. This result strongly suggests the formation of a Wigner crystalline state in a quantum wire. We analyze the dynamical response of the Wigner crystal to an electrostatic potential created by the adjacent drive wire within a hydrodynamic framework.