Falls are one of the major causes leading to injury of elderly people. Using wearable devices for fall detection has a high cost and may cause inconvenience to the daily lives of the elderly. In this paper, we present an automated fall detection approach that requires only a low-cost depth camera. Our approach combines two computer vision techniques-shape-based fall characterization and a learning-based classifier to distinguish falls from other daily actions. Given a fall video clip, we extract curvature scale space (CSS) features of human silhouettes at each frame and represent the action by a bag of CSS words (BoCSS). Then, we utilize the extreme learning machine (ELM) classifier to identify the BoCSS representation of a fall from those of other actions. In order to eliminate the sensitivity of ELM to its hyperparameters, we present a variable-length particle swarm optimization algorithm to optimize the number of hidden neurons, corresponding input weights, and biases of ELM. Using a low-cost Kinect depth camera, we build an action dataset that consists of six types of actions (falling, bending, sitting, squatting, walking, and lying) from ten subjects. Experimenting with the dataset shows that our approach can achieve up to 91.15% sensitivity, 77.14% specificity, and 86.83% accuracy. On a public dataset, our approach performs comparably to state-of-the-art fall detection methods that need multiple cameras.

The Dzyaloshinskii-Moriya interaction (DMI) at the heavy metal (HM) and ferromagnetic metal (FM) interface has been recognized as a key ingredient in spintronic applications. Here we investigate the chemical trend of DMI on the 5d band filling (5d^{3}-5d^{10}) of the HM element in HM/FM (FM=CoFeB,Co)/MgO multilayer thin films. DMI is quantitatively evaluated by measuring asymmetric spin wave dispersion using Brillouin light scattering. Sign reversal and 20 times modification of the DMI coefficient D have been measured as the 5d HM element is varied. The chemical trend can be qualitatively understood by considering the 5d and 3d bands alignment at the HM/FM interface and the subsequent orbital hybridization around the Fermi level. Furthermore, a correlation is observed between DMI and effective spin mixing conductance at the HM/FM interfaces. Our results provide new insights into the interfacial DMI for designing future spintronic devices.

Despite their great promise for providing a pathway for very efficient and fast manipulation of magnetization, spin-orbit torque (SOT) operations are currently energy inefficient due to a low damping-like SOT efficiency per unit current bias, and/or the very high resistivity of the spin Hall materials. This work reports an advantageous spin Hall material, Pd 1−x Pt x , which combines a low resistivity with a giant spin Hall effect as evidenced with three independent SOT ferromagnetic detectors. The optimal Pd 0.25 Pt 0.75 alloy has a giant internal spin Hall ratio of >0.60 (damping-like SOT efficiency of ≈0.26 for all three ferromagnets) and a low resistivity of ≈57.5 µΩ cm at a 4 nm thickness. Moreover, it is found that the Dzyaloshinskii-Moriya interaction (DMI), the key ingredient for the manipulation of chiral spin arrangements (e.g., magnetic skyrmions and chiral domain walls), is considerably strong at the Pd 1−x Pt x /Fe 0.6 Co 0.2 B 0.2 interface when compared to that at Ta/Fe 0.6 Co 0.2 B 0.2 or W/Fe 0.6 Co 0.2 B 0.2 interfaces and can be tuned by a factor of 5 through control of the interfacial spin-orbital coupling via the heavy metal composition. This work establishes a very effective spin current generator that combines a notably high energy efficiency with a very strong and tunable DMI for advanced chiral spintronics and spin torque applications.

Hematopoietic (Hem) and endothelial (End) lineages derive from a common progenitor cell, the hemangioblast: specifically, the human cord blood (CB) CD34+KDR+ cell fraction comprises primitive Hem and End cells, as well as hemangioblasts. In humans, the potential therapeutic role of Hem and End progenitors in ischemic heart disease is subject to intense investigation. Particularly, the contribution of these cells to angiogenesis and cardiomyogenesis in myocardial ischemia is not well established. In our studies, we induced myocardial infarct (MI) in the immunocompromised NOD-SCID mouse model, and monitored the effects of myocardial transplantation of human CB CD34+ cells on cardiac function. Specifically, we compared the therapeutic effect of unseparated CD34+ cells vs. PBS and mononuclear cells (MNCs); moreover, we compared the action of the CD34+KDR+ cell subfraction vs. the CD34+KDR- subset. CD34+ cells significantly improve cardiac function after MI, as compared with PBS/MNCs. Similar beneficial actions were obtained using a 2-log lower number of CD34+KDR+ cells, while the same number of CD34+KDR- cells did not have any effects. The beneficial effect of CD34+KDR+ cells may mostly be ascribed to their notable resistance to apoptosis and to their angiogenic action, since cardiomyogenesis was limited. Altogether, our results indicate that, within the CD34+ cell population, the CD34+KDR+ fraction is responsible for the improvement in cardiac hemodynamics and hence represents the candidate active CD34+ cell subset.

The antiferromagnet (AFM) / ferromagnet (FM) interfaces are of central importance in recently developed pure electric or ultrafast control of FM spins, where the underlying mechanisms remain unresolved. Here we report the direct observation of Dzyaloshinskii-Moriya interaction (DMI) across the AFM/FM interface of IrMn/CoFeB thin films. The interfacial DMI is quantitatively measured from the asymmetric spin-wave dispersion in the FM layer using Brillouin light scattering. The DMI strength is enhanced by a factor of 7 with increasing IrMn layer thickness in the range of 1-7.5 nm. Our findings provide deeper insight into the coupling at AFM/FM interface and may stimulate new device concepts utilizing chiral spin textures such as magnetic skyrmions in AFM/FM heterostructures.Control of spins in ferromagnets (FMs) utilizing antiferromagnets (AFMs) is an emerging branch of spintronics [1][2][3][4][5] . By placing an AFM layer adjacent to the FM layer, the unique electric, magnetic and transport properties of the AFM may be used to control the FM layer via interfacial coupling. Conventionally, the AFM layer has mostly played a passive role in device operations by either improving the hardness of FM via exchange bias [6][7][8] or increasing the magnetic damping of FM through spin pumping [9][10][11][12][13] . More recently, the AFMs have been used as active control elements, leading to promising breakthroughs in the electric and ultrafast control of FM spins. For instance, electric current-induced magnetization switching of FM without an external magnetic field has been realized in the AFM/FM systems [1][2][3][4] . These pioneering experiments have been shown to generate the pure spin current in the AFM or at the AFM/FM interface 1,2,[14][15][16] and to utilize the exchange bias to break the switching symmetry [1][2][3][4] . Moreover, coherent spin precession in the FM layer can be effectively excited by an ultrafast spin-exchange-coupling torque across the AFM/FM interface 5 . The laser pulse perturbs the AFM spin arrangement, which in turn generates an intense and non-thermal transient torque acting on the FM spins. Despite these promising achievements, certain limitations such as the incomplete magnetization switching by current remain in the AFM/FM system. Thus, elucidating interaction mechanisms across the AFM/FM interface is not only important from a scientific point of view, but also of great technologic relevance.In heterostructures with broken spatial inversion symmetry, the interfacial Dzyaloshinskii-Moriya interaction (DMI) has been identified as an important mechanism leading to a host of interesting phenomena. DMI promotes non-collinear spin alignments and determines the chirality and dynamics of chiral spin textures [17][18][19] . For instance, DMI stabilizes the magnetic skrymions and domain walls in the Né el configuration with certain chirality and lends a mechanism for driving skrymion and domain wall motion via spin torques [20][21][22][23][24][25] . Similarly, DMI likely contributes to the current-in...

Magnetic skyrmions as swirling spin textures with a nontrivial topology have potential applications as magnetic memory and storage devices. Since the initial discovery of skyrmions in non-centrosymmetric B20 materials, the recent effort has focused on exploring room-temperature skyrmions in heavy metal and ferromagnetic heterostructures, a material platform compatible with existing spintronic manufacturing technology. Here, we report the surprising observation that a room-temperature skyrmion phase can be stabilized in an entirely different class of systems based on antiferromagnetic (AFM) metal and ferromagnetic (FM) metal IrMn/CoFeB heterostructures. There are a number of distinct advantages of exploring skyrmions in such heterostructures including zero-field stabilization, tunable antiferromagnetic order, and sizable spin-orbit torque (SOT) for energy-efficient current manipulation. Through direct spatial imaging of individual skyrmions, quantitative evaluation of the interfacial Dzyaloshinskii-Moriya interaction, and demonstration of current-driven skyrmion motion, our findings firmly establish the AFM/FM heterostructures as a promising material platform for exploring skyrmion physics and device applications.

The interfacial Dzyaloshinskii-Moriya Interaction (DMI) in ultrathin magnetic thin film heterostructures provides a new approach for controlling spin textures on mesoscopic length scales. Here we investigate the dependence of the interfacial DMI constant on a Pt wedge insertion layer in Ta/CoFeB/Pt(wedge)/MgO thin films by observing the asymmetric spin wave dispersion using Brillouin light scattering. Continuous tuning of by more than a factor of three is realized by inserting less than one monolayer of Pt. The observations provide new insights for designing magnetic thin film heterostructures with tailored for controlling skyrmions and magnetic domain wall chirality and dynamics.

The emerging field of valleytronics aims to exploit the valley pseudospin of electrons residing near Bloch band extrema as an information carrier. Recent experiments demonstrating optical generation and manipulation of exciton valley coherence (the superposition of electron-hole pairs at opposite valleys) in monolayer transition metal dichalcogenides (TMDs) provide a critical step towards control of this quantum degree of freedom. The charged exciton (trion) in TMDs is an intriguing alternative to the neutral exciton for control of valley pseudospin because of its long spontaneous recombination lifetime, its robust valley polarization, and its coupling to residual electronic spin. Trion valley coherence has however been unexplored due to experimental challenges in accessing it spectroscopically. In this work, we employ ultrafast two-dimensional coherent spectroscopy to resonantly generate and detect trion valley coherence in monolayer MoSe2 demonstrating that it persists for a few-hundred femtoseconds. We conclude that the underlying mechanisms limiting trion valley coherence are fundamentally different from those applicable to exciton valley coherence.