Simultaneous electrical-field-effect modulation of both top and bottom Dirac surface states of epitaxial thin films of three-dimensional topological insulators.

It is crucial for the studies of the transport properties and quantum effects related to Dirac surface states of three-dimensional topological insulators (3D TIs) to be able to simultaneously tune the chemical potentials of both top and bottom surfaces of a 3D TI thin film. We have realized this in molecular beam epitaxy-grown thin films of 3D TIs, as well as magnetic 3D TIs, by fabricating dual-gate structures on them. The films could be tuned between n-type and p-type by each gate alone. Combined application of two gates can reduce the carrier density of a TI film to a much lower level than with only one of them and enhance the film resistance by 10,000%, implying that Fermi level is tuned very close to the Dirac points of both top and bottom surface states without crossing any bulk band. The result promises applications of 3D TIs in field effect devices.

Emergence of a coherent in-gap state in the SmB6 Kondo insulator revealed by scanning tunneling spectroscopy.

We use scanning tunneling microscopy to investigate the (001) surface of a cleaved SmB6 Kondo insulator. Variable temperature dI/dV spectroscopy up to 60 K reveals a gaplike density of state suppression around the Fermi level, which is due to the hybridization between the itinerant Sm 5d band and localized Sm 4f band. At temperatures below 40 K, a sharp coherence peak emerges within the hybridization gap near the lower gap edge. We propose that the in-gap resonance state is due to a collective excitation in magnetic origin with the presence of spin-orbital coupling and mixed valence fluctuations. These results shed new light on the electronic structure evolution and transport anomaly in SmB6.

Predicting willingness to donate blood based on machine learning: two blood donor recruitments during COVID-19 outbreaks.

Machine learning methods are a novel way to predict and rank donors' willingness to donate blood and to achieve precision recruitment, which can improve the recruitment efficiency and meet the challenge of blood shortage. We collected information about experienced blood donors via short message service (SMS) recruitment and developed 7 machine learning-based recruitment models using PyCharm-Python Environment and 13 features which were described as a method for ranking and predicting donors' intentions to donate blood with a floating number between 0 and 1. Performance of the prediction models was assessed by the Area under the receiver operating characteristic curve (AUC), accuracy, precision, recall, and F1 score in the full dataset, and by the accuracy in the four sub-datasets. The developed models were applied to prospective validations of recruiting experienced blood donors during two COVID-19 pandemics, while the routine method was used as a control. Overall, a total of 95,476 recruitments via SMS and their donation results were enrolled in our modelling study. The strongest predictor features for the donation of experienced donors were blood donation interval, age, and donation frequency. Among the seven baseline models, the eXtreme Gradient Boosting (XGBoost) and Support vector machine models (SVM) achieved the best performance: mean (95%CI) with the highest AUC: 0.809 (0.806-0.811), accuracy: 0.815 (0.812-0.818), precision: 0.840 (0.835-0.845), and F1 score of XGBoost: 0.843 (0.840-0.845) and recall of SVM: 0.991 (0.988-0.994). The hit rate of the XGBoost model alone and the combined XGBoost and SVM models were 1.25 and 1.80 times higher than that of the conventional method as a control in 2 recruitments respectively, and the hit rate of the high willingness to donate group was 1.96 times higher than that of the low willingness to donate group. Our results suggested that the machine learning models could predict and determine the experienced donors with a strong willingness to donate blood by a ranking score based on personalized donation data and demographical details, significantly improve the recruitment rate of blood donors and help blood agencies to maintain the blood supply in emergencies.

[Long-term clinical observation of an accommodative 1CU after implantation].

OBJECTIVE: To evaluate the clinical effectiveness and accommodative range after implanting the 1CU. METHODS: It was a prospective case series study. From March in 2004 to December in 2007, 23 cases (28 eyes) had phacoemulsification and implantation of 1CU (HumanOptics). Naked and best corrected distant acuity, Naked acuity at 35 cm and best corrected near, the amplitude of accommodation measured with subjective and objective techniques and the change in the anterior chamber depth were measured at 3-6 months, 18-24 months and over 36 months after surgery. RESULTS: After implantation, the 1CU had good centered and stable and no IOL-specific complications. Naked distant acuity of the three groups are 0.84+/-0.23, 0.81+/-0.19 and 0.78+/-0.17, between them there are no significantly statistical differences (F=0.759, P>0.05). The best corrected distant acuity of the three groups were 0.97+/-0.13, 0.99+/-0.17 and 1.00+/-0.17, between them there are no significantly statistical differences (F=0.17, P>0.05). The near acuity at 35 cm was 0.66+/-0.24, 0.52+/-0.14 and 0.47+/-0.12, between them there are significantly statistical differences (F=9.312, P<0.01). The best corrected near acuity were 0.97+/-0.13, 0.94+/-0.22 and 0.90+/-0.21, between them there are no significantly statistical differences (F=0.915, P>0.05). The accommodative range measured with subjective were 0.89+/-0.34, 0.72+/-0.17 and 0.56+/-0.16, between them there are significantly statistical differences (F=13.43, P<0.01). The accommodative range measured with objective were 3.58+/-0.54, 3.01+/-0.89 and 2.50+/-0.54, between them there were significantly statistical differences (F=17.886, P<0.01). The anterior chamber depth measured by application of 2% pilocarpine eyedrops were 0.88+/-0.40, 0.54+/-0.23 and 0.33+/-0.20, between them there were significantly statistical differences (F=26.589, P<0.01). CONCLUSIONS: The eyes with 1CU have good visual acuity and increased accommodative range more than the single-focus IOL. With the extension of time after surgery, the ability of 1CU regulation gradually declines, and nears point swift away gradually.

Magnetic quantum phase transition in Cr-doped Bi2(SexTe1-x)3 driven by the Stark effect.

The recent experimental observation of the quantum anomalous Hall effect has cast significant attention on magnetic topological insulators. In these magnetic counterparts of conventional topological insulators such as Bi2Te3, a long-range ferromagnetic state can be established by chemical doping with transition-metal elements. However, a much richer electronic phase diagram can emerge and, in the specific case of Cr-doped Bi2(SexTe1-x)3, a magnetic quantum phase transition tuned by the actual chemical composition has been reported. From an application-oriented perspective, the relevance of these results hinges on the possibility to manipulate magnetism and electronic band topology by external perturbations such as an electric field generated by gate electrodes-similar to what has been achieved in conventional diluted magnetic semiconductors. Here, we investigate the magneto-transport properties of Cr-doped Bi2(SexTe1-x)3 with different compositions under the effect of a gate voltage. The electric field has a negligible effect on magnetic order for all investigated compositions, with the remarkable exception of the sample close to the topological quantum critical point, where the gate voltage reversibly drives a ferromagnetic-to-paramagnetic phase transition. Theoretical calculations show that a perpendicular electric field causes a shift in the electronic energy levels due to the Stark effect, which induces a topological quantum phase transition and, in turn, a magnetic phase transition.

Magnetoresistance Behavior of Conducting Filaments in Resistive-Switching NiO with Different Resistance States.

The resistive switching (RS) effect in various materials has attracted much attention due to its interesting physics and potential for applications. NiO is an important system and its RS effect has been generally explained by the formation/rupture of Ni-related conducting filaments. These filaments are unique since they are formed by an electroforming process, so it is interesting to explore their magnetoresistance (MR) behavior, which can also shed light on unsolved issues such as the nature of the filaments and their evolution in the RS process, and this behavior is also important for multifunctional devices. Here, we focus on MR behavior in NiO RS films with different resistance states. Rich and interesting MR behaviors have been observed, including the normal and anomalous anisotropic magnetoresistance and tunneling magnetoresistance, which provide new insights into the nature of the filaments and their evolution in the RS process. First-principles calculation reveals the essential role of oxygen migration into the filaments during the RESET process and can account for the experimental results. Our work provides a new avenue for exploration of the conducting filaments in resistive switching materials and is significant for understanding the mechanism of RS effect and multifunctional devices.

Evolution of Ni nanofilaments and electromagnetic coupling in the resistive switching of NiO.

Resistive switching effect in conductor/insulator/conductor thin-film stacks is promising for resistance random access memory with high-density, fast speed, low power dissipation and high endurance, as well as novel computer logic architectures. NiO is a model system for the resistive switching effect and the formation/rupture of Ni nanofilaments is considered to be essential. However, it is not clear how the nanofilaments evolve in the switching process. Moreover, since Ni nanofilaments should be ferromagnetic, it provides an opportunity to explore the electromagnetic coupling in this system. Here, we report a direct observation of Ni nanofilaments and their specific evolution process for the first time by a combination of various measurements and theoretical calculations. We found that multi-nanofilaments are involved in the low resistance state and the nanofilaments become thin and rupture separately in the RESET process with subsequent increase of the rupture gaps. Theoretical calculations reveal the role of oxygen vacancy amount in the evolution of Ni nanofilaments. We also demonstrate electromagnetic coupling in this system, which opens a new avenue for multifunctional devices.

Erythrocyte concentrates recovered from under-collected whole blood: experimental and clinical results.

BACKGROUND: Although periodic blood shortages are widespread in major Chinese cities, approximately 1 x 10(5) U of whole blood are discarded yearly because of under-collection. To reduce the wastage of acid citrate dextrose solution B (ACD-B) anticoagulated under-collected whole blood (UC-WB), this study was performed to elucidate the effect of extracellular pH and holding time on erythrocyte quality. Mannitol-adenine-phosphate (MAP) erythrocyte concentrates (UC-RBCs) were prepared with UC-WB to assess the safety and efficacy of this component. METHODS: The effect of the different extracellular pH levels and storage times on erythrocytes was assessed by fluorescent probes, SDS-PAGE electrophoresis, electron microscopy and spectroscopy. In vitro properties of 34 UC-RBCs that were prepared with UC-WB at different times after collection were analyzed and compared to normal RBCs during 35 days of storage. The results of transfusion with UC-RBCs and the incidence of adverse reactions in 49 patients were determined. RESULTS: 1) Low extracellular pH levels and long storage time induced increases in RBC fluorescence polarization and mean microviscosity, changes in membrane fluidity, band 1, 2 and 3 protein expression, and erythrocyte morphology. 2) During storage for 35 days, difference in between-subjects effects of K+, hemolysis and supernatant erythrocyte membrane protein (EMP) were statistically significant (P = 0.041, 0.007 and 0.002, respectively), while the differences between these parameters in the 4 h group and comparable controls were less significant. 3) Clinical data from 49 patients confirmed that transfusions with UC-RBCs were satisfactory with no adverse reactions. CONCLUSION: These results suggest that it is feasible to prepare RBCs with ACD-B anticoagulated UC-WB at a minimum of 66% volume of the labeled collection. It was effective and safe to transfuse the UC-RBCs prepared within 4 h after collection and stored within 7 days. The use of UC-WB would be a welcome addition to limited blood resources in China. TRIAL REGISTRATION: Chinese Clinical Trial Registry ChiCTR-TRC-13003967.

Electrically tuned magnetic order and magnetoresistance in a topological insulator.

The interplay between topological protection and broken time reversal symmetry in topological insulators may lead to highly unconventional magnetoresistance behaviour that can find unique applications in magnetic sensing and data storage. However, the magnetoresistance of topological insulators with spontaneously broken time reversal symmetry is still poorly understood. In this work, we investigate the transport properties of a ferromagnetic topological insulator thin film fabricated into a field effect transistor device. We observe a complex evolution of gate-tuned magnetoresistance, which is positive when the Fermi level lies close to the Dirac point but becomes negative at higher energies. This trend is opposite to that expected from the Berry phase picture, but is intimately correlated with the gate-tuned magnetic order. The underlying physics is the competition between the topology-induced weak antilocalization and magnetism-induced negative magnetoresistance. The simultaneous electrical control of magnetic order and magnetoresistance facilitates future topological insulator based spintronic devices.

Experimental observation of the quantum anomalous Hall effect in a magnetic topological insulator.

The quantized version of the anomalous Hall effect has been predicted to occur in magnetic topological insulators, but the experimental realization has been challenging. Here, we report the observation of the quantum anomalous Hall (QAH) effect in thin films of chromium-doped (Bi,Sb)2Te3, a magnetic topological insulator. At zero magnetic field, the gate-tuned anomalous Hall resistance reaches the predicted quantized value of h/e(2), accompanied by a considerable drop in the longitudinal resistance. Under a strong magnetic field, the longitudinal resistance vanishes, whereas the Hall resistance remains at the quantized value. The realization of the QAH effect may lead to the development of low-power-consumption electronics.