Spin polarization in quantum point contact based on wurtzite topological quantum well.

Manipulating spin polarization in wide-gap wurtzite semiconductors is crucial for the development of high-temperature spintronics applications. A topological insulator revealed recently in wurtzite quantum wells (QWs) provides a platform to mediate spin-polarized transport through the polarization field-driven topological edges and large Rashba spin-orbit coupling (SOC). Here, we propose a spin-polarized device in a quantum point contact (QPC) structure based on ZnO/CdO wurtzite topological QWs. The results show that the QPC width can sufficiently control the lateral spin-orbit coupling (SOC) as well as the band gap of the edge states through the quantum size effect. As a result, the spin-polarized conductance exhibits oscillation due to the spin precession, which can be controlled by adjusting the voltage imposed on the split gate. The QPC-induced large spin splitting is highly nonlinear and becomes strong close to the gap. The spin splitting of the edge states will be suppressed for QPC widths greater than 50 nm, and thus lead to an extremely long spin precession length. This QPC width-dependent lateral SOC effect provides an emerging electrical approach to manipulate spin-polarized electron transport in topological wurtzite systems.

Piezoelectric manipulation of spin-orbit coupling in a Wurtzite heterostructure.

The combination of piezoelectricity and spin-orbit coupling (SOC) effect makes wurtzite semiconductors attractive for the development of exotic spin-related physics as well as spintronic applications. Triggering piezoelectricity, particularly by an external stimulus, provides a new perspective for manipulating SOC, but until now, a comprehensive understanding of this mechanism is lacking. Herein, by means of self-consistent calculations and Löwdin perturbation approach, we have explored the manipulation of SOC in the wurtzite (Al, Ga)N/GaN heterostructure by external stress-induced piezoelectric polarization. The results suggest that the Rashba SOC depends weakly on stress due to the wide-gap feature of the wurtzite crystal that makes Rashba SOC predominant by a bulk term instead of the structural inversion term. The piezoelectric polarization diminishes and even turns off Dresselhaus coupling by reducing the interfacial electric field. Moreover, piezoelectricity is shown to improve the poorly gate-tunable SOC. In the heterostructure with two occupied subbands, the Dresselhaus coupling of the second subband is more sensitive than the first one in response to stress. As an extension, we further demonstrate that the correlation effect in the wurtzite heterostructure can be significantly enhanced by piezoelectric polarization. This study offers an in-depth insight into piezoelectric modulation of spin-orbit physics, which has the potential for stimulating new quantum correlation states or designing functional spintronic devices.

Pressure pain threshold and somatosensory abnormalities in different ages and functional conditions of post-stroke elderly.

BACKGROUND: Somatosensory deficits and abnormal pain sensitivity are highly prevalent among stroke survivors, which negatively impacts their quality of life and recovery process. However, the factors for pressure pain threshold (PPT) and somatosensory abnormalities in post-stroke elderly remain unknown. The aim of this study was to explore the effects of age, side and other functional conditions, such as spasticity and motor functions, on PPT and sensory abnormalities among elderly after stroke. METHODS: The cross-sectional study finally included 43 post-stroke elderly aged over 60 and assessed the PPT of 14 bilateral muscles widely located in the whole body by using a digital force gage. Meanwhile, spasticity, motor function, joint pain and activity of daily living (ADL) were evaluated by the Modified Ashworth scale, Fugl-Meyer, and Barthel Index, respectively. All participants were divided into higher-aged and lower-aged groups based on the median age of all of them. RESULTS: Higher age tended to be associated with higher sensitivity but not significant except for one upper limb muscle, and the affected side showed significantly higher PPTs than the unaffected side in three out of seven muscles (p < 0.05). Furthermore, the somatosensory abnormalities in the affected side, particularly hypoalgesia, were more frequent in higher-aged than lower-aged patients in most assessed muscles. Meanwhile, patients with spasticity showed more increment of PPTs in affected muscles around the knee joint than patients without spasticity (p < 0.05). Patients with better motor functions, less joint pain and higher ADL performed less bilateral differences of PPTs than other patients in some muscles (p < 0.05). CONCLUSIONS: The age and side differences of mechanical pain sensitivity were found among post-stroke elderly. Older patients show higher sensitivity in both sides compared with the younger ones, and the affected side of the elder shows more somatosensory abnormalities, particularly hypoalgesia, than that of the younger ones. Post-stroke elderly in good functional conditions, such as normal muscle tone, better physical function and daily activities, and less joint pain, seems to have more equal pain sensitivity between both sides than those in poor conditions.

High-Performance Piezo-Phototronic Devices Based on Intersubband Transition of Wurtzite Quantum Well.

III-nitride semiconductors play much more important roles in the areas of modern photoelectric applications, whereas strong polarization in their heterostructures is always a challenge to restrict the efficiency and performance of photoelectric devices. In this study, piezo-phototronic effect on near-infrared intersubband absorption is explored based on polar GaN/AlN quantum wells. The results show that externally applied pressure leads to the redshift of absorption wavelength by reducing polarization field of the quantum well. The sensitivity to estimate pressure-dependent intersubband absorption wavelength is almost two orders of magnitude higher than interband photoelectric devices. Additionally, such sensitivity is further enhanced by 2.6 times at 20 GPa as a result of piezo-phototronic effect. This study paves avenue for designing high-performance near-infrared piezo-phototronic devices based on intersubband transition.

Understanding the role of Niobium, Molybdenum and Tungsten in realizing of the transparentn-type SnO2.

Based on the density functional theory, the defective band structures (DBSs), ionization energy and formation energy for Niobium (Nb), Molybdenum (Mo) and Tungsten (W)-doped SnO2are calculated. The DBSs show Nb, Mo and W substituting Sn (labeled as NbSn, MoSnand WSn) could form the localized impurity states which are above the conduction band minimum (CBM). These characteristics can be attributed to the energy of dopants' d-orbitals are much higher than that of Sn-s and -d orbital as well as O-2p orbitals, and the dopants with their neighboring atoms would form the non-bonding impurity states. The DBSs confirm NbSn, MoSnand WSnare typicaln-type defects in SnO2. The ionization energiesϵ(0/+) for NbSn, MoSnand WSnare higher than 0.22 eV above CBM, indicating these defects could be fully ionized. We find the NbO and MoO3are promising dopant sources, as the thermodynamic equilibrium fabrication scheme is considered. Taking Nb-doped SnO2as an example, we find a few NbSncould induce high conductivity (541 S cm-1). These results suggest that SnO2containing NbSn, MoSnand WSnare promisingn-type semiconductors. Our findings would provide a better understanding of then-type properties in Nb, Mo and W-doped SnO2.

The Effect of Inclines on Joint Angles in Stroke Survivors During Treadmill Walking.

Stroke severely affects the quality of life, specifically in walking independently. Thus, it is crucial to understand the impaired gait pattern. This gait pattern has been widely investigated when walking on a level treadmill. However, knowledge about the gait pattern when walking on inclines is scarce. Therefore, this study attempted to fulfill this knowledge gap. In this study, 15 stroke survivors and 15 age/height/weight healthy controls were recruited. The participants were instructed to walk on three different inclines: 0°, 3°, and 6°. The participants were required to walk on each incline for 2 min and needed to complete each incline two times. The dependent variables were the peak values for ankle/knee/hip joint angles and the respective variability of these peak values. The results showed that an increment of the incline significantly increased the peak of the hip flexion and the peak of the knee flexion but did not affect the peak values of the ankle joints in the paretic leg in these stroke survivors. In comparison with the healthy controls, lower hip extension, lower hip flexion, lower knee flexion, and lower ankle plantar flexion were observed in stroke survivors. A clinical application of this work might assist the physical therapists in building an effective treadmill training protocol.

Intra-rater and inter-rater reliability of pressure pain threshold assessment in stroke patients.

BACKGROUND: As pain is a common symptom following a stroke, pressure pain threshold (PPT) assessment can be used to evaluate pain status or pain sensitivity of patients. However, the reliability of PPT test in stroke patients is still unknown. AIM: To examine the intra- and inter-rater reliability of PPT measurements in poststroke survivors and explore their factors. DESIGN: An observational study. SETTING: The setting of the study is a rehabilitation hospital. POPULATION: The population of the study was represented by a total of 54 patients after stroke. METHODS: The study included 16 measured points on the affected and unaffected sides. PPT was assessed by two raters in turn. Intra- and inter-rater reliability was evaluated by intraclass correlation coefficients (ICC). RESULTS: All intra-rater (ICC=0.84-0.97) and inter-rater (ICC=0.83-0.95) reliability for PPT assessment were good or excellent in stroke patients. Of the 16 points, 12 showed higher intra-rater ICC values than inter-rater, whereas no evident difference was observed between the affected and unaffected sides. Furthermore, patients who were male, ischemic, or with higher motor function generally performed higher ICC values than those who were female (24 out of 32 results), hemorrhagic (28 out of 32 results), or mobility dysfunction (26 out of 32 results), respectively. CONCLUSIONS: PPT assessment with good or excellent reliability can be used in stroke patients. Neither of the two sides (affected or unaffected) affects PPT reliability, and intra-rater reliability is better than inter-rater reliability. In addition, gender, stroke type, and motor function can affect the reliability of measuring mechanical pain threshold in poststroke survivors. CLINICAL REHABILITATION IMPACT: The pressure algometer can be used as a reliable and portable tool to assess the mechanical pain tolerance and sensory function in stroke patients in clinics.

The Effects of Gender, Functional Condition, and ADL on Pressure Pain Threshold in Stroke Patients.

BACKGROUND: Somatosensory impairments and pain are common symptoms following stroke. However, the condition of perception and pain threshold for pressure stimuli and the factors that can influence this in individuals with stroke are still unclear. This study aimed to investigate the gender differences in pressure pain threshold (PPT) and positive somatosensory signs for pressure stimuli, and explore the effects of joint pain, motor function, and activities of daily living (ADL) on pain threshold in post-stroke patients. DESIGN: A cross-sectional study. METHODS: A total of 60 participants with stroke were recruited, and their pain condition, motor functions, and ADL were evaluated by the Fugl-Meyer assessment of joint pain scale, motor function scale, and Barthel index, respectively. PPTs in eight tested points at the affected and unaffected sides were assessed. RESULTS: Significant differences in PPTs were found between male and female patients in all measured muscles (p < 0.05). Positive somatosensory signs for pressure stimuli, including hypoalgesia and hyperalgesia, were frequently found at the affected side, particularly in the extremity muscles, but such signs were not significantly influenced by gender (p > 0.05). More equal PPTs between both sides and relatively lower PPTs at the affected side in the trunk and medial gastrocnemius muscles (p < 0.05) were observed in patients with less pain, better motor functions, and ADL. CONCLUSION: Gender differences widely exist in post-stroke survivors either at the affected or unaffected side, which are multifactorial. Sensory loss and central and/or peripheral sensitization, such as hypoalgesia and hyperalgesia for pressure stimuli, caused by a brain lesion are common signs in male and female stroke patients. Moreover, patients who are in a better condition show a more symmetrical pain sensitivity between both sides in the trunk and in female lower extremities, indicating the bidirectional improvement of somatosensory abnormalities caused by a possible neural plasticity.

Piezotronic Transistor Based on Topological Insulators.

Piezotronics and piezophototronics are emerging fields by coupling piezoelectric, semiconductor, and photon excitation effects for achieving high-performance strain-gated sensors, LEDs, and solar cells. The built-in piezoelectric potential effectively controls carrier transport characteristics in piezoelectric semiconductor materials, such as ZnO, GaN, InN, CdS, and monolayer MoS2. In this paper, a topological insulator piezotronic transistor is investigated theoretically based on a HgTe/CdTe quantum well. The conductance, ON/OFF ratio, and density of states have been studied at various strains for the topological insulator piezotronic transistor. The ON/OFF ratio of conductance can reach up to 1010 with applied strain. The properties of the topological insulator are modulated by piezoelectric potential, which is the result of the piezotronic effect on quantum states. The principle provides a method for developing high-performance piezotronic devices based on a topological insulator.