Topological Crystalline Insulator Nanomembrane with Strain-Tunable Band Gap

The ability to fine-tune band gap and band inversion in topological materials is highly desirable for the development of novel functional devices. Here we propose that the electronic properties of a free-standing nanomembrane of topological crystalline insulator (TCI) SnTe and Pb$_{1-x}$Sn$_x$(Se,Te) are highly tunable by engineering elastic strain and controlling membrane thickness, resulting in tunable band gap and giant piezoconductivity. Membrane thickness governs the hybridization of topological electronic states on opposite surfaces, while elastic strain can further modulate the hybridization strength by controlling the penetration length of surface states. We propose a frequency-resolved infrared photodetector using force-concentration induced inhomogeneous elastic strain in TCI nanomembrane with spatially varying width. The predicted tunable band gap accompanied by strong spin-textured electronic states will open up new avenues for fabricating piezoresistive devices, thermoelectrics, infrared detectors and energy-efficient electronic and optoelectronic devices based on TCI nanomembrane.Comment: 10 pages, 9 figure

Envelope function method for electrons in slowly-varying inhomogeneously deformed crystals

We develop a new envelope-function formalism to describe electrons in slowly-varying inhomogeneously strained semiconductor crystals. A coordinate transformation is used to map a deformed crystal back to geometrically undeformed structure with deformed crystal potential. The single-particle Schr\"{o}dinger equation is solved in the undeformed coordinates using envelope function expansion, wherein electronic wavefunctions are written in terms of strain-parametrized Bloch functions modulated by slowly varying envelope functions. Adopting local approximation of electronic structure, the unknown crystal potential in Schr\"{o}dinger equation can be replaced by the strain-parametrized Bloch functions and the associated strain-parametrized energy eigenvalues, which can be constructed from unit-cell level ab initio or semi-empirical calculations of homogeneously deformed crystals at a chosen crystal momentum. The Schr\"{o}dinger equation is then transformed into a coupled differential equation for the envelope functions and solved as a generalized matrix eigenvector problem. As the envelope functions are slowly varying, coarse spatial or Fourier grid can be used to represent the envelope functions, enabling the method to treat relatively large systems. We demonstrate the effectiveness of this method using a one-dimensional model, where we show that the method can achieve high accuracy in the calculation of energy eigenstates with relatively low cost compared to direct diagonalization of Hamiltonian. We further derive envelope function equations that allow the method to be used empirically, in which case certain parameters in the envelope function equations will be fitted to experimental data.Comment: 15 pages, 8 figure

Near Neutrality of an Oxygen Molecule Adsorbed on a Pt(111) Surface

The charge state of paramagnetic or nonmagnetic O2 adsorbed on a Pt(111) surface is analyzed using density functional theory. We find no significant charge transfer between Pt and the two adsorbed molecular precursors, suggesting these oxygen reduction reaction (ORR) intermediates are nearly neutral, and changes in magnetic moment come from self adjustment of O2 spin-orbital occupations. Our findings support a greatly simplified model of electrocatalyzed ORR, and also point to more subtle pictures of adsorbates or impurities interacting with crystal than literal integer charge transfers

Calculating Phase-Coherent Quantum Transport in Nanoelectronics with \u3cem\u3eab initio\u3c/em\u3e Quasiatomic Orbital Basis Set

We present an efficient and accurate computational approach to study phase-coherent quantum transport in molecular and nanoscale electronics. We formulate a Green’s-function method in the recently developed ab initio nonorthogonal quasiatomic orbital basis set within the Landauer-Büttiker formalism. These quasiatomic orbitals are efficiently and robustly transformed from Kohn-Sham eigenwave functions subject to the maximal atomic-orbital similarity measure. With this minimal basis set, we can easily calculate electrical conductance using Green’s-function method while keeping accuracy at the level of plane-wave density-functional theory. Our approach is validated in three studies of two-terminal electronic devices, in which projected density of states and conductance eigenchannel are employed to help understand microscopic mechanism of quantum transport. We first apply our approach to a seven-carbon atomic chain sandwiched between two finite crosssectioned Al(001) surfaces. The emergence of gaps in the conductance curve originates from the selection rule with vanishing overlap between symmetry-incompatible conductance eigenchannels in leads and conductor. In the second application, a (4,4) single-wall carbon nanotube with a substitutional silicon impurity is investigated. The complete suppression of transmission at 0.6 eV in one of the two conductance eigenchannels is attributed to the Fano antiresonance when the localized silicon impurity state couples with the continuum states of carbon nanotube. Finally, a benzene-1,4-dithiolate molecule attached to two Au(111) surfaces is considered. Combining fragment molecular orbital analysis and conductance eigenchannel analysis, we demonstrate that conductance peaks near the Fermi level result from resonant tunneling through molecular orbitals of benzene- 1,4-dithiolate molecule. In general, our conductance curves agree very well with previous results obtained using localized basis sets while slight difference is observed near the Fermi level and conductance edges

Adherence to medication interventions: Following attending physicians or online support?

Medication interventions are clinical interventions that delay or prevent the recurrence. In this research, we built upon the social network theory (SNT) to examine how trust in attending physicians and different sources of online social support would affect patients\u27 adherence to medication interventions. We conducted a mixed-method approach for different types of target populations. An online survey involving 311 patients with recent hospitalization experience was conducted, and the results confirmed that accessing support from online professionals made patients deviate from the medication interventions. Besides, patients’ trust in ability of their attending physicians would promote the adherence behaviors. Considering more senior patients, we conducted ten in-depth interviews to obtain further insight into patients\u27 dilemmas and challenges in integrating eHealth platforms into their treatment. This research contributes to the existing literature by revealing the potential problems in eHealth platform development and operation, in integrating the eHealth platform with physical healthcare systems

The Role of mHealth in Facilitating Prediabetic and Diabetic Patients’ Involvement in Health Interventions

Health interventions are useful tools for preventing and alleviating diabetes which show low adherence in medical practice for prediabetic and diabetic patients. mHealth technologies have the potential to facilitate health management and improve prediabetic and diabetic patients’ self-management outcomes. Building on Social Cognitive Theory, this research-in- progress paper proposes a research model to account for the role of physician’s recognition in promoting self-management behaviors for prediabetic and diabetic patients through mHealth technologies. To test the research model, authors developed a mobile diabetes management application and cooperated with a large tertiary hospital in China. In this research-in-progress, we propose to recruit 280 subjects who are in the prediabetic or diabetic conditions. This study is expected to contribute to the research on and practice of the health interventions through mHealth technologies

FAM222A encodes a protein which accumulates in plaques in Alzheimer's disease.

Alzheimer's disease (AD) is characterized by amyloid plaques and progressive cerebral atrophy. Here, we report FAM222A as a putative brain atrophy susceptibility gene. Our cross-phenotype association analysis of imaging genetics indicates a potential link between FAM222A and AD-related regional brain atrophy. The protein encoded by FAM222A is predominantly expressed in the CNS and is increased in brains of patients with AD and in an AD mouse model. It accumulates within amyloid deposits, physically interacts with amyloid-β (Aβ) via its N-terminal Aβ binding domain, and facilitates Aβ aggregation. Intracerebroventricular infusion or forced expression of this protein exacerbates neuroinflammation and cognitive dysfunction in an AD mouse model whereas ablation of this protein suppresses the formation of amyloid deposits, neuroinflammation and cognitive deficits in the AD mouse model. Our data support the pathological relevance of protein encoded by FAM222A in AD

Stress-driven crystallization via shear-diffusion transformations in a metallic glass at very low temperatures

At elevated temperatures, glasses crystallize via thermally activated diffusion. However, metallic glasses can also undergo deformation-induced crystallization at very low temperatures. Here we demonstrate the crystallization of Al[subscript 50]Fe[subscript 50] metallic glasses under cyclic deformation at 50 K using molecular dynamics simulations and reveal the underlying atomic-scale processes. We demonstrate that stress-driven nonaffine atomic rearrangements, or shear diffusion transformation (SDT) events, lead to successive metabasin-to-metabasin transitions and long-range ordering. We also illustrate that the nucleation and growth of the crystal proceed via collective attachment of ordered clusters, advancing the amorphous/crystal interface in an intermittent manner. The cooperative nature of the steplike crystallization is attributed to the large activation volume of Eshelby transformations which generate as a by-product nonaffine diffusive atomic displacements that accumulate over loading cycles. The dual nature of shear (affine) and diffusion (nonaffine) in low-temperature stress-driven SDT events thus unifies inelasticity with crystallization.National Basic Research Program of China (973 Program) (Grant 2012CB619402)National Basic Research Program of China (111 Program) (Grant B06025)National Science Foundation (U.S.) (Grant DMR-1120901)National Science Foundation (U.S.) (Grant DMR-1410636

Time-Dependent Density Functional Theory with Ultrasoft Pseudopotential: Real-Time Electron Propagation across Molecular Junction

A practical computational scheme based on time-dependent density functional theory (TDDFT) and ultrasoft pseudopotential (USPP) is developed to study electron dynamics in real time. A modified Crank-Nicolson time-stepping algorithm is adopted, under planewave basis. The scheme is validated by calculating the optical absorption spectra for sodium dimer and benzene molecule. As an application of this USPP-TDDFT formalism, we compute the time evolution of a test electron packet at the Fermi energy of the left metallic lead crossing a benzene-(1,4)-dithiolate junction. A transmission probability of 5-7%, corresponding to a conductance of 4.0-5.6muS, is obtained. These results are consistent with complex band structure estimates, and Green's function calculation results at small bias voltages

Exact Finite-Difference Schemes for d

The authors attempt to construct the exact finite-difference schemes for linear stochastic differential equations with constant coefficients. The explicit solutions to Itô and Stratonovich linear stochastic differential equations with constant coefficients are adopted with the view of providing exact finite-difference schemes to solve them. In particular, the authors utilize the exact finite-difference schemes of Stratonovich type linear stochastic differential equations to solve the Kubo oscillator that is widely used in physics. Further, the authors prove that the exact finite-difference schemes can preserve the symplectic structure and first integral of the Kubo oscillator. The authors also use numerical examples to prove the validity of the numerical methods proposed in this paper