Effect of temperature on resonant electron transport through stochastic conduction channels in superlattices

We show that resonant electron transport in semiconductor superlattices with an applied electric and tilted magnetic field can, surprisingly, become more pronounced as the lattice and conduction electron temperature increases from 4.2 K to room temperature and beyond. It has previously been demonstrated that at certain critical field parameters, the semiclassical trajectories of electrons in the lowest miniband of the superlattice change abruptly from fully localized to completely unbounded. The unbounded electron orbits propagate through intricate web patterns, known as stochastic webs, in phase space, which act as conduction channels for the electrons and produce a series of resonant peaks in the electron drift velocity versus electric-field curves. Here, we show that increasing the lattice temperature strengthens these resonant peaks due to a subtle interplay between the thermal population of the conduction channels and transport along them. This enhances both the electron drift velocity and the influence of the stochastic webs on the current-voltage characteristics, which we calculate by making self-consistent solutions of the coupled electron transport and Poisson equations throughout the superlattice. These solutions reveal that increasing the temperature also transforms the collective electron dynamics by changing both the threshold voltage required for the onset of self-sustained current oscillations, produced by propagating charge domains, and the oscillation frequency

Identification and estimation of a large factor model with structural instability

This paper tackles the identification and estimation of a high dimensional factor model with unknown number of latent factors and a single break in the number of factors and/or factor loadings occurring at unknown common date. First, we propose a least squares estimator of the change point based on the second moments of estimated pseudo factors and show that the estimation error of the proposed estimator is Op(1). We also show that the proposed estimator has some degree of robustness to misspecification of the number of pseudo factors. With the estimated change point plugged in, consistency of the estimated number of pre and post-break factors and convergence rate of the estimated pre and post-break factor space are then established under fairly general assumptions. The finite sample performance of our estimators is investigated using Monte Carlo experiments

Building use-wellbeing associations: A spatial perspective

This paper examines the effects of mixed and dense building use patterns on life satisfaction of local residents. The analysis is empirically conducted by using a combination of a cross-sectional individual survey data and point-of-interest big data in Beijing. The results show that mixed building uses are positively associated with subjective wellbeing, but residents tend to be less satisfied with dense building use patterns. Additional results quantify evidence that the building use-wellbeing association needs to be contingent upon human lived experiences for consumption and social interaction in the uncertain geographical context. Findings of this study suggest that the hybrid application of location-based big data and traditional survey in urban contexts provides an alternative channel for recovering the built environment-wellbeing associations at fine geographical scales.</p

Adenine Tautomers: Relative Stabilities, Ionization Energies, and Mismatch with Cytosine

In this study, we have investigated 12 tautomers of the DNA base adenine at the BP86/TZ2P and BP86/QZ4P levels of density functional theory. The vertical and adiabatic ionization energies of all tautomers were determined as the difference in energy between the radical cation and the corresponding neutral system. Furthermore, an evaluation is made for the eigenvalue spectra calculated with the SAOP functional, which is shown to lead to substantial improvements for orbital energies compared to BP86. We have also explored the correlations between the Kohn−Sham orbitals of the different tautomers at the BP86/QZ4P and SAOP/QZ4P levels. Finally, we discuss implications of the existence of the tautomeric forms of adenine for the DNA replication

Quantum Dynamics Study of Photoexcited Aniline

A model Hamiltonian based on the quadratic vibronic coupling model is developed to describe the photoinduced dynamics of aniline excited to the manifold of states comprising its first six singlet electronic states. The model Hamiltonian is parametrized by fitting to the results of extensive EOM-CCSD calculations and its validity tested through the calculation of the first two bands in the electronic absorption spectrum of aniline. It is found that two previously neglected 3p Rydberg states play an important role in the dynamics of aniline following excitation into the first two ¹ππ* states. Assignments of the vibrational structure seen in the experimental spectrum is made, and the role played by the Herzberg–Teller effect in excitation to the first ¹ππ* state is analyzed

Increasing Contaminant Burdens in an Arctic Fish, Burbot (Lota lota), in a Warming Climate

The temporal patterns of mercury (Hg), polychlorinated biphenyls (PCBs), and other contaminants in Arctic aquatic biota are usually attributed to changing atmospheric sources. However, climate variability and change is another means of altering contaminant fate and bioavailability. We show here that the concentrations of Hg and PCBs in Mackenzie River burbot (Lota lota), a top predator fish and important staple food for northern Canadian communities, have increased significantly over the last 25 years despite falling or stable atmospheric concentrations, suggesting that environmental processes subsequent to atmospheric transport are responsible. Using a dated sediment core from a tributary lake near the Mackenzie River sampling site, we show that variations in Hg concentrations downcore are strongly associated with labile, algal-derived organic matter (OM). Strong temporal correlations between increasing primary productivity and biotic Hg and PCBs as reflected by burbot suggest that warming temperatures and reduced ice cover may lead to increased exposure to these contaminants in high trophic level Arctic freshwater biota

Controlling Graphene Ultrafast Hot Carrier Response from Metal-like to Semiconductor-like by Electrostatic Gating

We investigate the ultrafast terahertz response of electrostatically gated graphene upon optical excitation. We observe that the photoinduced terahertz absorption increases in charge neutral graphene but decreases in highly doped graphene. We show that this transition from semiconductor-like to metal-like response is unique for zero bandgap materials such as graphene. In charge neutral graphene photoexcited hot carriers effectively increase electron and hole densities and increase the conductivity. In highly doped graphene, however, photoexcitation does not change net conducting carrier concentration. Instead, it mainly increases electron scattering rate and reduce the conductivity

Additional file 1: Table S1. of A retrospective paired study: efficacy and toxicity of nimotuzumab versus cisplatin concurrent with radiotherapy in nasopharyngeal carcinoma

Prognostic factors for overall survival (Univariate) (N = 104). Table S2. Prognostic factors for overall survival (multivariable) (N = 104). Table S3. Toxicities in stage III and IV patients with h-R3/RT and CDDP/RT (N = 78). Table S4. Assignment expressions for factors in the table of patients’ characteristics. Table S5. Patients’ compliance (104 cases). Table S6. Neoadjuvant chemotherapy was recommended by NCCN guidelines of Head and Neck Cancer. Table S7. General information for all 302 patients of CDDP/RT and h-R3/RT group. Table S8. Prognostic factors for Overall Survival of all 302 patients (Univariate). Table S9. Prognostic factors for Overall Survival of all 302 patients (Multivariable). (ZIP 437 kb

Additional file 2: Figure S1. of A retrospective paired study: efficacy and toxicity of nimotuzumab versus cisplatin concurrent with radiotherapy in nasopharyngeal carcinoma

Overall survival of stage II patients who received h-R3/RT or CDDP/RT. Figure S2. Overall survival of patients aged more than 60 years old who received h-R3/RT or CDDP/RT. Figure S3. Overall survival in stage III and IV patients with h-R3/RT and CDDP/RT. (ZIP 12 kb

Accurate X‑ray Absorption Spectra of Dilute Systems: Absolute Measurements and Structural Analysis of Ferrocene and Decamethylferrocene

X-ray absorption fine structure (XAFS) of ferrocene (Fc) and Decamethylferrocene (DmFc) have been determined on an absolute scale using transmission measurements of multiple solutions of differing concentrations (15 mM, 3 mM, pure solvent) at operating temperatures of 10–20 K. Mass attenuation coefficients and photoelectric absorption cross sections are measured and tabulated for both molecules for an extended energy range in excess of 1.5 keV from the Fe K-shell absorption edge. At these temperatures, the minimization of of dynamic disorder has enabled a critical determination of the oscillatory absorption structures created by multiple-scattering paths of the excited photoelectron. These oscillatory structures are highly sensitive to the local conformation environment of the iron absorber in organometallic structures. Crystallographic and scattering studies have reported both structures characterized by staggered cyclopentadienyl rings, in contrast with low temperature crystallography and recent density functional theoretical predictions. Phase changes in the crystallographic space groups are reported for Fc at different temperatures, raising the possibility of alternative conformation states. Robust experimental techniques are described which have allowed the measurement of XAFS spectra of dilute systems by transmission at accuracies ranging from 0.2% to 2%, and observe statistically significant fine structure at photoelectron wavenumbers extending to >12 Å–1. The subtle signatures of the conformations are then investigated via extensive analysis of the XAFS spectra using the full multiple scattering theory as implemented by the FEFF package. Results indicate a near-eclipsed D5h geometry for low-temperature Fc, in contrast with a staggered D5d geometry observed for DmFc. The ability of this experimental approach and data analysis methodology combined with advanced theory to investigate and observe such subtle conformational differences using XAFS is a powerful tool for future challenges and widens the capacity of advanced XAFS to solve a broad range of challenging systems