Effects of magnetic field on electron transport in semiconductor superlattices

Quantum superlattice with a narrow energy band is an artificial semiconductor structure demonstrating both nonlinear and active high-frequency electromagnetic properties. These types of superlattices are used as key elements in various miniature electronic devices including frequency multipliers and quantum cascade lasers. Interaction between terahertz radiation and magnetic field in semiconductor superlattices has been the subject of growing research interest, both theoretical and experimental. In this thesis, we study the nonlinear dynamics of electrons in minibands of the semiconductor superlattices subjected to a terahertz electric field and a magnetic field. Electron transport in a semiconductor superlattice with an electric field and a tilted magnetic field has been studied using semiclassical equations. In particular, we consider how dynamics of electron in superlattices evolve with changing the strength and the tilt of a magnetic field. In order to investigate the influence of a tilted magnetic field on electron transport, we calculate the drift velocity for different values of the magnetic field. Studies have shown that the resonance of Bloch oscillations and cyclotron oscillations produces additional peaks in drift velocity. We also found out that appearance of these resonances can promote amplification of a small ac signal applied to the superlattice. In the presence of the electromagnetic field, the superlattice is expected to demonstrate the Hall effect, which however should have a number of very specific features due to an excitation of Bloch oscillations and a significant electric anisotropy. Here, we theoretically study the Hall effect in a semiconductor superlattice both for the steady electron transport and for the transient response. We studied the coherent Hall effect in an extraordinary configuration where the electric field is applied in the transverse direction of the superlattice growth direction. By mapping the momentum dynamics to the pendulum equivalent, we distinguished the two regimes of the oscillations from the viewpoint of the effective potentials. We discuss the experimental manifestation of the Hall effect in a realistic superlattice. We also made the numerical simulations of the polarized THz field and the time-resolved internal electro-optic sampling (TEOS) signals where we found the unusual shaped waveforms of the THz signals

Fluorescence Probe Based on Hybrid Mesoporous Silica/Quantum Dot/Molecularly Imprinted Polymer for Detection of Tetracycline

A newly designed fluorescence probe made from a hybrid quantum dot/mesoporous silica/molecularly imprinted polymer (QD/MS/MIP) was successfully created, and the probe was used for the detection of tetracycline (TC) in serum sample. QD/MS/MIP was characterized by transmission electron microscope, Fourier transform infrared spectroscopy, UV spectroscopy, X-ray powder diffraction, nitrogen adsorption–desorption experiment and fluorescence spectroscopy. Tetracycline, which is a type of broad-spectrum antibiotic, was selected as the template. The monomer and the template were combined by covalent bonds. After the template was removed to form a binding site, a hydrogen bonding interaction formed between the hole and the target molecule. Moreover, when rebinding TC, a new complex was produced between the amino group of QD/MS/MIP and the hydroxyl group of TC. After that, the energy of the QDs could transfer to the complex, which explains the fluorescence quenching phenomenon. The fluorescent intensity of QD/MS/MIP decreased in 10 min, and an excellent linearity from 50 to 1000 ng mL^–1 was correspondingly obtained. This composite material has a high selectivity with an imprinting factor of 6.71. In addition, the confirmed probe strategy was successfully applied to serum sample analyses, and the recoveries were 90.2%–97.2% with relative standard deviations of 2.2%–5.7%. This current work offers a novel and suitable method to synthesize QD/MS/MIP with a highly selective recognition ability. This composite material will be valuable for use in fluorescence probe applications

Regioselective Formation of 2,4,5-Trisubstituted Oxazoles through Transition-Metal Free Heterocyclization of 1,3-Diynes with <i>N</i>,<i>O</i>‑Bis(trimethylsiyl)acetamide

Transition-metal free heterocyclization reaction of 1,3-diynes with <i>N</i>,<i>O</i>-bis­(trimethylsiyl)­acetamide was accomplished in the presence of <i>t</i>-BuOK and acetonitrile at 120 °C. This method regioselectively gave 2,4,5-trisubstituted oxazoles in yields up to 97%

Computational Design of Alloy-Core@Shell Metal Nanoparticle Catalysts

The alloy-core@shell nanoparticle structure combines the advantages of a robust noble-metal shell and a tunable alloy-core composition. In this study we demonstrate a set of linear correlations between the binding of adsorbates to the shell and the alloy-core composition, which are general across a range of nanoparticle compositions, size, and adsorbate molecules. This systematic tunability allows for a simple approach to the design of such catalysts. Calculations of candidate structures for the hydrogen evolution reaction predict a high activity for the PtRu@Pd structure, in good agreement with what has been reported previously. Calculations of alloy-core@Pt 140-atom nanoparticles reveal new candidate structures for CO oxidation at high temperature, including Au_0.65Pd_0.35@Pt and Au_0.73Pt_0.27@Pt, which are predicted to have reaction rates 200 times higher than that of Pt(111)

Data_Sheet_3_Componential usage patterns in dengue 4 viruses reveal their better evolutionary adaptation to humans.doc

There have been at least four types of dengue outbreaks in the past few years. The evolutionary characteristics of dengue viruses have aroused great concerns. The evolutionary characteristics of dengue 4 viruses are studied in the present study based on their base usage patterns and codon usage patterns. The effective number of codons and relative synonymous codon usage (RSCU) values of four types of dengue viruses were counted or calculated. The Kullback–Leibler (K–L) divergences of relative synonymous codon usage from dengue viruses to humans and the Kullback–Leibler divergences of amino acid usage patterns from dengue viruses to humans were calculated to explore the adaptation levels of dengue viruses. The results suggested that: (1) codon adaptation in dengue 4 viruses occurred through an evolutionary process from 1956 to 2021, (2) overall relative synonymous codon usage values of dengue 4 viruses showed more similarities to humans than those of other subtypes of dengue viruses, and (3) the smaller Kullback–Leibler divergence of amino acid usage and relative synonymous codon usage from dengue viruses to humans indicated that the dengue 4 viruses adapted to human hosts better. All results indicated that both mutation pressure and natural selection pressure contributed to the codon usage pattern of dengue 4 viruses more obvious than to other subtypes of dengue viruses and that the dengue 4 viruses adapted to human hosts better than other types of dengue viruses during their evolutionary process.</p

Data_Sheet_2_Componential usage patterns in dengue 4 viruses reveal their better evolutionary adaptation to humans.xls

There have been at least four types of dengue outbreaks in the past few years. The evolutionary characteristics of dengue viruses have aroused great concerns. The evolutionary characteristics of dengue 4 viruses are studied in the present study based on their base usage patterns and codon usage patterns. The effective number of codons and relative synonymous codon usage (RSCU) values of four types of dengue viruses were counted or calculated. The Kullback–Leibler (K–L) divergences of relative synonymous codon usage from dengue viruses to humans and the Kullback–Leibler divergences of amino acid usage patterns from dengue viruses to humans were calculated to explore the adaptation levels of dengue viruses. The results suggested that: (1) codon adaptation in dengue 4 viruses occurred through an evolutionary process from 1956 to 2021, (2) overall relative synonymous codon usage values of dengue 4 viruses showed more similarities to humans than those of other subtypes of dengue viruses, and (3) the smaller Kullback–Leibler divergence of amino acid usage and relative synonymous codon usage from dengue viruses to humans indicated that the dengue 4 viruses adapted to human hosts better. All results indicated that both mutation pressure and natural selection pressure contributed to the codon usage pattern of dengue 4 viruses more obvious than to other subtypes of dengue viruses and that the dengue 4 viruses adapted to human hosts better than other types of dengue viruses during their evolutionary process.</p

Data_Sheet_1_Componential usage patterns in dengue 4 viruses reveal their better evolutionary adaptation to humans.xls

There have been at least four types of dengue outbreaks in the past few years. The evolutionary characteristics of dengue viruses have aroused great concerns. The evolutionary characteristics of dengue 4 viruses are studied in the present study based on their base usage patterns and codon usage patterns. The effective number of codons and relative synonymous codon usage (RSCU) values of four types of dengue viruses were counted or calculated. The Kullback–Leibler (K–L) divergences of relative synonymous codon usage from dengue viruses to humans and the Kullback–Leibler divergences of amino acid usage patterns from dengue viruses to humans were calculated to explore the adaptation levels of dengue viruses. The results suggested that: (1) codon adaptation in dengue 4 viruses occurred through an evolutionary process from 1956 to 2021, (2) overall relative synonymous codon usage values of dengue 4 viruses showed more similarities to humans than those of other subtypes of dengue viruses, and (3) the smaller Kullback–Leibler divergence of amino acid usage and relative synonymous codon usage from dengue viruses to humans indicated that the dengue 4 viruses adapted to human hosts better. All results indicated that both mutation pressure and natural selection pressure contributed to the codon usage pattern of dengue 4 viruses more obvious than to other subtypes of dengue viruses and that the dengue 4 viruses adapted to human hosts better than other types of dengue viruses during their evolutionary process.</p

A Helix-Stabilizing Linker Improves Subcutaneous Bioavailability of a Helical Peptide Independent of Linker Lipophilicity

Stabilized peptides address several limitations to peptide-based imaging agents and therapeutics such as poor stability and low affinity due to conformational flexibility. There is also active research in developing these compounds for intracellular drug targeting, and significant efforts have been invested to determine the effects of helix stabilization on intracellular delivery. However, much less is known about the impact on other pharmacokinetic parameters such as plasma clearance and bioavailability. We investigated the effect of different fluorescent helix-stabilizing linkers with varying lipophilicity on subcutaneous (sc) bioavailability using the glucagon-like peptide-1 (GLP-1) receptor ligand exendin as a model system. The stabilized peptides showed significantly higher protease resistance and increased bioavailability independent of linker hydrophilicity, and all subcutaneously delivered conjugates were able to successfully target the islets of Langerhans with high specificity. The lipophilic peptide variants had slower absorption and plasma clearance than their respective hydrophilic conjugates, and the absolute bioavailability was also lower likely due to the longer residence times in the skin. Their ease and efficiency make double-click helix stabilization chemistries a useful tool for increasing the bioavailability of peptide therapeutics, many of which suffer from rapid in vivo protease degradation. Helix stabilization using linkers of varying lipophilicity can further control sc absorption and clearance rates to customize plasma pharmacokinetics

A Reactive Molecular Dynamics Study of <i>n</i>‑Heptane Pyrolysis at High Temperature

<i>n</i>-Heptane is the most important straight chain paraffin in the fossil-fuel industry. In this work, pyrolysis of <i>n</i>-heptane at high temperature is investigated by a series of ReaxFF based reactive molecular dynamic simulations. The pyrolysis correlated intermediate reactions, important product/intermediate distributions, and corresponding kinetics behaviors are systematically analyzed at atomistic level. The results indicate that the entire pyrolysis process is radical-dominated. The unimolecular dissociation is the main pathway of <i>n</i>-heptane decomposition. Initiation of the decomposition is mainly through C–C bond fission. Central C–C bonds would dissociate prior to the terminal ones. Besides, the Rice–Kossiakoff theory is proved for the pyrolysis of <i>n</i>-heptane at the atomistic level. To give a better description of the pyrolysis behavior, some alkane related intermolecular reactions should be considered in the mechanism. The apparent activation energy extracted from the present simulations is 43.02–54.49 kcal/mol in the temperature range 2400–3000 K, which is reasonably consistent with the experimental results

CO Oxidation at the Au–Cu Interface of Bimetallic Nanoclusters Supported on CeO₂(111)

DFT+U calculations of the structure of CeO₂(111)-supported Au-based bimetallic nanoclusters (NCs) show that a strong support–metal interaction induces a preferential segregation of the more reactive element to the NC–CeO₂ perimeter, generating an interface with the Au component. We studied several Au -based bimetallic NCs (Au-X, X: Ag, Cu, Pd, Pt, Rh, and Ru) and found that (Au–Cu)/CeO₂ is optimal for catalyzing CO oxidation via a bifunctional mechanism. O₂ preferentially binds to the Cu-rich sites, whereas CO binds to the Au-rich sites. Engineering a two-component system in which the reactants do not compete for binding sites is the key to the high catalytic activity at the interface between the components