Rheological Properties and Microstructures of Hydroxyethyl Cellulose/Poly(Acrylic Acid) Blend Hydrogels

A simple in-situ method was introduced to prepare hydroxyethyl cellulose/poly(acrylic acid) (HEC/PAA) blend hydrogels by forming an interpenetrating network (IPN). Storage modulus (G′) and loss modulus (G″) were improved dramatically compared to HEC. To prove that hydrogen bonds and chemical crosslinking played major roles in improving the hydrogel strength and toughening, and to optimize the components of HEC/PAA blend hydrogels, a series of blend hydrogels with different ratios of HEC to PAA were designed and the corresponding Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), rheological tests, and swelling properties were compared. Crosslinked HEC/PAA blend hydrogel (mol/mol = 1:1) showed the best properties appropriate for opening up biomedical applications of the hydrogel.     

Adsorption of Hydrogels Based on Cellulose for Cu(II) and Ni(II): Behaviors and Mechanisms

Hydrogels based on cellulose-graft-poly (acrylic acid) copolymers (C-g-AA) were synthesized by graft copolymerization in a phosphoric acid solvent. Fourier transform infrared (FT-IR) spectra confirmed the structure of the C-g-AA. The adsorption behaviors of the hydrogels for Cu(II) and Ni(II) were investigated. The results showed that their adsorption capacity increased as the initial concentrations of metal ions and the pH value of the solution increased. Freundlich and Langmuir isotherm models were employed to analyze the data from batch adsorption experiments. The results indicated that there were very good correlation coefficients for their linearized equations. The maximum adsorption amounts of the hydrogels for the metal ions, based on the Langmuir model, were 182 and 200 mg/g for Cu(II) and Ni(II), respectively. When the initial concentration of metal ions was 1000 mg/g the actual adsorption amounts of the hydrogels for Cu(II) and Ni(II) were 181 and 183 mg/g, respectively.     

Rapid Deswelling of Porous Poly[2-(N-morpholino)ethyl methacrylate] Hydrogel and Controlled Release of Ibuprofen

A novel, rapidly responsive, cross-linkedpoly[(2-N morpholino)ethyl methacrylate] (PMEMA) hydrogel was synthesized through free radical polymerization at room temperature. The highly swellable PMEMA gel displayed rapid deswelling kinetics in response to salt and temperature changes in its environment. During the deswelling test the hydrogel lost 75% of its water within 4 min in response to the salt effect, while it lost only 30% of its water in response to a temperature change within the same interval. Scanning electron microscopy revealed that the PMEMA gel has numerous open pore channels allowing rapid diffusion of water or water-soluble molecules from the gel matrix. Such a rapid response to environmental stimuli is promising for biomedical applications. Therefore, the designed gel was used as a potential drug carrier using water insoluble Ibuprofen (IBU) as a test drug. The results suggest that the PMEMA hydrogel would be beneficial for achieving a slow/controlled release of water-insoluble drugs.     

The exponent λ (x, Q2) of the proton structure functionF2(x, Q2) at lowx

The exponent λ of the structure function F₂ ∼x ^−λ is calculated using the solution of the DGLAP equation for gluon at lowx reported recently by the present authors. The quantity λ is calculated both as a function ofx at fixedQ ² and as a function ofQ ² at fixedx and compared with the most recent data from H1     

On Localization of Clay Nanoparticles in Polypropylene/poly(Lactic Acid) Blend Nanocomposites: Correlation with Mechanical Properties

Two polypropylene (PP)/polylactide (PLA)/clay ternary nanocomposite systems, i.e. PP-rich and PLA-rich ones, each containing various amounts of one of two types of clay, were prepared by one step melt compounding in a twin screw extruder. The microstructures of the developed systems were correlated with tensile and impact properties. A theoretical calculation using wetting coefficients was used for predicting the clay nanoparticles localization in the blends. The nanoparticles were almost completely located within the PLA phase in both the PP-rich and PLA-rich systems, in good agreement with the predictions. Addition of a compatibilizer led to localization of the nanoparticles at the interfaces of the blends. From the wide angle X-ray scattering (WAXS) spectra it was concluded that the incorporation of clay led to intercalated structures in the both systems. The increase in impact toughness of the compatibilized blend nanocomposites, with respect to the uncompatibilized ones, was attributed to the weakened interfacial debonding in the presence of the interfacial-localized nanoparticles.     

Structural,electronic and magnetic properties of the (001), (110) and (111) surfaces of rocksalt sodium sulfide: A first-principles study

First principles study of the structural, electronic and magnetic properties of the (111), (110) and (001) surfaces of rocksalt sodium sulfide (rs-NaS) are reported. The results show that the bulk half-metallicity of this compound is well preserved on the surfaces considered here except for Na-terminated (111) surface. The spin-flip gap at the S-terminated (111), (001) and (110) surfaces are close to the bulk value. Using ab-initio atomistic thermodynamics, we calculate the surface energies as a function of chemical potential to find the most stable surface. We find that the Na-terminated (111) surface is the most stable one over the whole allowed range of chemical potential, while the surface energies of the (001) and (110) surfaces approach the most stable surface energy at the sulfur rich environment. We have also calculated the interlayer exchange interaction in bulk and Na-terminated (111) surface by classical Heisenberg model and we found that the surface effects do not change these kinds of interactions significantly.     

Structural Investigation of (5-Amino-1,3,4-thiadiazolyl-2-thionato)trimethyltin(IV): 1D Chains Generated by Hydrogen Bonding

ABSTRACT

The geometry of the four-coordinated Sn atom in the title compound, (CH₃)₃Sn(C₂H₂N₃S₂), is distorted tetrahedral with three Sn–C bonds and one Sn–S bond. Two crystallographically distinct molecules a and b within the asymmetric unit are hydrogen bonded. Intermolecular “N–H?N” hydrogen bond interactions generate infinite 1D chains consisting of alternating, centrosymmetric R2,2(8) and R4,2(10) rings.     

Structural, vibrational, thermal and magnetic investigation of novel Co(II), Cu(II), Zn(II) and Hg(II) crystalline metal complexes with 2-amino-5-benzylmercapto-1,3,4-thiadiazole: a low weight model of protonated copolymer resin

The 2-amino-5-benzylmercapto-1,3,4-thiadiazole (C₉H₉N₃S₂) is a low weight model of a protonated copolymer resin used as a metal uptake agent. New monomeric crystalline metal complexes of C₉H₉N₃S₂ with Co(II), Cu(II), Zn(II) and Hg(II) were synthesized and investigated in order to facilitate the interpretation of the metal/resin binding mode. These materials have been studied by single crystal X-ray Diffraction and FTIR Spectroscopy at room temperature. Crystal data for these triclinic phases are reported. All frameworks consist of discrete monomeric units that provide crystalline stability through a network of hydrogen bond interactions. The Co(II), Zn(II) and Hg(II) ions are surrounded by a tetrahedral arrangement of two thioether monodentate ligands (each one coordinating by a N(1)_thiadiazole atom) and two chlorine atoms. The Cu(II) ion is coordinated by four thioether monodentate ligands (each one coordinating by a N(1)_thiadiazole atom) and one chlorine atom as nearest neighbor in a distorted square pyramidal polyhedron. The spectroscopic data are consistent with the structural model. FTIR spectra evidence changes in the H-bonds in the crystal packing when coordination with these divalent ions is present. Magnetic susceptibility at room temperature for Cu(II) and Co(II) complexes, EPR spectrum at room temperature for Cu(II) complex and thermal properties for all complexes were measured. These results could be useful for the interpretation of the binding mode of M(II)/1,3,4-thiadiazole-2-amino-5-thiol in protonated copolymer resin which are used as uptake agents of toxic metallic ions.     

Electronic structures and magnetism of Fe nanowires on Cu（001） and Ag（O01）： A first-principles study

The electronic structures and magnetism of Fe nanowires along the [110] direction on Cu（001） and Ag（001） [Fe（nw）/Cu（001） and Fe（nw）/Ag（001）] are investigated by using the all-electron full-potential linearized augmented plane wave method in the generalized gradient approximation. It is found that the magnetic moment of Fe atom for the Fe（nw）/Cu（001） is 2.99#B, which is slightly smaller than that （3.02μB） for the Fe（nw）/Ag（001） but much larger than that （2.22μB） for the bcc iron. The great enhancement of magnetic moment in the Fe nanowires can be explained by the Fe d-band narrowing and enhancement of the spin-splitting due to a reduction in coordination number, From the calculated spin-polarized layer-projected density of states, it is found that the Fe 3d-states are strongly hybridized with the adjacent Cu 3d-states in the Fe（nw）/Cu（001）, and there exists a strong hybridization between the Fe sp-and the adjacent Ag 4d-states in the Fe（nw）/Ag（001）.     

Structural and Electronic Properties of Li2Mg(NH)2 for Hydrogen Storage: First-principles Study

应用第一原理方法研究了储氢材料α-Li₂Mg(NH)₂和β-Li₂Mg(NH)₂两种构型的结构性质和电子性质．计算优化得到的晶胞参数和N-H键长符合实验得到的数据．通过Murnaghan状态方程得到了体积模量和零压力下的能量,计算结果表明α-Li₂Mg(NH)₂为基态构型．通过Mulliken布居分析说明α构型的N-Li/Mg的离子特性和N-H间的交互作用都弱于β构型．态密度分析结果表明,价带轨道主要由N原子的s轨道和p轨道占据,并与H原子的s轨道杂化．     

Structural and phonon dynamical properties of perovskite manganites: (Tb, Dy, Ho)MnO3

A shell model has been used to study the structure, phonon dynamics and phase coexistence of perovskite manganites RMnO₃ (R=Tb, Dy, Ho). The calculated crystal structure, Raman and IR frequencies and specific heats are found to be in good agreement with the available experimental data. The phonon density of states, elastic constants, elastic stiffness, shear constants and phonon dispersion curves have been computed for these manganites. A zone center imaginary A_u mode is revealed in these phonon dispersion curves, which indicates the occurrence of the metastability of the perovskite phase. The Gibbs free energy values calculated as a function of temperature and pressure for RMnO₃ in the orthorhombic phase, when compared with those of the hexagonal phase, reveal the possibility of coexistence of these two phases in the present multiferroic manganites under ambient conditions.     

Predicting Bitcoin (BTC) Price in the Context of Economic Theories: A Machine Learning Approach

Bitcoin (BTC)—the first cryptocurrency—is a decentralized network used to make private, anonymous, peer-to-peer transactions worldwide, yet there are numerous issues in its pricing due to its arbitrary nature, thus limiting its use due to skepticism among businesses and households. However, there is a vast scope of machine learning approaches to predict future prices precisely. One of the major problems with previous research on BTC price predictions is that they are primarily empirical research lacking sufficient analytical support to back up the claims. Therefore, this study aims to solve the BTC price prediction problem in the context of both macroeconomic and microeconomic theories by applying new machine learning methods. Previous work, however, shows mixed evidence of the superiority of machine learning over statistical analysis and vice versa, so more research is needed. This paper applies comparative approaches, including ordinary least squares (OLS), Ensemble learning, support vector regression (SVR), and multilayer perceptron (MLP), to investigate whether the macroeconomic, microeconomic, technical, and blockchain indicators based on economic theories predict the BTC price or not. The findings point out that some technical indicators are significant short-run BTC price predictors, thus confirming the validity of technical analysis. Moreover, macroeconomic and blockchain indicators are found to be significant long-term predictors, implying that supply, demand, and cost-based pricing theories are the underlying theories of BTC price prediction. Likewise, SVR is found to be superior to other machine learning and traditional models. This research’s innovation is looking at BTC price prediction through theoretical aspects. The overall findings show that SVR is superior to other machine learning models and traditional models. This paper has several contributions. It can contribute to international finance to be used as a reference for setting asset pricing and improved investment decision-making. It also contributes to the economics of BTC price prediction by introducing its theoretical background. Moreover, as the authors still doubt whether machine learning can beat the traditional methods in BTC price prediction, this research contributes to machine learning configuration and helping developers use it as a benchmark.     

Incorporation of Benzocyclobutene Cross-Linkable Moieties in Poly(Methyl Acrylate): A Novel Approach to Shape-Memory Polymers Accompanied with Microphase Separation

Benzocyclobutene (BCB) moieties were incorporated into a typical polyolefin, poly(methyl acrylate), by free radical copolymerization of benzocyclobutene-4-yl acrylate and methyl acrylate. The subsequent cross-linking of the generated copolymers by ring-opening reaction of BCB gave rise to shape-memory polymers. This new cross-linking process did not require cross-linker and yielded small molecules. Most importantly, submicron-sized particles within the cross-linked polymers, which were observed using atomic force microscope, were induced by this cross-linking strategy. The results of the shape-memory tests suggested that the cross-linked polymers displayed good shape-memory performance.     

Linear and nonlinear optical properties of 3-nitroaniline (m-NA) and 4-nitroaniline (p-NA) crystals: A DFT/TDDFT study

We have studied the electronic structure and optical responses of 3-nitroaniline and 4-nitroaniline crystals within the framework of density functional theory (DFT). In addition, the excitonic effects are investigated by using the recently published bootstrap exchange-correlation kernel within the time dependent density functional theory (TDDFT) framework. Our calculations based on mBJ approximation yield the indirect band gap for both crystals, but the larger one for m-NA. Due to the excitonic effects, the TDDFT calculations gives rise to the enhanced and red-shifted spectra (compared to RPA). Due to the weak intermolecular interactions, band-structure calculations yield bands with low dispersion for both crystals. This study shows that the substituent groups play an important role in the top of valence band and the bottom of conduction band. Due to the linear structure of p-NA molecule, the highest peaks are located in the optical spectra of p-NA crystal, while m-NA has more sharp peaks, especially at lower energies. Both DFT and TDDFT calculations for the energy loss spectra show plasmon peaks around 27 and 28 eV for p-NA and m-NA, respectively. Due to the non-centrosymmetric structure of m-NA crystal, we also have reported its nonlinear spectra and the 2ω/ω intra-band and inter-band contributions to the dominant susceptibilities. Findings indicate the opposite signs for these contributions, especially at higher energies. The comparison between nonlinear spectra and the linear spectra (as a function of both ω and 2ω) reveals the significant resemblance between linear and nonlinear patterns. In addition to the reasonable agreement between our results with experimental data, this study reveals the spectral similarities between crystalline susceptibility and molecular polarizability.     

High resolution XPS study of the large-band-gap semiconductor stibnite (Sb2S3): Structural contributions and surface reconstruction

Conventional X-ray photoelectron spectroscopy (XPS) and synchrotron radiation XPS (SRXPS) were used to probe the chemical state properties of stibnite (Sb₂S₃), a large-band-gap semiconductor of complex structure. The conventional spectra were obtained with a Kratos Axis Ultra XPS with magnetic confinement charge neutralization, which is very effective in minimizing both uniform charging and differential charging on this large-band-gap semiconductor. The narrow linewidths (much narrower than previously obtained) for single doublet fits (e.g. Sb 4d_5/2 of 0.57 eV and S 2p_3/2 of 0.63 eV) enabled the observation of a small peak on the low binding energy side of the Sb 3d and Sb 4d lines. With the aid of the very surface-sensitive Sb 4d SRXPS spectra, these low energy peaks are assigned to small Sb metal clusters at the surface after cleavage; the signal for these clusters increases with X-ray dose on the sample.A detailed analysis of the Sb 4d and S 2p linewidths concludes that the Sb 4d_5/2 linewidth is larger than expected based on the inherent linewidth of the instrument and the Sb 4d lifetime width, and on comparison with the As 3d linewidth (0.52 eV) for the analogous As₂S₃. Also, the S 2p_3/2 linewidth is substantially broader than the Sb 4d_5/2 linewidth. These larger than expected linewidths are due to two structurally distinct Sb atoms and three structurally distinct S atoms in the Sb₂S₃ crystal structure. Accordingly, the Sb 4d and S 2p spectra have been fitted to two and three doublets respectively, and the linewidth for all peaks is 0.53 eV. Using recent molecular orbital calculations, the doublets have been assigned to the different structural Sb and S sites.     

Comment on: “Solution of the Dirac equation for the Woods–Saxon potential with spin and pseudospin symmetry” [Phys. Lett. A 338 (2005) 90]

The bound-state method employed by Guo and Sheng [J.Y. Guo, Z.-Q. Sheng, Phys. Lett. A 338 (2005) 90] is shown inadequate since only one of their solutions remains compatible, in the spin-symmetric low-mass regime, with the physical boundary conditions. We clarify the problem and construct a new, correct solution in the pseudospin-symmetric regime.     

Structural,electronic, optical and elastic properties of the complex K2PtCl6-structure hydrides ARuH6 (A = Mg,Ca, Sr and Ba): first-principles study

We report a systematic study of the structural, electronic, optical and elastic properties of the ternary ruthenium-based hydrides A₂RuH₆ (A = Mg, Ca, Sr and Ba) within two complementary first-principles approaches. We describe the properties of the A₂RuH₆ systems looking for trends on different properties as a function of the A sublattice. Our results are in agreement with experimental ones when the latter are available. In particular, our theoretical lattice parameters obtained using the GGA-PBEsol to include the exchange-correlation functional are in good agreement with experiment. Analysis of the calculated electronic band structure diagrams suggests that these hydrides are wide nearly direct band semiconductors, with a very slight deviation from the ideal direct-band gap behaviour and they are expected to have a poor hole-type electrical conductivity. The TB-mBJ potential has been used to correct the deficiency of the standard GGA for predicting the optoelectronic properties. The calculated TB-mBJ fundamental band gaps are about 3.53, 3.11, 2.99 and 2.68 eV for Mg₂RuH₆, Ca₂RuH₆, Sr₂RuH₆ and Ba₂RuH₆, respectively. Calculated density of states spectra demonstrates that the topmost valence bands consist of d orbitals of the Ru atoms, classifying these materials as d-type hydrides. Analysis of charge density maps tells that these systems can be classified as mixed ionic-covalent bonding materials. Optical spectra in a wide energy range from 0 to 30 eV have been provided and the origin of the observed peaks and structures has been assigned. Optical spectra in the visible range of solar spectrum suggest these hydrides for use as antireflection coatings. The single-crystal and polycrystalline elastic moduli and their related properties have been numerically estimated and analysed for the first time.