An engineering theory of soil behaviour in unloading and reloading

Summary A constitutive law is proposed for describing the stress-strain characteristic of soils in unloading-reloading. The constitutive equations are valid piecewisely between subsequent, appropriately formulated, stress reversal loci. The stress-strain relationships are formulated in terms of generalized stress and strain differences referred to the last stress reversal point and connected through a variable compliance tensor. The shear compaction effect is modelled by a suitable formulation of the compliance tensor.Specialization to conventional triaxial condition is given. As well as fitting available experimental data in unloading-reloading of normally consolidated and overconsolidated clays, the proposed constitutive relation can model the dependence on OCR of the shape of the undrained effective stress paths, the phenomenon of cyclic mobility of clay in undrained compression and the unloading-reloading stress paths in the oedometer. The theory requires the identification of only three material constants in addition to those pertinent to the usual elastoplastic theory of soil with which it may be easily combined.

---

Sommario Si propone una legge costitutiva per descrivere il legame sforzi-deformazioni dei terreni sottoposti a processi di scarico e ricarico. Le equazioni costitutive sono formulate a tratti e definite su un dominio limitato dai luoghi di inversione di carico. Nella formulazione della legge costituitiva verranno introdotte delle variabili generalizzate di sforzo riferite all'ultimo punto di inversione di carico. Queste variabili sono legate alle deformazioni, riferite anche esse allo stato relativo all'ultimo punto di inversione di carico, da un tensore di cedevolezza variabile. Un'adeguata formulazione di questo tensore permette di modellare l'efferio di densificazione sotto carico deviatorico ciclico.Questa legge costitutiva interpreta bene i risultati sperimentali su argille normalmente consolidate e sovraconsolidate. La teoria permette anche di descrivere la dipendenza del percorso degli sforzi efficaci in condizioni non drenate dal grado di sovraconsolidazione, la mobilità ciclica dell'argilla in condizioni non drenate e il percorso degli sforzi efficaci in un processo di scarico e ricarico in un edometro.Per identificare il modello sono necessari solo tre parametri oltre a quelli necessari per identificare il comportamento del terreno vergine.

     

A first regularity result for the Armstrong–Frederick cyclic hardening plasticity model with Cosserat effects

The purpose of this article is to prove the Hölder continuity up to the boundary of the displacement vector and the microrotation matrix for the quasistatic, rate-independent Armstrong–Frederick cyclic hardening plasticity model with Cosserat effects. This model is of non-monotone and non-associated type. In the case of two space dimensions we use the hole-filling technique of Widman and Morrey's Dirichlet growth theorem.     

The effect of points fattening on Hirzebruch surfaces

The purpose of this note is to study initial sequences of 0–dimensional subschemes of Hirzebruch surfaces and classify subschemes whose initial sequence has the minimal possible growth.     

Polyelectrolyte coatings prevent interferences from charged nanoparticles in SPME speciation analysis

In this work we present a new approach for protection of the fiber in solid phase microextraction (SPME) from interfering charged particles present in the sample medium. It involves coating of commercial poly(dimethylsiloxane) extraction phase with polyelectrolyte layer composed of poly(diallyldimethylammonium chloride), and poly(sodium 4-styrenesulfonate). The modified fiber provides reproducible, convenient and fast extraction capabilities toward the model analyte, triclosan (TCS). A negatively charged polyelectrolyte coating prevents sorbing oxidic nanoparticles from both partitioning into the PDMS phase and aggregation at its surface. The results for the TCS/nanoparticle sample show that the polyelectrolyte layer-modified solid phase extracts just the free form of the organic compound and enables dynamic speciation analysis of the nanoparticulate target analyte complex.     

The Development and Validation of a Stability-Indicating UHPLC-DAD Method for Determination of Perindopril l-Arginine in Bulk Substance and Pharmaceutical Dosage Form

A stability-indicating ultra-high-performance liquid chromatography (UHPLC) method with a diode array detector was developed and validated for the determination of cis/trans isomers of perindopril l-arginine in bulk substance and pharmaceutical dosage form. The separation was achieved on a Poroshell 120 Hilic (4.6 × 150 mm, 2.7 µm) column using a mobile phase composed of acetonitrile–0.1 % formic acid (20:80 v/v) at a flow rate of 1 mL min^?1. The injection volume was 5.0 µL and the wavelength of detection was controlled at 230 nm. The selectivity of the UHPLC-DAD method was confirmed by determining perindopril l-arginine in the presence of degradation products formed during acid–base hydrolysis and oxidation as well as degradation in the solid state, at an increased relative air humidity and in dry air. The method’s linearity was investigated in the ranges 0.40–1.40 µg mL^?1 for isomer I and 0.40–2.40 µg mL^?1 for isomer II of perindopril l-arginine. The UHPLC-DAD method met the precision and accuracy criteria for the determination of the isomers of perindopril l-arginine. The limits of detection and quantitation were 0.1503 and 0.4555 µg mL^?1 for isomer I and 0.0356 and 0.1078 µg mL^?1 for isomer II, respectively.     

Photophysics,Excited‐state Double‐Proton Transfer and Hydrogen‐bonding Properties of 5‐Deazaalloxazines

The photophysical properties of 5‐deazaalloxazine and 1,3‐dimethyl‐5‐deazaalloxazine were studied in different solvents. These compounds have higher values of fluorescence quantum yields and longer fluorescence lifetimes, compared to those obtained for their alloxazine analogs. Electronic structure and S₀–S_i transitions were investigated using the ab initio methods [MP2, CIS(D), EOM‐CCSD] with the correlation‐consistent basis sets. Also the time‐dependent density functional theory (TD‐DFT) has been employed. The lowest singlet excited states of 5‐deazaalloxazine and 1,3‐dimethyl‐5‐deazaalloxazine are predicted to have the π, π* character, whereas similar alloxazines have two close‐lying π, π* and n, π* transitions. Experimental steady‐state and time‐resolved spectral studies indicate formation of an isoalloxazinic excited state via excited‐state double‐proton transfer (ESDPT) catalyzed by an acetic acid molecule that forms a hydrogen bond complex with the 5‐deazaalloxazine molecule. Solvatochromism of both 5‐deazaalloxazine and its 1,3‐dimethyl substituted derivative was analyzed using the Kamlet–Taft scale and four‐parameter Catalán solvent scale. The most significant result of our studies is that the both scales show a strong influence of solvent acidity (hydrogen bond donating ability) on the emission properties of these compounds, indicating the importance of intermolecular solute–solvent hydrogen‐bonding interactions in their excited state.     

Enantioselective addition of phenylacetylene to aldehydes catalyzed by a d-glucosamine-derived sulfonamide-titanium complex

We present the synthesis of β-hydroxy sulfonamides derived from d-glucosamine and their application as ligands in titanium tetraisopropoxide promoted enantioselective addition of phenylacetylene to benzaldehyde and selected aromatic and aliphatic aldehydes. The N-3,5-bis(trifluoromethyl)benzenesulfonamido-d-glucosamine derivative was chosen as the most efficient ligand for this addition. The reaction is highly enantioselective for several aromatic aldehydes and enantiomeric excesses up to 92% were obtained.     

The highly enantioselective 1,3-dipolar cycloaddition of alkyl glyoxylate-derived nitrones to E-crotonaldehyde catalyzed by hybrid diamines

1,3-Dipolar cycloaddition of alkyl glyoxylate-derived nitrones to E-crotonaldehyde can be catalyzed by hybrid diamines, obtained from (S)-BINAM and l-α-amino acids. The hybrid of (S)-BINAM and l-Phe was found to be the best organocatalyst. Products were obtained in good yield and diastereoselectivity as well as high enantioselectivity (82-91% ee). Subsequent transformations into functionalized pyrrolidinones have been demonstrated.     

Synthesis of new dendrimers—trimesic acid derivatives

The efficient synthesis of new dendrimeric polyesters up to generation 3 that consist of 1,3,5-benzenetricarboxylic acid building blocks with potential applications in drug delivery is described. The dendrimers possess hydroxy or allyl functional groups on the surface and were prepared through a divergent approach using readily available 2-(hydroxymethyl)-2-ethylpropan-1,3-diol and 1,3,5-benzenetrimethanol as central cores, with 3,5-bis[(allyloxy)methyl]benzoic acid being an essential unit of the dendrimer. The latter compound was synthesized, in high yield, from 1,3,5-benzenetricarboxylic acid, applying selective hydrolysis of the corresponding triester as the key step.