Mesoscopic to universal crossover of the transmission phase of multilevel quantum dots

Transmission phase alpha measurements of many-electron quantum dots (small mean level spacing delta) revealed universal phase lapses by pi between consecutive resonances. In contrast, for dots with only a few electrons (large delta), the appearance or not of a phase lapse depends on the dot parameters. We show that a model of a multilevel quantum dot with local Coulomb interactions and arbitrary level-lead couplings reproduces the generic features of the observed behavior. The universal behavior of alpha for small delta follows from Fano-type antiresonances of the renormalized single-particle levels.     

Some Physico-chemical Properties of Doxazosin Mesylate Polymorphic Forms and its Amorphous State

Seven polymorphic modifications of doxazosin mesylate, designed as forms A, D, E, F, G, H, I, and the amorphous state were studied by thermal methods (TG and DSC), temperature resolved X-ray powder diffractometry, hot stage and scanning electron microscopy and by FT-IR spectroscopy. Amorphous form was obtained either by fast evaporation of the solvent or by fast cooling of the melt in the DSC. Polymorphs A and F were found to be stable in the temperature range from room temperature to their melting points at 277.9 and 276.5°C, respectively. Form G, which melts at 270.8°C, was found to be hygroscopic. Polymorph D undergoes irreversible solid–liquid–solid phase transition at 235.5°C to polymorph I which melts at 274.9°C. Form H, which melts at 258.0°C, was found to be unstable at high temperatures. DSC examinations revealed that form H is irreversibly transformed to polymorph F during heating above the temperature of about 240°C. The amorphous state was found to be stable at room temperature but when heating above the glass transition (T _g=144.1°C) it crystallizes at 221.6°C, what leads into a mixture of polymorphic forms. The new polymorphic form designed as E was identified in the mixture. The polymorph E is converted by heating to the more stable form F. The solubilities at 25°C for forms A, and F in methanol are 3.5 and 7.7 mg mL⁻¹and in water they are 3.8 and 6.2 mg mL⁻¹, respectively. This revised version was published online in August 2006 with corrections to the Cover Date.     

In situ UV-Vis and ex situ IR spectroelectrochemical investigations of amorphous and crystalline electrochromic Nb2O5 films in charged/discharged states

Niobium oxide (Nb₂O₅) films and powders have been obtained via the sol-gel route from an NbCl₅ precursor. XRD spectra revealed that films with pseudohexagonal (TT-phase) and orthorhombic (T-phase) structure were formed at 500  °C and 800  °C, respectively, while at 300  °C films were amorphous. Infrared (IR) and Raman spectra of powders and films of Nb₂O₅ in different polymorphic forms were detected, and vibrational band assignments were made. Electrochromic properties of amorphous films and films with the TT-phase were established from in situ ultraviolet visible (UV-Vis) spectroelectrochemical measurements and correlated with ex situ IR transmission spectra of charged films. Ex situ IR spectra revealed that charging of amorphous films is accompanied by variations of the Nb-O stretching mode intensity, while, for films with the TT- and T-phase, splitting of the Nb₃-O stretching modes and the appearance of polaron absorption were noted with Li⁺ ion insertion. Ex situ X-ray diffraction (XRD) spectra of charged films with the TT-phase showed changes of the unit cell dimensions with charging. The influence of the polaron absorption on the ex situ near-grazing incidence angle (NGIA) IR reflection-absorption spectra of charged/discharged films is discussed in detail. Received: 21 August 1997 / Accepted: 9 October 1997     

1,3‐Dipolar cycloadditions of (4R*,5R*)‐1‐alkylidene‐4‐(benzoylamino)‐5‐phenyl‐3‐pyrazolidinon‐1‐azomethine imines

1,3‐Dipolar cycloadditions of azomethine imines 3a and 3b , available by acid‐catalyzed treatment of 3‐pyrazolidinone 1 with acetone ( 2a ) and butyraldehyde ( 2b ), respectively, were studied. Reactions of 3a with DMAD ( 4 ) afforded a mixture of products 9 and 10a , whilst treatment of 3b with DMAD ( 4 ) gave a mixture of compound 9 and epimeric cycloadducts 10 / 10′b . On the other hand, cycloadducts 13a,b‐16a,b were isolated as single diastereomers in 9–37% yields upon reactions of 3a,b with olefinic dipolarophiles 5–8 . The structures of cycloadducts 9, 10a, 10/10′b , and 13a,b‐16a,b were determined by ¹H nmr and NOESY spectroscopy. The structure of compound 13a was confirmed by X‐ray diffraction.     

A simple synthesis of 4-(2-aminoethyl)-5-hydroxy-1H-pyrazoles

A simple four-step synthesis of 4-(2-aminoethyl)-5-hydroxy-1H-pyrazoles 8 (or their 1H-pyrazol-3(2H)-one tautomers 8′) as the pyrazole analogues of histamine was developed. First, enamino lactam 3 was prepared as the key intermediate in two steps from 2-pyrrolidinone (1). Next, acid-catalysed ‘ring switching’ transformations of 3 with monosubstituted hydrazines 4 gave N-[(1-substituted 5-hydroxy-1H-pyrazol-4-yl)ethyl]benzamides 7a-k and N-[2-(2-heteroaryl-3-oxo-2,3-dihydro-1H-pyrazol-4-yl)ethyl]benzamides 7′l-o. Benzamides 7a-k and 7′l-o were finally hydrolysed by heating in 6 M hydrochloric acid to furnish 1-substituted 4-(2-aminoethyl)-5-hydroxy-1H-pyrazoles 8a-k and 4-(2-aminoethyl)-2-heteroaryl-1H-pyrazol-3(2H)-ones 8′l-o in good overall yields.     

Luttinger liquids with boundaries: Power-laws and energy scales

We present a study of the one-particle spectral properties for a variety of models of Luttinger liquids with open boundaries. We first consider the Tomonaga-Luttinger model using bosonization. For weak interactions the boundary exponent of the power-law suppression of the spectral weight close to the chemical potential is dominated by a term linear in the interaction. This motivates us to study the spectral properties also within the Hartree-Fock approximation. It already gives power-law behavior and qualitative agreement with the exact spectral function. For the lattice model of spinless fermions and the Hubbard model we present numerically exact results obtained using the density-matrix renormalization-group algorithm. We show that many aspects of the behavior of the spectral function close to the boundary can again be understood within the Hartree-Fock approximation. For the repulsive Hubbard model with interaction U the spectral weight is enhanced in a large energy range around the chemical potential. At smaller energies a power-law suppression, as predicted by bosonization, sets in. We present an analytical discussion of the crossover and show that for small U it occurs at energies exponentially (in -1/U) close to the chemical potential, i.e. that bosonization only holds on exponentially small energy scales. We show that such a crossover can also be found in other models. Received 8 February 2000 and Received in final form 25 April 2000