New books

Ohne Zusammenfassung

---

New books

     

The parabolic equation as a limiting case of a certain elliptic equation

Summary We consider the Dirichlet problem for the equation L_ε(u) ≡ u_xx+ɛu_yy++A(x, y)u_x−B(y)u_y+C(x, y)u=F(x, y) where B(y)>0 and ɛ is a small positive parameter. An asymptotic formula is proved, from which it follows that in a suitable part of the domain of definition u(x, y, ɛ)→U(x, y) as ɛ→0+, where U(x, y) is the solution of the corresponding boundary - value problem for the reduced equation L₀(U)≡U_xx+A(x, y)U_x−B(y)U+C(x, y)U=F(x, y). To Enrico Bompiani on his scientific Jubilee.     

Development and validation of an HPLC method for the determination of verapamil residues in supports of cleaning procedure

Analytical method validation, determining the recovery rate from the equipment surface, and stability of a potential contaminant are important steps of a cleaning validation process. An HPLC method for the determination of the verapamil residues on stainless steel surfaces of the equipment employed in drug manufacture is described. The cleaning validation sample impurities as well as excipients of the commercial sample did not interfere in the analysis which proved the selectivity of the method. The validation of the method demonstrated acceptable levels of the linearity, precision and accuracy. Cotton swabs, moistened with methanol were used to remove any residues of drugs from stainless steel surfaces, and give recoveries of above 78.59% for three diferent concentration levels. The precision of the results, reported as the relative standard deviation (RSD, %), were below 1.58%. Low quantities of the drug residues were determined by HPLC using a Hypersil ODS column (125 × 4.0 mm, 5 μm) at 25°C with the mobile phase metanol-water-triethylamine (70: 30: 0.2, v/v/v) at a flow rate of 0.6 mL/min, injection volume of 50 μL and detection at 278 nm.     

Fluorescence Anisotropy of Branched Molecules Containing 1-Aminopyrene Chromophores

Fluorescence anisotropy measurements were performed on a set of multichromophoric compounds, which contain a different number of aminopyrenyl moieties linked to a triazine ring, in order to reveal the nature of both the electronic excited states and relaxation pathways of the compounds. Our experimental results complement quantum chemical calculations. We propose that the lowest excited state from which fluorescence proceeds is localized on a single individual aminopyrene moiety. In contrast, excitation to a higher excited state is likely followed by a migration of energy to another nearby aminopyrene chromophore before the internal conversion to the emitting state takes place. We suggest that this migration is responsible for the experimentally measured decrease of fluorescence anisotropy of the studied compounds.     

Field Effect and Local Gating in Nitrogen-Terminated Nanopores (NtNP) and Nanogaps (NtNG) in Graphene

Functionalization of electrodes is a wide-used strategy in various applications ranging from single-molecule sensing and protein sequencing, to ion trapping, to desalination. We demonstrate, employing non-equilibrium Green′s function formalism combined with density functional theory, that single-species (N, H, S, Cl, F) termination of graphene nanogap electrodes results in a strong in-gap electrostatic field, induced by species-dependent dipoles formed at the electrode ends. Consequently, the field increases or decreases electronic transport through a molecule (benzene) placed in the nanogap by shifting molecular levels by almost 2 eV in respect to the electrode Fermi level via a field effect akin to the one used for field-effect transistors. We also observed the local gating in graphene nanopores terminated with different single-species atoms. Nitrogen-terminated nanogaps (NtNGs) and nanopores (NtNPs) show the strongest effect. The in-gap potential can be transformed from a plateau-like to a saddle-like shape by tailoring NtNG and NtNP size and termination type. In particular, the saddle-like potential is applicable in single-ion trapping and desalination devices.     

Neuro-fuzzy estimation of important coccoliths on abundances of foraminiferal species and fragments abundances

Journal of Radioanalytical and Nuclear Chemistry - The study's major goal was to identify the most significant coccoliths based on foraminiferal species and fragment abundances, oxygen isotope...     

Posets of Copies of Countable Non-Scattered Labeled Linear Orders

Order - We show that the poset of copies $\mathbb {P} (\mathbb {Q}_{n} )=\langle \{ f[X]: f\in \text {Emb} (\mathbb {Q}_{n} ) \},\subset \rangle $ of the countable homogeneous universal n-labeled...     

Chirality-Controlled Self-Assembly of Amphiphilic Dibenzo[6]helicenes into Langmuir–Blodgett Thin Films

Racemic and highly enantioenriched 3-methoxycarbonyl, 3-carboxy, and 3-hydroxymethyl derivatives of dibenzo[6]helicene were prepared. The Langmuir layers of these helicenes were formed at the air–water interface and transferred onto solid substrates to afford Langmuir–Blodgett films, which were then studied by ambient atomic force microscopy and (chir)optical spectroscopy. Significant differences were found in the behaviour of the Langmuir layers as well as in the morphology, UV/Vis, electronic circular dichroism (ECD), and fluorescence spectra of the Langmuir–Blodgett thin films depending on the molecular chirality and nature of the polar group. The experimental results were supported by molecular dynamics simulations.