Automated methods for the location of the boundaries of chromatographic peaks

Several simple techniques are presented for the identification of the boundaries of chromatographic peaks. These methods provide a significant reduction in the time needed to perform the rapid, automatic calculation of the central peak moments and to evaluate the quality of a separation while improving the accuracy of the measurements of column efficiencies. It was found that the identification of the peak boundaries as functions of the peak widths and the examination of the slope of the signal to noise versus time plot are viable alternatives to a manual determination.     

Molecular structure, vibrational spectra and nonlinear optical properties of l-Valine Hydrobromide: DFT study

FT-IR and Raman spectra of the nonlinear optical material l-Valine Hydrobromide crystal have been recorded and analyzed. The equilibrium geometry, bonding features and the harmonic vibrational wavenumbers of LVB have been calculated with the help of density functional theory (DFT) calculation. The lowering of NH stretching wavenumber indicates the formation of NH?Br hydrogen bonding. The calculated First order hyperpolarizability value shows that LVB is the potential candidate for the NLO applications. The electronic effects and the hydrogen bonding were explained using natural bond orbital analysis.     

Quantum chemical studies on structure of 1-3-dibromo-5-chlorobenzene

Molecular structure and vibrational frequencies of 1-3-dibromo-5-chlorobenzene (DBCB) have been investigated by density functional theory (DFT) calculations using Becke's three-parameter exchange functional combined with Lee–Yang–Parr correlation (B3LYP) and standard basis set 6-31G. DFT (B3LYP/6-31G) calculations have been performed giving energies, optimized structure, harmonic vibrational frequencies, IR intensities, and Raman activities. Raman and IR spectra of the DBCB were recorded and complete assignment of the observed vibrational bands of DBCB has been proposed. The predicted first-hyperpolarizability of DBCB is 1.221 × 10⁻³⁰ esu, which suggests that the title compound is an attractive object for future studies of non-linear optical properties. The impact of di-substituted halogens on the compound has also been discussed. Besides, molecular electrostatic potential (MEP), HOMO–LUMO analysis and NBO analysis were performed at DFT level of theory The UV–vis spectral analysis of DBCB has also been done which confirms the charge transfer of the title compound.     

Molecular structure, vibrational spectroscopic, first hyperpolarizability, NBO and HOMO, LUMO studies of P-Iodobenzene sulfonyl chloride

In this work, the experimental and theoretical vibrational spectra of P-Iodobenzene sulfonyl chloride (P-IBSC) were studied. P-IBSC and its derivatives present in many biologically active compounds. Because of their spectroscopic properties and chemical significance in particular, sulfonyl chloride and its derivatives have been studied extensively by spectroscopic (FTIR and FT-Raman spectra) and theoretical methods. The infrared spectra of these compounds were recorded in condensed states, while the Raman spectra were measured without polarization using both parallel and perpendicular polarizations of scattered light. The molecular geometry, highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), first order hyperpolarizability and thermodynamic properties of P-IBSC have been computed with the help of density functional theory (B3LYP) and ab initio (HF) methods with the LanL2DZ basis set. The HOMO and LUMO energy gap explains the charge transfer interactions taking place within the molecule. NBO study explains charge delocalization of the molecule. The contributions of the different modes to each wave number were determined using potential energy distributions (PEDs). The experimental and calculated results were consistent with each other.     

Boot Camp: A Novel Intensive Approach to Voice Therapy

It is well known in the disciplines of neurobiology, exercise physiology, motor learning, and psychotherapy that desirable learning and behavior changes occur primarily from practice that involves high-intensity overload, variability, and specificity of training. We propose a novel treatment approach called intensive short-term voice therapy that uses these practice parameters for recalcitrant dysphonia. Intensive short-term voice therapy involves multiple sessions with a variety of clinicians, incorporating multiple simultaneous therapeutic approaches. The intensive short-term voice therapy approach is characterized by voice therapy for 1–4 successive days each with an average of 5 hours of therapy and five clinicians. This form of intensive voice therapy provides rigorous practice, involving not only overload but also opportunities for specificity and individuality thereby facilitating better transfer of learned skills. This article discusses the conceptual, theoretical, and practical foundations of this novel therapy approach.     

First-principle calculations on optical properties of C-N-doped and C-N-codoped anatase TiO2

The electronic structures, dipole moment and optical properties of C-N-doped and C-N-codoped anatase titanium dioxide (TiO₂) are studied using the plane-wave ultrasoft pseudopotential method of density functional theory (DFT). The results revealed that the absorption coefficients of pure TiO₂ and N-doped TiO₂ are consistent with experimental values in the visible-light region. The bands originating from C/N-2p states lie in the band gap of doped TiO₂. A visible-light absorption edge red-shift can be observed. The atomic charges have changed, resulting in devation of the center of gravity of the negative electric charge from the positive electric charge in the super-cell, and their dipole moment would not be zero. The dipole moment has large influence on the optical responses in the visible region of TiO₂. Because of the small distance (0.531 nm) between C and N atoms, the covalent bond component was easily enhanced between C atom and adjacent O atom, the covalent bonds making it more difficult for the carrier transfer. Moreover, its optical absorption coefficient is going to reduce in the visible-light region. Under the condition of the larger distance (0.691 nm) between C and N atoms, their interaction can be reduced, which is beneficial to electrons transition; as a result, a significant improvement of the photocatalytic activity of TiO₂ has been found under the visible-light irradiation.     

Absorption line profile recovery based on residual amplitude modulation and first harmonic integration methods in photoacoustic gas sensing

Two methods for recovery of gas absorption line profiles are presented in this paper using photoacoustic spectroscopy and tunable diode laser spectroscopy (TDLS) with wavelength modulation (WM). A theoretical analysis based on Fourier coefficients is given in order to describe the various components that arise under simultaneous intensity and frequency modulation. The first method makes use of the residual amplitude modulation (RAM) signal which is always present in current modulation of distributed feedback (DFB) tunable diode lasers. The second method involves integration of a near-pure first harmonic derivative signal, separated from other distorting components by appropriate choice of the lock-in detection phase in the case of low modulation index. Good agreement is obtained with both methods between the experimental results and the theoretical simulation for the P17 absorption line of acetylene at 1535.39 nm but the second method gives a much improved accuracy and signal-to-noise ratio in lineshape recovery with photoacoustic spectroscopy.     

A novel collision free WDM optical switching network

To avoid burst collision in OBS-WDM ring network, a novel scheme called Estimated Traffic based Longest Queue First (ETLQF) has been proposed. In it, the scheduler considers both the queue length and the incoming traffic. The scheduler can adjust the queue lengths in advance to cater to the incoming traffic, targeting to reduce cell loss ratio (CLR) and improve the buffer utilization. The simulation results show that the ETLQF in OBS ring networks not only reduces CLR by 10-60%, but also achieves high throughput while saving 65% of wavelengths, when compared to conventional schemes with only destination delay.     

Spatial charge distribution and conductivities of the LaAlO3/SrTiO3 interfaces: A theoretical study

The electronic properties of the charge carriers at the LaAlO₃/SrTiO₃ interfaces are investigated by first principles studies. For the n-type interface, the carriers are located only on the SrTiO₃ side. For the p-type interface, the carriers are highly localized at the interface. A critical thickness of the LaAlO₃ overlayer exists, below which, the interface is insulating. Moreover, we show that the effective masses and mobilities of the carriers are spatially anisotropic and have a strong disparity for the two types of carriers. These results are consistent with experimental observations and are explained by the band structures and alignments of the consisting oxides and their interaction at the interfaces.