Relationships between dipole moments of diatomic molecules.

The dipole moment is one of the most important physical properties of a molecule. We present a combination rule for the dipole moments of related diatomic molecules. For molecules AB, AX, BY, and XY from two different element groups in the periodic table, if their elements make a small parallelogram, reliable predictions can be obtained. Our approach is particularly useful for systems with heavy atoms. For a large set of molecules tested, the average difference of the prediction from experimental data is less than 0.2 debye (D). The dipole moments for heavy molecules such as GaCl, InBr, SrCl, and SrS, for which no experimental data are available at present, are predicted to be 3.17, 3.76, 3.85 and 11.54 D, respectively.

Relationship between dipole moments and harmonic vibrational frequencies in diatomic molecules.

Electric dipole moments and harmonic vibrational frequencies are two of the most important molecular properties in many fields of chemistry and physics. With the aid of classical physics, an empirical relationship between them was obtained for diatomic molecules as µd = kq(2)/(ReµAωe(2))(1/2), where k is a constant and µd, q, Re, µA, and ωe are the dipole moment, atomic charge, equilibrium bond length, reduced mass, and equilibrium vibrational frequency, respectively. This relation also provides the atomic charge q as a function of molecular dipole moment. Comparisons with over 60 molecules were made to test this relationship. For typical ionic molecules such as the alkali halides, the predicted dipole moments are in good agreement with the observed data assuming the atomic charges are 1 e. For general polar molecules, the estimated atomic charges obtained from the electric dipole moments are in good agreement with ab initio results for natural bond orbital and/or Mulliken populations.

A single crystal row-column-array for 3D ultrasound imaging.

In vivo 3D ultrasound imaging with 2D-array transducers is of great importance for both clinical application and biomedical research, but it is complicated in fabrication and also very expensive in hardware due to thousands of electronic channels. In this work, we demonstrate a new fabrication process of 7-MHz 128 + 128 elements row-column-array (RCA) transducer with relaxor ferroelectric PMN-0.28PT single crystal. With piezoelectric single crystal and improved acoustic matching, the optimized performance of -6 dB bandwidth of ∼82 % and insertion loss of -44.6 dB is achieved. The axial and lateral imaging resolutions at different depth of the RCA transducer are quantified by the point spread function (PSF), and the results are respectively 0.20 mm and 0.41 mm at the depth of 7.7 mm, and 0.22 mm and 0.47 mm at the depth of 16.7 mm. The transducer is validated experimentally on a hyperechoic phantom, and 3D view and slices of B-mode images are obtained. The experimental results indicate that our developed RCA transducer can obtain high-quality 3D ultrasound images, demonstrating great potential on ultrafast 3D and functional imaging.

Relations between harmonic frequencies of diatomic molecules.

The relations between the harmonic frequencies of different molecules are revealed with the aid of the spring constants of atoms in molecules. Using the atomic spring constants in the related molecules, the force constants for a new molecule can be estimated. The simplest scheme to obtain the force constant of a given molecule is similar to a simple chemical reaction formula, such as A(2) + B(2) → AB, and the corresponding relation between the molecular force constants is k(AB)(-1) = (2k(A(2)))(-1) + (2k(B(2)))(-1). For a given molecule, one can design numerous schemes to obtain its force constant from the atomic spring constants in other molecules. A high degree of periodical regularity appears in the application of different kinds of schemes to the ground states. The reliable schemes for the ground electronic states can be adopted for the excited states. Over two hundred molecules with experimental data available for comparison have been tested. The discrepancies between the calculated and the experimental harmonic frequencies can reach 1% and better; the results show that the present approach is simple in theory and handy to use. The harmonic frequencies for dozens of hetero-nuclear molecules of the transition-metal elements are also predicted.

[Identification of spill oil species based on low concentration synchronous fluorescence spectra and RBF neural network].

In this paper, a new method was developed to differentiate the spill oil samples. The synchronous fluorescence spectra in the lower nonlinear concentration range of 10(-2) - 10(-1) g x L(-1) were collected to get training data base. Radial basis function artificial neural network (RBF-ANN) was used to identify the samples sets, along with principal component analysis (PCA) as the feature extraction method. The recognition rate of the closely-related oil source samples is 92%. All the results demonstrated that the proposed method could identify the crude oil samples effectively by just one synchronous spectrum of the spill oil sample. The method was supposed to be very suitable to the real-time spill oil identification, and can also be easily applied to the oil logging and the analysis of other multi-PAHs or multi-fluorescent mixtures.

A Novel Distal Micromotor-Based Side-Looking Intravascular Ultrasound Transducer.

Cardiovascular disease has become one of the leading causes of death in China, accounting for 45.5% of all deaths in rural areas and 43.16% in urban areas. Hence, its early diagnosis is important. With the development of intravascular imaging technology, the intravascular ultrasound (IVUS) is widely used. The available commercial mechanical rotary side-looking IVUS (SL-IVUS) transducers are driven by external motors that use long flexible shafts to transmit the rotation. However, when the transducer passes through a long-curved blood vessel, it easily causes the nonuniform rotation distortion (NURD) of the image. A catheter which contains a distal motor and sodium chloride (NaCl) solution is presented in this study as an attempt to solve such issues. The NaCl solution is used to connect the transducer and micromotor so that the motor can directly drive the transducer to rotate and acquire the information of the blood vessel. The results showed that the center frequency and -6-dB fraction bandwidth of the single element were 47 MHz and 98%, respectively. The SL-IVUS catheter consists of a distal motor, with speed stability and high resolution, and has the potential to diagnose cardiovascular disease. This novel structure can decrease the dimension at the top of the catheter and reduce the risks of clinical diagnosis.

Development of Cardiac Phased Array With Large-Size PZN-5.5 %PT Single Crystals.

In recent years, the manufacturing process of lead zinc niobate-lead titanate [Pb(Zn1/3Nb2/3)O3-PbTiO3, also called PZN-PT], has been enhanced with improvements in size, consistency, and a suitable compromise between piezoelectric properties and phase transition temperature, which means that it is possible to obtain PZN-PT single crystals in sufficient size for performance characterization studies and batch manufacturing to produce high-performance medical ultrasonic transducers. This article mainly focuses on the development of the 64-element phased array ultrasonic transducer based on novel large-size PZN-PT piezoelectric single crystals. The composition of the single crystal was chosen as PZN-5.5 %PT. The designed center frequency of the phased array is 3.0 MHz, which is suitable for cardiac ultrasound imaging. The array elements were spaced at a 0.254-mm pitch, and interconnected through a custom-designed flexible circuit. Double matching layers with a light backing structure were applied in the transducer fabrication process to improve the performance of the array. The test results of the developed phased array showed a center frequency of 3.0 MHz, and an average -6 dB fractional bandwidth of 72%. In the vicinity of the center frequency, the two-way insertion loss (IL) was about -46 dB, while a crosstalk between the adjacent elements was less than -31 dB. The wire phantom can be distinctly imaged with the phased array, and the axial and lateral resolutions were measured to be 660 and [Formula: see text], respectively. The image of a standard phantom was acquired to present the imaging performance of the transducer. The final results indicate that the transducer arrays based on novel large-size PZN-PT single crystals are quite promising for use in medical ultrasound imaging applications.

Atomic Charges in Highly Ionic Diatomic Molecules.

Atomic charges were investigated as functions of detectable atomic and molecular constants at equilibrium structures. It was found based upon the variation idea that atomic charges in highly ionic molecules can be expressed as a function of molecular dipole moments, polarizabilities of free cations, and polarizabilities of free neutral atoms of the corresponding anions. The function can be given in the form of classical Rittner's relationship (J. Chem. Phys. 1951, 19, 1030). For the ground states of alkali halide molecules, the predicted atomic charges are close to an elementary charge e and the predicted dipole moments are in good agreement with the observed values; for spin-restricted high-ionic systems such as the lowest 9Σ electronic states of BN, AlN, GaN, BP, AlP, GaP, BAs, AlAs, and GaAs molecules, the predicted atomic charges are also near 1e and in good agreement with the results of natural population analysis at MRCI/cc-pvqz and HF/6-311+G(3df) levels. Polarizabilities for the lowest quintet states of B-, Al-, Ga-, N+, P+, and As+ ions were also obtained based upon high-level ab initio computations. Atomic charges from other related methods are also investigated for comparison. The results demonstrate that high-quality atomic charges can be obtained with detectable variables, such as molecular dipole moment, vibrational frequency, as well as polarizabilities of the related free atoms and ions.