ABSTRACT
In a previous paper, a model was developed for the nonlinear acoustic resistance for compact insertion elements. Within the model, two loss coefficients are used to tune the model for each type of element, and data were used to empirically determine these coefficients for an area contraction. This paper extends the nonlinear model, developing expressions based on physical principles for the forward and reverse loss coefficients for both an area contraction and orifice. In addition, experimental data for the acoustic resistance of both elements was taken using an impedance tube. Utilizing the expressions developed, the model compares favorably with the experimental data.
ABSTRACT
In a previously published paper, a model for the nonlinear acoustic response of an area contraction including bias flow was presented. The model's prediction for the zero-driving resistance grew progressively worse as the steady-flow Mach number increased. This trend suggests that the forward loss coefficients should depend on the steady Mach number. This letter provides an empirical fitting of this Mach number dependence, along with additional validation data for the model. These additional validation data corroborate the model's prediction that the nonlinear impedance is frequency independent. This letter additionally provides an experimental methodology for determining the characteristic length with sample results.
Subject(s)
Acoustics , Nonlinear DynamicsABSTRACT
Acoustic instabilities are frequently the culprit for engine failure. To mitigate these instabilities, an accurate model of the nonlinear acoustic pressure profile of the system is necessary. This study develops a nonlinear model for the acoustic response of an area-contraction. The derivation begins with the unsteady Bernoulli equation which is formed into the pressure drop across the area-contraction. Each acoustic variable is assumed to be time-harmonic and is written as the sum of a steady and fundamental term. Using a Fourier transformation, nonlinear expressions for the pressure drop and impedance are derived as functions of the steady and acoustic velocity. These expressions capture the nonlinearity of the acoustic response when the flow can reverse out of the orifice, i.e., the amplitude of the mean velocity is less than the amplitude of the oscillating acoustic velocity. This impedance model is verified by archive quality acoustic response data from a previous study.
ABSTRACT
Experimental studies have noted the often surprising and unpredictable effect of ionic liquids as solvents on reaction kinetics for radical polymerisation. We theoretically investigate the energetic and structural effects of ionic liquids, both protic and aprotic, on radical stability, presenting stabilisation of the radical by the ionic liquid by up to -78.0 kJ mol-1. Kinetic data relating to propagating systems for several industrially viable monomers indicate that propagation rates can be increased or decreased (by up to 6 orders of magnitude) depending on the monomer and ionic liquid combination. The interplay of activation entropy and activation enthalpy, much of which depends on hydrogen bonding between the solvent and reactants, play a crucial role in controlling reaction kinetics. It is concluded that the use of cheaper protic ionic liquids as solvents may be viable for improved kinetic control over radical reactions.
ABSTRACT
The accurate prediction of physicochemical properties of condensed systems is a longstanding goal of theoretical (quantum) chemistry. Ionic liquids comprising entirely of ions provide a unique challenge in this respect due to the diverse chemical nature of available ions and the complex interplay of intermolecular interactions among them, thus resulting in the wide variability of physicochemical properties, such as thermodynamic, transport, and spectroscopic properties. It is well understood that intermolecular forces are directly linked to physicochemical properties of condensed systems, and therefore, an understanding of this relationship would greatly aid in the design and synthesis of functionalized materials with tailored properties for an application at hand. This review aims to give an overview of how electronic structure properties obtained from quantum chemical methods such as interaction/binding energy and its fundamental components, dipole moment, polarizability, and orbital energies, can help shed light on the energetic, physical, and spectroscopic properties of semi-Coulomb systems such as ionic liquids. Particular emphasis is given to the prediction of their thermodynamic, transport, spectroscopic, and solubilizing properties.
ABSTRACT
We report a rare case of thyrotoxicosis in a patient with anaplastic thyroid cancer. A 65-yr-old male presented with a 2-d history of rapidly enlarging neck mass and back pain. Physical examination revealed a large, hard thyroid mass and resting tachycardia. He did not have any symptoms suggestive of airway compression at presentation. Thyroid hormone levels were consistent with a hyperthyroid state. CT scan of the neck and thorax showed a heterogeneous mass replacing the thyroid, bilateral pulmonary nodules, and a metastasis with pathological fracture at the level of T-8. Technetium-pertechnetate scan failed to show any uptake in the region of the thyroid. Fine needle aspiration of the thyroid revealed anaplastic thyroid cancer. The patient was started on steroids and radiation therapy of his spine lesion. Brief surgical exploration of the thyroid revealed extensive local infiltration of adjacent neck tissues and marked tumor necrosis. Immunohistochemical stains of the tumor were positive for p53, thyroglobulin, and thyroid transcription factor-1. The tumor had an extremely aggressive course and the patient died of asphyxiation from severe airway compromise 11 d after his initial presentation.
