Nonequilibrium Thermodynamics And Quasielastic Light Scattering From Crystals. Ii. Piezoelectric Crystals

The methodology described and utilized previously by the author, involving the use of nonequilibrium thermodynamics in the analysis of the spectrum of light scattered quasielastically by crystals, is applied to piezoelectric crystals. An additional thermodynamic variable, the electric polarization, is taken into account and assumed to be a relaxing variable. Solution of the resulting equations in the case of KH2PO4 leads, as expected, to the appearance of a polarization relaxation line in the spectrum. The spectrum is calculated for several values of the two relevant parameters: the polarization relaxation frequency and the ratio of C66 isothermal elastic constants at constant electric field and constant polarization. For a fixed polarization-relaxation frequency, it is found that as the ratio of elastic constants decreases (the characteristic behavior as the ferroelectric phase transition in KH2PO4 is approached), the intensity of the relaxation line increases at the expense of the Brillouin lines. In contrast with standard treatments of coupled modes in piezoelectric crystals, no adjustable parameters are involved in determining the spectrum. © 1980 The American Physical Society.22126006601

Rheology of vitreous humour and pharmacological substitutes used in eye surgery

The Vitreous Humour (VH) is a transparent gel that fills the vitreous cavity in the Human eye. VH is mainly composed of water (99%) and includes a network of protein fibrils (collagen) and hyaluronan (1%). It is known that VH becomes progressively liquefied with age, or as a consequence of some diseases, and consequently the rheological, biomechanical and structural properties of the fluid also change. For the normal operation of the eye, when vitreoretinal pathologies appear, effective treatments must be performed. A common treatment for these diseases is the injection of a VH substitute in the vitreous cavity. The major vitreous substitutes commercially available are silicone oils and perfluorocarbon liquids, but currently there is little information about their rheological properties, which are known to be intimately linked to their functionality. The aim of this work is to measure the rheological properties of the VH and five commercial vitreous substitutes currently used in vitreoretinal surgeries. Six fluids were analysed: VH collected from rabbit eyes, two silicone oils (RS-Oil1000 and RS-Oil5000, Alchimia), two perflurocarbon liquids (HPF8 and HPF10, Alchimia) and a mixture of silicone oil with perfluorocarbon (Densiron68, Fluoron). The rheological characterization of the fluids was done using a shear rheometer (DHR-2, TA Instruments) to perform steady shear, small amplitude oscillatory shear (SAOS) and creep measurements. Extensional measurements using the Slow Retraction Method were performed with a capillary break-up extensional rheometer (Haake CaBER1, ThermoElectron) and an in-house extensional rheometer. Our results show that VH separates into two different phases (gel and liquid) and both phases exhibit viscoelastic behaviour. The liquid phase rheology is independent of time but the gel properties are time dependent, with the VH gel phase exhibiting storage (G’) and loss (G’’) moduli that increase with time after dissection (e.g. the maximum value of G’ and G’’ increase from 3.2 Pa and 0.9 Pa right after dissection to 11.4 Pa and 2.3 Pa a few hours after dissection). Despite being used for the same purpose, the pharmacological fluids show significantly different rheological properties between them and when compared with the VH. All pharmacological fluids tested display a Newtonian behaviour in steady shear flow and their viscosities vary from 0.49 mPa s to 4.57 Pa s, at 37°C

The loop prominence of May 13, 1971 and its associated effects

A study is presented about the formation of a loop prominence system (LPS) on May 13, 1971. The development of the phenomenon in found the follow the model of Jefferies and Orrall, and was associated with small radio bursts and several kind SID. From the spectral analysis a temperature of 13200 K has been deduced and a density of hydrogen atoms n(H) = 10¹⁰ cm⁻⁸ estimated. The existence of inclined emissions probably produced by rotatory motions is discussed. From the radio-data analysis it was inferred that an impulsive and a thermal component were present, the length of the emitting plasma cloud was found to be about 56000 Km. The LPS appeared, in accordance to previous results, in a región producing proton fiares. The paper in full will be published in Solar Physics.Asociación Argentina de Astronomí

The Role of Popliteal Vein Incompetence in the Diagnosis of Saphenous-popliteal Reflux Using Continuous Wave Doppler

AbstractIntroduction: continuous wave Doppler (CWD) has good discriminatory power at the groin in the assessment of saphenous femoral junction (SFJ); however, it is not as accurate as duplex ultrasound scanning (DUS) in the popliteal fossa for assessment of saphenous popliteal junction (SPJ) in patients with primary short saphenous vein incompetence.Aim: the aim of this study was to compare the findings of CWD with those of DUS at the SPJ and assess the role of popliteal vein incompetence in the accuracy of CWD. Method: prospective study of consecutive patients presenting to a vein clinic requiring a duplex scan of their SPJ. Each patient was examined by one surgeon using CWD and by one radiologist using DUS. Each observer was unaware of the other's findings. Additional information on the competence of the popliteal vein on DUS was also recorded. Results: some 171 limbs in 128 patients with varicose veins were studied. One hundred and sixteen limbs had reflux at SPJ on CWD whilst 55 did not. Their mean age was 54 (range 18–85). Female to male ratio was 3:1. Spearman's rank correlation between CWD and DUS has 0.49 (p =0.0001). CWD has a sensitivity of 92% and specificity of 53% (PPV=62%, NPV=89%, accuracy=70%). Twenty-nine limbs had an incompetent popliteal vein (IPV). Of those, 12 limbs also had incompetence on CWD and competence on DUS at the SPJ, which represent 28% of the total number of limbs with these findings (n =43). Conclusion: CWD is sensitive in detecting incompetence at SPJ, though its specificity is low. In this study 17% (n =29) of all patients had incompetence of popliteal vein. Up to 25% ( n =12) of patients with SPJ incompetence on CWD (Doppler +) and competence on DUS (duplex −) had incompetence of the underlying popliteal vein, which may explain the low specificity. The presence of SPJ incompetence on CWD should be confirmed on DUS prior to surgery

The loop prominence of May 13, 1971 and its associated effects

A study is presented about the formation of a loop prominence system (LPS) on May 13, 1971. The development of the phenomenon in found the follow the model of Jefferies and Orrall, and was associated with small radio bursts and several kind SID. From the spectral analysis a temperature of 13200 K has been deduced and a density of hydrogen atoms n(H) = 10¹⁰ cm⁻⁸ estimated. The existence of inclined emissions probably produced by rotatory motions is discussed. From the radio-data analysis it was inferred that an impulsive and a thermal component were present, the length of the emitting plasma cloud was found to be about 56000 Km. The LPS appeared, in accordance to previous results, in a región producing proton fiares. The paper in full will be published in Solar Physics.Asociación Argentina de Astronomí

The loop prominence of May 13, 1971 and its associated effects

A study is presented about the formation of a loop prominence system (LPS) on May 13, 1971. The development of the phenomenon in found the follow the model of Jefferies and Orrall, and was associated with small radio bursts and several kind SID. From the spectral analysis a temperature of 13200 K has been deduced and a density of hydrogen atoms n(H) = 10¹⁰ cm⁻⁸ estimated. The existence of inclined emissions probably produced by rotatory motions is discussed. From the radio-data analysis it was inferred that an impulsive and a thermal component were present, the length of the emitting plasma cloud was found to be about 56000 Km. The LPS appeared, in accordance to previous results, in a región producing proton fiares. The paper in full will be published in Solar Physics.Asociación Argentina de Astronomí

Prototype of an axial flux permanent magnet generator for wind energy systems applications

Small scale wind power applications require a cost effective and mechanically simple generator in order to be a reliable energy source. The use of direct driven generators, instead of geared machines, reduces the number of drive components, which offers the opportunity to reduce costs and increases system reliability and efficiency. For such applications, characterized by low speed of rotation, the axial flux permanent magnet generator is particularly suited, since it can be designed with a large pole number and high torque density. This paper presents a double-sided axial flux permanent magnet low-speed generator, with internal rotor and slotted stators. Such a structure gives a good compromise between performance characteristics and feasibility of construction. Test results obtained from the prototype are reported.FC

An axial flux permanent magnet synchronous generator for a gearless wind energy system

In low speed applications such as wind energy conversion systems, the use of direct driven generators, instead of geared machines, reduces the number of drive components, which offers the opportunity to reduce costs and increases system reliability and efficiency. The Axial Flux Permanent Magnet (AFPM) generator is particularly suited for such application, since it can be designed with a large pole number and a high torque density. This paper presents the design, construction and experimental validation of a double-sided AFPM synchronous generator prototype, with internal rotor and slotted stators. Design objectives embrace achieving a good compromise between performance characteristics and feasibility of construction, which results in a cost competitive machine

Atomic Charge Transfer-counter Polarization Effects Determine Infrared Ch Intensities Of Hydrocarbons: A Quantum Theory Of Atoms In Molecules Model

Atomic charge transfer-counter polarization effects determine most of the infrared fundamental CH intensities of simple hydrocarbons, methane, ethylene, ethane, propyne, cyclopropane and allene. The quantum theory of atoms in molecules/charge-charge flux-dipole flux model predicted the values of 30 CH intensities ranging from 0 to 123 km mol-1 with a root mean square (rms) error of only 4.2 km mol-1 without including a specific equilibrium atomic charge term. Sums of the contributions from terms involving charge flux and/or dipole flux averaged 20.3 km mol-1, about ten times larger than the average charge contribution of 2.0 km mol-1. The only notable exceptions are the CH stretching and bending intensities of acetylene and two of the propyne vibrations for hydrogens bound to sp hybridized carbon atoms. Calculations were carried out at four quantum levels, MP2/6-311++G(3d,3p), MP2/cc-pVTZ, QCISD/6-311++G(3d,3p) and QCISD/cc-pVTZ. 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