A new look at Theodorsen's method in aerofoil theory

Theodorsen's method for calculating the incompressible potential flow past an aerofoil is viewed afresh. It is found that some simple modifications to the computational process make the computations relatively faster, easier and more accurate. The new modifications are applicable to the analysis of conventional aerofoils with up to moderate thickness and camber ratios. Several examples are presented to show the effectiveness of the modifications.     

Differential Discrimination Technique for Incoherent Doppler Lidar to Measure Atmospheric Wind and Backscatter Ratio

A new incoherent Doppler lidar scheme is proposed using a high resolution Mach-Zehnder interferometer discriminator with sinusoidal transmission functions. A two-channel differential discrimination technique is developed which provides high sensitive velocity measurement. The aerosol and molecular backscatter signals can be separately measured and the backscatter ratio obtained. Principle of the measurement is described and the characteristics of this technique are analyzed and compared. Numerical calculation for a moderate size 1.064 μ lidar shows that an accuracy better than 1 m/s for the velocity measurement and 18% for the backscatter ratio measurement can be obtained up to a height of 10 km by a 500 shot average.     

Measuring the optical parameters of thin films by p-polarized laser beams

The refractive index n_f, extinction coefficient k_f and thickness d_f of a dip coated film are measured by using p-polarized laser beams. A sample is oblique illuminated with a p-polarized laser beam, and then two reflected beams, from the front and back surfaces, are received with a detector. After measuring their intensity ratio versus the angle of incidence, it is convenient to obtain the parameters of the film by means of data fitting. The films of polymethyltriethoxy silane (PMTES), which were made on a BK-7 glass substrate by dip coating, were measured. The method is non-contact, non-destructive and has the advantages of simplicity of both equipment and understanding. It is also shown that the values measured by this method are coincident with those measured by ellipsometry.     

Preliminaries to the body-cover theory of pitch control

Preliminary theoretical and empirical work suggest that increased thyroarytenoid muscle activity may either increase or decrease fundamental frequency, depending on cricothyroid muscle activity and a new cross-sectional area parameter. This parameter is defined as the ratio of muscular tissue in vibration to total tissue in vibration. Canine laryngeal nerves were stimulated to measure vocal-fold length changes. These data, combined with previously reported tissue density, passive stress, and passive frequency data, were used to construct a set of curves predicting canine fundamental frequency from thyroarytenoid and cricothyroid muscle activity and the area ratio. The results suggest that high cricothyroid muscle activity and small area ratios tend to cause fundamental frequency lowering with increased thyroarytenoid muscle activity.     

Adsorption mode change from adlayer- to restructuring-type with increasing coverage, evidenced by structural determination of c(2 × 2)→(4 × 4)→(5 × 5) sequence formed on Ni(001) by Li deposition

We determined surface structures in a structural sequence c(2 × 2)→(4 × 4)→(5 × 5) formed on Ni(001) at 370 K with increasing Li coverage by a dynamical low-energy electron diffraction analysis. The (4 × 4) and (5 × 5) are complex surface-structures involving restructuring of substrate surface atoms, and are analogous to the previously determined (3 × 3) and (4 × 4) structures formed for Li/Cu(001). The c(2 × 2) at low coverages is a Li adlayer, so a change of the adsorption mode from adlayer- to restructuring-type is evidenced in the course of increasing coverage within a monolayer range.     

Surface defects created by low energy (20 < E < 240 eV) ion bombardment of Ge(001)

Surface defects created on Ge(001) exposed to low energy Xe ions are characterized by in situ scanning tunneling microscopy (STM). The temperature of the sample during ion bombardment is 165 C and ion energies range from 20 to 240 eV. The ion collisions create defects (vacancies and adatoms) which nucleate and form vacancy and adatom islands. For fixed total vacancy creation, the vacancy island number density increases with increasing ion energy: the vacancy island number density is 1.6 × 10⁻²⁰ cm⁻² for 40 eV ion bombardment and increases to 4.4 × 10⁻²⁰ cm⁻² for 240 eV ion bombardment. The increased nucleation rate for vacancies is attributed to clustering of defects. The sputtering yield of Ge(001) is also measured by STM. The sputtering yield for 20 eV ions is approximately 10⁻³ per ion but the net yield for surface defects (sum of adatoms and vacancies) is an order of magnitude higher, 10⁻², due to adatom-vacancy pair creation.     

换热器传热管在静水中的挤压膜阻尼研究

本文通过求解三维Navier-Stokes方程,导出计算挤压膜阻尼的公式,对Mulcahy所提出的模型作了改进,并提出了stokes数的间隙修正因子的概念. 改进后的挤压膜阻尼模型计及管子振幅的影响,在管子振幅很小的情况下,它与Mulcahy提出的模型相似,实际上可把Mulcahy提出的模型看成改进后模型的一个特例. 为了验证改进后的模型,对传热管在空气和静水介质中的阻尼进行了实验研究.结果表明理论计算值与实验测量值符合良好.     

Evaluation of liquid junction potentials and determination of pH values of strong acids at moderate ionic strengths

A new experimental approach is proposed for the evaluation of liquid junction potentials and single ion activities. Neither of these quantities can be experimentally measured without assumption. Furthermore, they are concentration dependent but without clearly defined functional relationships. Thus, a given assumption may be satisfactory to obtain these quantities at a given concentration, but will fail at another concentration. It is the intent of this paper to establish a functional relationship between the ratio of activity coefficients and the ionic strength, through which the liquid junction potentials may be computed, as well as the pH values at moderate ionic strengths (<1.0 m). Experimental results are presented and uncertainties are discussed.     

X-ray diffraction measurements on PE 2000 between 10 K and 300

Summary It was possible to obtain film exposures of the WAXS-diagram (2 50°) of a PE-fraction in the temperature range from 10 K to 300 K by using a special low temperature Guinier-chamber. The crystallographica-,b-andc-axis has been calculated from the positions of all reflexions. The different behaviour of their expansion coefficients can be explained by activation of rotational- and torsional-vibrations. If we take the number of net planes as constant and consider a temperature-independent part resulting from paracrystalline disorder (built up during crystallization), we can describe the linear increasing of the integral widths of the reflexions with decreasing temperature (10 ... 100%) with building up of inherent stresses inside the crystals.

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Zusammenfassung Eine spezielle Tieftemperatur-Guinier-Kammer ermöglichte es, Filmaufnahmen der Röntgenweitwinkelstreukurve (2 50°) einer hochkristallinen Polyäthylen-Fraktion im Bereich von ca. 10 K bis 300 K zu erhalten. Das unterschiedliche Temperaturverhalten der Ausdehnungskoeffizienten der kristallographischena-,b- undc-Achse, berechnet aus der Lage aller auswertbaren Reflexe, kann durch Anregung von Torsions- und Rotationsschwingungen erklärt werden. Unter der Annahme konstanter Kristallitgrößen sowie eines temperaturunabhängigen parakristallinen Gitterstörungsanteils (hervorgerufen durch Defekteinbau bei der Kristallisation), kann die starke Zunahme der integralen Breiten der Reflexe (bis ca. 100%) zu tiefen Temperaturen auf Eigenspannungen in den Kristalliten zurückgeführt werden.

     

Size exclusive capillary electrophoresis separation of DNA oligonucleotides in small size linear polyacrylamide polymer solution

The mobility of analytes in capillary electrophoresis using polymer gels and solutions is usually described as having an inverse relationship with the molecular size (mobility decreases as molecular size increases). The most commonly used models for predicting such mobility are the Ogston model and the Reptation model. However, in this study a new separation phenomenon was observed in which the mobility of DNA oligonucleotides increased with molecular size in a capillary electrophoresis phase (CEP) coated capillary column. The polymer system used was a 11% linear polyacrylamide (Mr = 1500) solution. The log-transformed number of base pairs (log N) of three double stranded oligonucleotides had an inverse linear relationship (r2 > 0.9981) with their migration time in the capillary column. Such a relationship is similar to that observed with size exclusive chromatography.