固定资产投资对产业结构变动的影响分析

产业结构提升是一国或地区经济素质的重要表现,在产业结构演变的过程中,固定资产投资起着推动和促进的作用。本文运用成分分析的基本原理,对1980年以来我国产业结构的变化以及与固定资产投资活动的关系进行了测算分析。主要内容包括:产业结构成分变动的描述,产业结构成分变动检验,产业结构与固定资产投资之间关系的成分回归模拟等。     

Two-dimensional ultrasound Doppler velocimeter for velocity field measurements of liquid metal flows

We present a novel fluid flow measurement system based on the pulsed-wave ultrasound Doppler velocimetry being able to determine two-dimensional velocity fields. It applies for the measurement of unsteady liquid metal flows driven by electromagnetic forces concerning the research field of magnetohydrodynamics. The application of advanced processing techniques enable high data acquisition rates and concurrently a high spatial resolution facilitating to resolve transient liquid metal flow structures which could not been acquired so far. An experimental setup utilizing liquid metal in a cubic vessel exposed to a stationary rotating magnetic field was used to validate the reliability of the measurement system. The swirling fluid motion in its horizontal section could be resolved into a velocity field grid of 24 × 24 vectors while achieving frame rates of about 30 fps. Results from a further study driving liquid metal in a cylindrical vessel by a pulsed rotating magnetic field are presented. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Changes in the gait characteristics caused by external load,ground slope and velocity variation

The complexity of the human gait manifests itself by lots of parameters that can evoke different changes in the walking manner. They can be divided into two groups: inherent, like anthropometric features or peculiar psychomotor type, and those related to the external conditions. The aim of the paper is to analyze the influence of three parameters, i.e. external load, ground slope and gait velocity, on the locomotion characteristics and the gait stability. Within the framework of investigations for different values of the mentioned parameters a film registration of the trajectories of selected kinematic nodes during some gait cycles has been carried out. The obtained data was a subject of numerical calculation aimed at extracting the essential properties of the principal gait characteristics.     

An experimental study of the effect of fracture and operative intervention on acoustical properties of human tibial bone

Conclusions 1. The differences between the ultrasonic parameters c and determined for the right and left tibial bones as well as between values obtained directly on the bone and through the skin are statistically insignificant (p>0.1).2. Experimental fracture of the tibia leads to a significant decrease in the ultrasound speed (p<0.001) and increase in the ultrasound damping coefficient (p<0.001).3. Operative intervention, as a whole, and any of the surgical manipulations, in particular, significantly alter the initial acoustic parameters of the tibia with fracture or after osteotomy relative to fracture or osteotomy without osteosynthesis. These groups of patients should have different criteria for the degree of fracture repair.4. Weakening of the stability of the fixation of a fracture by screwing in or loosening screws attaching a splint plate to the bone cause an increase in the damping coefficient. This sign is rather sensitive for use in clinical practice to diagnose weakening of the rigidity of fixation.5. The ultrasound parameters c and depend on the magnitude of the cross-sectional defect of the diaphysis and in conjunction may be used for diagnosis of the degree of adhesion of a fracture or operation site after corrective osteotomy.6. The values for c and found for undamaged bone may be used to evaluate their values for a diaphysis used for preparing bone samples.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Riga Scientific Research Institute of Traumatology and Orthopedics. Translated from Mekhanika Polimerov, No. 1, pp. 88–96, January–February, 1978.     

The emergence of multiplicative thinking in children's solutions to paper folding tasks

Although children partition by repeatedly halving easily and spontaneously as early as the age of 4, multiplicative thinking is difficult and develops over a long period in school. Given the apparently multiplicative character of repeated halving and doubling, it is natural to ask what role they might play in the development of multiplicative thinking. We investigated this question by examining children's solutions to folding tasks, which involved predicting the number of equal parts created by a succession of given folds and determining a sequence of folds to create a given number of equal parts. Analyzing a combination of cross-sectional data and case studies from standardized clinical interviews, we found that children were most successful at coordinating folding sequences with multiplicative thinking when they used a conceptualization of doubling based upon recursion. This conceptualization tended to generate more sophisticated solutions.     

Modeling the influence of mineral content and porosity on ultrasound parameters in bone by using synthetic phantoms

Model composite media – 10×15×80 mm³ bone tissue phantoms based on an epoxy resin with fillers—were made to study the influence of porosity and mineral content on ultrasound velocity and attenuation. The pores were simulated by 1 mm³ particles of a soft rubber, while the mineral content was imitated by a mineral residue of natural bone obtained by burning and grinding. The porosity and mineral content were varied in the range of 0–70% by volume with a step of 10%. The velocity, attenuation, and prevalent frequency of ultrasound were measured by the pulse transition method, using transducers with nominal frequencies 0.1, 0.2, 0.5, and 1.0 MHz. It was experimentally found that the ultrasound velocity decreased nearly exponentially with growth in porosity, while the velocity dispersion was negligible at frequencies >0.2 MHz; the ultrasound attenuation increased linearly with growth in porosity and strongly depended on the frequency; the velocity increased nonlinearly with growth in mineral content above 40%; the attenuation did not exhibit a distinct dependence on the mineral content; the porosity provoked a shift in the prevalent frequency of transducers, tending to the common value of 0.2 MHz, while the mineral content did not excite similar changes. The complex measurement of velocity, frequency-dependent attenvation, and prevenlent frequency of ultrasound is proposed in ultrasonic diagnostics of bone for more precise determination of the influence of the porosity and the degree of mineralization on the bone condition.Published in Mekhanika Kompozitnykh Materialov, Vol. 35, No. 2, pp. 211–220, March–April, 1999.     

Modeling the influence of mineral content and porosity on ultrasound parameters in bone by using synthetic phantoms

Model composite media − 10×15×80 mm³ bone tissue phantoms based on an epoxy resin with fillers—were made to study the influence of porosity and mineral content on ultrasound velocity and attenuation. The pores were simulated by ∼ 1 mm³ particles of a soft rubber, while the mineral content was imitated by a mineral residue of natural bone obtained by burning and grinding. The porosity and mineral content were varied in the range of 0–70% by volume with a step of 10%. The velocity, attenuation, and prevalent frequency of ultrasound were measured by the pulse transition method, using transducers with nominal frequencies 0.1, 0.2, 0.5, and 1.0 MHz. It was experimentally found that the ultrasound velocity decreased nearly exponentially with growth in porosity, while the velocity dispersion was negligible at frequencies >0.2 MHz; the ultrasound attenuation increased linearly with growth in porosity and strongly depended on the frequency; the velocity increased nonlinearly with growth in mineral content above 40%; the attenuation did not exhibit a distinct dependence on the mineral content; the porosity provoked a shift in the prevalent frequency of transducers, tending to the common value of 0.2 MHz, while the mineral content did not excite similar changes. The complex measurement of velocity, frequency-dependent attenvation, and prevenlent frequency of ultrasound is proposed in ultrasonic diagnostics of bone for more precise determination of the influence of the porosity and the degree of mineralization on the bone condition.     

Reduction of vibration due to change in mass configuration

The paper concerns the elimination of vibration due to changing the centre of gravity of a system. It is shown that the damping effect can be generated in an oscillating pendulum by a continuous motion of an auxiliary mass. A simple system in form of a variable length pendulum is considered. It is seen that if the pendulum length function is correctly chosen, the Coriolis force will cause additional damping effect in the system. The Floquet method is used to investigate the linear system stability. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Stresses due to Heterogeneous Surface Tension in Solids

When surface‐active melt interacts with metal a zone with high dislocation density arises in the surface layer of metal. The interaction between melt and metal leads to a decrease of surface tension and to considerable stresses in the surface layer due to the surface tension gradient. The estimation shows that the stress distribution in the vicinity of the surface active melt perimeter is sufficient for nucleation and movement of dislocations in the surface layer.     

Ultrasonic velocity in epoxy resin at temperatures down to 4.2 K

Results are presented from measurements of the velocity of longitudinal and shear elastic waves (f=5 MHz) in ÉD-20 epoxy resin, at temperatures from 4.2 to 293 K. These data were used to calculate the moduli of elasticity E and G. Also, the moduli E (f=250 Hz) and G (f=2 Hz) of the ÉD-20 resin were measured directly. The calculated velocities of the low-frequency elastic waves c_t=(E/p)^1/2 and c_t=(G/p)^1/2 (where p is the density) were compared with the results from the ultrasonic measurements. The frequency dependence of elastic-wave velocity in the epoxy resin was evaluated. It was found that when the frequency was varied by four orders of magnitude, the dispersion of longitudinal-wave velocity was 18% at 4.2 K and 39% at 293 K. A quantitative criterion is proposed for estimation of the dispersion of sonic velocity from the results of measurements at any two frequencies. It was established that the sonic velocity at low temperatures varies linearly with the temperature, and in the case of longitudinal waves changes from c_l-3360 m/sec at 4.2 K to 2820 m/sec at 293 K. The shear-wave velocity changes from c_t=1630 m/sec at 5 K to 1340 m/sec at 293 K. The values of the dynamic Young's modulus E and shear modulus G at 4.2 K are 8.6 and 3.2 GPa, respectively. On a plot of c=f(T) for ED-20, a transition is observed at 180 K, due to reorientational rotation of methyl groups. The activation energy of the relaxation process is 3.6 kcal/mole. Large values are obtained for the dispersion of the dynamic modulus E:37.8% at 4.2 K and 93% at 293 K.Paper presented at 9th International Conference on the Mechanics of Composite Materials Riga, October, 1995.Moscow State Academy of Automotive Vehicle and Tractor Machinery Construction, Russia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 32, No. 4, pp. 460–466, July–August, 1996.