The Vibrational Behavior of Coupled Bladed Disks with Variable Rotational Speed

Low pressure steam turbine blades are subjected to high static and dynamic loads during operation. These loads strongly depend on the turbine's rotational speed, leading to entirely new load conditions. To avoid high dynamic stresses due to the forced vibrations, a coupling of the blades, such as shrouds or snubber coupling, is applied to reinforce the structure. In this work the influence of the rotational speed on the vibration behavior of shrouded blades is investigated. Two fundamental phenomena are considered: the stress stiffening and the spin softening effect. Both effects are caused by centrifugal forces and affect the structural mechanical properties, i.e. the stiffness matrix K , of the rotating system. Since the rotational speed Ω appears quadratically, it is possible to derive the stiffness matrix as a second order matrix polynomial in Ω² [3]. In the case of shrouded blades, contact forces between neighboring blades must be taken into account. The contact status and the pressure distribution in particular is strongly influenced by the rotational speed, respectively, centrifugal forces, caused by the untwisting and radial deformation of the blades. For the calculation, a three dimensional structural mechanical model including a spatial contact model is considered. The solution of the nonlinear equations of motion is based on the well known Multiharmonic Balance Method [2]. Here, the nonlinear forces are computed in the time domain and transferred in the frequency domain by the use of the Fast Fourier Transformation (FFT), also known as the Alternating Frequency Time method (AFT) [1]. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Computer-simulation analysis of the ESR spectra of mechanoradicals in PMMA

In this study, initially, we tried to obtain the mechanoradicals of PMMA (poly(methyl methacrylate)). For this purpose, we designed a simple drilling apparatus. Using this apparatus, we prepared some PMMA samples at 77 K in vacuum. Later, by using an ESR (electron spin resonance spectrometer), we observed ESR signals for these samples at 77 K. This means that mechanoradicals have been successfully produced by mechanical fracture in PMMA using our drilling apparatus. Secondly, we tried to identify the radicals from these spectra through using theoretical analyses and, some computer simulations have been done by suggesting two different theoretical models for these ESR signals. Finally, by using experimental and theoretical data, we showed that our simple apparatus could be used to obtain mechanoradicals from polymers. Results were seen to be in very good agreement with the literature. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 2195–2200, 1997     

A generalization of the Goldston–Pintz–Yildirim prime gaps result to number fields

D. A. Goldston, J. Pintz and C. Y. Y?ld?r?m [3] proved the existence of infinitely many prime pairs whose difference is arbitrarily small compared to the average gap, namely $$ \liminf_{n\to\infty} \frac{p_{n+1}-p_n}{\log p_n}=0. $$ In the present work we generalize their result to totally real number fields. We prove that if ω ₀ and ω ₁ run over distinct prime elements of the number field, then $$ \liminf_{\omega_0,\omega_1} \left|\frac{{\mathbf {N}}(\omega_1-\omega_0)}{{\mathbf {N}}\omega_0}\right|=0. $$      

Fourier transform infrared study of the effect of diabetes on rat liver and heart tissues in the CH region

Diabetes mellitus is characterized by hyperglycemia, a relative lack of insulin. The metabolic disturbances in diabetic patients are often associated with cardiac and liver dysfunctions. Generally, experimental diabetic models in animals have been used to study diabetes-related changes in organ function, but the complexity of intact tissues can cause contradictory results. For this reason, different techniques have been used to understand the mechanisms of these dysfunctions in diabetic organs. The purpose of the present study is to investigate the effects of streptozotocin (STZ)-induced diabetes on rat liver and heart tissues at the molecular level by Fourier Transform Infrared (FTIR) spectroscopy. Wistar rats of both sexes, weighing 200-250 g, were made diabetic by a single injection of 50 mg kg(-1) intraperitoneal (i.p.) streptozotocin dissolved in 0.05 M citrate buffer (pH 4.5) and they were kept for 4-5 weeks. The diabetes status was checked by measuring the blood glucose level. In the complex FTIR spectra, the bands in the CH region for example the CH(2) antisymmetric and symmetric stretching, the CH(3) symmetric and asymmetric stretching vibrations due to lipids and proteins in the 3000-2800 cm(-1) region and CH(2) scissoring around 1464 cm(-1) and the CH(3) scissoring at 1454 cm(-1) were analyzed. Characteristic spectral bands of these diabetic samples were compared with those of control group to confirm the effect of diabetes on liver and heart tissues. The FTIR spectra revealed dramatic differences in the band positions and bandwidths, signal intensity values and signal intensity ratios between diabetic and control tissues. Similar differences were observed for diabetic liver and heart tissues. A significant increase in the bandwidth of the CH(2) symmetric and antisymmetric stretching and the CH(3) symmetric and asymmetric stretching bands has been observed for both tissue types. The wavenumber of the CH(3) asymmetric stretching band shifts to lower values, indicating an increase in the order in the deep interior part of the lipid chains. The ratio of the CH(2) symmetric to CH(3) symmetric stretching band (lipid/protein ratio) decreases by 13% for diabetic heart and liver tissues. A decrease is also detected in the ratio of the CH(2) scissoring to the CH(3) scissoring mode. The overall intensity of these bands is seen to increase for diabetic tissues.     

Awareness on adverse effects of nanotechnology increases negative perception among public: survey study from Singapore

As has been demonstrated by recent societal controversies associated with the introduction of novel technologies, societal acceptance of a technology and its applications is shaped by consumers’ perceived risks and benefits. The research reported here investigates public perceptions of nanotechnology in Singapore, where technological innovation is an established part of the economy, and it might be expected that consumer perceptions of risk are low, and those of benefit are high. The contribution of socio-demographic variables, knowledge level and exposure to risk information in shaping risk perception about nanotechnology applications within different application sectors were analysed. About ~80 % of respondents have some understanding of nanotechnology, 60 % report having heard some negative information, and 39 % perceive nanotechnology as beneficial, while 27.5 % perceive it as risky. Nanotechnology application in food was reported to cause the most concern in the consumers included in the sample. Two-step cluster analysis of the data enabled grouping of respondents into those who expressed ‘less concern’ or ‘more concern’ based on their average scores for concern levels expressed with applications of nanotechnology in different sectors. Profiling of these clusters revealed that, apart from various socio-demographic factors, exposure to risk-related information, rather than awareness in nanotechnology itself, resulted in respondents expressing greater concern about nanotechnology applications. The results provide evidence upon which regulatory agencies and industries can base policies regarding informed risk–benefit communication and management associated with the introduction of commercial applications of nanotechnology.