Study of Single-Fiber Fiber Optic Lever Microphone

Fiber optic sensors are widely used in today\u27s technological applications, providing many advantages that conventional sensors lack. In particular, there is a demand in hypersonic applications to develop microphones to measure acoustic pressure that performs in high temperature and noisy surroundings. This thesis analyzes fiber optic lever microphones (FOLM), since they perform at high temperatures. An FOLM system is an intensity modulated sensor, which is simple to implement and is small in size. Two models of the FOLM have been fabricated and calibrated. The first model uses a seven-element fiber array while the second uses a single-fiber to transmit and receive light. The second model was found to be more stable at the expense of some reduced sensitivity. This microphone is able to detect acoustic pressures at temperatures of 1000° F with good sensitivity. The operating frequency range extends to 25 KHz, and the dynamic range is 190 dB. The microphone is also stable with temperature cycling, and the sensitivity remains within a tolerance of ± 3 dB. This thesis details the design of the single-fiber FOLM system, analysis of the transfer function of the system, laboratory calibration, noise analysis and the results of a field test. Computational algorithms are presented to predict the theoretical frequency response, determined primarily by the membrane parameters, and the gap between fiber and mirror to obtain maximum response. Calibration methods and instrumentation are explored to provide suitable procedures to calibrate the single-fiber FOLM system at room and high temperatures, which is believed to be done for the first time. A new data acquisition system was built to extend the frequency of an existing spectrum analyzer, and to serve as a portable system for field test purposes. The calibration data is analyzed to justify the theory of the system and to determine specifications. The noise analysis reveals the noise sources in the FOLM system and their contribution to the total background noise floor, which provides ideas to obtain better signal-to-noise ratio, that is, higher sensitivity for the microphone. This thesis also includes a field test result to show the ability of a single-fiber FOLM system in a high temperature and harsh environment, such as, in the Thermal Acoustic Fatigue Apparatus at NASA Langley Research Center. The results show stable response from the system in a high acoustic intensity, high temperature environment

Asymmetric Impacts of Public Debt on Economic Growth: Empirical Evidence From Vietnam

Purpose: The objective studies the influence of government debt on the expansion of the Vietnamese economy was the subject of the research presented in this article.   Theoretical framework: Most governments in developing nations have budget deficits due to excessive spending and inadequate revenue. When the government chooses to pay the budget deficit through borrowing, it incurs a liability known as public debt and public debt on economic growth.   Design/methodology/approach: In regression analysis involving time series data, if the regression model contains the variables' present values and the lagged values (past values), this model is known as the lagged distribution model. If the model's explanatory variables include one or more lagged values of the dependent variable, the model is called the autoregressive model. Nonlinear Auto Regressive Distributed Lag regression was applied.   Findings: The findings reveal that government debt has a considerable and disproportionate effect on sustained economic growth in the short and long run using a Nonlinear Autoregressive Distributed Lag (NARDL) model with quarterly data over twenty years beginning in 2000.   Research, Practical & Social implications: The results indicate a disproportional association between public sector debt levels and short- and long-term economic growth. The results are consistent with recent empirical studies showing a nonlinear relationship between some nations' public debt and economic development.   Originality/value: Government debt should support short- and long-term economic growth through funding production. Consequently, government debt should not burden the economy when the high amount of debt exceeds the capacity to repay

Trade Liberalization and Development in ICT Sector and its impact on household welfare in Viet Nam

The ICT sector in Viet Nam had not been developed until the 1980s. However, over the last decade of rapid growth, it has had a powerful impact on many aspects of life in this country. Although the ICT sector is still at an early stage of development and lags behind many other countries in the region, the government of Viet Nam made strong commitments to upgrade the nation’s ICT capability and implemented significant reforms in terms of trade and investment liberalization in ICT sector over the last decade.Trade Liberalization, ICT, Household welfare, Viet Nam

Evaluate the Results at Minimum 2-Years of Treating Rotator Cuff Tear by Arthroscopic Surgery

BACKGROUND: Rotator cuff tear (RCT) is a common injury of the shoulder, especially middle-aged people. Nonoperative treatment, cortisone injections are only effective at an early stage. Open surgery causes postoperative atrophy of the deltoid muscle, so results are limited. Arthroscopic rotator cuff repair surgery has been performed in Vietnam for about ten years, with many advantages such as the ability to accurately assess the lesions and less invasive procedure. In order to have a clearer view, we performed a mid-term assessment of the effectiveness of this surgery. AIM: Evaluate results over 2 years of patients with rotator cuff tears treated with arthroscopic surgery and their quality of life. METHOD: A group of 30 patients were diagnosed with RCT and surgery by arthroscopy to treat at Hanoi Medical University Hospital and Saint Paul Hospital between Jun 2015 and April 2017. The results of the surgeries were assessed by the degree of pain, muscle power, motion of the shoulder joint according to UCLA shoulder score. Evaluate the quality of life through the Rotator Cuff-Quality of Life (RC-QoL) index. RESULTS: The average age was 60.7 years. Female / male ratio was 1.3. Thirty-six months ± 6.41 was the average follow-up time (min 27 – max 50 months). The shoulder function is recorded according to UCLA has an average score of 30.9, therein good and excellent result were 90 %. The mean RC-QoL index was 91.5%. CONCLUSION: Treatment of RCT by arthroscopic surgery that has been evaluated for a minimum of 2 years follow-up showed good results and high quality of patient’s life

Study on model for cutting force when milling SCM440 steel

This article presents empirical study results when milling SCM440 steel. The cutting insert to be used was a TiN coated cutting insert with tool tip radius of 0.5 mm. Experimental process was carried out with 18 experiments according to Box-Behnken matrix, in which cutting speed, feed rate and cutting depth were selected as the input parameters of each experiment. In addition, cutting force was selected as the output parameter. Analysis of experimental results has determined the influence of the input parameters as well as the interaction between them on the output parameters. From the experimental results, a regression model showing the relationship between cutting force and input parameters was built. Box-Cox and Johnson data transformations were applied to construct two other models of cutting force. These three regression models were used to predict cutting force and compare with experimental results. Using parameters including coefficient of determination (R-Sq), adjusted coefficient of determination (R-Sq(adj)) and percentage mean absolute error (% MAE) between the results predicted by the models and the experimental results are the criteria to compare the accuracy of the cutting force models. The results have determined that the two models using two data transformations have higher accuracy than model not using two data transformations. A comparison of the model using the Box-Cox transformation and the model using the Johnson transformation was made with a t-test. The results confirmed that these two models have equal accuracy. Finally, the development direction for the next study is mentioned in this articl

Factors Affecting C02 Emission in Vietnam: a Panel Data Analysis

The purpose of this study is to investigate the major factors in the process of economic growth that influence the carbon dioxide (CO2) emission in Vietnam. An Autoregressive Distributed Lag (ARDL) model was used to evaluate the impact based on Environmental Kuznets curve (EKC) and Pollution haven hypothesis (PHH) in 1990–2011. The results indicate that the economic growth, energy consumption, financial development and trade openness  positively influence the CO2 emissions, whereas foreign direct investment has a negative impact in the short term. Coefficient of joining ASEAN is not statistically significant. The findings of this study also support the validity of EKC and PHH in the Vietnamese economy. Therefore, it is important to use green energy, examine requirements for foreign investment and adopt trade-related measures and policies to increase environmental protection

Development of surface roughness model in turning process of 3X13 steel using TiAlN coated carbide insert

Surface roughness that is one of the most important parameters is used to evaluate the quality of a machining process. Improving the accuracy of the surface roughness model will contribute to ensure an accurate assessment of the machining quality. This study aims to improve the accuracy of the surface roughness model in a machnining process. In this study, Johnson and Box-Cox transformations were successfully applied to improve the accuracy of surface roughness model when turning 3X13 steel using TiAlN insert. Four input parameters that were used in experimental process were cutting velocity, feed rate, depth of cut, and insert-nose radius. The experimental matrix was designed using Central Composite Design (CCD) with 29 experiments. By analyzing the experimental data, the influence of input parameters on surface roughness was investigated. A quadratic model was built to explain the relationship of surface roughness and the input parameters. Box-Cox and Johnson transformations were applied to develop two new models of surface roughness. The accuracy of three surface roughness models showed that the surface roughness model using Johnson transformation had the highest accuracy. The second one model of surface roughness is the model using Box-Cox transformation. And surface roughness model without transformation had the smallest accuracy. Using the Johnson transformation, the determination coefficient of surface roughness model increased from 80.43 % to 84.09 %, and mean absolute error reduced from 19.94 % to 16.64 %. Johnson and Box-Cox transformations could be applied to improve the acuaracy of the surface roughness prediction in turning process of 3X13 steel and can be extended with other materials and other machining processe

Possibilities of fly ash application in geopolymer composite for high temperature

56 s. :obr., tab., grafy +CD ROMTato bakalářská práce se věnuje změnou barvy popílku při ohřevu na vysokou teplotu. Další část práce se zabývá rozborem vlastností popílku a to především barvou, tvarem, chemickým složením a stlačitelností před a po zpracování při vysokých teplotách. Výsledky této práce lze uplatnit ve stavebním průmyslu (ovlivnění barvy popílu)