In the urban labor market, the rural labor force can choose whether to become self- employed or work for wages depending on their stock of human capital and local labor market conditions. A simple Mincer earnings regr...In the urban labor market, the rural labor force can choose whether to become self- employed or work for wages depending on their stock of human capital and local labor market conditions. A simple Mincer earnings regression shows that the rate of return to schooling for wage earners is two percentage points higher than that for the self-employed. After correcting for bias in sample selection, the expanded Mincer earnings equation estimated the rate of return to schooling for wage earners at between 5.3 and 6.8 percent. From the standpoint of training, we found that the simplest form of training, short-term training and formal training played an important role in promoting migrant workers’ repeat mobility. However, the simplest form of training did not have a significant effect on earnings,whereas short-term and formal training played an important determining role in this respect. Moreover, rights protection issues such as wage arrears also had an important effect on migrant workers’ repeat mobility. In handling heterogeneity and endogenous educational variables among migrant workers, the authors found that the years of schooling of the parents of migrant workers were not an ideal instrumental variable.展开更多
Medical diagnostic X-rays are the largest manmade source of ionizing radiation received by the members of the general public. The aim of this study was to evaluate the radiographic reject/repeat rate and also to deter...Medical diagnostic X-rays are the largest manmade source of ionizing radiation received by the members of the general public. The aim of this study was to evaluate the radiographic reject/repeat rate and also to determine dose to the patients from radiographic rejects/repeats in radiology centers of Urmia University of Medical Sciences. During a 4 month period the most frequently examinations were chosen in three radiology centers. A form was designed as a reject/repeat analysis form for radiographers to complete each time a film was rejected by radiologists or repeated. The collected data were compiled at the end of each week and entered into a computer for analysis at the end of study. The results of this study showed that highest and lowest repetition rates were for pelvis, 14.01% and upper limb, 4.17%, respectively. The main reasons of repetition of radiographs were due to exposure (54%) and positioning (18%) errors. The average repeat rate in all three hospitals was 7.20%. It was found that human error has important role to repetition of radiographs. It is demonstrated that those patients having repeated radiographs received an average of 3.23 Gy·cm2. Based on the findings of this study it must be remembered that the highest repetition rate was for pelvis. Considering the radiosensitive organs related to pelvis especially in pediatric patients some special considerations must be applied for pelvis examinations.展开更多
A novel Automatic repeat ReQuest (ARQ) protocol called cooperative ARQ is presented in this let-ter, where a relay terminal is requested to retransmit an erroneously received packet, instead of the source ter-minal. T...A novel Automatic repeat ReQuest (ARQ) protocol called cooperative ARQ is presented in this let-ter, where a relay terminal is requested to retransmit an erroneously received packet, instead of the source ter-minal. The data link layer Packet Error Rate (PER) performance of cooperative ARQ is derived in correlated wireless channel. The results show that even though the relay-destination channel is worse than the source-destination channel, the new protocol outperforms the traditional one as long as the average SNR of the relay-destination channel is better than a certain threshold. It is also demonstrated that a second order diversity gain can be achieved with the cooperative ARQ protocol.展开更多
Equation based TCP-friendly rate control (TFRC) protocol has been proposed to support video streaming applications. In order to improve TFRC performance in wireless channels, the link level automatic repeat request (A...Equation based TCP-friendly rate control (TFRC) protocol has been proposed to support video streaming applications. In order to improve TFRC performance in wireless channels, the link level automatic repeat request (ARQ) scheme is usually deployed. However, ARQ cannot ensure strict delay guarantees, especially over multihop links. This paper introduces a theoretical model to deduce an equation for packet size adjustment in transport layer to minimize retransmission delay by taking into con- sideration the causative reasons inducing retransmission in link layer. An enhanced TFRC (ETFRC) scheme is proposed inte- grating TFRC with variable packet size policy. Simulation results demonstrate that higher goodput, lower packet loss rate (PLR), lower frame transmission delay and jitter with good fairness can be achieved by our proposed mechanism.展开更多
文摘In the urban labor market, the rural labor force can choose whether to become self- employed or work for wages depending on their stock of human capital and local labor market conditions. A simple Mincer earnings regression shows that the rate of return to schooling for wage earners is two percentage points higher than that for the self-employed. After correcting for bias in sample selection, the expanded Mincer earnings equation estimated the rate of return to schooling for wage earners at between 5.3 and 6.8 percent. From the standpoint of training, we found that the simplest form of training, short-term training and formal training played an important role in promoting migrant workers’ repeat mobility. However, the simplest form of training did not have a significant effect on earnings,whereas short-term and formal training played an important determining role in this respect. Moreover, rights protection issues such as wage arrears also had an important effect on migrant workers’ repeat mobility. In handling heterogeneity and endogenous educational variables among migrant workers, the authors found that the years of schooling of the parents of migrant workers were not an ideal instrumental variable.
文摘Medical diagnostic X-rays are the largest manmade source of ionizing radiation received by the members of the general public. The aim of this study was to evaluate the radiographic reject/repeat rate and also to determine dose to the patients from radiographic rejects/repeats in radiology centers of Urmia University of Medical Sciences. During a 4 month period the most frequently examinations were chosen in three radiology centers. A form was designed as a reject/repeat analysis form for radiographers to complete each time a film was rejected by radiologists or repeated. The collected data were compiled at the end of each week and entered into a computer for analysis at the end of study. The results of this study showed that highest and lowest repetition rates were for pelvis, 14.01% and upper limb, 4.17%, respectively. The main reasons of repetition of radiographs were due to exposure (54%) and positioning (18%) errors. The average repeat rate in all three hospitals was 7.20%. It was found that human error has important role to repetition of radiographs. It is demonstrated that those patients having repeated radiographs received an average of 3.23 Gy·cm2. Based on the findings of this study it must be remembered that the highest repetition rate was for pelvis. Considering the radiosensitive organs related to pelvis especially in pediatric patients some special considerations must be applied for pelvis examinations.
基金Supported by the National Natural Science Foundation of China (No.60472079), and Natural Science Founda-tion of Zhejiang Province (No.Z104252).
文摘A novel Automatic repeat ReQuest (ARQ) protocol called cooperative ARQ is presented in this let-ter, where a relay terminal is requested to retransmit an erroneously received packet, instead of the source ter-minal. The data link layer Packet Error Rate (PER) performance of cooperative ARQ is derived in correlated wireless channel. The results show that even though the relay-destination channel is worse than the source-destination channel, the new protocol outperforms the traditional one as long as the average SNR of the relay-destination channel is better than a certain threshold. It is also demonstrated that a second order diversity gain can be achieved with the cooperative ARQ protocol.
基金Project supported by the National Natural Science Foundation ofChina (No. 60302004) and the Natural Science Foundation of HubeiProvince (No. 2005ABA264), China
文摘Equation based TCP-friendly rate control (TFRC) protocol has been proposed to support video streaming applications. In order to improve TFRC performance in wireless channels, the link level automatic repeat request (ARQ) scheme is usually deployed. However, ARQ cannot ensure strict delay guarantees, especially over multihop links. This paper introduces a theoretical model to deduce an equation for packet size adjustment in transport layer to minimize retransmission delay by taking into con- sideration the causative reasons inducing retransmission in link layer. An enhanced TFRC (ETFRC) scheme is proposed inte- grating TFRC with variable packet size policy. Simulation results demonstrate that higher goodput, lower packet loss rate (PLR), lower frame transmission delay and jitter with good fairness can be achieved by our proposed mechanism.
