Experimental Study of the Creep Behaviour of the Cold‐Drawn 304L Stainless Steel

Abstract: In this article, the material and physical parameters for the creep constitutive equations of cold‐drawn 304L stainless steel have been determined using experimental data. Austenitic stainless steel 304L is used mostly in power generation and petrochemical industries because of its high‐temperature creep resistance even at above yield stresses. Test samples have been obtained from cold‐drawn bars, and the material conforms to ASTM A276‐05a specifications. The creep behaviour and properties have been examined for this material by conducting uni‐axial creep tests. Constant temperature and constant load uni‐axial creep tests have been carried out at three temperatures of 680,700 and 720 °C, subjected to constant loads which produce below and above yield initial stresses of 200, 250, 320, 340 and 360 MPa. The experimental data have been used to obtain the creep constitutive parameters using numerical optimisation techniques. In addition, the temperature and stress dependency of the creep properties for this alloy have been investigated using Larson–Miller and Monkman–Grant parameters.     

Pyridine-functionalized mesoporous silica as an adsorbent material for the determination of nickel and lead in vegetables grown in close proximity by electrothermal atomic adsorption spectroscopy

A new, sensitive, and low cost solid-phase extraction method using pyridine-functionalized MCM-48 mesoporous silica for the extraction, pre-concentration, and electrothermal atomic absorption spectrometric determination of nickel and lead in food samples at ng mL⁻¹ levels is described herein. The levels of nickel and lead in different types of vegetables grow in Shiraz–Iran and Rafsanjan–Iran were determined by electrothermal atomic absorption spectrometry. The use of two standard reference materials and also comparing the results to a standard reference procedure ensured the accuracy of this method. Factors, such as flow rate of extraction, and the type, pH, concentration, and volume of eluent, were appraised. The effect of various ions on recovery was also investigated. Detection limits of 0.11 and 0.14 ng mL⁻¹ were obtained for lead and nickel, respectively.     

Design of a 12-bit high-speed CMOS D/A converter using a new 3D digital decoder structure useful for wireless transmitter applications

In this paper a 12-bit Nyquist current-steering digital-to-analog converter (DAC) is implemented using TSMC 0.35 μm standard CMOS process technology. The proposed DAC is an essential part in baseband section of wireless transmitter circuits. Using oversampling ratio (OSR) for it leads to avoid use of an active analog reconstruction filter. The optimum segmentation (75%) has been used to get the best DNL and reduce glitch energy. This segmentation ratio guarantees the monotonicity. Higher performance is achieved using a new 3D thermometer decoding method which reduces the area, power consumption and the number of control signals of the digital section. Using two digital channels in parallel, helps reach 1 GHz sampling frequency. Simulations indicate that the DAC has an accuracy better than 10.7-bit for upcoming higher data rate standards (IEEE 802.16 and 802.11n), and a spurious-free-dynamic-range (SFDR) higher than 64 dB in whole Nyquist frequency band. The post layout four corner Monte-Carlo simulated INL is better than 0.74 LSB while simulated DNL is better than 0.49 LSB. The analog voltage supply is 3.3 V while the digital part of the chip operates with only 2.4 V. Total power consumption in Nyquist rate measurement is 144.9 mW. Active area of chip is 1.37 mm².     

纳米微气泡存在下浮选机和浮选柱回收细粒磷酸盐矿物的比较

细粒浮选一直是许多矿物加工厂面临的主要问题之一.由于细颗粒的气泡粒子碰撞概率很低,因此降低了浮选效率.细粒的存在通常不利于浮选过程,影响了浮选精矿的选择性和质量,而且增加了试剂的消耗量.因此,在大多数加工厂中,会将部分颗粒输送到尾矿池中,以减少这些问题的影响,并提高浮选过程的选择性.由于d80小于30μm的颗粒的存在,...     

Peer acceptance, self-perceptions, and social skills of learning disabled students prior to identification.

This study addressed how learning disabled students prior to identification (LDPI), low-achieving (LA), average-achieving (AA), and high-achieving (HA) students compare on peer, teacher, and self assessments of social status and social skills in the fall and spring of kindergarten. Two hundred thirty-nine Black, Hispanic, and White students, 78% of a kindergarten population, participated. Controlling for age, sex, and achievement levels, four groups were identified: LDPI, LA, AA, and HA. In fall and spring of kindergarten all students were administered measures of peers' perceptions of social status, teacher's assessment of behavior problems and social skills, and self-perception. MANOVA and a stepwise discriminant function analysis revealed that as early as 8 weeks after entering kindergarten, LDPI students differed significantly from their peers on social variables and attention problems. Results suggest that later social difficulties of LD students are not solely a function of a history of low achievement and low teacher acceptance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Self-concept and peer acceptance in students with learning disabilities: A four- to five-year prospective study.

Examined the peer relations and self-concepts of students prior to and following their identification by the school district as learning disabled (LD) in a 4- to 5-yr prospective study. Self-concept ratings (kindergarten–4th grade) and peer acceptance ratings (kindergarten–3rd grade), as well as academic achievement scores, were compared across 3 groups: LD students who were placed in resource special education programs during 2nd grade, low-achieving (LA) students, and average-achieving/high-achieving (AA/HA) students. For peer acceptance, AA/HA students' scores were higher than LA students' scores only. No between-groups differences were obtained during any school year on the self-concept measure. Findings suggest that LD students' self-perceptions are not negatively affected by academic and social difficulties in the early grades or by the identification and labeling process. Though generalization is limited by the small sample size, few studies have examined students with learning disabilities longitudinally or prior to and following their identification. (PsycINFO Database Record (c) 2010 APA, all rights reserved)