Development of TiB<Subscript>2</Subscript> reinforced in-situ Ti aluminide matrix composite through reaction synthesis

TiB₂ reinforced in-situ titanium aluminide matrix composite was made through reaction synthesis process using high purity elemental powders of Ti, Al, Cr, Nb and B. XRD of the synthesized block showed presence of mainly Al₃Ti and TiB₂ phases. To obtain γ Ti aluminide based matrix, the material was homogenized in two phase region (α₂+γ). Presence of γ phase matrix alongwith α₂ was confirmed through XRD, SEM and TEM. Uniform distribution of TiB₂ phase was confirmed through elemental mapping and by analyzing specimens of different locations. Differential scanning calorimetry of powder mixture showed presence of endothermic peak for Al melting and exothermic peak of Ti aluminide and TiB₂ formation.     

Three-Stage Least-Squares Analysis of Time and Cost Overruns in Construction Contracts

Construction cost overrun and time overrun (delay) are a significant problem in highway-construction project delivery. Previous research studies have provided insight into the factors that affect overruns; however the findings may have been limited because they do not explicitly consider the simultaneous relationship between cost and time overruns. In this paper, we use data from Indiana highway projects to provide empirical evidence that a simultaneous relationship exists between cost and time overruns and that analysis of these two contractual outputs need to take due cognizance of such simultaneity. Using the three-stage least-squares technique, we identify a number of factors that significantly affect cost overrun and time overrun and we show how the effect of these variables vary by attributes such as project type and results of the bidding process. The models developed in this paper can help agencies enhance the estimation of the expected overruns of final cost and the delay in completion time for their planned projects.     

Characterization of slider-lubricant interaction with tribo-current

Lube-surfing recording combined with thermal fly-height control (TFC) technology is considered as a promising head-disk interface (HDI) scheme for further increasing magnetic areal density to 5?C10?Tbits/in². To realize this alternative technology, however, a lot of tricky issues are required to be solved. Among them, how to characterize the flying of slider in the lubricant or light lube-contact by the slider is probably one of the tough but inevitable challenges. In this study, the slider/lubricant/disk contact induced tribo-current is investigated with a modified media-tester in which the TFC slider is electrically isolated with the rest of the tester. The measured tribo-currents versus the heater voltages or the powers to the slider??s heater clearly indicate three different intensity regions of tribo-current, by which the three different contact types, namely, non-contact, lube-contact and solid-contact can be differentiated clearly. This method provides a promising way for accurately studying of lube-surfing recording.     

Low-power half-select free single-ended 10 transistor SRAM cell

This paper proposes a novel subthreshold 10T SRAM cell. The proposed design removes the half-select issue which is a problem in SRAM array as observed in the case of conventional 6T and 8T cells. Since the proposed cell is free from half-select disturb, bit-interleaving scheme can be implemented. A bit-interleaved architecture helps to reduce errors in multiple bits of a single word. This makes the proposed design immune to soft error caused by α particles or high-energy cosmic rays. The proposed cell uses data-dependent stack PMOS switching scheme (DSPS) to reduce the write access time and improve the write-ability. A single-ended read decoupled scheme used to perform read operation enhances the read stability. Various design metrics of the proposed SRAM cell have been compared with previously proposed cells such as SBI9T, DF9T and UDVS10T. The proposed cell shows 1.07×, 2.89× and 13.78× improvement in write access time while writing ‘0’ as compared to the SBI9T, DF9T and UDVS10T, respectively at a V _DD of 0.4 V. The proposed cell shows lesser spread in write delay as compared to DF9T cell, which signifies lower variability. There is 8.4, 10.3 and 6.5 % improvement in WSNM when compared to the three cells mentioned above, respectively. Also, 27.3 and 2.02 % improvements can be observed in RSNM when compared to the SBI9T and DF9T at a supply voltage of 0.4 V. RSNM of UDVS10T is same as that of the proposed design. As far as power consumption is concerned, the proposed design consumes 1.38× lesser read power as compared to UDVS10T and 1.67× and 5.02× lesser write power as compared to DF9T and UDVS10T respectively. The proposed design shows 1.8 % improvement in read current variability when compared to DF9T. Lastly, the proposed cell shows 2.21× and 5.25× higher I _READ/I _LEAK as compared to DF9T and UDVS10T.

     

Effect of prior cold rolling and test temperature on stress-strain rate behaviour of a Zr-2.5Nb alloy

Zr-2.5 wt% Nb alloy sheet, obtained by unfolding and straightening a pressure tube, was further cold rolled upto 39% reduction in thickness to investigate the effect of cold working on the stress ()-strain rate () behaviour over a strain rate range of 2 × 10–5 to 5 × 10–3 s–1 and a temperature range of 625 to 700 °C. Irrespective of the amount of rolling, the log vs log plots exhibit superplastic behaviour with strain rate sensitivity index, m, as high as 0.8, which decreases to 0.2 at higher strain rates. On the other hand, the activation energy for deformation, Q, increases from 171.1 kJ/mol for superplastic deformation to 249 kJ/mol in Region III. The tendency for improved superplasticity (m) is seen upon cold working by 22% or more at the test temperatures 675 and 700 °C.     

Partitioning and searching dictionary for correction of optically read Devanagari character strings

Abstract. This paper describes a method for the correction of optically read Devanagari character strings using a Hindi word dictionary. The word dictionary is partitioned in order to reduce the search space besides preventing forced matching to an incorrect word. The dictionary partitioning strategy takes into account the underlying OCR process. The dictionary words at the top level have been divided into two partitions, namely: a short-words partition and the remaining words partition. The short-word partition is sub-partitioned using the envelope information of the words. The envelope consists of the number of top, lower, core modifiers along with the number of core charactersp. Devanagari characters are written in three strips. Most of the characters referred to as core characters are written in the middle strip. The remaining words are further partitioned using tags. A tag is a string of fixed length associated with each partition. The correction process uses a distance matrix for a assigning penalty for a mismatch. The distance matrix is based on the information about errors that the classification process is known to make and the confidence figure that the classification process associates with its output. An improvement of approximately 20% in recognition performance is obtained. For a short word, 590 words are searched on average from 14 sub-partitions of the short-words partition before an exact match is found. The average number of partitions and the average number of words increase to 20 and 1585, respectively, when an exact match is not found. For tag-based partitions, on an average, 100 words from 30 partitions are compared when either an exact match is found or a word within the preset threshold distance is found. If an exact match or a match within a preset threshold is not found, the average number of partitions becomes 75 and 450 words on an average are compared. To the best of our knowledge this is the first work on the use of a Hindi word dictionary for OCR post-processing. Received August 6, 2001 / Accepted August 22, 2001     

Effect of zinc supplementation on cell-mediated immunity and lymphocyte subsets in preschool children

The pattern and distribution of periodontitis were investigated in 162 randomly selected dogs available for necropsy in veterinary practice. There were 82 males and 80 females of 50 different breeds (150 dogs were pure-bred and 12 were mongrels, aged between 7 months and 14 yr. Presence of periodontitis was determined by assessment of alveolar bone loss on radiographs of the skulls and jaws. Periodontitis occurred frequently with increasing age, although the prevalence varied markedly among and within different breeds. Of the breeds most represented in the sample, periodontitis was most frequently seen in poodles and dachshunds but was rarely recognized in German shepherd dogs. Regardless of age, the vast majority of the dogs displayed either one or both of two different radiographic patterns of alveolar bone loss. One pattern was characterized by slight, horizontal alveolar bone loss involving interradicular and interdental areas. The other pattern was one of predominantly crater-like, or narrow, vertical bone defects which, when advanced, often extended around a single root or tooth to surround the root apices. The two types of patterns did not seem to be breed-dependent. The posterior maxillary and mandibular premolars and molars were the most frequently affected teeth. Alveolar bone loss was most severe in the maxilla, while corresponding bone loss in the mandible was more often related to increasing age.     

Extended power method and stability of linear discrete-time systems

A computationally simple and efficient method is proposed to determine the stability of linear discrete-time systems. The method directly utilises the system (state-transition) matrix and avoids the evaluation of the characteristic polynomial. Another interesting feature of this approach is that it can be extended to extract the eigenvalues of matrices, in a recursive fashion.     

Leptin in human pregnancy: the relationship with gestational hormones

OBJECTIVES: The aims of the study were (1) to examine the relationship between leptin and placental hormones by measuring serial changes in serum levels of leptin during and after pregnancy and (2) to study the effects of several gestational hormones on leptin release from fully differentiated 3T3-L1 adipocyte cell cultures. STUDY DESIGN: Serum levels of leptin were measured throughout pregnancy and at 3 months post partum in 29 healthy women and were also measured in 18 healthy women at delivery by cesarean section and on postpartum day 3. In addition, 3T3-L1 mouse adipocytes were incubated for 24 hours in media containing various reproductive hormones and leptin production was measured. RESULTS: Serum leptin levels increased significantly (8.4 +/- 0.9 vs 13.5 +/- 1.5 ng/mL; P <.001) between the first 2 trimesters of pregnancy but not between the second and third trimesters. These changes in leptin did not correlate significantly with changes in body mass index. Leptin levels dropped significantly during the immediate postpartum period, from 34.1 +/- 4.9 at cesarean delivery to 7.3 +/- 1.4 ng/mL on postpartum day 3 (P <.001). Fasting insulin level did not correlate significantly with leptin level during pregnancy but did so during the postpartum period (r = 0.60; P <.05). Leptin secretion from 3T3-L1 adipocytes was increased significantly when cells were cultured with human chorionic gonadotropin (150%, P <.01) and also when they were cultured with estrogen (120%, P <.03). CONCLUSION: The data suggest that leptin production by adipose tissue is stimulated by several hormones of pregnancy, which may contribute to the increased leptin levels observed during gestation.