In this work, we studied the effect of initial grain size on the hot compression characteristics of super-304H austenitic stainless steel in a range of strain rates (0.001–1 s−1) at a fixed ...temperature of 1223 K. Analysis of the flow curves reveals that the flow stress is inversely proportional to the average sub-grain diameter in both coarse and fine-grained specimens at higher strain (≥0.5) levels. Further, the fine-grained specimen following deformation at a low strain rate (0.001 s−1) reveals the occurrence of both continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) mechanisms. In this condition, the CDRX is characterized by a progressive increase of boundary misorientation, while the DDRX is characterized by bulging and strain-induced boundary migration. In contrast, the CDRX characterized by the formation of microbands is majorly responsible for the grain refinement in the fine-grained specimen at higher strain rates (∼1 s−1) and in the coarse-grained specimen at all strain rates (0.001–1 s−1). The superposition of different DRX mechanisms leads to significant variations in grain refinement kinetics with strain rates and initial grain sizes. The findings of this investigation provide a foundation for the accurate control of the microstructures in the studied alloy with different initial grain sizes during the hot working at various strain rates.
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•Large strain hot compression in super-304H is conducted at 1223 K and 0.001–1 s−1.•Avrami exponent is weakly dependent on strain rate but varies with initial grain size.•Fine-grained specimen at 0.001 s−1 reveals both DDRX and CDRX mechanisms.•Fine and coarse-grained specimens at 1 s−1 reveal CDRX assisted by microbanding.•Superposition of DRX mechanisms leads to variations in grain refinement kinetics.
The road surface roughness is an important parameter that determines the quality of a road network. It has a direct influence on the grip and skid resistance of the vehicles. For this reason, this ...parameter has to be periodically monitored to keep track of its changes. Nowadays, road surface roughness is measured by driving measurement vehicles equipped with laser scanners all over the country. But, this approach is very costly, labor-intensive, and time-consuming. This article is done to evaluate the potential of high-resolution airborne polarimetric synthetic aperture radar (SAR) to remotely estimate the road surface roughness on a wide scale. Different SAR backscatter-based semi-empirical models and SAR polarimetry-based models for surface roughness estimation are implemented in this article. Also, a new semi-empirical model is proposed in this article, which is trained specifically for the road surface roughness estimation. Additive noise subtraction, upper sigma nought threshold masking, and lower signal-to-noise ratio threshold masking techniques were implemented in this article to improve the reliability of road surface roughness estimation. The feasibility of this approach is tested using fully polarimetric X-band datasets acquired with DLR's airborne radar sensor F-SAR. The surface roughness results estimated using these airborne SAR datasets show good agreement with the ground truth surface roughness values and the results are discussed in this article.
The complex microstructural changes following superplastic deformation in statically and continually recrystallizing Al-alloys are examined. Al alloy, AA 2004, exhibits continual recrystallization ...during deformation, whereas in two other alloys, AA 5456 and AA 7020, static recrystallization leads to the formation of equiaxed grains prior to the onset of superplastic deformation. Other features such as grain growth, grain rotation, dislocation accumulation and their influence on texture evolution during superplastic deformation are investigated. The observations clearly suggest that grain boundary sliding is the rate controlling process during steady state superplastic deformation.
Uniaxial hot deformation was carried out in a wide range of temperatures (1173 K to 1423 K) and strain rates (0.001 to 10 s
−1
) in a super austenitic stainless steel employing a Gleeble ...thermomechanical simulator. The evolution of fine grains due to dynamic recrystallization (DRX) with near-random texture was evident following deformation at strain rates 0.001 to 10 s
−1
and temperatures 1173 K to 1273 K. The deformed grains in this domain exhibited the typical formation of 〈110〉//ND or α fiber, and its volume fraction gradually increased when the resistance to deformation increases. Weak deformation texture was persisted in the fine DRX grains (≤ 3
µ
m) which gradually converted to a strong 〈001〉//ND fiber following grain growth. The deformation texture was simulated by employing a crystal plasticity finite element method (CPFEM). The texture inhomogeneity was observed in the typical compressed specimen which was associated with variation in stress/strain paths at different locations of the hot compressed specimen. Further, the ∑3 twin boundary evolution was analyzed employing Pande’s relationship and twin-related domains (TRDs) analysis. The growth accident was identified as the major mechanism of ∑3 twin boundary evolution during DRX in this alloy. Moreover, the ∑3 regeneration was also evident in a small domain of hot working (1323 K/0.001 s
−1
) which was substantiated by texture randomization and formation of relatively larger TRDs in the microstructure.
Hot deformation behavior of a phosphorous-modified super austenitic stainless steel was studied in the temperature range of 1173–1423K and strain rate range of 0.001–10s−1 employing thermomechanical ...simulator. The apparent activation energy for deformation in the above processing regime was estimated to be 482kJmol−1. The deformation parameters were modeled using Arrhenius equation and Zener–Hollomon parameter (Z). Peak stress, critical stress for dynamic recrystallization, stress at which flow softening is maximum as well as steady state stress was found to exhibit a linear relationship with ln(Z/A). Strains corresponding to these stresses were also found to exhibit the relation ε=CZAp. Processing maps were developed at different plastic strains employing dynamic materials modeling. Microstructures corresponding to the different processing conditions were characterized employing electron back scatter diffraction. Based on the analysis of microstructure and processing map, the optimum processing domain for hot deformation is identified as strain rate range of 0.01–0.1s−1 and temperature range of 1300–1350K. Although a significant recrystallization was observed following hot deformation in the strain rate ranges of 1–10s−1 and temperature ranges 1373–1423K, this domain was marked as unstable in the processing map.
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•Super austenitic stainless steel was hot-deformed at 1173-1423K and 0.001-10s−1 using a thermo-mechanical simulator•Hot deformation parameters were modeled using Arrhenius equation and Zener–Hollomon parameter (Z)•Peak, critical (for DRX), maximum flow softening and steady-state stresses vary linearly with ln(Z/A)•Processing map was constructed and microstructures at different processing domains were characterized•Optimum processing domain was identified as 1300-1350K and 0.01-0.1s−1
Airborne synthetic aperture radar (SAR) has the potential to monitor remotely the road traffic infrastructure on a large scale. Of particular interest is the road surface roughness, which is an ...important road safety parameter. For this task, novel algorithms need to be developed. Machine learning approaches, such as artificial neural networks and random forest regression, which can perform nonlinear regression, can achieve this goal. This work considers fully polarimetric airborne radar datasets captured with German Aerospace Center's (DLR)'s airborne F-SAR radar system. Several machine learning-based approaches were tested on the datasets to estimate road surface roughness. The resulting models were then compared with ground truth surface roughness values and also with the semiempirical surface roughness model studied in the previous work.
Abstract
Background:
Presently, computed tomography (CT) is the most important source of medical radiation exposure. CT radiation doses vary considerably across institutions depending on the protocol ...and make of equipment. India does not yet have national or region-specific CT diagnostic reference levels.
Aim:
To evaluate radiation doses of consecutive multidetector CT (MDCT) examinations based on anatomic region, performed in 1 month, collected simultaneously from seven tertiary care hospitals in Kerala.
Settings and Design:
Descriptive study.
Materials and Methods:
We collected the CT radiation dose data of examinations from the seven collaborating tertiary care hospitals in Kerala, performed with MDCT scanners of five different makes. The data included anatomic region, number of phases, CT dose index (CTDI
vol
), dose-length product (DLP), and effective dose (ED) of each examinations and patient demographic data.
Statistical Analysis:
We calculated the 25
th
, 50
th
, and 75
th
percentiles of the CTDI
vol
, DLP, and ED according to anatomic region. We made descriptive comparisons of these results with corresponding data from other countries.
Results:
Of 3553 patients, head was the most frequently performed examination (60%), followed by abdomen (19%). For single-phase head examinations, 75
th
percentile of CTDI
vol
was 68.1 mGy, DLP 1120 mGy-cm, and ED 2.1 mSv. The 75
th
percentiles of CTDI
vol
, DLP, and ED for single-phase abdomen examinations were 10.6, 509.3, and 7.7, and multiphase examinations were 14.6, 2666.9, and 40.8; single-phase chest examinations were 23.4, 916.7, and 13.38, and multiphase examinations were 19.9, 1737.6, and 25.36; single-phase neck were 24.9, 733.6, and 3.814, and multiphase neck were 24.9, 2076, and 10.79, respectively.
Conclusion:
This summary CT radiation dose data of most frequently performed anatomical regions could provide a starting point for institutional analysis of CT radiation doses, which in turn leads to meaningful optimization of CT.
Chronic obstructive pulmonary disease (COPD) is a common disease causing significant socioeconomic burden. COPD patients, commonly smokers develop resistance to inhaled steroids attributed to ...deficiency of histone deacetylase 2 (HDAC2). The study of relationship between systemic inflammation and functional performance demonstrated that increased CRP level is inversely related to six minute walk distance (SMWD) and Forced Expired Volume in one second (FEV1). Theophylline restores HDAC2 activity thereby unlocking steroid resistance and potentiating inhaled corticosteroids (ICS) action culminating in reduced airway inflammation and mortality.
To study the effects of addition of Theophylline to the combination of Formoterol plus Budesonide on various objective and subjective parameters in moderate to severe COPD patients and to assess the safety profile of the combination. Setting and Study design: A single blinded, prospective, randomized, placebo controlled study at a tertiary care hospital in Jaipur, India.
Fifty eight patients diagnosed with moderate to severe COPD were randomized into two groups. Group A patients received Formoterol 24μg plus budesonide 800μg daily in divided doses along with Theophylline while group B patients received Formoterol 24μg plus budesonide 800μg daily in divided doses along with placebo tablets. Both groups were followed up on 15th, 30th &60th day. During every visit all patients were assessed subjectively (symptom scoring) and objectively (spirometry, CRP, SMWT) and adverse effects if any were recorded. The obtained data subject to statistical analysis using"Graph pad Instat3" software.
Statistically significant improvement with a decline in total symptom score (p < 0.0001) was found with respect to "Night symptoms"&"SOB on rising" in group A. Theophylline group showed significant improvement in SMWD and FEV1.Mean fall in CRP was greater in Group A (not statistically significant). No side effects requiring withdrawal of drug were noted with Theophylline.
Addition of Theophylline to Formoterol plus Budesonide reduces dyspnea, improves exercise performance and pulmonary functions in moderate to severe COPD. Further studies are required to explore if reduced dosage would have equal efficacy with better safety and tolerability profile.
Dynamic recrystallization (DRX) kinetics and its association with annealing twins in alloy 617 has been studied in a range of strain rates (0.001s−1 to 10s−1) and temperatures (1173–1473K). In both ...low (< 0.1s−1) and high (≥ 1s−1) strain rate domains, DRX fraction is high as compared to intermediate strain rate (~ 0.1s−1). The lower critical strain for DRX initiation with higher growth of DRX grains is responsible for large DRX fraction with coarse grains microstructure in the low strain rate domain. In contrast, DRX at higher strain rates is mainly controlled by the large stored energy along with adiabatic temperature rise which leads to higher DRX nucleation. It is also noticed that the evolution of twins is greatly influenced by deformation temperature at all imposed strain rates. Here, the evolution of twins is quantified by measuring twin boundary length fraction and length density. The twin-length density increases with increase in DRX fraction at low temperatures (< 1423K) but decreases with increasing DRX fraction at high temperatures (≥ 1423K). An exponential rise in recrystallized grain size with DRX fraction is observed at a temperature ≥ 1423K. This suggests that rapid migration of high-angle boundaries happened at ≥ 1423K which may not be favorable for nucleation of twins during DRX.
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Dynamic microstructural evolution and recrystallization mechanism during hot deformation of intermetallic-hardened duplex Fe-9Al-10.8Mn-4.5Ni-0.7C (wt.%) lightweight steel have been comprehensively ...examined at various deformation temperatures at a fixed strain rate of 0.001 s−1. The flow curves are predicted employing Avrami exponent obtained from the strain dependent Johnson-Mehl-Avrami-Kolmogorov relation, which is further corroborated with the dynamic microstructural response. A detailed analysis of the intermetallic precipitates and elemental partitioning in both the ferrite and austenite phases are performed. The ferrite matrix having uniformly distributed nano-sized B2 (NiAl) precipitates has a higher micro-hardness as compared to the austenite matrix, which corroborates the strain partitioning in the austenite phase during hot deformation. Two distinct restoration mechanisms are observed in this alloy viz. continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) following hot deformation. The CDRX mechanism in the ferrite and austenite phase is characterised by the progressive misorientation development of subgrains into high-angle boundary during straining. The ferrite phase is associated with CDRX mechanism at all the deformation temperatures (1223–1423 K) albeit DDRX-like mechanism, facilitated by austenite/ferrite interphase is found to be an assisting mechanism towards the higher temperatures (1323–1423 K). The austenite phase, on the other hand, exhibits DDRX mechanism during the initial stage and dominant CDRX at the later stage of deformation at lower temperature (1223–1323 K). With the increasing deformation temperature to 1423 K, the dissolution of boundary-B2 precipitates in austenite facilitates the boundary migration, thus promoting the DDRX accompanied by the twinning in this phase.
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•Ferrite with nano-sized B2 precipitates has higher microhardness than austenite.•The flow curves in the steel are predicted employing the JMAK model.•Ferrite phase exhibits both CDRX and DDRX-like mechanism at 1323–1423 K.•CDRX is dominant mechanism in austenite in later stage of deformation at 1223 K.•Dissolution of B2 in austenite phase triggers DDRX and grain coarsening at 1423 K.
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