Inclusion of fibers can mostly enhance the mechanical properties of concrete; however, the role of those in reinforced concrete beams wherein the interaction between concrete, steel reinforcement, ...and fibers is crucial can be different. This paper provides an experimental study to evaluate the residual behavior of macro fiber-RC beams exposed to high temperatures. Thirty-six scaled reinforced concrete beams were designed and fabricated according to the ACI 318 criteria and requirements, subjected to high temperatures up to 800 °C. In this investigation, mechanical and deformation properties of heated RC beams, failure patterns, and confinement role of fibers were examined, discussed, and compared with non-heated specimens. This investigation indicated, adding steel fibers noticeably improved the residual bearing capacity and bond interaction between steel bars with concrete at high temperatures. Hence, this value for RC beams reinforced with steel and hybrid-synthetic fibers at 800 °C was 65% and 48% of their initial capacity, respectively; however, for plain concrete was about 40%. Moreover, the transformation of failure patterns depended on the type of used fibers and experienced temperatures.
With regard to the expansion of the use of carbon fiber reinforced polymer (CFRP) in strengthening civil engineering structures due to its high positive points (like high tensile strength and low ...thickness) as well as its weaknesses in high temperatures especially in buildings and weak points of existing thermal insulators, the experiments mentioned in this article have been carried out to investigate the post-fire conditions of CFRP retrofitting systems using the externally bonded reinforcement technique which resulted from the need to use insulation for this type of reinforcement system to improve its heat performance, as well as the weak points of common insulations. In the first phase, 12 samples of reinforced concrete (RC) beams strengthened with externally bonded carbon fiber reinforced polymer (UD200) were heated at 400 °C, 500 °C, 600 °C, and 800 °C and loaded after cooling, then they were compared with the results of the second phase of the tests which have been explained completely, consisting of 11 RC beams strengthened with CFRP having exactly the same properties as those in the first phase. They were also thermally insulated with intumescent paint that had some advantages like low thickness (1.1 mm) and the speed and ease of implementation and restoration. These results have clearly shown that the new insulating layer not only can maintain the positive feature of common insulations, but also unlike other common insulators, does not add to the thickness of the specimens. Moreover, the application of the intumescent paint both increased the performance of the specimens at high temperatures and covered the weaknesses of CFRP reinforcement system against heat so that the CFRP sheets unlike the ones on the non-insulated specimens did not completely disappear at the highest temperature.
African Americans (AA) have traditionally been thought to have higher immunologic risk than Caucasians (CA) for rejection and allograft loss. The impact of ethnicity on the outcome of simultaneous ...pancreas–kidney (SPK) transplant with basiliximab induction has not been reported. In this study, we retrospectively analyze the long‐term results of 36 AA and 55 CA recipients of primary SPK. The actual patient survival rates of AA and CA groups were 91.7% vs. 90.1% at 1 year, 93.3% vs. 88.1% at 3 years, and 94.4% vs. 83.3% at 5 years. The actual kidney survival of AA and CA were 91.7% vs. 89.1% at 1 year, 90% vs. 81% at 3 years, and 83.3% vs. 75% at 5 years. The actual pancreas survival of AA and CA were 88.9% vs. 85.5% at 1 year, 83.3% vs. 78.6% at 3 years and 72.2% vs. 70.8% at 5 years. Death‐censored analyses also found no difference in pancreas and kidney graft survival rates over 5 years. Higher rejection rate, but the same low CMV infection, and comparable quality of graft function were noted in AA group. AA may not have worse long‐term outcomes than CA recipients of SPK with basiliximab induction and tacrolimus (TAC), mycophenolate acid (MFA) and steroid maintenance immunotherapy.
Testing the post‐transplant HLA antibodies is critical to differentiating the diagnostic alternatives in patients with allograft dysfunction.
We review comprehensive observations of electromagnetic ion cyclotron (EMIC) wave-driven energetic electron precipitation using data collected by the energetic electron detector on the Electron ...Losses and Fields InvestigatioN (ELFIN) mission, two polar-orbiting low-altitude spinning CubeSats, measuring 50-5000 keV electrons with good pitch-angle and energy resolution. EMIC wave-driven precipitation exhibits a distinct signature in energy-spectrograms of the precipitating-to-trapped flux ratio: peaks at >0.5 MeV which are abrupt (bursty) (lasting ∼17 s, or
Δ
L
∼
0.56
) with significant substructure (occasionally down to sub-second timescale). We attribute the bursty nature of the precipitation to the spatial extent and structuredness of the wave field at the equator. Multiple ELFIN passes over the same MLT sector allow us to study the spatial and temporal evolution of the EMIC wave - electron interaction region. Case studies employing conjugate ground-based or equatorial observations of the EMIC waves reveal that the energy of moderate and strong precipitation at ELFIN approximately agrees with theoretical expectations for cyclotron resonant interactions in a cold plasma. Using multiple years of ELFIN data uniformly distributed in local time, we assemble a statistical database of ∼50 events of strong EMIC wave-driven precipitation. Most reside at
L
∼
5
−
7
at dusk, while a smaller subset exists at
L
∼
8
−
12
at post-midnight. The energies of the peak-precipitation ratio and of the half-peak precipitation ratio (our proxy for the minimum resonance energy) exhibit an
L
-shell dependence in good agreement with theoretical estimates based on prior statistical observations of EMIC wave power spectra. The precipitation ratio’s spectral shape for the most intense events has an exponential falloff away from the peak (i.e., on either side of
∼
1.45
MeV). It too agrees well with quasi-linear diffusion theory based on prior statistics of wave spectra. It should be noted though that this diffusive treatment likely includes effects from nonlinear resonant interactions (especially at high energies) and nonresonant effects from sharp wave packet edges (at low energies). Sub-MeV electron precipitation observed concurrently with strong EMIC wave-driven >1 MeV precipitation has a spectral shape that is consistent with efficient pitch-angle scattering down to ∼ 200-300 keV by much less intense higher frequency EMIC waves at dusk (where such waves are most frequent). At ∼100 keV, whistler-mode chorus may be implicated in concurrent precipitation. These results confirm the critical role of EMIC waves in driving relativistic electron losses. Nonlinear effects may abound and require further investigation.
Correction to: The ELFIN Mission Angelopoulos, V.; Tsai, E.; Bingley, L. ...
Space science reviews,
09/2020, Letnik:
216, Številka:
6
Journal Article
Recenzirano
Odprti dostop
Correction to: Space Sci. Rev. (2020) 216: 103
https://doi.org/10.1007/s11214-020-00721-7
Affiliation 2 in this article is the wrong affiliation that instead should read: “Institute of Geophysics and ...Planetary Physics, University of California, Los Angeles, CA, USA” which should be regarded as the final version by the reader.
Cyclosporine-associated thrombotic microangiopathy in renal allografts.
The association between cyclosporine (CsA) and thrombotic microangiopathy (TMA) in renal allografts is well documented. ...However, predisposing factors and therapy guidelines are not adequately characterized.
We reviewed 188 patients with kidney or kidney-pancreas transplants who were treated between January 1994 and December 1996 with prednisone, CsA, or tacrolimus, and azathioprine or mycophenolate. We analyzed 50 patients who had graft biopsies: 26 with TMA and 24 with no TMA, as well as 19 patients with well-functioning grafts who never required biopsy.
TMA was observed in 26 of 188 renal graft recipients (14%). TMA was confined to the allograft kidney without any systemic evidence in 24 of the 26 patients. At the time of the diagnosis of TMA, 24 of the patients were on CsA, with 19 on the microemulsion form. Conversely, 5 of 18 control patients with no graft dysfunction were on the microemulsion form of CsA (P = 0.0026). Graft loss was seen in 8 of 26 patients with TMA. Conversion from CsA to tacrolimus resulted in a one-year salvage of graft function in 13 of 16 (81%) patients.
TMA was the cause of renal graft dysfunction in 14% of renal graft recipients and was associated with the use of the microemulsion form of CsA. Systemic signs of TMA were rare, underscoring the importance of the graft biopsy in making the diagnosis. The most successful strategy was switching from CsA to tacrolimus, with good graft function in 81% of the recipients one year after the TMA episode.
We reviewed our initial experience with helical computed tomography (CT) angiography in the evaluation of living kidney donors which, until now, has necessitated arteriography. Nineteen donors (12 ...women, 7 men) have had their renal anatomy evaluated solely by CT angiography preoperatively.All scans demonstrated normal collecting systems and single ureters. Five donors (26%) had supernumerary renal arteries. Fourteen donors had single, 4 donors had two, and 1 donor had three renal arteries. Helical CT demonstrated small polar vessels in several donors. Two donors (10%) had supernumerary renal veins. Accuracy of vascular anatomy defined on CT was 90% when confirmed at operation. Anatomically all CT findings were consistent with operative findings except in 1 donor who was found to have a 0.8 cm lesion near the renal hilum.At our institution, the total charges for selective renal arteriography are $3845 and for helical CT with three‐dimensional (3‐D) reconstruction are $1546. The amount of contrast dye (approximately 100 mL) is equivalent. Patients uniformly reported that the CT scan was a convenient and painless procedure.The accuracy of helical CT angiography is equivalent to arteriography in assessing renal vascular anatomy (with the additional benefit of imaging venous and parenchymal anatomy). Charges for helical CT are 59% less. There is greater patient acceptance and potentially less morbidity associated with the non‐invasive nature of helical CT. We believe that CT angiography is the radiologic procedure of choice for the assessment of renal anatomy in potential living kidney donors.
Rupture of a renal allograft (RAR) is an uncommon but serious complication of renal transplantation. A recent RAR prompted a review of our experience, with the purpose of (1) identifying conditions ...that may predispose this complication and (2) defining strategies for prevention. A 5-yr, consecutive living-related (LRD) and cadaver donor (CD) cohort of 331 patients was studied retrospectively. Twelve patients (3.6%) had RAR. Donor characteristics, procurement and preservation conditions, and recipient characteristics were major study categories. Data analysis was computer-based and included multivariate analysis. The nine White and two Black cadaver donors were "ideal", mean age 29 yr, with mean high creatinine (CR) of 1.3 and terminal CR of 1.1 mg/dl and mean terminal urine output of 423 ml/min. Nine of 11 CD had low-dose dopamine use (terminal, mean 8, range 5-13 micrograms/kg/min). Eleven of 11 donors had procurement en-bloc, 9 of which were multiple organ procurement. All had 4+/4+ flush and cold storage with UW solution. Mean cold ischemia time (CIT) was 22 h, 28 min (range 15 h, 16 min to 40 h). For patients with RAR mean age was 39 yr; there were 12 Black patients and 7 males, 5 females. HLA match was 1 antigen (AG) for 3, 2 AG for 8, and 4 AG for 1 (mean 1.9). Nine patients had delayed or declining renal function requiring dialysis. The panel reactive antibody was at peak, mean 47% (range 0-100%) and current, mean 18% (range 0-84%). Six of 12 had OKT3 therapy at time of RAR and six had biopsies. Day of RAR was mean 10, median 9 (range 4-21). Pain and drop in hematocrit were observed in most. There was one fatality (8%), and all kidneys were removed. All kidneys showed at least minimal rejection but six had severe acute tubular necrosis (ATN) with edema and minimal rejection. Statistically significant associations with RAR were older recipient age (p = 0.01), donor-recipient race mismatch (White donor to Black recipient) (p = 0.007), and dialysis requirement (p < 0.001). Other variables were not statistically correlated: gender, race, CIT, transplant number, LRD vs. CD, peak or current PRA, and total HLA and BDR mismatch. The data suggest that ATN and rejection act synergistically to cause RAR and that early delayed function requires intensive and perhaps novel immunosuppression, especially in Black recipients.
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