570 research outputs found
Möglichkeiten und Grenzen der Berechnung von Rissbreiten in verÀnderlichen Verbundsituationen
Die vorliegende Arbeit reflektiert die aktuelle Diskussion von Modellen zur Vorhersage von Rissbreiten und versucht, objektive Vergleichskriterien aufzustellen sowie Folgerungen fĂŒr mögliche Lösungswege zu ziehen. Am Beginn steht eine ausfĂŒhrliche Auseinandersetzung mit dem Verbundmechanismus zwischen Betonstahl und Beton und den Möglichkeiten der Verbundanalyse. Ausgehend von eigenen Versuchen an kurzen VerbundlĂ€ngen zur Untersuchung des Verbundverhaltens von Bewehrung in hochfesten Betonen wird in der Arbeit nach Möglichkeiten zur Vorhersage von Gleit- und SprengbrĂŒchen gesucht. FĂŒr SprengbrĂŒche, also LĂ€ngsrissbildung, ist ein verbesserter Versuchsaufbau entwickelt worden, der RĂŒckschlĂŒsse auf die Verformungsentwicklung in der potentiellen SprengbruchflĂ€che und den Aufbau eines Verbundwiderstands unter Belastung ermöglicht. Es stellte sich trotz der Fortschritte in der Versagensanalyse dieser Versuche heraus, dass es wenig sinnvoll ist, die gewonnenen Verbundgesetze direkt auf lange VerbundlĂ€ngen zur Ermittlung von Rissbreiten anzuwenden. Zur Simulation der mit Bauteilsituationen vergleichbaren langen VerbundlĂ€ngen wird dagegen eine Hypothese ĂŒber den Widerstand einer potentiellen LĂ€ngsbruchflĂ€che verwendet. Dabei wird die mögliche Reaktion von gekoppelten und voneinander abhĂ€ngigen Betonzugringen um einen Betonstahl, vom Lasteintrag beginnend, sukzessive fortschreitend aufgebaut. Die Aufteilung der Zugringe folgt dabei einer Annahme ĂŒber die Entwicklung von lokalen Verbundrissen nach Goto. Damit ist die Zugringtheorie von Tepfers auf lange VerbundlĂ€ngen ĂŒbertragbar und Simulationen von ZugstĂ€ben nahe an Tepfers theoretischen AnsĂ€tzen werden so ermöglicht. Die Rechnersimulationen an langen VerbundlĂ€ngen im Vergleich zur Prognose nach MC 90 wurden fĂŒr Einzelrissbildung und abgeschlossene Rissbildung an zylindrischen Dehnkörpergeometrien durchgefĂŒhrt. Zur Verifizierung der zeitabhĂ€ngigen EinflĂŒsse wie ZwĂ€ngungen aus Schwinden und Zugkriechen sind einfache AnsĂ€tze entwickelt worden. Am Ende dieser Analysen steht eine Neubewertung normativer AnsĂ€tze (MC 90/DIN 1045-1 sowie EN 1992-1-1) zur Berechnung einer charakteristischen Rissbreite. Eine SchlĂŒsselstellung nimmt die richtige Prognose des wirksamen Rissabstands in allen Berechnungsmodellen ein. Anhand eines neu zusammengestellten Datensatzes und vorhandener VergleichsdatensĂ€tze wurde die Performance der Modelle untersucht. Anwendungsbereiche, die problematisch erscheinen, konnten eingegrenzt werden. Es war zu folgern, dass die AnsĂ€tze fĂŒr den effektiven Bewehrungsgrad und die Verbundspannung zu verbessern sind. Die daraufhin mit einem additiven Sicherheitselement und einem variablen Mindestwert entwickelte Modellalternative gegenĂŒber den normativen VorschlĂ€gen ist nun zielgerichteter und kann dabei eine effektivere und zuverlĂ€ssigere Prognose der Rissbreite und damit der konstruktiven Bewehrungslösung liefern. Die Anforderungen an die Performance eines Rechenwertes der Rissbreite wk sind um ein EffektivitĂ€tskriterium fĂŒr den Rissabstand srk ergĂ€nzt worden, dessen VorhersagequalitĂ€t entscheidend fĂŒr effiziente und zuverlĂ€ssige Vorhersagen der Rissbreite ist. Die ZuverlĂ€ssigkeit des DIN-Ansatzes fĂŒr Mindestbewehrung im Grenzzustand der Gebrauchstauglichkeit ist ebenfalls geprĂŒft worden. Umfangreiche Zusammenstellungen, Beispiele und Parameterstudien sind im Anhang der Arbeit hinzugefĂŒgt, um die theoretischen Ergebnisse zu stĂŒtzen und Lesern Vergleichsmöglichkeiten zu bieten. Dazu gehören auch zwei AblaufplĂ€ne und Hilfsmittel fĂŒr einfache Absicherungen, die die zu erwartenden Schwierigkeiten bei der Verwendung des normativen DIN 1045-1 Ansatzes zur BeschrĂ€nkung auf kleine Rissbreiten ausgleichen können.The doctoral thesis reflects the recent discussion on the finding of suitable verification models for crack width control. It tries to assemble criteria for the comparison in order to draw conclusions from the outcome. In the very beginning stands a widespread analysis of the bond mechanisms between the reinforcing steel and the concrete. Starting from own testing on short embedment lengths in HPC, opportunities are researched for the prediction of a sliding or splitting failure of the surrounding concrete during bar pull-out. An improved test setup is developed by the Author to verify the splitting failure mechanism that finally leads to longitudinal cover cracking. It enables to obtain better indications for the inner strain development in the later failure plane, showing the development of the bond resistance during loading. Although progress were made in the quality of analysis, it turned out that, a direct implementation of obtained bond laws is less successful to take care of the apparent problem of long embedment lengths. The description of that problem is essential within the crack width verification. Differently, a method is suggested to simulate a probable longitudinal splitting plane and its potential to resist an applied longitudinal load. In that method, the possible reaction of interlinked concrete tension rings around a steel bar is thought to form a growing global resistance with every added resistance ring in a sequential chain that are decreasingly loaded if the distance to the load application increases. The segmentation follows an approximation of the possibly development of local bond cracks acc. to Goto. In this, the application of the tension ring theory from Tepfers were successfully overtaken to the problem of long embedment lengths. It enables for simulations close to the original theory of tensile rings formed by concrete around the reinforcing steel. Comparing the results with MC 90, the simulation of long embedment lengths were performed using imaginary cylindrical test-specimen, enabling the verification of single and stabilized cracking. Simplified methods were developed in order to implement time-dependent influences like restraint from creep and shrinkage.An extensive evaluation of the normative methods (MC 90/ DIN 1045-1 and EN 1992-1-1) for verifications of a characteristic crack width stands at the end of the studies. A key position within the models is held by the realistic prognosis of the accountable crack distance. Using a newly compiled dataset and already existing data for comparison, the performances of current models were verified for predicting crack widths or distances. Complicated fields of its application could be marked and isolated. It was concluded that, the approaches for the determination of the effective reinforcement ratio and the bond stress should be improved. The developed alternative for calculation is assembled with an added safety feature and a variable minimum for the crack distance. It can lead to a more reliable prognosis for crack distances and the depending crack widths in order to design a more efficient reinforcement detailing. The requirements on the performance of a determined characteristic crack width wk are extended by the application of a criteria of effectiveness for the calculated crack distance srk. The reliability of the MC 90 -approach and the DIN-approach for minimum reinforcement has also been checked. Extensive compilations of data, examples and parameter studies are added to the appendix in order to backup the theoretical results and to invite others to compare. Two calculation flow charts and helptools are integrated to ensure the quality of crack width calculations also in cases where smaller crack widths must be verified, using informative and normative methods in MC 90/ DIN 1045-1
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Prevalence of iron deficiency in 62,685 women of seven race/ethnicity groups: The HEIRS Study.
BackgroundFew cross-sectional studies report iron deficiency (ID) prevalence in women of different race/ethnicity and ages in US or Canada.Materials and methodsWe evaluated screening observations on women who participated between 2001-2003 in a cross-sectional, primary care-based sample of adults ages â„25 y whose observations were complete: race/ethnicity; age; transferrin saturation; serum ferritin; and HFE p.C282Y and p.H63D alleles. We defined ID using a stringent criterion: combined transferrin saturation <10% and serum ferritin <33.7 pmol/L (<15 ÎŒg/L). We compared ID prevalence in women of different race/ethnicity subgrouped by age and determined associations of p.C282Y and p.H63D to ID overall, and to ID in women ages 25-44 y with or without self-reported pregnancy.ResultsThese 62,685 women included 27,079 whites, 17,272 blacks, 8,566 Hispanics, 7,615 Asians, 449 Pacific Islanders, 441 Native Americans, and 1,263 participants of other race/ethnicity. Proportions of women with ID were higher in Hispanics and blacks than whites and Asians. Prevalence of ID was significantly greater in women ages 25-54 y of all race/ethnicity groups than women ages â„55 y of corresponding race/ethnicity. In women ages â„55 y, ID prevalence did not differ significantly across race/ethnicity. p.C282Y and p.H63D prevalence did not differ significantly in women with or without ID, regardless of race/ethnicity, age subgroup, or pregnancy.ConclusionsID prevalence was greater in Hispanic and black than white and Asian women ages 25-54 y. p.C282Y and p.H63D prevalence did not differ significantly in women with or without ID, regardless of race/ethnicity, age subgroup, or pregnancy
Dietary Linolenic Acid and Adjusted QT and JT Intervals in the National Heart, Lung, and Blood Institute Family Heart Study
OBJECTIVES The goal of this study was to examine whether higher consumption of total linolenic acid was associated with rate-adjusted QT and JT intervals (QTrr and JTrr, respectively). BACKGROUND Higher intake of fish omega-3 fatty acids and plant omega-3 such as alpha-linolenic acid is associated with lower risk of myocardial infarction. While long-chain omega-3 can inhibit ventricular arrhythmia, it is not known whether alpha-linolenic acid influences ventricular repolarization. METHODS We studied 3,642 subjects from the National Heart, Lung, and Blood Institute Family Heart study who were free of myocardial infarction, left ventricular hypertrophy, pacemaker, and with QRS <120 ms. We used the 95th percentile of the gender-specific distribution of QTrr and JTrr to define abnormally prolonged repolarization. Within each gender, we created age-and energy-adjusted tertiles of linolenic acid and used regression models for analyses. RESULTS Mean age was 50 years, and average intake of total linolenic acid was 0.74 g/day. There was an inverse association between consumption of linolenic acid and QTrr and JTrr (p for trend 0.001 and 0.0005, respectively). From the lowest (reference) to the highest gender-, age-, and energy-adjusted tertile of linolenic acid, multivariable adjusted odds ratios for prolonged QTrr were 1.0, 0.74 (95% confidence interval [CI] 0.57 to 0.96), and 0.59 (95% CI 0.44 to 0.77), respectively (p for trend 0.0003). Corresponding values for JTrr were 1.0, 0.73 (95% CI 0.52 to 1.03), and 0.59 (95% CI 0.40 to 0.87), respectively (p for trend 0.009). Exclusion of subjects taking drugs known to influence QT did not influence this association. CONCLUSIONS Higher intake of dietary linolenic acid might be associated with a reduced risk of abnormally prolonged repolarization in men and women
Advances in standardization of laboratory measurement procedures: implications for measuring biomarkers of folate and vitamin B-12 status in NHANES1234
Population studies such as NHANES analyze large numbers of laboratory measurements and are often performed in different laboratories using different measurement procedures and over an extended period of time. Correct clinical and epidemiologic interpretations of the results depend on the accuracy of those measurements. Unfortunately, considerable variability has been observed among assays for folate, vitamin B-12, and related biomarkers. In the past few decades, the science of metrology has advanced considerably, with the development of improved primary reference measurement procedures and high-level reference materials, which can serve as the basis for accurate measurement. A rigorous approach has been established for making field methods traceable to the highest-level reference measurement procedures and reference materials. This article reviews some basic principles of metrology and describes their recent application to measurements of folate and vitamin B-12
Early progressive renal decline precedes the onset of microalbuminuria and its progression to macroalbuminuria
OBJECTIVE
Progressive decrease in the glomerular filtration rate (GFR), or renal decline, in
type 1 diabetes (T1D) is observed in patients with macroalbuminuria. However,
it is unknown whether this decline begins during microalbuminuria (MA) or
normoalbuminuria (NA).
RESEARCH DESIGN AND METHODS
The study group (second Joslin Kidney Study) comprises patients with T1D and NA
(n = 286) or MA (n = 248) who were followed for 4-10 years (median 8 years). Serial
measurements (median 6, range 3â16) of serum creatinine and cystatin C were
used jointly to estimate GFR (eGFRcr-cys) and assess its trajectories during
follow-up.
RESULTS
Renal decline (progressive eGFRcr-cys loss of at least 3.3% per year) occurred in
10% of the NA and 35% of the MA (P , 0.001). In both groups, the strongest
determinants of renal decline were baseline serum concentrations of uric acid
(P , 0.001) and tumor necrosis factor receptor 1 or 2 (TNFR-1 or -2, P , 0.001).
Other significant risk factors included baseline HbA1c, age/diabetes duration, and
systolic blood pressure. Relative impacts of these determinants were similar in NA
and MA. Renal decline was not associated with sex or baseline serum concentration of TNF-a, IL-6, IL-8, IP-10, MCP-1, VCAM, ICAM, Fas, or FasL.
CONCLUSIONS
Renal decline in T1D begins during NA and it is determined by multiple factors,
similar to MA. Thus, this early decline is the primary disease process leading to
impaired renal function in T1D. Changes in albumin excretion rate, such as the
onset of MA or its progression to macroalbuminuria, are either caused by or develop in parallel to the early renal declin
Pharmacogenetic Association of NOS3 Variants with Cardiovascular Disease in Patients with Hypertension: The GenHAT Study
Nitric oxide synthase 3 (NOS3) catalyzes production of NO in the endothelium and may play a role in cardiovascular disease (CVD). We assessed the pharmacogenetic associations of three NOS3 polymorphisms and three antihypertensive drugs with CVD outcomes. Hypertensive subjects (nâ=â30,280) from a multi-center, double-blind clinical trial were randomized to chlorthalidone, amlodipine, or lisinopril treatment (mean follow up, 4.9 years). Outcomes included coronary heart disease (CHD: fatal CHD and nonfatal myocardial infarction); stroke; heart failure (fatal, requiring hospitalization, or outpatient treatment); all-cause mortality; and end-stage renal disease (ESRD). Main effects of NOS3 variants on outcome and genotype-treatment interactions were tested. For NOS3 â690 C>T (rs3918226), a higher hazard ratio (HR) was found in minor allele carriers for CHD (CCâ=â1.00, CT+TTâ=â1.12 (95% confidence interval (CI)â=â1.00â1.26), Pâ=â0.048). For NOS3 â922 A>G (rs1800779), a higher HR was found in minor allele carriers for heart failure (AAâ=â1.00, AG+GGâ=â1.10 (CIâ=â1.00â1.21), Pâ=â0.046). Significant pharmacogenetic findings were observed for stroke and all-cause mortality. For â690 C>T, a lower HR was observed for stroke in minor allele carriers when treated with amlodipine versus lisinopril (CCâ=â0.85 (CIâ=â0.73â0.99), CT+TTâ=â0.49 (CIâ=â0.31â0.80), Pâ=â0.04). For glu298asp G>T (rs1799983), a lower HR was observed for all-cause mortality in minor allele carriers when treated with amlodipine versus lisinopril (GGâ=â1.01 (CIâ=â0.91â1.13), GT+TTâ=â0.85 (CIâ=â0.75â0.97), Pâ=â0.04). We observed significant associations with NOS3 variants and CHD and heart failure and significant pharmacogenetic effects for stroke and all cause mortality. This suggests that NOS3 variants may potentially provide useful clinical information with respect to treatment decisions in the future
Iterative Outlier Removal: A Method for Identifying Outliers in Laboratory Recalibration Studies
Extreme values that arise for any reason, including through non-laboratory measurement procedure-related processes (inadequate mixing, evaporation, mislabeling), lead to outliers and inflate errors in recalibration studies. We present an approach termed iterative outlier removal (IOR) for identifying such outliers
Lessons from morpholino-based screening in zebrafish
Morpholino oligonucleotides (MOs) are an effective, gene-specific antisense knockdown technology used in many model systems. Here we describe the application of MOs in zebrafish (Danio rerio) for in vivo functional characterization of gene activity. We summarize our screening experience beginning with gene target selection. We then discuss screening parameter considerations and data and database management. Finally, we emphasize the importance of off-target effect management and thorough downstream phenotypic validation. We discuss current morpholino limitations, including reduced stability when stored in aqueous solution. Advances in MO technology now provide a measure of spatiotemporal control over MO activity, presenting the opportunity for incorporating more finely tuned analyses into MO-based screening. Therefore, with careful management, MOs remain a valuable tool for discovery screening as well as individual gene knockdown analysis
Serum concentration of cystatin C and risk of end-stage renal disease in diabetes
OBJECTIVEdPatients with diabetes have a high risk of end-stage renal disease (ESRD). We
examined whether prediction of this outcome, according to chronic kidney disease (CKD) staging by creatinine-based estimates of the glomerular filtration rate (eGFRcreat), is improved by
further staging with serum cystatin Câbased estimates (eGFRcyst).
RESEARCH DESIGN AND METHODSdPatients with diabetes in CKD stages 1â3 were
selected from three cohorts: two from Joslin Diabetes Center, one with type 1 diabetes (N = 364)
and one with type 2 diabetes (N = 402), and the third from the Finnish Diabetic Nephropathy
(FinnDiane) Study of type 1 (N = 399). Baseline serum concentrations of creatinine and cystatin C
were measured in all patients. Follow-up averaged 8â10 years and onsets of ESRD (n = 246) and
death unrelated to ESRD (n = 159) were ascertained.
RESULTSdAlthough CKD staging by eGFRcyst was concordant with that by eGFRcreat for
62% of Joslin patients and 73% of FinnDiane patients, those given a higher stage by eGFRcyst
than eGFRcreat had a significantly higher risk of ESRD than those with concordant staging in all
three cohorts (hazard ratio 2.3 [95% CI 1.8â3.1]). Similarly, patients at a lower stage by eGFRcyst
than by eGFRcreat had a lower risk than those with concordant staging (0.30 [0.13â0.68]).
Deaths unrelated to ESRD followed the same pattern, but differences were not as large.
CONCLUSIONSdIn patients with diabetes, CKD staging based on eGFRcyst significantly
improves ESRD risk stratification based on eGFRcreat. This conclusion can be generalized to
patients with type 1 and type 2 diabetes and to diabetic patients in the U.S. and Finland
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