Risk based Fatigue Inspection Planning – State of the Art

AbstractThe present paper presents the methodology and the practical calculations for risk based inspection planning of fatigue cracks in welded offshore steel structures. Due to the uncertainty in the variables involved in the problem the planning has to be carried out by stochastic modeling and risk based assessments. Scatter in potential crack growth has to be analyzed by applied probabilistic facture mechanics and the uncertainty in the performance of the actual inspection technique has to be determined. With given risk acceptance criteria the practical outcome of the analyses is recommended inspection techniques and associated planned inspection time intervals. The classical theory is briefly outlined and the latest recommendations from a Joint Industry Project recently completed in Norway are included. A practical case study for life extension of an oil loading system in the North Sea is presented

Probabilistic models for the fatigue resistance of welded steel joints subjected to constant amplitude loading

S-N curves found in various rules and regulations are the basic tool for the practicing engineer when carrying out life predictions for welded details in dynamically loaded structures. The present work is investigating the expected fatigue life and associated scatter for welded steel joints subjected to Constant Amplitude (CA) loading. The objective is to obtain more reliable life predictions based on advancements in the probabilistic model fitted to collected life data. A Random Fatigue Limit Model (RFLM) is proposed to obtain fatigue resistance curves at given probability levels of survival. As a distinction to more conventional statistical methods, the model is treating both the fatigue life and the fatigue limit as random variables. The focus is on high cycle fatigue and long-life data and runouts are included in a rational and logical manner by using a maximum likelihood method. Life data for a transverse fillet welded attachment originally designated as a category 71 detail in Eurocode 3 Part 1-9 are collected and analysed. The plate thickness of the specimens ranges from 20 mm to 32 mm and the steel quality is mild and medium strength Carbon-Manganese steel. The results are compared with the results obtained by conventional S-N curves. The compatibility between the fitted probabilistic models and the underlying fatigue damage mechanisms is emphasized.publishedVersio

Crack growth models for multiaxial fatigue in a ship's propeller shaft

Abstract A premature fatigue failure of a large intermediate propeller shaft in a shuttle tanker is discussed and analyzed. The short fatigue life consists mainly of a crack growth phase. Life predictions are carried out by crack growth modelling based on engineering fracture mechanics. The purpose of the present investigation is to identify the most likely loading modes based on the evolution of the crack propagation. A Linear Elastic Fracture Mechanics Model (LEFM) is applied with the stress intensity factor range entering the Paris law as a key parameter. Existing formulas for the geometry functions are supplemented by more detailed stress intensity factor calculations pertaining to small semi-elliptical surface cracks subjected to stress mode I. Enhanced geometry functions are proposed as a function of the relative crack depth and the crack shape aspect ratio. The ability of the fracture mechanics model to reconstruct the observed crack path and crack shape development is emphasized. Various loading modes and multi-axial stress states are applied to pursue the observed crack behavior. The observed semi-elliptical crack shapes and the shift in crack planes are included in the analysis

Radiotherapy for marginally resected, unresectable or recurrent giant cell tumor of the bone: a rare cancer network study

The role of radiotherapy for local control of marginally resected, unresectable, and recurrent giant cell tumors of bone (GCToB) has not been well defined. The number of patients affected by this rare disease is low. We present a series of 58 patients with biopsy proven GCToB who were treated with radiation therapy. A retrospective review of the role of radiotherapy in the treatment of GCToB was conducted in participating institutions of the Rare Cancer Network. Eligibility criteria consisted of the use of radiotherapy for marginally resected, unresectable, and recurrent GCToB. Fifty-eight patients with biopsy proven GCToB were analyzed from 9 participating North American and European institutions. Forty-five patients had a primary tumor and 13 patients had a recurrent tumor. Median radiation dose was 50 Gy in a median of 25 fractions. Indication for radiation therapy was marginal resection in 33 patients, unresectable tumor in 13 patients, recurrence in 9 patients and palliation in 2 patients. Median tumor size was 7.0 cm. A significant proportion of the tumors involved critical structures. Median follow-up was 8.0 years. Five year local control was 85% . Of the 7 local failures, 3 were treated successfully with salvage surgery. All patients who received palliation achieved symptom relief. Five year overall survival was 94%. None of the patients experienced grade 3 or higher acute toxicity. This study reports a large published experience in the treatment of GCToB with radiotherapy. Radiotherapy can provide excellent local control for incompletely resected, unresectable or recurrent GCToB with acceptable morbidity

Elite Suppressor–Derived HIV-1 Envelope Glycoproteins Exhibit Reduced Entry Efficiency and Kinetics

Elite suppressors (ES) are a rare subset of HIV-1–infected individuals who are able to maintain HIV-1 viral loads below the limit of detection by ultra-sensitive clinical assays in the absence of antiretroviral therapy. Mechanism(s) responsible for this elite control are poorly understood but likely involve both host and viral factors. This study assesses ES plasma-derived envelope glycoprotein (env) fitness as a function of entry efficiency as a possible contributor to viral suppression. Fitness of virus entry was first evaluated using a novel inducible cell line with controlled surface expression levels of CD4 (receptor) and CCR5 (co-receptor). In the context of physiologic CCR5 and CD4 surface densities, ES envs exhibited significantly decreased entry efficiency relative to chronically infected viremic progressors. ES envs also demonstrated slow entry kinetics indicating the presence of virus with reduced entry fitness. Overall, ES env clones were less efficient at mediating entry than chronic progressor envs. Interestingly, acute infection envs exhibited an intermediate phenotypic pattern not distinctly different from ES or chronic progressor envs. These results imply that lower env fitness may be established early and may directly contribute to viral suppression in ES individuals

Effect of remote ischaemic conditioning on clinical outcomes in patients with acute myocardial infarction (CONDI-2/ERIC-PPCI): a single-blind randomised controlled trial.

BACKGROUND: Remote ischaemic conditioning with transient ischaemia and reperfusion applied to the arm has been shown to reduce myocardial infarct size in patients with ST-elevation myocardial infarction (STEMI) undergoing primary percutaneous coronary intervention (PPCI). We investigated whether remote ischaemic conditioning could reduce the incidence of cardiac death and hospitalisation for heart failure at 12 months. METHODS: We did an international investigator-initiated, prospective, single-blind, randomised controlled trial (CONDI-2/ERIC-PPCI) at 33 centres across the UK, Denmark, Spain, and Serbia. Patients (age >18 years) with suspected STEMI and who were eligible for PPCI were randomly allocated (1:1, stratified by centre with a permuted block method) to receive standard treatment (including a sham simulated remote ischaemic conditioning intervention at UK sites only) or remote ischaemic conditioning treatment (intermittent ischaemia and reperfusion applied to the arm through four cycles of 5-min inflation and 5-min deflation of an automated cuff device) before PPCI. Investigators responsible for data collection and outcome assessment were masked to treatment allocation. The primary combined endpoint was cardiac death or hospitalisation for heart failure at 12 months in the intention-to-treat population. This trial is registered with ClinicalTrials.gov (NCT02342522) and is completed. FINDINGS: Between Nov 6, 2013, and March 31, 2018, 5401 patients were randomly allocated to either the control group (n=2701) or the remote ischaemic conditioning group (n=2700). After exclusion of patients upon hospital arrival or loss to follow-up, 2569 patients in the control group and 2546 in the intervention group were included in the intention-to-treat analysis. At 12 months post-PPCI, the Kaplan-Meier-estimated frequencies of cardiac death or hospitalisation for heart failure (the primary endpoint) were 220 (8·6%) patients in the control group and 239 (9·4%) in the remote ischaemic conditioning group (hazard ratio 1·10 [95% CI 0·91-1·32], p=0·32 for intervention versus control). No important unexpected adverse events or side effects of remote ischaemic conditioning were observed. INTERPRETATION: Remote ischaemic conditioning does not improve clinical outcomes (cardiac death or hospitalisation for heart failure) at 12 months in patients with STEMI undergoing PPCI. FUNDING: British Heart Foundation, University College London Hospitals/University College London Biomedical Research Centre, Danish Innovation Foundation, Novo Nordisk Foundation, TrygFonden

"Det er relasjoner det går på" : hvilke strategier velger rektor for å forebygge mobbing?

I denne masteroppgaven undersøker jeg mulige strategier rektor kan velge når skolen skal utforme en beredskap mot mobbing. Tittelen, det er relasjoner det går på, har jeg hentet fra intervjuet med Kaja, en av rektorene som har deltatt i undersøkelsen. Dette med relasjoner ble etter hvert et veldig sentralt begrep når jeg arbeidet med datamaterialet mitt. Informantene er på ulikt vis opptatt av relasjoner mellom elevene, mellom lærerne og elevene, mellom rektor og lærerne og mellom rektor og elevene. Det å bygge opp gode relasjoner kan være en viktig del av skolens beredskap mot mobbing. Et annet sentralt begrep er skolekulturen. Er det sånn at enkelte skolekulturer virker slik at det blir grobunn for mobbing? På den annen side, kan en skolekultur virke forebyggende mot at det skjer mobbing? Mange hevder at skolekulturen legger sterke premisser for skolens muligheter til å utvikle seg. Er det kulturen som styrer eller kan kulturen styres? Dette er et sentralt spørsmål som blir drøftet i denne oppgaven. Jeg har valgt å bruke kvalitativ metode og har foretatt halvstrukturerte intervjuer av henholdsvis rektor og en gruppe lærere på to utvalgte ungdomsskoler. Rektors rolle i skolens arbeid mot mobbing er sentral i denne oppgaven. Jeg har tatt på ”skolelederbriller” og fokusert på ulike valg rektor kan ta. Med utgangspunkt i det innsamlede datamateriale har jeg prøvd å ha flere ulike perspektiver når jeg har drøftet empirien i forhold til aktuell teori både om ledelse generelt, skoleledelse, problematferd og mobbing spesielt. På bakgrunn av datamaterialet mitt har jeg valgt ut aktuell teori fra ledelsesfeltet, fra organisasjonsteori og fra skoleledelse spesielt. Følgende tema er sentrale; begrepet ledelse, ledelse i et distribuert perspektiv, ulike styringsdiskurser, ansvarsplikt, demokratisk ledelse, skolekultur, legalitet og legitimitet. Jeg har også valgt ut teori om mobbing og problematferd som omhandler ulike perspektiver på begrepet mobbing, nyere viten om implementering av ulike mobbeprogram og teori om problematferd i et systemperspektiv. Tidlig i arbeidet så jeg at det kan være to ulike hovedstrategier å velge når rektor skal initiere en god beredskap mot mobbing på skolen. Jeg har kalt disse, mobbing i et smalspektret perspektiv og mobbing i et bredspektret perspektiv. Et smalspektret perspektiv analyserer mobbing som et individuelt fenomen der man er mest opptatt av mobber og mobbeoffer og har lite fokus på konteksten mobbingen skjer i. I dette perspektivet velger ofte ledelsen et individualistisk- eller et systemperspektiv på ledelse (Møller og Fuglestad 2006:kap.14), der man er mest opptatt av personlige egenskaper eller systemrettede tiltak på skolen. I dette perspektivet blir kulturbegrepet ofte oppfattet som noe statisk som legger premisser for hvordan mennesker samhandler. Det kan også se ut som om effekten av smalspektrede mobbetiltak kan være av kortere varighet. I dette perspektivet er det ofte problematisk å påvise betydningen av rektors rolle. Et bredspektret perspektiv på mobbing analyserer skolens læringsmiljø som en helhet og en ser på problematferd i et systemteoretisk perspektiv (Nordahl et. al:2005). Det er viktig å analysere konteksten mobbingen skjer i. Teorifeltet innebefatter både litteratur om problematferd, pedagogikk og skoleledelse. I dette perspektivet kan det være nødvendig at ledelsen velger et relasjonelt eller et distribuert perspektiv på ledelse (Møller og Fuglestad 2006:kap.14), der rektor er opptatt av å bygge opp gode relasjoner mellom alle ledd på skolen og å myndiggjøre lærere og elever. Kulturbegrepet blir oppfattet som noe som både legger premisser for skolen men også kan utvikles og styres i ønsket retning. Det kan se ut som om effekten av bredspektrede mobbetiltak er mer varige enn de mer smalspektrede tiltakene. Betydningen av ledelsens rolle kan være lettere å påvise. Hva bør rektor velge når skolen skal utforme en beredskap mot mobbing? Mitt datamateriale viser at dilemmaet ikke er enten eller, men ja takk begge deler! Det kan se ut som om det kan være hensiktsmessig at rektor utvikler strategier i arbeidet mot mobbing som er basert på både et smalspektret og et bredspektret perspektiv. Det langsiktige arbeidet med å forebygge at mobbing skjer, kan med fordel skje i et bredspektret perspektiv. Det å jobbe med å utvikle skolekulturen samtidig som man har et opplegg for å lære elevene sosial kompetanse ser ut til å gi god effekt. På den annen side, akutte mobbesaker som oppstår på skolen bør høyst sannsynlig møtes med konkrete og håndfaste tiltak som er egnet til å sette en stopper for mobbingen der og da. Her kan det være en fordel med et smalspektret perspektiv, der en fokuserer på mobbingen og de personene som er involvert. Oppgaven viser likevel at for å oppnå varige forbedringer av læringsmiljøet og reduksjon i forekomst av mobbing over tid, kan det være en hensiktsmessig strategi for rektor å legge hovedvekten av arbeidet på et bredspektret perspektivet. Geithus 30.04.06. Tom Lassen Havnsun