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CAI combustion and the factors affecting it were intensively investigated in a single cylinder, air-assisted gasoline direct injection engine. CAI was achieved by means of residual gas trapping by utilising low-lift short duration camshafts and early closing of the exhaust valves. The effects of EVC (Exhaust Valve Closure) and IVO (Inlet Valve opening) timings, spark timing, single and split injection timings, coolant temperature, compression ratio, cam lift and duration on exhaust emissions and CAI operation were investigated experimentally. Engine speed throughout the course of the experiments, was varied from 1200rpm to 2400rpm and the air/fuel ratio was altered from stoichiometric to the misfire limit. The results show that the EVC timing, compression ratio, cam lift and duration had significant influences on CAI combustion and emissions. Early EVC when combined with higher compression ratio and higher cam lift, enhance CAI combustion operation and stability. IVO timing had minor effect on CAI combustion while spark timing hardly affects CAI operation as soon as fully-developed CAI conditions were established. Coolant temperature was revealed to have substantial impact on CAI combustion when the coolant temperature was below 65C. The results also show the importance of injection timing. Early injection gave faster and more stable combustion, less HC and CO emissions, but more prone to knocking combustion and higher NOx emissions. Furthermore, CAI operation range could considerably be extended with injection during the recompression process. Late injection led to slower and unstable combustion, higher HC and CO emissions but lower combustion noise and NOx emissions. Split injection gave even further extension of CAI range in both stoichiometric and lean mixture operations. All the above clearly suggest, that optimising injection timing and using split injection is an effective way to control and extend CAI operation in a direct injection gasoline engine.

Background Preterm birth is a leading cause of perinatal morbidity and mortality worldwide, resulting in a pressing need to identify risk factors leading to effective interventions. Limited evidence suggests potential relationships between maternal sleep or vital exhaustion and preterm birth, yet the literature is generally inconclusive. Methods We examined the relationship between maternal sleep duration and vital exhaustion in the first six months of pregnancy and spontaneous (non-medically indicated) preterm birth among 479 Peruvian women who delivered a preterm singleton infant (<37 weeks gestation) and 480 term controls who delivered a singleton infant at term (≥37 weeks gestation). Maternal nightly sleep and reports of vital exhaustion were ascertained through in-person interviews. Spontaneous preterm birth cases were further categorized as those following either spontaneous preterm labor or preterm premature rupture of membranes. In addition, cases were categorized as very (<32 weeks), moderate (32–33 weeks), and late (34- <37 weeks) preterm birth for additional analyses. Logistic regression was used to estimate adjusted odds ratios (aORs) and 95% confidence intervals (CIs). Results After adjusting for confounders, we found that short sleep duration (≤6 hours) was significantly associated with preterm birth (aOR = 1.56; 95% CI 1.11-2.19) compared to 7–8 hours of sleep. Vital exhaustion was also associated with increased odds of preterm birth (aOR = 2.41; 95% CI 1.79-3.23) compared to no exhaustion (Ptrend <0.001). These associations remained significant for spontaneous preterm labor and preterm premature rupture of membranes. We also found evidence of joint effects of sleep duration and vital exhaustion on the odds of spontaneous preterm birth. Conclusions The results of this case–control study suggest maternal sleep duration, particularly short sleep duration, and vital exhaustion may be risk factors for spontaneous preterm birth. These findings call for increased clinical attention to maternal sleep and the study of potential intervention strategies to improve sleep in early pregnancy with the aim of decreasing risk of preterm birth.

Master of Science / Department of Agronomy / J.A. Dille / The availability of ALS-inhibitor herbicide-resistant grain sorghum hybrids will provide an opportunity to control grass weeds post-emergence with the ALS-inhibiting herbicide nicosulfuron (Zest[superscript]TM). More information on impact of grass weeds on sorghum yield are needed to optimize the application of nicosulfuron. The research objectives were to evaluate the impact of time of grass weed removal on grain sorghum yield when grown in different crop row spacing and seeding rates and to determine the critical duration of grass weed competition. Field studies were conducted in 2014 and 2015 at the KSU Agricultural Research Center at Hays, KS and the KSU Department of Agronomy Research Farm near Manhattan, KS. Four main treatments were grain sorghum row spacing of 25 and 76 cm at Hays or 20 and 76 cm at Manhattan, and two seeding rates of 125,000 and 150,000 seed ha⁻¹. Within each main plot, seven treatments were established including: weed-free all season using pre-emergence herbicides, weed-free all season by hand, weedy for 2, 3, 4, and 5 weeks after crop emergence in 2014 or weedy for 2, 4, 6, and 8 weeks after crop emergence in 2015, and weedy all season. The main grass weeds were giant, green, and yellow foxtail species, large crabgrass, and barnyardgrass. Grass weed biomass increased through the season at both locations in 2014 and in Manhattan in 2015. Hays 2014 grain sorghum aboveground stem and leaf biomass across row spacing and seeding rates decreased as weed removal time was delayed through the growing season. Grain sorghum yield decreased with increasing duration of grass weed competition in both years in Manhattan and in 2014 at Hays. Yield loss reached 5% at 2.3 to 25 weeks after sorghum emergence in narrow row spacing and 3.3 to 6.3 weeks after sorghum emergence in wide row spacing, depending on location, demonstrating that removing grass weed competition during these time frames will prevent more than 5% loss in grain sorghum yields.

Introduction and Background: Central venous catheters (CVCs) are extensively used worldwide. Mechanical, infectious and thrombotic complications are well described with their use and may be associated with prolonged hospitalisation, increased medical costs and mortality. CVCs account for an estimated 90% of all catheter-related bloodstream infections (CRBSI) and a host of risk factors for CVC-related infections have been documented. These include, most importantly, the duration of catheterisation. The duration of use of CVCs remains controversial and the length of time such devices can safely be left in place has not been fully and objectively addressed in the critically ill patient. Over the past few years, antimicrobial impregnated catheters have been introduced in an attempt to limit catheter-related infection (CRI) and increase the time that CVCs can safely be left in situ. Recent meta-analyses concluded that antimicrobial-impregnated CVCs appear to be effective in reducing CRI. Materials and Methods: This was a prospective randomised double-blind study performed in the adult multidisciplinary Intensive Care Unit (ICU) at Charlotte Maxeke Johannesburg Academic Hospital (CMJAH) over a four year period. The study entailed a comparison of standard triple-lumen versus antimicrobial impregnated CVCs on the rate of CRI. The aim was to determine whether the duration of catheter insertion time could safely be increased from the standard practice of seven days at the CMJAH adult multidisciplinary ICU to 14 days, to assess the influence of the antimicrobial impregnated catheter on the incidence of CRI, and to elucidate the epidemiology and risks of CRI. Results: One hundred and eighteen critically ill patients were included in the study which spanned 34 951.5 catheter hours (3.99 catheter years). Sixty-two patients received a standard triple-lumen catheter and 56, a chlorhexidine-silver sulfadiazine (CSS) impregnated triple-lumen catheter. The mean duration of placement for the full sample of 118 CVCs was 12.3 days (range, 1-14). No statistically significant difference in CRI rates between the two types of catheters could be demonstrated. The most common source of primary CRBSI was skin, followed by hub and infusate. The site of CVC insertion (internal jugular versus subclavian vein) and the use of parenteral nutrition were not noted to be risk factors for catheter infection. There was no clinical evidence of catheter-related thrombosis in either of the study groups. Conclusion: This study was unable to demonstrate that antimicrobial catheters provided any significant benefit over standard catheters, which it is felt, can safely be left in place for up to 14 days with appropriate infection control measures. The most common source of CRI was the skin. The administration of parenteral nutrition and the site of catheter insertion (internal jugular vein versus subclavian vein) were not noted to be risk factors for CRI. There was no clinical evidence of thrombotic complications in either of the study groups. This study offers direction for the use of CVCs in critically ill patients and addresses many of the controversies that exist.

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Finding an explanation for the rise and persistence of European unemployment has been one of the main research programmes of labour economists during the last decade. In this doctoral thesis, we contribute to this literature by questioning the causes of unemployment persistence in Belgium. To that purpose, we conduct an in-depth econometric analysis of the flows out of unemployment in this country. In Chapters 2 and 3, we study the behaviour of the exit rate out of unemployment over duration and calendar time. In Chapter 3, we investigate whether this behaviour differs according to the place of living and the skill level, as measured by the level of education. Finally, in Chapter 4, we determine to what extent the divergences in the rate of flowing from unemployment between workers with different levels of education can be explained by a skill mismatch phenomenon and/or by a job competition story. By refining the causes of unemployment persistence in Belgium, our doctoral research also contributes to the design of more effective labour market policies.

Youth unemployment has been a persistent problem in the European Union for many years and the affected countries spend a substantial part of their budget on active labour market policies, with the aim to integrate young unemployed workers into the labour market. Employment subsidy programmes are one type of active labour market policies that have been implemented. Although important amounts of money have been spent for these programmes, little is known about the effects of participation in subsidised employment on the labour market transitions. This thesis incorporates several studies that aim to estimate the effect of a subsidised employment programme. The programme provides a reduction of the social insurance contribution for employers that hire eligible workers. All three studies provide estimates for the participation of long term unemployed school leavers. In order to evaluate whether programme participation is useful for their integration into the labour market, the effect on different duration outcomes has been investigated. A major difficulty in causal analysis with non-experimental data is that the characteristics of the group of participants may by systematically different from those of the group of non-participants. Estimates may therefore reflect both the effect of participation as well as the particular selection of participants. To control for this selection bias, multivariate mixed proportional hazard models have been applied and a large number of control variables have been incorporated. The results of this thesis show that participation in the employment subsidy programme accelerates the transitions into regular, non-subsidised employment. Moreover, the employment duration is increased, compared to a regular employment spell. Finally, the estimates show that the effect of a former participation on the duration of a subsequent unemployment spell is similar to the effect of a former regular employment spell.

Finding an explanation for the rise and persistence of European unemployment has been one of the main research programmes of labour economists during the last decade. In this doctoral thesis, we contribute to this literature by questioning the causes of unemployment persistence in Belgium. To that purpose, we conduct an in-depth econometric analysis of the flows out of unemployment in this country. In Chapters 2 and 3, we study the behaviour of the exit rate out of unemployment over duration and calendar time. In Chapter 3, we investigate whether this behaviour differs according to the place of living and the skill level, as measured by the level of education. Finally, in Chapter 4, we determine to what extent the divergences in the rate of flowing from unemployment between workers with different levels of education can be explained by a skill mismatch phenomenon and/or by a job competition story. By refining the causes of unemployment persistence in Belgium, our doctoral research also contributes to the design of more effective labour market policies.

This paper is analyzing the unemployment duration difference of individuals under different high school programs in Sweden. The cause of the analysis has from stemmed from different fields of study and its effect on employment positions in the labour market. We see education as a factor of key importance. In addition to research on an education level, the type of study also plays an important role. Therefore, how different school programs affect unemployment duration becomes the central question we try to answer in this paper. To pursue a clear analysis structure, we start with previous studies on an education level and show the author’s interest into the research of the field of study’s effect on unemployment. Job search theory is applied to do analysis on the data. Then, an empirical analysis of unemployment duration is conducted. This is done through linear regression using the least-squares method. Finally, conclusions are made as well as some policy implications and ideas for further research.