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Models for pattern formation in somitogenesis: a marriage of cellular and molecular biology

Somitogenesis, the process by which a bilaterally symmetric pattern of cell aggregations is laid down in a cranio-caudal sequence in early vertebrate development, provides an excellent model study for the coupling of interactions at the molecular and cellular level. Here, we review some of the key experimental results and theoretical models related to this process. We extend a recent chemical pre-pattern model based on the cell cycle Journal of Theoretical Biology 207 (2000) 305-316, by including cell movement and show that the resultant model exhibits the correct spatio-temporal dynamics of cell aggregation. We also postulate a model to account for the recently observed spatio-temporal dynamics at the molecular level

A mathematical formulation for the cell-cycle model in somitogenesis: analysis, parameter constraints and numerical solutions

In this work we present an analysis, supported by numerical simulations, of the formulation of the cell-cycle model for somitogenesis proposed in Collier et al.(J. Theor. Biol. 207 (2000), 305–316). The analysis indicates that by introducing appropriate parameter constraints on model parameters the cell-cycle mechanism can indeed give rise to the periodic pattern of somites observed in normal embryos. The analysis also provides a greater understanding of the signalling process controlling somite formation and allows us to understand which parameters influence somite length

Experiences of graduating students from a medical programme five years after curricular transformation: A descriptive study

Background. The University of the Witwatersrand introduced a new curriculum in 2003 where students could gain admission to the medicalprogramme at two levels: directly as school leavers or following a degree as graduate entrants at the third year of study. From this point both groups of students continue in a combined class in a single curriculum.Objective. To determine the experiences of the fifth cohort of graduating students from a medical programme following curricular transformation.Method. A quantitative descriptive study was undertaken using a semi-structured questionnaire with both open- and closed-ended questions. There were 201 students in the graduating class, all of whom were invited to complete the questionnaire.Results. A 74% response rate was obtained, of which 66% were school leaver entrants and 34% were graduates. Among the best experiences there were 59 comments relating directly to the programme. The worst experiences included perceptions of the lack of standardisation in clinical exams and feelings of inadequacy in relation to pharmacology and microbiology. Just under three-quarters of the participants felt ‘adequately prepared’ for the clinical years; 82% of the participants stated that they would make changes to the programme.Conclusion. The placement of this evaluation at the conclusion of formal assessments may have contributed to the depth of responses and openness of respondents in the completion of the questionnaire. We highly recommend the value of obtaining data on students’ experiences and opinions of a programme at the point of exit from the programme

The Effect of State Workers' Compensation Program Changes on the Use of Federal Social Security Disability Insurance

In addition to traditional forms of private and public medical insurance, two other large programs help pay for costs associated with ill health. In 2007, Workers Compensation (WC) insurance provided $55.4 billion in medical care and cash benefits to employees who are injured at work or contract a work-related illness, and Social Security Disability Insurance (DI) provided$99 billion to individuals who suffer from permanent disabilities and are unable to engage in substantial gainful activity. During the 1990s, real DI outlays increased nearly 70 percent, whereas real WC cash benefit spending fell by 12 percent. There has been concern that part of this relationship between two of the nation’s largest social insurance programs may be due to individuals substituting towards DI as state WC policies tightened. We test this hypothesis using a number of different WC and DI program parameters. We first show that this negative correlation between the national series does not hold over time within states, the level at which a causal relationship should operate. We then test how regulatory changes in state WC program parameters impact WC outcomes (intended effect) and DI outcomes (unintended effect). We find no compelling evidence of WC tightening causing DI rolls to increase, and conclude it is unlikely that state WC changes were a meaningful factor in explaining the rise in DI.

Job Satisfaction as Related to Safety Performance: A Case for a Manufacturing Firm

Many companies have made significant improvements in safety records, but have eventually reached a plateau. This article examines employee safety performance in regards to their job satisfaction and its implications to managers for improving employees safety performance through job redesign

Job Satisfaction as Related to Safe Performance: A Case for a Manufacturing Firm

Many companies have made significant improvements in safety records, but have eventually reached a plateau. This article examines employee safety performance in regards to their job satisfaction and its implications to managers for improving employees safety performance through job redesign

Pattern formation in the transverse section of a laser with a large Fresnel number

We experimentally investigate pattern formation in a single-wavelength long laser cavity with a large Fresnel number. Near the laser threshold, we observe a single frequency spatially periodic structure corresponding to titled waves theoretically predicted by the Maxwell-Bloch equations. We also show the presence of secondary instabilities at other wavelengths and polarization instabilities at the same wavelength for different parameter values. (S0031-9007(99)08512-9)

Timing and Reconstruction of the Most Recent Common Ancestor of the Subtype C Clade of Human Immunodeficiency Virus Type 1

Human immunodeficiency virus type 1 (HIV-1) subtype C is responsible for more than 55% of HIV-1 infections worldwide. When this subtype first emerged is unknown. We have analyzed all available gag (p17 and p24) and env (C2-V3) subtype C sequences with known sampling dates, which ranged from 1983 to 2000. The majority of these sequences come from the Karonga District in Malawi and include some of the earliest known subtype C sequences. Linear regression analyses of sequence divergence estimates (with four different approaches)were plotted against sample year to estimate the year in which there was zero divergence from the reconstructed ancestral sequence. Here we suggest that the most recent common ancestor of subtype C appeared in the mid- to late 1960s. Sensitivity analyses, by which possible biases due to oversampling from one district were explored, gave very similar estimates