Geometry and Dynamics with Time-Dependent Constraints

We describe how geometrical methods can be applied to a system with explicitly time-dependent second-class constraints so as to cast it in Hamiltonian form on its physical phase space. Examples of particular interest are systems which require time-dependent gauge fixing conditions in order to reduce them to their physical degrees of freedom. To illustrate our results we discuss the gauge-fixing of relativistic particles and strings moving in arbitrary background electromagnetic and antisymmetric tensor fields.Comment: 8 pages, Plain TeX, CERN-TH.7392/94 and MPI-PhT/94-4

Thermal Modification of Color in Red Alder Veneer. I. Effects of Temperature, Heating Time, and Wood Type

Red alder has become one of the most widely traded hardwood species in North America, and sliced red alder veneer is commonly applied as a decorative overlay on composite wood panels used by the furniture and cabinet industries. Red alder wood, however, acquires a mottled orange color following felling, which is undesirable when the wood is used for decorative purposes. Heating red alder wood remedies this problem to some extent, but there is still an unacceptable level of variability in the color of veneer sliced from heated veneer cants. This study examined the variation in color of red alder wood samples cut sequentially from the pith to the bark and subjected to heating under isothermal conditions. The aim was to examine whether within-tree variation in the susceptibility of red alder wood to thermal darkening can explain variation in color of veneer sliced from steamed red alder cants, and to determine the optimal thermal treatment (temperature and time) that can impart the tan color to red alder wood that industry is seeking. Results indicated that there was within-tree variation in the color of red alder samples following thermal treatment, but differences were pronounced only when wood was heated at a low temperature. Wood close to the bark tended to be redder than wood close to the pith when heated at 30°C, but such a difference was absent in wood heated at higher temperatures (50-90°C). Heating red alder wood, in vitro, at 70°C for 36 h produced wood that was evenly colored from pith to bark and matched the current industry color preference. It is suggested that the color of thermally modified red alder wood depends on the strength of reactions that produce orange/red chromophores in the wood, thermal darkening of the wood, and destruction of orange/red chromophores

Thermal Modification of Color in Red Alder Veneer. Part II. Effects of Season, Log Storage Time, and Location of Wood in Stems

The value of red alder lumber is diminished by discoloration caused by the enzyme-mediated polymerization of the diarylheptanoid xyloside, Oregonin that results in the formation of red-colored chromophores in freshly felled wood. This discoloration can be reduced by pre-steaming wood prior to kiln drying of lumber or veneer slicing, but in practice, there is still variation in the color of heat-treated wood, particularly in veneer sliced from heat-treated cants processed at different times of the year. There is seasonal variation in the concentration of Oregonin that is involved in the discoloration of red alder wood and it is hypothesized here that heat-treated red alder wood will be redder and darker when the wood is obtained from logs harvested during spring when the concentration of Oregonin is known to be higher than in other seasons. The aim of this research was to test this hypothesis, and also examine the effects of log storage time and location of wood in stems on the color of heat-treated red alder wood. The color of red alder wood subjected to an isothermal heat treatment at 70°C was strongly influenced by the season in which parent trees were harvested and the length of time that logs were stored prior to heat treatment of wood. In particular, wood harvested in spring and stored for 2 wk prior to heat treatment was significantly darker than similarly treated wood obtained from logs harvested in other seasons, and redder than wood harvested in summer and winter. If the storage time of logs harvested in spring and summer was extended to 4 wk, however, the heat-treated wood became lighter and less red. Heat-treated wood from the inner part of the logs was redder and darker than heat-treated wood from the outer part of the logs except occasionally, when the outer sapwood was obtained from logs harvested in spring or summer. Careful control of log storage time, heating temperature, and duration of heat treatment could be used to minimize seasonal variation in the color of veneer sliced from heated red alder cants

Inter-rater agreement in the scoring of abstracts submitted to a primary care research conference

BACKGROUND: Checklists for peer review aim to guide referees when assessing the quality of papers, but little evidence exists on the extent to which referees agree when evaluating the same paper. The aim of this study was to investigate agreement on dimensions of a checklist between two referees when evaluating abstracts submitted for a primary care conference. METHODS: Anonymised abstracts were scored using a structured assessment comprising seven categories. Between one (poor) and four (excellent) marks were awarded for each category, giving a maximum possible score of 28 marks. Every abstract was assessed independently by two referees and agreement measured using intraclass correlation coefficients. Mean total scores of abstracts accepted and rejected for the meeting were compared using an unpaired t test. RESULTS: Of 52 abstracts, agreement between reviewers was greater for three components relating to study design (adjusted intraclass correlation coefficients 0.40 to 0.45) compared to four components relating to more subjective elements such as the importance of the study and likelihood of provoking discussion (0.01 to 0.25). Mean score for accepted abstracts was significantly greater than those that were rejected (17.4 versus 14.6, 95% CI for difference 1.3 to 4.1, p = 0.0003). CONCLUSIONS: The findings suggest that inclusion of subjective components in a review checklist may result in greater disagreement between reviewers. However in terms of overall quality scores, abstracts accepted for the meeting were rated significantly higher than those that were rejected

Human Resource Needs and Demand for Post-Secondary Education in the Canadian Secondary Wood Products Industry

Skilled labor shortages in manufacturing industries are being reported in a number of countries. The extent to which such shortages are affecting Canadian wood manufacturing industries is not known. The aim of this study was to survey the skills and educational needs of Canadian wood manufacturing industries, the status, capacity, and challenges that post-secondary education institutes face in meeting industries' human resource needs, and finally the attractiveness of the industry to high school job-seekers. The majority (83%) of wood manufacturing companies in Canada are experiencing problems in hiring skilled tradespeople, and 54.5% of the companies face difficulties in hiring and retaining professionals and supervisory personnel. Skilled staff shortages and competitive pressures were nominated by companies as the two most important factors restricting their growth. The skills needs of companies have changed over the last 10 years, and companies now place a much higher premium on leadership and communication skills from management, and attitude and advanced technical skills from tradespeople. Most companies offered some kind of in-house training to redress skills gaps, but less than half were likely to use the Internet to deliver in-house training. The majority of high school students were not interested in pursuing a career in the wood manufacturing industry because of its association with unsustainable forestry practices and manual labor, and the availability of more attractive career options. Lack of student interest in wood manufacturing is affecting the institutions offering relevant vocational and professional training, and nine of the thirteen institutes suffer from under-enrollment in their wood manufacturing programs. Comprehensive strategies are required to address the labor market imbalances currently affecting Canada's wood manufacturing industries

Single-Bottleneck Approximation for Driven Lattice Gases with Disorder and Open Boundary Conditions

We investigate the effects of disorder on driven lattice gases with open boundaries using the totally asymmetric simple exclusion process as a paradigmatic example. Disorder is realized by randomly distributed defect sites with reduced hopping rate. In contrast to equilibrium, even macroscopic quantities in disordered non-equilibrium systems depend sensitively on the defect sample. We study the current as function of the entry and exit rates and the realization of disorder and find that it is, in leading order, determined by the longest stretch of consecutive defect sites (single-bottleneck approximation, SBA). Using results from extreme value statistics the SBA allows to study ensembles with fixed defect density which gives accurate results, e.g. for the expectation value of the current. Corrections to SBA come from effective interactions of bottlenecks close to the longest one. Defects close to the boundaries can be described by effective boundary rates and lead to shifts of the phase transitions. Finally it is shown that the SBA also works for more complex models. As an example we discuss a model with internal states that has been proposed to describe transport of the kinesin KIF1A.Comment: submitted to J. Stat. Mec