625 research outputs found
The Job Task Model as a Means for Understanding Computer Usage in the Work Place
A qualitative study of a workplace was conducted through the use of interviews and observation of ten participants working in hardware and software engineering. The study arose from a lack of information on computer usage in workplace settings and a lack of identified functional needs for skills-based training.
There were three primary guiding questions and areas of findings in this study: l.Does the job task model define the areas of computer literacy for the individual worker?
The job task model proved to be an effective method for analyzing tasks, tools, and the environment for usage of computer technologies in specialized professions. 2.Does the type of job task influence the functional needs for computer usage in the areas of training, hardware and software usage, application of individual anthropometric data, and workstation design?
The job tasks did not influence how the participants were trained in the use of computers. The primary method of learning to use computer hardware and software was through self-instruction. However, the type of job task did influence the type of hardware and software needed to perform a task. Professional employees needed to know how to use both general and specific types of hardware and software. The job task affected the ergonomic arrangement of work areas, but the participants generally lacked training in how to identify and correct risk factors that may lead to computer-related injury.3.What are the stress factors in this workplace setting? Do the stress factors influence computer-related injury rates in this workplace and if so, how can those types of injuries be reduced?
The stress factors identified in this setting included job demand factors, psychosocial factors, and ergonomic factors. Although these types of stress factors have been associated with computer-related injury through research, none of the participants reported injury associated with computer usage. It was also found that the participants did not consider musculoskeletal disorders to be injuries but rather illnesses.
Implications of the study suggest that the job task model provides a balanced approach to the design of instructional materials. Further, by allowing one category of the job task model to be dominant in the instructional content also appears to weaken the overall instructional validity
Absorption/Expulsion of Oligomers and Linear Macromolecules in a Polymer Brush
The absorption of free linear chains in a polymer brush was studied with
respect to chain size and compatibility with the brush by means of
Monte Carlo (MC) simulations and Density Functional Theory (DFT) /
Self-Consistent Field Theory (SCFT) at both moderate, , and
high, , grafting densities using a bead-spring model.
Different concentrations of the free chains are
examined. Contrary to the case of when all species are almost
completely ejected by the polymer brush irrespective of their length , for
we find that the degree of absorption (absorbed amount)
undergoes a sharp crossover from weak to strong () absorption,
discriminating between oligomers, , and longer chains. For a
moderately dense brush, , the longer species, ,
populate predominantly the deep inner part of the brush whereas in a dense
brush they penetrate into the "fluffy" tail of the dense
brush only. Gyration radius and end-to-end distance of absorbed
chains thereby scale with length as free polymers in the bulk. Using both
MC and DFT/SCFT methods for brushes of different chain length , we demonstrate the existence of unique {\em critical} value of
compatibility . For the energy of free
chains attains the {\em same} value, irrespective of length whereas the
entropy of free chain displays a pronounced minimum. At all density
profiles of absorbing chains with different intersect at the same distance
from the grafting plane. The penetration/expulsion kinetics of free chains into
the polymer brush after an instantaneous change in their compatibility
displays a rather rich behavior. We find three distinct regimes of penetration
kinetics of free chains regarding the length : I (), II (), and III (), in which the time of absorption grows with
at a different rate. During the initial stages of penetration into the
brush one observes a power-law increase of with power
whereby penetration of the free chains into the
brush gets {\em slower} as their concentration rises
Gender as a Moderator of the Relationship Between Preparty Motives and Event-Level Consequences
Prepartying is often associated with increased alcohol consumption and negative alcohol-related consequences among college students. General drinking motives are often only weakly related to preparty alcohol use, and few studies have examined the associations between preparty-specific drinking motives and alcohol-related consequences that occur during or after a preparty event. The current study utilizes event-level data to address this gap in the literature by examining the relationship between four types of preparty motives (prepartying to relax or loosen up, to increase control over alcohol use, to meet a dating partner, and to address concerns that alcohol may not be available later) and alcohol consequences as a function of gender. Participants (N = 952) reported on their most recent preparty event in the past month. After controlling for general drinking motives, all four preparty motives predicted greater event-level consequences for both males and females. Further, prepartying to increase control over alcohol consumed was associated with greater consequences for males as compared to females. The findings are consistent with research suggesting that preparty specific motives may further our understanding of prepartying outcomes over and above the use of general drinking motive measures
The temperature effect on electrokinetic properties of the silica–polyvinyl alcohol (PVA) system
The influence of polyvinyl alcohol (PVA) adsorption on the structure of the diffuse layer of silica (SiO2) in the temperature range 15–35 °C was examined. The microelectrophoresis method was used in the experiments to determine the zeta potential of the solid particles in the absence and presence of the polymer. The adsorption of PVA macromolecules causes the zeta potential decrease in all investigated SiO2 systems. Moreover this, decrease is the most pronounced at the highest examined temperature. Obtained results indicate that the conformational changes of adsorbed polymer chains are responsible for changes in electrokinetic properties of silica particles. Moreover, the structure of diffuse layer on the solid surface with adsorbed polymer results from the following effects: the presence of acetate groups in PVA chains, the blockade of silica surface groups by adsorbed polymer and the shift of slipping plane due to macromolecules adsorption
From Capillary Condensation to Interface Localization Transitions in Colloid Polymer Mixtures Confined in Thin Film Geometry
Monte Carlo simulations of the Asakura-Oosawa (AO) model for colloid-polymer
mixtures confined between two parallel repulsive structureless walls are
presented and analyzed in the light of current theories on capillary
condensation and interface localization transitions. Choosing a polymer to
colloid size ratio of q=0.8 and studying ultrathin films in the range of D=3 to
D=10 colloid diameters thickness, grand canonical Monte Carlo methods are used;
phase transitions are analyzed via finite size scaling, as in previous work on
bulk systems and under confinement between identical types of walls. Unlike the
latter work, inequivalent walls are used here: while the left wall has a
hard-core repulsion for both polymers and colloids, at the right wall an
additional square-well repulsion of variable strength acting only on the
colloids is present. We study how the phase separation into colloid-rich and
colloid-poor phases occurring already in the bulk is modified by such a
confinement. When the asymmetry of the wall-colloid interaction increases, the
character of the transition smoothly changes from capillary condensation-type
to interface localization-type. The critical behavior of these transitions is
discussed, as well as the colloid and polymer density profiles across the film
in the various phases, and the correlation of interfacial fluctuations in the
direction parallel to the confining walls. The experimental observability of
these phenomena also is briefly discussed.Comment: 36 pages, 15 figure
Hard sphere fluids confined between soft repulsive walls: A comparative study using Monte Carlo and density functional methods
Hard-sphere fluids confined between parallel plates a distance apart are
studied for a wide range of packing fractions, including also the onset of
crystallization, applying Monte Carlo simulation techniques and density
functional theory. The walls repel the hard spheres (of diameter ) with
a Weeks-Chandler-Andersen (WCA) potential , with range . We
vary the strength over a wide range and the case of simple hard
walls is also treated for comparison. By the variation of one can
change both the surface excess packing fraction and the wall-fluid
and wall-crystal surface free energies. Several
different methods to extract and from Monte Carlo
(MC) simulations are implemented, and their accuracy and efficiency is
comparatively discussed. The density functional theory (DFT) using Fundamental
Measure functionals is found to be quantitatively accurate over a wide range of
packing fractions; small deviations between DFT and MC near the fluid to
crystal transition need to be studied further. Our results on density profiles
near soft walls could be useful to interpret corresponding experiments with
suitable colloidal dispersions.Comment: 23 pages, 7 ps, eps figure
Adsorption transition of a self-avoiding polymer chain onto a rigid rod
The subject of this work is the adsorption transition of a long flexible
self-avoiding polymer chain onto a rigid thin rod. The rod is represented by a
cylinder of radius R with a short-ranged attractive surface potential for the
chain monomers. General scaling results are obtained by using renormalization
group arguments in conjunction with available results for quantum field
theories with curved boundaries [McAvity and Osborn 1993 Nucl. Phys. B 394,
728]. Relevant critical exponents are identified and estimated using geometric
arguments.Comment: 19 pages, 4 figures. To appear in: J. Phys.: Condens. Matter, special
issue dedicated to Lothar Schaefer on the occasion of his 60th birthda
Free energy of alternating two-component polymer brushes on cylindrical templates
We use computer simulations to investigate the stability of a two-component
polymer brush de-mixing on a curved template into phases of different
morphological properties. It has been previously shown via molecular dynamics
simulations that immiscible chains having different length and anchored to a
cylindrical template will phase separate into striped phases of different
widths oriented perpendicularly to the cylindrical axis. We calculate free
energy differences for a variety of stripe widths, and extract simple
relationships between the sizes of the two polymers, N_1 and N_2, and the free
energy dependence on the stripe width. We explain these relationships using
simple physical arguments based upon previous theoretical work on the free
energy of polymer brushes.Comment: 5 pages, 5 figures, accepted for publication in the Journal of
Chemical Physic
Effects of polymer polydispersity on the phase behaviour of colloid-polymer mixtures
We study the equilibrium behaviour of a mixture of monodisperse hard sphere
colloids and polydisperse non-adsorbing polymers at their -point, using
the Asakura-Oosawa model treated within the free-volume approximation. Our
focus is the experimentally relevant scenario where the distribution of polymer
chain lengths across the system is fixed. Phase diagrams are calculated using
the moment free energy method, and we show that the mean polymer size at which gas-liquid phase separation first occurs decreases with increasing
polymer polydispersity . Correspondingly, at fixed mean polymer size,
polydispersity favours gas-liquid coexistence but delays the onset of
fluid-solid separation. On the other hand, we find that systems with different
but the same {\em mass-averaged} polymer chain length have nearly
polydispersity-independent phase diagrams. We conclude with a comparison to
previous calculations for a semi-grandcanonical scenario, where the polymer
chemical potentials are imposed, which predicted that fluid-solid coexistence
was over gas-liquid in some areas of the phase diagram. Our results show that
this somewhat counter-intuitive result arose because the actual polymer size
distribution in the system is shifted to smaller sizes relative to the polymer
reservoir distribution.Comment: Changes in v2: sketch in Figure 1 corrected, other figures improved;
added references to experimental work and discussion of mapping from polymer
chain length to effective radiu
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