PubMed Health⌕ Search

Biomedical subjects

F Penna

Publications and source records attributed to F Penna.

6 recordsLinked to original sources

Dynamical correlations in Brownian hard rods.

We analyze the time decay of small amplitude density perturbations in systems of highly packed Brownian hard rods, relaxing towards a uniform density distribution. The results of Brownian dynamics simulations and those of the deterministic dynamic density functional (DDF) theory, are contrasted with a new theoretical approach beyond the DDF assumptions. We characterize dynamical correlation modes which, having the lowest relaxation time, determine the late time evolution of the system. The spectrum of possible time decays has a continuous band structure, with pockets of discrete values, near the minima of the DDF results, where the validity of that theory appears to be well established.

Journal Article↗

Colloidal hard-rod fluids near geometrically structured substrates.

Density functional theory is used to study colloidal hard-rod fluids near an individual right-angled wedge or edge as well as near a hard wall, which is periodically patterned with rectangular barriers. The Zwanzig model, in which the orientations of the rods are restricted to three orthogonal orientations but their positions can vary continuously, is analyzed by numerical minimization of the grand potential. Density and orientational order profiles, excess adsorptions, as well as surface and line tensions are determined. The calculations exhibit an enrichment [depletion] of rods lying parallel and close to the corner of the wedge (edge). For the fluid near the geometrically patterned wall, complete wetting of the wall-isotropic liquid interface by a nematic film occurs as a two-stage process in which first the nematic phase fills the space between the barriers until an almost planar isotropic-nematic liquid interface has formed separating the higher-density nematic fluid in the space between the barriers from the lower-density isotropic bulk fluid. In the second stage, a nematic film of diverging film thickness develops upon approaching bulk-isotropic-nematic coexistence.

Journal Article↗

Dynamic density functional study of a driven colloidal particle in polymer solutions.

The dynamic density functional (DDF) theory and standard Brownian dynamics simulations (BDS) are used to study the drifting effects of a colloidal particle in a polymer solution, both for ideal and interacting polymers. The structure of the stationary density distributions and the total induced current are analyzed for different drifting rates. We find good agreement with the BDS, which gives support to the assumptions of the DDF theory. The qualitative aspect of the density distribution are discussed and compared to recent results for driven colloids in one-dimensional channels and to analytical expansions for the ideal solution limit.

Colloids↗

Use of nucleotides in weanling rats with diarrhea induced by a lactose overload: effect on the evolution of diarrhea and weight and on the histopathology of intestine, liver and spleen.

Until recently, dietary sources of nucleotides were thought not to be essential for good nutrition. Certain states with higher metabolic demands may require larger amounts that cannot be provided by endogenous production. The objective of the present study was to determine the action of nucleotides on the recovery from lactose-induced diarrhea in weaned rats. Thirty-six weanling Fisher rats were divided into two groups. Group 1 received a standard diet and group 2 received a diet containing lactose in place of starch. On the 10th day, six animals per group were sacrificed for histopathological evaluation. The remaining animals were divided into two other subgroups, each with 6 animals, receiving a control diet, a control diet with nucleotides (0.05% adenosine monophosphate, 0.05% guanosine monophosphate, 0.05% cytidine monophosphate, 0.05% uridine monophosphate and 0.05% inosine monophosphate), a diet with lactose, and a diet with lactose and nucleotides. On the 32nd day of the experiment all animals were sacrificed. Animals with diarrhea weighed less than animals without diarrhea. The introduction of nucleotides did not lead to weight gain. Mean diet consumption was lower in the group that continued to ingest lactose, with the group receiving lactose plus nucleotides showing a lower mean consumption. Animals receiving lactose had inflammatory reaction and deposits of periodic acid-Schiff-positive material in intestinal, hepatic and splenic tissues. The introduction of nucleotides led to an improvement of the intestinal inflammatory reaction. In lactose-induced diarrhea, when the stimulus is maintained--lactose overload--the nucleotides have a limited action on the weight gain and on recovery of intestinal morphology, although they have a protective effect on hepatic injury and improve the inflammatory response.

Analysis of Variance↗

Growth-inhibitory activities of benzofuran and chromene derivatives toward Tenebrio molitor.

Growth-inhibitory activities of selected natural benzofurans (4-9), trans-cinnamic acid derivatives (10-13), chromene compounds (14 and 16), and some semisynthetic derivatives were determined in last instar larvae of Tenebrio molitor via topical administration in Me2CO. The most inhibitory of the tested compounds were 3-gamma, gamma-dimethylallyl-p-coumaric acid (10) and the benzofuran derivative 12-(p-cumaroyloxy)-tremetone (5), the former compound acting on the pupae and the latter on the last instar larvae. Several developmental deficiencies were observed, and some structure-activity relationships are discussed.

Animals↗

Hours of work, and perceptions of fatigue among truck drivers.

Drivers and companies operating in the heavy road transport industry were surveyed about drivers' hours of work and perceptions of the causes and magnitude of fatigue as an industry problem. These drivers were operating in a state which, at the time of the survey, did not restrict driving hours for heavy haulage drivers. On the day of the interview, estimates based on retrospective and prospective reports, suggest that in a 24 hour period about 38% of drivers exceed 14 hours of driving, and 51% exceed 14 hours of driving plus other non-driving work. About 12% of drivers reported less than 4 hours of sleep on one or more working days in the week preceding the interview. These drivers are likely to be operating their vehicles while having a significant sleep debt. About 20% of drivers reported less than 6 hours sleep before starting their current journey, but nearly 40% of dangerous events that occurred on the journey were reported by these drivers (p < 0.05). Many drivers and company representatives reported fatigue to be a problem for other drivers, but considered themselves or their companies' drivers to be relatively unaffected by fatigue. There were differences between drivers' and companies' perceptions about causes of fatigue, and strategies that should be used to manage it. The results obtained from these drivers in an unregulated state were compared with earlier findings from drivers in states where driving hours restrictions are in place.

Accidents, Occupational↗