Composite fermions traversing a potential barrier

Using a composite fermion picture, we study the lateral transport between two two-dimensional electron gases, at filling factor 1/2, separated by a potential barrier. In the mean field approximation, composite fermions far from the barrier do not feel a magnetic field while in the barrier region the effective magnetic field is different from zero. This produces a cutoff in the conductance when represented as a function of the thickness and height of the barrier. There is a range of barrier heights for which an incompressible liquid, at $\nu =1/3$, exists in the barrier region.Comment: 3 pages, latex, 4 figures available upon request from [email protected]. To appear in Physical Review B (RC) June 15t

PI-controlled bioreactor as a generalized Lienard system

It is shown that periodic orbits can occur in Cholette's bioreactor model working under the influence of a PI-controller. We find a diffeomorphic coordinate transformation that turns this controlled enzymatic reaction system into a generalized Lienard form. Furthermore, we give sufficient conditions for the existence and uniqueness of limit cycles in the new coordinates. We also perform numerical simulations illustrating the possibility of the existence of a local center (period annulus). A result with possible practical applications is that the oscillation frequency is a function of the integral control gain parameterComment: 15 pages, 5 figures, accepted version at Computers & Chem. En

Réseaux formels du savoir : une étude des expériences canadiennes

Version anglaise disponible dans la Bibliothèque numérique du CRDI: Formal knowledge networks : a study of Canadian experience

In vitro multiplication of Protea cynaroides L. microshoots and the effects of high phosphorous concentration on explant growth

Protea cynaroides L. is a slow-growing, difficult-to-propagate plant. Due to problems such as phenolic browning and their sensitivity to the phosphorous nutrient, in vitro multiplication of P. cynaroides explants have not been successful. The present study was conducted to induce shoot proliferation of established P. cynaroides microshoots, and investigate the effects of high phosphorous concentration during explant multiplication. Microshoots with either one or two nodes were cultured on Murashige and Skoog (MS) medium containing modified macronutrients and full strength micronutrients. Two concentrations of NH4H2PO4 were tested: 0 mg L-1 NH4H2PO4, and a high P concentration of 1400 mg L-1 NH4H2PO4. Both growth media were also supplemented with gibberellic acid (GA3) (30 mg L-1), 6-benzylaminopurine (BAP) (2 mg L-1), ethylenediaminetetraacetic acid (EDTA) (50 mg L-1) and indole-butyric acid (IBA) (0.5 mg L-1). Results show that, contrary to what is often reported, the presence of a high phosphorous concentration in the growth media did not adversely affect P. cynaroides explants. The survival rate and mean axillary shoot length of explants cultured on growth media containing 1400 mg L-1 NH4H2PO4 were not significantly different from those grown on 0 mg L-1 NH4H2PO4. No phosphorous toxicity symptoms were observed in explants cultured on media with high phosphorous levels. Results also show that explants with two nodes had a higher survival rate and produced significantly longer axillary shoots than those with one node, irrespective of phosphorous concentration. Multiplication of P. cynaroides microshoots was successfully achieved for the first time.This work was supported by the National Science Council of Taiwan (R.O.C) in the form of a research grant (NSC 100-2313-B-343-001).http://www.academicjournals.org/AJBam201

Multiple abiotic and biotic drivers of long-term wood decomposition within and among species in the semi-arid inland dunes:A dual role for stem diameter

Litter decomposition in sunny, semi-arid and arid ecosystems is controlled by both biotic factors including litter traits and abiotic factors including UV light, but for wood decomposition it still remains uncertain which of these environmental factors are the predominant controls among different woody species. In these dry ecosystems, it is likely that the stem diameter and spatial position of the dead wood are of particular importance especially where wood can be buried versus exposed due to substrate displacement by wind. Here we focus on the fact that stem diameter can affect decomposition rates both via the relative surface exposure to sunlight or soil and via higher resource quality of narrower stems to decomposers. In a field manipulation experiment, we investigated the relative importance of litter position (sand burial vs. surface vs. suspended above the surface), UV radiation (block versus pass) and stem diameter class (<2, 2–4, 4–8, 8–13 and 13–20 mm) on the mass loss of woody litters of four shrub species in an inland dune ecosystem in northern China. We found that after 34 months of in situ incubation, the mass loss of buried woody litters was three times faster than those of suspended and surface woody litters (53.5 ± 2.7%, 17.0 ± 1.0% and 14.4 ± 1.2%, respectively). In surface and suspended positions, litter decomposition rates were almost equally low and most mass loss was during the first 2 years, when bark was still attached and UV radiation had no significant effect on woody litter mass loss. These findings suggest that sand burial is the main environmental driver of wood decomposition via its control on microbial activity. Moreover, wood N and diameter class were the predominant factors driving woody litter decomposition. A key finding was that wider stems had slower litter decomposition rates not only directly (presumably via greater relative surface exposure) but also indirectly via their higher wood dry matter content or lower wood N; these effects were modulated by litter position. Our findings highlight a dual role of stem diameter on wood decomposition, that is, via relative surface exposure and via wood traits. The accuracy and confidence of global carbon cycling models would be improved by incorporating the different effects of stem diameter on woody litter decomposition and below-ground wood decomposition processes in drylands

Observed photodetachment in parallel electric and magnetic fields

We investigate photodetachment from negative ions in a homogeneous 1.0-T magnetic field and a parallel electric field of approximately 10 V/cm. A theoretical model for detachment in combined fields is presented. Calculations show that a field of 10 V/cm or more should considerably diminish the Landau structure in the detachment cross section. The ions are produced and stored in a Penning ion trap and illuminated by a single-mode dye laser. We present preliminary results for detachment from S- showing qualitative agreement with the model. Future directions of the work are also discussed.Comment: Nine pages, five figures, minor revisions showing final publicatio

Role and significance of total phenols during rooting of Protea cynaroides L. cuttings

Phenolic compounds, which are known to regulate root formation, are found abundantly in difficult-toroot Protea cynaroides stem cuttings. In this study, analysis of total phenol content was carried out on blanched and unblanched cuttings to observe its fluctuation throughout the entire rooting period (120 days) and establish its relationship with root formation. Results showed that blanching significantly increased the total phenol content in the basal ends of the cuttings. The high total phenol content was associated with significantly higher rooting percentage and increased the number of roots formed. Blanching reduced the time needed for the cuttings to root sufficiently to be transplanted to the field by 30 days. Analyses of different parts of cuttings throughout the entire rooting period showed continuous increase in total phenols at the basal end, while decrease in total phenols was observed in the leaves.http://www.academicjournals.org/AJ

The role of traditional foods in food-based dietary guidelines - a South African case study on maas (cultured milk)

With the revision of the South African food-based dietary guidelines (FBDGs) a new guideline specifically recommending the daily consumption of dairy products including maas (cultured milk) was introduced. This paper aims to evaluate the relevance of including maas as a traditional food product in the FBDGs. It was found that maas is a culturally relevant and traditional food product in South Africa. The nutrient profile of maas has changed notably over time since the first nutrient analysis was performed in 1995. The health benefits of maas, together with its popularity and its cultural relevance as part of the South African diet, make maas a suitable traditional food product to be included in the South African FBDGs.Clover Industries Limited2019-01-01hj2017Food Scienc

Simulation experiments for performance analysis of multiple-bus multiprocessor systems with nonexponential service times

A simulation model (program) is constructed for performance analysis of multiple-bus multiprocessor systems with shared memories. It is assumed that the service time of the common memory is either hypo- or hyperexponentially distributed. Process ing efficiency is used as the performance index. To investigate the effects of different service time distributions on the system perfor mance, comparative results are obtained for a large set of input parameters. The simulation results show that the error in approx imating the memory access time by an exponentially distributed random variable is less than 6% if the coefficient of variation is less than 1, but it increases drastically with this factor if it is greater than 1.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68518/2/10.1177_003754978905200104.pd