Growth Cone Pathfinding: a competition between deterministic and stochastic events

BACKGROUND: Growth cone migratory patterns show evidence of both deterministic and stochastic search modes. RESULTS: We quantitatively examine how these two different migration modes affect the growth cone's pathfinding response, by simulating growth cone contact with a repulsive cue and measuring the resultant turn angle. We develop a dimensionless number, we call the determinism ratio Ψ, to define the ratio of deterministic to stochastic influences driving the growth cone's migration in response to an external guidance cue. We find that the growth cone can exhibit three distinct types of turning behaviors depending on the magnitude of Ψ. CONCLUSIONS: We conclude, within the context of these in silico studies, that only when deterministic and stochastic migration factors are in balance (i.e. Ψ ~ 1) can the growth cone respond constructively to guidance cues

Investigation of the retronasal perception of palm wine (Elaeis Guineensis) aroma by application of sensory analysis and exhaled odorant measurement (exom).

The headspace profile of palm wine was evaluated by time-resolved sensory analysis showing significant changes of the diverse odour attributes with time after swallowing. Fruity and citrusy were the most intense aroma qualities perceived upon sample introduction into the mouth, while swallowing of the palm wine elicited a more acidic impression followed by citrusy and fruity nuances respectively. After swallowing, panelists described an increase in the nutty and popcorn-like aroma impressions. Based on these sensory observations, the retronasal aroma perception of palm wine was investigated by application of the modified Exhaled Odorant Measurement (EXOM)-approach. In EXOM analysis, odorants that are exhaled through the nose during food consumption and swallowing are collected and analysed by high resolution gas chromatography-olfactometry and mass spectrometry, respectively. EXOM results revealed an initial 24 odor-active compounds in the \'swallow\' breath with 23 of these odorants being identified on the basis of their odor qualities and intensities, as well as chromatographic and mass spectral data. Only 14 compounds were detectable in the exhaled breath 20 s after swallowing the palm wine and 11 of these were subsequently identified. Generally, the identified odorants belonged to very diverse odorant substance classes such as heteroaromatic compounds, esters, alcohols, carbonyl and thio compounds and many more. Among these, higher persistence intervals in the exhalation breath were obtained for the buttery smelling compounds butan-2,3-dione and 3-hydroxy-butan-2-one (acetoine), 3-isobutyl 2- methoxypyrazine with bell pepper-like aroma impression, the malty smelling 2- and 3-methylbutanols, and the coconut-like smelling γ-dodecalactone. The popcorn-like smelling 2-acetyl 1-pyrroline, the fresh flowery linalool and two unknown compounds with citrusy and buttery aroma impressions were only detectable at 20 s after swallowing. Dynamic changes were also observed in retronasal sensory evaluations that were attributed to specific palm wine odorants. Accordingly, both sensory and analytical data on retronasal aroma perception of palm wine monitored the dynamic flavour changes during palm wine consumption. Keywords: Retronasal, EXOM, swallow breath, 2-acetyl 1-pyrroline African Journal of Food, Agriculture, Nutrition and Development Vol. 9 (2) 2009: pp. 793-81

Changes in structure and aroma release from starch-aroma systems upon α-amylase addition

The influence of starch hydrolysis by α-amylase addition on structural properties and aroma release from starch-aroma systems was studied. A food model system composed of aqueous tapioca starch dispersion (4g dry starch/100g dispersion) and one aroma compound (menthone) was investigated. Structure breakdown and related changes in starch fraction (amylose) were measured by rheology and iodine-binding. Menthone release from the aroma-starch system in the headspace was followed by proton transfer reaction-mass spectrometry (PTR-MS) upon starch hydrolysis. A slightly higher viscosity was found for the starch-menthone system compared to the starch system without menthone upon α-amylase addition. One could hypothesise that menthone acts as a kind of nucleation agent for inducing structure build-up of starch segments, hindering starch degradation. An extensive aroma release from aroma-starch systems upon α-amylase addition was expected, but, instead, just a slight volatile increase was found after a starch hydrolysis time of 60min. It is suggested that aroma release is the result of several superimposed effects ranging from viscosity effects to interactions between aroma compounds and starch degradation product

The Parallel Persistent Memory Model

We consider a parallel computational model that consists of $P$ processors, each with a fast local ephemeral memory of limited size, and sharing a large persistent memory. The model allows for each processor to fault with bounded probability, and possibly restart. On faulting all processor state and local ephemeral memory are lost, but the persistent memory remains. This model is motivated by upcoming non-volatile memories that are as fast as existing random access memory, are accessible at the granularity of cache lines, and have the capability of surviving power outages. It is further motivated by the observation that in large parallel systems, failure of processors and their caches is not unusual. Within the model we develop a framework for developing locality efficient parallel algorithms that are resilient to failures. There are several challenges, including the need to recover from failures, the desire to do this in an asynchronous setting (i.e., not blocking other processors when one fails), and the need for synchronization primitives that are robust to failures. We describe approaches to solve these challenges based on breaking computations into what we call capsules, which have certain properties, and developing a work-stealing scheduler that functions properly within the context of failures. The scheduler guarantees a time bound of $O(W/P_A + D(P/P_A) \lceil\log_{1/f} W\rceil)$ in expectation, where $W$ and $D$ are the work and depth of the computation (in the absence of failures), $P_A$ is the average number of processors available during the computation, and $f \le 1/2$ is the probability that a capsule fails. Within the model and using the proposed methods, we develop efficient algorithms for parallel sorting and other primitives.Comment: This paper is the full version of a paper at SPAA 2018 with the same nam

Simulating the dynamics of linear forests in Great Plains agroecosystems under changing climates

Most forest growth models are not suitable for the highly fragmented, linear (or linearly shaped) forests in the Great Plains agroecosystems (e.g., windbreaks, riparian forest buffers), where such forests are a minor but ecologically important component of the land mosaics. This study used SEEDSCAPE, a recently modified gap model designed for cultivated land mosaics in the Great Plains, to simulate the effects of climate change on the dynamics of such linear forests. We simulated the dynamics of windbreaks with different initial planting species richness and widths flight changes as the selected resulting factor) using current climate data and nested regional circulation models (RegCMs). Results indicated that ( i ) it took 70-80 simulation years for the linear forests to reach a steady state under both normal (present-day) and warming climates; (ii) warming climates would reduce total aboveground tree biomass and the spatial variation in biomass, but increase dominance in the linear forests, especially in the upland forests; (iii) linear forests with higher planting species richness and smaller width produced higher aboveground tree biomass per unit area; and (iv) the same species performed very differently with different climate scenarios, initial planting diversity, and forest widths. Although the model still needs further improvements (e.g., the effects of understory species should be included), the model can serve as a useful tool in modeling the succession of linear forests in human-dominated land mosaics under changing climates and may also have significant practical implications in other systems

An in vitro assay of collagen fiber alignment by acupuncture needle rotation

BACKGROUND: During traditional acupuncture therapy, soft tissues attach to and wind around the acupuncture needle. To study this phenomenon in a controlled and quantitative setting, we performed acupuncture needling in vitro. METHODS: Acupuncture was simulated in vitro in three-dimensional, type I collagen gels prepared at 1.5 mg/ml, 2.0 mg/ml, and 2.5 mg/ml collagen, and either crosslinked with formalin or left untreated. Acupuncture needles were inserted into the gels and rotated via a computer-controlled motor at 0.3 rev/sec for up to 10 revolutions while capturing the evolution of birefringence under cross-polarization. RESULTS: Simulated acupuncture produced circumferential alignment of collagen fibers close to the needle that evolved into radial alignment as the distance from the needle increased, which generally matched observations from published tissue explant studies. All gels failed prior to 10 revolutions, and the location of failure was near the transition between circumferential and radial alignment. Crosslinked collagen failed at a significantly lower number of revolutions than untreated collagen, whereas collagen concentration had no effect on gel failure. The strength of the alignment field increased with increasing collagen concentration and decreased with crosslinking. Separate studies were performed in which the gel thickness and depth of needle insertion were varied. As gel thickness increased, gels failed at fewer needle revolutions. For the same depth of insertion, alignment was greater in thinner gels. Alignment increased as the depth of insertion increased. CONCLUSION: These results indicate that the mechanostructural properties of soft connective tissues may affect their response to acupuncture therapy. The in vitro model provides a platform to study mechanotransduction during acupuncture in a highly controlled and quantitative setting