Stability of hexagonal solidification patterns

We investigate the dynamics of cellular solidification patterns using three-dimensional phase-field simulations. The cells can organize into stable hexagonal patterns or exhibit unsteady evolutions. We identify the relevant secondary instabilities of regular hexagonal arrays and find that the stability boundaries depend significantly on the strength of crystalline anisotropy. We also find multiplet states that can be reached by applying well-defined perturbations to a pre-existing hexagonal array.Comment: Minor changes, mainly in introduction and conclusion, one reference adde

Pulsed electric field in combination with vacuum impregnation with trehalose improves the freezing tolerance of spinach leaves

Pulsed electric fields in combination with vacuum infusion have been utilized to impregnate cells with trehalose, aiming at substantially improving the freezing tolerance of spinach leaves. Spinach samples were first treated with ten trains of bi-polar, rectangular electric field pulses with a nominal electric field strength of 580 V/cm and immediately immersed in a 40% (w/w) solution of trehalose under vacuum for 20 min. The samples were kept in the trehalose solution for 2.5 h at atmospheric pressure, immersed in deionised water at 4 ºC overnight, frozen in liquid nitrogen and thawed in water at room temperature. The leaves were evaluated for cell damage with microscopic observations and wilting tests. The results provided evidence that the impregnation with trehalose by the combined actions of electric fields and vacuum impregnation drastically improved the freezing tolerance of the spinach leaves

Effect of pulsed electric fields on the germination of barley seeds

[Excerpt] Introduction: There is only little information available in the literature about the effect of reversible electropermeabilization on plant cells and tissues. We here present a first exploration of the effect of pulsed electric fields (PEF) on barley seed germination. PEF is used as a physical means of stressing the seeds and affect their metabolism. [...]info:eu-repo/semantics/publishedVersio

Pulsed electric field-induced cell permeabilisation of potato tissue lead to sustained metabolic changes

Metabolite profiling was used to characterize stress responses of potato tissue subjected to reversible electroporation, providing insights on how potato tissue responds to a physical stimulus such as pulsed electric fields (PEF), which is an artificial stress. Wounded potato tissue was subjected to field strengths ranging from 200 to 400 V/cm, with a single rectangular pulse of 1 ms. Electroporation was demonstrated by propidium iodide staining of the cells nucleae. Metabolic profiling of data obtained through GC/TOF-MS complemented with orthogonal projections to latent structures (OPLS) clustering analysis showed that 24 h after the application of PEF, potato metabolism shows PEF-specific responses characterized by the changes in the hexose pool that may involve starch and ascorbic acid degradation

Metabolomic evaluation of pulsed electric field-induced stress on potato tissue

Metabolite profiling was used to characterize stress responses of potato tissue subjected to reversible electroporation, providing insights on how potato tissue responds to a physical stimulus such as pulsed electric fields (PEF), which is an artificial stress. Wounded potato tissue was subjected to field strengths ranging from 200 to 400 V/cm, with a single rectangular pulse of 1 ms. Electroporation was demonstrated by propidium iodide staining of the cell nucleae. Metabolic profiling of data obtained through GC/TOF-MS and UPLC/TOF-MS complemented with orthogonal projections to latent structures clustering analysis showed that 24 h after the application of PEF, potato metabolism shows PEF-specific responses characterized by the changes in the hexose pool that may involve starch and ascorbic acid degradation.The Royal Physiographic Society in Lund, SwedenPortuguese Foundation of Science (FCT), PortugalDepartment of Cell and Organism Biology, Lund Universit

Effects of pulsed electrical fields on the texture of potato tissue

The application of pulsed electric fields (PEF) to cellular tissue is known to affect permanently or transiently the state of cell membranes, this is reflected in the electric properties of the tissue. Permanent permeabilization is known to affect the texture of the tissue. We have investigated whether low intensities of PEF would give rise to transient or permanent changes in texture. In this study, changes on the viscoelastic properties of potato tissues exposed to PEF during small-amplitude oscillatory dynamic rheological measurements were monitored. Potato tissue was subjected to field strengths ranging from 30 to 500 V/cm, with a single rectangular pulse of 10 µs, 100 µs or 1 ms. The elastic (G) and viscous (G&) moduli were measured every 30 s after the delivery of the pulse and the tan delta change calculated. The results were correlated with measurements of changes on electrical resistance during the delivery of the pulse. Interestingly, there is a drastic increase of tan delta 30 s after the application of the pulse, followed by a decrease 1 min after pulsation. This response is strongly influenced by the intensity and width of the pulse. Moreover, at high field strengths, the observed electroporation of the tissue reached similar levels when pulse widths of 1 ms and 100 µs were applied. Our results, supported by similar measurements on osmotically dehydrated control samples, clearly show that PEF causes a rapid change of the viscoelastic properties of the tissue that could be attributed to a partial loss in turgor pressure. This would be an expected consequence of electroporation. The recovery of the tan delta to values similar to those before pulsation, strongly suggests recovery of plasma membrane properties and turgor. These viscoelastic changes were shown to be independent of the total degree of permeabilization.info:eu-repo/semantics/publishedVersio

The association between low level exposures to ambient air pollution and term low birth weight: a retrospective cohort study

BACKGROUND: Studies in areas with relatively high levels of air pollution have found some positive associations between exposures to ambient levels of air pollution and several birth outcomes including low birth weight (LBW). The purpose of this study was to examine the association between LBW among term infants and ambient air pollution, by trimester of exposure, in a region of lower level exposures. METHODS: The relationship between LBW and ambient levels of particulate matter up to 10 um in diameter (PM(10)), sulfur dioxide (SO(2)) and ground-level ozone (O(3)) was evaluated using the Nova Scotia Atlee Perinatal Database and ambient air monitoring data from the Environment Canada National Air Pollution Surveillance Network and the Nova Scotia Department of Environment. The cohort consisted of live singleton births (≥37 weeks of gestation) between January1,1988 and December31,2000. Maternal exposures to air pollution were assigned to women living within 25 km of a monitoring station at the time of birth. Air pollution was evaluated as a continuous and categorical variable (using quartile exposures) for each trimester and relative risks were estimated from logistic regression, adjusted for confounding variables. RESULTS: There were 74,284 women with a term, singleton birth during the study period and with exposure data. In the analyses unadjusted for year of birth, first trimester exposures in the highest quartile for SO(2 )and PM(10)suggested an increased risk of delivering a LBW infant (relative risk = 1.36, 95% confidence interval = 1.04 to 1.78 for SO(2 )exposure and relative risk = 1.33, 95% confidence interval = 1.02 to 1.74 for PM(10)). After adjustment for birth year, the relative risks were attenuated somewhat and not statistically significant. A dose-response relationship for SO(2 )was noted with increasing levels of exposure. No statistically significant effects were noted for ozone. CONCLUSION: Our results suggest that exposure during the first trimester to relatively low levels of some air pollutants may be associated with a reduction in birth weight in term-born infants. These findings have implications for the development of effective risk management strategies to minimize the public health impacts for pregnant women

Dual-barrel conductance micropipet as a new approach to the study of ionic crystal dissolution kinetics

A new approach to the study of ionic crystal dissolution kinetics is described, based on the use of a dual-barrel theta conductance micropipet. The solution in the pipet is undersaturated with respect to the crystal of interest, and when the meniscus at the end of the micropipet makes contact with a selected region of the crystal surface, dissolution occurs causing the solution composition to change. This is observed, with better than 1 ms time resolution, as a change in the ion conductance current, measured across a potential bias between an electrode in each barrel of the pipet. Key attributes of this new technique are: (i) dissolution can be targeted at a single crystal surface; (ii) multiple measurements can be made quickly and easily by moving the pipet to a new location on the surface; (iii) materials with a wide range of kinetics and solubilities are open to study because the duration of dissolution is controlled by the meniscus contact time; (iv) fast kinetics are readily amenable to study because of the intrinsically high mass transport rates within tapered micropipets; (v) the experimental geometry is well-defined, permitting finite element method modeling to allow quantitative analysis of experimental data. Herein, we study the dissolution of NaCl as an example system, with dissolution induced for just a few milliseconds, and estimate a first-order heterogeneous rate constant of 7.5 (±2.5) × 10–5 cm s–1 (equivalent surface dissolution flux ca. 0.5 μmol cm–2 s–1 into a completely undersaturated solution). Ionic crystals form a huge class of materials whose dissolution properties are of considerable interest, and we thus anticipate that this new localized microscale surface approach will have considerable applicability in the future

Coal Home Heating and Environmental Tobacco Smoke in Relation to Lower Respiratory Illness in Czech Children, from Birth to 3 Years of Age

OBJECTIVE: The objective of this study was to evaluate how indoor pollution from tobacco and home heating may adversely affect respiratory health in young children. DESIGN: A birth cohort was followed longitudinally for 3 years to determine incidence of lower respiratory illness (LRI). PARTICIPANTS: A total of 452 children born 1994–1996 in two districts in the Czech Republic participated. EVALUATIONS: Indoor combustion exposures were home heating and cooking fuel, mother’s smoking during pregnancy, and other adult smokers in the household. Diagnoses of LRI (primarily acute bronchitis) from birth to 3 years of age were abstracted from pediatric records. Questionnaires completed at delivery and at 3-year follow-up provided covariate information. LRI incidence rates were modeled with generalized linear models adjusting for repeated measures and for numerous potential confounders. RESULTS: LRI diagnoses occurred more frequently in children from homes heated by coal [vs. other energy sources or distant furnaces; rate ratio (RR) = 1.45; 95% confidence interval (CI), 1.07–1.97]. Maternal prenatal smoking and other adult smokers also increased LRI rates (respectively: RR = 1.48; 95% CI, 1.10–2.01; and RR = 1.29; 95% CI, 1.01–1.65). Cooking fuels (primarily electricity, natural gas, or propane) were not associated with LRI incidence. For children never breast-fed, coal home heating and mother’s smoking conferred substantially greater risks: RR = 2.77 (95% CI, 1.45–5.27) and RR = 2.52 (95% CI, 1.31–4.85), respectively. CONCLUSIONS: Maternal smoking and coal home heating increased risk for LRI in the first 3 years of life, particularly in children not breast-fed. RELEVANCE: Few studies have described effects of coal heating fuel on children’s health in a Western country. Breast-feeding may attenuate adverse effects of prenatal and childhood exposures to combustion products