Purpose
The mechanical contribution of plant roots to the soil shear strength is commonly modelled using fibre bundle models (FBM), accounting for sequential breakage of roots. This study provides a ...generic framework, able to includes the many different existing approaches, to quantify the effect of various model assumptions.
Methods
The framework uses (1) a single model parameter determining how load is shared between all roots, (2) a continuous power-law distribution of root area ratio over a range of root diameters, and (3) power-law relationships between root diameters and biomechanical properties. A new load sharing parameter, closely resembling how roots mobilise strength under landslide conditions, is proposed. Exact analytical solutions were found for the peak root reinforcement, thus eliminating the current need for iterative algorithms. Model assumptions and results were validated against existing biomechanical and root reinforcement data.
Results
Root reinforcements proved very sensitive to the user-defined load sharing parameter. It is shown that the current method of discretising all roots in discrete diameter classes prior to reinforcement calculations leads to significant overestimations of reinforcement. Addition of a probabilistic distribution of root failure by means of Weibull survival functions, thus adding a second source of sequential mobilisation, further reduced predicted reinforcements, but only when the reduction due to load sharing was limited.
Conclusion
The presented solutions greatly simplify root reinforcement calculations while maintaining analytical exactness as well as clarity in the assumptions made. The proposed standardisation of fibre bundle-type models will greatly aid comparison and exchange of data.
Cooling Energy-Hungry Data Centers Meijer, G. I.
Science (American Association for the Advancement of Science),
04/2010, Letnik:
328, Številka:
5976
Journal Article
Recenzirano
Soon after the Internet took off in the mid-1990s, enterprise computing infrastructures with warehouses full of servers, known as data centers, became commonplace. The energy consumption challenges ...posed by such data centers are considerable. The power dissipation of servers has to be managed skillfully. Perhaps surprisingly, the power consumption of the cooling infrastructure that is required to keep the microelectronic components from overheating is on a par with that of the servers themselves.
CFTR, the cystic fibrosis (CF) gene, encodes for the CFTR protein that plays an essential role in anion regulation and tissue homeostasis of various epithelia. In the gastrointestinal (GI) tract CFTR ...promotes chloride and bicarbonate secretion, playing an essential role in ion and acid-base homeostasis. Cftr has been identified as a candidate driver gene for colorectal cancer (CRC) in several Sleeping Beauty DNA transposon-based forward genetic screens in mice. Further, recent epidemiological and clinical studies indicate that CF patients are at high risk for developing tumors in the colon. To investigate the effects of CFTR dysregulation on GI cancer, we generated Apc(Min) mice that carried an intestinal-specific knockout of Cftr. Our results indicate that Cftr is a tumor suppressor gene in the intestinal tract as Cftr mutant mice developed significantly more tumors in the colon and the entire small intestine. In Apc(+/+) mice aged to ~1 year, Cftr deficiency alone caused the development of intestinal tumors in >60% of mice. Colon organoid formation was significantly increased in organoids created from Cftr mutant mice compared with wild-type controls, suggesting a potential role of Cftr in regulating the intestinal stem cell compartment. Microarray data from the Cftr-deficient colon and the small intestine identified dysregulated genes that belong to groups of immune response, ion channel, intestinal stem cell and other growth signaling regulators. These associated clusters of genes were confirmed by pathway analysis using Ingenuity Pathway Analysis and gene set enrichment analysis (GSEA). We also conducted RNA Seq analysis of tumors from Apc(+/+) Cftr knockout mice and identified sets of genes dysregulated in tumors including altered Wnt β-catenin target genes. Finally we analyzed expression of CFTR in early stage human CRC patients stratified by risk of recurrence and found that loss of expression of CFTR was significantly associated with poor disease-free survival.
Transition metal oxides exhibiting a bistable resistance state are attractive for nonvolatile memory applications. The relevance of oxygen vacancies for the resistance‐change memory is investigated ...by X‐ray fluorescence (see figure), infrared microscopy, and X‐ray absorption spectroscopy using Cr‐doped SrTiO3 as an example. The microscopic origin of resistance switching in this class of materials may be due to an oxygen‐vacancy drift occurring in close proximity to one of the electrodes.
For an immiscible oil drop immersed in a stably stratified ethanol–water mixture, a downwards solutal Marangoni flow is generated on the surface of the drop, owing to the concentration gradient, and ...the resulting propulsion competes against the downwards gravitational acceleration of the heavy drop. In prior work of Li et al. (Phys. Rev. Lett., vol. 126, issue 12, 2021, 124502), we found that for drops of low viscosity, an oscillatory instability of the Marangoni flow is triggered once the Marangoni advection is too strong for diffusion to restore the stratified concentration field around the drop. Here we experimentally explore the parameter space of the concentration gradient and drop radius for high oil viscosities and find a different and new mechanism for triggering the oscillatory instability in which diffusion is no longer the limiting factor. For such drops of higher viscosities, the instability is triggered when the gravitational effect is too strong so that the viscous stress cannot maintain a stable Marangoni flow. This leads to a critical drop radius above which the equilibrium is always unstable. Subsequently, a unifying scaling theory that includes both the mechanisms for low and for high viscosities of the oil drops is developed. The transition between the two mechanisms is found to be controlled by two length scales: the drop radius $R$ and the boundary layer thickness $\delta$ of the Marangoni flow around the drop. The instability is dominated by diffusion for $\delta < R$ and by viscosity for $R<\delta$. The experimental results for various drops of different viscosities can well be described with this unifying scaling theory. Our theoretical description thus provides a unifying view of physicochemical hydrodynamic problems in which the Marangoni stress is competing with a stable stratification.
The fungus Fusarium oxysporum f.sp. cubense (Focub) causes Fusarium wilt of banana. Focub strains are divided into races according to their host specificity, but which virulence factors underlie ...these interactions is currently unknown. In the F. oxysporum f.sp. lycopersici (Fol)-tomato system, small secreted fungal proteins, called Six proteins, were identified in the xylem sap of infected plants. The Fol Six1 protein contributes to virulence and has an avirulence function by activating the I-3 immune receptor of tomato. The Focub tropical race 4 (TR4) genome harbors three SIX1 homologs: SIX1a, b and c. In this study, the role of Focub-SIX1a in pathogenicity was evaluated since this homolog is present in not only TR4 but also in other races. A deletion mutant of the SIX1a gene from Focub TR4 strain II5 was generated (FocubΔSIX1a) and tested in planta. Mutants were found to be severely compromised in their virulence. Ectopic integration of the Focub-SIX1a gene in the FocubΔSIX1a strain restored virulence to wild type levels. We conclude that Focub-SIX1a is required for full virulence of Focub TR4 towards Cavendish banana.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Optical cycling of AlF molecules Hofsäss, S; Doppelbauer, M; Wright, S C ...
New journal of physics,
07/2021, Letnik:
23, Številka:
7
Journal Article
Recenzirano
Odprti dostop
Abstract
Aluminium monofluoride (AlF) is a promising candidate for laser cooling and trapping at high densities. We show efficient production of AlF in a bright, pulsed cryogenic buffer gas beam, and ...demonstrate rapid optical cycling on the Q rotational lines of the
A
1
Π ↔
X
1
Σ
+
transition. We measure the brightness of the molecular beam to be >10
12
molecules per steradian per pulse in a single rotational state and present a new method to determine its velocity distribution in a single shot. The photon scattering rate of the optical cycling scheme is measured using three different methods, and is compared to theoretical predictions of the optical Bloch equations and a simplified rate equation model. Despite the large number of Zeeman sublevels (up to 216 for the Q(4) transition) involved, a high scattering rate of at least 17(2) × 10
6
s
−1
can be sustained using a single, fixed-frequency laser without the need to modulate the polarisation. We deflect the molecu-lar beam using the radiation pressure force and measure an acceleration of 8.7(1.5) × 10
5
m s
−2
. Losses from the optical cycle due to vibrational branching to
X
1
Σ
+
,
v
″ = 1 are addressed efficiently with a single repump laser. Further, we investigate two other loss channels, parity mixing by stray electric fields and photo-ionisation. The upper bounds for these effects are sufficiently low to allow loading into a magneto‐optical trap.
Falling poses a major threat to the steadily growing population of the elderly in modern-day society. A major challenge in the prevention of falls is the identification of individuals who are at risk ...of falling owing to an unstable gait. At present, several methods are available for estimating gait stability, each with its own advantages and disadvantages. In this paper, we review the currently available measures: the maximum Lyapunov exponent (λS and λL), the maximum Floquet multiplier, variability measures, long-range correlations, extrapolated centre of mass, stabilizing and destabilizing forces, foot placement estimator, gait sensitivity norm and maximum allowable perturbation. We explain what these measures represent and how they are calculated, and we assess their validity, divided up into construct validity, predictive validity in simple models, convergent validity in experimental studies, and predictive validity in observational studies. We conclude that (i) the validity of variability measures and λS is best supported across all levels, (ii) the maximum Floquet multiplier and λL have good construct validity, but negative predictive validity in models, negative convergent validity and (for λL) negative predictive validity in observational studies, (iii) long-range correlations lack construct validity and predictive validity in models and have negative convergent validity, and (iv) measures derived from perturbation experiments have good construct validity, but data are lacking on convergent validity in experimental studies and predictive validity in observational studies. In closing, directions for future research on dynamic gait stability are discussed.
The latter are essential for food security in the African Great Lakes Region where banana is a major staple crop that already suffers from manifold other pests and diseases, such as nematodes, ...weevils, Xanthomonas bacterial wilt, and black leaf streak disease, also known as Black Sigatoka. ...sooner or later, every diagnostic will retrieve false positives, such as by a non-TR4 strain that nevertheless tests positive 18. ...multiple diagnostics should be used that target different genomic areas for confirmatory reasons. ...comparative analyses of the genomes from new versus previous incursions enables only provisional associations. ...the proximity of the sampling sites to these farms and the applied disease management practices strongly suggest that TR4 was not successfully contained. ...TR4 was recently reported on Mayotte, an island in the Indian Ocean approximately 700 km from the infested farms in Mozambique 24.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
PDF
