A drastic transition at birth, from constant maternal nutrient supply in utero to intermittent postnatal feeding, requires changes in the metabolic system of the neonate. Despite their central role ...in metabolic homeostasis, little is known about how pancreatic β cells adjust to the new nutritional challenge. Here, we find that after birth β cell function shifts from amino acid- to glucose-stimulated insulin secretion in correlation with the change in the nutritional environment. This adaptation is mediated by a transition in nutrient sensitivity of the mTORC1 pathway, which leads to intermittent mTORC1 activity. Disrupting nutrient sensitivity of mTORC1 in mature β cells reverts insulin secretion to a functionally immature state. Finally, manipulating nutrient sensitivity of mTORC1 in stem cell-derived β cells in vitro strongly enhances their glucose-responsive insulin secretion. These results reveal a mechanism by which nutrients regulate β cell function, thereby enabling a metabolic adaptation for the newborn.
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•Nutritional changes after birth alter β cell function•β cells acquire glucose response via changes in mTORC1 nutrient sensitivity•Glucose response is independent of changes in canonical β cell markers expression•Nutrient-regulated mTORC1 activity controls stem cell-derived β cell function
At birth, metabolic adaptations prepare the newborn for its new nutritional environment. Helman et al. demonstrate a role of nutrient sensing by mTORC1 in adjusting insulin secretion in neonatal β cells. Exploiting this adaptative property of β cells results in improved glucose-responsive insulin secretion in human stem cell-derived β cells.
DLVO interactions are computed between a colloidal particle and heterogeneous collector, and a simple statistical approach is proposed for calculating the mean potential energy of interaction for ...randomly distributed heterogeneity.
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►Method to compute DVLO interactions with topographical and chemical heterogeneity. ►Topographical features increase attraction between heterogeneous surfaces. ►Explains deviations from mean-field predictions for surfaces with adsorbed patches. ►Simple statistical approach requires only two calculations with homogeneous surfaces.
The DLVO force and potential energy of interaction between microspheres and topographically and chemically heterogeneous surfaces in aqueous solution are computed using a modification of the surface element integration approach. The heterogeneous surface has an array of cylindrical pillars of varying height, diameter, and arrangement to model different nano-topographies. In agreement with previous studies, the nano-topography decreases the size of the potential energy barrier for unfavorable surfaces because the pillars limit the minimum separation distance. The influence of topography is significant even for pillars several nanometers high and is more pronounced if the surface potential of the pillar tops differs from that of the underlying surface. A new force- and energy-averaging model is introduced as a simple method to compute the mean interaction energy or force between the particle and a heterogeneous surface, which differs significantly from a mean-field approach based on the average or nominal surface potential. Small variations in topography are found to remove large energy barriers to colloidal deposition. These results help explain the increased attraction of patchy surfaces towards particles relative to expectations based on typical DLVO calculations, which is particularly significant for surfaces with adsorbed polyelectrolytes.
We present a method to generate complete arbitrary spatially variant polarization modulation of a light beam by means of a parallel aligned nematic liquid crystal spatial light modulator (SLM). We ...first analyze the polarization modulation properties in a transmission mode. We encode diffraction gratings onto the SLM and show how to achieve partial polarization control of the zero order transmitted light. We then extend the technique to a double modulation scheme, which is implemented using a single SLM divided in two areas in a reflective configuration. The polarization states of the transmitted beam from the first pass through the first area are rotated using two passes through a quarter wave plate. The beam then passes through the second area of the SLM where additional polarization information can be encoded. By combining previously reported techniques, we can achieve complete amplitude, phase and polarization control for the diffracted light that allows the creation of arbitrary diffractive optical elements including polarization control. Theoretical analysis based on the Jones matrix formalism, as well as excellent experimental results are presented.
Abruptly autofocusing vortex beams Davis, Jeffrey A; Cottrell, Don M; Sand, David
Optics express,
2012-Jun-04, 2012-06-04, 20120604, Letnik:
20, Številka:
12
Journal Article
Recenzirano
Odprti dostop
We generate abruptly autofocusing beams that produce vortices at the focus. We give explicit equations for the phase-only Fourier masks that generate these beams including explanations for ...controlling the focal distance and numerical aperture. We show experimental results for the focal distance, the vortex pattern and show that the diameter of the focused beam can be made smaller than the size of a comparable Airy beam from a lens. Finally we show how to move the focus spot in three dimensions by encoding additional optical elements onto the phase pattern.
Abstract
Interactions between quasiparticles are of fundamental importance and ultimately determine the macroscopic properties of quantum matter. A famous example is the phenomenon of ...superconductivity, which arises from attractive electron-electron interactions that are mediated by phonons or even other more exotic fluctuations in the material. Here we introduce mobile exciton impurities into a two-dimensional electron gas and investigate the interactions between the resulting Fermi polaron quasiparticles. We employ multi-dimensional coherent spectroscopy on monolayer WS
2
, which provides an ideal platform for determining the nature of polaron-polaron interactions due to the underlying trion fine structure and the valley specific optical selection rules. At low electron doping densities, we find that the dominant interactions are between polaron states that are dressed by the same Fermi sea. In the absence of bound polaron pairs (bipolarons), we show using a minimal microscopic model that these interactions originate from a phase-space filling effect, where excitons compete for the same electrons. We furthermore reveal the existence of a bipolaron bound state with remarkably large binding energy, involving excitons in different valleys cooperatively bound to the same electron. Our work lays the foundation for probing and understanding strong electron correlation effects in two-dimensional layered structures such as moiré superlattices.
Over the past few decades, inadvertent consequences have stemmed from the intensified use of neonicotinoids in agroecosystems. Neonicotinoid applications can result in both positive (e.g., reduced ...persistent virus transmission) and negative (e.g., increased host susceptibility) repercussions exhibiting ambiguity for their use in crop production. In soybean, aspects of neonicotinoid usage such as the impact on nonpersistent virus transmission and efficacy against nontarget herbivores have not been addressed. This study evaluated the interaction between the neonicotinoid thiamethoxam and soybean variety and the impact on different pest feeding guilds. Feeding and behavioral bioassays were conducted in the laboratory to assess the effect of thiamethoxam on the mortality and weight gain of the defoliator, Chrysodeixis includens (Walker). Bioassays evaluated impacts dependent and independent of soybean tissue, in addition to both localized and systemic efficacy within the soybean plant. Additionally, using the electrical penetration graph technique (EPG), the probing behavior of 2 piercing-sucking pests, Aphis gossypii Glover and Myzus persicae (Sulzer), was observed. Results from defoliator bioassays revealed thiamethoxam had insecticidal activity against C. includens. Distinctions in thiamethoxam-related mortality between bioassays dependent and independent of soybean tissue (∼98% versus ∼30% mortality) indicate a contribution of the plant towards defoliator-related toxicity. Observations of defoliator feeding behavior showed a preference for untreated soybean tissue relative to thiamethoxam-treated tissue, suggesting a deterrent effect of thiamethoxam. EPG monitoring of probing behavior exhibited a minimal effect of thiamethoxam on piercing-sucking herbivores. Findings from this study suggest neonicotinoids like thiamethoxam may provide some benefit via insecticidal activity against nontarget defoliators.
Feeding by insect herbivores activates plant signaling pathways, resulting in the enhanced production of secondary metabolites and other resistance-related traits by injured plants. These traits can ...reduce insect fitness, deter feeding, and attract beneficial insects. Organic and inorganic chemicals applied as a foliar spray, seed treatment, or soil drench can activate these plant responses. Azelaic acid (AA), benzothiadiazole (BTH), gibberellic acid (GA), harpin, and jasmonic acid (JA) are thought to directly mediate plant responses to pathogens and herbivores or to mimic compounds that do. The effects of these potential elicitors on the induction of plant defenses were determined by measuring the weight gains of fall armyworm, Spodoptera frugiperda (J. E. Smith) (FAW) (Lepidoptera: Noctuidae) larvae on four crop plants, cotton, corn, rice, and soybean, treated with the compounds under greenhouse conditions. Treatment with JA consistently reduced growth of FAW reared on treated cotton and soybean. In contrast, FAW fed BTH- and harpin-treated cotton and soybean tissue gained more weight than those fed control leaf tissue, consistent with negative crosstalk between the salicylic acid and JA signaling pathways. No induction or inconsistent induction of resistance was observed in corn and rice. Follow-up experiments showed that the co-application of adjuvants with JA failed to increase the effectiveness of induction by JA and that soybean looper Chrysodeixis includens (Walker), a relative specialist on legumes, was less affected by JA-induced responses in soybean than was the polyphagous FAW. Overall, the results of these experiments demonstrate that the effectiveness of elicitors as a management tactic will depend strongly on the identities of the crop, the pest, and the elicitor involved.
The source of water (H₂O) and hydroxyl radicals (OH), identified on the lunar surface, represents a fundamental, unsolved puzzle. The interaction of solar-wind protons with silicates and oxides has ...been proposed as a key mechanism, but laboratory experiments yield conflicting results that suggest that proton implantation alone is insufficient to generate and liberate water. Here, we demonstrate in laboratory simulation experiments combined with imaging studies that water can be efficiently generated and released through rapid energetic heating like micrometeorite impacts into anhydrous silicates implanted with solar-wind protons. These synergistic effects of solar-wind protons and micrometeorites liberate water at mineral temperatures from 10 to 300 K via vesicles, thus providing evidence of a key mechanism to synthesize water in silicates and advancing our understanding on the origin of water as detected on the Moon and other airless bodies in our solar system such as Mercury and asteroids.
•It was demonstrated that fly as particles can be grouped into compositionally distinct groups.•Fly ashes with similar bulk composition may produce different compressive strengths in concrete.•The ...compositional strength can be predicted using the particle group composition.•Linear modeling of the particle group composition has significant predictive power for concrete.•There are specific particle groups most strongly associated with early strength gain.
A new classification approach is presented that uses individual fly ash particle measurements to provide improved and more in-depth information about the properties of the concrete. The technique uses machine guided X-ray microanalysis to measure the compositions of 2000 randomly selected particles from 20 different fly ashes. This paper details the methods used to acquire the particle composition data and the derivation of the representative groups of the fly ash particles or classification groups. This method is named the Particle Model. To investigate the utility of these groups, 12 fly ashes were used at a 20% mass replacement of the cement in a series of concrete mixtures, which were tested for compressive strength at various times over 180 d of curing. Seven of the nine particle compositions identified were found to influence the compressive strength of the concrete with a linear model R-squared value of 0.99. The Particle Model showed a statistically significant improvement over the Class C or F classification from ASTM C618 and EN450. This work aims to establish the Particle Model and show that the classification shows promise to be used as a method to predict the physical properties of concretes that contain fly ash.
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