Pushing and pulling on OH- and H3O+ with electric fields across water’s surface

We use second harmonic generation (SHG) spectroscopy, molecular dynamics simulation, and theoretical modeling to study the response of the neat liquid water-air interface to changes in the potential of an external electrode positioned above the liquid. We observe a parabolic dependence of second harmonic intensity on applied potential. This dependence is reminiscent of bulk-phase electric field induced second harmonic (EFISH) but more complicated because it combines the second-order response of the topmost water layer and the potential dependent response of the interfacial electrical double-layer. Based on the literature values for these contributions, we derive a physical interpretation of our measurements that reveals new insight into the response of the neat water interface to external electric fields. Specifically, we find that the net dipolar orientation of water molecules within the double-layer is primarily responsive to the internal fields generated by the excess surface concentrations of OH- and H3O+ that arise to screen the external potential. Notably, this interpretation implies that the orientational response of water dipoles at the interface can actually oppose the direction of the external field, a subtle effect that is not captured by traditional models.

Evolution of a confluent gut epithelium under cyclic stretching

The progress of food in the gastrointestinal (GI) tract is driven by a peristaltic motion generated by the muscle belt surrounding the GI tract. In turn, the response of the intestinal epithelial cells to the peristaltic stresses affects the dynamics of the epithelial structure. In this work, we study the effect of cyclic stretching (0.125 Hz, 10% strain) on the spatial organization of the intestinal epithelium using intestinal cells deposited on a flat elastomeric substrate to mimic the peristaltic motion in vitro. A confluent monolayer of Caco-2 cells is grown on a PDMS chip to probe the morphological and orientational response of the tissue to cyclic stretching. The PDMS chips are either covalently or non-covalently coated with laminin to recapitulate the basement membrane. We observe a significant orientational response where the cells rearrange their long axes perpendicular to the stretching direction for both coating conditions. The experiment is modeled by a vertex model where the cells store elastic energy with varying strain and effectively have a rotational diffusive motion through rearrangements of their shapes. The model also predicts a transition between the perpendicular orientation and orientation at an oblique angle determined by the level of the cell elastic anisotropy. It provides a general framework to study cell response and relaxation dynamics under cyclic stretching across different cell types. We also discuss potential relevance of peristalsis in determining planar cell polarity in 3D architectures.

Влияние beta-дикетонатного комплекса европия(III) на ориентационные отклики в сигнале сверхбыстрого оптического эффекта Керра-=SUP=-*-=/SUP=-

Experiments on recording the ultrafast optical Kerr effect (OKE) in solution of europium(III) β‑diketonate complexes in toluene at a concentration of 10^–2 mol/L showed that the total OKE signal is not a superposition of two contributions, one of which is related to the vibrational–rotational dynamics of toluene molecules, while the other is due to the vibrational–rotational dynamics of the europium(III) complexes. This immediately indicates that the europium(III) complexes essentially change the structure of liquid toluene, which is reflected in the character of an orientational response in picosecond range.

Electric Field FT-IR: Analysis of a Liquid Crystalline Polymer

Fourier transform infrared spectroscopy in a reflective mode has been utilized to study the dynamics of molecular structure in a polymeric liquid crystalline melt. The experimental setup included a thermo-electric cell which allows heating, melting of the sample, and also application of an electric ([Formula: see text]) field during spectroscopic observation. It was therefore possible to monitor orientation of dipolar groups as a function of time during thermal and electrical treatments. The material studied was a liquid crystalline copolyester, and orientation was monitored through absorbance associated with stretching of carbonyl bonds. Measurements taken on a melt of this material reveal an orientational response of carbonyl groups which begins immediately upon application of a relatively low [Formula: see text]-field (3750 V cm−1) and continues over a period of approximately one hour. It was somewhat surprising that a measurable change in dipolar orientation was observed. Cooperative dipolar phenomena and the torque-transmitting elasticity of the mesomorphic fluid are thought to be important factors in the observed behavior.

A field study of homing and orientation to the home site in Ulvaria subbifurcata (Pisces: Stichaeidae)

The movements, homing behavior, and initial orientation to the capture site were investigated in Ulvaria subbifurcata using an underwater habitat and scuba. Field experiments showed that this benthic species restricts its activity to a small home range, less than 3 m2, is capable of returning to that home area after being displaced at least 270 m, and can orient in the direction of the home site after displacements of at least 30 m. The conditions under which the orientation experiments were conducted indicate that visual cues are not necessary for the orientational response.