Weak-anchoring effects in a thin pinned ridge of nematic liquid crystal.

A theoretical investigation of weak-anchoring effects in a thin two-dimensional pinned static ridge of nematic liquid crystal resting on a flat solid substrate in an atmosphere of passive gas is performed. Specifically, we solve a reduced version of the general system of governing equations recently derived by Cousins et al. [Proc. R. Soc. A 478, 20210849 (2022)10.1098/rspa.2021.0849] valid for a symmetric thin ridge under the one-constant approximation of the Frank-Oseen bulk elastic energy with pinned contact lines to determine the shape of the ridge and the behavior of the director within it. Numerical investigations covering a wide range of parameter values indicate that the energetically preferred solutions can be classified in terms of the Jenkins-Barratt-Barbero-Barberi critical thickness into five qualitatively different types of solution. In particular, the theoretical results suggest that anchoring breaking occurs close to the contact lines. The theoretical predictions are supported by the results of physical experiments for a ridge of the nematic 4^{'}-pentyl-4-biphenylcarbonitrile (5CB). In particular, these experiments show that the homeotropic anchoring at the gas-nematic interface is broken close to the contact lines by the stronger rubbed planar anchoring at the nematic-substrate interface. A comparison between the experimental values of and the theoretical predictions for the effective refractive index of the ridge gives a first estimate of the anchoring strength of an interface between air and 5CB to be (9.80±1.12)×10^{-6}Nm^{-1} at a temperature of (22±1.5)^{∘}C.

Young and Young-Laplace equations for a static ridge of nematic liquid crystal, and transitions between equilibrium states.

Motivated by the need for greater understanding of systems that involve interfaces between a nematic liquid crystal, a solid substrate and a passive gas that include nematic-substrate-gas three-phase contact lines, we analyse a two-dimensional static ridge of nematic resting on a solid substrate in an atmosphere of passive gas. Specifically, we obtain the first complete theoretical description for this system, including nematic Young and Young-Laplace equations, and then, making the assumption that anchoring breaking occurs in regions adjacent to the contact lines, we use the nematic Young equations to determine the continuous and discontinuous transitions that occur between the equilibrium states of complete wetting, partial wetting and complete dewetting. In particular, in addition to continuous transitions analogous to those that occur in the classical case of an isotropic liquid, we find a variety of discontinuous transitions, as well as contact-angle hysteresis, and regions of parameter space in which there exist multiple partial wetting states that do not occur in the classical case.

The ventilation of buildings and other mitigating measures for COVID-19: a focus on wintertime.

The year 2020 has seen the emergence of a global pandemic as a result of the disease COVID-19. This report reviews knowledge of the transmission of COVID-19 indoors, examines the evidence for mitigating measures, and considers the implications for wintertime with a focus on ventilation.

On the Effect of Substrate Viscoelasticity on the Evaporation Kinetics and Deposition Patterns of Nanosuspension Drops.

This study investigates the evaporation of sessile pure water and nanosuspension drops on viscoelastic polydimethylsiloxane (PDMS) films. We varied the viscoelasticity of the PDMS films by controlling the curing ratio and categorized them into three types: stiff (10:1, 20:1, 40:1), soft (60:1, 80:1), and very soft (100:1, 120:1, 140:1, 160:1). On stiff surfaces, pure water drops initially evaporate in a constant contact radius (CCR) mode, followed by a constant contact angle mode, and finally in a mixed mode of evaporation. Nanosuspension drops follow the same trend as water drops but with a difference toward the end of their lifetimes, when a short second CCR mode is observed. Complete evaporation of nanosuspension drops on stiff substrates leads to particle deposition patterns similar to a coffee ring with cracks and deposition tails. On soft surfaces, the initial spreading is followed by a pseudo-CCR mode. Complete evaporation of nanosuspension drops on soft substrates leads to deposits in the form of a uniform ring with a sharp ox-horn profile. Unexpectedly, the initial spreading is followed by a mixed mode on very soft substrates, on which wetting ridges (WRs) pulled up by the vertical component of surface tension are clearly observed in the vicinity of the contact line (CL). As the evaporation proceeds, the decreasing contact angle breaks the force balance in the horizontal direction at the CL and gives rise to a net horizontal force, which causes the CL to recede, transferring the horizontal force to the WR. Because of the viscoelastic nature of the very soft substrate, this horizontal force acting on the WR cannot be completely countered by the bulk of the substrate underneath. As a result, the WR moves horizontally in a viscous-flow way, which also enables the CL to be continuously anchored to the ridge and to recede relative to the bulk of the substrate. Consequently, a mixed mode of evaporation occurs. Complete evaporation of nanosuspension drops on very soft substrates leads to finger-like deposits.

Fatal Intoxication Involving 3-MeO-PCP: A Case Report and Validated Method.

We present in this case report a validated method for accurate quantitative analysis of 3-methoxy phencyclidine (3-MeO-PCP) to determine postmortem blood concentrations of this PCP analog. A 29-year-old male with a history of illicit drug use was found unresponsive in his bed with a bag of white powder next to him. Resuscitation efforts were unsuccessful and the individual was pronounced dead 9 minutes after arrival to the hospital. Initial ELISA screening suggested the presence of PCP in the decedent's blood. However, confirmatory testing revealed no detectable PCP. Instead, a large peak corresponding to a m/z 274.218 species with retention time similar to PCP was present on a LC-TOF-MS drug screen, suggesting a possible PCP analog. This mass corresponds specifically to a methoxy-PCP analog, several of which are available for purchase online. Standards for 3-MeO-PCP and 4-MeO-PCP were obtained and injected on the same instrument. Although the 3- and 4-MeO-PCP analogs have identical masses and retention times, they are still distinguishable through their mass spectra. The peak from the decedent's sample matched both the mass spectrum and the retention time of 3-MeO-PCP. A quantitative LC-MS-MS method was subsequently developed and validated for casework. Analysis using this method revealed a concentration of 139 ± 41 µg/L 3-MeO-PCP in the decedent's blood. Diphenhydramine (4.1 ± 0.7 mg/L), marijuana metabolite (presumptive positive, confirmation not performed) and a small amount of amphetamine (<0.10 mg/L) were also found in the decedent's blood. The cause of death was determined to be combined 3-MeO-PCP, diphenhydramine and amphetamine toxicity. The manner of death was certified as an accident.

Fluid-dynamical model for antisurfactants.

We construct a fluid-dynamical model for the flow of a solution with a free surface at which surface tension acts. This model can describe both classical surfactants, which decrease the surface tension of the solution relative to that of the pure solvent, and antisurfactants (such as many salts when added to water, and small amounts of water when added to alcohol) which increase it. We demonstrate the utility of the model by considering the linear stability of an infinitely deep layer of initially quiescent fluid. In particular, we predict the occurrence of an instability driven by surface-tension gradients, which occurs for antisurfactant, but not for surfactant, solutions.

Evaporation of droplets on strongly hydrophobic substrates.

The manner in which the extreme modes of droplet evaporation (namely, the constant contact radius and the constant contact angle modes) become indistinguishable on strongly hydrophobic substrates is described. Simple asymptotic expressions are obtained which provide good approximations to the evolutions of the contact radius, the contact angle, and the volume of droplets evaporating in the extreme modes for a wide range of hydrophobic substrates. As a consequence, on strongly hydrophobic substrates it is appropriate to use the so-called "2/3 power law" to extrapolate the lifetimes of droplets evaporating in the constant contact radius mode as well as in the constant contact angle mode.

Dynamics of a two-dimensional vapor bubble confined between superheated or subcooled parallel plates.

The dynamics of a long, two-dimensional vapor bubble confined in the gap between two superheated or subcooled parallel plates is analyzed theoretically. The unsteady expansion and/or contraction of the bubble is driven by mass transfer between the liquid and the vapor. The analysis uses the approach developed by Wilson [J. Fluid Mech. 391, 1 (1999)] for a situation with "large" gaps and "small" superheating or subcooling to consider a situation with small gaps and large superheating or subcooling in which the mass transfer from or to the semicircular nose of the bubble is comparable to that from or to the thin liquid films on the plates. In order to permit a (semi-) analytical treatment the analysis is restricted to low Prandtl number liquids. When both plates are superheated the bubble always expands. In this case there are two possible constant-velocity continuous-film solutions for the expansion of the bubble, namely, an unstable fast mode and a stable slow mode. The evolution of the bubble is calculated numerically for a range of values of the parameters. In particular, these calculations show that eventually the bubble expands either with the constant velocity of the slow mode or exponentially. When both plates are subcooled the bubble always collapses to zero length in a finite time. When one plate is subcooled and the other plate is superheated the situation is rather more complicated. If the magnitude of the subcooling is less than that of the superheating then if the magnitude of the subcooling is greater than a critical value then a variety of complicated behaviors (including the possibility of an unexpected "waiting time" behavior in which the bubble remains almost stationary for a finite period of time) can occur before the bubble eventually collapses to a finite length in an infinite time, whereas if it is less than this critical value then the bubble always expands and eventually does so exponentially. If the magnitude of the subcooling is greater than that of the superheating then the bubble always collapses to zero length in a finite time.

Postmortem distribution of the novel antipsychotic drug quetiapine.

The objective of this research was to determine the concentrations and distribution of the atypical antipsychotic drug, quetiapine, in postmortem tissues from eight Medical Examiner cases. Quetiapine was isolated from liquid specimens and tissue homogenates by extraction at an alkaline pH into 1-chlorobutane. The 1-chlorobutane was decanted, and quetiapine, plus the internal standard (prochlorperazine), was back-extracted into 0.1N sulfuric acid. The acid layer was made basic, and quetiapine, plus the internal standard, was re-extracted into 1-chlorobutane. Quantitation was by gradient, high-pressure liquid chromatography on a C-8 ODS (2.1 x 150 mm, 5 mu) column with acetonitrile/0.1M ammonium hydroxide (pH 10) mobile phase and a photodiode array detector set at 258 nm. The apparent linear range of the assay was from 0.05 to 5.0 microg/mL. At known concentrations of 0.1 and 0.5, interday accuracy (n = 5) was 103.8 and 107.2%, respectively. Interday precision (% cv) at the same concentrations was 9.8 and 9.0, respectively. In the cases where quetiapine was not considered to have contributed to the death, the postmortem concentrations in blood, liver, and bile ranged between 0.15 and 2.7 mg/L (n = 6), 1.3 and 9.5 mg/kg (n = 8), and 10 and 46 mg/L (n = 5), respectively. In the one case involving a quetiapine overdose, concentrations in blood (19.8 mg/L), liver (12.6 mg/kg), and bile (161 mg/L) exceeded the ranges of concentrations determined in specimens from the quetiapine-unrelated deaths.

Modeling the kinetics of enzymic reactions in mainly solid reaction mixtures.

There is currently considerable interest in using mainly solid reaction mixtures for enzymic catalysis. In these reactions starting materials dissolve into, and product materials crystalize out of, a small amount of liquid phase in which the catalytic reaction occurs. An initial mathematical model for mass transfer effects in such systems is constructed using some physically reasonable approximations. The model equations are solved numerically to determine how the reactant concentrations vary with time and position. To evaluate the extent to which mass transfer limits the overall rate of product formation, an effectiveness factor is defined as the ratio of the observed total reaction rate to the total reaction rate in the reaction limited limit. As expected, the value of the effectiveness factor in steady state is strongly dependent on the Thiele modulus. However, it is also observed that the effectiveness factor can vary widely as a result of changes in the other dimensionless groups characterizing the system. For example, there are situations with Thiele modulus equal to unity in which the value of the effectiveness factor varies between approximately 0.1 and 0.8 as the other parameters are varied in physically reasonable ranges. Analytical asymptotic solutions that provide good approximations to the numerically calculated results in various physically important limiting cases are also presented.