Robust Anti-Icing Surfaces Based on Dual Functionality─Microstructurally-Induced Ice Shedding with Superimposed Nanostructurally-Enhanced Water Shedding.

Research into anti-icing surfaces often conflates the two separate problems of ice accumulation: water adhesion and ice adhesion. The body feathers of perpetually ice-free penguins are very good natural examples of anti-icing surfaces, which use two different mitigation strategies for the two disparate problems. Herein, we mimic the form of the feather's wire-like structure, which is decorated with superimposed nanogrooves by laser micromachining fine woven wire cloths. Post-processing techniques also allow us to isolate the role of surface chemistry by creating both hydrophilic and hydrophobic versions of the synthetic anti-icing surfaces. Our results show that water-shedding and ice-shedding characteristics are indeed derived from different physical functions of the hierarchical structure. The microstructure of the woven wire cloth leads to facile interfacial cracking and therefore extremely low ice adhesion strengths; the superimposed laser-induced periodic surface structures with hydrophobic surface chemistry lead to water shedding. Our work shows that by first taking a fracture mechanics approach to designing the ice-shedding function, a robust anti-icing surface can be engineered by separately designing the water-shedding functions.

Leveraging Solidification Dynamics to Design Robust Ice-Shedding Surfaces.

The adhesion of ice to external surfaces is an important challenge in many industries. This has sparked much research into fabricating surfaces with low ice adhesion strengths. Our novel approach to designing ice-shedding surfaces leverages the dynamics of water solidification to induce beneficial stress concentrations throughout the iced interface. We have chosen a bare woven metal wire cloth substrate to demonstrate these principles. The pore geometries of the wire cloths lead to stress concentrations upon freezing and expansion of the water/ice, while their microstructural topography allows for facile crack opening. We have discovered that by leveraging knowledge of the underlying physical processes involved in ice formation and delamination, we can engineer a robust metal surface to have an extremely low ice adhesion strength (12.5 kPa) without using chemical coatings.

TinyLev acoustically levitated water: Direct observation of collective, inter-droplet effects through morphological and thermal analysis of multiple droplets.

HYPOTHESIS: Understanding the crystallization of atmospheric water can require levitation techniques to avoid the influence of container walls. Recently, an acoustic levitation device called the TinyLev was designed, which can levitate multiple droplets at room temperature. Proximal crystallization may affect droplet phase change and morphological characteristics. METHODOLOGY: In this study, acoustically levitated pure water droplets were frozen individually and in pairs or triplets using a TinyLev device. Nucleation, bulk crystal growth, and melting were observed using digital and infrared cameras concurrently. FINDINGS: Initially, the acoustic field forced the droplets into an oblate spheroid shape, though the counteracting force of the cooling stream caused them to circularize. Droplet geometry was thus the net result of streaming forces and surface tension at the acoustic boundary layer/air-liquid interface. Nucleation was determined to be neither homogeneous nor heterogeneous but secondary, and thus dependent on the cooling rate and not on the degree of supercooling. It was likely initiated by aerosolized ice particles from the air or from droplets that had already nucleated and broken up. The latter secondary ice production process resulted in multi-drop systems with statistically identical nucleation times. Notably, this meant that the presence of interfacial rupture at an adjacent droplet could influence the crystallization behaviour of another. After the formation of an initial ice shell around the individual droplets, dendritic protrusions grew from the droplet surface, likely seeded by the same ice particles that caused nucleation, but at a quasi-liquid layer. When freezing was complete, it was determined that the frozen core had undergone a volumetric expansion of 30.75%, compared to 9% for pure, sessile water expansion. This significantly greater expansion may have resulted from entrained air bubbles at the inner solid-liquid interface and oscillations at the moving phase boundary caused by changes in local acoustic forces. Soon after melting began, acoustic streaming, the buoyancy of the remaining ice, and convective currents caused by both an inner thermal gradient and thermocapillary effects along the air-liquid interface, all contributed to the droplet spinning about the horizontal axis.

A Practical Comparison of Beam Shuttering Technologies for Pulsed Laser Micromachining Applications.

In this report we investigate the performance of various beam shutter technologies when applied to femtosecond laser micromachining. Three different shutter options are considered: a mechanical blade shutter, a bistable rotary solenoid shutter, and an electro-optic modulator (EOM) shutter. We analyzed the behavior of each shutter type during repeated open/close commands (period of 10 ≤ T ≤ 200 ms) using both high-speed videography and practical micromachining experiments. To quantify the performance at varying cycle periods, we introduce a new variable called the compliance that characterizes the average state of the shutter with respect to its intended position. We found that the solenoid shutter responds poorly to sequential commands. The mechanical shutter provides reliable performance for cycled commands as short as T = 40 ms, but begins to lag significantly behind the control signal for T ≤ 20 ms. The EOM shutter provides the most precise and reliable performance, with an opening time of only 0.6 ms and a high compliance with the signal commands, even when cycled very quickly (T = 10 ms). Overall, this study acts as an extensive practical guide for other laser users when considering different shutter options for their laser system and desired application.

The Tuning of LIPSS Wettability during Laser Machining and through Post-Processing.

In this work, we investigate the fabrication of stainless-steel substrates decorated with laser-induced periodic surface structures (LIPSS) of both hydrophilic and hydrophobic wettability through different post-processing manipulation. In carrying out these experiments, we have found that while a CO2-rich atmosphere during irradiation does not affect final wettability, residence in such an atmosphere after irradiation does indeed increase hydrophobicity. Contrarily, residence in a boiling water bath will instead lead to a hydrophilic surface. Further, our experiments show the importance of removing non-sintered nanoparticles and agglomerates after laser micromachining. If they are not removed, we demonstrate that the nanoparticle agglomerates themselves become hydrophobic, creating a Cassie air-trapping layer on the surface which presents with water contact angles of 180°. However, such a surface lacks robustness; the particles are removed with the contacting water. What is left behind are LIPSS which are integral to the surface and have largely been blocked from reacting with the surrounding atmosphere. The actual surface presents with a water contact angle of approximately 80°. Finally, we show that chemical reactions on these metallic surfaces decorated with only LIPSS are comparatively slower than the reactions on metals irradiated to have hierarchical roughness. This is shown to be an important consideration to achieve the highest degree of hydro-philicity/phobicity possible. For example, repeated contact with water from goniometric measurements over the first 30 days following laser micromachining is shown to reduce the ultimate wettability of the surface to approximately 65°, compared to 135° when the surface is left undisturbed for 30 days.

Propagating and Debunking Conspiracy Theories on Twitter During the 2015-2016 Zika Virus Outbreak.

The present study investigates the characteristics of discussion of conspiracy theories about the Zika virus outbreak of 2015-16 on Twitter. Content and social network analysis of a dataset of 25,162 original Tweets about Zika virus conspiracy theories showed that relative to debunking messages, conspiracy theories spread through a more decentralized network, are more likely to invoke supposedly knowledgeable authorities in making arguments, and ask more rhetorical questions. These trends can be understood in the context of previous work on conspiracy theories, including the "just asking questions" style of rhetoric, the importance of sourcing and authority, and the tendency to simultaneously consider many different potential conspiracies that might underlie an important topic or event.

Conspiracy suspicions as a proxy for beliefs in conspiracy theories: Implications for theory and measurement.

Research on the psychology of conspiracy theories has shown recent steps towards a standardization of measures. The present article seeks to continue that trend by presenting the Flexible Inventory of Conspiracy Suspicions (FICS), a questionnaire template that can be adapted to measure suspicions of a conspiracy around nearly any topic of public interest. Compared to conspiracy belief measures that ask about specific theories on a given topic, the FICS is worded in such a way as to provide relatively stable validity across time and cultural context. Using a hybrid approach incorporating classical test theory and Rasch scaling, three questionnaire studies on Mechanical Turk demonstrate the validity of the FICS in measuring conspiracy suspicions regarding 9/11, vaccine safety, and US elections, with good psychometric properties in most situations. However, the utility of the FICS is limited in the case of climate change due to the existence of two opposing conspiracy theories that share essentially no common assumptions ('climate change is a hoax' vs. 'there is a conspiracy to make people believe that climate change is a hoax'). The results indicate that the FICS is a reliable and valid measure of conspiracy suspicions within certain parameters, and suggest a three-level model that differentiates general conspiracist ideation, relatively vague conspiracy suspicions, and relatively specific conspiracy beliefs.

Online communication as a window to conspiracist worldviews.

In spite of the social stigma surrounding them, conspiracy theories are a common topic of public debate on the Internet. The content and tone of these discussions provide a useful insight into the structure of conspiracist belief systems and the psychological characteristics of those who believe and disbelieve in conspiracy theories. In this focused review, we relate patterns of behavior found in online comments to the broader research literature on the psychology of conspiracy theories. Most notably, as conspiracism has its basis in disbelieving a mainstream or received narrative rather than in believing a specific alternative, most conspiracist arguments tend to fall along those same lines. Finally, we examine the implications of this methodology for future research into online discussion, particularly among hard-to-research populations.

"What about building 7?" A social psychological study of online discussion of 9/11 conspiracy theories.

Recent research into the psychology of conspiracy belief has highlighted the importance of belief systems in the acceptance or rejection of conspiracy theories. We examined a large sample of conspiracist (pro-conspiracy-theory) and conventionalist (anti-conspiracy-theory) comments on news websites in order to investigate the relative importance of promoting alternative explanations vs. rejecting conventional explanations for events. In accordance with our hypotheses, we found that conspiracist commenters were more likely to argue against the opposing interpretation and less likely to argue in favor of their own interpretation, while the opposite was true of conventionalist commenters. However, conspiracist comments were more likely to explicitly put forward an account than conventionalist comments were. In addition, conspiracists were more likely to express mistrust and made more positive and fewer negative references to other conspiracy theories. The data also indicate that conspiracists were largely unwilling to apply the "conspiracy theory" label to their own beliefs and objected when others did so, lending support to the long-held suggestion that conspiracy belief carries a social stigma. Finally, conventionalist arguments tended to have a more hostile tone. These tendencies in persuasive communication can be understood as a reflection of an underlying conspiracist worldview in which the details of individual conspiracy theories are less important than a generalized rejection of official explanations.

Temporal characteristics of overt attentional behavior during category learning.

Many theories of category learning incorporate mechanisms for selective attention, typically implemented as attention weights that change on a trial-by-trial basis. This is because there is relatively little data on within-trial changes in attention. We used eye tracking and mouse tracking as fine-grained measures of attention in three complex visual categorization tasks to investigate temporal patterns in overt attentional behavior within individual categorization decisions. In Experiments 1 and 2, we recorded participants' eye movements while they performed three different categorization tasks. We extended previous research by demonstrating that not only are participants less likely to fixate irrelevant features, but also, when they do, these fixations are shorter than fixations to relevant features. We also found that participants' fixation patterns show increasingly consistent temporal patterns. Participants were faster, although no more accurate, when their fixation sequences followed a consistent temporal structure. In Experiment 3, we replicated these findings in a task where participants used mouse movements to uncover features. Overall, we showed that there are important temporal regularities in information sampling during category learning that cannot be accounted for by existing models. These can be used to supplement extant models for richer predictions of how information is attended to during the buildup to a categorization decision.

Informed inferences of unknown feature values in categorization.

Many current computational models of object categorization either include no explicit provisions for dealing with incomplete stimulus information (e.g. Kruschke, Psychological Review 99:22-44, 1992) or take approaches that are at odds with evidence from other fields (e.g. Verguts, Ameel, & Storms, Memory & Cognition 32:379-389, 2004). In two experiments centered around the inverse base-rate effect, we demonstrate that people not only make highly informed inferences about the values of unknown features, but also subsequently use the inferred values to come to a categorization decision. The inferences appear to be based on immediately available information about the particular stimulus under consideration, as well as on higher-level inferences about the stimulus class as a whole. Implications for future modeling efforts are discussed.

Mucosal serotonin signaling is altered in chronic constipation but not in opiate-induced constipation.

OBJECTIVES: Changes in mucosal serotonin (5-HT) signaling have been detected in a number of functional and inflammatory disorders of the gastrointestinal (GI) tract. This study was undertaken to determine whether chronic constipation (CC) is associated with disordered 5-HT signaling and to evaluate whether constipation caused by opiate use causes such changes. METHODS: Human rectal biopsy samples were obtained from healthy volunteers, individuals with idiopathic CC, and individuals taking opiate medication with or without occurrence of constipation. EC cells were identified by 5-HT immunohistochemistry. 5-HT content and release levels were determined by enzyme immunoassay, and mRNA levels for the synthetic enzyme tryptophan hydroxylase-1 (TpH-1) and serotonin-selective reuptake transporter (SERT) were assessed by quantitative real-time reverse transcription PCR. RESULTS: CC was associated with increases in TpH-1 transcript, 5-HT content, and 5-HT release under basal and stimulated conditions, whereas EC cell numbers and SERT transcript levels were not altered. No changes in these elements of 5-HT signaling were detected in opiate-induced constipation (OIC). CONCLUSIONS: These findings demonstrate that CC is associated with a pattern of altered 5-HT signaling that leads to increased 5-HT availability but does not involve a decrease in SERT expression. It is possible that increased 5-HT availability due to increased synthesis and release contributes to constipation due to receptor desensitization. Furthermore, the finding that elements of 5-HT signaling were not altered in the mucosa of individuals with OIC indicates that constipation as a condition does not lead to compensatory changes in 5-HT synthesis, release, or signal termination.

The effects of daikenchuto (DKT) on propulsive motility in the colon.

BACKGROUND: The purpose of this study is to examine the use of daikenchuto (DKT), a traditional Japanese medicine, as a potential treatment for opiate-induced slowing of intestinal transit in an isolated guinea pig colon model of motility. METHODS: Isolated segments of distal guinea pig colon were mounted in a perfusion chamber and imaged with a digital video camera interfaced with a computer. Fecal pellets were inserted into the oral end of the colonic segment and the rates of propulsive motility over a 3 to 4 cm segment of colon were determined in the presence and absence of test compounds. In addition, intracellular recordings were obtained from intact circular muscle, and the responsiveness of inhibitory and excitatory junction potentials to DKT was evaluated. RESULTS: The addition of D-Ala2, N-Me-Phe4, Gly-ol5 (DAMGO), a selective µ-receptor agonist, caused a concentration dependent decrease in colon motility. Naloxone did not affect basal activity, but partially restored motility in the DAMGO treated preparations. DKT (1 × 10(-4)-3 × 10(-4)g/mL) also reversed the inhibitory effect of DAMGO treated colon in a concentration dependent manner. At higher concentrations (1 × 10(-3)-3 × 10(-3)g/mL), however, this effect was lost. Motility slowed even further when naloxone and DKT were combined with noticeable disruptions in spatiotemporal patterns. Interestingly, when added alone, DKT resulted in reverse peristalsis of the pellet. In electrophysiologic studies DKT inhibited both excitatory and inhibitory junction potentials. CONCLUSIONS: DKT appears to be as effective as naloxone in restoring motility in DAMGO treated colon. These two agents, however, do not appear to have an additive effect. When used on untreated colon segments, DKT appears to cause disruptions in the intrinsic reflex circuit of the gut resulting in a disruption of neuromuscular communication.

Catastrophic Clostridium difficile enteritis in a pelvic pouch patient: report of a case.

INTRODUCTION: In recent years, Clostridium difficile-associated infection has emerged as an increasingly problematic entity. More virulent strains have been isolated and new manifestations of the infection have been described. PURPOSE: The primary aim of this manuscript is to describe what we believe to be the first reported case of devastating C. difficile enteritis in a patient with an ileal reservoir. CONCLUSION: A high index of suspicion is required in the appropriate clinical setting in light of the apparently changing spectrum of C. difficile disease.

Control of outer vestibule dynamics and current magnitude in the Kv2.1 potassium channel.

In Kv2.1 potassium channels, changes in external [K+] modulate current magnitude as a result of a K+-dependent interconversion between two outer vestibule conformations. Previous evidence indicated that outer vestibule conformation (and thus current magnitude) is regulated by the occupancy of a selectivity filter binding site by K+. In this paper, we used the change in current magnitude as an assay to study how the interconversion between outer vestibule conformations is controlled. With 100 mM internal K+, rapid elevation of external [K+] from 0 to 10 mM while channels were activated produced no change in current magnitude (outer vestibule conformation did not change). When channels were subsequently closed and reopened in the presence of elevated [K+], current magnitude was increased (outer vestibule conformation had changed). When channels were activated in the presence of low internal [K+], or when K+ flow into conducting channels was transiently interrupted by an internal channel blocker, increasing external [K+] during activation did increase current magnitude (channel conformation did change). These data indicate that, when channels are in the activated state under physiological conditions, the outer vestibule conformation remains fixed despite changes in external [K+]. In contrast, when channel occupancy is lowered, (by channel closing, an internal blocker or low internal [K+]), the outer vestibule can interconvert between the two conformations. We discuss evidence that the ability of the outer vestibule conformation to change is regulated by the occupancy of a nonselectivity filter site by K+. Independent of the outer vestibule-based potentiation mechanism, Kv2.1 was remarkably insensitive to K+-dependent processes that influence current magnitude (current magnitude changed by <7% at membrane potentials between -20 and 30 mV). Replacement of two outer vestibule lysines in Kv2.1 by smaller neutral amino acids made current magnitude dramatically more sensitive to the reduction in K+ driving force (current magnitude changed by as much as 40%). When combined, these outer vestibule properties (fixed conformation during activation and the presence of lysines) all but prevent variation in Kv2.1 current magnitude when [K+] changes during activation. Moreover, the insensitivity of Kv2.1 current magnitude to changes in K+ driving force promotes a more uniform modulation of current over a wide range of membrane potentials by the K+-dependent regulation of outer vestibule conformation.