Low Tilt Research Articles

Mechanically durable liquid-impregnated honeycomb surfaces

Liquid repellent surfaces typically work by keeping the fouling liquid in a metastable state, with trapped pockets of air between the substrate and the liquid. An alternative method with greater long-term stability utilizes liquid-impregnated surfaces, where the liquid being repelled slides over an immiscible liquid immobilized on a porous surface. Here, we report a method for creating honeycomb surfaces amenable to liquid-impregnation. Polystyrene dissolved in a water-immiscible, volatile solvent was deposited in a humid environment on a variety of substrates to achieve the necessary porosity. Evaporative cooling results in condensation of water in a breath figure array of droplets, forming a sacrificial template for the drying polymer film. These honeycomb surfaces were further functionalized with fluorosilane and dipped in the lubricating liquid to result in a durable, liquid-repellent surface. These surfaces were found to exhibit repellency towards water and oils with extremely low tilt angles due to the smooth liquid–liquid contact between the lubricating liquid and the liquid being repelled.

Dynamic Defrosting on Scalable Superhydrophobic Surfaces.

Recent studies have shown that frost can grow in a suspended Cassie state on nanostructured superhydrophobic surfaces. During defrosting, the melting sheet of Cassie frost spontaneously dewets into quasi-spherical slush droplets that are highly mobile. Promoting Cassie frost would therefore seem advantageous from a defrosting standpoint; however, nobody has systematically compared the efficiency of defrosting Cassie ice versus defrosting conventional surfaces. Here, we characterize the defrosting of an aluminum plate, one-half of which exhibits a superhydrophobic nanostructure while the other half is smooth and hydrophobic. For thick frost sheets (>1 mm), the superhydrophobic surface was able to dynamically shed the meltwater, even at very low tilt angles. In contrast, the hydrophobic surface was unable to shed any appreciable meltwater even at a 90° tilt angle. For thin frost layers (≲1 mm), not even the superhydrophobic surface could mobilize the meltwater. We attribute this to the large apparent contact angle of the meltwater, which for small amounts of frost serves to minimize coalescence events and prevent droplets from approaching the capillary length. Finally, we demonstrate a new mode of dynamic defrosting using an upside-down surface orientation, where the melting frost was able to uniformly detach from the superhydrophobic side and subsequently pull the frost from the hydrophobic side in a chain reaction. Treating surfaces to enable Cassie frost is therefore very desirable for enabling rapid and low-energy thermal defrosting, but only for frost sheets that are sufficiently thick.

Coronal and heliospheric magnetic flux circulation and its relation to open solar flux evolution.

Solar cycle 24 is notable for three features that can be found in previous cycles but which have been unusually prominent: (1) sunspot activity was considerably greater in the northern/southern hemisphere during the rising/declining phase; (2) accumulation of open solar flux (OSF) during the rising phase was modest, but rapid in the early declining phase; (3) the heliospheric current sheet (HCS) tilt showed large fluctuations. We show that these features had a major influence on the progression of the cycle. All flux emergence causes a rise then a fall in OSF, but only OSF with foot points in opposing hemispheres progresses the solar cycle via the evolution of the polar fields. Emergence in one hemisphere, or symmetric emergence without some form of foot point exchange across the heliographic equator, causes poleward migrating fields of both polarities in one or both (respectively) hemispheres which temporarily enhance OSF but do not advance the polar field cycle. The heliospheric field observed near Mercury and Earth reflects the asymmetries in emergence. Using magnetograms, we find evidence that the poleward magnetic flux transport (of both polarities) is modulated by the HCS tilt, revealing an effect on OSF loss rate. The declining phase rise in OSF was caused by strong emergence in the southern hemisphere with an anomalously low HCS tilt. This implies the recent fall in the southern polar field will be sustained and that the peak OSF has limited implications for the polar field at the next sunspot minimum and hence for the amplitude of cycle 25.

Nematic fluctuations balancing the zoo of phases in half-filled quantum Hall systems

Half-filled Landau levels form a zoo of strongly correlated phases. These include non-Fermi liquids (NFL), fractional quantum Hall (FQH) states, nematic phases, and FQH nematic phases. This diversity poses the question: what keeps the balance between the seemingly unrelated phases? The answer is elusive because the Halperin-Lee-Read (HLR) description that offers a natural departure point is inherent strongly coupled. But the observed nematic phases suggest nematic fluctuations play an important role. To study this possibility, we apply a recently formulated controlled double expansion approach in large-$N$ composite fermion flavors and small $\epsilon$ non-analytic bosonic action to the case with both gauge and nematic boson fluctuations. In the vicinity of a nematic quantum critical line (NQCL), we find that depending on the amount of screening of the gauge- and nematic-mediated interactions controlled by $\epsilon$'s, the RG flow points to all four mentioned correlated phases. When pairing preempts the nematic phase, NFL behavior is possible at temperatures above the pairing transition. We conclude by discussing measurements at low tilt angles which could reveal the stabilization of the FQH phase by nematic fluctuations.

Field stabilization of Alvarez-type cavities

Alvarez-type cavities are commonly used to reliably accelerate high quality hadron beams. Optimization of their longitudinal field homogeneity is usually accomplished by post-couplers, i.e. additional rods being integrated into the cavity. This paper instead proposes to use the stems that keep the drift tubes for that purpose. As their individual azimuthal orientations do not change the cavity's undisturbed operational mode, they comprise a set of free parameters that can be used to modify higher mode field patterns. The latter have significant impact on the robustness of the operational mode w.r.t. eventual perturbations. Several optimized stem configurations are presented and benchmarked against each other. The path to obtain these configurations is paved analytically and worked out in detail through simulations. It is shown that the method provides for flat field distributions and very low field tilt sensitivities without insertion of post-couplers.

Tilt grain boundaries energy and structure in NiTi alloys

Energy and structure of tilt grain boundaries are studied in Nickel-Titanium (NiTi) alloys. Molecular dynamics (MD) simulations are utilized to investigate the excess energy of symmetric and asymmetric tilt grain boundaries as a function of the misorientation and inclination angles. Structural units of different symmetric grain boundaries are identified and the correlation between the structure and energy is investigated. It is shown that the Read-Shokley model can accurately predict the energy of low angle symmetric tilt grain boundaries in austenite NiTi alloy. Density functional theory (DFT) calculations are used to study two representative symmetric grain boundaries. Comparing to DFT calculations, it is shown that the MD results can predict the GB potential energies accurately. The Electron charge density distributions are studied and the bonding strength between atoms, and low/high charge density regions are investigated, and accosted with the structural units in the grain boundaries. It is shown that a symmetric arrangement of Ni and Ti atoms at the GB improved the uniformity of bonding and charge density distribution.

Are sagittal spinopelvic radiographic parameters significantly associated with quality of life of adult spinal deformity patients? Multivariate linear regression analyses for pre-operative and short-term post-operative health-related quality of life.

To evaluate the association in ASD patients between spinopelvic sagittal parameters and health-related quality of life (HRQL), adjusted for demographic and surgical variables. We constructed multiple linear regression models to investigate pre-operative (PreOp) and 6-month post-operative (PostOp) HRQL as assessed by the Oswestry Disability Index (ODI), with sagittal parameters as independent variables adjusted for potential confounders, such as age, sex, body mass index, past spine surgery, types of surgical treatment, and complications. A total of 204 patients (164 women, 40 men, mean age 53.1years) were included in this study. In multivariate models for PreOp ODI, no significant association was observed between PreOp HRQL and sagittal parameters when adjusted for covariates. Interestingly, age, sex, American Society of Anesthesiologists score, and body mass index were still significantly associated with PreOp HRQL. In contrast to PreOp analysis, there was a significant association between PostOp worse HRQL (higher ODI) and positive T1 sagittal tilt (T1ST: the angle between a line drawn from the center of the femoral head axis to the midpoint of the T1 vertebral body and a vertical line). Sagittal vertical axis had a weaker association with HRQL than T1ST. PostOp ASD patients lose flexibility in the fused spinal segment, and might be predisposed to symptoms related to spinal sagittal malalignment due to limited compensatory ability to maintain a balanced standing posture. Interestingly, in patients with sagittal imbalance, low pelvic tilt (PT) of<20 was significantly associated with PostOp worse HRQL; this suggests that lack of pelvic compensatory ability can cause significant disability after ASD surgery. Pre-operatively, the impact of sagittal parameters on HRQL was not as strong as reported in the previous studies that used univariate analysis. Not only sagittal parameters, but also the pre-operative patient's general condition should be carefully reviewed when considering indication for ASD surgery. In contrast, although this is a short-term follow-up study, PostOp HRQL was significantly associated with sagittal parameters. When ASD surgery has been indicated, restoration of spinal sagittal alignment is certainly important for PostOp HRQL.

Liquid-impregnated porous polypropylene surfaces for liquid repellency

Polypropylene is a popular plastic material used in consumer packaging. It would be desirable if such plastic containers were liquid repellent and not so easily fouled by their contents. Superomniphobic surfaces typically work by keeping the fouling liquid in a metastable state, with trapped pockets of air between the substrate and the liquid. An alternative method with greater long-term stability utilizes liquid-impregnated surfaces, where the liquid being repelled slides over an immiscible liquid immobilized on a porous surface. Here, we report a method for creating porous polypropylene surfaces amenable to liquid-impregnation. A solvent–nonsolvent polypropylene solution was deposited at high temperature to achieve the necessary porosity. Such surfaces were further functionalized with fluorosilane and dipped in the lubricating liquid to result in a durable, liquid-repellent surface. It is believed these liquid-impregnated surfaces will be more industrially viable than previous examples due to the ease of fabrication and their durability. These surfaces were found to exhibit repellency towards water, oils, shampoo, and laundry detergent with extremely low tilt angles due to the smooth liquid–liquid contact between the lubricating liquid and the liquid being repelled.

Methodology for finding and evaluating safe landing sites on small bodies

Here we develop and demonstrate a three-step strategy for finding a safe landing ellipse for a legged spacecraft on a small body such as an asteroid or planetary satellite. The first step, acquisition of a high-resolution terrain model of a candidate landing region, is simulated using existing statistics on block abundances measured at Phobos, Eros, and Itokawa. The synthetic terrain model is generated by randomly placing hemispheric shaped blocks with the empirically determined size-frequency distribution. The resulting terrain is much rockier than typical lunar or martian landing sites. The second step, locating a landing ellipse with minimal hazards, is demonstrated for an assumed approach to landing that uses Autonomous Landing and Hazard Avoidance Technology. The final step, determination of the probability distribution for orientation of the landed spacecraft, is demonstrated for cases of differing regional slope. The strategy described here is both a prototype for finding a landing site during a flight mission and provides tools for evaluating the design of small-body landers. We show that for bodies with Eros-like block distributions, there may be >99% probability of landing stably at a low tilt without blocks impinging on spacecraft structures so as to pose a survival hazard.

Interferometric Fiber-Optic Tilt Sensor Exploiting Taper and Lateral-Offset Fusing Splicing

An ultra-sensitive and low cost optical fiber interferometric tilt sensor has been proposed and experimentally demonstrated. The tilt sensor was based on a taper and lateral-offset fusion splicing. The interference spectra of the proposed sensor under different tilt angles and directions have been measured and theoretically analyzed. Due to the asymmetrical configuration, the proposed device is orientation-dependent, and the tilt angle sensitivity reaches up to 1.15 nm/deg with the $R^{2}$ value of 0.9931 no matter the sensor is operated in the $- \theta $ or $+ \theta $ directions. Therefore, it will be a promising candidate for civil engineering, aviation industry, and automobile industry, especially, for the applications where a high sensitivity is required in a small measurement range.

From Sponges to Nanotubes: A Change of Nanocrystal Morphology for Acute‐Angle Bent‐Core Molecules

AbstractThe crystalline (B4) phase made of acute‐angle bent‐core molecules (1,7‐naphthalene derivatives), which exhibits an unusual, highly porous sponge‐like morphology, is presented. However, if grown in the presence of low‐weight mesogenic molecules, the same crystal forms nanotubes with a very high aspect ratio. The nanotubes become unstable upon increasing the amount of dopant molecules, and the sponge‐like morphology reappears. The phase is optically active, and the optical activity is an order of magnitude smaller than in the B4 phase made of conventional bent‐core molecules. The optical activity is related to the spatial inhomogeneity of the layered structure and is reduced due to the low apex angle and low tilt of the molecules. The arrangement of molecules within the layers was deduced from the bathochromic absorption shift in the B4 phase.

From Sponges to Nanotubes: A Change of Nanocrystal Morphology for Acute‐Angle Bent‐Core Molecules

The crystalline (B4 ) phase made of acute-angle bent-core molecules (1,7-naphthalene derivatives), which exhibits an unusual, highly porous sponge-like morphology, is presented. However, if grown in the presence of low-weight mesogenic molecules, the same crystal forms nanotubes with a very high aspect ratio. The nanotubes become unstable upon increasing the amount of dopant molecules, and the sponge-like morphology reappears. The phase is optically active, and the optical activity is an order of magnitude smaller than in the B4 phase made of conventional bent-core molecules. The optical activity is related to the spatial inhomogeneity of the layered structure and is reduced due to the low apex angle and low tilt of the molecules. The arrangement of molecules within the layers was deduced from the bathochromic absorption shift in the B4 phase.

Studies of Parylene C Microfibrous Thin Films Electrical Properties

We have fabricated and measured the room-temperature capacitance in metal-insulator-metal (MIM) structures utilizing the Parylene C films as the insulators in the frequency range 1 kHz to 1 MHz. The Parylene-C films were of variable thicknesses and were either spin-on dense films or columnar microfibrous thin films (μFTFs) grown using oblique angle physicochemical vapor deposition. The values of the vapor tilt angle, χv, used were 30°, 60°, or 90°. Expectedly, columnar microfibrous thin film of Parylene C is observed to have lower values of k than the dense one. However, it is observed that the dielectric constant of the μFTFs is increased with increasing deposition tilt angle χv. This is explained in terms of film porosity as a function of χv, which is enhanced in films deposited at lower tilt angles. The dependence of k on measurement frequency suggests that molecular dipole effects dominate charge polarization in the films.

Tuning the wetting properties of siloxane-nanoparticle coatings to induce superhydrophobicity and superoleophobicity for stone protection

A water soluble siloxane emulsion enriched with silica nanoparticles (7nm) is sprayed on white marble and sandstone without the use of any organic solvent. A continuous rough structure, composed of numerous micro/nano structures, is formed at low nanoparticle concentration. Drops of water, glycerol, ethylene glycol and oil on coatings, which were prepared using siloxane and 2% w/w nanoparticles correspond to high static contact angles (>150o). Moreover, water and oil drops correspond to low tilt contact angles (<7o).SEM shows that the continuous structure collapses when high nanoparticle concentration (>2% w/w) is used for the production of the coatings, as large grooves are formed. These grooves have no significant effect on the contact angles of water and glycerol drops which correspond to high surface tensions. However, the grooves are responsible for a transition from the above described Cassie-Baxter state to the Wenzel state, which was observed for ethylene glycol and oil drops, that are liquids of low surface tensions.The evaporation of water drops on structured coatings prepared using siloxane and 2% w/w nanoparticles is monitored. It is shown that a set of stick-slip events of the contact line, accompanied by a decrease in contact angle, dominates the evaporation process.

Implementation of a cryo-electron tomography tilt-scheme optimized for high resolution subtomogram averaging.

Cryo-electron tomography (cryoET) allows 3D structural information to be obtained from cells and other biological samples in their close-to-native state. In combination with subtomogram averaging, detailed structures of repeating features can be resolved. CryoET data is collected as a series of images of the sample from different tilt angles; this is performed by physically rotating the sample in the microscope between each image. The angles at which the images are collected, and the order in which they are collected, together are called the tilt-scheme. Here we describe a “dose-symmetric tilt-scheme” that begins at low tilt and then alternates between increasingly positive and negative tilts. This tilt-scheme maximizes the amount of high-resolution information maintained in the tomogram for subsequent subtomogram averaging, and may also be advantageous for other applications. We describe implementation of the tilt-scheme in combination with further data-collection refinements including setting thresholds on acceptable drift and improving focus accuracy. Requirements for microscope set-up are introduced, and a macro is provided which automates the application of the tilt-scheme within SerialEM.

The Optic Nerve Head in Primary Open-Angle Glaucoma Eyes With High Myopia: Characteristics and Association With Visual Field Defects.

To evaluate the morphologic characteristics of optic neuropathy and its association with visual field (VF) defects in primary open-angle glaucoma (POAG) eyes with high myopia. In this cross-sectional study, we reviewed data from 375 Taiwanese patients (375 eyes) of POAG, ages 20 to 60 years. Optic disc photographs were used for planimetric measurements of morphologic variables. The myopic refraction was divided into high myopia (<-6.0 D) and nonhigh myopia (moderate myopia to hyperopia). The optic disc area was classified as moderate (1.59 to 2.85 mm(2)), large, and small. Differences in characteristics between groups, correlations with the disc area, and factors associated with VF defects were determined. Of the 142 highly myopic eyes, 33 (23%) had a large disc, 26 (18%) had a small disc, and 55 (39%) had a tilted disc. Large discs had a higher cup-to-disc (C/D) area ratio and a higher tilt ratio; small discs had a smaller rim area and a lower tilt ratio (all P<0.05). Characteristics associated with high myopia included a smaller rim area, a higher C/D area ratio, and a lower tilt ratio (all P<0.001). In logistic regression, the refraction, the C/D area ratio, the rim area, and the tilt ratio (all P<0.05) were associated with VF defects. In Taiwanese individuals with POAG, our study found that tilted, large, or small discs were prevalent in highly myopic eyes. Of these characteristics, only the disc tilt and high myopia by itself were associated with the severity of glaucomatous optic neuropathy.

Impact of inverter loading ratio on solar photovoltaic system performance

Due to decreasing solar module prices, some solar developers are increasing their projects’ inverter loading ratio (ILR), defined as the ratio of DC module capacity to AC inverter capacity. In this study, we examine the operational impacts of this trend. Using minute-level solar data, we examine the relationship between inverter induced clipping losses and AC generation. We find minimal clipping losses at an ILR of 1.25; at an ILR of 2.0, we observe that 16% of potential annual generation is lost. Minute-level data prove to be essential in determining the generation lost to clipping, as hourly data mask key clipping and ramping events. Higher ILRs lead to a greater frequency of time spent at maximum generation, but also a greater frequency and magnitude of large solar ramping events. Module degradation can attenuate the impacts of inverter clipping over time. We observe that the effective degradation rate (net of any changes to inverter clipping losses) can be as little as half the actual degradation rate for projects with high ILRs. The diurnal and seasonal trends in clipping correspond with solar insolation patterns, with the highest clipping occurring around noon. For fixed tilt installations with tilt angles at latitude, we observe the highest clipping near the autumnal and vernal equinoxes. Increasing the tilt angle leads to more winter clipping, while lower tilt angles shifts the clipping to summer months. Shifting from fixed tilt to north–south single axis tracking increases the generation lost to clipping significantly. At an ILR of 1.25, annual clipping approximately doubles to 1% compared to fixed tilt at latitude, while clipping under an ILR of 2.0 increases to 22%, compared to 16% for the fixed configuration. As expected, more clipping occurs during the hours preceding and following noon when using single axis tracking.

Finite temperature effect on mechanical properties of graphene sheets with various grain boundaries**Project supported by the Nation Natural Science Foundation of China (Grant Nos. 11347219 and 11404147), the Natural Science Foundation of Jiangsu Province, China (Grant No. BK20140519), the Training Project of Young Backbone Teacher of Jiangsu University, the Advanced Talents of Jiangsu University, China (Grant No. 11JDG118), the Practice

The mechanical properties of graphene sheets with various grain boundaries are studied by molecular dynamics method at finite temperatures. The finite temperature reduces the ultimate strengths of the graphenes with different types of grain boundaries. More interestingly, at high temperatures, the ultimate strengths of the graphene with the zigzag-orientation grain boundaries at low tilt angles exhibit different behaviors from those at lower temperatures, which is determined by inner initial stress in grain boundaries. The results indicate that the finite temperature, especially the high one, has a significant effect on the ultimate strength of graphene with grain boundaries, which gives a more in-depth understanding of their mechanical properties and could be useful for potential graphene applications.

Effect of Janus particle concentration on water-repellent finish of textile fabric

The surface of poly(ethylene terephthalate) (PET) filament fabric was modified with Janus Particles (Jps) for water-repellency property. Jps were characterized with zeta potential measurement, fluorescent microscopy and X-ray photoelectron spectroscopy. The hydrophilic part of Jps bound to the activated PET filament surface and hydrophobic part of Janus faced the environment. The wetting and morphology of modified polyester surface were investigated with scanning electronic microscope and DAT 1100-FIBRO System and DAT 1129 Tilt Table. It was found that with the increase in the concentration of Jps, modified surface showed higher water contact angle and lower tilt angle. From the surface morphology it was also noticed that higher concentration of Jps gave raspberry-like aggregations on modified filament textile surface. Finally it was demonstrated that highest concentration (20 wt. %) of Jps was very efficient for the design of water-repellent textile fabric.

Superhydrophobic, superoleophobic coatings for the protection of silk textiles

Abstract The fabrication of protective coatings on silk with special properties is presented. A water soluble siloxane emulsion enriched with silica nanoparticles (7 nm) is sprayed on silk, without the use of any organic solvent. By adjusting the nanoparticle concentration, treated silk obtains (i) superhydrophobic and superoleophobic properties, as evidenced by the high static contact angles of water and oil droplets (>150°) and (ii) water and oil repellent properties, as supported by the corresponding low tilt contact angles (