Revisiting mechanics of ice–skate friction : from experiments at a skating rink to a unified hypothesis

The mechanics underlying ice–skate friction remain uncertain despite over a century of study. In the 1930s, the theory of self-lubrication from frictional heat supplanted an earlier hypothesis that pressure melting governed skate friction. More recently, researchers have suggested that a layer of abraded wear particles or the presence of quasi-liquid molecular layers on the surface of ice could account for its slipperiness. Here, we assess the dominant hypotheses proposed to govern ice– skate friction and describe experiments conducted in an indoor skating rink aimed to provide observations to test these hypotheses. Our results indicate that the brittle failure of ice under rapid compression plays a strong role. Our observations did not confirm the presence of full contact water films and are more consistent with the presence of lubricating ice-rich slurries at discontinuous high-pressure zones (HPZs). The presence of ice-rich slurries supporting skates through HPZs merges pressure-melting, abrasion and lubricating films as a unified hypothesis for why skates are so slippery across broad ranges of speeds, temperatures and normal loads. We suggest tribometer experiments to overcome the difficulties of investigating these processes during actual skating trials.

Competition Between Red Blood Cell Aggregation and Breakup: Depletion Force due to Filamentous Viruses vs. Shear Flow

Human blood is a shear-thinning fluid with a complex response that strongly depends on the red blood cell’s (RBC’s) ability to form aggregates, called rouleaux. Despite numerous investigations, microscopic understanding of the break up of RBC aggregates has not been fully elucidated. Here, we present a study of breaking up aggregates consisting of two RBCs (a doublet) during shear flow. We introduce the filamentous fd bacteriophage as a rod-like depletant agent with a very long-range interaction force, which can be tuned by the rod’s concentration. We visualize the structures while shearing by combining a home-build counter-rotating cone-plate shear cell with microscopy imaging. A diagram of dynamic states for shear rates versus depletant concentration shows regions of different flow responses and separation stages for the RBCs doublets. With increasing interaction forces, the full-contact flow states dominate, such as rolling and tumbling. We argue that the RBC doublets can only undergo separation during tumbling motion when the angle between the normal of the doublets with the flow direction is within a critical range. However, at sufficiently high shear rates, the time spent in the critical range becomes too short, such that the cells continue to tumble without separating.

Study of peculiarities of intra- and postoperative state of the interface «intraocular lens - posterior capsule» in phacoemulsification of senile cataract

Presence of full contact of interface «intraocular lens (IOL) – posterior capsule (PC)» ensures the transparency of the latter in the early period after phacoemulsification (PE) of senile cataract (SC). The main reasons for absence of full contact of IOL with PC are: the presence of residuals of viscoelastic (VE) in the capsular bag, uneven tension of the capsule by the haptic elements of the IOL, and the incommensurability of the size of the IOL with the capsule. Purpose. To study the features of the intra- and postoperative state of interface «IOL – PC» during PE SC. Material and methods. Dynamic observation of 42 patients (42 eyes), who operated on immature senile cataracts, was carried out. All operations were performed using OPMI LUMERA 700 surgical microscope (Carl Zeiss Meditec AG, Jena, Germany) with integrated intra-operative OCT, state of interface «IOL – PC» was examined. 2 hours after and on the 1st day after the operation state of interface «IOL – PC» was studied in all eyes by OCT on Optovue RTVue-100 (Optovue, Inc., US) with module for anterior segment examining to protocols «Cornea Line» and «Cornea Cross Line». Results. During the operation, the presence of contact between IOL and PC was observed only in 9 eyes (21.4%). 2 hours after surgery, 40 eyes (95.2%) had absence of contact between lens and capsule. On the 1st day after surgery, the optimal interface between IOL and PC was observed in 32 eyes (76.2%). Conclusion. Studies have shown that state of interface «IOL – PC» on the 1st day does not depend on its characteristics revealed intraoperative and 2 hours after the operation. The main reason for absence of contact between IOL and PC is residues of VE, and the using «impulse-irrigation» technique allows completely removing VE from the central zone of the capsule in all cases. Key words: cataract, phacoemulsification, intraocular lens, lens capsule, viscoelastic, interface «IOL – PC».

Investigation of operational characteristics of axial displacement guides for thermal expansion systems of steam turbines

ТНЕ PURPOSE. To carry out a comparative analysis of the performance characteristics of the longitudinal movement guides of the external bearing housings of steam turbines, using the principle of rotation to ensure full contact of their lateral surfaces with the lateral surfaces of the guide groove at the base of the external bearing housing of the steam turbine. Compare the manufacturability of elements and their implementation for both existing and newly developed steam turbines .METHODS. The permissible transverse forces are determined from the strength conditions and compared for the traditional design of fixed longitudinal guides and the design of guides, in which the principle of rotation is used to avoid "biting" of the bearing housing on the guides when temperature misalignment appears along the flanges of the turbine cylinder. Also, the allowable forces are determined and compared from the condition of the absence of plastic deformations in any of the elements of the interface of the guides, the base frame and the bearing housing. Based on the results obtained, the value of the permissible temperature misalignment along the flanges of the turbine cylinder is estimated. The analysis was carried out in relation to the operating conditions of the front bearing housing and HPC of turbines of the T 100/120-130 UTZ family.RESULTS. It has been established that all the considered designs of guides with pivoting elements make it possible to exclude the occurrence of plastic deformations in the junction of the base frame and the outboard bearing housing at a temperature misalignment of 20°C regulated in most turbine operating instructions. CONCLUSION. The design of longitudinal keys proposed by UTZ does not require a change in the technology for manufacturing the foundation frames and allows the unit to be modernized during repairs in a CHP. The best performance disc guide design can be used in new turbine designs or factory retrofits.

Predictors and Correlates of Perceived Cognitive Decline in Retired Professional Rugby League Players

Objective: Rugby league is an international full-contact sport, with frequent concussive injuries. Participation in other full-contact sports such as American football has been considered to be a risk factor for neuropsychiatric sequelae later-in-life, but little research has addressed the mental and cognitive health of retired professional rugby league players. We examined predictors and correlates of perceived (self-reported) cognitive decline in retired National Rugby League (NRL) players.Methods: Participants were 133 retired male elite level rugby league players in Australia. Participants completed clinical interviews, neuropsychological testing, and self-report measures. The Informant Questionnaire on Cognitive Decline in the Elderly, self-report (IQCODE-Self), measured perceived cognitive decline.Results: The median age of the sample was 55.0 (M = 53.1, SD = 13.9, range = 30–89) and the median years of education completed was 12.0 (M = 11.9, SD = 2.6, range = 7–18). The retired players reported a median of 15.0 total lifetime concussions (M = 28.0, SD = 36.6, range = 0–200). The mean IQCODE-Self score was 3.2 (SD = 0.5; Range = 1.3–5.0); 10/133 (7.5%) and 38/133 (28.6%) scored above conservative and liberal cutoffs for cognitive decline on the IQCODE-Self, respectively. Perceived cognitive decline was positively correlated with current depressive symptoms, negatively correlated with years of professional sport exposure and resilience, and unrelated to objective cognition and number of self-reported concussions. A multiple regression model with perceived cognitive decline regressed on age, concussion history, professional rugby league exposure, depression, resilience, objective cognitive functioning, daytime sleepiness, and pain severity showed depression as the only significant predictor.Conclusion: This is the first large study examining subjectively experienced cognitive decline in retired professional rugby league players. Similar to studies from the general population and specialty clinics, no relationship was found between objective cognitive test performance and perceived cognitive decline. Depressive symptoms emerged as the strongest predictor of perceived cognitive decline, suggesting that subjective reports of worsening cognition in retired elite rugby league players might reflect psychological distress rather than current cognitive impairment.

Study of State of Interface “Intraocular Lens — Posterior Capsule” Depending on Size of Capsulorhexis in Senile Cataract Phacoemulsification

Purpose. To study the state of interface “intraocular lens (IOL) — posterior capsule (PC)” depending on diameter of capsulorhexis in phacoemulsification of senile cataract.Patients and methods. 227 patients (227 eyes) were examined after phacoemulsification of senile cataract at LenSx femtosecond laser (Alcon, USA). The study did not include patients with corneal opacities, signs of axial displacement of lens, with irido- and phacodonesis, glaucoma, axial length less than 22 mm and more than 26 mm. Depending on diameter of performed capsulorhexis, we formed 3 groups: 1st group — 76 eyes with diameter capsulorexis 5.5 mm; 2nd group — 73 eyes with 5.0 mm; 3rd group — 78 eyes with 4.5 mm. We studied type of interface “IOL — PC”, the maximum value of PC diastasis and the maximum depth of its folds using an RTVue-100 Optical Coherence Tomography (Optovue, USA) on the first day after the operation.Results. The maximum number of eyes with absence of contact between IOL and PC was noted in the 3rd group (62.8 %), the largest number of eyes with full contact between IOL and PC (63.2 %) was in the 1st group. The minimum average depth of the PC folds (111.1 ± 32.7 μm) was noted in the 1st group, and the maximum (165 ± 75.4 μm) — in the 2nd group.Conclusion. The analysis showed that type of interface “IOL — PC” in the first day after phacoemulsification of senile cataract depends on diameter of capsulorhexis. The largest number of eyes (64.6 %) with full contact between IOL and PC was observed in the group of patients with capsulorhexis 5.5 mm, and the smallest (6.4 %) — in eyes with diameter capsulorexis 4.5 mm. Presumably, the main reason for the absence or incomplete contact between IOL and PC is the presence of viscous dispersive between them. The deformation of PC in the form of folds does not directly depend on diameter of capsulorhexis and, obviously, is due to the uneven tension of the capsular bag by the IOL haptics.

Sex Work and Professional Risk Communication: Keeping Safe on the Streets

Risk communication is traditionally authored by institutions and addressed to the potentially affected publics for whom they are responsible. This study expands the scope of risk communication by analyzing safety guides produced by a hypermarginalized group for whom institutions show no responsibility: full-contact, street-level sex workers. Using corpus-assisted discourse analysis and keyword analysis to reveal patterns of word choices, the authors argue that the safety guides exhibit characteristics and qualities of professional communication: audience adaptation, social responsibility, and ethical awareness. This area of inquiry—the DIY, peer-to-peer, extrainstitutional risk communication produced by marginalized people—widens technical and professional communication's approach to risk communication.

A New Experimental Method for Measuring Improved Oil Recovery in Shales

Improved Oil Recovery, IOR, in shales is a topic of growing interest due to the low oil recovery observed in shales. Evaluating different IOR chemicals at the lab scale has proved difficult and time consuming due to their ultra-low permeability and low porosity. Conventional core procedures (such as core floods) are often not practical to use with such samples since they take too long. In this study, we introduce a new laboratory method for measuring the oil recovery in a huff-and-puff IOR process in shales. In huff-and-puff IOR, a treatment additive and a gas are typically injected in combination into the reservoir. Oil production is initiated after a shut-in period. Our experimental protocol starts by saturating preserved shales with oil by exposing them to the reservoir oil under pressure for an extended time. To speed up this process the preserved shale sample is crushed and sieved to 5-10 mesh. The pressure vessels are then loaded with these oil-saturated 5-10 mesh shale particles and the desired IOR fluid is injected into the pressure vessel. The vessel is rotated to ensure full contact with the shale. The samples are heated to ensure that the fluid is at reservoir pressure and temperature. Several tests were done to ensure that the fluid temperature and pressure inside the vessels were at the desired conditions throughout the 72-hour test period. T2 NMR scans were carried out before and after treatment to determine the amount of incremental oil recovery from the treatment. In tests where the two fluid phases were indistinguishable, deuterium was used in the treatment fluid in lieu of water. Excellent reproducible results were obtained with this method. This new method has been used to test a number of different treatment fluids, gases and solvents under a variety of conditions. The test can be completed in a matter of a few days as compared to several weeks that would be required for a core flood. Several tests can be run simultaneously, further speeding up the process. The results of the laboratory tests can be scaled to the field by using suitable surface-to-volume ratios in the lab and comparing them to the field. With this new method we have a fast and robust method for conducting these huff-and-puff experiments in a repeatable, and precise manner. This allows us to quickly evaluate different IOR fluids for a particular shale-fluid system at reservoir conditions.

Revisiting mechanics of ice–skate friction: from experiments at a skating rink to a unified hypothesis

The mechanics underlying ice–skate friction remain uncertain despite over a century of study. In the 1930s, the theory of self-lubrication from frictional heat supplanted an earlier hypothesis that pressure melting governed skate friction. More recently, researchers have suggested that a layer of abraded wear particles or the presence of quasi-liquid molecular layers on the surface of ice could account for its slipperiness. Here, we assess the dominant hypotheses proposed to govern ice–skate friction and describe experiments conducted in an indoor skating rink aimed to provide observations to test these hypotheses. Our results indicate that the brittle failure of ice under rapid compression plays a strong role. Our observations did not confirm the presence of full-contact water films and are more consistent with the presence of lubricating ice-rich slurries at discontinuous high-pressure zones (HPZs). The presence of ice-rich slurries supporting skates through HPZs merges pressure-melting, abrasion and lubricating films as a unified hypothesis for why skates are so slippery across broad ranges of speeds, temperatures and normal loads. We suggest tribometer experiments to overcome the difficulties of investigating these processes during actual skating trials.

Plantar Pressure Detection System Based on Flexible Hydrogel Sensor Array and WT-RF

This paper presents a hydrogel-based flexible sensor array to detect plantar pressure distribution and recognize the gait patterns to assist those who suffer from gait disorders to rehabilitate better. The traditional pressure detection array is composed of rigid metal sensors, which have poor biocompatibility and expensive manufacturing costs. To solve the above problems, we have designed and fabricated a novel flexible sensor array based on AAM/NaCl (Acrylamide/Sodium chloride) hydrogel and PI (Polyimide) membrane. The proposed array exhibits excellent structural flexibility (209 KPa) and high sensitivity (12.3 mV·N−1), which allows it to be in full contact with the sole of the foot to collect pressure signals accurately. The Wavelet Transform-Random Forest (WT-RF) algorithm is introduced to recognize the gaits based on the plantar pressure signals. Wavelet transform realizes the signal filtering and normalization, and random forest is responsible for the classification of the processed signals. The classification accuracy of the WT-RF algorithm reaches 91.9%, which ensures the precise recognition of gaits.