Large Gap Research Articles

Opinion: Strengthening research in the Global South – atmospheric science opportunities in South America and Africa

Abstract. To tackle the current pressing atmospheric science issues, as well as those in the future, a robust scientific community is necessary in all regions across the globe. Unfortunately, this does not yet exist. There are many geographical areas that are still underrepresented in the atmospheric science community, many of which are in the Global South. There are also larger gaps in the understanding of atmospheric composition, processes, and impacts in these regions. In this opinion, we focus on two geographical areas in the Global South to discuss some common challenges and constraints, with a focus on our strengths in atmospheric science research. It is these strengths, we believe, that highlight the critical role of Global South researchers in the future of atmospheric science research.

Design and Development of a Polymeric-Based Curcumin Nanoparticle for Drug Delivery Enhancement and Potential Incorporation into Nerve Conduits.

Peripheral nerve injuries (PNI) impact millions of individuals in the United States, prompting thousands of nerve repair procedures annually. Nerve conduits (NC) are commonly utilized to treat nerve injuries under 3 cm but larger gaps still pose a challenge for successful peripheral nerve regeneration (PNR) and functional recovery. This is partly attributed to the absence of bioactive agents such as stem cells or growth factors in FDA-approved conduits due to safety, harvesting, and reproducibility concerns. Therefore, curcumin, a bioactive phytochemical, has emerged as a promising alternative bioactive agent due to its ability to enhance PNR and overcome said challenges. However, its hydrophobicity and rapid degradation in aqueous solutions are considerable limitations. In this work, a nanoscale delivery platform with tannic acid (TA) and polyvinylpyrrolidone (PVP) was developed to encapsulate curcumin for increased colloidal and chemical stability. The curcumin nanoparticles (CurNPs) demonstrate significantly improved stability in water, reduced degradation rates, and controlled release kinetics when compared to free curcumin. Further, cell studies show that the CurNP is biocompatible when introduced to neuronal cells (SH-SY5Y), rat Schwann cells (RSC-S16), and murine macrophages (J774 A.1) at 5 μM, 5 μM, and 10 μM of curcumin, respectively. As a result of these improved physicochemical properties, confocal fluorescence microscopy revealed superior delivery of curcumin into these cells when in the form of CurNPs compared to its free form. A hydrogen peroxide-based oxidative stress study also demonstrated the CurNP's potential to protect J774 A.1 cells against excessive oxidative stress. Overall, this study provides evidence for the suitability of CurNPs to be used as a bioactive agent in NC applications.

Gap expansion is the dominant driver of canopy openings in a temperate mountain forest landscape

Abstract Natural disturbances are important drivers of forest dynamics, and canopy gaps are their fingerprints in forest ecosystems. Gaps form and persist because of the interplay of tree mortality and regeneration. They can have long‐lasting impacts on ecosystems, yet the temporal dynamics of gap formation and closure remains poorly quantified. We analysed 11,331 canopy gaps and their changes through time across 3999 ha of unmanaged temperate mountain forests at Berchtesgaden National Park (Germany). We assessed gap formation and closure using three repeat lidar acquisitions between 2009 and 2021, analysing canopy height changes at 1 m horizontal resolution. Our objective was to determine the dominant mode of gap formation, distinguishing the creation of new gaps from the expansion of existing ones. Additionally, we studied the rate of gap closure, considering closure from tree regeneration and lateral crown expansion. Gap formation was primarily driven by gap expansion rather than the initiation of new gaps. Gap expansion accounted for 81.3% of gap formation, although new gaps were on average twice as large as gap expansions. Only 1.4% of gaps did not expand over the 12‐year study period, and Norway spruce forests had the highest rate of gap expansion. Overall, gap closure rate (0.74 ha 100 ha−1 year−1) was higher than gap formation (0.58 ha 100 ha−1 year−1) in our study system. Ingrowth of the regenerating tree cohort was the primary mode of gap closure, with lateral crown expansion accounting for 20% of all gap area closed. Mixed‐species stands had the highest rate of gap closure, and gaps <0.1 ha closed faster than larger gaps. Synthesis. While canopy openings are generally small in the European Alps, we show that they keep growing over multiple years, underlining that gap expansion is an important driver of temperate forest dynamics. Canopy gaps closed faster than they were created, highlighting the resilience of European mountain forests to natural disturbances. However, as disturbances are projected to increase under climate change, this resilience might be challenged in the future, requiring a continuous monitoring of gap dynamics as an important early warning indicator of forest change.

Bashimyzon cheni, a new genus and species of sucker loach (Teleostei, Gastromyzontidae) from South China

Bashimyzon, new genus, is here established for Erromyzon damingshanensis, and a new species of the genus is described from the You-Jiang of the Pearl River (=Zhu-Jiang in mandarin Chinese) basin in Guangxi Province, South China. This new genus has a small gill opening above the pectoral-fin base and short pectoral fins extending backwards short of pelvic-fin insertions, both characters combined to separate it from all currently-recognized gastromyzontid genera except Erromyzon and Protomyzon, but differs from the two genera in having a larger gap between the posterior edge of eye and the vertical through the pectoral-fin insertion and very small fleshy lobes posterior to the maxillary-barbel bases. It is further distinct from its most similar genus Erromyzon in having a relatively larger gill opening, fewer branched pectoral-fin rays folded against body, and more posteriorly placed pectoral fins with a shorter fin base. Bashimyzon cheni, new species, and B. damingshanensis, the single congeneric species, differ in number of lateral-line pored scales, body coloration, and cephalic contour, and also in substantial genetic divergence.

Ultrabright Xanthene Fluorescence Probe for Mitochondrial Super-Resolution Imaging.

Mitochondria are important organelles that provide energy for cellular physiological activities. Changes in their structures may indicate the occurrence of diseases, and the super-resolution imaging of mitochondria is of great significance. However, developing fluorescent probes for mitochondrial super-resolution visualization still remains challenging due to insufficient fluorescence brightness and poor stability. Herein, we rationally synthesized an ultrabright xanthene fluorescence probe Me-hNR for mitochondria-specific super-resolution imaging using structured illumination microscopy (SIM). The rigid structure of Me-hNR provided its ultrahigh fluorescence quantum yield of up to 0.92 and ultrahigh brightness of up to 16,000. Occupying the para-position of the O atom in the xanthene skeleton by utilizing the smallest methyl group ensured its excellent stability. The study of the photophysical process indicated that Me-hNR mainly emitted fluorescence via radiative decay, and nonradiative decay and inter-system crossing were rare due to the slow nonradiative decay rate and large energy gap (ΔEst = 0.55 eV). Owing to these excellent merits, Me-hNR can specifically light up mitochondria at ultralow concentrations down to 5 nM. The unprecedented spatial resolution for mitochondria with an fwhm of 174 nm was also achieved. Therefore, this ultrabright xanthene fluorescence probe has great potential in visualizing the structural changes of mitochondria and revealing the pathogenesis of related diseases using SIM.

A new synonymy in the Lethaeini of the Neotropics (Heteroptera: Rhyparochromidae), with new country records for Petissius spinipes (Stål)

ABSTRACT Lethaeini is a diverse tribe within Rhyparochromidae, with Lethaeus Dallas being the most speciose genus. This study is focused on the poorly documented Lethaeus lepidus White, the only species in the genus recorded from the Neotropics. Through a reexamination, this species is considered a new synonym of Petissius spinipes Stål. The examined material is sourced from recent field expeditions in natural areas in Brazil, as well as from entomological collections. In addition, the types of the described species were studied from high-definition photographs. The distribution of P. spinipes is updated, indicating that the species is widely distributed in the Neotropics, and filling a large geographic gap with many new locality records. Distribution map including the new records and high-definition illustrations of the species and diagnostic characters are provided. As a result of the findings presented, there are currently no documented representatives of the genus Lethaeus in the New World. With the previouly significant geographical gap between Argentina and Guyana, the 12 new Brazilian state records substantially amplify our undertanding into the species’ range. This emphasizes the indispensable role of entomological collections and the need for dedicaded sampling expeditions to enhance our undertanding of overlooked taxa, as is often the case for Rhyparochromidae.

Predictive and Near-Optimal Sampling for View Materialization in Video Databases

Scalable video query optimization has re-emerged as an attractive research topic in recent years. The OTIF system, a video database with cutting-edge efficiency, has introduced a new paradigm of utilizing view materialization to facilitate online query processing. Specifically, it stores the results of multi-object tracking queries to answer common video queries with sub-second latency. However, the cost associated with view materialization in OTIF is prohibitively high for supporting large-scale video streams. In this paper, we study efficient MOT-based view materialization in video databases. We first conduct a theoretical analysis and establish two types of optimality measures that serve as lower bounds for video frame sampling. In order to minimize the number of processed video frames, we propose a novel predictive sampling framework, namely LEAP, exhibits near-optimal sampling performance. Its efficacy relies on a data-driven motion manager that enables accurate trajectory prediction, a compact object detection model via knowledge distillation, and a robust cross-frame associator to connect moving objects in two frames with a large time gap. Extensive experiments are conducted in 7 real datasets, with 7 baselines and a comprehensive query set, including selection, aggregation and top-k queries. The results show that with comparable query accuracy to OTIF, our LEAP can reduce the number of processed video frames by up to 9× and achieve 5× speedup in query processing time. Moreover, LEAP demonstrates impressive throughput when handling large-scale video streams, as it leverages a single NVIDIA RTX 3090ti GPU to support real-time MOT-based view materialization from 160 video streams simultaneously.

Aerodynamic investigation of the turbulent flow past a louvered-fin-and-tube automotive heat exchanger

Turbulent flow past a radiator contributes to noise emission when interacting with a downstream cooling fan. This study examines turbulent flow characteristics downstream of a radiator, focusing on turbulence production, dissipation, non-homogeneity, and anisotropy. We assess turbulence models based on isotropy and homogeneity for noise prediction in real applications. Results show significant non-homogeneity due to the radiator grid’s wakes, extending downstream to a region where the fan would be located. Flow in this region trends toward isotropy, especially when considering a downstream circularly-holed wood panel mimicking the flow contraction caused by a fan casing. The radiator core’s fins and louvers break down vortical structures more than generating large eddies, as reported in studies involving heat exchangers with larger gaps between cooling pipes. The von Kármán turbulence model approximates the experimental spectrum, but caution is needed with rapid flow acceleration. This investigation enhances our understanding of turbulence characteristics in the vicinity of radiators with implications for noise spectrum prediction and modeling in such systems.

What makes entrepreneurship counter-cyclical? Evidence from a shutdown of start-up subsidies in Denmark

ABSTRACT This paper examines how the presence of startup subsidies to the unemployed influences the relationship between business cycle and entrepreneurial activity, and the implications on individuals’ long-term earnings. We propose that on one hand, this measure fosters entrepreneurship, especially during recessions, by attracting individuals facing labour market constraints. On the other hand, the policy may unintentionally penalize counter-cyclical founders back to paid jobs if employers perceive them as less committed or of lower quality. Exploiting a change in Danish policy that abolishes a startup subsidy scheme for the unemployed, we compare the entrepreneurial population in two extended periods. Our findings indicate that entrepreneurship tends to be counter-cyclical during the subsidy period (1988–1996), while pro-cyclical in the post-reform period (1998–2006). Moreover, the results highlight an unintended consequence of the policy, i.e. a persistent and large (post-exit) wage gap between counter-cyclical and pro-cyclical founders, particularly pronounced for individuals with lower education, unobserved ability, and part-time job experience prior to transition.

Instrumentation for measurement: A case study on conceptual versus problem-solving knowledge

The problem under analysis looks at the overall comparison of about 1300 students’ performance considering separately their conceptual and problem-solving knowledge over 7 academic years of the course of Instrumentation for Measurement within the Mechanical Engineering Department, Faculty of Engineering, University of Porto . This course gives the relevant background for later content courses on Automation, Control, Mechatronics, Smart Factories, etc., in that Mechanical Engineering master's degree. It is important to note that such content deals with basic concepts in different science and technology topics, incorporating today's cyber systems and the Internet of Things (IoT). This content includes fundamental principles spanning traditional topics as physics, statistics, mechanical, dynamics, design, and electrical, foundational, technical, and technological knowledge, and informatics. Together, they permit access to very small changes in physical quantities making possible their measurement, interpreting them, and providing data in the cloud. Also, aspects related to a variety of specific prepared questions to motivate students to improve and enhance their comprehension instead of a pure sequence of memorization activities for a perfect “how-to-respond” are explained. The work describes details on the instructional course design, and the actions used to improve the difference in both performances, from the point of view of pedagogical strategies and their sequence of results. The main outcomes of the analysis performed on data from those 7-course editions indicate large differences between the scores of conceptual (/theoretical) and problem-solving components; steady improvement in student performance in conceptual knowledge over the years; stable performance concerning the problem-solving component; clear disruption in conceptual performance in the academic year disturbed by the pandemic situation, followed by great recovery in the following academic year. The results are discussed in the framework of the regulations and conditions in which the instruction takes place and the pedagogical strategies employed to balance conceptual and problem-solving knowledge. Finally, some suggestions are put forward to investigate further possible reasons behind the large gap in theoretical and problem-solving results. The authors hope to contribute with some helpful discussion and outcomes and to foster later feedback from the community.

Novel Solid-State Electrolyte Na3La5Cl18 with High Stability and Fast Ionic Conduction.

Motivated by the recent experimental synthesis of a LaCl3-based lithium superionic conductor [Yin, Y.-C. Nature 2023, 616, 77-83], we explore the potential of a LaCl3-based system for a sodium superionic conductor in this work. Using density functional theory combined with molecular dynamics simulation and a grand potential phase diagram analysis, we find that the resulting Na3La5Cl18 exhibits high energetic stability with a small energy-above-hull of 18 meV per atom, a large band gap of 5.58 eV, a wide electrochemical window of 0.41-3.76 V from the cathodic to the anodic limit, and a high Na+ conductivity of 1.3 mS/cm at 300 K. Furthermore, Na3La5Cl18 shows high chemical interface stability with the reported high-potential cathode materials such as NaCoO2, NaCrO2, Na2FePO4F, Na3V2(PO4)3, and Na3V2(PO4)2F3. These findings clearly suggest that the LaCl3-based framework can be used as a building block not only for Li-ion but also for Na-ion batteries.

OVERVIEW OF ROOT ZONE TECHNOLOGY

Central Pollution Control Board (2007) study found that discharge of untreated sewage is sthe single most important cause for surface and ground water pollution n India. There is a large gap between the generation and treatment of domestic wastewater in India. The problem is not only that India lacks sufficient treatment capacity but also that the existing sewage treatment plants are not operated and are not maintained. Most of the government-owned sewage treatment plants remain closed due to improper design, poor maintenance, or lack of reliable electricity supply to operate the plants, absentee employees, and poor management. The wastewater generated in these areas normally percolates in the soil or evaporates. The uncollected wastes accumulate in the urban areas cause unhygienic conditions and release pollutants that leach to surface and groundwater. Moreover, where these treatment plants exist, the cost of treatment is so high that industrialists favour not treating the waste generated and directly dumping the untreated waste into the rivers.The Root Zone Treatment system (RZTS) also known as the reed bed system or constructed wetland system is a sealed filter bed consisting of a sand/gravel/ soil system, occasionally with a cohesive element, planted with vegetation that can grow in wetlands. After removing coarse and floating material, the wastewater passes through the filter bed where biodegradation of the wastewater occurs. The functional mechanisms in the soil matrix responsible for the mineralization of biodegradable matter are characterized by complex physical, chemical and biological processes resulting from the combined effects of the filter bed material, wetland plants, micro-organisms and wastewater. The root zone treatment system also known as the reed bed or constructed wetland system is a sealed filter bed consisting of a sand /gravel/soil system.

Plasma Electrolytic Oxidation Synthesis of Heterostructured TiO2/CuxO Films for Photoelectrochemical Water Splitting Applications

TiO2 is a versatile photo-/electrochemically active material that finds a wide variety of applications in industry and science alike. Its main but often overlooked advantage is the abundance of Ti in nature, as it is the 9th most commonly found element in the Earth’s crust. Despite some drawbacks (e.g., large band gap) that limit its light conversion efficiency in comparison to some other materials, it is particularly inert in corrosive media, and its properties can be modified by various means. In this study TiO2 films are synthesized by an anodization-like procedure called plasma electrolytic oxidation. By varying synthesis conditions different morphologies and structures are obtained. Moreover, successful heterostructuring is achieved by adding a copper precursor into the solution. The TiO2/CuxO films are comprehensively characterized for their structural, optical, and photoelectrochemical properties. Interpretation of XPS and XANES spectra suggest that the content of Cu2+ increases in relation to the maximum voltage reached during synthesis. The UV–vis absorption was also found to display a distinct Cu2+ absorption footprint, as well as lower optical band gap values for the heterostructures. A comprehensive photoelectrochemical characterization for water splitting in 1 M KOH reveals that the TiO2/CuxO films exhibit improved activity overall.

TV cooking shows—Consumer entertainment or education?

AbstractThe current observational study aims to determine the extent to which main food safety principles are addressed in Slovenian cooking shows and whether the type of main actor or television channel significantly impacts adherence to good hygiene practices. In general, our results show that food handling presented to the audience in Slovenian TV cooking shows often deviates from the main food safety recommendations. A comparison between amateur and professional chefs has shown notable but statistically insignificant differences. While in the area of personal hygiene, more deviations were found among amateur than among professional chefs (p = 0.011), we can observe the opposite in the area of preparation practices, albeit with insignificant difference (p = 0.884). The current study provides further evidence that there is a large gap between what viewers see and what they should have seen in television cooking shows from a food safety perspective.

Anharmonic strong-coupling effects at the origin of the charge density wave in CsV3Sb5

The formation of charge density waves is a long-standing open problem, particularly in dimensions higher than one. Various observations in the vanadium antimonides discovered recently further underpin this notion. Here, we study the Kagome metal CsV3Sb5 using polarized inelastic light scattering and density functional theory calculations. We observe a significant gap anisotropy with 2Δmax/kBTCDW≈20\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$2{\\Delta }_{\\max }/{k}_{{{{{{{{\\rm{B}}}}}}}}}{T}_{{{{{{{{\\rm{CDW}}}}}}}}}\\, \\approx \\, 20$$\\end{document}, far beyond the prediction of mean-field theory. The analysis of the A1g and E2g phonons, including those emerging below TCDW, indicates strong phonon-phonon coupling, presumably mediated by a strong electron-phonon interaction. Similarly, the asymmetric Fano-type lineshape of the A1g amplitude mode suggests strong electron-phonon coupling below TCDW. The large electronic gap, the enhanced anharmonic phonon-phonon coupling, and the Fano shape of the amplitude mode combined are more supportive of a strong-coupling phonon-driven charge density wave transition than of a Fermi surface instability or an exotic mechanism in CsV3Sb5.

Compact remanence-free permanent magnet-based variable magnetic field source.

We demonstrate a simple and compact variable magnetic field source based on the permanent cube magnet array approximating a Halbach cylinder. The large air gap area accommodates standard cryostat tails while providing a high uniformity and magnetic field stability of up to 0.5T over regions of up to about a centimeter. It eliminates magnetic remanence effects and produces reproducible fields without the need for feedback. Thanks to the low cost and exceptional energy efficiency, it provides an accessible solution for modest magnetic field requirements in a wide range of research applications.

JWST MIRI MRS Observations of T Cha: Discovery of a Spatially Resolved Disk Wind

Understanding when and how circumstellar disks disperse is crucial to constrain planet formation and migration. Thermal winds powered by high-energy stellar photons have long been theorized to drive disk dispersal. However, evidence for these winds is currently based only on small (∼3–6 km s−1) blueshifts in [Ne ii] 12.81 μm lines, which does not exclude MHD winds. We report JWST MIRI MRS spectro-imaging of T Cha, a disk with a large dust gap (∼30 au in radius) and blueshifted [Ne ii] emission. We detect four forbidden noble gas lines, [Ar ii], [Ar iii], [Ne ii], and [Ne iii], of which [Ar iii] is the first detection in any protoplanetary disk. We use line flux ratios to constrain the energy of the ionizing photons and find that argon is ionized by extreme ultraviolet, whereas neon is most likely ionized by X-rays. After performing continuum and point-spread function subtraction on the integral field unit cube, we discover a spatial extension in the [Ne ii] emission off the disk continuum emission. This is the first spatially resolved [Ne ii] disk wind emission. The mostly ionic spectrum of T Cha, in combination with the extended [Ne ii] emission, points to an evolved stage for any inner MHD wind and is consistent with the existence of an outer thermal wind ionized and driven by high-energy stellar photons. This work acts as a pathfinder for future observations aiming at investigating disk dispersal using JWST.

Monetary incentives to improve tax compliance: A Brazilian case study

AbstractMotivationTo enhance tax education and increase citizen participation in combatting tax evasion, monetary incentives may be used. In December (2021), the state government of Rio Grande do Sul in Brazil launched the Receita Certa project. It aims to encourage new taxpayer habits, by refunding part of the tax collected by retailers on consumption back to citizens, contingent on its performance exceeding inflation rates. Taxpayers add their tax identification to receipts and request redemption every three months.PurposeWe analyse the impact of the Receita Certa project on the behaviour of consumers as taxpayers.MethodsWe evaluate the impacts of Receita Certa using difference‐in‐differences. The response variables are the monthly number and value of electronic receipts issued to beneficiaries. The treatment group consists of citizens eligible for the refund in its introduction month, while the remainder constitute the control group. The database includes receipts issued to 3.4 million taxpayers who added their tax identification to the receipt — spanning 11 months before and 18 months after the initiative, began resulting in 46.7 million records.FindingsThe Receita Certa proved ineffective, as it led to fewer tax documents issued. Distributing resources widely to many users does not seem the best solution, both in cost and results. Distribution goes first and foremost to people on higher incomes since they got larger prizes: the smaller prizes of people on lower incomes were often not claimed. The programme made tax more regressive. The programme was also costly.Policy implicationsStates that have a large tax gap need to improve their control systems. Initiatives like the Receita Certa that return resources widely to taxpayers to reduce tax evasion are widespread. Given the results shown, Receita Certa needs rethinking.

Bone formation in large/moderate gap after immediate implantation in response to different treatments: a pre-clinical study in the canine posterior mandible.

This study aims to investigate different treatments on new bone formation around immediate implants in the canine posterior mandible with varying sized mesial-distal gap. The 4th premolar and the 1st molar of six Labrador dogs were extracted from the mandible, and 4 dental implants were placed 1mm below the level of the buccal bone crest. Moderate/large mesial-distal gaps between the implants and the sockets were treated with one of four methods and divided into the following groups: (1) the blank group, (2) the collagen membrane (CM) group, (3) the deproteinized bovine bone mineral (DBBM) group, and (4) the DBBM + CM group. Sequential fluorescent labeling was performed at 4, 8, and 10 weeks after the operation. After 12 weeks, the dogs were euthanized, and specimens were collected for micro-CT scanning and histological analysis. The survival rate of immediate implant was 100%. Micro-CT showed significant differences in bone mineral density (BMD) and bone volume fraction (BVF) among groups (P = 0.040, P = 0.009); other indicators were not significantly different among groups. Histological analysis showed the proportion of new bone formation and bone-to-implant contact were not significantly different among groups. No significant difference in bone reduction height around dental implant among four groups and varied mesial-distal gap size. Owing to the restricted sample size, this pilot study lacks conclusive findings. Within the limitation, this study demonstrated that although DBBM significantly increase BMD and BVF, the use of DBBM/CM didn't significantly improve bone formation and healing in extraction sockets around the implants in both moderate and large mesial-distal gap. The use of deproteinized bovine bone in conjunction with collagen is a common practice in immediate implantation procedures in the posterior mandible. However, there is a lack of conclusive evidence regarding the timing and circumstances under which they should be employed.

Viscosimetric squeeze flow of suspensions.

The rheology of particle suspensions has been extensively explored in the case of a simple shear flow, but less in other flow configurations which are also important in practice. Here we investigate the behavior of a suspension in a squeeze flow, which we revisit using local pressure measurements to deduce the effective viscosity. The flow is generated by approaching a moving disk to a fixed wall at constant velocity in the low Reynolds number limit. We measure the evolution of the pressure field at the wall and deduce the effective viscosity from the radial pressure drop. After validation of our device using a Newtonian fluid, we measure the effective viscosity of a suspension for different squeezing speeds and volume fractions of particles. We find results in agreement with the Maron-Pierce law, an empirical expression for the viscosity of suspensions that was established for simple shear flows. We prove that this method to determine viscosity remains valid in the limit of large gap width. This makes it possible to study the rheology of suspensions within this limit and therefore suspensions composed of large particles, in contrast to Couette flow cells which require small gaps.