Equal Spacing Research Articles

Nonlinear dynamics of multiple Alfvén modes driven by trapped energetic ions in tokamaks: A triplet paradigm

Non-linear dynamics of multiple infernal Alfvén eigenmodes—a subset of global Alfvén eigenmodes in tokamak plasmas with extended low-shear central core [Marchenko et al., Phys. Plasmas 16, 092502 (2009)]—is studied. The analysis is carried out for a mode triplet with toroidal mode-numbers n=1, 2, 3. It was assumed that the n = 1 mode was linearly unstable due to precession resonance with trapped fast ions, whereas the other modes were linearly damped. The modes were coupled due to a non-linearity in a bounce-averaged drift kinetic equation for the distribution function of fast ions. Nonlinear equations for the mode amplitudes and phases are derived and solved numerically. It is found that the temporal evolution of the amplitudes and the phase (responsible for the frequency chirping) of the modes exhibit Hopf bifurcations to stable limit cycles. This can explain a synchronous cyclic destabilization of multiple modes in Alfvén avalanches (sudden growth of amplitudes of the mode cluster with different n and approximately equal frequency spacing) in NSTX and bursting modes in MAST—events, which resulted in enhanced loss of fast ions.

A numerical study on dynamic flows past three tandem inclined elliptic cylinders near moving wall

This numerical study focuses on the dynamic flows past three tandem inclined elliptic cylinders of equal spacing parallel to a moving wall using a lattice Boltzmann method. The gap ratio (G/D=0.6–2.5, where G and D are the gap between the wall surface and cylinder center and major axis, respectively), spacing ratio (L/D=1.5–10, where L is the distance of two adjacent cylinder centers), and inclination angle (α=±15°,±30°,±45°—the angle between normal vector and cylinder's major-axis) are explored at Reynolds number Re = 150 (based on D). The intended analysis links hydrodynamic coefficients, wake structures, and spectral analysis in parameter space of α−G/D−L/D to fluid mechanics. The flow is highly adjustable in this space, dividing into seven regimes: overshoot, continuous reattachment, alternative reattachment, wavy, meandering, quasi-coshedding, and coshedding, which are spatially classified into four modes due to flow interference: shear layer, primary, two-layered, and secondary vortex shedding modes. Transitions between adjacent modes determine three boundaries; and hydrodynamic coefficients differ substantially in parameter space. Due to shadowing, the upstream cylinder has a larger drag coefficient than the middle and downstream cylinders, reducing the drag coefficient of upstream cylinder and the lift coefficient of middle and downstream cylinders. α=±45° has the highest lift oscillation among the three cylinders and a small drag coefficient of the upstream cylinder. The moving wall's proximity effect increases the upstream cylinder's lift coefficient for α<0°, being negligible for high G/D across the full L/D range and stabilizing the lift oscillation of three cylinders.

Word learning by children with developmental language disorder: Identifying gaps in our understanding of spaced retrieval effects.

Current evidence shows that children with developmental language disorder (DLD) benefit from spaced retrieval during word learning activities. Word recall is quite good relative to recall with alternative word learning procedures. However, recall on an absolute basis can be improved further; many studies report that fewer than two-thirds of the words are learned, even with the assistance of spaced retrieval during the learning activities. In this article we identify details of spaced retrieval that are less well understood in an effort to promote more effective learning through retrieval practice. We discuss the importance of factors such as: (a) integrating immediate retrieval with spaced retrieval trials; (b) determining whether gradual increases in spacing have more than short-term benefits relative to equal spacing; (c) discovering the number of successful retrievals sufficient to ensure later recall; (d) using spaced retrieval to avoid erosion of phonetic details on later recall tests; and (e) whether the well-documented difficulties with learning word forms might be tied to a particular subgroup of children with DLD. We also speculate on some of the possible reasons why spaced retrieval is beneficial in the first place. Although many children with DLD make gains in word learning through procedures that incorporate spaced retrieval, there are numerous details involved in the process that can alter its success. Until we have a better understanding of the boundaries of spaced retrieval's effectiveness, we will not be taking full advantage of this promising addition to word learning procedures. Spaced retrieval activities can be an important addition to the resources that clinicians and educators have available to assist children in their word learning. With a deeper understanding of the issues discussed here, we should be able to put spaced retrieval to even greater use.

Validate robot-assisted total laparoscopic hysterectomy with four equally-spaced ports without an assistant port.

To evaluate the usefulness of robot-assisted total laparoscopic hysterectomy with four equally-spaced ports (RA-TLH/4e) without an assistant port. In RA-TLH/4e, four da Vinci ports were placed horizontally at a height of 4cm above the umbilicus with 8cm equal spacing. Poor development of the surgical field or difficult forceps manipulations were handled with the endoscope and forceps movement (port-hopping). Patient background, surgical outcomes, complications, port-hopping frequency were compared in three groups: RA-TLH/4e, RA-TLH with four unequally-spaced ports (RA-TLH/4u), and conventional RA-TLH with five ports (RA-TLH/5). There were no significant differences in patient background or surgical outcomes among the three groups except for age, preparation time, and hospital stay, and no cases of laparotomy conversion or serious complications. RA-TLH/4e had fewer port-hoppings than RA-TLH/4u. The minimum abdominal width showed a weak negative correlation with port-hopping frequency in RA-TLH/4u, but not in RA-TLH/4e. RA-TLH/4e allowed for a reduction in personnel and costs compared to RA-TLH/5. The equal placement of four ports allowed sufficient port spacing even for patients with narrow abdominal widths. In addition, the port-hopping technique was able to fully compensate for the lack of an assistant port. RA-TLH/4e is a highly useful technique that not only excels in safety but also reduces costs.

Near-moving-wall flows past three tandem elliptical cylinders at low Reynolds number of 150

Dynamic flows past three tandem elliptic cylinders of equal spacing in parallel arrangement with a moving wall are numerically conducted by the lattice Boltzmann method. The gap ratio (G/D, where G and D are the gap between the wall surface and cylinder center and major axis, respectively) from 0.6 to 2.5 and spacing ratio (L/D, where L is the distance of two adjacent cylinder centers) from 1.5 to 10 are examined at Reynolds number of Re = 150 (based on D). The desired analysis correlates variations of hydrodynamic coefficients, wake structures, and spectral analysis in wide space of G/D and L/D with underlying fluid mechanics. The flow is highly adjustable in G/D−L/D space, dividing into six distinct regimes: overshoot, continuous reattachment, alternative reattachment, wavy, meandering, and coshedding, which are spatially classified into four modes because of flow interference, namely, shear layer, primary, two-layered, and secondary vortex shedding modes. The transition between adjacent modes defines three boundaries. The first boundary always occurs behind the middle or downstream cylinder, whereas the second and third boundaries occur between the upstream and middle cylinders and the downstream cylinder wake. Due to the near-wall flow interference, the hydrodynamic coefficients are highly changeable in L/D−G/D space, signifying the crucially lower drag coefficient of the middle and downstream cylinders than that of a single cylinder. A small G/D determines the increase in lift coefficient of the upstream cylinder as a result of the ground effect, while the shadowing effect of the upstream cylinder induces identical Strouhal numbers of the middle and downstream cylinders.

A practical guide to calculating vocal tract length and scale-invariant formant patterns

Formants (vocal tract resonances) are increasingly analyzed not only by phoneticians in speech but also by behavioral scientists studying diverse phenomena such as acoustic size exaggeration and articulatory abilities of non-human animals. This often involves estimating vocal tract length acoustically and producing scale-invariant representations of formant patterns. We present a theoretical framework and practical tools for carrying out this work, including open-source software solutions included in R packages soundgen and phonTools. Automatic formant measurement with linear predictive coding is error-prone, but formant_app provides an integrated environment for formant annotation and correction with visual and auditory feedback. Once measured, formants can be normalized using a single recording (intrinsic methods) or multiple recordings from the same individual (extrinsic methods). Intrinsic speaker normalization can be as simple as taking formant ratios and calculating the geometric mean as a measure of overall scale. The regression method implemented in the function estimateVTL calculates the apparent vocal tract length assuming a single-tube model, while its residuals provide a scale-invariant vowel space based on how far each formant deviates from equal spacing (the schwa function). Extrinsic speaker normalization provides more accurate estimates of speaker- and vowel-specific scale factors by pooling information across recordings with simple averaging or mixed models, which we illustrate with example datasets and R code. The take-home messages are to record several calls or vowels per individual, measure at least three or four formants, check formant measurements manually, treat uncertain values as missing, and use the statistical tools best suited to each modeling context.

MODAL BEHAVIOUR OF LONGITUDINALLY PERFORATED NANOBEAMS

Nano-electro-mechanical systems (NEMS) require perforated beams for structural integrity. Hole sizes, hole numbers, and scale effects need to be modelled appropriately in their design. This paper presents a new finite element model to investigate the modal behaviour of longitudinally perforated nanobeams (LPNBs) using the classical Euler–Bernoulli beam theory. A symmetric array of holes arranged parallel to the length direction of the beam with equal spacing was assumed for the perforation. The non-local Eringen’s differential form was used to incorporate the nanoscale sizes. The accuracy of the proposed model was verified by comparing the obtained results with the available analytical solutions for fully filled nanobeams. The effects of aspect ratios, non-local parameters, boundary conditions, and perforation characteristics on the modal behaviour of LPNBs were investigated. The non-local parameter reduced the natural frequency owing to a decrease in the stiffness of the structures. However, the perforation filling ratio led to higher values of the fundamental frequency. Furthermore, compared with other boundary conditions, clamped–clamped boundary conditions demonstrated the best performance in terms of the maximum frequency.

How much do customer ordering practices drive medical supplies distribution (in)efficiency for primary care markets?

Companies across many industries seek to understand how customer ordering impacts supply chain distribution performance. In the US medical supplies industry, wholesalers are uniquely positioned to use information about downstream customers to study and potentially influence buyer policies and practices due to their industry scale and data visibility. In this study, wholesale medical supplies buyers are first examined based on their ordering practices over a 2‐year window using the theoretical lens of data clumpiness—patterns of data non‐conformity to equal spacing—to derive insights into how their ordering practices affect the distribution efficiency of the medical supplies wholesale distributor. The analysis also considers how different buyer and industry characteristics moderate these upstream ordering effects. The results reveal several significant findings for both theory and practice. First, buyers exhibiting less clumpiness in order sizing and greater clumpiness in order‐timing practices drive greater distribution efficiencies for the wholesale distributor. These effects are greater when buyers have more category experience and lower when ordering across multiple categories. Industry customers’ use of centralized purchasing also tends to lower wholesale distributor efficiency. Still, these negative effects can be mitigated when customer ordering practices favor replenishment based on customer needs and consistent order sizing. After discussing the implications of our analysis, we offer additional practical and theoretical extensions of our approach that can be applied to study other industry supply chains or that could affect related healthcare purchasing markets.

Large scale study on influence of biopolymer to mitigate wind induced sand erosion with durability analysis

The desertification is a serious threat that affects the sustainable agriculture, ecosystem, and economic progress of society. There is an urgent need for an environment friendly, cost-effective, durable, and practical approach to mitigate wind induced erosion. The present study introduces a novel approach through large scale testing using biopolymer, including durability analysis. The research investigates the influence of biopolymer namely Acacia gum (AG) to mitigate wind induced sand erosion. For the experimental setup, rectangular trays (180 cm × 60 cm × 15 cm) containing 11 erosion pins (three rows along the length, in a staggered way at equal spacing) have been filled with desert sand. Solutions have been prepared using biopolymer concentrations (1%, 2%, and 3%) mixed with water. The prepared solution was sprayed onto specimens and the treated samples were then left for air drying (7 and 28 days curing period). The study has been performed on summer days with an average temperature of 40 °C. After biotreatment, the specimens were examined in a wind tunnel at variable wind speeds of 6, 10, and 15 m/s to measure sand loss rate (SLR) for different wind intervals (i.e., 1, 2, 3, 4, and 5 min). Surface strengths were assessed using a pocket penetrometer. To check the durability of biotreated sand samples, 28 days curing period samples, with all biopolymer percentages have gone through 5 wetting and drying cycles (WDC). After the last WDC, samples were left again for 28 days and then experienced all tests. The minimum and maximum SLR for desert sand ranged from 17 kg/m² at 6 m/s and 1 min duration to 123 kg/m² at 15 m/s and 5 min duration respectively. Instead biotreated sand samples presented negligible SLR. Surface strength increased with increasing biopolymer concentration and a curing period. The maximum surface strength was 334.47 kPa recorded at 3% concentration during the curing period of 28 days. Further analysis involving SEM, EDX, and PXRD, confirmed sand particle bonding. For surface strength, 3% biopolymer concentration consistently produced positive outcomes, even after undergoing 5 WDC.

Impact of land use changes on the land surface thermal environment in Nanchang, Jiangxi province, China

Throughout human history, human activities have resulted in land use and land cover changes (LUCC) and can have a direct impact on the land surface thermal environment (LSTE). In the existing studies, the holistic nature of changes in land use and land cover (LULC) has been neglected in favor of focusing on the interactions between different LULC types and the land surface thermal environment. This study used ArcGIS Pro 3.0, ENVI 5.3, and SPSS software to construct a contribution index model and stepwise regression equation to investigate the relationship between LULC type, structure, and pattern changes and LSTE changes in Nanchang City, Jiangxi Province, China, from 1990 to 2020. The findings revealed that 1) rapid urbanization has led to a surge in the area of built-up land and a decrease in the area of arable land in Nanchang; between 1990 and 2020, the area of built-up land in Nanchang increased by 433.29 km2, while the area of arable land decreased by 291.99 km2; 2) The land surface temperature (LST) was divided into five classes according to the equal spacing method, and the areas with the highest and lowest temperature classes were the high temperature zone and the low temperature zone, respectively. Over the past 30 years, the LSTE in Nanchang has gradually deteriorated, with the area of the low temperature zone shrinking by 554.2 km2 and the area of other classes appearing to increase significantly; 3) the contribution index and stepwise regression equation demonstrate that the primary reasons for the worsening of the LSTE are an increase in the scale of cultivated land and construction land. It was found that rationalization of urban LULC type, structure, and pattern can effectively reduce land surface temperature.

Auto-setting multi-soliton temporal spacing in a fiber laser by a hybrid GA-PSO algorithm.

Multi-soliton operation in fiber lasers is a promising platform for the investigation of soliton interaction dynamics and high repetition-rate pulse. However, owing to the complex interaction process, precisely manipulating the temporal spacing of multiple solitons in a fiber laser is still challenging. Herein, we propose an automatic way to control the temporal spacing of multi-soliton operation in an ultrafast fiber laser by a hybrid genetic algorithm-particle swarm optimization (GA-PSO) algorithm. Relying on the intelligent adjustment of the electronic polarization controller (EPC), the on-demand temporal spacing of the double solitons can be effectively achieved. In particular, the harmonic mode locking with equal temporal spacing of double solitons is also obtained. Our approach provides a promising way to explore nonlinear soliton dynamics in optical systems and optimize the performance of ultrafast fiber lasers.

Meta-Analysis of the Effect of Subsurface Irrigation on Crop Yield and Water Productivity

Problems such as population growth and climate change have led to a reduction in the use of water for irrigated agriculture, constraining the growth of crops. Subsurface irrigation, as a widely used and efficient water-saving irrigation technology, varies in its effect on increasing yields and saving water under different environmental, management, and other conditions. To investigate the effects of subsurface irrigation on yield, water productivity (WP), and irrigation water productivity (IWP) of three typical crops (wheat, maize, and cotton), this paper conducted a meta-analysis of 528 pairs of studies from 64 papers worldwide to quantify the response of crop yield, WP, and IWP to subsurface irrigation. Overall, the yield, WP and IWP increased by 5.96%, 21.62%, and 27.72%, respectively, with subsurface irrigation compared with surface irrigation. Compared with other conditions, the greatest rate of change was observed at around 200–500 m above sea level, 10–15 °C average annual temperature, 1.45–1.55 g/cm3 soil bulk density, alkaline soil, and when the crops were planted with equal row spacing. Meanwhile, the amount of irrigation water, as well as the subsurface pipeline arrangement and burial depth, had significant effects on crop yield, WP, and IWP. The maximum increase in crop yield, WP, and IWP was favored when the irrigation volume of the subsurface irrigation was reduced by 50–100% compared with surface irrigation or when both had the same volume of irrigation but a mild water deficit. In addition, the yield, WP, and IWP were also affected by fertilization factors. The recommended fertilizer application rates were ≤90 kg P ha–1 (phosphorus) and <150 kg N ha–1 (nitrogen). Compared with surface irrigation, subsurface irrigation showed the greatest yield increase when fertilizer was applied in a one-time application, and the WP and IWP increased significantly when the number of fertilizer applications was <3.

Ergodic sampling: Acquisition design to maximize information from limited samples

AbstractData acquisition using equal spacing has been a standard practice in geophysics. The dense uniform sampling derived from Nyquist–Shannon sampling includes redundant samples, and it is sufficient but not necessary to adequately record target signals. We propose an ergodic sampling, which avoids the redundant samples in the dense uniform sampling and possesses the ability to capture the sufficiently similar information content as does Nyquist sampling. Ergodicity means that a key part of the system can represent the average performance of the entire system. Our ergodic samples are a critical subset of dense uniform samples and can represent the full uniform Nyquist samples. To find such a critical subset, we first examine the properties of different sampling patterns, including the sampling interval distribution, sampling angle distribution, areal sample density, and resolution in the spectral domain. We define the information sampling ability of sampling patterns based on these properties. The concept of information sampling ability that we have proposed serves as the criterion to compare different sampling patterns and assess their sampling performances. The sampling patterns with the same information sampling ability have the same capability to gather information, even though the appearance of sampling patterns may be different. We formulate an optimization problem to find this critical subset of sample locations, which has the fewest number of samples but has a similar information sampling ability as that of the desired dense uniform samples. This critical subset is irregularly located, has the optimized properties and forms the ergodic sampling pattern. We define this process of sampling design and associated understanding as the ergodic sampling. Ergodic sampling can be applied to gain two major benefits in practice. First, this approach can save a significant number of samples. We demonstrate ergodic sampling using one‐dimensional synthetic data and a two‐dimensional field geophysical dataset. The simulations confirm that, compared with other sampling strategies, ergodic sampling can use fewer samples to acquire the same amount of information, so that we can save cost. Alternatively, with the same budget, we can use the same number of samples through ergodic sampling to acquire more information. The new ergodic sampling can lead to a new generation of economic and efficient geophysical data acquisition, which could assist in increasing the discovery rate in resource exploration, tackling more earth science problems with a limited budget and can also benefit the environment in the process by reducing the invasiveness in potentially sensitive regions.

Numerical simulation of diverging plasma magneto-hydrodynamic acceleration channels

This paper presents a numerical study of plasma flow in a magneto-hydrodynamic acceleration channel. The results show that in the channel with equal electrode pair spacing, increasing the magnetic field strength reduces the Joule heat dissipation and the temperature. Increasing the applied voltage increases the external energy input, increasing both the exit Mach number and the internal temperature. Reducing the electrical conductivity achieves a balance between acceleration and temperature rise. For acceleration channels of different shapes, a constant cross section channel can only accelerate the fluid to near sonic speeds, whereas a diverging channel can achieve supersonic speeds. In addition, maintaining constant electrode spacing in the diverging channel effectively prevents fluid deceleration at the rear of the acceleration channel caused by the reverse Lorentz force under high magnetic field strength.

Dosimetric Study of Total Marrow and Lymphoid Irradiation on a Ring Gantry-Based Medical Linac with a Two-Layer Multi-Leaf Collimator

In this study, we aimed to evaluate dosimetric quality of total marrow and lymphoid irradiation (TMLI) plans for a ring gantry-based medical Linac with a two-layer multi-leaf collimator. We retrospectively retrieved treatment planning CT images, structure sets, and plan dose for four adult patients, two male and two female, who previously received TMLI treatments on helical tomotherapy (HT) at our institution. TMLI plans were optimized for a ring gantry-based medical Linac with a two-layer multi-leaf collimator (Halcyon, Varian Medical Systems, Inc., Palo Alto, CA). A prescription dose of 12 Gy in 8 fractions was prescribed to the skeletal bones from the skull to mid-thigh, spleen, spinal canal, and lymphoid volume. Five or six isocenters were placed with equal spacing along the patient's longitudinal direction in each TMLI plan with two 6-MV flattening filter-free volumetric modulated arc therapy (VMAT) fields at each isocenter. Isocenter separation ranged from 15 cm to 16.5 cm. Each VMAT field has a field size of 28 cm to 28 cm with the collimator at 90° and a full gantry rotation. The nominal dose rate was 800 MU/minute, and the maximum gantry rotation speed was 24°/sec. Institutional dosimetric constraints were used for optimization including a mean lung dose limit of less than 8 Gy. All the plans were normalized so that 85% the primary planning target volume received the prescription dose. The average mean doses to the target volumes ranged from 12.2 to 12.6 Gy in the Halcyon TMLI plans, while they ranged from 12.1 to 12.5 Gy in the HT TMLI plans. Relative to the prescription dose, the average mean dose for normal organs ranged from 21.3% to 56.6% in the Halcyon TMLI plans, while it ranged from 10.1% to 68.4% in the clinical HT plans. The difference in the average mean dose to normal organs was less than 0.5 Gy except two organs between the Halcyon and HT TMLI plans. The average median dose for normal organs ranged from 18.2% to 48.8% relative to the prescription dose in the Halcyon TMLI plans. The mean lung dose (MLD) in the Halcyon TMLI plans met the institutional limit with an average dose of 6.75±0.42 Gy (range: 6.44 - 7.36 Gy), while the average MLD was 6.54±0.77 Gy (range: 6.24 - 7.22 Gy) in the HT plans (p-value = 0.71 in the paired t-test). The average total monitor unit in the Halcyon TMLI plans was 4,425±906 MU (range: 3,470 - 5,575 MU) with an average beam-on time of 5.1±1.3 minutes (range: 4.1 - 7.0 minutes), which excludes isocenter setup time, while the average beam-on time was 22.2±3.2 minutes (range: 19.6 - 26.1 minutes) with the HT plans. Halcyon TMLI plans met our institutional dosimetric constraints with adequate normal organ sparing and target dose coverage. The beam-on time with the Halcyon plans was significantly shorter than that with the HT plans, which could lead to shorter treatment time and increased patient comfort. This study showed the feasibility of TMLI treatments on the Halcyon machine. The same method could be used for total body irradiation on Halcyon.

Numerical Study on Internal and External Flow Fields of the UHMWPE Cage

Ultra-high molecular weight polyethylene (UHMWPE) is a new kind of fishing gear material applied in deep-sea fishing cages, which is becoming a trend. Studies on the internal and external flow fields of cages made of UHMWPE have been scarce previously. Therefore, a three-dimensional numerical model for the UHMWPE cage is established herein, where the cage is modeled by a porous media model. The Darcy–Forchheimer coefficients of the porous media are obtained by physical model experiments and numerical simulations. Then, the cylindrical cage is divided into 16 planar nets circumferentially, along with an additional bottom net, to investigate its internal and external flow fields numerically. For a single cylindrical cage, the degree of deceleration decreases as the flow velocity increases, and this effect becomes less apparent when the flow velocity reaches a certain threshold. Finally, the flow field characteristics of double cages with different spacing and multiple cages with equal spacing are revealed.

Data-driven multi-stage sampling strategy for a three-dimensional geological domain using weighted centroidal voronoi tessellation and IC-XGBoost3D

Conventional site investigation schemes typically use an empirical sampling strategy, which involves equal sampling spacing with regular grid patterns. However, this approach assigns equal importance to the entire site and does not account for subsurface stratigraphic variations and site constraints. In this study, a data-driven multi-stage sampling strategy is proposed to adaptively optimize the borehole locations for a three-dimensional (3D) geotechnical site, considering the subsurface stratigraphic uncertainties and irregular site geometries. The initial sampling plan is determined based on weighted centroidal Voronoi tessellation, which assigns various sampling densities to zones depending on their importance. Measurements obtained in the previous sampling stage are combined with prior geological knowledge to establish and update a 3D geological domain using a physics-informed geological modelling method. The next optimal location for sampling is adaptively determined with the objective of maximizing the reduction in the stratigraphic uncertainty. The proposed method represents the first data-driven 3D site planning method that explicitly considers 3D subsurface stratigraphic variations. The performance of the proposed multi-stage sampling strategy is illustrated using a simulation study. The results indicate that the proposed method efficiently identifies the optimal sampling locations while comprehensively considering the 3D subsurface geological uncertainties and irregular site geometries.

Dissecting the phase separation and oligomerization activities of the carboxysome positioning protein McdB.

Across bacteria, protein-based organelles called bacterial microcompartments (BMCs) encapsulate key enzymes to regulate their activities. The model BMC is the carboxysome that encapsulates enzymes for CO2 fixation to increase efficiency and is found in many autotrophic bacteria, such as cyanobacteria. Despite their importance in the global carbon cycle, little is known about how carboxysomes are spatially regulated. We recently identified the two-factor system required for the maintenance of carboxysome distribution (McdAB). McdA drives the equal spacing of carboxysomes via interactions with McdB, which associates with carboxysomes. McdA is a ParA/MinD ATPase, a protein family well studied in positioning diverse cellular structures in bacteria. However, the adaptor proteins like McdB that connect these ATPases to their cargos are extremely diverse. In fact, McdB represents a completely unstudied class of proteins. Despite the diversity, many adaptor proteins undergo phase separation, but functional roles remain unclear. Here, we define the domain architecture of McdB from the model cyanobacterium Synechococcus elongatus PCC 7942, and dissect its mode of biomolecular condensate formation. We identify an N-terminal intrinsically disordered region (IDR) that modulates condensate solubility, a central coiled-coil dimerizing domain that drives condensate formation, and a C-terminal domain that trimerizes McdB dimers and provides increased valency for condensate formation. We then identify critical basic residues in the IDR, which we mutate to glutamines to solubilize condensates. Finally, we find that a condensate-defective mutant of McdB has altered association with carboxysomes and influences carboxysome enzyme content. The results have broad implications for understanding spatial organization of BMCs and the molecular grammar of protein condensates.

Estimating Public Transportation Accessibility in Metropolitan Areas: A Case Study and Comparative Analysis

Accessibility-oriented public transportation planning can improve the operational efficiency of public transportation, guide orderly urban development, and alleviate issues such as traffic congestion, environmental pollution, and resource consumption in large cities. To promote the practical application and widespread adoption of public transportation accessibility estimating systems, this study proposes an improved public transport accessibility levels (PTAL) method. It innovatively incorporates residents’ preference indices for different modes of transportation and addresses the challenge of missing timetable data in the calculation process. Using actual data from Shenzhen, a case study is conducted to analyze the public transportation accessibility index and compare the results obtained through k-means clustering, the equal spacing method, the quantile method, and the application of the London PTAL method. The research findings indicate that the optimal number of clusters for public transportation accessibility index analysis in large cities is six when using clustering algorithms. Among the statistical analysis methods, the quantile method shows favorable performance. Furthermore, a comprehensive comparison of different classification methods confirms that the improved PTAL method offers better discrimination in estimating public transportation accessibility levels compared to the London PTAL method. The study concludes by providing guidance on how cities with different characteristics can reference the improved PTAL method.

Fragmentation of inflated elastic brittle rings: Emergence of the quasi-equidistant spacing of cracks

The order of appearance and the position of meridional cracks in brittle domes is a delicate question of mechanics. This paper investigates a dimension-reduced model, a pressurized brittle ring constrained to the plane, to show that a simple, deterministic approach based on the Griffith theory of fracture predicts quasi-equidistant, i.e., close to an equal spacing of the emerging cracks. It is also demonstrated that the order of emergence is significantly affected by the variation of the in-plane elastic support as well the bending rigidity of the ring. In the model, the energy minimization is first recast into a sequence of coupled boundary value problems. The relationship between the mechanical model and geometric properties of the emerging pattern is studied numerically. The pattern is shown to be driven by elaborate co-dimension one bifurcations and by the requirement of global energy minimization.