Number Of Strands Research Articles

Enhancing the Biomimetic Mechanics of Bottlebrush Graft-Copolymers through Selective Solvent Annealing.

Self-assembled networks of bottlebrush copolymers are promising materials for biomedical applications due to a unique combination of ultra-softness and strain-adaptive stiffening, characteristic of soft biological tissues. Transitioning from ABA linear-brush-linear triblock copolymers to A-g-B bottlebrush graft copolymer architectures allows significant increasing the mechanical strength of thermoplastic elastomers. Using real-time synchrotron small-angle X-ray scattering, it is shown that annealing of A-g-B elastomers in a selective solvent for the linear A blocks allows for substantial network reconfiguration, resulting in an increase of both the A domain size and the distance between the domains. The corresponding increases in the aggregation number and extension of bottlebrush strands lead to a significant increase of the strain-stiffening parameter up to 0.7, approaching values characteristic of the brain and skin tissues. Network reconfiguration without disassembly is an efficient approach to adjusting the mechanical performance of tissue-mimetic materials to meet the needs of diverse biomedical applications.

The homology of a Temperley–Lieb algebra on an odd number of strands

The homology of a Temperley–Lieb algebra on an odd number of strands

Extensor Tendon Repair.

Extensor tendon injuries are a common condition that hand surgeons must be prepared to treat. The area of extensor tendon injury can traditionally be broken down into 9 zones. Physical examination is the best way to diagnose extensor tendon injury with a loss of active extension in the injured digit. The tenodesis effect may be utilized to aid in diagnosis: wrist flexion should cause passive extension at the metacarpophalangeal, proximal interphalangeal, and distal interphalangeal joints if the extensor tendon is in continuity. Repair of extensor tendon injuries depends on the zone of injury and the thickness of the tendon, which determines its ability to hold core sutures. For zone-I and II injuries, several "figure of 8" buried sutures can be utilized or a running type of suture may be employed. For zone-III to VII injuries, 1 or 2 core sutures and a supplementary running suture can be utilized. Several alternative techniques have been previously described. These include variations in the number of core strands, repair configuration, and suture caliber, as well as the use of epitendinous repair. Alternative treatments also include nonoperative treatment, which is typically reserved for partial tendon injuries and for patients who are unable to tolerate a surgical procedure. The techniques that we describe are tailored to the thickness of the tendon. Running sutures are applicable to any zone, whereas core sutures are best utilized in zones III through VII. The running interlocking horizontal mattress technique has been found to be stiffer and faster to accomplish compared with the other techniques, and was found to have good to excellent clinical results in a study of lacerations in zones IV and V1,2. Repair of extensor tendon lacerations has demonstrated good long-term outcomes if performed in a timely manner after injury. A previous study showed good to excellent function in up to 64% of acute extensor tendon repairs, more fingers lost the ability to flex fully than lost the ability to extend3. Systematic reviews have suggested that dynamic rehabilitation may not provide superior long-term benefit compared with static splinting4. The Elson test should be performed under a digital nerve block in order to properly assess the integrity of the central slip.In distal zone I and III injuries, suture anchors or bone tunnels may be utilized when there is no remaining tendon on the distal end of the laceration.When preparing the tendon ends for repair, it is important to handle the tendon delicately-preferably through the cut end of the tendon rather than the tendon itself.In zone-VII injuries, the injured tendon may lie beneath the extensor retinaculum. In such cases, windowing of the extensor retinaculum may decrease adhesion formation and facilitate repair. MCP = metacarpophalangealPIP = proximal interphalangealDIP = distal interphalangealIP = interphalangealROM = range of motionRMS = relative motion splintRIHM = running interlocking horizontal mattress.

Optimization and forecasting of reinforced wire ropes for tower crane by using hybrid HHO-PSO and ANN-HHO algorithms

Wire rope is a vital component of every crane. Wire rope faults are related to the operation, fabrication environment, etc., and the prevalent mode of failure is fatigue. The aim of this study is to develop an advanced tower crane applicable to wire rope with integrated reinforcement. Steel wire ropes are superiorly used in several tower crane applications, but they may create certain failures such as less fatigue and wear-resistant. In this study, steel wires are strengthened by granite and Zinc oxide (ZnO) reinforcement. Two sets of wire ropes are prepared as complete and partial reinforcement of steel wire with seven strands and 15 wires. The failure tests such as hardness, wear analysis, tensile strength, and fatigue life are optimized using hybrid Harris Hawk optimization-based Particle swarm Optimization (Hybrid HHO-PSO). Besides, the experimented wire rope performances are predicted using hybrid Artificial Neural Network based HHO (Hybrid ANN-HHO). Fully reinforced wire ropes provide better performances for both experimented and optimization behaviors. This provides 1818 MPa of maximum tensile strength, 0.23 mm of minimal wear depth, and 3.38x104 times better fatigue life. In the HHO-PSO optimization method, the obtained better tensile strength is 1822 MPa, wear depth is 0.66 mm, and Fatigue life is 3.57 x104 times. Besides, from the predicted outcomes, ANN-HHO provides a minimal error value than the ANN approach. The result of this study will open up different ways for the advancement of wire rope in tower crane application by improving its load bearing capacity. The outcomes from this research can be practically applicable for increasing the load bearing capacity of the tower crane without increasing the number of wires and strands in the wire rope.

Biomechanical analysis of cadaver rabbit Achilles tendons after full transection and suture: Comparison of U-Tang 4-strand with the cross-locked version of U-Tang 4-strand suture technique

IntroductionTendon injures rank as the second most common hand injuries, and unsatisfactory repair can significantly impact a patient's everyday life. Over the years, various suture techniques have been studied in the pursuit of finding the optimal repair method. The ideal tendon repair should achieve maximum strength, while being easy to perform and minimizing tissue trauma. This study aims to compare the mechanical properties of the cross-locked U-Tang 4-strand suture to its unmodified version, the U-Tang 4-strand suture, to assess which technique offers greater repair strength. MethodsSixteen Achilles tendons from New Zealand White rabbits were randomly assigned to one of two suture technique groups; an original U-Tang 4-strand suture or a cross-locked U-Tang 4-strand suture, both performed using a 4-0 Supramid thread. The specimens were tested in uniaxial tension after a preconditioning phase. Cross-sectional area, load until failure, gap formation, stiffness, elastic modulus, and failure stress were determined. ResultsThe standard U-Tang 4-strand suture withstood a maximum force of 25.48 ± 6.06 N, while the cross-locked version endured 33.90 ± 6.09 N. This indicates that the modified version demonstrated significantly greater strength (p = 0.021). The elastic modulus of the cross-locked U-Tang 4-strand suture (0.02 ± 0.003 MPa) was significantly higher than that of the original version (0.01 ± 0.006 MPa) (p = 0.028). No significant differences were observed regarding the cross-sectional area, load at 2 mm gap formation, stiffness and failure stress. ConclusionEmploying the cross-locked U-Tang 4-strand suture results in a significantly greater maximum force and elastic modulus compared to the original U-Tang 4-strand suture, utilizing the same thread and number of strands and knots. Therefore, the cross-locking version provides an alternative for achieving more stable initial repair strength.

First look at the distribution of deactivated dFADs used by the French Indian Ocean tropical tuna purse-seine fishery

Abstract The presence of abandoned, lost or otherwise discarded fishing gears, including drifting fish aggregating devices (dFADs), in marine ecosystems poses significant ecological and socioeconomic concerns. The estimation of the number of dFADs in the marine environment is challenging due to the loss of tracking information when dFAD tracking buoys are remotely deactivated. For the first time, a data set of dFADs buoy positions, including those that had previously been remotely deactivated, has been made available for the period July–August 2020. Data from this period provide valuable insights into the life expectancy, spatial distribution, and status of deactivated dFAD buoys, enabling a more accurate assessment of dFAD presence and impacts. Deactivated buoys represented a 17.2% increase in the total number of tracked objects, and we estimate the in-water half-life of deactivated dFAD tracking buoys to be 101 days. Including deactivated buoys increases the number of strandings during the SP by 23.7%. Nevertheless, the representativity of these results is unknown given the limited spatio-temporal and numerical extent of our data, highlighting the importance of availability of comprehensive data on dFADs to effectively estimate their total numbers and mitigate their environmental impacts.

Numerical investigation for shear behavior of pretensioned spun precast concrete pile

Pretensioned spun precast concrete (SPC) pile has emerged as a popular solution for deep foundation systems due to its ease of construction, enhanced bearing capacity, and overall cost-effectiveness. However, the hollowness of SPC piles, which reduces their sectional area, may become critical near the pile cap zone, especially in liquefaction scenarios during earthquake events. This study numerically investigates the shear behavior of hollow pre-tensioned SPC piles using the Finite Element (FE) technique. Primarily, the numerical results are validated with the test results of actual SPC piles where they were manufactured by high-strength concrete and high-tensioned steel strands for both with and without spirals. The numerical results show a good agreement with the experimental data in terms of strength, stiffness, and failure pattern for both types of spiral arrangements. The numerically obtained shear capacity is also found to be within close range of the code recommendations. A series of parametric studies have been conducted to understand the influence of essential pile parameters such as spiral’s spacing, effective prestress, number of strands, thickness-to-diameter ratio, concrete strength, and test orientation angle on the shear resistance of SPC pile. The study claimed that the addition of shear reinforcements to SPC piles boosts their shear capability, whereas the addition of strands and angle of test orientation have little effect on the piles' shear resistance. The optimum applied pre-stressing was found in a range of 4–8 MPa. The optimum values of t/d ratios in terms of material savings to shear resistance of the SPC pile fall in a range of 0.20 – 0.30. Morris Sensitivity Analysis (MSA) reveals that effective prestress and pile concrete strength are the most influential parameters of the shear capacity of SPC piles. This study provides important details for the SPC pile's shear design, illustrating its applicability in deep foundations in seismic areas.

Real-time Physically Guided Hair Interpolation

Strand-based hair simulations have recently become increasingly popular for a range of real-time applications. However, accurately simulating the full number of hair strands remains challenging. A commonly employed technique involves simulating a subset of guide hairs to capture the overall behavior of the hairstyle. Details are then enriched by interpolation using linear skinning. Hair interpolation enables fast real-time simulations but frequently leads to various artifacts during runtime. As the skinning weights are often pre-computed, substantial variations between the initial and deformed shapes of the hair can cause severe deviations in fine hair geometry. Straight hairs may become kinked, and curly hairs may become zigzags. This work introduces a novel physical-driven hair interpolation scheme that utilizes existing simulated guide hair data. Instead of directly operating on positions, we interpolate the internal forces from the guide hairs before efficiently reconstructing the rendered hairs based on their material model. We formulate our problem as a constraint satisfaction problem for which we present an efficient solution. Further practical considerations are addressed using regularization terms that regulate penetration avoidance and drift correction. We have tested various hairstyles to illustrate that our approach can generate visually plausible rendered hairs with only a few guide hairs and minimal computational overhead, amounting to only about 20% of conventional linear hair interpolation. This efficiency underscores the practical viability of our method for real-time applications.

An automated optimized design of practical post-tensioned slabs

In this paper, an efficient methodology that could be implemented within any analysis software is developed to automate the design process of post-tensioned slabs. Optimization techniques are used to compute the necessary number of strands. The present methodology is based on computing an innovative influence matrix that contains the effect of each strand on stresses at a set of control points (points of peak stresses). This matrix will be used in the optimization avoiding reanalysis in each optimization iteration. The sum of the squares of the difference between the allowable stress and the computed stresses at all control points is considered an objective function. The optimization is then carried out under the constraints that the stresses at each control point should not exceed the allowable limit and to ensure that the number of strands is an integer value. Alternatively, the proposed methodology could be used as a value-engineering tool. Practical examples are presented to demonstrate the efficiency of the developed methodology.

Modeling the Performance Parameters of Pollen Grains of Male Date Palms Using an Artificial Neural Network Based on the Mineral Composition and Morphological Properties of Their Leaves

One of the key factors for sustainability in agricultural systems, particularly, for cultivation of date palms, is the identification of the performance parameters of the pollen grains of male date palms (Phoenix dactylifera L.). This study was carried out to predict the performance parameters of pollen grains using an artificial neural network (ANN) model. The morphological features of spathe length, spathe weight, number of pinnae per leaf, leaf length, leaf width, length of the pinna part, pinna length, pinna width, length of the spathe stem, and spathe width, as well as the concentrations of minerals such as Mg, N, K, P, and Ca in their leaves were used as inputs to the ANN model. For this purpose, we collected the required data from nine male date palms grown in Saudi Arabia. The ANN model utilized in this work included an input layer with 15 parameters, a hidden layer of 30 neurons, and an output layer with 8 neurons. The ANN model was trained with 27 patterns. Seven patterns were utilized for testing purposes. The coefficient of determination (R2) obtained between the observed and predicted performance parameters’ values using the testing dataset was 0.902 for the number of strands per spathe, 0.967 for strand length, 0.963 for the number of flowers per strand, 0.941 for the number of flowers per spathe, 0.985 for the weight of pollen grains per spathe, 0.810 for the pollen grains’ viability, 0.936 for the pollen grains’ length, and 0.992 for the pollen grains’ width. The length of the spathe stem had the most critical effect on how the ANN model predicted the values of the dependent variables, i.e., the number of strands per spathe, with a percentage of contribution of 17.66%; the weight of pollen grains per spathe, with 17.85%; the pollen grains’ length, with 19.78%, and the pollen grains’ width, with a percentage of contribution of 30.59%. Spathe weight had the most critical influence on strand length and pollen grains’ viability, with percentages of 26.29% and 14.92%, respectively. Leaf width had the most critical effect on the number of flowers per spathe, with a percentage of 12.55%. The elemental concentration of K in the male date palm leaves had the most critical effect on the number of flowers per strand, with a percentage of 13.98%. It was therefore concluded that using a modeling process with the ANN technique can help estimate the performance parameters of male date palms’ pollen grains for different purposes, such as providing a starting point for mathematical analyses associated with the physiological mechanisms of male date palm. Moreover, the outcomes of this research work can be supportive as a practical tool in this field of study.

Evolution of RNA Viruses: Reasons for the Existence of Separate Plus, Minus, and Double-Strand Replication Strategies.

Plus, minus, and double-strand RNA viruses are all found in nature. We use computational models to study the relative success of these strategies. We consider translation, replication, and virion assembly inside one cell, and transmission of virions between cells. For viruses which do not incorporate a polymerase in the capsid, transmission of only plus strands is the default strategy because virions containing minus strands are not infectious. Packaging only plus strands has a significant advantage if the number of RNA strands produced per cell is larger than the number of capsids. In this case, by not packaging minus strands, the virus produces more plus-strand virions. Therefore, plus-strand viruses are selected at low multiplicity of infection. However, at high multiplicity of infection, it is preferable to package both strands because the additional minus virions produced are helpful when there are multiple infections per cell. The fact that plus-strand viruses are widespread while viruses that package both strands are not seen in nature suggests that RNA strands are indeed produced in excess over capsids, and that the multiplicity of infection is not sufficiently high to favor the production of both kinds of virions. For double-strand viruses, we show that it is advantageous to produce only plus strands from the double strand within the cell, as is observed in real viruses. The reason for the success of minus-strand viruses is more puzzling initially. For viruses that incorporate a polymerase in the virion, minus virions are infectious. However, this is not sufficient to explain the success of minus-strand viruses, because in this case, viruses that package both strands outcompete those that package only minus or only plus. Real minus-strand viruses make use of replicable strands that are coated by a nucleoprotein, and separate translatable plus strands that are uncoated. Here we show that when there are distinct replicable and translatable strands, minus-strand viruses are selected.

Single bundle hamstrings autograft preparation techniques for anterior cruciate ligament reconstruction: current concepts.

Anterior cruciate ligament reconstruction (ACLR) is one of the most common orthopedic procedures, and huge variation exists in the surgical technique. Single bundle hamstrings autograft reconstruction is a common method and has good clinical outcomes. A criticism of the hamstrings autograft is a small graft diameter, often less than 8-mm, which has been associated with increased re-rupture rates. Several graft preparation techniques for single bundle hamstrings autograft exist. Perioperative decisions include the number of tendons utilized, number of graft strands, graft configuration, and femoral and tibial fixation methods. Awareness of the minimum tendon and graft length required to produce each graft variation is necessary to avoid common pitfalls. However, intraoperative graft modification is possible to maximize graft diameter, and obtain proper fixation. The objective of this current concepts review is to describe the indications, surgical anatomy, technique, intraoperative tips, clinical outcomes, and complications for single bundle hamstrings autograft preparation techniques in ACLR.

Highly conductive AuNPs/Co-MOF nanocomposites synergistic hybridization chain reaction enzyme-free electrochemical aptasensor for ultrasensitive detection of Aflatoxin B1

Aflatoxin B1 (AFB1) is the most poisonous and carcinogenic pollutant among numerous mycotoxins, posing a serious risk to the health of humans. Herein, an electrochemical aptasensor was constructed for AFB1 detection using gold nanoparticles/cobalt-based metal–organic skeleton (AuNPs/Co-MOF) as a modifying material combined with an enzyme-free signal amplification strategy. AuNPs/Co-MOF have an extensive specific surface area and outstanding electrical conductivity, which allows for the loading of a large number of DNA strands and enhancement of the thionine (THi) redox signal, leading to a significant increase in signal response THi loaded bimetallic core–shell nanocomposites (Au@PtNPs) were synthesized as signal labels. Au@PtNPs have high catalytic activity towards THi while improving the efficiency of the loaded THi, which enables the electrochemical signal of THi to be amplified. In addition, the hybridization chain reaction (HCR) signal amplification strategies for enzyme-free amplification elicits a strong response in the electrochemical signal while ensuring sensor stability. The aptasensor has a detection range of 0.001–500 ng/mL and achieves the limit of detection (LOD) was 1.2 × 10-2 pg/mL and limit of quantification (LOQ) was 4.0 × 10-2 pg/mL under optimal experimental conditions. Therefore, applications for electrochemical aptasensors in the realm of food safety monitoring are quite promising.

The effect of the number of strands and knot throws of core suture techniques on the mechanical properties of the repaired flexor tendon.

Flexor tendon injury is a common hand trauma that requires surgical repair. The objective was to compare the repaired strength and gliding resistance with a varied number of repair strands and of square knots using a two-strand-overhand locking (TSOL) knot. First, isolated suture loops with different number of suture strands and number of closing knots were compared in mechanical strength and failure mode. Then, 90 flexor digitorum profundus (FDP) tendons from turkey digits were used for the tendon repair experiment. Both phases followed a similar 3 × 3 matrix comparing the knot type including TSOL+1SK (square knot), TSOL+2SK, and TSOL+3 SK and repair techniques including two-, four-, and six-strand repairs techniques respectively. The repaired tendons were tested for tendon resistance against pulley (friction), maximum force, force at 2 mm displacement, stiffness, and failure mode. Increasing the number of strands and closing square knots increases the tensile strength and stiffness of flexor tendon repairs and isolated suture loops without a significant effect on tendon friction. An increase in the number of square knots have shown increased strength only in Pennington repair, which correlated with the increased number of knot unraveling, a weak knot failure model. Our data demonstrated that increasing the number of strands is effective for improving the overall strength of tendon repair. When a two-strand repair is chosen, increasing knot number can improve repair strength. However, the number of knots appears not affecting repair strength in six-strand repair technique.

Spatial and temporal trends of Tamanend’s bottlenose dolphin (Tursiops erebennus) strandings in South Carolina, USA, 2006–2020

Marine mammal strandings data contribute towards overall assessments of cetacean populations, including seasonal, annual and life‐history trends which result from both natural and anthropogenic causes. We conducted spatial and temporal analyses of Tamanend’s bottlenose dolphin (Tursiops erebennus) strandings in the waters of South Carolina, USA, over a 15‐year period from 2006 to 2020, with the following objectives: (1) to determine spatial and temporal trends; (2) to analyse seasonal reproductive trends; (3) to determine life‐history parameters, such as sex ratio and age class; (4) to determine the extent to which human interaction contributed to strandings; and (5) to compare stranding patterns with historical data from 1992–2005. A total of 837 strandings occurred over the study period, with a mean of 55.8 strandings per annum. The season with most strandings was Spring (April–June), while March and April had the highest number of strandings. A relatively equal number of male and females dolphins stranded, and mortality was highest in neonates, first‐year calves and adults. Neonatal strandings comprised 22.1% of all strandings and were predominant in May. Ninety‐five human‐interaction (HI) cases were observed, representing 22.9% of strandings where HI or non‐HI could be determined. Confirmed crab‐pot buoy‐line entanglements were the predominant HI category (n = 31). Density maps and hot spot analysis showed most strandings, including live and neonatal strandings and HI cases, occurred in defined areas of Charleston and Beaufort Counties. While many trends were similar to historical data, some new trends emerged, particularly an increase of strandings in March and April. Neonatal strandings decreased in November and the historical spike during this month has essentially disappeared. The results of this analysis serve as a tool to predict stranding rates and inform conservation and management decisions to better protect bottlenose dolphins.

Conformational transformation of activator strand directly regulates CRISPR/Cas12a system activity for live cell sensing of multiple biomolecules

In recent years, biosensors designed based on the CRISPR/Cas12a system have opened up a new era in biosensing. However, the activator strand in the existing CRISPR/Cas12a-based sensing strategies are usually designed with 20 bases complementary to crRNA, it is difficult to completely shut down the trans-cleavage activity of the CRISPR/Cas12a system. To address this issue and simultaneously construct a biosensor with an “on-off-on” mode, we shortened the activator strand complementary to crRNA to 16 bases and embedded it into a hairpin structure depriving its ability to activate the Cas12a. We all know that the binding of aptamers with small molecules involves folding into a complex structure that is complementary to the surface of small molecules, thus forming a stable complex. To further expand the application of the CRISPR/Cas12a system in the field of biosensors, we selected small-molecule ATP and nucleolin as targets to confirm that the formation of the complex three-dimensional structure at the 3′- end of activator strand does not affect the activity of CRISPR/Cas12a system. Therefore, by designing only one allosteric activator strand, it is possible to regulate CRISPR/Cas12a system’s activity. This design not only reduces the number of DNA strands used in the sensing system, but also eliminates the need for complex concentration optimization operations. Furthermore, the stability of the intramolecular hairpin structure can minimize fluctuations in the background signal, ensuring stable and low-background signals in live cell applications, this further expands the toolbox of applications for the CRISPR/Cas12a system.

Noise and fading reduction in a phase-OTDR system using a multi-strand optical fiber sensing cable

This paper introduces an innovative architecture, to the best of our knowledge, for a phase-OTDR sensing system, employing a multi-strand optical fiber cable as the sensing element. Within the cable, the fiber strands are interconnected to form a single serpentine-shaped fiber. The key advantage of this architecture lies in its ability to enhance the detection performance of a phase-OTDR system by reducing missing alarms caused by interference fading. Additionally, noise reduction can be achieved by aggregating the sub-traces corresponding to all fiber strands. To further enhance performance, we associate the use of a multi-pulse averaging method, which involves aggregating traces obtained using multiple probe pulses with varying temporal widths. The results obtained indicate that the performance of this architecture is closely related to the number of fiber strands and the number of probe pulses used. We expect that the proposed phase-OTDR architecture is particularly well-suited for effective distributed intrusion monitoring applications in short- to medium-range sensitive infrastructures where high security is paramount.

Experimental study on the flexural performance of prestressed RC beams with post-tensioned CFRP strands

Carbon fiber reinforced polymer (CFRP) exhibits multiple advantages over conventional steel, such as high strength and corrosion resistance. By replacing prestressing steel with prestressing CFRP in new prestressed reinforced concrete (RC) structures, the corrosion issue of prestressing steel can be resolved. At present, there remains scarce research on the application of CFRP strands in the prestressed RC structures. An experimental study was conducted on prestressed RC beams with internal post-tensioned CFRP strands under flexure. The study aimed to analyze the effects of the prestress level, number of CFRP strands, layout shape of CFRP strands, bonding layer, and reinforcement ratio of steel bars on the flexural behavior. The test results indicated that all specimens experienced concrete crushing failure. After applying prestressing CFRP strands to ordinary RC beams, the cracking load increased by 50.0% to 102.2%, the yielding load increased by 20.2% to 38.6%, and the ultimate load increased by 20.3% to 41.4%. Reducing the reinforcement ratio of steel bars had a minor effect on the cracking load but resulted in a noticeable decrease in the yielding and ultimate loads of the prestressed CFRP strand-reinforced concrete beams. Moreover, the bonded specimen showed a slight increment in the cracking, yielding, and ultimate loads as well as stiffness compared to the unbonded specimen, while the deformation capacity of the unbonded specimen remained superior. The specimens with curved and straight prestressing CFRP strands exhibited very similar mechanical properties.

Khovanov homology, wedges of spheres and complexity

Our main result has topological, combinatorial and computational flavor. It is motivated by a fundamental conjecture stating that computing Khovanov homology of a closed braid of fixed number of strands has polynomial time complexity. We show that the independence simplicial complex I(w) associated to the 4-braid diagram w (and therefore its Khovanov spectrum at extreme quantum degree) is contractible or homotopy equivalent to either a sphere, or a wedge of two spheres (possibly of different dimensions), or a wedge of three spheres (at least two of them of the same dimension), or a wedge of four spheres (at least three of them of the same dimension). On the algorithmic side we prove that finding the homotopy type of I(w) can be done in polynomial time with respect to the number of crossings in w. In particular, we prove the wedge of spheres conjecture for circle graphs obtained from 4-braid diagrams. We also introduce the concept of Khovanov adequate diagram and discuss criteria for a link to have a Khovanov adequate braid diagram with at most 4 strands.

Sensitive detection of exosomes by an electrochemical aptasensor based on double nucleic acid amplifications

Exosomes are extracellular vesicles secreted by mammalian cells and recognized as a powerful non-invasive cancer marker because they carry the cellular components specific to parent cells. The development of a convenient, rapid and sensitive exosome detection method is very important for the early diagnosis of cancer. In this study, an electrochemical biosensor based on two signal amplification methods, primer exchange reaction (PER) and rolling circle amplification (RCA), was developed for the high sensitive detection of exosomes. First, exosomes were specifically captured by CD63 aptamer and DNA strands (T) were released through a chain replacement reaction. Then the T strands initiated the PER reaction, producing a large number of short strands of DNA (P). Afterwards, RCA reaction was carried out on the electrode surface. Finally, a large amount of horseradish peroxidase (HRP) was bound to the electrode surface to catalyze o-phenylenediamine (OPD) oxidation, and the reduction current signal was obtained to realize the quantitative detection of exosomes. Under the optimal experimental conditions, there was a good linear relationship between DPV signal and the logarithm of exosome concentration in the range of 88 ∼ 8.8 × 106 particle/μL with a low limit of detection of 22 particle/μL. This strategy could realize sensitive detection of exosomes and provide a new strategy for the detection of other tumor markers.