Clusters Of Loops Research Articles

Deciphering Solar Coronal Heating: Energizing Small-scale Loops through Surface Convection

The solar atmosphere is filled with clusters of hot small-scale loops commonly known as coronal bright points (CBPs). These ubiquitous structures stand out in the Sun by their strong X-ray and/or extreme-ultraviolet (EUV) emission for hours to days, which makes them a crucial piece when solving the solar coronal heating puzzle. In addition, they can be the source of coronal jets and small-scale filament eruptions. Here we present a novel 3D numerical model using the Bifrost code that explains the sustained CBP heating for several hours. We find that stochastic photospheric convective motions alone significantly stress the CBP magnetic field topology, leading to important Joule and viscous heating concentrated around the CBP’s inner spine at a few megameters above the solar surface. We also detect continuous upflows with faint EUV signals resembling observational dark coronal jets and small-scale eruptions when Hα fibrils interact with the reconnection site. We validate our model by comparing simultaneous CBP observations from the Solar Dynamics Observatory (SDO) and the Swedish 1‐m Solar Telescope (SST) with observable diagnostics calculated from the numerical results for EUV wavelengths as well as for the Hα line using the Multi3D synthesis code. Additionally, we provide synthetic observables to be compared with Hinode, Solar Orbiter, and the Interface Region Imaging Spectrograph (IRIS). Our results constitute a step forward in the understanding of the many different facets of the solar coronal heating problem.

Ultra-long-range interactions between active regulatory elements.

Contacts between enhancers and promoters are thought to relate to their ability to activate transcription. Investigating factors that contribute to such chromatin interactions is therefore important for understanding gene regulation. Here, we have determined contact frequencies between millions of pairs of cis-regulatory elements from chromosome conformation capture data sets and analyzed a collection of hundreds of DNA-binding factors for binding at regions of enriched contacts. This analysis revealed enriched contacts at sites bound by many factors associated with active transcription. We show that active regulatory elements, independent of cohesin and polycomb, interact with each other across distances of tens of megabases in vertebrate and invertebrate genomes and that interactions correlate and change with activity. However, these ultra-long-range interactions are not dependent on RNA polymerase II transcription or individual transcription cofactors. Using simulations, we show that a model of chromatin and multivalent binding factors can give rise to long-range interactions via bridging-induced clustering. We propose that long-range interactions between cis-regulatory elements are driven by at least three distinct processes: cohesin-mediated loop extrusion, polycomb contacts, and clustering of active regions.

Transition between a nano-sized prismatic dislocation loop and vacancy cluster in α-iron: An atomic scale study

Plastic deformation and the presence of hydrogen enhance the concentration of vacancy-type defects in α-iron, wherein monovacancies can accumulate as a planar vacancy cluster (VC). The planar VC can then be nucleated into a corresponding prismatic dislocation loop (PDL), which can also be directly generated through cross-slip mechanisms of a screw dislocation. Inversely, a PDL can be converted to a corresponding VC. High densities of VCs and PDLs can significantly influence the mechanical properties of iron-based materials. Here, a quantitative energy barrier is established for the transition between nano-sized 1/2 〈111〉 PDLs and VCs using the nudged elastic band method for different applied strains. It was concluded that a cluster size of more than 19 vacancies can easily nucleate into a PDL if a VC with planar configuration is formed in α-iron. Further, the nano-sized VC to PDL transition is enhanced under compressive strain while the nano-sized PDL to VC transition is enhanced under tensile strain. This result indicates that nano-sized VCs generated by tensile deformation are converted to a PDL after unloading and diffusing away. Inversely, nano-sized PDLs that form by deformation can easily diffuse to high tensile stress regions near stress singularities, such as crack tips and triple-junctions of grain boundaries, and then accumulate as high-density VCs.

Evolutionarily distinct and sperm-specific supersized chromatin loops are marked by Helitron transposons in Xenopus tropicalis

Transposable elements (TEs) are abundant in metazoan genomes and have multifaceted effects on host fitness. However, the mechanisms underlying the functions of TEs are still not fully understood. Here, we combine Hi-C, ATAC-seq, and ChIP-seq assays to report the existence of multimegabase supersized loop (SSL) clusters in the Xenopus tropicalis sperm. We show that SSL anchors are inaccessible and devoid of the architectural protein CTCF, RNA polymerase II, and modified histones. Nearly all SSL anchors are marked by Helitrons, a class II DNA transposon. Molecular dynamics simulations indicate that SSL clusters are likely formed via a molecular agent-mediated chromatin condensation process. However, only slightly more SSL anchor-associated genes are expressed at late embryo development stages, suggesting that SSL anchors might only function in sperm. Our work shows an evolutionarily distinct and sperm-specific genome structure marked by a subset of Helitrons, whose establishment and function remain to be explored.

Abdominal Cocoon Syndrome (ACS) or Idiopathic Sclerosing Peritonitis: An Extremely Rare Cause of Intestinal Obstruction

Introduction: Abdominal cocoon syndrome is an extremely rare cause of intestinal obstruction in which loops of small bowel are encapsulated by a fibro-collagenous membrane. This condition is also known in the literature as sclerosing peritonitis, and in the majority of cases, it has no known cause. The majority of patients exhibit long-standing signs and symptoms of partial intestinal obstruction. Presentation of case: A 15-year-old female patient presented with complete intestinal obstruction with no known co-morbidity and no history of prior laparotomy. Intraoperatively, the entire small bowel was found to be encapsulated by a dense fibrous sac. The peritoneal sac was excised, followed by lysis of the inter-loop adhesions with appendicectomy done at the same time. Discussion: Most patients with abdominal cocoon syndrome present with features of recurrent acute or chronic small bowel obstruction secondary to kinking and/or compression of the intestines within the constricting cocoon. An abdominal mass may also be present due to an encapsulated cluster of dilated small bowel loops. Conclusions: Abdominal cocoon is a rare condition causing intestinal obstruction, and diagnosis requires a high index of suspicion because of the non-specific clinical picture. Contrast-enhanced CT-scan (CT) of the abdomen is a useful radiological tool to aid in preoperative diagnosis. Peritoneal sac excision and adhesiolysis is the treatment, and the outcome is usually satisfactory.

Obstructed Left Paraduodenal Hernia with Spontaneous Reduction Demonstrated on Computed Tomography: A Case Report

Paraduodenal hernias (PDH) are the most frequently occurring internal hernia, caused due to nonfusion between inferior mesentery and parietal peritoneum. The herniation of the bowel through the fossa of Landzert results in the left paraduodenal hernia which constitutes 75% of PDH. A case of a 34-year-old male with obstructed left PDH and a spontaneous reduction is demonstrated on Computed Tomography (CT). The patient had a cluster of jejunal loops forming a sac-like mass in the left anterior pararenal space, with surrounding mass effect with twisting and stretching of the mesenteric vessels at the hernia orifice, which showed a spontaneous reduction on subsequent contrast-enhanced and delayed CT studies. Despite the imaging evidence of spontaneous reduction of left PDH in our case, surgery remains the mainstay in terms of management for left paraduodenal hernia.

Dislocation reaction-based formation mechanism of stacking fault tetrahedra in FCC high-entropy alloy

In conventional FCC metals and alloys, the formation mechanisms of stacking fault tetrahedron (SFT) based on the vacancy cluster and Frank loop have been widely accepted; however, the dislocation reaction-based formation mechanism of SFT without Frank loop and vacancy cluster remains controversial. In this work, we studied the formation of the SFTs in CoCrFeNiCu high-entropy alloy (HEA) bicrystals and their single-crystal counterparts subjected to shear deformation using molecular dynamics (MD) simulations. The migration and thickening of grain boundaries, and the nucleation and glide of dislocations from the grain boundaries are the predominant carriers of deformation, which are the prerequisite for the formation of SFT. We observed two types of dislocation reaction-based formation mechanisms, where there is no vacancy aggregation and Frank loop participation. The formation of SFT originates from the growth of the bottom face of the pyramid in the bicrystal HEA, while in the single-crystal HEA, SFT nucleates at its vertex, and extends towards its bottom.

Left paraduodenal hernia treated by single-incision laparoscopic surgery: a case report

BackgroundParaduodenal hernia is a rare internal hernia which accounts for only 1% of all intestinal hernias. There have been limited reported cases of paraduodenal hernia treated by laparoscopic surgery. We report a case of left paraduodenal hernia that was successfully treated by single-incision laparoscopic surgery (SILS).Case presentationA 17-year-old woman presented with left upper abdominal pain. An abdominal enhanced multi-detector computed tomography demonstrated encapsulated cluster of small bowel loops in the left upper quadrant which passed through the dorsal side of the inferior mesenteric vein, and showed that blood flow of the prolapsed small bowel was preserved. We preoperatively diagnosed left paraduodenal hernia without ischemia or necrosis. We performed elective SILS because she was a young actress training school student and cosmetic benefit was thought to be important. We pulled out the protruded small bowel and closed a defect with a running suture by SILS. The patient was discharged 3 days after the surgery with no complications.ConclusionsWe reported the case of left paraduodenal hernia successfully diagnosed and treated by SILS.

Pulsed laser melting of implant amorphized Si1-xGex thin films

Nanosecond pulsed laser annealing using a frequency doubled Nd:YAG laser (λ = 532 nm) was performed on undoped implant amorphized Si and 40 nm Si1-xGex epitaxial thin films ranging from x = 0.1 to 0.5. Ge+ implants were used to create ~ 15 nm thick surface amorphous layers. The microstructural evolution of the layers was investigated for laser powers that ranged from the sub-melt, partial amorphous layer melt, full amorphous layer melt, to full epi-layer melt regimes. Time resolved reflectometry and transmission electron microscopy was used to couple the impact of melt dynamics with resulting microstructures and to determine processing benchmarks as a function of Ge concentration. It was shown that for the right combination of power and amorphous layer thickness, defect free regrowth is possible. At melt depths ≥ 22 nm for the Si0.7Ge0.3 films, it was found that progressive liquid/solid interface roughening during solidification led to lateral germanium segregation coupled with the formation of dislocation half loops and dislocation loop clusters at the surface. These results are important for the exploration of pulsed laser melting of Si1-xGex for CMOS source/drain contact and channel strain engineering applications.

A light clustering model predictive control approach to maximize thermal power in solar parabolic-trough plants

This article shows how coalitional model predictive control (MPC) can be used to maximize thermal power of large-scale solar parabolic-trough plants. This strategy dynamically generates clusters of loops of collectors according to a given criterion, thus dividing the plant into loosely coupled subsystems that are locally controlled by their corresponding loop valves to gain performance and speed up the computation of control inputs. The proposed strategy is assessed with decentralized and centralized MPC in two simulated solar parabolic-trough fields. Finally, results regarding scalability are also given using these case studies.

Essential role of accessory subunit LYRM6 in the mechanism of mitochondrial complex I

Respiratory complex I catalyzes electron transfer from NADH to ubiquinone (Q) coupled to vectorial proton translocation across the inner mitochondrial membrane. Despite recent progress in structure determination of this very large membrane protein complex, the coupling mechanism is a matter of ongoing debate and the function of accessory subunits surrounding the canonical core subunits is essentially unknown. Concerted rearrangements within a cluster of conserved loops of central subunits NDUFS2 (β1-β2S2 loop), ND1 (TMH5-6ND1 loop) and ND3 (TMH1-2ND3 loop) were suggested to be critical for its proton pumping mechanism. Here, we show that stabilization of the TMH1-2ND3 loop by accessory subunit LYRM6 (NDUFA6) is pivotal for energy conversion by mitochondrial complex I. We determined the high-resolution structure of inactive mutant F89ALYRM6 of eukaryotic complex I from the yeast Yarrowia lipolytica and found long-range structural changes affecting the entire loop cluster. In atomistic molecular dynamics simulations of the mutant, we observed conformational transitions in the loop cluster that disrupted a putative pathway for delivery of substrate protons required in Q redox chemistry. Our results elucidate in detail the essential role of accessory subunit LYRM6 for the function of eukaryotic complex I and offer clues on its redox-linked proton pumping mechanism.

A Sensitivity Mapping Technique for Tensile Force and Case Depth Characterization Based on Magnetic Minor Hysteresis Loops

In the nondestructive testing and evaluation area, magnetic major hysteresis loop measurement technology are widely applied for ferromagnetic material evaluation. However the characterization ability of major hysteresis loop measurement technology greatly varies as the evaluated target properties. To solve this limitation, magnetic minor hysteresis loops, which reflect the responses of ferromagnetic material magnetization in a systematic way, is recommend. Inspired by plenty of information carried by the minor loops, the sensitivity mapping technique was developed to achieve the highest sensitivity of minor-loop parameters to the nondestructively evaluated targets. In this study, for the first time, the sensitivity mapping technique is used to measure the tensile force in a steel strand and evaluate the effective case depth in induction-hardened steel rods. The method and procedures for the sensitivity mapping technique are given before experimental detection. The obtained experimental results indicate that the linear correlation between the induced voltage (or the magnetic induction intensity) and the tensile force (or effective case depth) exists at most of the locations in the cluster of minor loops. The obtained sensitivity maps can be used to optimize the applied magnetic field (or excitation current) and the analyzed locations at the minor loops for achieving the highest sensitivity. For the purpose of tensile force measurement, it is suggested that the strand should be firstly magnetized to the near-saturation state and then restored to the remanent state. In this way, the highest sensitivity is obtained as about 15.26 mV/kN. As for the induction-hardened steel rods, the highest sensitivity of magnetic induction intensity to the effective case depth occurs under low magnetic field conditions and the absolute value of the highest sensitivity is about 0.1110 T/mm. This indicates that if the highest sensitivity is required in the case depth evaluation, the induction-hardened steel rods are only required to be weakly magnetized. The proposed sensitivity mapping technique shows the good performance in the high-sensitivity evaluation of tensile force and case depth in ferromagnetic materials and its application scope can be extended to other nondestructive detection fields.

Loop-Cluster Coupling and Algorithm for Classical Statistical Models.

Potts spin systems play a fundamental role in statistical mechanics and quantum field theory and can be studied within the spin, the Fortuin-Kasteleyn (FK) bond or the q-flow (loop) representation. We introduce a Loop-Cluster (LC) joint model of bond-occupation variables interacting with q-flow variables and formulate an LC algorithm that is found to be in the same dynamical universality as the celebrated Swendsen-Wang algorithm. This leads to a theoretical unification for all the representations, and numerically, one can apply the most efficient algorithm in one representation and measure physical quantities in others. Moreover, by using the LC scheme, we construct a hierarchy of geometric objects that contain as special cases the q-flow clusters and the backbone of FK clusters, the exact values of whose fractal dimensions in two dimensions remain as an open question. Our work not only provides a unified framework and an efficient algorithm for the Potts model but also brings new insights into the rich geometric structures of the FK clusters.

Formation of a tiny flux rope in the center of an active region driven by magnetic flux emergence, convergence, and cancellation

Aims. Flux ropes are generally believed to be core structures of solar eruptions that are significant for the space weather, but their formation mechanism remains intensely debated. We report on the formation of a tiny flux rope beneath clusters of active region loops on 2018 August 24. Methods. Combining the high-quality multiwavelength observations from multiple instruments, we studied the event in detail in the photosphere, chromosphere, and corona. Results. In the source region, the continual emergence of two positive polarities (P1 and P2) that appeared as two pores (A and B) is unambiguous. Interestingly, P2 and Pore B slowly approached P1 and Pore A, implying a magnetic flux convergence. During the emergence and convergence, P1 and P2 successively interacted with a minor negative polarity (N3) that emerged, which led to a continuous magnetic flux cancellation. As a result, the overlying loops became much sheared and finally evolved into a tiny twisted flux rope that was evidenced by a transient inverse S-shaped sigmoid, the twisted filament threads with blueshift and redshift signatures, and a hot channel. Conclusions. All the results show that the formation of the tiny flux rope in the center of the active region was closely associated with the continuous magnetic flux emergence, convergence, and cancellation in the photosphere. Hence, we suggest that the magnetic flux emergence, convergence, and cancellation are crucial for the formation of the tiny flux rope.

The First Passage Sets of the 2D Gaussian Free Field: Convergence and Isomorphisms

In a previous article, we introduced the first passage set (FPS) of constant level $-a$ of the two-dimensional continuum Gaussian free field (GFF) on finitely connected domains. Informally, it is the set of points in the domain that can be connected to the boundary by a path along which the GFF is greater than or equal to $-a$. This description can be taken as a definition of the FPS for the metric graph GFF, and it justifies the analogy with the first hitting time of $-a$ by a one-dimensional Brownian motion. In the current article, we prove that the metric graph FPS converges towards the continuum FPS in the Hausdorff metric. This allows us to show that the FPS of the continuum GFF can be represented as a union of clusters of Brownian excursions and Brownian loops, and to prove that Brownian loop soup clusters admit a non-trivial Minkowski content in the gauge $r\mapsto |\log r|^{1/2}r^2$. We also show that certain natural interfaces of the metric graph GFF converge to SLE$_4$ processes.

Effect of Cutting Crystal Directions on Micro-Defect Evolution of Single Crystal γ-TiAl Alloy with Molecular Dynamics Simulation

In this work, the distribution and evolution of micro-defect in single crystal γ-TiAl alloy during nanometer cutting is studied by means of molecular dynamics simulation. Nanometer cutting is performed along two typical crystal directions: [ 1 ¯ 00 ] and [ 1 ¯ 01 ] . A machined surface, system potential energy, amorphous layer, lattice deformation and the formation mechanism of chip are discussed. The results indicate that the intrinsic stacking fault, dislocation loop and atomic cluster are generated below the machined surface along the cutting crystal directions. In particular, the Stacking Fault Tetrahedron (SFT) is generated inside the workpiece when the cutting crystal direction is along [ 1 ¯ 00 ] . However, a “V”-shape dislocation loop is formed in the workpiece along [ 1 ¯ 01 ] . Furthermore, atomic distribution of the machined surface indicates that the surface quality along [ 1 ¯ 00 ] is better than that along [ 1 ¯ 01 ] . In a certain range, the thickness of the amorphous layer increases gradually with the rise of cutting force during nanometric cutting process.

Thermal balance of large scale parabolic trough plants: A case study

The main control objective in commercial solar parabolic plants is to track the average temperature of all the loops around a reference set by the operator, by manipulating the flow of a synthetic oil. Due to the large number of loops existing in current solar plants and the vast extension that they cover, obtaining a precise knowledge of every loops efficiency becomes a very challenging task. Parameters such as loops reflectivity, tube absorptance, optical efficiency may exhibit a great disparity due to dirt accumulated and atmospheric conditions. Because of this, the most efficient loops achieve higher temperatures and the collectors may have to be set out of focus in many cases.This paper presents a case study on a simulation model of a large scale parabolic plant, 50 MW, in which a control of the aperture of the solar field loops inlet valves is applied through a nonlinear optimization problem. The goal is to reduce the imbalance of loops temperature caused by the difference in efficiencies. The idea is opening the input valves of the most efficient loops to increase the incoming flow-rate and reducing the flow in the less efficient loops. This will prevent, in many cases, the activation of the defocus control avoiding energy losses and minimizing the deterioration of actuators.The optimization problem will need estimations of the loops states and parameters. An Unscented Kalman Filter is used to estimate the loops temperatures states and a concentrated parameter model is used to estimate the loops efficiencies. A loop clustering is implemented to avoid high computation times. Simulation results showing thermal balance of the field minimizing the defocusing actions are presented.

Parallel loop cluster quantum Monte Carlo simulation of quantum magnets based on global union-find graph algorithm

A large-scale parallel loop cluster quantum Monte Carlo simulation is presented. On 24,576 nodes of the K computer, one loop cluster Monte Carlo update of the world-line configuration of the S=1∕2 antiferromagnetic Heisenberg chain with 2.6×106 spins at inverse temperature 3.1×105 is executed in about 8.62 s, in which global union-find cluster identification on a graph of about 1.1 trillion vertices and edges is performed. By combining the nonlocal global updates and the large-scale parallelization, we have virtually achieved about 1013-fold speed-up from the conventional local update Monte Carlo simulation performed on a single core. We have estimated successfully the antiferromagnetic correlation length and the magnitude of the first excitation gap of the S=4 antiferromagnetic Heisenberg chain for the first time as ξ=1.040(7)×104 and Δ=7.99(5)×10−4, respectively.

Inverting the coupling of the signed Gaussian free field with a loop-soup

Lupu introduced a coupling between a random walk loop-soup and a Gaussian free field, where the sign of the field is constant on each cluster of loops. This coupling is a signed version of isomorphism theorems relating the square of the GFF to the occupation field of Markovian trajectories. His construction starts with a loop-soup, and by adding additional randomness samples a GFF out of it. In this article we provide the inverse construction: starting from a signed free field and using a self-interacting random walk related to this field, we construct a random walk loop-soup. Our construction relies on the previous work by Sabot and Tarrès, which inverts the coupling from the square of the GFF rather than the signed GFF itself.

Convergence of the two-dimensional random walk loop-soup clusters to CLE

We consider the random walk loop-soup of subcritical intensity parameter on the discrete half-plane \mathtt{H}:=\mathbb{Z}\times\mathbb{N} . We look at the clusters of discrete loops and show that the scaling limit of the outer boundaries of outermost clusters is a CLE _{\kappa} conformal loop ensemble.