Minimal Cores Research Articles

Bending performance and failure mechanisms of composite sandwich structures with 3D printed hybrid triply periodic minimal surface cores

In this paper, a novel hybrid triply periodic minimal surface (TPMS) core with a nonlinear transition region was designed by combining two types of TPMS (Diamond and Schwarz P) structures using the sigmoid function. The width of the transition region was precisely regulated by adjusting the gradient control parameter r in the sigmoid function. Composite sandwich structures (CSS) were fabricated by bonding two carbon fiber reinforced polymer (CFRP) face sheets to a 3D printed polylactic acid (PLA) core. The bending performance and failure mechanisms of the CSSs with the hybrid TPMS cores were analyzed through three-point bending tests and finite element analysis (FEA). The results indicate that as r increases, the transition region of the hybrid TPMS cores becomes narrower, leading to a gradual decrease in bending strength, bending stiffness, and core shear stress. The failure process of the CSSs in the experiment aligns well with the FEA results. Through comparative analysis of the stiffness-to-weight and strength-to-weight ratios of the CSSs with the native TPMS cores, the hybrid TPMS cores with a wider transition region enhance the structural efficiency of the CSSs, while those with a narrower transition region negatively impact the performance of the CSSs.

Impact behavior of periodic, stochastic, and anisotropic minimal surface-lattice sandwich structures

Recent advancements in 3D printing technologies have made it possible to fabricate intricate lattice architectures with high precision. These lattices can now be utilized to design lightweight sandwich structures that serve multiple functions. To enhance the impact loading performance of these structures, it is crucial to understand how the lattice's topological properties, particularly those with minimal surface attributes like periodic or stochastic Primitive and Gyroid triply periodic minimal surfaces (TPMS) and spinodal-like stochastic cellular materials, associate with the mechanical properties of sandwich structures while keeping the skin thickness fixed. Thus, this paper explores the low-velocity impact behavior of various sheet/shell-based minimal surface-latticed cores of sandwich structures with woven composite skins. The elasto-plastic-damage numerical simulations consider lattice core periodicity, randomness, and anisotropy while keeping the relative density constant. Core lattice randomness and anisotropy are designed using the Gaussian Random Field (GRF) method for spinodal-based stochastic cellular materials and stochastic TPMS. The simulation results showed that the periodic Primitive-lattice core exhibits high out-of-plane shearing strength, enabling the sandwich structure to demonstrate the highest perforation limit. GRF spinodal-based core achieved the highest peak load due to its anisotropic mechanical properties. However, the post-yielding bending of the lattice sheet limited its ability to resist perforation, and absorb and dissipated energy. Interestingly, the stochastic Gyroid TPMS topology, with its inherent densely-distributed microstructure, showed high sensitivity to loading rate, resulting in enhanced energy absorption and dissipation of the sandwich structure. These findings offer valuable insights for optimizing multifunctional sandwich structures with superior impact performance and their design for additive manufacturing.

Non-ribosomal peptide synthase profiles remain structurally similar despite minimally shared features across fungus-farming termite microbiomes

Abstract Fungus-farming termites (Macrotermitinae) engage in an obligate mutualism with members of the fungal genus Termitomyces, which they maintain as a monoculture on specialized comb structures. Both these comb structures and the guts of the termites host diverse bacterial communities that are believed to assist in sustaining monoculture farming through antagonist suppression. Among candidate bacteria-derived compounds serving this function are non-ribosomal peptides (NRPs), which are a highly bioactive class of specialized metabolites, frequently produced by symbionts within eukaryotic hosts. However, our understanding of specialized metabolites in termite-associated microbiomes is limited. Here we use amplicon sequencing to characterize both bacterial composition and NRP potential. We show that bacterial and NRP diversity are correlated and that the former varies more than the latter across termite host and gut and comb samples. Compositions of the two are governed by host species and sample type, with topological similarity indicating a diverse set of biosynthetic potential that is consistent with the long evolutionary history of the Macrotermitinae. The structure of both bacterial and NRP compositional networks varied similarly between guts and combs across the Macrotermitinae albeit with auxiliary termite genus-specific patterns. We observed minimal termite species-specific cores, with essentially no Macrotermitinae-wide core and an abundance of putatively novel biosynthetic gene clusters, suggesting that there is likely no single solution to antagonist suppression via specialized NRP metabolites. Our findings contribute to an improved understanding of the distribution of NRP potential in the farming termite symbiosis and will help guide targeted exploration of specialized metabolite production.

Plant Antimicrobial Peptides: Insights into Structure-Function Relationships for Practical Applications

Antimicrobial peptides (AMPs) are short polypeptide molecules produced by multicellular organisms that are involved in host defense and microbiome preservation. In recent years, AMPs have attracted attention as novel drug candidates. However, their successful use requires detailed knowledge of the mode of action and identification of the determinants of biological activity. In this review, we focused on structure-function relationships in the thionins, α-hairpinins, hevein-like peptides, and the unique Ib-AMP peptides isolated from Impatiens balsamina. We summarized the available data on the amino acid sequences and 3D structure of peptides, their biosynthesis, and their biological activity. Special attention was paid to the determination of residues that play a key role in the activity and the identification of the minimal active cores. We have shown that even subtle changes in amino acid sequences can affect the biological activity of AMPs, which opens up the possibility of creating molecules with improved properties, better therapeutic efficacy, and cheaper large-scale production.

Inductive Validity Cores

Symbolic model checkers can construct proofs of properties over highly complex models. However, the results reported by the tool when a proof succeeds do not generally provide much insight to the user. It is often useful for users to have traceability information related to the proof: which portions of the model were necessary to construct it. This traceability information can be used to diagnose a variety of modeling problems such as overconstrained axioms and underconstrained properties, measure completeness of a set of requirements over a model, and assist with design optimization given a set of requirements for an existing or synthesized implementation. In this paper, we present a comprehensive treatment of a suite of algorithms to compute inductive validity cores (IVCs), minimal sets of model elements necessary to construct inductive proofs of safety properties for sequential systems. The algorithms are based on the UNSAT core support built into current SMT solvers and novel encodings of the inductive problem to generate approximate and guaranteed minimal inductive validity cores as well as all inductive validity cores. We demonstrate that our algorithms are correct, describe their implementation in the JKind model checker for Lustre models, and present several use cases for the algorithms. We then present a substantial experiment in which we benchmark the efficiency and efficacy of the algorithms.

Finding Strategyproof Social Choice Functions via SAT Solving

A promising direction in computational social choice is to address research problems using computer-aided proving techniques. In particular with SAT solvers, this approach has been shown to be viable not only for proving classic impossibility theorems such as Arrow's Theorem but also for finding new impossibilities in the context of preference extensions. In this paper, we demonstrate that these computer-aided techniques can also be applied to improve our understanding of strategyproof irresolute social choice functions. These functions, however, requires a more evolved encoding as otherwise the search space rapidly becomes much too large. Our contribution is two-fold: We present an efficient encoding for translating such problems to SAT and leverage this encoding to prove new results about strategyproofness with respect to Kelly's and Fishburn's preference extensions. For example, we show that no Pareto-optimal majoritarian social choice function satisfies Fishburn-strategyproofness. Furthermore, we explain how human-readable proofs of such results can be extracted from minimal unsatisfiable cores of the corresponding SAT formulas.

On getting rid of the preprocessing minimization step in MUC-finding algorithms

When a constraint network is unsatisfiable, it can be of prime importance to provide the network designer with a full-fledged explanation of what causes the absence of any solution to the network. In this respect, minimal unsatisfiable cores (in short, MUCs) form the basis for such an explanation. Efficient MUC extractors are often made of an initial incomplete minimization step that delivers an upper-approximation of a MUC, followed by a refinement step. The first step is believed crucial for the global performance of the whole approach. In this paper, its actual importance is investigated. Especially, it is shown that the first step can be skipped when the refinement process dynamically exploits the information from its own search.

Accelerated Deletion-based Extraction of Minimal Unsatisfiable Cores

Various technologies are based on the capability to find small unsatisfiable cores given an unsatisfiable CNF formula, i.e., a subset of the clauses that are unsatisfiable regardless of the rest of the formula. If that subset is irreducible, it is called a Minimal Unsatisfiable Core (MUC). In many cases, the MUC is required not in terms of clauses, rather in terms of a preknown user-given set of high-level constraints, where each such constraint is a conjunction of clauses. We call the problem of minimizing the participation of such constraints high-level minimal unsatisfiable core (HLMUC) extraction. All the current state-of-the-art tools for MUC- and HLMUC-extraction are deletion-based, which means that they iteratively try to delete clauses from the core. We propose nine optimizations to this general strategy, although not all apply to both MUC and HLMUC. For both cases we achieved over a 2X improvement in run time comparing to the state-of-the-art and a reduction in the core size, when applied to a benchmark set consisting of hundreds of industrial test cases. These techniques are implemented in our award-winning solvers HaifaMUC and HaifaHLMUC.

Boosting MUC extraction in unsatisfiable constraint networks

One very fertile domain of applied Artificial Intelligence is constraint solving technologies. Especially, constraint networks that concern problems that can be represented using discrete variables, together with constraints on allowed instantiation values for these variables. Every solution to a constraint network must satisfy every constraint. When no solution exists, the user might want to know the actual reasons leading to the absence of global solution. In this respect, extracting mucs (Minimal Unsatisfiable Cores) from an unsatisfiable constraint network is a useful process when causes of unsatisfiability must be understood so that the network can be re-engineered and relaxed to become satisfiable. Despite bad worst-case computational complexity results, various muc-finding approaches that appear tractable for many real-life instances have been proposed. Many of them are based on the successive identification of so-called transition constraints. In this respect, we show how local search can be used to possibly extract additional transition constraints at each main iteration step. In the general constraint networks setting, the approach is shown to outperform a technique based on a form of model rotation imported from the sat-related technology and that also exhibits additional transition constraints. Our extensive computational experimentations show that this enhancement also boosts the performance of state-of-the-art DC(WCORE)-like MUC extractors.

Surgical Pathology of Lung Cancer

The diagnosis, treatment, and management of lung tumors represent a complex set of decision algorithms and require the cooperation and interaction of a team of experts and support systems. The surgical pathologist, an early, important member of the diagnostic team, uses clinical and radiological evidence to differentiate benign from malignant tumors and renders a unique diagnosis that provides both prognostic and treatment information. Using routine histopathologic criteria, histochemical and immunohistochemical stains, and molecular and genetic testing, surgical pathologists and cytopathologists may distinguish between small cell and other bronchogenic carcinomas, separate adenocarcinomas from squamous cell carcinomas, differentiate between pleural carcinomas and diffuse malignant mesotheliomas, and discriminate among the varieties of neuroendocrine carcinomas. Among adenocarcinomas, the pathological examination stratifies those tumors with absent or minimal central invasive cores that have an excellent prognosis from the more common adenocarcinomas with larger invasive components. These distinctions are necessary based on differences in tumor biology, response to therapy, and prognosis for these different histological types. Histopathologic analysis should attempt to provide a precise diagnosis and limit the usage of the term non-small cell carcinoma. The team approach also enables the optimal use of tumor tissue for diagnostic purposes as well as molecular genetic testing and the discovery of targetable sites for therapeutic management. Though low-stage tumors tend to be initially treated with surgical resection, more advanced stages will be approached with limited tissue acquisition, necessitating a strategy for best practices of scarce tissue resources. The awareness of diagnostic modalities and tissue handling by all members of the team ensures the best patient-centered care.

Minimal reductions and cores of edge ideals

We study minimal reductions of edge ideals of graphs and determine restrictions on the coefficients of the generators of these minimal reductions. We prove that when I is not basic, then coreI⊂mI, where I is an edge ideal in the corresponding localized polynomial ring and m is the maximal ideal of this ring. We show that the inclusion is an equality for the edge ideal of an even cycle with an arbitrary number of whiskers. Moreover, we show that the core is obtained as a finite intersection of homogeneous minimal reductions in the case of even cycles. The formula for the core does not hold in general for the edge ideal of any graph and we provide a counterexample. In particular, we show in this example that the core is not obtained as a finite intersection of general minimal reductions.

Long-term rotation and tillage effects on soil structure and crop yield

Tillage and rotation are fundamental factors influencing soil quality and thus the sustainability of cropping systems. Many studies have focused on the effects of either tillage or rotation, but few have quantified the long term integrated effects of both. We studied the issue using a 30-year old long-term rotation and tillage treatment experiment on a Canadian silt loam soil. Topsoil measurements were carried out for three different rotations: R1, (C–C–C–C) continuous corn (Zea mays L.), R6, (C–C–O(RC), B(RC)) corn, corn, oats (Avena fatua L.) and spring barley (Hordeum vulgare L.) and R8, (C–C–S–S) corn, corn, soybean (Glycine max L.), soybean. A red clover (Trifolium pretense L.) cover crop was under seeded in oats and spring barley in R6. In 2010, first year corn was grown in R6 and R8. The tillage treatments included no tillage, NT and mouldboard ploughing, MP. Topsoil structural quality was visually evaluated in early June and mid October. Minimal disturbed soil cores collected in early June were used for X-ray CT scanning and to quantify water content and porosity. Soil friability was determined on the soil samples using a drop shatter test. Crop yield was determined and correlated to the soil quality estimates. We found significant effect of both rotation and tillage on visual soil structure at both times of assessment. Poor soil structure was found for NT except when combined with a diverse crop rotation (R6). The soil core pore characteristics data also displayed a significant effect of tillage but only a weak insignificant effect of rotation. The drop shatter results were in accordance with the visual assessment data. Crop yield correlated significantly with the visual soil structure scores. We conclude that a diverse crop rotation was needed for an optimal performance of NT for the studied soil.

Extracting minimal unsatisfiable subformulas in satisfiability modulo theories

Explaining the causes of infeasibility of formulas has practical applications in various fields, such as formal verification and electronic design automation. A minimal unsatisfiable subformula provides a succinct explanation of infeasibility and is valuable for applications. The problem of deriving minimal unsatisfiable cores from Boolean formulas has been addressed rather frequently in recent years. However little attention has been concentrated on extraction of unsatisfiable subformulas in Satisfiability Modulo Theories(SMT). In this paper, we propose a depth-firstsearch algorithm and a breadth-first-search algorithm to compute minimal unsatisfiable cores in SMT, adopting different searching strategy. We report and analyze experimental results obtaining from a very extensive test on SMT-LIB benchmarks.

Improved usability and performance of SMT solvers for debugging specifications

It is now common to construct an extended static checker or software verification system using an SMT theorem prover as the underlying logical verifier. SMT provers have improved significantly in performance over the last several years. However, their usability as a component of software checking and verification systems still has gaps. This paper describes investigations in two areas: the reporting of counterexample information and the testing of vacuity, both of which are important to realistic use of such tools for typical software development. The use of solvers in verification is more effective if the solvers support minimal unsatisfiable cores and incremental construction, evolution and querying of satisfying assignments; current solvers only partially support these capabilities.

Pyromellitic Diimides: Minimal Cores for High Mobility n-Channel Transistor Semiconductors

Three pyromellitic diimides were synthesized in high yields by one conventional reaction between pyromellitic dianhydride and various amines. The films made from these pyromellitic diimides derivatives exhibit a mobility up to 0.079 cm2/(V.s). In addition, the on/off ratios of n-channel devices are as high as 1 000 000.

Reconstructing historical trends in metal input in heavily-disturbed, contaminated estuaries: studies from Bilbao, Southampton Water and Sicily

Estuaries may be important reservoirs for contaminants as they tend to act as sinks for fine, contaminant-reactive sediments, and, historically, they have acted as centres for industrial and urban development. Analysis of dated sediment cores from these areas may allow historical trends in heavy metal input to be reconstructed, and recent and historical inputs of metal contaminants to be compared. Undisturbed saltmarsh settings have been used widely in the reconstruction of historical trends in metal input as saltmarshes provide a stable, vegetated substrate of dominantly fine sediments, and are less prone to erosion and reworking than adjacent mudflat areas. In comparison, much less research on historical pollution trends has been undertaken at estuarine sites which are prone to severe local disturbance, such as intertidal areas which are routinely dredged or where sedimentary processes have been modified by human activities such as shipping, salt working, port activities, land claim etc. This paper assesses the usefulness of 210Pb and 137Cs dating, combined with geochemical studies, in reconstructing historical trends in heavy metal input and sediment accretion in 3 heavily-modified, industrialised estuarine areas in Europe: the Bilbao estuary (Spain), Southampton Water (UK), and the Mulinello estuary (Sicily). Of these sites, only a salt marsh core from the Mulinello estuary provides a high-resolution record of recent heavy metal inputs. In Southampton Water only a partial record of changing metal inputs over time is retained due to land-claim and possible early-diagenetic remobilisation, while at Bilbao the vertical distribution of heavy metals in intertidal flats is mainly controlled by input on reworked sediment particles and variations in sediment composition. Where 137Cs and 210Pb distributions with depth allow a chronology of sediment deposition to be established, and early-diagenetic remobilisation has been minimal, mudflat and saltmarsh cores from even the most heavily-disturbed estuarine sites can provide useful information on variations in historical contaminant input. When the sediments have been vigorously mixed or reworked, large-scale compositional variations are present, or significant early-diagenetic remobilisation has occurred, however, only general information on the scale of contamination can be obtained.

The Complete Sequences of the Galago and Rabbit β-Globin Locus Control Regions: Extended Sequence and Functional Conservation Outside the Cores of DNase Hypersensitive Sites

The locus control region (LCR) of mammalian β-globin genes covers at least 17 kb at the 5′ end of the gene cluster and has been implicated in chromatin domain opening, enhancement, and insulation from neighboring sequences. Functional dissection of the LCR has defined the minimal cores for four of the five major DNase hypersensitive sites (HSs) that mark this regulatory region. To examine fully the patterns of conserved sequences in the mammalian homologs to the β-globin LCR, we determined the complete DNA sequence of the galago β-globin LCR and completed previously unsequenced regions of the rabbit LCR. Simultaneous alignment of these sequences with the human, goat, and mouse LCRs revealed conserved sequences (phylogenetic footprints) detected using three largely independent methods. The most highly conserved segments are found both within the HS cores and in some but not all regions flanking the cores. These results argue for an extended pattern of well-conserved sequences, many of which lie outside the minimal cores, and we show that a key sequence required for domain opening by the region including HS3 maps about 1 kb 5′ to the minimal core. Differential phylogenetic footprints, containing sequences conserved in nonhuman mammals but not in humans, are found primarily around HS3, consistent with some species-specific differences in function that may be important for differences in hemoglobin switching during development.

Discriminatory von Neumann-Morgenstern solutions

A discriminatory von Neumann-Morgenstern (vN-M) solution assigns fixed payoffs to certain players and permits the remaining players to arbitrarily redistribute their payoffs. This paper gives a complete characterization of discriminatory vN-M solutions, describing the role of the players and their payoffs in terms of minimal vital coalitions and Cores of reduced games resembling the DavisMaschler reduced game. The characterization makes it computationally easy to verify proposed discriminatory vN-M solutions, and may be used to determine all discriminatory vN-M solutions.