bluuebunny/crossref_metadata_2025 huggingface dataset:
De-channeling in terms of instantaneous transition rates: computer simulations for 855 MeV electrons at (110) planes of diamond
Authors: Backe H.
Published: August 2022

Monte-Carlo simulation calculation have been performed for 855 MeV electrons channeling in (110) planes of a diamond single crystal. The continuum potential picture has been utilized. Both, the transverse potential and the angular distributions of the scattered electrons at screened atoms are based on the Doyle–Turner scattering factors which were extrapolated with the functional dependence of the Molière representation to large momentum transfers. Scattering cross-sections at bound electrons have been derived for energies less than 30 keV from the double differential cross-section as function of both, energy and momentum transfer, taking into account also longitudinal and transverse excitations. For energies above 30 keV the Møller cross-section is used. The dynamics of the particle in the continuum transverse potential has been described classically. Results of the channeling process are presented in terms of instantaneous transition rates as function of the penetration depth, indicating that channeling can be described by a single exponential function only after about 15 $$\mu $$
μ
m when the equilibration phase has been reached. As a byproduct, improved drift and diffusion coefficients entering the Fokker–Planck equation have been derived with which its predictive power can be improved.

Graphic abstract
Neutron waveguides with finite repulsive potential in clad
Authors: de la Peña I. Molina , Alvarez-Estrada R. F. , Calvo M. L.
Published: August 2022

The interaction of an incoming slow neutron with a straight semi-infinite material waveguide (physically, a very lengthy one) located in vacuum (clad) in the infinite three-dimensional (3D) space is studied. The waveguide creates an attractive potential on the neutron. The physical quantum-mechanical wave phenomena are: (i) reflection and scattering of the neutron by the waveguide and (ii) its confined propagation along the latter, in specific propagation modes. The direct application of standard scattering integral equations meets several difficulties, arising mainly from the infinite length of the waveguide and (ii). New and more convenient 3D scattering integral equations are proposed and discussed, using suitable Green functions, adequate for the semi-infinite waveguide and accounting for (i) and the above difficulties. Approximate formulae for the probability amplitudes and fluxes for (i) and (ii) are given: in particular, the formulas for slow neutron confined propagation extend the ones given previously for optical waveguides. Some detailed applications and numerical computations for two-dimensional media and waveguides are presented.
Structural Synthesis of PLC Program for Real-Time Specification Patterns
Authors: Xie Kai , Wei Zijian , Yin Kang , Li Songsong , Yao Xinyan , Zhou Xiaoyu
Published: August 2022

Among all the reactive synthesis methods, the results of the structural synthesis have the best interpretability and traceability. However, existing structural synthesis method cannot deal with real-time specifications and specifications with circular dependencies. A structural synthesis method for Programmable Logic Controller programs is proposed. First, a real-time specification pattern language, RTSPS4Syn, is proposed. Under the condition that there is no circular dependency between the specification items, the implementations of a specification item are assembled structurally from the implementation of its scope and property expression; and the programs for the specification items are concatenated according to the order of priority and dependency to obtain the synthesized program. This paper presents a method to eliminate the circular dependence of specifications, such that the synthesis approach can be applied to specifications with circular dependency. Furthermore, this paper presents an approach for setting the preset values of timers when considering tolerance on the duration of the delay. The synthesis method does not need to check the conflict and determine the nondeterministic part of the specifications. These problems are solved in existing research by constraint solving in PSPACE.
The Li–Sekatskii coefficients for the Selberg class
Authors: Mazhouda Kamel , Sodaïgui Bouchaïb
Published: August 2022

In this paper, we study a Li-type criterion for some [Formula: see text]-functions. First, we define a type of generalized Li-type coefficients and relate them with the generalized Riemann Hypothesis. Second, we provide arithmetic and asymptotic representations for these coefficients.
Bianchi Type I model of universe with customized scale factors
Authors: Sarmah Pranjal , Goswami Umananda Dev
Published: August 2022

According to standard cosmology, the universe is homogeneous and isotropic at large scales. However, some anisotropies can be observed at the local scale in the universe through various ways. Here, we have studied the Bianchi Type I model by customizing the scale factors to understand the anisotropic nature of the universe. We have considered two cases with slight modifications of scale factors in different directions in the generalized Bianchi Type I metric equation, and compared the results with the [Formula: see text]CDM model and also with available cosmological observational data. Through this study, we also want to predict the possible degree of anisotropy present in the early universe and its evolution to current time by calculating the value of density parameter for anisotropy [Formula: see text] for both low and high redshift [Formula: see text] along with the possible relative anisotropy that exist among different directions. It is found that there was a relatively higher amount of anisotropy in the early universe and the anisotropic nature of the universe vanishes at the near past and the present epochs. Thus, at near past and present stages of the universe there is no effective distinction between this anisotropic model and the standard [Formula: see text]CDM model.
A Novel SDMFO-MBSVM-Based Segmentation and Classification Framework for Glaucoma Detection Using OCT and Fundus Images
Authors: Rayavel P. , Murukesh C.
Published: August 2022

Glaucoma is an eye disease that causes loss of vision and blindness by damaging a nerve in the back of the eye called optic nerve. The optic nerve collects the visual information from the eyes and transmits to the brain. Glaucoma is mainly caused by an abnormal high pressure in the eyes. Over time, the increased pressure can erode the tissues of optic nerve, leading to vision loss or blindness. If it is diagnosed in advance, then only it can prevent the vision loss. To diagnose the glaucoma, it must accurately differentiate between the optic disc (OD), optic cup (OC), and the retinal nerve fiber layer (RNFL). The segmentation of the OD, OC, and RNFL remains a challenging issue under a minimum contrast image of boundaries. Therefore, in this study, an innovative method of Hybrid Symbiotic Differential Evolution Moth-Flame Optimization (SDMFO)-Multi-Boost Ensemble and Support Vector Machine (MBSVM)-based segmentation and classification framework is proposed for accurately detecting the glaucoma disease. By using Group Search Optimizer (GSO), the affected parts of the OD, OC and RNFL are segmented. The proposed SDMFO-MBSVM method is executed in MATLAB site, its performance is analyzed with three existing methods. From the comparison, the accuracy of the proposed method in OD segmentation gives better results of 3.37%, 4.54% and 2.22%, OC segmentation gives better results of 2.22%, 3.37% and 4.54%, and RNFL segmentation gives the better results of 3.37%, 97.21% and 5.74%.
Fibering flat manifolds of diagonal type and their fundamental groups
Authors: Chung Ho Yiu , Petrosyan Nansen
Published: August 2022

An [Formula: see text]-dimensional closed flat manifold is said to be of diagonal type if the standard representation of its holonomy group [Formula: see text] is diagonal. An [Formula: see text]-dimensional Bieberbach group of diagonal type is the fundamental group of such a manifold. We introduce the diagonal Vasquez invariant of [Formula: see text] as the least integer [Formula: see text] such that every flat manifold of diagonal type with holonomy [Formula: see text] fibers over a flat manifold of dimension at most [Formula: see text] with flat torus fibers. Using a combinatorial description of Bieberbach groups of diagonal type, we give both upper and lower bounds for this invariant. We show that the lower bounds are exact when [Formula: see text] has low rank. We apply this to analyze diffuseness properties of Bieberbach groups of diagonal type. This leads to a complete classification of Bieberbach groups of diagonal type with Klein four-group holonomy and to an application to Kaplansky’s Unit Conjecture.
FRACTAL ANALYSIS OF STOKES FLOW IN TORTUOUS MICROCHANNELS WITH HYDRAULICALLY ROUGH SURFACES
Authors: YI SHUANG , ZHENG SHENG , YANG SHANSHAN , ZHOU GUANGRONG
Published: August 2022

Previous studies have shown that the flow in porous media can be affected by the structure of microchannels. In this paper, the capillary bundle model is used to simplify the complex and irregular structure of porous media, which is assumed to be comprised of tortuous capillaries covered with statistical self-similar conical rough elements. Considering the boundary layer effect, a fractal geometry-based quantitative model has been proposed to investigate the relationship between the hydraulic roughness of capillaries and the micro-flow properties. According to the proposed model, the influence of roughened surfaces on the tortuosity of Stokes flow can be considered as the combination of every individual rough element in 2D flow fields, which is extended to 3D flow fields based on a series of assumptions and approximations. Analytical expressions of tortuosity and permeability of Stokes flow through roughened capillaries are derived. According to the results, the tortuosity of capillary flow increases with a higher relative roughness, while the permeability is inversely proportional to it. Predictions of permeability by the present model are compared with the previous models and experiment data, which show good agreement.
A DICHOTOMY OF STRONG OPEN SET CONDITION OF SELF-CONFORMAL SETS
Authors: HUANG LIANG-YI , ZHANG YUAN
Published: August 2022

Let [Formula: see text] be a [Formula: see text] self-conformal set. It is well known that [Formula: see text] satisfies the strong open set condition provided it satisfies the open set condition. A point [Formula: see text] is called a trivial point of [Formula: see text] if [Formula: see text] is a connected component of [Formula: see text]. Let [Formula: see text] be a strong open set for [Formula: see text]. In this paper, we show that whether [Formula: see text] contains a trivial point of [Formula: see text] determines several metrical and topological properties of [Formula: see text], including the maximal power law property and the dimension drop of the connected part of [Formula: see text].
NOVEL TRAVELING WAVE SOLUTIONS FOR THE FRACTAL ZAKHAROV–KUZNETSOV–BENJAMIN–BONA–MAHONY MODEL
Authors: WANG KANGLE
Published: August 2022

In this paper, the fractal Zakharov–Kuznetsov–Benjamin–Bona–Mahony model (FZKBBM) is studied based on the local fractional derivative sense on Cantor sets for the first time. The different types of traveling wave solutions of the FZKBBM are successfully obtained by using two reliable and efficient approaches, which are fractal Yang wave method (FYWM) and fractal variational method (FVM). The properties of the obtained traveling wave solutions of non-differential type are elaborated by using some three-dimensional simulation graphs.
A FRACTAL MODEL FOR GAS DIFFUSION IN DRY AND WET FIBROUS MEDIA WITH TORTUOUS CONVERGING–DIVERGING CAPILLARY BUNDLE
Authors: GAO JUN , XIAO BOQI , TU BILIANG , CHEN FENGYE , LIU YONGHUI
Published: August 2022

In this paper, a fractal model is proposed for gas diffusion in dry and wet fibrous media with tortuous converging–diverging capillary bundle on the basis of the fractal theory. The proposed theoretical model for the normalized gas diffusivity (NGD) can be expressed as an explicit functional relation of porosity, [Formula: see text], fluid saturation, [Formula: see text], fractal dimensions, [Formula: see text] and [Formula: see text], the minimum average radius, [Formula: see text], the maximum average radius, [Formula: see text], the straight capillary length of a unit cell [Formula: see text] as well as fluctuation amplitude [Formula: see text]. The predictions of the proposed model have been compared with the existing experimental data and the available model predictions, and a good agreement can be observed. The effect of various parameters on the NGD is studied alone. It is observed that the NGD decreases with an increase in the fluctuation amplitude. Also, it is seen that the NGD decreases with an increase in the tortuosity fractal dimension. Moreover, it is found that the NGD in wet fibrous media decreases with an increase in the fluid saturation. The present model has no empirical constant and each parameter contains clear physical meaning. These may better reveal the physical mechanisms of gas diffusion in fibrous media.
OPTION SURFACE STATISTICS WITH APPLICATIONS
Authors: MADAN DILIP B. , WANG KING
Published: August 2022

At each maturity a discrete return distribution is inferred from option prices. Option pricing models imply a comparable theoretical distribution. As both the transformed data and the option pricing model deliver points on a simplex, the data is statistically modeled by a Dirichlet distribution with expected values given by the option pricing model. The resulting setup allows for maximum likelihood estimation of option pricing model parameters with standard errors that enable the testing of hypotheses. Hypothesis testing is then illustrated by testing for the consistency of risk neutral return distributions being those of a Brownian motion with drift time changed by a subordinator. Models mixing processes of independent increments with processes related to solutions of Ornstein–Uhlenbeck (OU) equations are also tested for the presence of the OU component. Solutions to OU equations may be viewed as processes of perpetual motion responding continuously to their past movements. The tests support the rejection of Brownian subordination and the presence of a perpetual motion component.
Noncommutative quantum decomposition of Gegenbauer white noise process
Authors: Riahi Anis
Published: August 2022

The main purpose of this paper is to derive a general structure of Gegenbauer white noise analysis as a counterpart class of non-Lévy white noise. First, we start with a new detailed construction of the Gegenbauer Fock space [Formula: see text] which serves to obtain the quantum decomposition associated with the Gegenbauer white noise processes. More precisely, based on the notion of quantum decomposition and the orthogonalization of polynomials of noncommutative Gegenbauer white noise [Formula: see text], we study the chaos property of the noncommutative [Formula: see text]-space with respect to the vacuum expectation [Formula: see text]. Next, we determine the distribution of the Gegenbauer operator [Formula: see text] and as a consequence we give some useful properties of the Gegenbauer white noise process.
The Impact of Trade Credit on Financing Strategy in a Dual Capital-Constrained Supply Chain
Authors: Xie Xiaofeng , Yang Yang , Lyu Xingyang , Zhang Fengying , Hu Xiuying , Zhou Zongfang
Published: August 2022

This study analyzes the financing strategy of a two-echelon supply chain, consisting of a manufacturer and a retailer, both subject to capital constraints. Specifically, the bank provides loans to the manufacturer, who then grants trade credit to the retailer. Based on the three-party game analysis framework of the bank, manufacturer, and retailer, this paper constructs a supply chain financing model under the information symmetry and information asymmetry structures, respectively; measures the maximum financing ability of the manufacturer; and discusses the influence of trade credit, moral hazard, and information structure on the manufacturer’s and bank’s strategies. The results show that under the trade credit situation, it is critical for the bank to provide loan to manufacturer who does not have moral hazard. The maximum financing capacity of the manufacturer is affected by the rate of return on moral hazard and the intensity of trade credit default. The increase of trade credit default intensity and risk exposure will lead to the increase of the interest rate of bank loan, and in the case of information asymmetry, the bank will often ask for a higher interest rate to deal with the information disadvantage. The strategy for the bank to make the credit line is more complex, and the degree of information asymmetry plays a positive moderating effect on the influence of trade credit on the credit line. Our findings provide implications for participants who implement financing actions to improve their financial performance and control the moral hazard and default risk along a supply chain.
High-Performance Level and Innovation Capabilities in the Aerospace Industry of Mexico: A Qualitative Comparative Analysis
Authors: Rodríguez José Carlos , Manzo María Aline , Gómez Mario
Published: August 2022

This paper analyzes the necessary and sufficient conditions for successful innovation in design and engineering companies (DECs) of the aerospace industry in Mexico. It is argued that successful innovation activity is a condition for achieving a high-performance level (HPL) among DECs. Seven innovation capabilities are analyzed to determine whether an HPL exists. Based on the dynamic capabilities approach, this research suggests that learning capability (LRC), research and development capability (RDC), creative capability (CRC), collaborative innovation capability (CIC), knowledge sharing capability (KSC), and exploitation capability (EXTC) are necessary conditions to achieve an HPL in DECs of the aerospace industry in Mexico. The fuzzy-set qualitative comparative analysis (fsQCA) methods are applied in this research to get insight into the configuration complexity that determines configurational causal relationships between HPL and innovation capabilities among firms of this industry in Mexico.
Improved synthesis of tetrakis(porphyrin) molecular cleftviapalladium-mediated cross-coupling between a bis(porphyrin) boronic ester and bis(iodophenyl)butadiyne
Authors: Hisano Naoyuki , Hirao Takehiro , Tanabe Kouta , Haino Takeharu
Published: August 2022

Tetrakis(porphyrin) molecular cleft was prepared by Suzuki-Miyaura cross coupling between a bis(porphyrin) boronate ester and 1,4-bis(4-iodophenyl)-1,3-butadiyne. The overall yield of the Tetrakis(porphyrin) was found to be more than doubled compared to that reported previously. The successful preparation of tetrakis(porphyrin) was characterized by a combination of nuclear magnetic resonance (NMR) spectroscopy and high resolution mass spectrometry (HRMS). Furthermore, HRMS evidenced the formation of supramolecular polymeric species driven by bis(porphyrin)-bis(porphyrin) dimerization in the gas phase.
Photodynamic antimicrobial activities of halogenated 3,5-dimethyl- and 1,3,5,7-tetramethyl-meso-pentafluorophenyl BODIPY dyes
Authors: May Aviwe Khanya , Chiyumba Choonzo , Harris Jessica , Mack John , Nyokong Tebello
Published: August 2022

The photodynamic antimicrobial chemotherapy (PACT) activities of four meso-pentafluorophenylBODIPY dyes were studied against Staphylococcus aureus to identify structure-property relationships related to the introduction of different substituents on the BODIPY core. 1,3,5,7-Tetramethyl dyes with bromine and iodine atoms at the 2,6-positions (2a and 3a) were synthesized and characterized along with 3,5-dimethyl dyes that were either tetrabrominated at the 1,2,6,7-positions (2b) or diiodinated (3b) at the 2,6-positions. The incorporation of iodine atoms on the BODIPY core at the 2,6-positions enhanced the PACT activity relative to those of the di- and tetrabrominated dyes. Replacing the methyl groups at the 1,7-positions with protons to form 3b results in greater PACT activity than is the case with 3a since the absence of steric hindrance related to methyl groups at the 1,7-positions allows the meso-aryl ring to rotate closer to the plane of the [Formula: see text]-system of the BODIPY core. The tetrabrominated dye was found to have the lowest PACT activity due to a lack of stability in solution and poor uptake by the bacteria being studied. The electron-withdrawing pentafluorophenyl group was selected to lower the dipole moment of the BODIPY core dye since poor PACT activity was observed when a 2,6-dibromo-1,3,5,7-tetramethyl BODIPY dye was prepared with a thiomethylphenyl group (2c).
Open Quantum Random Walks and Quantum Markov chains on Trees I: Phase transitions
Authors: Mukhamedov Farrukh , Souissi Abdessatar , Hamdi Tarek
Published: August 2022

In the present paper, we construct QMC (Quantum Markov Chains) associated with Open Quantum Random Walks such that the transition operator of the chain is defined by OQRW and the restriction of QMC to the commutative subalgebra coincides with the distribution [Formula: see text] of OQRW. However, we are going to look at the probability distribution as a Markov field over the Cayley tree. Such kind of consideration allows us to investigate phase transition phenomena associated for OQRW within QMC scheme. Furthermore, we first propose a new construction of QMC on trees, which is an extension of QMC considered in [10]. Using such a construction, we are able to construct QMCs on tress associated with OQRW. Our investigation leads to the detection of the phase transition phenomena within the proposed scheme. This kind of phenomena appears for the first time in this direction. Moreover, mean entropies of QMCs are calculated.
Concurrent Learning of Patch and Image-Based Features by CNN for Diabetic Retinopathy Detection
Authors: Mohamed Jebran P. , Gupta Shweta
Published: August 2022

Diabetic Retinopathy (DR) is a disorder of the eyes allied with prolonged hyperglycemia and is the leading cause of blindness globally. The earliest signs of DR include the presence of microaneurysms (MA). This research proposes a paradigm that includes patch-level lesion classification and DR severity assessment. A framework is presented that utilizes a multi-task learning approach centered on a single data source and is capable of predicting two outcomes. The proposed method for patch-level MA categorization consists of only three stages and is based on the combination of auto feature extraction by deep learning and classification by the machine learning algorithm. After preprocessing, for feature descriptor learning, GoogLeNet is employed, followed by SVM for classification. A comprehensive approach is provided to use the patch and image-level feature vectors to grade DR severity. To assess the suggested technique for patch-level classification, an experiment was undertaken by using two widely known public datasets, namely E-ophtha and IDRiD datasets. The developed system achieved 98.67% accuracy, a sensitivity of 99.2%, specificity of 99.06% on e-ophtha-MA database, while a trained model is validated on the IDRiD database, it achieves an accuracy of 70.6%, the sensitivity of 67.62%, specificity of 73.58%. The MESSIDOR dataset is used to evaluate the performance of DR grading as well. The proposed system achieves an accuracy of 89.39%, a sensitivity of 91.1%, specificity of 79.31% for two-stage grade DR severity.
Slow Growth Damage Assessment of Bonded Metal-Composite Joint Using a Numerical Approach
Authors: Kabir Md. Imran , Wong Laurence , Wang John , Yang Chunhui , Zhang Y. X.
Published: August 2022

The applications of composite materials and adhesive-bonded joints in the aviation industry have significantly increased in recent years and their damage assessment attracts a lot of research interest. This study investigates the slow growth damages of bonded metal-composite joints and develops a finite element-based numerical procedure to capture mechanical behaviors of those damages in the joints. The residual static strength and strain energy release rates (SERRs) (which determine the damage growth rates) of the joints are the two quantities that can be determined to predict the fatigue life of adhesive bonded joints. The absence of extensive experimental and numerical assessments for predicting the slow growth damage of bonded metal-composite joints necessitates the development of a numerical procedure to determine these quantities. Toward this end, a three-dimensional (3D) finite element (FE) model was created. From the FE analyses, the residual static strength and SERRs of bonded metal-composite joints were calculated as a function of varying disbond crack lengths following the adhesive element failure criterion and fracture mechanics approach, respectively. Additionally, the residual strength and SERR for joints with delamination of the composite adherend were also calculated by implementing a linear fracture mechanics-based failure index. The results suggested that the stable crack length of the joint with 180[Formula: see text]mm long overlap length was about 140[Formula: see text]mm and 100[Formula: see text]mm when the crack was initiated from taper and gap end, respectively. These lengths were consistent for both disbond and delamination scenarios. Residual strength values were 89[Formula: see text]kN and 65[Formula: see text]kN for joints with 10[Formula: see text]mm disbonds initiated from the taper end and gap region, respectively. With the material properties considered, the delamination propagation strengths for delaminated joints were notably lower than their disbonded counterparts. Based on the findings of this study’s analysis, a systematic strategy was developed for applying the slow growth technique for bonded joints, which would aid in the creation of an actual sample for experimental validation. The experiment in turn will provide calibration for the parameters in the model for practical applications.
Cerium-based nanoparticles for cancer photodynamic therapy
Authors: Li Hui , Wei Min , Lv Xinyi , Hu Yanling , Shao Jinjun , Song Xuejiao , Yang Dongliang , Wang Wenjun , Li Buhong , Dong Xiaochen
Published: August 2022

Metal- and metal-oxide-based nanoparticles have been widely exploited in cancer photodynamic therapy (PDT). Among these materials, cerium-based nanoparticles have drawn extensive attention due to their superior biosafety and distinctive physicochemical properties, especially the reversible transition between the valence states of Ce(III) and Ce(IV). In this review, the recent advances in the use of cerium-based nanoparticles as novel photosensitizers for cancer PDT are discussed, and the activation mechanisms for electron transfer to generate singlet oxygen are presented. In addition, the types of cerium-based nanoparticles used for PDT of cancer are summarized. Finally, the challenges and prospects of clinical translations of cerium-based nanoparticles are briefly addressed.
Does “Swarm Intelligence” Support Reductive Physicalism?
Authors: Firt Erez
Published: August 2022

This paper discusses the collective intelligent behavior of wholes made out of numerous individuals, otherwise known as Swarm Intelligence (SI). By and large, SI is defined as a kind of a problem-solving ability that emerges when a large number of relatively simple information-processing units, whether animate or artificial, interact locally with each other and with the environment. In this paper, we examine whether SI systems can be thought of as intelligent, according to an accepted definition of Universal Intelligence, whether the emergence of such collective “mind behavior” can be deduced from the simple rules that govern the behavior of the individuals of the swarm, and whether we can reach, through analogical reasoning, new insights regarding physicalist–reductionist views about human intelligence.
Searching entangled program spaces
Authors: Koppel James , Guo Zheng , de Vries Edsko , Solar-Lezama Armando , Polikarpova Nadia
Published: August 2022

Many problem domains, including program synthesis and rewrite-based optimization, require searching astronomically large spaces of programs. Existing approaches often rely on building specialized data structures—version-space algebras, finite tree automata, or e-graphs—to compactly represent such spaces. At their core, all these data structures exploit independence of subterms; as a result, they cannot efficiently represent more complex program spaces, where the choices of subterms are entangled.

We introduce
equality-constrained tree automata
(ECTAs), a new data structure, designed to compactly represent large spaces of programs with entangled subterms. We present efficient algorithms for extracting programs from ECTAs, implemented in a performant Haskell library, ecta. Using the ecta library, we construct Hectare, a type-driven program synthesizer for Haskell. Hectare significantly outperforms a state-of-the-art synthesizer Hoogle+—providing an average speedup of 8×—despite its implementation being an order of magnitude smaller.
Monadic compiler calculation (functional pearl)
Authors: Bahr Patrick , Hutton Graham
Published: August 2022

Bahr and Hutton recently developed a new approach to calculating correct compilers directly from specifications of their correctness. However, the methodology only considers
converging
behaviour of the source language, which means that the compiler could potentially produce arbitrary, erroneous code for source programs that diverge. In this article, we show how the methodology can naturally be extended to support the calculation of compilers that address both convergent and divergent behaviour
simultaneously
, without the need for separate reasoning for each aspect. Our approach is based on the use of the partiality monad to make divergence explicit, together with the use of strong bisimilarity to support equational-style calculations, but also generalises to other forms of effect by changing the underlying monad.
Verified symbolic execution with Kripke specification monads (and no meta-programming)
Authors: Keuchel Steven , Huyghebaert Sander , Lukyanov Georgy , Devriese Dominique
Published: August 2022

Verifying soundness of symbolic execution-based program verifiers is a
significant challenge. This is especially true if the resulting tool needs to be
usable outside of the proof assistant, in which case we cannot rely on shallowly
embedded assertion logics and meta-programming. The tool needs to manipulate
deeply embedded assertions, and it is crucial for efficiency to eagerly prune
unreachable paths and simplify intermediate assertions in a way that can be
justified towards the soundness proof. Only a few such tools exist in the
literature, and their soundness proofs are intricate and hard to generalize or
reuse. We contribute a novel, systematic approach for the construction and
soundness proof of such a symbolic execution-based verifier. We first implement
a shallow verification condition generator as an object language interpreter in
a specification monad, using an abstract interface featuring angelic and demonic
nondeterminism. Next, we build a symbolic executor by implementing a similar
interpreter, in a symbolic specification monad. This symbolic monad lives in a
universe that is Kripke-indexed by variables in scope and a path condition.
Finally, we reduce the soundness of the symbolic execution to the soundness of
the shallow execution by relating both executors using a Kripke logical
relation. We report on the practical application of these techniques in
Katamaran, a tool for verifying security guarantees offered by instruction set
architectures (ISAs). The tool is fully verified by combining our symbolic
execution machinery with a soundness proof of the shallow verification
conditions against an axiomatized separation logic, and an Iris-based
implementation of the axioms, proven sound against the operational semantics.
Based on our experience with Katamaran, we can report good results on
practicality and efficiency of the tool, demonstrating practical viability of
our symbolic execution approach.
Datatype-generic programming meets elaborator reflection
Authors: Ko Hsiang-Shang , Chen Liang-Ting , Lin Tzu-Chi
Published: August 2022

Datatype-generic programming is natural and useful in dependently typed languages such as Agda. However, datatype-generic libraries in Agda are not reused as much as they should be, because traditionally they work only on datatypes decoded from a library’s own version of datatype descriptions; this means that different generic libraries cannot be used together, and they do not work on native datatypes, which are preferred by the practical Agda programmer for better language support and access to other libraries. Based on elaborator reflection, we present a framework in Agda featuring a set of general metaprograms for instantiating datatype-generic programs as, and for, a useful range of native datatypes and functions —including universe-polymorphic ones— in programmer-friendly and customisable forms. We expect that datatype-generic libraries built with our framework will be more attractive to the practical Agda programmer. As the elaborator reflection features used by our framework become more widespread, our design can be ported to other languages too.
Structural versus pipeline composition of higher-order functions (experience report)
Authors: Rivera Elijah , Krishnamurthi Shriram
Published: August 2022

In teaching students to program with compositions of higher-order
functions, we have encountered a sharp distinction in the difficulty
of problems as perceived by students. This distinction especially
matters as growing numbers of programmers learn about functional
programming for data processing. We have made initial progress on
identifying this distinction, which appears counter-intuitive to
some. We describe the phenomenon, provide some preliminary evidence
of the difference in difficulty, and suggest consequences for
functional programming pedagogy.
Multiparty GV: functional multiparty session types with certified deadlock freedom
Authors: Jacobs Jules , Balzer Stephanie , Krebbers Robbert
Published: August 2022

Session types have recently been integrated with functional languages, bringing message-passing concurrency to functional programming.
Channel endpoints then become first-class and can be stored in data structures, captured in closures, and sent along channels.
Representatives of the GV (Wadler's "Good Variation") session type family are of particular appeal because they not only assert session fidelity but also deadlock freedom, inspired by a Curry-Howard correspondence to linear logic.
A restriction of current versions of GV, however, is the focus on binary sessions, limiting concurrent interactions within a session to two participants.
This paper introduces Multiparty GV (MPGV), a functional language with multiparty session types, allowing concurrent interactions among several participants.
MPGV upholds the strong guarantees of its ancestor GV, including deadlock freedom, despite session interleaving and delegation.
MPGV has a novel redirecting construct for modular programming with first-class endpoints,
thanks to which we give a type-preserving translation from binary session types to MPGV to show that MPGV is strictly more general than binary GV.
All results in this paper have been mechanized using the Coq proof assistant.
Fusing industry and academia at GitHub (experience report)
Authors: Thomson Patrick , Rix Rob , Wu Nicolas , Schrijvers Tom
Published: August 2022

GitHub hosts hundreds of millions of code repositories written in hundreds of different programming languages. In addition to its hosting services, GitHub provides data and insights into code, such as vulnerability analysis and code navigation, with which users can improve and understand their software development process. GitHub has built Semantic, a program analysis tool capable of parsing and extracting detailed information from source code. The development of Semantic has relied extensively on the functional programming literature; this paper describes how connections to academic research inspired and informed the development of an industrial-scale program analysis toolkit.
‘do’ unchained: embracing local imperativity in a purely functional language (functional pearl)
Authors: Ullrich Sebastian , de Moura Leonardo
Published: August 2022

Purely functional programming languages pride themselves with reifying effects that are implicit in imperative languages into reusable and composable abstractions such as monads. This reification allows for more exact control over effects as well as the introduction of new or derived effects. However, despite libraries of more and more powerful abstractions over effectful operations being developed, syntactically the common 'do' notation still lags behind equivalent imperative code it is supposed to mimic regarding verbosity and code duplication. In this paper, we explore extending 'do' notation with other imperative language features that can be added to simplify monadic code: local mutation, early return, and iteration. We present formal translation rules that compile these features back down to purely functional code, show that the generated code can still be reasoned over using an implementation of the translation in the Lean 4 theorem prover, and formally prove the correctness of the translation rules relative to a simple static and dynamic semantics in Lean.
Staged compilation with two-level type theory
Authors: Kovács András
Published: August 2022

The aim of staged compilation is to enable metaprogramming in a way such that we
have guarantees about the well-formedness of code output, and we can also mix
together object-level and meta-level code in a concise and convenient manner. In
this work, we observe that two-level type theory (2LTT), a system originally
devised for the purpose of developing synthetic homotopy theory, also serves as
a system for staged compilation with dependent types. 2LTT has numerous good
properties for this use case: it has a concise specification, well-behaved model
theory, and it supports a wide range of language features both at the object and
the meta level. First, we give an overview of 2LTT's features and applications
in staging. Then, we present a staging algorithm and prove its correctness. Our
algorithm is "staging-by-evaluation", analogously to the technique of
normalization-by-evaluation, in that staging is given by the evaluation of 2LTT
syntax in a semantic domain. The staging algorithm together with its correctness
constitutes a proof of strong conservativity of 2LLT over the object theory. To our
knowledge, this is the first description of staged compilation which supports
full dependent types and unrestricted staging for types.
Entanglement detection with near-zero cost
Authors: Westrick Sam , Arora Jatin , Acar Umut A.
Published: August 2022

Recent research on parallel functional programming has culminated in a provably efficient (in work and space) parallel memory manager, which has been incorporated into the MPL (MaPLe) compiler for Parallel ML and shown to deliver practical efficiency and scalability. The memory manager exploits a property of parallel programs called disentanglement, which restricts computations from accessing concurrently allocated objects. Disentanglement is closely related to race-freedom, but subtly differs from it. Unlike race-freedom, however, no known techniques exists for ensuring disentanglement, leaving the task entirely to the programmer. This is a challenging task, because it requires reasoning about low-level memory operations (e.g., allocations and accesses), which is especially difficult in functional languages.

In this paper, we present techniques for detecting entanglement dynamically, while the program is running. We first present a dynamic semantics for a functional language with references that checks for entanglement by consulting parallel and sequential dependency relations in the program. Notably, the semantics requires checks for mutable objects only. We prove the soundness of the dynamic semantics and present several techniques for realizing it efficiently, in particular by pruning away a large number of entanglement checks. We also provide bounds on the work and space of our techniques.

We show that the entanglement detection techniques are practical by implementing them in the MPL compiler for Parallel ML. Considering a variety of benchmarks, we present an evaluation and measure time and space overheads of less than 5% on average with up to 72 cores. These results show that entanglement detection has negligible cost and can therefore remain deployed with little or no impact on efficiency, scalability, and space.
Aeneas: Rust verification by functional translation
Authors: Ho Son , Protzenko Jonathan
Published: August 2022

We present Aeneas, a new verification toolchain for Rust programs based on a lightweight functional translation. We leverage Rust’s rich region-based type system to eliminate memory reasoning for a large class of Rust programs, as long as they do not rely on interior mutability or unsafe code. Doing so, we relieve the proof engineer of the burden of memory-based reasoning, allowing them to instead focus on functional properties of their code.

The first contribution of Aeneas is a new approach to borrows and controlled aliasing. We propose a pure, functional semantics for LLBC, a Low-Level Borrow Calculus that captures a large subset of Rust programs. Our semantics is value-based, meaning there is no notion of memory, addresses or pointer arithmetic. Our semantics is also ownership-centric, meaning that we enforce soundness of borrows via a semantic criterion based on loans rather than through a syntactic type-based lifetime discipline. We claim that our semantics captures the essence of the borrow mechanism rather than its current implementation in the Rust compiler.

The second contribution of Aeneas is a translation from LLBC to a pure lambda-calculus. This allows the user to reason about the original Rust program through the theorem prover of their choice, and fulfills our promise of enabling lightweight verification of Rust programs. To deal with the well-known technical difficulty of terminating a borrow, we rely on a novel approach, in which we approximate the borrow graph in the presence of function calls. This in turn allows us to perform the translation using a new technical device called backward functions.

We implement our toolchain in a mixture of Rust and OCaml; our chief case study is a low-level, resizing hash table, for which we prove functional correctness, the first such result in Rust. Our evaluation shows significant gains of verification productivity for the programmer. This paper therefore establishes a new point in the design space of Rust verification toolchains, one that aims to verify Rust programs simply, and at scale.

Rust goes to great lengths to enforce static control of aliasing; the proof engineer should not waste any time on memory reasoning when so much already comes “for free”!
Multi types and reasonable space
Authors: Accattoli Beniamino , Dal Lago Ugo , Vanoni Gabriele
Published: August 2022

Accattoli, Dal Lago, and Vanoni have recently proved that the space used by the Space KAM, a variant of the Krivine abstract machine, is a reasonable space cost model for the λ-calculus accounting for logarithmic space, solving a longstanding open problem. In this paper, we provide a new system of multi types (a variant of intersection types) and extract from multi type derivations the space used by the Space KAM, capturing into a type system the space complexity of the abstract machine. Additionally, we show how to capture also the time of the Space KAM, which is a reasonable time cost model, via minor changes to the type system.
On Feller continuity and full abstraction
Authors: Barthe Gilles , Crubillé Raphaëlle , Dal Lago Ugo , Gavazzo Francesco
Published: August 2022

We study the nature of applicative bisimilarity in λ-calculi endowed with operators for sampling from contin- uous distributions. On the one hand, we show that bisimilarity, logical equivalence, and testing equivalence all coincide with contextual equivalence when real numbers can be manipulated through continuous functions only. The key ingredient towards this result is a notion of Feller-continuity for labelled Markov processes, which we believe of independent interest, giving rise a broad class of LMPs for which coinductive and logically inspired equivalences coincide. On the other hand, we show that if no constraint is put on the way real numbers are manipulated, characterizing contextual equivalence turns out to be hard, and most of the aforementioned notions of equivalence are even unsound.
The theory of call-by-value solvability
Authors: Accattoli Beniamino , Guerrieri Giulio
Published: August 2022

The semantics of the untyped (call-by-name) lambda-calculus is a well developed field built around the concept of solvable terms, which are elegantly characterized in many different ways. In particular, unsolvable terms provide a consistent notion of meaningless term. The semantics of the untyped call-by-value lambda-calculus (CbV) is instead still in its infancy, because of some inherent difficulties but also because CbV solvable terms are less studied and understood than in call-by-name. On the one hand, we show that a carefully crafted presentation of CbV allows us to recover many of the properties that solvability has in call-by-name, in particular qualitative and quantitative characterizations via multi types. On the other hand, we stress that, in CbV, solvability plays a different role: identifying unsolvable terms as meaningless induces an inconsistent theory.
Flexible presentations of graded monads
Authors: Katsumata Shin-ya , McDermott Dylan , Uustalu Tarmo , Wu Nicolas
Published: August 2022

A large class of monads used to model computational effects have natural presentations by operations and equations, for example, the list monad can be presented by a constant and a binary operation subject to unitality and associativity. Graded monads are a generalization of monads that enable us to track quantitative information about the effects being modelled. Correspondingly, a large class of graded monads can be presented using an existing notion of graded presentation. However, the existing notion has some deficiencies, in particular many effects do not have natural graded presentations.

We introduce a notion of flexibly graded presentation that does not suffer from these issues, and develop the associated theory. We show that every flexibly graded presentation induces a graded monad equipped with interpretations of the operations of the presentation, and that all graded monads satisfying a particular condition on colimits have a flexibly graded presentation. As part of this, we show that the usual algebra-preserving correspondence between presentations and a class of monads transfers to an algebra-preserving correspondence between flexibly graded presentations and a class of flexibly graded monads.