Micromechanical investigation of fines liberation and transport during coal seam dewatering

The reduction of subsurface hydrostatic pressure to allow natural gas desorption is an integral step in the production of coal seam gas (CSG). During this dewatering stage, viscous stresses can cause the liberation and transport of fines, which are predominantly comprised of inorganic clay groups such as smectite, illite and kaolin, from within the coal matrix. Dislodged particles migrate in production fluid through fractures towards the wellbore where capture and deposition can deteriorate the reservoir's permeability. Once in the wellbore, these particles can adversely affect the performance of mechanical equipment such as pumps. This study uses direct numerical simulation of a synthetic coal fracture to help elucidate the particle detachment process. This is approached using a coupled lattice Boltzmann-discrete element method to capture both physical and physicochemical interactions based on Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Preliminary testing with the developed model suggests that particles move almost freely along the bounding surface regardless of electrostatic interactions, and that Hele-Shaw predictions of particle lift in particular can be inadequate. Further, larger-scale simulations indicated that the DLVO parameters can significantly impact the vertical position of propagating fines with variations in eroded mass of over 100% observed for the range of tested salinity levels

Security Analysis of Isogeny-Based Cryptosystems

Let $E$ be a supersingular elliptic curve over a finite field. In this document we study public-key encryption schemes which use non-constant rational maps from $E$. The purpose of this study is to determine if such cryptosystems are secure. Supersingular Isogeny Diffie-Hellman (SIDH) and other supersingular isogeny-based cryptosystems are considered. The content is naturally divided by cryptosystem, and in the case of SIDH, further divided by type of cryptanalysis: SIDH when the endomorphism ring of the base elliptic curve is given (as is done in practice), repeated use of keys in SIDH, and endomorphism ring constructing algorithms. In each case the relevent background material is presented to develop the theory. In studying the security of SIDH when the endomorphism ring of the base curve $E$ is known, one of the main results is the following. This theorem is then used to reduce the security of such an SIDH instantiation to the problem of finding particular endomorphisms in \End(E). \begin{thm} Given \begin{enumerate} \item a supersingular elliptic curve E/\FQ such that $p = N_1 N_2 - 1$ for coprime $N_1\approx N_2$, where $N_2$ is $\log p$-smooth, \item an elliptic curve $E'$ that is the codomain of an $N_1$-isogeny $\phi:E\rightarrow E'$, \item the action of $\phi$ on $E[N_2]$, and \item a $k$-endomorphism $\psi$ of $E$, where $\gcd(k, N_1) = 1$, and if \g is the greatest integer such that $g\mid N_2^2$ and $g\mid k$, then \h := \frac{k}{g} < N_1, \end{enumerate} there exists a classical algorithm with worst case runtime \tilde{O}(\h^3) which decides whether $\psi(\ker\phi) = \ker\phi$ or not, but may give false positives with probability $\approx \frac{1}{\sqrt{p}}$. Further, if \h is $\log{p}$-smooth, then the runtime is \tilde{O} (\sqrt{\h}). \end{thm} In studying the security of repeated use of SIDH public keys, the main result presented is the following theorem, which proves that performing multiple pairwise instances of SIDH prevents certain active attacks when keys are reused. \begin{thm} Assuming that the CSSI problem is intractable, it is computationally infeasible for a malicious adversary, with non-negligible probability, to modify a public key $(E_B,\phi_B(P_A),\phi_B(Q_A))$ to some $(E_B,R,S)$ which is malicious for SIDH. \end{thm} It is well known that the problem of computing hidden supersingular isogenies can be reduced to computing the endomorphism rings of the domain and codomain elliptic curves. A novel algorithm for computing an order in the endomorphism ring of a supersingular elliptic curve is presented and analyzed to have runtime $O(p^{1/2}(\log p)^2)$. In studying non-SIDH cryptosystems, four other isogeny-based cryptosystems are examined. The first three were all proposed by the same authors and use secret endomorphisms. These are each shown to be either totally insecure (private keys can be recovered directly from public keys) or impractical to implement efficiently. The fourth scheme is a novel proposal which attempts to combine isogenies with the learning with errors problem. This proposal is also shown to be totally insecure

A Note on the Ending Elliptic Curve in SIDH

It has been suspected that in supersingular isogeny-based cryptosystems the two ending elliptic curves computed by the participants are exactly equal. Resolving this open problem has not been pressing because the elliptic curves are known to be isomorphic, and therefore share a $j$-invariant which can be used as a shared secret. However, this is still an interesting independent problem as other values of the elliptic curves may be valuable as shared information as well. This note answers this open problem in the affirmative

Key Compression for Isogeny-Based Cryptosystems

We present a method for key compression in quantum-resistant isogeny-based cryptosystems, which reduces storage and transmission costs of per-party public information by a factor of two, with no effect on the security level of the scheme. We achieve this reduction by compressing both the representation of an elliptic curve, and torsion points on said curve. Compression of the elliptic curve is achieved by associating each j-invariant to a canonical choice of elliptic curve, and the torsion points will be represented as linear combinations with respect to a canonical choice of basis for this subgroup. This method of compressing public information can be applied to numerous isogeny-based protocols, such as key exchange, zero-knowledge identification, and public-key encryption. The details of utilizing compression for each of these cryptosystems is explained. We provide implementation results showing the computational cost of key compression and decompression at various security levels. Our results show that isogeny-based cryptosystems achieve the smallest possible key sizes among all existing families of post-quantum cryptosystems at practical security levels

Structural Positional Encoding for knowledge integration in transformer-based medical process monitoring

Predictive process monitoring is a process mining task aimed at forecasting information about a running process trace, such as the most correct next activity to be executed. In medical domains, predictive process monitoring can provide valuable decision support in atypical and nontrivial situations. Decision support and quality assessment in medicine cannot ignore domain knowledge, in order to be grounded on all the available information (which is not limited to data) and to be really acceptable by end users. In this paper, we propose a predictive process monitoring approach relying on the use of a {\em transformer}, a deep learning architecture based on the attention mechanism. A major contribution of our work lies in the incorporation of ontological domain-specific knowledge, carried out through a graph positional encoding technique. The paper presents and discusses the encouraging experimental result we are collecting in the domain of stroke management

Current developments and challenges of underground mine ventilation and cooling methods

The mining industry has experienced a dramatic change over the past 20 years in terms of methods and equipment as well as human resource policies. These changes have had impacts on the design of mine ventilation systems. Although feasible developments have been implemented to some extent, in some other areas ventilation planning still requires further improvements to provide a healthy work environment at a reasonable cost. The boom in energy costs has also encouraged mine ventilation designers to seek for efficient use of energy and optimization strategies. The electricity consumption by mine refrigeration plants should be reduced possibly without any adverse effects on the safety of workers. This study presents an overview of the latest techniques used by the experts to address these issues. A revision of the novel ventilation strategies and mine refrigeration methods, and their ultimate effect on efficiency and mining costs would be identified. Finally, likely future developments in the area of mine cooling are outlined

Boston Hospitality Review: Winter 2018

Table of contents: Blockchain Technology & its Implications for the Hospitality Industry By Tarik Dogru, Makarand Mody, & Christie Leonardi -- How Does My Neighbor Feel About my Airbnb? By Makarand Mody, Courtney Suess & Tarik Dogru -- 5 Keys to Successful Hospitality Leadership By Sarah Andersen -- Cutting Through the Online Hospitality Clutter: 10 Best Practices for Organic Visibility By Leora Lanz & Juan Lesmes -- When is a Group a Chain, and a Chain a Brand? By Christopher Muller -- À la Carte Dining in a Banquet Setting: Is it Feasible? By Peter Szende and Ally Run

Development of a central-moment phase-field lattice Boltzmann model for thermocapillary flows: Droplet capture and computational performance

This study develops a computationally efficient phase-field lattice Boltzmann model with the capability to simulate thermocapillary flows. The model was implemented into the open-source simulation framework, waLBerla, and extended to conduct the collision stage using central moments. The multiphase model was coupled with both a passive-scalar thermal LB, and a RK solution to the energy equation in order to resolve temperature-dependent surface tension phenomena. Various lattice stencils (D3Q7, D3Q15, D3Q19, D3Q27) were tested for the passive-scalar LB and both the second- and fourth-order RK methods were investigated. There was no significant difference observed in the accuracy of the LB or RK schemes. The passive scalar D3Q7 LB discretisation tended to provide computational benefits, while the second order RK scheme is superior in memory usage. This paper makes contributions relating to the modelling of thermocapillary flows and to understanding the behaviour of droplet capture with thermal sources analogous to thermal tweezers. Four primary contributions to the literature are identified. First, a new 3D thermocapillary, central-moment phase-field LB model is presented and implemented in the open-source software, waLBerla. Second, the accuracy and computational performance of various techniques to resolve the energy equation for multiphase, incompressible fluids is investigated. Third, the dynamic droplet transport behaviour in the presence of thermal sources is studied and insight is provided on the potential ability to manipulate droplets based on local domain heating. Finally, a concise analysis of the computational performance together with near-perfect scaling results on NVIDIA and AMD GPU-clusters is shown. This research enables the detailed study of droplet manipulation and control in thermocapillary devices

Ellsworth American : January 28, 1903

Over the last two decades, lattice Boltzmann methods have become an increasingly popular tool to compute the flow in complex geometries such as porous media. In addition to single phase simulations allowing, for example, a precise quantification of the permeability of a porous sample, a number of extensions to the lattice Boltzmann method are available which allow to study multiphase and multicomponent flows on a pore scale level. In this article, we give an extensive overview on a number of these diffuse interface models and discuss their advantages and disadvantages. Furthermore, we shortly report on multiphase flows containing solid particles, as well as implementation details and optimization issues.Schlumberger-Doll Research CenterNetherlands Organization for Scientific Research (NWO/STW (Vidi grant 10787)Foundation for Fundamental Research on Matter (Netherlands) (FOM/Shell IPP (09iPOG14 - “Detection and guidance of nanoparticles for enhanced oil recovery”))Los Alamos National Laboratory (LDRD Program and Institutional Computing Program)Japan. Ministry of Education, Culture, Sports, Science and Technology (International Institute for Carbon Neutral Energy Research (WPI-I2CNER))National Science Fund for Distinguished Young Scholars (China) (Thousand Youth Talents Program