Affine monads and lazy structures for Bayesian programming

We show that streams and lazy data structures are a natural idiom for programming with infinite-dimensional Bayesian methods such as Poisson processes, Gaussian processes, jump processes, Dirichlet processes, and Beta processes. The crucial semantic idea, inspired by developments in synthetic probability theory, is to work with two separate monads: an affine monad of probability, which supports laziness, and a commutative, non-affine monad of measures, which does not. (Affine means that T(1)≅ 1.) We show that the separation is important from a decidability perspective, and that the recent model of quasi-Borel spaces supports these two monads. To perform Bayesian inference with these examples, we introduce new inference methods that are specially adapted to laziness; they are proven correct by reference to the Metropolis-Hastings-Green method. Our theoretical development is implemented as a Haskell library, LazyPPL

Which rhizobia nodulate which legumes in New Zealand soils?

Recent work which genotypically characterised rhizobia of native, crop and weed legumes in New Zealand and examined their cross-nodulation ability is reviewed and related to earlier work with focus on New Zealand pasture systems. The New Zealand native legumes were exclusively effectively nodulated by novel strains of Mesorhizobium which did not nodulate crop or weed legumes. Clovers, lucerne, Lotus and grain legumes were effectively nodulated by different genera, species and biovars of rhizobia primarily originating from inoculum. Rhizobial symbionts of white clover have established over wide areas in New Zealand. Weed legumes are effectively nodulated by different genera/species of rhizobia depending on species. Bradyrhizobia that cross-nodulate lupins, gorse, European broom and tagasaste are widespread in New Zealand

Alchemical Gold and the pursuit of the Mercurial Elixir: An analysis of two alchemical treatises from the Tibetan Buddhist Canon

This article focuses on the analysis of two Tibetan treatises on iatrochemistry, The Treatise on the Mercurial Elixir (Dngul chu grub pa’i bstan bcos) and the Compendium on the Transmutation into Gold (Gser ’gyur bstan bcos bsdus pa). These texts belong to the rasaśāstra genre that were translated from Sanskrit into Tibetan by Orgyenpa Rinchenpel (O rgyan pa Rin chen dpal, 1229/30–1309) and integrated into the Tibetan Buddhist Canon of the Tengyur (Bstan ’gyur). The treatises deal with the processing of mercury, which is indispensable to convert metals into gold (gser ’gyur) and to accomplish the ‘mercurial elixir’ (dngul chu’i bcud len). The texts start with the description of a ‘pink-coloured’ (dmar skya mdog) compound, which is described as the amalgam of ‘moonlight-exposed tin’ (gsha’ tshe zla ba phyogs), gold, and copper. According to the texts, mercury has to be ‘amalgamated’ (sbyor ba) with ‘minerals that devour its poisons’ (za byed khams) and with ‘eight metals that bind it’ (’ching khams brgyad); at the same time, mercury is cooked with ‘red substances’ (dmar sde tshan) and other herbal extracts, types of urine and salts, and reduced to ashes. Starting with an outline of the earliest Tibetan medical sources on mercury, I analyse the two treatises with regard to their entire materia alchemica and the respective purification methods aimed at ‘obtaining essences’ (snying stobs), which are then to be absorbed by mercury. I argue that the two thirteenth-century treatises were particularly significant in the process of consolidating pharmaceutical practices based on mercury and the merging of alchemical and medical knowledge in Tibet

Electric Field and Strain Tuning of 2D Semiconductor van der Waals Heterostructures for Tunnel Field-Effect Transistors

Heterostacks consisting of low-dimensional materials are attractive candidates for future electronic nanodevices in the post-silicon era. In this paper, using first-principles calculations based on density functional theory (DFT), we explore the structural and electronic properties of MoTe2/ZrS2 heterostructures with various stacking patterns and thicknesses. Our simulations show that the valence band (VB) edge of MoTe2 is almost aligned with the conduction band (CB) edge of ZrS2, and (MoTe2)m/(ZrS2)m (m = 1, 2) heterostructures exhibit the long-sought broken gap band alignment, which is pivotal for realizing tunneling transistors. Electrons are found to spontaneously flow from MoTe2 to ZrS2, and the system resembles an ultrascaled parallel plate capacitor with an intrinsic electric field pointed from MoTe2 to ZrS2. The effects of strain and external electric fields on the electronic properties are also investigated. For vertical compressive strains, the charge transfer increases due to the decreased coupling between the layers, whereas tensile strains lead to the opposite behavior. For negative electric fields a transition from the type-III to the type-II band alignment is induced. In contrast, by increasing the positive electric fields, a larger overlap between the valence and conduction bands is observed, leading to a larger band-to-band tunneling (BTBT) current. Low-strained heterostructures with various rotation angles between the constituent layers are also considered. We find only small variations in the energies of the VB and CB edges with respect to the Fermi level, for different rotation angles up to 30\ub0. Overall, our simulations offer insights into the fundamental properties of low-dimensional heterostructures and pave the way for their future application in energy-efficient electronic nanodevices