Causality and replication in concurrent processes

The replication operator was introduced by Milner for obtaining a simplified description of recursive processes. The standard interleaving semantics denotes the replication of a process P, written !P, a shorthand for its unbound parallel composition, operationally equivalent to the process P | P | …, with P repeated as many times as needed. Albeit the replication mechanism has become increasingly popular, investigations on its causal semantics has been scarce. In fact, the correspondence between replication and unbound parallelism makes it difficult to recover basic properties usually associated with these semantics, such as the so-called concurrency diamond. In this paper we consider the interleaving semantics for the operator proposed by Sangiorgi and Walker, and we show how to refine it in order to capture causality. Furthermore, we prove it coincident with the standard causal semantics for recursive process studied in the literature, for processes defined by means of constant invocations

The effect catabolite repression on a known secondary netabolite streptonycete

The possible involvement of carbon catabolite repression in control of synthesis of the polyether antibiotic M139603 was examined by culturing the producing organism S. Longisooroflavus in a variety of media containing a range of different carbon sources at different concentrations. From the results it has been tentatively concluded that carbon catabolite repression is not mediated by any of the carbon sources tested

Regular Expression Matching and Operational Semantics

Many programming languages and tools, ranging from grep to the Java String library, contain regular expression matchers. Rather than first translating a regular expression into a deterministic finite automaton, such implementations typically match the regular expression on the fly. Thus they can be seen as virtual machines interpreting the regular expression much as if it were a program with some non-deterministic constructs such as the Kleene star. We formalize this implementation technique for regular expression matching using operational semantics. Specifically, we derive a series of abstract machines, moving from the abstract definition of matching to increasingly realistic machines. First a continuation is added to the operational semantics to describe what remains to be matched after the current expression. Next, we represent the expression as a data structure using pointers, which enables redundant searches to be eliminated via testing for pointer equality. From there, we arrive both at Thompson's lockstep construction and a machine that performs some operations in parallel, suitable for implementation on a large number of cores, such as a GPU. We formalize the parallel machine using process algebra and report some preliminary experiments with an implementation on a graphics processor using CUDA.Comment: In Proceedings SOS 2011, arXiv:1108.279

Localized deformation in soft solids around spherical cavities

Biological tissue, like internal organs, brain, or skin, are soft solids that may be exposed to injury inducing mechanisms at a range of rates, resulting in damage. Sport injuries, car crashes, traumatic brain injury, and ballistic impacts can produce strain rates from 10−10^5 1/s. The parameters governing failure in these soft solids (moduli < 1 MPa) are challenging to quantify, requiring modifications or defying the use of traditional characterization techniques. Driving bubble/droplet growth or contraction provides a way to characterize these materials while avoiding some limitations of traditional techniques. Large deformations in these spherical geometries induce localized deformations at the surface of the cavity. In this thesis, I leverage these localized deformations, cracks during expansion and creases during contractions, to investigate fracture energy and strain stiffening, respectively. A Small-scale Ballistic Cavitation device uses a high-pressure air reservoir to generate spherical deformation at high rates within soft solids. Air accelerates through a needle, reaching the speed of sound at the tip before delivery to the sample. The energy density of the air pulse matches that of bullets, producing small, ballistic-like cavitations. Independent control of pressure, needle diameter, and valve cycle time provides flexibility in experimental control variables not available in other ultrasoft solid cavitation techniques. Using these needle-mediated, high rate spherical expansions, I investigate the parameters governing fracture initiation in soft solids by adapting a theory of fracture traditionally used in dynamic failure in hard materials. I present results from cavity expansions in silicone and gelatin samples. Increasing the rate of expansion increases the number of cracks initiated in the cavity surface, leading to multi-lobed cracks, as opposed to the penny-shaped cracks present in quasi-static cavitations. The elastic wave speed-dependent fracture correlation model I adapt suggests that counting the number of cracks provides a measure of the soft solid’s fracture energy. Additionally, I include the implications of this model for analytical calculations in very tough, nonlinear materials. Finally, I demonstrate the multiple fracture phenomenon in ballistic impacts and present a method for analyzing damage that draws upon the understanding gained in from the bench-scale cavity expansions. In the last chapter, I report on crease morphology and evolution at the surface of contracting cavities embedded within elastomeric solids of varying degrees of crosslinking. Cavity contraction is achieved through evaporation of an embedded water droplet. In validation of theoretical predictions, strain-stiffening is found to govern both crease onset and crease density. Neo-Hookean solids are found to prefer initiating creasing with many short creases that join to form a collapsed state with only a few creases, whereas creasing in Gent solids initiates with a few creases that propagate across the cavity surface

Health effects of home energy efficiency interventions in England: a modelling study

Objective: To assess potential public health impacts of changes to indoor air quality and temperature due to energy efficiency retrofits in English dwellings to meet 2030 carbon reduction targets. Design: Health impact modelling study. Setting: England. Participants: English household population. Intervention: Three retrofit scenarios were modelled: (1) fabric and ventilation retrofits installed assuming building regulations are met. (2) As with scenario (1) but with additional ventilation for homes at risk of poor ventilation. (3) As with scenario (1) but with no additional ventilation to illustrate the potential risk of weak regulations and non-compliance. Main Outcome: Primary outcomes were changes in quality adjusted life years (QALYs) over 50 years from cardiorespiratory diseases, lung cancer, asthma and common mental disorders due to changes in indoor air pollutants, including: second-hand tobacco smoke, PM2.5 from indoor and outdoor sources, radon, mould, and indoor winter temperatures. Results: The modelling study estimates showed that scenario (1) resulted in positive effects on net mortality and morbidity of 2,241 (95% credible intervals (CI) 2,085 to 2,397) QALYs per 10,000 persons over 50 years due to improved temperatures and reduced exposure to indoor pollutants, despite an increase in exposure to outdoor–generated PM2.5. Scenario (2) resulted in a negative impact of -728 (95% CI -864 to -592) QALYs per 10,000 persons over 50 years due to an overall increase in indoor pollutant exposures. Scenario (3) resulted in -539 (95% CI -678 to -399) QALYs per 10,000 persons over 50 years due to an increase in indoor exposures despite targeting. Conclusions: If properly implemented alongside ventilation, energy efficiency retrofits in housing can improve health by reducing exposure to cold and air pollutants. Maximising the health benefits requires careful understanding of the balance of changes in pollutant exposures, highlighting the importance of ventilation to mitigate the risk of poor indoor air quality

Ultrafast non-equilibrium dynamics of rotons in superfluid helium

Superfluid 4He, the first superfluid ever discovered, is in some ways the least well understood. Unlike 3He superfluid, or the variety of Bose-Einstein condensates of ultracold gases, superfluid 4He is a very dense liquid of strongly interacting quasiparticles. The theory is then necessarily phenomenological: the quasiparticle properties are found from experiment, and controversies over their description still remain, notably regarding vortex dynamics and the nature of rotons and roton pair creation. It is therefore important to develop new experimental tools for probing the system far from equilibrium. Here we describe a method for locally perturbing the density of superfluid helium through the excitation of roton pairs with ultrashort laser pulses. By measuring the time dependence of this perturbation, we track the non-equilibrium evolution of the two-roton states on a picosecond timescale. Our results reveal an ultrafast cooling of hot roton pairs as they thermalize with the colder gas of other quasiparticles. We anticipate that these findings, as well as future applications of the introduced ultrafast laser technique to different temperature and pressure regimes in bulk liquid 4He, will stimulate further experimental and theoretical investigations towards better understanding of superfluidity