Thermally-activated Non-Schmid Glide of Screw Dislocations in W using Atomistically-informed Kinetic Monte Carlo Simulations

Thermally-activated \small{\nicefrac{1}{2}} screw dislocation motion is the controlling plastic mechanism at low temperatures in body-centered cubic (bcc) crystals. Motion proceeds by the nucleation and propagation of atomic-sized kink pairs susceptible of being studied using molecular dynamics (MD). However, MD's natural inability to properly sample thermally-activated processes as well as to capture $\{110\}$ screw dislocation glide calls for the development of other methods capable of overcoming these limitations. Here we develop a kinetic Monte Carlo (kMC) approach to study single screw dislocation dynamics from room temperature to $0.5T_m$ and at stresses $0<\sigma<0.9\sigma_P$, where $T_m$ and $\sigma_P$ are the melting point and the Peierls stress. The method is entirely parameterized with atomistic simulations using an embedded atom potential for tungsten. To increase the physical fidelity of our simulations, we calculate the deviations from Schmid's law prescribed by the interatomic potential used and we study single dislocation kinetics using both projections. We calculate dislocation velocities as a function of stress, temperature, and dislocation line length. We find that considering non-Schmid effects has a strong influence on both the magnitude of the velocities and the trajectories followed by the dislocation. We finish by condensing all the calculated data into effective stress and temperature dependent mobilities to be used in more homogenized numerical methods

Pre-conceptual guidelines for men: a review of male infertility experience, including nutrition and lifestyle factors

Male fertility is declining and affects approximately one in seven couples. Reasons for this are multi-factorial and the subject of on-going research, though environmental contaminants (such xenoestrogens) are believed to be contributory factors. Semen parameters can be improved through a healthy diet and nutritional supplementation has also been shown to improve semen parameters, clinical pregnancy and live birth rates significantly. Despite this, in medical care dietary modification beyond alcohol reduction is rarely recommended. The aim of this review was to consider the psychosocial impacts of infertility in males whilst assessing other nutritional and lifestyle interventions that can be used in personalized nutrition care. More tailored nutrition care needs to consider this and the taboo surrounding the male infertility experience. A systematic approach was used. Three electronic databases (CINAHL, Medline and Academic Search Complete) were searched using predetermined Boolean search terms and identified 125 papers for review. Hand searches were undertaken to ensure recent evidence was included. Duplicates were removed and predefined inclusion and exclusion criteria were applied. Narrative synthesis was used for review and to develop preconceptual guidelines. Review data indicates dietary modification or supplementation with antioxidants such as vitamin C, vitamin E, coenzyme Q10, selenium, carnitine and zinc have been shown to improve markers of male fertility and reduce markers of seminal oxidative damage. Also, a Mediterranean style diet is also associated with higher quality sperm counts. Weight loss is beneficial in terms of normalizing endocrine profiles but at present it is not possible to determine if this is the effect of weight loss alone, or the combined effect of weight loss alongside other dietary improvement. Further research is therefore needed to understand the role of the many potential confounding factors. Despite this, infertility is emotionally challenging for men and nutrition, and personalised nutrition and lifestyle therapies have potential to support men trying to conceive. Pre-conceptual nutrition and lifestyle guidelines for men have been developed from this review and the use should be considered as the basis for more tailored nutrition care in practice

LINK and the dynamics of utterance interpretation.

The operation allows the derivation of inferential units as the result of syntactic processing. The same operation derives structure across a diffuse range of data; the differences between these are attributable to lexical information and the dynamics of the process. The thesis examines a range of data where clauses depend on some element in the main clause for interpretation. These are assigned structure as LINK trees in the framework of Labelled Deductive Systems for Natural Language outlined in Kempson, Meyer-Viol & Gabbay, (Dynamic Syntax: the Deductive Flow of Natural Language, in prep.). I describe the approach to utterance interpretation this proposes: linguistic structure is built incrementally according to lexically encoded procedural instructions and rules of construction constrained by pragmatic principles. This allows a perspective where problems previously divided between syntax, semantics and pragmatics can be addressed in a more unified manner. 1 outline the operation as it has been developed for relative clauses. This allows several trees to be built for the same utterance which are connected by a having a node description in common. I argue that this operation can be extended to cover the following data: extraposed relative clauses, reduced relative clauses, adjunct predicates and parenthetical constituents. To this end I introduce type (p) into the framework, which allows the representation of non-tensed propositions and I modify the operation to allow the creation of trees from discontinuous input. I develop context-dependent lexical rules to capture the difference between modifying and predicative uses of lexical items. The interaction of processing tasks, compilation and lexical information determines the precise nature of the structures which are built. The update procedure I develop allows a uniform characterisation of the way structure is derived across different contexts, shedding new light on the dynamics of building interpretation

Harnessing optical micro-combs for microwave photonics

In the past decade, optical frequency combs generated by high-Q micro-resonators, or micro-combs, which feature compact device footprints, high energy efficiency, and high-repetition-rates in broad optical bandwidths, have led to a revolution in a wide range of fields including metrology, mode-locked lasers, telecommunications, RF photonics, spectroscopy, sensing, and quantum optics. Among these, an application that has attracted great interest is the use of micro-combs for RF photonics, where they offer enhanced functionalities as well as reduced size and power consumption over other approaches. This article reviews the recent advances in this emerging field. We provide an overview of the main achievements that have been obtained to date, and highlight the strong potential of micro-combs for RF photonics applications. We also discuss some of the open challenges and limitations that need to be met for practical applications.Comment: 32 Pages, 13 Figures, 172 Reference

Future Contingents and the Logic of Temporal Omniscience

At least since Aristotle’s famous 'sea-battle' passages in On Interpretation 9, some substantial minority of philosophers has been attracted to the doctrine of the open future--the doctrine that future contingent statements are not true. But, prima facie, such views seem inconsistent with the following intuition: if something has happened, then (looking back) it was the case that it would happen. How can it be that, looking forwards, it isn’t true that there will be a sea battle, while also being true that, looking backwards, it was the case that there would be a sea battle? This tension forms, in large part, what might be called the problem of future contingents. A dominant trend in temporal logic and semantic theorizing about future contingents seeks to validate both intuitions. Theorists in this tradition--including some interpretations of Aristotle, but paradigmatically, Thomason (1970), as well as more recent developments in Belnap, et. al (2001) and MacFarlane (2003, 2014)--have argued that the apparent tension between the intuitions is in fact merely apparent. In short, such theorists seek to maintain both of the following two theses: (i) the open future: Future contingents are not true, and (ii) retro-closure: From the fact that something is true, it follows that it was the case that it would be true. It is well-known that reflection on the problem of future contingents has in many ways been inspired by importantly parallel issues regarding divine foreknowledge and indeterminism. In this paper, we take up this perspective, and ask what accepting both the open future and retro-closure predicts about omniscience. When we theorize about a perfect knower, we are theorizing about what an ideal agent ought to believe. Our contention is that there isn’t an acceptable view of ideally rational belief given the assumptions of the open future and retro-closure, and thus this casts doubt on the conjunction of those assumptions

Unraveling the temperature dependence of the yield strength in single-crystal tungsten using atomistically-informed crystal plasticity calculations

We use a physically-based crystal plasticity model to predict the yield strength of body-centered cubic (bcc) tungsten single crystals subjected to uniaxial loading. Our model captures the thermally-activated character of screw dislocation motion and full non-Schmid effects, both of which are known to play a critical role in bcc plasticity. The model uses atomistic calculations as the sole source of constitutive information, with no parameter fitting of any kind to experimental data. Our results are in excellent agreement with experimental measurements of the yield stress as a function of temperature for a number of loading orientations. The validated methodology is then employed to calculate the temperature and strain-rate dependence of the yield strength for 231 crystallographic orientations within the standard stereographic triangle. We extract the strain-rate sensitivity of W crystals at different temperatures, and finish with the calculation of yield surfaces under biaxial loading conditions that can be used to define effective yield criteria for engineering design models

Femtosecond quantification of void evolution during rapid material failure

Understanding high-velocity impact, and the subsequent high strain rate material deformation and potential catastrophic failure, is of critical importance across a range of scientific and engineering disciplines that include astrophysics, materials science, and aerospace engineering. The deformation and failure mechanisms are not thoroughly understood, given the challenges of experimentally quantifying material evolution at extremely short time scales. Here, copper foils are rapidly strained via picosecond laser ablation and probed in situ with femtosecond x-ray free electron (XFEL) pulses. Small-angle x-ray scattering (SAXS) monitors the void distribution evolution, while wide-angle scattering (WAXS) simultaneously determines the strain evolution. The ability to quantifiably characterize the nanoscale during high strain rate failure with ultrafast SAXS, complementing WAXS, represents a broadening in the range of science that can be performed with XFEL. It is shown that ultimate failure occurs via void nucleation, growth, and coalescence, and the data agree well with molecular dynamics simulations

A synthetic low-frequency mammalian oscillator

Circadian clocks have long been known to be essential for the maintenance of physiological and behavioral processes in a variety of organisms ranging from plants to humans. Dysfunctions that subvert gene expression of oscillatory circadian-clock components may result in severe pathologies, including tumors and metabolic disorders. While the underlying molecular mechanisms and dynamics of complex gene behavior are not fully understood, synthetic approaches have provided substantial insight into the operation of complex control circuits, including that of oscillatory networks. Using iterative cycles of mathematical model-guided design and experimental analyses, we have developed a novel low-frequency mammalian oscillator. It incorporates intronically encoded siRNA-based silencing of the tetracycline-dependent transactivator to enable the autonomous and robust expression of a fluorescent transgene with periods of 26 h, a circadian clock-like oscillatory behavior. Using fluorescence-based time-lapse microscopy of engineered CHO-K1 cells, we profiled expression dynamics of a destabilized yellow fluorescent protein variant in single cells and real time. The novel oscillator design may enable further insights into the system dynamics of natural periodic processes as well as into siRNA-mediated transcription silencing. It may foster advances in design, analysis and application of complex synthetic systems in future gene therapy initiatives