Marginally Deformed Starobinsky Gravity

We show that quantum-induced marginal deformations of the Starobinsky gravitational action of the form $R^{2(1 -\alpha)}$, with $R$ the Ricci scalar and $\alpha$ a positive parameter, smaller than one half, can account for the recent experimental observations by BICEP2 of primordial tensor modes. We also suggest natural microscopic (non) gravitational sources of these corrections and demonstrate that they lead generally to a nonzero and positive $\alpha$. Furthermore we argue, that within this framework, the tensor modes probe theories of grand unification with a large scalar field content.Comment: 5 pages, 1 figure, 2 column

A pedestrian approach to the high energy limits of branes and other gravitational systems

In this article we study limits of models that contain a dimensionful parameter such as the mass of the relativistic point-particle. The limits are analogous to the massless limit of the particle and may be thought of as high energy limits. We present the ideas and work through several examples in a (hopefully) pedagogical manner. Along the way we derive several new results.Comment: 19 pages, 1 figur

Model for reflection and transmission matrices of nanowire end facets

Nanowires show a large potential for various electrooptical devices, such as light emitting diodes, solar cells and nanowire lasers. We present a direct method developed to calculate the modal reflection and transmission matrix at the end facets of a waveguide of arbitrary cross section, resulting in a generalized version of the Fresnel equations. The reflection can be conveniently computed using Fast Fourier Transforms. We demonstrate that the reflection is qualitatively described by two main parameters, the modal field confinement and the average Fresnel reflection of the plane waves constituting the waveguide mode.Comment: 11 pages,14 figure

The Exact Geometry of a Kerr-Taub-NUT Solution of String Theory

In this paper we study a solution of heterotic string theory corresponding to a rotating Kerr-Taub-NUT spacetime. It has an exact CFT description as a heterotic coset model, and a Lagrangian formulation as a gauged WZNW model. It is a generalisation of a recently discussed stringy Taub-NUT solution, and is interesting as another laboratory for studying the fate of closed timelike curves and cosmological singularities in string theory. We extend the computation of the exact metric and dilaton to this rotating case, and then discuss some properties of the metric, with particular emphasis on the curvature singularities.Comment: 14 pages, 3 figure

Effects of pre- or postoperative morphine and of preoperative ketamine in experimental surgery in rats, evaluated by pain scoring and c-fos expression

Since Wall (1988) hypothesised a beneficial post surgical effect of preoperative analgesic treatment (so-called pre-emptive analgesic treatment) as a supplement to postoperative analgesic treatment, the concept has been subject to many scientific debates. According to the hypothesis, applying analgesics before the nociceptive stimulus is beneficial due to reduced wind-up and reduced central sensitisation resulting in diminished risk of postoperative hyperalgesia and allodynia (Woolf and Chong, 1993). The scientific literature provides conflicting evidence for this theory. Beneficial effect of preemptive analgesic treatment has been reported after pre-emptive treatment with local analgesics, opioids and NSAID´s compared with placebo (Woolf and Chong, 1993). Some clinical settings have showed beneficial analgesic effect of preemptive analgesia, when the same pre-emptive and postoperative treatments with lidocaine (Ejlersen et al., 1992; Doyle and Bowler, 1998) or opioids (Katz et al., 1992) were compared. However, Dahl et al. (1992) and Elhakim et al. (1995) did not obtained supportive results in their clinical studies.In the majority of studies using animal models addressing this concept, the nociceptive stimulus has been obtained by injection of irritating chemicals, in particular formalin. When somatic tissue is damaged or irritated, nociceptive receptors are activated by peripheral release of extracellular inflammatory mediators. The activated receptors lead the signal to the synapses in the dorsal horn of the spinal cord as a 2-phased signal. In the acute first phase, nociceptive stimuli are mediated centrally through Aä fibres fibres. During the slower and long-lasting second phase, the nociceptive stimuli are mediated mainly through C-fibres (Cross et al., 1994). The release of extracellular inflammatory mediators increases the peripheral excitability, which leads to hyperalgesia (Woolf, 1995). Repetitive peripheral nociceptive impulses mediated through C-fibres result in an increased central excitability of dorsal appears to be in part mediated through N-methylhorn neurones. This state is called wind-up and appears to be in part mediated through N-methyl- D-aspartate (NMDA) receptors on dorsal horn secondary nociceptive neurones. Transmission of multiple slow stimuli leads to release of glutamate, which removes the Mg++-block in the NMDA receptor and allows substantial Ca++-inflow (Urban et al., 1994). NMDA receptor antagonists bind to the same site as Mg++ and prevents Ca++- inflow (Hirota and Lambert, 1996; Kress, 1997). NMDA-receptor antagonists can prevent wind-up but not the initial responses of the neurones, whereas the reverse is true for opioids (Chapman and Dickenson, 1992). NMDA-antagonists have no effect on pain of the acute first phase, but may act synergistic to the analgesic effect of opioids (Chapman and Dickenson, 1992; Honoré et al., 1996). Only few studies deal with a postoperative experimental model in animals and those available are conflicting. Brennan et al. (1996) developed an elegant postoperative model in rats with surgical intervention on the plantar surface of the hind foot. In this study a relationship was found between behavioural pain observation scores and mechanical hyperalgesia. Ovariohysterectomized rats have also been used as animal models of postoperative pain (Lascelles et al. 1995). A commonly used method of determining the nociceptive activity caused by a peripheral stimulus is to identify and quantify the nuclear protein Fos expressed in secondary nociceptive neurones in the spinal cord. c-fos is an immediate early gene (IEG), that encodes for Fos. IEG’s are rapidly and transiently induced in neuronal cells within minutes of extracellular stimulation (Sheng and Greenberg, 1990). The c-fos mRNA accumulates, and reaches its peak after 30 to 40 minutes. The Fos level peaks approximately two hours after induction of c-fos (Harris, 1998). Since Hunt (1987) reported, that peripheral inflammation induced c-fos in neurones in the dorsal horn of the spinal cord, many studies have shown the relationship between nociception and cfos expression.The aim of the present investigation was to study the effect of pre-emptive versus postoperative opioid analgesic treatment by use of the surgical model of Brennan et al. (1996) and combine the pre-emptive and postoperative opioid treatment with pre-emptive ketamine. The effects were quantified by stereological estimation of the number of dorsal horn neurones expressing c-fos and pain scoring from the operated hind foot

Specifying and Verifying Concurrent Algorithms with Histories and Subjectivity

We present a lightweight approach to Hoare-style specifications for fine-grained concurrency, based on a notion of time-stamped histories that abstractly capture atomic changes in the program state. Our key observation is that histories form a partial commutative monoid, a structure fundamental for representation of concurrent resources. This insight provides us with a unifying mechanism that allows us to treat histories just like heaps in separation logic. For example, both are subject to the same assertion logic and inference rules (e.g., the frame rule). Moreover, the notion of ownership transfer, which usually applies to heaps, has an equivalent in histories. It can be used to formally represent helping---an important design pattern for concurrent algorithms whereby one thread can execute code on behalf of another. Specifications in terms of histories naturally abstract granularity, in the sense that sophisticated fine-grained algorithms can be given the same specifications as their simplified coarse-grained counterparts, making them equally convenient for client-side reasoning. We illustrate our approach on a number of examples and validate all of them in Coq.Comment: 17 page

Numerical modeling of phase-separation in binary media based on the cahn-hilliard equation

In the article numerical procedure for solution of the Cahn-Hilliard equation which is based on the forward Euler method in time and mixed (due to 4th order nature of differential operator) linear finite element formulation in space is described. Numerical examples consist of idealized model with double well potential (in 2 and 3 spatial dimensions) and more physically relevant model with logarithmic potential (in 2D only).У статті описано процедуру наближеного рішення рівняння Кана-Хіллярда в частинних похідних 4-го порядку, котра базується на явному методі Ейлера в часі та змішаній постановці з білінійними скінченими елементами в просторі. Наведено чисельні рішення для ідеалізованої моделі з двуямним потенціалом (в 2-х та 3-х просторових вимірах) та більш фізично релевантної моделі з логарифмічним потенціалом (тільки в 2-х просторових вимірах)

Udkomne Bøger.

Udkomne Bøger

Thomas Riise Segelcke. Fodt den 2. Maj 1831, død den 12. November 1902.

Thomas Riise Segelcke. Fodt den 2. Maj 1831, død den 12. November 1902