Brane worlds and dark matter

Two problems related to dark matter is considered in the context of a brane world model in which the confinement of gauge fields on the brane is achieved by invoking a confining potential. First, we show that the virial mass discrepancy can be addressed if the conserved geometrical term appearing in this model is considered as an energy momentum tensor of an unknown type of matter, the so-called X-matter whose equation of state is also obtained. Second, the galaxy rotation curves are explained by assuming an anisotropic energy momentum tensor for the X-matter.Comment: 13 pages, 1 figure, to appear in IJMP

Distributed Optimization of Multi-Robot Motion with Time-Energy Criterion

This paper is an application of a special case of distributed optimization problem. It is applied on optimizing the motion of multiple robot systems. The problem is decomposed into L subproblems with L being the number of robot systems. This decomposition reduces the problem to solving a single robot problem. The optimization problem is solved via a distributed algorithm, utilizing subgradient method. A global objective function is set as the sum of individual robot objectives in time and energy. Constraints are divided into two sets, namely, robot-individual constraints and robots’ interactions (collision) constraints. The approach is applied for the case of wheeled mobile robots: we are able to generate in parallel for each robot an optimized control input trajectory and then illustrate it in simulation examples

Biomass Torrefaction Process Review and Moving Bed Torrefaction System Model Development

Torrefaction is currently developing as an important preprocessing step to improve the quality of biomass in terms of physical properties, and proximate and ultimate composition. Torrefaction is a slow heating of biomass in an inert or reduced environment to a maximum temperature of 300°C. Torrefaction can also be defined as a group of products resulting from the partially controlled and isothermal pyrolysis of biomass occurring in a temperature range of 200–230ºC and 270–280ºC. Thus, the process can also be called a mild pyrolysis as it occurs at the lower temperature range of the pyrolysis process. At the end of the torrefaction process, a solid uniform product with lower moisture content and higher energy content than raw biomass is produced. Most of the smoke-producing compounds and other volatiles are removed during torrefaction, producing a final product that will have a lower mass but a higher heating value. An important aspect of research is to establish a degree of torrefaction where gains in heating value offset the loss of mass. There is a lack of literature on torrefaction reactor designs and a design sheet for estimating the dimensions of the torrefier based on capacity. This study includes a) conducting a detailed review on the torrefaction of biomass in terms of understanding the process, product properties, off-gas compositions, and methods used, and b) to design a moving bed torrefier, taking into account the basic fundamental heat and mass transfer calculations. Specific objectives include calculating the dimensions like diameter and height of the moving packed bed for different capacities, designing the heat loads and gas flow rates, and developing an interactive excel sheet where the user can define design specifications. In this report, 25–1000 kg/hr are used in equations for the design of the torrefier, examples of calculations, and specifications for the torrefier

A New Approach to Multi-Model Adaptive Control

Adaptive control is an approach used to deal with systems with uncertain or time-varying parameters. A classical adaptive controller typically consists of a linear time-invariant (LTI) control law together with a tuning mechanism which adjusts its parameters. Usually, though not exclusively, discrete-time adaptive controllers provide only asymptotic stability and possibly bounded-noise bounded-state stability; neither exponential stability nor a bounded noise gain is typically proven. Recently it has been shown that if we employ a parameter estimator based on the original Projection Algorithm together with projecting the parameter estimates onto a given compact and convex set, then the adaptive controller guarantees linear-like closed-loop behavior: exponential stability, a bounded noise gain and a convolution bound on the exogenous inputs. In this thesis, the overarching objective is to show that we can prove these same desirable linear-like properties in a wide range of adaptive control problems without the convexity assumption: the main idea is to use multiple estimators and a switching algorithm. Indeed, we show that those properties arise in a surprisingly natural way. We first prove a general result that exponential stability and a convolution bound on the closed-loop behavior can be leveraged to show tolerance to a degree of time-variations and unmodelled dynamics, i.e. such closed-loop properties guarantee robustness. After reviewing the original Projection Algorithm and introducing the reader to our slightly revised version, we turn our attention to controller design, with a focus on a non-convex set of plant uncertainty. As a starting point, we first consider first-order plants incorporating a simple switching algorithm. We then extend the approach to a class of nonlinear plants (which have stable zero dynamics); we consider both cases of convex and non-convex sets of parameter uncertainty. Afterwards, we turn to possibly non-minimum phase LTI plants; first we consider the stabilization problem for which we have two convex sets of uncertainty; then, we turn to the problem of tracking the sum of a finite number of sinusoids of known frequencies subject to an unknown plant order and a general compact set of uncertainty

Comparison of muscular tissue concentration of heavy metals in Sharpnose stinger (Himantura gerrardi) and Bigeye scade (Selar crumenophthalmus) of the Persian Gulf

We assessed concentration of heavy metals (Cu, Fe, Hg and Zn) in the muscular tissue of benthic species Himantura gerrardi and pelagic species Selar crumenophthalmus caught from the Persian Gulf during winter 2008. After biometrical measurements, the muscle tissues of 51 randomly selected samples were separated from 86 stations. Specimens were digested using the wet method and the concentrations of Cu, Fe and Zn were determined using Atomic Absorption Spectrophotometer (flame method) and also concentration of mercury was determined using Mercury Analyzer device. The mean concentration of heavy metals in muscle tissues of Himantura gerrardi were as follows: Fe: 74.78; Hg: 0.77; Zn: 875.99 and Cu: 3.5. However, these values for muscle tissues of Selar crumenophthalmus were: Fe: 25.07; Hg: 0.20; Cu: Zn: 15.54 and Zn: 2.31kg/g dry weight. Results showed that concentration of the selected heavy metals in H. gerrardi, were significantly higher than Selar crumenophthalmus (P <0.05)

Potential explanations for conflicting findings on abrupt versus gradual smoking cessation: a population study in England

BACKGROUND AND AIM: Observational and trial evidence conflict on the efficacy of two contrasting behavioural approaches to quitting smoking – gradual and abrupt. Observational data suggests an abrupt approach to quitting is superior to a gradual approach, whilst trials show no difference. One potential explanation is self-selection in observational data, whereby people can choose their quit approach and those who find it harder to quit may be more likely to choose a gradual quit approach. This study aims to investigate potential explanations for these conflicting findings. METHODS: We used observational data from a nationally representative sample of adults in England from November 2006 to February 2020 who reported smoking and had made at least one quit attempt in the past year (n=21,542). We used logistic regression models to assess the association between abrupt versus gradual quit attempts and quit success, adjusting for sociodemographic, smoking and quit attempt characteristics. FINDINGS: Abrupt, versus gradual, attempts were associated with improved quit success in an unadjusted model (OR=2.02, 95% CI=1.86-2.19). This association remained after adjusting for a broad range of relevant confounders (OR=1.75, 95% CI=1.59-1.93). CONCLUSIONS: Among a representative sample of adults who had smoked and made a quit attempt in the past year, there was evidence of an association between abrupt attempts and quit success before and after adjusting for relevant confounders. This suggests that the differences in quit success seen between abrupt and gradual quit attempt types are not completely driven by self-selection in observational data. IMPLICATIONS: We investigated explanations for conflicting findings on the efficacy of gradual versus abrupt approaches to quitting smoking between trial and observational data. Despite adjusting observational data for sociodemographic, smoking and quit attempt characteristics, an association between abrupt quitting and quit success remained. Therefore, differences in quit success were not completely driven by self-selection of a gradual approach by people who found it especially difficult to quit or differences in the use of quitting aids. However, characteristics adjusted for were limited by the data available, and future research should continue to investigate the difference in findings across study types to inform cessation support

Mechanisms of airfoil noise near stall conditions

The focus of this paper is on investigating the noise produced by an airfoil at high angles of attack over a range of Reynolds number Re≈2×10⁵–4×10⁵. The objective is not modeling this source of noise but rather understanding the mechanisms of generation for surface pressure fluctuations, due to a separated boundary layer, that are then scattered by the trailing edge. To this aim, we use simultaneous noise and surface pressure measurement in addition to velocimetric measurements by means of hot wire anemometry and time-resolved particle image velocimetry. Three possible mechanisms for the so-called “separation-stall noise” have been identified in addition to a clear link between far-field noise, surface pressure, and velocity fields in the noise generation

Cross-correlating Sunyaev-Zel'dovich and weak lensing maps

We present novel statistical tools to cross-correlate frequency cleaned thermal Sunyaev–Zel'dovich (tSZ) maps and tomographic weak lensing (wl) convergence maps. Moving beyond the lowest order cross-correlation, we introduce a hierarchy of mixed higher order statistics, the cumulants and cumulant correlators, to analyse non-Gaussianity in real space, as well as corresponding polyspectra in the harmonic domain. Using these moments, we derive analytical expressions for the joint two-point probability distribution function for smoothed tSZ (y) and convergence (κ) maps. The presence of tomographic information allows us to study the evolution of higher order mixed tSZ–wl statistics with redshift. We express the joint PDFs pκy(κ, y) in terms of individual one-point PDFs [pκ(κ), py(y)] and the relevant bias functions [bκ(κ), by(y)]. Analytical results for two different regimes are presented that correspond to the small and large angular smoothing scales. Results are also obtained for corresponding hotspots in the tSZ and convergence maps. In addition to results based on hierarchical techniques and perturbative methods, we present results of calculations based on the lognormal approximation. The analytical expressions derived here are generic and applicable to cross-correlation studies of arbitrary tracers of large-scale structure including, e.g., that of tSZ and soft X-ray background. We provide detailed comparison of our analytical results against state of the art Millennium Gas Simulations with and without non-gravitational effects such as pre-heating and cooling. Comparison of these results with gravity only simulations, shows reasonable agreement and can be used to isolate effect of non-gravitational physics from observational data