Momentum Characteristics Research Articles

An analysis of the influence of background subtraction and quenching on jet observables in heavy-ion collisions

Abstract Subtraction of the large background in reconstruction is a key ingredient in jet studies in high-energy heavy-ion collisions at RHIC and the LHC. Here we address the question to which extent the most commonly used subtraction techniques are able to eliminate the effects of the background on the most commonly discussed observables at present: single inclusive jet distributions, dijet asymmetry and azimuthal distributions. We consider two different background subtraction methods, an area-based one implemented through the FastJet package and a pedestal subtraction method, that resemble the ones used by the experimental collaborations at the LHC. We also analyze different ways of defining the optimal parameters in the second method. We use a toy model that easily allows variations of the background characteristics: average background level and fluctuations and azimuthal structure, but cross-checks are also done with a Monte Carlo simulator. Furthermore, we consider the influence of quenching using Q-PYTHIA on the dijet observables with the different background subtraction methods and, additionally, we examine the missing momentum of particles. The average background level and fluctuations affect both single inclusive spectra and dijet asymmetries, although differently for different subtraction setups. A large azimuthal modulation of the background has a visible effect on the azimuthal dijet distributions. Quenching, as implemented in Q-PYTHIA, substantially affects the di-jet asymmetry but little the azimuthal dijet distributions. Besides, the missing momentum characteristics observed in the experiment are qualitatively reproduced by Q-PYTHIA.

Absolute Momentum: A Simple Rule-Based Strategy and Universal Trend-Following Overlay

There is a considerable body of research on relative strength price momentum but much less on absolute momentum, also known as time series momentum. In this paper, we explore the practical side of absolute momentum. We first explore its sole parameter - the formation, or look back, period. We then examine the reward, risk, and correlation characteristics of absolute momentum applied to stocks, bonds, and real assets. We finally apply absolute momentum to a 60/40 stock/bond portfolio and a simple risk parity portfolio. We show that absolute momentum can effectively identify regime change and add significant value as an easy-to-implement, rule-based approach with many potential uses as both a stand-alone program and trend-following overlay.

一流110 m ハードル走選手のハードリング動作に関するバイオメカニクス的分析：角運動量保存則からの検討

The purpose of this study was to investigate the characteristics of the angular momentum of the limbs during the airborne phase of sprint hurdling. Twenty-nine male hurdlers participated in this study. Their hurdling motions at the seventh hurdle were videotaped using two high-speed cameras. During the first half of the airborne phase, the faster hurdlers required a large angular momentum of the lead leg, which they compensated for by a large counter direction of angular momentum in the trail leg. During the second half of the airborne phase, faster hurdlers swung the lead leg for a shorter duration by adjusting the head and trunk. However, if hurdlers overemphasise the downward motion of the lead leg, this can result in excessive backward and left leaning of the trunk upon landing.

Numerical simulation of the formation of a toxic cloud on outpouring ejection of liquefied chlorine to the atmosphere

UDC 536.24,614.83 The results of numerical investigation of the influence of wind velocity and degree of atmospheric stability on the process of toxic cloud formation on outpouring ejection of liquefied chlorine are presented. The computa- tional procedure is realized with the use of the hydrodynamic analysis package FLUENT. The proposed model describes the distribution of two clouds: primary and secondary. The primary aerosol cloud is formed as a result of instantaneous boiling up of a part of the liquid phase, and the secondary one, on evaporation (boiling) of a spill. Introduction. An analysis of the danger of emergencies often requires estimation of the propagation of toxic or explosive substances in the atmosphere. The source of information for predicting the evolution of the cloud is the intensity of entrance of the dangerous substance into the environment as a result of vaporization. The processes of va- porization and scattering of vapor in air are noted for the complex interrelation, which can hardly be taken into ac- count within the framework of simplified analytical and empirical relations. This requires using methods of numerical simulation based on packages of hydrodynamic analysis CFD for the solution of the above-mentioned problems. Within the framework of numerical simulation, the mutual effect of heat- and mass transfer processes that accompany the development of the emergency is taken into account directly by jointly solving differential equations of transfer of mass, momentum, energy, components, and turbulent characteristics. The problems of numerical simulation of the propagation of gaseous substances in the atmosphere were con- sidered in a large number of works, e.g., (1-9), however, in the existing models the description of the vaporization process is schematic only, which can be an obstacle to the reliable estimation of the zones of toxic injury or the di- mensions of a dangerous explosive cloud. With regard to the aforesaid, the problem of developing the mathematical apparatus for simulating the forma- tion of a vapor-air cloud in the case of emergency ejection of a liquefied gas as applied to the description of the source of ejection would seem urgent. In the present work, for determining the zones of toxic damage on outpouring ejection of liquefied chlorine, we suggest a model based on the program complex FLUENT. The model includes description of basic physical phe- nomena that determine the dynamics of formation of a toxic cloud: evaporation of aerosol in a cloud, vaporization in boiling (evaporation) of a spill, scattering of gas with droplet inclusions in the atmosphere, and condensation of steam in the cloud. Mathematical Model of Vaporization. On breakake of a vessel with a superheated liquid, instantaneous boil- ing up of a certain portion of the liquid phase takes place as a result of the sharp decrease in pressure and violation of the thermodynamic balance through the liberation of internal energy. This is followed by establishment of a new equilibrium state, with the temperature of the remaining portion of the liquid phase decreasing to the boiling point at atmospheric pressure. The instantaneous evaporation of liquid leads to the formation of the primary vapor cloud. To es- timate the fraction of substance x v that "instantaneously" converts into vapor, the following relation can be used (10):

Philip John Stephens. 9 October 1940 — 31 July 2012

Philip J. Stephens was a theoretical chemist who brought to fruition two new forms of optical spectroscopy, using circularly polarized light, for the determination of electronic structure and molecular stereochemistry. The first was magnetic circular dichroism (MCD), the wavelength dependence of the differential absorption of left and right circularly polarized light induced by a magnetic field applied parallel to the light beam. Stephens established a methodology for extracting from MCD spectra the angular momentum characteristics of ground and excited electronic states and demonstrated applications to the assignment of the optical spectra of coordination complexes of transition metals and to metalloproteins. In the second half of his career Stephens led the field of vibrational circular dichroism (VCD), the measurement of the natural circular dichroism (CD) arising from the vibrational transitions of chiral molecules. He developed instrumental techniques to measure this weak dichroism over a wide frequency range with high sensitivity. Subsequently he developed a quantum-mechanical method that yielded reliable calculations of VCD spectra by using density functional theory. Thus absolute configurations of all the chiral centres in an organic molecule are readily established. Given the increasing importance of enantiomerically pure chiral drugs, VCD has found widespread application in the pharmaceutical industry. Philip had not only a deep understanding of chemical theory but also a thorough grasp of experiments. His lectures on theoretical topics were models of clarity. He was also an accomplished pianist in demand, when a student at Oxford University, as an accompanist and for chamber concerts.

Laminar forced convection heat transfer from a heated square cylinder in a Bingham plastic fluid

In this work, the momentum and heat transfer characteristics of a heated cylinder of square cross-section immersed in a streaming Bingham plastic medium have been studied. The governing differential equations (continuity, momentum and thermal energy) have been solved numerically over wide ranges of conditions as: plastic Reynolds number, 0.1⩽Re⩽40, Prandtl number, 1⩽Pr⩽100 and the Bingham number, 0⩽Bn⩽100. Over this range of conditions, the flow is expected to be symmetric and steady. The detailed flow and temperature fields in the vicinity of the cylinder surface are examined in terms of streamline and isotherm profiles respectively. In particular, owing to the presence of the yield stress, the so-called yielded (fluid-like) and unyielded (solid-like) regions are delineated in the flow domain as functions of the Reynolds and Bingham numbers. This objective is accomplished by a detailed examination of the velocity profiles and shear rate profiles along the center planes. Further insights are developed in terms of the distribution of the pressure and local Nusselt number along the cylinder surface together with their average values in terms of drag coefficients and mean Nusselt number. The present numerical results on drag and Nusselt number (in the form of j-factor) have been correlated to the modified Bingham and Reynolds numbers via simple expressions thereby enabling their interpolation for the intermediate values of these dimensionless parameters.

New explicit approximate solution of MHD viscoelastic boundary layer flow over stretching sheet

In this paper, the study the momentum and heat transfer characteristics in an incompressible electrically conducting non‐Newtonian boundary layer flow of a viscoelastic fluid over a stretching sheet. The partial differential equations governing the flow and heat transfer characteristics are converted into highly nonlinear coupled ordinary differential equations by similarity transformations.The resultant coupled highly nonlinear ordinary differential equations are solved by means of, homotopy analysis method (HAM) for constructing an approximate solution of heat transfer in magnetohydrodynamic (MHD) viscoelastic boundary layer flow over a stretching sheet with non‐uniform heat source.The proposed method is a strong and easy to use analytic tool for nonlinear problems and does not need small parameters in the equations. The HAM solutions contain an auxiry parameter, which provides a convenient way of controlling the convergence region of series solutions. The results obtained here reveal that the proposed method is very effective and simple for solving nonlinear evolution equations. The method is straightforward and concise, and it can also be applied to other nonlinear evolution equations in physics. Copyright © 2012 John Wiley & Sons, Ltd.

Analyst Recommendations and Stock Price Momentum

This paper examines the role of sell-side security analysts in the stock price momentum phenomenon. We employ an indirect method that mitigates the “piggy-backing” effect to test the role of analysts. Our findings indicate that analyst recommendations are positively influenced by the momentum characteristics of stocks, that there is no momentum for neglected stocks, and, most importantly, that analysts cause momentum. The findings hold up to various robustness checks.

Momentum and heat transfer characteristics of a long parallelepiped submerged in power-law fluids in the laminar vortex shedding regime

The governing partial differential equations describing the flow and forced convection heat transfer characteristics of power-law fluids past a long parallelepiped at α=45° incidence have been solved numerically in the two-dimensional laminar flow regime. In particular, the major thrust of this work is to elucidate the influence of Reynolds number (Re), Prandtl number (Pr) and power-law index (n) on the detailed and macroscopic momentum and heat transfer characteristics in the laminar vortex shedding regime. The detailed features of the flow and heat transfer phenomena are visualized and analyzed in terms of the instantaneous streamlines, iso-vorticity and isotherm contours whereas the surface pressure and local Nusselt number distributions over the surface of the parallelepiped provide the next level of description of these phenomena. The gross features of the flow are captured in terms of the time-averaged drag coefficient, rms value of the lift coefficient, Strouhal number and Nusselt number. The trends seen here are qualitatively similar to that reported in the literature for a circular cylinder and a bar of square cross-section (with zero angle of incidence). Broadly, shear-thinning viscosity promotes heat transfer due to the lower effective viscosity of the fluid in the close proximity of the parallelepiped bar. As expected, shear-thickening behaviour shows the opposite effect. The ranges of the pertinent dimensionless groups spanned in this study are as follows: 0.3⩽n⩽1.8; 45⩽Re⩽120 and 0.7⩽Pr⩽80. Over this range of Reynolds number, the flow was found to be truly periodic. Finally, the numerical heat transfer results are correlated using a simple analytical form which facilitates the interpolation of the present results for the intermediate values of the parameters.

Experiments on evolution characteristics of momentum wakes generated by the towed sphere with a horizontal jet

The model of the towed sphere with a L-shape nozzle jet was used to generate both drag and jet momentum wakes due to the body and cooling discharge water of the underwater vehicle, the results of experiments were presented for the evolution characteristics of such combined momentum wakes in a stratified fluid. It is shown that for J D/ J C D, the evolution characteristics for the combined momentum wakes are mainly attributed to the drag momentum wake generated by the towed sphere, and the far wake becomes quasi two-dimensional (2D) in the form of a Karman-like dipolar vortex street, where J D is the drag momentum flux due to the towed sphere, J is the jet momentum flux due to the L-shape nozzle jet and C D is the drag coefficient of the sphere. For J D/ J C D, the evolution characteristics for the combined momentum wakes are strongly dependent of the ( Rej , Frj ) combinations, and the far wake can become quasi 2D in the form of an anti-Karman-like dipolar vortex street being mainly attributed to the jet momentum wake under some ( Rej , Frj ) combinations, but there may be no occurrence of large-scale coherent structures, where Rej and Frj are Reynolds and Froude numbers duo to the L-shape nozzle jet respectively. The conditions under different Reynolds and Froude numbers ( Rej , Frj ) combinations where the anti-Karman-like dipolar vortex streets can be formed by such combined momentum wakes were determined by use of data based on the present series experiments, and the dependence of the dimensionless formation time and inverse dimensionless average wavelength of the quasi 2D dipolar vortex streets on Frj for different values of Rej was obtained, results indicate that these parameters are independent of Rej and approximately follow some power exponent laws on Frj .

用归一化的光子态矢函数描述孪生双光子思想实验

根据Born对归一化波函数的概率解释，从量子力学的观点重新审视孪生双光子思想实验，着眼的对象不再是这对孪生光子本身，而是一群具有共同属性的光子集合。所有这些光子具有完全相同的能量和角动量特征，但是在动量的相反方向却具有相等的概率；或者说这是一群在相反动量方向具有相等的数量、而所有其它量子特征完全相同的光子集合。仿效先前对光学双孔效应进行量子力学分析的步骤，具体构造出描述孪生双光子思想实验总的归一化光子态矢函数，所描述的并不是两个光子之间的纠缠，而是单个光子的概率，从而得到光子的空间分布函数。当光子的总数达到形成完整图像的统计学要求时，宏观上将显示出明暗间隔的条纹。在追溯纠缠态历史渊源的基础上，返璞归真孪生双光子思想实验的量子力学观点，对所谓的EPR佯谬引发出来的双光子纠缠态作出了新的解释，提出了量子信息的新认识。 Based on Born’s statistical interpretation for the normalized wave function, the twin two-photon thought experiment is reexamined from point of view of quantum mechanics. The emphasis is no longer the pair of twin photons itself, but rather a group of photons with common attributes. All the photons have the characteristics of identical energy and angular momentum, but possess same probability in the opposite direction of momentum, that is to say, this is a group of photon collections, which have the same number in the opposite direction of momentum, while all other quantum characteristics are identical. Following the example of the previous procedure dealing with optical two-hole effect by use of quantum mechanics, the total normalized photonic state-vector function that described the twin two-photon thought experiment has been specifically constructed, which does not describe the entangled behavior of the two photons, but the probability of a single photon, and thus deduces the probability distribution of a photon in the space. When the total number of photons satisfies the statistical requirements to form a complete picture, some fringes of light and dark interval will be displayed. On the basis of retrospective historical origins of entanglement, the point of view of quantum mechanics about the twin two-photon thought experiment was reverted. The so-called EPR paradox, and the entangled two-photon state have been re-interpreted, and a new understanding of quantum information has been put forward.

The characteristics of turbulent momentum and heat similarity function and bulk transfer coefficient over grassland surface

The turbulent momentum and sensible heat transfer over land surface have a notable influence on the change of global climate and atmospheric circulation, and Monin-Obukhov similarity function is a most important method to calculate the turbulent momentum and sensible heat flux near the surface, and ascertaining the right bulk transfer coefficient is a most effective way of improving the atmospheric model simulation capabilities. The characteristic of Monin-Obukhov similarity function is analyzed and the empirical formula is fitted, and the changes of bulk transfer coefficients of momentum and sensible heat over grassland with mean wind speed at 10 m high are discussed by using the data of the flux observations over Xilin Gol grassland in Spring 2008. Comparison with the observation values by eddy correlation method shows that the revised Monin-Obukhov similarity function underestimates the momentum flux by 10.8% and over estimates the sensible heat flux by 6.5%, but the typical Businger-Dyer similarity function underestimates the momentum flux by 37.0% and over estimates the sensible heat flux by 16.1%. Under unstable stratification, the bulk transfer coefficients of momentum (CD) and sensible heat (CH) vary with mean wind speed at 10 m high (U) according to the power law, which take the forms CD=0.009U-0.322 and CH=0.184U-1.978 respectively. Under stable stratification, the bulk transfer coefficients are found to increase in the manner of the logarithm law over grassland surface and tend to neutral or nearly neutral values with wind speed increasing. The revised Monin-Obukhov similarity function can significantly improve the accuracy of turbulent momentum and sensible heat flux computed by average gradient data, and the relations between bulk transfer coefficients and wind speed at 10 m high provide the useful parameterization schemes for accurately expressing the transportation characteristics of near surface turbulence.

Heat Transfer in MHD Dusty Boundary Layer Flow over an Inclined Stretching Sheet with Non-Uniform Heat Source/Sink

This paper presents the study of momentum and heat transfer characteristics in a hydromagnetic flow of dusty fluid over an inclined stretching sheet with non-uniform heat source/sink, where the flow is generated due to a linear stretching of the sheet. Using a similarity transformation, the governing equations of the problem are reduced to a coupled third-order nonlinear ordinary differential equations and are solved numerically by Runge-Kutta-Fehlberg fourth-fifth-order method using symbolic software Maple. Our numerical solutions are shown to agree with the available results in the literature and then employ the numerical results to bring out the effects of the fluid-particle interaction parameter, local Grashof number, angle of inclination, heat source/sink parameter, Chandrasekhar number, and the Prandtl number on the flow and heat transfer characteristics. The results have possible technological applications in liquid-based systems involving stretchable materials.

Study on MHD Viscous Flow over a Stretching Sheet Using DTM-Pade’ Technique

In this paper, we present the study of momentum characteristics in a MHD viscous flow over a stretching sheet. First the partial differential equations of motion have been transformed to an ordinary differential equation. The analytical method called Differential Transformation Method (DTM) powered by the Pade’ approximation is applied to solve the nonlinear equation derived from MHD viscous flow over a stretching sheet, the effect of parameters variation has been investigated for two numerical cases and finally the analytical results have been compared with numerical one in a numerical case. The obtained results approve its efficiencies and capabilities beside numerical solutions achieved from Runge Kutta method.

Analysis of momentum characteristics of the miniengine of a microelectromechanical system operating on a solid mixed propellant

A self-consistent problem relating combustion parameters of a solid propellant in a miniengine of the microelectromechanical system to the engine’s structural characteristics is solved. The dependence of the pressure in the combustion chamber of this engine on the combustion rate of the propellant in it and the engine’s outlet diameter is determined. Recommendations are formulated for the choice of the composition of a mixed solid propellant based on glycidyl azide polymer doped with nitramines and for the geometry of the combustion chamber of the above miniengine, which provide the required values of its total momentum and the propulsive force.

Are Capital Markets Inefficient on a Macro Level?

Samuelson’s dictum (1998) states that capital markets are “macro inefficient”. If this conjecture is true, returns should be partially predictable across different asset classes. We test for the predictability of returns on an asset class level by exploiting the advantageous features of the parametric portfolio policy approach proposed by Brandt, Santa-Clara and Valkanov (2009). We apply the parametric portfolio policy framework in a multi asset investment universe and perform a number of robustness checks such as varying the degree of risk aversion, conducting out-of-sample analyses and including transaction costs. Our results demonstrate that the parametric portfolio policy approach generates positive excess returns after costs in an out-of-sample setting by parameterizing the asset weights as a function of the assets’ value and momentum characteristics. The optimal strategy is a combination of value and momentum investing and depends on the risk aversion of investors. Risk-averse investors benefit from focusing on value investing, while our results advise risk-seeking investors to favor momentum investing. Overall, our analysis indicates that capital markets are inefficient on a macro level.

Ridge correlation structure in high-multiplicity pp collisions with CMS

Results on two-particle angular correlations are presented in proton–proton collisions at center of mass energies of 7 TeV, over a broad range of pseudorapidity and azimuthal angle. In very high-multiplicity events at 7 TeV, a pronounced structure emerges in the two-dimensional correlation function for particle pairs with intermediate pT of 1–3 GeV/c, in the kinematic region 2.0 < |Δη| < 4.8 and small Δϕ. This structure, which has not been observed in pp collisions before, is similar to what is known as the ‘ridge’ in heavy-ion collisions. It is not predicted by commonly used proton–proton Monte Carlo models and is not seen in lower multiplicity pp collisions. Updated studies of this new effect as a function of particle transverse momentum, rapidity and event characteristics are shown.

Forced convection in power-law fluids from an asymmetrically confined heated circular cylinder

In this work, the influence of asymmetric confinement on momentum and heat transfer characteristics from a heated circular cylinder submerged in power-law liquids has been investigated numerically. The detailed flow and temperature fields are visualized in terms of the streamline and isotherm contours. Due to the asymmetry of the flow field, in addition to the drag force, there is also a net lift force acting on the cylinder. Furthermore, shear-thinning characteristics tend to modulate the influence of blockage and asymmetry on the rate of heat transfer. All else being equal, shear-thinning behaviour facilitates heat transfer. On the other hand, depending upon the degree of asymmetry, the heat transfer may increase or decrease thereby suggesting a non-monotonic relationship between Nusselt number and asymmetric placement of the cylinder. The results reported herein embrace the following ranges of conditions: Reynolds number, 0.1 ⩽ Re ⩽ 100 ; power-law index, 0.3 ⩽ n ⩽ 1 ; Prandtl number, 1 ⩽ Pr ⩽ 100 ; blockage ratio, β = 0.2, 0.3 and 0.4, and gap ratio, 0.25 ⩽ γ ⩽ 1 . The range of Reynolds number is such that the flow is likely to be in the steady and time-periodic flow regime, at least for an unconfined cylinder.

Effects of Non-Darcian and Inlet Conditions on the Forced Convection Along a Vertical Plate With Film Evaporation

The present study analyzes theoretically the non-Darcian effects and inlet conditions of forced convection flow with liquid film evaporation in a porous medium. The physical scheme includes a liquid–air streams combined system; the liquid film falls down along the plate and is exposed to a cocurrent forced moist air stream. The axial momentum, energy, and concentration equations for the air and water flows are developed based on the steady two-dimensional (2-D) laminar boundary layer model. The non-Darcian convective, boundary, and inertia effects are considered to describe the momentum characteristics of a porous medium. The paper clearly describes the temperature and mass concentration variations at the liquid–air interface and provides the heat and mass transfer distributions along the heated plate. Then, the paper further evaluates the non-Darcian effects and inlet conditions on the heat transfer and evaporating rate of liquid film evaporation. The numerical results show that latent heat transfer plays the dominant heat transfer role. Carrying out a parametric analysis indicates that higher air Reynolds number, higher wetted wall temperature, and lower moist air relative humidity will produce a better evaporating rate and heat transfer rate. In addition, a non-Darcy model should be adopted in the present study. The maximum error for predictions of heat and mass transfer performance will be 21% when the Darcy model is used.

Role of Analysts: Following Momentum or Creating Momentum?

This paper examines whether sell-side security analysts follow momentum or create momentum by themselves for recommending stocks. We employ an indirect method of testing the role of analysts by assigning projected recommendation scores for the neglected stocks to mitigate the so-called piggy-backing effect. Our results are not fully consistent with the notion that analysts follow past momentum to predict future stock recommendations. Using a data set of neglected stocks and creating projected recommendations of these stocks, we find evidence that analysts drive up the stocks’ momentum characteristics before recommending them. This finding suggests the fact that analysts not only follow momentum, rather they create momentum, at least to a great extent.