STABILITY NUMBER IN SUBCLASSES OF P5-FREE GRAPHS

Two new hereditary classes of P5-free graphs where the stability number can be found in polynomial time are proposed. They generalize several known results.     

Gargano,Lewinter and Malerba问题的解

§1　IntroductionLet G be a graph with vertex-set V(G) ={ v1 ,v2 ,...,vn} .A labeling of G is a bijectionL:V(G)→{ 1,2 ,...,n} ,where L (vi) is the label of a vertex vi.A labeled graph is anordered pair (G,L) consisting of a graph G and its labeling L.Definition1.An increasing nonconsecutive path in a labeled graph(G,L) is a path(u1 ,u2 ,...,uk) in G such thatL(ui) + 1相似文献   

翼型模型振动的实验研究与气动特性分析

通过在NF-3低速风洞专门研制的翼型模型及相应的俯仰和沉浮振动机构,选用NACA0012翼型进行大迎角下不同频率的振动实验,研究了模型振动平均状态下对其气动力特性的影响情况,并在N-S方程基础上对振动流场进行了初步分析。实验与计算研究的结果表明:在临近定常失速迎角的大迎角条件下,翼型的振动可以引起旋涡分离,导致翼型升力减小和失速迎角的提前;就所讨论的两种振动模式而言,俯仰振动的影响大于沉浮振动。所以,为了提高飞机模型,尤其是大展弦比飞机模型的风洞实验精准度,在模型设计和加工时要特别注意加强机翼弦向的扭转刚度。     

Effect of fiber orientation on fiber wetting processes

The current work incorporates a microscopic study of the effect of fiber orientation on the fiber wetting process and flow of liquid droplets along filter fibers when subjected to airflow and gravity forces. Glass filter fibers in various combinations were oriented at various angles within a plane defined by the airflow direction and were supplied with distilled water in aerosol form. The behavior and flow of the liquid collected by the fibers were observed and measured using a specially developed microscope cell, detailed in the paper. The experimental results were compared to a theoretical model developed to describe the behavior. The theory and experimental results showed good agreement. The developed theory allows an optimum angle to be determined for the internal filter fiber structure in the design of wet filters. A sensitivity analysis of the model was conducted to determine the most important parameters. This will aid design of wet filtration systems such that maximal self-cleaning can be accomplished with minimal water use.     

Particle capture processes and evaporation on a microscopic scale in wet filters

This paper details results of an experimental study of the capture of solid and liquid aerosols on fibrous filters wetted with water. A microscopic cell containing a single fibre (made from a variety of materials) was observed via a microscope, with a high speed CCD camera used to dynamically image the interactions between liquid droplets, zeolite and PSL particles and fibres. Variable quantities of liquid irrigation were used, and the possibility for subsequent fibre regeneration after clogging or drying was also studied. It was found that drainage of the wetting liquid (water) from the fibres occurred, even at very low irrigation rates when the droplet consisted almost completely of captured particles. It was also found that the fibre was rapidly loaded with captured particles when the irrigation was not supplied. However, almost complete regeneration (removal of the collected cake) by the liquid droplets occurred shortly after recommencement of the water supply. The study also examined the capture of oily liquid aerosols on fibres wetted with water. A predominance of the barrel shaped droplet on the fibre was observed, with oil droplets displacing water droplets (if the oil and fibre combination created a barrel shaped droplet), creating various compound droplets of oil and water not previously reported in literature. This preferential droplet shape implies that whatever the initial substance wetting a filter, a substance with a greater preferential adherence to the fibre will displace the former one.     

SERS from light localization positions

The proposed model allows to analyze reasons for surface enhanced Raman scattering (SERS) by molecules adsorbed onto surface of metal particles. It considers multiple inelastic scattering of a photon, which moves along a closed loop inside a system of closely packed small metallic particles. During this motion, the photon undergoes multiple exchanges with the medium by the same amount of energy corresponding to excitation in the system of charge density fluctuations, which are permanently present in the system. The energy of such fluctuations can be an arbitrary value, with magnitude of less than the energy of incident photon. Probability of the excitation is very high and comparable with the probability of resonance excitation of the dipole surface plasmon in a separate particle. Strong local fields related to these fluctuations exist over entire frequency range from infrared up to ultraviolet. The reason for the photon motion along the closed loop is related to constructive interference of amplitudes corresponding to two alternative ways of the loop passing; clockwise and counter clockwise. Probability of such motion is calculated. Peculiarities of behavior of charge density fluctuations allow explaining some specific features of flicker noise. Copyright © 2013 John Wiley & Sons, Ltd.     

Observation and modelling of barrel droplets on vertical fibres subjected to gravitational and drag forces

Extensive experimental investigation of the wetting processes of fibre/liquid systems during air filtration (when drag and gravitational forces are acting) has shown many important features, including droplet extension, oscillatory motion, and detachment or flow of drops from fibres as airflow velocity increases. A detailed experimental study of the aforementioned processes was conducted using glass filter fibres and H(2)O aerosol, which coalesce on the fibre to form barrel droplets with small contact angles. The droplets were predominantly observed in the Reynolds transition (or unsteady laminar) flow region. The droplet oscillation appears to be induced by the onset of vortexes in the flow field around the droplet as the increasing droplet size increases the Reynolds number. Flow in this region is usually modelled using the classical two-dimensional Karman vortex street, and there exist no 3D equivalents. Therefore to model such oscillation it was necessary to create a new conceptual model to account for the forces both inducing and inhibiting such oscillation. The agreement between the model and experimental results is acceptable for both the radial and transverse oscillations.     

Identification of Metal Contaminants on FCC Catalyst

FCC Catalyst deactivation is a major source of expense in the refining industry. Of concern is the deposition of contaminant metals onto the catalyst particles, leading to premature deactivation. Samples of used catalyst were collected from a working refinery using the standard sampling ports. These samples were subjected to surface examination by Scanning Electron Microscope, and to X‐ray Micro Analysis to determine elementary composition of key metals. Particle mapping was conducted to obtain cross sectional composition of both used and fresh catalyst. It was found that metals preferentially deposit onto the outside of the catalyst particles, presumably causing premature de‐activation to occur. Although the particles are found in a high attrition environment, the metal deposits formed a rough outer surface on the particle. Mild attrition of these particles was found to remove this outside layer of material and help to restore the original chemical make up of the particles surface. This work has shown how refineries can investigate metal deposition onto particles surfaces which will help them better manage FCCU catalyst usage.     

Stabilization of spinel structure during combustion synthesis of iron nanooxides

Iron oxide nanoparticles were synthesized by direct metal combustion in the oxygen-containing environment. A pure Fe powder as well as its mixtures with powders of some other metals (Mg, Co, Zn) were burnt in oxygen-containing environment. The synthesized oxide nanoparticles were examined with transmission electron microscopy, X-ray diffractometry, atomic adsorption spectroscopy, and magnetization measurements. The results of the study of the nanoparticle properties showed that the doping of the other metal to the Fe fuel led to the spinel phase stabilization. The synthesized non-agglomerated ferrimagnetic nanoparticles possess the extremely high magnetization, which makes them attractive for ferrofluid applications.This revised version was published online in August 2005 with corrections to one of the authors’ names.     

Observation and modelling of clamshell droplets on vertical fibres subjected to gravitational and drag forces

Extensive experimental investigation of the wetting processes of fibre-liquid systems during air filtration (when drag and gravitational forces are acting) has shown many important features, including droplet extension, oscillatory motion, and detachment of drops from fibres as airflow velocity increases, and also movement or flow of droplets along fibres. A detailed experimental study of the processes was conducted using stainless steel filter fibres and H2O aerosol, which coalesce on the fibre to form clamshell droplets. The droplets were predominantly observed in the Reynolds transition flow region, since this is the region where most of the above features occur. The droplet oscillation is believed to be induced by the onset of the transition from laminar to turbulent flow as the increasing droplet size increases Reynolds number for the flow around the droplet. Two-dimensional flow in this region is usually modelled using the classical Karman vortex street, however there exist no 3D equivalents. Therefore to model such oscillation it was necessary to create a new conceptual model to account for the forces both inducing and preventing such oscillation. The agreement between the model and experimental results is very good for both the radial and transverse oscillations.