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Diameter D (diameter + d)
Selected AbstractsVascular response to laser photothermolysis as a function of pulse duration, vessel type, and diameter: Implications for port wine stain laser therapyLASERS IN SURGERY AND MEDICINE, Issue 2 2002Sol Kimel PhD Abstract Background and Objective Treatment of port wine stains (PWS) by photothermolysis can be improved by optimizing laser parameters on an individual patient basis. We have studied the critical role of pulse duration (tp) on the treatment efficacy. Study Design/Materials and Methods The V-beam laser (Candela) allowed changing tp over user-specified discrete values between 1.5 and 40 milliseconds by delivering a series of 100 microsecond spikes. For the 1.5 and 3 millisecond pulses, three spikes were observed at intervals tp/2 and for tp,,,6 milliseconds, four spikes separated by tp/3. The ScleroPlus laser (Candela) has a smooth output over its fixed 1.5 milliseconds duration. Blood vessels in the chick chorioallantoic membrane (CAM) were irradiated at fixed wavelength (595 nm), spot size (7 mm), radiant exposure (15 Jcm,2), and at variable tp. The CAM contains an extensive microvascular network ranging from capillaries with diameter D,<,30 ,m to blood vessels of D,,,120 ,m. The CAM assay allows real-time video documentation, and observation of blood flow in pre-capillary arterioles (A) and post-capillary venules (V). Vessel injury was graded from recorded videotapes. Mathematical modeling was developed to interpret results of vessel injury when varying tp and D. A modified thermal relaxation time was introduced to calculate vessel wall temperature following laser exposure. Results Arterioles. For increasing tp, overall damage was found to decrease. For fixed tp, damage decreased with vessel size. Venules. For all D, damage was smaller than for corresponding arterioles. There was no dependence of damage on tp. For given tp, no variation of damage with D was observed. Photothermolysis due to spiked (V-beam) vs. smooth (Scleroplus) delivery of laser energy at fixed tp (1.5 milliseconds), showed similar vessel injuries for al values of D (P>0.05). Conclusions The difference between initial arteriole and venule damage could be explained by the threefold higher absorption coefficient at 595 nm in (oxygen-poor!) arterioles. In human patients, PWS consist of ectatic venules (characterized by higher absorption), so that these considerations favor the use of 595-nm irradiation for laser photothermolysis. For optimal treatment of PWS it is proposed that tp be between 0.1 and 1.5 milliseconds. This is based on a modified relaxation time ,d,, defined as the time required for heat conduction into the full thickness of the vessel wall, which is assumed to have a thickness ,D ,,0.1D. The corresponding ,d, will be a factor of about six smaller than given in the literature. For vessels with D between 30 and 300 ,m, ,d, ranges from 0.1 to 1.5 milliseconds. Lasers Surg. Med. 30:160,169, 2002. © 2002 Wiley-Liss, Inc. [source] Conditional diameter saturated graphsNETWORKS: AN INTERNATIONAL JOURNAL, Issue 4 2008C. Balbuena Abstract The conditional diameter D,,(G) of a connected graph G is a measure of the maximum distance between two subsets of vertices satisfying a given property ,, of interest. For any given integer k , 1, a connected graph G is said to be conditional diameter k -saturated if D,,(G) , k and there does not exist any other connected graph G, with order ,V(G,), = ,V(G),, size ,E(G,), > ,E(G),, and conditional diameter D,,(G,) , k. In this article, we obtain such conditional diameter saturated graphs for a number of properties ,,, generalizing the results obtained in (Ore, J Combin Theory 5(1968), 75,81) for the (standard) diameter D(G). © 2008 Wiley Periodicals, Inc. NETWORKS, 2008 [source] Isomorphisms of the De Bruijn digraph and free-space optical networksNETWORKS: AN INTERNATIONAL JOURNAL, Issue 3 2002D. Coudert Abstract The de Bruijn digraph B(d, D) has degree d, diameter D, dD vertices, and dD+1 arcs. It is usually defined by words of size D on an alphabet of cardinality d, through a cyclic left-shift permutation on the words, after which the rightmost symbol is changed. In this paper, we show that any digraph defined on words of a given size, through an arbitrary permutation on the alphabet and an arbitrary permutation on the word indices, is isomorphic to the de Bruijn digraph, provided that this latter permutation is cyclic. We use this result to improve from O(dD+1) to the number of lenses required for the implementation of B(d, D) by the Optical Transpose Interconnection System proposed by Marsden et al. [Opt Lett 18 (1993), 1083,1085]. © 2002 Wiley Periodicals, Inc. [source] Controlling the Diameter of Polyaniline Nanofibers by Adjusting the Oxidant Redox Potential,ADVANCED MATERIALS, Issue 3 2007H. Ding A self-assembly process with no external template and no added acidic dopant is reported as a method providing quantitative control over the diameter d of the polyaniline (PANI) nanofibers produced. An experimental formula relating d to the standard redox potential of the oxidants is established. The PANI nanofibers in the figure have d,,,15,nm. [source] Rheological properties of acrylic bone cement during curing and the role of the size of the powder particlesJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2002Gladius Lewis Abstract A dynamic compressive rheometric technique was used to determine the true or complex viscosity (,*) of three poly (methyl methacrylate), PMMA-based bone cement formulations (one commercially available and two experimental), as a function of the time that elapsed from commencement of hand mixing of the cement constituents (t). For each cement, two rheological parameters [namely, the time of onset of cure (tons) and the critical cure rate (CCR), which is herein defined as the complex viscosity rate computed at tons] were determined from the ,*,t data. For each cement, particle analysis was used to obtain the powder particle size distribution, from which the following parameters were obtained: (a) the overall mean particle diameter Dm, and (b) the relative amounts of small-sized PMMA beads (mean diameter d between 0 and 40 ,m) (,) and large-sized PMMA beads (d > 75 ,m) (,). It is seen that the key particle parameter is not Dmper se but , and ,. Thus, the highest values of tons and CCR were obtained from a cement with the highest values of , and ,. An explanation for these trends is given, and two areas for further research work in this field are outlined. © 2002 John Wiley & Sons, Inc. J Biomed Mater Res (Appl Biomater) 63: 191,199, 2002; DOI 10.1002/jbm.10127 [source] Nanoscale uniformity of pore architecture in diatomaceous silica: a combined small and wide angle x-ray scattering studyJOURNAL OF PHYCOLOGY, Issue 1 2000Engel G. Vrieling Combined small and wide angle X-ray scattering (SAXS and WAXS) analysis was applied to purified biogenic silica of cultured diatom frustules and of natural populations sampled on marine tidal flats. The overall WAXS patterns did not reveal crystalline phases (WAXS domain between 0.07 to 0.5 nm) in this biogenic silica, which is in line with previous reports on the amorphous character of the SiO2 matrix of diatom frustules. One exception was the silica of the pennate species Cylindrotheca fusiformis Reimann et Lewin, which revealed wide peaks in the WAXS spectra. These peaks either indicate the presence of a yet unknown crystalline phase with a repetitive distance (d -value ,0.06 nm) or are caused by the ordering of the fibrous silica fragments; numerous girdle bands. The SAXS spectra revealed the size range of pores (diameter d between 3.0 and 65 nm), the presence of distinct pores (slope transitions), and structure factors (oscillation of the spectra). All slopes varied in the range of ,4.0 to ,2.5, with two clear common regions among species: d < 10 nm (slopes ,4, denoted as region I and also called the Porod region), and 10.0 < d < 40.0 nm (slopes ,2.9 to ,3.8, denoted as region II). The existence of these common regions suggests the presence of comparable form (region I) and structure (region II) factors, respectively the shape of the primary building units of the silica and the geometry of the pores. Contrast variation experiments using dibromomethane to fill pores in the SiO2 matrix showed that scattering was caused by pores rather than silica particles. Electron microscopic analysis confirmed the presence of circular, elliptical, and rectangular pores ranging in size from 3 to 65 nm, determining the structure factor. The fine architecture (length/width ratio of pore diameters) and distribution of the pores, however, seemed to be influenced by environmental factors, such as the salinity of and additions of AlCl3 to the growth medium. The results indicate that diatoms deposit silica with pores <50 nm in size and are highly homologous with respect to geometry. Consequently, it is suggested that in diatoms, whether pennate or centric, the formation of silica at a nanoscale level is a uniform process. [source] On labeling the vertices of products of complete graphs with distance constraintsNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 2 2005D.J. Erwin Variations of Hale's channel assignment problem, the L(j, k)-labeling problem and the radio labeling problem require the assignment of integers to the vertices of a graph G subject to various distance constraints. The ,j,k -number of G and the radio number of G are respectively the minimum span among all L(j, k)-labelings, and the minimum span plus 1 of all radio labelings of G (defined in the Introduction). In this paper, we establish the ,j,k -number of ,K for pairwise relatively prime integers t1 < t2 < , < tq, t1 , 2. We also show the existence of an infinite class of graphs G with radio number |V(G)| for any diameter d(G). © 2003 Wiley Periodicals, Inc. Naval Research Logistics, 2005 [source] On the fault-tolerant diameter and wide diameter of ,-connected graphsNETWORKS: AN INTERNATIONAL JOURNAL, Issue 2 2005Jian-Hua Yin Abstract The fault-tolerant diameter, Dk, and wide diameter, dk, are two important parameters for measuring the reliability and efficiency of interconnection networks. It is well known that for any ,-connected graph G and any integer k, 1 , k , ,, we have Dk , dk. However, what we are interested in is how large the difference between dk and Dk can be. For any 2-connected graph G with diameter d, Flandrin and Li proved that d2 , D2 + 1 if d = 2 and d2 , (d , 1)(D2 , 1) if d , 3. In this article, we further prove that d2 , max{D2 + 1, (d , 1)(D2 , d) + 2} for d , ,(D2 , 1)/2, and d2 , max{D2 + 1,,(D2 , 1)2/4, + 2} for d , ,(D2 , 1)/2, + 1, and we also show that this upper bound can be achieved. Moreover, for any ,(, 3)-connected graph G, we prove that d, , D, + 1 if D, , 1 = 2 and d, , max{D, + 2,,(D,)2/4, + 2} if D, , 1 = 2 and D, , 1 , 3. © 2005 Wiley Periodicals, Inc. NETWORKS, Vol. 45(2), 88,94 2005 [source] Self-sustained oscillations in opposed impinging jets in an enclosureTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2000David A. Johnson Abstract The flow of jets in confining enclosures has significant application in many engineering processes. In particular, the impingement of axisymmetric jets in a confined space has been examined using flow visualization, laser Doppler anemometry, and numerical simulations. Several flow regions were found; stable steady, regular oscillatory, and irregular oscillatory. Initially, a steady flow field existed for all arrangements for Red < ,90 (based on the nozzle diameter d, the fluid kinematic viscosity v and the volumetric flow rate Q through the nozzle (Q = ,d2/4Uavg)) but subsequent increments in the fluid velocity caused a regularly oscillating flow field to emerge. The onset of the oscillations and the upper limit of finite oscillations were found to be a function of the Red, and the nozzle diameter to chamber dimension ratio. Steady numerical simulations predicted the steady flow field well and good agreement was obtained in unsteady simulations of the oscillating flow field. The oscillating flow field is considered to be a class of self-sustaining oscillations where instabilities in the jet shear layer are amplified because of feed back from pressure disturbances in the impingement region. L'écoulement de jets dans des espaces confinés a des applications importantes dans de nombreux precédés d'ingénierie. On a examiné en particulier la collision de jets axisymétriques dans un espace confiné au moyen de la visualisation des écoulements, de l'anémométrie par laser Doppler et de simulations numériques. On a trouvé plusieurs régions d'écoulement : stable-stationnaire, régulier-oscillatoire et irrégulier-oscillatoire. Initialement, il existe un champ d'écoulement stationnaire pour toutes les configurations lorsque Red < ,90 (basé sur le diamètre de tuyère d, la viscosité cinématique du fluide (et le débit volumétrique Q dans la tuyère (Q = ,d24Uavg)); mais une augmentation subséquente de la vitesse du fluide déclenche un champ d'écoulement oscillatoire régulier. On a trouvé que l'apparition des oscillations et la limite supérieure des oscillations finies sont fonction de Red et du rapport entre le diamètre de l'orifice et la dimension de la chambre. Des simulations numériques stationnaires prédisent bien le champ d'écoulement stationnaire et un bon accord est obtenu pour des simulations non stationnaires du champ d'écoulement oscillant. Le champ d'écoulement oscillant est considéré être une catégorie d'oscillations qui se maintiennent seules dans laquelle les instabilités dans la couche de cisaillement des jets sont amplifiés par un effet retour des perturbations de pression dans la région de collision. [source] Experimental study of stick-slip behaviourINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 6 2004Florence Adjemian Abstract Simple axi-symmetric uni-axial compression tests have been realized on dry loose samples of glass beads (diameters d: d=0.2 ± 0.05 mm, 0.75 ± 0.1 mm, or 3 mm) and on Hostun sand under small lateral confinement, ,3<60 kPa, using different sample sizes. The experiments with the two smallest spheres (d=0.2 and 0.75 mm) exhibit stick-slips, which are characterized by (i) a rapid release ,q of the deviatoric stress q and by (ii) the strain ,,1 separating two events. The samples which exhibit stick-slip also present a weakening of strength q(,1) as the rate of deformation d,1/dt is increased. No stick-slip is generated during the first part of the q,,1 curve, i.e. when q grows fast with ,1. Four different parameters helped us determine the statistics of ,q and ,,: the lateral pressure ,3,, the rate of deformation d,1/dt, the sample height H, and the diameter D. The statistics do not depend on rate history. They look like exponentials in small samples and/or in (large sample+fast d,1/dt), and they look like Poissonian or Gaussian in (Large sample+small d,1/dt). This change in statistics is attributed to a varying of triggering process starting from a single random event in small samples to multiple random events. We have interpreted this change of statistics as due to some finite size effect so that the representative elementary volume shall contain at least (200)3 grains. Localization of deformation is visible at the end of compression but cannot be detected from stick-slip statistics nor from q vs , curve. Copyright © 2004 John Wiley & Sons, Ltd. [source] | |||||||||||||