Статті в журналах з теми "Narrow rigid tube"

The earlier constitutive model of Fang & Owens (Biorheology, vol. 43, 2006, p. 637) and Owens (J. Non-Newtonian Fluid Mech. vol. 140, 2006, p. 57) is extended in scope to include non-homogeneous flows of healthy human blood. Application is made to steady axisymmetric flow in rigid-walled tubes. The new model features stress-induced cell migration in narrow tubes and accurately predicts the Fåhraeus–Lindqvist effect whereby the apparent viscosity of healthy blood decreases as a function of tube diameter in sufficiently small vessels. That this is due to the development of a slippage layer of cell-depleted fluid near the vessel walls and a decrease in the tube haematocrit is demonstrated from the numerical results. Although clearly influential, the reduction in tube haematocrit observed in small-vessel blood flow (the so-called Fåhraeus effect) does not therefore entirely explain the Fåhraeus–Lindqvist effect.

When blood flows slowly in a narrow tube, red-cell aggregation results in formation of an approximately cylindrical “core” of red cells, which moves as a rigid body. The core is denser than the surrounding fluid, and sedimentation is observed in horizontal tubes. To model this, the Stokes flow of a fluid surrounding a long solid cylinder (the core) contained in a long hollow cylinder (the tube) is considered. The cylinder axes are parallel but not coincident. An exact analytic expression for the resistance coefficient for motion perpendicular to the axes is given. This coefficient increases rapidly with the ratio of core radius to tube radius, and core eccentricity. The predicted rate of sedimentation is comparable to that observed experimentally. The apparent viscosity of a two-phase medium consisting of a core of aggregated particles and surrounding pure fluid is calculated. For a core radius corresponding to experimental conditions, the apparent viscosity increases rapidly with increasing eccentricity of the core.

Secondary bending moment and geometric nonlinearity should be taken into account in pipe tower design. Taking the 110kV double-circuit narrow-base steel pipe tower as an example, the 110 kV double-circuit narrow-base steel pipe tower is compared and analyzed through the tower structure design software and the general finite element software ANSYS. The analysis results show that the narrow-base steel tube tower should adopt a rigid-truss structure model, and the influence of the secondary bending moment of the main material and the geometric nonlinearity should be considered. The secondary bending moment effect accounts for about 10-20% of the strength stress of the steel pipe main material. Through comparative analysis, a number of design points are summarized, which provides a certain practical guiding significance for the design and application of the double-circuit narrow-base steel pipe tower.

An analysis is presented of the mechanics of red blood cells flowing in very narrow tubes. Mammalian red cells are highly flexible, but their deformations satisfy two significant constraints. They must deform at constant volume, because the contents of the cell are incompressible, and also at nearly constant surface area, because the red cell membrane strongly resists dilation. Consequently, there exists a minimal tube diameter below which passage of intact cells is not possible. A cell in a tube with this diameter has its critical shape: a cylinder with hemispherical ends. Here, flow of red cells in tubes with near-minimal diameters is analysed using lubrication theory. When the tube diameter is slightly larger than the minimal value, the cell shape is close to its shape in the critical case. However, the rear end of the cell becomes flattened and then concave with a relatively small further increase in the diameter. The changes in cell shape and the resulting rheological parameters are analysed using matched asymptotic expansions for the high-velocity limit and using numerical solutions. Predictions of rheological parameters are also obtained using the assumption that the cell is effectively rigid with its critical shape, yielding very similar results. A rapid decrease in the apparent viscosity of red cell suspensions with increasing tube diameter is predicted over the range of diameters considered. The red cell velocity is found to exceed the mean bulk velocity by an amount that increases with increasing tube diameter.

The hydrodynamic influence of deformable porous surface layers on the motion of a rigid sphere falling in a narrow cylindrical tube filled with a stationary Newtonian fluid is studied using lubrication theory. The porous layers on both the surface of the tube and the sphere are modelled as binary mixtures of solid and liquid components. The sphere is placed at an arbitrary position in the tube and is free to rotate. Effects of the clearance between the sphere and the tube, the eccentricity of the position of the sphere and the properties of the surface layers on the velocity and rotation of the sphere are studied. It is found that, when the lengthscale on which the velocity varies within the porous layer is much smaller than the clearance, the effects of the porous layer can be represented by an equivalent slip boundary condition, the slip velocity at the boundary being proportional to the local shear rate. The slip velocities have a strong influence on the motion of the sphere when the clearance is small. For a given clearance and slip parameters, both the falling and rotation velocities of the sphere increase with the sphere eccentricity. The shear stresses on the surfaces of both the tube and the sphere are greatly reduced when slip boundary conditions are applied, as is the pressure gradient in the region between the sphere and the tube wall. This work could have some relevance to the creeping motion of blood cells in the microcirculation where the glycocalyx, a polysaccharide-rich layer, covers the external surfaces of both endothelial and red blood cells.

The motion of a rigid ellipsoidal particle freely suspended in a Poiseuille flow of an incompressible Newtonian fluid through a narrow tube is studied numerically in the zero-Reynolds-number limit. It is assumed that the effect of inertia forces on the motion of the particle and the fluid can be neglected and that no forces or torques act on the particle. The Stokes equation is solved by a finite element method for various positions and orientations of the particle to yield the instantaneous velocity of the particle as well as the flow field around it, and the particle trajectories are determined for different initial configurations. A prolate spheroid is found to either tumble or oscillate in rotation, depending on the particle–tube size ratio, the axis ratio of the particle, and the initial conditions. A large oblate spheroid may approach asymptotically a steady, stable configuration, at which it is located close to the tube centreline, with its major axis slightly tilted from the undisturbed flow direction. The motion of non-axisymmetric ellipsoids is also illustrated and discussed with emphasis on the effect of the particle shape and size.

In the development of telemanipulated surgical robots, a class of continuum robots known as concentric tube robots has drawn particular interest for clinical applications in which space is a major limitation. One such application is transnasal surgery, which is used to access surgical sites in the sinuses and at the skull base. Current techniques for performing these procedures require surgeons to maneuver multiple rigid tools through the narrow confines of the nasal passages, leaving them with limited dexterity at the surgical site. In this article, we present a complete robotic system for transnasal surgery featuring concentric tube manipulators. It illustrates a bagging concept for sterility, and intraoperatively interchangeable instruments that work in conjunction with it, which were developed with operating room workflow compatibility in mind. The system also includes a new modular, portable surgeon console, a variable view-angle endoscope to facilitate surgical field visualization, and custom motor control electronics. Furthermore, we demonstrate elastic instability avoidance for the first time on a physical prototype in a geometrically accurate surgical scenario, which facilitates use of higher curvature tubes than could otherwise be used safely in this application. From a surgical application perspective, this article presents the first robotic approach to removing tumors growing behind the eyes in the orbital apex region, which has not been attempted previously with a surgical robot.

The main character distinguishing Minibiotus from Macrobiotus is the presence of peribuccal papulae instead of lamellae. However, most Minibiotus species also share a set of characters of the bucco-pharyngeal apparatus. This set is defined by ten morphological features (the first seven common to all species, the last three to most of them): antero-ventral mouth (1), teeth in oral cavity absent or strongly reduced (2), a rigid and narrow buccal tube (3), buccal tube wall thickened below the point of insertion of stylet supports (4), stylet supports inserted at considerable distance from the posterior end of the buccal tube (5), short ventral lamina (6), short macroplacoid row length (7), a double curvature of the buccal tube (8), first macroplacoid situated very close to the pharyngeal apophysis (9) and three almost rounded macroplacoids (10). We examined the original descriptions and/or the type material of several species belonging to the genus Macrobiotus that seemed to present this set of characters. It was concluded that several species should be transferred from Macrobiotus to Minibiotus. The following new combinations are proposed: Minibiotus subintermedius (Ramazzotti, 1962) comb. n., Minibiotus pustulatus (Ramazzotti, 1959) comb. n., Minibiotus julietae (de Barros, 1942) comb. n., Minibiotus marcusi (de Barros, 1942) comb. n., Minibiotus granatai (Pardi, 1941) comb. n., Minibiotus allani (Murray, 1913) comb. n., Minibiotus crassidens (Murray, 1907) comb. n. and Minibiotus acontistus (de Barros, 1942) comb. n.. As a result of these new combinations, the genera Minibiotus and Macrobiotus appear to be more homogeneous, but their monophyly has not yet been demonstrated. Further data are necessary to better analyze the systematic position of Macrobiotus lazzaroi Maucci, 1986, Macrobiotus spertii Ramazzotti, 1957 and Macrobiotus striatus Mihelčič, 1949.

Dear Editor: Time has proven that endoscopy is generally a safe and effective tool in the diagnosis and treatment of various conditions. It offers superior visualization with markedly decreased morbidity and mortality. In Otolaryngology, otoendoscopy has been gaining acceptance in providing improved otoscopic visualization and video recording of the tympanic membrane. We describe a technique of myringotomy and ventilation tube insertion under endoscopic visualization using a rigid Hopkins rod scope previously described by other authors based on their accepted clinical guidelines for myringotomy. 1,2 The use of rigid endoscopes provides visualization of the entire tympanic membrane with excellent resolution, better fidelity of color with a well-angled or side-to-side vision. The procedure is generally safe, convenient and can be performed in an out-patient setting. Correspondingly, the video recordings could improve disease documentation for baseline and post-myringotomy evaluation. They can also be a tool to enable better understanding for patients.3 Materials and Methods A total of seven (n=7) patients with symptomatic and non-resolving otitis media with effusion (OME) previously managed conservatively for 3-6 months from October 2009 to March 2010 were included in the study. The patients also had disabling otalgia with 4 of the subjects having more than 30 dB hearing loss. Subjects who had poor pain threshold, were deemed non-cooperative and those in the pediatric age group were excluded from the study. Informed consent with strict compliance to institutional ethical standards was signed by all patients. The procedures were all performed by the junior author at the E.N.T Diagnostic Unit of a private tertiary university hospital. Materials used for the procedure were the same as with conventional myringotomy (eg. aural speculum, Kley or sickle knife, Hartmann ear forceps and ventilation tube/s). The anesthetic used was an Eutectic Mixture of Local Anesthesia (EMLA®) cream 5 % (Astra-Zeneca, Sodertalje, Sweden) in a 1 cc tuberculin syringe, and 20-25% aqueous form of phenol solution. A 0 degree 4mm x 107.5mm rigid endoscope (KARL STORZ GmbH & Co. KG Mittelstr., Tuttlingen, Germany) was used. (Figure 1) First an otoendoscopy was performed and the clinical indications and risks for myringotomy were thoroughly discussed with each patient. EMLA® cream was applied to the ear canal and to the external surface of the tympanic membrane using a 1 cc tuberculin syringe. After 60 minutes, the external ear canal was cleared for complete visualization of the tympanic membrane. (Figure 2) The patient was then positioned seated on the examining chair with head tilted to the opposite side. Using a 0 degree 4mm x 107.5mm rigid endoscope, the posterior third of the external auditory canal and the tympanic membrane was visualized. The scope was held with the left hand only up to the anterior portion of the cartilaginous canal to avoid involuntary activation of the Xth cranial nerve and to allow further advancement of other instruments to the posterior canal. A shorter rigid otoendoscope (4mm x 45mm) or a smaller diameter pediatric rigid endoscope (2.7mm x 107.5mm) may be used if available. A Kley knife or myringotomy knife was dipped lightly in phenol solution and carefully advanced to the tympanic membrane for the preferred myringotomy stab incision. (Figure 3) Care was taken to avoid contact of the phenol and knife tip with the canal wall to avoid stimulating unnecessary movement, canal abrasion or dermal irritation from the phenol solution during the entire procedure. (Figure 3) The myringotomy incisions were made at the posterior-inferior tympanic membrane quadrant for ease of access and drainage. (Figure 4) Evacuation of middle ear fluid was performed using a 2 and 3 mm Frazer middle ear suction tip. The myringotomy incision was made large enough to admit the ventilation tube in four subjects with copious effusions. In these four, the tube was introduced and adjusted using a 1 mm x 8 cm (working length) Hartmann ear forceps. A 1.14 mm I.D. Armstrong beveled fluoroplastic grommet ventilation tube (Xomed, Jocksonville, FL) was used in 3 subjects while a Sheehy collar button tube without wire (Micromedics Inc, St. Paul, Minnesota,USA) was used in one. The choice of tube depended mainly on the authors’ preference, taking tube designs available for specific ear conditions into consideration. (Figure 4) All subjects were instructed to avoid vigorous activities for the first 48 hours post-myringotomy, with strict water precautions. Ofloxacin otic drops were then prescribed. Results There were a total of 7 patients, 3 males and 4 females, with age ranging from 25 to 65 years (mean=50). All of them tolerated the procedure well. Ventilation tubes were inserted in 4 subjects with copious middle ear effusions. All had minimal intra-operative (PAS 2-5) and post-operative pain (PAS 0-2). The procedures were done on an out-patient basis. Co-morbid conditions were likewise treated (Table 1). Six out of the seven subjects experienced immediate subjective relief of otalgia and hearing loss after myringotomy while one subject had persistent complaint of ear fullness. The main indication for the procedure was otitis media with effusion with significant hearing loss, otalgia and ear fullness non-responsive to 3 months conservative management. All patients had significant contributing factors for OME such as frequent infectious rhinitis or chronic persistent allergic rhinitis. Six of the 7 subjects had markedly improved hearing. Four subjects with a preoperative pure-tone evaluation of >30-40 dB hearing loss had pure-tone average improvement to 10-15 dB after subsequent hearing examinations. All subjects were evaluated post-operatively with otoendoscopy. One case was unresponsive and subsequently diagnosed with adhesive otitis media and advised to undergo myringoplasty. Discussion Endoscopic myringotomy under topical anesthesia is a generally safe and practical procedure. Its indications are the same with conventional myringotomy with or without ventilation tube insertion such as Otitis Media with Effusion persisting beyond 3 months with associated significant hearing loss, impending mastoiditis or intracranial complications, recurrent episodes of acute otitis media (> 3 episodes in 6 months or > 4 episodes in 12 months), chronic tympanic membrane or pars flaccida, barotrauma, autophony (hearing body sounds; eg. breathing) due to patulous or widely open eustachean tube, craniofacial anomalies predisposing to middle ear dysfunction (e.g. cleft palate), and middle ear dysfunction due to head and neck radiation and skull base surgery.4 Endoscopic visualization of the tympanic membrane enables better patient understanding of their ear conditions. Such has been the basis for the procedure along with the use of 5% EMLA® to decrease the pain and discomfort of patients undergoing out-patient myringotomy procedures.5 Phenol on the other hand aids in faster creation of tympanic membrane incision and decreases post-operative bleeding through its tissue vaporizing chemical cauterization effect with negligible toxicity if given in minute amount.6 Furthermore for post-operative cases of middle ear surgeries, it can be used for surveillance and middle ear cleaning. This can improve post-operative follow-up and possibly decrease the need for second look surgery.7 Generally, endoscopic myringotomy provides a complete and enhanced visualization of the tympanic membrane and some middle ear structures that only appear as silhouettes with conventional otoscopy. Rigid endoscopes may have less illumination and magnification compared to an operating microscope traditionally used in myringotomy procedures but it can provide an angled or “off line-of-site” visualization of the tympanic membrane and canal wall advantageous in trans-canal visualization of the tympanic membrane. Just like the conventional out-patient myringotomy, endoscopic myringotomy under topical anesthesia is less costly than performing the procedure under general anesthesia or through sedation requiring a more controlled clinical setting. Smaller diameter and shorter endoscopes may be more feasible for diagnostic otoendoscopy, but a rigid 4 mm endoscope is more widely available in most local clinics. The major disadvantage of this procedure is the instrumentation in very young or uncooperative patients with a narrow external auditory canal. One-handed instrumentation and lens fogging may also be encountered but can be reduced with familiarity with the procedure. The indications for endoscopic myringotomy as with those for traditional myringotomy remain suggestions and do not represent the standard of care. Clinicians can modify them when medically necessary as treatment options should always be individualized to meet each patient’s need. Failure to improve hearing may suggest another middle ear condition that necessitates further evaluation. Some cases may need myringotomy tube replacement while surgery is reserved for failed tympanic membrane healing. Lastly, like any other surgical technique and instrumentation, the major key to a successful endoscopic myringotomy is still good patient selection.

Abstract Objective: To test the null hypothesis that rapid maxillary expansion (RME) with a rigid bonded appliance has no effect on conductive hearing loss (CHL) in growing children. Materials and Methods: Fifteen growing subjects (mean age 13.43 ± 0.86 years) who had narrow maxillary arches and CHL participated in this study. Three pure-tone audiometric and tympanometric records were taken from each subject. The first records were taken before RME (T1), the second after maxillary expansion (T2) (mean = 0.83 months), and the third after retention (mean = 6 months) and fixed appliance treatment (approximately 2 years) periods (T3). The data were analyzed by means of analysis of variance (ANOVA) and least significant difference (LSD) tests. Results: Hearing levels of the patients were improved and air-bone gaps decreased at a statistically significant level (P < .001) during active expansion (T2–T1) and the retention and fixed appliance treatment (T2–T3) periods. Middle ear volume increased in all observation periods. However, a statistically significant increase was observed only in the T2–T3 period. No significant change was observed in the static compliance value. Conclusions: The hypothesis is rejected. RME treatment has a positive and statistically significant effect on both improvements in hearing and normal function of the eustachian tube in patients having transverse maxillary deficiency and CHL.

Carbon nanotubes (CNTs) have been proposed as one of the most promising materials for nanoelectro-mechanical system due to high elastic modulus, high failure strength and excellent resilience [1,. Recent development of many-body interaction [3, made possible realistic molecular dynamics (MD) simulations of carbon-made systems. We carried out such studies for carbon nanotubes under generic modes of mechanical load: axial compression, bending, and torsion. A singular behavior of the nanotube energy at certain levels of strain corresponds to abrupt change in morphology. In this letter, we report the torsional instability analysis of single wall carbon nanotube filled with hydrogen via molecular dynamics simulations. The simulations are carried out at a temperature 77K which previous study obtained the hydrogen storage inside CNT at this condition [A. C. Dillo. Here we use atomistic simulations to study a flexible surface narrow carbon nanotube with tube diameters 10.8 Å. According to conventional physisorption principles, the gas-adsorption performance of a porous solid is maximized when the pores are no larger than a few molecular diameters [8]. Under these conditions, the potential fields produced at the wall overlap to produce a stronger interaction force than that observed in adsorption on a simple plane. However, the mechanisms responsible for the adsorption and transportation of hydrogen in nanoporous solids or nanopores are not easily observed using experimental methods. As a result, the use of computational methods such as molecular dynamics (MD) or Monte Carlo (MC) simulations have emerged as the method of choice for examining the nanofluidic properties of liquids and gases within nanoporous materials [9,1. Several groups have performed numerical simulations to study the adsorption of water in CNTs [11-1, while others have investigated the diffusion of pure hydrocarbon gases and their mixtures through various SWNTs with diameters ranging from 2 ~ 8 nm [17-19] or the self-and transport diffusion coefficients of inert gases, hydrogen, and methane in infinitely-long SWNTs [20-21]. In general, the results showed that the transport rates in nanotubes are orders of magnitude higher than those measured experimentally in zeolites or other microporous crystalline solids. In addition, it has been shown that the dynamic flow of helium and argon atoms through SWNTs is highly dependent on the temperature of the nanotube wall surface [22]. Specifically, it was shown that the flow rate of the helium and argon atoms, as quantified in terms of their self-diffusion coefficients, increased with an increasing temperature due to the greater thermal activation effect. Previous MD simulations of the nanofluidic properties of liquids and gases generally assumed the nanoporous material to have a rigid structure. However, if the nanoporous material is not in fact rigid, the simulation results may deviate from the true values by several orders of magnitude. Several researchers have investigated the conditions under which the assumption of a rigid lattice is, or is not, reasonable [23, 24]. In general, the results showed that while the use of a rigid lattice was permissible in modeling the nanofluidic properties of a gas or liquid in an unconfined condition, a flexible lattice assumption was required when simulating the properties of a fluid within a constrained channel. Moreover, in real-world conditions, the thermal fluctuations of the CNT wall atoms impact the diffusive behavior of the adsorbed molecules, and must therefore be taken into account. This study performs a series of MD simulations to investigate the transport properties of hydrogen molecules confined within a narrow CNT with a diameter of 10.8 Å (~ 1 nm) at temperatures ranging from 100 ~ 800 K and particle loadings of 0.01~1 No/Å. To ensure the validity of the simulation results, the MD model assumes the tube to have a flexible wall. Hydrogen molecules are treated as spherical particles. In performing the simulations, the hydrogen molecules are assumed to have a perfectly spherical shape. In addition, the interactions between the molecule and the CNT wall atoms and the interactions between the carbon atoms within the CNT wall are modeled using the Lennard-Jones potential [25,2. The simulations focus on the hydrogen adsorption within the SWNT not adsorption in the interstices or the external surface of nanotube bundles.

Soft-bodied animals, such as earthworms, are capable of contorting their body to squeeze through narrow spaces, create or enlarge burrows, and move on uneven ground. In many applications such as search and rescue, inspection of pipes and medical procedures, it may be useful to have a hollow-bodied robot with skin separating inside and outside. Textiles can be key to such skins. Inspired by earthworms, we developed two new robots: FabricWorm and MiniFabricWorm. We explored the application of fabric in soft robotics and how textile can be integrated along with other structural elements, such as three-dimensional (3D) printed parts, linear springs, and flexible nylon tubes. The structure of FabricWorm consists of one third the number of rigid pieces as compared to its predecessor Compliant Modular Mesh Worm-Steering (CMMWorm-S), while the structure of MiniFabricWorm consists of no rigid components. This article presents the design of such a mesh and its limitations in terms of structural softness. We experimentally measured the stiffness properties of these robots and compared them directly to its predecessors. FabricWorm and MiniFabricWorm are capable of peristaltic locomotion with a maximum speed of 33 cm/min (0.49 body-lengths/min) and 13.8 cm/min (0.25 body-lengths/min), respectively.

In 2005 in sublittoral zone of Koryak coast 79 species of amphipods belonged to 43 genera, 20 families and two suborders are revealed. The main part of the fauna was endemics of Pacific boreal area. The biomass varied from the several 100-th shares of gram to 15.6 g/m2. The maximum biomass of amphipods at population density 230 ind./m2 was registered at Cape Hajtyrka. The average biomass was 2.0 ± 0.6 g/m2 or 0.4% from the total biomass of a benthos. In places of amphipods accumulations their part in the total biomass of a benthos could reach 56.9%. Quantity indicators of amphipods on a shelf of Koryak coast above, than in Anadyr Bay. In different places of the investigated water area dominating species was different (Atylus bruggeni, Pontogeneia rostrata, Anisogammarus pugettensis, Caprella paulina). Rigid soil are extended on main parts of water area of narrow geosynclinal shelf of Koryak coast, mobile filter feeder, building small houses-tubes in thickness of a soil (Byblis erythrops, Ampelisca macrocephala and some other) had here no such wide development as in of Anadyr Bay. The shelf of Koryak coast distinguishes from the other areas of the Far East seas by small species wealth of amphipods at the stations – basically no more than five species.

Vocal fold paralysis is an otolaryngologic disorder that is more prevalent in the adult population. Its occurrence in children has been documented in the literature. We report a case of congenital bilateral vocal fold paralysis and discuss the issues surrounding its ultimate diagnosis and management. CASE REPORT Three months prior to consult, a five–year-old girl started to have noisy (whistling), difficult breathing lasting throughout the day and becoming louder if she cried. She had no cough, colds, fever, or voice changes. Suspecting asthma, an attending pediatrician at a private tertiary hospital emergency room administered salbutamol nebulization affording temporary relief of dyspnea, but the noisy breathing persisted. The girl was discharged on salbutamol syrup to be taken for episodes of difficulty breathing, without any laboratory work-ups. Two months before consult, another pediatrician prescribed co-amoxiclav and bromhexine for the persistent noisy breathing, without any improvement. Still no work-ups were requested. A month later, the noisy breathing was louder and associated with difficulty breathing, alar flaring and dynamic chest movements. Suspecting foreign-body aspiration, a tertiary government hospital pediatrician requested chest radiographs that showed minimal infiltrates and no hyperinflation, inconsistent with the working impression. She was referred to our institution for bronchoscopy and possible foreign body extraction. At our institution, further review of history revealed a Caesarian section for premature rupture of membranes, with cord coil noted on delivery. The perinatal history was otherwise unremarkable. The girl had been diagnosed with bronchial asthma at two years of age when the noisy breathing was first noted, and had been given Salbutamol syrup as needed for episodes of difficulty breathing. There had been no feeding difficulties and her developmental milestones were at par with age. Immunizations were also complete. Physical examination revealed respiratory distress with biphasic stridorous breath sounds (heard louder over the neck) with bilateral alar flaring and subcostal and chest wall retractions. Examination of the throat, ears and nose was unremarkable, as was the neurological exam. A repeat Chest X-ray (Figure 1) showed confluent opacities in both lower lobes and shouldering of the subglottic trachea in the frontal projection. No foreign body was appreciated, and a subglottic stenosis and/or tracheomalacia were considered. Awake flexible laryngoscopy (Figure 2) revealed bilateral immobile vocal folds fixed in paramedian position. Tracheobronchoscopy under general anesthesia showed no hypopharyngeal or tracheal lesions up to the level of the carina. A tracheotomy was performed and a Shiley size 4.5 tracheostomy tube was inserted. After much consultation with her relatives, it was decided to follow her closely due to the possibility of spontaneous resolution of bilateral vocal fold paralysis. After two (2) years of regular follow-up, repeat awake flexible laryngocopy revealed no change in vocal fold status. Direct laryngoscopy with cordotomy and arytenoidectomy were then performed. (Figure 3) Two weeks post-operatively, the patient was successfully decannulated. DISCUSSION Stridor represents one of the most common complaints of children presenting with upper airway pathologies. It is defined as an “abnormal sound produced by air passing through an airway lumen of decreased caliber.”1 Despite the abundance of literature describing and differentiating this symptom, it would not be uncommon for physicians to mistake this for a wheeze2 – an adventitious lung sound. One important point in determining whether a certain breath sound is stridorous or not is the location where the sound is heard loudest: stridorous sounds being heard louder in the neck and wheezing sounds heard best in the lungs.3 Stridor may be classified based on timing -- whether it is expiratory, inspiratory or biphasic4,5 Determining the timing of stridor allows one to narrow a multitude of differentials. (Table 1) However, the co-existence of upper and lower airway pathologies in a patient with stridor may complicate the diagnosis. Hence, further workups may be required. There are no hard and fast indications of what imaging or modality to request in the assessment of a child with stridor. In this case, a chest X-ray showed equivocal findings. Flexible endoscopy followed, and revealed the disorder. Rigid tracheobronchoscopy ruled out concomitant tracheal lesions such as laryngomalacia, which is the most common associated anomaly.6 Congenital bilateral vocal fold paralysis, defined as reduced or absent mobility of both vocal folds in children is an uncommon disorder. A study by Ahmad et al. estimated the incidence of congenital bilateral vocal fold paralysis to about 0.9% of all cases of vocal fold paralysis.7 The causes of this rare disorder include central nervous system diseases (most common of which is Arnold-Chiari malformation), muscular dystrophies, autoimmune disorders and trauma (arytenoid dislocation). Most cases however are idiopathic.8 In our case, trauma (cord coil) seems to be the only positive event that may actually be the precipitating factor. However, even after repeated histories, there is a significant disparity between the presumed cause (cord coil) and the start of symptoms at about 2 years of age. Labeling this case as idiopathic may also be quite premature since an underlying neuromuscular disorder, though rare may present later in life between 4 months to 7 years.9 Case reports of bilateral vocal fold paralysis in the local literature are scarce.10-12 The most common complaint of this airway pathology is stridor with 32% presenting after one (1) year of age.8 One of the most controversial issues regarding this problem is the value of laryngeal electromyography in diagnosis. While its value in adults with vocal fold immobility is recognized, its role in children is questionable. A study by Berkowitz showed that a normal EMG may be a finding in children with bilateral vocal fold paralysis.13 These reasons, aside from the fact that the patient had no other history of neck trauma and that the procedure is technically difficult with the potential for more damaging complications on account of the smaller laryngeal apparatus of the child compared to an adult precluded the application of laryngeal electromyography in this case. Another controversy is the use of imaging modalities such as CT Scan and MRI. The role of these ancillaries is supposedly to rule out central nervous system and peripheral nerve lesions. But while neurological and thoracic pathologies must be considered in the assessment of vocal fold paralysis, in the face of a normal neurological and chest examination, such exams are unnecessary and may in fact cause untoward and needless stress on the patient. Our patient had a normal neurological and developmental exam as well as a normal chest and lung exam. In case of idiopathic bilateral vocal fold paralysis, Berkowitz et al.14 opined that “blockade of glycinergic inhibitory neurotransmission by strychnine acts pre-synaptically on postinspiratory laryngeal constrictor motorneurons to induce firing during inspiration” as a suggested mechanism and perhaps the reason why EMG findings may be normal in this condition. But the decision and timing to perform definitive surgery or observe (maintain tracheostomy tube) is perhaps the most significant issue to consider. Factors to consider include impact on language, emotional, and intellectual development, tracheostomy complications, capacity of caregivers to provide home care and possibility of spontaneous recovery.15 Each of these factors must be taken into consideration and weighed prior to decision making. Parents must also be informed and included in this process. The rationale for observation has been emphasized in a study by Daya et al.8 wherein some children showed recovery after age 5 with the longest time of recovery at age 11 years old. In case of non-resolution, a variety of surgical techniques can be done – none showing a clear advantage over the other.16 After 2 years of regular follow-up, observing no significant change in vocal fold status, the parents decided to opt for surgery. Laser arytenoidectomy and cordotomy were chosen because studies have shown it to be superior to other surgical techniques in terms of decannulation rate16 and voice preservation and it was a familiar procedure in our institution. In this procedure, in which an Accupulse Lumenis 40 ST (Yokneam, Israel distributed by Spectromed) carbon dioxide laser machine was used, the posterior one-third of the left vocal fold along with a portion of the left vocal process was ablated. (Figure 3) No major complications were noted during the procedure. Two weeks postoperatively, the patient was successfully decannulated. Four months after the procedure, the mother reported no further episodes of difficulty of breathing and very minimal speech deficiencies. She also noted increased confidence and cheerfulness. This case demonstrates how a careful history and physical examination (with minimal diagnostic studies) allows for precise diagnosis without the use of costly interventions such as a CT Scan, MRI or Electromyography and enumerates the factors that must be considered in choosing the best management for the patient. Acknowledgements We would like to thank Dr. Joel Romualdez and Dr. Ray Casile for their suggestions and encouragement that have made the writing of this manuscript possible.

Recent research is making progress in framing more precisely the basic dynamical and statistical questions about turbulence and in answering them. It is helping both to define the likely limits to current methods for modelling industrial and environmental turbulent flows, and to suggest new approaches to overcome these limitations. Our selective review is based on the themes and new results that emerged from more than 300 presentations during the Programme held in 1999 at the Isaac Newton Institute, Cambridge, UK, and on research reported elsewhere. A general conclusion is that, although turbulence is not a universal state of nature, there are certain statistical measures and kinematic features of the small-scale flow field that occur in most turbulent flows, while the large-scale eddy motions have qualitative similarities within particular types of turbulence defined by the mean flow, initial or boundary conditions, and in some cases, the range of Reynolds numbers involved. The forced transition to turbulence of laminar flows caused by strong external disturbances was shown to be highly dependent on their amplitude, location, and the type of flow. Global and elliptical instabilities explain much of the three-dimensional and sudden nature of the transition phenomena. A review of experimental results shows how the structure of turbulence, especially in shear flows, continues to change as the Reynolds number of the turbulence increases well above about 104 in ways that current numerical simulations cannot reproduce. Studies of the dynamics of small eddy structures and their mutual interactions indicate that there is a set of characteristic mechanisms in which vortices develop (vortex stretching, roll-up of instability sheets, formation of vortex tubes) and another set in which they break up (through instabilities and self- destructive interactions). Numerical simulations and theoretical arguments suggest that these often occur sequentially in randomly occurring cycles. The factors that determine the overall spectrum of turbulence were reviewed. For a narrow distribution of eddy scales, the form of the spectrum can be defined by characteristic forms of individual eddies. However, if the distribution covers a wide range of scales (as in elongated eddies in the ‘wall’ layer of turbulent boundary layers), they collectively determine the spectra (as assumed in classical theory). Mathematical analyses of the Navier–Stokes and Euler equations applied to eddy structures lead to certain limits being defined regarding the tendencies of the vorticity field to become infinitely large locally. Approximate solutions for eigen modes and Fourier components reveal striking features of the temporal, near-wall structure such as bursting, and of the very elongated, spatial spectra of sheared inhomogeneous turbulence; but other kinds of eddy concepts are needed in less structured parts of the turbulence. Renormalized perturbation methods can now calculate consistently, and in good agreement with experiment, the evolution of second- and third-order spectra of homogeneous and isotropic turbulence. The fact that these calculations do not explicitly include high-order moments and extreme events, suggests that they may play a minor role in the basic dynamics. New methods of approximate numerical simulations of the larger scales of turbulence or ‘very large eddy simulation’ (VLES) based on using statistical models for the smaller scales (as is common in meteorological modelling) enable some turbulent flows with a non-local and non-equilibrium structure, such as impinging or convective flows, to be calculated more efficiently than by using large eddy simulation (LES), and more accurately than by using ‘engineering’ models for statistics at a single point. Generally it is shown that where the turbulence in a fluid volume is changing rapidly and is very inhomogeneous there are flows where even the most complex ‘engineering’ Reynolds stress transport models are only satisfactory with some special adaptation; this may entail the use of transport equations for the third moments or non-universal modelling methods designed explicitly for particular types of flow. LES methods may also need flow-specific corrections for accurate modelling of different types of very high Reynolds number turbulent flow including those near rigid surfaces.This paper is dedicated to the memory of George Batchelor who was the inspiration of so much research in turbulence and who died on 30th March 2000. These results were presented at the last fluid mechanics seminar in DAMTP Cambridge that he attended in November 1999.

Abstract One of the fundamental phenomena associated with the transport of rigid particles by the fluid flow in narrow ducts and tubes is the Segre–Silberberg effect. Experimental observations show that a spherical particle transported by the fluid flow in a long channel occupies a position of equilibrium between the wall and the centerline of the channel. In this study, this effect was numerically investigated using a novel semi-implicit immersed boundary method based on the discrete forcing approach. A uniform Cartesian mesh is used for the duct, whereas a moving Lagrangian mesh is used to track the position of the particle. Unlike previous studies, both cases of the duct geometry are considered: a round tube and a flat channel. Good agreement is shown to the available theoretical and numerical results of other studies. The problem is described by two dimensionless parameters, the channel Reynolds number, and the relative particle diameter. Parametric studies to these parameters were carried out, showing fundamental dependencies of equilibrium position on Reynolds number from 20 to 500 and on relative particle diameter from 0.2 to 0.7. It is demonstrated that the position of equilibrium becomes closer to the wall with the increase of Reynolds number, as well as with the decrease of particle diameter. In addition, the dependence of particle velocity on its diameter is investigated. The obtained results are of both theoretical and practical interest, with possible applications ranging from proppant transport to the design of microfluidic devices.

Introduction: A limitation of mini-percutaneous nephrolithotomy (mPCNL) is the narrow working channel of mini-nephroscopes, typically restricting instrumentation to 5 F or smaller. We evaluated the efficacy of the 1.5 mm Swiss Lithoclast® Trilogy (Trilogy) rigid probe and compared the results to consecutive cases performed with a 30 W Holmium:YAG (Ho:YAG) laser. Methods: A retrospective review of 30 consecutive mPCNL cases using the Trilogy and 30 W Holmium laser was performed. A 12-French (F) MIPS nephroscope with a 16.5 F access sheath and 6.7 F working channel was used for all mPCNL cases. The Trilogy was used with a disposable 1.5 mm x 440 mm probe with dual ultrasonic and ballistic energy. The Ho:YAG laser was used with a 550 micron fibre and a maximum of 30 W. Stone clearance time (SCT) was defined by the total time interval between activation of the lithotripter until insertion of the nephrostomy tube and measured in mm2/minutes. SCT included time for fragment retrieval, equipment adjustments, and rigid and flexible nephroscopy during and after lithotripsy. Results: Eleven cases using a 1.5 mm Trilogy probe and 16 cases using a Ho:YAG laser met final inclusion criteria. Three cases using the Trilogy were excluded from final analysis due to conversion to alternative energy sources — two of those were upsized to standard PCNL and one was converted to laser. Mean stone diameter and density in the final Trilogy cohort was 26.7 mm and 1193 Hounsfield units (HU). Mean diameter and density in the laser cohort was 25.2 mm and 1049 HU. The mean stone area clearance time for Trilogy was 4.7±1.8 mm2/minute vs. 3.4±0.7 mm2/minute with Ho:YAG laser (p=0.21). For hard stones, defined as density >1000 HU, the Trilogy averaged 3.7±1.6 mm2/minutes, while the laser averaged 3.1±1.3 mm2/minutes (p=0.786). For soft stones, defined as <1000 HU, the Trilogy averaged 8.9±1.0 mm2/minutes compared to the Ho:YAG, which averaged 3.6±1.8mm2/minutes (p=0.019). No device0related complications occurred in either cohort. Conclusions: The 1.5 mm mPCNL Trilogy probe was comparable to 30 W Ho:YAG laser for clearing hard stones. The Trilogy performed better than laser on soft stones with a HU density <1000 HU.

This paper gives a summary of the technical evolution of medical endoscopy. The first documented redirection of sunlight into the human body dates back to the 16th century. Rigid tubes with candle light were given a trial later on. Low light intensity forced the development of alternative light sources. Some of these experiments included burning chemical components. Electric lighting finally solved the problems of heat production and smoke. Flexible endoscopy increased the range of medical examinations as it allowed access to tight and angular body cavities. The first cameras for endoscopic applications made taking photos from inside the human body possible. Later on, digital video endoscopy made endoscopes easier to use and allowed multiple spectators to observe the endoscopic intervention. Swallowable capsules called pill-cams made endoscopic examinations of the small intestine possible. Modern technologies like narrow band imaging and fluorescence endoscopy increased the diagnostic significance of endoscopic images. Today, image processing is applied to decrease noise and enhance image quality. These enhancements have made medical endoscopy an invaluable tool in many diagnostic processes. In closing, an example is given of an interdisciplinary examination, which is taken from the archaeological field.