bluuebunny/crossref_metadata_2025 huggingface dataset:
Differential responses of the mosquito Aedes albopictus from the Indian Ocean region to two chikungunya isolates
Authors: Martin Estelle , Moutailler Sara , Madec Yoann , Failloux Anna-Bella
Published: March 2010

Background

Aedes aegypti and Aedes albopictus are both vectors of chikungunya virus (CHIKV). The two Aedes species co-exist in the Indian Ocean region and were involved in the 2005-2006 CHIKV outbreaks. In the Reunion Island, a single mutation in the viral envelope has been selected that leads to high levels of replication in Ae. albopictus, and a short extrinsic incubation period as the virus could be found in saliva as early as two days after infection. An important question is whether this variant is associated with adverse effects impacting some mosquito life-history traits such as survival and reproduction.

Results

We performed experimental infections using three mosquito strains of Ae. aegypti Mayotte and Ae. albopictus (Mayotte and Reunion), and two CHIKV strains (E1-226A and E1-226V). Ae. aegypti Mayotte were similarly susceptible to both viral strains, whereas Ae. albopictus Mayotte and Ae. albopictus Reunion were more susceptible to CHIKV E1-226V than to E1-226A. In terms of life-history traits measured by examining mosquito survival and reproduction, we found that: (1) differences were observed between responses of mosquito species to the two viruses, (2) CHIKV infection only affected significantly some life-history traits of Ae. albopictus Reunion and not of the other two mosquito strains, and (3) CHIKV reduced the lifespan of Ae. albopictus Reunion and shortened the time before egg laying.

Conclusion

We demonstrated that CHIKV only reduces the survival of Ae. albopictus from the Reunion Island. By laying eggs just before death, reproduction of Ae. albopictus from the Reunion Island is not reduced since other parameters characterizing oviposition and hatching were not affected.
Visual acuity in larval zebrafish: behavior and histology
Authors: Haug Marion F , Biehlmaier Oliver , Mueller Kaspar P , Neuhauss Stephan CF
Published: March 2010

Background

Visual acuity, the ability of the visual system to distinguish two separate objects at a given angular distance, is influenced by the optical and neuronal properties of the visual system. Although many factors may contribute, the ultimate limit is photoreceptor spacing. In general, at least one unstimulated photoreceptor flanked by two stimulated ones is needed to perceive two objects as separate. This critical interval is also referred to as the Nyquist frequency and is according to the Shannon sampling theorem the highest spatial frequency where a pattern can be faithfully transmitted. We measured visual acuity in a behavioral experiment and compared the data to the physical limit given by photoreceptor spacing in zebrafish larvae.

Results

We determined visual acuity by using the optokinetic response (OKR), reflexive eye movements in response to whole field movements of the visual scene. By altering the spatial frequency we determined the visual acuity at approximately 0.16 cycles/degree (cpd) (minimum separable angle = 3.1°). On histological sections we measured the retinal magnification factor and the distance between double cones, that are thought to mediate motion perception. These measurements set the physical limit at 0.24 cpd (2.1°).

Conclusion

The maximal spatial information as limited by photoreceptor spacing can not be fully utilized in a motion dependent visual behavior, arguing that the larval zebrafish visual system has not matured enough to optimally translate visual information into behavior. Nevertheless behavioral acuity is remarkable close to its maximal value, given the immature state of young zebrafish larvae.
Are Nepali students at risk of HIV? A cross‐sectional study of condom use at first sexual intercourse among college students in Kathmandu
Authors: Adhikari Ramesh
Published: March 2010

Background

Condoms offer the best protection against unintended pregnancies and sexually transmitted infections. Little research has been conducted to determine the prevalence and investigate the influencing factors of condom use at first sexual intercourse among college students.

Methods

A self‐administered questionnaire was completed by 1137 college students (573 male and 564 female) in the Kathmandu Valley. Analyses were confined to 428 students who reported that they have ever had sexual intercourse. The association between condom use at first sexual intercourse and the explanatory variables was assessed in bivariate analysis using Chi‐square tests. The associations were further explored using multivariate logistic analysis in order to identify the significant predictors after controlling for other variables.

Results

Among the sexually active students, less than half (48%) had used condoms during first sexual intercourse. The results from the logistic regression analysis revealed that age, caste and/or ethnicity, age at first sexual intercourse, types of first sex partner, alcohol consumption and mass media exposure are significant predictors for condom use at first sexual intercourse among the college students. Students in the older age groups who had first sex were about four times (16 to 19 years old) (OR = 3.5) more likely and nine times (20 or older) (OR = 8.9) more likely than the students who had sex before 16 years of age to use condoms at first sexual intercourse.

Moreover, those students who had first sex with commercial sex worker were five times (OR = 4.9) more likely than those who had first sex with their spouse to use condoms at first sex. Furthermore, students who had higher exposure to both print and electronic media were about twice (OR = 1.75) as likely as those who had lower media exposure to use condoms. On the other hand, students who frequently consumed alcohol were 54% (OR = 0.46) less likely to use condoms at first sexual intercourse than those who never or rarely consumed alcohol.

Conclusions

The rate of condom use at first sexual intercourse is low among the students. It indicates students are exposed to health hazards through their sexual behaviour. If low use of condom at first sex continues, vulnerable sexual networks will grow among them that allow quicker spreading of sexually transmitted diseases and HIV. Findings from this study point to areas that policy and programmes can address to provide youth with access to the kinds of information and services they need to achieve healthy sexual and reproductive lives.
Lack of SIRT1 (Mammalian Sirtuin 1) Activity Leads to Liver Steatosis in the SIRT1+/− Mice: A Role of Lipid Mobilization and Inflammation
Authors: Xu Fen , Gao Zhanguo , Zhang Jin , Rivera Chantal A. , Yin Jun , Weng Jianping , Ye Jianping
Published: March 2010

Mammalian sirtuin 1 (SIRT1) may control fatty acid homeostasis in liver. However, this possibility and underlying mechanism remain to be established. In this study, we addressed the issues by examining the metabolic phenotypes of SIRT1 heterozygous knockout (SIRT1+/−) mice. The study was conducted in the mice on three different diets including a low-fat diet (5% fat wt/wt), mediate-fat diet (11% fat wt/wt), and high-fat diet (HFD, 36% fat wt/wt). On low-fat diet, the mice did not exhibit any abnormality. On mediate-fat diet, the mice exhibited a significant increase in hepatic steatosis with elevated liver/body ratio, liver size, liver lipid (triglyceride, glycerol, and cholesterol) content, and liver inflammation. The hepatic steatosis was deteriorated in the mice by HFD. In the liver, lipogenesis was increased, fat export was reduced, and β-oxidation was not significantly changed. Body weight and fat content were increased in response to the dietary fat. Fat was mainly increased in sc adipose tissue and liver. Inflammation was also elevated in epididymal fat. Whole body energy expenditure and substrate utilization were reduced. Food intake, locomotor activity, and fat absorption were not changed. These data suggest that a reduction in the SIRT1 activity increases the risk of fatty liver in response to dietary fat. The liver steatosis may be a result of increased lipogenesis and reduced liver fat export. The inflammation may contribute to the pathogenesis of hepatic steatosis as well. A reduction in lipid mobilization may contribute to the hepatic steatosis and low energy expenditure.
Sentry Selection in Wireless Networks
Authors: Balister Paul , Bollobás Béla , Sarkar Amites , Walters Mark
Published: March 2010

Letbe a Poisson process of intensity one in the infinite plane ℝ2. We surround each pointxofby the open disc of radiusrcentred atx. Now letSnbe a fixed disc of arean, and letCr(Sn) be the set of discs which intersectSn. WriteErkfor the event thatCr(Sn) is ak-cover ofSn, andFrkfor the event thatCr(Sn) may be partitioned intokdisjoint single covers ofSn. We prove that P(Erk∖Frk) ≤ck/ logn, and that this result is best possible. We also give improved estimates for P(Erk). Finally, we study the obstructions tok-partitionability in more detail. As part of this study, we prove a classification theorem for (deterministic) covers of ℝ2with half-planes that cannot be partitioned into two single covers.
New Classes of Random Tessellations Arising from Iterative Division of Cells
Authors: Cowan Richard
Published: March 2010

We present new ideas about the type of random tessellation which evolves through successive division of its cells. These ideas are developed in an intuitive way, with many pictures and only a modicum of mathematical formalism–so that the wide application of the ideas is clearly apparent to all readers. A vast number of new tessellation models, with known probability distribution for the volume of the typical cell, follow from the concepts in this paper. There are other interesting models for which results are not presented (or presented only through simulation methods), but these models have illustrative value. A large agenda of further research is opened up by the ideas in this paper.
Contact and Chord Length Distribution Functions of the Poisson-Voronoi Tessellation in High Dimensions
Authors: Muche L.
Published: March 2010

In this paper we present formulae for contact distributions of a Voronoi tessellation generated by a homogeneous Poisson point process in the d-dimensional Euclidean space. Expressions are given for the probability density functions and moments of the linear and spherical contact distributions. They are double and simple integral formulae, which are tractable for numerical evaluation and for large d. The special cases d = 2 and d = 3 are investigated in detail, while, for d = 3, the moments of the spherical contact distribution function are expressed by standard functions. Also, the closely related chord length distribution functions are considered.
Variance-Optimal Hedging in General Affine Stochastic Volatility Models
Authors: Kallsen Jan , Pauwels Arnd
Published: March 2010

We consider variance-optimal hedging in general continuous-time affine stochastic volatility models. The optimal hedge and the associated hedging error are determined semiexplicitly in the case that the stock price follows a martingale. The integral representation of the solution opens the door to efficient numerical computation. The setup includes models with jumps in the stock price and in the activity process. It also allows for correlation between volatility and stock price movements. Concrete parametric models will be illustrated in a forthcoming paper.
On the Distribution of the Nearly Unstable AR(1) Process with Heavy Tails
Authors: Olvera-Cravioto Mariana
Published: March 2010

We consider a nearly unstable, or near unit root, AR(1) process with regularly varying innovations. Two different approximations for the stationary distribution of such processes exist: a Gaussian approximation arising from the nearly unstable nature of the process and a heavy-tail approximation related to the tail asymptotics of the innovations. We combine these two approximations to obtain a new uniform approximation that is valid on the entire real line. As a corollary, we obtain a precise description of the regions where each of the Gaussian and heavy-tail approximations should be used.
Covariances Estimation for Long-Memory Processes
Authors: Wu Wei Biao , Huang Yinxiao , Zheng Wei
Published: March 2010

For a time series, a plot of sample covariances is a popular way to assess its dependence properties. In this paper we give a systematic characterization of the asymptotic behavior of sample covariances of long-memory linear processes. Central and noncentral limit theorems are obtained for sample covariances with bounded as well as unbounded lags. It is shown that the limiting distribution depends in a very interesting way on the strength of dependence, the heavy-tailedness of the innovations, and the magnitude of the lags.
Optimal Control of a Stochastic Processing System Driven by a Fractional Brownian Motion Input
Authors: Ghosh Arka P. , Roitershtein Alexander , Weerasinghe Ananda
Published: March 2010

We consider a stochastic control model driven by a fractional Brownian motion. This model is a formal approximation to a queueing network with an ON-OFF input process. We study stochastic control problems associated with the long-run average cost, the infinite-horizon discounted cost, and the finite-horizon cost. In addition, we find a solution to a constrained minimization problem as an application of our solution to the long-run average cost problem. We also establish Abelian limit relationships among the value functions of the above control problems.
On the Dual Relationship Between Markov Chains of GI/M/1 and M/G/1 Type
Authors: Taylor P. G. , Van Houdt B.
Published: March 2010

In 1990, Ramaswami proved that, given a Markov renewal process of M/G/1 type, it is possible to construct a Markov renewal process of GI/M/1 type such that the matrix transforms G(z, s) for the M/G/1-type process and R(z, s) for the GI/M/1-type process satisfy a duality relationship. In his 1996 PhD thesis, Bright used time reversal arguments to show that it is possible to define a different dual for positive-recurrent and transient processes of M/G/1 type and GI/M/1 type. Here we compare the properties of the Ramaswami and Bright dual processes and show that the Bright dual has desirable properties that can be exploited in the design of algorithms for the analysis of Markov chains of GI/M/1 type and M/G/1 type.
Insensitive Bounds for the Moments of the Sojourn Times in M/GI Systems Under State-Dependent Processor Sharing
Authors: Brandt Andreas , Brandt Manfred
Published: March 2010

We consider a system with Poisson arrivals and independent and identically distributed service times, where requests in the system are served according to the state-dependent (Cohen's generalized) processor-sharing discipline, where each request receives a service capacity that depends on the actual number of requests in the system. For this system, we derive expressions as well as tight insensitive upper bounds for the moments of the conditional sojourn time of a request with given required service time. The bounds generalize and extend corresponding results, recently given for the single-server processor-sharing system in Cheung et al. (2006) and for the state-dependent processor-sharing system with exponential service times by the authors (2008). Analogous results hold for the waiting times. Numerical examples for the M/M/m-PS and M/D/m-PS systems illustrate the given bounds.
Long-Time Behaviour in a Model of Microtubule Growth
Authors: Hryniv O. , Menshikov M.
Published: March 2010

We study a continuous-time stochastic process on strings made of two types of particle, whose dynamics mimic the behaviour of microtubules in a living cell; namely, the strings evolve via a competition between (local) growth/shrinking as well as (global) hydrolysis processes. We give a complete characterization of the phase diagram of the model, and derive several criteria of the transient and recurrent regimes for the underlying stochastic process.
The Busy Period of an M/G/1 Queue with Customer Impatience
Authors: Boxma Onno , Perry David , Stadje Wolfgang , Zacks Shelley
Published: March 2010

We consider an M/G/1 queue in which an arriving customer does not enter the system whenever its virtual waiting time, i.e. the amount of work seen upon arrival, is larger than a certain random patience time. We determine the busy period distribution for various choices of the patience time distribution. The main cases under consideration are exponential patience and a discrete patience distribution.
Stein's Method for Compound Geometric Approximation
Authors: Daly Fraser
Published: March 2010

We apply Stein's method for probabilistic approximation by a compound geometric distribution, with applications to Markov chain hitting times and sequence patterns. Bounds on our Stein operator are found using a complex analytical approach based on generating functions and Cauchy's formula.
On the Variety of Shapes on the Fringe of a Random Recursive Tree
Authors: Feng Qunqiang , Mahmoud Hosam M.
Published: March 2010

We consider a variety of subtrees of various shapes lying on the fringe of a recursive tree. We prove that (under suitable normalization) the number of isomorphic images of a given fixed tree shape on the fringe of the recursive tree is asymptotically Gaussian. The parameters of the asymptotic normal distribution involve the shape functional of the given tree. The proof uses the contraction method.
Optimal Allocation of Active Redundancies to k-out-of-n Systems with Heterogeneous Components
Authors: Li Xiaohu , Ding Weiyong
Published: March 2010

In this note we deal with the allocation of independent and identical active redundancies to a k-out-of-n system with the usual stochastic order among its independent components. The optimal policy is proved both to assign more redundancies to the weaker component and to majorize all other policies. This improves the corresponding one in Hu and Wang (2009) and serves as a nice supplement to that in Misra, Dhariyal and Gupta (2009) as well.
In vivo mechanical response of human Achilles tendon to a single bout of hopping exercise
Authors: Peltonen Jussi , Cronin Neil J. , Avela Janne , Finni Taija
Published: March 2010

Stiffness of the human Achilles tendon (AT) was determined in vivo before and after a single bout of hopping exercise. It was hypothesized, based on published data using in vitro specimens, that a reduction in AT stiffness may occur after just 1000 loading cycles at physiological stress levels. Ten healthy subjects performed two-legged hopping exercise consisting of 1150–2600 high impacts. Tendon stiffness was determined in several isometric ramp contractions [20%, 40%, 60%, 80% and 100% maximum voluntary contraction (MVC)] during which tendon elongation was measured using ultrasonography and two cameras. Tendon force was calculated by dividing measured ankle torque by magnetic resonance imaging-derived AT lever arm length. Tendon stiffness remained unchanged, being 430±200 N mm−1 before and 390±190 N mm−1 after the exercise [not significant (n.s.)]. Despite the lack of changes in stiffness, maximum tendon force during MVC was reduced from 3.5±0.6 kN to 2.8±0.7 kN (P<0.01). As the proposed decline in stiffness was not observed, it is concluded that mechanical fatigue did not take place in the AT of healthy individuals after a single bout of high-impact exercise performed until exhaustion.
Fuel switching and energy partitioning during the postprandial metabolic response in the ball python (Python regius)
Authors: Waas Stefan , Werner Roland A. , Starck J. Matthias
Published: March 2010

Digestion, absorption and assimilation of the meal are active processes that require start-up energy before the energy contained in a meal can be utilized. The energetic costs associated with feeding (specific dynamic action, SDA) are high in sit-and-wait foraging snakes that tolerate long fasting periods. We used 13C-labelled prey to partition between endogenous energy sources (i.e. snakes own resources) and exogenous energy sources (i.e. prey). A linear mixing model was then applied to determine the portion of 13C originating from the different sources. The snakes showed a normal and typical postprandial response. By four hours after feeding, the δ13C-values indicated fuel switching from endogenous to exogenous. From then on, fuel mixing continuously increased until, at 20 h after feeding, 75% of fuel was exogenous. Resource partitioning showed that throughout SDA, the amount of exogenous energy increased to ~60% of SDA, which was equivalent to ~4.5% of the energy contained in a meal.
Deployment of hagfish slime thread skeins requires the transmission of mixing forcesviamucin strands
Authors: Winegard T. M. , Fudge D. S.
Published: March 2010

Hagfishes are benthic marine protovertebrates that secrete copious quantities of slime when threatened. The slime originates as a two-component glandular exudate comprised of coiled bundles of cytoskeletal intermediate filaments (thread skeins) and mucin vesicles. Holocrine secretion of the slime into seawater results in the rapid deployment of both fibrous and mucin components, resulting in about a liter of dilute slime. Deployment of the thread skeins involves their unraveling in a fraction of a second from a 150 μm-long ellipsoid bundle to a thread that is 100× longer. We hypothesized that thread skein deployment requires both vigorous hydrodynamic mixing and the presence of mucin vesicles, both of which are required for whole slime deployment. Here we provide evidence that mixing and mucin vesicles are indeed crucial for skein unraveling. Specifically, we show that mucin vesicles mixed into seawater swell and elongate into high-aspect ratio mucin strands that attach to the thread skeins, transmit hydrodynamic forces to them and effect their unraveling by loading them in tension. Our discovery of mucin strands in hagfish slime not only provides a mechanism for the rapid deployment of thread skeins in vivo, it also helps explain how hagfish slime is able to trap such impressive volumes of seawater via viscous entrainment. We believe that the deployment of thread skeins via their interaction with shear-elongated mucins represents a unique mechanism in biology and may lead to novel technologies for transmitting hydrodynamic forces to microscale particles that would typically be immune to such forces.
It's tough to be small: dependence of burrowing kinematics on body size
Authors: Che James , Dorgan Kelly M.
Published: March 2010

Burrowing marine infauna are morphologically diverse and range in size over several orders of magnitude. Whilst effects of ontogenetic and morphological differences on running, flying and swimming are relatively well understood, similar analyses of burrowing mechanics and kinematics are lacking. The polychaete Nereis virens Sars extends its burrow by fracture, using an eversible pharynx to exert force on the walls of the burrow. The resulting stress is amplified at the anterior tip of the burrow, which extends when the stress exceeds the fracture toughness of the material. Here we show that the polychaete Cirriformia moorei extends its burrow by a similar mechanism, but by using its hydrostatic skeleton rather than an eversible pharynx. Based on the dimensionless wedge number, which relates work of fracture to work to maintain body shape against the elasticity of sediment, we predicted that smaller worms would exhibit behaviors characteristic of tougher sediments and that scaling of kinematics would reflect decreasing difficulty in fracturing sediment with increasing body size. We found that smaller worms were relatively blunter and thicker, and had a greater variation of thickness than larger worms as they burrowed. Although these kinematic differences increase the stress amplification at the crack tip, smaller worms still generate lower stress intensity factors. The greater relative body thickness and shape changes of smaller worms are consistent with ontogenetic changes in forces exerted by earthworms, and are likely driven by the challenge of exerting enough stress to extend a crack with a small body size.
Hydrodynamic sensing does not facilitate active drag reduction in the golden shiner (Notemigonus crysoleucas)
Authors: McHenry M. J. , Michel K. B. , Stewart W. , Müller U. K.
Published: March 2010

The lateral line system detects water flow, which allows fish to orient their swimming with respect to hydrodynamic cues. However, it is unclear whether this sense plays a role in the control of propulsion. Hydrodynamic theory suggests that fish could reduce drag by coordinating the motion of the head relative to detected flow signals. To test this hypothesis, we performed measurements of undulatory kinematics during steady swimming in the golden shiner (Notemigonus crysoleucas) at three speeds (4.5, 11.0 and 22.0 cm s−1). We found that the phase shift between yaw angle and lateral velocity (20.5±13.1 deg., N=5) was significantly greater than the theoretical optimum (0 deg.) and the amplitude of these variables created a hydrodynamic index (H=0.05±0.03, N=6) that was less than an order of magnitude below the theoretical prediction. Furthermore, we repeated these measurements after pharmacologically ablating the lateral line hair cells and found that drag reduction was not adversely influenced by disabling the lateral line system. Therefore, flow sensing does not facilitate active drag reduction. However, we discovered that ablating the lateral line causes the envelope of lateral displacement to nearly double at the envelope's most narrow point for swimming at 4.5 cm s−1. Therefore, fish may use hydrodynamic sensing to modulate the lateral amplitude of slow undulatory swimming, which could allow rapid responses to changes in environmental flow.
Prediction of Tensile Strength and Optimization of Process Parameters for Friction Stir Welded AZ31B Magnesium Alloy
Authors: Padmanaban G , Balasubramanian V
Published: March 2010

An attempt has been made to develop an empirical relationship to predict the tensile strength of friction stir welded AZ31B magnesium alloy by incorporating process parameters such as tool rotational speed, welding speed, and axial force. The experiments were conducted based on three factors, three levels of central composite face centred design with a full replications technique. The developed relationship can be effectively used to predict the tensile strength of friction stir welded joints at the 95 per cent confidence level. The results indicate that tool rotational speed has the greatest influence on tensile strength, followed by welding speed and axial force.
High Value Manufacturing: A Case Study in Transformation
Authors: Bititci U S , Mendibil K T , Maguire C
Published: March 2010

In a continuously and rapidly changing global landscape, manufacturing organizations have to undertake transformational changes in order to stay in business. The aim of the current paper is to present an analysis of the transformation story of Highland Spring Limited through a high-value manufacturing lens. In order to achieve this, literature on high value manufacturing and organizational transformation is reviewed; Highland Spring's transformation story is described, including the research methods used; and finally, Highland Spring's transformation story is analysed and discussed. Findings suggest that while the literature on high value manufacturing provides adequate direction as to what high value manufacturing is and various models that could be pursued, it is the organizational transformation literature that provides guidance on how transformation to a high-value manufacturing model may be achieved. Further, the paper concludes that high value transformation is an emergent process comprising of a series of radical waves of change that is shaped by a guiding vision and the contextual factors.
Studies on the Behaviour of the Green Particulate Fluid Lubricant in Its Nano Regime when Machining AISI 1040 Steel
Authors: Ramana S V , Ramji K , Satyanarayana B
Published: March 2010

Significant advances, both practical and theoretical, have been made in understanding the behaviour of engineering materials when machining at higher cutting conditions. Nano-integrated manufacturing is a subject of immense interest for various sustainable engineered systems. Metal removal processes involve the generation of high cutting forces and temperatures. The use of proper lubricant to reduce forces and temperatures and to improve total cutting phenomena overall is an important aspect. The present investigation analysed a green, petroleum-free lubricant that is produced by mixing two environmentally benign components, canola oil and nano-crystalline boric acid. To study the influence of variation of nano-level boric acid particle size and its weight percentage on the performance of the proposed green particulate fluid lubricant, various turning tests were conducted on AISI 1040 steel using tungsten carbide inserts. Variations in cutting forces, tool temperatures and surface roughness were studied. The experimental results revealed that both cutting forces and tool temperatures increased as the boric acid particle size decreased. The surface quality of the machined surface was reduced as the solid lubricant particle size was reduced to the nano-level. Interestingly, reductions in both cutting force and tool temperature were observed as the boric acid weight percentage decreased, tending towards the pure canola oil-based machining results. The surface quality of the machined surface was also improved as the volume fraction of boric acid was decreased.
Effects of Different Heat Flux Schemes in Modelling of Transport Phenomena during Gas Tungsten Arc Welding of AA1050
Authors: Kohandehghan A R , Serajzadeh S
Published: March 2010

A three-dimensional model is utilized to predict temperature distribution and fluid flow during the process of gas tungsten arc welding (GTAW). In order to evaluate the effect of the heat flux model on the accuracy of predictions, two types of heat sources — with different natures based on Gaussian surface heat flux and volumetric Goldak's double-ellipsoid heat flux distributions — are taken into account. These heat flux schemes are input into a model simulation of GTAW of AA1050. In the next stage, the transient temperature distribution within the metal being welded is predicted for each heat flux model using FLUENT computational fluid dynamics software. The fusion and heat-affected zones are then determined and compared with each other as well as with experimental observations. The results show that the distribution and intensity of heat flux over the top surface of a workpiece have an important effect on the shape and dimensions of predicted weld pool geometry. Furthermore, the double-ellipsoid heat flux model results produced more realistic data than the Gaussian surface heat flux distribution for the welding conditions considered here.
Fracture Toughness of a Zirconia Engineering Ceramic and the Effects Thereon of Surface Processing with Fibre Laser Radiation
Authors: Shukla P P , Lawrence J , Wu H
Published: March 2010

Vickers hardness indentation tests were employed to investigate the near-surface changes in the hardness of a fibre laser-treated and an as-received ZrO2 engineering ceramic. Indents were created using 5, 20, and 30 kg loads to obtain the hardness. Optical microscopy, white-light interferometry, and a coordinate measuring machine were then used to observe the crack lengths and crack geometry. Palmqvist and half-penny median crack profiles were found, which dictated the selection of the group of equations used herein. Computational and analytical approaches were then adapted to determine the K1 c of ZrO2. It was found that the best applicable equation was: K1 c = 0.016 ( E/ H)1/2 ( P/ c3/2), which was confirmed to be 42 per cent accurate in producing K1 c values within the range of 8 to 12 MPa m1/2 for ZrO2. Fibre laser surface treatment reduced the surface hardness and produced smaller crack lengths in comparison with the as-received surface. The surface crack lengths, hardness, and indentation loads were found to be important, particularly the crack length, which significantly influenced the end K1 c value when K1 c = 0.016 ( E/ H)1/2 ( P/ c3/2) was used. This is because, the longer the crack lengths, the lower the ceramic's resistance to indentation. This, in turn, increased the end K1 c value. Also, the hardness influences the K1 c, and a softer surface was produced by the fibre laser treatment; this resulted in higher resistance to crack propagation and enhanced the ceramic's K1 c. Increasing the indentation load also varied the end K1 c value, as higher indentation loads resulted in a bigger diamond footprint, and the ceramic exhibited longer crack lengths.
Investigation and development of an innovative pigging technique for the water-supply industry
Authors: Quarini G , Ainslie E , Herbert M , Deans T , Ash D , Rhys D , Haskins N , Norton G , Andrews S , Smith M
Published: March 2010

Water-supply companies monitor the state of their pipe networks and ensure that the pipes are clean and free of inert loose deposits by flushing and pigging. Flushing involves forcing high speed water through the pipes so as to carry away particulates, pigging consists of forcing an object (the pig) through the pipe so as to push or wipe away the loose material. Both systems have drawbacks; the first tends to use very large volumes of water, and it may be impossible to get the required velocities in large-diameter pipes. The second requires purpose built launch and receive stations and may run the risk of damaging the pipe walls. This paper presents an innovative alternative to water flushing or conventional pigging for the potable-water-supply industry. This alternative uses a phase change material (ice—water slurry), which can be introduced into and removed from existing pipe networks with minimal alterations. The underlying concept is that when an ice slurry is propelled through pipes at modest speeds, the wall shear is two to four orders of magnitude higher than that which would have been achieved had water (only) been travelling in the pipe at the same speed. Thus, even with relatively low speeds, the ‘ice pig’ is able to achieve efficient cleaning and removal of loose materials. This technology has the advantage that the ice pig changes its shape to fit the containing topology, hence it is able to navigate bends, contraction/expansions and partly open vales, while cleaning the containment walls and transporting particulates. Lastly, the ice pig is guaranteed never to get stuck, as it will simply melt away, if left for sufficient time.

The paper presents laboratory experimental data, qualitatively demonstrating the capability of the technique and quantitative data enabling engineers to scale and size the ice pig for full scale trials. Finally, preliminary work from full scale trails on live water trunk mains is briefly presented and discussed.
Model reference adaptive switching control of a linearized hypersonic flight vehicle model with actuator saturation
Authors: Dong C , Hou Y , Zhang Y , Wang Q
Published: March 2010

In order to address the control of an air-breathing hypersonic flight vehicle (AHFV) with actuator saturation, a model reference adaptive switching control (MRASC) approach is proposed. The design of the MRASC system is centred around a linearized longitudinal-motion flexible model at a Mach 8, altitude of 10 000 ft, and dynamic pressure of 1017 lb/ft2 flight condition. A switched reference system (SRS) is established to describe the desired dynamics of the AHFV with/without actuator saturation, and correspondingly, a switched adaptive controller (SAC) is constructed utilizing the hyperstability method. By switching between the subsystems of the SRS and the corresponding subcontrollers of the SAC, the MRASC system achieves the desired performance and is globally asymptotically stable under limited disturbances, provided that a simple linear-matrix-inequality-based sufficient condition holds. Although it is too early to say that the proposed scheme gives desired anti-saturation performance with respect to large disturbances, within a large flight envelope, there are still some advantages that will improve performance.
Reversible Formation and Destruction of Micelles of Amphiphilic Compounds in Aqueous Media. Competition with Pseudorotaxane Formation
Authors: Suzaki Yuji , Taira Toshiaki , Osakada Kohtaro
Published: March 2010

N-Alkyl-4,4′-bipyridiniums [4,4′-bpy-N-(CH2)nOAr]+(Cl−) (n = 6 and 10, Ar = C6H3-3,5-t-Bu2, C6H3-3,5-(OMe)2, and C6H2-2,4,6-Me3), having the cationic bipyridinium group and a long hydrophobic alkyl chain, were prepared from the reaction of 4,4′-bipyridine with the corresponding alkyl chlorides. The amphiphilic compounds in water form micelles which encapsulate added pyrene in the hydrophobic core. Addition of α-cyclodextrin to the micellar solution converts a part of the aggregated amphiphilic molecules to their pseudorotaxane with α-cyclodextrin. Formation of the pseudorotaxanes is favored at lower temperature, as is observed by temperature dependent change of the absorption spectra.
One-Pot Synthesis and Fluorescence Properties of 2-Arylquinolines
Authors: Sueki Shunsuke , Okamoto Chiharu , Shimizu Isao , Seto Keisuke , Furukawa Yukio
Published: March 2010

The one-pot synthesis of 2-arylquinoline with arylamines, arylaldehyde, and 1,1-diethoxyethane were studied using a catalytic amount ytterbium triflate. Various 2-arylquinolines showed fluorescence properties and the fluorescence was quenched by introducing the nitro group into aryl moiety of 2-arylquinolines.
Crystal Structures of Two Vancomycin Complexes with Phosphate and N-Acetyl–d-Ala. Structural Comparison between Low-Affinity and High-Affinity Ligand Complexes of Vancomycin
Authors: Kikuchi Takanori , Karki Shyam , Fujisawa Ikuhide , Matsushima Yoshitaka , Nitanai Yasushi , Aoki Katsuyuki
Published: March 2010

Crystal structures of two vancomycin complexes with phosphate and N-acetyl–d-Ala (AcDA) were determined. Each complex involves two crystallographically independent vancomycin molecules (V1 and V2) in the asymmetric unit, which form a usually observed back-to-back arranged vancomycin dimer V1–V2 with two disaccharide chains packed in a head-to-head manner, but only one of the two ligand-binding sites is occupied. Comparison of the published crystal structures of low-affinity (small in molecular size) ligand complexes of vancomycin with high-affinity (large) ligand complexes reveals that when the high-affinity ligand binds, three structural factors (hydrogen-bonding interactions between the two peptide-backbones and hydrophobic intra-dimer sugar–ring and ring (face)–ring (edge) interactions) work to enhance the stabilization of the back-to-back dimer-interface, an important factor that is believed to promote antibacterial activity. It has also been revealed, by examining the high-affinity ligand complexes (including N-acetyl–d-Ala–d-Ala), that sugar–ligand interaction could cause different affinities of the two halves of the dimer; this is a factor responsible for the failure of the ligand binding to V1 in the AcDA complex. Possible scenarios for the formation of vancomycin complexes with low-affinity as well as high-affinity ligands are presented.
One-year outcomes of radiofrequency ablation of incompetent perforator veins using the radiofrequency stylet device
Authors: Marsh P , Price B A , Holdstock J M , Whiteley M S
Published: March 2010

Objectives

Early success treating incompetent perforator veins (IPVs) with radiofrequency ablation (RFA) and the trend to move varicose vein surgery into a walk-in walk-out service led to the design of a specific device enabling RFA of IPVs using local anaesthesia (ClosureRFS™ stylet). Our aim was to assess one-year outcomes of a clinical series of patients undergoing treatment with this device. Truncal reflux, where present, was treated initially, and RFA of IPVs was performed as a secondary procedure.

Method

Duplex ultrasound examinations were performed and the presence of IPVs documented. Results were compared with preoperative scans. IPVs were classified as closed, not closed/reopened or de novo.

Results

Of the 75 patients invited for follow-up, 53 attended at a median time of 14 months (range 11–25). Sixty-seven limbs were analysed (M:F 1:2.1, median age 62, range 25–81). Of the 124 treated IPVs, 101 were closed (82%). Clinical, aetiological, anatomical and pathological clinical score was improved in 49.3% limbs. IPV closure was reduced in patients with recurrent varicose veins compared with primary varicose veins (72.3% versus 87%, P = 0.056).

Conclusion

These results demonstrate the radiofrequency stylet device to be an effective treatment for IPVs.
The use of prophylaxis in patients undergoing diagnostic tests for suspected venous thromboembolism
Authors: Lee J-A , Zierler B K
Published: March 2010

Objectives

The purpose of this study was to describe the use of pharmacological and mechanical prophylaxis and clinical outcomes of patients undergoing diagnostic tests for suspected venous thromboembolism (VTE).

Methods

The medical records of 660 consecutive inpatients referred for suspected VTE at an academic medical centre were retrospectively reviewed.

Results

Acute VTE was diagnosed in 138 (21%) of the 660 patients; the incidence of deep vein thrombosis and pulmonary embolism was 18–25%, respectively. Only 61% of eligible patients received pharmacological prophylaxis and 43% of patients received mechanical prophylaxis. The incidence of VTE was higher in patients who did not receive pharmacological prophylaxis (30%) compared with patients who did (16%, P value <0.001).

Conclusions

Preventive measures for VTE, including both pharmacological and mechanical prophylaxis, were underutilized in hospitalized patients undergoing diagnostic tests for suspected VTE.
Firm Size and Industry Structure Under Human Capital Intensity: Insights from the Evolution of the Global Advertising Industry
Authors: von Nordenflycht Andrew
Published: March 2010

Although existing literature assumes that the human capital intensity of professional services leads to small and flimsy firms, several professional services feature large, long-lived firms. To develop insights about firm size and industry structure in human capital intensive industries, I analyze the structure and evolution of the advertising industry. Drawing on a range of quantitative and qualitative evidence, I develop two hypotheses regarding the industry's structure and consolidation: (1) size differentiation, in which firm size and industry structure are connected to the size distribution of clients' projects, and (2) financial intermediation, in which the industry's consolidation is ascribed to organizational innovations that mitigate transaction costs between external investors and ad agency owners. I then discuss the applicability of these two hypotheses to other professional services. The analysis suggests several new insights about the value of capital, the nature of demand, and the nature of assets in human capital intensive industries.
Managing Organizational Change: Negotiating Meaning and Power-Resistance Relations
Authors: Thomas Robyn , Sargent Leisa D. , Hardy Cynthia
Published: March 2010

Theoretical developments in the analysis of organizations have recently turned to an “organizational becoming” perspective, which sees the social world as enacted in the microcontext of communicative interactions among individuals through which meaning is negotiated. According to this view, organizational change is endemic, natural, and ongoing; it occurs in everyday interactions as actors engage in the process of establishing new meanings for organizational activities. We adopt this approach to study how meanings were negotiated by senior and middle managers in a workshop held as part of a culture change program at a telecommunications company. Our study identifies two very different patterns in these negotiations, constituted by the particular communicative practices adopted by participants. We discuss the implications of these patterns for organizational change in relation to generative dialogue and power-resistance relations between senior and middle managers.
Too Good to Be True? The Unintended Signaling Effects of Educational Prestige on External Expectations of Team Performance
Authors: Sauer Stephen J. , Thomas-Hunt Melissa C. , Morris Patrick A.
Published: March 2010

In this paper we report the results of two experimental studies designed to test how demographic characteristics affect outsiders' assessments of a firm's top managers. We draw on theories of evaluation and status characteristics to examine the interactive effects of managers' racial characteristics and educational prestige on external perceptions. In the first study, we find that top executives' educational background and race affected analysts' valuation of a firm's stock. Outside analysts made the highest stock price projections for firms led by white executives who had highly prestigious educational backgrounds but made the lowest valuations for firms led by African Americans with the same prestigious education. We posit that the moderating effect of executives' racial characteristics stems from outsiders' assumptions that African American managers received preferential treatment in the admissions process for high prestige universities. In the second study, we find that when we explicitly removed the possibility of preferential selection, analysts gave the same stock valuation to firms led by white and African American executives with high educational prestige. We discuss the implications of these findings for theory and management.
Ilizarov principles of deformity correction
Authors: Spiegelberg B , Parratt T , Dheerendra SK , Khan WS , Jennings R , Marsh DR
Published: March 2010

Ilizarov frames provide a versatile fixation system for the management of bony deformities, fractures and their complications. The frames give stability, soft tissue preservation, adjustability and functionality allowing bone to realise its full osteogenic potential. It is important that we have a clear and concise understanding of the Ilizarov principles of deformity correction to best make use of this fixation system. In this review article, the history of Ilizarov frame, the basic sciences behind it, the mechanical principles governing its use and the clinical use of the fixation system are discussed.
Anatomical failure following laparoscopic antireflux surgery (LARS); does it really matter?
Authors: Dunne N , Stratford J , Jones L , Sohampal J , Robertson R , Booth MI , Dehn TCB
Published: March 2010

INTRODUCTION

Failure rates of laparoscopic antireflux surgery (LARS) vary from 2–30%. A degree of anatomical failure is common, and the most common failure is intrathoracic wrap herniation. We have assessed anatomical integrity of the crural repair and wrap using marking Liga clips placed at the time of surgery and compared this with symptomatic outcome.

PATIENTS AND METHODS

A prospective study was undertaken on 50 patients who underwent LARS in a single centre over a 3-year period. Each had an X-ray on the first postoperative day and a barium swallow at 6 months at which the distance was measured between the marking Liga clips. An increase in interclip distance of > 25–49% was deemed ‘mild separation’, and an increase of > 50% ‘moderate separation’. Patients completed a standardised symptom questionnaire at 6 months.

RESULTS

At 6 months' postoperatively, 22% had mild separation of the crural repair with a mean Visick score of 1.18, and 54% had moderate separation with a mean Visick score of 1.26. Mild separation of the wrap occurred in 28% with a mean Visick score of 1.21 and 22% moderate separation with a mean Visick score of 1.18. Three percent had mild separation of both the crural repair and wrap with a mean Visick score of 1.0, and 16% moderate separation with a mean Visick score of 1.13. Of patients, 14% had evidence of some degree of failure on barium swallow but only one of these was significant intrathoracic migration of the wrap which was symptomatic and required re-do surgery.

CONCLUSIONS

The prevalence of some form of anatomical failure, as determined by an increase in the interclip distance, is high at 6 months' postoperatively following LARS. However, this does not seem to correlate with a subjective recurrence of symptoms.