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Selected AbstractsGrowth and characterization of Nd, Yb , yttrium oxide nanopowders obtained by sol-gel methodCRYSTAL RESEARCH AND TECHNOLOGY, Issue 12 2007A. Rzepka Abstract Nanopowders of Y2O3 pure, doped and codoped by Nd3+, Yb3+ were obtained by sol-gel method. Solution with ethylene glycol was choosed as the proper solution where crystallites of powder with Nd and Yb dopants had the same size. Finally the one-phased compounds of Y2O3 doped 0.5 at% Nd and 1, 2 or 4 at% Yb were obtained. Grain growth and their morphology were investigated in various temperature and time of heating. The changes of crystallite sizes and lattice constants in relation to the heating time and temperature for the composition Y2O3 doped 0.5 at% Nd and 2 at% Yb are presented. Y2O3 containing 0,5 at% of Nd exhibits intense luminescence bands centered at 920 nm, 1100 nm and 1360 nm whereas a single band at about 1020 nm appears in samples co-doped with neodymium and ytterbium. Luminescence spectra recorded did not depend on the sample preparation procedure and size of grains. OH impurity affects critically the relaxation dynamics of luminescent ion in nanopowders. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Seismic response analysis of multidrum classical columnsEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 10 2005Dimitrios Konstantinidis Abstract This paper presents a numerical investigation on the seismic response of multidrum classical columns. The motivation for this study originates from the need to understand: (a) the level of ground shaking that classical multidrum columns can survive, and (b) the possible advantages or disadvantages of retrofitting multidrum columns with metallic shear links that replace the wooden poles that were installed in ancient times. The numerical study presented in this paper is conducted with the commercially available software Working Model 2DŌ, which can capture with fidelity the sliding, rocking, and slide-rocking response of rigid-body assemblies. This paper validates the software Working Model by comparing selected computed responses with scarce analytical solutions and the results from in-house numerical codes initially developed at the University of California, Berkeley, to study the seismic response of electrical transformers and heavy laboratory equipment. The study reveals that relative sliding between drums happens even when the g -value of the ground acceleration is less than the coefficient of friction, µ, of the sliding interfaces and concludes that: (a) typical multidrum classical columns can survive the ground shaking from strong ground motions recorded near the causative faults of earthquakes with magnitudes Mw=6.0,7.4; (b) in most cases multidrum classical columns free to dislocate at the drum interfaces exhibit more controlled seismic response than the monolithic columns with same size and slenderness; (c) the shear strength of the wooden poles has a marginal effect on the sliding response of the drums; and (d) stiff metallic shear links in-between column drums may have an undesirable role on the seismic stability of classical columns and should be avoided. Copyright © 2005 John Wiley & Sons, Ltd. [source] Demographics of the spawning aggregations of four catostomid species in the Savannah River, South Carolina and Georgia, USAECOLOGY OF FRESHWATER FISH, Issue 2 2008T. B. Grabowski Abstract,,, Differences in the life history strategies employed by otherwise ecologically similar species of a fish assemblage may be an important factor in the coexistence of these species and is an essential consideration in the conservation and management of these assemblages. We collected scales to determine age and growth of four species of the catostomid assemblage (northern hogsucker Hypentelium nigricans, spotted sucker Minytrema melanops, notchlip redhorse Moxostoma collapsum and robust redhorse Moxostoma robustum) of the Savannah River, Georgia,South Carolina in spring 2004 and 2005. Robust redhorse was the largest species; reaching sexual maturity at an older age and growing faster as a juvenile than the other species. Spotted sucker did not achieve the same size as robust redhorse, but reached sexual maturity at younger ages. Notchlip redhorse was intermediate between the abovementioned two species in age at maturity and size. Northern hogsucker was the smallest species of the assemblage and reached the sexual maturity at the age of three. Both robust redhorse and spotted sucker were sexually dimorphic in size-at-age. The range of life history strategies employed by Savannah River catostomids encompasses the range of life history strategies exhibited within the family as a whole. [source] A cost analysis of ranked set sampling to estimate a population meanENVIRONMETRICS, Issue 3 2005Rebecca A. Buchanan Abstract Ranked set sampling (RSS) can be a useful environmental sampling method when measurement costs are high but ranking costs are low. RSS estimates of the population mean can have higher precision than estimates from a simple random sample (SRS) of the same size, leading to potentially lower sampling costs from RSS than from SRS for a given precision. However, RSS introduces ranking costs not present in SRS; these costs must be considered in determining whether RSS is cost effective. We use a simple cost model to determine the minimum ratio of measurement to ranking costs (cost ratio) necessary in order for RSS to be as cost effective as SRS for data from the normal, exponential, and lognormal distributions. We consider both equal and unequal RSS allocations and two types of estimators of the mean: the typical distribution-free (DF) estimator and the best linear unbiased estimator (BLUE). The minimum cost ratio necessary for RSS to be as cost effective as SRS depends on the underlying distribution of the data, as well as the allocation and type of estimator used. Most minimum necessary cost ratios are in the range of 1,6, and are lower for BLUEs than for DF estimators. The higher the prior knowledge of the distribution underlying the data, the lower the minimum necessary cost ratio and the more attractive RSS is over SRS. Copyright © 2005 John Wiley & Sons, Ltd. [source] Investment in Mate Guarding May Compensate for Constraints on Ejaculate Production in the Cricket Gryllodes sigillatusETHOLOGY, Issue 12 2001Philip W. Bateman Although there is a corpus of evidence that females of many taxa are choosy about males, there is less information on how males may react to females of different ,quality' (i.e. potential fecundity). The cricket Gryllodes sigillatus shows distinct mate guarding behaviour. We examined how long males mate guard females of different sizes (reflecting egg load and potential fecundity). We also examined the sperm number in ampullae donated to females of different sizes to see if males make a concomitant difference in investment in ejaculate. We also examined mate-guarding behaviour and ejaculate size of males mated to virgin and nonvirgin females of the same size to see if males equate size with increased age and increased likelihood of mating (increased sperm competition). The results showed that males mate guard larger females for longer but make no difference in ejaculate investment between sizes of female. Males make no significant difference in mate guarding investment or ejaculate investment between virgins and nonvirgins of the same size. There is evidence that other species of crickets do alter their ejaculate depending on the female size and mating history, but have less distinct guarding behaviour. We suggest that mate-guarding investment in G. sigillatus may serve a similar function to that of ejaculate investment in other crickets. [source] A comparison of spreader penetration depth and load required during lateral condensation in teeth prepared using various root canal preparation techniquesINTERNATIONAL ENDODONTIC JOURNAL, Issue 8 2005S. F. Dulaimi Abstract Aim, To compare the influence of various root canal preparation techniques on spreader penetration depth and load required during lateral condensation with gutta-percha and sealer. Methodology, Eighty extracted human teeth with single and straight canals were used. Twenty teeth were instrumented using one of four root canal preparation techniques. The four preparation techniques were: step-back technique without Gates-Glidden drills, step-back technique with Gates-Glidden drills, crown-down pressureless technique and hybrid technique (step-down/step-back). After root canal preparation had been completed a simulated periodontal ligament was fabricated from a uniform layer of silicone impression material. The roots were then mounted in an acrylic resin to simulate the physical condition found in tooth socket. A standardized stainless steel hand spreader of the same size as the master apical file was mounted in an Instron testing machine and lateral compaction with gutta-percha and sealer was performed. The load value was recorded from the Instron testing machine. The spreader penetration depths were measured with an endodontic ruler. The data obtained were analysed statistically using anova and Student's t -tests. Results, No significant difference in initial spreader load needed to condense the master cone was found amongst the four canal preparation techniques (P > 0.05). The step-back technique with Gates-Glidden drills and the hybrid technique demonstrated the least difference between the initial spreader penetration and the working length (mean 1.925 and 2.25 mm, respectively). The step-back technique without Gates-Glidden drills and the crown-down pressureless technique had the greatest difference between initial spreader penetration and the working length (mean 4.425 and 4.75 mm, respectively). Conclusion, The flare created by canal preparation affected spreader penetration depth, but had no effect on the spreader load. [source] Evaluation of smear layer removal by EDTAC and sodium hypochlorite with ultrasonic agitationINTERNATIONAL ENDODONTIC JOURNAL, Issue 5 2002D. M. Z. Guerisoli Abstract Aim To evaluate smear layer removal by different irrigating solutions under ultrasonic agitation. Methodology Twenty recently extracted mandibular incisors with a single root canal were divided into four equal groups. Three groups were instrumented using the modified double-flared technique, the fourth remained unprepared. Each group was irrigated with either distilled water, 1.0% sodium hypochlorite alone or associated with 15% EDTAC between each file size. The final group was not instrumented but irrigated with 1.0% sodium hypochlorite and 15% EDTAC. A size 15 file energised by ultrasound was used with small amplitude filing movements against the canal walls in all groups. The teeth were split longitudinally and the roots measured to provide three sections of the same size (cervical, middle and apical). Samples were examined under the scanning electron microscope and assessed for the amount of smear layer by three independent and calibrated examiners. The scoring system ranged from 1 (no smear layer) to 4 (all areas covered by smear layer). Due to the non-parametric nature of the data, Friedman's test was used for statistical analysis. Results Canal walls were covered with smear layer in the group irrigated with 1% sodium hypochlorite alone and the group irrigated with distilled water. Canals irrigated with 1.0% sodium hypochlorite associated with 15% EDTAC had less smear layer throughout the canal (P < 0.001). There were no statistical differences for the amount of smear layer found on the cervical, middle and apical thirds when each group was analysed separately. Conclusions Under ultrasonic agitation, sodium hypochlorite associated with EDTAC removed the smear layer from root canal walls, whereas irrigation with distilled water or 1.0% sodium hypochlorite alone did not remove smear layer. [source] Effective elastic properties of the double-periodically cracked platesINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 15 2005G. S. Wang Abstract In this paper, the interaction of double-periodical cracks is accurately solved based on the isolating analysis procedure, superposition principle, pseudo-traction method, Chebyshev polynomial expansion and crack-surface collocation technique. The jump displacement crossing crack faces, the average additional strain and therefore the effective compliance of the double-periodically cracked plate are directly determined. The numerical results for axial-symmetrically distributed double-periodical cracks, general double-periodical cracks with one collinear direction as well as two sets of double-periodical cracks with same size and square distribution are given in this paper. And the partial typical numerical results are compared with the previous works. The analysis shows that the anisotropy induced by the general double-periodical cracks is generally not orthogonal anisotropy. Only when the double-periodical cracks are axial-symmetrically distributed, is the anisotropy orthogonal. In this special cases, the effective engineering constants (consist of effective elastic modulus, the effective Poisson's ratio, the effective shear modulus) of cracked plate versus crack spacing, in the plane stress and plane strain conditions, respectively, are analysed. Copyright © 2005 John Wiley & Sons, Ltd. [source] Intraepidermal animal-type melanomaINTERNATIONAL JOURNAL OF DERMATOLOGY, Issue 8 2006DiplomateNB, S. Punjabi MBBS Animal-type melanoma is a rare variant of melanoma in humans.1 Its name is derived from its histological appearance, which is similar to that described in melanomas occurring in white or gray horses.2 All tumors are dermally located, and characterized by a proliferation of deeply pigmented elongated or rounded cells, showing moderate atypia and a low mitotic rate. In some tumors, secondary infiltration of the epidermis has been noted. More than half of the patients are younger than 30 years, and prognosis seems to be much better than that expected for a superficial spreading or nodular melanoma of the same size. We report the first case of animal-type melanoma in situ. [source] An experimental and mathematical study of efforts of a novel photovoltaic-Trombe wall on a test roomINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 6 2008Ji Jie Abstract A novel photovoltaic-Trombe wall (PV-TW) is proposed and investigated experimentally and theoretically in this paper. The PV-TW was installed at the south-facing external wall of an environmental chamber that carried two identical test rooms. Both of the test rooms have a double window of the same size. One test room was installed with the PV-TW (known as the PV-TW room), and the other without PV-TW (known as the reference room). The influence of the PV-TW on the thermal environment of the test room was investigated under different operating conditions. The experimental results show the dual benefits of the PV-TW system: improving the room thermal condition and at the same time generating electricity. Compared with the reference room, the maximum indoor temperature was found to be 5,7°C higher in winter, and the daily electrical output reached about 0.3,kWh with a PV cell area of 0.72,m2. Also, a detailed model is given to evaluate the performance of PV-TW theoretically, and the PV-TW room is simulated under one certain operating condition. The simulated and measured air temperatures of PV-TW room are found to be in good agreement. Copyright © 2007 John Wiley & Sons, Ltd. [source] Shape of ,-crystallin analyzed by small-angle neutron scatteringJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2007Masaaki Sugiyama The size and shape of aggregates of human recombinant ,A-crystallin and ,B-crystallin are investigated with small-angle neutron scattering and dynamic light scattering. At a bioactive temperature (310,K), both polypeptides form aggregates with almost the same size and shape. The ,B-crystallin maintains an almost identical size and shape at 310 and 288,K, whereas the aggregate of ,A-crystallin shows deformation at 288,K. This result suggests that at the lower temperature there is a difference in structural stability between the two aggregates of the polypeptides. [source] Bone-specific heparan sulfates induce osteoblast growth arrest and downregulation of retinoblastoma proteinJOURNAL OF CELLULAR PHYSIOLOGY, Issue 1 2006Kerry J. Manton The heparan sulfate (HSs) sugars of the extracellular matrix (ECM) play a key role during both development and wound repair in regulating the flow of growth and adhesive factors across their cell surface receptors. The aim of this study was to assess the structural and functional differences of HS chains extracted from the conditioned media (soluble), cell surface, and ECM of primary human osteoblast cultures, and to analyze their effects on osteoblast cell growth. HS chains from these compartments were characterized through a combination of enzymatic degradation, anion exchange chromatography, and molecular sieving. Although the chains were all approximately the same size, they varied systematically in their sulfate content, suggesting differences in their protein-binding domains. When added to pre-confluent hFOB1.19 osteoblast cultures, HS doses exceeding 500 ng/ml inhibited proliferation, without affecting viability, irrespective of their origin. Furthermore, HS doses of 500 ng/ml also downregulated retinoblastoma, Cyclin A and CDK1 protein expression, indicating that high doses of osteoblast HS negatively regulate cell cycle, resulting in growth arrest; when high doses of HS were withdrawn after a prolonged period, linear cell growth was reestablished. Thus, despite differences in sulfation, HS from either the soluble, cell surface, or matrix compartments of primary human osteoblast cultures are functionally similar with respect to their effects on growth. Binding assays revealed that the HS chains bound TGF,1, a known inhibitor of osteoprogenitor growth, at higher affinity than a suite of other bone-related, heparin-binding growth factors. Overcoming such sugar-mediated inhibition may prove important for wound repair. J. Cell. Physiol. 209: 219,229, 2006. © 2006 Wiley-Liss, Inc. [source] The effect of temperature and somatic growth on otolith growth: the discrepancy between two clupeid species from a similar environmentJOURNAL OF FISH BIOLOGY, Issue 3 2006D. P. Fey Otolith growth rates of the early life stages of herring Clupea harengus (n= 472) and smelt Osmerus eperlanus (n= 348) collected in the Vistula Lagoon (Baltic Sea) during 1997,1999 were analysed. The larvae and early juveniles were not only collected in the same geographical area they were also of the same size (range 15,43 mm standard length, LS), similar ages and were collected during the same seasons (May to July). Although the two clupeid species experienced very similar environmental conditions, there were significant discrepancies in the analysed relationships. The otolith growth of larval and juvenile smelt was very strongly related to somatic growth while temperature had a minor effect. In herring, the effect of somatic growth, although clearly visible and statistically highly significant, was of less importance than temperature. Furthermore, variation in the otolith size and LS relationship was affected by temperature and somatic growth in both species, but the variance of otolith size at LS was higher for herring than for smelt. Although growth backcalculation from otoliths can presently be recommended as an appropriate method for use with both smelt and herring (despite possibly lower precision and accuracy with the latter), other methods referring directly to short-term increment width changes (e.g. marginal increment analysis) are recommended for smelt but not for herring. [source] Variation of reproductive behaviour and success of males adopting different tactics in Atlantic salmonJOURNAL OF FISH BIOLOGY, Issue 2003B. De Gaudemar Six males and five females anadromous Atlantic salmon were released in two sections of the Lapitxuri experimental stream (Southwest France), where they could reproduce naturally. Females had all the same size and age, contrary to males. We focussed our attention on the variation with time of spawning tactics and success of males. Two factors affected male spawning behaviour in the short term. An increase of the OSR increased the level of male competition around redds which resulted in a larger number of males adopting sneaking rather than fighting tactics. Changes in female activities also seemed to be detected by males, since male aggressiveness increased when females were close to oviposition. But whatever their activities, males preferentially courted the earlier spawning female when two females were active at the same time. Fighting in males was confirmed to be the most successful tactic at a given time. However, males adopting sneaking tactic at the beginning of the spawning season could dramatically increase their reproductive success in the long-term. Fighting males invested much more energy in contests than secondary males, which may constitute a handicap in terms of longevity. They could quickly lose their status or strength with time which, although placed in a situation of high OSR, resulted in greater numbers of previously low-ranking males adopting satellite and fighting tactics during the period preceding oviposition. Age more than size affected male status and reproductive success. Females seemed to select their mate directly in relation to their physiological condition, since they only attacked dull coloured males showing obvious wound marks. They also could indirectly choose their mate by repeatedly leaving the redd during the period preceding oviposition in a situation of high OSR. This behaviour might incite male competition and also promoted, by incessant attempts of secondary males to rob the more successful status of primary males, their chance to spawn with fitter males. These results emphasized the importance of environment, physiological condition and energy expenditure in allocation tactics and variations in salmon reproductive success throughout the spawning season. This led us to hypothesize that the choice of sneaking through conditional strategies might provide greater average fitness in salmon alternative life histories. [source] Structure of nanometre-sized Xe particles embedded in Al crystalsJOURNAL OF MICROSCOPY, Issue 3 2004M. SONG Summary The structure and lattice parameters of Xe particles about 1 nm to about 6 nm in size embedded in Al were investigated with off-Bragg condition high-resolution transmission electron microscopy. An Xe particle about 1 nm in size had different structural properties from those 2,6 nm in sizes. Some 1-nm Xe particles had an face-centred cubic (f.c.c.) structure with the same orientation as the Al matrix, whereas others of the same size had a non-f.c.c. structure. The lattice parameters of a 1-nm f.c.c. Xe particle were about 20% smaller than the average value obtained from electron diffraction, i.e. the particle was compressed by about 80%. The lattice parameters of Xe crystals about 2 nm to about 6 nm in size were almost the same as those obtained from diffraction results. One of the reasons for the extra compression seen with a 1-nm Xe particle is the increase in pressure inside an Xe particle with decreasing particle size. [source] Undergraduate students' understanding of falling bodies in idealized and real-world situationsJOURNAL OF RESEARCH IN SCIENCE TEACHING, Issue 6 2004M. Veronica Cahyadi This study investigates the understanding of 18 first-year undergraduate students when simultaneously presented with two contrasting dynamical situations: the idealized (without air resistance) and real-world cases of balls being dropped or thrown. Previous work has shown that getting students to recognize flaws in their mental models helps them develop their understanding. Our students were better able to answer correctly the problems in idealized cases than the problems in real-world cases. For the real-world cases, the students understood the impact of air resistance on the object's size better than the impact of air resistance on objects of the same size but different mass. In follow-up interviews, the students reported that using the two different situations in the same test did indeed encourage them to think more carefully. By recognizing the need to include air resistance, they activated their appropriate mental "resources" to deal with the situations. We conclude that using contrasting situations (i.e., with and without an idealization) is a useful teaching tool. © 2004 Wiley Periodicals, Inc. J Res Sci Teach 41: 569,583, 2004 [source] Bed Stability and Sedimentation Associated With Human Disturbances in Pacific Northwest Streams,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 2 2009Philip R. Kaufmann Abstract:, To evaluate anthropogenic sedimentation in United States (U.S.) Pacific Northwest coastal streams, we applied an index of relative bed stability (LRBS*) to summer low flow survey data collected using the U.S. Environmental Protection Agency's Environmental Monitoring and Assessment Program field methods in a probability sample of 101 wadeable stream reaches. LRBS* is the log of the ratio of bed surface geometric mean particle diameter (Dgm) to critical diameter (D*cbf) at bankfull flow, based on a modified Shield's criterion for incipient motion. We used a formulation of LRBS* that explicitly accounts for reductions in bed shear stress that result from channel form roughness due to pools and wood. LRBS* ranged from ,1.9 to +0.5 in streams within the lower quartile of human riparian and basin disturbance, and was substantially lower (,4.2 to ,1.1) in streams within the upper quartile of human disturbance. Modeling results suggest that the expected range of LRBS* in streams without human disturbances in this region might be generally between ,0.7 and +0.5 in either sedimentary or volcanic lithology. However, streams draining relatively soft, erodible sedimentary lithology showed greater reductions in LRBS* associated with disturbance than did those having harder, more resistant volcanic (basalt) lithology with similar levels of basin and riparian disturbance. At any given level of disturbance, smaller streams had lower LRBS* than those with larger drainages. In sedimentary lithology (sandstone and siltstone), high-gradient streams had higher LRBS* than did low-gradient streams of the same size and level of human disturbance. High gradient streams in volcanic lithology, in contrast, had lower LRBS* than low-gradient streams of similar size and disturbance. Correlations between Dgm and land disturbance were stronger than those observed between D*cbf and land disturbance. This pattern suggests that land use has augmented sediment supplies and increased streambed fine sediments in the most disturbed streams. However, we also show evidence that some of the apparent reductions in LRBS*, particularly in steep streams draining small volcanic drainages, may have resulted in part from anthropogenic increases in bed shear stress. The synoptic survey methods and designs we use appear adequate to evaluate regional patterns in bed stability and sedimentation and their general relationship to human disturbances. More precise field measurements of channel slope, cross-section geometry, and bed surface particle size would be required to use LRBS* in applications requiring a higher degree of accuracy and precision, such as site-specific assessments at individual streams. [source] Comparison of Development and Larval Growth of Four Venerid ClamsJOURNAL OF THE WORLD AQUACULTURE SOCIETY, Issue 2 2005Young-Baek Hur The development and larval morphology of four venerid calms, Ruditapes philippinarum, Mactra veneriformis, Cyclina sinensis, and Meretrix lusoria, which cohabit the intertidal zone in western coastal Korea, were compared using laboratory culture techniques. At 87 ,m, the fertilized eggs of C. sinensis and M. lusoria were the largest and at 53 ,m, those of M. veneriformis were the smallest. D-shaped larvae of M. lusoriu were the largest and those of M. veneriformis were the smallest measuring at 135 ,m and 89 ,m, respectively. D-shaped larvae of R. philippinarum and M. lusoria had symmetrical shoulder angles and an elliptical ventral form, in contrast to the asymmetrical shoulder angles and round ventral forms of M. veneriformis and C. sinensis. In general, pediveliger larvae of all species in the study were yellow, but those of M. veneriforks and C sinenis were a more pronounced yellow. In between the early D-shaped and pediveliger stage, 7 and 17 d elapsed for M. lusonia and C. sinensis larvae, respectively. In the early larval stages for all species, the sheU length was longer than the height. However, shell length and height later became approximately the same size in all species except R. philippinarum, which exhibited a flat shape. These results indicate that for these four venerid clams, the different characteristics in larval growth and external morphology provide the evidence necessary for larval identification of natural seed production despite the fact that they spawn concurrently in the intertidal zone. [source] Using scissors to quantify hardness of insects: do bats select for size or hardness?JOURNAL OF ZOOLOGY, Issue 4 2007P. W. Freeman Abstract Scissors are used to determine the hardness of fresh insects of different size and taxa. Our results indicate a strong relationship between the size of an insect and its hardness, which can be expressed as log(Fmax)=0.65 × log(V)+,. Fmax is the maximal force needed to cut the insect and is our measure of insect hardness. V is the volume of the insect and , is a constant that can be derived for different insect taxa. The value of 0.65 was found as an average of beetle and moth samples, and this number appears consistent across insect taxa. We found that beetles averaged about 3.2 times harder than moths of the same size. Beetles were also more variable in hardness than moths, with the softest beetles about equal in hardness to an average moth of the same size. Using our data on insect hardness coupled with data on the diets of bats and their bite forces from the literature, we attempt to determine whether the upper size limit of insects taken by a bat is limited by the insect's dimensions or its hardness. Our results indicate that both these factors may be important. [source] Relative fatigue life estimation of cylindrical hollow rollers in general pure rolling contactLUBRICATION SCIENCE, Issue 1 2008Wisam M. Abu Jadayil Solid and hollow cylindrical rollers in pure rolling contact have been modelled. The two rollers are subjected to a combined normal and tangential loading. The tangential loading is one-third of the normal loading value. The finite element package, ABAQUS, is used to study the stress distribution and the resulting deformations in the bodies of the rollers. Then the Ioannides,Harris fatigue life model for rolling bearings is applied on the ABAQUS numerical results to investigate the fatigue life of the solid and hollow rollers. Using the fatigue life of the solid rollers as the reference fatigue life, the relative fatigue lives of hollow rollers are determined. Four main different hollowness percentages are been studied: 20, 40, 60 and 80%. The hollowness percentage is the ratio of the diameter of the hole to the outer diameter of the cylinder. For each of those hollowness percentages, two cases are studied , when the two rollers in contact are hollow and when one hollow roller is in contact with a solid roller. This study includes two main models: Model 1, where the two cylindrical rollers in contact are of the same size, and Model 2, where the two rollers in contact are not of the same size. The estimated relative fatigue lives of hollow rollers showed a great improvement of the fatigue life compared with solid rollers under the same loading conditions. This was a result of the redistribution of stresses in the contact zone in the case of hollow rollers. Redistribution of stresses over a larger volume of the roller body decreased the peak stress and reduced the volume under risk. Increasing the hollowness percentage from 20 to 60% increased the flexibility of the roller, and better stress distribution was achieved, which resulted in improving the fatigue life. Although 80% of hollowness rollers have more flexibility than 60% of hollowness rollers, the bending stresses (,b) on the inner surface of the rollers tend to decrease the fatigue life. Copyright © 2007 John Wiley & Sons, Ltd. [source] Models of Irregular Hyperbranched Polymers: Topological Disorder and Mechanical ResponseMACROMOLECULAR THEORY AND SIMULATIONS, Issue 7 2006Thorsten Koslowski Abstract Summary: We study the impact of topological disorder on the mechanical response of hyperbranched macromolecules from a theoretical and numerical perspective. The polymer models are generated using a bond switching algorithm, and the emerging systems are described within the Zimm and Rouse pictures of macromolecular dynamics. The topological disorder is manifest in the frequency-dependent dynamic moduli, . These are clearly distinct from that of regular hyperbranched fractals of the same size, and they do not obey simple scaling rules. The dynamic moduli reflect the short-range order inherent in the model, and we thus suggest that the extent of disorder in branched tree-like polymers may be well-estimated experimentally using . Model of an irregular hyperbranched polymer. [source] Wide-range length metrology by dual-imaging-unit atomic force microscope based on porous aluminaMICROSCOPY RESEARCH AND TECHNIQUE, Issue 3 2004Dongxian Zhang Abstract A new dual-imaging-unit atomic force microscope (DIU-AFM) was developed for wide-range length metrology. In the DIU-AFM, two AFM units were combined, one as a reference unit, and the other a test one. Their probes with Z piezo elements and tips were horizontally set in parallel at the same height to reduce errors due to geometric asymmetry. An XY scanner was attached to an XY block that was able to move in the X direction with a step of about 500 nm. A standard porous alumina film was employed as the reference sample. Both reference sample and test sample were installed at the center of the XY scanner on the same surface and were simultaneously imaged. The two images had the same lateral size, and thus the length of the test sample image could be accurately measured by counting the number of periodic features of the reference one. The XY block together with the XY scanner were next moved in the X direction for about 1.5 ,m and a second pair of reference and test images were obtained by activating the scanner. In this way, a series of pairs of images were acquired and could be spliced into two wide-range reference and test images, respectively. Again, the two spliced images were of the same size and the length of test image was measured based on the reference one. This article presents a discussion about the structure and control of the DIU-AFM system. Some experiments were carried out on the system to demonstrate the method of length calculation and measurement. Experiments show a satisfactory result of wide-range length metrology based on the hexagonal features of the porous alumina with a periodic length of several tens of nanometers. Using this method the DIU-AFM is capable of realizing nanometer-order accuracy length metrology when covering a wide range from micron to several hundreds of microns, or even up to millimeter order. Microsc. Res. Tech. 64:223,227, 2004. © 2004 Wiley-Liss, Inc. [source] A Ka-band equal-branch waveguide power dividerMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 11 2007Yunchuan Guo Abstract A Ka-band equal-branch waveguide power divider is proposed in this letter. This waveguide power divider has the uniform main guide and all the branches in same size to minimize the difficulty and sensitivity in the mechanical fabrication. Full-wave simulation and in-door measurement are also carried to validate this design. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2637,2639, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22811 [source] Circularly polarized proximity-coupled microstrip antennasMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 5 2005Yi-Lung Lee Abstract A novel design for the production of circularly polarized radiation (CP) in proximity-fed microstrip antennas is presented. To achieve this circular-polarization design, the two orthogonal modes of the microstrip antenna are excited in series through the proximity coupling of an L-shaped open microstrip line. The experimental results show that the 3-dB axial-ratio CP bandwidth of the proposed design is increased by more than 30%, as compared to a conventional CP microstrip antenna of the same size. The details of the simulated and experimental results for the proposed design are presented and discussed. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 46: 429,430, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21006 [source] Evaluation of the reflected phase of a patch using waveguide simulator for reflectarray designMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 6 2005N. Lenin Abstract This paper presents the measured reflected phase-variation curves for microstrip-patch elements of variable size, which form the most essential part in the design of a reflectarray antenna. A waveguide simulator exploiting the concept of infinite array is successfully implemented in the characterization of reflected phase, which avoids the need for large arrays for the empirical design of an element. A set of seven microstrip-array samples, each consisting of three square elements of the same size designed at 10 GHz, is measured. A comparison of the simulations using the finite-element method and the measured results shows good agreement. The phase variation is in the range of +167° to ,178° for a patch-size variation of 5.5 to 13 mm. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 45: 528,531, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20869 [source] Heterogeneous genetic structure in a Fagus crenata population in an old-growth beech forest revealed by microsatellite markersMOLECULAR ECOLOGY, Issue 5 2004Y. Asuka Abstract The within-population genetic structure of Fagus crenata in a 4-ha plot (200 × 200 m) of an old-growth beech forest was analysed using microsatellite markers. To assess the genetic structure, Moran's I spatial autocorrelation coefficient was calculated. Correlograms of Moran's I showed significant positive values less than 0.100 for short-distance classes, indicating weak genetic structure. The genetic structure within the population is created by limited seed dispersal, and is probably weakened by overlapping seed shadow, secondary seed dispersal, extensive pollen flow and the thinning process. Genetic structure was detected in a western subplot of 50 × 200 m with immature soils and almost no dwarf bamboos (Sasa spp.), where small and intermediate-sized individuals were distributed in aggregations with high density because of successful regeneration. By contrast, genetic structure was not found in an eastern subplot of the same size with mature soils and Sasa cover, where successful regeneration was prevented, and the density of the small and intermediate-sized individuals was low. Moreover, genetic structure of individuals in a small-size class (diameter at breast height < 12 cm) was more obvious than in a large-size class (diameter at breast height , 12 cm). The apparent genetic structure detected in the 4-ha plot was therefore probably the result of the structure in the western portion of the plot and in small and intermediate-sized individuals that successfully regenerated under the favourable environment. The heterogeneity in genetic structure presumably reflects variation in the density that should be affected by differences in regeneration dynamics associated with heterogeneity in environmental conditions. [source] PY54, a linear plasmid prophage of Yersinia enterocolitica with covalently closed endsMOLECULAR MICROBIOLOGY, Issue 4 2003Stefan Hertwig Summary PY54 is a temperate phage isolated from Yersinia enterocolitica. Lysogenic Yersinia strains harbour the PY54 prophage as a plasmid (pY54). The plasmid has the same size (46 kb) as the PY54 genome isolated from phage particles. By electron microscopy, restriction analysis and DNA sequencing, it was demonstrated that the phage and the plasmid DNAs are linear, circularly permuted molecules. Unusually for phages of Gram-negative bacteria, the phage genome has 3,-protruding ends. The linear plasmid pY54 has covalently closed ends forming telomere-like hairpins. The equivalent DNA sequence of the phage genome is a 42 bp perfect palindrome. Downstream from the palindrome, an open reading frame (ORF) was identified that revealed strong DNA homology to the telN gene of Escherichia coli phage N15 encoding a protelomerase. Similar to PY54, the N15 prophage is a linear plasmid with telomeres. The N15 protelomerase has cleaving/joining activity generating the telomeres by processing a 56 bp palindrome (telomere resolution site tel RL). To study the activity of the PY54 protein, the telN -like gene was cloned and expressed in E. coli. A 77 kDa protein was obtained and partially purified. The protein was found to process recombinant plasmids containing the 42 bp palindrome. Telomere resolution of plasmids under in vivo conditions was also investigated in Yersinia infected with PY54. Processing required a plasmid containing the palindrome as well as adjacent DNA sequences from the phage including an additional inverted repeat. Regions on the phage genome important for plasmid maintenance were defined by the construction of linear and circular miniplasmid derivatives of pY54, of which the smallest miniplasmid comprises a 4.5 kb DNA fragment of the plasmid prophage. [source] Improving SNR of RF coils using composite coil elementsNMR IN BIOMEDICINE, Issue 9 2009Zhiyue J. Wang Abstract A composite coil element consists of up to three independent orthogonal loops. It improves the flexibility in shaping the radio frequency (RF) field in its vicinity, compared with a single-loop coil element. Computer simulations were conducted to explore the potential advantages of this type of coil configuration for improving the signal-to- noise ratio (SNR), including the intrinsic SNR (ISNR) and the realistic SNR, when the effects of resistive loss of the coil were included. A ,half-space' model was considered, with a variable B0 direction relative to the surface of a large conductive medium. The SNR performance of a square single-loop coil parallel to the surface of the medium was compared with that of a composite coil element where up to two additional orthogonal square loops of the same size were added to the single coil loop. The SNR performances of coil arrays consisting of single-loop elements and composite elements were also evaluated. The RF field was calculated using the finite-difference time-domain method. The results show that the composite coil element has a substantially better ISNR at all depths from the surface than that of a single-loop element covering the same surface area. Furthermore, the ISNR of a composite element is not sensitive to the surface orientation relative to the B0 field. The computer simulation also revealed that at 128,MHz, the resistive loss from the copper coil loops standing upright on the surface at room temperature is substantial compared to the loss in the medium. Consequently, the realistic SNR is significantly lower than ISNR at 128,MHz for a composite coil element. The coil loading by the medium becomes more dominant at 170 and 298,MHz, and the differences between the realistic SNR and ISNR become smaller at these higher frequencies. Copyright © 2009 John Wiley & Sons, Ltd. [source] Stem cell implantation in ischemic mouse heart: a high-resolution magnetic resonance imaging investigation,NMR IN BIOMEDICINE, Issue 6 2005Ekkehard Küstermann Abstract Advances in the biology of stem cells have evoked great interest in cell replacement therapies for the regeneration of heart tissue after myocardial infarction. However, results from human trials are controversial, since the destination of the injected cells, their engraftment and their long-term fate have remained unclear. Here we investigate whether transplanted cells can be identified in the intact and lesioned murine myocardium employing high-resolution MRI. Cardiac progenitor cells, expressing the enhanced green fluorescent protein (EGFP), were labeled with ultra-small paramagnetic iron-oxide (USPIO) nanoparticles and transplanted into the intact or injured myocardium of mice. Their precise location was determined with high-resolution MRI and compared with histological tissue sections, stained with Prussian blue for iron content. These experiments showed that iron nanoparticle-loaded cells could be identified at high resolution in the mouse heart. However, ischemic myocardium (after cryoinjury or left coronary artery ligation) was characterized by a signal attenuation similar to that induced by USPIO-labeled cells in T -weighted MR images, making detection of labeled stem cells in this area by T -sensitive contrast rather difficult. In animals with myocardial injury only, the signal attenuated areas were of the same size in proton density- and T -weighted MR images. In injured animals also receiving labeled cells the lesioned area appeared larger in T - than in proton density-weighted MR images. This sequence-dependent lesion size change is due to the increased signal loss caused by the iron oxide nanoparticles, most sensitively detectable in the T -sensitive images. Thus, using the novel combination of these two parameter weightings, USPIO-labeled cells can be detected at high resolution in ischemic myocardium. Copyright © 2005 John Wiley & Sons, Ltd. [source] Internal Atrial Defibrillation During Electrophysiological Studies and Focal Atrial Fibrillation Ablation ProceduresPACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 10 2001MARTIN R. KARCH KARCH, M.R., et al.: Internal Atrial Defibrillation During Electrophysiological Studies and Focal Atrial Fibrillation Ablation Procedures. Induction of sustained AF during electrophysiological studies requires electrical cardioversion to restore sinus rhythm for continuation of the electrophysiological study and mapping procedure. The study included 104 consecutive patients (age 59 ± 12 years, 74 men), who were in stable sinus rhythm at the beginning of the electrophysiological study, underwent internal atrial defibrillation (IAD) of AF (> 15 minutes) that was induced during electrophysiological study. In 21 patients, AF was regarded to be the clinical problem (group I), and in the remaining 83 patients other arrhythmias represented the primary target of the electrophysiological study (group II). A 7.5 Fr cardioversion catheter (EP Medical) equipped with a distal array was used and placed in the left pulmonary artery and a proximal array of the same size was located along the lateral right atrial wall. All patients were successfully cardioverted with a mean energy of 6.2 ± 4.0 J. In 18 (78%) of 21 group I patients and in 12 (14%) of 81 group II patients, AF recurred 3.7 ± 3.4 and 2.4 ± 1.4 times during electrophysiological study, respectively. The IAD shock did not suppress focal activity, thus the mapping of atrial foci responsible for AF could be continued even after several IADs. No IAD related complications occurred during the study. In conclusion, (1) IAD can be safely and successfully performed during electrophysiological study without using narcotic drugs or high electric energies; (2) IAD does not suppress focal activity; and (3) even if AF recurs frequently during the electrophysiological study, IAD can be performed several times without significant time delay. [source] | |||||||||||||||||||||||||||||||||||||