bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of a recombinantly expressed proteinase K‐like enzyme from a psychrotrophic Serratia sp.
Authors: Larsen Atle Noralf , Moe Elin , Helland Ronny , Gjellesvik Dag Rune , Willassen Nils Peder
Published: November 2005

The gene encoding a peptidase that belongs to the proteinase K family of serine peptidases has been identified from a psychrotrophic Serratia sp., and cloned and expressed in Escherichia coli. The gene has 1890 base pairs and encodes a precursor protein of 629 amino acids with a theoretical molecular mass of 65.5 kDa. Sequence analysis suggests that the peptidase consists of a prepro region, a catalytic domain and two C‐terminal domains. The enzyme is recombinantly expressed as an active ∼ 56 kDa peptidase and includes both C‐terminal domains. Purified enzyme is converted to the ∼ 34 kDa form by autolytic cleavage when incubated at 50 °C for 30 min, but retains full activity. In the present work, the Serratia peptidase (SPRK) is compared with the family representative proteinase K (PRK) from Tritirachium album Limber. Both enzymes show a relatively high thermal stability and a broad pH stability profile. SPRK possess superior stability towards SDS at 50 °C compared to PRK. On the other hand, SPRK is considerably more labile to removal of calcium ions. The activity profiles against temperature and pH differ for the two enzymes. SPRK shows both a broader pH optimum as well as a higher temperature optimum than PRK. Analysis of the catalytic properties of SPRK and PRK using the synthetic peptide succinyl‐Ala‐Ala‐Pro‐Phe‐pNA as substrate showed that SPRK possesses a 3.5–4.5‐fold higher kcat at the temperature range 12–37 °C, but a fivefold higher Km results in a slightly lower catalytic efficiency (kcat/Km) of SPRK compared to PRK.
Parvalbumin deficiency in fast‐twitch muscles leads to increased ‘slow‐twitch type’ mitochondria, but does not affect the expression of fiber specific proteins
Authors: Racay Peter , Gregory Patrick , Schwaller Beat
Published: November 2005

Parvalbumin (PV), a small cytosolic protein belonging to the family of EF‐hand calcium‐binding proteins, is highly expressed in mammalian fast‐twitch muscle fibers. By acting as a ‘slow‐onset’ Ca2+ buffer, PV does not affect the rapid contraction phase, but significantly contributes to increase the rate of relaxation, as demonstrated in PV–/– mice. Unexpectedly, PV–/– fast‐twitch muscles were considerably more resistant to fatigue than the wild‐type fast‐twitch muscles. This effect was attributed mainly to the increased fractional volume of mitochondria in PV–/– fast‐twitch muscle, extensor digitorum longus, similar to levels observed in the slow‐twitch muscle, soleus. Quantitative analysis of selected mitochondrial proteins, mitochondrial DNA‐encoded cytochrome oxidase c subunit I and nuclear DNA‐encoded cytochrome oxidase c subunit Vb and F1‐ATPase subunit β revealed the PV–/–tibialis anterior mitochondria composition to be almost identical to that in wild‐type soleus, but not in wild‐type fast‐twitch muscles. Northern and western blot analyses of the same proteins in different muscle types and in liver are indicative of a complex regulation, probably also at the post‐transcriptional level. Besides the function in energy metabolism, mitochondria in both fast‐ and slow‐twitch muscles act as temporary Ca2+ stores and are thus involved in the shaping of Ca2+ transients in these cells. Previously observed altered spatio‐temporal aspects of Ca2+ transients in PV–/– muscles are sufficient to up‐regulate mitochondria biogenesis through the probable involvement of both calcineurin‐ and Ca2+/calmodulin‐dependent kinase II‐dependent pathways. We propose that ‘slow‐twitch type’ mitochondria in PV–/– fast muscles are aimed to functionally replace the slow‐onset buffer PV based on similar kinetic properties of Ca2+ removal.
The three desulfoglucosinolate sulfotransferase proteins in Arabidopsis have different substrate specificities and are differentially expressed
Authors: Klein Marion , Reichelt Michael , Gershenzon Jonathan , Papenbrock Jutta
Published: November 2005

Sulfotransferases (SOTs) catalyse the transfer of a sulfate group from 3′‐phosphoadenosine 5′‐phosphosulfate (PAPS) to an appropriate hydroxy group of various substrates with the parallel formation of 3′‐phosphoadenosine 5′‐phosphate. In Arabidopsis thaliana, 18 SOT proteins (AtSOT) have been identified. Three of them, AtSOT16, AtSOT17 and AtSOT18, catalyse the sulfation of desulfoglucosinolates. The proteins were expressed in Escherichia coli, purified by affinity chromatography and used for enzyme kinetic studies. By establishing two types of enzyme assay using both 35S‐labelled and unlabelled PAPS, separation of the products by HPLC, and detection of the products by monitoring radioactivity or UV absorption, the substrate specificities of the three AtSOT proteins were determined. They show different maximum velocities with several desulfoglucosinolates as substrates and differ in their affinity for desulfobenzylglucosinolate and PAPS. The sequences encoding AtSOT18 were amplified from Arabidopsis ecotypes C24 and Col0; the two expressed proteins differ in two out of 350 amino acids. These amino‐acid variations led to different substrate specificities. Exchange of one of the two amino acids in AtSOT18 from C24 to the respective amino acid in AtSOT18 from Col0 gave the C24 protein the same substrate specificity as the wild‐type AtSOT18 protein from Col0. All three desulfoglucosinolate AtSOT proteins are localized in the cytoplasm, as demonstrated by transient expression of fusion constructs with the green fluorescent protein in Arabidopsis protoplasts. Northern blot analysis indicated differential expression of the three AtSOT genes in plant organs and tissues at different developmental stages and during a light/darkness cycle. High (500 µm) and low (50 µm) sulfate concentrations in the medium did not influence the levels of expression.
Factor substitution and factor intensities in models with more factors than goods
Authors: Wong Siu‐kee
Published: November 2005

This paper considers the commodity prices–factor prices relation in models with more factors than consumption goods. Under some simple factor substitutability assumptions, many results in the n × n cases have counterparts in the l × n cases. The proportional price changes of the “middle factors” will be trapped between those of the “extreme factors”. A weak and a strong Stolper–Samuelson theorem can also be proven. If the numbers of goods and perfectly complementary factors are equal and the production functions have the nested constant elasticity of substitution form, two of the complementary factors would have the most extreme relative price changes, regardless of the factor intensities.
Universal and group‐specific real‐time PCR diagnosis of flavescence dorée (16Sr‐V), bois noir (16Sr‐XII) and apple proliferation (16Sr‐X) phytoplasmas from field‐collected plant hosts and insect vectors
Authors: Galetto L. , Bosco D. , Marzachì C.
Published: November 2005

Three real‐time PCR–based assays for the specific diagnosis of flavescence dorée (FD), bois noir (BN) and apple proliferation (AP) phytoplasmas and a universal one for the detection of phytoplasmas belonging to groups 16Sr‐V, 16Sr‐X and 16Sr‐XII have been developed. Ribosomal‐based primers CYS2Fw/Rv and TaqMan probe CYS2 were used for universal diagnosis in real‐time PCR. For group‐specific detection of FD phytoplasma, ribosomal‐based primers fAY/rEY, specific for 16Sr‐V phytoplasmas, were chosen. For diagnosis of BN and AP phytoplasmas, specific primers were designed on non‐ribosomal and nitroreductase DNA sequences, respectively. SYBR® Green I detection coupled with melting curve analysis was used in each group‐specific protocol. Field‐collected grapevines infected with FD and BN phytoplasmas and apple trees infected with AP phytoplasma, together with Scaphoideus titanus, Hyalesthes obsoletus and Cacopsylla melanoneura adults, captured in the same vineyards and orchards, were used as templates in real‐time PCR assays. The diagnostic efficiency of each group‐specific protocol was compared with well‐established detection procedures, based on conventional nested PCR. Universal amplification was obtained in real‐time PCR from DNAs of European aster yellows (16Sr‐I), elm yellows (16Sr‐V), stolbur (16Sr‐XII) and AP phytoplasma reference isolates maintained in periwinkles. The same assay detected phytoplasma DNA in all test plants and test insect vectors infected with FD, BN and AP phytoplasmas. Our group‐specific assays detected FD, BN, and AP phytoplasmas with high efficiencies, similar to those obtained with nested PCR and did not amplify phytoplasma DNA of other taxonomic groups. Melting curve analysis was necessary for the correct identification of the specific amplicons generated in the presence of very low target concentrations. Our work shows that real‐time PCR methods can sensitively and rapidly detect phytoplasmas at the universal or group‐specific level. This should be useful in developing defence strategies and for quantitative studies of phytoplasma–plant–vector interactions.
Colonization of Tubú (Montanoa guatemalensis, Asteraceae) Windbreaks by Woody Species1
Authors: Piper Jon K.
Published: November 2005

Tubú (Montanoa guatemalensis, Asteraceae) is a popular tree used in windbreaks in the San Luis valley near the Monteverde cloud forests of Costa Rica. Seventy‐eight woody taxa from 32 families were found in the understory of 19 tubú windbreaks (five 4‐yr‐old, eight 12‐yr‐old, and six 20‐yr‐old). Mean size of tubú increased with stand age, but tubú was neither replacing itself nor spreading from the windbreaks. Density of other trees and shrubs ≥1 m was higher in 4‐yr‐old plots than in 20‐yr‐old plots, but density of other trees <1 m tall did not vary with windbreak age. Whereas richness of species ≥1 m was higher for 12‐ and 20‐yr‐old plots than for 4‐yr‐old plots, species richness of trees <1 m tall did not vary with windbreak stand age. Higher proportions of the woody colonists in 12‐ and 20‐yr‐old plots were animal dispersed than in 4‐yr‐old plots. Tubú windbreaks may undergo major changes in woody species composition, with Daphnopsis americana, Inga punctata, and Trichilia havanensis likely to predominate in the future.
Sugar Preferences in Nectar‐ and Fruit‐Eating Birds: Behavioral Patterns and Physiological Causes1
Authors: Lotz Chris N. , Schondube Jorge E.
Published: November 2005

Sucrose, glucose, and fructose are the three sugars that commonly occur in floral nectar and fruit pulp. The relative proportions of these three sugars in nectar and fruit in relation to the sugar preferences of pollinators and seed dispersers have received considerable attention. Based on the research of Herbert and Irene Baker and their collaborators, a dichotomy between sucrose‐dominant hummingbird‐pollinated flowers and hexose‐dominant passerine flowers and fruits was proposed. Data on sugar preferences of several hummingbird species (which prefer sucrose) vs. a smaller sample of passerines (which prefer hexoses) neatly fitted this apparent dichotomy. This hummingbird–passerine dichotomy was strongly emphasized until the discovery of South African plants with sucrose‐dominant nectars, which are pollinated by passerines that are able to digest, and prefer sucrose. Now we know that, with the exception of two clades, most passerines are able to assimilate sucrose. Most sugar preference studies have been conducted using a single, relatively high, sugar concentration in the nectar (ca 20%). Thus, we lack information about the role that sugar concentration might play in sugar selection. Because many digestive traits are strongly affected not only by sugar composition, but also by sugar concentration, we suggest that preferences for different sugar compositions are concentration‐dependent. Indeed, recent studies on several unrelated nectar‐feeding birds have found a distinct switch from hexose preference at low concentrations to sucrose preference at higher concentrations. Finally, we present some hypotheses about the role that birds could have played in molding the sugar composition of plant rewards.
Responses of a Specialized Insectivorous Mammal (Myrmecophaga tridactyla) to Variation in Ambient Temperature1
Authors: Camilo‐Alves Constança de Sampaio e Paiva , Mourão Guilherme de Miranda
Published: November 2005

This study reports the effect of daily mean ambient temperature on daily activity and habitat use by the giant anteater (Myrmecophaga tridactyla) in the Pantanal wetlands of Brazil. We equipped 11 giant anteaters with a global position system collar programmed to acquire a location every 10 min for 15 d. A temperature data logger left in the meteorological station at the study site registered data on ambient temperature. Giant anteaters were mainly active in open fields except during the coldest days, when they sought protection inside forests. Giant anteaters also used open habitats for resting but during the hottest or chilliest days they sheltered in forests. In the Pantanal, where temperatures are usually high, giant anteaters were active all night long, but as daily average ambient temperature decreased anteaters began and finished activity progressively earlier and reduced total activity. As a consequence, time spent active at daylight increased progressively and time spent active during the night decreased progressively, probably to allow the anteaters to expose themselves to solar radiation and to avoid heat loss during the night.
Behavioral Response of Resident Jamaican Birds to Dry Season Food Supplementation1
Authors: Brown David R. , Sherry Thomas W.
Published: November 2005

We used plot‐level manipulations and analyses to test the effects of food availability on the behavior and condition of resident dry‐forest birds in Jamaica. Two control plots were monitored in each of 2 yr. Food was supplemented on five plots over 2 yr with piles of cut oranges distributed around plots, which served as a direct source of carbohydrates and water, and an indirect source of ground arthropods due to increased above‐ground activity. We reduced ants on five plots over 2 yr; however, we found no difference in total ground arthropod biomass between control and reduction treatments, so we pooled these plots for analysis. We selected nine focal resident bird species for study of relative abundance, body condition, and breeding condition. Birds were sampled prior to, and 5 to 6 weeks after the initiation of treatments. Seven of nine species had higher relative abundance following food supplementation. Three species were recaptured more frequently in supplementation plots than in control plots. These abundance and persistence responses did not cause any changes in body condition. In one species, Bananaquit (Coereba flaveola), food supplementation resulted in higher concentrations of individuals in breeding condition. These results demonstrate a functional response to dry‐season food availability and suggest a limiting mechanism. This study helps explain mechanisms by which bird populations respond to resource availability, and is the first successful plot‐level food supplementation experiment for tropical forest birds.
Generations, Mobility and Community: Geographies of Three Generations of Greek and Italian Ancestry in Sydney
Authors: BURNLEY IAN. H.
Published: November 2005

Geographies of three generations of Greek and Italian ancestry in Sydney totalling 245 000 people in 2001 are identified. A model of community sequences is developed within a conceptual framework of intergenerational spatial, occupational and social absorption. Considerable intra‐ and inter‐generational occupational mobility took place and the third generations showed higher proportions as managers, professionals and associate professionals than persons of Australian ancestry. Second and third generations had occupational profiles which were much closer to the host society than the first generations. Despite occupational mobility, employment, residential and social trends associated with the first generations affected the adult second generations and to an extent the third. Several thousand members of three generations re‐grouped into successive local communities, patronised facilities in core communities, and maintained place identities.
The Changing Health Care Behaviour of the Hmong Refugee Population in Sydney
Authors: WANG JENNIFER A.
Published: November 2005

Health care behaviour of Hmong refugees in Sydney was investigated after research in the United States had shown that, within the Southeast Asian refugee community in that country, Hmong refugees not only had the lowest rates of use of Western medicine but also were the most likely to assess their quality of health as only fair (Brainard and Zaharlick, 1989, 849). In contrast, this study found that the Sydney Hmong generally used Western medicine as a system of first choice. At the same time, most continued to use traditional medicines, albeit in a modified form. Minimal costs, freedom to choose their own doctor and appropriate, long term health education were the most important factors in Hmong using Western medicine in Sydney. Other contributing factors included the structure and size of the community, the presence of a long‐term Hmong resident in Sydney upon arrival and familiarity with Western medicine. Thus, the Sydney Hmong community was able to maintain a reasonable quality of health at an affordable price. An unexpected finding was the improved social, economic and health status of Hmong women. Such differentiated results are a powerful argument for not looking at refugees as a homogenous group, even when investigating a single, national, ethnic or cultural group. This study highlighted both the multidisciplinary and transdisciplinary nature of health care behaviour and the contribution that a small in‐depth case study can make to health and migrant policy.
Regionalisation of Environmental Management: a Case Study of the Natural Heritage Trust, South Australia
Authors: FARRELLY MEGAN
Published: November 2005

Regional planning for and management of the environment and natural resources are the new foci of the Australian Government's funding initiative, the Natural Heritage Trust Phase Two (NHT2). NHT2 attempts to integrate and coordinate the efforts of the many local environmental community groups that work on‐ground. By operating at the regional scale, it is expected that more strategic and targeted outcomes will be achieved. This paper examines how the shift to regional‐scale delivery has affected key stakeholders in South Australia, focussing on the experiences of a sub‐regional environmental community group. Interviews with key regional stakeholders, participant observation and document analysis highlighted difficulties in the transition to regional delivery, for both regional and local groups. Limited funding, restrictive timelines, vague guidelines and prescriptive information, slowed the development of the regional plan and frustrated regional groups. A lack of communication and limited community participation in developing the regional plan created uncertainty and confusion in the sub‐regional community group, resulting in mistrust of and alienation from the regional groups. Concern was also expressed over the loss of the local‐scale focus, particularly as community leaders moved to higher decision‐making positions within the region. It is too early too assess the effectiveness of the regional groups. However, if the issues identified during the transitional phase are not addressed, then the regional groups may struggle to achieve their objectives.
Letting Indigenous People Talk About Their Country: a Case Study of Cross‐Cultural (Mis)communication in an Environmental Management Planning Process
Authors: LLOYD D. , VAN NIMWEGEN P. , BOYD W. E.
Published: November 2005

This paper presents a case study, based on the experiences of two senior Aboriginal traditional owners who were engaged in negotiations surrounding the establishment of a Regional Forest Agreement (RFA) in southeast Queensland. This case is notable as an illustration of the capacity of natural resource management planning, through negotiation within a formal process, to extinguish native title. Importantly, the personal experiences of two senior Aboriginal people provide an insight into a situation designed to enhance interactions between government and community, with the overt intention of improving natural resource management. However, the record of this personal experience indicates that the communication was less than satisfactory and that the outcomes, at least in terms of the experiences recorded here, of the individual senior Aboriginal community members, was less than satisfactory. We conclude that, despite best intentions, there is an important lack of provision for community influence or power, including any legal or administrative institutional framework. We also conclude that there are important institutional and social processes of engagement still to be developed, including ways of engaging the community more widely that has conventionally been the case.
Recent Storm Boulder Deposits on the Beecroft Peninsula, New South Wales, Australia
Authors: SAINTILAN N. , ROGERS K.
Published: November 2005

This paper documents the deposition of large boulders on the Beecroft Peninsula, New South Wales, during a one in four‐year swell event in October 1999. The size of the boulders in relation to the magnitude of the swell suggests that the boulder field at Whale Point on the Beecroft Peninsula is explicable in terms of storm swells alone.
Associations Among Risk Factors, Individual Resources, and Indices of School‐Related Asthma Morbidity in Urban, School‐Aged Children: A Pilot Study
Authors: Mitchell Daphne Koinis , Adams Sue K. , Murdock Karla Klein
Published: November 2005

Abstract: This paper presents a conceptual model including examples of risk and resource factors associated with indices of school‐related asthma morbidity (eg, missed sleep, participation in activities, school absences) in a group of urban, school‐aged children with asthma from ethnic minority backgrounds. Specifically, the current longitudinal study examines relations between a contextual risk factor (ie, family life stressors), an asthma‐related risk factor (ie, asthma symptoms), individual resources (ie, attention, children's problem‐solving beliefs, and self‐esteem), and aspects of asthma morbidity that have been shown to have an impact on children's academic performance. Participants of the study included 31 mother‐child dyads from low‐income, inner‐city neighborhoods. Results of hierarchical regression analyses revealed that after controlling for risk factors (ie, asthma symptoms and family life stressors) at baseline, children's individual characteristics (ie, children's problem‐solving beliefs and self‐esteem) functioned as resource factors for some indices of asthma‐related functioning (school absences, participation in activities, and missed sleep) at follow‐up (1 year later). Results suggest that contextual and individual risk and resource factors should be further explored in studies including larger samples of urban children with asthma in order to help guide the development of preventive interventions in school‐based and health care settings. (J Sch Health. 2005;75(10):375–383)
Bullying Perspectives: Experiences, Attitudes, and Recommendations of 9‐ to 13‐Year‐Olds Attending Health Education Centers in the United States
Authors: Brown Stephen L. , Birch David A. , Kancherla Vijaya
Published: November 2005

Abstract: Because 1 in 5 elementary school and 1 in 10 middle school students in the United States report being bullied, understanding student perspectives is crucial to prevention. This study solicited opinions of 9‐ to 13‐year‐olds regarding the magnitude of, causes of, and remedies for bullying. Data were obtained from 1229 students visiting 11 health education centers in seven states. Students responded via anonymous, electronic keypads. Half the respondents said they have been bullied at least once in a while. When bullied, almost half said they fight back, about a fourth tell an adult, and 20% do nothing; only 8% try to talk to the bully. Nearly two thirds claimed they tell or try to stop bullying when they see it, but 16% do nothing, and 20% join in. Almost three fourths believed bullying is “uncool,” yet 42% said they bully at least occasionally. Bullies and victims were more likely to be middle school age. Frequent bullies were more likely to think it is cool, to fight back when bullied, and to join in when others are bullied. Two classes of victims were apparent. Victims who also bully often said that bullying occurs because others are not friendly to bullies or because bullies want to get their way; many also admitted that they do not know how it can be stopped. Victims who do not bully were most likely to do nothing when bullied but to try to stop the bullying of others. Recommendations are given for using these findings to customize curricula or programs. (J Sch Health. 2005;75(10):384‐392)
What are the Relevant Parameters for the Geometrical Optimization of an Implantable Bioartificial Pancreas?
Authors: Dulong Jean-Luc , Legallais Cécile
Published: November 2005

A sphere within a cylinder representing the islet encapsulated in a hollow fiber can model an implantable bioartificial pancreas. Based on a finite element model for insulin response to a glucose load in the presence of various oxygen supplies, the present study aimed at pointing out the major parameters influencing this secretion. The computational results treated with the Taguchi method clearly demonstrated that geometrical parameters (fiber length and islet density) should be precisely optimized for an enhanced insulin response. This requires the collection of more relevant experimental data concerning the islet oxygen consumption. Moreover, the relative errors on glucose consumption or insulin secretion by the islets do not seem to affect the whole optimization process, which should focus on the oxygen supply to islets.
Local and Global Geometric Influence on Steady Flow in Distal Anastomoses of Peripheral Bypass Grafts
Authors: Giordana S. , Sherwin S. J. , Peiró J. , Doorly D. J. , Crane J. S. , Lee K. E. , Cheshire N. J. W. , Caro C. G.
Published: November 2005

We consider the effect of geometrical configuration on the steady flow field of representative geometries from an in vivo anatomical data set of end-to-side distal anastomoses constructed as part of a peripheral bypass graft. Using a geometrical classification technique, we select the anastomoses of three representative patients according to the angle between the graft and proximal host vessels (GPA) and the planarity of the anastomotic configuration. The geometries considered include two surgically tunneled grafts with shallow GPAs which are relatively planar but have different lumen characteristics, one case exhibiting a local restriction at the perianastomotic graft and proximal host whilst the other case has a relatively uniform cross section. The third case is nonplanar and characterized by a wide GPA resulting from the graft being constructed superficially from an in situ vein. In all three models the same peripheral resistance was imposed at the computational outflows of the distal and proximal host vessels and this condition, combined with the effect of the anastomotic geometry, has been observed to reasonably reproduce the in vivo flow split. By analyzing the flow fields we demonstrate how the local and global geometric characteristics influences the distribution of wall shear stress and the steady transport of fluid particles. Specifically, in vessels that have a global geometric characteristic we observe that the wall shear stress depends on large scale geometrical factors, e.g., the curvature and planarity of blood vessels. In contrast, the wall shear stress distribution and local mixing is significantly influenced by morphology and location of restrictions, particular when there is a shallow GPA. A combination of local and global effects are also possible as demonstrated in our third study of an anastomosis with a larger GPA. These relatively simple observations highlight the need to distinguish between local and global geometric influences for a given reconstruction. We further present the geometrical evolution of the anastomoses over a series of follow-up studies and observe how the lumen progresses towards the faster bulk flow of the velocity in the original geometry. This mechanism is consistent with the luminal changes in recirculation regions that experience low wall shear stress. In the shallow GPA anastomoses the proximal part of the native host vessel occludes or stenoses earlier than in the case with wide GPA. A potential contribution to this behavior is suggested by the stronger mixing that characterizes anastomoses with large GPA.
The Buckling of Spherical Liposomes
Authors: Pamplona D. C. , Greenwood J. A. , Calladine C. R.
Published: November 2005

In the classical “first approximation” theory of thin-shell structures, the constitutive relations for a generic shell element—i.e. the elastic relations between the bending moments and membrane stresses and the corresponding changes in curvature and strain, respectively—are written as if an element of the shell is flat, although in reality it is curved. In this theory it is believed that discrepancies on account of the use of “flat” constitutive relations will be negligible provided the ratio shell-radius∕thickness is of sufficiently large order. In the study of drawing of narrow, cylindrical “tethers” from liposomes it has been known for many years that it is necessary to use instead a constitutive law which explicitly describes a curved element in order to make sense of the mechanics; and indeed such tethers are generally of “thick-walled” proportions. In this paper we show that the proper constitutive relations for a curved element must also be used in the study, by means of shell equations, of the buckling of initially spherical thin-walled giant liposomes under exterior pressure: these involve the inclusion of what we call the “Mκ” terms, which are not present in the standard “first-approximation” theory. We obtain analytical expressions for both the bifurcation buckling pressure and the slope of the post-buckling path, in terms of the dimensions and elastic constants of the lipid bi-layer, and also the initial state of bending moment in the vesicle. We explain physically how the initial bending moment can affect the bifurcation pressure, whereas it cannot in “first-approximation” theory. We use these results to map the conditions under which the vesicle buckles into an oblate, as distinct from a prolate (“rugby-ball”) shape. Some of our results were obtained long ago by the use of energy methods; but our aim here has been to identify precisely what is lacking in “first-approximation” theory in relation to liposomes, and so to put the “shell equations” approach onto a firm footing in mechanics.
Effects of the Frequency and Duration of Cyclic Stress on the Mechanical Properties of Cultured Collagen Fascicles From the Rabbit Patellar Tendon
Authors: Yamamoto Ei , Kogawa Daisuke , Tokura Susumu , Hayashi Kozaburo
Published: November 2005

The effects of frequency or duration of cyclic stress on the mechanical properties of collagen fascicles were studied by means of in vitro tissue culture experiments. Collagen fascicles of approximately 300μm in diameter were obtained from rabbit patellar tendons. During culture, cyclic stress having the peak stress of approximately 2MPa was applied to the fascicles at 1Hz for 1hour∕day (1Hz-1h group), at 1Hz for 4hours∕day (1Hz-4h group), or at 4Hz for 1hour∕day (4Hz-1h group). The frequency of 4Hz and the duration of 1hour∕day are considered to be similar to those of the in vivo stress applied to fascicles in the intact rabbit patellar tendon. After culture for 1 or 2weeks, the mechanical properties of the fascicles were determined using a micro-tensile tester, and were compared to the properties of non-cultured, fresh fascicles (control group) and the fascicles cultured under no load condition (non-loaded group). The tangent modulus and tensile strength of fascicles in the 4Hz-1h group were similar to those in the control group; however, the fascicles of the 1Hz-1h and 1Hz-4h groups had significantly lower values than those of the control group. There was no significant difference in the tensile strength between the 1Hz-1h and non-loaded groups, although the strength in the 1Hz-4h group was significantly higher than that of the non-loaded group. It was concluded that the frequency and duration of cyclic stress significantly affect the mechanical properties of cultured collagen fascicles. If we apply cyclic stress having the frequency and duration which are experienced in vivo, the biomechanical properties are maintained at control, normal level. Lower frequencies or less cycles of applied force induce adverse effects.
A Numerical and Experimental Investigation of Transitional Pulsatile Flow in a Stenosed Channel
Authors: Beratlis N. , Balaras E. , Parvinian B. , Kiger K.
Published: November 2005

In the present paper, a closely coupled numerical and experimental investigation of pulsatile flow in a prototypical stenotic site is presented. Detailed laser Doppler velocimetry measurements upstream of the stenosis are used to guide the specification of velocity boundary conditions at the inflow plane in a series of direct numerical simulations (DNSs). Comparisons of the velocity statistics between the experiments and DNS in the post-stenotic area demonstrate the great importance of accurate inflow conditions, and the sensitivity of the post-stenotic flow to the disturbance environment upstream. In general, the results highlight a borderline turbulent flow that sequentially undergoes transition to turbulence and relaminarization. Before the peak mass flow rate, the strong confined jet that forms just downstream of the stenosis becomes unstable, forcing a role-up and subsequent breakdown of the shear layer. In addition, the large-scale structures originating from the shear layer are observed to perturb the near wall flow, creating packets of near wall hairpin vortices.
Thermo-Mechanical Responses of a Surface-Coupled AFM Cantilever
Authors: Wu Jianhua , Fang Ying , Yang Dong , Zhu Cheng
Published: November 2005

Atomic force microscopy (AFM) has been widely used for measuring mechanical properties of biological specimens such as cells, DNA, and proteins. This is usually done by monitoring deformations in response to controlled applied forces, which have to be at ultralow levels due to the extreme softness of the specimens. Consequently, such experiments may be susceptible to thermal excitations, manifested as force and displacement fluctuations that could reduce the measurement accuracy. To take advantage of, rather than to be limited by, such fluctuations, we have characterized the thermomechanical responses of an arbitrarily shaped AFM cantilever with the tip coupled to an elastic spring. Our analysis shows that the cantilever and the specimen behave as springs in parallel. This provides a method for determining the elasticity of the specimen by measuring the change in the tip fluctuations in the presence and absence of coupling. For rectangular and V-shaped cantilevers, we have derived a relationship between the mean-square deflection and the mean-square inclination and an approximate expression for the specimen spring constant in terms of contributions to the mean-square inclination from the first few vibration modes.
Quantifying Effects of Plaque Structure and Material Properties on Stress Distributions in Human Atherosclerotic Plaques Using 3D FSI Models
Authors: Tang Dalin , Yang Chun , Zheng Jie , Woodard Pamela K. , Saffitz Jeffrey E. , Sicard Gregorio A. , Pilgram Thomas K. , Yuan Chun
Published: November 2005

Background: Atherosclerotic plaques may rupture without warning and cause acute cardiovascular syndromes such as heart attack and stroke. Methods to assess plaque vulnerability noninvasively and predict possible plaque rupture are urgently needed. Method: MRI-based three-dimensional unsteady models for human atherosclerotic plaques with multi-component plaque structure and fluid-structure interactions are introduced to perform mechanical analysis for human atherosclerotic plaques. Results: Stress variations on critical sites such as a thin cap in the plaque can be 300% higher than that at other normal sites. Large calcification block considerably changes stress/strain distributions. Stiffness variations of plaque components (50% reduction or 100% increase) may affect maximal stress values by 20–50 %. Plaque cap erosion causes almost no change on maximal stress level at the cap, but leads to 50% increase in maximal strain value. Conclusions: Effects caused by atherosclerotic plaque structure, cap thickness and erosion, material properties, and pulsating pressure conditions on stress/strain distributions in the plaque are quantified by extensive computational case studies and parameter evaluations. Computational mechanical analysis has good potential to improve accuracy of plaque vulnerability assessment.
Methodology for Predicting Oxygen Transport on an Intravenous Membrane Oxygenator Combining Computational and Analytical Models
Authors: Guzmán Amador M. , Escobar Rodrigo A. , Amon Cristina H.
Published: November 2005

A computational methodology for accurately predicting flow and oxygen-transport characteristics and performance of an intravenous membrane oxygenator (IMO) device is developed, tested, and validated. This methodology uses extensive numerical simulations of three-dimensional computational models to determine flow-mixing characteristics and oxygen-transfer performance, and analytical models to indirectly validate numerical predictions with experimental data, using both blood and water as working fluids. Direct numerical simulations for IMO stationary and pulsating balloons predict flow field and oxygen transport performance in response to changes in the device length, number of fibers, and balloon pulsation frequency. Multifiber models are used to investigate interfiber interference and length effects for a stationary balloon whereas a single fiber model is used to analyze the effect of balloon pulsations on velocity and oxygen concentration fields and to evaluate oxygen transfer rates. An analytical lumped model is developed and validated by comparing its numerical predictions with experimental data. Numerical results demonstrate that oxygen transfer rates for a stationary balloon regime decrease with increasing number of fibers, independent of the fluid type. The oxygen transfer rate ratio obtained with blood and water is approximately two. Balloon pulsations show an effective and enhanced flow mixing, with time-dependent recirculating flows around the fibers regions which induce higher oxygen transfer rates. The mass transfer rates increase approximately 100% and 80%, with water and blood, respectively, compared with stationary balloon operation. Calculations with combinations of frequency, number of fibers, fiber length and diameter, and inlet volumetric flow rates, agree well with the reported experimental results, and provide a solid comparative base for analysis, predictions, and comparisons with numerical and experimental data.
An Application of Nanoindentation Technique to Measure Bone Tissue Lamellae Properties
Authors: Hoffler C. Edward , Guo X. Edward , Zysset Philippe K. , Goldstein Steven A.
Published: November 2005

Measuring the microscopic mechanical properties of bone tissue is important in support of understanding the etiology and pathogenesis of many bone diseases. Knowledge about these properties provides a context for estimating the local mechanical environment of bone related cells that coordinate the adaptation to loads experienced at the whole organ level. The objective of this study was to determine the effects of experimental testing parameters on nanoindentation measures of lamellar-level bone mechanical properties. Specifically, we examined the effect of specimen preparation condition, indentation depth, repetitive loading, time delay, and displacement rate. The nanoindentation experiments produced measures of lamellar elastic moduli for human cortical bone (average value of 17.7±4.0GPa for osteons and 19.3±4.7GPa for interstitial bone tissue). In addition, the hardness measurements produced results consistent with data in the literature (average 0.52±0.15GPa for osteons and 0.59±0.20GPa for interstitial bone tissue). Consistent modulus values can be obtained from a 500-nm-deep indent. The results also indicated that the moduli and hardnesses of the dry specimens are significantly greater (22.6% and 56.9%, respectively) than those of the wet and wet and embedded specimens. The latter two groups were not different. The moduli obtained at a 5‐nm∕s loading rate were significantly lower than the values at the 10- and 20‐nm∕s loading rates while the 10- and 20‐nm∕s rates were not significantly different. The hardness measurements showed similar rate-dependent results. The preliminary results indicated that interstitial bone tissue has significantly higher modulus and hardness than osteonal bone tissue. In addition, a significant correlation between hardness and elastic modulus was observed.
Cellular Response of Adipose Derived Passage-4 Adult Stem Cells to Freezing Stress
Authors: Devireddy Ram V. , Thirumala Sreedhar , Gimble Jeffrey M.
Published: November 2005

A differential scanning calorimeter technique was used to generate experimental data for volumetric shrinkage during cooling at 20°C∕min in adipose derived adult stem cells (ASCs) in the presence and absence of cryoprotective agents (CPAs). By fitting a model of water transport to the experimentally determined volumetric shrinkage data, the membrane permeability parameters of ASCs were obtained. For passage-4 (P4) ASCs, the reference hydraulic conductivity Lpg and the value of the apparent activation energy ELp were determined to be 1.2×10−13m3∕Ns and 177.8kJ∕mole, respectively. We found that the addition of either glycerol or dimethylsulfoxide (DMSO) significantly decreased the value of the reference hydraulic conductivity Lpg(cpa) and the value of the apparent activation energy ELp(cpa) in P4 ASCs. The values of Lpg(cpa) in the presence of glycerol and DMSO were determined as 0.39×10−13 and 0.50×10−13m3∕Ns, respectively, while the corresponding values of ELp(cpa) were 51.0 and 61.5kJ∕mole. Numerical simulations of water transport were then performed under a variety of cooling rates (5-100°C∕min) using the experimentally determined membrane permeability parameters. And finally, the simulation results were analyzed to predict the optimal rates of freezing P4 adipose derived cells in the presence and absence of CPAs.
Computational Modeling of a Dynamic Knee Simulator for Reproduction of Knee Loading
Authors: Guess Trent M. , Maletsky Lorin P.
Published: November 2005

As a first step towards reproducing desired three-dimensional joint loading and motion on a dynamic knee simulator, the goal of this study was to develop and verify a three-dimensional computational model that generated control profiles for the simulator using desired knee loading and motion as model inputs. The developed model was verified by predicting tibio-femoral loading on an instrumented analog knee for given actuator forces and the ability to generate simulator control profiles was demonstrated using a three-dimensional walking profile. The model predicted axial tibia loading for a sagittal-plane dual-limb squat within 1% of measured peak loading. Adding out-of-sagittal-plane forces decreased the accuracy of load prediction. The model generated control profiles to the simulator that produced axial tibia loading within 16% of desired for walking. Discrepancies in predicted and measured quadriceps forces influenced the accuracy of the generated control profiles. Future work will replace the analog knee in both the model and machine with a prosthetic knee.
Measurement of Strain in the Left Ventricle during Diastole with
cine-MRI and Deformable Image Registration
Authors: Veress Alexander I. , Gullberg Grant T. , Weiss Jeffrey A.
Published: November 2005

The assessment of regional heart wall motion (local strain) can localize ischemic myocardial disease, evaluate myocardial viability, and identify impaired cardiac function due to hypertrophic or dilated cardiomyopathies. The objectives of this research were to develop and validate a technique known as hyperelastic warping for the measurement of local strains in the left ventricle from clinical cine-magnetic resonance imaging (MRI) image datasets. The technique uses differences in image intensities between template (reference) and target (loaded) image datasets to generate a body force that deforms a finite element (FE) representation of the template so that it registers with the target image. To validate the technique, MRI image datasets representing two deformation states of a left ventricle were created such that the deformation map between the states represented in the images was known. A beginning diastolic cine-MRI image dataset from a normal human subject was defined as the template. A second image dataset (target) was created by mapping the template image using the deformation results obtained from a forward FE model of diastolic filling. Fiber stretch and strain predictions from hyperelastic warping showed good agreement with those of the forward solution (R2=0.67 stretch, R2=0.76 circumferential strain, R2=0.75 radial strain, and R2=0.70 in-plane shear). The technique had low sensitivity to changes in material parameters (ΔR2=−0.023 fiber stretch, ΔR2=−0.020 circumferential strain, ΔR2=−0.005 radial strain, and ΔR2=0.0125 shear strain with little or no change in rms error), with the exception of changes in bulk modulus of the material. The use of an isotropic hyperelastic constitutive model in the warping analyses degraded the predictions of fiber stretch. Results were unaffected by simulated noise down to a signal-to-noise ratio (SNR) of 4.0 (ΔR2=−0.032 fiber stretch, ΔR2=−0.023 circumferential strain, ΔR2=−0.04 radial strain, and ΔR2=0.0211 shear strain with little or no increase in rms error). This study demonstrates that warping in conjunction with cine-MRI imaging can be used to determine local ventricular strains during diastole.