bluuebunny/crossref_metadata_2025 huggingface dataset:
Piezoelectric, pyroelectric, dielectric and ferroelectric properties of Ba0.3Na0.7Ti0.3Nb0.7O3
Authors: Abdelkefi Helmi , Khemakhem Hamadi , Simon Annie , Maglione Mario
Published: December 2007

The ferroelectric, piezoelectric, and pyroelectric properties of Ba1−xNaxTi1−xNbxO3 with x=0.70 (BTNN0.70) lead-free ceramic were investigated. Polycrystalline sample with composition BTNN0.70 was prepared by using conventional dry ceramic technique. Sample was sintered at 1250°C for 3h under oxygen showed perovskite structure with high densities 4.92g∕cm3 (∼96% as relative density). X-ray analysis confirmed the formation of single-phase compound with cubic crystal structure. Dielectric properties were studied in detail as a function of frequency and temperature. From temperature variation of dielectric constant, Curie temperature (TC) was determined. Discussion on hysteresis behavior for the sample at room temperature is presented. An essential relation between the piezoelectric properties and the ferroelectric nature of the ceramics was detected. The piezoelectric and pyroelectric coefficients of the ceramic were studied as a function of temperature.
Fast growing mode of stimulated Raman scattering in a pure three-wave process
Authors: Lin Hai , Zha Xuejun , Shen Baifei , Li Ruxin , Chen Li-Ming , Xu Zhizhan
Published: December 2007

Stimulated Raman scattering (SRS) of a relativistic laser in plasmas is studied in the framework of the standard equation set of a three-wave process. As far as every wave involved in the process is concerned, its evolution has two aspects: time-dependent amplitude and time-dependent frequency. These two aspects affect each other. Strict analysis and numerical experiment on the full three-wave equation set reveal that a fast growing mode of the instability, which could reach a balance or saturation point during a period far shorter than an estimation based on conventional analysis, could take place in a standard three-wave process without coupling with a fourth wave. This fast growing mode is found to stem from the constraint set by the background density on the amplitude of the driven Langmuir wave. The effect of various parameters on the development of the SRS instability is studied by numerical calculation of the history of the instability in different cases.
A study on the disk-shaped piezoelectric transformer with multiple outputs
Authors: Guo Mingsen , Lam K. H. , Wang S. , Kwok K. W. , Chan Helen L. W. , Zhao X. Z.
Published: December 2007

In this study, a modified disk-shaped multiple-output piezoelectric transformer operated at the fundamental radial vibration mode has been presented. A derived equivalent circuit for the multioutput piezoelectric transformer was used to analyze the performance. Two piezoelectric transformers, a symmetrically electroded piezoelectric transformer with dual outputs and an asymmetrically electroded piezoelectric transformer with triple outputs, were fabricated with lead zirconate titanate piezoelectric ceramics. The characteristics of the two piezoelectric transformers were investigated experimentally. The piezoelectric transformer with multiple outputs has potential to be used in power supply units and other electronic circuits.
The effect of contact length on adhesion between carbon nanotubes on silicon dioxide
Authors: McElroy Kaylee , Davis Robert C. , Hawkins Aaron
Published: December 2007

The force of adhesion was measured for single walled carbon nanotubes grown over lithographically defined silicon dioxide trenches. We varied contact lengths between the nanotubes and silicon dioxide from 230to850nm. Suspended nanotubes were pushed vertically into the trenches with an atomic force microscope tip, causing them to slip along the surface. Previous work done at shorter contact lengths found that tension was constant with contact length [J. D. Whittaker et al., Nano Lett. 6, 953 (2006)]. This study finds that when the nanotube contact length approaches 1μm, the tension at which nanotubes slip begins to increase with contact length. This indicates that contact length independent adhesion is a uniquely nanoscale behavior.
Terahertz absorbance spectrum fitting method for quantitative detection of concealed contraband
Authors: Wang Yingxin , Zhao Ziran , Chen Zhiqiang , Kang Kejun , Feng Bing , Zhang Yan
Published: December 2007

We present a quantitative method for the nondestructive detection of concealed contraband based on terahertz transmission spectroscopy. Without knowing the prior information of barrier materials, the amount of concealed contraband can be extracted by approximating the terahertz absorbance spectrum of the barrier material with a low-order polynomial and then fitting the measured absorbance spectrum of the inspected object with the polynomial and the known standard spectrum of this kind of contraband. We verify the validity of this method using a sample of explosive 1,3,5-trinitro-s-triazine (RDX) covered with several different barrier materials which are commonly encountered in actual inspection, and good agreement between the calculated and actual value of the amount of RDX is obtained for the experiments performed under both nitrogen and air atmospheres. This indicates that the presented method can achieve quantitative detection of hidden contraband, which is important for security inspection applications.
Negative differential resistance induced by intermolecular interaction in a bimolecular device
Authors: Long Meng-Qiu , Chen Ke-Qiu , Wang Lingling , Zou B. S. , Shuai Z.
Published: December 2007

Using nonequilibrium Green’s functions in combination with the density-functional theory, we study the electronic transport properties of the molecular device constructed by two cofacial oligo(phenylene ethynylene) molecules and gold electrodes. The results show that negative differential resistance can be observed when the intermolecular distance closes to a certain value. We propose that a combination of the splitting of the molecular orbitals due to the intermolecular interaction and the change of the coupling between the molecules and the electrodes at different biases might be responsible for the negative differential resistance behavior.
Micromagnetic modeling of laser-induced magnetization dynamics using the Landau-Lifshitz-Bloch equation
Authors: Atxitia U. , Chubykalo-Fesenko O. , Kazantseva N. , Hinzke D. , Nowak U. , Chantrell R. W.
Published: December 2007

We present a dynamic approach to micromagnetics based on the Landau-Lifshitz-Bloch equation and Langevin dynamics. This type of modeling will be necessary at high temperatures when the magnetization length is not conserved, especially close to the Curie temperature. We model the laser-induced magnetization dynamics with various laser pulse fluences and show that the results are consistent with both experiments and atomistic modeling. Our results show different recovery rates depending on the final demagnetized state.
Stability of the mode-locked regime in quantum dot lasers
Authors: Viktorov E. A. , Mandel Paul , Kuntz M. , Fiol G. , Bimberg D. , Vladimirov A. G. , Wolfrum M.
Published: December 2007

We report on experimental and theoretical studies of the stability regime of passive mode-locked quantum dot lasers, which is decisively larger than in quantum well lasers. A small range of Q-switched instability is observed at low gain currents. Transition to Q switching is inhibited due to fast damping of the relaxation oscillations. A double pulse mode-locking regime appears for longer cavities, and exhibits bistability and coupling to the fundamental mode-locking operation.
Backward rectifying and forward Schottky behavior at Au∕Nb-1.0wt%-doped SrTiO3 interface
Authors: Cui Yimin , Wang Rongming
Published: December 2007

The Au∕Nb-1.0wt%-doped SrTiO3 junctions were successfully fabricated by magnetic controlled sputtering and annealing process. Backward diodelike behaviors were observed in as-prepared junction and the one annealed at 350°C. Transition to Schottky behavior was found in the junction annealed at 750°C; the Schottky junction shows linear capacitance-voltage (C−2-V) relationship in the reverse condition with barrier heights determined to be 1.6eV. The results of current-voltage (I-V) measurements reveal that high temperature annealing can alter interface barrier and thereby ameliorate the stability of leakage current remarkably.
Cavity polaritons from excited-subband transitions
Authors: Anappara Aji A. , Tredicucci Alessandro , Beltram Fabio , Biasiol Giorgio , Sorba Lucia , De Liberato Simone , Ciuti Cristiano
Published: December 2007

We report on the coupling of optical transitions between excited conduction subbands in GaAs∕AlGaAs heterostructures with the resonant photonic mode of a semiconductor microcavity. The coupling is found to increase with temperature, owing to the thermal excitation of carriers from the ground subband and, thanks to the large dipole-matrix element of the excited-state transition, a record splitting of 60meV is shown in the room-temperature reflectance. The importance of translating the angle-dependent spectra into energy-wavevector dispersion when the coupling is so large is highlighted, and a theoretical fitting procedure is used to extract the value of the vacuum-field Rabi energy.
Deep traps responsible for hysteresis in capacitance-voltage characteristics of AlGaN∕GaN heterostructure transistors
Authors: Polyakov A. Y. , Smirnov N. B. , Govorkov A. V. , Markov A. V. , Dabiran A. M. , Wowchak A. M. , Osinsky A. V. , Cui B. , Chow P. P. , Pearton S. J.
Published: December 2007

The origin of hysteresis in capacitance-voltage (C-V) characteristics was studied for Schottky diodes prepared on AlGaN∕GaN transistor structures with GaN (Fe) buffers. The application of reverse bias leads to a shift of C-V curves toward higher positive voltages. The magnitude of the effect is shown to increase for lower temperatures. The phenomenon is attributed to tunneling of electrons from the Schottky gate to localized states in the structure. A technique labeled “reverse” deep level transient spectroscopy was used to show that the deep traps responsible for the hysteresis have activation energies of 0.25, 0.6, and 0.9eV. Comparison with deep trap spectra of GaN buffers and Si doped n-GaN films prepared on GaN buffers suggests that the traps in question are located in the buffer layer.
Influence of sodium adsorption ratio on sodium and calcium breakthrough curves and hydraulic conductivity in soil columns
Authors: Dikinya Oagile , Hinz Christoph , Aylmore Graham
Published: December 2007

The paper examines the effects of electrolyte concentration and sodium adsorption ratio (SAR) on the relative saturated hydraulic conductivity (RHC) and the ionic behaviour of calcium (Ca) and sodium (Na) ions in the Na–Ca exchange complex. Batch binary exchange and saturated column transport experiments were carried out to quantify these effects using an agricultural Balkuling soil and a mining residue. Generally, RHC has been found to decrease with time, with increasing SAR, and with decreasing electrolyte concentration. The more rapid decrease in RHC in the mining residue, particularly at the lowest concentration (1 mmol/L), was consistent at all SAR values. The decreases in RHC were likely to be caused by partial blocking of pores by dispersed clay particles, as evidenced by the appearance of suspended clay particles in the effluent during leaching. Significant differences in RHC were observed in the passage of fronts of decreasing electrolyte concentrations for CaCl2 and SAR 15 solutions through the soil columns. These differences were attributable to structural alterations (slaking) of the media and the nature of the particles released and mobilised within the porous structure at any given point in the column. Measurements at the critical threshold concentration and turbidity concentration at SAR 15 revealed structural breakdown of the pore matrix system as evidenced by decreased RHC. The increase in SAR to 15 is initially accompanied by erratic RHC, presumably due to the break up of soil aggregates under the increased swelling forces. The less coherent mining residue soil was substantially more vulnerable to blockage of pores than the Balkuling soil in which clay particles are likely to be more readily mobilised, and hence available to re-deposit and occlude the matrix pores.
Can synchrotron micro-X-ray fluorescence spectroscopy be used to map the distribution of cadmium in soil particles?
Authors: Milham Paul J. , Payne Timothy E. , Lai Barry , Trautman Rachael L. , Cai Zhonghou , Holford Paul , Haigh Anthony M. , Conroy Jann P.
Published: December 2007

Plants take up cadmium (Cd) from the soil, and the concentration of Cd in some plant products is a health concern. Plant uptake of Cd is poorly predicted by its concentration in soils; consequently, there is interest in the binding and distribution of Cd in soil. Synchrotron micro-X-ray fluorescence spectroscopy (micro-XRFS) is the most sensitive method of observing this distribution. We used beam-line 2-ID-D of the Advanced Photon Source (APS), Argonne, to test whether this technique could map the Cd distribution in 5 soils from Greater Sydney that contained 0.3–6.4 mg Cd/kg. A subsample of one soil was spiked to contain ~100 mg Cd/kg. Cadmium was readily mapped in the Cd-enriched subsample, whereas in the unamended soils, only one Cd-rich particle was found; that is, sensitivity generally limited Cd mapping. We also examined a sample of Nauru phosphorite, which was a primary source of much of the Cd in farm soils on the peri-urban fringe of Greater Sydney. The phosphorite contained ~100 mg Cd/kg and the Cd was relatively uniformly distributed, supporting the findings of an earlier study on an apatite from Africa. The micro-XRFS at beam-line 2-ID-D of the APS can be reconfigured to increase the sensitivity at least 10-fold, which may allow the distribution of Cd and its elemental associations to be mapped in particles of most agricultural soils and facilitate other spectroscopic investigations.
Atrazine degradation and transport in runoff on a Black Vertosol
Authors: Rattray D. J. , Standley J. , Silburn D. M. , Freebairn D. M. , Spann K. P.
Published: December 2007

In Australia communities are concerned about atrazine being detected in drinking water supplies. It is important to understand mechanisms by which atrazine is transported from paddocks to waterways if we are to reduce movement of agricultural chemicals from the site of application. Two paddocks cropped with grain sorghum on a Black Vertosol were monitored for atrazine, potassium chloride (KCl) extractable atrazine, desethylatrazine (DEA), and desisopropylatrazine (DIA) at 4 soil depths (0–0.05, 0.05–0.10, 0.10–0.20, and 0.20–0.30 m) and in runoff water and runoff sediment. Atrazine + DEA + DIA (total atrazine) had a half-life in soil of 16–20 days, more rapid dissipation than in many earlier reports. Atrazine extracted in dilute potassium chloride, considered available for weed control, was initially 34% of the total and had a half-life of 15–20 days until day 30, after which it dissipated rapidly with a half life of 6 days. We conclude that, in this region, atrazine may not pose a risk for groundwater contamination, as only 0.5% of applied atrazine moved deeper than 0.20 m into the soil, where it dissipated rapidly. In runoff (including suspended sediment) atrazine concentrations were greatest during the first runoff event (57 days after application) (85 µg/L) and declined with time. After 160 days, the total atrazine lost in runoff was 0.4% of the initial application. The total atrazine concentration in runoff was strongly related to the total concentration in soil, as expected. Even after 98% of the KCl-extractable atrazine had dissipated (and no longer provided weed control), runoff concentrations still exceeded the human health guideline value of 40 µg/L. For total atrazine in soil (0–0.05 m), the range for coefficient of soil sorption (Kd) was 1.9–28.4 mL/g and for soil organic carbon sorption (KOC) was 100–2184 mL/g, increasing with time of contact with the soil and rapid dissipation of the more soluble, available phase. Partition coefficients in runoff for total atrazine were initially 3, increasing to 32 and 51 with time, values for DEA being half these. To minimise atrazine losses, cultural practices that maximise rain infiltration, and thereby minimise runoff, and minimise concentrations in the soil surface should be adopted.
Delineating soil landscape facets from digital elevation models using compound topographic index in a geographic information system
Authors: Yang X. , Chapman G. A. , Gray J. M. , Young M. A.
Published: December 2007

Soil landscapes and their component facets (or sub-units) are fundamental information for land capability assessment and land use planning. The aim of the study was to delineate soil landscape facets from readily available digital elevation models (DEM) to assist soil constraint assessment for urban and regional planning in the coastal areas of New South Wales (NSW), Australia. The Compound Topographic Index (CTI) surfaces were computed from 25 m DEM using a D-infinity algorithm. The cumulative frequency distribution of CTI values within each soil landscape was examined to identify the values corresponding to the area specified for each unmapped facet within the soil landscape map unit. Then these threshold values and CTI surfaces were used to generate soil landscape facet maps for the entire coastal areas of NSW. Specific programs were developed for the above processes in a geographic information system so that they are automated, fast, and repeatable. The modelled facets were assessed by field validation and the overall accuracy reached 93%. The methodology developed in this study has been proven to be efficient in delineating soil landscape facets, and allowing for the identification of land constraints at levels of unprecedented detail for the coast of NSW.
Agronomic values of greenwaste biochar as a soil amendment
Authors: Chan K. Y. , Van Zwieten L. , Meszaros I. , Downie A. , Joseph S.
Published: December 2007

A pot trial was carried out to investigate the effect of biochar produced from greenwaste by pyrolysis on the yield of radish (Raphanus sativus var. Long Scarlet) and the soil quality of an Alfisol. Three rates of biochar (10, 50 and 100 t/ha) with and without additional nitrogen application (100 kg N/ha) were investigated. The soil used in the pot trial was a hardsetting Alfisol (Chromosol) (0–0.1 m) with a long history of cropping. In the absence of N fertiliser, application of biochar to the soil did not increase radish yield even at the highest rate of 100 t/ha. However, a significant biochar × nitrogen fertiliser interaction was observed, in that higher yield increases were observed with increasing rates of biochar application in the presence of N fertiliser, highlighting the role of biochar in improving N fertiliser use efficiency of the plant. For example, additional increase in DM of radish in the presence of N fertiliser varied from 95% in the nil biochar control to 266% in the 100 t/ha biochar-amended soils. A slight but significant reduction in dry matter production of radish was observed when biochar was applied at 10 t/ha but the cause is unclear and requires further investigation. Significant changes in soil quality including increases in pH, organic carbon, and exchangeable cations as well as reduction in tensile strength were observed at higher rates of biochar application (>50 t/ha). Particularly interesting are the improvements in soil physical properties of this hardsetting soil in terms of reduction in tensile strength and increases in field capacity.
Climate change impacts on forestry
Authors: Kirilenko Andrei P. , Sedjo Roger A.
Published: December 2007

Changing temperature and precipitation pattern and increasing concentrations of atmospheric CO
2
are likely to drive significant modifications in natural and modified forests. Our review is focused on recent publications that discuss the changes in commercial forestry, excluding the ecosystem functions of forests and nontimber forest products. We concentrate on potential direct and indirect impacts of climate change on forest industry, the projections of future trends in commercial forestry, the possible role of biofuels, and changes in supply and demand.
Crop and pasture response to climate change
Authors: Tubiello Francesco N. , Soussana Jean-François , Howden S. Mark
Published: December 2007

We review recent research of importance to understanding crop and pasture plant species response to climate change. Topics include plant response to elevated CO2concentration, interactions with climate change variables and air pollutants, impacts of increased climate variability and frequency of extreme events, the role of weeds and pests, disease and animal health, issues in biodiversity, and vulnerability of soil carbon pools. We critically analyze the links between fundamental knowledge at the plant and plot level and the additional socio-economic variables that determine actual production and trade of food at regional to global scales. We conclude by making recommendations for current and future research needs, with a focus on continued and improved integration of experimental and modeling efforts.
Input–output robustness in simple bacterial signaling systems
Authors: Shinar Guy , Milo Ron , Martínez María Rodríguez , Alon Uri
Published: December 2007

Biological signaling systems produce an output, such as the level of a phosphorylated protein, in response to defined input signals. The output level as a function of the input level is called the system's input–output relation. One may ask whether this input–output relation is sensitive to changes in the concentrations of the system's components, such as proteins and ATP. Because component concentrations often vary from cell to cell, it might be expected that the input–output relation will likewise vary. If this is the case, different cells exposed to the same input signal will display different outputs. Such variability can be deleterious in systems where survival depends on accurate match of output to input. Here we suggest a mechanism that can provide input–output robustness, that is, an input–output relation that does not depend on variations in the concentrations of any of the system's components. The mechanism is based on certain bacterial signaling systems. It explains how specific molecular details can work together to provide robustness. Moreover, it suggests an approach that can help identify a wide family of nonequilibrium mechanisms that potentially have robust input–output relations.
Mesozooplankton grazing in the coastal Gulf of Alaska: Neocalanus spp. vs. other mesozooplankton
Authors: Liu Hongbin , Dagg Michael J. , Napp Jeffrey M. , Sato Riki
Published: December 2007

Liu, H., Dagg, J. M., Napp, J. M., and Sato, R. 2008. Mesozooplankton grazing in the coastal Gulf of Alaska: Neocalanus spp. vs. other mesozooplankton. – ICES Journal of Marine Science, 65: 351–360. Three species of large calanoid copepod, Neocalanus flemingeri, Neocalanus plumchrus, and Neocalanus cristatus, dominate the spring biomass of mesozooplankton in the Subarctic Pacific. We compared the grazing impact of Neocalanus species on phytoplankton with grazing by the remainder of the mesozooplankton community in the coastal and shelf waters of the Gulf of Alaska during spring and summer 2003. Neocalanus spp. and other mesozooplankton fed mainly on particles >20 µm, and phytoplankton in the smaller size-fractions (<20 µm) increased in the presence of mesozooplankton, possibly because of a trophic cascade resulting from mesozooplankton consumption of microzooplankton. Neocalanus spp. accounted for most of the mesozooplankton biomass and herbivory in the shelf water of the Gulf of Alaska and in the Prince William Sound (PWS) during April/May. The biomass of other mesozooplankton (mostly small copepods) varied seasonally and spatially; it did not increase in summer after the descent of Neocalanus spp. from the surface layer. On the basis of the clearance rates obtained from our experiments, in spring, grazing by Neocalanus spp. and the remaining mesozooplankton consumed ∼10% of daily growth of phytoplankton >20 µm in the outer-shelf region, where chlorophyll a concentrations were <0.5 mg m−3, and in PWS. Mesozooplankton consumed a smaller percentage of the >20 µm daily phytoplankton production in the inner- and mid-shelf regions where chlorophyll a concentrations were typically >5 mg m−3 with blooms of large diatoms. In summer, without Neocalanus spp. in the surface layer, mesozooplankton grazing accounted for a very small proportion of phytoplankton production across the whole shelf.
Randomised trial of laparoscopic Burch colposuspension versus tension‐free vaginal tape: long‐term follow up
Authors: Jelovsek JE , Barber MD , Karram MM , Walters MD , Paraiso MFR
Published: December 2007

Objective  To compare the long‐term efficacy of laparoscopic Burch colposuspension with tension‐free vaginal tape (TVT) for the treatment of urodynamic stress urinary incontinence (SUI).

Design  Long‐term follow up from a prospective randomised trial.

Setting  Academic tertiary referral centre.

Sample  Seventy‐two women with urodynamic SUI from two institutions.

Methods  Subjects were randomised to either laparoscopic Burch or TVT from August 1999 to August 2002. Follow‐up evaluations occurred 6 months, 1 year, 2 years, and 4–8 years after surgery.

Main outcome measures  Subjects completed the Incontinence Severity Index, Urogenital Distress Inventory 6 (UDI‐6), Incontinence Impact Questionnaire (IIQ‐7), and Patient Global Impression of Improvement (PGI‐I) scales.

Results  Median follow‐up duration was 65 months (range 12–88 months) with 92% completing at least one follow‐up visit. Seventy‐four percent of subjects had long‐term (4–8 years) follow up. Fifty‐eight percent of subjects receiving laparoscopic Burch compared with 48% of TVT subjects reported any urinary incontinence 4–8 years after surgery (Relative Risk (RR):1.19; 95% CI: 0.71–2.0) with no significant difference between groups. Bothersome SUI symptoms were seen in 11 and 8%, respectively, 4–8 years after surgery (P= 0.26). There was significant improvement in the postoperative UDI‐6 and IIQ‐7 scores in both groups at 1–2 years that were maintained throughout follow up with no significant differences between the groups.

Conclusions  TVT has similar long‐term efficacy to laparoscopic Burch for the treatment of SUI. A substantial proportion of subjects have some degree of urinary incontinence 4–8 years after surgery; however, the majority of incontinence is not bothersome.
The carotid bodies influence growth responses to moderate maternal undernutrition in late‐gestation fetal sheep
Authors: Burrage D , Green LR , Moss TJM , Sloboda DM , Nitsos I , Newnham JP , Hanson MA
Published: December 2007

Objective  To determine the role of carotid sinus innervation on differential fetal organ growth during maternal nutrient restriction in late pregnancy.

Design  Randomised controlled study.

Setting  University research facility.

Sample  Thirty‐nine Merino ewes.

Methods  At 113 days gestational age (dGA), fetuses were bilaterally carotid sinus denervated or sham denervated. From 118 dGA, the surgery groups were subdivided into two dietary groups, and their ewes were fed 100% of nutrient requirements or 50% until tissue collection at 140 dGA. This provided four groups (sham/control diet, sham/restricted diet, denervated/control diet and denervated/restricted diet).

Main outcome measures  Fetal organ weights and hormone levels and maternal weight change during the dietary restriction.

Results  Adrenal glands were larger in sham/restricted diet fetuses than in sham/control diet or denervated/restricted diet fetuses (P < 0.05). Fetal adrenal weight and brain‐to‐liver weight ratio were positively related to maternal weight change during the nutritional challenge in sham fetuses only (P < 0.05). Fetal liver weight was negatively related to maternal weight change during nutritional challenge in sham fetuses only (P < 0.05).

Conclusions  We have shown a reduction in liver growth but sparing of adrenal growth in response to moderate maternal undernutrition, which is dependent on intact carotid body innervation. This suggests a new role for the carotid bodies in the control of differential organ growth during such undernutrition.
Determining Ca2+‐sensor binding time and its variability in evoked neurotransmitter release
Authors: Yoon Ava Chomee , Kathpalia Vinnie , D'Silva Sahana , Cimenser Aylin , Hua Shao‐Ying
Published: December 2007

The speed and reliability of neuronal reactions are important factors for proper functioning of the nervous system. To understand how organisms use protein molecules to carry out very fast biological actions, we quantified single‐molecule reaction time and its variability in synaptic transmission. From the synaptic delay of crayfish neuromuscular synapses the time for a few Ca2+ ions to bind with their sensors in evoked neurotransmitter release was estimated. In standard crayfish saline at room temperature, the average Ca2+ binding time was 0.12 ms for the first evoked quanta. At elevated extracellular Ca2+ concentrations this binding time reached a limit due to saturation of Ca2+ influx. Analysis of the synaptic delay variance at various Ca2+ concentrations revealed that the variability of the Ca2+‐sensor binding time is the major source of the temporal variability of synaptic transmission, and that the Ca2+‐independent molecular reactions after Ca2+ influx were less stochastic. The results provide insights into how organisms maximize reaction speed and reliability.
Mechanical Stimulation of Tendon Tissue Engineered Constructs: Effects on Construct Stiffness, Repair Biomechanics, and Their Correlation
Authors: Shearn Jason T. , Juncosa-Melvin Natalia , Boivin Gregory P. , Galloway Marc T. , Goodwin Wendy , Gooch Cynthia , Dunn Michael G. , Butler David L.
Published: December 2007

The objective of this study was to determine how in vitro mechanical stimulation of tissue engineered constructs affects their stiffness and modulus in culture and tendon repair biomechanics 12weeks after surgical implantation. Using six female adult New Zealand White rabbits, autogenous tissue engineered constructs were created by seeding mesenchymal stem cells (0.1×106cells∕ml) in collagen gel (2.6mg∕ml) and combining both with a collagen sponge. Employing a novel experimental design strategy, four constructs from each animal were mechanically stimulated (one 1Hzcycle every 5min to 2.4% peak strain for 8h∕day for 2weeks) while the other four remained unstretched during the 2week culture period. At the end of incubation, three of the mechanically stimulated (S) and three of the nonstimulated (NS) constructs from each animal were assigned for in vitro mechanical testing while the other two autogenous constructs were implanted into bilateral full-thickness, full-length defects created in the central third of rabbit patellar tendons (PTs). No significant differences were found in the in vitro linear stiffnesses between the S (0.15±0.1N∕mm) and NS constructs (0.08±0.02N∕mm; mean±SD). However, in vitro mechanical stimulation significantly increased the structural and material properties of the repair tissue, including a 14% increase in maximum force (p=0.01), a 50% increase in linear stiffness (p=0.001), and 23–41% increases in maximum stress and modulus (p=0.01). The S repairs achieved 65%, 80%, 60%, and 40% of normal central PT maximum force, linear stiffness, maximum stress, and linear modulus, respectively. The results for the S constructs exceed values obtained previously by our group using the same animal and defect model, and to our knowledge, this is the first study to show the benefits of in vitro mechanical stimulation on tendon repair biomechanics. In addition, the linear stiffnesses for the construct and repair were positively correlated (r=0.56) as were their linear moduli (r=0.68). Such in vitro predictors of in vivo outcome hold the potential to speed the development of tissue engineered products by reducing the time and costs of in vivo studies.
Mechanical Stimulation of Tissue Engineered Tendon Constructs: Effect of Scaffold Materials
Authors: Nirmalanandhan Victor S. , Dressler Matthew R. , Shearn Jason T. , Juncosa-Melvin Natalia , Rao Marepalli , Gooch Cynthia , Bradica Gino , Butler David L.
Published: December 2007

Our group has shown that numerous factors can influence how tissue engineered tendon constructs respond to in vitro mechanical stimulation. Although one study showed that stimulating mesenchymal stem cell (MSC)–collagen sponge constructs significantly increased construct linear stiffness and repair biomechanics, a second study showed no such effect when a collagen gel replaced the sponge. While these results suggest that scaffold material impacts the response of MSCs to mechanical stimulation, a well-designed intra-animal study was needed to directly compare the effects of type-I collagen gel versus type-I collagen sponge in regulating MSC response to a mechanical stimulus. Eight constructs from each cell line (n=8 cell lines) were created in specially designed silicone dishes. Four constructs were created by seeding MSCs on a type-I bovine collagen sponge, and the other four were formed by seeding MSCs in a purified bovine collagen gel. In each dish, two cell-sponge and two cell-gel constructs from each line were then mechanically stimulated once every 5min to a peak strain of 2.4%, for 8h∕day for 2 weeks. The other dish remained in an incubator without stimulation for 2 weeks. After 14 days, all constructs were failed to determine mechanical properties. Mechanical stimulation significantly improved the linear stiffness (0.048±0.009 versus 0.015±0.004; mean±SEM (standard error of the mean ) N/mm) and linear modulus (0.016±0.004 versus 0.005±0.001; mean±SEM MPa) of cell-sponge constructs. However, the same stimulus produced no such improvement in cell-gel construct properties. These results confirm that collagen sponge rather than collagen gel facilitates how cells respond to a mechanical stimulus and may be the scaffold of choice in mechanical stimulation studies to produce functional tissue engineered structures.
Mechanical Properties of Stapedial Tendon in Human Middle Ear
Authors: Cheng Tao , Gan Rong Z.
Published: December 2007

Measurement on mechanical properties of the stapedial tendon in human middle ear has not been reported in the literature. In this paper, we used the material testing system to conduct uniaxial tensile, stress relaxation, and failure tests on stapedial tendon specimens harvested from human temporal bones. The digital image correlation method was employed to assess the boundary effect on experimental data. The stress-strain relationship of the tendon obtained from experiments was analyzed using the hyperelastic Ogden model. The results presented include (1) the constitutive equation of the tendon for stretch ratio of 1–1.4 or stress range of 0–1.45MPa, (2) the mean ultimate stress and stretch ratio of the tendon at 4.04MPa and 1.65, respectively, and (3) the hysteresis and normalized stress relaxation function of the tendon. The data reported in this paper contribute to ear mechanics, especially for theoretical analysis of human ear function.
The Coupled Motion of the Femur and Patella During In Vivo Weightbearing Knee Flexion
Authors: Li Guoan , Papannagari Ramprasad , Nha Kyung Wook , DeFrate Louis E. , Gill Thomas J. , Rubash Harry E.
Published: December 2007

The movement of the knee joint consists of a coupled motion between the tibiofemoral and patellofemoral articulations. This study measured the six degrees-of-freedom kinematics of the tibia, femur, and patella using dual-orthogonal fluoroscopy and magnetic resonance imaging. Ten normal knees from ten living subjects were investigated during weightbearing flexion from full extension to maximum flexion. The femoral and the patellar motions were measured relative to the tibia. The femur externally rotated by 12.9deg and the patella tilted laterally by 16.3deg during the full range of knee flexion. Knee flexion was strongly correlated with patellar flexion (R2=0.91), posterior femoral translation was strongly correlated to the posterior patellar translation (R2=0.87), and internal-external rotation of the femur was correlated to patellar tilt (R2=0.73) and medial-lateral patellar translation (R2=0.63). These data quantitatively indicate a kinematic coupling between the tibia, femur, and patella, and provide base line information on normal knee joint kinematics throughout the full range of weightbearing flexion. The data also suggest that the kinematic coupling of tibia, femur, and patella should be considered when investigating patellar pathologies and when developing surgical techniques to treat knee joint diseases.
New Modality for Maximizing Cryosurgical Killing Scope While Minimizing Mechanical Incision Trauma Using Combined Freezing-Heating System
Authors: Yan Jing-Fu , Deng Zhong-Shan , Liu Jing , Zhou Yi-Xin
Published: December 2007

Cryosurgery is a minimally invasive surgical technique using extremely low temperature to destroy undesired tissues. A surgical freezing margin of at least 1 cm is often recommended to avoid local tumor recurrence after surgery. For treating slender or elongated solid tumors in a conventional cryosurgery, simultaneous insertion of multiple cryoprobes is a necessity to guarantee an adequate killing scope. However, the risk of mechanical incision trauma may outweigh the benefits of such therapy. To resolve this difficulty, we proposed a new cryosurgical treatment modality, which can significantly maximize the killing scope while minimize the incision trauma, using the recently developed combined cryosurgical-hyperthermia treatment system (CCHTS). The method, named as one time’s percutaneous insertion while multiple times’ freezing∕heating ablation, is rather flexible in administrating a complex cryosurgical process and avoids certain shortcomings of conventional freezing strategies. Owing to the powerful heating function, the present probe can be easily moved back along its original incision tract to the desired positions immediately after initiating the heating. Then, a new iceball can be formed there while the iceballs generated before still remain unmelted in the following cycles. Consequently, a slender iceball could be generated to embrace the whole elongated tumor. This is, however, rather hard to achieve for a conventional cryosurgery with only one single freezing function or using only one probe. To visually demonstrate the feasibility and potential advantage of the present method, proof of concept in vitro gel experiments were performed. In addition, tests and corresponding theoretical simulations were performed on pork tissues. All the results indicate that the elongated iceball could be easily generated by using only one CCHTS probe owing to its strong freezing∕heating capability. In this way, a large number of incisions with multiple probes, commonly adopted in a conventional cryosurgery, can be avoided and the serious mechanical trauma including potential dangers can thus be significantly reduced. Meanwhile, the cost for the operation and postmedical care will be lowered. The present strategies are expected to be valuable in administrating a highly efficient and minimally invasive cryosurgery in the near future.
Compatibility of Segmenting Fluids in Continuous-Flow Microfluidic PCR
Authors: Walsh E. J. , King C. , Grimes R. , Gonzalez A. , Ciobanu D.
Published: December 2007

Continuous flow offers notable advantages over batch processing for analytical applications like gene expression profiling of biological material, which demands very high processing. The technology of choice for future genetic analyzers will most likely use the polymerase chain reaction (PCR); therefore, high-throughput, high-speed PCR devices have raised enormous interest. Continuous-flow, biphasic PCR can meet these requirements but segmenting∕carrier fluids chemically compatible with the PCR are needed. The present paper compares several fluids in terms of compatibility with PCR and fluidic dynamics in a continuous, two-phase flow microfluidic device, and PCR efficiency was assessed quantitatively. The results represent the first step toward rational fluid design for biphasic continuous PCR.
A New Medical Parallel Robot and Its Static Balancing Optimization
Authors: Lessard Simon , Bigras Pascal , Bonev Ilian A.
Published: December 2007

The preoperative procedure for treating peripheral arterial disease requires 3D mapping of the blood vessel of interest. Because the available technologies are costly and invasive, and have an iodizing effect, new 3D imaging systems are being developed from ultrasound scanning technology using a robot as the probe manipulator. The authors of this paper have designed a new parallel robot along these lines. In response to the great concern for safety generated by the use of robots in medicine, we present a new approach for static balancing to enhance the safety of the proposed robot. Because total balancing is not practical for this device, the approach we have chosen is an optimization based on the addition of torsion springs on the actuated and the passive revolute joints. The optimization consists of a sequence of objectives, which are met using a linear programming technique, since the equations of torques and forces are linear with respect to the unknown variables.
β-Catenin Defines Head Versus Tail Identity During Planarian Regeneration and Homeostasis
Authors: Gurley Kyle A. , Rink Jochen C. , Alvarado Alejandro Sánchez
Published: December 2007

After amputation, freshwater planarians properly regenerate a head or tail from the resulting anterior or posterior wound. The mechanisms that differentiate anterior from posterior and direct the replacement of the appropriate missing body parts are unknown. We found that in the planarian
Schmidtea mediterranea
, RNA interference (RNAi) of β
-catenin
or
dishevelled
causes the inappropriate regeneration of a head instead of a tail at posterior amputations. Conversely, RNAi of the β-catenin antagonist
adenomatous polyposis coli
results in the regeneration of a tail at anterior wounds. In addition, the silencing of β-
catenin
is sufficient to transform the tail of uncut adult animals into a head. We suggest that β-catenin functions as a molecular switch to specify and maintain anteroposterior identity during regeneration and homeostasis in planarians.
Evidence of autumn nitrogen limitation and contribution of picoplankton to carbon fixation in Lake Tahoe
Authors: Chang Cecily C. Y. , Petersen Richard
Published: December 2007

Water samples were collected from Lake Tahoe at midlake and nearshore stations at three depths (25, 50, and 75 m, corresponding to light intensities of approximately 10, 1, and 0.1% of surface light) in May and September. The water samples were evaluated to decide the following: (1) whether carbon fixation was N-limited and whether there were differences between picoplankton and larger phytoplankters and (2) the relative importance of picoplankton carbon fixation and related photosynthetic parameters. Evidence of N-limitation was observed only in September at the midlake station for the populations at 50 and 75 m, and to a lesser extent at the nearshore station at 75 m, but only for the nanoplankton fraction. The contribution of picoplankton to total carbon fixation ranged from 34 to 69% and did not increase with depth. Low values for Ik, the photoadaptation parameter, for deep water populations (0.1% light level) in September, but not May, suggested that these populations were adapted to low light in the fall but not the spring.
A wall jet to measure the attachment strength of zebra mussels
Authors: Ackerman Josef Daniel , Ethier C. Ross , Spelt Jan K. , Allen D. Grant , Cottrell Catherine M.
Published: December 2007

A wall jet is presented as a novel means of measuring the attachment strength of zebra mussels. Attachment strength was inferred from a fluid detachment parameter (DP), defined as the nominal wall shear stress at the detachment site × mussel length2. DP varied significantly on natural and artificial substrates: in tests with 288 Dreissena bugensis (≈8–10 mm long), the mean (±SE) DP was 8.9 ± 0.9 mPa∙m2 on limestone/dolomite, 5.6 ± 0.5 mPa∙m2 on polyvinylchloride, 4.3 ± 0.4 mPa∙m2 on stainless steel, 4.2 ± 0.5 mPa∙m2 on aluminum, and 2.5 ± 0.3 mPa∙m2 on polymethylmethacrylate (Plexiglas). The attachment strength of postlarval mussels (plantigrades; <1 mm) was two orders of magnitude less than adult mussels. These results were validated with conventional tensile loadings, in which 633 Dreissena bugensis and 26 Dreissena polymorpha were pulled off substrates with a calibrated force scale. The tensile loadings results were comparable with those of marine bivalves. Good correlation between pull-off force and DP was observed. Information of this nature is useful for the implementation of environmentally benign zebra mussel controls.
Introgression and fixation of Arctic char (Salvelinus alpinus) mitochondrial genome in an allopatric population of brook trout (Salvelinus fontinalis)
Authors: Bernatchez Louis , Glémet Hélène , Wilson Chris C. , Danzmann Roy G.
Published: December 2007

Although mitochondrial introgression between taxa has been increasingly documented, interspecific replacement of mtDNA is rare, particularly when the donor species is absent. We document evidence for a population of brook trout (Salvelinus fontinalis) in which all individuals possess the mitochondrial genome of Arctic char (S. alpinus) despite the present-day absence of the latter species in the watershed where the population is located. The mitochondrial genotype of 48 brook trout from Lake Alain (Québec) was characterized by RFLP analysis performed over the entire mtDNA molecule and/or a 2.5-kb PCR-amplified segment of the ND-5/6 region. Although the fish examined were morphologically indistinguishable from typical brook trout and homozygous for the diagnostic alleles characteristic of brook trout, the mtDNA of all individuals was identical to the Québec Arctic char haplotype. Together, these results indicate that the mtDNA haplotype observed in Lake Alain brook trout has resulted from ancient introgression with Arctic char rather than ancestral polymorphism or convergent evolution. They also demonstrate that introgressive hybridization between those two species can have significant and long-term effects on their genetic composition.
Allometric and environmental correlates of territory size in juvenile Atlantic salmon (Salmo salar)
Authors: Keeley Ernest R. , Grant James W. A.
Published: December 2007

We observed juvenile Atlantic salmon (Salmo salar) over a wide range of stream conditions and body sizes to determine the relative importance of environmental factors and body size as predictors of territory size. Defended and foraging areas were virtually identical in size. Eighty-eight percent of the variation in territory size was explained by differences in body size and age; territory size increased with body size, but young-of-the-year salmon had relatively larger territories for their body size than older fish. Territory size was inversely related to food abundance, the only significant environmental correlate of territory size, but food only explained an additional 2% of the variation in territory size. Intruder pressure, visual isolation, and current velocity were not significantly related to territory size. The allometric scaling of territory size was consistent with the hypothesis that Atlantic salmon maintain a maximum daily ration of drift flowing over their territory. Atlantic salmon in Catamaran Brook have larger territories than is reported in the literature for other stream-dwelling salmonids of a similar size.