bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamic Simulation Pericardial Bioprosthetic Heart Valve Function
Authors: Kim Hyunggun , Lu Jia , Sacks Michael S. , Chandran Krishnan B.
Published: September 2006

While providing nearly trouble-free function for 10–12 years, current bioprosthetic heart valves (BHV) continue to suffer from limited long-term durability. This is usually a result of leaflet calcification and/or structural degeneration, which may be related to regions of stress concentration associated with complex leaflet deformations. In the current work, a dynamic three-dimensional finite element analysis of a pericardial BHV was performed with a recently developed FE implementation of the generalized nonlinear anisotropic Fung-type elastic constitutive model for pericardial BHV tissues (W. Sun and M.S. Sacks, 2005, [Biomech. Model. Mechanobiol., 4(2-3), pp. 190–199]). The pericardial BHV was subjected to time-varying physiological pressure loading to compute the deformation and stress distribution during the opening phase of the valve function. A dynamic sequence of the displacements revealed that the free edge of the leaflet reached the fully open position earlier and the belly region followed. Asymmetry was observed in the resulting displacement and stress distribution due to the fiber direction and the anisotropic characteristics of the Fung-type elastic constitutive material model. The computed stress distribution indicated relatively high magnitudes near the free edge of the leaflet with local bending deformation and subsequently at the leaflet attachment boundary. The maximum computed von Mises stress during the opening phase was 33.8kPa. The dynamic analysis indicated that the free edge regions of the leaflets were subjected to significant flexural deformation that may potentially lead to structural degeneration after millions of cycles of valve function. The regions subjected to time varying flexural deformation and high stresses of the present study also correspond to regions of tissue valve calcification and structural failure reported from explanted valves. In addition, the present simulation also demonstrated the importance of including the bending component together with the in-plane material behavior of the leaflets towards physiologically realistic deformation of the leaflets. Dynamic simulations with experimentally determined leaflet material specification can be potentially used to modify the valve towards an optimal design to minimize regions of stress concentration and structural failure.
Effects of Inertia and Gravity on Liquid Plug Splitting at a Bifurcation
Authors: Zheng Y. , Fujioka H. , Grotberg J. C. , Grotberg J. B.
Published: September 2006

Liquid plugs may form in pulmonary airways during the process of liquid instillation or removal in many clinical treatments. During inspiration the plug may split at airway bifurcations and lead to a nonuniform final liquid distribution, which can adversely affect treatment outcomes. In this paper, a combination of bench top experimental and theoretical studies is presented to study the effects of inertia and gravity on plug splitting in an airway bifurcation model to simulate the liquid distributions in large airways. The splitting ratio, Rs, is defined as the ratio of the plug volume entering the upper (gravitationally opposed) daughter tube to the lower (gravitationally favored) one. Rs is measured as a function of parent tube Reynolds number, Rep; gravitational orientations for roll angle, ϕ, and pitch angle, γ; parent plug length LP; and the presence of pre-existing plug blockages in downstream daughter tubes. Results show that increasing Rep causes more homogeneous splitting. A critical Reynolds number Rec is found to exist so that when Rep⩽Rec, Rs=0, i.e., no liquid enters the upper daughter tube. Rec increases while Rs decreases with increasing the gravitational effect, i.e., increasing ϕ and γ. When a blockage exists in the lower daughter, Rec is only found at ϕ=60deg in the range of Rep studied, and the resulting total mass ratio can be as high as 6, which also asymptotes to a finite value for different ϕ as Rep increases. Inertia is further demonstrated to cause more homogeneous plug splitting from a comparison study of Rs versus Cap (another characteristic speed) for three liquids: water, glycerin, and LB-400X. A theoretical model based on entrance flow for the plug in the daughters is developed and predicts Rs versus Rep. The frictional pressure drop, as a part of the total pressure drop, is estimated by two fitting parameters and shows a linear relationship with Rep. The theory provides a good prediction on liquid plug splitting and well simulates the liquid distributions in the large airways of human lungs.
Anterior Displacement of the TMJ Disk: Repositioning of the Disk Using a Mitek System. A 3D Finite Element Study
Authors: Pérez del Palomar A. , Doblaré M.
Published: September 2006

In this paper the behaviors of the temporomandibular joint (TMJ) with an anteriorly displaced disk without reduction and with a surgically repositioned one were compared with the response of a healthy disk during jaw opening. The movement of each joint was obtained imposing the same opening path between incisors and assuming that the movement of the condyle is determined by the passive action of the masticatory muscles and the restrictions imposed by the articulating surfaces and the ligaments. A fiber-reinforced porohyperelastic model was used to simulate the behavior of the articular disk. The influence of the friction coefficient in the diseased joint was also analyzed, finding that the final displacement of the complex condyle-disk was smaller as the friction coefficient increased. On the other hand, its displacement in the repositioned joint was different than in the healthy case because the artificial sutures used in the surgery do not fully stabilize the disk posteriorly as the retrodiscal tissue does. The stress response of the disk changed in both pathologic cases: in the displaced joint the highest stresses moved from the intermediate zone (healthy case) to the posterior band, and in the reconstructed one the most loaded zone moved posteriorly at total opening. Besides, local stress concentrations appeared in the neighborhood of the artificial sutures and therefore damage of the disk and releasing of the sutures might be possible postoperatively.
Mitochondrial Dynamics in Chondrocytes and Their Connection to the Mechanical Properties of the Cytoplasm
Authors: Bomzon Ze’ev , Knight Martin M. , Bader Dan L. , Kimmel Eitan
Published: September 2006

Background: The motion and redistribution of intracellular organelles is a fundamental process in cells. Organelle motion is a complex phenomenon that depends on a large number of variables including the shape of the organelle, the type of motors with which the organelles are associated, and the mechanical properties of the cytoplasm. This paper presents a study that characterizes the diffusive motion of mitochondria in chondrocytes seeded in agarose constructs and what this implies about the mechanical properties of the cytoplasm. Method of approach: Images showing mitochondrial motion in individual cells at 30s intervals for 15min were captured with a confocal microscope. Digital image correlation was used to quantify the motion of the mitochondria, and the mean square displacement (MSD) was calculated. Statistical tools for testing whether the characteristic motion of mitochondria varied throughout the cell were developed. Calculations based on statistical mechanics were used to establish connections between the measured MSDs and the mechanical nature of the cytoplasm. Results: The average MSD of the mitochondria varied with time according to a power law with the power term greater than 1, indicating that mitochondrial motion can be viewed as a combination of diffusion and directional motion. Statistical analysis revealed that the motion of the mitochondria was not uniform throughout the cell, and that the diffusion coefficient may vary by over 50%, indicating intracellular heterogeneity. High correlations were found between movements of mitochondria when they were less than 2μm apart. The correlation is probably due to viscoelastic properties of the cytoplasm. Theoretical analysis based on statistical mechanics suggests that directed diffusion can only occur in a material that behaves like a fluid on large time scales. Conclusions: The study shows that mitochondria in different regions of the cell experience different characteristic motions. This suggests that the cytoplasm is a heterogeneous viscoelastic material. The study provides new insight into the motion of mitochondria in chondrocytes and its connection with the mechanical properties of the cytoplasm.
An Efficient Robotic Tendon for Gait Assistance
Authors: Hollander Kevin W. , Ilg Robert , Sugar Thomas G. , Herring Donald
Published: September 2006

A robotic tendon is a spring based, linear actuator in which the stiffness of the spring is crucial for its successful use in a lightweight, energy efficient, powered ankle orthosis. Like its human analog, the robotic tendon uses its inherent elastic nature to reduce both peak power and energy requirements for its motor. In the ideal example, peak power required of the motor for ankle gait is reduced from 250 W to just 77 W. In addition, ideal energy requirements are reduced from nearly 36 J to just 21 J. Using this approach, an initial prototype has provided 100% of the power and energy necessary for ankle gait in a compact 0.95kg package, seven times less than an equivalent motor/gearbox system.
Modified Bilston Nonlinear Viscoelastic Model for Finite Element Head Injury Studies
Authors: Shen F. , Tay T. E. , Li J. Z. , Nigen S. , Lee P. V. S. , Chan H. K.
Published: September 2006

This paper proposes a modified nonlinear viscoelastic Bilston model (Bilston et al., 2001, Biorheol., 38, pp. 335–345). for the modeling of brain tissue constitutive properties. The modified model can be readily implemented in a commercial explicit finite element (FE) code, PamCrash. Critical parameters of the model have been determined through a series of rheological tests on porcine brain tissue samples and the time-temperature superposition (TTS) principle has been used to extend the frequency to a high region. Simulations by using PamCrash are compared with the test results. Through the use of the TTS principle, the mechanical and rheological behavior at high frequencies up to 104rad∕s may be obtained. This is important because the properties of the brain tissue at high frequencies and impact rates are especially relevant to studies of traumatic head injury. The averaged dynamic modulus ranges from 130Pato1500Pa and loss modulus ranges from 35Pato800Pa in the frequency regime studied (0.01rad∕sto3700rad∕s). The errors between theoretical predictions and averaged relaxation test results are within 20% for strains up to 20%. The FEM simulation results are in good agreement with experimental results. The proposed model will be especially useful for application to FE analysis of the head under impact loads. More realistic analysis of head injury can be carried out by incorporating the nonlinear viscoelastic constitutive law for brain tissue into a commercial FE code.
A Novel Single-Photon Counting Technique Applied to Highly Sensitive Measurement of [Ca2+]i Transient in Human Aortic Smooth Muscle Cells
Authors: Tada Shigeru , Okazaki Ken
Published: September 2006

This study demonstrates that aequorin, a luminescent natural dye, is useful for vascular cell intracellular Ca2+ concentration ([Ca2+]i) determination. A new single-photon counting technique was developed to resolve the effects of fluid flow shear stress on [Ca2+]i in human aortic smooth muscle cells (HASMCs). Confluent HASMCs were grown on petri dishes loaded with aequorin. Then the dishes were placed in a luminometer chamber after the physiological level of shear stress was applied to the HASMC surfaces. The chamber was housed inside a highly sensitive photomultiplier tube. It detected ultraweak photon emission in response to the [Ca2+]i transient. In the presence of 2.0mM extracellular Ca2+, a shear stress of 12dyn∕cm2, applied for 60s to the top surface of the HASMC monolayer, elicited a sharp increase in [Ca2+]i.
Detecting and Predicting Early Faults of Complex Rotating Machinery Based on Cyclostationary Time Series Model
Authors: Chen Z. S. , Yang Y. M. , Hu Z. , Shen G. J.
Published: September 2006

Vibration signals of complex rotating machinery are often cyclostationary, so in this paper one novel method is proposed to detect and predict early faults based on the linear (almost) periodically time-varying autoregressive (LPTV-AR) model. At first the algorithms of identifying model parameters and order are presented using the higher-order cyclic-cumulant, which can suppress additive stationary noises and improve the signal to noise ratio (SNR). Then numerical simulations are done and the results indicate that this model is more effective for cyclostationary signals than the classical AR model. In the end the proposed method is used for detecting incipient gear crack fault in a helicopter gearbox. The results demonstrate that the approach can be used to detect and predict early faults of complex rotating machinery by the kurtosis of the residual signal.
Rapid Chemically Induced Changes of PtdIns(4,5)P
2
Gate KCNQ Ion Channels
Authors: Suh Byung-Chang , Inoue Takanari , Meyer Tobias , Hille Bertil
Published: September 2006

To resolve the controversy about messengers regulating KCNQ ion channels during phospholipase C–mediated suppression of current, we designed translocatable enzymes that quickly alter the phosphoinositide composition of the plasma membrane after application of a chemical cue. The KCNQ current falls rapidly to zero when phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P
2
or PI(4,5)P
2
] is depleted without changing Ca
2+
, diacylglycerol, or inositol 1,4,5-trisphosphate. Current rises by 30% when PI(4,5)P
2
is overproduced and does not change when phosphatidylinositol 3,4,5-trisphosphate is raised. Hence, the depletion of PI(4,5)P
2
suffices to suppress current fully, and other second messengers are not needed. Our approach is ideally suited to study biological signaling networks involving membrane phosphoinositides.
Sex differences in baseline neuropsychological function and concussion symptoms of collegiate athletes
Authors: Covassin T , Swanik C B , Sachs M , Kendrick Z , Schatz P , Zillmer E , Kaminaris C
Published: September 2006

Objective:To investigate sex differences in baseline neuropsychological function and concussion symptoms between male and female collegiate athletes.

Methods:A post-test only design was used to examine baseline neuropsychological test scores and concussion symptoms. A total of 1209 NCAA Division I collegiate athletes from five northeastern universities in the USA completed a baseline ImPACT test. ImPACT, a computerised neuropsychological test battery, was administered during an athlete’s pre-season.

Results:Female athletes performed significantly better than male athletes on baseline verbal memory scores (p = 0.001), while male athletes performed significantly better than female athletes on baseline visual memory scores (p = 0.001). Female athletes endorsed a significant number of mild baseline symptoms as compared to male athletes.

Conclusions:Male and female athletes exhibit differences on baseline neuropsychological test performance and concussion symptoms.
Heat-related and cold-related deaths in England and Wales: who is at risk?
Authors: Hajat S , Kovats R S , Lachowycz K
Published: September 2006

Background:Despite the high burden from exposure to both hot and cold weather each year in England and Wales, there has been relatively little investigation on who is most at risk, resulting in uncertainties in informing government interventions.

Objective:To determine the subgroups of the population that are most vulnerable to heat-related and cold-related mortality.

Methods:Ecological time-series study of daily mortality in all regions of England and Wales between 1993 and 2003, with postcode linkage of individual deaths to a UK database of all care and nursing homes, and 2001 UK census small-area indicators.

Results:A risk of mortality was observed for both heat and cold exposure in all regions, with the strongest heat effects in London and strongest cold effects in the Eastern region. For all regions, a mean relative risk of 1.03 (95% confidence interval (CI) 1.02 to 1.03) was estimated per degree increase above the heat threshold, defined as the 95th centile of the temperature distribution in each region, and 1.06 (95% CI 1.05 to 1.06) per degree decrease below the cold threshold (set at the 5th centile). Elderly people, particularly those in nursing and care homes, were most vulnerable. The greatest risk of heat mortality was observed for respiratory and external causes, and in women, which remained after control for age. Vulnerability to either heat or cold was not modified by deprivation, except in rural populations where cold effects were slightly stronger in more deprived areas.

Conclusions:Interventions to reduce vulnerability to both hot and cold weather should target all elderly people. Specific interventions should also be developed for people in nursing and care homes as heat illness is easily preventable.
Differential changes in β-adrenoceptor signal transduction in left and right ventricles of infarcted ratsThis paper is one of a selection of papers published in this Special issue, entitled Second Messengers and Phosphoproteins—12th International Conference.
Authors: Sethi Rajat , Saini Harjot K. , Wang Xi , Elimban Vijayan , Babick Andrea , Dhalla Naranjan S.
Published: September 2006

Although different experimental and clinical studies have revealed varying degrees of defects in β-adrenoceptors (β-ARs) during the development of heart failure, the mechanisms for differences in β-AR signal transduction between the left (LV) and right ventricle (RV) are not understood. Because biochemical alterations in the myocardium depend on the stage of heart disease, this study was undertaken to assess the status of β-ARs in the LV and RV at different stages of heart failure. Myocardial infarction was induced in rats by occluding the left coronary artery for 8 and 24 weeks. The β-AR signal transduction was monitored by measuring β1-AR density, the isoproterenol-induced positive inotropic effect, the increase in [Ca2+]i in cardiomyocytes, and the activation of adenylyl cyclase. The β-AR signal transduction parameters in the 8- and 24-week failing LV were depressed, whereas the RV showed upregulation at 8 weeks and downregulation at 24 weeks of these mechanisms. These results suggest that β-AR-mediated signal transduction in the LV and RV are differentially regulated and are dependent upon the stage of development of congestive heart failure due to myocardial infarction.
Phosphorylation and dephosphorylation of human myristoyltransferase type 1This paper is one of a selection of papers published in this Special issue, entitled Second Messengers and Phosphoproteins—12th International Conference.
Authors: Selvakumar Ponniah , Sharma Rajendra K.
Published: September 2006

N-Myristoyltransferase (NMT) is an essential eukaryotic enzyme that catalyzes the co-translational and (or) post-translational transfer of myristate to the amino terminal glycine residue of a number of important proteins, especially the non-receptor tyrosine kinases whose activity is important for tumorigenesis. Human NMT was found to be phosphorylated by non-receptor tyrosine kinase family members of Lyn, Fyn, and Lck and dephosphorylated by the Ca2+/calmodulin-dependent protein phosphatase, calcineurin. In this review, we discuss the cross-talk that exists between NMT and their N-myristoylated protein substrates. The cross-talk among NMT, tyrosine kinases, and phosphatases may be determined by their subcellular localization and by the physiological state of the cell.
AMP-activated protein kinase — the fat controller of the energy railroadThis paper is one of a selection of papers published in this Special issue, entitled Second Messengers and Phosphoproteins—12th International Conference.
Authors: Steinberg Gregory R. , Macaulay S. Lance , Febbraio Mark A , Kemp Bruce E.
Published: September 2006

AMP-activated protein kinase plays an important role in the regulation of lipid metabolism in response to metabolic stress and energy demand. It is also under endocrine control. AMPK acts at multiple steps and has a central role controlling fatty acid, triglyceride, and cholesterol synthesis, as well as the oxidation of fatty acids through direct phosphorylation effects and the control of gene transcription. As such, it can be considered to be the fat controller of the energy railroad. It is thought that AMPK may be a major mediator of the health benefits of exercise in mitigating the development of obesity and age-onset diseases.
PTP1B and TC-PTP: novel roles in immune-cell signalingThis paper is one of a selection of papers published in this Special issue, entitled Second Messengers and Phosphoproteins—12th International Conference.
Authors: Simoncic Paul D. , McGlade C. Jane , Tremblay Michel L.
Published: September 2006

It has recently been demonstrated that the protein tyrosine phosphatase (PTP) PTP1B and the T-cell PTP (TC-PTP) target several substrates involved in immune cell signaling. Recent data have furthered the view of these 2 PTP members as key regulators of the immune response. This review will focus on the substrate specificities of PTP1B and TC-PTP and their roles in immune cell signaling, and will discuss some new data implicating PTP1B and TC-PTP in myeloid development.
Vanadium and bone development: putative signaling pathwaysThis paper is one of a selection of papers published in this Special issue, entitled Second Messengers and Phosphoproteins—12th International Conference.
Authors: Barrio D.A. , Etcheverry S.B.
Published: September 2006

Vanadium is a trace element present in practically all cells in plants and animals. It exerts interesting actions in living systems. At pharmacological doses, vanadium compounds display relevant biological actions such as mimicking insulin and growth factors as well as having osteogenic activity. Some vanadium compounds also show antitumoral properties. The importance of vanadium in bone arises from the studies developed to establish the essentiality of this element in animals and humans. Bone tissue, where the element seems to play an important role, accumulates great amounts of vanadium. This paper reviews the physiology of osteoblasts, the involvement of different growth factors on bone development, and the effects of vanadium derivatives on the skeletal system of animal models and bone-related cells. Two cellular lines are discussed in particular; one derived from a rat osteosarcoma (UMR106) and the other is a nontransformed osteoblast cell line (MC3T3-E1). The effects of different growth factors and their mechanisms of action in these cellular lines are reviewed. These models of osteoblasts are especially useful in understanding the intracellular signaling pathways of vanadium derivatives in hard tissues. Vanadium uses an intricate interplay of intracellular mechanisms to exert different biochemical and pharmacological actions. The effects of vanadium derivatives on some cellular signaling pathways related to insulin are compiled in this review. The comprehension of these intracellular signaling pathways may facilitate the design of vanadium compounds with promising therapeutic applications as well as the understanding of secondary side effects derived from the use of vanadium as a therapeutic agent.
Role of the Go/i signaling network in the regulation of neurite outgrowthThis paper is one of a selection of papers published in this Special issue, entitled Second Messengers and Phosphoproteins—12th International Conference.
Authors: He John Cijiang , Neves Susana R. , Jordan J. Dedrick , Iyengar Ravi
Published: September 2006

Neurite outgrowth is a complex differentiation process stimulated by many neuronal growth factors and transmitters and by electrical activity. Among these stimuli are ligands for G-protein-coupled receptors (GPCR) that function as neurotransmitters. The pathways involved in GPCR-triggered neurite outgrowth are not fully understood. Many of these receptors couple to Gαo, one of the most abundant proteins in the neuronal growth cones. We have studied the Go signaling network involved in neurite outgrowth in Neuro2A cells. Gαo can induce neurite outgrowth. The CB1 cannabinoid receptor, a Go/i-coupled receptor expressed endogenously in Neuro2A cells, triggers neurite outgrowth by activating Rap1, which promotes the Gαo-stimulated proteasomal degradation of Rap1GAPII. CB1-receptor-mediated Rap1 activation leads to the activation of a signaling network that includes the small guanosine triphosphate (GTP)ases Ral and Rac, the protein kinases Src, and c-Jun N-terminal kinase (JNK), which converge onto the activation of signal transducer and activator of transcription 3 (Stat3), a key transcription factor that mediates the gene expression process of neurite outgrowth in Neuro2A cells. This review describes current findings from our laboratory and also discusses alternative pathways that Go/i might mediate to trigger neurite outgrowth. We also analyze the role neurotransmitters, which stimulate Go/i to activate a complex signaling network controlling neurite outgrowth, play in regeneration after neuronal injury.
EFFECT OF THICKNESS OF LIQUID CRYSTALLINE LAYER ON THE THERMOTROPIC AND THERMODYNAMICAL PROPERTIES OF NEMATIC-ISOTROPIC LIQUID AND ISTROPIC LIQUID-NEMATIC PHASE TRANSITIONS
Authors: POLAT ÖMER , NESRULLAJEV ARIF , OKTIK ŞENER
Published: September 2006

In this work, effect of thickness of the liquid crystalline layer on the morphologic, thermotropic and thermodynamical properties of the nematic–isotropic liquid and isotropic liquid–nematic phase transitions in Shiff based liquid crystals has been investigated.

The shift of temperatures of the nematic–isotropic liquid and isotropic liquid–nematic phase transitions to the lower temperatures and the widening of linear and temperature widths of the heterophase regions of these phase transitions by the increase in the thickness of liquid crystalline layer have been found.

The effect of thickness of liquid crystalline layer on morphologic, thermotropic and thermodynamical properties of liquid crystals under investigations is connected with change of interaction energy between liquid crystalline molecules and reference surfaces.
THERMAL STABILITY AND TRANSPORT PROPERTIES OF Na0.495CoO2 SINGLE CRYSTALS
Authors: XU Z. A. , XU Y. , CHEN X. Z. , SHEN J. Q. , CAO G. H. , GAN Z. H. , QIU L. M.
Published: September 2006

Single crystals of Na 0.495 CoO 2 were obtained through a flux method followed by de-intercalation of sodium. The resistivity (ρ) and thermal stability were studied for the de-intercalated samples exposed to humid air. It was found that the de-intercalated Na 0.495 CoO 2 crystal is vulnerable to water in the air, and a hydration process in which H 2 O molecules fill oxygen vacancies in CoO 2 layers instead of being intercalated between CoO 2 layers is suggested to be responsible for the remarkable change in resistivity induced by water absorption. The Na 0.495 CoO 2 sample shows a weak localization of carriers just below 200 K and Co 3+– Co 4+ charge ordering at about 40 K, lower than the corresponding charge ordering transition temperature reported in Na 0.5 CoO 2. The lower charge ordering transition temperature might be caused by the slight deviation of Na content (x) from 0.5.
THE ESR STUDY OF AMORPHOUS THIN FILMS OF MIXED OXIDES In2O3–SnO2 SYSTEM DEPOSITED BY CO-EVAPORATION
Authors: ANWAR M. , GHOURI I. M. , SIDDIQI S. A.
Published: September 2006

The ESR spectra of amorphous thin films of mixed oxides In 2 O 3– SnO 2 system is presented. An initial increase in the intensity of ESR signal at g=1.994, and decrease in the intensity of the signal at g=1.98 with an increase in Sn content in In 2 O 3 lattice is caused by the Sn atom substitution of In atom, giving out one extra electron. The decrease in the intensity of ESR signal at g=1.994 and an increase in the intensity of the signals at g=1.98 above the critical Sn content (10 mol% SnO 2) is caused by the defects formed by Sn atoms, which act as carrier traps rather than as electron donors. The increase in the intensity of ESR signal at g=1.89 with the increase in Sn content in mixed oxides In 2 O 3– SnO 2 system is caused by the increase in the concentration of oxygen vacancies, which are generated in the In 2 O 3 and SnO 2 lattices by thermal evaporation. The increase in the intensity of ESR signals at g=1.994, g=1.98 and g=1.89 with the increase in thickness is caused by the bulk properties of the films. The increase in the intensity of ESR signals at g=1.994, g=1.98 and g=1.89 with the increase in substrate temperatures is due to the increase in the concentration of oxygen vacancies, which are generated at higher substrate temperatures and to the diffusion of Sn atoms from interstitial locations into the In cation sites, which result in higher electron concentration. The decrease in the intensity of ESR signals at g=1.994, g=1.98 and g=1.89 with an increase in annealing temperature is attributed to the rearrangement of the atoms and to the removal of voids, which causes a decrease in the number of unsatisfied bonds and formation of indium and tin species of lower valence states. The new oxidation states, the In 2+ and the Sn 2+, formed due to the annealing of the samples can be attributed to the internal electron transfer from oxygen 2p to the In 5 s and Sn 5 s levels, both in In 2 O 3 and SnO 2.
MODEL EQUATION OF STATE OF LIQUID C60 BASED ON HARD SPHERE–YUKAWA POTENTIAL
Authors: KHEDR M. BAHAA
Published: September 2006

The series mean spherical approximation (SMSA) for the hard sphere–Yukawa (HSYK) fluid is applied to C 60. The energy and range parameters of HSYK potential have been reduced to one parameter by forcing the q→0 limit of the Fourier transform of the potential to be identical to that of the empirical potential of C 60. The new equation of state (EOS) allows us to investigate the liquid–vapor coexistence curve and calculate the thermodynamic properties of liquid C 60. The comparisons with computer simulation results suggest the importance of treating the attractive tail of the potential accurately. The estimated critical parameters Tc=1984.8 K , ρc=0.464 nm -3 and Pc=36.3 bar , which are in good agreement with NVT-Monte Carlo computer simulation predictions. The results are discussed by making reference to previous studies.
Effects of Lactobacillus casei Shirota, Bifidobacterium breve, and oligofructose-enriched inulin on colonic nitrogen-protein metabolism in healthy humans
Authors: De Preter Vicky , Vanhoutte Tom , Huys Geert , Swings Jean , De Vuyst Luc , Rutgeerts Paul , Verbeke Kristin
Published: September 2006

Pre- and/or probiotics can cause changes in the ecological balance of intestinal microbiota and hence influence microbial metabolic activities. In the present study, the influence of oligofructose-enriched inulin (OF-IN), Lactobacillus casei Shirota, and Bifidobacterium breve Yakult on the colonic fate of NH3 and p-cresol was investigated. A randomized, placebo-controlled, crossover study was performed in 20 healthy volunteers to evaluate the influence of short- and long-term administration of OF-IN, L. casei Shirota, B. breve Yakult, and the synbiotic L. casei Shirota + OF-IN. The lactose[15N,15N]ureide biomarker was used to study the colonic fate of NH3. Urine and fecal samples were analyzed for 15N content by combustion-isotope ratio mass spectrometery and for p-cresol content by gas chromatography-mass spectrometry. RT-PCR was applied to determine the levels of total bifidobacteria. Both short- and long-term administration of OF-IN resulted in significantly decreased urinary p-cresol and 15N content. The reduction of urinary 15N excretion after short-term OF-IN intake was accompanied by a significant increase in the 15N content of the fecal bacterial fraction. However, this effect was not observed after long-term OF-IN intake. In addition, RT-PCR results indicated a significant increase in total fecal bifidobacteria after long-term OF-IN intake. Long-term L. casei Shirota and B. breve Yakult intake showed a tendency to decrease urinary 15N excretion, whereas a significant decrease was noted in p-cresol excretion. In conclusion, dietary addition of OF-IN, L. casei Shirota, and B. breve Yakult results in a favorable effect on colonic NH3 and p-cresol metabolism, which, in the case of OF-IN, was accompanied by an increase in total fecal bifidobacteria.
A tale of two dogs: analyzing two models of canine ventricular electrophysiology
Authors: Cherry Elizabeth M. , Fenton Flavio H.
Published: September 2006

The extensive development of detailed mathematical models of cardiac myocyte electrophysiology in recent years has led to a proliferation of models, including many that model the same animal species and specific region of the heart and thus would be expected to have similar properties. In this paper we review and compare two recently developed mathematical models of the electrophysiology of canine ventricular myocytes. To clarify their similarities and differences, we also present studies using them in a range of preparations from single cells to two-dimensional tissue. The models are compared with each other and with new and previously published experimental results in terms of a number of their properties, including action potential morphologies; transmembrane currents during normal heart rates and during alternans; alternans onsets, magnitudes, and cessations; and reentry dynamics of spiral waves. Action potential applets and spiral wave movies for the two canine ventricular models are available online as supplemental material. We find a number of differences between the models, including their rate dependence, alternans dynamics, and reentry stability, and a number of differences compared with experiments. Differences between models of the same species and region of the heart are not unique to these canine models. Similar differences can be found in the behavior of two models of human ventricular myocytes and of human atrial myocytes. We provide several possible explanations for the differences observed in models of the same species and region of the heart and discuss the implications for the applicability of models in addressing questions of mechanism in cardiac electrophysiology.
Mechanism of the induction of brain c-Fos-positive neurons by lipid absorption
Authors: Lo Chun-Min , Ma Liyun , Zhang Dian Ming , Lee Rachel , Qin Abby , Liu Min , Woods Stephen C , Sakai Randall R. , Raybould Helen E. , Tso Patrick
Published: September 2006

Many gastrointestinal meal-related signals are transmitted to the central nervous system via the vagus nerve and thereby control changes in meal size. The c-Fos-positive neuron has been used as a marker of neuronal activation after lipid meals to examine the contribution of a selective macronutrient on brain neurocircuit activity. In rats fed Intralipid, the c-Fos-positive neurons were highly stimulated in the nucleus of the solitary tract (NTS) and in the hypothalamus, including the paraventricular nucleus (PVN), arcuate nucleus of the hypothalamus (ARC), and ventromedial hypothalamus at 4 h lipid feeding. However, c-Fos-like immunoreactivity was markedly attenuated in these brain regions when chylomicron formation/secretion was blocked by Pluronic L-81. After lymph was diverted from the lymph cannulated animals, the rats had a lower number of c-Fos-positive cells in the NTS and ARC. In contrast, the rats had higher c-Fos-positive neurons in PVN. The present study also revealed that c-Fos-positive neurons induced by feeding of Intalipid were abolished by CCK type 1 receptor antagonist, Lorglumide. We conclude that the formation and/or secretion of chylomicron are critical steps for initiating neuronal activation in the brain.
Effects of burn injury on myocardial signaling and cytokine secretion: possible role of PKC
Authors: Tan Jing , Maass David L. , White D. Jean , Horton Jureta W.
Published: September 2006

This study examined the effects of major burn injury on the cellular distribution of several PKC isoforms in adult rat hearts and examined the hypothesis that PKC plays a regulatory role in cardiomyocyte cytokine secretion. Burn trauma was given over 40% total body surface area in Sprague-Dawley rats. An in vitro model of burn injury included addition of burn serum, 10% by volume, to primary cardiomyocyte cultures (collagen perfusion). In vivo burn injury produced redistribution of PKCδ, PKCε, and PKCα from the cytosol (soluble) to the membrane (particulate) component of the myocardium. This activation of the PKC isoforms was evident 2 h after burn injury and progressively increased over 24 h postburn. Addition of burn serum to isolated myocytes produced similar PKC isoform redistribution from the soluble to the particulate compartment, promoted myocyte Ca2+and Na+loading, and promoted robust myocyte secretion of inflammatory cytokines similar to that reported after in vivo burn injury. Pretreating cardiomyocytes with either calphostin or PKCε inhibitory peptide, a potent inhibitor of PKCε, prevented burn serum-related redistribution of the PKCε isoform and prevented burn serum-related cardiomyocyte secretion of TNF-α, IL-1β, IL-6, and IL-10. These data suggest that the PKCε isoform plays a pivotal role in myocardial inflammatory response to injury, altering cardiac function by modulating cardiomyocyte inflammatory cytokine response to injury.
Increased temperature, not cardiac load, activates heat shock transcription factor 1 and heat shock protein 72 expression in the heart
Authors: Staib Jessica L. , Quindry John C. , French Joel P. , Criswell David S. , Powers Scott K.
Published: September 2006

The expression of myocardial heat shock protein 72 (HSP72) postexercise is initiated by the activation of heat shock transcription factor 1 (HSF1). However, it remains unknown which physiological stimuli govern myocardial HSF1 activation during exercise. These experiments tested the hypothesis that thermal stress and mechanical load, concomitant with simulated exercise, provide independent stimuli for HSF1 activation and ensuing cardiac HSP72 gene expression. To elucidate the independent roles of increased temperature and cardiac workload in the exercise-mediated upregulation of left-ventricular HSP72, hearts from adult male Sprague-Dawley rats were randomly assigned to one of five simulated exercise conditions. Upon reaching a surgical plane of anesthesia, each experimental heart was isolated and perfused using an in vitro working heart model, while independently varying temperatures (i.e., 37°C vs. 40°C) and cardiac workloads (i.e., low preload and afterload vs. high preload and afterload) to mimic exercise responses. Results indicate that hyperthermia, independent of cardiac workload, promoted an increase in nuclear translocation and phosphorylation of HSF1 compared with normothermic left ventricles. Similarly, hyperthermia, independent of workload, resulted in significant increases in cardiac levels of HSP72 mRNA. Collectively, these data suggest that HSF1 activation and HSP72 gene transcriptional competence during simulated exercise are linked to elevated heart temperature and are not a direct function of increased cardiac workload.
Physiological imaging of the lung: single-photon-emission computed tomography (SPECT)
Authors: Petersson Johan , Sánchez-Crespo Alejandro , Larsson Stig A. , Mure Margareta
Published: September 2006

Emission tomography provides three-dimensional, quantitative images of the distribution of radiotracers used to mark physiological, metabolic, or pathological processes. Quantitative single photon emission computed tomography (SPECT) requires correction for the image-degrading effects due to photon attenuation and scatter. Phantom experiments have shown that radioactive concentrations can be assessed within some percentage of the true value when relevant corrections are applied. SPECT is widely spread, and radiotracers are available that are easy to use and comparably inexpensive. Compared with other methods, SPECT suffers from a lower spatial resolution, and the time required for image acquisition is longer than for some alternative methods. In contrast to some other methods, SPECT allows simultaneous imaging of more than one process, e.g., both regional blood flow and ventilation, for the whole lung. SPECT has been used to explore the influence of posture and clinical interventions on the spatial distribution of lung blood flow and ventilation. Lung blood flow is typically imaged using macroaggregates of albumin. Both radioactive gases and particulate aerosols labeled with radioactivity have been used for imaging of regional ventilation. However, all radiotracers are not equally suited for quantitative measurements; all have specific advantages and limitations. With SPECT, both blood flow and ventilation can be marked with radiotracers that remain fixed in the lung tissue, which allows tracer administration during conditions different from those at image registration. All SPECT methods have specific features that result from the used radiotracer, the manner in which it is administered, and how images are registered and analyzed.
Tendon collagen synthesis at rest and after exercise in women
Authors: Miller Benjamin F. , Hansen Mette , Olesen Jens L. , Schwarz Peter , Babraj John A. , Smith Kenneth , Rennie Michael J. , Kjaer Michael
Published: September 2006

In general, there is a higher incidence of musculoskeletal injuries during physical activity in women than in men. We hypothesized that in women rates of tendon collagen synthesis would be lower than in men at rest and after exercise, especially in the later luteal phase when estrogen and progesterone concentrations are higher than the early follicular phase. We studied tendon collagen fractional synthesis rate (FSR) in 15 young, healthy female subjects in either the early follicular ( n = 8) or the late luteal phase ( n = 7) 72 h after an acute bout of one-legged exercise (60 min kicking at 67% workload maximum) (72 h) and compared the results with those previously obtained for men. Samples were taken from the patellar tendon in both the exercised and rested legs to determine collagen FSR by the incorporation of [15N]proline into tendon collagen hydroxyproline. There was no effect of menstrual phase on tendon collagen synthesis either at rest or after exercise. However, there was a significant difference between women and men at rest (women = 0.025 ± 0.002%/h, men = 0.045 ± 0.008%/h; P < 0.05) and 72 h after exercise (women = 0.027 ± 0.005%/h; men = 0.058 ± 0.008%/h). Furthermore, rest and 72-h tendon collagen synthesis were not different in women, whereas in men tendon collagen synthesis remained significantly elevated 72 h after exercise. It is concluded that both in the resting state and after exercise, tendon collagen FSR is lower in women than in men, which may contribute to a lower rate of tissue repair after exercise.
GABAAand GABABreceptors differentially modulate volume and frequency in ventilatory compensation in obese Zucker rats
Authors: Yang Ai-Lun , Lo Ming-Jae , Ting Hua , Chen Jwo-Sheng , Huang Chih-Yang , Lee Shin-Da
Published: September 2006

The aim of this study was to investigate whether GABAAand/or GABABreceptor-mediated mechanisms contribute to the impaired ventilatory response and reduced maximal aerobic exercise capacity in obese Zucker rats. Ten lean and 10 obese Zucker rats were studied at 12 wk of age. Minute ventilation (V̇e), tidal volume (Vt), and breathing frequency (f) during room air breathing and in response to 10 min of hypercapnia (8% CO2) and 30 min of hypoxia (10% O2) were measured by the barometric method, and peak oxygen consumption (V̇o2 peak) was measured by an enclosed metabolic treadmill following the randomized blinded subcutaneous administration of equal volumes of DMSO (vehicle), bicuculline (selective GABAAreceptor antagonist, 1 mg/kg), and phaclofen (selective GABABreceptor antagonist, 1 mg/kg). Administration of bicuculline and phaclofen to lean animals had no effect on V̇e and V̇o2 peak. Similarly, phaclofen failed to alter V̇e and V̇o2 peakin obese rats, although it did significantly increase f after 5–20 min of hypoxia. In contrast, bicuculline increased V̇e and Vt relative to DMSO during room air breathing and after 10–30 min of hypoxic exposure in obese rats, but it did not increase V̇e at 5 min of hypoxemia. Bicuculline increased V̇o2 peakrelative to DMSO in obese Zucker rats. We conclude that endogenous GABA acting on GABAAreceptors can modulate V̇e and V̇o2 peakin obese but not in lean Zucker rats, whereas endogenous GABA acting on GABABreceptors modulates f during hypoxia (5–20 min) in obese rats in a very different manner from that when acting on GABAAreceptors.
Fetal Head Biometry Assessed by Fetal Magnetic Resonance Imaging following in utero Myelomeningocele Repair
Authors: Danzer Enrico , Johnson Mark P. , Bebbington Michael , Simon Erin M. , Wilson R. Douglas , Bilaniuk Larrissa T. , Sutton Leslie N. , Adzick N. Scott
Published: September 2006

Objective: To examine the impact of fetal myelomeningocele (MMC) repair on fetal head biometry and cerebrospinal fluid (CSF) spaces assessed by magnetic resonance imaging (MR) studies. Study Design: Axial measurements of intracranial structures were taken at defined anatomical landmarks. Pre- and postnatal head biometry data and CSF spaces obtained from in utero repaired MMC fetuses (n = 22) were compared to the pre- and postnatal measurements of MMC patients that underwent standard neurosurgical MMC repair after birth (n = 16) and a cohort of age-matched control patients (prenatal, n = 52; postnatal, n = 9). Results: In fetuses with MMC, initial MR scans showed an almost complete absence of supratentorial and posterior fossa CSF spaces. No differences in postnatal CSF spaces were found between controls and prenatally repaired MMC newborns. In fetuses with postnatal MMC repair, CSF spaces remained significantly reduced (p < 0.0001). The mean ventricular diameter (VD) increase in the postnatal repaired MMC group was significantly higher compared to the mean percentage of VD increase in the fetal repaired MMC group (6.4 vs. 4.2 mm; p = 0.02). Pre- and postnatal brain thickness measurements were significantly reduced in both MMC populations compared to age-matched normal values (p < 0.0001). In contrast to postnatally repaired patients, in utero repair fetuses showed significant reversal of hindbrain herniation and normalization of the posterior fossa CSF spaces. Conclusion: Mid-gestational repair of MMC promotes normalization of extra-axial CSF spaces. Due to progressive ventriculomegaly, brain thickness remains decreased in both prenatal repaired and age-matched non-repaired MMC patients when compared to age-matched normal values. Restoration of CSF volume in the posterior fossa after in utero repair is indicative of reversal of hindbrain herniation.