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Comparable Conditions (comparable + condition)
Selected AbstractsMeasurement of the force and torque produced in the calcium response of reactivated rat sperm flagellaCYTOSKELETON, Issue 1 2001Mark J. Moritz Abstract Rat sperm that are demembranated with Triton X-100 and reactivated with Mg-ATP show a strong mechanical response to the presence of free calcium ion. At pCa < 4, the midpiece region of the flagellum develops a strong and sustained curvature that gives the cell the overall appearance of a fishhook [Lindemann and Goltz, 1988: Cell Motil. Cytoskeleton 10:420,431]. In the present study, the force and torque that maintain the calcium-induced hook have been examined quantitatively. In addition, full-length and shortened flagella were manipulated to evaluate the plasticity of the hooks and determined the critical length necessary for maintaining the curvature. The hooks were found to be highly resilient, returning to their original configuration (>95%) after being straightened and released. The results from manipulating the shortened flagella suggest that the force holding the hook in the curved configuration is generated in the basal 60 ,m of the flagellum. The force required to straighten the calcium-induced hooks was measured with force-calibrated glass microprobes, and the bending torque was calculated from the measured force. The force and torque required to straighten the flagellum were found to be proportional to the change in curvature of the hooked region of the flagellum, suggesting an elastic-like behavior. The average torque to open the hooks to a straight position was 2.6 (±1.4) × 10 -7 dyne × cm (2.6 × 10 -14 N × m) and the apparent stiffness was 4.3 (±1.3) × 10 -10 dyne × cm2 (4.3 × 10 -19 N × m2). The stiffness of the hook was determined to be approximately one quarter the rigor stiffness of a rat sperm flagellum measured under comparable conditions. Cell Motil. Cytoskeleton 49:33,40, 2001. © 2001 Wiley-Liss, Inc. [source] A Substrate-Selective Nanoreactor Made of Molecularly Imprinted Polymer Containing Catalytic Silver NanoparticlesADVANCED FUNCTIONAL MATERIALS, Issue 16 2009Song jun Li Abstract An original, substrate-selective nanoreactor is designed and characterized. The nanoreactor made of a 4-nitrophonel (NP)-imprinted polymer and Ag nanoparticles, can specifically recognize NP compared with its analogues 4-nitrophenyl acetate (NPA) and 2,6-dimethyl-4-nitrophenol (DNP). Under comparable conditions, this nanoreactor significantly accelerated the reduction of NP; however, much less acceleration is shown for its analogues. Unlike traditional Ag nanoreactors, which lack molecular recognition abilities, this unique nanoreactor is composed of molecularly imprinted networks, making substrate-selective catalysis feasible. [source] Impact of past and present land-management on the C-balance of a grassland in the Swiss AlpsGLOBAL CHANGE BIOLOGY, Issue 11 2008NELE ROGIERS Abstract Grasslands cover about 40% of the ice-free global terrestrial surface, but their quantitative importance in global carbon exchange with the atmosphere is still highly uncertain, and thus their potential for carbon sequestration remains speculative. Here, we report on CO2 exchange of an extensively used mountain hay meadow and pasture in the Swiss pre-Alps on high-organic soils (7,45% C by mass) over a 3-year period (18 May 2002,20 September 2005), including the European summer 2003 heat-wave period. During all 3 years, the ecosystem was a net source of CO2 (116,256 g C m,2 yr,1). Harvests and grazing cows (mostly via C export in milk) further increased these C losses, which were estimated at 355 g C m,2 yr,1 during 2003 (95% confidence interval 257,454 g C m,2 yr,1). Although annual carbon losses varied considerably among years, the CO2 budget during summer 2003 was not very different from the other two summers. However, and much more importantly, the winter that followed the warm summer of 2003 observed a significantly higher carbon loss when there was snow (133±6 g C m,2) than under comparable conditions during the other two winters (73±5 and 70±4 g C m,2, respectively). The continued annual C losses can most likely be attributed to the long-term effects of drainage and peat exploitation that began 119 years ago, with the last significant drainage activities during the Second World War around 1940. The most realistic estimate based on depth profiles of ash content after combustion suggests that there is an 500,910 g C m,2 yr,1 loss associated with the decomposition of organic matter. Our results clearly suggest that putting efforts into preserving still existing carbon stocks may be more successful than attempts to increase sequestration rates in such high-organic mountain grassland soils. [source] The First Reaction of Dimethoxycarbene with an Imine MoietyHELVETICA CHIMICA ACTA, Issue 9 2007Grzegorz Mlosto Abstract The nucleophilic dimethoxycarbene (DMC; 2) generated by thermal decomposition of 2,5-dihydro-1,3,4-oxadiazole derivative 1 in boiling toluene reacts smoothly with N -(9H -fluoren-9-ylidene)-4-methylbenzenesulfonamide (7b) to yield carbonimidoate derivative 10. A multi-step reaction pathway, initiated by the attack of DMC onto the CN bond and followed by the migration of the sulfonyl group (or via a sulfinate anion) is proposed to explain the formation of the final product. In contrast to the formal ketimine 7b, N -benzylidene-4-methylbenzenesulfonamide (7a), a formal aldimine, does not react with DMC under comparable conditions. [source] Polymer hydrogenation in pulsed flow systems with extrusionAICHE JOURNAL, Issue 4 2008Alan Bussard Abstract The hydrogenation of poly(styrene) over a Pd/Al2O3 catalyst was studied in reactors where pulsed flows are present due to both extrusion and forced pulsing. The reaction was investigated over a range of flow rates, polymer concentrations, and pulsing conditions. Observed activities were highly related to gas-to-liquid mass transfer rates predicted by a correlation for slug flow in catalyst monoliths. A reactor fed by a liquid-starved extruder is an attractive choice for hydrogenation at low polymer concentrations, where intrinsic reaction rates are approached. Higher polymer concentrations (10 wt %) lead to higher mass transfer resistances and a decrease in observed activity. But in this case forced pulsing has a greater effect on productivity; an optimum pulsing frequency was observed. Selectivity was higher and power input lower than in a stirred tank at comparable conditions. The optimal frequency is higher than those found in previous work on hydrogenations. © 2008 American Institute of Chemical Engineers AIChE J, 2008 [source] High-temperature kinetics of the homogeneous reverse water,gas shift reactionAICHE JOURNAL, Issue 5 2004F. Bustamante Abstract The high-temperature rate of reaction of the homogeneous, reverse water,gas shift reaction (rWGSR) has been evaluated in quartz reactors with rapid feed preheating under both low- and high-pressure conditions. The form of the power-law rate expression was consistent with the Bradford mechanism. The Arrhenius expressions for the reaction rate constant, corresponding to the empty reactor, were in very good agreement with the low-pressure results of Graven and Long, but yielded rate constants roughly four times greater than those obtained in our packed reactor and those reported by Kochubei and Moin and by Tingey. Reactor geometry was not responsible for these differences because computational fluid dynamics simulations revealed similar residence time distributions and comparable conversions when the same kinetic expression was used to model the rWGSR in each reactor. Most likely, the empty NETL reactor and the Graven and Long reactor did not attain an invariant value of the concentration of the chain carrier (H) at low reaction times, which led to an overestimation of the rate constant. Conversions attained in an Inconel® 600 reactor operating at comparable conditions were approximately two orders of magnitude greater than those realized in the quartz reactor. This dramatic increase in conversion suggests that the Inconel® 600 surfaces, which were depleted of nickel during the reaction, catalyzed the rWGSR. © 2004 American Institute of Chemical Engineers AIChE J, 50: 1028,1041, 2004 [source] Effects of stimulation frequency and pulse duration on fatigue and metabolic cost during a single bout of neuromuscular electrical stimulationMUSCLE AND NERVE, Issue 5 2010Julien Gondin PhD Abstract We have investigated the effects of stimulation frequency and pulse duration on fatigue and energy metabolism in rat gastrocnemius muscle during a single bout of neuromuscular electrical stimulation (NMES). Electrical pulses were delivered at 100 Hz (1-ms pulse duration) and 20 Hz (5-ms pulse duration) for the high (HF) and low (LF) frequency protocols, respectively. As a standardization procedure, the averaged stimulation intensity, the averaged total charge, the initial peak torque, the duty cycle, the contraction duration and the torque-time integral were similar in both protocols. Fatigue was assessed using two testing trains delivered at a frequency of 100 Hz and 20 Hz before and after each protocol. Metabolic changes were investigated in vivo using 31P-magnetic resonance spectroscopy (31P-MRS) and in vitro in freeze-clamped muscles. Both LF and HF NMES protocols induced the same decrease in testing trains and metabolic changes. We conclude that, under carefully controlled and comparable conditions, the use of low stimulation frequency and long pulse duration do not minimize the occurrence of muscle fatigue or affect the corresponding stimulation-induced metabolic changes so that this combination of stimulation parameters would not be adequate in the context of rehabilitation. Muscle Nerve, 2010 [source] Experimental superficial candidiasis on tissue modelsMYCOSES, Issue 4 2010J. A. M. S. Jayatilake Summary Candida species are common pathogens causing superficial mycoses primarily affecting the mucosa and the skin in humans. Crucial steps during pathogenesis of superficial candidiasis comprise fungal adhesion, colonisation and subsequent penetration of the respective tissues. Exploring these pathological events and perhaps fungal and tissue responses towards drug treatment is imperative in the management of this infection. Unfortunately, pathological biopsies of superficial candidiasis do not exhibit the early changes in the host,pathogen interaction as the tissues are already invaded by the fungi. In vivo experimental assessments of pathological processes of superficial candidiasis are also limited because of the difficulties in providing reproducible and comparable conditions in the host environment. Conversely, in vitro models have helped studying fungal,host interactions under more defined and controlled conditions. Some common in vitro models used to simulate superficial candidiasis are chick chorioallantoic membrane, mucosal explants and single layer or multiple layer cell cultures. Interestingly, these experimental approaches share advantages as well as disadvantages when compared with in vivo conditions. Hence, this review intends to discuss about the experimental superficial candidiasis produced in various tissue models and their advantages as well as disadvantages with a particular reference to further improvement of validity and reliability of such experiments. [source] Bladder wall tension during physiological voiding and in patients with an unstable detrusor or bladder outlet obstructionBJU INTERNATIONAL, Issue 6 2003S. Bross OBJECTIVE To develop and evaluate a new clinical method for measuring bladder wall tension (BWT) on detrusor contraction during physiological voiding and under pathological conditions, as in experimental trials during subvesical obstruction the ability to generate pressure increases, whereas the contractile force per cross-sectional area of detrusor muscle decreases. PATIENTS AND METHODS In all, 24 patients were divided into three equal groups: group 1 (mean age 58, sd 8.6 years) comprised men with bladder outlet obstruction in accordance with the Abrams-Griffiths nomogram; group 2 (four men and four women, 56, sd 7.2 years) had detrusor instability; and group 3 (54, sd 9.6 years) had normal bladder emptying. BWT, as the detrusor force per cross-sectional area of bladder tissue (in N/cm2), was calculated after a urodynamic evaluation and ultrasonographic estimate of bladder wall thickness. RESULTS In all patients it was possible to measure BWT; the mean (sd) maximum BWT in group 1 was 9.8 (3.9) N/cm2, in group 2 during bladder instability was 11.7 (2.6) N/cm2 and in group 3 was 2.8 (0.5) N/cm2. CONCLUSIONS Estimating BWT in humans is possible by combining a urodynamic evaluation with an ultrasonographic estimate of bladder wall thickness. Further clinical research should elucidate the clinical relevance of BWT under comparable conditions. [source] Construction of the Active Site of Metalloenzyme on Au NC MicellesCHINESE JOURNAL OF CHEMISTRY, Issue 7 2009Zhiming ZHANG Abstract For developing an efficient nanoenzyme system with self-assembly strategy, gold nanocrystal micelles (Au NC micelles) with inserted catalytic Zn(II) centers were constructed by self-assembly of a catalytic ligand [N,N -bis(2-aminoethyl)- N, -dodecylethylenediamine] Zn(II) complexes (Zn(II)L) on the surface of Au NC via hydrophobic interaction. The functionalized Au NC micelles acted as an excellent nanoenzyme model for imitating ribonuclease. The catalytic capability of the Au NC micelles was evaluated by accelerating the cleavage of 2-hydroxypropyl p -nitrophenyl phosphate (HPNP). These functionalized Au NC micelles exhibited considerable ribonuclease-like activities by a factor of 4.9×104 (kcat/kuncat) for the cleavage of HPNP in comparison to the spontaneous cleavage of HPNP at 37°C. The catalytic capability of the functionalized Au NC micelles can be considerably compared to other models reported previously as nanoenzymes under the comparable conditions. [source] | ||||||||||||||||