bluuebunny/crossref_metadata_2025 huggingface dataset:
Cryoprotection by urea in a terrestrially hibernating frog
Authors: Costanzo Jon P. , Lee Richard E.
Published: October 2005

The role of urea as a balancing osmolyte in osmotic adaptation is well known, but this `waste product' also has myriad other functions in diverse taxa. We report that urea plays an important, previously undocumented role in freezing tolerance of the wood frog (Rana sylvatica), a northern woodland species that hibernates terrestrially in sites where dehydration and freezing may occur. Wood frogs inhabiting an outdoor enclosure accumulated urea to 65 mmol l-1 in autumn and early winter, when soil moisture was scarce, but subsequently urea levels fell to ∼2 mmol l-1 as the availability of environmental water increased. Laboratory experiments showed that hibernating R. sylvatica can accumulate at least 90 mmol l-1 urea under relatively dry, warm conditions. During experimental freezing, frogs synthesized glucose but did not accumulate additional urea. Nevertheless, the concentrations of urea and glucose in some tissues were similar. We tested urea's efficacy as a cryoprotectant by measuring lysis and lactate dehydrogenase (LDH) leakage in samples of R. sylvaticaerythrocytes frozen/thawed in the presence of physiological levels of urea or other osmolytes. In conferring protection against freeze/thaw damage, urea was comparable to glycerol and as good as or better than glucose, cryoprotectants found in freeze-tolerant frogs and other animals. Urea treatment also improved the viability of intact tissues frozen in vitro, as demonstrated by post-thaw measures of metabolic activity and LDH leakage. Collectively, our findings suggest that urea functions both as an osmoprotectant and a cryoprotectant in terrestrially hibernating amphibians.
Does swarming cause honey bees to update their solar ephemerides?
Authors: Towne William F. , Baer Christopher M. , Fabiny Sarah J. , Shinn Lisa M.
Published: October 2005

Spatial orientation in the social insects offers several examples of specialized learning mechanisms that underlie complex learning tasks. Here we study one of these systems: the processes by which honey bees update, or fail to update, their memories of the sun's daily pattern of movement (the solar ephemeris function) in relation to the landscape. Specifically, we ask whether bees that have initially learned the solar ephemeris function relative to a conspicuous treeline at their natal site can later realign the ephemeris to a differently oriented treeline. We first confirm and clarify an earlier finding that bees transplanted passively (by being carried) do not re-learn the solar ephemeris in relation to the new treeline. When they cannot detect the sun directly, as on overcast days, these transplanted bees use a solar ephemeris function appropriate for their natal site, despite days or weeks of experience at the new site. We then ask whether bees put through a swarming process as they are transplanted are induced to re-learn the solar ephemeris function at the new site, as swarming is a natural process wherein bees transplant themselves. Most of the swarmed bees failed to re-learn, even though they did extensive learning flights (in comparison with those of non-swarmed controls)as they first emerged from the hive at the new site. We hypothesize that the bees' representation of the solar ephemeris function is stored in an encapsulated cognitive module in which the ephemeris is inextricably linked to the reference landscape in which it was learned.
Miniaturization (0.2 g) and evaluation of attachment techniques of telemetry transmitters
Authors: Naef-Daenzer B. , Früh D. , Stalder M. , Wetli P. , Weise E.
Published: October 2005

We have developed a miniaturized very high frequency (VHF) transmitter design for radio-tagging small animals. The average mass of the circuitry is 0.084 g (range 0.081-0.087), hence, with the smallest power cell, complete tags weigh 0.2 g and have a life of 18-22 days. We further demonstrate that with such small tags the technique of attaching the device to the animal's body strongly affects the effective radiated power, and thus transmission ranges. Ideally the attachment couples the electronics to the animal's body as a ground plane for improved radiation. The transmitter allows the application of radio-tracking to be expanded to new taxa whose spatial behaviour and population dynamics are largely unknown, for example arthropods, reptiles or amphibians. The new design is also suitable for miniature implants and signal modulation with sensors.
Ionoregulatory changes in different populations of maturing sockeye salmonOncorhynchus nerkaduring ocean and river migration
Authors: Shrimpton J. M. , Patterson D. A. , Richards J. G. , Cooke S. J. , Schulte P. M. , Hinch S. G. , Farrell A. P.
Published: October 2005

We present the first data on changes in ionoregulatory physiology of maturing, migratory adult sockeye salmon Oncorhynchus nerka. Fraser River sockeye were intercepted in the ocean as far away as the Queen Charlotte Islands (∼850 km from the Fraser River) and during freshwater migration to the spawning grounds; for some populations this was a distance of over 700 km. Sockeye migrating in seawater toward the mouth of the Fraser River and upriver to spawning grounds showed a decline in gill Na+,K+-ATPase activity. As a result, gill Na+,K+-ATPase activity of fish arriving at the spawning grounds was significantly lower than values obtained from fish captured before entry into freshwater. Plasma osmolality and chloride levels also showed significant decreases from seawater values during the freshwater migration to spawning areas. Movement from seawater to freshwater increased mRNA expression of a freshwater-specific Na+,K+-ATPase isoform(α1a) while having no effect on the seawater-specific isoform(α1b). In addition, gill Na+,K+-ATPase activity generally increased in active spawners compared with unspawned fish on the spawning grounds and this was associated with a marked increase in Na+,K+-ATPase α1b mRNA. Increases in gill Na+,K+-ATPase activities observed in spawners suggests that the fish may be attempting to compensate for the osmotic perturbation associated with the decline in plasma chloride concentration and osmolality.
Path integration in a three-dimensional maze: ground distance estimation keeps desert ants Cataglyphis fortis on course
Authors: Grah Gunnar , Wehner Rüdiger , Ronacher Bernhard
Published: October 2005

In this study, we investigate the ability of desert ants to gauge the ground distances of sloped sections in a three-dimensional (3D) outbound path. Ground distance estimation, as opposed to a simple measurement of walking distances, is a necessary prerequisite for precise path integration in undulating terrain. We trained ants to visit a feeder along a path that included an angular turn as well as a `hill', resulting in an outbound path with a distinct 3D structure. We then observed the ants' return path in a test field on level ground. From the angles of the ants' return path on the test field one can infer which property of the hill segment was fed into the ants'path integration module, the actual walking distance or the ground distance. The results show clearly that it is the ground distance that Cataglyphis fortis feeds into its path integrator, and suggest that the ants are able to keep an accurate home vector also in hilly terrain.
Oxygen delivery to the fish eye: Root effect as crucial factor for elevated retinalPO2
Authors: Waser W. , Heisler N.
Published: October 2005

Although the retina has one of the highest metabolic rates among tissues,certain teleost fishes lack any vascular supply to this organ which, in combination with the overall thickness of the organ, results in extremely long diffusion distances. As the only way to compensate for these obstacles, oxygen partial pressure (PO2) in the eyes of such fish is elevated far above atmospheric values. Although not supported by any direct evidence, the enhancement of PO2 is considered to be related to the Root effect, the release upon acidification of Hb-bound O2 into physical dissolution, possibly supported by counter-current multiplication similar to the loop of Henle.

The present study evaluates the magnitude of intraocular PO2 enhancement under tightly controlled physiological conditions, to directly confirm the involvement of the Root effect on intraocular PO2 in the retina of rainbow trout Oncorhynchus mykiss. Intraocular PO2 was determined with special polarographic microelectrodes inserted into the eye. PO2profiles established in vivo by driving electrodes through the entire retina yielded average PO2 values between 10 mmHg (1.3 kPa) at the inner retinal surface and 382 mmHg (50.9 kPa) close to the outer retinal limit (Bruch's membrane). According to estimates on the basis of the diffusion distances determined from sections of the retina(∼436 μm at the site of PO2 measurement)and literature data on specific oxygen consumption, the in vivodetermined values would be sufficient to cover the oxygen demand of the retina with some safety margin.

For a clear and direct in-tissue-test as to the involvement of the Root effect, an isolated in vitro eye preparation was established in order to avoid the problem of indirect blood supply to the eye from the dorsal aorta only via the pseudobranch, a hemibranch thought to modulate blood composition before entry of the eye. Any humoral effects (e.g. catecholamines)were eliminated by perfusing isolated eyes successively with standardized red blood cell (RBC) suspensions in Ringer, using trout (with Root) and human(lacking any Root effect) RBC suspension. To optimize perfusate conditions for maximal Root effect, the Root effect of trout RBCs was determined in vitro via graded acidification of individual samples equilibrated with standardized gas mixtures. During perfusion with trout RBC, PO2 at the outer retinal limit was 99 mmHg(13.2 kPa), but fell by a factor of 3.3 upon perfusion with human RBC in spite of higher total oxygen content (TO2 2.8 for trout vs 3.9 mmol l-1 for human RBC). Upon reperfusion with trout RBC, PO2 was restored immediately to the original value. This regularly observed pattern indicated a highly significant difference (P=0.003) between perfusion with trout (with Root effect;high retinal PO2) and perfusion with human (no Root effect; low retinal PO2) RBC suspension,thus clearly demonstrating that the Root effect is directly involved and a crucial prerequisite for the enhancement of PO2in the retina of the teleost eye.
Ontogenetic development of locomotion in small mammals - a kinematic study
Authors: Schilling Nadja
Published: October 2005

Comparative studies of locomotion indicate that limb design and performance are very similar in adult mammals of small to medium size. The present study was undertaken to test whether basic therian limb pattern is present during postnatal development. Kinematic data were collected from juveniles of two eutherian species in a cross-sectional study, using cinevideography. The tree shrew Tupaia glis and the cui Galea musteloides were selected because of their different reproductive strategies, which could result in differences in the development of locomotor abilities. The aims of this study were to describe the process by which young animals develop the adult pattern of locomotion and the extent to which this process varies in two species with very different postnatal ontogenies.

Despite their different life histories, the development of kinematic parameters in the altricial tree shrew and the precocial cui are surprisingly similar. General limb design, performance, and timing of segment and joint movements in the young animals were similar to adults in both species, even from the first steps. Touch-down of the forelimb occurred at the position below the eye in all individuals and limb position was highly standardized at touch-down; no major changes in segment and joint angles were observed. Significant changes occurred at lift-off. With increasing body mass, limb segments rotated more caudally, which resulted in larger limb excursions and relatively longer steps. Developmental changes in locomotor abilities were similar in both species; only the time necessary to reach the adult performance was different. Despite the widely assumed maturity of locomotor abilities in precocial young, the first steps of the cui juveniles were not similar to the movements of adults. The adult locomotor pattern was reached within the first postnatal week in the cui and by the time they leave the nest in the tree shrew (39 days after birth; individual P39).

These results suggest that during the evolution of precocial development only processes independent of exercise or gravity can be shifted into the intrauterine period. However, development of locomotor ability dependents on exercise, and adjustments and training occur during growth. Therefore, only the time necessary to reach maturity was clearly shortened in the precocial juvenile relative to the ancestral altricial condition.
Hearing measurements from a stranded infant Risso's dolphin, Grampus griseus
Authors: Nachtigall Paul E. , Yuen Michelle M. L. , Mooney T. Aran , Taylor Kristen A.
Published: October 2005

An infant Risso's dolphin (Grampus griseus) was rescued from the beach in Southern Portugal, and an audiogram was measured using auditory evoked potentials (AEP) and envelope following response (EFR) techniques for frequencies from 4 to 150 kHz. The stimuli used were custom sinusoidally amplitude-modulated (SAM) tone-bursts, and the AEP responses were collected,averaged and analyzed to quantify the animal's physiological response and,thereby, hearing thresholds. The infant animal showed a wide range of best sensitivity, with the lowest threshold of 49.5 dB re. 1 μPa at 90 kHz. The audiogram showed a typical mammalian ∪-shape with a gradual, low-frequency slope of 16.4 dB octave-1 and a sharp high-frequency increase of 95 dB octave-1. When compared with an audiogram of an older Risso's dolphin obtained using behavioral methods, the threshold values at upper frequencies were much lower for this infant animal, and this infant heard higher frequencies. These results redefine the hearing capabilities of Risso's dolphins by demonstrating very high-frequency sensitivity.
Determination of pH by microfluorometry: intracellular and interstitial pH regulation in developing early-stage fish embryos (Danio rerio)
Authors: Mölich Andreas , Heisler Norbert
Published: October 2005

Microfluorometric techniques were applied in vivo for continuous monitoring of specific acid-base parameters in zebrafish (Danio rerio) embryos during early stages of ontogeny. Dextran-coupled pH-sensitive single-excitation/dual-emission dye SNARF-1 was pressure-injected into individual cells or the interstitial space of 16- to 256-cell embryos,and pH was continuously recorded during subsequent development for time periods of up to 8 h. A novel calibration technique was developed, essentially characterized by in vitro inorganic buffer calibration of the optical system and mathematical post-processing according to the effects of in vivo dye modifiers through a correlation established by direct comparison of optical techniques with pH microelectrodes. This approach results in high accuracy of microfluorometry, comparable with that of pH electrodes, and a recovery only limited by the physical stability of the utilized optical system.

Intracellular pH (pHi) in Danio rerio embryos between 1k-cells stage and the end of epiboly was found to be well regulated to a mean value of 7.55±0.13 (± s.d.), a range distinctly more alkaline than typical values for adult fish but in accordance with embryonic pHi of a few non-fish species shortly after fertilization. Also, interstitial pH (pHint) was significantly higher (8.08±0.25) than values for extracellular pH in adult fish. Distributions of HCO3- across membranes and between interstitium and ambient fluid compared with respective potentials strongly suggest that pH in these early stages of ontogeny is already adjusted by active transfer processes. Non-respiratory changes in ambient pH between 7.7 and 8.5 did not significantly affect pHi, a result potentially attributable to low membrane leakage rate or to the potency of active transfer mechanisms. In order to assess the pH regulatory systems more quantitatively,embryos were exposed to ambient changes of carbon dioxide partial pressure(PCO2). The direct impact of PCO2 changes on cell pH was alleviated by cell non-bicarbonate buffering and subsequent rapid, almost complete, compensation by changes in cell[HCO3-] as an expression of transmembrane transfer of acid-base relevant ions. On the basis of these results, we conclude that the regulatory potency of embryonic cells is well developed, is active to resist extensive homoiostatic stress and is efficient to maintain critical metabolism in adverse conditions, even at early stages of ontogeny.
The contribution of tympanic transmission to fine temporal signal evaluation in an ultrasonic moth
Authors: Rodríguez Rafael L. , Schul Johannes , Cocroft Reginald B. , Greenfield Michael D.
Published: October 2005

In lesser waxmoths Achroia grisella, pair formation and female mate choice involve very fine discrimination of male ultrasonic signals. Female A. grisella prefer male signals with longer pulses and longer`asynchrony intervals', and evaluate differences in these characteristics in the range of 80-260 μs. The first step in the evaluation of these characteristics is the tympanic transmission of stimuli. We used laser vibrometry to describe the mode of vibration, frequency tuning and stimulus transmission of the tympana of A. grisella. The tympanic response consisted of a rotational mode of vibration, in which the anterior and posterior sections moved out of phase; the posterior section of the tympanum vibrated with all points moving in phase and maximum displacement at the attachment point of the scoloparium that contains the receptor cells. The tympana of A. grisella were tuned to high ultrasonic frequencies and had an estimated time constant (i.e. the limit to their temporal acuity) of about 20-50 μs. Pulse length and all but the shortest asynchrony interval were thus well resolved by the tympanum. We discuss implications for the evaluation of pulse length and asynchrony interval.
Three-Dimensional Measurement of Intervertebral Kinematics in Vitro Using Optical Motion Analysis
Authors: Holt C A , Evans S L , Dillon D , Ahuja S
Published: October 2005

Measurement of the stiffness of spinal motion segments is widely used for evaluating the stability of spinal implant constructs. A three-dimensional motion analysis technique has been developed that allows accurate measurement of the relative movement of the vertebral bodies about a well-defined anatomical axis system. The position of marker clusters on each vertebra is tracked using digital infrared cameras (Qualisys AB, Gothenburg). Landmarks are identified using a marked pointer, and an anatomical coordinate system is defined for each vertebra. The transformation relating the upper and lower vertebrae is calculated, using the joint coordinate system approach of Grood and Suntay to find the rotations and translations in each anatomical plane.

The stiffness of vertebrectomy constructs was investigated using a Synex vertebral body replacement and an anterior rod with one or two screws in each vertebral body, with or without damage to the posterior longitudinal ligament (PLL). A moment of 2 N m was applied about each anatomical axis, and the range of motion about each axis was calculated.

The range of motion in flexion-extension and lateral bending was significantly greater with only one screw. When the PLL was cut, there was no significant increase in the range of motion.
An In-Vitro Investigation into the Cement Pressurization Achieved During Insertion of Four Different Femoral Stems
Authors: Gozzard C , Gheduzzi S , Miles A W , Learmonth I D
Published: October 2005

Adequate cement pressurization during stem insertion improves the interdigitation of cement into bone. This increases the strength of the cement-bone interface, thus contributing to the reduction of the incidence of aseptic loosening, the commonest cause of revision surgery. This in-vitro study compared the cement pressurization achieved during insertion of four different stems of equivalent sizes: the Elite Plus (DePuy, UK), C-Stem (DePuy, UK), Exeter (Stryker, USA), and CPS-Plus (Plus Orthopedics, Switzerland). The maximum pressures attained at the time of stem insertion were recorded at proximal, mid and distal stem levels. The Elite Plus generated significantly higher distal pressures than the other stems. The CPS-Plus generated significantly greater proximal cement pressures than the Elite Plus, C-Stem, and Exeter prostheses. The triple taper of the C-Stem increased the cement pressurization medial to the stem.

The stem shape and the presence or absence of a proximal stem centralizer affect cement pressurization. The presence of a proximal stem centralizer, a large stem volume, and a lateral-medial taper are all factors associated with increased cement pressurization during stem insertion.
A 12-Station Anatomic Hip Joint Simulator
Authors: Saikko V
Published: October 2005

A novel 12-station hip joint simulator with an anatomic position of the prosthesis was designed and built. The motion of the simulator consists of flexion-extension and abduction-adduction. The load is of the double-peak type. The validation test was done with three similar 28 mm CoCr-polyethylene joints in diluted calf serum lubricant for 3.3 × 106 cycles. The bearing surfaces of the polyethylene cups were burnished, the CoCr heads were undamaged, the wear particles were in the 0.1-1 μm size range, and the mean wear factor of the polyethylene cups was 5.7 × 10−7 mm3/N m. These essential observations were in good agreement with clinical findings. In addition, three similar 50 mm CoCR/CoCr joints, representing the contemporary large-diameter metal-on-metal articulation were tested. The wear of the CoCr/CoCr joints was calculated from the Co and Cr concentrations of the used lubricant quantified with atomic absorption spectroscopy. The bearing surfaces of the CoCr/CoCr jonits showed mild criss-cross scratching only. The average wear factor of polyethylene cups was 275 times that of the CoCr/CoCr joints. The tribological behaviour of the large-dia. CoCr/CoCr appeared to be dominated by fluid film lubrication, as indicated by very low frictional heating and wear, making it tribologically superior to the conventional CoCr/polyethylene, and therefore very interesting clinically. In conclusion, the simulator proved to be a valid, reliable, practical, economical, and easy-to-operate tool for wear studies of various hip replacement designs.
A Three-Dimensional Dynamic Finite Element Model of the Prosthetic Knee Joint: Simulation of Joint Laxity and Kinematics
Authors: Barink M , Kampen A van , Malefijt M de Waal , Verdonschot N
Published: October 2005

For testing purposes of prostheses at a preclinical stage, it is very valuable to have a generic modelling tool, which can be used to optimize implant features and to avoid poor designs being launched on to the market. The modelling tool should be fast, efficient, and multipurpose in nature; a finite element model is well suited to the purpose. The question posed in this study was whether it was possible to develop a mathematically fast and stable dynamic finite element model of a knee joint after total knee arthroplasty that would predict data comparable with published data in terms of (a) laxities and ligament behaviour, and (b) joint kinematics. The soft tissue structures were modelled using a relatively simple, but very stable, composite model consisting of a band reinforced with fibres. Ligament recruitment and balancing was tested with laxity simulations. The tibial and patellar kinematics were simulated during flexion-extension. An implicit mathematical formulation was used. Joint kinematics, joint laxities, and ligament recruitment patterns were predicted realistically. The kinematics were very reproducible and stable during consecutive flexion-extension cycles. Hence, the model is suitable for the evaluation of prosthesis design, prosthesis alignment, ligament behaviour, and surgical parameters with respect to the biomechanical behaviour of the knee.
A First Approach to in vitro Simulation of Vascular Calcification by the Controlled Crystallization of Poorly Crystalline Calcium Phosphates onto Porous Cholesterol
Authors: Dorozhkin S V , Dorozhkina E I
Published: October 2005

A first approach to in vitro simulation of vascular calcification was elaborated. Vascular calcification was simulated by a slow crystallization of a non-stoichiometric poorly crystallized carbonateapatite from Kokubo's revised simulated body fluid (rSBF) on the surface of a porous pellet made of pure cholesterol. To achieve this, the crystallization experiments were performed under strictly controlled conditions (similar to physiological ones) provided by a constant-composition double-diffusion (CCDD) device. To obtain an even closer match to in vivo conditions, rSBF was enriched by the addition of glucose and bovine serum albumin (BSA) in physiological amounts. Precipitation took place on the surface of cholesterol and the precipitates consisted of poorly crystalline non-stoichiometric, sodium-and magnesium-containing carbonateapatite.
The Changes in the Tensile Properties of Tendons after Freeze Storage in Saline Solution
Authors: Ng Boon Ho , Chou Siaw Meng , Lim Beng Hai , Chong Alphonsus
Published: October 2005

The objective of this study is to evaluate the influence of saline solution (0.9 per cent NaCl) on the tensile properties of freeze-stored tendons. Firstly, 170 pieces of chicken flexor digitorum profundus tendons were retrieved and wrapped in saline-soaked gauze before they were stored at -40 °. Then specimens were tensile tested at various time points over 360 days, scanning electron microscopy (SEM) was performed on fresh specimens, and specimens were freeze-stored for 233 days to investigate microstructure change after freeze storage. The mean values of strain ultimate tensile strength (UTS) did not deviate significantly (analysis of variance; p = 0.249) following freeze storage while the UTS and elastic modulus increased gradually with the duration of freeze storage and the growth became significant ( p < 0.01) for durations longer than 70 and 40 days respectively. The SEM study showed that the collagen fibre density of specimens stored for 233 days decreased because of porosity growth. These findings suggested that the saline increased the tensile strength and modulus of the collagen.
Improving Contour Accuracy of Machine Tools Using an Integral-Gain Scheduler
Authors: Ko R C , Good M C
Published: October 2005

In high-precision machine tools, contour error at axis reversal can significantly reduce the quality of products. Resulting from non-linear friction behaviour, the reversal error is traditionally handled by the velocity controller, which highly relies on a high-performance current servo. However, the widely employed pulse width modulation (PWM) inverter in the power stage of the current servo operates with a severe non-linearity known as deadband. The deadband effect degrades the current-loop tracking performance and consequently hinders the velocity controller in responding to friction disturbances. The result is a significant and oscillatory tracking error, or contour error in a multiaxis system.

Unlike other approaches where the deadband is compensated via measurement or estimation, a control system approach is proposed in this paper where the deadband is treated as a voltage perturbation in the current loop. The proposed scheme incorporates a feedforward signal from the current command and schedules the integral action in the current controller accordingly. The proposed scheme was implemented in digital servo drives of a commercial grinding machine. Experiments show that the proposed scheme is an effective and practical solution for this type of problem.
Experimental and numerical investigation of effect of fuel on ion sensor signal to determine combustion timing in homogeneous charge compression ignition engines
Authors: Mehresh P , Flowers D , Dibble R W
Published: October 2005

Homogeneous charge compression ignition (HCCI) engines offer promise owing to low emissions and high efficiency. However, the control of the combustion process in HCCI engines, specifically the control of the start of combustion (SOC) or ignition timing, remains a challenge. Piezoelectric pressure transducers are used in research engines for determination of the start of combustion; however, these pressure transducers are too expensive and fragile for applications in commercial engines. Recent work by the authors as well as other investigators has shown the potential of inexpensive ion sensors in HCCI engines fuelled with propane or gasoline. However, the working range of ion sensors is limited in HCCI engines owing, in large part, to the fact that the peak cycle temperature in HCCI combustion is quite low (∼ 1700–1900 K). With the guidance of detailed chemical kinetic modelling it is shown that fuels or additives producing a higher concentration of CH radicals will probably produce higher ion concentrations. Acetylene (HC=CH) is known to produce large concentrations of CH radicals. Hence, various mixtures of propane and acetylene are numerically and experimentally studied. The ion concentration substantially increases with the addition of a small amount of acetylene. This research is an effort to understand the ion generation mechanism in HCCI engines with a view towards improving the ion signal.
Ion current measurement in a homogeneous charge compression ignition engine
Authors: Tanaka T , Narahara K , Tabata M , Yoshiyama S , Tomita E
Published: October 2005

An ion current probe using a spark plug was applied to gasoline-fuelled homogeneous charge compression ignition (HCCI) combustion with hot residual gas in order to verify the possibility of using it as a combustion sensor. The ion current signal for single-cycle HCCI combustion had a simple profile and effectively one maximum value. There is a possibility that a similar ion current signal corresponding to the completed reaction can be obtained, depending on the location of the probe during HCCI combustion. The ionization reaction for HCCI combustion is affected by the chemical ionization reaction with heat release, and there is a possibility that the ion current can be used to detect heat release corresponding to the chemical ionization reaction. A strong correlation between the timing of the integrated ion current and the timing of the mass fraction burned is observed. The timing of the mass fraction burned is assumed from the timing of the integrated ion current, and the mass fraction burned (up to 70 per cent) can be determined, even if the engine driving condition changes within the scope of the test. There is a correlation between the timing of the maximum ion-current and the maximum rate of heat release, and there is a possibility that the maximum value of the rate of heat release can be inferred by detecting the timing of the maximum ion current. There is a correlation between the timing of the maximum ion current and the timing of the maximum pressure at each cycle. Therefore, it may be possible to monitor the variation of the HCCI combustion phasing.
A study on premixed charge compression ignition combustion of natural gas with direct injection
Authors: Ishiyama T , Kawanabe H , Ohashi K , Shioji M , Nakai S
Published: October 2005

In order to extend the available load range and obtain higher thermal efficiency in natural gas premixed charge compression ignition (PCCI) engines, a strategy for controlling direct injection combustion is discussed. Experimental results from single-cylinder engine tests demonstrate the possibility to extend load range by direct fuel injection. Reduced nozzle orifice size and reduced injection angle provide higher combustion efficiency; however, this promotes the tendency to knock because of the formation of a locally rich mixture. Arising from discussions based on prediction by computational fluid dynamics (CFD) code, considering mixture heterogeneity, it is suggested that controlling probability density functions (PDFs) of fuel concentration could be a means to control the rate of pressure rise. Restricted air utilization is useful to activate combustion at low overall equivalence ratios; on the other hand, full utilization of in-cylinder air and formation of a quantity of lean mixture can provide mild combustion.
Performance of multi-dimensional models for simulating diesel premixed charge compression ignition engine combustion using low- and high-pressure injectors
Authors: Kong S-C , Ra Y , Reitz R D
Published: October 2005

An engine CFD model has been developed to simulate premixed charge compression ignition (PCCI) combustion using detailed chemistry. The numerical model is based on the KIVA code that is modified to use CHEMKIN as the chemistry solver. The model was applied to simulate ignition, combustion, and emissions processes in diesel engines operated to achieve PCCI conditions. Diesel PCCI experiments using both low- and high-pressure injectors were simulated. For the low-pressure injector with early injection (close to intake valve closure), the model shows that wall wetting can be minimized by using a pressure-swirl atomizer with a variable spray angle. In the case of using a high-pressure injector, it is found that late injection (SOI = 5 ° ATDC) benefits soot emissions as a result of low-temperature combustion at highly premixed conditions. The model was also used to validate the emission reduction potential of an HSDI diesel engine using a double injection strategy that favours PCCI conditions. It is concluded that the present model is useful to assess future engine combustion concepts, such as PCCI and low-temperature combustion (LTC).
Combustion optimization in the low-temperature diesel combustion regime
Authors: Yun H , Reitz R D
Published: October 2005

A microgenetic algorithm (μGA) code was applied to optimize experimentally an HSDI single-cylinder diesel engine equipped with a common rail fuel-injection system in order to reduce NOx, soot, and b.s.f.c. simultaneously. Four control factors were used, namely, start-of-injection (SOI) timing, intake boost pressure level, cooled exhaust gas recirculation (EGR) rate, and fuel-injection pressure. The search space was designed to be within the experimental capabilities of the engine and control system. The engine testing was done at 1550 r/min, and 25 per cent load. The optimum results showed significant improvements for the NOx and soot emissions. Through analysis of the combustion characteristics, the mechanisms of emission reduction were revealed. The optimum featured a long ignition delay due to retarded SOI timing, and low combustion temperatures as a result of high EGR rates. The resulting long time for mixing and low temperatures helps suppress soot formation. To explore further the effect of mixing on emissions in the low-temperature combustion regime, factors that enhance turbulent mixing rates, including the use of high injection pressures and post injections were examined. The results show that optimal post injections are useful further to reduce emissions when they feature a short injection pulse with an optimal dwell time between injections.
Computational fluid dynamics analysis of the effect of mixture heterogeneity on combustion process in a premixed charge compression ignition engine
Authors: Saijyo K , Kojima T , Nishiwaki K
Published: October 2005

We analyzed the interrelationships between mixture heterogeneity and reaction in a premixed charge compression ignition (PCCI) combustion, using large eddy simulation (LES) in conjunction with a reaction kinetics model. The aim of this analysis is to find the statistical characteristics of the mixture heterogeneity in a turbulent flowfield for moderating the PCCI combustion and for increasing an output limit, which is restricted by a severe knock. Several different initial conditions of heterogeneity of an air-fuel or air-fuel-EGR gas mixture were given at the intake valve closing time by a new method, which generated statistically reasonable turbulent fluctuations in both velocity and fuel mass fraction fields. The autoignition and combustion behaviours were analysed for several different sets of the r.m.s. and the length scale of the fluctuations in the fuel mass fraction. The analyses show that the combination of a larger r.m.s. value and a longer-length scale of the fluctuations in fuel mass fraction is effective to slow the combustion in a hot flame reaction phase and to avoid knocking. The analytical results also show that the heterogeneous distribution of an EGR gas has a considerable effect in making the combustion slower, even when a fuel-air mixture is homogeneous.
An Enhancement of Photoproperties of Solid-state TiO2|dye|CuI Type Cells by Coupling Mercurochrome with Natural Juice Extracted from Pomegranate Fruits
Authors: Sirimanne Prasad Manjusri , Senevirathna Indika , Tennakone Kirthi
Published: October 2005

Electrostatic coupling of mercurochrome with an anthocyanin pigment extracted from pomegranate fruits results an enhancement of the photovoltaic properties of TiO2|dye|CuI solid-state solar cells.
Uniform PbS Hopper (Skeletal) Crystals Grown by a Solution Approach [Retracted]
Authors: Zhu Jiping , Zhou Xiaoyuan , Chen Ke
Published: October 2005

Unique PbS hopper (skeletal) crystals were obtained in large quantities through solvothermal process by controlling the reaction conditions such as time, concentration, and temperature. A possible formation mechanism was proposed based on their shape evolution.
An artificial riboswitch for controlling pre-mRNA splicing
Authors: KIM DONG-SUK , GUSTI VERONICA , PILLAI SAILESH G. , GAUR RAJESH K.
Published: October 2005

Riboswitches, as previously reported, are natural RNA aptamers that regulate the expression of numerous bacterial metabolic genes in response to small molecule ligands. It has recently been shown that these RNA genetic elements are also present near the splice site junctions of plant and fungal introns, thus raising the possibility of their involvement in regulating mRNA splicing. Here it is shown for the first time that a riboswitch can be engineered to regulate pre-mRNA splicing in vitro. We show that insertion of a high-affinity theophylline binding aptamer into the 3′ splice site (3′ ss) region of a model pre-mRNA (AdML-Theo29AG) enables its splicing to be repressed by the addition theophylline. Our results indicate that the location of 3′ ss AG within the aptamer plays a crucial role in conferring theophylline-dependent control of pre-mRNA splicing. We also show that theophylline-mediated control of pre-mRNA splicing is highly specific by first demonstrating that a small molecule ligand similar in shape and size to theophylline had no effect on the splicing of AdML-Theo29AG pre-mRNA. Second, theophylline failed to exert any influence on the splicing of a pre-mRNA that does not contain its binding site. Third, theophylline specifically blocks the step II of the splicing reaction. Finally, we provide evidence that theophylline-dependent control of pre-mRNA splicing is functionally relevant.
Yeast Puf3 mutants reveal the complexity of Puf-RNA binding and identify a loop required for regulation of mRNA decay
Authors: HOUSHMANDI S. SEAN , OLIVAS WENDY M.
Published: October 2005

The eukaryotic Puf proteins regulate mRNA translation and degradation by binding the 3′ untranslated regions of target mRNAs. Crystal structure analysis of a human Puf bound to RNA suggested a modular mode of binding, with specific amino acids within each of eight repeat domains contacting a single nucleotide of the target RNA. Here we study the mechanism by which the yeast Puf3p binds and stimulates the degradation of COX17 mRNA. Mutation of the predicted RNA-binding positions of Puf3p to those found in Puf5p demonstrated that a single amino acid change in Puf3p abolished detectable binding to COX17. Since this amino acid position in both Puf3p and Puf5p is predicted to contact an adenine in the respective target RNAs, the amino acid in Puf3p must play a more critical role in promoting COX17 interaction. In contrast, an amino acid change in the third repeat of Puf3p, which interacts with the only divergent nucleotide between the Puf3p and Puf5p targets, had no effect on binding COX17. These results argue that a simple set of rules cannot reliably link specific amino acid positions with target specificity. Each of these amino acid changes in Puf3p enhanced binding to the Puf5p target HO RNA, suggesting a different mode of binding to this target. Finally, we identified an outer surface loop that was dispensable for binding but was required to promote both rapid deadenylation and subsequent decapping of the COX17 mRNA, most likely as a point of protein–protein interactions.
Solution probing of metal ion binding by helix 27 fromEscherichia coli16S rRNA
Authors: LAMBERT MEREDITH NEWBY , HOERTER JOHN A.H. , PEREIRA MIGUEL J.B. , WALTER NILS G.
Published: October 2005

Helix (H)27 fromEscherichia coli16S ribosomal (r)RNA is centrally located within the small (30S) ribosomal subunit, immediately adjacent to the decoding center. Bacterial 30S subunit crystal structures depicting Mg2+binding sites resolve two magnesium ions within the vicinity of H27: one in the major groove of the G886–U911 wobble pair, and one within the GCAA tetraloop. Binding of such metal cations is generally thought to be crucial for RNA folding and function. To ask how metal ion–RNA interactions in crystals compare with those in solution, we have characterized, using solution NMR spectroscopy, Tb3+footprinting and time-resolved fluorescence resonance energy transfer (tr-FRET), location, and modes of metal ion binding in an isolated H27. NMR and Tb3+footprinting data indicate that solution secondary structure and Mg2+binding are generally consistent with the ribosomal crystal structures. However, our analyses also suggest that H27 is dynamic in solution and that metal ions localize within the narrow major groove formed by the juxtaposition of the loop E motif with the tandem G894–U905 and G895–U904 wobble pairs. In addition, tr-FRET studies provide evidence that Mg2+uptake by the H27 construct results in a global lengthening of the helix. We propose that only a subset of H27–metal ion interactions has been captured in the crystal structures of the 30S ribosomal subunit, and that small-scale structural dynamics afforded by solution conditions may contribute to these differences. Our studies thus highlight an example for differences between RNA–metal ion interactions observed in solution and in crystals.
Rituximab Treatment of Refractory Rheumatoid Arthritis
Authors: Summers Kelly M , Kockler Denise R
Published: October 2005

OBJECTIVE

To review published literature using rituximab for treatment of refractory rheumatoid arthritis (RA).

DATA SOURCES

An English-language literature search was conducted using MEDLINE (1966–May 2005) and EMBASE (1980–May 2005). References of identified articles were subsequently reviewed for additional data.

DATA SYNTHESIS

Evidence suggests that B lymphocyte depletion in patients suffering from refractory RA may be a key component in the interruption of the disease pathogenesis. Successful depletion of B lymphocytes with rituximab in patients with RA has been reported in case reports, open-label pilot studies, and a randomized, double-blind, placebo-controlled trial.

CONCLUSIONS

Based on the limited published data, rituximab, when used in combination with other agents (ie, cyclophosphamide or methotrexate), appears to be a reasonable treatment option for refractory RA. However, additional controlled trials need to be conducted to further define optimal dosing, response rates, comparative long-term efficacy, and RA treatment algorithm placement of rituximab in this patient population.
Clinical Evaluation of a Lead Mobilization Test Using the Chelating Agent Dimercaptosuccinic Acid
Authors: Hoet Perrine , Buchet Jean-Pierre , Decerf Laurence , Lavalleye Benoît , Haufroid Vincent , Lison Dominique
Published: October 2005

Background: The lead mobilization test reflects the mobilizable and likely toxicologically active fraction of the lead body burden. We propose a safe and convenient protocol for this test, to assess concomitant copper and zinc excretion and to determine the size of the chelatable lead pool in nonoccupationally exposed adults.

Methods: The study population included 80 white adults: 40 controls [median blood lead concentration (PbB), 25 μg/L] and 40 lead-exposed individuals (315 μg/L). After collection of 4- and 24-h baseline urine specimens and a blood sample, dimercaptosuccinic acid (DMSA) was administered orally (1 g), and additional 4- and 24-h urine specimens were obtained. Determinants of the chelatable urinary lead (DMSA-PbU) were traced by linear regression analysis.

Results: Urinary DMSA and lead excretion peaked within 2–3 h after DMSA administration. The amounts of DMSA, lead, copper, and zinc recovered in the 4-h urinary collections were highly correlated with those in 24-h collections (r = 0.857, 0.859, 0.958, and 0.757, respectively). At PbB concentrations >300 μg/L, the relationship between DMSA-PbU and PbB showed a steep increase and a widespread dispersion of DMSA-PbU around the regression line. After DMSA, copper and zinc excretion rates were increased up to 91- and 33-fold, respectively. No side effects were reported after DMSA.

Conclusions: Determination of DMSA-PbU in a 4-h collection after DMSA is convenient, apparently safe, and inexpensive. An upper reference limit value of 22 μg/4 h is proposed for Belgian reference individuals. The diagnostic value of DMSA-PbU is likely to be contributive for PbB >300 μg/L.
Neural Correlates of Reach Errors
Authors: Diedrichsen Jörn , Hashambhoy Yasmin , Rane Tushar , Shadmehr Reza
Published: October 2005

Reach errors may be broadly classified into errors arising from unpredictable changes in target location, called target errors, and errors arising from miscalibration of internal models (e.g., when prisms alter visual feedback or a force field alters limb dynamics), called execution errors. Execution errors may be caused by miscalibration of dynamics (e.g., when a force field alters limb dynamics) or by miscalibration of kinematics (e.g., when prisms alter visual feedback). Although all types of errors lead to similar on-line corrections, we found that the motor system showed strong trial-by-trial adaptation in response to random execution errors but not in response to random target errors. We used functional magnetic resonance imaging and a compatible robot to study brain regions involved in processing each kind of error. Both kinematic and dynamic execution errors activated regions along the central and the postcentral sulci and in lobules V, VI, and VIII of the cerebellum, making these areas possible sites of plastic changes in internal models for reaching. Only activity related to kinematic errors extended into parietal area 5. These results are inconsistent with the idea that kinematics and dynamics of reaching are computed in separate neural entities. In contrast, only target errors caused increased activity in the striatum and the posterior superior parietal lobule. The cerebellum and motor cortex were as strongly activated as with execution errors. These findings indicate a neural and behavioral dissociation between errors that lead to switching of behavioral goals and errors that lead to adaptation of internal models of limb dynamics and kinematics.