bluuebunny/crossref_metadata_2025 huggingface dataset:
Finite Element Analysis of Woven Airbeams
Authors: Malm Christopher G. , Davids William G. , Peterson Michael L. , Zhang Hui
Published: April 2008

The underlying mechanics of airbeam structures continues to be a topic of current research. Airbeams are attractive because they have the advantage of outstanding strength-to-weight ratios, can deform without causing irreversible damage to the structure, and the deflated storage space is small. Major challenges in the analysis of airbeams include capturing fabric wrinkling under small compressive strains and incorporating the effects of internal pressure. This paper presents results from analyses of cylindrical woven airbeams using the commercial finite element software package ABAQUS. Models are created using a combination of shell and membrane elements, and loaded in three point bending. The models are solved as quasi-static using the ABAQUS/Explicit solver. The effects of mesh density and material damping on solution accuracy are investigated. Results of the finite element models are compared to experimental data.
Reliability of Cyclically Actuated Silicon Microcantilevers in Liquid Environments
Authors: Ali S. , Mantell Susan C. , Longmire Ellen K.
Published: April 2008

Microstructures are exposed to a variety of liquid environments in applications such as biosensors, BioMEMS, and microfluidic devices. Environmental interactions between the liquids and microstructures can undermine the reliability of MEMS in liquid environments. In this paper, reliability of silicon microcantilevers is investigated in two common liquids, de-ionized water and saline solution, and contrasted with results in air. These single crystal silicon microcantilevers have a magnetic Permalloy tip and are magnetically actuated. The microcantilevers are subjected to long-term cyclic actuation (108-109 cycles) in a liquid filled enclosure. Reliability of the microcantilevers is evaluated by periodically monitoring changes in resonance frequency. The microcantilevers are subjected to peak stresses of ~5 MPa, which is typical for MEMS applications in liquids, e.g. AFM tips and biosensors. Since the tensile strength of silicon (1-3 GPa) is much higher than the applied stresses, structural fatigue failures were neither expected nor observed in air, water or saline. Changes in resonance frequencies of microcantilevers tested in air and water were insignificant to within the limits of experimental accuracy. However, environmental interactions influenced the reliability of microcantilevers tested in saline as indicated by a gradual decrease in resonance frequency. This decrease in resonance frequency is attributed to gradual mass adsorption of ionic species on the microcantilevers from the saline solution as indicated by scanning electron microscope imaging and electron dispersive spectroscopy.
Experimental Study on the Stabilization of the No-Motion State in the Rayleigh-Benard Convection Problem
Authors: Remillieux Marcel C.
Published: April 2008

We demonstrate experimentally that through the use of proportional-differential control, it is possible to stabilize the no-motion state of a fluid layer heated from below, cooled from above, and confined in an upright, circular cylinder (the Rayleigh-Be´nard problem). An array of 24 independently controlled heaters (thermal actuators), microfabricated on a silicon wafer, constitutes the bottom boundary of the test cell. A cooling system maintains the top boundary at a constant temperature. Silicon diodes located at the mid-height of the cell, above the actuators, measure the fluid's temperature. The multi-input, multi-output controller adjusts the heaters' power in proportion to the deviation of the fluid's temperatures, as recorded by the diodes, from preset values associated with the no-motion, conductive state. First, a set of experiments was conducted in the absence of a controller to determine the uncontrolled, reference state. Advantage is taken of the linear dependence of the mid-height temperature on the power input in the no-motion state. The preset temperatures are determined by extrapolating the mid-height temperatures to the desired input power values. A proportional controller is then engaged. We show that as the controller's gain increases so does the critical Rayleigh number for the onset of convection. The proportional controller allows us to increase the critical Rayleigh number by as much as a factor of 1.4. When the controller's gain is larger than a critical value, the system becomes time-wise oscillatory (Hopf bifurcation) and the controller's performance deteriorates. The oscillatory convection can be significantly damped out by engaging a proportional-differential (PD) controller. The PD controller allows us to further increase the critical Rayleigh number for the onset of convection to as much as a factor or 1.7 compared to the uncontrolled case. Further increases in the critical Rayleigh number were not possible due to the actuators' saturation. We also compared the supercritical flow patterns at the mid-height of the test cell in the presence of the controller with the flow patterns in the absence of a controller. The proportional controller modified the flow pattern from a single convective cell with ascending fluid in one half of the cell and descending in the other half, to fluid ascending at the center of the cell and descending at near the lateral wall. Our work represents an improvement over previous experimental investigations on the stabilization of Rayleigh-Be´nard convection in which the critical Rayleigh number was increased by only a factor of 1.2. Almost uniform temperature distribution at the mid-height is obtained through the combined action of proportional and derivative controllers. The Rayleigh-Be´nard convection is suppressed under conditions when, in the absence of a controller, flow would persist.
Using Scenarios to Evaluate Technology Development Options for Power Generation Equipment
Authors: Franco Flavio J.
Published: April 2008

The world of power generation is currently facing a number of challenges and uncertainties, caused by technical, economic, political, geographical and social factors. Manufacturers of power generation equipment have to design their strategies for technology development taking into account these challenges and uncertainties. They have to set goals for the medium and the long term, which involve the commitment of huge amounts of resources. At the same time, given the uncertainty of the future, they have to try to reduce their risks. Scenario-Based Planning is a methodology to deal with uncertainty in making decisions for the long term. It does not tell planners what will probably happen but helps them to understand what may happen through an understanding of the relationships of cause and effect within the environment of interest. Taking gas turbines as an example, this paper shows an application of the method to the evaluation of the markets related to different primary energy sources and different technologies, within power generation scenarios given by the IEA and scenarios proposed in previous papers by the author. Although current power generation gas turbines are predominantly designed to burn natural gas, developments based on other primary energy sources will require gas turbines to run with different fuels (synthetic gas or hydrogen, for example), helium or CO2 (in high temperature nuclear reactor systems) or hot air (in hybrid solar thermal power systems). Wind power may also require backup from gas turbines, probably incorporating significant fuel flexibility. An estimate of the value of the potential markets related to these different applications of gas turbines is made in this paper. Historical and estimated experience curves for the technologies of interest and their dependence relationships are used in this analysis, with a system dynamics model as described in [1].
Numerical Simulations on Aerodynamic Drag of Ground Transportation System (GTS) Model
Authors: Sitlani Manish P. , Aung Kendrick
Published: April 2008

The aerodynamic drag characteristics of a heavy-duty truck with two configurations, a tractor and a single trailer, and a tractor and a tandem-trailer (two trailers), have been studied. The aerodynamic drag of a truck depends on geometry, frontal area and shape, and the speed of the truck. The basic geometry used in the simulation is a 1:8 scale Ground Transportation System (GTS). The effects of vehicle geometry, frontal shape, vehicle speed, and the gap size were investigated and the drag coefficients were computed. The effect of add-on devices such as aerodynamic boat-tail plates at the rear of the trailer on the aerodynamic drag of the truck has also been analyzed. In particular, the effects of the gap between tractor and trailer, and the gap between trailers on the aerodynamic drag of tractor and two trailers configuration were determined. The feasibility of Reynolds-Average Navier-Stokes (RANS) κ-ε model in the prediction of aerodynamic drag at various Reynolds numbers has also been studied. The CFD software from CD-adapco together with an expert tool, es-aero, was used for all the analyses reported in this paper. CFD simulations for tractor and single trailer configuration were performed for various Reynolds numbers. The simulation results were validated with available experimental data and good agreements were found. Validation of numerical results for tractor and single trailer with the experimental data formed the basis for analyzing tractor and double trailer configuration. The tractor and two trailers configuration for different gap sizes between the trailers at various speeds were analyzed. The results showed that closing the gaps and incorporating boat-tails at the rear of the trailer could reduce the drag by as much as 33 percent. Drag coefficient also reduced by 46 percent by introducing smooth frontal fillets in case of tractor and single trailer. The study also emphasizes flow structures around the vehicle that contribute to the total drag.
The effect of skin thickness determined using breast CT on mammographic dosimetry
Authors: Huang Shih‐Ying , Boone John M. , Yang Kai , Kwan Alexander L. C. , Packard Nathan J.
Published: April 2008

The effect of breast skin thickness on dosimetry in mammography was investigated. Breast computed tomography (CT) acquisition techniques, combined with algorithms designed for determining specific breast metrics, were useful for estimating skin thickness. A radial‐geometry edge detection scheme was implemented on coronal reconstructed breast CT (bCT) images to measure the breast skin thickness. Skin thickness of bilateral bCT volume data from 49 women and unilateral bCT volume data from 2 women (10 healthy women and 41 women with BIRADS 4 and 5 diagnoses) was robustly measured with the edge detection scheme. The mean breast skin thickness (‐breast standard deviation) was found to be . Since most current published normalized glandular dose coefficients are based on the assumption of a 4‐mm breast skin thickness, the values computed with Monte Carlo techniques will increase up to 18% due to the thinner skin layers (e.g., 6‐cm 50% glandular breast, 28 kVp Mo–Mo spectrum). The thinner skin dimensions found in this study suggest that the current values used for mammographic dosimetry lead to a slight underestimate in glandular dose.
Combined kV and MV imaging for real‐time tracking of implanted fiducial markersa)
Authors: Wiersma R. D. , Mao Weihua , Xing L.
Published: April 2008

In the presence of intrafraction organ motion, target localization uncertainty can greatly hamper the advantage of highly conformal dose techniques such as intensity modulated radiation therapy (IMRT). To minimize the adverse dosimetric effect caused by tumor motion, a real‐time knowledge of the tumor position is required throughout the beam delivery process. The recent integration of onboard kV diagnostic imaging together with MV electronic portal imaging devices on linear accelerators can allow for real‐time three‐dimensional (3D) tumor position monitoring during a treatment delivery. The aim of this study is to demonstrate a near real‐time 3D internal fiducial tracking system based on the combined use of kV and MV imaging. A commercially available radiotherapy system equipped with both kV and MV imaging systems was used in this work. A hardware video frame grabber was used to capture both kV and MV video streams simultaneously through independent video channels at 30 frames per second. The fiducial locations were extracted from the kV and MV images using a software tool. The geometric tracking capabilities of the system were evaluated using a pelvic phantom with embedded fiducials placed on a moveable stage. The maximum tracking speed of the kV/MV system is approximately 9 Hz, which is primarily limited by the frame rate of the MV imager. The geometric accuracy of the system is found to be on the order of less than 1 mm in all three spatial dimensions. The technique requires minimal hardware modification and is potentially useful for image‐guided radiation therapy systems.
Characteristics of megavoltage cone‐beam digital tomosynthesis
Authors: Descovich M. , Morin O. , Aubry J. F. , Aubin M. , Chen J. , Bani‐Hashemi A , Pouliot J.
Published: April 2008

This article reports on the image characteristics of megavoltage cone‐beam digital tomosynthesis (MVCB DT). MVCB DT is an in‐room imaging technique, which enables the reconstruction of several two‐dimensional slices from a set of projection images acquired over an arc of . The limited angular range reduces the acquisition time and the dose delivered to the patient, but affects the image quality of the reconstructed tomograms. Image characteristics (slice thickness, shape distortion, and contrast‐to‐noise ratio) are studied as a function of the angular range. Potential clinical applications include patient setup and the development of breath holding techniques for gated imaging.
Efficiency improvements for ion chamber calculations in high energy photon beams
Authors: Wulff J. , Zink K. , Kawrakow I.
Published: April 2008

This article presents the implementation of several variance reduction techniques that dramatically improve the simulation efficiency of ion chamber dose and perturbation factor calculations. The cavity user code for the EGSnrc Monte Carlo code system is extended by photon cross‐section enhancement (XCSE), an intermediate phase‐space storage (IPSS) technique, and a correlated sampling (CS) scheme. XCSE increases the density of photon interaction sites inside and in the vicinity of the chamber and results—in combination with a Russian Roulette game for electrons that cannot reach the cavity volume—in an increased efficiency of up to a factor of 350 for calculating dose in a Farmer type chamber placed at 10 cm depth in a water phantom. In combination with the IPSS and CS techniques, the efficiency for the calculation of the central electrode perturbation factor can be increased by up to three orders of magnitude for a single chamber location and by nearly four orders of magnitude when considering the variation with depth or with distance from the central axis in a large field photon beam. The intermediate storage of the phase‐space properties of particles entering a volume that contains many possible chamber locations leads to efficiency improvements by a factor larger than 500 when computing a profile of chamber doses in the field of a linear accelerator photon beam. All techniques are combined in a new EGSnrc user code egs_chamber. Optimum settings for the variance reduction parameters are investigated and are reported for a Farmer type ion chamber. A few example calculations illustrating the capabilities of the egs_chamber code are presented.
Region‐oriented CT image representation for reducing computing time of Monte Carlo simulations
Authors: Sarrut David , Guigues Laurent
Published: April 2008

Purpose. We propose a new method for efficient particle transportation in voxelized geometry for Monte Carlo simulations. We describe its use for calculating dose distribution in CT images for radiation therapy. Material and methods. The proposed approach, based on an implicit volume representation named segmented volume, coupled with an adapted segmentation procedure and a distance map, allows us to minimize the number of boundary crossings, which slows down simulation. The method was implemented with the GEANT4 toolkit and compared to four other methods: One box per voxel, parameterized volumes, octree‐based volumes, and nested parameterized volumes. For each representation, we compared dose distribution, time, and memory consumption. Results. The proposed method allows us to decrease computational time by up to a factor of 15, while keeping memory consumption low, and without any modification of the transportation engine. Speeding up is related to the geometry complexity and the number of different materials used. We obtained an optimal number of steps with removal of all unnecessary steps between adjacent voxels sharing a similar material. However, the cost of each step is increased. When the number of steps cannot be decreased enough, due for example, to the large number of material boundaries, such a method is not considered suitable. Conclusion. This feasibility study shows that optimizing the representation of an image in memory potentially increases computing efficiency. We used the GEANT4 toolkit, but we could potentially use other Monte Carlo simulation codes. The method introduces a tradeoff between speed and geometry accuracy, allowing computational time gain. However, simulations with GEANT4 remain slow and further work is needed to speed up the procedure while preserving the desired accuracy.
Peripheral dose measurement for CyberKnife radiosurgery with upgraded linac shielding
Authors: Chuang Cynthia F. , Larson David A. , Zytkovicz Andrea , Smith Vernon , Petti Paula L.
Published: April 2008

The authors investigated the peripheral dose reduction for CyberKnife radiosurgery treatments after the installation of a linac shielding upgrade. As in a previous investigation, the authors considered two treatment plans, one for a hypothetical target in the brain and another for a target in the thorax, delivered to an anthropomorphic phantom. The results of the prior investigation showed that the CyberKnife delivered significantly higher peripheral doses than comparable model C Gamma Knife or IMRT treatments. Current measurements, after the linac shielding upgrade, demonstrate that the additional shielding decreased the peripheral dose, expressed as a percentage of the delivered monitor units (MU), by a maximum of 59%. The dose reduction was greatest for cranial‐caudal distances from the field edge less than 30 cm, and at these distances, the CyberKnife peripheral dose, expressed as a percentage of the delivered MU, is now comparable to that measured for the other treatment modalities in our previous investigation. For distances between 30 and 70 cm from the field edge, the additional shielding reduced the peripheral dose by between 20% and 55%. At these distances, the CyberKnife peripheral dose remains higher than doses measured in our previous study for the model C Gamma Knife and IMRT.
Slides collection. Radiation Oncology Physics: A Handbook for Teachers and Students
Authors: Sethi Anil
Published: April 2008

Slides collection. Radiation Oncology Physics: A Handbook for Teachers and Students Podgorsak E. B. and Hartmann G. H. Based on the IAEA publication, ISBN: 92‐0‐107304‐6, Vienna, Austria. Free access at: http://www‐naweb.iaea.org/nahu/dmrp/slides.shtm.
Bats Limit Arthropods and Herbivory in a Tropical Forest
Authors: Kalka Margareta B. , Smith Adam R. , Kalko Elisabeth K. V.
Published: April 2008

Previous exclosure studies measuring the top-down control of arthropod abundance and herbivory combined the effects of birds and bats. We experimentally partitioned bird predation from bat predation in a lowland tropical forest in Panama and measured the direct effects (arthropod abundance) and indirect effects (herbivory). The exclusion of birds and bats each directly increased arthropod abundance on plants: Bird-exclosed plants contained 65% more, and bat-exclosed plants 153% more, arthropods than controls. Birds and bats also indirectly increased herbivory: Bird-exclosed plants suffered 67% more, and bat-exclosed plants 209% more, herbivory than controls. We conclude that bats have dramatic ecological effects that were previously overlooked.
Distribution of Dipeptidyl Peptidase IV in Patients with Chronic Tonsillitis
Authors: Stankovic Milan , Vlahovic Predrag , Avramovic Verica , Todorovic Miroljub
Published: April 2008

In the pathogeneses of recurrent tonsillitis (RT) and tonsillar hypertrophy (TH), different immunological mechanisms are involved. Dipeptidyl peptidase IV (DPP IV) and aminopeptidase N (APN) participate in the regulation of the immune response during inflammation. In this study, the localization of DPP IV and the enzymatic activities of DPP IV and APN in 32 patients, 13 with RT and 19 with TH, who underwent tonsillectomy were investigated. The localization of DPP IV in tonsils was studied using histochemical and immunohistochemical methods. The enzymatic activities of DPP IV and APN in tonsillar lymphocytes and the patients' sera were determined kinetically at 37°C using Gly-Pro-p-nitroanilide (for DPP IV) and Ala-p-nitroanilide (for APN) as chromogenic substrates. In samples from both RT and TH patients, DPP IV was found to localize mainly in extrafollicular areas of tonsillar tissue in a pattern corresponding to the T-cell distribution. Significantly higher (P< 0.001) levels of DPP IV and APN activities in sera from patients with TH than in sera from patients with RT were found. A correlation of DPP IV activities in sera and tonsillar lymphocytes from patients with TH was also found (r= 0.518;P< 0.05). Moreover, the results show that DPP IV and APN activities in sera decreased significantly with age. Tonsillar lymphocytes demonstrated a wide range of DPP IV and APN activities, without significant differences between the investigated groups. The results of this study show that the localization of DPP IV does not depend on the type of tonsillitis, whereas the variety in levels of DPP IV and APN activities in sera of patients with TH and RT suggests different patterns of participation of antigen-stimulated tonsils in the immune system.
Novel Human Adenovirus Causing Nosocomial Epidemic Keratoconjunctivitis
Authors: Ishiko Hiroaki , Shimada Yasushi , Konno Tsunetada , Hayashi Akio , Ohguchi Takeshi , Tagawa Yoshitsugu , Aoki Koki , Ohno Shigeaki , Yamazaki Shudo
Published: April 2008

In 2000, we encountered cases of nosocomial infections with epidemic keratoconjunctivitis (EKC) at a university hospital in Kobe, in the western part of Japan. Two human adenovirus (HAdV) strains, Kobe-H and Kobe-S, were isolated from patients with nosocomial EKC infection. They were untypeable by existing neutralizing antisera; however, the isolate was neutralized with homologous antisera. We then encountered several cases of EKC due to nosocomial infections in eye clinics in different parts of Japan. A total of 80 HAdVs were isolated from patients with EKC at eight different hospitals. The partial hexon gene sequences of the isolates were determined and compared to those of the prototype strains of 51 serotypes. All isolates had identical partial hexon nucleotide sequences. Phylogenetic analysis classified these isolates into species of HAdV-D. The isolates showed 93.9 to 96.7% nucleotide identity with HAdV-D prototype strains, while all 32 HAdV-D prototype strains ranged from 93.2 to 99.2% identity. The sequences of the loop 2 and fiber knob regions from the representative strain, Kobe-H, were dissimilar in all prototype strains of 51 serotypes. We believe that this virus is a novel serotype of HAdV that causes EKC.
Detection of the
Klebsiella pneumoniae
Carbapenemase Type 2 Carbapenem-Hydrolyzing Enzyme in Clinical Isolates of
Citrobacter freundii
and
K. oxytoca
Carrying a Common Plasmid
Authors: Rasheed J. Kamile , Biddle James W. , Anderson Karen F. , Washer Laraine , Chenoweth Carol , Perrin John , Newton Duane W. , Patel Jean B.
Published: April 2008

The
Klebsiella pneumoniae
carbapenemase (KPC) was detected in carbapenem-resistant isolates of
Citrobacter freundii
and
Klebsiella oxytoca
recovered from different patients in a Michigan hospital. Restriction analysis and hybridization with a KPC-specific probe showed the
bla
KPC-2
genes of these two genera of the family
Enterobacteriaceae
are carried on a common plasmid.
Structural Basis for the Receptor Binding Specificity of Norwalk Virus
Authors: Bu Weiming , Mamedova Aygun , Tan Ming , Xia Ming , Jiang Xi , Hegde Rashmi S.
Published: April 2008

Noroviruses are positive-sense, single-stranded RNA viruses that cause acute gastroenteritis. They recognize human histo-blood group antigens as receptors in a strain-specific manner. The structures presented here were analyzed in order to elucidate the structural basis for differences in ligand recognition of noroviruses from different genogroups, the prototypic Norwalk virus (NV; GI-1) and VA387 (GII-4), which recognize the same A antigen but differ in that NV is unable to bind to the B antigen. Two forms of the receptor-binding domain of the norovirus coat protein, the P domain and the P polypeptide, that were previously shown to differ in receptor binding and P-particle formation properties were studied. Comparison of the structures of the NV P domain with and without A trisaccharide and the NV P polypeptide revealed no major ligand-induced changes. The 2.3-Å cocrystal structure reveals that the A trisaccharide binds to the NV P domain through interactions with the residues Ser377, Asp327, His329, and Ser380 in a mode distinct from that previously reported for the VA387 P-domain-A-trisaccharide complex. Mutational analyses confirm the importance of these residues in NV P-particle binding to native A antigen. The α-GalNAc residue unique to the A trisaccharide is buried deeply in the NV binding pocket, unlike in the structures of A and B trisaccharides bound to VA387 P domain, where the α-fucose residue forms the most protein contacts. The A-trisaccharide binding mode seen in the NV P domain complex cannot be sterically accommodated in the VA387 P domain.
A Point Mutation Leading to Hepatitis C Virus Escape from Neutralization by a Monoclonal Antibody to a Conserved Conformational Epitope
Authors: Keck Zhen-Yong , Olson Oakley , Gal-Tanamy Meital , Xia Jinming , Patel Arvind H. , Dreux Marlène , Cosset Francois-Loïc , Lemon Stanley M. , Foung Steven K. H.
Published: April 2008

A challenge in hepatitis C virus (HCV) vaccine development is defining conserved protective epitopes. A cluster of these epitopes comprises an immunodominant domain on the E2 glycoprotein, designated domain B. CBH-2 is a neutralizing human monoclonal antibody to a domain B epitope that is highly conserved. Alanine scanning demonstrated that the epitope involves residues G523, G530, and D535 that are also contact residues for E2 binding to CD81, a coreceptor required for virus entry into cells. However, another residue, located at position 431 and thus at a considerable distance in the linear sequence of E2, also contributes to the CBH-2 epitope. A single amino acid substitution at this residue results in escape from CBH-2-mediated neutralization in a genotype 1a virus. These results highlight the challenges inherent in developing HCV vaccines and show that an effective vaccine must induce antibodies to both conserved and more invariant epitopes to minimize virus escape.
Head, face and neck injury in youth rugby: incidence and risk factors
Authors: McIntosh A S , McCrory P , Finch C F , Wolfe R
Published: April 2008

Objectives

In this study, the incidence of head, neck and facial injuries in youth rugby was determined, and the associated risk factors were assessed.

Design

Data were extracted from a cluster randomised controlled trial of headgear with the football teams as the unit of randomisation. No effect was observed for headgear use on injury rates, and the data were pooled.

Setting

General school and club-based community competitive youth rugby in the 2002 and 2003 seasons.

Participants

Young male rugby union football players participating in under-13, under 15, under 18 and under 21 years competitions. Eighty-two teams participated in year 1 and 87 in year 2.

Main outcome measures

Injury rates for all body regions combined, head, neck and face calculated for game and missed game injuries.

Results

554 head, face and neck injuries were recorded within a total of 28 902 h of rugby game exposure. Level of play and player position were related to injury risk. Younger players had the lowest rates of injury; forwards, especially the front row had the highest rate of neck injury; and inside backs had the highest rate of injuries causing the player to miss a game. Contact events, including the scrum and tackle, were the main events leading to injury.

Conclusion

Injury prevention must focus on the tackle and scrum elements of a youth rugby game.
Personal best marathon performance is associated with performance in a 24-h run and not anthropometry or training volume
Authors: Knechtle B , Wirth A , Knechtle P , Zimmermann K , Kohler G
Published: April 2008

Objective:

In this study, the influence of anthropometric and training parameters on race performance in ultra-endurance runners in a 24-h run was investigated.

Design:

Descriptive field study.

Setting:

24-h run in Basel 2007.

Participants:

15 male Caucasian ultra-runners (mean (SD) 46.7 (5.8 years), 71.1 (6.8 kg), 1.76 (0.07 m), body mass index 23.1 (1.84 kg/m2)).

Interventions:

None.

Main outcome measures:

Age, body mass, body height, length of lower limbs, skin-fold thicknesses, circumference of extremities, skeletal muscle mass, body mass, percentage of body fat, and training volume in 15 successful finishers were determined to correlate anthropometric and training parameters with race performance.

Results:

No significant association (p>0.05) was found between the reached distance and the anthropometric properties. There was also no significant association between the reached distance with the weekly training hours, running years, the number of finished marathons and the number of finished 24-h runs. The reached distance was significantly (p<0.05) positively correlated with the personal best marathon performance (r2 = 0.40) and the personal best 24-h run distance (r2 = 0.58). Furthermore, the personal best marathon performance was significantly and positively correlated (p<0.01) with the best personal 24-h run distance (r2 = 0.76).

Conclusions:

Anthropometry and training volume does not seem to have a major effect on race performance in a 24-h run. Instead, a fast personal best marathon time seems to be the only positive association with race performance in a 24-h run.
Zero blood alcohol concentration limits for drivers under 21: lessons from Canada
Authors: Chamberlain E , Solomon R
Published: April 2008

Graduated licensing programs (GLPs) that include zero or low blood alcohol concentration (BAC) restrictions have proven to be a popular and effective measure for improving traffic safety among young people. However, a major drawback of such programs, at least in Canada, is that the BAC restriction is lifted on completion of the GLP, which typically occurs around the age of 18 or 19. This corresponds to the legal drinking age in Canada, a time when alcohol consumption and rates of binge drinking increase. It is not surprising, then, that 18–20 year-old drivers are dramatically overrepresented in alcohol-related deaths and injuries. One way to address this problem is to raise the legal drinking age, as has occurred in the United States. In jurisdictions, like Canada, that are unlikely to raise the legal drinking age, other measures are necessary to separate drinking from driving among 18–20 year-olds. This article recommends that the zero BAC restrictions be extended beyond the completion of the GLP, until drivers reach the age of 21. The scientific evidence for such a measure is reviewed, and the growing government support for enacting such BAC limits in Canada is described.
Meiotic configurations in the oospore of Phytophthora capsici
Authors: Stephenson L. W. , Erwin D. C. , Leary J. V.
Published: April 2008

Photomicrographs of chromosomal configurations in nuclei of squashed whole mounts of mature oospores (cultures 32 days old) of Phytophthora capsici stained with iron hematoxylin were interpreted to indicate that meiosis occurred in the oospore. Chromosomes in dividing oospore nuclei were observed in synapsis, diakinesis, metaphase I, and metaphase II. Comparison of polar metaphase I and metaphase II plates revealed a reduction in chromosome size and number and nuclear size. The haploid number of chromosomes was interpreted to be 6.
Litter decomposition studies using mesh bags: spillage inaccuracies and the effects of repeated artificial drying
Authors: Suffling Roger , Smith David W.
Published: April 2008

A modified method of measuring litter decomposition using mesh bags is suggested in which the bags are reused during several time increments. The chief objections to this method are that litter may be lost through spillage and that repeated artificial drying may affect decomposition rates. Experimental results are presented to show that spillage represents a significant source of error with finely divided litter, even using conventional litter bag methods. A method for handling litter bags is suggested in which corrections may be made for spillage. In a second experiment it was found that decomposition rates were not significantly altered by repeated artificial drying of old-field litter so that repeated drying of litter in field experiments may be valid.
Reproductive biology of Rumex crispus. Phenology, surface area of chlorophyll-containing tissue, and contribution of the perianth to reproduction
Authors: Maun M. A.
Published: April 2008

Rumex crispus (curled dock) overwinters as a rosette. Growth of the rosette begins in the middle of April and the panicles emerge after about 4 to 6 weeks. Anthesis starts in the middle of a panicle and proceeds basipetally and acropetally on the main rachis and outward on the primary and secondary branches. The seeds mature from the end of July to the middle of August.The perianth is a major portion of the total chlorophyll-containing tissue of the panicle. Perianth segments enclosing the seeds contribute significantly to the dry matter of seeds. The contribution is highest when the perianth is young. The growth in length and width of seeds is complete 8 days after anthesis.
Quiescent cell populations in apical meristems of Helianthus annuus
Authors: Langenauer Haviva D. , Davis Edward L. , Webster Peter L.
Published: April 2008

Quiescent cell populations in both root and shoot apical meristems of Helianthus annuus are compared. Histoautoradiographs prepared after 12-h provision of [3H]thymidine in the growth medium demonstrate the presence of a quiescent center located subterminally in the apical meristem of cultured and attached Helianthus roots. Similar techniques (using [3H]-thymidine in the medium for 24–48 h) show that while cells of the shoot meristem undergo DNA synthesis, a central zone that does not incorporate the precursor exists at the summit of the cultured vegetative shoot apex. Central zone cells contain larger nuclei than do surrounding cells in the shoot apex, while quiescent-center nuclei are smaller than those in the surrounding meristem of the root apex.Growth of excised roots in medium without carbohydrates causes temporary arrest of proliferative activity in most of the meristem. When sucrose is provided after this treatment, cells of the meristem as well as most cells of the root quiescent center are stimulated into DNA synthesis. In shoots cultured in sucrose-deficient medium, few cells continue to synthesize DNA, but subsequent transfer to medium with carbohydrates stimulates no cells of the central zone into DNA synthesis, although progression through the cycle is resumed by other cells of the meristem. These and other considerations suggest that the quiescent regions in root and shoot apical meristems are not comparable.
Glucose inhibition of the characteristic melanoid pigment of Xanthomonas phaseoli var. fuscans
Authors: Basu P. K.
Published: April 2008

The brown melanoid pigment of Xanthomonas phaseoli var. fuscans is a reliable cultural character to distinguish this pathogen, the cause of fuscous blight of beans (Phaseolus vulgaris), from X. phaseoli, the causal organism of common bean blight. The pigment appears to be exogenous because it developed mainly in nutrient agar and only slightly in water agar held side by side in the same petri plate inoculated by a single streak of X. phaseoli var. fuscans. Both pathogens produced similar tyrosinase-type diffusible enzymes in nutrient agar plates as detected by DL-dopa (3,4-dihydroxy-DL-phenylalanine) reaction. Presently unknown specific factors, besides the detectable enzymes, may be involved in pigment production.High glucose concentration in culture media caused inhibition of pigment development. One of the reasons for this inhibition seemed to be the repressive effect of glucose on the synthesis or secretion of tyrosinase-type enzymes as well as on the autooxidation of substrates, like dopa. Therefore, the amount of glucose in culture media should be carefully regulated when the characteristic brown pigment of X. phaseoli var. fuscans is used to distinguish this pathogen from X. phaseoli.
Activity of glucose-6-phosphate dehydrogenase from lettuce seeds (Lactuca sativa)
Authors: Speer Henry L.
Published: April 2008

The effects of phosphate, arsenate, arsenite, and sulfate on lettuce seed (Lactuca sativa L.) glucose-6-phosphate dehydrogenase were investigated. All four substances inhibited the enzyme and inhibition was substrate dependent. The reaction was specific for glucose-6-phosphate and NADP. No effect of red or far-red light could be observed on enzyme activity. All enzyme activity was confined to the supernatant fraction.
Lecanora vaenskaei Roux et C. Coste sp.nov. (Lichens, Ascomycotina), sa position systématique et celle des Rhizoplaca (Lecanorales, Lecanoraceae)
Authors: Roux Claude , Coste Clother , Ménard Thierry , Bellemère André , Bricaud Oliver
Published: April 2008

Lecanora vaenskaei Roux et C. Coste sp.nov. is described as a new saxicolous, calcifugous lichen species, discovered in southeastern France (Var Department). It differs from Lecanora chlorophaeodes Nyl. in its thallus, apothecia, paraphyses, spores and distribution. The classification of the new species is considered with respect to the genus Rhizoplaca, which is shown to belong to the family Lecanoraceae rather than the Parmeliaceae. Key words: lichens, Lecanoraceae, Lecanora, morphology, structure, distribution, ecology, systematics, Parmeliaceae, Rhizoplaca.
Effects of Streptomyces corchorusii, Streptomyces mutabilis, pendimethalin, and metribuzin on the control of bacterial and Fusarium wilt of tomato
Authors: El-Shanshoury Abd El-Raheem R. , El-Sououd Soad M. Abu , Awadalla Omima A. , El-Bandy Nabila B.
Published: April 2008

Two Streptomyces spp. and two herbicides were used to control the pathogens of tomato wilt disease in vitro and in vivo. In vitro studies showed inhibitory effects of Streptomyces corchorusii against Fusarium oxysporum f.sp. lycopersici (Sacc.) and inhibitory effects of Streptomyces mutabilis against Pseudomonas solanacearum. In cultures amended with pendimethalin or metribuzin, the growths of P. solanacearum and F. oxysporum were inhibited. The degree of growth inhibition was proportional to the herbicide concentration, with pendimethalin being more effective than metribuzin, and maximum inhibition was at 2.0 × 10−3 M. The growth of S. corchorusii and S. mutabilis was slightly inhibited or enhanced by the herbicides. Supplementation of the herbicides to culture media of the antagonistic Streptomyces spp. increased their inhibitory effects against P. solanacearum and F. oxysporum that were proportional to the herbicide concentrations. Soaking seeds of tomato in the herbicides prior to sowing in sterilized and raw soils and applying S. corchorusii and (or) S. mutabilis to the soils artificially infested with P. solanacearum and (or) F. oxysporum f.sp. lycopersici (Sacc.) 40 days after transplanting revealed significant interactions that gave better control of wilt than either applied alone. The combination of antagonistic Streptomyces spp. was more effective with pendimethalin than with metribuzin and in nonsterilized soil than in sterilized soil. The combination of pendimethalin with S. corchorusii, S. mutabilis, or S. corchorusii plus S. mutabilis was more effective than the single treatment with microbial antagonists or the herbicide against F. oxysporum, P. solanacearum, and Pseudomonas plus Fusarium, respectively. In both soils, the combination of microbial antagonists with pendimethalin was most effective at 2.0 × 10−3 M, disease incidence being reduced to zero and the percent colonization of either pathogen being the lowest. The results also revealed that these combinations minimized the negative effects of the pathogens on tomato growth. This work demonstrates that two compatible control agents, biological and chemical, can be combined to give additional control of a plant pathogen. Keywords: Streptomyces spp., herbicides, Pseudomonas solanacearum, Fusarium oxysporum f.sp. lycopersici (Sacc.), wilt, Lycopersicon esculentum Mill.
Ecophysiology of a snow-bed bryophyte Kiaeria starkei during snowmelt and uptake of nitrate from meltwater
Authors: Woolgrove C. E. , Woodin S. J.
Published: April 2008

Snow is a very efficient scavenger of atmospheric pollutants and because of the dynamics of snowmelt, much of the pollutant load of a snowpack is released at very high concentrations in episodes known as the acid flush. The ecological effects of this are largely unknown, but any effects on the bryophyte-dominated vegetation of snow beds will depend in part on the physical environment and physiological state of plants under and just out of snow cover. These factors were investigated at a snow bed in the Cairngorm Mountains, Scotland. The subnivean environment is characterized by slightly elevated CO2 concentrations (up to 70 μL/L above ambient), temperatures at and just above 0 °C, and very low light intensity, with no light penetrating through more than 50 cm depth of snow. Despite overwinter storage in these conditions, the bryophyte Kiaeria starkei is shown to be capable of photosynthetic activity immediately after removal of snow cover, and tissue chlorophyll and carbohydrate concentrations increase by 250 and 60%, respectively, during the 2 weeks thereafter. Comparison of photosynthetic light responses at 5 and 18 °C in plants collected from under and out of snow cover demonstrates acclimatization to seasonal environmental change that must enable maximization of growth during the short growing season available. Kiaeria starkei is also shown to be capable of nitrate reductase activity even at 2 °C and to assimilate more than 90% of the pollutant nitrate coming into contact with it in snowmelt. As nitrate is known to be damaging to bryophytes in excess, this demonstrates a real threat of pollutant deposition to rare snow-bed communities in Scotland today and is an important warning for other regions where snow-bed vegetation is important. Keywords: snow, bryophyte, atmospheric pollution, nitrate, photosynthesis.
La relation entre le Striga hermonthica et ses hôtes: une synthèse
Authors: Olivier Alain
Published: April 2008

The parasitic weed Striga hermonthica causes considerable yield losses in maize, pearl millet, and sorghum in Africa. The extent of the damage caused to crops is related to their close interaction with the parasite. The S. hermonthica seed germinates in response to germination stimulants exuded by cereal roots. The rootlet extremity then turns into a haustorium that attaches itself to the host root and penetrates its tissue. In this manner, a connection is established between the vascular systems of both plants, allowing absorption of water, minerals, and organic compounds that are essential for the parasite's development. S. hermonthica also affects the host's metabolism and photosynthesis. No effective control method against the parasite is available for the African peasants. The utilization of germination stimulants and herbicides, the rotation practice, and intercropping as well as biological control and varietal selection have given disappointing results so far. A better understanding of host resistance mechanisms is necessary to develop new methods for the control of the parasite. Keywords: Striga hermonthica, germination, haustorium, host–parasite interaction, control methods, resistance.
Continuing variation in successive asexual generations of Phytophthora cinnamomi following sexual reproduction
Authors: Zheng X. B. , Ko W. H.
Published: April 2008

Colony-type stability of asexual progeny of selfed-oospore cultures of Phytophthora cinnamomi was investigated. Progeny were divided into parental type A, types B to E for those different from type A but with a distinct uniform pattern, and type M for those with the overlapping appearance of two different types. Colonies derived from three successive zoospore generations of isolate P630 were of the same parental A type. However, colonies from oospores of the same isolate consisted of types A, B, C, D, E, and M. Some of the oospore cultures of type A or B and all the type M oospore cultures produced zoospores containing more than one type. Oospore cultures of types C, D, or E that were tested produced zoospores with the same colony type as their respective parent. Among the five cultures randomly selected from asexual progeny produced by oospore isolates P630-21 and P630-6, four displayed continuing variation in colony type in the three to five successive zoospore generations tested. Keywords: asexual variation, continuing variation, Phytophthora cinnamomi, sexual reproduction.
The influence of pasture age, plant density, and genotype on intraspecific diversity of Trifolium repens (white clover)
Authors: Maze Jack , Turkington Roy
Published: April 2008

Morphological variation, as expressed in PCA axis scores, for clovers growing in different aged pastures, was apportioned to pasture age, quadrats within pastures, intraspecific densities within quadrats, and genets within densities. Of those factors that have an effect on variation, genets is the greatest, followed by quadrats, intraspecific density, and age of the pasture. There is also an age-related decline in variation in plants of Trifolium repens as seen in genetic origin, quadrats within a pasture, and intraspecific density. These results indicate a need to determine more accurately the relationship between genetic and phenotypic responses in the decline in among-plant variation over time. Keywords: Trifolium repens, variation.