Measurement of circumnutation in maize roots

The movement of growing primary roots of maize was measured using a computer driven video-digitizer system. Real time measurements with two perpendicularly mounted video cameras permit measurements of growth movements in three dimensions and allow precise control of growth experiments. The spatial reconstruction and the angular orientation of the oscillating tips revealed that roots fluctuate in growth rate, straight growth and tip orientation. The movements of roots were less uniform than circumnutational activity of shoots and occurred in roots growing in the dark or light, submersed in buffer or suspended in air. The movements led to tip orientation deviating more than 30 degrees from the vertical without causing gravi-reaction. Large angular fluctuations occurred in cycles lasting on average 80 min. and could be observed even in decapped roots. The data suggest that endogenous movements are the result of internal growth regulation, possibly derived from differential sensitivity or adaptation of the elongating tissue. The ability of roots to respond to reorientation seems to depend upon the extent and direction of previous movements. Endogenous movements are likely to contribute to the gravitropic response and to irregular growth under conditions of microgravity.     

Risk of formation of cracks on the rolling surface of solid railroad wheels damaged during braking

Conclusion Analysis by fracture mechanics approaches of stresses on the level corresponding to the threshold range of the SIF K_th showed that the structural elements weakened by crack can operate for long periods of time under specific conditions. The methods of statistical fracture mechanics can be used to determine the permissible crack dimensions not leading to failure.The solid railroad wheels damaged by braking cannot be regarded as long-term structures. The presence of radial cracks and the possibility of their continuous formation during service must be taken into account. Therefore, the service rules of solid wheels specified by the German National Railway Board are completely justified.The article was received in the German language. Authorized translation by S. Ya. Yarema.Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 26, No. 4, pp. 90–95, July–August, 1990.     

Man's Impact on Water Resources

ABSTRACT

The SSARR model is applied to simulate flood levels in the Mekong river delta. The Mekong and Bassac rivers which are two main rivers and the Vaico river are interlaced together with canals and floodplains with storage. The flow exchanges between these rivers, and the tidal influences in their estuarial reaches make it necessary to utilize the backwater mode of the SSARR model in the simulation. In addition to the backwater mode, the diversion algorithm of the SSARR model is also used to take into account the over bank flow conditions.

Since the river storages during the flood periods are considerable, the rivers have been divided into several storage reaches or reservoirs. The flow between these storage reaches depends on the water level differences between each pair. Moreover, the various flood plain storages are also represented by a network of interconnected storage reaches or reservoirs. The upstream boundary condition is the discharge in the Mekong river at Phnom Penh, and the downstream boundary conditions are the tides at the mouths of the three rivers. Rainfall over the study area is also considered as input to the model.

In general, very close agreement is obtained in the calibration and verification except at thte stations Can Tho and My Thuan where tidal influences are significant. However, good results are obtained for the envelope of high tides at these two stations. Sensitivity analysis is made to determine the effects of the overbank flow parameters, and the exchange flow parameters on the flow in the rivers. More data collection of delta discharges and water levels is recommended for the future to improve the existing backwater relationship for better simulation of tidal fluctuation in the estuarial reaches of the delta.     

A new device for performing reference point indentation without a reference probe

Here we describe a novel, hand-held reference point indentation (RPI), instrument that is designed for clinical measurements of bone material properties in living patients. This instrument differs from previous RPI instruments in that it requires neither a reference probe nor removal of the periosteum that covers the bone, thus significantly simplifying its use in patient testing. After describing the instrument, we discuss five guidelines for optimal and reproducible results. These are: (1) the angle between the normal to the surface and the axis of the instrument should be less than 10°, (2) the compression of the main spring to trigger the device must be performed slowly (>1 s), (3) the probe tip should be sharper than 10 μm; however, a normalized parameter with a calibration phantom can correct for dull tips up to a 100 μm radius, (4) the ambient room temperature should be between 4?°C and 37 °C, and (5) the effective mass of the bone or material under test must exceed 1 kg, or if under 1 kg, the specimen should be securely anchored in a fixation device with sufficient mass (which is not a requirement of previous RPI instruments). Our experience is that a person can be trained with these guidelines in about 5 min and thereafter obtain accurate and reproducible results. The portability, ease of use, and minimal training make this instrument suitable to measure bone material properties in a clinical setting.     

The influence of the extraction voltage on the energetic electron population of an electron cyclotron resonance ion source plasma

An influence of the extraction voltage on the high energy slope of bremsstrahlung radiation spectra has been reported in ECRIS experiments, which is not well understood so far. In order to provide more detailed data on this effect, we have measured bremsstrahlung radiation spectra accompanying especially the evolution of highly charge ions (i.e., by monitoring the Ar(14+) charge state) as the extraction voltage is changed from 0 to 20 kV, in dedicated experiments at the Frankfurt 14 GHz-ECRIS.     

Emotion understanding and performance during computer-supported collaboration

Individuals collaborating around and through computers benefit from receiving information that helps them understand one another, which is often termed awareness. This article explores what collaborators understand about each other’s emotions and the potential benefits for performance that might come from raising this understanding. In Experiment 1 co-located collaborators judged each other’s emotions after playing a game that required cooperative data collection and analysis. Their judgements were largely inaccurate and based on their own emotions, suggesting limited emotion understanding. Experiment 2 explored if this could be overcome by making collaborators aware of each other’s emotions. Co-located and remote collaborators played a cooperative puzzle-solving game under conditions of awareness or no awareness. Awareness was manipulated by making collaborators share their self-reported emotions during key moments of their game play. Both remote and co-located collaborators improved their performance after sharing their emotions. However, unlike co-located collaborators, remote collaborators also improved their understanding of each other’s emotions and experienced more positive affect. We conclude by discussing the content of collaborators’ emotion understanding and the probable mechanisms underlying the observed effects of being made aware of a partner’s emotions.     

Multi-product sequencing and lot-sizing under uncertainties: A memetic algorithm

The paper deals with a stochastic multi-product sequencing and lot-sizing problem for a line that produces items in lots. Two types of uncertainties are considered: random lead time induced by machine breakdowns and random yield to take into account part rejects. In addition, sequence dependent setup times are also included. This study focuses on maximizing the probability of producing a required quantity of items of each type for a given finite planning horizon. A decomposition approach is used to separate sequencing and lot-sizing algorithms. Previous works have shown that the sequencing sub-problem can be solved efficiently, but the lot-sizing sub-problem remains difficult. In this paper, a memetic algorithm is proposed for this second sub-problem. Computational results show that the algorithms developed can be efficiently used for large scale industrial instances.     

Effects of user age and target-expansion methods on target-acquisition tasks using a mouse

Target expansion, i.e., the increase of target size according to cursor movement, can be a practical scheme to improve the usability of target-selection tasks using a mouse. This study examined the effects of different user age groups and target-expansion methods on target-acquisition tasks with grouped icons. Twenty-eight subjects performed acquisition tasks under eight experimental conditions: combinations of four expansion areas (no, one-icon, fish-eye, and group expansion) and two expansion techniques (occlusion and push). Older users took longer to acquire targets than younger users; however, they showed no significant difference in accuracy. Target expansion did not substantially improve performance speed compared to the static condition. However, the error rate was lowest when group area was expanded with the push technique, and both age groups were most satisfied with one-icon area expansion with the occlusion technique. We suggest alternative guidelines in designing target-expansion schemes.