Nitrogen resorption and fractionation during leaf senescence in typical tree species in Japan

In northeastern Japan,an area of high precipitation and mountains,beech(Fagus creanata Blume),larch(Larix kaempferi Lamb.),cedar(Cryptomeria japonica D.Don)and black locust(Robinia pseudoacacia L.)were evaluated for N resorption and N isotope fractionation in preand post-abscission leaves in comparison to green leaves.The highest leaf N concentration in summer corresponded to the N-fi xing black locust,followed in decreasing order by the deciduous beech and larch and evergreen cedar.On the other hand,the lowest N resorption effi ciency corresponded to black locust and the highest to beech,in increasing order by larch and cedar.All tree species returned signifi cant amounts of N before leaf abscission;however,N isotope fractionation during leaf N resorption was only found for beech,with a depleted N isotope value from green to pre-abscission leaf.The most N,however,was resorbed from pre-abscission to post-abscission.This result may indicate thatδ15 N fractionation took place during N transformation processes,such as protein hydrolysis,when the concentration of free amino acids increased sharply.The diff erence in the type of amino acid produced by each species could have infl uenced the N isotope ratio in beech but not in the other tree species.The results of this study showed that it is possible to infer the type and timing of processes relevant to N resorption by analyzing leafδ15 N variation during senescence.

A force measurement platform for a vitreoretinal surgical simulator using an artificial eye module integrated with a quartz crystal resonator

To provide quantitative feedback on surgical progress to ophthalmologists practicing inner limiting membrane(ILM)peeling,we developed an artificial eye module comprising a quartz crystal resonator(QCR)force sensor and a strain body that serves as a uniform force transmitter beneath a retinal model.Although a sufficiently large initial force must be loaded onto the QCR force sensor assembly to achieve stable contact with the strain body,the highly sensitive and wide dynamic-range property of this sensor enables the eye module to detect the slight forceps contact force.A parallel-plate strain body is used to achieve a uniform force sensitivity over the 4-mm-diameter ILM peeling region.Combining these two components allowed for a measurable force range of 0.22 mN to 29.6 N with a sensitivity error within−11.3 to 4.2%over the ILM peeling area.Using this eye module,we measured the applied force during a simulation involving artificial ILM peeling by an untrained individual and compensated for the long-term drift of the obtained force data using a newly developed algorithm.The compensated force data clearly captured the characteristics of several types of motion sequences observed from video recordings of the eye bottom using an ophthalmological microscope.As a result,we succeeded in extracting feature values that can be potentially related to trainee skill level,such as the mean and standard deviation of the pushing and peeling forces,corresponding,in the case of an untrained operator,to 122.6±95.2 and 20.4±13.2 mN,respectively.