New Polymer Tensiometers: Measuring Matric Pressures Down to the Wilting Point

Tensiometers are commonly used for measuring soil water matric pressures. Unfortunately, the water-filled reservoir of conventional tensiometers limits their applicability to soil water matric pressures above approximately –0.085 MPa. Tensiometers filled with a polymer solution instead of water are able to measure a larger range of soil water matric pressures. We designed and constructed six prototype polymer tensiometers (previously called osmotic tensiometers) consisting of a wide-range pressure transducer with a temperature sensor, a stainless steel casing, and a ceramic plate with a membrane preventing polymer leakage. A polymer chamber (0.1–2.2 cm3) was located between the pressure transducer and the plate. We tested the polymer tensiometers for long-term operation, the effects of temperature, response times, and performance in a repacked sandy loam under laboratory conditions. Several months of continuous operation caused a gradual drop in the osmotic pressure, for which we developed a suitable correction. The osmotic potential of polymer solutions is temperature dependent, and requires calibration before installation. The response times to sudden and gradual changes in ambient temperature were found to be affected by polymer chamber height and polymer type. Practically useful response times (<0.2 d) are feasible, particularly for chambers shorter than 0.20 cm. We demonstrated the ability of the instrument to measure the range of soil water pressures in which plant roots are able to take up water (from 0 to –1.6 MPa), to regain pressure without user interference and to function properly for time periods of up to 1 yr

Impulse-response functions of several detectors used in flow-injection analysis

A procedure for the determination of the impulse-response function of a detector is given. Its application to photometers, ion-sensitive field effect transistors, a potentiometric detector at constant current and a voltammetric detector shows that the impulse-response function can be used to obtain specific information about the performance of the detector in the manifold. This function clearly shows the contribution of the detector to the peak broadening and how the detector generates the final signal from the presented concentration profile. From this information one could derive improvements to the detector, such as changing the construction of the detector cell, minimizing the influence of other parts of the manifold or adapting the attached electronics

Oxidative coupling of methane over doped Li/MgO catalysts

A series of zirconia doped Li/MgO catalysts with a fixed amount of zirconia and varying concentrations of lithium was used for the oxidative coupling of methane. It was found that an increase in lithium concentration resulted in a decrease in initial activity, while the selectivity was not affected. The life-time of Zr doped Li/MgO catalysts with a fixed concentration of ZrO2 is a function of the lithium concentration. Previous results have shown that Li2Mg3ZrO6 is active and selective but it is now shown to be instable under reaction conditions

The Role of Brain Aging in Cognition and Motor Function

__Abstract__ Aging of the population is accompanied by many challenges, such as the maintenance of health and quality of life during older age. An important aspect of living longer is that old age is related to disease and loss of functions. The loss of brain functions poses a large problem in older age. Changes that occur in the brain can already be visualized when no symptoms or clinical disease are apparent. Magnetic resonance imaging (MRI) is often used to visualize subtle brain changes. The subclinical brain changes can however be used as markers of future clinical disease. Furthermore, subclinical, subtle changes in brain function can cause considerable discomfort in daily living

De economie van het veenrietweidebedrijf : een quickscan voor West-Nederland

Deze quickscan onderzoekt of en hoe het voor bestaande melkveehouders aantrekkelijk kan zijn om deels − of geheel − over te schakelen op rietteelt. Het concept is bedoeld om de overstap aantrekkelijk te maken naar ‘natte landbouw’ in (landbouw)gebieden die vernatten. Wanneer wordt het interessant om over te stappen op rietteelt in een gebied waar de traditionele landbouw niet meer kan onderneme

Measuring very negative water potentials with polymer tensiometers: principles, performance and applications

In recent years, a polymer tensiometer (POT) was developed and tested to directly measure matric potentials in dry soils. By extending the measurement range to wilting point (a 20-fold increase compared to conventional, water-filled tensiometers), a myriad of previously unapproachable research questions are now open to experimental exploration. Furthermore, the instrument may well allow the development of more water-efficient irrigation strategies by recording water potential rather than soil water content. The principle of the sensor is to fill it with a polymer solution instead of water, thereby building up osmotic pressure inside the sensor. A high-quality ceramic allows the exchange of water with the soil while retaining the polymer. The ceramic has pores sufficiently small to remain saturated even under very negative matric potentials. Installing the sensor in an unsaturated soil causes the high pressure of the polymer solution to drop as the water potentials in the soil and in the POT equilibrate. As long as the pressure inside the polymer chamber remains sufficiently large to prevent cavitation, the sensor will function properly. If the osmotic potential in the polymer chamber can produce a pressure of approximately 2.0 MPa when the sensor is placed in water, proper readings down to wilting point are secured. Various tests in disturbed soil, including an experiment with root water uptake, demonstrate the operation and performance of the new polymer tensiometer and illustrate how processes such as root water uptake can be studied in more detail than before. The paper discusses the available data and explores the long term perspectives offered by the instrument

The influence of additives on the current carrying capacity of bulk YBa2Cu3OX

We studied the influence of using different powders and several additives on the shaping process and critical current density of sintered bulk YBa2Cu3OX. It was found that all additives used facilitated the shaping process. Silver and most organic additives influenced the critical current density only little, Zinc reduced it to zero, but an ethylenebisstearoylamide compound doubled the critical current density as compared to samples without additives

Stability constants for some divalent metal ion/crown ether complexes in methanol determined by polarography and conductometry

Stability constants in methanol at 25.0°C were evaluated for the complexes of the divalent cations Ca2+, Ni2+, Zn2+, Pb2+, Mg2+, Co2+ and Cu2+ with the macrocyclic polyethers 15-crown-5 (15C5), 18-crown-6 (18C6), dicyclohexyl-18-crown-6 (DC18C6) and dibenzo-24-crown-8 (DB24C8). The log K values of the 1:1 complexes were generally in the range 2.1–4.2, which is low in comparison to the values of the corresponding crown ether/alkali metal ion complexes. M2L complexes were observed for the systems Pb2+/18C6, Pb2+/DC18C6, Ca2+/DC18C6 and Cu2+/D18C6, whereas ML2 complexes were found for Ca2+/18C6 and Cu2+/18C6. Within the series of complexes studied, there was no clear relationship between cation diameter and hole size

Het Beter Leven-kenmerk : de beleving van biologische consumenten

The aim of this qualitative study is to gain an insight into how and to what extent the Animal Protection Society’s Beter Leven (Better Life) mark contributes to the attractiveness of organic animal products in the opinion of light users. In order to investigate this, LEI conducted a qualitative study among 14 light users in 200