High-bandwidth, variable-resistance differential noise thermometry.

We have developed Johnson noise thermometry applicable to mesoscopic devices with variable source impedance with high bandwidth for fast data acquisition. By implementing differential noise measurement and two-stage impedance matching, we demonstrate noise measurement in the frequency range of 120 MHz-250 MHz with a wide sample resistance range of 30 Ω-100 kΩ tuned by gate voltages and temperature. We employed high-frequency, single-ended low noise amplifiers maintained at a constant cryogenic temperature in order to maintain the desired low noise temperature. We have achieved thermometer calibration with temperature precision up to 650 µK measuring a 200 mK temperature modulation on a 10 K background with 30 s of averaging. Using this differential noise thermometry technique, we measured thermal conductivity on a bilayer graphene sample spanning the metallic and semiconducting regimes in a wide resistance range, and we compared it to the electrical conductivity.

[Effect of low temperature on the resistance and functional activity of the photosynthetic apparatus of wheat plants].

The dynamics of cold resistance and the activity of the photosynthetic apparatus (PSA) of wheat germs at 4 degrees C were studied. It was shown that in the first hours of cold, a certain functional readjustment to the changed conditions takes place in the plant organism. A decrease in the activity of the PSA and cessation of the linear growth of the leaf are registered at this stage along with an increase in resistance, as well as an increase in the coefficient of nonphotochemical extinguishing of the fluorescence of chlorophyll. In one to four days, when resistance reaches its maximum, photosynthesis and the rate of electron transport are stabilized, the chlorophyll content in the lightcollecting complex increases, and the growth recommences. The final stage of adaptation (days 4-7) is characterized not only by the steady level of resistance but also by new functional organization of the PSA, which allows the plants to endure the lowered temperature successfully.

[Setaria viridis tolerance of high zinc concentrations].

The effect of high zinc concentrations on the growth and photosynthetic apparatus of Setaria viridis (L.) Beauv. was investigated under laboratory conditions and a vegetation experiment. The experiments showed that zinc concentrations of 10(-6) to 10(-3) M did not influence seed germination. Moreover, zinc in concentrations of 40 and 80 mg kg(-1) substrate had no significant effect on most of the plant growth parameters. However, higher metal concentrations (160 and 320 mg kg(-1) substrate) inhibited shoot biomass, leaf area, inflorescence length, and biomass. At the same time, parameters such as the content of chlorophyll (a + b), F0, F(v), and the F(v)/F(m) rate were not reduced even in the presence of zinc in the highest concentrations (320 mg kg(-1) substrate). S. viridis tolerance of high zinc concentrations, as well as its capacity to accumulate zinc in roots and shoots, suggests the plant can be used for phytoremediation of zinc polluted soils.

[Effect of lead on the photosynthetic apparatus of annual grasses].

The effect of lead (in the form of Pb(CH3COO)2 x 3H2O at concentrations of 200, 400, and 800 mg/kg substrate) on the photosynthetic apparatus of barley (cultivar Dina) and oat (cultivar Falenskii) was studied. Exposure to low concentrations of lead (200 mg/kg) slightly increased the content of chlorophyll in leaves and the rate of photosynthesis. Medium concentrations of lead (400 mg/kg) had no marked effect on the parameters analyzed, whereas high concentrations (800 mg/kg) decreased the area of leaves, the content of green pigments in them, and the rate of photosynthesis.