Low Negative Temperature Research Articles

Temperature compensated high efficiency inductor current sensor

Inductor current sensing is very important in the control and monitoring of switching power converters. Traditional low cost implementation using a sensing resistor in series with the inductor will reduce the overall efficiency of the power converter. Conventional Hall effect current sensor could also be used to detect the inductor current. However, it will significantly increase the production cost of power converters. One simple and low cost implementation is to add a resistor–capacitor (RC) network in parallel with the inductor so that the inductor current can be derived from the added circuitry. The problem with RC sensing network is that the sensed variable is very sensitive to temperature variations. In this paper, a novel inductor current sensor using low cost negative temperature coefficient (NTC) thermistors to compensate the variation in the parasitic resistance of the inductor due to temperature changes is proposed. The changes in the cutoff frequency and steady state gain are also compensated by the added NTC thermistor circuit. With the compensated network, the sensed inductor current derived from the modified RC network will be independent of temperature variations. The compensated network can be applied to inductors fitted to power converters. Although experimental studies based on a buck converter were carried out to illustrate the correctness of the improved sensing technique, the proposed technique is applicable to other converter topologies.

Correlations between electric, magnetic, and galvanomagnetic quantities in stable icosahedral phases based on aluminum

On the basis of the results of the experimental investigation of the correlations between the electric, magnetic, and galvanomagnetic properties, the nature of the electronic phenomena leading to the difference of icosahedral quasicrystals from typical metals and insulators (low conductivity and negative temperature coefficient of resistance, diamagnetism of the ground state and its decrease with increasing temperature, and existence of residual and thermally induced charge carriers) is discussed.

Low threshold current density and negative characteristic temperature 1.3μm InAs self-assembled quantum dot lasers

By combining optimized growth of the GaAs spacer layers and p-type modulation doping of the quantum dots, a 1.3μm emitting self-assembled quantum dot laser exhibiting both a low threshold current density and negative-T0 temperature behavior at room temperature is achieved. Spontaneous emission measurements provide no evidence for enhanced Auger recombination in doped devices. The negative T0 exhibited by the doped device is consistent with a delayed thermalization of carriers within the quantum dot ensemble.

High-performance 1.3 µm InAs/GaAs quantum-dot lasers with low threshold current and negative characteristic temperature

A high-growth-temperature GaAs spacer layer (HGTSL) is shown to significantly improve the performance of 1.3 µm multilayer InAs/GaAs quantum-dot (QD) lasers. The HGTSL inhibits threading dislocation formation, resulting in enhanced electrical and optical characteristics and hence improved performance of QD lasers. To further reduce the threshold current density and improve the room-temperature characteristic temperature (T0), the high-reflection (HR) coating and p-type modulation doping have been incorporated with the HGTSL technique. A very low continuous-wave room-temperature threshold current of 1.5 mA and a threshold current density of 18.8 A cm−2 are achieved for a three-layer device with a 1 mm HR/HR cavity, while a very low threshold current density of 48 A cm−2 and a negative T0 are achieved in the p-doped lasers.

A wide-ranging kinetic modeling study of methyl butanoate combustion

A detailed chemical kinetic model has been used to study methyl butanoate (a model compound for biodiesel fuels) oxidation over a wide range of conditions. New experimental results obtained in a jet stirred reactor (JSR) at 0.101 MPa, Φ = 1.13 and 800 < T (K) < 1350 were obtained and used to test and modify an earlier model. In addition, new experimental data generated in an opposed-flow diffusion flame at 0.101 MPa and in the Princeton variable pressure flow reactor (VPFR) at 1.266 MPa, 0.35 < Φ < 1.5 and 500 < T (K) < 900 are presented and compared against the revised model. The numerical model consists of 295 chemical species and 1498 chemical reactions and gives a good description of the data. Experimentally, the oxidation of methyl butanoate shows very little low temperature and negative temperature coefficient behaviour, with hot ignition occurring at about 800 K. Modeling results show similar diminished low temperature oxidation character, but reasonably reproduce hot ignition behaviour found in the VPFR. At higher temperature conditions, the model well describes the intermediate species found in the jet stirred reactor and in opposed flow diffusion flame experiments.

Influence of the clearance between initiating unit and main high explosive charge on jet perforator efficiency

Influence of the clearance between initiating unit and main high explosive charge on penetration depth of a jet perforator at low ambient temperatures is investigated. Experiments were conducted on jet perforators, which consisted of an initiating unit (including detonator and an intermediate high explosive charge enclosed in a thin metal cylindrical shell) and a main high explosive charge with metal-lined cavity. External diameter of the perforator was 42 mm. We observed significant decrease (up to 50%) of penetration depth at low ambient temperatures. It has been observed during the experiments that the effect of the decrease of penetration depth at low negative temperature was absent, when a small clearance existed between the initiating unit and the main high explosive charge. Thus, it has been determined that a clearance between the initiating unit and the main high explosive charge can be used to improve the perfection of detonation front. The problem of parameter optimization for the transition zone between the initiating unit and the main charge was studied using the methods of numerical modeling provided by ODVAX software. Numerical and theoretical analysis of the detonation initiation process for various values of the initiating unit wall thickness (0.5, 1.0, 2.0 mm), and for different materials for its shell has revealed that maximum reduction of the acceleration stage, after which the detonation reaches stationary mode, is achieved when: – Thickness of the initiating unit wall facing the high explosive charge equals to the permissible minimum for required mechanical properties. – Clearance width equals to 2–3 times the wall thickness. – Shapes of the main charge and the initiating unit wall are congruent at the moment of collision.

The Temperature Regime of the Surface Layer of the Phobos Regolith in the Region of the Potential Fobos–Grunt Space Station Landing Site

Because of the absence of the atmosphere, the short duration of the Phobos day (7.7 hours), and the presence of a highly porous and fine-grained soil on the Phobos surface, all components of the future Russian Fobos–Grunt lander will operate under frequent and sharp temperature changes: from positive to extremely low negative temperatures. As a consequence, information about the temperature regime directly on the surface of the Martian satellite and in the near-surface layer appears to be extremely important. The proposed publication contains both the information about the thermophysical properties of the surface regolith of Phobos, derived from observations made with the Mariner 9 orbiter, the Viking orbiter, the Fobos-2 spacecraft, and the Mars Global Surveyor orbiter, and the results of the numerical modeling of the thermal regime of the surface regolith layer (on diurnal and seasonal time scales) in the area of the potential Fobos–Grunt landing site. We performed this modeling by taking into account the seasons on Mars and the effects due to the eclipse of Phobos by Mars.

Temperature effects of electrical resistivity of conductive silicone rubber filled with carbon blacks

AbstractThe temperature effects of electrical resistivity of conductive silicone rubber filled with widely varying concentrations of carbon blacks (CBs: GPF 660 carbon black, HAF N‐330 carbon black, VXC‐72 conductive carbon black, and BP2000 superconductive carbon black) were studied from 30 to 200°C. Both low positive temperature coefficient (L‐PTC) and negative temperature coefficient (NTC) phenomena were observed, whose intensity and temperature range depend on the type and the concentration of CBs. A stronger temperature dependency of resistivity was observed when the CB concentration was in the percolation region. Unlike crystalline polymers/CBs composites, the high positive temperature coefficient (H‐PTC) phenomenon was not observed in CB‐filled silicone rubber when the CB concentration was near the percolation threshold. Generally, pronounced the NTC phenomenon appears in composites with small particles of CBs at concentrations near the percolation threshold, whereas a pronounced PTC phenomenon appears in composites with large CB particles of at concentrations exceeding the percolation region. If both PTC and NTC phenomena were in the same sample of conductive silicone rubber, the PTC phenomenon always appeared at relatively low temperatures and NTC at relatively high temperatures. The results were discussed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3889–3895, 2003

Cold hardening of plants is a result of maintenance of an increased photosynthesis/respiration ratio at low temperature

The capacity of plants for hibernation is ensured by the presence of significant food resources, like in hibernating mammals. In plants, these resources are accumulated in autumn due to maintenance of the rates of true CO2 assimilation elevated with reference to the dark respiration. This becomes possible as a result of higher thermoresistance of photosynthesis, as compared to respiration, and low light requirements for photosynthesis saturation at low positive or negative temperatures.

Anomalous spin-lattice relaxation in dilute RhFe at positive and negative nanokelvin temperatures

We report investigations at ultra low positive and negative spin temperatures on the spin-lattice relaxation in a rhodium sample with 6 ppm of iron impurities. A strong decrease in the Korringa constant κ, dependent on the inverse of nuclear spin temperature 1/T, was observed in fields below 1 mT; at B=0, the κ was almost two times smaller at T=0.8nK than at -0.8 nK. These results indicate strong modification of magnetic impurity scattering by the large nuclear susceptibility of the host material.

Low temperature characteristics of electrical parameters in amorphous Si/Si heterojunction bipolar transistors

Measurement of the low temperature characteristics of current gain, H FE, and cut-off frequency, ƒT, in amorphous emitter silicon heterojunction bipolar transistor is reported. The current gain, H FE,, has a positive temperature coefficient and falls with increasing base concentration, N B, at both room temperature and low temperatures. Because of the low-temperature avalanche multiplication effect in the collector-base junction, H FE, increases with increasing applied voltage, V BC, at low temperature. The cut-off frequency, ƒT, has positive temperature coefficient at low current levels and negative temperature coefficient at high current levels. It is concluded finally that the value of H FE of this device at low temperatures is adequate for most applications.

Floating Potential in Negative-Ion-Containing Plasma

For a feasibility study of low-energy etching at low pressures, the floating potential in negative-ion-containing plasma was theoretically investigated. The sheath equations into which the effect of the negative ion was incorporated was numerically solved. The results showed that the floating potential with respect to the plasma potential decreased in its absolute value with an increase in the negative ion concentration, and thus it is suggested that low-energy etching would be possible even in low-pressure plasma. A particular emphasis was given on the floating potential showing an abrupt decrease at a certain value of the negative ion concentration with relatively low negative ion temperature, and this was applicable to the digital etching technique.

Substitution of Cu by Fe in the superconducting ceramic oxide EuBa2Cu3Oy: Structure, electrical conductivity, and microwave response

A series of EuBa2(Cu1−x Fe x )3Oy (0.0⩽x⩽0.15) ceramics were prepared and examined by thermogravimetric analysis, X-ray powder diffraction, electrical resistance measurements, and a magnetically modulated microwave absorption technique. The oxygen content (y=6.98±0.03), determined by thermogravimetric analysis in a reducing atmosphere, was independent of the iron concentration forx⩽0.12. The introduction of iron into the EuBa2Cu3O y lattice, via substitution into copper sites, effects a progressive decrease in the superconducting transition temperature with increasing iron concentration. Normal-state conductivity similarly progresses from a low resistivity and negative temperature coefficient behavior, to a semiconducting-like response at the high iron concentrations. X-ray powder diffraction measurements indicate that material containing 6% iron and above is tetragonal, yet it remains superconducting with up to at least 12% iron.

Some Characteristics of Clear-Air Turbulence in the Middle Stratosphere

Abstract Analysis of clear-air turbulence measurements obtained from highly sensitive balloon-borne instrumentation is presented. Emphasis is placed on the structure of the turbulent velocity field in the inertial range. Regions of weak turbulence are found to be associated with low Richardson numbers and negative temperature gradients. Measurements of the turbulent energy intensity are presented. The extension of the inertial range is found to be consistent with theoretical values in the case of stably stratified flow. The turbulence intensity varies significantly over a two-hour time interval. An important result is the observational evidence for a 2/3 law behavior in the structure function at scales where the turbulent velocity field cannot be isotropic: this behavior cannot be explained by a two-dimensional turbulence field.

The ohmic stability and low temperature coefficient of resistance of Cu-Ni/Au-Ni multilayers obtained in ultrahigh vacuum by controlled co-evaporation

For compositions around 43 at.% Ni, thin films of CuNi alloys more than 1200 Å thick deposited in ultrahigh vacuum (UHV) onto a fused silica substrate by controlled co-evaporation from two separate copper and nickel sources show low negative temperature coefficients of resistance (TCRs) (-10 -4 to -10 -6 ° C -1) and a satisfactorily high stability in the temperature range 20–300 °C in UHV. In the atmosphere, however, the ohmic behaviour of the films shows hysteresis and appreciable instability due to oxidation. Thin Au-Ni films (38 at.% Ni) have a higher positive TCR (+2 × 10 -4 ° C -1) but they have the advantage of being less oxidized in atmospheric air up to 150 °C. In order to obtain unoxidizable multilayers with a low TCR we prepared CuNi films 1300 Å thick and stabilized them by annealing. AuNi films 200 Å thick were then deposited onto the CuNi films by controlled co-evaporation. After the annealing process the TCR was about -3 × 10 -6 ° C -1 from 20 to 150 ° C. The ohmic stability tested from 20 to 150 °C in nitrogen and then in the atmosphere showed no appreciable zero balance drift or ohmic instability.

Low temperature dry cells

Influence of the clearance between initiating unit and main high explosive charge on penetration depth of a jet perforator at low ambient temperatures is investigated. Experiments were conducted on jet perforators, which consisted of an initiating unit (including detonator and an intermediate high explosive charge enclosed in a thin metal cylindrical shell) and a main high explosive charge with metal-lined cavity. External diameter of the perforator was 42 mm. We observed significant decrease (up to 50%) of penetration depth at low ambient temperatures. It has been observed during the experiments that the effect of the decrease of penetration depth at low negative temperature was absent, when a small clearance existed between the initiating unit and the main high explosive charge. Thus, it has been determined that a clearance between the initiating unit and the main high explosive charge can be used to improve the perfection of detonation front. The problem of parameter optimization for the transition zone between the initiating unit and the main charge was studied using the methods of numerical modeling provided by ODVAX software. Numerical and theoretical analysis of the detonation initiation process for various values of the initiating unit wall thickness (0.5, 1.0, 2.0 mm), and for different materials for its shell has revealed that maximum reduction of the acceleration stage, after which the detonation reaches stationary mode, is achieved when:–Thickness of the initiating unit wall facing the high explosive charge equals to the permissible minimum for required mechanical properties.–Clearance width equals to 2–3 times the wall thickness.–Shapes of the main charge and the initiating unit wall are congruent at the moment of collision.