High Temperature Oscillations Research Articles

High-temperature magneto-inter-chirality oscillations in 2D systems with strong spin–orbit coupling

Conventional Shubnikov–de Haas oscillations of conductivity in 3D are washed out as the temperature exceeds the spacing between the Landau levels. This is due to smearing of the Fermi distribution. In 2D, in the presence of two or more size-quantization subbands, there is an additional type of magneto-oscillations, usually referred to as magneto-inter-subband oscillations, which do not decay exponentially with temperature. The period of these oscillations is determined by the condition that the energy separation between the subbands contains an integer number of Landau levels. Under this condition, which does not contain the Fermi distribution, the inter-subband scattering rate is maximal. Here we show that, with only one subband, high-temperature oscillations are still possible. They develop when the electron spectrum is split due to the spin–orbit coupling. For these additional oscillations, the coupling enters both the period and the decay rate.

From Laboratory to Field: The Effect of Controlling Oscillations in Temperature on the Growth of Crops

Crops are grown in natural conditions. Environmental factors such as temperature, humidity, and light irradiance have a regular pattern. A grower chamber is usually used to test the effect of environmental factors on the crops. If crops were cultivated under fixed environmental conditions, the results would be different from that for plants that are grown in a natural environment. Limits in the capability of an apparatus mean that most studies use a fixed temperature, a fixed relative humidity, or a fixed light intensity. In an accumulated temperature study, Pak choi and strawberry were used to compare the difference between fixed and oscillating temperature conditions in a growth chamber. There were three temperature patterns: the high-temperature (HVT) oscillation pattern (day: 22–32 °C; night: 19–25 °C), low-temperature (LVT) oscillation pattern (day: 21–29 °C; night: 19–23 °C), and the fixed temperature (CT) regime (day: 25 °C; night: 22 °C). The light intensity was 80 μmol∙m−2s−1. The environments used for the Pak choi experiments were the HVT oscillation pattern, the CT pattern, and the inside air temperature for a net house. The strawberries had three treatments: the HVT and LVT oscillation patterns, and the CT pattern. The fresh weight of total plants, the leaf area, the leaf number, and the chlorophyll content were measured for the two crops. For strawberries, the fresh weight of the leaves and the Brix value were measured. The experimental results show that there is a significant difference in the growth characteristics for these three regimes. The results of the growth characteristics of Pak choi and strawberry for an oscillating temperature are better than those for a fixed temperature environment with a statistically significant difference. For the biological and agricultural experiments, an oscillating temperature in the growth chamber realistically simulates a natural environment.

Developmental timing of Drosophila pachea pupae is robust to temperature changes

Rearing temperature is correlated with the timing and speed of development in a wide range of poikiloterm animals that do not regulate their body temperature. However, exceptions exist, especially in species that live in environments with high temperature extremes or oscillations. Drosophila pachea is endemic to the Sonoran desert in Mexico, in which temperatures and temperature variations are extreme. We wondered if the developmental timing in D. pachea may be sensitive to differing rearing temperatures or if it remains constant. We determined the overall timing of the Drosophila pachea life-cycle at different temperatures. The duration of pupal development was similar at 25 °C, 29 °C and 32 °C, although the relative progress differed at particular stages. Thus, D. pachea may have evolved mechanisms to buffer temperature effects on developmental speed, potentially to ensure proper development and individual's fitness in desert climate conditions.

Thermally-Induced Wedging–Ratcheting Failure Mechanism in Rock Slopes

A thermally induced wedging–ratcheting mechanism for slope stability is investigated using a large-scale physical model and using a three-dimensional version of the numerical Distinct Element Method (3DEC). The studied mechanism consists of a discrete block that is separated from the rock mass by a tension crack filled with a wedge block or rock fragments. Irreversible block sliding is assumed to develop down a gently dipping sliding plane in response to climatic thermal fluctuations and consequent contraction and expansion of the sliding and wedge block materials. A concrete block assembly representing the rock mass is placed in a specially designed climate controlled room. An integrated measurement system tracks the block displacement and temperature evolution over time. Results of the numerical 3DEC model and an existing analytical solution are compared with the experimental results and the sensitivity of the numerical and analytical solutions to the input thermo-mechanical parameters is explored. To test the applicability of our physical and numerical models to the field scale, we compare our numerical simulations with monitored displacements of a slender block that was mapped in the East slope of Mount Masada, as up until recently the governing mechanism for this block displacement has been assumed to be seismically driven. By application of our numerical approach to the physical dimensions of the block in the field we find that, in fact, thermal loading alone can explain the mapped accumulated displacement that has surpassed by now 200 mm. We believe this new, thermally-induced, failure mechanism may play a significant role in slope stability problems due to the cumulative and repetitive nature of the displacement, particularly in rock slopes in fractured rock masses that are exposed to high temperature oscillations.

Silicon Carbide MESFET High Frequency Oscillator for Microwave Applications

The Gouriet oscillator is mainly dealing with 4H-SiC metal semiconductor field effect transistor is fabricated with HPSI substrate and passive integrated elements are based on design for demand of the required function of frequency 1GHz. This high frequency or temperature oscillator is operated from 30 to 200˚C, the gain of the delivered power of 21.8dbm at the frequency of 1GHz and the temperature of 200˚C. The oscillator transistor output response is at 200˚C, the improved percentage is 15%. This output response of the difference in between the frequency around the vary of temperature is less than 0.5%.

Silicon Carbide BJT Oscillator Design Using S-Parameters

Radio frequency (RF) oscillator design typically requires large-signal, high-frequency simulation models for the transistors. The development of such models is generally difficult and time consuming due to a large number of measurements needed for parameter extraction. The situation is further aggravated as the parameter extraction process has to be repeated at multiple temperature points in order to design a wide-temperature range oscillator. To circumvent this modelling effort, an alternative small-signal, S-parameter based design method can be employed directly without going into complex parameter extraction and model fitting process. This method is demonstrated through design and prototyping a 58 MHz, high-temperature (HT) oscillator, based on an in-house 4H-SiC BJT. The BJT at elevated temperature (up to 300 0C) was accessed by on-wafer probing and connected by RF-cables to the rest of circuit passives, which were kept at room temperature (RT).

Study on properties of aluminum alloy welded by friction stir welding

In order to meet the special requirements of aerospace industry for materials of aluminum alloy, the precisely controlled heat treatment was studied. The 2219 aluminum alloy welded plate was prepared by friction stir welding, and its microstructure and mechanical properties were studied correspondingly. The reasons for strength reduction of welded joints are analyzed and summarized. The research results showed that the average tensile strength of the welded joints increased to 393 Mpa and the elongation increased to 12.6% of the base metal. With the special recrystallization technology of high temperature oscillation heat treatment, the fine grains can be maintained, the plasticity of aluminum alloy can be restored, which means that the softening problem can be eliminated and the mechanical strength can be improved.

Effect of Landau quantization on linear magnetoresistance of a periodically modulated two-dimensional electron gas

The linear response of two-dimensional electron gas in a perpendicular magnetic field in the presence of a spatially dependent classically smooth electrostatic potential is studied theoretically, by application of the Kubo formula for nonlocal conductivity tensor. In the classical transport regime, a general expression for the conductivity tensor through the correlation functions of the homogeneous electron gas is derived. The quantum transport regime, when Landau quantization is essential, is studied for the case of unidirectional periodic potential modulation. Apart from the Shubnikov-de Haas oscillations, the resistivity can demonstrate quantum oscillations with larger periods and smaller amplitudes, which survive when temperature increases. These oscillations exist when the modulation amplitude considerably exceeds the cyclotron energy so the Landau subbands, formed out of the Landau levels by the modulation potential, overlap in the energy domain. Both diagonal components of the resistivity tensor demonstrate oscillations related to modification of the density of states by the modulation. In addition, the resistivity component perpendicular to the modulation axis, which is caused by the scattering-assisted hopping transport, shows another kind of oscillations related to enhancement of the hopping probability when the guiding center of cyclotron orbit shifts by the doubled cyclotron radius. It is suggested that such high-temperature oscillations can be detected under conditions when the modulation period considerably exceeds the cyclotron radius.

An experimental critique on the existence of fragile-to-strong transition in glass-forming liquids

A number of recent studies in the literature have reported the existence of unusual temperature dependence of the shear viscosity for a variety of glass-forming liquids that cannot be described with a single fragility index. Rather, these liquids display an apparent fragile-to-strong transition (FST) with lowering of temperature that was suggested to be indicative of a structural transition. In the present work we critique the accuracy of the high-temperature oscillation viscometry technique that was used almost exclusively for viscosity measurements of these liquids above their liquidus temperature. Viscosity measurements are carried out on binary Ge-Se chalcogenide liquids in their supercooled and stable states using conventional capillary and parallel-plate rheometry techniques and are compared with the oscillation viscometry data in the literature. Such comparisons conclusively demonstrate that the latter measurement technique often underestimates the viscosity by nearly an order of magnitude, especially at high temperatures. These results, when taken together, indicate that the observation of FST in glass-forming liquids is likely an artifact of the inaccuracy of the oscillation viscometry technique. Moreover, these results cast serious doubt on the reliability of the high-temperature oscillation viscometry data for metals and alloys that are prevalent in the literature.

Effect of inclination angle and fill ratio on geyser boiling phenomena in a two-phase closed thermosiphon – Experimental investigation

Geyser boiling is a complex phenomenon which may occur in heat pipes causing high temperature and pressure oscillation leading to noticeable vibration. Therefore, understanding of such process is essential to improve heat pipes thermal performance and avoid damage. In this experimental study, a comprehensive investigation of several parameters on the characteristics of the geyser boiling has been conducted during the operation of two-phase closed thermosiphon (TPCT) using water as the working fluid. The effect of different inclination angles (90, 60, 30 and 10°) at various fill ratios defined as volume of liquid in the evaporator to the volume of the evaporator (25%, 65% and 100%) on the geyser boiling has been investigated at a broad range of heat load and for various mass flow rates and inlet temperatures of the cooling water. These important parameters have been examined to report the occurrence and period of the geyser effect at each heat input. The results showed that the orientation and the liquid charge have a significant impact on the occurrence and period of the geyser boiling at low and high heat inputs. For example, at a fill ratio of 100%, the geyser boiling occurs at a lower heat input compared with that for fill ratios 25%, 65% at all inclination angles, while it happens at a higher heat load at a low inclination 10° compared with other angles at all fill ratios. In addition, at high input energies, it almost disappears at orientations of 90 and 60° for all liquid charges. Also, comparing with fill ratios of 25% and 65%, a shorter period is observed for a fill ratio of 100% at angles of 90, 30 and 10°, whereas it is longer at 60° and low heat inputs. This work highlights the effects of the operating conditions on geyser boiling in heat pipes.

Possibilities and prospects of using energy of high-temperature oscillation plasma flow in treatment of ventral hernias

OBJECTIVE. This work investigated an influence of high-temperature oscillation plasma flow on hypoderma and determined the degree of influence on lymphatic vessels. MATERIAL AND METHODS. The experiment was carried out on 15 guinea pigs, that were divided into 5 groups (3 species in each group). An incision of derma and hypoderma was performed in dorsal area. The control group was the first and their incised tissues were used for comparative morphological analysis. Hypoderma has been treated by high-temperature oscillation plasma flow using Plasma.Jet to achieve coagulation homeostasis in the second group. Excisional biopsy was made immediately after tissue processing by Plasma.Jet in this group. Biopsy was performed on the third day in the third group. It was on the fifth day in the fourth group and on the seventh day in the fifth group. RESULTS. According to histological and immunohistochemical study, it was stated that optimal hemostasis was achieved due to coagulation without necrotic changes and absence of lymphorrhea. CONCLUSIONS. The developed method of hemostasis allowed doctors to reduce complication rate in postoperative period.

Water-flow Gazing Curtain-wall and Ground Source Heat Pump as an Energy Saving Strategy in Buildings

Background: The thermal challenge raised by the use of traditional air-chamber glazing in contemporary architecture is not coherent with the current goals for buildings in terms of energy efficiency Methods: This paper explores the possibilities of the active water-flow glazing technology in the form of a curtain-wall, and its integration with a geothermal heat exchanger. A simulation is carried out in order to evaluate such installation, and the results of this simulation are then compared to real data collected from a built and functioning example in Spain. Findings: In order to evaluate the energy savings resulted from this installation, the two studies (simulation and real data) are followed by two parallel estimations of energy savings when compared to a theoretical electric energy expense in HVAC of a building with a more conventional building technology. The active water-flow glazing tackles the problem by flowing water through the chamber between glass panes; the windows become solar energy collectors, and a closed water circuit provides the building with the thermal inertia needed to prevent high temperature oscillations. Combining this emerging technology of active waterflow glazing with low-cost heating and cooling strategies such as geothermal exchangers, free cooling and seasonal heat storage would enable maximum use of daylight by a transparent glass facade and, at the same time, achieve Zero Energy Building performance. Applications: When compared to a traditional double-pane curtain-wall connected to an air-water heat pump, a combination of water-flow glazing and ground source heat pump proves to entail substantial energy savings (close to 40%) in a building’s overall cooling costs.

Kinetic phenomena in organic conductors in high magnetic fields (Review Article)

A review of experimental and theoretical studies of transport phenomena in strongly anisotropic organic conductors is presented. Considerable attention is paid to the phenomena that are specific to quasi-2D and quasi-1D conductive structures and have no analogues both in ordinary metals and in truly 2D or 1D conducting systems. Angular magnetoresistance oscillations, de Haas–van Alphen and Shubnikov–de Haas phenomena, high-temperature quantum oscillations of the magnetoresistance, and high-frequency resonances, including those arising due to the motion of electrons open trajectories, are discussed. The resonant angular oscillations of high-frequency conductivity and weakly damped electromagnetic waves in quasi-2D organic conductors under strong spatial dispersion are considered.

Laser cooling of a high-temperature oscillator by a three-level system

We study the laser cooling of a mechanical oscillator through the coupling with a dissipative three-level system. Under a background temperature beyond the Lamb-Dicke regime, we extend the standard cooling analysis by separately studying the classical motion and the quantum dynamics of the oscillator. In Ladder-system cooling, the cooling rate degrades by orders of magnitude at large classical motion. This phenomenon causes a critical transition of the final temperature at a hot background. In stark contrast, electromagnetic-induced-transparency (EIT) cooling with a $\Lambda$-system produces significant negative cooling rate at high motional excitation. At steady state, the oscillator could exhibit both cooling and lasing behaviours. We argue that a successful EIT cooling requires either a poor quality oscillator to suppress the lasing effect, or terminating the cooling process at a transient stage.

A novel pyroelectric generator utilising naturally driven temperature fluctuations from oscillating heat pipes for waste heat recovery and thermal energy harvesting

Low temperature thermal to electrical energy converters have the potential to provide a route for recovering waste energy. In this paper, we propose a new configuration of a thermal harvester that uses a naturally driven thermal oscillator free of mechanical motion and operates between a hot heat source and a cold heat sink. The system exploits a heat induced liquid-vapour transition of a working fluid as a primary driver for a pyroelectric generator. The two-phase instability of a fluid in a closed looped capillary channel of an oscillating heat pipe (OHP) creates pressure differences which lead to local high frequency temperature oscillations in the range of 0.1–5 K. Such temperature changes are suitable for pyroelectric thermal to electrical energy conversion, where the pyroelectric generator is attached to the adiabatic wall of the OHP, thereby absorbing thermal energy from the passing fluid. This new pyroelectric-oscillating heat pipe (POHP) assembly of a low temperature generator continuously operates across a spatial heat source temperature of 55 °C and a heat sink temperature of 25 °C, and enables waste heat recovery and thermal energy harvesting from small temperature gradients at low temperatures. Our electrical measurements with lead zirconate titanate (PZT) show an open circuit voltage of 0.4 V (AC) and with lead magnesium niobate–lead titanate (PMN-PT) an open circuit voltage of 0.8 V (AC) at a frequency of 0.45 Hz, with an energy density of 95 pJ cm−3 for PMN-PT. Our novel POHP device therefore has the capability to convert small quantities of thermal energy into more desirable electricity in the nW to mW range and provides an alternative to currently used batteries or centralised energy generation.

Effects of Measurement Conditions on Operating Limits of Solar Horizontal Heat Pipes

In this work operating limit measurements are presented for one self-fabricated and one commercial solar heat pipe at horizontal and small inclination angles. While for the self-fabricated test sample heat transfer is limited by entrainment, dry-out limit is observed for the commercial solar heat pipe. Operating limit measurements of the commercial solar heat pipe show good reproducibility, whereas the detected operating limit of the self-fabricated heat pipe varies drastically. When tested at slight inclination, high temperature oscillations indicating geyser boiling effects are observed for the commercial test sample. Finally, operating limit definitions given by the literature are discussed regarding their applicability for solar thermal applications.

Heritage Earth Construction and Hygrothermal Comfort: The Challenge of Rebuilding in Central Chile

According to the latest official census of 2002, earth construction represented 5.5% of the Chilean building stock. These buildings of traditional construction techniques of unfired earth and straw blocks (adobe), rammed earth (tapial) or wattle and daub (quincha) form a large proportion of Chile’s National Monuments and heritage buildings. In addition to their heritage value, these buildings with their high thermal mass, respond well to the climate conditions of both the altiplano of northern Chile and the Central Valley, zones with high diurnal temperature oscillations, with typical daily temperature differences of up to 20°C. However following the 2005 earthquake in Tarapacá, northern Chile and that of the 27th February 2010 in Central Chile a serious rethink has been required as to the retention and restoration of adobe buildings. Public opinion has labelled earth construction as unsafe and most reconstruction to date has taken place with prefabricated timber solutions which lack the necessary thermal mass to respond well to the climatic conditions. At the same time research into the structural integrity, seismic resistance, maintenance and the living conditions provided by earth construction has been undertaken. In this wider context this paper presents the compilation of international and Chilean research into the hygrothermal properties of adobe construction, in addition to the authors insitu measurements of the temperature and relative humidity in two surviving adobe dwellings in the earthquake hit village of Chépica located in Chile´s Central valley. These measurements are compared with those of a dwelling rebuilt with straw bales and earth render in the same location. Based on this information the paper studies the challenge of rebuilding and restoring heritage buildings whilst providing occupants with the necessary levels of environmental comfort.

Investigation of the Temperature Dependence of the Oscillation of the Magnetic Susceptibility in Semiconductors

The temperature dependence of the magnetic susceptibility oscillations semiconductors was considered in a quantizing magnetic field. With the help of mathematical modeling of the thermal broadening of the energy levels, the temperature dependence of the de Haas-van Alphen effect in quantizing magnetic field was investigated. The influence of temperature on the de Haas-van Alphen with the help of free energy of electrons ( ) ( ) , χ HT in semiconductors was determined. Theoretical results of the mathematical simulation were compared with experimental data for bismuth. Using the proposed model of the low-temperature ( ) ( ) , χ HT , high-temperature oscillation magnetic susceptibility in semiconductors was calculated.

Nuclear DNA content variation among perennial taxa of the genus Cyanus (Asteraceae) in Central Europe and adjacent areas

The genome size of 265 plants and the GC content of 126 plants from 63 populations of the Cyanus triumfetti and Cyanus montanus groups, collected across the Carpathians, Pannonia, Bohemian Massif, and Western and Dinaric Alps were determined by PI and DAPI flow cytometry. Variation of the nuclear DNA content among homoploid species, and intraspecific and interpopulation variation were confirmed in simultaneous analyses. The 2C-value at the diploid level (the C. triumfetti group) varied from 2.53 for Cyanus dominii subsp. sokolensis to 3.06 pg for C. triumfetti s.s. (1.21-fold range). At the tetraploid level (the C. montanus group), the 2C-value varied from 5.19 for Cyanus mollis to 5.84 pg for C. montanus (1.13-fold range). High intraspecific and interpopulation variation in the amount of nuclear DNA in the C. triumfetti group correlates with the extensive morphological variation found in this group. Significant between-species differences in genome size indicate that this attribute may be used as a supportive taxonomic marker for both of the groups studied. The GC content varied by 2.93 %, from 39.46 % for “Cyanus axillaris” to 40.61 % for Cyanus adscendens; this character is of no value for taxonomic purposes. Genome size of the studied populations is significantly higher in southern parts of the distribution area and at higher elevations. Plants with smaller genomes tend to occur in dry areas at low altitudes with high diurnal and annual temperature oscillations. The GC content of the populations studied is significantly correlated with longitude, increasing from east to west; and plants with GC-rich genomes are concentrated in the coldest areas with low minimum temperatures.

Amplitude Shift Keyed Radio Communications for Hostile Environments

This work presents the amplitude modulation radio transmission system for communications in hostile environments. The commissioning of a high temperature oscillator and AM mixer system for the purpose of Amplitude Shift Keyed modulation is presented. While previous work has demonstrated oscillators in the Ultra High Frequency (UHF) band, these have been targeted at applications such as radar and mobile telephones. In this paper we have concentrated on the shortwave bands to maximize the range between a sensor unit and the receiver within wireless networks. The work demonstrates that simple communication systems are already possible for hostile environments and allow for simple sensor data to be wirelessly transmitted to safer working areas.