Ends Of Stack Research Articles

Analysis of forming mechanism and influencing factors of thermoacoustic plate end temperature difference

In order to explore the formation mechanism and influencing factors of the temperature difference between two ends of the plate stack, an expression of the temperature change of the stack with time was established based on the two-dimensional heat conduction equation. Based on this, the finite element model of heat transfer between a single thermoacoustic plate stack and the gas above it is established in Ansys, and the temperature of the plate stack is solved. When the sound field is constant, the variation law of the temperature of the stack with the working time and space is obtained, and the formation mechanism of the temperature difference between the two ends of the plate stack is revealed. From the calculation results, it is found that the net heat transfer between the gas and the plate stack is mainly reflected in the two ends of the plate stack, and the contribution of the air mass in the middle part is mainly the relay heat transfer. In the process of working, part of the sound work is converted into the internal energy of the air mass, which makes the gas temperature on the surface of the plate rise as a whole. The working frequency, stack length and stack thermal conductivity are taken as the influencing factors. When no load is added, the variation of the temperature of the high and low end of the stack with the working time under different working conditions is analyzed. And the theory of series between short plates is put forward to explain the formation mechanism of large temperature difference between the two ends of the plates. In order to further reduce the cooling temperature of thermoacoustic refrigerator, a new research method and exploration direction are proposed.

Tertiary folds of the SL5 RNA from the 5′ proximal region of SARS-CoV-2 and related coronaviruses

Coronavirus genomes sequester their start codons within stem-loop 5 (SL5), a structured, 5' genomic RNA element. In most alpha- and betacoronaviruses, the secondary structure of SL5 is predicted to contain a four-way junction of helical stems, some of which are capped with UUYYGU hexaloops. Here, using cryogenic electron microscopy (cryo-EM) and computational modeling with biochemically determined secondary structures, we present three-dimensional structures of SL5 from six coronaviruses. The SL5 domain of betacoronavirus severe-acute-respiratory-syndrome-related coronavirus 2 (SARS-CoV-2), resolved at 4.7 Å resolution, exhibits a T-shaped structure, with its UUYYGU hexaloops at opposing ends of a coaxial stack, the T's "arms." Further analysis of SL5 domains from SARS-CoV-1 and MERS (7.1 and 6.4 to 6.9 Å resolution, respectively) indicate that the junction geometry and inter-hexaloop distances are conserved features across these human-infecting betacoronaviruses. The MERS SL5 domain displays an additional tertiary interaction, which is also observed in the non-human-infecting betacoronavirus BtCoV-HKU5 (5.9 to 8.0 Å resolution). SL5s from human-infecting alphacoronaviruses, HCoV-229E and HCoV-NL63 (6.5 and 8.4 to 9.0 Å resolution, respectively), exhibit the same coaxial stacks, including the UUYYGU-capped arms, but with a phylogenetically distinct crossing angle, an X-shape. As such, all SL5 domains studied herein fold into stable tertiary structures with cross-genus similarities and notable differences, with implications for potential protein-binding modes and therapeutic targets.

Experimental study on the effect of hydraulic radius of stack on the performance of thermoacoustic prime mover with open resonator

<p class="Abstract">Thermoacoustic prime mover is a device which converts thermal energy into acoustic work. The device mainly consists of a resonator pipe, a stack (a porous medium), and two heat exchangers. Four stacks were made of a pile of stainless wire-mesh screens with various mesh numbers of #12, #14, #16, and #18, providing the effective hydraulic radius of 0.32 mm, 0.28 mm, 0.25 mm, 0.23 mm, respectively. Each stack has 4 cm length. By using the wire-mesh screens, it is easier to vary the hydraulic radius of stack than any other material. The stack is sandwiched between a hot heat exchanger and an ambient heat exchanger. The resonator is made of a stainless-steel pipe with one end open and the other closed. The stack and heat exchangers are placed inside a resonator pipe near the closed end. The thermal energy were provided by using an electric heater which is installed at the hot heat exchanger. Ambient water was flowing through the ambient heat exchanger. Sound is produced by the stack when the temperature difference between the both ends of stack reachs an onset point. This experiments were performed by recording the temperatures at both ends of stack and the pressure amplitudes of the sound at several points along the resonator for various hydraulic radius of stack. It is found that the effective hydraulic radius of 0.28 mm gives the lowest onset temperature, the shortest time to reach onset condition, and the highest pressure amplitude which are 314°C, 299 s, and 2.89 kPa, respectively. The frequency of sound is not altered by the change of hydraulic radius of stack.</p>

Development of diverted plasma discharge and plan for advanced divertor study in VEST

Operational scenario for diverted plasmas has been developed in Versatile Experiment Spherical Torus (VEST) not only for improving plasma performance but also for preparing upcoming experiments on advanced divertor concepts such as snowflake and x-point divertor. Diverted discharge scenario is designed using an in-house simulation code and experimentally realized by adjusting turn-on time of two partial solenoid (PF2) coils located at both ends of the center stack. With the diverted scenario, we achieve the improvement in plasma duration by ∼20% compared to the limited plasma operation, mainly due to the mitigation of impurity influxes from the center stack made of tungsten. Indeed, the impurity O-I line is observed to be decreased to 50% of the limited plasma operation. Fast camera images and equilibrium reconstruction based on magnetic diagnostics clearly shows the successful generation of diverted plasmas as well. This paper presents the first results on the diverted plasma operation in VEST and future plan for the experiments on the advanced divertor concept.

Helix Capping in RNA Structure

Helices are an essential element in defining the three-dimensional architecture of structured RNAs. While internal basepairs in a canonical helix stack on both sides, the ends of the helix stack on only one side and are exposed to the loop side, thus susceptible to fraying unless they are protected. While coaxial stacking has long been known to stabilize helix ends by directly stacking two canonical helices coaxially, based on analysis of helix-loop junctions in RNA crystal structures, herein we describe helix capping, topological stacking of a helix end with a basepair or an unpaired nucleotide from the loop side, which in turn protects helix ends. Beyond the topological protection of helix ends against fraying, helix capping should confer greater stability onto the resulting composite helices. Our analysis also reveals that this general motif is associated with the formation of tertiary structure interactions. Greater knowledge about the dynamics at the helix-junctions in the secondary structure should enhance the prediction of RNA secondary structure with a richer set of energetic rules and help better understand the folding of a secondary structure into its three-dimensional structure. These together suggest that helix capping likely play a fundamental role in driving RNA folding.

The Effects of Stack Parameters on the Performances of Acoustic-Refrigeration Thermoacoustic Conversion System

In this research, the acoustic-refrigeration thermoacoustic conversion system numerical model was constructed, the combined influences of structural and positional parameters of stack on the temperature difference at two ends (DT) and the coefficient of performance (COP) were analyzed. Besides, the acoustic-refrigeration thermoacoustic conversion test system was built up. Finally, experiments were performed to testify the calculation results of the conversion system. The results showed that within the common ranges of the parameters values, the porosity of stack affected the COP slightly while the temperature difference seriously, the temperature difference at the two ends of stack increased with the increase of the porosity of stack; for stacks which have the same porosity and gaps between each parallel plate, two values for the center position of stack were exist of which one could make the temperature difference get to the best value, the other one made the COP achieve the maximum value; when the porosity and the center position of stack remained constant, the temperature difference increased first and decreased afterwards with the increase of the gaps height between each parallel plate. In the selected model, the temperature difference at the ends of stack got an ideal value when 2y0=0.45 mm (the gaps height between each parallel plate was nearly about 2.4 times than thermal penetration depth). The results provided the theoretical basis and experimental evidences for improving the performance of acoustic-refrigeration thermoacoustic conversion system.

Experimental Investigation on Effect of Stack on Thermoacoustic Conversion System Performance

The thermoacoustic conversion system is designed, while the position and structure parameter of stack are calculated and analysed. At the same time, the parameters of stack and the input working frequency which influence the system are researched by experiment. The results show that the center position of stack in the standing-wave tube and the length of stack have great influence on the system, and exists a best value in the same input power and frequency; Meanwhile, the pore diameter and wall thickness of stack are also exist the best values, the temperature difference at both ends of stack will be reduced if the value is too big or too small; The best working frequency of the system is migrated due to the stack, working fluid and so on.

Initial plasma start-up using partial solenoid coils in Versatile Experiment Spherical Torus (VEST)

Initial plasma start-up experiments based on ohmic discharge using partial solenoid coils located at both vertical ends of a center stack have been carried out in Versatile Experiment Spherical Torus (VEST) at Seoul National University. Ohmic discharges with the help of microwave pre-ionization have been performed according to the pre-programed start-up scenario which was experimentally verified by a series of vacuum field measurements using an internal magnetic probe array. A plasma current of around 0.4kA has been achieved by ohmic discharge using partial solenoid coils, under the toroidal magnetic field of 0.1T. The vacuum field calculation and fast camera image have revealed that the small plasma current even with significant amount of loop voltage up to 9.7V is attributed to the imbalance of poloidal field for equilibrium. Modification of the start-up scenario and upgrade of power supplies are proposed to be carried out in order to achieve higher plasma current in the future experiments.

Design Features and Commissioning of the Versatile Experiment Spherical Torus (VEST) at Seoul National University

A new spherical torus called VEST (Versatile Experiment Spherical Torus) is designed, constructed and successfully commissioned at Seoul National University. A unique design feature of the VEST is two partial solenoid coils installed at both vertical ends of a center stack, which can provide sufficient magnetic fluxes to initiate tokamak plasmas while keeping a low aspect ratio configuration in the central region. According to initial double null merging start-up scenario using the partial solenoid coils, appropriate power supplies for driving a toroidal field coil, outer poloidal field coils, and the partial solenoid coils are fabricated and successfully commissioned. For reliable start-up, a pre-ionization system with two cost-effective homemade magnetron power supplies is also prepared. In addition, magnetic and spectroscopic diagnostics with appropriate data acquisition and control systems are well prepared for initial operation of the device. The VEST is ready for tokamak plasma operation by completing and commissioning most of the designed components.

A novel approach to design and fabrication of thermo-acoustic refrigerator using high amplitude sound waves

The basic object of this paper is compression of refrigerant by the consumption of high amplitude sound waves that results the generation thermal Energy. For generation of sound waves a loud speaker (or common audio speaker) has been employed for creating high amplitude sound waves which compresses refrigerant (helium) by the well Known thermodynamics process of heat absorption. A Thermo acoustic refrigerator is fabricated with a cooler and loud speaker. The acoustic power produced by a loud speaker as a sound waves reaches to heat the pump. The cooler works on a reverse Carnot cycle by incorporating a compact acoustic network to create the travelling wave phasing necessary to operate. As the acoustic wave propagates temperature difference occurs at the ends of stack, heat and cold is trap by the heat exchangers regenerator from a cold heat exchanger to an ambient one. Instead of using co-axial topology network, the toroidal is used. The design, construction and performance measurement of the cooler are also discussed. Finally, at 8 0 C a

Stability analysis of a gas turbine exhaust stack

Stability analysis, based on finite element method, was carried out on a gas turbine exhaust stack following obvious appearances of significant gaps between its silencer casings and embracing rings. The finite element model was developed by referring to the corresponding technical drawing of the exhaust stack and the information obtained during the site inspection. In the case of axial constraint at both ends of the exhaust stack, the original design was found incapable of withstanding the thermal loading experienced during operation of the gas turbine, leading to instability of the structure. A design modification of the exhaust stack was proposed to rectify this problem. The outcome of the finite element analysis indicated that the modified design of the exhaust stack had improved stability as compared to the original design when subjected to typical thermal loading of the gas turbine operation.

A DNA-porphyrin minor-groove complex at atomic resolution: the structural consequences of porphyrin ruffling.

The crystal structure of a B-type DNA hexanucleotide duplex complexed with the porphyrin molecule nickel-[tetra-N-methyl-pyridyl] porphyrin has been solved by multiwavelength anomalous diffraction phasing and refined to an R factor of 11.5% at a resolution of 0.9 A. The structure has been solved and refined as two crystallographically independent duplexes, stacked end to end. Contrary to expectation, the porphyrin molecule is not intercalated into the duplex but is stacked onto the ends of the two-duplex stack. The porphyrin molecule is highly buckled as a consequence of the nickel coordination, which produces large changes in local DNA structure. A second mode of porphyrin binding is apparent as a consequence of crystal packing, which places the ligand in the minor groove of an adjacent duplex. This structure thus provides, to our knowledge, the first atomic visualization of minor-groove binding for a porphyrin molecule. The geometry of groove binding provides a ready explanation for porphyrin-induced DNA strand cleavage at deoxyribose residues.

Three‐Dimensional Thermal Modeling of Lithium‐Polymer Batteries under Galvanostatic Discharge and Dynamic Power Profile

A three‐dimensional model is developed to simulate and compare heat generation and transport within a lithium polymer electrolyte battery under galvanostatic discharges and a dynamic power profile [the Simplified Federal Urban Driving Schedule (SFUDS)]. Emphasis is placed on the maintenance of the operational temperature and temperature uniformity within a battery by designing a suitable thermal management system. The results indicate that the anisotropic thermal conductivity within the battery is an important factor influencing thermal performance and should be taken into consideration in battery design. On the one hand, because of the low effective thermal conductivity across a laminated cell stack, steep temperature distributions may be caused if cooling channels or electric heaters are placed at the two ends of a cell stack. On the other hand, the relatively large average thermal conductivity along the width and height directions allows more efficient heat removal or addition, and thus facilitates the maintenance of uniform operating temperature. Under the SFUDS power profile, the time‐averaged heat generation rate is low, and therefore a high‐performance insulation material is required to maintain the operating temperature. The thermal model has been applied to study the effectiveness of different arrangements of cooling channels and electric heaters and to select suitable heating intensities and insulating materials.

Stress relief for flextensional transducer

This invention is a device that permits a flextensional transducer to function after the flextensional transducer experiences a pressure equal to or greater than the pressure found at the survival depth of prior art flextensional transducers. The foregoing is achieved by not bonding at least one end of the transducer's piezoelectric stack to the transducer's shell and having the other end or ends of the piezoelectric stack held in the vicinity of the transducer's shell by a pair of guide rails, etc. This permits the transducer's shell to move away from at least one end of the piezoelectric stack at pressures equal to or greater than the pressure at which the stack would experience tensile stresses in a conventional flextensional design. Thus, the piezoelectric stack will not fracture since it receives no tensile stress. Hence, when the transducer experiences a hydrostatic pressure less than the pressure at the survival depth, the shell of the transducer will recontact the free end of the piezoelectric stack permitting the transducer to function.

In situ localization of the sites of paraquat action

Abstract. Effects of paraquat were monitored by electron microscopic, cytochemical, and in vivo spectrophotometric procedures. Electron microscopy of paraquat‐treated pea leaf discs indicates that the chloroplasts are affected primarily with both thylakoid dilation and apparent lamellar fusions, resulting in a ‘honeycomb’ of lamellae. No ultra‐structural effects were noted when leaf discs were incubated in both DCMU and paraquat. Paraquat‐induced peroxide was located cytochemically along the stroma lamellae, on the ends of the grana stack and in the dilated thylakoids. Less destruction was noted in those samples where peroxide was precipitated by cerium chloride, indicating that peroxide or one of its products is one of the major causes of paraquat toxicily. In C4 plants mesophyll plastids exhibited much more peroxide deposition than was detected in bundle sheath plastids. No plastid peroxide depositions were noted in a photobleaching mutant that is resistant to paraquat. In situ cytochrome f oxidation‐reduction was followed during paraquat treatments and resulted in a hastening of the dark re‐reduction of cytochrome f after only 1 h of treatment. This effect was prevented by DCMU or CeCI3. Electron transport, as measured by cytochrome f oxidation‐reduction, was completely obliterated by a 24 h paraquat treatment. These in situ studies on paraquat confirm previous studies that the primary effect in the light is on the plastid and involves peroxide or further products generated by peroxide.