高温超导电缆冷却系统现状与发展

结合国内外高温超导电缆工程实例从制冷原理,系统形式等方面介绍了几种常用的高温超导电缆冷却系统;同时从适用条件、运行可靠性、经济性等方面对它们进行比较;分析国际上对高温电缆冷却系统的研究趋势,并对其研究发展提出建议。     

主动式冷却系统微型化发展现状

常规的制冷系统在一些特殊场合下不能用作消除热害的理想解决方案.得益于微系统工艺和微尺度传热传质理论的不断完善,以蒸气压缩系统、吸收式系统和热电系统为代表的主动冷却系统在微型化和轻量化方面取得显著进展.文中基于国内外最新文献分别介绍了这三种主动冷却系统的优、缺点及发展现状,通过实例对比说明蒸气压缩系统具有较大发展潜力,就...     

Nuclear magnetic resonance microscopy of the development of the parasitoid wasp Venturia canescens within its host moth Plodia interpunctella

Nuclear magnetic resonance microscopy was used to image the parasitoid wasp Venturia canescens (Hymenoptera: Ichneumonidae) within larval and pupal instars of its host, the Indian meal moth, Plodia interpunctella (Lepidoptera: Pyralidae). The images were obtained using gradient-echo and chemical shift selective pulse sequences and clearly showed the location and shapes of the parasitoid as it developed from the L₁ larva to a pupal stage within the host. The digestive, nervous, and tracheal systems of the host were identified and changes were observed as the host underwent metamorphosis. Destruction of the host tissues by the parasitoid was visible. It was found that the parasitoid first ate the fat body and digestive system of the host, allowing the host to continue to grow, and only progressed to the vital organs when its own development had neared pupation.     

On the development of an ion-beam stochastic cooling system for the nuclotron superconducting accelerator complex

The Joint Institute for Nuclear Research (JINR) initiated the creation of a unique heavy-ion collider, the Nuclotron-based ion collider facility (NICA), which is planned to be put into commission in 2016. According to the calculation data, the collider luminosity, which should be kept at a record high level of 10²⁷ cm^?2 s^?1, will gradually decrease, mainly due to intrabeam scattering. To maintain luminosity at a high level, it is necessary to include a cooling system in the base project of the accelerator. Among the two cooling methods (electron and stochastic) most frequently used for heavy ion beams, stochastic cooling seems more attractive. However, there has been a lack of experience in the development and commissioning of such systems in Russia. For this reason, an experiment on stochastic cooling on the Nuclotron accelerator is being prepared to explore the technology and possibilities of this method. In this work, the method of stochastic cooling, the technique for calculating the cooling dynamics, and the experimental setup under development are briefly described.     

Laser cooling of atoms, ions, or molecules by coherent scattering

We point out a laser cooling method for atoms, molecules, or ions at low saturation and large detuning from the particles' resonances. The moving particle modifies the field inside a cavity with a time delay characteristic of the cavity linewidth, while the field acts on the particle via the light shift. The dissipative mechanism can be interpreted as Doppler cooling based on preferential scattering rather than preferential absorption. It depends on particle properties only through the coherent scattering rate, opening new possibilities for optically cooling molecules or interacting atoms.     

Axialisation, cooling and quenching of ions in a Penning trap

On the basis of a macroscopic ground state population it was argued recently that Bose-Einstein condensation should occur in a one-dimensional harmonic potential. We examine this situation by drawing analogies to bosons in a two-dimensional box, where the thermodynamic limit is well-defined. We show that in both systems although the ground state populations show sharp onsets at the critical temperature, the behaviour of the specific heat is analytic, which proves the absence of a phase transition in these systems. Received: 17 February 1997 / Revised: 3 September 1997 / Accepted: 13 October 1997     

Guiding, focusing, and cooling of atoms in a strong dipole potential

01 ^* (doughnut) modes for atomic beam manipulation. A slow atomic beam is guided over up to 0.3 m and focused down to 6.5 μm radius. The doughnut mode is used as a strong mesoscopic dipole potential with vibrational level spacings up to the photon recoil energy. Polarization gradient cooling in this system generates a bimodal momentum distribution with a narrow component momentum width of 4 ?k. Received: 26 June 1998     

Ultrastructure of carp Cyprinus carpio permatozoa after cooling,dilution and freeze-thawing

Dilution of the carp spermatozoa with a cryoprotective medium was shown to inflict serious injuries to the fine structures of some spermatozoa. The amount of the injured spermatozoa increases after cryopreservation. Examination of the freeze-fracture micrographs of the heads of the carp spermatozoa, showed that their protoplasmic faces were covered with the particles in high concentrations. These particles do not form clusters after cooling the spermatozoa down to +5 degrees C and dilution with a cryoprotective medium. For the first time the authors observed the particles to form geometrically shaped regular formations on the outer membranes of the carp spermatozoa[pf1]. On the basis of the results obtained the authors propose that high susceptibility of the carp spermatozoa to osmotic exposures is apparently due to some particular features of the fine structures of their membranes and to their expected probably low heterogeneity.     

Intensification of cooling by a pulsed gas-droplet flow: Equipment,parameters, and results

A bench for studying heat exchange between a pulsed spray and a surface heated to a temperature below the boiling point is designed. A calorimeter to measure the integral heat exchange accurate to 1.5–3.0% and equipment generating the pulse spray are described. The main parameters of the forming gas-drop-let flow (the gas and liquid velocities, the variation of the hydropulse duration and the size of flow-constituting droplets when moving toward a heat exchanger, and the liquid concentration distribution over the cross section and along the flow) and respective measuring techniques are given. It is shown that the duration of a droplet train in the flow influences heat-and-mass transfer.     

Prospects for sympathetic cooling of molecules in electrostatic, ac and microwave traps

We consider how trapped molecules can be sympathetically cooled by ultracold atoms. As a prototypical system, we study LiH molecules co-trapped with ultracold Li atoms. We calculate the elastic and inelastic collision cross sections of ⁷LiH + ⁷Li with the molecules initially in the ground state and in the first rotationally excited state. We then use these cross sections to simulate sympathetic cooling in a static electric trap, an ac electric trap, and a microwave trap. In the static trap we find that inelastic losses are too great for cooling to be feasible for this system. The ac and microwave traps confine ground-state molecules, and so inelastic losses are suppressed. However, collisions in the ac trap can take molecules from stable trajectories to unstable ones and so sympathetic cooling is accompanied by trap loss. In the microwave trap there are no such losses and sympathetic cooling should be possible.     

Ultra-fast dynamics of electron thermalization,cooling and transport effects in Ru(001)

Time-resolved two-photon photoelectron spectroscopy is used to study the dynamics of non-equilibrium electron and hole distributions at bare and D₂O-covered Ru(001) following optical excitation (55-fs, 800-nm pulses) with variable fluence (0.04–0.6 mJcm^-2). Within the first 0.5 ps we observe an ultra-fast transient of the excited-carrier population and energy density at the surface which is accompanied by pronounced deviations of the electron-energy distribution from a (thermalized) Fermi–Dirac distribution. Comparison of the transient energy density of the photoexcited electrons at the surface with predictions of the two-temperature model provides fair agreement up to 400 fs, but exhibits a systematically lower energy density at later times, where electrons and phonons are equilibrated. We propose that this reduced energy density at the surface originates from ultra-fast energy transport of non-thermal electrons into the bulk in competition to electron–phonon coupling at the surface. This is corroborated by extending the two-temperature model to account for non-thermal, photoexcited electrons, whereby quantitative agreement with experiment can only be achieved if ballistic transport and reduced electron–phonon coupling is incorporated for non-thermal electrons. Implications for surface femtochemistry are discussed. PACS 78.47.+p; 71.38.-k; 73.40.-c     

All-solid-state continuous-wave laser systems for ionization,cooling and quantum state manipulation of beryllium ions

We describe laser systems for photoionization, Doppler cooling, and quantum state manipulation of beryllium ions. For photoionization of neutral beryllium, we have developed a continuous-wave 235 nm source obtained by two stages of frequency doubling from a diode laser at 940 nm. The system delivers up to 400 mW at 470 nm and 28 mW at 235 nm. For control of the beryllium ion, three laser wavelengths at 313 nm are produced by sum-frequency generation and second-harmonic generation from four infrared fiber lasers. Up to 7.2 W at 626 nm and 1.9 W at 313 nm are obtained using two pump beams at 1051 and 1551 nm. Intensity drifts of around 0.5 % per hour have been measured over 8 h at a 313 nm power of 1 W. These systems have been used to load beryllium ions into a segmented ion trap.     

L1,L2 maps of distortion-product otoacoustic emissions from a moth ear with only two auditory receptor neurons

The tympanal organ of the moth Empyreuma affinis emits physiologically vulnerable distortion-product otoacoustic emissions. To assess the nature of underlying mechanical nonlinearities, we measured L1,L2 maps by varying both stimulus levels. Two types of maps were found: (1) Maps containing dominant islands centered at the L1=L2 diagonal as it is typical for saturating nonlinearities that can be described by Boltzmann functions. In contrast to maps published for mammals and frogs, the shape of such islands includes sharp ridges at L1 or L2 levels close to 70 dB sound pressure level. This could be produced by a strongly asymmetric operating point of the respective transfer functions, consistent with the fact that the auditory sensory cells are not hair cells but primary mechanoreceptors with a single cilium. The saturating map components could be selectively reduced by acoustic suppression. (2) Maps where separated islands were less conspicuous but in which the dominant feature consisted of contour lines which were orthogonal to the L1=2L2 diagonal and could be generated by an expansive nonlinearity. Maps showing strong islands were found for f2 frequencies between 26.7 and 45 kHz, maps without strong islands for f2 between 42 and 57.5 kHz. This suggests a frequency-dependent change regarding the involved mechanical nonlinearities.     

Study of the influence of cooling on the parameters of millimeter-wave high-frequency amplifiers, mixers, and mixer-amplifier modules of industrial manufacturing

We briefly describe equipment and methods for a study of the influence of deep cooling on the parameters of sensors of millimeter-wave receivers, which are not designed for operation under such conditions, and present the data on improvement of their sensitivity and the ranges of optimal temperatures.     

New ultrasonic assisted technology of freezing,cooling and thawing in solid food processing: A review

Solid foods include fish, shrimp, shellfish, and other aquatic products, fruits, and vegetables. These products are commonly used for food freezing, cooling, and thawing. However, traditional freezing, cooling, and thawing of solid food technologies have limitations in quality, such as protein denaturation and water loss in food. Ultrasound-assisted technology has become a useful method in solid food processing due to improved preservation quality of solid food. This paper comprehensively reviews the mechanism and application of ultrasonic in solid food processing technology. Although the application of ultrasound-assisted ultrasound in solid food processing is relatively comprehensive, the energy saving of food cold processing is essential for practical application. This paper analyzes the optimization of ultrasonic in solid food processing, including orthogonal/multi-frequency technology and the combination of ultrasonic and other technologies, which provides new ideas for freezing, cooling, and thawing of solid food processing.     

Open discharges: Structure, development, and role of photoemission

The research reported in three preceding papers is summarized. The photoelectron mechanism for the formation of electron beams in an open discharge with a grid anode is revised. Revision of the discharge mechanism also requires revision of the optimal conditions for its excitation. A new method for pumping lasers by beams of fast atoms formed in an open discharge with an inverted voltage is proposed. Zh. Tekh. Fiz. 68, 33–38 (March 1998)     

Formation, cascade development, and rupture of the X-pinch neck

Data from high-resolution x-ray shadow photography of an X-pinch in the diode of a high-power dense-plasma generator are presented. The processes leading to the formation of a minidiode, the compression of the neck arising in it, and the cutoff and subsequent emptying of the neck are studied. Cascade formation of short-lived structures, which consistently reproduce the form of the minidiode on small scales before the x-ray burst, is observed in the course of the implosion. The position of the x-ray emission points is determined.     

Cryopreservation of Quercus suber and Quercus ilex embryonic axes: in vitro culture,desiccation and cooling factors

This study examines different factors included in the cryopreservation protocols for Quercus ilex and Q. suber embryonic axes. In vitro incubation temperature played an important role in the appropriate development of Q. ilex axes, as 15 degrees C was superior to 25 degrees C. Q. suber axes proved to be more sensitive to desiccation and cooling. Poor survival (35%) was observed when axes were included into cryovials and then in liquid nitrogen, and none when immersed in sub-cooled liquid nitrogen (-210 degrees C). Q. ilex axes showed poorly organised development in vitro (c. 50% of non-cooled axes showed shoot development). However, c. 80% survival was observed after cryopreservation (either in liquid nitrogen or sub-cooled liquid nitrogen at 0.34 g water / g dry weight), of which c. 15% showed shoot development.