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The Bi2Te3/FeTe heterostructure intersects several phenomena and key classes of materials in condensed matter physics: topological insulators, superconductivity, magnetism, and the physics of interfaces. While neither the topological insulator (Bi2Te3) nor the iron chalcogenide (FeTe) are themselves superconductors, superconductivity forms in a thin 7nm interfacial layer between the two. The restricted dimensionality and the extraordinarily conductive normal state, possibly sourced by the topologically protected surface states, have led to the observation of novel phenomena such as the Likharev vortex explosion and transitions in behavior resulting from the interplay between current induced depairing and the Berezinski-Kosterlitz-Thouless regime. Bi2Te3/FeTe also displays the anomalous oscillatory magnetoresistance phenomenon, which we had previously observed in cuprates. [ABSTRACT FROM AUTHOR]

The flow behaviors of clusters in the riser of a two-dimensional (2D) circulating fluidized bed was numerically studied based on the Euler-Lagrangian approach. Gas turbulence was modeled by means of Large Eddy Simulation (LES). Particle collision was modeled by means of the direct simulation Monte Carlo (DSMC) method. Clusters’ hydrodynamic characteristics are obtained using a cluster identification method proposed by sharrma et al. (2000). The descending clusters near the wall region and the up- and down-flowing clusters in the core were studied separately due to their different flow behaviors. The effects of superficial gas velocity on the cluster behavior were analyzed. Simulated results showed that near wall clusters flow downward and the descent velocity is about -45 cm/s. The occurrence frequency of the up-flowing cluster is higher than that of down-flowing cluster in the core of riser. With the increase of superficial gas velocity, the solid concentration and occurrence frequency of clusters decrease, while the cluster axial velocity increase. Simulated results were in agreement with experimental data. The stochastic method used in present paper is feasible for predicting the cluster flow behavior in CFBs. [ABSTRACT FROM AUTHOR]

In this contribution the low-excitation structural properties of the doubly mid-shell nucleus 170Dy are discussed, with a special empasis on the evolution of the ground state rotational band within the dysprosium isotopic chain. Recent results from an experiment with the EURICA setup at RIKEN are shown in the context of previous measurements at the PRISMA+CLARA as well as the PRISMA+AGATA setups at Laboratori Nazionali di Legnaro. A brief outlook on future planned measurements is also given. [ABSTRACT FROM AUTHOR]

In order to use high temperature superconductivity for current lead applications, it is necessary to determine the thermal, mechanical, and electrical properties in the temperature range planned for the application. In this work, we measured the temperature dependence of the thermal conductivity and thermal expansion of two types of commercial BSCCO tapes. The measurements were carried out on a GM cryocooler based apparatus in a temperature range of 10 K to 300 K. In addition, the results were used to investigate the influence of the different material components on the performance of the conductor. [ABSTRACT FROM AUTHOR]

Cryogenic mechanical properties are generally considered to be some of the most important parameters in cryogenic engineering. Therefore, it is very important to test and investigate mechanical properties at low temperatures. Most systems for cryogenic mechanical property testing are cooled using liquid nitrogen (300 K-77 K) or liquid helium (77 K-4.2 K). As we know, liquid helium is relatively rare and thus expensive. In this study, to attain accurate and stable intermediate temperatures and reduce testing cost, a cryogenic mechanical property testing system cooled by a G-M cryocooler was studied and developed. In this system, the sample can be cooled down to 10.5 K after about 10 hours of running. The tension, bending and compression testing (load range up to 50 kN) can be carried out. [ABSTRACT FROM AUTHOR]

Low-density alloys include aluminum alloys, titanium alloys and magnesium alloys. Aluminum alloys and titanium alloys have been widely investigated and used as structural materials for cryogenic applications because of their light weight and good low-temperature mechanical properties. For aerospace applications, persistent efforts are being devoted to reducing weight and improving performance. Magnesium alloys are the lightest structural alloys among those mentioned above. Therefore, it is necessary to pay attention to magnesium alloys and to investigate their behaviors at cryogenic temperatures. In this paper, we have investigated the mechanical properties and microstructures of some magnesium alloys at cryogenic temperatures. Experimental results on both titanium and magnesium alloys are taken into account in considering these materials for space application. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Using a Langevin-transport approach, the current noise power spectrum of a multi Quantum Well Infrared Photodetector (QWIP) is obtained considering a discrete distribution of generation-recombination centers (quantum wells). The inhomogeneous charge distribution in the quantum well structure affects the intensity and the frequency dependence of the noise power spectrum, giving rise to features different than what expected on the basis of a model based on fully uncorrelated fluctuation processes in homogeneous structures. This model reproduces the behavior of the current noise power spectral density. In particular, its relation to the discrete structure of the device, i.e. to the number of quantum wells N, arises as a consequence of the imbalance between the current injected at the emitter and the stream of photoelectrons drifting through the structure. The 1/N scaling of noise is an issue whose interest exceeds the application area of QWIP and is under intense investigation in periodic substrates, in devices based on chain of organic molecules, in superlattice and others. Understanding the origins of the unavoidable deviations of noise from a simple 1/N dependence, exhibited by the aforementioned and many other devices in different operative conditions, represents one of the most intriguing and fascinating problem that the noise community is facing in the last decade. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Low-frequency current noise and current-voltage (I-V) characteristics have been studied in InAs/GaAs self-assembled Quantum Dot Infrared Photodetectors in dark conditions and under illumination, at T = 77K and T = 5K. The noise behavior is consistent with a generation-recombination fluctuation process mainly related to thermally excited charge carriers at T = 77K. At T = 5K the current noise is consistent with a mechanism of fluctuations driven by the electric field, related to tunneling rather than emission-capture of charge carriers from the Quantum Dots. A very effective noise suppression mechanism, related to the tunneling regime, determines a decrease of fluctuation intensity as a function of the voltage. At T = 5K, an interesting behavior is observed in the current-voltage and noise power spectra for some of nominally identical QDIP structures in the presence of irradiation. Some devices indeed exhibit (i) a very high photoresponse and (ii) a 1/f-shaped noise spectrum at low frequencies. The noise suppression mechanism still acts in the presence of radiation, thus reducing the noise intensity proportionally to the photocurrent intensity. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

C and Si powders of different sizes were doped into MgB2 separately or together. Samples were made by a solid-state reaction method. It was found that the C doping had a strong negative effect on critical temperature (Tc) while the Si doping did not significantly depress Tc. All of these doping materials increased Jc at higher fields when the doping particles were of nanometer sizes. At 20 K and 4 T, Jc of the sample doped with nano-Si achieved 104A/cm2, which is 2 orders of magnitude higher than that of coarse Si doped MgB2. Jc of the sample doped with nano-carbon is one order of magnitude higher than for the sample doped with coarse carbon particles. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Ag/Bi-2223 tapes were fabricated using the Powder-In-Tube method, involving intermediate deformation techniques of sandwich rolling (SR), pressing (P) and normal rolling (NR). Magnetic field B dependence of J[sub c] was measured. Depending on the relationship between J[sub c] and B, the irreversible magnetic field B[sub irr] was determined and pinning force density F was calculated. The experimental results showed that self-field-J[sub c] was linear with the relative density for SR-, P- and NR-tapes. Our experimental results support that NR-, P-, and SR-tapes have a same sort of pinning center and the intermediate deformation processing cannot change property of pinning centers, but can effect the pinning force strength. Our experimental results also support that sandwich rolling is the best technique for fabricating Ag/Bi-2223 tapes. [ABSTRACT FROM AUTHOR]

Flux dynamics of an MgB[sub 2] bulk sample have been studied by systematic measurements of the fundamental and third harmonic ac susceptibility. The irreversibility line T[sub irr](B) has been obtained by fitting the onset temperature T[sub on] (f,B) of the third harmonics at different frequencies to T[sub on](f,B) = C(2πf)[sup 1/[(z-1)ν]] + T[sub irr](B). The flux creep activation energy U(j,B,T) has been derived as U[sub 0][1-(T/T[sub irr])²]²(B/B[sub 0])[sup -n](j/j[sub 0])[sup -μ], with n=1.33 and μ=0.2. The steep decline of the activation energy as a function of the magnetic field U(B) ∝ B[sup -1.33] leads to the steep drop in the critical current density with magnetic field. The relaxation of the current density j(t) of the sample has been detected in a time window of 10[sup -4]∼10[sup -1]s, as the frequency is in the range of 10Hz-10kHz, which extends the time window l∼10[sup 4]s of the conventional dc magnetic relaxation to a much smaller one. The obtained activation energy and the irreversibility line indicate that the pinning properties of the MgB[sub 2] sample will need to be improved for practical applications. [ABSTRACT FROM AUTHOR]

A thermoacoustic engine is a new type of pressure-wave generator that possibly has a very long lifetime because of no mechanical moving parts. A thermoacoustic engine operating in standing wave mode is also called a natural engine with intrinsic thermodynamic irreversibility, so it shows a poor thermodynamic performance in converting thermal energy to acoustic energy. The conversion efficiency is around 10 to 25 percent of Carnot. By analyzing the generation rate of acoustic workflow and the local critical temperature gradient in the traveling-wave and standing wave modes, a thermoacoustic engine with local traveling-wave loop was designed, built and studied. In addition, a miniature coaxial pulse tube refrigerator was attached to the engine, and about 80K temperature difference was achieved with nitrogen in preliminary tests. [ABSTRACT FROM AUTHOR]

Thermally self-excited thermoacoustic engines are currently considered to drive regenerative refrigerators because of no moving parts in such a system. There are many factors that can affect the efficiency and miniaturization of the thermoacoustic systems. Among them, the operating frequency is most important one. To actively control the resonant frequency, we propose a new method. In our system, a unit made of a bellows attached by a metallic block is in introduced in the thermoacoustic system. Using different metallic bellows and blocks can easily control the operating frequency of the system. The design methodology is reported in the paper. [ABSTRACT FROM AUTHOR]

In this paper, external acoustic loads on the performances of a quarter-wavelength traveling-wave thermoacoustic pressure generator are analyzed. First, we derived the maximal frequency and the critical temperature gradient of the thermoacoustic systems by analyzing the conversion between passive network and active network. Then, we considered the effect of the external loads on operating frequency and obtain some qualitative results. [ABSTRACT FROM AUTHOR]

We report the polarized optical absorption spectra of 0.4 nm-sized single-walled carbon nanotubes which are arrayed in channels of an AlPO[sub 4]-5 single crystal. When the electric field (E) of light is polarized parallel to the tube direction (c), the spectra show a sharp absorption band at 1.3 eV, and two broad bands at 2.1eV and 3.1 eV, respectively. The intensities of these absorption bands gradually decrease as the light polarization is turned from E...c to E...c. In the E...c configuration, the tube shows nearly transparent in the measured energy region 0.5 - 4 eV. The measured absorption spectra could be well explained by density-of-states calculated using a local density function approximation. [ABSTRACT FROM AUTHOR]

Axisymmetrical and three dimentional flows through single circular and rectangular microchannel with diaphragm are studied in this paper to imitate the performance of micro-machined membrane particle filter with grid of through holes. The microchannel flows are studied using both the DSMC method and the information preservation (IP) method which yield the result of pressure drop across the diaphragm in better agreement with the experimental data for the membrane filter, than the NS equation calculation with slip boundary condition. [ABSTRACT FROM AUTHOR]

We calculate the probability distribution P(k⊥) for the momentum perpendicular to its original direction of motion that an energetic quark or gluon picks up as it propagates through weakly coupled quark-gluon plasma in thermal equilibrium. [ABSTRACT FROM AUTHOR]