Rows Of Wires Research Articles

Molecular dynamics simulation of periodic flow containing contaminant in the regenerator

The lifespan of regenerative refrigerators is predominantly influenced by contamination. This paper studies the interaction between N2 and regenerator wire at a microscopic scale for the first time. A section of regenerator wire is simulated using molecular dynamics to investigate the impacts of temperature, charging pressure, and contamination amount. Based on the single-wire model, it indicates that N2 initially forms clusters and then adheres to the wire surface when the temperature is below 80 K. Clusters decrease in size as the temperature rises from 80 K to 90 K. The quantity of N2 attached to the wire decreases by 50% when the temperature reaches 130 K and decreases to 0 at 170 K. Charging pressure and contamination amount slightly affect adsorption. When a row of wires is aligned perpendicular to the flow, adsorption rates are fast and the adsorption process is completed in several cycles. At 50 K, the size of the largest cluster decreases by 80.6%, marking the greatest reduction. Based on this, the paper proposes that N2 will mostly congeal within the regenerator between 90 K and 70 K while the refrigerator operates. This study establishes a theoretical foundation for further exploration of contamination-induced failure mechanisms.

Mean compression ratio of a self-expandable valve is associated with the need for pacemaker implantation after transcatheter aortic valve replacement

BackgroundThe risk and timing of permanent pacemaker implantation (PPMI) after transcatheter aortic valve replacement (TAVR) is still hard to predict. We aimed to analyze the relationship between the compression ratio of a self-expandable valve (SEV) and the need for PPMI after TAVR.MethodsA total of 106 patients who were implanted with the VitaFlow transcatheter aortic valve system and for whom complete imaging information was available were included in this retrospective cohort study. Eight lines perpendicular to the long axis of the SEV were drawn (the top and bottom of the SEV and the intersection of each row of wires) for measurement purposes. The compression ratio was calculated as 1 − (in vivo meridian/in vitro meridian) and compared between patients undergoing and those not undergoing PPMI after adjusting for implantation depth. Multivariable logistic regression and Cox proportional hazards models were used to assess factors associated with the risk and timing of the need for PPMI.ResultsFifteen (14.2%) patients underwent PPMI after TAVR. Patients with a higher mean compression ratio (20%, odds ratio [OR] = 214.82; p < 0.001) and prior right bundle branch block (OR = 51.77; p = 0.015) had a higher risk of the need for PPMI after TAVR. These two factors were also associated with the timing of PPMI, according to the Cox proportional hazards model.ConclusionsThe compression ratio of the SEV was positively associated with the risk of PPMI after TAVR, and the association was most significant in the annular and supravalvular planes. The compression ratio may also affect the time to PPMI.

Aerodynamic Effects of Knitted Wire Meshes—CFD Simulations of the Flow Field and Influence on the Flow Separation of a Backward-Facing Ramp

Passive flow control techniques are needed to reduce flow separation and enhance aerodynamic performance. In this work, the effect of a knitted wire mesh on the flow separation of a backward-facing ramp was numerically investigated for a Reynolds number of 3000. A grid independence study and a RANS turbulence model sensitivity analysis were conducted. The CFD simulations exhibited counter-rotating streamwise vortices emerging from the knitted wire mesh, and the reattachment length was significantly reduced. A variation of the knitted wire rows revealed a maximum reduction of the reattachment length of 25.7% for the case of four rows. A comparison with a different knitted wire mesh geometry yielded a decreased reattachment length reduction.

X-ray pulse shaping in experiments with planar wire arrays at the 1.6 MA Zebra generator

The shaping of the x-ray radiation pulse is very important in both radiation physics research and Inertial Confinement Fusion studies. The novel planar wire array (PWA) was found to be the effective radiator tested at the university-scale 1.6 MA, 100 ns Zebra generator. The single PWA consists of a single row of wires that are parallel to each other, while the double planar wire array (DPWA) and triple planar wire array (TPWA) include two or three parallel plane wire rows, respectively. All multi-planar geometries resulted in a cascade-type array implosion with a complicated multi-step precursor formation before plasma stagnation. The PWAs (without additional core foam target) feature a dynamic precursor evolution that is a powerful tool for x-ray pulse shaping. The shape and timing of the x-ray pulse from different PWAs were theoretically predicted and experimentally analyzed for a variety of planar wire arrays.

Toward a constructive homogenization theory of composite metamaterials

AbstractIn the homogenization of composite metamaterials the role played by the relative positions of the wires and resonators is not well understood, though essential. We present an effective medium approach which can systematically account for these effects. It involves independently homogenizing rows of wires and planes of resonators as slabs with negative permittivity and permeability respectively. The metamaterial is then treated as a 1D single negative anisotropic stack. Using this approach we show that it is in principle possible to satisfy the requirements of Pendry's superlens, [mu]=[epsilon]=-1 , up to losses. We propose a class of structure geometries which seems promising for achieving this holy grail of metamaterial science.

Resonant frequencies of post–wall waveguide cavities

A new method is presented for predicting the resonant frequencies of post–wall rectangular waveguide cavities, in which the narrow walls of the guide are composed of rows of vias. By interpreting the fields inside the guide as a superposition of plane waves, the surface impedance of a row of wires, when illuminated by a plane wave, is used to model the narrow walls of the waveguide. The derivation leads to equivalent rectangular waveguide dimensions that are then used to calculate the resonant frequencies of the cavity. Theoretical results are compared with the observed TE10m resonant frequencies of several post–wall waveguide cavities fabricated in low temperature cofired ceramic (LTCC). The results confirm that the method improves the resonant frequency prediction when the pitch of the vias is at least ten times greater than their radius.

AC Loss in the Coil of a Nonideal Type 2 Superconductor. I. A Row of Wires in a Transverse Magnetic Field

A theoretical expression for the AC loss of the row of wires of nonideal type 2 superconductors in a transverse AC magnetic field is derived with the aid of the critical-state model. The applicability of the present calculation is limited to the so-called semi-quasistatic AC loss of the wires with a pinning force of the Bean-London type in a high DC bias field. Compared with the usual simple slab approximation for a coil, a striking difference is found in some cases with regard to the flux penetration and the value of the AC loss.

THE SENSITIVITY OF ECHOLOCATION IN BATS

1. The distance at which bats (Myotis lucifugus) react to the presence of a row of small wires has been measured by a photographic determination of the distance at which the pulse repetition rate first increases as the bats fly towards the wires. Distinct changes in this rate were measured in almost every flight towards wires spaced 30 cm. apart and ranging in diameter from 0.18 to 3 mm. 2. The interval between successive pulses averaged 60 to 80 msec as the bats flew along the room towards the row of wires, and dropped to 20-40 msec just before the barrier. The intervals decreased less with the smaller sizes of wire. 3. All but the largest of these wires are well below one wave-length of the emitted sounds of these bats (50-60 kc, or 6-7 mm., at the peak intensity and 120 kc, or about 3 mm., at the very beginning of some pulses). 4. Clear evidence that the wires had been detected was furnished at the point where the interval between pulses first dropped significantly below the level that prevailed before and after the approach to the row of wires. This average distance of first vocal reaction to the row of wires was 215 cm. for 3-mm. wire, 185 cm. for 1.07-mm., 150 cm. for 0.65-mm., 120 for 0.54-mm., 105 cm. for 0.28-mm., and 90 cm. for 0.18-mm. A conservative correction for reaction time and the acoustic delay between the bat and the microphone indicates that the distance of first detection must have been at least 10 cm. greater than these distances of reaction. 5. Since small wires can be detected at distances of as much as 5500 times the wire diameter, and well before the bat gives evidence by its flight pattern that it is aware of them, it appears likely that larger objects are detected at considerably greater distances.