Ultra-high temperature stability Joule-Thomson cooler with capability to accomodate pressure variations

A Joule-Thomson cryogenic refrigeration system capable of achieving high temperature stabilities in the presence of varying temperature, atmospheric pressure, and heat load is provided. The Joule-Thomson cryogenic refrigeration system includes a demand flow Joule-Thomson expansion valve disposed in a cryostat of the refrigeration system. The expansion valve has an adjustable orifice that controls the flow of compressed gas therethrough and induces cooling and partial liquefaction of the gas. A recuperative heat exchanger is disposed in the cryostat and coupled to the expansion valve. A thermostatically self-regulating mechanism is disposed in the cryostat and coupled to the J-T expansion valve. The thermostatically self-regulating mechanism automatically adjusts the cross sectional area of the adjustable valve orifice in response to environmental temperature changes and changes in power dissipated at a cold head. A temperature sensing and adjusting mechanism is coupled to a cold head for adjusting the temperature of the cold head in response to the change in heat flow in the cold head. The temperature sensing and adjusting mechanism comprises a temperature sensitive diode, a wound wire heater, and an electrical feedback control circuit coupling the diode to the heater. An absolute pressure relief valve is interposed between the output of the cryostat and an exhaust port for maintaining a constant exhaust temperature in the refrigerating system, independent of the changes in atmospheric pressure

A freeze, melt valve and dispensing system for cesium

Design and operation of freeze, melt valve used in vacuum encapsulating cesium for thermionic diode

Spin Diode Based on Fe/MgO Double Tunnel Junction

We demonstrate a spin diode consisting of a semiconductor free nano-scale Fe/MgO-based double tunnel junction. The device exhibits a near perfect spin-valve effect combined with a strong diode effect. The mechanism consistent with our data is resonant tunneling through discrete states in the middle ferromagnetic layer sandwiched by tunnel barriers of different spin-dependent transparency. The observed magneto-resistance is record high, ~4000%, essentially making the structure an on/off spin-switch. This, combined with the strong diode effect, ~100, offers a new device that should be promising for such technologies as magnetic random access memory and re-programmable logic.Comment: 14 page

Local spin valve effect in lateral (Ga,Mn)As/GaAs spin Esaki diode devices

We report on a local spin valve effect observed unambiguously in lateral all-semiconductor all-electrical spin injection devices, employing p+-(Ga,Mn)As/n+-GaAs Esaki diode structures as spin aligning contacts. We discuss the observed local spin-valve signal as a result of interplay between spin-transport-related contribution and tunneling anisotropic magnetoresistance of magnetic contacts. The magnitude of the spin-related magnetoresistance change is equal to 30 Ohm which is twice the magnitude of the measured non-local signal.Comment: submitted to Appl. Phys. Let

Evaluation of Fluid Diodes as Pulmonary Heart Valve Replacements

Children born with congenital heart disease often times suffer from severe chronic pulmonary insufficiency. Palliative treatments for this condition may come early on in the life of the patient; however, if it becomes severe enough, a pulmonary valve replacement may be required. There currently is not a permanent option for a replacements valve. Therefore, a need exists to develop a permanent solution. Knowing that the right heart circulation is more tolerant of moderate levels of regurgitation (0 - 35%) and pressure gradient (0 - 30 mmHg), this study investigates the hypothesis that a fluid diode, a motionless valve that offers low resistance to forward flow and high resistance to reverse flow, could serve as a permanent solution. The diode valve concept was tested in vitro in a mock pulmonary circulatory system (MPCS). Transvalvular pressure gradient (TVG) and regurgitant fraction (RF%) were used to assess valve performance. The valve was tested in vitro over a range of pulmonary vascular resistances (PVR). In vivo testing was completed using a swine model. A parametric study was also done to find the effect of changing geometries on the flow regulating capabilities of the valves. Finally, flow field studies were performed using particle image velocimetry (PIV). The flow patterns, viscous shear and Reynolds shear stresses were analyzed, and the potential for platelet activation and thrombus formation was determined. In the in vitro studies, the fluid diode maintained the RF% between 2% and 17% and TVG less than 17 mmHg for PVR values between 1 and 5 mmHg/Lpm. The diode performed acceptably in the animal model as well for PVR between 2.3 and 3mmHg/Lpm and pulmonary vascular compliance (PVC) between 2 to 3 mL/mmHg. The parametric study identified the angle of impingement and beta ratio as two dimensions that affect the valve performance. The total shear stress level and exposure times were found using the PIV data. The level of activation was found to be a function of PVR and, for PVR values below 6 mmHg/Lpm, the threshold reported to trigger platelet activation was not exceeded. As a whole, the study has shown that the diode valve concept shows promise as a replacement pulmonary valve. The fluid diode is capable of regulating flow to acceptable levels for some ranges of PVR and PVC

Pulsed energy power system Patent

Pulsed energy power system for application of combustible gases to turbine controlling ac voltage generato

Elastomeric microfluidic diode and rectifier work with Newtonian fluids

We report on two microfluidic elastomeric autoregulatory devices—a diode and a rectifier. They exhibit physically interesting and complex nonlinear behaviors (saturation, bias-dependent resistance, and rectification) with a Newtonian fluid. Due to their autoregulatory properties, they operate without active external control. As a result, they enable increased microfluidic device density and overall system miniaturization. The demonstrated diode and rectifier would also be useful components in future microfluidic logic circuitry

Size Dependence of the Magnetic and Electrical Properties of the Spin-Valve Transistor

The electrical and magnetic properties of the spin-valve transistor (SVT) are investigated as a function of transistor size. A new fabrication process, designed to study the size dependence of the SVT properties, uses: silicon-on-insulator (SOI) wafers, a combination of ion beam and wet etching and a negative tone photoresist (SU8) as an insulating layer. The Si/Pt emitter and Si/Au collector Schottky barrier height do not depend on the transistor dimensions. The parasitic leakage current of the Si/Au collector is, however, proportional to its area. The relative collector current change with magnetic field is 240%, independent of size, while the transfer ratio starts to decrease for SVTs with an emitter area below 25 × 25 ¿m2. The maximum input current is found to be limited by the maximum current density allowed in the base (1.7 × 107 A/cm2), which is in agreement with the maximum current density for spin valve

On-off switch and sign change for non-local Josephson diode in spin-valve Andreev molecules

Andreev molecules consist of two coherently coupled Josephson junctions and permit non-local control over supercurrents. By making the barriers magnetic and thus creating a spin-valve, we predict that a non-local Josephson diode effect occurs that is switchable via the magnetic configuration of the barriers. The diode effect is turned on, off, or changes its sign depending on whether the spin-valve is in a parallel, normal, or antiparallel configuration. These results offer a way to exert complete control over a non-local Josephson diode effect via the spin degree of freedom rather than varying a global magnetic flux which affects the entire system and likely neighbouring components in a device architecture.Comment: 5 pages, 4 figure