Operational Stability Limits in Rotating Detonation Engine Numerical Simulations

An instability is described which arises in computational fluid dynamic (CFD) simulations of semi-idealized rotating detonation engines (RDE) configured with a throat at the exit. Its existence is verified by examining output from two independently developed CFD codes simulating the same configuration and producing solutions that agree well. The instability is shown to be thermo-acoustic in that a spatial integral of the product of pressure and heat release fluctuations develops a regular oscillation which grows in time. The instability can become severe enough to cause detonation failure. Its onset is shown to be closely linked to the size of the exit throat and the size of the inlet restriction; both parameters that strongly influence RDE performance. It is shown that the instability places a cap on ideal RDEperformance, but that an optimized exhaust throat and inlet restriction combination still yields substantial pressure gain. Other parametric sensitivities are also examined in terms ofinstability growth. These include axial length, inlet manifold pressure, and air-fuel ratio

CFD modeling of microwave electrothermal thrusters

Microwave-heated plasmas in convergent nozzles are analyzed using a coupled Maxwell and Navier-Stokes solver to examine relevant issues associated with microwave thermal propulsion. Parametric studies are conducted to understand the effect of power, pressure, and plasma location with respect to the nozzle throat. For nozzles in the 0.5 to 3 N range with helium flow, results show that specific impulses up to 550-650 seconds are possible, with further increases being limited by severe wall-heating. Coupling efficiencies of over 90 percent are consistently obtained, with overall efficiencies ranging from 40 percent to 80 percent. Size scale-up studies-done by scaling the frequency from 2.45 GHz to 0.91 GHz-indicate that plasma migration toward the walls occurs more frequently for the lower frequency. Increasing the cavity aspect ratio and detuning the cavity are found to be effective ways of keeping the plasma on axis

The role of chemotherapy in the management of newly diagnosed brain metastases: a systematic review and evidence-based clinical practice guideline

TARGET POPULATION: This recommendation applies to adults with newly diagnosed brain metastases; however, the recommendation below does not apply to the exquisitely chemosensitive tumors, such as germinomas metastatic to the brain. RECOMMENDATION: Should patients with brain metastases receive chemotherapy in addition to whole brain radiotherapy (WBRT)? Level 1 Routine use of chemotherapy following WBRT for brain metastases has not been shown to increase survival and is not recommended. Four class I studies examined the role of carboplatin, chloroethylnitrosoureas, tegafur and temozolomide, and all resulted in no survival benefit. Two caveats are provided in order to allow the treating physician to individualize decision-making: First, the majority of the data are limited to non small cell lung (NSCLC) and breast cancer; therefore, in other tumor histologies, the possibility of clinical benefit cannot be absolutely ruled out. Second, the addition of chemotherapy to WBRT improved response rates in some, but not all trials; response rate was not the primary endpoint in most of these trials and end-point assessment was non-centralized, non-blinded, and post-hoc. Enrollment in chemotherapy-related clinical trials is encouraged