Mach 4 Performance of a Fixed-Geometry Hypersonic Inlet with Rectangular-to-Elliptical Shape Transition
Wind-tunnel testing of a hypersonic inlet with rectangular-to-elliptical shape transition has been conducted at Mach 4.0. These tests were performed to investigate the starting and back-pressure limits of this fixed-geometry inlet at conditions well below the Mach 5.7 design point. Results showed that the inlet required side spillage holes in order to self-start at Mach 4.0. Once started, the inlet generated a compression ratio of 12.6, captured almost 80% of available air and withstood a back-pressure ratio of 30.3 relative to tunnel static pressure. The spillage penalty for self-starting was estimated to be 4% of available air. These experimental results, along with previous experimental results at Mach 6.2 (Smart, M.K, “Experimental Testing of a Hypersonic Inlet with Rectangular-to-Elliptical Shape Transition”, Journal of Propulsion and Power, Vol. 17, No. 2, pp 276-283, 2001)indicate that fixed-geometry inlets with rectangular-toelliptical shape transition are a viable configuration for airframe-integrated scramjets that operate over a significant Mach number range.
Design of Three-Dimensional Hypersonic Inlets with Rectangular-to-Elliptical Shape Transition
A methodology has been devised for the design of three-dimensional hypersonic Inlets, This methodology makes extensive use of inviscid stream-tracing techniques to generate an inlet with smooth shape transition from a rectangular-like capture to an elliptical throat. Highly swept leading edges and a significantly notched cowl enable use of these inlets in fixed geometry configurations. The design procedure includes a three-dimensional viscous correction and uses established correlations to check for boundary-layer separation caused by shock wave interactions. Complete details of the design procedure are presented and the characteristics of a modular inlet with a design point of Mach 6.0 are examined. Comparison with a classical two-dimensional inlet optimized for maximum total pressure recovery indicates that these three-dimensional inlets demonstrate good inviscid performance even when operating well below the design point. An estimate of the on-design viscous performance corresponds with that of an efficient inlet for scramjet applications.
Negatively charged phospholipids trigger the interaction of a bacterial Tat substrate precursor protein with lipid monolayers.
Folded proteins can be translocated across biological membranes via the Tat machinery. It has been shown in vitro that these Tat substrates can interact with membranes prior to translocation. Here we report a monolayer and infrared reflection-absorption spectroscopic (IRRAS) study of the initial states of this membrane interaction, the binding to a lipid monolayer at the air/water interface serving as a model for half of a biological membrane. Using the model Tat substrate HiPIP (high potential iron-sulfur protein) from Allochromatium vinosum, we found that the precursor preferentially interacts with monolayers of negatively charged phospholipids. The signal peptide is essential for the interaction of the precursor protein with the monolayer because the mature HiPIP protein showed no interaction with the lipid monolayer. However, the individual signal peptide interacted differently with the monolayer compared to the complete precursor protein. IRRA spectroscopy indicated that the individual signal peptide forms mainly aggregated β-sheet structures. This β-sheet formation did not occur for the signal peptide when being part of the full length precursor. In this case it adopted an α-helical structure upon membrane insertion. The importance of the signal peptide and the mature domain for the membrane interaction is discussed in terms of current ideas of Tat substrate-membrane interactions.