The Loss of Hydrophobic Polypeptides during Fermentation and Conditioning of High Gravity and Low Gravity Brewed Beer

The object of this study was to investigate the loss of hydrophobic polypeptides, which are important for foam quality and stability in finished beer. Loss of hydrophobic polypeptide due to fermenter foaming occurs during transfer of fermented wort since a gradient of hydrophobic polypeptides towards the surface is created during fermentation. Due to higher polyphenol levels in high gravity (20°Plato) wort, more hydrophobic polypeptides are lost due to cold break (cold trub) precipitation compared to low gravity (12°Plato) wort. Another important factor affecting the loss of hydrophobic polypeptides could be proteinase A activity during fermentation, especially in high gravity fermentation where the yeast is exposed the higher stress. During high gravity fermentation, where osmotic pressures are higher, ethanol levels become greater, and nitrogen‐carbohydrate ratios are lower, more proteinase A is released by the yeast. This release of proteinase A into fermenting wort could have implications for the foam stability of the finished product.     

The effect of mischmetal addition on the structure and mechanical properties of a cast Al-7Si-0.3Mg alloy containing excess iron (up to 0.6 Pct)

The effect of Fe content (0.2 to 0.6 pct) on the microstructure and mechanical properties of a cast Al-7Si-0.3Mg (LM 25/356) alloy has been investigated. Further, 1 pct mischmetal (MM) additions (a mixture of rare-earth (RE) elements) were made to these alloys, and their mechanical properties at room and at elevated temperatures (up to 200 °C) were evaluated. A structure-property correlation on this alloy was attempted using optical microstructure analysis, fractographs, X-ray diffraction, energy-dispersive analysis of X-rays (EDX), and quantitative metallography by image analysis. An increase in Fe content increased the volume percentage of Fe-bearing intermetallic compounds (β and π phases), contributing to the loweryield strength (YS), ultimate tensile strength (UTS), percentage elongation, and higher hardness. An addition of 1 pct MM to the alloys containing 0.2 and 0.6 pct Fe was found to refine the microstructure; modify the eutectic silicon and La, Ce, and Nd present in the MM; form different intermetallic compounds with Al, Si, Fe, and Mg; and improve the mechanical properties of the alloys both at room and elevated temperatures.     

Equal-channel angular extrusion of beryllium

The equal-channel angular extrusion (ECAE) technique has been applied to a powder metallurgy (P/M) source Be alloy. Extrusions have been successfully completed on Ni-canned billets of Be at approximately 425°C. No cracking was observed in the billets, and significant grain refinement was achieved. In this article, microstructural features and dislocation structures are discussed for a singlepass extrusion, including evidence of <c> and <c+a> dislocations. Significant crystallographic texture developed during ECAE, which is discussed in terms of this unique deformation processing technique and the underlying physical processes which sustain the deformation. S.R. AGNEW, formerly with the Oak Ridge National Laboratory, Oak Ridge, TN 37831-6115 This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee.     

Terahertz/optical mixing in symmetric semiconductor quantum wells embedded in optical microcavities

A quantum well (QW) in the simultaneous presence of a terahertz field polarized in the growth direction and an incident optical field near an excitonic resonance results in substantial frequency mixing between the terahertz and optical fields. In particular, a response at new frequencies given by the input optical frequency plus or minus multiples of the terahertz frequency occurs-the terahertz sidebands. In a symmetric QW, the dominant contribution to terahertz-sideband formation is the high-frequency modulation of the overlap integral of the relevant conduction- and valence-subband envelope functions that determine the strength of the interband dipole moment. terahertz-sideband generation is shown to be strongly enhanced in a high quality-factor optical microcavity. Numerical values of the reflected intensity into the first terahertz sideband normalized with respect to the reflected intensity at the fundamental as large as /spl sim/10% are estimated. This suggests that terahertz-sideband generation in semiconductor microcavities is a promising option worthy of exploration for wavelength conversion for wavelength-division multiplexing applications.     

A network management architecture for robust packet routing in meshoptical access networks

We describe an architecture for an optical local area network (LAN) or metropolitan area network (MAN) access. The architecture allows for bandwidth sharing within a wavelength and is robust to both link and node failures. The architecture can be utilized with an arbitrary, link-redundant mesh network (node-redundancy is necessary only to handle all node failures), and assumes neither the use of a star topology nor the ability to embed such a topology within the physical mesh. Reservation of, bandwidth is performed in a centralized fashion at a (replicated) head end node, simplifying the implementation of complex sharing policies relative to implementation on a distributed set of routers. Unlike a router, however, the head end does not take any action on individual packets and, in particular, does not buffer packets. The architecture thus avoids the difficulties of processing packets in the optical domain while allowing for packetized shared access of wavelengths. We describe the route construction scheme and prove its ability to recover from single link and single node failures, outline a flexible medium access protocol and discuss the implications for implementing specific policies, and propose a simple implementation of the recovery protocol in terms of state machines for per-link devices     

Investigation of the power dissipation during IGBT turn-off using a new physics-based IGBT compact model

New compact models of the IGBTs (both non-punch through IGBT (NPTIGBT) and punch-through IGBT (PTIGBT)) are presented in this paper. The models are implemented in the SABER circuit simulator and used for a study of IGBT anode current and voltage characteristics during a device turn-off (clamped inductive load circuit with gate controlled turn-off), since these parts of the transient characteristics essentially predict the power dissipation (V×I) inside the device. It is shown that PTIGBTs are faster than NPTIGBTs, this becoming more apparent at higher clamp voltages.     

The Onsager relations analyzed using an ellipsoidal statistical equation

Validity on the well-known Onsager reciprocal relations L ₁₂=L ₂₁ is verified in the kinetic theory of gases taking into account mass and heat transfer near the surface. Using an analytical solution to the ellipsoidal statistical equation (providing for the true Prandtl number), it is demonstrated that the Onsager relations are obeyed, at least to within exponential corrections of the type exp(−1/Kn) in the Knudsen number.     

阻止抬升盆地原油生物降解的深埋灭菌作用

微生物活动造成的原油生物降解作用发生地球中大多数的油藏中，人们认为生物降解作用大大降低油藏中原油的质量，为成功寻找工业油藏，理解地质建造中生物降解作用发生的条件与过程是十分重要的，尽管最近的研究推测微生物活动在温度在150℃仍能有效地发生，但是人们普遍认为在地质时代，有效的石油生物降解作用通常发生在温度低于80℃的储层中，然而奇怪的是在温度低于80℃的储层中，还可发现未降解的原油，本文收集了一些油藏中有关生物降解程度的数据，发现未降角原油局限于埋藏浅的冷盆地，这些盆地曾是地球中更深，更热的部位，后经抬升作用形成的，我们认为这石油储层在深埋过程中，在温度为80－90℃时经历了灭菌作用，使得深部生物圈中降解烃类的生物停止活动，尽管这些储层后期抬升到较冷的部位并再次发生石油充注，也不会发生生物降解作用，表明灭菌后的沉积物不再适合降解烃类的细菌生长。     

Inertia effects on non-parallel thermal instability of natural convection flow over horizontal and inclined plates in porous media

The inertia effect on the onset of thermal instability in natural convection flow over heated horizontal and inclined flat plates embedded in fluid-saturated porous media is analyzed. The linear non-parallel flow model is employed in the instability analysis, which takes into account the streamwise variation as well as the transverse variation of the disturbance amplitude functions. The set of partial differential equations for the disturbance amplitude functions are converted to a system of homogeneous linear ordinary differential equations with homogeneous boundary conditions by the local non-similarity method. The resulting eigenvalue problem is then solved by an implicit finite-difference method. Representative neutral stability curves and critical Rayleigh numbers are presented. It has been found that as the angle of inclination relative to the horizontal increases, the surface heat transfer rate increases, whereas the flow becomes more stable to the vortex mode of instability. Also, as the inertia effect, expressed in terms of Forchheimer number, Fr, increases, the heat transfer rate decreases, but the flow becomes more stable. It is demonstrated that the non-parallel flow model predicts a more stable flow than the parallel flow model.