The noncavitating performance and life of a small vane-type positive displacement pump in liquid hydrogen

The low flow rate and high head rise requirements of hydrogen/oxygen auxiliary propulsion systems make the application of centrifugal pumps difficult. Positive displacement pumps are well-suited for these flow conditions, but little is known about their performance and life characteristics in liquid hydrogen. An experimental and analytical investigation was conducted to determine the performance and life characteristics of a vane-type, positive displacement pump. In the experimental part of this effort, mass flow rate and shaft torque were determined as functions of shaft speed and pump pressure rise. Since liquid hydrogen offers little lubrication in a rubbing situation, pump life is an issue. During the life test, the pump was operated intermittently for 10 hr at the steady-state point of 0.074 lbm/sec (0.03 kg/sec) flow rate, 3000 psid (2.07 MPa) pressure rise, and 8000 rpm (838 rad/sec) shaft speed. Pump performance was monitored during the life test series and the results indicated no loss in performance. Material loss from the vanes was recorded and wear of the other components was documented. In the analytical part of this effort, a comprehensive pump performance analysis computer code, developed in-house, was used to predict pump performance. The results of the experimental investigation are presented and compared with the results of the analysis. Results of the life test are also presented

Identification of New mRNA Targets of Puf Protein-Mediated Decay in Yeast

Precise regulation of gene expression is accomplished at many levels. Puf proteins are a widely conserved family of RNA binding proteins that regulate gene expression by influencing the stability of their target mRNA transcripts. Puf family members have been characterized as transcript-specific repressors in Drosophila, Dictyostelium, mouse, C. elegans, and Xenopus. In S. cerevisiae, there are 5 conserved Puf family members. Two of them, Puf3p and Puf5p, are known to destabilize their mRNA targets, down-regulating gene expression. The remaining yeast Pufs, Puf1p, Puf2p and Puf4p, are homologous to Puf3p and Puf5p, suggesting that they too have regulatory roles not yet observed. In this work, I attempt to identify new mRNA targets of Puf mediated decay in yeast. In particular, I am interested in targets of the uncharacterized yeast Pufs. The ability of a Puf protein to regulate its target transcript is dependent on Puf binding to a conserved element in the 3¿UTR of the target mRNA. A search for similar 3¿UTR elements and previous microarray data helped to identify numerous potential mRNA targets of Puf-mediated decay. In this work, experimental analysis of the candidate mRNAs positively identified three new targets of Puf mediated mRNA decay. Two of the targets, HXK1 and TIF1, are destabilized in vivo by Puf1p and Puf5p, respectively. The third target, YHB1, is actually stabilized by Puf2p. Interestingly, while the TIF1 and HXK1 3¿UTRs are sufficient for Puf mediated decay as expected, the YHB1 3¿UTR is not sufficient to confer Puf2p mediated decay onto the MFA2 coding region. In addition to these functional studies, I also demonstrate Puf interaction with conserved sequence elements in each 3¿UTR. Together, my work provides evidence that all yeast Puf proteins selectively regulate mRNA decay, and in some cases, Puf proteins may up-regulate gene expression

Puf1p-MEDIATED mRNA DECAY AND COMBINATORIAL CONTROL OF mRNA STABILITY BY THE YEAST Puf PROTEINS

The stability of a messenger RNA (mRNA) is a highly regulated and important aspect of gene expression. Proteins that regulate mRNA stability often bind to 3\u27 untranslated region (UTR) sequence elements. The eukaryotic Puf proteins are one class of 3\u27UTR binding proteins that regulate the stability and expression of their target transcripts. Several global genome analyses have identified hundreds of potential mRNA targets of the Saccharomyces cerevisiae Puf proteins, however only three mRNA targets for these proteins have been characterized thus far. After direct testing of nearly forty candidate mRNAs, I have established three of these as true mRNA targets of Puf-mediated decay in yeast, YHB1, HXK1 and TIF1. In a novel finding, multiple Puf proteins, including Puf1p, regulate HXK1 and TIF1 mRNAs in combination. TIF1 mRNA decay can be stimulated individually by Puf1p and Puf5p, but the combination of both proteins is required for full regulation. This Puf-mediated decay requires the presence of two UGUA binding sites within the TIF1 3\u27UTR, with one site regulated by Puf5p and the other by both Puf1p and Puf5p. The stability of the endogenously transcribed HXK1 mRNA, cellular levels of Hxk1 protein activity, and HXK1 3\u27UTR-directed decay are affected by Puf1p and Puf5p as well as Puf4p. YHB1 mRNA decay is mediated by Puf5p and also requires a UGUA sequence element. This work has discovered the first targets of Puf1-mediated decay. Since much of our knowledge of the mechanism suggests that Puf protein target recognition and mechanism of action varies with each of these proteins, I investigate the mechanism of Puf1p-mediated decay using a variety a techniques. The results of this research aid in our understanding of the similar, yet distinct, decay regulation of Puf proteins in yeast and higher organisms

In-Situ Defect Detection in Laser Powder Bed Fusion by Using Thermography and Optical Tomography—Comparison to Computed Tomography

Among additive manufacturing (AM) technologies, the laser powder bed fusion (L-PBF) is one of the most important technologies to produce metallic components. The layer-wise build-up of components and the complex process conditions increase the probability of the occurrence of defects. However, due to the iterative nature of its manufacturing process and in contrast to conventional manufacturing technologies such as casting, L-PBF offers unique opportunities for in-situ monitoring. In this study, two cameras were successfully tested simultaneously as a machine manufacturer independent process monitoring setup: a high-frequency infrared camera and a camera for long time exposure, working in the visible and infrared spectrum and equipped with a near infrared filter. An AISI 316L stainless steel specimen with integrated artificial defects has been monitored during the build. The acquired camera data was compared to data obtained by computed tomography. A promising and easy to use examination method for data analysis was developed and correlations between measured signals and defects were identified. Moreover, sources of possible data misinterpretation were specified. Lastly, attempts for automatic data analysis by data integration are presented

Tracking spin and charge with spectroscopy in spin-polarised 1D systems

We calculate the spectral function of a one-dimensional strongly interacting chain of fermions, where the response can be well understood in terms of spinon and holon excitations. Upon increasing the spin imbalance between the spin species, we observe the single-electron response of the fully polarised system to emanate from the holon peak while the spinon response vanishes. For experimental setups that probe one-dimensional properties, we propose this method as an additional generic tool to aid the identification of spectral structures, e.g. in ARPES measurements. We show that this applies even to trapped systems having cold atomic gas experiments in mind.Comment: 5 pages, 4 figure

Modelling and control of a water jet cutting probe for flexible surgical robot

Surgical removal of cancerous tissue from the spine is limited by the inability of hand held drills and cutting tools to reach small crevices present in complex bones such as the spinal column, especially on the anterior side. In addition, the high speed rotating mechanisms used presently are subject to stability issues when manoeuvring around tortuous bone forms. We report on the design and experimental testing of a novel flexible robotic surgical system which addresses these issues. The robot consists of a flexible probe, a water jet cutting system, and a haptic feedback controller. The water jet cutting system consists of a flexible end effector capable of bending around the anterior of the spinal column for tissue removal. A new experimental method of controlling the depth of water jet cut is described. The haptic feedback controller is based on a constraint set approach to define 3D boundaries, based on five key types of constraints. Experimental outcomes of measuring the depth of water jet cut were combined with haptic regional constraints with the aim of improving the safety of surgical procedures. The reliability, accuracy and performance of the prototype robot were tested in a mock surgical procedure on the lower lumbar vertebrae. Results show promise for the implementation of water jet cutting for robotic surgical spinal procedures