Centrifugal Compressor Configuration, Selection and Arrangement: A User's Perspective

TutorialThe detailed sizing and selection of centrifugal compressors may be somewhat of a mystery to the typical user. Once the suction and discharge process conditions and required flow rates are established, they are submitted to an equipment supplier for sizing and selection. The resulting combination of impeller diameters, casing sizes and operating speed determined by the equipment supplier can be puzzling to the engineer charged with evaluating the selections. This tutorial is intended to introduce the dimensional and dimensionless similarity parameters that can be utilized to perform an independent, equivalent selection for a compression application or provide a more thorough evaluation of the selections provided by an equipment supplier. These performance parameters will allow prediction of design point head and efficiency, approximate impeller diameters, and approximate compressor operating speeds. Furthermore, the inter-relationship between impeller diameter and rotational speed will be investigated to highlight the trade-offs in changing either of these design variables. The tutorial will also investigate useful mechanical parameters and guidelines that allow comparative preliminary assessment of proposed designs. When significant head and/or flow requirements exist for a specific application, it becomes necessary to divide the compression service into multiple sections and in some situations multiple casings. Although a few different ways to configure multiple compressor sections exist, there are benefits and issues associated with each of these configurations. The potential benefits and issues of different arrangement options will also be addressed in this tutorial

Application of Dynamic pressure-balanced Seals in a Multi-stage Centrifugal Compressor

LectureTest results for an ASME Power Test Code 10 (PTC) Type 1 test of a 4,500 psia (310 Bara) discharge pressure gas lift centrifugal compressor outfitted with dynamic pressure-balanced seals at the impeller eyes; shaft interstage and division wall locations are presented and compared to the same testing with conventional labyrinth seals. Both aerodynamic performance and rotor dynamic stability, obtained via operational modal analysis (OMA), are presented. A client’s motivation, along with the design and testing of dynamic pressure-balanced (DPB) seals for turbomachinery are also presented in this paper. With the DPB seals installed the test results indicate 2.8 percent lower power was required for the same head level across the entire range of inlet flows and pressure ratios, when compared to the same testing with conventional labyrinth seals. Rotordynamic stability, obtained via operational modal analysis (OMA), showed the dynamic pressure-balanced (DPS) seals exhibited log decs similar to standard labyrinth seals across the entire range of flows and pressure ratios. The foregoing demonstrates both the aerodynamic and mechanical/rotordynamic integrity of the dynamic pressure-balanced seals for oil and gas, turbomachinery applications

Hitchhiker’s Guide to Voltammetry: Acute and Chronic Electrodes for in Vivo Fast-Scan Cyclic Voltammetry

Fast-scan cyclic voltammetry (FSCV) has been used for over 20 years to study rapid neurotransmission in awake and behaving animals. These experiments were first carried out with carbon-fiber microelectrodes (CFMs) encased in borosilicate glass, which can be inserted into the brain through micromanipulators and guide cannulas. More recently, chronically implantable CFMs constructed with small diameter fused-silica have been introduced. These electrodes can be affixed in the brain with minimal tissue response, which permits longitudinal measurements of neurotransmission in single recording locations during behavior. Both electrode designs have been used to make novel discoveries in the fields of neurobiology, behavioral neuroscience, and psychopharmacology. The purpose of this Review is to address important considerations for the use of FSCV to study neurotransmitters in awake and behaving animals, with a focus on measurements of striatal dopamine. Common issues concerning experimental design, data collecti..

Intra- and inter-individual genetic differences in gene expression

Genetic variation is known to influence the amount of mRNA produced by a gene. Given that the molecular machines control mRNA levels of multiple genes, we expect genetic variation in the components of these machines would influence multiple genes in a similar fashion. In this study we show that this assumption is correct by using correlation of mRNA levels measured independently in the brain, kidney or liver of multiple, genetically typed, mice strains to detect shared genetic influences. These correlating groups of genes (CGG) have collective properties that account for 40-90% of the variability of their constituent genes and in some cases, but not all, contain genes encoding functionally related proteins. Critically, we show that the genetic influences are essentially tissue specific and consequently the same genetic variations in the one animal may up-regulate a CGG in one tissue but down-regulate the same CGG in a second tissue. We further show similarly paradoxical behaviour of CGGs within the same tissues of different individuals. The implication of this study is that this class of genetic variation can result in complex inter- and intra-individual and tissue differences and that this will create substantial challenges to the investigation of phenotypic outcomes, particularly in humans where multiple tissues are not readily available.

&#xa

A quantitative account of genomic island acquisitions in prokaryotes

<p>Abstract</p> <p>Background</p> <p>Microbial genomes do not merely evolve through the slow accumulation of mutations, but also, and often more dramatically, by taking up new DNA in a process called horizontal gene transfer. These innovation leaps in the acquisition of new traits can take place via the introgression of single genes, but also through the acquisition of large gene clusters, which are termed Genomic Islands. Since only a small proportion of all the DNA diversity has been sequenced, it can be hard to find the appropriate donors for acquired genes via sequence alignments from databases. In contrast, relative oligonucleotide frequencies represent a remarkably stable genomic signature in prokaryotes, which facilitates compositional comparisons as an alignment-free alternative for phylogenetic relatedness.</p> <p>In this project, we test whether Genomic Islands identified in individual bacterial genomes have a similar genomic signature, in terms of relative dinucleotide frequencies, and can therefore be expected to originate from a common donor species.</p> <p>Results</p> <p>When multiple Genomic Islands are present within a single genome, we find that up to 28% of these are compositionally very similar to each other, indicative of frequent recurring acquisitions from the same donor to the same acceptor.</p> <p>Conclusions</p> <p>This represents the first quantitative assessment of common directional transfer events in prokaryotic evolutionary history. We suggest that many of the resident Genomic Islands per prokaryotic genome originated from the same source, which may have implications with respect to their regulatory interactions, and for the elucidation of the common origins of these acquired gene clusters.</p

Marketing and advertising online sports betting: a problem gambling perspective

In this article, online sports betting is explored with the objective of critically examining the potential impact on problem gambling of the emerging product features and advertising techniques used to market it. First, the extent of the issue is assessed by reviewing the sports betting prevalence rates and its association with gambling disorders, acknowledging the methodological difficulties of an unambiguous identification of what exactly constitutes sports-related gambling today. Second, the main changes in the marketization of online betting products are outlined, with specific focus on the new situational and structural characteristics that such products present along with the convergence of online betting with other adjacent products. Third, some of the most prevalent advertising master narratives employed by the betting industry are introduced, and the implications for problem gamblers and minors are discussed

Surface Phenotype and Functionality of WNV Specific T Cells Differ with Age and Disease Severity

West Nile virus (WNV) infection can result in severe neuroinvasive disease, particularly in persons with advanced age. As rodent models demonstrate that T cells play an important role in limiting WNV infection, and strong T cell responses to WNV have been observed in humans, we postulated that inadequate antiviral T cell immunity was involved in neurologic sequelae and the more severe outcomes associated with age. We previously reported the discovery of six HLA-A*0201 restricted WNV peptide epitopes, with the dominant T cell targets in naturally infected individuals being SVG9 (Env) and SLF9 (NS4b). Here, memory phenotype and polyfunctional CD8+ T cell responses to these dominant epitopes were assessed in 40 WNV seropositive patients displaying diverse clinical symptoms. The patients' PBMC were stained with HLA-I multimers loaded with the SVG9 and SLF9 epitopes and analyzed by multicolor flow cytometry. WNV-specific CD8+ T cells were found in peripheral blood several months post infection. The number of WNV-specific T cells in older individuals was the same, if not greater, than in younger members of the cohort. WNV-specific T cells were predominantly monofunctional for CD107a, MIP-1β, TNFα, IL-2, or IFNγ. When CD8+ T cell responses were stratified by disease severity, an increased number of terminally differentiated, memory phenotype (CD45RA+ CD27− CCR7− CD57+) T cells were detected in patients suffering from viral neuroinvasion. In conclusion, T cells of a terminally differentiated/cytolytic profile are associated with neuroinvasion and, regardless of age, monofunctional T cells persist following infection. These data provide the first indication that particular CD8+ T cell phenotypes are associated with disease outcome following WNV infection

N-terminal Domain of Prion Protein Directs Its Oligomeric Association

The self-association of prion protein (PrP) is a critical step in the pathology of prion diseases. It is increasingly recognized that small non-fibrillar ?-sheet-rich oligomers of PrP may be of crucial importance in the prion disease process. Here, we characterize the structure of a well defined ?-sheet-rich oligomer, containing ?12 PrP molecules, and often enclosing a central cavity, formed using full-length recombinant PrP. The N-terminal region of prion protein (residues 23-90) is required for the formation of this distinct oligomer; a truncated form comprising residues 91-231 forms a broad distribution of aggregated species. No infectivity or toxicity was found using cell and animal model systems. This study demonstrates that examination of the full repertoire of conformers and assembly states that can be accessed by PrP under specific experimental conditions should ideally be done using the full-length protein

Inhibition of the inositol kinase Itpkb augments calcium signaling in lymphocytes and reveals a novel strategy to treat autoimmune disease

Emerging approaches to treat immune disorders target positive regulatory kinases downstream of antigen receptors with small molecule inhibitors. Here we provide evidence for an alternative approach in which inhibition of the negative regulatory inositol kinase Itpkb in mature T lymphocytes results in enhanced intracellular calcium levels following antigen receptor activation leading to T cell death. Using Itpkb conditional knockout mice and LMW Itpkb inhibitors these studies reveal that Itpkb through its product IP4 inhibits the Orai1/Stim1 calcium channel on lymphocytes. Pharmacological inhibition or genetic deletion of Itpkb results in elevated intracellular Ca2+ and induction of FasL and Bim resulting in T cell apoptosis. Deletion of Itpkb or treatment with Itpkb inhibitors blocks T-cell dependent antibody responses in vivo and prevents T cell driven arthritis in rats. These data identify Itpkb as an essential mediator of T cell activation and suggest Itpkb inhibition as a novel approach to treat autoimmune disease