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Normal Pressure (normal + pressure)

Distribution by Scientific Domains
Chemistry57%

Terms modified by Normal Pressure

  • normal pressure hydrocephalus
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    Selected Abstracts

    Alternative stripper configurations for CO2 capture by aqueous amines

    AICHE JOURNAL, Issue 12 2007
    Babatunde A. Oyenekan
    Abstract Aqueous absorption/stripping is a promising technology for the capture of CO2 from existing or new coal-fired power plants. Four new stripper configurations (matrix, internal exchange, flashing feed, and multipressure with split feed) have been evaluated with seven model solvents that approximate the thermodynamic and rate properties of 7m (30 wt %) monoethanolamine (MEA), potassium carbonate promoted by piperazine (PZ), promoted MEA, methyldiethanolamine (MDEA) promoted by PZ, and hindered amines. The results show that solvents with high heats of absorption (MEA, MEA/PZ) favor operation at normal pressure. The relative performance of the alternative configurations is matrix > internal exchange > multipressure with split feed > flashing feed. MEA/PZ and MDEA/PZ are attractive alternatives to 7m MEA. The best solvent and process configuration, matrix with MDEA/PZ, offers 22 and 15% energy savings over the baseline and improved baseline, respectively, with stripping and compression to 10 MPa. The energy requirement for stripping and compression to 10 MPa is about 20% of the power output from a 500 MW power plant with 90% CO2 removal. © 2007 American Institute of Chemical Engineers AIChE J, 2007 [source]

    The self-hosting structure of ,-Ta

    ACTA CRYSTALLOGRAPHICA SECTION B, Issue 1 2002
    Alla Arakcheeva
    Using electrodeposition from a bath of molten fluorides, single crystals of tetragonal ,-tantalum have been obtained for the first time at normal pressure. The unit-cell parameters are a = 10.211,(3), c = 5.3064,(10),Å, space group P21m. The ,-Ta structure belongs to the ,-type Frank,Kasper structures which are typical for binary intermetallic compounds and ,-U. In comparison to the ,-type, additional intercalated Ta atoms (population factor ,0.01) have been detected between the atoms located in the channels of the structure. The shorter interatomic distances observed between the channel atoms in comparison with the atoms of the framework justify the `self-hosting' characteristic. ,-Ta exhibits common features with the complex tetragonal structures of the high-pressure phases for the elements Rb, Ba, Sr, Bi and Sb. [source]

    Reversal of benign prostate hyperplasia by selective occlusion of impaired venous drainage in the male reproductive system: novel mechanism, new treatment

    ANDROLOGIA, Issue 5 2008
    Y. Gat
    Summary The prostate is an androgen-regulated exocrine gland producing over 30% of the noncellular components of the semen and promoting optimal conditions for survival and motility of sperm in the vagina. Benign prostate hyperplasia (BPH) is the most common benign neoplasm in men. Its aetiology is not clear, and therefore, current medical treatments are directed towards the symptoms. Though testosterone is known to be the promoter of prostate cell proliferation, no causal relation between serum testosterone levels and BPH has been found. In this study, we propose a novel and tested pathophysiological mechanism for the evolution of BPH and suggest a tested and effective treatment. We found that in all BPH patients, the one-way valves in the vertically oriented internal spermatic veins are destroyed (clinically manifested as varicocele), causing elevated hydrostatic pressure, some 6-fold greater than normal, in the venous drainage of the male reproductive system. The elevated pressure propagates to all interconnected vessels leading to a unique biological phenomenon: venous blood flows retrograde from the higher pressure in the testicular venous drainage system to the low pressure in the prostatic drainage system directly to the prostate (law of communicating vessels). We have found that free testosterone levels in this blood are markedly elevated, with a concentration of some 130-fold above serum level. Consequently, the prostate is exposed to: (i) increased venous pressure that causes hypertrophy; (ii) elevated concentration of free testosterone causing hyperplasia. We have treated 28 BPH patients using a technique that restores normal pressure in the venous drainage in the male reproductive system. The back-pressure and the back-flow of blood from the testicular to the prostate drainage system were eliminated and, consequently, a rapid reduction in prostate volume and a regression of prostate symptoms took place. [source]

    Enantioselective [4+2]-Cycloaddition Reaction of a Photochemically Generated o -Quinodimethane: Mechanistic Details, Association Studies, and Pressure Effects

    CHEMISTRY - A EUROPEAN JOURNAL, Issue 9 2004
    Benjamin Grosch Dipl.
    Abstract 1,2,3,4-Tetrahydro-2-oxoquinoline-5-aldehyde (2) was prepared from m -aminobenzoic acid and 3-ethoxyacryloyl chloride (4) in 19,% overall yield. Compound 2 underwent a photochemically induced [4+2]-cycloaddition reaction with various dienophiles upon irradiation in toluene solution. The exo product 10,a was obtained with acrylonitrile (9,a) as the dienophile, whereas methyl acrylate (9,b) and dimethyl fumarate (9,c) furnished the endo products 11,b and 11,c (69,77,% yield). The reactions proceeded at ,60,°C in the presence of the chiral complexing agent 1 (1.2 equiv) with excellent enantioselectivity (91,94,% ee). The enantiomeric excess increases in the course of the photocycloaddition as a result of the lower product association to 1. The intermediate (E)-dienol 8 was spectroscopically detected at ,196,°C in an EPA (diethyl ether/isopentane/ethanol) glass matrix. The association of the substrate 2 to the complexing agent 1 was studied by circular dichroism (CD) titration. The measured association constant (KA) was 589,M,1 at room temperature (25,°C) and normal pressure (0.1 MPa). An increase in pressure led to an increased association. At 400 MPa the measured value of KA was 703,M,1. Despite the stronger association the enantioselectivity of the reaction decreased with increasing pressure. At 25,°C the enantiomeric excess for the enantioselective reaction 2 + 9,a,10,a decreased from 68,% ee at 0.1 MPa to 58,% ee at 350 MPa. This surprising behavior is explained by different activation volumes for the diastereomeric transition states leading to 10,a and ent - 10,a. 1,2,3,4-Tetrahydro-2-oxochinolin-5-aldehyd (2) wurde ausgehend von m -Aminobenzoesäure und 3-Ethoxyacryloylchlorid (4) in fünf Schritten und einer Gesamtausbeute von 19,% hergestellt. Die Verbindung ließ sich in Toluol als Lösungsmittel mit verschiedenen Dienophilen in einer photochemisch induzierten [4+2]-Cycloaddition umsetzen (69,77,% Ausbeute), wobei als Hauptprodukt mit Acrylnitril (9,a) das exo -Produkt 10,a entstand. Methylacrylat (9,b) und Dimethylfumarat (9,c) lieferten die endo -Produkte 11,b and 11,c. In Gegenwart des chiralen Komplexierungsreagenz, 1 (1.2 Äquiv.) verliefen die Reaktionen mit exzellenter Enantioselektivität (91,94,% ee). Der Enantiomerenüberschuß nahm im Verlauf der photochemischen Umsetzung zu, was man auf die relativ zum Substrat 2 niedrigere Assoziation des Produkts zurückführen kann. Das intermediär gebildete (E)-Dienol 8 wurde spektroskopisch in einer EPA (Ether/i -Pentan/Ethanol) Glasmatrix bei ,196,°C nachgewiesen. Die Assoziation des Substrats 2 an das Komplexierungsreagenz 1 wurde durch CD-Titration genauer untersucht. Die Assoziationskonstante (KA) wurde bei Zimmertemperatur (25,°C) und Normaldruck (0.1 MPa) zu 589,M,1bestimmt. Bei höherem Druck beobachtete man eine verstärkte Assoziation und bei 400 MPa wurde eine Assoziationskonstante von KA=703,M,1bestimmt. Trotz der stärkeren Assoziaion nahm die Enantioselektivität mit wachsendem Druck ab. Bei 25,°C sank der Enantiomerenüberschuß der enantioselektiven Reation 2 + 9,a,10,a von 68,% ee bei 0.1 MPa auf 58,% ee bei 350 MPa. Dieses überraschende Verhalten läßt sich möglicherweise durch die unterschiedlichen Aktivierungsvolumina für die Übergangszustände erklären, die zu 10,a und ent - 10,a führen. [source]

    Preparation of Lanthanide Hydrides of Nanometric Size by the Catalytic Method

    CHINESE JOURNAL OF CHEMISTRY, Issue 11 2002
    Yin-Heng Fan
    Abstract Rare-earth metals were hydrogenated in the presence of TICI4 catalyst in tetrahydrofuran (THF) at 45 °C under normal pressure. Transmission electron micrographs showed that the resulting lanthanide hydrides were in the form of nanoparticles. The rate of hydrogenation decreased with increasing atomic number of the rare-earth elements. [source]

    Development and modeling of a frictional wall damper and its applications in reinforced concrete frame structures

    EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 7 2004
    Chang-Geun Cho
    Abstract A wall-type friction damper is newly proposed in this paper to improve the performance of reinforced concrete (RC) framed structures under earthquake loads. Traditionally, the damper was generally invented as a brace-type member. However, it has been seen to cause problems in the RC frame structures in that concrete is apt to be damaged in the connection regions of the RC member and the brace-type damper under earthquake loads. The proposed wall-type damper has an advantage in the retrofit of RC structures. The system consists of a Teflon® slider and a RC wall. The damper is also designed to control normal pressures acting on a frictional slider. The numerical applications show that the proposed damper can be effective in mitigating the seismic responses of RC frame structures and reducing the damage to RC structural members. Copyright © 2004 John Wiley & Sons, Ltd. [source]

    Lubricants under high local pressure: Liquids act like solids

    MATERIALWISSENSCHAFT UND WERKSTOFFTECHNIK, Issue 10-11 2004
    M. H. MüserArticle first published online: 21 OCT 200
    Schmierstoff; Druck; plastisches Fliessen; Reibungsgesetz Abstract A lubricant layer solidifies when it is confined between two walls at large normal pressures. The atomic scale motion that occurs when the two confining surfaces slide past each other induces flow in the lubricant layer that is akin of plastic flow. This results in friction-velocity relationships similar to Coulomb's law of friction. Moreover, the lubricant layer does not necessarily melt, even when the two solids are in stick slip motion. In this paper, atomic-scale details of the plastic flow mechanism are investigated by means of molecular dynamics simulations. Schmierstoffe unter hohem lokalem Druck: Flüssigkeiten verhalten sich wie Feststoffe Eine molekular dünne Schicht Schmierstoff verfestigt sich, wenn sie zwischen zwei Festkörpern großen Drücken ausgesetzt ist. Die atomaren Bewegungsmechanismen, die in dem Schmierstofffilm auftreten, wenn die Festkörper gegeneinander verschoben werden, können als plastisches Fliessen verstanden werden. Dieser Mechanismus führt zu einer Kraft-Geschwindigkeitsrelation, die dem Coulomb'schen Reibungsgesetz ähnlich ist. Selbst wenn die beiden Wände in Stick-Slip Bewegung sind, verflüssigt sich der Schmiermittelfilm nicht automatisch. In dieser Arbeit werden die Details des angesprochenen plastischen Fliessens anhand von Molekular-Dynamik Simulationen im Detail untersucht. [source]