Total pressure

About: Total pressure is a research topic. Over the lifetime, 5199 publications have been published within this topic receiving 66658 citations.

Monte Carlo Prediction of Radiative Heat Transfer in Inhomogeneous, Anisotropic, Nongray Media

Abstract: A Monte Carlo solution technique has been formulated to predict the radiative heat transfer in three-dimensional, inhomogeneous participating media which exhibit spectrally dependent emission and absorption and anisotropic scattering. Details of the technique and selected numerical sensitivities are discussed. The technique was applied to a problem involving a medium composed of a gas mixture of carbon dioxide and nitrogen and suspended carbon particles. A homogeneous medium was modeled to examine the effect of total pressure and carbon-particle concentration on radiative heat transfer. Variation in total pressure, over the range studied, had minimal effect on the amount of heat radiated to the enclosure walls and on the radiative-flux distribution within the medium. Increases in the carbon particle concentration produced significantly higher heat fluxes at the boundaries and altered the radiative flux distribution. The technique was then applied to an inhomogeneous medium to examine effects of specific temperature and carbon particle concentration distributions on radiative heat transfer. For the inhomogeneous conditions examined, the largest radiative flux divergence occurs near the center of the medium and the regions near some enclosure walls act as energy sinks.

Improving curved subsonic diffuser performance with vortex generators

Abstract: The objective of this research was to use vortex generators to reduce total pressure distortion (ie, total pressure nonuniformity) and improve total pressure recovery within a curved subsonic diffuser In this study more than 20 configurations of both co- and counter-rotating arrays of vortex generators were tested in a diffusing S duct Surface static pressure, surface flow visualization, and exit plane total pressure and transverse velocity data were acquired The aerodynamic performance of each configuration was assessed by calculating total pressure recovery and spatial distortion elements The best configuration tested reduced distortion by more than 50% while improving total pressure recovery by 05% The results indicate that the mechanism responsible for improved aerodynamic performance is not boundary-layer re-energization from shed axial vortices but rather the suppression of detrimental secondary flows by redirecting the flow

Role of Pressure in the Growth of Hexagonal Boron Nitride Thin Films from Ammonia-Borane

Abstract: We analyze the optical, chemical, and electrical properties of chemical vapor deposition (CVD) grown hexagonal boron nitride (h-BN) using the precursor ammonia-borane (H3N–BH3) as a function of Ar/H2 background pressure (PTOT). Films grown at PTOT ≤ 2.0 Torr are uniform in thickness, highly crystalline, and consist solely of h-BN. At larger PTOT, with constant precursor flow, the growth rate increases, but the resulting h-BN is more amorphous, disordered, and sp3-bonded. We attribute these changes in h-BN grown at high pressure to incomplete thermolysis of the H3N–BH3 precursor from a passivated Cu catalyst. A similar increase in h-BN growth rate and amorphization is observed even at low PTOT if the H3N–BH3 partial pressure is initially greater than the background pressure PTOT at the beginning of growth. h-BN growth using the H3N–BH3 precursor reproducibly can give large-area, crystalline h-BN thin films, provided that the total pressure is under 2.0 Torr and the precursor flux is well-controlled.

Nonlinear indicial response of complex nonstationary oscillations as pulmonary hypertension responding to step hypoxia (degree of nonlinearityyFourier spectrumyHilbert spectrumynonlinear relationships)

Abstract: This paper is devoted to the quantization of the degree of nonlinearity of the relationship between two biological variables when one of the variables is a complex nonstationary oscillatory signal. An example of the situation is the indicial responses of pulmonary blood pressure (P) to step changes of oxygen tension (DpO2) in the breathing gas. For a step change of DpO2 beginning at time t1, the pulmonary blood pressure is a nonlinear function of time and DpO2, which can be written as P(t-t1 z DpO2). An effective method does not exist to examine the nonlinear function P(t-t1 z DpO2). A systematic approach is proposed here. The definitions of mean trends and oscillations about the means are the keys. With these keys a practical method of calculation is devised. We fit the mean trends of blood pressure with analytic functions of time, whose nonlinearity with respect to the oxygen level is clarified here. The associated oscillations about the mean can be transformed into Hilbert spectrum. An integration of the square of the Hilbert spectrum over frequency yields a measure of oscillatory energy, which is also a function of time, whose mean trends can be expressed by analytic functions. The degree of nonlinearity of the oscillatory energy with respect to the oxygen level also is clarified here. Theoretical extension of the experimental nonlinear indicial functions to arbitrary his- tory of hypoxia is proposed. Application of the results to tissue remodeling and tissue engineering of blood vessels is discussed. In biomedical science, we often have to deal with variables that are stochastic, oscillatory, and nonstationary and the relationship of these variables to other chemical, mechanical, physical, and pharmacological variables. In the cardiovascular system blood pressure is such a variable. This paper illustrates the mathematical approach to deal with the question of linearity or nonlinearity of the dependence of blood pressure on other variables. As a specific illustration, we consider the changes that occur in the lung when a sea-level dwelling animal is flown to a ski resort at a higher altitude where the partial pressure of oxygen in the gas that the animal breathes is lower. What happens is that the pulmonary arterial blood pressure becomes higher (1-3), the arterial blood vessel wall becomes thicker (3-5), the different layers of the arteries thicken with different rates and different courses of time (2-6), the mechanical properties of the blood vessel wall change with specific historical courses (7-9), cells in the wall modify, grow, proliferate, or move (5, 6, 10-13), intercellular matrix and interstitial space change (14, 15), the stress and strain distribution in the vessel wall change with time in a specific way (16), and because of cellular and extracellular changes the zero-stress state of the blood vessel wall changes with time (7-9). The crucial fact is the blood pressure change, because the blood pressure imposes load on the blood vessel wall, causing stress and strain, and the subsequent tissue and mechanical properties remodeling are believed to be the results of these stress and strain changes. Therefore, the exact behavior of blood pressure when the oxygen tension changes is of paramount importance. But blood pressure is stochastic (see Fig. 1). To get a meaningful and precise description of the blood pressure history is the first step. We used a catheter that was implanted in the pulmonary arterial trunk of a rat to get the instantaneous reading of blood pressure continuously over many days in a simulated laboratory chamber. The oxygen tension in the breathing gas was controlled as a constant or varied as a step decrease in time or a step increase in time. Typical blood pressure records are shown in Fig. 1. Previous reports (17) have demonstrated various features of pulmonary hypertension caused by hypoxia, but no mathematical analysis of the blood pressure-oxygen relationship was shown. The present paper shows a systematic use of the method pre- sented in refs. 18 and 19 to the study of the nonlinearity of the pulmonary blood pressure-oxygen tension relationship. METHODS Sixteen male Sprague-Dawley rats (Harlan, San Diego, CA), 358.9 6 4.9 g body weight, were used in the study. The protocol and experimental methods are presented in refs. 19 and 20. Briefly, each rat was implanted with an indwelling catheter in the pulmonary arterial trunk when breathing a gaseous anesthetic of isoflurane. After the implantation of the catheter, the rat could move freely in a standard-sized cage in a quiet room that was illuminated from 0600 to 1800 h. The catheter tubing had 0.305 mm i.d. and 0.635 mm o.d. and floated in the pulmonary arterial trunk facing downstream. The other end of the tubing was connected to a Statham pressure transducer (P23ID, Hato Rey, PR). The pressure recorded therefore was the stagnation or total pressure. The pressure was recorded continuously by a computer at a sampling rate of 100 pointsysec over a 36-h period with a time lag of 2 sec in every 60 sec for computer processing. The analog-to-digital conversion was accomplished by a data trans- lation board (DT31-EZ, Data Translation, Marlboro, MA). After 6 h in normal sea-level air with 20.9% oxygen, the rats were exposed to a hypoxic gas containing nitrogen and 17.2% O2, 13.6% O2 ,o r 10% O 2 for 24 h followed by returning to breathing normal sea-level air for 6 h. The changeover from one level of oxygen tension to the next was accomplished in 1.5 6 0.5 min each time. Hence, in the perspective of 1 day we say approximately that the oxygen level was changed as a step function of time. Four rats were used at each hypoxic level; four served as control without hypoxia. For mathematical analysis of the pressure signal, we begin by considering the time between successive extrema as the local time scale and define an intrinsic mode function (IMF) as a function that satisfies two conditions: (i) in the whole data set,

JET quasistationary internal-transport-barrier operation with active control of the pressure profile.

Abstract: Quasistationary operation has been achieved on the Joint European Torus tokamak in internal-transport-barrier (ITB) scenarios, with the discharge time limited only by plant constraints. Full current drive was obtained over all the high performance phase by using lower hybrid current drive. For the first time feedback control on the total pressure and on the electron temperature profile was implemented by using, respectively, the neutral beams and the ion-cyclotron waves. Although impurity accumulation could be a problem in steady state ITBs, these experiments bring some elements to answer to it.