Diffusion and flow of gases and vapours through micropores I. Slip flow and molecular streaming

1950 ◽  
Vol 203 (1072) ◽  
pp. 55-74 ◽  
Keyword(s):  
Transition Region ◽  
Cross Sections ◽  
Slip Flow ◽  
Gradual Change ◽  
Considerable Uncertainty ◽  
Fine Powders ◽  
True Value ◽  
Pore Texture ◽  
Wide Range

It has been shown that the slight minimum found by Knudsen in the plot of G against p for circular capillaries is very much exaggerated for non-circular cross-sections. Since the pore-system in a porous medium must correspond to non-circular sections, a similar minimum might be expected. Such a possibility would give rise to considerable uncertainty in applying gas permeabilities to the determination of specific surfaces of very fine powders, when flow takes place mainly by molecular streaming. The minimum should appear when d e = λ (transition region). By using a number of powders of different particle size and four different gases, a very wide range of values of d e /λ on both sides of unity has been covered. It has been established clearly that, while the plot of G against p sometimes undergoes a small and very gradual change of gradient in the transition region, no sign of a minimum has been detected. For all practical purposes, it is sufficient to assume that G against p is linear for all values of p . For a powder of Pyrex glass microspheres, the value of δ/k´ = 0·46, which agrees in magnitude with theoretical expectations. For different plugs, and also for the same plug, when G against p is curved, δ/k´ has different values, but the total range of variation is not large. The foregoing conclusions are not dependent on porosity or pore texture. The pore texture of fine powders at high porosities is so non-uniform that the surface calculated from permeability is 50% or less of its true value, but the transition from slip flow to streaming is unaffected and values of δ/k´ are normal.

Valence shell absolute photoabsorption oscillator strengths, constrained dipole oscillator strength distributions, and dipole properties for CH3NH2, (CH3)2NH, and (CH3)3N

1994 ◽  
Vol 72 (3) ◽  
pp. 529-546 ◽  
Author(s):  
Gordon R. Burton ◽  
Wing Fat Chan ◽  
Glyn Cooper ◽  
C.E. Brion ◽  
Ashok Kumar ◽  
...  
Keyword(s):  
Oscillator Strength ◽  
Cross Sections ◽  
Oscillator Strengths ◽  
Valence Shell ◽  
Reliable Determination ◽  
Sum Rule ◽  
Wide Range ◽  
Dipole Oscillator ◽  
Strength Distributions

Dipole (e,e) spectroscopy has been used to measure the absolute photoabsorption oscillator strengths (cross sections) for the valence shells of CH3NH2, (CH3)2NH, and (CH3)3N from the photoabsorption threshold to 250 eV at low resolution (∼1 eV fwhm) and to 31 eV at high resolution (0.048 eV fwhm). The observed peaks in the photoabsorption spectra of the methylamines have been assigned to transitions to Rydberg orbital upper states. Our measured photoabsorption data, augmented by mixture rule estimates for high photon energies, have been used in conjunction with Thomas–Reiche–Kuhn sum rule and molar refractivity constraints, to construct constrained dipole oscillator strength distributions for each of the methylamines. From these constrained dipole oscillator strength distributions a wide range of related dipole properties have been calculated for each of the methylamines, and in most cases the results so obtained represent the first (reliable) determination of these properties.

New in Old: Simplified Equations for Linear-elastic Symmetric Arches and Insights on Their Behavior

2020 ◽  
Vol 61 (3) ◽  
pp. 227-240
Author(s):  
Branko Glisic
Keyword(s):  
Cross Sections ◽  
Normal Force ◽  
Approximate Equation ◽  
Structural Behavior ◽  
Structural Systems ◽  
Linear Elastic ◽  
Wide Range ◽  
Different Types ◽  
Internal Forces

Closed-form equations for determination of reactions and internal forces of linear-elastic symmetric arches with constant cross-sections are derived. The derivation of the equations was initially made for segmental, threehinged, two-hinged, and hingeless arches. Not all derived equations are simple, but still not excessively complex to apply, and they reveal several new insights into the structural behavior of arches. The first is an extremely simple approximate equation for horizontal reactions of a hingeless arch under self-weight, which could be also applied with excellent accuracy to catenary and parabolic arches, and with a desirable level of accuracy to two- and three-hinged arches with a relatively wide range of geometries. The second insight is an approximately linear relationship between reactions and between internal forces of arches with different structural systems, which helps understand the global structural behavior of arches in a new way and enables inference of some other insights presented in the paper. The third insight reflects the relationships between normal force distribution and its eccentricity in different types of arches. Finally, the fourth insight regards the comparison of behavior of arches under the self-weight with those loaded with uniformly distributed load along their span.

Analysis of STEM micrographs of thick objects

1978 ◽  
Vol 36 (2) ◽  
pp. 106-107
Author(s):  
S. Golladay
Keyword(s):  
Inelastic Scattering ◽  
Multiple Scattering ◽  
Mass Distribution ◽  
Cross Sections ◽  
Phase Contrast ◽  
Image Point ◽  
Contrast Effects ◽  
Total Cross Sections ◽  
Elastic And Inelastic Scattering

The theory of multiple scattering has been worked out by Groves and comparisons have been made between predicted and observed signals for thick specimens observed in a STEM under conditions where phase contrast effects are unimportant. Independent measurements of the collection efficiencies of the two STEM detectors, calculations of the ratio σe/σi = R, where σe, σi are the total cross sections for elastic and inelastic scattering respectively, and a model of the unknown mass distribution are needed for these comparisons. In this paper an extension of this work will be described which allows the determination of the required efficiencies, R, and the unknown mass distribution from the data without additional measurements or models. Essential to the analysis is the fact that in a STEM two or more signal measurements can be made simultaneously at each image point.

A quantitative approach to inner shell losses

1978 ◽  
Vol 36 (1) ◽  
pp. 526-527 ◽  
Author(s):  
R.D. Leapman ◽  
P. Rez ◽  
D.F. Mayers
Keyword(s):  
Energy Transfer ◽  
Cross Section ◽  
Cross Sections ◽  
Accurate Determination ◽  
Background Intensity ◽  
Core Excitation ◽  
Quantitative Basis ◽  
Cross Section Differential ◽  
Bound Electrons

Microanalysis by EELS has been developing rapidly and though the general form of the spectrum is now understood there is a need to put the technique on a more quantitative basis (1,2). Certain aspects important for microanalysis include: (i) accurate determination of the partial cross sections, σx(α,ΔE) for core excitation when scattering lies inside collection angle a and energy range ΔE above the edge, (ii) behavior of the background intensity due to excitation of less strongly bound electrons, necessary for extrapolation beneath the signal of interest, (iii) departures from the simple hydrogenic K-edge seen in L and M losses, effecting σx and complicating microanalysis. Such problems might be approached empirically but here we describe how computation can elucidate the spectrum shape.The inelastic cross section differential with respect to energy transfer E and momentum transfer q for electrons of energy E0 and velocity v can be written as

Preparation And elemental analysis of ancient fibers

1987 ◽  
Vol 45 ◽  
pp. 410-411
Author(s):  
Allen Angel ◽  
Kathryn A. Jakes
Keyword(s):  
Cross Sections ◽  
Physical Structure ◽  
Energy Dispersive ◽  
Archaeological Sites ◽  
X Ray ◽  
Long Term Storage ◽  
Backscattered Electron ◽  
Electron Imaging

Fabrics recovered from archaeological sites often are so badly degraded that fiber identification based on physical morphology is difficult. Although diagenetic changes may be viewed as destructive to factors necessary for the discernment of fiber information, changes occurring during any stage of a fiber's lifetime leave a record within the fiber's chemical and physical structure. These alterations may offer valuable clues to understanding the conditions of the fiber's growth, fiber preparation and fabric processing technology and conditions of burial or long term storage (1).Energy dispersive spectrometry has been reported to be suitable for determination of mordant treatment on historic fibers (2,3) and has been used to characterize metal wrapping of combination yarns (4,5). In this study, a technique is developed which provides fractured cross sections of fibers for x-ray analysis and elemental mapping. In addition, backscattered electron imaging (BSI) and energy dispersive x-ray microanalysis (EDS) are utilized to correlate elements to their distribution in fibers.

Gender determination of caucasoid hair using image analysis

1993 ◽  
Vol 51 ◽  
pp. 216-217
Author(s):  
T.B. Ball ◽  
W.M. Hess
Keyword(s):  
Image Analysis ◽  
Cross Sections ◽  
Scalp Hair ◽  
The Body ◽  
Equivalent Diameter ◽  
Cross Sectional ◽  
Hair Samples ◽  
Length Width ◽  
Morphological Differences

It has been demonstrated that cross sections of bundles of hair can be effectively studied using image analysis. These studies can help to elucidate morphological differences of hair from one region of the body to another. The purpose of the present investigation was to use image analysis to determine whether morphological differences could be demonstrated between male and female human Caucasian terminal scalp hair.Hair samples were taken from the back of the head from 18 caucasoid males and 13 caucasoid females (Figs. 1-2). Bundles of 50 hairs were processed for cross-sectional examination and then analyzed using Prism Image Analysis software on a Macintosh llci computer. Twenty morphological parameters of size and shape were evaluated for each hair cross-section. The size parameters evaluated were area, convex area, perimeter, convex perimeter, length, breadth, fiber length, width, equivalent diameter, and inscribed radius. The shape parameters considered were formfactor, roundness, convexity, solidity, compactness, aspect ratio, elongation, curl, and fractal dimension.

DINAMIKA POLITIK PERSETUJUAN BERSAMA TENTANG PENETAPAN DESA ADAT DI KABUPATEN ROKAN HULU TAHUN 2014

2017 ◽  
Vol 15 (1) ◽  
pp. 21
Author(s):  
Haryo Suganda ◽  
Raja Muhammad Amin
Keyword(s):  
Regulatory Region ◽  
Field Research ◽  
Analysis Techniques ◽  
Political Dynamics ◽  
Political Interests ◽  
Wide Range ◽  
Information Method ◽  
Qualitative Descriptive ◽  
The Village

This study is motivated the identification of policies issued by the regional Governmentof Rokan Hulu in the form of Regulatory region number 1 by 2015 on the determination of thevillage and Indigenous Village. Political dynamics based on various interests against themanufacture of, and decision-making in the process of formation of the corresponding localregulations determination of Indigenous Villages in the Rokan Hulu is impacted to a verysignificantamount of changes from the initial draft of the number i.e. 21 (twenty one) the villagebecame Customary 89 (eighty-nine) the Indigenous Villages who have passed. Type of thisresearch is a qualitative descriptive data analysis techniques. The research aims to describe theState of the real situation in a systematic and accurate fact analysis unit or related research, aswell as observations of the field based on the data (information). Method of data collectionwas done with interviews, documentation, and observations through fieldwork (field research).The results of the research on the process of discussion of the draft local regulations andmutual agreement about Designation of Indigenous Villages in the Rokan Hulu is, showed thatthe political dynamics that occur due to the presence of various political interests, rejectionorally by Villagers who were judged to have met the requirements of Draft Regulations to beformulated and the area for the set to be Indigenous Villages, and also there is a desire fromsome villages in the yet to Draft local regulations in order to set the Indigenous village , there isa wide range of interests of these aspects influenced the agreement to assign the entire localVillage which is in the Rokan Hulu become Indigenous village, and the village of Transmigrationinto administrative Villages where the initiator of the changes in the number of IndigenousVillages in the Rokan Hulu it is the desire of the local Government of its own.

Modal frequencies of bridges from GNSS (GPS) monitoring data: Experimental, statistical evidence

2021 ◽  
Vol 17 (1-2) ◽  
pp. 3-14
Author(s):  
Stathis C. Stiros ◽  
F. Moschas ◽  
P. Triantafyllidis
Keyword(s):  
Signal To Noise Ratio ◽  
Vertical Axis ◽  
Bridge Monitoring ◽  
Low Snr ◽  
True Value ◽  
Gps Satellites ◽  
Wide Range ◽  
Spectral Peaks ◽  
Monitoring Survey ◽  
True Frequency

GNSS technology (known especially for GPS satellites) for measurement of deflections has proved very efficient and useful in bridge structural monitoring, even for short stiff bridges, especially after the advent of 100 Hz GNSS sensors. Mode computation from dynamic deflections has been proposed as one of the applications of this technology. Apart from formal modal analyses with GNSS input, and from spectral analysis of controlled free attenuating oscillations, it has been argued that simple spectra of deflections can define more than one modal frequencies. To test this scenario, we analyzed 21 controlled excitation events from a certain bridge monitoring survey, focusing on lateral and vertical deflections, recorded both by GNSS and an accelerometer. These events contain a transient and a following oscillation, and they are preceded and followed by intervals of quiescence and ambient vibrations. Spectra for each event, for the lateral and the vertical axis of the bridge, and for and each instrument (GNSS, accelerometer) were computed, normalized to their maximum value, and printed one over the other, in order to produce a single composite spectrum for each of the four sets. In these four sets, there was also marked the true value of modal frequency, derived from free attenuating oscillations. It was found that for high SNR (signal-to-noise ratio) deflections, spectral peaks in both acceleration and displacement spectra differ by up to 0.3 Hz from the true value. For low SNR, defections spectra do not match the true frequency, but acceleration spectra provide a low-precision estimate of the true frequency. This is because various excitation effects (traffic, wind etc.) contribute with numerous peaks in a wide range of frequencies. Reliable estimates of modal frequencies can hence be derived from deflections spectra only if excitation frequencies (mostly traffic and wind) can be filtered along with most measurement noise, on the basis of additional data.

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