Number density predictions for primeval galaxies

2007 ◽  
pp. 242-249 ◽  
Author(s):  
Edward Thommes ◽  
Klaus Meisenheimer
Keyword(s):  
Number Density

Mass Determination by Direct Measurement of Electron Scattering

1975 ◽  
Vol 33 ◽  
pp. 240-241
Author(s):  
M. K. Lamvik ◽  
A. V. Crewe
Keyword(s):  
Cross Section ◽  
Electron Scattering ◽  
Mass Density ◽  
Variable Mass ◽  
Scattering Cross Section ◽  
Mass Determination ◽  
Number Density ◽  
Cross Sectional ◽  
Thin Slice ◽  
Scattering Cross

If a molecule or atom of material has molecular weight A, the number density of such units is given by n=Nρ/A, where N is Avogadro's number and ρ is the mass density of the material. The amount of scattering from each unit can be written by assigning an imaginary cross-sectional area σ to each unit. If the current I0 is incident on a thin slice of material of thickness z and the current I remains unscattered, then the scattering cross-section σ is defined by I=IOnσz. For a specimen that is not thin, the definition must be applied to each imaginary thin slice and the result I/I0 =exp(-nσz) is obtained by integrating over the whole thickness. It is useful to separate the variable mass-thickness w=ρz from the other factors to yield I/I0 =exp(-sw), where s=Nσ/A is the scattering cross-section per unit mass.

PEMBUATAN SURFAKTAN DARI ASAM OLEAT

2019 ◽  
Vol 1 (3) ◽  
pp. 68
Author(s):  
Puguh Setyopratomo ◽  
Edy Purwanto ◽  
H. Yefrico ◽  
H. Yefrico
Keyword(s):  
Oleic Acid ◽  
Optimum Condition ◽  
Reaction Temperature ◽  
Catalyst Concentration ◽  
Acid Number ◽  
Esterification Reaction ◽  
Number Density ◽  
Sample Analysis ◽  
Reaction Conversion ◽  
Glycerol Mono

The synthesis of glycerol mono oleic from oleic acid and glycerol is classified as an esterification reaction. This research is aimed to study the influent of reaction temperature and catalyst concentration on reaction conversion. During the experiment the temperature of reaction mixture was varied as 110 oC, 130 oC, and 150 oC, while the catalyst concentration of 1%, 3 %, and 5% was used. The batch experiment was conducted in a glass reactor equipped with termometer, agitator, and reflux condensor. The oleic acid – glycerol mol ratio of 1 : 2 was used as a mixture feed. To maintain the reaction temperature at certain level, the oil bath was used. After the temperature of reaction mixture was reached the expected value, then H2SO4 catalyst was added to the reactor.  To measure the extent of the reaction, every 30 minutes the sample was drawn out from the reactor vessel. The sample analysis include acid number, density, and viscosity measurement. From this research the optimum condition which is the temperature of reaction of 150 oC and 1% catalyst concentration was obtained. At this optimum condition the convertion reach 86% and the analysis of other physical properties of the product show the acid number of 24.12, the density of 0.922 g/cc, and the viscosity of 118.4 cp.

Combining First-Principles and Data Modeling for the Accurate Prediction of the Refractive Index of Organic Polymers

2017 ◽  
Author(s):  
Mohammad Atif Faiz Afzal ◽  
Chong Cheng ◽  
Johannes Hachmann
Keyword(s):  
First Principles ◽  
Data Modeling ◽  
Accurate Prediction ◽  
Index Of Refraction ◽  
Structure Theory ◽  
Organic Polymers ◽  
Number Density ◽  
Lorenz Equation ◽  
In Silico Studies ◽  
Wide Range

Organic materials with a high index of refraction (RI) are attracting considerable interest due to their potential application in optic and optoelectronic devices. However, most of these applications require an RI value of 1.7 or larger, while typical carbon-based polymers only exhibit values in the range of 1.3–1.5. This paper introduces an efficient computational protocol for the accurate prediction of RI values in polymers to facilitate in silico studies that an guide the discovery and design of next-generation high-RI materials. Our protocol is based on the Lorentz-Lorenz equation and is parametrized by the polarizability and number density values of a given candidate compound. In the proposed scheme, we compute the former using first-principles electronic structure theory and the latter using an approximation based on van der Waals volumes. The critical parameter in the number density approximation is the packing fraction of the bulk polymer, for which we have devised a machine learning model. We demonstrate the performance of the proposed RI protocol by testing its predictions against the experimentally known RI values of 112 optical polymers. Our approach to combine first-principles and data modeling emerges as both a successful and highly economical path to determining the RI values for a wide range of organic polymers.

scholarly journals Dark matter freeze-in from semi-production

2021 ◽  
Vol 2021 (6) ◽  
Author(s):  
Andrzej Hryczuk ◽  
Maxim Laletin
Keyword(s):  
Dark Matter ◽  
Early Universe ◽  
Cross Section ◽  
Thermal Equilibrium ◽  
Indirect Detection ◽  
Production Mechanism ◽  
Number Density ◽  
Matter Production ◽  
Relic Density ◽  
Standard Formalism

Abstract We study a novel dark matter production mechanism based on the freeze-in through semi-production, i.e. the inverse semi-annihilation processes. A peculiar feature of this scenario is that the production rate is suppressed by a small initial abundance of dark matter and consequently creating the observed abundance requires much larger coupling values than for the usual freeze-in. We provide a concrete example model exhibiting such production mechanism and study it in detail, extending the standard formalism to include the evolution of dark matter temperature alongside its number density and discuss the importance of this improved treatment. Finally, we confront the relic density constraint with the limits and prospects for the dark matter indirect detection searches. We show that, even if it was never in full thermal equilibrium in the early Universe, dark matter could, nevertheless, have strong enough present-day annihilation cross section to lead to observable signals.

scholarly journals A Simple Gas-Kinetic Model For Dilute and Weakly Charged Plasma Micro-Jet Flows

Fluids ◽  
2021 ◽  
Vol 6 (7) ◽  
pp. 250
Author(s):  
Shiying Cai ◽  
Chunpei Cai
Keyword(s):  
Simple Model ◽  
Electric Fields ◽  
Neutral Condition ◽  
Jet Flows ◽  
Far Field ◽  
Convection Term ◽  
Number Density ◽  
Simulation Based ◽  
Analytical Formulas ◽  
Electric Field Force

This paper presents a simple model for slightly charged gas expanding into a vacuum from a planar exit. The number density, bulk velocity, temperature, and potential at the exit are given. The electric field force is assumed weaker than the convection term and is neglected in the analysis. As such, the quasi-neutral condition is naturally adopted and the potential field is computed with the Boltzmann relation. At far field, the exit degenerates as a point source, and simplified analytical formulas for flow and electric fields are obtained. The results are generic and offer insights on many existing models in the literature. They can be used to quickly approximate the flowfield and potential distributions without numerical simulations. They can also be used to initialize a simulation. Based on these results, more advanced models may be further developed.

A New theory for evaluating the number density of inclusions in films

2006 ◽  
Vol 252 (23) ◽  
pp. 8235-8238 ◽  
Author(s):  
Zhi Lin Xia ◽  
Zheng Xiu Fan ◽  
Jian Da Shao
Keyword(s):  
Number Density
Sign in / Sign up

Export Citation Format

Share Document