Theoretical Model Analysis of Absorption of a Three Level Diode Pumped Alkali Laser

This paper models the absorption phenomena of light in a three level diode pumped alkali laser system. Specifically this model calculates for a user defined set of system parameters the attenuation of the input pump beam and characteristics of the bleached wave. Using Wolfram\u27s Mathematical 6.0 software all necessary physics for an accurate description of absorption was modeled from first principles: energy levels, cross sections, spin-orbit kinetic processes, saturation frequencies, pump attenuation, and differential transmittance, which is a representation of the bleached wave. A specific DPAL scenario was simulated, 455K system temperature, alkali concentration of 6.1 - 1013, and a system pressure of 200 torr of He and 600 torr of Ethane. For a range of initial input intensities the linear approximation to the beam attenuation predicted consistently a differential transmittance value of 70%. It was concluded that the linear approximation is a good indicator of the distance a bleached wave penetrates an absorbing cell. This model was also benched marked against the quasi two level model. In the limit of high system pressure the simulated model converged to the same population inversion as that of the quasi two level regime. Finally, within the quasi two level regime a closed analytic equation was developed to describe under what conditions the system would lase

Non-Adiabatic Atomic Transitions: Computational Cross Section Calculations of Alkali Metal-Noble Gas Collisions

Diode Pumped Alkali Lasers operate by exciting a gaseous cell of alkali metal to its P3/2 excited energy state. A noble gas, present in the cell, collisionally de-excites the alkali metal to its P1/2 state. The alkali atoms then relax to their S1/2 ground state by emitting photons. The non-radiative de-excitation due to inert gas atoms represents an interesting juncture for DPALs operation. This process must be faster than the radiative relaxation back to the S1/2 state for lasing to occur. The rate of non-radiative de-excitation is related to the collisional cross section and the cross section is related to the S-Matrix. A time-dependent algorithm, the Channel Packet Method, was implemented to predict S-Matrix elements for alkali metal - noble gas (MNg) collisions. The S-Matrix contains the close-coupled Hamiltonian of the MNg system in body-fixed coordinates represented in the P-Manifold of states. There were two major state-to-state coupling phenomena responsible for intramultiplet mixing: spin-orbit and Coriolis. A total of nine collisions were computationally simulated between Potassium, Rubidium, and Cesium and the noble gases Helium, Neon, and Argon. Temperature averaged cross-sections were calculated for the P1/2 to P3/2 transition and compared to experiment

The Rotational Raman Effect in Polyatomic Gases

An account is given of the relation of the theory of the Raman effect developed by Placzek to the theory based upon the Kramers Heisenberg dispersion formula. The equivalence of the two is shown in the general case. An outline is given of the procedure used by Prof. W.V. Houston and the writer in evaluating the integrals resulting from this theory for the intensities of the individual rotation lines for molecules of the symmetrical top class. The results of this calculation are verified experimentally in the case of ammonia gas, using accurate photometric technique. It is shown (1) that the general intensity distribution over the pure rotation band is as predicted; (2) that the effect of the nuclear spin of the hydrogen atoms must be taken into account; (3) that the relative intensity of the R-branch lines and S-branch lines corresponds to a molecule which is nearly planar, in agreement with results from the infra red spectra. The frequencies of the rotation and vibration lines are also discussed. The line at 3219 cm-1 is interpreted as due to the unsymmetrical vibration of the hydrogen nuclei, not previously observed. The rotation structure of a series of the simpler hydrocarbons, as well as carbon dioxide, has been investigated. Methane shows no pure rotation, in agreement with theory. The rotation band of acetylene has been obtained, and gives the value 23.45·10-40 gm cm2 for the moment of inertia. Ethylene shows a structure with slight irregularities which have not been fully accounted for; the moment of inertia is found to be approximately 30.1·10-40 gm cm2. An interpretation is suggested for the results with ethane which yields A 38.2·10-40 gm cm2. The resolution in the case of carbon dioxide is entirely unambiguous, and gives A 70.2·10-40 gm cm2</p

Determining the Climate Change Mitigation Potential of Countryside Stewardship

© All rights are reserved by Lewis KA. This work is licensed under a Creative Commons Attribution-Non Commercial 4.0 International License. https://creativecommons.org/licenses/by-nc/4.0/Short communication explaining the approach adopted to a research project aimed at understanding the climate change mitigation benefits of England's Countryside Stewardship SchemePeer reviewe

How Much Does It Cost to Buy Healthy Food in the Illawarra?

Why measure the Affordability of Current & Recommended Diets in the Illawarra? The rising cost of living in Australia is contributing to increased food insecurity, making it difficult for many households to afford nutritious food. Measuring the cost and affordability of diets in the Illawarra region can identify economic barriers that prevent residents from accessing healthy foods. This information can help guide public health policies to promote better nutrition in the community

Artificial egg-strip surveying for detection of pond-breeding newts: Does egg-strip substrate matter?

Survey methods for detecting newts (Salamandridae: Pleurodelinae) in ponds by identifying presence of eggs laid during their aquatic breeding condition are useful and often deployed across various population surveillance activities. Egg-strip surveying is an effective way of detecting newt presence in a pond by providing an egg-laying medium for newts that can be selectively inspected by a surveyor. In this study we deployed a series of different plastic substrates to investigate substrate laying preference by three species of newts; Lissotriton helveticus, L. vulgaris and Triturus cristatus. Our results revealed that L. helveticus and L. vulgaris significantly preferred green and longer varieties of black egg-strip substrate over a thicker less pliable plastic substrate. Contrastingly T. cristatus exhibited no significant preference between substrates. Results from this study indicate that if surveyors choose to use black long, black short, black, green, yellow, or red coloured substrates, or thicker black plastic substrates for egg-strip surveys, detection for T. cristatus remains constant but with improved detection and mild preference on more pliable plastic substrates. However, for L. vulgaris and L. helveti­ cus the thicker gauge black egg-strips may significantly reduce the effectiveness of detection and are discriminated against compared to more pliable grades of green and longer varieties of black plastic substrate. We recommend that surveyors constructing and deploying their own home-made egg-strip substrates should carefully consider their choice of which plastic substrate material to use in constructing the equipment

The Relation Between Galaxy ISM and Circumgalactic OVI Gas Kinematics Derived from Observations and Λ\LambdaCDM Simulations

We present the first galaxy-OVI absorption kinematic study for 20 absorption systems (EW>0.1~{\AA}) associated with isolated galaxies (0.15$<z<$0.55) that have accurate redshifts and rotation curves obtained using Keck/ESI. Our sample is split into two azimuthal angle bins: major axis ($\Phi<25^{\circ}$) and minor axis ($\Phi>33^{\circ}$). OVI absorption along the galaxy major axis is not correlated with galaxy rotation kinematics, with only 1/10 systems that could be explained with rotation/accretion models. This is in contrast to co-rotation commonly observed for MgII absorption. OVI along the minor axis could be modeled by accelerating outflows but only for small opening angles, while the majority of the OVI is decelerating. Along both axes, stacked OVI profiles reside at the galaxy systemic velocity with the absorption kinematics spanning the entire dynamical range of their galaxies. The OVI found in AMR cosmological simulations exists within filaments and in halos of ~50 kpc surrounding galaxies. Simulations show that major axis OVI gas inflows along filaments and decelerates as it approaches the galaxy while increasing in its level of co-rotation. Minor axis outflows in the simulations are effective within 50-75 kpc beyond that they decelerate and fall back onto the galaxy. Although the simulations show clear OVI kinematic signatures they are not directly comparable to observations. When we compare kinematic signatures integrated through the entire simulated galaxy halo we find that these signatures are washed out due to full velocity distribution of OVI throughout the halo. We conclude that OVI alone does not serve as a useful kinematic indicator of gas accretion, outflows or star-formation and likely best probes the halo virial temperature.Comment: 24 pages, 21 figures, 4 tables. Accepted to ApJ on November 14, 201

Temperature controlled motion of an antiferromagnet- ferromagnet interface within a dopant-graded FeRh epilayer

Chemically ordered B2 FeRh exhibits a remarkable antiferromagnetic-ferromagnetic phase transition that is first order. It thus shows phase coexistence, usually by proceeding though nucleation at random defect sites followed by propagation of phase boundary domain walls. The transition occurs at a temperature that can be varied by doping other metals onto the Rh site. We have taken advantage of this to yield control over the transition process by preparing an epilayer with oppositely directed doping gradients of Pd and Ir throughout its height, yielding a gradual transition that occurs between 350 K and 500 K. As the sample is heated, a horizontal antiferromagnetic-ferromagnetic phase boundary domain wall moves gradually up through the layer, its position controlled by the temperature. This mobile magnetic domain wall affects the magnetisation and resistivity of the layer in a way that can be controlled, and hence exploited, for novel device applications

Taking the tool analogy seriously: Forms and naming in the cratylus

Copyright © The Author(s) 2014. Published by Cambridge University Press. It has been suggested that the so-called tool analogy passage of Plato's Cratylus presents us with a moderate linguistic naturalism that can stand or fall independently of the more unpalatable etymological and mimetic theories advanced later in the dialogue. This paper offers a reading of the tool analogy which argues that Socrates' employment of Forms (and in particular Species-Forms), together with a careful distinction between the types of knowledge associated with making and using tools, aims to establish a radical linguistic naturalism that constrains the intrinsic properties of names. This should be clear if we take Socrates' claim seriously that names are tools: tools in general can only function successfully if they exhibit the relevant structural, compositional and (to some extent) material properties. Since Socrates claims that names are a class of tools and not merely like tools in some respects, as many have supposed, then what holds for tools in general must also hold for names

Spatial distribution of O VI covering fractions in the simulated circumgalactic medium

We use adaptive mesh refinement cosmological simulations to study the spatial distribution and covering fraction of O VI absorption in the circumgalactic medium (CGM) as a function of projected virial radius and azimuthal angle. We compare these simulations to an observed sample of 53 galaxies from the Multiphase Galaxy Halos Survey. Using MOCKSPEC, an absorption-line analysis pipeline, we generate synthetic quasar absorption-line observations of the simulated CGM. To best emulate observations, we studied the averaged properties of 15,000 “mock samples,” each of 53 sight lines having a distribution of D/Rvir and sight-line orientation statistically consistent with the observations. We find that the O VI covering fraction obtained for the simulated galaxies agrees well with the observed value for the inner halo (D/Rvir ≤ 0.375) and is within 1.1σ in the outer halo (D/Rvir > 0.75), but is underproduced within 0.375 < D/Rvir ≤ 0.75. The observed bimodal distribution of the O VI covering fraction with azimuthal angle, showing a higher frequency of absorption along the projected major and minor axes of galaxies, is not reproduced in the simulations. Further analysis reveals the spatial-kinematic distribution of O VI-absorbing gas is dominated by outflows in the inner halo mixed with an inflowing gas that originates from farther out in the halo. Though the CGM of the individual simulated galaxies exhibits spatial structure, the flat azimuthal distribution occurs because the individual simulated galaxies do not develop a CGM structure that is universal from galaxy to galax