Population Distribution Of Levels Research Articles

Theoretical and experimental study of the pump pulse width optimization of the Yb-doped fiber amplifier

In order to suppress the amplified spontaneous emission (ASE) in the low repetition rate high energy fiber master oscillator power amplifier (MOPA) system and achieve the best amplification results, it is necessary to optimize the pump pulse width. Based on solving a set of time-dependent rate and power transfer equations, the optimum pump pulse width is obtained by studying the transient response of the upper level population distribution, stored energy and ASE of the Yb-doped fiber amplifier under pulsed pump. The ASE built-up time is measured and the optimum value is found by tuning the width of pump pulse in the experiment, and the results show the validity of the numerical simulation.

掺镱光纤放大器泵浦脉宽优化

In order to suppress the amplified spontaneous emission (ASE) in the low-repetition rate high-energy fiber master-oscillator-power-amplifier (MOPA) system and achieve the best amplification results, it is necessary to optimize the pump pulse width. Based on solving a set of time-dependent rate and power transfer equations, the transient response of the upper level population distribution, stored energy and ASE of the Yb-doped fiber amplifier under pulsed pump are numerically studied. And the numerical optimum pump pulse width is 793 s under specific parameters given in the paper, including the pump power, fiber length, core area, Yb-doped concentration, etc. In the experiment the ASE built-up time is measured, and the optimum value is 800 s which is found by tuning the width of the pump pulse and measuring the amplification results of the fiber amplifier. The experiment shows the validity of the numerical simulation. 

Theoretical and experimental study of transient response of the Yb-doped fiber amplifier

Some analysis of the transient response of the Yb-doped fiber amplifier are performed by solving a set of time-dependent rate and power transfer equations based on finite-difference method. Meanwhile, the variation of time to reach the steady state for upper level population distribution, the forward and backward amplified spontaneous emissions (ASEs) and stored energy on the system parameters including pump power, fiber length, Yb-doped concentration, and core area are numerically simulated, respectively. The results show that, by optimizing pump pulse width, stored energy can reach or even exceed the steady state value of continuous wave (CW) pump. By increasing Yb-doped concentration and core area, stored energy is increased, the ASE is suppressed and the ASE built-up time is postponed. In addition, the experimental results show the validity of the theoretical ASE built-up time. The obtained results can provide important guiding for the optimization of pump pulse width and fiber parameters.

Singlet molecular nitrogen in the Auroral ionosphere and under the conditions of laboratory discharge

Using the suggested model of the electron kinetics of N2 singlet states, the population of the vibrational levels in the molecular nitrogen states (a′)1Σ − , a 1Π g , and w 1Δ u is calculated for the case when fast auroral electrons penetrate into the Earth’s ionosphere. It is shown for the first time that the population distribution of the vibrational levels v = 0−6 in the state a 1Π g in the auroral ionosphere and also in a laboratory discharge varies with atmospheric pressure insignificantly. Similar calculations for pure nitrogen atmosphere show a considerable increase in the populations of lower vibrational levels (v = 0−2) with rising pressure.

The PD1/PD-L1 Axis in the Classical Hodgkin Lymphoma Microenvironment: PD-1 Is Rarely Expressed but Identifies Patients with High-Risk Disease

Abstract 1560 Introduction:Classical Hodgkin lymphoma (CHL) is histologically unique: the malignant Hodgkin Reed-Sternberg cell (HRS) represents a fraction of tumour bulk, the majority being inflammatory cells: a combination of inadequate immune response and tumor-supportive microenvironment. PD-1 is a T-cell expressed CD28-analogue that inhibits activity of the expressing cell by interactions with ligands including the B7 analogue PD-L1. PD-L1 is upregulated in a range of immune and non-immune cells including malignant cells. Immunosuppression through this axis may contribute to failed immune response and adverse outcome in some tumors (Keir et al. Annu Rev Immunol, 2008; 26: 677–704) and there are reports regarding expression levels and pathway activity (Chemnitz et al. Blood, 2007; 110: 3226–33) as well as biological importance in CHL (Yamamoto et al. Blood, 2008; 111: 3220–3224). PD-L1 is overexpressed by HRS cells and encoded by a chromosomal region showing recurrent copy number gains in CHL (Steidl et al. Blood, 2010; 116: 418- 427). PD1/PD-L1 interactions are also essential to the survival of germinal centre B cells (Good-Jacobson et al. Nature Imm; 2010; 11: 535–42) the normal counterparts of the HRS, implying a potential direct supportive role for this pathway independent of the immune response. While the mechanistic importance of this axis in CHL is widely stated, little published evidence exists to substantiate it. This immunohistochemical (IHC) study set out to determine levels and variability of expression of PD-1 and PD-L1 at diagnosis in CHL and determine prognostic importance. Methods:IHC analysis was performed on tissue microarrays (TMAs) from 122 previously untreated CHL patients with known clinical outcome: median age 30 (range 18–80), 35% female, 71% advanced stage, median follow up 16.5 (range 2–40) years. Triplicate cores were made from areas of high cellularity avoiding fibrotic or acellular portions, arrayed and stained for PD-1 or PD-L1. Positive cells were counted across all cores using an automated image analysis system (Ariol), output confirmed by expert histopathologists, and means calculated corrected to % infiltration per 1mm2. 105 cases (86%) had tissue of sufficient quality for full IHC assessment. Groups were determined based on population distribution of infiltration levels and confirmed using the test/validation set method. Outcomes of freedom from first-line treatment failure (FFTF), disease-specific survival (DSS) and overall survival (OS) were assessed using the Kaplan Meier method with statistically significant differences between groups calculated using the log-rank test. Results:PD-1 expression was strikingly low or absent in the microenvironment of the majority of cases: <1% of cells in 40% of cases and <5% of cells in 80%. Median expression was 0.14% of all nucleated cells (range 0–8.9%). When present, this was predominantly as a low-level background infiltrate with frequent clusters/nodules of PD-1 positive lymphoid cells aggregating around HRS cells. Notably, the rare patients with high expression of PD-1 had adverse outcome. The 20% of patients with infiltration >0.5% cells had DSS 61% vs 89% at both 5 and 10 years (p=0.03). In contrast, PD-L1 was expressed at a high level in both HRS and the microenvironment in the majority of cases: >10% cells in 38% of cases, and <1% in only 5%. Median expression was 6.1% (range 0.2%–40%). Level of PD-L1 expression in the microenvironment was not associated with any measure of clinical outcome. Conclusions:PD-1 may have biological significance, as measured by impact on prognosis in a minority of patients with CHL, where overexpression is associated with an increased chance of CHL-related death. This may relate to immunosuppression, but the very low overall levels of expression and tendency to cluster around the malignant cells (a pattern seen more often in nodular lymphocyte predominant HL) imply a more localised HRS interactive role perhaps equivalent to the pathway's activity in a normal germinal centre. Its ligand PD-L1 is highly expressed in the microenvironment as well as in the HRS, which may relate to an activated rather than suppressive microenvironment, but without association with prognosis. We conclude that for the majority of patients with CHL, the definitive role for this pathway remains to be demonstrated conclusively. [Display omitted] Disclosures:Gribben:Roche: Honoraria; Celgene: Honoraria; GSK: Honoraria; Mundipharma: Honoraria; Gilead: Honoraria; Pharmacyclics: Honoraria.

The population distribution of argon atoms in Paschen 1s levels in an inductively coupled plasma

The population distribution of argon atoms in Paschen 1s levels in inductively coupled plasmas is investigated using a collisional–radiative model and the optical emission spectroscopy method. The modelling results of population densities are in good agreement with the experimental ones. According to this model, the population distribution of 1s levels is affected mainly by the electron impact transfer and the resonance radiation processes. As a result, a simple relationship on the population ratio of 1s4 and 1s5 is obtained. From this relationship, three kinetic regimes with different electron densities and discharge pressures are identified, which can be used to characterize the population distribution of argon 1s levels in inductively coupled plasmas.

Velocity map imaging the dynamics of the reactions of Cl atoms with neopentane and tetramethylsilane

The reactions of ground state Cl((2)P(3/2)) atoms with neopentane and tetramethylsilane have been studied at collision energies of 7.9+/-2.0 and 8.2+/-2.0 kcal mol(-1), respectively. The nascent HCl(v=0,J) products were probed using resonance enhanced multiphoton ionization spectroscopy combined with velocity map imaging (VMI) to determine the rotational level population distributions, differential cross sections (DCSs), and product translational energy distributions. The outcomes from PHOTOLOC and dual beam methods are compared and are discussed in light of previous studies of the reactions of Cl atoms with other saturated hydrocarbons, including a recent crossed molecular beam and VMI investigation of the reaction of Cl atoms with neopentane [Estillore et al., J. Chem. Phys. 132, 164313 (2010)]. Rotational distributions were observed to be cold, consistent with the reactions proceeding via a transition state with a collinear Cl-H-C moiety. The DCSs for both reactions are forward peaked but show scatter across a broad angular range. Interpretation using a model based on linear dependence of scattering angle on impact parameter indicates that the probability of reaction is approximately constant across all allowed impact parameters. Product translational energy distributions from dual beam experiments have mean values, expressed as fractions of the total available energy, of 0.67 (Cl+neopentane) and 0.64 (Cl+tetramethylsilane) that are consistent with a kinematic model for the reaction in which the translational energy of the reactants is conserved into product translational energy.

Self-Reversal in Hydrogen Lyman-α Line Profile

A detailed spectral profile of the Lyman-α line of neutral hydrogen, i.e., the transition from n = 2 to the ground state, where n is the principal quantum number, was measured with a vacuum ultraviolet spectrometer for the plasma in the Large Helical Device. Self-reversal was observed in the spectral profile when the plasma density was increased with repetitive injection of hydrogen pellets. A one-dimensional radiation transport model was used for creating the Lyman-α spectral profile, for which an emission and absorption medium with a slab geometry and constant plasma parameters were assumed. The population density of the n = 2 level generally has a peaked spatial profile even with constant ground state density because of the reabsorption effect which is essential for the emergence of self-reversal in the spectral profile. We used the n = 2 level population distribution in the medium by Molisch et al. [Radiation Trapping in Atomic Vapours, Oxford University, Oxford, 1998] and evaluated the Lyman-α spectral profile as a function of the optical thickness. The observed line profile was found to be well fitted, for example, with a ground state density of 5.2 × 1018 m−3 and a medium thickness of 10 cm when a Lorentzian profile having a full width at half maximum of 0.0018 nm is adopted for the emission and absorption coefficients.

Spatial Autoregressive Model for Population Estimation at the Census Block Level Using LIDAR-derived Building Volume Information

The collection of population by census is laborious, time consuming and expensive, and often only available at limited temporal and spatial scales. Remote sensing based population estimation has been employed as a viable alternative for providing population estimates based on indicators that make use of two-dimensional areal information of buildings or one-dimensional length information of roads The recent advancement of LIDAR remote sensing provides the opportunity to add the third dimension of height information into the modeling of population distribution. This study explores the use of building volumes derived from LIDAR as a population indicator. Our study shows the volume-based model consistently outperforms area and length-based models at the census block level. Additionally, the study examines the impact of spatial autocorrelation, the presence of which violates the independence assumption of the traditional OLS models. To address this problem, a spatial autoregressive model is employed to account for the spatial autocorrelation in the regression residuals. By incorporating the spatial pattern, the volume-based spatial error model achieves a goodness of fit (R2) of 85 percent, with a significant improvement in model performance and estimation accuracies in comparison with its OLS counterpart. The study confirms building volume as a more valuable indicator and estimator for block level population distribution, especially if an appropriate spatial autoregressive model is adopted.

A simple collisional–radiative model for low-temperature argon discharges with pressure ranging from 1 Pa to atmospheric pressure: kinetics of Paschen 1s and 2p levels

A simple collisional–radiative model for the Paschen 1s and 2p levels is proposed for low-temperature argon discharges. This model can predict the population distribution of 1s and 2p levels over a wide discharge pressure range 1–105 Pa and ionization ratio range 10−6–10−3. The modelling results are found to be in good agreement with observed optical emissions from several different types of argon discharges at 1, 100 and 105 Pa. By using the model, the dominant kinetic processes of 1s and 2p levels are investigated for an electron beam plasma, an inductively coupled plasma, a capacitively coupled plasma and a microwave microplasma. A kinetic diagram is given, which can be used to identify the kinetic state of 1s and 2p levels in many low-temperature argon discharges reported in the literature. This model is also useful for obtaining discharge parameters from optical emissions in low-temperature argon discharges.

A 236 GHz Fe3+ EPR Study of Nanoparticles of the Ferromagnetic Room-Temperature Semiconductor Sn1−x Fe x O2 (x = 0.005)

High-frequency (236 GHz) electron paramagnetic resonance (EPR) studies of Fe3+ ions at 255 K are reported in a Sn1−x Fe x O2 powder with x = 0.005, which is a ferromagnetic semiconductor at room temperature. The observed EPR spectrum can be simulated reasonably well as the overlap of spectra due to four magnetically inequivalent high-spin (HS) Fe3+ ions (S = 5/2). The spectrum intensity is calculated, using the overlap I(BL) + (I(HS1) + I(HS2) + I(HS3) + I(HS4)) × exp(−0.00001B), where B is the magnetic field intensity in Gauss, I represents the intensity of an EPR line (HS1, HS2, HS3, HS4), and BL stands for the baseline (the exponential factor, as found by fitting to the experimental spectrum, is related to the Boltzmann population distribution of energy levels at 255 K, which is the temperature of the sample in the spectrometer). These high-frequency EPR results are significantly different from those at X-band. The large values of the zero-field splitting parameter (D) observed here for the four centers at the high frequency of 236 GHz are beyond the capability of X-band, which can only record spectra of ions with much smaller D values than those reported here.

Charge-state distribution in a photoionized laser-produced plasma

We present the first x-ray spectroscopic measurements of the ionization balance relevant to astrophysics with intense laser. Independent measurement of the radiation flux indicates values of the ionization parameter ξ ∼ 10 erg cm s-1 and Planckian radiation source of 80 eV to photoionize the nitrogen gas. The observed emission spectra of nitrogen of relatively low density (ni = 1.4 × 1019 cm−3) shows a good agreement with the synthetic spectra by a time-dependent DCA (Detailed Configuration Accounting) atomic model. In this model, it solves the rate equations for level population distributions by considering collisional and radiative atomic processes based on screened hydrogenic model. The jj configuration atomic states and transition probabilities are calculated with Hullac to synthesize spectrum. With this model, we can obtain a reasonable range of the electron temperatures of 20 — 30 eV. Comparisons of charge-state distribution with a non-LTE atomic model FLYCHK show reasonable agreement.

HCN to HCO+Millimeter Line Diagnostics of AGN Molecular Tori. I. Radiative Transfer Modeling

We explore millimeter line diagnostics of an obscuring molecular torus modeled by a hydrodynamic simulation with three-dimensional non-local thermodynamic equilibrium radiative transfer calculations. Based on the results of a high-resolution hydrodynamic simulation of the molecular torus around an active galactic nucleus, we calculate the intensities of the HCN and HCO+ rotational lines as two representative high-density tracers. Three-dimensional radiative transfer calculations shed light on a complicated excitation state in the inhomogeneous torus, even though a spatially uniform chemical structure is assumed. We find that similar transition coefficients for the HCN and HCO+ rotational lines lead to a natural concordance of the level population distributions of these molecules and a line ratio RHCN/HCO+ 1 for the same molecular abundance value over 2 orders of magnitude. Our results suggest that HCN must be much more abundant than HCO+ (yHCN 10y) in order to obtain the high ratio (RHCN/HCO+ ~ 2) observed in some nearby galaxies. There is a remarkable dispersion in the relation between integrated intensity and column density, indicative of possible shortcomings of the HCN(1-0) and HCO+(1-0) lines as high-density tracers. The internal structures of inhomogeneous molecular tori down to subparsec scales in external galaxies will be revealed by the forthcoming Atacama Large Millimeter/submillimeter Array. Three-dimensional radiative transfer calculations of molecular lines with a high-resolution hydrodynamic simulation prove to be a powerful tool to provide a physical basis for molecular-line diagnostics of the central regions of external galaxies.

Commentary: Rare alleles, modest genetic effects and the need for collaboration

of the complex issues facing those trying to identify genetic variants underlying common complex disease. They focus on the common disease—common variant model where effect sizes associated with individual genetic variants are small. Undoubtedly this will be the case for most, but not all, variants. An L-shaped or exponential distribution of mutation effect sizes has wide support 2–4 with many variants with small effects, a smaller number with intermediate effects and relatively few with large effects. It could be argued that the genetic variants related to human disease that have been identified to date primarily reflect the study designs used to identify them. Linkage studies conducted among families with multiple cases of disease were successful in identifying highly penetrant variants with large effects. Association studies conducted in general population samples using common genetic markers typically find low penetrance variants with (very) small effects, as noted by Khoury. This is not unexpected given that these common genetic variants are ancient and will have been subject to some selective pressure over time. 3 We can predict that re-sequencing studies in the near future which study rarer variants (say 0.05–5%) will identify many variants of intermediate effect associated with common complex disease. This paradigm shift has already begun with the seminal work of Cohen, who compared non-synonymous sequence variations in individuals at the extremes of the population distribution of LDL-cholesterol levels, and determined that a significant fraction of genetic variance is due to multiple alleles with intermediate effects that are present at low frequencies (0.05–5%) in the population, particularly persons of African ancestry. 5 Until many such studies are reported it will be premature to decide on the relative importance of the common variant—common disease model and the alternative rare variant—common disease model which states that disease susceptibility to common diseases is the result of multiple low frequency/rare variants with larger phenotypic effects. As Cohen notes, although individually rare, these variants may be collectively common in the population. This has important consequences since the issues of causal inference and clinical application, described well by Khoury, maybe somewhat different for these variants. Our view of the genetic contribution to common complex disease is becoming clearer but is still biased as it is highly determined by available genetic technology and its cost. 6 Nevertheless, the questions raised by Khoury with respect to the common variants currently employed in genetic association studies are important to consider. The most immediate questions are perhaps how to interpret the findings of the increasing number of genome-wide association (GWA) studies which are now being conducted and how this global research effort could be most efficiently marshalled.

The model of level broadening in condensed phase

We study a model of non-Markovian kinetics for a harmonic oscillator embedded in a harmonic heat bath. We present a new scheme for approximately solving the quantum relaxation equation for the density matrix to find a distribution of level populations. It is found to be an extended Lorentzian with the width depending on the energy. A more convenient non-Markovian distribution called square root Fourier distribution that was implemented in the preceding paper [M. V. Basilevsky et al., J. Chem. Phys. 125, 194513 (2006)] is closely related to this extended Lorentzian model. Both distributions decay exponentially far away from their centers and reproduce well standard Lorentzian widths in the vicinity of the central region. A conventional Lorentzian model with such widths results when the Redfield approximation is applied in the frame of the present procedure.

FLYCHK: Generalized population kinetics and spectral model for rapid spectroscopic analysis for all elements

FLYCHK is a straightforward, rapid tool to provide ionization and population distributions of plasmas in zero dimension with accuracy sufficient for most initial estimates and in many cases is applicable for more sophisticated analysis. FLYCHK solves rate equations for level population distributions by considering collisional and radiative atomic processes. The code is designed to be straightforward to use and yet is general enough to apply for most laboratory plasmas. Further, it can be applied for low-to-high Z ions and in either steady-state or time-dependent situations. Plasmas with arbitrary electron energy distributions, single or multiple electron temperatures can be studied as well as radiation-driven plasmas. To achieve this versatility and accuracy in a code that provides rapid response we employ schematic atomic structures, scaled hydrogenic cross-sections and read-in tables. It also employs the jj configuration averaged atomic states and oscillator strengths calculated using the Dirac–Hartree–Slater model for spectrum synthesis. Numerous experimental and calculational comparisons performed in recent years show that FLYCHK provides meaningful estimates of ionization distributions, well within a charge state for most laboratory applications.

Velocity and metastable state population distributions of neodymium atoms produced by laser ablation

Laser-induced fluorescence spectroscopy has been employed to characterize the plume produced in nanosecond laser ablation of metallic neodymium. The kinetic-energy distributions of the neutral and ionized atoms in the plume under both vacuum and gas environments have been investigated. The population distribution of metastable levels in the ablated atoms was also derived. The results show that some metastable states are more heavily populated than predicted by a Boltzmann-type distribution. These investigations provide preliminary data for the design of a new type of resonance photo-ionization laser ion source as well as for high-resolution laser spectroscopy of refractory elements.

Triplet line shape simulation in continuous wave electron paramagnetic resonance experiments

We present a simple yet powerful method of simulating continuous wave electron spin resonance line shape of triplets in frozen and liquid solutions. The analysis enables one to consider cases such as immobilized triplets with random distribution, anisotropic slow and fast rotation of the triplet molecules, exchange between triplets with different Hamiltonians, anisotropic relaxation rates, and triplets with non-Boltzmann population distribution of the spin levels. Theoretical basis for the method is provided, along with several examples of simulated and experimental spectra for various physical conditions. A short “Matlab” routine, which can be used in the numerical spectra simulation, is given in the Appendix. © 2005 Wiley Periodicals, Inc. Concepts Magn Reson Part A 25A: 18–39, 2005

Photoionization Modeling and the K Lines of Iron

We calculate the efficiency of iron K line emission and iron K absorption in photoionized models using a new set of atomic data. These data are more comprehensive than those previously applied to the modeling of iron K lines from photoionized gases, and allow us to systematically examine the behavior of the properties of line emission and absorption as a function of the ionization parameter, density and column density of model constant density clouds. We show that, for example, the net fluorescence yield for the highly charged ions is sensitive to the level population distribution produced by photoionization, and these yields are generally smaller than those predicted assuming the population is according to statistical weight. We demonstrate that the effects of the many strongly damped resonances below the K ionization thresholds conspire to smear the edge, thereby potentially affecting the astrophysical interpretation of absorption features in the 7-9 keV energy band. We show that the centroid of the ensemble of K(alpha) lines, the K(beta) energy, and the ratio of the K(alpha(sub 1)) to K(alpha(sub 2)) components are all diagnostics of the ionization parameter of our model slabs.

The product branching and dynamics of the reaction of chlorine atoms with methylamine

Nascent rotational level population distributions have been measured for the HCl and DCl products of photo-initiated reaction of Cl atoms with CH3NH2, CD3NH2, CH3ND2 and CD3ND2. The use of the different isotopomers of methylamine enables the dynamics of abstraction of H/D atoms from carbon or nitrogen atoms to be distinguished, and the former channel is found to produce HCl or DCl with greater rotational excitation than the latter channel. Mean HCl rotational energies for the two reactions Cl + CH3ND2 → HCl + CH2ND2 and Cl + CD3NH2 → HCl + CD3NH are, respectively, 501 ± 84 and 122 ± 12 cm−1. Fits of the HCl and DCl rotational distributions for reaction of Cl atoms with the CH3NH2 and CD3ND2 molecules with distributions obtained from reactions of the two partially deuterated isotopomers yield branching ratios for C–H ∶ N–H and C–D ∶ N–D abstraction of 0.48 ∶ 0.52 and 0.58 ∶ 0.42, respectively. Ab initio electronic structure theory calculations of the energetics and geometries of transition states and molecular complexes along the reaction pathways for the two competing channels provide key insights to aid the interpretation of the experimental data. The computed bond angle of the N–H–Cl moiety (142.0°) in the transition state for the CH3NH forming channel deviates more from linearity than the C–H–Cl bond angle (171.1°) in the competing transition state, but leads to lower rotational excitation of the nascent HCl products. This counter-intuitive outcome is explained in terms of dipole–dipole interactions between the HCl and organic radical products as they separate.