Gain Distribution Research Articles

Parity-time symmetry in coherently coupled vertical cavity laser arrays

We report parity-time (PT) symmetry breaking in electrically injected, coherently coupled, vertical cavity surface emitting laser arrays. We predict beam steering, mode evolution and mode hopping as a consequence of the non-Hermiticity of the array analyzed by temporal coupled mode theory with both asymmetric gain distribution and local frequency detuning. We present experimental confirmation of the predicted mode evolution, mode hopping and PT symmetry breaking with quantitative agreement with the theory.

Erratum to: Spatial–temporal gain distribution of a CuBr vapor brightness amplifier

Erratum to: Spatial–temporal gain distribution of a CuBr vapor brightness amplifier

Theoretical analysis of uniform longitudinal gain for a double-end-pumped Yb:YAG multi-slab pulsed amplifier

For high average power lasers with double-end-pumped multi-slab (DEPMS) configuration, a non-uniform gain distribution within each slab caused by the step-doped multi-slab will lead to the amplified spontaneous emission (ASE) effect and then reduce the laser performance. As an example, longitudinal gradient doping is used in a DEPMS Yb:YAG pulsed amplifier to create uniform longitudinal gain (ULG) and then the ASE effect is effectively reduced. The ULG is theoretically derived and we show that the energy storage can be increased by 9% with ULG compared with the step-doped DEPMS. We found that the optimal pump efficiency, longitudinal gain-length product and columnar doping density are determined by the launched pump intensity. Numerical simulation also demonstrated that optimization of the amplifier with uniform gain and high pump efficiency can be achieved by placing additional gradient slabs to the original gradient doping slabs. Our investigations might provide an efficient way to carefully optimize a DEPMS pulsed amplifier with higher efficiency.

Low-profile patch antennas for biomedical and wireless applications

Printed microstrip-fed antennas based on a slotted radiating patch are proposed herein. First, a basic rectangular antenna without any slots was designed, being suitable for wideband applications and showing impedance bandwidth of 2714 MHz for $$S_{11} < -10$$S11<-10 dB. Next, dual-band operation for worldwide interoperability for microwave access (WiMAX, from 3.11 to 3.97 GHz) and wireless local-area network (WLAN, 4.97---5.71 GHz) was obtained by including slots only on the left side of the basic design. Then, using a structure with slots on the right side of the radiating patch, WLAN operation was obtained in the frequency range of 2.865---2.096 GHz. The fourth antenna, with slots on both sides of the patch, was characterized and realized for biomedical applications at 2.45 GHz ($$S_{11} <-10$$S11<-10 dB). The proposed antennas can be realized with small ground plane size and total antenna area of only $$27.5 \times 21\,\hbox {mm}^{2}$$27.5×21mm2. This reduction in total antenna area is achieved by using a truncated patch. All the simulations were carried out using Empire XCcel. The designs were characterized based on their radiation pattern, return loss, voltage standing wave ratio (VSWR), gain, and current distribution. The simulated and measured results show good compatibility.

General coupled-mode analysis of a geometrically symmetric waveguide array with nonuniform gain and loss

The exceptional point (EP) is one of the typical properties of parity–time-symmetric systems, arising from modes coupling with identical resonant frequencies or propagation constants in optics. Here we show that in addition to two different modes coupling, a nonuniform distribution of gain and loss leads to an offset from the original propagation constants, including both real and imaginary parts, resulting in the absence of EP. These behaviors are examined by the general coupled-mode theory from the first principle of the Maxwell equations, which yields results that are more accurate than those from the classical coupled-mode theory. Numerical verification via the finite element method is provided. In the end, we present an approach to achieve lossless propagation in a geometrically symmetric waveguide array.

X-ray energy self-adaption high dynamic range (HDR) imaging based on linear constraints with variable energy

In X-ray imaging, the image quality is related to the ray energy, imaging detector, object construction, etc. For complex workpieces, if all imaging conditions are identical, not all of the construction projection information can be captured with a fixed energy and limited dynamic range. This will result in over- and underexposed regions, which will affect projection quality. Thus, this paper presents an approach to extend the dynamic range of X-ray imaging systems based on linear constraints with variable energy. First, we study the relationship of grey variation between the adjacent energy images and present the grey gain distribution and linear dispersion. Then, based on a piecewise curve linear approximation, auto-self-adaption variation of ray energy is used to capture the image sequences under the linear constraint of the grey gain distribution. Also, based on the linear assumption, we obtain the weighting fusion coefficient to fuse the image sequences to extend the dynamic range. Finally, experiments demonstrate that this method has an advantage for ray energy auto-control and fusion coefficient calculation, which can realize optimal matching between the X-ray imaging system and the testing object to extend the dynamic range of the imaging system.

Suppression of far-field blooming in high-power broad-area diode lasers by optimizing gain distribution

Far-field blooming, a serious far-field dependence on driving current, affects the stability of beam quality and applications of broad-area (BA) diode lasers. In this Letter, the lateral ridge waveguide (LRW) is introduced to BA lasers by a simple and cost-effective approach to control the far-field stability and beam divergence. The influences of LRW length on output power, near- and far-field, are investigated and it is found that the optimized LRW length is able to improve both the far-field blooming and output power. The mechanism behind this is analyzed and a 0.13°/A dependence of lateral divergence angle on the injection current is achieved.

1 J, 1 Hz lamp-pumped high-gain Nd: phosphate glass laser amplifier

We present a lamp-pumped Nd: phosphate glass laser amplifier delivering up to 1 J of pulse energy at 1053 nm with a repetition rate of 1 Hz and an injected pulse energy of 2.5 mJ. The amplifier system employs a beam-shaping module and a four-pass, lamp-pumped amplifier. The thermally induced wavefront distortion is mitigated and a uniform gain distribution is obtained by a four-lamp-pumped laser head in the amplifier. Thus, an excellent beam quality is obtained.

Secrecy Outage Analysis of k-th Best Link in Random Wireless Networks

In this paper, we analyze the secrecy characteristics of random wireless networks using stochastic geometric tools. The locations of the source and eavesdropper nodes are modeled as independent 2-D Poisson point processes. We investigate the secrecy outage probability of such networks from the perspective of the $k$ th best source, which has still not been well characterized. In particular, we derive the received path gain distributions of the typical destination and the eavesdropper from the $k$ th best source. Furthermore, we introduce a novel concept of security-region based on the $k$ th best source index. This is pragmatic in creating a protected communication zone for the typical destination and also to bind the number of sources that can coordinate in a coordinated multi-point transmission (CoMP) network. We further derive the secrecy outage probability for these CoMP sources based on the security-region. We also provide a closed-form expression for the maximum number of eavesdroppers for a given secrecy outage constraint, which can effect the secure communication. Tractable numerical, and simulation results are presented under various assumptions of densities, path loss exponents, and antenna figures.

Establishment and Verification of Solar Radiation Calculation Model of Glass Daylighting Roof in Hot Summer and Warm Winter Zone in China

In this paper, solar heat gain through glass daylighting roof is deeply studied by theoretical calculation method, taking Guangzhou in the Hot Summer and Warm Winter (HSWW) zone as an example. The direct solar radiation is calculated by Bouguer formula whereas the diffuse solar radiation is calculated by Berlage formula, representing the basis for the calculation method of the solar radiation intensity through the glass daylighting roof. Through the establishment of solar radiation calculation model, the solar heat gain of the commonly used glass types has been calculated and analyzed, especially comparatively analyzing of Low-E cored-glass with double-coated silver and 6+12A+6 insulating glass. Then, comparison between solar heat gain as calculated and measured by field measurement tested the indoor solar radiation heat gain distribution by using adjacent rooms with different glass types in a hot summer area, with the aim of demonstrating the effectiveness of the model. The research in this paper is expected to further improve the calculation accuracy of both thermal load and indoor temperature.

Economics of fairness within the food supply chain in context of the EU

The paper broaches the issue of unfair trading practices (UTPs) at the expense of, economically spoken, weaker actors among the food supply chain in context of the EU. For illustrating the concept of UTPs and delivering a theoretical basis for scrutinizing the term of fairness in respective trading practices the paper suggests the three variables 1) bargaining power, 2) market power/anti competitive practices and 3) unequal gain distribution. Subsequently the article presents selected national food-specific legislative based reactions towards UTPs evolved in context of the three variables. Ultimately the paper presents a qualitatively generated hypothesis which presumes that legislative food-specific measurements focussing on protecting suppliers lead to a beneficial monetary share for farmers, by means of influencing the producer price to a monetarily advantageous extent. The hypothesis was generated unprejudiced in the run-up to the paper. The research design which led to the hypothesis mentioned will be presented.

517: The distribution of gestational weight gain and associated adverse neonatal outcomes

517: The distribution of gestational weight gain and associated adverse neonatal outcomes

Low-energy LED lighting heat gain distribution in buildings, part II: LED luminaire selection and test results

Lighting heat gains are a significant contributor to space cooling load in buildings and it is important to determine the lighting heat gain distribution—specifically, the fraction of convective and radiative heat gains, as well as the fraction of conditioned space and plenum space heat gains. Traditional lighting's heat gain distribution has been determined and the data are available on the ASHRAE Handbook. However, there is a lack of relevant data for the light-emitting diodes lighting heat gain. As the light-emitting diodes technology and application are rapidly growing, the need to identify light-emitting diodes lighting heat gain becomes highly demanded. In this project (ASHRAE RP-1681), 14 commercially available light-emitting diodes lighting luminaries’ heat gain distributions were determined through systematically designed experiments. The split between the convective heat gain and the radiative heat gain, and the split between the conditioned space heat gain and ceiling plenum heat gain were determined for these luminaries. A companion article describes the test approach and pilot test results. This article introduces luminaires selection and analyses the formal test results.

Simulations of the gain profile and performance of a diode side-pumped QCW Nd:YAG laser.

A design of a diode side-pumped Nd:YAG laser module and simulations of the gain distribution inside the active medium are presented in this paper. The code is based on a nonsequential ray-tracing Monte Carlo method for the light generated by the laser diodes. The fluorescence image of the active medium was analyzed in order to compare it with the simulations, which were found to be in good agreement with experimental data. The laser was tested in QCW mode and provided a maximum average power of 220 W while maintaining constant energy per pulse in the 100-1000 Hz range.

Low-energy LED lighting heat gain distribution in buildings, part 1: Approach and pilot test

Lighting heat gains are a significant contributor to space cooling load in buildings and it is important to determine the lighting heat gain distribution—specifically, the fraction of convective and radiative heat gains, as well as the fraction of conditioned space and plenum space heat gains. Traditional lighting's heat gain distribution has been determined and the data are available on the ASHRAE Handbook. However, there is a lack of relevant data for the light-emitting diode lighting heat gain. As the light-emitting diode technology and application are rapidly growing, the need to identify light-emitting diode lighting heat gain becomes highly demanded. In this project (ASHRAE RP-1681), 14 commercially available light-emitting diode lighting luminaries’ heat gain distributions were determined through systematically designed experiments. The split between the convective heat gain and the radiative heat gain, and the split between the conditioned space heat gain and ceiling plenum heat gain were determined for these luminaries. This article describes the test approach and pilot test results, and a companion article introduces luminaires selection and analyses the formal test results.

Gestational weight gain rate in third trimester relates to maternal and neonatal outcomes in pregnancies with normal glucose tolerance

Objective To investigate the association between third-trimester gestational weight gain rate (GWGR) and both maternal and neonatal health outcomes in a normal glucose tolerance obstetric population. Methods This was a retrospective cohort study of full-term singleton live births (n=1 967) in women with a normal oral glucose tolerance test (OGTT) tested at 24-28 gestational weeks, who gave birth at Beijing Obstetrics and Gynecology Hospital, Capital Medical University, between January and December in 2013. The subjects were divided into three groups based on third-trimester GWGR category of the 2009 Institute of Medicine (IOM) guidelines. Each group was divided into three subgroups by pre-pregnancy body mass index (BMI): low (<18.5), normal (≥18.5-<25.0), and high (≥25.0). One-way analysis of variance, Chi-square or Fisher's exact test, Logistic regression and corrected analysis were performed for statistical analysis. Results (1) Of the 1 967 women analyzed, third-trimester weight gain distribution was normal in 575(29.2%), excessive in 982(49.9%), and insufficient in 410(20.8%). No significant differences were found in terms of age, parity, education level, family history of diabetes or hypertension among the GWGR groups (all P>0.05). (2) The mean third-trimester weight gain in the 1 967 normal OGTT women was (0.56±0.23) kg/week and the mean neonatal birth weight was (3 442±396) g. The above two parameters were linearly correlated (Y=103.839X+3383.752, r=0.621, P 0.05). (3) Compared to the normal GWGR group, the excessive GWGR group had an increased incidence of cesarean section [30.2% (297/982) vs 22.2% (128/575)] and hypertensive disorders of pregnancy [4.0% (39/982) vs 1.9% (11/575)] (all P 0.05). (4) In the normal and insufficient GWGR groups, no differences in neonatal birth weight or risk of small-for-gestational age (SGA) or large-for-gestational age (LGA) were seen in any of the BMI subgroups (all P>0.05). In the excessive GWGR group, the high pre-pregnant BMI subgroup showed higher neonatal birth weight than the normal pre-pregnant BMI subgroup [(3 552.3±445.0) vs (3 481.8±416.1) g, P<0.01], and the low pre-pregnant BMI subgroup showed lower neonatal birth weight (3 352.7±371.2) g than the normal pre-pregnant BMI subgroup (P<0.01). Moreover, the high pre-pregnant BMI subgroup in the excessive GWGR group had an increased risk of fetal macrosomia (OR=1.60, 95%CI: 1.11-2.81). Conversely, the low pre-pregnant BMI subgroup in the excessive GWGR group had a decreased risk of fetal macrosomia (OR=0.52, 95%CI: 0.29-0.97) (all P<0.05). The high BMI subgroup had a greater risk of hypertensive disorders of pregnancy than the normal BMI subgroup in all GWGR groups (all P<0.05). The incidence of surgical delivery or NICU admission was not significantly different among the three GWGR subgroups. Conclusions Excessive weight gain in third-trimester is common in normal OGTT women. Excessive gestational weight gain is associated with adverse maternal and neonatal outcomes. Thus, gestational weight gain in the third-trimester should be adequately monitored and a balance in weight gain within the range recommended by the 2009 IOM guidelines should be established in normal OGTT pregnant women. Key words: Pregnancy; Weight gain; Pregnancy trimester, third; Body mass index; Birth weight; Infant, newborn; Pregnancy outcome

High-efficiency, 154 W CW, diode-pumped Raman fiber laser with brightness enhancement.

We demonstrate a high-power, high-efficiency Raman fiber laser pumped directly by laser diode modules at 978nm. 154W of CW power were obtained at a wavelength of 1023nm with an optical to optical efficiency of 65%. A commercial graded-index (GRIN) core fiber acts as the Raman fiber in a power oscillator configuration, which includes spectral selection to prevent generation of the second Stokes. In addition, brightness enhancement of the pump beam by a factor of 8.4 is attained due to the Raman gain distribution profile in the GRIN fiber. To the best of our knowledge this is the highest power and highest efficiency Raman fiber laser demonstrated in any configuration allowing brightness enhancement (i.e., in either cladding-pumped configuration or with GRIN fibers, excluding step-index core pumped), regardless of pumping scheme (i.e., either diode pumped or fiber laser pumped).

On dividends in the phase–type dual risk model

The dual risk model assumes that the surplus of a company decreases at a constant rate over time, and grows by means of upward jumps which occur at random times with random sizes. In the present work, we study the dual risk renewal model when the waiting times are phase-type distributed. Using the roots of the fundamental and the generalized Lundberg’s equations, we get expressions for the ruin probability and the Laplace transform of the time of ruin for an arbitrary single gain distribution. Then, we address the calculation of expected discounted future dividends particularly when the individual common gains follow a phase-type distribution. We further show that the optimal dividend barrier does not depend on the initial reserve. As far as the roots of the Lundberg equations and the time of ruin are concerned, we address the existing formulae in the corresponding Sparre-Andersen insurance risk model for the first hitting time, and we generalize them to cover also the situations where we have multiple roots. We do that working a new approach and technique, approach we also use for working the dividends, unlike others, it can be also applied for every situation.

Effects of initiating moderate wine intake on abdominal adipose tissue in adults with type 2 diabetes: a 2-year randomized controlled trial.

To generate evidence-based conclusions about the effect of wine consumption on weight gain and abdominal fat accumulation and distribution in patients with type 2 diabetes. In the 2-year randomized controlled CASCADE (CArdiovaSCulAr Diabetes & Ethanol) trial, patients following a Mediterranean diet were randomly assigned to drink 150 ml of mineral water, white wine or red wine with dinner for 2 years. Visceral adiposity and abdominal fat distribution were measured in a subgroup of sixty-five participants, using abdominal MRI. Ben-Gurion University of the Negev, Soroka-Medical Center and the Nuclear Research Center Negev, Israel. Alcohol-abstaining adults with well-controlled type 2 diabetes. Forty-eight participants (red wine, n 27; mineral water, n 21) who completed a second MRI measurement were included in the 2-year analysis. Similar weight losses (sd) were observed: red wine 1·3 (3·9) kg; water 1·0 (4·2) kg (P=0·8 between groups). Changes (95 % CI) in abdominal adipose-tissue distribution were similar: red wine, visceral adipose tissue (VAT) -3·0 (-8·0, 2·0) %, deep subcutaneous adipose tissue (DSAT) +5·2 (-1·1, 11·6) %, superficial subcutaneous adipose tissue (SSAT) -1·9 (-5·0, 1·2) %; water, VAT -3·2 (-8·9, 2·5) %, DSAT +2·9 (-2·8, 8·6) %, SSAT -0·15 (-3·3, 2·9) %. No changes in antidiabetic medication and no substantial changes in energy intake (+126 (sd 2889) kJ/d (+30·2 (sd 690) kcal/d), P=0·8) were recorded. A 2-year decrease in glycated Hb (β=0·28, P=0·05) was associated with a decrease in VAT. Moderate wine consumption, as part of a Mediterranean diet, in persons with controlled diabetes did not promote weight gain or abdominal adiposity.

The parameterization of microchannel‐plate‐based detection systems

AbstractThe most common instrument for low‐energy plasmas consists of a top‐hat electrostatic analyzer (ESA) geometry coupled with a microchannel‐plate‐based (MCP‐based) detection system. While the electrostatic optics for such sensors are readily simulated and parameterized during the laboratory calibration process, the detection system is often less well characterized. Here we develop a comprehensive mathematical description of particle detection systems. As a function of instrument azimuthal angle, we parameterize (1) particle scattering within the ESA and at the surface of the MCP, (2) the probability distribution of MCP gain for an incident particle, (3) electron charge cloud spreading between the MCP and anode board, and (4) capacitive coupling between adjacent discrete anodes. Using the Dual Electron Spectrometers on the Fast Plasma Investigation on NASA's Magnetospheric Multiscale mission as an example, we demonstrate a method for extracting these fundamental detection system parameters from laboratory calibration. We further show that parameters that will evolve in flight, namely, MCP gain, can be determined through application of this model to specifically tailored in‐flight calibration activities. This methodology provides a robust characterization of sensor suite performance throughout mission lifetime. The model developed in this work is not only applicable to existing sensors but also can be used as an analytical design tool for future particle instrumentation.