Political factors, entrepreneurship and female employment vulnerability in sub-Saharan Africa.

This study examines the relationship between political factors, entrepreneurship, and female employment vulnerability in sub-Saharan Africa. Using data from the World Development Indicators (WDI) and World Governance Indicators (WGI) of the World Bank for the period 2001 - 2022, the study employs the Generalised Method of Moments to control for endogeneity. The results show that there exists an elastic relationship between voice and accountability and female vulnerability to employment in these sub-regions. It implies that a percentage increase in voice and accountability will result in a 11.9%, 3.07%, 1.08% decrease in female vulnerability to employment in Central, East, West and Southern Africa, respectively. These findings suggest that improving political institutions and reducing corruption could help to promote female entrepreneurship and reduce vulnerability in Sub-Saharan Africa.

Cette étude examine la relation entre les facteurs politiques, l'entrepreneuriat et la vulnérabilité de l'emploi des femmes en Afrique subsaharienne. Utilisant les données des Indicateurs de développement dans le monde (WDI) et des Indicateurs de gouvernance mondiale (WGI) de la Banque mondiale pour la période 2001-2022, l'étude utilise la méthode généralisée des moments pour contrôler l'endogénéité. Les résultats montrent qu'il existe une relation élastique entre la voix et la responsabilité et la vulnérabilité des femmes à l'emploi dans ces sous-régions. Cela implique qu'une augmentation en pourcentage de la voix et de la responsabilité entraînera une diminution de 11,9 %, 3,07 % et 1,08 % de la vulnérabilité des femmes à l'emploi en Afrique centrale, orientale, occidentale et australe, respectivement. Ces résultats suggèrent que l'amélioration des institutions politiques et la réduction de la corruption pourraient contribuer à promouvoir l'entrepreneuriat féminin et à réduire la vulnérabilité en Afrique subsaharienne.

Apparent change of the 3C/3D line intensity ratio in neonlike ions.

The resonance 3C ([(2p5)1/23d3/2]J=1 → [2p6]J=0) to intercombination 3D ([(2p5)3/23d5/2]J=1 → [2p6]J=0) line intensity ratio of neonlike ions has been studied. The measured line intensity ratio for neonlike Xe44+ ions shows an apparent change, which is reproduced by the calculations using the relativistic configuration interaction plus many-body perturbation theory. It is clearly elucidated that the change in the 3C/3D line intensity ratio is caused by strong configuration mixing between the upper levels of the 3D and 3F ([(2p5)1/23s]J=1 → [2p6]J=0) lines. The present measurement allows us to discuss the 3C/3D line intensity ratio for the highest-Z ions hitherto, which suggests that the experiment-theory discrepancy in the 3C/3D line intensity ratio of neonlike ions diminishes with increasing atomic number Z and further trends to vanish at higher-Z ions. Furthermore, the present study provides benefits to better understand configuration mixing effect in the radiative opacity of hot plasmas.

Transition energies and oscillator strengths for the intrashell and intershell transitions of the C-like ions in a thermodynamic equilibrium plasma environment.

We present a theoretical study of the transition energies ω and the oscillator strengths gf for the C-like ions (with Z from 14-36) subject to plasma environment for atomic transitions, which meet the spatial and temporal criteria of the Debye-Hückel (DH) approximation. Two strong dipole-allowed transitions, viz., the intrashell transition 2s2p^{3}^{3}D_{1}→2s^{2}2p^{2}^{3}P_{0}, and the intershell transition 2s^{2}2p3d^{3}D_{1}→2s^{2}2p^{2}^{3}P_{0} are investigated in detail. We found that both ω and gf increase for the intrashell transition under the Debye-Hückel screening potential V_{DH} in terms of the Debye length D, which is linked to the ratio between the plasma density N_{e} and its temperature kT. In contrast, both ω and gf decrease for the intershell transition. Our theoretically estimated data have led to a general scaling feature for the change in ω of both intershell and intrashell transitions for ions with different nuclear charge Z. A similar general feature for the change in gf is also found for the intrashell transition. However, due to the change of the electron correlations between electrons in different shells with respect to the relativistic spin-orbit interaction as Z varies, the variation of gf subject to the surrounding plasma is more complicated for the intershell transition. The results presented in this work may facilitate the plasma diagnostic to determine the plasma temperature and density for the astrophysical objects and the controlled fusion facilities.

Assisting target recognition through strong turbulence with the help of neural networks.

Imaging and target recognition through strong turbulence is regarded as one of the most challenging problems in modern turbulence research. As the aggregated turbulence distortion inevitably degrades remote targets and makes them less recognizable, both adaptive optics approaches and image correction methods will become less effective in retrieving correct attributes of the target. Meanwhile, machine learning (ML)-based algorithms have been proposed and studied using both hardware and software approaches to alleviate turbulence effects. In this work, we propose a straightforward approach that treats images with turbulence distortion as a data augmentation in the training set, and investigate the effectiveness of the ML-assisted recognition outcomes under different turbulence strengths. Retrospectively, we also apply the recognition outcomes to evaluate the turbulence strength through regression techniques. As a result, our study helps to build a deep connection between turbulence distortion and imaging effects through a standard perceptron neural network (NN), where mutual inference between turbulence levels and target recognition rates can be achieved.

Quadrant Fourier transform and its application in decoding OAM signals.

We present a new, to the best of our knowledge, concept of using quadrant Fourier transforms (QFTs) formed by microlens arrays (MLAs) to decode complex optical signals based on the optical intensity collected per quadrant area after the MLAs. From a computational optics viewpoint, we show the most promising use of the QFT in low-cost and passive decoding of laser signals carrying optical angular momenta (OAM) that are prevalent in research frontiers of optical communications, computation, and imaging. There are numerous ways of creating, adding, and combining OAM states in optical waves, while decoding or demultiplexing approaches often turn out to be complicated or expensive. The simple OAM decoder formed by a pair of identical MLAs, which are concatenated in the focal plane and transversely offset by half-pitch length, can accomplish the imaging task with four pixels per cell. By sorting the gradient curls of the optical wave into local quadrant cells, the decoder analyzes the intensity reallocation that is proportional to the gradients and computes the gradient curls accordingly. The low-cost, compactness, and simplicity of the proposed OAM sensor will further promote OAM-based applications, as well as many other applications that exploit the spatial complexity of optical signals.

Lossy wavefront sensing and correction of distorted laser beams.

The art of rectifying a laser beam carrying amplitude and phase distortions has been demonstrated through several competing methods. Both wavefront sensor and wavefront sensor-less approaches show that the closed-loop correction of a laser beam can be accomplished by exploiting high-resolution sampling of the beam distortion in its spatial or time domain, respectively. Moreover, machine-learning-based wavefront sensing has emerged recently, and uses training data on an arbitrary sensing architecture to map observed data to reasonable wavefront reconstructions. This offers additional options for beam correction and optical signal decoding in atmospheric or underwater propagation. Ideally, wavefront sensing can be achieved through any resolution in spatial samples, provided that more frequent sampling in the time domain can be achieved for a reduced number of spatial samples. However, such trade-offs have not been comprehensively studied or demonstrated experimentally. We present a fundamental study of lossy wavefront sensing that reduces the number of effective spatial samples to the number of actuators in a deformable mirror for a balanced performance of dynamic wavefront corrections. As a result, we show that lossy wavefront sensing can both simplify the design of wavefront sensors and remain effective for beam correction. In application, this concept provides ultimate freedom of hardware choices from sensor to sensorless approaches in wavefront reconstruction, which is beneficial to the frontier of study in free-space optical communication, lidar, and directed energy.

Light field camera study of near-ground turbulence anisotropy and observation of small outer-scales.

Understanding turbulence effects on laser beam propagation is critical to the emerging design, study, and test of many long-range free space optical (FSO) communication and directed energy systems. Conventional studies make the prevalent assumption of isotropic turbulence, while more recent results suggest anisotropic turbulence for atmospheric channels within a few meters elevation above the ground. As countless FSO systems have been and continue to be deployed in such channels, analysis of anisotropic modelings has become one of the fastest growing areas in FSO research. This in turn motivates new tools that can distinguish anisotropic characteristics to improve both modeling accuracy and physical interpretations. Wavefront sensors such as Shack-Hartmann sensors, interferometers, and plenoptic sensors have been devised and used in experiments; however, they all require rigid alignments that lack resilience against temperature gradient buildup and beam wander. We find that by using a light field camera (LFC) that extracts perturbation of individual light rays, the wave structure function of turbulence can be retrieved with high reliability. Furthermore, we find through experiments that the outer scales of near-ground turbulence tend to be a magnitude smaller than conventional theoretical assumptions, agreeing with new findings by others but being absent in current theoretical modelings. As a result, we believe that the LFC is an ideal candidate in the frontier of turbulence research; it is both commercially available and easy to adapt to turbulence experiments.

Measuring the turbulence profile in the lower atmospheric boundary layer.

Optical turbulence can have a severe effect on the propagation of laser beams through the atmosphere. In free space optics and directed energy applications, these laser beams quite often propagate along a slant or vertical path. In these cases, the refractive index structure function parameter cannot be assumed constant, since it varies with height. How it varies with height, especially in the first few meters above the ground, is not well behaved. Turbulence height profiles have been measured since the 1970s, mainly for astronomical observations. These profiles are usually measured for the atmospheric boundary layer (the layer of air from the ground up to approx. 1 km during day and 100 m during night) and some kilometers above it. We have measured the temperature fluctuations in the first few meters above ground level using a system containing eight resistance thermometer devices, mounted in a row at different spacings. Measurements were made flying this system under a tethered balloon or mounted on a telescoping mast. The temperature structure function parameter, CT2, can be estimated from the temperature fluctuations measured by the 28 different probe pairs and the unique distances between the two probes. Finally, Cn2 is estimated from this temperature structure function parameter and compared to values predicted by a turbulence profile model.

A Novel AURKA Mutant-Induced Early-Onset Severe Hepatocarcinogenesis Greater than Wild-Type via Activating Different Pathways in Zebrafish.

Aurora A kinase (AURKA) is an important regulator in mitotic progression and is overexpressed frequently in human cancers, including hepatocellular carcinoma (HCC). Many AURKA mutations were identified in cancer patients. Overexpressing wild-type Aurka developed a low incidence of hepatic tumors after long latency in mice. However, none of the AURKA mutant animal models have ever been described. The mechanism of mutant AURKA-mediated hepatocarcinogenesis is still unclear. A novel AURKA mutation with a.a.352 Valine to Isoleucine (V352I) was identified from clinical specimens. By using liver-specific transgenic fish overexpressing both the mutant and wild-type AURKA, the AURKA(V352I)-induced hepatocarcinogenesis was earlier and much more severe than wild-type AURKA. Although an increase of the expression of lipogenic enzyme and lipogenic factor was observed in both AURKA(V352I) and AURKA(WT) transgenic fish, AURKA(V352I) has a greater probability to promote fibrosis at 3 months compared to AURKA(WT). Furthermore, the expression levels of cell cycle/proliferation markers were higher in the AURKA(V352I) mutant than AURKA(WT) in transgenic fish, implying that the AURKA(V352I) mutant may accelerate HCC progression. Moreover, we found that the AURKA(V352I) mutant activates AKT signaling and increases nuclear ß-catenin, but AURKA(WT) only activates membrane form ß-catenin, which may account for the differences. In this study, we provide a new insight, that the AURKA(V352I) mutation contributes to early onset hepatocarcinogenesis, possibly through activation of different pathways than AURKA(WT). This transgenic fish may serve as a drug-screening platform for potential precision medicine therapeutics.

Change of the relative line strengths due to the resonance induced population transfer between Fe XVII and FeXVI ions.

We present a detailed study to resolve the discrepancy between the existing theoretically estimated oscillator strengths and the recently observed result from the X-ray free electron laser (XFEL) experiment performed at the Linac Coherent Light Source (LCLS) for the intensity ratio between two of the strongest emission lines from Ne-like Fe XVII (Fe16+) ion. By including the dynamic resonance induced population transfer due to autoionization between the coexisting Fe XVII and Fe XVI (Fe15+) ions in the XFEL experiment, we are able to successfully resolve this difference in theory and experiment. Further experimental works are suggested for a more detailed understanding of the dynamic resonance processes for ions.

Using turbulence scintillation to assist object ranging from a single camera viewpoint.

Image distortions caused by atmospheric turbulence are often treated as unwanted noise or errors in many image processing studies. Our study, however, shows that in certain scenarios the turbulence distortion can be very helpful in enhancing image processing results. This paper describes a novel approach that uses the scintillation traits recorded on a video clip to perform object ranging with reasonable accuracy from a single camera viewpoint. Conventionally, a single camera would be confused by the perspective viewing problem, where a large object far away looks the same as a small object close by. When the atmospheric turbulence phenomenon is considered, the edge or texture pixels of an object tend to scintillate and vary more with increased distance. This turbulence induced signature can be quantitatively analyzed to achieve object ranging with reasonable accuracy. Despite the inevitable fact that turbulence will cause random blurring and deformation of imaging results, it also offers convenient solutions to some remote sensing and machine vision problems, which would otherwise be difficult.

Phase and amplitude beam shaping with two deformable mirrors implementing input plane and Fourier plane phase modifications.

We find that ideas in optical image encryption can be very useful for adaptive optics in achieving simultaneous phase and amplitude shaping of a laser beam. An adaptive optics system with simultaneous phase and amplitude shaping ability is very desirable for atmospheric turbulence compensation. Atmospheric turbulence-induced beam distortions can jeopardize the effectiveness of optical power delivery for directed-energy systems and optical information delivery for free-space optical communication systems. In this paper, a prototype adaptive optics system is proposed based on a famous image encryption structure. The major change is to replace the two random phase plates at the input plane and Fourier plane of the encryption system, respectively, with two deformable mirrors that perform on-demand phase modulations. A Gaussian beam is used as an input to replace the conventional image input. We show through theory, simulation, and experiments that the slightly modified image encryption system can be used to achieve arbitrary phase and amplitude beam shaping within the limits of stroke range and influence function of the deformable mirrors. In application, the proposed technique can be used to perform mode conversion between optical beams, generate structured light signals for imaging and scanning, and compensate atmospheric turbulence-induced phase and amplitude beam distortions.

Multi-aperture laser transmissometer system for long-path aerosol extinction rate measurement.

We present the theory, design, simulation, and experimental evaluations of a new laser transmissometer system for aerosol extinction rate measurement over long paths. The transmitter emits an ON/OFF modulated Gaussian beam that does not require strict collimation. The receiver uses multiple point detectors to sample the sub-aperture irradiance of the arriving beam. The sparse detector arrangement makes our transmissometer system immune to turbulence-induced beam distortion and beam wander caused by the atmospheric channel. Turbulence effects often cause spatial discrepancies in beam propagation and lead to miscalculation of true power loss when using the conventional approach of measuring the total beam power directly with a large-aperture optical concentrator. Our transmissometer system, on the other hand, combines the readouts from distributed detectors to rule out turbulence-induced temporal power fluctuations. As a result, we show through both simulation and field experiments that our transmissometer system works accurately with turbulence strength Cn2 up to 10-12 m-2/3 over a typical 1-km atmospheric channel. In application, our turbulence- and weather-resistant laser transmissometer system has significant advantages for the measurement and study of aerosol concentration, absorption, and scattering properties, which are crucial for directed energy systems, ground-level free-space optical communication systems, environmental monitoring, and weather forecasting.

Imaging through strong turbulence with a light field approach.

Under strong turbulence conditions, object's images can be severely distorted and become unrecognizable throughout the observing time. Conventional image restoring algorithms do not perform effectively in these circumstances due to the loss of good references on the object. We propose the use a plenoptic sensor as a light field camera to map a conventional camera image onto a cell image array in the image's sub-angular spaces. Accordingly, each cell image on the plenoptic sensor is equivalent to the image acquired by a sub-aperture of the imaging lens. The wavefront distortion over the lens aperture can be analyzed by comparing cell images in the plenoptic sensor. By using a modified "Laplacian" metric, we can identify a good cell image in a plenoptic image sequence. The good cell image corresponds with the time and sub-aperture area on the imaging lens where wavefront distortion becomes relatively and momentarily "flat". As a result, it will reveal the fundamental truths of the object that would be severely distorted on normal cameras. In this paper, we will introduce the underlying physics principles and mechanisms of our approach and experimentally demonstrate its effectiveness under strong turbulence conditions. In application, our approach can be used to provide a good reference for conventional image restoring approaches under strong turbulence conditions. This approach can also be used as an independent device to perform object recognition tasks through severe turbulence distortions.

Using a plenoptic sensor to reconstruct vortex phase structures.

A branch point problem and its solution commonly involve recognizing and reconstructing a vortex phase structure around a singular point. In laser beam propagation through random media, the destructive phase contributions from various parts of a vortex phase structure will cause a dark area in the center of the beam's intensity profile. This null of intensity can, in turn, prevent the vortex phase structure from being recognized. In this Letter, we show how to use a plenoptic sensor to transform the light field of a vortex beam so that a simple and direct reconstruction algorithm can be applied to reveal the vortex phase structure. As a result, we show that the plenoptic sensor is effective in detecting branch points and can be used to reconstruct phase distortion in a beam in a wide sense.

Plenoptic mapping for imaging and retrieval of the complex field amplitude of a laser beam.

The plenoptic sensor has been developed to sample complicated beam distortions produced by turbulence in the low atmosphere (deep turbulence or strong turbulence) with high density data samples. In contrast with the conventional Shack-Hartmann wavefront sensor, which utilizes all the pixels under each lenslet of a micro-lens array (MLA) to obtain one data sample indicating sub-aperture phase gradient and photon intensity, the plenoptic sensor uses each illuminated pixel (with significant pixel value) under each MLA lenslet as a data point for local phase gradient and intensity. To characterize the working principle of a plenoptic sensor, we propose the concept of plenoptic mapping and its inverse mapping to describe the imaging and reconstruction process respectively. As a result, we show that the plenoptic mapping is an efficient method to image and reconstruct the complex field amplitude of an incident beam with just one image. With a proof of concept experiment, we show that adaptive optics (AO) phase correction can be instantaneously achieved without going through a phase reconstruction process under the concept of plenoptic mapping. The plenoptic mapping technology has high potential for applications in imaging, free space optical (FSO) communication and directed energy (DE) where atmospheric turbulence distortion needs to be compensated.

Determining the phase and amplitude distortion of a wavefront using a plenoptic sensor.

We have designed a plenoptic sensor to retrieve phase and amplitude changes resulting from a laser beam's propagation through atmospheric turbulence. Compared with the commonly restricted domain of (-π,π) in phase reconstruction by interferometers, the reconstructed phase obtained by the plenoptic sensors can be continuous up to a multiple of 2π. When compared with conventional Shack-Hartmann sensors, ambiguities caused by interference or low intensity, such as branch points and branch cuts, are less likely to happen and can be adaptively avoided by our reconstruction algorithm. In the design of our plenoptic sensor, we modified the fundamental structure of a light field camera into a mini Keplerian telescope array by accurately cascading the back focal plane of its object lens with a microlens array's front focal plane and matching the numerical aperture of both components. Unlike light field cameras designed for incoherent imaging purposes, our plenoptic sensor operates on the complex amplitude of the incident beam and distributes it into a matrix of images that are simpler and less subject to interference than a global image of the beam. Then, with the proposed reconstruction algorithms, the plenoptic sensor is able to reconstruct the wavefront and a phase screen at an appropriate depth in the field that causes the equivalent distortion on the beam. The reconstructed results can be used to guide adaptive optics systems in directing beam propagation through atmospheric turbulence. In this paper, we will show the theoretical analysis and experimental results obtained with the plenoptic sensor and its reconstruction algorithms.

From sparse to dense and from assortative to disassortative in online social networks.

Inspired by the analysis of several empirical online social networks, we propose a simple reaction-diffusion-like coevolving model, in which individuals are activated to create links based on their states, influenced by local dynamics and their own intention. It is shown that the model can reproduce the remarkable properties observed in empirical online social networks; in particular, the assortative coefficients are neutral or negative, and the power law exponents γ are smaller than 2. Moreover, we demonstrate that, under appropriate conditions, the model network naturally makes transition(s) from assortative to disassortative, and from sparse to dense in their characteristics. The model is useful in understanding the formation and evolution of online social networks.

Do scientists trace hot topics?

Do scientists follow hot topics in their scientific investigations? In this paper, by performing analysis to papers published in the American Physical Society (APS) Physical Review journals, it is found that papers are more likely to be attracted by hot fields, where the hotness of a field is measured by the number of papers belonging to the field. This indicates that scientists generally do follow hot topics. However, there are qualitative differences among scientists from various countries, among research works regarding different number of authors, different number of affiliations and different number of references. These observations could be valuable for policy makers when deciding research funding and also for individual researchers when searching for scientific projects.