Dynamics of prey–predator model with strong and weak Allee effect in the prey with gestation delay

This study proposes two prey–predator models with strong and weak Allee effects in prey population with Crowley–Martin functional response. Further, gestation delay of the predator population is introduced in both the models. We discussed the boundedness, local stability and Hopf-bifurcation of both nondelayed and delayed systems. The stability and direction of Hopfbifurcation is also analyzed by using Normal form theory and Center manifold theory. It is shown that species in the model with strong Allee effect become extinct beyond a threshold value of Allee parameter at low density of prey population, whereas species never become extinct in weak Allee effect if they are initially present. It is also shown that gestation delay is unable to avoiding the status of extinction. Lastly, numerical simulation is conducted to verify the theoretical findings.&nbsp

Transmitter Selection for Secrecy Against Colluding Eavesdroppers with Backhaul Uncertainty

Due to the exponential growth of interconnected devices and reduced cell coverage, beyond fifth-generation networks will be dense. Thus, instead of wired backhaul, wireless backhaul will be cost-effective and flexible. For security in multi-transmitter systems, sub-optimal and optimal transmitter selection schemes exist. However, including backhaul activity knowledge available (BKA) and backhaul activity knowledge unavailable (BKU) cases and transmitter selection schemes, there is no generalized secrecy analysis method. Moreover, evaluation of the ergodic secrecy rate (ESR) of the optimal selection schemes is impossible using existing solution approaches. To address these, we propose two sub-optimal and optimal transmitter selection schemes for a small-cell multi-transmitter system in BKU or BKA cases in the presence of multiple colluding eavesdroppers. We derive the distribution of the ratio of the destination channel SNR and eavesdropping channel SNR, thereby providing different secrecy performance metrics uniformly irrespective of selection schemes and BKU or BKA cases. Simplified asymptotic expressions are provided to elucidate the influence of the system parameters and of the backhaul reliability. We observe that the secrecy performance improves when the knowledge of backhaul link activity is utilized, and the improvement is most noticeable when the backhaul is highly unreliable. We also observe that while the secrecy performance degrades with an increasing number of eavesdroppers, neither the asymptotic saturation value of the secrecy outage probability nor the rate of improvement of the ESR with signal-to-noise-ratio depends on the number of eavesdroppers

Optimal harvesting policy of a prey–predator model with Crowley–Martin-type functional response and stage structure in the predator

In this paper, a three-dimensional dynamical model consisting of a prey, a mature predator, and an immature predator is proposed and analysed. The interaction between prey and mature predator is assumed to be of the Crowley–Martin type, and both the prey and mature predator are harvested according to catch-per-unit-effort (CPUE) hypothesis. Steady state of the system is obtained, stability analysis (local and global both) are discussed to explore the long-time behaviour of the system. The optimal harvesting policy is also discussed with the help of Pontryagin's maximum principle. The harvesting effort is taken as an effective control instrument to preserve prey and predator and to maintain them at an optimal level

Influence of laser spot size at diffuser plane on the longitudinal spatial coherence function of optical coherence microscopy system

Coherence properties and wavelength of light sources are indispensable for optical coherence microscopy/tomography as they greatly influence the signal to noise ratio, axial resolution, and penetration depth of the system. In the present letter, we investigated the longitudinal spatial coherence properties of the pseudo-thermal light source (PTS) as a function of spot size at the diffuser plane, which is controlled by translating microscope objective lens towards or away from the diffuser plane. The axial resolution of PTS is found to be maximum ~ 13 microns for the beam spot size of 3.5 mm at the diffuser plane. The change in the axial resolution of the system as the spot size is increased at the diffuser plane is further confirmed by performing experiments on standard gauge blocks of height difference of 15 microns. Thus, by appropriately choosing the beam spot size at the diffuser plane, any monochromatic laser light source depending on the biological window can be utilized to obtain high axial-resolution with large penetration depth and speckle-free tomographic images of multilayered biological specimens irrespective of the source temporal coherence length. In addition, PTS could be an attractive alternative light source for achieving high axial-resolution without needing chromatic aberration corrected optics and dispersion-compensation mechanism, unlike conventional setups.Comment: 11 pages, 4 figures. arXiv admin note: text overlap with arXiv:1810.0199

Characterization of color cross-talk of CCD detectors and its influence in multispectral quantitative phase imaging

Multi-spectral quantitative phase imaging (QPI) is an emerging imaging modality for wavelength dependent studies of several biological and industrial specimens. Simultaneous multi-spectral QPI is generally performed with color CCD cameras. However, color CCD cameras are suffered from the color crosstalk issue, which needed to be explored. Here, we present a new approach for accurately measuring the color crosstalk of 2D area detectors, without needing prior information about camera specifications. Color crosstalk of two different cameras commonly used in QPI, single chip CCD (1-CCD) and three chip CCD (3-CCD), is systematically studied and compared using compact interference microscopy. The influence of color crosstalk on the fringe width and the visibility of the monochromatic constituents corresponding to three color channels of white light interferogram are studied both through simulations and experiments. It is observed that presence of color crosstalk changes the fringe width and visibility over the imaging field of view. This leads to an unwanted non-uniform background error in the multi-spectral phase imaging of the specimens. It is demonstrated that the color crosstalk of the detector is the key limiting factor for phase measurement accuracy of simultaneous multi-spectral QPI systems.Comment: 16 pages, 8 figure

Optimal Friendly Jamming and Transmit Power Allocation in RIS-assisted Secure Communication

This paper analyzes the secrecy performance of a reconfigurable intelligent surface (RIS) assisted wireless communication system with a friendly jammer in the presence of an eavesdropper. The friendly jammer enhances the secrecy by introducing artificial noise towards the eavesdropper without degrading the reception at the destination. Approximate secrecy outage probability (SOP) is derived in closed form. We also provide a simpler approximate closed-form expression for the SOP in order to understand the effect of system parameters on the performance and to find the optimal power allocation for the transmitter and jammer. The optimal transmit and jamming power allocation factor is derived by minimizing the SOP assuming a total power constraint. It is shown that the SOP performance is significantly improved by the introduction of the jammer and a gain of approximately $3$ dB is achieved at an SOP of $10^{-4}$ by optimally allocating power compared to the case of equal power allocation

Metabolic and infectious pathologies in Brazilian medical literature: a review

OBJECTIVE: This review of original reports on metabolic and infectious diseases that were recently published in Brazilian journals is designed to inform the readership of CLINICS about their content. METHODS: I conducted a search in PubMed for original research articles (clinical or basic research) recently published (2008-2009) by Brazilian medical and biological periodicals. Papers on metabolic pathologies were retrieved by searching for appropriate keywords such as metabolic syndrome and obesity. Papers on infectious disease were obtained by entering 15 different keywords for the most commonly occurring pathologies. Review articles, editorials, letters to the editor, and case reports were manually excluded. Selected titles were then categorized into appropriate sub-categories. RESULTS: This search produced a total of 123 articles, which filtered down to 72 articles after eliminating editorials, review articles, letters to the Editor and case reports. Reviewed periodicals were Arquivos Brasileiros de Cardiologia, Arquivos Brasileiros de Endocrinologia e Metabologia, Brazilian Journal of Biological and Medical Research, Brazilian Journal of Infectious Diseases, Jornal de Pediatria, Jornal de Pneumologia, Revista da Associação Médica Brasileira, Revista da Escola de Enfermagem da Universidade de São Paulo, and São Paulo Medical Journal. The articles were then briefly summarized