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According to official statistics, cancer remains the main reason of death and over 50% of patients with cancer receive radiotherapy. However, adverse consequences after radiation exposure like radiation-induced skin reactions (RISR) have negative or even fatal impact on patients’ quality of life (QoL). In this review we summarize the mechanisms and managements of RISRs, a process that involve a variety of extracellular and intracellular signals, among which oxidative stress (OS) are now commonly believed to be the initial part of the occurrence of all types of RISRs. As for the management of RISRs, traditional treatments have been widely used but without satisfying outcomes while some promising therapeutic strategies related to OS still need further researches. In the context we discuss how OS leads to the happening of RISRs of different types, hoping it can shed some light on the exploration of new countermeasures.

For a spatial twisted central configuration of the Newtonian ($ 2N $+1)-body problem where $ 2N $ masses are at the vertices of two paralleled regular $ N $-polygons with distance $ h > 0 $, and the twist angle between the two regular $ N $-polygons is $ 0\leq\theta < 2\pi $, we study the sufficient and necessary conditions for the existence of the spatial twisted central configuration. Additionally, we obtain the uniqueness of the spatial twisted central configuration.

For double pyramidal central configurations of the Newtonian (N+2)-body problem where N point particles are positioned at the vertices of a regular N-polygon, and the (N+1)-th and (N+2)-th point-particles are positioned the opposite sides of the plane containing the polygon, and the two point particles are located on a line, which is perpendicular to the regular N-polygon, we obtain some properties of the positions, masses and values of N of these N+2 point-particles

Intensity-modulated direct-detection (IM/DD) optical systems are most widely employed in short-reach optical interconnects due to their simple structure and cost-effectiveness. However, IM/DD systems face mixed linear and nonlinear channel impairments, mainly induced by the combination of square-law detection and chromatic dispersion, as well as the utilization of low-cost non-ideal transceivers. To solve this issue, recent years have witnessed a growing trend of introducing machine learning technologies such as neural networks (NNs) into IM/DD systems for channel equalization. NNs usually present better system performance than traditional approaches, and various types of NNs have been investigated. Despite the excellent system performance, the associated high computational complexity is a major drawback that hinders the practical application of NN-based equalizers. This paper focuses on the performance and complexity trade-off of NNs employed in IM/DD systems, presenting a systematic review of the current status of NN-based equalizers as well as a number of effective complexity reduction approaches. The future trends of leveraging advanced NN in IM/DD links are also discussed.

Abstract Immune checkpoint inhibitors (ICIs) targeting CTLA-4 and PD-1/PD-L1 to boost tumor-specific T lymphocyte immunity have opened up new avenues for the treatment of various histological types of malignancies, with the possibility of durable responses and improved survival. However, the development of acquired resistance to ICI therapy over time after an initial response remains a major obstacle in cancer therapeutics. The potential mechanisms of acquired resistance to ICI therapy are still ambiguous. In this review, we focused on the current understanding of the mechanisms of acquired resistance to ICIs, including the lack of neoantigens and effective antigen presentation, mutations of IFN‐γ/JAK signaling, and activation of alternate inhibitory immune checkpoints, immunosuppressive tumor microenvironment, epigenetic modification, and dysbiosis of the gut microbiome. Further, based on these mechanisms, potential therapeutic strategies to reverse the resistance to ICIs, which could provide clinical benefits to cancer patients, are also briefly discussed.

The electrolytic refining of crude tin is generally carried out in the fluorosilicic acid (H2SiF6) system with the assistance of bone glue and β-naphthol. However, the high saturated vapor pressure and low stability of H2SiF6 present environmental concerns and do not align with sustainable development goals. In this paper, the electrochemical behavior of tin on a glassy carbon (GC) electrode was studied in a relatively green and environmentally friendly methanesulfonic acid (MSA) system. Bone glue, sodium lignosulfonate, and β-naphthol were used as additives to make the deposit morphology smooth and to ensure grain refinement. The electrochemical reduction process of Sn2+ in an MSA system is a quasi-reversible process controlled by diffusion. The apparent activation energy Ea = 14.189 kJ/mol for the ion diffusion of Sn2+ was further calculated. The results of chronoamperometry showed that the electrocrystallization of Sn2+ on the GC electrode gradually tended to three-dimensional instantaneous nucleation with the increase in applied potential. The morphology and phase of the deposits were analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results showed that the deposits were uniform and dense pure tin. This work elucidates the electrochemical behavior of tin in a methanesulfonic acid system.

Radiotherapy (RT) is an effective treatment option for multiple thoracic malignant tumors, including lung cancers, thymic cancers, and tracheal cancers. Radiation-induced lung injury (RILI) is a serious complication of radiotherapy. Radiation causes damage to the pulmonary cells and tissues. Multiple factors contribute to the progression of Radiation-induced lung injury, including genetic alterations, oxidative stress, and inflammatory responses. Especially, radiation sources contribute to oxidative stress occurrence by direct excitation and ionization of water molecules, which leads to the decomposition of water molecules and the generation of reactive oxygen species (ROS), reactive nitrogen species (RNS). Subsequently, reactive oxygen species and reactive nitrogen species overproduction can induce oxidative DNA damage. Immune cells and multiple signaling molecules play a major role in the entire process. Mesenchymal stem cells (MSCs) are pluripotent stem cells with multiple differentiation potentials, which are under investigation to treat radiation-induced lung injury. Mesenchymal stem cells can protect normal pulmonary cells from injury by targeting multiple signaling molecules to regulate immune cells and to control balance between antioxidants and prooxidants, thereby inhibiting inflammation and fibrosis. Genetically modified mesenchymal stem cells can improve the natural function of mesenchymal stem cells, including cellular survival, tissue regeneration, and homing. These reprogrammed mesenchymal stem cells can produce the desired products, including cytokines, receptors, and enzymes, which can contribute to further advances in the therapeutic application of mesenchymal stem cells. Here, we review the molecular mechanisms of radiation-induced lung injury and discuss the potential of Mesenchymal stem cells for the prevention and treatment of radiation-induced lung injury. Clarification of these key issues will make mesenchymal stem cells a more fantastic novel therapeutic strategy for radiation-induced lung injury in clinics, and the readers can have a comprehensive understanding in this fields.

Abstract In this paper, we consider the existence of multiple periodic solutions for a class of second-order difference equations with quadratic–supquadratic growth condition at infinity. Moreover, we give three examples to illustrate our main result.

Driven by emerging technologies such as the Internet of Things, 4K/8K video applications, virtual reality, and the metaverse, global internet protocol traffic has experienced an explosive growth in recent years. The surge in traffic imposes higher requirements for the data rate, spectral efficiency, cost, and power consumption of optical transceivers in short-reach optical networks, including data-center interconnects, passive optical networks, and 5G front-haul networks. Recently, a number of self-coherent detection (SCD) systems have been proposed and gained considerable attention due to their spectral efficiency and low cost. Compared with coherent detection, the narrow-linewidth and high-stable local oscillator can be saved at the receiver, significantly reducing the hardware complexity and cost of optical modules. At the same time, machine learning (ML) algorithms have demonstrated a remarkable performance in various types of optical communication applications, including channel equalization, constellation optimization, and optical performance monitoring. ML can also find its place in SCD systems in these scenarios. In this paper, we provide a comprehensive review of the recent progress in SCD systems designed for high-speed optical short- to medium-reach transmission links. We discuss the diverse applications and the future perspectives of ML for these SCD systems.

Apoptosis plays particularly important roles in tumorigenesis through various mechanisms. Apoptosis can be initiated by both extrinsic and intrinsic signals centered in and coming from the mitochondria. Antiapoptotic proteins promote tumor progression, and the occurrence and progression of tumors are closely related to antiapoptotic protein expression. As the only member of the septin gene family with proapoptotic function, apoptosis-related proteins in the TGF-β signaling pathway (ARTS) has received extensive attention for its unique structure. In contrast, unlike other known inhibitors of apoptosis protein (IAP) antagonists, ARTS exhibits a stronger tumor suppressor potential. Recent research has shown that ARTS can bind and inhibit XIAP and Bcl-2 directly or assist p53 in the degradation of Bcl-XL. Here, we review recent advances in the molecular mechanisms by which the proapoptotic protein ARTS, with its unique structure, inhibits tumorigenesis. We also discuss the possibility of mimicking ARTS to develop small-molecule drugs.

Abstract Consider the following stochastic differential equation (SDE): X t = x + ∫ 0 t b ( s , X s ) d s + ∫ 0 t σ ( s , X s ) d B s , 0 ≤ t ≤ T , x ∈ R , $$ X_{t}=x+ \int _{0}^{t}b(s,X_{s})\,ds+ \int _{0}^{t}\sigma (s,X_{s}) \,dB_{s}, \quad 0\leq t\leq T, x\in \mathbb{R}, $$ where { B s } 0 ≤ s ≤ T $\{B_{s}\}_{0\leq s\leq T}$ is a 1-dimensional standard Brownian motion on [ 0 , T ] $[0,T]$ . Suppose that q ∈ ( 1 , ∞ ] $q\in (1,\infty ]$ , p ∈ ( 1 , ∞ ) $p\in (1,\infty )$ , b = b 1 + b 2 $b=b_{1}+b_{2}$ , b 1 ∈ L q ( 0 , T ; L p ( R ) ) $b_{1}\in L^{q}(0,T;L^{p}(\mathbb{R}))$ such that 1 / p + 2 / q < 1 $1/p+2/q 0 $\delta >0$ such that σ 2 ≥ δ $\sigma ^{2}\geq \delta $ . Then there exists a weak solution to the above equation. Moreover, (i) if σ ∈ C ( [ 0 , T ] ; C u ( R ) ) $\sigma \in \mathcal{C}([0,T];\mathcal{C}_{u}(\mathbb{R}))$ , all weak solutions have the same probability law on 1-dimensional classical Wiener space on [ 0 , T ] $[0,T]$ and there is a density associated with the above SDE; (ii) if b 2 = 0 $b_{2}=0$ , p ∈ [ 2 , ∞ ) $p\in [2,\infty )$ and σ ∈ L 2 ( 0 , T ; C b 1 / 2 ( R ) ) $\sigma \in L^{2}(0,T;{\mathcal{C}}_{b}^{1/2}({\mathbb{R}}))$ , the pathwise uniqueness holds.

Abstract Objective To evaluate the association of human papilloma virus (HPV) infection with prognosis, specifically overall survival (OS) and disease‐free survival (DFS), in laryngeal squamous cell carcinoma (LSCC) patients. Method A systematic review and meta‐analysis were performed according to the Preferred Reporting Items for Systematic Reviews and Meta‐Analyses (PRISMA) guidelines. LSCC was confirmed on the basis of histopathology, whereas HPV status was confirmed by polymerase chain reaction. Results A total of 6539 articles were initially searched from 8 databases, of which 11 studies were eligible for our review. A total of 1442 LSCC cases were included in this analysis. Eight studies examined 3‐year OS for LSCC. The pooled hazard ratio (HR) from the 8 studies was 0.29 (95% CI: 0.25‐0.33). There was a statistically significant difference in 3‐year OS between the HPV‐negative and ‐positive groups, with the latter having a better survival. There was no statistically significant differences in 5‐ and 10‐year OS. Five studies examined 3‐ and 5‐year DFS for LSCC, whereas only 3 studies examined 10‐year DFS. There was no statistically significant difference in 3‐, 5‐, and 10‐year DFS between the HPV groups. Conclusion This study evaluated the survival impact of HPV infection in LSCC patients. The OS of the HPV‐positive group was better than that of the HPV‐negative group in terms of short‐term survival. Compared with the HPV‐negative group, the HPV‐positive group had a better trend of DFS, suggesting that a larger sample size and further exploration of the pathology and local control of HPV‐positive tumors are needed.

Abstract We consider nonlocal PDEs driven by additive white noises on Rd ${\mathbb{R}}^{d}$. For Lq $L^{q}$ integrable coefficients, we derive the existence and uniqueness, as well as Hölder continuity, of mild solutions. Precisely speaking, the unique mild solution is almost surely Hölder continuous with Hölder index 0

Abstract In this paper, we prove a new quantitative deformation lemma, and then gain a new mountain pass theorem in Hilbert spaces. By using the new mountain pass theorem, we obtain the new existence of two nontrivial periodic solutions for a class of nonlinear second-order discrete systems, which greatly improves the result in (Zhou et al. in Proc. R. Soc. Edinb. A 134:1013–1022, 2004).

BackgroundEpisil® is a bioadhesive barrier-forming oral liquid gel that can relieve oral mucositis (OM) caused by radiotherapy (RT) and hence relieves pain effectively. In this study, we observed the effects of Episil® on the OM and nutritional status of patients with head and neck cancers (HNCs) undergoing RT.MethodsA total of 50 HNC patients were divided into the Episil® (25 patients) and control (25 patients) groups. Patients in the Episil® group were sprayed with Episil®. In the control group, the kangfuxin solution or Kangsu™ oral gargle was used. Medical staff assessed the OM extent and timing as well as the nutritional status during treatment and recorded adverse reactions other than OM. The nutritional status assessment included the following indicators: Patient Generated-Subjective Global Assessment (PG-SGA) score, body mass index (BMI), body weight, albumin levels, and other hematological indicators.ResultsThe incidence of high-level OM (III–IV) after RT was lower in the Episil® group than in the control group (P < 0.05). Nutritional status assessments showed that the Episil® group had a lower percentage of weight loss than the control group at weeks 4 and 7 after RT. Similar results were also obtained for BMI and albumin levels (P < 0.05). Moreover, according to PG-SGA scores, fewer patients in the Episil® group were malnourished and more patients were well-nourished (P < 0.05) compared with the control group.ConclusionEpisil® effectively improved OM and malnutrition in HNC patients who received RT and has a good clinical application value.

BackgroundMicroRNAs (miRNAs) have been discovered to dictate the development of various tumors. However, studies on the roles of miRNAs in the progression of gastric cancer (GC) are still lacking.MethodsHerein, by analyzing GC cell lines and patients samples, we observed that miR-148b-5p was significantly downregulated in GC. We also confirmed that miR-148b-5p overexpression significantly inhibited GC cell proliferation and invasion in vitro and in vivo.ResultsOverexpression of miR-148b-5p not only reprogrammed the metabolic properties of GC but also regulated the immune microenvironment by shifting lymphocyte and myeloid populations. Mechanistically, ATPIF1, an important glycolysis-associated gene, was identified as a direct target of miR-148b-5p and mediated the effect of miR-148b-5p. Notably, the low level of miR-148b-5p was significantly related with poor prognosis of GC patients (P < 0.001). Importantly, the levels of miR-148b-5p significantly changed the sensitivity of GC cells to several anti-cancer drugs (Doxorubicin, P < 0.05, Paclitaxel, P < 0.01, Docetaxel, P < 0.05).ConclusionsTargeting miR-148b-5p inhibits immunity microenvironment and gastric cancer progression.

Human papillomavirus (HPV) is a risk factor for squamous cell carcinoma of the head and neck (HNSCC). This study aimed to investigate the feasibility of IHC- p16INK4a (p16) as an alternative modality for diagnosing HPV infection. We searched PubMed, EMBASE, Web of Science, and Cochrane library for studies that evaluated the diagnostic accuracy of IHC-p16 staining. A total of 30 studies involving 2,963 patients were included from 2007 to 2019. The combined sensitivity was 0.94 (95% CI: 0.92–0.95); specificity, 0.90 (95% CI: 0.89–0.91); positive likelihood ratio (LR), 6.80 (95% CI: 5.63–8.21); negative LR, 0.10 (95% CI: 0.07–0.16); diagnostic odds ratio, 85.98 (95% CI: 55.57–133.03); and area under the curve value, 0.9550. Subgroup analysis showed that the IHC-p16 test was more consistent with the in situ hybridization (ISH) test and has greater diagnostic value for oropharyngeal squamous cell carcinoma. The diagnostic efficacy of IHC-p16 varied among countries. In conclusion, IHC-p16 has high sensitivity and specificity for diagnosing HPV infection in HNSCC. The consistency of IHC-p16 findings with those of ISH indicate that their combination can be used to improve the specificity of diagnosis.

Radiotherapy has significantly improved the survival of cancer patients but is also associated with several adversities, including radiation-induced carotid injury (RICI). The RICI mechanisms are complex, including vessel inflammatory injury, carotid atherosclerosis, intimal proliferation, media necrosis, and peri-adventitial fibrosis. The main manifestation and adverse consequence of RICI is carotid artery stenosis (CAS), which can lead to stroke and transient ischemic attack. Currently, carotid artery injury is primarily diagnosed via color-coded duplex sonography. Early detection of traumatic changes in the carotid artery depends on measurements of carotid intima-media thickness; serum biomarker testing also shows great potential. CAS is mainly treated with carotid endarterectomy or carotid angioplasty and stent implantation. Notably, bone marrow mesenchymal stem cells are advantageous in RICI treatment and reduce carotid inflammation, oxidative stress, and delaying atherosclerosis. This review summarizes the mechanisms, examination methods, and latest treatments for RICI to provide data for its clinical prevention and treatment.

Radiation-induced fibrosis (RIF) is a severe long-term complication of the normal tissue following radiotherapy. Its prototypical characteristic is the persistent activation of myofibroblasts, resulting in proportion disorder and hyperplasia remodeling of the extracellular matrix comprising collagen. The continuous progress of RIF may contribute to multiple clinical manifestations such as hollow organ stenosis, impaired gaseous diffusion, and loss of tissue compliance significantly affecting the overall quality of daily life in patients with irradiated cancer. Traditionally, the potential mechanism of myofibroblast activation and differentiation has not been elucidated, and the process has been considered as static and irreversible. Recent studies have shown that RIF is a dynamic, multi-step process mediated by many regulated chemokines and cytokines. The RIF process includes release of reactive oxygen species (ROS), microvascular injury, recruitment of inflammatory cells, and activation of myofibroblasts. Numerous signaling pathways are involved in the initiation and progression of RIF, of which SMAD-regulated CTGF expression mediated by TGF-β1 is referred as the main axis. Current management strategies applied in clinical practice for patients with RIF are only supportive treatments, such as anti-inflammatory therapy using steroids; however, the efficacies achieved by these interventions are limited and unsatisfactory. Therefore, this review explores advances in RIF pathogenesis and anti-fibrosis therapy. We hope to provide clinicians with improved awareness and enormous promise in the management of RIF.

Abstract Background Sevoflurane preconditioning induces brain ischemic tolerance, but the mechanism remains poorly elucidated. Nitration is an important form of post-translational modification in pathological signaling. This study was to investigate the role of thioredoxin-1 (Trx-1) nitration in neuroprotection effect induced by sevoflurane preconditioning in a transient stroke model in rats. Methods Adult male Sprague–Dawley rats were preconditioned with 2% sevoflurane or vehicle oxygen exposure, 1 h per day, for 5 consecutive days. At 24 h after the last exposure, rats were subjected to focal brain ischemia induced by middle cerebral artery occlusion (MCAO) for 90 min, followed by 72-h reperfusion. Trx-1 expression and activity, as well as the content of nitrotyrosine at penumbra were detected at 24 h after preconditioning and 2, 8, 24, 72 h after MCAO. Nitrated Trx-1 was examined by immunoprecipitation at 8 h after MCAO. The role of Trx-1 nitration in ischemic tolerance was assessed by administration of nitrated human-Trx-1 prior to MCAO. Neurological scores, brain infarct volumes and TUNEL staining were evaluated at 24 h after reperfusion. Results Ischemic stroke decreased Trx-1 activity but not the expression in penumbra tissue. The content of nitrotyrosine was elevated after MCAO. Preconditioning with sevoflurane increased Trx-1 activity and reduced its nitration at 8 h after MCAO in comparison with vehicle preconditioning. The decrement of Trx-1 activity was correlated with its nitration level. Exogenous administration of nitrated human-Trx-1 reversed the brain ischemic tolerance of sevoflurane preconditioning, exacerbating brain infarct volume, neurobehavioral defects and apoptosis, while administration of human-Trx-1 had no effect on the sevoflurane preconditioning-induced neuroprotection. Conclusion Ischemic stroke reduces Trx-1 activity via post-translational nitrative modulation in rats. Sevoflurane preconditioning induces brain ischemic tolerance and anti-apoptosis by partially preserving Trx-1 activity via inhibiting nitration.

In this paper, we propose a faster-than-Nyquist non-orthogonal frequency-division multiplexing (NOFDM) scheme for visible light communications (VLCs) where the multiplexing/demultiplexing employs the inverse fractional cosine transform (IFrCT)/FrCT. Different to the common fractional Fourier transform-based NOFDM (FrFT-NOFDM) signal, FrCT-based NOFDM (FrCT-NOFDM) signal is real-valued, which can be directly applied to the VLC systems without the expensive up-conversion and thus it is more suitable for the cost-sensitive VLC systems. Under the same transmission rate, FrCT-NOFDM signal occupies smaller bandwidth compared to OFDM signal. When the bandwidth compression factor α is set to 0.8, 20% bandwidth saving can be obtained. Therefore, FrCT-NOFDM has higher spectral efficiency and suffers less high-frequency distortion compared to OFDM, which benefits the bandwidth-limited VLC systems. As the simulation results show, bit error rate performance of FrCT-NOFDM with α of 0.9 or 0.8 is better than that of OFDM. Meanwhile, FrCT-NOFDM has a superior security performance. In conclusion, FrCT-NOFDM shows the potential for application in the future VLC systems.

This article mainly observed the protective effect of sulforaphane (SFN) on radiation-induced skin injury (RISI). In addition, we will discuss the mechanism of SFN’s protection on RISI. The RISI model was established by the irradiation of the left thigh under intravenous anesthesia. Thirty-two C57/BL6 mice were randomly divided into control group (CON), SFN group, irradiation (IR) group, and IR plus SFN (IR/SFN) group. At eight weeks after irradiation, the morphological changes of mouse skin tissues were detected by H&E staining. Then, the oxidative stress and inflammatory response indexes in mouse skin tissues, as well as the expression of Nrf2 and its downstream antioxidant genes, were evaluated by ELISA, real-time PCR, and Western blotting. The H&E staining showed the hyperplasia of fibrous tissue in the mouse dermis and hypodermis of the IR group. Western blotting and ELISA results showed that the inflammasome of NLRP3, caspase-1, and IL-1β, as well as oxidative stress damage indicators ROS, 4-HNE, and 3-NT, in the skin tissues of mice in the IR group were significantly higher than those in the control group (p < 0.05). However, the above pathological changes declined sharply after SFN treatment (p < 0.05). In addition, the expressions of Nrf2 and its regulated antioxidant enzymes, including CAT and HO-1, were higher in the skin tissues of SFN and IR/SFN groups, but lower in the control and IR groups (p < 0.05). SFN may be able to suppress the oxidative stress by upregulating the expression and function of Nrf2, and subsequently inhibiting the activation of NLRP3 inflammasome and DNA damage, so as to prevent and alleviate the RISI.

Radiotherapy (RT) is currently one of the leading treatment for various cancers and it may cause injury to healthy tissue, with both short-term and long-term side effects. Inflammatory responses play an important role in the adverse reactions of early and late ionizing radiation. Nucleotide-binding domain and leucine-rich-repeat-containing family pyrin 3 (NLRP3) inflammasome as a multi-protein complex that activates caspase-1 can give rise to the proinflammatory cytokines such as interleukin-18 (IL-18) and interleukin-1 beta (IL-1β) maturation. Recent experiments and studies have shown that up-regulation of NLRP3 inflammasome have a big impact on radiation damage, which include radiation-induced oral mucositis, radiation-induced skin reactions, radiation-induced lung damage, radiation-induced intestinal injury and radiation-induced changes in other systems. In this paper, we will review the role of NLRP3 inflammasome in radiation damage, to explore possible therapeutic strategies for radiation damage.

A novel low-cost and energy-efficient approach for reaching 40 Gb/s signals is proposed for cost-sensitive optical access networks. Our proposed design is constituted of an innovative low-complex high-performance digital signal processing (DSP) architecture for pulse amplitude modulation (PAM-4), reuses existing commercial cost-effective 10-G components and eliminates the need of a power-hungry radio frequency (RF) component in the transmitter. Using a multi-functional 17-tap reconfigurable adaptive Volterra-based nonlinear equalizer with noise suppression, significant improvement in receiver optical power sensitivity is achieved. Results show that over 30 km of single-mode fiber (SMF) a link power budget of 33 dB is feasible at a bit-error-rate (BER) threshold of 10−3.

In order to meet the increasing capacity requirements, network operators are extending their optical infrastructure closer to the end-user while making more efficient use of the resources. In this context, long reach passive optical networks (LR-PONs) are attracting increasing attention.Coherent LR-PONs based on high speed digital signal processors represent a high potential alternative because, alongside with the inherent mixing gain and the possibility of amplitude and phase diversity formats, they pave the way to compensate linear impairments in a more efficient way than in traditional direct detection systems. The performance of coherent LR-PONs is then limited by the combined effect of noise and nonlinear distortion. The noise is particularly critical in single channel systems where, in addition to the the elevated fibre loss, the splitting losses should be considered. In such systems, Kerr induced self-phase modulation emerges as the main limitation to the maximum capacity. In this work, we propose a novel clustering algorithm, denominated histogram based clustering (HBC), that employs the spatial density of the points of a 2D histogram to identify the borders of high density areas to classify nonlinearly distorted noisy constellations. Simulation results reveal that for a 100 km long LR-PON with a 1:64 splitting ratio, at optimum power levels, HBC presents a Q-factor 0.57 dB higher than maximum likelihood and 0.21 dB higher than k-means. In terms of nonlinear tolerance, at a BER of 2×10 − 3 , our method achieves a gain of ∼2.5 dB and ∼1.25 dB over maximum likelihood and k-means, respectively. Numerical results also show that the proposed method can operate over blocks as small as 2500 symbols.

We are concerned with the initial value problem for a multidimensional balance law with multiplicative stochastic perturbations of Brownian type. Using the stochastic kinetic formulation and the Bhatnagar-Gross-Krook approximation, we prove the uniqueness and existence of stochastic entropy solutions. Furthermore, as applications, we derive the uniqueness and existence of the stochastic entropy solution for stochastic Buckley-Leverett equations and generalized stochastic Burgers type equations.

Neural networks (NNs) have been successfully applied to channel equalization for optical communications. In optical fiber communications, the linear equalizer and the nonlinear equalizer with traditional structures might be more appropriate than NNs for performing real-time digital signal processing, owing to its much lower computational complexity. However, the optimization algorithms of NNs are useful in many optimization problems. In this paper, we propose and evaluate the tap estimation schemes for the equalizer with traditional structures in optical fiber communications using the optimization algorithms commonly used in the NNs. The experimental results show that adaptive moment estimation algorithm and batch gradient descent method perform well in the tap estimation of equalizer. In conclusion, the optimization algorithms of NNs are useful in the tap estimation of equalizer with traditional structures in optical communications.

Coherent optical orthogonal frequency division multiplexing (CO-OFDM) has attracted a lot of interest in optical fiber communications due to its simplified digital signal processing (DSP) units, high spectral-efficiency, flexibility, and tolerance to linear impairments. However, CO-OFDM’s high peak-to-average power ratio imposes high vulnerability to fiber-induced non-linearities. DSP-based machine learning has been considered as a promising approach for fiber non-linearity compensation without sacrificing computational complexity. In this paper, we review the existing machine learning approaches for CO-OFDM in a common framework and review the progress in this area with a focus on practical aspects and comparison with benchmark DSP solutions.

To address the continuous growth in high-speed ubiquitous access required by residential users and enterprises, Telecommunication operators must upgrade their networks to higher data rates. For optical fiber access networks that directly connect end users to metro/regional network, capacity upgrade must be done in a cost- and energy-efficient manner. 40 Gb/s is the possible lane rate for the next generation passive optical networks (NG-PONs). Ideally, existing 10 G PON components could be reused to support 40 Gb/s lane-rate NG-PON transceiver, which requires efficient modulation format and digital signal processing (DSP) to alleviate the bandwidth limitation and fiber dispersion. The major contribution of this work is to offer insight performance comparisons of 40 Gb/s lane rate electrical three level Duobinary, optical Duobinary, and four-level pulse amplitude modulation (PAM-4) for incorporating low complex DSPs, including linear and nonlinear Volterra equalization, as well as maximum likelihood sequence estimation. Detailed analysis and comparison of the complexity of various DSP algorithms are performed. Transceiver bandwidth optimization is also undertaken. The results show that the choices of proper modulation format and DSP configuration depend on the transmission distances of interest.