Scheme for a WDM-PON with colorless optical network units based on a flat optical frequency comb.

A new, to the best of our knowledge, scheme for a wavelength division multiplexing passive optical network (WDM-PON) based on a flat optical frequency comb (OFC) is proposed. Using an OFC as the optical source of the system can realize the colorlessness of optical network units (ONUs), and the direct detection of the downlink data further simplifies the ONU structure. The coherent demodulation of the uplink data improves the system performance due to the coherence of the comb lines. In this research, the proposed system is studied for its performance and power budgeting. The results show the flexibility, effectiveness, and practicability of the proposed scheme, which can be applied to future high-capacity optical access networks.

Classification of quantum correlation using deep learning.

Quantum correlation, as an intrinsic property of quantum mechanics, has been widely employed to test the fundamental physical principles and explore the quantum-enhanced technologies. However, such correlation would be drowned and even destroyed in the conditions of high levels of loss and noise, which drops into the classical realm and renders quantum advantage ineffective. Especially in low light conditions, conventional linear classifiers are unable to extract and distinguish quantum and classical correlations with high accuracy. Here we experimentally demonstrate the classification of quantum correlation using deep learning to meet the challenge in the quantum imaging scheme. We design the convolutional neural network to learn and classify the correlated photons efficiently with only 0.1 signal photons per pixel. We show that decreasing signal intensity further weakens the correlation and makes an accurate linear classification impossible, while the deep learning method has a strong robustness of such task with the accuracy of 99.99%. These results open up a new perspective to optimize the quantum correlation in low light conditions, representing a step towards diverse applications in quantum-enhanced measurement scenarios, such as super-resolution microscope, quantum illumination, etc.

Frequency measurement of microwave signals in a wide frequency range based on an optical frequency comb and channelization method.

We propose a new, to the best of our knowledge, scheme for the frequency measurement of wideband microwave signals by applying the optical frequency comb (OFC) and channelization technique. Unlike the usual method of using radio-frequency driving signals to generate an OFC, our scheme uses digital driving signals, which makes the comb spacing adjustable and the comb bandwidth wider. In the measurement process, multiple sets of beat signals can be obtained at the same time, and multiple frequency components of the microwave signals can be measured at the same time. The theoretical analysis model of the scheme is established, and the scheme is validated by VPI simulation software. The results show that the range of frequency measurement is 0∼50GHz, and it can be further expanded by extending the width of the OFC.

Colony composition and nutrient analysis of Polyrhachis dives ants, a natural prey of the Chinese pangolin (Manis pentadactyla).

The Chinese pangolin (Manis pentadactyla) is a critically endangered mammal with a highly specialized diet. To enhance nutritional knowledge of its diet, we analyzed the colony composition of a nest of Polyrhachis dives ants, which is the key natural prey in the Chinese pangolin's diet. In addition, we determined the nutrient composition of the total colony compared with adult ants. Nutrients quantified in this study included: crude protein, crude fat, carbohydrate, and amino acids, minerals, and vitamins, as well as formic acid and chitin, which have not been reported in previous diet studies. Our results showed that the colony consisted of adults (82%), pupae (10%), larvae (7%), and eggs (1%) (fresh mass). Both the total colony and adult ants, respectively, contained high concentrations of crude protein (62.97% and 64.68%), chitin (49.25% and 60.40%), crude fat (10.12% and 9.91%) (dry matter basis), and formic acid (2.06% and 3.07%) (fresh mass). This implies that Chinese pangolin might prefer prey with high protein, high chitin, low fat, and low formic acid content. Colony and adult ants differed in chemical composition in many aspects, thus it might be unsuitable to feed Chinese pangolin with only adult ants. Chitin and formic acid may play important roles in the diet and selectivity of Chinese pangolin. This study provides reference information that may be useful for developing better artificial diets with more comprehensive nutrient compositional data to meet the nutritional requirements of the Chinese pangolin under managed feeding programs.

Thresholded single-photon underwater imaging and detection.

Optical underwater target imaging and detection have been a tough but significant challenge in deep-sea exploration. Distant reflected signals drown in various underwater noises due to strong absorption and scattering, resulting in degraded image contrast and reduced detection range. Single-photon feature operating at the fundamental limit of the classical electromagnetic waves can broaden the realm of quantum technologies. Here we experimentally demonstrate a thresholded single-photon imaging and detection scheme to extract photon signals from the noisy underwater environment. We reconstruct the images obtained in a high-loss underwater environment by using photon-limited computational algorithms. Furthermore, we achieve a capability of underwater detection down to 0.8 photons per pulse at Jerlov type III water up to 50 meters, which is equivalent to more than 9 attenuation lengths. The results break the limits of classical underwater imaging and detection and may lead to many quantum-enhanced applications, like air-to-sea target tracking and deep-sea optical exploration.

Ultra-flat optical frequency comb generation based on a polarization modulator and a Butterworth band-stop filter.

A new, to the best of our knowledge, scheme for the generation of ultra-flat optical frequency combs (OFCs) is proposed, which mainly uses a polarization modulator (PolM) and a first-order Butterworth band-stop filter. The PolM is driven by a digital periodic square-wave signal, and the output of the PolM is an uneven OFC. The function of the Butterworth band-stop filter is to obtain flat and stable OFCs by changing its bandwidth. The comb spacing of the OFCs can be adjusted by changing the period of the square-wave signal. The theoretical model for the scheme is also established. The simulation results show that the generator constructed according to the proposed scheme can produce 64, 128, and 256 comb lines with 200 MHz comb spacing and with spectral flatness lower than 0.3 dB. The comb spacing can be further increased by using the square-wave signal at GHz rates, and the generated OFCs exhibit good frequency tunability.

Flat optical frequency comb generation based on a dual-parallel Mach-Zehnder modulator and a single recirculation frequency shift loop.

To generate a flat optical frequency comb (OFC), a new scheme based on a dual-parallel Mach-Zehnder modulator and a single recirculation frequency shift loop is proposed and analyzed. Compared with the traditional single loop recirculation frequency shift method, the quantity of comb lines is doubled, and the comb flatness is better when the number of cycles is the same. The theoretical analysis model is established, and the simulation results show that a 111-line OFC with frequency spacing of 10 GHz, flatness of 1.32 dB, and optical signal to noise ratio of 27.4 dB can be obtained by adopting the proposed scheme.

Reproductive behavior of the captive Sunda pangolin (Manis javanica Desmarest, 1822).

Understanding reproductive behavior is important for the conservation of endangered species, but research on the reproductive behavior of Sunda pangolins (Manis javanica Desmarest, 1822) is still very scarce. In this study, we used focal animal sampling and all-occurrence recording by an infrared monitor to observe the behaviors of two Sunda pangolins during a 5-day breeding period at the Pangolin Research Base for Artificial Rescue and Conservation Breeding of South China Normal University (PRB-SCNU). The behavioral characteristics and breeding strategies were analyzed, and the results were discussed together with information on other captive Sunda pangolin pairs at PRB-SCNU. The results found that there was no obvious estrus behavior in the captive female, while the male could exhibit sexual excitement and courtship behavior after a brief introduction period. Repeated copulation continued over many days after the female accepted the courtship. The average duration of copulatory behavior was 248.9 ± 148.7 s (n = 25), and all copulation occurred between 20:00 and 08:00 hr in the natural day-night photoperiod. The mating position of Sunda pangolins was lateral-ventral and was classified as the ninth or eleventh pattern under both Dewsbury's and Dixson's classification systems. This study can provide scientific guidance for the captive breeding and management of Sunda pangolins and other pangolin species, which is of great significance for ex situ conservation tactics.

Microwave multi-frequency measurement based on an optical frequency comb and a photonic channelized receiver.

A new method, to the best of our knowledge, to measure frequencies of received microwave signal based on an optical frequency comb (OFC) and a photonic multi-channel receiver is proposed and simulated. The measurement system mainly includes a seed laser, an OFC generator composed of two cascaded Mach-Zehnder modulators, a frequency shifter, an intensity modulator, a wavelength-division demultiplexer, photodiodes (PDs), and electrical filters. Two sets of beat signals need to be obtained in the measurement process. By analyzing the two sets of beat signals, multiple frequency components of the microwave signal can be measured at a time. The validity of the proposed scheme is verified by VPI simulation software. It is shown that microwave frequencies within dozens of gigahertz can be precisely measured, and factors affecting the frequency measurement range are also studied.

Keeping and breeding the rescued Sunda pangolins (Manis javanica) in captivity.

The Sunda pangolin (Manis javanica Desmarest, 1822) is a Critically Endangered species. Given that this species lacks effective policies for in situ conservation and prevention of poaching in the wild, ex situ conservation and a captive breeding program are urgently needed to save this species from extinction. However, techniques for the maintenance and captive breeding of pangolins have not been well developed. In June 2010, we established the Pangolin Research Base for Artificial Rescue and Conservation Breeding of South China Normal University (PRB-SCNU). To date, a total of 34 Sunda pangolin cubs have been born at PRB-SCNU, 26 of which were captive bred, indicating great progress in keeping and breeding the Sunda pangolin. The techniques for maintenance-including housing, transitioning to an artificial diet, husbandry, and captive breeding-are described in this paper. The purpose of this manuscript is to share our successful experiences and techniques in the maintenance, management, and captive breeding of Sunda pangolins, and to provide guidance and a reference for the captive care and management of Sunda pangolins and other pangolin species.

Conservation genomics of the critically endangered Chinese pangolin.

The Chinese pangolin (Manis pentadactyla, MP) has been extensively exploited and is now on the brink of extinction, but its population structure, evolutionary history, and adaptive potential are unclear. Here, we analyzed 94 genomes from three subspecies of the Chinese pangolin and identified three distinct genetic clusters (MPA, MPB, and MPC), with MPB further divided into MPB1 and MPB2 subpopulations. The divergence of these populations was driven by past climate change. For MPB2 and MPC, recent human activities have caused dramatic population decline and small population size as well as increased inbreeding, but not decrease in genomic variation and increase in genetic load probably due to strong gene flow; therefore, it is crucial to strengthen in situ habitat management for these two populations. By contrast, although human activities have a milder impact on MPA, it is at high risk of extinction due to long-term contraction and isolation, and genetic rescue is urgently needed. MPB1 exhibited a relatively healthy population status and can potentially serve as a source population. Overall, our findings provide novel insights into the conservation of the Chinese pangolin and biogeography of the mammals of eastern Asia.

Observation of a Photonic Orbital Gauge Field.

Gauge field is widely studied in natural and artificial materials. With an effective magnetic field for uncharged particles, many intriguing phenomena are observed in several systems like photonic Floquet topological insulator. However, previous researches about the gauge field mostly focus on limited dimensions such as the Dirac spinor in graphene materials. Here, an orbital gauge field based on photonic triangular lattices is first proposed and experimentally observed. Disclination defects with Frank angle Ω created on such lattices breaks the original lattice symmetry and generates purely geometric gauge field operating on orbital basis functions. Interestingly, it is found that bound states near zero energy with the orbital angular momentum (OAM) l = 2 are intensively confined at the disclination as gradually expanding Ω. Moreover, the introduction of a vector potential field breaks the time-reversal symmetry of the orbital gauge field, experimentally manifested by the chiral transmission of light on helical waveguides. The orbital gauge field further suggests fantastic applications of manipulating the vortex light in photonic integrated devices.

Only Sunda and Chinese pangolin (Pholidota) are naturally distributed in China.

Actually, only two pangolin species occur naturally in China, namely the Chinese pangolin (Manis pentadactyla) and the Sunda pangolin (Manis javanica). The Sunda pangolin was found to occur naturally in Yunnan, China, but only with a narrow distribution in the Xishuangbanna and Pu'er City. The Indian pangolin (Manis crassicaudata) did not occur in China. The previous claim that this species is naturally distributed in China was found to originate from a mistake in the book "The Mammals of China and Mongolia" written by Allen in 1938.

Weaning period and growth patterns of captive Sunda pangolin (Manis javanica) cubs.

This study tracked and recorded the weight changes of 13 captive Sunda pangolin cubs from lactation to maturity to explored the appropriate weaning time and reveal the rules of its weight growth. SPSS 25.0 was used to build a cubic equation model to fit the body weight change rules of 4 individuals who nonvoluntarily ingested artificial feed (NIAF) at 127 days after birth and 5 individuals who voluntarily ingested artificial feed (VIAF) at 86-108 days after birth. The body weight of NIAF cubs aged 0-120 days and VIAF cubs aged 0-150 days were estimated according to the fitting model. An independent sample T-test was performed on the mean body weight of the two groups during the late lactation period. The results showed that at 105 days after birth, the body weight of the VIAF group was significantly higher than that of the NIAF group (P = 0.049), and the body weight of the VIAF group was extremely significantly higher than that of the NIAF group at 114 days (P = 0.008); The peak cumulative body weight of the NIAF cubs during lactation appeared around 130 days of age (n = 3); The mortality rate was 66.7% (n = 3) after about 150 days if the feed was continuously consumed nonvoluntarily. It was concluded that the milk secretion period of the mother is about 0-5 months after giving birth; the weaning period of the cubs should be 4-5 months after birth. If the cubs don't follow the mother to eat artificial feed for 3 months after birth, it can start be induced with artificial diet which adds termites, and the time point cannot be later than 130 days, otherwise it is not conducive to the survival of the cubs; When sexually mature, the body length and body weight of female cubs account for about 84% and 60% of the adult, respectively; the body maturity and body weight of female cubs tend to be stable about 15.3 months and 16.4 months, respectively. Finally, a special needle-shaped nipples and nursing patterns of female Sunda pangolins were also recorded in this study. These findings play an important role in guiding the nursing of captive Sunda pangolin cubs and other pangolin cubs. It is expected to improve the survival rate of the cubs by exploring the appropriate weaning time and the rules of weight growth. By scientifically planning the reproductive cycle of the female Sunda pangolins, our goal is to expand the population size and eventually release to the wild, meanwhile improving knowledge of this critically endangered species.

The gut microbiome of the Sunda pangolin (Manis javanica) reveals its adaptation to specialized myrmecophagy.

BACKGROUND: The gut microbiomes of mammals are closely related to the diets of their hosts. The Sunda pangolin (Manis javanica) is a specialized myrmecophage, but its gut microbiome has rarely been studied. METHODS: Using high-throughput Illumina barcoded 16S rRNA amplicons of nine fecal samples from nine captive Sunda pangolins, we investigated their gut microbiomes. RESULTS: The detected bacteria were classified into 14 phyla, 24 classes, 48 orders, 97 families, and 271 genera. The main bacterial phyla were Firmicutes (73.71%), Proteobacteria (18.42%), Actinobacteria (3.44%), and Bacteroidetes (0.51%). In the PCoA and neighbor-net network (PERMANOVA: pangolins vs. other diets, weighted UniFrac distance p < 0.01, unweighted UniFrac distance p < 0.001), the gut microbiomes of the Sunda pangolins were distinct from those of mammals with different diets, but were much closer to other myrmecophages, and to carnivores, while distant from herbivores. We identified some gut microbiomes related to the digestion of chitin, including Lactococcus, Bacteroides, Bacillus, and Staphylococcus species, which confirms that the gut microbiome of pangolins may help them to digest chitin. SIGNIFICANCE: The results will aid studies of extreme dietary adaption and the mechanisms of diet differentiation in mammals, as well as metagenomic studies, captive breeding, and ex situ conservation of pangolins.

Body temperatures of Manis pentadactyla and Manis javanica.

Body temperature is an important parameter for assessing animal health and physiological function. An iButton thermometer was used to measure the body temperatures of three Chinese pangolins (Manis pentadacyla) and three Sunda pangolins (M. javanica). The body temperature of Chinese pangolins was 33.2 ± 0.95°C (30.6-34.2°C, n = 3) and that of Sunda pangolins was 32.8 ± 0.48°C (31.7-34.2°C, n = 3). The daily variation in body temperature was 1.0-2.9°C in three Chinese pangolins and 1.2-1.9°C in three Sunda pangolins. The body temperature of Sunda pangolins tended to rise at night, with the highest body temperatures occurring mostly at night. This study provides valuable body temperature data for Chinese and Sunda pangolins and lays the foundation for future research on their mechanisms of body temperature regulation.

Vitamin A deficiency and its treatment in captive Sunda pangolins.

The high incidence of disease in captive pangolins is a major obstacle in pangolin-conservation breeding programs. Therefore, elucidating pangolins' susceptibility to disease is the key to conservation progress. At the Pangolin Research Base for Artificial Rescue and Conservation Breeding of South China Normal University (PRB-SCNU), vitamin A deficiency was diagnosed in 14 captive Sunda pangolins. Typical eye signs included lacrimal eyes, keratopathy and a blank, milky orb. The afflicted pangolins were treated with vitamins A and D for 15-30 days; all individuals recovered. We report the detection and treatment of vitamin A deficiency in captive Sunda pangolins at the PRB-SCNU. Our results could provide guidance for the future prevention and treatment of vitamin A deficiency and associated diseases in pangolin species, both to reduce the incidence of these diseases in captive pangolins and to aid conservation efforts.

Expression Profile of the Digestive Enzymes of Manis javanica Reveals Its Adaptation to Diet Specialization.

The expression of animal digestive enzymes reflects important dietary adaptations. The pangolin, also known as scaly anteater, is a specialized myrmecophage that consumes mainly ants and termites, but its digestive enzymes have not been fully investigated. Therefore, in this study, we used shotgun proteomic analysis to examine the protein components of the saliva and intestinal juice of a Sunda pangolin (Manis javanica) that died shortly after being rescued. The intestinal juice contained greater variety of digestive enzymes, including α-amylase, maltase-glucoamylase, α,α-trehalase, sucrase-isomaltase, pepsin A, trypsin, pancreatic endopeptidase E, carboxypeptidase A1, carboxypeptidase B, dipeptidyl-peptidase 4, and pancreatic triacylglycerol lipase. The digestive enzymes identified in the saliva were maltase-glucoamylase and trypsin, and chitinase which was also found in the intestinal juice. Compared with other animals, the Sunda pangolin has less intestinal protease diversity and lacks key digestive enzymes, such as chymotrypsin and pancreatic elastase. The expression profile of the digestive enzymes of the Sunda pangolin reveals animal's adaptation to a diet consisting mainly of ants and termites. Our results will facilitate the preparation of artificial food for rescued pangolins and for those in captivity for conservation breeding efforts.

A note on captive breeding and reproductive parameters of the Chinese pangolin, Manis pentadactyla Linnaeus, 1758.

The Chinese pangolin (Manis pentadactyla Linnaeus, 1758) is a critically endangered species, and documents on its captive breeding and reproductive parameters are scarce. MP8, kept in the Pangolin Research Base for Artificial Rescue and Conservation Breeding of South China Normal University (the PRB-SCNU), gave birth to a male offspring (MP86) on 19 October 2011. The baby pangolin was well developed, with a weight of 120 g and a total length of 23.2 cm. The gestation length of MP8 was estimated to be from 182 to 225d. Reproductive parameters of the Chinese pangolin are discussed based on collected data about this species. The Chinese pangolin has an obvious reproductive seasonality and its gestation length is typically six to seven months. In this observation, estrus and mating principally occurred in a one-year period from February to July. Parturition principally took place from September to February of the next year. Chinese pangolins usually give birth to one offspring at a time (n = 27). Sex ratio at birth was 0.71:1 (♀:♂, n = 12). Average weight for the reproducible females was 3.57 ± 1.38 kg (2.14-6.8 kg, n = 15). We estimated that Chinese pangolins could reach sexual maturity before they were one year old.

[A preliminary study on burrow ecology of Manis pentadactyla].

A total of 61 pangolin(Manis pentadactyla) burrows at Dawuling Natural Reserve were recorded and measured from June 2000 to May 2001, and 40 of them were dissected. The results indicated that all the burrows were blind without branch. The long diameter of entrance was 14.20 +/- 2.79 cm(n = 61), and the short one was 12.50 +/- 2.83 cm(n = 61). These burrows could be divided into two types, i.e., winter burrows and summer burrows. Winter burrows were relatively deeper(1.44 +/- 0.73 m, n = 28), and summer burrows were relatively shallower (0.32 +/- 0.11 m, n = 12). The soil in burrows was usually soft, damp and thick, with a thick surface layer of organic matter. The main motive of digging burrows was to prey on termites, hibernate, rest, breed, hide, and defense. The mean residing duration of pangolin in a burrow was 12.25 +/- 2.25 d. Pangolin rarely utilized the used burrows, and the reutilization rate of used burrows was only 8.33%. The surroundings factors of 61 burrows were recorded, and divided into 9 categories and 27 subcategories. According to the occurrence frequency of each factor and the cluster analysis results of 61 burrows, the habitat selection of pangolin was discussed, which showed that pangolin preferred creating burrows at the sites with weak human disturbance (distance from disturbance source beyond 1,000 m), steep slope(30 degrees-60 degrees), half sunny and half shady slope, mixed coniferous and broadleaf forest, moderate elevation(760-1,500 m), good hiding conditions at entrance(full cover or partial cover), middle or lower slope location, and easily accessing to water source(distance from water source within 500 m). Pangolin was averse to establish burrows at the habitats with shady slope, poor hiding condition at entrance(bare), sharp steeper(> 60 degrees) or gentle (< 30) slope, higher elevation (over 1,500 m), and coniferous forest. Pangolin preferred south facing, and strongly avoided north facing entrance.