On prediction of chaotic dynamics in semiconductor lasers by reservoir computing.

Studying the chaotic dynamics of semiconductor lasers is of great importance for their applications in random bit generation and secure communication. While considerable effort has been expended towards investigating these chaotic behaviors through numerical simulations and experiments, the accurate prediction of chaotic dynamics from limited observational data remains a challenge. Recent advancements in machine learning, particularly in reservoir computing, have shown promise in capturing and predicting the complex dynamics of semiconductor lasers. However, existing works on laser chaos predictions often suffer from the need for manual parameter optimization. Moreover, the generalizability of the approach remains to be investigated, i.e., concerning the influences of practical laser inherent noise and measurement noise. To address these challenges, we employ an automated optimization approach, i.e., a genetic algorithm, to select optimal reservoir parameters. This allows efficient training of the reservoir network, enabling the prediction of continuous intensity time series and reconstruction of laser dynamics. Furthermore, the impact of inherent laser noise and measurement noise on the prediction of chaotic dynamics is systematically examined through numerical analysis. Simulation results demonstrate the effectiveness and generalizability of the proposed approach in achieving accurate predictions of chaotic dynamics in semiconductor lasers.

Rogue wave generation using a chaotic semiconductor laser with energy redistribution.

We demonstrate for the first time that optical rogue waves (RWs) can be generated using a chaotic semiconductor laser with energy redistribution. Chaotic dynamics are numerically generated using the rate equation model of an optically injected laser. The chaotic emission is then sent to an energy redistribution module (ERM) that consists of a temporal phase modulation and a dispersive propagation. The process enables a temporal energy redistribution of the chaotic emission waveforms, where coherent summation of consecutive laser pulses leads to random generation of giant intensity pulses. Efficient generation of optical RWs are numerically demonstrated by varying the ERM operating parameters in the entire injection parameter space. The effects of the laser spontaneous emission noise on the generation of RWs are further investigated. The RW generation approach offers a relatively high flexibility and tolerance in the choice of ERM parameters according to the simulation results.

Predicting the dynamical behaviors for chaotic semiconductor lasers by reservoir computing.

We demonstrate the successful prediction of the continuous intensity time series and reproduction of the underlying dynamical behaviors for a chaotic semiconductor laser by reservoir computing. The laser subject to continuous-wave optical injection is considered using the rate-equation model. A reservoir network is constructed and trained using over 2 × 104 data points sampled every 1.19 ps from the simulated chaotic intensity time series. Upon careful optimization of the reservoir parameters, the future evolution of the continuous intensity time series can be accurately predicted for a time duration of longer than 0.6 ns, which is six times the reciprocal of the relaxation resonance frequency of the laser. Moreover, we demonstrate for the first time, to the best of our knowledge, that the predicted intensity time series allows for accurate reproduction of the chaotic dynamical behaviors, including the microwave power spectrum, probability density function, and the chaotic attractor. In general, the demonstrated approach offers a relatively high flexibility in the choice of reservoir parameters according to the simulation results, and it provides new insights into the learning and prediction of semiconductor laser dynamics based on measured intensity time series.

Chaotic time-delay signature suppression with bandwidth broadening by fiber propagation.

Chaotic emission of a semiconductor laser is investigated through propagation over a fiber for achieving broadening of the bandwidth and suppression of the time-delay signature (TDS). Subject to delayed optical feedback, the laser first generates chaos with a limited bandwidth and an undesirable TDS. The laser emission is then delivered over a standard single-mode fiber for experiencing self-phase modulation, together with anomalous group-velocity dispersion, which leads to the broadening of the optical bandwidth and suppression of the TDS in the intensity signal. The effects are enhanced as the input power launched to the fiber increases. By experimentally launching up to 340 mW into a 20 km fiber, the TDS is suppressed by 10 times to below 0.04, while the bandwidth is broadened by six times to above 100 GHz. The improvement of the chaotic signal is potentially useful in random bit generation and range detection applications.

Effect of long-term fertilization on wheat yield under different precipitation patterns.

Rational application of nitrogen and phosphorus is one of the main pathways to enhance wheat yield. The optimum dosage of nitrogen and phosphorus used in different precipitation patterns was studied using the binary quadratic regression equation, which could provide a basis for fertilization of wheat in Loess Plateau. The results showed that the amount of nitrogen and phosphorus ferti-lizer required for the maximum yield was dependent on precipitation patterns. The maximum wheat yield in normal years was 4229 kg·hm-2, with the dosage of nitrogen and phosphorus applied being 172 and 164 kg·hm-2, respectively. The maximum wheat yield in wet years was 4896 kg·hm-2, with the dosage of nitrogen fertilizer being 2% more than that in normal years, 175 kg·hm-2, and the dosage of phosphorus was about 1% less than that in normal years, 162 kg·hm-2. The application of nitrogen and phosphorus in dry years was about 16% and 5% less than that in normal years. When the dosage was more than that, wheat yield began to decline. The economic optimum fertilization differed in different precipitation patterns. The economic optimum nitrogen and phosphorus fertilization in normal years was 161 and 151 kg·hm-2, while in dry years it was 135, 143 kg·hm-2, respectively. The economic optimum fertilization in wet years was about 3% and 1% more than that in normal years, 167 and 153 kg·hm-2. The economic optimum fertilization was 6%-8% lower than optimum amount of fertilization. In actual production, it was recommended to reduce the amount of nitrogen and phosphorus by 10% in order to improve the utilization rate of fertilizer and get the maximum benefit.

Repression effect of metformin on photo-damage of human skin fibroblasts induced by UVA / 基础医学与临床

Objective To determine the inhibitory effect and mechanism of metformin ( MF) on photo-damage of human skin fibroblasts ( HSF) induced by UVA .Methods Human skin fibroblasts were randomly divided into con-trol group, UVA group and UVA+MF group.The proliferation of HSF was detected by CCK-8 assay kit.SA-β-gal staining was performed to evaluate the senescence state .The level of ROS was examined by fluorescence probe DCF-DA staining using flow cytometry .Real-time PCR was used to determine mRNA expression of senescence -asso-ciated signals of MMP 1 and MMP3.The protein expression of MMP 1, MMP3, SOD1 and SOD2 were measured by Western blot .R esults To the proliferation of HSF , 0.01 mmol/L Metformin had no significant effect , but 0.1 and 1 mmol/L Metformin depressed significantly ( P<0.05 ) .Compared with the Control group , it showed that UVA irradiation increased the positive rate of SA-β-gal staining ( P<0.01 ) , the level of ROS ( P<0.05 ) , mRNA and protein expression of MMP1 and MMP3 significantly(P<0.01);Also decreased the expression of SOD1 and SOD2 ( P<0.01) .Compared with the UVA group , it showed that metformin decreased the positive rate of SA-β-gal staining (P<0.05), the level of ROS(P<0.05), mRNA and protein expression of MMP1 and MMP3 significantly(P<0.05);Also increased the expression of SOD 1 ( P<0.01 ) and SOD2.Conclusions Metfomin can inhibit photo-damage of human skin fibroblasts induced by UVA via decreasing ROS and metal matrix protease generation , also the improvement of cellular antioxidant capacity .

Frequency-modulated microwave generation with feedback stabilization using an optically injected semiconductor laser.

Generation of frequency-modulated continuous-wave (FMCW) microwave signals is investigated using the period-one (P1) dynamics of a semiconductor laser. A modulated optical injection drives the laser into P1 oscillation with a modulated microwave frequency, while adding feedback to the injection reduces the microwave phase noise. Using simply a single-mode laser, the tunability of P1 dynamics allows for wide tuning of the central frequency of the FMCW signal. A sweep range reaching 7.7 GHz is demonstrated with a sweep rate of 0.42 GHz/ns. When the external modulation frequency matches the reciprocal of the feedback delay time, feedback stabilization is manifested as an increase of the frequency comb contrast by 30 dB for the FMCW microwave signal.

Randomness evaluation for an optically injected chaotic semiconductor laser by attractor reconstruction.

State-space reconstruction is investigated for evaluating the randomness generated by an optically injected semiconductor laser in chaos. The reconstruction of the attractor requires only the emission intensity time series, allowing both experimental and numerical evaluations with good qualitative agreement. The randomness generation is evaluated by the divergence of neighboring states, which is quantified by the time-dependent exponents (TDEs) as well as the associated entropies. Averaged over the entire attractor, the mean TDE is observed to be positive as it increases with the evolution time through chaotic mixing. At a constant laser noise strength, the mean TDE for chaos is observed to be greater than that for periodic dynamics, as attributed to the effect of noise amplification by chaos. After discretization, the Shannon entropies continually generated by the laser for the output bits are estimated in providing a fundamental basis for random bit generation, where a combined output bit rate reaching 200 Gb/s is illustrated using practical tests. Overall, based on the reconstructed states, the TDEs and entropies offer a direct experimental verification of the randomness generated in the chaotic laser.

Square-wave oscillations in a semiconductor ring laser subject to counter-directional delayed mutual feedback.

Square-wave (SW) switching of the lasing direction in a semiconductor ring laser (SRL) is investigated using counter-directional mutual feedback. The SRL is electrically biased to a regime that supports lasing in either counter-clockwise (CCW) or clockwise (CW) direction. The CCW and CW modes are then counter-directionally coupled by optical feedback, where the CCW-to-CW and CW-to-CCW feedback are delayed by τ1 and τ2, respectively. The mutual feedback invokes SW oscillations of the CCW and CW emission intensities with a period of T≈τ1+τ2. When τ1=τ2, symmetric SWs with a duty cycle of 50% are obtained, where the switching time and electrical linewidth of the SWs can be reduced to, respectively, 1.4 ns and 1.1 kHz by strengthening the feedback. When τ1≠τ2, asymmetric SWs are obtained with a tunable duty cycle of τ1/(τ1+τ2). High-order symmetric SWs with a period of T=(τ1+τ2)/n can also be observed for some integer n. Symmetric SWs of order n=13 with a period of T=10.3 ns are observed experimentally.

Random bit generation at tunable rates using a chaotic semiconductor laser under distributed feedback.

A semiconductor laser with distributed feedback from a fiber Bragg grating (FBG) is investigated for random bit generation (RBG). The feedback perturbs the laser to emit chaotically with the intensity being sampled periodically. The samples are then converted into random bits by a simple postprocessing of self-differencing and selecting bits. Unlike a conventional mirror that provides localized feedback, the FBG provides distributed feedback which effectively suppresses the information of the round-trip feedback delay time. Randomness is ensured even when the sampling period is commensurate with the feedback delay between the laser and the grating. Consequently, in RBG, the FBG feedback enables continuous tuning of the output bit rate, reduces the minimum sampling period, and increases the number of bits selected per sample. RBG is experimentally investigated at a sampling period continuously tunable from over 16 ns down to 50 ps, while the feedback delay is fixed at 7.7 ns. By selecting 5 least-significant bits per sample, output bit rates from 0.3 to 100 Gbps are achieved with randomness examined by the National Institute of Standards and Technology test suite.

Modulation instability in a highly nonlinear fiber for discrete-time pulsed random bit generation.

A simple yet high-speed scheme by utilizing modulation instability (MI) on the discrete-time generation of random bits is proposed and demonstrated experimentally. We develop MI pulses by pumping a highly nonlinear fiber in the anomalous dispersion regime using a mode-locked laser. MI pulses contain fluctuating pulse-to-pulse variations of peak intensities for extraction into random bits. At a repetition rate of 10 GHz, 5 bits are extracted from each pulse in generating random bits at 50 Gbps, as verified by the National Institute of Standards and Technology test suite.

[Detection of organophosphorus pesticide residue on the surface of apples using SERS].

Traditional pesticide residue detection methods are usually complicated, time-consuming, and destructive. Rapid, nondestructive, online real-time is the development direction of the pesticide testing. In the present paper, we use surface enhanced Raman spectroscopy (SERS) technique to detect the organophosphorus pesticide residue of phorate and fenthion on apple to investigate a fast, nondestructive detection method for the pesticide of phorate and tiguron on apples. The results show that the characteristic frequencies of the two organophosphorus pesticides are easier to identify using surface-enhanced Raman spectroscopy. We select Raman signal at 728 cm(-1) for phorate and that at 1 512 cm(-1) for fenthion as target peak for quantitative analysis, and use an internal standard to establish phorate and fenthion linear regression model. This method can be used as a quantitative analysis reference of phorate and fenthion.

[Diagnosis of Down's syndrome using short tandem repeat loci D21S11, D21S1440 and Penta D].

OBJECTIVE: To investigate the feasibility of genetic diagnosis of Down's syndrome (DS) using short tandem repeat (STR), and to develop a rapid and accurate method for diagnosing DS. METHODS: Quantitative fluorescence polymerase chain reaction (QF-PCR) was used to amplify STR loci D21S11, D21S1440 and Penta D of 719 samples. Three hundred and eighty-nine samples were peripheral blood, 282 were amniotic fluid, 48 were chorionic villous samples. The products were analyzed using eleterophoresis to detect DS. RESULTS: Among 652 samples with a normal karyotype, 635 showed 2 bands with a 1:1 ratio or a single band. The remaining 17 samples showed 3 bands, and were regarded as false positive results. For 67 DS samples, 53 showed 3 bands/peaks with a 1:1:1 ratio and 14 showed 2 bands/peaks with a 2:1 ratio. The sensitivity and specificity of STR loci D21S11, D21S1440 and Penta D were 76.12% and 98.62%, 71.64% and 98.93%, 89.55% and 99.85%, respectively. The overall sensitivity and specificity of 3 STR loci were 100% (67/67) and 97.39% (635/652), respectively. CONCLUSION: Compared with conventional method, author's method is simpler, more stable and rapid, and can be used for large-scale prenatal screening of DS.

Random bit generation using an optically injected semiconductor laser in chaos with oversampling.

Random bit generation is experimentally demonstrated using a semiconductor laser driven into chaos by optical injection. The laser is not subject to any feedback so that the chaotic waveform possesses very little autocorrelation. Random bit generation is achieved at a sampling rate of 10 GHz even when only a fractional bandwidth of 1.5 GHz within a much broader chaotic bandwidth is digitized. By retaining only 3 least significant bits per sample, an output bit rate of 30 Gbps is attained. The approach requires no complicated postprocessing and has no stringent requirement on the electronics bandwidth.

[Surface enhanced Raman spectroscopy (SERS) of saliva for the diagnosis of lung cancer].

Surface enhanced Raman spectroscopy (SERS) has shown the advantage of detecting low concentration biofluids presently. Saliva SERS of 21 lung cancer patients and 22 normal people were measured and differentiated in the present paper. Intensities of most peaks of lung cancer patients are weaker than that of normal people, while some stronger but with a small change rate. Those peaks were assigned to proteins and nucleic acids which indicate a corresponding decrease of those substances in saliva. Principal component analysis (PCA) and linear discriminant analysis (LDA) were used to deduce and discriminate the two groups of data, resulting in accuracy, sensitivity, and specificity being 84%, 94%, and 81%, respectively.

A spatial scan statistic for nonisotropic two-level risk cluster.

Spatial scan statistic methods are commonly used for geographical disease surveillance and cluster detection. The standard spatial scan statistic does not model any variability in the underlying risks of subregions belonging to a detected cluster. For a multilevel risk cluster, the isotonic spatial scan statistic could model a centralized high-risk kernel in the cluster. Because variations in disease risks are anisotropic owing to different social, economical, or transport factors, the real high-risk kernel will not necessarily take the central place in a whole cluster area. We propose a spatial scan statistic for a nonisotropic two-level risk cluster, which could be used to detect a whole cluster and a noncentralized high-risk kernel within the cluster simultaneously. The performance of the three methods was evaluated through an intensive simulation study. Our proposed nonisotropic two-level method showed better power and geographical precision with two-level risk cluster scenarios, especially for a noncentralized high-risk kernel. Our proposed method is illustrated using the hand-foot-mouth disease data in Pingdu City, Shandong, China in May 2009, compared with two other methods. In this practical study, the nonisotropic two-level method is the only way to precisely detect a high-risk area in a detected whole cluster.

Influence of Ginkgo biloba extract on the proliferation, apoptosis of ACC-2 cell and Survivin gene expression in adenoid cystic carcinoma of lacrimal gland

OBJECTIVE@#To explore the influence of extract of Ginkgo biloba (EGB) on the proliferation, apoptosis of ACC-2 cell and Survivin gene expression in adenoid cystic carcinoma (ACC) of lacrimal gland.@*METHODS@#ACC-2 cell in human with ACC of lacrimal gland was in vitro cultured. MTT method was used for cell proliferation detection. Annexin V/PI double-staining flow cytometer was used to detect cell apoptosis and cell cycle. Survivin gene expression was analyzed by RT-PCR and Western blotting.@*RESULTS@#EGB had inhibitory effect on the proliferation of ACC-2 cell with significant dose-effect relationship, and there was statistical difference when compared with the control group (P<0.01). The inhibitory concentration 50 % (IC(50)) is 88 mg/L. The flow cytometer test indicated that EGB can gradually increase ACC-2 cell in G(0)-G(1) stage and decrease it in G(2)-M and S stage. With the increase of dose, the apoptosis rate of ACC-2 cell was obviously increased (P<0.05 or P<0.01). EGB had certain inhibitory effect on Survivin gene expression of ACC-2 cell, and Survivin gene expression was decreased with the increasing of the EGB concentration (P<0.01).@*CONCLUSIONS@#EGB can effectively inhibit Survivin gene expression of ACC-2 cell in human with ACC of lacrimal gland, induce the apoptosis of ACC-2 cell and inhibit tumor cell proliferation.

Area disease estimation based on sentinel hospital records.

BACKGROUND: Population health attributes (such as disease incidence and prevalence) are often estimated using sentinel hospital records, which are subject to multiple sources of uncertainty. When applied to these health attributes, commonly used biased estimation techniques can lead to false conclusions and ineffective disease intervention and control. Although some estimators can account for measurement error (in the form of white noise, usually after de-trending), most mainstream health statistics techniques cannot generate unbiased and minimum error variance estimates when the available data are biased. METHODS AND FINDINGS: A new technique, called the Biased Sample Hospital-based Area Disease Estimation (B-SHADE), is introduced that generates space-time population disease estimates using biased hospital records. The effectiveness of the technique is empirically evaluated in terms of hospital records of disease incidence (for hand-foot-mouth disease and fever syndrome cases) in Shanghai (China) during a two-year period. The B-SHADE technique uses a weighted summation of sentinel hospital records to derive unbiased and minimum error variance estimates of area incidence. The calculation of these weights is the outcome of a process that combines: the available space-time information; a rigorous assessment of both, the horizontal relationships between hospital records and the vertical links between each hospital's records and the overall disease situation in the region. In this way, the representativeness of the sentinel hospital records was improved, the possible biases of these records were corrected, and the generated area incidence estimates were best linear unbiased estimates (BLUE). Using the same hospital records, the performance of the B-SHADE technique was compared against two mainstream estimators. CONCLUSIONS: The B-SHADE technique involves a hospital network-based model that blends the optimal estimation features of the Block Kriging method and the sample bias correction efficiency of the ratio estimator method. In this way, B-SHADE can overcome the limitations of both methods: Block Kriging's inadequacy concerning the correction of sample bias and spatial clustering; and the ratio estimator's limitation as regards error minimization. The generality of the B-SHADE technique is further demonstrated by the fact that it reduces to Block Kriging in the case of unbiased samples; to ratio estimator if there is no correlation between hospitals; and to simple statistic if the hospital records are neither biased nor space-time correlated. In addition to the theoretical advantages of the B-SHADE technique over the two other methods above, two real world case studies (hand-foot-mouth disease and fever syndrome cases) demonstrated its empirical superiority, as well.

A spatial scan statistic for multiple clusters.

Spatial scan statistics are commonly used for geographical disease surveillance and cluster detection. While there are multiple clusters coexisting in the study area, they become difficult to detect because of clusters' shadowing effect to each other. The recently proposed sequential method showed its better power for detecting the second weaker cluster, but did not improve the ability of detecting the first stronger cluster which is more important than the second one. We propose a new extension of the spatial scan statistic which could be used to detect multiple clusters. Through constructing two or more clusters in the alternative hypothesis, our proposed method accounts for other coexisting clusters in the detecting and evaluating process. The performance of the proposed method is compared to the sequential method through an intensive simulation study, in which our proposed method shows better power in terms of both rejecting the null hypothesis and accurately detecting the coexisting clusters. In the real study of hand-foot-mouth disease data in Pingdu city, a true cluster town is successfully detected by our proposed method, which cannot be evaluated to be statistically significant by the standard method due to another cluster's shadowing effect.

Hand, foot and mouth disease: spatiotemporal transmission and climate.

BACKGROUND: The Hand-Foot-Mouth Disease (HFMD) is the most common infectious disease in China, its total incidence being around 500,000~1,000,000 cases per year. The composite space-time disease variation is the result of underlining attribute mechanisms that could provide clues about the physiologic and demographic determinants of disease transmission and also guide the appropriate allocation of medical resources to control the disease. METHODS AND FINDINGS: HFMD cases were aggregated into 1456 counties and during a period of 11 months. Suspected climate attributes to HFMD were recorded monthly at 674 stations throughout the country and subsequently interpolated within 1456 × 11 cells across space-time (same as the number of HFMD cases) using the Bayesian Maximum Entropy (BME) method while taking into consideration the relevant uncertainty sources. The dimensionalities of the two datasets together with the integrated dataset combining the two previous ones are very high when the topologies of the space-time relationships between cells are taken into account. Using a self-organizing map (SOM) algorithm the dataset dimensionality was effectively reduced into 2 dimensions, while the spatiotemporal attribute structure was maintained. 16 types of spatiotemporal HFMD transmission were identified, and 3-4 high spatial incidence clusters of the HFMD types were found throughout China, which are basically within the scope of the monthly climate (precipitation) types. CONCLUSIONS: HFMD propagates in a composite space-time domain rather than showing a purely spatial and purely temporal variation. There is a clear relationship between HFMD occurrence and climate. HFMD cases are geographically clustered and closely linked to the monthly precipitation types of the region. The occurrence of the former depends on the later.