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We proposed and numerically studied a traceless encryption approach for physical layer security in coherent optical communications system, the most attractive advantage of which is that it is hard for eavesdroppers to be aware that the transmission signal has been encrypted because the modulation formats of encrypted signal are still the regular ones, i.e. traceless encryption. In the proposed approach, the phase only or the combination of phase and amplitude dimensions can be used for encryption and decryption. Three simple encryption rules are designed and used to investigate the encryption security performance of the scheme, in which the QPSK signal can be encrypted to be as 8PSK, QPSK and 8QAM. The results show that three simple encryption rules can cause 37.5%, 25%, 62.5% of user signal binary codes to be misinterpreted by the eavesdroppers, respectively. When the modulation formats of encrypted signal and user signal are identical, the scheme can not only cover up the real information, but also have a potential application at misleading eavesdroppers. The impacts of the control light peak power at the receiver on the decryption performance are also analysed, the results indicate that the decryption performance of the scheme has a good tolerance to the peak power fluctuation of control light at the receiver.

Estimating large and sparse inverse covariance matrix plays a fundamental role in modern multivariate analysis, because the zero entries capture the conditional independence between pairs of variables given all other variables. This estimation task can be realized by penalizing the maximum likelihood estimation with an adaptive group lasso penalty imposed directly on the elements of the inverse, which allows the estimated to have a blockwise sparse structure that is particularly useful in some applications. In the paper, we are particularly interested in studying the implementation of optimization algorithms for minimizing a class of log-determinant model. This considered minimization model, one the one hand, contains a large number of popular sparse models as special cases, but on the other hand, it poses more challenges especially in high-dimensional situations. Instead of targeting the challenging optimization problem directly, we employ the symmetric Gauss–Seidel (sGS) iteration based alternating direction method of multipliers (ADMM) to tackle the 3-block nonsmooth dual program. By choosing an appropriate proximal term, it was shown that the implemented sGS-ADMM is equivalent to the 2-block ADMM, so its convergence is followed directly from some existing theoretical results. Numerical experiments on synthetic data and real data sets, including the performance comparisons with the directly extended ADMM, demonstrate that the implemented algorithm is effective in estimating large and sparse inverse covariance matrices.

The impact of 1-(4-amino-2-hydroxyphenyl)ethanone (AHPE) from the metabolites of endophytic fungus Phomopsis liquidambari on quorum sensing (QS) of Agrobacterium tumefaciens was evaluated for the first time in this study. Exposure to AHPE at concentrations ranging from 12.5 to 50 μg/mL, the β-galactosidase activity, acyl-homoserine lactone level, swimming motility, chemotaxis, and flagella formation were significantly inhibited. qRT-PCR quantification combined with the docking analysis demonstrated that AHPE affected the QS system of A. tumefaciens by repressing the transcriptional levels of traI and traR rather than signal mimicry. 1H NMR-based metabolic analysis indicated that the metabolism of A. tumefaciens was notably disturbed with AHPE treatment. AHPE treatment also resulted in the enhanced oxidative stress in A. tumefaciens. The enhanced oxidative stress lead to the disorder of energy supply, protein synthesis, and nucleotide metabolism, and ultimately attenuated the pathogenicity of A. tumefaciens. Our study indicated that AHPE can serve as a potential pesticide to defend against A. tumefaciens.

An acousto-optic switch scheme based on optical tamm state (OTS) is proposed. The acousto-optic switch’s structure is one-dimensional photonic crystal heterostructure, which is composed of three materials: silicon dioxide, gallium arsenide and tellurium dioxide. All three materials are acousto-optic materials, which can ensure the acousto-optic effect when the ultrasonic wave and the light wave are incident at the same time. Due to the acousto-optic effect, the refractive index and thickness of one-dimensional photonic crystal heterostructures are changed by ultrasonic. The acousto-optic switch changes the ultrasonic amplitude to shift the intrinsic wavelength of OTS to the shorter wave direction. With the increase of ultrasonic amplitude, the intrinsic wavelength of OTS hardly changes after the amplitude exceeds 0.4 nm. This means that the ultrasonic wave with an amplitude of 0.4 nm can shift the intrinsic wavelength to 1538 nm. The acousto-optic switch realizes the on-off function within the permitted range. In this paper, the theoretical model of the acousto-optic switch is established. The propagation of ultrasonic wave in one-dimensional photonic crystal heterostructure is analyzed by theoretical model. The propagation of light in the medium after acousto-optic effect is analyzed by transmission matrix method. The simulation is carried out through COMSOL Multiphysics software. The results show OTS exists and localization can be seen in the electric field diagram. The acousto-optic switch of 1548.8–1551.7 nm can be realized by applying certain amplitude of ultrasonic or not. In this wavelength range, the extinction ratio is not lower than 12 dB and the insertion loss is not higher than 0.97 dB. The maximum extinction ratio is 13.17 dB, and the minimum insertion loss is only 0.65 dB. The acousto-optic switch of 1536.6–1543.3 nm can be realized by applying ultrasonic wave with amplitude corresponding to the length of incident light. In this wavelength range, the extinction ratio is not lower than 12 dB, and the insertion loss is not higher than 0.99 dB. The maximum extinction ratio is 13.15 dB, and the minimum insertion loss is only 0.65 dB. The response time of the acousto-optic switch is less than 13 ns. The acousto-optic switch has the characteristics of high extinction ratio and low insertion loss. It has a good application prospect and can be effectively applied in future optical communication.

A novel scheme for all-optical ultra-wideband signal source based on semiconductor fiber ring laser (SFRL) is proposed, in which three monocycle signals can be generated simultaneously. The effect of the bias current of the semiconductor optical amplifier (SOA) in the SFRL, the wavelength of the lasing light, the power and the wavelength of input signal light on the performance of the monocycle signals are analyzed through numerical simulation. The results show that the output monocycle pulses with better symmetry can be obtained when the bias current of SOA is in a range of 200−220 mA. The average power, the amplitude of the positive and negative pulses of the output monocycle pulses increase as the wavelength of the lasing light increases. A better performance of the monocycle pulses can be obtained under lower input signal optical power. The wavelength of the input signal light has a little effect on the output monocycle pulses.

In this paper, we propose a novel scheme for ultrafast multifunctional all-optical logic gates, which can achieve not only simple logic gates including AND, NOR, Smacr 1Smacr2,Smacr1Smacr2,XNOR, and XOR but also complex logic gates including half adder, half subtracter, decoder, and comparer based on four-wave mixing in semiconductor optical amplifiers (SOAs) with polarization-shift-keying (PolSK) modulated signals. A comprehensive polarization-dependent broadband dynamic model of this kind of ultrafast multifunctional all-optical logic gates is presented. By numerical simulation, the multifunctional all-optical logic gates are theoretically realized at 40 Gbit/s. The effects of two input signal powers, injected current, frequency detuning, and polarization dependence of SOA on the output performance of the multifunctional all-optical logic gates are theoretically investigated in detail. The results indicate that this scheme is free of pattern effect due to using the PolSK modulation format. Moreover, the nice eye opening of the logic gates indicates the good performance of the proposed ultrafast multifunctional all-optical logic gates. This scheme is potential for applications in future high bit rate optical networks.

Plasmid conjugation systems are composed of two components, the DNA transfer and replication system, or Dtr, and the mating pair formation system, or Mpf. During conjugal transfer an essential factor, called the coupling protein, is thought to interface the Dtr, in the form of the relaxosome, with the Mpf, in the form of the mating bridge. These proteins, such as TraG from the IncP1 plasmid RP4 (TraG RP4 ) and TraG and VirD4 from the conjugal transfer and T-DNA transfer systems of Ti plasmids, are believed to dictate specificity of the interactions that can occur between different Dtr and Mpf components. The Ti plasmids of Agrobacterium tumefaciens do not mobilize vectors containing the oriT of RP4, but these IncP1 plasmid derivatives lack the trans -acting Dtr functions and TraG RP4 . A. tumefaciens donors transferred a chimeric plasmid that contains the oriT and Dtr genes of RP4 and the Mpf genes of pTiC58, indicating that the Ti plasmid mating bridge can interact with the RP4 relaxosome. However, the Ti plasmid did not mobilize transfer from an IncQ relaxosome. The Ti plasmid did mobilize such plasmids if TraG RP4 was expressed in the donors. Mutations in traG RP4 with defined effects on the RP4 transfer system exhibited similar phenotypes for Ti plasmid-mediated mobilization of the IncQ vector. When provided with VirD4, the tra system of pTiC58 mobilized plasmids from the IncQ relaxosome. However, neither TraG RP4 nor VirD4 restored transfer to a traG mutant of the Ti plasmid. VirD4 also failed to complement a traG RP4 mutant for transfer from the RP4 relaxosome or for RP4-mediated mobilization from the IncQ relaxosome. TraG RP4 -mediated mobilization of the IncQ plasmid by pTiC58 did not inhibit Ti plasmid transfer, suggesting that the relaxosomes of the two plasmids do not compete for the same mating bridge. We conclude that TraG RP4 and VirD4 couples the IncQ but not the Ti plasmid relaxosome to the Ti plasmid mating bridge. However, VirD4 cannot couple the IncP1 or the IncQ relaxosome to the RP4 mating bridge. These results support a model in which the coupling proteins specify the interactions between Dtr and Mpf components of mating systems.

Two regions of the nopaline-type Ti plasmid pTiC58 are important for conjugal transfer of this element to recipient bacteria. These two regions were cloned into two independent replicons to produce a binary transfer system. For one region, oriT/tra, we constructed two derivatives, pFRtra and pDCtra-5. Each contains the oriT site and the two flanking, divergently transcribed tra operons that encode the DNA processing functions associated with the relaxosome. These two plasmids also carry traR, which encodes the transcriptional activator necessary for expression of transfer genes. The two plasmids differ by the amounts of traB sequence or sequence downstream of traG present in the construct. The second replicon, pPLE2, carries the traI/trb region. The traI gene confers production of the Agrobacterium tumefaciens N-acyl homoserine lactone autoinducer, while the remaining genes in the trb operon encode components of the mating bridge. Donors harboring the two plasmids mobilized the transfer of the plasmid carrying the oriT/tra region to an A. tumefaciens recipient at frequencies similar to that at which the intact Ti plasmid transferred. Plasmid pFRtra, which encodes most of traB, was mobilized at a frequency almost 10-fold higher than was pDCtra-5, which lacks most of the gene. A. tumefaciens donors also mobilized pFRtra to Escherichia coli and Pseudomonas fluorescens recipients at frequencies similar to those observed with A. tumefaciens recipients. Rhizobium meliloti harboring the binary system also transferred the oriT/tra component to these recipients. However, E. coli or P. fluorescens donors harboring the binary system did not transfer pFRtra to any of the recipients. Furthermore, while the A. tumefaciens and R. meliloti donors produced high levels of the autoinducer, the P. fluorescens and E. coli donors produced only trace amounts of this signal molecule. These results indicate that the tra system of pTiC58 is fully contained within the characterized tra and trb regions of the Ti plasmid, that conjugation does not require functions encoded by the vir system for maximal activity, and that while the Ti plasmid tra system recognizes diverse gram-negative bacteria as recipients, of the hosts tested, it functions only in members of the family Rhizobiaceae.

Conjugal transfer of the nopaline-type Agrobacterium Ti plasmid pTiC58 is regulated by a transcriptional activator, TraR, and a diffusible signal molecule, conjugation factor (CF). CF is a member of a family of substituted homoserine lactones (HSLs) that act as coinducers for regulating gene expression in diverse Gram-negative bacteria by a mechanism called autoinduction. In Vibrio fischeri HSL production is conferred by the luxI gene. Homologues of this gene are responsible for HSL production by other Gram-negative bacteria. A gene that we call traI, conferring production of material with CF activity, was localized to a 1-kb region at the upstream end of tra3 of pTiC58. Spectroscopy showed that the activity was authentic CF. Sequence analysis showed that traI could encode a protein of 211 amino acids, TraI, that is related to the proteins responsible for HSL production by other bacteria. A second, partial open reading frame immediately downstream of traI could encode a protein related to TrbB of plasmid RP4, which is required for conjugal transfer. Transcription of traI and of the downstream tra3 genes requires TraR and CF and initiates from the traI promoter. The results show that traI is responsible for CF production, that it is the first gene of the tra3 operon, and that expression of this operon is regulated by autoinduction.

The replicator ( rep ) of the nopaline-type Ti plasmid pTiC58 is located adjacent to the trb operon of this conjugal element. Previous genetic studies of this region (D. R. Gallie, M. Hagiya, and C. I. Kado, J. Bacteriol. 161:1034–1041, 1985) identified functions involved in partitioning, origin of replication and incompatibility, and copy number control. In this study, we determined the nucleotide sequence of a 6,146-bp segment that encompasses the rep locus of pTiC58. The region contained four full open reading frames (ORFs) and one partial ORF. The first three ORFs, oriented divergently from the traI-trb operon, are closely related to the repA , repB , and repC genes of the octopine-type Ti plasmid pTiB6S3 as well as to other repA , - B , and - C genes from the Ri plasmid pRiA4b and three large plasmids from Rhizobium spp. The fourth ORF and the partial ORF are similar to y4CG and y4CF , respectively, of the Sym plasmid pNGR234a. The 363-bp intergenic region between traI and repA contained two copies of the tra box which is the cis promoter recognition site for TraR, the quorum-sensing activator of Ti plasmid conjugal transfer. Expression of the traI-trb operon from the tra box II-associated promoter mediated by TraR and its acyl-homoserine lactone ligand, AAI, was negatively influenced by an intact tra box III. On the other hand, the region containing the two tra boxes was required for maximal expression of repA , and this expression was enhanced slightly by TraR and AAI. Copy number of a minimal rep plasmid increased five- to sevenfold in strains expressing traR but only when AAI also was provided. Consistent with this effect, constitutive expression of the quorum-sensing system resulted in an apparent increase in Ti plasmid copy number. We conclude that Ti plasmid copy number is influenced by the quorum-sensing system, suggesting a connection between conjugal transfer and vegetative replication of these virulence elements.