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We propose a machine learning-based nonsymmetrical demodulation technique relying on clustering to mitigate time-varying distortions derived from several impairments such as IQ imbalance, bias drift, phase noise and interchannel interference. Experimental results show that those impairments cause centroid movements in the received constellations seen in time-windows of 10k symbols in controlled scenarios. In our demodulation technique, the k-means algorithm iteratively identifies the cluster centroids in the constellation of the received symbols in short time windows by means of the optimization of decision thresholds for a minimum BER. We experimentally verified the effectiveness of this computationally efficient technique in multicarrier 16QAM Nyquist-WDM systems over 270 km links. Our nonsymmetrical demodulation technique outperforms the conventional QAM demodulation technique, reducing the OSNR requirement up to ∼0.8 dB at a BER of 1 × 10−2 for signals affected by interchannel interference.

This paper presents a characterization of interchannel interference (ICI) effects in gridless Nyquist-WDM systems due to two contributions, namely, overlapping among optical carriers and stimulation of nonlinear optical fiber impairments. ICI is assessed regarding bit error rate (BER) at 16 and 32 Gbaud, as a function of several system parameters. Nonlinear impairment compensation based on the digital back-propagation algorithm is implemented in the DSP-based coherent receiver. Results demonstrated that ICI due to channels overlapped has a higher impact concerning BER than nonlinear optical fiber impairments. Besides, the use of the back-propagation algorithm improves system performance, reducing up to 3 and 0.7 orders of magnitude of BER in QPSK and 16QAM cases, respectively. It means that this algorithm can minimize nonlinear effects under varying system parameters, but its performance is limited in sub-Nyquist cases. Resumen: en este artículo, se presenta una caracterización sistemática de los efectos de la interferencia intercanal (ICI) en sistemas Nyquist-wdm debido a dos contribuciones: i) traslape espectral de las portadoras y ii) estimulación de los efectos no lineales de la fibra óptica. La ICI se evalúa en términos de la tasa de error de bit (VER) a 16 Gbaudios y 32 Gbaudios, como función de la potencia de diversos parámetros del sistema. Se implementa en el dsp del receptor coherente un ecualizador no lineal basado en el algoritmo backpropagation, para compensar los efectos no lineales en la señal recibida. Los resultados demostraron que la ICI debido a los canales traslapados tiene mayor impacto en la BER que la ICI debido a las no linealidades de la fibra óptica sin traslape. Además, el ecualizador no lineal mejora el desempeño del sistema al reducir la BER hasta 3 y 0.7 órdenes de magnitud para QPSK y 16QAM, respectivamente. Esto significa que el algoritmo backpropagation puede minimizar efectos no lineales de la ICI bajo variaciones en los parámetros del sistema, pero su desempeño se limita en escenarios con espaciamiento espectral sub-Nyquist.

In order to improve the quality of service for the final user, content operators are implementing regional data centers to have the content closer to end users and optimize network latencies. This implies a change in the internet architecture. Traditional transport networks are migrating to data center or inter-cloud interconnection networks to satisfy the demands of the market. The objective of this paper is to propose a migration methodology from the current transport networks to the intercloud networks in order to the operators adapt their networks to take care of the investments and remain in force in the market, analyzing different fiber types, and networks scenarios that can help to improve the quality, latency and flexibility of the telecommunication system.

In this paper, we present a comb generation conformed by twenty one subcarriers with a fixed space, following the ITU-T G.694.1 recommendation for Elastic Optical Networks. This generation is done through optical frequency comb generator (OFCG) using a single Mach Zehnder Modulator (MZM). The performance of 3 subcarriers is evaluated as a function of transmission distance in a wavelength division multiplexing (WDM) system based on coherent detection. It is demonstrated a successful transmission up to 100 km. Improvement in terms of BER by using combs centered at 193.2875 THz and 193.3250 THz are obtained in comparison with single lasers.

Actualmente en Colombia ha comenzado el despliegue de la fi bra optica hasta el hogar, con el fi n de que los operadores de telecomunicaciones ofrezcan servicios de mayor capacidad, aprovechando el gran ancho de banda que proporciona la fi bra optica. Para la masifi cacion de esta tecnologia y el cubrimiento de todos los usuarios fi nales, las redes deben ser de bajo costo, por lo cual los sistemas modulados en intensidad con deteccion directa ( IM-DD) siguen vigentes a pesar de las ventajas de los receptores opticos coherentes. No obstante, en los sistemas IM-DD, las senales transmitidas se ven mas afectadas ante las imperfecciones de la fi bra optica como lo es la dispersion cromatica, causante de la interferencia inter-simbolo, la cual provoca el aumento de la tasa de error de bit ( BER ) . En este articulo se presenta una red optica IM-DD simulada en Virtual Photonics®( VPI ) , para transmision de senales con modulacion No-Return-to-Zero On-Off-Keying ( NRZ-OOK) de hasta 40 Gbps, con longitudes de fi bra optica monomodo estandar hasta de 80 km. Se plantea la compensacion de los efectos del canal optico mediante la ecualizacion electrica usando el algoritmo de LMS ( Least-Mean-Square ) , estimando los coefi cientes del canal a traves de secuencias de entrenamiento, presentando una reduccion signifi cativa del BER a 10 Gbps con respecto a la relacion senal a ruido ( SNR ) . Ademas, se comparan los resultados con un ecualizador MLSE ( Maximunlikelihood sequence estimation ) , el cual reduce en menor medida el BER en comparacion a la ecualizacion LMS..

We study and experimentally evaluate the modulation index influence on Mach-Zehnder Modulator in external modulation at low-radio frequency voltage (2.277 V pp ) to improve the system performance of a coherent receiver based-on 3×3 coupler. The system achieves a sensitivity of −29 dBm in the error-free condition, after propagation through 60 km-long fiber link at a frequency carrier of 15 GHz, offering a cost-effective solution for centralized radio access network (C-RAN).

This paper presents the analysis by simulation of the incidence of the RS error correction technique in the performance of an EPON point-to-point link. The RS technique is based on the Euclidean algorithm and is modified by including the solution system of linear equations Gauss Jordan in the determination of the error value. Mathematical processes are performed in the field of finite number. The measurements show that the RS(255.239) coding scheme gives the EPON system a coding gain of 0.98 dB.

A phase-offset compensation by dual-stage ring fragmentation and clustering of 16-QAM and APSK constellation is demonstrated experimentally in RoF scenario. OSNR improvements of 3.3 dB and 1.4 dB for 16-QAM and 12+4 PSK, respectively, are obtained.

Background Clinical decision support for Clostridioides difficile infection (CDI) diagnostics reduces inappropriate testing, leading to decreased need for isolation and antibiotic use. Our institution utilized manual discontinuation by laboratory staff of CDI testing for inappropriate specimens, including formed stool and age < 1 year. We aimed to assess the financial impact of instituting a CDI best practice alert at a quaternary care children’s hospital. Methods A multidisciplinary team mapped inappropriate testing criteria identified from literature review with discrete fields in our electronic health record (EHR, EpicCare) to design an alert. The exclusion criteria identified included: (1) age < 1 year; (2) positive C. difficile test within past 14 days; (3) less than or equal to 3 unformed stools in past 24 hours; (4) current receipt of CDI-directed therapy; or (5) laxative use or barium exposure in prior 48 hours. 6 months of data prior to implementation were reviewed to estimate impact of the alert. At implementation, any exclusion criteria detected in the EHR at the time of order entry triggered an alert to deter CDI testing. Cost estimates for averted tests (Quick Check Complete Assay/Illumigene) included cost of test ($50), cost of isolation/personal protective equipment ($159/day), and cost of treatment with oral vancomycin in false-positives ($2250/treatment course). Results In a 6-month pre-implementation period, 586 tests for CDI were ordered; of which, 23% were identified by our criteria as inappropriate. During the first 3 months of alert implementation, 256 tests were ordered, of which 105 (41%) caused the alert to fire. Of those, 56 tests were not ordered, for a 22% reduction in testing. Laboratory staff continued to manually stop tests not meeting criteria, such as patient age Conclusion Implementation of an alert for select patients using a bioinformatics algorithm reduced inappropriate CDI testing. Clinical decision support for CDI can lead to substantial cost savings for both antibiotic use and isolation precautions. Disclosures All authors: No reported disclosures.

Background Human adenovirus (HAdV) is a documented source of morbidity and mortality after hematopoietic cell transplant (HCT); however, there are limited data documenting HAdV species and type in this population. Understanding the molecular characteristics of HAdV could inform the development and assessment of interventions. The species and type of HAdV-positive specimens are detailed using an archived convenience sample of specimens obtained in pediatric HCT recipients. Methods The cohort included autologous and allogeneic HCT recipients between January 2000 and December 2013. An archived clinical repository of frozen specimens was interrogated to identify residual HAdV-positive specimens, which were sent to Lovelace Respiratory Research Institute (LRRI) to determine species and type. Medical chart review was performed to determine whether an isolate was related to HAdV disease or HAdV-attributable death. Results There were 547 HAdV PCR-positive clinical specimens from 87 HCT recipients. Of the 547 specimens, 289 were identified from an archived repository and sent to LRRI to determine species and type, and HAdV was successfully isolated and typed from 61 (Figure 1). Species C was the most common species (59.0%) with C2 being the most frequent type (34.4%). Of the 15 recipients with type C2, plasma was the most common specimen source (57.1%). Three recipients with C2 had this species and type detected from multiple sources (Tables 1 and 2). Among those with a typing result, type C2 also was responsible for 33.3% of all HAdV-attributed disease and 38.1% of all HAdV-attributed death. Conclusion Species C was the most common species to be isolated in a convenience sample of HAdV-positive clinical specimens from a single-center cohort of pediatric HCT recipients. Type C2 was most commonly associated with HAdV disease and attributable death. These results suggest HAdV species and type influence the impact of HAdV in this patient population. The findings need to be confirmed in prospective cohorts but suggest real-time molecular typing may be relevant and provide possible targets for the development of future interventions. These results must be interpreted with caution; not all clinical specimens were available for molecular typing, and it is possible C2 is easier to isolate from archived specimens. Disclosures All authors: No reported disclosures.

Mycoplasmas, including Ureaplasma and Mycoplasma species, are uncommon but important causes of septic arthritis, especially affecting immunosuppressed patients. Many of the reported cases have been associated with congenital immunodeficiency disorders, especially hypogammaglobulinemia. Mycoplasmas are difficult to grow in the laboratory, and these infections may be underdiagnosed using culture techniques. We report a case of a 21-year-old woman with juvenile idiopathic arthritis and hip arthroplasties treated with rituximab and adalimumab who developed urogenital infections and soft tissue abscesses followed by knee arthritis with negative routine cultures. Ureaplasma species was identified from synovial fluid on 2 separate occasions using a broad-range 16S ribosomal RNA gene polymerase chain reaction. Azithromycin led to rapid improvement in symptoms, but after completion of therapy, involvement of the hip prosthesis became apparent, and again, 16S rRNA gene polymerase chain reaction was positive for Ureaplasma species. The literature is reviewed with a discussion of risk factors for Mycoplasma septic arthritis, clinical presentation, methods of diagnosis, and treatment.

Extended-spectrum β-lactamases (ESBLs) pose a threat to public health because of their ability to confer resistance to extended-spectrum cephalosporins such as cefotaxime. The CTX-M β-lactamases are the most widespread ESBL enzymes among antibiotic resistant bacteria. Many of the active site residues are conserved between the CTX-M family and non-ESBL β-lactamases such as TEM-1, but the residues Ser237 and Arg276 are specific to the CTX-M family, suggesting that they may help to define the increased specificity for cefotaxime hydrolysis. To test this hypothesis, site-directed mutagenesis of these positions was performed in the CTX-M-14 β-lactamase. Substitutions of Ser237 and Arg276 with their TEM-1 counterparts, Ala237 and Asn276, had a modest effect on cefotaxime hydrolysis, as did removal of the Arg276 side chain in an R276A mutant. The S237A:R276N and S237A:R276A double mutants, however, exhibited 29- and 14-fold losses in catalytic efficiency for cefotaxime hydrolysis, respectively, while the catalytic efficiency for benzylpenicillin hydrolysis was unchanged. Therefore, together, the Ser237 and Arg276 residues are important contributors to the cefotaximase substrate profile of the enzyme. High-resolution crystal structures of the CTX-M-14 S70G, S70G:S237A, and S70G:S237A:R276A variants alone and in complex with cefotaxime show that residues Ser237 and Arg276 in the wild-type enzyme promote the expansion of the active site to accommodate cefotaxime and favor a conformation of cefotaxime that allows optimal contacts between the enzyme and substrate. The conservation of these residues, linked to their effects on structure and catalysis, imply that their coevolution is an important specificity determinant in the CTX-M family.

In this paper, performance evaluation of different transmitters enabling colorless operation for WDM— PONs applications is carried out. Injected Locked Fabry Perot Laser Diode (IL-FPLD) and Reflective Semiconductor Optical Amplifier (RSOA) in external seeding and wavelength reuse scheme are modeled in VPITransmissionMaker® simulation platform. Upstream transmissions are performed at 1.25 Gb/s with distances up to 40 km, achieving a BER of ∼ 1×10−10, with an aggregate capacity of 40 Gb/s by using IL-FPLD. For the RSOA with external seeding, upstream transmission rates of 1.25 Gb/s and downstream transmission of 5 Gb/s are achieved in 43 km of fiber link achieving a BER of ∼ 1×10−10. For a RSOA in wavelength reuse scheme, symmetric rates of 1.25 Gb/s per lambda for transmission distances up to 20 km, are achieved with a BER of ∼ 1×10−12.

Urinary tract infections are one of the most common reasons for health care visits. Diagnosis and optimal treatment often require a urine culture, which takes an average of 1.5 to 2 days from urine collection to results, delaying optimal therapy. Faster, but accurate, alternatives are needed. Light scatter technology has been proposed for several years as a rapid screening tool, whereby negative specimens are excluded from culture. A commercially available light scatter device, BacterioScan 216Dx (BacterioScan, Inc.), has recently been advertised for this application. Paired use of mass spectrometry (MS) for bacterial identification and automated-system-based susceptibility testing straight from the light scatter suspension might provide dramatic improvement in times to a result. The present study prospectively evaluated the BacterioScan device, with culture as the reference standard. Positive light scatter specimens were used for downstream rapid matrix-assisted laser desorption ionization–time of flight (MALDI-TOF) MS organism identification and automated-system-based antimicrobial susceptibility testing. Prospective evaluation of 439 urine samples showed a sensitivity of 96.5%, a specificity of 71.4%, and positive and negative predictive values of 45.1% and 98.8%, respectively. MALDI-TOF MS analysis of the suspension after density-based selection yielded a sensitivity of 72.1% and a specificity of 96.9%. Antimicrobial susceptibility testing of the samples identified by MALDI-TOF MS produced an overall categorical agreement of 99.2%. Given the high sensitivity and negative predictive value of results obtained, BacterioScan 216Dx is a reasonable approach for urine screening and might produce negative results in as few as 3 h, with no downstream workup. Paired rapid identification and susceptibility testing might be useful when MALDI-TOF MS results in an organism identification, and it might decrease the time to a result by more than 24 h.

We propose an adaptive nonsymmetrical demodulation technique enabling the mitigation of time-varying distortions. The approach is experimentally verified in multichannel coherent 16QAM Nyquist links, with nonlinear effects and overlapped channels.

In this paper, clustering techniques such as k-means and Fuzzy c-means (FCM) are applied for phase recovery and demodulation of m-ary non-symmetrical constellations, distorted by linear and nonlinear impairments in optical fiber transmission systems. The effect of distortions on data-symbols corresponds to an emulation of electro-optical conversion plus system components impairments, and other phenomenal arisen during optical propagation. These distortions can be observed in a constellation diagram as data-symbol forming irregular elliptical shapes with angular-rotations taking as a reference the ideal positions of the data-symbols in classical modulation. By numerical simulation, the results show that the k-means algorithm according to index values using Silhouette coefficient, find the centroids and estimate the symbols that belong to that cluster in a lower computational time, improving among 2.12 and 3.19 times with respect to FCM. The system performance for the bit error rate (BER) is increased by using the k-means algorithm in 0.44 decades for BPSK, 0.34 decades using QPSK, 0.38 decades for 8-QAM, and 0.36 decades for 16-QAM. For FCM, lower improvements comparing to k-means in m-PSK, but attain gains of 0.20 and 0.33 decades for 8-QAM and 16-QAM, respectively. Although these improvements are conservatives, the whole set of constellations exhibit a better performance than conventional demodulation method for OSNR levels higher than 15 dB. We believe that clustering techniques are promissory for phase-recovery and signal demodulation in non-symmetrical m-ary modulation schemes under irregular decision boundaries.

We propose and numerically validate a method to redistribute QAM symbols on the constellation diagram aiming to minimize channel transmission impairment effects. The pre-distortion method is based on the design of digital complex multipliers and it is tested by simulation in a Radioover-Fiber (RoF) system. Assuming different channel responses, ten types of redistributed formats are generated by applying the proposed digital pre-distortion method of data-symbols in the constellation diagram on classical 8-QAM and 16-QAM formats. The robustness of the redistributed modulation formats is evaluated in comparison with classical m-QAM formats in terms of the bit-error-rate (BER), for a transmission distance of 40 and 80 km over uncompensated single-mode fiber links at 1 and 10 Gb/s respectively. It is shown that 8-QAM Offset-π /4 at 80 km with a bit rate of 10 Gb/s attains a gain in log(BER) of 2.3 decades, and improves the reach up to 94.5 km when compared to classical 8-QAM. On the other hand, 16-QAM Offset-π/4 at 40 km achieves a gain of 1.7 decades improving the reach up to 50 km for the same error level having the classical 16-QAM as reference. With these results the future work will enable a methodology to design robust constellations against linear impairments of optical channel.

Future terabit optical communication systems will rely on higher order Quadrature Amplitude Modulation (QAM) formats to improve the spectral efficiency (SE). However, these formats exhibit a higher sensitivity to linear as well as non-linear impairments throughout the optical link [1, 2]. These impairments may be time-varying in nature arising from mechanical disturbance in optical fibers, temperature variations in the components and small variations of the bias control of the IQ optical modulators for example. Unlike optical noise, these degradations may have a probability density function (PDF) that is non-Gaussian and therefore may shift the centroids (mean value) of the received symbols from their ideal constellation positions by different extents, Fig 1a. Thus, employing non-symmetrical decision boundaries by means of machine learning techniques may improve the overall system performance with high computational efficiency in contradistinction to complex linear equalization or computationally heavy non-linear mitigation techniques [2, 3]. Furthermore, an area that has not been well explored is the use of digital techniques at the receiver for tracking and compensating the effects of fast time-varying link parameters. Here, we demonstrate an adaptive machine learning-based nonsymmetrical decision technique relying on clustering to mitigate time-varying impairments such as IQ imbalance, bias drift, and phase noise. We experimentally verified its effectiveness in a 16QAM Nyquist system at 16 Gbaud for back-to-back (B2B) and 250 km links.

Linear carrier pre-distortion specifically designed to rearrange the spatial distribution of data-symbols in the constellation diagram is proposed for Intercarrier Interference Mitigation in an electrical multicarrier (MC) system. The linear carrier pre-distortion is achieved by convolving a pre-designed transfer function with each radiofrequency carrier previous by means of a redistribution of the QPSK data-symbols over IQ plane for each carrier composing the MC signal before the up-conversion to RF. At the receiver, an adaptive linear equalizer (Least Mean Squared) re-constructs the QPSK constellations for each radiofrequency carrier after signal demodulation. Our proposal is numerically validated by simulation in a 3 × 0.5 Gbaud Nyquist PSK multicarrier system. For BPSK, the inter-carrier overlapping percentage (IOP) takes values from 90% down to 75%, this enables a reduction of 15% in carrier spacing, and a symbol error rate (SER) gain of 1.2 dB for a Nyquist separation of 0.75. Whereas for QPSK, the reduction achieved is 15%, and the SER gain is 1.8 dB for a Nyquist separation of 0.85 (Being ideal a carrier spacing equal to 100% as carrier bandwidth). We believe that the proposed linear carrier pre-distortion technique enables further investigations on signal constellation re-distributions allowing controlled inter-carrier interference in the context of next broadband generation technologies.

Pathogenic bacteria require iron to replicate inside mammalian hosts. Recent studies indicate that heme acquisition in Gram-positive bacteria is mediated by proteins containing one or more near-iron transporter (NEAT) domains. Bacillus anthracis is a spore-forming, Gram-positive pathogen and the causative agent of anthrax disease. The rapid, extensive, and efficient replication of B. anthracis in host tissues makes this pathogen an excellent model organism for the study of bacterial heme acquisition. B. anthracis secretes two NEAT hemophores, IsdX1 and IsdX2. IsdX1 contains a single NEAT domain, whereas IsdX2 has five, a novel property among hemophores. To understand the functional significance of harboring multiple, non-identical NEAT domains, we purified each individual NEAT domain of IsdX2 as a GST fusion and analyzed the specific function of each domain as it relates to heme acquisition and transport. NEAT domains 1, 3, 4, and 5 all bind heme, with domain 5 having the highest affinity. All NEATs associate with hemoglobin, but only NEAT1 and -5 can extract heme from hemoglobin, seemingly by a specific and active process. NEAT1, -3, and -4 transfer heme to IsdC, a cell wall-anchored anthrax NEAT protein. These results indicate that IsdX2 has all the features required to acquire heme from the host and transport heme to the bacterial cell wall. Additionally, these results suggest that IsdX2 may accelerate iron import rates by acting as a “heme sponge” that enhances B. anthracis replication in iron-starved environments.

Nyquist optical multicarrier transmission based on gridless wavelength division multiplexing (WDM) technology suffers by inter-channel interference (ICI) due to carrier overlapping. Even though the unpredictable effect of the ICI has been treated as a non-linear noise, temporal correlations of data symbols may partially allow ICI mitigation by linear equalization techniques. In this research, we systematically evaluate and mitigate the impact of the ICI for sub-Nyquist carrier spacing in a multicarrier system by applying a linear equalization technique. System characterization is presented in terms of bit-error-rate (BER) estimation as a function of carrier frequency spacing variations, the roll-off factor of the digital Nyquist pulse-shaping filter, and transmission distance scenarios. The mitigation of the ICI effects is carried out by the linear constant modulus algorithm (CMA) equalizer after compensating fiber linear impairments and before the sampling process at the digital coherent receiver, in a 3 × 32 Gbaud single-polarization Nyquist quadrature phase shift keying (QPSK) multicarier system. The CMA updates the coefficients of an adaptive digital filter based on a blind estimation technique to minimize the error function defined by the constant modulus of QPSK signals. System performance is improved after the linear equalization, reaching optical transmission distance without amplification of up to 130 km assuming a 15% FEC limit. Furthermore, the linear equalization allows a sub-Nyquist spacing of 30.5 GHz assuming a 15% FEC limit. Moreover, the adopted equalization technique relaxes the computational cost of the digital filtering, enabling roll-off factor values of up to 0.3 for 120 km transmission assuming 9% FEC limit.

Multicarrier optical systems are expected to allow data transmission above 100 Gbps in the next generation long-haul optical networks with a minimum spectral separation between carriers to increase spectral efficiency. Nevertheless, closely separation between optical carriers cause Interchannel interference (ICI) due to the inherent non-linear effects associated to optical fiber such as self-phase modulation (SPM) and cross-phase modulation (XPM). Both SPM and XPM induce a phase shifting in transmitted frequency multiplexed signals. This phase shifting can be observed as a rotated constellation diagram of phase-modulated signals and it degrades system performance by increasing the Bit-Error-Rate (BER). In this paper, a phase offset estimation and compensation using k-means clustering algorithm is validated by simulation in a multicarrier optical system. The optical carriers are modulated in PSK and 16-QAM formats at 32 Gbaud and signal transmission is simulated over standard single-mode fiber (SSMF). System performance is analyzed as a function of frequency carrier spacing and transmission distances. After Phase correction a decrease of the BER is achieved, demonstrating the feasibility and robustness of the proposed clustering technique to compensate induced nonlinear constellations rotations in future multicarrier optical networks.

Multi-carrier optical transmission with ideal spectrum occupancy per-carrier equal to data baud rate (Nyquist criteria) with overall spectral efficiency higher than 2 bit/s/Hz is expected to replace currently deployed single-carrier 100 Gb/s DP-QPSK systems. However, ideal Nyquist shaping per carrier is not easily achievable due to the bandwidth resolution in optical filtering and the high computational complexity in digital filtering. This paper investigates and characterizes in terms of bit-error-rate (BER) performance degradation, the impact of spectral overlapping between adjacent optical carriers known as inter-channel interference (ICI), under variations of the following system parameters: roll-off factor of the digital Nyquist filter, channel spacing, linewidth laser and transmission distance. ICI is numerically studied in a 3×32-Gbaud 384-Gb/s scenario with QPSK and 16-QAM modulation formats. Results show a high impact in the non-ideal spectral channel generation due to the roll-off factor. Channel spacing of an ideal 32 GHz spectrum separation has a high impact in BER, 4 decades of BER difference compared with a 34 GHz separation. Besides, a dependency between ICI and transmitted sequences per channel has been identified. This bit sequences influence, can lead a new bit-probability-awareness codification technique to mitigate ICI effects in future optical scenarios.

In this article we propose a new methodology to estimate the change in the bandwidth demand in time, mainly in residential areas. The bandwidth demand forecast is a basic aspect to decide the evolution of metropolitan optical networks. The word evolution refers to the necessity of making changes in networks, either by upgrading or replacing different elements that are part of the network. This analysis, along with a technological alternatives analysis, provides the operator the needed information to achieve the appropriate network planning and to make investment decisions.

Nyquist-WDM systems have been proposed as a promising solution in multicarrier transmissions to be a technology which could face the elastic networks challenges. In the spectrum, Nyquist-WDM requires an ideal rectangle, characteristic that is impossible in practice. With a channel spacing near or equal to baud rate, the roll-off factor of the pulse shaping filter has influence in the channel spreading, generating spectral overlapping between adjacent channels. This phenomenon is called Interchannel Interference (ICI). This research evaluates the impact of the ICI effects in a 5 × 32 Gbaud Nyquist-WDM system, with 16-QAM modulation. The impact of the Roll-off and channel spacing value is analyzed for distances up to 5 km. Error Vector Magnitude in constellation and bit error rate are estimated according to channel spacing penalty, roll-off factor, and transmission distance variation. ICI effects minimization using LMS algorithm in the digital coherent receiver is proposed. LMS adapts the coefficients of the adaptive filter making equalization by a training sequence, superchannels signals are received in independent coherent receivers in a joint equalization among channels. The performance of the systems is improved with LMS equalization, reducing the log(BER) from −1 to −11 for 5 km in a channel spacing equal to the symbol rate, and from ∼2 to ∼20 for a channel spacing penalty of 1.5 GHz, with roll-off factor Nyquist filter of 0.15, which is feasible in practice in the pulse shaping filter at the transmitter.

Extended spectrum β-lactamases (ESBLs) pose a significant threat to public health because of their ability to confer resistance to third generation cephalosporins such as cefotaxime. CTX-M-14 β-lactamase is one of the most widespread ESBL enzymes among antibiotic resistant bacteria and was used in this study to identify residues that facilitate resistance to cephalosporins. We investigated the roles of Ser237 and Arg276 in CTX-M-14 β-lactamase using site-directed mutagenesis, kinetic analysis and X-ray crystallography. We show that, together, Ser237 and Arg276 residues are key determinants of cefotaxime hydrolysis by the CTX-M-14 β-lactamase. X-ray structures of S70G:S237A:R276A and S70G:S237A variants of CTX-M-14 alone and in complex with cefotaxime revealed changes in the orientation of the aminothiazole ring on the cefotaxime side chain suggesting that these residues form a cooperative network which allows cefotaxime to assume a more buried position in the active site thereby facilitating catalysis. Fi...

In this paper I want to show experimentally as is possible to create a multicarrier system from a single source, emulating an 8-channel WDM system. This was used for BLS (Broadband Light Source), in this case an FPL (Fabry Perot laser). then using techniques SS (Spectrum Slicing), is achieved only filter out of the source 8 channels were independently modulates amplitude at a transmission rate of 1 Gbps. to determine the signal to noise ratio (SNR) provided by the eye diagrams of each of the channels for this two methods were used, one statistical and the other showing the oscilloscope used.

We propose a broadband all optical wavelength conversion scheme based on a dual driven Mach-Zendher modulator along the entire C band. Successful signal demodulation of 5 shifted 100 Gbps Nyquist QPSK channels separated by 50GHz between each other around the original optical modulated signal is reported. The propose wavelength conversion schemes enables dynamic bandwidth allocation on next generation optical superchannels.

In the context of gridless optical multicarrier systems, we propose a method for intercarrier interference (ICI) mitigation which allows bit error correction in scenarios of nonspectral flatness between the subcarriers composing the multicarrier system and sub-Nyquist carrier spacing. We propose a hybrid ICI mitigation technique which exploits the advantages of signal equalization at both levels: the physical level for any digital and analog pulse shaping, and the bit-data level and its ability to incorporate advanced correcting codes. The concatenation of these two complementary techniques consists of a nondata-aided equalizer applied to each optical subcarrier, and a hard-decision forward error correction applied to the sequence of bits distributed along the optical subcarriers regardless of prior subchannel quality assessment as performed in orthogonal frequency-division multiplexing modulations for the implementation of the bit-loading technique. The impact of the ICI is systematically evaluated in terms of bit-error-rate as a function of the carrier frequency spacing and the roll-off factor of the digital pulse-shaping filter for a simulated 3×32-Gbaud single-polarization quadrature phase shift keying Nyquist-wavelength division multiplexing system. After the ICI mitigation, a back-to-back error-free decoding was obtained for sub-Nyquist carrier spacings of 28.5 and 30 GHz and roll-off values of 0.1 and 0.4, respectively.

The development of technologies for optical access networks and user demand for more bandwidth has enabled consider increasing rates and improve the current coverage of access networks. Currently there are various ways to achieve this goal, one relates to the use of modulations in the signal processing in both the OLT and the ONU. This process has already begun studying for transport networks with highly complex formats and costly implementation. DPSK (Diferencial Phase Shift Key) modulation has been identified for possible implementation in the context of access. This paper describes how we implement to 10Gpbs and testing with 2 different types of fibers.

Orotidine 5'-monophosphate decarboxylase (ODCase) catalyzes the decarboxylation of orotidine 5'-monophosphate to uridine 5'-monophosphate during pyrimidine nucleotide biosynthesis. This enzyme is one of the most proficient known, exhibiting a rate enhancement of over 17 orders of magnitude over the uncatalyzed rate. An interesting question is whether the high proficiency of ODCase is associated with a highly optimized sequence of active site residues. This question was addressed by randomizing 24 residue positions in and around the active site of the E. coli ODCase (pyrF) by site-directed mutagenesis. The libraries of mutants were selected for function from a multicopy plasmid or by single-copy replacement at the pyrF locus on the E. coli chromosome. Stringent sequence requirements for function were found for the mutants expressed from the chromosomal pyrF locus. Six positions were not tolerant of substitutions and several others accepted very limited substitutions. In contrast, all positions could be substituted to some extent when the library mutants were expressed from a multicopy plasmid. For the conserved quartet of charged residues Lys44-Asp71-Lys73-Asp76, a cysteine substitution was found to provide function at positions 71 and 76. A lower pK(a) for both cysteine mutants supports a mechanism whereby the thiolate group of cysteine substitutes for the negatively charged aspartate side chain. The partial function mutants such as D71C and D76C exhibit reduced catalytic efficiency relative to wild type but nevertheless provide a rate enhancement of 15 orders of magnitude over the uncatalyzed rate indicating the catalytic proficiency of the enzyme is robust and tolerant of mutation.