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(2R,3R)-2,3-Butanediol dehydrogenase (R,R-BDH) from Bacillus coagulans 2-6 is a zinc-dependent medium-chain alcohol dehydrogenase. Recombinant R,R-BDH with a His6 tag at the C-terminus was expressed in Escherichia coli BL21 (DE3) cells and purified by Ni2+-chelating affinity and size-exclusion chromatography. Crystals were grown by the hanging-drop vapour-diffusion method at 289 K. The crystallization condition consisted of 8%(v/v) Tacsimate pH 4.6, 18%(w/v) polyethylene glycol 3350. The crystal diffracted to 2.8 A resolution in the orthorhombic space group P212121, with unit-cell parameters a = 88.35, b = 128.73, c = 131.03 A.

Biosynthetic alanine racemase (AlrPA) fromPseudomonas aeruginosaPAO1 carrying a His6tag was expressed inEscherichia coliBL21 (DE3) cells and purified by Ni2+-chelating affinity and anion-exchange chromatography for X-ray crystallographic analysis. Crystals were grown by the hanging-drop vapour-diffusion method at 289 K in a solution consisting of 4%(v/v) Tacsimate pH 5.0, 14%(w/v) polyethylene glycol 3350 with a protein concentration of 8 mg ml−1. The crystal diffracted to 2.76 Å resolution and belonged to the orthorhombic space groupP212121, with unit-cell parametersa= 74.12,b= 76.97,c= 154.80 Å, α = β = γ = 90°.

Alanine dehydrogenase (OF4Ald) from the alkaliphilic Bacillus pseudofirmus OF4 was expressed and purified with a His6 tag in a form suitable for X-ray crystallographic analysis. Crystals were grown by the hanging-drop vapour-diffusion method at 289 K using a solution consisting of 0.1 M Tris–HCl pH 8.0, 0.2 M LiSO4, 22%(w/v) PEG 3350. X-ray diffraction data were collected to 2.8 A resolution. The crystal belonged to the triclinic space group P1, with unit-cell parameters a = 88.04, b = 105.59, c = 120.53 A, α = 88.37, β = 78.77, γ = 82.65°.

Alanine dehydrogenase (l-AlaDH) from Bacillus megaterium WSH-002 catalyses the NAD+-dependent interconversion of l-alanine and pyruvate. The enzyme was expressed in Escherichia coli BL21 (DE3) cells and purified with a His6 tag by Ni2+-chelating affinity chromatography for X-ray crystallo­graphic analysis. Crystals were grown in a solution consisting of 0.1 M HEPES pH 8.0, 12%(w/v) polyethylene glycol 8000, 8%(v/v) ethylene glycol at a concentration of 15 mg ml−1 purified protein. The crystal diffracted to 2.35 A resolution and belonged to the trigonal space group R32, with unit-cell parameters a = b = 125.918, c = 144.698 A.

Two different semi-analytical methods for error probability estimation in PDM-QPSK optical communication systems are investigated. We consider the accuracy of a stochastic semi-analytical method based on Gaussian noise statistics and a deterministic semi-analytical method where the noise probability density function is estimated analytically against Monte-Carlo simulation. Linear coherent PDM-QPSK systems with distortions induced by filtering only, and nonlinear coherent PDM-QPSK systems with or without inline dispersion compensation are studied. Our results suggest that the stochastic semi-analytical method based on Gaussian noise statistics works very well for practical fiber-optic communication systems.

To explore the clinical and prognostic values of serum carbohydrate antigen (CA125), neuron-specific enolase (NSE), calcitonin (CT) levels in patients with lung cancer before operation.Ninety two untreated patients with lung cancer confirmed histologically were studied. Serum CA125, NSE, and CT were detected in 92 lung cancer patients by ELISA before operation. Thirty healthy volunteers were chosen as controls.The sensitivity of CA125, NSE, and CT for the diagnosis of lung cancer were 48.9%, 21.7%, and 7.6% respectively. The level of CA125 in lung cancer patients was significantly higher than that of control (P0.05). The level of NSE in patients with small cell lung cancer was significantly higher than that of control (P0.01). The level of CT in lung cancer patients was higher than that of control, but without significant difference. The 3-year survival rate of patients with increased serum CA125 level before operation was 44.4% (20/45), whereas that of patients with normal CA125 level was 66.0% (31/47) (P0.05). The 3-year survival rate of patients with increased serum NSE and CT levels was 45.0% (9/20) and 42.8% (3/7) respectively, whereas that of patients with normal serum NSE and CT level was 58.3% (42/72) and 56.5% (48/85) respectively. The 3-year survival rate of patients with increased serum NSE or CT level had no significant difference with that of patients with normal level (P0.05).The diagnostic values of CA125, NSE and CT are limited. CA125 can be used as an prognostic parameter in patients with lung cancer after operation.

The amplified spontaneous emission (ASE) of inline amplifiers gives rise to amplitude fluctuations of the optical field envelope and the fiber nonlinearity translates them into phase fluctuations. This is known as nonlinear phase noise. This type of noise is first studied by Gordon and Mollenauer [1] and hence, this noise is also called “Gordon–Mollenauer phase noise.” The nonlinear phase noise leads to performance degradation in fiberoptic systems based on phase-shift keying (PSK) or differential phase-shift keying (DPSK) [1–4]. Gordon and Molleneuer pointed out that two degrees of freedoms (DOFs) of the noise field are of importance [1]. These noise components have the same form as the signal pulse. One of the noise components is in phase with the signal and the other in quadrature. The in-phase component of the noise changes the amplitude of the signal pulse and hence, leads to energy change while the quadrature component leads to a linear phase shift. The energy change is translated into an additional phase shift due to fiber nonlinearity. Gordon and Mollenauer argued that the noise components other than the above-mentioned modes have less significant effects if the optical bandwidth is not too large and they derived a simple analytical expression for the variance of nonlinear phase noise by ignoring fiber dispersion. When the receiver filter bandwidth is larger than the signal bandwidth, it has been found that two DOFs are not sufficient to describe the noise process [5]. Analytical expressions for the probability density function of nonlinear phase noise have been derived in [6–8] by ignoring fiber dispersion. The interaction between the nonlinearity and ASE is the strongest when the dispersion is zero because of phase matching and therefore, the analyses of [1, 5–8] over estimate the impact of nonlinear phase noise. Attempts have been made to calculate the impact of nonlinearphase noise in the presence of dispersion [–23]. By assuming that the signal is CW and using the approach typically used in the study of modulational instability, it has been found that the variance of nonlinear phase noise becomes quite small in dispersion-managed transmission lines when the absolute dispersion of the transmission fiber becomes large [9]. Later in [10], the variance of nonlinear phase noise is calculated for a Gaussian pulse in a dispersion-managed transmission line and results showed that variance of nonlinear phase noise due to self-phase modulation (SPM) is quite small as compared to the case of no dispersion.

We show that for coherent 112 Gbps PDM-QPSK systems employing inline dispersion management, and for a wide range of birefringence parameters, spinning reduces the benefit of local birefringence in the mitigation of nonlinear impairments.

We experimentally explore several optical fibers for all-Raman systems. We find that while NZ-DSF with small A eff may require slightly smaller pump power, its OSNR disadvantage is approximately 5 dB compared to ultra-low loss fibers.

We experimentally demonstrate transmission of 40 × 112 Gb/s PM-QPSK channels over a 365 km unrepeatered span enabled by ultra-low loss fibres in an effective area-managed configuration using only backward-pumped Raman with 25 dB gain and EDFA amplification.

We derive an analytical formula to estimate the variance of nonlinear phase noise caused by the interaction of amplified spontaneous emission (ASE) noise with fiber nonlinearity such as self-phase modulation (SPM), cross-phase modulation (XPM), and four-wave mixing (FWM) in coherent orthogonal frequency division multiplexing (OFDM) systems. The analytical results agree very well with numerical simulations, enabling the study of the nonlinear penalties in long-haul coherent OFDM systems without extensive numerical simulation. Our results show that the nonlinear phase noise induced by FWM is significantly larger than that induced by SPM and XPM, which is in contrast to traditional WDM systems where ASE-FWM interaction is negligible in quasi-linear systems. We also found that fiber chromatic dispersion can reduce the nonlinear phase noise. The variance of the total phase noise increases linearly with the bit rate, and does not depend significantly on the number of subcarriers for systems with moderate fiber chromatic dispersion.

We propose a simple adaptive step size method for band-limited signals based on analytic double commutator estimates. The proposed adaptive step size method efficiently suppresses numerical artifacts in high-speed DWDM systems and is several times more efficient than other common methods.

We show that a nonlinear adaptive MLSE receiver based on Volterra theory with 4-bit ADC and 3-fold oversampling can result in a reach of 960 km over 10 Gb/s NZ-DSF fiber-optic communication systems.

We show that blind adaptive MLSE and fractionally-spaced DFE receivers based on nonlinear Volterra theory can extend the reach beyond 300 km in uncompensated 10 Gbit/s fiber-optic transmission systems dominated by fiber nonlinearity.

We present a two-fold oversampling maximum-likelihood-sequence-estimation receiver for 10 Gb/s fiberoptic communication systems. We use the Volterra theory to model the channel nonlinearity, and least mean square algorithm to update the channel characteristics without training sequence.

A two-fold oversampling adaptive maximum likelihood sequence estimation (MLSE) receiver based on Viterbi algorithm has been implemented for 10 Gb/s fiber optical communication systems, taking into account the amplified spontaneous emission noise, uncompensated chromatic dispersion, and nonlinearity due to square-law detection. We use the Volterra theory to model the channel nonlinearity, and Recursive Least Square (RLS) algorithm to update the channel characteristics. We estimate the error probability of the adaptive MLSE receiver for return-to-zero (RZ) on-off-keying (OOK) modulation format using standard Monte-Carlo simulation. Our results show that, when propagated along standard single-mode fibre for a bit-error-ratio (BER) of 10-3, the dispersion tolerance for two-fold oversampling adaptive MLSE receiver is 1.7 times of that for optimum threshold receiver employing no electronic dispersion compensation (EDC) for RZ-OOK signal with 60 % duty cycle. We have also compared the effects of two-fold oversampling and synchronous sampling for the adaptive MLSE receiver, and our results show that the error probability of MLSE receiver can be reduced by an order of magnitude for the same system parameters when the two-fold oversampling is used.© (2007) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The effect of nonlinear phase noise in dispersion-managed optical transmission systems is studied. The variance of the nonlinear phase noise in systems based on differential phase-shift keying (DPSK) in the presence of dispersion is examined analytically, and a semianalytical expression to calculate the error probability including intrachannel four-wave mixing, linear phase noise, and nonlinear phase noise for systems based on DPSK is derived. In addition, for the on-off keying (OOK) format, the formula for the error probability including amplified spontaneous emission noise and intrachannel nonlinear effects has been given. On the basis of the semianalytical expressions, we have compared the error probability of systems based on DPSK and OOK, and the results show that, to reach a given bit error rate of 10-9 for a specific long-haul system, the difference between the signal-to-noise ratio required by the DPSK format and that required by the OOK format is around 6 dB for the launch power of 0 dBm, and the difference becomes larger as the launch power increases.

Variance of nonlinear phase noise in dispersion-managed systems based on differential phase-shift keying is examined analytically. Error probabilities for systems based on DPSK and OOK formats are evaluated and compared.

A correction is made to the article by Lu et al. (2013). Acta Cryst. F69, 934–936., A correction is made to the Matthews coefficient in the article by Lu et al. (2013, Acta Cryst. F69, 934–936).

Ultra-long-haul transmission at distances greater than 10,000 km is investigated for 112 Gb/s PM-QPSK signals using span lengths of 75 km and 100 km and all-Raman amplification. Two different ultra-low loss and large effective area optical fibers are studied. We demonstrate a reach length of 10,200 km for a 40 channel system using a fiber with effective area 112 μm(2) with 100 km spans, and a reach length of 13,288 km for a system with 75 km spans using a fiber with effective area of 134 μm(2).

We investigate the performance of a maximum likelihood sequence estimation (MLSE) receiver at 10.7 Gb/s in the presence of two optical nonlinear impairments, cross-phase modulation (XPM) and stimulated Brillouin scattering (SBS). We find that the tolerance to both nonlinearities decreases with larger levels of uncompensated dispersion. Our results also suggest that the MSLE receiver loses its linear regime advantage in comparison to a standard receiver at some dispersion levels in the presence of the nonlinear effects. We demonstrate that long uncompensated links up to 160 km may show better tolerance to the nonlinear effects with a lower dispersion fiber when using an MLSE receiver.