V- and W-band microwave generation and modulation using semiconductor lasers at period-one nonlinear dynamics.

Microwave generation and modulation over the V- and W-bands are investigated using a semiconductor laser subject to both comb-like optical injection and direct modulation. The former not only excites period-one (P1) nonlinear dynamics for tunable microwave generation but also improves the stability and purity of such generated microwaves. The latter upconverts data onto the generated microwaves by superimposing the data effectively only onto the lower oscillation sideband of the P1 dynamics, which prevents the data from dispersion-induced degradation over fiber distribution. As a result, microwaves that are continuously tunable from 40 to 110 GHz with a 3-dB linewidth of less than 1 Hz and with phase noise better than -95dBc/Hz at 10-kHz offset are generated. A bit-error ratio better than the forward error correction limit, 3.8×10-3, is achieved for 12-Gb/s 16-quadrature amplitude modulation data after 25-km fiber distribution.

Structural insights into the duplex DNA processing of TREX2.

The three prime repair exonuclease 2 (TREX2) is an essential 3'-to-5' exonuclease that functions in cell proliferation, genome integrity and skin homeostasis maintenance. The abnormal expression level of TREX2 can result in broken chromosome, increased susceptibility to skin carcinogenesis and Psoriasis. However, the molecular mechanisms of how TREX2 binds and processes its natural substrates, dsDNA or chromosomal DNA, to maintain genome stability remain unclear. In this study, we present four new crystal structures: apo-TREX2, TREX2 in complex with two different dsDNA substrates, and TREX2 in complex with a processed dsDNA product. Analysis of the structures reveals that TREX2 stacks with the 5'-terminal of dsDNA by a Leu20-Pro21-Asn22 cluster for precisely trimming the 3'-overhang. In addition, TREX2 specifically interacts with the non-scissile strand of dsDNA by an α-helix-loop region. The unique interaction patterns of the TREX2-dsDNA complex highlight the requirement of long double-stranded region for TREX2 binding and provide evidence of the functional role of TREX2 in processing chromosomal DNA. Moreover, the non-processive property of TREX2 is elucidated by the structure of TREX2-product complex. Our work discloses the first structural basis of the molecular interactions between TREX2 and its substrates and unravels the mechanistic actions of TREX2.

The effect of Xenopus laevis egg extracts with/without BRG1 on the development of preimplantation cloned mouse embryos.

SummaryMuch effort has been devoted to improving the efficiency of animal cloning. The aim of this study was to investigate the effect of BRG1 contained in Xenopus egg extracts on the development of cloned mouse embryos. The results showed that mouse NIH/3T3 cells were able to express pluripotent genes after treatment with egg extracts, indicating that the egg extracts contained reprogramming factors. After co-injection of Xenopus egg extracts and single mouse cumulus cells into enucleated mouse oocytes, statistically higher pronucleus formation and development rates were observed in the egg Extract- co-injected group compared with those in the no egg extract-injected (NT) group (38-66% vs 18-34%, P<0.001). Removal of BRG1 protein from Xenopus egg extracts was conducted, and the BRG1-depleted extracts were co-injected with single donor cells into recipient oocytes. The results showed that the percentages of pronucleus formation were significantly higher in both BRG1-depleted and BRG1-intact groups than that in the nuclear transfer (NT) group (94, 64% vs 50%, P<0.05). Furthermore, percentages in the BRG1-depleted group were even higher than in the BRG1-intact group (94% vs 64%). More confined expression of Oct4 in the inner cell mass (ICM) was observed in the blastocyst derived from the egg extract-injected groups. However, Nanog expression was more contracted in the ICM of cloned blastocysts in the BRG1-depleted group than in the BGR1-intact group. Based on the present study, BRG1 might not play an essential role in reprogramming, but the factors enhancing pronucleus formation and development of cloned mouse embryos are contained in Xenopus egg extracts.

On channel estimation schemes for APD-based DDM-OFDM-PONs under sub-Nyquist sampling.

Implementing preprocessing in a delay-division multiplexing (DDM) orthogonal frequency-division multiplexing (OFDM) passive optical network (PON) requires a priori knowledge of channel responses, which need to be estimated under the constraint of sub-Nyquist analog-to-digital sampling. The localized approach allocates subcarriers in different frequency zones to training symbols in different time slots for channel estimation without spectral overlap. Unfortunately, the localized scheme is susceptible to inaccurate estimation when using an avalanche photodiode (APD), due to variations in APD saturation associated with different training symbols. Instead of localizing all subcarriers of a training symbol in a single frequency zone, we propose distributing training subcarriers through various frequency zones. This distributed scheme would prevent spectral overlap and also reduce the degree of variation in APD saturation, thereby improving the accuracy of channel estimation. Alternatively, we propose an orthogonal scheme in which each training symbol uses all of the subcarriers simultaneously. The orthogonality specified among consecutive training symbols should make it possible to estimate the channel response with low computational complexity. We conducted experiments to compare various schemes used for channel estimation in a 25-Gbps APD-based OFDM-PON. Our results revealed that the orthogonal scheme achieved the best results, and the localized scheme provided the worst channel estimates. We demonstrate the application of the orthogonal scheme in a penalty-free DDM system at 1/32 of the Nyquist rate, which provided a loss budget of 28 dB after fiber transmission over a distance of 25 km.

DFT/IDFT-free receiving scheme for spread-OFDM signals employing low-sampling-rate ADCs.

This paper presents a DFT/IDFT-free receiving scheme for spread-OFDM signals. Leveraging sub-Nyquist sampling and proper sampling delay, the proposed scheme enables each user to receive the requested data without the need for DFT and IDFT; thus, the complexity at receiver can be greatly reduced. Nonetheless, DC component is altered in an AC coupling system, such that severe waveform distortion is caused when the process of DFT/IDFT is omitted. Thus, a DC-zeroing algorithm is proposed to guarantee constant DC after sub-Nyquist sampling, thereby eliminating such distortion. To experimentally verify the concept of proposed scheme, a 27.15-Gbit/s optical spread-OFDM signal was transmitted over fiber and received by the DFT/IDFT-free scheme with sub-Nyquist sampling. More users will reduce the required sampling rate at receiver; for the case of 16 users, the required sampling rate for the 27.15-Gbit/s signal is as low as 1 GSample/s. The experimental results show that error-free transmission was achievable, and the penalty due to lowering sampling rate (i.e., increasing the number of users) is insignificant.

V-band gapless OFDM RoF system with power detector down-conversion and novel Volterra nonlinear filtering.

This Letter presents a V-band gapless orthogonal frequency division multiplexing (OFDM) RoF system at 60 GHz employing a power detector to support vector signal down-conversion. Additional RF tone is generated and transmitted from a central station to replace the local oscillator at a wireless receiver for power detector down-conversion. To enhance the spectrum efficiency, the gap between the OFDM signal and the RF tone is not needed. However, the down-converted signal will suffer signal-to-signal interference (SSBI). In this Letter, we propose and successfully employ a novel Volterra nonlinear compensation to mitigate SSBI, resulting in a 22% data rate improvement with a bit-loading algorithm.

Spectrally efficient polarization multiplexed direct-detection OFDM system without frequency gap.

We experimentally demonstrate a spectrally efficient direct-detection orthogonal frequency-division multiplexing (DD-OFDM) system. In addition to polarization-division multiplexing, removing the frequency gap further improves the spectral efficiency of the OFDM system. The frequency gap between a reference carrier and OFDM subcarriers avoids subcarrier-to-subcarrier beating interference (SSBI) in traditional DD-OFDM systems. Without dynamic polarization control, the resulting interference after square-law direct detection in the proposed gap-less system is polarization-dependent and composed of linear inter-carrier interference (ICI) and nonlinear SSBI. Thus, this work proposes an iterative multiple-input multiple-output detection scheme to remove the mixed polarization-dependent interference. Compared to the previous scheme, which only removes ICI, the proposed scheme can further eliminate SSBI to achieve the improvement of ∼ 7 dB in signal-to-noise ratio. Without the need for polarization control, we successfully utilize 7-GHz bandwidth to transmit a 39.5-Gbps polarization multiplexed OFDM signal over 100 km.

60-GHz optical/wireless MIMO system integrated with optical subcarrier multiplexing and 2x2 wireless communication.

This paper proposes a 2x2 MIMO OFDM Radio-over-Fiber scheme based on optical subcarrier multiplexing and 60-GHz MIMO wireless transmission. We also schematically investigated the principle of optical subcarrier multiplexing, which is based on a dual-parallel Mach-Zehnder modulator (DP-MZM). In our simulation result, combining two MIMO OFDM signals to drive DP-MZM gives rise to the PAPR augmentation of less than 0.4 dB, which mitigates nonlinear distortion. Moreover, we applied a Levin-Campello bit-loading algorithm to compensate for the uneven frequency responses in the V-band. The resulting system achieves OFDM signal rates of 61.5-Gbits/s with BER of 10(-3) over 25-km SMF transmission followed by 3-m wireless transmission.

W-band OFDM Radio-over-Fiber system with power detector for vector signal down-conversion.

This Letter proposes a W-band OFDM RoF system at 103.5 GHz employing power detector to support vector signal down-conversion. Additional RF tone is generated and transmitted from central office to replace the local oscillator at a wireless receiver. With a proper frequency gap and power ratio between the RF tone and the OFDM-modulated signal, the impact from signal-to-signal beating interference can be minimized. The data rate can achieve a 40 Gbps 16 QAM OFDM signal over 25 km fiber and 2 m wireless transmission.

Let-7-mediated suppression of mucin 1 expression in the mouse uterus during embryo implantation.

Mucin 1 (Muc1) is an integral transmembrane mucin glycoprotein expressed on the apical surface of most epithelia. It is considered to be a barrier to the regulation of embryo implantation by inhibiting attachment of the embryo to the endometrium. Therefore, loss of Muc1 on the surface of uterine epithelial cells is necessary for embryo implantation. Studies have demonstrated that microRNAs (miRNAs) play a key role in enhancing embryo implantation in mammals. In this study, we investigated the regulatory role of two miRNAs (let-7a and let-7b) on the expression of Muc1 in mouse uteri during implantation. Western blotting indicated that Muc1 expression was highest on day1 of pregnancy and constantly decreased thereafter until day 4. In contrast to Muc1 expression, increased expression of let-7a and let-7b was evident on day 4 of pregnancy as measured by real-time reverse transcription-polymerase chain reaction (real-time RT-PCR). We demonstrated direct binding of let-7a and let-7b to the 3'untranslated region of muc1. Furthermore, Muc1 expression was suppressed after transfection of mouse uterine epithelial cells isolated from day 1 of pregnancy with let-7a and let-7b. In summary, the present study provides evidence that Muc1 is a direct target of let-7a and let-7b. Additionally, the current study suggests that miRNAs are novel targets which can be used to facilitate a successful pregnancy and repair implantation failure.

High spectral efficient W-band optical/wireless system employing single-sideband single-carrier modulation.

With broader available bandwidth, W-band wireless transmission has attracted a lot of interests for future Giga-bit communication. In this article, we experimentally demonstrate W-band radio-over-fiber (RoF) system employing single-sideband single-carrier (SSB-SC) modulation with lower peak-to-average-power ratio (PAPR) than orthogonal frequency division multiplex (OFDM). To overcome the inter-symbol interference (ISI) of the penalty from uneven frequency response and SSB-SC modulation, frequency domain equalizer (FDE) and decision feedback equalizer (DFE) are implemented. We discuss the maximum available bandwidth of different modulation formats between SSB-SC and OFDM signals at the BER below forward error correction (FEC) threshold (3.8 × 10(-3)). Up to 50-Gbps 32-QAM SSB-SC signals with spectral efficiency of 5 bit/s/Hz can be achieved.

100-GHz DD-OFDM-RoF system over 150-km fiber transmission employing pilot-aided phase noise suppression and bit-loading algorithm.

This study extended the transmission distance of a 100-GHz DD-OFDM-RoF system through the reduction of chromatic dispersion-induced phase noise. The implementation of a pilot-aided phase noise suppression (PPNS) scheme enabled the transmission of distance-insensitive 16.97-Gbps QPSK OFDM over 0~150-km fiber and 2-m air transmission via a DFB laser with linewidth of 1~10-MHz. We applied a bit-loading algorithm in conjunction with PPNS to maximize spectral efficiency, resulting in a 93% improvement in the data rate from 11.53 to 22.27 Gbps at a fiber transmission of 150 km.

Ultrahigh capacity 2 × 2 MIMO RoF system at 60 GHz employing single-sideband single-carrier modulation.

This article proposes and experimentally demonstrates a radio-over-fiber system employing single-sideband single-carrier (SSB-SC) modulation at 60 GHz. SSB-SC modulation has a lower peak-to-average-power ratio than orthogonal frequency division multiplex (OFDM) modulation; therefore, the SSB-SC signals provide superior nonlinear tolerance, compared to OFDM signals. Moreover, multiple-input multiple-output (MIMO) technology was used extensively to enhance spectral efficiency. A least-mean-square-based equalizer was implemented, including MIMO channel estimation, frequency response equalization, and I/Q imbalance compensation to recover the MIMO signals. Thus, using 2×2 MIMO technology and 64-QAM SSB-SC signals, we achieved the highest data rate of 84 Gbps with 12 bit/s/Hz spectral efficiency using the 7-GHz license-free band at 60 GHz.

MicroRNA-199a mediates mucin 1 expression in mouse uterus during implantation.

Embryo implantation is a complicated process involving interactions between the blastocyst and the luminal epithelium of the receptive uterus. Mucin 1 (MUC1) is an integral membrane glycoprotein expressed apically by secretory epithelial cells and the glandular epithelium in different organs, including the uterus. It is believed that loss of MUC1 on the surface of uterine epithelial cells is necessary for embryo implantation. The endogenous non-protein coding microRNAs (miRNAs) of 21-24 nucleotides are found in diverse organisms. It has been shown that miRNAs participate in a range of cellular processes by regulating gene expression at the post-transcriptional level. In the present study, the regulatory role of miRNA-199a on the expression of MUC1 in mouse uterus during implantation was investigated for its effect on embryo implantation. Western blotting and immunohistochemistry results showed high MUC1 expression on Day 0.5 and low expression by Day 4.5 of pregnancy. In contrast with MUC1 expression, increased miRNA-199a expression was evident at Day 4.5 of pregnancy, as measured by real-time reverse transcription-polymerase chain reaction. In addition, we demonstrated direct binding of miRNA-199a to the 3'-untranslated region of MUC1. Transfection of miRNA-199a into mouse uterine epithelial cells isolated from Day 0.5 of pregnancy also downregulated expression of MUC1. Therefore, the present study provides evidence that MUC1 is a direct target of miRNA-199a and suggests that development of novel strategies to facilitate a successful pregnancy and repair implantation failure humans may include miRNA.

Protein degradation of Lsd1 is mediated by Bre1 yet opposed by Lsd1-interacting lncRNAs during fly follicle development.

Tissue development, homeostasis, and repair all require efficient progenitor expansion. Lysine-specific demethylase 1 (Lsd1) maintains plastic epigenetic states to promote progenitor proliferation while overexpressed Lsd1 protein causes oncogenic gene expression in cancer cells. However, the precise regulation of Lsd1 protein expression at the molecular level to drive progenitor differentiation remains unclear. Here, using Drosophila melanogaster oogenesis as our experimental system, we discovered molecular machineries that modify Lsd1 protein stability in vivo. Through genetic and biochemical analyses, an E3 ubiquitin ligase, Bre1, was identified as required for follicle progenitor differentiation, likely by mediating Lsd1 protein degradation. Interestingly, specific Lsd1-interacting long non-coding RNAs (LINRs) were found to antagonize Bre1-mediated Lsd1 protein degradation. The intricate interplay discovered among the Lsd1 complex, LINRs and Bre1 provides insight into how Lsd1 protein stability is fine-tuned to underlie progenitor differentiation in vivo.

High spectral efficient W-band OFDM-RoF system with direct-detection by two cascaded single-drive MZMs.

W-band wireless transmission has attracted a lot of interest due to its wider available bandwidth (i.e. 75-110 GHz). In this article, we propose a direct-detection orthogonal frequency division multiplexing radio over fiber (OFDM-RoF) system via two cascaded single-drive MZMs at center frequency of 103 GHz. We discuss maximum bandwidth of different modulation formats under forward error correction (FEC) threshold (3.8 x 10(-3)). Up to 40-Gbps 16-QAM OFDM signals is achieved over 25-km fiber and 2-m wireless transmission. To overcome the penalty from uneven frequency response, bit-loading algorithm is applied to discuss data rate and spectral efficiency with signal bandwidth from 5 to 10 GHz. With 10-GHz bandwidth, 46.4-Gb/s data rate and 4.64-bit/s/Hz spectral efficiency was achieved. To achieve 40-Gbps data rate, the required bandwidth of OFDM signal with bit-loading is 2 GHz less than that without bit-loading.

Seasonality can override the effects of anthropogenic activities on microplastic presence in invertebrate deposit feeders in an urban river system.

Microplastic pollution is an urgent threat to the biota of aquatic ecosystems and is generally recognized as a global issue. Identifying the sources of microplastics is acknowledged as the most effective approach for mitigating microplastic pollution. However, the factors that regulate the spatiotemporal dynamics of microplastics in urban river networks, such as microplastic sources and other variables, have not been studied together at the watershed scale, let alone regarding their impact on internal microplastics. Here, we define "internal microplastics" as microplastics in biota, either in the digestive system or internal organs of organisms. We estimated the effects of anthropogenic activities (land cover and wastewater treatment plants) and seasonality on the concentration of internal microplastics in midge larvae (Diptera: Chironomidae) in an urban river system at a watershed scale in Taiwan. Agricultural activities, but not industrial activities, had a significant negative nonlinear effect on microplastic concentration. However, seasonality was the most crucial factor, as the microplastic concentration was significantly lower during the wet season. Although the presence of a wastewater treatment plant significantly increased the microplastic concentration at downstream sampling sites, its effect appeared to be minor. We conclude that seasonality overrides the effects of anthropogenic activities on the variation in the concentration of internal microplastics in midge larvae in an urban river system.

PMD tolerant direct-detection polarization division multiplexed OFDM systems with MIMO processing.

This work proposes a novel direct-detection polarization division multiplexed OFDM scheme without the need of dynamic polarization control at a polarization-diverse receiver, and the proposed scheme is robust against polarization mode dispersion. Setting the frequency difference between two polarization-orthogonal reference carriers as one subcarrier spacing, possible signal fading can be avoided, and the corresponding interference from adjacent subcarriers is eliminated by a novel MIMO algorithm. The penalty caused by high channel matrix condition number can be decreased by inserting empty tones among subcarriers, and the polarization-dependent OSNR penalty at the BER of 10⁻³ is <3.6 dB with an empty tone inserted every 8 subcarriers. Moreover, the numerical results demonstrate the 16 × 10³-ps/nm chromatic dispersion and the 300-ps differential group delay will not induce additional penalty.

2 × 2 MIMO radio-over-fiber system at 60 GHz employing frequency domain equalization.

This work experimentally demonstrates the efficacy of the 2 × 2 multiple-input multiple-output (MIMO) technique for capacity improvement of a 60-GHz radio-over-fiber (RoF) system employing single-carrier modulation format. We employ frequency domain equalization (FDE) to estimate the channel response, including frequency response of the 60 GHz RoF system and the MIMO wireless channel. Using FDE and MIMO techniques, we experimentally demonstrate the doubling the of wireless data capacity of a 60 GHz RoF system to 27.15 Gb/s using 16-QAM modulation format, with transmission over 25 km of standard single-mode fiber and 3 m wireless distance.