High sensitivity 10Gb/s Si photonic receiver based on a low-voltage waveguide-coupled Ge avalanche photodetector

We demonstrate low-voltage germanium waveguide avalanche photodetectors (APDs) with a gain × bandwidth product above 100GHz. A photonic receiver based on such a Ge APD, including a 0.13μm SiGe BiCMOS low-noise trans-impedance amplifier and a limiting amplifier, is realized. A 5.8dB sensitivity improvement is demonstrated at -5.9V bias at an avalanche gain of 6 through bit error ratio measurements. The absolute sensitivity in avalanche mode is -23.4dBm and -24.4dBm at a bit error ratio of 1 × 10(-12) and 1 × 10(-9) respectively.

Novel supramolecular elastomer films based on linear carboxyl-terminated polydimethylsiloxane oligomers: preparation, characterization, biocompatibility, and application in wound dressings

A novel supramolecular elastomer (SESi) based on multiple hydrogen bond associations between low-molecular-weight polydimethylsiloxane chains was obtained through a two-step reaction of linear carboxyl-terminated polydimethylsiloxane oligomers with diethylenetriamine and urea, and the reaction mechanism was characterized. The results of differential scanning calorimetry and X-ray diffraction analyses indicated that the supramolecular network structure is completely amorphous, endowing SESi with rubber-like elastic behavior at room temperature. The transparent SESi film prepared by hot pressing displayed nice viscoelasticity, benign water absorption, water vapor transition rates, and ideal biocompatibility; and did not show cytotoxicity or skin irritation. These properties allow the elastomer to function as an occlusive wound dressing. To demonstrate its potential in wound dressings, a detailed comparison of commercial 3M Tegaderm(™) film and the SESi film was conducted. The SESi film exhibited similar effects in wound healing, and the wound bed was covered by the SESi film without the occurrence of significant adverse reactions.

Impacts of the ubiquitous factor Zelda on Bicoid-dependent DNA binding and transcription in Drosophila

The Drosophila transcription factor Bicoid (Bcd) binds thousands of genomic sites during early embryogenesis, but it is unclear how many of these binding events are functionally important. Here, Small and colleagues test the role of the maternal factor Zelda (Zld) in Bcd-mediated binding and transcription. Embryos lacking Zld show enhanced Bcd binding to a subset of genomic locations, causing early activation of target genes normally silent until later stages. This study demonstrates a critical role for Zld in controlling Bcd binding and target gene activation in the early embryo.

In vivo cross-linking studies suggest that the Drosophila transcription factor Bicoid (Bcd) binds to several thousand sites during early embryogenesis, but it is not clear how many of these binding events are functionally important. In contrast, reporter gene studies have identified >60 Bcd-dependent enhancers, all of which contain clusters of the consensus binding sequence TAATCC. These studies also identified clusters of TAATCC motifs (inactive fragments) that failed to drive Bcd-dependent activation. In general, active fragments showed higher levels of Bcd binding in vivo and were enriched in predicted binding sites for the ubiquitous maternal protein Zelda (Zld). Here we tested the role of Zld in Bcd-mediated binding and transcription. Removal of Zld function and mutations in Zld sites caused significant reductions in Bcd binding to known enhancers and variable effects on the activation and spatial positioning of Bcd-dependent expression patterns. Also, insertion of Zld sites converted one of six inactive fragments into a Bcd-responsive enhancer. Genome-wide binding experiments in zld mutants showed variable effects on Bcd-binding peaks, ranging from strong reductions to significantly enhanced levels of binding. Increases in Bcd binding caused the precocious Bcd-dependent activation of genes that are normally not expressed in early embryos, suggesting that Zld controls the genome-wide binding profile of Bcd at the qualitative level and is critical for selecting target genes for activation in the early embryo. These results underscore the importance of combinatorial binding in enhancer function and provide data that will help predict regulatory activities based on DNA sequence.

Enzymatic synthesis of feruloylated lysophospholipid in a selected organic solvent medium

Feruloylated lysophospholipids (FLPs) were firstly synthesized from phosphatidylcholine (PC) and ethyl ferulate (EF) using lipase-catalysed interesterification in selected solvents at controlled water content. Kinds of lipases and single solvents were screened. Novozym 435 and toluene were found to be the suitable biocatalyst and solvent, respectively. Then tert-butanol, n-butanol, chloroform, isopropanol, acetone and DMSO were respectively added into toluene in order to increase conversion of products. The results showed that toluene/chloroform could significantly increase the conversion and the optimal combination of toluene and chloroform was 90:10 (v/v). The optimal conditions generated for FLPs production were a substrate molar ratio of 5:1 (PC/EF), a PC's hydrolytic time of 1.5h, an enzyme load of 60 mg/ml, a solvent dosage of 5 ml and a molecular sieves concentration (4Å) of 100mg/ml. Under these conditions, 40.51% of EF can be converted to FLPs, which were identified by TLC and HPLC-MS.

A practical implementation of multifrequency widefield frequency-domain fluorescence lifetime imaging microscopy

Widefield frequency-domain fluorescence lifetime imaging microscopy (FD-FLIM) is a fast and accurate method to measure the fluorescence lifetime, especially in kinetic studies in biomedical researches. However, the small range of modulation frequencies available in commercial instruments makes this technique limited in its applications. Herein, we describe a practical implementation of multifrequency widefield FD-FLIM using a pulsed supercontinuum laser and a direct digital synthesizer. In this instrument we use a pulse to modulate the image intensifier rather than the more conventional sine-wave modulation. This allows parallel multifrequency FLIM measurement using the Fast Fourier Transform and the cross-correlation technique, which permits precise and simultaneous isolation of individual frequencies. In addition, the pulse modulation at the cathode of image intensifier restores the loss of optical resolution caused by the defocusing effect when the cathode is sinusoidally modulated. Furthermore, in our implementation of this technique, data can be graphically analyzed by the phasor method while data are acquired, which allows easy fit-free lifetime analysis of FLIM images. Here, our measurements of standard fluorescent samples and a Föster resonance energy transfer pair demonstrate that the widefield multifrequency FLIM system is a valuable and simple tool in fluorescence imaging studies.

A system of repressor gradients spatially organizes the boundaries of Bicoid-dependent target genes

The homeodomain (HD) protein Bicoid (Bcd) is thought to function as a gradient morphogen that positions boundaries of target genes via threshold-dependent activation mechanisms. Here, we analyze 66 Bcd-dependent regulatory elements and show that their boundaries are positioned primarily by repressive gradients that antagonize Bcd-mediated activation. A major repressor is the pair-rule protein Runt (Run), which is expressed in an opposing gradient and is necessary and sufficient for limiting Bcd-dependent activation. Evidence is presented that Run functions with the maternal repressor Capicua and the gap protein Kruppel as the principal components of a repression system that correctly orders boundaries throughout the anterior half of the embryo. These results put conceptual limits on the Bcd morphogen hypothesis and demonstrate how the Bcd gradient functions within the gene network that patterns the embryo.

Electro-optic directed logic circuit based on microring resonators for XOR/XNOR operations

We report the implementation of the XOR and XNOR operations using an electro-optic directed logic circuit based on two cascaded silicon microring resonators (MRRs), which are both modulated through the plasma dispersion effect. PIN diodes are embedded around the MRRs to achieve the carrier-injection modulation. The inherent resonance wavelength mismatch between the two nominally identical MRRs caused by fabrication errors is compensated by two local microheaters above each MRR through the thermo-optic effect. Two electrical modulating signals applied to the MRRs represent the two operands of the two operations. Simultaneous bitwise XOR and XNOR operations at 100 Mbit/s are demonstrated.

Ultra-low-power carrier-depletion Mach-Zehnder silicon optical modulator

We demonstrate a 26 Gbit/s Mach-Zehnder silicon optical modulator. The doping concentration and profile are optimized, and a modulation efficiency with the figure of merit (VπL) of 1.28 V·cm is achieved. We design an 80-nm-wide intrinsic silicon gap between the p-type and n-type doped regions to reduce the capacitance of the diode and prevent the diode from working in a slow diffusion mode. Therefore, the modulator can be driven with a small differential voltage of 0.5 V with no bias. Without the elimination of the dissipated power of the series resistors and the reflected power of the electrical signal, the maximum power consumption is 3.8 mW.

Simultaneous rupture of bilateral quadriceps tendon and rotator cuff tear: a case report

This is a case report of a patient who sustained both a bilateral quadriceps tendon rupture and a complete rotator cuff tear. Overuse is a known risk factor for rotator cuff tears, but this case suggests that it can also be a risk factor for quadriceps tendon rupture.

Low-voltage, high-extinction-ratio, Mach-Zehnder silicon optical modulator for CMOS-compatible integration

We demonstrate a carrier-depletion Mach-Zehnder silicon optical modulator, which is compatible with CMOS fabrication process and works well at a low driving voltage. This is achieved by the optimization of the coplanar waveguide electrode to reduce the electrical signal transmission loss. At the same time, the velocity and impedance matching are both considered. The 12.5 Gbit/s data transmission experiment of the fabricated device with a 2-mm-long phase shifter is performed. The driving voltages with the swing amplitudes of 1 V and 2 V and the reverse bias voltages of 0.5 V and 0.8 V are applied to the device, respectively. The corresponding extinction ratios are 7.67 and 12.79 dB.

Oxygen vacancy density-dependent transformation from infrared to Raman active vibration mode in SnO2 nanostructures

Raman spectra acquired from spherical, cubic, and cuboid SnO2 nanocrystals (NCs) reveal a morphologically independent Raman mode at ∼302 cm(-1). The frequency of this mode is slightly affected by the NC size, but the intensity increases obviously with decreasing NC size. By considering the dipole changes induced by oxygen vacancies and derivation based on the density functional theory and phonon confinement model, an oxygen vacancy density larger than 6% is shown to be responsible for the transformation of the IR to Raman active vibration mode, and the intensity enhancement is due to strong phonon confinement.

Five-port optical router for photonic networks-on-chip

We experimentally demonstrate a spatially non-blocking five-port optical router, which is based on microring resonators tuned through the thermo-optic effect. The characteristics of the microring-resonator-based switching element are investigated to achieve balanced performances in its two output ports. The optical router is fabricated on the SOI platform using standard CMOS processing. The effective footprint of the device is about 440×660 μm2. The microring resonators have 3-dB bandwidths of larger than 0.31 nm (38 GHz), and extinction ratios of better than 21 dB for through ports and 16 dB for drop ports. Finally, 12.5 Gbps high-speed signal transmission experiments verify the routing functionality of the optical router.

Microring-resonator-based four-port optical router for photonic networks-on-chip

We design and fabricate a four-port optical router, which is composed of eight microring-resonator-based switching elements, four optical waveguides and six waveguide crossings. The extinction ratio is about 13 dB for the through port and larger than 30 dB for the drop port. The crosstalk of the measured optical links is less than -13 dB. The average tuning power consumption is about 10.37 mW and the tuning efficiency is 5.398 mW/nm. The routing functionality and optical signal integrity are verified by transmitting a 12.5 Gb/s PRBS optical signal.

Demonstration of a directed optical decoder using two cascaded microring resonators

We propose and demonstrate a directed optical decoder that can perform the decoding function from a two-bit electrical signal to a four-bit optical signal based on two cascaded microring resonators. We use two electrical signals regarded as a two-bit electrical signal to modulate the two microring resonators through the thermo-optic effect and four optical signals regarded as a four-bit optical signal appear at the output ports, respectively. The device operating at 10 kbps is demonstrated.

Proof of concept of directed OR/NOR and AND/NAND logic circuit consisting of two parallel microring resonators

We propose and demonstrate a directed OR/NOR and AND/NAND logic circuit consisting of two parallel microring resonators (MRRs). We use two electrical signals representing the two operands of the logical operation to modulate the two MRRs through the thermo-optic effect, respectively. The final operation results are represented by the output optical signals. Both OR/NOR and AND/NAND operations at 10 kbps are demonstrated.

Vibrational imaging of tablets by epi-detected stimulated Raman scattering microscopy

Proper chemical imaging tools are critical to the pharmaceutical industry due to growing regulatory demand for intermediate and end-product content uniformity testing. Herein we demonstrate stimulated Raman scattering (SRS) imaging of active pharmaceutical ingredient (API) and four excipients within tablets. Tablets from six manufactures were imaged with a speed of 53 s per frame of 512 × 512 pixels (i.e., 200 μs per pixel) and a lateral spatial resolution as high as 0.62 μm. The SRS chemical imaging was compared to confocal Raman mapping and coherent anti-Stokes Raman scattering (CARS) chemical imaging in terms of speed and chemical selectivity. The acquisition speed of SRS imaging is ca. 10(4) times faster than confocal Raman mapping and SRS technique showed superior to CARS chemical selectivity for studied samples. Our data demonstrate the potential of SRS microscopy in high-speed screening of pharmaceutical solid dosage forms.

Characterization of yeasts colonizing in healthy individuals

Opportunistic yeast pathogens may switch from harmless commensal to pathogenic relationships with the host under different conditions. They usually cause superficial infections, but may be the agents of more significant infections in immunocompromised patients. To investigate yeast colonization in the oral cavities of clinically healthy individuals, we collected oral swabs from 323 students and staff at the National Health Research Institutes, Taiwan. A total of 49 (15.2%) volunteers were colonized by low levels of yeasts and of these, only 3 (6.1%) were co-colonized by more than one species. Among the 52 isolates, comprising seven fungal genera and 13 species, Candida albicans (57.7%) was the dominant species, followed by Candida parapsilosis (15.4%). There was only one isolate of C. parapsilosis that showed, in vitro, a high (2 μg/ml) minimum inhibitory concentration (MIC) to amphotericin B. There were six (11.5%) isolates with fluconazole MICs ≥ 64 μg/ml and all of them were non-Candida species. With the exception of Cryptococcus albidus, the remaining five isolates had voriconazole MICs ≥ 4 μg/ml. In addition, there was one C. albicans isolate with relatively high fluconazole (32 μg/ml) and voriconazole (4 μg/ml) MICs.

[Effect of the first water-sediment regulation on the variations of dissolved inorganic nutrients' concentrations and fluxes in the lower main channel of the Yellow River]

The variations and fluxes of dissolved inorganic nutrients were studied, based on continuously monitored data in the lower main channel of Yellow River (Lijin) during the period of water-sediment regulation in July 2002. Concentrations rang from 169.3 to 273.2 micromol x dm(-3) for NO3- -N, 0.08 to 0.84 micromol x dm(-3) for NO2- -N, 1.39 to 5.04 micromol x dm(-3) for NH4+ -N, with average of 218.6, 0.16, 2.27 micromol x dm(-3), respectively. Concentrations rang from 0.36 to 0.56 micromol x dm(-3) for PO4(3-) -P, 161.4 to 195.8 micromol x dm(-3) for SiO3(2-) -Si, with average of 0.48, 166.7 micromol x dm(-3), respectively. No significant relationship was found between nitrate, phosphate and water discharge during the period of water-sediment regulation, while silicate correlated well with suspended sediment discharge. Water-sediment regulation has no significant effect on the variation of dissolved inorganic nutrients concentrations during 2002 to 2003. But the fluxes proportion of dissolved inorganic nutrients during water-sediment regulation to the whole year is about 50%.

Syntheses and growth mechanisms of 3C-SiC nanostructures from carbon and silicon powders

Cubic silicon carbide (3C-SiC) nanostructures such as needle- and Y-shaped nanowhiskers, smooth and pagoda-shaped nanorods are synthesized on a large scale from activated carbon and silicon powders at 1250 degrees C under atmospheric pressure. The use of ball-milled silicon powders results in the formation of nanowires and nanowhiskers, whereas non-milled silicon powders lead to nanorods together with unreacted silicon powders. Residual oxygen in the growth chamber initiates the carburization reactions which can proceed without further oxygen consumption. The size and morphology of the as-synthesized 3C-SiC nanostructures are observed to be related to the size and morphology of the starting silicon particles. An oxygen-assisted gas-solid model is proposed to explain the observed nanostructures.

Synthesis and characteristics of cubic silicon carbide nanospheres with smooth surfaces

Large quantities of cubic silicon carbide (3C-SiC) nanospheres are synthesized on silicon wafer using zinc sulphide (ZnS) and activated carbon powder. The synthesized nanospheres have smooth surfaces and their diameters range from 20 to 430 nm. The growth of these nanospheres can be explained by a gas-solid model. ZnS powder plays a key role in the formation of activated Si and SiOx. Carburization of the activated Si and SiOx by CO gas leads to the formation of the 3C-SiC nanospheres. Special three-dimensional structure of the product is related to high concentrations of the reactants.

High-speed vibrational imaging and spectral analysis of lipid bodies by compound Raman microscopy

Cells store excess energy in the form of cytoplasmic lipid droplets. At present, it is unclear how different types of fatty acids contribute to the formation of lipid droplets. We describe a compound Raman microscope capable of both high-speed chemical imaging and quantitative spectral analysis on the same platform. We used a picosecond laser source to perform coherent Raman scattering imaging of a biological sample and confocal Raman spectral analysis at points of interest. The potential of the compound Raman microscope was evaluated on lipid bodies of cultured cells and live animals. Our data indicate that the in vivo fat contains much more unsaturated fatty acids (FAs) than the fat formed via de novo synthesis in 3T3-L1 cells. Furthermore, in vivo analysis of subcutaneous adipocytes and glands revealed a dramatic difference not only in the unsaturation level but also in the thermodynamic state of FAs inside their lipid bodies. Additionally, the compound Raman microscope allows tracking of the cellular uptake of a specific fatty acid and its abundance in nascent cytoplasmic lipid droplets. The high-speed vibrational imaging and spectral analysis capability renders compound Raman microscopy an indispensible analytical tool for the study of lipid-droplet biology.