Study of dynamic biasing InGaAs/InAlAs avalanche photodiodes with different active areas.

In this work, by comparing and analyzing dynamic biasing InGaAs/InAlAs avalanche photodiodes(APDs) with different active areas, it is found that they have different noise suppression frequency ranges. The upper limit frequency(defined as the frequency at which the noise suppression effect begins to fail) of InGaAs/InAlAs APDs with active area diameter of 50 µm, 100 µm and 200 µm are 2400 MHz, 1990MHz and 1400 MHz respectively. In addition, for InGaAs/InAlAs APDs with an active area diameter of 50 µm, 100 µm and 200 µm, their optimal frequencies of dynamic biasing (defined as the frequency corresponding to the optimal SNR) are 1877MHz, 1670 MHz and 1075 MHz respectively. At last, applying dynamic biasing technology, it achieves a useful gain of 6698.1, which is much greater than that of DC bias (47.2), and this technology has the potential to be applied in high sensitivity laser radar receivers.

Repair of Finger Pulp Defect and Sensory Reconstruction Using Reverse Homodigital Artery Island Flap With Palmar Cutaneous Branches of the Proper Digital Nerve.

OBJECTIVE: To illustrate the clinical outcomes of the reverse digital proper artery island flap with anastomosing the palmar cutaneous branches of the proper digital nerve for the reconstruction of finger pulp defects. METHODS: From December 2007 to December 2017, a total of 20 patients with finger pulp defects were treated with reverse digital proper artery island flap for innervated construction. Functional outcomes, aesthetic appearance, and complications were evaluated. Functional outcomes were assessed according to range of motion, sensory grade (S0-S4), static 2-point discrimination, Semmes-Weinstein monofilament test, and Cold Intolerance Severity Score. Aesthetic appearance was evaluated according to the Michigan Hand Outcomes Questionnaire. RESULTS: All flaps survived completely without any complications, and all patients were followed up for at least 12 months. The average static 2-point discrimination, Semmes-Weinstein monofilament, and Cold Intolerance Severity Score results of the injured fingers were 6.35 mm (range, 5-8 mm), 3.64 (range, 2.83-4.17), and 19 (range, 8-24), respectively. All patients achieved recovery in sensation from S3+ to S4. The active ranges of motion of the metacarpophalangeal, proximal interphalangeal, and distal interphalangeal joints of the affected fingers were satisfactory. Based on the Michigan Hand Outcomes Questionnaire, 11 patients were strongly satisfied, and 9 were satisfied with the appearance of the injured finger. CONCLUSIONS: The reverse digital proper artery island flap with anastomosing the palmar cutaneous branches of the proper digital nerve is an effective and reliable alternative for the reconstruction of finger pulp defect. In the recovery of sensation, this flap leads to satisfactory effects.

Herders' adaptation strategies and animal husbandry development under climate change: A panel data analysis.

The frequent occurrence of extreme climate events has become an indisputable fact. However, the role of adaptation to extreme climate change in the development of livestock husbandry is still insufficiently understood. This study empirically analyzed the impact of herders' adaptation strategies to extreme drought on livestock husbandry development and aimed to explore the optimal grassland management path under continuous climate change. A panel dataset of surveyed herders from the Xilingol League, a traditional pastoral area in China, was used. The results indicated that the average frequency of extreme drought in the Xilingol League from 1980 to 2020 was 4.94 months/year, and the occurrence of extreme drought showed a slightly upward trend. The average technical efficiency of livestock husbandry was 0.721, which can still be improved. Hay purchases can effectively promote livestock technical efficiency (p<0.01) and is the main adaptation strategy of herders to extreme drought. Further analysis showed that non-farming and pastoral employment has a positive regulatory effect in the impact of purchased hay on livestock technical efficiency. The results of this study deepen the understanding of effective adaptation to extreme weather events in pastoral areas due to climate change and provide useful information to policymakers engaged in grassland management.

Reverse digital artery island flap with versus without sensory nerve coaptation for finger pulp reconstruction.

PURPOSE: Whether an innervated reverse digital artery island flap is superior to a non-innervated reverse digital artery island flap still remains controversial. We aimed to compare the clinical outcomes of the two flaps in repairing finger pulp soft tissue defects. METHODS: Medical records of patients who underwent finger pulp reconstruction between January 2007 and December 2017 were evaluated retrospectively. A total of 45 patients were included. Twenty underwent sensory nerve reconstruction with cutaneous branches of the proper digital nerve, and 25 underwent the surgery without sensory nerve reconstruction. Surgical results, complications and sensory function were collected for analysis. Sensory function was assessed by static two-point discrimination and the modified sensory evaluation standard of British Medical Research Council. RESULTS: The average operation time of innervated flaps was 23 min longer than non-innervated flaps. All 45 flaps survived completely. There was no significant difference in complications between groups. The average follow-up was 22 months. At the final follow-up, five non-innervated flaps had no recovery of static two-point discrimination. The average static two-point discrimination of the remaining 20 non-innervated flaps was larger than that of innervated flaps. Innervated flaps consistently achieved higher sensory function grades according to the modified sensory evaluation standard of British Medical Research Council. CONCLUSION: An innervated reverse digital artery island flap can achieve better sensory function recovery in a shorter time. This procedure did not increase the incidence of complications, although it extended the operation time. It has proven to be a good technique for finger pulp reconstruction.

High signal-noise ratio avalanche photodiodes with dynamic biasing technology for laser radar applications.

In this work, a high signal-noise ratio (SNR) dynamic biasing InGaAs/InAlAs avalanche photodiode (APD) is demonstrated experimentally and first applied in a laser radar system. Combining with the dynamic biasing technology, the APDs are operated in an unexploited voltage range between linear mode and Geiger mode, which, in this work, is defined as a transition zone. Surprisingly, it is found that the excess noise of dynamic biasing APDs decreases with the gain in this transition zone. As expected, the maximum useful gain is as high as 620 in the dynamic biasing mode, which shows a greater promotion than that of the DC biasing mode (17.5). Compared with the traditional DC biasing mode, the optimal SNR for dynamic biasing mode is improved by 14 dB without the degradation of response time as the peak optical power is 525 nW. Moreover, when SNR = 10, the peak optical power for the dynamic biasing mode is 43.4 nW, which shows a 57.5-fold (17.6 dB) reduction in comparison with the DC biasing mode (2495 nW). Therefore, we believe this new optical receiver will pave a new way in high-sensitivity and high-speed light detection.

Photon-Trapping Microstructure for InGaAs/Si Avalanche Photodiodes Operating at 1.31 µm.

With the rapid development of photo-communication technologies, avalanche photodiode (APD) will play an increasingly important role in the future due to its high quantum efficiency, low power consumption, and small size. The monolithic integration of optical components and signal processing electronics on silicon substrate chips is crucial to driving cost reduction and performance improvement; thus, the technical research on InGaAs/Si APD is of great significance. This work is the first to demonstrate the use of a photon-trapping (PT) structure to improve the performance of the InGaAs/Si APD based on an SOI substrate, which exhibits very high absorption efficiency at 1310 nm wavelength while the thickness of the absorption layer is kept at 800 nm. Based on the optical and electrical simulations, an optimized InGaAs/Si PT-APD is proposed, which exhibits a better performance and a higher responsivity compared to the original InGaAs/Si APD.

A Self-Assembled Nanoindicator from Alizarin Red S-Borono-Peptide for Potential Imaging of Cellular Copper(II) Ions.

Recently, smart nanomaterials from peptide self-assembly have received extensive attention in the field of biological and medical applications. Through rationally designing the molecular structure, we constructed a borono-peptide that self-assembled into well-defined nanofibers. Relying on the specific recognition between the vicinal diol compound and boronic acid, a novel alizarin red S (ARS)-borono-peptide (BP) spherical nanoindicator was fabricated, accompanying with the emission of strong fluorescent signal. The fluorescent nanoindicator displayed an intense response to copper(II) ions and underwent the fluorescent "turn-off" due to the strong binding-induced displacement. Originating from the high selectivity toward copper(II) ions, good biocompatibility and cancer cell targeting, the nanoindicator offered the opportunity to image copper(II) ions in cancer cells via fluorescent change.

A Lyotropic Liquid Crystal from a Flexible Oligopeptide Amphiphile in Dimethyl Sulfoxide.

Despite the rapid progress in peptide liquid crystals (LCs) due to their prominent properties, our investigation on flexible peptide-based LCs is incomplete, mainly resulted from their unclear formation mechanisms and unexploited applications in organic solvents. Here, we develop a lyotropic LC based on a flexible oligopeptide amphiphile, which aggregates into aligned cylinder-like nanostructures in dimethyl sulfoxide (DMSO). The formation mechanism of lyotropic LC in DMSO was probed by the experimental investigation and molecular dynamics simulation, indicating that the hydrogen bonding and hydrophobic and electrostatic interactions contribute to the formation of ordered nanostructures in the organic solvent. Arising from the orientational order and suitable fluidity, we exploit the application of lyotropic LC as an aligned medium to measure the residual dipolar couplings of bioactive molecules. This study not only offers the understanding of the mechanism to create LC systems without rigid aromatic groups but also expands the applications of ordered bottom-up nanomaterials in organic solvents.

Directing an oligopeptide amphiphile into an aligned nanofiber matrix for elucidating molecular structures.

A novel aligned nanofiber matrix was obtained from the self-assembly of an oligopeptide amphiphile. The alignment properties can be applied to measure residual dipolar couplings (RDCs) for the structural elucidation of molecules by liquid-state NMR.

Novel oligopeptide nanoprobe for targeted cancer cell imaging.

Here we designed and constructed a tryptophan-phenylalanine-phenylalanine-tryptophan (WFFW) tetrapeptide, which generated photostable and tunable fluorescence emission signals from 340 nm to 500 nm. The WFFW tetrapeptide could self-assemble into a spherical nanostructure with enhanced fluorescence intensity. Driven by π-π stacking and hydrogen bond interaction, WFFW co-assembled with arginine-glycine-aspartic acid (RGD) modified WFFW to form a cancer-targeted fluorescent nanoprobe, which could selectively image the cancer cells.

A Water-Stable Cl@Ag14 Cluster Based Metal-Organic Open Framework for Dichromate Trapping and Bacterial Inhibition.

Decoding the principles of cluster-based framework assembly at the molecular level remains a persistent challenge. Herein, we isolated and characterized a novel water-stable three-dimensional (3D) metal-organic open framework [Cl@Ag14(cPrC≡C)10Cl2·(p-TOS)·1/3H2O]n (SD/Ag14, cPrC≡CH = cyclopropylacetylene; p-TOS = p-toluenesulfonate), which contains a chloride-templated Ag14 cluster as building block. For SD/Ag14, one chloride acts as the template to shape the Ag14 cluster and the other bridges the clusters to a 3D pcu-h open framework. As revealed by high resolution electrospray mass spectrometry (HRESI-MS), the Ag12-Ag14 species are potential cluster-based intermediates to the 3D pcu-h framework, which authenticates a preconceived idea that the 3D framework is hierarchically assembled from the silver clusters as observed in solid state. Interestingly, SD/Ag14 can be used effectively to remove the environmental pollutant Cr2O72- from wastewater through anion exchange in a single-crystal-to-single-crystal (SC-SC) transformation fashion. Furthermore, SD/Ag14 exhibits excellent antibacterial activity against Staphylococcus aureus, thus making it a potential antibacterial agent.

Modifying Surface Chemistry of Metal Oxides for Boosting Dissolution Kinetics in Water by Liquid Cell Electron Microscopy.

Dissolution of metal oxides is fundamentally important for understanding mineral evolution and micromachining oxide functional materials. In general, dissolution of metal oxides is a slow and inefficient chemical reaction. Here, by introducing oxygen deficiencies to modify the surface chemistry of oxides, we can boost the dissolution kinetics of metal oxides in water, as in situ demonstrated in a liquid environmental transmission electron microscope (LETEM). The dissolution rate constant significantly increases by 16-19 orders of magnitude, equivalent to a reduction of 0.97-1.11 eV in activation energy, as compared with the normal dissolution in acid. It is evidenced from the high-resolution TEM imaging, electron energy loss spectra, and first-principle calculations where the dissolution route of metal oxides is dynamically changed by local interoperability between altered water chemistry and surface oxygen deficiencies via electron radiolysis. This discovery inspires the development of a highly efficient electron lithography method for metal oxide films in ecofriendly water, which offers an advanced technique for nanodevice fabrication.

Nanoscale Engineering in VO2 Nanowires via Direct Electron Writing Process.

Controlling phase transition in functional materials at nanoscale is not only of broad scientific interest but also important for practical applications in the fields of renewable energy, information storage, transducer, sensor, and so forth. As a model functional material, vanadium dioxide (VO2) has its metal-insulator transition (MIT) usually at a sharp temperature around 68 °C. Here, we report a focused electron beam can directly lower down the transition temperature of a nanoarea to room temperature without prepatterning the VO2. This novel process is called radiolysis-assisted MIT (R-MIT). The electron beam irradiation fabricates a unique gradual MIT zone to several times of the beam size in which the temperature-dependent phase transition is achieved in an extended temperature range. The gradual transformation zone offers to precisely control the ratio of metal/insulator phases. This direct electron writing technique can open up an opportunity to precisely engineer nanodomains of diversified electronic properties in functional material-based devices.