A method for evaluating the selectivity of electrodes implanted fornerve simulation

The scale of stimulating electrodes possible for use in functional electrical stimulation to restore motor and sensory function is rapidly approaching that of individual neurons. Although the electrodes may approach the dimensions of single nerve cells, it is unclear if the region of excitation elicited by each electrode will be correspondingly small. Previous techniques for evaluating this have either been tedious or have lacked the resolution necessary. This paper describes a method that uses the refractory interaction of the compound action potentials elicited by a stimulus pulse pair, along with high-resolution recording of those potentials, to achieve measurements of the selectivity of stimulation down to the scale of a few axon diameters. The feasibility of this technique is demonstrated in sciatic nerves of frogs (Rana Catesbiana) acutely implanted with a sapphire electrode array.     

Transient response of ARROW VCSELs

The transient response of antiresonant reflecting optical waveguide (ARROW) vertical-cavity surface-emitting lasers (VCSELs) is analyzed. It is found that under current modulation, the radiation loss of the transverse-leaky mode decreases during the state of the lasers but increases during the state. Numerical analysis shows that this variation in radiation loss is due to the carrier-induced refractive-index depression that arises from spatial-hole-burning of carrier concentration. It is noted that the increment in radiation loss during the state can be used to prevent net modal gain of the transverse-leaky mode from reacquiring threshold after turn-off. Hence, a new method to design ARROW, based on the variation in radiation loss, is proposed to eliminate the excitation of secondary pulsation in VCSELs. The influence of thermal lensing effects on the excitation of secondary pulsation during the state of the lasers is also investigated.     

Enzymatic Writing to Soft Films: Potential to Filter,Store, and Analyze Biologically Relevant Chemical Information

Sensor‐based chemical analyses commonly enlist either the molecular recognition capabilities of biology (e.g., enzyme biosensors) or advanced information processing algorithms (e.g., the electronic nose). Here, a hybrid approach is proposed in which an enzyme is used to “filter” chemical information and write this information to a film which then serves as a permanent storage medium that can be ‘read’ repeatedly, interactively, and by multiple sensor modalities. This approach is demonstrated by analyzing common dietary phenols that are reported to offer health benefits. Specifically, the enzyme tyrosinase is used to convert these phenols into reactive quinones that graft (i.e., write) to a chitosan film. Grafting can be detected by optical, mechanical, and electrochemical sensors. Importantly, grafting confers redox activity to the films and this redox activity can be probed interactively by advanced electrochemical methods that allow the intrinsic redox reactivities to be compared, redox interactions to be identified, and biologically relevant redox activities to be examined. The transfer of chemical and biological information to a film is envisioned to provide broader access to the extensive capabilities offered by sensor technologies and signal processing methodologies.     

Band‐Offset Engineering for Enhanced Open‐Circuit Voltage in Polymer–Oxide Hybrid Solar Cells

The power conversion efficiency of organic and hybrid solar cells is commonly reduced by a low open‐circuit voltage (V_OC). In these cases, the V_OC is significantly less than the energy of the lowest energy absorbed photon, divided by the elementary charge q. The low photovoltage originates from characteristically large band offsets between the electron donor and acceptor species. Here a simple method is reported to systematically tune the band offset in a π‐conjugated polymer–metal oxide hybrid donor–acceptor system in order to maximize the V_OC. It is demonstrated that substitution of magnesium into a zinc oxide acceptor (ZnMgO) reduces the band offset and results in a substantial increase in the V_OC of poly(3‐hexylthiophene) (P3HT)–ZnMgO planar devices. The V_OC is seen to increase from 500 mV at x = 0 up to values in excess of 900 mV for x = 0.35. A concomitant increase in overall device efficiency is seen as x is increased from 0 to 0.25, with a maximum power‐conversion efficiency of 0.5 % obtained at x = 0.25, beyond which the efficiency decreases because of increased series resistance in the device. This work provides a new tool for understanding the role of the donor–acceptor band offset in hybrid photovoltaics and for maximizing the photovoltage and power‐conversion efficiency in such devices.     

PMBus--数字电源开放标准协议

近年来,许多相关的因素导致对数字电源管理的需求急剧上升。许多板卡设计人员已经转向开发中间总线电源结构,通过使用多个单板DC/DC转换器来产生不同硅器件所需要的多样化的电源要求。这导致一个很明显的结果就是在产品的设计、生产测试及日常使用的过程中,配置、控制及监控这些电源将变得更加的复杂。光是控制上电/下电时序就需要专门的可编程集成电路及大量的额外部件,更别说用于灵活的系统级控制和诊断所需要的配置或实时反馈设施。     

Synchronized External Pulsation for Improved Tolerance to Acceleration Stress: Model Studies and Preliminary Experiments

Synchronized external pulsation is proposed as a method to improve tolerance to acceleration stress. This technique uses a modified anti-G suit which is pressurized and depressurized synchronously with the heart cycle. The feasibility of the procedure has been studied using a computer model of the cardiovascular system which includes the effects of Gz stress, and contains simulations of baroreceptor control of heart rate and venous tone. Model predictions indicate that for unprotected subjects, carotid pressure at eye level (ophthalmic artery pressure) decreases to 20 mmHg (beginning of central light loss) at approximately +3.6 Gz. Applying standard anti-G suit pressure to the model increases this level to 5.3 Gz. When synchronized external pulsation of 2 psi is superimposed on the standard anti-G suit pressure, the tolerance to acceleration stress is further augmented by at least 0.9 G above the protection afforded by the standard anti-G suit alone. A set of preliminary experiments on human subjects to test the feasibility of using the technique in the high-G environment has also been carried out. The results under various protection modes compare favorably to the model predictions. Our results suggest that the computer model presented here is a useful tool for studying cardiovascular responses under +GZ stress. It also indicates that using synchronized external pulsation pressure superimposed on the standard anti-G suit pressure may offer extra protection to acceleration stress.     

Mechanistic-based comparisons of stabilised base and granular surface layers of low-volume roads

Granular surface and base layers of low-volume roads (LVRs) are frequently subjected to severe damage that adversely affects safety and requires regular repair and maintenance. Various stabilisation methods have been evaluated for mitigating damage and improving serviceability of LVR systems. However, few well-documented comparisons exist of the field mechanical performance, durability and construction costs of different stabilisation methods under the same set of geological, climate, and traffic conditions. Therefore, the present study was conducted to identify the most effective and economical among several stabilisation methods for repairing or reconstructing granular surface and base layers of LVRs. In this study, a range of promising technologies from a comprehensive literature review was selected and examined using field demonstration sections. A total of nine geomaterials, three chemical stabilisers, and three types of geosynthetics were used to construct various test sections over a 3.22 km stretch of granular-surfaced road. Extensive falling weight deflectometer (FWD) and dynamic cone penetrometer tests were performed to evaluate the multilayered elastic moduli and strengths of the various sections. This paper details the design and construction of each test section, compares the as-constructed mechanistic performance of all test sections, and assesses stiffness changes of several sections one year after construction. To provide a statistical basis for the comparisons, a pairwise multiple-comparison procedure applied for unequal sample sizes and variances and the paired t-test were used to analyse the FWD test results, demonstrating that the performance measures of the various sections were significantly different.     

Elaboration,characterization and study of a novel affinity membrane made from electrospun hybrid chitosan/nylon-6 nanofibers for papain purification

Electrospun hybrid chitosan/nylon-6 nanofibrous mats with fiber diameters in the range of 80–310 nm were successfully fabricated using an electrospinning method. Nanofibrous membranes were prepared by nucleophilic reaction of the chitosan’s hydroxyl and amidocyanogen with the triazinyl chloride of Cibacron Blue F3GA (CB) ligand. This system was used to study the purification of papain. Physical and chemical properties of the affinity membrane were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (ATR-FTIR), differential scanning calorimetry (DSC), contact angle (CA) and element analysis (EA). The equilibrium adsorption capacity (from Langmuir isotherm data) for papain was 93.46 mg/g affinity membrane. Fifteen layers of the composite affinity membrane were packed into a spin column to separate papain from raw material. Significant amount of the adsorbed papain (about 90.4%) was eluted by 1.0 M NaSCN at pH 9.0, and 4.8-fold purification was achieved in a single step. Experiments on regeneration and dynamic adsorption were also performed. It is shown that this system has the potential to be developed for the industrial purification of the papain.     

High Salinity Relaying to Reduce Vibrio parahaemolyticus and Vibrio vulnificus in Chesapeake Bay Oysters (Crassostrea virginica)

Cases of Vibrio infections in the United States have tripled from 1996 to 2009 and these infections are most often associated with the consumption of seafood, particularly oysters (Crassostrea virginica). Information is needed on how to reduce numbers of Vibrio parahaemolyticus and Vibrio vulnificus in bi‐valve molluscan shellfish (for example, oysters). The purpose of this study was to evaluate the effectiveness of high salinity relaying or treatment in recirculating aquaculture systems (RASs) as methods to reduce the abundance of V. parahaemolyticus and V. vulnificus in oysters. For relaying field trials, oysters were collected from approved harvest waters, temperature abused outside under a tarp for 4 h, and then transferred to high (29 to 33 ppt.) and moderate (12 to 19 ppt.) salinities. For RAS treatment trial, oysters were transferred to 32 to 34 ppt. salinity at 15 °C. After 7, 14, 21, and in some instances 28 d, oysters were collected and analyzed for V. parahaemolyticus and V. vulnificus levels using multiplex real‐time PCR. Initial levels of V. parahaemolyticus and V. vulnificus ranged from 3.70 to 5.64 log₁₀ MPN/g, and were reduced by 2 to 5 logs after 21 to 28 d in high salinity water (29 to 34 ppt.). Oyster mortalities averaged 4% or less, and did not exceed 7%. Relaying of oysters to high salinity field sites or transfer to high salinity RAS tanks was more effective in reducing V. vulnificus compared with V. parahaemolyticus. These results suggest that high salinity relaying of oysters is more effective in reducing V. vulnificus than V. parahaemolyticus in the oyster species used in this study.