High‐efficiency microcrystalline silicon single‐junction solar cells

This short communication highlights our latest results towards high‐efficiency microcrystalline silicon single‐junction solar cells. By combining adequate cell design with high‐quality material, a new world record efficiency was achieved for single‐junction microcrystalline silicon solar cell, with a conversion efficiency of 10.69%, independently confirmed at ISE CalLab PV Cells. Such significant conversion efficiency could be achieved with only 1.8 µm of Si. Copyright © 2013 John Wiley & Sons, Ltd.     

Design and calibration of a high-frequency oscillatory ventilator

High-frequency ventilation (HFV) is a modality of mechanical ventilation which presents difficult technical demands to the clinical or laboratory investigator. The essential features of an ideal HFV system are described, including wide frequency range, control of tidal volume and mean airway pressure, minimal dead space, and high effective internal impedance. The design and performance of a high-frequency oscillatory ventilation system is described which approaches these requirements. The ventilator utilizes a linear motor regulated by a closed loop controller and driving a novel frictionless double-diaphragm piston pump. Finally, the ventilator performance is tested using the impedance model of Venegas [1].     

Capacity of Differential Versus Nondifferential Unitary Space–Time Modulation for MIMO Channels

Differential unitary space-time modulation (DUSTM) and its earlier nondifferential counterpart, USTM, permit high-throughput multiple-input multiple-output (MIMO) communication entirely without the possession of channel state information by either the transmitter or the receiver. For an isotropically random unitary input we obtain the exact closed-form expression for the probability density of the DUSTM received signal, permitting the straightforward Monte Carlo evaluation of its mutual information. We compare the performance of DUSTM and USTM through both numerical computations of mutual information and through the analysis of low- and high-signal-to-noise ratio (SNR) asymptotic expressions. In our comparisons the symbol durations of the equivalent unitary space-time signals are equal to T. For DUSTM the number of transmit antennas is constrained by the scheme to be M=T/2, while USTM has no such constraint. If DUSTM and USTM utilize the same number of transmit antennas at high SNRs the normalized mutual information of the two schemes expressed in bits/s/Hz are asymptotically equal, with the differential scheme performing somewhat better. At low SNRs the normalized mutual information of DUSTM is asymptotically twice the normalized mutual information of USTM. If, instead, USTM utilizes the optimum number of transmit antennas then USTM can outperform DUSTM at sufficiently low SNRs     

Sensor allocation in diverse environments

Sensor coverage varies with location due to factors such as weather, terrain, and obstacles. If a field can be partitioned into zones of homogeneous sensing areas, then the area covered by a random deployment of sensors can be optimized by controlling the number of sensors deployed in each zone. This paper provides formulas to directly calculate the optimal sensor partition in runtime asymptotically equal to the number of zones; to determine the minimum sensor count required to achieve a specific coverage threshold; and to bound the maximum increase in coverage over a strategy oblivious to differences in sensing areas. Results show that this bound is no greater than 13% for a field with two zones. While the analytical solutions assume that each zone is covered independently, sensors are allowed to affect neighboring zones in simulations. Nevertheless, the simulation results support the optimality of the solutions.     

Nanotechnology‐Enabled Closed Loop Insulin Delivery Device: In Vitro and In Vivo Evaluation of Glucose‐Regulated Insulin Release for Diabetes Control

Recently, a new multifunctional, bio‐inorganic nanocomposite membrane with the ability to self‐regulate the release of insulin in response to blood glucose (BG) levels was reported. Herein, the application of this material as part of a small, implantable, closed‐loop insulin delivery device designed to continuously monitor BG concentrations and regulate insulin release is proposed. The insulin delivery device consists of a nanocomposite glucose‐responsive plug covalently bound to an insulin reservoir made of surface‐modified silicone. The plug is prepared with crosslinked bovine serum albumin (BSA) and enzymes (glucose oxidase (GOx) and catalase (CAT)), pH‐responsive hydrogel nanoparticles, and multifunctional MnO₂ nanoparticles. The plug functions both as a glucose sensor and controlled delivery unit to release higher rates of insulin from the reservoir in response to hyperglycemic BG levels and basal insulin rates at normal BG concentration. The surfaces of the device are modified by silanization followed by PEGylation to ensure its safety and biocompatibility and the stability of encased insulin. Our results show that insulin release can be modulated in vitro in response to glucose concentrations. In vivo experiments show that the glycemia of diabetic rats can be controlled with implantation of the prototype device. The glucose‐responsiveness of the device is also demonstrated by rapid drop in BG level after challenging diabetic rats with bolus injection of glucose solution. In addition, it is demonstrated that surface PEGylation of the device is necessary for reducing the immune response of the host to the implanted foreign object and maintaining insulin stability and bioactivity. With this molecular architecture and the bio‐inorganic nanocomposite plug, the device has the ability to maintain normal BG levels in diabetic rats.     

Nanoscale Characterization of Energy Generation from Piezoelectric Thin Films

We report on the use of nanoindentation to characterize in situ the voltage and current generation of piezoelectric thin films. This work presents the controlled observation of nanoscale piezoelectric voltage and current generation, allowing accurate quantification and mapping of force function variations. We characterize both continuous thin films and lithographically patterned nano­islands with constrained interaction area. The influence of size on energy generation parameters is reported, demonstrating that nanoislands can exhibit more effective current generation than continuous films. This quantitative finding suggests that further research into the impact of nanoscale patterning of piezoelectric thin films may yield an improved materials platform for integrated microscale energy scavenging systems.     

Toward a Theory Relating Political Discourse, Media, and Public Opinion

This paper presents a multimethod investigation of framing in the government–media–public interaction during the so-called partial-birth abortion (PBA) debate in the U.S. Operationalizing framing as the use of the word "baby" or "fetus," content analysis first shows that opposing political elites employed almost exclusive vocabularies in attempts to justify their views and shape attitudes. Time-series analysis then charts the path of "baby's" discursive dominance from congressional discourse through news and editorials to citizens. Finally, experimental results support 2 microlevel hypotheses. First, uptake—exposure to articles featuring the exclusive use of "baby" or "fetus," respectively, increased or decreased support for banning PBA. Second, emergence—participants exposed to discourse using both terms converged upon a response independent of the words' relative proportions. In contrast to probabilistic survey response models, these findings support the idea that a kind of public reason can emerge from the interaction of citizens' judgment processes and elite communication.     

Conventional Electron Microscopy and Electron Holography of Organic Solar Cells

Organic solar cells are a promising route towards large‐area and low‐price photovoltaic systems. The devices are composed of at least two layers: the hole‐transport layer and the electron‐transport layer. The light absorption can occur in one or both layers. At the interface of the layers the excitons are separated into charge carriers, and every layer deals with one type of carrier. Higher efficiencies of the separation process can be obtained by using a mixed layer containing both materials to obtain a very high interface area. Although the structure of the mixed layers used plays a crucial role for the device performance, until now the morphologies have not been elucidated. In order to correlate physical and optical findings with structure and morphology for the materials in question, electron microscopy experiments were performed on the single components as well as on the layer systems. The conventional electron microscope is a poor phase microscope. As consequence, weak‐phase objects like organic molecules have to be stained or imaged under strong defocus to produce an observable contrast. Artifacts caused by chemical staining and the appearance of Fresnel diffraction using the defocus technique represent the main problems of conventional microscopy. These artifacts can be avoided using electron holography. Holograms of ultrathin sections of thin layers composed of organic dye molecules were recorded. Subsequently, the phase images were reconstructed. In this manner, we succeeded in obtaining high‐contrast electron micrographs without applying staining or defocus. In addition, holograms of crystalline C₆₀ and zinc phthalocyanine were successfully recorded. Holography has been shown to be a useful tool to image beam‐sensitive and weak‐phase objects without artifacts.     

MOCVD制备过掺杂GaN基稀磁半导体微结构研究

应用MOCVD方法我们在c轴取向的蓝宝石衬底上生长出Fe掺杂和Mn掺杂GaN薄膜。通过改变前驱物的通入量,我们制备出不同掺杂浓度的样品。应用高分辨透射电镜,我们对样品的微结构进行了分析。对于Fe过掺杂GaN样品,我们发现了六角结构的Fe3N团簇的存在,并且Fe3N(0002)面平行于GaN(0002)面;对于Mn过掺杂GaN样品,我们发现了六角结构的Mn6N2.58相的存在,并且Mn6N2.58(0002)面平行于GaN(0002)面。同时,由于晶格中掺入了大量掺杂离子,GaN晶格取向遭到了破坏,导致了部分GaN(0002)面的倾斜。磁学测量表明均一相的Fe掺杂GaN显现铁磁性,而均一相Mn掺杂GaN没有铁磁性。由于铁磁性Fe单晶和Fe3N团簇的存在,相比于均一性Fe掺杂GaN,过掺杂GaN样品的磁性大幅度增强,而Mn过掺杂GaN样品显现出很弱的铁磁性,这有可能来源于Mn6N2.58相。