Concept and demonstration of an intermediate band tandem device for solar energy conversion

We have realized a tandem solar cell design that combines a pin‐junction with a photovoltaic intersubband absorber. This concept allows harvesting light in the visible range and the near‐ and mid‐infrared at the same time, and theoretically, energy conversion efficiencies beyond the Shockley–Queisser‐limit could be achieved. A test structure was grown, and the operation of this concept could be confirmed, in principal with an optical two‐beam experiment. The basic characteristics of the device can be explained with an equivalent circuit design that consists of three individual cells, and we find an obvious analogy to the concept of the intermediate band solar cell with noteworthy advantages at some points. Our results show, that for a working device it is crucial to adjust the properties of the photovoltaic intersubband absorber for optimal charge separating performance at the working point of the solar cell. Copyright © 2015 John Wiley & Sons, Ltd.     

Understanding selective oxidations

Functionalizing organic molecules is an important value-creating step throughout the entire chemical value-chain. Oxyfunctionalization of e.g. C-H or C=C bonds is one of the most important functionalization technologies used industrially. The major challenge in this field is the prevention of side reactions and/or the consecutive over-oxidation of the desired products. Despite its importance, a fundamental understanding of the intrinsic chemistry, and the subsequent design of a tailored engineering environment, is often missing. Industrial oxidation processes are indeed to a large extent based on empirical know-how. In this mini-review, we summarize some of our previous work to help to bridge this knowledge gap and elaborate on our ongoing research.     

Dicing of hard and brittle materials with on-machine laser-dressed metal-bonded diamond blades

The ultra-precision dicing of hard and brittle materials causes high wear on the abrasive tool which results in the deterioration of blade cross section as well as the decrease of diamond grain exposure. Resin-bonded diamond blades are used due to their in-process self-sharpening capability. Nevertheless, the shape of the blade cross section generated by self-sharpening is random which leads to poor accuracy when precise grooves need to be produced. Metal-bonded diamond blades feature higher tool lifetime and shape accuracy compared to resin-bonded blades, but are not capable of performing self-sharpening. In this study, the laser dressing of metal-bonded diamond blades is investigated to enable their use in the ultra-precision dicing of hard and brittle materials by continuous laser dressing. We investigated laser dressing with and without the presence of cooling water. The sharpness (grain exposure) after dressing is measured by the cutting face surface roughness. The dicing performance is evaluated by observing the dicing results in terms of cutting depth consistency and by monitoring the spindle power during dicing. Dicing blades which have been laser dressed in an environment with coolant feature less grain exposure than dicing blades which have been laser dressed in dry condition. The dicing results show an improvement in the sharpness and durability of laser-dressed dicing blades in comparison with new or conventionally dressed blades. The ability to apply and perform laser dressing on a dicing machine in an environment with coolant shows the feasibility of laser technology for continuous dressing.     

Silk for Drug Delivery Applications: Opportunities and Challenges

Silk fibers have been used in textiles for more than 5,000 years and as a suturing material for many centuries. The recent development of new applications for silks include drug delivery. An overview of this new field is provided, summarizing the development of emerging drug delivery applications which include silk-based nanomedicines and transdermal delivery systems We also highlight some of the challenges in developing silk-based drug delivery systems.     

CO2 savings of ground source heat pump systems – A regional analysis

In the current study the savings of CO₂ emissions due to the use of ground source heat pump (GSHP) systems was investigated in comparison to conventional heating systems. Based on a subsidy program for GSHP systems in southwest Germany, the regional, average, and total CO₂ savings of 1105 installed GSHP systems were determined on a regional scale. The emitted CO₂ per kWh of heating demand for the studied scenario resulted in 149 g CO₂/kWh for GSHP using the German electricity mix and 65 g CO₂/kWh using the regional electricity mix, which results in CO₂ savings of 35% or 72%, respectively. Similar CO₂ avoidances of GSHP systems were found in American and European studies ranging between 15% and 77% strongly depending on the supplied energy for the heat pumps and the efficiency of installation. The resulting CO₂ savings for one installed GSHP unit in the present study therefore range between 1800 and 4000 kg per year. Nevertheless, the minimum average total annual CO₂ savings of all installed GSHP systems due to the subsidy program amounted to 2000 tons per year. The maximum regional avoided additional CO₂ emissions are primarily associated with the affluent suburbs of the most densely populated area in the region. In 2006 the total contribution of CO₂ savings due to GSHP systems in Germany was only about 3.4% of the total renewable energies. However, continuously rising numbers of installed GSHP units and the increasing use of renewable electricity demonstrate that there is a fine opportunity to substantially avoid additional CO₂ emissions associated with the provision of heating (and cooling) of buildings and other facilities.     

Exploring Internal Structure of Nanoporous Glasses Obtained by Leaching of Phase‐Separated Alkali Borosilicate Glasses

Mesoporous glasses – the leaching products of phase‐separated alkali borosilicate glasses – are widely used in fundamental research and practical applications. In this work, the option to control their internal mesopore structure by varying the conditions of microphase separation has been studied. Structure and transport characterization of a family of nanoporous glasses obtained under different conditions has been performed using a combination of several experimental techniques, including gas adsorption, nuclear magnetic resonance cryoporometry and diffusometry.     

The effectiveness of producer‐side machine‐independent optimizations for mobile code

Portable mobile code is often executed by a host virtual machine using just‐in‐time compilation. In this context, the compilation time in the host virtual machine is critical. This compilation time can be reduced if optimizations are performed ahead‐of‐time before distribution of the mobile code. Unfortunately, the portable nature of mobile code limits ahead‐of‐time optimizations to those that are machine‐independent. This work examines the effect of machine‐independent optimizations on the performance of mobile code applications. All experiments use the SafeTSA Format, a mobile code format that is based on Static Single Assignment Form (SSA Form). The experiments, which are performed on both the PowerPC and IA32 architectures, indicate that the effects of performing classical machine‐independent optimizations are—in fact—quite machine‐dependent. Nevertheless, the results demonstrate that applying such optimizations in a mobile code system can be beneficial. Copyright © 2009 John Wiley & Sons, Ltd.