Methodical selection of thermal conductivity models for porous silica-based media with variation of gas type and pressure

If the effective thermal conductivity of a silica powder in any gas atmosphere is to be calculated analytically, one is faced with a whole series of decisions. There are a lot of different models for the gas thermal conductivity in the pores, the thermal accommodation coefficient or the effective thermal conductivity itself in the literature. Furthermore, it has to be decided which input parameters should be used. This paper gives an overview and recommendations as to which calculation methods are best suited for the material classes of precipitated silica, fumed silica, silica gel and glass spheres. All combinations of the described methods result in a total of 2800 calculation models which are compared with pressure-dependent thermal conductivity measurements of 15 powdery materials with 7 different gases using Matlab computations. The results show that with a model based on a spherical unit cell, which considers local Knudsen numbers, the measuring points of all powder-gas combinations can be determined best with an average variance of about 18.5%. If the material class is known beforehand, the result can be predicted with an average accuracy of about 10% with the correspondingly determined methods

Passive room conditioning using phase change materials—Demonstration of a long-term real size experiment

The thermal properties of lightweight buildings can be efficiently improved by using phase change materials (PCMs). The heat storage capacity of the building can be extended exactly at the desired temperature level, which leads to an enormous increase in residential comfort. This is shown in the present paper using the example of a prefabricated wooden house. The house was divided into two identical rooms. One of them was equipped with almost one ton of phase change material based on salt hydrates with a melting temperature of approx. 21°C. The material was encapsulated in 1-l Polyethylene containers and installed in two back-ventilated layers inside of the walls. The house was monitored for a period of 87 days in terms of temperatures, solar radiation and air velocity inside the PCM wall system. A considerable temperature buffering could be observed in the PCM room compared to the reference room. An overall reduction of the temperature fluctuations of 57% and a reduction of the day/night fluctuations of 62% compared to the reference room could be obtained. In addition, a prediction regarding the energy demand of such buildings is discussed on the basis of a simulation program. Thus, the annual cooling capacity can be reduced by 36.5% compared to the regular timber construction technique by introducing PCM. Furthermore, the good correlation of the simulation results with the experimental ones allows using the simulation as a tool to design a house with additional thermal storages

A customized stand-alone photometric Raman sensor applicable in explosive atmospheres: a proof-of-concept study

This paper presents an explosion-proof two-channel Raman photometer designed for chemical process monitoring in hazardous explosive atmospheres. Due to its design, alignment of components is simplified and economic in comparison to spectrometer systems. Raman spectrometers have the potential of becoming an increasingly important tool in process analysis technologies as part of molecular-specific concentration monitoring. However, in addition to the required laser power, which restricts use in potentially explosive atmospheres, the financial hurdle is also high. Within the scope of a proof of concept, it is shown that photometric measurements of Raman scattering are possible. The use of highly sensitive detectors allows the required excitation power to be reduced to levels compliant for operation in potentially explosive atmospheres. The addition of an embedded platform enables stable use as a self-sufficient sensor, since it carries out all calculations internally.Multi-pixel photon counters (MPPCs) with large detection areas of 1350&thinsp;µm2 are implemented as detectors. As a result, the sensitivity of the sensor is strongly increased. This gain in sensitivity is primarily achieved through two characteristics: first, the operating principle avalanche breakdown to detect single photons is used; second, the size of the image projected onto the MPPC is much bigger than the pixel area in competing Raman-Spectrometers resulting in higher photon flux. This combination enables reduction of the required excitation power to levels compliant for operation in potentially explosive atmospheres. All presented experiments are performed with strongly attenuated laser power of 35&thinsp;mW. These include the monitoring of the analytes ethanol and hydrogen peroxide as well as the reversible binding of CO2 to amine. Accordingly, the described embedded sensor is ideally suited as a process analytical technology (PAT) tool for applications in environments with limitations on power input.</p

Degradation of cellular mir-27 by a novel, highly abundant viral transcript is important for efficient virus replication in vivo.

Cytomegaloviruses express large amounts of viral miRNAs during lytic infection, yet, they only modestly alter the cellular miRNA profile. The most prominent alteration upon lytic murine cytomegalovirus (MCMV) infection is the rapid degradation of the cellular miR-27a and miR-27b. Here, we report that this regulation is mediated by the ∼1.7 kb spliced and highly abundant MCMV m169 transcript. Specificity to miR-27a/b is mediated by a single, apparently optimized, miRNA binding site located in its 3'-UTR. This site is easily and efficiently retargeted to other cellular and viral miRNAs by target site replacement. Expression of the 3'-UTR of m169 by an adenoviral vector was sufficient to mediate its function, indicating that no other viral factors are essential in this process. Degradation of miR-27a/b was found to be accompanied by 3'-tailing and -trimming. Despite its dramatic effect on miRNA stability, we found this interaction to be mutual, indicating potential regulation of m169 by miR-27a/b. Most interestingly, three mutant viruses no longer able to target miR-27a/b, either due to miRNA target site disruption or target site replacement, showed significant attenuation in multiple organs as early as 4 days post infection, indicating that degradation of miR-27a/b is important for efficient MCMV replication in vivo

Functional interdependence of BRD4 and DOT1L in MLL leukemia.

Targeted therapies against disruptor of telomeric silencing 1-like (DOT1L) and bromodomain-containing protein 4 (BRD4) are currently being evaluated in clinical trials. However, the mechanisms by which BRD4 and DOT1L regulate leukemogenic transcription programs remain unclear. Using quantitative proteomics, chemoproteomics and biochemical fractionation, we found that native BRD4 and DOT1L exist in separate protein complexes. Genetic disruption or small-molecule inhibition of BRD4 and DOT1L showed marked synergistic activity against MLL leukemia cell lines, primary human leukemia cells and mouse leukemia models. Mechanistically, we found a previously unrecognized functional collaboration between DOT1L and BRD4 that is especially important at highly transcribed genes in proximity to superenhancers. DOT1L, via dimethylated histone H3 K79, facilitates histone H4 acetylation, which in turn regulates the binding of BRD4 to chromatin. These data provide new insights into the regulation of transcription and specify a molecular framework for therapeutic intervention in this disease with poor prognosis

Thermal accommodation in nanoporous silica for vacuum insulation panels

The thermal accommodation coefficient is a measure for the quality of thermal energy exchange between gas molecules and a solid surface. It is an important parameter to describe heat flow in rarefied gases, for example, in aerospace or vacuum technology. As special application, it plays a decisive role for the thermal transport theory in silica filled vacuum insulation panels. So far, no values have been available for the material pairings of silica and various gases. For that reason, this paper presents thermal conductivity measurements under different gas-pressure conditions for precipitated and fumed silica in combination with the following gases: helium, air, argon, carbon dioxide (CO$_{2}$), sulfur dioxide (SO$_{2}$), krypton, and sulfur hexafluoride (SF$_{6}$). Additionally, a calculation method for determining thermal accommodation coefficients from the thermal conductivity curves in combination with the pore size distribution of silica determined by mercury intrusion porosimetry is introduced. The results are compared with existing models