Mathematical modeling of scroll compressors — part II: overall scroll compressor modeling

This paper presents the development of a comprehensive simulation model of a horizontal scroll compressor, which combines a detailed compression process model (Chen Y., Halm N., Groll E., Braun J. Mathematical modelling of scroll compressors — part I: compression process modeling, International Journal of Refrigeration 2002;25(6):731–750) and an overall compressor model. In the overall model, compressor components are analyzed in terms of nine different elements. Steady state energy balance equations are established applying the lumped capacitance method. In combination with the detailed compression process model, these equations were implemented into computer code and solved recursively. In this way, the temperature and pressure of the refrigerant in different compressor chambers, the temperature distributions in the scroll wraps, and the temperatures of the other compressor elements can be obtained. Thereafter, power consumption and efficiency of the compressor can be calculated. Tests were used to verify the overall model on a macroscopic basis. Using the simulation program based on the overall compressor model, a parametric study of the scroll compressor was performed, and the effects of internal leakage and heat transfer losses were investigated and some preliminary results were obtained. These results indicate that the comprehensive scroll compressor model is capable of predicting real compressor behavior and useful to the design and optimization of scroll compressors.     

Fluorine Scan of Inhibitors of the Cysteine Protease Human Cathepsin L: Dipolar and Quadrupolar Effects in the π‐Stacking of Fluorinated Phenyl Rings on Peptide Amide Bonds

The π‐stacking of fluorinated benzene rings on protein backbone amide groups was investigated, using a dual approach comprising enzyme–ligand binding studies complemented by high‐level quantum chemical calculations. In the experimental study, the phenyl substituent of triazine nitrile inhibitors of human cathepsin L (hCatL), which stacks onto the peptide amide bond Gly67?Gly68 at the entrance of the S3 pocket, was systematically fluorinated, and differences in inhibitory potency were measured in a fluorimetric assay. Binding affinity is influenced by lipophilicity (clog P), the dipole and quadrupole moments of the fluorinated rings, but also by additional interactions of the introduced fluorine atoms with the local environment of the pocket. Generally, the higher the degree of fluorination, the better the binding affinities. Gas phase calculations strongly support the contributions of the molecular quadrupole moments of the fluorinated phenyl rings to the π‐stacking interaction with the peptide bond. These findings provide useful guidelines for enhancing π‐stacking on protein amide fragments.     

Studies on the Solidification Path of Single Crystal Superalloys

Single crystal superalloys are widely used in high temperature sections of turbines, where they are able to withstand extended exposure to high temperatures. As these alloys are commonly cast and directionally solidified via the Bridgman process, the knowledge of their solidification path is of great importance. This paper gives an overview of aspects of the solidification path in superalloys, as studied experimentally and from a modeling and simulation point of view. The implications of microsegregation, and sequence of phase formation are discussed. Attention is given to the processes leading to the formation of interdendritic γ′, also often referred to as the γ/γ′ eutectic.     

Full angle spatial compounding for improved replenishment analyses in contrast perfusion imaging: in vitro studies

For contrast enhanced perfusion imaging semi-quantitative methods (such as the bolus-, replenishment- or depletion-method) are commonly used to analyze the dynamic changes in concentration of contrast agent induced by insonification. In order to apply these methods and to decrease artifacts from tissue nonlinearity, perfusion imaging is conducted using decreased transmit power. However, echo signals from deeper structures are often too weak to be successfully analyzed. Furthermore, shadowing artifacts may occur as a result of high concentration of contrast agent in the beam path. Thus, those semi-quantitative methods often fail or yield ambiguous diagnoses. Imaging an object (e.g., the female breast) from multiple viewing angles (spatial compounding) may overcome these issues. In addition, spatial compounding achieves an isotropic resolution and reduces speckle and further common artifacts. In this paper we present results obtained from a combination of spatial compounding with contrast enhanced perfusion imaging. Applying the replenishment method, we extracted perfusion-related parameters and compared the conventional parametric images with the compound parametric images. We found that the compounded parametric images outperform the conventional images due to reduced noise and suppression of artifacts.     

Semi-Godunov schemes for general triangular systems of conservation laws

General m × m triangular systems of conservation laws in one space dimension are considered. These systems arise in applications like multi-phase flows in porous media and are non-strictly hyperbolic. Simple and efficient finite-volume schemes of the Godunov type are devised. These are based on a local decoupling of the system into a series of single conservation laws with discontinuous coefficients and are hence termed semi-Godunov schemes. These schemes are not based on the characteristic structure of the system. Some useful properties of the schemes are derived and several numerical experiments demonstrate their robustness and computational efficiency.     

Ultrafast spin dynamics in colloidal ZnO quantum dots

Time-resolved Faraday rotation measurements in the ultraviolet have been performed to reveal the ultrafast spin dynamics of electrons in colloidal ZnO quantum dots. Oscillating Faraday rotation signals are detected at frequencies corresponding to an effective g factor of g = 1.96. Biexponential oscillation decay is observed that is due to (i) rapid depopulation of the fundamental exciton (tau = 250 ps) and (ii) slow electron spin dephasing ( T 2 = 1.2 ns) within a metastable state formed by hole-trapping at the quantum dot surface.     

Synthesis and Structure–Activity Relationship Study of Organometallic Bioconjugates of the Cyclic Octapeptide Octreotate

The chemically stabilized somatostatin‐derived cyclic octapeptide octreotate has a number of interesting applications in medicinal chemistry. Here, a number of different organometallic derivatives of octreotate were prepared, and their properties were investigated. Specifically, we report the synthesis and characterization of ruthenocene, ferrocene, and cobaltocenium octreotate derivatives and their fluorophore‐labeled conjugates as well as a dicobalt hexacarbonyl alkyne functionalized octreotate. To provide further insights into their characteristics, the log P values and electrochemical properties of the novel metal conjugates were compared. For biological activity, we determined their toxicity in three different cell lines. Cellular uptake and colocalization of selected compounds were studied by fluorescence microscopy with particular focus on efficiency and specificity of their uptake through the somatostatin receptor SSTR to elucidate the value of the metallocene head group for its potential use as a nontoxic and universal peptide label.     

„In Stockholm hatte man offenbar irgendwelche Gegenbewegung” – Ferdinand Sauerbruch (1875–1951) und der Nobelpreis

The archive of the Nobel Assembly for Physiology or Medicine in Solna, Sweden, is a remarkable repository that contains reports and dossiers of the Nobel Prize nominations of senior and junior physicians from around the world. Although this archive has begun to be used more by scholars, it has been insufficiently examined by historians of surgery. No other German surgeon was nominated as often as Ferdinand Sauerbruch for the Nobel Prize for Physiology or Medicine in the first half of the 20th century. This contribution reconstructs why and by whom Sauerbruch was nominated, and discusses the Nobel committee evaluations of his work. Political factors did not play an obvious role in the Nobel committee discussions, in spite of the fact that Adolf Hitler in 1937 had prohibited all German citizens to accept the Nobel Prize. The main reasons why Sauerbruch ultimately was not considered prize-worthy were that Sauerbruch’s achievements were marked by scientific priority disputes, and that his work was not seen as original enough.     

Contact-free exhaust system for vacuum compatible gas bearing guides

Using linear gas bearing guides in a high vacuum environment, the common method to keep the vacuum quality is to exhaust the gas emitted by the bearing pads before leaking into the vacuum chamber. Thereby the exhaust tubes between the guide and the exhaust pumps should interfere with the guide as little as possible while maintaining a flexible connection and a highly effective exhaustion rate. A novel exhaust system that implements these requirements is described within this paper. The major achievement was the realization of two exhaust tubes slidable into one another combined with the known method of non-contact clearance seals, thus enabling an highly efficient and yet disturbance free exhaustion. This setup was developed and characterized at static and dynamic conditions. An analytical model for dimensioning the non-contact seal was worked out and experimentally verified. The number of seal stages and the clearance height were identified as the major impact factors on the leakage rate of the setup. It is concluded that the investigated approach is very suitable for vacuum compatible gas bearing guides since a vacuum level in the order of 10⁻⁴ Pa was maintained during the experiments.