Exact enumeration of three-dimensional lattice proteins

We present an algorithm for the exhaustive enumeration of all monomer sequences and conformations of short lattice proteins as described by the hydrophobic-polar (HP) model. The algorithm is used for an exact identification of all designing sequences of HP proteins consisting of up to 19 monomers whose conformations are represented by interacting self-avoiding walks on the simple cubic lattice. Employing a parallelized implementation on a Linux cluster, we generate the complete set of contact maps of such walks.     

Untersuchung von Schmelz‐ und Rekristallisationsprozessen sowie Riss‐, Oxid‐ und Porenbildung beim Schweißen

Investigation of melting and re‐crystallization processes and of crack, oxide and pore formation during welding In the paper some known investigation methods of the primary re‐crystallization and of the structure of the crystallization front are discussed. All these methods have disadvantages, in some cases they cause a limited validity or are expensive. The presented new method is based on the micrographic recording of the melting and solidifying metal surfaces. The method overcomes the above‐mentioned disadvantages. It is able to investigate in the welding seams not only the primary re‐crystallization processes but also the secondary ones including the formation of cracks and pores and the appearance of non‐metallic inclusions like oxides. The facilities of the method are demonstrated on some examples of use.     

B1 field-insensitive transformers for RF-safe transmission lines

Objective: Integration of transformers into transmission lines suppresses radiofrequency (RF)-induced heating. New figure-of-eight-shaped transformer coils are compared to conventional loop transformer coils to assess their signal transmission properties and safety profile. Materials and methods: The transmission properties of figure-of-eight-shaped transformers were measured and compared to transformers with loop coils. Experiments to quantify the effect of decoupling from the B₁ field of the MR system were conducted. Temperature measurements were performed to demonstrate the effective reduction of RF-induced heating. The transformers were investigated during active tracking experiments. Results: Coupling to the B₁ field was reduced by 18 dB over conventional loop-shaped transformer coils. MR images showed a significantly reduced artifact for the figure-of-eight- shaped coils generated by local flip-angle amplification. Comparable transmission properties were seen for both transformer types. Temperature measurements showed a maximal temperature increase of 30K/3.5 K for an unsegmented/ segmented cable. With a segmented transmission line a robotic assistance system could be successfully localized using active tracking. Conclusion: The figure-of-eight-shaped transformer design reduces both RF field coupling with the MR system and artifact sizes. Anatomical structure close to the figure-of-eight-shaped transformer may be less obscured as with loop-shaped transformers if these transformers are integrated into e.g. intravascular catheters.     

Velocity navigator for motion compensated thermometry

Object  

Proton resonance frequency shift thermometry is sensitive to breathing motion that leads to incorrect phase differences. In this work, a novel velocity-sensitive navigator technique for triggering MR thermometry image acquisition is presented.     

Solving nonlinear dynamic models by iterative dynamic programming

The paper presents a discrete-time dynamic programming algorithm that is suitable to track nonlinearities in intertemporal optimization problems. In contrast to using linearization methods for solving intertemporal models, the proposed algorithm operates globally by iteratively computing the value function and the controls in feedback form on a grid. A conjecture of how the trajectories might behave is analytically obtained by letting the discount rate approach infinity. The dynamic found serves as a useful device for computing the trajectories for finite discount rates employing the algorithm. Commencing with a large step and grid size, and then pursuing time step and grid refinements allows for the replication of the nonlinear dynamics for various finite discount rates. As the time step and grid size shrink, the discretization errors vanish. The algorithm is applied to three economic examples. Two examples are of deterministic type; the third is stochastic. In the deterministic cases limit cycles are detected.The present paper draws on joint work with Malte Sieveking whom I want to thank for many discussions.     

Vorwort anlässlich des 70. Geburtstages von Em. o. Univ.-Prof. Dipl.-Ing. Dr. mont. Horst Wagner

Ohne Zusammenfassung     

Two eyes see more than one: double echo stereoscopic MRA for rapid 3D visualization of vascular structures

Object

A three-dimensional (3D) visualization of the target region during intravascular interventions in real-time is challenging since the acquisition of a time-consuming 3D dataset is required. In this work, a novel stereoscopic double echo sequence for achieving 3D depth perception by sampling only two oblique projection images is presented.

Materials and methods

A double echo (DE) FLASH pulse sequence was developed to acquire continuously stereoscopic image pairs of the vascular target anatomy. Stereo image data were displayed on a stereoscopic 3D LCD monitor in real time after image reconstruction. Phantom experiments followed by a depth perception test were performed to assess the usability of the stereo image pairs for 3D visualization. In an animal experiment the sequence was tested in vivo and was compared with a slower interleaved (IL) sequence variant.

Results

In the phantom experiments an SNR difference of 6?% between left and right image was found which did not influence the depth perception. The DE acquisition was superior to the IL sequence (SNR_DE?=?10.3, 2.3 images/s over SNR_IL?=?7.1, 1.7 images/s), and during contrast enhancement the abdominal arterial vasculature was clearly perceived as a 3D structure.

Conclusion

A novel stereoscopic DE pulse sequence can be utilized for the fast 3D stereoscopic visualization of vascular structures in real-time.     

Effects of Postidentification Feedback on Eyewitness Identification and Nonidentification Confidence.

Two experiments investigated new dimensions of the effect of confirming feedback on eyewitness identification confidence using target-absent and target-present lineups and (previously unused) unbiased witness instructions (i.e., "offender not present" option highlighted). In Experiment 1, participants viewed a crime video and were later asked to try to identify the thief from an 8-person target-absent photo array. Feedback inflated witness confidence for both mistaken identifications and correct lineup rejections. With target-present lineups in Experiment 2, feedback inflated confidence for correct and mistaken identifications and lineup rejections. Although feedback had no influence on the confidence-accuracy correlation, it produced clear overconfidence. Confidence inflation varied with the confidence measure reference point (i.e., retrospective vs. current confidence) and identification response latency. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Liver and spleen enhancement after intravenous injection of carboxydextran magnetite: effect of dose, delay of imaging, and field strength in an ex vivo model

It has been predicted that liver and spleen enhancement after administration of superparamagnetic contrast agents may be different, depending on the strength of the main magnetic field. With the use of an ex vivo model, we investigated at 0.3, 0.5, and 1.5 T the effects on liver and spleen signal intensity of 5, 15, and 45 mumol/kg body weight of dextran magnetite (SHU 555A) in 54 rats. Nine rats served as controls. At different time delays since injection, the animals were killed, and after perfusion with saline, the liver, brain, and spleen were fixed in formalin. The specimens were embedded in an agar gel matrix and imaged with inversion recovery T1-weighted, proton density spin echo, and T2*-weighted gradient recalled echo (GRE) sequences. At each magnetic field strength, peak liver and spleen signal loss increased with increasing dose of the contrast medium. Signal loss was significantly more conspicuous after a dose of 15 than 5 mumol/kg body weight, but not after a dose of 45 compared with 15 mumol/kg. No signal change was observed in the brain. GRE images showed higher enhancement than proton density-weighted spin echo and inversion recovery images but were noisier. The enhancement showed a plateau between 30 min and 24 hours. Only the signal decrease of the liver after a low dose of contrast medium on GRE images was significantly higher (p < 0.01) at 1.5 than at 0.5 and 0.3 T. Other differences in respect to the field strength were less significant (p < 0.05) or nonsignificant. Differences in the spleen enhancement were nonsignificant. SHU 555A at a dose of 15 mumol/kg is an efficient intracellular contrast agent for liver and spleen at low, mid, and high field strength. Proton density spin echo images are probably the sequence of choice to exploit SHU 555A contrast effects and a wide time window for imaging after its intravenous injection does exist.