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Christian Blum

Publications and source records attributed to Christian Blum.

5 recordsLinked to original sources
PubMed2006

Single oligomer spectra probe chromophore nanoenvironments of tetrameric fluorescent proteins.

When analyzing the emission of a large number of individual chromophores embedded in a matrix, the spread of the observed parameters is a characteristic property for the particular chromophore-matrix system. To quantitatively assess the influence of the matrix on the single molecule emission parameters, it is imperative to have a system with a well-defined chromophore nanoenvironment and the possibility to alter these surroundings in a precisely controlled way. Such a system is available in the form of the visible fluorescent proteins, where the chromophore nanoenvironment is defined by the specific protein sequence. We analyze the influence of the chromophore embedding within this defined protein environment on the distribution of the emission maximum wavelength for a number of variants of the fluorescent protein DsRed, and show that this parameter is characteristic of the chromophore-protein matrix combination and largely independent of experimental conditions. We observe that the chemical changes in the vicinity of the chromophore of different variants do not account for the different distributions of emission maximum positions but that the flexibility of the chromophore surrounding has a dominant role in determining the distribution. We find, surprisingly, that the more rigid the chromophore surrounding, the broader the distribution of observed maximum positions. We hypothesize that, after a thermally induced reorientation in the chromophore surrounding, a more flexible system can easily return to its energetic minimum position by fast reorientation, while in more rigid systems the return to the energetic minimum occurs in a stepwise fashion, leading to the broader distribution observed.

Luminescent Proteins↗
PubMed2005

Midvastus approach in total knee arthroplasty: a randomized, double-blinded study on early rehabilitation.

The medial parapatellar approach has become the standard technique in total knee arthroplasty (TKA). However, recent studies have reported superior results regarding functional recovery when using the midvastus approach. It was the aim of this study to evaluate the early functional outcome of both surgical techniques. In a prospective, double-blinded, randomized study, 50 patients for TKA were consecutively operated on either by the medial parapatellar or the midvastus approach. Exclusion criteria were defined as previous open knee surgery and leg deformity of more than 10 degrees varus or valgus. TKA was performed in all patients by one surgeon using the same type of implants in both groups. Pain scores (VAS) were documented and follow-up data including quadriceps strength and proprioception were obtained 3 weeks and 6 weeks postoperatively. Both groups were comparable in preoperative demographic data. Postoperatively, patients in the midvastus group demonstrated significantly lower pain in rest (VAS: mean 2.25 vs. 3.03) and under movement (VAS: mean 2.92 vs. 3.13). Further, they showed superior isometric quadriceps strength at 3 weeks (41.4 vs. 27.6 Nm) and 6 weeks (47.6 vs. 35.5 Nm). Moreover, this group showed a superior postoperative proprioception, while the range of motion was similar in both groups. The midvastus approach offers advantages over the standard parapatellar arthrotomy, in the early rehabilitation period. No adverse effects were observed associated with this approach. Therefore, the midvastus approach should be considered as a valuable alternative in TKA.

Aged↗
PubMed2004

Room temperature spectrally resolved single-molecule spectroscopy reveals new spectral forms and photophysical versatility of aequorea green fluorescent protein variants.

It is known from ensemble spectroscopy at cryogenic temperatures that variants of the Aequorea green fluorescent protein (GFP) occur in interconvertible spectroscopically distinct forms which are obscured in ensemble room temperature spectroscopy. By analyzing the fluorescence of the GFP variants EYFP and EGFP by spectrally resolved single-molecule spectroscopy we were able to observe spectroscopically different forms of the proteins and to dynamically monitor transitions between these forms at room temperature. In addition to the predominant EYFP B-form we have observed the blue-shifted I-form thus far only seen at cryogenic temperatures and have followed transitions between these forms. Further we have identified for EYFP and for EGFP three more, so far unknown, forms with red-shifted fluorescence. Transitions between the predominant forms and the red-shifted forms show a dark time which indicates the existence of a nonfluorescent intermediate. The spectral position of the newly-identified red-shifted forms and their formation via a nonfluorescent intermediate hint that these states may account for the possible photoactivation observed in bulk experiments. The comparison of the single-protein spectra of the red-shifted EYFP and EGFP forms with single-molecule fluorescence spectra of DsRed suggest that these new forms possibly originate from an extended chromophoric pi-system analogous to the DsRed chromophore.

Animals↗
PubMed2004

The hyper-cube framework for ant colony optimization.

Ant colony optimization is a metaheuristic approach belonging to the class of model-based search algorithms. In this paper, we propose a new framework for implementing ant colony optimization algorithms called the hyper-cube framework for ant colony optimization. In contrast to the usual way of implementing ant colony optimization algorithms, this framework limits the pheromone values to the interval [0,1]. This is obtained by introducing changes in the pheromone value update rule. These changes can in general be applied to any pheromone value update rule used in ant colony optimization. We discuss the benefits coming with this new framework. The benefits are twofold. On the theoretical side, the new framework allows us to prove that in Ant System, the ancestor of all ant colony optimization algorithms, the average quality of the solutions produced increases in expectation over time when applied to unconstrained problems. On the practical side, the new framework automatically handles the scaling of the objective function values. We experimentally show that this leads on average to a more robust behavior of ant colony optimization algorithms.

Algorithms↗