Publications by authors named "Cornelius Weiss"

10 Publications

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Reversible Photoinduced Conversion of Unprecedented Norbornadiene-Based Photoswitches with Redox-Active Naphthalene Diimide Functionalities.

Chemistry 2022 Jul 1. Epub 2022 Jul 1.

Friedrich-Alexander-Universitat Erlangen-Nurnberg, Department of Chemistry and Pharmacy & Interdisciplinary Center for Molecular Materials (ICMM), Nikolaus-Fiebiger-Straße 10, 91058, Erlangen, GERMANY.

An unprecedented compound class of functional organic hybrids consisting of a photoswitchable norbornadiene building block and a redoxactive chromophore, namely naphthalene diimide, were designed and synthesized. Within these structures the capability of rylene chromophores to function as a redox active catalyst upon their photoexcitation was utilized to initiate the oxidative back-conversion of the in-situ formed quadricyclane unit to its norbornadiene analogue. In this way successive photoexcitation at two differenr wavelengths enabled a controlled photoswitching between the two isomerical states of the hybrids. Beyond this prove of concept, the dependency of the reaction rate to the intramolecular distance of the two functional molecular building blocks as well as the concentration of the photoexcited sample was monitored. The experimental findings and interpretations were furthermore supported by quantum chemical investigations.
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http://dx.doi.org/10.1002/chem.202201446DOI Listing
July 2022

Surface Chemistry of the Molecular Solar Thermal Energy Storage System 2,3-Dicyano-Norbornadiene/Quadricyclane on Ni(111).

Chemphyschem 2022 May 25:e202200199. Epub 2022 May 25.

Lehrstuhl für Physikalische Chemie II, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstr. 3, 91058, Erlangen, Germany.

Molecular solar thermal (MOST) systems are a promising approach for the introduction of sustainable energy storage solutions. We investigated the feasibility of the dicyano-substituted norbornadiene/quadricyclane molecule pair on Ni(111) for catalytic model studies. This derivatization is known to lead to a desired bathochromic shift of the absorption maximum of the parent compound. In our experiments further favorable properties were found: At low temperatures, both molecules adsorb intact without any dissociation. In situ temperature-programmed HR-XPS experiments reveal the conversion of (CN) -quadricyclane to (CN) -norbornadiene under energy release between 175 and 260 K. The absence of other surface species due to side reactions indicates full isomerization. Further heating leads to the decomposition of the molecular framework into smaller carbonaceous fragments above 290 K and finally to amorphous structures, carbide and nitride above 400 K. DFT calculations gave insights into the adsorption geometries. (CN) -norbornadiene is expected to interact stronger with the surface, with flat configurations being favorable. (CN) -quadricyclane exhibits smaller adsorption energies with negligible differences for flat and side-on geometries. Simulated XP spectra are in good agreement with experimental findings further supporting the specific spectroscopic fingerprints for both valence isomers.
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http://dx.doi.org/10.1002/cphc.202200199DOI Listing
May 2022

[Evaluation of a Manualized Group Program for Siblings of Children with Diseases or Disabilities].

Prax Kinderpsychol Kinderpsychiatr 2020 May;69(3):203-217

Klinik und Poliklinik für Psychiatrie und Psychotherapie Medizinische Fakultät am Universitätsklinikum Carl Gustav Carus Technische Universität Dresden Deutschland Klinik und Poliklinik für Psychiatrie und Psychotherapie.

This study evaluates a manualized group program for siblings of children with life-threatening/life-limiting diseases or disabilities. The program aims to activate resources and to reduce emotional and behavioral problems, using cognitive-behavioral methods and experience-based interventions. In this multi-center study, 13 GeschwisterTREFFs were conducted by 11 study sites in Germany. Prior to and after the intervention 97 siblings aged 7 to 14 years and their parents were examined with standardized questionnaires. At baseline, the siblings of children with diseases or disabilities showed significant more emotional and behavioral problems compared to the respective norm samples. After the intervention, the siblings reported declined problem behavior scores that were mostly in the range of the particular norm values. Furthermore, the children indicated a significant improvement of self-esteem, self-efficacy, school competences and relations to their siblings. However, parents reported more problem behavior and less health-related quality of life of their children at both assessments. The present multi-center study showed the interventions' feasibility in different settings and confirmed expected improvements of target variables during the intervention period. Randomized-controlled trails are warranted to verify our results.
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http://dx.doi.org/10.13109/prkk.2020.69.3.203DOI Listing
May 2020

[Work and Training Conditions of Young German Physicians in Internal Medicine - Results of a Second Nationwide Survey by Young Internists from the German Society of Internal Medicine and the German Professional Association of Internists.]

Dtsch Med Wochenschr 2018 Apr 3;143(7):e42-e50. Epub 2018 Apr 3.

Sektionen Infektiologie und Tropenmedizin, I. Medizinische Klinik und Poliklinik, Universitätsklinikum Hamburg-Eppendorf.

Background:  Medical specialty training is the basis for career development of young internists and it is vital for the delivery of high-quality medical care. In 2014 the young internists of two professional bodies in Germany conducted a survey among their young members and described major factors influencing training and working conditions. We present the results of a follow-up survey to describe changes of these factors over time. An additional focus is set on the difficulties of balancing medical career and family.

Methods:  In the end of 2016 we conducted an online-based survey of all members in training of the German Society of Internal Medicine (DGIM) and the Professional Association of German Internists (BDI). The questionnaire used in the 2014 survey was modified and items investigating the balance between career and family were added.

Results:  A total of 1587 questionnaires were returned and analysed. Mayor findings did not change over time. Psychosocial strain remains very high among medical trainees in internal medicine. A structured training curriculum and meaningful feedback are associated with lower psychosocial strain and higher work satisfaction. Internists - and here especially women - with children experience the daily balance of medical career and family as extremely challenging.

Conclusion:  These results demonstrate that there is still a serious need for adjusting training and working conditions of young internists in Germany. Especially the role and increasing importance of female physicians has to be recognized by enabling a successful integration of medical career and family.
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http://dx.doi.org/10.1055/a-0543-4544DOI Listing
April 2018

Novel λ(3)-iodane-based functionalization of synthetic carbon allotropes (SCAs)-common concepts and quantification of the degree of addition.

Chemistry 2014 Dec 24;20(50):16644-51. Epub 2014 Oct 24.

Department of Chemistry and Pharmacy and Institute of Advanced Materials and Processes (ZMP), Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Henkestrasse 42, 91054 Erlangen (Germany), Fax: (+49) 9131-85-26864.

The covalent functionalization of carbon allotropes represents a main topic in the growing field of nano materials. However, the development of functional architectures is impeded by the intrinsic polydispersibility of the respective starting material, the unequivocal characterization of the introduced functional moieties, and the exact determination of the degree of functionalization. Based on a novel carbon allotrope functionalization reaction, utilizing λ(3) -iodanes as radical precursor systems, we were able to demonstrate the feasibility to separate and to quantify thermally detached functional groups, formerly covalently linked to carbon nanotubes and graphene through thermogravimetric GC-MS.
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http://dx.doi.org/10.1002/chem.201404662DOI Listing
December 2014

Vibration transfer in the ball-stem contact interface of artificial hips.

Med Eng Phys 2013 Oct 23;35(10):1513-7. Epub 2013 May 23.

TUHH - Hamburg University of Technology, Institute of Biomechanics, Denickestrasse 15, 21073 Hamburg, Germany.

Audible squeaking has put the reputation of ceramic bearings for total hip replacements into question. Inter-articular friction induces vibrations in the ceramic head which are transferred through the head-taper interface to the femoral stem. If excited to sufficient amplitudes, squeaking can be emitted by the stem. Hence, the damping and amplification properties of this interface have a crucial influence on stem vibrations. The aim of this study was to determine the vibration transfer behavior between the head and the taper of a femoral stem and its dependence on the assembly force, in order to assess its influence on the development of audible squeaking. A ceramic head was assembled on a titanium femoral stem taper with high and low forces. Frequency response functions characterizing the head-stem interface were determined experimentally. The interface demonstrated negligible influence on vibration transfer in the squeaking frequency range (1-5 kHz). However its damping effect in lower and higher frequency ranges was significant and some areas of amplification were also found. Although squeaking vibration was not influenced by the particular interface studied, the method established can be utilized to trace taper designs with dynamic properties that decrease the susceptibility to squeaking.
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http://dx.doi.org/10.1016/j.medengphy.2013.04.001DOI Listing
October 2013

Friction-induced whirl vibration: root cause of squeaking in total hip arthroplasty.

J Biomech 2012 Jan 17;45(2):297-303. Epub 2011 Nov 17.

Institute of Mechanics and Ocean Engineering, Hamburg University of Technology, Hamburg, Germany.

Squeaking is reported for ceramic-on-ceramic hip arthroplasty, and risk factors leading to this phenomenon have been investigated empirically in the past, this way giving hints to when this phenomenon occurs. The aim of this study is to present an experimentally validated explanation for the dynamical mechanism underlying the squeak, i.e. a description of what happens when noise is generated. First the kinematics of the ceramic bearing couple in relative motion are reconsidered. The relative motion at the contact zone can be understood as superposition of relative rotation and translation. The relative weight of both components depends substantially on the instantaneous load vector, which primarily determines the position of the contact area, and the instantaneous relative rotation vector. For the investigated gait scenarios, both load vector and rotation axis vary strongly during the gait cycle. Second, experimental vibration analysis during squeak is performed. A pronounced micrometer scale elliptical motion of the ball inside the liner is found. It is shown that the rotational component of the relative kinematics during gait indeed leads to friction induced vibrations. We show that a generic whirl type friction induced flutter instability, also known from similar (non bio-) mechanical systems, is the root cause of the emitted squeaking noise. Based on the identified mechanism, the role of THA system parameters (materials, design), patient risk factors, as well as the role of the gait cycle, will have to be reconsidered and linked in the future to develop effective measures against squeaking.
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http://dx.doi.org/10.1016/j.jbiomech.2011.10.025DOI Listing
January 2012

The influence of component design, bearing clearance and axial load on the squeaking characteristics of ceramic hip articulations.

J Biomech 2011 Mar 4;44(5):837-41. Epub 2011 Feb 4.

TUHH, Hamburg University of Technology, Institute of Biomechanics, Denickestrasse 15, 21073 Hamburg, Germany.

Squeaking of hip replacements with ceramic-on-ceramic bearings has put the use of this material into question despite its superior wear behavior. Squeaking has been related to implant design. The purpose of this study was to determine the influence of particular acetabular cup and femoral stem designs on the incidence of squeaking and its characteristics. The dynamic behavior of the stem, head and stem assembled with head was investigated by determining their eigenfrequencies using experimental and numerical modal analysis. Four different stem and three different cup designs were investigated. Operational system vibrations resulting in audible squeaking were reproduced in a hip simulator and related to the respective component eigenfrequencies. The applied joint load and bearing clearance were varied in the clinically relevant range. Stems with lower eigenfrequencies were related to lower squeaking frequencies and increased acoustic pressure (loudness), and therefore to a higher susceptibility to squeaking. Higher load increased the squeaking frequency, while the acoustic pressure remained unchanged. No influence of the clearance or the cup design was found. Stem design was found to have an important influence on squeaking characteristics and its incidence, confirming and explaining similar clinical observations. Cup design itself was found to have no major influence on the dynamic behavior of the system but plays an important indirect role in influencing the magnitude of friction: Squeaking only occurs if the friction in the joint articulation is sufficient to excite vibrations to audible magnitudes. If friction is low, no squeaking occurs with any of the designs investigated.
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http://dx.doi.org/10.1016/j.jbiomech.2010.12.012DOI Listing
March 2011

Deformation characteristics and eigenfrequencies of press-fit acetabular cups.

Clin Biomech (Bristol, Avon) 2011 Jan;26(1):46-51

TUHH, Hamburg University of Technology, Biomechanics Section, Denickestrasse 15, 21073 Hamburg, Germany.

Background: elastic deformation of press-fitted acetabular cups during implantation provides primary stability. Excessive deformation can lead to chipping or improper seating of ceramic inlays and is dictated by cup stiffness, which also affects its vibrational characteristics. Purpose was to investigate the influence of cup design on deformation during press-fitting and on vibration properties.

Methods: deformation of ten acetabular cups (with and without ceramic inlay) was tested for radial loads clinically occurring during press-fitting (0-2000N). Eigenfrequencies were measured using experimental modal analysis and related to mass and stiffness.

Findings: the first eigenfrequency of the shells varied greatly (4-9kHz); insertion of inlays caused an increase (16-33 kHz). The range of shell stiffness was high (2.7-48.4kN/mm), increasing due to inlay insertion (124.7-376.2kN/mm). Stiffness and mass were sufficient predictors for eigenfrequencies (p<0.001,R²=0.94).

Interpretation: the cups investigated represent a large stiffness range. Lower cup stiffness can increase primary stability but jeopardize inlay seating, and a suitable balance must be achieved by the designer. Eigenfrequencies also decrease with decreasing stiffness but were all found to lie considerably above clinically observed squeaking frequencies, indicating that these cup designs play no predominant role in the squeaking phenomenon. The observed relation between eigenfrequencies and the quotient of stiffness and mass might be used in the development of new thin walled cup designs so that their contribution to system vibrations is prevented. Presently, surgeons should be aware of the deformation characteristics of cups in order to select a suitable press-fit magnitude.
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http://dx.doi.org/10.1016/j.clinbiomech.2010.08.015DOI Listing
January 2011

Squeak in hip endoprosthesis systems: An experimental study and a numerical technique to analyze design variants.

Med Eng Phys 2010 Jul 16;32(6):604-9. Epub 2010 Mar 16.

Institute of Mechanics and Ocean Engineering, Hamburg University of Technology, Eissendorfer Str. 42, 21073 Hamburg, Germany.

Hip endoprosthesis systems are analyzed with respect to their susceptibility to self-excited vibrations and sound or noise generation. Experimental studies reveal that certain configurations can become unstable causing exponentially growing regular high-frequency oscillations that asymptotically approach a limit-cycle with considerable amplitude. Ultimately the vibrations do also lead to the emission of sound that is perceived as squeaking or squeal. To identify dominant influence factors and critical parameters, stability analyses were conducted on the basis of finite-element modeling. The resulting numerical approach, based on the determination of complex eigenvalues and eigenvectors, is shown to be an effective tool to analyze and show differences between endoprosthesis designs with respect to their susceptibility to develop squeaking phenomenons.
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http://dx.doi.org/10.1016/j.medengphy.2010.02.006DOI Listing
July 2010
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