Time-Resolved Chiral Vibrational Spectroscopy

Advances in infrared laser technology and detection sensitivity have made time-resolved chiral vibrational spectroscopy experimentally feasible. Here we describe our recent efforts in detecting, for the first time, transient vibrational circular dichroism (VCD) signals with picosecond time resolution. The absorption changes of the cobalt (?)-sparteine complex Co(sp)Cl2 after visible excitation of a d-d excited state was probed in the CH-stretch region by alternating left- and right-handed circular polarized mid IR laser pulses. VCD spectra can be sensitive reporters of peptide and protein secondary structure or the absolute configuration of chiral organic compounds in solution. Recent developments are presented, which may in the future allow us to access this information in the course of fast chemical reactions

Vibrational chiral spectroscopy with femtosecond laser pulses

Vibrational circular dichroism and optical rotary dispersion spectra can provide detailed information about molecular structure and the conformation of biomolecules. Their artefact-free recording with high time resolution is a current experimental challenge. We outline recent progress

Data on face-to-face contacts in an office building suggests a low-cost vaccination strategy based on community linkers

Empirical data on contacts between individuals in social contexts play an important role in providing information for models describing human behavior and how epidemics spread in populations. Here, we analyze data on face-to-face contacts collected in an office building. The statistical properties of contacts are similar to other social situations, but important differences are observed in the contact network structure. In particular, the contact network is strongly shaped by the organization of the offices in departments, which has consequences in the design of accurate agent-based models of epidemic spread. We consider the contact network as a potential substrate for infectious disease spread and show that its sparsity tends to prevent outbreaks of rapidly spreading epidemics. Moreover, we define three typical behaviors according to the fraction $f$ of links each individual shares outside its own department: residents, wanderers and linkers. Linkers ($f\sim 50\%$) act as bridges in the network and have large betweenness centralities. Thus, a vaccination strategy targeting linkers efficiently prevents large outbreaks. As such a behavior may be spotted a priori in the offices' organization or from surveys, without the full knowledge of the time-resolved contact network, this result may help the design of efficient, low-cost vaccination or social-distancing strategies

Development of Ultrafast Time-Resolved Chiral Infrared Spectroscopy

Among the different techniques available to study the molecular structure, chiral spectroscopy is a fast, reliable method, where molecules can be investigated in the liquid phase. Chiral spectroscopy is based on optical activity. A molecule is said to be optically active if it interacts differently with left- and right-circular polarised light. The difference of absorption between the two circular states is referred to as circular dichroism (CD), whereas the difference of refraction is known as optical rotatory dispersion (ORD). Because the optical activity finds its origin in asymmetry, it is directly dependent of the molecular geometry. Probing optically active vibrational transitions allows to retrieve even more structural information as infrared spectra are usually more resolved than electronics ones. Extension of this technique to the recording of time-resolved chiral vibrational signals may enable the dynamics of conformation changes in biomolecules such as peptides and proteins to be followed with unprecedented details. Toward this goal, we report the first pulsed laser set-up capable of recording both static infrared CD and ORD spectra and photo-induced changes in vibrational circular dichroism (VCD) with picosecond time resolution. A femtosecond laser system is synchronized to a photo elastic modulator to produce alternating left- and right-circular polarised mid-IR pulses. Transient changes in vibrational circular dichroism of the CH-stretch vibrations of the cobalt-sparteine complex Co(sp)Cl2 are presented in a first proof-of-principle experiment. Both static and transient vibrational chiral spectroscopy suffer two important drawbacks: Chiral signals are usually small and sensitive to polarisation-based artefacts, which mainly originate from the interaction between an imperfect probe beam polarisation and a non isotropic sample. We report on a new scheme for synchronizing the laser system and the photo elastic modulator which generates almost perfect probe polarisation states. The technique reduces possible polarisation-based artefacts and allows multichannel detection of the chiral signals normally obscured by polarisation sensitive optics of the monochromator. To increase signal size, a self-heterodyning configuration is implemented where a part of the probe pulse acts as a phase-locked local oscillator heterodyning the chiral signal. The technical improvements presented in this thesis should open the door to measurements of transient vibrational chiral spectra of biomolecules

Pulsed-Active Microwave Thermography

Active microwave thermography (AMT) is a thermographic nondestructive testing and evaluation technique that utilizes an electromagnetic-based excitation with a subsequent infrared measurement of the surface thermal profile of the material or structure of interest. AMT has been successfully applied to several aerospace and civil infrastructure applications. This work seeks to expand the performance of AMT by incorporating a signal processing technique common to traditional (flash-lamp) thermography, referred to as pulsed thermography (PT). PT operates on the premise of a pulsed excitation, as opposed to a constant or step excitation (ST) over a given time-period that is typical to traditional active thermography. This work applies the pulsed approach to AMT, herein referred to as P-AMT, and compares the thermal contrast (TC) and signal-to-noise ratio (SNR) of traditional and pulsed AMT inspections as applied to a moisture ingress detection need. The results suggest that the optimal heating time (indicated through SNR) for P-AMT is less than that of traditional AMT with a reduced overall (absolute) temperature. This is important as it relates to any inspection with concerns for thermal damage as well an overall reduction in required inspection time

«Let’s Biodesign!» : vom Operationssaal zum disruptiven Medizinprodukt

Der Biodesign-Ansatz ist eine innovative Ausbildungsmethodik für die Entwicklung radikaler Produktinnovationen in Healthcare-Unternehmen. Sie zielt konsequent auf die Praxis und vermittelt Studierenden unternehmerische Kompetenzen

Augmented and virtual reality in dermatology : where do we stand and what comes next?

As the skin is an accessible organ and many dermatological diagnostics still rely on the visual examination and palpation of the lesions, dermatology could be dramatically impacted by augmented and virtual reality technologies. If the emergence of such tools raised enormous interest in the dermatological community, we must admit that augmented and virtual reality have not experienced the same breakthrough in dermatology as they have in surgery. In this article, we investigate the status of such technologies in dermatology and review their current use in education, diagnostics, and dermatologic surgery; additionally, we try to predict how it might evolve in the near future

Modeling stratum corneum swelling for the optimization of electrode-based skin hydration sensors

We present a novel computational model of the human skin designed to investigate dielectric spectroscopy electrodes for stratum corneum hydration monitoring. The multilayer skin model allows for the swelling of the stratum corneum, as well as the variations of the dielectric properties under several hydration levels. According to the results, the stratum corneum thickness variations should not be neglected. For high hydration levels, swelling reduces the skin capacitance in comparison to a fixed stratum corneum thickness model. In addition, different fringing-field electrodes are evaluated in terms of sensitivity to the stratum corneum hydration level. As expected, both conductance and capacitance types of electrodes are influenced by the electrode geometry and dimension. However, the sensitivity of the conductance electrodes is more affected by dimension changes than the capacitance electrode leading to potential design optimization

Using lock-in thermography to investigate stimuli-responsive nanoparticles in complex environments

​© 2021 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.The use of nanoparticles (NP) has been dramatically rising in the recent years and NPs can nowadays be found in various products ranging from food to composite materials or cosmetics. Currently, the most frequently employed NP types are titania (TiO 2 ), as a typical color additive, silica (SiO 2 ), as anticoagulation agent, and silver (Ag) NPs, which are added to textiles, due to their antimicrobial properties. Because of their outstanding physical and mechanical properties, carbon-containing nanomaterials, such as graphene and carbon nanotubes, have also experienced a surge in industrially relevant applications. About 30% of the NPs are suspended in liquids, ranging from water to creams and lotions to car lubricants, followed by applications containing surface-bound (e.g., in textiles) NPs and finally nanocomposites (e.g., polymer-CNT composites). Together with biological and physiological fluids, these matrices render the detection and quantification of NPs fairly complex. The broad range of chemical and biological compositions of these environments, including pH and ionic strength, are often detrimental to the colloidal stability of NPs, potentially causing aggregation or even dissolution effects and therefore render NP analysis fairly challenging

Pulsed-active microwave thermography

Active microwave thermography (AMT) is a thermographic nondestructive testing and evaluation techniquethat utilizes an electromagnetic-based excitation with a subsequent infrared measurement of the surface thermal profile of the material or structure of interest. AMT has been successfully applied to several aerospace and civil infrastructure applications. This work seeks to expand the performance of AMT by incorporating a signal processing technique common to traditional (flash-lamp) thermography, referred to as pulsed thermography (PT). PT operates on the premise of a pulsed excitation, as opposed to a constant or step excitation (ST) over a given time-period that is typical to traditional active thermography. This work applies the pulsed approach to AMT, herein referred to as P-AMT, and compares the thermal contrast (TC) and signal-to-noise ratio (SNR) of traditional and pulsed AMT inspections as applied to a moisture ingress detection need. The results suggest that the optimal heating time (indicated through SNR) for P-AMT is less than that of traditional AMT with a reduced overall (absolute) temperature. This is important as it relates to any inspection with concerns for thermal damage as well an overall reduction in required inspection time