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

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

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

Photonically-activated molecular excitations for thermal energy conversion in porphyrinic compounds

This document is the Accepted Manuscript version of a Published Work that appeared in final form in the Journal of Physical Chemistry C, copyright ©American Chemical Society after peer review and technical editing by the publisher.Heterocyclic, macrocycle organic compounds, structurally characterized with porphyrins, are not only abundant in nature but also environmentally friendly. These porphyrinic compounds have recently been extensively studied for their fascinating structures, physical properties, and high potentials in engineering applications. We report experimental results on the photonically activated thermal energy conversion via irradiations of white light (simulated solar light). The photothermal effects have been well studied for metallic conductors with a large number of charge carriers based on the so-called localized surface plasmon resonance (LSPR). However, the LSPR model may not apply to the porphyrinic materials with a very limited number of charge carriers. In this study, we have found several porphyrinic compounds to exhibit pronounced photothermal effects including chlorophyll, chlorophyllin, hemoglobin, and phthalocyanine, which all share similar structural characteristics. Raman data show characteristic molecular vibrations from these compounds that are responsible for photon-to-thermal energy conversions near the optical absorption frequencies. We attribute the porphyrin molecular vibrations to the photothermal effects observed from these compounds and predict that all porphyrinic materials can be optically activated for pronounced photothermal effects. Also established is a newly defined specific photothermal coefficient (SPC), a unique photothermal property of the thin films investigated in this study

Diphtheria in the Postepidemic Period, Europe, 2000–2009

Efforts must be made to maintain high vaccination coverage

A lock-in-based method to examine the thermal signatures of magnetic nanoparticles in the liquid, solid and aggregated states

We propose a new methodology based on lock-in thermography to study and quantify the heating power of magnetic nanoparticles. Superparamagnetic iron oxide nanoparticles exposed to a modulated alternating magnetic field were used as model materials to demonstrate the potency of the system. Both quantitative and qualitative information on their respective heating power was extracted at high thermal resolutions under increasingly complex conditions, including nanoparticles in the liquid, solid and aggregated states. Compared to conventional techniques, this approach offers a fast, sensitive and non-intrusive alternative to investigate multiple and dilute specimens simultaneously, which is essential for optimizing and accelerating screening procedures and comparative studies

An Outbreak of Rift Valley Fever in Northeastern Kenya, 1997-98

In December 1997, 170 hemorrhagic fever-associated deaths were reported in Carissa District, Kenya. Laboratory testing identified evidence of acute Rift Valley fever virus (RVFV). Of the 171 persons enrolled in a cross-sectional study, 31(18%) were anti-RVFV immunoglobulin (Ig) M positive. An age-adjusted IgM antibody prevalence of 14% was estimated for the district. We estimate approximately 27,500 infections occurred in Garissa District, making this the largest recorded outbreak of RVFV in East Africa. In multivariate analysis, contact with sheep body fluids and sheltering livestock in one’s home were significantly associated with infection. Direct contact with animals, particularly contact with sheep body fluids, was the most important modifiable risk factor for RVFV infection. Public education during epizootics may reduce human illness and deaths associated with future outbreaks

Determinants of fatal outcome in patients admitted to intensive care units with influenza, European Union 2009–2017

Free PMC article: https://www.ncbi.nlm.nih.gov/pmc/articles/pmid/32258201/Background: Morbidity, severity, and mortality associated with annual influenza epidemics are of public health concern. We analyzed surveillance data on hospitalized laboratory-confirmed influenza cases admitted to intensive care units to identify common determinants for fatal outcome and inform and target public health prevention strategies, including risk communication. Methods: We performed a descriptive analysis and used Poisson regression models with robust variance to estimate the association of age, sex, virus (sub)type, and underlying medical condition with fatal outcome using European Union data from 2009 to 2017. Results: Of 13 368 cases included in the basic dataset, 2806 (21%) were fatal. Age ≥40 years and infection with influenza A virus were associated with fatal outcome. Of 5886 cases with known underlying medical conditions and virus A subtype included in a more detailed analysis, 1349 (23%) were fatal. Influenza virus A(H1N1)pdm09 or A(H3N2) infection, age ≥60 years, cancer, human immunodeficiency virus infection and/or other immune deficiency, and heart, kidney, and liver disease were associated with fatal outcome; the risk of death was lower for patients with chronic lung disease and for pregnant women. Conclusions: This study re-emphasises the importance of preventing influenza in the elderly and tailoring strategies to risk groups with underlying medical conditions.info:eu-repo/semantics/publishedVersio

Variations of skin thermal diffusivity on different skin regions

Background and Objective: Skin thermal diffusivity plays a crucial role in various applications, including laser therapy and cryogenic skin cooling.This study investigates the correlation between skin thermal diffusivity and two important skin parameters, melanin content and erythema, in a cohort of 102 participants. Methods: An in-house developed device based on transient temperature measurement was used to assess thermal diffusivity at different body locations. Melanin content and erythema were measured using a colorimeter. Statistical analysis was performed to examine potential correlations. Results: The results showed that the measured thermal diffusivity values were consistent with previous reports, with variations observed among subjects. No significant correlation was found between thermal diffusivity and melanin content or erythema. This suggests that other factors, such as skin hydration or epidermis thickness, may have a more dominant influence on skin thermal properties. Conlcusion: This research provides valuable insights into the complex interplay between skin thermal properties and physiological parameters, with potential implications for cosmetic and clinical dermatology applications