Time-domain THz spectroscopy

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Time-domain THz spectroscopy of the characteristics of hydroxyapatite provides a signature of heating in bone tissue

Time-domain THz spectroscopy of the characteristics of hydroxyapatite provides a signature of heating in bone tissue

Abstract Because of the importance of bone in the biomedical, forensic and archaeological contexts, new investigation techniques are constantly required to better characterize bone ultrastruc- ture. In the present paper, we provide an extended investigation of the vibrational features of bone tissue in the 0.1-3 THz frequency range by time-domain THz spectroscopy. Their assignment is supported by a combination of X-ray diffraction and DFT-normal modes calculations. We investigate the effect of heating on bone tissue and synthetic calcium- phosphates compounds with close structure and composition to bone mineral, including stoichiometric and non-stoichiometric hydroxyapatite (HA), tricalcium phosphate, calcium pyrophosphate and tetracalcium phosphate. We thus demonstrate that the narrow vibra- tional mode at 2.1 THz in bone samples exposed to thermal treatment above 750 ˚C arises from a lattice mode of stoichiometric HA. This feature is also observed in the other synthetic compounds, although weaker or broader, but is completely smeared out in the non-stoichio- metric HA, close to natural bone mineral composition, or in synthetic poorly crystalline HA powder. The THz spectral range therefore provides a clear signature of the crystalline state of the investigated bone tissue and could, therefore be used to monitor or identify structural transitions occurring in bone upon heating.
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Time-domain THz spectroscopy of the characteristics of hydroxyapatite provides a signature of heating in bone tissue

Time-domain THz spectroscopy of the characteristics of hydroxyapatite provides a signature of heating in bone tissue

Abstract Because of the importance of bone in the biomedical, forensic and archaeological contexts, new investigation techniques are constantly required to better characterize bone ultrastruc- ture. In the present paper, we provide an extended investigation of the vibrational features of bone tissue in the 0.1-3 THz frequency range by time-domain THz spectroscopy. Their assignment is supported by a combination of X-ray diffraction and DFT-normal modes calculations. We investigate the effect of heating on bone tissue and synthetic calcium- phosphates compounds with close structure and composition to bone mineral, including stoichiometric and non-stoichiometric hydroxyapatite (HA), tricalcium phosphate, calcium pyrophosphate and tetracalcium phosphate. We thus demonstrate that the narrow vibra- tional mode at 2.1 THz in bone samples exposed to thermal treatment above 750 ˚C arises from a lattice mode of stoichiometric HA. This feature is also observed in the other synthetic compounds, although weaker or broader, but is completely smeared out in the non-stoichio- metric HA, close to natural bone mineral composition, or in synthetic poorly crystalline HA powder. The THz spectral range therefore provides a clear signature of the crystalline state of the investigated bone tissue and could, therefore be used to monitor or identify structural transitions occurring in bone upon heating.
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Terahertz Time-Domain Spectroscopy of Thermoresponsive Polymers in Aqueous Solution

Terahertz Time-Domain Spectroscopy of Thermoresponsive Polymers in Aqueous Solution

Polymer characterization SI1; parameter extraction from THz-TDS, with signal processing of time-domain pulses and frequency domain amplitude and phase to extract the refractive index and[r]

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Towards broadband THz spectroscopy and analysis of sub-wavelength-size biological samples

Towards broadband THz spectroscopy and analysis of sub-wavelength-size biological samples

Abstract—We report on our recent progress toward bio- photonic applications of terahertz time-domain spectroscopy. First, we developed a technique for the confinement of broadband terahertz pulses to a sub-wavelength-volume, and will present its applications to study biological samples. Second, we will discuss the analysis of terahertz time-trace data from bio samples using our Fit@TDS software based on the time-domain optimization algorithm that enables direct fitting of sample parameters. The combination of those (the experimental and the modelling) techniques is a robust tool for terahertz bio-photonics.
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Device for broadband THz spectroscopy of 1-nL-volume samples

Device for broadband THz spectroscopy of 1-nL-volume samples

I. I NTRODUCTION NCREASING light-matter interactions by confining light to a subwavelength volume is crucial for nonlinear-optical effects and is especially important for the detection of small objects in the Terahertz (THz) range, such as molecules or biosamples – its volume is usually smaller than the cube of the THz wavelength, thus the light-matter interactions are extremely reduced. Moreover, confining light to an object with low refractive index (such as biosamples and their environment) is still a challenge for several spectral ranges. In the THz range this has been achieved using near-field microscopy [1] and wave guiding structures that confines the light in one direction using a parallel plate metallic waveguide (PPMW) [2] ideal for time-domain spectroscopy (TDS) experiments [3]. However, a specific coupling scheme is needed to properly excite the mode of interest. Our method combines the curved tapered antenna approach (similarly to Ref. [4]) to properly inject the beam into the waveguide together with the approach of Ref. [5], using a fully planar
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Development of a prototype Time Domain Spectroscopy
system for in vivo terahertz thermal imaging.

Development of a prototype Time Domain Spectroscopy system for in vivo terahertz thermal imaging.

0.4. ÉVALUATION DES PERFORMANCES DU SYSTÈME xxxiii Enfin, puisque chaque pixel contient toutes les informations spectrales portées par le TH Z , nous avons également évalué la transformée de Fourier ˆ F de chaque trace (pixel) et comparé ses valeurs à certaines fréquences sélectionnées. Les grandeurs de la transformation à ν = 0.5 THz, 0.75 THz et 1 THz sont affichées dans les panneaux i, j et k, tandis que le panel l rapporte l’intégrale de la magnitude de 0.4 THz à 0.7 THz : toutes les images identifient clairement la zone brûlée avec un bon contraste, bien que se rapprochant de 1 THz l’image devient plus faible et plus difficile à distinguer par rapport à la tache lumineuse déjà observée dans les panneaux de e à h. Le spectre intégré du panel l n’est pas très différent des valeurs à 0.5 THz, ce qui indique que les composants spectraux à des fréquences plus élevées ne sont pas suffisamment intenses pour influencer le résultat d’une approche aussi simple. Pour exploiter pleinement les capacités spectrales du système, il est nécessaire de mettre en œuvre une fonction de pondération appropriée.
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Subnanosecond single electron source in the time-domain

Subnanosecond single electron source in the time-domain

time, high transmission part of the curve becomes more noisy as the integration window incorporates more noise. Finally all the results obtained for different values of the gate voltage and excitation amplitude can be represented on a two-dimensional colorplot, Fig.7, where the current is represented in colorscale. We observe again at low amplitudes the periodic oscillations reflecting the periodicity of the dot density of states (horizontal axis). Broadening of the current peaks occurs at low transmission as the escape time becomes longer (vertical axis). For 2eV exc = ∆, the oscillations vanish as one electron is emitted at each period and one
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Time-Domain Harmonic Balance Method for Turbomachinery Aeroelasticity

Time-Domain Harmonic Balance Method for Turbomachinery Aeroelasticity

ONERA–The French Aerospace Lab, 92322 Châtillon, France The present paper investigates a time-domain harmonic balance method as an alternative to classical time- marching schemes for stability studies of turbomachineries toward flutter. A weak-coupling approach is applied, which requires computing the fluid response to prescribed harmonic motions of the structure. The harmonic balance method, formulated in the arbitrary Lagrangian/Eulerian framework, is adapted to single-passage reduction using phase-lag boundary conditions expressed purely in the time domain. Validation against experimental data for the 11th standard configuration for aeroelasticity is performed, showing good agreement. Finally, an industrial test case is presented: a fan designed by Safran Snecma. The results show the good accuracy of the proposed harmonic balance method as well as significant reductions in computational time.
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A Time Domain Characterization of 2-microlocal Spaces

A Time Domain Characterization of 2-microlocal Spaces

Unité de recherche INRIA Rocquencourt Domaine de Voluceau - Rocquencourt - BP 105 - 78153 Le Chesnay Cedex France Unité de recherche INRIA Lorraine : LORIA, Technopôle de Nancy-Brabois -[r]

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An upscaled DGTD method for time-domain electromagnetics

An upscaled DGTD method for time-domain electromagnetics

Local problems are independent i.e. can be solved in parallel Local time-stepping is possible i.e. local problems can be time advanced with their own time step (or time scheme) In the discrete case, first level problem is a linear system with a symetric positive definite matrix

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Molecular frame reconstruction using time-domain photoionization interferometry

Molecular frame reconstruction using time-domain photoionization interferometry

In this Letter, time-domain measurements, utilizing molecular alignment techniques, have been demonstrated as a means to “complete” photoionization studies. The time- domain data provided sufficiently high information content to reliably extract the axis distributions and matrix elements for three different ionization channels. A bootstrapping fitting methodology provided a flexible and robust analysis route, and MF reconstructions provided an additional stringent test of the physical parameters so determined, as well as an illustration of their predictive power. The main advantage of this methodology is that it is completely general in principle (although it may be restricted by symmetry in certain cases, and may require noncylindrically symmetric polarization geometries [34] ), and is applicable to any molecular ionization problem, provided that the prepa- ration and propagation of the rotational wave packet remains decoupled from other molecular dynamics. All relative magnitudes and phases of the ionization matrix elements can be determined and MF interferograms can be obtained without experimentally challenging MF measurements, which require molecular orientation or fragmentation. The disadvantage is that this fitting methodology is not a black-box procedure, and requires detailed analysis (see Supplemental Material [34] ). While this methodology has been demonstrated herein for the simplest case of a homonuclear linear molecule, the theory and analysis protocol allows for arbitrary asymmetric molecules. Equation (3) can provide a sense of the limitations of this. The degree of rotational excitation determines the number of C L;M K;Q that can be extracted from the data. These then provide a set of multivariate quadratic equations in the dipole matrix elements. The nature and solubility of this equation set for asymmetric top molecules will be the subject of a future publication [70] . Some improvements may be possible here, for example, the use of other fitting algorithms (genetic algorithms and homotopy methods [71] ), which may allow for a more robust approach less sensitive to local minima in the solution hyperspace, and the use of graphics processing units (GPUs) to massively parallelize the computations.
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Time-resolved photoemission spectroscopy on a metal/ferroelectric heterostructure

Time-resolved photoemission spectroscopy on a metal/ferroelectric heterostructure

IV. CONCLUSION We have provided a proof of concept for the investiga- tion of realistic devices in operating conditions with time- resolved photoemission spectroscopy. The chemical, elec- tronic and depth sensitivity of core level photoemission is used to probe the transient response of different parts of the upper electrode/ferroelectric interface to voltage pulse induced polarization switching. With the spatial and time resolution available, valuable information on the physics of the interface is accessible.

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Time-resolved Bell Correlation Spectroscopy of Molecular Vibrations

Time-resolved Bell Correlation Spectroscopy of Molecular Vibrations

(Dated: December 11, 2019) Quantum states of bulk oscillators can be important resources for quantum technologies. The development of versatile techniques to prepare and measure such states can in turn shed new light on the processes and time scales of decoherence in vibrational excitations. Here, we present a new scheme leveraging universal properties of Raman scattering to create quantum correlations between light and vibration that are strong enough to violate a Bell inequality. We measure the decay of these hybrid photon-phonon Bell correlations with sub-picosecond time-resolution and observe the decoherence of a vibrational qubit encoded in two time bins. The experiment relies on a molecular vibrational mode featuring a record number of ∼ 1000 quantum coherent oscillations at ambient conditions, which scatters light inelastically and can therefore be addressed by time-resolved single photon Raman spectroscopy. It paves the way for the study of quantum correlations in highly complex solid-state and molecular systems in their natural state, i.e. without any engineering of their coherence properties or interaction mechanisms.
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Casimir forces in the time domain: I. Theory

Casimir forces in the time domain: I. Theory

Our goal is then to compute G ij via the FDTD method. The straightforward way to achieve this involves com- puting the Fourier transform of the electric field in re- sponse to a short pulse. However, in most methods a crucial step for evaluating the resulting frequency inte- gral is the passage to imaginary frequencies, correspond- ing to imaginary time. We show that, in the FDTD, this gives rise to exponentially growing solutions and is therefore unsuitable. Instead, we describe an alternative formulation of the problem that exploits a recently pro- posed equivalence in which contour deformations in the complex frequency-domain ω(ξ) correspond to introduc- ing an effective dispersive, dissipative medium at a real “frequency” ξ. From this perspective, it becomes simple to modify the FDTD Maxwell’s equations for the pur- pose of obtaining well-behaved stress tensor frequency integrands. We illustrate our approach by considering a contour corresponding to a medium with frequency- independent conductivity σ. This contour has the ad- vantage of being easily implemented in the FDTD, and in fact is already incorporated in most FDTD solvers. Finally, we show that it is possible to abandon the fre- quency domain entirely in favor of evaluating the force integral directly in the time domain, which offers several conceptual and numerical advantages.
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Time-resolved photoelectron spectroscopy : from wavepackets to observables

Time-resolved photoelectron spectroscopy : from wavepackets to observables

TRPES has been the subject of a number of reviews 21–33 and these cover various aspects of the field. Here, we intend to give a pedagogical overview of TRPES and its application to non-adiabatic excited dynamics in polyatomic molecules. We aim not only at readers who are already somewhat familiar with the field, but also at a more general audience, particularly new researchers and graduate students. Therefore, a signifi- cant amount of background is included and is, necessarily, somewhat lengthy. Readers with a grounding in molecular dynamics and TRPES should feel free to skim or skip some parts. The subsequent sections of this paper are arranged as follows. In Section 2, a conceptual framework for time- resolved photoionization measurements is presented, followed by more detailed discussion of the underlying theory. Empha- sis is placed on understanding excited state dynamics and following these dynamics with TRPES. The salient points are illustrated with simple model examples, which provide intuitive and faithful pictures illustrating the important concepts. In Section 3, a brief introduction to TRPES experimental tech- niques is given, followed by three prototypical experimental examples chosen to highlight the application of TRPES to different problems: from the simplest vibrational wavepacket on a single potential energy surface, to disentangling intrinsi- cally coupled electronic and nuclear motions, to identifying character of the intermediate states involved in dynamics by making measurements in the molecular frame—the most complete measurement. We end with a short conclusion and outlook.
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Drug/protein interactions studied by time-resolved fluorescence spectroscopy

Drug/protein interactions studied by time-resolved fluorescence spectroscopy

Keywords: drugs, flurbiprofen, albumin, time-resolved fluorescence, femtosecond, fluorescence upconversion 1. INTRODUCTION The transport and distribution of drugs in the body is a complex mechanisms governed by many different processes. An important role is played by specific transport proteins, responsible for the fixing and release of the drugs. Obtaining a better understanding of the factors that govern the structure and dynamics of drug-protein complexes is therefore of great interest.

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Recent Achievements on a DGTD Method for Time-Domain Electromagnetics

Recent Achievements on a DGTD Method for Time-Domain Electromagnetics

time advanced with a global time step which is approximately 4.7 times larger than the smallest time step of the mesh. The linear system of equations associated to the implicit elements is solved using an optimized sparse direct solver and the factorization of the implicit matrix is performed once for all before entering the time stepping loop. The simulations have been carried out on a workstation equipped with an Intel Xeon 2.3 GHz and 16 GB of RAM. The simulation time for the fully explicit DGTD-P 1 method is 14 h 22 mn for a total of

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Locally implicit discontinuous Galerkin method for time domain electromagnetics

Locally implicit discontinuous Galerkin method for time domain electromagnetics

8 Con lusion We have presented the results of a study aiming at over oming the grid-indu ed stiness in high order DGTD methods formulated on non-uniform simpli ial meshes for the solu- tion of the system of time domain Maxwell equations. For that purpose, we have adopted an hybrid expli it-impli it time integration strategy. First, the elements of the underlying mesh are assumed to be partitioned into two sets a ording to an appropriate geometri riterion. Then, the time integration method onsidered here ombines an impli it Crank- Ni olson s heme applied to the semi-dis retized equations asso iated to the mesh elements belonging to one of the subsets (typi ally , the elements lo alized in the rened zones of the mesh), with an expli it Leap-Frog s heme applied to the semi-dis retized equations for the elements in the omplementary subset. The resulting strategy is a omponent splitting based CNLF (Crank-Ni olson-Leap-Frog) DGTD method following the terminology adopted in [Ver09℄. A stability analysis of the hybrid expli it-impli it DGTD method using energeti onsiderations shows that the referen e (global) time step an be omputed from a ondi- tion essentially ensuring that the Leap-F rog s heme alone is stable for the mesh elements of the orresponding subset. The temporal onvergen e of the CNLF time integration s heme has re ently been studied in [Ver09℄ where a onvergen e ondition is derived that guaran- tees se ond order temporal onvergen e uniformly in the spatial dis retization parameter. The a ura y of the CNLF DGTD method has been assessed here numeri ally in the two- dimensional ase by onsidering wave propagation problems for whi h analyti al solutions are available.
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ON THE FREQUENCY DOMAIN DETECTION OF HIGH DIMENSIONAL TIME SERIES

ON THE FREQUENCY DOMAIN DETECTION OF HIGH DIMENSIONAL TIME SERIES

In this paper, we address the problem of detection, in the frequency domain, of a M -dimensional time series modeled as the output of a M × K MIMO filter driven by a K-dimensional Gaussian white noise, and disturbed by an additive M -dimensional Gaussian col- ored noise. We consider the study of test statistics based of the Spectral Coherence Matrix (SCM) obtained as renormalization of the smoothed periodogram matrix of the observed time series over N samples, and with smoothing span B. To that purpose, we con- sider the asymptotic regime in which M, B, N all converge to infin- ity at certain specific rates, while K remains fixed. We prove that the SCM may be approximated in operator norm by a correlated Wishart matrix, for which Random Matrix Theory (RMT) provides a precise description of the asymptotic behaviour of the eigenvalues. These results are then exploited to study the consistency of a test based on the largest eigenvalue of the SCM, and provide some numerical illustrations to evaluate the statistical performance of such a test.
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Time-domain simulation of large electric power systems using domain-decomposition and parallel processing methods

Time-domain simulation of large electric power systems using domain-decomposition and parallel processing methods

I wish to express my gratitude to each member of the examining committee, for devot- ing their time to read this report. During my stay in Liège, Professors Patricia Rousseaux, Christophe Geuzaine, and Damien Ernst have offered concrete support both as members of my dissertation committee but also through our enriching discussions. A special thanks to Professor Costas Vournas who was the first one to introduce me to the world of power system dynamics and has supported and advised me over the years. I would also like to thank Dr. Mevludin Glavic for the insightful discussions during our coffee breaks outside the department entrance, but also for transferring his experience to help me make some impor- tant decisions in my life. I wish to thank Professor Xavier Guillaud, his support and feedback on my work have been valuable for my PhD. Many thanks to Simon Lebeau (TransÉnergie di- vision, Hydro-Québec) and Patrick Panciatici (RTE) for providing a valuable input to my work based on real engineering problems. Upon arriving in Liège, I was welcomed by Professor
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