scholarly journals Measuring non-radiative relaxation time of fluorophores with biomedical applications by intensity-modulated laser-induced photoacoustic effect

2011 ◽  
Vol 2 (10) ◽  
pp. 2749 ◽  
Author(s):  
Behrouz Soroushian ◽  
Xinmai Yang
Keyword(s):  
Relaxation Time ◽  
Biomedical Applications ◽  
Radiative Relaxation ◽  
Photoacoustic Effect ◽  
Intensity Modulated

scholarly journals The Stability of Mars’s Annular Polar Vortex

2017 ◽  
Vol 74 (5) ◽  
pp. 1533-1547 ◽  
Author(s):  
William J. M. Seviour ◽  
Darryn W. Waugh ◽  
Richard K. Scott
Keyword(s):  
Relaxation Time ◽  
Time Scales ◽  
Time Scale ◽  
Thermal Relaxation ◽  
Polar Vortex ◽  
Radiative Relaxation ◽  
Equilibrium Profile ◽  
Rotating Shallow Water ◽  
The Stability ◽  
Topographic Forcing

Abstract The Martian polar atmosphere is known to have a persistent local minimum in potential vorticity (PV) near the winter pole, with a region of high PV encircling it. This finding is surprising, since an isolated band of PV is barotropically unstable, a result going back to Rayleigh. Here the stability of a Mars-like annular vortex is investigated using numerical integrations of the rotating shallow-water equations. The mode of instability and its growth rate is shown to depend upon the latitude and width of the annulus. By introducing thermal relaxation toward an annular equilibrium profile with a time scale similar to that of the instability, a persistent annular vortex with similar characteristics as that observed in the Martian atmosphere can be simulated. This time scale, typically 0.5–2 sols, is similar to radiative relaxation time scales for Mars’s polar atmosphere. The persistence of an annular vortex is also shown to be robust to topographic forcing, as long as it is below a certain amplitude. It is therefore proposed that the persistence of this barotropically unstable annular vortex is permitted owing to the combination of short radiative relaxation time scales and relatively weak topographic forcing in the Martian polar atmosphere.

scholarly journals An adapted Coffey model for studying susceptibility losses in interacting magnetic nanoparticles

2015 ◽  
Vol 6 ◽  
pp. 2173-2182 ◽  
Author(s):  
Mihaela Osaci ◽  
Matteo Cacciola
Keyword(s):  
Relaxation Time ◽  
Magnetic Fields ◽  
Biomedical Applications ◽  
Tumor Therapy ◽  
Linear Response Theory ◽  
Orientation Model ◽  
Specific Loss Power ◽  
Acceptable Range ◽  
Nanoparticle System ◽  
Néel Relaxation

Background: Nanoparticles can be used in biomedical applications, such as contrast agents for magnetic resonance imaging, in tumor therapy or against cardiovascular diseases. Single-domain nanoparticles dissipate heat through susceptibility losses in two modes: Néel relaxation and Brownian relaxation. Results: Since a consistent theory for the Néel relaxation time that is applicable to systems of interacting nanoparticles has not yet been developed, we adapted the Coffey theoretical model for the Néel relaxation time in external magnetic fields in order to consider local dipolar magnetic fields. Then, we obtained the effective relaxation time. The effective relaxation time is further used for obtaining values of specific loss power (SLP) through linear response theory (LRT). A comparative analysis between our model and the discrete orientation model, more often used in literature, and a comparison with experimental data from literature have been carried out, in order to choose the optimal magnetic parameters of a nanoparticle system. Conclusion: In this way, we can study effects of the nanoparticle concentration on SLP in an acceptable range of frequencies and amplitudes of external magnetic fields for biomedical applications, especially for tumor therapy by magnetic hyperthermia.

scholarly journals Optical decomposition of DNA gel and modification of object mobility on micrometre scale

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Suguru Shimomura ◽  
Takahiro Nishimura ◽  
Yusuke Ogura ◽  
Jun Tanida
Keyword(s):  
Thermal Energy ◽  
Dna Sequences ◽  
Biomedical Applications ◽  
State Transitions ◽  
Dye Molecules ◽  
Radiative Relaxation ◽  
Polystyrene Beads ◽  
Object Mobility ◽  
Detection Of Biomolecules ◽  
Viscosity Changes

AbstractDNA gels can be engineered to exhibit specific properties through the choice of DNA sequences and modification with dye molecules, and can therefore be useful in biomedical applications such as the detection of biomolecules. State transitions of DNA gels on the micrometre scale can generate a viscosity gradient, which can be used to modify the mobility of micrometre-sized objects. In this paper, we propose a method for changing the viscosity of DNA gels using optical decomposition. The use of light allows for decomposition on the micrometre scale, which can be used to achieve patterned viscosity changes within DNA gels. Decomposition was induced by thermal energy released through non-radiative relaxation of excited quenchers. We demonstrated the decomposition of DNA gels in response to irradiation patterns on the micrometre scale. In addition, as a result of changes in DNA gel viscosity due to decomposition, the mobility of polystyrene beads was shown to increase. This technique could provide a new optical approach for controlling the mobility of micrometre-sized objects.

Enhancing the carrier thermalization time in organometallic perovskites by halide mixing

2016 ◽  
Vol 18 (7) ◽  
pp. 5219-5231 ◽  
Author(s):  
Mohamed El-Amine Madjet ◽  
Alexey V. Akimov ◽  
Fadwa El-Mellouhi ◽  
Golibjon R. Berdiyorov ◽  
Sahel Ashhab ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Relaxation Time ◽  
Molecular Dynamics Simulations ◽  
Charge Carriers ◽  
Relaxation Dynamics ◽  
Radiative Relaxation ◽  
Carrier Relaxation ◽  
Thermalization Time ◽  
Dynamics Simulations ◽  
Carrier Thermalization

Non-adiabatic molecular dynamics simulations of non-radiative relaxation dynamics of charge carriers in hybrid perovskites show that the carrier relaxation time can be considerably increased by halide mixing.

scholarly journals Iterative method for determination of the laser beam profile and τV-T

2008 ◽  
Vol 6 (1) ◽  
pp. 71-76
Author(s):  
Mihailo Rabasovic ◽  
Dragan Markushev
Keyword(s):  
Relaxation Time ◽  
Laser Beam ◽  
Photoacoustic Signal ◽  
Linear Process ◽  
Beam Profile ◽  
Photoacoustic Tomography ◽  
Spatial Profile ◽  
Photoacoustic Effect ◽  
Laser Beam Profile

Measuring the vibrational-to-translational relaxation time ?V-T in gases is one of the first applications of the photoacoustic effect. The spatial profile of the laser beam is crucial in these measurements because the multiphoton excitation is investigated. The multiphoton absorption is a non-linear process. Because of this, the top hat profile is preferable. It allows one to deal with nonlinearity in a simple manner. In order to reveal the real laser beam profile, we have slightly changed the theoretical profiles in such a manner that the best matching is obtained between theoretical and experimental photoacoustic signals. Still, there was a question: Is it possible to deduce the laser beam profile directly from the photoacoustic signal, thus avoiding manual changing of the laser beam profile? According to this paper, it is possible. The appropriate method has been found in another photoacoustics application: photoacoustic tomography. Thus, the method for the simultaneous determination of the spatial profile of the laser beam and vibrational-to-translational relaxation time is presented in this paper. It employs pulsed photoacoustics and an algorithm developed for photoacoustic tomography.

scholarly journals Nanoparticle Probes for Structural and Functional Photoacoustic Molecular Tomography

2015 ◽  
Vol 2015 ◽  
pp. 1-11 ◽  
Author(s):  
Haobin Chen ◽  
Zhen Yuan ◽  
Changfeng Wu
Keyword(s):  
Molecular Imaging ◽  
Biomedical Applications ◽  
High Sensitivity ◽  
Biological Tissues ◽  
Structure And Function ◽  
Photoacoustic Tomography ◽  
Optical Contrast ◽  
Photoacoustic Effect ◽  
Nanoparticle Probes ◽  
And Function

Nowadays, nanoparticle probes have received extensive attention largely due to its potential biomedical applications in structural, functional, and molecular imaging. In addition, photoacoustic tomography (PAT), a method based on the photoacoustic effect, is widely recognized as a robust modality to evaluate the structure and function of biological tissues with high optical contrast and high acoustic resolution. The combination of PAT with nanoparticle probes holds promises for detecting and imaging diseased tissues or monitoring their treatments with high sensitivity. This review will introduce the recent advances in the emerging field of nanoparticle probes and their preclinical applications in PAT, as well as relevant perspectives on future development.

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