Non-Fourier heat transport in metal-dielectric core-shell nanoparticles under ultrafast laser pulse excitation

Relaxation dynamics of embedded metal nanoparticles after ultrafast laser pulse excitation is driven by thermal phenomena of different origins the accurate description of which is crucial for interpreting experimental results: hot electron gas generation, electron-phonon coupling, heat transfer to the particle environment and heat propagation in the latter. Regardingthis last mechanism, it is well known that heat transport in nanoscale structures and/or at ultrashort timescales may deviate from the predictions of the Fourier law. In these cases heat transport may rather be described by the Boltzmann transport equation. We present a numerical model allowing us to determine the electron and lattice temperature dynamics in a spherical gold nanoparticle core under subpicosecond pulsed excitation, as well as that of the surrounding shell dielectric medium. For this, we have used the electron-phonon coupling equation in the particle with a source term linked with the laser pulse absorption, and the ballistic-diffusive equations for heat conduction in the host medium. Either thermalizing or adiabatic boundary conditions have been considered at the shell external surface. Our results show that the heat transfer rate from the particle to the matrix can be significantly smaller than the prediction of Fourier's law. Consequently, the particle temperature rise is larger and its cooling dynamics might be slower than that obtained by using Fourier's law. This difference is attributed to the nonlocal and nonequilibrium heat conduction in the vicinity of the core nanoparticle. These results are expected to be of great importance for analyzing pump-probe experiments performed on single nanoparticles or nanocomposite media

Cooling Dynamics of a Gold Nanoparticle in a Host Medium Under Ultrafast Laser Pulse Excitation: A Ballistic-Diffusive Approach

We present a numerical model allowing to determine the electron and lattice temperature dynamics in a gold nanoparticle under subpicosecond pulsed excitation, as well as that of the surrounding medium. For this, we have used the electron-phonon coupling equation in the particle with a source term linked with the laser pulse, and the ballistic-diffusive equations for heat conduction in the host medium. Our results show that the heat transfer rate from the particle to the matrix is significantly smaller than the prediction of Fourier's law. Consequently, the particle temperature rise is much larger and its cooling dynamics is much slower than that obtained using Fourier's law, which is attributed to the nonlocal and nonequilibrium heat conduction in the vicinity of the nanoparticle. These results are expected to be of great importance for interpreting pump-probe experiments performed on single nanoparticles or nanocomposite media

'Spillout' effect in gold nanoclusters embedded in c-Al2O3(0001) matrix

Gold nanoclusters are grown by 1.8 MeV Au^\sup{2+} implantation on c-Al\sub{2}O\sub{3}(0001)substrate and subsequent air annealing at temperatures 1273K. Post-annealed samples show plasmon resonance in the optical (561-579 nm) region for average cluster sizes ~1.72-2.4 nm. A redshift of the plasmon peak with decreasing cluster size in the post-annealed samples is assigned to the 'spillout' effect (reduction of electron density) for clusters with ~157-427 number of Au atoms fully embedded in crystalline dielectric matrix with increased polarizability in the embedded system.Comment: 14 Pages (figures included); Accepted in Chem. Phys. Lett (In Press

Resonant Raman Scattering by quadrupolar vibrations of Ni-Ag Core-shell Nanoparticles

Low-frequency Raman scattering experiments have been performed on thin films consisting of nickel-silver composite nanoparticles embedded in alumina matrix. It is observed that the Raman scattering by the quadrupolar modes, strongly enhanced when the light excitation is resonant with the surface dipolar excitation, is mainly governed by the silver electron contribution to the plasmon excitation. The Raman results are in agreement with a core-shell structure of the nanoparticles, the silver shell being loosely bonded to the nickel core.Comment: 3 figures. To be published in Phys. Rev.

Thermal Excitation of Broadband and Long-range Surface Waves on SiO 2 Submicron Films

We detect thermally excited surfaces waves on a submicron SiO 2 layer, including Zenneck and guided modes in addition to Surface Phonon Polaritons. The measurements show the existence of these hybrid thermal-electromagnetic waves from near-(2.7 $\mu$m) to far-(11.2 $\mu$m) infrared. Their propagation distances reach values on the order of the millimeter, several orders of magnitude larger than on semi-infinite systems. These two features, spectral broadness and long range propagation, make these waves good candidates for near-field applications both in optics and thermics due to their dual nature.Comment: Applied Physics Letters, American Institute of Physics, 201

Wetting to Non-wetting Transition in Sodium-Coated C_60

Based on ab initi and density-functional theory calculations, an empirical potential is proposed to model the interaction between a fullerene molecule and many sodium atoms. This model predicts homogeneous coverage of C_60 below 8 Na atoms, and a progressive droplet formation above this size. The effects of ionization, temperature, and external electric field indicate that the various, and apparently contradictory, experimental results can indeed be put into agreement.Comment: 4 pages, 4 postscript figure

Structural, Functional, and Evolutionary Implications of a Histidine Moieity in Cardiac Troponin I.

Regulation of cardiac output is mediated by intrinsic and extrinsic factors that modulate the rhythmic transitions between contraction (systole) and relaxation (diastole). At the level of cardiac myofilaments, the troponin complex (troponin I (TnI), troponin C (TnC), and troponin T (TnT)) is the allosteric regulatory unit that controls the transition between active and inactive actomyosin cross-bridges. This is accomplished by the C-terminal switch arm of TnI toggling between actin during diastole and cTnC during systole in a calcium-dependent manner. These studies elucidate new knowledge regarding the structural, functional, and evolutionary implications of a histidine residue in the switch arm of troponin I. Molecular modeling of TnI isoforms and large scale bioinformatics analysis of chordate phylogenies were used to study the evolution of the cardiac troponin complex. At the molecular level, a single histidine to alanine substitution in the cTnI switch arm was the most effective mechanism for decreasing the binding free energy at the regulatory interface of TnI and TnC. Evidence suggests that this single amino acid substitution increases the intrinsic relaxation potential of the cTn complex enhancing diastolic performance to meet mammalian lusitropic demands. A histidine button in TnI is known to provide a therapeutic basis for pH responsive titratable inotropy in response to various cardiac stresses. As such, the physiological implications of a histidine button in mammalian cardiac TnI (cTnI A164H) were studied. Whole organ in vivo cardiac hemodynamic analysis shows that cTnI A164H Tg mice protect cardiac function from age-induced cardiomyopathy. Furthermore, cTnI A164H Tg hearts sustain cardiac performance during severe hypercapnic acidosis compared to complete pump failure with 100% mortality observed in control mice. In situ and in silico site-directed protein mutagenesis, in vitro cellular biophysics, and atomic resolution molecular dynamics simulations were used to analyze the therapeutic basis for a histidine button in cTnI. Evidence suggests that differential ionization of histidine mediates the titratable inotropy observed in myofilaments containing cTnI A164H.Ph.D.Molecular and Integrative PhysiologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/64822/1/npalpant_1.pd

A Track for Change: Roller derby’s impact on primary role identity

Study Aim: To explore how participation in competitive roller derby affects identity formation in women’s primary occupational roles

pH-Responsive Titratable Inotropic Performance of Histidine-Modified Cardiac Troponin I

AbstractCardiac troponin I (cTnI) functions as the molecular switch of the thin filament. Studies have shown that a histidine button engineered into cTnI (cTnI A164H) specifically enhances inotropic function in the context of numerous pathophysiological challenges. To gain mechanistic insight into the basis of this finding, we analyzed histidine ionization states in vitro by studying the myofilament biophysics of amino acid substitutions that act as constitutive chemical mimetics of altered histidine ionization. We also assessed the role of histidine-modified cTnI in silico by means of molecular dynamics simulations. A functional in vitro analysis of myocytes at baseline (pH 7.4) indicated similar cellular contractile function and myofilament calcium sensitivity between myocytes expressing wild-type (WT) cTnI and cTnI A164H, whereas the A164R variant showed increased myofilament calcium sensitivity. Under acidic conditions, compared with WT myocytes, the myocytes expressing cTnI A164H maintained a contractile performance similar to that observed for the constitutively protonated cTnI A164R variant. Molecular dynamics simulations showed similar intermolecular atomic contacts between the WT and the deprotonated cTnI A164H variant. In contrast, simulations of protonated cTnI A164H showed various potential structural configurations, one of which included a salt bridge between His-164 of cTnI and Glu-19 of cTnC. This salt bridge was recapitulated in simulations of the cTnI A164R variant. These data suggest that differential histidine ionization may be necessary for cTnI A164H to act as a molecular sensor capable of modulating sarcomere performance in response to changes in the cytosolic milieu