Single photon double ionization of the helium dimer

We show that a single photon can ionize the two helium atoms of the helium dimer in a distance up to 10 {\deg}A. The energy sharing among the electrons, the angular distributions of the ions and electrons as well as comparison with electron impact data for helium atoms suggest a knock-off type double ionization process. The Coulomb explosion imaging of He_2 provides a direct view of the nuclear wave function of this by far most extended and most diffuse of all naturally existing molecules.Comment: 10 pages, 5 figure

Ion impact induced Interatomic Coulombic Decay in neon and argon dimers

We investigate the contribution of Interatomic Coulombic Decay induced by ion impact in neon and argon dimers (Ne$_2$ and Ar$_2$) to the production of low energy electrons. Our experiments cover a broad range of perturbation strengths and reaction channels. We use 11.37 MeV/u S$^{14+}$, 0.125 MeV/u He$^{1+}$, 0.1625 MeV/u He$^{1+}$ and 0.150 MeV/u He$^{2+}$ as projectiles and study ionization, single and double electron transfer to the projectile as well as projectile electron loss processes. The application of a COLTRIMS reaction microscope enables us to retrieve the three-dimensional momentum vectors of the ion pairs of the fragmenting dimer into Ne$^{q+}$/Ne$^{1+}$ and Ar$^{q+}$/Ar$^{1+}$ (q = 1, 2, 3) in coincidence with at least one emitted electron

Interatomic Coulombic Decay following Photoionization of the Helium Dimer: Observation of Vibrational Structure

Using synchrotron radiation we simultaneously ionize and excite one helium atom of a helium dimer (He_2) in a shakeup process. The populated states of the dimer ion (i.e. He^[*+](n = 2; 3)-He) are found to deexcite via interatomic coulombic decay. This leads to the emission of a second electron from the neutral site and a subsequent coulomb explosion. In this letter we present a measurement of the momenta of fragments that are created during this reaction. The electron energy distribution and the kinetic energy release of the two He^+ ions show pronounced oscillations which we attribute to the structure of the vibrational wave function of the dimer ion.Comment: 8 pages, 5 figure

Vocal tract resonances in singing: variation with laryngeal mechanism for male operatic singers in chest and falsetto registers

International audienceSeven male operatic singers sang the same notes and vowels in their chest and their falsetto registers, covering the overlap frequency range where two main laryngeal mechanisms can be identified by means of electroglottography: M1 in chest register and M2 in falsetto register. Glottal contact quotients determined using electroglottography were typically lower by 0.27 in M2 than in M1. Vocal tract resonance frequencies were measured by using broadband excitation at the lips and found to be typically lower in M2 than in M1 sung at the same pitch and vowel; R1 typically by 65 Hz and R2 by 90 Hz. These shifts in tract resonances were only weakly correlated with the changes in the contact quotient or laryngeal height that were measured simultaneously. There was considerable variability in the resonance tuning strategies used by the singers, and no evidence of a uniform systematic tuning strategy used by all singers. A simple model estimates that the shifts in resonance frequencies are consistent with the effective glottal area in falsetto register (M2) being 60%-70% of its value in chest register (M1)

Mononuclear Phagocyte System Depletion Blocks Interstitial Tonicity-Responsive Enhancer Binding Protein/Vascular Endothelial Growth Factor C Expression and Induces Salt-Sensitive Hypertension in Rats

We showed recently that mononuclear phagocyte system (MPS) cells provide a buffering mechanism for salt-sensitive hypertension by driving interstitial lymphangiogenesis, modulating interstitial Na(+) clearance, and increasing endothelial NO synthase protein expression in response to very high dietary salt via a tonicity-responsive enhancer binding protein/vascular endothelial growth factor C regulatory mechanism. We now tested whether isotonic saline and deoxycorticosterone acetate (DOCA)-salt treatment leads to a similar regulatory response in Sprague-Dawley rats. Male rats were fed a low-salt diet and received tap water (low-salt diet LSD), 1.0% saline (high-salt diet HSD), or DOCA+1.0% saline (DOCA-HSD). To test the regulatory role of interstitial MPS cells, we further depleted MPS cells with clodronate liposomes. HSD and DOCA-HSD led to Na(+) accumulation in the skin, MPS-driven tonicity-responsive enhancer binding protein/vascular endothelial growth factor C-mediated hyperplasia of interstitial lymph capillaries, and increased endothelial NO synthase protein expression in skin interstitium. Clodronate liposome MPS cell depletion blocked MPS infiltration in the skin interstitium, resulting in unchanged tonicity-responsive enhance binding protein/vascular endothelial growth factor C levels and absent hyperplasia of the lymph capillary network. Moreover, no increased skin endothelial NO synthase protein expression occurred in either clodronate liposome-treated HSD or DOCA-salt rats. Thus, absence of the MPS-cell regulatory response converted a salt-resistant blood-pressure state to a salt-sensitive state in HSD rats. Furthermore, salt-sensitive hypertension in DOCA-salt rats was aggravated. We conclude that MPS cells act as onsite controllers of interstitial volume and blood pressure homeostasis, providing a local regulatory salt-sensitive tonicity-responsive enhancer binding protein/vascular endothelial growth factor C-mediated mechanism in the skin to maintain normal blood pressure in states of interstitial Na(+) and Cl(-) accumulation. Failure of this physiological extrarenal regulatory mechanism leads to a salt-sensitive blood pressure response

Adapted to Roar: Functional Morphology of Tiger and Lion Vocal Folds

Vocal production requires active control of the respiratory system, larynx and vocal tract. Vocal sounds in mammals are produced by flow-induced vocal fold oscillation, which requires vocal fold tissue that can sustain the mechanical stress during phonation. Our understanding of the relationship between morphology and vocal function of vocal folds is very limited. Here we tested the hypothesis that vocal fold morphology and viscoelastic properties allow a prediction of fundamental frequency range of sounds that can be produced, and minimal lung pressure necessary to initiate phonation. We tested the hypothesis in lions and tigers who are well-known for producing low frequency and very loud roaring sounds that expose vocal folds to large stresses. In histological sections, we found that the Panthera vocal fold lamina propria consists of a lateral region with adipocytes embedded in a network of collagen and elastin fibers and hyaluronan. There is also a medial region that contains only fibrous proteins and hyaluronan but no fat cells. Young's moduli range between 10 and 2000 kPa for strains up to 60%. Shear moduli ranged between 0.1 and 2 kPa and differed between layers. Biomechanical and morphological data were used to make predictions of fundamental frequency and subglottal pressure ranges. Such predictions agreed well with measurements from natural phonation and phonation of excised larynges, respectively. We assume that fat shapes Panthera vocal folds into an advantageous geometry for phonation and it protects vocal folds. Its primary function is probably not to increase vocal fold mass as suggested previously. The large square-shaped Panthera vocal fold eases phonation onset and thereby extends the dynamic range of the voice

The anisotropic hyperelastic biomechanical response of the vocal ligament and implications for frequency regulation: A case study

One of the primary mechanisms to vary one's vocal frequency is through vocal fold length changes. As stress and deformation are linked to each other, it is hypothesized that the anisotropy in the biomechanical properties of the vocal fold tissue would affect the phonation characteristics. A biomechanical model of vibrational frequency rise during vocal fold elongation is developed which combines an advanced biomechanical characterization protocol of the vocal fold tissue with continuum beam models. Biomechanical response of the tissue is related to a microstructurally informed, anisotropic, nonlinear hyperelastic constitutive model. A microstructural characteristic (the dispersion of collagen) was represented through a statistical orientation function acquired from a second harmonic generation image of the vocal ligament. Continuum models of vibration were constructed based upon Euler–Bernoulli and Timoshenko beam theories, and applied to the study of the vibration of a vocal ligament specimen. From the natural frequency predictions in dependence of elongation, two competing processes in frequency control emerged, i.e., the applied tension raises the frequency while simultaneously shear deformation lowers the frequency. Shear becomes much more substantial at higher modes of vibration and for highly anisotropic tissues. The analysis was developed as a case study based on a human vocal ligament specimen

Do red deer stags (Cervus elaphus) use roar fundamental frequency (F0) to assess rivals?

It is well established that in humans, male voices are disproportionately lower pitched than female voices, and recent studies suggest that this dimorphism in fundamental frequency (F0) results from both intrasexual (male competition) and intersexual (female mate choice) selection for lower pitched voices in men. However, comparative investigations indicate that sexual dimorphism in F0 is not universal in terrestrial mammals. In the highly polygynous and sexually dimorphic Scottish red deer Cervus elaphus scoticus, more successful males give sexually-selected calls (roars) with higher minimum F0s, suggesting that high, rather than low F0s advertise quality in this subspecies. While playback experiments demonstrated that oestrous females prefer higher pitched roars, the potential role of roar F0 in male competition remains untested. Here we examined the response of rutting red deer stags to playbacks of re-synthesized male roars with different median F0s. Our results show that stags’ responses (latencies and durations of attention, vocal and approach responses) were not affected by the F0 of the roar. This suggests that intrasexual selection is unlikely to strongly influence the evolution of roar F0 in Scottish red deer stags, and illustrates how the F0 of terrestrial mammal vocal sexual signals may be subject to different selection pressures across species. Further investigations on species characterized by different F0 profiles are needed to provide a comparative background for evolutionary interpretations of sex differences in mammalian vocalizations