The surrounding microenvironment limits tumour expansion, imposing a compressive stress on the tumour, but little is known how pressure propagates inside the tumour. Here we present non-destructive cell-like microsensors to locally quantify mechanical stress distribution in three-dimensional tissue. Our sensors are polyacrylamide microbeads of well-defined elasticity, size and surface coating to enable internalization within the cellular environment. By isotropically compressing multicellular spheroids (MCS), which are spherical aggregates of cells mimicking a tumour, we show that the pressure is transmitted in a non-trivial manner inside the MCS, with a pressure rise towards the core. This observed pressure profile is explained by the anisotropic arrangement of cells and our results suggest that such anisotropy alone is sufficient to explain the pressure rise inside MCS composed of a single cell type. Furthermore, such pressure distribution suggests a direct link between increased mechanical stress and previously observed lack of proliferation within the spheroids core.

The laser induced dispersed fluorescence spectra (L.I.D.F.S.) of jet cooled NO2 molecules in emission from 11 different vibronic levels located between 22 006 and 23 625 cm−1 was recorded. The corresponding variety of Franck–Condon accesses has allowed the observation of the complete set of the 191 lowest vibrational levels of the X̃ 2A1 ground state, located up to 10 000 cm−1. The vibrational band origins were measured to within typically 0.3 cm−1, assigned (n1, n2, n3), and fitted with a 24 coefficient Dunham expansion giving a typical residual error of 0.5 cm−1. Furthermore, the vibrationless Ã 2B2 level has probably also been observed at 9737 cm−1. A perturbative model of the X̃ 2A1–Ã 2B2 vibronic interaction has been used in order to calculate the energy shift of the high vibrational levels (around 10 000 cm−1) of the X̃ 2A1 state.

Laser induced dispersed fluorescence spectra of jet cooled NO2: The complete set of vibrational levels up to 10000 cm−1 and the onset of the X2 A 1-A2 B 2 vibronic interaction J. Chem. Phys. 95, 5686 (1991); 10.1063/1.461617 Vibronic analysis of the A2 A 1-X2 E laserinduced fluorescence of jetcooled CH3S J. Chem. Phys. 95, 66 (1991); 10.1063/1.461786 Laser fluorescence excitation spectrum of jetcooled tropolone: The A1 B 2-X1 A 1 system zero point energy separation of7392 cm -1 and very recently Blahous et al. 14 have found an intermediate value of 8540

The visible excitation spectrum of jet cooled NO2: Statistical analysis of rovibronic interactions J. Chem. Phys. 103, 7740 (1995); 10.1063/1.470295 NO2 jet cooled visible excitation spectrum: Vibronic chaos induced by the X2 A 1-A2 B 2 interaction J. Chem. Phys. 95, 5701 (1991); 10.1063/1.461620Laser induced dispersed fluorescence spectra of jet cooled NO2: The complete set of vibrational levels up to 10 000 cm−1 and the onset of the X2 A 1-A2 B 2 vibronic interaction J. Chem. Phys. 95, 5686 (1991);We have observed a set of 350 2 B 2 vibronic levels of NO 2 in the 16 000-19 360 cm Ϫ1 energy range by the laser induced fluorescence ͑LIF͒ technique combined with a supersonic jet. This work extends ͑i.e., a larger energy range͒ and improves ͑i.e., a better detection threshold͒ our previous study ͓J. Chem. Phys. 95, 5701 ͑1991͔͒. 42 new 2 B 2 vibronic levels have been detected in this range where 159 vibronic levels were previously observed. In the 16 580-19 360 cm Ϫ1 energy range we estimate that the 315 observed levels represent 96% of the existing 2 B 2 levels. The correlation properties of this large and almost complete set of 315 2 B 2 vibronic levels have been analyzed. We present the next neighbor distribution, the ⌺ 2 (L), and ⌬ 3 (L) statistics, the Fourier transform ͑FT͒ of the stick spectrum with constant intensities ͉͑FT͉ 2 ͒, and the intensity distribution. The results of these analyses confirm the chaotic behavior of the 2 B 2 vibronic levels in this energy range: there are strong level repulsion, long range correlations and a Porter-Thomas intensity distribution. The correlation ''hole'' observed in the ͉FT͉ 2 of the stick vibronic spectrum is close to the one of the Gaussian orthogonal ensemble ͑GOE͒. However we have found a significant deviation from completely chaotic behavior ͑GOE type͒. Two peaks in the FT indicate recurrences ͑periods of 50 and 150 fs͒ i.e., periodic motions. We conclude that chaos is established within the 2 B 2 vibronic levels of NO 2 , after few hundred femtoseconds.