Search results for "Hydrostatic pressure"

Effect of Combined Physical Stresses on Cells: The Role of Water

2010

International audience; The role of water in microorganism viability was assessed through the application of combined physical perturbations. The combination of different physical parameters could allow to balance the properties variations (especially water related) resulting from the increase of one parameter alone. Thus, it is possible to optimize the survival of cells in controlling these parameters. This was tested through two different examples. The first example shows that combination of osmotic level and temperature can allow optimizing yeast cell survival in following membrane fluidity variation. Moreover this analysis has allowed a better comprehension of cell inactivation during r…

Spectroscopic and quantum chemical study of pressure effects on solvated chlorophyll

2004

Abstract Hydrostatic pressure effects up to 907 MPa on absorption spectra of chlorophyll a molecules dissolved in diethyl ether have been studied at ambient temperature both experimentally and theoretically using quantum chemistry methods. The fluorescence spectra are studied only experimentally. The data suggest that coordination interactions between the central Mg atom of the chlorophyll and solvent molecules along with interactions that modify the porphyrin skeleton of the solute are responsible for the observed differences of pressure dependence of the Q y , Q x , and Soret spectral bands. The coordination number of the Mg atom changes from five to six between 400 and 600 MPa.

Prevention of ventricular catheter obstruction and slit ventricle syndrome by the prophylactic use of the Integra antisiphon device in shunt therapy …

2010

Object This 25-year follow-up study was performed on 120 children with hypertensive hydrocephalus to evaluate the influence of the early prophylactic implantation of the Integra antisiphon device (ASD, Integra Neurosciences Ltd.) on the rate of proximal shunt obstructions and the frequency of symptomatic slit ventricle syndrome (SVS). The adaptability of the ASD to growth, proper positioning of the ASD as a necessity for its successful performance, and the 3 phases of SVS development are discussed. Method Since 1978, the ASD has consistently been implanted either at the time of primary shunt insertion (66 neonates, mean follow-up 11 years) or during revisions of preexisting shunts (54 chil…

Evaluation of urodynamic studies by computer

1978

In an attempt to simplify urodynamic evaluation, the data obtained from cystometry, urethral profile and flowmetry were analysed using the ICS recommendations for standardization and terminology. All studies were compiled from check lists feasible for computation. The aim was to establish standards and "typical" changes for the normal bladder and pathological states to enable automatic readout of computed data. The results did, in fact, show "typical" changes but failed to establish standard measurements suitable for completely computed diagnoses.

Effects of hydrostatic pressure on the thermoelectric properties of the ϵ-polytype of InSe, GaSe, and InGaSe2 semiconductor compounds: anab initiostu…

2017

Nonlinear mode coupling in a birefringent microstructured fiber tuned by externally applied hydrostatic pressure

2015

We studied the effect of power coupling between two linearly polarized modes, which occurs during nonlinear propagation in an externally tuned birefringent microstructured fiber. We investigated both experimentally and numerically the possibility of measuring hydrostatic pressure by tracking the nonlinear power coupling between the fiber polarization modes. We analyzed the impact of the fiber length exposed to pressure and the input polarization state on the coupling efficiency. We also revealed that the observation of nonlinear power coupling between the polarization modes is limited by linear coupling occurring in the leadthroughs to the pressure chamber. Moreover, we demonstrated that th…

Effect of pressure on structural properties and energy band gaps of γ-InSe

2003

We have investigated theoretically the effect of hydrostatic pressure on interatomic bond lengths and energy band gaps of γ-InSe. Total energy calculations were performed using the linear augmented plane wave (LAPW) method, taking into account scalar relativistic corrections as well as spin-orbit coupling. Internal structural parameters were optimized for different pressures by adopting as input the unit cell parameters known from experiment. Our theoretical results for the nearest-neighbor In-Se bond length are in excellent agreement with a recent experimental determination from high-pressure EXAFS measurements. The covalent In-In bond is found to be more compressible than the partially io…

Zinc-blende AlN and GaN under pressure: structural, electronic, elastic and piezoelectric properties

2004

In this paper we report a theoretical study of the structural, elastic, electronic and piezoelectric properties of zinc-blende AlN and GaN under the pressure effect. The study is focused on the first-principles all electron full-potential augmented plane wave plus local orbitals calculations within the density-functional theory. The results of bulk properties, including lattice constants, bulk modulus and derivatives and band structures are obtained and compared using both the local density approximation (LDA) and the generalized gradient approximation (GGA) for the exchange-correlation functional. We find that the GGA does not give a significant improvement over LDA. We also report calcula…

High-pressure structural study of the scheelite tungstatesCaWO4andSrWO4

2005

Angle-dispersive x-ray-diffraction and x-ray-absorption near-edge structure measurements have been performed on ${\mathrm{CaWO}}_{4}$ and ${\mathrm{SrWO}}_{4}$ up to pressures of approximately 20 GPa. Both materials display similar behavior in the range of pressures investigated in our experiments. As in the previously reported case of ${\mathrm{CaWO}}_{4}$, under hydrostatic conditions ${\mathrm{SrWO}}_{4}$ undergoes a pressure-induced scheelite-to-fergusonite transition around 10 GPa. Our experimental results are compared to those found in the literature and are further supported by ab initio total-energy calculations, from which we also predict the instability at larger pressures of the …

Measurement of brain tissue pressure in cold induced cerebral oedema.

1973

Experiments were performed in order to evaluate the concept that brain oedema is associated with an increase in local interstitial fluid pressure. Assuming that the pressure measured by the cotton wick technique represents the hydrostatic interstitial fluid pressure, the tissue pressure was recorded with pressure transducers in the white matter adjacent and remote to a local cold injury, in the opposite hemisphere, and in the cisterna magna. In 9 cats during steady-state conditions mean tissue pressures between 1.20±0.30 mm Hg and 2.33±0.80 mm Hg were found, as compared to a mean CSF pressure of 5.17±0.82 mm Hg. The tissue pressure was found to increase significantly adjacent to the lesion …