Lower Transition Pressure Research Articles

Classification of Pressure Range Based on the Characterization of Escherichia coli Cell Disruption in High Pressure Homogenizer

Problem statement: High pressure Homogenizer was used for cell disruption in many studies. But no work was carried out to study the characteristics of cell disruption in a wide range of pressure. Approach: The characteristics of Escherichia coli cell disruption was studied in Avestin small scale homogenizer by varying the operating pressure (50-1500 bar), cell concentration in the feed (1.39-12.51 g dry cell weight L-1) and number of passes (1-5 passes). Results: It was found that cell concentration between 1.39 g dry cell weight L-1 and 12.51 g dry cell weight L-1 has no effect on cell disruption while the pressure applied and number of passes gave different effects on cell disruption characteristics. In between 100 and 250 bar, the protein release was mainly due to point break. In this case, the variation in cell size was not significant with increasing number of passes and maximum protein release was not achieved even after many numbers of pass. However, selectivity of specific protein (interferon-α2b) was high as it is located predominantly in periplasmic region. In between 1000 and 1500 bar, the maximum protein release, maximum interferon-α2b release and drastic reduction of cell size was observed after the first pass. In subsequent passes, micronization of cell debris was observed but without much variation in protein release. There was no reduction in antigenicity of interferon-α2b even at 1500 bar. At 500 bar, the protein release and reduction of cell size were significantly increased with increasing number of passes. Conclusion: The pressure range for E. coli cell disruption was classified as low pressure range (100-250 bar), transition pressure (500 bar) and high pressure range (1000-1500 bar). The working pressure for the homogenizer could be selected by considering the operating cost and further downstream processing.

Pressure Induced Superconductivity inCaFe2As2

CaFe2As2 has been found to be exceptionally sensitive to the application of hydrostatic pressure and can be tuned to reveal all the salient features associated with FeAs superconductivity without introducing any disorder. The ambient pressure, 170 K, structural/magnetic, first-order phase transition is suppressed to 128 K by 3.5 kbar. At 5.5 kbar a new transition is detected at 104 K, increasing to above 300 K by 19 kbar. A low temperature, superconducting dome (T(c) approximately 12 K) is centered around 5 kbar, extending down to 2.3 kbar and up to 8.6 kbar. This superconducting phase appears to exist when the low pressure transition is suppressed sufficiently, but before the high pressure transition has reduced the resistivity too dramatically.

Lattice dynamics of wurtzite and rocksalt AlN under high pressure: Effect of compression on the crystal anisotropy of wurtzite-type semiconductors

Raman spectra of aluminum nitride (AlN) under pressure have been measured up to $25\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$, i.e., beyond the onset of the wurtzite-to-rocksalt phase transition around $20\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. The experimental pressure coefficients for all the Raman-active modes of the wurtzite phase are reported and compared to those obtained from ab initio lattice dynamical calculations, as well as to previous experimental and theoretical results. The pressure coefficients of all the Raman-active modes in wurtzite-type semiconductors (AlN, GaN, InN, ZnO, and BeO), as well as the relatively low bulk modulus and phase transition pressure in wurtzite AlN, are discussed in the light of the pressure dependence of the structural crystal anisotropy in wurtzite semiconductors. On pressure release, AlN partially returns to the wurtzite phase below $1.3\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ but the presence of a rocksalt phase in AlN was observed at pressures as low as $1.3\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$, as evidenced by comparing the experimental Raman spectra to calculated one- and two-phonon densities of states of the rocksalt phase.

Dynamically driven phase transformations in heterogeneous materials. I. Theory and microstructure considerations

A theoretical model recently developed for heterogeneous materials undergoing dynamically driven thermodynamic phase transitions [F. L. Addessio et al. J. Appl. Phys. 97, 083509 (2005)] has been extended to allow for complex material microstructures. The model is applied to silicon carbide—titanium (SiC–Ti) unidirectional metal matrix composites where the aligned SiC fibers are filler and Ti is the matrix. Ti is known to undergo a low pressure and temperature solid-solid first-order phase transition. The microstructural analysis uses the generalized method of cells, which partitions a representative volume element into subcells containing the SiC fibers and the Ti matrix. The thermomechanical analysis has been reformulated from the previous work. In the reformulation it is found that thermodynamic quantities are naturally expressed as mass fraction averages over the two coexisting phases while the mechanical quantities are expressed naturally as volume averages. Consequently, the thermomechanical reformulation merges the mass averages typically found in thermodynamics with the volume averages used for mechanical properties of composites. Simulations have been pursued to study the complex interplay between loading, microstructure, and the thermomechanical response of the system as it undergoes the solid-solid Ti phase transformation. This is done for several different representative volume elements. For different orientations of loads relative to the fiber axes, the effect of local microstructure on the macroscopic stress-strain and thermodynamic response of the SiC–Ti composite is investigated.

Electron-phonon coupling in high-pressure Nb

The Fermi surface, phonon spectrum, and electron-phonon coupling parameter for metallic Nb under high pressure have been investigated with a full potential linearized augmented plane wave, linear muffin-tin orbital, and pseudopotential plane-wave methods. The results support the experimental observation of electronic topological transitions at 5 and 60 GPa. The lower pressure transition is related to a very subtle change in the topology of the Fermi surface as revealed in accurate calculations of the Hall coefficient. The transition at 60 GPa is identified with a change in the Fermi-surface topology due to the crossing of the electronic band along the $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\Gamma}}N$ (\ensuremath{\Sigma}) direction in the cubic Brillouin zone. The calculated electron-phonon coupling parameters are in qualitative agreement with those derived from high-pressure experiment.

Electrical properties and phase transition of CoFe2O4 nanocrystals under pressure

The electric resistance CoFe2O4 nanocrystals of different sizes, obtained by the coprecipitation method was investigated under pressure up to 20 GPa in a diamond anvil cell at ambient temperature. The experimental results indicate that the phase transition (from the spinel to a tetragonal structure) takes place at 7.5 and 12.5 GPa for 6 and 80 nm, nanocrystals, respectively, in agreement with the prediction of scaling theory of the phase transition of nanocrystals. The relatively low transition pressure for CoFe2O4 is related to the high d-electron coupling between magnetic ions and to the small band gap in CoFe2O4 as compared to the other spinel ferrites. These results are discussed in terms of decreasing band gap with increasing pressure. The smaller the size of nanocrystals, the higher the phase transition pressure. The resistance of CoFe2O4 nanocrystal decreases exponentially under pressure, according to R∝exp(−CP), where C=0.7634 GPa−1 for large nanocrystals (80 nm) and C=0.5124 GPa−1 for CoFe2O4 of 6 nm.

Enhancing low pressure hydrogen storage in sodium alanates

We investigated the dehydrogenation of NaAlH4 and the reversible low-pressure rehydrogenation from NaH to Na3AlH6. Highly purified NaAlH4 requires relatively high temperatures to decompose to NaH and long durations to rehydride to the Na3AlH6 phase in hydrogen gas. However, any degradation of the purity of this material, whether through ball milling with diamond powder or ball milling with diamond plus Al powders, mixing the purified material with Pt powder, or doping with a Ti organometallic compound, lowers the decomposition temperature and facilitates rehydriding the product NaH+Al to Na3AlH6. Diamond ball milling of NaAlH4 seems to be the best of these procedures; it substantially decreases the decomposition temperatures, with significant dehydrogenation starting at 180°C rather than 250°C for the purified material, and with formation of NaH substantially complete at 235°C rather than 290°C. Rather surprisingly, it also facilitates rehydrogenation from NaH+Al to Na3AlH6. Similarly, NaAlH4 doped with Ti according to the recipe of Bogdanović lowers the decomposition temperatures and improves the hydrogenation kinetics for the low pressure transition from NaH+Al to Na3AlH6. Pressure–composition isotherms show that the rehydrogenation of the resulting NaH+Al decomposition phases into the Na3AlH6 intermediate phase at pressures below 3.6 MPa is similar for the diamond ball milled and Ti-doped material. Diamond ball milling NaAlH4 with excess Al did not improve the rehydrogenation kinetics.

Pressure induced structural transitions in nanocrystalline grained selenium

Using diamond anvil cell technique, energy-dispersive X-ray diffraction and Raman spectroscopy were employed to study pressure induced phase transitions in nanocrystalline selenium up to 30 GPa. A complex phase transition behavior was observed, with lower transition pressure and more phase transitions than in conventional coarse-grained Se. This is considered a new kind of pressure induced phase transition behavior for a nanocrystalline material.

Conformations of Short-Chain Poly(ethylene oxide) Lipopolymers at the Air−Water Interface: A Combined Film Balance and Surface Tension Study

The interfacial behavior of a short-chain poly(ethylene oxide) (PEO) lipopolymer, PEO (molecular weight 2000) grafted distearoylphosphatidylethanolamine (PEO2K-DSPE), and its mixtures with distearoylphosphatidylcholine (DSPC) have been studied using Langmuir film balance and surface tension methods. Surface pressure−area isotherms for pure PEO2K-DSPE and PEO2K-DSPE/DSPC mixtures (with 2, 5, 10, 15, or 20 mol % of PEO2K-DSPE) revealed two phase transitions. The simple additivity in the molecular area of lipid mixtures with increasing incorporation of PEO lipopolymer below the low-pressure transition indicates the existence of a two-dimensional thin layer of PEO and lipid. The low-pressure transition is interpreted as desorption of surface-adsorbed PEO molecules into the aqueous subphase. Correlation of film balance experiments with PEO lipopolymer and surface tension experiments with PEO aqueous solutions suggests dehydration of the PEO in the lipopolymer film by expulsion of PEO-associated water molecules as surface pressure increases. Theoretical models, based on scaling theories of polymers at interfaces, fit the observed isotherms well in the low-pressure regime below the first transition but poorly in the high-pressure regime above the first transition. The high-pressure transition is interpreted as ordering of lipid tails in lipopolymers, as driven by the enthalpic gain from lipid alignment and balanced by the entropic loss for lipid ordering and most importantly by dehydration of the PEO chains.

Polarization effects in the simulation of lead (II) fluoride

An interionic potential to describe the interactions in PbF2 is constructed from ab initio calculations. The potential is based upon formal ionic charges and includes polarization effects arising from the induced dipoles on both anions and cations. The cation polarization effects are shown to be crucial to explain observable differences between PbF2 and alkaline-earth fluorides of comparable cation size (SrF2 and BaF2). In particular, the lower transition pressure between the - (fluorite) and - (cotunnite) phases and the qualitative difference between the shapes of the phonon dispersion for PbF2 and the alkaline earths are reproduced. Simulations show a transition to a superionic conducting state in the -phase, though at a temperature slightly higher than that observed experimentally. No ionic conduction is observed in the -phase at comparable temperatures, in agreement with experiment. The pattern of diffuse neutron scattering predicted by the simulations in the superionic domain is shown to reproduce the distinctive distribution of intensity observed experimentally.

The low-pressure transition from diffusion-controlled to multipacting gas breakdown

The transition region from diffusion-controlled to multipacting discharge conditions in a parallel geometry, when the gas pressure is decreased and attains values below the so-called mean-free-path limit, is investigated using a Monte Carlo simulation technique. An ideal gas, without excitation states at energies below the ionization level and with a velocity-independent electron-molecule collision frequency, is considered. The results are plotted as breakdown voltages, properly normalized to the electron energy for which the secondary-electron emission yield of the electrodes is unity, vs. the gas pressure, given as the ratio of the electron collision frequency over the applied electric field frequency. Curves for various sets of dimensionless variables, representing size, electrode and gas parameters, are given and interpreted in terms of the changing relative importance of electron collisions with gas molecules and with electrodes, when the gas pressure is decreased and vacuum conditions are approached.

Electronic structure of cerium in the self-interaction corrected local spin density approximation

The electronic structure of cerium is calculated in the self-interaction corrected, local spin density approximation. In this formalism the electronic eigenstates may be described as either localized or delocalized. Two competing local minima of the total energy functional are found. The \ensuremath{\gamma} phase is found to be excellently described with one f electron per atom being localized. In contrast, the \ensuremath{\alpha} phase is best described with delocalized f electrons. The total energy is approximately equal in the two phases allowing for a low-pressure transition between them in accordance with experiment.

A high pressure Raman study of KTP and pressure induced phase transitions

Potassium titanate orthrophosphate KTiOPO 4 (KTP) has been studied by high pressure Raman technique to 17 GPa using a diamond cell. The Raman data reveal that two phase transitions occur in the system: one near 5.5 GPa and another near 10 GPa. The Lower-pressure transition is definitely first-order but appears to be driven by the phonon mode near 56 cm −1, which exhibits marked softening. A mean field-like behavior is observed. It is hypothesized that this transition is likely to be from ferroelectric (FE) to an antiferroelectric (AF) phase. The 10 GPa transition may be due to AF-PE (paraelectric) transition driven by pressure from high temperature to room temperature. From the larger pressure responce of the PO 4 vibrational modes it is believed that the PO 4 polyhedral compression is larger than the TiO 6 polyhedral compression. leading to polyhedral tilt transitions.

Laser Induced Osmosis

AbstractPressure transients are observed in absorbing gases at low pressure in a non‐resonant spectrophone. At very low pressure (transition saturated) the transient is negative on irradiation. Interpretation is given in terms of thermodynamics of laser driven systems. The local value of the partition function of resonant molecules is shwon to be a function of the driving beam's intensity. The law of mass action predicts then accumulation of the resonant particles in the high intensity regions of the beam.

The mechanical properties of PVC under high pressure

The deformation properties of PVC have been studied under high pressure. Craze initiation and yield criteria have been proposed. The brittle-to-ductile transition was observed between 1×107 and 2×107 Pa, which is a relatively low transition pressure compared to polystyrene. Deformation in the post-yield region occurred by neck formation and subsequent drawing to produce chain orientation. When PVC was exposed to the pressure-transmitting fluid, silicon oil, a strong environmental stress cracking effect was observed.

Shock compression data for liquids. III. Substituted methane compounds, ethylene glycol, glycerol, and ammonia

Hugoniot data are presented for the liquid forms of the substituted methanes—dichloromethane, dibromomethane, di-iodomethane, and chloroform—ethylene glycol, glycerol, and ammonia. High explosive techniques were used to cover the range of dynamic pressures of 0.7 to 82.0 GPa. Chloroform transforms to a new form at 25.0 GPa pressure. Di-iodomethane data indicate a low pressure transition at 2.3 GPa and a second transition at a pressure greater than 66.0 GPa. The shock velocity–particle velocity (Us–Up) data for these two liquids are best represented by a linear relationship over the various forms. The Us–Up data for dichloromethane, dibromomethane, ethylene glycol, and glycerol are best fit by a quadratic expression in Up. Ammonia Us–Up data fit a linear relationship. Only dibromonethane and ammonia Us–Up curves extrapolate to the known sound speed. The others intercept at values that are 13% to 33% higher than the measured sound speed, indicative of low pressure transitions.

A method for determining a solid solution of the Pb(Hf1−yZry)1−xTixO3 type used for electromechanical energy conversion

The mechanical stress-forced Ferroelectric F→Antiferroelectric AF transition energy conversion is reviewed. The temperature-composition phase diagram of PbHf1−xTixO3+1%La2O3 is established. The composition of a suitable material such as a ternary solid solution of the Pb(Hf1−yZry)1−xTixO3+1%La2O3 type, characterized by a low transition pressure, is theoretically determined by a graphic construction using the Goldschmidt factor. Experimental results on the prepared material are given.

Equations of state of FeO and CaO

New shock-wave (Hugoniot) and release-adiabatic data for Fe_(0.94)O and CaO, to 230 and 175 GPa (2.3 and 1.75 Mbar) respectively, show that both oxides transform from their initial B1 (NaCl-type) structures at about 70 (±10) GPa. CaO transforms to the B2 (CsCl-type) structure and FeO is inferred to do the same. Alternatively, FeO may undergo an electronic transition, but it probably does not disproportionate under shock to Fe and Fe_2O_3 or Fe_3O_4. The Hugoniot data for the B1 phases of FeO and CaO agree with the ultrasonically-determined bulk moduli (K_0= 185, 112 GPa, respectively) and with the ultrasonically-determined pressure derivative for CaO (K′_0= 4.8); K′_0∼ 3.2 for FeO is determined from the present data. The Hugoniot data for both FeO and CaO are consistent with low- and high-pressure phases having identical K_0 and K′_0. Volume changes for B1/B2 transitions in oxides agree with theoretical expectations and with trends among the halides: -ΔV/V_1 ~ 4 per cent and 11 per cent for FeO and CaO respectively. Also, the transition pressures increase with decreasing cation/anion radius ratio for the oxides. The Hugoniot data show that the density of the outer core is equal to that of a 50–50 mix (by weight) of Fe and FeO (∼10 wt per cent oxygen), consistent with geochemical arguments for the presence of oxygen in the core. In terms of a mixture of simple oxides, the density of the lower mantle is satisfied by Fe/(Mg + Fe) ∼ 0.12, however, arbitrarily large amounts of CaO can be present; an enrichment of refractory components in the lower mantle is allowed by the shock-wave data. Because of the relatively low transition pressure in FeO, a B1/B2 transition in (Mg, Fe)O is likely to occur in the lower mantle even if MgO transforms at 150–170 GPa. Such a transition may contribute to the scattering of seismic waves and change in velocity gradient found near the base of the mantle.

Flow in capillary systems: II. Low pressure transition flow of gases in short capillaries, rectangular slits, beds of spheres and parallel capillary bundles

The permeability equation for the transition from molecular to viscous flow in long cylinders has been modified to include any system. The general equation contains geometry-dependent correction factors which can be applied to the viscous, slip and molecular flow terms separately. It is found that the Knudsen permeability minimum is influenced by all three contributions to the total flow. In short cylinders the minimum disappears at a length to radius ratio of about 15, but can reappear in very short sections. Agreement with available experimental data is moderately good. Very deep minima are predicted for rectangular slits in accord with Gaede's (1913) results, while a slight downward curvature to the pressure axis is predicted for beds of uniform spheres. Equations for transition flow in parallel bundles of long cylinders with a Poisson or Gaussian radius distribution are derived, and it appears that at no radius distribution does the minimum vanish, although considerable distortions in this region are possible.

Transitions and phases of polytetrafluoroethylene (teflon)

Transitions in polyfluoroethylene (Teflon) have been studied as a function of pressure and temperature. A high-pressure transition (5, 000 atm) and a lower pressure transition were studied. These are believed to result from three polymorphic forms. The pressure of the high-pressure transition decreases and that of the low-pressure transition increases with increasing temperature. A triple point is indicated at approximately 70° C, and a third equilibrium line is found to proceed to higher pressures with increasing temperature from this point. Experimental errors involved render tests of all thermodynamic conditions at the triple point indeterminate.