Rt-PA thrombolytic therapy in patients with acute posterior circulation stroke: A retrospective study.

At present, recombinant tissue-type plasminogen activator (rt-PA) thrombolytic therapy is widely used in patients with acute ischemic stroke within 4.5 h following stroke onset. However, the efficacy of intravenous alteplase thrombolytic therapy for posterior circulation stroke (PCS) has been rarely described. The present study aimed to predict the outcome of patients with PCS following rt-PA thrombolytic therapy in a more efficient manner. Data were collected from patients who had suffered from posterior circulation ischemic stroke, who had been treated with rt-PA over a period of 4 years (2016-2020), and had been treated at a stroke center. All patients were treated with alteplase at a standard dose of 0.9 mg/kg. According to the onset to needle time (ONT), these patients were divided into the 0-3 and 3-4.5 h groups, and the National Institutes of Health Stroke Scale (NIHSS) score was compared before thrombolysis and at 24 h after thrombolysis. Subsequently, the patients with acute PCS whose ONT was ≤3 h were divided into the NIHSS score >3 points and NIHSS score ≤3 points groups, and the NIHSS score improvement rate was compared 24 h later. A total of 989 patients were included in the study; there were 783 patients with acute anterior circulation stroke (ACS) and 203 patients with acute PCS (of note, 2 patients had negative results from brain magnetic resonance imaging); 63 patients were treated with urokinase (UK) thrombolysis and 140 patients were treated with alteplase intravenous thrombolysis. The 140 patients that received alteplase thrombolytic therapy were divided into two groups, namely the ≤3 h group and 3-4.5 h group, which, on the basis of the ONT, no significant differences were found between the two the groups according to the NIHSS score before thrombolysis (P>0.05). The NHISS scores in the ≤3 h group were significantly lower than those in the 3-4.5 h group following thrombolysis therapy, and the differences between the two groups were statistically significant (P<0.05); the patients with acute PCS treated with rt-PA in the ≤3 h group were divided into the NIHSS score ≤3 points group and the NIHSS score >3 points group. In this ≤3 h group, the average NIHSS score improvement rate following rt-PA thrombolysis was 0.535 (53.5%) in the NIHSS score ≤3 points group and that in the NIHSS score >3 points group was 0.336 (33.6%); the difference between the two groups was statistically significant (P<0.05). The patients treated with intravenous alteplase thrombolysis within 3 h following stroke onset benefited more than those treated with thrombolysis therapy within 3 to 4.5 h after stroke onset. On the whole, the present study demonstrates that the patients with mild stroke (NIHSS score ≤3 points) who were treated at an earlier stage (received alteplase thrombolysis therapy within 3 h after stroke onset) benefited to a greater extent from the therapy.

A method for isotope exchange kinetics in mineral-water system-an in-situ study on oxygen isotope exchange in Na2CO3-H2O system.

The experiments on the exchange reaction rate of the oxygen isotopes in the mineral-water system with initial conditions of 100 °C and 240 MPa, 100 °C and 924 MPa, 118 °C and 170 MPa are taken. The oxygen isotope 18O exchange reactions between aqueous C16O32- and H218O are mainly traced by measuring the Raman peak intensity of oxygen-containing elements (CO32-) in sodium carbonate solution. The inconsistent trends between the molar fraction and the concentration of C18O216O2- indicate oxygen isotope exchange between sodium carbonate and heavy water accompanied by dissolution and recrystallization between supersaturated sodium carbonate solution and solid sodium carbonate. In the heterogeneous experimental systems the order of oxygen isotope exchange reactions are more than 1 and the dynamics of oxygen isotope exchange conform to JMAK kinetics model with the nucleation and growth processes of sodium carbonate crystal.

Stability of copper acetate at high P-T and the role of organic acids and CO2 in metallic mineralization.

Many metal deposits were formed by carbonic fluids (rich in CO2) as indicated by fluid inclusions in minerals, but the precise role of CO2 in metal mineralization remains unclear. The main components in fluid inclusions, i.e. H2O and CO2, correspond to the decomposed products of organic acids, which lead us to consider that in the mineralization process the organic acids transport and then discharge metals when they are stable and unstable, respectively. Here we show that the thermal stability of copper acetate solution at 15-350 °C (0.1-830 MPa) provides insight as to the role of organic acids in metal transport. Results show that the copper acetate solution is stable at high P-T conditions under low geothermal gradient of <19 °C/km, with an isochore of P = 1.89 T + 128.58, verifying the possibility of copper transportation as acetate solution. Increasing geothermal gradient leads to thermal dissociation of copper acetate in the way of 4Cu(CH3 COO)2 + 2H2O = 4Cu + 2CO2 + 7CH3COOH. The experimental results and inferences in this contribution agree well with the frequently observed fluid inclusions and wall-rock alterations of carbonate, sericite and quartz in hydrothermal deposits, and provide a new dimension in the understanding of the role of CO2 during mineralization.

An experimental investigation of n-hexane at high temperature and pressure.

At present, no high temperature experiments on phase change are reported. In this study, we have measured the Raman bands νs(CH3), νs(CH2), νas(CH3), and νas(CH2) of n-hexane in a hydrothermal diamond cell up to 588 K. We determined that the liquid-solid phase transition pressure of n-hexane is 1.17 GPa, and we also gave a number of high temperatures and pressures data on phase change which are not reported previously. In addition, we defined the solidus of n-hexane which can be represented by the equation P = 8.581T-1550.16, and the relation dP/dT = 8.581 which can be used to calculate the thermodynamic parameters for n-hexane in the liquid-solid phase transition. For all we know, the above two equations are presented here for the first time. Furthermore, it is the first report here in a graphic way on high-temperature phase change in n-hexane, and it is also the first to be shown in the 3-D figure.

An in-situ Raman study on pristane at high pressure and ambient temperature.

The CH Raman spectroscopic band (2800-3000cm-1) of pristane was measured in a diamond anvil cell at 1.1-1532MPa and ambient temperature. Three models are used for the peak-fitting of this CH Raman band, and the linear correlations between pressure and corresponding peak positions are calculated as well. The results demonstrate that 1) the number of peaks that one chooses to fit the spectrum affects the results, which indicates that the application of the spectroscopic barometry with a function group of organic matters suffers significant limitations; and 2) the linear correlation between pressure and fitted peak positions from one-peak model is more superior than that from multiple-peak model, meanwhile the standard error of the latter is much higher than that of the former. It indicates that the Raman shift of CH band fitted with one-peak model, which could be treated as a spectroscopic barometry, is more realistic in mixture systems than the traditional strategy which uses the Raman characteristic shift of one function group.

Raman spectroscopic study of cyclohexane at pressures below 1000MPa.

At present, the room temperature freezing pressure of cyclohexane is still uncertain, and the phase transition pressure of solid I - solid III is not reliable at ambient temperature. In this work, we have performed a Raman spectroscopic study of cyclohexane in a Moissanite anvil cell at pressures below 1000MPa at 25°C, and analyzed the characteristic of Raman brands νs(CH2), νas(CH2) and νb(Ring). Two phase transition pressures 80MPa and 550MPa were determined by a quartz pressure gauge, and they are the room temperature freezing pressure of cyclohexane and the phase transition pressure of solid I to solid III, respectively. Furthermore, from the phase diagram of cyclohexane, it is inferred that pressure plays an important role on the stability of cyclohexane as the main constituent of oil, and it can be beneficial to understanding the formation, migration and preservation of petroleum in subterranean rock strata.

The influence of ionic strength on carbonate-based spectroscopic barometry for aqueous fluids: an in-situ Raman study on Na2CO3-NaCl solutions.

The Raman wavenumber of the symmetric stretching vibration of carbonate ion (ν1-CO32-) was measured in three aqueous solutions containing 2.0 mol·L-1 Na2CO3 and 0.20, 0.42, or 0.92 mol·L-1 NaCl, respectively, from 122 to 1538 MPa at 22 °C using a moissanite anvil cell. The ν1 Raman signal linearly shifted to higher wavenumbers with increasing pressure. Most importantly, the slope of ν1-CO32- Raman frequency shift (∂ν1/∂P)I was independent of NaCl concentration. Moreover, elevated ionic strength was found to shift the apparent outline of the carbonate peak toward low wavenumbers, possibly by increasing the proportion of the contact ion pair NaCO3-. Further investigations revealed no cross-interaction between the pressure effect and the ionic strength effect on the Raman spectra, possibly because the distribution of different ion-pair species in the carbonate equilibrium was largely pressure-independent. These results suggested that the ionic strength should be incorporated as an additional constraint for measuring the internal pressure of various solution-based systems. Combining the ν1-CO32- Raman frequency slope with the pressure herein with the values for the temperature or the ionic strength dependencies determined from previous studies, we developed an empirical equation that can be used to estimate the pressure of carbonate-bearing aqueous solutions.

In Situ Raman Spectroscopic Study of Barite as a Pressure Gauge Using a Hydrothermal Diamond Anvil Cell.

In situ Raman measurements of barite were performed at temperatures in the range of 298-673 K and pressures in the range of 105-1217 MPa using a hydrothermal diamond anvil cell combined with laser Raman spectroscopy. The Raman frequency and the full width at half maximum (FWHM) of the most intense ν1 Raman peak for barite as a function of pressure and temperature were obtained. In the experimental P-T ranges, the ν1Raman band systematically shifted toward low wavenumbers with increasing pressure and temperature. The positive pressure dependence of ν1Raman frequency indicates stress-induced shortening of the S-O bond, whereas the negative temperature dependence shows temperature-induced expansion of the S-O bond. In contrast, the observed ν1Raman band became broadened, which should be attributed to the reduced ordering of molecular structure. Based on the obtained data, the established relationships among the Raman shift or the FWHM, pressure and temperature can be used to obtain good estimates of the internal pressure in natural barite-bearing fluid inclusions or hydrothermal diamond anvil cell. This is a sensitive and reliable approach to the accurate determination of geological pressure.

[A Simple but Effective Device to Avoid Objective Lens Overheating: An Air Blower Device].

The interior of the Earth is a high temperature and high pressure environment. High temperatures cause important changes in the physical and chemical properties of minerals. An increase in temperature leads to significant changes in the molecular and lattice vibrations, elasticity, and seismic velocity of minerals. The high temperature vibrational spectroscopy (infrared and Raman) used to study these changes can provide highly significant understanding of the Earth's interior. During high temperature spectroscopy, the heating device that is used to heat the sample can work at a very high temperature (e.g., 1 500 ℃) because it has a cooling device surrounding it that is used to prevent the temperature of its environments from getting too high. However, radiation from its heating elements is intense and this will shine on and heat the objective lens of the focusing system for the spectroscopic light source, and this would result in damage to the lens. Thus, to avoid damage to the objective lens, an upper limit is placed on the heater temperature. The significance of this work is that it presents a method to exceed the present instrument's temperature limit so that we can perform in situ spectroscopy on samples at higher temperatures. This work extended the temperature limit for the sample to a higher temperature by using an air blower around the objective lens to create a gas flow around it. The gas flow serves to remove heat from the objective lens by forced convection and its turbulent flow also served to increase the rate of heat transport from the lens to the moving gas stream, which together prevented overheating of the objective lens. Our results have shown that although this device is simple, it was highly effective: for a sample temperature of 1 000 ℃, the objective lens temperature was reduced from ～235 to ～68 ℃. Using this device, we performed in situ high temperature Raman spectroscopy of forsterite up to a sample temperature of 1 300 ℃. The results agreed well with previous studies and demonstrated that with our simple air blower device, we can perform in situ high temperature spectroscopy up to 1 300 ℃ without damaging the objective lens and without expensive components like a high temperature composite objective lens or a long focus objective lens.

[Raman Spectroscopic Study on the Determination of SO4(2-) Concentration in Aqueous Solution under High Temperature and Pressure].

In the present work, the Raman spectra of SO4(2-) ions in aqueous solutions were studied. The quantitative analysis shows that there is a significant correlation between the Raman intensity ratio(R) and the SO4(2-) concentration. The SO4(2-) concentration in aqueous solution at ambient temperature and pressure can be determined by the Raman intensity according to the linear fitting equation c (SO4(2-) = 4.779 6R (r2 = 0.999 4). Furthermore, the research proves that the temperature and pressure will af- fect the relationship between the Raman intensity ratio and the concentration of SO4(2-) ions. The quantitative equation for measur- ing the SO4(2-) concentration in aqueous solution at high temperature and high pressure is c(SO4(2-)) = 4.779 6(R + 1.469 x 10(-4)ΔT + 1.340 x 10(-4)ΔP), where R is defined as the ratio of the SO4(2-) ions band intensity to the OH stretching single band intensity, T is the temperature relative to 23 °C, ΔP is the pressure relative to 0.1 MPa, 23 °C ≤ T ≤ 390 °C, the concentration range of the SO4(2-) ions is 0.5-1.5 mol · L(-1), and the uncertainty of the equation is 6.5%. Raman spectroscopy can be used to measure the concentration of the Raman-active species in aqueous solutions.

Raman spectroscopic quantitative study of NaCl-CaCl2-H2O system at high temperatures and pressures.

Raman spectra features of the ternary system NaCl-CaCl2-H2O under high temperatures and high pressures were systematically studied in the present work by using hydrothermal diamond anvil cell (HDAC) and Raman shifts of quartz to determine pressures, and it has been obtained for the quantitative relationship between Raman shifts of the O-H stretching band of water, mass fractions of solutes and pressures was obtained. The mass fractions of salts, where salinity of NaCl equal to that of CaCl2, are 4.0 mass %, 8.0 mass %, and 12.0 mass %, respectively. Experimental results indicate that the standardized Raman frequency shift differences of the O-H stretching vibration (deltav(O0H)) rise with the increasing temperatures when the mass fractions of salts and pressures of the NaCl-CaCl2-H2O system remain constant. deltav(O-H) increases with the increase in mass fractions of salts in the system when the temperatures and pressures are constant. Linear relationship between deltav(O-H) and pressure with similar slopes can be found for the NaCl-CaCl2-H2O system with different salinities. The quantitative relationship between deltav(O-H), temperature (T), pressure (P), and mass fraction of solute (M) is P = -31.892 deltav(O-H) + 10.131T + 222.816M - 3 183.567, where the valid PTM range of the equation is 200 MPa < or = P < or = 1 700 MPa, 273 K < or = T < or = 539 K and M < or = 12 mass %. The equation can be used as a geobarometer in the studies of fluid inclusions of NaCl-CaCl2-H2O system with equal salinities. The method, as a direct geological detecting technique, has a potential application value.

[Research on Raman spectra of chalcopyrite under 0-1400 MPa and ambient temperature].

The variation characters of the A1 mode Raman spectra of chalcopyrite under 0.1-1400 MPa and ambient temperature were researched using diamond anvil cell. The results show that the shape and intensity of the Raman peak remains constant under experimental conditions, indicating that the chemical bounds of Cu-S and Fe-S remain unchanged. The authors have also noticed that the position of the Raman peak shifts to higher frequency with increasing pressure, which could be described as: nu(290) = 0.031 2p + 290.60 (0.1< or =p<58.8 MPa) and nu(290) = 0.00572p+292.10 (58.8 < or =p<1400 MPa). The rate of the Raman peak shifting with increasing pressure changed abruptly at about 58.8 MPa, the d(nu)/dp is 31.2 and 5.72 cm(-1) x GPa(-1) below and above 58.8 MPa respectively, which perhaps indicate that some structural changes occurred in the chalcopyrite.

Determination of the internal pressure of fluid inclusions by using Raman spectroscopy.

In situ Raman spectroscopic measurements of H2O-NaCl systems with three different salinities (0, 5.0, and 10.0 wt% NaCl) in the region of O-H stretching vibration were obtained at pressures up to 1800 MPa and temperatures from 298 to 453 K, with a hydrothermal diamond-anvil cell. The peak position was determined by fitting the obtained O-H stretching band with one Gaussian component. At a given temperature, the shift of the band decreased systematically with increasing pressure, and the data show a good linear relationship. For systems of different salinity, the slopes of the isotherms seem to be independent of temperature under the conditions investigated. With increasing salinity, the slope of the isotherm gradually increases. The relationships measured for the shift of the O-H stretching band with temperature, salinity, and pressure can be used to determine the internal pressure and isochore of fluid inclusions as well as the formation temperature and pressure of host minerals.

[Research on Raman spectra of oxalic acid during decarboxylation under high temperature and high pressure].

The present research studied the thermal stability of oxalic acid under high temperature and pressure and its in-situ transformation by Raman spectroscopy using a hydrothermal diamond anvil cell. Raman spectra allow the detection of ionic and covalent atomic aggregates through the acquisition of vibrational spectra that are characteristic of their structures and molecular bond types. The result showed that there was no change in characteristic vibrational Raman peaks of oxalic acid in the low-temperature stage. With the increase in temperature and pressure, the characteristic vibrational Raman peaks of oxalic acid became weaker and the peaks disappeared at a certain high temperature, and decarboxylation happened. Oxalic acid decomposes to produce CO2 and H2, according to the reaction: C2 H2O4-2CO2 + H2. It was found that the decarboxylation was highly related with pressure and that the decarboxylation would be hindered at high pressure. Decarboxylation of oxalic acid under high temperature and pressure showed a linear relationship between temperature and pressure. The data fitting generated the formula: P(MPa) = 12. 839T(K)-5 953.7, R2 = 0.99. The molar volume change of decarboxylation of oxalic acid can be described by deltaV(cm(-3) x mol(-1)) = 16.69-0.002P (MPa) + 0.005 2T(K), R = 0.99.

[Raman spectroscopic study on the fluid effects in dissolution and phase transition mechanisms of gypsum].

Raman spectroscopic studies on the process of dissolution and phase transition of gypsum in different fluids were taken. Gypsum took phase transition to be anhydrite in the range from 170 degrees C to 190 degrees C in pure water, and no more change happened with decreasing temperature to room temperature. Gypsum took phase transition to be anhydrite in the range from 170 degrees C to 190 degrees C too in Na2 SO4 solution, but anhydrite can regain to be gypsum when temperature decreases to room temperature. The process of phase transition of gypsum in pure water is not reversible, but it happens in Na2 SO4 solution. The study shows that fluid effects can influence the dissolution and phase transition mechanisms of minerals and cannot be ignored.

[Research on Raman spectra of isooctane at ambient temperature and ambient pressure to 1. 2 GPa].

The experimental study of the Raman spectral character for liquid isooctane (2,2,4-trimethylpentane, ATM) was con ducted by moissanite anvil cell at the pressure of 0-1.2 GPa and the ambient temperature. The results show that the Raman peaks of the C-H stretching vibration shift to higher frenquencies with increasing pressures. The relations between the system pressure and peaks positions is given as following: v2 873 = 0.002 8P+2 873.3; v2 905 = 0.004 8P+2 905.4; v2 935 = 0.002 7P+ 2 935.0; v2 960 = 0.012P+2 960.9. The Raman spectra of isooctane abruptly changed at the pressure about 1.0 GPa and the liquid-solid phase transition was observed by microscope. With the freezing pressure at ambient temperature and the melting temperature available at 1 atm, the authors got the liquid-solid phase diagram of isooctane. According to Clapeyron equation, the authors obtained the differences of volume and entropy for the liquid-solid phase transition of isooctane: deltaV(m) = 4.46 x 10(-6) m3 x mol-1 and deltaS = -30.32 J x K(-1) x mol(-1).

[In situ experimental study of phase transition of calcite by Raman spectroscopy at high temperature and high pressure].

The phase transitions of calcite at high temperature and high pressure were investigated by using hydrothermal diamond anvil cell combined with Raman spectroscopy. The result showed that the Raman peak of 155 cm(-1) disappeared, the peak of 1 087 cm(-1) splited into 1083 and 1 090 cm(-1) peaks and the peak of 282 cm(-1) abruptly reduced to 231 cm(-1) at ambient temperature when the system pressure increased to 1 666 and 2 127 MPa respectively, which proved that calcite transformed to calcite-II and calcite-III. In the heating process at the initial pressure of 2 761 MPa and below 171 degrees C, there was no change in Raman characteristic peaks of calcite-III. As the temperature increased to 171 degrees C, the color of calcite crystal became opaque completely and the symmetric stretching vibration peak of 1 087 cm(-1), in-plane bending vibration peak of 713 cm(-1) and lattice vibration peaks of 155 and 282 cm(-1) began to mutate, showing that the calcite-III transformed to a new phase of calcium carbonate at the moment. When the temperature dropped to room temperature, this new phase remained stable all along. It also indicated that the process of phase transformation from calcite to the new phase of calcium carbonate was irreversible. The equation of phase transition between calcite-III and new phase of calcium carbonate can be determined by P(MPa) = 9.09T x (degrees C) +1 880. The slopes of the Raman peak (v1 087) of symmetrical stretching vibration depending on pressure and temperature are dv/dP = 5.1 (cm(-1) x GPa(-1)) and dv/dT = -0.055 3(cm(-1) x degrees C(-1)), respectively.

In situ high-pressure and high-temperature experiments on n-heptane.

The Raman spectroscopy of n-heptane was investigated in a moissanite anvil cell at ambient temperatures and a diamond anvil cell under pressures of up to ~2000 MPa and at temperature range from 298 to 588 K. The results show that at room temperature the vibration modes, assigned to the symmetric and antisymmetric stretching of CH(3) and CH(2) stretching, shifted to higher frequency according to quasi-linearity with increasing pressure, and a liquid-solid phase transition occurred at near 1150 MPa. The high-temperature solidus line of n-heptane follows a quadratic function of P = 0.00737T(2) + 5.27977T - 1195.76556. Upon phase change, fitting the experimental data obtained in the temperature range of 183∼412 K to the Clausius-Clapeyron equation allows one to define the thermodynamic parameters of n-heptane of dP/dT = 0.01474T + 5.27977.

[Research on Raman spectra of calcite phase transition at high pressure].

The present research studied the process of phase transition from calcite-I to calcite-III under the condition of high hydrostatic pressure using hydrothermal diamond anvil cell and Raman spectrum technique. The hydrothermal diamond anvil cell is the most useful instrument to observe sample in-situation under high temperature and high pressure. The authors can get effective results from this instrument and pursue further research. The method of Raman spectra is the most useful measure tool and it can detect the material according to the spectrum. The result shows that three characteristic Raman peaks of calcite-I move to high-position with adding pressure. Water media in system becomes frozen at the pressure of 1103 MPa, and there is no change in the structure of calcite-I. The abrupt change of characteristic Raman peaks of calcite-I happens when the system pressure reaches 1752 MPa, and changed characteristic Raman peaks explain that calcite-I changes to calcite-III. There are two types of calcite-III, and type A happens in the system because of the effect of hydrostatic pressure. The characteristic Raman peak in different areas of minerals shows that the degree of phase transition becomes larger from inner part to edge part. The research also shows the advantage of hydrothermal diamond anvil cell and Raman spectrum for qualitative analysis of mineral structure using in-situ technique.

[Raman spectra study of barite at the pressure of 0-1 GPa and ambient temperature].

The variation characters of Raman spectra of S-O symmetric stretching vibration v987 and symmetric bending vibration v452 and V462 of barite at high pressure were studied using moissanite anvil cell. The experimental results show that barite is stable at the pressure of 0-1 GPa and ambient temperature, and the Raman peak positions of barite shift to higher frequency with increasing pressure. The relations between the Raman shifts and system pressure are given as follows: v987 = 0.004 4p+987.42, v452 = 0.002 3p+452.6, v462 = 0.001 8p+ 462.42, and that stretching vibrations are more affected by pressure than bending vibrations. The intensity of 987 cm(-1) Raman peak of barite is six times greater than that of 464 cm(-1) Raman peak of quartz, so barite can be used as a good pressure gauge. Besides, the relation between the system pressure and Raman shift of 987 cm(-1) peak position of barite is given as follows: p(MPa) = 223.16 X (deltav(p))987 -90.35 (987 cm(-1) < v(p) < 992 cm(-1)). The difference in the measured relative pressure-shift of the Raman line of the symmetric stretching vibration among various sulfate minerals shows the compressibility and strength of the S-O bond in the SO4 group.