In situ investigation of laser-induced ignition and the early stages of methane-air combustion at high pressures using a rapidly tuned diode laser at 2.55 microm

The laser-induced ignition of methane/air-mixtures at elevated pressures was investigated by an absorption spectroscopic technique. A room temperature continuous wave InGaAsSb/AlGaAsSb quantum well ridge diode laser was wavelength tuned around 2.55 mum by periodically modulating the injection current from 0 to 174 mA at a 5 kHz repetition rate. The laser heat sink temperature was fixed at 291 K. The infrared laser beam was sent through the pressurized combustion vessel perpendicularly to the igniting laser beam (Nd:YAG laser, 10 ns pulse duration, 20 mJ) at the position of the ignition spark. Fuel-rich to fuel-lean mixtures of methane/air (air equivalence ratio 0.89, 1.06, 1.42, 2.50) were investigated at initial pressures of up to 3 MPa. The initial temperature was 473 K, the volume of the combustion vessel 0.9x10(-3) m(3). The formation of water vapor in the vicinity of the laser spark was tracked by the diode laser. The time resolution of the measurements was 0.2 ms for a total continuous measurement time of up to 1 s. In this way, the laser-induced ignition and its accompanying effects could be investigated on a time scale spanning four orders of magnitude. Apart from the absorbance of water vapor which could be determined semi-quantitatively (due to the effects of severe pressure broadening at high pressures and the ignorance of the exact temperature distribution after ignition), the emissions from the flame (broadband, 1-10 mum) and a gas inhomogeneity index were recorded. The gas inhomogeneity index was obtained by extracting a frequency variable from the time-dependent fluctuations of the transmitted laser intensities and calculating its derivation. The absorbance of water vapor, the emissions from the flame and the gas inhomogeneity index were found to be a powerful tool to characterize laser-induced ignition. Major implications of in situ species concentration measurements at high pressures for the design and development of high-load combustors are presented.     

Application of primary plasma standardization to Nd-YAG laser-induced shock wave plasma spectrometry for quantitative analysis of high concentration Au–Ag–Cu alloy

A study was performed on a laser-induced shock wave plasma generated on high concentration Au–Ag–Cu alloys by a Q-switched Nd-YAG laser of 4.8 mJ under reduced air pressure of 2 torr. It was found that the total emission intensity of the secondary plasma is proportional to the intensity of the primary plasma. Assuming linear proportionality between the intensity of the primary plasma and the number of atoms vaporized from the target, it is proposed that quantitative analysis can be applied to the intensities of the analytical emission lines normalized by the total intensity of the primary plasma. This experimental result demonstrated for each metal element shows an excellent linear relationship between the normalized emission line intensity and the content of the corresponding element.     

Chitosan‐based hydrogels: A new polymer‐based system with excellent laser‐damage threshold properties

Two types of chitosan hydrogel systems have been prepared that have a laser damage threshold (LDT) up to 35 times higher than commercial PMMA bulk materials. For these samples, the LDT increases with increasing water content. The mechanism of laser damage and the contribution of water to their high laser damage resistance have been examined. DSC measurements indicate water within the hydrogels exist in various states, each with different laser damage resistance properties. These various states play a key role in determining the LDT by controlling the dissipation of laser energy and providing a mechanism for self‐healing. This preliminary research shows that polymer hydrogels have potential for high power laser applications because they combine good mechanical integrity due to the polymer frame and good energy dissipation and healing characteristics due to the molecular mobility of water. These two traits allow for bulk shape‐retaining films with high laser damage thresholds and potential reversibility in damage processes. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 769–778, 1999     

Approximate analytic solution for the dissociation of molecular iodine in the presence of singlet oxygen

A computational study including sensitivity, nondimensional, and stedy-state analyses of the gas-phase kinetics associated with Chemical Oxygen-Iodine Lasers (COIL) was performed to develop a simplified kinetic model and assess kinetic limitations to laser performance. A minimal set of 13 reactions is developed that adequately describes the time evolution of the major chemical constituents of a COIL device. A characteristic time for the dissociation of molecular iodine by singlet oxygen is established in terms of iodine fraction, water content, yield of singlet oxygen, and rate parameters. Finally, an approximate analytic solution to the iodine dissociation problem is established for a broad range of reagent concentrations. The current study is limited in applicability due to the exclusion of chemical heat release and reactive mixing phenomenon. © 1995 John Wiley & Sons, Inc.     

The non-linear model of sound wave diffusion in Chrysanthemum callus

There are non-linear effects during sound wave diffusing in biological tissues. It is necessary to further research the process of sound wave diffusion. In this article, we have primarily established the non-linear model of sound diffusion in Chrysanthemum callus, which can theoretically predict the attenuation tendency of sound wave in biological tissues, and the intensity received by tissues, the model provides us a primary model to further explore the mechanism of sound wave. Generally, due to the non-linear effects in tissue for sound wave diffusion, the efficient factor η and the effective diffusion distance are reduced, the effective attenuation coefficient _eff is increased. On the other hand, the conversion relation of sound intensity and sound pressure is primarily explored in this paper. We can gain the magnitude of pressure in tissue, which provides the basis of stress–growth relation studies for tissues and cells.     

Thermochemical properties of some bis(trifluoromethyl-sulfonyl)imide based room temperature ionic liquids

Cartilage thermoforming is an emerging surgical technology which uses heat to accelerate stress relaxation in mechanically deformed tissue specimens. Heat induced shape change in cartilage is associated with complex thermo-mechanical behavior of which the mechanisms are still a subject of debate. Differential scanning calorimetry (DSC) was used to characterize the threshold temperatures and enthalpies in cartilage as a function of water content. The DSC identified two enthalpic events in porcine nasal septal cartilage, which depend on the water content. The change in the water content of cartilage impacts the interactions between matrix macromolecules and water molecules, which may be associated with a bound-free water transformation (reversible process) and a denaturation of cartilage (irreversible process).     

Corrélation entre les conditions de traitement thermique par laser co2 de puissance et les modifications structurales de surface d'alliage de titane TA6V

The transfer of electromagnetic wave energy to the metallic material is done by an exchange between the laser photons and the lattice electrons via the inverse bremstrahlung. This process induces the passage of an electron from the valence to the conduction band in which it becomes free and energetic and it provokes, by collision with others electrons of the crystal lattice, the heating of the sample surfaces. The laser energy is then transformed, at the surface, into thermal energy (heat) which diffuses into the sample.For the same kind of materials with surfaces prepared in the same conditions, only laser beam parameters vary, following the relation: Qs = P τ / S, where Qs is the specific energy at the lighted surface, P the power of the laser, τ the interaction time and S the surface lighted by the laser beam. This factor indicates if the laser treatments are done without microstructural modification of the samples or with melting of the material surface.The martensitic phase α' obtained after the laser treatment is metastable, with a small grain size compared to those obtained with the classical thermal treatments. The size of α' grains depends on the energy density (Qs = P τ / S ) received by the specimen from the laser wave.     

Excitation of nanoscale vapor bubbles at the surface of gold nanoparticles in water

Intense nonequilibrium femtosecond laser excitation of gold nanoparticles in water leads to a transient heating of the nanoparticles, which decays via heat transfer to the water phase. It is shown that the water temperature rises to near the critical temperature and the water undergoes an explosive evaporation in the subnanosecond range. The formation of vapor bubbles shows a threshold dependence on laser fluence. The nascent nanoscale vapor bubbles change the heat dissipation drastically. The nanoscale structure is resolved directly with a combination of x-ray scattering methods sensitive to the particle lattice expansion and the change in the water structure factor.     

Heat capacity of water in poly(methyl methacrylate) hydrogel membrane for an artificial kidney

The heat capacities of a poly(methyl methacrylate) hydrogel membrane for an artificial kidney have been determined over the range of temperatures from 228 to 298 K as a function of water content. At least two kinds of water were found: freezable water and nonfreezable water. The partial specific heat capacities of both waters were calculated from the dependence of heat capacity of the hydrogel on the water content. The heat capacities of freezable water were estimated to be 1.04 cal g⁻¹ K⁻¹ at 298 K and 0.47 cal g⁻¹ K⁻¹ at 228 K. The mobility must therefore be similar to that of bulk water at 298 K, though the melting temperature was lower than that of bulk water. Consequently, the freezable water was not assigned to bound water but to pore water for which the melting temperature was depressed due to interfacial tension. On the other hand, the heat capacities of nonfreezable water were estimated to be 1.02 cal g⁻¹ K⁻¹ at 298 K and 1.06 cal g⁻¹ K⁻¹ at 228 K. The mobility of the water would be similar to that of free water at both 298 and 228 K. © 1995 John Wiley & Sons, Inc.     

IR laser and heat-induced changes in annulus fibrosus collagen structure

The purpose of this study was to characterize essential changes in the structure of annulus fibrosus (AF) after hydrothermal and infrared (IR) laser treatment and to correlate these results with alterations in tissue state. Polarization-sensitive optical coherence tomography imaging was used to measure collagen birefringence in AF. Differential scanning calorimetry was used as a complementary technique, providing detailed information on thermodynamic processes in the tissue. Birefringence, peak of the denaturation endotherm, and the enthalpy of denaturation (DeltaHm) were determined before and after hydrothermal heat treatment (85 degrees C for 15 min) and non-ablative Er:glass fiber laser exposures on AF in the whole disk (vertebrae-disk-vertebrae complex). Our data have demonstrated quantitative differences between results of laser and hydrothermal heating. Birefringence did not disappear and DeltaHm did not change after treatment in the water bath, but loss of birefringence and a decrease in the enthalpy did occur after laser exposure. These results could be explained by the photomechanical effect of laser irradiation. We suggest that thermo-mechanical stress played a dominant role in the disruption of the collagen network of AF under non-homogeneous laser heating.     

Heat of adsorption of water vapors on active carbons

The initial stage of adsorption of water vapors on active carbons is due to the reaction of the water molecules with inorganic and organic polar sites. For the lowest degrees of filling, the heats of adsorption of H₂O on active carbons evacuated at 500°C are overestimated due to the strong physical and chemical reaction with the primary active sites. Adsorption on secondary active sites (second coordination sphere of the active site) results in the formation of aqueous clusters with stressed hydrogen bonds and with heats below the heat of vapor condensation (). Filling of micropores containing water clusters and capillary condensation in mesopores simultaneously take place in the middle region and in the region of saturation. Micropores containing no water clusters do not fill with water even for P/P_s=1. In this region, q > by 3%. Desorption of water from the micropores is almost totally controlled by capillary evaporation of the liquid from the mesopores, and the sorption volume distribution curve by Kelvin radii reflects the distribution of the total volume of meso- and micropores by the radii of the cylindrical mesopores.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2183–2186, October, 1989.     

Effects of thermal treatment on the surface properties of a wide pore silica gel

A mesoporous silica gel Davidson 59 was thermally treated in vacuo, in the temperature range 20–1000°C. Effects of thermal treatment on the water contents, nitrogen surface areas, pore structure and heats of immersion in water were investigated and discussed. The temperatures selected were 20, 110, 200, 290, 380, 480, 510 and 1000°C. These temperatures were found to cover all the various textural changes resulting from the heat effect.It could be shown that the heats of immersion in water depend primarily on the water content of the sample and are proportional, at least qualitatively to the number of hydroxyl groups on the surface and their availability for interaction with liquid water. The interesting result obtained is that a second factors is involved, namely the pore structure of the adsorbent. A qualitative parallelism exists between the normalized heat of immersion per unit area, and the average pore radius. Apparently the packing of water molecules in narrow pores leads to a decrease in the heat of immersion due to repulsion between the permanent dipoles of the molecules. In narrower pores, the heat of immersion in water is smaller than in wide pores.     

IV-VI semiconductor growth on silicon substrates and new mid-infrared laser fabrication methods

This paper reviews results from research conducted at the University of Oklahoma on the development of new IV-VI semiconductor (lead salt) epitaxial growth and laser fabrication procedures that can ultimately lead to dramatic increases in mid-IR laser operating temperatures. Work has focused on growth of IV-VI semiconductor laser structures on silicon substrates using buffer layers that contain BaF2. Recent experiments show that it is possible to obtain high crystalline quality IV-VI semiconductor layer structures on (111)-oriented silicon substrates using molecular beam epitaxy (MBE) or on (100)-oriented silicon using a combination of MBE and liquid phase epitaxy (LPE). Experimental data for IV-VI semiconductor layer structures grown on silicon substrates including crystalline quality information as determined by high resolution X-ray diffraction (HRXRD) measurements and absorption edge information as determined by Fourier transform infrared (FTIR) transmission measurements are presented. Results show that these materials can be used to fabricate lasers that cover the 3 microns (3333 cm-1) to 16 microns (625 cm-1) spectral range. Removal of IV-VI semiconductor laser structures from the silicon growth substrate by dissolving BaF2 buffer layers with water is also demonstrated. This allows epitaxially-grown laser structures to be sandwiched between two heat sinks with a minimum of thermally resistive IV-VI semiconductor material. Theoretical modeling predicts that IV-VI lasers fabricated this way will have maximum continuous wave (cw) operating temperatures at least 60 degrees higher than those of IV-VI lasers fabricated on PbSe or PbTe substrates.     

Characterization of lipid extracts from brain tissue and tumors using Raman spectroscopy and mass spectrometry

Brain tissue is characterized by high lipid content. The amount of lipids decreases, and its composition changes in the most frequent primary brain tumor, the glioma. Scope of the current paper was to extract quantitatively lipids from porcine and human brain tissue as well as from five human gliomas using a modified protocol according to Folch. The lipid extracts were studied by Raman spectroscopy with 785 nm excitation and by mass spectrometry with electron impact ionization. Porcine and human brain tissues have similar water and lipid content and show similar Raman and mass spectra. In contrast, gliomas are characterized by increased water content and decreased lipid content. Elevated phosphatidylcholine to cholesterol ratios in lipid extracts of gliomas were indicated by Raman bands of the choline group and cholesterol. Due to its higher sensitivity, mass spectrometry detected increased levels of cholesterol ester relative to cholesterol in lipid extracts of gliomas. For comparison, thin tissue sections were prepared from the glioma specimens before lipid extraction; infrared spectroscopic images were recorded and analyzed by a supervised classification model. This study demonstrates how to improve the analysis of brain tumors and to complement the diagnosis of brain pathologies using a multimodal approach.     

Analysis of the effect mechanism of water and CH4 concentration on gas explosion in confined space

In order to study the effect of water and CH₄ concentration on gas explosion, a 20L spherical explosive device was used to carry out a water-containing gas explosion experiment, and the explosion simulation was carried out with CHEMKIN-PRO, the mechanism of water on gas explosion was analyzed from the perspective of free radicals and energy. The results showed that the upper limit of gas explosion, maximum explosion pressure and temperature decreased significantly with the increase of water content. The higher the concentration of CH₄, the more obvious the inhibitory effect of water on gas explosion pressure, and the optimal explosion concentration of CH₄ decreased with the increase of water content. As the water content and CH₄ concentration increase, the residual CH₄ content increases after the explosion, the O₂ content decreases, and the CO content produced increases. When the CH₄ concentration is lower than the optimal concentration, water promotes the formation of CO₂ to a certain extent; when the CH₄ concentration is higher than the optimal explosive concentration, the CO₂ content decreases with the increase of water content. Overall, water inhibits methane explosion, the addition of water on the one hand reduces the concentration of active free radicals H, O, OH, on the other hand, it interferes with the generation of gas explosion energy and consumes the kinetic energy of the gas explosion flame shock wave through heat absorption, thus inhibiting the intensity of gas explosion.     

A myelin-specific contrast agent for magnetic resonance imaging of myelination

Myelination is one of the most fundamental biological processes in the development of vertebrate nervous systems. Abnormal or disrupted myelination occurs in many acquired or inherited neurodegenerative diseases, including multiple sclerosis (MS) and various leukodystrophies. To date, magnetic resonance imaging (MRI) has been the primary tool for diagnosing and monitoring the progression of MS and related diseases; however, any change in signal intensity of conventional MRI reflects a change only in tissue water content, which is a nonspecific measure of the overall changes in macroscopic tissue injury. Thus, the use of MRI as a primary measure of disease activity was shown to be disassociated from the clinical outcome due to the lack of specificity for myelination. In order to increase the MRI specificity for myelin pathologies, we designed and synthesized the first Gd-based T(1) MR contrast agent (MIC) that binds to myelin with high specificity. In this Communication, we demonstrate that MIC localizes in brain regions in proportion to the extent of myelination. In addition, MIC possesses promising MR contrast properties, which allow for direct detection of myelin distribution through T(1) mapping in the mouse brain.     

Resonance fluorescence spectroscopy in laser-induced cavitation bubbles

Laser-induced breakdown spectroscopy (LIBS) in liquids using a double-pulse Q-switched Nd:YAG laser system has provided reliable results that give trace detection limits in water. Resonant laser excitation has been added to enhance detection sensitivity. A primary laser pulse (at 532 nm), transmitted via an optical fiber, induces a cavitation bubble and shockwave at a target immersed in a 10 mg l⁻¹–100 mg l⁻¹ indium (In) water suspension. The low-pressure rear of the shockwave induces bubble expansion and a resulting reduction in cavity pressure as it extends away from the target. Shortly before the maximum diameter is expected, a secondary laser pulse (also at 532 nm) is fed into the bubble in order to reduce quenching processes. The plasma field generated is then resonantly excited by a fiber-guided dye laser beam to increase detection selectivity. The resulting resonance fluorescence emission is optically detected and processed by an intensified optical multichannel analyzer system.      

水合和pH对蛋白酶K热诱发转变影响的量热法研究

用差示扫描量热法, 在310～450 K温度范围、0.048～4.39克水/克干酶以及pH3～9范围内研究了蛋白酶K(EC 3.4.21.14)的热变性。分别提出表征热变性过程的三个主要热力学参数: 热变性温度T_d、比变性焓△H_d及超额表观比热C_(ex)~(max)和总水量h以及pH的关系。除Td和h的关系属于Flory-Garrett类型外, 蛋白酶K的热变性热力学特征和已报道的球蛋白、双螺旋蛋白及三螺旋蛋白不相同。一级水合水对蛋白酶K热变性热力学特征有最大的影响, pH也是影响该酶热稳定性的重要因素。     

Calorimetric Study of the Glass Transition Process in Humid Proteins and DNA

By method of differential scanning calorimetry the absolute values of heat capacity for the systemwater–biopolymer (globular and fibrillar proteins and DNA) were measured in a wide range of temperatures (from -30 up to 130°C) and concentrations of proteins both in native and denatured states. Thermal properties of humid denatured biopolymers demonstrate a characteristic anomaly in the form of the heat capacity jump at temperature depending on the bound water content. It has been shown that in the systems studied a glass transition, where water serves as a native plasticizer, is observed. It has been established that the S-shaped character of all heat capacity curves obtained on dehydration for native and denatured biopolymers is due to the gradual transition to the glassy state of both native and denatured samples. It was found that thermally denatured humid small globular proteins at subsequent dissolving in water at room temperature are able to restore their native structure. This revised version was published online in July 2006 with corrections to the Cover Date.