In-situ measurement of pyrolysis and combustion gases from biomass burning using swept wavelength external cavity quantum cascade lasers.

Broadband high-speed absorption spectroscopy using swept-wavelength external cavity quantum cascade lasers (ECQCLs) is applied to measure multiple pyrolysis and combustion gases in biomass burning experiments. Two broadly-tunable swept-ECQCL systems were used, with the first tuned over a range of 2089-2262 cm-1 (4.42-4.79 µm) to measure spectra of CO2, H2O, and CO. The second was tuned over a range of 920-1150 cm-1 (8.70-10.9 µm) to measure spectra of ammonia (NH3), ethene (C2H4), and methanol (MeOH). Absorption spectra were measured continuously at a 100 Hz rate throughout the burn process, including inhomogeneous flame regions, and analyzed to determine time-resolved gas concentrations and temperature. The results provide in-situ, dynamic information regarding gas-phase species as they are generated, close to the biomass fuel source.

Physical conditions for UO formation in laser-produced uranium plumes.

We investigate the oxidation of uranium (U) species, the physical conditions leading to uranium monoxide (UO) formation and the interplay between plume hydrodynamics and plasma chemistry in a laser-produced U plasma. Plasmas are produced by ablation of metallic U using nanosecond laser pulses. An ambient gas environment with varying oxygen partial pressures in 100 Torr inert Ar gas is used for controlling the plasma oxidation chemistry. Optical emission spectroscopic analysis of U atomic and monoxide species shows a reduction in the emission intensity and persistence with increasing oxygen partial pressure. Spectral modelling is used for identifying the physical conditions in the plasma that favor UO formation. The optimal temperature for UO formation is found to be in the temperature range of ∼1500-5000 K. The spectrally integrated and spectrally filtered (monochromatic) imaging of U atomic and molecular species reveals the evolutionary paths of various species in the plasma. Our results also highlight that oxidation in U plasmas predominantly occurs at the cooler periphery and is delayed with respect to plasma formation, and the dissipation of molecular species strongly depends on oxygen partial pressure.

Standoff analysis of laser-produced plasmas using laser-induced fluorescence.

We report the use of laser-induced fluorescence (LIF) of laser ablation (LA) plumes for standoff applications. The standoff analysis of Al, as major and minor species in samples, is performed in a nanosecond laser-produced plasma created at a distance of ∼10 m. The LIF of LA plumes is carried out by resonantly exciting an Al transition at 394.4 nm (S1/22-P1/22) using a continuous wave (cw) tunable laser and by collecting the direct-line fluorescence signal at 396.15 nm. The spectral resolution of LIF is obtained by scanning the cw tunable LIF laser across the selected Al transition. Our results highlight that LIF provides enhanced signal intensity, emission persistence, and spectral resolution when compared to thermally excited emission.

Tracking of oxide formation in laser-produced uranium plasmas.

We use a spatially and temporally resolved emission tracking technique based on optical emission spectroscopy to map the evolution of emission features from uranium and its compounds in a plasma produced by a nanosecond laser. We observe quenching of the emission from neutral uranium (591.538 nm) and uranium monoxide (593.55 nm) species with increasing oxygen concentration and discuss possible reaction pathways for dissociation or formation of higher uranium oxides (UxOy). We further identify spectral features between 320 nm and 380 nm and between 520 nm and 640 nm, which we attribute to UxOy.

High-resolution spectroscopy of laser ablation plumes using laser-induced fluorescence.

We report laser-induced fluorescence spectroscopy (LIF) of laser-produced plasmas under varying nitrogen pressure levels up to atmospheric pressure. The plasmas were generated on a glass target containing minor amounts of U and Al using 1064 nm, 6 ns pulses from a Nd:YAG laser. A frequency-doubled continuous-wave Ti:Sapphire laser was used as an ultra-narrowband tunable LIF excitation source to increase the magnitude and persistence of emission from selected U and Al atomic transitions in a laser-produced plasma. 2D-fluorescence spectroscopy (2D-FS) absorption/emission images were recorded at various nitrogen pressure levels, showing both excitation and emission spectral features. At lower pressure levels (⪝100 Torr), fluorescence emission was found to be well separated in time from thermally-excited emission. However, as the ambient pressure increased, the thermally-excited emission persisted for longer times along with a reduction of LIF emission persistence and intensity. The excitation spectral features showed the inherent linewidths of various transitions in the plasma, which have significantly narrower spectral linewidths than observed in emission spectra. We evaluated two nearby transitions separated by only 18 pm to demonstrate the effectiveness of fluorescence spectra over thermally-excited spectra for high-resolution studies. The present results highlight the importance of LIF as a diagnostic tool employing continuous-wave laser re-excitation, addressing some of the limitations of traditional emission and absorption spectroscopic methods.

Quantitative isotopic measurements of gas-phase alcohol mixtures using a broadly tunable swept external cavity quantum cascade laser.

A swept-ECQCL is used for broadband IR spectroscopy of isotopic mixtures of CH3OH, CH3OD, CH3CH2OH, and CH3CH2OD in a static gas cell over a wavelength range of 9.5 to 10.4 µm. A weighted least squares fitting approach with quantitative library spectra illustrates that significant spectral congestion does not negatively impact the ability for in situ quantification of large isotopic species in a mixture. The noise equivalent concentrations for CH3OH, CH3OD, CH3CH2OH, and CH3CH2OD are 19 ppbv m, 28 ppbv m, 450 ppbv m, and 350 ppbv m respectively for a 50 seconds integration time. Based on the observed NECs, isotopic precisions of 0.07‰ and 0.79‰ for a 50 s integration time are calculated for measurements of the [MeOD]/[MeOH] and [EtOD]/[EtOH] isotope ratios, respectively, for the species concentrations in the gas cell.

Consequences of femtosecond laser filament generation conditions in standoff laser induced breakdown spectroscopy.

The combination of femtosecond laser filament ablation and emission spectroscopy is a potential analytical tool for standoff characterization of samples of interest. We compare the emission features and physical conditions of plasmas generated from metal targets using either by loosely focused femtosecond filaments or by lens-free filaments. Our results show that the filament generation conditions influence the plasma properties appreciably which include the atomic and molecular emission features, persistence and plasma fundamentals (temperature and density). The loosely focused fs pulse filaments are found to generate ablation plumes with higher temperature and density along with increased persistence compared to plumes generated by lens-free filaments.

Two-dimensional fluorescence spectroscopy of laser-produced plasmas.

We use a two-dimensional laser-induced fluorescence spectroscopy technique to measure the coupled absorption and emission properties of atomic species in plasmas produced via laser ablation of a solid aluminum target at atmospheric pressure. Emission spectra from the Al I 394.4 nm and Al I 396.15 nm transitions are measured while a frequency-doubled, continuous wave (cw) Ti:sapphire laser is tuned across the Al I 396.15 nm transition. The resulting two-dimensional spectra show the energy coupling between the two transitions via increased emission intensity for both transitions during resonant absorption of the cw laser at one transition. Time-delayed, gated detection of the emission spectrum is used to isolate resonantly excited fluorescence emission from thermally excited emission from the plasma. In addition, the tunable cw laser measures the absorption spectrum of the Al transition with ultrahigh resolution after the plasma has cooled, resulting in narrower spectral linewidths than observed in emission spectra. Our results highlight that fluorescence spectroscopy employing cw laser re-excitation after pulsed laser ablation combines benefits of both traditional emission and absorption spectroscopic methods.

Plasma temperature clamping in filamentation laser induced breakdown spectroscopy.

Ultrafast laser filament induced breakdown spectroscopy is a very promising method for remote material detection. We present characteristics of plasmas generated in a metal target by laser filaments in air. Our measurements show that the temperature of the ablation plasma is clamped along the filament channel due to intensity clamping in a filament. Nevertheless, significant changes in radiation intensity are noticeable, and this is essentially due to variation in the number density of emitting atoms. The present results also explain the near absence of ion emission but strong atomic neutral emission from plumes produced during fs LIBS in air.

Morphological changes in ultrafast laser ablation plumes with varying spot size.

We investigated the role of spot size on plume morphology during ultrafast laser ablation of metal targets. Our results show that the spatial features of fs LA plumes are strongly dependent on the focal spot size. Two-dimensional self-emission images showed that the shape of the ultrafast laser ablation plumes changes from spherical to cylindrical with an increasing spot size from 100 to 600 µm. The changes in plume morphology and internal structures are related to ion emission dynamics from the plasma, where broader angular ion distribution and faster ions are noticed for the smallest spot size used. The present results clearly show that the morphological changes in the plume with spot size are independent of laser pulse width.

Differential laser absorption spectroscopy of uranium in an atmospheric pressure laser-induced plasma.

A two-beam differential laser absorption technique is used to measure 238U absorption spectra with high signal-to-noise ratios in an atmospheric pressure laser-induced plasma. High-resolution absorption spectra are presented for the 238U 861 nm transition in the presence of dry air at pressures up to 760 Torr. A spectral linewidth (FWHM) of 2.23±0.13 GHz was found for the 238U line in dry air at 760 Torr. Absorption spectrum measurements using a low 238U concentration NIST glass standard were used to demonstrate sensitivity of the approach.

Feasibility and Safety of a Combined Metabolic Strategy in Glioblastoma Multiforme: A Prospective Case Series.

Background: Glioblastoma multiforme (GBM) may be susceptible to metabolic strategies such as fasting and ketogenic diets, which lower blood glucose and elevate ketones. Combining these two strategies may be an ideal approach for sustaining a potentially therapeutic glucose ketone index (GKI). In this prospective case series, we observed whether a combined metabolic strategy was feasible, safe, and capable of sustaining a GKI <6 in patients with GBM. Methods: We provided recommendations and guidelines to 10 GBM patients at various stages of tumour progression and treatment that enabled them to complete a 5-7-day fast every 1-2 months combined with a modified ketogenic diet during the intervening weeks. Patients monitored their blood glucose and ketone levels and body weight. Adverse effects were assessed. Results: Patients completed a mean of 161 ± 74 days of the combined metabolic strategy, with 34 ± 18 (21%) days of prolonged fasting (mean fast duration: 6.0 ± 1.4 days) and 127 ± 59 (79%) days on the ketogenic diet. The mean GKI for all 10 patients was 3.22 (1.28 during the fasts, 5.10 during the ketogenic diet). Body weight decreased by 8.4 ± 6.9 kg (11.2% decrease in baseline weight). The most common adverse effects attributed to the fasts and ketogenic diet were fatigue, irritability, and feeling lightheaded. The metabolic strategy did not interfere with standard oncological treatments. Conclusion: This is the first study to observe the feasibility and safety of repeated, prolonged fasting combined with a modified ketogenic diet in patients with GBM. Using minimal support, patients maintained the combined metabolic strategy for 5-6 months while sustaining a potentially therapeutic mean GKI of 3.22. Weight loss was considerable. Adverse effects attributed to the metabolic strategy were mild, and it did not interfere with standard oncological treatments. Study Registration: This study is registered on the Australia New Zealand Clinical Trials Registry, number ACTRN12620001310954. The study was registered on 4 December 2020.

Time-resolved absorption spectroscopic characterization of ultrafast laser-produced plasmas under varying background pressures.

Time-resolved tunable laser absorption spectroscopy is used to characterize the physical properties of ultrafast laser-produced plasmas. The plasmas were produced from an Inconel target, with ≤0.4wt% Al, using ∼35fs, ∼800nm, ∼5mJ laser pulses at varying Ar background pressures from 1 to 100 Torr. The absorption spectrum of atomic Al is measured with high spectral and temporal resolution when the probe laser is stepped across the selected Al transition at 394.4 nm. Spectral fitting is used to infer linewidths, kinetic temperature, Al column density, and pressure broadening coefficient. The late time physical properties of plasmas are compared for various pressure levels. Our studies highlight that a significant lower state population exists even at early times of ultrafast laser-produced plasma evolution, and lower state population persistence decreases with increasing ambient pressure. We also show that the fundamental optical properties, such as pressure broadening, can be measured using ultrafast laser-produced plasmas combined with laser absorption spectroscopy.

Cyclodextrins as catalysts for the removal of cholesterol from macrophage foam cells.

Low concentrations of cyclodextrins (< 1.0 mM) added to serum act catalytically, accelerating the exchange of cholesterol between cells and lipoproteins. J774 macrophages incubated with serum and 2-hydroxypropyl-beta-cyclodextrin (< or = 1 mM) released fivefold more labeled cholesterol than with serum alone. Increased efflux was not accompanied by a change in cell cholesterol mass; thus, cyclodextrin functioned as a cholesterol shuttle, enhancing cholesterol bidirectional flux without changing the equilibrium cholesterol distribution between cells and medium. The addition of phospholipid vesicles to serum and cyclodextrin shifted the equilibrium distribution to favor the medium, producing rapid and extensive depletion of cell cholesterol mass. The combination of serum, phospholipid vesicles, and cyclodextrin also stimulated the rapid clearance of both free and esterified cholesterol from mouse peritoneal macrophages loaded with free and esterified cholesterol. This study: (a) demonstrates that a compound can function as a catalyst to enhance the movement of cholesterol between cells and serum, (b) illustrates the difference between cholesterol exchange and net transport in a cell/serum system, (c) demonstrates how net movement of cholesterol is linked to concentration gradients established by phospholipids, (d) provides a basis for the development of the shuttle/sink model for the first steps in reverse cholesterol transport, (e) validates the model using artificial shuttles (cyclodextrins) and sinks (large unilamellar vesicles), and (f) suggests that cyclodextrin-like cholesterol shuttles might be of pharmacological significance in treating unstable atherosclerotic plaques.

Effects of membrane lipids and -proteins and cytoskeletal proteins on the kinetics of cholesterol exchange between high density lipoprotein and human red blood cells, ghosts and microvesicles.

To better understand the effects of plasma membrane lipids and proteins and the cytoskeleton on the kinetics of cellular cholesterol efflux, the effects of (1), selectively depleting either sphingomyelin (SM) or phosphatidylcholine (PC); (2), cross-linking the cytoskeleton, and (3), removing certain cytoskeletal and integral membrane proteins on radiolabelled cholesterol efflux from red blood cells (RBC) have been studied. When RBC were treated with either phospholipase A2 or sphingomyelinase C to hydrolyze either 30-40% of the PC or 40-50% of the SM, respectively, the halftimes (t1/2) for cholesterol efflux to excess HDL3 were not significantly altered, with the values being 4.4 +/- 0.8 h or 3.7 +/- 0.4 h, respectively, compared to 4.6 +/- 0.6 h for control RBC. To investigate the effects of the cytoskeleton on the rate of free cholesterol (FC) desorption from the plasma membrane, the cytoskeletal proteins were cross-linked by either heat-treatment or exposure to diamide and cholesterol efflux from ghosts of these cells was measured. Cross-linking the cytoskeletal proteins by diamide treatment resulted in no significant change in t1/2 for treated (3.6 +/- 0.6 h) compared to control (4.2 +/- 0.4 h) ghosts: this suggests that the cytoskeleton does not play a large role in modulating cholesterol efflux. To investigate the effects of membrane proteins on cholesterol efflux, RBC microvesicles, containing mainly band 3 and 4 proteins and little of the cytoskeletal proteins, such as spectrin (bands 1,2) or actin (band 5), were obtained by incubation with the ionophore A23187. With excess HDL3 present, microvesicles exhibited a t1/2 of 4.2 +/- 1.9 h (compared to the t1/2 of 4.2 +/- 0.4 h for control ghosts). The results described in this paper suggest that neither changing the SM/PC ratio in the membrane nor cross-linking the cytoskeletal proteins nor removing the cytoskeleton changes the t1/2 for cholesterol efflux to excess HDL3. Presumably, the cholesterol-phospholipid interactions are insensitive to these perturbations in membrane structure.

The helical hydrophobic moments and surface activities of serum apolipoproteins.

The mean helical hydrophobic moments (muH) have been used to compare the amphipathic helices of several apolipoprotein classes with the helices in membrane proteins, water-soluble globular proteins and surface-active peptides. The amphipathic helices in serum apolipoproteins have similar muH and mean hydrophobicities to helices in water-soluble globular proteins. The intrinsic surface activities of proteins and peptides, as determined by surface pressure at the air/water interface, correlate with the product (muH . F) where muH is the average value of muH for all helices in the molecule, and F is the fraction of alpha-helix structure in the protein.

Cholesterol transfer from small and large unilamellar vesicles.

The rates of transfer of [14C]cholesterol from small and large unilamellar cholesterol/egg yolk phosphatidylcholine vesicles to a common vesicle acceptor were compared at 37 degrees C. The rate of exchange of cholesterol between vesicles of identical cholesterol concentrations (20 mol%) did not differ from the rate of transfer from donor vesicles containing 20 mol% cholesterol to egg yolk PC vesicles. Further, the rate of transfer of [14C]cholesterol from vesicles containing 15 mol% dicetyl phosphate (to confer a negative charge) was not different from the rate of transfer from neutral vesicles. However, the half-time for transfer of [14C]cholesterol from large unilamellar donor vesicles was about 5-times greater (10.2 h, 80 nm diameter) than from small unilamellar vesicles (2.3 h, 23 nm diameter). These data suggest that increased curvature in small unilamellar vesicles reduces cholesterol-nearest neighbor interactions to allow a more rapid transfer of cholesterol into the aqueous phase.

Effects of membrane lipid composition on the kinetics of cholesterol exchange between lipoproteins and different species of red blood cells.

To better understand the effects of plasma membrane structure on the kinetics of cellular cholesterol efflux to extracellular lipoprotein particles, the influence of plasma membrane sphingomyelin (SM) on the kinetics of cholesterol exchange was examined in both a model membrane system comprised of egg SM/egg phosphatidylcholine (PC) unilamellar vesicles and in various types of mammalian red blood cells (RBC) containing differing levels of SM. The kinetics and mechanism of the bidirectional flux of unesterified cholesterol (FC) between RBC and lipoproteins were established by using human RBC (labeled with [14C]FC) incubated with varying concentrations of human [3H]FC high-density lipoprotein (HDL3) or [3H]FC low-density lipoprotein (LDL). A maximal rate constant for FC efflux was obtained when the lipoprotein FC was in excess (6-fold and 15-fold, for HDL3 and LDL, respectively) of RBC FC; under this condition, the rate-limiting step is desorption of cholesterol molecules from the RBC membrane into the extracellular aqueous phase. At 37 degrees C, the halftime (t1/2) for efflux was 4.6 +/- 0.6 h for HDL3 and 6.2 +/- 0.2 h for LDL; FC efflux exhibited first-order kinetics and the RBC FC comprised a single kinetic pool. To investigate the effect of different membrane SM/PC ratios on the rate of FC desorption from the plasma membrane, the kinetics of cholesterol efflux from bovine RBC (5:1, w/w ratio of SM/PC), human RBC (1:1 ratio), rabbit RBC (0.6:1 ratio) and rat RBC (0.3:1 ratio) were compared. With excess HDL3 present, bovine, rabbit, and rat RBC exhibited t1/2 of 5.5 +/- 0.8, 4.0 +/- 0.2, and 3.7 +/- 0.6 h, respectively, for cholesterol efflux. Changing the ratio from 0.3:1 to 3:1 in egg SM/egg PC small unilamellar vesicles increased the t1/2 for cholesterol efflux at 45 degrees C from 1.1 to 6.9 h. The results described in this paper suggest that increasing membrane SM content raises the t1/2 for cholesterol exchange in both the RBC plasma membrane and in simple mixed SM/PC bilayers. However, the influence of SM is less in the natural plasma membrane, perhaps because of modulating factors such as membrane proteins and the presence of a complex phospholipid mixture.

Differences in the interaction of inorganic and organic (hydrophobic) cations with phosphatidylserine membranes.

The interaction of phosphatidylserine dispersions with "hydrophobic", organic cations (acetylcholine, tetraethylammonium ion) is compared with that of simple inorganic cations (Na+, Ca2+); differences in the hydration properties of the two classes of ions exist in the bulk phase as evident from spin-lattice relaxation time T1 measurements. It is shown that the reaction products (cation-phospholipid) differ markedly in their physicochemical behaviour. With increasing concentration both classes of ions reduce the zota-potential of phosphatidylserine surfaces, the monovalent inorganic cations being only slightly more effective than the hydrophobic cations. Inorganic cations cause precipitation of the lipid once the surface charge of the bilayer is reduced to a certain threshold value. This is not the case with the organic cations. The difference is probably associated with the different hydration properties of the resulting complexes. Thus binding of Ca2+ causes displacement of water of hydration and formation of an anhydrous, hydrophobic calcium-phosphatidylserine complex which is insoluble in water, whereas the product of binding of the organic cations is hydrated, hydrophilic and water soluble. The above findings are consistent with NMR results which show that the phosphodiester group is involved in the binding of both classes of cations as well as being the site of the primary hydration shell. Besides affecting interbilayer membrane interactions such as those involved in cell adhesion and membrane fusion, the binding of both classes of cation can affect the molecular packing within a bilayer.

Cholesterol transport between cells and high-density lipoproteins.

Various types of studies in humans and animals suggest strongly that HDL is anti-atherogenic. The anti-atherogenic potential of HDL is thought to be due to its participation in reverse cholesterol transport, the process by which cholesterol is removed from non-hepatic cells and transported to the liver for elimination from the body. Extensive studies in cell culture systems have demonstrated that HDL is an important mediator of sterol transport between cells and the plasma compartment. The topic of this review is the mechanisms that account for sterol movement between HDL and cells. The most prominent and easily measured aspect of sterol movement between HDL and cells is the rapid bidirectional transfer of cholesterol between the lipoprotein and the plasma membrane. This movement occurs by unmediated diffusion, and in most situations its rate in each direction is limited by the rate of desorption of sterol molecules from the donor surface into the adjacent water phase. The net transfer of sterol mass out of cells occurs when there is either a relative enrichment of sterol within the plasma membrane or a depletion of sterol in HDL. Recent studies suggest that certain minor subfractions of HDL (with pre-beta mobility on agarose gel electrophoresis and containing apoprotein A-I but no apo A-II) are unusually efficient at promoting efflux of cell sterol. To what extent efflux to these HDL fractions is balanced by influx from the lipoprotein has not yet been established clearly. The prevention and reversal of atherosclerosis require the mobilization of cholesterol from internal (non-plasma membrane) cellular locations. To some extent, this may involve the retroendocytosis of HDL. However, most mobilization probably involves the transport of internal sterol to the plasma membrane, followed by desorption to extracellular HDL. Several laboratories are investigating the transport of sterol from intracellular locations to the plasma membrane. Studies on biosynthetic sterol (probably originating mostly in the smooth endoplasmic reticulum) suggest that there is rapid transport to the plasma membrane in lipid-rich vesicles. Important features of this transport are that it bypasses the Golgi apparatus and may be positively regulated by the specific binding of HDL to the plasma membrane.(ABSTRACT TRUNCATED AT 400 WORDS)