Phase-difference and spectroscopic imaging for monitoring of human brain temperature during cooling

Decrease of the human brain temperature was induced by intranasal cooling. The main purpose of this study was to compare the two magnetic resonance methods for monitoring brain temperature changes during cooling: phase-difference and magnetic resonance spectroscopic imaging (MRSI) with high spatial resolution. Ten healthy volunteers were measured. Selective brain cooling was performed through nasal cavities using saline-cooled balloon catheters. MRSI was based on a radiofrequency spoiled gradient echo sequence. The spectral information was encoded by incrementing the echo time of the subsequent eight image records. Reconstructed voxel size was 1×1×5 mm³. Relative brain temperature was computed from the positions of water spectral lines. Phase maps were obtained from the first image record of the MRSI sequence. Mild hypothermia was achieved in 15–20 min. Mean brain temperature reduction varied in the interval <−3.0; − 0.6>°C and <−2.7; − 0.7>°C as measured by the MRSI and phase-difference methods, respectively. Very good correlation was found in all locations between the temperatures measured by both techniques except in the frontal lobe. Measurements in the transversal slices were more robust to the movement artifacts than those in the sagittal planes. Good agreement was found between the MRSI and phase-difference techniques.     

Controlled fabrication of Si nanostructures by high vacuum electron beam annealing

Silicon nanostructures, called Si nanowhiskers, have been successfully synthesized on Si(1 0 0) substrate by high vacuum electron beam annealing (EBA). Detailed analysis of the Si nanowhisker morphology depending on annealing temperature, duration and the temperature gradients applied in the annealing cycle is presented. A correlation was found between the variation in annealing temperature and the nanowhisker height and density. Annealing at 935 °C for 0 s, the density of nanowhiskers is about 0.2 μm⁻² with average height of 2.4 nm grow on a surface area of 5×5 μm, whereas more than 500 nanowhiskers (density up to 28 μm⁻²) with an important average height of 4.6 nm for field emission applications grow on the same surface area for a sample annealed at 970 °C for 0 s. At a cooling rate of −50 °C s⁻¹ during the annealing cycle, 10–12 nanowhiskers grew on a surface area of 5×5 μm, whereas close to 500 nanowhiskers grew on the same surface area for samples annealed at the cooling rate of −5 °C s⁻¹. An exponential dependence between the density of Si nanowhiskers and the cooling rate has been found. At 950 °C, the average height of Si nanowhiskers increased from 4.0 to 6.3 nm with an increase of annealing duration from 10 to 180 s. A linear dependence exists between the average height of Si nanowhiskers and annealing duration. Selected results are presented showing the possibility of controlling the density and the height of Si nanowhiskers for improved field emission properties by applying different annealing temperatures, durations and cooling rates.     

A fibre-optic thermometric sensor based on the thermo-optic effect of titanium dioxide coatings

An experimental determination of the thermo-optic effect of titanium dioxide is described in which the test element is a thin film deposited onto the end face of an optical fibre. The film acts as an etalon. The reflectivity of titanium dioxide films was measured as a function of temperature experimentally over the range 20 °C to 500 °C, and modelled theoretically to yield a value of the thermo-optic coefficient of − 1.49 × 10⁻⁴ K⁻¹. The use of the data in the design of a thin-film optical fibre temperature sensor is described.     

Temperature measurements using fiber optic polarization interferometer

A novel measurement method of temperature based on the phenomena that the phase difference between principle polarization states in the optical retarder is function of temperature is described. The polarization state of optical beam is changed as it passes through the optical retarder, which depends on the temperature. The temperature of optical retarder is determined by comparison of the power difference between principal polarization states. We demonstrate successfully the temperature measurement by using a polarization maintaining fiber as the optical retarder. With a 100 mm length of the fiber optic retarder, the change rate of phase difference on temperature was 0.236 rad/°C and the measurement error was ±0.038°C over the temperature range of −2.6 – +3.4°C. With a 11.5 mm length of the fiber optic retarder, the change rate of phase difference on temperature was 0.021 rad/°C and the measurement error was ±0.79°C over the temperature range of −8.5 – +86.5°C.     

Cryo-scanning electron microscopic study on freezing behavior of xylem ray parenchyma cells in hardwood species

Differential thermal analysis (DTA) has indicated that xylem ray parenchyma cells (XRPCs) of hardwood species adapt to freezing of apoplastic water either by deep supercooling or by extracellular freezing, depending upon the species. DTA studies indicated that moderately cold hardy hardwood species exhibiting deep supercooling in the XRPCs were limited in latitudinal distribution within the −40°C isotherm, while very hardy hardwood species exhibiting extracellular freezing could distribute in colder areas beyond the −40°C isotherm. Predictions based on the results of DTA, however, indicate that XRPCs exhibiting extracellular freezing may appear not only in very hardy woody species native to cold areas beyond the −40°C isotherm but also in less hardy hardwood species native to tropical and subtropical zones as well as in a small number of moderately hardy hardwood species native to warm temperate zones. Cryo-scanning electron microscopic (cryo-SEM) studies on the freezing behavior of XRPCs have revealed some errors in DTA. These errors are originated mainly due to the overlap between exotherms produced by freezing of water in apoplastic spaces (high temperature exotherms, HTEs) and exotherms produced by freezing of intracellular water of XRPCs by breakdown of deep supercooling (low temperature exotherms, LTEs), as well as to the shortage of LTEs produced by intracellular freezing of XRPCs. In addition, DTA results are significantly affected by cooling rates employed. Further, cryo-SEM observations, which revealed the true freezing behavior of XRPCs, changed the previous knowledge of freezing behavior of XRPCs that had been obtained by freeze-substitution and transmission electron microscopic studies. Cryo-SEM results, in association with results obtained from DTA that were reconfirmed or changed by observation using a cryo-SEM, revealed a clear tendency of the freezing behavior of XRPCs in hardwood species to change with changes in the temperature in the growing conditions, including both latitudinal and seasonal temperature changes. In latitudinal temperature changes, XRPCs in less hardy hardwood species native to tropical and subtropical zones exhibited deep supercooling to −10°C, XRPCs in moderately hardy hardwood species native to temperate zones exhibited a gradual increase in the supercooling ability to −40°C from warm toward cool temperate zones, and XRPCs in very hardy hardwood species native to boreal forests exhibited extracellular freezing via an intermediate form of freezing behavior between deep supercooling and extracellular freezing. In seasonal temperature changes, XRPCs in hardwood species native to temperate zones changed their supercooling ability from a relatively low degree in summer to a high degree in winter. XRPCs in hardwood species native to boreal forests changed their freezing behavior from deep supercooling to −10°C in summer to extracellular freezing in winter. These results indicate that the freezing behavior of XRPCs in hardwood species tends to shift gradually from supercooling of −10°C, to a gradual increase in the deep supercooling ability to −40°C or less, and finally to extracellular freezing as a result of cold acclimation in response to both latitudinal and seasonal temperature changes. It is thought that these temperature-dependent changes in the freezing behavior of XRPCs in hardwood species are mainly controlled by changes in cell wall properties, although no distinct changes were detected by electron microscopic observations in cell wall organization between hardwood species or between seasons. Evidence of temperature-dependent changes in the freezing behavior of XRPCs in hardwood species provided by the results of studies using a cryo-SEM has indicated the need for further investigation to clarify cold acclimation-induced cell wall changes at the sub-electron microscopic level in order to understand the mechanisms of freezing adaptation.     

Pyroelectric properties in three phases coexistence Pb[(Mn0.33Nb0.67)0.5(Mn0.33Sb0.67)0.5]0.08(ZrxTi1−x)0.92O3 lead ceramics

The bulk dense Pb[(Mn_0.33Nb_0.67)_0.5(Mn_0.33Sb_0.67)_0.5]_0.08(Zr_xTi_1−x)_0.92O₃ pyroelectric ceramics have been successfully prepared by the conventional solid method. The effect of three phases coexistence in the ceramics is studied. When x = 0.95 and 0.85 in the ceramics, the maximum pyroelectric coefficient peaks appear at 23 °C and 45 °C, and the maximum values are 26.5 × 10⁻⁴ C/m² °C and 25.5 × 10⁻⁴ C/m² °C, respectively. The maximum pyroelectric coefficient appears large while the peaks widths are small. When the two kinds of ceramic powders mixed with the mol ratio of 2:1, the pyroelectric coefficient of the ceramics is above 10.0 × 10⁻⁴ C/m² °C in a broad temperature range from 20 °C to 55 °C. The possible physical mechanism of the temperature broadened phenomenon is briefly discussed.     

Proton conductivity and phase relationship in solid KOH between 248 and 406°C

Existing evidence indicates that between 248°C and the melting point at 406°C, KOH is a rotator phase. We have shown that, as might be expected, this results in enhanced proton conductivity, and a value of 2×10⁻³ ohms⁻¹ cm⁻¹ was found at 350°C, which is the highest reported for proton conducting solid electrolytes in this temperature range. Excess protons are provided by water molecules residing on the normal OH^- sites, and charge compensation is provided by CO²⁻₃ ions in the solid solution of KOH(≈ 1 m/o K₂CO₃, 1.3m/o H₂O). The activation energy for proton hopping between adjacent H₂O and OH⁻ species probably accounts for most of the observed activation energy of 53±3 kJ mol⁻¹. From TGA studies the isobars at 0.05 and 10 Torr were established for KOH-rich compositions in the KOH---H₂O system, and it was shown that the rotator phase of KOH is stable between these vapour pressures.     

Refractive index of standard oils as a function of wavelength and temperature

The refractive indices (n) of eight standard oils from Physikalisch Technische Bundesanstalt, Germany were determined with an accuracy of ±1×10⁻⁴ by using Abbe Refractometer. The measurements were performed at temperature 20°C in the spectral range 0.4–0.7 μm. The experimental data were fitted to the simple Cauchy dispersion formula and the results were found to be consistent within the limits of experimental error. In all cases, the refractive index decreased monotonically with increasing wavelength. The refractive indices (n) of these oils have been measured as a function of the temperature t (20°C up to 50°C) at λ=0.589 μm and were found to have linear temperature dependencies. The refractive indices of the studied oils and the uncertainty in their values are calculated at λ=0.589. The Lorentz–Lorenz (L–L) formula has been tested and it was found to be valid with a maximum deviation of 0.4% and was used to calculate the molecular polarizability θ.     

N Chemical Shift Tensor Magnitude and Orientation in the Molecular Frame of Uracil Determined via MAS NMR

The potential of heteronuclear MAS NMR spectroscopy for the characterization of ¹⁵N chemical shift (CS) tensors in multiply labeled systems has been illustrated, in one of the first studies of this type, by a measurement of the chemical shift tensor magnitude and orientation in the molecular frame for the two ¹⁵N sites of uracil. Employing polycrystalline samples of ¹⁵N₂ and 2-¹³C,¹⁵N₂-labeled uracil, we have measured, via ¹⁵N–¹³C REDOR and ¹⁵N–¹H dipolar-shift experiments, the polar and azimuthal angles (θ, ψ) of orientation of the ¹⁵N–¹³C and ¹⁵N–¹H dipolar vectors in the ¹⁵N CS tensor frame. The (θ_NC, ψ_NC) angles are determined to be (92 ± 10°, 100 ± 5°) and (132 ± 3°, 88 ± 10°) for the N1 and N3 sites, respectively. Similarly, (θ_NH, ψ_NH) are found to be (15 ± 5°, −80 ± 10°) and (15 ± 5°, 90 ± 10°) for the N1 and N3 sites, respectively. These results obtained based only on MAS NMR measurements have been compared with the data reported in the literature.     

Electrical conductivity of Ag/Na ion-exchanged titanosilicate glasses

The Ag₂O–TiO₂–SiO₂ glasses were prepared by Ag⁺/Na⁺ ion-exchange method from Na₂O–TiO₂–SiO₂ glasses at 380–450 °C below their glass transition temperatures (T_g), and their electrical conductivities were investigated as functions of TiO₂ content and the ion-exchange ratio (Ag/(Ag+Na)). In a series of glasses 20R₂O·xTiO₂·(80−x)SiO₂ with x=10, 20, 30 and 40 in mol%, the electrical conductivities at 200 °C of the fully ion-exchanged glasses of R=Ag were in the order of 10⁻⁵ or 10⁻⁴ S cm⁻¹ and were 1 or 2 orders of magnitude higher than those of the initial glasses of R=Na. The glass of x=30 exhibited the highest increase of conductivity from 3.8×10⁻⁷ to 1.3×10⁻⁴ S cm⁻¹ at 200 °C by Ag⁺/Na⁺ ion exchange among them. When the ion-exchange ratio was changed in 20R₂O·30TiO₂·50SiO₂ system, the electrical conductivity at 200 °C exhibited a minimum value of 7.6×10⁻⁸ S cm⁻¹ around Ag/(Ag+Na)=0.3 and increased steeply in the region of Ag/(Ag+Na)=0.5–1.0. When the ion-exchange temperature was changed from 450 to 400 °C, the conductivity of the ion-exchanged glass of x=30 decreased. The infrared spectroscopy measurement revealed that the ion-exchange temperature of 450 °C induced a structural change in the glass of x=30. The T_g of the fully ion-exchanged glass of x=30 was 498 °C. It was suggested that the incorporated silver ions changed the average coordination number of titanium ions to form higher ion-conducting pathway and resulted in high conductivity in the titanosilicate glasses.     

Optical characterization of the silicon photodiodes for the establishment of national radiometric standards

Optical properties of the silicon photodiodes are investigated in the visible spectral regime. Non-linearity measurement standard was established by using Hamamatsu S1337-11 type windowless silicon photodiode whose non-linearity value was found to be better than 6×10⁻⁵ at photocurrent level of 10⁻⁹ to 10⁻⁴ A. Temperature effects on the spectral responsivity for S1337-11, S1337-1010BQ and S1227-1010BQ type photodiodes were analyzed between 20°C and 40°C at 488.1, 514.7 and 632.8 nm vacuum wavelengths. The spatial uniformities of the responsivity for three type photodiodes are performed with a laser beam having 1 mm diameter by using home made two-axis micro translation system. Results of the reflectance measurements for three elements of reflection-based trap detectors were compared with the predicted values obtained from Fresnel equations.     

A multi-parameter optical fiber sensor with interrogation and discrimination capabilities

A multi-parameter and multi-function, but low-cost, optical fiber grating sensor with self-interrogation and self-discrimination capabilities is presented theoretically and experimentally. The sensor bases on three fiber Bragg gratings (FBG) and one fiber long period grating (LPG). Strain, vibration, pressure, ordinary temperature (−10 to 100 °C) and high temperature (100–800 °C) can be measured by the sensor. When high temperature (100–800 °C) is measured, the LPG is used as a high temperture sensor head and FBG₁ is used as an interrogation element. Alternatively, when one of the other four measurands is measured, FBG₁ (or FBG₂) is used as a sensor head and LPG is used as an interrogation element. When two of the other four measurands are measured simultaneously, FBG₁ and FBG₂ are used as sensor heads and LPG is used as a shared interrogation element. FBG₃ is used as a reference element to eliminate the errors resulted from light source fluctuation and the cross-sensitivity between measurand and environmental temperature. The measurands can be interrogated according to the signals of the photodiodes (PDs), which are related to the relative wavelength shift of the LPG and the FBGs. Experimental results agree well with theoretical analyses. The interrogation scheme is immune to light source fluctuation and the cross-sensitivity between measurands and enviromental temperature, and also the dynamic range is large.     

Effect of heat treatment on structure, magnetization and magnetostriction of Fe81Ga19 melt-spun ribbons

Structure, magnetization and magnetostriction of melt-spun Fe₈₁Ga₁₉ ribbons were investigated both before and after heat treatment. The matrix of melt-spun Fe₈₁Ga₁₉ ribbons kept a body-centered-cubic (bcc) structure (A2) at room temperature. [1 0 0] preferred orientation was formed during melt-spinning process and became stronger with the increase of the ribbon thickness. For the ribbons with a thickness of 110 μm, maximum saturation magnetostrictive strain of −189 ppm along ribbon length was obtained in the samples heat treated at 800 °C for 3 h and then quenched into water. This value was about 16% larger than that of melt-spun ones, which could be contributed to the single disordered A2 structure and the enhancement of [1 0 0]-oriented texture. However, when the ribbon samples were cooled at 2 and 0.5 °C/min after heat treatment at 800 °C for 3 h, a minor quantity of ordered D0₃ and L1₂ phase was found to precipitate in the A2 matrix, respectively, which resulted in the reduction of both magnetization and magnetostrictive strain.     

Photoluminescence of GeSi/Si(0 0 1) self-assembled islands with dome and hut shape

The photoluminescence spectra of GeSi/Si (0 0 1) self-assembled islands produced by solid source molecular beam epitaxy in a wide range (460–700°C) of growth temperatures were investigated. The results showed a blue shift of the island-related photoluminescence peak with a growth temperature lowering from 600°C to 550°C. The observed blue shift of the island photoluminescence peak is associated with a sharp decrease in the average height of the island, which occurs through a change of its shape from dome to hut as the growth temperature lowers from 600°C to 550°C.     

Bond-Shift Rearrangement in Solid Li3P7(Monoglyme)3: A P MAS NMR Study

The ³¹P MAS NMR spectrum of solid Li₃P₇(monoglyme)₃ has been reinvestigated over a wide temperature range (−70 to +77°C) and under conditions of better resolution (Larmor frequency of 162 MHz and spinning rate of 30 kHz) than previously measured (121 MHz and 13 kHz). At low temperatures three spinning sideband (ssb) manifolds are observed: a singlet (centered at −45 ppm relative to 85% H₃PO₄) due to the apical atom (A) of the P₇-cage trianion; a 1 : 1 : 1 triplet (at −110, −117, and −124.5 ppm) due to the negatively charged equatorial (E) atoms, and a one to two doublet (at −161 and −168.5 ppm) due to the basal (B) atoms. These results are consistent with the P₇ cage having nearly, but not perfect, C_3v symmetry. The compound appears to be well ordered in the solid state with very little structural dispersity. On heating, the NMR lines broaden and eventually coalesce into a single ssb manifold. This behavior is ascribed to bond-shift rearrangement similar to the Cope rearrangement in bullvalene. A MAS 2D exchange experiment and a quantitative analysis of the 1D NMR lineshapes indicate that, unlike in solution where the rearrangement involves a single bond shift at a time, in the solid the process involves a succession of two bond shifts: The first leads to an intermediate species in which the rearranged P₇ cage is inverted, while in the subsequent step a second bond shift takes place that also restores the original orientation of the cage in the lattice. The overall effect of the double bond shift is equivalent to cyclic permutation of the phosphorus atoms within the five member rings of the P₇-cage. The quantitative analysis of the dynamic lineshapes shows that this cyclic permutation proceeds at a different rate in one ring (k_d¹) than in the other two (k_d^2,3). The kinetic parameters for these processes are E_a¹=18.7 kJ/mol, E_a^2,3=58.0 kJ/mol, k_d¹(17°C)=k_d^2,3(17°C)=10⁴ s⁻¹. No indications for independent threefold molecular jumps of the P₇ cage were found.     

The microwave spectrum, structure, and barrier to internal rotation of selenoacetaldehyde, CH3CHSe

The rotational spectrum of the unstable molecule selenoacetaldehyde, CH₃CHSe, has been studied by microwave spectroscopy between 26.5 and 40 GHz. Transitions have been measured for five abundant selenium isotopic variants. These measurements have, together with structural information from the related molecules CH₃CHS and CH₃CHO, allowed reliable data on the C=Se bond length (1.758 ± 0.01 Å) and the e angle (125.7 ± 0.3°) to be derived. The spectral lines show splittings due to hindered internal rotation and using these together with the derived structure, barrier heights of 1602 cal mole⁻¹ (6703 J mole⁻¹) and 1648 cal mole⁻¹ (6859 J mole⁻¹) have been determined for the ground and first torsionally excited states, respectively.     

Effect of lower growth temperature on C incorporation in GeC epilayers on Si(0 0 1) grown by MBE

Effect of lower growth temperature T_s on C incorporation to substitutional sites in Ge_1−xC_x/Si(0 0 1) grown by molecular beam epitaxy was investigated. To enhance the non-equilibrium growth condition, the temperature T_s was lowered from 600°C down to 300°C. The C incorporation into substitutional sites of GeC epilayers was very sensitive to T_s. X-ray diffraction (XRD) measurement indicated that the substitutional C composition x increased with decrease in T_s from 600°C to 400°C. At T_s350°C, the estimation of x by the XRD analysis was impossible because of polycrystallization. The Raman shift measurement enables to estimate x for T_s350°C, as consequently larger x than that grown at T_s=400°C was verified. The enhancement of non-equilibrium growth condition by decreasing T_s was important to increase x.     

Thermally tuned optical fiber for true time delay generation

A new technique for generating a continuous range of true time delay values is introduced. Heating optical fiber in order to change the effective index of the guided mode produces time delays. A 45-m section of single-mode silica fiber is demonstrated to produce a continuous range of time delay values from 0 to 211 ps over a temperature tuning range of 50°C (30–80°C). A thermal time delay factor is introduced and found to be 0.096 ps/m°C for Corning LEAF fiber. A 7.66-m section of multimode Lucina polymer fiber is demonstrated to produce a range of time delay values from 0 to 32 ps over a temperature tuning range of 30°C (30–60°C). The thermal time delay factor for this fiber is −0.1427 ps/m°C.     

Studies on the preparation and ethanol gas sensing properties of spinel Zn0.6Mn0.4Fe2O4 nanomaterials

Zn_1−xMn_xFe₂O₄ (x = 0, 0.2 and 0.4) nanomaterials were synthesized by sol–gel citrate method and studied structural and gas sensing properties. The structural characteristics of synthesized nanomaterials were studied by X-ray diffraction measurement (XRD) and transmission electron microscope (TEM). The results revealed that the particle size is in the range of 30–35 nm for Mn–Zn ferrite with good crystallinity. The gas sensing properties were studied towards reducing gases like LPG, CH_4, CO and ethanol and it is observed that Mn–Zn ferrite shows high response to ethanol at relatively lower operating temperature. The Zn_0.6Mn_0.4Fe₂O₄ nanomaterial shows better sensitivity towards ethanol at an operating temperature 300 °C. Incorporation of 1.5 wt.% Pd improved the sensitivity, selectivity, response time and reduced the operating temperature from 300 °C to 230 °C for ethanol sensor. The response time of 200 ppm ethanol in air is about 10s.     

GaInAsSb/AlGaAsSb lasers in the wavelength range between 2.73 μm and 2.93 μm

Compressively strained multiple quantum well lasers in the GaInAsSb/AlGaAsSb material system are reported. Indium concentrations between 40% and 47.5% were chosen for the GaInAsSb quantum wells. Compressive strains varied between 1.16% and 1.43%. The lasers worked continuous wave at room temperature up to a wavelength of 2.81 μm. For a laser with 2.93 μm wavelength continuous wave operation was found up to a temperature of −23°C. This laser worked in pulsed operation at 15°C.