Accurate monitoring of an interferometric fiber-optic sensor with a multimode semiconductor laser

A technique for monitoring interferometric sensors by correlation of the optical signal from the sensor with the signal from a phase-modulated reference interferometer is described. The technique is applied to temperature measurement with a fiber Fabry-Perot sensing head. We extend the 7 degrees C unambiguous measurement range obtained with a 1.3-mum laser diode as the light source to 43 degrees C by adding a second laser diode emitting at 1.55mum . Experimentally, a rms phase-measurement error of +/-0.28rad , corresponding to a temperature error of +/-0.32 degrees C , was achieved with a low-quality multimode Fabry-Perot laser. The phase error was improved to +/-0.14rad , corresponding to a temperature error of +/-0.16 degrees C , by use of a distributed-feedback laser diode.     

Thermal response of contrast agent microbubbles: preliminary results from physico-chemical and US-imaging characterization

Hyperthermia (HT) is a therapeutic strategy based on the selective damaging of tumoral cells when heated at temperatures in the range 41-45 degrees C. We are currently investigating the feasibility of Ultrasound (US) imaging to perform a non-invasive, efficient and cost effective temperature monitoring of heated tissues. Commercial US contrast agents (Sonovue, Bracco), consisting in microbubbles of SF(6) coated with a phospholipidic shell, greatly improve the US echo signal from tissues. Further investigations have been performed, consisting in physico-chemical and US-imaging characterization. In conclusion, we demonstrate that Sonovue microbubbles reach their maximal diameter at 40 degrees C, and then a sharp decrease is observed, possible due to the occurrence of gel-sol transition of the phospholipidic shell. At the same temperature the maximal backscattering intensity is predicted and actually experimentally observed. Sonovue, as well as other contrast agents based only on phospholipids, are, therefore, not suitable for use as non-invasive temperature monitoring medium since it is sensitive to temperatures below the hyperthermic range. Although microbubbles are in principle thermally effective, other coating materials should be investigated in order to increase their operative thermal range.     

High-performance optical code generation and recognition by use of a 511-chip, 640-Gchip/s phase-shifted superstructured fiber Bragg grating

The generation and recognition of a record-length 511-chip optical code is experimentally demonstrated by use of a superstructured fiber Bragg grating (SSFBG) with a chip rate of 640 Gchips/s. Very high reflectivity (92%) is achieved with high-quality correlation properties. The temperature deviation tolerance is approximately +/- 0.3 degrees C, which is within the package's temperature stability range (+/- 0.1 degrees C). Experimental results show good agreement with the theory. They indicate the SSFBG's potential for processing a long optical code with an ultrahigh chip rate, which could significantly improve the system's performance.     

Measurement of regional brain temperature using proton spectroscopic imaging: validation and application to acute ischemic stroke

A magnetic resonance proton spectroscopic imaging (SI) technique was developed to measure regional brain temperatures in human subjects. The technique was validated in a homogeneous phantom and in four healthy volunteers. Simulations and calculations determined the theoretical measurement precision as approximately +/-0.3 degrees C for individual 1-ml voxels. In healthy volunteers, repeated measurements on individual voxels had an S.D. = 1.2 degrees C. In a clinical study, 40 patients with acute ischemic stroke were imaged within 26 h (mean, 10 h) of onset. Temperatures were highest in the region that appeared abnormal (i.e., ischemic) on diffusion-weighted imaging (DWI) compared with a normal-appearing brain. The mean temperature difference between the DWI "lesion" area and the "normal brain" was 0.17 degrees C [P < 10(-3); range, 2.45 degrees C (hotter)-2.17 degrees C (cooler)]. Noninvasive temperature measurement by SI has sufficient precision to be used in studies of pathophysiology in stroke and in other brain disorders and to monitor therapies.     

A robust technique for two-dimensional separation of undistorted chemical-shift anisotropy powder patterns in magic-angle-spinning NMR

A robust magic-angle-spinning experiment for separating undistorted, quasi-static chemical-shift powder patterns is presented. It is derived from the technique of R. Tycko, G. Dabbagh, and P. Mirau (1989, J. Magn. Reson. 85, 265), but uses 360 degrees instead of 180 degrees pulses. In combination with a suitable phase sequence, this makes the spectral patterns very insensitive to pulse-length errors and other imperfections, as demonstrated both experimentally and theoretically. This method, termed separation of undistorted powder patterns by effortless recoupling (SUPER), can be used at standard spinning speeds, between 2.5 and 5 kHz, and with standard radiofrequency power levels (in particular, for protons, a decoupling field strength gammaB(1)/2pi of less than 80 kHz). No significant artifacts are observed even for samples extending to the ends of the radiofrequency coil. The method has been applied to samples containing various sp(2)- and sp(3)-hybridized carbon sites. Even for the methylene groups in polyethylene, a system with very strong C-H and H-H dipolar couplings and only moderate chemical-shift anisotropy (CSA), a useful CSA powder pattern has been obtained. With a CSA scaling factor of 0.155, accuracies of +/-5, +/-3, and +/-1 ppm of the principal values can be achieved for protonated aromatic carbons, unprotonated sp(2)-hybridized groups, and aliphatic sites, respectively. Examples of CSA-based assignment of COOC vs other COO or CON groups, and of aromatic vs olefinic C=C carbons are shown, for both small molecules and polymers.     

The effect of saccharides on the post-thaw recovery of cane toad (Bufo marinus) spermatozoa

The effect of monosaccharides (glucose, fructose) and disaccharides (maltose, sucrose, trehalose) as diluents, in cryoprotective additives containing 15% (v/v) DMSO or glycerol as cryoprotectants, were investigated on the recovery of sperm motility after cryopreservation of cane toad (Bufo marinus) spermatoazoa at low (approximately 5 degrees C/min(-1)) and high cooling rates (approximately 35 degrees C/min(-1)). The results show that: 1. recovery of percentage motility was higher with slow cooling than with high cooling rates (37.0 +/- 2.5%, 15.3 +/- 1.6%, P<0.001, respectively), 2. disaccharides were more effective than monosaccharides in protecting spermatozoa with slow cooling (43.9 +/- 1.2%, 26.8 +/- 2.5%, P<0.02, respectively), 3. glycerol was more effective than DMSO with fast cooling (18.3 +/- 2.2%, 12.6 +/- 2.3%, P<0.02, respectively), 4. trehalose with glycerol was the most effective cryoprotective additive with fast cooling (31.0 +/- 3.2%, P<0.05), and 5. overall the recovery of degree (vigour) of motility (range, 1.9 - 3.2) was more resilient to cryopreservation than recovery of percentage motility (range, 8.9 - 51.5 %). Comparison of post-thaw percentage and vigour of sperm motility up to 24 minutes after activation showed disaccharides supported greater duration sperm motility than monosaccharides This result and the recovery of spermatozoa immediately after freeze-thaw, show the main effect of saccharides are as cryoprotectants and not as exogenous energy substrates.     

Functional MR imaging of the human brain using FLASH: influence of various imaging parameters.

In this study the influence of a large variety of imaging parameters on the signal increase (DeltaS) and the contrast-to-noise ratio (CNR) of functional magnetic resonance imaging experiments was determined using FLASH imaging at 2 T. During visual stimulation of the brain we detected significant variations of DeltaS as a function of the echo time (30 ms: 3.5 +/- 0.4%, 60 ms: 6.8 +/- 0.7%), slice thickness (2.5 mm: 6.8 +/- 0.7%, 10.0 mm: 3.3 +/- 0.3%), and pixel size (4.69 mm: 3.1 +/- 0.3%, 1.88 mm: 5.9 +/- 0.5%). Significant changes of DeltaS with flip angle occurred for TE = 20 ms (15 degrees : 2.1 +/- 0.2%, 60 degrees : 3.2 +/- 0.5%). At TE = 30 ms there still was a slight increase (15 degrees : 3.0 +/- 0.4%, 60 degrees : 3.8 +/- 0.5%), while at TE = 50 ms no changes of DeltaS could be detected with flip angle. Furthermore, DeltaS decreased with the use of first-order flow and motion compensation (off: 5.8 +/- 0.6%, on: 4.5 +/- 0.5%). The purpose of this study was to identify the optimal imaging parameters for blood oxygenation level dependent contrast using FLASH imaging at 2 T. Relying on a time normalized contrast-to-noise ratio (CNR(n)) we found the following parameters to be optimal: TE approximately 40-50 ms, a rather low spatial resolution (slice thickness approximately 5.0-7.5 mm, pixel size approximately 2.3-4.6 mm, matrix size 64 x 48), and flip angles lower than 30 degrees. Flow compensation should not be applied, and a rather low bandwidth of approximately 2.5 kHz is favorable, as it yields a superior signal-to-noise ratio.     

Influence of concentration of substances used in ultrasonic cleaning in alkaline solutions on cavitation intensity

Cavitation intensity vs. temperature of aqueous solutions of three substances most frequently used in ultrasonic cleaning: sodium carbonate, metasilicate and phosphate were measured. Shapes of cavitation - temperature curves for 0-10% solutions during heating and cooling in the 20-70 degrees C temperature range were compared. Maximal cavitation intensity curves for these solutions at 60 degrees C (most frequently used temperature of ultrasonic cleaning in aqueous solutions), in identical conditions and at various ultrasound frequencies are presented as diagrams.     

Picosecond snapshot of the speckles from ferroelectric BaTiO3 by means of x-ray lasers

A picosecond x-ray laser speckle has been conducted to study the dynamics of a disordered surface domain structure (BaTiO3 with 90 degrees c/a domains) as a function of temperature for the first time. The transient surface structures induced by ferroelectric domains decrease as temperature increases towards the Curie temperature T(c) and completely disappear above T(c). The dramatic change of the spatial configuration of the c/a domains was observed to occur from a temperature 2 degrees C below T(c), near which the average correlated domain size at equilibrium decreases as (T(c)-T)(0.37+/-0.02).     

Enhanced stability of low temperature processed perovskite solar cells via augmented polaronic intensity of hole transporting layer

The commercial mass production of perovskite solar cells requires full compatibility with roll‐to‐roll processing with enhanced device stability. In line with this, the present work addresses following issues simultaneously from multiple fronts: (i) low temperature processed (140 °C) ZnO is used as electron transport layer (ETL) for fabricating the mixed organic cation based perovskite solar cells, (ii) the expensive hole transporting layer (HTL) spiro‐OMeTAD is replaced with F4TCNQ doped P3HT and (iii) the fabrication method does not incorporate the dopant TBP which is known to induce degradation processes in perovskite layer. All the devices under study were fabricated in ambient conditions. The F4TCNQ doped P3HT (HTL) based devices exhibits 14 times higher device stability compared to the conventional Li‐TFSI/TBP doped P3HT devices. The underlying mechanism behind the enhanced device lifetime in F4TCNQ doped P3HT (HTL) based devices was investigated via in‐depth electronic, ionic and polaronic characterization. The enhanced polaronic property in F4TCNQ doped P3HT HTL device ascertains its superior hole extraction and electron blocking capability; and consequently higher stability retained even after a month of ageing.

     

Applications of differential scanning calorimetry in developing cryopreservation strategies for Parkia speciosa, a tropical tree producing recalcitrant seeds

Shoot-tips of Parkia speciosa, a recalcitrant seed producing tropical leguminous tree withstood cryopreservation using encapsulation-vitrification in combination with trehalose preculture. Differential scanning calorimetry (DSC) revealed that trehalose moderated the thermal characteristics of the shoot-tips. A 30 min PVS2 treatment had the lowest glass transition temperature (Tg) (-50.2 +/- 1.1 degree C) when applied in combination with 5% (w/v) trehalose. The Tg increased to -40.2 +/- 1.0 degree C as the sugar concentration was decreased to 2.5 percent (w/v). Tg heat capacity for shoot-tips treated with 2.5 percent and 5 percent (w/v) trehalose and exposed to PVS2 for 30 min increased from 0.17 +/ 0.05 to 0.23 +/- 0.01 J per gram, respectively. Enthalpies of the melt-endotherm varied in proportion to trehalose concentration, for the 30 min PVS2 treatment, whereas the melt enthalpy for control shoots was greater than 150 J per gram and decreased to ca. 60 J per gram with 2.5 percent (w/v) trehalose. For 5 percent and 10 percent (w/v) trehalose treatments, enthalpy declined to ca. 24 and 12 J per gram respectively and freezing points were depressed to -75 degree C and -85 degree C with 2.5 percent and 5 percent trehalose (w/v), respectively. DSC elucidated the critical points at which vitrification occurred in germplasm exposed to trehalose and PVS2. A 60 min PVS2 treatment supporting ca. 70 percent survival was found optimal for stable glass formation during cooling and on rewarming.     

Cold tolerance and overwintering of an introduced New Zealand frog, the brown tree frog (Litoria ewingii)

The overwintering strategy of Litoria ewingii in Otago, New Zealand, was studied under laboratory and field conditions. Microhabitat temperature measurements showed that the frogs were often exposed to subzero temperatures. In the laboratory, Litoria ewingii tolerated freezing for up to 6 hrs at -1 degrees C, and after the completion of the freezing event (about 1 hr) at -2 degrees C. Frogs frozen with insulation survived freezing for 12 hrs at -1 degrees C. Frogs supercooled to -1.2 +/- 0.1 degrees C and -1.7 +/- 0.3 degrees C on wet and dry substrates respectively. L. Ewingii tolerated up to 47.5% of its body water frozen. Plasma glucose levels and osmolality were not increased during freezing. It is concluded that l. Ewingii cannot avoid freezing and is sufficiently freeze tolerant to survive the subzero temperatures encountered during winter in Otago.     

微流控芯片系统中测温及控温装置的研制

报道了一种结构简单、成本低、操作方便、应用于微流控芯片系统中温度测量及温度控制的装置。该系统以CCD摄像机、荧光显微镜及图像采集卡构成的非接触荧光指示剂测温装置,实现了微流体空间温度分布测量以及随时间变化的温度测量。提出了以透明氧化铟锡薄膜玻璃作为加热元件,采用PID控制算法的温度控制平台,稳态时温度控制精度可达到±0.1 ℃。采用该测温和控温装置研究了玻璃微流控芯片微通道内溶液温度在空间上和随时间的变化情况,结果表明该方法简单、有效,可达到μm级的空间分辨率和ms级的时间分辨率。     

Effects of coil dimensions and field polarization on RF heating inside a head phantom

Deterioration of radiofrequency (RF) inhomogeneity with increasing static magnetic field in magnetic resonance imaging (MRI) is one of the fundamental challenges preventing their clinical rendition and posing safety hazards. Variation in RF coil designs could help redistribute RF energy absorption over the imaged object. This work is intended to determine experimentally the difference in RF heating produced within a human head phantom by in situ measurement of RF inhomogeneity as a function of coil design utilized at 8 T. The heating patterns of 1/4 wavelength (long) and 1/8 wavelength 11-cm (short) transverse electromagnetic (TEM) coils loaded with a homogeneous human head phantom at 340 MHz were evaluated. In addition, different transmit/receive (T/R) configurations were used in search for the possibility of "hot-spot" formation. Fluoroptic thermometry was used to measure temperatures in multiple positions in a head phantom made of ground turkey breast for RF powers corresponding to a specific absorption rate (SAR) of 4.0 W/kg for 10 min. Numerical simulations were performed to study the general RF power deposition patterns in phantoms at 340 MHz including the effects of field polarization. The temperature increases varied from 0 to 0.8 degrees C for the long RF coil, while the short RF coil produced a maximum temperature change of 0.5 degrees C. Similar to ultra high-field electromagnetic simulations, these measurements revealed low peripheral and high deep-tissue heating at 8 T. The findings indicated that the largest temperature changes for both cases were less than 1 degrees C. While these results showed an increase in localized heating due to RF pulses at 8 T, they highlight that RF inhomogeneity could be redistributed using different RF coil designs through which the hot spots could be made cooler.     

芦丁热稳定性的红外光谱法实时原位跟踪

本文首次利用傅叶变换红外光谱法和变温附件」产时原位跟踪了天然药物芦丁折为性过程。结果表明：２５℃－２７０℃温度范围内,芦丁的热变性过程是一个伴随着芦丁氧化的热分解过程。在较低温度下（７５℃）芦丁的分子结构就开始发生变化,不仅暗示了中国态的存在,还进一步验证芦丁的稳定性较差;在较高温度下（２７０℃）芦丁分解成两种产物。该方法快速、准确、无溶剂效应,可进行榈的无损原位检测。     

Effects of hypothermia on ischaemic depolarisation in brain : a comparison of responses in rat and gerbil

The latency of development of ischaemic depolarization (LID) has been used to compare the relative effects of different levels of hypothermia on ischaemic responses in brains of rat and gerbil, using a model with imposed complete cessation of cerebral blood flow (CBF=0). At temperatures reducing from 37 degrees C to 20 degrees C, the LIDs were consistently shorter in the gerbil than in the rat. For example, at 37 degrees C the LID in the gerbil was 0.71+/- 01.2 min, and in the rat, 1.37 +/- 0.02 min respectively (P<0.01), whilst at 20 degrees C, the values were 5.48 +/- 0.25 min and 7.30 +/- 0.76 min (P<0.01). However, the relative effects of hypothermia on each species were similar (by linear regression with slopes of -0.29 and -0.35 min/degree C in the two species). There may be underlying differences in brain biophysics or structure between species, but in spite of this, applied hypothermia still imposes a similar depression on the development of ischaemic damage. Both models may thus be used in studies of brain hypothermia as long as the intrinsic differences are appreciated.     

Effect of alcohol consumption on the liver detoxication capacity as measured by [13C]methacetin- and [methyl-13C]methionine-breath tests

The aim of this study was to investigate the hepatic microsomal and mitochondrial functions by using the 13CO2-breath test in healthy subjects either before or after the consumption of red wine. Fourteen adults received [13C]methacetin and [methyl-13C]methionine together with a standardised dinner. Expired air samples were taken over 6 h. After a wash-out period, the subjects consumed 0.4 ml ethanol/kg/day together with dinner over a 10-day period. Thereafter, 13C-tracer administration was repeated under identical conditions. The 13CO2-enrichments were measured by isotope ratio mass spectrometry. The mean cumulative percentage 13C-dose recovery (CPDR) after administration of [13C]methacetin and [methyl-13C]methionine either without or with red wine consumption amounted to 38.2+/-6.3 vs. 36.3+/-6.7% (p=0.363) and 9.5+/-3.3 vs. 8.8+/-2.5% (p=0.47), respectively. Moderate alcohol consumption does not induce significant short-term changes of the microsomal and the mitochondrial functions of the human liver in healthy subjects.     

The use of ultrasound-stimulated acoustic emission in the monitoring of modulus changes with temperature

It has been previously shown that the amplitude of the ultrasound-stimulated acoustic emission (USAE) signal is sensitive to tissue temperature and, therefore, can help detect it. Its amplitude, however, is sensitive to both acoustical and mechanical parameters, that at most frequencies have opposite effects due to temperature. In this paper, we explore the feasibility of using a frequency shift of the resonant peaks of the USAE signal for monitoring the tissue stiffness variation with temperature. In a numerical simulation, the variation of the frequency shift at different temperatures is shown. Then, in a series of experiments involving a gel phantom and porcine muscle tissue, the frequency shift variation is shown to follow the known stiffness changes due to temperature. It is also shown that this shift indicates reversible changes as well as the onset of thermal coagulative necrosis. The necrosis is marked by a monotonically increasing positive frequency shift. It was thus shown that the USAE spectrum peaks undergo a negative shift (or, downshift) when the stiffness decreases and a positive shift (or, upshift) when the stiffness increases. The experimental frequency shifted around a peak at 22.1-22.5 kHz within a range of -250 to 80 Hz and -200 to 250 Hz for the gel and muscle tissue for the temperatures of 25-70 and 30-70 degrees C, respectively. Simulation and ex vivo experimental results indicate that the USAE frequency shift method can help decouple the mechanical from the acoustical parameter dependence as well as detect the onset of thermal coagulative necrosis.     

The effects of ultrasound on the mechanical properties of rat cardiac muscle

The mechanical properties of cardiac muscle during ultrasonic irradiation have been studied in vitro. Left anterior papillary muscle from normal rats was suspended in buffered lactated Ringers solution equilibrated with 95% O2, and 5% CO2 and maintained at 20 degrees C. The muscles were stimulated to contract isometrically three times per minute at the length which produced maximum tension. Each muscle was irradiated with a MHz ultrasound at an average power of 2.4 Wcm-2 for a period of 10 min with a 10 min recovery period. Irradiation caused an average increase in temperature of the muscle of 1.7 +/- 0.2 degrees C (mean +/- SEM). Irradiation caused the resting tension (1.46 +/- 0.13g) to decrease by 17.8 +/- 4.7% and the developed tension (3.33 +/- 0.61g) to decrease by 4.1 +/- 0.9%. Since changes in contractile properties have been reported with temperature the bath temperature was raised and changes in contraction observed. When compensated for effects of temperature, the changes in resting tension became - 13.3 +/- 4.1% while the change in developed tension became + 1.6 +/- 2.3%. The change in resting tension is highly significant (p less than 0.05 paired t-test) while the change in developed tension is not. Thus 1 MHz ultrasound at an intensity of 2.4 Wcm-2 appears to affect resting tension of cardiac muscle without affecting the active tension. Since changes in cardiac mechanics of this type have not been described previously the effects of ultrasound appears to be unique.     

石英拉曼峰进行压力标定的误差研究

在常温常压下进行了作为压标的石英颗粒的拉曼光谱测量和研究。研究结果发现,在25℃和常压条件下,不同的石英颗粒测得的Si—O振动模在463.59～464.65cm-1范围内变化,误差为(±0.1～±0.3)cm-1。其中不同石英颗粒拉曼峰的最大差异达1.06cm-1,远远大于其测量误差。我们认为这是由于石英破碎时使石英颗粒内产生的应力所致。因此,在进行金刚石压腔高温高压实验的压力确定时,必须以常压下实测的Si—O振动模测量值为零压参考点。另外,拉曼光谱仪的波数漂移以及环境温度的不稳定均会造成不可忽视的压力测量误差,应对此进行校正。