Crystal Sheet Research Articles

Quantitative measurements in thermo-fluid dynamics based on colour processing

Colour can be expressed as a weighted combination of three attributes: hue, intensity, and saturation. Non-coherent light reflected by thermo-sensitive liquid crystals holds a variable hue, moving in a generally narrow temperature interval and also depending on its inclination with respect to the plane of the crystals and on the characteristics of the impinging light. In experimental practice it is not feasible to ensure uniform lighting over an extensive area and its entire view under the same angle. Thus, the acquired hue field is non-uniform even if the liquid crystal sheet is isothermal. However, by means of proper filtering and calibration of the colour attribute, this optical technique, besides being non-intrusive and inexpensive, is capable of mapping the temperature with an accuracy better than 5% of its measuring-range amplitude. A similar method can be applied for measuring the thickness of a thin liquid film. In this case, the colour attribute to be processed is its intensity. In fact, the light transmitted through a dyed liquid decreases with an increasing thickness of the layer. Again, a perfectly uniform light source is unattainable and the recorded intensity field is non-homogeneous even if the liquid free surface is flat. Nevertheless, the film thickness can be determined by this colour-processing procedure with an accuracy better than 8% of the measuring-range amplitude, which is dictated by the utilised dyestuff concentration. Further thermo-fluid dynamic measurements performed over extensive areas could be handled with analogous methodologies. Surface temperature by emitted infrared waves and void fraction in ducts by light absorption are particular examples.

Model pharmaceutical co-crystallization: Guest-directed assembly of caffeine and aromatic tri-hydroxy and dicarboxylic acids into different heteromolecular hydrogen bonding networks in solid state

Three model pharmaceutical caffeine-containing co-crystals of 1,3,5-trihydroxybenzene (phloroglucinol), isophthalic acid and 5-hydroxyisophthalic acid were synthesized and characterized via single-crystal X-ray diffraction. The three crystalline forms reported are an anhydrous co-crystal and other two are co-crystal hydrates. Also their binding properties were studied by UV–vis analysis. In each of these structures, an organised intermolecular hydrogen bonding motif was observed. A comparison of hydrogen bonding motifs in the crystal sheets was presented.

Measurement of Heat Transfer During Drop-Wise Condensation of Water on Polyethylene

Heat transfer coefficients associated with drop-wise condensation are quite large. Because the ensuing driving temperature difference is small, experimental determination of heat transfer coefficient is a challenge. The statistical nature of droplet distribution in the ensemble contributes to the intricacy of analysis and interpretation. Against this background, the spatial distribution of temperature during drop-wise condensation over a polyethylene substrate was measured using liquid crystal thermography (LCT) simultaneously with actual visualization of the condensation process by videography. Experiments were conducted in such a way that pendant drops form on the underside of the liquid crystal sheet. Temperature variation at the base of the droplets, as small as 0.4 mm, were satisfactorily resolved. The signature of the drop shape was visible in the LCT images. The drop size distribution on the substrate was simultaneously visualized. Static contact angles of water on polyethylene are measured and drop shapes were estimated via a mathematical model for comparison. Using a one-dimensional heat transfer approximation, heat flux profiles through individual droplets were obtained. The temperature profiles from LCT combined with drop sizes from direct visualization provide sufficient data for understanding the heat transfer mechanism during drop-wise condensation. Results show that the measured heat flux as a function of drop diameter matches published data for large drop sizes but fails for small drops where the thermal resistance of the LCT sheet is a limiting factor. To a first approximation, the present work shows that drop size can be correlated to the local heat flux. Hence, the average heat flux over a surface can be obtained entirely from the drop size distribution.

Heat Transfer under Buoyancy-Induced Flow at the Chemical Reaction Front Using Thermochromic Liquid Crystal Sheet

Heat transfer and hydrodynamics at the chemical reaction front have been investigated experimentally using a thermochromic liquid crystal sheet. If the chemical reaction occurs, a band region where the temperature, due to the heat of reaction, is higher than the initial temperature appears at the reaction front. Natural convection due to the temperature difference at the reaction front plays an important role in conveying the higher temperature fluid. For the hydrochloric acid (HCl)–sodium hydroxide (NaOH) system, as the frequency of contact between HCl and NaOH due to convection increases with the concentration of ethanol, the temperature beyond the stagnation point becomes higher than that in other areas. On the other hand, for the acetic acid (CH3COOH)–NaOH system, the heat transfer depends mainly on the heat of reaction, because the rate of CH3COOH dissolution is smaller than that of HCl.

Experimental Study on Control of an Impinging Jet Heat Transfer Using Triangular Tabs

This paper describes the heat transfer enhancement by triangular tabs attached to the nozzle exit of the jet. Experiments on the impinging jet were performed to clarify the effect of the triangular tabs on the heat transfer. In particular, the attention is paid on the relationship between tab pitch angle θ and heat transfer enhancement ratio defined as NuTab/Nu0. Temperature distribution was measured by a thermosensitive liquid crystal sheet on the impingement plate of a glass coated by ITO (Indium Tin Oxide) film. In the case of θ =90 or 135 deg, the region of heat transfer enhancement is wider than the case of θ =45 deg. The velocity field was also measured by a hot-wire anemometer in the jet and over the impinging plate to investigate the relation between the flow field and the temperature field. It is found that the flow fluctuation by the tabs clearly contributes to the heat transfer promotion.

Orientation effect on recovery and recrystallization of cold rolled niobium single crystals

Single crystal sheets of niobium with initial orientations of (0 0 1) [ 1 1 ¯ 0 ] , (1 1 0) [ 1 1 ¯ 0 ] and (1 1 1) [ 1 1 ¯ 0 ] were rolled at room temperature in the strain range of 25–50%. The deformed specimens were vacuum annealed at temperatures of 800 °C, 1000 °C, and 1200 °C for 3 h. TEM, SEM-OIM and optical microscopy revealed orientation stability in (0 0 1) and (1 1 0) rolled samples with no recrystallization observed after annealing. Samples rolled along (1 1 1) partially recrystallized after annealing at 1000 °C and 1200 °C. A relatively small increase was observed in hardness of (0 0 1) rolled crystals between 25% and 50% strain, implying low work hardening rates. (1 1 1) rolled samples showed higher hardening rates, and enhanced recovery in hardness values after annealing, due to partial recrystallization. Conditions have been identified for the deformation and annealing of niobium single crystals, enabling the preservation of single crystal structure and near-complete recovery of mechanical properties. A simple crystallographic model is proposed, giving an explanation for the observed orientation stability in (0 0 1) and (1 1 0) rolled samples, and the tendency towards instability and recrystallization in (1 1 1) rolled samples.

Hydrogen-bonding sheets in crystals for chirality recognition: synthesis and application of (2 S,3 S) -2,3-dihydroxy- and (2 S,3 S) -2,3-dibenzyloxy-1,4-bis(hydroxyamino)butanes

Two enantiopure bis(hydroxyamino) compounds were successfully prepared from dialkyl tartrate by a chiral-pool method and applied as basic resolving agents in the enantioseparation of 2-arylpropanoic acids and arylglycolic acids. (2 S,3 S) -2,3-Dihydroxy-1,4-bis(hydroxyamino)butane (2 S,3 S) - 1a could moderately recognize the chirality of the 2-arylpropanoic acids, while (2 S,3 S) -2,3-dibenzyloxy-1,4-bis(hydroxyamino)butane (2 S,3 S) - 1b could not due to the low crystallinity of both the corresponding diastereomeric salts. On the other hand, (2 S,3 S) - 1b showed a similar chirality-recognition ability for the arylglycolic acids. The ability of (2 S,3 S) - 1b was different from those generally observed for widely used primary amine-type resolving agents with regard to the relationship between the resolution efficiency and the similarity in the relative molecular length of a resolving agent and a target racemate. The X-ray crystallographic analyses of the less-soluble diastereomeric salts revealed that in the salts (2 S,3 S) - 1a formed a supramolecular sheet, of which the distance was variable to make the resultant dissymmetric space fit to the shape of the target acids, and that (2 S,3 S) - 1b was constructed from a robust supramolecular sheet, consisting of hydrogen-bonding 2 1 columns, with the participation of the hydroxy group of the arylglycolic acids. These X-ray crystallographic analyses also suggested that for the formation of a supramolecular sheet, the coexistence of two hydroxyamino groups is essential.

Oscillation Effect of Impingement Surface on Two-Dimensional Impingement Heat Transfer

This paper describes the oscillation effect of impingement surface on two-dimensional impingement heat transfer with confined wall. The local temperature distribution on an impingement surface was measured using a thermosensitive liquid crystal sheet and an image processor. Experiments were conducted by using air as a working fluid. Experimental conditions were as follows: Reynolds number Re=1000–10,000, dimensionless distance between nozzle and impingement surface h∕B=1.0–4.0, frequency f=0–100Hz, and amplitudes a=0.5mm and 1.0mm. The local Nusselt number was improved for the comparatively low Reynolds number and low frequency and was depressed for high frequency. In the case of heat transfer enhancement, vortices on the impingement surface were renewed frequently, and on the other hand, in the case of heat transfer depression, thermal boundary layer thickness increased in appearance by the vibration of the impingement surface.

Size effects on thin film ferroelectrics: Experiments on isolated single crystal sheets

Thin lamellae were cut from bulk single crystal BaTiO3 using a focused ion beam microscope. They were then removed and transferred onto single crystal MgO substrates, so that their functional properties could be measured independent of the original host bulk ferroelectric. The temperature dependence of the capacitance of these isolated single crystal films was found to be strongly bulklike, demonstrating a sharp Curie anomaly, as well as Curie–Weiss behavior. In addition, the sudden change in the remanent polarization as a function of temperature at TC was characteristic of a first order phase change. The work represents a dramatic improvement on that previously published by Saad et al. [J. Phys.: Condens. Matter 16, L451 (2004)], as critical shortcomings in the original specimen geometry, involving potential signal contributions from bulk BaTiO3, have now been obviated. That the functional properties of single crystal thin film lamellae are comparable to bulk, and not like those of conventionally deposited heterogeneous thin film systems, has therefore been confirmed.

NANOSCALE FERROELECTRICS MACHINED FROM SINGLE CRYSTALS

ABSTRACT This paper summarises some of the most recent work that has been done on nanoscale ferroelectrics as a result of a joint collaborative research effort involving groups in Queen's University Belfast, the University of Cambridge and the University of St. Andrews. Attempts have been made to observe fundamental effects of reduced size, and increasing morphological complexity, on ferroelectric behaviour by studying the functional response and domain characteristics in nanoscale single crystal material, whose size and morphology have been defined by Focused Ion Beam (FIB) patterning. This approach to nanoshape fabrication has allowed the following broad statements to be made: (i) in single crystal BaTiO3 sheets, permittivity and phase transition behaviour is not altered from that of bulk material down to a thickness of ∼ 75 nm; (ii) in single crystal BaTiO3 sheets and nanowires changes in observed domain morphologies are consistent with large scale continuum modeling.

Photorefractive Properties of Potassium Lithium Niobate Crystals with CeO 2 and Nd 2O 3

KLN and Ce:Nd:KLN crystals were grown by Czochralski method and polarized into single ferroelectrics domain along c-axis. The properties of KLN and Ce:Nd:KLN crystals, such as Curie temperature, Raman spectra, exponential gain coefficient ( T) and thin crystal sheet effect, were measured. The results showed that the two spectra resembling Ce:Nd:KLN crystal were of tetragonal tungsten bronze structure, the exponential gain coefficient of Ce:Nd:KLN crystal was higher than that of KLN crystals and Ce:Nd:KLN crystal had thin crystal sheet effect, for its exponential gain coefficient increasing with crystal sheet thinning. The thin crystal sheet effect of Ce:Nd:KLN crystal was also discussed.

Phase transition characteristics of Bi/Sn doped Ge 2Sb 2Te 5thin film for PRAM application

The Bi and Sn were doped to Ge 2Sb 2Te 5 (GST) to investigate and modify the phase transition characteristics. The Bi/Sn doped GST thin film was prepared by RF magnetron co-sputtering and its crystal structure, sheet resistance, and phase transition kinetics were analyzed. By the doping of Bi/Sn, the crystallization temperature or stable phase was changed slightly compared with GST. For the PRAM application, the optimum doping concentration was Bi 5.9 and Sn 17.7 at.%, and its minimum time for crystallization was shorten more than 30% compared with GST. The sheet resistance difference between amorphous and crystalline state was higher than 10 4 Ω/□.

Thermal effect of microbubbles in the focused ultrasound field

High-intensity focused ultrasound (HIFU) has been developed for the treatment of tumor, and additionally the medical applications with microbubbles such as ultrasound imaging have attracted much attention. In the field of the bubble dynamics, it is known that the microbubble is an energy converter of ultrasound mechanical energy to heat when subjected to an acoustic field. The goal is the tissue heating enhanced by microbubbles. In this study, the relationship between the heating effect and the behavior of microbubbles is analyzed. The temperature rise was measured by a thermocouple and a thermal liquid crystal sheet, and the bubble behavior was simultaneously observed with a camera. The ultrasound frequency is 2.2 MHz and the intensity is 100–2000 W/cm2. The temperature rise became larger as the number density of microbubbles (Levovist) around the focal region increased. As the number density became too large, the conversion efficiency from ultrasound energy to heat became smaller because the shielding effect of ultrasound by the existence of too many bubbles became larger. From these results, it is indicated that it is important to choose the optimal conditions of microbubbles and ultrasound in order to control the heat deposition from microbubbles.

Positioning Annihilation Photon Interactions in a Thin LSO Crystal Sheet With a Position-Sensitive Avalanche Photodiode

Using scintillation crystal sheets instead of discrete crystal arrays in high-resolution PET has the immediate advantage of reduced complexity as well as a potential for increased sensitivity. In order to evaluate the positioning capability of a position sensitive avalanche photodioide (PSAPD) using a sheet Lutetium Oxyorthosilicate (LSO) crystal scintillator, we studied the dependence of detected event position versus the known source position. In particular, we studied positioning in a continuous 8 mmtimes8 mm LSO sheet coupled to a PSAPD with an 8 mmtimes8 mm active area experimentally, studied optical transport in the sheet crystal with Monte Carlo simulation, and used two positioning methods to evaluate PSAPD pincushioning effects. Both collimated <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">57</sup> Co 122 keV and coincidence-triggered <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">22 </sup> Na 511 keV sources were used in the experiments performed. We analyze the energy resolution, sensitivity, photopeak position and spatial resolution as a function of source position. An average point spread function (PSF) resolution of 2.86 and 1.12 mm FWHM for <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">57 </sup> Co and <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">22</sup> Na respectively was observed. Within 1.2 mm from the edge of the LSO sheet, the average photopeak position change was 5%. Simulations using annihilation photon interactions from GATE and scintillation photon transport from DETECT2000, as well as utilizing a pincushion-reduction posioning algorithm, have confirmed that the positioning and energy response observed experimently at the edge of the crystal is due to optical transport near those edges

On Magnetic Field Control Experiments of Ferrofluid Convection Motion

Summary The experiments have been performed on the stability of buoyancy-driven flows of a ferrofluid for the cases of an inclined and vertical orientation of thin cylindrical encloser. Visualization of flow patterns is provided by a temperature-sensitive liquid crystal sheet which serves as the lower surface of a transparent heat exchanger. The local temperature sensor is used for measurement of heat transport across the fluid layer. The results indicate that with the help of an external homogeneous transversal magnetic field it is possible to control the stability of thermogravitational shear flow under vertical orientation of the layer, i.e. induce the thermomagnetic mode of instability with vertical orientation of longitudinal convection rolls. As numerous experimental investigations show the origin of concentration density gradients due to gravity sedimentation of magnetic particles and their aggregates results in traveling wave regimes of Rayleigh and thermomagnetic convection flows.

10303 集束超音波音場における微小気泡を含む媒質内の温度分布(流体(1))

HIFU (High Intensity Focused Ultrasound) treatment combined with microbubbles as a heat transducer has currently been investigated. It has been indicated that microbubbles have a potential to enhance the heat deposition around the focal region of ultrasound. In order to realize this method, it is needed that the coagulation region in the tissue which contains microbubbles is well-controlled. In this study, the temperature distribution in the medium with microbubbles is analyzed in detail. This time, a thermal liquid crystal (TLC) sheet is used for the measurement of temperature distribution in a polyacrylamide gel. In the case of no bubbles, the shape of the high temperature region was ellipse. In the case of some bubbles, the shape grew more complicated and its area became larger. The microbubbles radiate heat energy around them, and the attenuation effect of ultrasound becomes larger. In the case of too many bubbles, the temperature at the geometric focus didn't become so high. The bubbles shield the most of ultrasound energy. It is very important to choose the optimal conditions of microbubble-enhanced HIFU treatment, considering these phenomena.

On features of ferrofluid convection caused by barometrical sedimentation

The experimental and numerical studies of Rayleigh convection in a thin cylindrical layer have been conducted for a ferrofluid containing magnetite particles suspended in kerosene carrier liquid. Near the onset of convection, the wave oscillatory convection was observed both in the experiments and in the numerical finite volume simulations. Time periods of temperature oscillations obtained using thermocouples were investigated using wavelet analysis. Thermosensitive liquid crystal sheet visualizations of flow patterns revealed irregular spatiotemporal behavior of convection, close to the threshold. Numerical simulations using a two-phase mixture model indicated that the initial sedimentation gradient may lead to spatiotemporally chaotic convection. Experimentally observed hysteresis and strong dependence of the measured heat flux from the prehistory of the experiments allude to non-Newtonian nature of ferrocolloids.

Scintillation crystal design features for a miniature gamma ray camera

A miniature scintillation camera with a 5 cm /spl times/ 5 cm field-of-view (FOV) is being developed to aid in surgical staging of cancer. This paper reports on certain interesting design aspects of the scintillation crystal array. Simulations and measurements of different types of crystal materials revealed that lutetium oxyorthosilicate (LSO), which is ordinarily used in PET, has appealing properties for detecting 140 keV photons. For example, LSO requires only 3 mm of thickness for 95% detection efficiency at 140 keV. This small thickness is appealing for high light collection efficiency, narrow light distribution, and minimizing the LSO volume in order to reduce intrinsic background events produced by /sup 176/Lu (2.6% abundance). Studies of both discrete and sheet crystals revealed that discrete crystal arrays have the advantage of increased spatial linearity and dynamic range compared to crystal sheets. For optimizing sensitivity and spatial resolution, several crystal array conditions were investigated, including ground crystal pixels packed tightly together with internal reflectors and with optical coupling grease. This design focuses the light, but also allows adequate light sharing for positioning with the position sensitive photomultiplier tube (PSPMT) that will be used in the gamma camera.

Stereochemistry Driven Distribution of 1,4-Diaminocyclohexane Residues over the Crystalline and Amorphous Phase in Copolyamides 4.14/1,4-DACH.14. A Solid-State NMR and Temperature-Dependent WAXD Study

Following our previous study on the stereoselective cocrystallization of linear and cyclic dicarboxylic acid residues in copolyamides 12.6/12.1,4-cyclohexanedicarboxylic acid (12.6/12.1,4-CHDA, Vanhaecht et al., Macromolecules 2004, 37, 421), we have now investigated a series of copolyamides containing trans or cis isomers of 1,4-diaminocyclohexane (1,4-DACH), viz. 4.14/1,4-DACH.14. Solid-state NMR studies and WAXD experiments demonstrate that the cis isomer is present in the amorphous regions of the copolyamide, whereas the trans isomer is located in both the crystalline and the amorphous phase. Similar to the results for the trans-1,4-CHDA-based copolyamides, trans-1,4-DACH moieties are probably built into the crystalline structure with the cycloaliphatic ring oriented perpendicular to the hydrogen-bonded crystal sheets. Temperature-dependent WAXD patterns show that, unlike in the homopolyamide 4.14, a pseudohexagonal phase is not formed at the Brill temperature in the copolyamide. Instead, crossing rat...

GRAVITATIONAL AND MAGNETIC CONVECTION IN MAGNETIC FLUID

Experiments were performed to examine the influence of external homogeneous magnetic field on ferrofluid convection in thin cylindrical layer heated from one wide sidewall and cooled from another. Gravitational and magnetic mechanisms of convection as well as the influence of gravitational sedimentation of particles and their aggregates on stability and structure of fluid flows are studied. The integral and local temperature sensors were used for measurement of heat transport across the layer. Visualization of flow patterns was provided by a temperature-sensitive liquid crystal sheet. The results indicate that with the help of a magnetic field it is possible to control the stability and the form of convection motions. Besides, the concentration gradients of solid phase can have material role to convection instability and heat transfer.