Modeling of an isolated liquid hydrogen droplet evaporation and combustion

In this model, diffusive governing equations of Liquid Hydrogen (LH) evaporation and combustion were solved. The simulation reveals that, there exists a critical radius (a_cri) where radiation heat is equal to conduction heat (Q_rad = Q_cond) and a_cri is a function of ambient temperature during LH droplet evaporation process. Under pure evaporation condition, for large liquid hydrogen droplets (a > a_cri) radiation heat is dominant at a given environment temperature, but as liquid droplet size decreases, radiation heat becomes insignificant and thermal conduction will be dominant for liquid evaporation. When LH droplet is burned in a cold environment (T_∞ = 300 K), there are two films above the LH surface, Film I is from LH surface to flame front within which a dense hydrogen gas cloud is formed; Film II is from flame front to the free stream where oxygen is diffused inward to react with hydrogen. The flame front is located about 95 times of the droplet radius (r_f = 95a) and the flame temperature could rise up to 2077 K. When an LH droplet is immersed in a hot environment (T_∞ = 2050 K), the flame front is located at a similar distance to the LH droplet (r_f/a = 114) and flame temperature could go up to 3769 K.     

Rotatable liquid crystal waveplate

A photoresist well of size 60 × 60 × 15 μm³ has been used to confine a droplet of nematic liquid crystal to create a rotatable waveplate. The optical texture of the droplet between crossed polarisers is consistent with the nematic n-director running substantially along a diameter of the droplet and connecting two nematic defects on the curved edges of the droplet. Electric field induced azimuthal rotation of the axis of the nematic liquid crystal droplet has been demonstrated. At higher temperatures, 30 °C and above, the droplet is more circular in shape and can be switched to arbitrary rotation angles. At lower temperatures, 25 °C and below, the sides of the droplet are straightened by the interaction with the well walls and the switching tends to favour discrete orientations of the optic axis. The shape of the time–voltage switching response curve for rotation by an angle of 40° also depends on the temperature of the droplet. A switching time that is inversely proportional to the voltage squared results when the droplet is nearest to circular in shape.     

Synthesis of nanostructured TiO2 particles in room temperature ionic liquid and its photocatalytic performance

Nanostructured TiO₂ particles were synthesized by sol-gel method with room temperature ionic liquid (RTIL) 1-n-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF₆]) as a reaction medium. The structure and morphology of TiO₂ nanoparticles were characterized with X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). The as-prepared TiO₂ nanoparticles present anatase crystal phase even without being calcined at high temperature, and show better photocatalytic performance in the degradation of methyl orange. The photocatalytic efficiency increases evidently along with increasing the concentration of nanostructure TiO₂, and the degradation percent can reach 100% at the optimal catalyst concentration (2.0 g/L).     

Analysis of dichroic dye-doped polymer-dispersed liquid crystal materials for display devices

Dichroic polymer-dispersed liquid crystals (DPDLCs) based on nematic liquid crystal materials with azo dye were investigated in detail for the application of display devices. Polarizing optical microscopy, differential scanning calorimeter and electro-optic experiments all have shown that the DPDLC containing low concentration of dyes modifies the basic properties of these materials like optical transmission, threshold voltage, contrast ratio and absorbance factor. A minimum amount of dye needs to be added to the liquid crystal with the polymer matrix for its effective phase separation and to minimize the transmittance in the OFF state and therefore gives rise to an overall improvement in contrast ratio of the devices. Molecular orientation and dynamics in droplet sizes are readily controlled in these DPDLC materials. These findings imply that the value of the threshold electric field E_th is approximately 8 V/μm for pure polymer-dispersed liquid crystal (without dye) where the threshold electric field E_th values are approximately 4.0 V/μm, 2.0 V/μm, 1.7 V/μm 1.0 V/μm, for 0.0625%, 0.125%, 0.25% and 0.5% with azo dye in DPDLCs, respectively. From the results we can also infer that the maximum contrast is approximately 2.55 times the minimum contrast observed in the experiment for DPDLCs. The results show that the DPDLC with proscribed dye concentration will be possibly suitable and promising functional electronic materials for green technology flexible liquid crystal display.     

Optical properties of BaCaBO3F crystal

The optical transmission spectra of BaCaBO₃F (abbr. BCBF) crystal have been measured at room temperature. The refractive indices have been measured with the minimum deviation method and fitted to the Sellmeier equations. The nonlinear optical coefficient d₂₂ of BCBF crystal determined by the Maker fringe technique is 0.74d₃₆(KDP).     

An Approach to Use a Raw Single Crystal Whisker as Intrinsic Josephson Junctions Stack

We have developed a technique to observe the intrinsic Josephson effect in Bi₂Sr₂CaCu₂O_8+δ (Bi-2212) single crystal whiskers. In this technique, a raw Bi-2212 single crystal whisker used as intrinsic Josephson junctions (IJJs) along the c-axis. The technique is simple, quick, and less-cost processing. First, a whisker made to stand on ac-plane and then two electrodes were made in ab-planes on either side. The standing whisker with this configuration worked as IJJs. The standing whisker (1.6 mm×40 μm×3 μm) showed the transition temperature of about 84 K. The critical current was about 15 mA at 8 K (critical current density ～23 A/cm²). We observed voltage gap of about 500 mV in current–voltage (I–V) characteristics. This corresponds to a few hundred of IJJs out of ～2,000 IJJs in the whisker thickness. Observations reflect that the technique can be further improved with the single crystal quality, shape of single crystal whisker, and annealing conditions.     

Effect of frequency on dielectric properties of liquid crystal doped with side-chain liquid crystalline polymer

The frequency and applied bias voltage dependence of the dielectric properties and dielectric anisotropy of liquid crystal (LC) doped with side-chain liquid crystalline polymer (SLCP) mixture have been investigated using the admittance spectroscopy method (C–V and G/ω–V) in the frequency range of 10 kHz to 10 MHz at room temperature. The liquid crystal used in this experiment is E63. The doping material used in this study is SLCP and its concentration is ensured 1 wt % in E63. Dielectric constant (?′), dielectric loss (?), dielectric loss tangent (tan δ) and real and imaginary parts of electrical modulus (M′ and M″) of the E63/SLCP mixture was also calculated. Moreover, dielectric anisotropy (Δ?) as a function of frequency was obtained. Results show that the values of the all dielectric parameters are strong functions of frequency and applied bias voltage. After a critical frequency, dielectric anisotropy has negative values according to p/n type changing.     

Colloidal Material Box: In-situ Observations of Colloidal Self-Assembly and Liquid Crystal Phase Transitions in Microgravity

To study the self-assembly behavior of colloidal spheres in the solid/liquid interface and elucidate the mechanism of liquid crystal phase transition under microgravity, a Colloidal Material Box (CMB) was designed which consists of three modules: (i) colloidal evaporation experimental module, made up of a sample management unit, an injection management unit and an optical observation unit; (ii) liquid crystal phase transition experimental module, including a sample management unit and an optical observation unit; (iii) electronic control module. The following two experimental plans will be performed inside the CMB aboard the SJ-10 satellite in space. (i) Self-assembly of colloidal spheres (with and without Au shell) induced by droplet evaporation, allowing observation of the dynamic process of the colloidal spheres within the droplet and the change of the droplet outer profile during evaporation; (ii) Phase behavior of Mg₂Al LDHs suspensions in microgravity. The experimental results will be the first experimental observations of depositing ordered colloidal crystals and their self-assembly behavior under microgravity, and will illustrate the influence of gravity on liquid crystal phase transition.     

A room temperature solution-phase method to synthesize β-Ni(OH)2 nanoneedles

A simple room temperature solution-phase method has been employed to synthesize β-Ni(OH)₂ nanoneedles in the presence of a suitable cationic surfactant cetyltrimethylammonium bromide for the first time. The chemical composition and morphology of the as-prepared β-Ni(OH)₂ nanoneedles were characterized by X-ray powder diffraction and transmission electron microscopy. The effect of surfactant and NH₄OH on the morphology and size of β-Ni(OH)₂ nanoparticles was discussed in detail. The growth mechanism of the as-synthesized nanoneedles was discussed based on the experimental results. The results indicate that the binding between CTAB and β-Ni(OH)₂ crystal nuclei inhibits crystal growth randomly and favors needle-like single crystal growth with their preferred facets.     

Specific features of attenuated light transmission by liquid-crystal twist cells in constant and alternating electric fields

Optical transmission characteristics of dual-frequency nematic liquid crystal (NLC) twist cells with different alignment layers (rubbed polyimide and obliquely deposited cerium dioxide) have been studied in constant and alternating electric fields. It has been established that a change in the optical (twist effect) threshold and dynamic range of attenuated transmission depend both on the boundary conditions (that influence the screening of applied voltage) and on the parameters of the applied electric field. The maximum dynamic range (49.5 dB) has been obtained in the cell with a CeO₂ alignment layer controlled by a constant potential. In the case of an alternating electric field, the dynamic range decreases because of reduced effective voltage.     

Synthesis of nanostructure rutile TiO2 in a carboxyl-containing ionic liquid

Nanostructure rutile TiO₂ was prepared in a carboxyl-containing ionic liquid, 1-methylimidazolium-3-acetate chlorine ([AcMIm]Cl), by using TiOCl₂ solution as a precursor at low temperature. The obtained nanostructure TiO₂ was analyzed with fourier transform infrared (FTIR), X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). The as-prepared TiO₂ present only rutile crystal phase and a novel flower-like morphology. The as-prepared rutile TiO₂ shows better photocatalytic performance in the degradation of methyl orange. The template-directing performance of ionic liquid is due to the bidentate chelating complexation between the carboxylic functional group of ionic liquid and titania.     

Physicochemical properties and theoretical explanation of ZnCd(SCN)4 crystal

The crystal density and Mohs hardness of zinc cadmium thiocyanate (ZCTC), ZnCd(SCN)₄ have been measured at room temperature. The specific heat of the crystal is 699.5 J mol⁻¹ K⁻¹ at 300 K. The thermal expansion coefficient (TEC) along the a and c axes, respectively, is interpreted on the basis of crystal structure. The thermal decomposition process is characterized by thermogravimetry analysis and differential scanning calorimetry (TGA/DSC). The intermediates and final products of the thermal decomposition were identified by X-ray powder diffraction at room temperature. The high-temperature effect in air on the optical transmission of the crystal was also studied.     

Investigation of nonionic diazo dye-doped polymer dispersed liquid crystal film

Sudan black B (SBB) was used to investigate as the nonionic diazo dye-doped in polymer dispersed liquid crystal (PDLC) display, by polymerization-induced phase separation (PIPS) method. The maximum absorbance, contrast ratio, dichroic ratio and the order parameter of nonionic diazo dye in nemetic host (TL203) were investigated using UV?CVis polarized spectroscopy. The orientation of the dye molecules was controlled by electric field, which enabled the contrast ratio of the dye to be obtained by electrically switching. The change occurring on droplet morphologies and electro-optical properties of PDLC film with the change in contents of Sudan black dye and liquid crystals (LC) contents was investigated. We found an increase in LC droplet sizes with the increase of diazo dye and LC contents. Moreover the addition of small amount of nonionic diazo dye reduced the threshold voltage (V $_{\boldsymbol{\rm th}})$ , increased off-state transmittance, enhanced the contrast ratio and decreased the response time of dye-doped PDLC. Additionally the change in transition temperature of LC and changes in LC droplet morphologies with the addition of dye were also observed. Such changes were observed with the images taken by polarized optical microscope (POM). The detail discussions on such behaviours were also made.     

Surface tension and density data for Fe–Cr–Mo,Fe–Cr–Ni,and Fe–Cr–Mn–Ni steels

The temperature dependence of surface tension and density for Fe–Cr–Mo (AISI 4142), Fe–Cr–Ni (AISI 304), and Fe–Cr–Mn–Ni TRIP/TWIP high-manganese (16 wt% Cr, 7 wt% Mn, and 3–9 wt% Ni) liquid alloys are investigated using the conventional maximum bubble pressure (MBP) and sessile drop (SD) methods. In addition, the surface tension of liquid steel is measured using the oscillating droplet method on electromagnetically levitated (EML) liquid droplets at the German Aerospace Centre (DLR, Cologne). The data of thermophysical properties for Fe–Cr–Mn–Ni is of major importance for modeling of infiltration and gas atomization processes in the prototyping of a “TRIP-Matrix-Composite.” The surface tension of TRIP/TWIP steel increased with an increase in temperature in MBP as well as in SD measurement. The manganese evaporation with the conventional measurement methods is not significantly high within the experiments (?_Mn < 0.5 %). The temperature coefficient of surface tension (dσ/dT) is positive for liquid steel samples, which can be explained by the concentration of surface active elements. A slight influence of nickel on the surface tension of Fe–Cr–Mn–Ni steel was experimentally observed where σ is decreased with increasing nickel content. EML measurement of high-manganese steel, however, is limited to the undercooling state of the liquid steel. The manganese evaporation strongly increased in excess of the liquidus temperature in levitation measurements and a mass loss of droplet of 5 % was observed.     

Control of liquid crystal alignment by deposition of silicon oxide thin film

We investigated liquid crystal alignment on a-SiO_x thin films by means of X-ray diffraction and X-ray photoemission spectroscopy as we varied the deposition temperature and the target-to-substrate distance. We found that liquid crystal molecules can be aligned vertically on a-SiO_x film when the stoichiometry parameter x of a-SiO_x is smaller than 1.56, but they can be aligned homogeneously when x is larger than 1.56. We also found that whether liquid crystals can be aligned vertically or homogeneously on a-SiO_x film can be predicted simply by measuring the change in optical transmittance by deposition of a-SiO_x thin film layers.     

Study of Defect Modes in 1d Photonic Crystal Structure Containing High and Low T c Superconductor as a Defect Layer

The present paper describes the study of defect modes in a one-dimensional photonic crystal (1d-PC) containing a high and low temperature superconductor as a defect layer at different temperatures below the superconducting transition temperature (T _c ). Since the refractive index of the superconducting material is dependent on the penetration depth, which depends on the temperature of the superconducting material, hence by changing the temperature of the superconducting material its refractive index can also be changed. Analysis of the transmission spectra of defect modes in the reflection band of 1d-PC structure shows a shift in the wavelength peak of the defect mode. The shift in peak is different for different superconducting materials and it increases with the increase in temperature whether the defect layer is high T _c or low T _c superconductors. We also study the presence two defect layers in a 1d-PC structure, one with high T _c and other with a low T _c superconductor. Further, the effect of variation in the thickness of the defect layer on the defect modes of the PC structure has also been studied In order to obtain the transmission (reflection) spectra of a 1d-PC structure with a defect, we employ the transfer matrix method (TMM). This property of the defective PC structure can be exploited in designing the temperature sensor and narrow optical filters. Further, this tunable feature of superconductor photonic crystal has technical use in the superconducting electronics and photonics.     

Phase Transitions in Liquid Crystal Doped with Magnetic Particles of Different Shapes in Combined Electric and Magnetic Fields

We have studied the influence of electric and magnetic fields on the orientational structure of ferronematics based on a thermotropic nematic 4-trans-4 \(^{\prime }\) -n-hexylcyclohexyl-isothiocyanato-benzene (6CHBT). The 6CHBT liquid crystal has been dissolved in phenyl isothiocyanate and doped with rod-like or chain-like magnetic particles. In such a mixture, the phase transition from an isotropic to a nematic phase is via a droplet state, i.e., coexistence of nematic and isotropic phases. The obtained results showed that a combination of the electric and magnetic fields can change the character of a phase transition from the isotropic to the nematic phase via the droplet state in such systems. Moreover, magneto-dielectric measurements of structural transitions showed the magnetic field induced a shift of the phase transition temperature from the isotropic to the droplet state.     

Preparation of PbS-type PbO nanocrystals in a room-temperature ionic liquid

In a strong polar environment of ionic liquid 1-n-butyl-3-ethylimidazolium tetrafluoroborate [BEIM]BF₄, PbO nanocrystals with PbS-type crystal structure were successfully synthesized by the thermal decomposition of Pb(OH)₂ at 180 °C for 3 h under ambient pressure. The product was characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), electric diffraction (ED), X-ray photoelectron spectrum (XPS) and elemental analysis.     

Evaporation of additive droplets in a pulse MHD generator

Theoretical investigation into evaporation of additive droplets in the combustion chamber of a pulse MHD generator were undertaken. Flow in the chamber is considered as stationary and one-dimensional; mixing in a direction perpendicular to flow is believed to be ideal, and mixing is lacking in the flow direction. It is suggested that droplets are monodisperse, spherical, and motionless relative to the gas medium. The droplet evaporation can be taken as occurring in the diffusion mode. The specific heat c _p and heat conductivity coefficient are taken to be constant and independent of temperature and the concentration of components. The Lewis number is believed to be the unit value; and the Soret and Dufour effects, negligible. A formula for calculation of the droplet evaporation rate with allowance made for chemical reactions occurring in liquid and gas media is obtained.     

Crystal growth and characterization of Ho-doped Lu3Ga5O12 for 2 μm laser

Ho:LuGG single crystal was successfully grown by the Czochralski growth method, and its lattice parameter was found to be 12.2371 Å. Its thermal conductivity was measured to be 5.29 W mK⁻¹ at 300 K. Meanwhile, transmission spectra were recorded at room temperature, and then its absorption spectra were obtained combining with the transmission spectra of LuGG crystal. The transition intensity parameters Ω_t (t = 2, 4, 6), the oscillator strengths, fluorescence branching ratios, transition probabilities and the lifetimes of Ho³⁺ in LuGG crystal were all evaluated by the Judd–Ofelt theory. Furthermore, its emission spectra were also determined and analyzed.