Return flux budget of polychromatic laser guide stars

The polychromatic laser guide star (PLGS) is one of the solutions proposed to extend the sky coverage by large telescopes to 100% by enabling a complete knowledge of all perturbation orders of the wavefront. The knowledge of the tip-tilt is deduced from the monitoring of the chromatic components of the PLGS, from 330 nm to the visible or near infrared. Here we study the original scheme to create the PLGS by resonant excitation of the mesospheric sodium by two pulsed lasers (tens of kilohertz repetition rate, tens of watts average power, tens of nanoseconds pulse duration), at 589 and 569 nm, respectively. The efficiency of this process is investigated numerically by means of both Bloch equation and rate equation models. The influence of numerous laser parameters is studied. In the best case, having optimized all laser parameters, the return flux at 330 nm should not exceed 7x10(4) photons/s/m2 for 2x18 W laser average power at the mesosphere. This maximum is obtained for a modeless laser whose spot diameter corresponds to 4 times the diffraction limit. For a diffraction-limited spot, the return flux falls down to 4x10(4)photons/s/m2.     

Characterization of a high-brilliance soft x-ray laser at 13.9 nm by use of an oscillator-amplifier configuration

We have improved a highly coherent x-ray laser at 13.9 nm using an oscillator-amplifier configuration. To improve a high-brilliance x-ray laser, we adopted traveling wave pumping for the amplifier target and rotated the amplifier target 3-4 mrad in the counterclockwise direction. Thereby, a seed x-ray laser can be amplified by medium plasma of the amplifier target with a high gain coefficient. The amplified x-ray laser has the output energy of approximately 1.3 microJ, corresponding to a large photon flux of 6.5 x 10(10) photons/pulse and a high peak brilliance of 5 x 10(26) photons/(s x mm(2) x mrad(2) x 0.01% bandwidth).     

Micro/nanoscale spatial resolution temperature probing for the interfacial thermal characterization of epitaxial graphene on 4H-SiC

Limited internal phonon coupling and transfer within graphene in the out-of-plane direction significantly affects graphene-substrate interfacial phonon coupling and scattering, and leads to unique interfacial thermal transport phenomena. Through the simultaneous characterization of graphene and SiC Raman peaks, it is possible, for the first time, to distinguish the temperature of a graphene layer and its adjacent 4H-SiC substrate. The thermal probing resolution reaches the nanometer scale with the graphene (≈1.12 nm) and is on the micrometer scale (≈12 μm) within SiC next to the interface. A very high thermal resistance at the interface of 5.30 (-0.46) (+0.46) x 10(-5) Km2 W(-1) is observed by using a Raman frequency method under surface Joule heating. This value is much higher than those from molecular dynamics predictions of 7.01(-1.05) (+1.05) x 10(-1) and 8.47(-0.75) (+0.75) x 10(-10) Km2 w(-1) for surface heat fluxes of 3 × 10(9) and 1 × 10(9) and 1 x 10(10) W m(-2) , respectively. This analysis shows that the measured anomalous thermal contact resistance stems from the thermal expansion mismatch between graphene and SiC under Joule heating. This mismatch leads to interface delamination/separation and significantly enhances local phonon scattering. An independent laser-heating experiment conducted under the same conditions yielded a higher interfacial thermal resistance of 1.01(-0.59) (+1.23) x 10(-4) Km2 W(-1). Furthermore, the peak width method of Raman thermometry is also employed to evaluate the interfacial thermal resistance. The results are 3.52 × 10(-5) and 8.57 × 10(-5) K m2 W(-1) for Joule-heating and laser-heating experiments, respectively, confirming the anomalous thermal resistance between graphene and SiC. The difference in the results from the frequency and peak-width methods is caused by the thermal stress generated in the heating processes.     

Rayleigh-calibrated fluorescence quantum yield measurements of acetone and 3-pentanone

We measured fluorescence quantum yields of acetone and 3-pentanone as a pure gas and with nitrogen diluent at room temperature at 20, 507, and 1013 mbar using 248, 266, and 308 nm excitation by calibrating the optical collection system with Rayleigh scattering from nitrogen. At 20 mbar with 308-nm excitation, the fluorescence quantum yields for acetone and 3-pentanone are 7 +/- 1 x 10(-4) and 1.1 +/- 0.2 x 10(-3), respectively, and each decreases with decreasing excitation wavelength. These directly measured values are significantly lower than earlier ones that were based on a chain of relative measurements. The observed pressure and excitation wavelength dependence is in qualitative agreement with a previously developed fluorescence quantum yield model, but the absolute numbers disagree. Changing acetone's fluorescence rate constant to 3 x 10(5) s(-1) from its previous value of 8 x 10(5) s(-1) resulted in good agreement between our measurements and the model.     

Isotope selective near-resonant two-photon ionization of 41Ca isotope via the 4s11s 1S0 intermediate state

Isotope selective excitation of a 41Ca isotope using a near-resonant two-photon ionization scheme 4s2 1S0-->422.7924 nm,413.3685 nm4s11s 1S0-->514.5 nmCa+ has been proposed for using the 41Ca isotope in applications as a tracer in biomedical studies. The ionization efficiency and optical selectivity have been calculated for various powers of the excitation and ionization laser. Under the optimized excitation and ionization laser powers the ionization efficiency for the studied scheme is found to be 1.7x10(-4). The optical selectivity value is approximately 1.0x10(5) and both of these values are either comparable or slightly better than the earlier published work by our group. The overall ionization efficiency for the two-photon ionization scheme considering the throughput factor is 5x10(-3), which is 2 orders of magnitude higher than the stepwise excitation process. Therefore, the higher ionization efficiency of the process enables monitoring of the tracer isotope for longer durations. In combination with a mass spectrometer, an abundance sensitivity of approximately 10(10) can be obtained, which is adequate for biomedical applications.     

Photodiode array for position-sensitive detection using high X-ray flux provided by synchrotron radiation

Synchrotron radiation provides a high intensity source over a large range of wavelengths. This is the prominent quality that has laid the foundations of the EXAFS development (Extended X-ray Absorption Fine Structure). EXAFS data can be collected in different ways. A full scan requires 5 to 10 min, compared to the one-day data collection of a conventional Bremsstrahlung X-ray tube.Recently, by using the new photodiode array (R 1024 SFX) manufactured by Reticon, it has been possible to reduce the data collection time to less than 100 ms. The key elements of this new EXAFS method are a dispersive optics combined with a position sensitive detector able to work under very high flux conditions. The total aperture of 2500 μm × 25 μm for each pixel is well suited to spectroscopic applications. Besides its high dynamic range (> 10⁴) and its linearity, the rapidity of the readout allows a flux of 10⁹–10¹⁰ photons/s over the 1024 sensing elements.     

Photophysics of resonantly and non-resonantly excited erbium doped Ge nanowires

We have fabricated Er doped germanium nanowires of different diameters by pulsed laser deposition and chemical methods. Er induced photoluminescence emission due to the intra-4f (4)I(13/2)→(4)I(15/2) transition of Er energy levels at 1.53 μm has been achieved at room temperature using both resonant (980 nm) and non-resonant (325 nm) excitation of Er ions. The observed 1.53 μm photoluminescence signal upon non-resonant 325 nm excitation is attributed to the Ge related oxygen deficiency centers surrounding the Ge core. For direct excitation, the infrared photoluminescence characteristics have been studied as a function of Er concentration, photon flux, and diameter of the nanowires. The Er related emission signal is found to be enhanced with increase in Er concentration, pump flux of 980 nm, and the nanowire diameter. The time resolved characteristics of the Er induced emission peak have been studied as a function of the pump flux as well as the diameter of the Ge nanowires.     

Field tests on human tolerance to (LNG) fire radiant heat exposure, and attenuation effects of clothing and other objects

A series of field tests exposing mannequins clothed with civilian clothing to a 3m x 3m square liquefied natural gas (LNG) pool fire was conducted. Both single layer clothing and double layer clothing were used. The radiant heat flux incident outside the clothing and incident on the skin covered by clothing were measured using wide-angle radiometers, for durations of 100-200 s (per test). The levels of heat flux incident on the clothing were close to 5 kW/m(2). The magnitude of the radiant heat attenuation factor (AF) across the thickness was determined. AF varies between 2 and higher for cotton and polyester clothing (thickness 0.286-1.347 mm); AF value of 6 was measured for 1.347 mm thickness. Single sheet newspaper held about 5 cm in front of mannequins and exposed to incident flux of 5 kW/m(2) resulted in AF of 5, and AF of 8 with double sheets. AF decreases linearly with increasing heat flux values and linearly increases with thickness. The author exposed himself, in normal civilian clothing (of full sleeve cotton/polyester shirt and jean pants), to radiant heat from a LNG fire. The exposure was for several tens of seconds to heat flux levels ranging from 3.5 kW/m(2) to 5(+) kW/m(2) (exposure times from 25s to 97 s at average heat flux values in the 4 kW/m(2) and 5 kW/m(2)range). Occasionally, he was exposed to (as high as) 7 kW/m(2) for durations of several seconds. He did not suffer any unbearable or even severe pain nor did he experience blisters or burns or any other injury on the unprotected skin of his body. The incident heat fluxes on the author were measured by a hand-held radiometer (with digital display) as well as by strapped on wide-angle radiometers connected to a computer. He could withstand the US regulatory criterion of 5 kW/m(2) (for 30 s) without suffering any damage or burns. Temperature measured on author's skin covered by clothing did not rise above the normal body temperature even after 200 s of exposure to 4 kW/m(2) average heat flux.     

Fabrication of a W/W-Mo/Mo System Layered Flier-Plate Material

A kind of W/W-Mo/Mo system layered flier-plate material (LFP) was fabricated in this study by the methods of powder metallurgy and bonding together. Such LFP had high parallelism, planeness and densification and its density varied from 17.25x10(3) kg/m(3) to 10.22x10(3) kg/m(3) through a total thickness of 3.0 mm. The W-Mo interlayer of this LFP was obtained by hot-press sintering and its densification at 1573 K was studied. Then by using additives 4Ni-3Cu (in wt pct), the LFP was fabricated under 1573 K-30 MPa-60 min. The mechanism of the interfacial bonding of the W/W-Mo/Mo system LFP was also mainly investigated.     

Using anisotropic heat flux sensors in aerodynamic experiments

We present the results of comparative measurements of the heat flux to a flat plate in a supersonic flow at a Mach number of M = 6, which were performed using the two following anisotropic heat sensors with different thicknesses of sensor elements: (i) Atomic Layer Thermo Pile (ALTP, Fortech GmbH, Germany) with a thickness of ～0.5 × 10^?6 m and (ii) gradient heat flux sensor (GHFS, St. Petersburg State Polytechnic University, Russia) with a thickness of ～2 × 10^?4 m. The ALTP sensor can be used for directly measuring heat fluxes in processes with a characteristic time above 10^?6 s. A method for mathematically processing the GHFS response signal is proposed that allows heat flux oscillations to be revealed in gasdynamic process with a characteristic time on the order of 10^?4 s.     

助熔剂法合成钨氧氯化合物Li23CuW10O40Cl5

由于不同阴离子之间的电负性、离子半径、极化率和氧化态之间的差异, 混合阴离子化合物可以产生不同于单一类型阴离子的新特性。混合阴离子金属材料在电子、湿度探测器、气体传感器、太阳能电池电极等领域有着广泛的应用前景。助熔剂方法是一种广泛应用于混合离子晶体生长的方法, 它以适当的金属盐作为助熔剂, 在较温和的条件下进行复分解反应。助熔剂法在混合阴离子化合物的合成中具有重要意义。钨氧氯化合物Li₂₃CuW₁₀O₄₀Cl₅单晶以高质量的Li₄WO₅为前驱体, 以CuCl₂为助熔剂通过两步法合成。通过X射线单晶衍射确定其晶体结构。结果表明, Li₂₃CuW₁₀O₄₀Cl₅结晶属于P6₃/mcm空间群, 晶胞参数分别为a=1.02846(3) nm, c=1.98768(9) nm, V=1.82076(11) nm³, Z=2。单胞中分别包含五个晶体学独立的Li原子, 两个W原子, 一个Cu原子, 两个Cl原子以及五个O原子。结构中, W(1)原子和一个Cl原子及五个O原子相连接, 形成畸变八面体, 而W(2)原子与四个O原子相连接形成四面体, Cu原子与六个O原子相连形成八面体。因此, Li₂₃CuW₁₀O₄₀Cl₅的晶体结构主要由[CuO₆]和[W(1)O₅Cl]八面体以及[W(2)O₄]四面体构成。助熔剂法合成钨氧氯化合物Li₂₃CuW₁₀O₄₀Cl₅对今后探索新型的混合阴离子化合物具有重要意义。     

Increasing the resolution of single pair fluorescence resonance energy transfer measurements in solution via molecular cytometry

We report a method to increase the resolution of single pair fluorescence resonance energy transfer (spFRET) measurements in aqueous solutions. Solution-based spFRET measurements of fluorescently labeled biological molecules (proteins, RNA, DNA) are often used to obtain histograms of molecular conformation without resorting to sample immobilization. However, for solution-phase spFRET studies, the number of photons detected from a single molecule as it diffuses through an open confocal volume element are quite limited. An "average" transit may yield on the order of 40 photons. Shot noise on the number of detected photons substantially limits the resolution of the measurement. The method reported here uses a hydrodynamically focused sample stream to ensure molecules traverse the full width of an excitation laser beam. This substantially increases the average number of photons detected per molecular transit (approximately 85 photons/molecule), which increases measurement precision. In addition, this method minimizes another source of heterogeneity present in diffusive measures of spFRET: the distribution of paths taken through the excitation laser beam. We demonstrate here using a FRET labeled protein sample (a FynSH3 domain) that superior resolution (a factor of approximately 2) can be obtained via molecular cytometry compared to spFRET measurements based upon diffusion through an open confocal volume element.     

Superior thermal conductivity of single-layer graphene

We report the measurement of the thermal conductivity of a suspended single-layer graphene. The room temperature values of the thermal conductivity in the range approximately (4.84+/-0.44)x10(3) to (5.30+/-0.48)x10(3) W/mK were extracted for a single-layer graphene from the dependence of the Raman G peak frequency on the excitation laser power and independently measured G peak temperature coefficient. The extremely high value of the thermal conductivity suggests that graphene can outperform carbon nanotubes in heat conduction. The superb thermal conduction property of graphene is beneficial for the proposed electronic applications and establishes graphene as an excellent material for thermal management.     

溴水的膜吸收性能研究

研究了溴水的膜吸收分离性能,并采用回归正交试验设计方法优化溴水膜吸收工艺条件.以NaOH溶液作为吸收剂,采用PVDF中空纤维膜,研究了吸收时间、溴水温度、吸收液浓度及其流速等操作条件对溴水膜吸收性能的影响.结果表明:溴的吸收率随吸收时间的增加而增大,溴水膜吸收过程进料温度与传质系数之间符合阿伦尼斯关系.吸收液侧NaOH的浓度从0.003 mol/L增加至0.01 mol/L时,传质系数从4.75×10-4 cm/s增至6.02×10-4cm/s,对应的膜通量从2.4×10-3 kg/(m2·h)增至3×10-3 kg/(m2·h).吸收液的流体动力学条件对于溴水膜吸收过程通量无显著影响.采用回归正交试验确定的PVDF膜溴水膜吸收分离最佳工艺为:当NaOH吸收溶液浓度为0.01 mol/L,流量为2 L/h时,浓度为220 mg/L的溴水在进料温度为50℃、进料流速为22.24 cm/s的条件下,膜吸收通量达到6.17×10-3kg/(m2·h).     

Evaluation of glass materials by using the line-focus-beam ultrasonic-material-characterization system

We developed experimental procedures to evaluate glass materials using the line-focus-beam ultrasonic-material-characterization (LFB-UMC) system. We prepared 28 specimens of a commercial borosilicate glass from random lots, and measured the velocities of leaky-surface acoustic waves (LSAWs) and leaky-surface-skimming compressional waves (LSSCWs), VLSAW and VLSSCW, using V(z) curve measurements at 225 MHz and 23 degrees C. The velocities for VLSAW ranged from 3121.83 m/s to 3149.77 m/s, with a maximum deviation of 27.94 m/s. The velocities for VLSSCW ranged from 5547.7 m/s to 5585.0 m/s, with a maximum deviation of 37.3 m/s. To investigate these observed variations in VLSAW and VLSSCW, we measured the bulk acoustic wave (BAW) properties, viz., longitudinal and shear velocities, then the densities and the chemical compositions of 8 of the 28 specimens. The LFB-UMC measurements confirmed that decreases in VLSAW and VLSSCW occur mainly with the B2O3 dopant concentrations, corresponding to the decrease of shear-wave and longitudinal-wave velocities that are caused by the decrease of the stiffness constants c44 and c11, respectively, rather than with decreased densities. The sensitivities are -6.36 x 10(-2) wt%/(m/s) for VLSAW and -4.87 x 10(-2) wt%/(m/s) for VLSSCW. This demonstrates that the LFB-UMC system is effective for evaluating glass materials and controlling production processes, by analyzing variations in chemical composition through the super-accurate velocity measurements of LSAWs and LSSCWs.     

Orange-red phosphorescent OLEDs using iridium(III) complexes with benzoylphenylpyridine ligands containing fluorine and trifluoromethyl groups

We have designed and synthesized four orange-red phosphorescent Ir(III) complexes based on the benzoylphenylpyridine ligand with fluorine and trifluoromethyl substitution. Multilayered OLEDs were fabricated using these complexes as dopant materials. Particularly, by using 1 as a dopant in the emitting layer, a highly efficient orange-red OLED was fabricated, showing a maximum luminance of 10410 cd/m2 at 10 V, a luminous efficiency of 17.47 cd/A, a power efficiency of 7.19 Im/W, an external quantum efficiency of 6.27% at 20 mA/cm2, respectively, and CIE(x,y) coordinates of (0.51, 0.48) at 10 V. Furthermore, a red OLED using dopant 2, with CIE(x,y) coordinates of (0.61, 0.39), exhibited a maximum luminance of 5797 cd/m2 at 10 V, a luminous efficiency of 11.43 cd/A at, a power efficiency of 4.12 Im/W, and an external quantum efficiency of 6.62% at 20 mA/cm2, respectively.     

Rotational Line Strengths and Self-Pressure-Broadening Coefficients for the 1.27-microm, a (1)D(g)-X (3)?(g)(-), v = 0-0 Band of O(2)

We measured at 296 K the rotational line strengths and pressure-broadening coefficients for the 1.27-mum, a (1)D(g)-X (3)?(g)(-), v = 0-0 band of O(2) with a Fourier transform infrared spectrometer using an optical path length of 84 m, a spectral resolution of 0.01 cm(-1), and sample pressures between 13 and 104 kPa. The integrated band strength is 7.79(17) x 10(-6) m(-2) Pa(-1) [7.89(17) x 10(-5) cm(-2) atm(-1)], and the Einstein Acoefficient for spontaneous emission is 2.237(51) x 10(-4) s(-1), which corresponds to an upper-state1/e lifetime of 1.24(3) h. The pressure-broadening coefficients decrease with increasing N and range from 19 to 38 MHz/kPa (FWHM). The mean value for the transitions studied is 30.3(21) MHz/kPa [0.1024(71) cm(-1)/atm] (FWHM). The Einstein A coefficient determined here is in good agreement with the widely accepted value of 2.58 x 10(-4) s(-1) initially obtained by Badgeret al. [J. Chem. Phys. 43, 4345 (1965)] more than 30 years ago. The standard uncertainties given above are one standard deviation.     

Upconversion fluorescence in Sm3+-doped zinc phosphate glassy matrix

The mechanism governing the upconversion fluorescence from the ⁴G_5/2 level of Sm³⁺ ion has been investigated in zinc phosphate glass matrices under infrared (1.06?µm) laser excitation. This visible emission is centred at 590?nm and corresponds to the ⁴G_5/2?→?⁶H_7/2 transition. The dependence of the integrated intensity on the excitation power confirms that this emission is due to the three-photon absorption process and is in agreement with the existing theory. The intensity of the upconversion fluorescence has a cubic dependence on the excitation power. An absolute upconversion efficiency of about 10^?7 was obtained for the sample doped with 0.5?wt% Sm³⁺ ions. A quantitative estimate of the number of photons leaving the sample was also determined.     

Highly efficient blue light-emitting materials based on arylamine substituted DPVBi derivatives

A series of arylamine substituted DPVBi derivatives (1-4) were synthesized via the Horner-Wadsworth-Emmons reaction. Their electroluminescent properties were examined by fabricating a multilayer OLED device with the following structure: ITO/DNTPD (40 nm)/NPB (20 nm)/2% DPVBi derivatives (1-4) doped in MADN (20 nm)/Alq3 (40 nm)/Liq (1.0 nm)/Al. All devices showed efficient blue emission. In particular, a high efficiency blue OLED was fabricated using compound 1 as a dopant in the emitting layer. The maximum luminance, luminous efficiency, power efficiency and CIE coordinates of the blue OLED using compound 1 as a dopant were 16110 cd/m2 at 10 V, 10.1 cd/A at 20 mA/cm2, 4.37 Im/W at 20 mA/cm2, and (x = 0.197, y = 0.358) at 8 V, respectively. Moreover, a device using compound 4 as the dopant exhibited efficient deep blue emission with a luminance, luminous efficiency, power efficiency and CIE coordinates of 7005 cd/m2 at 10 V, 6.25 cd/A at 20 mA/cm2, 2.50 Im/W at 20 mA/cm2 and (x = 0.151, y = 0.143) at 8 V, respectively.     

Permeation of solvents through disk type rice husk silica membrane modified with alkyl silylation reagents

Rice husk silica (RHS) which was obtained with thermal treatment of rice husk has the size of approximately 10 micrometer with 4-5 nm pore. RHS can be mold to a disk type membrane. The membrane may have submicron pore originated from the space among the particles, and the nano pores of the rice husk silica (RHS pore). Even it is difficult to adjust the size of the pores, we can suggest that the membrane shows different permeability for the organic/inorganic solvents if the affinity between the surface of the pores and the permeating molecule is changed. In this study, we investigated the permeation of the typical solvents such as water, ethanol and toluene to the RHS membranes sintered at 1100 degrees C, 1150 degrees C and 1200 degrees C and modified with triethoxymethyl silane (CH3)Si(C2H5O)3, diethoxydiemethyl silane (CH3)2Si(C2H5O)2 and ethoxytriemethyl silane (CH3)3Si (C2H5O). The result showed that permeability of original membranes for water (e.g., 1100 degrees C, 2.87 x 10(-3) mol/m2 s Pa) was larger than ethanol (1100 degrees C, 5.51 x 10(-4) mol/m2 s Pa) and toluene (1100 degrees C, 3.09 x 10(-4) mol/m2 s Pa) at the sintering temperatures. For the silane modified membranes, the permeability for water decreased drastically while those for ethanol and toluene increased.