Concentration-cancellation for the velocity fields in two dimensional incompressible fluid flows

We show that the weak-L ² limit of a sequence of solutions of the two dimensional incompressible Euler equation is still a solution, provided that a (strong) concentration set for the reduced defect measure has locally finite one dimensional Hausdorff measure in space and time.     

铋镓共掺的高浓度掺铒石英基光纤中铒离子团簇率的实验研究

使用MCVD法结合溶液掺杂技术制作了铒铋镓共掺的石英基光纤.根据光纤吸收谱，得出其中铒离子浓度是5.24×10²⁵/m³.然后提出了一种新的利用透射率测定掺铒光纤的团簇率的实验方法，该方法相比于以前的方法更简单有效.利用该方法，测得了自制铒铋镓共掺光纤中团簇率.通过与前人的结果相比较，充分说明铋和镓的掺入大大提高了铒离子在石英基光纤中的溶解度，抑制了铒离子形成团簇.     

铋镓共掺的高浓度掺铒石英基光纤中铒离子团簇率的实验研究

使用MCVD法结合溶液掺杂技术制作了铒铋镓共掺的石英基光纤.根据光纤吸收谱,得出其中铒离子浓度是5.24×10²⁵/m³.然后提出了一种新的利用透射率测定掺铒光纤的团簇率的实验方法,该方法相比于以前的方法更简单有效.利用该方法,测得了自制铒铋镓共掺光纤中团簇率.通过与前人的结果相比较,充分说明铋和镓的掺入大大提高了铒离子在石英基光纤中的溶解度,抑制了铒离子形成团簇. 关键词： 掺铒光纤 石英基光纤 团簇 高浓度     

Effects of entanglement concentration on Tg and local segmental motions

The process of spin-coating to fabricate thin polymer films with high molecular weight can produce samples with entanglement concentrations that are far below the equilibrium value. It is not clear whether or not such low entanglement concentrations are responsible for the depression of the glass temperature in thin polymer films. In this work, we measure the calorimetric glass temperature and viscoelastic response of polystyrenes with molecular weights ranging from 3×10³ to 43.7×10⁶ g/mol, for both bulk material and for samples freeze-dried from dilute solution. We conclude that the reduction of the glass temperature observed in thin polymer films cannot be due to the reduced entanglement concentration in the samples. Received 15 August 2001 and Received in final form 2 March 2002     

Measurement of oxidation states for transition elements with a small spot tabletop XANES instrument

Development of a compact, high sensitivity, low‐power and low‐cost, tabletop instrument for x‐ray absorption near edge structure, XANES, measurements will make possible chemical speciation and characterization studies in a broad variety of applications in medicine, science and industry. Such a system utilizing a low‐power (<50 W) microfocus x‐ray source combined with a toroidal doubly curved crystal (DCC) optic has been used to differentiate Mn metal and Mn²⁺ and Mn⁷⁺ solution (2, 3% respectively) or Cr metal and Cr³⁺ and Cr⁶⁺ in aqueous (0.1% concentration) solution by measurement of their XANES spectra. This prototype system can measure Cr at 100‐ppm concentration levels. Improvements in the system should make measurements at <10 ppm levels or very short (<1 s) measurement time possible for a large variety of elements. By using this system, rapid reduction of Cr⁶⁺ to Cr³⁺ in cultured cells was directly observed. Copyright © 2009 John Wiley & Sons, Ltd.     

An optical absorption method of detecting iodine-containing substances in liquid acid media formed during the reprocessing of spent nuclear fuel

We propose an absorption method for determining the concentrations of iodine-containing substances (I₂ and IO ₃ ^? ) in real time in liquid acid media formed when spent nuclear fuel is reprocessed at nuclear fuel cycle plants. The essence of the method is to measure simultaneously at two wavelengths the intensity of the radiation that passes through the solution being analyzed. The sensitivity of this method allows reliable and real-time control to be exercised over both the technological process of fuel reprocessing and the operations of purification systems.     

Experimental evidence of electron neutrino oscillations and validation of MSW-LMA model with Borexino

We report the real time measurements of ⁷Be and ⁸B solar neutrino fluxes performed with the Borexino experiment at the Laboratori Nazionali del Gran Sasso. The achievement of these measurements was possible thanks to the excellent levels of the radiopurity reached. The measurement of the ⁷Be in real time is the first direct measurements of the survival probability for solar electron neutrinos in the vacuum region. For ⁸B we reached a threshold energy of 3MeV which is the lowest achieved so far in real time. For the first time, the same apparatus can measure two different oscillation regions (vacuum-driven and matter-enhanced) predicted by the MSW-LMA model. Borexino also quotes the ratio between the survival probabilities, corresponding to 1.93 ± 0.75, and validates the presence of the transition region between the two oscillation regimes, according to the MSW-LMA solution.In addition, a preliminary result on the Day-Night Asymmetry (ADN) for the ⁷Be neutrino flux is presented and corresponds to 0.007 ± 0.073. This measurement makes Borexino able to give once more an independent confirmation of the MSW-LMA solution.     

Development of new chemical dosimeter for low dose range

Accurate measurement of low dose radiation in complex systems is of utmost importance in radiation biology and related areas. Ferrous Benzoic acid Xylenol orange (FBX) system is being widely used for measurement of low dose gamma radiation because of its reproducibility and precision. However, an additional step, i.e., dissolution of benzoic acid in water at higher temperature followed by cooling at room temperature is involved for the preparation of this dosimeter. This makes it inconvenient as a ready to use dosimeter. In the present work, the organic molecule, sorbitol has been used for measurement of low doses of radiation. The advantages of using sorbitol are its ready availability and instantaneous water solubility. Owing to its dissolution at room temperature, possible errors those are involved in calculation of dose due to thermal oxidation of ferrous ions during preparation of the FBX dosimetric solution could be made insignificant in the proposed dosimeter. In the present system, sorbitol acts as radiolytic sensitizer for the oxidation of ferrous ion, and xylenol orange forms a 1:1 complex specifically with ferric ions. Thus, the analytical detection limit of ferric ions is enhanced compared to other systems. Final composition of the dosimetric solution is; 0.5 mol/m³ xylenol orange, 10 mol/m³ sorbitol and 0.2 mol/m³ ferrous ion in 50 mol/m³ sulfuric acid. Radiolytic sensitization in combination with analytical enhancement of the ferrous based system, allows us to measure radiation dose in the range of 0.05 Gy–12 Gy with ease and high reproducibility.     

pep neutrino detection by a lithium detector as a direct way to seek oscillations of solar neutrinos

The high sensitivity of a lithium detector to pep and ⁷Be neutrinos renders a radiochemical lithium detector a powerful tool for seeking solar-neutrino oscillations. The first phase of the lithium experiment with an apparatus involving 10 t of metallic lithium will allow collecting data within 1 yr of measurements to provide very definite information about a MSW SMA solution. The second phase with ten modules 10 t each will measure the semiannual variations of the signal, whereby the contributions of pep and ⁷Be lines will be weighted, which will give “smoking-gun” evidence for the “just-so” solution for large mixing angles and Δm ² about 10^?10–10^?9 eV². If both regions are not confirmed, the results of the lithium detector can be interpreted in favor of the MSW LMA solution.     

Carrier concentration and shallow electron states in In-doped hydrothermally grown ZnO

Single-crystal ZnO has been hydrothermally grown with additional In₂O₃ in the solution. Schottky barrier contacts have been deposited by electron beam evaporation of Pd onto the face. Capacitance–voltage measurements have been performed to reveal the carrier concentration as a function of the In₂O₃ content in the solution, and secondary-ion mass spectrometry was used to measure the resulting In concentration in the samples. For an In₂O₃ content of 2×10¹⁹ cm⁻³, the average free electron concentration increased to 5×10¹⁸ cm⁻³ compared to 4×10¹⁷ cm⁻³ for the non-doped material. An increase of the In₂O₃ content to 4×10¹⁹ cm⁻³ leads to a measured carrier concentration of approximately 1×10¹⁹ cm⁻³; however, only up to a quarter of the incorporated In became electrically active. From thermal admittance spectroscopy measurements two prominent electronic levels are found, and compared with to the non-doped material case, the freeze-out of the shallow doping in the In-doped samples takes place at lower temperatures (below 80 K).     

XAS spectroelectrochemistry: reliable measurement of X‐ray absorption spectra from redox manipulated solutions at room temperature

The design and operation of a low‐volume spectroelectrochemical cell for X‐ray absorption spectroscopy (XAS) of solutions at room temperature is described. Fluorescence XAS measurements are obtained from samples contained in the void space of a 50 µL reticulated vitreous carbon (sponge) working electrode. Both rapid electrosynthesis and control of the effects of photoreduction are achieved by control over the flow properties of the solution through the working electrode, where a good balance between the rate of consumption of sample and the minimization of decomposition was obtained by pulsing the flow of the solution by 1–2 µL with duty cycle of ～3 s while maintaining a small net flow rate (26–100 µL h^?1). The performance of the cell in terms of control of the redox state of the sample and minimization of the effects of photoreduction was demonstrated by XAS measurements of aqueous solutions of the photosensitive Fe^III species, [Fe(C₂O₄)₃]^3?, together with that of the electrogenerated [Fe(C₂O₄)₃]^4? product. The current response from the cell during the collection of XAS spectra provides an independent measure of the stability of the sample of the measurement. The suitability of the approach for the study of small volumes of mM concentrations of protein samples was demonstrated by the measurement of the oxidized and electrochemically reduced forms of cytochrome c.     

The anionic chain process mechanism for reactions of perchlorofluoroethanes with nucleophiles in solution: a theoretical study

Anionic chain process mechanism (including reactions (1)–(4)) suggested by the experimental investigations for the reactions of nucleophile (CH₃O^?) with perchlorofluoroethanes CF₂ClCCl₃ ( 1 ), CF₂ClCCl₂F ( 2 ), and CF₃CCl₃ ( 3 ) in solution is examined by performing calculations using the B3LYP method and the SCIPCM (self‐consistent isodensity polarizable continuum) model for simulating solution effects. The SCIPCM‐B3LYP calculations indicate that anionic species have large solvation energies and solvation energy values for different kinds of anions are quite different, which effects changes in ΔH's for the reactions in solution. Competition between anionic hyperconjugation and solvation leads to negative ΔH values for reactions (2) from 1 and 2 in solution. Reactions (3) and (4) from 1 , 2 , and 3 in solution are predicted to be exothermic or highly exothermic. Since the ΔH values for reactions (1) and (2) from 1 and 2 in solution are negative or small positive values, the reactions of CH₃O^? with 1 and 2 in solution proceed via the anionic chain process. For 3 in solution, reactions (1) and (2) are endothermic while reactions (3) and (4) are exothermic or highly exothermic. The reactions of CH₃O^? with 3 in solution may proceed via the anionic chain process. All these conclusions are in agreement with the experimental indications for reactions of nucleophiles with 1 , 2 , and 3 in solution. Copyright © 2007 John Wiley & Sons, Ltd.     

Wavelength modulated cavity enhanced absorption spectroscopy of ammonia at 1994 nm

We describe the sensitive detection of ammonia by wavelength modulated cavity enhanced infrared tunable diode laser absorption spectroscopy at 1994 nm. The spectrometer can measure a fractional absorption of ∼10^-5 for an absorption pathlength of a few kilometers. The spectral resolution and sensitivity are sufficient to measure ammonia isotopomers (¹⁴NH₃, ¹⁵NH₃) in planetary atmospheres. The spectrometer is miniaturisable, so a future multiple-species version will be highly suitable for in situ planetary exploration and life-detection. PACS 42.62.Fi; 33.20.-t; 33.20.Ea     

Invariant Measures of Gaussian Type for 2D Turbulence

Gaussian measures ?? ^??,?? are associated to some stochastic 2D models of turbulence. They are Gibbs measures constructed by means of an invariant quantity of the system depending on some parameter ?? (related to the 2D nature of the fluid) and the viscosity???. We prove the existence and the uniqueness of the global flow for the stochastic viscous system; moreover the measure ?? ^??,?? is invariant for this flow and is the unique invariant measure. Finally, we prove that the deterministic inviscid equation has a ?? ^??,?? -stationary solution (for any ??>0).     

Observation of Andreev-Pushkarov vacancy clusters in phase-separated solid solutions of 4He in 3He

New features are observed for the pressure in a phase-separated dilute solid solution of ⁴He in ³He subjected to multiple temperature cycling within the phase-separation region. The results are explained within the framework of the hypothesis of A.F. Andreev and D.I. Pushkarov that the vacancies in a crystal without ideal periodicity are surrounded by clusters with a periodic structure. The equation for determining the radius of a cluster of pure ⁴He in a solution of ⁴He in ³He is refined. This hypothesis is shown to provide quantitative agreement between the calculated and experimental data under the assumption that the homogenization of the phase-separated solution is accompanied by the formation of metastable vacancies with a concentration of ～(4–5)×10^?5.     

Representation of solutions of the Burgers equation using functional integrals

In the paper, a representation of a solution of the Burgers equation in ℝ ⁿ is obtained by using integrals with respect to the Wiener measure on the space of trajectories in ℝ ⁿ . The Burgers equation is considered in a rigged Hilbert space. It is proved that, in the infinite-dimensional case, there is an analog of the Cole-Hopf transformation relating the Burgers equation and an analog of the heat equation with respect to measures. The Feynman-Kac formula for the heat equation (with potential) with respect to measures in a rigged Hilbert space is obtained.     

Cooling dilute 3He4He mixtures to 0.6 mK

We have cooled a ³He⁴He solution to the lowest temperatures yet achieved, 0.58 mK, and find no evidence for a superfluid transition in the dissolved ³He. We have measured the thermal boundary resistance between this solution and sintered 700 Å silver powder, and find that R is proportional to T^?2 between 0.8 mK and 4 mK.     

细胞灌注-核磁共振联用方法的研究

该文报道了研制的一套细胞灌注装置,并运用该细胞灌注装置与核磁共振连用的方法在线监测药物作用下肿瘤细胞的能量代谢过程. 结果表明核磁共振细胞灌注方法可有效观察到细胞能量代谢的变化,可作为追踪筛选药物的活性成分及探索药物治疗肿瘤细胞的作用机理的一种有力手段.     

Optical measurement of <Superscript>3</Superscript>He nuclear polarization for metastable exchange optical pumping studies at high magnetic field

An accurate optical method to measure the nuclear polarization of ³He atoms in the 1¹S ground state is described. The absorption of a weak, probe laser beam is used to measure the relative populations of two hyperfine sublevels of the 2³S metastable state that are not addressed by the pumping laser beam. Since a common spin temperature between the ground and metastable states is established by metastable exchange collisions, the nuclear polarization can be derived from these absorption measurements. The method is highly sensitive, robust, and can be used to monitor the dynamics of optical pumping and relaxation processes without interfering with them. It was successfully implemented and tested in the 0.45–2.0 T magnetic field range at the ³He gas pressure up to 67 mbar.     

An integrated optical sensor for measuring glucose concentration

We used an optical sensor combined with a Mach-Zehnder interferometric waveguide and optical fibers to measure slight changes of aqueous sugar concentrations. The merits of this sensor are simplicity, reliability, high sensitivity and continuous monitoring. The technique is based on the fact that the refractive index of sugar solution changes with the concentration of sugar. In the experiment, one arm of the interferometer is clad with glue and is thus isolated from the sugar solution. The other one is exposed to the sugar solution. A single mode fiber is directly glued onto the interferometric waveguide, to guide the light into the interferometer. If the concentration of sugar covering the waveguide changes, the phase of propagating light in the exposed arm will be changed, while the phase in the other arm is fixed. Hence the output intensity from the interferometer is directly related to the concentration of the sugar solution. The result of this experiment yields the relation between the sugar concentration and output signal. From 0% to 1% concentration of sugar solution, there is only a 1.4×10^–3 refractive index difference. Two sets of experimental data have been obtained, showing a linear relation between the sugar concentration and the output signal from our sensor. This sensor could be used for continuous monitoring of blood sugar in the human body.