Critical behavior of the free surface of liquid 4He near the λ point

The noncriticality of the free surface of liquid ⁴He near the point and the finite-size scaling postulate are combined to show that the surface tension can have two singularities, one due to rounding and another due to shifting. The rounding singularity can be reduced, via a further scaling assumption, to that previously suggested by Sobyanin and Hohenberg. Results from calculations based on continuous symmetry models and experiments on topologically 2D ⁴He films are used to argue that the shift singularity is ¦t¦^1–, which is consistent with the leading singularity observed by Magerlein and Sanders.     

The effect of potassium on the adsorption of gold on the TiO(2)(110)-1 × 1 surface

Density functional theory (DFT) total-energy calculations have been used to investigate the effect of potassium on the adsorption geometry of gold on a TiO(2)(110)- 1 × 1 surface. The gold prefers to sit between the two bridge oxygen atoms above the sixfold titanium atom. The addition of potassium significantly affects the bonding geometry of the gold. Potassium displaces gold from the bridge site and causes its migration to the top of the fivefold titanium atom. Our calculations suggest that potassium is bonded to the bridging oxygen atoms, and to the sixfold titanium atom as well as to gold. This excludes the formation of a K(2)O-like compound at the surface.     

The irradiation effect of a Nd–YAG pulsed laser on the CeO2 target in the liquid

The irradiation of an Nd–YAG pulsed laser on the CeO₂ target in water was investigated. The reaction products depend mainly on the energy density of the Nd–YAG laser. The CeO₂ nanoparticles with sizes of 20–80 nm were formed in water, while the energy density was larger than 32 kJ/cm². The nanocrystalline films with grain sizes of 50–150 nm were formed on the target with the energy density of 20–25 kJ/cm². Finally, the amorphous films were formed with the energy density of 6–15 kJ/cm². The formation mechanisms of the nanoparticles and the films were discussed according to the triple-point phase diagram of CeO₂.     

The response of a small liquid scintillation counter for low energy (γ, p) experiments

In this paper we present the experimental details and the performance of a small NE213 counter operating at high pressure used in low energy (γ, p) experiments. The p/γ discrimination techniques used to select a low event rate of protons in a high photon background are described.     

Fabrication of a PVC membrane samarium(III) sensor based on N,N′,N″-tris(4-pyridyl)trimesic amide as a selectophore

A new ion-selective electrode for Sm^3 + ion is described based on the incorporation of N,N′,N″-tris(4-pyridyl)trimesic amide (TPTA) in a poly(vinylchloride) (PVC) matrix. The membrane sensor comprises nitrobenzene (NB) as a plasticizer, and oleic acid (OA) as an anionic additive. The sensor with the optimized composition shows a Nernstian potential response of 19.8 ± 0.5 mV decade^? 1 over a wide concentration range of 1.0 × 10^? 2 and 1 × 10^? 6 mol L^? 1, with a lower detection limit of 4.7 × 10^? 7 mol L^? 1 and satisfactor applicable pH range of 3.6–9.2. Having a short response time of less than 10 s and a very good selectivity towards the Sm^3 + over a wide variety of interfering cations (e.g. alkali, alkaline earth, transition and heavy metal ions) the sensor seemed to be a promising analytical tool for determination of the Sm^3 +. Hence, it was used as an indicator electrode in the potentiometric titration of samarium ion with EDTA. It was also applied to the direct samarium recovery in binary mixtures.     

BCC vs. HCP—The Effect of Crystal Symmetry on the High Temperature Mobility of Solid 4He

We report results of torsional oscillator (TO) experiments on solid ⁴He at temperatures above 1?K. We have previously found that single crystals, once disordered, show some mobility (decoupled mass) even at these rather high temperatures. The decoupled mass fraction with single crystals is typically 20–30%. In the present work we performed similar measurements on polycrystalline solid samples. The decoupled mass with polycrystals is much smaller, ～1%, similar to what is observed by other groups. In particular, we compared the properties of samples grown with the TO’s rotation axis at different orientations with respect to gravity. We found that the decoupled mass fraction of bcc samples is independent of the angle between the rotation axis and gravity. In contrast, hcp samples showed a significant difference in the fraction of decoupled mass as the angle between the rotation axis and gravity was varied between zero and 85 degrees. Dislocation dynamics in the solid offers one possible explanation of this anisotropy.     

The effect of temperature instability on the threshold sensitivity of photodetectors based on A<Superscript>III</Superscript>–B<Superscript>V</Superscript> photodiodes

The dependence of the sensitivity of photodetectors based on A^III–B^V photodiodes on accidental variations of the temperature of its elements is analyzed. It is shown that the temperature drift of the bias level in input circuits of op-amps strongly contributes to the resulting photodetector noise up to frequencies on the order of 1 MHz. To reach the limiting sensitivities of the sensors, it is necessary to stabilize the temperature of not only the photodiode chip, but also the integrated circuit of the first amplifier stage. For most of applications, the required stabilization accuracy does not exceed ±0.1°C. As a result of the analysis, prototype high-sensitivity medium-wavelength (2–5 μm) sensors were developed that operate without forced cooling and have a detection threshold of tens of nanowatts at a detection bandwidth of 0–1 MHz.     

Selective dispersive liquid–liquid microextraction and preconcentration of Ni(II) into a micro droplet followed by ETAAS determination using a yellow Schiff's base bisazanyl derivative

A simple, rapid and sensitive method was developed for the selective separation and preconcentration of Ni(II) using dispersive liquid–liquid microextraction, by a yellow Schiff's base bisazanyl derivative, as a selective complexing agent. In this method, a mixture of 45 μL chloroform (extraction solvent) and 450 μL tetrahydrofuran (dispersive solvent) is rapidly injected by syringe into a 5 mL aqueous sample containing 3% (w/v) sodium chloride and an appropriate amount of the Schiff's base. As a result, a cloudy solution is formed by entire dispersion of the extraction solvent into the aqueous phase. After centrifuging for 5 min at 5000 rpm, the sedimented phase is directly injected into the electrothermal atomic absorption spectrometry for Ni(II) determination. Some important parameters, such as kind and volume of extraction and dispersive solvents, extraction time, salt effect, pH and concentration of the chelating agent have been optimized. Under the optimum conditions, the enrichment factor for the presented method is 138. The calibration curve was linear over a nickel concentration range of 10–50 ng mL^? 1. The detection limit and relative standard deviation were 0.04 ng mL^? 1 and 2.1%, respectively. The method was successfully applied to the extraction and determination of Ni(II) in different water samples.     

The effect of thermodynamic properties of Me–Ti (Me = In,Sn, Ga,Au, and Ge) melts on the wetting of the CaF<Subscript>2</Subscript> substrate

The effect of Ti additions on the wetting behavior of CaF₂ by non-reactive liquid metals (In, Sn, Ga, Au, Ge) was investigated. Pure metals do not wet CaF₂ while minor additions of Ti improve wetting. Small changes of the contact angle were observed in the CaF₂/Au–Ti and CaF₂/Ge–Ti systems, which are characterized by strong Me–Ti interaction in the melt, while considerable decrease of contact angle was obtained in the CaF₂/In–Ti, CaF₂/Sn–Ti and CaF₂/Ga–Ti systems, which display a relatively weak Me–Ti interaction. According to a thermodynamic analysis and experiential observations, Ti does not react with the substrate to form condensed phases at the metal/CaF₂ interface. Therefore, it was assumed that the mechanism of the wetting improvement is attributed to the Ti segregation at the interface. The results of the XPS analysis confirm a Ti enrichment of the region close to the interface, moreover, according to the high resolution XPS spectrum, obtained from this region, the position of the In4d peak has a chemical shift, which is typical for In–Ti intermetallic compounds. The XPS analysis does not provide sufficient evidence for the formation of the intermetallic interfacial layer at elevated temperature. Thus, further investigations have to be designed and conducted in order to clarify this issue.     

Construction and properties of a gamma-ray detector based on D(γ, n)H neutron counting

The photodisintegration of deuterium with subsequent neutron counting has been used in a system to detect high-energy γ-rays. The system consists of a cylindrical tank filled with 242 l of heavy water and surrounded by 30 ³He-filled proportional counters. Details of the construction, specifications and characteristics of the detector are described. The detector has been used to measure the hexadecapole strength of the 2506 (J^π = 4⁺) → 0 (J^π = 0⁺) keV γ-ray transition in ⁶⁰Ni (E4 = 78 nuclear physics applications, it is proposed that the detector be used for studies relevant to nuclear astrophysics, in particular for the study of capture reactions induced on highly radioactive targets (up to about 1 Ci). The detector is also useful for neutron work (18% neutron efficiency).     

Mechanical Response of <Superscript>4</Superscript>He Films Adsorbed on Graphite with a Quartz Tuning Fork

We have carried out quartz-crystal microbalance (QCM) experiments of 32 kHz quartz tuning fork for ⁴He films adsorbed on Grafoil, and have measured the temperature dependence of the resonance frequency and Q value for various areal densities. It was found that the frequency does not decrease exactly in proportion to the areal density. This means that the film still undergoes decoupling partly, although it is strongly suppressed from that of 5 MHz QCM measurements. Above the three-atom thick film, the decoupling due to the superfluidity of the overlayer is observed. In addition, we found that the competition between the superfluidity and the slippage takes place for a large oscillation amplitude. From the comparison with 5 MHz QCM measurements, it is concluded that the acceleration of substrate plays an important role in the slippage.     

Growth of copper nanoislands on the Si(100)-<Emphasis Type="Italic">c</Emphasis>(4 × 12)-Al surface studied by scanning tunneling microscopy

The growth of copper island films on the Si(100)-c(4 × 12)-Al surface phase has been studied using scanning tunneling microscopy (STM). The dependence of the island concentration on their size and the substrate temperature is determined. The diffusion activation energy and the binding energy of copper dimers are determined from an analysis of the experimental STM data in terms of the kinetic theory of nucleation. The critical temperature corresponding to a change in the growth regime is evaluated from an Arrhenius plot. It is established that the c(4 × 12)-Al surface phase exhibits an orienting action on the crystalline structure of Cu nanoislands.     

The effect of titanium dioxide nano-filler on the conductivity,morphology and thermal stability of poly(methyl methacrylate)—poly(styrene-<Emphasis Type="Italic">co</Emphasis>-acrylonitrile) based composite solid polymer electrolytes

The composite solid polymer electrolyte (CSPE) samples, comprising of poly(methylmethacrylate) (PMMA)/poly(styrene-co-acrylonitrile) (SAN)/ethylene carbonate (EC)/propylene carbonate (PC)/lithium trifluoromethanesulfonate (LiCF₃SO₃)/anatase-TiO₂ as nano-filler (0, 5, 6, 7, 8 and 9 wt% for samples T0, T1, T2, T3, T4 and T5 respectively) were prepared by solution casting technique. Fourier transform infrared (FT-IR) spectral studies indicate the interaction of PMMA and plasticizers (EC, PC) with Lithium ion and nano-filler TiO₂ in samples. From AC impedance studies ionic conductivity, dielectric constant increase with increase in the concentration of nano-filler TiO₂ up to 9 wt%. The sample T5 shows lowest activation energy (E_a) of 0.14 eV, very short relaxation time (τ) of 1.49?×?10^?7 s and exhibits maximum ionic conductivity of 1.05?×?10^?4 S cm^?1 at room temperature. The conductivity-temperature dependence studies showed that the conductivity of all samples depict Arrhenius behaviour suggesting ion-hopping mechanism. Dielectric studies reveal ion conducting nature of CSPE samples. Thermogravimetric analysis indicate the thermal stability of CSPE sample T5 up to 333 °C with maximum degradation at 388 °C. DSC studies reveal absence of glass transition temperature (T_g) of atactic component of PMMA in CSPE sample T5 indicating amorphous nature. X-ray diffraction patterns shows shift in the position of peaks confirming the complex formation of the PMMA-SAN-EC-PC-LiCF₃SO₃-TiO₂ system. SEM analysis indicates that the presence of lithium salt and filler TiO₂ on polymer host does not lead to heterogenous polymer blend thus retaining its amorphous nature.     

Effect of Si(100)-<Emphasis Type="Italic">c</Emphasis>(4 × 12)-Al and Si(111)-(5.55 × 5.55)-Cu reconstructions on the deposition of cobalt onto silicon surface

The use of surface reconstructions for modifying properties of single crystal silicon substrates with a view to the creation of new nanostructures is a promising direction in the development of nanotechnologies. Systems Si(100)-c(4 × 12)-Al and Si(111)-(5.55 × 5.55)-Cu occupy special positions among stable reconstructions of the silicon surface, which have been recently demonstrated to be promising templates. The adsorption of cobalt on these surfaces at various temperatures has been studied using scanning tunneling microscopy. The room-temperature deposition leads to the formation of a weakly ordered layer of metallic Co with retained initial reconstructions at the Co/Si interface. An increase in the temperature leads to the formation of faceted cobalt silicide islands on both reconstructed surfaces.     

Enzymatic degradation of the hydrogels based on synthetic poly(α-amino acid)s

Biodegradable hydrogels are studied as potential scaffolds for soft tissue regeneration. In this work biodegradable hydrogels were prepared from synthetic poly(α-amino acid)s, poly(AA)s. The covalently crosslinked gels were formed by radical copolymerization of methacryloylated poly(AA)s, e.g. poly[N ⁵-(2-hydroxy-ethyl)-l-glutamine-ran-l-alanine-ran-N ⁶-methacryloyl-l-lysine], as a multifunctional macro-monomer with a low-molecular-weight methacrylic monofunctional monomer, e.g. 2-hydroxyethyl methacrylate (HEMA). Methacryloylated copolypeptides were synthesized by polymerization of N-carboxyanhydrides of respective amino acids and subsequent side-chain modification. Due to their polypeptide backbone, synthetic poly(AA)s are cleavable in biological environment by enzyme-catalyzed hydrolysis. The feasibility of enzymatic degradation of poly(AA)s alone and the hydrogels made from them was studied using elastase, a matrix proteinase involved in tissue healing processes, as a model enzyme. Specificity of elastase for cleavage of polypeptide chains behind the l-alanine residues was reflected in faster degradation of l-alanine-containing copolymers as well as of hydrogels composed of them.     

The effect of strontium (Sr) on the ignition temperature of magnesium (Mg): a look at the pre-ignition stage of Mg–6 wt% Sr

The effect of strontium (Sr) addition on the ignition and oxidation behavior of magnesium has been investigated. Continuous heating experiments carried out in dry air-flow reveal that the ignition temperature (T _i) is raised from 640 °C (of pure Mg) to up to 854 °C at 6 wt% Sr addition. The oxidation behavior of Sr containing alloys was investigated during (i) isothermal oxidation experiments above the liquidus temperature (~640 °C) and (ii) during pre-ignition heating to 700 °C. The change in the ignition temperature of various alloy compositions is related to the amount of Sr that can be segregated to the surface and to the activity of the elements in the surface in the stages prior to ignition.     

The effect of Y on the hot-tearing resistance of Al–5 wt.% Cu based alloy

It is well known that the continuing quest for Al–Cu alloy with improved casting defects is driven by the need in aerospace industries. Especially, the wide crystallization range of Al–5 wt.% Cu based alloys results in generation of hot-tearing. In Al–5 wt.% Cu alloy, the hot-tearing susceptibility is influenced by the larger crystallization range, the quantity and distribution of the eutectic microstructure in the grain boundary and the size of primary α (Al) particles. The effect of Y content on the hot-tearing resistance in Al–5 wt.% Cu based alloys was studied by ZQS-2000 twin Bar Tester of Thermo-Cracking-Linear Contraction Tester. The hot-tearing behavior was studied by thermal analysis, optical microscopy (OM) and scanning electron microscopy (SEM). It was found that Y promoted the end-solidification temperature and decreased the quantity of eutectic in grain boundary. Y-rich phase precipitation caused a depression of the begin-solidifying temperature of α (Al), narrowed the crystallization range, increased the hot-tearing resistance and decreased the hot-tearing susceptibility significantly.     

Errata to “The effect of an axial temperature gradient on the steady motion of a large droplet in a tube” by S. K. Wilson

Errata to The effect of an axial temperature gradient on the steady motion of a large droplet in a tube by S. K. Wilson J. Eng. Maths 29 (1995) 205–217     

Studying the electric conductivity of the Si(100)<Emphasis Type="Italic">c</Emphasis>(4×12)-Al surface phase during deposition of indium and aluminum

The dependence of the electric conductivity of the Si(100)c(4×12)-Al surface phase on the surface morphology has been studied using low-energy electron diffraction, scanning tunneling microscopy, and four-point probe conductivity measurement techniques in the course of the vacuum deposition of In and Al. The growth of adsorbate islands acting as additional centers of charge carrier scattering leads to a decrease in the conductivity.