Carbon Paste Electrode Modified with Functionalized Nanoporous Silica Gel as a New Sensor for Determination of Silver Ion

A new dipyridyl‐functionalized silica gel (DPSG) was synthesized. The potentiometric response of silver ion was investigated at a carbon paste electrode chemically modified with functionalized nanoporous silica gel. The electrodes with a DPSG proportions of 10.1% (w/w), showed very stable potential. Calibration plots with Nernstian slopes for Ag⁺ were observed, 58.7 (±0.9) mV decade^?1, over a wide linear range of concentration (5.0×10^?7 to 1.0×10^?1 M). The electrode has a detection limit of 1.0×10^?7 M. The selectivity coefficients measured by the match potential method in acetate buffer, pH 5.5, were investigated. The electrode has fast response time, high performance, high sensitivity in wide cation activity ranges, and good long term stability (more than 6 months). The method was satisfactory and used to determine the concentration of silver ion in waste waters contaminated by this metal.     

Accelerator mass spectrometry of small biological samples

Accelerator mass spectrometry (AMS) is an ultra-sensitive technique for isotopic ratio measurements. In the biomedical field, AMS can be used to measure femtomolar concentrations of labeled drugs in body fluids, with direct applications in early drug development such as Microdosing. Likewise, the regenerative properties of cells which are of fundamental significance in stem-cell research can be determined with an accuracy of a few years by AMS analysis of human DNA. However, AMS nominally requires about 1 mg of carbon per sample which is not always available when dealing with specific body substances such as localized, organ-specific DNA samples. Consequently, it is of analytical interest to develop methods for the routine analysis of small samples in the range of a few tens of microg. We have used a 5 MV Pelletron tandem accelerator to study small biological samples using AMS. Different methods are presented and compared. A (12)C-carrier sample preparation method is described which is potentially more sensitive and less susceptible to contamination than the standard procedures.     

Stripping Voltammetry of Cerium(IIl) with a Chemically Modified Carbon Paste Electrode Containing Functionalized Nanoporous Silica Gel

This research introduces the design of an adsorptive stripping voltammetric method for the cerium(III) determination at a carbon paste electrode, chemically modified with dipyridyl‐functionalized nanoporous silica gel (DPNSG‐CPE). The electroanalytical procedure comprised two steps: the Ce(III) chemical accumulation at ?200 mV followed by the electrochemical detection of the Ce(III)/dipyridyl complex, using anodic stripping voltammetry. The factors, influencing the adsorptive stripping performance, were optimized including the modifier quantity in the paste, the electrolyte concentrations, the solution pH and the accumulation potential or time. The resulting electrode demonstrated a linear response over a wide range of Ce(III) concentration (1.0–28 ng mL^?1). The precision for seven determinations of 4 and 10 ng mL^?1 Ce(III) was 3.2% and 2.5% (relative standard deviation), respectively. The prepared electrode was used for the cerium determination in real samples and very good recovery results were obtained.     

Numerical investigation of boiling heat transfer in a quenching process of jet impingement considering solid temperature distribution

Boiling jet impingements are being widely used in various industries. Hence, a quenching jet impingement is simulated numerically. A solver code based on volume of fluid method was modified to analyze the effects of conjugation and mass transfer, and validated against an experimental study. Then, optimized cooling factor (OCF) was defined to involve temperature uniformity of the block and the cooling rate simultaneously. Subsequently, in laminar two-jet configurations, the effects of velocity inlet function, jet-to-surface and jet-to-jet spacing on standard temperature uniformity index (STUI) and OCF in a highly heated block were investigated. Heaviside function of time for the inlet velocity and periods of pulse between 0 and 0.2 were considered. Some remarkable results are achieved by the proposed configurations. In all cases with pulsating jets, improvements in STUI and OCF relative to pulse-free ones were observed; when V?=?0.4 m s^?1, OCF peaked at 2 in P?=?0.06, which was almost eight times greater than OCF of pulse-free configuration (OCF?=?0.24). As velocity decreased, the temperature uniformity improved; however, OCF showed the highest value at higher velocities occurring for lower periods of pulses. This happens because of more uniform temperature distribution in both plate sides and continual destroying film boiling layers generated on the surface. Also, in a jet-to-jet spacing of about one-third of the block length, for all plate lengths, optimal temperature uniformity with maximum OCF was obtained, due to formation of two stagnation points having the highest heat transfer rate by positioning in an ideal distance from each other.

     

The effects of Knudsen-dependent flow velocity on vibrations of a nano-pipe conveying fluid

In this paper, we investigate the effect of nano-flow on vibration of nano-pipe conveying fluid using Knudsen (Kn). We use Euler–Bernoulli plug-flow beam theory. We modify no-slip condition of nano-pipe conveying fluid based on Kn. We define a Kn-dependent flow velocity. We consider effect of slip condition, for a liquid and a gas flow. We reformulate Navier–Stokes equations, with modified versions of Kn-dependent flow velocity. We observe that for passage of gas through nano-pipe with nonzero Kn, the critical flow velocities decreased considerably as opposed to those for zero Kn. This can show that ignoring Kn effect on a gas nano-flow may cause non-conservative design of nano-devices. Furthermore, a more impressive phenomenon happens in the case of clamped-pinned pipe conveying gas fluid. While we do not observe any coupled-mode flutter for a zero Kn, we can see the coupled-mode flutter, accompanying the second-mode divergence, for a nonzero Kn.     

Atomically Precise Lanthanide-Iron-Oxo Clusters Featuring the ϵ-Keggin Ion

Atomically precise molecular metal-oxo clusters provide ideal models to understand metal oxide surfaces, self-assembly, and form-function relationships. Devising strategies for synthesis and isolation of these molecular forms remains a challenge. Here, the synthesis of four Ln-Fe oxo clusters that feature the ϵ-{Fe₁₃} Keggin cluster in their core is reported. The {Fe₁₃} metal-oxo cluster motif is the building block of two important iron oxyhydroxyide phases in nature and technology, ferrihydrite (as the δ-isomer) and magnetite (the ϵ-isomer). The reported ϵ-{Fe₁₃} Keggin isomer as an isolated molecule provides the opportunity to study the formation of ferrihydrite and magnetite from this building unit. The four currently reported isostructural lanthanide-iron-oxo clusters are fully formulated [Y₁₂Fe₃₃(TEOA)₁₂(Hyp)₆(μ₃-OH)₂₀(μ₄-O)₂₈(H₂O)₁₂](ClO₄)₂₃ ⋅ 50 H₂O ( 1 , Y₁₂Fe₃₃ ), [Gd₁₂Fe₃₃(TEOA)₁₂(Hyp)₆(μ₃-OH)₂₀(μ₄-O)₃₂(H₂O)₁₂](ClO₄)₁₅ ⋅ 50 H₂O ( 2 , Gd₁₂Fe₃₃ ) and [Ln₁₆Fe₂₉(TEOA)₁₂(Hyp)₆(μ₃-OH)₂₄(μ₄-O)₂₈(H₂O)₁₆](ClO₄)₁₆(NO₃)₃ ⋅ n H₂O (Ln=Y for 3 , Y₁₆Fe₂₉ , n=37 and Ln=Gd for 4 , Gd₁₆Fe₂₉ n=25; Hyp=trans-4-Hydroxyl-l -proline and TEOA=triethanolamine). The next metal layer surrounding the ϵ-{Fe₁₃} core within these clusters exhibits a similar arrangement as the magnetite lattice, and Fe and Ln can occupy the same positions. This provides the opportunity to construct a family of compounds and optimize magnetic exchange in these molecules through composition tuning. Small-angle X-ray scattering (SAXS) and high-resolution electrospray ionization mass spectrometry (HRESI-MS) show that these clusters are stable upon dissolution in both water and organic solvents, as a first step to performing further chemistry towards building magnetic arrays or investigating ferrihydrite and magnetite assembly from pre-nucleation clusters.     

Directed paths on percolation clusters

We consider a variant of the problem of directed polymers on a disordered lattice, in which the disorder is geometrical in nature. In particular, we allow a finite probability for each bond to be absent from the lattice. We show, through the use of numerical and scaling arguments on both Euclidean and hierarchical lattices, that the model has two distinct scaling behaviors, depending upon whether the concentration of bonds on the lattice is at or above the directed percolation threshold. We are particularly interested in the exponents and, defined by ft and xt , describing the free-energy and transverse fluctuations, respectively. Above the percolation threshold, the scaling behavior is governed by the standard random energy exponents (=1/3 and =2/3 in 1+1 dimensions). At the percolation threshold, we predict (and verify numerically in 1+1 dimensions) the exponents=1/2 and =v/v, where v and v are the directed percolation exponents. In addition, we predict the absence of a free phase in any dimension at the percolation threshold.     

Copper (II) Nitrate-Silica Gel Mediated Regeneration of Carbonyl Compounds from Oximes Under Microwave Irradiation

Cu(NO₃)₂ supported on silica gel can be used as an effective and mild oxidizing agent for the direct conversion of oximes to carbonyl compounds under microwave irradiation in good yield.     

Finite Order Batalin-Fradkin-Tyutin Method for Chiral Bosons in Non-commutative Space

The recently improved finite order BFT Hamiltonian embedding method is applied to the two dimensional chiral bosons in non-commutative space. It is then systematically converted to a first class constraint model. Performing the momentum integrations, the corresponding fully gauge symmetry Lagrangian as well as its partition function in phase space are obtained.