Synthesis of carbon nanotubes by catalytic vapor decomposition (CVD) method: Optimization of various parameters for the maximum yield

This paper describes an effect of flow rate, carrier gas (H₂, N₂ and Ar) composition, and amount of benzene on the quality and the yield of carbon nanotubes (CNTs) formed by catalytical vapour dcomposition (CVD) method. The flow and mass control of gases and precursor vapors respectively were found to be interdependent and therefore crucial in deciding the quality and yield of CNTs. We have achieved this by modified soap bubble flowmeter, which controlled the flow rates of two gases, simultaneously. With the help of this set-up, CNTs could be prepared in any common laboratory. Raman spectroscopy indicated the possibilities of formation of single-walled carbon nanotubes (SWNTs). From scanning electron microscopy (SEM) measurements, an average diameter of the tube/bundle was estimated to be about 70 nm. The elemental analysis using energy dispersion spectrum (EDS) suggested 96 at.wt.% carbon along with ca. 4 at.wt.% iron in the as-prepared sample. Maximum yield and best quality CNTs were obtained using H₂ as the carrier gas.      

Development and Validation of a Stability-Indicating LC Method for Simultaneous Analysis of Aceclofenac and Paracetamol in Conventional Tablets and in Microsphere Formulations

A stability-indicating reversed-phase LC method for analysis of aceclofenac and paracetamol in tablets and in microsphere formulations has been developed and validated. The mobile phase was 80:20 (v/v) methanol–phosphate buffer (10 mM at pH 2.5 ± 0.02). UV detection was at 276 nm. The method was linear over the concentration ranges 16–24 and 80–120 μg mL^?1 for aceclofenac and paracetamol, respectively, with recovery in the range 100.9–102.22%. The limits of detection and quantitation for ACF were 0.0369 and 0.1120 μg mL^?1, respectively; those for PCM were 0.0631 and 0.1911 μg mL^?1, respectively.     

A method for characterizing adsorption of flowing solutes to microfluidic device surfaces

We present a method for characterizing the adsorption of solutes in microfluidic devices that is sensitive to both long-lived and transient adsorption and can be applied to a variety of realistic device materials, designs, fabrication methods, and operational parameters. We have characterized the adsorption of two highly adsorbing molecules (FITC-labeled bovine serum albumin (BSA) and rhodamine B) and compared these results to two low adsorbing species of similar molecular weights (FITC-labeled dextran and fluorescein). We have also validated our method by demonstrating that two well-known non-fouling strategies [deposition of the polyethylene oxide (PEO)-like surface coating created by radio-frequency glow discharge plasma deposition (RF-GDPD) of tetraethylene glycol dimethyl ether (tetraglyme, CH(3)O(CH(2)CH(2)O)(4)CH(3)), and blocking with unlabeled BSA] eliminate the characteristic BSA adsorption behavior observed otherwise.     

A constrained variational approach to the designing of low transport band gap materials: A multiobjective random mutation hill climbing method

Neutral polythiophene (PT) and polyselenophene (PSe) are semiconductors with band gaps of about 2 eV. We have proposed and implemented a constrained variational method in which total energy of neutral PT or PSe oligomers is minimized under the constraint that the band gap measured by HOMO–LUMO energy difference is also a minimum in each case. The constrained (bimodal) minimization has been carried out by an adaptive random mutation hill climbing method within the basic framework of Su‐Schrieffer‐Heeger type of model. We show that the “band‐gap constrained minimization” automatically creates electron deficient quinoid regions (QR) in the PT or PSe chains, embedded in aromatic regions (ARs), on both sides. We have investigated how the number and distribution of such QRs can reduce the band gap. Band gap constrained electronic structure calculations thus provide designing clues for low transport band gap materials based on molecular chromophores. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

FTIR,powder XRD,TEM and dielectric studies of pure and zinc doped nano‐hydroxyapatite

Hydroxyapatite, Ca₁₀(PO₄)₆(OH)₂ or HAP, is an important bio‐material, which is having application in bone implants and dentistry. In the present study, zinc doped nano‐hydroxyapatite (Zn‐HAP) was synthesized via chemical precipitation route using surfactant mediated approach. The doping of zinc was confirmed by EDAX. The powder X‐ray diffraction (XRD) pattern revealed the typical hydroxyapatite pattern with broadening and extra peaks were observed for higher concentration. The average crystallite size was calculated by applying the Scherrer's formula to powder XRD pattern and was found in the range of 16 to 33 nm. The morphology of synthesized nano‐particles was also confirmed using TEM. FTIR spectroscopy was used to confirm the presence of various bonds. The dielectric study was carried out at room temperature within the frequency range from 10² Hz to 10⁷ Hz and the variations of dielectric constant with frequency of applied field as well as with the concentration of zinc were studied. It was found that as the concentration of zinc increased the dielectric constant increased. The variations of dielectric loss and a.c. conductivity with frequency of applied field were studied. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and synthesis of Sr<Subscript>3</Subscript>MgSi<Subscript>2</Subscript>O<Subscript>8</Subscript>:Dy<Superscript>3+</Superscript> nanorod arrays by a solid state reaction method

Sr₃MgSi₂O₈:Dy³⁺ Nano-rods were synthesized by using solid state reaction method. The structural properties, morphology and band structure properties of the phosphor was studied. The structural properties were examined by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Bonding behaviour of the phosphor was also determined by recording the FTIR spectra of the phosphor. Band structure i.e. band gap of the phosphor was determined by recording the absorption spectrum. The absorption spectrum was recorded for the sample and the band gap was determined by using Tauc plot. Band gap of the phosphor was found around 5.4 eV.     

Soft X-ray microscopy and spectroscopy at the molecular environmental science beamline at the Advanced Light Source

We present examples of the application of synchrotron-based spectroscopies and microscopies to environmentally relevant samples. The experiments were performed at the molecular environmental science beamline (11.0.2) at the Advanced Light Source, Lawrence Berkeley National Laboratory. Examples range from the study of water monolayers on Pt(1 1 1) single crystal surfaces using X-ray emission spectroscopy and the examination of alkali halide solution/water vapor interfaces using ambient pressure photoemission spectroscopy, to the investigation of actinides, river water biofilms, Al-containing colloids and mineral–bacteria suspensions using scanning transmission X-ray spectromicroscopy. The results of our experiments show that spectroscopy and microscopy in the soft X-ray energy range are excellent tools for the investigation of environmentally relevant samples under realistic conditions, i.e., with water or water vapor present at ambient temperature.     

Role of confinements on the melting of Wigner molecules in quantum dots

We explore the stability of a Wigner molecule (WM) formed in confinements with differentgeometries emulating the role of disorder and analyze the melting (or crossover) of such asystem. Building on a recent calculation [D. Bhattacharya, A. Ghosal, Eur. Phys. J.B 86, 499 (2013)] that discussed the effects of irregularities on thethermal crossover in classical systems, we expand our studies in the untested territory byincluding both the effects of quantum fluctuations and ofdisorder. Our results, using classical and quantum (path integral)Monte Carlo techniques, unfold complementary mechanisms that drive the quantum and thermalcrossovers in a WM and show that the symmetry of the confinement plays no significant rolein determining the quantum crossover scale n_X. This is because thezero-point motion screens the boundary effects within short distances. The phase diagramas a function of thermal and quantum fluctuations determined from independent criteria isunique, and shows “melting” from the WM to both the classical and quantum “liquids”. Anintriguing signature of weakening liquidity with increasing temperature, T, is found in the extreme quantum regime. The crossover is associated with production of defects. However, thesedefects appear to play distinct roles in driving the quantum and thermal “melting”. Ouranalyses carry serious implications for a variety of experiments on many-particle systems? semiconductor heterostructure quantum dots, trapped ions, nanoclusters, colloids and complex plasma.     

Conventionality of Simultaneity and the Tippe Top Paradox in Relativity

In this paper we critically examine a recently posed paradox (tippe top paradox in relativity) and its suggested resolution. A tippe top when spun on a table, tips over after a few rotations and eventually stands spinning on its stem. The ability of the top to demonstrate this charming feat depends on its geometry (all tops are not tippe tops). To a rocket-bound observer the top geometry should change because of the Lorentz contraction. This gives rise to the possibility that for a sufficiently fast observer the geometry of the top may get altered to such an extent that the top may not tip over! This is certainly paradoxical since a mere change of the observer cannot alter the fact that the top tips over on the table. In an effort to resolve the issue the authors of the paradox compare the equations of motion of the particles of the top from the perspective of the inertial frames of the rocket and the table and observe among other things that (1) the relativity of simultaneity plays an essential role in resolving the paradox and (2) the puzzle in some way is connected with one of the corrolaries of special relativity that the notion of rigidity is inconsistent with the theory. We show here that the question of the incompatibility of the notion of rigidity with special relativity has nothing to do with the current paradox and the role of the lack of synchronization of clocks in the context of the paradox is grossly over-emphasized. The conventionality of simultaneity of special relativity and the notion of the standard (Einstein) synchrony in the Galilean world have been used to throw light on some subtle issues concerning the paradox.