Calorimetry In Vapor Absorption And Binary Mixture Vapor Compression Refrigeration And Heatpump Systems

The use of binary fluid systems in thermally driven vapour absorption and mechanically driven vapour compression refrigeration and heatpump cycles has provided an impetus for obtaining experimental date on caloric properties of such fluid mixtures. However, direct measurements of these properties are somewhat scarce in spite of the calorimetric techniques described in the literature being quite adequate. Most of the design data are derived through calculations using theoretical models and vapour-liquid equilibrium data. This article addresses the choice of working fluids and the current status on the data availability vis-a-vis engineering applications. Particular emphasis is on organic working fluid pairs.

Electronic absorption and emission spectroscopic investigations of the interaction of the fullerenes, C60 and C70, with amines and aromatic molecules

Electronic absorption spectroscopy and fluorescence spectroscopy have been used to investigate the interaction of the fullerenes C60 and C70 with diethylaniline, and with aromatic solvents such as benzene. C60 interacts weakly with aromatic amines in the ground state while C70 does not interact at all. Steady state fluorescence emission and lifetime measurements show that both C60 and C70 form excited state complexes (exciplexes) with the amines in non-aromatic solvents such as methylcyclohexane, but not in benzene. In benzene, only fluorescence quenching is observed due to the interaction between the π systems of the aromatic solvent and the fullerene in the ground state. This is also borne out by the systematic study of solvent effects on the absorption and emission spectra of the fullerenes.

Spectrally broadened excitonic absorption and enhanced optical nonlinearities in Dy3+-doped ZnO nanoparticles

We have synthesized Dy3+-doped ZnO nanoparticles at room temperature through the sol-gel method. X-ray diffraction and Scanning electron microscopic studies confirm the crystalline nature of the particles. Excitonic absorption of ZnO shows three different bands, and we observe that incorporation of Dy3+ results in the shifting and broadening of the n=1 absorption band of ZnO. Photoluminescence studies done at the excitation wavelength of 335 nm show broad emission containing five different bands. Open-aperture z-scan studies done at 532 nm using 5 ns laser pulses show an optical limiting behavior, which numerically fits to a three-photon type absorption process. The nonlinearity is essentially resonant, as it is found to increase consistently with Dy3+ concentration. This feature makes Dy3+-doped ZnO a flexible optical limiter for potential device applications.

Optical absorption and photoluminescence studies of Nd3 doped alkali boro germanate glasses

Optical absorption and photoluminescence studies have been carried out at room temperature in 25 R2O-25 GeO2-49.5 B2O3-0.5 Nd2O3 glass systems, (Composition in mol%, R= Li, Na, K and Rb). Judd Ofelt Intensity parameters and other parameters like Racah (E-1, E-2 and E-3), Slater-Condon-Shortley (F-2, F-4 and F-6) Spin-Orbit Coupling (xi(4f)) and Configuration Interaction (alpha,beta and gamma) for Nd3+ ion in the glass system are calculated. The variation of the 02 parameters are interpreted in terms of the covalency of the RE ion in the glass matrix. Further the hypersensitive transition I-4(9/2) -> (4)G(5/2), (2)G(7/2) is analyzed with respect to the intensity ratio I-L/I-S and is found to be dependent on the type of alkali in the glass matrix. The Photoluminescence studies do not show any appreciable shift in the peak emission wavelength of the F-4(3/2) to I-4(11/2) transition with the change in alkali type. (C) 2010 Elsevier B.V. All rights reserved.

The effect of host glass on optical absorption and fluorescence of Nd3+ in xNa(2)O-(30-x)K2O-70B(2)O(3) glasses

The effect of host glass composition on the optical absorption and fluorescence spectra of Nd3+ has been studied in mixed alkali borate glasses of the type xNa(2)O-(30-x)K2O-69.5B(2)O(3)-0.5Nd(2)O(3) (X = 5,10,15,20 and 25). Various spectroscopic parameters such as Racah (E-1, E-2 and E-3), spin-orbit (xi(4f)) and configuration interaction (alpha, beta) parameters have been calculated. The Judd-Ofelt intensity parameters (Omega(lambda)) have been calculated and the radiative transition probabilities (A(rad)), radiative lifetimes (tau(r)), branching ratios (beta) and integrated absorption cross sections (Sigma) have been obtained for certain excited states of the Nd3+, ion and are discussed with respect to x. From the fluorescence spectra, the effective fluorescence line widths (Deltalambda(eff)) and stimulated emission cross sections (sigma(p)) have been obtained for the three transitions F-4(3/2) --> I-4(9/2), F-4(3/2) --> I-4(11/2) and F-4(3/2) --> I-4(13/2) of Nd3+. The stimulated emission cross section (sigma(p)) values are found to be in the range (2.0-4.8) x 10(-2)0 cm(2) and they are large enough to indicate that the mixed alkali borate glasses could be potential laser host materials.

Probing ultrafast carrier dynamics, nonlinear absorption and refraction in core-shell silicon nanowires

We investigate the relaxation dynamics of photogenerated carriers in silicon nanowires consisting of a crystalline core and a surrounding amorphous shell, using femtosecond time-resolved differential reflectivity and transmission spectroscopy at 3.15 eV and 1.57 eV photon energies. The complex behaviour of the differential transmission and reflectivity transients is the mixed contributions from the crystalline core and the amorphous silicon on the nanowire surface and the substrate where competing effects of state-filling and photoinduced absorption govern the carrier dynamics. Faster relaxation rates are observed on increasing the photogenerated carrier density. Independent experimental results on crystalline silicon-on-sapphire (SOS) help us in separating the contributions from the carrier dynamics in crystalline core and the amorphous regions in the nanowire samples. Further, single-beam z-scan nonlinear transmission experiments at 1.57 eV in both open- and close-aperture configurations yield two-photon absorption coefficient beta (similar to 3 cm/GW) and nonlinear refraction coefficient gamma (-2.5 x 10 (-aEuro parts per thousand 4) cm(2)/GW).

New solid forms of the anti-HIV drug etravirine: salts, cocrystals, and solubility

Thirteen new solid forms of etravirine were realized in the process of polymorph and cocrystal/salt screening to improve the solubility of this anti-HIV drug. One anhydrous form, five salts (hydrochloride, mesylate, sulfate, besylate, and tosylate), two cocrystals (with adipic acid and 1,3,5-benzenetricarboxylic acid), and five solvates (formic acid, acetic acid, acetonitrile, and 2:1 and 1:1 methanolates) were obtained. The conformational flexibility of etravirine suggests that it can adopt four different conformations, and among these, two are sterically favorable. However, in all 13 solid forms, the active pharmaceutical ingredient (API) was found to adopt just one conformation. Due to the poor aqueous solubility of the API, the solubilities of the salts and cocrystals were measured in a 50% ethanol water mixture at neutral pH. Compared to the salts, the cocrystals were found to be stable and showed an improvement in solubility with time. All the salts were dissociated within an hour, except the tosylate, which showed 50% phase transformation after 1 h of the slurry experiment. A structure property relationship was examined to analyze the solubility behavior of the solid forms.

Solvent-induced changes on the polarity of the triplet excited state of 2-chlorothioxanthone: From time-resolved absorption and resonance Raman spectroscopies

Solvent polarity has been known to influence the triplet state structure and reactivity. Here, we present our experimental and theoretical study on the effect of solvent on the lowest triplet excited state structure of 2-chlorothioxanthone (CTX). Time-resolved absorption (TA) spectroscopy has been employed to understand the triplet state electronic structure; whereas solvent-induced structural changes have been studied using time-resolved resonance Raman (TR3) spectroscopy. Both the DFT and TD-DFT calculations have been performed in the solution phase employing self-consistent reaction field implicit solvation model to support the experimental data. It has been observed that CO stretching frequencies of the excited triplet state are sensitive to the solvent polarity and increase with the increase in the solvent polarity. Both TA and TR3 studies reveal that specific solvent effect (H-bonding) is more pronounced in comparison to the nonspecific solvent effect. (C) 2013 Elsevier B.V. All rights reserved.

Nonlinear Optical Properties and Temperature-Dependent UV-Vis Absorption and Photoluminescence Emission in 2D Hexagonal Boron Nitride Nanosheets

Recently, a lot of interest has been centred on the optical properties of hexagonal boron nitride (h-BN), which has a similar lattice structure to graphene. Interestingly, h-BN has a wide bandgap and is biocompatible, so it has potential applications in multiphoton bioimaging, if it can exhibit large nonlinear optical (NLO) properties. However, extensive investigation into the NLO properties of h-BN have not been done so far. Here, NLO properties of 2D h-BN nanosheets (BNNS) are reported for the first time, using 1064-nm NIR laser radiation with a pulse duration of 10 ns using the Z-scan technique. The reverse saturable absorption occurs in aqueous colloidal solutions of BNNS with a very large two-photon absorption cross section (sigma(2PA)) of approximate to 57 x 10(-46) cm(4) s(-1) photon(-1). Also, by using UV-Vis absorption spectroscopy, the temperature coefficient of the bandgap (dE(g)/dT) of BNNS is determined to be 5.9 meV K-1. Further defect-induced photoluminescence emission in the UV region is obtained in the 283-303 K temperature range, under excitations of different wavelengths. The present report of large sigma(2PA) combined with stability and biocompatibility could open up new possibilities for the application of BNNS as a potential optical material for multiphoton bioimaging and advanced photonic devices.

Resonant absorption of Alfven waves and the associated phenomenon of magnetic reconnection

It is proposed that the mathematical analysis of the Alfven wave equation in inhomogeneous magnetic fields which explain the resonance absorption of Alfven surface waves near a resonant layer can also be used to show that the magnetic reconnection process can arise near the zero-frequency resonant layer driven by VLF Alfven surface waves. It is suggested that the associated phenomena of resonant absorption and magnetic reconnection can account for the recent observations of intense magnetic activity in the long-period geomagnetic micropulsation range, at cusp latitudes, during flux transfer events.

Absorption, translocation and metabolism of fluchloralin in groundnut (Arachis hypogaea) and pigweed (Amaranthus viridis)

Root absorption and translocation of [C-14]fluchloralin were determined in groundnut (Arachis hypogaea L.) cv. TMV-2 and pigweed (Amaranthus viridis L.) grown in nutrient solution culture under greenhouse conditions. Root-applied fluchloralin toxicity to groundnut and pigweed was also examined. A growth reduction of 50% occurred in groundnut that received fluchloralin at a concentration of 9.0 mum. Root absorption was similar for both groundnut and pigweed at one day after application (DAA), but groundnut absorbed about twice the amount of fluchloralin during 4 and 8 days of continuous application, compared with pigweed. Groundnut absorbed 25% of the total applied fluchloralin after 8 days. Translocation to leaves from treated roots was low and roots of groundnut contained 80% of the total absorbed C-14, 8 DAA. Contrary to the observations in groundnut, transport from the roots and leaves following root application in pigweed was rapid: 1 and 8 DAA, leaves of pigweed contained 45 and 70% of the total absorbed C-14, respectively. Different patterns of fluchloralin metabolism were observed in pigweed and groundnut. Pigweed metabolized most of the fluchloralin absorbed by roots. The fluchloralin tolerance of pigweed could partially be accounted for by absorption, translocation and metabolism.

Influence of two photon absorption induced free carriers on coherent polariton and phonon generation in ZnTe crystals

Combination of femtosecond Kerr, two photon absorption, and impulsive stimulated Raman scattering (ISRS) experiments have been carried out to investigate the effect of pulse energy and crystal temperature on the generation of coherent polaritons and phonons in 〈110〉 cut ZnTe single crystals of three different resistivities. We demonstrate that the effect of two photon induced free carriers on the creation of both the polaritons and phonons is largest at 4 K where the free carrier lifetime is enhanced. The temperature dependant ISRS on high and low purity ZnTe crystals allows us to unambiguously assign the phonon mode at 3.5 THz to the longitudinal acoustic mode at X-point in the Brillouin zone, LA(X).

Non-bonded interactions in 2,2,4,4-tetramethyl-1,3-cyclobutanedithione and 2,2,4,4-tetramethyl-3-thio-1,3-cyclobutanedione

Electronic absorption and emission spectra as well as He(I) photoelectron spectra of 2,2,4,4-tetramethyl-,3-cyclobutanedithione and 2,2,4,4-tetramethyl-1-3-thio-1,3-cyclobutanedione have been interpreted on the basis of molecular orbital calculations. The results show that the non-bonded orbital of the dithione is split owing to through-bond interaction, the magnitude of splitting being 0.4 eV. The π* orbital of the dithione appears to be split by about 0.2 eV. Electronic absorption spectra show evidence for the existence of four n—π* transitions, arising out of the splitting of the orbitals referred to above, just as in the case of 2,2,4,4-tetramethyl-1,3-cyclobutanedione. Electronic and photoelectron spectra of the thio-dione show evidence for weak interaction between the C=S and C&.zdbnd;O groups, probably via π* orbitals. Infrared spectra of both the dithione and the thio-dione are consistent with the planar cyclobutane ring; the ring-puckering frequency responsible for non-bonded interactions is around 67 cm−1 in both the dithione and the thio-dione, the value not being very different from that in the dione. The 1,3-transannular distance is also similar in the three molecules.

Hydrogen bonding with mono- and di-carbonyls

The electronic absorption and i.r. spectroscopic studies are reported for the hydrogen bonding systems involving alcohol and various ketones. It is shown that the hydrogen bonding abilities of ketones are determined by the extent of delocalization of the lone pair electrons in their non-bonding molecular orbitals. Evidence for the formation of very weak intermolecular hydrogen bonds between alcohol and the π-electron part of the dicarbonyls has also been presented from the i.r. studies in the 3400–3700 cm−1 region.

Valence states and magnetic properties of LaNi1-xMnxO3 (for 0≤x≤0.2 and x=0.5)

Single-phase LaNi1-xMnxO3 samples in the compositional range 0and La2NiMnO6 was prepared from a mixture of carbonates. All the samples contained a disordered array of nickel and manganese ions. X-ray absorption and XPS measurements indicate the presence of Mn(III) and Ni(III) valence states at room temperature for x=0.1, 0.2 and 0.5. Magnetic susceptibility data suggest Mn4+ solute ions and Stoner-enhanced Pauli paramagnetism of the metallic solvent for x=0.01 with a smooth transition to Mn3+ solute ions and a spontaneously magnetised solvent conduction band at x=0.05. Below 200K, the x=0.05 sample forms superparamagnetic clusters, and below 40K there is evidence for an antiferromagnet spin-density wave. Comparisons with LaCo0.95Mn0.05O3 and La0.98Sr0.02CoO3 confirm that the long-range magnetic coupling occurs via solvent electrons in a narrow conduction band. The conductivity changes from that of a narrow-band metal for x<0.01 to that more characteristic of diffusive motion for x>0.05, but any motional enthalpy appears to remain small ( Delta Hm approximately=0). The x=0.1 sample exhibits ferrimagnetic spin glass behaviour below 40K, and the ferromagnetic interactions increase with manganese concentration. The oxide with x=0.50 is ferromagnetic with a well defined Curie temperature.