Effects of electric fields on thermal convection in gases

Summary Extensive measurements of the coefficient of electroconvective heat transfer have been carried out in gases: air, Ar, N₂, O₂, freon-12 and freon-22, using a single platinum wire mounted along the axis of a copper cylinder. The diameter of the cylinder was 53 mm, while that of the wire was 0.025 mm. Electroconvective heat transfer coefficients have been measured as a function of electric field, pressure, orientation and frequency of the applied electric field in the earth's gravitational field. The results reveal a complicated interaction between the electric-field gradient and thermal convection. The present work indicates that the Senftleben mechanism alone cannot account for the observed phenomena.     

Automation of the direct current comparator resistance bridge

The direct current comparator resistance bridge, Model 9975, manufactured by Guildline Instruments, Inc., which permits electrical resistance measurements up to eight digits, has been fully automated. Details of this automation are described in this paper. The performance of the automated bridge is demonstrated with applications to electrical resistivity studies on some metallic alloys.     

The Crystal and Molecular Structure of Atipamezole Base and Atipamezole Hydrochloride

Abstract  

Crystal structures of alpha₂-adrenergic antagonist atipamezole base (1) and its hydrochloric acid salt (2) have been determined using X-ray diffraction methods. Atipamezole base crystallized in the monoclinic space group P2₁, with unit cell parameters a = 13.238(4), b = 9.747(4), c = 14.609(5) ?, β = 107.75(4)o, V = 1,795.3(12) ?³ and Z = 6 (three independent molecules of 1). Atipamezole hydrochloride crystallized in the monoclinic space group Cc, with unit cell parameters a = 12.052(1), b = 32.561(9), c = 13.668(5) ?, β = 102.64(1)o, V = 5,233(2) ?³ and Z = 16 (four independent molecules of 2). Each of the three atipamezole moieties in 1 has an intramolecular C–H···N H-bond. In both structures the molecules are H-bonded to form extended chains.     

Electrical resistivity and antiferromagnetism of chromium-platinum alloys

Electrical resistivity, ?, has been measured as a function of temperature, T, of Cr alloys containing 0.47, 0.93, and 1.63 at.% Pt. The onset of antiferromagnetism causes anomalies in the ? vs T curves which increase with increasing Pt concentrations. Using the criterion that at the Néel temperature, T_N, d?/dT is minimum, it has been determined that the values of T_N are (430 ± 10)K, (490 ± 5)K, and (535 ± 5)K for the above-mentioned alloys. The nature of the antiferromagnetic state and the corresponding anomalies in the electrical resistivity in the Cr-Pt system are very similar to those found in Cr-Ir solid solutions.     

Electrical resistivity of iron-vanadium alloys between 78 and 1200 K

Electrical resistivity (?) of FeV alloys containing 0.5, 0.9, 2.7, and 6.1 at% V has been measured as a function of temperature (T) between 78 and 1200 K. The ? vs. T curves exhibit a change in the slope at the ferromagnetic Currie temperature (T_c). The d?/dT vs. T curves in the neibhorhood of T_c are similar to the corresponding plot for pure Fe. Our studies confirm the previously observed anomalous effect of V on T_c of Fe, i.e., that T_c increase with small additions of V to Fe. The critical index λ⁺ associated with the power law of d?/dT just above T_c has been determined as a function of V concentration.     

Study of PEGylated lipid layers as a model for PEGylated liposome surfaces: molecular dynamics simulation and Langmuir monolayer studies

We have combined Langmuir monolayer film experiments and all-atom molecular dynamics (MD) simulation of a bilayer to study the surface structure of a PEGylated liposome and its interaction with the ionic environment present under physiological conditions. Lipids that form both gel and liquid-crystalline membranes have been used in our study. By varying the salt concentration in the Langmuir film experiment and including salt at the physiological level in the simulation, we have studied the effect of salt ions present in the blood plasma on the structure of the poly(ethylene glycol) (PEG) layer. We have also studied the interaction between the PEG layer and the lipid bilayer in both the liquid-crystalline and gel states. The MD simulation shows two clear results: (a) The Na(+) ions form close interactions with the PEG oxygens, with the PEG chains forming loops around them and (b) PEG penetrates the lipid core of the membrane for the case of a liquid-crystalline membrane but is excluded from the tighter structure of the gel membrane. The Langmuir monolayer results indicate that the salt concentration affects the PEGylated lipid system, and these results can be interpreted in a fashion that is in agreement with the results of our MD simulation. We conclude that the currently accepted picture of the PEG surface layer acting as a generic neutral hydrophilic polymer entirely outside the membrane, with its effect explained through steric interactions, is not sufficient. The phenomena we have observed may affect both the interaction between the liposome and bloodstream proteins and the liquid-crystalline-gel transition and is thus relevant to nanotechnological drug delivery device design.     

Convective specific-heat transfer in liquids in the presence of non-uniform electric field

Summary The electroconvective specific-heat transfer coefficient has been measured in various liquids (methanol, kerosene, silicon oil and ethanol) from a single platinum wire (diameter=0.025 mm) mounted along the axis of a copper cylinder (diameter=53 mm). The heat transfer coefficient has been evaluated under the influence of a.c. and d.c. fields. An a.c. field always causes an enhancement in the heat transfer coefficient. A d.c. field causes an inhibition in heat transfer in methanol. A similar trend is noticed in kerosene, but the heat transfer coefficient increases again as the field is increased. An enhancement in the heat transfer coefficient is observed in silicon oil, and a similar trend is noticed in ethanol, but the heat transfer coefficient decreases again as the field is increased. The effect of cylinder orientation on convection is studied. The efficiency of convection has been calculated for various liquids using an empirical relation. The efficiency obtained in a d.c. field is found to be higher than in the a.c. field. A similar trend is also noticed for the electric Nusselt number.     

Magnetization of lutetium iron garnet near the critical point

A study has been made of the critical magnetic properties of lutetium iron garnet. Values of the critical exponents, β, δ and λ were seen to fulfill the scaling relation, β(δ?1)=λ, within the limits of experimental error. The critical temperature, obtained from the kink-point plot of applied magnetic field vs break-point temperature, was reaffirmed through utilization of the Kouvel-Fisher analysis.